CA2136254A1 - Method for fabrication of wavelength selective electro-optic grating for dfb/dbr lasers - Google Patents

Method for fabrication of wavelength selective electro-optic grating for dfb/dbr lasers

Info

Publication number
CA2136254A1
CA2136254A1 CA002136254A CA2136254A CA2136254A1 CA 2136254 A1 CA2136254 A1 CA 2136254A1 CA 002136254 A CA002136254 A CA 002136254A CA 2136254 A CA2136254 A CA 2136254A CA 2136254 A1 CA2136254 A1 CA 2136254A1
Authority
CA
Canada
Prior art keywords
accordance
waveguide
depositing
grating
cladding
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.)
Abandoned
Application number
CA002136254A
Other languages
French (fr)
Inventor
Tien-Heng Chiu
Michael D. Williams
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.)
AT&T Corp
Original Assignee
American Telephone and Telegraph Co 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 American Telephone and Telegraph Co Inc filed Critical American Telephone and Telegraph Co Inc
Publication of CA2136254A1 publication Critical patent/CA2136254A1/en
Abandoned legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S5/00Semiconductor lasers
    • H01S5/10Construction 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
    • H01S5/12Construction 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
    • H01S5/125Distributed Bragg reflector [DBR] lasers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S5/00Semiconductor lasers
    • H01S5/10Construction 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
    • H01S5/12Construction 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
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S5/00Semiconductor lasers
    • H01S5/06Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/062Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
    • H01S5/0625Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes in multi-section lasers
    • H01S5/06255Controlling the frequency of the radiation
    • H01S5/06256Controlling the frequency of the radiation with DBR-structure
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S5/00Semiconductor lasers
    • H01S5/10Construction 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
    • H01S5/1046Comprising interactions between photons and plasmons, e.g. by a corrugated surface
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES 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
    • H01S5/00Semiconductor lasers
    • H01S5/10Construction 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
    • H01S5/12Construction 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
    • H01S5/1231Grating growth or overgrowth details

Abstract

A method is described for the preparation of a DFB/DBR laser which includes an electro-optic grating formed by periodically modulating the index of refraction of the cladding employed. The method involves depositing a waveguide upon a semi-insulating or doped substrate and then depositing an active layer upon the resultant structure. The active layer is subsequently selectively etched and a cladding material deposited adjacent thereto and electrically isolated therefrom. The cladding is then selectively patterned with a conductive material by photolithographic techniques to yield a grating to periodically modulate the index of refraction.

Description

21352~

.

METHOD FOR FABRICATION OF WAVELENGTH SELECTIVE
ELECTRO-OPTIC GRATING FOR DFB/DBR LASERS

Field of the Invention.
More particularly, the present invention relates to a method for the preparation of a wavelength selective electro-optic grating for DFB/DBR lasers and related structures wherein etched corrugation wavelength gratings are replaced with a grating formed by periodically modulating the index of refraction of the cladding employed or the waveguide itself.

Background of the Invention During the past decade, rapid advances have been made in laser technology. These advances have led to the integration of lasers with other active optical elements such as detectors, optical amplifiers, optical modulators and switches on one semiconductor chip. Interconnections employed for this purpose are miniature, transparent, passive waveguides which pipe light from one device to the next and function in a manner similar to metals which carry electricity in conventional circuits. Further enhancements in this technology have been attained from advances in crystal growth and large area wafer processing.

Among the more recent developments in photonic integrated circuitry has been the corrugated-waveguide grating. The fabrication of these gratings became routine after the distributed feedback (DFB) laser was adopted 21362S~

worldwide as the preferred optical telecommunications source where high spectral purity is required. These gratings provide high quality on-chip resonators without encountering the restraints imposed by the usual cleaved-facet resonators employed in semiconductor lasers.
Additionally, the gratings function as filters in certain receiver and amplifier applications.
Scanning electron micrographs in distributed feedback lasers reveal a corrugated interface between a higher index core material and a lower index cladding material.
As a light beam propagates down such a waveguide, each bump reflects a small portion of the light. If the beam's wavelength is not close to the Bragg wavelength, all the reflections are out of phase and interfere destructively.
At the Bragg wavelength, all reflections add in phase, so leading to a large cumulative reflection.
At the present time, the control of output wavelength of semiconductor lasers in distributed feedback (DFB) and tuning in distributed Bragg reflector (DBR) based lasers is achieved by means of the incorporation therein of the above-noted corrugated waveguide grating. In the DBR
configuration, gratings of this type are typically installed by etching back a portion of the active layer and exposing the surface of an underlying passive waveguide. Alternatively, the grating may be installed in the substrate prior to the growth of the waveguide. In subsequent processing, an interference pattern formed by ultraviolet lasers is typically used to expose photoresist deposited on the exposed waveguide. The developed photoresist then forms the mask for etching the grating corrugation. The exposed portion of the structure is then regrown and contacts attached for operation. In the DFB
configuration, the grating is usually installed prior to growth of the active layer or waveguide. This end is typically attained by using an interference pattern, as described above, to expose photoresist deposited on the exposed passive waveguide. The exposed photoresist forms a mask for etching the corrugation. The active layer is then grown over the grating and suitable contacts are added to effect operation.

Summary of the Invention.
In accordance with the present invention, the etched corrugation waveguide grating in the aforementioned structures is replaced with a grating formed by periodically modulating the index of refraction of either the cladding material or the waveguide. The modulated media chosen may be either bulk material or, more specifically, contain quantum well structures. In the case of the latter, it would effect large changes in the index of refraction by means of the quantum confined Stark effect or phase space absorption quenching with the application of an electric field. In the case of bulk material, current injection is the preferred mode of operation since the field induced change in the refractive index (Franz-Keldysh effect) is less efficient. The periodicity of the described device is established by means of conducting media, for example, metal, conductive polymer, etc. The conductive media is employed in the form of strip lines through which current is passed or an electric field is established through the media.
Alternatively, periodicity may be established simply by the plasmon interaction of the periodically spaced conductive strip lines with the media.

Brief Description of the Drawing.
The invention will be more readily understood by reference to the following detailed description taken in conjunction with the accompanying drawing wherein:
FIG 1. is a front elevational view, in cross-section, of a semiconductor substrate suitable for use in the practice of the present invention;
Fig. 2 is a front elevational view, in cross-section, of the substrate of Fig. 1 after growth thereon of a conductive plane;
Fig. 3 is a front elevational view, in cross-section, of the structure of Fig. 2 after the growth thereon of a waveguide containing multiple quantum wells;
Fig. 4 is a front elevational view, in cross-section of the structure of Fig. 3 after growth thereon of a conductive plane on the waveguide;
Fig. 5 is a front elevational view, in cross-section of the structure of Fig. 4 after the growth thereon of active quantum well laser layers;
Fig. 6 is a front elevational view, in cross-section of the structure of Fig. 5 after removal of laser and conductive material in all areas but for the area destined 213625~

for use as the gain region of the desired device;
Fig. 7 is a front elevational view, in cross-section of the structure of Fig. 6 after the deposition thereon of cladding/spacer material;
Fig. 8 is a front elevational view, in cross section of the structure of Fig. 7 after the formation thereon of an electro-optic grating and deposition of a conductive polymer film; and Fig. 9 is a front elevational view, in perspective, of the structure of Fig. 8.

Det~;led Description of the Invention.
The first step in the practice of the present invention involves selection of a suitable substrate material. Most of the optoelectronic devices currently manufactured are designed for long wavelength systems (1.3 and l.S5 micrometers) and are typically fabricated from indium gallium arsenide phosphide materials on indium phosphide substrates. However, in some cases aluminum gallium arsenide/gallium arsenide substrates are employed for short wavelength systems. The substrate chosen is normally n-doped. Fig. 1 depicts a typical semi-insulating n-type indium phosphide substrate member 11 in front elevational view.
Following, an n-type buffer layer (conducting plane) 12 is deposited upon the substrate 11 by conventional epitaxial growth techniques. This contact layer is required in those instances in which a semi-insulating substrate is used to provide the required conductivity.

213fi25~
-The epitaxial growth process preserves the crystalline symmetry of the substrate. Typical procedures suitable for this purpose include molecular beam epitaxy using only elemental sources or metal organic chemical vapor deposition using easily vaporized molecular sources.
Next, there is deposited upon conducting plane 12 a waveguide 13, shown in Fig. 3. The waveguide selected for use in the practice of the present invention may be chosen from among any of the conventional prior art materials commonly used for this purpose and may comprise bulk materials or quantum well layers. The waveguide is grown in the base structure in an appropriate stoichiometry for achieving or propagating a particular wavelength suitable for waveguiding properties. The thickness of the waveguide is dictated by considerations relating to the optical mode desired.
Then, an n-type contact layer (conductive plane) 14 is deposited upon waveguide 13 as shown in Fig. 4.
Thereafter, a laser 15 is deposited upon conductive layer 14, as shown in Fig. 5, by conventional epitaxial growth techniques. The laser is selected from among any of the materials commonly employed in distributed feedback (DFB) lasers and distributed Bragg reflector (DBR) lasers.
Typical of such materials are the III-V semiconductor materials such as indium gallium arsenide phosphide.
The next step in the fabrication of the desired structure involves etching down the assembly to expose the waveguide materials. This end may be effected, for example, by anisotropic dry etching or low frequency 213625~
-plasma etching in which the direction of the ion bombardment enhances the etch rate. A variety of etchants may be chosen for this purpose. Typical etchants suitable for such use are HC1, Br:CH3OH, H2SO4:H2O2 and HBr:H2O2 for wet etching and CF2Cl2, CH4:H2 and CH4H2 for dry etching.
Surface preparation is also critical in the preparation of contacts and to effect adhesion, so requiring reproducible surface preparation techniques.
This typically involves multiple organic solvent cleaning followed by a light etch of the material, and the removal of surface oxides. The resultant etched down structure is shown in Fig. 6.
Following the etching procedure in which the wavegulde materials are exposed, cladding 16, as shown in Fig. 7, is deposited thereon. Then, a conductive material is deposited upon the cladding region 16 in the form of a grating 17 as shown in Fig. 8 by photolithographic techniques. A front elevational view, in perspective, of the structure of Fig. 8 is shown in Fig. 9.
The conductive material selected for use in the practice of the present invention may be chosen from among any of the conventional prior art materials used for this purpose and may comprise metals, semiconductors, or polymers. Polymer systems suitable for this purpose evidence metallic conductivity, are soluble, processable and environmentally stable. The most commonly used material for this purpose is polyaniline of the general formula:

-Of the various oxidative states of this material, the emeraldine form (y = 0.5) has been the most widely used.
This polymer, in the undoped form, is solution processable from both organic and aqueous acid solutions. The conductivity of the polyaniline does not degrade upon exposure to ambient conditions. Numerous derivatives of the material are also feasible since substituents such as alkyl groups can be easily incorporated on either the aromatic rings or the nitrogen atoms. This permits tailoring of the properties of the polyanilines.
Recent advances in the art have resulted in inducing doping of the polymer by incorporating onium salts or amine triflate salts in the polyaniline which decompose upon being subjected to radiation or thermal treatment to generate active dopant species, namely protonic acids.
The thickness and refractive index of the cladding/spacer layer for the conductive material is determined by the optical mode required and would be apparent to those skilled in the art.
The structures prepared in the described manner are suitable for use in a typical DBR laser system. The application of a difference of potential across the cladding periodically will result in the preparation of a grating of controlled refractive index, such control being attained by regulation of the voltage bias. The prime 213625~

advantage of this technology resides in the substitution of conventional prior art gratings with an elctro-optic grating which enhances the lifetime of the device and improves the yield while reducing processing costs.
While the invention has been described in detail in the foregoing specification, it will be understood by those skilled in the art that variations may be made without departing from the spirit and scope of the lnventlon.

Claims (11)

1. Method for the fabrication of a wavelength selective electro-optic grating for DFB/DBR lasers which comprises the steps of (a) depositing a first n-type contact layer upon the surface of a semi-insulating or doped III-V semiconductor substrate, (b) depositing a waveguide upon the n-type contact layer, (c) depositing a second n-type contact layer upon the waveguide, (d) depositing an active layer upon the said second n-type contact layer, (e) selectively etching the active layer down to the waveguide layer in a region of the structure designed for formation of a grating, (f) growing a cladding/spacer material upon said region designed for formation of a grating, (g) depositing and patterning a photoresist on the resultant structure, and (h) depositing a conductive material upon the cladding region in the form of a grating by photolithographic techniques.
2. Method in accordance with claim 1 wherein said substrate is indium phosphide.
3. Method in accordance with claim 1 wherein the waveguide comprises quantum well layers.
4. Method in accordance with claim 1 wherein the waveguide comprises bulk materials.
5. Method in accordance with claim 1 wherein the n-type contact layers are deposited by molecular beam epitaxy using elemental or organometallic sources.
6. Method in accordance with claim 1 wherein the n-type contact layers are deposited by metal organic chemical vapor deposition techniques.
7. Method in accordance with claim 1 wherein the active material is a laser selected from the group consisting of DBR and DFB lasers.
8. Method in accordance with claim 1 wherein etching of the active layer is effected by anisotropic dry etching.
9. Method in accordance with claim 1 wherein said conductive material is polyaniline.
10. Method in accordance with claim 1 wherein the cladding comprises bulk materials.
11. Method in accordance with claim 1 wherein the cladding comprises quantum well layers.
CA002136254A 1993-12-21 1994-11-21 Method for fabrication of wavelength selective electro-optic grating for dfb/dbr lasers Abandoned CA2136254A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US171,126 1993-12-21
US08/171,126 US6194240B1 (en) 1993-12-21 1993-12-21 Method for fabrication of wavelength selective electro-optic grating for DFB/DBR lasers

Publications (1)

Publication Number Publication Date
CA2136254A1 true CA2136254A1 (en) 1995-06-22

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ID=22622634

Family Applications (1)

Application Number Title Priority Date Filing Date
CA002136254A Abandoned CA2136254A1 (en) 1993-12-21 1994-11-21 Method for fabrication of wavelength selective electro-optic grating for dfb/dbr lasers

Country Status (4)

Country Link
US (1) US6194240B1 (en)
EP (1) EP0660469A3 (en)
JP (1) JPH07202330A (en)
CA (1) CA2136254A1 (en)

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KR100413527B1 (en) * 2002-01-29 2004-01-03 한국전자통신연구원 Method for fabricating monolithic integrated semiconductor photonic devices
TWI229751B (en) * 2003-12-26 2005-03-21 Ind Tech Res Inst Adjustable filter and manufacturing method thereof
CN115411612B (en) * 2022-09-05 2023-08-01 武汉敏芯半导体股份有限公司 Narrow linewidth semiconductor laser and preparation method thereof

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Also Published As

Publication number Publication date
US6194240B1 (en) 2001-02-27
EP0660469A2 (en) 1995-06-28
JPH07202330A (en) 1995-08-04
EP0660469A3 (en) 1995-11-29

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EEER Examination request
FZDE Discontinued