EP1258065A4 - High power distributed feedback ridge waveguide laser - Google Patents

High power distributed feedback ridge waveguide laser

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Publication number
EP1258065A4
EP1258065A4 EP01920104A EP01920104A EP1258065A4 EP 1258065 A4 EP1258065 A4 EP 1258065A4 EP 01920104 A EP01920104 A EP 01920104A EP 01920104 A EP01920104 A EP 01920104A EP 1258065 A4 EP1258065 A4 EP 1258065A4
Authority
EP
European Patent Office
Prior art keywords
laser diode
semiconductor laser
waveguide region
ridge structure
distributed feedback
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01920104A
Other languages
German (de)
French (fr)
Other versions
EP1258065A1 (en
Inventor
Joseph H Abeles
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Trumpf Photonics Inc
Original Assignee
Trumpf Photonics Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Trumpf Photonics Inc filed Critical Trumpf Photonics Inc
Publication of EP1258065A1 publication Critical patent/EP1258065A1/en
Publication of EP1258065A4 publication Critical patent/EP1258065A4/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/12—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q23/00—Antennas with active circuits or circuit elements integrated within them or attached to them
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G02F1/2257—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure the optical waveguides being made of semiconducting material
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
    • G02F1/31—Digital deflection, i.e. optical switching
    • G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
    • G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
    • G02F1/31—Digital deflection, i.e. optical switching
    • G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
    • G02F1/3137—Digital deflection, i.e. optical switching in an optical waveguide structure with intersecting or branching waveguides, e.g. X-switches and Y-junctions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/26—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture
    • H01Q3/2682—Time delay steered arrays
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/011—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  in optical waveguides, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/212—Mach-Zehnder type
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/16—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 series; tandem
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/05—Function characteristic wavelength dependent
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/15—Function characteristic involving resonance effects, e.g. resonantly enhanced interaction
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/58—Multi-wavelength, e.g. operation of the device at a plurality of wavelengths
    • G02F2203/585—Add/drop devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1039—Details on the cavity length
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2036—Broad area lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser

Definitions

  • the present invention relates to a ridge waveguide (RWG) semiconductor laser diode
  • FIG. 1 shows the RIN performance achieved and 300 MHz
  • High-power ridge waveguide (RWG) lasers use a cold-cavity index, i.e., effective
  • antiguiding Although antiguiding is quantitatively difficult to estimate accurately and is
  • the width limits the power that can be achieved by the laser for several reasons: Firstly, the
  • any RWG laser such as a DFB RWG
  • a semiconductor laser diode comprises a body of a semiconductor material having a
  • the diode also includes a distributed feedback structure associated with at
  • the width of the ridge can be
  • FIG. 1 is a graph plotting linewidth vs. power output of a prior art broadened
  • FIG. 2 is a graph plotting power output vs. injection current of a prior art broadened
  • FIG. 3 is a perspective view of a DFB RWG semiconductor laser diode according to an exemplary embodiment of the present invention.
  • FIG. 3 there is shown a DFB RWG semiconductor laser diode 10
  • the laser diode 10 comprises a body 12 of a semiconductor material or materials having a bottom surface 14,
  • the body 12 includes a waveguide
  • the active region 24 may be of any structure well known in the laser diode art which is
  • the active region 24 comprises one or more quantum wells.
  • the waveguide region 22 includes a
  • the first and second layers 25 and 26 of undoped semiconductor material have a
  • doping level of no greater than about 5X10 16 atoms/cm 3 .
  • a first clad region 28 is disposed on the first side of the waveguide region 22.
  • first clad region 28 may be composed of a semiconductor material of a P-type conductivity.
  • the first clad region 28 is etched so as expose portions
  • a distributed feedback structure formed by corrugations 33, is etched in
  • the doping level in the first and second clad regions 28 and 30 are typically between about 5X10 17 atoms/cm 3 and 2X10 19 atoms/cm 3 .
  • a contact layer 32 of a conductive material, such as a metal, is on and in ohmic
  • the contact layer 32 is in
  • the contact layer 34 extends across the
  • the thickness of the waveguide region 22 and the composition of the waveguide are The thickness of the waveguide region 22 and the composition of the waveguide
  • active region 24 does not overlap from the waveguide region 22 into the more heavily doped
  • clad regions 28 and 30 by more than 5%, and preferably by not more than 2%.
  • the clad regions 28 and 30 by more than 5%, and preferably by not more than 2%.
  • the amount of overlap of the photons into the clad regions 28 and 30 need not be less than 1%. This means that the amount of the optical mode, which is mainly in the waveguide region
  • the thickness of the waveguide region should be at least
  • the various regions of the body 12 may be made of any of the well known semiconductor materials used for making laser
  • diode such as but not limited to gallium arsenide, aluminum gallium arsenide, indium
  • 30 may be doped uniformly throughout their thickness or may be graded with little or no
  • the laser diode 10 of the present invention can be made longer than conventional
  • laser diodes i.e., in lengths of substantially 3 millimeters or longer, because there is lower
  • semiconductor material surrounding the ridge structure 31 is substantially reduced to between about 0.0007 and 0.002. This, in turn, permits width Wof the ridge to be

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • Semiconductor Lasers (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

A distributed feedback ridge waveguide semiconductor laser diode (10) having a waveguide region (22) with a typical thickness of at least 500 nanometers and an effective refractive index difference between the ridge structure (31) and exposed portions of the waveguide region (25) which surround the ridge structure of less than 0.001. This permits the width (W) of the ridge (31) to be expanded beyond 3.5 microns thus translating directly to higher power outputs at 1.55 νm wavelengths, where carrier diffusion and carrier heating limit current density injected into the active region (24).

Description

HIGH POWER DISTRIBUTED FEEDBACK RIDGE WAVEGUIDE LASER
PROVISIONAL APPLICATION
This application claims the benefit of Provisional application 60 176,915 filed
January 20, 2000.
FIELD OF THE INVENTION
The present invention relates to a ridge waveguide (RWG) semiconductor laser diode
having increased output power, to a distributed feedback (DFB) RWG semiconductor laser
diode of this kind which exhibits dynamic single longitudinal mode along with increased
output power, and, more particularly, to a high power RWG semiconductor laser diode, such
as a DFB RWG semiconductor laser diode, having reduced antiguiding effects within the
waveguide which permits a larger single mode guide to be utilized.
BACKGROUND OF THE INVENTION
High efficiency, high power lasers have long been pursued for such applications as optical pumping of solid state and fiber lasers, direct material processing, printing,
communications, sensing, etc. For example, U.S. Patent 5,818,860, entitled High Power
Semiconductor Laser Diode, assigned to David Sarnoff Research Center, Inc., describes a
broadened-waveguide technique for producing high-power DFB lasers.
The broadened waveguide concept described in U.S. Patent 5,818,860 permits low
loss and therefore high-power lasing in multimode sources. Other characteristics inherent in this concept are of particular promise for high-power single-spatial-mode and dynamic-
single- longitudinal-mode lasing. Results of an initial attempt in which the broadened
waveguide was incorporated into a 1.55 μm single mode DFB RWG diode laser has
provided encouragement; as there was attained a 200 mW power output single mode, -165
dBm/Hz RIN from 0 to 2 GHz, and 200 kHz linewidths for 1.5 mm cavity length implementations. Further, FIG. 1 shows the RIN performance achieved and 300 MHz
linewidth with a broadened waveguide DFB laser. As shown in FIG. 2, this laser emitted
200 mW cw at 1.55 μm wavelength.
High-power ridge waveguide (RWG) lasers use a cold-cavity index, i.e., effective
index, stepof ~Δ« = 0.01, but this value under current injection is diminished by
antiguiding. Although antiguiding is quantitatively difficult to estimate accurately and is
variable, proprietary experiments and extensive published accounts of conventional RWG
laser structures lead one to conclude that latitude in the choice of n is severely
compromised by the antiguiding phenomenon. As a result, Δ« must be designed to
substantially exceed the maximum anticipated antiguiding diminution. For RWG lasers of
the prior art, antiguiding has required n values so great that ridge widths must be limited to
~3.5 μm or narrower to attain a stable, single waveguide mode. The restriction in ridge
width limits the power that can be achieved by the laser for several reasons: Firstly, the
maximum current density that can be usefully pumped into a semiconductor active region
may be limited by phenomena such as the maximum attainable conduction band offsets or
other phenomena which affect the maximum power attainable. For wider ridges, a greater
current per unit length can usefully be pumped into the active region, causing higher powers to be emitted. Such effects limit the maximum power emitted by the RWG laser under both
cw and pulsed conditions. Secondly, an increased ridge width would provide a greater
surface area for heat dissipation. Since laser diode performance is severely restricted as
temperature rises, wider ridges would permit greater currents to be pumped into the RWG
laser and greater powers to be emitted. Such effects presently limit the maximum power
emitted by a RWG laser under cw conditions
Therefore, a high-power RWG laser having a ridge width greater than -3.5 μm is
needed to provide further gains in power output from any RWG laser such as a DFB RWG
laser
SUMMARY OF THE INVENTION
A semiconductor laser diode comprises a body of a semiconductor material having a
length of at least substantially 3 millimeters; a low-propagation-loss waveguide region
formed in the body, having a thickness of at least 500 nanometers; a ridge structure disposed
over a side of the waveguide region. For applications requiring dynamic single-longitudinal- mode operation, the diode also includes a distributed feedback structure associated with at
least one of the waveguide region and ridge structure. The effective refractive index
difference between the ridge structure and exposed portions of the waveguide region which
surround the ridge structure is less than 0.003. Accordingly, the width of the ridge can be
expanded beyond 3.5 microns. BRIEF DESCRIPTION OF THE DRAWINGS
The advantages, nature, and various additional features of the invention will appear
more fully upon consideration of the illustrative embodiments now to be described in detail
in connection with accompanying drawings wherein:
FIG. 1 is a graph plotting linewidth vs. power output of a prior art broadened
waveguide DFB laser;
FIG. 2 is a graph plotting power output vs. injection current of a prior art broadened
waveguide DFB laser; and
FIG. 3 is a perspective view of a DFB RWG semiconductor laser diode according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The high-power DFB RWG laser of the present invention set forth in greater detail
further on employs the broadened-waveguide technology described in U.S. Patent 5,818,860,
the entire disclosure of which is incorporated herein by reference, to expand the ridge width
of the laser beyond 3.5 μm. The reduced propagation losses due to reduced modal overlap
with doped regions permits the laser to operate with reduced overlap with the quantum
wells, as occurs in the broadened-waveguide laser of the '860 patent, and causes the active region to operate with lower gain (and lower carrier concentration)which concomitantly
reduces antiguiding. This is because it is the nature of the antiguiding effect that a reduction
in index is proportional to the increase in the optical gain per unit length, as compared to the
materials surrounding the ridge. This effect permits a smaller effective refractive index or index difference Dn between the ridge region and the surrounding etched region, in turn
permitting wider single mode ridge waveguides. This translates directly to higher power
outputs at wavelengths such as 1.55 mm, where carrier diffusion and carrier heating limit
current density which can usefully injected into the active region, particularly in InGaAsP
laser.
Turning now to FIG. 3, there is shown a DFB RWG semiconductor laser diode 10
according to an exemplary embodiment of the present invention. The laser diode 10 comprises a body 12 of a semiconductor material or materials having a bottom surface 14,
top surface 16, end surfaces 18 and side surfaces 20. The body 12 includes a waveguide
region 22 extending thereacross. Within the waveguide region 22 is an active region 24 in
which photons are generated when an appropriate electrical bias is placed across the diode
10. The active region 24 may be of any structure well known in the laser diode art which is
capable of generating photons consistent with the requirement of attaining low optical
propagation losses through a broadened waveguide design, or equivalent. Preferably, the
active region 24 comprises one or more quantum wells. The waveguide region 22 includes a
first layer 25 of "undoped" semiconductor material on a first side of the active region 24 and a second layer 26 of "undoped" semiconductor material on a second side of the active
region 24. The first and second layers 25 and 26 of undoped semiconductor material have a
doping level of no greater than about 5X1016 atoms/cm3.
A first clad region 28 is disposed on the first side of the waveguide region 22. The
first clad region 28 may be composed of a semiconductor material of a P-type conductivity.
A second clad region 30, which may be formed of a N-type conductivity, is disposed on the second side of the waveguide region. The first clad region 28 is etched so as expose portions
of the underlying first layer 25 of undoped semiconductor material. The etched clad region
28 defines a ridge-like structure 31 having a width W. For dynamically single longitudinal
mode operation, a distributed feedback structure, formed by corrugations 33, is etched in
either the ridge-shape first clad region 28 as shown or in the first layer 25 of undoped
semiconductor material.
The composition of the first and second clad regions 28 and 30 of a semiconductor
material is of a lower refractive index than the materials of the first and second layers 25 and
26 of the waveguide region 22. The doping level in the first and second clad regions 28 and 30 are typically between about 5X1017 atoms/cm3 and 2X1019 atoms/cm3.
A contact layer 32 of a conductive material, such as a metal, is on and in ohmic
contact with the P-type conductivity ridge-shaped clad region 28. The contact layer 32 is in
the form of a strip which extends between the end surfaces 18 of the body 12 and may be
narrower than the width of the body 12, i.e., the distance between the side surfaces 20 of the
body 12. A contact layer 34 of a conductive material, such as a metal, is on and in ohmic
contact with the N-type conductivity clad region 30. The contact layer 34 extends across the
entire area of the bottom surface 14 of the body 12.
The thickness of the waveguide region 22 and the composition of the waveguide
region 22 and the clad regions 28 and 30 must be such that the optical mode generated by the
active region 24 does not overlap from the waveguide region 22 into the more heavily doped
clad regions 28 and 30 by more than 5%, and preferably by not more than 2%. However, the
amount of overlap of the photons into the clad regions 28 and 30 need not be less than 1%. This means that the amount of the optical mode, which is mainly in the waveguide region
22, that extends into (overlaps) the clad regions 28 and 30 is no greater than about 5% of the
total optical mode. To achieve this, the thickness of the waveguide region should be at least
500 nanometers (nm) and the composition of the waveguide region 22 and the clad regions
28 and 30 should be such that the refractive index of the regions provides the confinement of the optical mode in the waveguide region 22 to the extent that the overlap of the optical
mode into the clad regions 28 and 30 is not greater than 5%. The various regions of the body 12 may be made of any of the well known semiconductor materials used for making laser
diode, such as but not limited to gallium arsenide, aluminum gallium arsenide, indium
phosphide, indium gallium arsenide and such quaternary materials as indium, gallium
arsenide phosphide. However, the materials used for the various regions must have refractive
indices which provide the desired confinement of the optical mode. The clad regions 28 and
30 may be doped uniformly throughout their thickness or may be graded with little or no
doping at their junction with the waveguide region 22 and the heaviest doping at the
respective surface of the body 12.
The laser diode 10 of the present invention can be made longer than conventional
laser diodes, i.e., in lengths of substantially 3 millimeters or longer, because there is lower
optical propagation loss in the laser diode of the invention. Moreover, the broadened
waveguide region 22, with its reduced antiguiding effects, enables the ridge structure 31 to
be etched so that the effective refractive index Δn, i.e., index difference, between the ridge
structure 31 and the exposed portions of the underlying first layer 25 of undoped
semiconductor material surrounding the ridge structure 31 is substantially reduced to between about 0.0007 and 0.002. This, in turn, permits width Wof the ridge to be
increased substantially beyond the 3.5 μm widths of conventional designs to widths of 5 μm
and greater, therefore translating directly to higher power outputs per unit length at 1.55 μm
wavelengths, where carrier diffusion and carrier heating limit current density injected into
the active region, particularly in InGaAsP. That is, power increases due to increased length of the diode as taught in the '860 patent are further extended by 50% to 100% in the
structure taught here by increase of the ridge width for an index-guided RWG laser such as a RWG DFB laser diode.
Additionally, the distributed feedback structure produces a coupling constant K which
is about 3 times greater than similar structures in conventional laser diodes because of the 3
times greater width of the ridge structure. Consequently, further improvements in thermal
dissipation and power density are realized with the laser structure of the present invention.
While the foregoing invention has been described with reference to the above
embodiments, various modifications and changes can be made without departing from the
spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.

Claims

What is claimed is:
1. A semiconductor laser diode comprising:
a body of a semiconductor material having a length of at least 2.5 millimeters;
a waveguide region formed in the body, the waveguide region including active region for generating an optical mode of photons, the waveguide region having a thickness which
supports a mode exhibiting a 5% or less overlap with a highly doped p-clad layer;
a ridge structure disposed over a side of the waveguide region; and wherein the effective refractive index difference between the ridge structure and
exposed portions of the waveguide region which surround the ridge structure is less than
0.002.
2. The semiconductor laser diode of claim wherein a distributed feedback structure is
associated with at least one of the waveguide region and ridge structure
3. The semiconductor laser diode of claim 1 wherein the waveguide region has a doping
level of no greater than 5X1016 atoms /cm3.
4. The semiconductor laser diode of claim 1 wherein the ridge structure is defined by
one of two clad regions disposed on opposing sides of the waveguide region, the clad regions being at least partially doped to be of opposite conductivity types.
5. The semiconductor laser diode of claim 3 wherein the materials of the waveguide
region and the clad regions have a refractive index which provides confinement of the
optical mode to the waveguide region with an overlap of the optical mode into the clad
regions of no greater than 5%.
6. The semiconductor laser diode of claim 3 wherein the clad regions are of a
semiconductor material having a lower index of refraction than the materials of the portions of the waveguide region adjacent the clad regions.
7. The semiconductor laser diode of claim 3 wherein the ridge structure has a width that
is 5 microns or greater.
8. The semiconductor laser diode of claim 1 wherein the distributed feedback structure
comprises corrugations.
9. The semiconductor laser diode of claim 1 wherein the distributed feedback structure
is formed in the ridge structure.
10. The semiconductor laser diode of claim 1 wherein the distributed feedback structure
is formed in the waveguide region.
11. The semiconductor laser diode of claim 1 wherein at least a portion of the body is
made from a semiconductor material selected from the group consisting of gallium arsenide,
aluminum gallium arsenide, indium phosphide, indium gallium arsenide and indium, gallium
arsenide phosphide.
12. The semiconductor laser diode of claim 1 wherein the ridge structure has a P-type
conductivity.
13. A semiconductor laser diode comprising:
a body of a semiconductor material having a length of at least 3 millimeters;
a waveguide region formed in the body, the waveguide region including active region for
generating an optical mode of photons, the waveguide region having a thickness which
supports a mode exhibiting a 5% or less overlap with a highly doped p-clad layer;
a ridge structure disposed over a side of the waveguide region; and
wherein the ridge structure has a width that is greater than 3.5 microns.
14. The semiconductor laser diode of claim 13 wherein a distributed feedback structure
is associated with at least one of the waveguide region and ridge structure;
15. The semiconductor laser diode of claim 13 wherein the effective refractive index
difference between the ridge structure and exposed portions of the waveguide region which
surround the ridge structure is less than 0.002.
16. The semiconductor laser diode of claim 13 wherein the waveguide region has a
doping level of no greater than 5X1016 atoms /cm3.
17. The semiconductor laser diode of claim 13 wherein the ridge structure is defined by one of two clad regions disposed on opposing sides of the waveguide region, the clad
regions being at least partially doped to be of opposite conductivity types.
18. The semiconductor laser diode of claim 17 wherein the materials of the waveguide
region and the clad regions have a refractive index which provides confinement of the
optical mode to the waveguide region with an overlap of the optical mode into the clad
regions of no greater than 5%.
19. The semiconductor laser diode of claim 17 wherein the clad regions are of a
semiconductor material having a lower index of refraction than the materials of the portions
of the waveguide region adjacent the clad regions.
20. The semiconductor laser diode of claim 13 wherein the distributed feedback structure
comprise corrugations.
21. The semiconductor laser diode of claim 13 wherein the distributed feedback structure
is formed in the ridge structure.
22. The semiconductor laser diode of claim 13 wherein the distributed feedback structure
is formed in the waveguide region.
23. The semiconductor laser diode of claim 13 wherein at least a portion of the body is
made from a semiconductor material selected from the group consisting of gallium arsenide, aluminum gallium arsenide, indium phosphide, indium gallium arsenide and indium, gallium
arsenide phosphide.
24. The semiconductor laser diode of claim 13 wherein the ridge structure has a P-type conductivity.
EP01920104A 2000-01-20 2001-01-22 High power distributed feedback ridge waveguide laser Withdrawn EP1258065A4 (en)

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US17691500P 2000-01-20 2000-01-20
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PCT/US2001/002019 WO2001054240A1 (en) 2000-01-20 2001-01-22 High power distributed feedback ridge waveguide laser

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US7920770B2 (en) 2008-05-01 2011-04-05 Massachusetts Institute Of Technology Reduction of substrate optical leakage in integrated photonic circuits through localized substrate removal
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EP1258065A1 (en) 2002-11-20
WO2001055814A2 (en) 2001-08-02
WO2001053881A1 (en) 2001-07-26
CA2398833A1 (en) 2001-07-26
AU2001247192A1 (en) 2001-07-31
AU2001241424A1 (en) 2001-07-31
JP2003520455A (en) 2003-07-02
WO2001055814A3 (en) 2002-02-07
AU2001262901A1 (en) 2001-08-07

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