Recently, the emerging 2 μm waveband has gained increasing interest due to its great potential for a wide scope of applications. Compared with the existing optical communication windows at shorter wavelengths, it also offers distinct advantages of lower nonlinear absorption, better fabrication tolerance, and larger free carrier plasma effects for silicon photonics, which has been a proven device technology. While much progress has been witnessed for silicon photonics at the 2 μm waveband, the primary challenge still exists for on-chip detectors. Despite the maturity and compatibility of the waveguide coupled photodetectors made of germanium, the 2 μm regime is far beyond its cutoff wavelength. In this work, we demonstrate an efficient and high-speed on-chip waveguide-coupled germanium photodetector operating at the 2 μm waveband. The weak sub-bandgap absorption of epitaxial germanium is greatly enhanced by a lateral separation absorption charge multiplication structure. The detector is fabricated by the standard process offered by a commercial foundry. The device has a benchmark performance with responsivity of 1.05 A/W and 3 dB bandwidth of 7.12 GHz, which is able to receive high-speed signals with up to 20 Gbit/s data rate. The availability of such an efficient and fast on-chip detector circumvents the barriers between silicon photonic integrated circuits and the potential applications at the 2 μm waveband.

We have experimentally demonstrated 30 Gbit/s coupling modulation based on silicon racetrack ring resonator operating at 2 μm waveband. The modulator has EO bandwidth beyond 18 GHz and modulation efficiency of 0.75 V•cm.

Silicon photonic tunable flat-top filters are demonstrated via the 5th-order and the 10th-order CROW structure at 2-μm waveband. Box-like transmission spectra are measured with 3-dB bandwidth of 3.34 nm and 5.34 nm, respectively.

The short-wavelength mid-infrared spectral range of the 2 μm waveband has the advantages of low transmission loss and broad gain bandwidth, making it a promising candidate for the next optical fiber communication window. It is thus highly desired to develop high-performance silicon photonic components in this waveband. Here, an efficient dual-layer grating coupler was designed on a 220 nm thick silicon-on-insulator based on raised polysilicon to address the low directionality issue. For the fiber tilted at an angle of 10°, the grating coupler’s simulated coupling efficiency reaches 80.3% (−0.95 dB) at a wavelength of 2002 nm. The 1 dB bandwidth is 66 nm. The structure is completely compatible with the standard silicon photonic fabrication process, making it suitable for large volume fabrication.

A fabrication-friendly polarization splitter-rotator is designed by particle swarm optimization. The device has a short length of 26.62 µm and <1 dB loss with 127 nm optical bandwidth.

A tunable silicon photonic microring resonator with radius of 2 µm is demonstrated at 2-µm waveband. Ultra-large free spectral range of 75.312 nm and extinction ratio of 23.93 dB are achieved.

Driven by the demand to extend optical fiber communications wavelengths beyond the C + L band, the 2 mu m wave band has proven to be a promising candidate. Extensive efforts have been directed into developing high-performance and functional photonic devices. Here we report an integrated silicon photonic arrayed waveguide grating (AWG) fabricated in a commercial foundry. The device has 64 channels with a spacing of approximately 50 GHz (0.7 nm), covering the bandwidth from 1967 nm to 2012 nm. The on-chip insertion loss of the AWG is measured to be approximately 5 dB. By implementing a TIN metal layer, the AWG spectrum can be thermally tuned with an efficiency of 0.27 GHz/mW. The device has a very compact configuration with a footprint of 23 mm x 2 mm. The demonstrated AWG can potentially be used for dense wavelength division multiplexing in the 2 mu m spectral band. (C) 2022 Optica Publishing Group

Driven by the demand to extend optical fiber communications wavelengths beyond the C + L band, the 2 µm wave band has proven to be a promising candidate. Extensive efforts have been directed into developing high-performance and functional photonic devices. Here we report an integrated silicon photonic arrayed waveguide grating (AWG) fabricated in a commercial foundry. The device has 64 channels with a spacing of approximately 50 GHz (0.7 nm), covering the bandwidth from 1967 nm to 2012 nm. The on-chip insertion loss of the AWG is measured to be approximately 5 dB. By implementing a TiN metal layer, the AWG spectrum can be thermally tuned with an efficiency of 0.27 GHz/mW. The device has a very compact configuration with a footprint of 2.3 mm × 2 mm. The demonstrated AWG can potentially be used for dense wavelength division multiplexing in the 2 µm spectral band.

An integrated 1×N switch is proposed and experimentally demonstrated via tunable silicon photonic metasurface which has an insertion loss of 3 dB and extinction ratio of 5 dB in the C band.

Polarization and mode division multiplexing are powerful tools for large-capacity parallel optical communications. Dual-polarization and mode-division multiplexed silicon photonic integrated circuit with ultra-small footprint is proposed and experimentally demonstrated. The circuits consist of a mode multiplexer, 3-dB power splitter and two demultiplexers which can simultaneously handle TE0, TE1, TM0 and TM1 mode. Compared with conventional device structure, the device footprint is scaled down via pixelated waveguide meta-structure. The mode multiplexer and the splitter have a footprint of only 6.8 μm × 6 μm and 6 μm × 5.25 μm, respectively. The fabrication tolerance on the nanohole size variations are studied, and the fabricated devices are systematically characterized. The measured insertion losses of the multiplexer and 3-dB power splitter are below 1.4 dB and 4.5 dB for all four modes within the wavelength range from 1530 nm-1570 nm. In the meantime, the measured maximum inter-mode cross talk is below -15 dB over a 30 nm bandwidth. The experimental results also indicate the power imbalance of the splitter is within 0.4 dB from 1530 nm-1570 nm. Since the demonstrated polarization and mode handling devices via pixelated meta-structures occupy significantly smaller chip area than conventional wisdoms, this work shows the potential for large scale and dense integration of polarization and mode division multiplexing system on photonic chip.

Recently, 2-μm wave band has gained increasing interest due to its potential application for next-generation optical communication. But the development of 2-μm optical communications is substantially hampered by the modulation speed due to the device bandwidth constraints. Thus, a high-speed modulator is highly demanded at 2 μm. Motivated by this prospect, we demonstrate a high-speed silicon Mach–Zehnder modulator for a 2-μm wave band. The device is configured as a single-ended push–pull structure with waveguide electrorefraction via the free carrier plasma effect. The modulator was fabricated via a multiproject wafer shuttle run at a commercial silicon photonic foundry. The modulation efficiency of a single arm is measured to be 1.6 V · cm . The high-speed characterization is also performed, and the modulation speed can reach 80 Gbit/s with 4-level pulse amplitude modulation (PAM-4) formats.