The manipulation of optical modes directly in a multimode waveguide without affecting the transmission of undesired signal carriers is of significance to realize a flexible and simple structured optical network-on-chip. In this Letter, an arbitrary optical mode and wavelength carrier access scheme is proposed based on a series of multimode microring resonators and one multimode bus waveguide with constant width. As a proof-of-concept, a three-mode (de)multiplexing device is designed, fabricated, and experimentally demonstrated. A new, to the best of our knowledge, phase-matching idea is employed to keep the bus waveguide width constant. The mode coupling regions and transmission regions of the microring resonators are designed carefully to selectively couple and transmit different optical modes. The extinction ratio of the microring resonators is larger than 21.0 dB. The mode and wavelength cross-talk for directly (de)multiplexing are less than −12.8 dB and −19.0 dB, respectively. It would be a good candidate for future large-scale multidimensional optical networks.

Reconfigurable optical directed logic circuits (RODLC) aim to perform arbitrary logic operations using the optical switch network, in which the electrical signals regarded as the logic operands are applied to the optical switch to control the propagation of light over time, and the logic operation results are obtained at the output ports of the optical switch network in the form of light. In this paper, a novel RODLC is proposed and experimentally demonstrated by utilizing an optical switch array with the prosperous optical mode division multiplexing (MDM) technology to perform arbitrary logic functions. As a proof of concept, a RODLC with two optical mode (de)multiplexers and twelve thermo-optic microring resonators on a silicon-on-insulator substrate is fabricated based on standard microfabrication technology. To demonstrate its reconfigurability to perform arbitrary logic functions, eight logic operations: NOT, AND, NAND, OR, NOR, XOR, XNOR, as well as one combination operation of four-operand, with the operation speed of 10 Kbps are successfully implemented as examples. The demonstrated RODLC characterized with reconfigurability, scalability, and ability for large-scale integration, will contribute to the flourishing development of optical computing and information processing in large-scale optical hybrid integrated circuits.

Lithium niobate on insulator (LNOI) is a promising platform for realizing high-performance photonic integrated circuits (PICs) for communication applications due to LN's excellent electro-optic properties. Multimode photonic devices are attractive as they can improve the communication capacity of PICs by multiplexing orthogonal modes. For connecting multimode photonic components on the same chip, multimode waveguide bends are indispensable. In this contribution, multimode waveguide bends are proposed, simulated, and experimentally demonstrated with double air grooves to ensure low crosstalk for three different transverse electric (TE) modes by improving the mode overlap at the interface between the straight and bent waveguide when the waveguide is bent. This enables demonstration of S-shaped waveguide bends (two 90 o bent waveguides) with insertion losses below 1.42, 1.12, and 2.5 dB in the wavelength range of 1525-1575 nm for the transmitted TE 0 , TE 1 , and TE 2 modes, respectively. The mode crosstalk is lower than −12.2 dB for all three modes. The demonstrated device provides a compact solution for multimode waveguide bends in the LNOI platform, paving the way for high-speed, high-data-capacity PICs for on-chip communication systems.

On-chip photonic neural network (PNN) is emerging as an attractive solution for artificial neural networks due to its high computing density, low energy consumption, and compact size. Matrix-vector multiplication (MVM) plays a key role in on-chip PNN, which can achieve high-speed multiply-accumulate operation. Most of the current schemes implement MVM by adopting wavelength division multiplexing technology to accumulate the power of different wavelengths together, resulting in using a mass of laser sources. Additionally, real-number-field MVM is inevitable for realizing precise PNNs, while limited by the nature of light, effective solutions to perform negative value computing are still inadequate. Here, we propose and demonstrate a PNN accelerator based on wavelength and mode hybrid multiplexing technology to reduce the use of multi-wavelength lasers, which can satisfactorily play real-number-field computing (including positive and negative domain) based on a newly presented transformation mapping approach, avoiding the demanding experimental setup and the sacrificing weight modulation depth. As a proof-of-concept, a fabricated accelerator for image convolution and letter pattern detection has been demonstrated successfully, achieving a computing density of 1.37 TOPS/mm2 under the 22.38 Gbaud modulation rate.