Analysis and assessment of the gain of optically pumped surface-normal optical amplifiers

This paper analyzes and assesses the gain of optically pumped surface-normal MQW optical amplifiers. The proposed amplifiers have the advantage of polarization independence, high coupling efficiency to and from optical fibers, and flexibility of operating wavelength. We analyzed the gain characteristics of 100- to 200-period MQWs and verified the dependence of gain on a strained lattice and selective doping. Theoretical analysis' of such MQWs shows a single-pass gain of 3 dB with broad operation bandwidth. A single-pass gain of 2.6 dB is obtained experimentally in an InGaAs/lnGaA1As MQW amplifier, which is compared with calculations. The use of a Fabry-Perot interferometer (FPI) structure in an optical amplifier is a useful way to increase the gain, but causes a problem of narrow operation bandwidth when the single-pass gain is low. Therefore, a single-pass gain above 2 to 3 dB is a prerequisite to achieve both a high gain and moderate operation bandwidth in FPI-structured optical amplifiers. We have designed an FPI-structured surface-normal optical amplifier both with a high gain of 10.1 dB and broad operation bandwidth of 4.6 nm, when a single-pass gain is 3 dB.