ABSTRACT
In the optical communication system, the power of the optical signal should be greater than the minimum detectable power of the receiver and should also be smaller than the maximum allowable power of the receiver to assure the allowable bit error rate. Attenuator is used to adjust the optical power to be in the allowable power range of receiver. Also in front of the optical amplifier, the optical power should be adjusted in a specific range and an attenuator is sometimes required. In the wavelength division multiplexing (WDM) system, the multiplexed signals are simultaneously amplified. When the wavelength multiplexed signal passes several amplifiers in a long distance optical fiber transmission system, the nonuniformity of power profile of wavelength channels is accumulated and emphasized. As a result, some of wavelength channels cannot satisfy the allowable power range of optical amplifier. To solve this problem, variable optical attenuator is used to adjust the uniformity of wavelength channels in WDM systems.
