Ultrasound has strong penetrability in opaque media, which makes it one of the most important detection tools for structural safety monitoring. Compared with the traditional piezoelectric transducers(PZTs) used for ultrasonic detection, fiber-optic ultrasonic sensing system based on optical adaptivity of two-wave mixing (TWM) photorefractive crystal has strong characteristics of anti-electromagnetic interference, high sensitivity and strong multiplexing, as well as the adaptive detection for optical phase modulation and permanent dynamic recording of the interference pattern current position, which has a large quantity of applications in structural health monitoring. For the interferometric properties and ultrasonic detection technology of TWM in the field of structural safety monitoring, this paper introduces the principle of adaptive two-wave mixing interferometry, the sensing devices, and methods in various fiber Bragg grating (FBG) sensor systems and dynamic signal detection of Er-doped fiber gratings and discusses the application of fiber-optic ultrasonic sensing systems in ultrasonic detection based on adaptive TWM technology. Finally, the problems and solutions in the sensing system are analyzed. By miniaturizing the TWM interferometer and integrating the entire sensing system, it is expected to further improve the detection performance of the device and expand future research directions.
Two-wave mixing interferometry based on photorefractive crystals stands out among many techniques for monitoring dynamic strain because it can provide multiple dynamic sensing and does not require electronic feedback to actively compensate for any quasi-static drift. However, the traditional optical signal sensing processing system has shortcomings such as large, occupied space, various types of optical components, and complex optical path structure, which is not conducive to practical applications. Thanks to the development of photonic integrated circuits, photonic integrated can effectively solve these shortcomings. In this paper, based on the experimental study of two-wave mixing interferometry in InP:Fe spatial optics configuration, a photonic integrated two-wave mixing photorefractive interferometer is designed, which consists of curved waveguide, directional couple, unbalanced Mach-Zehnder interferometer structure, crossed waveguide, electrodes, etc. To minimize the loss of light in transmission and achieve the best demodulation performance for a two-wave mixing photorefractive interferometer, each structure is optimized by finite element method simulations. The feasibility of the optimized structure is verified in theory and the demodulation curve of transmitted signal light varying with time is obtained.
Due to the wave nature of light and the influence of optical material properties, the design and performance of photonic circuits can be relatively complex. While computer-aided software tools such as CAD can improve the efficiency of photonic circuit development, they still face challenges in handling large-scale photonic integrated circuit (PIC) designs. In this paper, we develop a photonics design automation tool, called GT Photonics, which provides a flexible development environment capable of handling large-scale PIC designs. The GT Photonics platform integrates multiple high-performance photonic devices, including passive and active components, and allows users to freely develop and adjust the parameters of individual photonic devices. To enhance development efficiency, the platform offers various design methods, modular development, parameter unit reuse, customizability, and intelligent routing capabilities. These features streamline the development of complex photonic integrated circuits. To facilitate development, the platform defines a netlist view to record photonic device information and employs visual design methods for circuit visualization. Once the design is completed, the photonic circuit can be exported as a Graphic Data System version 2 (GDSII) file for performance simulation and validation. This article presents a case study involving the design of an optical phased array (OPA) using the GT Photonics platform. The case study encompasses the design process, design outcomes, and various design details. Photonic design automation holds significant importance for engineering and research endeavors.
Distributed sensing technology provides engineers with powerful tools for position sensing, 3D sensing, shape sensing, and model validation applications. A new method for fiber-optic 3D shape sensing that can be used in minimally invasive biomedical devices is presented. A shape sensor was made using a heat-shrink tube, a Teflon hard tube and three strings of fiber Bragg grating (FBG). The sensor has compact structure, good flexibility. Besides, a shape reconstruction algorithm is established, for the location of each FBG array on the sensor, the calculation method of curvature and torsion is designed, and the continuous functions of curvature and torsion are constructed by cubic spline interpolation. The shape reconstruction under different bending conditions is realized by using the coordinate system rotation method. In the error analysis stage, the curvature error and torsion angle error of the sensor are optimized by introducing the scale factor. The results show that the optimized algorithm has good shape reconstruction effect.
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