Inverse Design of a Wavelength (De)Multiplexer for 1.55- and 2-μm Wavebands by Using a Hybrid Analog-Digital Method

Recently, the emerging 2-μm waveband has gained increasing interest due to its great potential for a wide scope of applications. The 2-μm waveband is considered a novel communication window with distinct advantages of lower signal loss, better fabrication tolerance and broader gain bandwidth. Considering the advantages of 2-μm waveband, wavelength division multiplexing of 1.55- and 2-μm wavebands is one of the effective means to solve the current communication capacity crisis. Therefore, wavelength (de)multiplexer for 1.55- and 2-μm wavebands is a crucial component. However, traditional design methods make it challenging to create a wavelength (de)multiplexer with a large bandwidth and compact footprint. Here, we proposed and experimentally demonstrated a wavelength demultiplexer for 1.55- and 2-μm wavebands with an ultra-compact footprint of 3 × 3 μm2 utilizing an inverse design method called hybrid analog-digital algorithm to reduce computational cost and improve the device performance. Based on this algorithm, we further created three adjustable optimization parameters to achieve optimal device performance. We provide detailed explanations for the selection of these optimization parameters. The designed device has experimentally achieved a bandwidth of 100 nm for 1.55- and 2-μm wavebands, with the insertion loss less than 1.2 and 0.9 dB, and the crosstalk less than -17.7 and -16.4 dB, respectively. Furthermore, based on a fabricated wavelength division multiplexing chip, we demonstrated a dual-wavebands data transmission system that achieved a data rate of 138 Gbps at 1550 nm and 84 Gbps at 2004 nm, drawing a promising application for high-speed optical communications in the future.