LASER DIODE LASER DIODE INTRODUCTION Laser Diode (LD) is a semiconductor device with p-n junction which emit laser radiation by applying a current in forward direction. The term laser is an acronym that stands for "Light Amplification by Stimulated Emission of Radiation". The basic operating mechanisms of laser diodes are similarly based on the electrical and optical properties of p-n junctions and semiconductor materials. Laser diodes are devices emitting coherent light produced in a stimulated emission process whereas LEDs under injection excitation emit light produced in a spontaneous emission process. The light emission process in laser diodes is therefore more complicated than that in LEDs. The materials used in laser diodes are quite similar to those used in LEDs, and the lasing wave length ranges from the visible to the infrared wave length range depending on the material of the active layer. The infrared 780 nm-band AlGaAs/AlGaAs and visible 635~650 nm-band AlGaInP/AlGaInP material systems are commonly used. Typical laser diodes emitting visible light are composed of III-V compound semiconductors, but some II-Vi compound semiconductors such as (Zn, Cd)Se/ZnSe are also used in laser diodes emitting visible light. On the developmental stage of laser diodes, continuous-wave(cw) lasing at room temperature was achieved in an AlGaAs/GaAs double-hetero structure has been a common one for laser diodes. FEATURE AND APPLICATION Feature - The product is a semiconductor device with p-n junction which emit laser radiation by applying a current. - The product is widely used in IT/AV/Industrial application. - Lasing wave length of this products are 780nm, 650nm and 635nm. Application - Pointer - Laser Printer - Barcode Scanner & Measuring Instrument - Data Storage & Optical Pick-up : CD-P, CD-ROM, CD-RW, DVD-P, DVD-ROM -1- LASER DIODE STRUCTURE -2- LASER DIODE PART NUMBERING SLD 1 650 2 18 2 7 1 X 4 5 6 7 3 1 Samsung Laser Diode 2 Wave Length 3 Package Type 4 Optical Power 5 Operating Temperature 6 Pin Configuration 7 Suffix 1 Abbreviation of SAMSUNG Laser Diode 2 Wave Length Symbol Wave Length 635 635 650 650 780 780 3 Package Type Symbol Package Type 09 9.0 (TO-9 CAN) 18 5.6 (TO-18 CAN) 38 3.8 Small Package The suffix 'F' symbol shows the lead-frame mold type package. (Example: 78018261F) 4 Optical Power Symbol Optical Power 2 5 3 7 8 50 9 90 -3- LASER DIODE 5 Operating Temperature Symbol Optical Temperature 4 4 5 5 6 60 7 70 6 Pin Configuration Symbol LD Lead PD Lead 0 anode cathode 1 anode anode 2 cathode anode Drawing 7 Suffix This symbol shows the derivative parts. -4- LASER DIODE PACKAGING Tray Packing 168 o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Tray Side Marking : (Ex.) 48 SLD65018371 LOT : 305-1 - Tray Packing Amount : 100EA LD/TRAY - Tray Side Lot No. Marking : (Example) Symbol 3 05 Manufactured Month Meaning (ex) 3 : March A : October C : December - 1 MOCVD (Epitaxial Growth) Wafer No. Batch No. Box Packing Inside Box Outside Box 362 166 LASER DIODE 240 LASER DIODE 256 336 350 - Inside Box Packing Amount : 60EA TRAYS/INSIDE BOX (10EA : Capping Trays) 5,000EA LD/INSIDE BOX - Outside Box Packing Amount : 2EA INSIDE BOXES/OUTSIDE BOX 10,000EA LD/OUTSIDE BOX -5- LASER DIODE Labeling Top View ESD Warning Label SLD65018371 Side View Customer P/N Customer P/N Customer P/N Customer P/N Customer P/N Semco P/N Customer P/N Production Lot Number -6- LASER DIODE APPLICATION MANUAL (OPERATIONAL ATTENTION) Operating Characteristics Laser Diode (LD) is a semiconductor device with p-n junction which emit laser / strong coherency / radiation by applying a current in forward direction. However, in difference from usually semiconductor diodes LD have the next peculiarities: 1. LD usually operates at operation current 20~40mA for a low power LD and 80~120mA for a high power LD and low applied forward voltage (usually ~2). But, very important peculiarity of LD is high current densities (~2000~4000A/cm2) during LD operation. Therefore, LD operation generates a significant heat thin active layer. 2. In normal operation mode, LD has a relatively small volume for laser output power (3~7mW for low power LD and 25~220mW for high power LD). But, they have a very high density of laser radiation in a active layer and on output mirror facet (~1.0MW/cm2 and more). Therefore, there is a optical power limit caused by optical damage of output mirror facet / COD (Catastrophic Optical Damage) /. Regular Lasing P (c) (b) (a) Operating Power Regular Lasing After COD o COD w After COD Low Power e r Ith High Iop Iop [ Forward Current (mA) ] Fig. 1 COD (Catastrophic Optical Damage) Fig.1 shows us typical COD phenomenon of laser diode. When you operate LD after occurrence of COD, operating current at a specific power would be much higher than before COD -Fig.1(b)-. In the worst case, laser power could not reach a required power due to COD -Fig.1(c)-. When you drive LD, please pay attention to LD operation under COD power level. 3. LD has a very quick electrical and light response (lower than a few nano-second and less). In connection with these features LD are extremely susceptible to damage caused by current surges. It must be stressed here that even an instantaneous application extra pulse current causes a rapid LD's deterioration. Whenever, You handle LD, please pay strict attention to the following precautions. -7- LASER DIODE Electrostatic Surge Prevention It is necessary to strike that LD are even more sensitive to electrostatic discharge than Si-based Laser MM C=200pF semiconductor chips and require more careful Diode preventive measures. COD also could be happened by small surge due to electrostatic discharge. Fig. 2 shows us a static electricity test Fig. 2 Static Electricity Test Circuit circuit of Samsung. When shipping the laser diodes, they would be inserted in anti-static bags to prevent electrostatic charging by transportation. D Example of a typical workbench for operation with B Laser Diode Fig. 3 : D A 1. Ground work tables and floors using C conductive table mats and floor mats; 1 MOhm 2. Ground operators using conductive wrist E 1 MOhm bands; 3. All used tools as well as soldering irons A- Conductive floor mat B- Conductive table mat should be ground C- Antistatic shoes 1 MOhm D- Wrist strap E- Grounded soldering iron The grounding should be connected through a Fig. 3 Workbench for LD Operation resistor of approximately 1. Precautions for Current Driving Circuits LD AC100V 1 2 1- AC Noise Filter; 2- Slow Starter; 3 3- APC Driver Fig. 4 General LD Operation Circuit 1. While operating, LD can be easily damaged by surge currents which may occur during power on and off of the drive circuit or while adjusting the optical power output. 2. If possible, for standard testing process, we recommend to use the special industrial laser diode current driver, for example, the Melles Griot current source 06 DLD 201 or other type. 3. When you use nonindustrial self designed drivers, please make it sure that the spike current generated in on-off switching of power supplies does not exceed the maximum LD operation current. It is recommended to insert an appropriate filter consisting of a appropriate CR circuit -8- LASER DIODE or other slow start circuit when chattering or overshoot shown in Fig. 4. Care must also be taken to prevent surge currents from entering the circuit from external sources. Use an AC noise filter. In Po Output Laser Power pulse mode operation, overshoot in Maximum optical power output is sometimes observed. Power Rating In this case, try to suppress the overshoot or lower the overshoot power level below t 0 Ith the maximum LD operation current shown in Fig. 5. Pumping Pulse Current t 4. Make all electrical connections secure. An open or short circuit while the LD is on, Fig. 5 LD Pulse Mode Operation will result in deterioration. It is desirable to use shielded cables. 5. Use a reliable control for setting the operation current. Improper contacts may result in current surges. 6. While LD is powered up, don't touch probes from a oscilloscope or volt-meter against the circuit or LD terminals. 7. Don't CONNECT OR DISCONNECT the laser diode terminals while the POWER is ON. Heat Diffusion Precautions 1. All main LD's parameters depend on a temperature. Because of LD in operation during generation of heat at the p-n junction/ active layer/ it is necessary to provide a good heat conduction mechanism. Usually, LD chip is mounted on a heat sink within the package to facilitate effective heat diffusion. Because the heat sink conducts the generated heat to the package flange, it is advisable LD to attach a heat radiator to the LD package flange for better heat diffusion. Thermal contact between the package flange and the heat radiator plate must be good. Furthermore heat diffusion also depends on the design of the radiator plate, i.e. , shape, size and material. An appropriate design is required for each industrial application. 2. Ineffective heat diffusion can cause a positive feed back of driving current and limit the usability of the LD. Namely, high temperature of LD package reduces an optical output power below an expected level, which requires higher driving current to maintain the nominal output. As a result, this raises the temperature and requires more higher current. Thus excessive driving current can destroy LD. -9- LASER DIODE On the Safety of Laser Light Avoid to look into the laser light directly or directly D AN G ER ! V is ib le L a s e r R a d ia tio n A v o id D ire c t E y e E x p o s u re CLASS 3B LASER PRODUCT through an optical system. It is very DANGEROUS! Samsung red and IR laser diodes correspond to the class III B of the International Radiation Standard of the Laser Products. Although the typical optical output power of Samsung low power laser ranges from a several mW to 5mW, their power density can reach 1/. For observing laser beam safely, you always have to use safety goggles that block infrared rays. - 10 - LASER DIODE NOTICE Electrical & Optical Parameters & Definitions Parameter Symbol Output optical power Pop Definition Typical optical output power in pulse or CW mode. Up to this output level, there are no kinks in the Light- Current curve. The forward current through the LD which necessary for the LD to Operating current Iop produce its specified typical optical Operating voltage Vop Wavelength p output power The forward voltage across the LD by forward operating current The wavelength of the laser spectral line with the greatest intensity The value of the incremental change in laser beam Watt-ampere power for an SE incremental change in forward current above the threshold current. / Slope / Efficiency The monitoring photodiode current Monitoring current is proportional to LD laser output Im power [ at a specified reverse bias voltage ] The forward current value at which the LD begins to produce laser Threshold current Ith output The Laser beam divergency // laser beam's full angular at the half-maximum intensity points(FWHM), measured in horizontal plane [ parallel to the LD p-n in horizontal plane junction plane ] The Laser beam divergency laser beam's full angular at the half-maximum intensity points(FWHN), measured in vertical plane in vertical plane [ perpendicular to the LD p-n junction plane ] Maximum admissible reverse bias voltage, which may be applied to LD reverse voltage VR the LD without a damage Maximum admissible reverse bias voltage, which may be applied to PD bias voltage VRp the monitoring PD without a damage Operating temperature Topr Storage temperature Tstg Range of the case temperature within which LD may be safety stored Range of the ambient temperature within which LD may be safety stored Forward current If Current through the forward biased LD Forward bias voltage Vf Laser diode voltage by an applied forward bias - 11 -