WO2007057807A2 - Vcsel with coating for polarization control - Google Patents

Vcsel with coating for polarization control Download PDF

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Publication number
WO2007057807A2
WO2007057807A2 PCT/IB2006/054064 IB2006054064W WO2007057807A2 WO 2007057807 A2 WO2007057807 A2 WO 2007057807A2 IB 2006054064 W IB2006054064 W IB 2006054064W WO 2007057807 A2 WO2007057807 A2 WO 2007057807A2
Authority
WO
WIPO (PCT)
Prior art keywords
coating
mirror
laser
polarization state
polarization
Prior art date
Application number
PCT/IB2006/054064
Other languages
French (fr)
Other versions
WO2007057807A3 (en
Inventor
Marcel F. C. Schemmann
Armand Pruijmboom
Dirk J. Broer
Original Assignee
Koninklijke Philips Electronics N.V.
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 Koninklijke Philips Electronics N.V. filed Critical Koninklijke Philips Electronics N.V.
Publication of WO2007057807A2 publication Critical patent/WO2007057807A2/en
Publication of WO2007057807A3 publication Critical patent/WO2007057807A3/en

Links

Classifications

    • 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
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18355—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a defined polarisation
    • 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
    • H01S2301/00—Functional characteristics
    • H01S2301/14—Semiconductor lasers with special structural design for lasing in a specific polarisation mode
    • 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
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08059—Constructional details of the reflector, e.g. shape

Definitions

  • the present invention relates to a mirror, such as a mirror for reflecting light in a laser and in particular to a mirror which controls the polarization state of laser light.
  • lasers operate in one or more of several polarization states, each state being defined according to the direction of oscillation of the associated E-f ⁇ eld.
  • lasers will often switch from one polarization state to another state, or combination of states.
  • a sudden change in polarization state can lead to power fluctuations, which directly influences the efficiency by which light can be coupled within an optical system.
  • Various methods are employed to overcome this change in polarization state, including the use of asymmetry in the laser cavity, mechanical strain, off crystal-axis orientation of the gain media and optical gratings. Each of these methods aim to encourage the oscillation of the E-f ⁇ eld of the laser light along a preferred direction and thus maintain a preferred polarization state. The preferred polarization state will then attain lasing threshold before other polarization states and so will operate in a stable manner.
  • Lasers which have an asymmetric laser cavity design will have a polarization dependent effective mirror reflectivity, due to asymmetric mode profiles. However, lasers which develop symmetric mode profiles do not suffer from this polarization dependence of reflectivity.
  • Symmetric mode profiles are generally desired in optical systems and since mechanical strain can conflict with reliability requirements, off-axis crystal growth can affect material properties and the incorporation of gratings can be expensive.
  • the present invention aims to alleviate at least some of these problems.
  • a mirror comprising a coating, wherein said coating creates a polarization dependent reflectivity of the mirror so that the mirror predominantly reflects light of a pre-determined polarization state.
  • a mirror can be advantageously used for reflecting light in a laser cavity of a laser thereby enabling said laser to operate stably in the pre-determined polarization state.
  • the coating may be optically anisotropic.
  • the coating causes laser light having a polarization state different to the pre-determined polarization state and which in use is reflected from opposite interfaces of the coating to be attenuated by interference.
  • the coating absorbs laser light having a polarization state different to the pre-determined polarization state.
  • a laser comprising at least one such mirror.
  • Fig. 1 schematically illustrates a laser.
  • a laser 1 comprises laser cavity 2 having output mirror 3 and end mirror 5.
  • the output mirror 3 comprises a coating 4.
  • the coating 4 has a polarization dependent loss, retardation and/or reflectivity.
  • the coating 4 defines a laser mirror in combination with interfaces between the laser material (not shown) and other optional coatings (not shown), and air.
  • the inclusion of any of the polarization dependent properties in the coating 4 (or any of the optional coating layers) will result in a polarization dependence of the overall reflectivity of the mirror 3.
  • the laser round trip gain becomes polarization dependent and a preferred mode can be defined in which the laser will operate.
  • Two types of coating which may provide the polarization dependent reflectivity of the coating 4, are anisotropic coatings and polarization coatings.
  • An anisotropic coating is one in which there exists a directional dependence of the properties of the coating. This coating typically provides a quarter wavelength phase shift for one of the two polarization states, such that in reflection to the outer surface to air, one of the polarization states is attenuated by destructive interference. In contrast, a polarization coating will only transmit one type of polarization state with the result that only one polarization state will become reflected from the outer surface. The orthogonal polarization states will then become absorbed.
  • the vapor deposition process involves the application of a physical vapor deposition process of serial bideposition to uniaxial optical coatings.
  • the vapor impinges at an angle of about 70° on to the laser substrate and a stepwise axial rotation of 180° increments of the substrate causes a columnar structure to grow normal to the substrate.
  • the stepwise increments ensure that the film is achiral with an in-plane linear birefringence.
  • the application of an organic coating involves spincoating an organic mixture on top of the outer surface of a laser mirror, which has previously been provided with an alignment layer of rubbed polyimide.
  • the spin conditions for a liquid crystal monomer mixture prepared by dissolving 2g RM257 (l,4-di(4-(3-acryloyloxypropyloxy)benzoyloxy)- 2-methylbenzene), 0.5g RM82 (l,4-di(4-(3-acryloyloxyhexyloxy)benzoyloxy)-2- methylbenzene), 0.5g 4-(6-acryloyloxyhexyloxy)-4-(hexyloxy)benzoyloxy)benzene, 0.03g Irgacure 184 (1-hydroxycyclohexyl phenylketone) and 0.015g BDH1533, into 6g xylene at 70 0 C containing 0.07 mg/g paramethoxyphenol are 60 seconds at 2500rpm, yielding
  • the formation of the single crystal without defects is facilitated by an anneal step on a hot plate at 70 0 C for 30 seconds.
  • the aligned liquid crystal monomer is then photopolymerised by an ultra-violet exposure for 2 minutes at 120 0 C with an ultra-violet intensity of 3.5mW/cm 2 .
  • Such an alignment of the liquid crystals creates the desired anisotropy in the coating .
  • a polarization coating the outer surface of a laser mirror, when mounted on the wafer as an array of many individual solid-state lasers, is coated with a solution of lyotropic dye dissolved in water.
  • the dye molecules are based on perylene containing molecules that stack into columns when dissolved in water.
  • the molecules are applied by a doctor-blade-coating unit that induces a shear during the film formation. The shear forces align the columns and when the water evaporates, which is usually quick since the films are very thin, the film crystallizes into a single crystal or quasi-single crystal with a large anisotropy in the optical absorbance.
  • the coating provides for the selective control of the polarization state.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Optical Elements Other Than Lenses (AREA)
  • Lasers (AREA)
  • Polarising Elements (AREA)

Abstract

There is described a mirror (3) comprising a coating (4) that creates a polarization dependent reflectivity of the mirror (3) so that the mirror (3) predominantly reflects light of a pre-determined polarization state. The mirror (3) can be advantageously used in a laser (1) comprising a laser cavity (2) thereby enabling the laser (1) to operate stably in the pre-determined polarization state. The laser (1) has an end mirror (5). Preferably the laser (1) is a VCSEL.

Description

Mirror
The present invention relates to a mirror, such as a mirror for reflecting light in a laser and in particular to a mirror which controls the polarization state of laser light.
Many types of laser operate in one or more of several polarization states, each state being defined according to the direction of oscillation of the associated E-fϊeld. During operation, lasers will often switch from one polarization state to another state, or combination of states. A sudden change in polarization state can lead to power fluctuations, which directly influences the efficiency by which light can be coupled within an optical system.
Various methods are employed to overcome this change in polarization state, including the use of asymmetry in the laser cavity, mechanical strain, off crystal-axis orientation of the gain media and optical gratings. Each of these methods aim to encourage the oscillation of the E-fϊeld of the laser light along a preferred direction and thus maintain a preferred polarization state. The preferred polarization state will then attain lasing threshold before other polarization states and so will operate in a stable manner.
Lasers which have an asymmetric laser cavity design will have a polarization dependent effective mirror reflectivity, due to asymmetric mode profiles. However, lasers which develop symmetric mode profiles do not suffer from this polarization dependence of reflectivity.
A specific laser type that is finding a wide range of applications in data communications and consumer electronics is the semiconductor based VCSEL (Vertical Cavity Surface Emitting Laser). VCSELs typically have symmetric modes and suffer from polarization instability. Usually the output mirror of these lasers is coated to affect the overall mirror reflectivity, and replacing this coating with, or adding to this coating, polarization dependent layers, is found to stabilize the operation of the VCSEL.
Symmetric mode profiles are generally desired in optical systems and since mechanical strain can conflict with reliability requirements, off-axis crystal growth can affect material properties and the incorporation of gratings can be expensive.
The present invention aims to alleviate at least some of these problems.
In accordance with this invention as seen from a first aspect, there is provided a mirror comprising a coating, wherein said coating creates a polarization dependent reflectivity of the mirror so that the mirror predominantly reflects light of a pre-determined polarization state. Such a mirror can be advantageously used for reflecting light in a laser cavity of a laser thereby enabling said laser to operate stably in the pre-determined polarization state.
The coating may be optically anisotropic.
In one embodiment the coating causes laser light having a polarization state different to the pre-determined polarization state and which in use is reflected from opposite interfaces of the coating to be attenuated by interference.
In another embodiment the coating absorbs laser light having a polarization state different to the pre-determined polarization state.
In accordance with this invention as seen from a second aspect, there is provided a laser comprising at least one such mirror.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter, with reference to the following drawing, in which, Fig. 1 schematically illustrates a laser.
Referring to Fig. 1 a laser 1 comprises laser cavity 2 having output mirror 3 and end mirror 5. The output mirror 3 comprises a coating 4. The coating 4 has a polarization dependent loss, retardation and/or reflectivity. The coating 4 defines a laser mirror in combination with interfaces between the laser material (not shown) and other optional coatings (not shown), and air. The inclusion of any of the polarization dependent properties in the coating 4 (or any of the optional coating layers) will result in a polarization dependence of the overall reflectivity of the mirror 3. As a result, the laser round trip gain becomes polarization dependent and a preferred mode can be defined in which the laser will operate.
Two types of coating, which may provide the polarization dependent reflectivity of the coating 4, are anisotropic coatings and polarization coatings.
An anisotropic coating is one in which there exists a directional dependence of the properties of the coating. This coating typically provides a quarter wavelength phase shift for one of the two polarization states, such that in reflection to the outer surface to air, one of the polarization states is attenuated by destructive interference. In contrast, a polarization coating will only transmit one type of polarization state with the result that only one polarization state will become reflected from the outer surface. The orthogonal polarization states will then become absorbed.
There are a number of ways of applying an anisotropic coating to the outer surface of a laser including the vapor deposition of inorganic coatings, and the spin coating and alignment of organic coatings.
The vapor deposition process involves the application of a physical vapor deposition process of serial bideposition to uniaxial optical coatings. During the coating process, the vapor impinges at an angle of about 70° on to the laser substrate and a stepwise axial rotation of 180° increments of the substrate causes a columnar structure to grow normal to the substrate. The stepwise increments ensure that the film is achiral with an in-plane linear birefringence.
The application of an organic coating involves spincoating an organic mixture on top of the outer surface of a laser mirror, which has previously been provided with an alignment layer of rubbed polyimide. The spin conditions for a liquid crystal monomer mixture, prepared by dissolving 2g RM257 (l,4-di(4-(3-acryloyloxypropyloxy)benzoyloxy)- 2-methylbenzene), 0.5g RM82 (l,4-di(4-(3-acryloyloxyhexyloxy)benzoyloxy)-2- methylbenzene), 0.5g 4-(6-acryloyloxyhexyloxy)-4-(hexyloxy)benzoyloxy)benzene, 0.03g Irgacure 184 (1-hydroxycyclohexyl phenylketone) and 0.015g BDH1533, into 6g xylene at 700C containing 0.07 mg/g paramethoxyphenol are 60 seconds at 2500rpm, yielding a layer thickness of about 1.4μm. The rubbed polyimide establishes nearly planar alignment of the liquid crystal monomers with the director (i.e. the common axis along which the liquid crystal molecules point) being parallel to the rubbing direction.
The formation of the single crystal without defects is facilitated by an anneal step on a hot plate at 700C for 30 seconds. The aligned liquid crystal monomer is then photopolymerised by an ultra-violet exposure for 2 minutes at 1200C with an ultra-violet intensity of 3.5mW/cm2. Such an alignment of the liquid crystals creates the desired anisotropy in the coating .
In forming a polarization coating, the outer surface of a laser mirror, when mounted on the wafer as an array of many individual solid-state lasers, is coated with a solution of lyotropic dye dissolved in water. The dye molecules are based on perylene containing molecules that stack into columns when dissolved in water. The molecules are applied by a doctor-blade-coating unit that induces a shear during the film formation. The shear forces align the columns and when the water evaporates, which is usually quick since the films are very thin, the film crystallizes into a single crystal or quasi-single crystal with a large anisotropy in the optical absorbance.
Alternatively, employing the same technique which is used in applying an anisotropic organic coating (as explained above) but adding a dichroic dye, which absorbs light in the wavelength range of the laser, causes the polarization of laser light which is parallel to the director to become absorbed, whereas the laser light perpendicular to the director can pass through the coating. In this manner, the coating provides for the selective control of the polarization state.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parentheses shall not be construed as limiting the claims. The word "comprising" and "comprises", and the like, does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The singular reference of an element does not exclude the plural reference of such elements and vice-versa. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:
1. A mirror (3) comprising a coating (4), wherein said coating (4) creates a polarization dependent reflectivity of the mirror (3) so that the mirror (3) predominantly reflects light of a pre-determined polarization state.
2. A mirror (3) as claimed in claim 1, wherein said coating (4) is optically anisotropic.
3. A mirror (3) as claimed in claim 1, wherein said coating (4) causes laser light having a polarization state different to the pre-determined polarization state and which in use is reflected from opposite interfaces of the coating (4) to be attenuated by interference.
4. A mirror (3) as claimed in claim 1, wherein said coating (4) absorbs laser light having a polarization state different to the pre-determined polarization state.
5. A mirror (3) as claimed in claim 1 wherein the coating (4) comprises inorganic material.
6. A mirror (3) according to claim 5 wherein the coating (4) comprises organic material.
7. A laser (1) comprising at least one mirror (3) as defined in claim 1.
PCT/IB2006/054064 2005-11-17 2006-11-02 Vcsel with coating for polarization control WO2007057807A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP05110895 2005-11-17
EP05110895.9 2005-11-17

Publications (2)

Publication Number Publication Date
WO2007057807A2 true WO2007057807A2 (en) 2007-05-24
WO2007057807A3 WO2007057807A3 (en) 2007-11-01

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011084047A1 (en) 2010-11-17 2012-05-24 Vertilas Gmbh Polarization-stable surface-emitting laser diode

Citations (9)

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Publication number Priority date Publication date Assignee Title
JPH03118198A (en) * 1989-09-30 1991-05-20 Toppan Printing Co Ltd Card and image forming method
EP0689065A1 (en) * 1994-06-24 1995-12-27 F. Hoffmann-La Roche AG Optical component
EP0795941A1 (en) * 1996-03-13 1997-09-17 Sharp Kabushiki Kaisha An optoelectronic semiconductor device
US5928819A (en) * 1996-12-19 1999-07-27 Xerox Corporation Methods to fabricate optical equivalents of fiber optic face plates using reactive liquid crystals and polymers
US6324002B1 (en) * 1999-10-26 2001-11-27 Agilent Technologies, Inc. Polarization-dependent imaging element
US20030048827A1 (en) * 2001-09-11 2003-03-13 Wen-Yen Hwang Method and apparatus for polarizing light in a VCSEL
EP1306699A2 (en) * 2001-10-23 2003-05-02 Dai Nippon Printing Co., Ltd. Process of producing optical element and optical element
US6785320B1 (en) * 1999-07-10 2004-08-31 Qinetiq Limited Control of polarisation of vertical cavity surface emitting lasers
WO2006052328A1 (en) * 2004-10-29 2006-05-18 3M Innovative Properties Company Polarized led

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH03118198A (en) * 1989-09-30 1991-05-20 Toppan Printing Co Ltd Card and image forming method
EP0689065A1 (en) * 1994-06-24 1995-12-27 F. Hoffmann-La Roche AG Optical component
EP0795941A1 (en) * 1996-03-13 1997-09-17 Sharp Kabushiki Kaisha An optoelectronic semiconductor device
US5928819A (en) * 1996-12-19 1999-07-27 Xerox Corporation Methods to fabricate optical equivalents of fiber optic face plates using reactive liquid crystals and polymers
US6785320B1 (en) * 1999-07-10 2004-08-31 Qinetiq Limited Control of polarisation of vertical cavity surface emitting lasers
US6324002B1 (en) * 1999-10-26 2001-11-27 Agilent Technologies, Inc. Polarization-dependent imaging element
US20030048827A1 (en) * 2001-09-11 2003-03-13 Wen-Yen Hwang Method and apparatus for polarizing light in a VCSEL
EP1306699A2 (en) * 2001-10-23 2003-05-02 Dai Nippon Printing Co., Ltd. Process of producing optical element and optical element
WO2006052328A1 (en) * 2004-10-29 2006-05-18 3M Innovative Properties Company Polarized led

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011084047A1 (en) 2010-11-17 2012-05-24 Vertilas Gmbh Polarization-stable surface-emitting laser diode
WO2012065834A1 (en) 2010-11-17 2012-05-24 Vertilas Gmbh Polarization-stable surface-emitting laser diode
US8971375B2 (en) 2010-11-17 2015-03-03 Vertilas, GmbH Polarization-stable surface-emitting laser diode
KR101527299B1 (en) * 2010-11-17 2015-06-09 버티라스 게엠베하 Polarization-stable surface-emitting laser diode

Also Published As

Publication number Publication date
WO2007057807A3 (en) 2007-11-01
TW200736665A (en) 2007-10-01

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