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OC: Fixed or Wireless Optical Access or Transport Systems & Networks


Terrestrial fiber-optic networks - Gerson Flavio Mendes de Lima


An optical network is a communication system that uses light signals, instead of electronic ones, to send information between two or more points. The points could be computers in an office, large urban centers or even nations in the global telecommunications system. Optical networks comprise optical transmitters and receivers, fiber optic cables, optical switches and other optical components. Optical and electronic networks can take several different forms. Point-to-point networks make permanent connections among two or more points so any pair of nodes can communicate with each other; point to multipoint networks broadcast the same signals simultaneously to many different nodes; switched networks like the telephone system include switches that make temporary connections among pairs of nodes. The basic building blocks of these networks are fiber-optic cables-the so-called “pipes”-which carry signals from node to node, with switches directing them to their destination.


The Signal


An optical signal consists of a series of pulses produced by switching a laser beam off and on. Its speed depends on how fast the beam can be switched on and off, and how much the pulses spread in length during transmission, an effect called dispersion. The amount of dispersion depends on the type of fiber, the fiber length and the nature of the optical signal. The more dispersion, the more difficult it is to distinguish between adjacent pulses. With current technology, different types of fiber can be combined to reduce dispersion effects, allowing transmission at 10 gigabits per second for a few thousand kilometers. To achieve faster transmission speeds, researchers are exploring ways to actively compensate for dispersion.


A single fiber can transmit many separate signals simultaneously at different wavelengths of light, a technique called wavelength-division multiplexing. This is analogous to broadcasting many radio and television signals through the air at different frequencies. 


Like the number of radio stations, the maximum number of optical channels is limited by the slice of spectrum used for each channel and the total amount of spectrum available. Devices called “demultiplexers” separate the optical channels and distribute them to separate optical receivers. Demultiplexers slice the spectrum into very narrow chunks, isolating each optical channel from adjacent ones.


Multiplying the number of optical channels by the data rate on each optical channel gives total transmission capacity of a fiber. Laboratory experiments have transmitted more than 10 trillion bits (10 terabits) per second through more than 100 kilometers of fiber. However, commercial transmission rates typically do not exceed a few hundred gigabits per second.


Achieving these high data rates and multiple channels requires sophisticated components. Semiconductor lasers-which generate the light pulses used in almost all fiber optic communications systems-must emit only a very narrow range of wavelengths to limit dispersion. Fibers also are designed to limit dispersion.




The clearest optical fibers can transmit signals more than 100 kilometers without amplification-much farther than copper wires. When the signal must span a longer distance, it is passed through an optical amplifier, which multiplies the strength of the optical signal. The most widely used optical amplifiers are fibers doped with atoms of erbium, a rare-earth element that absorbs light energy from an external pump laser. The erbium atoms then release that energy to amplify weak optical signals across the entire band of wavelengths that the laser transmits. With careful control, a string of dozens of optical fiber amplifiers can transmit signals thousands of kilometers across the ocean.


Optical Switches


One challenge to optical networking is how to switch light signals. When a signal arrives at its destination, it must be separated from the rest of the channels. To drop one signal at an intermediate point, an optical filter separates the proper wavelength from the rest. Equipment at that point may also add a new signal to the now unoccupied wavelength.


Optical switches may operate on a single wavelength, or on all the wavelengths transmitted through a fiber. A fixed filter, like the one described above, could be replaced by a switch that selects one of several filters to divert the desired wavelength to the intermediate point. A third kind of switch separates the wavelengths into separate beams, and a moving mirror directs one or more of the wavelengths in a different direction. Other optical switches simultaneously switch all wavelengths passing through a fiber; one example is a mirror at the fiber output that could tilt between two different positions to reroute all optical channels in case of a fiber break.


The preceding examples are called “all-optical” switches because they operate on light signals. A different class of switches convert optical signals into an electronic form which can be switched electronically; the resulting electronic signal then feeds into an optical transmitter to generate a new optical signal. These are called opto-electro-optical switches.


As the technology continues to advance, optical networks will need to convert signals from one wavelength to another. This can be done now with opto-electro-optical wavelength converters that convert the input optical signal into electronic form to drive a transmitter at the second wavelength. All-optical wavelength converters have been demonstrated in the laboratory, but are not yet used in practical systems. Laser sources that can be tuned to many different wavelengths also will be needed; several types have been demonstrated, and some are in commercial production. - Jeff Hecht – MIT TR - January 22, 2002


Fiber-optic transmission and networking: the previous 20 and the next 20 years

Scaling capacity of fiber-optic transmission systems via silicon photonics

Optical Communication Systems

Optical Networks: Optical Network Services in Future Broadband Networks

Optical Transport Networks & Technologies Standardization Work Plan-ITU

ITU standards enhance capabilities of the Optical Transport Network - ITU Hub

Optical Transport Networks (itu.int)



About TACS

TACS Consulting Delivers The Insight and Vision on Information Communication and Energy Technologies for Strategic Decisions.

TACS is Pioneer and Innovator of many Communication Signal Processors, Optical Modems, Optimum or Robust Multi-User or Single-User MIMO Packet Radio Modems, 1G Modems, 2G Modems, 3G Modems, 4G Modems, 5G Modems, 6G Modems, Satellite Modems, PSTN Modems, Cable Modems, PLC Modems, IoT Modems and more..

TACS consultants conducted fundamental scientific research in the field of communications and are the pioneer and first inventors of PLC MODEMS, Optimum or Robust Multi-User or Single-User MIMO fixed or mobile packet radio structures in the world.

TACS is a leading top consultancy in the field of Information, Communication and Energy Technologies (ICET). The heart of our Consulting spectrum comprises strategic, organizational, and technology-intensive tasks that arise from the use of new information and telecommunications technologies. TACS Consulting offers Strategic Planning, Information, Communications and Energy Technology Standards and Architecture Assessment, Systems Engineering, Planning, and Resource Optimization.



TACS is a leading top consultancy in the field of information, communication and energy technologies (ICET).


The heart of our consulting spectrum comprises strategic, organizational, and technology-intensive tasks that arise from the use of new information, communication and energy technologies. 
The major emphasis in our work is found in innovative consulting and implementation solutions which result from the use of modern information, communication and energy technologies.



  • Delivers the insight and vision on technology for strategic decisions
  • Drives innovations forward as part of our service offerings to customers worldwide 
  • Conceives integral solutions on the basis of our integrated business and technological competence in the ICET sector 
  • Assesses technologies and standards and develops architectures for fixed or mobile, wired or wireless communications systems and networks
  • Provides the energy and experience of world-wide leading innovators and experts in their fields for local, national or large-scale international projects.






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