Experimental study of the impact of carrying a telecom signal on LOCSET-based coherent beam combining

Abstract

We report on what is, to our knowledge, one of the first realizations of a CBC (coherent beam combining)-based laser emitter carrying a 10.66 Gb/s telecom signal in free-space optics, within the laboratory environment. Two telecom modulations have been tested: NRZ (non-return-to-zero, in amplitude) and DPSK (differential phase-shift keying, in phase). The modulated signal is split and amplified in three fiber amplifiers, delivering up to 3 W each. CBC of data amplified signals is achieved with residual phase errors well below < λ/60 RMS, using a phase-tagging technique (LOCSET). A first analysis of the influence of various parameters (such as phase-tagging modulation depth, optical path difference, number of channels, amplifier power) on the locking and data transmission quality is investigated. The study shows that the phase-tagging modulation depth and optical path difference are the main critical issues when carrying data on a CBC signal.