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1/19/2011 4-1 ECE 415 EXPERIMENT NO. 3 CHARACTERISTICS OF LIGHT EMITTING DIODES AND INJECTION LASER DIODES PURPOSE : To determine the LI characteristic and the far-field radiation patterns of light emitting diodes (LEDs) and GaAlAs (infrared) (or InGaAlP (red)) injection laser diodes (ILDs). REFERENCES : 1. C. L. Chen, , Irwin, (1996), Chapter 4. 2. S. von Fe hren, “Red - light diode lasers”, Elektor Electronics USA , April 1992. (attached) 3. Electrical connections, power supplies etc. from an unknown source. WARNING : Don't stare at the ILD beam at close range directly . You can't see the infrared (IR) light. But the IR (or red) light can certainly damage your eyes! PROCEDURES : NOTE : 1. The center conductor of the coax may be positive or negative, depending on the particular LED and ILD packages. Refer to the label of the diode mount. 2. The maximum operating current for a LED and the threshold current for an ILD are different for diodes of different brand and different model. Ask your instructor for the maximum operating current and threshold current before proceed any further. I. LED: 1. Place an index card or a sheet of thick paper in front of, and at a distance of a few centimeters from, the LED. Gradually increase the driving current. Don’t exceed the current limit specified by your instructor. Use a Find-R-Scope to observe the beam pattern displayed on the paper. Does the LED emit a circular beam?
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1/19/2011 4-2 2. Place a power meter or a photodiode 3 to 5 cm from the LED. Use a lens with a short focal length (5 cm or less) to collect light for LED (Figure 1). Align the detector with respect to the LED with the aid of a Find-R-Scope. 3.
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