WO2022127138A1 - 谐振腔、激光器和激光雷达 - Google Patents

谐振腔、激光器和激光雷达 Download PDF

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WO2022127138A1
WO2022127138A1 PCT/CN2021/110735 CN2021110735W WO2022127138A1 WO 2022127138 A1 WO2022127138 A1 WO 2022127138A1 CN 2021110735 W CN2021110735 W CN 2021110735W WO 2022127138 A1 WO2022127138 A1 WO 2022127138A1
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grating
fiber
resonant cavity
gain chip
interval
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PCT/CN2021/110735
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English (en)
French (fr)
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易昌申
李大汕
任文建
沈渊
向少卿
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上海禾赛科技有限公司
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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
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/185—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only horizontal cavities, e.g. horizontal cavity surface-emitting lasers [HCSEL]
    • H01S5/187—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only horizontal cavities, e.g. horizontal cavity surface-emitting lasers [HCSEL] using Bragg reflection
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/2004—Confining in the direction perpendicular to the layer structure
    • H01S5/2009—Confining in the direction perpendicular to the layer structure by using electron barrier layers
    • H01S5/2013—MQW barrier reflection layers
    • H—ELECTRICITY
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    • 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
    • H01S5/3086—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure doping of the active layer
    • H01S5/309—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure doping of the active layer doping of barrier layers that confine charge carriers in the laser structure, e.g. the barriers in a quantum well structure
    • 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/3407—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers characterised by special barrier 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
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/34346—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser characterised by the materials of the barrier layers
    • H01S5/34353—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser characterised by the materials of the barrier layers based on (AI)GaAs

Definitions

  • the invention relates to the field of lasers, in particular to a resonant cavity, a laser and a laser radar.
  • Lidar is a commonly used ranging sensor, which has the characteristics of long detection distance, high resolution, and little environmental interference. It is widely used in intelligent robots, unmanned aerial vehicles, unmanned vehicles and other fields. In recent years, autonomous driving technology has developed rapidly, and lidar, as the core sensor of its distance perception, has become indispensable. Laser, as one of the core components of lidar, its performance has a great influence on the performance of lidar.
  • External cavity semiconductor lasers are composed of semiconductor laser chips and external cavity feedback elements such as plane mirrors, Fabry-Pérot etalons or gratings.
  • External cavity semiconductor lasers have many excellent characteristics unmatched by other types of lasers, such as narrow output spectral linewidth, tunable wavelength width, ultra-short pulse output, and high-frequency amplitude modulation.
  • narrow output spectral linewidth a laser that is a lasers
  • tunable wavelength width such as narrow output spectral linewidth
  • ultra-short pulse output such as ultra-short pulse output
  • high-frequency amplitude modulation such as narrow output spectral linewidth
  • tunable wavelength width such as narrow output spectral linewidth
  • ultra-short pulse output such as ultra-short pulse output
  • high-frequency amplitude modulation such as narrow output spectral linewidth
  • tunable wavelength width a laser that is a laser that is a laser that is a laser that is a laser that is a laser
  • Fiber Bragg grating semiconductor external cavity lasers have extremely narrow output linewidths and good dynamic single-mode characteristics.
  • Multi-wavelength semiconductor lasers are widely used in Dense Wavelength Division Multiplexing (DWDM) systems, all-optical network systems, lidar systems, precision measurement and other fields.
  • DWDM Dense Wavelength Division Multiplexing
  • all-optical network systems lidar systems
  • precision measurement and other fields precision measurement and other fields.
  • the multi-wavelength semiconductor external cavity laser still has long external cavity cavity, difficult packaging, and the large difference in the external cavity length, which is fatal for the multi-wavelength semiconductor external cavity laser operating with ultra-short pulses. of.
  • the problem solved by the present invention is to provide a resonant cavity, a laser and a laser radar, so as to overcome the problem that the cavity length of the multi-wavelength external cavity laser is too long to be packaged, and to solve the problem that the cavity length of each external cavity differs greatly, which is not conducive to ultra-short pulses. work problem.
  • the present invention provides a resonant cavity, comprising:
  • a gain chip the gain chip has an output surface from which light exits; a fiber grating, the fiber grating is located on one side of the output surface, the fiber grating includes a first grating, and the first grating has a plurality of first grating bars , there is a first interval between the adjacent first grid bars; the second grid, the second grid has a plurality of second grid bars, and there is a second interval between the adjacent second grid bars; the The second grid bars are located in the first interval, and the first interval is not equal to the second interval.
  • the fiber grating is a fiber Bragg grating.
  • the grid bar closest to the gain chip is the initial grid bar; the interval closest to the gain chip is the initial interval;
  • Initial second bars of the second grating are located within initial intervals of the first grating.
  • it further includes: a third grating, the third grating has a plurality of third grid bars, and a third interval is provided between adjacent third grid bars; the third grid bars are located in the first In the interval, the third interval is not equal to the first interval and the second interval.
  • it further includes: a reflective film, the reflective film is disposed opposite to the fiber grating, and is located on the side of the gain chip away from the fiber grating.
  • the gain chip has a rear surface, and the rear surface is arranged opposite to the output surface; the reflective film is located on the rear surface.
  • it further includes: a first anti-reflection film, the first anti-reflection film is located on the output surface.
  • it further includes: a fiber lens, the fiber lens is located between the gain chip and the fiber grating.
  • it further includes: a second anti-reflection film, the second anti-reflection film is located on the end face of the optical fiber lens facing the gain chip.
  • the fiber lens has a wedge angle; the angle of the wedge angle of the fiber lens corresponds to the divergence angle of the light emitted by the gain chip.
  • the gain chip is a semiconductor gain chip, which has a divergence angle along the fast axis direction and a divergence angle along the slow axis direction, and the angle of the wedge angle of the fiber lens is respectively the same as the divergence angle along the fast axis direction.
  • the angle corresponds to the divergence angle along the slow axis.
  • the fiber lens is at least one of a single wedge-shaped fiber lens, a square tapered fiber lens, and a conical fiber lens.
  • the end face of the fiber lens facing the gain chip is a curved surface that protrudes toward the gain chip.
  • the present invention also provides a laser, comprising:
  • a resonant cavity, the resonant cavity is the resonant cavity of the present invention.
  • thermoly conductive substrate the surface of the thermally conductive substrate has a prefabricated solder area; the gain chip is mounted on the prefabricated solder area.
  • it further includes: an optical fiber fixing block, the surface of the optical fiber fixing block has a groove; the fiber grating is fixed in the groove.
  • it further includes: a temperature controller, wherein the thermally conductive substrate and the optical fiber fixing block are located on the surface of the temperature controller.
  • the present invention also provides a laser radar, comprising:
  • a light source the light source includes the laser of the present invention; a detector, the number of the detectors corresponds to the number of gratings included in the fiber grating in the laser.
  • it further includes: a diffractive element, the diffractive element is located downstream of the optical path of the light generated by the light source.
  • the second grating of the second grating is located in the first interval of the first grating, and the first interval is not equal to the second interval, that is, the first interval is not equal to the second interval.
  • the grating constant of the grating is not equal to the grating constant of the second grating, and the gratings with different grating constants are intertwined, and the gratings of the two gratings are staggered. within the same region of the fiber grating.
  • the first grating and the second grating are used as cavity mirrors and the gain chip respectively form an external cavity resonator, since the writing is in the same area, the length of the cascaded external cavity resonator is short and the external cavity occupies space. Small, easy to control the temperature of each grating, good temperature consistency, easy to miniaturize the package; and the cavity length is similar, after the current is injected, the light-emitting time of each wavelength of the light pulse is basically the same, which can effectively improve its application in narrow-pulse lidar. performance.
  • the resonant cavity further includes: a transparent film located on the output surface of the gain chip to suppress the end surface reflection of the output surface of the gain chip, thereby suppressing the intra-cavity mode oscillation of the gain chip and improving the performance of the laser stability.
  • the resonant cavity further includes: an optical fiber lens; the end face of the optical fiber lens facing the gain chip is a convex curved surface toward the gain chip; and the angle of the wedge angle of the optical fiber lens is the same as that of the gain chip.
  • the divergence angle of the light emitted by the gain chip corresponds to that, that is, the direction with a large divergence angle has a large wedge angle, and the direction with a small divergence angle has a small wedge angle, so that as much of the light generated by the gain chip as possible is coupled through the fiber lens head into the fiber grating, effectively improving the coupling efficiency and increasing the output power.
  • the gain chip is mounted on the prefabricated solder area of the thermally conductive substrate; the fiber grating is fixed in the groove of the optical fiber fixing block by the thermally conductive material; and the thermally conductive substrate and the optical fiber fixing block are arranged in the temperature control
  • a temperature feedback loop is formed together with the temperature controller to precisely control the temperature of the gain chip and the fiber grating, thereby improving the temperature stability of the laser.
  • the laser of the present invention is used as the light source.
  • the laser can simultaneously generate multiple lasers of different wavelengths;
  • the use of grating can increase the output channel without increasing the number of lasers, and can effectively improve the performance of lidar.
  • FIG. 1 is a schematic structural diagram of a multi-wavelength semiconductor external cavity laser using fiber Bragg grating cascades
  • FIG. 2 is a schematic structural diagram of an embodiment of a resonant cavity of the present invention.
  • Figure 3 is a schematic diagram of the working principle of the fiber Bragg grating
  • Fig. 4 is the schematic diagram of the fiber grating writing process in the resonant cavity embodiment shown in Fig. 1;
  • FIG. 5 is a schematic structural diagram of the optical fiber lens 130 in the embodiment shown in FIG. 1;
  • Fig. 6 is the projection schematic diagram of arrow A direction among Fig. 5;
  • FIG. 7 is a three-dimensional schematic diagram of an embodiment of the laser of the present invention.
  • FIG. 8 is a schematic top-view structural diagram of the embodiment of the laser shown in FIG. 7 .
  • FIG. 9 is the transmission spectrum of the fiber grating in the embodiment of the laser shown in FIG. 7 .
  • FIG. 10 is a schematic diagram of an optical path structure of an embodiment of a laser radar according to the present invention.
  • the multi-wavelength semiconductor external cavity laser in the prior art has the problem that the length of the external cavity is greatly different from that of each external cavity.
  • a schematic diagram of the structure of a multi-wavelength semiconductor external cavity laser using fiber Bragg gratings the reasons for the large external cavity cavity length and the large difference between the external cavity cavity lengths are analyzed:
  • FIG. 1 a schematic structural diagram of a multi-wavelength semiconductor external cavity laser using fiber Bragg gratings cascaded is shown.
  • the resonant cavity of the laser includes: a gain chip 11, the gain chip 11 has a light exit surface (not marked in the figure) and a rear surface (not marked in the figure) opposite to the light exit surface; the reflective film 20, The reflective film 20 is located at the rear end of the gain chip 11; the fiber Bragg grating 30 is located on the optical path of the light generated by the gain chip 1; the first grating 31, the second grating 32 and the third grating 33; the reflective film 20 and the first grating 31, the second grating 32 and the third grating 33 respectively form resonators with different cavity lengths .
  • the laser uses a fiber Bragg grating with multiple gratings (respectively the first grating 31 , the second grating 32 and the third grating 33 ) to select multiple wavelengths, corresponding to different gratings, to form
  • the cavity lengths of the outer cavity are L1, L2 and L3, respectively.
  • the cavity length of the outer cavity formed is relatively large, which is prone to packaging difficulties; and the difference between the cavity lengths of the outer cavities is at least The width of a grating, that is, the length of each cavity is very different. Therefore, after the current is injected, the light-emitting time of each wavelength of the light pulse is quite different (that is, the switching of multiple wavelengths is inconsistent), which is not conducive to the use of narrow-pulse lasers.
  • Radar as in current time-of-flight (TOF) ranging based lidar applications.
  • the present invention provides a resonant cavity, including: a gain chip, the gain chip has an output surface from which light exits; a fiber grating, the fiber grating is located on one side of the output surface, and the fiber grating It includes a first grating, the first grating has a plurality of first grid bars, and a first interval is formed between adjacent first grid bars; a second grating, the second grating has a plurality of second grid bars, A second interval is provided between the adjacent second grid bars; the second grid bars are located in the first interval, and the first interval and the second interval are not equal.
  • the second grating of the second grating is located in the first interval of the first grating, and the first interval is not equal to the second interval, that is, the first interval is not equal to the second interval.
  • the grating constant of the grating is not equal to the grating constant of the second grating, and the gratings with different grating constants are intertwined, and the gratings of the two gratings are staggered. within the same region of the fiber grating.
  • the first grating and the second grating are used as cavity mirrors and the gain chip 110 to respectively form an external cavity resonator, since the first grating and the second grating are written in the same area, the cascaded external The cavity length of the cavity resonator is short, the space occupied by the outer cavity is small, the temperature of each grating is easy to control, the temperature consistency is good, and the package is easy to miniaturize; and the cavity length of each outer cavity is similar, and after the current is injected, the light-emitting time of the light pulse of each wavelength is basically The same, can effectively improve the performance of its application in narrow pulse lidar.
  • FIG. 2 a schematic structural diagram of an embodiment of a resonant cavity of the present invention is shown.
  • the resonant cavity includes: a gain chip 110 .
  • the gain chip 110 is used as a gain medium of the resonant cavity.
  • the gain chip 110 has an output surface 111 of the fiber output.
  • the gain chip 110 is a semiconductor laser gain chip.
  • the resonant cavity further includes: a first anti-reflection film (not shown in the figure), and the first anti-reflection film is located on the output surface of the gain chip 110, that is, directly on the output surface of the gain chip 110.
  • the output surface of the gain chip is coated to obtain the first anti-reflection coating.
  • the first anti-reflection film can effectively improve the transmittance of the output surface of the gain chip 110 and reduce the reflectivity of the output surface, thereby effectively suppressing the oscillation of the cavity mode of the gain chip 110, which is beneficial to improve the stability of the laser performance sex.
  • the reflectivity of the first anti-reflection film is less than 0.1%.
  • the resonant cavity further includes: a fiber grating 120, which is used as a cavity mirror of the resonant cavity to reflect light.
  • the resonant cavity further includes: a reflective film 113 , the reflective film 113 is disposed opposite to the fiber grating 120 , and is located at a position of the gain chip 110 away from the fiber grating 120 . side.
  • the reflective film 113 is used as another cavity mirror of the resonant cavity to form a resonant cavity with the fiber grating 120.
  • the light generated by the gain chip 110 is between the reflective film 113 and the fiber grating 120. reflections back and forth.
  • the gain chip 110 has a rear end surface 112, and the rear end surface 112 is disposed opposite to the output surface 111; the reflective film 113 is located on the rear end surface, that is, it can be directly on the The rear surface 112 of the gain chip 110 is coated to form the reflective film 113 .
  • the reflectivity of the reflective film 113 is greater than 90% to reduce the loss of the resonant cavity.
  • the fiber grating 120 is located on one side of the output surface 111 of the gain chip 110 .
  • the fiber grating 120 includes a first grating 121 and a second grating 122.
  • the first grating 121 has a plurality of first gratings, and adjacent first gratings have a first interval;
  • the second grating has a plurality of first gratings.
  • the second gratings of the second grating 122 are located in the intervals of the first gratings of the first grating 121, that is, the second gratings and the first gratings are interwoven, and the gratings of the two gratings are staggered; and
  • the first interval is not equal to the second interval, that is, the grating constant of the second grating is not equal to the grating constant of the first grating, that is, the two gratings whose grating constants are not equal are written in the the same region of the fiber grating described above.
  • the first grating 121 and the second grating 122 are used as two external cavity resonators formed by cavity mirrors and the gain chip 110 respectively, since the first grating 121 and the second grating 122 are written on the In the same area, the length of the cascading external cavity resonator is short, the external cavity occupies a small space, the temperature of each grating is easy to control, the temperature consistency is good, and the package is easy to miniaturize; , the light-emitting time of each wavelength light pulse is basically the same, which can effectively improve the performance of its application in narrow-pulse lidar.
  • the resonant cavity further includes: a third grating 123, the third grating 123 has a plurality of third grid bars, and adjacent third grid bars have a third interval; the third grid bars are located in the first interval, and the third interval is not equal to the first interval and the second interval.
  • multiple gratings can be written in the same area of the fiber grating, which can effectively reduce the cavity length of the cascaded external cavity resonator and the space occupied by the external cavity, thereby reducing the difficulty of temperature control of each grating and improving the efficiency of each grating.
  • the temperature of the grating is consistent, and the miniaturization of the package can be improved; the lengths of the external cavities are similar, and after the current is injected, the light-emitting time of the light pulse of each wavelength is basically the same, which can effectively improve its application in narrow-pulse lidar. performance.
  • the grating closest to the gain chip 110 is the initial grating; the interval closest to the gain chip is the initial interval; the initial interval of the second grating is The second grating is located within the initial interval of the first grating, that is, the extending direction of the resonator, the plurality of first gratings of the first grating 121 and the plurality of second gratings of the second grating 122
  • the staggered arrangement is started from the beginning, so as to minimize the cavity length, reduce the space occupied by the outer cavity, and minimize the resonant cavity formed by the first grating 121 and the second light 122 respectively.
  • the cavity length gap can effectively improve the laser performance.
  • the resonant cavity further includes: a third grating 123 having a plurality of third gratings, and the initial third gratings of the third grating 123 are also located within the initial interval of the first grating . That is to say, in this embodiment, the first grating 121 , the second grating 122 and the third grating 123 are all written in the same area, so that the cavity length can be minimized and the external cavity can be reduced to the greatest extent. The space occupied can also be minimized, and the cavity length gap of different resonators can be minimized, which can effectively improve the performance of the laser.
  • the fiber grating 120 is a fiber Bragg grating.
  • FIG. 3 shows a schematic diagram of the working principle of the fiber Bragg grating
  • FIG. 4 shows a schematic diagram of the writing process of the fiber grating in the resonant cavity embodiment shown in FIG. 1 .
  • Fiber Bragg Grating is a spatial phase grating formed in the fiber core.
  • the forward-transmitted fiber core mode is coupled.
  • the energy of the core mode is transferred to the backward propagating core mode, resulting in a reflection of the incident wave.
  • Fiber Bragg grating can be written by mask method, chemical etching method, femtosecond method, etc.
  • FIG. 4 shows a schematic diagram of writing the fiber Bragg grating by the mask method.
  • the UV beam is irradiated on the phase mask 124, the incident beam is divided into a -1st-order diffracted beam and a +1st-order diffracted beam, and the optical power of the -1st-order diffracted beam and the +1st-order diffracted beam are equal, and the two interfere with each other to form light and dark Alternating stripes.
  • the refractive index of the fiber core material changes with the light intensity after exposure to UV light. Therefore, the interference light with varying light intensity can modulate the refractive index of the fiber core material through the light intensity, thereby forming a fiber Bragg grating.
  • the grating constant is 1/2 of the period of the phase mask. Therefore, the grating constant of the fiber grating written by the mask method has nothing to do with the wavelength of the incident light, but is only related to the period of the phase mask.
  • the fiber grating in the embodiment of the resonant cavity shown in FIG. 2 is repeatedly written three times in the same area with phase masks of different periods, so as to form three fiber gratings with different grating constants in the same area, that is, in the same area , gratings with different grating constants are intertwined, so that the length of the region in which the gratings are formed in the optical fiber can be reduced.
  • the fiber grating in the embodiment of the resonant cavity shown in FIG. 2 is repeatedly written three times in the same area with phase masks of different periods, so as to form three fiber gratings with different grating constants in the same area, that is, in the same area , gratings with different grating constants are intertwined, so that the length of the region in which the gratings are formed in the optical fiber can be reduced.
  • the corresponding grating constants are ⁇ 1, ⁇ 2 and ⁇ 3 respectively, and the phase mask used in writing is
  • the template periods are 2 ⁇ 1, 2 ⁇ 2, and 2 ⁇ 3, respectively.
  • the resonant cavity further includes: a fiber lens 130 , and the fiber lens 130 is located between the gain chip 110 and the fiber grating 120 .
  • the fiber lens 130 can couple the light generated by the gain chip 110 into the fiber grating 120 as much as possible, thereby reducing the loss of the resonant cavity.
  • FIG. 5 shows a schematic structural diagram of the optical fiber lens 130 in the embodiment shown in FIG. 1
  • FIG. 6 is a schematic projection diagram of the direction of arrow A in FIG. 5 .
  • the fiber lens 130 has a wedge angle; the angle of the wedge angle of the fiber lens 130 corresponds to the divergence angle of the light emitted by the gain chip 110, and also That is to say, the larger the divergence angle of the light emitted by the gain chip 110 is, the larger the wedge angle of the fiber lens 130 is; The smaller the value, the more light generated by the gain chip 110 can be coupled into the fiber grating 120 through the fiber lens 130 as much as possible, thereby effectively improving the coupling efficiency and increasing the output power.
  • the above wedge angle refers to the opening angle formed by the fiber optic lens 130 in a given direction.
  • the gain chip 110 is a semiconductor gain chip
  • the semiconductor gain chip has a divergence angle along the fast axis direction and a divergence angle along the slow axis direction
  • the angle of the wedge angle of the fiber lens 130 is respectively the same as that of the The divergence angle along the fast axis direction corresponds to the divergence angle along the slow axis direction, that is, the angle size of the wedge angle of the fiber lens 130 is the size of the divergence angle along the fast axis direction and the divergence angle along the slow axis direction.
  • the fiber lens 130 is a square tapered fiber lens.
  • the fiber lens may also be a single wedge-shaped fiber lens or a conical fiber lens.
  • the end face of the optical fiber lens 130 facing the gain chip 110 is a curved surface that protrudes toward the gain chip 110 .
  • the curved surface protruding toward the gain chip 110 can converge light, so that more light can enter the fiber grating 120 , thereby effectively improving the coupling efficiency and increasing the output power.
  • the fiber lens 130 is formed by, for example, processing, for example, grinding, the fiber core at the end face of the fiber waveguide where the fiber grating 120 is located.
  • the resonant cavity further includes: a second anti-reflection film, and the second anti-reflection film is located on the end face of the optical fiber lens 130 facing the gain chip.
  • the second anti-reflection coating can effectively increase the intensity of light transmitted through the end face of the fiber lens 130, suppress the reflection of the end face of the fiber lens 130 toward the end face of the gain chip 110, so that the light can be directly coupled into the fiber waveguide, so that the fiber waveguide and the
  • the gain chip 110 is mode-matched, and the coupling efficiency is improved (for example, the coupling can be made less than or greater than 60%), so that the cavity mode oscillation of the gain chip 110 can be effectively suppressed, and the stability of the resonant cavity can be improved.
  • the reflectivity of the second anti-reflection film is less than 0.1%.
  • the present invention also provides a laser, the laser comprises: a resonant cavity, and the resonant cavity is the resonant cavity of the present invention.
  • FIGS. 7 and 8 a schematic structural diagram of an embodiment of a laser of the present invention is shown; wherein FIG. 7 is a three-dimensional schematic diagram of the laser embodiment, and FIG. 8 is a top-view structural schematic diagram of the laser embodiment.
  • the resonant cavity is the resonant cavity of the present invention.
  • the resonant cavity includes a gain chip 210, a fiber grating 220 and a fiber lens 230 located therebetween.
  • the resonant cavity includes a gain chip 210, a fiber grating 220 and a fiber lens 230 located therebetween.
  • the fiber grating 220 has a certain reflectivity and bandwidth in the target wavelength range, and has multiple reflection peaks corresponding to multiple (three in this embodiment) Bragg periods, so that it can be used as the mode selection of the external cavity laser. element.
  • the multiple gratings in the fiber grating 220 and the gain chip respectively form multiple external cavity resonators. When the laser resonance conditions are met, multiple laser wavelengths resonate simultaneously to output multi-wavelength laser light.
  • the fiber grating 220 includes three gratings with different grating constants and written in the same area.
  • the fiber grating 220 and the reflective film (not shown in the figure) on the rear surface 212 (shown in FIG. 8 ) of the gain chip 210 are used as cavity mirrors of the external cavity resonator respectively, and the fiber grating 220 also serves as the external cavity Model selection components.
  • the fiber grating 220 writes three gratings in the same area, and the grating constants of each grating are unequal, and the Bragg wavelengths of each grating are unequal, so the fiber grating 220 has a certain bandwidth at the positions of different design wavelengths. (corresponding to the concave part of the transmission spectrum in Figure 9).
  • the fiber grating 220 writes a plurality of gratings in the same area.
  • the length of the cascading external cavity resonator cavity is short and the cavity length is similar.
  • the light-emitting time of the light pulse of each wavelength is basically the same (that is, the switching of multiple wavelengths is the same). .
  • the length of the grating region in the fiber grating 220 is about 2 mm
  • the Bragg wavelengths corresponding to the three gratings are 1530 nm, 1550 nm and 1570 nm respectively
  • the reflectivity is about 20%
  • the -3dB bandwidth of the reflection spectrum is 0.4nm.
  • the laser further includes: a thermally conductive substrate 240 having a prefabricated solder area on the surface; the gain chip 210 is mounted on the prefabricated solder area.
  • the thermally conductive substrate 240 provides positive and negative electrodes for the gain chip 210 to supply power.
  • the thermally conductive substrate 240 is a highly thermally conductive substrate, that is, the thermally conductive substrate 240 has high thermal conductivity and low thermal resistance, which can efficiently dissipate heat, which is beneficial to improve the heat dissipation conditions of the gain chip 210 .
  • the material of the thermally conductive substrate 240 may be materials such as aluminum nitride, beryllium oxide, and aluminum oxide. Specifically, in this embodiment, the material of the thermally conductive substrate 240 is aluminum nitride, and the thermal conductivity is 200W/m.k.
  • the surface of the thermally conductive substrate 240 has a prefabricated solder area (not shown in the figure), and the prefabricated solder area is prefabricated with solder to realize the welding between the gain chip 210 and the thermally conductive substrate 240 , so as to not only realize the thermally conductive substrate 240
  • the electrical connection between the gain chip 210 and the gain chip 210 also realizes the fixed connection between the gain chip 210 and the thermally conductive substrate 240 .
  • Au/Sn solder is prefabricated on the prefabricated solder region.
  • the upper and lower surfaces of the thermally conductive substrate 240 are gold-plated.
  • the thermally conductive substrate 240 is divided into a plurality of regions, and different regions are respectively used for setting the lead pads of the positive and negative electrodes of the gain chip 210, the temperature sensor thermistor, and the like.
  • the temperature sensor thermistor is close to the position patch of the gain chip 210 .
  • the laser further includes: an optical fiber fixing block 250, the surface of the optical fiber fixing block 250 has a groove (not marked in the figure); the fiber grating 220 is fixed in the groove.
  • the optical fiber fixing block 250 is used to support and fix the optical fiber waveguide.
  • the optical fiber fixing block 250 defines a groove along the longitudinal center portion for arranging the optical fiber grating 220 .
  • the grooves of the optical fiber fixing block 250 are filled with thermally conductive materials, on the one hand, the fiber grating 220 is fixed, and on the other hand, the heat dissipation of the fiber grating 220 is accelerated to improve its heat dissipation conditions.
  • the material of the optical fiber fixing block 250 can be set to aluminum nitride ceramics, alumina ceramics, tungsten-copper alloys, and other materials with certain hardness and high thermal conductivity, so as to take into account the effects of fixing and heat dissipation .
  • the laser further includes: a temperature controller 260, and the thermally conductive substrate 240 and the optical fiber fixing block 250 are located on the surface of the temperature controller 260 to precisely control
  • the temperature of the gain chip 210 and the fiber grating 220 helps to keep the external cavity length stable and improve the temperature stability of the laser.
  • the laser further includes: a packaging tube 270, the packaging tube 270 includes a shell, a PIN pin, a nozzle, and a shell cover, and the packaging tube 270 provides sealing for various components of the laser Stable and reliable space environment, and provide PIN pins for electrical connection.
  • the temperature controller is a semiconductor cold chip temperature controller (Thermoelectric Cooler, TEC).
  • the temperature controller 260 is a semiconductor Peltier temperature device, which is soldered on the bottom plate of the package tube 270 by a reflow soldering process, and the thermally conductive substrate 240 and the fiber grating fixing block 250 are soldered by a reflow soldering process.
  • the temperature controller 260 and the temperature sensor thermistor form a temperature feedback loop, which can control the temperature of the gain chip 210 and the fiber grating 220, and the temperature stability is better than 0.005°C.
  • the PIN pins of the positive and negative electrodes for supplying power to the gain chip 210 on the package casing 270 are arranged at a relatively small spacing, which can optimize the parasitic inductance between the electrodes under pulsed working conditions and improve the working performance of the laser pulse.
  • the present invention also provides a laser radar, the laser radar includes: a light source, the light source includes the laser of the present invention; a detector, the number of the detectors is the same as the number of gratings included in the fiber grating in the laser Corresponding.
  • FIG. 10 a schematic diagram of an optical path structure of an embodiment of a laser radar of the present invention is shown.
  • the laser 310 is the laser of the present invention.
  • the resonant cavity of the laser 310 includes a gain chip and a fiber grating, and the fiber grating includes a plurality of gratings.
  • the fiber grating includes a plurality of gratings.
  • the light source of the lidar includes the laser 310 of the present invention, that is, the fiber grating in the resonator of the laser 310 has multiple gratings, which can be combined with gain chips to form multiple external cavity resonators, so the light source of the lidar Able to achieve multi-wavelength output.
  • the lidar further includes: a diffractive element 320 , and the diffractive element 320 is located downstream of the optical path of the light generated by the light source.
  • the lidar further includes: a collimating lens 320, and the light generated by the laser 310 is collimated by the collimating lens 320 and projected onto the diffractive element 320;
  • the laser 310 outputs multiple wavelengths, so the generated light contains multiple wavelengths of light, so the diffractive element 320 can divide the multiple wavelengths of light into multiple channels for output, thereby forming multiple beams of probe light to out for detection.
  • the number of channels formed is equal to the number of wavelengths in the light generated by the laser, that is, equal to the number of gratings in the fiber grating.
  • the lidar further includes: detectors (not shown in the figure), and the number of the detectors corresponds to the number of gratings included in the fiber grating in the laser. Since the diffractive element 320 divides the multi-wavelength light generated by the laser into a plurality of channels for output to form multi-beam detection light, the number of the detectors corresponds to the number of gratings included in the fiber grating in the laser to realize multi-beam detection Detection of echoes formed by light.
  • the laser 310 can output laser light including three wavelengths of 1530 nm, 1550 nm and 1570 nm.
  • the diffraction element 320 is a diffraction grating. After the laser light generated by the laser 310 is collimated by the collimating lens 320, it is incident on the diffraction grating at a certain angle (for example, a near littrow angle); , 1570nm output light 420, 1530nm output light 430, that is to say, one channel becomes 3 channels output after being split by the diffraction grating, and the number of output channels is 3 times the original.
  • the second grating of the second grating is located in the first interval of the first grating, and the first interval is not equal to the second interval, that is, the grating constant of the first grating
  • the grating constants of the second grating are not equal, and the gratings with different grating constants are intertwined, and the gratings of the two gratings are staggered. within the area.
  • the first grating and the second grating are used as cavity mirrors and the gain chip respectively form an external cavity resonator, since the writing is in the same area, the length of the cascaded external cavity resonator is short and the external cavity occupies space.
  • the light-emitting time of each wavelength of the light pulse is basically the same, which can effectively improve its application in narrow-pulse lidar. performance.

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Abstract

一种谐振腔、激光器和激光雷达，谐振腔包括：增益芯片（110），增益芯片（110）具有光线出射的输出面（111）；光纤光栅（120），光纤光栅（120）位于输出面（111）一侧，光纤光栅（120）包括第一光栅（121），第一光栅（121）具有多个第一栅条，相邻第一栅条之间具有第一间隔；第二光栅（122），第二光栅（122）具有多个第二栅条，相邻第二栅条之间具有第二间隔；第二栅条位于第一间隔中，第一间隔与第二间隔不等。能够缩短外腔腔长，减小各外腔腔长差。

Description

谐振腔、激光器和激光雷达 技术领域
本发明涉及激光器领域，特别涉及一种谐振腔、激光器和激光雷达。
背景技术
激光雷达是一种常用的测距传感器，具有探测距离远、分辨率高、受环境干扰小等特点，广泛应用于智能机器人、无人机、无人驾驶等领域。近年来，自动驾驶技术发展迅速，激光雷达作为其距离感知的核心传感器，已不可或缺。激光器，作为激光雷达核心部件之一，其性能的好坏对激光雷达的性能有着的很大的影响。
外腔半导体激光器是由半导体激光器芯片和平面镜、法布里-珀罗(Fabry–Pérot)标准具或光栅等外腔反馈元件构成的。外腔半导体激光器具有许多其他类型激光器所无法比拟的优良特性，如输出光谱线宽窄、波长可调谐宽、可产生超短脉冲输出及实现高频幅度的调制等。但是由于光栅和反射镜的体积庞大、价格高，与半导体激光芯片封装工艺复杂，作为外腔结构反馈元件又有诸多缺点。
随着光纤光栅制作技术的不断进步，人们将普通半导体激光器(增益)芯片的一端面上镀增透膜，另一端面镀高反膜，增益芯片与光纤光栅形成外腔半导体激光器，这样解决了分离反馈元件与半导体激光器、光纤耦合封装的问题。
光纤光栅半导体外腔激光器具有极窄的输出线宽和良好的动态单模特性。多波长半导体激光器在密集型光波复用(Dense Wavelength Division Multiplexing，DWDM)系统、全光网络系统、激光雷达系统、精密测量等领域具有广泛的应用。为了简化系统设计， 人们希望用一个能发射多个波长的激光器替代多个激光器光谱合束的方案，基于布拉格(Bragg)光纤光栅的多波长半导体外腔激光器受到广泛关注。
但是即使采用布拉格光纤光栅，多波长半导体外腔激光器依旧存在外腔腔长长，封装困难，以及各外腔腔长相差很大，对于超短脉冲工作的多波长半导体外腔激光器来说是致命的。
发明内容
本发明解决的问题是提供一种谐振腔、激光器和激光雷达，以克服多波长外腔激光器腔长过长封装困难的问题，又解决了各个外腔腔长相差很大，不利于超短脉冲工作的问题。
为解决上述问题，本发明提供一种谐振腔，包括：
增益芯片，所述增益芯片具有光线出射的输出面；光纤光栅，所述光纤光栅位于所述输出面一侧，所述光纤光栅包括第一光栅，所述第一光栅具有多个第一栅条，相邻所述第一栅条之间具有第一间隔；第二光栅，所述第二光栅具有多个第二栅条，相邻所述第二栅条之间具有第二间隔；所述第二栅条位于所述第一间隔中，所述第一间隔与所述第二间隔不等。
可选的，所述光纤光栅为布拉格光纤光栅。
可选的，最靠近所述增益芯片的栅条为初始栅条；最靠近所述增益芯片的间隔为初始间隔；
所述第二光栅的初始第二栅条位于所述第一光栅的初始间隔内。
可选的，还包括：第三光栅，所述第三光栅具有多个第三栅条，相邻所述第三栅条之间具有第三间隔；所述第三栅条位于所述第一间隔中，所述第三间隔与所述第一间隔和所述第二间隔均不等。
可选的，还包括：反射膜，所述反射膜与所述光纤光栅相对设置，位于所述增益芯片远离所述光纤光栅的一侧。
可选的，所述增益芯片具有后端面，所述后端面与所述输出面相背设置；所述反射膜位于所述后端面。
可选的，还包括：第一增透膜，所述第一增透膜位于所述输出面。
可选的，还包括：光纤透镜，所述光纤透镜位于所述增益芯片和所述光纤光栅之间。
可选的，还包括：第二增透膜，所述第二增透膜位于所述光纤透镜朝向所述增益芯片的端面。
可选的，所述光纤透镜具有楔形角；所述光纤透镜的楔形角的角度与所述增益芯片发射光线的发散角相对应。
可选的，所述增益芯片为半导体增益芯片，其具有沿快轴方向的发散角和沿慢轴方向的发散角，所述光纤透镜的楔形角的角度分别与所述沿快轴方向的发散角和所述沿慢轴方向的发散角相对应。
可选的，所述光纤透镜为单楔形光纤透镜、四方锥形光纤透镜和圆锥形光纤透镜中的至少一种。
可选的，所述光纤透镜朝向所述增益芯片的端面为朝向所述增益芯片凸出的曲面。
相应的，本发明还提供一种激光器，包括：
谐振腔，所述谐振腔为本发明的谐振腔。
可选的，还包括：导热基板，所述导热基板表面具有预制焊料区；所述增益芯片贴片于所述预制焊料区。
可选的，还包括：光纤固定块，所述光纤固定块表面具有凹槽；所述光纤光栅固定于所述凹槽内。
可选的，还包括：温度控制器，所述导热基板和所述光纤固定块位于所述温度控制器表面。
此外，本发明还提供一种激光雷达，包括：
光源，所述光源包括本发明的激光器；探测器，所述探测器的个数与所述激光器中光纤光栅包括的光栅数量相对应。
可选的，还包括：衍射元件，所述衍射元件位于所述光源所产生光线的光路下游。
与现有技术相比，本发明的技术方案具有以下优点：
本发明的技术方案中，所述第二光栅的第二栅条位于第一光栅的第一间隔中，而且所述第一间隔与所述第二间隔不等，也就是说，所述第一光栅的光栅常数与所述第二光栅的光栅常数不相等，而且不同光栅常数的光栅相互交织，两个光栅的栅条交错设置，即所述第二光栅和所述第一光栅刻写在所述光纤光栅的同一区域内。当所述第一光栅和所述第二光栅分别作为腔镜与所述增益芯片分别构成外腔谐振腔时，由于刻写在同一区域，因此级联外腔谐振腔腔长短，外腔所占空间小，各光栅温度易控制，温度一致性好，封装易于小型化；而且腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同，能够有效改善其在窄脉冲激光雷达中应用的性能表现。
本发明可选方案中，所述谐振腔还包括：位于所述增益芯片的输出面的透膜，以抑制增益芯片输出面的端面反射，从而压制所述增益芯片内腔模式振荡，提高激光器性能稳定性。
本发明可选方案中，所述谐振腔还包括：光纤透镜；所述光纤透镜朝向所述增益芯片的端面为朝向所述增益芯片凸出的曲面；而且所述光纤透镜的楔形角的角度与所述增益芯片发射光线的发散角相对应，即发散角大的方向楔形角大，发散角小的方向，楔形角小，从而使增益芯片所产生光线中尽可能多经所述光纤透镜头耦合入所述光纤光栅，有效提高耦合效率，增大输出功率。
本发明的激光器中，所述增益芯片贴片于导热基板的预制焊料区；所述光纤光栅通过导热材料固定于所述光纤固定块的凹槽内；而导热基板和光纤固定块设置于温度控制器的测温基板上，与所述温度控制器一起构成温度反馈回路，以精确控制增益芯片和光纤光栅的温度，从而提高激光器的温度稳定性。
本发明的激光雷达中，所述光源采用本发明的激光器，当所述光纤光栅中不同光栅的栅条间的间隔不相等时，所述激光器能够同时产生不同波长的多种激光；在配合衍射光栅的使用，能够在不增加激光器数量的同时，增加输出通道，能够有效提高激光雷达性能。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是一种采用布拉格光纤光栅级联的多波长半导体外腔激光器的结构示意图；
图2是本发明谐振腔一实施例的结构示意图；
图3是布拉格光纤光栅的工作原理示意图；
图4是图1所示谐振腔实施例中光纤光栅刻写过程的示意图；
图5是图1所示实施例中所述光纤透镜130的结构示意图；
图6是图5中箭头A方向的投影示意图；
图7是本发明激光器一实施例的立体示意图；
图8是图7所示激光器实施例的俯视结构示意图。
图9是图7所示激光器实施例中光纤光栅的透射谱。
图10是本发明激光雷达一实施例的光路结构示意图。
具体实施方式
由背景技术可知，现有技术中的多波长半导体外腔激光器存在外腔腔长长和各外腔腔长相差大的问题。现结合一种采用布拉格光纤光栅的多波长半导体外腔激光器的结构示意图分析其外腔腔长大、各外腔腔长相差大问题的原因：
参考图1，示出了一种采用布拉格光纤光栅级联的多波长半导体外腔激光器的结构示意图。
所述激光器的谐振腔包括：增益芯片11，所述增益芯片11具有光线出射的出光面(图中未标示)以及与所述出光面相背的后端面(图中未标示)；反射膜20，所述反射膜20位于所述增益芯片11的后端面；布拉格光纤光栅30，所述布拉格光纤光栅30位于所述增益芯片1所产生光线的光路上；所述布拉格光纤光栅包括沿延伸方向依次排列的第一光栅31、第二光栅32以及第三光栅33；所述反射膜20与所述第一光栅31、所述第二光栅32以及所述第三光栅33分别形成不同腔长的谐振腔。
如图1所示，所述激光器利用具有多个光栅(分别为第一光栅31、第二光栅32以及第三光栅33)的布拉格光纤光栅选出多个波长，对应于不同的光栅，所形成外腔的腔长分别为L1、L2和L3。
由于所述多个光栅是沿光纤延伸方向依次排列且相互之间并无交叠；因此所形成外腔的腔长较大，从而容易出现封装困难；而且各外腔腔长的差值至少为一个光栅的宽度，即各腔长相差很大，因此在注入电流后，各波长光脉冲的出光时刻相差较大(即多个波长的开关不一致)，不利于所述激光器在使用窄脉冲的激光雷达，如当前基于飞行时间(TOF)测距的激光雷达中的应用。
为解决所述技术问题，本发明提供一种谐振腔，包括：增益芯片，所述增益芯片具有光线出射的输出面；光纤光栅，所述光纤光栅位于所述输出面一侧，所述光纤光栅包括第一光栅，所述第一光栅具有多个第一栅条，相邻所述第一栅条之间具有第一间隔；第二光栅，所述第二光栅具有多个第二栅条，相邻所述第二栅条之间具有第二间隔；所述第二栅条位于所述第一间隔中，所述第一间隔与所述第二间隔不等。
本发明的技术方案中，所述第二光栅的第二栅条位于第一光栅的第一间隔中，而且所述第一间隔与所述第二间隔不等，也就是说，所述第一光栅的光栅常数与所述第二光栅的光栅常数不相等，而且不同光栅常数的光栅相互交织，两个光栅的栅条交错设置，即所述第二光栅和所述第一光栅刻写在所述光纤光栅的同一区域内。当所述第一光栅和所述第二光栅作为腔镜与所述增益芯片110分别构成外腔谐振腔时，由于所述第一光栅和所述第二光栅刻写在同一区域，因此级联外腔谐振腔腔长短，外腔所占空间小，各光栅温度易控制，温度一致性好，封装易于小型化；而且各外腔腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同，能够有效改善其在窄脉冲激光雷达中应用的性能表现。
为使本发明的上述目的、特征和优点能够更为明显易懂，下面结合附图对本发明的具体实施例做详细的说明。
参考图2，示出了本发明谐振腔一实施例的结构示意图。
如图2所示，所述谐振腔包括：增益芯片110。
所述增益芯片110用以作为所述谐振腔的增益介质。所述增益芯片110具有光纤输出的输出面111。本发明一些实施例中，所述增益芯片110为半导体激光增益芯片。
需要说明的是，本实施例中，所述谐振腔还包括：第一增透膜(图中未示出)，所述第一增透膜位于所述增益芯片110的输出面，即直 接在所述增益芯片的输出面上镀膜以获得所述第一增透膜。所述第一增透膜能够有效提高所述增益芯片110输出面的透射率、降低所述输出面上的反射率，从而能够有效抑制增益芯片110内腔模式振荡，有利于提高激光器性能的稳定性。具体的，所述第一增透膜的反射率小于0.1％。
所述谐振腔还包括：光纤光栅120，作为所述谐振腔的一个腔镜以反射光线。
需要说明的是，本发明一些实施例中，所述谐振腔还包括：反射膜113，所述反射膜113与所述光纤光栅120相对设置，位于所述增益芯片110远离所述光纤光栅120的一侧。
所述反射膜113作为所述谐振腔的另一个腔镜，用以与所述光纤光栅120构成谐振腔，所述增益芯片110所产生的光线在所述反射膜113和所述光纤光栅120之间来回反射。
具体的，本实施例中，所述增益芯片110具有后端面112，所述后端面112与所述输出面111相背设置；所述反射膜113位于所述后端面，即可以直接在所述增益芯片110的后端面112镀膜以形成所述反射膜113。本发明一些实施例中，所述反射膜113的反射率大于90％以降低所述谐振腔的损耗。
所述光纤光栅120位于所述增益芯片110的输出面111的一侧。所述光纤光栅120包括第一光栅121和第二光栅122，所述第一光栅121具有多个第一栅条，相邻第一栅条之间具有第一间隔；所述第二光栅具有多个第二栅条，相邻所述第二栅条之间具有第二间隔。所述第二栅条位于所述第一间隔中，所述第一间隔与所述第二间隔不等。
所述第二光栅122的第二栅条位于第一光栅121的第一栅条的间隔中，即所述第二光栅与所述第一光栅相互交织，两个光栅的栅条交错设置；而且所述第一间隔与所述第二间隔不等，即所述第二光栅的光栅常数与所述第一光栅的光栅常数不相等，也就是说，两个光栅常 数不相等的光栅刻写在所述光纤光栅的同一区域。当所述第一光栅121和所述第二光栅122作为腔镜与所述增益芯片110分别构成的两个外腔谐振腔时，由于所述第一光栅121和所述第二光栅122刻写在同一区域，因此所构成级联外腔谐振腔腔长短，外腔所占空间小，各光栅温度易控制，温度一致性好，封装易于小型化；而且各外腔腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同，能够有效改善其在窄脉冲激光雷达中应用的性能表现。
如图1所示，本发明一些实施例中，所述谐振腔还包括：第三光栅123，所述第三光栅123具有多个第三栅条，相邻所述第三栅条之间具有第三间隔；所述第三栅条位于所述第一间隔中，所述第三间隔与所述第一间隔和所述第二间隔均不等。
也就是说，所述光纤光栅的同一区域能够刻写多个光栅，能够有效减小级联外腔谐振腔的腔长，减小外腔所占空间，从而降低各光栅温度控制的难度，提高各光栅温度的一致性，而且能够提高封装的小型化程度；此各外腔腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同，能够有效改善其在窄脉冲激光雷达中应用的性能表现。
本发明一些实施例中，所述光纤光栅的各个光栅中，最靠近所述增益芯片110的栅条为初始栅条；最靠近所述增益芯片的间隔为初始间隔；所述第二光栅的初始第二栅条位于所述第一光栅的初始间隔内，即所述谐振腔延伸方向，所述第一光栅121的多个第一栅条和所述第二光栅122的多个第二栅条从一开始即开始交错设置，从而能够最大限度的减小腔长，减小外腔所占空间，还能够最大限度的减小第一光栅121和所述第二光线122分别所构成谐振腔的腔长差距，能够有效提高激光器性能。
此外，本实施例中，所述谐振腔还包括：具有多个第三栅条的第三光栅123，所述第三光栅123的初始第三栅条也位于所述第一光栅的初始间隔内。也就是说，本实施例中，所述第一光栅121、所述第二 光栅122和所述第三光栅123均刻写在同一区域内，从而能够最大限度的减小腔长，减小外腔所占空间，还能够最大限度的减小不同谐振腔的腔长差距，能够有效提高激光器性能。
本发明一些实施例中，所述光纤光栅120为布拉格光纤光栅。
结合参考图3和图4，其中图3示出布拉格光纤光栅的工作原理示意图；图4示出了图1所示谐振腔实施例中光纤光栅刻写过程的示意图。
布拉格光纤光栅(Fiber Bragg Grating，FBG)是在光纤纤芯内形成的空间相位光栅，通过光栅前向传输的纤芯模式与后向传输的纤芯模式之间发生耦合，而使前向传输的纤芯模式的能量传递给后向传输的纤芯模式，形成对入射波的反射。其中，反射波长(即布拉格波长)为λB＝2neffΛ，其中Λ为光栅常数(即光栅周期)，neff为纤芯等效折射率。布拉格光纤光栅可以通过掩模板法、化学腐蚀法、飞秒法等方式进行刻写。
图4所示的是采用掩模板法刻写布拉格光纤光栅的示意图。UV光束照射在相位掩膜板124上，入射光束分为-1级衍射光束和+1级衍射光束，而且-1级衍射光束和+1级衍射光束的光功率相等，两者相互干涉形成明暗相间的条纹。光纤纤芯材料的折射率在受到UV光照射后会随着光强的不同而改变。因此光强变化的干涉光能够通过光强调制光纤纤芯材料的折射率，从而形成布拉格光纤光栅。
掩模板法刻写的布拉格光纤光栅，光栅常数是相位掩模板周期的1/2。因此掩模板法所刻写的光纤光栅的光栅常数与入射光波长无关，只与相位掩模板的周期相关。
所以，图2所示谐振腔实施例中的光纤光栅，是在同一区域分别用不同周期的相位掩模板重复刻写三次，从而在同一区域形成三个具有不同光栅常数的光纤光栅，即同一区域内，不同光栅常数的光栅相互交织，从而能够减少光纤中，形成有光栅的区域的长度。图2所示 实施例中，所述光纤光栅120的第一光栅121、第二光栅122和第三光栅123中，所对应的光栅常数分别为Λ1、Λ2和Λ3，刻写时所采用的相位掩模板周期分别为2Λ1、2Λ2和2Λ3。
继续参考图2，本发明一些实施例中，所述谐振腔还包括：光纤透镜130，所述光纤透镜130位于所述增益芯片110和所述光纤光栅120之间。所述光纤透镜130能够使所述增益芯片110所产生的光线尽可能的耦合进入所述光纤光栅120，从而降低所述谐振腔损耗。
结合参考图5和图6，其中图5示出了图1所示实施例中所述光纤透镜130的结构示意图，图6是图5中箭头A方向的投影示意图。
如图5和图6所示，本发明一些实施例中，所述光纤透镜130具有楔形角；所述光纤透镜130的楔形角的角度与所述增益芯片110发射光线的发散角相对应，也就是说，所述增益芯片110发射光线发散角越大的方向，所述光纤透镜130的楔形角越大；所述增益芯片110发射光线发散角越小的方向，所述光纤透镜130的楔形角越小，从而使增益芯片110所产生光线中尽可能多经所述光纤透镜130耦合入所述光纤光栅120，有效提高耦合效率，增大输出功率。上文中的楔形角即指在给定方向上光纤透镜130所成的张角。
本实施例中，所述增益芯片110为半导体增益芯片，所述半导体增益芯片具有沿快轴方向的发散角和沿慢轴方向的发散角，所述光纤透镜130的楔形角的角度分别与所述沿快轴方向的发散角和所述沿慢轴方向的发散角相对应，即所述光纤透镜130的楔形角的角度大小与沿快轴方向的发散角大小和沿慢轴方向的发散角大小相适应，也就是说，沿快轴方向的发散角大，则光纤透镜130该方向上的楔形角较大；沿慢轴方向的发散角小，则光纤透镜130该方向上的楔形角较小。
具体的，本实施例中，所述光纤透镜130为四方锥形光纤透镜。本发明其他实施例中，所述光纤透镜还可以为单楔形光纤透镜、圆锥形光纤透镜。
需要说明的是，如图5和图6所示，本发明一些实施例中，所述光纤透镜130朝向所述增益芯片110的端面为朝向所述增益芯片110凸出的曲面。朝向所述增益芯片110凸出的曲面，能够对光线起到汇聚作用，从而能够使更多的光线进入所述光纤光栅120内，从而有效提高耦合效率，增大输出功率。光纤透镜130例如是对光纤光栅120所在光纤波导的端面处的纤芯进行加工，例如研磨，而形成的。
需要说明的是，本实施例中，所述谐振腔还包括：第二增透膜，所述第二增透膜位于所述光纤透镜130朝向所述增益芯片的端面。第二增透膜能够有效提高经端面透射入所述光纤透镜130的光线强度，抑制光纤透镜130朝向所述增益芯片110的端面的端面反射，使光线能直接耦合进光纤波导，使光纤波导与所述增益芯片110模式匹配，耦合效率提升(例如能够使耦合小于大于60％)，从而能够有效抑制增益芯片110内腔模式振荡，有利于提高谐振腔稳定性。具体的，所述第二增透膜的反射率小于0.1％。
相应的，本发明还提供一种激光器，所述激光器包括：谐振腔，所述谐振腔为本发明的谐振腔。
参考图7和图8，示出了本发明激光器一实施例的结构示意图；其中图7是激光器实施例的立体示意图，图8是激光器实施例的俯视结构示意图。
所述谐振腔为本发明的谐振腔。具体的，所述谐振腔包括增益芯片210和光纤光栅220以及位于两者之间的光纤透镜230。所述谐振腔的具体技术方案参考前述谐振腔的实施例，本发明在此不再赘述。
所述光纤光栅220在目标波长范围内均具有一定的反射率和带宽，具有与多个(本实施例中为3个)布拉格周期对应的多个反射峰值，从而能够作为外腔激光器的选模元件。所述光纤光栅220中的多个光栅分别与所述增益芯片构成多个外腔谐振腔，当满足激光谐振条件时，多个激光波长同时谐振，输出多波长激光。
具体的，本实施例中，所述光纤光栅220包括3个不同光栅常数且刻写在同一区域的光栅。所述光纤光栅220与所述增益芯片210后端面212(如图8所示)的反射膜(图中未标示)一起分别作为外腔谐振腔的腔镜，所述光纤光栅220还作为外腔选模元件。
所述光纤光栅220在同一区域内刻写3个光栅，且每个光栅的光栅常数均不等，每个光栅的布拉格波长均不等，因此所述光纤光栅220在不同设计波长的位置存在一定带宽的反射峰(对应图9中透射谱的凹陷部分)。当满足激光谐振条件时，多个激光波长同时谐振，输出多波长激光。所述光纤光栅220在同一区域内刻写多个光栅，级联外腔谐振腔腔长短，腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同(即多个波长的开关一致)。
具体的，本实施例中，所述光纤光栅220中光栅区域的长度约为2mm，3个光栅对应的布拉格波长分别为1530nm、1550nm和1570nm，反射率约为20％，反射谱-3dB带宽为0.4nm。
继续参考图7和图8，所述激光器还包括：导热基板240，所述导热基板240表面具有预制焊料区；所述增益芯片210贴片于所述预制焊料区。
所述导热基板240为所述增益芯片210提供正负电极以实现供电。所述导热基板240为高导热基板，即所述导热基板240材料的导热率高、热阻小，能够实现热量的高效散逸，有利于改善所述增益芯片210的散热条件。
本发明一些实施例中，所述导热基板240的材料可以是氮化铝、氧化铍、氧化铝等材料。具体的，本实施例中，所述导热基板240的材料为氮化铝，导热系数为200W/m.k。
所述导热基板240的表面具有预制焊料区(图中未示出)，所述预制焊料区上预制了焊料以实现所述增益芯片210和导热基板240之间的焊接，从而不仅实现导热基板240和所述增益芯片210之间的电性 连接，还实现所述增益芯片210在所述导热基板240之间的固定连接。具体的，本实施例中，所述预制焊料区上预制了Au/Sn焊料。
如图7所示，所述导热基板240上下表面均镀金。所述导热基板240被分为多个区域，不同区域分别用于设置所述所述增益芯片210正负电极的引线焊盘、温度传感器热敏电阻等。其中温度传感器热敏电阻靠近所述谐所述增益芯片210的位置贴片。
继续参考图7和图8，所述激光器还包括：光纤固定块250，所述光纤固定块250表面具有凹槽(图中未标示)；所述光纤光栅220固定于所述凹槽内。
所述光纤固定块250用以支撑固定光纤波导。所述光纤固定块250沿纵向中央部分开设凹槽用以设置所述光纤光栅220。所述光纤固定块250的凹槽内填充导热材料，一方面固定所述光纤光栅220，另一方面加速所述光纤光栅220的热量散逸以改善其散热条件。
因此，本发明一些实施例中，所述光纤固定块250的材料可以设置为氮化铝陶瓷、氧化铝陶瓷、钨铜合金等具有一定硬度且高导热率的材料，以兼顾固定和散热的效果。
继续参考图7和图8，本发明一些实施例中，所述激光器还包括：温度控制器260，所述导热基板240和所述光纤固定块250位于所述温度控制器260表面，以精确控制增益芯片210和光纤光栅220的温度，从而有助于保持外腔腔长稳定，提高激光器的温度稳定性。
需要说明的是，所述激光器还包括：封装管壳270，所述封装管壳270包括壳体、PIN脚、管嘴、壳盖，所述封装管壳270为激光器的各种元器件提供密封稳定可靠的空间环境，并提供电连接的PIN脚。
本发明一些实施例中，所述温度控制器为半导体冷片温度控制器(Thermoelectric Cooler，TEC)。具体的，本实施例中，所述温度控制器260为半导体珀尔帖温度器件，通过回流焊工艺焊接于封装管壳270的底板上，导热基板240和光纤光栅固定块250通过回流焊工艺 焊接在温度控制器260的上表面上，温度控制器260与温度传感器热敏电阻构成温度反馈回路，可以控制所述增益芯片210和所述光纤光栅220的温度，温度稳定性优于0.005℃。
此外，所述封装管壳270上给所述增益芯片210供电的正负电极PIN脚排布间距较小，可优化脉冲工作条件电极之间的寄生电感，提高激光器脉冲工作性能。
相应的，本发明还提供一种激光雷达，所述激光雷达包括：光源，所述光源包括本发明的激光器；探测器，所述探测器的个数与所述激光器中光纤光栅包括的光栅数量相对应。
参考图10，示出了本发明激光雷达一实施例的光路结构示意图。
所述激光器310为本发明的激光器，具体的，所述激光器310的谐振腔包括增益芯片和光纤光栅，所述光纤光栅包括多个光栅。所述激光器310的具体技术方案参考前述激光器的实施例，本发明在此不再赘述。
由于所述激光雷达的光源包括本发明的激光器310，即所述激光器310的谐振腔中的光纤光栅具有多个光栅，能够结合增益芯片形成多个外腔谐振腔，因此所述激光雷达的光源能够实现多波长输出。
如图10所示，本实施例中，所述激光雷达还包括：衍射元件320，所述衍射元件320位于所述光源所产生光线的光路下游。
需要说明的是，本实施例中，所述激光雷达还包括：准直透镜320，所述激光器310所产生的光线经所述准直透镜320准直，投射至所述衍射元件320上；由于所述激光器310是多波长输出，因此所产生的光线中包含有多个波长的光，因此所述衍射元件320能够将多个波长的光分为多个通道输出，从而形成多束探测光以出射进行探测。而且所形成通道数量与激光器产生光线中波长数量相等，即与光纤光栅中的光栅数量相等。
因此，所述激光雷达还包括：探测器(图中未示出)，所述探测器的个数与所述激光器中光纤光栅包括的光栅数量相对应。由于衍射元件320将激光器产生的多波长的光分为多个通道输出以形成多束探测光，因此所述探测器的数量与所述激光器中光纤光栅包括的光栅数量相对应从而实现多束探测光所形成回波的探测。
具体的，本实施例中，所述激光器310能够输出包括1530nm、1550nm和1570nm三个波长的激光。所述衍射元件320为衍射光栅。所述激光器310所产生的激光经准直透镜320准直后，以一定角度(例如近littrow角度)入射至所述衍射光栅；衍射光栅将光束分为3束光输出，分别为1550nm输出光410、1570nm输出光420、1530nm输出光430，也就是说，一个通道经衍射光栅分光后变为3个通道输出，输出的通道数量是原来的3倍。
综上，所述第二光栅的第二栅条位于第一光栅的第一间隔中，而且所述第一间隔与所述第二间隔不等，也就是说，所述第一光栅的光栅常数与所述第二光栅的光栅常数不相等，而且不同光栅常数的光栅相互交织，两个光栅的栅条交错设置，即所述第二光栅和所述第一光栅刻写在所述光纤光栅的同一区域内。当所述第一光栅和所述第二光栅分别作为腔镜与所述增益芯片分别构成外腔谐振腔时，由于刻写在同一区域，因此级联外腔谐振腔腔长短，外腔所占空间小，各光栅温度易控制，温度一致性好，封装易于小型化；而且腔长相近，在注入电流后，各波长光脉冲的出光时刻基本相同，能够有效改善其在窄脉冲激光雷达中应用的性能表现。
虽然本发明披露如上，但本发明并非限定于此。任何本领域技术人员，在不脱离本发明的精神和范围内，均可作各种更动与修改，因此本发明的保护范围应当以权利要求所限定的范围为准。

Claims (19)

  1. 一种谐振腔，其特征在于，包括：
    增益芯片，所述增益芯片具有光线出射的输出面；
    光纤光栅，所述光纤光栅位于所述输出面一侧，所述光纤光栅包括第一光栅，所述第一光栅具有多个第一栅条，相邻所述第一栅条之间具有第一间隔；第二光栅，所述第二光栅具有多个第二栅条，相邻所述第二栅条之间具有第二间隔；
    所述第二栅条位于所述第一间隔中，所述第一间隔与所述第二间隔不等。
  2. 如权利要求1所述的谐振腔，其特征在于，所述光纤光栅为布拉格光纤光栅。
  3. 如权利要求1所述的谐振腔，其特征在于，最靠近所述增益芯片的栅条为初始栅条；最靠近所述增益芯片的间隔为初始间隔；
    所述第二光栅的初始第二栅条位于所述第一光栅的初始间隔内。
  4. 如权利要求1所述的谐振腔，其特征在于，还包括：第三光栅，所述第三光栅具有多个第三栅条，相邻所述第三栅条之间具有第三间隔；
    所述第三栅条位于所述第一间隔中，所述第三间隔与所述第一间隔和所述第二间隔均不等。
  5. 如权利要求1所述的谐振腔，其特征在于，还包括：反射膜，所述反射膜与所述光纤光栅相对设置，位于所述增益芯片远离所述光纤光栅的一侧。
  6. 如权利要求5所述的谐振腔，其特征在于，所述增益芯片具有后端面，所述后端面与所述输出面相背设置；所述反射膜位于所述后端面。
  7. 如权利要求1所述的谐振腔，其特征在于，还包括：第一增透膜，所述第一增透膜位于所述输出面。
  8. 如权利要求1所述的谐振腔，其特征在于，还包括：光纤透镜，所述光纤透镜位于所述增益芯片和所述光纤光栅之间。
  9. 如权利要求8所述的谐振腔，其特征在于，还包括：第二增透膜，所述第二增透膜位于所述光纤透镜朝向所述增益芯片的端面。
  10. 如权利要求8所述的谐振腔，其特征在于，所述光纤透镜具有楔形角；
    所述光纤透镜的楔形角的角度与所述增益芯片发射光线的发散角相对应。
  11. 如权利要求8或10所述的谐振腔，其特征在于，所述增益芯片为半导体增益芯片，其具有沿快轴方向的发散角和沿慢轴方向的发散角，所述光纤透镜的楔形角的角度分别与所述沿快轴方向的发散角和所述沿慢轴方向的发散角相对应。
  12. 如权利要求8或10所述的谐振腔，其特征在于，所述光纤透镜为单楔形光纤透镜、四方锥形光纤透镜和圆锥形光纤透镜中的至少一种。
  13. 如权利要求8所述的谐振腔，其特征在于，所述光纤透镜朝向所述增益芯片的端面为朝向所述增益芯片凸出的曲面。
  14. 一种激光器，其特征在于，包括：
    谐振腔，所述谐振腔为权利要求1～13任一项所述的谐振腔。
  15. 如权利要求14所述的激光器，其特征在于，还包括：导热基板，所述导热基板表面具有预制焊料区；
    所述增益芯片贴片于所述预制焊料区。
  16. 如权利要求14所述的激光器，其特征在于，还包括：光纤固定块， 所述光纤固定块表面具有凹槽；所述光纤光栅固定于所述凹槽内。
  17. 如权利要求14所述的激光器，其特征在于，还包括：温度控制器，所述导热基板和所述光纤固定块位于所述温度控制器表面。
  18. 一种激光雷达，其特征在于，包括：
    光源，所述光源包括权利要求14～17任一项所述的激光器；
    探测器，所述探测器的个数与所述激光器中光纤光栅包括的光栅数量相对应。
  19. 如权利要求18所述的激光雷达，其特征在于，还包括：衍射元件，所述衍射元件位于所述光源所产生光线的光路下游。
PCT/CN2021/110735 2020-12-16 2021-08-05 谐振腔、激光器和激光雷达 WO2022127138A1 (zh)

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