An Optical Tapped Delay Line (OTDL), which resolves multiple wavelength signals having extremely narrow wavelength spacing, is combined with other known optical devices to provide a wide variety of optical signal processing applications, including: multiplexing and de-multiplexing a multi-channel signal; adding a signal to, or dropping a signal from, a multi-channel optical signal; specialized coding processing such as generating code division multiple access signals; wavelength locking (stabilizing) a signal; filtering a signal; and analyzing and monitoring a signal spectrum. The OTDL spatially separates individual channels to allow separate processing on each channel. Fixed and tunable embodiments are identified in appropriate cases. Bulk, hybrid, and integrated optical embodiment and methods of fabrication are described, as are curved self-focusing and evanescent embodiments of OTDL devices. The devices and processes disclosed have particular application to dense wavelength division multiplexing (DWDM) and permit a significant improvement in the quantity of information that can be carried on DWDM signals while enhancing signal quality.

1. Field of the Invention
The present invention relates to optical communications, and more particularly to devices and methods for manipulating a multi-frequency input signal, such as a WDM or DWDM signal, to perform a variety of optical signaling processes.
2. Background of the Invention
Fiber optic cable is widely used for data transmission and other telecommunication applications. The relatively high cost of installing new fiber optic cable presents a barrier to increased carrying capacity, however, so it is highly desirable to increase the data carrying capabilities of existing fiber. Wavelength division multiplexing (WDM) enables different wavelengths to be carried over a common fiber optic waveguide. WDM can separate the fiber bandwidth into multiple discrete channels through a technique referred to as dense wavelength division multiplexing (DWDM). This provides a relatively low cost and proven method of substantially increasing long-haul telecommunication capacity over existing fiber optic transmission lines. Techniques and devices are required, however, for performing a variety of processing procedures on the input signals, such procedures including: multiplexing and de-multiplexing the different discrete carrier wavelengths, adding new signals to and dropping existing signals from the multiplexed signal, specialized coding processing such as code division multiple access, precisely controlling the wavelength of laser sources throughout the WDM communications process, improving signal quality (filtering) by reducing crosstalk and signal power loss as channel frequency spacings decrease, and channel interleaving and de-interleaving, among others.
Multiplexing and De-multiplexing. As part of the mux/demux process, individual optical signals should be combined onto a common fiber optic waveguide and then later separated again into the individual signals or channels at the opposite end of the fiber optic cable. Thus, the ability to effectively combine and then separate individual wavelengths (or wavelength bands) from a broad spectral source is of growing importance to the fiber optic telecommunications field and other fields employing optical instruments.
Devices that assemble multiple tightly spaced carrier wavelengths within a single fiber are called multiplexers. Devices that separate the carrier wavelengths at the receiving end of a fiber are called de-multiplexers or channelizers. WDM channelizers known in the prior art include Fabry-Perot interferometers, Lummer-Gehrcke interferometers, Virtually Imaged Phased Array (VIPA) generators, Thin film interference filters, arrayed waveguide gratings, and optical fiber Bragg gratings.
The Fabry-Perot interferometer is a known device for resolving light into its component frequencies, or equivalently, its component wavelengths. FIG. 1 illustrates one example of a prior art Fabry-Perot interferometer. It includes two parallel partially reflective mirrors 70 and 71. The mirrors are separated by a cavity 72, which might be an air space or alternatively, a solid transparent material. Light from a spectrally broadband source, i.e., a laser, is input at plane 75. In particular, a multi-spectral light ray input from point P1 entering through the partially reflective mirror 70 at an angle θ undergoes multiple reflections between mirrors 70 and 71. The emerging light rays 76, having a common wavelength λ, interfere constructively along a circular locus P2 in the output plane 77 where an appropriate detector might be positioned. The condition for constructive interference that relates a particular angle θ and a particular wavelength λ is given by the formula2d cos θ=mλwhere d is the separation of the reflecting surfaces and m is an integer known as the order parameter. The Fabry-Perot etalon thereby separates the component frequencies of the input light by using multiple beam reflections and interferences. It is apparent from the equation above that the output light pattern of the system, i.e., the interference fringes, in the case of a diverging input beam, is a set of concentric circular rings. One ring is present for each wavelength component of the input light for each integer m, with the diameter of each ring being proportional to the corresponding light frequency.
The Fabry-Perot interferometer is not well suited for use as a WDM channelizer due to the difficulty in obtaining high optical throughput efficiency. If the input beam is divergent, e.g., the direct output of an optical fiber, then the output pattern for a given wavelength is a set of rings. Multiple wavelengths produce nested sets of concentric rings. It is difficult to collect this light efficiently and concentrate it at multiple detector points, or couple it to multiple output fibers, especially while maintaining the separation of wavelength components that the interferometer has produced. If the input beam is collimated, e.g., the collimated output of an optical fiber, then the beam can be fanned over a narrow range of angles to produce only a single-order output (e.g., m=+1) for each wavelength of interest. This fanning makes it easy to concentrate the output light at multiple detector points or fibers, but there is inherently high loss. The throughput efficiency can be no greater than 1/N, where N is the number of wavelength components to be separated.
FIG. 2 illustrates an example of a prior art Lummer-Gehrcke interferometer. The illustrated interferometer comprises an uncoated glass plate P and a prism R for coupling a beam of light B into the plate. Internally, the plate is highly reflective at internal incidence angles that approach the critical angle. The internal incidence angle controls the reflectivity of the surfaces. The output of the illustrated Lummer-Gehrcke interferometer is a series of multiple reflected beams b1, b2, b3 that have a frequency-dependent phase shift from beam to beam and that are focused at the output plane S by a lens L. The interference fringes that are formed at the output plane in the case of a diverging input beam and a particular wavelength λ are a family of hyperbolae H near the center of the output plane. Each wavelength component of the input beam gives rise to a unique set of hyperbolic fringes.
The Lummer-Gehrcke interferometer relies upon a glass plate that is uncoated. However, the absence of a surface coating means that it is not possible to tailor the fringe intensity profile. This makes the Lummer-Gehrcke interferometer impractical for use in WDM applications in which the fringe profile controls the channel filter shape.
The Lummer-Gehrcke interferometer also is not well suited for use as a WDM channelizer due to the difficulty in obtaining high optical throughput efficiency. If the input beam is divergent, e.g., the direct output of an optical fiber, then the output pattern for a given wavelength is a family of hyperbolae. Multiple wavelengths produce nested sets of hyperbolae. It is difficult to collect this light efficiently and concentrate it at multiple detector points, or couple it to multiple output fibers, especially while maintaining the separation of wavelength components that the interferometer has produced. If the input beam is collimated, e.g., the collimated output of an optical fiber, then the output pattern for a given wavelength is a set of focused spots corresponding to multiple interference orders. Again, it is difficult to collect this light efficiently, and there is generally an inherent loss. The throughput efficiency can be no greater than 1/N, where N is the number of focused spots per wavelength.
FIG. 3 illustrates an example of a prior art virtually imaged phased array (commonly referred to as a VIPA). The VIPA illustrated in FIG. 3 includes a rectangular glass plate 100 that has a 100% reflective coating 101 on a first side and a partially reflective coating 102 on an opposing side. Light enters the plate 100 below the reflective coating 101 in the form of a focused line source 105 produced by a cylinder lens 106.
FIG. 4 illustrates an operational side view of the VIPA. Input light rays 107 and 110 represent the boundaries of the line-focused input beam. The lens 106 focuses the input rays at the point 111, after which the rays diverge as the beam propagates. The focused input rays 107 and 110 are partially reflected by the coating 102 and then totally reflected by the coating 101. This reflection produces a virtual image of point 111 at location 112. The reflective process is continued, producing additional receding virtual images at locations 115 and 116. This process produces virtual images of the line source that recede away from the input side of the glass plate (i.e., to the left of element 100 in FIG. 3) and that are distributed in the y direction.
FIG. 5 illustrates an example of the optical distribution of the diverging light beams at the exit surface of the glass plate. The numbered circles 117, 120 and 121 are intended to call the reader's attention to the areas of interest on the coated surface 102. The circles represent the size of the light beams exiting the plate. The line focused input is illustrated at point 111, the twice reflected light that has diverged due to propagation is illustrated at circle 117, the four-times reflected light that has diverged even more is illustrated at circle 120, and the six-times reflected light that has diverged even more is illustrated at circle 121. In the example illustrated in FIG. 5, after more than six reflections the diverging light beams overlap and blend into an interference pattern.
As shown in FIG. 5, each of the successive beams 117, 120 and 121 that exits the surface 102 of the VIPA plate 100 appears to originate from the line source images 112, 115 and 116, respectively, as shown in FIG. 4. The light from these images diverges as the light propagates inside the glass plate 100. Part of the light from each image exits the plate through the partially reflective coating 102. The exiting beams interfere with each other. The interference pattern is collected by a lens 122 and focused onto a 1-dimensional detector array 125 (FIG. 3).
In the illustrated VIPA the beams diverge and overlap at the partially reflective surface 102. This overlap effect makes weighting the individual virtual sources possible only in an area-average sense, thus limiting the degree to which the channel filter shape can be tailored.
The VIPA requires a line-focused input. The line-focused input means that the VIPA may provide a relatively compact device for coarse channelization (i.e., wide channel spacing on the order of one hundred GHz). However, the line-focused input makes the VIPA impractical for fine channelization (i.e., narrow channel spacing on the order of one GHz) due to the fact that a thicker plate is needed, which would result in excessive beam divergence and overlap at the exit surface.
Thin film interference filters require a different coating design to separate each wavelength component of an input beam. A stacked thin-film multiplexer is taught in U.S. Pat. No. 6,111,474. Since the interference filters produced by thin film coatings tend to have relatively wide passbands, they cannot achieve high resolution (twenty-five GHz or finer). In addition, stacking thin-film filters such as the device in U.S. Pat. No. 6,111,474 produces loss that effectively limits the number of channels.
In the classical diffraction grating, as used for WDM channelization applications, the dispersive element is a grating embedded in a monoblock of silica. The input optical fibers may be directly fixed to the block. The grating may comprise several tens of grooves to several thousands of grooves per millimeter. The grooves may be fabricated, for example, by etching with a diamond tool or by holographic photo-exposure. The grating diffracts incident light in a direction related to the wavelength of the light, the groove spacing, and the incidence angle. Consequently, an incident beam comprising several wavelength components will be angularly separated into different directions. Conversely, a reverse mode of operation is possible in which several beams of different wavelengths coming from different directions may be combined (multiplexed) into the same output direction.
Diffraction gratings of reasonable size do not have sufficient resolution for HWDM. For example, for a channel separation of 1 GHz, a grating would have to be significantly longer than twelve inches to achieve an adequate channel filter shape. They also have high optical insertion loss, making them inefficient for use in high-resolution WDM systems.
Diffraction gratings tend to produce undesirable polarization effects. The diffraction efficiency depends on the polarization of the incident beam. For a given wavelength, this effect increases when the groove spacing decreases. Typically this effect is small when the groove spacing is at least ten times larger than the wavelength, but the effect becomes important when the groove spacing is reduced to a few wavelengths in order to achieve higher angular dispersions.
The prior art arrayed waveguide grating (AWG) is an integrated-optic passive delay line device that performs channelization. The AWG is designed to increase the resolving power, i.e. the fine splitting of the wavelengths, over that obtainable with classical diffraction gratings. Around 1990, AWGs were first proposed both by Takahashi and others in Japan, and by Dragone and others in the United States. Arrayed waveguides gratings increase the optical path difference between the diffracting elements by using a waveguide structure that is equivalent to the well-known Michelson echelon gratings in classical optics. AWGs have the inherent disadvantage of a much smaller free spectral range that limits the total number of channels and increases the near-end crosstalk that affects bidirectionality. It is difficult to achieve resolution better than fifty GHz using an AWG. AWG devices capable of one GHz resolution would be physically large, expensive, and have very high loss.
A fiber grating is made by recording a Bragg grating inside the core of a single-mode fiber, which is made photosensitive by doping it with germanium, for example. This grating may be used as a narrowband filter. It is important to use one grating per wavelength channel, so there is an inherent limitation on the number of channels that can be de-multiplexed with such devices due to the shear bulk of the resulting system. A primary disadvantage of a fiber grating is that it can reflect only one wavelength. An N channel system therefore requires N fiber gratings.
Optical Add-Drop Multiplexers. Techniques and devices are known for multiplexing the discrete wavelengths in DWDM transmission systems, i.e., for combining individual optical signals onto a common fiber optic waveguide. Then, the optical signals are separated again into the individual signals or channels at the opposite end of the fiber optic cable. The ability to effectively combine and then separate individual wavelengths (or wavelength bands) from a broad spectral source is of significant importance to the fiber optic telecommunications field. Similarly, this technique is important in many other fields employing optical networking devices.
As fiber optic transmissions enter and leave metropolitan and local area networks (LANs), each data-carrying wavelength is usually switched through various points along the fiber optic network. These points are known as "nodes." At node locations, optical signals can be forwarded to the next node or "dropped" towards their final destination via the best possible path. The best possible path may be determined by such factors as distance, cost, and the reliability of specific routes. In addition, specific data-carrying wavelengths may be recombined or "added" to the multiplexed optical signal at node sites. The devices that perform these functions in DWDM network systems are called add/drop multiplexers (ADMs).
A conventional way to drop a data signal from a DWDM fiber is to de-multiplex the signal into its constituent wavelengths. Next, the light is detected using a photodetector, thus converting the signals to an electronic form (OE conversion). The electronic signal is switched and/or routed, as appropriate. The remaining signals are converted back to an optical signal (EO conversion). The optical signal is then sent down the proper fiber. During this last step, a signal can be added to the remaining signals. Such OE and EO conversion operations are both protocol and data rate dependent. These operations also require inflexible devices that are costly and difficult to upgrade as system capacity demand is increased.
Optical add/drop multiplexers (OADMs) have several significant advantages. First, OADMs cost less because they eliminate the need for much of the expensive high-speed electronics in conventional devices. Second, OADMs require smaller packaging because removing the electrical conversion step results in a reduced component count within the switches. Finally, optical devices are relatively future-proof because the optics can accommodate any bit-rate, whereas electrical devices should always be customized for the bit-rate and protocol of the signals.
Optical add/drop systems are comprised of two major subsystems. The first subsystem is the de-multiplexing and multiplexing subsystem for selecting and recombining the appropriate wavelength. The second subsystem is the add/drop apparatus for routing the wavelength to the desired optical fiber output. Existing techniques for wavelength separation from a multiplexed signal using optical architectures include thin film bandpass filters, Fabry-Perot filters, fiber Bragg or diffraction grating filters, and polarization controllers. Each of these optical filtering methods may have different forms.
Thin film bandpass filters have traditionally been used in OADM devices to select single wavelengths from a multi-channel optical signal. Although such filters have good channel isolation, they tend to exhibit a transmission light loss of approximately 10%. Such filters are also highly temperature-sensitive. Further, they often operate in only one direction. In addition, such filters are limited to a single, fixed wavelength. Thus, to construct a multi-channel OADM device, multiple filters must be combined. This results in increased complexity, optical loss, and cost.
In U.S. Pat. No. 5,751,456, Koonen disclosed an example of a solution to some of these issues wherein a narrow-bandpass Fabry-Perot filter was utilized in a bi-directional OADM. As Fabry-Perot filters can have a bandpass of 1-2 nm or less, they can provide better isolation and lower loss factors than other thin film interference filters. FIG. 6 illustrates an example of the Koonen prior art. The device illustrated in FIG. 6 is limited in that it can add/drop only a single wavelength. As illustrated in this example, a circulator 127 is used to pass four wavelengths λ1-λ4 to a Fabry-Perot filter 130. Filter 130 selects one wavelength λ1 for continuation on to a receiver 131. The remaining wavelengths λ2-λ4 are reflected by the filter 130 back to circulator 127. A transmitter 132 sends a new wavelength λ1′ to the filter 130. The new wavelength λ1′ is multiplexed with the original wavelengths λ2-λ4. The resulting wavelength is returned to the circulator 127 for continuation
The issue of such interference filter-based ADM devices being fixed in nature has been addressed in the prior art with the invention of "tunable" filters. Tunable filters can be selectively tuned to different wavelengths within a multi-channel optical signal. However, tuning thin-film optical filters requires that either the incident optical beam be repositioned with respect to the filter surface or that the filter itself be repositioned with respect to the input beam. Both scenarios require mechanical movement of components such as actuators or stepper motors. The mechanical movement of these components makes these OADM devices active in nature. This results in increased complexity and cost.
FIG. 7 illustrates an example of a prior art tunable filter as disclosed in U.S. Pat. No. 6,292,299. FIG. 7 illustrates the mechanical nature of selecting a single wavelength. FIG. 7 also illustrates the potential complexity of matching the add/drop wavelengths to output fibers. An electronic controller 135 controls an x-z filter positioner 138 to direct an optical filter 136 to move in the x and z directions to a specific location where a single wavelength from an incoming fiber 137 is intercepted. Once selected, the wavelength is passed or dropped to a fiber 140. The unselected wavelengths are reflected to continue on a fiber 141. A wavelength can be added from fiber 140 at the same time. As can be seen from the example illustrated in FIG. 7, the electronic controller should be mechanically manipulated to select a single wavelength.
Diffraction gratings and fiber Bragg grating filters (FBGs) offer alternative means of selecting and isolating single wavelengths from a multi-channel input beam in OADM devices. Diffraction gratings can be used in an OADM device to separate an input beam into its components in one direction, and recombine the wavelengths in the reverse direction. However, with diffraction grating systems, the component count can rise rapidly. Lenses, collimators, and focusing optics are required to refine, direct, and couple the light beams into fibers.
Because FBGs are constructed from optical fibers, rather than individual thin-film filter substrates, they allow for all-fiber systems to be constructed. Fiber Bragg grating systems offer high levels of selectivity. However, they are limited in that several fiber gratings must be combined, along with optical circulators, in order to handle a multiplexed optical signal with a high channel count. The result can be a very large device with a high component count, increased complexity, and a higher cost. In addition, the combination or cascading of multiple-fiber Bragg gratings can significantly reduce signal strength as the insertion loss of multiple devices is compounded throughout the system.
A recent development in the area of wavelength selectivity and separation of multiplexed optical signals has been the utilization of polarization controllers. As disclosed by U.S. Pat. No. 6,285,478, polarization-controlling elements can also be used within OADM devices to separate a multi-channel WDM input signal into odd and even channels. This is done, for example, by splitting the signal into its vertically and horizontally polarized components. When combined with birefringent beam displacing optics, the separated signals can then be directed to appropriate output paths. This method provides an add/drop device that can accommodate the high channel counts and narrow channel spacing of current DWDM networks, where channels are separated by 50 GHz or less. This channel-separation technique is expandable and can adapt to increasing channel counts. However, this technique is subject to very high optical component count. Included in the optical component count are multiple polarization controllers, birefringent elements and beam splitters. These components are required to manipulate dense multiplexed signals. Assembling and aligning these optical components within a device can be extremely expensive. This is particularly true when high levels of precision are required. FIG. 8 illustrates an example of the prior art requirement for a large number of components to separate eight channels.
With the continued development of WDM fiber optic systems, it is becoming increasingly important to control the direction of wavelengths to desired output ports (i.e., routers). It is likewise important to permit a new signal to replace an existing signal at a specific wavelength (i.e., add/drop) using optical systems. Furthermore, since the development of DWDM sends hundreds and even thousands of wavelengths through a fiber, the ability to selectively control a single or several wavelengths without affecting the other wavelengths is very important. This ability is important because the optical to electrical to optical conversion process is expensive and uses significant power as well as space. In particular, optical add/drops are important components in WDM regional-access ring or star networks to provide broadband access to users.
Prior art optical subsystems that perform add/drop functions include mirrors and micro-electro-mechanical systems (MEMS) using movable and fixed micro-mirrors and etalons. These micro-mirrors are a reconfigurable switching matrix capable of directing the output of wavelengths in multiple directions.
It is also known in the art to use a tunable optical add/drop that employs an optical filter device, such as a multi-layer dielectric wedge filter. This technique is successful using tunable Mach-Zehnder interferometers, acoustic tuning filters, tunable thin film interference filters, tunable Fabry-Perot etalons, and tunable Fabry-Perot interferometers. However, it is only possible to interact with a single wavelength at one time using this technique.
A wedged etalon with an actuator that moves the etalon to the position of the channel to be added or dropped may also be employed. However, this system can only accommodate adding or dropping a single channel simultaneously. Further, the added or dropped channel must be at the same frequency.
Accordingly, in light of the limitations of the prior art, it is desirable to have an optical add/drop system which is simpler then those known in the art, has low optical loss characteristics, operates on single or multiple channels, and is capable of adding or dropping finely-spaced channels with separations as close as 50 MHz.
Optical Code Division Multiple Access. Code-Division Multiple Access (CDMA) is a spread spectrum encoding method that enables many users to simultaneously transmit separate signals over the same spectral bandwidth. In CDMA, a data signal of bandwidth D is modulated by a higher rate coded waveform of bandwidth C. The resulting signal has a bandwidth of D+C, which, for large ratios of C to D is approximately equal to C. The ratio C/D is commonly referred to as the spreading ratio, the spreading gain, or the processing gain. The intended receiver modulates the received signal by an exact replica of the coded waveform to remove the code modulation and recover the data signal. The coded waveform may be any of many types but the primary one of interest here is a binary coded bi-phase modulation, also referred to as binary phase shift keying, or BPSK, modulation. The signaling rate of the coded spreading waveform is commonly called the chip rate.
The number of users that could occupy the same spreading bandwidth C is regulated by the processing gain of the high rate modulation, i.e., the ratio of the modulation rate to the data rate, C/D. In theory, this ratio is equal to the number of users. But in practice, due to the need to maintain low cross-correlation properties between the high rate sequences, the number of usable sequences, hence users, is somewhat less than the processing gain.
There has been considerable interest within the communications industry in recent years on the potential for Optical CDMA (OCDMA) to make more efficient use of the bandwidth available in fiber optic communications systems. The main problem with fiber optic systems is the inefficient nature of dedicated bandwidth allocation architectures. Many communications, particularly Internet Protocol communications, are extremely bursty. Therefore, as more users are added and depart, the bandwidth resource must be dynamically re-allocated. This may not be feasible.
The traditional method of signal processing used to address this problem in fiber optic systems is a frequency domain multiplexing protocol called wavelength division multiplexing (WDM). In WDM, the optical efficiency is increased by the creation of a plurality of wavelengths, each carrying a separate signal. Still, the number of wavelengths or channels that can be supported is constrained by the stability of each discrete wavelength and the tuning range of the diode laser. OCDMA is suggested as an alternative or in conjunction with WDM to increase the efficient use of fiber communications systems. The primary advantage of code division multiple access, as opposed to other optical multiple access or multiplexing techniques, is the reduced requirement on coordination of exact timing and frequency allocations to the multiple users. In OCDMA, all of the users occupy the same time and frequency space and are precisely separated using their specific chipping code, a much simpler task.
Earlier inventions have been described to implement OCDMA, which can be grouped in three categories: simple spectral domain methods, complex spectral domain methods, and time-domain based systems.
In a spectrally encoded OCDMA system, each user is identified by a particular pattern of spectral (frequency) components. These patterns can be encoded with a simple periodic optical filter, as disclosed by Pfeiffer in U.S. Pat No. 5,784,506 and U.S. Pat. No. 6,215,573. In U.S. Pat. No. 5,784,506, Pfeiffer discloses an electronic decoding of the spectral encoded signal. In U.S. Pat. No. 6,215,573, Pfeiffer discloses an optical receiver with filtering characteristics for decreasing cross talk. In U.S. Pat. No. 5,867,290, Dutt et al. disclose a system whereby the spectrally encoded signal is created by selectively attenuating certain wavelengths from a broadband light source.
Typical OCDMA proposed systems use unipolar codes that use plus ones (+1) and zeros (0), generally called on-off keying. Such codes are used because they are easily optically detected. This inherently reduces optical efficiency because a "0" code removes or discards available light. To increase optical efficiency, it is far better to use bi-polar codes, i.e. those consisting of plus one (+1) and minus one (−1). However, detection of bi-polar codes requires detection in the presence of an unmodulated reference beam, i.e., coherent detection. Coherent detection is difficult and expensive to achieve in a practical system.
The Dutt system is not very optically efficient due to the use of unipolar codes and it has a limited code set. The Pfeiffer systems are more efficient but also have a limited code set resulting in a limited number of users.
In U.S. Pat. No. 5,760,941, Young et al. disclose a method and system for transmitting bi-polar codes using pairs of unipolar codes. This method requires each of the pairs of unipolar codes to be separately transmitted on separate fibers or opposite polarization.
In U.S. Pat. No. 6,236,483, Dutt et al. disclose a system based upon Young U.S. Pat. No. 5,760,941 with the addition of the use of sub-band encoding to divide the spectra into sub-groups.
Both the Dutt and Young systems are based upon attenuating the optical carrier using unipolar codes. This scheme cannot achieve optimal optical efficiency.
In U.S. Pat. No. 6,313,771, Munroe et al. disclose an OCDMA system based upon use of fiber Bragg gratings to encode a short pulse into a sequence of plus one (+1) and minus one (−1) coded pulses, i.e., optically efficient bi-polar codes. In order to overcome inherent limitations of fiber Bragg gratings, this method specifically uses two stages of encoding to achieve a relatively long encoding pattern. This multi-stage system is complex to build and relies on two fiber Bragg gratings. This is less optically efficient than using a single grating.
In U.S. Pat. No. 6,292,282, Mossberg et al. disclose a time wavelength multiple access communication system whereby the optical signal of a user is separated into a small number of spectral bands. The resulting bands are transmitted in a specific time-sequence order. A decoder for a specific user removes the time sequencing of the spectral bands such that a signal from the intended user is time-aligned. The number of frequency bands, and hence, the number of available codes, and therefore users, is limited in a practical system.
In summary, the existing methods of OCDMA are not very efficient which yields a lower number of potential users. Furthermore, they rely upon grating technologies that have limited resolution. Lastly, some of the more efficient methods are complex and costly to manufacture.
Wavelength Stabilization and Locking. Wavelength division multiplexing (WDM) systems communicate multiple signals through a single optical fiber by utilizing a different optical wavelength for each carrier signal. In the multiplexing process, an information signal is combined with a carrier signal and multiple such combined signals, called channels, are multiplexed into a single optical fiber for simultaneous transmission. De-multiplexing involves the separation of channels into individual data-carrying signals. The International Telecommunications Union has developed standards for WDM with predefined frequencies at channel spacings of 100 GHz (or 0.8 nm). By reducing the channel spacing, increased numbers of data-carrying channels may be added. Because of ever-increasing bandwidth requirements, telecommunications carriers need more channels of information and narrow channel spacings of 25 GHz and below are being intensely studied.
For a number of reasons, practical systems utilizing 25 GHz and narrower spacing are developing slowly. In particular, maintaining increasingly narrower channel spacing demands extreme precision in the frequency stability from the source laser—a precision that is not reliably achievable. The wavelength of most lasers has a tendency to drift, and if the channel spacing is sufficiently close, crosstalk is introduced as the wavelength of one channel drifts closer to an adjacent channel. Factors such as equipment aging, device tolerances, power source fluctuations, and temperature changes all serve to complicate the problem.
It is well known that the frequency stability of WDM systems is highly temperature dependent. Temperature changes cause variations in the optical devices that have a direct impact on optical properties, for example, by expanding or contracting a material to alter its physical dimensions or by changing the index of refraction of a material. The likely result is that the frequency of interest "drifts" relative to the target or detector with a corresponding degradation of the signal. Active compensation systems employ heater/coolers to maintain the components at a constant temperature. These devices effectively solve the problem of frequency drift, but at relatively high cost and with a loss of overall efficiency due to the power requirements.
As a result of this problem, prior art solutions have been found that attempt to eliminate or minimize temperature-induced frequency drift. The various alternative devices to which this type of solution is applied are commonly referred to as wavelength references, wavelength lockers, or wavelength monitors. These devices vary in size, complexity and cost. Among the best performing wavelength lockers, from the standpoint of size, accuracy and cost, are those utilizing etalons.
A well-known etalon-based optical device for performing wavelength locking is a Fabry-Perot etalon, an example of which was previously illustrated and described with respect to FIG. 1. When used in a wavelength locker, a portion of the modulated laser output beam is commonly split. One segment of the beam is routed directly to an output while a second segment first passes through the etalon before reaching a detector. Only the single wavelength λ exits the etalon and the device is designed to ensure that λ is the "lock" wavelength. Tuning is commonly achieved by physically rotating the etalon slightly during device fabrication. This position, and hence the lock wavelength of the device, is permanent once construction of the device is completed. Once the device is initially designed and calibrated, it defines a precise fixed relationship between the two signals provided to the detector. Variation of the relationship resulting from laser wavelength changes is monitored and the laser driver input is altered via a feedback loop to minimize detected differences. A more complete description of such a system may be found in the technical article entitled "Wavelength Lockers Make Fixed and Tunable Lasers Precise," WDM Solutions, January 2002, p. 23.
The Fabry Perot etalon does not serve well as a WDM channelizer due to the difficulty in obtaining high optical throughput efficiency. If the input beam is divergent, e.g., the direct output of an optical fiber, then the output pattern for a given wavelength is a set of rings. Multiple wavelengths produce nested sets of concentric rings. It is difficult to collect this light efficiently and concentrate it at multiple detector points, or couple it to multiple output fibers, especially while maintaining the separation of wavelength components that the etalon has produced. If the input beam is collimated, e.g., the collimated output of an optical fiber, then the beam can be fanned over a narrow range of angles to produce only a single-order output (e.g., m=+1) for each wavelength of interest. This fanning makes it easy to concentrate the output light at multiple detector points or fibers, but there is inherently high loss.
U.S. Pat. Nos. 5,428,700, 5,798,859 and 5,825,792 to Hall, Colbourne et al, and Villeneuve et al. respectively all reveal laser stabilization systems employing Fabry-Perot etalons of the type described above.
U.S. Pat. No. 6,345,059 to Flanders describes a highly complex laser wavelength compensation system in which the tuned wavelength is maintained by controlling the optical length of the laser cavity. This disclosure states that the wavelength precision of this system is 0.1 nm accuracy, which equals 12.5 GHz channel spacing.
U.S. Pat. No. 6,289,028 B1 to Munks, et al. discloses the simultaneous monitoring, stabilizing, tuning, and control of laser source wavelengths with the aid of an error feedback loop. A rotatable optical filter provides wavelength tuning by tilting the filter in accordance with feedback signals.
An alternative type of wavelength locking is taught in PCT application IPO Number WO 01/35505 A1 to Sappey. A one or two-dimensional array of lasers at different spatial positions within an external resonating cavity illuminates a diffraction grating. Opposing the diffraction grating is either a mirror (in the one-dimensional case) or a second grating (in the two-dimensional case). Light fed back to the lasers causes the laser to lock to the wavelength of the feedback, resulting in each laser lasing as a discrete, well-controlled wavelength. Each channel of a WDM system requires its own stabilized laser.
Significant channel spacing reductions in WDM systems will require substantial improvements in wavelength stability, with the corresponding precision ability to monitor, tune and lock those wavelengths as needed.
Flat-Top Filter Shape. A common identifier of signal filtering capability for a WDM device is called the passband. The shape of the passband determines the ability of the filter to efficiently separate channels. The most desirable passband shape, a horizontal top and vertical sides, would discriminate all of the light energy corresponding to a desired channel and would pass no other light energy from, for example, an adjacent channel. It is currently impossible to obtain such a filter in practice, but the more closely a device approximates this ideal the better its signal processing capability becomes. Prior art references are replete with references to "top hat" filters in reference to efforts to approximate the ideal filter shape.
Grating-based technologies are effectively limited to 50 GHz resolution. They commonly obtain a flat-top response by first widening and then flattening the Gaussian filter shape, as is described in U.S. Pat. No. 6,298,186 to He. An adverse effect of this technique is an approximate 3 dB loss in signal strength because of the abnormal shape of the resulting passband.
Polarization based devices are known to provide better peak flatness and isolation for narrow channel spacings than can be obtained with interferometric devices as is taught in U.S. Pat. No. 6,208,444 to Wong.
The present invention resolves many of the disadvantages in the prior art by providing more nearly ideal flat-top passbands at resolutions less than 50 GHz.
Interleaving and De-interleaving. An interleaver is an optical device in a wavelength division multiplexing fiber optic network that separates (de-interleaves) and combines (interleaves) alternating channels, i.e., even and odd channels. U.S. Pat. No. 6,275,322 describes a well-known architecture based upon a Michelson interferometer combined with a Fabry-Perot etalon. FIG. 10, when considered as having the input at Port A, illustrates an example of the functional operation of a typical de-interleaver. Multiplexed signals λ1, λ2, λ3, . . . enter interleaver 169 with a channel spacing of 100 GHz. Port B receives odd signals λ1, λ3, λ5, . . . with a channel spacing of 200 GHz. Port C receives even signals λ2, λ4, λ6, . . . , also with a channel spacing of 200 GHz. FIG. 10, when considered as having the inputs at Ports B and C, illustrates an example of the functional operation of a typical interleaver. Odd signals as described above enter at Port B synchronously with even signals entering at Port C. Interleaver 169 combines the signals to produce an output signal containing channels λ1, λ2, λ3, . . . with 100 GHz channel spacing. The channel spacing is always tied to the commercial telecommunications standard such as 100 GHz, 50 GHz, 25 GHz, etc., associated with DWDM signals. Interleavers work in this situation because even and odd channels have a frequency spacing that is double the frequency spacing for the combined set of channels. For example, in a 100 GHz spaced network, the odd channels are spaced by 200 GHz and the even channels are spaced at 200 GHz. By separating the even and odd channels, devices that are designed to work with 200 GHz spaced channels can interface with 100 GHz network devices.
By stacking interleavers, telecommunication carriers are able to improve bandwidth utilization and increase channel counts. Normally a fiber with channels spaced at 100 GHz carries 40 channels. Prior art FIG. 9 illustrates an example of how a carrier can increase this channel count by a factor of eight using seven interleavers. It is apparent from FIG. 9 that the prior art interleaver architecture is relatively complex and requires multiple devices, which introduces undesirable power losses into the system and increases device size and costs.
U.S. Pat. No. 6,275,322 B1 to Tai describes a prior art interleaver having a Michelson interferometer combined with a Fabry-Perot etalon. U.S. Pat. Nos. 6,212,313 B1 and 6,208,444 B1 describe optical interleavers that use the polarization property of light to separate odd and even channels. Their functional outputs are limited to two ports having one polarity or another.
There is a need for an optical interleaver suitable for the high data rate requirements of DWDM signal processing, that has the structural simplicity of a single device, and that does not have other disadvantages found within the prior art.
Optical Spectrum Analyzer. High-resolution spectrometers, or optical spectrum analyzers (OSAs), are used in a wide variety of optical applications. In particular, they are very important in fiber optic communication systems such as WDM where transmission power and laser performance is important to transmit information-carrying wavelengths. The higher the resolution of the OSA, the greater is the ability to monitor the fiber optic carrier.
Most all OSAs are based upon diffraction gratings. The gratings are many closely spaced grooves that scatter the incident light. The light scattered from each of the grooves creates an interference pattern some distance away from the grating that is used to obtain power estimates. In order to increase the ability to resolve the far-field pattern, the number of grooves must be increased as well as the spacing between the grooves must become more closely spaced. Although this can be accomplished, the size of the diffraction gratings and the expense of making such a large device creates a practical limit on the resolution of diffraction-grating based OSAs at 30 to 50 picometers. For example, U.S. Pat. No. 66,262,879 B1 claims a resolution of 4 GHz, which is equivalent to 32 picometers.
In a WDM system, the wavelengths of light being measured are on the order of 1.5 microns and they are spaced 50 to 100 GHz apart. Because of the high cost of laying optical fibers, achieving greater efficiency using existing fiber resources has become increasingly important. One trend in this direction is decreasing the spacing between wavelengths to 25 GHz, 12.5 GHz and less However, as channel spacing decreases common WDM network problems such as transmitter wavelength drift, filter concatenation, and signal distortion can more easily cause cross-talk between these closely-spaced channels. This makes it very important to continuously monitor all the channels in a functioning WDM system spaced at 25 GHz or less.
Integrated Optics. As with many technologies today, a principal goal of fiber optic telecommunication component manufacturing is to create WDM devices that are smaller, easier to fabricate, more reliable, and significantly cheaper than conventional products. To this end, multiplexer/demultiplexers, modulators, optical add/drop multiplexers (OADM), wavelength switches, and channel-monitoring equipment with integrated optical (IO) packaging and planar structures are increasingly populating the WDM component industry, including arrayed waveguide gratings (AWG) devices and planar lightwave circuits (PLC).
Several companies commercially produce integrated optic WDM devices, including Nortel, Lucent Technologies, JDS Uniphase, Corning, Bookham, and others, which are based on AWG and planar technologies. These devices perform a variety of functions within fiber optic networks and are becoming increasingly important as fiber optic systems and networks are required to handle larger volumes of data and voice traffic at faster rates. However, current WDM integrated optic technologies suffer from the same channel spacing and resolution limitations as their bulk optic counterparts. Wavelength separation closer than 50 GHz, within the ITU DWDM grid, has remained illusive to current planar and hybrid device technologies.
As is the case with their bulk counterparts, integrated optic (IO) WDM multiplexer and demultiplexer devices require optical elements to combine and separate the multiple wavelengths of the input signal. Many of the methods of wavelength separation used in bulk WDM demultiplexing equipment have also been incorporated into IO devices including diffraction gratings, AWGs, thin film filters, and Fabry-Perot interferometers. The operation, advantages, and disadvantages of these, and other dispersive methods, are addressed elsewhere in this patent application, and can be applied to integrated optical devices, as well.
A standard method of fabricating IO WDM demultiplexers/multiplexers devices is to place an AWG between a diffraction grating and a focusing lens. In such a configuration, the diffraction grating disperses the wavelengths, and lenses are used to couple discrete wavelengths into individual optical fiber. Examples of a planar 10 wavelength demultiplexers/multiplexer based upon this fundamental AWG structure are described in U.S. Pat. No. 5,799,118, in EP 0 984 304, and in U.S. Pat. No. 6,404,946. Although integrated optical diffraction grating-based devices, such as the aforementioned examples, are being used in WDM systems, their resolution is limited. An IO WDM device with a diffraction grating and an AWG would need to be very large and expensive to have sub-50 GHz channel resolution, and would suffer from very high loss.
An IO multi/demultiplexer that uses an echelon grating is described in U.S. Pat. No. 4,715,027, wherein the grating is formed on a dielectric substrate by photolithographic and etching techniques. In this case, the echelon grating could be made either wavelength-transmissive or reflective, depending on fabrication methods. This type of grating overcomes the size-dependency limitations and fabrication difficulties of other diffraction grating-based WDM devices. However, this device cannot produce the narrow channel spacing and high channel counts of an OTDL-based integrated optical demultiplexer.
In U.S. Pat. No. 4,279,464 Colombini describes and integrated optical wavelength demultiplexer that improves upon diffraction grating-based IO WDM demuxes by replacing the grating with a dispersive thin film prism within a multi-layer stack deposited onto a silicon wafer. By using a thin-film prismatic layer to angularly disperse and separate the wavelengths, the proposed device would have lower insertion losses and higher channel capacity. However, the fabrication of this IO demultiplexer could be extremely difficult and expensive due the precision required in the thin film deposition process to lay down the prism and lens layers, as well as the nature of the stack materials.
FIG. 57 shows a prior art a planar waveguide integrated optical multiplexer and demultiplexer device, as disclosed by Bhagavatula in U.S. Pat. No. 6,111,674. In this device, a multiple-wavelength input signal is demultiplexed using a Fabry-Perot thin film stack consisting of alternating partially reflective and transmissive layers. The angularly dispersed wavelengths emerge from the "optical path length difference generator" and are individually coupled to a fan-shaped output array of waveguides by means of a focusing lens. This device could be fabricated as either a planar or a Hybrid IO structure. The drawback to this type of integrated optical WDM demultiplexer/multiplexer is the inherently high loss associated with the thin film wavelength-separation elements, which limits the number of channels that can be effectively demultiplexed, as well as the level of channel spacing within a DWDM system.
The OTDL technology and devices described herein allow for fabrication of WDM products with much finer wavelength channel spacing than currently possible with optical communications equipment, by operating in very narrow bands within each 100 GHz ITU DWDM channel. One can achieve data-carrying channels that are as narrow as 2.5 Hz per bit without pulse shaping, and can reach 0.8 Hz per bit with pulse shaping using OTDL technology. In practical application, this means that an OTDL device can carry sixteen OC-48 (2.5 Gbits/sec) data channels over each 100 GHz DWDM channel.
One approach for fabrication of OTDL devices is a bulk optical approach composed of discrete components with free-space optical connections, as disclosed herein and in co-pending U.S. patent application Ser. No. 09/687,029. Such a method of construction could be very labor intensive and expensive as each optical component and sub-system must be aligned and fixed in place. Maintaining important fabrication and functional tolerances can be difficult. In addition, as functionality of the bulk OTDL device is increased, so are the part count and device size. In today's WDM networks, this can be a disadvantage as component dimensions are crucial to system construction and cost.
The fundamental operation of the OTDL is similar to that of AWG technology, based on performing a Fourier Transformation of a set of time-offset signal samples. However, AWG technology relies on a set of individual waveguides, each of a different length, to create the time-offset samples, while the OTDL technology uses an optical cavity with a partially transmissive surface as an optical delay line. This method allows the creation of a larger array (more elements) of time-offset samples, and greater time delay between samples, leading to higher resolution and an increased channel count. Furthermore, the optical cavity technique affords a smaller package footprint than that of an AWG device performing an equivalent function.

Method and apparatus for optical signal processing using an optical tapped delay line


An integral laser imaging and coagulation apparatus, and associated systems and methods that allow an ophthalmologist to perform laser retinal surgical procedures with an integral laser imaging and coagulation apparatus disposed at a first (i.e. local) location from a control system disposed at a second (i.e. remote) location, e.g., a physician's office. In some embodiments, communication between the integral laser imaging and coagulation apparatus and control system is achieved via the Internet®.

As is well known in the art, various eye disorders, such as diabetic retinopathy, vascular occlusion, neovascularization and age macular degeneration, can, and in most instances will, have an adverse effect on the retina. Indeed, if not treated at the appropriate stage, noted diseases, particularly, diabetic retinopathy, can lead to severe losses in vision.
Various methods and systems have thus been developed to aid in the diagnosis of the noted eye diseases. The method often employed by eye care specialist, such as an ophthalmologist, is to examine the ocular fundus (the inside back surface of the eye containing the retina, blood vessels, nerve fibers, and other structures) with an ophthalmoscope.
The ophthalmoscope is a small, hand-held device, which, when appropriately positioned, shines light through a subject's pupil to illuminate to fundus. By properly focusing the light reflected from the subject's fundus, an examiner can observe the fundus structures.
As is well known in the art, examination of the ocular fundus can also be achieved using a fundus or slit lamp camera. Illustrative are the apparatus and systems disclosed in U.S. Pat. Nos. 5,713,047, 5,943,116, 5,572,266, 4,838,680, 6,546,198, 6,636,696, 4,247,176; 5,742,374 and 6,296,358.
Various method and systems have also been developed to treat eye disorders, such as diabetic retinopathy, glaucoma and age macular degeneration. One known method of treating the noted eye disorders, as well as retinal detachment, is laser coagulation of predetermined biological structures of the eye, such as the retina.
As is well known in the art, during laser coagulation of an eye structure, laser energy is transmitted to the structure to effect coagulation thereof. A typical laser coagulation system thus includes a laser energy or beam source, such as a beam projector, a slit image projector or lamp for forming a slit image on the eye, and observation equipment for observing the slit image and laser spot(s) in the eye. Illustrative are the laser coagulation systems disclosed in U.S. Pat. Nos. 4,759,360 and 4,736,744.
A major drawback associated with each of the noted conventional systems, as well as most known laser coagulation systems (and associated methods), is that the conventional slit lamp systems require a contact lens to neutralize the refractive power of the cornea. A contact lens is also necessary to provide a variable field of view of the retina up to 130°.
As is well known in the art, the contact lens must be appropriately positioned on the surface of the cornea and held at the desired position by the specialist, e.g., surgeon, while looking through the slit lamp microscope.
There are several drawbacks associated with the use of a contact lens during laser coagulation. A major drawback is that the use of a contact lens requires topical anesthesia and a dilated pupil for laser application. As is well known in the art, a contact lens can, and in many instances will, cause corneal abrasion on an anesthetized cornea.
A further drawback associated with conventional laser coagulation procedures is that the laser procedures are dependent on the steadiness of the physician's hands and the subject's head.
Another apparatus that is often used for laser energy delivery to the peripheral retina is the indirect ophthalmoscope. Use of the indirect ophthalmoscope requires a physician to hold an appropriate convex lens in front of the eye (pupil) with one hand to focus the laser beam on the retina, while the eye is indented with another hand to bring the peripheral retina into the field of view for laser application.
Although laser delivery with an indirect ophthalmoscope eliminates the need for a contact lens, there are still drawbacks and disadvantages associated with use of an indirect ophthalmoscope, A major drawback is that during laser delivery (and, hence, coagulation of a desired eye structure), the ophthalmoscope is often carried on the physician's head for 30-60 mins. This extended period causes extreme fatigue for the physician.
The indentation of the eye for the extended period is also very unpleasant for the subject or patient.
A further drawback associated with the use of an indirect ophthalmoscope for laser coagulation is that the indirect ophthalmoscope does not provide a retained record or documentation for future evaluation. Further, in most instances, the subject typically requires subsequent fundus photography.
It would thus be desirable to provide non-contact systems and methods for laser coagulation of eye structures to treat eye disorders
It is therefore an object of the present invention to provide non-contact systems and methods for laser coagulation of eye structures that substantially reduce or overcome the noted drawbacks and disadvantages associated with conventional contact-based laser coagulation systems and methods.
It is another object of the present invention to provide non-contact apparatus, systems and methods for laser imaging and coagulation of an eye structure.
It is another object of the present invention to provide non-contact apparatus, systems and methods for laser imaging and coagulation of the retina and its periphery to treat retina and choroideal disorders and/or diseases.

This patent is subject to a terminal disclaimer.

Laser coagulation of an eye structure from a remote location


A process for preparing lactide or glycolide from a lactic acid oligomer or glycolic acid oligomer is disclosed where the molecular weight of the synthesis reactor residue is controlled to no more than 1.2 times that in the feed. The process is carried out at 130.degree. to 280.degree. C. and preferably 180.degree. to 210.degree. C. using from 1 to 6 weight percent catalyst in the oligomer feed to the synthesis reactor. The catalysts are tin or tin compounds, yttrium or rare earth metal compounds, or antimony compounds which are known as alphahydroxycarboxylic acid cyclic dimerization or polymerization catalysts.

1. Field of the Invention
Polylactide and polyglycolide are biodegradable polymers which are manufactured commercially. The monomer used is lactide or glycolide which are cyclic dimers of lactic acid or glycolic acid and which are prepared from lactic acid or glycolic acid.
2. Prior Art
U.S. Pat. No. 5,023,349 discloses a process for the rapid conversion of oligomers of alpha-hydroxycarboxylic acids, esters or salts thereof to cyclic dimer esters in high yields by rapidly passing an inert gas through the reaction mixtures at a temperature such that the cyclic dimer is rapidly removed from the reaction mixture as it is formed. The process uses 0.1 to 1.5% and preferably 0.3 to 0.9% stannous octoate catalyst.
U.S. Pat. No. 5,053,522 discloses heating lactic acid, glycolic acid, or polylactic or polyglycolic acid of molecular weight 400 to 2,000, preferably 500 to 800, at 130.degree. to 230.degree. C., preferably 180.degree. to 200.degree. C., in the presence of 0.05 to 1.0 weight percent, preferably 0.1 to 0.8 weight percent of a tin catalyst to form lactide. The lactide formed is distilled off and additional polylactic acid is fed in continuously or batchwise.
The higher molecular weight oligomer produced by the presently used processes requires treatment to lower its molecular weight before it can be recycled to the lactide or glycolide preparation step. The need for this treatment to lower the molecular weight of the oligomer is a necessary part of the conventional lactide or glycolide production.
This high molecular weight material presents two problems. First, if the molecular weight is allowed to go too high, the viscosity increases to the point where the material becomes intractable. Second, to prevent yield loss, this high molecular weight material must be re-hydrolyzed and recycled.
Dilution is a technique which can be used to control molecular weight of the oligomer remaining in the reaction mixture after cyclic dimer production. The reactions which produce cyclic dimer are uni-molecular whereas the dehydration reactions are bi-molecular. Thus the rate of dimer production is linearly proportional to oligomer concentration while dehydration is proportional to the square of the oligomer concentration. Reducing the concentration of monomer in the reactor by one half would lower the dimer production rate by one half but reduce the rate of molecular weight increase of oligomer by one half squared or one quarter. At present this is the only method known to limit the increase in molecular weight of the oligomer remaining in the reactor and this method has only marginal success. Dilution however reduces productivity and thus increases costs.

Process for the synthesis of lactide or glycolide from lactic acid or glycolide acid oligomers


Antibodies that specifically bind to toxins of C. difficile, antigen binding portions thereof, and methods of making and using the antibodies and antigen binding portions thereof are provided herein.

Clostridium difficile (C. difficile) is a gram-positive bacterium that causes gastrointestinal disease in humans. C. difficile is the most common cause of infectious diarrhea in hospital patients, and is one of the most common nosocomial infections overall (Kelly et al., New Eng. J. Med., 330:257-62, 1994). In fact, disease associated with this pathogen may afflict as many as three million hospitalized patients per year in the United States (McFarland et al., New Eng. J. Med., 320:204-10, 1989; Johnson et al., Lancet, 336:97-100, 1990).
Treatment with antibiotics such as ampicillin, amoxicillin, cephalosporins, and clindamycin that disrupt normal intestinal flora can allow colonization of the gut with C. difficile and lead to C. difficile disease (Kelly and Lamont, Annu. Rev. Med., 49:375-90, 1998). The onset of C. difficile disease typically occurs four to nine days after antibiotic treatment begins, but can also occur after discontinuation of antibiotic therapy. C. difficile can produce symptoms ranging from mild to severe diarrhea and colitis, including pseudomembranous colitis (PMC), a severe form of colitis characterized by abdominal pain, watery diarrhea, and systemic illness (e.g., fever, nausea). Relapsing disease can occur in up to 20% of patients treated for a first episode of disease, and those who relapse are at a greater risk for additional relapses (Kelly and Lamont, Annu. Rev. Med., 49:375-90, 1998).
C. difficile disease is believed to be caused by the actions of two exotoxins, toxin A and toxin B, on gut epithelium. Both toxins are high molecular weight proteins (280-300 kDa) that catalyze covalent modification of Rho proteins, small GTP-binding proteins involved in actin polymerization, in host cells. Modification of Rho proteins by the toxins inactivates them, leading to depolymerization of actin filaments and cell death. Both toxins are lethal to mice when injected parenterally (Kelly and Lamont, Annu. Rev. Med., 49:375-90, 1998).
C. difficile disease can be diagnosed by assays that detect the presence or activity of toxin A or toxin B in stool samples, e.g., enzyme immunoassays. Cytotoxin assays can be used to detect toxin activity. To perform a cytotoxin assay, stool is filtered to remove bacteria, and the cytopathic effects of toxins on cultured cells are determined (Merz et al., J. Clin. Microbiol., 32:1142-47, 1994).
C. difficile treatment is complicated by the fact that antibiotics trigger C. difficile associated disease. Nevertheless, antibiotics are the primary treatment option at present. Antibiotics least likely to cause C. difficile associated disease such as vancomycin and metronidazole are frequently used. Vancomycin resistance evolving in other microorganisms is a cause for concern in using this antibiotic for treatment, as it is the only effective treatment for infection with other microorganisms (Gerding, Curr. Top. Microbiol. Immunol., 250:127-39, 2000). Probiotic approaches, in which a subject is administered non-pathogenic microorganisms that presumably compete for niches with the pathogenic bacteria, are also used. For example, treatment with a combination of vancomycin and Saccharomyces boulardii has been reported (McFarland et al., JAMA., 271(24):1913-8, 1994. Erratum in: JAMA, 272(7):518, 1994).
Vaccines have been developed that protect animals from lethal challenge in infectious models of disease (Torres et al., Infect. Immun. 63(12):4619-27, 1995). In addition, polyclonal antibodies have been shown to protect hamsters from disease when administered by injection or feeding (Giannasca et al., Infect. Immun. 67(2):527-38, 1999; Kink and Williams, Infect. Immun., 66(5):2018-25, 1998). Murine monoclonal antibodies have been isolated that bind to C. difficile toxins and neutralize their activities in vivo and in vitro (Corthier et al., Infect. Immun., 59(3):1192-5, 1991). There are some reports that human polyclonal antibodies containing toxin neutralizing antibodies can prevent C. difficile relapse (Salcedo et al., Gut., 41(3):366-70, 1997). Antibody response against toxin A has been correlated with disease outcome, indicating the efficacy of humoral responses in controlling infection. Individuals with robust toxin A ELISA responses had less severe disease compared to individuals with low toxin A antibody levels (Kyne et al., Lancet, 357(9251):189-93, 2001).
The individual role of toxin A and toxin B in disease pathogenesis, and the role of anti-toxin antibodies in protection from C. difficile disease are controversial and may depend on the host. In humans, the anti-toxin A antibody response has been correlated to disease outcome, suggesting a requirement for anti-toxin A response for protection. This observation is in contrast with reports of disease-causing C. difficile organisms that express only toxin B, implying that toxin B can contribute to disease in humans. These toxin A-negative strains can also cause disease in hamsters (Sambol et al., J. Infect. Dis., 183(12):1760-6, 2001).

Antibodies against clostridium difficile toxins and uses thereof


A disconnect apparatus by which a cryogenic inductor can be both thermally and electrically isolated from a workload and a generator. The disconnect apparatus includes an input disconnect and an output disconnect. The input and output disconnects, when opened, thermally and electrically isolate the inductor, thereby enabling the inductor to more efficiently be cryogenically cooled. This represents a great savings in cryogenic coolant. The input and output disconnects can be simultaneously or sequentially actuated into the connected and disconnected configuration. Provision is made by which a thermal barrier can be interposed between the switch contacts of the input disconnect leading to the inductor and, the output disconnect can be evacuated to reduce heat transfer respective to the load.

It is often necessarry to cryogenically cool an electrical apparatus, such as an electrical inductor, especially an inductor used for carrying extremely high current. The amount of liquified gas employed in cryogenically cooling the inductor is directly proportional to the heat transfer mechanism associated with the inductor. It would therefore be desirable to insulate the inductor in a superior manner in order to achieve very low heat flow thereinto.
A well insulated cryogenically cooled inductor of the type having tremendous current flow therethrough necessarily entails large current flow conductors connected thereto. The conductors, being excellent electrical conductors, are also excellent heat conductors. Accordingly, under ordinary circumstances, the electrical conductors connected to the inductor represent a tremendous heat sink by which heat transfer into the conductor requires an enormous amount of coolant in order to achieve the desirable current carrying capabilities of the inductor.
It is therefore desirable to be able to both electrically and thermally isolate an inductor from both its workload as well as its generator. This is especially so when utilizing an inductor in conjunction with a homopolar generator and a workload therefor.

Electrical disconnect method and apparatus


A medical monitor, such as a fetal monitor, is provided with a code reader, e.g. a bar code reader. A manual contains clear text instructions as well as predefined codes in their correct sequential form. The instructions help the unskilled user to operate the monitor, and the actual monitor functions are triggered by scanning the codes, instead of pushing buttons, turning knobs etc. A questionnaire may also be provided to enter answers to anamnesis data. These answers, together with vital signs data, may be transmitted via telephone lines to a hospital, which makes the medical monitor ideally suited for home monitoring applications.

Operation of medical monitors is an issue of major importance. In most cases, such monitors are operated by personnel without technical education, such as nurses. The increasing complexity of state-of-the-art medical monitors, and the additional functionality provided by such equipment, as compared to prior art monitors, makes it necessary to focus on an easy-to-operate "man-machine" interface. In the field of medical monitoring, this is a particularly important problem, not only due to the time it takes to train a non-technical person, but also for reasons of patient safety. For example, if a nurse accidentally switches off the alarm capability of a medical monitor, this may well lead to the death of the patient.
There have already been attempts in the prior art to overcome the restrictions of the "knob and button" approach. For example, buttons not required for everyday operation of a monitor have been hidden behind a cover. Likewise, operation of the monitors has been automated, in order to reduce the amount of human interactions.
Another approach is the use of softkeys, i.e., keys without a fixed label, and with dynamically assigned function. One successful attempt to implement such a softkey concept in a medical monitor is disclosed in U.S. Pat. No. 5,056,059. This prior art human interface uses two- or three-level input sequences, wherein the meaning of the softkeys changes from level to level.
However, it will be noted that a softkey concept requires expensive hardware components, like a display (which is used to depict the various softkey labels). Therefore, the softkey approach is useful in applications which require an expensive monitor, and a display anyway (as is the case in the configurable monitor according to U.S. Pat. No. 5,056,059).
In contrast, the softkey concept does not meet the needs of small or stand-alone monitors which are not equipped with a display, and the necessary number of keys. It will be understood that it would be an extremely costly measure to provide a display simply for the purpose of labelling the softkeys.
Another attempt to make the user interface easier relies on menu-driven user interaction. That is, the user is guided through several steps, and the monitor may propose adequate measures. However, such menus require the provision of a display as well.
The above concepts are also not suited for operation by the patient himself, e.g., in home monitoring applications (i.e., a monitor located at the patient's home). Whatever operating concept is used during home monitoring, the patient will have to study complex instructions. In this context, it is particularly important to note that a medical monitor includes a multiplicity of functions which are partially sensitive to patient safety; likewise, the order of the steps is important. Consider, for example, a calibration procedure wherein the sequence of steps has to be performed in the correct order. If this order is not kept, the monitor will be incorrectly calibrated and therefore not indicate a dangerous situation of the patient.
Yet another problem associated with home monitoring is the correct anamnesis. During home monitoring, the vital signs (like the electrocardiogram, respiration, temperature etc.) are usually recorded by a remote monitor and transmitted to the hospital, or the doctor's office, via telephone lines. However, home monitoring requires not only that the vital signs of the patient are picked up by various transducers, but also some additional information which cannot be measured by a medical monitor, such as general feeling, skin color, weight etc. In the prior art, this additional information has been communicated over the phone. A person at the receiving end (doctor, nurse) recorded the answers and coded them for electronic processing. However, it will be appreciated that this process as such is very labour-intensive, costly and uncomfortable for the patient--a person recording his answers will not always be available, an extra telephone connection has to be set up, and the monitoring cycle is interrupted.
Although it would be possible to use an interactive and/or menu-driven system to record the patient's answers, this solution suffers from the same drawbacks as outlined above. That is, a display is required, the system is error-prone etc.
It is understood that this is not only a problem in home monitoring; in contrast, it applies whenever the patient provides an auto-anamnesis.
The above considerations apply particularly in cases of fetal monitoring with a "home monitor", i.e., when a fetal monitor is used in the pregnant woman's home. The well-being of the mother, pain etc. is clinically important information which cannot be transmitted to the hospital, or the obstetrician's office, in a cost-effective and convenient manner by the equipment provided by prior art solutions.

Method and apparatus for medical monitoring


A transmittance control method of electrochromic element, mainly comprising the following step: firstly, a total current flux input required is obtained by adding current value of each second together by the relationship between different current value and different rate of change of the electrochromic element obtained in terms of the same transmittance and different input voltages, then the total current flux for fixed transmittance is input into the electrochromic element in usage so as to achieve a transmittance of fixed value. In this manner, the electrochromic element can quickly achieve a transmittance of fixed value in precise manner, without repeated adjustment. Further, there is not such case happened as to influence the accuracy of its transmittance even after aging time lapse.

1. Field of the Invention
The present invention relates to a transmittance control method of electrochromic element, particularly to a transmittance control method of electrochromic element, whereby the electrochromic element can quickly achieve a transmittance of fixed value precisely without repeated adjustment, and there is not such case happened as to influence the accuracy of its transmittance even after aging time lapse.
2. Brief Description of Prior Art
Accompanying with the rapid progress of science and technology, a variety of specific materials have been developed, among which, electrochromic element refers to a component of reversibly changing color when voltage is applied. For example, the electrochromic element changes from transparent colorless to colored state when activated. Electrochromic element is basically a multi-layer electrochemical device in its structure. When a voltage is applied to the electrochromic element, the substances within it conduct reversible oxidation or reduction reaction which leads to a phenomena of color change. The electrochromic element can be used in our daily life. If sunshine is too strong in the outside or if internal privacy is desired, this technology can be applied to change glass transmittance.
In the operation and usage, the transmittance is lowered, the light absorbance is increased and the color becomes darker if a positive electricity is input into the electrochromic element, as depicted in FIG. 10 showing schematically the oxidation reaction of an electrochromic element; on the other hand, the transmittance is increased, the light absorbance is decreased and the color becomes lighter if a negative electricity is input into the electrochromic element, as depicted in FIG. 11 showing schematically the reduction reaction of an electrochromic element. By repeatedly applying positive or negative electricity to an electrochromic element, the electrochromic element can conduct oxidation or reduction reaction so as to reach a desired transmittance.
The above electrochromic element can reach expected effect of adjusting its light transmittance by the change of inputting positive or negative electricity. However, it is found in practical implementation that the magnitude of input voltage and current might affect the rate of change and service life of the electrochromic element. Thus, the abovementioned process of repeatedly applying positive or negative electricity for conducting oxidation or reduction reaction so as to reach desired transmittance takes a long time due to repeated adjustment; and repeated change of voltage and current might cause shrinkage of its service life. Therefore, there are still space for improvement in its overall operation and implementation.
In view of the above facts, the inventor of the present invention hereby proposes a novel transmittance control method of electrochromic element according to the research and improvements conducted on the defects of conventional method, and based on his abundant experience in R&D and manufacturing activities in relevant fields for past many years, so as to achieve the purpose of better practical value.

Transmittance control method of electrochromic component


The present invention provides methods for optimizing oligonucleotide hybridization probes for use in basic and clinical research. Specifically, the invention involves hybridizing serially diluted genomic sample to the oligonucleotide probes on the array, such that a signal intensity is produced for each of the probes; computationally identifying optimized probes which exhibit signal intensities that correspond to the serial dilutions of genomic sample and are reproducibly strong relative to non-optimized probes.

The advent of DNA microarray technology makes it possible to build an array of hundreds of thousands of DNA sequences in a very small area, such as the size of a microscopic slide. See, e.g., U.S. Pat. Nos. 6 375,903 and 5,143,854, each of which is hereby incorporated by reference in its entirety. The disclosure of U.S. Pat. No. 6,375,903, also incorporated by reference in its entirety, enables the construction of so-called maskless array synthesizer (MAS) instruments in which light is used to direct synthesis of the DNA sequences, the light direction being performed using a digital micromirror device (DMD). Using an MAS instrument, the selection of DNA sequences to be constructed in the microarray is under software control so that individually customized arrays can be built to order. In general, MAS based DNA microarray synthesis technology allows for the parallel synthesis of over 786,000 unique oligonucleotides in a very small area of a standard microscope slide. The microarrays are generally synthesized by using light to direct which oligonucleotides are synthesized at specific locations on an array, these locations being called features. Typically, one nucleotide sequence is synthesized at each feature of the array, i.e., there are multiple probes in each feature, but all those probes have the same nucleotide sequence. For certain applications, oligonucleotides of different sequences can be present within one feature of the array, and the ratio and direction (5′-3′, or 3′-5′) of these oligonucleotides can be controlled.
With the availability of the entire genome of hundreds of organisms, for which a reference sequence has generally been deposited into a public database, microarrays have been used to perform sequence analysis on DNA isolated from such organisms. Microarray methods that for example, allow the measurement of changes in DNA copy number are useful for the determination of chromosomal aberrations in higher eukaryotes that are often linked to disease states. Changes in copy number are typically the result of amplification or deletions of stretches of chromosomes. While large amplification and deletion or translocations can be readily detected by traditional karyotyping methods, the amplification or deletion of smaller DNA fragments within a chromosome can be difficult or impossible to detect by these methods. Accordingly, it has become increasingly important for genetic analysis to utilize the most accurate oligonucleotide probes.
Recently, several research groups have developed methods to optimize probes. For example, to avoid cross-hybridization of highly similar sequences on a microarray, researchers have developed an approach to determine the optimal number and length of gene-specific probes for accurate transcriptional profiling studies. The study surveyed probe lengths from 25 to 1000 nt. It was found that long probes yielded a better signal intensity than short probes. However, the signal intensity of short probes could be improved by addition of spacers or using higher probe concentration for spotting. (see Chou et al., Optimization of probe length and the number of probes per gene for optimal microarray analysis of gene expression. Nucleic Acids Res. 2004 Jul. 8; 32 (12):e99.) It is believed that alternative methods for optimizing probes for use in identifying genetic modifications would be a desirable contribution to the art.