40 Gb/s multimode all-optical regenerator based on the low-loss silicon-based nanowaveguide.

With the increasing demand for communication capacity, all-optical regeneration of multimode signals is a helpful technology of network nodes and optical signal processors. However, the difficulty of regenerating signal in higher-order modes hinders the practical application of multimode all-optical regenerators. In this study, we experimentally demonstrate the 40 Gb/s all-optical regeneration of NRZ-OOK signal in TE0 and TE1 modes via four-wave mixing (FWM) in the low-loss silicon-based nanowaveguide. By optimizing the parameters of waveguide section to enhance FWM conversion efficiency of two modes, and introducing Euler bending to reduce crosstalk between modes, the transmission loss of the silicon waveguide is 0.3 dB/cm, and the FWM conversion efficiency of the multimode regenerator is as high as -9.6 dB (TE0) and -13.0 dB (TE1). Both modes achieve extinction ratio enhancement of about 6 dB after regeneration. This silicon-based all-optical regenerator has great application potential in all-optical signal processing systems.

Towards a photonic integrated all-optical phase regenerator.

All-optical phase regeneration aims at restoring the phase information of coherently encoded data signals directly in the optical domain so as to compensate for phase distortions caused by transceiver imperfections and nonlinear impairments along the transmission link. Although it was proposed two decades ago, all-optical phase regeneration has not been seen in realistic networks to date, mainly because this technique entails complex bulk modules and relies on high-precision phase sensitive nonlinear dynamics, both of which are adverse to field deployment. Here, we demonstrate a new, to the best of our knowledge, architecture to implement all-optical phase regeneration using integrated photonic devices. In particular, we realize quadrature phase quantization by exploring the phase-sensitive parametric wave mixing within on-chip silicon waveguides, while multiple coherent pump laser tones are provided by a chip-scale micro-cavity Kerr frequency comb. Multi-channel all-optical phase regeneration is experimentally demonstrated for 40 Gbps QPSK data, achieving the best SNR improvement of more than 6 dB. Our study showcases a promising avenue to enable the practical implementation of all-optical phase regeneration in realistic long-distance fiber transmission networks.

Simultaneous full set of three-input canonical logic units in a single nonlinear device for an all-optical programmable logic array.

All-optical canonical logic units-based programmable logic array (CLUs-PLA) is an important combinational logic device owing to its flexibility and user-defined feature. However, the limited number of three-input CLUs generated in a single nonlinear device hinders their practical application. In this study, we overcome this limitation and experimentally demonstrate the simultaneous generation of a full set of three-input CLUs in only one nonlinear device. By performing bidirectional four-wave mixing (FWM) and wavelength spacing optimization, the all-optical three-input PLA with a full set of CLUs enables arbitrary functions. We experimentally demonstrate the implementation of a series of combinational logic functions including, user-defined logic functions, full adder, and full subtractor, exhibiting error-free performances for all logic operations at 40 Gb/s. The scheme can reduce the number of nonlinear devices in CLUs-PLA, which simplifies the computing system and reduces power consumption. Therefore, the scheme has great potential for future high-speed optical computing systems.

Seven-channel all-optical reconfigurable canonical logic units multicasting at 40 Gb/s based on a nonlinearity-enhanced silicon waveguide.

All-optical canonical logic unit (CLU) is the basic building block of high-speed optical logic operation and complex optical computing. By utilizing the parallelism of optical signals, multichannel multicasting of all-optical CLUs can expand the capacity of the computing system effectively. Here, we propose and experimentally demonstrate the 40 Gb/s all-optical reconfigurable two-input CLUs generated in seven wavelength channels via four-wave mixing (FWM) in the nonlinearity-enhanced silicon waveguide. By introducing reverse-biased PIN junctions to reduce nonlinear loss, the output power of converted light can be increased over 10 dB. Moreover, pumped by two optical signals and a continuous wave beam, a full set of reconfigurable CLUs is multicasted in seven parallel wavelength channels. All logic signals with error-free performance are realized. Attributing to the rate transparency of FWM and parallel multicasting of logic functions, the proposed scheme offers more flexibility and expandability in future high-speed optical logic processing and complex optical computing.

Photonic matrix multiplication lights up photonic accelerator and beyond.

Matrix computation, as a fundamental building block of information processing in science and technology, contributes most of the computational overheads in modern signal processing and artificial intelligence algorithms. Photonic accelerators are designed to accelerate specific categories of computing in the optical domain, especially matrix multiplication, to address the growing demand for computing resources and capacity. Photonic matrix multiplication has much potential to expand the domain of telecommunication, and artificial intelligence benefiting from its superior performance. Recent research in photonic matrix multiplication has flourished and may provide opportunities to develop applications that are unachievable at present by conventional electronic processors. In this review, we first introduce the methods of photonic matrix multiplication, mainly including the plane light conversion method, Mach-Zehnder interferometer method and wavelength division multiplexing method. We also summarize the developmental milestones of photonic matrix multiplication and the related applications. Then, we review their detailed advances in applications to optical signal processing and artificial neural networks in recent years. Finally, we comment on the challenges and perspectives of photonic matrix multiplication and photonic acceleration.

Wavelength-division multiplexing communications using integrated soliton microcomb laser source.

In this Letter, we report an investigation of the feasibility and performance of wavelength-division multiplexed (WDM) optical communications using an integrated perfect soliton crystal as the multi-channel laser source. First, we confirm that perfect soliton crystals pumped directly by a distributed-feedback (DFB) laser self-injection locked to the host microcavity has sufficiently low frequency and amplitude noise to encode advanced data formats. Second, perfect soliton crystals are exploited to boost the power level of each microcomb line, so that it can be directly used for data modulation, excluding preamplification. Third, in a proof-of-concept experiment, we demonstrate seven-channel 16-quadrature amplitude modulation (16-QAM) and 4-level pulse amplitude modulation (PAM4) data transmissions using an integrated perfect soliton crystal as the laser carrier; excellent data receiving performance is obtained for various fiber link distances and amplifier configurations. Our study reveals that fully integrated Kerr soliton microcombs are viable and advantageous for optical data communications.

Integrated all-optical programmable logic array based on semiconductor optical amplifiers.

The all-optical programmable logic array (PLA) is one of the most important optical complex logic devices that can implement combinational logic functions. In this Letter, we propose and experimentally demonstrate an integrated all-optical PLA at the operation speed of 40 Gb/s. The PLA mainly consists of a delay interferometer (DI) and semiconductor optical amplifiers (SOAs) of different lengths. The DI is used to pre-code the input signals and improve the reconfigurability of the scheme. The longer SOAs are nonlinear media for generating canonical logic units (CLUs) using four-wave mixing. The shorter SOAs are used to select the appropriate CLUs by changing the working states; then reconfigurable logic functions can be output directly. The results show that all the CLUs are realized successfully, and the optical signal-to-noise ratios are above 22 dB. The exclusive NOR gate and exclusive OR gate are experimentally demonstrated based on output CLUs.

40 Gb/s reconfigurable optical logic gates based on FWM in silicon waveguide.

Here we experimentally demonstrate reconfigurable logic gates via four-wave-mixing (FWM) in silicon waveguide with an operating speed of up to 40 Gb/s. After demodulated by a 40-GHz delay interferometer (DI), four non-return-to-zero differential phase shift keying (NRZ-DPSK) signals with carefully selected wavelengths are launched into the waveguide at the same time. Thanks to the effective FWM in silicon nano-waveguide, a full set of the two-input logic minterms can be generated simultaneously, and arbitrary combinational logic functions are able to be realized by properly combining these minterms.

Expanded all-optical programmable logic array based on multi-input/output canonical logic units.

We present an expanded all-optical programmable logic array (O-PLA) using multi-input and multi-output canonical logic units (CLUs) generation. Based on four-wave mixing (FWM) in highly nonlinear fiber (HNLF), two-input and three-input CLUs are simultaneously achieved in five different channels with an operation speed of 40 Gb/s. Clear temporal waveforms and wide open eye diagrams are successfully observed. The effectiveness of the scheme is validated by extinction ratio and optical signal-to-noise ratio measurements. The computing capacity, defined as the total amount of logic functions achieved by the O-PLA, is discussed in detail. For a three-input O-PLA, the computing capacity of the expanded CLUs-PLA is more than two times as large as that of the standard CLUs-PLA, and this multiple will increase to more than three and a half as the idlers are individually independent.