GB2180985A - Laser device with stabilised power output - Google Patents

Laser device with stabilised power output Download PDF

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Publication number
GB2180985A
GB2180985A GB08622658A GB8622658A GB2180985A GB 2180985 A GB2180985 A GB 2180985A GB 08622658 A GB08622658 A GB 08622658A GB 8622658 A GB8622658 A GB 8622658A GB 2180985 A GB2180985 A GB 2180985A
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GB
United Kingdom
Prior art keywords
laser device
control resistor
laser diode
laser
power output
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.)
Granted
Application number
GB08622658A
Other versions
GB8622658D0 (en
GB2180985B (en
Inventor
Albrecht Mozer
Olaf Hildebrand
Klaus Wunstel
Gerhard Luz
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.)
International Standard Electric Corp
Original Assignee
International Standard Electric Corp
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 International Standard Electric Corp filed Critical International Standard Electric Corp
Publication of GB8622658D0 publication Critical patent/GB8622658D0/en
Publication of GB2180985A publication Critical patent/GB2180985A/en
Application granted granted Critical
Publication of GB2180985B publication Critical patent/GB2180985B/en
Expired legal-status Critical Current

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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
    • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
    • H01S5/068—Stabilisation of laser output parameters
    • 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
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/06804—Stabilisation of laser output parameters by monitoring an external parameter, e.g. 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
    • H01S5/20—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
    • H01S5/22—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 having a ridge or stripe structure
    • H01S5/227—Buried mesa structure ; Striped active layer
    • H01S5/2275—Buried mesa structure ; Striped active layer mesa created by etching
    • H01S5/2277—Buried mesa structure ; Striped active layer mesa created by etching double channel planar buried heterostructure [DCPBH] laser
    • 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
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
    • 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
    • H01S5/068—Stabilisation of laser output parameters
    • H01S5/06808—Stabilisation of laser output parameters by monitoring the electrical laser parameters, e.g. voltage or current

Abstract

A laser device with stabilised power output comprises a control resistor (1) and a laser diode (2) which are thermally-coupled. The pump current is controlled via the control resistor (1). The resistance of the control resistor (1) has a temperature dependence suitable for regulating the power output at the respective operating temperature via the pump current (Ip). The control resistor may be connected in series with the diode (2) to a constant voltage source or alternatively connected in parallel with the diode to a constant current source. The resistor may be formed from a semiconductor material and connected to the diode to form an integrated circuit. Alternatively, discrete components may be used. <IMAGE>

Description

SPECIFICATION Laser device with stabilised power output The present invention relates to a laser device with stabilised power output, comprising a control and a laser diode.
The power output of a laser diode is strongly temperature-dependent. As the temperature rises, a higher pump current is needed to maintain the optical power output at the same level. If a laserdiodewith constant power output is required, and the cost of maintaining the temperature ofthe laser diode at a constantvalue is prohibitive, the pump current must be regulated.
Means for providing such regulation is disclosed in DE-OS 2606225. It uses a circuit with quickly responding negative feedback in which the driver amplifier is a transistor operated in a common-emitter configuration. The laser diode is interposed between the collector and the emitter of thetransistor. A photodetector is connected between the base and the emitter of the transistor, and the input signal is applied between the base and the emitterofthetransistor. Regulation is accomplished by feeding a portion ofthe output power of the laser diode backto the photodetector. The photo-currentthus produced controls the transistor base current of the driver amplifier.
The disadvantage ofthis known regulation lies in the optical feedback, forwhich partofthe output power must be converted back to an electric signal. This requires an additional adjustment step when mounting the necessary detector diode. As this known regulating system consists of several components, it is complicated and susceptible to trouble.
An objectofthe invention isto provide a simple laser device with stabilised power output, especially in case of temperature variations.
According to the invention in its broadest aspect a laser device with stabilised power output, comprising a control and a laser diode is characterised in that the control is formed by a control resistorwhich is thermally coupled with the laser diode.
The main advantages ofthe invention arethatthe laser device is of simple design, because the temperature-compensating control element is merely a resistor, and that this resistor is thermally coupled with the laser diode. The resistor can also be integrated into the laser diode.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which Figure lisa graph in which the optical output power of a laser diode is plotted againstthe pump current in a parametric representation, with T1 < T2 < T3, Figure2 isa schematic diagram of a first embodiment ofthe laser device, Figure 3 is a graph in which the pump current of the laser device of Figure 2 is plotted againsttemperature, Figure 4 is a cross-sectiona I view of a possible realisation of the laser device of Figure 2, Figure 5is a cross-sectional view of another realisation of the laser device of Figure 2, Figure 6 is a cross-sectional view of a further realisation of the laser device of Figure 2, Figure 7is a schematic diagram of a second embodimentofthe laser device, and Figure 8 is a graph which illustrates the interaction between the pump current and the control current ofthe laser device offigure 7.
Figure 1 illustrates the effectoftemperature on the optical power output of a laser diode. As the temperaturnT < T2 < T3 rises, an increasing pump current l1 < 1p2 < 1p3 is needed to maintain the optical power output P0 at a constant level.
Figure 2 shows a first embodiment of a laser device 3.Aconstant-voltage source U0 delivers the pump current Ip. Connected to the constant-voltage source is a series combination of a control resistor 1 and a laser diode 2. The control resistor 1 and the laser diode 2 are thermally coupled. The control resistor 1 hasthe characteristic resistivity profile of a semiconductor, i.e., R1 = R10 exp Eg (Eq.1) '2kT" where R10 is the temperature-dependent component of the resistance, given by the geometry and size of the resistor, Eg isth e band gap of the semiconductor, k is Boltzmann's constant, and Tisthetemperaturein kelvins.The voltage appearing across this laser device 3 of Figure 2 is UO = constant = U1 + U2, (Eq.2) where U2 is the voltage drop across the laser diode 2.
For U1 = Rill, (Eq.3) Eq. 2 becomes R,lp+Up = constant. (Eq.4) Substituting Eq.1 into Eq.4 gives Rt0exp(2kT) ip + U2 = constant. (Eq.5) In Figure 3, the pump current Ip of the laser device 3 for delivering constant output power PO is plotted against the operating temperatureT. Thevalues ofthe pump current and the operating temperature are typical of laser diodes. It can be seen that at higher operating temperatures, the pump current must be increased to obtain constant output power. The pump current is controlled via the control resistor 1,which isthermally coupled with the laser diode 2 and is controlled directly via the operating temeprature.Since the laser device 3 is supplied from a constant-voltage source U,, a temperature rise results in an increase in the pump current Ip because ofthe decrease inthevalue Ri ofthe control resistor 1. To obtain the correct pump current Ip atany operating temperature in the device of Figure 3, Eq.5 must be satisfied. To this end, the free parameters Rlo and Eg are adapted in a suitable manner. The poweroutput is more sensitive to R10thanto Eg.These parameters must be set with an accuracy depending on the predetermined tolerance of the temperature dependence of the power output.
Materials especially suited forthe control resistor 1 are quaternary semiconducting compounds of GalnSbP, GalnAsSb or InAsSbP, which show different values for Eg according to composition. It is also possible to use ternary semiconducting compounds, such as GalnAs with Eg = 750 meV, or other semiconductor materials, such as germanium, where Eg = 660 meV.
Afirst realisation of the laser device 3 is shown in Figure 4. A substrate 41 bears an n-type InP layer42.
Disposed over the layer 42 is an active GalnAsP layer 43 which is covered by a p-type InP layer 44.The layers 41 to44form the laser diode 2. Part ofthe layer44 is covered by a GalnAs layer45forming the control resistor 1. The GalnAs layer45 is covered by a metal layer46. This layer46 and a metal layer40 on the opposite side of the substrate41 form the contacts. The free parameter R10 in Eq.5 is determined by the lateral limits and the thickness ofthe GalnAs layer45.
Asecond embodiment of the laser device 3 is shown in Figure 5. A GalnAs layer 51 on the underside ofthe substrate 52 forms the control resistor 1. It is covered by a thick metal layer 50, which serves as both a heat sink and a contact. The upperside of the substrate 52 bears an n-type InP layer 53, oven which an active GalnAsP layer 54 is disposed. The latter bears a p-type InP layer 55 which is covered by a metal layer 56. The layers 52 to 55 form the laser diode.
Unlikethe case in the embodiment of Figure 4,the layerofthe control resistor 51 and the active layer54are congruent, i.e. Rio can be set only via the layerthickness. The layer of the control resistor 51 and the active layer 54 lie on opposite sides of the substrate and, thus, are far apart, with the layer of the control resistor 51 still adjoining the metal layer 50.
The two realisations of Figures 4and 5 are both designed to keep the layerofthe control resistor 45,51 and the active layer 43,54 at a uniform operating temperature which is as low as possible. Depending on the external temperature effects, one orthe other ofthese realisations has greater advantages. The first realisation ensures more reliably that the control resistor and the active layer are kept at a uniform temperature. The second realisation causes a lower operating temperature.
In the realisation of Figure 6, which shows the structure of a DCPBH (double-channel planar buried heterostructure) laser representative of complicated laser structures, the laser device 3 is deposited on an InP substrate 61 having its underside covered with a metal layer 60. The lnP substrate 61 bears an n-type InP layer 62, on which an active GalnAsP layer 63 is deposited. The active layer 63 is interrupted in two places and,thus, consists of two marginal portions and a centre portion. Atthetwo interruptions, the n-type lnP layer 62 has two etched depressions. The p-type InP layer 64 covers the marginal portions of the active layer 63 and both depressions of the n-type InP layer 62. The p-type InP layer 64 is covered by an n-type InP layer 65.The latter is covered by a p-type InP layer 66 having a depression etched in the middle thereof and covered by an SiO2 insulating layer 67 which is interrupted in the area ofthe depression. The SiO2 insulating layer 67, the area of its interruption, and the depression in the p-type InP layer 66 are covered by a GalnAs layer 68, which forms the control resistor 1. A portion ofthis layer 68 is covered by a metal layer 69. The depressions in the layer 62 and 66 are grooves. The two metal layers 60 and 69 form the electric contacts of the laser device 3. The resistance valueR10 is determined by taking into account the size and position of the metal layer 69. Ifthe metal layer 69 is located at the edge of the laser device, R10 increases, and the Joule heat generated is distributed over a greater area. The GalnAs layer 68 may be covered by a second metal layer which may be disposed symmetrically with respect two the metal layer 69.
In the realisations explained so far, the control resistor 1 ofthe laser device 3 is integrated in the laser diode.
The structures exhibit mirror symmetry.
The laser device 3 can also be constructed from discrete components, in which case the control resistor 1 and the laser diode 2 are preferably mounted on a common heatsink4 (Figure 2).
Figure 7 shows a second embodiment of the laser device 5. Connected to a constant-cu rrent sou rce 1o is a parallel combination of a control resistor 6 and a laser diode 2. The control resistor 6 and the laser diode 2 are thermally coupled via a common heat sink 4. The value R6 Of the control resistor6 has a positivetemperature coefficient, such thatthe control current land the pump current Ip (Figure8) have the desired relationshipto each otherfor obtaining the desired constant optical power output Po. The following relation holds: loop = constant.
Like the laser device 3, the laser 5 can be constructed from discrete components or in integrated form.

Claims (6)

1. A laser device with stabilised power output, comprising a control and a laser diode, characterised in thatthe control is formed by a control resistor which is thermally coupled with the laser diode (2).
2. A laser device as claimed in claim 1, characterised in thatthe control resistor is formed by a resistive layer integrated in the laser diode (2).
3. A laser device as claimed in claim 1, characterised in that the control resistor and the laser diode (2) are mounted as discrete components on a heat sink (4) effecting the thermal coupling.
4. A laser device as claimed in anyone of claims 1 to3, characterised in that the control resistor (1) is made of semiconductor material and connected in series with the laser diode (2), and that the control resistor(1) and the laser diode (2) are supplied from a constant-voltage source.
5. A laser device as claimed in any one ofclaims 1 to 3, characterised inthatthe control resistor (6) hasa positive temperature coefficient and is connected in parallel with the laser diode (2), and that the control resistor (6) and the laser diode (2) are supplied from a constant-current source.
6. A laser device substantially as described with reference to the accompanying drawings.
GB8622658A 1985-09-28 1986-09-19 Laser device with stabilised power output Expired GB2180985B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19853534744 DE3534744A1 (en) 1985-09-28 1985-09-28 LASER DEVICE WITH STABILIZED OUTPUT

Publications (3)

Publication Number Publication Date
GB8622658D0 GB8622658D0 (en) 1986-10-22
GB2180985A true GB2180985A (en) 1987-04-08
GB2180985B GB2180985B (en) 1989-10-25

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Family Applications (1)

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GB8622658A Expired GB2180985B (en) 1985-09-28 1986-09-19 Laser device with stabilised power output

Country Status (3)

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AU (1) AU586279B2 (en)
DE (1) DE3534744A1 (en)
GB (1) GB2180985B (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2197126A (en) * 1986-11-04 1988-05-11 Samsung Semiconductor Tele A light emitting semi- conductor device having current overload protection
EP0578883A1 (en) * 1991-06-27 1994-01-19 Xerox Corporation Diode Lasers
US5303251A (en) * 1990-08-17 1994-04-12 Linotype-Hell Ag Method and circuit arrangement for driving a laser diode

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3907423C2 (en) * 1989-03-08 1993-12-16 Kommunikations Elektronik Circuit arrangement for the transmission of optical signals via optical fibers
JP3518834B2 (en) * 1996-12-14 2004-04-12 株式会社東芝 Semiconductor light emitting device and optical fiber transmission system
DE102017112101A1 (en) * 2017-06-01 2018-12-06 Osram Opto Semiconductors Gmbh Optoelectronic semiconductor module
CN108988122A (en) * 2018-09-30 2018-12-11 无锡源清瑞光激光科技有限公司 A kind of quasi-continuous semiconductor laser control system of QCW suitable for laser spot welding
DE102018127977A1 (en) * 2018-11-08 2020-05-14 Osram Opto Semiconductors Gmbh DIODE LASER AND METHOD FOR OPERATING A DIODE LASER

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2038538A (en) * 1978-12-28 1980-07-23 Amann M Semiconductor laser diode
GB2052841A (en) * 1979-05-08 1981-01-28 Canon Kk Semiconductor laser device and an image recording apparatuus the same
GB2054949A (en) * 1979-07-26 1981-02-18 Standard Telephones Cables Ltd Cooling arrangement for laser diode
US4484331A (en) * 1981-07-20 1984-11-20 Rca Corporation Regulator for bias current of semiconductor laser diode

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2038538A (en) * 1978-12-28 1980-07-23 Amann M Semiconductor laser diode
GB2052841A (en) * 1979-05-08 1981-01-28 Canon Kk Semiconductor laser device and an image recording apparatuus the same
GB2054949A (en) * 1979-07-26 1981-02-18 Standard Telephones Cables Ltd Cooling arrangement for laser diode
US4484331A (en) * 1981-07-20 1984-11-20 Rca Corporation Regulator for bias current of semiconductor laser diode

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2197126A (en) * 1986-11-04 1988-05-11 Samsung Semiconductor Tele A light emitting semi- conductor device having current overload protection
US5303251A (en) * 1990-08-17 1994-04-12 Linotype-Hell Ag Method and circuit arrangement for driving a laser diode
EP0578883A1 (en) * 1991-06-27 1994-01-19 Xerox Corporation Diode Lasers

Also Published As

Publication number Publication date
AU586279B2 (en) 1989-07-06
GB8622658D0 (en) 1986-10-22
AU6265586A (en) 1987-04-02
DE3534744A1 (en) 1987-04-09
GB2180985B (en) 1989-10-25

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Legal Events

Date Code Title Description
732 Registration of transactions, instruments or events in the register (sect. 32/1977)
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19920919