OPTICALINSTRUMENTATION

SATYAJIT DASAssistant Professor,

Department of Electronics and Communication,Amrapali Institutue of Technology and Sciences,

Haldwani, Nainital, Uttarakhand

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Telecommunication networks based on fiber-optic technology have become a major information transmissionsystem. Optoelectronic devices and fiber optic technology is the latest development in telecommunicationnetworking and also it is the fastest as it uses light as a medium of transmission. Optoelectronic devicesare far better compared to their electric and magnetic counterparts. More research is still being conductedand better devices are still coming to the market.

This book provides you a vital study about optoelectronic devices and laser instrumentation. ManyUniversities are running it as a course with slight variation in the name of the subject. Such as OpticalInstrumentation, Fiber optics and laser instrumentation, optoelectronic devices and instrumentation,optoelectronics and laser based instrumentation, Fiber optic instrumentation, Laser and optical instrumentationetc. I have tried to cover the syllabus of almost all the universities.

In this book, I have discussed the basics and core of optoelectronics. From where it all started to wherewe are now. It covers the devices which are based on Fiber-optic communication technology such as photosources, photo detectors, optoelectronic modulators, optoelectronic sensors etc.

This book is divided into 11 chapters. Each chapter provides an insight of some aspect of optoelectronics.

Chapter 1: This chapter introduces you to optoelectronics. What exactly optoelectronics is? and how is itdifferent from optical fiber communication? How is fiber optic technology better than older technologies.

Chapter 2: This chapter befriends you with light and its properties. What is light? Histories and theoriesof light. Various properties of light, grating theory etc. has been explained.

Chapter 3: This chapter opens a gateway to optical fiber and its various properties. It discusses all aspectsof optical fiber starting from the basic laws governing to the various types of fibers and their properties.

Chapter 4: This chapter talks about optoelectronic sources and detectors. Two basic sources LED andLASERS have been almost completely covered. It includes structure, definition, working, processes, materials,design, modes, drive circuitry etc. All types of lasers that are used today have been included in the chapter.Also basics and types of detectors have been discussed.

Chapter 5: This chapter takes the laser study to the next level by discussing the industrial application oflasers and their future scope.

Chapter 6: This chapter covers all types of optoelectronic amplifiers and modulators. The basic concept,types of devices, advantages, drawback and comparisons are discussed.

Chapter 7: This chapter tries to cover some off the track topics of optoelectronics. They are mainly focusedon interferometry, types of instruments and techniques.

Chapter 8: This chapter discusses another very important aspect of optoelectronics. Holography. Holographyis one of the most important and fast growing 3-D image capturing technology which has changed thetechnology of image capturing. It also discusses the famous Michelson-Morley experiment and some othertypes of interferometers. This chapter also opens a discussion on Fourier optics.

Chapter 9: This chapter talks about Fiber-optic sensors. All types of optical sensors have been discussedin detail.

Chapter 10: This chapter is an extension to chapter 4, and this has been written to cover measuringinstruments, such as Power meters, Attenuators, Spectrum analyzers, OTDRs etc.

Chapter 11: In this chapter, optical computing, an another associated branch of optical communication isdiscussed optical mathematics and shadow casting are also discussed.

Hope you enjoy reading this book.Satyajit Das

Preface

This book is a result of dedication and encouragement of many individuals. I would like to thankall those who directly or indirectly contributed to this project.

Firstly, I would like to thank Mr. C.L. Dhingra (Chairman, AITS), Mr. Sanjay Dhingra (CEO,AITS), Mr. Narendra Dhingra (Secretary, AITS), Mr. R.C. Monga (Vice-Chairman, AITS),Col. R.C. Bhandari (Director-Administration, AITS), Dr. Vikas Narayan (Director, AITS) forsupporting me in writing this book.

I would like to thank Mrs. Mukta Jukaria (Head of Department, ECE, AITS), Dr. D.C. Joshi(Dean, AITS), Mr. Jeetendra Pandey (Asst. Dean, AITS), Prof. Y.K. Shah, Prof. P.C. Sah, Prof.A.K. Mathur, Mr. Nihar Ranjan Pandey, Mr. Hem C. Joshi, Mr. Inder S. Bisht, Mr. Upendra KrSingh, Mr. Mudit Gupta and all those who were the source of inspiration and positiveness duringwriting this book.

Also, I would like to extend my heartiest thanks to Miss Usha Koshyari and Miss NehaMelkani for helping me with the contents of the book. I would also like to thank my ex-studentsMr. Sanjay Satyapal, Miss Kavita Upadhyay and Miss Chetna Arora for their valuable contributionto the book.

I would also like to express my gratitude to Mrs. Anishka Jain, who was the one who actuallyinspired me to write the book. I also extend my sincere thanks to Dr. Amit Ganguly (SRMUniversity), Miss. Ankita Thakur (JSS Academy, Noida), Mr. Ravindra Tiwari (Department ofPhysics, AITS), Mr. Raghav Dixit (HCL Technologies, Noida) and Mr. Rajul Sharma (Essel ShyamLtd.) for their expertise, guidance and support in their respective fields.

Finally, I would like to express my heartiest thanks to Mr. Sanjeev Kataria of M/s Kataria &Sons for publishing this book and making this project a reality. Special thanks are due toMr. Sharda Singh for his support and guidance and Mr. Dinesh for word processing the contentsof the book and making the diagrams.

I enjoyed writing this book, and hope you enjoy reading it and using it for your courses andprojects.

Satyajit Das

Acknowledgements

Dedicated toMaa, Baba & Savya

1. INTRODUCTION TO OPTOELECTRONICS 1–9

1.1 Fiber Optics and Optoelectronics ........................................................................................................ 11.2 Historical Developments ..................................................................................................................... 21.3 Configuration of Fiber Optic Communication System ...................................................................... 4

1.3.1 Analog Fiber Optic Communication System .......................................................................... 51.3.2 Digital Fiber Optic Communication System ........................................................................... 5

1.4 Advantages of Fiber Optics and Optoelectronics ................................................................................ 61.5 Role of Fiber-optic Technology ........................................................................................................... 7

Summary ............................................................................................................................................... 8Review Questions ................................................................................................................................... 9

2. LIGHT AND ITS PROPERTIES 10–32

2.1 Concept of Light ................................................................................................................................ 102.2 Classification of different Phenomenon based on Theories of Light .............................................. 10

2.2.1 Corpuscular Theory .............................................................................................................. 102.2.2 Wave Theory ......................................................................................................................... 112.2.3 Electromagnetic Theory ....................................................................................................... 112.2.4 Quantum Theory .................................................................................................................. 11

2.3 Basic Light Sources and its Characterisation .................................................................................... 122.4 Polarization ........................................................................................................................................ 12

2.4.1 Linear Polarization ................................................................................................................ 132.4.2 Elliptical and Circular Polarization ........................................................................................ 14

2.5 Coherent and Incoherent Sources .................................................................................................... 162.6 Grating Theory .................................................................................................................................. 17

2.6.1 Diffraction .............................................................................................................................. 172.6.2 Difference between Interference and Diffraction ................................................................. 172.6.3 Single Slit Diffraction Pattern ................................................................................................ 182.6.4 Fraunhoffer’s Diffraction at a Double Slit ............................................................................. 23

2.7 Application of Diffraction Grating ..................................................................................................... 27Summary ............................................................................................................................................. 32Review Questions ................................................................................................................................. 32

3. OPTICAL FIBRE AND ITS PROPERTIES 33–58

3.1 Introduction to Optical Waveguide ................................................................................................... 333.1.1 Basic Laws of Optics ............................................................................................................. 343.1.2 Concept of TIR ..................................................................................................................... 35

3.2 Principle of Light Propagation through a Fiber ............................................................................... 353.2.1 Fractional Refractive Index Change ..................................................................................... 373.2.2 Numerical Aperture .............................................................................................................. 373.2.3 Skew Rays ............................................................................................................................. 40

3.3 Different Types of Fibers (Waveguides) and their Properties ........................................................... 423.3.1 Planar Waveguide also known as Dielectric Slab WG ........................................................... 42

Contents

Contents ix

3.3.2 Maxwell’s Equations ............................................................................................................. 433.3.3 Propagating Modes in a Symmetric Slab Waveguide ........................................................... 473.3.4 Asymmetric and Three-dimensional Waveguide (fibre) ...................................................... 473.3.5 Channel Waveguide (fiber) ................................................................................................... 483.3.6 Strip-loaded Waveguide (fiber) ............................................................................................. 48

3.4 Fiber Characteristics .......................................................................................................................... 493.5 Fiber Losses ....................................................................................................................................... 49

3.5.1 Absorption Loss .................................................................................................................... 493.5.2 Scattering Loss ...................................................................................................................... 503.5.3 Bending Loss ........................................................................................................................ 50

3.6 Dispersion .......................................................................................................................................... 513.7 Connectors and Splicers .................................................................................................................... 543.8 Fiber Termination ............................................................................................................................. 55

Summary ............................................................................................................................................. 55Review Questions ................................................................................................................................. 57

4. OPTOELECTRONIC SOURCES/DETECTORS AND LASER FUNDAMENTALS 59–139

4.1 Photosources/Optical Sources/Optoelectronics Sources ................................................................... 594.1.1 Light Emitting Diode (LED) ................................................................................................. 60

4.1.1.1 Structure and Working of LED .......................................................................... 604.1.1.2 Radiative Recombination Processes ................................................................... 634.1.1.3 Quantum Efficiency/Response Time and LED Power ....................................... 644.1.1.4 Materials used to Fabricate LED and Laser ........................................................ 654.1.1.5 LED Construction/Design of LED for Optical Communication ........................ 674.1.1.6 LED Drive Circuitry ............................................................................................ 68

4.1.2 Laser Fundamentals ........................................................................................................ 734.1.2.1 Fundamental Characteristics of Lasers .............................................................. 74

4.1.2.1.1 Three Level Laser .......................................................................... 774.1.2.1.2 Four Level Laser ............................................................................ 77

4.1.2.2 Properties of Laser .............................................................................................. 784.1.2.3 Laser Modes ........................................................................................................ 794.1.2.4 Main Components of a Laser ............................................................................. 814.1.2.5 Action of Optical Resonator/Resonator Configuration ..................................... 824.1.2.6 Mode Locking ..................................................................................................... 834.1.2.7 Q-Switching and Cavity Damping ...................................................................... 854.1.2.8 Laser Drive Circuitry .......................................................................................... 884.1.2.9 Applications of Laser .......................................................................................... 884.1.2.10 Comparison Chart of LED and Lasers .............................................................. 89

4.1.3 Types of Laser/Laser Classification ....................................................................................... 904.1.3.1 Introduction ........................................................................................................ 904.1.3.2 Laser Devices ...................................................................................................... 90

4.1.3.2.1 Basic Structure and Types of Laser Diodes ................................... 904.1.3.2.2 Quantum-Well Laser Diodes .......................................................... 934.1.3.2.3 Fabry-Perot Laser Diodes .............................................................. 95

4.1.3.3 Distributed-Feedback (DFB) Laser Diodes......................................................... 964.1.3.3.1 Vertical-Cavity Surface-Emitting Lasers (VCSEL) ........................ 984.1.3.3.2 Characteristics of Light Emitted by Laser Diodes ......................... 994.1.3.3.3 Solid Lasers (Ruby Laser) ............................................................ 102

4.1.3.4 Neodymium : Yittrium Aluminium Garnet (Nd : Yag Laser) ......................... 104

x Contents

4.1.3.4.1 Gas Lasers [Helium—Neon (He–Ne) Laser] .............................. 1054.1.3.4.2 Carbon Dioxide Laser (CO2 Lasers) ........................................... 1074.1.3.4.3 Semiconductor Lasers .................................................................. 1094.1.3.4.4 Hetrojunction Lasers ................................................................... 1144.1.3.4.5 Ion Lasers-The Argon Laser ........................................................ 1204.1.3.4.6 Liquid Lasers (Dye Laser) ............................................................ 122

4.2 Photodetectors/Optical Detectors/Optoelectronic Detectors .......................................................... 1254.2.1 Photodiode: Basic Principle of Detection ............................................................................ 1254.2.2 p-n Photodiode .................................................................................................................... 1284.2.3 p-i-n Photodiode .................................................................................................................. 1294.2.4 Avalanche Photodiode ......................................................................................................... 1294.2.5 Photoconductors ................................................................................................................. 1304.2.6 Solar Cells ........................................................................................................................... 1334.2.7 Phototransistors .................................................................................................................. 135Summary ........................................................................................................................................... 137Review Questions ............................................................................................................................... 138

5. INDUSTRIAL APPLICATIONS OF LASER 140–153

5.1 Laser for Measurement ................................................................................................................... 1405.1.1 Measurement of Distance .................................................................................................... 140

5.1.1.1 Light Detection and Ranging (LIDAR) ............................................................... 1415.1.2 Measurement of Length ..................................................................................................... 1445.1.3 Measurement of Velocity .................................................................................................... 1455.1.4 Measurement of Acceleration ............................................................................................. 1465.1.5 Measurement of Current .................................................................................................... 1465.1.6 Measurement of Voltage ..................................................................................................... 1465.1.7 Measurement of Atmospheric Effect .................................................................................. 146

5.2 Material Processing .......................................................................................................................... 1485.2.1 Laser Heating ...................................................................................................................... 1485.2.2 Laser Welding...................................................................................................................... 1505.2.3 Laser Melting and Trimming .............................................................................................. 1505.2.4 Laser Removal and Vaporization ........................................................................................ 151Summary ........................................................................................................................................... 152Review Questions ............................................................................................................................... 153

6. OPTOELECTRONIC AMPLIFIERS AND MODULATORS 154–210

6.1 Introduction ..................................................................................................................................... 1546.2 Review of Basic Concepts ............................................................................................................... 155

6.2.1 Optical Polarization ............................................................................................................. 1556.2.2 Birefringence ....................................................................................................................... 1576.2.3 Huygen’s Principle .............................................................................................................. 158

6.3 Repeaters and Optoelectronics Amplifiers ..................................................................................... 1616.3.1 Repeater .............................................................................................................................. 1616.3.2 Optoelectronic Amplifier ..................................................................................................... 162

6.4 Semiconductor Amplifiers ............................................................................................................... 1636.5 Erbium-doped Fiber Amplifiers (EDFAS) ....................................................................................... 1666.6 System Application .......................................................................................................................... 1696.7 Raman Optical Amplifier ................................................................................................................. 1716.8 Modulation/FO Instrumentation System........................................................................................ 173

Contents xi

6.8.1 LED Analog Modulation ..................................................................................................... 1746.8.2 LED Digital Modulation ...................................................................................................... 1776.8.3 Laser-Diode Modulation ..................................................................................................... 179

6.8.3.1 LD Analog Modulation ..................................................................................... 1796.8.3.2 LD Digital Modulation ...................................................................................... 180

6.9 Electro-optic Retardation (Retardation Plates) ............................................................................... 1816.10 Electro-optic modulators ...................................................................................................... 182

6.10.1 Electro-Optic Effect ........................................................................................................... 1826.10.2 Longitudinal Electro-Optic Modulator ............................................................................. 183

6.10.2.1 E-O Phase Modulator ..................................................................................... 1836.10.2.2 E-O Amplitude Modulator ............................................................................. 1846.10.2.3 E-O Intensity Modulator ................................................................................ 187

6.10.3 Transverse Electro-optic Modulator ................................................................................. 1896.10.4 Kerr Modulators ............................................................................................................... 1916.10.5 Coupled Waveguide Modulators ...................................................................................... 193

6.11 Magneto-optic Modulators .............................................................................................................. 1956.12 Acousto-optic Modulators ............................................................................................................... 197

6.12.1 Acousto-Optic Effects ....................................................................................................... 1976.12.2 Raman-Nath Modulator .................................................................................................. 1986.12.3 Bragg Modulator .............................................................................................................. 200

6.13 Application Areas of Optoelectronic Modulations .......................................................................... 2006.14 Non-linear Optics ............................................................................................................................ 201

6.14.1 Second Harmonic Generation .......................................................................................... 2046.14.2 Parametric Oscillation ....................................................................................................... 204Summary ........................................................................................................................................... 207Review Questions ............................................................................................................................... 209

7. INTERFEROMETRY 211–248

7.1 Introduction: The Interference Effect ............................................................................................ 2117.2 Young’s Experiment ........................................................................................................................ 2127.3 Radio Metry ..................................................................................................................................... 2137.4 Types of Interference Phenomenon and its Applications ............................................................... 214

7.4.1 Parallel-sided Plates ............................................................................................................. 2147.4.2 Interference in very Thin Films .......................................................................................... 2157.4.3 Newton’s Rings ................................................................................................................... 2157.4.4 Applications of Interference Phenomenon ......................................................................... 216

7.5 Interferometry ................................................................................................................................. 2177.5.1 Michelson’s Interferometer ................................................................................................ 217

7.5.1.1 Types of Fringes ................................................................................................ 2187.5.1.2 Visibility of Fringes ........................................................................................... 219

7.5.2 Applications of Michelson Interferometer .......................................................................... 2207.5.2.1 Wavelength of Monochromatic Light .............................................................. 2207.5.2.2 Difference in Wavelength between Two Neighbouring Spectral

Lines (Resolution of the Spectral Lines) .......................................................... 2237.5.2.3 Refractive Index of Thin Transparent Plates ................................................... 2257.5.2.4 Standardisation of the Meter ............................................................................ 227

7.5.3 Fabry-Perot Interferometer ................................................................................................ 2277.5.3.1 Visibility of Fringes ........................................................................................... 2307.5.3.2 Resolving Power of Fabry-Perot Interferometer ............................................. 2327.5.3.3 Resolving Power of a Fabry-Perot Interferometer (Rayleigh’s Criterion) ...... 233

xii Contents

7.6 Refractometer .................................................................................................................................. 2377.6.1 Jamin’s Refractometer ...................................................................................................... 2377.6.2 Mach-Zehnder Refractrometer ........................................................................................... 2387.6.3 Rayleigh’s Refractometer .................................................................................................... 239

7.7 Spectrograph ................................................................................................................................... 2407.8 Spectrophotometer / Spectrometer / Spectroscope ........................................................................ 241

7.8.1 µ of the Material of a Prism ................................................................................................. 2437.9 Monochromator (or Constant Deviation Spectrometer) ............................................................... 244

7.10 Calorimeter ..................................................................................................................................... 2467.11 Medical Optical Instruments ...................................................................................................... 247

Summary ........................................................................................................................................... 248Review Questions ............................................................................................................................... 248

8. HOLOGRAPHY AND FOURIER OPTICS 249–299

8.1 Introduction ..................................................................................................................................... 2498.1.1 Recording a Hologram ....................................................................................................... 2508.1.2 Reconstructing the 3-D Image ............................................................................................ 251

8.2 Holography of a Point Object ......................................................................................................... 2528.2.1 Off-axis Holography ........................................................................................................... 2528.2.2 On-axis Holography ........................................................................................................... 254

8.3 Spatial Frequency and Limit of Resolution..................................................................................... 2558.4 Speckle Phenomenon and Method of Measurement ..................................................................... 2598.5 Interference and Interference Fringes/Moire Fringes .................................................................... 2628.6 Michelson - Morley Interferometer ................................................................................................ 2658.7 Laser Interferometer ...................................................................................................................... 2708.8 Holographic Interferometer ........................................................................................................... 271

8.8.1 Double Exposure Interferometer ....................................................................................... 2748.8.2 Real Time Interferometer .................................................................................................. 2758.8.3 Contour Generation Interferometer .................................................................................. 276

8.9 Holography for Non-destructive Testing ....................................................................................... 2768.9.1 Optical Data Storage ........................................................................................................... 276

8.10 Holographic Components/Applications of Holography ................................................................ 2788.10.1 Holographic Optical Elements (HOE) ............................................................................... 278

8.11 Fourier Optics .................................................................................................................................. 2818.11.1 LENS ................................................................................................................................... 281

8.11.1.1 Convex and Concave Lenses ............................................................................ 2828.11.1.2 Principal Axis of a Lens ..................................................................................... 2828.11.1.3 Optical Center of a Lens ................................................................................... 2828.11.1.4 Principal Foci and Focal Length ........................................................................ 2838.11.1.5 Lens Power – Diopters ...................................................................................... 284

8.11.2 Image Forming Property of Lenses .................................................................................... 2848.11.3 Phase Transformation of a Thin Lens or Thin Lens as a Phase Transformation ............. 2878.11.4 The Phase Transformation of Thin Lens & its Physical Meaning ...................................... 289Summary ........................................................................................................................................... 297Review Questions ............................................................................................................................... 298

9. OPTICAL FIBER SENSORS 300–332

9.1 Introduction ..................................................................................................................................... 3009.2 Classification of Fiber-Optic Sensors .............................................................................................. 301

9.2.1 Classification I ..................................................................................................................... 302

Contents xiii

9.2.2 Classification II .................................................................................................................... 3029.2.3 Classification III .................................................................................................................. 302

9.3 Advantages of Optical Sensors ........................................................................................................ 3029.4 Multimode FOS and Single Mode FOS .......................................................................................... 303

9.4.1 Passive Multimode Fiber Optic Sensors ............................................................................. 3039.4.1.1 Displacement Sensor ........................................................................................ 3039.4.1.2 Pressure Sensor ................................................................................................ 3049.4.1.3 Stress Sensors ................................................................................................... 3059.4.1.4 Strain Sensors ................................................................................................... 3069.4.1.5 Micro-bend Optical Fiber Sensor ...................................................................... 3079.4.1.6 Temperature Sensors ....................................................................................... 3089.4.1.7 Liquid Level Sensor .......................................................................................... 309

9.4.2 Active Multimode Fiber Optic Sensors ............................................................................... 3109.4.2.1 Current Sensors/Voltage Sensors ..................................................................... 3109.4.2.2 Magnetic Sensors .............................................................................................. 311

9.5 Single Mode Fiber Optic Sensors .................................................................................................... 3159.5.1 Intensity - Modulated Sensors ............................................................................................ 3159.5.2 Differential Fiber-Optic Sensor ........................................................................................... 3169.5.3 Phase–Modulated Sensors .................................................................................................. 317

9.5.3.1 Fiber-Optic Mach-Zehnder Interferometric Sensor ......................................... 3199.5.3.2 Fiber-Optic Gyroscope ...................................................................................... 320

9.5.4 Spectrally Modulated Sensors ............................................................................................. 3229.5.5 Polarisation Modulated Sensors ......................................................................................... 324Summary ........................................................................................................................................... 330Review Questions ............................................................................................................................... 332

10. FIBER OPTIC FUNDAMENTALS AND MEASUREMENTS 333–354

10.1 Fundamentals of fibers .................................................................................................................... 33310.2 Fiber Optic Communication System ............................................................................................... 33310.3 Measurement Standards and Test Procedures ............................................................................... 33510.4 Test Equipments .............................................................................................................................. 336

10.4.1 Optical Power Meters ....................................................................................................... 33610.4.2 Optical Attenuators ........................................................................................................... 33710.4.3 Tunable Laser Sources ..................................................................................................... 33710.4.4 Optical Spectrum Analyzers .............................................................................................. 33810.4.5 Optical Time-Domain Reflectometer (OTDR) ................................................................ 33910.4.6 Multifunction Optical Test Systems .................................................................................. 340

10.5 Attenuation Measurements ............................................................................................................. 34010.5.1 The Cutback Techniques .................................................................................................. 34010.5.2 Insertion Loss Method ..................................................................................................... 341

10.6 Dispersion Measurements ............................................................................................................... 34310.6.1 Intermodal Dispersion ...................................................................................................... 343

10.6.1.1 Time-Domain Dispersion Measurements ....................................................... 34410.6.1.2 Frequency-Domain Dispersion Measurements ............................................... 346

10.6.2 Chromatic Dispersion ....................................................................................................... 34710.6.3 Polarization-Mode Dispersion .......................................................................................... 348

10.7 OTDR Field Applications ................................................................................................................ 34910.7.1 OTDR Trace ..................................................................................................................... 34910.7.2 Attenuation Measurement ................................................................................................ 350

xiv Contents

10.7.3 Fiber Fault Location .......................................................................................................... 35110.8 Laser Doppler Velocimeter ............................................................................................................. 352

Summary ........................................................................................................................................... 353Review Questions ............................................................................................................................... 354

11. OPTICAL COMPUTING 355–402

11.1 Analog Linear Optic processing : An introduction ......................................................................... 35511.2 Halftone Processing ........................................................................................................................ 35511.3 Non-Linear Optical Processing ....................................................................................................... 36211.4 Arithmetic Operations ..................................................................................................................... 366

11.4.1 Addition/Subtraction ......................................................................................................... 36611.4.2 Multiplication and Division ............................................................................................... 36711.4.3 Averaging .......................................................................................................................... 36811.4.4 Differentiation and Integration ........................................................................................ 370

11.5 Number System .............................................................................................................................. 37111.5.1 Number Representation ................................................................................................... 371

11.5.1.1 Decimal Number ............................................................................................. 37111.5.1.2 Base-2n Number Systems ................................................................................ 37211.5.1.3 Negative Number Representations ................................................................ 37611.5.1.4 Multiple-Valued Number System .................................................................... 37711.5.1.5 Modified Signed Digit Number System .......................................................... 37811.5.1.6 Residue Number System................................................................................. 37811.5.1.7 Logarithmic Number Systems ........................................................................ 380

11.5.2 Arithmetic Operations Based on Codes ........................................................................... 38111.5.2.1 Codes ............................................................................................................... 38111.5.2.2 Binary Arithmetic ............................................................................................ 38211.5.2.3 BCD Arithmetic ............................................................................................... 38511.5.2.4 Arithmetic ........................................................................................................ 38611.5.2.5 Signal Logarithmic Arithmetic ........................................................................ 389

11.6 Threshold Devices .......................................................................................................................... 39011.6.1 Spatial Light Modulators .................................................................................................. 391

11.6.1.1 Electronically Addressed SLM ......................................................................... 39111.6.1.2 Magneto-Optic SLM ........................................................................................ 39311.6.1.3 Optically Addressed SLM ................................................................................ 394

Summary ........................................................................................................................................... 400Review Questions ............................................................................................................................... 401

MULTIPLE CHOICE QUESTIONS 403–414

APPENDICES 415–424

MODEL QUESTION PAPERS 425–428

EXAMINATION PAPERS 429–432

INDEX 433–436

Optoelectronics is the study and application of electronic devices that source, detect and controllight, usually considered a sub-field of photonics. In this context, light often includes invisibleforms of radiation such as gamma-rays, X-rays, ultra-violet and infrared rays in addition to visiblelight.

Optoelectronics is a field of technology that combines the physics of light with electricity.It encompasses the study, design and manufacture of hardware devices that convert electric signalsinto photon signals and vice-versa. It is based on the quantum mechanical effects of light onsemiconducting materials, sometimes in the presence of an electric field.

Any device that operates as an electrical-to-optical or optical-to-electrical transducer is consideredan optoelectronic device.

Optoelectronic technologies include:

1. Fiber optics communication2. Laser system3. Electric eyes4. Remote sensing systems5. Medical diagnostic system6. Optical information system.

1.1 FIBER OPTICS AND OPTOELECTRONICS

Fiber optic communication and optoelectronics are very closely related to each other. Fiber opticdeals with the transmission of light in a medium, whereas optoelectronics deals with the conversionprocess of an electrical signal into optical signal and vice-versa.

Till now, we have studied how an electric signal travels from one end to other by wiredmedium. Lot of research work has been done over the years to improve the speed and efficiencyof the medium in which electric signal travels.

We know that light travels at the fastest possible speed in the universe. If somehow, we cantame light and use it to transport our data from one end to other; we can have a much improvedtransmission of our data. Our data can travel at the speed of 3 × 108 m/sec which is much faster

1

Introduction to Optoelectronics

1ChapterChapterChapterChapterChapter

2 Optical Instrumentation

than the wired medium of data transmission (although speed of light decreases in glass or othermedium but even though it is more than 10000 times faster than wired medium).

Let us now discuss, how all this began and how optoelectronics has reached where we see ittoday.

1.2 HISTORICAL DEVELOPMENTS

1. In 1800 century, man was completely unaware of the fact that light can be used as amedium for data transmission. Signal fires, reflecting mirrors, signal lamps, etc. wereused to transfer limited information.

2. In 1880, Alexander Graham Bell was the first person to observe the transmission of speechusing light signal. He showed the world that light can be used as the fastest medium tocarry data, if successfully tamed. He modulated sunlight with a diaphragm giving speechtransmission over a distance of 200 m.

3. The term fiber optics was first used by Dr. N. S. Kapany in 1956 when he along with hiscolleagues at Imperial College of Science and Technology, London, developed an imagetransmitting device called the ‘flexible fiberscope’. This device soon found application ininspecting inaccessible points inside reactor vessels and jet aircraft engines. It later becamequite popular in medical field.

4. A continuous and thorough research led to the invention of lasers in 1960. T. Maimanat the Hughes Research Laboratory invented lasers which provided a powerful coherentlight source together with the possibility of modulation at high frequencies.Also, low beam divergence of laser made enhanced free space optical transmission apractical possibility.

(Sir Alexander Graham Bell) (Dr. Narinder Singh Kapany) (Dr. Theodore H. Maiman)

5. Then in 1966, Charles Kao and George Hockham, working at the standardtelecommunication laboratory in England, proposed that an optical fiber might be usedas a means of communication, provided the signal loss could be made less than 20 decibelsper kilometer (dB/km). At that time optical fibers exhibited losses of the order of1000 dB/km.

Optical Instrumentation

Publisher : S K Kataria and Sons( KATSON ) ISBN : 9789350142974 Author : Satyajit Das

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