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Diffraction, Fourier Optics

and Imaging

OKAN K. ERSOY

WILEY-INTERSCIENCE

A JOHN WILEY & SONS, INC., PUBLICATION

Copyright # 2007 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any

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Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

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Library of Congress Cataloging-in-Publication Data

Ersoy, Okan K.

Diffraction, fourier optics, and imaging / by Okan K. Ersoy. p. cm.

Includes bibliographical references and index. ISBN-13: 978-0-471-23816-4

ISBN-10: 0-471-23816-3

1. Diffraction. 2. Fourier transform optics. 3. Imaging systems. I. Title.

QC415.E77 2007

 

 

 

 

 

5350.42--dc22

 

 

 

 

 

2006048263

Printed in the United States of America

10

9

8

7

6

5

4

3

2

1

Contents

Preface

xiii

1. Diffraction, Fourier Optics and Imaging

1

1.1 Introduction

1

1.2Examples of Emerging Applications with Growing

 

Significance

2

 

1.2.1 Dense Wavelength Division Multiplexing/Demultiplexing

 

 

(DWDM)

3

 

1.2.2 Optical and Microwave DWDM Systems

3

 

1.2.3 Diffractive and Subwavelength Optical Elements

3

 

1.2.4 Nanodiffractive Devices and Rigorous Diffraction Theory

4

 

1.2.5 Modern Imaging Techniques

4

2. Linear Systems and Transforms

6

2.1

Introduction

6

2.2

Linear Systems and Shift Invariance

7

2.3

Continuous-Space Fourier Transform

10

2.4

Existence of Fourier Transform

11

2.5

Properties of the Fourier Transform

12

2.6

Real Fourier Transform

18

2.7

Amplitude and Phase Spectra

20

2.8

Hankel Transforms

21

3. Fundamentals of Wave Propagation

25

3.1

Introduction

25

3.2

Waves

26

3.3

Electromagnetic Waves

31

3.4

Phasor Representation

33

3.5

Wave Equations in a Charge-Free Medium

34

3.6Wave Equations in Phasor Representation

 

in a Charge-Free Medium

36

3.7

Plane EM Waves

37

4. Scalar Diffraction Theory

41

4.1

Introduction

41

4.2

Helmholtz Equation

42

v

vi

CONTENTS

4.3 Angular Spectrum of Plane Waves

44

4.4Fast Fourier Transform (FFT) Implementation of the Angular

 

Spectrum of Plane Waves

47

4.5

The Kirchoff Theory of Diffraction

53

 

4.5.1

Kirchoff Theory of Diffraction

55

 

4.5.2

Fresnel–Kirchoff Diffraction Formula

56

4.6

The Rayleigh–Sommerfeld Theory of Diffraction

57

 

4.6.1

The Kirchhoff Approximation

59

 

4.6.2 The Second Rayleigh–Sommerfeld Diffraction Formula

59

4.7Another Derivation of the First Rayleigh–Sommerfeld

Diffraction Integral

59

4.8The Rayleigh–Sommerfeld Diffraction Integral For

 

Nonmonochromatic Waves

61

5. Fresnel and Fraunhofer Approximations

63

5.1

Introduction

63

5.2

Diffraction in the Fresnel Region

64

5.3

FFT Implementation of Fresnel Diffraction

72

5.4

Paraxial Wave Equation

73

5.5

Diffraction in the Fraunhofer Region

74

5.6

Diffraction Gratings

76

5.7

Fraunhofer Diffraction By a Sinusoidal Amplitude Grating

78

5.8

Fresnel Diffraction By a Sinusoidal Amplitude Grating

79

5.9

Fraunhofer Diffraction with a Sinusoidal Phase Grating

81

5.10

Diffraction Gratings Made of Slits

82

6. Inverse Diffraction

84

6.1

Introduction

84

6.2

Inversion of the Fresnel and Fraunhofer Representations

84

6.3

Inversion of the Angular Spectrum Representation

85

6.4

Analysis

86

7.Wide-Angle Near and Far Field Approximations

for Scalar Diffraction

90

7.1

Introduction

90

7.2

A Review of Fresnel and Fraunhofer Approximations

91

7.3

The Radial Set of Approximations

93

7.4

Higher Order Improvements and Analysis

95

7.5

Inverse Diffraction and Iterative Optimization

96

7.6

Numerical Examples

97

7.7

More Accurate Approximations

110

7.8

Conclusions

111

CONTENTS

 

vii

8. Geometrical Optics

112

8.1

Introduction

112

8.2

Propagation of Rays

112

8.3

The Ray Equations

117

8.4

The Eikonal Equation

118

8.5

Local Spatial Frequencies and Rays

120

8.6

Matrix Representation of Meridional Rays

123

8.7

Thick Lenses

130

8.8

Entrance and Exit Pupils of an Optical System

132

9.Fourier Transforms and Imaging with

Coherent Optical Systems

134

9.1

Introduction

134

9.2

Phase Transformation With a Thin Lens

134

9.3

Fourier Transforms With Lenses

136

 

9.3.1 Wave Field Incident on the Lens

136

 

9.3.2 Wave Field to the Left of the Lens

137

 

9.3.3 Wave Field to the Right of the Lens

138

9.4

Image Formation As 2-D Linear Filtering

139

 

9.4.1 The Effect of Finite Lens Aperture

141

9.5

Phase Contrast Microscopy

142

9.6

Scanning Confocal Microscopy

144

 

9.6.1 Image Formation

144

9.7

Operator Algebra for Complex Optical Systems

147

10. Imaging with Quasi-Monochromatic Waves

153

10.1

Introduction

153

10.2

Hilbert Transform

154

10.3

Analytic Signal

157

10.4Analytic Signal Representation of a Nonmonochromatic

 

Wave Field

161

10.5

Quasi-Monochromatic, Coherent, and Incoherent Waves

162

10.6

Diffraction Effects in a General Imaging System

162

10.7

Imaging With Quasi-Monochromatic Waves

164

 

10.7.1

Coherent Imaging

165

 

10.7.2

Incoherent Imaging

166

10.8Frequency Response of a Diffraction-Limited

Imaging System

166

10.8.1

Coherent Imaging System

166

10.8.2

Incoherent Imaging System

167

10.9 Computer Computation of the Optical Transfer Function

171

10.9.1

Practical Considerations

172

10.10 Aberrations

173

10.10.1

Zernike Polynomials

174

viii

 

 

CONTENTS

11. Optical Devices Based on Wave Modulation

177

11.1

Introduction

177

11.2

Photographic Films and Plates

177

11.3

Transmittance of Light by Film

179

11.4

Modulation Transfer Function

182

11.5

Bleaching

183

11.6

Diffractive Optics, Binary Optics, and Digital Optics

184

11.7

E-Beam Lithography

185

 

11.7.1

DOE Implementation

187

12. Wave Propagation in Inhomogeneous Media

188

12.1

Introduction

188

12.2

Helmholtz Equation For Inhomogeneous Media

189

12.3

Paraxial Wave Equation For Inhomogeneous Media

189

12.4

Beam Propagation Method

190

 

12.4.1 Wave Propagation in Homogeneous Medium with

 

 

 

Index n

191

 

12.4.2 The Virtual Lens Effect

192

12.5

Wave Propagation in a Directional Coupler

193

 

12.5.1 A Summary of Coupled Mode Theory

193

 

12.5.2 Comparison of Coupled Mode Theory and BPM

 

 

 

Computations

194

13. Holography

 

198

13.1

Introduction

198

13.2

Coherent Wave Front Recording

199

 

13.2.1

Leith–Upatnieks Hologram

201

13.3

Types of Holograms

202

 

13.3.1 Fresnel and Fraunhofer Holograms

203

 

13.3.2 Image and Fourier Holograms

203

 

13.3.3

Volume Holograms

203

 

13.3.4

Embossed Holograms

205

13.4

Computer Simulation of Holographic Reconstruction

205

13.5

Analysis of Holographic Imaging and Magnification

206

13.6

Aberrations

210

14.Apodization, Superresolution, and Recovery

of Missing Information

212

14.1

Introduction

212

14.2

Apodization

213

 

14.2.1

Discrete-Time Windows

215

14.3

Two-Point Resolution and Recovery of Signals

217

14.4

Contractions

219

 

14.4.1

Contraction Mapping Theorem

220

CONTENTS

 

ix

14.5

An Iterative Method of Contractions for Signal Recovery

221

14.6

Iterative Constrained Deconvolution

223

14.7

Method of Projections

225

14.8

Method of Projections onto Convex Sets

227

14.9

Gerchberg–Papoulis (GP) Algorithm

229

14.10

Other POCS Algorithms

229

14.11

Restoration From Phase

230

14.12

Reconstruction From a Discretized Phase Function

 

 

by Using the DFT

232

14.13

Generalized Projections

234

14.14

Restoration From Magnitude

235

 

14.14.1 Traps and Tunnels

237

14.15

Image Recovery By Least Squares and the

 

 

Generalized Inverse

237

14.16

Computation of Hþ By Singular Value

 

 

Decomposition (SVD)

238

14.17

The Steepest Descent Algorithm

240

14.18

The Conjugate Gradient Method

242

15. Diffractive Optics I

244

15.1

Introduction

244

15.2

Lohmann Method

246

15.3

Approximations in the Lohmann Method

247

15.4

Constant Amplitude Lohmann Method

248

15.5

Quantized Lohmann Method

249

15.6

Computer Simulations with the Lohmann Method

250

15.7

A Fourier Method Based on Hard-Clipping

254

15.8A Simple Algorithm for Construction of 3-D Point

 

Images

 

257

 

15.8.1

Experiments

259

15.9 The Fast Weighted Zero-Crossing Algorithm

261

 

15.9.1

Off-Axis Plane Reference Wave

264

 

15.9.2

Experiments

264

15.10 One-Image-Only Holography

265

 

15.10.1

Analysis of Image Formation

268

 

15.10.2

Experiments

270

15.11

Fresnel Zone Plates

272

16. Diffractive Optics II

275

16.1

Introduction

275

16.2

Virtual Holography

275

 

16.2.1

Determination of Phase

276

 

16.2.2

Aperture Effects

278

 

16.2.3

Analysis of Image Formation

279

x

CONTENTS

16.2.4Information Capacity, Resolution, Bandwidth, and

Redundancy

282

16.2.5 Volume Effects

283

16.2.6Distortions Due to Change of Wavelength and/or Hologram Size Between Construction and

Reconstruction

284

16.2.7 Experiments

285

16.3The Method of POCS for the Design of Binary

DOE

287

16.4 Iterative Interlacing Technique (IIT)

289

16.4.1 Experiments with the IIT

291

16.5Optimal Decimation-in-Frequency Iterative Interlacing

Technique (ODIFIIT)

293

16.5.1 Experiments with ODIFIIT

297

16.6 Combined Lohmann-ODIFIIT Method

300

16.6.1Computer Experiments with the Lohmann-ODIFIIT

Method

301

17.Computerized Imaging Techniques I:

Synthetic Aperture Radar

306

17.1

Introduction

306

17.2

Synthetic Aperture Radar

306

17.3

Range Resolution

308

17.4

Choice of Pulse Waveform

309

17.5

The Matched Filter

311

17.6

Pulse Compression by Matched Filtering

313

17.7

Cross-Range Resolution

316

17.8

A Simplified Theory of SAR Imaging

317

17.9

Image Reconstruction with Fresnel Approximation

320

17.10

Algorithms for Digital Image Reconstruction

322

 

17.10.1 Spatial Frequency Interpolation

322

18.Computerized Imaging II: Image

Reconstruction from Projections

326

18.1

Introduction

326

18.2

The Radon Transform

326

18.3

The Projection Slice Theorem

328

18.4

The Inverse Radon Transform

330

18.5

Properties of the Radon Transform

331

18.6Reconstruction of a Signal From its

 

Projections

332

18.7

The Fourier Reconstruction Method

333

18.8

The Filtered-Backprojection Algorithm

335

CONTENTS

 

 

xi

19. Dense Wavelength Division Multiplexing

338

19.1

Introduction

338

19.2

Array Waveguide Grating

339

19.3

Method of Irregularly Sampled Zero-Crossings (MISZC)

341

 

19.3.1 Computational Method for Calculating the

 

 

 

Correction Terms

345

 

19.3.2 Extension of MISZC to 3-D Geometry

346

19.4

Analysis of MISZC

347

 

19.4.1

Dispersion Analysis

349

 

19.4.2

Finite-Sized Apertures

350

19.5

Computer Experiments

351

 

19.5.1

Point-Source Apertures

351

 

19.5.2 Large Number of Channels

353

 

19.5.3

Finite-Sized Apertures

355

 

19.5.4 The Method of Creating the Negative Phase

355

 

19.5.5

Error Tolerances

356

 

19.5.6

3-D Simulations

356

 

19.5.7

Phase Quantization

358

19.6

Implementational Issues

359

20.Numerical Methods for Rigorous

Diffraction Theory

361

20.1

Introduction

361

20.2

BPM Based on Finite Differences

362

20.3

Wide Angle BPM

364

20.4

Finite Differences

367

20.5

Finite Difference Time Domain Method

368

 

20.5.1 Yee’s Algorithm

368

20.6

Computer Experiments

371

20.7

Fourier Modal Methods

374

Appendix A: The Impulse Function

377

Appendix B: Linear Vector Spaces

382

Appendix C: The Discrete-Time Fourier Transform,

 

 

The Discrete Fourier Transform and

 

 

The Fast Fourier Transform

391

References

 

397

Index

403

Preface

Diffraction and imaging are central topics in many modern and scientific fields. Fourier analysis and sythesis techniques are a unifying theme throughout this subject matter. For example, many modern imaging techniques have evolved through research and development with the Fourier methods.

This textbook has its origins in courses, research, and development projects spanning a period of more than 30 years. It was a pleasant experience to observe over the years how the topics relevant to this book evolved and became more significant as the technology progressed. The topics involved are many and an highly multidisciplinary.

Even though Fourier theory is central to understanding, it needs to be supplemented with many other topics such as linear system theory, optimization, numerical methods, imaging theory, and signal and image processing. The implementation issues and materials of fabrication also need to be coupled with the theory. Consequently, it is difficult to characterize this field in simple terms. Increasingly, progress in technology makes it of central significance, resulting in a need to introduce courses, which cover the major topics together of both science and technology. There is also a need to help students understand the significance of such courses to prepare for modern technology.

This book can be used as a textbook in courses emphasizing a number of the topics involved at both senior and graduate levels. There is room for designing several one-quarter or one-semester courses based on the topics covered.

The book consists of 20 chapters and three appendices. The first three chapters can be considered introductory discussions of the fundamentals. Chapter 1 gives a brief introduction to the topics of diffraction, Fourier optics and imaging, with examples on the emerging techniques in modern technology.

Chapter 2 is a summary of the theory of linear systems and transforms needed in the rest of the book. The continous-space Fourier transform, the real Fourier transform and their properties are described, including a number of examples. Other topics involved are covered in the appendices: the impulse function in Appendix A, linear vector spaces in Appendix B, the discrete-time Fourier transform, the discrete Fourier transform, and the fast Fourier transform (FFT) in Appendix C.

Chapter 3 is on fundamentals of wave propagation. Initially waves are described generally, covering all types of waves. Then, the chapter specializes into electromagnetic waves and their properties, with special emphasis on plane waves.

The next four chapters are fundamental to scalar diffraction theory. Chapter 4 introduces the Helmholtz equation, the angular spectrum of plane waves, the Fresnel-Kirchoff and Rayleigh-Sommerfeld theories of diffraction. They represent wave propagation as a linear integral transformation closely related to the Fourier transform.

xiii

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