Receivers
An optical fiber communication system consists of 3 main sub-segments-
Transmitter, Receiver and the fiber itself. The receiver acts as the
converter from optical to electric energy. The fiber optic receiver is
actually a transducer which is coupled to the optical fiber at the
receiving end. In normal wires or cables, the passage of information is
in electric form. So there is no need for a special receiving circuit,
but the optical communication system uses optical i.e. light signals to
transmit the information. This necessitates a special dedicated
circuitry at the sending and the receiving ends.
The main requirements of an optical receiver are - Small size, low
power consumption, and high responsivity. The small size is essential
because the receiver has to be coupled to the fiber. Responsivity is
the factor which determines the minimum input which the receiver can
detect.
Optical receivers can be classified into 2 primary types: PIN photodetector and the APD.
PIN stands for the structure of the device which has a p-type doped semiconductor and an n-doped semiconductor with an intrinsic layer sandwiched between them. APD stands for Avalanche Photo Diode, which operates on the principle of Avalanche breakdown.
Both the above types are made of Semiconductor, but the difference is that in the PIN photodetector, the output voltage is directly proportional to the intensity of light incident on it from the optical fiber, while the APD uses the principle of Avalanche breakdown to multiply the produced voltage so that it is amplified.
The photodetector is the common name given to devices which can detect and respond to incidence of light. It operates on the principle that when a photon strikes the reverse biased junction of a pn diode or a pin device, it transfers it energy to the electrons in the device. This results in the formation of an electron hole pair which gives rise to a current in the external circuit.
In the APD, this current is amplified by the phenomenon of avalanche effect, where the barrier potential is exceeded and device breakdown occurs. In the PIN diode, there is no amplification factor, thus the output is directly proportional to the incident light intensity, after accounting for effects of noise.
Another very critical feature of an optical receiver is that it should be capable of operating at very high speeds, so that the transfer of data can occur at high speeds. Apart from the photodetector, the optical receiver contains devices like de-modulator, amplifier and other devices which condition the signal, before the final output is delivered to the user.
For more information on fiber optics and receivers one can refer Optical Fiber Communications by Gerd Kaiser.
Optical receivers can be classified into 2 primary types: PIN photodetector and the APD.
PIN stands for the structure of the device which has a p-type doped semiconductor and an n-doped semiconductor with an intrinsic layer sandwiched between them. APD stands for Avalanche Photo Diode, which operates on the principle of Avalanche breakdown.
Both the above types are made of Semiconductor, but the difference is that in the PIN photodetector, the output voltage is directly proportional to the intensity of light incident on it from the optical fiber, while the APD uses the principle of Avalanche breakdown to multiply the produced voltage so that it is amplified.
The photodetector is the common name given to devices which can detect and respond to incidence of light. It operates on the principle that when a photon strikes the reverse biased junction of a pn diode or a pin device, it transfers it energy to the electrons in the device. This results in the formation of an electron hole pair which gives rise to a current in the external circuit.
In the APD, this current is amplified by the phenomenon of avalanche effect, where the barrier potential is exceeded and device breakdown occurs. In the PIN diode, there is no amplification factor, thus the output is directly proportional to the incident light intensity, after accounting for effects of noise.
Another very critical feature of an optical receiver is that it should be capable of operating at very high speeds, so that the transfer of data can occur at high speeds. Apart from the photodetector, the optical receiver contains devices like de-modulator, amplifier and other devices which condition the signal, before the final output is delivered to the user.
For more information on fiber optics and receivers one can refer Optical Fiber Communications by Gerd Kaiser.
