Ultra-narrow linewidth vertical external cavity surface emitting laser

Abstract

The invention belongs to the technical field of laser equipment, and particularly discloses an ultra-narrow linewidth vertical external cavity surface emitting laser which comprises a laser resonance unit and an intracavity control unit, the laser resonance unit is used for generating laser oscillation, and the intracavity control unit is used for carrying out polarization control, mode control, wavelength tuning and linewidth narrowing on fundamental frequency light; the laser resonance unit comprises a pump light emitting system, a gain chip, a folding output mirror and a rear end mirror; the intracavity control unit comprises a beam splitter, a polarization element, a mode control element, a wavelength tuning element, a line width narrowing element and an output coupling mirror; second harmonic self-suppression of a mode control element is adopted to control a laser mode in a resonant cavity to realize single-frequency lasing, so that the design and adjustment difficulty of the mode control element in the resonant cavity of the vertical cavity surface emitting laser can be simplified; the output line width of the laser is narrowed by using the self-injection locking characteristic of the microcavity device in the line width narrowing element, so that the effect of deeply narrowing the laser line width can be achieved, and ultra-narrow line width output is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of laser equipment, and in particular relates to an ultra-narrow linewidth vertical external cavity surface emitting laser. Background Art

[0002] Different from diode lasers and fiber lasers, vertical external cavity surface emitting lasers have unique properties such as high-precision external cavity structure, high intracavity power density, wide wavelength coverage and large tuning range. By placing frequency conversion elements and mode control elements in the resonant cavity, high-power single-frequency lasing with output wavelength covering the ultraviolet to near-infrared band can be achieved. At present, it has become a very potential single-frequency laser platform in the fields of quantum computing, atomic and molecular physics, and high-precision spectroscopy.

[0003] However, in order to obtain single-frequency output, a combination of a birefringent filter and an etalon is usually used as a mode control element. In this way, their thickness needs to be reasonably optimized according to the longitudinal mode spacing of the laser. In addition, in order to obtain higher output power, the etalon is usually designed with low finesse, and the maximum transmittance peaks of the etalon and the birefringent filter also need to be matched, which undoubtedly increases the difficulty of designing and adjusting the mode control element. In terms of narrowing the laser linewidth, since the etalon used is usually designed with low finesse, the output linewidth of the laser is generally in the order of hundreds of kHz to tens of MHz, and it is difficult to achieve narrow linewidth output. Summary of the invention

[0004] The object of the present invention is to provide an ultra-narrow linewidth vertical external cavity surface emitting laser to solve the problems of complex intracavity mode control and limited laser linewidth narrowing in existing vertical external cavity surface emitting lasers.

[0005] In order to achieve the above-mentioned object, the technical solution of the present invention is: an ultra-narrow linewidth vertical external cavity surface emitting laser, comprising a laser resonance unit and an intracavity control unit, wherein the laser resonance unit is used to generate laser oscillation, and the intracavity control unit is used to perform polarization control, mode control, wavelength tuning and linewidth narrowing on fundamental frequency light;

[0006] The laser resonance unit comprises a pump light emission system, a gain chip, a folded output mirror and a rear mirror, wherein the pump light emission system is used to emit pump light to the gain chip; the gain chip, the folded output mirror and the rear mirror constitute a laser resonance cavity; the gain chip is used to absorb the energy of the pump light and generate stimulated radiation, and reflect the stimulated radiation to the folded output mirror; the folded output mirror can reflect the stimulated radiation to the rear mirror and can output ultra-narrow linewidth doubled frequency light; the rear mirror can reflect the stimulated radiation and doubled frequency light to the folded output mirror; the stimulated radiation forms laser oscillation under the action of the laser resonance cavity to generate fundamental frequency light;

[0007] The intracavity control unit includes a beam splitter, a polarization element, a mode control element, a wavelength tuning element, a line width narrowing element and an output coupling mirror; the beam splitter and the polarization element are both located between the gain chip and the folded output mirror, and the polarization element is used to convert the fundamental frequency light into horizontally polarized light; the beam splitter is located on the side close to the gain chip, and the beam splitter is used to reflect a part of the fundamental frequency light generated by the laser resonant cavity to the output coupling mirror, and the output coupling mirror can output the fundamental frequency light to the line width narrowing element; the line width narrowing element adopts a whispering gallery microcavity, and the line width narrowing element is used to narrow the line width and produce The narrowband filtered signal is generated by the output coupling mirror and reflected by the beam splitter, and then received by the gain chip, and participates in the laser oscillation of the laser resonant cavity to form ultra-narrow linewidth doubled frequency light; the mode control element is located between the folding output mirror and the rear end mirror, and the mode control element is used to convert the fundamental frequency light into doubled frequency light and suppress the longitudinal laser mode in the cavity to achieve doubled frequency single frequency lasing; the wavelength tuning element is located on the side of the rear end mirror away from the folding output mirror, and the wavelength tuning element is used to tune the output wavelength of the laser to match the resonant wavelength of the linewidth narrowing element.

[0008] Furthermore, the linewidth narrowing element adopts a discrete structure, and the linewidth narrowing element includes a temperature control element, a discrete coupling device and a crystal microcavity, and the discrete coupling device and the crystal microcavity are installed on the temperature control element; the discrete coupling device is used to couple the single-frequency fundamental frequency light into the crystal microcavity, and the crystal microcavity can resonate with the single-frequency fundamental frequency light and form forward transmission light and reverse transmission light respectively; the reverse transmission light can be circulated and transmitted in the crystal microcavity in the form of total reflection, and finally form a narrow-band filtered signal; the narrow-band filtered signal passes through the discrete coupling device and is transmitted in the opposite direction to the single-frequency fundamental frequency light.

[0009] Furthermore, the linewidth narrowing element adopts an integrated structure, and the linewidth narrowing element includes a temperature control element, a first protective layer, a coupling waveguide and a spherical microcavity, the first protective layer is installed on the temperature control element, and the first protective layer is used to form a coupling environment and to fix the coupling waveguide and the spherical microcavity; the coupling waveguide is used to transmit the single-frequency fundamental frequency light to the spherical microcavity, and the spherical microcavity can resonate with the single-frequency fundamental frequency light and form forward transmission light and reverse transmission light respectively; the reverse transmission light can be circulated and transmitted in the spherical microcavity in the form of total reflection, and finally form a narrow-band filtered signal; the narrow-band filtered signal passes through the coupling waveguide and is transmitted in the opposite direction to the single-frequency fundamental frequency light.

[0010] Furthermore, the gain chip includes a reflective layer, an active layer and a second protective layer arranged in sequence, the reflective layer can reflect stimulated radiation, the active layer can provide light amplification for stimulated radiation; and the second protective layer is used to prevent the gain chip from being oxidized.

[0011] Furthermore, the wavelength tuning element is driven by direct current high voltage and has a telescopic effect.

[0012] Furthermore, the pump light emission system includes a pump source, and the pump source is a semiconductor laser diode whose lasing wavelength is shorter than the wavelength of the fundamental frequency light.

[0013] Furthermore, the pump light emission system further comprises a collimating focusing lens, and the pump light pumped out by the pump source is focused onto the gain chip after passing through the collimating focusing lens.

[0014] Furthermore, the polarization element is capable of being rotated.

[0015] Furthermore, the polarizing element is placed at a Brewster angle.

[0016] Furthermore, the beam splitter is coated with a splitting film layer for splitting the wavelength of the fundamental frequency light; the folding output mirror is coated with a first high-reflection film layer for reflecting the wavelength of the fundamental frequency light and a first high-transmission film layer for transmitting the wavelength of the doubled frequency light; the rear end mirror is coated with a second high-reflection film layer for reflecting the wavelength of the fundamental frequency light and the wavelength of the doubled frequency light; and the mode control element is coated with a second high-transmission film layer for transmitting the wavelength of the fundamental frequency light and the wavelength of the doubled frequency light.

[0017] The working principle of this technical solution is:

[0018] Under the action of the pump source, the gain chip generates stimulated radiation, which forms laser oscillation and generates fundamental frequency light under the action of the laser resonant cavity composed of the gain chip, folded output mirror and rear mirror. The frequency conversion and second harmonic self-suppression characteristics of the mode control element are used to realize the conversion between fundamental frequency light and doubled frequency light, as well as the suppression of the longitudinal laser mode in the cavity, to obtain doubled frequency single-frequency lasing; then, the polarization element and wavelength tuning element are used to realize the control of the laser output polarization state and the tuning of the laser wavelength, so as to achieve the matching of the laser wavelength with the resonant wavelength in the line width narrowing element; finally, the narrowband filtering signal generated in the line width narrowing element is used to generate the self-injection locking characteristic to deeply narrow the output line width of the laser.

[0019] The working principle of the discrete linewidth narrowing element is as follows: the single-frequency fundamental frequency light generated by the laser resonance unit enters the crystal microcavity in the form of an evanescent wave through the discrete coupling device after passing through the output coupling mirror. Forward and reverse transmission light are formed in the crystal microcavity respectively. Subsequently, the two beams of light are circulated in the crystal microcavity in the form of total reflection. Among them, the reverse transmission light is used to form a narrowband filtering signal with narrowed linewidth. The narrowband filtering signal has a narrow linewidth and matches the wavelength of the single-frequency fundamental frequency light. Finally, the narrowband filtering signal is transmitted in the opposite direction of the single-frequency fundamental frequency light through the discrete coupling device. After coupling by the output coupling mirror and reflection by the beam splitter, it will be received by the gain chip and participate in the laser oscillation between the gain chip, the folded output mirror and the back-end mirror.

[0020] The working principle of the integrated linewidth narrowing element is as follows: the single-frequency fundamental frequency light generated by the laser resonance unit enters the spherical microcavity in the form of an evanescent wave through the coupling waveguide after passing through the output coupling mirror. Forward and reverse transmission light are formed in the spherical microcavity respectively. Subsequently, the two beams of light are circulated in the spherical microcavity in the form of total reflection. Among them, the reverse transmission light is used to form a narrowband filtering signal with narrowed linewidth. The narrowband filtering signal has a narrow linewidth and matches the wavelength of the single-frequency fundamental frequency light. Finally, the narrowband filtering signal is transmitted through the coupling waveguide in the opposite direction of the single-frequency fundamental frequency light. After coupling by the output coupling mirror and reflection by the beam splitter, it will be received by the gain chip and participate in the laser oscillation between the gain chip, the folded output mirror and the back-end mirror.

[0021] The beneficial effects of this technical solution are: using the second harmonic self-suppression of the mode control element to control the laser mode in the resonant cavity to achieve single-frequency lasing can simplify the design and adjustment difficulty of the mode control element in the resonant cavity of the vertical cavity surface emitting laser; using the self-injection locking characteristics of the microcavity device in the line width narrowing element to narrow the output line width of the laser, it can play a role in deeply narrowing the laser line width and achieve ultra-narrow line width output. The present invention can solve the problems of complex intracavity mode control and limited laser line width narrowing of existing vertical external cavity surface emitting lasers, and is conducive to promoting the application of narrow line width vertical external cavity surface emitting lasers in technical fields such as quantum computing, atomic and molecular physics, and high-precision spectroscopy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the ultra-narrow linewidth vertical external cavity surface emitting laser of the present invention;

[0023] Figure 2 for Figure 1 Schematic diagram of the structure of the medium gain chip;

[0024] Figure 3 for Figure 1 A schematic diagram of the structure of a line width narrowing element of a discrete structure;

[0025] Figure 4for Figure 1 A schematic diagram of the structure of the line width narrowing element of the integrated structure;

[0026] Figure 5 This is a diagram showing the evolution of the relationship between the theoretical simulation of the laser line width and the feedback amount of the microcavity;

[0027] Figure 6 This is a diagram showing the evolution of the relationship between the theoretical simulation of the laser line width and the Q value of the microcavity. DETAILED DESCRIPTION

[0028] The following is further described in detail through specific implementation methods:

[0029] The figure marks in the drawings of the specification include: pump source 1, collimating focusing lens 2, gain chip 3, heat sink 4, beam splitter 5, polarization element 6, folded output mirror 7, mode control element 8, back-end mirror 9, wavelength tuning element 10, output coupling mirror 11, linewidth narrowing element 12, narrowband filtering signal 13, ultra-narrow linewidth doubled frequency light 14, reflection layer 15, active layer 16, second protective layer 17, temperature control element 18, discrete coupling device 19, crystal microcavity 20, single-frequency fundamental frequency light 21, forward transmission light 22, reverse transmission light 23, first protective layer 24, coupling waveguide 25, spherical microcavity 26.

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The embodiment is basically as shown in the attached Figure 1 As shown: An ultra-narrow linewidth vertical external cavity surface emitting laser includes a laser resonance unit and an intracavity control unit. The laser resonance unit is used to generate laser oscillation, and the intracavity control unit is used to perform polarization control, mode control, wavelength tuning and linewidth narrowing on the fundamental frequency light, thereby obtaining an ultra-narrow linewidth laser output.

[0032] The laser resonance unit includes a pump light emission system, a gain chip 3, a folded output mirror 7 and a rear mirror 9. The pump light emission system is used to emit pump light to the gain chip 3. The pump light emission system includes a pump source 1 and two sets of collimating and focusing lenses 2. The pump source 1 is a semiconductor laser diode whose lasing wavelength is smaller than the wavelength of the fundamental frequency light. The pump light pumped by the pump source 1 is focused on the gain chip 3 after passing through the collimating and focusing lens 2.

[0033] The gain chip 3, the folded output mirror 7 and the rear mirror 9 constitute a laser resonant cavity; the gain chip 3 is used to absorb the energy of the pump light and generate stimulated radiation, and reflect the stimulated radiation to the folded output mirror 7. The stimulated radiation forms laser oscillation under the action of the laser resonant cavity to generate fundamental frequency light.

[0034] The gain chip 3 is mounted on a heat sink 4, which is used to dissipate heat from the gain chip 3. The heat sink 4 is made of a diamond sheet. Figure 2 As shown, the gain chip 3 includes a reflective layer 15, an active layer 16 and a second protective layer 17 arranged in sequence. The reflective layer 15 is a high reflective layer, and the reflective layer 15 can reflect stimulated radiation. The active layer 16 is a semiconductor material, adopts a multi-quantum well design, and the active layer 16 can provide light amplification for stimulated radiation. The second protective layer 17 is used to prevent the gain chip 3 from being oxidized.

[0035] The folding output mirror 7 adopts a plano-concave mirror, which can reflect the stimulated radiation to the rear mirror 9 and can output the ultra-narrow linewidth doubled frequency light 14. The folding output mirror 7 is coated with a first high-reflection film layer that reflects the wavelength of the fundamental frequency light and a first high-transmission film layer that transmits the wavelength of the doubled frequency light. The rear mirror 9 can reflect the stimulated radiation and the doubled frequency light to the folding output mirror 7, and the rear mirror 9 is coated with a second high-reflection film layer that reflects the wavelength of the fundamental frequency light and the wavelength of the doubled frequency light.

[0036] The intracavity control unit includes a beam splitter 5, a polarization element 6, a mode control element 8, a wavelength tuning element 10, a line width narrowing element 12 and an output coupling mirror 11; the beam splitter 5 and the polarization element 6 are both located between the gain chip 3 and the folded output mirror 7, the polarization element 6 is placed at the Brewster angle, and the polarization element 6 is used to convert the fundamental frequency light into horizontally polarized light; the polarization element 6 can rotate with the normal line of the plane in which it is located as the axis, and can play a role in coarse tuning the output wavelength of the fundamental frequency light. The beam splitter 5 is located on the side close to the gain chip 3, and the beam splitter 5 is used to reflect a part of the fundamental frequency light generated by the laser resonant cavity to the output coupling mirror 11, and the other part is used to maintain the laser oscillation between the gain chip 3, the folded output mirror 7 and the rear end mirror 9. The beam splitter 5 is coated with a spectroscopic film layer for splitting the wavelength of the fundamental frequency light. The output coupling mirror 11 can output the fundamental frequency light to the line width narrowing element 12. The linewidth narrowing element 12 adopts a whispering gallery microcavity, and the linewidth narrowing element 12 is used to narrow the linewidth and generate a narrowband filter signal 13; the narrowband filter signal 13 is coupled by the output coupling mirror 11 and reflected by the beam splitter 5, and then received by the gain chip 3, and participates in the laser oscillation of the laser resonant cavity to form an ultra-narrow linewidth frequency-doubled light 14.

[0037] The mode control element 8 is located between the folding output mirror 7 and the rear mirror 9. The mode control element 8 is used to convert the fundamental frequency light into the double frequency light and suppress the longitudinal laser mode in the cavity to achieve double frequency single frequency lasing. The mode control element 8 is coated with a second high transmission film layer that transmits the wavelength of the fundamental frequency light and the double frequency light. The wavelength tuning element 10 is located on the side of the rear mirror 9 away from the folding output mirror 7. The wavelength tuning element 10 is used to precisely tune the output wavelength of the laser to match the resonant wavelength of the line width narrowing element 12. The wavelength tuning element 10 is driven by DC high voltage and has a telescopic effect.

[0038] The line width narrowing element 12 has a specific resonant wavelength and has two typical structures, namely a discrete structure and an integrated structure. Figure 3 As shown, the discrete structure line width narrowing element 12 includes a temperature control element 18, a discrete coupling device 19 and a crystal microcavity 20, and the discrete coupling device 19 and the crystal microcavity 20 are mounted on the temperature control element 18; the discrete coupling device 19 is used to couple the single-frequency fundamental frequency light 21 into the crystal microcavity 20. The crystal microcavity 20 is made of a crystal material, and the crystal microcavity 20 can resonate with the single-frequency fundamental frequency light 21, and form a forward transmission light 22 and a reverse transmission light 23 respectively; the reverse transmission light 23 can be circulated and transmitted in the crystal microcavity 20 in the form of total reflection, and finally form a narrowband filter signal 13; the narrowband filter signal 13 passes through the discrete coupling device 19 and is transmitted in the opposite direction of the single-frequency fundamental frequency light 21.

[0039] like Figure 4 As shown, the linewidth narrowing element 12 of the integrated structure includes a temperature control element 18, a first protective layer 24 with a low refractive index, a coupling waveguide 25 and a spherical microcavity 26. The first protective layer 24 is installed on the temperature control element 18. The first protective layer 24 is used to form a coupling environment with a refractive index close to that of air, so as to reduce the coupling loss and obtain a higher Q value whispering gallery microcavity. The first protective layer 24 is also used to fix the coupling waveguide 25 and the spherical microcavity 26. The coupling waveguide 25 is used to transmit the single-frequency fundamental frequency light 21 to the spherical microcavity 26, and the spherical microcavity 26 is formed by burning the tail end of the optical fiber. The spherical microcavity 26 can resonate with the single-frequency fundamental frequency light 21, and form a forward transmission light 22 and a reverse transmission light 23 respectively; the reverse transmission light 23 can be circulated and transmitted in the spherical microcavity 26 in the form of total reflection, and finally form a narrowband filter signal 13. The narrowband filter signal 13 passes through the coupling waveguide 25 and is transmitted in the opposite direction to the single-frequency fundamental frequency light 21.

[0040] The specific implementation process is as follows:

[0041] Under the action of the pump source 1, the gain chip 3 generates stimulated radiation, and the stimulated radiation forms laser oscillation under the action of the laser resonant cavity composed of the gain chip 3, the folded output mirror 7 and the rear mirror 9, generating fundamental frequency light. The frequency conversion and second harmonic self-suppression characteristics of the mode control element 8 are used to realize the conversion between fundamental frequency light and frequency-doubled light, as well as the suppression of the longitudinal laser mode in the cavity, to obtain frequency-doubled single-frequency lasing; then, the polarization element 6 and the wavelength tuning element 10 are used to realize the control of the laser output polarization state and the tuning of the laser wavelength, so as to achieve the matching of the laser wavelength with the resonant wavelength in the line width narrowing element 12; finally, the narrowband filtering signal 13 generated in the line width narrowing element 12 is used to generate the self-injection locking characteristic to deeply narrow the output line width of the laser.

[0042] The working principle of the discrete linewidth narrowing element 12 is as follows: the single-frequency fundamental frequency light 21 generated by the laser resonance unit enters the crystal microcavity 20 in the form of an evanescent wave through the discrete coupling device 19 after passing through the output coupling mirror 11. Forward transmission light 22 and reverse transmission light 23 are formed in the crystal microcavity 20 respectively. Subsequently, the two beams of light are cyclically transmitted in the crystal microcavity 20 in the form of total reflection. Among them, the reverse transmission light 23 is used to form a narrow-band filter signal 13 with narrowed linewidth. The narrowband filter signal 13 has a narrow linewidth and matches the wavelength of the single-frequency fundamental frequency light 21. Finally, the narrowband filter signal 13 is transmitted in the opposite direction of the single-frequency fundamental frequency light 21 through the discrete coupling device 19, and after coupling by the output coupling mirror 11 and reflection by the beam splitter 5, it will be received by the gain chip 3, and participate in the laser oscillation between the gain chip 3, the folded output mirror 7 and the rear mirror 9, and finally form an ultra-narrow linewidth doubled frequency light 14 output.

[0043] The working principle of the integrated linewidth narrowing element 12 is as follows: the single-frequency fundamental frequency light 21 generated by the laser resonance unit enters the spherical microcavity 26 in the form of an evanescent wave through the coupling waveguide 25 after passing through the output coupling mirror 11. Forward transmission light 22 and reverse transmission light 23 are formed in the spherical microcavity 26 respectively. Subsequently, the two beams of light are circulated in the spherical microcavity 26 in the form of total reflection. Among them, the reverse transmission light 23 is used to form a narrow-band filter signal 13 with narrowed linewidth. The narrowband filter signal 13 has a narrow linewidth and matches the wavelength of the single-frequency fundamental frequency light 21. Finally, the narrowband filter signal 13 is transmitted in the opposite direction of the single-frequency fundamental frequency light 21 through the coupling waveguide 25. After coupling by the output coupling mirror 11 and reflection by the beam splitter 5, it will be received by the gain chip 3 and participate in the laser oscillation between the gain chip 3, the folded output mirror 7 and the rear mirror 9, and finally form an ultra-narrow linewidth doubled frequency light 14 output.

[0044] The following is a specific example to illustrate:

[0045] The reflective layer 15 in the gain chip 3 has 30 pairs of GaAs / AlAs layers, providing a reflectivity of up to 99.99% for fundamental frequency light with a wavelength of 1020nm. The active layer 16 is composed of In0.15GaAs / GaAs / GaAsP0.05 multiple quantum wells, the fluorescence peak wavelength of the quantum well is 1020nm, and stimulated radiation with a lasing wavelength of 1020nm can be generated. The second protective layer 17 is a GaAs layer, which can prevent the gain chip 3 from being oxidized.

[0046] The pump source 1 is a semiconductor laser diode with an operating wavelength of 808nm. The beam splitter 5 is a plane reflector, and the splitting ratio of its beam splitting film layer at a wavelength of 1020nm is 9:1. The folding output mirror 7 is a plano-concave reflector with a curvature radius of 100mm. The concave reflective surface is coated with a high reflectivity film layer (first high reflective film layer) and a high transmittance film layer (first high transmittance film layer) at wavelengths of 1020nm and 510nm, respectively, and the plane will also be coated with a film layer with high transmittance at a wavelength of 510nm (first high transmittance film layer), which is used for folding the optical path of the arm where the gain chip 3 and the rear mirror 9 are located, and the output of the doubled frequency light. The rear mirror 9 is a plano-concave reflector with a curvature radius of 50mm, and its concave surface is coated with a second high reflective film layer with high reflectivity at wavelengths of 1020nm and 510nm.

[0047] The polarizing element 6 is a birefringent filter with a thickness of 1 mm. When it is placed at the Brewster angle, the stimulated radiation of the laser can be horizontally polarized. In addition, rotating the polarizing element 6 with the normal line of the plane where the polarizing element 6 is located as the axis can roughly tune the wavelength of the fundamental frequency resonant light. The mode control element 8 is a 3*3*15 mm 3 The LBO frequency doubling crystal is located between the rear mirror 9 and the folded output mirror 7. The second harmonic self-suppression effect of the mode control element 8 can be used to control the laser mode in the laser resonant cavity to achieve single-frequency lasing. When the phase matching is met, the mode control element 8 will also realize the conversion of the fundamental frequency light to the doubled frequency light. The wavelength tuning element 10 is a piezoelectric ceramic tube of 12mm*10mm*12mm (outer diameter*inner diameter*height), driven by DC high voltage, with a telescopic effect, which is used to precisely tune the output wavelength of the laser to match the resonant wavelength of the line width narrowing element 12.

[0048] The linewidth narrowing element 12 has a specific resonant wavelength and is composed of a whispering gallery microcavity device with an integrated temperature control unit, which includes two structures: discrete and integrated. Among them, in the discrete structure, the temperature control element 18 is a TEC temperature control module with a control accuracy of 0.01°C, the discrete coupling device 19 is a right-angle prism made of glass material, which is mainly used for coupling between single-frequency fundamental frequency light and the whispering gallery microcavity, and the crystal microcavity 20 is a calcium fluoride or magnesium fluoride microcavity with a high Q value. The single-frequency fundamental frequency light 21 is coupled into the crystal microcavity 20 in the form of evanescent waves, and forms forward transmission light 22 and reverse transmission light 23 respectively. The reverse transmission light 23 can be circulated in the crystal microcavity 20 in the form of total reflection, and finally forms a narrow-band filter signal 13 with a line width of MHz or 100kHz. The signal is transmitted in the opposite direction of the single-frequency fundamental frequency light 21 through the discrete coupling device 19, coupled by the output coupling mirror 11, and reflected by the beam splitter 5. It will be received by the gain chip 3 and participate in the laser oscillation between the gain chip 3, the folded output mirror 7 and the rear mirror 9. By tuning the wavelength of the laser or changing the temperature of the line width narrowing element 12, the narrow-band filter signal 13 is matched with the wavelength of the single-frequency fundamental frequency light 21, and finally forms an ultra-narrow line width doubled frequency light 14 output.

[0049] The evolution relationship between the laser line width and the feedback amount of the microcavity is as follows: Figure 5 As shown, for a free-running linewidth of 100kHz, the Q value and linewidth enhancement factor are 10 6 and 3 lasers, using a Q value of 10 9 The whispering gallery microcavity is used as a linewidth narrowing element 12. When the feedback amount of the microcavity increases to -20dB, the linewidth of the laser can be narrowed from 100kHz to the Hz level.

[0050] The evolution relationship between the laser line width and the Q value of the microcavity is as follows: Figure 6 As shown, for a free-running linewidth of 100kHz, the Q value and linewidth enhancement factor are 10 6 and 3, using a whispering gallery microcavity with a feedback of -21 dB as the linewidth narrowing element 12. When the Q value of the microcavity increases to 10 9 The line width of the laser can be narrowed from 100 kHz to tens of Hz.

[0051] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0052] The above is only an embodiment of the present invention. The common sense such as the known specific structure and characteristics in the scheme is not described in detail here. The ordinary technicians in the relevant field know all the common technical knowledge in the technical field of the invention before the application date or priority date, can obtain all the existing technologies in the field, and have the ability to apply the conventional experimental means before that date. The ordinary technicians in the relevant field can improve and implement this scheme in combination with their own abilities under the enlightenment given by this application. Some typical known structures or known methods should not become obstacles for ordinary technicians in the relevant field to implement this application. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent. The protection scope required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. Ultra-narrow linewidth vertical external cavity surface emitting laser, characterized by: It includes a laser resonance unit and an intracavity control unit, wherein the laser resonance unit is used to generate laser oscillation, and the intracavity control unit is used to perform polarization control, mode control, wavelength tuning and line width narrowing on the fundamental frequency light; The laser resonance unit comprises a pump light emission system, a gain chip (3), a folded output mirror (7) and a rear mirror (9); the pump light emission system is used to emit pump light to the gain chip (3); the gain chip (3), the folded output mirror (7) and the rear mirror (9) constitute a laser resonance cavity; the gain chip (3) is used to absorb the energy of the pump light and generate stimulated radiation, and reflect the stimulated radiation to the folded output mirror (7); the folded output mirror (7) can reflect the stimulated radiation to the rear mirror (9) and can output ultra-narrow linewidth doubled frequency light (14); the rear mirror (9) can reflect the stimulated radiation and the doubled frequency light to the folded output mirror (7); the stimulated radiation forms laser oscillation under the action of the laser resonance cavity to generate fundamental frequency light; The intracavity control unit comprises a beam splitter (5), a polarization element (6), a mode control element (8), a wavelength tuning element (10), a line width narrowing element (12) and an output coupling mirror (11); the beam splitter (5) and the polarization element (6) are both located between the gain chip (3) and the folded output mirror (7); the polarization element (6) is used to convert fundamental frequency light into horizontally polarized light; the beam splitter (5) is located on a side close to the gain chip (3); the beam splitter (5) is used to reflect a part of the fundamental frequency light generated by the laser resonant cavity to the output coupling mirror (11); the output coupling mirror (11) can output the fundamental frequency light to the line width narrowing element (12); the line width narrowing element (12) adopts a whispering gallery microcavity; the line width narrowing element (12) is used to The line width is narrowed and a narrowband filter signal (13) is generated; after the narrowband filter signal (13) is coupled by the output coupling mirror (11) and reflected by the beam splitter (5), it is received by the gain chip (3) and participates in the laser oscillation of the laser resonant cavity to form ultra-narrow line width doubled frequency light (14); the mode control element (8) is located between the folding output mirror (7) and the rear end mirror (9), and the mode control element (8) is used to convert the fundamental frequency light into doubled frequency light and suppress the longitudinal laser mode in the cavity to achieve doubled frequency single frequency lasing; the wavelength tuning element (10) is located on the side of the rear end mirror (9) away from the folding output mirror (7), and the wavelength tuning element (10) is used to tune the output wavelength of the laser so as to match the resonant wavelength of the line width narrowing element (12).

2. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The linewidth narrowing element (12) adopts a discrete structure, and comprises a temperature control element (18), a discrete coupling device (19) and a crystal microcavity (20), wherein the discrete coupling device (19) and the crystal microcavity (20) are mounted on the temperature control element (18); the discrete coupling device (19) is used to couple the single-frequency fundamental frequency light (21) into the crystal microcavity (20), and the crystal microcavity (20) can resonate with the single-frequency fundamental frequency light (21) and form forward transmission light (22) and reverse transmission light (23) respectively; the reverse transmission light (23) can be circulated and transmitted in the crystal microcavity (20) in the form of total reflection, and finally forms a narrowband filter signal (13); the narrowband filter signal (13) passes through the discrete coupling device (19) and is transmitted in the opposite direction to the single-frequency fundamental frequency light (21).

3. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The line width narrowing element (12) adopts an integrated structure, and comprises a temperature control element (18), a first protective layer (24), a coupling waveguide (25) and a spherical microcavity (26); the first protective layer (24) is mounted on the temperature control element (18); the first protective layer (24) is used to form a coupling environment and to fix the coupling waveguide (25) and the spherical microcavity (26); the coupling waveguide (25) is used to transmit the single-frequency fundamental frequency light ( 21) is transmitted to a spherical microcavity (26), the spherical microcavity (26) can resonate with the single-frequency fundamental frequency light (21), and form forward transmission light (22) and reverse transmission light (23) respectively; the reverse transmission light (23) can be circulated and transmitted in the spherical microcavity (26) in the form of total reflection, and finally form a narrow-band filter signal (13); the narrow-band filter signal (13) passes through the coupling waveguide (25) and is transmitted in the opposite direction to the single-frequency fundamental frequency light (21).

4. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The gain chip (3) comprises a reflective layer (15), an active layer (16) and a second protective layer (17) which are arranged in sequence; the reflective layer (15) is capable of reflecting stimulated radiation; the active layer (16) is capable of providing light amplification for stimulated radiation; and the second protective layer (17) is used to prevent the gain chip (3) from being oxidized.

5. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The wavelength tuning element (10) is driven by direct current high voltage and has a telescopic effect.

6. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The pump light emission system comprises a pump source (1), wherein the pump source (1) is a semiconductor laser diode whose lasing wavelength is shorter than the wavelength of the fundamental frequency light.

7. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 6, characterized in that: The pump light emission system further comprises a collimating focusing lens (2), and the pump light pumped out by the pump source (1) passes through the collimating focusing lens (2) and is focused onto the gain chip (3).

8. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The polarization element (6) is capable of rotating.

9. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 8, characterized in that: The polarizing element (6) is placed at the Brewster angle.

10. The ultra-narrow linewidth vertical external cavity surface emitting laser according to claim 1, characterized in that: The beam splitter (5) is coated with a splitting film layer for splitting the wavelength of the fundamental frequency light; the folding output mirror (7) is coated with a first high reflection film layer for reflecting the wavelength of the fundamental frequency light and a first high transmission film layer for transmitting the wavelength of the doubled frequency light; the rear end mirror (9) is coated with a second high reflection film layer for reflecting the wavelength of the fundamental frequency light and the wavelength of the doubled frequency light; and the mode control element (8) is coated with a second high transmission film layer for transmitting the wavelength of the fundamental frequency light and the wavelength of the doubled frequency light.

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