The use of fiber optic systems is expanding at a amazing rate. Only in the past Ten years, fiber optic communications systems have replaced just about all coaxial and twisted pair cables particularly in network backbones. This is also true in almost any long distance communication links.

This can be explained simply. Optical fiber cable is easier to set up, lighter than traditional copper cable, and much smaller than its electronic counterpart. The most crucial factor is it has much more bandwidth. Because fiber optic cables are lighter, they are simpler to survive existing ducts and cable raceways. There are other big benefits of fiber optic cables including their immunity to electromagnetic interference, longer repeater distances, lower power requirements, and better flexibility.

All the above pros make fiber optic cables very attractive and most important of all, very economical. The unstoppable trend for fiber optic applications would be the change from the long haul (long distance) to our desk, our house, and our office. The terms include FTTC ( fiber towards the curb), FTTD (fiber towards the desk), FTTH (fiber towards the home) and FTTB( fiber to the building). Fiber optic cables enable our imagine integrating all our phone, Internet and TV services. Fiber’s wide bandwidth makes this possible. It offers more than enough ability to meet all our voice, data and video requirements.

The transformation from copper to fiber is greatly accelerated through the invention of optical fiber amplifier. Optical fiber amplifiers enable optical signal transmission over very long distances without the expensive procedure for conversion to electronic signals, electronic amplification and the conversion to optical signal again as in traditional regenerators.

Today most of the network traffic switching continue to be done by electronic switches such as those from Cisco. But tremendous interest and effort of utilizing all-optical devices for those network switching are accumulating in the industry. The most important sign of all-optical switching lies in its almost unlimited transmission capacity. However, it is still within the prototype stage for controlling light with light, so optical swith circuits continue to be controlled by electronic circuits now. The switching matrix may be optical circuits but the control are still done by electronic circuits.

Optical fiber is nearly the perfect medium for signal transmission available today and in the foreseeable future. The excellent sign of optical fiber is its immunity to electromagnetic interference. Optical circuits can be crossed inside a common space without cross interference among them. But you will find problems which are impeding the rate of all-optical system development. The most obvious and basic reason may be the compatibility requirements with legacy fiber optic systems.

Another huge advantage of optical fiber is based on the opportunity to multiplex its capacity via WDM (wavelength division multiplexer). WDM modulates each of several data streams right into a different part of the light spectrum. WDM is the optical equivalent of FDM (frequency division multiplexer). The use of WDM can increase the capacity of merely one channel fiber optic communication system by countless times.

In additional to optical communication systems, fiber optic technology is also widely used in medicine, illumination, sensing, endoscopy, industry control and more.

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.

Source: FiberStore