For real-time monitoring of engineering structure, according to the principle of displacement sensing, a fiber Bragg grating(FBG) displacement sensor with tension cantilever beam is designed. During the displacement measurement, the relative displacement of the fulcrum at both ends of the sensor is generated, and the displacement is transmitted to the cantilever beam through the spring. The displacement is measured by measuring the strain of the cantilever beam. The sensitivity can be adjusted by changing the section size and length of the cantilever beam, the size of the cantilever beam is determined according to the technological constraints and theoretical calculation, and the aperture value is determined through the finite element analysis of the effect of the aperture size of the cantilever beam end on its strain. Finally, the performance of the sensor is tested, the results show that the sensitivity of the FBG displacement sensor with tension cantilever beam is 101.3 pm/mm, and the measuring range can reach 30 mm. Compared with the general commercial FBG displacement sensor, the sensitivity of FBG displacement sensor with tension cantilever beam is greatly improved, and the linear fitting degree reaches 0.994.

Aiming at the center wavelength shift problem in the fiber Bragg grating(FBG) sensing system, an FBG wavelength shift predict and generalization method based on extreme learning machine(ELM) is proposed. The method trains the neural network by constructing the mapping relationship between the center wavelength and the wavelength shift. It can realize the prediction and generalization of the wavelength shift. The experiment results show that the predicted error of FBG wavelength shift is less than 1 pm and the generalized error of FBG wavelength shift is less than 2 pm, which provides a useful exploration for the field calibration of FBG sensor system.

In order to solve the problems of easy damage and low sensing sensitivity of fiber grating, a micro spot welding machine and prestressed platform are designed and customized. Firstly, the optical fiber is nickel plated and metallized, then the optical fiber is encapsulated in capillary steel pipe by capillary resistance spot welding, and the temperature sensing characteristics are detected. The test results show that the surface of the electroplated nickel layer is bright and smooth, and the optical fiber is closely combined with the electroplated nickel layer. The fitting linearity between the central wavelength and the temperature change of the optical fiber sensor is very good, which can reach more than 0.999, and its temperature sensitivity is about 2.8 times compared with the bare grating sensor.

In order to solve the problem of traditional electromagnetic geophone which can only be measured in point and high engineering cost, a distributed optical fiber acoustic sensing system is proposed. Firstly, the optical structure of the system is designed, then the key module PIN photodetector is designed. Finally, the single vibration signal in the range of 50~500 Hz is tested by using 24-core armored optical cable in four groups of frequency tests. The experimental results show that the distributed optical fiber acoustic sensing system has a good detection effect on vibration signals generated by vibroseis, and can realize the precise positioning and frequency detection of vibration sources.

In order to monitor the deformation of transformer windings, wings, bridges and other equipment or engineering structures, the distributed optical fiber sensing system based on optical frequency domain reflection(OFDR) is used to study deformation reconstruction in this paper. Firstly, the transformation relationship between strain and curvature is introduced, and then the curve deformation reconstruction based on tangent recursive algorithm is deduced, and the improvement of reconstruction algorithm is proposed on the basis of tangent recursive algorithm. In the experiment, the spatial resolution of OFDR strain measurement system is set to 2 cm, and the concentrated force is loaded in the middle of the simple beam. When the concentrated load is 11.76 N, the maximum deformation reaches 40 mm. After eliminating the system error, the maximum error of the tangent recursive algorithm is 0.667 mm, and the maximum error of the improved reconstruction algorithm is 0.59 mm.

In response to the communication needs of marine resource exploration, underwater environmental monitoring and other fields in recent years, this paper proposes a new type of underwater image acquisition and transmission scheme, and designs a set of high-speed visible light video transmission system based on blue light-emitting diode(LED) according to this scheme. It has been tested and verified that the system can collect and transmit 720P high-definition video images underwater with a transmission distance of 1.4 m.

In order to study the visible light communication system in the case of non-line-of-sight link, this experiment establishes a non-line-of-sight link communication space model. On such basis, this paper designs the sender and receiver of the visible light communication system to complete the communication based on the non-line-of-sight link. The experimental results show that in the process of visible light communication, when the receiver only receives the signal transmitted by the non-line-of-sight link, the communication system can still complete the communication normally, non-line-of-sight communication can solve the problem that communication cannot be carried out because of the line-of-sight light is blocked.

In order to solve the common problem of clock synchronization between transmitter and receiver in communication system based on time difference of arrival(TDOA), a high accurate indoor visible light positioning algorithm based on double photo detectors(PDs) is proposed in this paper. The algorithm uses three light emitting diodes(LEDs) with different transmitting frequency and one receiver with two PDs. Considering the receiver’s scale, the time difference of arrival of the received signals is used to determine the three-dimensional location information of the indoor receiver. In a moderate model room, the proposed algorithm is analyzed via simulation. The simulation results show that the algorithm can determine the horizontal coordinates and height information of the receiver, with the positioning error is about 11 cm, which is suitable for various indoor location-based services.

optoelectronic oscillator is widely used in radar, communication and measurement fields, and is a research hotspot in microwave photonics. The introduction of new concepts and technologies promotes the development of optoelectronic oscillator and further expands the application of optoelectronic oscillators in modern electronic systems. This paper introduces the new concepts and technologies in optoelectronic oscillator, including parity-time symmetric optoelectronic oscillator, Fourier domain mode-locking optoelectronic oscillator, parametric optoelectronic oscillator, and integrated optoelectronic oscillator, points out the future development direction of photoelectric oscillator.

In order to facilitate subsequent processing, this paper proposes a polarization-insensitive terahertz dual-band narrowband absorber, its unit structure is a metal resonance layer-dielectric layer-metal substrate layer, with a area of 25 μm×25 μm and thickness of only 3 μm. Through the S parameter, the relationship between the size parameter of the device unit structure and the resonance frequency and absorptance is analyzed. The simulation results show that the absorption rate of the absorber at the resonance frequencies of 1.508 THz and 2.464 THz are both above 98.8%, and there is no limit to the polarization mode of the incident electromagnetic wave, and the good absorption performance is still maintained in the incident angle range of 0°~40°.

Reverse modulation wireless optical communication has broad application prospects in unmanned aerial vehicle, miniaturized platform and other fields, but it is easy to be affected by atmospheric turbulence, the received signal will have large low-frequency random fluctuation, and the bit error rate is high when using the hard decision method with fixed threshold. In order to improve the accuracy of signal decision, a signal decision method based on K-means algorithm is proposed. By learning the internal characteristics of the received sample points, the sample points in the window are dynamically and adaptively classified according to their similarity. The research results show that under the condition of turbulent channel, compared with the traditional hard decision method, the signal decision method based on K-means algorithm has better bit error performance. When the bit error rate is 10-6, the signal-to-noise ratio requirement is reduced by about 2 dB.

The existing international submarine cable system and terrestrial cable transmission system are designed independently according to their respective specifications, the two types of systems are connected through back-to-back method in the submarine cable landing station. In view of problems of relatively high investment and operating costs problems in existing methods, this paper elaborates the developing requirements of the joint network design of the submarine cable and terrestrial cable optical transmission system. Based on the analysis of the design specifications of submarine cable system and terrestrial cable system, it is suggested to use the generalized signal-to-noise ratio index to measure the overall transmission system performance. Finally, the joint design of the submarine cable and terrestrial cable optical transmission system is studied based on examples, deploying suggestions are given as well.noise ratio

In order to solve the problems of multiple levels, multiple systems, multiple types and unbalanced and insufficient role of the current optical transmission network, the existing optical transmission network is effectively integrated by using the cloud system theory to give full play to the overall efficiency. The framework structure of "optical transmission cloud" is proposed, and the construction methods of white licensing, automatic adaptation, integrated network management mode and packet transmission network(PTN) transmission mode are described, which makes it possible to realize a dynamic and stable "optical transmission cloud" with global coverage, multipoint deployment, random access and plug and play.