Fiber-coupled integrated modulation transfer spectroscopy lock-in device and method

Abstract

The application provides a kind of modulation transfer optical spectrum frequency locking device and method of fiber coupling integration, device includes: laser, optical fiber beam splitter, atom gas chamber filled with alkali metal atom, first fiber collimator, second fiber collimator, third fiber collimator, fiber electro-optic modulator, beam splitting prism, photoelectric detector, DDS signal generator, modulation and demodulation circuit and PID control circuit.Wherein, between laser and optical fiber beam splitter, between optical fiber beam splitter and first fiber collimator, between optical fiber beam splitter and fiber electro-optic modulator, between fiber electro-optic modulator and second fiber collimator, between third fiber collimator and photoelectric detector are connected by transmission fiber.It is realized that optical integration is realized by the way of fiber coupling for optical path, i.e., laser, optical elements and photoelectric detector and other devices are integrated on fiber platform, which reduces the volume and weight of modulation transfer optical spectrum frequency locking device, and improves portability and maintainability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser frequency locking, and particularly relates to a modulation transfer spectrum frequency locking device and method integrated with optical fiber coupling. BACKGROUND

[0002] The laser frequency output by a laser usually has a drift condition, and the laser frequency changes more significantly especially when the environmental temperature and vibration conditions change. In some application scenarios with high requirements for laser frequency, the laser frequency output by a laser needs to be locked, that is, frequency locking. The laser frequency locking usually refers to locking the laser frequency on a frequency reference which is not easily affected by the outside world and has high stability, such as atomic resonance absorption transition spectrum.

[0003] The modulation transfer spectrum (MTS) frequency locking technology is one of the laser frequency locking technologies, and the modulation transfer spectrum frequency locking technology mainly eliminates the atomic absorption Doppler background through the modulation transfer spectrum of the nonlinear four-wave mixing process, and has extremely high sensitivity and fineness. Since the laser itself does not need to be modulated, the interference of the modulation signal in the spectrum is reduced.

[0004] However, the current modulation transfer spectrum frequency locking technology is realized through a spatial optical path, and the structure of the transmission spatial optical path is complex and large in size. As a result, the modulation transfer spectrum locking device is large in size and weight, and has low portability and maintainability. SUMMARY

[0005] The present application solves the technical problem that the existing modulation transfer spectrum locking device is large in size, resulting in low portability and maintainability.

[0006] To solve the above technical problems, the present application provides a modulation transfer spectrum frequency locking device and method integrated with optical fiber coupling, and specifically adopts the following technical solutions:

[0007] In a first aspect, the present application provides a fiber-coupled integrated modulation transfer spectroscopy frequency locking device, comprising a laser, a fiber beam splitter, an atomic cell filled with alkali metal atoms, a first fiber collimator, a second fiber collimator, a third fiber collimator, a fiber electro-optical modulator, a beam splitting prism, a photodetector, a direct digital frequency synthesis (DDS) signal generator, a modulation-demodulation circuit and a proportional-integral-derivative (PID) control circuit. The laser is connected to the fiber beam splitter, the fiber beam splitter is connected to the first fiber collimator, the fiber beam splitter is connected to the fiber electro-optical modulator, the fiber electro-optical modulator is connected to the second fiber collimator, and the third fiber collimator is connected to the photodetector through transmission fibers. The laser is connected to the PID control circuit, the PID control circuit is connected to the modulation-demodulation circuit, the modulation-demodulation circuit is connected to the photodetector, the fiber electro-optical modulator is connected to the DDS signal generator, and the DDS signal generator is connected to the modulation-demodulation circuit through electric wires. The laser is configured to output a laser beam with a first frequency, and the laser beam is coupled into the transmission fiber, the first frequency being associated with the alkali metal atoms. The laser beam is transmitted to the fiber beam splitter through the transmission fiber, and the laser beam is split into a probe light beam and a pump light beam by the fiber beam splitter. The probe light beam is injected into the atomic cell through the first fiber collimator. The pump light beam is phase-modulated by the fiber electro-optical modulator according to a high-frequency modulation electrical signal output by the DDS signal generator, and then is injected into the atomic cell through the second fiber collimator and the beam splitting prism. The phase-modulated pump light beam and the probe light beam are opposite and coincide in the atomic cell. When the phase-modulated pump light beam and the probe light beam generate a four-wave mixing effect, the probe light beam after the four-wave mixing effect is coupled into the transmission fiber through the beam splitting prism and the third fiber collimator after passing through the atomic cell, and is transmitted to the photodetector through the transmission fiber. The probe light beam is converted into a beat frequency electrical signal by the photodetector and is output to the modulation-demodulation circuit. The beat frequency electrical signal and a reference signal output by the DDS signal generator are combined into a frequency discrimination signal by the modulation-demodulation circuit and are output to the PID control circuit. The frequency discrimination signal is processed into a feedback signal by the PID control circuit and is output to the laser. The laser adjusts the first frequency according to the feedback signal to realize frequency locking.

[0008] The device can ensure the stability and anti-interference ability of the laser beam in the transmission process through the excellent transmission characteristics of the optical fiber, thereby improving the precision and stability of the laser frequency locking. Moreover, the optical integration is realized by coupling the optical path with the optical fiber, i.e., the laser, the fiber beam splitter and other optical elements, and the photodetector, the fiber electro-optical modulator and other devices are integrated on the optical fiber platform, which greatly reduces the volume and weight of the modulation transfer spectroscopy frequency locking device, and improves the portability and maintainability.

[0009] In combination with the first aspect, in an optional implementation manner, the fiber beam splitter is an unequal power beam splitter, and the power of the probe light beam is less than the power of the pump light beam.

[0010] In the present implementation, the modulated pump light beam and the probe light beam are facilitated to realize the four-wave mixing effect, so that the modulation signal is transferred from the modulated pump light beam to the probe light beam, thereby improving the accuracy of frequency locking.

[0011] In combination with the first aspect, in an alternative implementation, the above-mentioned optical fiber beam splitter is an equal-power beam splitter, and the device further comprises an optical fiber attenuator, which is arranged between the optical fiber beam splitter and the first optical fiber collimator. The optical fiber attenuator is connected to the optical fiber beam splitter and the first optical fiber collimator through transmission optical fibers. The probe light beam passes through the optical fiber attenuator and then enters the atomic cell through the first optical fiber collimator; the optical fiber attenuator is configured to attenuate the power of the probe light beam according to a preset ratio.

[0012] In the present implementation, the power of the probe light beam can be accurately attenuated by the optical fiber attenuator, so that the ratio of the power of the attenuated probe light beam to the power of the pump light beam meets the application requirements.

[0013] In combination with the first aspect, in an alternative implementation, the above-mentioned alkali metal atoms are one of the following: potassium K atoms, rubidium Rb atoms, and cesium Cs atoms. In the case of K atoms, the first frequency corresponds to the D1 line of the K atom saturated spectrum, or the first frequency corresponds to the D2 line of the K atom saturated spectrum. In the case of Rb atoms, the first frequency corresponds to the D1 line of the Rb atom saturated spectrum, or the first frequency corresponds to the D2 line of the Rb atom saturated spectrum. In the case of Cs atoms, the first frequency corresponds to the D1 line of the Cs atom saturated spectrum, or the first frequency corresponds to the D2 line of the Cs atom saturated spectrum.

[0014] In combination with the first aspect, in an alternative implementation, the above-mentioned transmission optical fiber is a single-mode polarization maintaining optical fiber.

[0015] In the present implementation, the single-mode polarization maintaining optical fiber is used as the transmission optical fiber, which can ensure the stability and anti-interference ability of the laser beam during transmission, thereby improving the precision and stability of the laser frequency locking.

[0016] In combination with the first aspect, in an alternative implementation, the above-mentioned beam splitting prism is a polarization beam splitting prism.

[0017] In the present implementation, the polarization beam splitting prism can stably and accurately reflect the modulated pump light beam into the atomic cell.

[0018] In combination with the first aspect, in an alternative implementation manner, the high-frequency modulation electrical signal generated by the DDS signal generator has a frequency range of 1MHz-30MHz.

[0019] In the implementation manner, the high-frequency modulation electrical signal generated by the DDS signal generator can meet the application requirement of the modulation transfer optical frequency locking, thereby improving the applicability of the modulation transfer optical frequency locking device.

[0020] In combination with the first aspect, in an alternative implementation manner, one end of the first fiber collimator is connected to the transmission optical fiber through a capillary glass tube, and the other end of the first fiber collimator is bonded to the atomic cell. One end of the second fiber collimator is connected to the transmission optical fiber through a capillary glass tube, and the other end of the second fiber collimator is bonded to the beam splitting prism. One end of the third fiber collimator is connected to the transmission optical fiber through a capillary glass tube, and the other end of the third fiber collimator is bonded to the beam splitting prism.

[0021] In the implementation manner, the first fiber collimator, the second fiber collimator and the third fiber collimator are all connected to the transmission optical fiber through capillary glass tubes, so that the collimation of the light emitted by the transmission optical fiber can be realized.

[0022] In combination with the first aspect, in an alternative implementation manner, one light path of the fiber beam splitter is connected to the first fiber collimator through polarization maintaining fusion splicing, another light path of the fiber beam splitter is connected to the fiber electro-optical modulator through polarization maintaining fusion splicing, and the fiber electro-optical modulator is connected to the second fiber collimator through polarization maintaining fusion splicing.

[0023] In the implementation manner, the linear polarization direction of the light beam can be ensured unchanged during transmission. In this way, the stability and anti-interference capability of the light beam during transmission can be ensured.

[0024] Secondly, the laser beam is divided into a probe light beam and a pump light beam, the power of the probe light beam is less than the power of the pump light beam. The pump light beam is phase-modulated according to a preset high-frequency modulation electrical signal, to obtain a modulated pump light beam. Next, the modulated pump light beam and the probe light beam are oppositely and coincidently injected into an atomic cell filled with alkali metal atoms, so that the modulated pump light beam and the probe light beam generate a four-wave mixing effect. The probe light beam after the four-wave mixing effect is converted into a beat frequency electrical signal. Further, the beat frequency electrical signal and a reference signal are combined into a frequency discrimination signal, the reference signal is associated with the high-frequency modulation electrical signal. A feedback signal is determined according to the frequency discrimination signal, the feedback signal is used to represent a frequency error. Finally, the first frequency is adjusted according to the feedback signal, to realize frequency locking. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Structure diagram of the fiber-coupled integrated modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application Figure 1 ;

[0026] Figure 2 Structure diagram of the fiber-coupled integrated modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application Figure 2 ;

[0027] Figure 3 Flowchart of the fiber-coupled integrated modulation transfer spectroscopy frequency locking method provided by the embodiment of the present application.

[0028] The accompanying drawings illustrate:

[0029] 101-laser; 102-fiber beam splitter; 103-atomic cell; 104-first fiber collimator; 105-second fiber collimator; 106-third fiber collimator; 107-fiber electro-optical modulator; 108-beam splitting prism; 109-photoelectric detector; 110-DDS signal generator; 111-modulation and demodulation circuit; 112-PID control circuit; 113-fiber attenuator. DETAILED DESCRIPTION

[0030] The embodiments will be described in detail below with reference to examples thereof as illustrated in the accompanying drawings. When the following description refers to the drawings, same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following embodiments are not meant to represent all implementations consistent with the present application. Rather, they are merely examples of systems and methods consistent with some aspects of the present application as detailed in the appended claims.

[0031] The laser frequency output by the laser often has a drift, especially when the environmental temperature, vibration condition, etc. change, the laser frequency changes more significantly. In some applications with high requirements for laser frequency, it is necessary to lock the laser frequency output by the laser, i.e. frequency locking. The frequency locking of laser generally refers to locking the laser frequency on a frequency reference which is not easily affected by the outside world and has high stability, such as atomic resonance absorption transition spectrum line, etc.

[0032] The modulation transfer spectroscopy frequency locking technology is one of the laser frequency locking technologies. The modulation transfer spectroscopy frequency locking technology mainly eliminates the atomic absorption Doppler background through the modulation transfer spectroscopy of the nonlinear four-wave mixing process, and has extremely high sensitivity and fineness. Since the laser itself does not need to be modulated, the interference of the modulation signal in the spectrum is reduced.

[0033] However, the modulation transfer spectroscopy frequency locking technology is realized by a spatial light path at present. Due to the complex structure and large volume of the transmission spatial light path, the volume and weight of the modulation transfer spectroscopy frequency locking device are large, and the portability and maintainability are low.

[0034] To solve the above problems, the embodiment of the present application provides a fiber-coupled integrated modulation transfer spectroscopy frequency locking device and method. The device integrates the laser, optical elements and detectors on a compact fiber platform by using the excellent transmission characteristics of the optical fiber, which can greatly reduce the volume and weight of the modulation transfer spectroscopy frequency locking device, and improve its portability and maintainability. At the same time, the excellent transmission characteristics of the optical fiber can ensure the stability and anti-interference ability of the laser signal in the transmission process, thereby improving the precision and stability of the laser frequency locking.

[0035] The fiber-coupled integrated modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application can be widely applied in the fields of quantum sensing, laser radar, optical communication, spectral analysis and the like. Especially in the applications requiring high-precision and high-stability laser output, the modulation transfer spectroscopy frequency locking device has significant advantages and potential.

[0036] The scheme provided by the embodiment of the present application will be introduced below in combination with the drawings.

[0037] Specifically, referring to Figure 1 the structure of the fiber-coupled integrated modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application is shown in the figure. Figure 1 As shown in the figure, Figure 2 the fiber-coupled integrated modulation transfer spectroscopy frequency locking device provided by the present application comprises a laser 101, a fiber beam splitter 102, an atomic cell 103 filled with alkali metal atoms, a first fiber collimator 104, a second fiber collimator 105, a third fiber collimator 106, a fiber electro-optic modulator (EOM) 107, a beam splitting prism 108, a photoelectric detector 109, a DDS signal generator 110, a modulation-demodulation circuit (Mixer) 111 and a PID control circuit 112.

[0038] Among them, the laser 101 and the fiber beam splitter 102, the fiber beam splitter 102 and the first fiber collimator 104, the fiber beam splitter 102 and the fiber electro-optic modulator 107, the fiber electro-optic modulator 107 and the second fiber collimator 105, and the third fiber collimator 106 and the photoelectric detector 109 are connected through transmission optical fibers.

[0039] The laser 101, the PID control circuit 112, the modulation demodulation circuit 111, the photodetector 109, the fiber-optic electro-optic modulator 107 and the DDS signal generator 110 are connected by wires. The wires can be high-frequency conductive wires.

[0040] Specifically, the laser 101 is configured to output a laser beam with a first frequency, and couple the laser beam into a transmission fiber. The first frequency is associated with an alkali metal atom. The laser beam is transmitted to the fiber-optic beam splitter 102 through the transmission fiber, and is split into a probe light beam and a pump light beam through the fiber-optic beam splitter 102.

[0041] The probe light beam is injected into the atomic cell 103 through the first fiber collimator 104, and the pump light beam is phase-modulated by the fiber-optic electro-optic modulator 107 according to the high-frequency modulation electrical signal output by the DDS signal generator 110, and then is injected into the atomic cell 103 through the second fiber collimator 105 and the beam-splitting prism 108. The phase-modulated pump light beam is opposite to and coincides with the probe light beam in the atomic cell 103.

[0042] The first fiber collimator 104 is configured to collimate the probe light beam, and the second fiber collimator 105 is configured to collimate the phase-modulated pump light beam. The shape of the atomic cell 103 can be cylindrical or cuboid, or the shape of the atomic cell 103 can be specially shaped according to the actual application requirements.

[0043] The fiber-optic electro-optic modulator 107 is driven by the high-frequency modulation electrical signal generated by the DDS signal generator 110, and phase-modulates the pump light beam passing through the fiber-optic electro-optic modulator 107. The high-frequency modulation electrical signal can be generated by the DDS signal generator 110 according to a preset value.

[0044] The frequency of the phase-modulated pump light beam includes a carrier frequency (i.e., the first frequency) ω0 and sidebands ω0±nω m , ω m is a modulation frequency. In the embodiment of the present application, the first-order sidebands ω0±ω m can be considered. In this case, the phase-modulated pump light beam and the probe light beam can form a four-wave mixing condition, and the modulation signal can be transferred from the phase-modulated pump light beam to the probe light beam. Since this phenomenon only occurs in the sub-Doppler condition, the generated modulation transfer spectrum does not have a Doppler background.

[0045] Further, in the case that the phase-modulated pump light beam and the probe light beam generate four-wave mixing effect, the probe light beam after the four-wave mixing effect passes through the atomic cell 103, and then is coupled into the transmission fiber through the beam splitter prism 108 and the third fiber collimator 106, and is transmitted to the photoelectric detector 109 through the transmission fiber. The photoelectric detector 109 converts the beat frequency electrical signal into an electrical signal and outputs it to the modulation-demodulation circuit 111.

[0046] Specifically, taking the first-order sideband ω0±ω m of the probe light beam as an example, the first-order sideband ω0±ω m of the probe light beam generates a beat frequency ω m with the center frequency ω0of the probe light, and the signal is received by the photoelectric detector 109. The photoelectric detector 109 includes an amplification circuit, which converts the signal of the beat frequency ω m into a beat frequency electrical signal and outputs it to the modulation-demodulation circuit 111.

[0047] Further, the modulation-demodulation circuit 111 combines the beat frequency electrical signal and the reference signal transmitted by the DDS signal generator 110 into a frequency discrimination signal and outputs it to the PID control circuit 112, and the PID control circuit 112 processes the frequency discrimination signal into a feedback signal and outputs it to the laser 101, wherein the feedback signal is used to represent the frequency error. Finally, the laser 101 can adjust the first frequency according to the feedback signal to achieve frequency locking.

[0048] Wherein, the reference signal transmitted by the DDS signal generator 110 is associated with the high-frequency modulation electrical signal, for example, the reference signal can be the same as the high-frequency modulation electrical signal. That is, the DDS signal generator 110 generates a high-frequency modulation electrical signal into the fiber electro-optical modulator 107, and at the same time generates a reference signal into the PID control circuit 112.

[0049] Because the hyperfine structure energy level transition of alkali metal atoms corresponds to the peak of the saturated absorption spectrum, the zero-crossing point of the frequency discrimination curve obtained after modulation-demodulation corresponds to the first derivative of the peak value of the saturated absorption spectrum. In this way, by adjusting the frequency position of the laser 101, the laser 101 can be locked at a specific peak value of the saturated absorption spectrum through the frequency discrimination signal.

[0050] The modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application is optically coupled and integrated, and the excellent transmission characteristics of the optical fiber can ensure the stability and anti-interference capability of the laser beam during transmission, thereby improving the precision and stability of the laser frequency locking. Moreover, the optical integration is realized by coupling the optical path with the optical fiber, that is, the laser, the optical fiber beam splitter, the optical fiber collimator and other optical elements and the photodetector, the fiber-optic electro-optic modulator and other devices are integrated on the optical fiber platform, thereby greatly reducing the volume and weight of the modulation transfer spectroscopy frequency locking device and improving the portability and maintainability.

[0051] In some embodiments, the optical fiber beam splitter 102 can be an unequal power beam splitter, that is, the optical fiber beam splitter 102 can divide the laser beam into a probe light beam and a pump light beam with different powers. The power of the probe light beam is less than the power of the pump light beam.

[0052] For example, the power of the probe light beam can be one third of the power of the pump light beam, so that the modulated pump light beam and the probe light beam realize the four-wave mixing effect, so that the modulation signal is transferred from the modulated pump light beam to the probe light beam.

[0053] In some embodiments, the optical fiber beam splitter 102 can also be an equal power beam splitter. In this case, the optically coupled and integrated modulation transfer spectroscopy frequency locking device further comprises an optical fiber attenuator 113. Figure 2 Structure of the optically coupled and integrated modulation transfer spectroscopy frequency locking device provided by the embodiment of the present application Figure 2 As shown in Figure 2 The optical fiber attenuator 113 is arranged between the optical fiber beam splitter 102 and the first optical fiber collimator 104. The optical fiber attenuator 113 is connected to the optical fiber beam splitter 102 and the first optical fiber collimator 104 through transmission optical fibers.

[0054] In the case of the optical fiber attenuator 113, the probe light beam passes through the optical fiber attenuator 113 to obtain an attenuated probe light beam, and the attenuated probe light beam is then injected into the atomic cell 103 through the first optical fiber collimator 104. The optical fiber attenuator 113 is used to attenuate the power of the probe light beam according to a preset ratio, so that the power of the attenuated probe light beam is less than the power of the pump light beam. For example, the power of the attenuated probe light beam can be one third of the power of the pump light beam.

[0055] In some embodiments, the optical power of the optical fiber attenuator 113 can be adjustable in a preset ratio, i.e., the relative size of the power of the probe light beam and the pump light beam can be adjustable. In this way, the power of the probe light beam can be accurately attenuated by the optical fiber attenuator 113, so that the ratio of the power of the attenuated probe light beam and the power of the pump light beam meets the application requirements.

[0056] In some embodiments, the alkali metal atoms filled in the atomic cell 103 are one of the following: potassium K atoms, rubidium Rb atoms, and cesium Cs atoms.

[0057] Specifically, in the case of K atoms as alkali metal atoms, the first frequency corresponds to the D1 line of the K atom saturated spectrum, or the first frequency corresponds to the D2 line of the K atom saturated spectrum. In the case of Rb atoms as alkali metal atoms, the first frequency corresponds to the D1 line of the Rb atom saturated spectrum, or the first frequency corresponds to the D2 line of the Rb atom saturated spectrum. In the case of Cs atoms as alkali metal atoms, the first frequency corresponds to the D1 line of the Cs atom saturated spectrum, or the first frequency corresponds to the D2 line of the Cs atom saturated spectrum.

[0058] For example, in the case of Cs atoms as alkali metal atoms, the first frequency of the laser 101 can correspond to the D2 line of the Cs atom saturated spectrum, i.e., can correspond to a wavelength of 852 nanometers (nm).

[0059] In some embodiments, the transmission optical fiber is a single-mode polarization maintaining optical fiber. The single-mode polarization maintaining optical fiber can only transmit a single fundamental mode, is suitable for large-capacity long-distance transmission, and can ensure that the linear polarization direction of the transmitted light is unchanged. In this way, the stability and anti-interference ability of the laser beam during transmission can be ensured, thereby improving the precision and stability of the laser frequency locking.

[0060] In some embodiments, the wavelength band of the transmission optical fiber corresponds to the wavelength of the laser 101, so that the laser beam emitted by the laser 101 can be stably transmitted in the transmission optical fiber.

[0061] In some embodiments, the above-mentioned beam splitting prism 108 is a polarization beam splitting prism. The polarization beam splitting prism has the characteristics of small stress, high extinction ratio, good imaging quality, and small beam deflection angle. In this way, the beam splitting prism 108 can stably and accurately reflect the modulated pump light beam into the atomic cell 103.

[0062] In some embodiments, the frequency range of the high-frequency modulation electrical signal generated by the above-mentioned DDS signal generator 110 is 1 MHz-30 MHz. In this way, the high-frequency modulation electrical signal generated by the DDS signal generator can meet the application requirements of the modulation transfer spectrum locking, thereby improving the applicability of the modulation transfer spectrum locking device.

[0063] In some embodiments, the first fiber collimator 104, the second fiber collimator 105, and the third fiber collimator 106 may be miniature collimators to further reduce the size of the modulation transfer spectrum frequency locking device.

[0064] For example, the first fiber collimator 104, the second fiber collimator 105, and the third fiber collimator 106 may be composed of Clens lenses or Lens lenses.

[0065] In some embodiments, one end of the first fiber collimator 104 is connected to the transmission fiber via a capillary glass tube, and the other end of the first fiber collimator 104 is bonded to the atomic gas chamber 103. One end of the second fiber collimator 105 is connected to the transmission fiber via a capillary glass tube, and the other end of the second fiber collimator 105 is bonded to the beam splitter prism 108. One end of the third fiber collimator 106 is connected to the transmission fiber via a capillary glass tube, and the other end of the third fiber collimator 106 is bonded to the beam splitter prism 108.

[0066] In some embodiments, one optical path of the fiber optic beam splitter 102 is connected to the first fiber optic collimator 104 via polarization-maintaining fusion splicing, and the other optical path of the fiber optic beam splitter 102 is connected to the fiber optic electro-optic modulator 107 via polarization-maintaining fusion splicing. The fiber optic electro-optic modulator 107 is connected to the second fiber optic collimator 105 via polarization-maintaining fusion splicing.

[0067] In some embodiments, with Figure 3 Taking the modulation-transfer spectrum frequency-locking device including the fiber optic attenuator as an example, the fabrication and frequency-locking steps of the fiber-coupled integrated modulation-transfer spectrum frequency-locking device provided in this application embodiment are illustrated as follows:

[0068] First, an atomic gas cell 103 coupled with a miniature fiber optic collimator is fabricated. The first fiber optic collimator 104, the second fiber optic collimator 105, and the third fiber optic collimator 106 can be constructed from cylindrical lenses (clens). All three collimators are connected to the transmission fiber via capillary glass tubes to achieve collimation of the light emitted from the transmission fiber. A beam-splitting prism 108 is attached to one end of the atomic gas cell 103. The first fiber optic collimator 104 is attached to one end of the atomic gas cell 103, while the second fiber optic collimator 105 and the third fiber optic collimator 106 are attached to two surfaces of the beam-splitting prism 108, respectively. During the attachment process, it is ensured that the light emitted from the first fiber optic collimator 104, the second fiber optic collimator 105, and the third fiber optic collimator 106 converges to a single point, and that the light emitted from the first fiber optic collimator 104 and the second fiber optic collimator 105 overlaps.

[0069] Then, the laser beam emitted by the laser 101 is coupled into a transmission optical fiber and connected to an optical fiber beam splitter 102. The optical fiber beam splitter 102 divides the laser beam into a probe light beam and a pump light beam. One way of the optical fiber beam splitter 102 is connected to an optical fiber attenuator 113 through polarization maintaining fusion splicing, and the other end of the optical fiber attenuator 113 is connected to a first optical fiber collimator 104 through polarization maintaining fusion splicing. The other way of the optical fiber beam splitter 102 is connected to an optical fiber electro-optical modulator 107 through polarization maintaining fusion splicing. The other end of the optical fiber electro-optical modulator 107 is connected to a second optical fiber collimator 105 through polarization maintaining fusion splicing.

[0070] Secondly, the probe light beam after the four-wave mixing effect is coupled into the third optical fiber collimator 106, and the probe light beam after the four-wave mixing effect is received by the photodetector 109. The spectral signal is converted into an electrical signal by the amplification circuit of the photodetector 109 and sent to the modulation and demodulation circuit 111.

[0071] Further, the DDS signal generator 110 generates a high-frequency modulation electrical signal and inputs the high-frequency modulation electrical signal into the optical fiber electro-optical modulator 107, and generates a reference signal and inputs the reference signal into the PID control circuit 112.

[0072] Finally, the modulation and demodulation circuit 111 demodulates the signal of the photodetector 109 to obtain a frequency discrimination signal, inputs the frequency discrimination signal into the PID control circuit 112, and inputs the feedback signal obtained by the PID control circuit 112 into the laser 101 to realize frequency locking of the laser.

[0073] The embodiment of the present application also provides a modulation transfer spectrum frequency locking method integrated with optical fiber coupling, which can be applied to the modulation transfer spectrum frequency locking device integrated with optical fiber coupling provided in the above embodiment. Figure 3 As shown in the flowchart of the modulation transfer spectrum frequency locking method integrated with optical fiber coupling provided in the embodiment of the present application, ​ The modulation transfer spectrum frequency locking method integrated with optical fiber coupling provided in the embodiment of the present application includes the following steps S101-S108.

[0074] S101, output a laser beam with a first frequency.

[0075] The first frequency is associated with an alkali metal atom.

[0076] S102, divide the laser beam into a probe light beam and a pump light beam.

[0077] The power of the probe light beam is less than the power of the pump light beam.

[0078] S103, phase modulate the pump light beam according to a preset high-frequency modulation electrical signal to obtain a modulated pump light beam.

[0079] S104, the modulated pump light beam and the probe light beam are injected into the atomic cell filled with alkali metal atoms in opposition and coincidence, so that the modulated pump light beam and the probe light beam generate a four-wave mixing effect.

[0080] S105, the probe light beam after the four-wave mixing effect is converted into a beat frequency electrical signal.

[0081] S106, the beat frequency electrical signal and the reference signal are combined into a frequency discrimination signal.

[0082] The reference signal is associated with the high-frequency modulated electrical signal.

[0083] S107, the feedback signal is determined according to the frequency discrimination signal, and the feedback signal is used to characterize the frequency error.

[0084] S108, the first frequency is adjusted according to the feedback signal to achieve frequency locking.

[0085] In this way, by the method shown in S101-S108, the precision and stability of laser frequency locking can be improved.

[0086] Through the description of the above embodiments, those skilled in the art can clearly understand that, for the convenience and brevity of description, only the division of the above functional modules is exemplified, and in actual application, the above functions can be completed by different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules to complete all or part of the functions described above.

[0087] In the description of the present application, it should be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, such as two, three, etc., unless otherwise specifically limited.

[0088] In the present application, unless otherwise specifically defined and limited, the terms "mounting", "connection", "connection", "fixing" and the like should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise specifically limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0089] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0090] The similar parts among the embodiments provided in the present application can be referred to each other, and the specific embodiments provided above are only a few examples under the general concept of the present application, and do not constitute a limitation on the protection scope of the present application. Any other implementation manner extended according to the present application scheme without creative labor belongs to the protection scope of the present application for the person skilled in the art.

Claims

1. A fiber-coupled integrated modulation-transfer spectrum frequency-locking device, characterized in that, include: Laser, fiber beam splitter, atomic gas cell filled with alkali metal atoms, first fiber collimator, second fiber collimator, third fiber collimator, fiber electro-optic modulator, beam splitter prism, photodetector, direct digital frequency synthesis (DDS) signal generator, modulation and demodulation circuit, and proportional-integral-derivative (PID) control circuit. The laser and the fiber optic beam splitter, the fiber optic beam splitter and the first fiber optic collimator, the fiber optic beam splitter and the fiber optic electro-optic modulator, the fiber optic electro-optic modulator and the second fiber optic collimator, and the third fiber optic collimator and the photodetector are all connected by transmission optical fibers. The laser and the PID control circuit, the PID control circuit and the modulation and demodulation circuit, the modulation and demodulation circuit and the photodetector, the fiber electro-optic modulator and the DDS signal generator, and the DDS signal generator and the modulation and demodulation circuit are all connected by wires. The laser is used to output a laser beam of a first frequency and couple the laser beam into the transmission optical fiber, the first frequency being associated with the alkali metal atom; the laser beam is transmitted through the transmission optical fiber to the fiber beam splitter, which splits it into a probe beam and a pump beam; the probe beam enters the atomic gas cell through the first fiber collimator; the pump beam is phase-modulated by the fiber electro-optic modulator according to the high-frequency modulation electrical signal output by the DDS signal generator, and then enters the atomic gas cell through the second fiber collimator and the beam splitting prism; the phase-modulated pump beam and the probe beam are opposite and coincident within the atomic gas cell; after phase modulation... When the pump beam and the probe beam produce a four-wave mixing effect, the probe beam after the four-wave mixing effect passes through the atomic gas cell, is coupled into the transmission fiber through the beam splitter prism and the third fiber collimator, and is transmitted to the photodetector through the transmission fiber. The photodetector converts the signal into a beat frequency electrical signal and outputs it to the modulation and demodulation circuit. The modulation and demodulation circuit combines the beat frequency electrical signal and the reference signal transmitted by the DDS signal generator into a frequency discrimination signal and outputs it to the PID control circuit. The PID control circuit processes the frequency discrimination signal into a feedback signal and outputs it to the laser. The laser adjusts the first frequency according to the feedback signal to achieve frequency locking.

2. The apparatus according to claim 1, characterized in that, The fiber optic beam splitter is an unequal power beam splitter; the power of the probe beam is less than the power of the pump beam.

3. The apparatus according to claim 1, characterized in that, If the fiber optic beam splitter is an equal-power beam splitter, then the device further includes: a fiber optic attenuator, which is disposed between the fiber optic beam splitter and the first fiber optic collimator; the fiber optic attenuator and the fiber optic beam splitter, as well as the fiber optic attenuator and the first fiber optic collimator, are all connected by transmission optical fibers. The probe light beam passes through the fiber optic attenuator and then through the first fiber optic collimator into the atomic gas cell; the fiber optic attenuator is used to attenuate the power of the probe light beam according to a preset ratio.

4. The apparatus according to any one of claims 1-3, characterized in that, The alkali metal atom is one of the following: potassium (K) atom, rubidium (Rb) atom, or cesium (Cs) atom; When the alkali metal atom is a K atom, the first frequency corresponds to the D1 line of the saturated spectrum of the K atom, or the first frequency corresponds to the D2 line of the saturated spectrum of the K atom. When the alkali metal atom is an Rb atom, the first frequency corresponds to the D1 line of the saturated spectrum of the Rb atom, or the first frequency corresponds to the D2 line of the saturated spectrum of the Rb atom. When the alkali metal atom is a Cs atom, the first frequency corresponds to the D1 line of the saturated spectrum of the Cs atom, or the first frequency corresponds to the D2 line of the saturated spectrum of the Cs atom.

5. The apparatus according to any one of claims 1-3, characterized in that, The transmission fiber is a single-mode polarization-maintaining fiber.

6. The apparatus according to any one of claims 1-3, characterized in that, The beam splitter is a polarizing beam splitter.

7. The apparatus according to any one of claims 1-3, characterized in that, The frequency range of the high-frequency modulated electrical signal generated by the DDS signal generator is 1MHz-30MHz.

8. The apparatus according to any one of claims 1-3, characterized in that, One end of the first fiber collimator is connected to the transmission fiber through a capillary glass tube, and the other end of the first fiber collimator is bonded to the atomic gas cell. One end of the second fiber collimator is connected to the transmission fiber through a capillary glass tube, and the other end of the second fiber collimator is bonded to the beam splitter prism. One end of the third fiber collimator is connected to the transmission fiber through a capillary glass tube, and the other end of the third fiber collimator is bonded to the beam splitter prism.

9. The apparatus according to any one of claims 1-3, characterized in that, One optical path of the fiber optic beam splitter is connected to the first fiber optic collimator via polarization-maintaining fusion splice, and the other optical path of the fiber optic beam splitter is connected to the fiber optic electro-optic modulator via polarization-maintaining fusion splice. The fiber optic electro-optic modulator is connected to the second fiber optic collimator via polarization-maintaining fusion splice.

10. A fiber-coupled integrated modulation-transfer spectrum frequency locking method, characterized in that, include: Output a laser beam with a first frequency, which is associated with alkali metal atoms; The laser beam is divided into a probe beam and a pump beam, wherein the power of the probe beam is less than the power of the pump beam; The pump beam is phase-modulated according to a preset high-frequency modulation electrical signal to obtain a modulated pump beam. The modulated pump beam and the probe beam are directed toward each other and overlapped into an atomic gas cell filled with alkali metal atoms, so that the phase-modulated pump beam and the probe beam produce a four-wave mixing effect. The probe beam after generating the four-wave mixing effect is converted into a beat frequency electrical signal; The beat frequency electrical signal and the reference signal are combined into a frequency discrimination signal, wherein the reference signal is associated with the high-frequency modulation electrical signal; A feedback signal is determined based on the frequency discrimination signal, and the feedback signal is used to characterize the frequency error. The first frequency is adjusted according to the feedback signal to achieve frequency locking.

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