WO2009106278A2 - Dispositif de mesure de vitesse laser-doppler - Google Patents

Dispositif de mesure de vitesse laser-doppler Download PDF

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Publication number
WO2009106278A2
WO2009106278A2 PCT/EP2009/001270 EP2009001270W WO2009106278A2 WO 2009106278 A2 WO2009106278 A2 WO 2009106278A2 EP 2009001270 W EP2009001270 W EP 2009001270W WO 2009106278 A2 WO2009106278 A2 WO 2009106278A2
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WO
WIPO (PCT)
Prior art keywords
frequency
light beam
laser
light
semiconductor laser
Prior art date
Application number
PCT/EP2009/001270
Other languages
German (de)
English (en)
Other versions
WO2009106278A3 (fr
Inventor
Georg Bastian
Original Assignee
Fachhochschule Trier
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 Fachhochschule Trier filed Critical Fachhochschule Trier
Publication of WO2009106278A2 publication Critical patent/WO2009106278A2/fr
Publication of WO2009106278A3 publication Critical patent/WO2009106278A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4911—Transmitters
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4912—Receivers
    • 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
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
    • 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
    • H01S5/1092—Multi-wavelength lasing
    • H01S5/1096—Multi-wavelength lasing in a single cavity
    • 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

Definitions

  • the invention relates to a device for laser Doppler speed measurement, and a method for measuring the laser Doppler speed and a use of such a device.
  • the prior art has disclosed methods and apparatus for laser Doppler velocity measurement.
  • the sign of the velocity v of the object changes and the frequency decreases or increases relative to the frequency of the non-reflected light beam.
  • One problem with measuring the velocity of the object is that while the amount of frequency shift can be measured, it does not easily measure its direction. In order to be able to determine the direction of travel of the moving object relative to the detection unit, it has therefore not directly detected the changed frequency of the light in the prior art, but beats between two light beams, namely a first light beam having a frequency fo + f ⁇ shifted by the Doppler frequency and a second light beam, which is specifically shifted by a frequency fs with respect to the reference frequency f 0 .
  • the movement direction can be determined by measuring the beat frequency f.sub.sw between the light beam with the frequency f.sub.o + fs frequency-shifted in frequency by the frequency f.sub.s and the Doppler-shifted light beam with the frequency fo + f.sub.p.
  • the beat frequency f S w that is to say the frequency of the beat oscillation obtained by the superimposition of the two partial oscillations in the frequencies fo + gla and f o + fs, the following applies:
  • fsw is greater than fs for a moving object and fsw is less than fs for an approaching object.
  • a disadvantage of such an arrangement is that a separate acousto-optical component is needed to achieve the frequency shift.
  • This separate acousto-optic component must be placed exactly in the beam path and requires a very complex electrical control for an efficient frequency shift.
  • frequency shifts require high frequencies with high power, which in particular has a negative impact on the size of the measuring system.
  • the object of the invention is therefore to overcome the disadvantages of the prior art and in particular to provide a system that provides a simple way a stable frequency-shifted signal, wherein an additional device for moving the reference beams or means for moving the laser should be largely avoided.
  • the object is achieved in that in a device for laser Doppler velocity measurement means for generating a first light beam having a frequency f 0 and a second light beam which is frequency-shifted by f s and a second frequency fo + fs, available is provided.
  • the first light beam is reflected at a moving object and then has a Doppler-shifted frequency f o + f D.
  • the device comprises, in addition to the device for generating the first and second light beams, a detection device for determining a beat frequency f S w from the second light beam with the frequency f o + fs and the reflected light beam with the frequency fo + fFD Device for generating the first light beam having the first frequency and the second frequency-shifted by f s light beam comprises at least one semiconductor laser.
  • the first light beam is reflected at a moving object and the distance between the means for generating the first light beam and the moving object on the one hand and the moving object and the detection means on the other hand greater than the coherence length of the light of first light beam is.
  • the distance is preferably more than 1 m, in particular more than 5 m, very particularly preferably more than 10 m.
  • two waves are superposed in one detector. This does not necessarily require coherence.
  • the device for generating the first and the second light beam comprises two semiconductor lasers, which are preferably arranged at a small distance from one another on one and the same substrate.
  • a single semiconductor laser is provided for generating the first and the second light beam.
  • the advantage of using a single semiconductor laser is that it allows for transit time measurement, which is not possible when using two continuously operated lasers.
  • the distance between the semiconductor lasers can be between 100 ⁇ m and 1000 ⁇ m.
  • the different wavelengths of the two VCSELs which are constructed on the same substrate, is preferably set by temperature-stabilizing each of the two semiconductor lasers and operating it with a current source having low noise.
  • the semiconductor laser is preferably a so-called VCSEL (Vertical Cavity Surface Emitting Laser).
  • VCSELs are semiconductor lasers in which the light is radiated normal to the plane of the wafer on which the semiconductor laser is mounted Contrary to edge-emitting semiconductor lasers, in which the light exits at one or two edges of the semiconductor chip.
  • the laser resonator in a VCSEL is formed by two parallel to the wafer plane arranged DBR mirror (so-called distributed Bragg reflectors), between which an active zone for the generation of light is embedded.
  • the DBR mirrors are composed of layers of alternating low and high refractive index, each having an optical thickness of one quarter of the laser wavelength in the material.
  • intensity reflectivities of more than 95% can be realized within the VCSEL.
  • the charge carrier injection takes place in VCSEL by a pair of electrodes on the top and bottom of the VCSEL.
  • the laser-active zone formed between the two DBR mirrors is typically rotationally symmetrical, for example cylindrical.
  • the diameter of the cylindrical active region is, for example, 10 ⁇ m, the diameter 3 ⁇ m.
  • a VCSEL such that two vibration modes are capable of propagation in the resonator.
  • Such a VCSEL then emits two light beams with different wavelengths, the wavelengths having a defined frequency spacing.
  • the propagation of two modes in a VCSEL is possible, for example, if the rotational symmetry of the laser-active zone is refracted and the laser-active zone has, for example, an elliptical shape in cross-section instead of a circular shape.
  • the propagation of two beams in the defined frequency spacing simultaneously succeeds in particular for transverse modes. It is then advantageously emitted simultaneously from the VCSEL two light beams of different frequencies.
  • the VCSEL could also be driven so that two mutually orthogonally polarized modes are formed.
  • the semiconductor laser While in a first embodiment of the invention, the semiconductor laser emits two frequency-shifted light waves at the same time, it is in the excitation of different orthogonal polarized modes so that the modes are emitted with a time delay. In such a case, therefore, a certain switching time is to be included.
  • the switching times are to be chosen such that it is ensured that at any distance between the transmitter and the object within a certain measurement time always a beat can be measured. This means that a time window is needed in which the back-reflected signal arrives and at the same time the laser transmits in the other mode.
  • Fig. 5a-b and Fig. 6a-b are examples of the laser transmits in the other mode.
  • two beams with a stable frequency spacing from one another are provided by one and the same component, namely the semiconductor laser.
  • the invention provides two light beams with a single component. This has compared to the previous structures a considerable simplification result.
  • each of the two lasers emits slightly different wavelengths, for example, the first laser, the first wavelength f 0 and the second laser, the second wavelength f 0 + f s .
  • the detection device of the measuring device preferably comprises a
  • the evaluation unit essentially comprises an evaluation unit for detecting the beat frequency between a first reflected Doppler-shifted light signal and a second light signal which is frequency-shifted with respect to the first light signal.
  • the one electronic component is preferably designed as an integrated electrical component, ie the individual components are arranged on a common substrate or combined in a chip. In such a case, compared to the prior art substantially smaller design can be realized. It is then possible to also provide a compact component comprising all the necessary equipment, on a size ranging between 10 x 10 mm 2 and 0.01 x 0.01 mm 2 .
  • the invention also provides a method of measuring the laser Doppler velocity.
  • the method according to the invention comprises the following steps:
  • a first light beam with a first frequency f 0 is emitted by a semiconductor laser and a second light beam with a second frequency f o + fs. Then, with a detection device from the beat frequency, which is determined by the superposition of the shifted by the Doppler frequency beam with frequency fo + f s and the frequency-shifted beam with fo + fs, the direction of the body which provides the signal shifted by the Doppler frequency f D is determined.
  • the beat frequency fsw is greater than fs for a moving object and less than fs for an approaching object.
  • the signal with the first and the second frequency is made available at the same time in the method.
  • the first and second beams are provided with a time offset, for example, by switching the semiconductor laser from a first mode to a second mode.
  • driver assistance systems which can determine, for example, relative speeds between vehicles and absolute speeds.
  • the distance between the moving object and the device which makes the first or the second laser beam available is preferably more than 1 m, in particular more than 5 m, very particularly preferably more than 10 m. In particular, it is longer than the coherence length of the lasers used.
  • Fig. 1 shows the basic structure of a VCSEL
  • Fig. 2 shows a three-dimensional structure of the active zone of a
  • FIG. 3 shows an embodiment of a semiconductor laser with an active zone, which has a symmetry offset for the emission of different orthogonally polarized laser beams;
  • Fig. 4 shows an overall system of semiconductor laser detection devices and
  • 5a-b show a first embodiment of a pulse train for two modes of a semiconductor laser
  • 6a-b show a second alternative embodiment of a pulse sequence with different time intervals for two modes of a semiconductor laser.
  • FIG. 1 shows a sectional view of a VCSEL 1.
  • the VCSEL 1 comprises on its sides so-called distributed Bragg reflectors (DBR) 3.1, 3.2, which result from a plurality of alternating layers with different refractive indices, for example GaAs alternating layers 5.1, 5.2, 5.3 with different refractive indices.
  • DBR distributed Bragg reflectors
  • the active region 7 is preferably rotationally symmetrical about the axis of rotation RA, that is to say that the active region ideally has a cylindrical shape with a circular cross section.
  • the laser activity is essentially controlled by the charge carrier injection via the electrodes 10. 1, 10. 2 at the upper and lower end of the semiconductor laser 1.
  • the light 20 emitted from the active region 7 by laser action is emitted parallel to the axis of rotational symmetry of the semiconductor laser.
  • the active region is shown in more detail again.
  • the active region 7 has a cylindrical shape, wherein the
  • Cross-section of the cylinder 7 is a circle 40 with radius r.
  • Distributed Bragg reflectors 3.1, 3.2 are applied on the outer sides of the cylindrical cavity 7 .
  • the light emitted from the cavity light usually has only one frequency f 0 and there is due to the rotational symmetry no excellent polarization direction.
  • the epitaxial growth of the layers of the distributed Bragg reflectors 3.1, 3.2 is accompanied by stresses and thus asymmetric refractive indices.
  • the cavity can then no longer have a circular shape but, for example, an elliptical shape 50 with the ellipse axes a and b in cross section.
  • the same components as in Figure 2 are marked with the same reference numerals.
  • the laser light 100 emitted from such an asymmetrical component has different modes with different frequency and different polarization 110. Switching from one mode to the other and vice versa can be obtained by changing the injection current across the electrodes 10.1, 10.2.
  • two gate electrodes G1 and G2 can be arranged laterally on the active zone, as shown in phantom in FIG.
  • the rotational symmetry can be broken.
  • the same effect as described in Figure 3 is achieved, namely the emission of two modes with different frequency and polarization.
  • a voltage between at least one gate and a source electrode 10.1, 10.2 can be applied.
  • Switching between the modes can be accomplished by applying different voltages to the gate electrodes (G1, G2), i. H. a change to the gate capacity can be achieved.
  • the light emitted from a laser according to FIG. 3 consists of two partial beams with a stable frequency shift relative to each other and can be used for the Inventive device as shown in Figure 4 used for Doppler speed measurement.
  • the laser in FIG. 4 is labeled 200. It is formed according to the invention as a semiconductor laser, preferably from a VCSEL.
  • the laser 200 emits a first light beam 210 having a frequency f 0 and a second light beam 220 having a frequency fo + f s .
  • the first light beam with frequency f 0 strikes a moving object 250 and is reflected by it.
  • the reflected light beam 230 has a frequency f 0 + fo where fo
  • Doppler shift due to the movement of the object 250 is.
  • Both the light beam with the frequency f 0 + f s and the light beam f 0 + fo are recorded by a detection device 260.
  • the two light beams recorded by the detection device 260 with f 0 + f s and fo + fo are superimposed, yielding a superimposed signal with a beat frequency fo + f s / 2
  • Signal 270 with the beat frequency f D + f s / 2 is transmitted to the evaluation unit 280.
  • the size of the beat signal can then be used to deduce the speed of the object and in particular the direction of the object 250 in the evaluation unit 280.
  • the components 200, 260 and 280 are formed on a single chip.
  • This compact component can be used as a Doppler velocity measuring device with a size of only a few mm and has considerable space and manufacturing advantages over conventional devices.
  • two lasers could also be arranged side by side, for example on a substrate. The first of the two lasers would then emit a first wavelength f 0 , the second laser a wavelength fo + f s .
  • both semiconductor lasers preferably VCSELs
  • FIGS. 5a to 5b and 6a to 6b illustrate the case where a laser does not simultaneously emit two beams of the same frequency, ie a first light beam with a reference frequency fo and a second light beam with a frequency f 0 + f s , but rather the laser between two modes is switched back and forth or the two lasers on and off.
  • a laser can be switched back and forth between two orthogonally polarized modes, and these two modes can be emitted with a time delay. If one wishes to implement the present measuring method with such a system, it is crucial to ensure that, regardless of the distances between transmitter and object within a certain measuring time, a beat of the signal shifted by the Doppler frequency of the first frequency f 0 + fp with the second by a frequency f s with respect to the reference f 0 specifically frequency-shifted signal with a frequency f 0 + f s is measurable.
  • the transmitter is identified by the reference numeral 1000.
  • the transmitter according to the invention is a semiconductor laser, for example a VCSEL, which emits two modes. A first mode having a frequency fo and a second mode that is shifted by a frequency f s from the frequency f 0th
  • the laser can be switched such that it emits a first mode with the frequency f 0 and, after a certain time t, frequency-shifted a second mode by the frequency f s , ie a mode the frequency f 0 + f s - It is important that the modes are emitted in different directions. As described with reference to FIG.
  • FIG. 5b shows a completely different situation. Identical components are again identified by the same reference numbers as in FIG. 5a.
  • the distance between the transmitter 1000 and the object 1100 such that it f o + f s is a superposition of the frequency-shifted signal with the reflected-back shifted by the Doppler frequency signal fo + f ⁇ .
  • the Doppler frequency signal fo + f ⁇ With such a distance of the laser light source 1000, it is thus possible to produce the beat frequency necessary for determining the direction of movement.
  • a clocking for switching between the different frequencies is made such that not at the same time pulses of different Frequencies are emitted, but pulse packets, in which the time duration, for example, the frequency emitted at a frequency f 0 modes decreases, and then increase again.
  • the pulses which, for example, result in the different modes by current injection are equal in their time intervals, but the clock is not constant.
  • the desired beat frequency f sw occurs from the frequency f 0 + f s and the frequency f 0 + f D. Therefore, a non-continuous timing of the light source 1000 as in Figures 6a and 6b timing preferred according to Figure 5a to 5b, since then completely independent of the distance of the moving object to the light source within a sufficiently long time interval always beating frequency according to the invention can be determined ,
  • the working distance is preferably greater than the coherence length of the individual lasers.

Abstract

L'invention concerne un dispositif de mesure de vitesse laser-Doppler, comprenant un dispositif de production d'un premier faisceau lumineux d'une fréquence f0 et d'un second faisceau lumineux dont la fréquence est décalée en fréquence, par rapport à la première fréquence, d'une fréquence fs et présente ainsi une seconde fréquence fo+fs, le premier faisceau lumineux étant réfléchi sur un objet mobile, et le premier faisceau lumineux réfléchi présentant une fréquence fo+fD décalée en Doppler, et un dispositif de détection pour la détection d'une fréquence de battement fsw résultant de la superposition du second faisceau lumineux de fréquence fo+fs et du premier faisceau lumineux réfléchi fo+fD. L'invention est caractérisée en ce que le dispositif de production d'un premier faisceau lumineux et d'un second faisceau lumineux décalé en fréquence de fs comprend au moins un laser semi-conducteur.
PCT/EP2009/001270 2008-02-29 2009-02-23 Dispositif de mesure de vitesse laser-doppler WO2009106278A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102008012028.6 2008-02-29
DE102008012028A DE102008012028A1 (de) 2008-02-29 2008-02-29 Vorrichtung zur Laser-Doppler-Geschwindigkeitsmessung

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WO2009106278A2 true WO2009106278A2 (fr) 2009-09-03
WO2009106278A3 WO2009106278A3 (fr) 2009-12-03

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Publication number Priority date Publication date Assignee Title
DE102014207965A1 (de) * 2014-04-28 2015-10-29 Robert Bosch Gmbh Vorrichtung zur Objekterkennung

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GB2101832A (en) * 1981-06-16 1983-01-19 Nissan Motor A light pulse radar system
US5493395A (en) * 1991-05-02 1996-02-20 Canon Kabushiki Kaisha Wavelength variation measuring apparatus
US5926276A (en) * 1996-04-15 1999-07-20 Canon Kabushiki Kaisha Apparatus having an afocal lens system used in optical measurement of displacement
WO2001038884A1 (fr) * 1999-11-22 2001-05-31 California Institute Of Technology Capteur de particules microphotoniques
US20010009458A1 (en) * 2000-01-20 2001-07-26 Kimio Asaka Coherent laser radar system and target measurement method
WO2003084006A2 (fr) * 2002-04-03 2003-10-09 Esko-Graphics A/S Systeme laser
US20070121095A1 (en) * 2005-11-28 2007-05-31 Robert Lewis Distance measurement device with short range optics

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JP3606067B2 (ja) * 1998-10-30 2005-01-05 スズキ株式会社 振動測定方法および装置
JP4087247B2 (ja) * 2000-11-06 2008-05-21 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ 入力デバイスの移動の測定方法
US6885438B2 (en) * 2002-05-29 2005-04-26 Kent L. Deines System and method for measuring velocity using frequency modulation of laser output

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GB2101832A (en) * 1981-06-16 1983-01-19 Nissan Motor A light pulse radar system
US5493395A (en) * 1991-05-02 1996-02-20 Canon Kabushiki Kaisha Wavelength variation measuring apparatus
US5926276A (en) * 1996-04-15 1999-07-20 Canon Kabushiki Kaisha Apparatus having an afocal lens system used in optical measurement of displacement
WO2001038884A1 (fr) * 1999-11-22 2001-05-31 California Institute Of Technology Capteur de particules microphotoniques
US20010009458A1 (en) * 2000-01-20 2001-07-26 Kimio Asaka Coherent laser radar system and target measurement method
WO2003084006A2 (fr) * 2002-04-03 2003-10-09 Esko-Graphics A/S Systeme laser
US20070121095A1 (en) * 2005-11-28 2007-05-31 Robert Lewis Distance measurement device with short range optics

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Title
GESKE J ET AL: "Dual-wavelength vertical-cavity surface-emitting laser arrays fabricated by nonplanar wafer bonding" 2002 IEEE 18TH. INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE. GARMISCH, GERMANY, SEPT. 29 - OKT. 3, 2002; [IEEE INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE], NEW YORK, NY : IEEE, US, Bd. CONF. 18, 29. September 2002 (2002-09-29), Seiten 141-142, XP010609201 ISBN: 978-0-7803-7598-7 *

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DE102008012028A1 (de) 2009-09-10

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