A laser based on a Brewster window atomic filter and its implementation method

Abstract

The present invention discloses a laser based on a Brewster window atomic filter and a method for realizing the same. Fluorescence is emitted by a laser diode coated with an antireflection film, and after being collimated by a collimating lens, it is incident on an anomalous dispersion atomic filter based on a Brewster window. Only the light with a polarization direction satisfying the polarization selection effect of the incident surface of the Brewster window atomic filter is incident into the interior of the Brewster window atomic cell; the hyperfine energy levels of the atoms undergo Zeeman splitting, and only the light near the resonance transition frequency can pass through the exit surface of the Brewster window atomic cell again, reach the resonant cavity mirror, and then a part of the light returns along the original path to the laser diode coated with an antireflection film. After resonance is formed, it is then emitted by the resonant cavity mirror; the anomalous dispersion atomic filter based on a Brewster window realizes the function of the filter based on the resonance Faraday rotation effect generated when light and atoms interact in the atomic cell; the anomalous dispersion atomic filter based on a Brewster window includes: a Brewster atomic cell with the incident surface of the incident window perpendicular to the incident surface of the exit window, a permanent magnet, and a heating device.

Description

Technical Field

[0001] The present invention relates to the technical fields of atomic filtering and quantum frequency selection lasers, and particularly relates to a laser based on a Brewster window atomic filter and a method for realizing the same. Background Art

[0002] An atomic filter is a general term for devices that utilize the spectroscopic characteristics of atomic resonance transitions to achieve a filtering function. The commonly used Faraday anomalous dispersion atomic filter and Voigt anomalous dispersion atomic filter based on the Faraday rotation effect have characteristics such as a high background noise suppression ratio, narrow bandwidth, high transmittance, and high response rate, and play an irreplaceable and important role in research such as free optical communication, lidar remote sensing imaging, Faraday lasers, Voigt lasers, Faraday active optical frequency standards, quantum networks, quantum key distribution, ghost imaging, single-photon light sources, and precision spectroscopy.

[0003] However, the anomalous dispersion atomic filters used in the above-reported research and applications currently all adopt a structure in which a polarizer and an analyzer are respectively placed before and after an atomic gas cell, and then an external magnetic field is applied. This structure will first lead to an increase in the noise of the system. Especially in applications such as Faraday lasers, Voigt lasers, and Faraday active optical frequency standards, although the polarizer, analyzer, and atomic gas cell placed before and after the atomic gas cell all have a high transmittance, even up to more than 90%, there is still inevitably feedback noise from the reflected light of the polarizer, analyzer, and atomic gas cell. Although the angle of the above devices can be adjusted significantly so that the reflected light is not in the optical axis direction, it will cause a large energy loss; at the same time, the presence of the polarizer and analyzer before and after the atomic gas cell will also cause instability of the cavity length of the resonant cavity, affecting the system performance; secondly, the stability and reliability of the system decrease, and the effective failure time depends on four devices, which will inevitably increase uncertainty.

[0004] In summary, a laser based on a Brewster window atomic filter and a method for realizing the same are problems that urgently need to be solved. Summary of the Invention

[0005] The present invention provides a laser based on a Brewster window atomic filter and a method for realizing the same. The present invention takes the polarization selection of the Brewster angle as the basic principle, aiming to achieve an anomalous dispersion atomic filter with high stability, reliability, and low noise generation, as described in detail below:

[0006] A laser based on a Brewster window atomic filter, the laser takes the Faraday resonance rotation as the basic principle, and realizes the anomalous dispersion atomic filter through the polarization selection principle of the Brewster angle, including: an antireflection-coated laser diode, an anomalous dispersion atomic filter based on a Brewster window, a resonant cavity mirror, and a piezoelectric ceramic;

[0007] The laser diode coated with an anti-reflection film emits fluorescence. After being collimated by a collimating lens, it is incident on an anomalous dispersion atomic filter based on a Brewster window. Only the light with a polarization direction that satisfies the polarization selection effect of the incident surface of the Brewster window atomic filter is incident into the interior of the Brewster window atomic cell; the hyperfine energy levels of the atoms undergo Zeeman splitting, and by heating, the internal atomic density reaches the requirement for the polarization direction of the light at the resonance transition frequency to rotate; only the light near the resonance transition frequency can pass through the exit surface of the Brewster window atomic cell again, reach the resonant cavity mirror, and then a part of the light returns along the original path to the laser diode coated with an anti-reflection film. After resonance, it is then emitted from the resonant cavity mirror;

[0008] The anomalous dispersion atomic filter based on a Brewster window realizes the function of the filter based on the resonance Faraday rotation effect generated when light and atoms interact in the atomic cell;

[0009] The anomalous dispersion atomic filter based on a Brewster window includes: a Brewster atomic cell with the incident window and the exit window incident surfaces perpendicular, a permanent magnet, and a heating device,

[0010] When the first and second incident lights are incident on the incident window of the Brewster window atomic cell, the light with a polarization direction parallel to the incident surface formed by the optical axis and the normal of the incident window enters the Brewster window atomic cell;

[0011] The light with a polarization direction perpendicular to the incident surface formed by the optical axis and the normal of the incident surface is reflected on the surface of the incident surface;

[0012] The light that enters the Brewster window atomic cell, under the action of an external magnetic field, will rotate under the action of Faraday resonance rotation. Only the light with a polarization direction parallel to the optical axis direction and the normal of the exit window and parallel to the incident surface of the exit window can pass through the exit window.

[0013] Among them, the atomic species in the Brewster atomic cell are rubidium, potassium, cesium, sodium, strontium, or a buffer gas is filled.

[0014] Among them, the material of the Brewster atomic cell is high borosilicate glass, sapphire glass, Schott glass, or GE180 glass.

[0015] Furthermore, the magnet is in an integrated form or a discrete form.

[0016] Among them, the resonant cavity mirror is a plane mirror, or a corner cube and a corner cube array, and the corner cube or the corner cube array includes a hollow corner cube and a solid corner cube.

[0017] A method for realizing a laser of an atomic filter based on a Brewster window, the method includes:

[0018] Select the material of the Brewster window atomic gas cell and determine the refractive index in the target filter band.

[0019] The incident window and the exit window of the Brewster window atomic gas cell are perpendicular to ensure that the light passing through the incident window has a polarization direction that meets the requirements for passing through the exit window after Faraday resonance optical rotation.

[0020] Apply an external magnetic field. The magnetic field direction is parallel to the optical axis, corresponding to a Faraday anomalous dispersion atomic filter; or the magnetic field direction is perpendicular to the optical axis, corresponding to a Voigt anomalous dispersion atomic filter.

[0021] Apply a heating device to heat the Brewster window atomic gas cell to meet the atomic density requirements for the occurrence of Faraday resonance optical rotation.

[0022] A method for realizing a laser based on a Brewster window atomic filter, the method comprising:

[0023] The fluorescence emitted by the antireflection-coated laser diode, after being collimated by a collimating lens, is incident in front of an anomalous dispersion atomic filter based on a Brewster window, and the light with a vertical polarization direction can pass through the anomalous dispersion atomic filter.

[0024] After the vertically polarized light enters the anomalous dispersion atomic filter, due to the presence of the external magnetic field, the energy levels of the atoms undergo Zeeman splitting. By heating, the internal atomic density reaches the requirement for the polarization direction of the light at the resonance transition frequency to rotate.

[0025] Only the light near the resonance transition frequency can pass through the exit surface of the Brewster window atomic gas cell again, reach the resonator mirror, and then a part of the light returns along the original path to the antireflection-coated laser diode. After resonance, it is then emitted by the resonator mirror.

[0026] Piezoelectric ceramics are used to provide the tunable function of the resonator.

[0027] The beneficial effects of the technical solution provided by the present invention are:

[0028] 1. The anomalous dispersion atomic filter based on the Brewster window of the present invention includes a Faraday anomalous dispersion atomic filter and a Voigt anomalous dispersion atomic filter, etc., which can meet the requirements for forming laser oscillation in quantum frequency selection lasers and active optical frequency standards; at the same time, improve its stability and reliability and reduce noise generation.

[0029] 2. The quantum frequency-selective laser of the present invention based on the Brewster window's anomalous dispersion atomic filter includes a Faraday laser, a Voigt laser, etc. It not only realizes that the output wavelength automatically corresponds to the atomic spectral line, and the output frequency is immune to current and temperature fluctuations, but also through the new system of the anomalous dispersion atomic filter, it can reduce the feedback noise in the laser cavity and improve the system performance; at the same time, by reducing the system components, the stability and reliability of the system can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 FIG. is a device diagram of an anomalous dispersion atomic filter based on the Brewster angle, where the magnetic field direction is parallel to the optical axis direction, that is, a Faraday anomalous dispersion atomic filter;

[0031] Figure 2 FIG. is a device diagram of an anomalous dispersion atomic filter based on the Brewster angle, where the magnetic field direction is perpendicular to the optical axis direction, that is, a Voigt anomalous dispersion atomic filter;

[0032] Figure 3 FIG. is a device diagram of an atomic filter laser based on the Brewster window, where the magnetic field direction is parallel to the optical axis direction, that is, a Faraday laser;

[0033] Figure 4 FIG. is a device diagram of an atomic filter laser based on the Brewster window, where the magnetic field direction is perpendicular to the optical axis direction, that is, a Voigt laser.

[0034] In the drawings, the list of components represented by each reference numeral is as follows:

[0035] 1: Optical axis direction; 2: Normal of the incident window;

[0036] 3-1: First incident light (vertically polarized); 3-2: Second incident light (horizontally polarized);

[0037] 4: First schematic of the rotation of the polarization direction when entering the gas cell; 5: Second schematic of the rotation of the polarization direction when entering the gas cell;

[0038] 6: Third schematic of the rotation of the polarization direction when entering the gas cell; 7: Normal of the exit window;

[0039] 8: Exit light; 9: Brewster window atomic gas cell;

[0040] 10: Permanent magnet module; 11: Heating module;

[0041] 12: Laser diode coated with an antireflection film; 13: Collimating lens;

[0042] 14: Anomalous dispersion atomic filter based on the Brewster window; 15: Resonator mirror;

[0043] 16: Piezoelectric ceramic. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the implementation manners of the present invention in detail.

[0045] An anomalous dispersion atomic filter based on Brewster angle mainly selects laser frequencies based on the Faraday rotation generated by the interaction between light and atoms, that is, it realizes the function of the filter based on the resonance Faraday rotation effect generated when light and atoms interact in an atomic gas cell. Due to the presence of an externally applied magnetic field, when light propagating in the same or perpendicular direction to the magnetic field direction passes through the atomic gas cell, the resonance Faraday interaction between light and atoms will change the polarization state of the outgoing light, making it different from the polarization direction of the incident light. By coordinating the polarization state selection before incidence and the polarization state selection before emergence, signals with an emergence-incidence direction deviation of 90° or an odd multiple of 90° are selected to achieve filtering. Specifically, the linearly polarized light entering the medium can be regarded as the superposition of left-handed and right-handed circularly polarized lights. Under the action of an externally applied magnetic field, the magnetic sub-levels of atoms will undergo Zeeman splitting, resulting in a difference in the transition frequencies of the left-handed and right-handed components, causing the dispersion curves of the left and right circularly polarized lights to split. Since the dispersion intensity is directly related to the refractive index of the incident light, at the same frequency of the incident light, the left-handed and right-handed components have different refractive indices. When the incident light propagates the same optical path, the left-handed and right-handed components have different phase changes, and the polarization direction of the incident light rotates.

[0046] When incident lights 3-1 and 3-2 are incident on the incident window of the Brewster window atomic gas cell 9, due to the polarization selection effect of the Brewster window, only the light with the polarization direction parallel to the incident plane formed by the optical axis 1 and the incident window normal 2, that is, 3-1, can enter the Brewster window atomic gas cell 9; the light with the polarization direction perpendicular to the incident plane formed by the optical axis 1 and the incident plane normal 2, such as 3-2, will be reflected on the surface of the incident plane. The light entering the Brewster window atomic gas cell 9 will rotate under the action of the externally applied magnetic field under the action of the Faraday resonance rotation. The rotation process is shown in 4, 5, and 6. Only the light with the polarization direction parallel to the emergence window incident plane formed by the optical axis direction 1 and the emergence window normal 7, such as 8, can pass through the emergence window, and lights with other frequency components are filtered out due to the polarization direction selection effect, thereby realizing the filtering function. More specifically, when the intensity of the incident light is determined, the rotation effect is directly related to the magnitude of the externally applied magnetic field, the length of the Brewster window atomic gas cell, and the atomic density (atomic gas cell temperature) in the Brewster window atomic gas cell. Through the coordination of the above parameters, an excellent filtering effect can be achieved. The magnetic field direction can be parallel to the optical axis direction, which is a Faraday anomalous dispersion atomic filter; the magnetic field direction can also be parallel to the optical axis direction, which is a Voigt anomalous dispersion atomic filter.

[0047] A quantum frequency-selective laser based on a Brewster window atomic filter uses anomalous dispersion based on the Brewster angle and an atomic filter for external cavity frequency selection to achieve laser resonance, thereby outputting a new type of external cavity semiconductor laser with a laser frequency near the atomic transition line and immune to laser diode current and temperature fluctuations; effectively suppressing the feedback noise in the cavity and improving the performance of the laser; at the same time, the structure is more stable and the reliability is higher.

[0048] This embodiment of the invention introduces a method for realizing an anomalous dispersion atomic filter based on the Brewster angle. Based on the principle of Faraday resonance optical rotation, through the polarization selection principle of the Brewster angle, anomalous dispersion atomic filtering is realized. Compared with the traditional anomalous dispersion atomic filter based on a polarizer, an atomic gas cell, and an analyzer structure, using a Brewster window atomic gas cell for the anomalous dispersion atomic filter can make the structure of the filter more stable and the reliability higher; at the same time, this form of anomalous dispersion atomic filter is more stable in structure, smaller in volume, and stronger in feedback noise suppression ability in applications such as Faraday lasers, Voigt lasers, and Faraday active optical frequency standards that require multiple passes through the anomalous dispersion atomic filter to form laser oscillation, and can well increase its anti-interference ability and environmental adaptability.

[0049] Embodiment 1

[0050] The Brewster window atomic gas cell in this embodiment of the invention is illustrated by taking high borosilicate glass, cesium atoms, and rubidium atoms as examples. The method includes the following steps:

[0051] 101: First, select the material of the Brewster window atomic gas cell 9 and determine the refractive index in the target filtering band;

[0052] Among them, the refractive index of high boron silicon material glass for the D2 line of cesium atoms is 1.47. Then, according to the condition satisfied by the Brewster angle, the corresponding Brewster angle can be calculated as 55.8°.

[0053] 102: For the incident window and the exit window of the Brewster window atomic gas cell 9, since the polarization directions of the transmitted light are perpendicular to each other, the incident surfaces of the incident window and the exit window must be perpendicular to ensure that the light passing through the incident window satisfies the requirement of passing through the exit window after Faraday resonance optical rotation;

[0054] 103: Apply an external magnetic field. The magnetic field direction can be parallel to the optical axis, corresponding to a Faraday anomalous dispersion atomic filter; the magnetic field direction can also be perpendicular to the optical axis, corresponding to a Voigt anomalous dispersion atomic filter;

[0055] 104: Apply a heating device to heat the Brewster window atomic gas cell 9 to meet the atomic density requirement for the occurrence of Faraday resonance optical rotation.

[0056] Example 2

[0057] The embodiment of the present invention introduces a method for realizing a laser of an anomalous dispersion atomic filter based on Brewster angle, as described in detail below:

[0058] 201: The fluorescence emitted by the antireflection-coated laser diode 12 is collimated by the collimating lens 13 and then incident on the anomalous dispersion atomic filter 14 based on the Brewster window. Here, the transmittance should be ensured to be the maximum. As Figure 3 and Figure 4 shown, before the fluorescence is incident on the anomalous dispersion atomic filter 14 based on the Brewster window, the polarization direction of the fluorescence has both horizontal and vertical directions. Only the light with the vertical polarization direction can pass through the anomalous dispersion atomic filter 14;

[0059] 202: After the vertically polarized light enters the anomalous dispersion atomic filter 14, due to the presence of the external magnetic field, the hyperfine energy levels of the atoms undergo Zeeman splitting. At the same time, by heating, the internal atomic density is made to meet the requirement that the polarization direction of the light at the resonance transition frequency rotates;

[0060] 203: Only the light whose polarization direction rotates near 90°, that is, only the light near the resonance transition frequency can pass through the exit surface of the Brewster window atomic cell 9 again, reach the resonant cavity mirror 15, and then a part of the light returns along the original path to the antireflection-coated laser diode 12. After resonance, it is then emitted by the resonant cavity mirror 15;<>

[0061] 204: The piezoelectric ceramic 16 is used to provide the tunable function of the resonant cavity.

[0062] In summary, the embodiment of the present invention is based on the principle of Faraday resonance optical rotation, and through the polarization selection principle of the Brewster angle, a highly reliable anomalous dispersion atomic filter is realized. The quantum frequency selection laser realized by using the Brewster window, compared with the structure of traditional polarizers, atomic cells, and analyzers, greatly reduces the complexity of the device and significantly improves the stability and reliability; the embodiment of the present invention will play an active role in basic scientific research such as quantum precision measurement, such as Faraday lasers, Voigt lasers, Faraday active optical frequency standards, etc., atomic physics, quantum optics, and practical engineering applications such as aerospace.

[0063] [[ID=]27]For the models of the various devices in the embodiment of the present invention, except for those with special instructions, the models of other devices are not limited, as long as the devices can perform the above functions.

[0064] Those skilled in the art can understand that the drawings are only schematic diagrams of a preferred embodiment, and the serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0065] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A laser of an atomic filter based on a Brewster window, characterized in that, The laser is based on the principle of Faraday resonance optical rotation. Through the polarization selection principle of Brewster angle, it realizes the atomic filtering of anomalous dispersion, that is, the Voigt laser, including: an antireflection-coated laser diode, an anomalous dispersion atomic filter based on a Brewster window, a resonant cavity mirror, and a piezoelectric ceramic; The Voigt anomalous dispersion atomic filter based on a Brewster window: The refractive index of high-borosilicate glass for the D2 line of cesium atoms is 1.

47. According to the condition satisfied by the Brewster angle, the corresponding Brewster angle is calculated to be 55.8°; An external magnetic field is applied, and the magnetic field direction is perpendicular to the optical axis, that is, corresponding to the Voigt anomalous dispersion atomic filter, to form a Voigt laser; Select the material of the Brewster window atomic cell and determine the refractive index in the target filtering band; The incident window and the exit window of the Brewster window atomic cell are perpendicular to ensure that the light passing through the incident window satisfies the requirement of the polarization direction for passing through the exit window after Faraday resonance optical rotation; An external heating device is used to heat the Brewster window atomic cell to meet the atomic density requirement for the occurrence of Faraday resonance optical rotation; The antireflection-coated laser diode emits fluorescence. After being collimated by a collimating lens, it is incident on the anomalous dispersion atomic filter based on a Brewster window. Only the light with a polarization direction that satisfies the polarization selection effect of the incident surface of the Brewster window atomic filter is incident into the interior of the Brewster window atomic cell; The hyperfine energy levels of the atoms undergo Zeeman splitting, and by heating, the internal atomic density reaches the requirement for the rotation of the polarization direction of the light at the resonance transition frequency; Only the light near the resonance transition frequency can pass through the exit surface of the Brewster window atomic cell again, reach the resonant cavity mirror, and then a part of the light returns to the antireflection-coated laser diode along the original path. After resonance, it is then emitted by the resonant cavity mirror; The anomalous dispersion atomic filter based on a Brewster window realizes the function of the filter based on the resonance Faraday rotation effect generated when light and atoms interact in the atomic cell; The anomalous dispersion atomic filter based on a Brewster window includes: a Brewster atomic cell with the incident window and the exit window incident surface perpendicular, a permanent magnet, and a heating device, When the first and second incident lights are incident on the incident window of the Brewster window atomic cell, the light with a polarization direction parallel to the incident surface formed by the optical axis and the normal of the incident window enters the Brewster window atomic cell; The light with a polarization direction perpendicular to the incident surface formed by the optical axis and the normal of the incident surface is reflected on the incident surface; The light entering the Brewster window atomic cell will have its polarization direction rotated under the action of an external magnetic field and the Faraday resonance optical rotation. Only the light with a polarization direction parallel to the exit window incident surface formed by the optical axis direction and the normal of the exit window can pass through the exit window.

2. The laser of an atomic filter based on a Brewster window according to claim 1, characterized in that, The atomic species of the Brewster atomic cell are rubidium, potassium, cesium, sodium, or strontium.

3. The laser of an atomic filter based on a Brewster window according to claim 1, characterized in that, The material of the Brewster atomic cell is high-borosilicate glass, sapphire glass, Schott glass, or GE180 glass.

4. A laser of an atomic filter based on a Brewster window according to claim 1, characterized in that, The permanent magnet is in an integrated form or a discrete form.

5. The laser of an atomic filter based on a Brewster window according to claim 1, characterized in that, The resonant cavity mirror is a plane mirror, or a corner cube and a corner cube array, and the corner cube or the corner cube array includes a hollow corner cube and a solid corner cube.

6. A method for implementing a laser for an atomic filter based on a Brewster window according to claim 1, characterized in that, The method includes: The fluorescence emitted by the laser diode coated with an antireflection film, after being collimated by a collimating lens, is incident on the front of an anomalous dispersion atomic filter based on a Brewster window. The light energy with a vertical polarization direction can pass through the anomalous dispersion atomic filter; After the vertically polarized light enters the anomalous dispersion atomic filter, due to the presence of an external magnetic field, the energy levels of the atoms undergo Zeeman splitting. By heating, the internal atomic density is made to meet the requirement for the rotation of the polarization direction of the light at the resonance transition frequency; Only the light energy near the resonance transition frequency can pass through the exit surface of the Brewster window atomic gas cell again, reach the resonant cavity mirror, and then a part of the light returns along the original path to the laser diode coated with an antireflection film. After resonance, it is then emitted by the resonant cavity mirror; The piezoelectric ceramic is used to provide the tunable function of the resonant cavity.

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