We introduce an all-optical approach-optical parametric amplification (OPA) processer to suppress the impact of sun outage in laser satellite communication systems, which is implemented by only one nonlinear semiconductor optical amplifier driven by both the electrical and optical pumps. The optimized OPA processer with the current of 539mA and the pump-to-signal ratio of 16dB could significantly improve the signal quality by 3.5dB in experiment for the elevation angle of sun radiation of 0 rad. The signal-quality improvement is observed at the whole range of elevation angle, confirming the effectiveness of the proposed OPA processer in the field of sun-radiation mitigation.

In order to alleviate the impact of turbulence on the performance of underwater wireless optical communication (UWOC) in real time, and achieve high-speed real-time transmission and low cost and miniaturization of equipment, a 2×2 real-time MIMO high-speed miniaturized underwater wireless optical communication system based on FPGA and high-power LED array is designed in this letter. In terms of multiplexing gain, the imaging MIMO spatial multiplexing and high order modulation for the first time is combined and the real-time high-speed transmission of PAM-4 signal based on the LED array light source in 12m underwater channel at 100Mbps rate is implemented, which effectively improves the throughput of UWOC system with high-power commercial LED light source. In light of diversity gain, the system employs the diversity of repeated coding scheme to receive two identical NRZ-OOK signals, which can compensate the fading or flickering sub-links in real time under the bubble-like simulated turbulence condition, and has high robustness. To our knowledge, this is the first instance of a high rate and long distance implementation of a turbulent-resistant real-time MIMO miniaturized UWOC system based on FPGA and high-power LED arrays. With spatial diversity or spatial multiplexing capabilities, its low cost, integrity, and high robustness make the system have important practical prospects.

The lens-free on-chip microscopy with RGB LED (LFOCM-RGB) provides a portable, cost-effective, and high throughput imaging tool for resource-limited environments. However, the weak coherence of LEDs limits the high-resolution imaging, and the luminous surfaces of the LED chips on the RGB LED do not overlap, making the coherence-enhanced executions tends to undermine the portable and cost-effective implementation. Here, we propose a specially designed pinhole array to enhance coherence in a portable and cost-effective implementation. It modulates the three-color beams from the RGB LED separately so that the three-color beams effectively overlap on the sample plane while reducing the effective light-emitting area for better spatial coherence. And the separate modulation of the spatial coherence allows the temporal coherence to be modulated separately by single spectral filters rather than by expensive triple spectral filters. Based on the pinhole array, the LFOCM-RGB simply and effectively realizes the high-resolution imaging in a portable and cost-effective implementation, offering much flexibility for various applications in resource-limited environments.

A flexible-grid 1×(2×3) mode- and wavelength-selective switch which comprises counter-tapered couplers and silicon microring resonators has been proposed, optimized, and demonstrated experimentally in this paper. By carefully thermally tuning phase shifters and silicon microring resonators, mode and wavelength signals can be independently and flexibly conveyed to each any one of the output ports and different bandwidths can be generated as desired. The particle swarm optimization algorithm and finite difference time domain method are employed to optimize structural parameters of the two-mode (de)multiplexer and crossing waveguide. The bandwidth-tunable wavelength-selective optical router composed of twelve microring resonators is studied by taking advantage of the transfer matrix method. Measurement results show that, for the fabricated module, the crosstalk less than −10.18 dB, extinction ratio larger than 17.41 dB, the in-band ripple lower than 0.79 dB, and 3-dB bandwidth changing from 0.38 to 1.05 nm are obtained, as the wavelength-channel spacing is 0.40 nm. The corresponding response time is measured to be 13.64 μs.

The heterogeneous integration of photonic integrated circuits (PICs) with a diverse range of optoelectronic materials has emerged as a transformative approach, propelling photonic chips towards larger scales, superior performance, and advanced integration levels. Notably, two-dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and hexagonal boron nitride (hBN) exhibit remarkable device performance and integration capabilities, offering promising potential for large-scale implementation in PICs. In this paper, we first present a comprehensive review of recent progress, systematically categorizing the integration of photonic circuits with 2D materials based on their types, while emphasizing their unique advantages. Then we discuss the integration approaches of 2D materials with PICs. We also summarize the technical challenges in heterogeneous integration of 2D materials in photonics and envision their immense potential for future applications in PICs.

We present our efforts towards power scaling of Er:Lu2O3 lasers at 2.85 µm. By applying a dual-end diode-pumped resonator scheme, we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slope efficiency of 26%. In a single-end pumped resonator scheme, an output power of 10.1 W is reached under 41.9 W of absorbed pump power. To the best of our knowledge, this is the first single crystalline mid-infrared rare-earth-based solid-state laser with an output power exceeding 10 W at room temperature.

We propose a laser speckle contrast imaging method based on uniting spatiotemporal Fourier transform (LSCI-uSTFT). First, the raw speckle images are entirely transformed to the spatiotemporal frequency domain with a three-dimensional(3D) fast Fourier Transform. Second, the dynamic and static speckle components are extracted by applying 3D low-pass and high-pass filtering in the spatiotemporal frequency domain and inverse 3D Fourier transform. Third, we calculate the time-averaged modulation depth with the average of both components to map the 2D blood flow distribution. The experiments demonstrated that the proposed method could effectively improve computational efficiency and imaging quality.

We propose an absolute distance measurement method that employs heterodyne and superheterodyne combined interferometer to achieve synchronous detection and demodulation of multi-wavelengths. Coarse and fine synthetic wavelengths are generated by a dual-longitudinal-mode He-Ne laser and four acoustic optical frequency shifters (AOFS). Further, to improve phase synchronization measurement for multi-wavelengths, we analyze the demodulation characteristics of coarse and fine measurement signals and adopts a demodulation method suitable for both signals. Experimental results demonstrate that the proposed method can achieve high-precision synchronous demodulation of multi-wavelengths, and standard deviation (STD) is 1.7×10-5 m in a range of 2 m.

Edge detection for low-contrast phase objects cannot be performed directly by spatial difference of intensity distribution. In this work, an all-optical diffractive neural network (DPENet) based on the differential interference contrast principle to detect the edges of phase objects in an all-optical manner has been proposed. Edge information is encoded into interference light field by dual Wollaston prisms without lenses and light-speed processed by the diffractive neural network to obtain the scale-adjustable edges. Results show that DPENet achieves F-scores of 0.9293 (MNIST) and 0.9356 (NIST) and enables real-time edge detection of biological cells, achieving an F-score of 0.7547.

Optical coherence tomography (OCT) allows a direct and precise measurement of laser welding depth by coaxially measuring the keyhole depth and can be used for process monitoring and control. When OCT measurement was taken during single-beam laser welding, the keyhole instability of aluminum welding resulted in highly scattered OCT data and complicated the welding depth extraction methods. As a combination of an inner core beam and an outer ring beam, a novel adjustable ring mode (ARM) laser for producing stable keyhole was applied to the OCT measurement. Different ARM laser power arrangements were conducted on aluminum and copper. Results indicated that the ring beam greatly improved the stability of the core beam-induced keyhole, and smooth welding depth can be extracted from the concentrated OCT data.