Fiber Communication System: Multiplexing And Demultiplexing Techniques

The main focus of this report is on the fiber communication system. The optical fiber is the backbone of the modern communication network. It carries all long distances voice data and other multimedia forms of communication.

1.REPORT AIMS & OBJECTIVES

2.Fiber communication systems

3.Optical sensors

4.Multiplexing Mechanisms

Overview of the Fiber Communication System

1.REPORT AIMS & OBJECTIVES 

a). To determine the physical quantities that the optical fiber technology measures

b). To categorize the fiber optic sensor with respect to their technical operating principles.

c). To explain the operation of the fiber optic sensors in their surroundings or implementation environment.

2.Fiber communication systems

The optical fiber is the backbone of the modern communication network. It carries all long distances voice data and other multimedia forms of communication. The information revolution can be attributed to the evolution of optical fiber in data communications. It is preferred because of the low attenuation, very high bandwidth in the communication channel especially in the single mode fiber, its enormous capacity, and the system adds an optical layer that guarantees flexibility. Fiber communication systems are used in many fields such as the power engineering, biomedical, optical sensing for structural monitoring and VLSI in intra-chip communications.

The fiber optic cable, FOC, transmits data over very long distance. One very common example is the sea or ocean underground cable that connect continents on the planet earth. According to the basic model, the bandwidth of the fiber optic communication system determines the maximum data rate [1]. A FOC link denotes the signal pathway between two points using the cable. The pathway is the mode or channel that enables transmission of the data from the sender to the receiver points. The links are often described in terms of their ability to send and receive signals as part of the communication system. There are two modes of communication generally referred to as the simplex and duplex. The fiber carries light signals as single mode, multimode, step index, and as graded index fiber. The optical transmitter converts the electrical information for the computer network to the optical format. For the multi-mode fiber, a light emitting diode is used while for a single mode fiber, a laser diode is used. The reverse procedure is carried out on the receiving end. The communication system transmits information over very long distances and as a result, repeaters are used to receive weak light signals, clean them up, and amplify them for retransmission.

With the advent of newer technology in the data and network communications field, the transmitted signals need further processing such as switching, wavelength conversion, signal reshaping, and add-drop multiplexing. The scheme we focus on in this report is the multiplexing and demultiplexing technique used to transmit multiple sources of data along a single mode fiber for very long distances. The flow can be illustrated as shown below,

The Optical Fiber in Communication Networks

The input is usually format, set within a given bandwidth following a given data and network protocol. The optical transmitter performs modulation, power alterations, and wavelength modifications. The communication channel, in this case, the single mode fiber, experiences loss, light signal dispersion, 4-wave mixing, distortion and in most cases amplification using repeaters. The optical receiver checks on the bandwidth on reception and compares it to the sending one. Amount of information that can be transmitted is directly related to the frequency range over which the carrier operates, increasing the carrier frequency theoretically increases the available transmission bandwidth and therefore larger capacity.

3.Optical sensors

An optical sensor is a device that picks up external stimulus of the physical quantities such as the temperature, pressure, and strain. The device detects events or changes in the physical quantities and provide a corresponding optical output. The sensor will modulate an optical signal which when demodulated yields precise quantitative information about the measurand. Some of the problems associated with optical sensors are portability, remote monitoring, cost, ruggedness, and efficiency. The solutions to the optical sensors are obtained from optical fibers and the OE components for sensing such as the Fiber optic sensors. According to the alternate school of thought, the realization of the high sensitivity of optical fibers to external perturbations such as the phase modulation, micro bending loss in cabling, modal noise and its exploitation for development of sensors [2]. The high sensitivity of fibers due to long interaction length of light with the physical variable. Some of the merits of using the fiber optic sensors:

• Large bandwidth
• Efficient transmission or low loss
• Immunity to Electromagnetic interference or radio frequency interference and EMP.
• Information security is guaranteed
• The geometric versatility
• They are small in size and lightweight
• It guarantees no sparking or fire hazards with single fiber serves both as sensor and data transmitting channel.
• Allows for multiplexing and spatially distributed sensing and ensures very high performance.

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 [3]. 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.

Multiplexing and Demultiplexing Techniques Used in Fiber Communication

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 [4].

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.

4.Multiplexing Mechanisms

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 [5]. 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 [6]. 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 [7].

Optical Sensors

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 [8]. 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 [4]. 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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