Bragg light generation system and method applicable to Bragg-type atomic interferometers

Abstract

This invention relates to a Bragg light generation system and method suitable for Bragg-type atomic interferometers. The system includes: a laser for generating a first laser beam with a frequency in a preset atomic absorption peak band; an optical circulator for propagating the first laser beam to a cascaded acousto-optic modulator and receiving two third laser beams returned from the cascaded acousto-optic modulator; a cascaded acousto-optic modulator for diffracting the first laser beam into two second laser beams with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; an optical assembly for performing secondary diffraction on the two second laser beams and reflecting the two mutually perpendicular second laser beams to the cascaded acousto-optic modulator; and an output module for splitting and sampling the two third laser beams and modulating the sampled third laser beams into Bragg laser beams in the target frequency band. This invention reduces the path separation of the two Bragg laser beams by using a quasi-common optical path, thereby reducing phase noise and improving measurement accuracy.

Description

Technical Field

[0001] This invention belongs to the field of cold atom interferometry precision measurement technology, specifically relating to a Bragg light generation system and method suitable for Bragg-type atomic interferometers. Background Technology

[0002] With the rapid development of laser cooling technology, cold atom interferometry is playing an increasingly important role in precision measurement. Interferometers based on stimulated Raman transitions are called Raman atomic interferometers. In Raman atomic interferometers, after atoms absorb and emit photons, their internal states change, and their momentum states undergo a two-photon momentum change. Interferometers based on Bragg diffraction of atoms are called Bragg atomic interferometers. In Bragg atomic interferometers, the internal states of atoms do not change; only their momentum states change. In both types of interferometers, atomic wave packets are split, reflected, and converged under the action of three laser pulses to complete the interference. However, Bragg interferometers have a larger interference area due to multi-photon momentum transfer, thus increasing the interference phase shift and providing the possibility of further improving resolution. Furthermore, the internal states of atoms do not change during the interference process, thus reducing the influence of external electromagnetic fields on the interferometer. Therefore, Bragg interferometers have great potential in terms of measurement accuracy and environmental adaptability.

[0003] According to current literature, the Bragg laser in a Bragg interferometer is usually obtained by polarization combining two acousto-optic modulators with dual optical paths. Although this optical path can produce two laser beams with perpendicular polarization, similar frequencies, and tunability, which can form the optical lattice required for atomic Bragg diffraction, the separate paths of the two Bragg laser beams may cause optical path fluctuations due to vibrations, thus introducing phase noise. The phase noise of the Bragg laser is currently one of the important noise sources that restricts the measurement accuracy of Bragg-type atomic gravimeters. Summary of the Invention

[0004] To reduce the phase noise of a Bragg interferometer, a Bragg light generation system suitable for a Bragg-type atomic interferometer is provided in a first aspect of the present invention, comprising: a laser for generating a first laser with a frequency in a preset atomic absorption peak band; an optical circulator for propagating the first laser to a cascaded acousto-optic modulator and receiving two third laser beams returned from the cascaded acousto-optic modulator; a cascaded acousto-optic modulator for diffracting the first laser into two second laser beams with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; and propagating the two third laser beams to the optical circulator; an optical component for performing secondary diffraction on the two second laser beams and reflecting the two mutually perpendicular second laser beams obtained by diffraction to the cascaded acousto-optic modulator; and an output module for splitting and sampling the two third laser beams and modulating the sampled third laser beams into Bragg lasers in a target frequency band.

[0005] In some embodiments of the present invention, the cascaded acousto-optic modulator operates at a wavelength of 780 nm.

[0006] Furthermore, the radio frequency loading directions of the two acousto-optic crystals are opposite.

[0007] Furthermore, the diffraction direction of the two acousto-optic crystals is upward or downward.

[0008] In some embodiments of the present invention, the optical component includes: a lens for transmitting a second laser beam and causing two second laser beams to propagate symmetrically along both sides of the zero-order light; a baffle for blocking the zero-order light; a waveplate for adjusting the polarization direction of one second laser beam so that the polarization directions of the two second laser beams are perpendicular; and a zero-degree reflector for reflecting the second laser beam.

[0009] Furthermore, the focal length of the lens is 50mm.

[0010] In the above embodiments, the output module includes: a beam splitter for splitting and sampling two third laser beams; a cascaded acousto-optic modulator for acousto-optic modulation of the sampled third laser beam; and an optical fiber collimator for outputting the modulated third laser beam.

[0011] Furthermore, it also includes an optical phase-locked loop for phase locking of the modulated third laser.

[0012] A second aspect of the present invention provides a method for generating Bragg light suitable for a Bragg-type atomic interferometer, comprising: generating a first laser with a frequency in a preset atomic absorption peak band; propagating the first laser to a cascaded acousto-optic modulator and receiving two third laser beams returned from the cascaded acousto-optic modulator; diffracting the first laser into two second laser beams with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; propagating the two third laser beams to an optical circulator; performing secondary diffraction on the two second laser beams and reflecting the two mutually perpendicular second laser beams obtained by diffraction to the cascaded acousto-optic modulator; performing beam splitting and sampling on the two third laser beams, and modulating the sampled third laser beams into Bragg lasers in a target frequency band.

[0013] The beneficial effects of this invention are:

[0014] The Bragg laser generation scheme of this invention adopts a quasi-common optical path design, which is different from the traditional two-beam Bragg laser path separation scheme. In this invention, the spatial separation of the two Bragg lasers is smaller, resulting in less phase noise, which helps to improve the measurement accuracy of the Bragg interferometer. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the basic structure of the Bragg light generation system of a Bragg-type atomic interferometer in some embodiments of the present invention;

[0016] Figure 2 This is a schematic diagram of the specific structure of the Bragg light generation system in some embodiments of the present invention;

[0017] Figure 3 This is a schematic flowchart of a Bragg light generation method in some embodiments of the present invention;

[0018] Figure Labels

[0019] 1. Laser, 2. Optical circulator, 3. Cascaded acousto-optic modulator, 4. Optical components, 5. Output module; Detailed Implementation

[0020] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] refer to Figure 1 and Figure 2 In a first aspect of the invention, a Bragg light generation system suitable for a Bragg-type atomic interferometer is provided, comprising: a laser 1 for generating a first laser with a frequency in a preset atomic absorption peak band; an optical circulator 2 for propagating the first laser to a cascaded acousto-optic modulator 3 and receiving two third laser beams returned from the cascaded acousto-optic modulator; the cascaded acousto-optic modulator 3 for diffracting the first laser into two second laser beams with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; propagating the two third laser beams to the optical circulator 2; and performing a second Bragg diffraction on the two second laser beams returned by an optical component 4 to obtain two third laser beams; the optical component 4 for performing a second diffraction on the two second laser beams and reflecting the two mutually perpendicular second laser beams obtained by diffraction to the cascaded acousto-optic modulator 3; and an output module 5 for splitting and sampling the two third laser beams and modulating the sampled third laser beams into Bragg lasers in a target frequency band.

[0022] It's important to note that cascaded AOM (Acousto-optic Modulator) refers to an acousto-optic modulator. An acousto-optic modulator is a device that modulates optical signals using the interaction between sound waves and light waves. This type of modulator generates sound waves within a crystal or glass material, thereby changing the material's refractive index and modulating the passing light beam. Acousto-optic modulators can be used to control the intensity, frequency, or direction of laser beams and are widely used in optical communication, optical signal processing, laser technology, and other fields.

[0023] In some embodiments of the present invention, the cascaded acousto-optic modulator 3 operates at a wavelength of 780 nm.

[0024] The laser input uses a frequency doubling module connected by a pigtail, which doubles the frequency of a high-power 1560nm fiber laser to obtain a 780nm laser of over 6W. Laser 1 uses modulation-transfer spectral frequency stabilization technology to lock the frequency at the absorption peak of rubidium-87 atoms. The laser generated by the frequency doubling module is incident on port 1 of optical circulator 2 and output from port 2. After output, it enters the cascaded AOM. The AOM operates in the 780nm band and contains two acousto-optic crystals. The radio frequency loading directions of the two acousto-optic crystals are opposite. Crystal 1 is frequency-shifted by -80MHz, and the diffracted light propagates downward. Crystal 2 is frequency-shifted by -80MHz and the diffracted light propagates upward. The two diffracted beams are incident on a 780nm zero-degree mirror after passing through a lens with a focal length of 50mm. The angle of the zero-degree mirror is adjusted so that the laser returning through the mirror returns along the original path and undergoes secondary diffraction.

[0025] In some embodiments of the present invention, the optical component 4 includes: a lens for transmitting the second laser and making the two second laser beams propagate symmetrically along both sides of the zero-order light; a baffle for blocking the zero-order light; a waveplate for adjusting the polarization direction of one of the second laser beams so that the polarization directions of the two second laser beams are perpendicular; and a zero-degree reflector for reflecting the second laser.

[0026] Specifically, the two secondary diffracted beams return to port 2 of the circulator 2 and exit from port 3. A quarter-wave plate can be added to one of the diffracted beams, thus making the polarization directions of the two diffracted beams perpendicular. During the atom's fall, adjusting the driving frequency of one of the diffracted beams can compensate for the laser frequency, ensuring that the Bragg frequency condition is satisfied throughout the atom's fall. To minimize the change in the direction of the secondary diffracted beams during tuning, the acousto-optic crystal to be tuned is placed near the focal point of the lens.

[0027] In the above embodiments, the output module 5 includes: a beam splitter for splitting and sampling two third laser beams; a cascaded acousto-optic modulator 3 for acousto-optic modulation of the sampled third laser beam; and an optical fiber collimator for outputting the modulated third laser beam.

[0028] Specifically, after output from the circulator, the beam is sampled by a 1:99 beam splitter, the sampled beam is monitored by a PD, the remaining beam is modulated by another AOM, and the diffracted beam is output by an optical fiber collimator, which is the desired Bragg laser.

[0029] Furthermore, it also includes an optical phase-locked loop for phase locking of the modulated third laser beam.

[0030] This invention presents a quasi-common-path Bragg laser generation scheme. The laser input first enters a free-space optical circulator, then a custom-designed cascaded optical array (AOM). The cascaded AOM contains two acousto-optic crystals with opposite radio frequency loading directions. By adjusting the angle between the crystals and the incident light, the diffracted beams from the two crystals are made to have the same polarity but propagate symmetrically along both sides of the zero-order beam. The zero-order beam is blocked by a baffle. After passing through a lens, the two diffracted beams are reflected by mirrors and return to the AOM for secondary diffraction. One diffracted beam can pass through a quarter-wave plate to make its polarization perpendicular to the other beam. The laser beam after secondary diffraction and beam combining exits from the third port of the circulator. After optical power detection by a sampling mirror and a photodiode (PD), the two Bragg laser beams undergo diffraction within the AOM, and the diffracted beams are output from the collimator, which is the desired Bragg laser. Because the two Bragg beams have similar and tunable frequencies and perpendicular polarization, they meet the conditions for optical lattice generation and can be used as Bragg lasers.

[0031] Example 2

[0032] refer to Figure 3 A second aspect of the present invention provides a method for generating Bragg light suitable for a Bragg-type atomic interferometer, comprising: S100. generating a first laser with a frequency in a preset atomic absorption peak band; S200. propagating the first laser to a cascaded acousto-optic modulator and receiving two third laser beams returned from the cascaded acousto-optic modulator; S300. diffracting the first laser into two second laser beams with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; and propagating the two third laser beams to an optical circulator; S400. performing secondary diffraction on the two second laser beams and reflecting the two mutually perpendicular second laser beams obtained by diffraction to the cascaded acousto-optic modulator; S500. performing beam splitting and sampling on the two third laser beams and modulating the sampled third laser beams into Bragg lasers in the target frequency band.

[0033] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0034] 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 within the protection scope of the present invention.

Claims

1. A Bragg light generation system suitable for Bragg-type atomic interferometers, characterized in that, include: A laser used to generate a first laser beam with a frequency in the preset atomic absorption peak band; An optical circulator is used to propagate the first laser beam to the cascaded acousto-optic modulator and to receive two third laser beams returned from the cascaded acousto-optic modulator. A cascaded acousto-optic modulator is used to diffract a first laser into two second lasers with opposite propagation directions through Bragg diffraction of two acousto-optic crystals; and to propagate two third lasers to an optical circulator. An optical component is used to perform secondary diffraction on two second laser beams and reflect the two mutually perpendicular second laser beams obtained by diffraction to a cascaded acousto-optic modulator. The output module is used to split and sample the two third laser beams and modulate the sampled third laser beams into Bragg lasers of the target frequency band.

2. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 1, characterized in that, The cascaded acousto-optic modulator operates at a wavelength of 780nm.

3. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 2, characterized in that, The radio frequency loading directions of the two acousto-optic crystals are opposite.

4. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 2, characterized in that, The diffraction directions of the two acousto-optic crystals are upward or downward.

5. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 1, characterized in that, The optical components include: A lens is used to transmit the second laser beam and to make the two second laser beams propagate symmetrically on both sides of the zeroth order light. A baffle plate is used to block zero-order light. A waveplate is used to adjust the polarization direction of a second laser beam so that the polarization directions of the two second laser beams are perpendicular. The zero-degree reflector is used to reflect the second laser beam.

6. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 5, characterized in that, The focal length of the lens is 50mm.

7. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 1, characterized in that, The output module includes: A beam splitter is used to separate and sample two third laser beams. A cascaded acousto-optic modulator is used to perform acousto-optic modulation on the sampled third laser beam. Fiber collimator is used to output the modulated third laser beam.

8. The Bragg light generation system for a Bragg-type atomic interferometer according to claim 7, characterized in that, Also includes: An optical phase-locked loop is used to lock the phase of a modulated third laser beam.

9. A method for generating Bragg light suitable for a Bragg-type atomic interferometer, characterized in that, include: The first laser beam with a frequency in the preset atomic absorption peak band is generated. The first laser beam is propagated to the cascaded acousto-optic modulator, and two third laser beams are received from the cascaded acousto-optic modulator. The first laser beam is diffracted into two second laser beams with opposite propagation directions by Bragg diffraction of two acousto-optic crystals; and the two third laser beams are propagated to the optical circulator. The two second laser beams are diffracted twice, and the two mutually perpendicular second laser beams obtained by diffraction are reflected to the cascaded acousto-optic modulator. The two third laser beams are split and sampled, and the sampled third laser beams are modulated into Bragg lasers of the target frequency band.

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