Application of PIN diode

A PIN diode is used in a variety of different applications from low to high radiofrequency. PIN diodes are very good for RF switching and photodiode. Here is some application related to the PIN diode to know more details about PIN diode 

Application of Photodiode

• A PIN diode is used as a photodetector for most fiber optic applications.
• There are used as a variable resistor in at RF and microwave frequency.
• They are used in electric Pre - Amplifier to boost sensitivity.
• It used as a high voltage rectifier.
• Audio CD players, Computer CD drive, DVD players.
• In a phase shifter circuit considered as a lumped variable impedance microwave circuit element.
• Nuclear radiation detector.
• It can be also used limiter circuit and modulator.
• PIN diodes are utilized as series or shunt connected switches in a phase shifter design.

Fiber optic cable disadvantages

The main features of fiber optic cable are that it is a flexible, transparent fiber made by drawing plastic or glass to a diameter as a means to transmit light between the two ends of the fiber and also find wide usage in fiber-optic communication. So now let use check about the disadvantages of optical fiber cable to know more details about fiber optic cable. 

Disadvantages of fiber optic cable :

• Special training required to attach the connector to the cable
• Difficult to splice
• Can't be curved
• Low power
• The distance between the transmitter and receiver should keep short or repeater are needed to boost the signal
• Difficult to work with and difficult to install
• Higher initial cost installation
• More expensive to repair or maintain
• Interfacing cost
• Connector problem
• Highly susceptible
• Expensive in comparison with conventional electrical cables
• Limited application
• More vulnerable damage compare to copper wires
• Cost is higher than copper cable
• Require specific skills
• Affected by chemical

Fiber optic cable color code

Fiber color code:

In optical fiber terms inside the cable each tube in a loose tube cable, Individual fiber will be color-coded for different identification. So now in optical fiber communication, the fiber allows the convention created for telephone wire except fiber are identified individually, not pairs. Color fiber is spliced to ensure continuity of color codes throughout a cable run. The figure shows the color coding in optical fiber communication.

Fiber color codes

Connector color codes :

The earliest days of fiber optics cable like, orange, black or gray was multimode and yellow single mode. However, the advent of metallic connectors like the FC and ST mode connector color coding difficult, so colored strain relief boots were often used.

Fiber optic cable bandwidth

Introduction : 

In general, bandwidth is referred to as the range of a particular fiber optic cable. In reality, different cable has a different bandwidth capacity of transmitting data from one point to another. The bandwidth of fiber optic cable determines the maximum speed of the data pulses to the fiber cable can handle it. We know that the bandwidth is normally stated in terms of megahertz-kilometers.  For instance, there those which are most suitable is carrying large quantity data over long distances within a short time. Consequently, there are those most suited in transmitting a large quantity of data over short distances. In this case, the cable made to transmit data over very long distance cannot be used to transmit the same data over a short distance and if that is done, then the frequency will too much lower. For that reason, it is very important to study that bandwidth of particular fiber optic cable.

As the length of the fiber cable is increased, the bandwidth decreases in propagation. In general, a common 62.5/125 micrometer cable has a bandwidth in the 100 to 300 MHz-km range.

The speed of optical fiber cable while in using a single mode fiber cable can run from a few meters to 40 kilometers Where a multimode fiber optic cable is used for much shorter ranges.

Fiber types and bandwidth  :

Single mode - 100 Ghz-km

Graded index - 560 MHz-km at 1300 nm, 160 MHz-km at 850 nm 

Step index - 20 MHz-km

Conclusion :

The cost of fiber cables with the bandwidth capacity of fiber optic cable. You can have also found that fiber cable with efficiently and faster bandwidth capacity is more expensive than others. The greater the frequency and larger the bandwidth of fiber optic cable the more efficient is the cable. So and we already know that different people have got different reasons to purchase a fiber cable, the variation of bandwidth has indeed been beneficial to many. Therefore, the bandwidth capacity of fiber optic cable before purchasing it.

Fiber optic cable definition

A fiber optic cable is a flexible, high-speed data transmission medium, transparent fiber made by drawing plastic or glass to a diameter slightly thicker than that of a human hair. It is a high-speed data transmission medium.

The optical fiber cable is generally used as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communication. Digital data is transmitted through the cable via the rapid pulses of light. The receiving end of fiber optic transmission translates the light pulses into binary values, which can be read by a computer. Color fiber is spliced to ensure continuity of color codes throughout a cable run.

Since fiber optic cable provides fast transfer speed and large bandwidth, They are used for a large part of the internet backbone. For example, most transatlantic telecommunication cables between the U.S and Europe are fiber optic. In recent years, fiber optic technology has become increasingly popular for local internet connection as well. 

• Fiber optic cable can be used as a medium for computer networking and telecommunication because it is flexible and can be bundled as cables
• It also is used in telephone, military and space application
• It can be used an easy, economical and attractive solution for a lighting project
• It can be used to transmit power using a photovoltaic cell to convert the light into electricity. 

Fiber optic cable uses

A definition of fiber optic cable is a flexible, as well as transparent fiber made by drawing plastic or glass to a diameter slightly thicker than that of a human hair. Optical fiber cable can be generally used most often as a means to transmit light between the two ends of the fiber and find wide usage in the fiber optic communication system. So now let use check about where to uses of fiber optic to know more details about fiber optic cable.

Fiber optic cable can accommodate a variety of needs is given below :

• It can be used in communication, fiber optic sensors, as well as illumination,
• It is used a medical treatment like light guides, imaging tools and also as lasers for surgeries
• It is used hydrophones seismic or SONAR application, submarines, like wiring in aircraft, and other vehicles and also for field networking
• It used in computer networking, telephone, military as well as space application
• It can provide an easy, economical and attractive solution for a lighting project
• It is used for data transmission
• It can be also used microscopy and biomedical research
• It is used to transmit power using a photovoltaic cell to convert the light-electricity
• It is used to connect in a variety of network settings 
• And also help increase the speed and accuracy of data transmission
• Broadcast/cable companies are using fiber optic cable for wirings like HDTV, CATV, internet, video on demand and other applications

Fiber optic cable speed

A fiber optic cable is a flexible, as well as transparent fiber made by drawing plastic or glass to a diameter as a means to transmit light between the two ends of the fiber and find wide usage in fiber optic communication system. allow data to be transmitted high speeds over a great distance.

There are two types of fiber :

• Single mode fiber 
• Multimode fiber.

The two types of fiber and speed from these two fibers are different. A single-mode fiber cable can run from a few meters to 40 kilometers While multimode fiber optic cable is used for too much shorter ranges. 

Speeds :

  

Fiber optic cable is generally in single mode fiber uses only (OS1) while in multimode uses different (OM1, OM2, OM3, OM4). Single mode fiber optic can reach speed up to 100GB whereas multimode fiber optic run at speed from 100 Mb to 10 GB.

In fiber optic cable transmit at different speed over varying length depending on the size is used.

OM1 - 275 m ,33 m (Gigabit range)

OM2  - 550 m, 82 m (Gigabit range)

OM3 - 800 m, 300 m, 100 m, 100 m (Gigabit range)

OM4 - 1100 m, 550 m, 150 m (Gigabit range)

OS1 - 40km (Gigabit range)

Here we have to also compare the speed of Coaxial cable vs fiber optic cable. 

Fiber optic cable is just flat out faster. Fiber optic cable speed up to 10 Gbps, symmetrical upload as well as download bandwidth.

While in cable internet speed vary by provider and range from 10 Mbps to 1Gbps download speed and upload speed from 3 Mbps to 50 Mbps.

Fiber optic cable types

The fiber optic cable is to be used a variety of situations such as underground, outdoor poles or submerged underwater. The structure of cable depends on the situation where it is to be used,  but the basic cable design principles remain the same.

The requirement of optical fiber material is to be transparent for the efficient transmission of light.

The mechanical property of cable is one of the most important factors for using any specific cable. The maximum allowable axial load on cable decides to the length of the cable can be reliably installed. That are several benefits of a fiber optic cable is a flexible, transparent fiber made by drawing plastic or glass to a diameter slightly thicker than that of human hair.

Fiber arrangements :

• Several arrangements of fiber cables are done to use it for different application in a cable. The most basic form is two fiber cable is proper design. Shows basic two fiber cable design as given below. It is also known as a basic building block of fiber cable.
• Multiple fiber cables can be combined together using some similar techniques. 
• The basic fiber building blocks are used to form a large cable. These units are bound on a buffer material which acts as strength element along with an insulated copper conductor types of materials. The fiber building blocks are surrounded by paper tape, PVC jacket, yarn, and an outer sheath. 

Fiber optic  cable 

There are many types of fiber optic cable available in fiber optical communication. In general, there are two types of fiber optic cables are available :

1. Simplex cable

2. Duplex cable

1. Simplex cable :

In simplex cable single strand surrounded by around  900 um tight buffer then the aramid yarn and finally the outer jacket are available.

A jacket is used in 2 mm or 3 mm plenum or riser types of jacket.

2. Duplex cable:

In duplex cable strands of fiber optic cable attached at the center point. Cable surrounded by a 900 um buffer then a layer of kevlar and finally the outer jacket there.

A jacket is used in 2 mm or 3 mm plenum or riser types of jacket.

A number of a core are bundled in a plastic type of ducts. In case, ease identification of individual fibers is color-coded types. Shows some example of the color coding in the optical cable used by manufactures.

1 - Blue

2 - Orange

3 - Green

4 - Brown

5 - Grey

6 - White

7 - Red

8 - Black

9 - Yellow

10 - Violet

11 - Pink or light blue

12 - Turquoise or netutral

Fiber optic cable material

Materials are used for optical fiber :

The material requirement of fiber optic cable for glass and plastic. They offer widely different characteristics and therefore fibers made from the two different substances and find uses in very different applications.

The main requirement of fiber optic material to be given below :

• Fiber material must be required with compatible the cladding material
• It must be possible to draw long thin fiber from the material used
• The material must be used to be transparent for efficient transmission of light

Glass and plastics materials have fulfilled this requirement:

Most fiber consists of silica or silicate. Various types of low loss and high loss glass fiber are available to suit the requirement. Plastic fibers are not too much popular because of its high attenuation so they have better mechanical strength.

Glass fiber :

Glass fiber made by materials fusing mixtures of metal oxides having a refractive index of 1458 at 850 nm. For changing the refractive index different oxides like B₂O₃, GeO₂ and P₂O₅ are added as dopants. 

One important criterion is that the refractive index of the core is greater than that of the cladding, hence some important composition is used such as given below :

Composition :

1 : Core type -  GeO₂ - SiO₂  Cladding type - SiO₂ 

2 : Core type  -  P₂O₅  - SiO₂  Cladding type - SiO₂ 

3 : Core type - SiO₂  Cladding - B₂O_{3 -} SiO₂ 

4 : Core type - GeO₂ - B₂O₃ -  SiO₂  Cladding type - B₂O_{3  -} SiO₂ 

The principal raw material for silica is sand and glass materials. The fiber materials composed of pure silica is called as silica glass. The desirable properties of silica glass are given below:

• Resistance to deformation even at high temperatures.
• Good chemical durability. 
• Better transparency.
• Resistance to breakage from chemical thermal shocks.

Other types of glass fibers are :

• Halide glass fibers.
• Active glass fiber.
• Chalcogenide glass fiber.
• plastic optical fibers. 

Graded index fiber

Definition of Graded-index fiber :

An optical fiber with a core having a refractive index that decreases with increases radial distance from the fiber axis. The most common refractive index for a graded index fiber is very nearly parabolic. The parabolic result in continual refocusing of the rays in the core, and compensates for multimode distortion.

The graded index fiber has a core is made from many layers of glass. In the graded index fiber the refractive index is not uniform within the core, it is highest at the center and decreases smoothly and continuously with distance towards the cladding side. The refractive index profile across the core that takes place in the look like parabolic nature.

In graded-index fiber, the light waves are bent by refraction towards the core axis and they follow the curved path down the fiber length side. This result because of change in refractive index as moved away from the center of the core side.

Graded index fiber 

Multimode graded-index fiber :

The core size of multimode graded index fiber cable is varying from 50 to 100-micrometer range. 

In this fiber, the light ray enters the fiber at many different angles. So in graded index fiber, the light propagates across the core toward the center it is intersecting a less dense to more dense medium. This article gives some advantages of graded index fiber to know more details about it 

Therefore the light rays are being constantly being refracted and the ray is bending continuously. This cable is mostly used for long distance communication system.

Multimode graded index fiber

Some important point of graded index fiber :

• Graded index fiber data rate is very high.
• The path of light is helical in manner.
• Graded index fiber is of only one types that is a multimode fiber.
• Coupling efficiency is low.
• In graded-index fiber, the diameter of the core is about 50 micrometer in the case of multimode fiber.
• Attenuation is less.
• Refractive index is non-uniform.
• Graded index the bandwidth is high.  
• It is mostly used in local and wide area networks.

Step index fiber

The step index fiber is a cylindrical waveguide core with inner core has a uniform refractive index of n₁ and the core is surrounded by an outer cladding with a uniform refractive index of n_2.

In this fiber, the cladding refractive index ( n₂ ) is less than the core refractive index ( n₁ ) but there is some abrupt change in the refractive index at the core-cladding interface for using simple step-index fiber. 

The propagation of light wave within the core of step index fiber takes the path of a meridional ray. Ray follows a Zig Zag path of straight line segment. 

Depending on the refractive index profile of fiber and modes of fiber there exist two types of step index fiber  called as : 

1. Single mode step index fiber type
2. Multimode step-index fiber type

1. Single mode step index fiber

Single mode step index fiber has a central core that is sufficiently so small so that there is essentially only one path for light ray through the cable. 

The light ray propagates in the fiber through reflections. Typical core size is 2 to 15 micrometer. so single mode fiber is also known as the fundamental or monomode fiber.

Single mode fiber will permit only one mode to propagate and also does not suffer from mode delay difference. 

These are primarily developed for the 1300 nm window but they can be also be used effectively with time multiplex and wavelength division multiplex system operating in 1550 nm wavelength region.

The core fiber of a single mode fiber is very narrow compared to the wavelength of light is to be used. Therefore, only one single path exists through the cable core through which light can travel. 

(a) Multimode step index fiber type,  (b) Step index fiber type

2. Multimode step index fiber 

Multimode step-index fiber is the most widely used in optical fiber communication. It is easy to manufacture and also its core diameter is 50 to 1000 micrometer. 

In this mode, the light ray is propagated using the principle of total internal reflection. Since the core index of refraction is too much higher than the cladding index of refraction, so the light enters at less than the critical angle is guided along the fiber.

Light rays passing through the fiber are continuously reflected off the glass cladding towards the center of the core at different angles and also have lengths, limiting overall bandwidth.

One of the disadvantages of multimode step-index fibers is that the different optical length caused by various angles at which light is propagated relative to the core devices, causes the transmission bandwidth to be fairly small. So multimode step index fiber is typically only used in an application requiring of less than 1 km.  

Some important point of step index fiber :

• The data rate is very slow.
• The ray path of light propagation is looked like Zig Zag manner.
• Step index fiber of two types of mono-mode fiber and multimode fiber whereas using step index coupling efficiency with fiber is too high.
• In step index fiber the diameter of the core is about 50 - 200 micrometer while in the case of multimode fiber and 10 micrometers in the case of single mode fiber type.
• Attenuation is more.
• The refractive index of the core is high.
• The bandwidth is low.
• It is mostly used in local network communication.

Explore more information:

1. Difference between step index fiber and graded index fiber 

Raman amplifier

Introduction to Raman amplifier :

Raman amplifier is an optical amplifier based on main to be Raman gain, which results from the effect of stimulated called as Raman scattering. In this medium, the active medium is generated or often at an optical fiber, although it can also be a bulk crystal, a waveguide in a photonic integrated circuit, or a cell with a liquid or gas medium device. An input signal can be amplified while a counterpropagating with a pump of a beam, the wavelength of which is typically a few tens of nanometers shorter. For silica fibers, the maximum gain is obtained for a frequency offset of around = 10-15 THz between pump and signal depending on the composition of the fiber core. Here this article gives information about the most important amplifier known as the Raman amplifier to better understanding this topic.

Features of Raman amplifier :

• It can be operated in the different wavelength region
• Provided that a suitable pump source is available
• In this amplifier the gain spectrum can be tailored by using different pump wavelength simultaneously
• This amplifier also requires high pump power, it also requires high pump brightness but it can also generate high output powers
• A greater length of fiber is required
• It can have a lower noise figure
• This amplifier also has a fast reaction to changes in pump power, particularly for copropagating pump and very different saturation characteristics 

Working principle :

It is based on the stimulated Raman scattering effect. Power transferred in the optical signal is known as the Raman effect and amplification. In this above method, Raman amplification provides self-phase matching between the pump and signal with a broad gain bandwidth response generated. The pumping signal can be propagated in either direction of fiber called as forward and backward pumping.

Basically, the Raman gain is dependent on several terms following  given below :

• Fiber length
• Fiber length
• Fiber attenuation
• Fiber core diameter
• Optical pump power 

The figure is shown that below a typical Raman amplifier. The circulator as well as a pump shown in the figure, it lases comprise the two key elements of the Raman optical amplifier. The circulator is basically used for injecting light back into the transmission path minimal optical loss.

Typical Raman amplifier configuration

Advantages of Raman amplifier :

• Compatible with installed SM fiber.
• Variable wavelength amplification possible.
• A very broadband operation may be possible.
• Lower crosstalk.
• Can be used extends  EDFAs full form.

Disadvantages of Raman amplifier :

• High pump power requirements.
• Sophisticated gain control needed.
• Noise is also an issue.

Applications of Injection laser

A LASER full form is one type of device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. 

An injection laser is also known as a laser diode or diode laser. It is a semiconductor device, Nowadays it can be used optical fiber, compact disk, remote control device etc

Application of injection laser: 

• Laser diodes are performed where too much high radiance is required. This high radiance is generated due to the amplifying effects of stimulated emission. So it can supply optical power in milliwatts.
• Where narrow linewidth of the order of 1 nm ( approximately 10 A°) or less is required narrow linewidth is useful in minimizing the effects of material dispersion.
• Laser diodes are preferred where modulation is needed in the high gigahertz range.
• Where temporal coherence is required.
• Where good spatial coherence is required, it allows the output to be focused by a lens into a spot that has a  too much greater intensity than the dispersed unfocused beam.

Types of laser

Before we learn about types of LASER first let we understand what is full form of LASER. Here this article gives information about different types of laser mode to know more details about LASER in optical communication devices.

Single-Mode Lasers :

Single-mode lasers are preferred for high-speed long-distance communications. The single mode lasers that contain only a ( single longitudinal mode and a single transverse mode). Therefore, the spectral width of the optical emission is very narrow for this mode.

To restrict laser only for one longitudinal mode, its length of the lasing cavity is reduced such that only a single longitudinal mode falls within the gain-bandwidth of a device. Because of this device becomes hard to handle and output power is limited to a few mill watts only.

Modulation of Laser Diodes :

Imposing information on light stream is called as modulation of a laser diode.

Imposing information on light stream is called as (modulation of laser diode The / produce a varying optical power or by using an external modulator to modify optical power.

The limitation of the direct modulating rate of laser diodes depends on spontaneous (radiative) and stimulated carrier lifetimes and the photon lifetime

Spontaneous lifetime :

It is a function semiconductor band type structure and the concentration.

Stimulated carrier lifetime :

It is a function of optical density in the lasing cavity and it is typically 10 ps.

Photon lifetime :

In this laser average time that the photon resides in the lasing cavity before being lost by absorption.

Light Source Materials

In light source materials the spontaneous emission is due to the carrier recombination called the carrier recombination of electroluminescence.  

To encourage electroluminescence is necessary to select an appropriate semiconductor type of material. The semiconductors depending on energy band-gap can be categorized into the following way :

• Direct band-gap semiconductors 
• Indirect band-gap semiconductors. 
• Indirect band-gap semiconductors, electrons, and also holes on either side of band gap have the same value of crystal momentum. Hence, direct recombination is ban possible
• In the indirect gap semiconductors, the maximum and minimum energies occur at different values of crystal momentum. The recombination in these semiconductors is quite slow.
• In this laser, the active layer semiconductor material must have a direct band gap. Indirect bandgap semiconductor, electrons, and also holes recombine directly without need of the third particle to conserve momentum.
• In these materials, the optical radiation is sufficiently too muchhigh. 
• The peak output power is obtained at (810 nm ) The width of emission at half power (0.5) is referred to as (full-width half maximum (FWHM spectral width. For the given LED FWHM is 36 nm.

The fundamental quantum mechanical relationship between the gap energy E and frequency v is given as :

 E = hv

 E = hc / ɣ

 ɣ = hc / E

Where energy = joules, and wavelength = meter.  So expressing the gap energy in electron volts and wavelength in micrometers for this application.

What is light emitting diodes

A light-emitting diode (LED) is a component that converts the electrical signal into a corresponding light that is injected into the fiber. Basically, the light emitter is a key element in any fiber optic system. Essentially LED is a PN junction diode. 

p-n Junctions 

A basically conventional p-n junction is called as homojunction as the same semiconductor material.

The electron-hole recombination occurs in a relatively wide layer = 10 micrometers. As the carriers are not confined to the immediate vicinity of a junction, hence high current densities cannot be realized.

The carrier confinement problem can be resolved by sandwiching a thin layer of 0.1 micrometers between the p-type and n-type layers. 

 When the carrier confinement occurs due to bandgap discontinuity of the junction. Such a junction is called heterojunction and its device is called a double heterostructure. 

In an optical communication system when the requirement is an LED is 

1) In LED bit rate of 100-200 Mb/sec.

2) In LED optical power in tens of microwatts. 

LED Structures

Heterojunctions

A (heterojunction) is an interface between two adjoining single crystal semiconductors device with different band gap.

Heterojunctions are of two types, Antisotype ( p-n ) or,  Isotype (n-n or p-p)

Double Hetero-junctions (DH) 

In order to achieve efficient confinement of emitted radiation double hetero-junctions are used in LED structures.

In double hetero-junction, the crosshatched regions represent the energy levels of free charge recombination occurs only inactive InGaAsP layer.

A hetero-junction is a junction formed by dissimilar semiconductors. Double heterojunction ( DH) is formed by two different semiconductors on each side of the active region. The figure shows double heterojunction (DH) light emitter.

Double heterojunction emitter ( DH )

The two materials have different refractive indices and different band gap energies. The changes in band gap energies create the potential barrier for both holes and electrons. The free charges can recombine only in narrow, well defined active layer side.

A double hetero-junction (DH) structure will confine both electrons and holes a narrow active layer. Under forward bias, it will be a large number of carriers injected into the active region where they are efficiently confined. 

Main LED materials or Type :

• Gallium Arsenide ( GaAs ) - infra-red
• Gallium Phosphide ( GaP ) - Red, yellow and green
• Aluminum Gallium Phosphide ( AlGaP ) - Green
• Gallium Indium Nitride ( GaInN ) - near ultraviolet, bluish-green and blue
• Aluminium Gallium Arsenide Phosphide ( AlGaAsP ) - High brightness red, orange-red, orange and yellow
• Silicon Carbide ( SiC ) - Blue as a substrate
• Gallium Nitride ( GaN ) - green, emerald green
• Zinc Selenide ( ZnSe ) - Blue
• Aluminium Gallium Nitride ( AlGaN ) - Ultraviolet

Advantages of LED structure :

• Carrier recombination occurs in a small region 
• light emission occurs in an optical waveguide, which serves to narrow the output beam
• Smaller Size
• Light in weight
• Longer lifetime
• Operate very fast

For detailed information

Read more >> Advantages and Disadvantages of LED 

Application of LED diode :

• Sensor application
• Mobile application
• Sign application
• Indicator
• Remote  control
• Optoisolator
• LED signal
• Illumination
• Automotive uses

For detailed information

Read more >> Application of LED