Generation of wavelength-tunable single-mode picosecond pulses from a self-seeded gain-switched Fabry–Perot laser diode with a high-birefringence fiber loop mirror

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Abstract
We demonstrate a simple self-seeding scheme for generating wavelength-tunable single-mode picosecond pulses at a fixed repetition rate with a Fabry–Perot (FP) laser diode. In this scheme, the FP laser diode is self-seeded from a high-birefringence (HiBi) fiber loop mirror that acts as a periodic multichannel wavelength filter. By setting the channel spacing of the filter properly, stepwise wavelength tuning over a wide range can be achieved by either changing the FP cavity roundtrip phase shift or tuning the fiber loop mirror filter. With this scheme, fast electrical tuning is also possible by incorporating a phase-control section into the FP cavity. Using a HiBi fiber loop mirror with a channel spacing of 1.56 nm and a FP laser diode with a mode spacing of 1.45 nm, we were able to generate picosecond pulses at a repetition rate of approximately 2 GHz, whose wavelength could be tuned stepwise over ten successive laser cavity modes by either changing the temperature of the laser diode or tensioning/pressing a section of the HiBi fiber in the loop mirror. A side-mode suppression ratio over 15 dB over the entire tuning range was achieved.