Optical Multiplexers

• Make full use of the low loss band of the optical fiber to increase the transmission capacity of the optical fiber and double the physical limit of transmitting information through one optical fiber. At present, we just use a very small part of the optical loss spectrum (1310nm-1550nm). Wavelength division multiplexing can make full use of the huge bandwidth of single-mode optical fiber to about 25THz and sufficient transmission bandwidth.
• The ability to transmit two or more unsynchronized signals in the same optical fiber facilitates the compatibility between digital signals and analog signals, and has nothing to do with the data rate and modulation mode, and can flexibly remove or join channels in the middle of the line.
• For optical fiber cables already built, especially those with few cores laid early, as long as the original system has power headroom, it can be further compatibilized to realize the transmission of multiple one-way signals or two-way signals without using the original system Great changes, with strong flexibility.
• As a result of a substantial reduction in the amount of optical fiber used, the construction cost is greatly reduced. Due to the small number of optical fibers, it is also quick and easy to recover when a fault occurs.
• The sharing of active optical equipment reduces the cost of transmitting multiple signals or increasing new services.
• The active devices in the system have been greatly reduced, thus improving the reliability of the system. At present, due to the requirements of optical transmitters, optical receivers and other equipment for optical wavelength division multiplexing of multiple carriers, the implementation of the technology has a certain degree of difficulty. Meanwhile, the application of the multi-core optical cable does not appear to be particularly scarce for the traditional broadcast and television transmission services. So the actual application of optical multiplexersis not much. However, with the development of integrated cable television service, the increasing demand for network bandwidth, the implementation of various selective services, and the consideration of the economic costs of upgrading the network, etc., the features and advantages of optical multiplexers gradually emerge in the CATV transmission system, showing a broad application prospects, and even affect the development of CATV network pattern.

The bandwidth properties of optical fiber are well known and make it the media of choice for high-speed data and video applications. However, various forms of multiplexing are required to take advantage of this bandwidth. Time division and wavelength division multiplexing are the two most commonly used.

As fiber is best suited to digital transmission, many low-rate digital signals can be time division multiplexed (TDM) using electronic parallel-to-serial converters like the Agilent G-Link or the Cypress Hotlink. Several low rate signals are combined into a single high-speed channel for transmission and then reconstructed or broken out at the receiving end.

Although high-speed TDM devices are available for aggregate data rates of 10-40 Gbps for telecommunications applications, affordable components, e.g.TDM ICs, fiber optic transceivers and test equipment, are currently limited to 2.5 Gbps. TDM can also be done in several stages, e.g. programmable logic devices (PLDs) can be used to combine many low-rate signals. Over-sampling using a common clock is required when the signals are asynchronous.

Wavelength division multiplexing (WDM) is used to transmit more than one high-speed digital data stream on a single optical fiber. Different wavelengths of light, i.e. different colors, propagate in a single fiber without interfering as shown below. The devices that do the optical combining and separation are referred to as WDMs. These are passive optical devices that typically employ optical filters or gratings.