ent wavelengths different amounts condition in Eq. 6.1.40). At the input the 4 wavelengths and thereby sharpen the pulse in time. Dispersion are divided SO that 50% of each wavelength goes into compensating FBGs of up to 1500 ps/nm in the wave- each arm. Due to the FBGs A2 will be reflected from length region around 1550 nm are commercially each arm and the other three wavelengths will be available. transmitted. The two streams of transmitted light are The second application is concerned with add/drop subsequently combined in the right coupler and in- multiplexer/demultiplexers (mux/demux). One exam- terfering in such a way that all the transmitted light will ple of such a device is shown in Fig. 6.1-35 [33]. The exit through port 4. Similarly, the two portions of A2 purpose of such a device is to insert or remove a par- will be combined and interfere in the left coupler to ticular wavelength in a wavelength-division system. For emerge at port 2. example, to remove one wavelength out of a stream of Due to the inherent symmetry of these balanced wavelengths one can use the combination of a Mach- Mach-Zehnder interferometers they can simultaneously Zehnder interferometer in conjunction with FBGs. perform both multiplexing and demultiplexing. Assuming one would want to remove wavelength A2, it A commercial mux/demux device is capable of adding or is necessary to have two identical FBGs, one in each of dropping wavelengths that are < 1 nm apart (< 100 GHz the two interferometer arms (Fig. 6.1-35) and both @ 1550 nm) with less than -30 dB crosstalk between optimized for A2 (i.e., only A2 satisfies the Bragg different wavelengths. Input Optical fiber coupler gratings coupler Output Fig. 6.1-35 Example of a mux/demux device utilizing a FGB in a Mach-Zehnder interferometer. CHAPTER 6.1 Optical fiber, cable and connectors References 1. Webb, J. R., and U. L. Österberg. 16. Shibata, N., and T. Edahiro. 1982. Bandwidth Optical Waveguide 1995. In Optoelectronics for Trans. Inst. Electron. Commun. Eng. Transmission Filters: A