In order to improve the detection accuracy, detection dose range and the number of monitoring points of radiation sensing technology, the optical time domain reflectometer(OTDR) technology is used to observe the radiation induced attenua-tion(RIA) effect of single-mode optical fiber, so as to realize the feasibility of distributed radiation sensing application. The linear relationship between radiation dose and RIA of single-mode fiber is established by calculating the attenuation slope of optical power in OTDR curve. Using single-mode fiber with suitable RIA effect is expected to realize long-distance distributed radiation dose monitoring with high spatial resolution.

In distributed optical fiber acoustic sensing(DAS) system, the birefringence of single-mode optical fibers results in the polarization state change of the output light in the optical fibers, which is not matched with the polarization state of the reference light, resulting in the polarization fading phenomenon. This paper designs a DAS system based on polarization diversity technology. The Rayleigh scattering light interferes with the reference light in two polarization states, and then photo-electric conversion and data acquisition are carried out. The polarization fading phenomenon is removed, and therefore the false alarm rate of DAS system is reduced, which makes the system much practicable for real applications. Experiment results show that in DAS system, the polarization diversity technology can eliminate the system misjudgment caused by polarization fading phenomena along the fiber, and can improve the alarm accuracy of the DAS system.

To meet the high demand for high precision refractive index measurement in different fields such as medicine and chemistry, based on high precision sweep spectrum measurement technology, combined with tilt fiber grating for refractive index measurement, a high precision refractive index change sensor system is proposed. The spectral measurement of the cut-off mode of tilted fiber grating is carried out under the condition of slightly different refractive index, and the sensitivity of the cut-off mode to the external refractive index response is 28.3 nm/RIU. The accuracy of measuring the peak center wavelength of a cut-off mode at a fixed refractive index is calibrated. The measurement accuracy of refractive index change of 1.15 × 10-6 RIU is obtained, and the measurement accuracy of 6.5 × 10-7 RIU can be further achieved in the case of static measurement.

Raman fiber amplifier (RFA) can effectively improve the sensing distance of phase sensitive optical time domain refl-ectometer(Φ-OTDR) system. In order to further improve the system sensing distance of Φ-OTDR, the particle swarm optimiza-tion(PSO) algorithm is used to optimize the pump optical power value of the third-order bidirectional RFA. The theoretical farth-est sensing distance of Φ-OTDR system based on third-order bidirectional RFA is calculated and a simulation experiment is designed. The simulation and analysis results show that when the detection pulse width is greater than 200 ns, the Φ-OTDR system can reach more than 200 km through the third-order bidirectional RFA amplification sensing distance.

Due to the limitation of structure and material, the sensitivity of traditional optical fiber pressure sensor is difficult to be further improved. Based on the principle of Mach Zehnder interferometer, transverse pressure sensing structure of doped dual core photonic crystal fiber(DC-PCF) is designed. The relationship between pressure sensitivity and fiber structure is analyzed according to the influence of different doping materials and cross-section structure parameters of optical fiber on the pressure-sensitive characteristics, the DC-PCF structure with high pressure sensitivity is obtained by synthesizing the modefield area. The simulation results show that when the incident transmission wavelength is 1550 nm and the length of the dual core photonic crystal is 6 cm, the X polarization pressure sensitivity can reach 37.56 nm/MPa and the Y polarization pressure sensitivity can reach 35.27 nm/MPa. Compared with the traditional photonic crystal transverse pressure sensor, the pressure sensitivity of the sensor structure is increased by nearly 60 times.

To improve the system capacity, the utilization rate of optical fiber and reduce the cost of network construction, this paper proposes a quantum and classical fusion communication system based on dense wavelength division multiplexing(DWDM) technology. To eliminate or reduce the impact of classical signal on quantum signal in the system, it designs an unequal wavelength allocation method and an optical isolator are to deal with the four wave mixing noise and Raman scattering noise of the fusion system respectively. The simulation results show that the quantum bit error rate(QBER) of the quantum and classical fusion communication system is reduced by 33.3% due to four wave mixing and Raman scattering noise after noise processing.

Aiming at the requirement of miniaturization of Brillouin analog signal processing system, this paper presents a stimulated Brillouin scattering instantaneous frequency measurement(SBS-IFM) scheme based on the doped silica waveguide. In this scheme, the reflected light is effectively filtered out, and the Brillouin gain signal in the doped silica waveguide is amplified and observed by adding a lock-in amplifier and a filter. SBS-IFM based on the doped silica waveguide is realized by relatively moving the modulation frequency of pump light and the probe light, the IFM range of this scheme is about 15 GHz and the accuracy can reach 60 MHz.

In order to achieve stable multi-wavelength output, a multi-wavelength fiber laser based on nonlinear polarization rotation(NPR) of semiconductor optical amplifiers(SOA) is proposed and demonstrated. Due to the NPR effect of SOA, the intensity-dependent loss (IDL) is induced by the combination consisting of SOA and other polarization devices to suppress mode competition within homogenous broadening linewidth of SOA. Stable multi-wavelength lasing with wavelength spacing as small as 0.63 nm and wavelength number up to 35 is achieved at room temperature. Moreover, 12 nm wavelength tuning is implemented by tuning polarization. Finally, experimental investigation is carried out to show the stable multi-wavelength output with smaller wavelength spacing can be achieved by increasing the length polarization-maintaining fiber (PMF).

In order to meet the market demand for all kinds of optical fiber fusion splicer products, the basic platform of optical fiber fusion splicer is designed from the perspective of product modularization. In this paper, the overall design scheme of the basic platform is given together with the system block diagram, and the main components of the basic platform are introduced in detail, and then the verification test scheme and test results are described. Experimental results indicate that the scheme is reasonable and feasible, it meets the needs of optical fiber fusion splicer products to quickly respond to the market.

In order to improve the stability of two-dimensional servo stability system in mobile laser communication equipment "communication in motion" environment, in this paper, gyroscope installation and correction optimization method, charge coupled device(CCD) centroid optimization algorithm, fast convergence of small values in the same direction of gyroscope and CCD and other methods are used to optimize the dynamic performance of the two-dimensional servo stability system. The optimized system is installed on a six-axis swing table to simulate the dynamic environment, so as to verify the stability of the servo stability system under the excitation conditions of different amplitudes and frequencies. The experimental results show that the receiving power variation range of the optimized system is significantly reduced, and the stability accuracy of servo system is improved by at least 27% under the same excitation condition.

Aiming at the problem that indoor visible light positioning(VLP) generally requires multiple light emitting diode (LED) beacons, a high robustness three-dimensional VLP system based on a single LED beacon and a single complementary metal oxide semiconductor(CMOS) sensor is proposed. A modulable LED beacon with mark on the edge is used as transmitter, CMOS sensors as receiver for VLP systems and the collected image is regarded as an ellipse with geometric features. Perform feature extraction and demodulation of the elliptical light spot on the acquired image to identify predetermined information, and the undetermined position is solved by combining the monocular ranging and the angle of arrival(AOA) algorithm. The performance of the proposed VLP system is evaluated by experiments. The average positioning accuracy is 9.7 cm in the region of 1.8 m×1.8 m×2 m, and the positioning error of 13.1 cm with 80% confidence can be achieved.

National aeronautics and space administration(NASA) laser communications relay demonstration(LCRD) project is the USA first long-term satellite laser relay project, is also a pathfinder project for USA next generation of satellite relay system. In order to facilitate the study of new satellite laser relay technology, this paper gives a detailed description of the project, including the background, current status and future development. Besides, this paper gives out a list of technical specifics of the project.

Non-linear distortion caused by excessively high peak-to-average power ratio(PAPR) is one of the problems to be sol-ved urgently in direct-current biased optical orthogonal frequency division multiplexing(DCO-OFDM) technology. Aiming at this problem, an algorithm based on time frequency interleaving(TFI) and selection mapping(SLM) which called TFI-SLM peak-to-average ratio suppression algorithm is designed. This algorithm firstly performs TFI on the input signal to reduce the autocorrelation of the input signal, and then uses a small m sequence to generate a random phase factor to selectively map the transformed signal. Simulation results show that compared with the traditional algorithm, the algorithm not only avoids sending too much redundant information of phase factor sequence, but also reduces PAPR by 2.8 dB when the complementary cumulative distribution function(CCDF) value is 10-5.

With the rapid development of the internet industry, the expansion of data centers optical interconnection has become an inevitable trend. Insufficient wavelength resources in data centers will become an important factor restricting the development of data centers. this paper proposes a wavelength reuse passive optical interconnection scheme, two signals are modulated on the same optical carrier, and the optical orthogonal modulation technique is used to achieve error-free signal transmission. At the same time, polarization multiplexing technology is used to reduce the number of wavelengths required for data centers optical interconnection to 14, thereby improving the utilization of wavelength resources.

With the rapid development of the internet industry, the expansion of data centers optical interconnection has become an inevitable trend. Insufficient wavelength resources in data centers will become an important factor restricting the development of data centers. this paper proposes a wavelength reuse passive optical interconnection scheme, two signals are modulated on the same optical carrier, and the optical orthogonal modulation technique is used to achieve error-free signal transmission. At the same time, polarization multiplexing technology is used to reduce the number of wavelengths required for data centers optical interconnection to 14, thereby improving the utilization of wavelength resources.