Nonlinear polarization rotation (NPR) mode-locked lasers have attracted numerous attention due to their compact structure and high reliability. Based on this mold locking principle, an ytterbium-doped fiber femtosecond laser was designed and built. When the bidirectional pumping power reached 380 mW, the laser was mode-locked with a fundamental frequency repetition rate of 22.8 MHz. The output pulse was centered at 1030 nm with 224 fs for the pulse duration, 180 mW for the average power, 8 nJ for pulse energy, and 40 nm for the bandwidth at 10 dB. The beam had a good quality with signal-to-noise ratio greater than 50 dB. The laser can realize self-start mode locking with a ring laser structure. Besides, the third order passive harmonic mode locking with 68.5 MHz for the repeat frequency was observed by increasing the pump power to 1.6 W. Due to the advantages of line width, pulse width and pulse energy, the laser has application significance in spectral measurement, Raman imaging and other fields.

In the process of face expression analysis, head pose changes often cause asymmetry in face information, and it is difficult to obtain features that are robust to pose by traditional operations related to cropping and aligning face images only. In order to obtain structured features of faces, a face image frontalization processing method is proposed in the paper. The method maps the detected face landmarks to a new two-dimensional space for frontalization of landmarks, then restores the frontalized landmarks to the original image as new landmarks, and guides the image deformation from the original landmarks to the new landmarks by moving least squares to obtain the frontalized face image. The face images are preprocessed on public RAF-DB and ExpW face expression datasets using the proposed processing method, models are trained in VGG16 and ResNet50 deep learning networks for face expression classification tasks. The effectiveness of the frontalization method in the paper for face expression analysis is evaluated by the accuracy of the classification tasks. The experimental results show that this proposed method outperforms traditional pre-processing methods of deep learning in face expression analysis and can effectively improve the quality of face information.

Cell microscopic imaging is an important tool for cell phenotype detection. Traditional fluorescence imaging techniques are widely used in the cell imaging. However, the fluorescence imaging instruments have complex structure and high cost. Besides, staining could cause damage to cells. To address this problem, this paper proposes a virtual staining technique that performs strict alignment of bright field and fluorescence image datasets using a multimodal alignment algorithm, and improves network architecture, loss function, post-processing, and hardware adaptation for training optimization. The staining conversion bias is calculated by the evaluation criteria of the virtual staining. The method presented in this paper could simplify the fluorescence imaging equipment and eliminates the need for various staining operations, which could reduce the burden of research and diagnostic processes for biologists and pathologists.

A method for achieving the Raman signal excited by the longitudinal component of radially polarized light is proposed in this paper to solve the problem that ordinary polarized Raman signal cannot detect samples with vertical molecular orientation. In this method, the focused azimuthally polarized light and radially polarized light are used to excite the sample, and then the Raman signals generated by the two excitation lights are calculated to obtain the Raman signals excited by the pure longitudinal light field. We use Si(0 0 1) samples and Si(1 1 0) samples to verify the feasibility of this method. This work has certain significance for measuring longitudinally oriented molecules and longitudinal molecular vibration modes by Raman scattering.

The error of photoelectric encoder detection system is mainly affected by the angle measurement error of the reference photoelectric encoder, data acquisition error and coaxial error. The angle measurement error can be compensated. In this paper, an algorithm based on extreme gradient boosting (XGBoost) machine learning is designed to compensate the error of the reference photoelectric encoder. After compensation, the static accuracy is improved by 35 times. The standard deviation is decreased from 3.62" to 0.13", and the maximum error value is reduced from 5.53" to 0.39". Compared with the traditional back progagation (BP) neural network algorithm and radial basis function (RBF) neural network algorithm, XGBoost's compensation is better than the others. XGBoost machine learning algorithm compensation effectively reduces the measurement error of the reference photoelectric encoder and improves the detection accuracy of the photoelectric encoder detection system.

A long-term stability control scheme of the dynamic cavity length based on coupled optoelectronic oscillator is proposed. When the cavity length of the optical resonator changes, the resonant phase variation of two selected positions in the optical resonator is measured by the IQ mixer, and the optical delay line in the regeneration cavity is feedback-controlled to following compensation of the regeneration cavity length, and the controlled mode-locked output of the coupled optoelectronic oscillator with variable cavity length is realized, to convert the changing cavity length into the changing resonator frequency for measurement. After systematic experiments, the optoelectronic oscillator can output a variable locked microwave signal, and keep the side mode suppression ratio better than 47.26 dB, the power jitter less than 0.28 dB, and the lock phase error jitter within ±1.5° within 1 hour.

The main method for melanoma is photodynamic therapy (PDT), and the design of more efficient photosensitizers is the key point to melanoma therapy. To promote the therapeutic effect of PDT, a novel photosensitizer was designed. The substrate was the Protoporphyrin IX (PpIX), then the demethylated drug SGI-1027 and PpIX were encapsulated by the synthesized PMHC18-mPEG to form the SGI@PpIX-mPEG complex system. PpIX exposed to illumination causes cells to produce a large amount of reactive oxygen species (ROS), which would increase the content of the downstream protein Caspase-3. The demethylated drug increases the content of GSDME. Research indicates that the synthesized novel photosensitizer drug can not only generate reactive oxygen species to kill cancer cells, but also further lead to pyroptosis and enhance the effect of photodynamic therapy through the interaction between Caspase-3 and GSDME.

Microscopic techniques cannot resolve subwavelength scale structures due to the diffraction limit of optical imaging systems. Super-resolution imaging of single nanoparticles has been achieved by saturation scattering suppression imaging techniques, but when it comes to ensembles of nanoparticles, the coupling between nanoparticles needs to be considered. Far-field super-resolution optical imaging can be achieved on ordered gold nanorod arrays using a two-beam method beyond the diffraction limit. In this paper, a 5×5 gold nanorod array with an aspect ratio of 2 is designed, the thermal distribution of the gold nanorod array under continuous-wave laser is calculated by the vector light field theory and thermal diffusion theory, and the scattering imaging under dual-beam laser, i.e., pulsed excitation light and continuous-wave suppression light, is simulated. The simulation results show that the continuous-wave laser can effectively suppress the pulsed laser scattering of gold nanorod arrays, and the two-beam approach achieves super-resolution imaging with 80 nm resolution.

Optical information processing technology has the characteristics of high speed and parallelism. The wavelength of light is short and the information capacity is large. At the same time, it has many attributes such as amplitude, phase, wavelength and polarization, which could be the carrier of multi-dimensional information. Therefore, optical encryption is of great significance in the field of information security transmission and is widely used in the field of image encryption. For multiple image encryption, this paper proposes a multi image encryption algorithm based on cascaded phase iteration and computational ghost imaging. This method can encrypt multiple images efficiently at the same time, which is simple, safe and reliable, and has less transmission data. The encryption effect of this method is evaluated by using correlation coefficient, and the effectiveness and security of this method are verified by simulation.

This paper mainly solves the problem of accurate positioning of reference points in deflection measurement of concrete structures. The fitting algorithm of Gaussian spot is derived. The existence of the parameter Krame-Rowe lower bound is proved, and the corresponding parameters are optimized by the Levenberg-Marquardt method. The experimental results show that the root mean square error attenuated by the center extracted by the Gaussian fitting spot localization algorithm based on nonlinear parameter optimization is 0 when the signal-to-noise ratio is 40 dB. As the contrast decreases, the extraction accuracy of the three methods deteriorates. The Gaussian fitted spot localization algorithm based on nonlinear parameter optimization is superior to other algorithms before the contrast drops to 25% of the original image, but this advantage disappears when the contrast continues to decrease. It shows that in the case of good contrast, it can not only ensure accuracy but also improve robustness.

The region segmentation is an important pre-processing step in optical interferogram processing, in which the effective region is extracted from interferogram. The region segmentation of interferogram widely exists in the experimental testing and data processing of various digital wavefront interferometers. It has important influence on accurate wavefront retrieval and reliable implementation of phase unwrapping. The paper introduces the region segmentation technology of three kinds of popular interferogram, including single-frame interferogram, simultaneous phase-shifting interferogram and lateral shearing interferogram. The related research progress is systematically summarized, and the research trend in this field is also prospected.

In order to design coated fiber for optical frequency domain reflectometer (OFDR) temperature sensing, improve the temperature sensitivity of OFDR and increase its applicable scenarios, this paper theoretically analyzes and simulates the effects of one and two layers of coating on the temperature sensitivity of Rayleigh frequency shift in single-mode fiber. Firstly, the effects are analyzed by using the Lame solution theory in term of the geometrical, thermal and mechanical properties of the coating. Secondly, a simplified solution with only one layer of coating is proposed based on the relationship of axial strain in optical fiber caused by temperature and the force balance between optical fiber and one layer of coating. Finally, the temperature sensitivity of Rayleigh frequency shift of the one-layer and two-layer coated optical fiber is simulated on the basis of the established theoretical model. The results show that the sensitivity increases with the increase of Young's modulus, radius and thermal expansion coefficient of the outer coating. However, it is almost independent of Poisson's ratio of the coating. The results of this paper could broaden the application of OFDR in high temperature sensitive and cryogenic temperature scenarios.

In order to overcome the problems of traditional fabrication of semiconductor field effect transistors (FET), such as material damage, limited alignment accuracy, the difficulty of transferring the electrode and high cost, a fabrication technique of semiconductor FET based on a flexible stencil technology was proposed. Ultra-violet lithography technology can be used to fabricate the flexible stencil. Then, the stencil was directly scooped up, heated and dried. The metal was deposited by ion beam sputtering technique, and N-channel depletion FET was obtained by transferring semiconductor CdSe nanobelts to the electrode, which confirmed the functionality and the feasibility of this technique. The technique has low cost and low material damage, and it provides a new way to fabricate integrated semiconductor devices.