Measurement of attenuation loss in Optical Fiber



Objective : 
The aim of the experiment is to study various types of losses that occur in optical fibers and measure the loss in dB of two fiber patch cords.

Introduction :
The optical Fiber Loss has been designed for fundamental studies on optical fibers and optical fiber communication. The experiments included for study, introduce the student to basic concepts of this state of art technology in a simple style. The setup includes all the accessories to conduct experiments covered in the manual.

The three major Fiber optic components / instruments, viz, the optical fiber patch cord, LED source and the Optical Power.

Apparatus :

  1. One - meter PMMA Fiber patch cord (Cable 1).
  2. Five - meter PMMA patch cord (Cable 2).
  3. In – line SMA adaptor.
  4. LED source.
  5. Optical power meter.

A.   Specifications of Fiber Optics Cable:

  1. Core material :  Polymethyl Methacylate ( PMMC )
  2. Cladding material :  Fluorinated Polymer
  3. Fiber structure :  Step index type
  4. Core / cladding diameter :  960 µ / 1000 µ
  5. Core refractive index :  1.492
  6. Cladding refractive index :  1.405 to 1.417
  7. Numerical aperture :  0.5 ( typical)
  8. Acceptance angle :  55 to 60 degrees
  9. Attenuation at 660 nm :  Typical 0.3 dB per meter
  10. Jacket material :  Polythene ( Black ); 2.2 mm OD.

Loss in Patch cords ( Nominal values )

  • One meter :  1.3 dB
  • Five meters :  2.5 dB

 
B.    Fiber optics 660 nm LED used in LED Source
The Fiber Optics LED used in LED source. Operating at 660nm, it couples 40 to 50 µ W of power into a 1000 micron PMMA fiber. The LED is terminated with an optical SMA connector. The LED is suitable for speed above 500 KHz.
Specifications of Fiber Optics LED
1.    Material                :    GaALAs
2.    Wavelength            :    660nm
3.    Spectral Line Width        :    45nm
4.    Forward voltage ( Vf)        :    1.7 at 10 mA
5.    Reverse voltage ( Vr)        :    5 Volts
6.    Capacitance            :    100 pF
7.    Forward current ( max)        :    30 mA
8.    Optical power            :    30 – 40 µW at 10 mA
9.    Turn –on / Turn – off time    :    < 800 ns
10.    Termination            :    SMA 


C.    Fiber Optic Phototransistor  used in Optical Power meter
The Fiber Optic Phototransistor used in Optical power meter. The device has a responsivity of 50 µA / µW of incident light at 660 nm, when coupled to a 1mm PMMA fiber. The device is terminated with an optical SMA connector. The Photo transistor is suitable for speeds upto 100 KHz.

Specifications of Fiber Optics Phototransistor:

1.    Peak Responsivity        :    850nm
2.    Spectral range            :    400 to 1100nm
3.    Dark current            :    100 nA
4.    Spectral Response        :    50 µA / µW  at 660nm
5.    CE breakdown voltage        :    30 V ( Min)
6.    EC Breakdown Voltage        :    5 V(Min)
7.    VCE (sat)                :    0.2 V (typical)
8.    Rise / Fall time            :    5 µs ( typical)
9.    Connector            :    SMA
 


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