Maximizing Fiber Optic Bandwidth: TDM and WDM
Maximizing Fiber Optic Bandwidth: TDM and WDM
Fiber optic transmission is a powerful method of communication that has untapped potential for bandwidth. The theoretical capacity of the 1550 nm window in fiber optic transmission is in the terabits. However, current fiber optic systems have yet to fully utilize this bandwidth.
To increase bandwidth, there are two methods - Time Division Multiplexing (TDM) and Wavelength Division Multiplexing (WDM). TDM is achieved by increasing the modulation rate of a single carrier to allow multiple channels to be transmitted on the same carrier. This method requires high-speed electronics, both at the receiving and transmitting ends of the link. As bit rates increase, inherent modulation limitations of optical fibers become dominant resulting in pulse spreading due to chromatic and polarization mode dispersion. This can affect signal quality in longer transmission distances.
WDM, on the other hand, allows for increased bandwidth by using multiple optical carriers or wavelengths on a single fiber. By adding a second transmitter and receiver of a different wavelength on an optical fiber, the capacity of the communication system can be doubled without the need for expensive and faster transmitter/receiver pairs. The two wavelengths are multiplexed, or coupled, together and sent through a single fiber. At the receiving end, the wavelengths are separated, or demultiplexed, and sent to their respective receivers.
One of the reasons for the appeal of WDM is that it does not require the replacement of existing transmitter and receiver pairs. This differs from TDM, which would require the replacement of the existing pair with a more expensive and faster pair. The wavelengths used in WDM are chosen because they lie in the “windows” or ranges of least attenuation, allowing signals to travel farther. For a system utilizing a 1310 nm laser, a 1550 nm laser is usually added.
In conclusion, the potential for fiber optic transmission is vast, with theoretical bandwidths in the terabits. While TDM is one method of increasing bandwidth, it requires the replacement of existing hardware with more sophisticated and faster equipment. WDM, on the other hand, can double bandwidth while using existing hardware with the simple addition of a second transmitter and receiver. The versatility of WDM makes it a popular choice for increasing bandwidth and improving communication systems.
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