An optical frequency comb generation device

Abstract

An embodiment of the present invention discloses an optical frequency comb generation device. The optical frequency comb generation device includes a pump source, a gain medium, a coupled input mirror, a coupled output mirror, at least one first reflection cavity mirror, a second reflection cavity mirror, a beam splitter, a photodetector, a self-reference interferometer, and a phase-locked loop; the coupled input mirror, the first reflection cavity mirror, the second reflection cavity mirror, and the coupled output mirror form a resonant cavity, and the gain medium is located in the resonant cavity; the beam splitter is located at the output end of the resonant cavity, the photodetector is located at the first output end of the beam splitter, and the self-reference interferometer is located at the second output end of the beam splitter; the second reflection cavity mirror includes a lead magnesium niobate-lead titanate substrate and a reflection layer located on one side of the lead magnesium niobate-lead titanate substrate. The high-locking-bandwidth optical frequency comb generated by the embodiment of the present invention has the advantages of narrow comb tooth linewidth, good stability, good integration, etc., and can be used in aspects such as laser frequency measurement, time-frequency transfer, ultra-stable microwave source generation, astronomical observation, etc.

Description

Technical Field

[0001] The present invention relates to the field of optical technologies, and in particular, to an optical frequency comb generating device. Background Art

[0002] An optical frequency comb is a special femtosecond pulsed light. It is a series of ultrashort pulses with a pulse width on the femtosecond scale in the time domain, and a series of equally spaced single spectral lines with a wide spectral range in the frequency domain. Due to its characteristics of both narrow linewidth and wide spectrum, it has broad application prospects in many fields such as laser frequency measurement, time-frequency transfer, generation of ultra-stable microwave sources, astronomical observation, high-precision spectroscopy, and absolute distance measurement.

[0003] In order to obtain a series of frequency-stable frequency comb teeth, it is necessary to accurately lock the repetition frequency and the carrier-envelope offset frequency of the optical frequency comb. The repetition frequency is usually detected by a high-speed photodetector and controlled by a piezoelectric ceramic in the cavity, while the carrier-envelope offset frequency is usually detected by an f-2f self-reference interferometer and controlled by the drive current source of the pump laser. However, limited by the resonance frequency of the piezoelectric ceramic, the linewidth of a single comb tooth of the optical frequency comb is usually on the order of hundreds of kHz, and it is difficult to increase the bandwidth of the optical frequency comb. Summary of the Invention

[0004] An embodiment of the present invention provides an optical frequency comb generating device, which introduces a new type of piezoelectric ceramic to generate an optical frequency comb with a high locking bandwidth. The new type of piezoelectric ceramic is formed based on lead magnesium niobate titanate, and it has characteristics of high transparency, high piezoelectric effect, and high electro-optic effect. A high-reflection film is directly deposited on the lead magnesium niobate titanate substrate as one of the cavity mirrors of the resonant cavity, which can achieve a piezoelectric ceramic without load, effectively improve the resonance frequency of the piezoelectric ceramic, and further increase the locking bandwidth of the femtosecond frequency comb.

[0005] According to an aspect of the present invention, there is provided an optical frequency comb generating device, including a pump source, a gain medium, a coupling input mirror, a coupling output mirror, at least one first reflection cavity mirror, a second reflection cavity mirror, a beam splitter, a photodetector, a self-reference interferometer, and a phase-locked loop;

[0006] The coupling input mirror, the first reflection cavity mirror, the second reflection cavity mirror, and the coupling output mirror form a resonant cavity, and the gain medium is located in the resonant cavity;

[0007] The beam splitter is located at the output end of the resonant cavity, the photodetector is located at the first output end of the beam splitter, and the self-reference interferometer is located at the second output end of the beam splitter;

[0008] The photodetector and the second reflection cavity mirror are connected through the phase-locked loop, and the self-reference interferometer and the pump source are connected through the phase-locked loop;

[0009] The second reflecting mirror includes a lead magnesium niobate-lead titanate substrate and a reflecting layer located on one side of the lead magnesium niobate-lead titanate substrate.

[0010] Optionally, the pump light output by the pump source is transmitted through the coupling input mirror and then transmitted to the gain medium;

[0011] The pulsed light beam generated by the gain medium is output from the coupling output mirror and then incident on the beam splitter, and is divided into a first light beam and a second light beam. The first light beam is incident on the photodetector, and the second light beam is incident on the self-reference interferometer;

[0012] The photodetector measures the repetition frequency of the first light beam and feeds it back to the second reflecting mirror through the phase-locked loop to adjust the cavity length of the resonant cavity;

[0013] The self-reference interferometer measures the carrier-envelope offset frequency of the second light beam and feeds it back to the pump source through the phase-locked loop to adjust the pump current, so that the resonant cavity outputs an optical frequency comb.

[0014] Optionally, the phase-locked loop includes a repetition frequency locking circuit of the optical frequency comb and a carrier-envelope offset frequency locking circuit;

[0015] The photodetector and the second reflecting mirror are connected through the repetition frequency locking circuit. The repetition frequency locking circuit generates a first feedback signal according to the signal collected by the photodetector, and the first feedback signal is applied to the electrode of the lead magnesium niobate-lead titanate substrate in the form of a DC bias voltage to adjust the cavity length of the resonant cavity;

[0016] The self-reference interferometer and the pump source are connected through the carrier-envelope offset frequency locking circuit. The carrier-envelope offset frequency locking circuit generates a second feedback signal according to the signal collected by the self-reference interferometer, and the second feedback signal is used to adjust the pump current of the pump source.

[0017] Optionally, it further includes a lead-filled copper block, and the lead-filled copper block is located on the side of the second reflecting mirror away from the resonant cavity, and the second reflecting mirror is attached to the surface of the lead-filled copper block.

[0018] Optionally, it further includes a coupling lens group, and the coupling lens group includes at least one lens located between the pump source and the coupling input mirror.

[0019] Optionally, the thickness of the lead magnesium niobate-lead titanate substrate is 0.5 mm to 5 mm.

[0020] Optionally, the reflecting layer includes an anti-reflection enhancement film, and the dispersion of the anti-reflection enhancement film is less than 20 fs2 。

[0021] Optionally, the gain medium includes a laser crystal, and the thickness of the laser crystal is greater than or equal to 1 mm and less than or equal to 1 cm.

[0022] Optionally, the pump source includes a single-mode semiconductor laser or a fiber laser.

[0023] Optionally, the self-reference interferometer includes an f-2f self-reference interferometer based on a photonic crystal fiber.

[0024] The optical frequency comb generation device provided by the embodiment of the present invention includes a pump source, a gain medium, a coupled input mirror, a coupled output mirror, at least one first reflection cavity mirror, a second reflection cavity mirror, a beam splitter, a photodetector, a self-reference interferometer, and a phase-locked loop; pump light is provided by the pump source, a resonant cavity is formed by the coupled input mirror, the first reflection cavity mirror, the second reflection cavity mirror, and the coupled output mirror, and a stable optical frequency comb is output through the feedback of the phase-locked loop. The device directly deposits a high-reflection film on a lead magnesium niobate-lead titanate substrate as one of the cavity mirrors of the resonator, which can realize the piezoelectric ceramic without load, effectively improve the resonance frequency of the piezoelectric ceramic, and further improve the locking bandwidth of the femtosecond frequency comb.

[0025] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present invention, nor is it used to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is a schematic structural diagram of an optical frequency comb generation device provided by an embodiment of the present invention;

[0028] Figure 2 It is a schematic structural diagram of another optical frequency comb generation device provided by an embodiment of the present invention. Detailed Embodiments

[0029] To enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0030] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily need to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0031] The resonance frequency formula of the piezoelectric ceramic is: where k T is the hardness of the piezoelectric ceramic, and m eff is the payload of the piezoelectric ceramic. When there is no load, the payload of the piezoelectric ceramic is one-third of its own weight. When there is a load, the payload of the piezoelectric ceramic is one-third of its own weight plus the weight of the load. Obviously, reducing the load of the piezoelectric ceramic can increase its resonance frequency. Currently, the main methods to increase the resonance frequency of the piezoelectric ceramic are: reducing the weight of the piezoelectric ceramic, reducing the weight of the load (lens), selecting an adhesive with a larger elastic modulus, and bonding the back of the piezoelectric ceramic to a lead-filled copper block or an aluminum-iron alloy. However, the solutions in the prior art have limited effects and are difficult to provide an optical frequency comb with high stability and high bandwidth.

[0032] To solve the above problems, an embodiment of the present invention provides an optical frequency comb generating device. Figure 1 It is a schematic structural diagram of an optical frequency comb generating device provided by an embodiment of the present invention. Refer to Figure 1, the optical frequency comb generating device provided in this embodiment includes a pump source 1, a gain medium 2, a coupling input mirror 3, a coupling output mirror 4, at least one first reflecting cavity mirror 5, a second reflecting cavity mirror 6, a beam splitter 7, a photodetector 8, a self-reference interferometer 9, and a phase-locked loop 10; the coupling input mirror 3, the first reflecting cavity mirror 5, the second reflecting cavity mirror 6, and the coupling output mirror 4 form a resonant cavity, and the gain medium 2 is located in the resonant cavity; the beam splitter 7 is located at the output end of the resonant cavity, the photodetector 8 is located at the first output end of the beam splitter 7, and the self-reference interferometer 9 is located at the second output end of the beam splitter 7; the photodetector 8 and the second reflecting cavity mirror 6 are connected through the phase-locked loop 10, and the self-reference interferometer 9 and the pump source 1 are connected through the phase-locked loop; the second reflecting cavity mirror 6 includes a lead magnesium niobate-lead titanate substrate and a reflective layer located on one side of the lead magnesium niobate-lead titanate substrate ( Figure 1 not shown in

[0033] ). Optionally, the working process of the optical frequency comb generating device provided in this embodiment is as follows: the pump light output by the pump source 1 is transmitted through the coupling input mirror 3 and then transmitted to the gain medium 2; the pulsed light beam generated by the gain medium 2 is output from the coupling output mirror 4 and then incident on the beam splitter 7, and is divided into a first light beam a and a second light beam b. The first light beam a is incident on the photodetector 8, and the second light beam b is incident on the self-reference interferometer 9; the photodetector 8 measures the repetition frequency of the first light beam a and feeds it back to the second reflecting cavity mirror 6 through the phase-locked loop 10 to adjust the cavity length of the resonant cavity; the self-reference interferometer 9 measures the carrier envelope offset frequency of the second light beam b and feeds it back to the pump source 1 through the phase-locked loop 10 to adjust the pump current, so that the resonant cavity outputs an optical frequency comb.

[0034] Among them, Figure 1Only taking one first reflection mirror 5 as an example does not limit the embodiments of the present invention. In this embodiment, the coupling input mirror 3, the first reflection mirror 5, the second reflection mirror 6, and the coupling output mirror 4 form a butterfly-shaped resonant cavity. In other embodiments, the number of cavity mirrors of the resonant cavity can be more than four. For example, a total of six cavity mirrors (three first reflection mirrors) are provided to form a butterfly cavity, which can be designed according to actual situations during specific implementation. The pump source 1 is used to provide pump light. Optionally, the pump source 1 includes a single-mode semiconductor laser or a fiber laser, with an output power greater than 50 mW and an output light wavelength matching the absorption peak of the gain medium 2. The gain medium 2 includes, but is not limited to, common laser crystals such as titanium-doped sapphire and ytterbium-doped yttrium aluminum garnet. Optionally, the thickness of the laser crystal is greater than or equal to 1 mm and less than or equal to 1 cm. The coupling input mirror 3 is a dichroic mirror, which is used to transmit the pump light and reflect the pulsed light beam generated by the gain medium 2. The coupling output mirror 4 reflects a part of the pulsed light beam and outputs a part of the pulsed light beam. The specific reflectivity and transmittance can be selected according to actual situations. The first reflection mirror 5 is a high-reflectivity mirror, which is used to reflect the pulsed light beam. The second reflection mirror 6 is formed by plating a high-reflection film (reflection layer, located on the side close to the coupling output mirror 4) on a lead magnesium niobate-lead titanate substrate. The working wavelength of the high-reflection film matches the emission wavelength of the gain medium 2, the incident angle is 0°, and the dispersion within the working wavelength range is less than 20 fs 2。Lead magnesium niobate-lead titanate is a new type of piezoelectric material with characteristics of high transparency, high piezoelectric effect, and high electro-optic effect. Coating a high-reflection film on a lead magnesium niobate-lead titanate substrate and directly using it as the cavity mirror of a resonant cavity can make the piezoelectric ceramic unloaded, greatly improving the resonant frequency of the piezoelectric ceramic. Therefore, it can effectively increase the locking bandwidth of the optical frequency comb, making the generated optical frequency comb have advantages such as narrow comb tooth linewidth, good stability, and good integration, and can be used in aspects such as laser frequency measurement, time-frequency transfer, generation of ultra-stable microwave sources, and astronomical observations. During specific implementation, the thickness of the lead magnesium niobate-lead titanate substrate can be 0.5 mm to 5 mm, such as 0.5 mm, 1 mm, 2 mm, or 5 mm, and its cross-sectional size can be 8 mm × 8 mm, where the ratio of lead magnesium niobate to lead titanate can be arbitrary. The beam splitter 7 divides the beam output by the coupled output mirror 4 into two beams. One beam is transmitted to the photodetector 8. The working wavelength of the photodetector 8 matches the emission wavelength of the gain medium 2, and the response bandwidth should be higher than the repetition frequency of the optical frequency comb. During specific implementation, it can be selected according to the actual situation. The other beam is transmitted to the self-reference interferometer 9. The self-reference interferometer 9 includes an f-2f self-reference interferometer based on a photonic crystal fiber. The photonic crystal fiber realizes spectral broadening. The high-frequency part in the octave spectrum and the second-harmonic part of the low-frequency part achieve beat frequency in the interferometer, and the obtained beat frequency signal is the carrier-envelope offset frequency signal of the optical frequency comb. The phase-locked loop 10 includes a repetition frequency locking circuit 101 and a carrier-envelope offset frequency locking circuit 102 of the optical frequency comb. The photodetector 8 and the second reflection cavity mirror 6 are connected through the repetition frequency locking circuit 101. The repetition frequency locking circuit 101 generates a first feedback signal according to the signal collected by the photodetector 8, and the first feedback signal is applied to the electrode of the lead magnesium niobate-lead titanate substrate in the form of a DC bias voltage to adjust the cavity length of the resonant cavity. The self-reference interferometer 9 and the pump source 1 are connected through the carrier-envelope offset frequency locking circuit 102. The carrier-envelope offset frequency locking circuit 102 generates a second feedback signal according to the signal collected by the self-reference interferometer 9, and the second feedback signal is used to adjust the pump current of the pump source 1. During specific implementation, the circuit structures of the repetition frequency locking circuit 101 and the carrier-envelope offset frequency locking circuit 102 can be designed according to the actual situation, and the embodiments of the present invention do not limit this.

[0035] The technical solution of the embodiment of the present invention provides pump light through a pump source, forms a resonant cavity through a coupled input mirror, a first reflection cavity mirror, a second reflection cavity mirror, and a coupled output mirror, and outputs a stable optical frequency comb through the feedback of a phase-locked loop. This device directly coats a high-reflection film on a lead magnesium niobate-lead titanate substrate as one of the cavity mirrors of the resonator, can achieve an unloaded piezoelectric ceramic, effectively improve the resonance frequency of the piezoelectric ceramic, and further increase the locking bandwidth of the femtosecond frequency comb.

[0036] Figure 2This is a schematic structural diagram of another optical frequency comb generation device provided by an embodiment of the present invention. Refer to Figure 2 Optionally, the optical frequency comb generation device provided in this embodiment further includes a lead-filled copper block 11. The lead-filled copper block 11 is located on the side of the second reflecting cavity mirror 6 away from the resonant cavity, and the second reflecting cavity mirror 6 is attached to the surface of the lead-filled copper block 11.

[0037] By setting the lead-filled copper block 11, the low-frequency vibration of the second reflecting cavity mirror 6 can be absorbed, and the stability of the optical frequency comb generation device can be improved. Specifically, in implementation, the lead-filled copper block 11 is a copper shell filled with lead. The top of the lead is a right circular cone with a length of 7.5 mm, and the tip is 1 mm away from the outer wall of the copper shell. The bottom of the lead is a cylinder with a diameter of 15 mm and a length of 16.5 mm. The diameter of the top of the copper shell is 8 mm, and the wall thickness of the bottom is 2.5 mm. The lead and the copper shell need to be closely connected, and there should be no bubbles or impurities in the middle.

[0038] Continue to refer to Figure 2 Optionally, the optical frequency comb generation device further includes a coupling lens group 12. The coupling lens group 12 includes at least one lens located between the pump source 1 and the coupling input mirror 3.

[0039] Exemplarily, Figure 2 it is schematically shown in that the coupling lens group 12 includes a convex lens for converging the pump light to the gain medium 2. In other embodiments, other numbers of lenses can also be set, and the embodiments of the present invention do not limit this.

[0040] The above specific implementation manners do not constitute a limitation to the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An optical frequency comb generating device, characterized in that, It includes a pump source, a gain medium, a coupling input mirror, a coupling output mirror, at least one first reflecting cavity mirror, a second reflecting cavity mirror, a beam splitter, a photodetector, a self-reference interferometer and a phase-locked loop; The coupling input mirror, the first reflecting cavity mirror, the second reflecting cavity mirror and the coupling output mirror form a resonant cavity, and the gain medium is located in the resonant cavity; The beam splitter is located at the output end of the resonant cavity, the photodetector is located at the first output end of the beam splitter, and the self-reference interferometer is located at the second output end of the beam splitter; The photodetector and the second reflecting cavity mirror are connected through the phase-locked loop, and the self-reference interferometer and the pump source are connected through the phase-locked loop; The phase-locked loop includes a repetition frequency locking circuit and a carrier envelope offset frequency locking circuit; The photodetector is connected to the second reflecting cavity mirror through the repetition frequency locking circuit, and the self-reference interferometer is connected to the pump source through the carrier envelope offset frequency locking circuit; The second reflecting cavity mirror includes a lead magnesium niobate-lead titanate substrate and a reflecting layer located on one side of the lead magnesium niobate-lead titanate substrate; 2. The optical frequency comb generating device according to claim 1, characterized in that, The pump light output by the pump source is transmitted through the coupling input mirror and then transmitted to the gain medium; The pulsed light beam generated by the gain medium is output from the coupling output mirror and then incident on the beam splitter, and is divided into a first light beam and a second light beam. The first light beam is incident on the photodetector, and the second light beam is incident on the self-reference interferometer; The photodetector measures the repetition frequency of the first light beam and feeds it back to the second reflecting cavity mirror through the phase-locked loop to adjust the cavity length of the resonant cavity; The self-reference interferometer measures the carrier envelope offset frequency of the second light beam and feeds it back to the pump source through the phase-locked loop to adjust the pump current, so that the resonant cavity outputs an optical frequency comb.

3. The optical frequency comb generation device according to claim 2, characterized in that, The phase-locked loop includes a repetition frequency locking circuit of the optical frequency comb and a carrier envelope offset frequency locking circuit; The photodetector and the second reflecting cavity mirror are connected through the repetition frequency locking circuit. The repetition frequency locking circuit generates a first feedback signal according to the signal collected by the photodetector, and the first feedback signal is applied to the electrode of the lead magnesium niobate-lead titanate substrate in the form of a DC bias voltage to adjust the cavity length of the resonant cavity; The self-reference interferometer and the pump source are connected through the carrier envelope offset frequency locking circuit. The carrier envelope offset frequency locking circuit generates a second feedback signal according to the signal collected by the self-reference interferometer, and the second feedback signal is used to adjust the pump current of the pump source.

4. The optical frequency comb generating device according to claim 1, wherein It further includes a lead-filled copper block, the lead-filled copper block is located on the side of the second reflecting cavity mirror away from the resonant cavity, and the second reflecting cavity mirror is attached to the surface of the lead-filled copper block.

5. The optical frequency comb generating device according to claim 1, characterized in that, It further includes a coupling lens group, and the coupling lens group includes at least one lens located between the pump source and the coupling input mirror.

6. The optical frequency comb generating device according to claim 1, wherein The thickness of the lead magnesium niobate-lead titanate substrate is 0.5 mm to 5 mm.

7. The optical frequency comb generating device according to claim 1, characterized in that The reflective layer includes an anti-reflection film, and the dispersion of the anti-reflection film is less than 20 fs 2 .

8. The optical frequency comb generation device according to claim 1, wherein, The gain medium includes a laser crystal, and the thickness of the laser crystal is greater than or equal to 1 mm and less than or equal to 1 cm.

9. The optical frequency comb generating device according to claim 1, characterized in that, The pump source includes a single-mode semiconductor laser or a fiber laser.

10. The optical frequency comb generating device according to claim 1, wherein, The self-reference interferometer includes an f-2f self-reference interferometer based on photonic crystal fiber.

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