Active and passive combined optical clock stabilization system and time measurement device

Abstract

The present application provides an active-passive combined optical clock stabilization system and time measurement device, the system comprising: an active optical clock, a cavity locking component, and a passive optical clock; the active optical clock comprising a pump laser system and an active optical clock resonant cavity, the pump laser system being used to emit a first laser, and emitting the first laser to the active optical clock resonant cavity to form coherent stimulated radiation in the active optical clock resonant cavity to generate an active optical clock signal; the passive optical clock being used to generate a passive optical clock signal, and emitting it to the cavity locking component; the cavity locking component modulating the passive optical clock signal by a first electrical signal, and emitting the modulated optical signal to the active optical clock resonant cavity, and obtaining a second electrical signal corresponding to a reflected optical signal reflected by the active optical clock resonant cavity from the modulated optical signal, obtaining a first error signal by mixing the first electrical signal and the second electrical signal, and then adjusting the cavity length of the active optical clock resonant cavity according to the first error signal. The present application improves the long-term stability of the active optical clock.

Description

Technical Field

[0001] The present application relates to the technical field of optical quantum frequency standards, and in particular to an active-passive combined optical clock stabilization system and a time measurement device. Background Art

[0002] A quantum frequency standard is one that uses quantum transition frequencies to generate a standard frequency signal. Implementation of this quantum frequency standard enables metrological devices used for frequency and time measurement. Optical atomic clocks are currently a commonly used metrological device capable of implementing this quantum frequency standard. These clocks utilize the interaction of laser light with atomic clock transition energy levels to generate optical signals with the most accurate and stable frequencies available.

[0003] Active optical clocks are a key research area in optical frequency atomic clocks. Active optical clocks generate optical frequency standards by generating multi-atom coherent stimulated emission between atomic transition energy levels through weak feedback from an optical resonant cavity. Because active optical clock systems operate in deep bad cavity modes, their output frequency is naturally immune to the Brownian thermal noise generated by the resonant cavity. This significantly reduces the perturbations of cavity thermal noise on the output clock laser frequency, overcoming the current reliance of passive optical clocks on the linewidth of the local oscillator laser. Therefore, active optical clocks can theoretically achieve ultra-narrow linewidth optical frequency standards, providing narrow-linewidth laser sources in different frequency bands for other precision measurements, thereby promoting the development of optical frequency precision measurement.

[0004] However, the drift of the active optical clock resonant cavity will make the long-term stability of the active optical clock poor. Summary of the Invention

[0005] The present application provides an active-passive combined optical clock stabilization system to solve the problem of poor long-term stability of active optical clocks.

[0006] On the one hand, the present application provides an active-passive combined optical clock stabilization system, comprising: an active optical clock, a cavity locking component, and a passive optical clock;

[0007] The active optical clock includes a pump laser system and an active optical clock resonant cavity. The pump laser system is used to emit a first laser, and emit the first laser into the active optical clock resonant cavity to form coherent stimulated radiation in the active optical clock resonant cavity to generate an active optical clock signal.

[0008] The passive optical clock is used to generate a passive optical clock signal and emit the passive optical clock signal to the cavity locking component;

[0009] The cavity locking component is used to modulate the passive optical clock signal through a first electrical signal, emit the modulated optical signal to the active optical clock resonant cavity, and obtain a second electrical signal corresponding to a reflected optical signal reflected by the active optical clock resonant cavity to the modulated optical signal, obtain a first error signal by mixing the first electrical signal and the second electrical signal, and adjust the cavity length of the active optical clock resonant cavity according to the first error signal.

[0010] Optionally, the cavity locking assembly includes an electro-optic modulator, a first half-wave plate, a first polarization beam splitter, a quarter-wave plate, a signal generator, a high-speed photodetector, a mixer, and a control circuit;

[0011] The electro-optical modulator is connected to the passive optical clock and the signal generator respectively, and the mixer is connected to the high-speed photodetector, the signal generator and the control circuit respectively;

[0012] The signal generator is used to generate the first electrical signal and transmit the first electrical signal to the electro-optical modulator and the mixer;

[0013] The electro-optical modulator is used to modulate the passive optical clock signal by the first electrical signal, and emit the modulated optical signal to the first polarization beam splitter prism through the first half-wave plate;

[0014] The first polarization beam splitter prism is used to transmit the modulated light signal to the quarter-wave plate. The modulated light signal is emitted into the active optical clock resonant cavity through the quarter-wave plate. The modulated light signal oscillates in the active optical clock resonant cavity and is reflected to become a reflected light signal. The reflected light signal is emitted to the first polarization beam splitter prism through the quarter-wave plate.

[0015] The first polarization beam splitter prism is further configured to reflect the reflected light signal to the high-speed photodetector;

[0016] The high-speed photodetector is used to detect a second electrical signal corresponding to the reflected light signal and transmit the second electrical signal to the mixer;

[0017] The mixer is used to mix the first electrical signal and the second electrical signal to obtain the first error signal, and transmit the first error signal to the control circuit;

[0018] The control circuit adjusts the cavity length of the active optical clock resonant cavity according to the first error signal.

[0019] Optionally, the active optical clock resonant cavity includes a first cavity mirror, a first quantum reference system, a second cavity mirror, and a piezoelectric ceramic, wherein the first quantum reference system is arranged between the first cavity mirror and the second cavity mirror, and the piezoelectric ceramic is connected to the second cavity mirror;

[0020] The first quantum reference system is used to generate coherent stimulated radiation to generate an active optical clock signal;

[0021] The control circuit is specifically configured to provide a servo control voltage to the piezoelectric ceramic according to the first error signal, so as to move the piezoelectric ceramic to adjust the cavity length of the active optical clock resonant cavity.

[0022] Optionally, the first cavity mirror and the second cavity mirror are coated with an anti-reflection film at a wavelength corresponding to the first laser.

[0023] Optionally, the first cavity mirror and the second cavity mirror are coated with a reflective film at a wavelength corresponding to the passive optical clock signal.

[0024] The first cavity mirror and the second cavity mirror are coated with a reflective film at the wavelength of the active optical clock signal so that the cavity mode bandwidth of the active optical clock signal wavelength is greater than the clock transition linewidth in the first quantum reference system to form a bad cavity.

[0025] Optionally, the passive optical clock includes a clock laser system, a second half-wave plate, a second polarization beam splitter prism, an acousto-optic modulator, a third half-wave plate, a third polarization beam splitter prism, an ultra-stable laser locking system and a second quantum reference system; wherein

[0026] The clock laser system is used to emit a second laser. After passing through the second half-wave plate and the second polarization beam splitter prism, the second laser is split into a first polarization light and a second polarization light. The first polarization light is emitted to the third half-wave plate through the acousto-optic modulator, and then emitted to the third polarization beam splitter prism through the third half-wave plate. The second polarization light is emitted to the ultra-stable laser locking system.

[0027] The ultra-stable laser locking system is used for closed-loop feedback control of the clock laser system according to the error signal detected by the second polarized light;

[0028] The third polarization beam splitter prism is used to split the first polarized light into a third polarized light and a fourth polarized light, and the fourth polarized light is emitted to the second quantum reference system;

[0029] The second quantum reference system is connected to the acousto-optic modulator, and the second quantum reference system controls the acousto-optic modulator through closed-loop feedback according to the atomic spectral lines detected by the fourth polarized light;

[0030] The third polarized light that has been feedback controlled is a passive optical clock signal emitted to the cavity locking component.

[0031] Optionally, the passive optical clock is an optical lattice clock, an ion optical clock, or an atomic beam optical clock.

[0032] Optionally, the quantum system of the active optical clock is hot atoms, cold atoms, or ions, the energy level structure of the quantum system is a two-level system, a three-level system, or a four-level system, and the quantum system is used for the first quantum reference.

[0033] On the other hand, the present application provides a time measurement device, which includes the active and passive combined optical clock stabilization system as described above.

[0034] The present application provides a combined active and passive optical clock stabilization system comprising an active optical clock, a cavity-locked component, and a passive optical clock. The active optical clock includes a pump laser system and an active optical clock resonant cavity. A passive optical clock signal is generated by the passive optical clock and emitted to the cavity-locked component. The cavity-locked component modulates the passive optical clock signal with a first electrical signal and emits the modulated optical signal to the active optical clock resonant cavity. A second electrical signal corresponding to the reflected optical signal obtained by the active optical clock resonant cavity reflecting the modulated optical signal is obtained. A first error signal is then obtained by mixing the first and second electrical signals. Finally, the cavity length of the active optical clock resonant cavity is adjusted based on the first error signal to compensate for the drift of the active optical clock resonant cavity, thereby ensuring that the long-term stability of the active optical clock resonant cavity is consistent with that of the passive optical clock used as a reference. Furthermore, because the active optical clock suppresses the cavity pulling effect, the long-term instability of the active optical clock is reduced by two orders of magnitude compared to that of the passive optical clock, thereby improving the long-term stability of the active optical clock. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0036] Figure 1 A schematic diagram of the structure of the active and passive combined optical clock stabilization system provided in an embodiment of the present application;

[0037] Figure 2 A schematic structural diagram of an active and passive combined optical clock stabilization system provided in another embodiment of the present application.

[0038] The above drawings illustrate specific embodiments of the present application, which will be described in more detail below. These drawings and the textual description are not intended to limit the scope of the present application in any way, but rather to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments. DETAILED DESCRIPTION

[0039] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0040] The following examples of the present application are described with reference to the accompanying drawings. Therefore, those skilled in the art will recognize that various changes, equivalents, and / or substitutions may be made to the examples described herein without departing from the scope and spirit of the present application. In the description of the drawings, similar components may be represented by similar reference numerals.

[0041] In this application, the expressions "have", "may have", "include" and "contain", or "may include" and "may contain" may be used herein to indicate the presence of corresponding features (for example, elements such as values, functions, operations or components), but do not exclude the existence of additional features.

[0042] In this application, the expressions "A or B", "at least one of A and / or B", or "one or more of A and / or B" etc. used herein may include all combinations of one or more of the relevant listed items. For example, the terms "A or B", "at least one of A and B", or "at least one of A or B" may refer to all of the following situations: (1) including at least one A, (2) including at least one B, and (3) including at least one A and at least one B.

[0043] The terms used in this application are used to describe the purpose of the application's examples, rather than to limit the scope of the application. Unless otherwise indicated, the terms in the singular may include the plural form. Unless otherwise defined herein, all terms used herein (including technical or scientific terms) may have the same meanings as those skilled in the art would normally understand. It will also be understood that the terms defined in the dictionary or commonly used terms should also be interpreted as the customary manner of the relevant technology, and should not be idealized or too formally used, unless clearly defined as such in each example of the application. In some cases, even if a term is a term defined in the application, the term should not be interpreted as excluding the example of the application.

[0044] As today's most sophisticated scientific instruments capable of outputting quantum frequency standards, atomic clocks play a vital role in redefining the second, promoting satellite navigation and positioning, precision scientific measurement, verifying physical theories (such as the time dilation effect in Einstein's theory of relativity), volcano monitoring, quantum simulation, depth mapping, and gravitational measurements. In particular, optical atomic clocks (optical clocks), which use optical frequency transitions as their reference spectrum, achieve superior accuracy and stability compared to microwave atomic clocks, which use microwave transitions as their reference spectrum. Furthermore, the rapid adoption of femtosecond optical combs has made the application of optical frequency standard signals (optical frequency standards) a reality. Consequently, research on optical clocks has been intense both domestically and internationally in recent years, with a continuous stream of new research findings.

[0045] At present, the realization of optical frequency standards is mostly based on traditional passive optical clock technology. The general method is to stabilize the frequency of the laser output on a precisely designed passive optical resonant cavity to achieve a more accurate resonant frequency and thus obtain a highly coherent optical frequency standard signal. The local oscillator laser of the passive optical clock uses the Pound-Drever-Hall (PDH) technology to lock the laser on an ultra-stable resonant cavity to narrow the laser linewidth. However, due to the unavoidable Brownian thermal noise of the resonant cavity, the laser linewidth is limited to be further narrowed. However, if the Brownian motion of the resonant cavity is to be suppressed, the resonant cavity needs to be set to work in an extremely low temperature environment to reduce the thermal noise limit, which will greatly increase the complexity of the system.

[0046] To overcome the limitations of passive optical frequency standards, the concept of active optical clocks was proposed. Active optical clocks generate optical frequency standards by generating multi-atom coherent stimulated emission between atomic transition energy levels through weak feedback from an optical resonator. Because active optical clock systems operate in deep bad cavity modes, their output frequency is naturally immune to the Brownian thermal noise generated by the resonator, significantly reducing the perturbations of the cavity thermal noise on the output clock laser frequency. This overcomes the current optical clock's reliance on the linewidth of the local oscillator laser. Furthermore, active optical clocks offer a significant advantage in short-term stability over passive optical clocks. Therefore, active optical clocks can theoretically achieve ultra-narrow linewidth optical frequency standards, providing narrow-linewidth laser sources in different frequency bands for other precision measurements, thereby promoting the development of optical frequency precision measurement.

[0047] Although active optical clocks are naturally immune to the Brownian thermal noise generated by the resonant cavity, breaking through the thermal noise limit of traditional passive optical clock PDH frequency stabilization systems, the resonant cavity of the active optical clock will drift because the cavity length is not locked, resulting in poor long-term stability of the active optical clock.

[0048] Currently, passive optical clocks offer the best long-term stability available with existing technology. To address the issue of long-term stability of active optical clocks being limited by resonant cavity drift, this application proposes a combined active and passive optical clock stabilization system that can enhance the long-term stability of active optical clocks. This system compensates for the drift of the active optical clock's resonant cavity by referencing it to a passive optical clock, ensuring that the long-term stability of the active optical clock's resonant cavity is consistent with that of the referenced passive optical clock. Furthermore, because the active optical clock suppresses the cavity pulling effect, the long-term instability of the active optical clock is reduced by two orders of magnitude compared to that of the passive optical clock, thereby improving its long-term stability.

[0049] The following specific embodiments describe in detail the technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0050] Figure 1 This is a schematic diagram of the structure of the active and passive combined optical clock stabilization system provided in the embodiment of the present application. Figure 1 As shown, the optical clock stabilization system provided by the present application includes: an active optical clock 100, a cavity locking component 200 and a passive optical clock 300. The active optical clock 100 includes a pump laser system 101 and an active optical clock resonant cavity 102.

[0051] The cavity locking component 200 can control the cavity length of the active optical clock resonant cavity 102 based on the passive optical clock signal emitted by the passive optical clock 300, thereby compensating for the drift of the active optical clock resonant cavity 102, so that the long-term stability of the active optical clock resonant cavity 102 is consistent with that of the passive optical clock used for reference.

[0052] First, the direction of the passive optical clock signal is described starting from the passive optical clock 300 , to the cavity locking assembly 200 , and then to the active optical clock 100 .

[0053] The passive optical clock 300 is used to generate a passive optical clock signal and emit the passive optical clock signal to the cavity locking component 200 .

[0054] Optionally, the passive optical clock is an optical lattice clock, an ion optical clock, or an atomic beam optical clock.

[0055] Among them, the optical lattice clock is a kind of atomic clock. The so-called atomic clock is a clock that uses the vibration of electrons in atoms as its oscillator. If the frequency of the vibration is in the optical band, the clock is called an optical clock. The optical lattice clock is a type of optical clock. For example, the optical lattice clock developed by ytterbium atoms theoretically has an error of 1 second in 30 billion years, and an error of only 10 seconds per day. -18 Square seconds.

[0056] Single-ion optical clocks are one of the most accurate atomic clocks currently available, with uncertainty and stability indicators reaching the E-18 level, such as calcium ion optical clocks.

[0057] Atomic beam optical clocks are currently the most portable and stable type of optical clocks. For example, Andrew Ludlow's group at the National Institute of Standards and Technology in the United States used a scheme for energy level transfer detection using thermal atomic beams to detect excited states. 3 The energy level detection of the P1 state realizes the Ramsey spectrum with high signal-to-noise ratio and achieves a frequency stability of less than 10 -16 Calcium atomic beam optical frequency standard of the order of magnitude.

[0058] It can be seen that the uncertainty and stability indicators of optical lattice clocks, ion optical clocks and atomic beam optical clocks, which are passive optical clocks, have reached the current best level. Therefore, passive optical clocks are selected to provide passive optical clock signals for active optical clocks.

[0059] The cavity locking component 200 is used to modulate the passive optical clock signal through a first electrical signal, and emit the modulated optical signal to the active optical clock resonant cavity 102, and obtain a second electrical signal corresponding to the reflected optical signal reflected by the active optical clock resonant cavity 102 to the modulated optical signal, obtain a first error signal by mixing the first electrical signal and the second electrical signal, and adjust the cavity length of the active optical clock resonant cavity 102 according to the first error signal.

[0060] Specifically, the cavity locking component 200 generates a first electrical signal and modulates the passive optical clock signal emitted by the passive optical clock 300 using the first electrical signal to obtain a modulated optical signal. The modulated optical signal is then emitted to the active optical clock resonant cavity 102. The modulated optical signal oscillates in the active optical clock resonant cavity 102 and is reflected as a reflected optical signal, which carries information about the active optical clock resonant cavity. The reflected optical signal is then emitted to the cavity locking component 200. After receiving the reflected optical signal, the cavity locking component 200 converts the reflected optical signal into a second electrical signal and mixes the first and second electrical signals to obtain a first error signal. Finally, the cavity length of the active optical clock resonant cavity 102 is adjusted based on the first error signal.

[0061] Next, the process of generating an active optical clock signal in the present application is described.

[0062] Active optical clock 100 includes a pump laser system 101 and an active optical clock resonant cavity 102. Pump laser system 101 is used to emit a first laser beam, which is then emitted into active optical clock resonant cavity 102 to generate coherent stimulated emission within active optical clock resonant cavity 102 to generate an active optical clock signal.

[0063] Optionally, the active optical clock resonant cavity is made of a material with a low thermal expansion coefficient.

[0064] Through the operation of cavity locking assembly 200 and passive optical clock 300, the cavity length of active optical clock resonant cavity 102 is adjusted, compensating for the drift of the active optical clock resonant cavity. The active optical clock signal generated by active optical clock resonant cavity 102 provides an ultra-narrow linewidth optical frequency standard, which can provide a narrow linewidth laser source for precision measurement.

[0065] The active-passive combined optical clock stabilization system provided in the embodiments of the present application includes: an active optical clock 100, a cavity-locking component 200, and a passive optical clock 300. The active optical clock 100 includes a pump laser system 101 and an active optical clock resonant cavity 102. The passive optical clock 300 generates a passive optical clock signal and transmits the passive optical clock signal to the cavity-locking component 200. The cavity-locking component 200 modulates the passive optical clock signal using a first electrical signal and transmits the modulated optical signal to the active optical clock resonant cavity 102. The modulated optical signal oscillates in the active optical clock resonant cavity and is reflected as a reflected optical signal, which is then transmitted to the cavity-locking component 200. The cavity-locking component 200 obtains a second electrical signal corresponding to the reflected optical signal and then mixes the first and second electrical signals to obtain a first error signal. The cavity length of the active optical clock resonant cavity 102 is adjusted based on the first error signal to compensate for the drift of the active optical clock resonant cavity, thereby ensuring that the long-term stability of the active optical clock resonant cavity is consistent with that of the passive optical clock used as a reference. On this basis, since the active optical clock has an inhibitory effect on the cavity pulling effect, the long-term instability of the active optical clock is reduced by two orders of magnitude compared with the passive optical clock, thereby improving the long-term stability of the active optical clock.

[0066] Figure 2 This is a structural diagram of an active and passive optical clock stabilization system provided in another embodiment of the present application. Figure 1 Based on the above, the structure and function of the optical clock stabilization system are described in detail. Figure 2 As shown, the active optical clock resonant cavity includes a first cavity mirror 2, a first quantum reference 3, a second cavity mirror 4 and a piezoelectric ceramic 5; the cavity locking component includes an electro-optical modulator 9, a first half-wave plate 8, a first polarization beam splitter prism 7, a quarter-wave plate 6, a signal generator 10, a high-speed photodetector 11, a mixer 12 and a control circuit 13; the passive optical clock includes: a clock laser system 14, a second half-wave plate 15, a second polarization beam splitter prism 16, an acousto-optic modulator 18, a third half-wave plate 19, a third polarization beam splitter prism 20, an ultra-stable laser locking system 17 and a second quantum reference system 21.

[0067] First, the principle of providing a passive optical clock signal by the passive optical clock of the present application is described in detail.

[0068] The clock laser system 14, the second half-wave plate 15, the second polarization beam splitter prism 16, the acousto-optic modulator 18, the third half-wave plate 19, and the third polarization beam splitter prism 20 provided in this application can be as follows: Figure 2 The positional relationship shown is arranged in sequence; it can also be arranged on the base according to actual needs to form a connection of the mechanical structure, and this application does not make specific restrictions.

[0069] Among them, the clock laser system 14 is used to emit a second laser. After the second laser passes through the second half-wave plate 15 and the second polarization splitter prism 16, it is divided into a first polarization light and a second polarization light. The first polarization light is emitted to the third half-wave plate 19 through the acousto-optic modulator 18, and then emitted to the third polarization splitter prism 20 through the third half-wave plate 19. The second polarization light is emitted to the ultra-stable laser locking system 17; the ultra-stable laser locking system 17 is used to control the clock laser system 15 through closed-loop feedback based on the error signal detected by the second polarization light.

[0070] Specifically, clock laser system 14 emits a second laser beam. By adjusting the position of second half-wave plate 15, for example by pre-rotating second half-wave plate 15 to an appropriate position, second polarization beam splitter prism 16 can be used to split the second laser beam into two paths with appropriate light intensities, namely, first polarized light and second polarized light. This application does not impose any specific restrictions on the positioning of the second half-wave plate and the second polarization prism, as long as the second laser beam can be split into two paths with appropriate light intensities.

[0071] The first polarized light is emitted to the third half-wave plate 19 through the acousto-optic modulator 18 , and then emitted to the third polarization beam splitter prism 20 through the third half-wave plate 19 .

[0072] The acousto-optic modulator is a commonly used frequency-shifting component that can adjust the laser frequency within a certain range. It can match the laser frequency with the atomic transition frequency and be used to detect the atomic transition energy levels.

[0073] Among them, the second polarized light is injected into the ultra-stable laser locking system 17 to feedback control the clock laser system 14. That is, the ultra-stable laser locking system 17 references the clock laser system 14 to the ultra-stable optical resonant cavity in the ultra-stable laser locking system 18, thereby narrowing the laser linewidth emitted by the clock laser system.

[0074] Specifically, the ultra-stable laser locking system includes components included in an ultra-stable optical cavity and a locking loop, which is a laser frequency stabilization method commonly used in the field of quantum frequency standards, namely the PDH (Pound-Drever-Hall) laser frequency stabilization technology. The ultra-stable laser locking system can control the clock laser system through closed-loop feedback based on the error signal detected by the second polarized light in the ultra-stable laser locking system, thereby narrowing the linewidth of the first polarized light to detect extremely narrow atomic spectral lines.

[0075] The third polarization beam splitter prism 20 is used to split the first polarized light into a third polarized light and a fourth polarized light. The fourth polarized light is emitted to the second quantum reference system 21. The second quantum reference system 21 is connected to the acousto-optic modulator 18. The second quantum reference system 21 controls the acousto-optic modulator 18 through closed-loop feedback based on the atomic spectral lines detected by the fourth polarized light. The third polarized light that undergoes feedback control is the passive optical clock signal emitted to the cavity-locked component.

[0076] Specifically, by adjusting the position of the third half-wave plate 19, for example by pre-rotating the third half-wave plate 19 to an appropriate position, the third polarization beam splitter prism 20 can be configured to split the first polarized light into two paths with an appropriate light intensity ratio, namely, the third polarized light and the fourth polarized light. This application does not impose any specific restrictions on the positioning of the third half-wave plate 19 and the third polarization prism 20, as long as the first polarized light can be split into two paths with an appropriate light intensity ratio.

[0077] The second quantum reference system 21 includes components of a quantum reference and a locking loop. The fourth polarized light is used to detect the atomic transition spectrum of the quantum reference. The locking loop then feedback-controls the acousto-optic modulator, thereby locking the frequency of the third polarized light to the atomic transition frequency. The third polarized light then becomes a passive optical clock signal, which is emitted to the electro-optic modulator 9 of the cavity-locked component, providing a stable passive optical clock signal for the cavity-locked component.

[0078] Secondly, the specific working principle of the cavity locking assembly of the present application is described in detail.

[0079] The cavity-locked component includes an electro-optical modulator 9, a first half-wave plate 8, a first polarization beam splitter prism 7, a quarter-wave plate 6, a signal generator 10, a high-speed photodetector 11, a mixer 12 and a control circuit 13; wherein the electro-optical modulator 9 is respectively connected to the signal generator 10, and the mixer 12 is respectively connected to the high-speed photodetector 11, the signal generator 10 and the control circuit 13.

[0080] Specifically, the electro-optical modulator 9 is connected to the passive optical clock and the signal generator 10 respectively, and the mixer 12 is connected to the high-speed photodetector 11 and the signal generator 10 and the control circuit 13 respectively. In addition, the electro-optical modulator 9, the first half-wave plate 8, the first polarization beam splitter prism 7, and the quarter-wave plate 6 can be as follows: Figure 2 The positional relationship shown is arranged in sequence; it can also be arranged on the base according to actual needs to form a connection of the mechanical structure, and this application does not make specific restrictions.

[0081] Among them, the signal generator 10 is used to generate a first electrical signal and transmit the first electrical signal to the electro-optical modulator 9 and the mixer 12; the electro-optical modulator 9 is used to modulate the passive optical clock signal by the first electrical signal, and emit the modulated optical signal through the first half-wave plate 8 to the first polarization splitter prism 7.

[0082] Specifically, the signal generator 10 generates a first electrical signal and transmits it to the electro-optical modulator 9 and the mixer 12. The electro-optical modulator 9 modulates the passive optical clock signal emitted by the passive optical clock with the first electrical signal, and emits the modulated optical signal through the first half-wave plate 8 to the first polarization beam splitter prism 7.

[0083] Among them, modulation achieved using the electro-optic effect is called electro-optic modulation. The physical basis of electro-optic modulation is the electro-optic effect, which states that the refractive index of certain crystals changes under the influence of an external electric field. When light waves pass through this medium, their transmission characteristics are affected and altered. The modulating crystal is the core component of an electro-optic modulator. An electro-optic modulator is an optical modulator that utilizes the electro-optic effect. The process of loading information into a laser is called modulation, and the device that accomplishes this is called a modulator. Electro-optic modulation is external modulation, meaning that the modulation occurs within the optical path outside the laser.

[0084] The first polarization beam splitter prism 7 is used to transmit the modulated optical signal to the quarter-wave plate 6 , and the modulated optical signal is emitted into the active optical clock resonant cavity through the quarter-wave plate 6 .

[0085] Specifically, by setting the position of the first half-wave plate 8, for example, by pre-rotating the first half-wave plate 8 to an appropriate position, the first polarization beam splitter prism 7 can be used to completely transmit the modulated light signal to the quarter-wave plate 6. After passing through the quarter-wave plate 6, the modulated light signal is emitted into the active optical clock resonant cavity. This application does not impose any specific restrictions on the position setting of the first half-wave plate 8 and the first polarization beam splitter prism 7, as long as the modulated light signal is completely transmitted to the quarter-wave plate 6.

[0086] The modulated optical signal oscillates in the active optical clock resonant cavity and is reflected to become a reflected optical signal. The reflected optical signal is emitted to the first polarization beam splitter prism 7 through the quarter-wave plate 6 .

[0087] The first cavity mirror and the second cavity mirror are coated with a reflective film at a wavelength corresponding to the passive optical clock signal. The wavelength of the modulated optical signal and the passive optical clock signal are the same.

[0088] Specifically, the modulated light signal is emitted into the active optical clock resonant cavity and oscillates in the cavity, and the first cavity mirror 2 and the second cavity mirror 4 of the active optical clock resonant cavity are coated with a reflective film at the wavelength corresponding to the passive optical clock signal. Since the wavelength of the modulated light signal and the passive optical clock signal are the same, the modulated light signal is reflected by the active optical clock resonant cavity to become a reflected light signal, wherein the reflected light signal carries the information of the active optical clock resonant cavity, and the reflected light signal is emitted to the first polarization beam splitter prism 7 through the quarter wave plate 6.

[0089] The first polarization beam splitter prism 7 is further configured to reflect the reflected light signal to the high-speed photodetector 11 ; the high-speed photodetector 11 is configured to detect a second electrical signal corresponding to the reflected light signal and transmit the second electrical signal to the mixer 12 .

[0090] Specifically, by setting the position of the quarter-wave plate 6, for example, by pre-rotating the quarter-wave plate 6 to an appropriate position, the first polarization beam splitter prism can be made to completely reflect the reflected light signal to the high-speed photodetector 11. The high-speed photodetector 11 detects a second electrical signal corresponding to the reflected light signal and transmits the second electrical signal to the mixer 12. The present application does not impose any specific restrictions on the position setting of the quarter-wave plate 6 and the first polarization beam splitter prism 7, as long as the reflected light signal can be completely reflected to the high-speed photodetector 11.

[0091] The mixer 12 is used to mix the first electrical signal and the second electrical signal to obtain a first error signal, and transmit the first error signal to the control circuit 13; the control circuit 13 adjusts the cavity length of the active optical clock resonant cavity according to the first error signal.

[0092] Specifically, mixer 12 mixes the first electrical signal transmitted by signal generator 10 and the second electrical signal transmitted by high-speed photodetector 11 to generate a first error signal, and transmits the first error signal to control circuit 13. Control circuit 13 generates a servo signal based on the first error signal and provides a servo control voltage to piezoelectric ceramic 5 to move piezoelectric ceramic 5. Since piezoelectric ceramic 5 is connected to second cavity mirror 4, second cavity mirror 4 moves with the movement of piezoelectric ceramic 5, thereby adjusting the cavity length of the active optical clock resonant cavity and compensating for the drift of the active optical clock resonant cavity.

[0093] Finally, the specific working principle of the active optical clock of this application is described in detail.

[0094] The active optical clock includes a pump laser system and an active optical clock resonant cavity. The active optical clock resonant cavity includes a first cavity mirror 2, a first quantum reference system 3, a second cavity mirror 4 and a piezoelectric ceramic 5. The first quantum reference system 3 is arranged between the first cavity mirror 2 and the second cavity mirror 4, and the piezoelectric ceramic 5 is connected to the second cavity mirror 4.

[0095] Specifically, the piezoelectric ceramic 5 is connected to the second cavity mirror 4, and the first quantum reference system 3 is arranged between the first cavity mirror 2 and the second cavity mirror 4. Among them, the pump laser system 1, the first cavity mirror 2, the first quantum reference system 3, and the second cavity mirror 4 can be as follows: Figure 2 The positional relationship shown is arranged in sequence, and can also be arranged on the base according to actual needs to form a connection of the mechanical structure. This application does not make specific restrictions.

[0096] The pump laser system 1 is used to emit a first laser and emit the first laser to the active optical clock resonant cavity; the first quantum reference system 3 is used to form coherent stimulated radiation to generate an active optical clock signal.

[0097] Specifically, the pump laser system 1 emits a first laser to the active optical clock resonant cavity, which generates coherent stimulated radiation through the first quantum reference system 3 to generate an active optical clock signal.

[0098] Optionally, the quantum system of the active optical clock is hot atoms, cold atoms, or ions, and the energy level structure of the quantum system is a two-level, three-level, or four-level system. The quantum system is used as the first quantum reference. The hot atoms can be a hot atom gas cell or a hot atom beam, while the cold atoms can be optical cohesion, an optical lattice, or a trapped ion.

[0099] Optionally, the first cavity mirror 2 and the second cavity mirror 4 are coated with a reflective film at the wavelength of the active optical clock signal so that the cavity mode bandwidth of the active optical clock signal wavelength is greater than the clock transition linewidth in the first quantum reference system 3 to form a bad cavity.

[0100] Optionally, the first cavity mirror 2 and the second cavity mirror 4 are coated with an anti-reflection film at a wavelength corresponding to the first laser.

[0101] Specifically, after the first laser is emitted by the pump laser system 1, it needs to pass through the first cavity mirror 2 to reach the active optical clock resonant cavity. Therefore, the first cavity mirror 2 and the second cavity mirror 4 are coated with an anti-reflection film at the wavelength of the first laser to ensure that the first laser is emitted into the active optical clock resonant cavity as much as possible.

[0102] The control circuit 13 is specifically configured to provide a servo control voltage to the piezoelectric ceramic 5 according to the first error signal, so as to move the piezoelectric ceramic 5 to adjust the cavity length of the active optical clock resonant cavity.

[0103] Specifically, the control circuit 13 in the feedback control component provides a servo control voltage to the piezoelectric ceramic 5 according to the first error signal to move the piezoelectric ceramic 5. Since the piezoelectric ceramic 5 is connected to the second cavity mirror 4, the second cavity mirror 4 moves with the movement of the piezoelectric ceramic 5, thereby adjusting the cavity length of the active optical clock resonant cavity.

[0104] This embodiment of the application compensates for the drift of the active optical clock's resonant cavity by referencing it to a passive optical clock. This ensures that the long-term stability of the active optical clock's resonant cavity matches that of the passive optical clock used as a reference. Furthermore, because the active optical clock suppresses the cavity pulling effect, the long-term instability of the active optical clock is reduced by two orders of magnitude compared to that of the passive optical clock. This improves the long-term stability of the active optical clock.

[0105] On the other hand, an embodiment of the present application further provides a time measurement device, which includes the optical clock stabilization system as described in any of the above embodiments.

[0106] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, and the true scope and spirit of the present application are indicated by the following claims.

[0107] It should be understood that the present application is not limited to the exact structure described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. An active and passive combined optical clock stabilization system, characterized in that: The system comprises: an active optical clock, a cavity locking component and a passive optical clock; wherein The active optical clock includes a pump laser system and an active optical clock resonant cavity. The pump laser system is used to emit a first laser, and emit the first laser into the active optical clock resonant cavity to form coherent stimulated radiation in the active optical clock resonant cavity to generate an active optical clock signal. The passive optical clock is used to generate a passive optical clock signal and emit the passive optical clock signal to the cavity locking component; The cavity locking component is used to modulate the passive optical clock signal using a first electrical signal, emit the modulated optical signal to the active optical clock resonant cavity, and obtain a second electrical signal corresponding to a reflected optical signal of the modulated optical signal reflected by the active optical clock resonant cavity. A first error signal is obtained by mixing the first electrical signal and the second electrical signal. The cavity length of the active optical clock resonant cavity is adjusted according to the first error signal to compensate for the drift of the active optical clock resonant cavity, so that the long-term stability of the active optical clock resonant cavity is consistent with that of the referenced passive optical clock.

2. The system according to claim 1, wherein: The cavity locking assembly includes an electro-optic modulator, a first half-wave plate, a first polarization beam splitter, a quarter-wave plate, a signal generator, a high-speed photodetector, a mixer, and a control circuit; The electro-optical modulator is connected to the passive optical clock and the signal generator respectively, and the mixer is connected to the high-speed photodetector, the signal generator and the control circuit respectively; The signal generator is used to generate the first electrical signal and transmit the first electrical signal to the electro-optical modulator and the mixer; The electro-optical modulator is used to modulate the passive optical clock signal by the first electrical signal, and emit the modulated optical signal to the first polarization beam splitter prism through the first half-wave plate; The first polarization beam splitter prism is used to transmit the modulated light signal to the quarter-wave plate. The modulated light signal is emitted into the active optical clock resonant cavity through the quarter-wave plate. The modulated light signal oscillates in the active optical clock resonant cavity and is reflected to become a reflected light signal. The reflected light signal is emitted to the first polarization beam splitter prism through the quarter-wave plate. The first polarization beam splitter prism is further configured to reflect the reflected light signal to the high-speed photodetector; The high-speed photodetector is used to detect a second electrical signal corresponding to the reflected light signal and transmit the second electrical signal to the mixer; The mixer is used to mix the first electrical signal and the second electrical signal to obtain the first error signal, and transmit the first error signal to the control circuit; The control circuit adjusts the cavity length of the active optical clock resonant cavity according to the first error signal.

3. The system according to claim 2, characterized in that The active optical clock resonant cavity includes a first cavity mirror, a first quantum reference system, a second cavity mirror, and a piezoelectric ceramic, wherein the first quantum reference system is arranged between the first cavity mirror and the second cavity mirror, and the piezoelectric ceramic is connected to the second cavity mirror; The first quantum reference system is used to generate coherent stimulated radiation to generate an active optical clock signal; The control circuit is specifically configured to provide a servo control voltage to the piezoelectric ceramic according to the first error signal, so as to move the piezoelectric ceramic to adjust the cavity length of the active optical clock resonant cavity.

4. The system according to claim 3, characterized in that The first cavity mirror and the second cavity mirror are coated with an anti-reflection film at a wavelength corresponding to the first laser.

5. The system according to claim 3, wherein: The first cavity mirror and the second cavity mirror are coated with a reflective film at a wavelength corresponding to the passive optical clock signal.

6. The system according to claim 3, wherein: The first cavity mirror and the second cavity mirror are coated with a reflective film at the wavelength of the active optical clock signal so that the cavity mode bandwidth of the active optical clock signal wavelength is greater than the clock transition linewidth in the first quantum reference system to form a bad cavity.

7. The system according to claim 1, wherein: The passive optical clock includes a clock laser system, a second half-wave plate, a second polarization beam splitter prism, an acousto-optic modulator, a third half-wave plate, a third polarization beam splitter prism, an ultra-stable laser locking system and a second quantum reference system; wherein The clock laser system is used to emit a second laser. After passing through the second half-wave plate and the second polarization beam splitter prism, the second laser is split into a first polarization light and a second polarization light. The first polarization light is emitted to the third half-wave plate through the acousto-optic modulator, and then emitted to the third polarization beam splitter prism through the third half-wave plate. The second polarization light is emitted to the ultra-stable laser locking system. The ultra-stable laser locking system is used for closed-loop feedback control of the clock laser system according to the error signal detected by the second polarized light; The third polarization beam splitter prism is used to split the first polarized light into a third polarized light and a fourth polarized light, and the fourth polarized light is emitted to the second quantum reference system; The second quantum reference system is connected to the acousto-optic modulator, and the second quantum reference system controls the acousto-optic modulator through closed-loop feedback according to the atomic spectral lines detected by the fourth polarized light; The third polarized light that has been feedback controlled is a passive optical clock signal emitted to the cavity locking component.

8. The system according to claim 7, characterized in that The passive optical clock is an optical lattice clock, an ion optical clock or an atomic beam optical clock.

9. The system according to claim 3, wherein: The quantum system of the active optical clock is hot atoms, cold atoms or ions, the energy level structure of the quantum system is a two-level system, a three-level system or a four-level system, and the quantum system is used for the first quantum reference system.

10. A time measuring device, characterized in that: The time measurement device includes the active-passive combined optical clock stabilization system according to any one of claims 1 to 9.

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