In fiber optic networks, optical active devices are key components. It can convert electrical signals and optical signals to each other, the optical transmission system of the heart. Optical active devices are divided into the following three categories.
A. Light Source
The device that converts electrical signal into optical signal is called light source. The main light sources are light emitting diodes (LED) and laser diodes (LD).
B. Optical Detector
The device that converts optical signal into electrical signal is called optical detector. The main optical detectors are photodiode and avalanche photodiode.
The optical signal transmitted through the optical fiber reaches the receiving end, the receiving end has a light receiving element signal. But since we know of light has not yet reached the level of awareness of the electricity, so we can not direct the optical signal obtained by reducing the original signal. Between them, there are still one of the optical signals into electrical signals, and then by the electronic circuit to amplify the process, and finally restore the original signal. The reception switching element is called the light detector, or photodetector, short detector, also known as photo-detector or a photodiode. Common optical detector comprising PN photodiodes, PIN photodiodes and avalanche photodiodes (APD). Optical fiber communication systems require optical detector to be high sensitivity, fast response, low noise, stable and reliable.
C. Optical Amplifier
Optical fiber amplifier has become active devices rookie. Erbium-doped fiber amplifier (EDFA) has currently a large number of applications , while optical fiber Raman amplifier (FRA) is very promising.
Fiber amplifiers can not only amplify the optical signal directly, but also have real-time, high gain, broadband, online, low-noise, low-loss optical zoom function. They are essential key components in the new generation of fiber optic communication systems.
Since this technology not only solved the attenuation of optical network transmission speed and distance limitations, more importantly, it created a 1550nm band WDM, which can enable ultra high-speed, large-capacity, ultra-long haul wavelength division multiplexing (WDM), Dense Wavelength Division Multiplexing (DWDM), optical transmission, optical soliton transmission becomes a reality. It is epoch-making milestone in the history of optical fiber optic communication development.
In practical optical fiber amplifiers, there are mainly EDFA, semiconductor optical amplifier (SOA) and FRA, of which the EDFA amplifier with its superior performance is now widely used in long-distance , large capacity, high-speed optical fiber communication systems, access networks, optical fiber CATV networks, military systems in areas such as power amplifiers, repeater amplifiers and preamplifiers. Optical Fiber Amplifier is generally constituted of the gain medium optical fiber amplifier, the pump light input-output coupling structure.