Yan Joe LeeENGN1690GOAL: Measure the I-V and I-P curves for a LED and a laser diodeAnticipated Problems/Required Steps:1. Setup correct equipment to measure voltage and power.2. Control current supply to the setup.3. Measure voltage drop across LED/laser diode. 4. Direct laser beam/light to phtotodiode to measure power. 5. Automate measurement process to produce high quality I-V and I-P curves.

Proposed Solution/Procedure:A) To measure current-voltage characteristics1. Connect the laser diode/LED to the Agilent E3631A Variable Power Supply in series with a resistor. 2. Set the power supply to provide a drive current in mA. 3. Use a code to increase the current by steps of 1mA. Stop at 50mA for both LED and laser diode (value determined by referencing data sheet). 4. Measure the voltage across the laser diode/LED using the digital multimeter. Alternatively, measure the voltage across the resistor and the voltage drop across the LED/laser diode will be the voltage supplied voltage drop across resistor. 5. Use a code to automate the current and voltage measurement process and produce an I-V curve.

B) To measure current-output (power) characteristicsGeneral Procedure:1. Connect LED/laser diode to power supply. Set the power supply to provide a drive current in mA.2. Connect the PD300 photodiode sensor to the Ophir Vega Laser Power meter. The photodiode sensor measures laser power and displays is on the power meter. 3. Turn on the power supply. Direct the light emitted by the LED/laser diode to the photodiode sensor. Since light emitted by a LED diverges significantly, the light has to be focused before taking measurements using the photodiode sensor. As suggested in the Thorlabs website aspheric condenser lens can be used to collimate LED light emission. A second lens can be placed after the first lens to focus the light on the photodiode sensor. However, significant side emission cannot be collimated by lens. In this case a parabolic mirror can be used to collimate the side emission. Light emitted by a laser diode is easier to direct to the photodiode sensor because it is collimated. In both cases (LED and laser diode) the angle dependence of the PD 300 photodiode sensor should be taken into consideration. The sensitivity and accuracy of the sensors depends on the angle of incidence the beam should be aligned to hit the photodiode sensor as close to normal incidence as possible (using mirrors etc.)Power supply-Controls current

LED/laser diode

Multimeter- voltage measurements

Resistor

A) Measuring current-voltage characteristics

Photodiode sensorLED/laser diode

Lenses, mirrors etc.Power meterPower supply-Controls current

B) Measuring current-output characteristics