Probabilistic shaping technology can improve the channel capacity of visible light communication system by changing the probability distribution of transmitting source. A new probabilistic shaping algorithm is proposed. Firstly, orthogonal frequency division multiplexing modulation is introduced to establish the visible light communication model. Then, the false sign rate of constellation points is derived theoretically. The simulation results show that the source generated by this algorithm can not only adapt to the current channel condition better, but also avoid the process of obtaining the false sign rate of the receiver through multiple transmission training. Compared with the existing probabilistic shaping algorithms, the proposed algorithm can achieve a higher information transmission rate.

In order to meet the requirements of underwater high-speed laser communication and improve the error code performance of the system, an underwater high-speed laser communication system based on on-off keying(OOK) modulation is designed. The sliding window average filtering method is used to denoise the received data, and the threshold decision is made after the joint threshold is obtained according to the fixed threshold and the adaptive threshold. The system test results show that the bit error performance of the joint threshold decision mode is better than that of the fixed threshold decision mode and the adaptive threshold decision mode. The bit error rate of the system is about 0 and 10-2 respectively when communicating with clean water and water containing a small amount of suspended impurities.

Aiming at the problem of low data transmission security of visible light communication(VLC) link, the data transmission security problem of VLC link is becoming more and more prominent. In orthogonal frequency division multiplexing(OFDM) VLC system, a three-level physical layer encryption scheme with specific level, symbol level and phase joint encryption is proposed. Firstly, the chaotic sequence encryption method of Logistic mapping is introduced to reduce the correlation of encrypted data, improve the security of encrypted data and the transmission performance of the system. Then, the constellation mapping based on S replacement table is proposed, and the corresponding constellation mapping relationship is generated according to different S replacement tables, so that the characteristics of gray mapping are always maintained between the original binary bit data and the digital modulation signal generated after encryption, and the gray gain is guaranteed. The simulation results show that compared with the existing schemes, the proposed physical layer encryption scheme not only has higher security, but also reduces the pek-per-power ratio of the data sent by the OFDM VLC system, alleviates the nonlinear distortion generated by the light-emitting diode(LED) transmitter, and improves the bit error rate performance of the system.

In order to solve the energy supply problem of the perception terminal of the internet of things in underwater environment, the multifunctional photoelectric characteristics of gallium nitride quantum well diode and compatible manufacturing process are utilized to integrate energy, lighting, communication and perception components on the same gallium nitride chip, and realize interconnection among the devices, so as to prepare gallium nitride energy communication and perception integrated chip. Experiments of visible light wireless energy transmission and communication are carried out on the chip. The experimental results show that the chip can absorb external optical pulse signal and generate stable signal output, and the signal transmission rate can reach 1 Mb/s, which has the potential of relay communication. The chip can also realize energy acquisition and signal communication in underwater environment.

Aiming at the problems of low data transmission rate and difficulty in synchronization between receiver and transmitter in visible light communication(VLC) technology, an optical camera communication(OCC) system with color light-emitting diode(LED) array as transmitter and mobile camera as receiver is proposed. Firstly, a special frame structure was designed to solve the synchronization problem of the receiving and sending ends of the system, and an image processing algorithm was established to extract gray statistical characteristics of each channel of color LED to distinguish the color of LED. Then, the back propagation neural network classifier is introduced to improve the color recognition accuracy. Finally, the m pseudo-random sequence is used as the test data to measure the system communication bit error rate, and the impact of the transmitter refresh rate, camera deflection angle, transmission distance, LED color number on the bit error rate is studied. The experimental results show that the designed frame structure can ensure the stability of information transmission. The system can realize real-time communication with bit error rate of 10-6 magnitude and communication rate of 4.824 kb/s within 20~30 cm.

In order to deal with the spectrum crisis of the new generation of communication technology, according to the physical phenomenon of overlapping area between quantum well diode emission spectrum and detection spectrum, and a single channel full duplex visible light communication system based on GaN integrated optoelectronic chip is proposed. A pair of blue light and green light gallium nitride quantum well diode devices with the same quantum well structure are used as optical transmitter and optical receiver, respectively. The devices are integrated with TiO2/SiO2 distributed Bragg reflector(DBR). Incident light and emitted light are isolated to realize single-channel full-duplex optical communication. The test results show that the visible light communication system can save the channel space through the integration of gallium nitride optoelectronic chip, which is of great significance for the development of future 6G visible light communication technology.

In order to improve the performance of the visible light communication system, the heterogeneous integration of visible light communication technology and other communication technologies can make various technologies learn from each other, enhance the capacity of the communication system and improve the utilization rate of resources. The methods and development status of the integration of visible light communication with power line communication(PLC), WiFi, ethernet, long term evolution(LTE) network and fifth generation/sixth generation mobile communication technology(5G/6G) are introduced. The future development of visible light communication heterogeneous integration system is prospected.

In order to improve the transmission performance of indoor visible light communication system, a hybrid scheme of carrierless amplitude and phase(CAP)-digital pulse interval modulation(DPIM) based on generalized spatial modulation(GSM) is proposed. Based on the joint idea of space-time, CAP signals are loaded onto DPIM slot pulses in signal domain to construct mixed modulation signals, and multiple antennas are activated simultaneously through GSM technology in optical domain for information transmission. The theoretical expression of the frame error rate of the GSM-CAP-DPIM hybrid system in visible Gaussian channel is derived. The accuracy of the analytical expression is verified by simulation, and the influence of different space time parameter selection on the system frame error performance is explored. The experimental results show that the reliability of GSM-CAP-DPIM hybrid system is better than that of traditional hybrid modulation system with the same spectral efficiency.

Aiming at the low accuracy of traditional indoor positioning algorithm, an indoor positioning algorithm based on Elman neural network was proposed. The Elman neural network is used to expand the fingerprint database interpolation, complete the fingerprint database, and reduce the positioning error, and the algorithm model is verified by experiments. The experimental results show that the average positioning error of the proposed algorithm is 4.6 cm in 0.8 m × 0.8 m×0.8 m environment, which meets the accuracy requirements of indoor positioning.

The traditional static Lambert and non Lambert beam configuration is difficult to solve the problem of limited transmitter site. Aiming at the application scenario of a single transmitter, a coverage method of restricted visible light communication based on sectionalized optical beam switching is proposed. This method uses commercially available slanted non-Lambert optical beams to dynamically determine the candidate optical beams that can provide the best coverage signal-to-noise ratio according to the state information feedback from the receiver at different locations, and then builds a directional transmission link. Simulation results show that, compared with the traditional static Lambert beam configuration, the proposed method can achieve an average SNR gain of 4.48 dB and 5.94 dB respectively, by adding two or three candidate sector beam switching options in a typical indoor environment.

In order to further improve the accuracy of indoor visible light three-dimensional positioning, an indoor visible light three-dimensional positioning method based on minimum triangle algorithm is proposed. In this method, the line-of-sight link model is adopted, and the positioning terminal receives the light intensity signal carrying the light-emitting diode position information. The minimum triangle algorithm and the received signal strength indication method are used to calculate the three-dimensional position information of the receiver in the room, and then the weighted centroid algorithm is introduced to reduce the impact of optical path occlusion. The simulation results show that the average positioning error of the proposed positioning method is about 4.35 cm and the average height error is about 1.65 cm in the indoor positioning area of 5 m×5 m×3 m. The positioning accuracy is better than that of the traditional indoor visible light three-dimensional positioning method.

Aiming at the technical problems of large volume and low bandwidth of traditional lithium niobate electro-optic modulator, a new design method of electro-optic modulator based on thin film lithium niobate modulator chip is proposed. The high-frequency transmission simulation model of thin film lithium niobate electro-optic modulator is given. The design of high frequency signal feed in thin film lithium niobate electro-optic modulator and high frequency impedance matching design of transition film substrate are introduced in detail, the key specifications of 40 GHz small size thin film lithium niobate electro-optic modulator are tested. The test results show that the insertion loss, half wave voltage, 3 dB bandwidth and product size of the designed thin film lithium niobate electro-optic modulator are 4.1 dB, 3.9 V, 40 GHz and 30 mm ×10 mm×5 mm respectively, superior to the traditional lithium niobate electro-optic modulator.

In order to develop a miniaturized anti-irradiation erbium-doped fiber amplifier(EDFA) for satellite laser communication, the failure mechanism of erbium-doped fiber(EDF) in the irradiation environment is introduced, the irradiation performance of different erbium-doped concentrations EDF is studied, and the anti-irradiation performance of different material composite shielding structures is compared. Finally, a high-performance miniaturized anti-irradiation EDFA with a size of 60 mm×60 mm×15 mm, an output power of more than 23 dBm and an output power fluctuation of less than 0.1 dB at 20 krad(SI) irradiation dose is realized.

In order to solve the problems of long test cycle, high research and development cost and unstable product quality in the research and development to production stage of optical fiber products in the field of optical communication, based on the six Sigma quality management method, the invention problem solving theory(TRIZ)-design of experiments(DOE)-process capability Cpk model was established and applied to the development of anti-bending fiber G.657-B3. This model is beneficial to carry out efficient test design and test cost control, determine the best combination of refractive index profile parameters of G.657.B3 fiber, and apply to mass production. The experimental results show that at the wavelength of 1550 nm and 1625 nm, the typical loss of macro bending is 0.063 dB and 0.165 dB, respectively, when the bending radius is 5 mm and one circle is made, and the macro bending performance of the fiber is good.