Handbook Of Optical Through The Air
Communications David A Johnson
TABLE OF CONTTENTS
Preface …………………………………………………………………………… 1
Table of Contents ……………………………………………………………. 3
Introduction: ……………………………………………………………………. 5
Brief History ……………………………………………………………. 5
Why Optical Communications? ……………………………………………. 7
Why through-the-air communications? ………………………………………. 7
What are some of the limitations of through-the-air
communications? …….. 7
How can these light-beam techniques be used? …..………………………………
8
Possible uses for optical through-the-air communications
……………. 8
Chapter One – LIGHT THEORY …….…………………………….…….…… 10
The Spectrum, Human Eye Response ………………………………….…. 10
Silicon Detector Response ……………………..……………………………… 11
Units of Light …………………………………………………………….. 11
Light Power and Intensity ………………………..…………………………… 13
Miscellaneous Stuff ………………………………..…………………………… 13
Chapter Two – LIGHT DETECTORS ……………………………………. 14
What Does a Light Detector Do? ……………………………………………………... 14
The Silicon PIN Photodiode …………………………………………………… 14
InGaAs PIN Diode ………………………………………………….………………… 14
Typical PIN Diode Specifications …………………………………………………… 16
Package …………………………………………………………………… 16
Active Area …………………………………………………………………… 17
Response Time …………………………………………………………… 17
Capacitance …………………………………………………………… 17
Dark Current …………………………………………………………… 18
Noise Figure …………………………………………………………………… 18
Other Light Detectors ………………………………………………..…………... 18
Photo Transistor ……………………………………………………………. 18
Avalanche Photodiode ……………………………………………………. 19
Photo Multiplier Tube ……………………………………………………. 20
Optical Heterodyning …………………………………………………….. 21
Future Detectors ……………………………………………………………. 21
Detector Noise ……………………………………………………………. 21
Minimum Detectable Light Levels …………………………………………………….. 22
Optical Through-the-Air Communications Handbook -David A.
Johnson, PE Page 4 of 68
Chapter Three – LIGHT EMITTERS ………………………….………….. 23
Introduction to Light Emitters …………………………………………………….. 23
Light Emitting Diodes (LEDs) …………………………………………………….. 23
GaAlAs IR LED …………………………………………………………………….. 23
GaAs IR LED ………………………………………………………………. 24
GaAsP Visible Red LEDs …………………………………………………….. 25
Solid State Semiconductor Lasers …………………………………………………….. 25
GaAs (Hetrojunction) Lasers …………………………………………………….. 25
GaAlAs (CW) Lasers ……………………………………………………………... 26
Surface Emitting Lasers ………………………………………….…………. 27
Externally Excited Solid State Lasers …………………………..………………… 27
Gas Lasers …………………………………………………………………………….. 27
Fluorescent Light Sources …………………………………………………………….. 29
Fluorescent Lamps …………………………………………………………….. 29
Cathode Ray Tubes (CRT) …………………………………………………….. 29
Gas Discharge Sources …………………………………………………………….. 30
Xenon Gas Discharge Tubes …………………………………………………….. 30
Nitrogen Gas (air) Sparks …………………………………………………….. 31
Other Gas Discharge Sources …………………………………………………….. 31
External Light Modulators …………………………………………………………….. 32
Chapter Four –LIGHT SYSTEMS CONFIGURATIONS …………….. 33
Opposed Configuration …………………………………………………………….. 33
Diffuse Reflective Configuration …………………………………………………….. 34
Retro Reflective Configuration …………………………………………………….. 35
Chapter Five –LIGHT PROCESSING THEORY …………………….. 37
Lenses as Antennas …………………………………………………………………….. 37
Mirrors and Lenses …………………………………………………………………….. 37
Types of Lenses ……………………………………………………………………... 37
Divergence Angle …………………………………………………………………….. 38
Acceptance Angle …………………………………………………………………….. 38
Light Collimators and Collectors …………………………………………………….. 38
Multiple Lenses, Multiple Sources …………………………………………………….. 39
Optical Filters …………………………………………………………………….. 39
Make your own optical low-pass filter …………………………………………….. 41
Inverse Square Law …………………………………………………………………….. 41
Range Equation …………………………………………………………………….. 42
Chapter Six - OPTICAL RECEIVER CIRCUITS …………………….. 43
Light Collector …………………………………………………………………….. 43
Light Detector …………………………………………………………………….. 43
Stray Light Filters …………………………………………………………………….. 44
Current to Voltage Converter Circuits …………………………………………….. 44
High Impedance Detector Circuit …………………………………………….. 44
Transimpedance Amplifier Detector Circuit
with resistor feedback …………………………………………………… 45
Optical Through-the-Air Communications Handbook -David A.
Johnson, PE Page 5 of 68
Transimpedance Amplifier Detector Circuit
with inductor feedback …………………………………………………….. 46
Transimpedance Amplifier Detector Circuit
with limited Q feedback …………………………………………………….. 47
Post Signal Amplifiers …………………………………………………………….. 48
Signal Pulse Discriminators …………………………………………………………….. 49
Frequency to Voltage Converters …………………………………………………….. 49
Modulation Frequency Filters …………………………………………………….. 49
Audio Power Amplifiers …………………………………………………………….. 49
Light Receiver Noise Considerations …………………………………………….. 50
Other Receiver Circuits …………………………………………………………….. 50
Sample of Receiver Circuits ………………………………..………………. 52 - 58
Chapter Seven - OPTICAL TRANSMITTER CIRCUITS …………….. 59
Audio Amplifier with Filters …………………………………………………….. 59
Voltage to Frequency Converters …………………………………………………….. 59
Pulsed Light Emitters …………………………………………………………….. 60
Light Collimators …………………………………………………………………….. 60
Multiple Light Sources for Extended Range ……………………………………..
61
Wide Area Light Transmitters …………………………………………………….. 63
Wide Area Information Broadcasting …………………………………………….. 63
Samples of Transmitter Circuits ………………………………………………….. 65-66
