Fast, accurate and nondestructive spectral analysis technique is important and widely used in the fields of scientific research, information, biomedical, pharmaceutical detection, agriculture, environment, and security. However, the existing spectroscopic analysis equipments are usually bulky and complex, which are difficult to adapt to portable application scenarios such as on-site rapid detection, light-load platform, etc. In recent years, miniature spectroscopic detection technology and equipment have received extensive attention, and have been rapidly developed, with significant advantages in size, weight, and power consumption. In particular, the computational spectral analysis technology based on the speckle detection can obtain high-precision spectral information by recording and analyzing the speckle pattern formed by the scattering element on the measured light. This paper will first introduce the related technical principles and technological developments, then analyze the existing techniques including the advantages and disadvantages, and finally discuss and summarize the future development direction and application prospects.

Distributed acoustic sensing (DAS) technology can detect acoustic or vibration signals with high sensitivity and wide dynamic range by receiving the phase information from coherent Rayleigh scattered light. Linear quantization is used to measure high fidelity restoration of the signals. With the increasing demand of practical applications, the optical fiber intrusion detection field has put forward higher requirements for event location and identification, which is manifested as the accurate classification of intrusion events. Therefore, the combination of distributed acoustic sensing and pattern recognition (PR) technology is a hot research topic at present. This is beneficial to promote the application and development of distributed optical fiber sensing technology. The research progress of the pattern recognition technology applied to distributed optical fiber intrusion detection in recent years is summarized in this paper, which can be used for feature extraction and classification algorithm research progress. In this paper, several feature extraction methods for realizing intrusion event signal recognition and their feature selection difficulties in different application situations are reviewed. Meanwhile, the advantages and disadvantages of specific event recognition algorithm are analyzed and summarized.

The traditional respiratory rate measurement technologies have several deficiencies, such as subjective appraised results, complicated signal extraction processes, difficult access to equipment, and inconvenience to move due to the wired connection setting. The respiratory airflow can directly reflect the human breath, and the respiratory frequency is usually 10?12 breaths/min (1 ventilation every 5?6 seconds). The humidity difference between exhalation and inhalation can be directly used to measure respiratory rate. In the present work, a wireless respiratory rate monitoring system based on inorganic halide perovskite humidity sensor was developed. The sensor exhibits an ultrasensitive humidity sensing performance, which overcomes the long response/recovery time (> 10 seconds) of the commercial humidity sensors. The system utilized a Zigbee wireless communication to transmit the measurement signal, which separates the signal detection and processing parts, making it easier for the tester to move. The upper computer software was designed and used for data processing to calculate the breathing rate. The system can accurately monitor the respiratory rate in real-time, recognize and alarm the apnea successfully by comparing with a setting threshold value. The test results show that the system can accurately monitor the breathing rate with a maximum error of 1 time per minute. The system possesses great potential for application in respiratory rate monitoring due to its high accuracy, simple operation, portability, and low cost.

In view of the limitations of the existing methods when the camera has no common field of view, this paper proposes a method of using two plane calibration plates to calibrate two cameras at the same time. By deriving the coordinate transformation between the two cameras and two calibration plates, the solution of the relative pose relationship between any camera and the reference camera is transformed into a more mature hand-eye calibration equation. The experimental results show that this method can achieve simultaneous calibration of two cameras, and the absolute error is less than 0.089 mm. In the dual vision 3D measurement system, the cumulative error with phase height is less than 0.116 mm, which can provide a reliable initial value for the next step of data fusion.

Array microstructure optical elements are widely used in various beam homogenization occasions, but conventional processing methods cannot meet the accuracy requirements of large-sagittal convex cylindrical arrays. In this paper, the ultra-precision turning forming method is used to analyze the main factors affecting diamond turning, the sequential search method and the binary search method are designed to find the turning track, and the advantages and disadvantages of the two methods are compared. Furthermore, the binary search method is successfully found by combining the Matlab software turning trajectory and the numerical control program. As proof-of-concept demonstrations, turning experiments are carried on an ultra-precision lathe, and a large-vector high-array microstructure with a surface profile error of 135 nm is obtained. It proves that the force binary search method can accurately obtain the turning trajectory, and this method can be applied to both spherical and aspherical contours, showing important engineering application value.

In order to realize the non-destructive and real-time dynamic stress monitoring method of the construction machinery surface in complex and harsh environments, a fiber Bragg grating (FBG) stress sensor packaging method based on magnetron sputtering technology is proposed. Two packaging methods of complete embedding (the capillary copper tube embedded in the entire grating area) and two sides embedding (capillary copper tube nested at both ends of the grating area) are studied. The sensitization effect of the sensor is analyzed from the perspective of theory and finite element, and the results are consistent. The physical sensors are made, and temperature, stress, and comparison experiments are carried out. Simulation and experiment show that the FBG sensor improves the sensitivity by about 7.5% under this model. The temperature experiment shows that the temperature feedback correlation coefficient R2 of the second package structure reaches 0.99948, which shows good linearity in the range of 30 ℃?80 ℃; the stress experiment correlation coefficient R2 also reaches 0.99924, and the sensitivity is 6.14 pm/MPa. The accuracy of demodulation system reaches 0.05 MPa, it can demodulate stress quickly and accurately. Comparative experiments show that the monitoring system composed of grating demodulator has higher accuracy than the monitoring system composed of strain gauges, and maximum deviation value smaller 59.8%. The packaging structure of metallization method of embedded capillary copper tube combined with organic glue fixed is simple, high sensitivity, and precision, can meet the needs of large-scale construction machinery surface non-destructive real-time health monitoring.

In order to reduce the error and improve the measurement accuracy, a more detailed error model is established for the Hartmann method of focal power measurement in this paper. It focuses on the analysis of several problems that cause the error of refraction problems, including the dispersion error of the light source, the inaccurate of the photodetector’s central positing, the tilt of lens, misalignment between incidence axis and main axis of lens, and the incident light and the lens are not perpendicular. At last, it is concluded that the inaccuracy of the center extraction on the photodetector will cause a large error to the final result. For all these reasons, a method of dual bilinear interpolation combined with a fitting method to find the centroid is proposed, proving its effectiveness and accuracy.

The variation of ambient refractive index and ambient temperature is the main factor affecting the error of optical fiber strain measurement. In this paper, a strain sensor based on the dual-mode fiber (DMF) long period fiber grating (LPFG) is designed. The sensor model structure was designed, and the sensor samples with optimized parameters were produced. The experiment tested the response of the DMF-LPFG sensing structure to the strain, temperature and refractive index in the external environment. Through the Bragg grating (fiber Bragg grating, FBG) written on the single-mode fiber with a UV laser, the cross effect of the ambient temperature is solved. The results of the axial strain experiment show that the axial strain sensitivity of the new structure sensor can reach -5.4 pm/με in the strain range of 0 με~840 με, which is greatly improved compared to the ordinary LPFG. The sensitivity is 58.86 pm/℃ in the temperature range of 25 ℃~80 ℃, showing good linearity. At the same time, the sensor is insensitive to changes in ambient refractive index. The dual-parameter matrix is used to process the strain and temperature sensitivity of the few-mode LPFG and FBG to achieve dual-parameter simultaneous demodulation. The new composite grating structure has good sensing performance and engineering application prospects.

A photonic crystal fiber (PCF) for long distance communication was proposed in this paper. The circular and elliptical air holes distribute in the cladding, and there are two small elliptical air holes around the core in cross section of the PCF. The characteristics of the PCF were analyzed by using the finite element method (FEM) systematically. The results show that the PCF offers an ultrahigh birefringence of 3.51×10-2 and the confinement loss as low as 1.5×10-9 dB/m with the optimal structure at the wavelength of 1550 nm. Compared with the existing photonic crystal fibers with elliptical air holes, the birefringence has a large increase, and the confinement loss reduces by 5 orders of magnitude. Additionally, we also analyzed the relationship between the dispersion of the PCF and the wavelength, and obtained the Brillouin gain spectrum characteristics. In general, the PCF can be used in long distance communication system.