A commercial balanced optical front-end for 2.5 Gbit/s continuous phase frequency shift keying (CPFSK) coherent transmission system

Abstract

In this paper, a balanced optical front-end and IF module for a coherent heterodyne optical receiver are presented. The balanced optical front-end is realized with two commercially available GaInAs/InP p-i-n photodiodes and a full custom designed GaAs MMIC transimpedance amplifier. In this front-end a transimpedance, 3 dB bandwidth, and bandwidth- average input-referred noise current density of 58 dB(Omega) , at 1.7 GHz through 6.3 GHz, and 10 pA(root)Hz, have been measured. The IF module consists of three amplifier stages, a variable attenuator, a pass-band filter, and a broadband coupler. The amplifier stages and the variable attenuator are realized with commercially available MMICs chips. The filter and coupler have been built in hybrid technology. The measured characteristics are 47 dB gain with +/- 1.5 dB ripple, and more than 12 dB input/output port return losses. A transimpedance of 104 dB(Omega) has been measured in this complete optical receiver.