We propose two designs of low‐loss and temperature‐insensitive single‐mode waveguide crossing on silicon‐on‐insulator (SOI) platform with 415‐nm operation bandwidth covering all optical communication bands. Both designs are enabled by subwavelength grating (SWG) modeled as an anisotropic metamaterial. The initial design applies straight SWG as the lateral cladding of the waveguide crossing to minimize the refractive index contrast and reduce the insertion loss (IL), but needs a relatively long taper. An improved design is then proposed where the curved SWG is introduced to replace the straight SWG to decrease the taper length and improve the performance. The waveguide crossing with the improved design achieves a calculated maximum IL of 0.229 dB and maximum crosstalk of −35.6 dB over a 415‐nm wavelength range from 1260 nm to 1675 nm. The proposed devices are fabricated and characterized. Measured results of the improved design show a maximum IL of 0.264 dB and maximum crosstalk of −30.9 dB over a 230‐nm wavelength range including O‐, C‐, and L‐bands, which accord well with the simulation. Low temperature sensitivity has also been demonstrated in both simulations and experiments.

We demonstrate a polarization-insensitive 2 × 2 thermo-optic switch on a 220-nm silicon-on-insulator platform. This device is based on a balanced Mach-Zehnder interferometer with arms consisting of square-cross-section waveguides. In simulations, the Mach-Zehnder switch (MZS) exhibits extinction ratios (ERs) > 9.5 dB for the transverse electric (TE) and transverse magnetic (TM) polarized modes from 1500 nm to 1600 nm. Experimental results verify the broadband operation of the MZS: switching the two polarizations with ERs > 10 dB over an 85-nm wavelength range. Across the C-band (1530 $\sim$ 1565 nm), the fabricated MZS has insertion losses of 0.2 $\sim$ 4.3 dB and ERs > 16 dB (14 dB) at the cross (bar) port for both the TE and TM polarizations. The polarization-dependent losses are around 2 dB within a 100-nm wavelength range, showing the low polarization diversity of the MZS. The proposed MZS is a promising building block for implementing on-chip polarization-division-multiplexed optical interconnects.

The fast growth of data traffic in short-reach optical communications drives the demand for high-speed and low-cost optical modules. Here we demonstrate a silicon photonic (SiP) phase-diverse receiver based on our recently proposed asymmetric self-coherent detection (ASCD) scheme with Mach-Zehnder interferometers (MZI). The SiP MZI-ASCD receiver has a hardware-efficient architecture and recovers complex double-sideband signals via the beatings between a signal portion and a delayed signal portion from an asymmetric MZI using only 2 single-ended photodiodes and 2 analog-to-digital converters. The removal of the local oscillator in the direct detection receiver enables low-cost uncooled lasers, whereas the phase diversity closes the gap with coherent detection in terms of electrical spectral efficiency (ESE). Using a SiP MZI-ASCD receiver with a 15 ps delay, we detect a 60 Gbaud single-polarization 16-QAM signal transmitted over 40 km of single-mode fiber (SMF) below 20% overhead (OH) SD-FEC threshold of 2×10 ^-2 with a net bit rate of 200 Gbps and a record net ESE of 5.86 b/s/Hz per wavelength per polarization. Using a SiP MZI-ASCD receiver with a different delay of 7.5 ps, transmission of single-polarization 16-QAM DSB signal up to 80 Gbaud over 40 km is achieved below 24% OH SD-FEC threshold of 4.5×10 ^-2 with a record net bit rate of 258 Gbps and a net ESE of 5.31 b/s/Hz per wavelength per polarization.