Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2002-01-03
2004-09-28
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C324S762010
Reexamination Certificate
active
06797936
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus and method of automatically testing laser devices. More particularly, the invention relates to an apparatus and method of automatically testing laser diode sub-assemblies.
BACKGROUND OF THE INVENTION
Laser diode assemblies are constructed using a vertical surface laser die mounted onto a post. The vertical surface laser die generates a divergent light, similar to a flashlight and requires an external lense to lase. The die is bonded to the top of a metal post that is used to provide a secure base for the die as well as conduct electricity, but most importantly to conduct heat away from the die. The post and one contact of the die are wired together, and a wire or thin metal ribbon is extended from the other contact on the die. The extended wire or thin metal ribbon is called a tab and serves only as an electrical contact. Such a configuration is referred to as a chip-on-post, or COP. At this stage, the die has yet to be tested. When testing the COP, the objective is to simulate actual conditions by applying power to the COP and measuring the light output characteristics. Two characteristics are typically measured to determine whether or not the die is functioning correctly, the power and the light spectrum. The spectrum of the light output generally measures the number and shape of pulses, and the power of the light measures the light power output versus the power input.
To test the COP, a mechanical mount is used to hold the post and the tab in place. In typical test situations, up to 5 amps are pulled through the COP. If the heat is not sufficiently dissipated, the tab and/or the die will burn up. The COP is typically mechanically clamped in a conductive metal fixture to draw away the heat generated during testing and act as an electrode.
Once the COP is mechanically and electrically clamped, the divergent light from the die needs to be focused and reflected using an external lens. That is, the light is focused into a parallel beam that makes a laser light. Lasing the divergent light is accomplished by properly positioning a lens within the path of the divergent light. This arrangement is referred to as a laser diode sub-assembly.
FIG. 1
illustrates a laser diode sub-assembly of the prior art. A die
20
is bonded and wired to a post
10
. A tab
30
is coupled to the die
20
and the post
10
via the wired connection. The post
10
, the die
20
and the tab
30
together form a COP. When power is applied to the COP, a divergent light output
40
is generated. A lens
50
is properly positioned in the path of the divergent light output
40
to focus the divergent light
40
into laser light
60
.
Conventionally, both the lens and the COP are mounted on optical mounts. The mounts holding the lens and COP are coupled to micrometers that move the mounts, and therefore the lens and COP, in very small, incremental steps. A human operator, usually a highly trained optical technician, manually turns the knobs on the micrometers to obtain proper COP and lens alignment. The operator turns the micrometer knobs that in turn move the lens and COP back and forth, up and down, as well as tilting to obtain proper alignment for lasing. The operator monitors the output of a measuring device while moving the knobs to determine if the lens is being moved in the proper direction. The operator continues to adjust the micrometers and monitor the measurement device until the lens and COP are approximately positioned. The operator continues to adjust the micrometers until the highest readings are obtained and then manually records the final measurements. Such a process is very time consuming and subject to operator expertise and training, not to mention the inability to securely couple data taken with the device tested. This process is also potentially dangerous since lasing of the divergent light is performed in an open, unsafe environment. Operators are required to wear laser-proof glasses to prevent injury, but accidents can happen.
The power and the spectrum of the laser light are tested. This requires two different tests, each test requiring a different detection device. One detection device is used to detect the spectrum or frequency of the laser light. This detection device is coupled to a spectrum analyzer to measure spectrum characteristics. A second detection device is used to detect the power of the laser output. This detection device is then coupled to a power meter and the results of the voltage-ampere curve and peak power output of the laser light are recorded. Once the first test is completed, the COP is then aligned the second detection device in order to perform the second test. Either the detectors are interchanged or the COP may be moved to a different test setup. As a rule, the lens will need to be re-aligned when performing the second test. Even when the lens does not need to be re-aligned, changing the detection devices or moving the COP into different setups is very time consuming and prone to errors.
When performing a test on a different COP, re-alignment of the lens is necessary due to the irregularities from one COP to the next. Each die will be different due to the nature of the wafer fabrication process. Additionally, there are irregularities associated with mounting the die to the post. Mounting of the die is done using a special epoxy that mechanically and thermally bonds the die to the post. The assembly is then put in an oven to allow curing of the epoxy before the next step. Manufacturing processes associated with bonding a die on a post specify tolerances within which the die is to be placed on the post. Preferably, die are placed in the center of the post and flat relative to the top of the post. However, manufacturing processes introduce undesirable variables, so that every die is not positioned exactly the same as the next die.
SUMMARY OF THE INVENTION
A preferred embodiment of the present invention automatically tests a laser diode sub-assembly using a testing system. The testing system automatically loads, positions, transports, aligns, tests, records data and unloads each serialized laser diode sub-assembly to be tested without need of user interaction. While the preferred embodiment of the present invention is used to perform automated testing of COP laser diode subassemblies, the testing system of the present invention is also capable of performing automated testing on most laser diode assemblies as well as other devices under test (DUTs) with power up to 25 watts.
According to an aspect of the present invention, a testing system includes a handling system for automatically loading and positioning within a given tolerance each of a plurality of laser diode sub-assemblies, an optical system for automatically receiving each laser diode subassembly from the handling system and automatically performing one or more tests to measure functionality of each laser diode sub-assembly, a detection system for detecting characteristics associated with one or more tests performed by the optical system for each laser diode sub-assembly, and a control system for automatically receiving detected characteristics from the detection system, comparing the detected characteristics to stored expected characteristics for a properly functioning laser diode sub-assembly thereby forming a comparison, and providing control instructions to the optical system based on the comparison. The one or more tests are performed by automatically positioning a lens such that light generated from the laser diode sub-assembly is formed into laser light, and each test measures a desired characteristic of the laser light. The detection system includes one or more detection devices, each detection device corresponding to one of the one or more tests performed. The testing system also includes a mirror assembly properly positioned to direct the laser light to the one detection device corresponding to the test currently being performed by the optical system. Each detection device detects data associated with the desired characteristic and tr
Chiu Jim Tark
Kessler Jack Stephen
Haverstock & Owens LLP
Le Que T.
Opto Electronic Systems, Inc.
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