High extinction ratio waveform generation using a directly modulated laser and transmissive fiber Bragg grating filter

The ability to efficiently generate high modulation Extinction Ratio (ER) waveforms is important for many optical communication applications such as those employing high-sensitivity low-duty cycle waveforms like M-ary pulse-position modulation (M-PPM). Here, we report on a simple and efficient technique using a Directly Modulated Laser (DML) and a high-contrast narrow-band transmissive multiple-phase-shift Fiber Bragg Grating (FBG) filter. The FBG features low insertion loss < 0.5 dB, steep transition edges with a 3 dB bandwidth of 4.2 GHz and 40 dB bandwidth of 8.5 GHz, and deep out-of-band rejection > 60 dB. When used with a commercial DFB laser with fast chirp factor of 0.42 GHz/mA, waveforms with high ER may be generated with low modulation current ⪅ 20 mA, voltage ⪅ 1 V, and power < 20 mW. Performance and characterization of the DML, FBG, and DML-FBG generating high |ER| ⪆ 30 dB waveforms at 2.88 GHz are presented.