High-concentration CO2 has a great impact on the accuracy of H2S detection. Thus, this paper proposed a H2S and CO2 detection system based on fiber amplifier enhanced photoacoustic spectroscopy. A single distributed feedback (DFB) laser in series with a high-power erbium-doped fiber amplifier (EDFA) was taken as the photoacoustic excitation source for the high-precision detection of H2S and CO2 simultaneously. In addition, we analyzed the interference of CO2 on H2S detection at the selected H2S absorption line and corrected the measured H2S concentration with the detected CO2 concentration. The results show that the deviation of the corrected H2S concentration remains within -5% to 5%. Moreover, we used Allan variance analysis to calculate the detection limit of the system. When the integral time is 1 s, the detection limits to H2S and CO2 are 656.3×10 -9 and 25.2×10 -6, respectively; when the time is 100 s, the detection limits can reach 61×10 -9 and 2.6×10 -6, respectively. For trace H2S detection, the normalized noise equivalent absorption (NNEA) coefficient is calculated to be 5.5×10 -9 cm -1·W·Hz -1/2. In conclusion, the proposed system has high detection accuracy and good stability.

In this paper, we proposed a photonic crystal fiber (PCF) with a sandwiched structure to improve the sensitivity of the transverse pressure sensors and decrease the interference caused by temperature. In addition, we used a finite element method (FEM) to simulate the sensing characteristics of its Brillouin dynamic grating. Furthermore, we investigated the birefringence-induced frequency shift of the proposed PCF at different pressures and temperatures and analyzed the influence of the PCF structure on its sensing characteristics. The results show that the designed PCF has high sensing precision. At 0--40 ℃, the pressure sensitivity on the slow and fast axes was about 692 MHz/MPa and -404 MHz/MPa, respectively; the temperature sensitivity was only 0.18 MHz/℃ at 0--40 MPa. In comparison with the pressure sensing system designed with a conventional polarization-maintaining PCF, with a sensitivity of 199 MHz/MPa, the sensitivity of our PCF was increased by 493 MHz/MPa. In conclusion, the PCF proposed in this work improves the sensitivity of the transverse pressure sensors and eliminates the interference of temperature, having potential applications in high-precision transverse pressure sensing.

We proposed a novel intelligent system for long-distance optical fiber pre-warning and investigated its predictive accuracy in real working environment. The system mainly includes two parts: distributed sensing and signal recognition. Specifically, the phase-sensitive optical time domain reflection (Φ-OTDR) technology was used for distributed sensing and the neural network technology was used for signal recognition so as to recognize and classify intrusion events. In addition, an improved neural network structure was proposed in the signal recognition and compared with a neural network based on wavelet packet decomposition and that with three hidden layers. Finally, we performed three different experiments to explore the recognition accuracy of the system. The results show that the proposed system can well recognize and classify the intrusion events with an average recognition rate above 95%.

In this study, we use multiple independent parallel spatial channels in multi-core fibers to achieve spatial diversity in solving the signal fading and limited signal-to-noise ratio of distributed fiber acoustic sensing systems based on traditional single-mode fibers. We use the fan-in and fan-out modules for independent transmission and centralized reception of signals in four cores of the multi-core fiber, and multiple signals can be aggregated effectively using a coherent aggregation method. The experimental results show a well-reconstructed external disturbance signal, suppressed signal fading, and reduced noise floor by 5.2 dB compared with that of the optimized single-mode fiber system. The sensor exhibits high-level performance: lowest noise floor of -85 dB and bandwidth of 10 kHz.

In this study, a dual-channel probe type 81° tilted fiber grating (81°TFG) sensor is proposed and used for the evaluation of alpha-fetoprotein (AFP) immunoassays. First, the end face of 81°TFG is plated with a silver film to form the reflective type 81°TFG, and a dual-channel sensor is constructed by a 2×2 coupler and two 81°TFG probes. Then, large-size AuNs and GO are modified on the grating surface, and AFP monoclonal antibodies are used as the specific recognition unit to modify the grating surface to achieve a dual-channel probe type 81°TFG local surface plasmon resonance (LSPR) AFP immunosensor. Finally, the immune detection experiment is completed in a complex serum environment. The results demonstrated that the detection limit of the sensor for the mass concentration of AFP antigen is within the range of 1--10 pg/mL, the detection saturation point and sensitivity are ~200 ng/mL and ~0.155 nm/log(pg/mL), respectively, it has a satisfactory specific response to the serum of liver cancer patients is observed. Compared with the single-channel transmission type 81°TFG sensor, the sensor could simultaneously control the detection of positive and negative samples of the target molecules; therefore, enhancing the reliability in clinical detection applications, and the operation is simpler and the application potential is greater.

In underwater optical wireless communication (UOWC), optical transmission can occur near the water surface. Therefore, the influence of water surface wave disturbance on communication performance cannot be ignored. In this study, a near-surface UOWC system is developed in a laboratory environment. The water surface wave disturbance scene is generated by fan control, and the influence of the water surface wave disturbance on the communication performance is studied. In the experiment, non-return-to-zero on-off keying (NRZ-OOK) modulation is adopted to study the influence of input light intensity and water surface wave disturbance on the bit error rate (BER) of a pseudo-random signal with a rate of 500 Mbit/s transferred in a 10 m tap water channel. The results show that the BER of the system is closely related to the input light intensity when the optical signal is transmitted near the water surface. The water surface wave disturbance has a significant impact on the quality of communication, which is related to the range of the water surface wave disturbance in the optical transmission link and also to the depth of the water surface wave disturbance. Moreover, the BER presents a certain statistical law with the range and depth of the disturbance. This statistical law has a certain guiding significance for receiving, tracking, and aiming devices of the near-water surface optical link, water-air link, and air-water link of a wireless optical communication system.

Pansharpening aims to obtain hyperspectral images with high spatial resolutions by fusing hyperspectral images with low spatial resolutions and panchromatic images with high spatial resolutions together. This paper introduces a remote sensing image fusion method based on a deep convolutional neural network (CNN), which extracts spectral and spatial features step by step from hyperspectral and panchromatic images using two independent branch networks. The proposed fusion network is composed of two branches and a main network. The two independent branch networks are used for extracting the spatial-spectral features from hyperspectral and panchromatic images, while based on the features extracted from the branch network, the main network is used to reconstruct and the final fused hyperspectral images with high spatial resolutions are obtained. The experimental verifications were conducted on both CAVE and Pavia Center datasets. Through comparison, one can see that the proposed fusion algorithm outperforms the prevailing algorithms in terms of spatial detail and spectral fidelity.

In the process of imaging, the division-of-focal-plane (DoFP) polarization detector is often disturbed by noise, and it affects the quality and accuracy of the polarization images. In this paper, first, based on the non-local self-similarity of the image and the correlation between images with different polarization directions, the image is divided into blocks by using the spatial distribution characteristics of the DoFP polarization image, and similar image blocks are selected to form a similar block matrix. Then, principal component analysis (PCA) is used to obtain the eigenvalue matrix and eigenvector matrix of the similar block matrix, based on the eigenvalue distribution characteristics of the noise and the similar block matrix, and use dimensionality reduction to denoise the image in the PCA domain. Finally, simulated and real DoFP polarization images are used to evaluate the denoising effect of the algorithm. Experimental results show that the algorithm can effectively suppress the noise in the image and preserve the texture and edge details of the image, which is at least 1 dB higher than the peak signal-to-noise ratio of existing algorithms.

Terahertz focal plane imaging is a practical imaging technology with characteristics of rapid imaging and simple structure, which exhibits advantages for terahertz imaging of biological tissue. In this paper, a reflective continuous-wave terahertz focal plane imaging system is built to image fresh pork tissue, rat brain tissue, and human glioma tissue. It is found that the scattering of targets’ uneven surface can be reduced by adding imaging window. Meanwhile, non-uniform illumination can be eliminated by flat field correction. The results show that reflective continuous-wave terahertz focal plane imaging system can be used for the real-time imaging of biological tissue, which provides an effective technical method for the rapid label-free imaging of biological tissue.

The passive infrared remote sensing system for gas detection has the advantages of low costs, small volume, and easy expansion. Due to signal drift and background noise interference in passive infrared gas detection based on narrow-band pass filters, it is necessary to modulate, filter and phase-lock the signal. In addition, the measurement signal received by the system is greatly by photochopper radiation, so we should establish a radiation model for the measurement process. In light of this, we investigated a radiation model for passive infrared detection based on a lock-in amplifier in this paper and proposed a signal processing method with phase judgment after the lock-in amplifier. Furthermore, we designed and built a passive multispectral system for gas detection, which was calibrated in the laboratory, and we also carried out blackbody measurements at different temperatures. The results show that the measured radiance on each channel is consistent with that from the established model. This study provides a model basis and experimental verification for passive infrared signals based on lock-in amplifiers, as well as a reference for the development of portable remote sensing systems for gas detection in a short range.

A recirculating delayed self-heterodyne method with a short fiber is proposed for the precise measurement of sub-kHz laser linewidth. Using the recirculating delayed self-heterodyne interferometer with an only 2 km delayed fiber, a series of beat signals with different delay times are simultaneously measured. By simulating and fitting the power spectra of multiple high-order beat signals, the average linewidth of 944 Hz for a laser is obtained, which is basically in agreement with that obtained by the traditional beat frequency method. The proposed method can not only avoid a single measurement error, but also effectively reduce the frequency broadening induced by the 1/f frequency noise, therefore it can be used as an accurate detection tool for the linewidth measurement of a narrow linewidth laser.

We proposed a polarization-insensitive 1×3 optical power splitter with broadband performance. Ion assisted deposition was used to change the refractive index of the core SiNx in a sandwiched structure, so that the beat lengths of the orthogonal polarization modes were equal and thus polarization insensitivity was achieved. A combined structure of trapezoidal multimode interference waveguide and tapered waveguide was introduced to realize broad bandwidth, low loss, and good beam splitting uniformity. Furthermore, a finite-difference time-domain method was applied to simulation and optimization, and the results demonstrate that the length of the multimode interference waveguide is only 13.2 μm; the excess loss and imbalance of the splitter are lower than 0.07 dB and 0.03 dB, respectively. In addition, the 0.5 dB-loss bandwidth is as high as 255 nm, which can cover S, C, L, U, and part of E bands. Therefore, the proposed splitter has potential application value in the future integrated optical systems.

In the paper, zinc nitrate aqueous solution is used as electrodeposition solution to prepare zinc oxide (ZnO) nanowalls by the electrochemical deposition method. The effects of deposition voltage on the surface morphology, crystalline structure, Raman spectrum, photoluminescence spectrum, transmittance and ultraviolet detection performance are investigated. The experimental results show that the ZnO nanowalls fabricated by the proposed method have rather good uniformity, exhibit a wurtzite structure, grow preferentially along the (002) crystal plane, and have an obvious E2(high) mode peak. In addition, the ZnO nanowalls have a strong ultraviolet excitation peak at 394 nm. The ultraviolet detection experiments show that the photocurrent of ZnO nanowalls quickly reaches saturation under the irradiation of ultraviolet light and has the maximum value at the deposition voltage of 1.6 V. The corresponding response time and recovery time are 1.36 s and 2.23 s, respectively. The photo-to-dark current ratio is 38.96 and the photoelectric responsivity is 0.611 A/W at the bias voltage of 5 V.

Infrared dome, located at the forefront of an infrared missile, is one of the main components in the missile. According to the requirements of its working environment, the infrared dome should have good optical, mechanical, and thermal properties. At present, the main materials for fabricating infrared domes on the mid-infrared missiles are MgF2, sapphire, spinel, ALON, and nanocomposite ceramic. In this paper, we proposed a ZrO2 nano infrared transparent ceramic dome stabilized by high strength rare earth oxides. The research on the characteristics of the ceramic proved that the material could be used in the mid-infrared missiles. Furthermore, the material was applied to the development of the infrared dome sample. The compatibility test and the simulated dynamic casting test of the sample at the service environment of a missile verified the performance of the material.

In order to reduce the volume and weight of the hand-held binocular telescope, based on the principle of the single-chip multi-surface optical system, this paper establishes the model of the single-chip multi-surface telescope, constructs the relationship expression between the center thickness and the shielding ratio, obtains the initial structure of the system by calculation, and further optimizes a portable multi-surface reflective telescope. The telescope consists of a single lens, in which the light is reflected for four times in the lens, and each reflecting surface is an even aspheric surface. The working band of the system is visible light band, the magnification is 5×, the base of the lens is PMMA, the diameter is 15 mm, the total length is 5 mm, and the full field of view is 1.15°. The optimized full-field wave aberration of the lens meets the requirements of use, the optical modulation transfer function (MTF) curve is smooth and greater than 0.2 at 60 lp/mm, and the image quality is good. By comparing the optimized system with the traditional Galileo telescope system, it is found that the system meets the market demand for portable telescope systems.

Acousto-optic tunable filter (AOTF) imaging spectrometer can acquire image, spectrum and polarization information simultaneously. It has been successfully applied to the aerospace, agriculture, forestry, medicine, food safety, and other fields, thus having good development prospects. Optical system is one of the key parts in an AOTF imaging spectrometer to obtain information. Therefore, the optical systems of common AOTF imaging spectrometers are studied in this paper, and the working principle of AOTF and the general design scheme of the spectrometers are introduced. Furthermore, the optical design parameters of the whole system, such as the front, collimating and imaging sub-systems are calculated, and the common-aperture optical system is simulated. The front optical system has an off-axis three-mirror structure based on free-form surface, which matches with the aperture stop of the collimating system, and the collimating and imaging systems are off-axis three-mirror systems with front offset of the aperture stop. The simulation results show that the system has an MTF values close to the diffraction limit and greater than 0.57 at the bands of 0.4--1.0 μm, 1.0--3.0 μm, and 3.0--5.0 μm, a distortion less than 5%, and good imaging quality, in the case of the working band of 0.4--5.0 μm, F number 5, field of view angle of 5.3°.

Optical phased array is a technical solution to realize non-mechanical beam steering in laser radar. In view of the large size and difficulty of two-dimensional integration of the existing optical phased arrays, we propose a new two-dimensional optical phased array reflector that can realize two-dimensional beam steering. The reflector adopts an easy-to-integrate area array structure and employs the dispersion characteristics of the Gires-Tournois resonant near the resonance wavelength to amplify the phase shift. Simulation results showed that the structure has a high phase shift efficiency near the resonance wavelength, and provides a new solution for realizing two-dimensional beam steering.

As a kind of electromagnetic wave localized between metal and medium, surface plasmons is related to the collective oscillation of free electrons on the metal surface and has the characteristics of high-level localization and near-field enhancement. Therefore, an infrared narrow-spectrum enhanced imaging device is designed by using surface plasmon resonator. A single nanometer plasmon resonator is composed of two silver layers. The simulation results show that the resonator plays a narrow-spectrum absorption role in the infrared band. In the nanometer plasmon resonator, the absorption band is greatly enhanced by an electric field, and the undesired bands can be shielded at the same time. Such a narrow-spectrum CCD (Charge Coupled Device) is expected to be used in high-resolution imaging and daily infrared CCD, and the design demonstrates the commercial value of using a silicon-semiconductor CMOS (Complementary Metal Oxide Semiconductor) platform to fabricate near-infrared CCD with wavelengths around 800 nm.

This paper reports a method of fabricating the Cu2O-Ag SERS substrate by in-situ growth on a copper sheet. The as-fabricated substrate has considerable Raman enhancement after we optimized the annealing temperature and time for Cu2O fabrication and the AgNO3 concentration and reaction time for Cu2O-Ag fabrication. In addition, the concave spaces on the substrate surface and the uniformly distributed Ag NPs provided rich SERS “hot spots”. The substrate also has good hydrophobicity, homogeneity, stability, and sensitivity, and it can detect R6G with the limit of detection (LOD) of 0.78 nM. Furthermore, the substrate has great sensitivity towards several prohibited drugs, and the Raman intensity has an excellent quantitative relationship with drug concentration. To be specific, the LODs for malachite green, enrofloxacin, and nitrofurazone are 4.9 nM, 0.72 μM, and 0.12 μM, respectively. In conclusion, the proposed method has a simple process, low costs, and high SERS activity, indicating bright application prospects for environmental monitoring.

To eliminate the interference of ambient temperature drift in the dynamic refractive index measurement, we propose a refractive index sensor based on a metamaterial structure with alternating grating and graphene. The effect of structure parameters on the response spectra is numerically simulated by the finite-difference time-domain method, the coupling mechanism is analyzed, and the designed structure is optimized. The research results indicate that this sensor with a composite structure possesses the dual spectral characteristics of multi-channel and ultra-narrow linewidth. In addition, the high absorption spectrum at near-infrared region is attributed to the coupling and excitation by F-P cavity resonance effect, magnetic polariton resonance effect, and destructive interference. Based on the differences in refractive index and temperature sensitivity under different resonance modes, with two resonant peak position wavelengths as information carrier and under the help of a matrix equation, the refractive index sensitivity reaches 358.6 nm/RIU after temperature compensation. The results show that the proposed sensor is effective in the real-time dynamic monitoring of samples in the wide refractive index range (1--1.6 RIU), and can avoid the influence of temperature drift, and thus it has more practicability.

Due to the complex vertical distribution of aerosols in the atmosphere, the commonly used gradient method and wavelet covariance transform (WCT) method still have large uncertainties in automatically and continuously identifying the planetary boundary layer height (PBLH). For this reason, we applied the 2-D matrix method to the retrieval of PBLH in two cases observed by a dual-wavelength lidar over Jinhua city. The 2-D matrix method optimizes PBLH retrieval results from the distance and time dimensions. The results show that in the case of profiles with multi-layer aerosols, the 2-D matrix method is superior to the WCT method in terms of PBLH retrieval. The correlation coefficient between the PBLH retrieved by the 2-D matrix method at 532 nm and that by the WCT method at 1064 nm is 0.87. However, the correlation coefficient is only 0.37 if the 2-D matrix method is replaced by the WCT method at 532 nm. Additionally, the consistent variation trend in PBLH and surface temperature indicates reliable PBLH retrieval results. The 2-D matrix method provides a reference for the automatic and continuous identification of the PBLH by lidar in the absence of low clouds (no clouds appearing below 3 km).

Resting on the translation framework of spatially separated images, we proposed a cycle-consistent generative adversarial network (GAN) based on spatial disentangled representation to address the large mode difference and difficult translation between synthetic aperture radar images and optical remote sensing images. The proposed model separates images into style and content features by a deeper network layer and jump connection. Furthermore, the content features are translated by content mapping learning and combined with target style features for image translation. In addition, PatchGAN, as the discriminator, enhances the image detail generation, and target error loss and generation & reconstruction loss are introduced to limit the translation task to one-to-one mapping, thus reducing the information added and constraining the GAN. The experimental results in SEN1-2, SARptical, and WHU-SEN-City datasets show that compared with other image translation algorithms, the proposed method can translate two types of remote sensing images and generate images of high resolution, complete detail features, and strong authenticity.

A micron spectral domain optical coherence tomography (SDOCT) system built by us is used to conduct depth resolution, noncontact, and nondestructive measurement of glass subsurface defects. In addition, a single scattering model is used to calculate the obtained tomographic images, and obtain the glass scattering coefficient of glass subsurface defects. The experimental results revealed that the use of scattering coefficient is effective in distinguishing damage structures at different depths on the glass subsurface. The depth resolution measurement of the glass subsurface scattering coefficient is beneficial to the analysis of the optical characteristics of glass subsurface defects, and is essential for the processing and testing of precision optical components.

Hyperspectral images contain rich spectral information, and the hyperspectral image reconstruction from a single RGB image is of great value to military target recognition and medical diagnosis. Since traditional algorithms cannot reconstruct RGB images with unknown spectral response from cameras, this paper proposes a reconstruction algorithm based on an improved residual dense network. First, with an improved residual dense block as the basic module, we apply the adaptive weight module for feature recalibration, which improves the accuracy of hyperspectral image reconstruction. Additionally, our algorithm solves the hyperspectral image reconstruction instead of image super-resolution through replacing the spatial transformation layer with a feature one, which transforms the network from the spatial dimension to the spectral dimension. The experimental results show that the proposed algorithm is superior to the traditional methods and deep learning methods in both subjective effect and objective evaluation indicators. Compared with those of the sparse dictionary method, the mean relative absolute error (MRAE) and root mean square error (RMSE) of the proposed algorithm are reduced by 46.7% and 44.8%, respectively.

The observation of solar spectral imaging provides an importance data source for solar physics and space weather research. However, it faces a serious challenge from the dynamic solar atmosphere in the extreme ultraviolet (EUV) band. Only by time-consuming push-broom imaging can the traditional slit-type imaging spectrometer acquire 2D images of the solar disk due to a limited instantaneous field of view (FOV). Moreover, its system is unable to capture the rapid evolution of the solar transition region and corona since it does not have a high time resolution. Although an EUV imager can observe at a large 2D FOV and high time resolution, it cannot get the spectral resolution. For this reason, relying on the aberration-corrected elliptical varied line-space (EVLS) grating, we proposed a new slitless imaging spectrometer in this paper, which can simultaneously work in three diffraction orders (m=-1, 0, or +1). Besides, three EUV narrowband (29.4--31.4 nm) images of the solar disk with a FOV of 20 arcmin×20 arcmin can be obtained in a single snapshot without the mechanical motion of any component, which demonstrates the high time resolution and large FOV of our instrument. Additionally, the zero-order system without spectral dispersion, equivalent to an EUV imager, can directly obtain high-resolution spatial information (0.6 arcsec). In contrast, the images from the ±1-order systems with spectral dispersion carry spatial and spectral overlapping information, which is similar to the imaging principle of computed tomography. High-resolution spectral information (0.0035 nm) can be extracted from the 3-order images by a data inversion algorithm.

Film thickness uniformity in a magnetron sputtering system is one of the key indicators. The effects of magnetic field intensity, distance between target and substrate and gas pressure on the thickness uniformity of Si3N4 and SiO2 films are analyzed. The plasma density is analyzed by using Langmuir probe, and the longitudinal uniformity is adjusted by binary gradient inflation mode. By loading sine half-wave voltage to the target and using MATLAB software to determine the amplitude and phase parameters, so as to adjust the uniformity of the transverse. The experiment results show that for the Si3N4 film, the transverse uniformity is ±1.27%, ±0.62%, and ±1.33% respectively at the top, middle, and bottom, and the longitudinal uniformity is ±0.33%. For the SiO2 film, the transverse uniformity is ±1.12%, ±0.42%, and ±1.23% respectively at the top, middle, and bottom, and the longitudinal uniformity is ±0.25%.