A Brillouin laser

Abstract

The present invention discloses a Brillouin laser, comprising: a pump source emitting pump light of a first frequency, which, after beam aperture adjustment and collimation by a telescope device, passes sequentially through an optical isolator, a sampling lens, a first half-wave plate, and a focusing lens, before entering a Brillouin oscillator composed of a concave reflector, a Brillouin crystal, a convex lens device, and a volume Bragg grating; the pump light excites Stokes light of a second frequency in the Brillouin crystal, and the volume Bragg grating is placed on a piezoelectric ceramic displacement platform. The displacement of the piezoelectric ceramic displacement platform is controlled by a frequency-locked controller to adjust the Brillouin oscillator cavity length. The present invention effectively suppresses the generation of cascaded Stokes light, significantly increasing the output power of the Brillouin laser. The operable wavelength covers the ultraviolet, visible, and infrared bands, depending on the selected materials.

Description

Technical Field

[0001] The present invention relates to the field of lasers, and in particular to a high-power Brillouin laser. Background Art

[0002] Lasers with narrow linewidth have broad application prospects in the fields of lidar, interferometric sensors, metrology, quantum physics and microwave photonics. In particular, ultra-narrow linewidth laser light sources with high power, low noise and high beam quality have become irreplaceable and powerful tools in cutting-edge scientific research. With the increasing interest in space exploration, narrow linewidth lasers with high power, low noise and high beam quality are expected to significantly improve the distance of space communications and detection accuracy. Therefore, the research on light sources that meet this characteristic has important practical significance. The current methods for obtaining narrow linewidth lasers include direct radiation from semiconductors, distributed feedback (DFB) fiber lasers and Fabry-Perot (FP) longitudinal mode selective solid lasers. Although the output linewidth of some narrow linewidth semiconductor lasers and DFB fiber lasers can reach the kHz level and the stability and beam quality can also achieve good indicators, the output power is low. In addition to the above methods, Brillouin lasers based on stimulated Brillouin scattering (SBS) effect are regarded as a potential technical approach to obtain ultra-narrow linewidth and low-noise lasers. Currently, ultra-narrow linewidth laser output of sub-Hz has been achieved, which is 10 times narrower than other technical means. 3 -10 6 times.

[0003] Although waveguide-type Brillouin lasers have achieved low-threshold and narrow-linewidth output, they still face some difficult-to-overcome challenges, such as complex manufacturing processes, difficulty in suppressing cascaded Stokes light, low output power, and a very limited operating wavelength (usually limited to a few specific near-infrared wavelengths). Summary of the Invention

[0004] The present invention provides a high-power Brillouin laser. The purpose of the present invention is to overcome the technical shortcomings of the above-mentioned waveguide-type Brillouin laser, effectively suppress the generation of cascade Stokes light, and significantly increase the output power of the Brillouin laser. The operating wavelength covers the ultraviolet, visible light, and infrared bands depending on the selected materials. Details are described below:

[0005] A Brillouin laser, comprising:

[0006] The pump source emits pump light of the first frequency, which passes through the telescope device, the optical isolator, the sampling lens, the first half-wave plate and the focusing lens, and then enters the Brillouin oscillator composed of a concave reflector, a Brillouin crystal, a convex lens device and a volume Bragg grating;

[0007] The pump light excites Stokes light of the second frequency in the Brillouin crystal. The volume Bragg grating is placed on a piezoelectric ceramic displacement platform. The displacement of the piezoelectric ceramic displacement platform is controlled by a frequency-locked controller to adjust the cavity length of the Brillouin oscillator.

[0008] Among them, the frequency-locked controller is used to realize the measurement of the polarization signal of the resonant cavity, convert the optical signal into an electrical signal, perform subtraction operation, and then send it to the piezoelectric ceramic displacement platform. The piezoelectric ceramic displacement platform moves according to the electrical signal output by the frequency-locked controller. The frequency-locked controller consists of an attenuator, a quarter-wave plate, a polarization splitter prism, a first photodetector, a second photodetector and a subtractor.

[0009] The pump source is a solid laser, semiconductor laser or fiber laser that operates continuously or quasi-continuously, and the emitted laser is linearly polarized light.

[0010] Furthermore, the telescope device is composed of two convex lenses, the focusing lens is composed of a convex lens, and the convex lens device is composed of a convex lens. The light-transmitting surfaces of the convex lenses are all coated with a dielectric film that increases the transmittance of the pump light; the sampling lens is composed of a flat optical glass that partially reflects the pump light.

[0011] Furthermore, the optical isolator is used for unidirectional passage of pump light, and the optical isolator consists of a second half-wave plate, a first polarizer, a Faraday rotator, a third half-wave plate and a second polarizer.

[0012] The concave reflector is a plano-concave mirror, the flat surface of which is coated with a dielectric film that increases the transmittance of the pump light, and the concave surface of which is coated with a dielectric film that is highly reflective of the pump light.

[0013] Furthermore, both end faces of the volume Bragg grating are plated with anti-reflection films for pump light, the volume Bragg grating is reflective, and the center frequency is equal to the first frequency.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] 1. The laser directly achieves dual resonance of pump light and Stokes light in free space through a frequency-locked controller. By increasing the power of the pump light in the cavity and lowering the Brillouin laser threshold through cavity enhancement, it can effectively improve the quantum conversion efficiency of the laser and reduce the thermal load of the crystal.

[0016] 2. The present invention forms a free spatial operation mode through the Brillouin laser system composed of a concave reflector, a Brillouin crystal, a convex lens device, and a volume Bragg grating. Compared with the waveguide-type Brillouin laser, it does not require complex manufacturing processes and procedures, and can effectively increase the cross-sectional area and mode volume of the beam, increase the design freedom of the Brillouin laser, improve the energy extraction efficiency, and add temperature control capabilities. In addition, the operating wavelength range is wider than that of the waveguide-type Brillouin laser;

[0017] 3. By selecting bulk crystals such as diamond and TeO2 as Brillouin crystals, the laser can achieve outputs of different wavelengths, output linewidths and powers;

[0018] 4. The laser uses a volume Bragg grating to effectively suppress the generation of cascade Stokes light, achieving pure high-power, narrow-linewidth Brillouin laser output. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of a high-power Brillouin laser;

[0020] Figure 2 Schematic diagram of the structure of the optical isolator;

[0021] Figure 3 This is a structural diagram of the frequency-locked controller.

[0022] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0023] 1: Pump source; 2: Telescope device;

[0024] 3: Optical isolator; 4: Sampling lens

[0025] 5: First half wave plate; 6: Focusing lens;

[0026] 7: Concave reflector; 8: Brillouin crystal;

[0027] 9: Convex lens device; 10: Volume Bragg grating;

[0028] 11: Piezoelectric ceramic displacement platform; 12: Frequency-locked controller;

[0029] 13: Second half-wave plate; 14: First polarizer;

[0030] 15: Faraday rotator; 16: Third half-wave plate;

[0031] 17: second polarizer; 18: attenuation plate;

[0032] 19: Quarter wave plate; 20: Polarization beam splitter prism;

[0033] 21: first photodetector; 22: second photodetector;

[0034] 23: Subtractor. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0036] By studying the problems existing in the background technology, it is found that free-space Brillouin laser has become a potential way to break through the bottleneck of waveguide-type Brillouin laser and realize high-power narrow-linewidth laser output. In the free-space operation structure, in order to achieve high-power Brillouin laser operation output, the material needs to have a high Brillouin gain coefficient and high thermal conductivity; in addition, in order to meet the requirements of different working wavelengths and obtain high conversion efficiency, the material also needs to have a wide transmission spectrum and less negative nonlinear effects. Crystal materials represented by diamond have an extremely wide spectral transmission range and extremely high thermal conductivity. They are optical crystals that can achieve high-power and high-beam quality Brillouin laser output that is almost unaffected by heat. They are effective materials for realizing high-power free-space Brillouin laser output.

[0037] In summary, the present invention proposes to use a crystal material with a high gain coefficient and extremely high thermal conductivity as a Brillouin gain medium, directly pump the Brillouin oscillator cavity, and combine it with a volume Bragg grating (VBG) to achieve frequency control to obtain free-space operation of a high-power Brillouin laser.

[0038] In order to solve the problem of low output power of existing Brillouin lasers, the present invention proposes a high-power Brillouin laser based on free space operation of crystal materials. Figure 1 A high-power Brillouin laser includes: a pump source 1, a telescope device 2, an optical isolator 3, a sampling lens 4, a first half-wave plate 5, a focusing lens 6, a concave reflector 7, a Brillouin crystal 8, a convex lens device 9, a volume Bragg grating 10, a piezoelectric ceramic displacement platform 11, and a frequency-locked controller 12.

[0039] Among them, the pump source 1 emits a first frequency (ν p) is a continuous or quasi-continuous linearly polarized pump light, which is adjusted and collimated by the telescope device 2, and then passes through the optical isolator 3, the sampling lens 4, the first half-wave plate 1 and the focusing lens 6, and enters the Brillouin oscillator composed of a concave reflector 7, a Brillouin crystal 8, a convex lens device 9 and a volume Bragg grating 10; the volume Bragg grating 10 is placed on the piezoelectric ceramic displacement platform 11; the back-reflected pump light is reflected by the sampling lens 4 and then enters the frequency-locked controller 12, which monitors the polarization state change of the incident light and feeds back the signal to the piezoelectric ceramic displacement platform 11, and the piezoelectric ceramic displacement platform 11 moves in real time according to the feedback signal.

[0040] The adjustment and collimation of the beam aperture of the telescope device 2 are well known to those skilled in the art, and will not be elaborated in detail in the embodiment of the present invention.

[0041] In a specific implementation, the first half-wave plate 5 is used to adjust the polarization of the incident pump light so that its polarization state matches the maximum gain polarization angle of the Brillouin crystal 8. The concave reflector 7 is a plano-concave mirror, with a dielectric coating on the flat surface that increases the transmittance of the pump light and a dielectric coating on the concave surface that highly reflects the pump light. The pump light emitted from the pump source is incident on the flat surface reflected by the concave surface.

[0042] See also Figure 2 The optical isolator 3 is composed of a second half-wave plate 13, a first polarizer 14, a Faraday rotator 15, a third half-wave plate 16 and a second polarizer 17. On the one hand, the incident pump light is allowed to pass through the optical isolator 3 in one direction, and the reversely transmitted light is deflected and emitted through the first polarizer 14 or the second polarizer 17 due to the change in polarization state, and therefore cannot pass through the optical isolator 3, thereby protecting the pump source 1. At the same time, by adjusting the second half-wave plate 13, the power of the pump light incident on the Brillouin crystal 8 can be continuously adjusted without changing the quality of the pump light beam and the spot size.

[0043] That is, the optical isolator 3 is used to achieve unidirectional transmission of the incident pump light, and the light transmitted in the reverse direction cannot pass through, thereby playing the role of adjusting the power of the incident pump light and protecting the pump source.

[0044] See also Figure 3 The frequency-locked controller 12 is used to measure the polarization signal of the resonant cavity, convert the optical signal into an electrical signal, perform a subtraction operation, and then send it to the piezoelectric ceramic displacement platform. The piezoelectric ceramic displacement platform 11 moves according to the electrical signal output by the frequency-locked controller 12. The frequency-locked controller is composed of an attenuator 18, a quarter-wave plate 19, a polarization beam splitter prism 20, a first photodetector 21, a second photodetector 22, and a subtractor 23.

[0045] The laser line width emitted by the pump source 1 is δν, and the Brillouin gain line width of the Brillouin crystal 8 is ΓB , satisfying δν≤2Γ B ; Pump source 1 emits a frequency of ν p The pump light undergoes stimulated Brillouin scattering in the Brillouin crystal 8, and the frequency of the generated Stokes light is ν S .

[0046] Among them, both end faces of the volume Bragg grating 10 are plated with a frequency of ν p The volume Bragg grating 10 is a reflective type, and its center frequency is equal to the frequency ν emitted by the pump source 1 p , which is for frequency ν p The reflectivity of the pump light is R p , for frequency ν S The reflectivity of Stokes light is R S , R S <R p .

[0047] The frequency-locked controller 12 controls the piezoelectric ceramic displacement platform 11 so that the physical length L of the Brillouin oscillator composed of the concave reflector 7, the Brillouin crystal 8, the convex lens 9 and the volume Bragg grating 10 is equal to a positive integer multiple of c / (ν p -ν S ), where c is the speed of light in vacuum, thereby achieving dual resonance of pump light and Stokes light in the Brillouin oscillator to obtain high-efficiency Stokes light amplification output.

[0048] In practical applications, the Brillouin crystal 8 is a diamond crystal, a TeO2 crystal, a quartz crystal, a chalcogenide compound, or a rod-shaped optical fiber, and the Brillouin gain linewidth of the Brillouin crystal 8 is Γ B ; The cutting angles of the two ends of the Brillouin crystal 8 are flat-flat, or Brewster angle, and the two ends of the Brillouin crystal 8 are plated with a frequency of ν p Pump light anti-reflection coating.

[0049] When the two end faces of the Brillouin crystal 8 are cut at a flat-flat angle, the angle between the pump light and the incident surface of the Brillouin crystal 8 is 0°; when the two end faces of the Brillouin crystal 8 are cut according to the Brewster angle, the angle between the pump light and the incident surface of the Brillouin crystal 8 is equal to the Brewster angle.

[0050] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0051] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Brillouin laser, characterized in that The laser comprises: The pump source emits pump light of a first frequency, which, after being adjusted and collimated by the telescope device, passes through an optical isolator, a sampling lens, a first half-wave plate and a focusing lens in sequence, and then enters a Brillouin oscillator composed of a concave reflector, a Brillouin crystal, a convex lens device and a volume Bragg grating. The pump source is a solid-state laser, a semiconductor laser or a fiber laser operating continuously or quasi-continuously, and the emitted laser light is linearly polarized light. The optical isolator is used for unidirectional passage of the pump light, and the optical isolator is composed of a second half-wave plate, a first polarizer, a Faraday rotator, a third half-wave plate and a second polarizer. The telescope device is composed of two convex lenses, the focusing lens is composed of a convex lens, and the convex lens device is composed of a convex lens. The light-transmitting surfaces of the convex lenses are all coated with a dielectric film that increases the transmittance of the pump light. The first half-wave plate is used to adjust the polarization state of the pump light to a polarization state that matches the maximum gain polarization angle of the Brillouin crystal. The concave reflector is a plano-concave mirror, and the plane is coated with a dielectric film that increases the transmittance of the pump light. A dielectric film for optical anti-reflection, with a concave surface coated with a dielectric film that is highly reflective of pump light; the sampling lens is composed of a flat optical glass that partially reflects the pump light; the physical length of the Brillouin oscillator is equal to a positive integer multiple of the product of the inverse of the difference between the first frequency and the second frequency and the speed of light in a vacuum; the pump light excites Stokes light of a second frequency in the Brillouin crystal; the volume Bragg grating is placed on a piezoelectric ceramic displacement platform, and the displacement of the piezoelectric ceramic displacement platform is controlled by a frequency-locked controller to adjust the cavity length of the Brillouin oscillator; the laser linewidth of the pump light is less than or equal to twice the Brillouin gain linewidth of the Brillouin crystal; both end faces of the volume Bragg grating are coated with an anti-reflection film for pump light, the volume Bragg grating is reflective, and the center frequency is equal to the first frequency; the reflectivity of the volume Bragg grating to Stokes light of the second frequency is less than the reflectivity to pump light of the first frequency; the volume Bragg grating is used to suppress the generation of cascaded Stokes light and output pure, high-power, narrow-linewidth Brillouin laser light; The frequency-locked controller is used to measure the polarization signal of the resonant cavity, convert the optical signal into an electrical signal, perform a subtraction operation, and then send it to the piezoelectric ceramic displacement platform. The piezoelectric ceramic displacement platform moves according to the electrical signal output by the frequency-locked controller. The frequency-locked controller is composed of an attenuator, a quarter-wave plate, a polarization beam splitter, a first photodetector, a second photodetector, and a subtractor. The cutting angle of the two ends of the Brillouin crystal is flat-flat or Brewster angle, and the two ends of the Brillouin crystal are coated with a pump light anti-reflection film with a first frequency. When the two end faces of the Brillouin crystal are cut at a flat-flat angle, the angle between the pump light and the incident surface of the Brillouin crystal is 0°; when the two end faces of the Brillouin crystal are cut according to the Brewster angle, the angle between the pump light and the incident surface of the Brillouin crystal is equal to the Brewster angle.

Images