Ultra-narrow linewidth vertical external cavity surface-emitting laser

Abstract

This invention belongs to the field of laser equipment technology, specifically disclosing an ultra-narrow linewidth vertical external cavity surface-emitting laser (VECS), including a laser resonator unit and an intracavity control unit. The laser resonator 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 of the fundamental frequency light. The laser resonator unit includes a pump light emission system, a gain chip, a folded output mirror, and a back-end mirror. The intracavity control unit includes a beam splitter, a polarization element, a mode control element, a wavelength tuning element, a linewidth narrowing element, and an output coupling mirror. The second harmonic self-suppression of the mode control element is used to control the laser mode in the resonant cavity to achieve single-frequency lasing, which simplifies the design and adjustment difficulty of the mode control element in the resonant cavity of the VECS. The self-injection locking characteristic of the microcavity device in the linewidth narrowing element is used to narrow the output linewidth of the laser, which can achieve a deep narrowing of the laser linewidth and realize ultra-narrow linewidth output.

Description

Technical Field

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

[0002] Unlike diode lasers and fiber lasers, vertical-cavity surface-emitting lasers (VCSELs) possess unique properties such as highly precise external cavity structure, high intracavity power density, wide wavelength coverage, and a large tuning range. By placing frequency conversion and mode control elements within the resonant cavity, high-power single-frequency lasing covering the ultraviolet to near-infrared wavelength range can be achieved. Currently, it has become a promising single-frequency laser platform in fields such as quantum computing, atomic and molecular physics, and high-precision spectroscopy.

[0003] However, to achieve single-frequency output, a combination of a birefringent filter and an etalon is typically used as the mode control element. In this approach, their thicknesses need to be optimized based on the laser's longitudinal mode spacing. Furthermore, to obtain higher output power, the etalon is usually designed with low precision, and the peak maximum transmittance of the etalon and the birefringent filter also needs to be matched, which undoubtedly increases the difficulty of designing and adjusting the mode control element. Regarding narrowing the laser linewidth, due to the typically low-precision design of the etalon, the laser's output linewidth is generally in the range of hundreds of kHz to tens of MHz, making it difficult to achieve narrow linewidth output. Summary of the Invention

[0004] The purpose of this invention is to provide an ultra-narrow linewidth vertical external cavity surface-emitting laser (VECS) to solve the problems of complex intracavity mode control and limited laser linewidth in existing VECS.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: an ultra-narrow linewidth vertical external cavity surface-emitting laser, comprising a laser resonant unit and an intracavity control unit, wherein the laser resonant 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 of the fundamental frequency light;

[0006] The laser resonant unit includes a pump light emitting system, a gain chip, a folded output mirror, and a back-end mirror. The pump light emitting system emits pump light to the gain chip. The gain chip, folded output mirror, and back-end mirror constitute a laser resonant cavity. The gain chip absorbs the energy of the pump light and generates stimulated emission, reflecting the stimulated emission to the folded output mirror. The folded output mirror reflects the stimulated emission to the back-end mirror and outputs ultra-narrow linewidth frequency-doubled light. The back-end mirror reflects the stimulated emission and frequency-doubled light to the folded output mirror. The stimulated emission forms laser oscillation under the action of the laser resonant cavity, generating fundamental frequency light.

[0007] The intracavity control unit includes a beam splitter, a polarization element, a mode control element, a wavelength tuning element, a linewidth narrowing element, and an output coupling mirror. The beam splitter and polarization element are both located between the gain chip and the folded output mirror. The polarization element converts the fundamental frequency light into horizontally polarized light. The beam splitter is located near the gain chip and reflects a portion of the fundamental frequency light generated by the laser resonant cavity to the output coupling mirror. The output coupling mirror outputs the fundamental frequency light to the linewidth narrowing element. The linewidth narrowing element employs a whispering-gallery microcavity and is used to narrow the linewidth and produce... A narrowband filtered signal is generated; after being coupled by the output coupling mirror and reflected by the beam splitter, the narrowband filtered signal is received by the gain chip and participates in the laser oscillation of the laser resonant cavity to form ultra-narrow linewidth frequency-doubled light; the mode control element is located between the folded output mirror and the rear mirror, and the mode control element is used to convert the fundamental frequency light into frequency-doubled light and suppress the longitudinal laser mode in the cavity to realize frequency-doubled single-frequency lasing; the wavelength tuning element is located on the side of the rear mirror away from the folded 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, comprising a temperature control element, a discrete coupling device, and a crystal microcavity. The discrete coupling device and the crystal microcavity are mounted on the temperature control element. The discrete coupling device is used to couple single-frequency fundamental light into the crystal microcavity. The crystal microcavity can resonate with the single-frequency fundamental light, forming forward-propagating light and reverse-propagating light, respectively. The reverse-propagating light can circulate within the crystal microcavity in the form of total internal reflection, ultimately forming a narrowband filtered signal. The narrowband filtered signal passes through the discrete coupling device and propagates in the opposite direction to the single-frequency fundamental light.

[0009] Furthermore, the linewidth narrowing element adopts an integrated structure, comprising a temperature control element, a first protective layer, a coupling waveguide, and a spherical microcavity. The first protective layer is mounted on the temperature control element and serves to form a coupling environment and to fix the coupling waveguide and the spherical microcavity. The coupling waveguide transmits single-frequency fundamental light to the spherical microcavity, which resonates with the single-frequency fundamental light to form forward and reverse transmission light, respectively. The reverse transmission light can circulate within the spherical microcavity in the form of total internal reflection, ultimately forming a narrowband filtered signal. The narrowband filtered signal passes through the coupling waveguide and propagates in the opposite direction to the single-frequency fundamental light.

[0010] Furthermore, the gain chip includes a reflective layer, an active layer, and a second protective layer arranged sequentially. The reflective layer can reflect stimulated emission, and the active layer can provide optical amplification for stimulated emission. The second protective layer is used to prevent oxidation of the gain chip.

[0011] Furthermore, the wavelength tuning element is driven by a DC high voltage and has a stretching effect.

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

[0013] Furthermore, the pump light emission system also includes a collimating and focusing lens, through which the pump light pumped by the pump source is focused onto the gain chip.

[0014] Furthermore, the polarizing element is capable of rotation.

[0015] Furthermore, the polarization element is positioned at Brewster angle.

[0016] Furthermore, the beam splitter is coated with a beam-splitting film layer that splits the fundamental frequency wavelength; the folded output mirror is coated with a first high-reflectivity film layer that reflects the fundamental frequency wavelength and a first high-transmission film layer that transmits the second-order frequency wavelength; the rear end mirror is coated with a second high-reflectivity film layer that reflects both the fundamental frequency wavelength and the second-order frequency wavelength; and the mode control element is coated with a second high-transmission film layer that transmits both the fundamental frequency wavelength and the second-order frequency wavelength.

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

[0018] Under the action of the pump source, the gain chip generates stimulated emission. This stimulated emission, under the action of the laser resonant cavity formed by the gain chip, the folded output mirror, and the rear mirror, forms laser oscillations, generating fundamental frequency light. By employing the frequency conversion and second harmonic self-suppression characteristics of the mode control element, the conversion between the fundamental frequency light and the frequency-doubled light is achieved, as well as the suppression of the longitudinal laser mode within the cavity, resulting in frequency-doubled single-frequency lasing. Then, polarization elements and wavelength tuning elements are used to control the laser output polarization state and tune the laser wavelength, thereby achieving laser wavelength matching with the resonant wavelength in the linewidth narrowing element. Finally, the narrowband filter signal generated in the linewidth narrowing element is used to generate a self-injection-locked characteristic deep narrowing laser output linewidth.

[0019] The working principle of the discrete linewidth narrowing element is as follows: The single-frequency fundamental light generated by the laser resonator unit enters the crystal microcavity in the form of an evanescent wave after passing through the output coupling mirror and discrete coupling devices. Forward and reverse propagation beams are formed in the crystal microcavity. Subsequently, the two beams circulate within the crystal microcavity via total internal reflection. The reverse propagation beam is used to form a narrowband filter signal for linewidth narrowing. This narrowband filter signal has a narrow linewidth and matches the wavelength of the single-frequency fundamental light. Finally, this narrowband filter signal is propagated in the opposite direction to the single-frequency fundamental light through discrete coupling devices. After coupling by the output coupling mirror and reflection by the beam splitter, it is received by the gain chip and participates 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 light generated by the laser resonator unit enters the spherical microcavity in the form of an evanescent wave through the output coupling mirror and the coupling waveguide. Forward and reverse propagation beams are formed in the spherical microcavity. Subsequently, the two beams circulate within the spherical microcavity via total internal reflection. The reverse propagation beam is used to form a narrowband filter signal for linewidth narrowing. This narrowband filter signal has a narrow linewidth and matches the wavelength of the single-frequency fundamental light. Finally, this narrowband filter signal propagates in the opposite direction to the single-frequency fundamental light through the coupling waveguide. After coupling by the output coupling mirror and reflection by the beam splitter, it is received by the gain chip and participates 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 as follows: Using the second harmonic self-suppression of the mode control element to control the laser mode within the resonant cavity to achieve single-frequency lasing simplifies the design and adjustment of the mode control element within the resonant cavity of the vertical-cavity surface-emitting laser (VCSEL); utilizing the self-injection locking characteristic of the microcavity device in the linewidth narrowing element to narrow the laser's output linewidth achieves a significant reduction in laser linewidth, resulting in ultra-narrow linewidth output. This invention solves the problems of complex intracavity mode control and limited laser linewidth narrowing in existing VCSELs, and is beneficial for promoting the application of narrow-linewidth VCSELs in quantum computing, atomic and molecular physics, and high-precision spectroscopy. Attached Figure Description

[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 a medium-gain chip;

[0024] Figure 3 for Figure 1 A schematic diagram of a discrete-structure linewidth narrowing element;

[0025] Figure 4for Figure 1 A schematic diagram of a component with narrower linewidth in a mid-integrated structure;

[0026] Figure 5 A graph showing the evolution of the laser linewidth and the feedback amount of the microcavity in a theoretical simulation.

[0027] Figure 6 This is a graph showing the evolution of the laser linewidth and the Q value of the microcavity in a theoretical simulation. Detailed Implementation

[0028] The following detailed description illustrates the specific implementation method:

[0029] The reference numerals in the accompanying drawings include: 1. Pump source; 2. Collimating and focusing lens; 3. Gain chip; 4. Heat sink; 5. Beam splitter; 6. Polarizing element; 7. Folded output mirror; 8. Mode control element; 9. Rear end mirror; 10. Wavelength tuning element; 11. Output coupling mirror; 12. Linewidth narrowing element; 13. Narrowband filtered signal; 14. Ultra-narrow linewidth frequency doubling light; 15. Reflective layer; 16. Active layer; 17. Second protective layer; 18. Temperature control element; 19. Discrete coupling device; 20. Crystal microcavity; 21. Single-frequency fundamental light; 22. Forward transmission light; 23. Reverse transmission light; 24. First protective layer; 25. Coupled waveguide; 26. Spherical microcavity.

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] The basic implementation examples are as follows: Figure 1 As shown: An ultra-narrow linewidth vertical external cavity surface-emitting laser includes a laser resonator unit and an intracavity control unit. The laser resonator 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 of the fundamental frequency light, thereby obtaining ultra-narrow linewidth laser output.

[0032] The laser resonant 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 emits pump light to the gain chip 3 and includes a pump source 1 and two collimating and focusing lenses 2. The pump source 1 is a semiconductor laser diode with a lasing wavelength shorter than the fundamental frequency wavelength. The pump light emitted from the pump source 1 is focused onto the gain chip 3 after passing through the collimating and focusing lenses 2.

[0033] The gain chip 3, the folded output mirror 7, and the rear mirror 9 constitute the laser resonant cavity. The gain chip 3 is used to absorb the energy of the pump light and generate stimulated emission, and then reflects the stimulated emission to the folded output mirror 7. Under the action of the laser resonant cavity, the stimulated emission forms laser oscillation and generates fundamental frequency light.

[0034] Gain chip 3 is mounted on heat sink 4, which is used to dissipate heat from gain chip 3. Heat sink 4 is specifically made of 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 sequentially. The reflective layer 15 is a high-reflectivity layer capable of reflecting stimulated emission. The active layer 16 is made of semiconductor material and employs a multi-quantum-well design, providing optical amplification for stimulated emission. The second protective layer 17 is used to prevent oxidation of the gain chip 3.

[0035] The folding output mirror 7 is a plano-concave mirror. It can reflect stimulated emission to the rear mirror 9 and output ultra-narrow linewidth frequency-doubled light 14. The folding output mirror 7 is coated with a first high-reflectivity film that reflects the fundamental frequency wavelength and a first high-transmission film that transmits the frequency-doubled light wavelength. The rear mirror 9 can reflect stimulated emission and frequency-doubled light to the folding output mirror 7. The rear mirror 9 is coated with a second high-reflectivity film that reflects both the fundamental and frequency-doubled light wavelengths.

[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 linewidth narrowing element 12, and an output coupling mirror 11. Both the beam splitter 5 and the polarization element 6 are located between the gain chip 3 and the folded output mirror 7. The polarization element 6 is positioned at a Brewster angle and is used to convert the fundamental frequency light into horizontally polarized light. The polarization element 6 can rotate about the normal to its plane, thus providing coarse tuning of the output wavelength of the fundamental frequency light. The beam splitter 5 is located closer to the gain chip 3. It reflects a portion of the fundamental frequency light generated by the laser resonant cavity to the output coupling mirror 11, and the remaining portion is used to maintain laser oscillation between the gain chip 3, the folded output mirror 7, and the rear mirror 9. The beam splitter 5 is coated with a beam-splitting film to split the wavelength of the fundamental frequency light. The output coupling mirror 11 outputs the fundamental frequency light to the linewidth narrowing element 12. The linewidth narrowing element 12 adopts a whispering galvanic microcavity. The linewidth narrowing element 12 is used to narrow the linewidth and generate a narrowband filter signal 13. After being coupled by the output coupling mirror 11 and reflected by the beam splitter 5, the narrowband filter signal 13 is received by the gain chip 3 and participates in the laser oscillation of the laser resonant cavity to form an ultra-narrow linewidth frequency doubling light 14.

[0037] The mode control element 8 is located between the folded output mirror 7 and the rear mirror 9. The mode control element 8 is used to convert the fundamental frequency light into frequency-doubled light and suppress the longitudinal laser mode within the cavity, achieving frequency-doubled single-frequency lasing. The mode control element 8 is coated with a second high-transmittance film layer that transmits both the fundamental frequency wavelength and the frequency-doubled light wavelength. The wavelength tuning element 10 is located on the side of the rear mirror 9 away from the folded output mirror 7. The wavelength tuning element 10 is used to precisely tune the output wavelength of the laser, thereby matching it with the resonant wavelength of the linewidth narrowing element 12. The wavelength tuning element 10 is driven by a DC high voltage and exhibits a stretching effect.

[0038] The linewidth narrowing element 12 has a specific resonant wavelength and two typical structures: discrete and integrated. For example... Figure 3 As shown, the discrete linewidth narrowing element 12 includes a temperature control element 18, a discrete coupling device 19, and a crystal microcavity 20. 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 light 21 into the crystal microcavity 20. The crystal microcavity 20 is made of ground crystal material. The crystal microcavity 20 can resonate with the single-frequency fundamental light 21 and form forward transmission light 22 and reverse transmission light 23, respectively. The reverse transmission light 23 can circulate in the crystal microcavity 20 in the form of total internal reflection, and finally form a narrowband filtered signal 13. The narrowband filtered signal 13 passes through the discrete coupling device 19 and is transmitted in the opposite direction to the single-frequency fundamental light 21.

[0039] like Figure 4 As shown, the integrated linewidth narrowing element 12 includes a temperature control element 18, a low-refractive-index 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 and is used to create a coupling environment close to the refractive index of air to reduce coupling loss and obtain a high Q-value whispering-gallery microcavity. The first protective layer 24 also serves to fix the coupling waveguide 25 and the spherical microcavity 26. The coupling waveguide 25 is used to transmit the single-frequency fundamental light 21 to the spherical microcavity 26, which is formed by burning the end of an optical fiber. The spherical microcavity 26 can resonate with the single-frequency fundamental light 21, forming forward transmission light 22 and reverse transmission light 23, respectively. The reverse transmission light 23 can circulate within the spherical microcavity 26 in the form of total internal reflection, ultimately forming a narrowband filtered signal 13. The narrowband filtered signal 13 passes through the coupling waveguide 25 and propagates in the opposite direction to the single-frequency fundamental light 21.

[0040] The specific implementation process is as follows:

[0041] Under the action of pump source 1, gain chip 3 generates stimulated emission. Stimulated emission, under the action of the laser resonant cavity formed by gain chip 3, folded output mirror 7 and rear mirror 9, forms laser oscillation and generates fundamental frequency light. By using the frequency conversion and second harmonic self-suppression characteristics of mode control element 8, the conversion between fundamental frequency light and frequency-doubled light is realized, as well as the suppression of longitudinal laser mode in the cavity, to obtain frequency-doubled single-frequency lasing. Then, the polarization element 6 and wavelength tuning element 10 are used to control the laser output polarization state and tune the laser wavelength, thereby achieving laser wavelength matching with the resonant wavelength in linewidth narrowing element 12. Finally, the narrowband filter signal 13 generated in linewidth narrowing element 12 is used to generate the output linewidth of the self-injection locked characteristic depth narrowing laser.

[0042] The working principle of the discrete linewidth narrowing element 12 is as follows: The single-frequency fundamental light 21 generated by the laser resonator unit enters the crystal microcavity 20 in the form of an evanescent wave through the output coupling mirror 11 and the discrete coupling device 19. A forward transmission light 22 and a reverse transmission light 23 are formed in the crystal microcavity 20. Subsequently, the two beams circulate in the crystal microcavity 20 in the form of total internal reflection. The reverse transmission light 23 is used to form a narrowband filter signal 13 for linewidth narrowing. This narrowband filter signal 13 has a narrow linewidth and matches the wavelength of the single-frequency fundamental light 21. Finally, the narrowband filter signal 13 is transmitted in the opposite direction to the single-frequency fundamental light 21 through the discrete coupling device 19. After coupling by the output coupling mirror 11 and reflection by the beam splitter 5, it is received by the gain chip 3 and participates in the laser oscillation between the gain chip 3, the folded output mirror 7, and the rear mirror 9, ultimately forming an ultra-narrow linewidth frequency-doubled light 14 output.

[0043] The working principle of the integrated linewidth narrowing element 12 is as follows: The single-frequency fundamental light 21 generated by the laser resonator unit enters the spherical microcavity 26 in the form of an evanescent wave through the output coupling mirror 11 and the coupling waveguide 25. A forward transmission light 22 and a reverse transmission light 23 are formed in the spherical microcavity 26. Subsequently, the two beams circulate in the spherical microcavity 26 in the form of total internal reflection. The reverse transmission light 23 is used to form a narrowband filter signal 13 for linewidth narrowing. This narrowband filter signal 13 has a narrow linewidth and matches the wavelength of the single-frequency fundamental light 21. Finally, the narrowband filter signal 13 is transmitted in the opposite direction to the single-frequency fundamental light 21 through the coupling waveguide 25. After being 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 between the gain chip 3, the folded output mirror 7, and the rear mirror 9, ultimately forming an ultra-narrow linewidth frequency-doubled light 14 output.

[0044] The following is an example to illustrate this:

[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 1020 nm. The active layer 16 is composed of In0.15GaAs / GaAs / GaAsP0.05 multiple quantum wells, with a fluorescence peak wavelength of 1020 nm, capable of generating stimulated emission with a lasing wavelength of 1020 nm. The second protective layer 17 is a GaAs layer, which prevents the gain chip 3 from being oxidized.

[0046] Pump source 1 is a semiconductor laser diode with an operating wavelength of 808nm. Beam splitter 5 is a plane mirror with a beam splitting ratio of 9:1 at a wavelength of 1020nm. Folded output mirror 7 is a plano-concave mirror with a radius of curvature of 100mm. The concave reflective surface is coated with a high reflectivity film (first high reflectivity film) and a high transmittance film (first high transmittance film) for wavelengths of 1020nm and 510nm, respectively. The plane surface is also coated with a film with high transmittance for wavelength of 510nm (first high transmittance film), used for folding the optical path of the arm containing gain chip 3 and back-end mirror 9, as well as for the output of frequency-doubled light. Back-end mirror 9 is a plano-concave mirror with a radius of curvature of 50mm. Its concave surface is coated with a second high reflectivity film for wavelengths of 1020nm and 510nm.

[0047] Polarizing element 6 is a 1mm thick birefringent filter. When placed at Brewster's angle, it can cause the stimulated emission of the laser to be horizontally polarized. Furthermore, rotating this element about the normal to the plane containing it can coarsely tune the wavelength of the fundamental resonant light. Mode control element 8 has dimensions of 3*3*15mm. 3 The LBO frequency-doubling crystal, located between the rear mirror 9 and the folded output mirror 7, utilizes the second harmonic self-suppression effect of the mode control element 8 to control the laser mode within the laser resonant cavity, achieving single-frequency lasing. When phase matching is satisfied, the mode control element 8 will also convert the fundamental frequency light to the frequency-doubled light. The wavelength tuning element 10 is a 12mm*10mm*12mm (outer diameter*inner diameter*height) piezoelectric ceramic tube, driven by DC high voltage, and has a stretching effect. It is used to precisely tune the output wavelength of the laser to match the resonant wavelength of the linewidth 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, including both discrete and integrated structures. In the discrete structure, the temperature control element 18 is a TEC temperature control module with a control accuracy of 0.01℃, the discrete coupling device 19 is a right-angle prism made of glass, mainly used for coupling between the single-frequency fundamental light and the whispering-gallery microcavity, and the crystal microcavity 20 is a calcium fluoride or magnesium fluoride microcavity with a high Q value. A single-frequency fundamental light 21 is coupled into a crystal microcavity 20 in the form of an evanescent wave, forming a forward transmission light 22 and a reverse transmission light 23. The reverse transmission light 23 can circulate within the crystal microcavity 20 in the form of total internal reflection, ultimately forming a narrowband filtered signal 13 with a linewidth in the order of MHz or 100kHz. This signal is transmitted in the opposite direction to the single-frequency fundamental light 21 through a discrete coupling device 19, coupled by the output coupling mirror 11, reflected by the beam splitter 5, and received by the gain chip 3, participating in the laser oscillation between the gain chip 3, the folded output mirror 7, and the back-end mirror 9. By tuning the wavelength of the laser or changing the temperature of the linewidth narrowing element 12, the wavelength of the narrowband filtered signal 13 is matched with that of the single-frequency fundamental light 21, ultimately forming an ultra-narrow linewidth frequency-doubled light 14 output.

[0049] The evolution relationship between laser linewidth and microcavity feedback is as follows: Figure 5 As shown, for a free-running state with a linewidth of 100kHz, and a Q value and a linewidth enhancement factor of 10, 6 A laser with a Q value of 10 and 3. 9 The whispering galvanic microcavity 12 serves as a linewidth narrowing element. When the feedback 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 laser linewidth and the Q value of the microcavity is as follows: Figure 6 As shown, for a free-running state with a linewidth of 100kHz, and a Q value and a linewidth enhancement factor of 10, 6 The laser of type 3 uses a whispering-gallery microcavity with a feedback of -21dB as a linewidth narrowing element 12. When the Q value of the microcavity increases to 10... 9 At this time, the linewidth of the laser can be narrowed from 100kHz to the tens of Hz level.

[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0052] The above descriptions are merely embodiments of the present invention. Commonly known structures and characteristics are not described in detail here. Those skilled in the art are aware of all common technical knowledge in the field prior to the application date or priority date, are aware of all existing technologies in that field, and have the ability to apply conventional experimental methods prior to that date. Those skilled in the art can, under the guidance of this application, improve and implement this solution in combination with their own capabilities. Some typical known structures or methods should not be obstacles for those skilled in the art to implement this application. It should be noted that those skilled in the art can make several modifications and improvements without departing from the structure of the present invention. These should also be considered within the scope of protection of the present invention, and will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. An ultra-narrow linewidth vertical-external-cavity surface-emitting laser characterized in that: The laser resonant unit is used for generating laser oscillation, and the intracavity control unit is used for polarization control, mode control, wavelength tuning and line width narrowing of the fundamental light; The laser resonant unit includes a pump light emitting system, a gain chip (3), a folded output mirror (7) and a back mirror (9), the pump light emitting system is used for emitting pump light to the gain chip (3), the gain chip (3), the folded output mirror (7) and the back mirror (9) constitute a laser resonant cavity, the gain chip (3) is used for absorbing the energy of the pump light and generating stimulated radiation, and reflecting the stimulated radiation to the folded output mirror (7), the folded output mirror (7) can reflect the stimulated radiation to the back mirror (9) and output super-narrow line width frequency-doubled light (14), the back mirror (9) can reflect the stimulated radiation and the frequency-doubled light to the folded output mirror (7), and the stimulated radiation forms laser oscillation under the action of the laser resonant cavity to generate the fundamental light; 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 used for converting the fundamental light into horizontal polarization light, the beam splitter (5) is located on the side close to the gain chip (3), the beam splitter (5) is used for reflecting a part of the fundamental light generated by the laser resonant cavity to the output coupling mirror (11), the output coupling mirror (11) can output the fundamental light to the line width narrowing element (12), the line width narrowing element (12) adopts an echo wall microcavity, the line width narrowing element (12) is used for narrowing the line width and generating a narrow-band filtered signal (13), the narrow-band filtered signal (13) is received by the gain chip (3) after being coupled by the output coupling mirror (11) and reflected by the beam splitter (5), and participates in the laser oscillation of the laser resonant cavity to form super-narrow line width frequency-doubled light (14), the mode control element (8) is located between the folded output mirror (7) and the back mirror (9), the mode control element (8) is used for converting the fundamental light into frequency-doubled light and suppressing intracavity longitudinal laser modes to realize frequency-doubled single-frequency lasing, the wavelength tuning element (10) is located on the side of the back mirror (9) away from the folded output mirror (7), and the wavelength tuning element (10) is used for tuning the output wavelength of the laser to match the resonant wavelength of the line width narrowing element (12). The mode control element (8) is an LBO frequency doubling crystal; the wavelength tuning element (10) is a piezoelectric ceramic tube; the line width narrowing element (12) adopts a discrete structure, and comprises a temperature control element (18), a discrete coupling device (19) and a crystal microcavity (20); or 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).

2. The ultra-narrow linewidth VECSEL according to claim 1, characterized in that: When the line width narrowing element (12) adopts the discrete structure, 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 for coupling the single-frequency fundamental light (21) into the crystal microcavity (20), the crystal microcavity (20) can resonate with the single-frequency fundamental light (21) and form forward transmission light (22) and reverse transmission light (23) respectively; the reverse transmission light (23) can be circularly transmitted in the crystal microcavity (20) in the form of total reflection, and finally form a narrow-band filter signal (13); the narrow-band filter signal (13) is transmitted through the discrete coupling device (19) and in the direction opposite to that of the single-frequency fundamental light (21).

3. The ultra-narrow linewidth VECSEL according to claim 1, characterized in that: When the line width narrowing element (12) adopts the integrated structure, the first protective layer (24) is mounted on the temperature control element (18), and is used for forming a coupling environment and fixing the coupling waveguide (25) and the spherical microcavity (26); the coupling waveguide (25) is used for transmitting the single-frequency fundamental light (21) to the spherical microcavity (26), the spherical microcavity (26) can resonate with the single-frequency fundamental light (21) and form forward transmission light (22) and reverse transmission light (23) respectively; the reverse transmission light (23) can be circularly 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) is transmitted through the coupling waveguide (25) and in the direction opposite to that of the single-frequency fundamental light (21).

4. The ultra-narrow linewidth VECSEL of claim 1, wherein: The gain chip (3) comprises a reflective layer (15), an active layer (16) and a second protective layer (17) arranged in sequence, the reflective layer (15) can reflect stimulated radiation, and the active layer (16) can provide optical amplification for the stimulated radiation; the second protective layer (17) is used for preventing the gain chip (3) from being oxidized.

5. The ultra-narrow linewidth VECSEL of claim 1, wherein: The wavelength tuning element (10) adopts direct current high voltage driving and has a telescopic effect.

6. The ultra-narrow linewidth VECSEL of claim 1, wherein: The pump light emitting system comprises a pump source (1), and the pump source (1) is a semiconductor laser diode with a lasing wavelength less than that of the fundamental light.

7. The ultra-narrow linewidth VECSEL according to claim 6, characterized in that: The pump light emitting system further comprises a collimating focusing lens (2), and the pump light pumped out by the pump source (1) is focused on the gain chip (3) after passing through the collimating focusing lens (2).

8. The ultra-narrow linewidth VECSEL of claim 1, wherein: The polarization element (6) can be rotated.

9. The ultra-narrow linewidth VECSEL according to claim 8, characterized in that: The polarization element (6) is placed at the Brewster angle.

10. The ultra-narrow linewidth VECSEL of claim 1, wherein: The beam splitter (5) is coated with a light splitting film layer for splitting the fundamental light wavelength; the folding output mirror (7) is coated with a first high reflection film layer for reflecting the fundamental light wavelength and a first high transmission film layer for transmitting the second harmonic light wavelength; the rear end mirror (9) is coated with a second high reflection film layer for reflecting the fundamental light wavelength and the second harmonic light wavelength; and the mode control element (8) is coated with a second high transmission film layer for transmitting the fundamental light wavelength and the second harmonic light wavelength.

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