U.S. patent application number 09/833368 was filed with the patent office on 2001-09-13 for method and apparatus for modulated integrated optically pumped vertical cavity surface emitting lasers.
Invention is credited to Jiang, Wenbin, Lee, Hsing-Chung.
Application Number | 20010021214 09/833368 |
Document ID | / |
Family ID | 27028664 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021214 |
Kind Code |
A1 |
Jiang, Wenbin ; et
al. |
September 13, 2001 |
Method and apparatus for modulated integrated optically pumped
vertical cavity surface emitting lasers
Abstract
Modulated integrated optically pumped vertical cavity surface
emitting lasers are formed by integrating an electrically pumped
semiconductor laser and a vertical cavity surface emitting laser
(VCSEL) together with a means of direct modulation of the
electrically pumped semiconductor laser. In the preferred
embodiments, the electrically pumped semiconductor laser is a type
of folded cavity surface emitting laser (FCSEL). In a number of
embodiments, the FCSEL is partitioned into two sections by a gap in
material layers. In these embodiments, one section of the FCSEL is
biased so as to maintain the generation of photons at a constant
power level to pump the optically pumped VCSEL while the second
section of the FCSEL is used for modulation and causes the
optically pumped VCSEL to be modulated above the threshold. In
another embodiment, an electric-absorption modulator is sandwiched
between an electrically pumped FCSEL and an optically pumped VCSEL.
The electric-absorption modulator acts similar to a camera shutter
and allows photons to pass through from the electrically pumped
FCSEL to the optically pumped VCSEL when in one state and
attenuates photons before reaching the optically pumped VCSEL when
in another state.
Inventors: |
Jiang, Wenbin; (Calabasas,
CA) ; Lee, Hsing-Chung; (Calabasas, CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
27028664 |
Appl. No.: |
09/833368 |
Filed: |
April 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09833368 |
Apr 12, 2001 |
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09560008 |
Apr 27, 2000 |
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09560008 |
Apr 27, 2000 |
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09430570 |
Oct 29, 1999 |
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Current U.S.
Class: |
372/50.1 |
Current CPC
Class: |
H01S 5/4025 20130101;
H01S 5/1085 20130101; H01S 5/18369 20130101; H01S 5/0216 20130101;
H01S 5/2027 20130101; H01S 5/026 20130101; H01S 5/041 20130101;
H01S 5/06216 20130101; H01S 5/2231 20130101; H01S 5/18 20130101;
H01S 5/06226 20130101; H01S 5/0608 20130101; H01S 5/2214 20130101;
H01S 5/0265 20130101 |
Class at
Publication: |
372/50 |
International
Class: |
H01S 005/00 |
Claims
What is claimed is:
1. A modulated integrated optically pumped vertical cavity surface
emitting laser comprising: an electrically pumped surface emitting
laser having a first section and a second section, the first
section being biased at a threshold level to generate first photons
of a first power level, the second section being modulated in
response to a modulation signal to modulate the first photons
between the first power level and a second power level; and an
optically pumped vertical cavity surface emitting laser coupled to
the electrically pumped surface emitting laser, the optically
pumped vertical cavity surface emitting laser to receive the first
photons emitted from the electrically pumped surface emitting laser
at a second power level and lase thereby emitting second photons
from the modulated integrated optically pumped vertical cavity
surface emitting laser.
2. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the optically pumped
vertical cavity surface emitting laser to receive the first photons
emitted from the electrically pumped surface emitting laser at the
first power level and remain at or near a threshold state.
3. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the electrically pumped
surface emitting laser is formed to emit photons at a wavelength
over a wavelength range of 600 nanometers to 1150 nanometers when
being electrically pumped.
4. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the optically pumped
vertical cavity surface emitting laser is formed to operate at a
wavelength over a wavelength range of 1200 nanometers to 1750
nanometers when being optically pumped.
5. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the modulation signal is
responsive to a data signal.
6. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the electrically pumped
surface emitting laser includes, an active region having one or
more quantum well structures, and, an internal-angled beam steering
element and an external-angled beam steering element formed in the
active region to reflect photons.
7. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the electrically pumped
surface emitting laser includes, an active region having one or
more quantum well structures, and, an internal-angled beam steering
element and a cleaved or etched facet at a ninety degree angle
formed in the active region to reflect photons.
8. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 6 wherein, the active region has
one or more Indium-Gallium-Arsenide quantum well structures, and
the electrically pumped surface emitting laser further includes, a
p-type Gallium-Arsenide cladding layer coupled to the active
region, and an oxide confinement region formed within the cladding
layer.
9. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 6 wherein, the active region has
one or more Gallium-Arsenide quantum well structures, and the
electrically pumped surface emitting laser further includes, a
p-type Aluminum-Gallium-Arseni- de cladding layer coupled to the
active region, and an oxide confinement region formed within the
cladding layer.
10. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 6 wherein, the electrically pumped
surface emitting laser further includes, a substrate, a distributed
Bragg reflector coupled to the substrate, a first and second
semiconductor cladding layer separated by a gap, a first and second
semiconductor contact layer separated by the gap, and a first and
second contact terminal coupled respectively to the first and
second semiconductor contact layer, the first and second contact
terminal being separated.
11. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 10 wherein, the substrate is an
n-type Gallium-Arsenide substrate, the distributed Bragg reflector
is an n-type Aluminum-Gallium-Arsenide distributed Bragg reflector,
the first and second semiconductor cladding layer is a p-type
Aluminum-Gallium-Arsenide cladding layer, the first and second
semiconductor contact layer is a p-type Gallium-Arsenide contact
layer, and the first and second contact terminal are formed of a
metal layer.
12. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 10 wherein, the gap is formed in
the first and second semiconductor contact layer and extends into
the cladding layer by implanting one of the set of protons, helium
and oxygen.
13. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 10 wherein, the gap is formed in
the first and second semiconductor contact layer by dry or wet
etching the semiconductor contact and the cladding layer.
14. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 6 wherein, the electrically pumped
surface emitting laser further includes, a first section and a
second section of a distributed Bragg reflector having a gap
separating the first and second section, and a first and second
contact terminal coupled respectively to the first section and the
second section of the distributed Bragg reflector, the first and
second contact terminal being separated.
15. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 14 wherein, the gap is formed in
the distributed Bragg reflector by dry etching or wet etching
layers of the distributed Bragg reflector.
16. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the optically pumped
vertical cavity surface emitting laser includes, a first
distributed Bragg reflector, an active region coupled to the first
distributed Bragg reflector, the active region having one or more
quantum well structures, a second distributed Bragg reflector
coupled to the active region, and a substrate coupled to the second
distributed Bragg reflector.
17. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 16 wherein, the first distributed
Bragg reflector is formed of dielectric materials, the one or more
quantum well structures of the active region are one or more
Indium-Gallium-Arsenide-P- hosphide quantum well structures, the
second distributed Bragg reflector is formed of layers of the pair
of materials of Indium-Gallium-ArsenidePh-
osphide/Indium-Phosphide, and the substrate is an Indium-Phosphide
substrate.
18. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 1 wherein, the optically pumped
vertical cavity surface emitting laser is coupled to the
electrically pumped surface emitting laser through one of the set
of atomic bonding, wafer bonding, metal bonding, and epoxy
bonding.
19. A modulated integrated optically pumped vertical cavity surface
emitting laser comprising: an electrically pumped surface emitting
laser to generate photons; an electric-absorption modulator coupled
to the electrically pumped surface emitting laser to receive the
generated photons, the electric-absorption modulator to
periodically absorb the generated photons from the electrically
pumped surface emitting laser in response to a modulation signal,
the electric-absorption modulator to periodically pass through the
generated photons from the electrically pumped surface emitting
laser in response to a modulation signal; and an optically pumped
vertical cavity surface emitting laser coupled to the
electric-absorption modulator, the optically pumped vertical cavity
surface emitting laser to receive the pass through photons from the
electric-absorption modulator generated by the electrically pumped
surface emitting laser, the optically pumped vertical cavity
surface emitting laser further to lase in response to the pass
through photons and emit photons from the modulated integrated
optically pumped vertical cavity surface emitting laser.
20. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the electric-absorption
modulator includes, an active region having one or more quantum
well structures, and a pair of contact terminals coupled across the
active region of the electric-absorption modulator to modulate the
electric-absorption modulator.
21. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 20 wherein, the one or more quantum
well structures of the electric-absorption modulator are formed to
absorb photons at a wavelength over a wavelength range of 600
nanometers to 1150 nanometers when in an absorption state.
22. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the electrically pumped
surface emitting laser is formed to emit photons at a wavelength
over a wavelength range of 600 nanometers to 1150 nanometers when
being electrically pumped.
23. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser is formed to operate at a
wavelength over a wavelength range of 1200 nanometers to 1750
nanometers when being optically pumped.
24. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the modulation signal
is responsive to a data signal.
25. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the electrically pumped
surface emitting laser is an electrically pumped folded cavity
surface emitting laser.
26. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 25 wherein, the electrically pumped
folded cavity surface emitting laser includes, an active region
having one or more quantum well structures, and, an internal-angled
beam steering element and an external-angled beam steering element
formed in the active region to reflect photons.
27. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 26 wherein, the active region of
the electrically pumped folded cavity surface emitting laser has
one or more Indium-Gallium-Arsenide quantum well structures, and
the electrically pumped folded cavity surface emitting laser
further includes, a p-type Gallium-Arsenide cladding layer coupled
to the active region, and an oxide confinement region formed within
the cladding layer.
28. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 26 wherein, the active region of
the electrically pumped folded cavity surface emitting laser has
one or more Gallium-Arsenide quantum well structures, and the
electrically pumped folded cavity surface emitting laser further
includes, a p-type Aluminum-Gallium-Arsenide cladding layer coupled
to the active region, and an oxide confinement region formed within
the cladding layer.
29. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 26 wherein, the electrically pumped
folded cavity surface emitting laser further includes, a substrate,
a distributed Bragg reflector coupled to the substrate, a
semiconductor cladding layer, a semiconductor contact layer, and a
top contact terminal coupled to the semiconductor contact layer and
a base contact terminal coupled to the substrate.
30. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 29 wherein, the substrate is an
n-type Gallium-Arsenide substrate, the distributed Bragg reflector
is an n-type Aluminum-Gallium-Arsenide distributed Bragg reflector,
the semiconductor cladding layer is a p-type
Aluminum-Gallium-Arsenide cladding layer, the semiconductor contact
layer is a p-type Gallium-Arsenide contact layer, and the top
contact terminal and the base terminal are formed of metal
layers.
31. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 26 wherein, the internal-angled
beam steering element and the external-angled beam steering element
are laser cavity mirrors formed by etching a facet at an angle to
amplify the energy of the photons in the laser cavity and to steer
photons to the optically pumped vertical cavity surface emitting
laser.
32. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 26 wherein, the internal-angled
beam steering element is a laser cavity mirror formed by etching a
facet at an angle to amplify the energy of the photons in the laser
cavity and to steer photons to the optically pumped vertical cavity
surface emitting laser, and the external-angled beam steering
element is a facet formed by cleaving or etching at a ninety degree
angle to reflect the photons back into the electrically pumped
laser cavity.
33. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 31 wherein, the angle that the
facets are etched is in the range from thirty-five degrees to
fifty-five degrees.
34. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 31 wherein, the angle that the
facet are etched is in the range from forty-two degrees to
forty-eight degrees.
35. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser is a long wavelength
optically pumped vertical cavity surface emitting laser having an
active region formed of one or more
Indium-Gallium-Arsenide-Phosphide quantum wells to be optically
pumped and emit photons of a relatively long wavelength.
36. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser is a long wavelength
optically pumped vertical cavity surface emitting laser having an
active region formed of one or more
Indium-Aluminum-Gallium-Arsenide quantum wells to be optically
pumped and emit photons of a relatively long wavelength.
37. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser is a long wavelength
optically pumped vertical cavity surface emitting laser having an
active region formed of one or more Gallium-Arsenide-Antimonide
quantum wells to be optically pumped and emit photons of a
relatively long wavelength.
38. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser is a long wavelength
optically pumped vertical cavity surface emitting laser having an
active region formed of one or more Indium-Gallium-Arsenide-Nitride
quantum wells to be optically pumped and emit photons of a
relatively long wavelength.
39. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser includes a first distributed
Bragg reflector mirror formed of Aluminum-Gallium-Arsenide
monolithically grown on a top layer of the in-plane surface
emitting laser during its semiconductor manufacturing.
40. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 wherein, the optically pumped
vertical cavity surface emitting laser includes an active region of
one or more quantum wells, a first distributed Bragg reflector and
a second distributed Bragg reflector.
41. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 40 wherein, the second distributed
Bragg reflector of the optically pumped vertical cavity surface
emitting laser is a dielectric mirror deposited on top of the
active region.
42. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 40 wherein, the first distributed
Bragg reflector of the optically pumped vertical cavity surface
emitting laser is a dielectric mirror.
43. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 40 wherein, the optically pumped
vertical cavity surface emitting laser includes an oxide region in
the first or the second distributed Bragg reflector to guide
photons to emit at a single mode transversely.
44. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 40 wherein, the optically pumped
vertical cavity surface emitting laser includes one or more mesa
regions patterned in the first or second distributed Bragg
reflector to index guide photons to emit at a single mode
transversely.
45. The modulated integrated optically pumped vertical cavity
surface emitting laser of claim 19 further comprising: a third
laser to generate a small spot pump beam to couple to the optically
pumped vertical cavity surface emitting laser to gain guide photons
to emit at a single mode transversely.
46. A semiconductor laser apparatus comprising: a first
semiconductor laser and a second semiconductor laser integrated
with the first semiconductor laser, said first semiconductor laser
being responsive to electrical pumping and said second
semiconductor laser being responsive to optical pumping by said
first semiconductor laser; means for modulating photons of said
first semiconductor laser in order to modulate the photon emission
of said second semiconductor laser; and at least one beam steering
element to steer photons of said first semiconductor laser in a
direction towards said second semiconductor laser.
47. The semiconductor laser apparatus of claim 46 wherein: the
means for modulating is an electric-absorption modulator that is
modulated by a data modulation signal across its terminals.
48. The semiconductor laser apparatus of claim 46 wherein: the
means for modulating is the first semiconductor laser having a
first section and a second section, the first section being biased
to a threshold level and the second section being modulated by a
data modulation signal across terminals of the second section.
49. A method of modulating an optically pumped vertical cavity
surface emitting laser, the method comprising: providing an
electrically pumped surface emitting laser; modulating the photonic
emission of the electrically pumped surface emitting laser in
response to a data modulation signal; and steering the modulated
photonic emission of the electrically pumped surface emitting laser
into the optically pumped vertical cavity surface emitting laser,
the optically pumped vertical cavity surface emitting laser
generating a modulated laser beam output in response to the
modulating the photonic emission of the electrically pumped surface
emitting laser.
50. The method of claim 49 wherein, the electrically pumped surface
emitting laser generates photons of a relatively short wavelength
and the optically pumped vertical cavity surface emitting laser
generates a modulated laser beam having a relatively long
wavelength.
51. The method of claim 49 wherein, the electrically pumped surface
emitting laser is an electrically pumped folded cavity surface
emitting laser.
52. The method of claim 51 wherein, the electrically pumped folded
cavity surface emitting laser is a two section folded cavity
surface emitting laser having a first section and a second section,
the first section being biased at a threshold state, the second
section being modulated by the data modulation signal to modulate
the photonic emission of the electrically pumped surface emitting
laser.
53. The method of claim 49 wherein, an electric-absorption
modulator is coupled to the electrically pumped surface emitting
laser and is modulated by the data modulation signal to modulate
the photonic emission of the electrically pumped surface emitting
laser.
54. A fiber optic communication system for transmitting, receiving
or transceiving information over optical fibers, the fiber optic
communication system including: a modulated integrated optically
pumped vertical cavity surface emitting laser, the modulated
integrated optically pumped vertical cavity surface emitting laser
including, an electrically pumped semiconductor laser to emit
photons of a relatively short wavelength, the electrically pumped
semiconductor laser being electrically pumped to generate the
photons of the relatively short wavelength; an electric-absorption
modulator coupled to the electrically pumped semiconductor laser,
the electric-absorption modulator to modulate the photons of the
relatively short wavelength emitted from the electrically pumped
semiconductor laser; and a vertical cavity surface emitting laser
coupled to the electric-absorption modulator, the vertical cavity
surface emitting laser to receive modulated photons of the
relatively short wavelength emitted from the in-plane semiconductor
laser through the electric-absorption modulator, the vertical
cavity surface emitting laser being optically pumped by the
modulated photons of the relatively short wavelength emitted from
the in-plane semiconductor laser through the electric-absorption
modulator and emitting photons of a long wavelength from a
surface.
55. The fiber optic communication system of claim 54 for
transmitting, receiving or transceiving information over optical
fibers, wherein, the electrically pumped semiconductor laser is an
electrically pumped folded cavity surface emitting laser.
56. The fiber optic communication system of claim 54 for
transmitting, receiving or transceiving information over optical
fibers, wherein, the electric-absorption modulator modulates the
photons of the relatively short wavelength emitted from the
electrically pumped semiconductor laser in response to a data
modulation signal received across its terminals.
57. A method of constructing modulated integrated optically pumped
vertical cavity surface emitting lasers, the method comprising:
forming a wafer of electrically pumped folded cavity surface
emitting lasers; forming a wafer of optically pumped vertical
cavity surface emitting lasers; aligning the wafer of the
electrically pumped folded cavity surface emitting lasers and the
wafer of optically pumped vertical cavity surface emitting lasers
together; coupling the wafer of the electrically pumped folded
cavity surface emitting lasers and the wafer of optically pumped
vertical cavity surface emitting lasers together; and removing the
substrate from the wafer of the electrically pumped folded cavity
surface emitting lasers; removing a portion of material from a
distributed Bragg reflector in the wafer of the electrically pumped
folded cavity surface emitting lasers to form a gap which separates
the distributed Bragg reflector into two sections; and forming a
first contact terminal on one side of the gap in the distributed
Bragg reflector and a second contact terminal on another side of
the gap.
58. The method of claim 57, further comprising: cutting through the
coupled wafers to separated the modulated integrated optically
pumped vertical cavity surface emitting lasers.
59. A method of constructing modulated integrated optically pumped
vertical cavity surface emitting lasers, the method comprising:
forming a wafer of electrically pumped surface emitting lasers;
forming a wafer of electric-absorption modulators; forming a wafer
of optically pumped vertical cavity surface emitting lasers;
aligning the wafer of the electrically pumped surface emitting
lasers, the wafer of electric-absorption modulators, and the wafer
of optically pumped vertical cavity surface emitting lasers
together; and coupling the wafer of the electrically pumped surface
emitting lasers, the wafer of electric-absorption modulators and
the wafer of optically pumped vertical cavity surface emitting
lasers together.
60. The method of claim 59, further comprising: cutting through the
coupled wafers to separated the modulated integrated optically
pumped vertical cavity surface emitting lasers, and forming a first
contact terminal on one side of each of the electric-absorption
modulators and a second contact terminal on another side of each of
the electric-absorption modulators.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application and
claims the benefit of U.S. application Ser. No. 09/430,570,
Attorney Docket No. 003918.P005, filed Oct. 29, 1999 by inventors
Wenbin Jiang et al, the disclosure of which prior application is
hereby incorporated by reference, verbatim and with the same effect
as though it were fully and completely set forth herein, both of
which are to be assigned to E2o Communication, Inc.
FIELD OF THE INVENTION
[0002] The present invention relates generally to semiconductor
lasers. More particularly, the present invention relates to
modulation of semiconductor lasers.
BACKGROUND OF THE INVENTION
[0003] Semiconductor lasers have become more important. One of the
most important applications of semiconductor lasers is in
communication systems where fiber optic communication media is
employed. With growth in electronic communication, communication
speed has become more important in order to increase data bandwidth
in electronic communication systems. Improved semiconductor lasers
can play a vital roll in increasing data bandwidth in communication
systems using fiber optic communication media such as local area
networks (LANs), metropolitan area networks (MANs) and wide area
networks (WANs). A preferred component for optical interconnection
of electronic components and systems via optical fibers is a
semiconductor laser.
[0004] One type of well known semiconductor laser is a vertical
cavity surface emitting laser (VCSEL). The current state of design
and operation of VCSELs is well known. Due to optical properties of
optical fibers, photons emitted at longer wavelengths from a laser
tend to propagate longer distances and are less disturbed by
optical noise sources. Thus, forming a VCSEL that can operate at
longer wavelengths, such as a wavelength greater than 1.25 .mu.m,
is desirable.
[0005] Lasers can be excited or pumped in a number of ways.
Typically, VCSELs have been electrically excited (i.e. electrically
pumped) by a power supply in order to stimulate photon emission.
However, achieving photon emission at long wavelengths using
electrical pumping has not been commercially successful due to a
number of disadvantages. More recently it has been shown that a
VCSEL can be optically excited (i.e. optically pumped) to stimulate
photon emission.
[0006] In order to use a semiconductor laser in communication
systems, the laser output needs to be modulated somehow to
communicate a signal. One type of laser modulation scheme varies
the intensity of the light generated by the laser. Oftentimes this
has been done externally from the laser, similar to a camera's
shutter allowing light to pass through to an unexposed film.
However, this requires additional elements. It is more desirable to
directly modulate a semiconductor laser. However previously, direct
modulation of semiconductor lasers at the desired high frequencies
of communication systems has been limited by jitter and chirping in
addition to turn-on delays. Turn-on delay is the time it takes for
a semiconductor laser to emit photons in response to receiving an
electric turn on signal. Jitter refers to the variations in the
pulses of emitted photons in relation to a constant pulse train of
an electric signal. Chirping refers to changes in the wavelengths
of the emitted photons from a semiconductor laser.
[0007] It is desirable to overcome the limitations of the prior
art.
BRIEF SUMMARY OF THE INVENTION
[0008] Briefly, the present invention includes methods, apparatus
and systems as described in the claims.
[0009] Modulated integrated optically pumped vertical cavity
surface emitting lasers are formed by integrating an electrically
pumped semiconductor laser and a vertical cavity surface emitting
laser (VCSEL) together with a means of direct modulation of the
electrically pumped semiconductor laser. In the preferred
embodiments, the electrically pumped semiconductor laser is a type
of folded cavity surface emitting laser (FCSEL). In a number of
embodiments, the FCSEL is partitioned into two sections by a gap in
material layers. In these embodiments, one section of the FCSEL is
biased so as to maintain the generation of photons without causing
the optically pumped VCSEL to lase while the second section of the
FCSEL is used for modulation and causes the optically pumped VCSEL
to lase. In another embodiment, an electric-absorption modulator is
sandwiched between an electrically pumped FCSEL and an optically
pumped VCSEL. The electric-absorption modulator acts similar to a
camera shutter and allows photons to pass through from the
electrically pumped FCSEL to the optically pumped VCSEL when in one
state and blocks photons from reaching the optically pumped VCSEL
when in another state.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0010] FIG. 1A is a magnified side view of an integrated optically
pumped vertical cavity surface emitting laser.
[0011] FIG. 1B is a magnified cross-sectional front view of the
integrated optically pumped vertical cavity surface emitting laser
of FIG. 1A.
[0012] FIG. 2A is a magnified side view of a first embodiment of
the modulated integrated optically pumped VCSEL of the present
invention.
[0013] FIG. 2B is a magnified side view of a second embodiment of
the modulated integrated optically pumped VCSEL of the present
invention.
[0014] FIG. 3A is a magnified cross-sectional view of a third
embodiment of the modulated integrated optically pumped VCSEL of
the present invention.
[0015] FIG. 3B is a magnified back side view of the integrated
optically pumped vertical cavity surface emitting laser of FIG.
3A.
[0016] FIG. 4 is a magnified side view of a fourth embodiment of
the modulated integrated optically pumped VCSEL of the present
invention.
[0017] FIG. 5A is a block diagram of a system for modulating the
modulated integrated optically pumped VCSELs of FIG. 2A, FIG. 2B,
and FIGS. 3A-3B.
[0018] FIG. 5B is a block diagram of a system for modulating the
modulated integrated optically pumped VCSEL of FIG. 4.
[0019] Like reference numbers and designations in the drawings
indicate like elements providing similar functionality.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] In the following detailed description of the present
invention, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. However,
it will be obvious to one skilled in the art that the present
invention may be practiced without these specific details. In other
instances well known methods, procedures, components, and circuits
have not been described in detail so as not to unnecessarily
obscure aspects of the present invention.
[0021] For operation at high frequencies, an optically pumped long
wavelength vertical cavity surface emitting laser (VCSEL) seems to
be the preferable type of semiconductor laser. A VCSEL that is
optically pumped need not be doped to lase. Therefore an optically
pumped VCSEL need not have its high frequency operation limited by
parasitic capacitance and inductance caused by dopants and metal
contact pads that would otherwise have been added. The only high
frequency limits of an optically pumped VCSEL would be as a result
of its intrinsic carrier transport time and thermionic emission.
The high frequency limits due to intrinsic carrier transport time
and thermionic emission do not usually take effect until modulation
frequencies of twenty giga-Hertz (20 GHz) or more are reached.
Furthermore, VCSEL-emission frequency is strongly confined by its
high cavity-Q and cavity resonance, and thus laser modulation
chirping is not as pronounced as an electrically pumped
conventional in-plane semiconductor laser. Therefore, an optically
pumped VCSEL has greater commercial potential for operation at high
frequencies of modulation.
[0022] In order to modulate an optically pumped VCSEL at high
frequencies, the present invention directly modulates the pump
laser, which in turn modulates the optically pumped VCSEL. To
minimize the turn-on delay and pulse jitter, the present invention
pre-biases the optically pumped VCSEL just above its threshold to
ensure the maximum extinction ratio. In NRZ (non-return-to-zero)
modulation, the extinction ratio (ER) is the ratio of the power
output of photons in a data-on state input to the power output of
photons in a data-off state input. In communications systems, a
larger ER is preferred but it is usually difficult to achieve due
to poor laser performance. The threshold of an optically pumped
VCSEL is the input optical pump power needed for the VCSEL to reach
lasing threshold. With an optically pumped VCSEL being close to its
threshold level, the power output of photons from it corresponding
to the data-off state is very low. Thus the ER can be very large
with the optically pumped VCSEL in this condition. To accomplish
this, the present invention maintains a minimum pump laser power
output level just above the VCSEL threshold power level. Modulating
the pump laser well beyond its own threshold current level reduces
jitter and the turn-on delay becomes negligible. Additionally, any
chirping of the pump laser from modulation will have a minimal
impact on the optically pumped VCSEL. This is so because the
optically pumped VCSEL is insensitive to wavelength variations of
photons generated by the pump laser.
[0023] A limiting factor of the pump laser that effects the
optically pumped VCSEL is the parasitics of the pump laser.
Parasitics, such as resistance, capacitance and inductance, tend to
limit the achievable direct modulation frequency of the
electrically pumped laser, which in turn can impact the direct
modulation frequency of the long wavelength VCSEL. The present
invention substantially reduces the problem posed by parasitics. In
a number of embodiments the pump laser has two sectional areas. One
of the two sectional areas is always biased with a current so as to
keep the pump laser turned on. This one sectional area is always
sufficiently biased by a current to keep the optically pumped VCSEL
just at its lasing threshold. The second of the two sectional areas
is used to modulate the pump laser, which in turn modulates the
optically pumped VCSEL. Splitting the pump laser into two sectional
areas partitions the parasitics so that a lower level of parasitics
in the pump laser need only be modulated. In another embodiment, an
electric-absorption (EA) modulator is used to modulate the light or
photons generated by the pump laser before being coupled into the
optically pumped VCSEL. The parasitics associated with modulating
the electric-absorption (EA) modulator are minimal such that
modulation of the optically pumped VCSEL can occur at high
frequencies.
[0024] The present invention provides a modulated integrated
optically pumped VCSEL, which is optically pumped by an
electrically pumped folded cavity surface emitting laser (FCSEL).
The modulated integrated optically pumped VCSEL can be modulated at
high frequencies and is preferably formed to generated photons of
relatively long wavelengths. The FCSEL is electrically pumped and
its photon output modulated in order to modulate the optically
pumped VCSEL at high speeds. The integrated optically pumped
vertical cavity surface emitting laser (VCSEL) is formed by
integrating the electrically pumped FCSEL with an optically pumped
VCSEL. Preferably, the FCSEL is designed to emit photons of
relatively short wavelengths while the optically pumped VCSEL is
designed to emit photons of relatively long wavelengths. The
electrically pumped FCSEL and optically pumped VCSEL can be
integrated together in a number of ways including atomic bonding,
wafer bonding, metal bonding, epoxy glue or other well known
semiconductor bonding techniques. A number of embodiments of the
modulated integrated optically pumped VCSEL are disclosed.
[0025] The electrically pumped FCSEL is preferably designed to
operate at relatively short wavelengths (from 770 nanometers (nm)
to 1100 nanometers (nm)) with an optically pumped VCSEL designed to
operate preferably at relatively long wavelengths (from 1250 nm to
1700 nm). The optically pumped VCSEL operates without the use of
electric power by being optically pumped by the electrically pumped
FCSEL. Integration of the lasers depends upon the type of
semiconductor materials utilized in forming the two lasers. The two
lasers are integrated into one unit through semiconductor
processing methods such as monolithic epitaxial growth or by
joining outer layers of the two lasers together through atomic
bonding, wafer bonding, metal bonding, epoxy glue or other well
known semiconductor bonding techniques. Additionally, the optically
pumped VCSEL can be bonded to the FCSEL at an angle in order to
avoid reflected light from the long wavelength VCSEL being directly
returned to the in-plane laser to thereby avoiding optical noise
being fed back into the FCSEL. A third laser can also be used to
generate a small spot pump beam to couple to the optically pumped
VCSEL in order to gain guide photons to emit at a single mode
transversely. Although the electrically pumped FCSEL, also referred
to as the pump laser, can be multimode either longitudinally or
transversely, the output from the optically pumped VCSEL is single
mode longitudinally. The output from the optically pumped VCSEL can
be single mode transversely depending upon the geometric
integration scheme and patterning. It is preferred that the
optically pumped VCSEL operate in a single transverse mode to
optimally couple with a single mode fiber. Modulation of the
optically pumped VCSEL can be achieved through direct electrical
modulation of the pump laser or an electric-absorption
modulator.
[0026] Referring now to FIG. 1A, an integrated optically pumped
VCSEL 100 is illustrated. The integrated optically pumped VCSEL 100
includes a folded cavity surface emitting laser (FCSEL) 140
integrated with an optically pumped VCSEL 150. The folded cavity
surface emitting laser 140 includes a substrate 101, a distributed
Bragg reflector (DBR) 102, an active area 104, a confinement layer
105, a cladding layer 106, a semiconductor contact layer 107, a
first metal layer as a top contact terminal 108, a second metal
layer as a base terminal 110, and the facets or beam steering
elements 111A and 111B.
[0027] Substrate 101 of the FCSEL 104 is preferably an n-type doped
Gallium-Arsenide (GaAs) layer. Alternatively, the substrate 101 can
be a layer of an n-type doped Indium-Phosphide (InP) or other
semiconductor materials.
[0028] The DBR 102 is preferably doped to match the substrate 101.
For example, in the case that the substrate 101 is an n-type doped
Indium-Phosphide (InP) or Gallium-Arsenide (GaAs) substrate, the
DBR 102 is n-type doped as well. The layers of the DBR 102 are
preferably formed from n-type
Al.sub.xGal.sub.1-xAs/Al.sub.yGa.sub.1-yAs pairs of material with x
ranging from 0 and 0.5, and y ranging from 0.5 and 1 for a GaAs
substrate. The number of pairs may range from as few as five to as
many as forty with the typical number of pairs being about twenty
pairs of layers. Alternatively, an
Indium-Aluminum-Gallium-Arsenide/Indium-Phosphi- de (InAlGaAs/InP)
distributed Bragg Reflector (DBR), an
Indium-Gallium-Arsenide-Phosphide/Indium-Phosphide (InGaAsP/InP)
DBR, or other monolithic grown DBR mirror can be grown onto the
substrate 101 if it is an InP substrate. If wafer bonding
techniques are used, a Gallium-Arsenide/Aluminum-Gallium-Arsenide
(GaAs/AlGaAs) distributed Bragg reflector (DBR) or a dielectric DBR
can be bonded to the substrate 101 and the active area 104. In the
case of wafer bonding, the substrate 101 is preferably GaAs.
Exemplary dielectric materials for a dielectric DBR include
titanium di-oxide (TiO.sub.2), silicon di-oxide (SiO.sub.2), and
silicon nitrogen di-oxide (SiNO.sub.2).
[0029] The active area 104 can be a Gallium-Arsenide (GaAs), an
Aluminum-Gallium-Arsenide (AlGaAs), or an Indium-Gallium-Arsenide
(InGaAs) quantum well structure. The active area 104 of the FCSEL
140 in the preferred embodiment is a GaAs quantum well The quantum
well structure can be formed of a single quantum well or multiple
quantum wells but in the preferred embodiment one to three quantum
wells are utilized.
[0030] The cladding layer 106 of the FCSEL 140 is a p-type GaAs and
can alternately be a p-type AlGaAs layer.
[0031] The confinement layer 105 of the FCSEL 140 is preferably an
Aluminum-Gallium-Arsenide (AlGaAs) layer with aluminum content at
larger than 90% and preferably larger than 95%. The
Aluminum-Gallium-Arsenide (AlGaAs) layer 105 is formed within a
part of the cladding 106 to allow lateral oxidation during device
fabrication. Alternately, the confinement layer 105 is formed by
oxidizing a portion of an Aluminum-Arsenide (AlAs) layer into an
Aluminum-Oxide (Al.sub.2O.sub.3) region. The confinement layer 105
provides both current confinement and optical confinement for the
FCSEL 140. Referring momentarily to FIG. 1B, the confinement layer
105 is oxidized to form a narrow conductive stripe above the active
region 104 as illustrated.
[0032] The semiconductor contact layer 107 is provided so as to
make an ohmic contact to the metal layer of the top contact
terminal 108 deposited on its top surface. The semiconductor
contact layer 107 is preferably a Gallium-Arsenide (GaAs) layer
highly doped to be p-type semiconductor so as to provide an ohmic
contact.
[0033] The first metal layer of the top contact terminal 108 forms
a first terminal of the integrated optically pumped VCSEL 100.
Referring momentarily to FIG. 1B, the metal layer for the top
contact terminal 108 is only left deposited in certain areas of the
semiconductor contact layer 107 so as not to block areas where
photons are emitted or interfere with the coupling to the optically
pumped VCSEL 150.
[0034] The second metal layer for the base terminal 110 is
deposited on the bottom surface of the substrate 101 in order to
form the second terminal of the integrated optically pumped VCSEL
100.
[0035] The FCSEL 100 is an electrically pumped semiconductor laser
which has a folded laser cavity provided by a pair facets (also
referred to as reflectors or beam steering elements) 111A and 111B
at opposite ends. Preferably the external-angled beam steering
element 111B and the internal-angled beam steering element 111A are
approximately forty five degree angles with the incident light to
form the folded cavity of the folded cavity surface emitting laser
140. The beam steering elements 111A and 111B are preferably
parallel to each other and formed by cleaving, etching, ion milling
or other well known semiconductor process. The active area 104 of
the FCSEL has the external-angled beam steering element 111B and
the internal-angled beam steering element 111A formed from
processing its material layers. The external-angled beam steering
element 111B and the internal-angled beam steering element 111A may
continue and be formed into the cladding 106, the contact layer
107, and a portion 103 of the DBR 102 as illustrated in the
Figures. A dielectric coating (not shown) may be added to the
facets 111A and 111B to act as a mirror coating to increase the
reflectivity efficiency or as a surface passivation.
[0036] To manufacture the FCSEL 140, the layers of materials are
first deposited or grown from the beginning layer of the substrate
101. After forming a monolithic structure consisting of the
substrate 101, the DBR 102, the active region 104, the cladding
layer 106 with the confinement layer 105, and the contact layer
107, the facets 101A and 101B can be formed. The facets 101A and
101B are formed by cleaving, etching, ion milling or other
semiconductor process to remove material.
[0037] The optically pumped VCSEL 150 includes a first distributed
Bragg reflector (DBR) 112, a quantum well active area 114, a second
distributed Bragg reflector (DBR) 116, and a substrate 118. The
first DBR 112 can be an Al.sub.xGa.sub.1-xAs/Al.sub.yGa.sub.1-yAs
DBR, an InP/InGaAsP DBR, or a dielectric DBR, and is preferably a
dielectric DBR. The active area 114 can be InGaAsP, InAlGaAs,
InGaAs, InGaAsN, or GaAsSb quantum well structure having multiple
quantum wells. The second DBR 116 can be an
Al.sub.xGa.sub.1-xAs/Al.sub.yGa.sub.1-yAs DBR, an InGaAsP/InP DBR
or a dielectric DBR, and is preferably made of pairs of
InGaAsP/InP. The substrate 118 of the optically pumped VCSEL 150
can be a layer of GaAs or of Indium-Phosphide (InP), and is
preferably an InP substrate. DBRs 112 and 116 are preferably made
of thicknesses to provide substantial (preferably 99% or more)
reflection of long wavelengths at 1.3 .mu.m or 1.55 .mu.m to
amplify and stimulate emission. In FIGS. 1A and 1B, the folded
cavity surface emitting laser 140 and the optically pumped VCSEL
150 are integrated together at the interface 120 by either fusing,
gluing, metal bonding, epoxy bonding or other well-known
semiconductor bonding methods. In this case, interface 120
represents the joining of the surfaces and a layer of material, if
any, to join the surfaces. The interface 120 can alternately be an
air gap in the case where the FCSEL 140 and the optically pumped
VCSEL 150 are held mechanically aligned together.
[0038] In operation, the folded cavity surface emitting laser 140
generates a short wavelength laser beam 109 which is reflected
between the beam steering element 111A, beam steering element 111B,
DBR 102, and the contact layer 107 as the laser beam elements 109A,
109B and 109C. The in-plane laser beam 109A is reflected by beam
steering element 111A into the substantially perpendicular beam
109B for coupling into the VCSEL 150 to optically pump it. After
becoming sufficiently pumped to reach lasing threshold, the
optically pumped VCSEL 150 emits photons 144 preferably of a
relatively long wavelength as a laser beam.
[0039] Referring now to FIG. 2A, a magnified side view of a
modulated integrated optically pumped VCSEL 200 is illustrated. The
modulated integrated optically pumped VCSEL 200 includes the VCSEL
150 and a two-section FCSEL 140'. But for those described below,
the elements of optically pumped VCSEL 150 are the same as those
described with reference to FIGS. 1A-1B and are not repeated here.
The two-section FCSEL 140' is similar to FCSEL 140 except that the
two-section FCSEL 140' is separated into two sections, a first
section 201 and a second section 202 by a gap 205. The gap 205 may
be an airgap or a gap filed with an insulative or dielectric
material. The gap 205 separates the semiconductor contact layer 107
of FCSEL 140 into two sections, semiconductor contact layer 207A
and semiconductor contact layer 207B of FCSEL 140' in FIG. 2A. Each
of the sections 201 and 202 also has its own separate contact
terminal, first contact terminal 208A and second contact terminal
208B respectively, which are formed out of a deposited metal layer
in the desired contact area. The separate contact terminals 208A
and 208B provide for separate control of the FCSEL 140'. The gap
205 essentially forms two separate sections, first section 201 and
second section 202, of the FCSEL 140'. The first section 201 of the
FCSEL 140' is separately controlled by the first contact terminal
208A. The second section 202 of the FCSEL 140' is separately
controlled by the second contact terminal 208B. Interface 120'
couples FCSEL 140' to the VCSEL 150 and is formed similarly to
interface 120 of FIGS. 1A-1B but for the gap 205.
[0040] The second section 202 of the FCSEL 140' is DC biased, while
the first section 201 of the FCSEL 140' is modulated by data at a
data rate, or alternatively the first section 201 can be DC biased
while the second section 202 is modulated by data at a data rate.
The two sections, the first section 201 and the second section 202,
are controlled in such a way that the FCSEL 140' is always "on" and
generating photons at one power level. When the first section 201
is "off", the second section 202 is controlled so that the pump
power of the FCSEL 140' generates photons having a power level at
or slightly above the lasing threshold of the optically pumped
VCSEL 150. The second section 202 in this case is said to be at a
threshold biased state. In this case, VCSEL 150 does not lase or
minimally lases with emitted photons 244 being of a low power level
and therefore can be considered turned "off". When the first
section 201 is "on" in combination with the second section 202
being in a threshold biased state, the combined pump power from the
first section 201 and the second section 202 of the FCSEL 140'
generate photons of a second power level exceeding the threshold
pump power of the VCSEL 150 so that it lases and emits photons 244.
In this case, VCSEL 150 can be considered turned "on" when it lases
and emits photons 244. Optically pumped VCSEL 150 is preferably a
long wavelength optically pumped VCSEL to generate photons 244 at a
relatively long wavelength such as 1300 nm. The elements of the
optically pumped VCSEL 150 are the same as those described with
respect to FIGS. 1A-1B and are not repeated here.
[0041] Referring now to FIG. 2B, a magnified side view of a
modulated integrated optically pumped VCSEL 200' is illustrated.
The modulated integrated optically pumped VCSEL 200' of FIG. 2B is
similar to the modulated integrated optically pumped VCSEL 200 of
FIG. 2A except that an unnecessary portion of the optically pumped
VCSEL 150 is removed. Optically pumped VCSEL 150' is smaller that
the optically pumped VCSEL 150 and utilizes semiconductor materials
more efficiently. Additionally, the modulated integrated optically
pumped VCSEL 200' can have a larger surface contact for the metal
contact terminal 208B. VCSEL 200' retains the gap 205 to split the
FCSEL 140' into two sections, the first section 201 and the second
section 202. Alternatively, gap 205 may be larger or formed
differently due to the fact the portion of the optically pumped
VCSEL 150' is not covering the gap as in FIG. 2A.
[0042] In operation of the modulated integrated optically pumped
VCSEL 200 or 200', a data modulated waveform is coupled into the
first contact terminal 208A to modulate the FCSEL 140' and thereby
modulate the optically pumped VCSEL 150 to emit photons 244 or not
emit photons 244. A threshold bias signal is coupled into the
second contact terminal 208B while a reference level is coupled
into the base terminal 110. While a voltage waveform is supplied
between the first contact terminal 208A and the base terminal 110
and between the second contact terminal 208B and the base terminal
110, currents generated thereby in the FCSEL 140' actually form the
threshold bias and modulate the FCSEL 140' into the emission of
high or low energy photons into the optically pumped VCSEL 150.
[0043] Referring now to FIG. 3A, a magnified cross-sectional side
view of a modulated integrated optically pumped VCSEL 300 is
illustrated. The modulated integrated optically pumped VCSEL 300
includes a FCSEL 140" and the optically pumped VCSEL 150 as
illustrated in FIGS. 3A-3B. The material layers of the modulated
integrated optically pumped VCSEL 300 of FIGS. 3A-3B are the same
as those of the integrated optically pumped VCSEL 100 unless
discussed below and are otherwise not repeated here for brevity. A
wafer of optically pumped VCSELs 150 and a wafer of FCSELs 140 are
initially formed in the manufacture of the modulated integrated
optically pumped VCSEL 300 and joined together. To further
manufacture the VCSEL 300, portions of material layers are removed.
The substrate 101 (not shown in FIG. 3A) used to initially form the
FCSEL 140" is removed from the VCSEL 300. In comparison with FIGS.
1, 2A, and 2B, a portion of the DBR 102 of the FCSEL is removed,
including a gap 305, to form a first DBR section 312A and a second
DBR section 312B.
[0044] Initially before the removal of materials, wafer boding is
used to join together in alignment, the optically pumped VCSELs 150
in a wafer format with the FCSELs 140 in a wafer format. The device
fabrication process of the modulated integrated optically pumped
VCSELs 300 starts from the exposed substrate 101 of the FCSELs 140
in the joined wafers. First the substrate 101 is removed and a
portion of the DBR 102 of the FCSELs is removed, including a gap
305, to form a first DBR section 312A and a second DBR section 312B
of the FCSELs 140". A metal layer is then deposited in two desired
contact terminal areas onto the first DBR section 312A and the
second DBR section 312B to form a first contact terminal 310A and a
second contact terminal 310B. On the FCSEL side of the joined
wafers, sufficient portions of FCSEL material layers are etched
away to expose an area of the semiconductor contact layer 107 for
making p-type electrical contact from the same side as the n-type
metal contacts. A metal layer is then deposited onto desired areas
of the semiconductor contact layer 107 to form the p-contact
terminal 308 and the DBR sections 312A and 312B to form the
n-contact terminals 310A and 310B respectively. Referring now to
FIG. 3B, the p-contact terminal 308 couples to the semiconductor
contact layer 107 and the n-contact terminal 310B couples to the
DBR section 312B as illustrated. The p-contact terminal 308 extends
across the first section 301 and the second section 302 of the
FCSEL 140".
[0045] FCSEL 140" is a sectional FCSEL having the first section 301
and the second section 302 formed by the gap 305. The gap 305 may
be an airgap or a gap filed with an insulative or dielectric
material. The gap 305 separates the DBR 102 of FCSEL 140 into two
sections, a first DBR section 312A and a second DBR section 312B of
the FCSEL 140". Each of the DBR sections 312A and 312B also has its
own separate metal contact terminal, first contact terminal 310A
and second contact terminal 310B respectively, which are formed out
of a deposited metal layer in the desired contact area. The
separate contact terminals 310A and 310B provide for separate
control of the FCSEL 140". The first section 301 of the FCSEL 140"
is separately controlled by the first contact terminal 310A. The
second section 302 of the FCSEL 140" is separately controlled by
the second contact terminal 310B.
[0046] The second section 302 of the FCSEL 140" is DC biased, while
the first section 301 of the FCSEL 140" is modulated by data at a
data rate, or alternatively the first section 301 can be DC biased
while the second section 302 is modulated by data at a data rate.
The first section 301 and the second section 302 are controlled in
such a way that the FCSEL 140" is always "on" and generating
photons but not necessarily at the same power level. When the first
section 301 is "off", the second section 302 is controlled so that
the pump power of the FCSEL 140" generates photons having a power
level at the lasing threshold of the optically pumped VCSEL 150.
The second section 302 is said to be at a threshold biased state.
In this case, VCSEL 150 does not lase or minimally lases with
emitted photons 344 being of a low power level and therefore can be
considered turned "off". When the first section 301 is "on" in
combination with the second section 302 being in a threshold biased
state, the combined pump power from the first section 301 and the
second section 302 of the FCSEL 140" is at a level exceeding the
threshold pump power of the VCSEL 150 so that it lase and emits
photons 344. In this case, VCSEL 150 can be considered turned "on"
when it lases and emits photons 344.
[0047] In operation, a data modulated waveform is coupled into the
first contact terminal 310A to modulate the FCSEL 140" and thereby
modulate the optically pumped VCSEL 150 to emit photons 344 or not
emit photons 344. A threshold bias signal is coupled into the
second contact terminal 310B while a reference level is coupled
into the contact terminal 308. While a voltage or current waveform
is supplied between the first contact terminal 310A and the contact
terminal 308 and between the second contact terminal 310B and the
contact terminal 308, currents generated thereby in the FCSEL 140"
actually form the threshold bias and modulate the FCSEL 140" into
the emission of high or low energy photons into the optically
pumped VCSEL 150.
[0048] In the embodiments illustrated in FIGS. 2A, 2B, and 3A-3B of
the present invention, the pump laser is split into two sections.
In FIGS. 2A and 2B, FCSEL 140' is split into the first section 201
and the second section 202 by a gap 205. In FIGS. 3A-3B, FCSEL 140"
is split into the first section 301 and the second section 302. The
parasitics as seen from the point of view of the electrical
connections to the pump laser are also split in two. As a result,
the dynamic parasitics associated with data modulation of the first
section 201 through the first contact terminal 208A and of the
first section 301 through the first contact terminal 310A are
reduced from that of modulating the top contact terminal 108 of
FIGS. 1A-1B. The dynamic parasitic reduction at the first contact
terminal 208A is because only a small section of the pump FCSEL
140', the first section 201, needs to be modulated. The dynamic
parasitic reduction at the first contact terminal 310A is because
only a small section of the pump FCSEL 140", the first section 301,
needs to be modulated. With a low level of dynamic parasitics at
the pump laser, higher pump modulation frequencies can be obtained.
The higher pump modulation frequencies enable a higher modulation
frequency in the optically pumped VCSEL 150 and 150' as well.
[0049] Referring now to FIG. 4, a magnified side view of a
modulated integrated optically pumped VCSEL 400 is illustrated. The
modulated integrated optically pumped VCSEL 400 which is the
preferred embodiment includes an electrically pumped surface
emitting laser, the optically pumped VCSEL 150 and a surface
integrated electric-absorption (EA) modulator 405 sandwiched
there-between along with the interface 120'". The electrically
pumped surface emitting laser can be an electrically pumped
in-plane surface emitting laser, an electrically pumped grating
surface emitting laser, an electrically pumped VCSEL, or an
electrically pumped FCSEL 140 as shown in FIG. 4. The elements of
the material layers of the FCSEL 140 and the VCSEL 150 of the
modulated integrated optically pumped VCSEL 400 are the same as
those described with reference to FIGS. 1A-1B and are not repeated
herein for brevity.
[0050] The electric-absorption (EA) modulator 405 is formed of
multiple quantum wells sandwiched between cladding layers and
contact layers. The optically pumped VCSEL 150 is coupled to the EA
modulator 405 through the interface 120'". Interface 120'" is
formed similarly to interface 120 of FIGS. 1A-1B. The EA modulator
405 couples to the semiconductor contact layer 107 of the
electrically pumped FCSEL 140. The EA modulator 405 is used to
modulate the light or photons generated by the electrically pumped
FCSEL 140 before they are coupled into the optically pumped VCSEL
150. The EA modulator 405 acts similar to a shutter of a still
camera. In the "on" state, the photons generated by the
electrically pumped FCSEL 140 is transmitted through the EA
modulator 405 into the optically pumped VCSEL 150 without being
absorbed. In the "off" state, the EA modulator 405 is highly
absorptive and attenuates the photons emitted by the electrically
pumped FCSEL 140 before they reach the optically pumped VCSEL 150.
The EA modulator 405 includes contact terminals 410 and 408 for
modulation control. A modulated voltage is provided between the
contact terminals 410 and 408 to modulate the modulated integrated
optically pumped VCSEL 400. The modulated voltage is generated in
response to a desired data modulation signal and causes the EA
modulator 405 to attenuate photons at one voltage level and allow
them to pass at another voltage level.
[0051] The parasitics associated with modulating the EA modulator
405 are minimal such that modulation of the optically pumped VCSEL
can occur at high frequencies. The EA modulator 405 inherently has
chirping but does not effect the optically pumped VCSEL 150. The
optically pumped VCSEL 150 is relatively insensitive to variations
of the input pump wavelength. The EA modulator 405 may have a poor
extinction ratio of photons but this does not pose a problem for
the modulated integrated optically pumped VCSEL 400. This is
because it is not necessary to completely turn off the electrically
pumped FCSEL 140 during an "off" state in order that photons 444
are not emitted. The pump power need only be maintained at or near
the threshold pump level of the optically pumped VCSEL 150 so that
photons 444 are not emitted. Essentially the modulation frequency
of the modulated integrated optically pumped VCSEL 400 is limited
only by the carrier transport and the thermionic emission effect of
the optically pumped VCSEL 150.
[0052] Referring now to FIG. 5A, a block diagram of a system 500
for modulation of the embodiments of the modulated integrated
optically pumped VCSELs 200, 200', and 300 is illustrated. The
system 500 receives a data input 501 through an electronic
interface 502 such as a wire, cable, or pins. By means of an
optical interface 503, such as a collimating lens or fiber pigtail,
the system 500 couples to an optical fiber 504. Drive circuitry 506
generates the proper drive currents for a serial data modulation
signal 510A and a threshold bias signal 510B with respect to the
reference 508. The serial data modulation signal 510A and the
threshold bias signal 510B are respectively coupled to terminals
208A and 208B of VCSEL 200, terminals 208A and 208B of VCSEL 200',
or terminals 310A and 310B of VCSEL 300. The reference signal 508
of the drive circuitry 506 is coupled to the base terminal 110 of
VCSEL 200 and VCSEL 200', and top contact terminal 308 of VCSEL
300.
[0053] Referring now to FIG. 5B, a block diagram of a system 500'
for modulation of the preferred embodiment of the modulated
integrated optically pumped VCSEL 400 is illustrated. System 500'
is similar to system 500 but for drive circuitry 506' which
generates a varying voltage between the serial data modulation
terminals 410 and 408 of the EA modulator 405. The drive circuitry
506' also provides a voltage or current across terminals 408 and
110 for the FCSEL 140 of the modulated integrated optically pumped
VCSEL 400.
[0054] In each of the embodiments disclosed herein, the turn-on
delay was minimized by maintaining the pump laser, the electrically
pumped FCSEL, in a biased state generating photons with its power
at or slightly above the optically pumped VCSEL threshold. Jitter
is minimized in the embodiments as well for this same reason
because the pump laser, the electrically pumped FCSEL, is
maintained in a biased state constantly generating photons.
Chirping was minimized in the embodiments of modulated integrated
optically pumped VCSELs 200, 200', 300 and 400 because the VCSEL is
relatively insensitive to the pump wavelength variation.
[0055] The present invention has many advantages over the prior
art. One advantage of the present invention is that dynamic
modulation parasitics are reduced so that modulation frequencies
can be greater. Another advantage is that modulated integrated
optically pumped VCSEL can be commercially manufactured. Other
advantages of the present invention will become obvious to those of
ordinary skill in the art after thoroughly reading this
disclosure.
[0056] The preferred embodiments of the present invention are thus
described. While the present invention has been described in
particular embodiments, the present invention should not be
construed as limited by such embodiments, but rather construed
according to the claims that follow below.
* * * * *