A narrow-linewidth external cavity laser device based on a semi-confocal cavity

Abstract

The embodiment of the application discloses a narrow linewidth external cavity laser device based on a semi-confocal cavity. The laser device comprises: a seed light source for outputting a seed light beam; a semi-confocal cavity for feeding back the seed light beam to the seed light source after internal reflection to form a feedback light path, the semi-confocal cavity satisfying an external cavity self-injection locking condition to form a frequency-locked laser; the semi-confocal cavity comprises a reflecting plane opposite to a reflecting spherical surface, the reflecting spherical surface is convex towards a side away from the reflecting plane, and the reflecting plane is located on a focal plane of the reflecting spherical surface; the reflecting plane is inclined relative to an optical path of the seed light beam, and a focal point of the reflecting spherical surface on the reflecting plane is located on the optical path of the seed light beam, and the seed light beam is emitted from the original optical path after being reflected between the reflecting plane and the reflecting spherical surface for multiple times. The embodiment of the application solves the problem of a large volume of the existing narrow linewidth laser device, realizes the narrow linewidth frequency-locked laser, and makes the feedback external cavity smaller in volume, which is conducive to the miniaturization of the laser device.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of laser technology, and in particular to a narrow linewidth external cavity laser device based on a semi-confocal cavity. Background Technology

[0002] A laser is a device that emits laser light. The light emitted by a laser is pure and spectrally stable. Compared to ordinary light sources, lasers possess superior coherence and monochromaticity, and are widely used in various fields such as national defense, communications, and construction. To meet the demands of future intercity and space-based laser coherent communications with further performance improvements, as well as the needs of frequency-modulated continuous-wave lidar for artificial intelligence environmental perception, space gravity detection, and atomic and molecular measurements, higher requirements are being placed on the linewidth, size, power consumption, and production cost of lasers.

[0003] A laser consists of an excitation source, a gain medium, and a resonant cavity. The excitation source provides energy during laser generation, and the optical amplification process is realized in the gain medium. Since photons move in random directions after being generated in the gain medium, only an ordinary beam can be obtained if they are not restricted. Therefore, a resonant cavity is needed to control the beam and obtain different laser outputs to meet different applications.

[0004] One important parameter of a laser is its linewidth. The linewidth of a laser is mainly affected by external factors such as spontaneous emission of excited-state atoms or ions, phase noise, mechanical vibration of the resonant cavity, and temperature fluctuations. The smaller the linewidth value, the higher the purity of the spectrum, that is, the better the monochromaticity of the laser and the stronger the coherence, which is manifested as an extremely long coherence length.

[0005] Currently, narrow-linewidth lasers include solid-state narrow-linewidth lasers, fiber narrow-linewidth lasers, and semiconductor narrow-linewidth lasers. Solid-state or fiber narrow-linewidth lasers can achieve linewidths in the 1-kHz range, but they are large in size, cover limited wavelengths, have high production costs, and their performance has stagnated. Semiconductor lasers, on the other hand, can be mass-produced at low cost, are small in size, have low power consumption, and cover a wide wavelength range, making them widely favored. However, semiconductor lasers have relatively high intrinsic frequency noise, with even the best distributed feedback lasers only reaching the hundreds of kHz level. Summary of the Invention

[0006] This invention provides a narrow-linewidth external cavity laser device based on a semi-confocal cavity, which reduces the volume of the resonant cavity and the size of the external cavity laser while meeting the narrow linewidth requirement.

[0007] This invention provides a narrow-linewidth external cavity laser device based on a semi-confocal cavity, comprising:

[0008] Seed light source, used to output seed beam;

[0009] A semi-confocal cavity is configured to feed back the seed beam to the seed light source after internal reflection to form a feedback light path, and the semi-confocal cavity satisfies an external cavity self-injection locking condition to form a frequency-locked laser;

[0010] The semi-confocal cavity comprises a reflecting plane and a reflecting spherical surface, the reflecting spherical surface is convex towards a side away from the reflecting plane, and the reflecting plane is located on a focal plane of the reflecting spherical surface.

[0011] The reflecting plane is inclined relative to the light path of the seed beam, and a focal point of the reflecting spherical surface on the reflecting plane is located on the light path of the seed beam, and the seed beam is emitted from the original light path after multiple reflections between the reflecting plane and the reflecting spherical surface.

[0012] Optionally, the semi-confocal cavity comprises a plano-convex lens, and the plano-convex lens comprises the reflecting plane and the reflecting spherical surface.

[0013] Optionally, the semi-confocal cavity comprises a plane mirror and a spherical mirror, the plane mirror comprises the reflecting plane, and the spherical mirror comprises the reflecting spherical surface.

[0014] Optionally, on the light path of the seed beam, the reflecting spherical surface is located on a side of the reflecting plane away from the seed light source, and the reflectivity of the reflecting spherical surface is greater than the reflectivity of the reflecting plane.

[0015] Alternatively, on the light path of the seed beam, the reflecting plane is located on a side of the reflecting spherical surface away from the seed light source, and the reflectivity of the reflecting plane is greater than the reflectivity of the reflecting spherical surface.

[0016] Optionally, a phase adjustment module is further included, and the phase adjustment module is located on the light path of the seed beam and is configured to adjust the phase of the seed beam so that the semi-confocal cavity satisfies the external cavity self-injection locking condition to form the frequency-locked laser.

[0017] Optionally, the phase adjustment module comprises a temperature-controlled optical element or an electro-optic effect optical element, the temperature-controlled optical element is configured to change its refractive index according to temperature change to adjust the phase of the seed beam, and the electro-optic effect optical element is configured to change its refractive index according to electro-optic effect to adjust the phase of the seed beam.

[0018] Optionally, a cavity length adjustment module is further included, and the cavity length adjustment module is configured to change the length of the circulating reflection path of the seed beam in the semi-confocal cavity to generate frequency-locked lasers of different frequencies.

[0019] Optionally, further comprising a light cavity position adjusting module, configured to change the position of the semi-confocal cavity on the light path of the seed light beam, so as to generate a frequency-locked laser with different frequencies.

[0020] Optionally, further comprising a light beam coupling module, configured to couple the seed light beam into the semi-confocal cavity, and further configured to couple the feedback light beam of the semi-confocal cavity into the seed light source.

[0021] Optionally, the seed light source comprises a semiconductor laser; or the seed light source comprises a gain chip and a filter, and the filter is located on the light path of the seed light beam.

[0022] The semi-confocal cavity-based narrow-linewidth external cavity laser device provided by the embodiment of the present application comprises a seed light source and a semi-confocal cavity, the seed light source is configured to output a seed light beam, and the semi-confocal cavity is configured to feedback the seed light beam after internal reflection to the seed light source to form a feedback light path, the semi-confocal cavity satisfies the external cavity self-injection locking condition, and a frequency-locked laser is formed. Wherein, the semi-confocal cavity comprises a reflecting plane and a reflecting spherical surface, the reflecting spherical surface is convex towards a side away from the reflecting plane, and the reflecting plane is located on the focal plane of the reflecting spherical surface; the reflecting plane is inclined relative to the light path of the seed light beam, and the focal point of the reflecting spherical surface on the reflecting plane is located on the light path of the seed light beam, the seed light beam is emitted from the original light path after being reflected multiple times between the reflecting plane and the reflecting spherical surface, and laser external cavity resonance is realized. The embodiment of the present application solves the problem of large volume of the existing narrow-linewidth laser device, utilizes the reflecting plane and the reflecting spherical surface to form the semi-confocal cavity, uses the semi-confocal cavity as the feedback external cavity, realizes the narrow-linewidth frequency-locked laser, and adopts the feedback external cavity structure composed of the plane and the spherical surface, so that the volume of the feedback external cavity is smaller, the layout of the feedback external cavity is more convenient, and the miniaturization of the narrow-linewidth laser device is facilitated. In addition, the semi-confocal cavity can reduce the number of spherical surfaces relative to the spherical cavity, reduce the machining difficulty of the feedback external cavity, improve the control ability of the cavity length precision, and be more helpful for practical application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a structure schematic diagram of a semi-confocal cavity-based narrow-linewidth external cavity laser device provided by the embodiment of the present application;

[0024] Figure 2 is Figure 1 is a feedback light path schematic diagram of the semi-confocal cavity shown in the figure;

[0025] Figure 3 is a structure schematic diagram of another narrow-linewidth external cavity laser device provided by the embodiment of the present application;

[0026] Figure 4is a structure schematic diagram of still another narrow linewidth external cavity laser device provided by an embodiment of the present application;

[0027] Figure 5 is a structure schematic diagram of still another narrow linewidth external cavity laser device provided by an embodiment of the present application;

[0028] Figure 6 is a structure schematic diagram of still another narrow linewidth external cavity laser device provided by an embodiment of the present application;

[0029] Figure 7 is a schematic diagram of an incident feedback light path of another semi-confocal cavity provided by an embodiment of the present application;

[0030] Figure 8 is a structure schematic diagram of still another narrow linewidth laser device provided by an embodiment of the present application;

[0031] Figure 9 is a structure schematic diagram of still another narrow linewidth laser device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, but not all the structures.

[0033] It is found through research that using a high-quality factor (also known as Q value, reflecting the relationship between the energy storage and loss of a resonant cavity, the lower the loss of the cavity, the longer the average lifetime of the photon in the cavity, and the narrower the linewidth) resonant cavity can significantly narrow the semiconductor laser linewidth. Among them, using an FP cavity as a high-Q optical cavity can significantly reduce thermal absorption and nonlinear effects, and achieve narrow linewidth laser.

[0034] The confocal cavity has the advantages of being insensitive to the angle and mode field of the incident light, and the incident light can be obliquely incident, which is conducive to the formation of feedback. Common FP confocal cavity forms include parallel plane cavity and spherical cavity. However, the existing parallel plane cavity has a large mode volume, the laser radiation in the cavity has no focusing phenomenon, but the diffraction loss is high, and the mirror adjustment is difficult. The spherical confocal cavity requires two spherical mirrors with the same curvature radius, and the optical axis length and the curvature radius are equal. If there is a deviation, it will affect the fineness of the resonant cavity, and the conditions are harsh. In addition, the surface of the spherical mirror needs to be polished and ground, which is difficult to process. The smaller the curvature radius of the spherical mirror, the more difficult it is to process. The accuracy requirement of the optical axis length is also high. However, the size of the self-injection external cavity laser used for optical fiber sensing has strict requirements, and the traditional spherical cavity is not conducive to the miniaturization of laser products.

[0035] To solve the above problems, the embodiment of the present application provides a narrow linewidth external cavity laser device based on a semi-common focus cavity, Figure 1 is a structural schematic diagram of a narrow linewidth external cavity laser device based on a semi-common focus cavity provided by the embodiment of the present application, referring to Figure 1 The narrow linewidth external cavity laser device comprises: a seed light source 10, configured to output a seed light beam 100; and a semi-common focus cavity 20, configured to feedback the seed light beam 100 after internal reflection to the seed light source 10 to form a feedback light path, wherein the semi-common focus cavity 20 satisfies the external cavity self-injection locking condition to form a frequency-locked laser; the semi-common focus cavity 20 comprises a reflection plane 21 and a reflection spherical surface 22 opposite to each other, the reflection spherical surface 22 is convex towards a side away from the reflection plane 21, and the reflection plane 21 is located on a focal plane of the reflection spherical surface 22; the reflection plane 21 is inclined relative to an optical path of the seed light beam 100, and a focal point f of the reflection spherical surface 22 on the reflection plane 21 is located on the optical path of the seed light beam 100, and the seed light beam 100 is emitted from the original light path after being reflected multiple times between the reflection plane 21 and the reflection spherical surface 22.

[0036] For the structure of the semi-common focus cavity 20 provided by the embodiment of the present application, first of all, it is known to those skilled in the art that the focal length F of the reflection spherical surface 22 is equal to one half of the radius of curvature R thereof, and the embodiment of the present application sets the reflection plane 21 on the focal plane of the reflection spherical surface 22, which is essentially to set the reflection plane 21 at a position of one half of the radius of curvature R of the reflection spherical surface 22, that is, the center distance L of the reflection plane 21 and the reflection spherical surface 22 and the radius of curvature R of the reflection spherical surface 22 satisfy: L=R / 2. At this time, the light beam reflected by the reflection spherical surface 22 is focused on the reflection plane 21. Further, Figure 2 is Figure 1 the incident feedback light path schematic diagram of the semi-common focus cavity, referring to Figure 1 and Figure 2In the embodiment, the reflection plane 21 is inclined relative to the light path of the seed light beam 100, and the focal point f of the reflection spherical surface 22 on the reflection plane 21 is located on the light path of the seed light beam 100. In essence, the seed light source 10 is arranged to emit light towards the focal point f of the reflection spherical surface 22 on the reflection plane 21. It can be understood that, since the seed light beam 100 passes through the focal point f of the reflection spherical surface 22, when the seed light beam 100 is incident on the reflection surface (position a) of the reflection spherical surface 22, the light beam is reflected for the first time along a direction perpendicular to the reflection plane 21. Then, when the light beam reaches the reflection plane 21 (position b), the reflection plane 21 reflects the light beam along the original path for the second time. Then, the light beam is reflected for the third time towards the focal point f of the reflection plane 21 at the same position (position a) of the reflection spherical surface 22. The reflected light beam is reflected for the fourth time at the focal point position f of the reflection plane 21. The fourth reflected light beam is reflected in a mirror image manner at the lower half of the reflection spherical surface 22 (at position c of the reflection spherical surface 22 and at position d of the reflection plane 21) and again reaches the focal point position f of the reflection plane 21. Thus, the seed light beam 100 is reflected along the path a-b-a-f-c-d-c-f-a between the reflection plane 21 and the reflection spherical surface 22 in turn after being incident on the focal point f, thereby forming resonance. It should be noted that, in the embodiment, the reflection plane 21 at least at the position f has the ability of partial transmission and partial reflection, that is, when the reflected light beam in the cavity is incident from position a to position f, part of the light beam is transmitted by the reflection plane 21 and fed back to the seed light source 10 along the original path of the seed light beam 100, thereby forming external cavity resonance.

[0037] In the embodiment, the semi-confocal cavity 20 is essentially an external cavity of the seed light source 10, which is responsible for feeding back the seed light beam 100 along the original path after being internally reflected, so that the seed light beam 100 resonates in the external cavity to form external cavity frequency self-injection locking. In this process, the semi-confocal cavity 20 as an external cavity resonates with the seed light beam 100, thereby achieving external cavity frequency self-injection locking, and also serving as a high-Q FP cavity to form frequency self-injection locking by itself. The high-Q semi-confocal cavity 20 can further narrow the linewidth of the seed light beam 100 on the basis of narrowing the linewidth of the seed light beam 100 by external cavity frequency self-injection locking, in cooperation with its own frequency self-injection locking.

[0038] The narrow-linewidth external cavity laser device based on the semi-confocal cavity provided by the embodiment of the present application comprises a seed light source and a semi-confocal cavity, the seed light source is used to output a seed light beam, the semi-confocal cavity is used to feedback the seed light beam to the seed light source after internal reflection to form a feedback light path, the semi-confocal cavity satisfies the external cavity self-injection locking condition to form a frequency-locked laser. In the embodiment, the semi-confocal cavity comprises a reflecting plane and a reflecting spherical surface, the reflecting spherical surface is convex towards the side away from the reflecting plane, and the reflecting plane is located on the focal plane of the reflecting spherical surface; the reflecting plane is inclined relative to the light path of the seed light beam, and the focal point of the reflecting spherical surface on the reflecting plane is located on the light path of the seed light beam, the seed light beam is emitted from the original light path after multiple reflections between the reflecting plane and the reflecting spherical surface, and the laser external cavity resonance is realized. The embodiment of the present application solves the problem of large volume of the existing narrow-linewidth laser device, utilizes the reflecting plane and the reflecting spherical surface to form the semi-confocal cavity, uses the semi-confocal cavity as the feedback external cavity, realizes the narrow-linewidth frequency-locked laser, and adopts the feedback external cavity structure composed of the plane and the spherical surface to be smaller in size and more convenient for the feedback external cavity layout, which is conducive to the miniaturization of the narrow-linewidth laser device. In addition, the semi-confocal cavity can reduce the number of spherical surfaces relative to the spherical cavity, reduce the processing difficulty of the feedback external cavity, improve the control ability of the cavity length precision, and be more helpful for practical application.

[0039] It should be noted that the above Figure 1 It should be noted that the above

[0040] The narrow-linewidth external cavity laser device based on the semi-confocal cavity provided by the embodiment of the present application comprises a seed light source and a semi-confocal cavity, the seed light source is used to output a seed light beam, the semi-confocal cavity is used to feedback the seed light beam to the seed light source after internal reflection to form a feedback light path, the semi-confocal cavity satisfies the external cavity self-injection locking condition to form a frequency-locked laser. In the embodiment, the semi-confocal cavity comprises a reflecting plane and a reflecting spherical surface, the reflecting spherical surface is convex towards the side away from the reflecting plane, and the reflecting plane is located on the focal plane of the reflecting spherical surface; the reflecting plane is inclined relative to the light path of the seed light beam, and the focal point of the reflecting spherical surface on the reflecting plane is located on the light path of the seed light beam, the seed light beam is emitted from the original light path after multiple reflections between the reflecting plane and the reflecting spherical surface, and the laser external cavity resonance is realized. The embodiment of the present application solves the problem of large volume of the existing narrow-linewidth laser device, utilizes the reflecting plane and the reflecting spherical surface to form the semi-confocal cavity, uses the semi-confocal cavity as the feedback external cavity, realizes the narrow-linewidth frequency-locked laser, and adopts the feedback external cavity structure composed of the plane and the spherical surface to be smaller in size and more convenient for the feedback external cavity layout, which is conducive to the miniaturization of the narrow-linewidth laser device. In addition, the semi-confocal cavity can reduce the number of spherical surfaces relative to the spherical cavity, reduce the processing difficulty of the feedback external cavity, improve the control ability of the cavity length precision, and be more helpful for practical application. Figure 3 is another structure schematic diagram of the narrow-linewidth external cavity laser device provided by the embodiment of the present application, referring to Figure 3 In the embodiment, the semi-confocal cavity 20 comprises a plano-convex lens 200, the plano-convex lens 200 comprises a reflecting plane 21 and a reflecting spherical surface 22.

[0041] In the embodiment, the plane and the spherical surface in the plano-convex lens 200 have the light transmission ability, and at the same time, can also realize the internal multiple reflection, that is, the plane and the spherical surface of the plano-convex lens 200 can be used as the reflecting plane 21 and the reflecting spherical surface 22 in the above embodiment. The plano-convex lens 200 as a single solid structure has the reflecting plane 21 and the reflecting spherical surface 22 to realize the semi-confocal cavity, and the number of optical elements of the laser device is further reduced, and the processing process of the optical elements is simplified.

[0042] It should be noted that for the plano-convex lens 200, when the seed beam 100 is incident at the focal point f position of the reflection plane 21, there will be at least partial energy transmission, the transmitted light enters the plano-convex lens 200, and forms a circulating reflection between the reflection plane 21 and the reflecting spherical surface 22. At the same time, partial energy transmission will also occur at the reflection positions of the reflection plane 21 and the reflecting spherical surface 22 in this process. At this time, a transmitted light beam can be selected as the frequency-locked laser output according to the laser light output direction, and of course a beam splitting device can be additionally provided on the optical path of the seed beam to be responsible for the output of the frequency-locked laser. Figure 4 is a structural schematic diagram of another narrow linewidth external cavity laser device provided by an embodiment of the present application, compared with Figure 3 and Figure 4 In the embodiment of the present application, the beam splitter 30 can be arranged on the optical path of the seed beam 100 to split the seed beam 100 as the frequency-locked laser output, and the reflected light of the beam splitter can be specifically arranged as the frequency-locked laser output (as shown in Figure 3 ), or the transmitted light of the beam splitter 30 can be specifically arranged as the frequency-locked laser output (as shown in Figure 4 ).

[0043] Figure 5 is a structural schematic diagram of another narrow linewidth external cavity laser device provided by an embodiment of the present application, compared with Figure 5 In this embodiment, the semi-confocal cavity 20 includes a plane mirror 210 and a spherical mirror 220, the plane mirror 210 includes a reflection plane 21, and the spherical mirror 220 includes a reflecting spherical surface 22.

[0044] In this embodiment, the plane mirror 210 and the spherical mirror 220 are separately prepared optical elements, at this time, the reflectivity of the reflection plane 21 and the reflecting spherical surface 22 and whether they have light transmission capability can be designed separately, for example, a reflective film or an anti-reflection film can be coated on the surface or the back surface of the plane mirror 210 and the spherical mirror 220, so as to optimize the external cavity resonance of the semi-confocal cavity 20, improve the energy utilization rate, and increase the frequency-locked laser output energy.

[0045] Further, the seed light source in the embodiment of the present application can include a semiconductor laser, or the seed light source includes a gain chip and a filter, and the filter is arranged on the optical path of the seed beam.

[0046] Referring to Figure 1 The seed light source 10 essentially belongs to an optical cavity with gain, and a semiconductor laser 11 can be selected to generate a seed beam with a relatively wide linewidth. Figure 6 is a structural schematic diagram of another narrow linewidth external cavity laser device provided by an embodiment of the present application, compared with Figure 6The seed light source 10 can also adopt a combination of the gain chip 12 and the filter 13, the gain chip 12 has high gain for a specific waveband (for example, C waveband), and the filter 13 can select a laser wavelength within the gain spectrum line range (tens of nm) of the gain chip 12.

[0047] With reference to Figure 3 and Figure 5 , the embodiment of the present application can also be optionally provided with a beam coupling module 40, which is used for coupling the seed light beam 100 into the semi-confocal cavity 20, and also used for coupling the feedback light beam of the semi-confocal cavity 20 into the seed light source 10. Figure 3 and Figure 5 The beam coupling module 40 is shown in

[0048] As shown above Figure 2 , when the reflecting plane and the reflecting spherical surface have both reflecting and transmitting capabilities, the cavity energy output of the whole semi-confocal cavity includes five positions a, b, c, d and f as shown in Figure 2 , of which the positions b and d on the reflecting plane 21 have output in only one direction, and the other three positions a, c and f have output in two directions. Thus, the cavity energy output of the semi-confocal cavity has a total of 8 ports, and the output energy of the position f along the original path of the seed light beam 100 is at most 1 / 8. Based on this, considering the feedback energy size of the seed light beam in the semi-confocal cavity, the reflectivity and the transmissivity of the reflecting plane and the reflecting spherical surface can be designed respectively in the embodiment of the present application.

[0049] Figure 7 is another schematic diagram of an incident feedback light path of a semi-confocal cavity provided by the embodiment of the present application, with reference to Figure 7 , in the semi-confocal cavity of the embodiment, the reflecting spherical surface 22 is located on the side of the reflecting plane 21 away from the seed light source 10 in the light path of the seed light beam 100, and the reflectivity of the reflecting spherical surface 22 is greater than the reflectivity of the reflecting plane 21.

[0050] At this time, when the seed beam 100 is incident into the semi-confocal cavity 20, the reflectivity of the beam on the reflecting spherical surface 22 is greater than that on the reflecting plane 21, thereby improving the reflection capability of the beam on the reflecting spherical surface 22, reducing the transmission of the beam on the reflecting spherical surface 22, and concentrating the beam energy at the reflecting plane 21. More specifically, the reflectivity of the reflecting spherical surface can be set to be much greater than that of the reflecting plane, or the reflecting spherical surface can be set to have no transmission capability. In this case, there is only light reflection at positions a and c on the reflecting spherical surface, but no light transmission, reducing the energy output ports of the four semi-confocal cavities 20, and increasing the energy of the laser fed back from position f along the original path of the seed beam 100 to 1 / 4.

[0051] It should be noted that the reflectivity design of the reflecting sphere and reflecting plane needs to be determined based on their positions in the seed beam's optical path. It is understood that the purpose of this embodiment is to increase the feedback laser energy. Therefore, when the reflecting plane is located on the side of the reflecting sphere away from the seed source in the seed beam's optical path, the reflectivity of the reflecting plane can be selected to be greater than that of the reflecting sphere. In this case, the reflecting sphere acts as the transmission surface for the feedback laser. Relatively increasing the reflectivity of the reflecting plane and reducing its transmittance allows more energy within the cavity to be transmitted through the reflecting sphere, thereby increasing the feedback laser energy.

[0052] Furthermore, considering practical applications, the embodiments of the present invention provide more specific structural examples for the aforementioned narrow linewidth laser device. Figure 8 This is a schematic diagram of another narrow linewidth laser device provided in an embodiment of the present invention, for reference. Figure 8 Based on the above embodiments, the narrow linewidth laser device further includes a phase adjustment module 50, which is located in the optical path of the seed beam 100 and is used to adjust the phase of the seed beam 100 so that the semi-confocal cavity 20 meets the external cavity self-injection locking condition to form a frequency-locked laser.

[0053] Specifically, the phase adjustment module 50 may include a temperature-controlled optical element or an electro-optic effect optical element disposed on the optical path of the seed beam 100. Figure 8 (Not shown in the image), a temperature-controlled optical element is used to adjust the phase of the seed beam by changing its refractive index according to temperature changes, and an electro-optical effect optical element is used to adjust the phase of the seed beam by changing its refractive index according to the electro-optic effect. The change in refractive index essentially changes the optical path of the beam, thus achieving phase adjustment of the beam, ensuring that the entire laser device meets the external cavity self-injection locking condition, forming a frequency-locked laser. Furthermore, a detection unit can be added to the phase adjustment module 50 (…). Figure 8For example, a beam splitter and a light detecting element (not shown in the figure) are arranged to detect the intensity of the seed light beam 100 entering the semi-confocal cavity 20 and the feedback laser light exiting the semi-confocal cavity 20, so that the frequency-locked position of the feedback light wave peak of the semi-confocal cavity 20 can be determined, which is used as the basis for adjusting the feedback phase.

[0054] On the basis of the above-mentioned embodiments, the narrow linewidth laser device provided by the embodiments of the present application can further be provided with a frequency continuous adjustment function. Figure 9 is a structural schematic diagram of another narrow linewidth laser device provided by the embodiments of the present application, which is similar to the above-mentioned narrow linewidth laser device, and the same parts are not described herein. Figure 9 The narrow linewidth laser device can further comprise a cavity length adjustment module 60, which is used to change the circulating reflection path length of the seed light beam 100 in the semi-confocal cavity 20, so as to generate lock-in laser light of different frequencies.

[0055] As known by those skilled in the art, for an FP cavity, the cavity length determines the resonant frequency to a certain extent. Here, the cavity length adjustment module 60 changes the cavity length of the semi-confocal cavity 20, aiming to dynamically adjust the frequency resonance state of the semi-confocal cavity 20 and change the frequency of the lock-in laser light, so that the narrow linewidth laser device can output narrow linewidth lock-in laser light of different frequencies. It should be noted that the cavity length of the semi-confocal cavity 20 here does not refer to the center distance between the reflecting plane and the reflecting spherical surface, but the circulating reflection length inside the semi-confocal cavity 20, which can also be understood as the optical path of the light beam in the semi-confocal cavity 20. The cavity length adjustment module 60 of the semi-confocal cavity 20 can be a piezoelectric ceramic or an electrically controlled position device. For example, the piezoelectric ceramic or the electrically controlled position device can be used to adjust the inclination angle of the semi-confocal cavity 20. At this time, the reflection path of the seed light beam 100 in the semi-confocal cavity 20 changes, and the reflection positions on the reflecting plane and the reflecting spherical surface, except the focal point f, move, and the optical path of the light beam in the semi-confocal cavity 20 changes. In addition, the cavity length adjustment module 60 can also be a temperature control device, which changes the refractive index of the medium in the semi-confocal cavity 20, so as to change the optical path of the semi-confocal cavity 20, change its resonance state, and adjust the frequency of the lock-in laser light.

[0056] In addition to the above-mentioned adjustment of the frequency of the entire lock-in laser light by changing the frequency-locked state of the semi-confocal cavity, the external cavity in the embodiments of the present application can also be adjusted to adjust the frequency of the entire lock-in laser light. Continuing to refer to Figure 9 The narrow linewidth laser device can further comprise a light cavity position adjustment module 70, which is used to change the position of the semi-confocal cavity 20 in the light path of the seed light beam 100, so as to generate lock-in laser light of different frequencies.

[0057] The piezoelectric ceramic or the electrically controlled position device can translate the whole half-cofocus cavity 20 on the light path of the seed light beam 100, at this time, the external cavity structure of the laser device changes, the optical path changes, thereby realizing the adjustment of the external cavity resonance state, the external cavity resonance frequency changes, thereby realizing the adjustment of the frequency-locked laser frequency.

[0058] It should be noted that when the frequency of the whole frequency-locked laser is adjusted, not only the resonance frequencies of the half-cofocus cavity and the external cavity need to be adjusted synchronously to make the half-cofocus cavity resonance and the external cavity resonance generate a cooperative resonance, but also the intrinsic frequency of the seed light source needs to be adjusted, and the three frequencies are in a state of substantially alignment, so as to satisfy the frequency locking of the whole laser device and dynamically output laser of different frequencies. The phase adjustment module, the cavity length adjustment module and the optical cavity position adjustment module provided in the above embodiment can adjust the resonance state of the external cavity or the half-cofocus cavity respectively, and based on the at least two adjustment modules, the half-cofocus cavity and the external cavity can be adjusted synchronously, and the intrinsic frequency of the seed light source is adjusted, thereby realizing the frequency-locked laser frequency adjustment of the whole laser device.

[0059] Note that the above are only the preferred embodiments of the present application and the applied technical principles. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, re-adjustments, mutual combinations and substitutions without departing from the scope of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments, and can include more other equivalent embodiments without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims.

Claims

1. A narrow-linewidth external-cavity laser device based on a semi-confocal cavity, characterized in that, The application relates to a seed laser source and a method for generating a frequency-locked laser. The seed laser source comprises: a seed light source for outputting a seed light beam; and a semi-confocal cavity for feeding back the seed light beam after internal reflection to form a feedback light path, wherein the semi-confocal cavity satisfies an external cavity self-injection locking condition to form a frequency-locked laser. The semi-confocal cavity comprises a reflecting plane and a reflecting sphere, wherein the reflecting sphere is convex towards a side away from the reflecting plane, and the reflecting plane is located on a focal plane of the reflecting sphere. The reflecting plane is inclined relative to the light path of the seed light beam, and a focal point of the reflecting sphere on the reflecting plane is located on the light path of the seed light beam, and the seed light beam is emitted from the original light path after multiple reflections between the reflecting plane and the reflecting sphere. The semi-confocal cavity comprises a plano-convex lens, and the plano-convex lens comprises the reflecting plane and the reflecting sphere.

2. The narrow-linewidth external cavity laser device of claim 1, wherein, The semi-confocal cavity comprises a plane mirror and a spherical mirror, wherein the plane mirror comprises the reflecting plane, and the spherical mirror comprises the reflecting sphere.

3. The narrow-linewidth external cavity laser device of claim 1, wherein, On the light path of the seed light beam, the reflecting sphere is located on a side of the reflecting plane away from the seed light source, and the reflectivity of the reflecting sphere is greater than that of the reflecting plane.

4. The narrow-linewidth external cavity laser device of claim 1, wherein, Or, on the light path of the seed light beam, the reflecting plane is located on a side of the reflecting sphere away from the seed light source, and the reflectivity of the reflecting plane is greater than that of the reflecting sphere. The application further comprises a phase adjustment module located on the light path of the seed light beam, which is used for adjusting the phase of the seed light beam to make the semi-confocal cavity satisfy the external cavity self-injection locking condition to form a frequency-locked laser.

5. The narrow-linewidth external cavity laser device of claim 1, wherein, The phase adjustment module comprises a temperature-controlled optical element or an electro-optic effect optical element, wherein the temperature-controlled optical element is used for changing the refractive index of the temperature-controlled optical element according to temperature change to adjust the phase of the seed light beam, and the electro-optic effect optical element is used for changing the refractive index of the electro-optic effect optical element according to the electro-optic effect to adjust the phase of the seed light beam.

6. The narrow-linewidth external cavity laser device of claim 5, wherein, The application further comprises a cavity length adjustment module, which is used for changing the circulating reflection path length of the seed light beam in the semi-confocal cavity to generate frequency-locked lasers with different frequencies.

7. The narrow-linewidth external cavity laser device of claim 1, wherein, The application further comprises a light cavity position adjustment module, which is used for changing the position of the semi-confocal cavity on the light path of the seed light beam to generate frequency-locked lasers with different frequencies.

8. The narrow-linewidth external cavity laser device of claim 1, wherein, The application further comprises a beam coupling module, which is used for coupling the seed light beam into the semi-confocal cavity and coupling the feedback light beam of the semi-confocal cavity into the seed light source.

9. The narrow-linewidth external cavity laser device of claim 1, wherein, The seed light source comprises a semiconductor laser, or the seed light source comprises a gain chip and a filter, and the filter is located on the light path of the seed light beam.

10. The narrow-linewidth external cavity laser device of claim 1, wherein, ​

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