Linewidth Reduction and Wavelength Tuning of an Erbium-Doped Fiber Laser by Use of a Single-Mode-Selected and Side-Mode-Suppressed Fabry-Perot Laser Diode

A single-mode and highly side-mode-suppressed 1.55- (mu)m Fabry-Perot laser diode (FPLD) is achieved by feedback injection with an erbium-doped fiber laser (EDFL). For selection of the strongest longitudinal mode from the gain spectrum of the FPLD for lasing in the EDFL, the FPLD is operated at just below the threshold condition and is feedback injected by 0.02% of the EDFL output power. The lasing mode and center wavelength of the proposed singlemode FPLD source are decided by cross-correlated gain profiles of the EDFL and the FPLD; however, the effect of FPLD injection modes is found to be more pronounced. The optimized lasing linewidth (system limitation) and sidemode suppression ratio of 0.01 nm and >49 dB are obtained, which are far better than those of a FPLD at free-running condition. The worst linewidths at 3- and 10-dB decay are observed to be at approximately 0.016 and 0.05 nm, respectively. Linear wavelength tuning of as much as 4.5 nm (from 1558.7 to 1563.2 nm) by adjustment of the temperature of the FPLD from 10 °C to 40 °C at just below threshold is reported. The wavelength-tuning slope is approximately 0.14 nm °C under temperature accuracy of 0.1 °C.