CN100350683C - Error signal generation system - Google Patents

Error signal generation system Download PDF

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Publication number
CN100350683C
CN100350683C CNB028103181A CN02810318A CN100350683C CN 100350683 C CN100350683 C CN 100350683C CN B028103181 A CNB028103181 A CN B028103181A CN 02810318 A CN02810318 A CN 02810318A CN 100350683 C CN100350683 C CN 100350683C
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China
Prior art keywords
compensating unit
laser
exocoel
gain media
speculum
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CNB028103181A
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Chinese (zh)
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CN1547790A (en
Inventor
A·V·图加诺夫
M·S·赖斯
M·E·麦唐纳
B·V·约翰森
P·C·－H·林
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Intel Corp
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Intel Corp
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Priority claimed from US09/814,464 external-priority patent/US6816516B2/en
Priority claimed from US09/900,443 external-priority patent/US6658031B2/en
Application filed by Intel Corp filed Critical Intel Corp
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  by interference
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
    • 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
    • H01S5/14—External cavity lasers

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • Electromagnetism (AREA)
  • Lasers (AREA)
  • Semiconductor Lasers (AREA)

Abstract

A laser apparatus (20) and method that uses active thermalization of a reflective element to minimize losses and provide wavelength stability. The laser comprises first and second reflectors (24,28) defining an external cavity, and a compensating member (16) coupled to at least one of the reflectors (24) and configured to thermally position one reflector (24) with respect to the other reflector (28). The thermal positioning may be carried out by a thermoelectric controller (18) operatively coupled to the compensating member (16) and configured to thermally adjust the compensating member (16) by heating or cooling thereof. The laser apparatus (20) may comprise a gain medium (22) having first and second output facets (26,28) and emitting a coherent beam from the first facet along an optical path (32). The first reflector (24) is positioned in the optical path (32), with the second output facet (28) and first reflector (24) defining an output cavity.

Description

Has the initiatively laser aid of thermal tuning of exocoel
Technical field
Optical fiber telecommunications constantly need increase bandwidth.By wherein in single optical fiber the dense wave division multipurpose (DWDM) of a plurality of independent data stream of coexistence utilize the modulation appear at each data flow on the different channels to realize a kind of approach of bandwidth expansion.Each data stream modulates on the output beam of the corresponding semiconductor emitting laser of specific channel wavelength work, and is incorporated on the single optical fiber so that transmit in its each self-channel from the modulation output of semiconductor laser.International Telecommunication Union requires the channel spacing of about 0.4 nanometer or about 50GHz at present.This channel spacing allows to utilize single bearing optical fiber up to 128 channels in the bandwidth range of at present available optical fiber and fiber amplifier.The raising of optical fiber technology and might produce less channel spacing in the future to the continuous increase that big bandwidth needs.
Background technology
The driving of big bandwidth is caused the use of the specific DWDM equipment of accurate wavelength, for transmission output, the meticulous adjustment of DWDM equipment requirements that wavelength is specific are provided on the channel spacing of narrow separation.Along with tuned element is disposed for narrower channel spacing, reduction component tolerances and heat fluctuation become and become more and more important.Particularly, owing to cause that wavelength is unstable and reduce the environment heat fluctuation of launching power output, tunable telecommunication emitting laser is subject to the non-best influence that is provided with of tuned element.Need a kind of telecommunication emitting laser at present, it provides simple and the adjustment of tuned element accurately, to reduce the consume relevant with other environmental factor with the heat fluctuation that exists and wavelength stability is provided during laser works.
Summary of the invention
The present invention is that a kind of active (active) heat of laser cavity reflecting element of using is adjusted the laser aid and the method for consuming and wavelength stability is provided to minimize.Device of the present invention is generally a kind of laser, comprising: first and second speculum that limits laser cavity; Be coupled at least one speculum and be configured to compensating unit with respect to the speculum in another speculum heat location.Compensating unit can be directly coupled to first speculum and be configured to locatees first speculum with respect to second speculum.Carry out the heat location by being coupled to compensating unit in the operation and being configured to by the thermoelectric controller that heating or cooling come heat to adjust compensating unit.
More particularly, laser aid comprises the gain media that has first and second output facet (facet) and launch light beam along light path (optical path) from the first output facet.First speculum is arranged in light path, and the second output facet and first speculum limit laser cavity.Compensating unit can be heat conduction and have a high thermal coefficient of expansion.
Particularly, the invention provides a kind of outside cavity gas laser, comprising: comprise that (a) first and second exports faceted gain media, described gain media along light path from the described first output facet emission coherent beam; (b) be arranged in the end mirror of described light path, described end mirror and the described second output facet limit exocoel; (c) be coupled to the compensating unit of described end mirror; (d) thermoelectric controller is used for the described compensating unit of thermal control, to adjust the optical path length between described gain media and the described end mirror.
The present invention also provides a kind of external cavity laser apparatus, comprising: comprise that (a) first and second exports faceted gain media, described gain media along light path from the described first output facet emission coherent beam; (b) be arranged in the end mirror of described light path, described end mirror and the described second output facet limit exocoel; (c) be coupled to the compensating unit of described end mirror, described compensating unit has first thermal coefficient of expansion; (d) thermoelectric controller is used for the described compensating unit of thermal control, to adjust the optical path length between described gain media and the described end mirror; (e) heat conducting base, described heat conducting base has second thermal coefficient of expansion, and described gain media and described heat controller are coupled to described pedestal.
The present invention provides a kind of laser device again, comprising: first and second speculum that limits laser cavity; Gain media is used for along the emission of the light path between described first and second speculum light; Compensating unit, described compensating unit is coupled to one of described first and second speculum, and is configured to locate one of described first and second speculums by heat and comes underground heat initiatively to adjust optical path length between the described speculum; And thermoelectric controller, described thermoelectric controller is coupled to described compensating unit, so that the described compensating unit of thermal control on one's own initiative.
In certain embodiments, the gain media and first speculum can be passive (passively) adiabatic or relative to each other be heat-staple.In this respect, laser also comprises pedestal, and compensating unit and gain media are installed on pedestal.Pedestal has first thermal coefficient of expansion of selecting, and compensating unit has second thermal coefficient of expansion of selecting, and pedestal and compensating unit are processed to needed size and are configured to the passive exocoel thermal insulation that makes.Passive heat is stable can to carry out simultaneously with the active thermal control of end mirror by heating or cooling compensating unit.
Laser device also comprises and is arranged in the grid generator of light path before end mirror, can also comprise in certain embodiments being arranged in light path before end mirror and be configured to tuning or adjust the channel selector of the output wavelength of laser.Grid generator can comprise the grid etalon (etalon) that is installed to pedestal.Channel selector can be coupled to pedestal by drive unit or tuning equipment.It is stable that grid etalon and channel selector can also be subjected to passive heat by pedestal.The grid etalon can be coupled to thermoelectric controller in addition and be subjected to initiatively thermal control.
In other embodiments, laser can also comprise the detector that combines (associated) with exocoel, and it is configured to detect the loss situation of exocoel.Detector can be arranged to monitor the photodetector from the light output of exocoel, perhaps is arranged to monitor the voltage sensor that passes gain media voltage.Utilize the error signal that derives in the self-detector output to adjust exocoel by controller by heating or cooling compensating unit heat location end mirror.
Laser can also comprise being coupled to exocoel in the operation and being configured to and is incorporated into dither element in the exocoel detecting frequency modulation(FM).The dither element can be relevant with end mirror or be arranged in other position of exocoel.The frequency modulation(FM) of being introduced by the dither element has produced known in the feedback of the light to gain media from exocoel or predictable intensity and/or phase change.This from monitoring voltage that the intensity and/or the phase change of dither element are being passed gain media or in the light output of exocoel, be detectable.End mirror location by heating or cooling compensating element, influences the phase place and the intensity of modulation signal, and can use the amplitude and the phase place of modulating detected modulator signal by voltage or luminous power to generate error signal.According to locating end mirror by compensating unit heat, error signal can be used for the location or adjust end mirror in addition, so that error signal is invalid.
Method of the present invention is a kind of laser operation method, and it generally comprises: first and second speculum of limiting laser cavity is provided and adjusts laser cavity by the compensating unit that at least one speculum is coupled in the heat adjustment.The heat adjustment of compensating unit comprises and utilizes the thermoelectric controller be coupled to compensating unit to heat or cool off compensating unit.This method also comprises adiabatic passively or thermally-stabilised laser cavity, and the monitoring external losses relevant with laser cavity.Carry out heat adjustment according to the error signal that in the loss monitoring relevant, derives with external cavity.This method also comprises frequency modulation(FM) is incorporated into exocoel, and derives error signal according to the amplitude and the phase place of the frequency modulator that detects.
Description of drawings
Fig. 1 is the exocoel schematic diagram that adopts the heat of the end mirror of band compensating unit to locate according to the present invention.
Fig. 2 is the outside cavity gas laser according to band exocoel active thermal control of the present invention.
Fig. 3 A-3C is the graphic extension of pass-band performance of outside cavity gas laser that is used for Fig. 2 of channel selector, grid etalon and exocoel with respect to the selective channel in the wavelength grid.
Fig. 4 A-4C is the graphic extension that response is used for the tuning gain of the outside cavity gas laser of Fig. 2 of a plurality of channels of wavelength grid.
Fig. 5 is another embodiment of external cavity laser device.
Fig. 6 is the graphic extension from the error signal of the frequency modulation(FM) derivation of exocoel.
Fig. 7 A and 7B are comprising the graphic extension of using according to the passive thermal insulation of exocoel of the present invention.
Embodiment
In particular with reference to accompanying drawing, for illustrative purposes, the present invention is presented as the apparatus and method shown in Fig. 1 to 7.Be appreciated that not break away from basic principle disclosed herein, this device can change about the details of configuration and parts, and this method also can change about the order of details and enforcement.Aspect the outside cavity gas laser use the present invention is being disclosed mainly.But the present invention uses with other Laser Devices and optical system and it will be apparent to those skilled in the art that.It should also be understood that used technical term only is for the purpose of specific embodiment is described here, is not as limiting.
With reference to Fig. 1, show the exocoel device 10 of application according to the thermal control of outer cavity optical path length of the present invention.Device 10 comprises first reflecting element 12 and second reflecting element 14, and it limits the exocoel with optical path length l together.As described below, between reflecting element 12,14, the gain media (not shown) can be set, perhaps one of speculum 12,14 comprises the minute surface or the partial mirror of gain media.As described below equally, in the exocoel that limits by speculum 12,14, can also be provided with various other can be used on optics in the outside cavity gas laser, for example grid generator and channel selector (not shown). Reflecting element 12,14 can be installed on the conventional pedestal (not shown) or with conventional pedestal and combine.
First speculum 12 is coupled or joins compensating element, or parts 16 to, and this element or parts 16 are configured at the whole reflecting element 12 of position rise by the active thermal control.Compensating unit 16 is made of the material with height or relative high thermal expansion coefficient (CTE), for example aluminium, zinc or other metal or metal alloy.For example, the aluminium and zinc that have 24*10^-6/ ℃ CTE with 30.2*10^-6/ ℃.Can also use KOVAR with 4.8*10^-6/ ℃ of medium coefficient Alloy.According to content disclosed herein, those of ordinary skills can expect various other appropriate C TE materials.
Be to the material ideal of compensating unit 16 heat conduction so that these parts 16 can promptly be heated and cool off.Thermoelectric controller 18 is coupled to compensating unit 16 and is configured to heating or cooling compensating unit 16 in operation, it stands corresponding thermal expansion successively or shrinks to adjust the speculum 12 that is coupled to compensating unit 16 on the position.
Thus, cause compensating unit 16 thermal expansions by thermoelectric controller 18 heating compensating units 16, its speculum 12 shifts near speculum 14 to shorten optical path length l.Cause compensating unit 16 thermal contractions so that speculum 12 moves to increase outer cavity optical path length l away from speculum 14 by thermoelectric controller 18 cooling compensating units 16.In certain embodiments, compensating unit 16 can be coupled to speculum 12,14, so that the heating of compensating unit and consequent thermal expansion are used to make speculum to remove increasing outer cavity optical path length l, and the cooling of compensating unit 16 and consequent contraction are moved together to shorten optical path length l speculum 12,14.As described below, additional controller 19 can be coupled to thermoelectric controller 18 in operation provide heating or cooling to instruct with the error signal according to the loss characteristic that is derived from the exocoel that monitoring limits by speculum 12,14.
Referring now to Fig. 2, show according to external cavity laser device 20 of the present invention, wherein use the identical identical parts of label representative.Device 20 comprises gain media 22 and end face reflection element 24.Gain media 22 comprise conventional method Fabry-Perot-type led lighting chip and have the preceding facet 26 of coating antireflection (AR) and partial reflection after facet 28.Outer laser chamber touches off profile by back facet 28 and end mirror 24, and has optical path length l.Gain media 22 is from preceding facet 26 emission coherent beams, and preceding facet 26 is aimed at lens 30 with the light path 32 of qualification with exocoel optical axis conllinear.Preceding and the back facet 26,28 of gain media 22 also with the optical axis alignment of exocoel.Conventional output coupling optical device (not shown) combines with back facet 28 and is used for optical fiber (also not shown) is coupled in the output of outside cavity gas laser 20.End mirror 24 is coupled to aforesaid compensating unit 16, and its material by heat conduction, high thermal expansion coefficient constitutes.Compensating unit 16 is coupled to thermoelectric controller 18, and thermoelectric controller 18 is coupled to controller 19 on operating in regular turn.
Outside cavity gas laser 20 comprises grid generator element and tuned element, and it is respectively grid etalon 34 and wedge etalon channel selector 36 in the light path 32 between gain media 22 and end mirror 24 as shown in Figure 2.Typically, grid etalon 34 is arranged in before light path 32 tuned elements 36, and has reflected in parallel surface (face) 38,40.Grid etalon 34 is as interference light filter, the refractive index of the grid etalon 34 that the spacing by surperficial 38,40 limits and the optical thickness of grid etalon 34, the lowest-order in the wavelength consistent with the centre wavelength of the selection wavelength grid that for example comprises ITU (International Telecommunications Union) grid produces communication band.Can also select the grid of other wavelength as an alternative.The grid etalon have and between the grid line of ITU grid the corresponding Free Spectral Range of spacing (FSR), grid etalon 34 is used to provide each grid line that occupy the wavelength grid supercentral a plurality of passbands thus.Grid etalon 34 has the finesse (by the Free Spectral Range of wide maximum of half-wave or FWHM division) that suppresses the contiguous mould of outside cavity gas laser at each interchannel of wavelength grid.
Grid etalon 34 can be parallel-plate solid, liquid or channel interval etalon, and can be by through temperature controlled thermal expansion with shrink the tuning grid etalon 34 of optical thickness accurately measure between surperficial 38,40.As an alternative can by tilt with change between surface 38,40 optical thickness or by apply the tuning grid etalon 34 of electric field to electric light etalon material.Grid etalon 34 can also by on one's own initiative be tuned to select the communication grid, as the U.S. Patent application 09/900474 of co-applications herewith, inventor AndrewDaiber, title " Extemal Cavity Laser with Continous Tuning of Grid Generator " is introduced, and it is cited in this is for reference.
Have the wedge etalon 36 that non-parallel reflecting surface 42,44 is arranged to trapezoidal shape and can also be used as interferometric filter.Wedge etalon 36 comprises trapezoidal transparent substrate, trapezoidal airspace or film wedge interferometric filter between the reflecting surface of contiguous transparent substrate.Wedge etalon 36 as shown in Figure 2 can only be a tuned element that is used for outside cavity gas laser according to the present invention.Can for example grating device and electro-optical device rather than an etalon replace wedge etalon 36 with a plurality of tuned elements.Use the airspace wedge etalon open in United States Patent (USP) 6108355 as channel selector, wherein " wedge " is the trapezoidal airspace that is limited by adjacent substrate.Use the adjustable grating device of this pivot as adjusting tuning channel selector by the grating angle and using in outside cavity gas laser and apply the tuning tunable channel selector of use electric light of voltage and in United States Patent (USP), ask in 09/814646 open by selection, inventor Andrew Daiber, the March 21 calendar year 2001 applying date.Use the tuning classification thin-film interference filters of translation open in the U.S. Patent application 09/814646 of co-applications therewith and U.S. Patent application 09/900412, name is called " Graded Thin Film Wedge Interference Filterand Method of Use for Laser Tuning ", inventor Hopkins etc.Above-mentionedly be cited in openly that this is for reference.
In some is given an example,, amplified relative size, shape and distance between each optics of outside cavity gas laser 20, and needn't be shown to scale for clear.Outside cavity gas laser 20 comprises the optional feature (not shown), for example focuses on and aligning parts, with the polarizing optics that is configured to eliminate the parasitic feedback relevant with each parts of outside cavity gas laser 20.
Wideer than the passband of grid etalon 34 basically by the passband that wedge etalon 36 limits, the having basically and by the at interval corresponding cycle between limit the shortest of grid etalon 34 and the long wavelength channels of wedge etalon 36 than broad passband.In other words, the Free Spectral Range of wedge etalon 36 is corresponding with the whole wave-length coverage of the wavelength grid that is limited by grid etalon 34.Wedge etalon 36 has the finesse of the channel that suppresses the adjacent specific selective channel.
Use wedge etalon 36 between a plurality of communication channels, to select by the optical thickness that changes between the surface 42,44 of wedge etalon 36.This can be by realizing that along translation of x axle or driving wedge etalon 36 the x axle is parallel with the trapezoidal direction of the accurate tool 36 in wedge shape border and vertical with the optical axis of outside cavity gas laser 20 with light path 32.Each passband that is limited by wedge etalon 36 carries selectable channels, and along with the development of wedge shape or move in the light path 32, the light beam that moves along light path 32 pass the wedge etalon 36 that is carried on constructive interference between the longer-wavelength channels apparent surface 42,44 significantly than thickness portion.Take wedge etalon 36 from light path 32 away, light beam will experience the significantly thin part of wedge etalon 36 and passband will be exposed to the light path 32 of the corresponding shorter wavelength channel of carrying.As mentioned above, the Free Spectral Range of wedge etalon 36 is corresponding with the complete wave-length coverage of grid etalon 34, is tuned at the interior independent loss minimum value of communication band so that can pass the wavelength grid.Feed back the laser that is carried on selective channel centre wavelength from grid etalon 34 and wedge etalon 36 to the combination of gain media 22.Pass tuning range, the Free Spectral Range of wedge etalon 36 is wideer than grid etalon 34.
Wedge etalon 36 is equipped on the position by tuning by tuning, and tuning equipment comprises driving element or wavelength tuning device 46, wavelength tuning device 46 structures or be configured to according to adjustable ground of selective channel position wedge etalon 36.Tuner 46 comprises the stepper motor that combines with the appropriate hardware that is used for wedge etalon 36 accurate translations.As an alternative, tuner 46 comprises polytype actuator, includes but not limited to linear actuators known in the art such as DC servomotor, solenoid, voice coil actuator, piezoelectric actuator, ultrasonic drivers, shape store device.
Wavelength tuning device 46 is coupled to controller 19 in operation, controller 19 provides signal with the location by tuner 36 control wedge etalon 36.Controller 19 comprises data processor and memory (not shown), and storage is used for and the locating information look-up table that can select the corresponding wedge etalon 36 of channel wavelength in data storage.Controller 19 also is coupled to thermoelectric controller 18 and provides control command to wavelength tuning device 46 and thermoelectric controller 18 as shown.Can use the controller (not shown) of separation to be used for wavelength tuning device 46 as an alternative, and can share by the servo function of other tuning part and outside cavity gas laser 20 in the inside of tuner 46 or externally.
When outside cavity gas laser 20 be tuned to during different communication channel, controller 19 signals to tuner 46 according to the locator data of storing in look-up table, and tuner 46 is wedge etalon 36 conversion or be driven into correct position, and the optical thickness that wherein is arranged in the part wedge etalon 36 of light path 32 provides being longer than mutually of selective channel of carrying to relate to.Use linear encoder 50 to combine with wedge etalon 36 and tuner 46 to guarantee by tuner 46 correct position wedge etalon 36.
Wedge etalon 36 is included in the opacity 52,54 of its end, and opacity the 52, the 54th is detectable and can be as the position of check wedge etalon 36 when it is tuned to the longest of it or short channel length on the position on the optics.Opacity 52,54 provides the additional encoder mechanism of the position that is used in wedge etalon 36 in tuning.When wedge etalon 36 moves to a position so that one of opacity 52,54 when entering light path 32, light beam will or be weakened along light path obstruction in opacity 52,54.As following further specifying, weakening of this light can detect.Because can determine the position of opacity 52,54 on wedge etalon 36 exactly, so when opacity 52,54 will enter light path 32, controller 38 can be predicted.In light path 32 be not the appearance of some opacity 52,54 of expection with the presentation code mistake, and controller 19 exists opacity 52,54 to make suitable correction according to detecting in light path 32.Additional opacity (not shown) can be included in other position on the wedge etalon 36.
At laser 20 duration of works, transmission or the passband of whole wedge etalon 36 to select to limit by grid etalon 34 raised in the position in light path 32.Locate end mirror 34 tuning exocoels exocoel is locked onto the channel length of selection by heating or cooling compensating unit 16.Diagram shows grid etalon 34, wedge etalon 36 and the passband of the exocoel that limited by back facet 28 and end mirror 24 concerns that it shows exocoel passband PB1, grid etalon pass band PB2 and wedge etalon pass band PB3 in Fig. 3 A to 3C.Show relative gain at the longitudinal axis, show wavelength at transverse axis.As can be seen, the Free Spectral Range (FSR of wedge etalon 36 Channel selector) than the Free Spectral Range (FSR of grid etalon 34 Grid generator) big, and the Free Spectral Range (FSR of grid etalon 34 Grid generator) than the Free Spectral Range (FSR of exocoel The chamber) big.The passband peak value PB1 of exocoel is periodically consistent with the centre wavelength of the passband PB2 that the wavelength grid by grid etalon 34 limits.The passband that existence is extended on wedge etalon 36 and all passband PB2 at the wavelength grid.In the particular instance shown in Fig. 3 A-3C, the wavelength grid extends on by 0.5 nanometer (nm) or isolated 64 channels of 62GHz, and the shortest wavelength channel is at 1532nm, and the longest wavelength channel is at 1563.5nm.
Grid etalon 34 and wedge etalon 36 etc. strong reflection bundle significant figure determine weakening of contiguous mould or channel.As mentioned above, finesse equals the Free Spectral Range on half-wave is wide, perhaps finesse=FSR/FWHM.Fig. 3 B shows the width at the wide grid etalon pass band PB2 of half-wave, and Fig. 3 C shows the width at the wide wedge etalon pass band PB3 of half-wave.Improved the septate mode inhibition at outside cavity gas laser position decided at the higher level but not officially announced grid etalon 34 and wedge etalon 36.
Diagram illustrates center tuning at the passband PB3 of the channel of 1549.5nm and the wedge etalon between the 1550nm adjacent channel 36 in Fig. 4 A4C, wherein shows weakening of the selective channel that produced by grid etalon 34 and adjacent channel or mould.In order to know the exocoel passband PB1 that in Fig. 4 A-4C, has omitted shown in Fig. 3 A-3C.Grid etalon 34 is selected periodically longitudinal mode of the exocoel corresponding with the grid channel spacing, the contiguous mould of elimination simultaneously.Wedge etalon 36 is chosen in particular channel and all other channels of elimination in the wavelength grid.At a particular channel that is used to filter the skew in about plus or minus 0.5 channel spacing scope, selective channel or mode of laser are stable.For bigger channels offset, mode of laser jumps to next contiguous channel.
In Fig. 4 A, wedge etalon pass band PB3 is positioned at respect to the center at 1549.5nm grid channel.Very high with the relative gain that interrelates at 1549.5nm passband PB2, and be suppressed with respect to the 1549.5nm channel of selecting with relative gain value that nearby pass PB2 at 1549.0nm and 1550.0nm interrelates.The gain that interrelates with passband PB2 at 1550.5nm and 1548.5nm further is suppressed.The relative gain of the passband PB2 that the wedge etalon 36 of representing dotted line not to be subjected to suppresses.
Fig. 4 B is illustrated in the wedge etalon pass band PB that takes place during the channel switch in the position of 1549.5nm and 1550.0nm interchannel.The relative gain value that interrelates with passband PB2 at 1549.5nm and 1550.0nm is all very high, and the neither one channel is suppressed.The relative gain value that interrelates with passband PB2 at 1549.0nm and 1550.5nm is suppressed with respect to 549.5nm and 1550.0nm channel.The relative gain of the passband PB2 that the wedge etalon 36 of representing dotted line not to be subjected to suppresses.
Fig. 4 C is illustrated in the wedge etalon pass band PB3 that is positioned at 1550.0nm grid channel center relatively, the relative gain relevant with passband PB2 on 1550.0nm is very high, be suppressed simultaneously with at the 1550.0nm channel of the relevant relative gain of the passband PB2 of 1549.5nm and 1550.0nm, and the gain relevant with passband PB2 on 1551.0nm and 1549.0nm further is suppressed with respect to selection.And dotted line represents not to be subjected to the relative gain of the passband PB2 that wedge etalon 36 suppresses.
The exocoel passband PB1 that does not illustrate in Fig. 4 A-4C is an important consideration in outside cavity gas laser 20 tuning.It is desirable to, when outside cavity gas laser 20 is tuned to the selective channel wavelength, an exocoel passband PB1 will aim at or be locked into selection grid generator passband PB2 and channel selector passband PB3.End mirror 24 by hot positioning belt compensating unit 16 has realized adjusting by this way exocoel passband PB1 to adjust outer cavity optical path length according to invention.
Now,, show another embodiment, use the identical identical parts of label representative with tuning external cavity laser apparatus of hot exocoel 56 with reference to Fig. 5.In device 56, as described below, various parts are installed to conventional pedestal 58 or stablize with concentrated, the passive heat of generation device 56 each parts by conventional pedestal 58 supports.Gain media 12 is coupled to thermoelectric controller 60, and thermoelectric controller 60 is installed on bearing or the platform 62.Platform 62 is installed on the pedestal 58 in regular turn.Platform 62 is as being positioned properly gain media 12 so that collimater 30, grid etalon 34, wedge etalon 36 and end mirror 24 are arranged in the light path 32 that is limited by facet 26 emitted light beams from gain media 22.Thermoelectric controller 18 is installed on the pedestal 58, so that compensating unit 16 and end mirror 24 are installed to pedestal 58 by thermoelectric controller 18.Thermoelectric controller 60 provides thermal control can change the heat fluctuation of the gain media of the optical thickness between the facet 26,28 with prevention to gain media 22.Grid generator 34 is coupled to thermoelectric controller 64, and thermoelectric controller 64 is installed on the pedestal 58.Thermoelectric controller 64 provides temperature control to avoid or to be minimized in the change of the optical thickness between the surface 38,40 to grid etalon 34, and it will change the communication grid that is limited by grid generator 34.
Pedestal 58, platform 62 and compensating unit are made of the material with excellent heat conductivity, and the material of selection thermal coefficient of expansion as described below (CTE) provides passive heat stable.Pedestal 58, compensating unit 16 and platform 62 comprise copper-tungsten, and it provides good thermal conductivity and passes through to change the height tailorability of copper to the ratio of tungsten or aluminium and/or aluminium alloy.As an alternative, pedestal 58, platform 62 and compensating unit 16 comprise the multiple material that thermal conductivity is provided and can accurately selects CTE.Required CTE material is chosen in and is known in the art, and for example suitable material comprises various metals, metal alloy, metal nitride, metal carbides and/or their composition, compound, mixture and alloy.
Electrode 66,68 is coupled to gain media 12, is coupled to drive current source 70 in electrode 66 operations, and electrode 68 is ground connection suitably.Be coupled to controller 19 in drive current source 70 operations, controller 19 is regulated the electric current that is transferred to gain media 22 as required.Be coupled to electrode 66 and controller 19 in voltage sensor 72 operations.Voltage sensor 72 is configured to monitor at the laser run duration and passes the voltage of gain media 22 and transducer output is sent on the controller 19 of indication monitoring voltage.Because the light feedback from end mirror 24 is passed through facet 26 reflected back gain medias 22, so monitoring voltage indication and the relevant optical loss of exocoel that limits by end mirror 24 and gain media facet 28.Thus,, use it to relocate end mirror 24, adjust exocoel and deactivate error signal by heating or cooling compensating unit 16 by controller 19 by the output generation error signal of voltage sensor 72.Light from the surface 42,44 of the surface 38,40 of grid etalon 34 and wedge etalon 36 feeds back also reflected back gain media 22, in certain embodiments, the sensing voltage that passes gain media provides and can be used for adjusting grid etalons 34 and adjusting the error signal of wedge etalon 36 by tuner 46 by thermoelectric controller 64.
At laser 56 duration of works, provide electric current by drive current source 70 to gain media 22 by electrode 66,68 according to the instruction of self-controller 19.Measure the voltage that passes gain media 22 by voltage sensor 72, and voltage transmission is arrived controller 19.Because external environmental factor for example vibrates or heat fluctuation, or therein since aforesaid position wedge etalon wittingly 36 with the result of the channel variation of selecting different transmission channels, if exocoel passband PB1 is not that grid etalon pass band PB2 and wedge etalon pass band PB3 are best to be provided with respect to selecting, so various situations may take place.In these situations, meeting produces loss in the exocoel that is limited by end mirror 24 and gain media facet 28, and the instruction that controller 19 optionally sends by thermoelectric controller 18 heating or cooling compensating unit 16 minimizes the instruction that outer cavity loss there is no the effect error signal with location or tuning end mirror 24.
External cavity laser apparatus 56 also comprises the dither element 74 that is configured to frequency modulator is incorporated into exocoel.As described below, in laser external cavity, there is known frequency modulator to provide to be used to the good mechanism that enlarges the error signal of cavity loss outside the expression.As shown in the embodiment of Fig. 5, dither element 74 comprises the transparent electrooptic cell that is coupled to end mirror 2.Be coupled to controller 19 in 74 operations of dither element.Dither element 74 can be according to pass the voltage modulated generation frequency modulation(FM) that element 74 applies by the electrode (not shown).The electrooptical material of dither element 74 can comprise for example lithium niobate, or is to other the transparent electrooptical material of light beam along light path 32 transmission.End mirror 24 comprises the reflecting surface on the electrooptical material that directly is deposited to dither element 74.The modulation of being introduced by dither element 74 for example comprises the approximately frequency modulation(FM) of 20KHz.The voltage adjustment of passing the electrooptical material of element 74 has changed effective optical thickness of element 74, and the whole optical path length l is passed the exocoel (between diode facet 18 and end mirror 14) of outside cavity gas laser 56 thus.
As an alternative, dither element 74 comprises acousto-optic or press polish material, or other can provide warbled material or device to laser 56 exocoels.Dither element 74 can not be coupled with end mirror 24, and is arranged in other position of exocoel, perhaps can and suitably locate frequency modulation(FM) is incorporated into end mirror 24 to be incorporated in the exocoel thus outside exocoel.Use the electric light dither element be not coupled to end mirror in the U.S. Patent application 09/900426 of co-applications therewith, to describe, title " Evaluation and Adjustment of LaserLosses According to Voltage Across Gain Medium ", inventor Daiber etc., outside optics cavity, use piezoelectricity dither element in U.S. Patent application 09/814646, to describe, title " Error SignalGeneration System ", inventor Andrew Daiber, on the March 21 calendar year 2001 applying date, it is cited in this is for reference.U.S. Patent application 09/900426 as mentioned above, title " Evaluation and Adjustmentof Laser Losses According to Voltage Across Gain Medium " also disclose to can be used for having and have been configured to so that the control system of the outside cavity gas laser of warbled dither element to be provided to end mirror or other losser.
As mentioned above, in the power output of outside cavity gas laser 56, produced Strength Changes by the dither element modulation light path length l of introducing by element 58.Because feed back to the light in it from exocoel, this being modulated in the monitoring voltage that passes gain media 22 is detectable.Along with laser chamber mould or passband are aimed at the centre wavelength of the passband of grid generator 34 and channel selector 36 qualifications, these Strength Changes will reduce in amplitude and phase error.In other words, when passband PB1, PB2 and PB3 are optimal arrangement shown in Fig. 3 A-3C, nominally Strength Changes in modulation signal and phase error are minimum or be zero.The following use that further illustrates Strength Changes and phase error in the modulation signal of determining about error signal with reference to Fig. 6.
Outside cavity gas laser 56 duration of works with dither element 74, voltage signal is sent to controller 19 from voltage sensor 72, controller 19 is derived error signal from the modulation of being introduced by the frequency dither, and compensating signal is sent to thermoelectric controller 18, heating of this thermoelectric controller or cooling compensating unit 16, this compensating unit 16 is tuning or adjust optical path length l and expand or shrink according to adjusted end mirror 24 by the position.At laser 56 duration of works, controller 19 also is controlled to the drive current of gain media 12 and utilizes the location of the channel selector 36 of tuner 46.Controller 19 is also controlled the temperature of grid etalons 34 by thermoelectric controller 66.
With reference to Fig. 6, by wavelength to relative intensity graphic extension be incorporated in the exocoel the dither modulation signal with pass the relation of the detection voltage modulated of gain media 12.Fig. 6 illustrates grid etalon pass band PB2, and respectively with outside cavity gas laser mould 78A, 78B and 78C correspondent frequency or dither modulation signal 76A, 76B, 76C.Voltage modulated by electrooptic cell 58 is incorporated into laser external cavity to frequency modulated signal 76A-C in the above described manner.As shown in Figure 6, mode of laser 78A is with respect to the shorter wavelength lateral deviation decentre of passband PB2 towards passband PB2, and mode of laser 78B is positioned at about centre wavelength position of passband PB2, and mode of laser 78C is positioned at the longer wavelength side position of passband PB2.Mode of laser wavelength 78B is corresponding to the wavelength locking position and show the best loss profile of exocoel.Mode of laser 78A and 78C are with respect to passband PB2 off-center and caused non-best cavity loss profile, and it will need to adjust external cavity length l by effective optical thickness of adjusting electrooptic cell 58 or by locating end mirror 14 as mentioned above.
Conduct respectively is shown passes the voltage that gain media 22 detects at voltage modulation signal 80A, the 80B on Fig. 6 right side and dither modulation signal 76A, 76B and the 76C of 80C by voltage sensor 72, it corresponds respectively to mode of laser wavelength 78A, 78B and 78C.The position of mode of laser 78A that is shorter than the centre wavelength of passband PB2 at wavelength has produced the voltage signal 80A with the modulation in the band dither modulation signal 76A phase place.Produced modulation at wavelength greater than the position of the mode of laser 78C of the centre wavelength of passband PB2 with the voltage signal 80C outside the relevant dither modulation signal 76C phase place.
Act on the amplitude of relevant voltage signal with respect to the position of each optical maser wavelength of the gradient of passband PB2.Thus, and have bigger modulation amplitude than the mode of laser 78A wavelength correspondent voltage signal 80A on the steep gradient, and the mode of laser 78C correspondent voltage signal 80C relevant with the PB2 part with steep gradient not has corresponding less modulation amplitude at passband PB2.Because the cycle of dither modulation signal 76B and the centre wavelength of PB2 approximately symmetry take place, so have minimum modulation amplitude with center mode of laser 78B correspondent voltage signal 80B.In this case, main intensity frequency is the twice of dither modulation signal 76B frequency in voltage signal 80B.
As can be seen from Figure 6 the modulation amplitude that detects in the voltage that passes gain media 22 by detector 72 is represented correction or the adjusting range that laser external cavity is required, and the voltage signal phase modulation is represented the direction adjusted.The amplitude of selecting dither modulation signal 76A-C is to remain on acceptable level for the specific use of outside cavity gas laser to the Strength Changes of voltage signal modulation during wavelength locking.Select the dither modulating frequency enough high so that coherent control to be provided, and enough hang down with between the prevention transmission period to the interference of the information on the carrying signal that provides by exocoel is provided.As mentioned above, approximately the dither frequency of 20KHz is effective to specific tuning shown in Fig. 4 A-4C.
Use the passive heat of the exocoel of aforesaid active thermal control that is used to locate end mirror 24 and laser 56 and light parts wherein stable.Passive heat stable or " adiathermance device " in its minimum form, comprise using and distinguish end to the thermal coefficient of expansion (CTE) of end handing-over and have length and passive device that element CTE ratio is inversely proportional to.In this case, though the length of each element changes along with variation of temperature, the distance between the not handing-over end of element will not depend on temperature, keep constant.Use above-mentioned principle to set up the optical texture of a plurality of complexity.The principle of passive adiathermance device is known, and is presented in " Opto-mechanical Systems Design " second edition of Yoder etc.,, Marcel Dekker company, 14 chapters in 1993; " OpticalInstrument Structural Design " is cited in it that this is for reference.
In outside cavity gas laser, only use passive heat stable, and need not be favourable, but be difficult in certain laser mechanism, apply unerringly by exocoel active thermal control provided by the invention.Thus, because the stable thermal gradient and the variations in temperature that can not compensate easily of passive heat will produce the change of laser characteristic.As mentioned above, the present invention is provided for this variation in the detection laser characteristic by voltage detecting or other method, then changes the temperature of the structure member that combines with exocoel to adjust outer cavity optical path length according to change detected.
During laser works, variations in temperature acts on the refractive index of whole chamber length and chamber and its inner part, and it will cause the output wavelength relevant with the exocoel mould " non-locking " of selecting the transmission channel wavelength certainly and the variation of optical loss.The sum of the half-wavelength of carrying in the chamber is along with outer cavity optical path length changes with respect to variations in temperature.The optical path length of exocoel is the function of each element physical thickness, is included in the interior optics of exocoel and the refractive index of air and each parts and air.Two elements with identical optical thickness and different refractivity will carry the half-wavelength by its varying number separately.As mentioned above, in a single day selected output wavelength, the optical loss in the output beam that any variation in the cavity optical path length outside will cause not produced with selecting the grid passband to aim at by the exocoel passband for outside cavity gas laser.
Fig. 7 A and 7B schematically show respectively the passive heat stable scheme relevant with outside cavity gas laser 82,84, make to be denoted by like references identical parts.Outside cavity gas laser 82,84 comprises base or pedestal 58 separately, is with the gain media 22 of facet 26, is installed in end mirror or speculum 24 and tuned cell or channel selector 36 on the compensating unit 16.A plurality of additional optics jointly are shown Optical devices 86, and it comprises grid generator, collimating optics device, polarizing optics and/or other optics (not shown).As mentioned above, the thermoelectric controller (not shown) is coupled to compensating unit 16 and is used for its initiatively thermal control.Gain media 22 is installed to pedestal 58 by installation elements 88, and compensating unit 16 is installed to pedestal 58 by installation elements 90.
In each of outside cavity gas laser 82,84, be formed on that length is L between back facet 28 and the end mirror 24 OplThe resonance exocoel.In outside cavity gas laser 82, compensating unit 16 is configured to reduce passively length L during thermal expansion Opl, end mirror 24 moves in the exocoel during these parts 16 thermal expansions.In outside cavity gas laser 84, compensating unit 16 is configured to increase passively length L during thermal expansion Opl, end mirror 24 moves to the outside with respect to exocoel during these parts 16 thermal expansions.Between the phase of expansion, installation elements 88,90 will move each other and separate at heat susceptor.
Compensating unit 16 is configured and is configured to keep light path degree L ideally OplDo not change (except during the active thermal control of compensating unit 16) with temperature.Shown in Fig. 7 A, optical path length L OplCan be expressed as summation, comprise gain media 22, channel selector 36, common optical element 86 and the air gap La between said elements by laser 82 each parts light paths 1, La 2, La 3Optical thickness or path by gain media 22 are L d, are L by the optical path length of element 86 l, by the optical path length L of channel selector 36 tOptical path length by air gap between gain media 22 and the optical element 86 is La 1, be La by the optical path length of air gap between optical element 86 and the channel selector 36 2, the optical path length between channel selector 36 and the end mirror 24 is La 3Because laser 82 all elements all are coupled to pedestal 58 directly or indirectly, along with the rising of pedestal 58 temperature, their relative physical separation will typically increase.This will cause cavity optical path length L OplChange.
The optical path length of element is generally equal to its refractive index and its product along the light path size.The optical path length of outside cavity gas laser is the refractive index of a plurality of elements of existing in passing the light path of exocoel and the summation of optical thickness product, is included in the air that exists in the chamber.The optical path length of outside cavity gas laser can be expressed as thus:
L Opl＝∑n i·l i (1)
N wherein iBe refractive index along each element of light path, l iBe the thickness of each element along light path.Use the physical size of lowercase l representation element, capital L is represented optical dimensions.Increase along with the increase of element refractive index by the summation of the half-wavelength of element carrying as can be seen by the Huygens law with fixed endpoint.This is slow and crest is correspondingly tightr and draw in the Light in Medium transmission of high index by observing.Thus, on identical distance, have the wavelength of the element carrying greater number of high index, optical path length is not physical path length but measuring more accurately by the half-wavelength summation of exocoel carrying.
Approximate as first rank, compensating unit 16 needs thermal expansion to keep exocoel physical path length size (L Opl) constant.For the structure shown in Fig. 7 A, need satisfy dl F1/ dT=dl C/ dT.Be given in the physical distance between the fixing point 88,90 and the thermalexpansioncoefficient of pedestal 58 F, can determine constant in conjunction with material and thickness between installed part 90 and the end mirror 24 on demand with the physical distance that maintains between the chamber end points that limits by facet 28 and end mirror 24.In first rank are approximate, there are several potential error sources.Light path is different with physical path length at first, as mentioned above.Alternatively, for light path (L for example d, L I, L t, La 1, La 3) each section, constant for half-wavelength sum in the holding chamber must be considered the refractive index of each element.Secondly, when determining number of wavelengths that each element can carry, expansion that must computing element.The expansion of each element changes according to its thermal coefficient of expansion with along the section thickness of light path.In addition, during variations in temperature, some chambeies elements expand, and other component shrinkage, change the average weighted refractive index in chamber thus.For each element that is separated by the physical length in chamber, the average weighted refractive index is the summation of the product of physical length and refractive index.For example, during temperature raises,, reduced airspace L because compensating unit 16 inside Rapid Thermal expand A3, optical element has increased thickness simultaneously.Thirdly error source comes from each fact that the element refractive index changes along with temperature and variable quantity is different.Need a kind of method all these variations to be incorporated in the selection of the material of compensating unit 16 and size so that exocoel at the temperature range optical stabilization of broadness.
Provide the material of determining compensating unit 16 and the method more accurately of thickness or size combination by equation (2), wherein expressed the variation of temperature correlation in the optical path length that variation and change of refractive owing to each element physical length cause.
0 = d L Opl dT = Σ d ( n i · l i ) dT = Σ ( n i · αi + dni dT ) · li · · · ( 2 )
In equation (2), the rate of change of optical path length Lopl is zero need satisfying condition with respect to temperature: optical path length is the invariant of temperature.Optical path length is expressed as the refractive index n of each element i, each element thermalexpansioncoefficient iPhysical length l with each element iThe derivative of product.As mentioned above, each element of exocoel comprises gain media 22, channel selector 36, other optics 86 and the air that exists and other gas in light path.
The light path of outside cavity gas laser 82 is by the summation that constitutes its each section optical path length in Fig. 7 A, comprises the zone of air or other gas partitions optics.This relation of solution by equation (1) can be expressed as equation (3):
L Opl＝L d+L l+L t+L a123＝n dl d+n ll l+n tl t+n al a123 (3)
The airspace length l A123Expanded and effect of contraction by pedestal 58 and compensating unit 16, the airspace of expressing according to the size of pedestal 58 is l F1, the airspace that the size of compensating unit 16 is expressed is l CEquation (3) can be expressed as so:
L Opl＝n dl d+n ll l+n tl t+n a(l F1-l d-l l-l t-l c) (4)
Equation (4) can be expressed as following equation (5), with the optical path length L according to pedestal 58 F1, the additional light path length L O that produces by optical element in the chamber 86 and the optical path length L of compensating unit 16 COptical path length is shown:
L Opl＝[n al F1]+[(n d-n a)l d+(n l-n a)l l+(n t-n a)l t]-[n al c] (5)
Equation (5) can be expressed as:
L Opl＝L F+L O-L C (6)
Determine L as can be seen by above-mentioned equation (2) OplDerivative and it be set equal zero.As explanation in the following equation (7), this provides a kind of optical path length derivative L by pedestal 58 F' and in exocoel, pass through the optical path length derivative L that optical element 86 produces O' summation represent the derivative L of the optical path length of compensating unit 16 C' separate.The thermalexpansioncoefficient of difference using compensation parts 16, pedestal 58, gain media 22 and optics 86 in the process of differentiating C, α F, α d, α lIn addition, use the refractive index n of air, gain media 22, optical element 86 and channel selector 36 respectively a, n d, n lAnd n t, obtain following equation:
[n al c]′＝[n al F]′+[(n d-n a)l d+(n l-n a)l l+(n t-n a)l t]′ (7)
Equation (7) can also be expressed as:
L C′＝L F′+L O′ (8)
Derivative in can solve equation (7) is separated with the thermal coefficient of expansion that is compensated parts 16 and length product.
Fig. 7 B illustrates compensating unit 16 and places with respect to the difference of pedestal 58, and the expansion of compensating unit 16 causes increasing the outer cavity optical path length of laser 84.This relation has been provided in the separating of the equation (1) that provides in equation (9):
L Opl＝L d+L l+L t+L a124＝n dl d+n ll l+n tl t+n al a124 (9)
As mentioned above, airspace length L A123Be subjected to the expansion and the effect of contraction of pedestal 58 and compensating unit 16.But in this case, the expansion of compensating unit 16 is opposite with the effect shown in Fig. 7 A.Can be according to the size l of pedestal FlSize L with compensating unit 16 CExpress airspace length.Equation (9) can be expressed as equation (10):
L Opl＝n dl d+n ll l+n tl t+n a(l F1-l d-l l-l t+l c) (10)
Optical length L according to pedestal 58 F1, the additional optical length L that provides by optics 86 OOptical length L with compensating unit 16 CExpress equation (10):
L Opl＝[n al F1]+[(n d-n a)l d+(n l-n a)l l+(n t-n a)l t]-[n al c] (11)
Perhaps, more simplify:
L Opl＝L F+L O+L C (12)
Calculate L OplDerivative and establish it and be that zero provides the derivative L according to the optical path length of pedestal 58 F' and the derivative L of optics 86 optical path lengths O' the derivative L of optical path length of the compensating unit 16 represented of summation C' separate, shown in the following equation (13).The thermalexpansioncoefficient of difference using compensation parts 16, pedestal 58, gain media 22, optics 86 and channel selector 36 in the process of differentiating C, α F, α d, α lIn addition, use the refractive index n of air, gain media 22, optical element 86 and channel selector 36 respectively a, n d, n lAnd n t, obtain derivative:
-[n al c]′＝[n al F]′+[(n d-n a)l d+(n l-n a)l l+(n t-n a)l t]′ (13)
It can also be expressed as:
-L C′＝L F′+L O′ (14)
The thermal coefficient of expansion that the separating of equation (13) provides compensating unit 16 and the product of size, this compensating unit provides passive heat stable to the outside cavity gas laser structure of Fig. 7 B.
Though with reference to specific embodiment the present invention has been described, has it will be understood by those skilled in the art that not breaking away from the spirit and scope of the present invention can make various modification and be equal to alternative.In addition, for compound, technology, processing step or the step that makes specific situation, material, material adapts to purpose of the present invention, spirit and scope, can make multiple improvement.All these improve all within the scope of the appended claims.

Claims (25)

1. outside cavity gas laser comprises:
(a) comprise that first and second exports faceted gain media, described gain media along light path from the described first output facet emission coherent beam;
(b) be arranged in the end mirror of described light path, described end mirror and the described second output facet limit exocoel;
(c) be coupled to the compensating unit of described end mirror; With
(d) thermoelectric controller is used for the described compensating unit of thermal control, to adjust the optical path length between described gain media and the described end mirror.
2. the outside cavity gas laser of claim 1 also comprises being arranged in the grid generator of described light path in described end mirror front.
3. the outside cavity gas laser of claim 2 also comprises being arranged in the channel selector of described light path in described end mirror front.
4. the outside cavity gas laser of claim 1, also comprise pedestal, described gain media and described compensating unit are installed on the described pedestal, described pedestal has first thermal coefficient of expansion, described compensating unit has second thermal coefficient of expansion, and described pedestal and described compensating unit are processed to needed size and are configured to make passively described exocoel thermal insulation.
5. the outside cavity gas laser of claim 3, also comprise pedestal, wherein said gain media, described grid generator, described channel selector and described compensating unit are installed on the described pedestal, described compensating unit has first thermal coefficient of expansion, and described pedestal has second thermal coefficient of expansion, and described pedestal and described compensating unit are processed to needed size and are configured to make passively described exocoel thermal insulation.
6. the outside cavity gas laser of claim 1 also comprises:
(a) detector is relevant with described laser cavity and be configured to detect the loss relevant with described laser cavity; With
(b) controller is operatively coupled to described compensating unit and described detector, and is configured to come heat to adjust the length of described compensating unit according to the error signal that derives from described detector.
7. the outside cavity gas laser of claim 6, wherein said detector is the voltage detector that is positioned to monitor the voltage between the described gain media two ends.
8. the outside cavity gas laser of claim 6 also comprises the dither element that is operatively coupled to described exocoel and is configured to frequency modulation(FM) is incorporated into exocoel.
9. the outside cavity gas laser of claim 1, wherein said compensating unit comprises the material with high thermal coefficient of expansion.
10. the outside cavity gas laser of claim 9, wherein said compensating unit is heat conduction.
11. an external cavity laser apparatus comprises:
(a) comprise that first and second exports faceted gain media, described gain media along light path from the described first output facet emission coherent beam;
(b) be arranged in the end mirror of described light path, described end mirror and the described second output facet limit exocoel;
(c) be coupled to the compensating unit of described end mirror, described compensating unit has first thermal coefficient of expansion;
(d) thermoelectric controller is used for the described compensating unit of thermal control, to adjust the optical path length between described gain media and the described end mirror; With
(e) heat conducting base, described heat conducting base has second thermal coefficient of expansion, and described gain media and described thermoelectric controller are coupled to described pedestal.
12. the external cavity laser apparatus of claim 11 also comprises:
(a) detector is relevant with described exocoel and be configured to detect the loss relevant with described exocoel; With
(b) controller is operatively coupled to described compensating unit and described detector, and wherein said controller is configured to come heat to adjust the length of described compensating unit in response to the error signal that derives from described detector.
13. the external cavity laser apparatus of claim 12, wherein said detector are the voltage detectors that is positioned to monitor the voltage between the described gain media two ends.
14. the external cavity laser apparatus of claim 12 also comprises the dither element that is operatively coupled to described exocoel and is configured to frequency modulation(FM) is incorporated into exocoel.
15. the external cavity laser apparatus of claim 11, wherein said compensating unit comprises the material with high thermal coefficient of expansion.
16. the external cavity laser apparatus of claim 15, wherein said compensating unit is heat conduction.
17. a laser device comprises:
Limit first and second speculum of laser cavity;
Gain media is used between described first and second speculum along light path emission light beam;
Compensating unit, described compensating unit is coupled to one of described first and second speculum, and is configured to locate one of first and second speculums by heat and comes underground heat initiatively to adjust optical path length between the described speculum; And
Thermoelectric controller, described thermoelectric controller is coupled to this compensating unit, so that the described compensating unit of thermal control on one's own initiative.
18. the laser device of claim 17, wherein said compensating unit are used for locating described first speculum with respect to described second speculum.
19. the laser device of claim 17, wherein said thermoelectric controller are configured to the length that heat is adjusted described compensating unit.
20. the laser device of claim 18, wherein gain media has first and second output facet, the described first output facet is launched described light beam along described light path, described first speculum is arranged in described light path, the described second output facet limits described second speculum, and described first speculum and the described second output facet limit described laser cavity.
21. the laser device of claim 18, wherein said compensating unit is heat conduction.
22. the laser device of claim 18, wherein said compensating unit has high thermal coefficient of expansion.
23. the laser device of claim 20, wherein said gain media and described first speculum are relative to each other passively by thermal insulation.
24. the laser device of claim 17 also comprises:
Detector, relevant with described laser cavity, and be configured to detect the loss relevant with described laser cavity; With
Controller is operatively coupled to described compensating unit and described detector, and is configured to come heat to adjust the length of described compensating unit according to the error signal that derives from described detector.
25. the laser device of claim 24 also comprises the dither element that is operatively coupled to described laser cavity and is configured to frequency modulation(FM) is incorporated into described laser cavity.
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