At the end of the transmitter section, the multiplexer is used to combine the signals as well as at the end of the receiver section, the de-multiplexer for dividing the signals separately. The main function of WDM at the multiplexer is for uniting various light sources into only light sources, and this light can be changed into numerous light sources at the de-multiplexer.
The high data rate of this FOC cable is superior to the data rate of the metallic transmission cable. The TDM is one kind of method for transmitting a signal over a channel of particular communication by separating the time edge into slots. Like single slot is used for each message signal. TDM is mainly useful for analog and digital signals, in which several channels with low speed are multiplexed into high-speed channels used for transmission.
Depending on the time, every low-speed channel will be assigned to an exact position, wherever it works in the mode of synchronization. The synchronous TDM is very useful in both analogs as well as digital signals. In this type of TDM, the connection of input is allied to a frame. For example, if there are n-connections in the frame, then a frame will be separated into n-time slots, and for every unit, each slot is assigned to every input line.
In this type of TDM, the multiplexer assigns a similar slot for each device at every time. If the device has nothing for transmitting, then the time slot is assigned to a new device. Once the switch releases at the surface of the multiplexer ahead of a connection, then it has a chance of sending a unit into the lane.
Similarly, once the switch releases at the surface of the de-multiplexer ahead of a connection a chance to receiving a unit from the lane. This procedure is named interleaving. The statistical TDM is applicable to transmit different types of data simultaneously across a single cable. The transmission of data can be done from the input devices which are connected to networks like computers, fax machines, printers, etc. The statistical TDM can be used in the settings of telephone switchboards to control the calls.
This type of technique is comparable to dynamic bandwidth distribution, and a communication channel is separated into a random data stream number. The term CDM stands for code division multiplexing. It is one kind of technology that works with spread spectrum communication. In this type of communication, a narrowband signal can be transmitted through division across several channels or over a larger frequency band.
It does not compress the bandwidths of frequencies otherwise digital signals. The multiplexer may be replaced by a simple optical coupler, but losses will increase. Obviously, when the light propagation is reversed, the multiplexer becomes the demultiplexer, and conversely. It is important to note, however, that the coupling efficiency is not necessarily preserved in reverse operation.
For example, if the multiplexer uses single-mode entrance fibers and a multimode output fiber, the coupling losses would be excessive in the reversed use. Multiplexers designed with identical input and output fibers are usually reversible. For the multiplexing or separation of wavelengths, interference filters or gratings can be used. However, wavelength division multiplexers using interference filters cannot be used when the number of channels is too high or when the wavelengths are too close.
The main advantage of the grating is the simultaneous diffraction of all wavelengths and so it is possible to construct simple devices with a very large number of channels with the exception of fiber gratings. There are three types of gratings: classical, arrayed waveguide, or fiber. In the classical grating, we use gratings in the Stimax configuration Figure 3. The dispersive element was a grating embedded in a monoblock of silica, and the optical fibers were directly fixed to the block.
The number of grooves on the grating several tens to several thousands per millimeter are obtained by using a diamond tool or by holographic photoetching.
The grating has the property of diffracting light in a direction related to its wavelength Figure 4. Hence an incident beam with several wavelengths is angularly separated in different directions.
The diffraction angle depends on the groove spacing and on the incidence angle. The arrayed waveguide grating was designed to increase the resolving power, i. It was proposed around by Takahashi and others in Japan, and Dragone and others in the U. They increased the optical path difference between the diffracting elements by using a waveguide structure equivalent to the well-known Michelson echelon gratings in classical optics.
The advantage is a smaller channel spacing. The disadvantages are a much smaller free spectral range that will limit the total number of channels and near-end crosstalk that affects bidirectionality. A fiber grating is made by recording a Bragg grating in the core of single-mode fiber made photosensitive by doping with, for example, germanium.
This grating can be used as an narrowband filter. It is necessary to use one grating per wavelength. So there is some limitation to the number of channels that can be obtained with these devices.
Please tell me about the history of WDMs and your part in it. The optical multiplexing concept is not new. Denton and T. About 20 years later, the first practical components for multiplexing were proposed from different laboratories, mainly in the U.
We started our research on gratings in We took part in the engineering of ruling engines and to the introduction and development of holographic gratings in at Jobin Yvon. In those days, the main application was spectroscopy, and we had no idea of the possible applications to optical telecommunications. We realized that possibility only after having participated in the Summer School in Electromagnetism in Centre National d'tudes des Telecommunications in Lannion France devoted to guided waves in optical communication.
Soon after, we developed a new grating optics coupler in , but this component was only used for optical spectroscopy research and did not find application in optical telecommunications. In order to satisfy this requirement, several technologies have been suggested and developed, and one of the most attractive approaches is known as massive multiple-input multiple-output MIMO , and that is where, for example, spatial multiplexing comes to use [ 9 ]. From signal processing side, for instance, employing multiple carriers all the way to arranging antennas and network management, multiplexing technique provides accessing resources by dividing and sharing it among users.
In the other side, de-multiplexing has to be applied at the receiver side to inverse all the processes and extract the information sent. One particular example for application of multiplexing is seen in orthogonal frequency division multiplexing OFDM systems [ 10 ].
The signal is spread between different subcarriers, and the frequency bandwidth is efficiently used [ 11 ]. This chapter is an introduction to the book titled Multiplexing. A variety of definitions of multiplexing from different points of view are presented, and a short history of the origin of multiplexing is briefly discussed. The potential and application for existing and future technologies are also discussed.
Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications. Edited by Somayeh Mohammady.
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