The diagnosis of osteoporosis is eventually converted to the measurement of bone mineral density (BMD) in clinical trials. Since our previous work had proved the ability of using photoacoustic spectral analysis (PASA) to efficiently detect osteoporosis, in this contribution, we proposed a fully connected multi-layer deep neural network combined with PASA to semi-quantify BMD values corresponding to varying degrees of bone loss and to further evaluate the degree of osteoporosis. Experiments were carried out on swine femur heads, and the performance of our proposed method is satisfying for future clinical screening.

Space-division multiplexing (SDM) has attracted significant attention in recent years because larger transmission capacity is enabled by more degrees of freedom (DOFs) in few-mode fibers (FMFs) compared with single-mode fibers (SMFs). To transmit independent information on spatial modes without or with minor digital signal processing (DSP), weakly-coupled FMFs are preferred in various applications. Several cases with different use of spatial DOFs in weakly-coupled FMFs are demonstrated in this work, including single-mode or mode-group-multiplexed transmission, and spatial DOFs combined with time or frequency DOF to improve the system performance.

We propose and analyze a silicon hybrid plasmonic polarization splitter-rotator with an ultra-short footprint using an asymmetric bent directional coupler on a silicon-on-insulator platform. Benefitting from the large birefringence induced by the bent structure and plasmonic effect, the cross-polarization coupling length is only 5.21 μm. The transverse magnetic to transverse electric polarization conversion efficiency is over 99.9%, with an extinction ratio of 20.6 dB (32.5 dB) for the transverse magnetic (transverse electric) mode at 1.55 μm. Furthermore, the polarization conversion efficiency is higher than 90% while maintaining cross talk below ?19 dB within the bandwidth of 80 nm.

A new disordered crystal Nd:SrAl12O19 (Nd:SRA) with an Nd3+ doping concentration of 5% was successfully grown using the Czochralski method. A diode-pumped Nd:SRA Q-switched laser operating at 1049 nm was demonstrated for the first time, to the best of our knowledge. Based on an MXene Ti3C2Tx sheet, a high repetition rate of 201 kHz and a Q-switched pulse width of 346 ns were obtained when the absorbed pump power was 2.8 W. The peak power and single pulse energy were 1.87 W and 0.65 μJ, respectively.

A deep convolutional neural network is employed to simultaneously measure the beam-pointing and phase difference of sub-beams from a single far-field interference fringe for coherent beam combining systems. The amplitudes of sub-beams in the measurement path are modulated in order to prevent measuring mistakes caused by the symmetry of beam-pointing. This method is able to measure beam-pointing and phase difference with an RMS accuracy of about 0.2 μrad and λ/250, respectively, in a two-beam coherent beam combining system.

For the first time, a group-VI single element nanomaterial was used as the optical saturable absorber (SA) to generate laser pulses. With two-dimensional (2D) tellurene as a passive Q-switch, 1.06 μm and 1.3 μm pulse laser operations were realized from a diode-pumped Nd:YAG crystal. The shortest pulse widths were 98 ns and 178 ns, and the highest peak powers were 2.68 W and 2.45 W, respectively. Our research determines that tellurene is an excellent SA material in the near-infrared region.

The Laguerre–Gaussian (LG) mode beam has very important applications in many research fields. Here, the Theon sieve is first introduced into the laser resonator to generate petal-like laser beams by coherently superimposing two high-order LG modes. The effectiveness was verified by GLAD software. The petal-like laser beam is derived from the light field redistribution and coherent superposition caused by the diffraction effect of the Theon sieve. The relationship between the order of the petal-like laser and the cavity structures has also been investigated in detail. Light field operation in the laser cavity greatly simplifies the optical structure and is more beneficial to optical diagnostics and imaging.

We demonstrate a novel multifunctional radar receiver scheme based on photonic parametric sampling. The working principle of photonic parametric sampling based on four-wave mixing (FWM) process is presented. To experimentally verify the multifunctional feasibility, the scheme is individually implemented to carry out a four-channel phased array radar reception and a dual-band radar reception.

In this Letter, vortex phase and sinusoidal phase modulations of Hermite–Gaussian beams are studied theoretically and experimentally. The coding method of the experiment is introduced in detail, and the evolution law of focus under different beam order (m, n) and topological charge (l) is given. In order to verify the accuracy of the generation experiment, the optical field distribution under sinusoidal vortex modulation is analyzed deeply. The relevant analysis and methods provided in this Letter have certain practical significance for the development of laser mode analysis, optical communication, and other fields.

We investigate the influence of the source’s energy fluctuation on both computational ghost imaging and computational ghost imaging via sparsity constraint, and if the reconstruction quality will decrease with the increase of the source’s energy fluctuation. In order to overcome the problem of image degradation, a correction approach against the source’s energy fluctuation is proposed by recording the source’s fluctuation with a monitor before modulation and correcting the echo signal or the intensity of computed reference light field with the data recorded by the monitor. Both the numerical simulation and experimental results demonstrate that computational ghost imaging via sparsity constraint can be enhanced by correcting the echo signal or the intensity of computed reference light field, while only correcting the echo signal is valid for computational ghost imaging.

We experimentally demonstrated optical wireless power transfer (OWPT) using a near-infrared laser diode (LD) as the optical power transmitter. We considered a photovoltaic (PV) cell and a photodiode (PD) as the optical power receivers. We investigated the characteristics of the LD, PD, and PV cell in order to determine the optimum operating condition from the viewpoint of transfer efficiency. We also experimentally demonstrated a whole system optimization process to maximize the DC-to-DC transfer efficiency of the OWPT. Our experimental results showed that the optimization process can improve the OWPT efficiency by up to 48%.

Imaging through scattering media via speckle autocorrelation is a popular method based on the optical memory effect. However, it fails if the amount of valid information acquired is insufficient due to a limited sensor size. In this Letter, we reveal a relationship between the detector and object sizes for the minimum requirement to ensure image reconstruction by defining a sampling ratio R, and propose a method to enhance the image quality at a small R by capturing multiple frames of speckle patterns and piecing them together. This method will be helpful in expanding applications of speckle autocorrelation to remote sensing, underwater probing, and so on.

We propose a metalens for coaxial double wavelength focusing. One focusing spot is a circular solid spot, and the other focusing spot is a doughnut-shaped spot that is circling the solid spot. The designed metalens was composed of a meta-molecular nanostructured cell array. Each meta-molecular nanostructured cell was divided into four squares. Two slots with exactly the same shape, but usually with the rotation angle measured clockwise from the positive x axis, are etched into the gold film in two diagonally connected squares. Another two slots with the same shape but with the rotation angle measured counter-clockwise from the positive x axis are etched into another two diagonally connected squares in the same cell. The lasers with two different wavelengths are transformed into right-handed and left-handed circularly polarized beams, respectively. The two sets of slots with different azimuthal rotations modulated the phases of incident right-handed and left-handed circularly polarized beams independently. The numerical simulation with finite-difference time-domain (FDTD) software was carried out, and the experimental verification was also implemented. Both the experimental result and the numerical simulation agree well with the theoretical design.

This study provides a rapid method for quantification of mineral oil in rapeseed oil using near-infrared spectroscopy. The data were processed by direct orthogonal signal correction (DOSC), successive projections algorithm (SPA), partial least squares, and principal component regression (PCR). Good correlation coefficients (R) of 0.998 and root-mean-squared error (RMSE) of 0.005 were obtained, and the DOSC-SPA-PCR model was identified as the optimal method. A satisfactory accuracy with R and RMSE of prediction by DOSC-SPA-PCR of 0.990 and 0.006, was obtained. The results demonstrate that the proposed methodology is a promising method for the rapid quantitative detection of mineral oil in vegetable oil.

The photoelectric properties of conductive films are improved by doping Ag on aluminum-doped zinc oxide (AZO) films by laser induced forward transfer (LIFT). Firstly, the picosecond laser induced transfer mechanism of Ag films was revealed by numerical simulation; then, different-thickness Ag films were deposited on the AZO films by picosecond LIFT. When the film thickness is 30 nm and 50 nm, we have successfully obtained some Ag-AZO films with better optoelectronic properties by adjusting the laser parameters.

In recent years, multi-wavelength fiber lasers play a significant role in plenty of fields, ranging from optical communications to mechanical processing and laser biomedicine, owing to their high beam quality, low cost, and excellent heat dissipation properties. Benefitting from increasing maturity of optical elements, the multi-wavelength fiber laser has made rapid developments. In this review, we summarize and analyze diverse implementation methods covering continuous wave and pulsed fiber lasers at room temperature conditions: inserting an optical filter device and intensity-dependent loss structure in the resonant cavity, and applying ultrafast nonlinear optical response of materials and a dual-cavity structure. Finally, future challenges and perspectives of the multi-wavelength fiber laser are discussed and addressed.