Optical Detector basics
This page describes optical detector basics and mention quantum efficiency and responsivity of optical detector.
The optical detector is used in fiber optic communication system in the receiver part. It is used to convert light sources into corresponding voltage pulses. Refer fiber optic tutorial for more.
Optical detector used is normally avalanche photo diode or PIN diode. Optical detector must have high sensitivity, high fidelity, short response time and stability within the range of operation.
Quantum Efficiency of Optical Detector
Quantum efficiency of optical detector is given by
ηD = electron generation rate/incident photon rate
ηD = re/rp,
Where re and rp are electron generation rate and photon generation rate respectively.
Responsivity of Optical Detector
Responsivity gives the transfer characteristics of detector and is equal to following:
R = Ip/Po A/W ,
Ip is the photo current
Po is incident photon power
Po = Photon rate x hf
Po = rp x hf
re = η*Po/hf
Now, R = Ip/Po = e*re/Po = ηD*e/hf ,
Where, Ip = e*re
There is always a trade-off between speed of operation and sensitivity of detector.