Tunable single-mode fiber laser with a low-cost active Fabry-Perot filter of ultra-narrow-linewidth and high side-mode-suppressing ratio

Abstract

We demonstrate a novel approach for generating a narrow-linewidth and highly side-mode suppressed Erbium-doped fiber laser (EDFL) by combining it with an intracavity feedback-injected 1.55mum Fabry-Perot laser diode (FPLD) via optical couplers. To help selecting the strongest longitudinal mode from the gain-spectrum of FPLD for lasing in the EDF ring cavity, the intracavity FPLD is operated at just below threshold condition associated with an intracavity feedback optical power ratio of <1%. The lasing mode and center wavelength of the proposed EDFL source are decided by both the cross-correlated gain profile of EDFA and FPLD, however, the effect of FPLD injection modes is found to be more pronounced. The optimized lasing linewidth (system limitation) and side-mode suppression ratio of 0.01 nm and > 49 dB are obtained. The worst linewidth at 3-dB and 10-dB decay are observed to maintain at about 0.016 nm and 0.05 nm, respectively. Linear wavelength tuning of up to 6 nm (from 1551.5 nm to 1557.7 nm) by adjusting temperature of FPLD from 10 degreesC to 50 degreesC at just below threshold is reported. The wavelength-tuning slope is about 0.155 nm/degreesC under temperature accuracy of 0.1 degreesC.