A method for regulating brillouin gain, laser and light generated microwave source

Abstract

The application discloses a method for regulating Brillouin gain, a laser and an optical microwave source, and specifically relates to the method for regulating Brillouin gain. a The application discloses a method for regulating Brillouin gain, a laser and an optical microwave source, and specifically relates to the method for regulating Brillouin gain. The method for regulating Brillouin gain adopts the gradual change of the angle between the circular light path and the crystal axis, so that the speed of the generated acoustic phonon is continuously changed, and then the widened backward Brillouin gain feature is generated, the threshold of the backward Brillouin laser is reduced, the linewidth of the Brillouin laser is reduced in one step, and the diversity of the Brillouin laser application is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, and in particular to a method for regulating and controlling Brillouin gain, a laser and an optical microwave source. BACKGROUND

[0002] In recent years, Brillouin lasers have been widely used in fiber sensors, optical communication, spectral analysis, atomic clocks, gyroscopes and optical microwave generation due to their low noise and narrow linewidth characteristics. Stimulated Brillouin scattering is a non-elastic scattering effect caused by a third-order nonlinear effect, which results in the interaction of light waves and acoustic waves. In order to effectively realize the Brillouin laser based on Brillouin scattering, the interaction between photons and phonons is usually enhanced by using optical fibers and optical resonant cavities. In long-distance transmission optical fibers, the threshold of backward Brillouin scattering is low, so it can be applied to many fields such as slow light, pulse manipulation and optical storage. In the field of optical resonant cavities, the process of preparing low-threshold Brillouin lasers has developed from fusion and grinding methods to integrated photon resonant cavities based on chip micro-nano etching processes. For example, in the field of silicon nitride integrated photonics, a racetrack resonant cavity has been used to realize a narrow-linewidth Brillouin laser. The traditional Brillouin gain bandwidth is very narrow. In a crystal (such as a fluoride optical crystal), the Brillouin gain bandwidth is generally only a few megahertz to tens of megahertz. Therefore, it is a great challenge to design a low-threshold Brillouin laser with a wide gain bandwidth, and the process precision requirement is high, which greatly limits the implementation and application of Brillouin lasers. SUMMARY

[0003] In view of the above technical problems, the present application provides a method for regulating and controlling Brillouin gain, a laser and an optical microwave source. The method for regulating and controlling Brillouin gain gradually changes the angle between the circular light path and the crystal axis of the Brillouin gain crystal, so that the speed of the generated acoustic phonon changes continuously, thereby generating a widened backward Brillouin gain feature, which can reduce the threshold of the backward Brillouin laser, reduce the linewidth of the Brillouin laser in one step, and increase the diversity of Brillouin laser applications.

[0004] A method for regulating and controlling Brillouin gain, a resonant cavity adopts a Brillouin gain crystal with a curved boundary. A designed curved light path is used as the transmission path of acoustic phonons. The angle φ between the acoustic phonon and the crystal axis of the Brillouin gain crystal changes continuously during the transmission process, resulting in a change in the propagation speed V a (φ) of the acoustic phonon in the crystal, and a backward Brillouin gain envelope is generated to realize the regulation and control of Brillouin gain.

[0005] As a preferred embodiment of the above technical solution, the laser entering the resonant cavity is transmitted along the curved boundary of the Brillouin gain crystal after total reflection, and the laser is resonantly enhanced during the transmission process in the Brillouin gain crystal.

[0006] As the preferred technical scheme, the curved boundary of the Brillouin gain crystal is used to constantly change the transmission direction of the laser in the resonant cavity, so as to constantly change the angle φ between the laser transmission direction and the crystal axis and simultaneously realize the frequency shift regulation of the Brillouin laser, and the relationship is Ω B (φ) / 2π=2n eff v a (φ)。

[0007] As the preferred technical scheme, the relationship between the gain coefficient of the Brillouin laser and the frequency shift regulation of the Brillouin laser is Wherein, Γ B is the traditional Brillouin gain line width, L is the optical path, and Ω / 2π is the frequency difference between the pump laser and the Stokes signal light.

[0008] A laser adopts any one of the above-mentioned Brillouin gain regulation methods, and comprises a pump source, a coupler and a resonant cavity. The pump source generates acoustic phonons through electrostriction. The acoustic phonons are injected into the crystal resonant cavity through the coupler, are transmitted along the curved boundary through total reflection, and the laser is resonated and enhanced in the transmission plane.

[0009] As the preferred technical scheme, the shape of the resonant cavity includes but is not limited to one of a disc, a ring, and a track-type curved light path.

[0010] As the preferred technical scheme, the size of the resonant cavity includes but is not limited to one of millimeter level, hundred-micron level and tens-of-micron level.

[0011] As the preferred technical scheme, the Brillouin gain crystal adopts a single crystal or a polycrystal.

[0012] As the preferred technical scheme, the coupler includes but is not limited to one of a prism coupler, a micro-nano fiber coupler and an integrated optical waveguide coupler.

[0013] An optical microwave source adopts the laser adopting any one of the above-mentioned Brillouin gain regulation methods.

[0014] The beneficial effects of the present application are as follows:

[0015] Compared with the prior art, the crystal Brillouin laser and the optical microwave source provided by the present application utilize the gradual change of the angle between the circular light path and the crystal axis, so that the speed of the generated acoustic phonon is constantly changed, and then the widened backward Brillouin gain feature is generated. On the other hand, the high-quality factor crystal resonant cavity can reduce the threshold of the backward Brillouin laser, and further reduce the line width of the Brillouin laser. In addition, the wide-range Brillouin gain can generate a wide-range optical microwave signal, and increase the diversity of the Brillouin laser application. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A schematic diagram of the Brillouin laser generated in the Z-cut magnesium fluoride disc resonator cavity is provided for the embodiments of the present application.

[0017] Figure 2 A schematic diagram of the Z-cut magnesium fluoride disc resonator cavity longitudinal acoustic wave speed Va three-dimensional projection onto the unit sphere is provided for the embodiments of the present application.

[0018] Figure 3 A theoretical comparison diagram of the conventional Brillouin gain and the wide-range Brillouin gain spectrum is provided for the embodiments of the present application.

[0019] Figure 4 A reverse Brillouin laser spectrum diagram is provided for the embodiments of the present application.

[0020] Figure 5 A microwave signal source spectrum diagram of four Brillouin lasers and pump laser beat frequencies generated in a single crystal cavity is provided for the embodiments of the present application.

[0021] Figure 6 A histogram of the Brillouin frequency shift data measured in the experiment and a theoretical curve of the wide-range Brillouin gain are provided for the embodiments of the present application. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described clearly and completely in combination with the drawings of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative labor belong to the scope of protection of the present application.

[0023] As Figure 1 described, the present application discloses a laser for regulating Brillouin gain, which comprises a pump source 1, a coupler 2 and a resonator cavity 3, the resonator cavity 3 comprises a Brillouin gain crystal with a circular boundary, and the pump laser 101 emitted by the pump source 1 is coupled into the resonator cavity 3 through the coupler 2.

[0024] In the present embodiment, the pump laser 101 emitted by the pump source 1 is coupled with the Z-cut magnesium fluoride crystal disc resonator cavity 3 obtained by mechanical grinding through the evanescent wave coupler 2. By continuously scanning the pump laser 101 and adjusting the coupling distance and position, the pump beam 301 and the Stokes beam 302 interfere with each other and generate an electrostrictive effect to generate acoustic phonons 303. The included angle φ of the acoustic phonons 303 with the crystal axis 304 of the designed curved light path changes constantly during the transmission process, and the propagation speed of the acoustic phonons in the crystal changes constantly V a (φ), the gain range of the generated backward Brillouin signal 302 is regulated and greatly improved.

[0025] In this embodiment, the pump laser 101 is injected into the crystal resonant cavity via a coupler and then propagates along the curved boundary via total internal reflection as an intracavity pump beam 301, resulting in enhanced resonance of the laser within the propagation plane. This coupler is not limited to integrated optical waveguides, optical prisms, or micro / nano optical fibers.

[0026] like Figure 2 The sound velocity V of the longitudinal acoustic phonon in the circular cavity within the Z-cut magnesium fluoride disk resonant cavity. a (φ) A schematic diagram of three-dimensional projection onto a unit sphere. In the case of a Z-cut disk resonator, the longitudinal phonon phase velocity varies significantly along the periphery of the disk, with minimum and maximum values ​​of 6.640 km / s and 8.137 km / s, respectively. This enables Brillouin laser frequency shift Ω covering a wide frequency range. B (φ) / 2π=2n eff v a (φ), thereby reducing the requirements of cavity design accuracy for the dual resonance condition of the Brillouin laser and better realizing the low-threshold dual resonance Brillouin laser emission.

[0027] like Figure 3 The diagram shows a theoretical comparison between traditional Brillouin gain and the wide-range Brillouin gain produced by modulation. Modifying the Brillouin laser frequency shift is equivalent to modulating the Brillouin gain coefficient. Γ B Let L be the optical path length, Ω / 2π be the frequency difference between the pump laser and the Stokes signal light, and L be the linewidth of the traditional Brillouin gain. The Brillouin gain bandwidth of traditional fluoride crystals is only a few megahertz to tens of megahertz. The corresponding backward Brillouin gain curve can be obtained using this formula. The calculated Brillouin gain in the Z-cut circular magnesium fluoride cavity has two peaks near 11.75 GHz and 14.38 GHz, while the gain curve in the middle is relatively flat. Compared with the traditional Brillouin gain range, the range has broadened by a factor of one hundred.

[0028] like Figure 4 The reverse Brillouin laser spectrum shown clearly demonstrates the backward Brillouin laser signal generated by this invention in a magnesium fluoride crystal cavity with a diameter of approximately 1.9 mm. In this example, the threshold of the Brillouin laser is as low as 3.4 mW. The shape of the crystal resonator cavity includes, but is not limited to, one of the following: disk, ring, and racetrack type, and is not limited to block or chip-level platforms.

[0029] like Figure 5 The beat spectra of multiple Brillouin lasers and pump lights measured in a single magnesium fluoride crystal cavity clearly show that, due to the introduction of a change in the angle between the beam and the crystal axis, the Brillouin gain is modulated, resulting in a significant enhancement of its gain envelope coverage. The actual measured Brillouin laser frequency shift can span several GHz, which is in stark contrast to the traditional MHz level.

[0030] As Figure 6 The Brillouin shift data histogram and the wide-range Brillouin gain theoretical curve are shown in the two crystal cavities, by scanning the Brillouin mode near the wavelength window of 1550nm and 1555nm, in the generation of more than 2.5GHz wide Brillouin gain spectrum, the observed Brillouin shift frequency range from 11.729GHz to 14.466GHz. It can be seen that the probability of finding stimulated Brillouin scattering according to the Brillouin shift is in good agreement with the theoretical gain curve. It is proved that the wide-range Brillouin gain curve characteristics in the application.

[0031] Based on the above wide gain Brillouin laser, the application also provides an optical microwave source, which comprises the above Brillouin laser, by combining the pump and the Brillouin laser into a superfast photoelectric detector, the laser signal can be up-converted into a microwave signal, and due to the narrow linewidth characteristic of the high-quality factor resonant cavity, the optical microwave signal has the characteristics of low phase noise.

[0032] The above is only the preferred embodiment of the application and is not used to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for controlling Brillouin gain, characterized in that: The resonant cavity employs a Brillouin gain crystal with curved boundaries. A pre-designed curved optical path serves as the propagation path for acoustic phonons. The angle between the acoustic phonons and the crystal axis of the Brillouin gain crystal during propagation is... The constant changes cause the propagation speed of the acoustic phonons in the crystal to change. It also constantly changes, generating a backward Brillouin gain envelope, thus achieving Brillouin gain modulation; the laser entering the resonant cavity, after total internal reflection, propagates along the curved boundary of the Brillouin gain crystal, and resonance enhancement occurs during the laser's propagation in the Brillouin gain crystal; the curved boundary of the Brillouin gain crystal is used to continuously change the propagation direction of the laser in the resonant cavity, achieving the angle between the laser propagation direction and the crystal axis. The constant changes in frequency shift of the Brillouin laser are synchronously controlled, and the relationship is as follows: The relationship between the gain coefficient of the Brillouin laser and the frequency shift modulation of the Brillouin laser is as follows: ,in, The linewidth is the traditional Brillouin gain, and L is the optical path length. This represents the frequency difference between the pump laser and the Stokes signal light.

2. A laser, characterized in that: The Brillouin gain control method described in claim 1 includes a pump source, a coupler, and a resonant cavity. The pump source generates acoustic phonons through electrostriction. After the acoustic phonons are injected into the crystal resonant cavity through the coupler, they are transmitted along the curved boundary through total internal reflection, and the laser generates resonance enhancement in the transmission plane.

3. The laser according to claim 2, characterized in that: The shape of the resonant cavity includes one of the following: disk, ring, or racetrack-shaped curved optical path.

4. The laser according to claim 3, characterized in that: The cavity size of the resonant cavity includes one of the following: millimeter-level, hundred-micrometer-level, and tens of micrometer-level.

5. The laser according to claim 2, characterized in that: The Brillouin gain crystal can be a single crystal or a polycrystalline crystal.

6. The laser according to claim 2, characterized in that: The coupler includes one of the following: prism coupler, micro / nano fiber coupler, and integrated optical waveguide coupler.

7. A photogenerated microwave source, characterized in that: A laser employing any one of claims 2-6 that utilizes the Brillouin gain modulation method.

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