Some sensors are extrinsic such that when the light leaves the transmitting fiber to be changed before it continues to the detector by means of the return or receiving fiber . The intrinsic sensors are different in that the light beam does not leave the optical fiber but it is changed whilst still contained within it.
The point sensor detects the variable being measured based on its variation only in the surrounding of the sensor. The multiplexed sensor tends to have multiple localized sensors that are placed at intervals along the fiber length and the distributed sensor performs sensing in a distributed format along the length of the fiber .
Other components used are the fiber gratings which are sensing elements. These are photos inscribed into silica fibers and are a periodic perturbation of the optical fiber core refractive index created by exposure to intense ultraviolet radiation.
It provides high resolution, well-localized sensing regions, absolute measurement, and linear output. It is insensitive to optical systems and intensity fluctuations. It is capable of multiplexing several sensors along one fiber and it is very cost-effective.
For digital systems, the commonly implemented systems are the Synchronous optical networks such as SONET . It is the time division multiplexing optical network standard employed in North America. It is considered as the de-facto standard for fiber backhaul networks. The linear multiplexing and de-multiplexing is possible with add-drop-multiplexers.
With the evolution of the internet and data communications, the many carriers are finding that their estimates of fiber needs may have been underestimated. There are three ways to expand the capacity of a data communication system. It can be achieved by installing more cables, increasing the system bit rate to ensure that more signals can be multiplexed and to perform the wavelength division multiplexing.
In summary, the frequency division multiplexing, wavelength division multiplexing, time division multiplexing and code division multiplexing are the key techniques used in multiplexing and demultiplexing in the FOC communication system . It simultaneously aims at transmitting two or more signals on a single circuit. The economic perspective of multiplexing benefits the organization hosting the FOC as the transmission costs less in terms of physical resources such as cables and time. A corresponding multiplexer, or demultiplexer, is on the end of the high-speed line and it is used to separate the multiplexed signals .
The fiber has the capability to transmit hundreds of wavelengths. Once the fiber is in place, the additional wavelength can be launched by upgrading transceivers. The fiber optic cable multiplexes many signals from different senders. The multiplexing uses a set of techniques that allow the simultaneous transmission of multiple signals across a single data link. Under the analog signals, the frequency and wavelength division multiplexing techniques are used. Under the digital signals, the time division multiplexing is used . In the FOC communication system, the wavelength division multiplexing is used to multiplex multiple optical carrier signals on a single optical fiber by using different colors of the laser light to carry different signals. This is commonly done when a single mode FOC is used as it transmits data over very long distances compared to the multi-mode fiber.
he ISDN multiplexer streams is a continuous stream of frames. Each frame contains various control and sync information.
In a nutshell, a medium can carry at least one signal at any moment in time, especially in the case of the single mode fiber. The multiple signals sent at the senders point share one medium and the medium must be divided so as to give each signal a portion of the total bandwidth.
Trends and future scenario
Radio frequency signals are transmitted over fiber to provide broadband wireless access. It is an emerging trend in the data communications field . Some of the places that have considered the implementation of the same are such as Olympics London and Niagara Tunnel. The single Radio over frequency link can support both voice and data simultaneously. The new generation of optical communication is still evolving. Not only long-haul optic communication, the fiber to home and the local networks may be controlled optically and fully in the coming decade. There are plans to increase the number of underwater and underground fiber network cables to ensure faster and reliable data communication.
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