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VI Characteristics of Optical Laser Diode


To study fiber optics Laser Diode voltage vs current (VI) characteristics.


Apparatus Required



The semiconductor junction laser is also called an injection laser because its pumping method is electron-hole injection in a p-n junction. The semiconductor that has been extensively used for junction is the Gallium Arsenide. The features of semiconductor lasers are

  • Extreme mono chromaticity
  • High directionality

Three basic transition process related to operation of Lasers are

  • Absorption
  • Spontaneous emission
  • Stimulated emission

The starting material is an n-type GaAS doped with silicon in the range of 2-4x10 18 cm -3.A p-type is grown on the wafer by the liquid-phase epitaxial process. The wafer is lapped to a thickness of 75 μm and surfaces are metalized. The wafer is then cleaved into slivers. The next step is to evaporate are flective coating onto one of the cleared facts of the silver so that the laser can emit from only one facet.

Working Principle Diagram


  • Connect +12V adapter Laser Diode module.
  • Measure the series resistance R.
  • Switch (sw1) ON Laser Diode Module and Multi meter.
  • Connect the Multi meter probe, positive to P1 and negative to Ground P2.
  • Now we get a DC voltage output on Multi meter and vary the pot meter min to max range (0V to 5V).
  • Connect P1 and P6 test point, P2 and P7 test point using patch chord.
  • Keep pot meter at minimum position.
  • Now vary the pot meter min to max and note down the reading of Resistor across voltage (Vr) and Diode across voltage (Vd).
  • Tabulate all the readings in below tabular column.
  • And plate voltage vs current curve.

Tabular column

Series Resistance R = 150Ω



Resistor across Voltage

( Vr) in V

Diode across Voltage

(Vd) in V

Diode current

(Id=Vr/R) in mA


Model Graph


Thus the VI characteristic of Optical Laser Diode was plated.