A bulk optical interleaver with flat passband by using cascaded Mach-Zehnder Interferometers

A bulk design of optical interleaver with 50 GHz free spectral range (FSR) is experimentally demonstrated. The optical interleaver consists of three cascaded stages of modified Mach-Zehnder interferometers (MZIs), which are fabricated with beam splitters, end-mirror and delay-blocks. Beam splitters are used to split a propagating beam into two beams or coherently recombine two split beams, and delay-blocks located in one arm of each MZI are used to control the phase difference. The interleaver processes square-like spectral response with nearly zero ripple, wide fiat-top, and rather low crosstalk, sharp steepness, and ease in fabrication as well. The bandwidth of passband at -0.5 dB and stopband at -15 dB are over 30 GHz and about 25 GHz, respectively. The insertion loss is smaller than 1.5 dB and the polarization dependent loss (PDL) is about 0.15 dB. The crosstalk is lower than -25 dB. The return loss is larger than 45 dB.