In order to improve the accuracy of indoor visible light positioning, a single light-emitting diode (LED) lamp indoor po-sitioning algorithm based on double back propagation(BP) neural network is proposed. The algorithm first uses the BP neural net-work to determine the rough position range of the target in the positioning area, and then uses the position range as a limiting condition to use the BP neural network again to achieve more accurate positioning. The indoor positioning system uses a single LED lamp as the transmitter and three horizontal photodetectors as the receiver to receive optical power, which avoids the inter-symbol interference caused by using multiple LED lamps during positioning. The simulation results show that in the positioning area of 3 m×3 m×3.5 m, the average positioning accuracy of the algorithm in the paper can reach 0.0042 m, which is higher than the traditional indoor visible light positioning algorithm.

There are many disadvantages in manual identification of optical cable inkjet code characters, so the automatic identification technology of optical cable is urgently needed. Aiming at the characteristics of dot matrix characters in optical cable, an online optical cable character recognition system is proposed, the simulation research and parameter optimization of three character recognition algorithms such as template matching, artificial neural network and support vector machine are carried out, and the advantages and disadvantages of these three algorithms are compared. The influence of parameters of artificial neural network and support vector machine on recognition accuracy and training time is analyzed. The simulation results show that under the same test set, the artificial neural network algorithm has the highest recognition rate, the support vector machine algorithm has excellent performance when the number of training samples is small, and the template matching algorithm has the lowest complexity.

Facing people's increasing demand for optical fiber sensing, the capacity advantage of multimode optical fiber provides new ideas for solving the capacity barrier of single mode fiber and realizing high-precision multi-parameter optical fiber sensing measurement. This paper analyzes the mode characteristics of multimode fiber theoretically, reviews the research progress of multimode fiber mode coupling and polarization, and focuses on the dynamic development of the threshold, gain spectrum and Brillouin frequency shift of Brillouin scattering in multimode fiber, and analyzes the future development direction of optical fiber sensing.

Fiber taper is an important technology in optical fiber device manufacture. In order to research the relationship between the taper wasit shape and the taper parameters in the fast reciprocating moving hot-zone fused taper system, a theoretical model of the reciprocating moving hot-zone fused taper system is established based on the principle of volume invariance under the condition that the hot-zone moving speed is greater than the fiber tapering speed. The deformation processing of the tapered optical fiber is depicted in detail. Quantitative relationships between the diameter of the taper waist, the length of the taper waist and the moving number of the hot-zone, the moving speed of the hot-zone, tapering speed of the fiber, the reciprocating moving distance of the hot-zone, the width of the hot-zone and the initial optical fiber diameter are deduced in this paper. Experiments are also carried out to verify the validity of the proposed theory and the experimental results have good agreement with the theory.

In view of the growing demand for special optical fiber, the working principle of heterostructured cladding(HC) structure all-solid photonic bandgap fiber(AS-PBGF) based on multiresonant coupling mechanism is introduced, and the advantages of this structure fiber in realizing large mode field area, single-mode operation and low bending loss are introduced. From the point of view of passive optical fiber and active optical fiber, this paper summarizes and analyzes the research reports and progress of this kind of optical fiber in recent years. Finally, the research and application of HC structure AS-PBGF based on multiresonant coupling mechanism are prospected.

Aiming at the problem of secure communication in physical layer of optical network, a coherent communication quantum noise stream encryption(QNSC) system scheme based on low density parity check(LDPC) code is proposed. The LDPC code with a bit rate of 9/10 and discrete Fourier transform orthogonal frequency division multiplexing(DFT-OFDM) technology are applied in the system scheme. Finally, the scheme is verified by experiments. The experimental results show that after transmitting the standard single-mode fiber with the span of 40 km, 80 km, 120 km and 160 km, The LDPC code effectively reduces the bit error rate of the system, improves the communication security of the system, and does not affect the basic performance of the system.

In order to transmit ethernet packets over E1 link reliably and stably, a high-level data link control(HDLC) frame-forming and frame-de-framing processing circuit based on E1 link is proposed. This circuit adopts HDLC protocol to encapsulate ethernet packets sent by media independent interface(MII) in the sending part of the system and send them through wide area network(WAN) interface. In the receiving part of the system, the data received by WAN interface is unsealed. The simulation results show that the initial ethernet data frames can be recovered successfully at the receiving end when ethernet packets are sent through MII at the sending end.

Single carrier 400 Gb/s transmission is the main application rate of next generation communication system. In order to improve the transmission efficiency of this rate communication in practical engineering application, the relationship between different modulation modes and transmission spectrum width in high-speed communication system is analyzed theoretically. Based on five different modulation formats of 16 order quadrature amplitude modulation(16QAM), 16QAM/32QAM, 32QAM, 32QAM/64QAM and 64QAM, the single wave input power, transmission capacity and transmission distance of 400 Gb/s transmission system are experimentally studied. The experimental results show that there are obvious differences in transmission capacity and transmission distance between mixed transmission mode and single transmission mode.

Aiming at the problem that atmospheric turbulence reduces the bit error performance of communication system in free space optical communication, a new decoding method of segmented polarization code cyclic redundancy check serial cancellation list (PC-CRC-SCL) based on relaxed polarization code is proposed. The algorithm is applied to free space optical communication system and simulated under weak atmospheric turbulence intensity. The simulation results show that when the bit error rate is 10-4, compared with the segmented CRC-SCL decoding algorithm of the fully polarized code, the segmented PC-CRC-SCL decoding method based on the relaxed polarizatio code obtains an additional coding gain of 0.3 dB, and the complexity of the polarization code encoding and decoding is reduced by 10% to 20%, and the bit error performance of free space optical communication system is significantly improved.

Aiming at the problems of the rotating biprism system, such as the difficulty of solution, many error sources and low pointing accuracy, a correction method is proposed to compensate the rotation angle of the rotating biprism pointing system. In this paper, the relationship between the beam pointing error and the prism angle error is established by solving the partial derivative and establishing the total differential equation, and the compensation angle is calculated. Experiments have verified that in 99.57% of the pointing area, the maximum pointing deviation is reduced from 1.8742° to 1.4753°, and the root mean square is reduced from 0.1401° to 0.0893°. The compensation prism angle correction method can effectively improve the pointing accuracy.

Aiming at the problem of high insertion loss of current electro-optic modulator, a photonic crystal electro-optic modulator based on a width modulation (WM) cavity is proposed in this paper. The device is composed of a nanowire waveguide at the input port, silicon-based photonic crystal waveguide and a WM-type resonator. The connection between the first two structures uses a tapered structure to reduce the cascade loss between two different waveguides. According to the time-domain coupled mode theory and plasma dispersion effect, WM-type resonant cavity and PN doping structure are used to realize the modulation of transverse electric(TE) mode. The performance is simulated and analyzed by two-dimensional finite difference time domain method. The simulation results show that the device can realize the TE mode narrow-band on-off modulation function with a center wavelength of 1553.91 nm when the modulation voltage is 1.24 V. The insertion loss is 0.16 dB at 1550~1560 nm, and the extinction ratio is 19.73 dB. The modulation depth is 0.9894, the Q value reaches 1.5×104, and footprint is about 20 μm×9 μm.

Due to the high cost and long development cycle of monolithic integrated technology, a four-channel external-modulated electro-optic convertor module based on optoelectronic hybrid integrated package is proposed. The module uses optoelectronic hybrid integration technology, using space optical lens coupling instead of the original optical fiber interconnection mode, transmission microstrip instead of the traditional cable interconnection mode, gold wire/gold belt instead of the traditional low-frequency wire mode, and micro assembly process to realize multi professional bare chip integrated hermetic packaging instead of separate module hybrid assembly mode, so as to greatly compress the volume and improve the integration level. The test results show that the module realizes four channels of 2~18 GHz electro-optical conversion function, the wavelength sequence meets the requirements of 8 channels 200 GHz channel spacing, the radio frequency index S21value is -4 dB±3 dB, the standing wave is less than 1.5, and the noise figure is less than 23 dB.

In order to reduce the impact of white noise and random multipath noise in power grid optical communication system, two monitoring schemes based on linear frequency modulation-optical time domain reflectometer(LFM-OTDR) technology are proposed, namely single frequency LFM-OTDR scheme and frequency division multiplexing LFM-OTDR(FDM-LFM-OTDR) scheme. In this scheme, LFM optical pulse signal is used as the detection signal, and the backscattered detection signal is transformed into the fractional Fourier domain by fractional Fourier transform for signal processing and scattered light power calculation, so that the detection signal and backscattered noise can be separated more effectively. Compared with the single pulse OTDR scheme, the experimental results show that the dynamic range of OTDR is improved by 8.3 dB and 11 dB respectively by using single frequency LFM-OTDR scheme and FDM-LFM-OTDR scheme.

Aiming at the problem that the frequency synchronization of communication optical cable fault monitoring is limited by the length of optical cable, and the monitoring accuracy is easy to decline, a fault monitoring method for ultra-long-distance communication optical cable based on wide area measurement is proposed. In this method, the global positioning system(GPS) precise synchronous vector measurement unit (PMU) is used to provide frequency, phase and amplitude information, and the optical time domain reflectometer (OTDR) technology is used to determine the optical cable fault point, and the ultra long distance optical cable fault monitoring is completed. The experimental results show that: the frequency of optical cable fault signal changes obviously, and the fitting degree with the actual monitoring results is higher than 90%, the measurement time is short, and the monitoring effect of ultra -long-distance communication optical cable fault is better.