With the exponential growth in communications, caused mainly by the wide acceptance of the Internet, people’s demands of bandwidth and large data capacity have increasingly grown. However, from a technical perspective, fiber attenuation, dispersion and nonlinearity can significantly limite the bit rate and the spanning distance of the optical communication. With the improvement of fiber manufacturing and the invention of EDFA (erbium-doped fiber amplifier), the war against attenuation has been won, while dispersion and nonlinearity are still taken into main consideration in today’s high speed optical communication systems. Today, we are maily explaining the dispersion in fiber optics and the dispersion compensation, as well as introducing the Fiberstore‘s dispersion compensation module solution in this paper.
Dispersion in Optical Fibers
The broadening of light pulses, called dispersion, is a critical factor limiting the quality of signal transmission over optical links. Dispersion is a consequence of the physical properties of the transmission medium. In general, there are three main types of dispersion in a fiber:
Modal Dispersion – Modal dispersion occurs only in Multimode fibers. In a multimode fiber with a step profile of the refraction index all rays travel with the same speed – the rays traveling along the fiber axis have the same speed as the rays traveling close to the core-cladding interface. As they cover the optical paths of different length at the same speed they reach the detector at different times. This leads to the temporal pulse broadening at the end of the fiber. This type of temporal broadening is called the modal dispersion. Polarization mode dispersion (PMD) is a form of modal dispersion where two different polarizations of light in a waveguide, which normally travel at the same speed, travel at different speeds due to random imperfections and asymmetries, causing random spreading of optical pulses.
Waveguide Dispersion – Waveguide dispersion is chromatic dispersion which arises from waveguide effects: the dispersive phase shifts for a wave in a waveguide differ from those which the wave would experience in a homogeneous medium. Waveguide dispersion is important in waveguides with small effective mode areas. But for fibers with large mode areas, waveguide dispersion is normally negligible, and material dispersion is dominant.
Material Dispersion – Material dispersion is the phenomena whereby materials cause a “bundle” of light to spread out as it propagates. It is also a kind of chromatic dispersion. Material dispersion is not helpful in optical communications that it limits how much data can be sent, as the pulses will overlap and information will be lost.
Waveguide dispersion and material dispersion both belong to chromatic dispersion.
In fiber optical high bit rate (such as 10G or 40G bit/s) long-haul transmission systems, dispersion compensation is one of the most important items to be considered for design. Management or optimization of residual dispersion are required for photonic networks, i.e., for fibers, repeaters and optical interfaces.In addition, PMD compensation is also required especially for 40Gbit/s or higher bit rate long-haul systems. In a word, dispersion compensation is an important issue for fiber-optic links. Nowadays, there are many solution of dispersion compensation in fiber optics, such as dispersion compensation module (DCM), disperison compensation fiber (DCF), typical bragg grating operation and chirped fiber bragg grating etc.
In optical fiber communications, dispersion compensation modules (DCM) can be used for compensating the chromatic dispersion of a long span of transmission fiber. Typically, such a module provides a fixed amount of dispersion (e.g. normal dispersion in the 1.6-μm spectral region), although tunable dispersion modules are also available. A module can easily be inserted into a fiber-optic link because it has fiber connectors for the input and output. The insertion losses may be compensated with a fiber amplifier, e.g. an EDFA in a 1.5-μm telecom system. A dispersion compensation module is often placed between two fiber amplifiers.
Fiberstore Dispersion Compensation Module Solution
The Dispersion Compensation Modules (DCMs) are building blocks of the Fiberstore CWDM&DWDM Optical Transport System and serve at optical communication nodes to provide negative chromatic dispersion known as pulse spread phenomenon that limits the high-bit rateand maximal transmission distance of data along optical fibers.
The FS-DCM series modules, based on mature and reliable Disperison Compensation Fiber(DCF) technoloty, are desinged for 19-inch Rack Mount configuration which is used to compensate chromatic dispersion at any rates including 10Gbps, 40Gbps and even 100Gbps data rates in ultra long haul coherent networks, such as SDH high-bit transmission system, DWDM networks, CATV long haul transmission systems. These modules can achieve -10 to -2100 ps/nm of dispersion values at 1550nm wavelength and supply broad band dispersion slop compensation for standard singlemode fiber(SMF28 – G.652 fiber) across entire C-Band while maintaining an extremely low and flat insertion loss as well as low latency.
The FS-DCM series is a single-slot module that typically connects to the mid-stage of a Fiberstore Optical Amplifier, eg. EDFA, in long hual transmission system. The optical budget is not affected if the FS-DCM series is connected with an optical amplification with Mid-Stage. Futermore, compensation distance ranging from 10KM to 140 KM is available.
|40KM||FMT40-DCM||40KM Passive Dispersion Compensation, Plug-in Type, LC/UPC|
|80KM||DCM-80||80KM Passive Dispersion Compensation Module, 1U 19″ Rack Mount, LC/UPC|
|FMT80-DCM||80KM Passive Dispersion Compensation, Plug-in Type, LC/UPC|
|100KM||DCM-100||100KM Passive Dispersion Compensation Module, 1U 19″ Rack Mount, LC/UPC|
|10KM-140KM||DCM||Customized Passive Dispersion Compensation Module, LC/SC/FC, UPC/APC|
Typical Application Cases of FS-DCM Series
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