Communication
Telecommunications:Tele: “Over a distance”
Communications: “Exchange of information”
Similarly,
Telephone: Speech over a distance
Television: Vision over a distance
Telecommunications is the exchange of information over a certain distance using some type of EQUIPMENT
Fiber Optic Communication
Advantages:
- Because of the deployment of “Photons” as carriers of information
- Bandwidth - the raw bandwidth: 50 Tb/s (so far only partially exploited)
- Speed - light takes less than 2 second to travel from earth to moon- a blazing speed
- Low attenuation (0.16dB/km)
- Security
- Safety
- Electromagnetic immunity
- Light weight
- Small size
- Not susceptible to weather conditions
Example
- Each time you
- Pick up your Phone
- Turn on your TV
- Transmit documents over a Fax
- Give a cashier your Credit Card
- Use a bank ATM
- Surf the World Wide Web
Optical Fiber Transmit Of Light
Principle: Optical fiber works on the principle of total internal reflection. Once light ray enters into core, it propagates by means of multiple total internal reflection’ s at core-cladding interface.
The light in a fiber-optic cable travels through the core by constantly bouncing from the cladding, a principle called total internal reflection (TIR).
Advantage Of Optical Fiber Communication
- The optical fiber transmission is noise-free
- The rate of transmission of information is directly proportional to signal frequency
- Optical fibers are used more easily than copper cables because they are of small diameter and light weight
- The light signals conducted in optical fibers are harmless, but in copper cables, electricity is conducted which is dangerous sometimes
- The cross-talk becomes negligible in optical febers
- Optical fibers have longer life (20-30 years) than copper cables (12-15 years)
Classification of optical fibers based on modes of propagation:
1. Single mode fiber
2. Multi mode fiber
Optical fibers are classified into three types based on the refractive index profile: They are:
1. Step index single mode fiber
2. Step index multimode fiber.
3. Graded index multimode fiber.
Step Index Single Mode Fiber
- SMF- Only one mode propagates.
- This is achieved by very small core diameter (5-10 µm)
- SMF offers highest bit rate, most widely used in telecom
Characteristics of SMF:
- The diameter of the core is very small
- A very small numerical aperture value
1. It has high capacity
2. Nearly 80% of the fibers manufactured are of this type
Applications of SMF:
- It is used as undersea cables
- It finds particular application in submarine cable system
- It is used as telephone lines in long distance communications.
- When the incident angle is smaller the acceptance angle, light will propagate via TIR
- Sustains many modes
- Modes travel with same velocity
- Modes arrive at the end in different times
- It has high core diameter
- It has high numerical aperture
- It has low bandwidth
- Source- Either laser or LED can be used as the source of light.
- Application-They are used in data links.
- Disadvantage-They cannot be used over long distances.
Solution: GRIN fiber: Core refractive index is maximum at the centre and decreases gradually until it meets core-cladding boundary.
Modes propagating closer to the cladding-longer distance-propagate at higher speed (less RI).
Modes traveling around the centerline-shortest distance-travel at the lowest speed (high RI).
Characteristics of Step index Multi mode fiber:
- It is a high quality fiber
- It has a small numerical aperture
- It has intermediate bandwidth and capacity
- Source- Either LED or laser can be used as the source for the GRIN multimode fiber.
- Application-They are used to connect telephone trunks between central offices.
- Disadvantage: It is expensive
The losses in optical fibers are due to either dispersion or due to attenuation
Dispersion: Spreading of pulse width is called dispersion
Types of dispersion:
1. Material dispersion: Pulses at different wavelengths travel with different velocities in material dispersion
2. Wave guide dispersion: Pulses at different wavelengths travel with different angles
3.Intermodel dispersion: In multimode fiber, The pulse arrive at the fiber end at slightly different times
Attenuation
The loss of light energy of the optical signal as it propagates through the fiber is called attenuation. It is also called fiber loss.
The net attenuation can be determined by a factor called, attenuation coefficient () expressed in dB/km
= -
where Pout is the power output and Pin is the power coupled into the fiber& L is the length of the fiber.
The main reason for the loss of light intensity over the length of the cable is due to
(1) Light Absorption:
(2) Scattering:
(3)Radiation Losses:
(1) Light Absorption: Absorption loss is classified into two types.
(1) Absorption by impurities or extrinsic:
The absorption in the fiber glass occurs due to the presence of impurities like copper, chromium, iron etc (ie, transition metals).
Therefore they fail to undergo total internal reflection and hence it is a loss.
(2) Intrinsic Absorption:
Even if the material has no impurities, the material itself may absorb some light energy. This is called intrinsic absorption
(2) Scattering:
Since glass is a heterogeneous mixture of many oxides like SiO2, P2O5 (Phosphorous pentaoxide) etc., the composition of the molecular distribution varies from point to point, Hence due to the in homogeneity in the material there will be sharp variation in refractive index value inside the glass over a distance
(3) Radiation Losses:
Because of the bending of the fiber during installation, which are known as macroscopic bending, the curvatures in the fiber also leads to attenuation. Bending due to uneven forces on the interface leading to change in the refractive indices of core and clad also result in microscopic losses
Types Of OFC
Working: Transmitter block:
1. Analog information such as voice of a telephone user gives rise to electrical signals in analog form in the transmitter section of the telephone.
2. These electrical signals are transformed into optical signals with the help of optical transmitter
3. It is modulated and carried by the light emitted by an optical source such as LED or Laser diode.
4. This optical signal is then fed into the fiber
2. These electrical signals are transformed into optical signals with the help of optical transmitter
3. It is modulated and carried by the light emitted by an optical source such as LED or Laser diode.
4. This optical signal is then fed into the fiber
Working: Receiver block:
1. As a final point the receiving end, the optical signal from the fiber is fed into a photodetector.
2. The photodetector detects the optical signal and convers it to pulses of electric current.
3. Same information will be received as output from the receiver.
4.This is how the information is transferred from one end to other in an optical fiber communication system
2. The photodetector detects the optical signal and convers it to pulses of electric current.
3. Same information will be received as output from the receiver.
4.This is how the information is transferred from one end to other in an optical fiber communication system
ReplyDeleteIn the world of technology Optical Fiber Communication Fiber is the first preference over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances. C3 Pure Fibre is committed to fulfil your communications and information technology needs.