Abstract

The transmission distance in optical fiber communications has been greatly increased by the development of erbium-doped fiber amplifiers. As a result, the main factor limiting the transmission distance is now chromatic dispersion. We have reported a planar lightwave circuit (PLC) dispersion equalizer with design flexibility and high tolerance whose configuration is shown in Fig. 1.^1,2 This equalizer is basically composed of asymmetrical Mach-Zehnder interferometers cascaded in series. All the couplers have a 3 dB coupling ratio. It is confirmed that the lower and higher frequency components f_L = f₀−W/2 and f_H = f₀ + W/2 pass mainly through the shorter and longer arms of the interferometers, respectively, where f₀ is the center frequency of the operational range and W is typically 10 GHz. Thus positive dispersion can be achieved whose inclination is opposite to that of 1.3 µm zerodispersion fiber at 1.55 µm. The device is fabricated with a silica optical waveguide by flame hydrolysis deposition and reactive ion etching.^1,2 A chromium heater is deposited on every asymmetrical arm to provide thermo-optic phase shift control between the two arms of the interferometers. In this equalizer, the dispersion can be adjusted to both positive and negative values by appropriately setting the phase shift.¹ Therefore, it can compensate for both positive and negative dispersion around the zero-dispersion wavelength of a 1.55 µm dispersion-shifted fiber.

© 1995 IEEE