US20030011357A1 - Bar tester - Google Patents
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- US20030011357A1 US20030011357A1 US09/738,108 US73810800A US2003011357A1 US 20030011357 A1 US20030011357 A1 US 20030011357A1 US 73810800 A US73810800 A US 73810800A US 2003011357 A1 US2003011357 A1 US 2003011357A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/0014—Measuring characteristics or properties thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
Definitions
- the present invention relates generally to testing of semiconductors, and particularly to testing of laser bars, which are an intermediate structure in the manufacture of laser devices.
- Laser devices such as semiconductor diode lasers or laser chips, have become important commercial components. They are used in a wide variety of applications ranging from the readout sources in compact disks to the transmitters in optical fiber communication systems. While new applications in high-speed telecommunication networks continue to emerge, how to ensure that diode lasers are reliable and manufacturable is the most challenging issue.
- One proven approach to this issue is to deploy tight quality control by using laser bar testing systems that characterize diode lasers in many aspects and in an efficient manner.
- Diode lasers are manufactured on wafers or substrates which are processed and further divided into sections or quarters.
- the sections are further divided into laser bars by breaking or cleaving the sections along the scribe lines, to form facets along the elongated sides of the sections.
- the laser bar contain many laser diodes.
- the first stage where these lasers exhibit both electrical and optical characteristics is when laser bars are formed. Therefore, it is desired to characterize lasers at this early stage by probing and testing all the lasers when they are still in the form of a laser bar.
- the laser devices that do not meet specifications will be scrapped before entering into further labor-costing or time-costing stages, i.e. packaging and life-testing or bum-in.
- a full procedure of bar testing includes six measurements for each laser that is being probed: front-facet light versus current, back-facet light versus current, voltage versus current, horizontal far field pattern, vertical far field pattern and an optical spectrum analysis.
- a system that performs one or all of these measurement functions is called a laser bar tester.
- One aspect of the present invention is a tester for characterizing individual ones of a semiconductor laser devices of a laser bar, wherein the tester includes a holder for securing the laser bar in a fixed position.
- a movable measurement system is provided for characterizing the individual ones of the semiconductor laser devices as a function of the at least one relative direction.
- the present invention includes a pair of detectors, each moving in arc paths around the laser bar to sample the far-fields.
- FIG. 1 is a schematic view of a laser bar tester, in accordance with the present invention:
- FIG. 2 is a blow-up perspective portion of the vacuum held and temperature controlled laser bar assembly, held laser bar, and prober of FIG. 1, with reference to the far-field scans of FIG. 1, in accordance with the present invention
- FIG. 3 is a blow-up perspective portion of the vacuum held and temperature controlled laser bar assembly and laser bar of FIG. 2, in accordance with the present invention:
- FIG. 4 is a blow-up perspective drawing of the vertically movable probe pin 241 of FIG. 3 for contacting the selected laser device at the preselected indexed position, in accordance with the present invention.
- a laser bar tester that characterizes laser bars in all categories in a fast and accurate manner is taught. Additionally, this laser bar tester system is also compact in size.
- the laser bar testing system includes a fixture for holding the laser bar, a mechanism for probing individual lasers, and individual measurement modules.
- FIG. 1 An exemplary embodiment of the bar tester of the present invention is shown in FIG. 1, and is designated generally throughout by reference numeral 10 .
- the present invention for a tester and method for characterizing individual ones of a semiconductor laser devices of a laser bar 11 includes a holder 12 for securing the laser bar in a fixed position.
- the advantages of a fixed laser bar mounting is the minimization of testing errors due to the movement of the laser bar 11 .
- other movable detector systems surrounding a fixed laser bar can be implemented, in accordance with the teachings of the present invention.
- the holder 12 includes a selective application of vacuum suction 14 applied to the laser bar 11 abutted against a suitable fixture, such as a vacuum chuck, for releasing or securing the laser bar 11 in its fixture.
- a suitable fixture such as a vacuum chuck
- Other fixed holder arrangements could include clamping or other mounting applications to form a fixed reference for measurement purposes.
- the present invention for the bar tester 10 may further include a movable measurement system 16 for moving in at least one relative direction 21 , 22 , 23 with respect to the laser bar 11 for characterizing the individual ones of the semiconductor laser devices as a function of the at least one relative direction 21 , 22 , 23 .
- the movable measurement system 16 minimizes alignment and tolerance problems and provides a fast, flexible, and accurate characterization of the laser bar 11 .
- the movable measurement system 16 includes a prober or probing fixture 24 for selectively probing a selected laser device of the laser bar 11 in a selected fixed position, defined by the probed position.
- the movable measurement system 16 further includes a first detector, in the form of a photodetector or back-facet power detector 226 feeding signals to a back-facet power monitor module 26 .
- this first detector 226 is preferably mounted with the prober 24 in a fixed relative position with the selected laser device for collecting a back-facet power measurement of the laser device.
- a slidable integrating sphere 28 is connected to a slider 32 for laterally moving, in the horizontal direction 23 , towards the selected laser device for collecting a front-facet power measurement as measured by a power meter 34 whose power measurements are integrated by the sphere 28 .
- a controller 36 is preferably used to automatically control, by programmable computer software, the sequencing or indexing and movements of the measurement system and of the initially aligned position of selective laser device of the laser bar 11 in a controlled temperature environment.
- the same movable measurement system 16 is capable of making all other optical measurments by selectively using appropriate detectors and moving the detectors around the a selected laser device 111 of the laser bar 11 , as seen in FIGS. 2 - 4 , to make the desired measurement.
- a pair of second detectors 41 and 42 is further provided for collecting a far-field power measurement of the selected laser device.
- a first motor-driven arm 43 moves a first one 42 of the pair of second detectors in a horizontal arc path 22 relative to the selected laser device to sample the horizontal far-field.
- a second motor-driven arm 44 moves a second one 41 of the pair of second detectors in a vertical arc path 21 relative to the selected laser device to sample the vertical far-field.
- a programmable motor or another suitable motion controller 46 actuates the arms 43 and 44 .
- the arms 43 and 44 can be moved by other electrical or mechanical mechanisms.
- an optical spectrum analyzer (OSA) 52 is connected to the integrating sphere 28 and the controller 36 for providing further optical spectrum analysis, as seen in FIG. 1.
- Optical spectrum is preferably measured using a miniature fiber spectrometer based on the CCD-array silicon detector and fixed grating technology for keeping the cost of the spectrometer low while providing a reliable and sensitivive spectrometer,
- the miniature spectrometer is configured to collect data using a long integration period.
- pulsed optical signals of 5 mW peak power with 0.2% duty cycle have been measured. Because an A/D card is used to sample the signal from the CCD array, the speed is much faster than conventional spectrometers based on rotating gratings. Different miniature spectrometers may also be used for lasers operated at different wavelengths.
- the measurement system 16 automatically records wavelength of the lasers at different current levels programably supplied by a current supply 162 .
- FIGS. 1 - 4 an enlargement of the laser bar 11 of FIG. 1 is shown in FIGS. 2 - 4 , with reference to particular portions of the measurement system 16 of FIG. 1.
- a properly designed bar fixture provides a method of easy loading and unloading laser bars, a method of providing good electrical conductivity and a method of controlling temperature.
- the temperature is controlled and monitored as close to the laser bar 11 as possible.
- a reference of portions of the laser bar, in its vaccuum holder 12 , to portions of the measurement system 16 is first described to show where the measurements are referenced-off or indexed from.
- the P-contact surface 201 of the laser bar 11 is facing upward for the prober 24 to access.
- the output side or a laser emitting facet 204 of the laser bar 11 is near a stop block feature 121 located on top of a base portion 123 of the holder 12 of FIG. 1 for facilitating bar alignment while enabling measurements. such as the far-field scans along the arc paths 21 and 22 as seen in FIG. 2.
- a first one of a pair of probes of the prober 24 , the signal probe or probe tip 241 makes contact to the top surface 201 of the laser bar 11 , as seen in FIGS. 1 - 2 .
- This single reference point of the probe tip 241 will be used as the fixed reference for all optical measurements.
- the other probe makes contact to a striker plate 122 as the electrical ground.
- the probes 241 and 242 are preferably each in the form of a flexible pin, such as a pogo-pin.
- One advantage of having such a double-probe design is the minimization of microwave reflection when doing pulsed current operation for certain laser bar testing measurements.
- the striker plate 122 is on the opposite side of the stop block feature 121 to mount the bar 11 in the holder 12 between the elevated stop block feature 121 and the striker plate 122 . Plated with a layer of gold for good electrical conductivity, the striker plate 122 is physically and electrically attached to the base portion 123 of the holder by screws 222 .
- An advantage of using a separate striker plate, other than the base portion 123 of the holder for probing, is that a smaller worn-out striker plate need only be replaced instead of a complete, bigger, and more complexed holder 12 .
- the N-contact 202 of the laser bar 11 is electrically and thermally grounded to the base portion 123 of the holder 12 , preferably implemented as a gold plated fixture.
- a thermoelectric (TE) cooler 104 and a heat sink 102 are added underneath the vacuum holder 12 to control the temperature surrounding the bar 11 under testing, as seen in FIGS. 1 - 3 .
- the temperature is monitored with the temperature controller module 126 fed by the thermal signals picked-up by a thermal sensor 124 mounted inside the holder 21 for feeding-back temperature near the laser bar 11 .
- the temperature is controlled by a computer module, referenced as the temperature controller 126 , for regulating the testing temperature in the range of ⁇ 20 to 80 degrees C.
- the vaccuum holder 12 for the bar 11 of FIG. 1 is shown in more detail in FIGS. 2 - 3 .
- the laser bar 11 is preferably held by the vaccum suction 14 applied through a vacuum slot 214 in the base portion 123 of the holder or fixture 12 .
- the vacuum switch 114 of FIG. 1 By turning or activating the vacuum switch 114 of FIG. 1 “ON” or “OFF”, as controlled by the controller 36 , the bar 11 can be easily loaded to or unloaded from the holder 12 .
- four bars 11 are mounted at the same time, thus down-time due to loading/unload is minimized. For simplicity, only one bar 11 is shown in FIG. 3.
- the front edge of the vacuum holder 12 has a triangular-shaped protrusion used as a stop block feature 121 to position the laser bar 11 on the output side 204 .
- An appropriately designed tool (not shown) pushes the bar 11 against the stop block portion 121 of the holder and aligns the bar 11 into an indexable position on top of the base portion 123 of the holder.
- the height of the stop block portion 121 is preferably designed such that the active top region of the bar 11 is about 50 um above the top point of the stop block 121 to protect the laser bar from contact damage. Bars 11 are loaded to the testing system 16 in situ or in process, that is, the chuck or holder 12 is not relocated to a remote location for loading/unloading. This in situ procedure not only minimizes the down time of the system but also allows automatic loading/unloading.
- the individual lasers 111 on the bar 11 are indexed by a probing mechanism or system consisting of a horizontal motorized X-stage 152 which is supporting the laser bar holder 12 above through the use of an adapter plate 151 that is mounted to the X stage 152 and the prober 24 , already described having dual probes in a probe tip assembly, including a back-facet power monitor, that is connected to a vertical motorized Y-stage 154 .
- the X stage 152 horizontally moves the laser bar 11 which is placed on top of the X stage 152 , as seen in FIGS, 1 - 2 .
- the horizontal X-stage 152 translates the bar fixture or holder 12 with respect to the tip of the signal probe or probe tip 241 .
- the vertical stage 154 lowers the probe tip 241 to make the electrical contact and measurements are taken.
- the vertical stage 154 of FIG. 1 raises the probe tip 241 off the laser surface 201 and waits for the next laser to move in. Also controlled by the motion controller 36 , the vertical stage 154 is raised and lowered every time a specfic laser 111 .
- one of the many lasers 111 on the bar 11 is translated or indexed next, underneath the probe tip 241 for testing.
- the probe tip, as part of the prober 24 is attached only to the Y stage 154 for minimizing the movement of the laser bar 11 .
- the prober 24 is lowered to make contact and all the other detectors move around that particular laser 111 for various measurements. This procedure repeats itself until all the lasers 111 on the bar 11 are characterized.
- the probing system manages to create no scratch marks by using an inventive step-and-check or step-approximation approach.
- the software in the controller 36 that controls the probing system moves the vertical stage 154 towards the top laser bar surface 201 in small increments or small steps that get even smaller as the expected contact is approached.
- the testing software is facilitated by the controller 36 , implementable using a Pentium computer, and an ILX Lightwave semiconductor laser controller, that is also capable of performing optical tests, in the form of various modules 162 , 126 , 26 , and 34 , as seen in FIG. 1.
- the software in the controller 36 checks if there exists a close electrical loop between the laser bar 11 and the associated electronic instrument, such as whether the current supply 162 can pass a current to enable the current to be read. A contact position is obtained when such a close loop is found, for example, when a current measurement can be read.
- the controlling software in the controller 36 also calculates the parameters of the bar surface plane, such as the location of the next expected contact point, based on lasers 111 that have been successfully probed: these parameters are used to help obtain a faster contacting approach time for the rest of the lasers 111 on the bar 11 . This step-wise contacting approach also allows successful probing on rough or uneven laser bar surfaces.
- the slider 32 for the integrating sphere 28 are also aligned to the position where the probe tip 241 is lowered for making contact with a laser 111 .
- This position was determined when the system was initially setup.
- Each of many individual lasers 111 on a bar 11 is moved to that same initial setup position for test. Therefore, the proper alignment of individual laser 111 with all the detectors is preserved.
- the contacted laser bar 11 and the contacting probe tip 241 are maintained still in a fixed position.
- the optical measurements obtained include the most important characteristics for semiconductor diode lasers, such as the threshhold current measurable by knowing the value of the current supply 162 .
- Other important measurements include turn-on voltage, slope efficiency, series resistance, and front/back power ratio.
- the integration sphere 28 collects the front power. The use of the integration sphere 28 has two advantages: first, it allows measuring high optical power since the optical signal entering the sphere is scattered by the cavity walls and there is only a small portion of light that reaches the photo detector 226 in FIG. 1.
- the sphere 28 has a relatively large aperture 281 to allow easy coupling of a highly divergent optical signal from the diode laser 111 into the sphere's cavity.
- the sphere 28 is mounted on the computer controlled motion slider 32 that moves the integration sphere 28 to the lasers 111 when a front-facet power versus current test is performed.
- the back-facet power is collected by the large-area photo detector 226 (shown in FIG. 2) which is mounted on the probe assembly or prober 24 .
- the detector 226 will not be saturated by a high incident power because the back-facet of the bar 11 is usually high-reflectively coated.
- the kink-detection scheme utilizes a reduced aperture to measure a LI curve in order to enhance the occurrence of the kinks by moving in a lateral direction 23 the sphere 28 at a known distance to the laser 111 via the slider 32 .
- the measurement system 16 has the capability of continuously varying the numerical aperture 28 by allowing the aperture 281 to van, its distance from the laser 111 .
- a computer program in the controller 36 uses a binomial weighted averaging scheme, then processes the LI data to reveal the kinks.
- Another example of an optical measurement is the far-field scan which is very important in characterizing beam quality.
- Far-field patterns are defined as the angular dependence of optical intensity.
- the far-field characteristics determine the laser-to-fiber coupling efficiency.
- a semiconductor laser has an elliptical beam shape because the width of a laser waveguide is much larger than the thickness. Therefor a complete characterization of the far-field requires scanning cross the divergent beam along two orthogonal axes 21 and 22 .
- the measurement system 16 uses two mini-motor driven arms 43 and 44 to move two pin-size photo detectors 41 and 42 , one on each arm 43 and 44 , to sample across both the horizontal and vertical far-fields 21 and 22 .
- An encoder on the motor of the motion controller 46 allows positioning the detectors 41 and 42 with high accuracy (within 0.02 degree) and a preamplifier each in the detectors 41 and 42 guarantees a large dynamic gain range for each of the detectors 41 and 42 .
- the size of each of the detectors 41 and 42 is chosen to be about 100 um in diameter, and the distance from one of the detectors 41 or 42 to the laser emitting facet 204 is about 60 mm.
- the angular far-field resolution is estimated to be about 0.2 degree.
- far-field patterns Another application of far-field patterns is for kink-detection.
- the far-field patterns become asymmetric. Therefore, far-field measurements can first be taken at different current levels and any changes in the far-field patterns can be associated with kinks.
- the control software in the controller 36 automatically executes this far-field and kink association procedure.
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- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Testing Of Individual Semiconductor Devices (AREA)
- Testing Or Measuring Of Semiconductors Or The Like (AREA)
- Semiconductor Lasers (AREA)
Abstract
Description
- 1. Field of the Invention
- The present invention relates generally to testing of semiconductors, and particularly to testing of laser bars, which are an intermediate structure in the manufacture of laser devices.
- 2. Technical Background
- Laser devices, such as semiconductor diode lasers or laser chips, have become important commercial components. They are used in a wide variety of applications ranging from the readout sources in compact disks to the transmitters in optical fiber communication systems. While new applications in high-speed telecommunication networks continue to emerge, how to ensure that diode lasers are reliable and manufacturable is the most challenging issue. One proven approach to this issue is to deploy tight quality control by using laser bar testing systems that characterize diode lasers in many aspects and in an efficient manner.
- Diode lasers are manufactured on wafers or substrates which are processed and further divided into sections or quarters. The sections are further divided into laser bars by breaking or cleaving the sections along the scribe lines, to form facets along the elongated sides of the sections. The laser bar contain many laser diodes.
- During the process of diode laser fabrication from the wafer to the final packaging of individual laser devices or diodes, the first stage where these lasers exhibit both electrical and optical characteristics is when laser bars are formed. Therefore, it is desired to characterize lasers at this early stage by probing and testing all the lasers when they are still in the form of a laser bar. The laser devices that do not meet specifications will be scrapped before entering into further labor-costing or time-costing stages, i.e. packaging and life-testing or bum-in. Usually, a full procedure of bar testing includes six measurements for each laser that is being probed: front-facet light versus current, back-facet light versus current, voltage versus current, horizontal far field pattern, vertical far field pattern and an optical spectrum analysis. A system that performs one or all of these measurement functions is called a laser bar tester.
- In a conventional laser bar tester, after a laser bar holder or chuck has been removed to load/unload laser bars at a remote station, the laser bar and a single long contact probe are mounted on a rotational stage and detectors are scattered around the laser bar. In order to make a specific measurement, i.e. light versus current, the laser under test or the selected laser device and the probe have to rotate to face one particular detector with the probe engaged. Thus testing of all characteristics involves moving the laser bar and probe many times. This mechanism enabling multiple movements of the probe and the laser bar is prone to vibration that can cause the lift-off of the probe from the laser surface of the selected laser device, potentially damaging the laser because of transient electrical discharges during or in-between measurements.
- Therefore, there is a need to improve the laser bar tester to minimize damage to the laser devices due to the testing process while maximizing efficiency.
- One aspect of the present invention is a tester for characterizing individual ones of a semiconductor laser devices of a laser bar, wherein the tester includes a holder for securing the laser bar in a fixed position. For moving in at least one relative direction with respect to the laser bar, a movable measurement system is provided for characterizing the individual ones of the semiconductor laser devices as a function of the at least one relative direction.
- In another aspect, the present invention includes a pair of detectors, each moving in arc paths around the laser bar to sample the far-fields.
- Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
- It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.
- FIG. 1 is a schematic view of a laser bar tester, in accordance with the present invention:
- FIG. 2 is a blow-up perspective portion of the vacuum held and temperature controlled laser bar assembly, held laser bar, and prober of FIG. 1, with reference to the far-field scans of FIG. 1, in accordance with the present invention;
- FIG. 3 is a blow-up perspective portion of the vacuum held and temperature controlled laser bar assembly and laser bar of FIG. 2, in accordance with the present invention: and
- FIG. 4 is a blow-up perspective drawing of the vertically
movable probe pin 241 of FIG. 3 for contacting the selected laser device at the preselected indexed position, in accordance with the present invention. - A laser bar tester that characterizes laser bars in all categories in a fast and accurate manner is taught. Additionally, this laser bar tester system is also compact in size. The laser bar testing system includes a fixture for holding the laser bar, a mechanism for probing individual lasers, and individual measurement modules.
- Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. An exemplary embodiment of the bar tester of the present invention is shown in FIG. 1, and is designated generally throughout by
reference numeral 10. - In accordance with the invention, the present invention for a tester and method for characterizing individual ones of a semiconductor laser devices of a
laser bar 11 includes aholder 12 for securing the laser bar in a fixed position. The advantages of a fixed laser bar mounting is the minimization of testing errors due to the movement of thelaser bar 11. Eventhough only one example is shown, other movable detector systems surrounding a fixed laser bar can be implemented, in accordance with the teachings of the present invention. - As embodied herein as one example out of other various fixed holder arrangements, and depicted in FIG. 1, the
holder 12 includes a selective application ofvacuum suction 14 applied to thelaser bar 11 abutted against a suitable fixture, such as a vacuum chuck, for releasing or securing thelaser bar 11 in its fixture. Other fixed holder arrangements could include clamping or other mounting applications to form a fixed reference for measurement purposes. - In accordance with the invention, the present invention for the
bar tester 10 may further include amovable measurement system 16 for moving in at least onerelative direction laser bar 11 for characterizing the individual ones of the semiconductor laser devices as a function of the at least onerelative direction movable measurement system 16 minimizes alignment and tolerance problems and provides a fast, flexible, and accurate characterization of thelaser bar 11. - As embodied herein, and depicted in FIG. 1, the
movable measurement system 16 includes a prober or probingfixture 24 for selectively probing a selected laser device of thelaser bar 11 in a selected fixed position, defined by the probed position. Themovable measurement system 16 further includes a first detector, in the form of a photodetector or back-facet power detector 226 feeding signals to a back-facetpower monitor module 26. As seen in FIG. 2, thisfirst detector 226 is preferably mounted with theprober 24 in a fixed relative position with the selected laser device for collecting a back-facet power measurement of the laser device. - As part of the
movable measurement system 16, aslidable integrating sphere 28 is connected to aslider 32 for laterally moving, in thehorizontal direction 23, towards the selected laser device for collecting a front-facet power measurement as measured by apower meter 34 whose power measurements are integrated by thesphere 28. For compiling the front-facet power measurement as a function of the distance of theslidable integrating sphere 28 to the selected laser device and for characterizing the front-facet power measurement against the back-facet power measurement, acontroller 36 is preferably used to automatically control, by programmable computer software, the sequencing or indexing and movements of the measurement system and of the initially aligned position of selective laser device of thelaser bar 11 in a controlled temperature environment. - The same
movable measurement system 16 is capable of making all other optical measurments by selectively using appropriate detectors and moving the detectors around the a selectedlaser device 111 of thelaser bar 11, as seen in FIGS. 2-4, to make the desired measurement. For example, as seen in FIGS. 1-2, a pair ofsecond detectors arm 43 moves afirst one 42 of the pair of second detectors in ahorizontal arc path 22 relative to the selected laser device to sample the horizontal far-field. Similarly, a second motor-drivenarm 44 moves asecond one 41 of the pair of second detectors in avertical arc path 21 relative to the selected laser device to sample the vertical far-field. A programmable motor or anothersuitable motion controller 46 actuates thearms arms - As another example of further measurement capabilities, an optical spectrum analyzer (OSA)52 is connected to the integrating
sphere 28 and thecontroller 36 for providing further optical spectrum analysis, as seen in FIG. 1. Optical spectrum is preferably measured using a miniature fiber spectrometer based on the CCD-array silicon detector and fixed grating technology for keeping the cost of the spectrometer low while providing a reliable and sensitivive spectrometer, To measure weak optical signals, the miniature spectrometer is configured to collect data using a long integration period. In themeasurement system 16 of the present invention, pulsed optical signals of 5 mW peak power with 0.2% duty cycle have been measured. Because an A/D card is used to sample the signal from the CCD array, the speed is much faster than conventional spectrometers based on rotating gratings. Different miniature spectrometers may also be used for lasers operated at different wavelengths. - To complete the optical spectrum analysis, the
measurement system 16 automatically records wavelength of the lasers at different current levels programably supplied by acurrent supply 162. - Referring to FIGS.1-4, an enlargement of the
laser bar 11 of FIG. 1 is shown in FIGS. 2-4, with reference to particular portions of themeasurement system 16 of FIG. 1. A properly designed bar fixture provides a method of easy loading and unloading laser bars, a method of providing good electrical conductivity and a method of controlling temperature. - To provide a more accurate laser bar measurement system, the temperature is controlled and monitored as close to the
laser bar 11 as possible. A reference of portions of the laser bar, in itsvaccuum holder 12, to portions of themeasurement system 16 is first described to show where the measurements are referenced-off or indexed from. As seen in FIGS. 3-4, the P-contact surface 201 of thelaser bar 11 is facing upward for theprober 24 to access. The output side or alaser emitting facet 204 of thelaser bar 11 is near astop block feature 121 located on top of abase portion 123 of theholder 12 of FIG. 1 for facilitating bar alignment while enabling measurements. such as the far-field scans along thearc paths - A first one of a pair of probes of the
prober 24, the signal probe orprobe tip 241, preferably flexible, makes contact to thetop surface 201 of thelaser bar 11, as seen in FIGS. 1-2. This single reference point of theprobe tip 241 will be used as the fixed reference for all optical measurements. - The other probe, a
ground probe 242, makes contact to astriker plate 122 as the electrical ground. For greater flexibility, in case the surfaces of thelaser bar 11 is uneven, theprobes - Referring to FIG. 3, the
striker plate 122 is on the opposite side of thestop block feature 121 to mount thebar 11 in theholder 12 between the elevatedstop block feature 121 and thestriker plate 122. Plated with a layer of gold for good electrical conductivity, thestriker plate 122 is physically and electrically attached to thebase portion 123 of the holder byscrews 222. An advantage of using a separate striker plate, other than thebase portion 123 of the holder for probing, is that a smaller worn-out striker plate need only be replaced instead of a complete, bigger, and morecomplexed holder 12. - The N-
contact 202 of thelaser bar 11 is electrically and thermally grounded to thebase portion 123 of theholder 12, preferably implemented as a gold plated fixture. A thermoelectric (TE) cooler 104 and aheat sink 102 are added underneath thevacuum holder 12 to control the temperature surrounding thebar 11 under testing, as seen in FIGS. 1-3. - Referring also to FIG. 4, the temperature is monitored with the
temperature controller module 126 fed by the thermal signals picked-up by athermal sensor 124 mounted inside theholder 21 for feeding-back temperature near thelaser bar 11. Preferably, the temperature is controlled by a computer module, referenced as thetemperature controller 126, for regulating the testing temperature in the range of −20 to 80 degrees C. - To provide a fixed and indexable position for the
laser bar 11, thevaccuum holder 12 for thebar 11 of FIG. 1 is shown in more detail in FIGS. 2-3. Thelaser bar 11 is preferably held by thevaccum suction 14 applied through avacuum slot 214 in thebase portion 123 of the holder orfixture 12. By turning or activating thevacuum switch 114 of FIG. 1 “ON” or “OFF”, as controlled by thecontroller 36, thebar 11 can be easily loaded to or unloaded from theholder 12. Preferably, fourbars 11 are mounted at the same time, thus down-time due to loading/unload is minimized. For simplicity, only onebar 11 is shown in FIG. 3. - The front edge of the
vacuum holder 12 has a triangular-shaped protrusion used as astop block feature 121 to position thelaser bar 11 on theoutput side 204. An appropriately designed tool (not shown) pushes thebar 11 against thestop block portion 121 of the holder and aligns thebar 11 into an indexable position on top of thebase portion 123 of the holder. The height of thestop block portion 121 is preferably designed such that the active top region of thebar 11 is about 50 um above the top point of the stop block 121 to protect the laser bar from contact damage.Bars 11 are loaded to thetesting system 16 in situ or in process, that is, the chuck orholder 12 is not relocated to a remote location for loading/unloading. This in situ procedure not only minimizes the down time of the system but also allows automatic loading/unloading. - Referring to FIGS,1-4, the
individual lasers 111 on thebar 11 are indexed by a probing mechanism or system consisting of a horizontal motorized X-stage 152 which is supporting thelaser bar holder 12 above through the use of anadapter plate 151 that is mounted to theX stage 152 and theprober 24, already described having dual probes in a probe tip assembly, including a back-facet power monitor, that is connected to a vertical motorized Y-stage 154. Controlled by themotion controller 36, theX stage 152 horizontally moves thelaser bar 11 which is placed on top of theX stage 152, as seen in FIGS, 1-2. To moveindividual lasers 111 of thebar 11 into or out from the indexed measurement position, thehorizontal X-stage 152 translates the bar fixture orholder 12 with respect to the tip of the signal probe orprobe tip 241. While alaser 111 is in the measurement position, thevertical stage 154 lowers theprobe tip 241 to make the electrical contact and measurements are taken. After alaser 111 is fully characterized, thevertical stage 154 of FIG. 1 raises theprobe tip 241 off thelaser surface 201 and waits for the next laser to move in. Also controlled by themotion controller 36, thevertical stage 154 is raised and lowered every time aspecfic laser 111. one of themany lasers 111 on thebar 11, is translated or indexed next, underneath theprobe tip 241 for testing. The probe tip, as part of theprober 24, is attached only to theY stage 154 for minimizing the movement of thelaser bar 11. Once alaser 111 is moved underneath theprobe tip 241, theprober 24 is lowered to make contact and all the other detectors move around thatparticular laser 111 for various measurements. This procedure repeats itself until all thelasers 111 on thebar 11 are characterized. - One of key issues in probing is how to avoid scratching the
laser surface 201 by theprobe tip 241. The probing system manages to create no scratch marks by using an inventive step-and-check or step-approximation approach. The software in thecontroller 36 that controls the probing system moves thevertical stage 154 towards the toplaser bar surface 201 in small increments or small steps that get even smaller as the expected contact is approached. Preferably, the testing software is facilitated by thecontroller 36, implementable using a Pentium computer, and an ILX Lightwave semiconductor laser controller, that is also capable of performing optical tests, in the form ofvarious modules controller 36 checks if there exists a close electrical loop between thelaser bar 11 and the associated electronic instrument, such as whether thecurrent supply 162 can pass a current to enable the current to be read. A contact position is obtained when such a close loop is found, for example, when a current measurement can be read. The controlling software in thecontroller 36 also calculates the parameters of the bar surface plane, such as the location of the next expected contact point, based onlasers 111 that have been successfully probed: these parameters are used to help obtain a faster contacting approach time for the rest of thelasers 111 on thebar 11. This step-wise contacting approach also allows successful probing on rough or uneven laser bar surfaces. - Referring back to FIG. 1, all of the other detectors, such as the
OSA 52, theslider 32 for the integratingsphere 28 are also aligned to the position where theprobe tip 241 is lowered for making contact with alaser 111. This position was determined when the system was initially setup. Each of manyindividual lasers 111 on abar 11, is moved to that same initial setup position for test. Therefore, the proper alignment ofindividual laser 111 with all the detectors is preserved. - For all optical measurements, the contacted
laser bar 11 and the contactingprobe tip 241 are maintained still in a fixed position. The optical measurements obtained include the most important characteristics for semiconductor diode lasers, such as the threshhold current measurable by knowing the value of thecurrent supply 162. Other important measurements include turn-on voltage, slope efficiency, series resistance, and front/back power ratio. As one example of an optical measurment, theintegration sphere 28 collects the front power. The use of theintegration sphere 28 has two advantages: first, it allows measuring high optical power since the optical signal entering the sphere is scattered by the cavity walls and there is only a small portion of light that reaches thephoto detector 226 in FIG. 1. Second, thesphere 28 has a relativelylarge aperture 281 to allow easy coupling of a highly divergent optical signal from thediode laser 111 into the sphere's cavity. Thesphere 28 is mounted on the computer controlledmotion slider 32 that moves theintegration sphere 28 to thelasers 111 when a front-facet power versus current test is performed. The back-facet power is collected by the large-area photo detector 226 (shown in FIG. 2) which is mounted on the probe assembly orprober 24. Thedetector 226 will not be saturated by a high incident power because the back-facet of thebar 11 is usually high-reflectively coated. - One known issue for weakly guided high-power lasers is the existence of higher-order modes due to spatial hole burning. The occurrence of this effect is usually accompanied by “kinks” on a power or optical invensity versus current (LI) curve. However, the kinks are not obvious and can be very difficult to detect. In accordance with the teachings of the present invention, the kink-detection scheme utilizes a reduced aperture to measure a LI curve in order to enhance the occurrence of the kinks by moving in a
lateral direction 23 thesphere 28 at a known distance to thelaser 111 via theslider 32. With such a lateral movement of the sphere, themeasurement system 16 has the capability of continuously varying thenumerical aperture 28 by allowing theaperture 281 to van, its distance from thelaser 111. A computer program in thecontroller 36, using a binomial weighted averaging scheme, then processes the LI data to reveal the kinks. - Another example of an optical measurement is the far-field scan which is very important in characterizing beam quality. Far-field patterns are defined as the angular dependence of optical intensity. For example, the far-field characteristics determine the laser-to-fiber coupling efficiency. Usually a semiconductor laser has an elliptical beam shape because the width of a laser waveguide is much larger than the thickness. Therefor a complete characterization of the far-field requires scanning cross the divergent beam along two
orthogonal axes - In accordance with the teachings of the present invention, the
measurement system 16 uses two mini-motor drivenarms size photo detectors arm fields motion controller 46 allows positioning thedetectors detectors detectors detectors detectors laser emitting facet 204 is about 60 mm. The angular far-field resolution is estimated to be about 0.2 degree. - Another application of far-field patterns is for kink-detection. When kink occurs, the far-field patterns become asymmetric. Therefore, far-field measurements can first be taken at different current levels and any changes in the far-field patterns can be associated with kinks. The control software in the
controller 36 automatically executes this far-field and kink association procedure. - It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
Claims (10)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US09/738,108 US6501260B1 (en) | 2000-12-15 | 2000-12-15 | Bar tester |
EP01127548A EP1220394A3 (en) | 2000-12-15 | 2001-11-19 | Laser bar tester |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/738,108 US6501260B1 (en) | 2000-12-15 | 2000-12-15 | Bar tester |
Publications (2)
Publication Number | Publication Date |
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US6501260B1 US6501260B1 (en) | 2002-12-31 |
US20030011357A1 true US20030011357A1 (en) | 2003-01-16 |
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Application Number | Title | Priority Date | Filing Date |
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US09/738,108 Expired - Lifetime US6501260B1 (en) | 2000-12-15 | 2000-12-15 | Bar tester |
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US (1) | US6501260B1 (en) |
EP (1) | EP1220394A3 (en) |
Cited By (3)
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US8729696B2 (en) * | 2012-03-06 | 2014-05-20 | Hon Hai Precision Industry Co., Ltd. | Testing device for laser diode |
CN105467291A (en) * | 2015-12-30 | 2016-04-06 | 中国科学院西安光学精密机械研究所 | Semiconductor laser chip test fixing device and method thereof |
WO2020167512A1 (en) * | 2019-02-15 | 2020-08-20 | Agilent Technologies, Inc. | Method and apparatus for characterizing laser gain chips |
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SE517273C2 (en) * | 2001-06-12 | 2002-05-21 | Ericsson Telefon Ab L M | Procedure for bringing laser chips mounted on separate supports to a measuring station |
US6734959B2 (en) * | 2001-07-12 | 2004-05-11 | Labsphere, Inc. | Prober for testing light-emitting devices on a wafer |
DE10250777B4 (en) * | 2002-10-30 | 2006-07-06 | Finisar Corp.(N.D.Ges.D.Staates Delaware), Sunnyvale | Method and device for characterizing edge-emitting optical transmission elements |
US7256879B2 (en) * | 2003-12-11 | 2007-08-14 | Corning Incorporated | Semiconductor array tester |
US7733114B2 (en) * | 2008-10-21 | 2010-06-08 | Asm Assembly Automation Ltd. | Test handler including gripper-type test contactor |
US8456185B2 (en) | 2010-08-17 | 2013-06-04 | Avago Technologies General Ip (Singapore) Pte. Ltd. | Test adapter and method for achieving optical alignment and thermal coupling thereof with a device under test |
US8670109B2 (en) | 2010-12-02 | 2014-03-11 | Corning Incorporated | Laser characterization system and process |
CN104638510B (en) * | 2013-11-14 | 2018-01-02 | 山东华光光电子股份有限公司 | A kind of semiconductor laser storehouse junior unit test, the device and method of aging |
TWI530700B (en) * | 2015-03-11 | 2016-04-21 | 旺矽科技股份有限公司 | Testing machine and operation method thereof |
US10746945B1 (en) | 2017-10-09 | 2020-08-18 | Waymo Llc | Systems and methods for laser diode alignment |
CN111443273B (en) * | 2020-05-12 | 2021-07-09 | 中南大学 | Laser bar testing device |
US11781904B2 (en) * | 2020-12-01 | 2023-10-10 | Mpi Corporation | Chip chuck for supporting light emitting chip under optical inspection and chip supporting device having the same |
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US4795976A (en) | 1987-01-15 | 1989-01-03 | American Telephone And Telegraph Company At&T Bell Laboratories | Apparatus and derivative technique for testing devices |
JPH02240990A (en) * | 1989-03-15 | 1990-09-25 | Hitachi Ltd | Characteristic measuring device |
US5293516A (en) | 1992-01-28 | 1994-03-08 | International Business Machines Corporation | Multiprobe apparatus |
JPH075032A (en) * | 1993-06-15 | 1995-01-10 | Mitsubishi Electric Corp | Estimation apparatus for semiconductor laser |
US5454002A (en) * | 1994-04-28 | 1995-09-26 | The Board Of Regents Of The University Of Oklahoma | High temperature semiconductor diode laser |
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US5498973A (en) | 1994-12-22 | 1996-03-12 | International Business Machines Corporation | Apparatus for testing semiconductor laser devices |
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JP3635600B2 (en) * | 1996-08-29 | 2005-04-06 | キヤノン株式会社 | Feeder |
JP3601645B2 (en) | 1997-04-24 | 2004-12-15 | 澁谷工業株式会社 | Bonding method for solid-state laser oscillator |
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US6137305A (en) | 1998-10-26 | 2000-10-24 | Lucent Technologies Inc. | Method and apparatus for testing laser bars |
US6248604B1 (en) * | 1999-09-14 | 2001-06-19 | Lucent Technologies, Inc. | Method for design and development of a semiconductor laser device |
-
2000
- 2000-12-15 US US09/738,108 patent/US6501260B1/en not_active Expired - Lifetime
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2001
- 2001-11-19 EP EP01127548A patent/EP1220394A3/en not_active Withdrawn
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
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US8729696B2 (en) * | 2012-03-06 | 2014-05-20 | Hon Hai Precision Industry Co., Ltd. | Testing device for laser diode |
CN105467291A (en) * | 2015-12-30 | 2016-04-06 | 中国科学院西安光学精密机械研究所 | Semiconductor laser chip test fixing device and method thereof |
WO2020167512A1 (en) * | 2019-02-15 | 2020-08-20 | Agilent Technologies, Inc. | Method and apparatus for characterizing laser gain chips |
CN113412561A (en) * | 2019-02-15 | 2021-09-17 | 安捷伦科技有限公司 | Method and apparatus for characterizing a laser gain chip |
GB2598667A (en) * | 2019-02-15 | 2022-03-09 | Agilent Technologies Inc | Method and apparatus for characterizing laser gain chips |
GB2598667B (en) * | 2019-02-15 | 2023-10-04 | Agilent Technologies Inc | Method and apparatus for characterizing laser gain chips |
Also Published As
Publication number | Publication date |
---|---|
US6501260B1 (en) | 2002-12-31 |
EP1220394A2 (en) | 2002-07-03 |
EP1220394A3 (en) | 2004-09-22 |
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