Channel-spacing tunable silicon comb filter using two linearly chirped Bragg gratings

We propose a novel silicon-based comb filter with tunable channel spacing using a Michelson interferometer consisting of a pair of apodized linearly chirped Bragg gratings (ALC-BGs). The channel spacing of the proposed comb filter can be continuously tuned with a large tuning range by changing the effective refractive index of one of the ALC-BGs through the thermo-optic effect. Our numerical calculation shows that the channel spacing can be continuously tuned form 8.21 nm to 0.19 nm with an out-of-band rejection ratio of greater than 30 dB.