ocusing optics, you need to align the optics to minimize loss. To do SO, you should follow a standard industry technique, which is to first focus light on a spot similar to the size of the waveguide MFD. Once the preceding is accomplished, you would position the waveguide until its endface is located at the focal point. Because MFDs of communications systems are approximately 10 um or less, it is very difficult to perform the positioning mentioned above. This is because positioning equipment that supports submicrometer resolution along all three axes (x, y, and z) necessary to align a waveguide is bulky, expensive, and difficult to use. As an alternative, you can first attach a lens to the waveguide to generate a collimated beam. This enables you to work with collimated optics and obviates the need to consider the distance between the waveguide and the bulk optics. This technique also reduces the precision required for lateral alignment; however, similar to the fact that there is no free lunch, working with a collimated beam is not prob- lem-free. The key problem is the fact that sensitivity to angular misalign- ment will now increase. One method for correcting this problem involves the use of a tilt-adjustable coupler. This type of coupler uses screws to adjust the tilt angle between the focusing optics and the collimated beam. This enables the use of the screws to adjust the tilt angle, which in turn permits adjustment of the focused rays to strike the core of the fiber. Types of Couplers and Connectors There are numerous types of couplers. Some couplers couple light from a collimated source into either single-mode, multimode, or polarization- Chapter Four maintaining fibers. Couplers are available for different wavelengths and for different input powers. In addition, couplers vary according to the light source as well as the connector. Concerning the latter, common connectors include a receptacle-style physical contact, receptacle-style noncontact style, and pigtail-style couplers. Each coupler has advantages 