Gain improvement in L‐band EDFA using unpumped EDF in a double pass system

A new gain improvement technique for L‐band EDFA is presented. It uses an unpumped EDF in a double‐pass configuration in order to effectively suppress and completely exploit the backward ASE. Compared to a conventional single‐pass amplifier, the gain coefficient can be improved from 1.5 dB/mW to 3.1 dB/mW without much noise figure penalty. The L‐band EDFA can also reduce the pump power necessary to achieve a specified gain by about half, however, this occurs at the cost of noise figure increasing by 1.6 dB. The optimum length for an unpumped EDF is experimentally measured to be 3 m for both single‐pass and double‐pass systems. The maximum gain improvement of 15.5 dB was observed at a signal wavelength of 1572 nm while signal and pump powers were fixed at −30 dBm and 103 mW, respectively. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 154–156, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10706