- Fiber Optics
- Fiber Connectby Technology Explained Date Added: Tuesday 07 February, 2012High speed PIN photodiodes
To reduce the response time of a photodiode, the capacitance of the PN junction must be reduced. One of the ways to do that is to expand the depletion layer. The structure of the PN junction is designed to have a large N-type material. Usually the layer of the P-type material is very thin in order to have good sensitivity at the short wavelength range. Large N-type material ensures large depletion region is generated.
To expand the depletion region further, a layer of intrinsic undoped material is used between the PN junction, to form a PIN junction. Such photodiode is called PIN photodiode. PIN structure decreases the capacitance, and increases the sensitivity of the diode by providing larger area where the electron-hole pair can be generated by absorption of the energy from incident photons.
Negatively biased photodiode (working under photoconductive mode) further expands the depletion region, and hence is the usual way that high speed photodiode is used.
High speed photodiode usually has very small active area. This puts a low limit on the maximum optical power permitted on a photodiode and the maximum photocurrent generated. Velocity matched planar waveguide photodiodes have multiple PIN diodes integrated and coupled together, hence they can achieve large bandwidth (several tens of gigahertz), and at the same time produce high (tens of mA) photocurrent.Rating: [5 of 5 Stars!]
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- Fiber Optics