Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-1

ECEG287 Optical Detection Course Notes

Part 3: Noise and Photon Detection

Profs. Charles A. DiMarzio

and

Stephen W. McKnight

Northeastern University, Spring 2004

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-2

Topic Outline

• Noise Sources– Overview of Noise Sources– A Simple Noise Model

• Photon Noise - Fundamental Limit• Photon Detectors

– Quantum Efficiency– Gain– Types and Examples

• Other Noise Sources

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-3

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Noise Sources

• Photon Noise - Fundamental Limit

• Johnson Noise• G-R Noise • Background Noise• Electronic Noise

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-4

Classical Noise Model

Add Field Amplitudes

Re U

Im U

Us

Un

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-5

Photon Noise

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n

n

RMS

RMS

RMS

ei

ei

RMSn RMS

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-6

Photon Detector Concepts

• Quantum Efficiency (spectral dependence)• Gain• Responsivity

– Current or Voltage

• Noise– Current or Voltage

• Mechanisms of Detection– Later, for Specific Devices

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-7

Photon Detector Responsivity

e-

h

Photon Energy: E=h=hc/Total Energy: PtPhoton Count: np=Pt/hElectron Count: ne=qPt/hElectron Rate: ne /t=qP/hCurrent: i = ene /t=(qe/h)P

wqe/h

hW

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-8

Photon Detector Gain

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qG

Signal

Noise

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-9

Photon Counting (1)

0 5

Clock

GateCounter

tClock Signal

t

Photon Arrival

t

Photon Count3 1 2

Probability Density

n

Experimental Setup to measure the probability distribution of photon number.

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-10

Photon Counting (2)

t

Photon Arrival

t

Anode Electrons

t

Anode Electronsand Threshold

Photon counting threshold removes gain fluctuations but misses multiple counts. It does not reduce dark counts.

t

Photocathode Electrons

Error 1: Dark Count: Counted an electron when no photon was present.

Error 2: Missed Count: Counted one electron when two photons were present.

t

Photocathode Electron Count1

2

0

t

True Count1

2

0

1

1 2

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-11

Photon Detector Types

• Photoemissive– Vacuum Photodiodes

– Photomultipliers

– Low Quantum Efficiency, High Gain

• Semiconductor– Photoconductive

• Intrinsic and Extrinsic

• High Quantum Efficiency

• High Gain

• Example: Avalanche Photodiode

– Photovoltaic• Intrinsic and Extrinsic

• High Quantum Efficiency

• No Gain

• Low Noise

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-12

Photon Detector Characteristics

• Advantages– Sensitivity– Low Noise– Speed– Small Size

• Disadvantages– Difficult Calibration– Damage Susceptibility

• Other– Ruggedness (?)– Narrow Spectral Range– Cooling Requirement (?)

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-13

Other Noise Sources

• Johnson Noise

• G-R Noise

• Background Noise

• Electronic Noise

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-14

Thermal Noise

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Stopped here Wed 14 Jan 04

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-15

NEP Example

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-16

Detectivity, D*

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-17

Background Noise

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Signal

Bkg

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-18

Some Simplified Backgrounds

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-19

Background Noise

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Signal

Bkg withFluctuations

Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-20

Background NEP

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-21

Detectivity Limits and Example

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Jan 2004 Chuck DiMarzio, Northeastern University 10464-3b-22

Detector Examples: Spectral Photon Radiance

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Detector Examples: Detectivity, D*

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Detector Examples: Total Background Power

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Detector Examples: NEP

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