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| 9.1 |
INTRODUCTION : |
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A photodetector is a device which absorbs light and converts the optical energy to measurable electric current. Detectors are classified as |
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Thermal detectors |
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Photon detectors |
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Thermal detectors : |
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When light falls on the device, it raises its temperature, which, in turn, changes the electrical properties of the device material, like its electrical conductivity. Examples of thermal detectors are thermopile (which is a series of thermocouples), pyroelectric detector etc. |
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Photon detectors : |
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Photon detectors work on the principle of conversion of photons to electrons. Unlike the thermal detectors, such detectors are based on the rate of absorption of photons rather than on the rate of energy absorption. However, a device may absorb photons only if the energy of incident photons is above a certain minimum threshold. Photon detectors, in terms of the technology, could be based on |
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Vacuum tubes - e.g. photomultipliers |
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Semiconductors - e.g. photodiodes |
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For optical fiber applications, semiconductor devices are preferred because of their small size, good responsivity and high speed. |
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