Tunable vertical-cavity SOAs: a unique combination of tunable filtering and optical gain

In this paper the design and performance of novel micromechanically-tunable vertical-cavity semiconductor optical amplifiers (VCSOAs) are presented. Theoretical design issues include overviews of the signal gain, wavelength tuning characteristics, saturation properties, and noise figure of these unique devices. Using general Fabry-Pérot relationships it is possible to model both the wavelength tuning characteristics and the peak signal gain of tunable VCSOAs, while amplifier rate equations are used to describe the saturation and noise properties. It is found that these devices follow many of the same design trends as fixed-wavelength VCSOAs. However, with tunable devices, the tuning mechanism is found to result in varying amplifier properties over the wavelength span of the device. Experimental results for three generations of devices are given. The culmination of this work is a new bottom-emitting design in which the optical cavity is inverted and the MEMS-tuning structure serves as the high-reflectivity back mirror. By suppressing the variation in mirror reflectance with tuning, this configuration exhibits a two-fold increase in the effective tuning range as compared with our initial devices—with a minimum of 5 dB fiber-to-fiber gain (12 dB on-chip gain) over a wavelength span of roughly 21 nm, from 1557.36 nm to 1536.43 nm. Furthermore, these devices exhibit saturation, bandwidth and noise properties similar to state-of-the-art fixed-wavelength VCSOAs, including a fiber-coupled saturation output power of -1.36 dBm and an average gain bandwidth and noise figure of 65.2 GHz and 7.48 dB.