Analog performance of 1310-nm gain-clamped semiconductor optical amplifiers

We report on the analog performance of gain-clamped semiconductor optical amplifiers (GC-SOAs) with a full 50-550 MHz 77-channel NTSC loading. The optical gain of such an amplifier is linear i.e., independent of input power, when operated under gain-clamped conditions. The amplifier has distributed Bragg reflectors (DBR) at each end, which cause wavelength-selective feedback and hence, laser action at the DBR wavelength. This fixes the carrier concentration, effectively damping the optical gain of the device. The laser light serves as a reservoir of optical power and determines the maximum input power for which the device operates under linear conditions. Once the input level exceeds this limit the gain will no longer be clamped, and the device will exhibit the nonlinearities as observed for conventional SOAs. The gain-clamped amplifier developed for this study has a fiber-to-fiber gain of 21 dB at 1310 nm, and operates at input powers up to -12 dBm.