What is a photo detector ? Theory

INTRODUCTION

                                 An optical detector is a transducer that convert an optical signal into an electrical signal this is done by generating an electrical current prepartional to the intensity of incident optical radiation the relationship between the input optical radiation and the output electrical current it given by the detector responstivity.
                             Photo conductors are semiconductor device that can convert optical signals into electrical signals basically there are three processes for a general photo conductors .

a) Generation of carrier by incident signal.
b) Carrier transport and / or multiplication by                    whatever current gain mechanism my be present.
c) Interaction of current with external circuitry to             provide the output signal .

Important points of photo detector

  •  high responsibility or sensitivity at the operating wavelength.
  •  High speed of response or bandwidth of operation.
  • The detector should have minimum contribution towards noise. Thus dark current should be low., Leakage current must be low, shunt conductance should be low, thus noise equivalent power(NEP) must be low.
  • The detector should have minimum susceptibility to changes in ambient conditions, such as sensitives, noise performance, including the mechanical rigidity for digital device.

Optical detector

  • Compatible dimensions.
  • High sensitivity.
  • Fast response and sufficient bandwidth to handle the desire data rates.

Characteristics of detector

  • High sensitivity .
  • Dark current, leakage current and shunt conductance very low .
  • Stability .
  • Low basing voltage.
  • Low price.

Response time of a photo detector

The response time of a photo detector is the minimum amount of time for an input optical signal variation to manifest itself in the output signal of the photo detector an ideal detector has zero response time.


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