Handbook of Optical Wireless Communication

Preface
	Optical Communication: From Wired to Wireless
	Fiber Communication
	Optical Wireless Communication
	Trends in Optical Wireless Communication
		High Data Rates
		Networks
		Multipurpose Applications
		Integration
		All-in-One Systems
		Full Photoluminescence
		Multispectral Communication
		Beaconless Light
		Non-Co-Optical Axis
	Structure of This Book
Contents
About the Author
1 Optical Wireless Communication
	Introduction
	Optical Wireless Communication Development Status
		Foreign Development Status
			United States
			Europe
			Japan
		Domestic Development Status
	Optical Wireless Communication Systems
		Components of Optical Wireless Communication Systems
		Features of Optical Wireless Communication Systems
			Wide Communication Bandwidth and Large Information Capacity
			Large Optical Gain and Small Laser Beam Dispersion Angle
			High Immunity to Electromagnetic Interference and High Confidentiality
			Small Device Size, Light Weight, and Low Power Consumption
		Problems of Optical Wireless Communication Systems
			Coherent Detection Must Satisfy More-Demanding Matching Conditions
			Matching the Complexity of the Adaptive-Optics Algorithm with the Atmospheric Environment
			Atmospheric Turbulence Reduces the Efficiency of Spatial Light-to-Fiber Coupling
			Atmospheric Turbulence Complicates Beam Alignment in Long-Range Optical Wireless Communication Systems
	Key Technologies
		High-Quality Optical System Design
			Near Diffraction Limit Angle Optical System Design Technology
			Multi-optical Axis Consistency Mounting Technology
			Optical Abutment Light and Small Design Technology
		Fast, Accurate, and Stable Capture Alignment Tracking Technology
		High-Rate, High Power-Emitting Lasers
		Atmospheric Channel Impact Compensation Technology
	Summary
	References
2 Research Progress on Satellite Laser Communication Networks
	Introduction
	Satellite Laser Communication
	Foreign Research Progress
	Domestic Research Progress
	Key Technologies for Satellite Laser Communication
		Key Optical Technology
		Key Signal-Processing Technologies
		APT Technology
		Opto-Mechanical Design Technology
	Satellite Laser Communication Networks
		Satellite Orbits
		Satellite Network Architectures
			Single-Layer Satellite Networks
			Multilayer Satellite Networks
		Satellite-Network Topologies
			Network Topology
			Star Topology
			Ring Topology
			Mesh Topology
		Interstellar Laser Links
			Interstellar Laser Link Geometry
			Interstellar Laser Link Performance Calculation
		Satellite-Routing Algorithms
			Centralized Satellite-Routing Algorithm
			Distributed Satellite-Routing Algorithm
			Hybrid Satellite Routing Algorithm
	Summary
	References
3 Pulse-Like Position Modulation Technology
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Pulse-Position Modulation Technology
		Symbol-Structure Analysis of Various Modulation Modes
		Performance Analysis of the Modulation Modes
			Average Symbol Length
			Bandwidth Demand and Utilization
			Average Transmit Power
			Performance Analysis
		Slot Error Rate Analysis
			Slot Error Rate Analysis Under a Gaussian Channel Model
			Average Slot Error Rate Under a Weak Turbulence Channel Model
			Average Slot-Error Rate Under a Medium-Strong Turbulence Channel Model
			Average Slot-Error Rate Under a Strong Turbulence Channel Model
		Channel Capacity
			Transmission Capacity
			Average Channel Capacity Under a Turbulent Channel
			Average Channel Capacity of Different Modulation Modes and Turbulence Intensities
		Adaptive Threshold Detection
		Factors Affecting the Laser-Modulation Rate
	Summary
	References
4 Communication Lasers and Their Modulation Technology
	Introduction
	Lasers and Optical Wireless Communication
		Wireless Communication Systems
		Laser Structure
		Laser Modulation Modes
	Laser Research Progress and Present Situation
		Solid-State Lasers
		Gas Lasers
		Semiconductor Lasers
			Edge-Emitting Semiconductor Lasers
			Surface-Emitting Semiconductor Lasers
		Fiber Lasers
		Low-Coherence Lasers
		Ultraviolet Lasers
	Modulation Technology
		Internal Modulation
		External Modulation
			Parameter Optimization
			Photonic Integration and Thin-Film Lithium Niobate (TFLN)
			IQ Modulation
	Lasers and Modulation Technology
		Laser-Characteristic Optimization
			Response Characteristics
				Modulation-Response Characteristics
				Impulse-Response Characteristics
			Compensation Scheme
			Power Control System
	Modulation Experiment
		Internal Modulation
		Electro-optic Modulation
			Influence of the Temperature on the Refractive Index of an Electro-optic Crystal
			Influence of the Temperature Electro-optic Modulator on the Output Light Intensity
			Influence of the Temperature on the Light-Modulator Transmittance
	Summary
	References
5 Research Progress on Passive Modulation in Free-Space Optical Communication
	Introduction
		Passive Modulation and Its Performance Index
			Passive Modulation
		Performance Analysis
			Bit-Error Rate Analysis
			Interruption-Probability Analysis
			Channel-Capacity Analysis
			Power Analysis
		Modulation-Form Analysis
	Foreign Research Progress
	Domestic Research Progress
	Working Principle of an MRR FSO System
		MRR FSO-System Composition
		Main-Parameter Analysis
			Wavelength Choice
			Beam-Divergence Angle
			Optical-Receiver Diameter
	Modulated Retro-Reflector
		Angular-Reflector MRR
		Cat´s-Eye MRR
			Cat´s-Eye Effect
			Echo-Power Analysis
			Defocusing the Cat´s-Eye MRR
				Theoretical Analysis of Non-defocusing
				Theoretical Analysis of Defocusing
			Electro-Absorption Cat´s-Eye MRR
	MRR FSO Application Prospects and Development Trends
		Applications
		Development Tendencies
	Summary
	References
6 Detectors and Their Noise Models
	Introduction
	Photodetectors
		Photodetector Classification
			Photoconductive Effect
			Photovoltaic Effect
			Photoelectron-Emission Effect
		Photodetector Performance Indicators
			Quantum Efficiency
			Noise-Equivalent Power
			Responsivity
			Spectral Responsivity
			Frequency Responsivity
			Detectivity and Normalized Geochemical-Exploration Measures
	Photodetector Types
		Source Noises
		Photomultiplier Tubes
			Working Principle
			Research Progress
			Typical Application Scenarios
		Avalanche Photodetector
			Working Principle
			Research Progress
			Typical Application Scenarios
		PIN Photodetectors
			Working Principle
			Research Progress
			Typical Application Scenarios
		Four-Quadrant Detectors
			Working Principle
			Research Progress
			Typical Application Scenarios
		Quantum-Dot Infrared Detectors
			Working Principle
			Research Progress
			Bottlenecks and Breakthroughs
			Typical Application Scenarios
		Balanced Detectors
			Working Principle
			Research Progress
			Typical Application Scenarios
		Double Balanced Probes
			Working Principle
			Research Progress
			Typical Application Scenarios
	Photodetector Noise
		Sources of Photodetector Noise
			Loose-Particle Noise
			Generation-Compound Noise
			Thermal Noise
			1/f Noise
		Typical Photodetector-Noise Models
			Noise Model of an Avalanche Photodetector
				Thermal Noise
				Loose-Particle Noise Generated by the Dark Current
				Excess Noise
			PIN Photodetectors
				Thermal Noise
				Loose-Particle Noise
				Generation-Compound Noise
				1/f Noise
			Photomultiplier Tubes
				Signal-to-Noise Ratio
				Scattered-Particle Noise Current
				Simplified Photomultiplier Model
			Four-Quadrant Detector
				Thermal Noise
				1/f Noise
				Generation-Compound Noise
			Quantum-Dot Detector
				Dark Current
				Noise Gain
				Noise
			Balanced Detector
				Thermal Noise
				Loose-Particle Noise
			Double-Balanced Detector
				Loose-Particle Noise
				Thermal Noise
				Relative-Intensity Noise
	Summary
	References
7 Noise Models in Optical Wireless Communication Systems
	Introduction
	Noise Distribution in Optical Wireless Communication Systems
	Source Noise
		Research Progress
		Noise Models
			Laser Relative-Intensity Noise Model
			Laser Phase-Noise Model
	Channel Noise
		Research Progress
		Noise Model
			Transmission-Attenuation Model
			Turbulent-Noise Model
				Lognormal Model
				- Model
				K-Distribution Model
				Negative-Exponential Distribution Model
				Malaga Distribution Model
				Exponential-Generalized Gamma Distribution Model
			Phase-Noise Model
			Aiming-Noise Model
			Background-Light Noise Model
			Ke´s Model
	Beacon Noise
		Research Progress
		Noise Models
			Poisson Noise Model
			Photon-Counting Noise Model
			Multiplicative-Noise Model
			Photodetector-Amplification Noise Model
			Dark-Current Noise Model
			Thermal Noise Model
			Shot Noise Model
			1/f Noise Model
	Performance Analysis of Optical Wireless Communication Systems Under the Influence of Turbulence
	Conclusion
	References
8 Adaptive-Threshold Detection Technology
	Introduction
	Domestic and Foreign Research Progress
		Adaptive-Threshold Detection
		Foreign Research Progress
		Domestic Research Progress
	System Structure and Model
		Optical Wireless Communication System Structure
		Photoelectric Detection Noise
		Error Rate
		Optimal Threshold Detection
	Typical Adaptive-Threshold Detection Models
		LMS Filter Adaptive-Threshold Detection Model
		Kalman-Filter Adaptive-Threshold Detection Model
		Adaptive-Threshold Detection Model with a Fading Kalman Filter
	High-Order Cumulant Adaptive-Threshold Detection
		Decision-Guided Adaptive-Filtering Algorithm
		Sliding-Correlation Adaptive-Threshold Algorithm
		Adaptive-Threshold Detection in a Strong-Turbulence Channel
	Summary
	References
9 Four-Quadrant Detector Light-Spot Detection Principle
	Introduction
	Light-Spot Model and Detection Principle
		Light-Spot Model
		QD-Based Spot-Position Detection Principle
	Four-Quadrant Detector-Based Spot-Position Detection
		Foreign Research Progress
		Domestic Research Progress
	QD Spot-Detection Influence Factors
		Effect of Different Light-Spot Modes on the QD Output
		Effect of Different Spot Radii on the QD Output
		Effect of Different Dead-Zone Widths on the QD Output
		Effect of Different Background Lights on the QD Output
		Effect of Different Signal-to-Noise Ratios on the QD Output
		Effect of Different Positioning Algorithms on the QD Output
	Spot-Detection Algorithms
		Addition-Subtraction Algorithm
		Diagonal Algorithm
		Difference-Ratio-Sum Algorithm
		Logarithmic Algorithm
		Function-Fitting Methods
	QD Light-Spot Detection System
		Beam-Alignment Detection System
		Missing-Spot Detection Test
		System Alignment Test
		QD Composite Tracking and Communication System
		Micro- and Nano-laser-communication Terminal
	Summary
	References
10 Optical-Antenna Technologies
	Introduction
	Basic Structure of an Optical Antenna
	Cassegrain Optical Antennas
		Large-Aperture Cassegrain Antenna
		Cassegrain Optical-Antenna Array
		Freeform-Surface Cassegrain Antenna
		Cassegrain Optical Antenna Based on a Beam-Shaping Scheme
		Off-Axis Dual-Reflection Cassegrain Optical Antenna
		Maksutov-Cassegrain Optical Antenna with Off-Axis Emission of a Gaussian-Beam Array
		Pre-Collimated Cassegrain Optical Antenna
	Beacon-Free Tracking
	Point-to-Multipoint Communication Optical Antennas
	Summary
	References
11 Research Progress on One-to-Many Transmitting Antennas for Optical Wireless Communication
	Introduction
	Optical Antennas
		Reflective Telescope Systems
			Newtonian Telescopic System
			Cassegrain Telescope System
			Gregorian Telescope System
			Off-Axis Triple-Reflex Telescope System
		Refractive Telescope Systems
			Galileo Telescope System
			Kepler Telescope System
		Catadioptric Telescope System
			Schmidt-Cassegrain System
			Maksutov-Cassegrain System
		Problems of Point-to-Point Antennas
	Foreign and Domestic Research Progress
	One-to-Many Optical Communication
		Basic Principles of One-to-Many Optical Communication
		Acquisition, Pointing, and Tracking (APT)
	Optical Principle of One-to-Many Communication
		Multi-optical Terminal Combination Type
		Multi-reflector Type
		TSAT Networking
		Double Optical-Wedge Group Combined Type
		Fiber-Array Type
		Multi-transmission, Multi-receiver Structure
		Three-Concentric-Sphere Structure
		Rotating-Paraboloid Structure
	Development Trends
	Summary
	References
12 Acquisition, Pointing, and Tracking
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Research Progress in the Automatic Aiming of Optical Wireless Communication Systems at Xi´an University of Technology
		Coarse- and Fine-Grading Control System
		Beam Detection System
		Automatic Tracking Control System for Space-Based Relay Optical Wireless Communication
		Field Experiments for Acquisition, Aiming, and Tracking in Optical Wireless Communication
			1.3-km Far-Field Experiment
			5.2-km Far-Field Experiment
			10.2-km Far-Field Experiment
			100-km Far-Field Experiment
		Non-common Visual Axis Two-Dimensional Mirror Rapid Aiming System
			Basic Principle
			Coarse Tracking and Control Model
			Two-Dimensional Mirror Model
			Fine Tracking and Its Control Model
		Chapter Review
	Summary
	References
13 Spatial Optical-Fiber Coupling Technology
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Research Progress on Spatial Optical-Fiber Coupling Technology
		Space-Light-Single-Mode-Fiber Coupling in Atmospheric Turbulence
			Coupling Efficiency of a Lens Array in Atmospheric Turbulence
			Coupling Efficiency of a Maka Antenna Under Atmospheric Turbulence
			Comparison of the Coupling System with a Lens Array and a Maka Antenna Under Atmospheric Turbulence
		Integrated Maka Antenna Transmitting and Receiving Technology
		Automatic Spatial Optical-Coupling Alignment
			Application of a Simulated-Annealing Algorithm to Automatic Spatial Optical-Coupling Alignment
			Application of the SPGD Algorithm to Automatic Spatial Optical-Coupling Alignment
		Mode-Conversion Method
		Adaptive-Optical Wavefront Correction
		Correction of Non-common Path Aberrations by Reverse-Transmission Calibration
			Reverse-Transmission Calibration of a Non-common Optical-Path Aberration
			Adaptive-Optical System
			Simulation Analysis
			Experimental Results and Analysis
		Comparison of Several Different Methods to Improve the Spatial Optical-Fiber Coupling Efficiency
			Comparison of Different Methods to Improve Fiber Coupling
			Comparison of Domestic and Foreign Research on the Automatic-Alignment Method
			Comparison of Domestic and Foreign Research on Adaptive-Optical Wavefront Correction
	Summary
	References
14 Atmospheric-Turbulence Models
	Introduction
	Atmospheric Refractive-Index Power Spectra
		Turbulence Formation
		Atmospheric Refractive-Index Fluctuation
		Atmospheric Structure Constants
		Atmospheric Turbulence Effects
			Beam Divergence
			Beam Drift
			Beam Spreading
			Light-Intensity Flicker
			Angle-of-Arrival Fluctuation
	Spectral Models of Atmospheric Turbulence
		Foreign Research Progress
		Domestic Research Progress
	Power-Spectrum Models of Atmospheric Turbulence
		Kolmogorov Spectrum
		Tatarskii Spectrum
		Von Krmn Spectrum
		Greenwood-Tarazano Spectrum
		Hill Spectrum
		Andrews Spectrum
		Non-Kolmogorov Spectrum
		Turbulence Spectra Varying with Altitude
	Atmospheric-Turbulence Channel Models
		Log-Normal Distribution
		Gamma-Gamma Distribution
		Negative-Exponential Distribution
		K Distribution
		Malaga Distribution
		Ke´s Model
	Summary
	References
15 Atmospheric-Turbulence Suppression Methods in Optical Wireless Communication
	Introduction
	Optical Wireless Communication Systems
	Atmospheric Turbulence
		Atmospheric-Turbulence Formation Mechanism
		Impact of Atmospheric Turbulence on Optical-Communication Systems
			Light-Intensity Scintillation
			Beam Drift
			Beam Expansion
			Phase Fluctuation
	Key Technologies for Suppressing Atmospheric Turbulence
		Large-Aperture Receiving Technology
			Current Research Status
			Suppression Principle
		Partially Coherent Optical Technology
			Current Research Status
			Suppression Principle
		Diversity Technology
			Current Research Status
			Suppression Principle
		Adaptive-Optics Technology
			Current Research Status
			Suppression Principle
				Adaptive-Optics Systems with Wavefront Sensors
				Adaptive-Optics Systems Without Wavefront Sensors
	Development Trends
	Summary and Outlook
	References
16 Propagation of Partially Coherent Beams in Atmospheric Turbulence
	Introduction
	Research History and Current Situation
		Foreign Research Progress
		Domestic Research Progress
	Gaussian-Schell Model of a Partially Coherent Beam
	Properties of Partially Coherent Beam Propagation in Atmospheric Turbulence
		Intensity Distribution
			Comparison of the Intensity Distributions of a GSM Beam on Horizontal and Slanted Transmission Paths
			Influence of Light Source Parameters on the Intensity Distribution
			Effect of Atmospheric Turbulence on the Intensity Distribution
			Effect of the Zenith Angle on the Intensity Distribution
		Beam Spreading
			Spreading of a GSM Beam in Horizontal and Slanted Paths
			Angle Spreading of a GSM Beam in Horizontal and Slanted Paths
		Beam Wandering
			Beam Wandering of a GSM Beam on a Horizontal Transmission Path
			GSM Beam Wandering on a Slanted Transmission Path
		GSM Beam Scintillation
			Scintillation in Strong and Weak Turbulence
			Scintillation of Fully and Partially Coherent Beams
		Angle-of-Arrival Fluctuation
			Effect of Light Source Parameters on the Angle-of-Arrival Fluctuation
			Effect of Atmospheric Turbulence on the Angle-of-Arrival Fluctuation
		Polarization Characteristics
			Polarization Characteristics of Partially Coherent EGSM Beams in Uplink and Downlink Paths
			Comparison of the Polarization Degree
				Comparison of Polarization Direction Angles
			Polarization Comparison of Partially Coherent EGSM Beams on Horizontal and Slanted Paths
		Speckle Characteristics
			Influence of Light Source Parameters
			Influence of Atmospheric Turbulence Parameters
	Summary
	References
17 Progress in Research on Channel Equalization in Optical Wireless Communication
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Key Channel Equalization Technologies
		Linear Equalization
			Zero-Forcing Equalization Algorithm
			Minimum Mean Square Error Equalization Algorithm
		Nonlinear Equalization
			Decision Feedback Equalizer
			Maximum-Likelihood Criterion
			Channel Equalization Algorithms Based on Neural Networks
	Summary
	References
18 Error-Correction Coding
	Introduction
	Research Progress in Error-Correction Codes
	Applying Error-Correction Codes to Optical Wireless Communication
	Error-Correction Coding Simulations in an Optical Wireless Communication System
		Error-Correction Control Based on RS Codes
		Error Control Based on LDPC Codes
		Error Control Based on Turbo Codes
		Error Control Based on Fountain Codes
			LT Codes
			Raptor Codes
		Error Control Based on Polarization Codes
			SC Decoding Algorithm Performance Simulation
			Polarization Code Performance Under PPM Modulation
			Simulation and Experiment of Polarization Code Performance Under Subcarrier-Modulation Technology
	Experimental Measurements
		RS Codes
		Turbo Codes
		LDPC Codes
	Summary
	References
19 Optical Wireless MIMO Technology and Space-Time Coding
	Introduction
	Research Status of Optical MIMO Technology
		Foreign Development Status
		Domestic Development Status
	Optical MIMO Systems
		Composition of Optical MIMO Systems
		Classification of Optical MIMO Technologies
			Diversity Technology
			Diversity Combining Technology
				Equal-Gain Combining-Receiving Diversity
			Equal-Gain Combining of Transmit and Receive Diversity
			Spatial Multiplexing Technology in MIMO Systems
	Evolution from SISO to MIMO Channels
	Urgent FSO-OFDM Problems
	References
20 Space-Time Coding
	Introduction
	Overview of Space-Time Coding Research
		Rise of Optical Wireless MIMO
		Domestic Research on Optical Wireless MIMO
	Multi-Aperture Transmitting/Receiving Experiment
		Multibeam-Emission System Composition and Experiment
		Multi-aperture Receiving-System Composition and Related Experiments
	Layered Space-Time Codes
		Layered Space-Time Coding Models
		Layered Space-Time Codes
		Horizontal Layered Space-Time Coding
		Diagonal Layered Space-Time Codes
		Helical Layered Space-Time Coding
		Vertical Layered Space-Time Coding
			Performance Analysis of the Maximum-Likelihood Decoding Algorithm
			Performance Analysis of Linear-Decoding Algorithms
				Zero-Forcing Decoding Algorithm
				Minimum Mean-Squared Error Decoding Algorithm
	Space-Time Codes
		Orthogonal Space-Time Coding
		Space-Time Trellis Coding
		Differential Space-Time Coding
		Unitary Space-Time Coding
		Hybrid Space-Time Coding
		Summary
	Concatenated Code
		Cascaded Orthogonal Space-Time Coding
			Cascaded Orthogonal Space-Time Block-Code Model
			Performance Analysis of Cascaded Orthogonal Space-Time Coding
		Cascaded Layered Space-Time Codes
			Cascaded Layered Space-Time Code Model
			Analysis of Cascaded Layered Space-Time Codes
				Simulation of the LDPC+D-BLAST System
				LDPC+T-BLAST System
	References
21 Experimental Study on Optical Wireless Coherent Communication
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Experiment on Coherent Detection in Radio Optical Communication
		Coherent-Detection Techniques
		Analysis of Coherent Detection Systems Under Atmospheric Turbulence
			Effect of Arrival-Angle Fluctuation on Coherent-Detection Systems
			Effect of Amplitude Fluctuation on Coherent Detection Systems
			1.3-km Heterodyne-Detection System Experiment
		Analysis of a Coherent-Detection System Under the Influence of Channel Noise
			Signal-to-Noise Ratio Analysis
			Analysis of the Influence of Relative-Intensity Noise
			Thermal Noise-Effect Analysis
		Analysis of the Influence of Optical-Signal Polarization on Coherent Detection Systems
			Advantages of the Three Algorithms
			Comparison of the Three Algorithms
		Performance Analysis of the Light Source on a Coherent Detection System
			Analysis of the Local-Vibration Optical Power on the Coherent-Detection System Performance
			Analysis of the Light-Source Linewidth on the Performance of a Coherent Detection System
		Performance Analysis of a Subcarrier-Modulated (SCM) Nonoptical Outlier-Detection System
			Ideal-Channel NOHD
			Nonideal-Channel NOHD
			NOHD System Experiment
		Color Difference of a Dual-Wavelength Free-Space Optical Communication System
			Correlation Function of Arrival-Angle Fluctuation at Different Wavelengths
			Different Wavelength Arrival-Angle Compensation Coefficients
			Phase Relationship Between Gaussian Beams of Different Wavelengths
			Wavefront-Distortion Correction for Dual-Wavelength Free-Space Optical Communication Systems
			Experimental Results and Analysis
	Coherent-Detection Performance Optimization
		Influence of the Polarization State of Partially Coherent Light on the Sensitivity of Coherent Detection in Non-Kolmogorov Atm...
			Theoretical Analysis
			Experimental Study
	Effect of the Optical Spatial Distribution on the Mixing Efficiency
		Coherent Detection System
			Mixing Efficiency of Coherent Detection Under Ideal Conditions
			Mixing Efficiency of Coherent Detection in a Turbulent Flow
		Mixing Efficiency of a Gaussian-Distributed Signal Light and Various Local Vibration Lights
			Local Vibration Light Is Uniformly Distributed
			Local Vibration Light Has a Gaussian Distribution
			Local Oscillator Light Has an Airy Distribution
		Mixing Efficiency When the Signal Light Has an Airy Distribution with Varying Local Vibration Lights
			Local Vibration Light Is Uniformly Distributed
			Local Oscillator Light Has an Airy Distribution
			Local Light Has a Gaussian Distribution
		Mixing Efficiency When the Signal Light Is a Vortex Beam with Varying Local Vibration Lights
			Local Light Has a Gaussian Distribution
			Local Oscillator Light Has an Airy Distribution
			Local Vibration Light Is Uniformly Distributed
			Local Oscillator Light Is an LG Beam
			Experimental Study
	Influence of Wavefront Distortion on Coherent Detection Performance
		Theoretical Analysis
			Mixing Efficiency and Bit-Error Rate
			Phase Wavefront Distortion
		Numerical Analysis
			Influence of the Wavefront Distortion on the Mixing Efficiency and Bit-Error Rate
			Evaluation of the Mixing Efficiency and Bit-Error Rate in Coherent Detection
			Evaluation of the Mixing Gain in Coherent Detection
		Experimental Study
	References
22 Factors Affecting Coherent-Detection Sensitivity
	Introduction
	Direct Detection and Coherent Detection
		Direct Detection
		Coherent Detection
			Principle of Coherent Detection
			Zero-Difference Detection
			Heterodyne Detection
			Internal-Difference Detection
		Signal-to-Noise Ratio and Sensitivity of Coherent-Detection Systems
	Foreign Research Progress
	Domestic Research Progress
	Factors Affecting the Coherent-Detection Limit
		Thermal and Shot Noise
		Wavefront Distortion of the Signal Light
		Polarization Mismatch Between the Signal Light and Local-Oscillator Light
		Spot-Size Deviation and Optical-Axis Deflection
		Coupling Efficiency
		Detector Performance
		Preoptical Amplifier
	Development Trends
		High-Detection Sensitivity and Resolution
		Wider Applications
		Simpler and More Efficient Detection Methods
		Further Research
	Future Prospects
	References
23 Adaptive Optics Technology
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Adaptive Optics in the Optical Wireless Communication Field
		Adaptive Optical System with Wavefront Measurement
			Classic Control
			Intelligent Control
		Adaptive Optical System Without Wavefront Measurement
			Mode Methods
			Non-mode Methods
		Wavefront Correction Using Liquid Crystal Spatial Light Modulators
		Combined Wavefront Correction Using Tilt and Deformable Mirrors
		Spatial Optical Fiber-Coupled Adaptive Optical Wavefront Correction
			Automatic Fiber Coupling Alignment
			Mode Conversion
			Adaptive Optical Fiber Coupling Experiment
	Summary
	References
24 Mode Methods in Adaptive Optics
	Introduction
	Research Progress at Home and Abroad
	Mode Methods
		Zernike Mode
			Definition of a Zernike Polynomial
			Physical Meaning of Zernike Polynomials
			Zernike Polynomials for Simulating Turbulent Phase Screens
			Aberration of a Zernike Term Represents a Face Shape
			Principle of Zernike-Mode Wavefront-Distortion Correction
		Lukosz Mode
		Deformable-Mirror Eigenmode Method
			Definition of the Deformable-Mirror Eigenmode Method
			Correction Principle of the Deformable-Mirror Eigenmode Method
				System Function
				Correction Coefficient
		Legendre Mode
			Definition of the Legendre Polynomial
			Two-Dimensional Legendre Polynomials
			Orthogonality of Two-Dimensional Legendre Polynomials
	Wavefront-Distortion Correction Quality-Evaluation Method
	Application of Mode Methods to Wavefront Correction
		Application of Zernike Mode
		Application of the Deformable-Mirror Eigenmode Method
	Summary
	References
25 Research on a Decoupling Algorithm for a Dual-Deformable-Mirror Wavefront-Correction System
	Introduction
	Domestic and Foreign Research Progress
	Wavefront-Correction Principle with Dual-Deformable Mirrors
		Principle of a Dual-Deformable-Mirror Correction System
		Principle of the Separation Coefficient Algorithm
	Numerical Simulation Analysis
	Experimental Research
	Coupling Analysis
	Conclusion
	References
26 Optical Phase-Locked Loops
	Introduction
	Development of Phase-Locked Loops
		Development of Electric Phase-Locked Loops
		Development of Optical Phase-Locked Loops
	Electronic Phase-Locked Loops
		Basic Structure of an Electronic Phase-Locked Loop
		Classification of Electric Phase-Locked Loops
			Different Circuit Structures
				Analog Phase-Locked Loops
				All-Digital Phase-Locked Loops
				Classification of All-Digital Phase-Locked Loops
					Type-I All-Digital Phase-Locked Loop
					Type-II All-Digital Phase-Locked Loop
					Digital-Analog Hybrid Phase-Locked Loop
					Software Phase-Locked Loops
			Comparison of Analog and Digital Phase-Locked Loops
			Other Classifications
				Phase-Locked Loops with Different Frequency-Division Coefficients
				Phase-Locked Loops of Different Types and Numbers
				Narrowband and Broadband Phase-Locked Loops
		Parameters of Electronic Phase-Locked Loops
		Applications of Electric Phase-Locked Loops
	Optical Phase-Locked Loops in Optical Communication
		Basic Structure of an Optical Phase-Locked Loop
			Optical Hybrids
			Photoelectric Detection Circuit
			Loop Filter
			Tunable Laser
		Classification of Optical Phase-Locked Loops
			Balanced Optical Phase-Locked Loop
			Costas Optical Phase-Locked Loop
			Decision-Driven Optical Phase-Locked Loop
			SyncBit Optical Phase-Locked Loop
			Dither Optical Phase-Locked Loop
			Subcarrier Optical Phase-Locked Loop
		Parameters of the Optical Phase-Locked Loop
		Performance Comparison of Various Optical Phase-Locked Loops
	Optical Phase-Locked Loops in Optical Wireless Coherent Communication
		Optical Phase-Locked Loop for Coherent Optical Communication
		Typical Applications of Optical Phase-Locked Loops
	Summary
	References
27 Deformable Mirrors and Their Control Algorithms
	Introduction
	Foreign Research Progress
	Domestic Research Progress
	Deformable Mirrors
		Classification of Deformable Mirrors
			Divided by Surface Shape
			Divided by Driving Mode
		Typical Deformable Mirrors
			Separation-Actuator Continuous-Surface Deformable Mirror
			Spliced Deformable Mirror
			Thin-Film Deformable Mirror
			Dual-Piezoelectric Deformable Mirror
			MEMS Deformable Mirror
			Voice-Coil Deformable Mirror
		Performance Index of Deformable Mirrors
		Model of a Deformable Mirror
		Deformable-Mirror Control Algorithms
			Control Algorithm Based on the PI Hysteresis Model
			Decoupling Control Algorithm
				Decoupling Control Algorithm of a Single Deformable Mirror
				Decoupling Control Algorithm of Dual-Deformable Mirrors
			Laplace-Eigenfunction Decoupling Control Algorithm
			Sparse-Sampling Control Algorithm
		Application of Deformable-Mirror Control Algorithms in Adaptive-Optics Systems
	Summary
	References
28 Liquid-Crystal Spatial Light Modulators and Their Applications
	Introduction
	Liquid-Crystal Spatial Light Modulators
		Liquid Crystal and Spatial Light Modulators
		Research Progress
			Foreign Research Progress
			Domestic Research Progress
	LC-SLM Basic Working Principle
		Electronically Controlled Birefringence Properties of Liquid Crystals
		Directional Distribution of Liquid Crystals
	Reasons for and Experiments with the Phase Calibration of Liquid-Crystal Spatial Light Modulators
		Double-Slit Interference
		Twyman-Green Interference (Fig. 28.7)
		Turbulence-Simulation Principle of a Liquid-Crystal Spatial Light Modulator
		Wavefront-Distortion Correction Principle of a Liquid-Crystal Spatial Light Modulator
		Classification of Liquid-Crystal Spatial Light Modulators
	Research Status of Optical-Modulation Technology
		Foreign Research Progress
		Domestic Research Status
		Performance Evaluation of Liquid-Crystal Spatial Light Modulators
			Amplitude-Modulation Characteristics
			Phase-Modulation Characteristics
	Application of Liquid-Crystal Spatial Light Modulators to Adaptive Optics
		Phase-Screen Simulation of a Liquid-Crystal Spatial Light Modulator
		LC-SLM Coherent Optical Communication Wavefront-Correction Technology
			Static Wavefront-Correction Experiment
			1.3-Km Field Experiment
			Adaptive-Optical System of a Dual Liquid-Crystal Spatial Light Modulator
			Combined Liquid-Crystal-Deformable-Mirror Adaptive-Optics System
	Summary
	References
29 Mixers
	Introduction
	Tube Mixers
	RF Mixers
		Schottky-Diode Mixers
			Diode Types
				Schottky Barrier Diodes
				Planar Schottky Diodes
			Diode Mixers
		CMOS Mixers
	Mixer Circuit Structures
		Single-Ended Structures
		Single-Balanced Structures
		Double-Balanced Structures
		Triple-Balanced Structures
		Mixer Linearity
	Optical Mixers
		Working Principle
		Research Progress and Current Status
		3-dB Coupler and Phase Shifters
		Mach-Zehnder Interference Optical Mixers
			Mach-Zehnder Interference Optical Mixer Structure
			Mach-Zehnder Interference Optical Mixing
		Polarized Optical Mixers
			Polarized Optical Mixer Structure
			Research Progress of Polarization Optical Mixers
		Crystal Optical Mixers
			Material Properties of Crystal Optical Mixers
			Crystal Optical Mixers
		Other Types of Optical Mixers
		Multimode Interference Coupler Optical Mixer
			4 x 4 MMI Coupler Combination Types
			2 x 2 MMI Coupler Combination Types
			Different Phase Demodulation Types of MMI Couplers
		MMI Optical Mixer Classification
			Interference-Coupled MMI Coupler
			Paired-Interferometric MMI Coupler
			Symmetrical Interferometric MMI Coupler
		Arrayed Waveguide Grating Structured Optical Mixer
			Basic Principle of the Arrayed Waveguide Grating
			Research Progress on Arrayed Waveguide Gratings
	Comparison of the Material Properties of Optoelectronic Devices
		Common Materials for Optical Mixers
		Comparison of Material Properties
		Mixing-Error Analysis
			Phase Error
			Insertion Loss
				Fiber Collimating Lens
				Polarization Beam-Splitting Prism (PBS) and Waveplate
			Splitting Ratio Error
	Analysis of the Mixing Efficiency of an Optical mixer in a Coherent Optical Communication System
		Light Field Pattern Matching
			Optical Field Distribution
			Mixing Efficiency
		Light-Spot Size Mismatch
		Wavefront Mass
		Vibration and Tracking Errors
		Polarization Characteristics
			Influence of the Optical Vector Direction of the Linear Polarization Signal on the Mixing Efficiency
			Influence of Circular Polarization and Elliptical-Polarization Signal Lights on the Mixing Efficiency
	Research on Optical Mixers at Xi´an University of Technology
		Structural Design of an Optical mixer
		Structural Optimization
		Experimental Verification
	Summary
	References
30 Principles and Development of Optical Amplifiers
	Introduction
	Optical-Amplifier Classification
	Principle of Optical Amplifiers
	Erbium-Doped Optical-Fiber Amplifiers (EDFA)
		Principle of the Erbium-Doped Fiber Amplifier
			Features of Erbium-Doped Fiber Amplifiers
		Research Progress on Erbium-Doped Fiber Amplifiers
	Raman Fiber Amplifiers (RFA)
		Principle of the Raman Amplifier
			Features of the Raman Amplifier
		Research Progress on Raman Amplifiers
	Semiconductor Optical Amplifiers (SOAs)
		Principle of Semiconductor Optical Amplifiers
		Classification of Semiconductor Optical Amplifiers
		Characteristics of Semiconductor Optical Amplifiers
		Research Progress on Semiconductor Optical Amplifiers
			Recent Advances in Quantum-Dot Semiconductor Optical Amplifiers (QDSOA)
			Recent Advances in Reflective Semiconductor Optical Amplifiers (SOA)
	Summary and Outlook
		Summary
		Outlook
	References
31 Key Technologies in Underwater Optical Wireless Communication
	Introduction
	Underwater Wireless Communication
		Acoustic Communication
		Radio Frequency Communication
		Optical Communication
	Model and Research Status of Underwater Optical Wireless Communication Systems
		System Model
		Foreign Research Status
		Domestic Research Status
	Key Technologies in Underwater Optical Wireless Communication
		Channel Modeling of Underwater Optical Wireless Communication Systems
			Optical Properties of Water
			Model of an Underwater Turbulent Channel
			Channel Attenuation Model
				Direct Viewing Model
				Indirect Viewing Model
			Modeling Cross-Media Transmissions
		Light Source Selection
		Modulation Technology
		Coding Technology
		Detection Technology
	Underwater Optical Wireless Communication System Design Model
	Summary
	References
32 Experimental Study on Underwater Optical Wireless Channel Models
	Introduction
	Foreign and Domestic Research Status
		Foreign Research Status
		Domestic Research Status
	Characteristics of Seawater Channels
		Ocean Turbulence Spectrum Models
		Attenuation Characteristics of Underwater Particles
			Absorption Properties
				Light Absorption by Pure Water
				Light Absorption Characteristics of Phytoplankton
				Light Absorption Properties of Yellow Matter
				Light Absorption Characteristics of Suspended Particles
			Scattering Characteristics
				Light-Scattering Properties of Pure Water
				Phytoplankton Light-Scattering Characteristics
				Suspended Particle Light-Scattering Characteristics
					Specific Light-Scattering Properties of Small Particles
					Light-Scattering Characteristics of Large Particles
	Experimental Measurements of Underwater Optical Wireless Communication
		Experimental System
		Statistical Analysis of Data
		Underwater Structure Constant
		Probability Density Function
	Performance Analysis of Underwater Optical Wireless Communication Experiments
		Scintillation Index
		Optical Power Loss
		BER at Different SNR
	Optical Cross-Medium Transmission Characteristics
		Optical Transmedia Model
		Experiment
			Spatial Distribution of the Spot Intensity
			Spot Center Offset
	References
33 Principles and Research Progress on LEDs
	Introduction
	Basic LED Principles and Photoelectric Characteristics
		LED Fundamentals
			SRH Recombination
			Radiative Recombination
			Auger Recombination
		Electrical Properties of LEDs
		Optical Properties of LEDs
	LED Research and Status
		Research and Development of Red LEDs
		Research and Development of Yellow LEDs
		Research and Development of Green LEDs
		Research and Development of Blue LEDs
		Research and Development of White LEDs
		Research and Development of UV LEDs
		LED Device Material History
	Visible Light Full-Duplex Communication
		Research and Development of Visible Light Communication
		Overall Full-Duplex Communication System Structure
		LED Optical Design
		LED Driver Circuit
	Experimental Verification
		Overall Uplink Design
		System Experiment
	Summary
		LED Industry Opportunities
			Promote LED Lighting Products and Provide National Policy Support
			LED Lighting Technology Continues to Develop and Prices Continue to Decline
			LED Lighting Products Continue to Expand Their Application Fields
			China Has a Complete LED Lighting Industry Chain and the Industry Is in a Mature Period of Development
			China´s LED Industry Standards and Development Continue to Improve
		LED Industry Challenges
			The Core Technology Is Relatively Weak
			The Brand Influence of Domestic LED Lighting Enterprises Is Weak
			The Homogeneous Competition Phenomenon Is Serious
	References
34 Principle and Research Progress of Visible Light Communication
	Introduction
	Visible LED Communications
		LED Light-Emitting Principle
		LED Communications
	Current Domestic and Foreign Research Status
		Current Foreign Research Status
		Current Status of Domestic Research
	Key Technologies in LED Visible Light Communication Systems
		Link Technology
			Uplinks and Downlinks
			Direct Vision Links vs. on-Direct Vision Links
		Reverse Modulation Techniques
		Equalization Technology
			Pre-Equalization Technology
			Post-Equalization Technology
		Information Modulation Technology
			Digital Pulse Modulation
			Color Shift Keying
			Orthogonal Frequency-Division Multiplexing
		Bandwidth Extension Technology for White LED Light Sources
		Optical Camera Communication Technology
	Indoor Visible Light Communication LED Layouts
		Indoor Visible Light System Modeling
		Light Source Layout Design
	Visible Light Positioning
		Visible Light Positioning Technology
		Positioning Enablement Program
	Visible Light Networking
		Networking Overview
			Fundamental Principle
			Multiple Access Technology
		Heterogeneous Networking
			VLC-Wi-Fi Networking
			VLC-PLC Networking
			Other Heterogeneous Networking Examples
	Application Scenarios
		Smart Home
		Health Care
		Intelligent Transportation
		Aviation Applications
		Ship Communication
		Intelligent Industrial Lighting
		Museum Environment Monitoring
		Library Navigation
		Underwater Applications
		Emergency Applications
	Development Trends
	Summary and Outlook
	References
35 Indoor Visible-Light Communication and Its Heterogeneous Fusion Networks
	Introduction
	Domestic and Foreign Research Progress
	Indoor Visible-Light Communication Systems
		Link Modes and Channel Models
			Link Modes
			Channel Models
		Uplink Communication Links
	Visible-Light Communication Heterogeneous-Fusion Networks
		VLC and Power-Line Communication Integration
			Fusion Scheme
			Fusion-Network Structure
			Channel Model of the Fusion System
		Heterogeneous Integration of VLC and WiFi
			Indoor VLC-WiFi Heterogeneous Networking Scheme
			Characteristics of Indoor VLC-WiFi Heterogeneous Networking
			Indoor VLC-WiFi Heterogeneous Network AP Layout
		VLC and Ethernet System Integration
			Two-Way Communication Systems
			Optical Communication Medium-Conversion Module
				Network-Interface Circuit
				Protocol Conversion
				Mutual Fusion of Local Area Networks
		VLC and LTE Network Interconnections
			Network Architecture
			Indoor VLC and LTE Network-Interconnection Model
		Interconnection of a VLC and Radio-over-Fiber (RoF) System
	Summary
	References
36 Optical-Camera Communication
	Introduction
	Domestic and Foreign Research Progress
	System Model
		Working Principle of CMOS Image Sensors in Optical-Camera Communication
		Design of Data Frames for the OCC Sending End
	Design of the Demodulation Algorithm
		Selection of ROI
		Distortion Correction for Visible-Light Imaging
			Correction of Perspective Distortions
			Correction of Tilt Distortions
		Improved Center/Surround Retinex Image-Processing Algorithm
			Center/Surround Retinex Theory
			Improved Center/Surround Retinex Algorithm
		Decoding Data
	Experimental Results and Analysis
		Bit-Error Rate Testing
		Analysis of Experimental Results
	Conclusion
	References
37 Indoor Visible Light Positioning Technology
	Introduction
	Visible Light Positioning Systems
		Geometric Ranging
		Scene Analysis
		Proximity Sensing
		Image Sensor Imaging
	Domestic and Foreign Research Progress on Indoor Visible Light Localization
		Foreign Research Progress
		Domestic Research Status
	Research Progress on Key Technologies
		LED Layout
		Light Source Modulation Modes
		Intelligent Optimization Algorithms
		Multifeature Fusion Localization
	Summary
	References
38 Research Progress on Visible-Light Communication Uplinks
	Introduction
	Visible-Light Communication Systems and Uplinks
		Visible-Light Communication-System Composition
		Visible-Light Communication Links
		Visible-Light Communication Uplinks
		Uplink Schemes for Visible-Light Communication
		Infrared Communication Uplinks
	Domestic and Foreign Research Progress on Uplinks
	RF Uplinks
		Composition of an RF-VLC Two-Way Communication System
		Uplink RF Communication-Link Channel
		WiFi-VLC Communication System
	Power-Carrier Uplinks
		PLC-VLC-Fusion Communication-System Structure
		Channel Model of a PLC-VLC-Fusion Communication System
		PLC-VLC-Fusion Communication-System Scheme
	Uplinks with Reverse-Modulation Technology
		Structure of a Reverse-Modulation System
		Reverse-Modulation Uplinks
	Summary
	References
39 Research Progress on Indoor Visible Light-Source Layouts
	Introduction
	Visible-Light Communication Systems
		Principle of Visible-Light Communication Systems
		Channel Model and Light-Source Layout for Visible-Light Communications
	Domestic and Foreign Research Progress on VLC Light-Source Layouts
		Geometric-Layout Methods
		Light-Source-Location Optimization Methods Based on Intelligent-Optimization Algorithms
		Methods for Optimizing the Light-Source Parameters Based on Intelligent Optimization Algorithms
		Summary of Research Progress
	Visible-Light Communication Light-Source-Layout Analysis
		Light-Source-Layout Principles
		Light-Source Spatial Layout
			Thiessen Polygon Layout
			Center-of-Mass Thiessen Polygon Layout
			Wireless-Communication Network Layout
		LED-Array Light-Source Layouts
		Key Algorithms for Light-Source Layout Parameters
			Particle-Swarm Algorithm
			Genetic Algorithm
			Ant-Colony Algorithm
			Application of Intelligent Neural-Network Algorithms
	Research on VLC Light-Source Layouts at Xi´an University of Technology
		Received-Power Analysis
		Optimal Design of a Light-Source Layout
		Layout-Model Simulation Analysis
			Optimal Layout Design under Different Numbers of White LED-Array Light Sources
			Influence of White LED-Array Light-Source Design Parameters on the Light-Intensity Distribution
	Summary
	References
40 Resource-Allocation Strategy for VLC/RF Systems
	Introduction
	Domestic and Foreign Research Progress
	System Model
		Downlink Communication
			VLC Channel Model
			RF channel model
		Uplink Communication
		OFDMA System Model
		Queue Model
	Optimization Theory
		AP Allocation
		VLC AP Joint Subcarrier and Power Allocation
		RF AP Joint Resource Block and Power Allocation
	Algorithm Simulation Results Analysis
	Conclusion
	References
41 Indoor Visible-Light Location Based on a Fusion Clustering Algorithm
	Introduction
	Indoor Model and Algorithm Principle
		System Model
		Channel Model
		Fingerprint-Location Method
	Improved Fingerprint Method
		Offline Phase
			K-medoids Algorithm
			DBSCAN Algorithm
		Online Phase
	Simulation Verification
		Fingerprint Method
		Improved Fingerprint Method
		Discussion
	Conclusions
	References
42 Experimental Study on Chromaticity Control in Visible-Light Communication Systems
	Introduction
	Multicolor VLC-System Model and Foreign and Domestic Research Progress
		System Model
		Domestic Research Progress
		Foreign Research Progress
	Theoretical Basis
	Research on RGB LED Dimming
		Dimming and Calculation Methods
		Simulation Analysis of Dimming
			Simulating Color-Coordinate Changes
			Simulating Color-Temperature Changes
			Simulating Different Transmission Distances
		Dimming Experiment
	Design and Experiment of an RGB-LED Visible-Light Communication System
		System Working Principle and Experimental Device
		Analysis of Experimental Results
	Conclusion
	References
43 Visible-Light Channel-Equalization Algorithm Based on the Fusion of a Neural Network and a Temporal-Feature Memory Structure
	Introduction
	Research Progress
		Status of Traditional Equilibrium-Technology Research
		Balanced-Technology Research Status of Deep Learning
	Channel Balancing in Visible-Light Communication Systems
		Time-Domain Balance-Filtering Principle
		Communication-System Analysis and Simulation
		Performance Analysis of a VLC System in a Multipath Channel
	CNN-LSTM Neural Network Equalization Algorithm
		Overall Structure
		Robustness Analysis of the Algorithm
	Simulation Analysis of the CNN-LSTM Model Performance
		Structural Parameters of the CNN-LSTM Algorithm
		CNN-LSTM Model Parameter Settings
		Simulation Analysis of the Structural Effectiveness of the CNN-LSTM Algorithm
			Mobile Receiver-Compensation Method Based on the CNN-LSTM Algorithm Structure
		Comparative Simulation Analyses of Different Equalization Algorithms
		Simulation Analysis of the Structural Parameters of the CNN-LSTM Algorithm
	Conclusion
	References
44 Ultraviolet Non-Line-of-Sight Communication
	Introduction
	Research Progress at Home and Abroad
		Foreign Research Progress in Ultraviolet Optical Communication
		Domestic Research Progress in Ultraviolet Optical Communication
	Channel Model
		Single-Scattering Model
		Multiple-Scattering Model
	UV NLOS Communication Link Model
		Pulse-Broadening Effect of NLOS Ultraviolet Communication
		Influence of Atmospheric Turbulence on Ultraviolet NLOS Communication
	Key Technologies of UV Self-Organizing Networks
		Node-Localization Algorithm of an Ultraviolet Optical Communication Network
		Ultraviolet Self-Organizing-Network Multiuser Detection Technology
		MAC-Layer Protocol
		UV Ad hoc: Network Routing Protocol
		Analysis of Energy Saving in UV Wireless Sensor Networks
	Summary
	References
45 Experimental Study on Ultraviolet Optical Communication Noise
	Introduction
	Foreign and Domestic Research Progress
		Foreign Research Status
		Domestic Research Status
	Theoretical Model of Ultraviolet Background Light
		Theoretical Model of Solar Radiation to the Earth
			Photon Energy
			Blackbody Radiation Model
			Solar Radiation Model
			Atmospheric Parameters
			Solar-Blind Zone UV Background Light Radiation Model
		UV Optical Communication Path Loss Model
			Single-Scattering Model and Theory
			Multiple-Scattering Model and Theory
			Path Loss Analysis of Ultraviolet Optical Communications
		UV Light Scattering Channel Characteristics Under Different Weather Conditions
			UV Light Scattering Channel Characteristics on Rainy Days
			UV Light Scattering Channel Characteristics on Foggy Days
			UV Light Scattering Channel Characteristics on Dusty Days
	Experimental Study of the Noise Model Under Different Weather Conditions
		Experimental Setup
		Near Earth Background Light Noise Model
			Measured Data Analysis on Sunny Days
			Measured Data Analysis on Cloudy Days
			Measured Data Analysis on Rainy Days
			Analysis of Measured Data on Hazy Days
			High-Altitude Background Light Noise Model
			Xi´an-Urumqi 10-km Altitude
			Xi´an-Beijing 8-km Altitude
			Xi´an-Nanjing 8-Km Altitude
			Xi´an-Yantai 7-km Altitude
			Data Correlation Function Analysis
		Analysis of Light Intensity Distribution Characteristics of Ultraviolet Optical Communication
			Ultraviolet Indirect Turbulence Model
			Ultraviolet Indirect Vision PDF Experimental Measurements
	Summary
	References
46 Research Progress on OWC/RF Hybrid Communication Systems
	Introduction
	Foreign and Domestic Research Progress
		Foreign Research Progress
		Domestic Research Progress
	System Model
		OWC/RF Hybrid Parallel System Model
			Hard Switching
				Single Threshold Switching
				Dual-Threshold Switching
			Soft Switching
	OWC/RF Hybrid Relay System Model
		Multiuser Hybrid Relay System
		Intelligent Reflecting Surface-Assisted Hybrid Relay System
	Application Scenarios for OWC/RF Hybrid Communication
		Hybrid System for Space Communication
		Hybrid Systems in Vehicle Communications
		Hybrid Systems in Underwater Communication
		Hybrid Systems in 5G Retransmission
	Hybrid System Performance
		OWC Subsystem
		RF Subsystem
		Hybrid System
			Signal-to-Noise Ratio
			Outage Probability
			Average Bit Error Rate
	Problems, Challenges, and Solutions
		Weather Conditions
		Atmospheric Turbulence
		Pointing Errors
		Multipath Effect
	Summary
	References
47 Performance Analysis of a Hybrid FSO/RF/THz Relay Communication System
	Introduction
	Foreign and Domestic Research Progress
	System and Channel Models
		Channel Model
		FSO Link
		RF Link
		THz Link
	Performance Analysis
		Outage Probability
		Average Bit Error Rate
	Simulation Results
	Conclusion
	References
48 Orbital Angular Momentum Beam Techniques
	Introduction
	Basic OAM Concepts
		OAM Properties
		OAM Beam Types
	Research Progress on Vortex Beam Generation
		Single Vortex Beam Generation
		Generation of Superimposed Vortex Beams
	Research Progress on Vortex Beam Transmissions
		Vortex Beam Transmission Characteristics
		Beam Transmission Characteristics of Partially Coherent Vortex Beams
		Vector Vortex Beam Transmission Characteristics
		Adaptive Wavefront Correction for Vortex Beams
	Vortex Beam Separation Measurement
	OAM Technology in Optical Wireless Communication Systems at Xi´an University of Technology
		Generation of Vortex Beams Carrying OAM
			Optical-Fiber Generation Method
				Few-Mode Fiber-Generation Method
				Improved Inverted-Parabolic Fiber Structure
				Improved Photonic-Crystal Fiber Structure
			Spatial-Generation Method
				Fractional-Order LG Beam Generation
				LG Beam Superposition State Generation
				High-Order Radial LG Beam Superposition State Generation
		Vortex Beam OAM Transmission
			Transmission Characteristics After Turbulence
			Adaptive Optical Wavefront Correction
			Others
		Vortex Beam Separation and Detection
			Vortex Beam Detection
				Vortex Beam Interference Detection Method
				Aperture-Detection Method
				Grating Detection Method
				Phase Singularity Evolution
				Orientation Angle of Polarization
			Vortex Beam OAM Separation and Detection
		Vortex Beam OAM Applications
			Vortex Beam OAM Coding and Decoding
			Vortex Beam OAM Information Exchange
			Vortex Beam OAM Through Maca-Antenna Emission-Efficiency Analysis
	Research Outlook of OAM Technology for Optical Wireless Communication Systems
	References
49 Research Progress on Aircraft Relay Optical Wireless Communication
	Introduction
	Overview of UAV Relay Optical Communication Systems
		UAV Relays
		Relay Collaboration Technology
			Relay Forwarding Strategy
			Relay System Models
			Relay Communication Protocol
			Relay Performance Evaluation Metrics
			Interruption Probability
				Average Bit Error Rate
				Signal-to-Noise Ratio
				Channel Capacity
				Relay System Throughput
	Research Status of UAV Relays
		Status of Foreign Research
		Status of Domestic Research
	Key Technologies for UAV Relay Optical Communication
		Channel-Influencing Factors and Their Suppression Techniques
			Channel Model
				Optical Wireless Communication Link
				RF Communication Link
			Channel Characteristics
				Path Loss
				Doppler Effect
				Multipath Effect
				Atmospheric Turbulence
				Aiming Error
				Arrival Angle Undulation
		High-Precision Capture, Alignment, and Tracking Technology
		Modulation and Demodulation Techniques
		Lightweight and Miniaturization Design Technology
	Non-Co-axial Aircraft-Relay Technology
	Application of Optical Wireless Communication to UAV Relaying
	Summary
	References
50 Research Progress on Optical Wireless Communication in Industrial Internets
	Introduction
	Optical Wireless Communication and the Industrial Internet
	Related Applications of Optical Wireless Communication in Industrial Scenarios
		Data Transmission
		Indoor Positioning
		Environmental Monitoring
	Foreign and Domestic Research Progress
	Key Technologies of Optical Wireless Communication in the Industrial Internet
		Visible Light Channel Model
		Multiple-Input Multiple-Output Technology
			Spatial Diversity
			Spatial Multiplexing
		Coding and Modulation Techniques
		Adjacent-Channel Interference Suppression Technology
		Multiple-Access Technology
		Heterogeneous RF/VLC Technology
			Double-Hop RF/VLC System
			Independent RF/VLC System
			Parallel-Transmission RF/VLC System
	Optical Wireless Communication Problems in the Industrial Internet
		Long Transmission Range
		Indoor Attenuation
		Multipath Reflections
		Signal Loss and Blocking
		Theoretical Problems of Heterogeneous RF/VLC Transmissions
	Summary
		Device Positioning and SIGNAL Transmission
		Integrated Wearable Security Devices
		Underwater Industrial IoT
		Augmented-Reality Technology
	References