ABSTRACT
The temperature dependence of lightwave devices is a serious and outstanding problem. This characteristic is mostly caused by the temperature dependence of optical path length. To avoid the use of a precise and sophisticated temperature control unit, a technique to eliminate the temperature dependence of optical path length is required. The chapter discusses the absolute athermal condition. Since the central wavelength of multipath interferometers such as a Mach-Zehnder interferometer and an Arrayed Waveguide Grating (AWG) filters is determined by the optical path difference, the central wavelength can be made independent of temperature by equating the temperature coefficient of the optical path length difference. An athermalization method of AWG is the use of polymer material filled in a groove. In optical fibers, the athermalization of optical path length can be achieved by using some special methods to reduce thermal expansion. One of methods to reduce the thermal expansion is the use of special polymer jacket with a negative value of α.
