A multi-channel laser injection locking device based on whispering gallery microcavity

Abstract

The present invention discloses a multi-channel laser injection locking device based on a whispering gallery microcavity, which belongs to the technical field of quantum precision measurement and sensing. The device includes a pumping laser, a detection laser, a beam splitter, a fiber coupler, a fiber polarization controller, a fiber combiner, a whispering gallery optical microcavity and a temperature control module. Based on the wide transmission spectrum characteristics of the whispering gallery optical microcavity and the principle of laser injection locking, the characteristic backscattering Rayleigh scattering spectrum generated by the microcavity is used to achieve simultaneous injection locking of two or more laser frequencies with different central wavelengths, effectively combining the whispering gallery optical microcavity, light injection locking, and optical pumping and light detection technologies. The whole device is simple, the optical path structure is compact, the locking adjustment is convenient, and the noise reduction effect is significant. The present invention is suitable for precision instruments that require the simultaneous locking of the frequencies of single or multiple lasers, such as atomic magnetometers, atomic gyroscopes, atomic gravimeters, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum precision measurement and sensing, and specifically relates to a two-channel narrow-linewidth semiconductor laser light source system used in a hybrid pumping high-precision atomic magnetic field / inertial measurement system, and in particular to a multi-channel laser injection locking device based on a whispering gallery microcavity. Background Art

[0002] Quantum precision measurement and sensing has broad application prospects in extremely weak magnetic fields, inertia, gravity and cutting-edge basic fields. Atomic gyroscopes based on the SERF effect usually use hybrid optical pumping, that is, a gas chamber containing two alkali metal atoms (such as potassium atoms and rubidium atoms) is used as a sensitive element to detect the angular velocity of the moving carrier. Therefore, two narrow linewidth lasers corresponding to the central wavelength of alkali metal atomic absorption are required for optical pumping and signal detection respectively. Semiconductor lasers have the advantages of small size and low power consumption and are widely used in quantum sensor devices. However, they are limited by the short cavity length of semiconductor lasers, and the laser linewidth is mostly a few MHz. At more than ten MHz, the line width needs to be further compressed to reduce the light source noise. At the same time, in actual quantum sensors, due to the existence of pressure broadening and frequency shift, the optimal working point usually needs to deviate from the resonant absorption peak of alkali metal atoms, and the two lasers need to be stabilized at a frequency detuned or even far detuned position. The existing detuned or far detuned laser frequency locking system requires laser frequency locking, frequency shifting and other processes. The system is complex and large in size, and many components are prone to interference, which is not suitable for quantum precision measurement instruments such as atomic gyroscopes. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a multi-channel laser injection locking device based on a whispering gallery microcavity. By designing the parameters such as the size of the whispering gallery microcavity, the operating wavelengths of the pumping and detection lasers are respectively consistent with the wavelengths corresponding to a certain resonance mode generated by the microcavity. Then, the two lasers are respectively connected to the whispering gallery microcavity using the optical path designed by the device to achieve laser injection frequency locking, while compressing the line widths of the two lasers and reducing the frequency noise of the light source system. The invented device makes full use of the wide transmission spectrum range of the whispering gallery microcavity and the self-injection active locking to simultaneously narrow the line widths of the two lasers, effectively reducing the frequency noise of the light source system, and the entire device has a simple structure and is easy to operate.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A multi-channel laser injection locking device based on a whispering gallery microcavity, the device comprising a pumping laser, a detection laser, a first beam splitter prism, a second beam splitter prism, a first fiber coupler, a second fiber coupler, a first fiber polarization controller, a second fiber polarization controller, a fiber combiner, a whispering gallery optical microcavity and a temperature control module;

[0006] Among them, after the light output by the pump laser and the detection laser is split by the first beam splitter prism and the second beam splitter prism respectively, most of the light enters the atomic gyroscope optical path as pump light or detection light, and a small part of the light is coupled into the optical fiber through the first fiber coupler and the second fiber coupler for propagation. The two input ends of the fiber combiner are respectively connected to the first fiber coupler and the second fiber coupler, and the first fiber polarization controller and the second fiber polarization controller of the optical fiber are used to adjust the polarization state of the light in the optical fiber. The output end of the fiber combiner is connected to the whispering gallery optical microcavity. The whispering gallery optical microcavity is connected to the temperature control module, and the resonant wavelength of the microcavity can be adjusted by changing the temperature.

[0007] Furthermore, the pump laser is a DBR semiconductor laser, whose operating wavelength covers the resonance line wavelength of the alkali metal atom D1 line or D2 line, has a maximum output power of 120 mW, and the operating wavelength is continuously adjustable within a certain range near the resonance line wavelength.

[0008] Furthermore, the detection laser is a DBR semiconductor laser, whose operating wavelength covers the resonance line wavelength of the alkali metal atom D1 line or D2 line, has a maximum output power of 120 mW, and the operating wavelength is continuously adjustable within a certain range near the resonance line wavelength.

[0009] Furthermore, the first beam splitter prism and the second beam splitter prism are both cubic prisms formed by gluing two right-angle prisms, and their operating wavelengths cover the operating wavelengths of the pump laser and the detection laser, and are used to split the incident light corresponding to their respective optical paths into two beams of light according to a fixed light intensity ratio. The ratio of the light intensity output at the transmission end and the reflection end of each of the first beam splitter prism and the second beam splitter prism is a constant value, which has nothing to do with the polarization state of the incident light.

[0010] Furthermore, the first fiber coupler and the second fiber coupler are both mechanical devices with fiber interfaces, and have a lens inside for focusing incident spatial light, and are both used to couple the incident light corresponding to their respective optical paths into the optical fiber connected at the rear end. The lens position and angle are fine-tuned by multiple screws, and the focused light spot is aligned with the core of the connected optical fiber, achieving high-efficiency coupling of spatial light energy with the optical fiber core.

[0011] Furthermore, the first optical fiber polarization controller and the second optical fiber polarization controller are both mechanical devices that can clamp optical fibers, and can arbitrarily adjust the polarization state of light propagating in the clamped optical fibers by twisting the optical fibers. They are both used to arbitrarily control the polarization state of incident light transmitted in the optical fibers corresponding to their respective optical paths, and the polarization state control range covers the entire Poincaré sphere.

[0012] Furthermore, the fiber combiner is a fiber device, such as a 2×1 combiner, whose operating band covers the operating wavelengths of the pump laser and the detection laser, and can combine the light incident from the two fiber input ends into one beam and output it from the fiber output end, and can also be used in reverse as a beam splitting device.

[0013] Furthermore, the whispering gallery optical microcavity is a device made of materials such as crystal or quartz that can confine a high-energy-density light field to a cavity with a size of micrometer to millimeter through a whispering gallery mode. The central wavelength range of the resonance mode generated by the whispering gallery optical microcavity can cover the sum of the operating wavelengths of the pump laser and the detection laser used, the quality factor of the resonance mode can reach a very high level, and the damage power threshold of the whispering gallery optical microcavity is greater than the sum of the maximum output powers of the pump laser and the detection laser.

[0014] Furthermore, the temperature control module includes a thermistor, a semiconductor cooling sheet and a control circuit, which can measure the temperature of the whispering gallery optical microcavity packaging structure through the thermistor, and achieve the stability of the microcavity temperature by using the semiconductor cooling sheet combined with the feedback control algorithm in the control circuit.

[0015] The beneficial effects of the present invention are:

[0016] The present invention is mainly used for the laser light source system of the hybrid pumped atomic gyroscope, and has the advantages of simple optical path structure, convenient adjustment and significant noise reduction effect. The present invention utilizes the wide transmission spectrum characteristics of the whispering gallery optical microcavity and the basic principle of laser injection locking, combines the light of different wavelengths emitted by the pumping and detection lasers and introduces them into a single whispering gallery optical microcavity, and utilizes the back-scattered Rayleigh light of different wavelengths generated by the pre-designed microcavity to perform injection locking on the two lasers with different wavelengths. The present invention can effectively reduce the frequency noise of the pumping and detection lasers in the hybrid pumped light source system, and improve the spin polarization stability and detection sensitivity of the hybrid pumped atomic gyroscope. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of a multi-channel laser injection locking device based on a whispering gallery microcavity according to the present invention.

[0018] Figure numerals: 1. pumping laser, 2. detection laser, 3. first beam splitter prism, 4. second beam splitter prism, 5. first fiber coupler, 6. second fiber coupler, 7. first fiber polarization controller, 8. second fiber polarization controller, 9. fiber combiner, 10. whispering gallery optical microcavity, 11. temperature control module. DETAILED DESCRIPTION

[0019] The specific implementation of the present invention is described below in conjunction with the accompanying drawings for a better understanding of the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, these descriptions will be omitted here.

[0020] Existing hybrid pumped atomic gyroscope light source systems usually use two DBR semiconductor lasers with different wavelengths as pumping and detection lasers for optical pumping and signal detection. The line width of DBR semiconductor lasers is relatively wide, which will affect the polarization effect and detection accuracy of the atomic gyroscope. By adopting the above technical solution, two lasers with different wavelengths are injection-locked with different resonant wavelengths of the same whispering gallery microcavity, respectively, to achieve narrow linewidth and low noise output of the entire hybrid pumped atomic gyroscope optical system. Moreover, only one whispering gallery microcavity device is needed to achieve injection locking of the two lasers.

[0021] According to the above principle, if Figure 1 As shown, the present invention provides a multi-channel laser injection locking device based on a whispering gallery microcavity, which is mainly composed of a pump laser 1, a detection laser 2, a fiber combiner 9 and a whispering gallery optical microcavity 10. After the light emitted by the pump laser 1 and the detection laser 2 is split by the first beam splitter prism 3 and the second beam splitter prism 4, 90% of the light energy enters the atomic gyroscope pumping or detection light path as pumping light or detection light, and 10% of the light energy is coupled into the optical fiber through the first fiber coupler 5 and the second fiber coupler 6 to propagate. The two input ends of the fiber combiner 9 are respectively connected to the first fiber coupler 5 and the second fiber coupler 6 to combine the two paths of light into one path of light. At the same time, the two input ends of the fiber combiner 9 are respectively connected to the first fiber polarization controller 7 and the second fiber polarization controller 8, which are used to adjust the polarization state of the two incident lights so that they can excite more whispering gallery resonance modes. The output end of the fiber combiner 9 is connected to the whispering gallery optical microcavity 10. The back-scattered Rayleigh light generated by the whispering gallery optical microcavity 10 is split by the fiber combiner 9 and then propagates in the opposite direction into the pump laser 1 and the detection laser 2, thus realizing the self-injection locking of the two lasers. The temperature control module 11 can perform thermal tuning on the resonant wavelength of the whispering gallery optical microcavity 10 and can also keep the working environment temperature of the whispering gallery optical microcavity 10 stable to ensure the stability of injection locking.

[0022] The pump laser 1 is a DBR semiconductor laser with a central wavelength of 770 nm. DBR semiconductor lasers are called distributed Bragg feedback lasers. This type of laser uses a Bragg grating as a mode selection device and has a narrower output linewidth than ordinary FP cavity semiconductor lasers. The 770 nm band is the transition wavelength of the D1 line of the alkali metal atom potassium commonly used in atomic gyroscopes. The maximum output power of the laser of 120 milliwatts can meet the demand for pumping light in atomic gyroscopes. The laser can continuously change its output wavelength within a certain range by adjusting the operating temperature or injecting current.

[0023] The detection laser 2 is a DBR semiconductor laser with a central wavelength of 795 nm. The 795 nm band is the transition wavelength of the D1 line of the alkali metal atom rubidium commonly used in atomic gyroscopes. The maximum output power of the laser of 120 mW can meet the demand for detection light in atomic gyroscopes. The laser can continuously change its output wavelength within a certain range by adjusting the operating temperature or injecting current.

[0024] The first beam splitter prism 3 and the second beam splitter prism 4 are both polarization-independent beam splitters with a beam splitting ratio of 90:10, and their operating wavelengths cover 770 795 nm band. Since the whispering gallery microcavity injection locking does not require high optical power, and too high optical power in the microcavity will induce nonlinear effects and affect the effect of injection locking, only about 10% of the light is separated from the main path for injection locking to meet the requirements, and most of the remaining main path light can be used for pumping or detection of the atomic gyroscope.

[0025] The first fiber coupler 5 and the second fiber coupler 6 are both fiber couplers with multiple degrees of freedom. Since the whispering gallery optical microcavity device is coupled through a tapered fiber, and the beam combining devices in the system are also fiber devices, a fiber coupler is required to couple the spatial light separated by the laser into the fiber device connected at the back end for propagation.

[0026] The first optical fiber polarization controller 7 and the second optical fiber polarization controller 8 are both three-paddle polarization controllers that can produce birefringence by mechanically squeezing the optical fiber, thereby arbitrarily adjusting the polarization state of the light in the optical fiber. Since the excitation effect of the resonant mode in the whispering gallery microcavity is related to the polarization state of the incident light, it is necessary to use such an optical fiber polarization controller to adjust the output light of the two lasers incident into the whispering gallery microcavity to the appropriate polarization state.

[0027] The optical fiber combiner 9 is a 2×1 optical fiber combiner, which can combine two optical paths at the incident end into one optical path, and its operating wavelength covers 770 795 nm band. At the same time, the fiber combiner can also be used as a beam splitter in reverse, dividing the backscattered Rayleigh light generated by the whispering gallery optical microcavity into two paths of light propagation. At this time, the splitting ratio of the beam splitter is 50:50.

[0028] The whispering gallery optical microcavity 10 can be a fiber-coupled micro-cylindrical cavity made of quartz material through micro-nano processing technology. External input light is coupled into the microcavity in the form of evanescent waves through a tapered optical fiber, and light of a specific wavelength that meets the resonance condition can propagate stably in the microcavity, forming an enhanced whispering gallery resonance mode. At the same time, the back-scattered Rayleigh light generated by the whispering gallery resonance mode is also enhanced, and is coupled into the tapered optical fiber again to propagate backward into the laser, realizing self-injection locking of the laser.

[0029] The temperature control module 11 can measure the temperature of the whispering gallery optical microcavity 10 through a thermistor, and can also control the temperature of the microcavity at a set temperature point through a semiconductor refrigerator combined with a feedback control algorithm, so as to provide a stable working environment for the whispering gallery optical microcavity 10. Temperature can change the shape and refractive index and other parameters of the whispering gallery optical microcavity 10, and then change the resonant wavelength of the whispering gallery optical microcavity 10, so the resonant wavelength of the whispering gallery optical microcavity 10 can be thermally tuned by the temperature control module to produce a specific resonant wavelength. However, changes in the external ambient temperature will affect the stability of the resonant wavelength of the whispering gallery optical microcavity 10. Since a large amount of light energy is usually bound in the whispering gallery optical microcavity 10, the heat generated by it will cause the temperature in the whispering gallery optical microcavity 10 to gradually increase, and will also affect the stability of the resonant wavelength of the whispering gallery optical microcavity 10. Therefore, it is necessary to stably control the temperature of the whispering gallery optical microcavity 10 to maintain the stability of injection locking.

[0030] The working principle of the present invention is as follows:

[0031] Atomic gyroscopes based on the SERF effect usually use hybrid optical pumping to improve the sensitivity of quantum precision measurement, that is, two alkali metal atoms are placed in the atomic gas chamber, one alkali metal atom is pumped by the pumping laser, and then the precession signal of the other alkali metal atom is detected by the detection laser. The wavelengths of the resonance spectra of the two atoms are usually quite different, so the center wavelengths of the pumping laser and the detection laser are also far apart, generally in the order of tens of nanometers. By analyzing the atomic gyroscope theory, the precise optimal working wavelengths of the pumping laser and the detection laser under different gas chamber parameters can be obtained, and the pumping or detection effect of the atomic gyroscope can be optimized at this pumping or detection wavelength.

[0032] For the whispering gallery microcavity, light that meets the total reflection condition will propagate in a polygonal path in the microcavity, and its propagation path is approximately equal to the circumference of the circular microcavity. Based on the above analysis, it can be obtained that the resonant wavelength of the whispering gallery optical microcavity meets the following conditions:

[0033] (1)

[0034] In the formula, is the radius of the microcavity, is the microcavity effective refractive index, is the resonant wavelength, is the order of the resonance mode. The radius of the microcavity can be preliminarily calculated by the above formula, so that the wavelengths of the two lasers in the present invention can meet this resonance condition. In addition, with the help of tools such as finite element simulation and time-domain finite difference simulation, combined with the set parameters such as the material, shape, size and coupling method of the whispering gallery optical microcavity, a more accurate resonance wavelength corresponding to each order mode of the microcavity can be calculated, and finally a microcavity that can generate a whispering gallery resonance mode at the optimal wavelength of the pumping laser and the optimal wavelength of the detection laser is obtained.

[0035] In the present invention, the light emitted by the pump laser 1 and the detection laser 2 is combined by the fiber combiner 9 to form light with two wavelength components and enter the whispering gallery optical microcavity 10. According to the previous analysis, these two different wavelengths of light can form a stable whispering gallery resonance mode in the microcavity, so the enhanced back-Rayleigh scattered light generated by the microcavity will also contain two wavelength components. Since the beam splitting process of the fiber combiner 9 is not wavelength selective, the light that is reversely incident back to the pump laser 1 will not only contain the wavelength component output by itself, but also the wavelength component output by another laser. The same is true for the light that is reversely incident back to the detection laser 2. According to the relevant principles of semiconductor laser injection locking, the frequency range for achieving stable injection locking is as follows: It can be expressed as:

[0036] (2)

[0037] In the formula, is the injection parameter value of the externally injected light field, and are the light field amplitudes of the injected laser and the injected laser, and are the frequencies of the injected laser and the injected laser, is the line width enhancement factor of the injected laser, For time, is the cycle period of light in the laser cavity. It can be proved that the frequency difference between the two lasers has exceeded the frequency range that can achieve stable injection locking, so the light of the detection laser 2 that is incident back to the pump laser 1 will not affect the pump laser 1. It is similar for the detection laser 2. This is also one of the theoretical principles that the present invention can work normally without splitting the back Rayleigh scattered light.

[0038] Although the above describes the illustrative specific embodiments of the present invention to facilitate the understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A multi-channel laser injection locking device based on a whispering gallery microcavity, characterized in that: The device comprises a pumping laser (1), a detection laser (2), a first beam splitter prism (3), a second beam splitter prism (4), a first optical fiber coupler (5), a second optical fiber coupler (6), a first optical fiber polarization controller (7), a second optical fiber polarization controller (8), an optical fiber combiner (9), a whispering gallery optical microcavity (10), and a temperature control module (11); A pumping laser (1), a first beam splitter prism (3), a first optical fiber coupler (5), and a first optical fiber polarization controller (7) are sequentially connected through an optical path and then connected to a whispering gallery optical microcavity (10) via an optical fiber combiner (9); a detection laser (2), a second beam splitter prism (4), a second optical fiber coupler (6), and a second optical fiber polarization controller (8) are sequentially connected through another optical path and then connected to a whispering gallery optical microcavity (10) via an optical fiber combiner (9); The whispering gallery optical microcavity (10) is connected to a temperature control module (11) via a circuit; The operating wavelength of the pump laser (1) covers the wavelength of the resonance spectrum line of the alkali metal atom D1 line or D2 line, and the operating wavelength is continuously adjustable within a preset range of the resonance spectrum line wavelength, and the maximum output power is 120 milliwatts; The working wavelength of the detection laser (2) covers the wavelength of the resonance spectrum line of the alkali metal atom D1 line or D2 line, and the working wavelength is continuously adjustable within a preset range of the resonance spectrum line wavelength, and the maximum output power is 120 milliwatts; The first optical fiber polarization controller (7) and the second optical fiber polarization controller (8) are both used to arbitrarily control the polarization state of the incident light transmitted in the optical fiber corresponding to the respective optical paths, and the polarization state control range covers the entire Poincaré sphere; The optical fiber combiner (9) is a 2×1 combiner, which is used to combine two optical fiber beams into one beam and is used as a beam splitter in reverse. The operating wavelength range covers the operating wavelengths of the pump laser (1) and the detection laser (2) used. The whispering gallery optical microcavity (10) is used to confine a light field with high energy density within a cavity made of a crystal or quartz material through a whispering gallery mode; the central wavelength of the resonance mode generated by the whispering gallery optical microcavity (10) covers the sum of the operating wavelengths of a pumping laser (1) and a detection laser (2) used; and the damage power threshold of the whispering gallery optical microcavity (10) is greater than the sum of the maximum output powers of the pumping laser (1) and the detection laser (2).

2. According to claim 1, a multi-channel laser injection locking device based on a whispering gallery microcavity is characterized in that: The first beam splitter prism (3) and the second beam splitter prism (4) are used to split the incident light corresponding to their respective optical paths into two beams of light according to a fixed light intensity ratio, and the operating wavelength ranges of the first beam splitter prism (3) and the second beam splitter prism (4) cover the operating wavelengths of the pumping laser (1) and the detection laser (2) used.

3. The multi-channel laser injection locking device based on whispering gallery microcavity according to claim 1 is characterized in that: The first optical fiber coupler (5) and the second optical fiber coupler (6) are both used to couple the incident light corresponding to their respective optical paths into the optical fiber connected at the rear end.

4. The multi-channel laser injection locking device based on whispering gallery microcavity according to claim 1 is characterized in that: The temperature control module (11) is used to measure and adjust the temperature of the whispering gallery optical microcavity (10), and to control the temperature at a set value.

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