This book analyzes the development of space light-fiber coupling research, highlights its importance, examines the underlying theory and key problems, and elaborates on methods to improve the space light-fiber coupling efficiency. Starting from the basic theory of electromagnetic field, the transmission characteristics of light in optical fibers are expounded, and the coupling characteristics of optical signals of different modes are investigated. The spatial light-fiber coupling techniques such as mode conversion method, lens coupling method, and wavefront distortion correction method are discussed in detail, and the key technologies involved are verified by experiments. This book is suitable for the vast majority of engineering and technical personnel and teachers in colleges and institutions who are engaged in wireless optical communication. It can also be used to train senior undergraduates and graduate students in relevant fields.
Author(s): Xizheng Ke
Series: Optical Wireless Communication Theory and Technology
Publisher: Springer-Science Press
Year: 2023
Language: English
Pages: 232
City: Beijing
Preface
Contents
1 Introduction
1.1 Research Background and Significance
1.1.1 Transmitter
1.1.2 Receiver
1.1.3 Optical Antenna
1.1.4 Advantages of Spatial Light–Fiber Coupling
1.2 Development Status of Optical-Wireless Communication Technology
1.2.1 Current Foreign-Development Status
1.2.2 Domestic Development Status
1.3 Spatial Light–Fiber Coupling Technology
1.3.1 Research Progress Abroad
1.3.2 Domestic Research Progress
1.4 Spatial Light–Fiber Coupling
1.4.1 Optical Modes
1.4.2 Hermitian–Gaussian Beams
1.4.3 Laguerre–Gaussian Beams
1.4.4 Spatial Light–Fiber Coupling
1.5 Summary
References
2 Fiber-Optic Mode Theory
2.1 Fiber Optics
2.1.1 Basic Structure
2.1.2 Inverted Parabolic Fiber
2.2 Model Theory
2.2.1 Wave Equation
2.2.2 Wave-Equation Solution
2.3 Light-Wave Propagation Mode in Optical Fiber
2.3.1 Vector Mode
2.3.2 Scalar-Mode Solution
2.3.3 Normalized Operating Frequency
2.3.4 Coupling Efficiency of Gaussian Modes [15]
2.4 Mode Effective Refractive Index
2.4.1 Effective Refractive Index of a Vector Mode
2.4.2 Effective Refractive-Index Difference Between Modes
2.4.3 Dispersion Characteristics
2.4.4 Nonlinear Effects
2.4.5 Ideal Mode
References
3 Single-Lens Single-Mode Fiber Coupling Under Ideal Conditions
3.1 Plane-Wave Coupling
3.1.1 Geometrical-Optics Analysis of Coupling Efficiency
3.1.2 Mode-Field Analysis of Coupling Efficiency
3.1.3 Coupling Efficiency of Lens End Face
3.2 Coupling-Efficiency Decline Caused by Assembly Error
3.2.1 Radial Error
3.2.2 Axial Error
3.2.3 Axis Tilt Error
3.3 Adaptive-Optics System Errors
3.3.1 Calibration Errors
3.3.2 Fitting Errors
3.3.3 Measurement-Noise Errors
3.3.4 Bandwidth Errors
3.4 Non-common Path Aberrations
3.4.1 Research Status of Non-common Optical-Path-Aberration Calibration
3.4.2 Generation of Non-common Optical-Path Aberrations
3.4.3 Conversion of Non-common Optical-Path Aberrations
3.5 Gaussian-Beam Coupling
3.5.1 Coupling Efficiency
3.5.2 Experiment of Manually Eliminating Non-common Optical-Path Aberrations
3.5.3 Experiment of Automatically Eliminating Non-common Optical-Path Aberrations
3.6 Summary
References
4 Spatial Plane-Wave Single-Lens Single-Mode Fiber Coupling in Weakly Turbulent Atmospheres
4.1 Light-Field Distribution and Refractive-Index Power Spectrum in Atmospheric Turbulence
4.1.1 Born Solution for the Light-Field Distribution in Atmospheric Turbulence
4.1.2 Rytov Solution for the Light-Field Distribution in Atmospheric Turbulence
4.1.3 Refractive-Index Power-Spectrum Model
4.2 Lens Coupling in Atmospheric Turbulence
4.2.1 Coupling-Efficiency Model Under the Kolmogorov Turbulence Spectrum
4.2.2 Coupling-Efficiency Model Under the Von Kármán Turbulence Spectrum
4.2.3 Comparison of the Coupling Efficiency Under the Kolmogorov and Von Kármán Turbulence Spectra
4.2.4 Coupling Efficiency of an Oblique-Range Transmission Under the Von Kármán Turbulence Spectrum
4.3 Relative Fluctuation Variance of the Lens-Coupling Light Power in Atmospheric Turbulence
4.3.1 Relative Undulation Variance of Single-Lens Single-Mode Fiber-Coupling Power in Atmospheric Turbulence
4.3.2 Experimental Studies
4.3.3 Effect of Coupling Efficiency and Coupling-Power Jitter Variance on the BER of a Wireless-Optical Communication System
4.4 Spatial Optical Coupling of Lens Arrays in Atmospheric Turbulence
4.4.1 Coupling Efficiency
4.4.2 Coupling Experiment
4.5 Summary
References
5 Automatic Fiber-optic-coupling Alignment System
5.1 Auto-alignment Systems
5.1.1 Principle of the Auto-alignment System
5.1.2 Automatic-alignment System Components
5.1.3 Piezoelectric Ceramics
5.2 Basic Principles of Control Algorithms
5.2.1 Basic Principles of Simulated-annealing Algorithms
5.2.2 Flow of the Simulated-annealing Algorithm
5.2.3 Simulated-annealing Algorithm Features
5.2.4 Stochastic Parallel Gradient-descent Algorithm
5.2.5 Simulation of Different SPGD-algorithm Parameters
5.3 Effect of Alignment Errors on the Efficiency of Spatial Optical-fiber Coupling
5.3.1 Alignment Error and Coupling Efficiency
5.3.2 Radial, End-face, and Axial Errors
5.4 Two-dimensional Auto-alignment Experiments
5.4.1 Piezoelectric-ceramic and Fiber-fixing Method
5.4.2 Two-dimensional Alignment Experiments
5.5 Five-dimensional Auto-alignment Experiments
5.5.1 Piezoelectric-ceramic Combinations and Methods of Fixing Them to Optical Fibers
5.5.2 Analysis of Experimental Results
5.6 Summary
References
6 Mode-conversion Methods
6.1 Research Status of Mode Transformations
6.2 Basic Mode-conversion Theory
6.3 Spatial Phase-modulation Mode Conversions
6.3.1 Conversion from High-order Mode to LP01 Mode
6.3.2 Conversion-efficiency Analysis
6.4 Mode-conversion Improvements
6.4.1 Mode Conversion Based on the Simulated-annealing Algorithm
6.4.2 Comparison of Mode-conversion Effects
6.5 Experimental Study
6.5.1 Mode-conversion Experiment
6.5.2 Coupling-efficiency Experiment
References
7 Adaptive-optical Wavefront Correction
7.1 Introduction
7.2 System Composition
7.2.1 Zernike Polynomial
7.2.2 Influence of Wavefront Distortion on Coupling Efficiency
7.2.3 Power in the Barrel
7.2.4 Strehl Ratio
7.2.5 Wavefront Sensors
7.2.6 Wavefront Correctors
7.3 Simulation Analysis and Experimental Research
7.3.1 Simulation Analysis
7.3.2 Experimental Study
References
