WO2011000153A1 - 连续无跳模可调谐光栅外腔半导体激光器 - Google Patents

连续无跳模可调谐光栅外腔半导体激光器 Download PDF

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WO2011000153A1
WO2011000153A1 PCT/CN2009/072560 CN2009072560W WO2011000153A1 WO 2011000153 A1 WO2011000153 A1 WO 2011000153A1 CN 2009072560 W CN2009072560 W CN 2009072560W WO 2011000153 A1 WO2011000153 A1 WO 2011000153A1
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laser
diffraction grating
diffraction
tuning
output
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PCT/CN2009/072560
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English (en)
French (fr)
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张光志
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山东远普光学股份有限公司
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Priority to EP09846682A priority Critical patent/EP2451033A4/en
Priority to PCT/CN2009/072560 priority patent/WO2011000153A1/zh
Priority to JP2012517997A priority patent/JP2012531754A/ja
Publication of WO2011000153A1 publication Critical patent/WO2011000153A1/zh

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    • 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
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S2301/00—Functional characteristics
    • H01S2301/02—ASE (amplified spontaneous emission), noise; Reduction thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/105—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
    • H01S3/1055—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length one of the reflectors being constituted by a diffraction grating
    • 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
    • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
    • H01S5/0064—Anti-reflection components, e.g. optical isolators
    • 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
    • H01S5/022—Mountings; Housings
    • H01S5/0225—Out-coupling of light
    • H01S5/02251—Out-coupling of light using optical fibres
    • 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
    • H01S5/028—Coatings ; Treatment of the laser facets, e.g. etching, passivation layers or reflecting layers
    • 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
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H01S5/143—Littman-Metcalf configuration, e.g. laser - grating - mirror
    • 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
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4031—Edge-emitting structures
    • H01S5/4056—Edge-emitting structures emitting light in more than one direction
    • 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
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4031—Edge-emitting structures
    • H01S5/4062—Edge-emitting structures with an external cavity or using internal filters, e.g. Talbot filters

Definitions

  • the present invention relates to the field of semiconductor laser technology, and more particularly to a continuous mode-free tunable grating external cavity semiconductor laser. Background of the invention
  • the wavelength tuning technology of the light source is an important part of the laser technology, and the GTECL (Grating-tuned external cavity lasers) have high optical transmission purity, wide wavelength coverage and compact structure. It has outstanding advantages such as high conversion efficiency, single-mode output, low cost, and good reliability. It has been widely used in optical communication, optical switching, optical storage, fiber optic gyroscopes, metrology, high-resolution optical transmission measurement, and biomedical applications. In many fields, it has great application prospects.
  • tunable grating external cavity semiconductor lasers are generally of two types. One is a Littrow-type tunable grating external cavity semiconductor laser, and the other is a Litman-Mitkoff Littman-Metcalf-type tunable grating external cavity semiconductor laser. The two types of lasers are described below.
  • the Littrow-type tunable grating external cavity semiconductor laser produces a frequency-tunable laser beam with very narrow linewidth and very high optical coherence, and in the production of actual products, the Littrow-type GTECL laser is very compact and simple in form.
  • a resonant cavity structure that typically includes only three optics: a semiconductor laser as a laser gain medium, a diffraction grating as a frequency selective element, and a collimating lens that collimates the laser beam, thereby achieving a very simplified and low cost Manufacturing process.
  • a tunable grating external cavity semiconductor laser proposed by Wieman and Hollberg (see “Using Diode Lasers for Atomic Physics” by Carl E. Wieman and Leo Hollberg, Review of Scientific Instruments, Vol. 62, Pages 1-19, January, 1991 " ) is a typical Littrow-type tunable grating external cavity semiconductor laser.
  • Fig. 1 is a schematic view of a prior art Littrow type tunable grating external cavity semiconductor laser.
  • the tunable grating external cavity semiconductor laser includes: a semiconductor diode 101, a collimating lens 102, and a diffraction grating 103.
  • the semiconductor laser 101 has a rear surface 106 and a front surface 107.
  • the light beam generated in the semiconductor laser 101 passes through the collimator lens 102 to obtain parallel light.
  • the parallel light is incident on the diffraction grating 103 and is then used by the diffraction grating.
  • Narrow line width single longitudinal mode (SLM, single longitudinal mode) laser output Narrow line width single longitudinal mode (SLM, single longitudinal mode) laser output.
  • the diffraction grating 103 is rotatable about a fixed rotation axis passing through the G point and perpendicular to the plane of the paper, wherein the G point is the intersection of the optical axis 100 and the surface of the diffraction grating 103.
  • Tuning of the frequency or wavelength of the output laser can be achieved when the diffraction grating 103 is rotated about the fixed axis of rotation described above.
  • the single longitudinal mode of the above laser may suddenly jump from one longitudinal mode to the other longitudinal mode, thereby causing mod hopping.
  • the phenomenon of the mode hopping at the laser output frequency produces a frequency jump corresponding to the longitudinal mode spacing of the laser, which in turn destroys the continuous tuning of the laser frequency, the accuracy of the frequency tuning, the tuning linearity and other frequency-dependent tuning characteristics.
  • Applications have an adverse effect and should be avoided as much as possible, thus requiring MHF, mod-hop-free continuous frequency tuning or wavelength tuning.
  • N represents the modulus of the Nth longitudinal mode in the cavity, and N is an integer;
  • ⁇ represents the wavelength of the laser oscillation, that is, the wavelength of the laser selected by the grating dispersion, The laser wavelength is related to, that is, the value of (the value will vary with the change;
  • MG represents the optical distance from the M point (i.e., the intersection of the optical axis 100 and the rear surface 106 of the semiconductor laser 101) to the G point, that is, the optical length of the outer cavity.
  • ⁇ is generally constant; when the diffraction grating 103 rotates around the above fixed rotation axis, the magnitude of the diffraction angle changes. From the formula (1.2), the laser output laser or laser at this time The wavelength will also change; and from equation (1.3), when the magnitude of the diffraction angle changes, the modulus N will also change, that is, the change of the modulus N relative to the diffraction angle is not constant, and thus is diffracted. When the angle change is large, the mode hopping will occur (ie, the value of the modulus N will change by +1 or -1); that is, the laser shown in Figure 1 is used to rotate the diffraction grating to the laser frequency or laser.
  • the Littrow-type GTECL described above can only achieve very small or limited MHF tuning, but cannot perform MHF continuous tuning of the laser frequency or wavelength.
  • a tunable grating external cavity semiconductor laser is disclosed in U.S. Patent No. 6,731,661.
  • 2 is a schematic diagram of a Littrow-type tunable grating external cavity semiconductor laser in the prior art 2.
  • the tunable grating external cavity semiconductor laser also includes a semiconductor laser 101, a collimator lens 102, and a diffraction grating 103.
  • the tunable grating external cavity semiconductor laser differs in that the diffraction axis of the diffraction grating 103 in FIG.
  • L 2 is L, which is located at the intersection of the diffraction surface extension line of the diffraction grating 103 and the extension line of the rear surface 106 of the semiconductor laser 101. And the rotation axis L is perpendicular to the paper surface direction. Tuning of the output laser frequency or wavelength can also be achieved when the diffraction grating 103 is rotated about a fixed axis of rotation L.
  • ⁇ represents the distance from the defect point on the back surface 106 of the semiconductor laser 101 to the center of the surface of the diffraction grating 103, that is, the length of the outer cavity; the length of the outer cavity is related, that is, the value of Me ( It varies with the change; ⁇ represents the distance from the rotation axis L to the point M on the rear surface 106 of the semiconductor laser 101.
  • the tunable grating external cavity semiconductor laser of FIG. 2 can generate a relatively large MHF tuning range, but its mode N still depends on the diffraction angle ⁇ .
  • a broadband MHF tunable GTECL laser that is, a Littman-Metcalf type tunable grating external cavity semiconductor laser
  • a Littman-Metcalf resonator structure The construction of resonant cavities for this type of laser has been disclosed in numerous documents or patents. For example, U.S. Patent No. 5, 319, 512 to Luecke, U.S. Patent No.
  • the Littman-Metcalf type tunable grating external cavity semiconductor laser includes a planar mirror 108 in addition to the semiconductor laser 101, the collimator lens 102, and the diffraction grating 103.
  • the rotation axis L is located at an intersection of the extension line of the rear surface 106 of the semiconductor laser 101, the diffraction surface extension line of the diffraction grating 103 and the extension surface of the reflection surface of the plane mirror 108, and the rotation axis L is perpendicular to the paper surface direction; The point is the intersection of the reflected ray passing through the G point and the plane mirror 108.
  • the diffraction grating 103 is fixed, and the plane mirror 108 is rotatable about a fixed rotation axis L.
  • the diffraction angle changes, and the length of the outer cavity (ie, the distance between the two points of M and G and the sum of the optical paths between the two points of G and Q) also changes;
  • the modulus N at this time can be kept constant, so that the modulus N can be maintained while the laser frequency is changed, thereby achieving continuous mode-free tuning of the laser frequency.
  • the laser design shown in FIG. 3 is in an ideal working state, for example, the optical device used in the cavity of the laser does not have light dispersion, or the optical device in the cavity can be accurately aligned.
  • a semiconductor laser of the Littman-Metcalf type is capable of producing a maximum MHF tuning range covering the entire spectral range produced by the diffraction grating.
  • due to limitations of industrial manufacturing techniques and assembly and debugging means in the actual products of the tunable grating external cavity semiconductor laser shown in FIG. 3, there is generally a problem of device dispersion and misalignment of the optical device, which greatly limits the problem.
  • the MHF tuning range of the laser due to limitations of industrial manufacturing techniques and assembly and debugging means, in the actual products of the tunable grating external cavity semiconductor laser shown in FIG. 3, there is generally a problem of device dispersion and misalignment of the optical device, which greatly limits the problem.
  • the MHF tuning range of the laser due to limitations of industrial manufacturing techniques and assembly and debugging
  • Zhang and Hakuta proposed a cavity structure with automatic adjustment of the position of the optics and passive compensation to achieve the above-described broadband MHF tuning. Even so, in the manufacturing process of the above lasers, there are still many problems such as complicated optical and mechanical alignment, additional material cost of the optical device, large cavity size, and very slow tuning speed.
  • Embodiments of the present invention provide a continuous mode-free tunable grating external cavity semiconductor laser, thereby enabling seamless mode-free tuning of the laser frequency and reducing the production cost of the laser.
  • a continuous mode-free tunable grating external cavity semiconductor laser comprising: at least one optical component consisting of a gain medium and a collimating lens, and tuning a device and at least one diffraction grating;
  • a coherent light beam emitted by the gain medium passes through the collimating lens to become parallel light.
  • part of the diffracted light directly becomes the first output laser that is output, and another part of the diffracted light returns to the gain medium along the original incident optical path, and oscillates and amplifies in the gain medium.
  • the second output laser is formed; the diffraction grating is disposed on the tuning device; the tuning device drives the diffraction grating to rotate around a rotation axis located on the back surface of the diffraction grating; The axis is parallel to the diffractive surface of the diffraction grating and perpendicular to the optical axis of the laser.
  • the position of the pre-set rotation axis satisfies the condition:
  • the modulus of the longitudinal mode selected by the cavity of the laser is a constant.
  • the radius of rotation of the diffraction grating when the rotation is performed is the vertical distance of the rotation axis to the diffraction surface of the diffraction grating.
  • the tuning device is further configured to change the position of the rotating shaft in real time or to change the relative position of the rotating shaft and the diffraction grating in real time.
  • the tuning device includes: a driving device and a rotating base; the rotating base is connected to the driving device;
  • the rotating base for supporting or mounting the diffraction grating
  • the driving device is configured to drive the rotating base to drive the diffraction grating to rotate around the rotating shaft; and to change the position of the rotating shaft in real time, or to change the rotating shaft and the diffraction in real time The relative position of the grating.
  • the drive device is a rotary motor, a stepper motor or a microelectromechanical system.
  • the tuning device further includes: a control device and an encoder
  • the encoder is configured to track movement of the rotating base and send the tracking result to the control device;
  • the control device is configured to selectively control movement of the spin base according to the selected output laser wavelength and the tracking result, thereby outputting a desired frequency
  • the laser simultaneously performs the mode-free continuous tuning of the output laser frequency.
  • the laser includes a plurality of diffraction gratings
  • the plurality of diffraction gratings are disposed on the tuning device; the tuning device drives the plurality of diffraction gratings to rotate about the same rotation axis; the rotation axis is parallel to the diffraction surface of the diffraction grating and is opposite to the laser The optical axis is vertical;
  • the optical assembly utilizes any one of the diffraction gratings disposed on the tuning device to effect continuous mode-free tuning of the desired output laser frequency.
  • the laser further includes: a partial mirror disposed on a light path between the collimating lens and the diffraction grating;
  • the partial mirror is for generating a third output laser and a fourth output laser that filters out spectral noise.
  • the partial mirror is a beam splitter, a spatial filter or a coupled fiber.
  • the laser further includes: a coupling device
  • the coupling means is adapted to couple at least one output laser of the laser into a desired single mode or multimode fiber.
  • the laser further includes: one or more sets of optical components disposed around the tuning device;
  • Each set of optical components utilizes any one of the diffraction gratings disposed on the tuning device to achieve no mode hop continuous tuning of the desired output laser frequency.
  • an embodiment of the present invention provides a continuous mode-free tunable grating external cavity semiconductor laser. Since the continuous mode-free tunable grating external cavity semiconductor laser includes a tuning device and at least one diffraction grating, the diffraction grating is disposed on the tuning device; and the tuning device is configured to drive the diffraction grating around a preset The axis of rotation of the back side of the diffraction grating is rotated, and the axis of rotation is parallel to the diffraction surface of the diffraction grating and perpendicular to the optical axis of the laser, thereby enabling continuous mode-free tuning of the laser frequency and reducing the The production cost of the laser. BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a schematic view of a prior art Littrow type tunable grating external cavity semiconductor laser.
  • FIG. 2 is a schematic view of a Littrow-type tunable grating external cavity semiconductor laser in the prior art 2.
  • 3 is a schematic diagram of a Littman-Metcalf type tunable grating external cavity semiconductor laser in the prior art 3.
  • FIG. 4 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 1 of the present invention.
  • FIG. 5 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 1 of the present invention.
  • 6 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 2 of the present invention.
  • FIG. 7 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 3 of the present invention.
  • FIG. 8 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 4 of the present invention. Mode for carrying out the invention
  • the tunable grating external cavity semiconductor laser of the present invention comprises: a gain medium 401, a collimating lens 402, and a diffraction grating 403.
  • the gain medium 401 and the collimating lens 402 may constitute an optical component; the gain medium 401 is configured to generate a stable optical gain and emit a coherent light beam; for example, the gain medium 401 may include a total reflection or a portion a reflective rear surface 406, a front output surface 407 coated with an anti-reflection (AR) coating, and a semiconductor laser chip (the The chip may be a commonly used Fabry-Pero type semiconductor laser chip, or other devices having similar functions); point M in the figure is the intersection of the optical axis 400 and the rear surface 406 of the gain medium 401; G point is the optical axis The intersection of 400 and 4 the smear grating 403; therefore, the external cavity of the laser (abbreviated as the outer cavity, the same below) is defined by the back surface 406 of the gain medium 401 and the diffraction grating 403.
  • the external cavity of the laser abbreviated as the outer cavity, the same below
  • the gain medium 401 emits a coherent light beam from the front output surface 407, and the coherent light beam passes through the collimating lens 402 to become parallel light, which is diffracted after being incident on the diffraction grating 403; the light diffracted by the diffraction grating 403 is partially diffracted Light (eg, zero-order diffracted light) may directly become the first output laser that is output (eg, output laser 404), while another portion of the diffracted light (eg, first-order diffracted light, or higher order diffraction orders) is along
  • the original incident optical path returns to the back surface 406 of the gain medium 401, which in turn reflects the returned light back to the diffraction grating 403, and so on, until the diffracted light is oscillated and amplified in the gain medium 401
  • the diffracted light can be used as the second output laser (for example, the output laser 405). It can be seen that the length of the outer cavity in the resonant
  • the laser shown in FIG. 4 further includes a tuning device 409, which can form a tuning component with the diffraction grating 403 described above;
  • the diffraction grating is disposed on the tuning device; and the tuning device 409 is configured to drive the diffraction grating 403 such that the diffraction grating 403 is rotatable about a rotating axis disposed on a back surface of the diffraction grating; a rotation axis parallel to the diffraction surface of the diffraction grating and perpendicular to the optical axis 400 of the laser (ie, the rotation axis is a rotation axis passing through a zero point and perpendicular to the paper surface direction), that is, the rotation axis is not in the diffraction grating
  • An extension line of the diffraction surface of 403 is located on the back side of the diffraction grating
  • the tuning device 409 can also be used to change the position of the O point in real time (ie, change the position of the rotating axis), or to change the relative position of the 0 point and the diffraction grating 403 in real time (ie, change the rotating axis and the diffraction grating). Relative position of 403).
  • the diffraction grating 403 is performed
  • the radius of rotation of the above rotation is: the vertical distance from the point O (ie, the axis of rotation) to the diffraction surface of the diffraction grating 403, which distance can be represented by ⁇ ; wherein the point P is from the point O to the diffraction surface of the diffraction grating 403 The intersection of the perpendicular to the diffractive surface of the diffraction grating 403.
  • the back surface of the diffraction grating 403; and the position of the rotation axis and/or the rotation axis and the diffraction grating 403 may be used in advance or in real time.
  • the relative position of the tunable grating can be flexibly designed according to the requirements of laser frequency tuning, and the modulus N of the longitudinal mode selected by the cavity of the laser is constant.
  • FIG. 5 is a schematic diagram of a tunable grating external cavity semiconductor laser according to Embodiment 1 of the present invention.
  • the diffraction grating 403 is rotated by an angle / / around the rotation axis of the above-mentioned O point, the position of the diffraction grating 403 is moved, and therefore, the diffraction angle is changed from (9 to ⁇ ', G point At the G' point, the diffraction angle of the laser and the length of the outer cavity are changed, so that the above-described variation can be utilized to achieve tuning of the laser frequency.
  • the diffraction angle is 6», and the diffraction density of the diffraction grating 403 is set.
  • the center wavelength of the laser light selected by the diffraction grating 403 at this time is known. For:
  • the length of the outer cavity of the laser is 1 ⁇ 2 of the sum of the optical paths between the point M and the point G, according to the grating equation:
  • N represents the modulus of the Nth longitudinal mode in the cavity of the tunable grating outer cavity semiconductor laser when the diffraction angle is /, and N (is an integer).
  • the tuning device 409 drives the diffraction grating 403 to rotate a certain angle around the rotation axis passing through the zero point, for example, when the diffraction grating 403 is rotated to a position where the diffraction angle is, the G point on the diffraction surface of the diffraction grating 403 is moved to G'.
  • the position of the point, at this time, the outer cavity length of the laser is the sum of the optical paths between the M point and the G' point, that is, the length of the outer cavity of the laser changes:
  • GG ⁇ & ,0 r o - ⁇ : 1 0 ⁇ (4.4)
  • r. And t. Is a parameter having a certain relationship with the position of 0 o'clock; when the position of the O point is determined, or when the relative position of the 0 point and the diffraction grating 403 is determined, r. And ⁇ . The value is then determined; on the other hand, it can also be based on r. And t. The value is determined to determine the position of point 0 or to determine the relative position of point 0 to diffraction grating 403.
  • N( ) denote the modulus of the Nth longitudinal mode in the cavity of the tunable grating outer cavity semiconductor laser, and N (which is an integer, which is the laser selected by the diffraction grating 403)
  • N( ) denote the modulus of the Nth longitudinal mode in the cavity of the tunable grating outer cavity semiconductor laser
  • N which is an integer, which is the laser selected by the diffraction grating 403
  • ⁇ , ⁇ ) ⁇ , or I )- N( )
  • the continuous mode tuning condition of the mode hopping ensures continuous mode-free tuning in a given frequency range within the above finite gain bandwidth.
  • r in the formula (4.6) it is only necessary to appropriately adjust r in the formula (4.6).
  • ⁇ can easily meet the above-mentioned no-jump continuous tuning conditions, so that MHF continuous tuning can be easily realized for all laser frequencies.
  • a change in the position of the diffraction grating 403 and/or the axis of rotation (i.e., the position of the zero point) will result in the above r. And t.
  • the value of the change therefore, in the technical solution of the present invention, the position of the O point (ie, the position of the rotation axis) can be adjusted in real time by means of external feedback control, or by the diffraction grating 403 and O
  • the real-time adjustment of the absolute position or relative position of the point changes the two coordinates r described above.
  • ⁇ The value allows the above-described no-jump continuous tuning condition to be satisfied over a larger frequency tuning range.
  • the position of the defect may be selected in advance or in real time according to the actual application, or may be Or the relative position of the O-point to the diffraction grating 403 is selected in real time such that the diffraction grating 403 has a suitable cavity length of the laser in which the diffraction grating 403 is located when rotating about a rotation axis perpendicular to the paper plane passing through the O point. The length is used to output the laser at the desired frequency and achieve no mode-hop continuous tuning of the output laser frequency.
  • the selection of the position of the point O or the relative position of the zero point and the diffraction grating 403 and the rotation of the diffraction grating 403 can be realized by the tuning device 409.
  • the tuning device 409 can be any of a variety of fixed or dynamic position adjustment devices commonly used in the art.
  • the tuning device 409 can include a drive and a base (neither shown in Figures 4 and 5).
  • the diffraction grating 403 is disposed on the rotating base, and the rotating base is connected to a driving device, and the rotating base can be used for supporting or mounting the diffraction grating 403, and can change diffraction according to driving of the driving device.
  • the driving device may be configured to drive the rotating base to drive the diffraction grating 403 to rotate around the rotating axis, or to change the position of the 0 point or the relative point of the 0 point and the diffraction grating 403
  • the position is such that the diffraction grating 403 is rotatable to a desired position about a rotation axis passing through the O point and perpendicular to the plane of the paper.
  • the driving device may be a rotating motor, a stepping motor, a micro-electro-mechanical system (MEMS), or other device capable of implementing the above driving;
  • the connecting manner of the driving device and the rotating base may be directly fixed (for example, The rotary bearing of the rotary motor or the stepping motor is directly connected to the rotating base or through the universal joint and fixedly connected with the rotating base; the connection of the rotating bearing ensures that the rotating base can pass through 0 points and is perpendicular to the paper surface.
  • the rotation axis rotates or moves the shaft), or other connection methods commonly used in the art, and will not be described herein.
  • a control device and an encoder may be further included.
  • the encoder is configured to track the movement of the rotating base and send the tracking result to the control device.
  • the movement of the rotating base may be translational, rotational or translational plus rotation.
  • the translation of the pedestal may change the position of the rotating shaft or change the relative position of the rotating shaft and the diffraction grating; and the rotation of the rotating base may cause the diffraction grating on the rotating base to wrap around The rotating shaft rotates.
  • the control device is configured to selectively control the movement of the rotating base according to the selected wavelength of the output laser and the tracking result, so as to output the laser frequency while outputting the laser of the desired frequency. Perform no mode hop continuous tuning. From this, it can be seen that by the tuning device 409 as described above, the mode-free continuous tuning of the output laser frequency can be realized while outputting the laser light of the desired frequency.
  • the output laser there are: 1) an output laser 404 formed by laser light directly reflected by the diffraction surface of the diffraction grating 403; 2) by the diffraction grating 403 The diffractive surface is reflected back to the gain medium 401, and after being oscillated and amplified in the gain medium 401, the output laser 405 is output from the rear surface 406 of the gain medium 401.
  • spectral "noise” is present, which is derived from the source spontaneous emission (SSE) and the amplified spontaneous emission in the gain medium 401.
  • SSE source spontaneous emission
  • ASE amplified spontaneous emission.
  • a partial mirror can also be added to the tunable grating external cavity semiconductor laser shown in FIG. 5 for "clearing” the light in the output laser by "noise” (ie, output) ASE and SSE components in the laser).
  • the tunable grating external cavity semiconductor laser of the present invention includes a gain medium 401, a collimating lens 402, a diffraction grating 403, and a tuning device 409, and a collimating lens 402 and a diffraction grating.
  • a partial mirror 601 on the optical path between 403, the partial mirror 601 can be set or rotated to any desired angle according to actual needs Degree, used to filter out spectral noise in the output laser.
  • the partial mirror 601 can be a beam splitter or other form of spatial filter.
  • the above-mentioned spectral “noise” can be driven away from or deviated from the optical path of the output laser by diffraction of the diffraction grating 403. Therefore, the above-mentioned spectral "noise” in the output laser can be completely “cleared” by inserting the above-described partial mirror (for example, a beam splitter, a spatial filter, or a coupling fiber).
  • the above-described partial mirror for example, a beam splitter, a spatial filter, or a coupling fiber.
  • the partial mirror 601 can separately split the laser light passing through the partial mirror 601 into two laser beams, and one of the laser beams is an output laser 602, which is "cleared by the partial mirror 601". "acting such that the above-mentioned optical "noise” is no longer contained in the output laser 602 (i.e., the output laser 602 does not contain ASE and SSE components); the other laser is the output laser 603, which is conventional
  • the tunable laser beam still contains the above-mentioned optical "noise” (i.e., the output laser 603 still contains the ASE and SSE components) and is opposite to the direction of the output laser 602 described above.
  • tunable grating external cavity semiconductor laser as shown in Fig. 6, we can obtain the removal of the optical "noise" while obtaining a conventional tunable laser beam (for example, output lasers 404, 405, 603, etc.) That is, a laser beam having high coherence and high optical purity (for example, output laser 602) that does not include the ASE and SSE components, thereby improving the performance of the tunable grating external cavity semiconductor laser, and effectively expanding the above tunable The application range of grating external cavity semiconductor lasers.
  • a conventional tunable laser beam for example, output lasers 404, 405, 603, etc.
  • the tunable grating external cavity semiconductor laser is coupled in order to couple the mode-free continuous tuning laser generated by the tunable grating external cavity semiconductor laser to the corresponding single mode or multimode fiber 620.
  • a coupling device 610 as shown in FIG. 6 can also be included, which can be used to couple the output laser of the laser to the desired single mode or multimode fiber 620.
  • the coupling device 610 includes: a beam picking device 611, an optical isolator 612, and a collimating lens 613.
  • the beam collecting device 611 is configured to collect the output laser 405 outputted from the rear surface 406 of the gain medium 401, and deliver the collected output laser to the optical isolator 612; the optical isolator 612 is used to prevent external feedback. Interference of light, and unidirectional output of the output laser; the calibration lens 613 is configured to collimate the laser outputted in the optical isolator 612, so that the output laser becomes a parallel laser beam; The laser light outputted from the optical isolator 612 is focused such that the output laser light is coupled into the corresponding optical fiber 620.
  • the above-described coupling means 610 may be used separately to couple the above-described output laser light into a desired optical fiber.
  • the tuning component in the above tunable grating external cavity semiconductor laser can be further improved to improve the repetition sweeping rate and tuning speed of the tunable grating external cavity semiconductor laser.
  • FIG. 7 is a schematic illustration of a tunable grating external cavity semiconductor laser in accordance with a third embodiment of the present invention.
  • the tunable grating external cavity semiconductor laser of the present invention comprises: a gain medium 401, a collimating lens 402, a tuning device 409, a partial mirror 601, a coupling device 610, and at least one diffraction grating 403.
  • the tunable grating external cavity semiconductor laser may include one or more diffraction gratings 403, but in order to better introduce the technical solution of the present invention, the tunable grating external cavity semiconductor will be hereinafter
  • the laser includes three diffraction gratings 403 as an example for description.
  • the above three diffraction gratings 403 are disposed on the tuning device 409 to form a tuning component with the tuning device 409.
  • the tuning device 409 includes: a rotating base and a driving device for mounting and supporting the diffraction grating 403; the rotating base is connected to the driving device; the connection may be in the art Common connection For example, the rotating base and the stepping motor may be connected by a rotation bearing.
  • the three diffraction gratings 403 are disposed on a rotating base of the tuning device 409; the rotating base is rotatable about a rotation axis passing through a zero point and perpendicular to the paper surface direction; the stepping motor can be used to pass through the
  • the rotary bearing drives the rotating base such that the rotating base can rotate at a set rotational speed to change the position of each diffraction grating 403 disposed on the rotating base, so that the plurality of The position of one of the three diffraction gratings 403, shown as three), can satisfy the no-jump continuous tuning condition, thereby achieving no mode-hop continuous tuning of the laser frequency required for the laser output.
  • the tuning device can drive the plurality of gratings to rotate around the same rotation axis (ie, the above-mentioned rotation axis passing through the zero point and perpendicular to the paper surface direction), each diffraction grating
  • the radius of rotation may be the same or different, and may be adjusted according to actual needs, that is, the position of the three diffraction gratings on the tuning device 409 (including the angle between the respective diffraction gratings, each diffraction grating and 0 points).
  • each diffraction grating and the distance from each diffraction grating to 0 o'clock can be determined according to formula (4.6) and the actual application environment; in addition, the above-mentioned driving device can be a stepping motor or other device that can realize the above driving.
  • each of the tuning devices 409 rotates one round around the rotation axis passing through the O point and perpendicular to the paper surface direction.
  • An optical component consisting of a gain medium and a collimating lens can utilize any diffraction grating provided on the tuning device to achieve continuous mode-free tuning of the laser frequency of the desired output, thus the tunable grating external cavity semiconductor laser.
  • the laser beam outputted by the plurality of diffraction gratings described above may be subjected to multiple mode-free continuous tuning, thereby reducing the period between each mode-free continuous tuning, and improving the tunable grating external cavity semiconductor laser. Scan rate and tuning speed.
  • the diffraction grating may also include a plurality of diffraction gratings.
  • the number of the above diffraction gratings can be set in advance according to specific practical needs.
  • the partial mirror 601 and/or the coupling device 610 may be selected according to actual needs. It is not an essential component in the above tunable grating external cavity semiconductor laser.
  • FIG. 8 is a schematic view of a tunable grating external cavity semiconductor laser in Embodiment 4 of the present invention.
  • one or more sets of optical components may be disposed around the tuning device 409 in the tunable grating external cavity semiconductor laser.
  • Each of the optical components includes a gain medium 401 and a collimating lens 402, and may also include a partial mirror 601 and a coupling device 610.
  • each set of optical components can independently utilize any one of the diffraction gratings disposed on the tuning device 409 to achieve the desired output laser frequency.
  • No mode-hopping continuous tuning thereby further improving the utilization of the above-mentioned diffraction grating, reducing the period between each continuous mode-free tuning, and improving the scanning rate and tuning speed of the tunable grating external cavity semiconductor laser, achieving more Optical path laser output.
  • different sets of optical components may select different gain media, different collimating lenses, different diffraction gratings or different partial mirrors to generate output lasers of different wavelengths.
  • different gain media different collimating lenses
  • different diffraction gratings different partial mirrors
  • the continuous mode-free tunable grating external cavity semiconductor laser provided in the technical solution of the present invention is a Littrow-type tunable grating external cavity semiconductor laser
  • the resonant cavity structure of the laser is very compact and simple in form, and can be realized.
  • the versatile output enables a very simplified and low-cost manufacturing process with low cost, mass production, high stability and compact construction.

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Description

连续无跳模可调谐光栅外腔半导体激光器
技术领域
本发明涉及半导体激光器技术领域， 尤其是指一种连续无跳模可调 谐光栅外腔半导体激光器。 发明背景
光源的波长调谐技术是激光技术中的重要组成部分， 而可调谐光栅 夕卜月空半导体激光器 ( GTECL, Grating-tuned external cavity lasers ) 由于 其具有光傳纯度高、 波长覆盖范围广、 结构紧凑、 转换效率高、 单模输 出、 成本低、 可靠性好等突出的优点， 因此已被广泛应用于光通信、 光 交换、 光存储、 光纤陀螺、 计量测量、 高分辨率光傳测量以及生物医学 等诸多领域， 有着极大的应用前景。
在现有技术中， 可调谐光栅外腔半导体激光器一般有两种类型。 一 种是利特洛（Littrow ) 型可调谐光栅外腔半导体激光器， 另一种是利特 曼-迈特考夫 Littman-Metcalf型可调谐光栅外腔半导体激光器。以下将分 别对这两种类型的激光器进行介绍。
Littrow型的可调谐光栅外腔半导体激光器可产生线宽非常窄、光学 相干性非常高的频率可调的激光束， 且在实际产品的生产中， Littrow型 的 GTECL激光器具有非常紧凑并且形式简单的谐振腔结构， 该谐振腔 一般仅包括三个光学器件： 作为激光增益介质的半导体激光器、 作为选 频元件的衍射光栅和将激光光束准直的准直透镜， 从而可实现非常简化 且低成本的制造过程。 例如， Wieman和 Hollberg所提出的一种可调谐 光栅外腔半导体激光器 （参见文献 " 'Using Diode Lasers for Atomic Physics ' by Carl E. Wieman and Leo Hollberg, Review of Scientific Instruments, Vol. 62, Pages 1-19, January, 1991 " ) 就是一种比较典型的 Littrow型可调谐光栅外腔半导体激光器。
图 1为现有技术一中 Littrow型可调谐光栅外腔半导体激光器的示 意图。 如图 1所示， 该可调谐光栅外腔半导体激光器包括： 半导体激光 器 （Laser diode ) 101、 准直透镜 102和衍射光栅 ( diffraction grating ) 103。 其中， 半导体激光器 101具有一个后表面 106和一个前表面 107; 该半导体激光器 101 中所产生的光束经过准直透镜 102后可得到平行 光， 该平行光入射到衍射光栅 103上后被该衍射光栅 103衍射； 其中， 零级衍射光可直接作为输出激光 104， 而一级衍射光则沿原入射光路返 回半导体激光器 101中， 在半导体激光器 101中经过振荡、 放大后， 成 为输出激光 105 , 从而实现窄线宽的单纵模 ( SLM , single longitudinal mode ) 激光输出。
在上述的可调谐光栅外腔半导体激光器中， 衍射光栅 103可绕通过 G点的且垂直于纸面方向的固定旋转轴旋转，其中，所述 G点为光轴 100 与衍射光栅 103表面的交点。 当将衍射光栅 103绕上述的固定旋转轴旋 转时， 可实现对输出激光的频率或波长的调谐。 但是， 当根据上述谐振 腔的设计进行连续调谐时， 上述激光器的单纵模模式有可能会由一个纵 模突然跳跃到另一个纵模， 从而产生跳模（mod hopping )的现象。 该跳 模的现象在激光输出频率上， 产生相当于激光器纵模间隔的频率跳跃， 继而破坏了激光频率连续调谐的特点， 对于频率调谐的精确度， 调谐 线性度以及其他依赖于频率调谐特性的应用都会产生不利的影响， 因此 应当尽量避免， 从而要求实现无跳模（MHF， mod-hop-free ) 连续频率 调谐或波长调谐。
对于上述的跳模的现象， 可通过如下所述的公式进行相应的说明。 根据光栅方程： ( = 2 · sm ( 1.1 ) 以及谐振条件： N . = LMG ( 1.2 ) 可知： N = Lmg ( 1.3 )
dg · sin Θ 其中， N表示谐振腔中的第 N个纵模的模数， 且 N为整数； ^)表示 激光振荡波长， 即由光栅色散（ grating dispersion )所选择的激光的波长， 该激光波长与 有关， 即 ( 的值将随 的变化而变化； MG表示从 M点 (即光轴 100与半导体激光器 101的后表面 106的交点 )到 G点的光学 距离， 即外腔的光学长度（可简称为外腔长度， 下同）； 表示衍射光栅 103的刻划密度（ grooving density ); 表示激光束入射到衍射光栅 103 的入射角， 也是衍射角。
由图 1可知， Μσ和 一般都为常量； 当衍射光栅 103绕上述的固定 旋转轴旋转时， 衍射角 的大小将发生改变， 由公式（ 1.2 )可知， 此时 该激光器输出的激光频率或激光波长也将发生改变； 而由公式（ 1.3 )可 知， 当衍射角 的大小发生改变时， 模数 N也将随之发生改变， 即模数 N 相对于衍射角 的改变并不是常量， 从而在衍射角 的改变较大时， 将 发生跳模 (即模数 N的值发生 +1 或 -1的数量改变）； 也就是说， 图 1所 示的激光器在通过旋转衍射光栅来对激光频率或激光波长进行调谐 (即 改变输出激光的频率） 时， 将发生跳模的现象。 因此， 上述的 Littrow型 GTECL仅能实现非常小的或者是有限的 MHF调谐，而不能对激光频率或 波长进行 MHF连续调谐。
在现有技术中， 还有另一种 Littrow型可调谐光栅外腔半导体激光 器。 例如， Trutna Jr.在美国专利 No. 6,731 ,661中所公开一种可调谐光栅 外腔半导体激光器。 图 2为现有技术二中 Littrow型可调谐光栅外腔半 导体激光器的示意图。 如图 2所示， 该可调谐光栅外腔半导体激光器也 包括： 半导体激光器 101、 准直透镜 102和衍射光栅 103。 与图 1 中的 可调谐光栅外腔半导体激光器不同的是， 图 2中衍射光栅 103的旋转轴 为 L， 该旋转轴 L位于衍射光栅 103的衍射表面延长线与半导体激光器 101的后表面 106延长线的交点上， 且该旋转轴 L垂直于纸面方向。 当 衍射光栅 103绕固定的旋转轴 L旋转时， 也可实现对输出激光频率或波 长的调谐。
同理， 根据光栅方程： ( ) = 2dg -sin » (2.1 ) 以及谐振条件： N'^ = LMG{6) (2.2) 且谐振腔内部的光学部件均处于理想状态的情况下， 可有：
LMG(0) = OM 'tan Θ (2.3) 由此可知： N= 0M (2.4)
dg · cos θ 其中， ^ 表示从半导体激光器 101的后表面 106上的 Μ点到衍 射光栅 103表面的中心的距离， 即外腔长度； 该外腔长度与 有关， 即 Me( 的值将随 的变化而变化； ^表示从旋转轴 L到半导体激光器 101的后表面 106上的 M点的距离。
由公式 （2.4) 可知， 当^和 不变时， 如果旋转衍射光栅 103, 使得衍射角 发生改变， 则模凄 N也将发生改变， 即模！ ^N相对于衍射角 的改变也不是常量。 当衍射角 的改变较大时， 将发生跳模（即模数 N的值发生 +1 或 -1的数量改变）。 因此， 与图 1 中的可调谐光栅外腔半 导体激光器相比， 图 2中的可调谐光栅外腔半导体激光器虽然可以产生 相对较大的 MHF调谐范围， 但其模 N仍然依赖于衍射角 Θ, 因此， 当 衍射角 的变化范围较大时， 仍然无法保持 N为常量。 所以， 在图 2所 示的可调谐光栅外腔半导体激光器中， 也无法实现对激光频率的 MHF连 续调谐。 为了解决上述的问题， 在现有技术中， 已通过使用 Littman-Metcalf 谐振腔结构， 制造了一种宽带 MHF 可调 GTECL 激光器， 即 Littman-Metcalf型可调谐光栅外腔半导体激光器。 该类型的激光器的谐 振腔的构造已在多篇文献或专利中被公开。 例如， Luecke 的美国专利 ( No.5，319,668 )、 Sacher的美国专利（No.5,867,512 )、 Lang的美国专利 ( No.5,771,252 )、 Zhang 的美国专利 （ No.5,802,085 ) 和美国专利 ( No.6,606,340 ), Zhang 的美国专利 （ No.6,608,847 )、 Zhang 的美国专 利 （No.6,788，726 )、 Zhang的美国专利 （ No.6,940,879 ) 以及 Le的美国 专利 ( No.7,388,890 ) 等。
图 3为现有技术三中 Littman-Metcalf型可调谐光栅外腔半导体激光 器的示意图。 如图 3所示， 该 Littman-Metcalf型可调谐光栅外腔半导体 激光器除了包括半导体激光器 101、准直透镜 102和衍射光栅 103之外， 还包括一个平面反射镜 108。 其中， 旋转轴 L位于半导体激光器 101的 后表面 106延长线、 衍射光栅 103的衍射表面延长线与平面反射镜 108 的反射表面延长线的交点上， 且该旋转轴 L垂直于纸面方向； Q点为通 过 G点的反射光线与平面反射镜 108的交点。在该可调谐光栅外腔半导 体激光器， 衍射光栅 103固定不动， 而平面反射镜 108则可绕固定的旋 转轴 L旋转。当平面反射镜 108绕旋转轴 L旋转时，衍射角 发生改变， 外腔腔长（即 M、 G两点之间的距离与 G、 Q点两点之间的光路的总和） 也发生改变； 当旋转轴 L处于合适的位置时， 可使得此时的模数 N保持 为一个常量， 因而可以在激光频率发生变化的同时维持模数 N不变， 从 而实现对激光频率的无跳模连续调谐。
从原理上分析可知， 假如图 3所示的激光器设计处于理想工作状态 时， 例如， 该激光器的谐振腔内所使用的光学设备不发生光色散， 或者 腔内 的光学器件能够被准确地对准到相应的位置时， 则该 Littman-Metcalf类型的半导体激光器能够产生覆盖整个由衍射光栅所产 生的光谱范围的最大的 MHF调谐范围。 但是， 由于工业制造技术以及 装配调试手段的限制， 在图 3所示的可调谐光栅外腔半导体激光器的实 际产品中， 一般都存在设备色散和光学器件位置不对准的问题， 从而也 大大限制了该激光器的 MHF调谐范围。
为了克服上述的问题， Zhang和 Hakuta提出了一种具有光学器件位 置自动调整和被动补偿的谐振腔结构， 以便实现上述的宽带 MHF调谐。 但是即使如此， 在上述激光器的制造过程中， 仍然存在着复杂的光学和 机械对准、 光学器件的额外的材料成本、 超大的腔体尺寸和很慢的调谐 速度等诸多问题。
综上可知，现有技术中所使用的激光器中都存在着上述的诸多问题， 从而大大限制了可调谐光栅外腔半导体激光器在各种领域中的应用。 因 此， 人们非常需要一种连续无跳模、 且制造成本低、 可批量生产、 高稳 定性以及结构紧凑的可调谐光栅外腔半导体激光器， 以实现对激光频率 的无跳模连续调谐。 发明内容
本发明的实施例提供了一种连续无跳模可调谐光栅外腔半导体激 光器， 从而可实现对激光频率的无跳模连续调谐， 并降低所述激光器的 生产成本。
为达到上述目的， 本发明实施例的技术方案是这样实现的： 一种连续无跳模可调谐光栅外腔半导体激光器， 该激光器包括： 至 少一个由增益介质和准直透镜组成的光学组件、 调谐装置和至少一个衍 射光栅；
所述增益介质所发出的相干光束经过所述准直透镜后成为平行光， 所述平行光被所述衍射光栅衍射后， 部分衍射光直接成为被输出的第一 输出激光， 另一部分衍射光沿原入射光路返回所述增益介质中， 在所述 增益介质中振荡、 放大到超过激光器振荡阈值时， 成为第二输出激光； 所述衍射光栅设置于所述调谐装置上； 所述调谐装置驱动所述衍射 光栅绕一位于所述衍射光栅的背面的旋转轴旋转； 所述旋转轴与所述衍 射光栅的衍射表面平行且与激光器的光轴垂直。
所述预先设置的旋转轴的位置满足条件： 在所述激光器的输出激光 频率的调谐过程中， 由所述激光器的谐振腔所选择的纵模的模数为一个 常量。
所述衍射光栅进行所述旋转时的旋转半径为所述旋转轴到所述衍 射光栅的衍射表面的垂直距离。
所述调谐装置， 还用于实时改变所述旋转轴的位置， 或者用于实时 改变所述旋转轴与所述衍射光栅的相对位置。
所述调谐装置包括： 驱动装置和旋转基座； 所述旋转基座与所述驱 动装置连接；
所述旋转基座， 用于支撑或安装所述衍射光栅；
所述驱动装置， 用于驱动所述旋转基座以带动所述衍射光栅绕所述 旋转轴旋转； 并用于实时改变所述旋转轴的位置， 或者用于实时改变所 述旋转轴与所述衍射光栅的相对位置。
所述驱动装置为旋转马达、 步进电机或微电子机械系统。
所述调谐装置还包括： 控制装置和编码器；
所述编码器， 用于跟踪所述旋转基座的移动， 并将跟踪结果发送给 所述控制装置；
所述控制装置， 用于根据所选定的输出激光波长以及所述跟踪结 果， 对所述旋转基座的移动进行选择性地控制， 从而在输出所需频率的 激光的同时对所输出的激光频率进行无跳模连续调谐。
所述激光器包括多个衍射光栅；
所述多个衍射光栅设置于所述调谐装置上； 所述调谐装置驱动所述 多个衍射光栅均绕同一个旋转轴旋转； 所述旋转轴与所述衍射光栅的衍 射表面平行且与激光器的光轴垂直；
所述光学组件利用所述调谐装置上所设置的任意一个衍射光栅实 现对所需输出的激光频率的无跳模连续调谐。
所述激光器还包括： 设置于所述准直透镜与所述衍射光栅之间的光 路上的部分反射镜；
所述部分反射镜， 用于产生第三输出激光以及滤除了光谱噪声的第 四输出激光。
所述部分反射镜为分光镜、 空间滤波片或耦合光纤。
所述激光器还包括： 耦合装置；
所述耦合装置， 用于将所述激光器的至少一束输出激光耦合到所需 的单模或多模光纤中。
所述激光器还包括： 设置于所述调谐装置四周的一组或多组光学组 件；
每组光学组件均利用所述调谐装置上所设置的任意一个衍射光栅 实现对所需输出的激光频率的无跳模连续调谐。
综上可知， 本发明的实施例中提供了一种连续无跳模可调谐光栅外 腔半导体激光器。 由于该连续无跳模可调谐光栅外腔半导体激光器中包 括一个调谐装置和至少一个衍射光栅， 衍射光栅设置于调谐装置上； 而 调谐装置则用于驱动所述衍射光栅绕一预先设置的位于该衍射光栅的 背面的旋转轴旋转， 且该旋转轴与该衍射光栅的衍射表面平行且与激光 器的光轴垂直， 因此可实现对激光频率的无跳模连续调谐， 并降低所述 激光器的生产成本。 附图简要说明
图 1为现有技术一中 Littrow型可调谐光栅外腔半导体激光器的示 意图。
图 2为现有技术二中 Littrow型可调谐光栅外腔半导体激光器的示 意图。
图 3为现有技术三中 Littman-Metcalf型可调谐光栅外腔半导体激光 器的示意图。
图 4为本发明实施例一中可调谐光栅外腔半导体激光器的示意图。 图 5为本发明实施例一中可调谐光栅外腔半导体激光器的原理图。 图 6为本发明实施例二中可调谐光栅外腔半导体激光器的示意图。 图 7为本发明实施例三中可调谐光栅外腔半导体激光器的示意图。 图 8为本发明实施例四中可调谐光栅外腔半导体激光器的示意图。 实施本发明的方式
下面结合附图和实施例， 对本发明的具体实施方式作进一步详细描 述。
图 4 为本发明实施例一中的可调谐光栅外腔半导体激光器的示意 图。 如图 4所示， 本发明中的可调谐光栅外腔半导体激光器包括： 增益 介质 （gain medium ) 401、 准直透镜 402和衍射光栅 403。 其中， 所述 增益介质 401和准直透镜 402可组成一个光学组件；所述增益介质 401 , 用于产生稳定的光增益， 并发出相干光束； 例如， 该增益介质 401可以 包括一个全反射或部分反射的后表面 406、 一个涂覆有防反射 （AR, anti-reflection )涂层的前输出表面 407 以及一个半导体激光器芯片 （该 芯片可以是常用的 Fabry-Pero型半导体激光器芯片， 也可以是其它的具 有类似功能的器件）； 图中的 M点为光轴 400与增益介质 401的后表面 406的交点； G点为光轴 400与 4汙射光栅 403的交点； 因此， 该激光器 的外部谐振腔 (简称外腔， 下同 )被增益介质 401的后表面 406与衍射 光栅 403所限定。 增益介质 401从前输出表面 407发出相干光束， 该相 干光束经过所述准直透镜 402后成为平行光， 该平行光入射到衍射光栅 403上后发生衍射； 被衍射光栅 403所衍射的光， 一部分衍射光（例如， 零级衍射光） 可以直接成为被输出的第一输出激光（例如， 输出激光 404 ), 而另一部分†射光（例如， 一级衍射光， 或更高阶的衍射级） 则 沿着原入射光路返回至增益介质 401的后表面 406, 该后表面 406再将 所返回的光反射回衍射光栅 403 , 依此类推， 直到该衍射光在所述增益 介质 401中被振荡、 放大到超过激光器振荡阐值时， 该衍射光可作为第 二输出激光（例如， 输出激光 405 )。 由此可知， 该激光器的谐振腔中的 外腔长度即为 M点与 G点之间的光路的总和。
为了实现对激光频率的无跳模连续调谐， 在本发明的技术方案中， 图 4所示的激光器中还包括一个调谐装置 409, 该调谐装置 409可与上 述的衍射光栅 403组成一个调谐组件； 所述衍射光栅设置于所述调谐装 置上； 且该调谐装置 409, 用于驱动上述衍射光栅 403 , 使得该衍射光 栅 403可绕预先设置的位于所述衍射光栅的背面的旋转轴旋转； 所述旋 转轴与所述衍射光栅的衍射表面平行且与激光器的光轴 400垂直（即所 述旋转轴为通过 0点且与纸面方向垂直的旋转轴）， 即所述旋转轴不在 所述衍射光栅 403的衍射表面的延长线上， 而位于所述衍射光栅 403的 背面。 此外， 该调谐装置 409还可用于实时改变 O点的位置（即改变所 述旋转轴的位置），或用于实时改变 0点与衍射光栅 403的相对位置（即 改变所述旋转轴与衍射光栅 403的相对位置）。 所述衍射光栅 403进行 上述旋转时的旋转半径为： 所述 O点 （即所述旋转轴） 到衍射光栅 403 的衍射表面的垂直距离， 该距离可用^表示； 其中， P点为 O点到衍射 光栅 403的衍射表面的垂线与该衍射光栅 403的衍射表面的交点。
在本发明的实施例中， 当上述衍射光栅 403绕上述旋转轴旋转时， 所述衍射光栅 403 的背面； 而且还可预先或实时对该旋转轴的位置和 / 或该旋转轴与衍射光栅 403的相对位置进行设置， 因此上述的可调谐光 栅外腔半导体激光器可以根据激光频率调谐的要求， 进行灵活的设计， 满足由所述激光器的谐振腔所选择的纵模的模数 N为一常量的 MHF调 谐， 所以不需要任何其它外加的控制方式或手段即可实现对激光频率的 无跳模连续调谐， 且能够产生覆盖整个由衍射光栅所产生的光傳范围的 最大的 MHF调谐范围， 从而简化激光器的谐振器结构， 降低所述激光 器的生产成本。 以下将对上述实现无跳模连续调谐的具体原理进行介 绍。
图 5 为本发明实施例一中的可调谐光栅外腔半导体激光器的原理 图。 如图 5所示， 当上述衍射光栅 403绕上述过 O点的旋转轴旋转一个 角度/ /时， 衍射光栅 403的位置发生了移动， 因此， 衍射角由（9变为 θ', G点移动到了 G'点， 即该激光器的衍射角和外腔长度都发生了变化， 从 而可以利用上述的变化来实现对激光频率的调谐。
当衍射光栅 403处于初始状态， 还未开始旋转时， 衍射角为 6», 设衍 射光栅 403的刻划密度为 ， 则根据谐振条件可知， 此时通过该衍射光 栅 403所选择的激光的中心波长为：
l(0) = 2dg ' sia e ( 4.1 )
如图 5所示， 当衍射角为 Θ时， 该激光器的外腔长度为 M点到 G 点之间的光路总和 ½ ， 则根据光栅方程可知：
Figure imgf000014_0001
其中， N( 表示当衍射角为 / 时， 在上述可调谐光栅外腔半导体激 光器的谐振腔中的第 N个纵模的模数， 且 N( 为整数。
当调谐装置 409驱动上述衍射光栅 403绕上述过 0点的旋转轴旋转 一定角度后， 例如， 衍射光栅 403旋转到衍射角为 的位置时， 衍射光 栅 403的衍射表面上的 G点移动到了 G'点的位置， 此时， 该激光器的外 腔长度为 M点到 G'点之间的光路总和 , 即该激光器的外腔长度发 生了变化：
Lit(el) = Lit(e)-GG'(e',e) (4.3 ) 其中， 'φ',θ)即为该激光器的外腔长度的变化量。
根据图 5中的光路可知：
l_cos(6>_6>') + sin^-^')
GG\& ,0) = ro-〜： 10 · (4.4) 其中， rQ=W> = ~d' , t0 =GP, OP, ^和^分别表示点◦到点 P、 P'和点 G之间的距离 , ^表示 G点到 P点之间的距离。 根据图 5所示 可知， r。和 t。是与 0点的位置有确定关系的参数； 当 O点的位置确定后， 或者当 0点与衍射光栅 403的相对位置确定后， r。和 ί。的值也就随之被 确定； 反过来说， 也可以根据 r。和 t。的取值来确定点 0的位置或者确定 0点与衍射光栅 403的相对位置。
当衍射角为 时， 设 N( )表示在上述可调谐光栅外腔半导体激光器 的谐振腔中的第 N个纵模的模数， 且 N ( 为整数， 为通过该衍射 光栅 403所选择的激光的中心波长， 此时有：
A(0') = 2dg'sme' , (4.5 )
Figure imgf000014_0002
根据上述的公式 （4.1) ~ (4.5) 可知： Ν(θ') _ sin(6>) l-cos(6>-6>') sin(6>_6>')
- , -« (4.6)
Ν(β) ― sin( ) cos(^) cos(^)
其中， 和 2= /½(6 。 所述的 和《2表示可通过改变 旋转轴的位置 r。和 t。， 或改变旋转轴与衍射光栅的相对位置来调整激光 器的谐振腔纵模的模数 N的值的大小。
由上述公式 （4.6) 可知， 为了实现对所有的激光频率都实现 MHF 连续调谐， 则在整个激光频率的调谐过程中， 都需要使得由谐振腔所选 择的級模的模数 N '为一个常量， 即满足无跳模连续调谐条件：
Νφ、、ΙΝ{β) = \, 或 I )- N( )|≤1 ( 4.7 ) 在实际应用环境中的激光器中，由于增益介质 11的增益带宽是有限 的， 因此只需满足上述的无跳模连续调谐条件， 即可保证在上述有限增 益带宽内的给定频率范围内进行无跳模连续调谐。 由上述公式（ 4.6 )可 知， 只需适当调整公式 （4.6) 中的 r。和^ 则可很容易地满足上述的无 跳模连续调谐条件， 从而可容易地实现对所有的激光频率都实现 MHF 连续调谐。
由于衍射光栅 403和 /或旋转轴的位置 (即 0点的位置 )的改变将导 致上述的 r。和 t。的值的改变， 因此， 在本发明的技术方案中， 也可通过 对 O点的位置（即所述旋转轴的位置 )用外加反馈控制的方式进行实时 调整，或者通过对衍射光栅 403与 O点的绝对位置或相对位置的实时调 整， 来改变上述的两个坐标 r。和 ί。的值， 使得上述的无跳模连续调谐条 件可在更大频率调谐范围上得到满足。
由图 5可知， 当 0点的位置确定后， 或者当 Ο点与衍射光栅 403 的相对位置确定后， r。和 ί。的值也随之被确定。 因此， 在本发明的技术 方案中， 可根据实际应用情况， 预先或实时选定 Ο点的位置， 或者预先 或实时选定 O点与衍射光栅 403的相对位置，使得所述衍射光栅 403在 绕通过 O点的垂直于纸面方向的旋转轴旋转时，该衍射光栅 403所在的 激光器的谐振腔长度具有合适的长度以输出所需频率的激光， 并实现对 所输出的激光频率的无跳模连续调谐。
在本发明的技术方案中， 上述对 O点的位置或 0点与衍射光栅 403 的相对位置的选定以及衍射光栅 403 的旋转均可由调谐装置 409 来实 现。 所述调谐装置 409可以是本技术领域中常用的各种固定的或动态的 位置调节装置。 例如， 在本发明的具体实施例中， 所述调谐装置 409中 可以包括一个驱动装置和旋转基座 （base ) (图 4和图 5中均未示出）。 所述衍射光栅 403设置于所述旋转基座上， 且所述旋转基座与驱动装置 连接， 该旋转基座可用于支撑或安装所述衍射光栅 403 , 并可根据驱动 装置的驱动来改变衍射光栅 403的位置； 所述驱动装置， 可用于驱动所 述旋转基座以带动所述衍射光栅 403绕所述旋转轴旋转 , 也可以用于改 变 0点的位置或 0点与衍射光栅 403的相对位置，从而使得该衍射光栅 403可绕通过 O点且与纸面方向垂直的旋转轴旋转到所需的位置。其中， 所述驱动装置可以是旋转马达、 步进电机、 微电子机械系统 （MEMS ), 或其它可以实现上述驱动的设备； 所述驱动装置与旋转基座的连接方式 可以使用直接固定方式 （例如， 旋转马达或步进电机的旋转轴承直接与 旋转基座固定连接， 或通过万向节过渡并与旋转基座固定连接； 旋转轴 承的连接保证旋转基座可通过 0 点且与纸面垂直的旋转轴旋转或移动 转轴）， 或其它本领域中常用的连接方式， 在此不再赘述。
另外， 在所述调谐装置 409中， 还可包括控制装置和编码器 (例如， 线性编码器或电机旋转编码器； 图 4和图 5 中均未示出）。 其中， 所述 编码器，用于跟踪旋转基座的移动，并将跟踪结果发送给所述控制装置。 所述旋转基座的移动可以是平动、 转动或平动加转动。 其中， 通过旋转 基座的平动可以改变所述旋转轴的位置或改变所述旋转轴与所述衍射 光栅的相对位置； 而所述旋转基座的转动则可使得所述旋转基座上的衍 射光栅绕所述旋转轴转动。 所述控制装置则用于根据所选定的输出激光 的波长以及所述跟踪结果， 对旋转基座的移动进行选择性地控制， 从而 在输出所需频率的激光的同时对所输出的激光频率进行无跳模连续调 谐。 由此可知， 通过如上所述的调谐装置 409, 可在输出所需频率的激 光的同时， 实现对所输出的激光频率的无跳模连续调谐。
在图 5所示的可调谐光栅外腔半导体激光器中， 可以作为输出激光 的有： 1 ) 由衍射光栅 403 的衍射表面反射后直接输出的激光所形成的 输出激光 404; 2 ) 由衍射光栅 403的衍射表面反射回增益介质 401 , 并 在增益介质 401中经过振荡放大后， 从增益介质 401的后表面 406输出 的输出激光 405。
但是， 在上述输出激光 404和输出激光 405中， 均存在相对较高的 光谱"噪声"， 该光谱 "噪声 "为来源于增益介质 401 中的光源自发辐射 ( SSE, source spontaneous emission )和放大自发 i射 ( ASE， amplified spontaneous emission )。 上述光谱"噪声"的存在， 对于所输出的激光的相 干性和强度造成了不利的影响。 因此， 在本发明的技术方案中， 还可在 图 5所示的可调谐光栅外腔半导体激光器中加入一个部分反射镜， 用于 "清除 "上述输出激光中的光借"噪声" (即输出激光中的 ASE和 SSE成 分）。
图 6 为本发明实施例二中的可调谐光栅外腔半导体激光器的示意 图。 如图 6所示， 本发明中的可调谐光栅外腔半导体激光器除了包括增 益介质 401、 准直透镜 402、 衍射光栅 403和调谐装置 409之外， 还包 括一个设置于准直透镜 402与衍射光栅 403之间的光路上的部分反射镜 601 , 该部分反射镜 601 可根据实际需求被设置或旋转到所需的任意角 度， 用于滤除输出激光中的光谱噪声。 较佳的， 该部分反射镜 601可以 是分光镜或其它形式的空间滤波片。 由于所述光语"噪声"的波长不同于 所输出的激光波长 ,在空间分布上，上述光谱"噪声 "可通过衍射光栅 403 的衍射而被驱离或被偏离所述输出激光的光路。 因此， 可通过插入上述 的部分反射镜（例如， 分光镜、 空间滤波片或耦合光纤） 来彻底 "清除" 所述输出激光中的上述光谱"噪声"。
在本发明的实施例中， 上述部分反射镜 601可将通过该部分反射镜 601的激光分成两束激光后分别输出， 其中的一束激光为输出激光 602, 由于上述部分反射镜 601的"清除"作用， 从而使得该输出激光 602中不 再包含上述的光语"噪声"（即该输出激光 602中不包含 ASE和 SSE成 分）； 另一束激光为输出激光 603 , 该输出激光 603为传统的可调谐激光 束， 其中仍然包含上述的光语"噪声"（即该输出激光 603中仍包含 ASE 和 SSE成分）， 且与上述输出激光 602的方向相反。
通过如图 6所示的可调谐光栅外腔半导体激光器， 我们在获得传统 的可调谐激光束（例如， 输出激光 404、 405、 603等） 的同时， 还可以 获得去除了光语"噪声" (即不包含 ASE和 SSE成分） 的、 具有高相干 性、 高光语純度的激光束（例如， 输出激光 602 ), 从而提高了上述可调 谐光栅外腔半导体激光器的性能， 有效地拓展了上述可调谐光栅外腔半 导体激光器的应用范围。
此外， 在本发明的实施例中， 为了使上述可调谐光栅外腔半导体激 光器所产生的无跳模连续调谐激光与相应的单模或多模光纤 620实现耦 合， 上述可调谐光栅外腔半导体激光器中还可以包括一个如图 6所示的 耦合装置 610, 该耦合装置 610可用于将上述激光器的输出激光耦合到 所需的单模或多模光纤 620中。 以下， 我们将以输出激光 405为例， 对 本发明的技术方案进行介绍。 该耦合装置 610包括： 光束采集装置 611、 光隔离器 612和校准透 镜 613。 其中， 光束采集装置 611用于釆集从上述增益介质 401的后表 面 406 输出的输出激光 405 , 并将采集到的输出激光输送到光隔离器 612; 所述光隔离器 612 用于防止外部反馈光的干扰， 并实现上述输出 激光的单向输出； 所述校准透镜 613， 用于对所述光隔离器 612中输出 的激光进行准直， 使得该输出的激光成为平行的激光束； 或者用于对所 述光隔离器 612中输出的激光进行聚焦， 使得该输出的激光被耦合到相 应的光纤 620中。
此外， 在上述可调谐光栅外腔半导体激光器的输出激光 404、 603 或 602的方向上， 也可分别使用上述的耦合装置 610, 从而将上述的输 出激光耦合到所需的光纤中。
在本发明的技术方案中， 还可对上述可调谐光栅外腔半导体激光器 中的调谐组件进行进一步的改进， 以提高上述可调谐光栅外腔半导体激 光器的重复扫描速率 （ sweeping rate ) 以及调谐速度。
图 7 为本发明实施例三中的可调谐光栅外腔半导体激光器的示意 图。 如图 7所示， 本发明中的可调谐光栅外腔半导体激光器包括： 增益 介质 401、 准直透镜 402、调谐装置 409、部分反射镜 601、耦合装置 610 和至少一个衍射光栅 403。 在本发明的具体实施例中， 上述可调谐光栅 外腔半导体激光器可以包括一个或多个衍射光栅 403 , 但为了更好地对 本发明的技术方案进行介绍， 以下将以该可调谐光栅外腔半导体激光器 中包括三个衍射光栅 403为例进行说明。
如图 7所示， 上述三个衍射光栅 403设置于调谐装置 409上， 从而 与该调谐装置 409组成一个调谐组件。 所述调谐装置 409包括： 用于安 装和支撑所述衍射光栅 403的旋转基座（base )和驱动装置； 所述旋转 基座与所述驱动装置连接； 所述连接的方式可以是本领域中常用的连接 方式， 例如， 所述旋转基座与所述步进电机可通过旋转轴 ( rotation bearing )连接。 其中， 所述三个衍射光栅 403设置于调谐装置 409的旋 转基座上； 该旋转基座可绕通过 0点且垂直于纸面方向的旋转轴旋转； 所述步进电机， 可用于通过所述的旋转轴承驱动所述的旋转基座， 使得 该旋转基座可按照设置的旋转速度进行旋转， 以改变设置在旋转基座上 的各个衍射光栅 403的位置， 使得上述多个（图 7所示为三个）衍射光 栅 403中的某一个衍射光栅 403的位置可以满足无跳模连续调谐条件， 从而实现对激光器所需输出的激光频率的无跳模连续调谐。
在上述的可调谐光栅外腔半导体激光器中， 所述调谐装置可驱动上 述多个光栅均绕同一个旋转轴 (即上述通过 0点且垂直于纸面方向的旋 转轴）旋转， 每个衍射光栅的旋转半径可以相同， 也可以不同， 可根据 实际需要进行调整， 即所述三个衍射光栅在所述调谐装置 409上的位置 (包括各个衍射光栅之间的夹角、各个衍射光栅与 0点的相对位置以及 各个衍射光栅到 0点的距离）， 均可以根据公式 （4.6 ) 以及实际的应用 环境来确定； 另外， 上述的驱动装置可以是步进电机或其它可以实现上 述驱动的设备。
如图 7所示可知， 由于上述可调谐光栅外腔半导体激光器中具有多 个衍射光栅， 因此在所述调谐装置 409绕通过 O点且垂直于紙面方向的 旋转轴旋转一周的过程中， 每个由增益介质和准直透镜组成的光学组件 均可利用所述调谐装置上所设置的任意一个衍射光栅实现对所需输出 的激光频率的无跳模连续调谐， 因此该可调谐光栅外腔半导体激光器可 分别通过上述的多个衍射光栅对所输出的激光进行多次无跳模连续调 谐， 从而减小了每次无跳模连续调谐之间的周期， 提高了上述可调谐光 栅外腔半导体激光器的扫描速率以及调谐速度。
另外， 在图 7所示的可调谐光栅外腔半导体激光器中， 可包括一个 衍射光栅， 也可包括多个衍射光栅。 上述衍射光栅的数目可根据具体实 际需求而预先设置。
此外， 在图 7所示的可调谐光栅外腔半导体激光器中， 还可根据实 际需要选择是否设置上述的部分反射镜 601和 /或耦合装置 610, 即上述 的部分反射镜 601和耦合装置 610并不是上述可调谐光栅外腔半导体激 光器中的必要组成部分。
图 8 为本发明实施例四中的可调谐光栅外腔半导体激光器的示意 图。 如图 8所示， 为了更好的提高上述衍射光栅的利用率， 还可以在可 调谐光栅外腔半导体激光器中的调谐装置 409的四周， 设置一组或多组 光学组件。 其中， 每组光学组件都包括一个增益介质 401和一个准直透 镜 402 , 也可包括部分反射镜 601和耦合装置 610。 因此， 当调谐装置 409绕通过 O点且垂直于纸面方向的旋转轴转动时， 每组光学组件都可 单独利用调谐装置 409上所设置的任意一个衍射光栅实现对所需输出的 激光频率的无跳模连续调谐， 从而可进一步提高对上述衍射光栅的利用 率， 减小每次无跳模连续调谐之间的周期， 提高上述可调谐光栅外腔半 导体激光器的扫描速率以及调谐速度， 实现多光路激光输出。
此外， 图 8中所设置的多组光学组件中， 不同组的光学组件可以选 择不同的增益介质、 不同的准直透镜、 不同的衍射光栅或不同的部分反 射镜， 来产生不同波长的输出激光， 以实现独特的多波长、 多光路激 光输出。
综上可知， 在本发明的技术方案中， 提供了多种形式的连续无跳模 可调谐光栅外腔半导体激光器。 通过使用本发明实施例中所提供的上述 结构紧凑的、 可实现多功能输出连续无跳模可调谐光栅外腔半导体激光 器， 可实现对激光频率的无跳模连续调谐， 并可降低生产成本， 提高激 光器的扫描速率以及调谐速度， 从而使得上述连续无跳模可调谐光栅外 腔半导体激光器具有较大的 MHF调谐能力， 因此可以广泛应用于高分 率激光光语；则量 ( high-resolution laser metrology ) 以及诸 ^口原子钟、 激光冷却 /激光阱、战地（ on-field )生化分析器等光语传感器（ spectroscopic sensor ) 中。
此外， 由于本发明的技术方案中所提供的连续无跳模可调谐光栅外 腔半导体激光器是 Littrow 型的可调谐光栅外腔半导体激光器， 因此激 光器的谐振腔结构非常紧凑并且形式简单， 且可实现多功能输出， 从而 可实现非常简化且低成本的制造过程， 并具有成本低、 可批量生产、 高 稳定性以及结构紧凑等优点。
以上所述仅为本发明的较佳实施例而已， 并不用以限制本发明， 凡 在本发明的精神和原则之内所做的任何修改、 等同替换和改进等， 均应 包含在本发明的保护范围之内。

Claims

权利要求书
1、 一种连续无跳模可调谐光栅外腔半导体激光器， 其特征在于， 该激光器包括： 至少一个由增益介质和准直透镜组成的光学组件、 调谐 装置和至少一个衍射光栅；
所述增益介质所发出的相干光束经过所述准直透镜后成为平行光， 所述平行光被所述衍射光栅衍射后， 部分衍射光直接成为被输出的第一 输出激光， 另一部分衍射光沿原入射光路返回所述增益介质中， 在所述 增益介质中振荡、 放大到超过激光器振荡阁值时， 成为第二输出激光； 所述衍射光栅设置于所述调谐装置上； 所述调谐装置驱动所述衍射 光栅绕一位于所述衍射光栅的背面的旋转轴旋转； 所述旋转轴与所述衍 射光栅的衍射表面平行且与激光器的光轴垂直。
2、 根据权利要求 1所述的激光器， 其特征在于，
所述预先设置的旋转轴的位置满足条件： 在所述激光器的输出激光 频率的调谐过程中， 由所述激光器的谐振腔所选择的纵模的模数为一个 常量。
3、 根据权利要求 1所述的激光器， 其特征在于：
所述衍射光栅进行所述旋转时的旋转半径为所述旋转轴到所述衍 射光栅的衍射表面的垂直距离。
4、 根据权利要求 1所述的激光器， 其特征在于：
所述调谐装置， 还用于实时改变所述旋转轴的位置， 或者用于实时 改变所述旋转轴与所述衍射光栅的相对位置。
5、根据权利要求 4所述的激光器， 其特征在于， 所述调谐装置包括： 驱动装置和旋转基座； 所述旋转基座与所述驱动装置连接；
所述旋转基座， 用于支撑或安装所述衍射光栅；
所述驱动装置， 用于驱动所述旋转基座以带动所述衍射光栅绕所述 旋转轴旋转； 并用于实时改变所述旋转轴的位置， 或者用于实时改变所 述旋转轴与所述衍射光栅的相对位置。
6、 根据权利要求 5所述的激光器， 其特征在于：
所述驱动装置为旋转马达、 步进电机或微电子机械系统。
7、 根据权利要求 5所述的激光器， 其特征在于， 所述调谐装置还包 括： 控制装置和编码器；
所述编码器， 用于跟踪所述旋转基座的移动， 并将跟踪结果发送给 所述控制装置；
所述控制装置， 用于根据所选定的输出激光波长以及所述跟踪结 果， 对所述旋转基座的移动进行选择性地控制， 从而在输出所需频率的 激光的同时对所输出的激光频率进行无跳模连续调谐。
8、 根据权利要求 1所述的激光器， 其特征在于，
所述激光器包括多个衍射光栅；
所述多个衍射光栅设置于所述调谐装置上； 所述调谐装置驱动所述 多个衍射光栅均绕同一个旋转轴旋转； 所述旋转轴与所述衍射光栅的衍 射表面平行且与激光器的光轴垂直；
所述光学组件利用所述调谐装置上所设置的任意一个衍射光栅实 现对所需输出的激光频率的无跳模连续调谐。
9、根据权利要求 1所述的激光器， 其特征在于， 所述激光器还包括： 设置于所述准直透镜与所述衍射光栅之间的光路上的部分反射镜；
所述部分反射镜， 用于产生第三输出激光以及滤除了光谱噪声的第 四输出激光。
10、 根据权利要求 9所述的激光器， 其特征在于：
所述部分反射镜为分光镜、 空间滤波片或耦合光纤。
11、 根据权利要求 1或 9所述的激光器， 其特征在于， 所述激光器还 包括： 耦合装置；
所述耦合装置， 用于将所述激光器的至少一束输出激光耦合到所需 的单模或多模光纤中。
12、 根据权利要求 1所述的激光器， 其特征在于， 所述激光器还包 括： 设置于所述调谐装置四周的一组或多组光学组件；
每组光学组件均利用所述调谐装置上所设置的任意一个衍射光栅 实现对所需输出的激光频率的无跳模连续调谐。
PCT/CN2009/072560 2009-06-30 2009-06-30 连续无跳模可调谐光栅外腔半导体激光器 WO2011000153A1 (zh)

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