Gain measurements of InGaAsP 1.5-μm optical amplifiers

Abstract

Optical amplifiers will be important components in future optical communication and signal processing systems. Semiconductor Fabry-Perot amplifiers (FPA), i.e., injection lasers driven below threshold, have actually been demonstrated in experimental systems.1 However, FPA suffer from extremely narrow gain bandwidth and low saturated output power.2 On the other hand, traveling wave amplifiers (TWA)3 (ideally with zero reflectivity facets) have the potential for extremely wide bandwidth operation and high saturated output power. In practice, of course, zero reflectivity facets are impossible to achieve. Therefore, all semiconductor injection amplifiers may be viewed as FPA with a continuum of facet reflectivities ranging from that of cleaved mirrors to the lowest obtainable reflectivities. Since the facet reflectivities, however low, are always finite, the amplifier gain spectrum is not flat, and these wavelength-dependent gain variations must be considered when wide-bandwidth amplification is desired. The gain spectrum of a semiconductor optical amplifier can be approximated using a simple model which incorporates a single-pass gain g in the simple Fabry-Perot transmission equations.4 The gain spectrum G(λ) is then, where R is the facet reflectivity, and δ = 2π, (i/λ), i is the amplifier length, and λ. is the wavelength inside the amplifier. K is a coupling coefficient including coupling into and out of the amplifier.