What is Fiber Optics?

What is Fiber Optics?

Optical fiber is a next generation Transmission media . It is made of pure glass and Refractive index is changed by adding impurities in the glass. It is a long thin thread of glass through which information,signals etc can be passed in the form of light.


Types of Optics fiber:-

mainly two types of fiber;-
1. Single Mode.
2. Multimode.
     (a) Step index.
     (b) Graded index.
Optical fibers also classified by its reflective index profile are-
1. Single Mode--- Step Index.
2. Multi Mode --- Step Index.
3. Multi Mode --- Graded Index.

Single mode fiber d~6-8 micro meter
Multi mode fiber d ~ 50-100 micro meter.
Cladding diameter =125 micro meter.

MM has large dispersion.

SM has no dispersion.

In Single Mode Fiber light launching is very difficult because the size of the core diameter is very small about 6-8 micro meter.

MM, step index optical fiber only for academic interest.will be used in laboratory

MM, Graded index fiber for Local area network(LAN)

Most of the time fiber is single mode used in everywhere. It is the building blocks or backbone of telecommunication and long distance communication with ultra-high  bandwidth (Thz), low loss ,security of transmission and many more  offered by Single mode fibers. 



Electromagnetic Spectrum:-
      -----------------------------------------------------------------------------
      |                                                                                                        |
      --------|----------------|--------|-------------|-----------------|--------------
lambda     10 m             1 m       10 cm           1 mm             1micro m
frquency 30M           300M    3G               300G             300T
                 |<--Cox-cab-->|      |<-wave guide-->|           |<--optical fiber-->|

Types of Transmission medium:-

1. Twisted pair(point to point).
----telephone lines.
----low data rate.
----high EMI.
----lossy at Rf.
2. Coaxial Cable(point to pint).
----LAN.
----data rate few Mbps.
----low EMI.
----moderate loss.
3. Microwave link(point to point).
----long distance.
----large B/W.
----Line of sight.
----high free space loss.
4. Satellite communication(point to multi point).
----larger B/W.
---data monitoring.
---large delay.
---mobile environment.
---moderate life.
5. Fiber Optical Cable
---Larger B/W.
---Avoid EMI.
---Low loss in media.
---Light weight.

Satellite versus Fiber optics:-

1. Point to multi point   1. Point to point.
2. B/w GHz                    2. B/w THz.
3. Maintenance free      3. Needs maintenance.
4. Short life 7~8 yr        4. Long life.
5. No Upgrade ability   5. Upgradable.
6. Mobile,air, sea             6. On ground only.

Two will coexist due their complementary nature.

Basic of Light

What is light?

Light is an electromagnetic radiation.

Characteristics of Light:-

1. Intensity
2. Wavelength(color).
3. Spectral Width(purity of color) that is directly related to the data rate.
4. Polarization.
               ---Linear.
               ---Circular.
               ---Elliptical.
               ---Random.
Where the difference between reflecting index of core and cladding is small then we have called Linear Polarized mode(LMP). For a practicle fiber the model representative could be in the form of Linear polarized mode.

Light can be considered  as a three types of model:-

1. Ray Model.
2. Wave Model.
3. Quantum Model.

Ray Model does not show what is happening in cladding side.

Propagation of light depends upon the Wavelength.

Advantages of Optical fiber cable:-

1. Ultra-high bandwidth.
2. Low loss.(0.2 dB/km)
3. Low EMI.
4. Security of transmission.
5. Low manufacturing cost.
6. Low Weight,Low volume.
7. Point to point communication.

I like pint 1 and 2 of advantages.

Three Wavelength is :-(a) 800 nm  (b) 1300 nm (c) 1550 nm is mostly used in optics fiber communication.

Types of Optical Amplifier:-

1. Semiconductor Amplifier.
2. Erbium doped Fiber Amplifier.

Comparison of  both Amplifier:-

      Semiconductor                EDFA
1.1300 or 1500 nm band    1. 1550 nm only.
2. High power output       2. Low cross talk.
3. Higher coupling loss    3. High gain.
4. Integrable                     4. Low coupling loss.
5. Non-Linearity              5. Low noise.

Fiber Geometry

An Optical fiber consists of a core of optically transparent material usually silica or borosilicate glass surrounded by a cladding of the same material but a slightly lower refractive index. Fiber themselves have exceedingly  small diameters.cross section of the core and cladding diameters of commonly used fibers. The diameters of the core and cladding are given below.
Core (micro meter)  cladding(micro meter)
         8                                 125
        50                                125
       62.5                              125
       100                               140
Fiber sizes are usually expressed by first giving the core size followed by the cladding size. Thus, 50/125 means a core diameter of 50 micrometers and a cladding diameter of 125 micrometers

Structure  of fiber

The reflective index of the Core is larger compare to the Cladding.


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