Optical Communication, Fiber Optics, Electro-Optic Conversion Devices

Optical Communication and Optical Fiber:

Optical communication, also known as optical telecommunication, is communication at a distance using light to carry information. It can be performed visually or by using electronic devices. An optical communication system uses at the transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message from the received optical signal. When electronic equipment is not employed the 'receiver' is a person visually observing and interpreting a signal, which may be either simple (such as the presence of a beacon fire) or complex (such as lights using color codes or flashed in aMorse Code sequence).

Visual techniques such as smoke signals,hydraulic telegraphs,ship flags and semaphore lines were the earliest forms of optical communication.However , The transmitters in optical fiber links are generally light-emitting diode(LEDs) or laser diodes.Infrared light, rather than visible light is used more commonly because optical fibers transmit infrared wavelengths with less attenuation and dispersion. The signal encoding is typically simple intensity modulation, although historically optical phase frequency modulation have been demonstrated in the lab. The need for periodic signal regeneration was largely superseded by the introduction of the erbium-doped fiber amplifier, which extended link distances at significantly lower cost.

Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature. A basic fiber optic system consists of a transmitting device that converts an electrical signal into a light signal, an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal. The complexity of a fiber optic system can range from very simple (i.e., local area network) to extremely sophisticated and expensive (i.e., long distance telephone or cable television trunking ). For example, the system shown in Figure above could be built very inexpensively using a visible LED, plastic fiber, a silicon photodetector, and some simple electronic circuitry. On the other hand, a typical system used for long-distance, high-bandwidth telecommunication that employs wavelength-division multiplexing, erbium-doped fiber amplifiers, external modulation using DFB lasers with temperature compensation, fiber Bragg gratings, and high-speed infrared photodetectors could cost tens or even hundreds of thousands of dollars.

Benefits of Fiber optics:

Optical fiber systems have many advantages over metallic-based communication systems. These advantages include:

1.Long-distance signal transmission:

The low attenuation and superior signal integrity found in optical systems allow much longer intervals of signal transmission than metallic-based systems. While single-line, voice-grade copper systems longer than a couple of kilometers (1.2 miles) require an in-line signal for satisfactory performance, it is not unusual for optical systems to go over 100 kilometers (km), or about 62 miles, with no active or passive processing.

2.Large bandwidth, light weight, and small diameter:

Today’s applications require an ever-increasing amount of bandwidth. Consequently, it is important to consider the space constraints of many end users. It is commonplace to install new cabling within existing duct systems or conduit. The relatively small diameter and light weight of optical cable make such installations easy and practical, saving valuable conduit space in these environments.

3. Nonconductivity :

Another advantage of optical fibers is their dielectric nature. Since optical fiber has no metallic components, it can be installed in areas with electromagnetic interference (EMI), including radio frequency interference (RFI). Areas with high EMI include utility lines, power-carrying lines, and railroad tracks. All-dielectric cables are also ideal for areas of high lightning-strike incidence.

4. Security:

Unlike metallic-based systems, the dielectric nature of optical fiber makes it impossible to remotely detect the signal being transmitted within the cable. The only way to do so is by accessing the optical fiber. Accessing the fiber requires intervention that is easily detectable by security surveillance. These circumstances make fiber extremely attractive to governmental bodies, banks, and others with major security concerns.

5. Designed for future applications needs :

Fiber optics is affordable today, as electronics prices fall and optical cable pricing remains low. In many cases, fiber solutions are less costly than copper. As bandwidth demands increase rapidly with technological advances, fiber will continue to play a vital role in the long-term success of telecommunication.

Electro-optic conversion devices:

The device which converts electrical energy into the optical(photo-ionic) energy are termed asElectro-optic conversion devices. Eg-LED(light emitting diode), Laser-diode, Photo emissive cells etc .

The device which converts optical(photo-ionic) into the electrical energy are termed asElectro-optic conversion devices. Eg- Photo-diode , a photo transistor , LDR(light dependent resistor), solar cells, photoconductive cells etc.

References-

1.https://en.wikipedia.org/wiki/Fiber-optic_communication

2.https://spie.org/Documents/Publications/00 STEP Module 08.pdf