ASE spectral slice gain-clamping of EDFA

An erbium-doped (Er-doped) fiber amplifier operating in the C-band is gain clamped, at about 26 dB with noise figures below 6 dB by multiple fiber Bragg gratings. These gratings are placed at the amplifier output with center wavelengths in between communication channels so that unwanted amplified spontaneous emission is removed but put to good use. A 0.5-dB gain compression point at -15 dBm of input signal powers for two simultaneous signal channels is also demonstrated.

I. Introduction

Gain-Clamped erbium-doped fiber amplifiers (EDFAs) using fiber Bragg gratings (FBGs), traditionally are used to create Fabry–Pérot resonators [1], [2] which allow for the out-of-band laser to oscillate and limit the population inversion. Fig. 1. Two simultaneous signals propagate through the 980-nm forward pumped amplifier. Fig. 2. Transmission spectra of the three FBGs showing −30.47-, −26.83-, and −33.51-dB loss at 1549, 1551, and 1555 nm, respectively. The signals wavelengths are located between these FBG wavelengths. Alternatively, the FBGs have also been used to reflect an externally injected out-of-band signal [3] that provides a similar population limitation as the former case. An early attempt to gain-clamp an EDFA just by passive amplification of backward amplified spontaneous emission (ASE) produced satisfactory results [4] but with a gain of 21 dB for eight channels.