Multimode fibers (MMFs) are a promising solution for high-throughput signal transmission in the time domain. However, crosstalk among different optical modes within the MMF scrambles input information and creates seemingly random speckle patterns at the output. To characterize this process, a transmission matrix (TM) can be used to relate input and output fields. Recent innovations use TMs to manipulate the output field by shaping the input wavefront for exciting advances in deep-brain imaging, neuron stimulation, quantum networks, and analog operators. However, these approaches consider input/output segments as independent, limiting their use for separate signal processing, such as logic operations. Our proposed method, which makes input/output segments as interdependent, adjusts the phase of corresponding output fields using phase bias maps superimposed on input segments. Coherent superposition enables signal logic operations through a 15-m-long MMF. In experiments, a single optical logic gate containing three basic logic functions and cascading multiple logic gates to handle binary operands is demonstrated. Bitwise operations are performed for multi-bit logic operations, and multiple optical logic gates are reconstructed simultaneously in a single logic gate with polarization multiplexing. The proposed method may open new avenues for long-range logic signal processing and transmission via MMFs.

Optical modulators have been and will continue to be essential devices for energy- and cost-efficient optical communication networks. Heterogeneous silicon and lithium niobate modulators have demonstrated promising performances of low optical loss, low drive voltage, and large modulation bandwidth. However, DC bias drift is a major drawback of optical modulators using lithium niobate as the active electro-optic material. Here, we demonstrate high-speed and bias-drift-free Mach–Zehnder modulators based on the heterogeneous silicon and lithium niobate platform. The devices combine stable thermo-optic DC biases in silicon and ultra-fast electro-optic modulation in lithium niobate, and exhibit a low insertion loss of 1.8 dB, a low half-wave voltage of 3 V, an electro-optic modulation bandwidth of at least 70 GHz, and modulation data rates up to 128 Gb/s.

Multicore fiber (MCF) which contains more than one core in a single fiber cladding has attracted ever increasing attention for application in optical sensing systems owing to its unique capability of independent light transmission in multiple spatial channels. Different from the situation in standard single mode fiber (SMF), the fiber bending gives rise to tangential strain in off-center cores, and this unique feature has been employed for directional bending and shape sensing, where strain measurement is achieved by using either fiber Bragg gratings (FBGs), optical frequency-domain reflectometry (OFDR) or Brillouin distributed sensing technique. On the other hand, the parallel spatial cores enable space-division multiplexed (SDM) system configuration that allows for the multiplexing of multiple distributed sensing techniques. As a result, multi-parameter sensing or performance enhanced sensing can be achieved by using MCF. In this paper, we review the research progress in MCF based distributed fiber sensors. Brief introductions of MCF and the multiplexing/de-multiplexing methods are presented. The bending sensitivity of off-center cores is analyzed. Curvature and shape sensing, as well as various SDM distributed sensing using MCF are summarized, and the working principles of diverse MCF sensors are discussed. Finally, we present the challenges and prospects of MCF for distributed sensing applications.

Passive all-optical signal processors that overcome the electronic bottleneck can potentially be the enabling components for the next-generation high-speed and lower power consumption systems. Here, we propose and experimentally demonstrate a CMOS-compatible waveguide and its application to the all-optical analog-to-digital converter (ADC) under the nonlinear spectral splitting and filtering scheme. As the key component of the proposed ADC, a 50 cm long high-index doped silica glass spiral waveguide is composed of a thin silicon-nanocrystal (Si-nc) layer embedded in the core center for enhanced nonlinearity. The device simultaneously possesses low loss (0.16 dB/cm at 1550 nm), large nonlinearity (305W 1/km at 1550 nm), and negligible nonlinear absorption. A 2-bit ADC basic unit is achieved when pumped by the proposed waveguide structure at the telecom band and without any additional amplification. Simulation results that are consistent with the experimental ones are also demonstrated, which further confirm the feasibility of the proposed scheme for larger quantization resolution. This demonstrated approach enables a fully monolithic solution for all-optical ADC in the future, which can digitize broadband optical signals directly at low power consumption. This has great potential on the applications of high-speed optical communications, networks, and signal processing systems.