A corrugated silver diaphragm-based optical fiber microphone (OFM), formed by extrinsic Fabry-Perot interferometric structure, was proposed. The sensor's sensitivity was improved by releasing diaphragm's initial stress with the help of corrugations. A simple ``gray-scale exposure'' method was proposed to fabricate the corrugation. Experimental results indicated that the mechanical sensitivity of the fabricated corrugated diaphragm (CD) was 52 nm/Pa, which was twice that of the planar diaphragm under the same parameters. Other characteristics of the fabricated microphone were also tested in detail. The proposed CD-based OFM showed the advantages of high sensitivity, simplicity and low cost, which was expected to be applied in the field of weak acoustic sensing.

Synthetic aperture radar (SAR) is an active earth observation system with a certain surface penetration capability and can be employed to observations all-day and all-weather. Ship detection using SAR is of great significance to maritime safety and port management. With the wide application of in-depth learning in ordinary images and good results, an increasing number of detection algorithms began entering the field of remote sensing images. SAR image has the characteristics of small targets, high noise, and sparse targets. Two-stage detection methods, such as faster regions with convolution neural network (Faster RCNN), have good results when applied to ship target detection based on the SAR graph, but their efficiency is low and their structure requires many computing resources, so they are not suitable for real-time detection. One-stage target detection methods, such as single shot multibox detector (SSD), make up for the shortage of the two-stage algorithm in speed but lack effective use of information from different layers, so it is not as good as the two-stage algorithm in small target detection. We propose the two-way convolution network (TWC-Net) based on a two-way convolution structure and use multiscale feature mapping to process SAR images. The two-way convolution module can effectively extract the feature from SAR images, and the multiscale mapping module can effectively process shallow and deep feature information. TWC-Net can avoid the loss of small target information during the feature extraction, while guaranteeing good perception of a large target by the deep feature map. We tested the performance of our proposed method using a common SAR ship dataset SSDD. The experimental results show that our proposed method has a higher recall rate and precision, and the F-Measure is 93.32%. It has smaller parameters and memory consumption than other methods and is superior to other methods.

We present a dual-wavelength off-axis quasi-common-path digital holography for quantitative phase imaging using polarization-multiplexing in a single shot. Employing an off-axis nearly common-path configuration, our approach separates the two-wavelength information using a polarizing beam splitter, while modulates the orthogonal fringe directions for each wavelength using two retro-reflector mirrors, and thus generates a single multiplexed off-axis interferogram on a monochrome CCD camera. The information of a specimen, including phase and height, is reconstructed through a division algorithm for dual wavelengths with the help of a specimen-free multiplexed interferogram. The experimental results obtained on a square step target and a circular step target illustrate the validity and stability of our setup.

A parallel two-step spatial carrier phase-shifting common-path interferometer with a Ronchi grating placed outside the Fourier plane is proposed in this paper for quantitative phase imaging. Two phase-shifted interferograms with spatial carrier can be captured simultaneously using the proposed interferometer. The dc term can be eliminated by subtracting the two phase-shifted interferograms, and the phase of a specimen can be reconstructed through Fourier transform. The validity and stability of the interferometer proposed are experimentally demonstrated via the measurement of a phase plate.

High-sensitivity extrinsic Fabry-Perot cantilever accelerometers were proposed and tested. Micro-machined 45° angled fiber was adopted to form the cantilever to measure the acceleration. The Fabry-Perot cavity was formed by the sidewall of the fiber and the inner surface of commercial ceramic sleeves. The stepped cantilever fiber was fabricated by etching method to improve the sensitivity without enlarging the cantilever's length or adding extra proof-mass. Detailed theoretical analysis, simulation and experimental results of the proposed accelerometers were given. The measured results were in good agreement with the simulated results. The proposed accelerometers show the advantages of high flexibility, simplicity, compactness and low-cost, which are expected to be applied in the field of miniaturized vector hydrophone and seismic monitoring.

In this manuscript, optical fiber Fabry-Perot acoustics sensors based on corrugated PET diaphragms were proposed, fabricated and tested. Corrugations of different depths were introduced into the PET by simple hot-embossing process. The performances of the fabricated acoustics sensors were tested and analyzed. The results showed the corrugations could effectively improve the performances of the sensors. The proposed fabrication method of the corrugated diaphragm showed the advantages of simplicity and low-cost, and the acoustic sensors showed flexible control of corrugated structure, which were suitable for weak acoustic sensing.