A broadband wavelength demultiplexer assisted by SWG-based directional couplers

By using subwavelength grating (SWG), an ultra-compact directional coupler (DC) based wavelength demultiplexer operating at O-band and C-band is proposed. A designed embedded SWG structure is fabricated in the entire coupling section of DC, which can adjust the effective refractive indices for the first even and odd modes, leading to varying beat lengths resulted from the carefully tuned parameters of transmission grating. Shorter beat lengths of our proposed scheme effectively shrink the device footprint. Consequently, an ultra-compact wavelength demultiplexer is obtained with a total length of 13.5 mu m, which is similar to 20% of those conventional ones without SWG. Apart from that, it also exhibits a wide 1-dB bandwidth of similar to 140 nm across O-band (similar to 1310 nm) and similar to 125 nm across C-band (similar to 1550 nm). The insertion losses are 0.27 dB and 0.08 dB for the operating central wavelengths of 1310 nm and 1550 nm, respectively, while the extinction ratio for the two central wavelengths are both better than 15 dB.