All-fiber type cold atom laser beam generation method and device

Abstract

The invention discloses a method and a device for generating an all-fiber cold atom laser beam, and belongs to the field of atomic physics and quantum optics. The device comprises a master laser module, a slave laser module, an optical fiber beam splitting and combining module, an optical fiber electro-optical modulation module, a locking feedback module, an optical fiber monitoring module, a bi-pass optical fiber acousto-optic modulation optical path module and an optical fiber attenuation module. And after main laser of the master-slave laser module is subjected to frequency shift through the optical fiber EOM, a-1-level sideband is locked on resonance signal peaks from F = 3 to F '= 4 of the Rb85 atom D2 line by using a modulation transfer spectrum method. And slave laser of the master-slave laser module locks master laser on a reference signal source by using an optical phase-locked loop method. Raman laser is prepared in a blue detuning mode in frequency shift, so that sideband modulation is locked, and all-fiber probe light, repump light, cooling light and Raman light beams for cold atom laser beams meet the requirements of atom capture, polarization gradient cooling, state selection, interference and detection of a plurality of cold atom physical stages. The invention has the advantages of small size, large frequency tuning range, good environmental adaptability and the like.

Description

Technical Field

[0001] The invention belongs to the field of atomic physics and quantum optics, and relates to a laser beam splitting, transmission and frequency power control method, and in particular to an all-fiber type method and device for generating a cold atom laser beam. Background Art

[0002] With the in-depth development of atomic cooling technology, cold atom interference physics technology has gradually become the core and key in many fields such as quantum communication and precision measurement. The cold atom interference physics experimental process mainly includes cold atom trapping, atomic state preparation, matter wave interference, and population number detection. In addition, the experiment requires multiple MHz-level laser beams that can be tuned within ms, requiring the frequency of the laser output by the laser system to be locked and modulated to achieve the specified frequency, line width, etc. Taking the cold atom absolute gravimeter as an example, laser frequency tuning and power control are particularly important. Ultra-high precision requires frequency locking stability better than 10 -9 , Raman laser has ultra-low phase noise -100dBc / √Hz, etc.

[0003] The existing spatial optical path scheme is not only susceptible to temperature, but also sensitive to vibration. In particular, the overall size is large and difficult to integrate. Currently, most of them use single-pass fiber AO modulators, but due to the low switch isolation ratio, additional switch devices are often required for optical isolation, and the frequency shift and tuning range are small, and arbitrary frequency changes cannot be achieved. Using two fiber AO modulators in series will lead to large overall experimental losses, waste of additional RF drive, and the need to use fiber switches, which have problems such as difficult control of polarization isolation ratio. Raman laser preparation uses red detuning. The frequency difference between Raman laser and cooling laser is about 1GHz, the device is complex, and the laser power loss is large. Summary of the invention

[0004] In order to solve the shortcomings of the laser optical path device required for the current cold atom experiment, such as complexity, large size, difficulty in adjustment, and easy fluctuation, and to meet the requirements of large-range tuning of laser frequency and high-precision power control, the purpose of the present invention is to provide a method and device for generating a cold atom laser beam using an all-fiber type, and the frequency shift adopts a blue detuning method to prepare Raman laser, so that the sideband modulation is locked, and the all-fiber type detection laser, re-pumping laser, cooling laser and Raman laser beam of the cold atom laser beam are used to meet the requirements of generating cold atom laser beams in multiple cold atom physical stages such as atomic capture, polarization gradient cooling, state selection, interference, and detection. The present invention has the advantages of small size, large frequency tuning range, and good environmental adaptability.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] The present invention discloses an all-fiber type method for generating a cold atom laser beam, comprising the following steps:

[0007] Step 1: After the master laser of the master-slave laser module is frequency-shifted by the fiber EOM, the -1 level sideband is locked to the resonance signal peak of F=3 to F'=4 of the D2 line of the Rb85 atom by the modulation transfer spectroscopy method. At this time, the 0-level signal, that is, the master laser output is blue-shifted by Δf2-Δf1 relative to the resonance transition frequency of the D2 line of the Rb87 atom F=1 to F'=2, thus achieving the frequency locking of the master laser.

[0008] Step 2: The slave laser of the master-slave laser module uses an optical phase-locked loop method to lock the master laser to the reference signal source. The frequency of the slave laser is changed by changing the frequency of the reference signal source, and the phase locking of the slave laser is achieved by using the reference signal source to hop the frequency.

[0009] Step 3: Each frequency-shifted light is generated by the following method:

[0010] ① The light output by the slave laser of the master-slave laser module is shifted by -Δf1 through the double-pass fiber acousto-optic modulation optical path module to generate a detection laser;

[0011] ② The light output by the master laser of the master-slave laser module is frequency-shifted by Δf1-Δf2 through the double-pass fiber acousto-optic modulation optical path to generate re-pumping light laser.

[0012] ③ The light output by the slave laser of the master-slave laser module is shifted by -Δf1 through the double-pass fiber acousto-optic modulation optical path to generate cooling laser.

[0013] ④ After the master and slave lasers of the master-slave laser module are combined, the Raman laser is generated after the frequency is shifted by Δf2-Δf1 through the double-pass fiber acousto-optic modulation optical path.

[0014] The master laser of the master-slave laser module is locked on the Rb atomic saturation absorption spectrum, the master laser output laser frequency remains unchanged, and the re-pumping laser and Raman laser are output after frequency shifting through the double-pass fiber acousto-optic modulation optical path module; the output light of the slave laser of the master-slave laser module beats with the master laser, and the fiber detector detects the signal, which is fed back to the slave laser DC modulation input end through the servo, and the phase is locked on the specified phase near the atomic cooling laser, and the frequency of the slave laser output light is changed by changing the frequency of the phase-locked loop reference signal source to meet the frequency change requirements of the cooling laser and polarization gradient cooling, as well as the requirements of the Raman laser frequency chirp; thus, an all-fiber detection laser, re-pumping light laser, cooling laser and Raman laser beam for cold atom laser beams are obtained, and based on the all-fiber detection laser, re-pumping light laser, cooling laser and Raman laser beam, cold atom laser beams are provided for atom capture, polarization gradient cooling, state selection, interference, and detection of multiple cold atom physical stages.

[0015] Furthermore, the frequencies of the double-pass fiber optic acousto-optic modulation optical path module for the cooling laser and the double-pass fiber optic acousto-optic modulation optical path module for the detection laser are consistent, and the frequencies of the double-pass fiber optic acousto-optic modulation optical path module for the Raman laser and the double-pass fiber optic acousto-optic modulation optical path module for the re-pumping laser are consistent. A time-division multiplexing method is used to switch between different timing states, thereby reducing the number of double-pass fiber optic acousto-optic modulation modules and reducing the complexity and cost of the all-fiber type cold atom laser beam generation device.

[0016] The invention discloses an all-fiber type cold atom laser beam generating device, which is used to realize the all-fiber type cold atom laser beam generating method. An all-fiber type cold atom laser beam generating device comprises a master-slave laser module, a fiber beam splitting and combining module, a fiber electro-optic modulation module, a locking feedback module, a fiber monitoring module, a dual-pass fiber acousto-optic modulation optical path module and a fiber attenuation module.

[0017] The master-slave laser module is used to output master frequency light and slave frequency light. The master frequency light is locked at a specific frequency. The master and slave frequency lights perform beat frequency, so that the slave laser completes phase locking.

[0018] The optical fiber splitting and combining module is used to split the master and slave frequency lights into multiple beams for output or combine them into one beam, which are used to control the frequency and power separately.

[0019] The optical fiber electro-optic modulation module is used to modulate the main frequency light to generate sidebands, thereby achieving wide-range sideband modulation locking.

[0020] The optical fiber monitoring module is used for real-time optical power monitoring and provides light intensity feedback.

[0021] The dual-pass optical fiber acousto-optic modulation optical path module is connected to an optical fiber beam splitter or an optical fiber beam combiner to control the frequency and power of each beam of light, and is also used as an optical switch to perform arbitrary timing switching.

[0022] The optical fiber attenuation module is used to attenuate the input optical power to avoid damage to the receiving device due to excessive input optical power.

[0023] Furthermore, the double-pass fiber optic acousto-optic modulation optical path module is composed of a fiber optic acousto-optic modulator, a fiber optic circulator, and a fiber optic reflector, and is used to achieve frequency shifting and switching of light, wherein the fiber optic circulator has a non-reciprocal characteristic.

[0024] Furthermore, the dual-pass fiber AO modulation optical path module is composed of a fiber AO modulator, a fiber polarization beam splitter, and a fiber Faraday reflector, which is used to achieve frequency shift and switching of light. The fiber Faraday reflector can reflect the polarization state SOP of the incident light in a 90° orthogonal polarization direction, minimizing the change of polarization state caused by thermal and mechanical disturbances in the optical fiber.

[0025] Beneficial effects:

[0026] 1. The stability of the free-space optical path device is poor and is easily affected by environmental factors. The present invention discloses an all-fiber type method for generating a cold atom laser beam. After the master laser is frequency-shifted by the optical fiber EOM, the -1 level sideband is locked to the resonance signal peak of the Rb85 atom D2 line F=3 to F'=4 by the modulation transfer spectroscopy method. At this time, the 0-level signal, that is, the master laser output is blue-shifted by Δf2-Δf1 relative to the resonance transition frequency of the Rb87 atom D2 line F=1 to F'=2, that is, the master laser is frequency-locked. The slave laser uses an optical phase-locked loop method to lock the master laser to the reference signal source. The frequency of the slave laser is changed by changing the frequency of the reference signal source, and the phase locking of the slave laser is achieved by using the reference signal source to hop the frequency. The present invention uses an all-fiber optical path system to generate a cold atom laser beam. Compared with the free-space optical path, it has the advantages of being temperature-insensitive, highly stable, small in overall size, and easy to integrate.

[0027] 2. The present invention discloses an all-fiber method for generating a cold atom laser beam. The frequency shifting adopts a blue detuning method to obtain Raman laser, and the sideband modulation locking method is used to achieve the frequency locking of the laser. The present invention can simplify the cold atom laser beam generating device and reduce the complexity and cost of the supporting electronic control system.

[0028] 3. The present invention discloses an all-fiber method for generating a cold atom laser beam, which utilizes the advantages of double-pass optical fiber for light transmission and frequency shifting. No additional switch is required, the optical path switching speed can reach the us level, and the tuning range is large. Any frequency shift can be achieved as long as the frequency is covered by the bandwidth of the acousto-optic modulator.

[0029] 4. The present invention discloses an all-fiber method for generating cold atom laser beams, which uses a double-pass fiber acousto-optic modulation optical path to generate detection laser, re-pumping laser, cooling laser and Raman laser, all of which are implemented using an all-fiber device to form an optical path, which is helpful for laser frequency tuning and power control. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the principle of an all-fiber type cold atom laser beam generation device provided by the present invention;

[0031] Figure 2 A diagram of energy level transitions of rubidium atoms in a frequency shift locking scheme of an all-fiber type method for generating a cold atom laser beam provided by the present invention;

[0032] Figure 3 It is a schematic diagram of a double-pass fiber acousto-optic modulator according to an embodiment of the present invention;

[0033] Among them, 1-master-slave laser module, 2-optical fiber splitting and combining module, 3-optical fiber electro-optic modulation module, 4-locking feedback module, 5-optical fiber monitoring module, 6-dual-pass optical fiber acousto-optic modulation module, 7-optical fiber attenuation module. DETAILED DESCRIPTION

[0034] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0035] Embodiment 1:

[0036] like Figure 1 As shown, the present embodiment discloses an all-fiber atomic interference laser generating device, which is composed of a master-slave laser module 1, a fiber splitting and combining module 2, a fiber electro-optic modulation module 3, a locking feedback module 4, a fiber monitoring module 5, a dual-pass fiber acousto-optic modulation module 6, and a fiber attenuation module 7.

[0037] The master and slave laser modules 1 use narrow linewidth fiber lasers and are dual-channel output lasers that output 780nm light. Both the master and slave laser modules 1 have analog voltage input terminals with an input voltage range of 0V-5V. The laser frequency variation range for laser output is about 500MHz.

[0038] The master laser output by the master-slave laser module 1 outputs four paths of light through the optical fiber splitting and combining module 2, which are frequency-locked laser, re-pumping laser, Raman master laser and monitoring laser. The first path of light is the Raman master laser part of the master laser output by the master-slave laser module 1, which is combined with the Raman slave laser part of the slave laser output by the master-slave laser module 1 through the 2x2 optical fiber splitting and combining module 2 and then split into two parts. One part is incident on the optical fiber high-speed light detector after passing through the optical fiber attenuation module 7, and a beat frequency signal is generated on the optical fiber high-speed light detector for use in the optical phase-locked loop system; the other part is transmitted to the vacuum cavity as Raman laser after being frequency-shifted by +800MHz through the dual-pass optical fiber acousto-optic modulation optical path module 6. The second light path is a frequency-locked laser used to lock the frequency of the master laser output by the master-slave laser module 1 after being attenuated by the optical fiber attenuation module 7; the third light path is used as a re-pumping laser after being frequency-shifted by -800MHz by the double-pass optical fiber acousto-optic modulation optical path module 6; the fourth light path is a monitoring laser used to monitor the output optical frequency and power of the master laser output by the master-slave laser module 1 in real time;

[0039] The slave laser output by the master-slave laser module 1 outputs four paths of light through the fiber splitter module 2, which are cooling laser, detection laser, Raman slave laser and monitoring laser. The first path of light is the Raman slave laser part of the slave laser output by the master-slave laser module 1. It is combined with the Raman master laser part of the master laser output by the master-slave laser module 1 through the 2x2 fiber splitter and combiner module 2 and then split into two parts. One part is incident on the fiber high-speed light detector after passing through the fiber attenuation module 7, and a beat frequency signal is generated on the fiber high-speed light detector for use by the optical phase-locked loop system; the other part is transmitted to the vacuum cavity as Raman laser after being frequency-shifted by +800MHz through the dual-pass fiber acousto-optic modulation optical path module 6. The second path of light is transmitted to the vacuum cavity as cooling laser after being frequency-shifted by -250MHz through the dual-pass fiber acousto-optic modulation optical path module 6; the third path of light is the detection laser, which is transmitted to the vacuum cavity as detection laser after being frequency-shifted by -250MHz through the dual-pass fiber acousto-optic modulation optical path module 6. The fourth light is a monitoring laser, which is used to monitor the output optical frequency and power of the slave laser output by the master-slave laser module 1 in real time.

[0040] In this embodiment, the fiber splitting and combining module 2 is used to split the laser output into several beams or combine multiple laser beams into one beam, and the splitting power ratio can be freely customized; the fiber attenuation module 7 is used to appropriately attenuate the laser power to facilitate the use of laser frequency locking and phase locking; the dual-pass fiber optic acousto-optic modulation optical path module 6 is the core part of the method of the present invention. The use of all-fiber devices to form this optical path can facilitate laser frequency tuning and power control. The dual-pass fiber optic acousto-optic modulation optical path is composed of a fiber optic acousto-optic modulator, a fiber optic circulator, a fiber optic reflector, a fiber optic Faraday reflector, and a fiber optic polarization beam splitter. The fiber optic acousto-optic modulator is driven by a 30dBm RF signal, which causes the passing laser to generate diffracted light. The laser frequency changes and the transmission direction is also deflected. By controlling the RF drive of the fiber optic acousto-optic modulator, arbitrary switching of the optical path can be achieved. Please refer to the dual-pass fiber optic acousto-optic modulation optical path module 7. Figure 3 .

[0041] The present embodiment discloses an all-fiber atomic interference laser generation method, which is implemented by the following steps:

[0042] Step 1: After the master laser of the master-slave laser module is frequency-shifted by the fiber EOM, the -1 level sideband is locked to the F=3 to F'=4 resonance signal peak of the Rb85 atomic D2 line using the modulation transfer spectroscopy method. At this time, the 0-level signal, that is, the master laser output is blue-shifted by 800MHz relative to the resonance transition frequency of the Rb87 atomic D2 line F=1 to F'=2, thus achieving frequency locking of the master laser.

[0043] Step 2: The slave laser of the master-slave laser module uses an optical phase-locked loop method to lock the master laser to the reference signal source. The frequency of the slave laser is changed by changing the frequency of the reference signal source, and the phase locking of the slave laser is achieved by using the reference signal source to hop the frequency.

[0044] Step 3: Each frequency-shifted light is generated by the following method:

[0045] ① The light output by the slave laser of the master-slave laser module is shifted by -250MHz through the double-pass fiber acousto-optic modulation optical path module to generate a detection laser;

[0046] ② The light output by the master laser of the master-slave laser module is frequency-shifted by -800MHz through the double-pass fiber acousto-optic modulation optical path to generate re-pumping light laser.

[0047] ③ The light output by the slave laser of the master-slave laser module is frequency-shifted by -250MHz through a double-pass optical fiber acousto-optic modulation optical path to generate a cooling laser.

[0048] ④ After the master and slave lasers of the master-slave laser module are combined, the frequency is shifted by +800MHz through the double-pass fiber acousto-optic modulation optical path to generate Raman laser.

[0049] The energy level transition diagram of the rubidium atom in the frequency shift locking method is shown in FIG. Figure 2 shown.

[0050] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of 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. An all-fiber method for generating a cold atom laser beam, characterized in that: The steps include: Step 1: After the master laser of the master-slave laser module is frequency-shifted by the fiber EOM, the -1 level sideband is locked to the resonance signal peak of the F=3 to F'=4 of the D2 line of the Rb85 atom by the modulation transfer spectroscopy method. At this time, the 0-level signal, that is, the master laser output is blue-shifted by Δf2-Δf1 relative to the resonance transition frequency of the D2 line of the Rb87 atom F=1 to F'=2, that is, the frequency locking of the master laser is achieved; Step 2: The slave laser of the master-slave laser module uses an optical phase-locked loop method to lock the master laser to the reference signal source; the frequency of the slave laser is changed by changing the frequency of the reference signal source, and the phase locking of the slave laser is achieved by using the reference signal source to hop the frequency; Step 3: Each frequency-shifted light is generated by the following method: ① The light output by the slave laser of the master-slave laser module is shifted by -Δf1 through the double-pass fiber acousto-optic modulation optical path module to generate a detection laser; ② The light output by the master laser of the master-slave laser module is frequency-shifted by Δf1-Δf2 through the double-pass fiber acousto-optic modulation optical path to generate re-pumping laser; ③ The light output by the slave laser of the master-slave laser module is shifted by -Δf1 through the double-pass fiber acousto-optic modulation optical path to generate cooling laser; ④ After the master and slave laser beams of the master and slave laser modules are combined, the Raman laser is generated after the frequency is shifted by Δf2-Δf1 through the double-pass fiber acousto-optic modulation optical path; The master laser of the master-slave laser module is locked on the Rb atomic saturation absorption spectrum, the master laser output laser frequency remains unchanged, and the re-pumping laser and Raman laser are output after frequency shifting through the double-pass fiber acousto-optic modulation optical path module; the output light of the slave laser of the master-slave laser module beats with the master laser, and the fiber detector detects the signal, which is fed back to the slave laser DC modulation input end through the servo, and the phase is locked on the specified phase near the atomic cooling laser, and the frequency of the slave laser output light is changed by changing the frequency of the phase-locked loop reference signal source to meet the frequency change requirements of the cooling laser and polarization gradient cooling, as well as the requirements of the Raman laser frequency chirp; thus, an all-fiber detection laser, re-pumping laser, cooling laser and Raman laser beam for cold atom laser beams are obtained, and cold atom laser beams are provided for atom capture, polarization gradient cooling, state selection, interference, and detection of multiple cold atom physical stages based on the all-fiber detection laser, re-pumping laser, cooling laser and Raman laser beam.

2. The all-fiber method for generating a cold atom laser beam according to claim 1, characterized in that: The frequencies of the double-pass fiber optic acousto-optic modulation optical path module for the cooling laser and the double-pass fiber optic acousto-optic modulation optical path module for the detection laser are consistent, and the frequencies of the double-pass fiber optic acousto-optic modulation optical path module for the Raman laser and the double-pass fiber optic acousto-optic modulation optical path module for the re-pumping laser are consistent. A time-division multiplexing method is used to switch different timing states, thereby reducing the number of double-pass fiber optic acousto-optic modulation optical path modules.

3. An all-fiber type cold atom laser beam generating device, used to implement an all-fiber type cold atom laser beam generating method as claimed in claim 1 or 2, characterized in that: It includes a master-slave laser module, a fiber splitting and combining module, a fiber electro-optic modulation module, a locking feedback module, a fiber monitoring module, a dual-pass fiber acousto-optic modulation optical path module and a fiber attenuation module; The master-slave laser module is used to output master frequency light and slave frequency light, the master frequency light is locked at a specific frequency, the master and slave frequency lights perform beat frequency, so that the slave laser completes phase locking; The optical fiber splitting and combining module is used to split the master and slave frequency lights into multiple beams for output or combine them into one beam, which are used to control the frequency and power separately; The optical fiber electro-optic modulation module is used to modulate the main frequency light to generate sidebands, so as to achieve wide range sideband modulation locking; The optical fiber monitoring module is used for real-time optical power monitoring and provides light intensity feedback; The dual-pass optical fiber acousto-optic modulation optical path module is connected to an optical fiber beam splitter or an optical fiber beam combiner to control the frequency and power of each beam of light, and is also used as an optical switch to perform arbitrary timing switching. The optical fiber attenuation module is used to attenuate the input optical power to avoid damage to the receiving device due to excessive input optical power.

4. The all-fiber type cold atom laser beam generating device according to claim 3, characterized in that: The double-pass fiber optic acousto-optic modulation optical path module is composed of a fiber optic acousto-optic modulator, a fiber optic circulator, and a fiber optic reflector, and is used to realize frequency shifting and switching of light, wherein the fiber optic circulator has a non-reciprocal characteristic.

5. The all-fiber type cold atom laser beam generating device according to claim 3, characterized in that: The double-pass fiber AO modulation optical path module consists of a fiber AO modulator, a fiber polarization beam splitter, and a fiber Faraday reflector, which is used to achieve frequency shifting and switching of light. The fiber Faraday reflector can reflect the polarization state SOP of the incident light in an orthogonal polarization direction of 90°, thereby minimizing the change of polarization state caused by thermal and mechanical disturbances in the optical fiber.

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