Pulse driven laser diode
Introduction
The relatively high peak power and work efficiency make pulsed laser diode the ideal choice for the solid-state laser pump and range determination of such applications.
Pulsed laser diodes usually work at a relatively low level, so the average power is low, which can reach a higher peak Power.
So it's not very high.
On the other hand, the continuous wave laser diode is higher than the pulse laser.
This is because the thermal resistance of the device increases the junction temperature significantly during the continuous wave operation.So continuous wave laser diode generally needs to be good Heat sink encapsulation and/or refrigeration with thermal power.Pulsed laser diode is a powerful analytical tool for testing its quality and thermal efficiency.
Why pulse a continuous wave laser diode?
The ability of pulse-driven continuous wave laser diode in low duty ratio is very useful in diode evaluation.Its application can be divided into two broad areas.The first is the pre-packaged pass/fail test;The second is the device characteristic evaluation.Both applications take advantage of the impulse driveA laser diode does not produce a lot of heat.The test and characteristic evaluation can be completed under the minimum heat effect.
Prepackaged test
For this kind of application, the pulse of low duty ratio can be used for wafer or bar test after semiconductor manufacturing process.A single light measurement or L/I curve (light output vs. drive current) can be used to "pre-filter" the wafer after processing.It can remove defective wafers before the cost of bandit cutting and packaging operations, and establish the yield and performance of the manufacturing process.(note that the relative measurements of these tests are more important than absolute precision.)
Characteristics of the test
The second application area of pulse testing is the characterization test for packaged devices.Many industrial documents relating to laser diode characteristics are recommended for continuous wave testing as well as pulse wave testing.(this is the case with the technical consulting document ta-tsy-000983, which was published in the study titled "the reliability assurance practice of optoelectronic devices.")By comparing pulse and continuous wave mode, the parameters such as output power, wavelength and threshold current can be measured.The L/I curve of a typical laser diode is shown in figure 1.These curves show both the low duty ratio pulse mode and the continuous wave mode.The increase of the threshold current of the continuous wave curve and the slight decrease of the slope efficiency (compared to the pulse curve) are mainly caused by the temperature rise caused by the thermal resistance of the device.(the pulse width of the pulse L/I curve is generally 100 to 500 ns, which accounts for less than 1% of the air ratio, so the thermal effect is not obvious.)The comparison of pulse and continuous wave L/I curves can also be used to test the heat transfer quality of the chip/package interface.The temperature coefficient can be determined by calculating the equivalent temperature rise in continuous wave mode.This test method is much faster than the temperature cycle.There is also the possibility that the difference between continuous wave and pulse L/I curve may indicate poor connection or leakage of the chip, which usually means that the laser is of poor quality.Absolute precision is important for these test applications.Because of the need to modify the continuous wave performance, the pulse drive amplitude must be very accurate.Repeatability is also important for any test application.