Fiber Optic Transmission Multiplexing Technique

Multiplexing of fiber optic communication carrier for optical wave. Fiber optic communication multiplexing technique is mainly divided into three categories: optical multiplexed, optical signal multiplexing and subcarrier multiplexing with (SCM). Optical wave multiplexing wavelength division multiplexing (WDM) and space division multiplexing (SDM), the optical signal multiplexing comprises time-division multiplexing (TDM) and frequency division multiplexing with a (FDM).

1. Optical wave wavelength Division Multiplexing
At the transmitting end, the optical multiplexer to two or more different wavelength of the optical carrier signal converge together, and coupled to the same fiber in the optical lines for transmission; optical splitter at the receiving end via the various wavelengths of optical carrier separation, and then by the optical receiver, for further processing in order to restore the original signal. This is the wavelength division multiplexing. Suitable for multimode and single-mode system, one-way, two-way transmission, both assigned transmission loop transmission. The operating wavelength from 0.8μm to 1.7μm, low dispersion windows of the low attenuation of the optical fiber. Multiplexer requires a low insertion loss (1.0-2.5dB), sufficient bandwidth and good isolation. WDM technology allows the communication capability of the optical fiber communication system increases exponentially. Used for a set of optical amplifiers along the long-distance trunk and undersea fiber optic cable systems.

2. The Space Division Multiplexing
Including two aspects: First, the fiber multiplexed bunched fiber combination: two beam split along the space of a multidimensional communicaiton in an optical fiber. Multidimensional the modulation and demodulation of the degree of coherence can be used to realize multiplex space division multiplexing communication. Image bundles is a special the space division multiplexing. Image using the space division multiplexing transmission, the transmission speed will be orders of magnitude improvement. Hundreds of thousands of multi-core pixel image transmission fiber optic technology has matured, its color retention characteristics and translucent quite good.

3. Optical Frequency Division Multiplexing
Frequency division multiplexing and wavelength division multiplexing, in essence, there is no difference. If the optical carrier of the same fiber transmission few large ones, and the carrier asked larger spacing, referred to as WDM: wavelength interval smaller and if more optical carrier ones dense, that is, frequency division multiplexing. Frequency division multiplexing may be dozens, or even hundreds of times to improve the communication capacity. In the dense frequency point, without the conventional optical multiplexer and demultiplexer, but rely on the tuning device, the optical power coupler, or an optical filter and so on. At the receiving end there are two differnet tuning methods to achieve dense frequency division multiplex, a coherent heterodyne detection of the optical fiber communication and tuning the local oscillatior laser, second is the direct detection by a conventional optical fiber communication and tunable fiber filter. Mainly used in fiber optic subscriber network and fiber optic LAN, and is particularly suitable for the frequency division multiple access applications.

4. Optical Time Division Multiplexing
Optical time division multiplexing (OTDM) is optical digital communication in an efficient multiplexing method. It is the communication time is divided into equal intervals, each interval transmitting only a fixed channel, each channel is transmitted in accordance with a certain time sequence. General frame synchronization and bit synchronization both synchronous manner. As electronic devices limit too high digital rate and the optical time division multiplex required the retrocession access and difficult to tap technology, little progress in the past. But in recent years, a number of key technological breakthroughs, such as optical time division multiplex/ demultiplexing, transform limit ultrashort optical pulse generation, all-optical clock extraction technology, all-optical regeneration technology, optical modulator and optical zoom and optical linearand nonlinear transmission technology and so on, which makes the realization of the whole optical information processing system to become possible.

5. Subcarrier Multiplexing
Subcarrier multiplexing the signal to be transmitted is first used to modulate a radio frequency wave, and then the radio frequency wave to modulate the emission source. After the photoelectric conversion at the receiving end to restore the signal RF wave, and then restored to the original signal through the RF detector. Subcarrier fiber optic transmission to go through two modulation and twice demodulation, two-tier carrier are optical wave and radio frequency (RF) waves, radio frequency waves, also known as a subcarrier. The sub-carrier multiplex transmission system is by increasing the band width to achieve multi-channel transmission, bandwidth is increased as the carrier wave frequency and the number of channels increases. Its advantages can be mature microwave technology is not high optical devices, technically easy to implement.
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