In this paper, for improving the performance and stability of MoS2 saturable absorber, graphene oxide (GO) as colloidal surfactant is used to exfoliate MoS2 bulk material for obtaining few-layer GO-MoS2 nano-flakes. Further research on few-layer GO-MoS2 saturable absorber to mode-lock erbium-doped fiber laser (EDFL) is then conducted. In the experiment, a stable mode-locked pulsed laser is achieved with a center wavelength of 1558 nm, a repetition rate of 7.86 MHz and a pulse width of 1.9 ps. When the pump power reaches 60.5 mW, the output power is 0.48 mW and the pulse peak power is calculated to be 32.1 W. This work shows that the new composite 2D material prepared by this method is beneficial to maintain the stability of few-layer MoS2 and increase the damage threshold of the MoS2 saturable absorber for passive mode-locking.

We demonstrate a tunable actively mode-locked fiber laser at 2 μm band. A segment of 4 m Tm-Ho-co-doped fiber is used as gain medium. Active mode locking pulse is realized by using intensity modulation and the signal source is high frequency sinusoidal signal. A tunable narrow bandwidth optical filter is used to narrow laser linewidth, suppress noise and achieve wavelength tuning. Stable actively mode-locked pulses with up to 2.2 GHz repetition rate is obtained, corresponding to 649 order harmonic mode-locked pulse train. The pulse width is about 200 ps. The signal-to-noise ratio of RF spectrum is 68 dB. The optical tuning range is 1907 nm~1927 nm.

The accuracy of centroid estimation for Shcak-Hartmann wavefront sensor is highly dependent on noise, especially for the centre of gravity (CoG) method. Therefore, threshold selection is very important. This paper proposes a local adaptive threshold segmentation method based on statistical rank, which can reduce the influence of uneven background noise and decrease the wavefront reconstruction error more effectively, comparing with the traditional global threshold method. An experiment measuring static aberration was conducted, the accuracy of centroid estimation and wavefront reconstruction both testify the effectiveness of this method. Besides, we found that combing the local adaptive threshold method and intensity weighted centroiding (IWC) method can improve the performance of traditional centre of gravity method. It achieves higher centroiding accuracy under SNRp between 10~40 conditions.

A continuously tunable Q-switched all-fiber Er-doped laser based on a 45° tilted fiber grating and tunable bandpass filter is demonstrated. The 45° tilted fiber grating is used to achieve the nonlinear polarization rotation (NPR) along with two polarization controllers (PCs), Q-switching is realized due to the fact that the NPR effect in- duced intensity-dependent loss. Under the pump power of 655 mW, the Q-switched optical spectrum can be continuously tuned from 1512 nm to 1552 nm by simply rotating the tunable bandpass filter. During the wavelength tuning process, the average output power increases from 0.282 mW to 4.884 mW while the repetition rate enhances from 27.3 kHz to 119 kHz. To the best of our knowledge, this is the widest continuously tunable range of Q-switched fiber Lasers based on nonlinear polarization rotation effect and spectral bandpass filter.

In order to realize fast and accurate detection of moving targets under complex dynamic background, a moving object detection method based on BRISK (binary robust invariant scalable keypoints) algorithm is proposed. Firstly, the image is divided into blocks, and the image blocks are filtered by using image entropy. Then, aiming at the problem of large number of mismatch in the process of feature matching, the k-nearest neighbor algorithm and Euclidean distance are used to perform feature matching. Finally, the improved sequential sampling consistency algorithm is used to refine the feature points and further completes the background motion compensation, and morphological processing is used to segment the moving target. Through the verification of multiple video images, the proposed algorithm removes 32.7% of the feature points based on the original BRISK algorithm and improves the matching efficiency by 75%. The proposed algorithm has faster processing speed than previous algorithms and strong anti-noise performance.

In order to detect and analyze the complex multi-mode dynamics of fiber ring laser (FRL), in this experiment, based on the heterodyne detection method together with radio-frequency spectrum, the output of FRL intensities on two kinds of modulation condition are synchronously detected and analyzed. From the low dimension to high dimension chaos, the total intensity and multi-mode characters can be synchronously acquired. These experimental results show the relationships between real-time intensity and frequency evolution behaviors about single mode and total mode. Moreover, according to experimental results, the chaotic characteristics and inner relationships of erbium- doped fiber ring laser (EDFRL) output mode dynamic can be analyzed.

In order to analyze and process the random error of the fiber optic gyroscope (FOG) and improve its use precision, an error modeling method that combined empirical mode decomposition (EMD) and time series model was proposed. On the basis of the intrinsic mode functions (Imf) which was obtained by empirical mode decomposition, auto-regressive and moving average model (ARMA) modeling is performed hierarchically for each Imf. Then, Kalman filtering is performed layer by layer on the basis of the model to remove the random drift signals from the real angular velocity information. At the end of the algorithm, the signal which had been filtered need to be reorganized, and through the above steps, the conception of analyzing and modeling in connection with the random error of FOG from full frequency’s point of view was realized. Compared with other modeling methods, this method has a higher degree of simulation matching to the original data, at the same time, the experimental results have further shown that this method can effectively remove the signal of random drift from the fiber optic gyroscope’s output signal and improve its use precision significantly.

The evolution of cosine-super Gaussian (CSG) pulses propagating in a conventional single mode fiber (SMF) has been proposed. The propagation properties of CSG pulses are numerically studied by using split-step Fourier method, and the effects of initial phase φ0 and order of the pulse m are analyzed. Results show that when φ0 is increased to 80 rad, the first order CSG pulse will be compressed in a relatively long fiber, and then broaden monotonically; the higher order CSG pulses will experience a short compression first, and then broaden monotonically. In addition, the CSG pulses are compared with simple Gaussian pulses and Hyperbolic secant pulses. The results indicate that the Hyperbolic secant pulse broaden fastest; the simple Gaussian pulse broaden secondly; CSG pulses broaden slowest, which is most insensitive to the dispersion of fiber. The research work will pave a way to realize a special pulse in large-capacity, and long-range communications.

The optical aperture of the antenna is an important technical indicator of the liquid crystal optical phased array. Based on the multi-subarray parallel driving and two-level device cascade method (PAPA), in this paper, an improved i-PAPA method was proposed. Large area phased beam control is realized on a single phased array antenna by subdivision of the COM electrodes, and it has the advantages of single device operation and low insertion loss. Through numerical simulation, the results show that the antenna near field phase has continuous distribution; when the point angle varies from 0 degrees to +6 degrees, the far-field diffraction efficiency drops smoothly and monotonously as the point angle increases, the diffraction efficiency is greater than 48%; When the point angle varies from 0 degrees to +3 degrees, the diffraction the efficiency is greater than 80%.

With the widespread application of ultraviolet spectroscopy, low-cost portable ultraviolet spectrometer has become a research focus in this field. Firstly, the optical structure of the portable UV-VIS spectrometer was designed based on the crossed-asymmetric Czerny-Turner structure in the paper. Secondly, the key devices of ultraviolet spectrometer, namely ultraviolet detectors and blazed gratings, were studied. The coated UV-enhanced CCDs were fabricated using Lumogen fluorescent materials and vacuum coating methods. The influence of the position on the CCD surface of the fluorescent film on the resolution was analyzed. The effect of blazed gratings on the multi-order diffraction efficiency in the ultraviolet region was theoretically studied. Finally, the test results of performance of a portable UV-VIS spectrometer prototype show that the resolution of the 200 nm~900 nm band, 25 μm slit width, 600 lp/mm, 300 nm blazed grating configuration is less than 1.5 nm and the spectral responsivity increases to 20% in the spectral range varying from 200 nm to 300 nm, which meets the design requirements of the portable UV-VIS spectrometer.

Because of the size limit of the spectrometer, the resolution of the micro-spectrometer is usually difficultly less than 0.1 nm when it meets certain spectral range. While some special applications require that the spectrometer not only has small size, but also requires extremely high spectral resolution. We used Zemax (optical design software) to choose the initial structure parameters and evaluation function to automatically optimize angle and distance of focus lens, cylindrical lens and CCD to design an optical system of spectrometer of Czerny-Turner structure. Its resolution is better than 0.05 nm, and the volume of the system is 90 mm×130 mm×40 mm. On this basis, eight grating slanting angles were optimized, and the spectral resolution of the micro-spectrometer is better than 0.05 nm, while the band range reaches 820 nm～980 nm. So the spectrometer has the characteristics of high resolution, wide spectrum and small volume.