Compact silica dual-band wavelength demultiplexer based on asymmetric-defined multimode interference coupler

Limited refractive index difference of silica waveguide brings great size challenges in wavelength demultiplexing. A silica dual-band wavelength demultiplexer (DBWD) based on an asymmetric multimode interference coupler (MMI) is demonstrated. The selective separation and output of target dual bands can be implemented using the proposed design method based on asymmetric-defined MMI couplers. The beam propagation method is adopted to verify the proposed design principle. Standard CMOS fabrication is used in demultiplexer preparation. At λ=1350 nm, insertion loss (IL) and crosstalk (CT) at port Output ₁ are 1.94 dB and -24.92 dB, respectively. At λ=1550 nm, IL and CT at port Output ₂ are 2.44 dB and -29.00 dB, respectively. The 3-dB bandwidth (BW₃ dB) for Output ₁ and Output ₂ are 82 nm (1297-1379 nm) and 87 nm (1492-1579 nm), respectively. The corresponding CT for Output ₁ and Output ₂ are < -7.16 dB and < -12.9 dB, respectively. Due to the introduction of asymmetric MMI coupler, the footprint is reduced to 0.1 mm² (25 µm × 4000 µm). Because of the periodic characteristic, the wavelength demultiplexing can be extended from O/C bands to E/L bands by a reshaped asymmetric-MMI coupler. Even by combining more asymmetric-MMI couplers with different etched sections, all 18 channels of coarse wavelength division multiplexing (CWDM) transmission (1270-1610 nm) can be covered. The favorable manufacturing tolerance facilitates large-scale integration and mass production.