Aim

To Study the Characteristics of Optical Photo Diode in Zero Bias

Apparatus Required

• Fiber Optics Light Emitting Diode Module – 01
• Fiber Optics Photo Diode module – 01
• Plastic Fiber cable 1 meter – 01
• Multi meter – 01
• Adapter +12V/ DC – 02
• Patch Chords – 04

Principle of Optical Photo Diode

Photodiodes are frequently used photo detectors. They are semiconductor devices which contain a p–n junction, and often an intrinsic (undoped) layer between n and p layers. Devices with an intrinsic layer are called P-I-N or PIN photodiodes. Light absorbed in the depletion region or the intrinsic region generates electron–hole pairs, most of which contribute to a photocurrent. The photocurrent can be quite precisely proportional to the absorbed (or incident) light intensity over a wide range of optical powers.

Operation Modes

Photodiodes can be operated in two very different modes:

Photovoltaic mode

In this process like a solar cell, the illuminated photodiode generates a voltage which can be measured. However, the dependence of this voltage on the light power is nonlinear, and the dynamic range is fairly small. Also, the maximum speed is not achieved.

Photo conductive mode

Here, a reverse voltage is applied to the diode (i.e., a voltage in the direction where the diode is not conducting without incident light) and measures the resulting photocurrent. (It may also suffice to keep the applied voltage close to zero.) The dependence of the photocurrent on the light power can be very linear over six or more orders of magnitude of the light power, e.g. in a range from a few nanowatts to tens of milliwatts for a silicon p–i–n photodiode with an active area of a few mm2. The magnitude of the reverse voltage has nearly no influence on the photocurrent and only a weak influence on the (typically small) dark current (obtained without light), but a higher voltage tends to make the response faster and also increases the heating of the device.

Zero Bias Operation

Procedure

• Connect +12V adapter LED module and Photo Diode module.
• Switch (sw1) ON the LED Module and Multi meter.
• Connect P1 and P6 test point, P2 and P7 test point using patch chord in LED module.
• Vary the DC Source at maximum position in LED Module.
• Connect Fiber cable between LED and Photo Diode module.
• Now measure the series Resistance R in Photo Diode module.
• Switch (sw1) ON the Photo Diode module.
• Connect P3 and P4 test point, P4 and P6 test point using patch chord.
• Now note down the reading of Resistor across voltage (Vr).
• Calculate Diode current (Id), Dark current Id = Vr/R

Result

Thus the characteristic of Optical Photo Diode in Zero bias was calculated.