U.S. patent application number 09/168035 was filed with the patent office on 2002-01-10 for method and apparatus for collecting light from an array of light emitting devices.
Invention is credited to FREUND, JOSEPH M., PRZYBYLEK, GEORGE J., ROMERO, DENNIS M., STAYT, JOHN JR..
Application Number | 20020003428 09/168035 |
Document ID | / |
Family ID | 22609821 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003428 |
Kind Code |
A1 |
FREUND, JOSEPH M. ; et
al. |
January 10, 2002 |
METHOD AND APPARATUS FOR COLLECTING LIGHT FROM AN ARRAY OF LIGHT
EMITTING DEVICES
Abstract
A method for testing the light emitted by a group of
semiconductor light emitting devices arranged to emit light over a
testing area, each light emitting device having a p-contact, the
method including connecting a plurality of selectively connectable
p-contact probes to the p-contacts of respective light emitting
devices in the group of light emitting devices, selectively
activating one of the light emitting devices in the group of light
emitting devices to emit light over the testing area by selectively
supplying a predetermined electrical current to the p-contact of
the selected light emitting device via its respective p-contact
probe, guiding the light emitted by the selected light emitting
device via a light funnel having a collection end and a detection
end, the collection end being in juxtaposition with all the light
emitting devices in the group of light emitting devices, and
detecting light exiting the detection end of the light funnel.
Inventors: |
FREUND, JOSEPH M.;
(FOGELSVILLE, PA) ; PRZYBYLEK, GEORGE J.;
(DOUGLASVILLE, PA) ; ROMERO, DENNIS M.;
(ALLENTOWN, PA) ; STAYT, JOHN JR.; (SCHNECKSVILLE,
PA) |
Correspondence
Address: |
DARBY & DARBY
805 THIRD AVENUE
NEW YORK
NY
10022
|
Family ID: |
22609821 |
Appl. No.: |
09/168035 |
Filed: |
October 7, 1998 |
Current U.S.
Class: |
324/754.23 |
Current CPC
Class: |
G01J 1/0422 20130101;
G01R 31/2635 20130101; G01J 1/04 20130101; G01J 2001/4247
20130101 |
Class at
Publication: |
324/750 |
International
Class: |
G01R 031/302 |
Claims
What is claimed:
1. Apparatus for testing the light emitted by a group of
semiconductor light emitting devices arranged to emit light over a
testing area, each light emitting device having a p-contact, the
apparatus comprising: a light detector; a light funnel having a
collection, constructed to capture light substantially over the
entire testing area to collect light emitted by any of the light
emitting devices, and a detection end adapted to direct the
collected light to the light detector; and an electrical probe
arrangement including a plurality of p-contact probes selectively
connectable with the p-contacts of respective light emitting
devices in the group of light emitting devices.
2. Apparatus according to claim 1 and further comprising a support
device for securely positioning the group of semiconductor light
emitting devices aligned with the collection end of the light
funnel.
3. Apparatus according to claim 2 wherein said support device
comprises a support surface having a plurality of vacuum suction
apertures adapted to temporarily and securely hold a substrate
bearing a semiconductor bar including said series of light emitting
devices.
4. Apparatus according to claim 1 and further comprising a
switching device for selectively supplying a predetermined current,
via the p-contact probes, to the p-contacts of selected ones of the
light emitting devices.
5. Apparatus according to claim 2 and further comprising a
switching device for selectively supplying a predetermined current,
via the p-contact probes, to the p-contacts of selected ones of the
light emitting devices.
6. Apparatus according to claim 1 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting laser devices on a semiconductor bar, each laser device
having a light emitting edge along a given edge of the
semiconductor bar, and wherein the light collecting end of the
light funnel is constructed to be placed in juxtaposition with
substantially the entire edge of the semiconductor bar.
7. Apparatus according to claim 1 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting LED devices on a semiconductor bar, each LED device having
a light emitting edge along a given edge of the semiconductor bar,
and wherein the light collecting end of the light funnel is
constructed to be placed in juxtaposition with substantially the
entire edge of the semiconductor bar.
8. Apparatus according to claim 2 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting laser devices on a semiconductor bar, each laser device
having a light emitting edge along a given edge of the
semiconductor bar, and wherein the light collecting end of the
light funnel is constructed to be placed in juxtaposition with
substantially the entire edge of the semiconductor bar.
9. Apparatus according to claim 2 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting LED devices on a semiconductor bar, each LED device having
a light emitting edge along a given edge of the semiconductor bar,
and wherein the light collecting end of the light funnel is
constructed to be placed in juxtaposition with substantially the
entire edge of the semiconductor bar.
10. Apparatus according to claim 4 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting laser devices on a semiconductor bar, each laser device
having a light emitting edge along a given edge of the
semiconductor bar, and wherein the light collecting end of the
light funnel is constructed to be placed in juxtaposition with
substantially the entire edge of the semiconductor bar.
11. Apparatus according to claim 4 wherein the group of
semiconductor light emitting devices comprises a group of edge
emitting LED devices on a semiconductor bar, each LED device having
a light emitting edge along a given edge of the semiconductor bar,
and wherein the light collecting end of the light funnel is
constructed to be placed in juxtaposition with substantially the
entire edge of the semiconductor bar.
12. A method for testing the light emitted by a group of
semiconductor light emitting devices arranged to emit light over a
testing area, each light emitting device having a p-contact, the
method comprising: connecting a plurality of selectively
connectable p-contact probes to the p-contacts of respective light
emitting devices in the group of light emitting devices,
selectively activating one of the light emitting devices in the
group of light emitting devices to emit light over the testing
area, by selectively supplying a predetermined electrical current
to the p-contact of the selected light emitting device via its
respective p-contact probe; guiding the light emitted by the
selected light emitting device via a light funnel having a
collection end and a detection end, the collection end being in
juxtaposition with all the light emitting devices in the group of
light emitting devices; and detecting light exiting the detection
end of the light funnel.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to testing of semiconductor
light emitting devices, more particularly, the invention relates to
a method and apparatus for collecting light from a linear array of
edge emitting semiconductor laser or LED devices.
BACKGROUND OF THE INVENTION
[0002] Semiconductor light emitting devices, e.g., edge emitting
laser diodes or light emitting diodes (LED), are well known in the
art. Such devices are manufactured on wafers which, after initial
manufacture and processing (e.g. thinning down and trimming), are
separated into a predetermined number (e.g., three) of smaller
units, generally referred to as wafer sections. These sections are
typically further trimmed in one dimension, generally referred to
as length, to a predetermined size. Semiconductor laser or LED bars
are produced from a semiconductor wafer section by a scribing and
cleaving procedure, wherein predefined shapes of bars are
delineated by scribing lines and the bars are separated by cleaving
along the scribing lines. Accurate cleaving along the scribed lines
is possible because of the brittle nature of the sections.
[0003] A typical semiconductor LED or laser bar includes a
p-contact surface, generally referred to as the top surface, and an
n-contact surface, generally referred to as the back surface. The
p-contacts and n-contacts are produced by a fabrication sequence
including a metallization process in which the surfaces of a
semiconductor wafer are selectively coated with a metallic layer.
Individual semiconductor laser or LED devices on the bars may be
activated by applying an electric current across the n-contacts and
p-contacts, respectively, of the devices. During processing, the
bars are typically supported by a flexible, adhesive, holding
surface. After processing, the bars may be removed from the holding
surface for testing or the devices may be tested while the bars are
attached to the holding surface.
[0004] Testing of edge emitting semiconductor lasers or LEDs
involves measurement of the light intensity emitted by the laser or
LED devices at a predefined wavelength spectrum, while applying a
predetermined current using electrical probes, namely, a p-contact
probe and an n-contact probe. To ensure accurate comparative
testing of the laser or LED devices, the light emitted by the
devices must be collected at a precise, reproducible manner, e.g.,
at a predefined distance or angle, and delivered to a light
detector using appropriate optics. Typically, a plurality of laser
or LED devices are included in each semiconductor bar. To test
individual laser or LED devices along the bar, the light detector
and associated optics, as well as the p-side electrical probe, must
be separately aligned for each device being tested. For reliable
comparative testing of the laser or LED devices, the p-contact
alignment procedure requires complex and tedious positioning
equipment and/or software to ensure consistency in collecting and
detecting the light emitted by the laser or LED devices. The
n-contact does not require realignment for each device being tested
because the semiconductor bar includes a common n-contact for all
the laser or LED devices thereon.
SUMMARY OF THE INVENTION
[0005] The present inventors have developed a method and apparatus
for testing light emission from a series of edge emitting
semiconductor laser diodes or LEDs, using a light collection
arrangement and a p-contact electrical probe, without requiring
movement and/or realignment of the laser or LED bar, the light
collection arrangement or the contact electrical probe.
[0006] In accordance with the present invention, the light emitted
by individual laser or LED devices along a laser or LED bar is
collected sequentially by a fixed funnel-shaped light guide
(hereinafter referred to as: "light funnel") which directs the
light emitted by the individual laser or LED devices to a light
detector. In accordance with an aspect of the present invention, a
series of laser or LED bars, which may be mounted on a holding
substrate, may be sequentially brought to a predefined position
aligned with the light funnel. A selectively activated electrical
probe arrangement, including a plurality of individually
addressable p-contact probes, is brought into contact with the
laser or LED bar, such that each p-contact probe is in contact with
a respective p-contact. A switching device may be used to
selectively apply biasing voltage to the to the individual laser or
LED devices along the bar, via the respective p-contact probes, and
the light emitted by each individual laser or LED device is
collected by the fixed light funnel. Thus, once the laser or LED
bar is appropriately positioned with respect to the light funnel,
and the p-contact probe arrangement is brought into contact with
the respective p-contacts of the bar, the relative physical
positions of the bar, the light funnel and the p-contact probe
arrangement remain fixed during testing of all the laser or LED
devices on the bar.
[0007] An embodiment of the present invention thus provides
apparatus for sequentially testing the light emitted by a group of
semiconductor light emitting devices, each device having a
p-contact, arranged to emit light over a testing area. The
apparatus includes a light detector and a light funnel which has a
collection end, constructed to capture light over substantially the
entire testing area, and a detection end. The detection collects
light emitted by any of the light emitting devices and the
detection end directs the collected light to the light detector.
The apparatus further includes an electrical probe arrangement
including a plurality of p-contact probes which are selectively
connectable with the p-contacts of respective light emitting
devices in the group of light emitting devices. The apparatus may
further include a support device for securely positioning the group
of semiconductor light emitting devices aligned with the collection
end of the light funnel. Additionally, the apparatus may include a
switching device for selectively supplying a predetermined
electrical current, via the p-contact probes, to the p-contacts of
selected ones of the light emitting devices.
[0008] The present invention also provided a method for
sequentially testing the light emitted by a group of semiconductor
light emitting devices, each light emitting device having a
p-contact, arranged to emit light over a testing area. The method
includes placing an electrical probe arrangement including a
plurality of p-contact probes in contact with the p-contacts of
respective light emitting devices in the group of light emitting
devices, selectively activating selected ones of the light emitting
devices in the group of light emitting devices to emit light over
the testing area, guiding the light emitted by the selectively
activated light emitting devices via a light funnel which captures
light substantially over the entire testing area, and detecting the
light guided by the light funnel. In an embodiment of the present
invention, the light emitting devices are selectively activated by
selectively supplying an electrical current to the p-contacts of
the selected light emitting devices via their respective p-contact
probes. The group of semiconductor light emitting devices are
preferably securely positioned at a fixed position with respect to
the collection end of the light funnel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will be understood and appreciated
more fully from the following detailed description of an embodiment
of the invention, taken in conjunction with the accompanying
drawings in which:
[0010] FIG. 1 is a schematic front view of a semiconductor laser or
LED testing apparatus in accordance with an embodiment of the
present invention, shown in preparation for testing in accordance
with the present invention;
[0011] FIG. 2 is a schematic front view of the semiconductor laser
or LED testing apparatus of FIG. 1, during testing of semiconductor
laser or LED devices in accordance with an embodiment of the
present invention;
[0012] FIG. 3 is a schematic side view of part of the semiconductor
laser or LED testing apparatus of FIG. 1, during testing of
semiconductor laser or LED devices in accordance with an embodiment
of the present invention; and
[0013] FIG. 4 is a schematic, cross-sectional, front view of part
of the testing apparatus of FIG. 1, showing a light funnel aligned
with a selectively activated edge emitting laser or LED bar, in
accordance with an embodiment of the present invention; and
[0014] FIG. 5 is a schematic top view of part of the testing
apparatus of FIG. 1, showing two light funnels aligned with
respective edges of a selectively activated edge emitting laser
bar, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] The present invention will be hereinafter described in the
context of testing the light output of edge emitting semiconductor
laser devices. It should be understood however, that the invention
is also suitable for testing the light output of other light
emitting devices, for example, light emitting diode (LED)
devices.
[0016] Reference is made to FIG. 1 which schematically illustrates
a front view of a testing apparatus in accordance with an
embodiment of the present invention, and to FIGS. 2 and 3 which
schematically illustrate a front view and a side view respectively,
of the testing apparatus of FIG. 1 during testing in accordance
with an embodiment of the present invention. The testing apparatus
includes a testing assembly 10 having a head portion 12, a head
support structure 14 and two light funnels 18, each having a light
collection end 42 and a detection end 44. As shown particularly in
FIG. 3, head assembly 10 also includes an electrical probe
arrangement 16 including a plurality of separately addressable
p-contact electrical probes 48, as described in detail below.
[0017] The testing apparatus further includes a test sample support
device 24 having a surface 25 for supporting a holding substrate
22, e.g., an adhesive film. A plurality of semiconductor laser bars
20, each having opposite edges 50 and 52 and a top surface 54, are
mounted on substrate 22 such that top surface 54 faces testing
assembly 10. As shown particularly in FIG. 3, each semiconductor
bar 20 includes a series of semiconductor laser devices 45 having
p-contacts 46 on top surface 54. Each laser device 45, when
activated, emits light through edges 50 and 52 of bar 20. Support
device 24 may include a plurality of vacuum suction channels 26
which extend through the support device and have suction apertures
27 at surface 25.
[0018] As shown particularly in FIGS. 1 and 2, surface 25 may
include a generally level region 36 directly underneath probe
arrangement 16. Region 36 is adapted for placing one of laser bars
20 at a desired position relative to probe arrangement 16 and light
funnels 18, for testing as described below. Surface 25 is slanted
downwardly and outwardly on either side of region 36, such that the
laser bars 20 not being tested will not block or reflect the light
emitted by the laser devices 45 on the laser bar 20 being tested.
Testing assembly 10 further includes a switching device 40 which is
electrically connected, via conductors 38, to p-contact probes 48
in probe arrangement 16.
[0019] Testing assembly 10 further includes two light detectors 32
which are optically coupled to detection ends 44 of respective
light funnels 18, via optical guides 34 which may include optical
fibers and/or lenses as are known in the art.
[0020] As shown in FIG. 2, during operation, a vacuum is produced
in channels 26, e.g., by a vacuum suction pump (not shown in the
drawings), in the direction indicated by arrows 28. The vacuum
suction produced at apertures 27, pulls substrate 22 towards
surface 25, conforming the shape of flexible substrate 22 to the
shape of surface 25. The vacuum at apertures 27 also ensures that
substrate 22 is securely mounted on surface 25. In an embodiment of
the present invention, before suction is applied to channels 26,
substrate 22 is positioned on surface 25, using suitable alignment
means, for example, precision X-Y-Z Axis servo stages, as is known
in the art, such that the laser bar 20 to be tested is correctly
positioned on region 36 underneath testing assembly 10.
[0021] Once the bar 20 to be tested is positioned on region 36,
testing assembly 10 may be lowered, using any suitable mechanical
means known in the art, until probe arrangement 16 is brought into
contact with the bar 20 being tested, as shown particularly in FIG.
3. At this point, contact is made between the plurality of
electrical probes 48 of arrangement 16 and respective p-contacts 46
of laser devices 45 on surface 54 of bar 20. Alternatively, probe
arrangement 16 may be brought into contact with the bar 20 being
tested by raising support device 24. Using switching device 40,
which may be controlled by suitable hardware or software known in
the art, a predetermined bias current is selectively applied to
p-contacts 46 of selected ones of laser devices 45. Switching
device 40 preferably supplies a bias current in a predetermined
bandwidth suitable for activating the laser devices, as is known in
the art, and includes an electrostatic discharge (ESD) protection
circuit for protecting the laser devices from potentially damaging
ESD. The n-contacts to laser devices 45 are provided via a common
n-contact on the bottom surface of bar 20, as is known in the art,
which may be continuously connected to a predetermined electric
potential. In this manner, laser devices 45 may be sequentially
activated to emit light via edges 50 and 52 of bar 20 over testing
areas 62 and 64, respectively, alongside collection ends 42 of
light funnels 18.
[0022] As shown in FIG. 2, light 30 emitted from edges 50 and 52,
over testing areas 62 and 64, is collected by collecting ends 42 of
respective light funnels 18 which carry the light, via respective
detection ends 44 and optical guides 34, to light detectors 32.
Light detectors 32 monitor the intensity of light emitted from
edges 50 and 52, respectively, of each of sequentially tested laser
devices 45. Thus, the present invention enables reliable
comparative testing of different laser devices 45 as well as
comparative testing between the emissions from edges 50 and 52 for
each tested laser device 45. Any suitable method and apparatus may
be used to analyze the laser or LED emissions of edges 50 and 52,
as detected by light detectors 32, for example, the method and
apparatus described in U.S. Pat. No. 4,795,976 to Pawlik, the
disclosure of which is incorporated herein by reference.
[0023] Reference is now made to FIGS. 4 and 5. FIG. 4 schematically
illustrates a cross-sectional front view of one of light funnels 18
juxtaposed edge 52 of one of laser bars 20, during activation of
one of laser devices 45 by switching apparatus 40 to emit light
over testing area 64. FIG. 5 schematically illustrates a top view
of light funnels 18 aligned with respective edges 50 and 52 of bar
20, during activation of one of laser devices 45. As shown
particularly in FIG. 4, the light 30 emitted via edge 52 over
testing area 64 is received via a front surface 60 of collection
end 42 and is carried by multiple reflection off inner surfaces 56
of light funnel 18 to detection end 44. The geometry of light
funnel 18 may be designed such that the beam of light 30 exiting
detection end 44 will be a generally parallel light beam. The beam
of light 30 exiting detection end 44 enters optical guide 34, via
an input surface 58, and is carried by the optical guide to light
detector 32, as described above. In an embodiment of the present
invention, front surface 60 of funnel 18 and input surface 58 of
optical guide 58 are slightly angled to prevent direct reflection
of light 30 off inner surfaces 56 of light funnel 18 and to ensure
that a maximum, consistent, portion of light 30 will reach detector
32.
[0024] Light funnel 18 can be made of any suitable light guiding
material, such as glass or optical fiber, which may be shaped,
using shaping methods for optical fibers known in the art, to have
the funnel shape shown in FIG. 4. Alternatively, light funnel 18
may include a hollow tube having polished surfaces 56, or a tube
filled with a highly light-transmissive fluid having a
predetermined index of refraction. It should be appreciated that
the specific geometry of light funnel 18 may depend on the
materials composition of the funnel as well as the geometry of
other parts of the testing apparatus. To obtain maximum reflection
of light 30, surfaces 56 of light funnel 18 are preferably polished
and coated with a highly reflective coating, for example, a gold or
"pure white" coating.
[0025] It will be appreciated by persons skilled in the art that
positioning light funnels 18 in juxtaposition with the entire
length of edges 50 and 52 of bar 20, for sequentially testing all
the laser devices 45 on bar 20 over testing areas 62 and 64,
respectively, enables efficient, reliable, testing of a large
number of laser devices. This testing arrangement is shown most
clearly in FIG. 5.
[0026] While certain specific embodiments of the invention are
disclosed as typical, the invention is not limited to these
particular forms, but rather is applicable broadly to all such
variations as fall within the scope of the appended claims. Many
modifications and adaptations will be apparent to those skilled in
the art to which the invention pertains. Thus, the specific
structures and methods discussed in detail above are merely
illustrative of specific embodiments of the invention.
* * * * *