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Optical Fibre Systems- windows

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Optical Fibre Systems Transmission Windows (Bands) Due to optical fiber attenuation and dispersion, but also because of the characteristics of available opto-electronic components, transmission windows, are defined, which are wavelength bands with specific properties, within which wavelength division multiplexing can be practiced. First Window, from 0.8 to 0.9 µm say about 0.85 µm , (Short Wavelength Band) This was the first band used for optical fibre communication in the 1970s and early 1980s
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  Optical Fibre Systems Transmission Windows (Bands) Due to optical fiber attenuation and dispersion, but also because of the characteristics of available opto-electronic components, transmission windows, are defined, which arewavelength bands with specific properties, within which wavelength divisionmultiplexing can be practiced. First Window,   from 0.8 to 0.9 µm say about 0.85 µm , (Short Wavelength Band)  This was the first band used for optical fibre communication in the 1970s and early1980s. It was attractive because of a local dip in the attenuation profile (of fibre at thetime) but also (mainly) because you can use low cost optical sources and detectors in thisband. That is, it is not an attenuation or dispersion minimum, but it is an optimum for theuse of the most economical (and efficient) components: silicon for detectors, GaAs for transmitters; this window allows inexpensive short distance links or local area network over multimode fibers at low or medium bit rates. It has a new use for high bit rate shortdistance interconnections (Gbps and above), with VCSEL laser diodes over multimodefibers. Second Window (Medium Wavelength Band) This is the band around 1310 nm which came into use in the mid 1980s.This band is attractive today because there is zero fibre dispersion here (on single-modefibre). While sources and detectors for this band are more costly than for the short waveband the fibre attenuation is only about 0.4 dB/km. This is the band in which the majorityof long distance communications systems operate today. Third Window, from 1.510 µm to 1.600 µm say about 1.55 µm (Long WavelengthBand) This band has the lowest attenuation available on current optical fibre (about 0.26dB/km). In addition optical amplifiers are available which operate in this band. However,it is difficult (expensive) to make optical sources and detectors that operate here. Also,standard fibre disperses signal in this band. That is, it corresponds to the absoluteminimum of attenuation but requires more expensive components, because of thechromatic dispersion problem (monochromatic laser DFB diodes must be used, andeventually dispersion compensators). Used more recently, it is mostly used for longdistance links over single-mode fibers (terrestrial or submarine) with ranges exceeding100 km without amplifier, at bit rates of several Gbps. The optical amplification is usedat this wavelength and large scale wavelength division multiplexing is practiced. In thelate 1990s this band is where almost all new communications systems operate.  The 2 nd and 3 rd windows can also be multiplexed in both directions over the same fiber,which is performed in the new access network standard GPON.Transmission windows for silica fibres  
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