Characterization of an ASE reflector-based gain-clamped erbium-doped fiber amplifier

We develop a simulation tool for an all-optical gain-clamped erbium-doped fiber amplifier (GC-EDFA) based on an amplified spontaneous emission (ASE) reflector and thoroughly verify its validity by comparing simulation data with experimental ones. We carry out simulation work as changing conditions like reflection ratio and bandwidth of the ASE reflector, EDF length, and pump power. From this work, we have an exact understanding about the gain clamping principle that a reflected ASE acts like an intensity reservoir against input signal intensity variation. In general, as a reflected ASE power becomes higher, both a dynamic range and a noise figure (NF) increase; on the other hand, a clamped gain value decreases. The ASE reflector-based gain clamping scheme can be used for EDFAs with low NF characteristics at small input signal range in case a reflected ASE power is set at a level much lower than powers required for normal gain clamping function.

I. Introduction

Gain clamping is one of key functions required for erbium-doped fiber amplifiers (EDFAs) in wavelength-division-multiplexed (WDM) optical transmission systems and WDM optical networks where dynamic channels adding–dropping or abrupt failure of the other signal channels can occur. Fig. 1. Experimental (squares) and simulation (lines) data versus (a) input signal power at 1550 nm and (b) wavelength at −25 dBm. Definition of dynamic range and the GC-EDFA configuration are also shown in (a) and (b), respectively. Optical feedback schemes based on a lasing mechanism are a simple and effective way to achieve constant gain characteristics regardless of input power variations. However, the optical feedback schemes usually have some shortcomings like high noise figure (NF) and transient power excursion in surviving channels due to relaxation oscillation (RO). Various optical and optical–electrical hybrid approaches have been reported to solve such problems [1]–[3]. The approaches, however, must have a limitation to improve the shortcomings since they still use lasing-based gain clamping schemes. Recently, we reported a novel gain-clamping scheme for EDFA by using an amplified spontaneous emission (ASE) reflector composed of a coarse WDM (CWDM) coupler and a fiber mirror [4]. The gain-clamped EDFA (GC-EDFA) has been free from RO phenomena since it comprised no optical cavity. In this letter, we investigate the characteristics of the ASE reflector-based GC-EDFA with respect to operation conditions like reflection ratio, bandwidth, and center wavelength of the ASE mirror by using a theoretical simulation tool.