High-efficient subwavelength structure engineered grating couplers for 2-µm waveband high-speed data transmission.

The 2-µm waveband is becoming an emerging window for next-generation high-speed optical communication. To enable on-chip high-speed data transmission, improving the signal-to-noise ratio (SNR) by suppressing the coupling loss of a silicon chip is critical. Here, we report grating couplers for TE and TM polarized light at the 2-µm waveband. With a single-step fully etched process on the 340 nm silicon-on-insulator (SOI) platform, the devices experimentally demonstrate high coupling efficiency of -4.0 dB and 1-dB bandwidth of 70 nm for the TE polarized light, while -4.5 dB coupling efficiency and 58 nm 1-dB bandwidth for the TM polarized light. For comprehensive performance, both of them are among the best grating couplers operating in the 2-µm waveband so far. We also demonstrate 81Gbps high-speed on-chip data transmission using pulse amplitude modulation 8-level (PAM-8) signals.

Subwavelength structure engineered passband filter for the 2-µm wave band.

In this work, we experimentally demonstrate a passband filter for the 2-µm wave band on the silicon-on-insulator platform. The device consists of a strip waveguide and an apodized subwavelength-structured waveguide. Fabricated on a 340-nm-thick silicon membrane, the proposed passband filter shows a 3-dB bandwidth of 16-33 nm, a high sidelobe suppression ratio (SLSR) of 24 dB, and a low insertion loss (IL) of 0.4 dB.

High-efficiency mid-infrared on-chip silicon grating couplers for perfectly vertical coupling.

We present, to our knowledge, the first experimental demonstration of two on-chip gratings for perfectly vertical coupling at wavelengths of 3350 nm and 3550 nm, respectively. An anti-backreflection unit containing a fully etched trench and a subwavelength pillar is introduced in each grating period, together with a binary-approximated blazed unit, interleaving fully and shallow-etched slots in 500-nm thick silicon film. Both gratings show a strong ability to eliminate backreflection and provide predicted directionality of around 80%. The physical theoretical analysis is applied during further apodization for mitigating the computation of the optimization algorithm, improving the efficiency and optimization reliability, and increasing the fabrication robustness. The measured coupling efficiencies (CEs) of the gratings are -5.58 dB and -4.34 dB at wavelengths of 3350 nm and 3550 nm, with a 3-dB bandwidth of at least 87 nm and 210 nm, respectively.

Ultra-compact polarization-independent 3 dB power splitter in silicon.

We experimentally demonstrate an ultra-compact polarization-independent 3 dB power splitter on the silicon-on-insulator platform. Subwavelength structure engineering is employed to balance the coupling coefficients of TE and TM polarizations as well as a footprint reduction. The device possesses ultra-compact (1.2µm×2.62µm) and polarization-independent features with an operating bandwidth over 50 nm (from 1540 to 1590 nm).