Optical networks - Devices
In this chapter, we have the different components of optical devices.
Isolator is a non-reciprocal device that allows light to pass along a fiber in one direction and provides very high attenuation in the opposite direction. Insulators are needed in the optical system to prevent unwanted reflections, pulling back a fiber, and disrupting the operation of a laser (producing noise). In the manufacture of insulators, the " Faradays effect " is used, which depends on the polarization.
Isolators are constructed using optical polarizers, analyzers and Faradays rotators. The optical signal passes through the polarizer, oriented parallel to the state polarization input. The Faradays rotator will rotate the polarization of the optical signal 45 degrees.
The signal then passes through the lens.analyzer, which is oriented 45 degrees to the input polarizer. The isolator transmits an optical signal from left to right and changes its polarization 45 degrees and produces a loss of approximately 2 dB.
Circulators are micro-optical devices and can be used with any number of ports, however, 3 port / 4 port circulators are generally used. It has a relatively low loss of 0.5dB to 1.5dB port to port.
The basic function of a circulator is shown in the figure above. Light entering a particular port (say port 1) moves around the circulator and goes out to the next port (let's say port 2). Light entering port 2 goes to port 3, and so on. The device works symmetrically around a circle. Circulators are micro devices. optical and can be manufactured with any number of ports. However, circulators3 and 4 port are very common. Circulators have very low losses. Typical port-to-port loss is approximately 0.5 to 1.5 dB.
Splitters and couplers
Couplers and splitters are used to combine optical signals and / or
Three important characteristics are -
Return Loss - The amount of reflected and lost energy .
Insertion Loss - The amount of signal lost in total transit through a device.
Excessive loss - Additional loss of a device above the loss ttheoretical.
Types of couplers
- Y couplers
- Star couplers
- Fused fiber
- Mixing plate
- Planar (free space)
- 3 dB coupler
- Beam splitter
Filters are used to select the signal in the trans path and the receiver among many signals . Grids are filters. Switches, modulators, AWG, multiplexers, etc. are considered to be types of filters.
Here are the types of filters -
- Fabry- Perot
- Adjustable filter
- Filter fiber Bragg grating
Filters are used in front of an LED to reduce the width of the line before transmission. Filters will be very useful in WDM networks for -
A filter placed in front of an inconsistent receiver can be used to selectonnering a particular signal among many arrivals
WDM networks are proposed which use filters to control the path through a network that a signal will take.
Bragg fiber networks are the most important optical filter in the world of communications.
Modulators are made of a material which changes its optical properties under the influence of an electric or magnetic field. In general, three approaches are used -
- Electro-optical and magneto-optical effects
- Electro- absorption effects
- Acoustic modulators
Due to mechanical vibrations Ref Material change index Acoustic modulators use very high frequency sound By controlling the intensity of the sound we can control the amount of deflected light and therefore build a modulator.
Here are some of its advantages-
They can handle quite high power.
The amount of refracted light is linearly proportional to the intensity of sound waves.
They can modulate different wavelengths at the same time.
An optical filter is used to isolate or drop the wavelength of several wavelengths arriving on a fiber . Once a wavelength is removed, another channel using the same wavelength can be added or inserted on the fiber, as it leaves OADM.
A simple ADM has only 4 input and output channels, each with four wavelengths. In OADM, wavelengths can be amplified, equalized or further processed. OADM arranges the wavelengths from input fiber to output fiber using optical interconnect.
An optical x-connect can takefour input fibers, each carrying four wavelengths, and rearrange the 16 wavelengths, on the four output fibers. A single transponder inside OXC will mix one of the wavelengths to an available channel.