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Engineering Physics Lab Experiments

To study V-I characteristics of LED and laser diode



Aim

To study V-I characteristics of LED and laser diode

Apparatus Required:

LED and laser trainer kit, digital multimeter, power supply.

Principle

The light emitting diode (LED) and Laser diode are popular electronic devices which work on the principle of electroluminescence.

Characteristics of LED and LASER diodes:

Procedure:

V-I characteristics of LED

  1. Switch on the power supply.
  2. Adjust the set P0 Knob to extreme anti clock position to give minimum output power and observe the power in the power meter.
  3. Slowly turn set Po knob clockwise a little and then note load voltage (V L) across the LED, output terminal also note the readings in ammeter I L
  4. Repeat step 3 for noting various values of voltage and current
  5. Plot graph of VLL and I L

Current-Power (I-P) Characteristics of LED and LASER diode

The I-P characteristics of laser diode may be well utilized for the determination of quantum efficiency of the light emitting device the differential slope efficiency (dt/dl) is the slope of the L-I characteristics at a particular current.

The light emitted by LED is coupled to the power meter through the optical fiber cable. The power received is measured by the digital millimeter. The driving current is supplied using a continuous variable linear regulated DC power supply of 0- 32 volts through a series resistance of 100Ω.

P-I characteristics of LED

  1. Adjust the set Po knob to extreme anticlockwise position to give the minimum output in the power meter and observe the output power in the power meter.
  2. Slowly turn the set Po knob clockwise a little and then note current (I L) through the LED terminals. Also note the reading in the power meter (P O).
  3. Repeat step 2 for noting various values of I L and P O
  4. Plot a graph between I L and Po take closer reading to plot a fine graph.

To study the I-P characteristics of LASER :

The above procedure can be followed with change to laser to study the I-P characteristics of laser.

Observation:

V-I characteristics of LED

S.No Voltage (V) Current (I) mA
1
2
3

I-P characteristics of LED

S.No Current (I) mA Optical power (mW)
1
2
3

V-I characteristics of LASER

S.No Current (I) mA Optical power (mW)
1
2
3

I-P characteristics of LASER

S.No Current (I) mA Optical power (mW)
1
2
3

Precautions:

  1. Adjusting of knob should be done properly.
  2. Increasing of voltage to LED and laser diode should be done gradually.

Result:

The laser and LED characteristics are observed with different current, voltage and power readings and the graphs are drawn.