We propose and experimentally demonstrate an on-chip switchable mode exchange utilizing a Mach-Zehnder interferometer assisted by a phase shifter. The switchable functionality, which is essential for an advanced and reconfigurable optical network, can be realized by controlling the induced phase difference. The measured extinction ratio is ∼24  dB over the C band for OFF-ON switchover. For demonstration, open and clear-eye diagrams can be observed when processing non-return-to-zero on-off keying signals at 10 Gb/s. The bit error rate measurements indicate a reasonable power penalty of less than 1 dB for two-mode exchange. The proposed device can further promote advanced and flexible mode-multiplexing optical networks.

A dual-mode 3 dB power coupler based on silicon-on-insulator platform for mode division multiplexing system is proposed and demonstrated. The device, which consists of a tapered directional coupler and two output bend waveguides, has a 50:50 coupling ratio around the wavelength of 1550 nm for both fundamental and first order transverse magnetic (TM0 and TM1) modes. Based on asymmetrical tapered structure, a short common coupling length of ~15.2 μm for both modes is realized by optimizing the width of the tapered waveguide. The measured insertion loss for both modes is less than 0.7 dB. The crosstalks are about −14.3 dB for TM0 mode and −18.1 dB for TM1 mode.

Due to the excellent electrical and optical properties and their integration capability without lattice matching requirements, low-dimensional materials have received increasing attention in silicon photonic circuits. Bi2O2Se with high carrier mobility, narrow bandgap, and good air stability is very promising for high-performance near-infrared photodetectors. Here, the chemical vapor deposition method is applied to grow Bi2O2Se onto mica, and our developed polycarbonate/polydimethylsiloxane-assisted transfer method enables the clean and intact transfer of Bi2O2Se on top of a silicon waveguide. We demonstrated the Bi2O2Se/Si waveguide integrated photodetector with a small dark current of 72.9 nA, high responsivity of 3.5 A·W–1, fast rise/decay times of 22/78 ns, and low noise-equivalent power of 15.1 pW·Hz–0.5 at an applied voltage of 2 V in the O-band for transverse electric modes. Additionally, a microring resonator is designed for enhancing light–matter interaction, resulting in a wavelength-sensitive photodetector with reduced dark current (15.3 nA at 2 V) and more than a 3-fold enhancement in responsivity at the resonance wavelength, which is suitable for spectrally resolved applications. These results promote the integration of Bi2O2Se with a silicon photonic platform and are expected to accelerate the future use of integrated photodetectors in spectroscopy, sensing, and communication applications.

We propose and experimentally demonstrate an ultra-compact multimode waveguide crossing that can process two modes simultaneously. The symmetric Y-junction is introduced to split the high-order modes into fundamental ones, easing the subsequent processing. The footprint of the proposed crossing is as compact as 21  μm×21  μm. The measured results show an insertion loss of ∼1.82  dB for the TE mode and ∼0.46  dB for the TE mode at 1550 nm, as well as a crosstalk of <-18  dB from 1510 to 1600 nm.

We propose and experimentally demonstrate a sharply bent multimode silicon waveguide by introducing a pair of mode converters. The principle of the multimode bend is based on the eigenmode conversion between straight and bent waveguides, and the particle swarm optimization is adopted to engineer the geometry. The device is fabricated on the standard silicon-on-insulator platform using one lithography/etching, and no additional steps are required. The measured results show that the insertion loss is <0.2  dB, and the inter-mode crosstalk is <-22  dB with a bend radius of 5 μm, from 1500 to 1600 nm. A comparable performance can be achieved using a conventional scheme with 40 μm radius.

A novel adiabatic couplers (ACs) based broadband and fabrication-tolerant two-mode multiplexer (MUX) is designed using silicon-on-insulator (SOI) platform. Being different from the previously reported ACs-based scheme, the converted and multiplexed signals are on conventional modes, rather than supermodes. The experimental results are in good agreement with the simulations. Over a wavelength range of 75 nm measured, the crosstalk is lower than −20 dB, and the insertion loss is ~1 dB. The eye diagram and bit error rate measurements validate the good performance of the proposed mode MUX. The investigation on fabrication tolerance indicates reasonable performance degradation for a large gap deviation from −30 to 30 nm and etching depth deviation from −50 to 50 nm.

Data exchange is an important function for flexible optical network, and it has been extensively investigated for the time and wavelength domains. The mode division multiplexing (MDM) has been proposed to further increase the transmission capacity by carrying information on different modes with only single wavelength carrier. We propose and experimentally demonstrate a novel on-chip data exchange circuit for the MDM signals by utilizing two micro-ring resonator (MRR) based mode converters. For demonstration, single and four wavelengths non-return-to-zero on-off-keying (NRZ-OOK) signals at 10 Gb/s carried on different modes are successfully processed, with open and clear eye diagrams. Measured bit error ratio (BER) results show reasonable power penalties. The proposed circuit can be potentially used in advanced and flexible MDM optical networks.

Integrated spectrometers provide the possibility of compact, low-cost portable spectroscopy sensing, which is the critical component of the lab-on-a-chip system. However, using existing on-chip designs is challenging to realize a high-resolution miniature spectrometer over a broad wavelength range. Here, we demonstrate an on-chip time-sampling narrowband filter array spectrometer that enables simultaneous acquisition of high-resolution spectra via optical Fabry−Peŕot cavities and a large spectral range with tunable free spectral range free filters. Two spectrometers consisting of five and seven filter cells with a compact footprint are fabricated and experimentally characterized, demonstrating a resolution of <0.43 and <0.51 nm and a spectral range of 73.2 and 102.7 nm, respectively. Unknown broad bandwidth input signal spectra can be successfully retrieved. Integrating more filter cells with thermal isolation trenches can dramatically boost the operational spectral range. Such spectrometers may open up new pathways toward spectral analytical applications.