With the rapid development of electronic industry, higher and higher requirements are placed on the surface quality of optical components in electronic devices. Structured-Light Modulation Analysis Technique (SMAT) was recently proposed to detect the contamination and defects on specular surfaces. In this paper, the proposed mechanisms and mathematical models of SMAT are analyzed and established based on the theory of photometry and the optical characteristics of contamination and defects for the first time. What’s more, a novel transmission system adopting SMAT is especially designed for the defect detection of transparent objects. For both reflection and transmission system, simulations and experiments were conducted, and comparative studies with uniform planar illumination were also carried out. Simulations on the influence of incident light source region showed that SMAT can eliminate the interference of ambient light while uniform planar illumination technique cannot. Experiments on samples with specular surface and transparent material demonstrated that the modulation values at the contamination and defects are much less than that at clean and intact place, and defects and contaminations were clearly distinguished based on SMAT, while they were almost indiscernible with uniform planar illumination. Therefore, SMAT can be applied to the whole-field inspection of optical components in industrial environments.

Phase Measuring Deflectometry (PMD) and Structured-Light Modulation Analysis Technique (SMAT) perform effectively in shape and defect measurements of specular objects, but the difficulty of giving consideration to accuracy and speed has also restricted the further development and application of them. Inspired by recent successes of deep learning techniques for computational imaging, we demonstrate for the first time that deep learning techniques can be used to recover high-precision modulation distributions of specular surfaces from a single-frame fringe pattern under SMAT, enabling fast and high-quality defect detection of specular surfaces. This method can also be applied to recover higher-precision phase distributions of specular surfaces from a single-frame fringe pattern under PMD, so as to realize the 3D shape measurement. In this paper, we combine depthwise separable convolution, residual structure and U-Net to build an improved U-Net network. The experimental results prove that the method has excellent performance in the phase and modulation retrieval of specular surfaces, which almost reach the accuracy of the results obtained by ten-step phase-shifting method.

In order to solve the difficulty of traditional phase measuring deflectometry (PMD) in considering precision and speed, an orthogonal encoding PMD method based on deep learning is presented in this paper. We demonstrate for, what we believe to be, the first time that deep learning techniques can be combined with dynamic-PMD and can be used to reconstruct high-precision 3D shapes of specular surfaces from single-frame distorted orthogonal fringe patterns, enabling high-quality dynamic measurement of specular objects. The experimental results prove that the phase and shape information measured by the proposed method has high accuracy, almost reaching the results obtained by the ten-step phase-shifting method. And the proposed method also has excellent performance in dynamic experiments, which is of great significance to the development of optical measurement and fabrication areas.

We first report a single-light-source orthogonally pumped triaxial atomic magnetometer with a double-cell structure. By using a beam splitter to equally allocate the pump beam, the proposed triaxial atomic magnetometer is responsive to magnetic fields in all three directions, and without sacrificing system sensitivity. The experimental results indicate that, the magnetometer achieves a sensitivity of 22 fT/Hz^1/2 in x-direction with a 3-dB bandwidth of 22 Hz, a sensitivity of 23 fT/Hz^1/2 in y-direction with a 3-dB bandwidth of 23 Hz, and a sensitivity of 21 fT/Hz^1/2 in z-direction with a 3-dB bandwidth of 25 Hz. This magnetometer is useful for the applications that require the measurements of the three components of the magnetic field.

Among numerous mature optical 3D measurement techniques, phase-shift profilometry (PSP) has been widely used because of its high precision and insensitivity to ambient light, and high-speed PSP has become a research hotspot in recent years. Current mainstream high-frame rate PSP projection techniques employ binary defocusing projection schemes, which limit the available measurement depth. We propose a high-frame rate, large-depth-range sinusoidal fringe projection technique based on step-designed LED chips array. In principle, on the one hand, the LED chips array still produces a binary pattern, so high-frame rate switching can be achieved, on the other hand, whether focusing or defocusing can generate sinusoidal fringes, avoiding the limit of defocusing projection on the depth range of measurement. A PSP projector is designed and manufactured, and 3D reconstruction of static human face mask and dynamic rotating fan is carried out at 1 kHz frame rate. In another experiment, the PSP projector projected the fringes at a 100kHz frame rate and detected the fringes with a single point photodetector, and the output waveform showed that the projection technique had the potential to be much higher than the 100 kHz frame rate. These results show that the PSP projection technology has the advantages of high-frame rate and large-depth-range, and is very useful for three-dimensional measurement of moving targets.

In this paper, we investigate the output performance of a continuous-wave Ho³⁺-doped fluoride fiber laser operating at 3.92 µm from the ⁵I₅ → ⁵I₆ transition of Ho³⁺ using numerical simulation. A double-clad Ho³⁺-doped fluoroindate fiber with a doping concentration of 10.0 mol.% is assumed, with direct pumping at 888 nm. We propose simultaneous lasing on the ⁵I₆ → ⁵I₇ transition to enhance the slope efficiency while reducing the threshold and heat accumulation. Simulation results indicate that a slope efficiency of 17% and a threshold of 2.5 W can be obtained using a 9 cm-long fiber. Moreover, with the heat accumulation reduced by >40%, watt level laser output can be achieved in this cascade system at room temperature without the gain fiber being damaged by heat accumulation. The theoretical maximum output power of 1.27 W is 6 times higher than the highest reported value (197 mW), which is limited by the fiber damage due to excess heat load.