CN112213938A - Optical frequency atomic clock - Google Patents
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Abstract
The invention relates to the technical field of atomic clocks, and discloses an optical frequency atomic clock, which is characterized in that when the optical frequency atomic clock generates a required optical frequency comb signal by adopting a microcavity-based optical comb technology, two beams of frequency-stabilized laser are respectively locked with two nearest comb frequencies on the frequency spectrum of the optical frequency comb signal through a phase-locked loop, so that the direct locking of a repetition frequency and two laser frequency differences is realized, the initial frequency is locked by referring to the comb frequencies by carrying out frequency doubling treatment on the comb frequencies in advance as a typical optical frequency atomic clock system does not need, therefore, in the microwave frequency output process, only the repetition frequency is required to be within the working bandwidth of a common photoelectric detector and the spectrum width of the optical frequency comb signal covers the two beams of frequency-stabilized laser, the spectrum width does not need to reach one octave, and the requirement of the optical frequency comb system on the optical frequency spectrum width is greatly reduced, therefore, the microcavity optical comb can be applied to an optical clock system, and is beneficial to the miniaturization and even chip design of the optical frequency atomic clock.
Description
Technical Field
The invention belongs to the technical field of atomic clocks, and particularly relates to an optical frequency atomic clock.
Background
The atomic transition frequency is only related to the atomic energy level theoretically and does not change along with the time, and the atomic clock establishes the atomic energy level-based time frequency standard by mapping the stability of the atomic transition frequency with extremely narrow line width and extremely high stability to the microwave frequency band. The theoretical expression for the stability of the atomic clock frequency can be as follows:
in the formula, σy(t) represents the frequency stability of the atomic clock, χ represents the linear constant of the atomic clock transition line, υ represents the transition frequency of the atomic clock, Δ υ represents the line width of the atomic clock transition line, SNRepresenting the signal-to-noise ratio, t, of the detected signalCDenotes a measurement period and τ denotes a measurement time. From the above formula, the relative stability of the atomic clock is inversely proportional to the clock transition frequency (i.e., the atomic clock transition frequency v), and the clock transition frequencies of the conventional microwave atomic clocks are all in the microwave frequency band, for example, the cesium atomic clock transition frequency is 9.192631770GHz, and the rubidium atomic clock transition frequency is 6.834684211 GHz. With the development of the scientific and technical field, the performance of the traditional atomic clock is gradually difficult to meet the requirements, so that the optical frequency atomic clock with the clock transition frequency in the optical frequency band becomes an important technical path for further improving the frequency standard performance of the atomic clock. The transition frequency of the optical frequency atomic clock is 4 orders of magnitude higher than that of the traditional microwave atomic clock, and in addition, the transition energy level difference of the optical frequency atomic clock is larger than that of the traditional microwave atomic clock, so that compared with the traditional microwave atomic clock, the stability of the optical frequency atomic clock is greatly improved, and the frequency stability of the atomic optical frequency clock with the best performance to date reaches 10-18Magnitude.
However, the optical frequency atomic clock needs to complete the measurement of the optical frequency clock transition and transfer the stability of the optical frequency clock transition to the microwave frequency band, and a mature scheme which is widely adopted at present is to utilize a femtosecond optical frequency comb generated by a mode-locked laser to complete the coherent link between the optical frequency clock transition and the output microwave clock signal.
An optical frequency comb is essentially a pulsed laser signal that appears in the frequency domain as a collection of equally frequency-spaced and phase-locked laser lines, as shown in fig. 1, with a pulse repetition frequency frepI.e. the frequency spacing between the teeth of each frequency comb. In dispersive media, the difference between the burst velocity and the phase velocity results in a carrier-envelope phase difference Δ φ, which results in an overall initial bias frequency f for the optical frequency combceo＝frepDelta phi/2 pi, so that the frequency of each frequency comb of the optical frequency comb can be used as the initial frequency fceoAnd repetition frequency frepShown is that: f. ofk＝fceo+kfrepWherein the initial frequency fceoAnd repetition frequency frepAre all in the radio frequency band and k can be up to 106This, in turn, makes the optical frequency comb act like a frequency scale with a repetition frequency scale up to hundreds of THz (optical frequency band).
A typical optical frequency atomic clock system is shown in fig. 2, which realizes coherent link between clock frequency and microwave frequency by a femtosecond optical frequency comb generated by a conventional mode-locked laser, and the system operating principle is as follows: the repetition frequency f of the optical frequency comb signal is realized by the third photodetector PD3repDetecting the value of (2); by passing the k-th1Frequency of comb teeth of optical comb
After frequency multiplication, with 2k1Frequency of comb teeth of optical comb
Beat frequency to obtain the initial frequency of the optical comb
Then the pumping power of the mode-locked laser is controlled by a first phase-locked loop PLL1 to make the initial frequency f of the optical combceoLocking to repetition frequency frepTo obtain
Controlling the cavity length of the mode-locked laser by a second phase-locked loop PLL2 to make the kth optical comb2Frequency of comb teeth of optical comb
Locking to optical frequency clock transition frequency frTo obtain:
in the formula, k2And alpha and beta are constants, and the whole system is realized by two phase-locked loops:
at this time, the system will repeat the optical comb at the frequency frepLocked to the transition frequency f of the atomic optical frequency clockrAnd the output of the microwave frequency of the optical clock is realized.
The above method requires that the optical frequency comb must satisfy two conditions: (1) repetition frequency f of optical frequency combrepTo be within the operating range of the photodetector PD (typically tens of GHz); (2) the spectral width of the optical frequency comb is to reach an octave, so that the frequencies of the two comb teeth are equal
And
the initial frequency f of the optical frequency comb can be realized by frequency doubling and beat frequencyceoIs locked (i.e., self-referenced). The traditional optical frequency comb signal is generated by mode-locked lasers, such as a Ti sapphire mode-locked laser, an Er-doped fiber mode-locked laser, an Er Yb Glass mode-locked laser and the like, which can simultaneously satisfy the repetition frequency frepWithin the operating bandwidth of a common photodetector and the requirement that the spectral width exceeds one octave.
Although the optical frequency comb based on the mode-locked laser has been successfully applied to the engineering of the optical clock (i.e. the optical frequency atomic clock) as a mature technology, the size and power consumption of the optical frequency atomic clock still seriously restrict the miniaturization and even the chip miniaturization of the optical frequency atomic clock. The recently emerged microcavity optical comb technique generates an optical frequency comb by exciting a nonlinear Four-wave mixing (FWM) effect with a localized strong optical field in an optical microcavity, as shown in fig. 3. Compared with the traditional mode-locked laser, the optical microcavity generating the microcavity optical comb signal has the micron-scale size and the potential of on-chip integration, and the complexity and the volume of an optical comb system are greatly simplified, so that the microcavity optical comb technology is an important technical approach for realizing miniaturization and even chip formation of the optical frequency atomic clock.
The microcavity optical comb at present realizes the repetition frequency f from GHz to THz magnitude by adjusting the microcavity designrepHowever, it is difficult to achieve a spectral width of one octave while the repetition frequency is within the operating bandwidth of a common photodetector, and thus it is difficult to achieve the initial frequency fceoThis makes the typical optical clock scheme based on microcavity optical combs (as shown in fig. 2) difficult to implement.
Disclosure of Invention
In order to solve the problem that the self-reference locking of the initial frequency is difficult to realize when the microcavity optical comb technology is adopted in the traditional optical clock scheme, the invention aims to provide the novel optical frequency atomic clock based on the microcavity optical comb technology, which can realize the direct locking of the repetition frequency and the frequency difference of two lasers, does not need to firstly carry out frequency doubling treatment on comb tooth frequency to automatically lock the initial frequency like a typical optical frequency atomic clock system, and further does not need the optical comb spectrum width to reach one octave, so that the microcavity optical comb technology can be applied to the optical clock system.
The technical scheme adopted by the invention is as follows:
an optical frequency atomic clock comprises a microcavity optical comb module, a frequency stabilization laser source module and a phase-locked loop module;
the microcavity optical comb module is used for generating a frequency f ═ fceo+kfrepWherein f isceoRepresenting the initial frequency, f, of the optical frequency comb signalrepRepresenting the repetition frequency of the optical frequency comb signal, k being a positive integer;
the frequency stabilized laser source module is used for generating a first frequency stabilized laser and a second frequency stabilized laser, wherein the frequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2Unequal and respectively located within spectral width coverage of the optical frequency comb signals;
the phase-locked loop module is used for carrying out frequency f according to the nth comb toothn＝fceo+nfrepMth comb frequency fm＝fceo+mfrepFrequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2To control the power and wavelength of the pumping light signal of the microcavity optical comb module to make the repetition frequency f of the newly generated optical frequency comb signalrepLocking to frequency fr1And frequency fr2The difference between the first comb tooth frequency and the second comb tooth frequency is used for realizing the microwave frequency output of the optical frequency atomic clock, wherein the nth comb tooth frequency fn＝fceo+nfrepFor the nearest frequency f in the optical frequency comb signalr1The mth comb frequency fm＝fceo+mfrepFor the nearest frequency f in the optical frequency comb signalr2N and m are positive integers respectively.
Based on the above invention, a novel optical frequency atomic clock based on the microcavity optical comb technology is provided, that is, when the optical frequency atomic clock adopts the optical frequency comb technology to generate the required optical frequency comb signal, two beams of frequency-stabilized laser are respectively locked with the two nearest comb frequencies on the frequency spectrum of the optical frequency comb signal through a phase-locked loop, so as to realize direct locking of the repetition frequency and the frequency difference of the two lasers, without needing to firstly carry out frequency doubling processing on the comb frequencies to obtain a reference locking initial frequency like a typical optical frequency atomic clock system, so that in the process of realizing the microwave frequency output of the optical frequency atomic clock, only the repetition frequency is required to be within the working bandwidth of a common photoelectric detector and the spectral width of the optical frequency comb signal is required to cover the two beams of frequency-stabilized laser, and the spectral width is not required to reach one frequency doubling pass, thereby greatly reducing the requirement of the optical frequency comb system on the optical frequency spectral width, therefore, the microcavity optical comb can be applied to an optical clock system, and is beneficial to the miniaturization and even chip design of the optical frequency atomic clock.
Preferably, the microcavity optical comb module comprises a pump light source and an optical microcavity, wherein a pump light signal output end light path of the pump light source is communicated with an optical signal input end of the optical microcavity, and an optical signal output end of the optical microcavity is used for outputting the optical frequency comb signal.
Specifically, the optical microcavity is prepared from silicon nitride, silicon dioxide, aluminum nitride, lithium niobate, fused quartz or fluoride materials and can generate the repetition frequency frepMicro-cavity structures from GHz to THz scale.
Preferably, the first frequency stabilized laser and the second frequency stabilized laser are generated in the same physical system.
Preferably, the frequency-stabilized laser source module adopts a laser source which excites the frequency-stabilized laser based on an atomic transition spectral line, a molecular transition spectral line or an ion transition spectral line.
Specifically, the atomic transition spectral line includes a hydrogen atomic transition spectral line, a potassium atomic transition spectral line, a rubidium atomic transition spectral line, or a cesium atomic transition spectral line.
Specifically, the molecular transition line includes an ammonia molecular transition line and a hydrogen cyanide molecular transition line.
Specifically, the ion transition spectral line includes a calcium ion transition spectral line, a mercury ion transition spectral line, and an aluminum ion transition spectral line.
Preferably, the phase-locked loop module comprises a first phase-locked loop and a second phase-locked loop;
the first phase-locked loop is used for carrying out frequency f according to the nth comb toothn＝fceo+nfrepAnd the frequency f of the first frequency stabilized laserr1To control the pump light signal power of the microcavity optical comb module to make the nth comb frequency f of the optical frequency comb signal generated newlyn＝fceo+nfrepLocking to frequency fr1To obtain fr1＝fn+frep/a＝fceo+(n+1/a)frepWherein a is a preset constant；
The second phase-locked loop is used for carrying out frequency f according to the mth comb toothm＝fceo+mfrepAnd the frequency f of the second frequency stabilized laserr2To control the wavelength of the pump light signal of the microcavity optical comb module to make the mth comb frequency f of the optical frequency comb signal generated newlym＝fceo+mfrepLocking to frequency fr2To obtain fr2＝fm+frep/b＝fceo+(m+1/b)frepWherein b is a preset constant.
Specifically, the device also comprises a first photoelectric detector, a second photoelectric detector and a third photoelectric detector;
the output end of the first photoelectric detector is in communication connection with the first phase-locked loop and is used for detecting the nth comb frequency fn＝fceo+nfrepWith said frequency fr1The frequency difference therebetween;
the output end of the second photoelectric detector is in communication connection with the second phase-locked loop and is used for detecting the mth comb frequency fm＝fceo+mfrepWith said frequency fr2The frequency difference therebetween;
the output end of the third photoelectric detector is respectively in communication connection with the first phase-locked loop and the second phase-locked loop and is used for detecting the repetition frequency frepThe numerical value of (c).
The invention has the beneficial effects that:
(1) the invention provides a novel optical frequency atomic clock based on a microcavity optical comb technology, namely when the optical frequency atomic clock adopts the optical frequency comb technology based on the microcavity to generate a required optical frequency comb signal, two beams of frequency-stabilized laser are respectively locked with two nearest comb tooth frequencies on the frequency spectrum of the optical frequency comb signal through a phase-locked loop, so that the direct locking of a repetition frequency and two laser frequency differences is realized, the initial frequency is locked by referring to the comb tooth frequencies by carrying out frequency doubling treatment on the comb tooth frequencies in advance like a typical optical frequency atomic clock system, therefore, in the process of realizing the microwave frequency output of the optical frequency atomic clock, only the repetition frequency is required to be within the working bandwidth of a common photoelectric detector and the spectral width of the optical frequency comb signal covers the two beams of frequency-stabilized laser, the spectral width does not need to reach one octave, and the requirement of the optical frequency comb system on the optical comb spectral width is greatly reduced, therefore, the microcavity optical comb can be applied to an optical clock system, and is beneficial to the miniaturization and even chip design of the optical frequency atomic clock;
(2) the difference between the repetition frequency and the frequency between two beams of atom frequency stabilized laser generated in the same physical system can be locked, instead of locking the repetition frequency and the frequency of a single beam of atom frequency stabilized laser, so that the interference caused by the environmental disturbance such as temperature drift, mechanical vibration and the like can be eliminated by utilizing the differential effect.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is an exemplary plot of the frequency domain and time domain characteristics of an optical frequency comb provided by the present invention.
FIG. 2 is a schematic diagram of a system architecture of a typical optical frequency atomic clock provided by the present invention.
FIG. 3 is an exemplary diagram of a microcavity optical comb system and its generation mechanism provided by the present invention.
FIG. 4 is a schematic diagram of the system structure of the optical frequency atomic clock based on the microcavity optical comb technology.
Detailed Description
The invention is further described with reference to the following figures and specific embodiments. It should be noted that the description of the embodiments is provided to help understanding of the present invention, but the present invention is not limited thereto. Specific structural and functional details disclosed herein are merely illustrative of example embodiments of the invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to the embodiments set forth herein.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention.
It should be understood that, for the term "and/or" as may appear herein, it is merely an associative relationship that describes an associated object, meaning that three relationships may exist, e.g., a and/or B may mean: a exists alone, B exists alone, and A and B exist at the same time; for the term "/and" as may appear herein, which describes another associative object relationship, it means that two relationships may exist, e.g., a/and B, may mean: a exists independently, and A and B exist independently; in addition, for the character "/" that may appear herein, it generally means that the former and latter associated objects are in an "or" relationship.
It will be understood that when an element is referred to herein as being "connected," "connected," or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Conversely, if a unit is referred to herein as being "directly connected" or "directly coupled" to another unit, it is intended that no intervening units are present. In addition, other words used to describe the relationship between elements should be interpreted in a similar manner (e.g., "between … …" versus "directly between … …", "adjacent" versus "directly adjacent", etc.).
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.
It should also be noted that, in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed substantially concurrently, or the figures may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
It should be understood that specific details are provided in the following description to facilitate a thorough understanding of example embodiments. However, it will be understood by those of ordinary skill in the art that the example embodiments may be practiced without these specific details. For example, systems may be shown in block diagrams in order not to obscure the examples in unnecessary detail. In other instances, well-known processes, structures and techniques may be shown without unnecessary detail in order to avoid obscuring example embodiments.
Example one
As shown in fig. 4, the optical frequency atomic clock provided in this embodiment includes a microcavity optical comb module, a frequency-stabilized laser source module, and a phase-locked loop module; the microcavity optical comb module is used for generating a frequency f ═ fceo+kfrepWherein f isceoRepresenting the initial frequency, f, of the optical frequency comb signalrepRepresenting the repetition frequency of the optical frequency comb signal, k being a positive integer; the frequency stabilized laser source module is used for generating a first frequency stabilized laser and a second frequency stabilized laser, wherein the frequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2Unequal and respectively located within spectral width coverage of the optical frequency comb signals; the phase-locked loop module is used for carrying out frequency f according to the nth comb toothn＝fceo+nfrepMth comb frequency fm＝fceo+mfrepFrequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2To controlThe pumping light signal power and wavelength of the microcavity optical comb module enable the newly generated optical frequency comb signal to have the repetition frequency frepLocking to frequency fr1And frequency fr2The difference between the first comb tooth frequency and the second comb tooth frequency is used for realizing the microwave frequency output of the optical frequency atomic clock, wherein the nth comb tooth frequency fn＝fceo+nfrepFor the nearest frequency f in the optical frequency comb signalr1The mth comb frequency fm＝fceo+mfrepFor the nearest frequency f in the optical frequency comb signalr2N and m are positive integers respectively.
As shown in fig. 4, in a specific structure of the optical frequency atomic clock, the microcavity optical comb module may include, but is not limited to, a pump light source and an optical microcavity, where a pump light signal output end optical path of the pump light source is communicated with an optical signal input end of the optical microcavity, and an optical signal output end of the optical microcavity is used for outputting the optical frequency comb signal. The pump light source is also called as a pump laser, and is an existing laser used for emitting continuous laser; the optical microcavity can be, but is not limited to, one made of silicon nitride, silicon dioxide, aluminum nitride, lithium niobate, fused silica, fluoride or the like and capable of generating the repetition frequency frepMicro-cavity structures of the order of GHz to THz, e.g. using on-chip silicon nitride micro-ring cavities of a continuous-optical-pumped laser for generating a repetition frequency frepAn optical frequency comb signal at 35GHz and a spectral range from 170THz (corresponding to a wavelength of 1700nm) to 200THz (corresponding to a wavelength of 1500 nm).
The frequency stabilized laser source module is a laser source which utilizes the existing frequency stabilization technology to stabilize the frequencies of the first frequency stabilized laser and the second frequency stabilized laser on corresponding values respectively. Specifically, the frequency-stabilized laser source module may be, but is not limited to, a laser source that excites a frequency-stabilized laser based on an atomic transition spectral line, a molecular transition spectral line, or an ion transition spectral line, and the like, where the atomic transition spectral line may be, but is not limited to, a hydrogen atomic transition spectral line, a potassium atomic transition spectral line, a rubidium atomic transition spectral line, or a cesium atomic transition spectral line; the molecular transition line may be, but is not limited to, a packetContains ammonia molecule transition spectral line, hydrogen cyanide molecule transition spectral line, etc.; the ion transition line can include, but is not limited to, a calcium ion transition line, a mercury ion transition line, an aluminum ion transition line, and the like. For example, two narrow linewidth lasers with the wavelengths of 1590nm and 1560nm are frequency-doubled and then respectively locked on rubidium atom D1 and D2 transition spectral lines (the corresponding wavelengths are 795nm and 780nm) to form two narrow linewidth lasers with the frequencies of fr1And fr2The atomic frequency stabilized laser reference source of (1).
The phase-locked loop module is used for stabilizing the frequency of the two beams of the atomic system and the frequency is fr1And fr2The laser of (a) is respectively locked with the two nearest comb frequencies on the frequency spectrum of the optical frequency comb signal (namely, the pumping light signal power and wavelength of the microcavity optical comb module are controlled in a conventional feedback control mode), so that the repetition frequency f is realizedrepFrequency difference f fromr1-fr2Locking of (2).
Therefore, through the detailed principle description of the optical frequency atomic clock, a novel optical frequency atomic clock based on the microcavity optical comb technology is provided, that is, when the optical frequency atomic clock adopts the optical frequency comb technology based on the microcavity to generate a required optical frequency comb signal, two beams of frequency-stabilized laser can be respectively locked with two nearest comb frequencies on the frequency spectrum of the optical frequency comb signal through a phase-locked loop, so as to realize direct locking of a repetition frequency and two laser frequency differences, without firstly carrying out frequency doubling processing on the comb frequencies to lock an initial frequency from a reference, as in a typical optical frequency atomic clock system, in the process of realizing the microwave frequency output of the optical frequency atomic clock, only the repetition frequency is required to be within the working bandwidth of a common photoelectric detector and the spectral width of the optical frequency comb signal covers two beams of frequency-stabilized laser, without the spectral width reaching one frequency doubling pass, the requirement of the optical clock system on the spectral width of the optical comb is greatly reduced, so that the microcavity optical comb can be applied to the optical clock system, and the optical frequency atomic clock is favorably subjected to miniaturization and even chip design.
Preferably, the first frequency stabilized laser and the second frequency stabilized laser are generated in the same physical system. The same physical system isThe two frequency stabilization lasers are excited based on different transition spectral lines of the same atom, molecule or ion, and the repetition frequency f can be adjustedrepLocking with the difference in frequency between two atomic frequency stabilized lasers generated in the same physical system, rather than the repetition frequency frepAnd the frequency of the laser is locked with the frequency of the single-beam atomic frequency stabilized laser, so that the interference caused by the environmental disturbance such as temperature drift, mechanical vibration and the like can be partially eliminated by utilizing the differential effect.
Optimally, the phase-locked loop module comprises a first phase-locked loop PLL1 and a second phase-locked loop PLL 2; the first phase-locked loop PLL1 for generating the n-th comb frequency fn＝fceo+nfrepAnd the frequency f of the first frequency stabilized laserr1To control the pump light signal power of the microcavity optical comb module to make the nth comb frequency f of the optical frequency comb signal generated newlyn＝fceo+nfrepLocking to frequency fr1To obtain fr1＝fn+frep/a＝fceo+(n+1/a)frepWherein a is a preset constant; the second phase-locked loop PLL2 is used for obtaining the mth comb frequency fm＝fceo+mfrepAnd the frequency f of the second frequency stabilized laserr2To control the wavelength of the pump light signal of the microcavity optical comb module to make the mth comb frequency f of the optical frequency comb signal generated newlym＝fceo+mfrepLocking to frequency fr2To obtain fr2＝fm+frep/b＝fceo+(m+1/b)frepWherein b is a preset constant.
As shown in fig. 4, by the locking action of the two phase-locked loops, it can be obtained: f. ofr1-fr2＝(n+1/a-m-1/b)frepNamely:
thereby generating the repetition frequency f of the optical frequency comb signalrepCan be locked to frequency fr1And frequency fr2And on the difference, realizing the microwave frequency output of the optical frequency atomic clock. For example, a repetition frequency f can be realizedrepWith rubidium atomsLocking of frequency difference between the D1 and D2 transition spectral lines: upsilon isD2-υD1＝2fr1-2fr2＝2(n+1/a-m-1/b)frepNamely:
wherein upsilon isD2Representing the transition frequency, upsilon, of the spectral line corresponding to the transition of rubidium atom D2D1Representing the transition frequency of the transition spectral line corresponding to the rubidium atom D2.
Further optimized, the system also comprises a first photodetector PD1, a second photodetector PD2 and a third photodetector PD 3; the output end of the first photodetector PD1 is communicatively connected with the first phase-locked loop PLL1 and is used for detecting the nth comb frequency fn＝fceo+nfrepWith said frequency fr1The frequency difference therebetween; the output end of the second photoelectric detector is in communication connection with the second phase-locked loop and is used for detecting the mth comb frequency fm＝fceo+mfrepWith said frequency fr2The frequency difference therebetween; the output terminal of the third photo detector PD3 is respectively connected to the first phase-locked loop PLL1 and the second phase-locked loop PLL3 in communication for detecting the repetition frequency frepThe numerical value of (c). The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 may all be implemented by using existing conventional photodetectors, so as to obtain the magnitude of the frequency responsible, and further facilitate performing repetition frequency locking control on the corresponding phase-locked loop.
In summary, the optical frequency atomic clock provided by the embodiment has the following technical effects:
(1) the embodiment provides a novel optical frequency atomic clock based on a microcavity optical comb technology, namely when the optical frequency atomic clock adopts the optical frequency comb technology based on the microcavity to generate a required optical frequency comb signal, two beams of frequency-stabilized laser are respectively locked with two nearest comb frequencies on the frequency spectrum of the optical frequency comb signal through a phase-locked loop, so that direct locking of a repetition frequency and two laser frequency differences is realized, and the condition that the initial frequency is locked by referring to the comb frequencies by carrying out frequency doubling processing on the comb frequencies as a typical optical frequency atomic clock system is not required, so that in the process of realizing microwave frequency output of the optical frequency atomic clock, only the repetition frequency is required to be within the working bandwidth of a common photoelectric detector and the spectrum width of the optical frequency comb signal covers the two beams of frequency-stabilized laser, the spectrum width does not need to reach one octave, and the requirement of the optical frequency comb system on the optical comb spectrum width is greatly reduced, therefore, the microcavity optical comb can be applied to an optical clock system, and is beneficial to the miniaturization and even chip design of the optical frequency atomic clock;
(2) the difference between the repetition frequency and the frequency between two beams of atom frequency stabilized laser generated in the same physical system can be locked, instead of locking the repetition frequency and the frequency of a single beam of atom frequency stabilized laser, so that the interference caused by the environmental disturbance such as temperature drift, mechanical vibration and the like can be eliminated by utilizing the differential effect.
The various embodiments described above are merely illustrative, and may or may not be physically separate, as they relate to elements illustrated as separate components; if reference is made to a component displayed as a unit, it may or may not be a physical unit, and may be located in one place or distributed over a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: modifications of the technical solutions described in the embodiments or equivalent replacements of some technical features may still be made. And such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Finally, it should be noted that the present invention is not limited to the above alternative embodiments, and that various other forms of products can be obtained by anyone in light of the present invention. The above detailed description should not be taken as limiting the scope of the invention, which is defined in the claims, and which the description is intended to be interpreted accordingly.
Claims (10)
1. An optical frequency atomic clock is characterized by comprising a microcavity optical comb module, a frequency stabilization laser source module and a phase-locked loop module;
the microcavity optical comb module is used for generating a frequency f ═ fceo+kfrepWherein f isceoRepresenting the initial frequency, f, of the optical frequency comb signalrepRepresenting the repetition frequency of the optical frequency comb signal, k being a positive integer;
the frequency stabilized laser source module is used for generating a first frequency stabilized laser and a second frequency stabilized laser, wherein the frequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2Unequal and respectively located within spectral width coverage of the optical frequency comb signals;
the phase-locked loop module is used for carrying out frequency f according to the nth comb toothn＝fceo+nfrepMth comb frequency fm＝fceo+mfrepFrequency f of the first frequency stabilized laserr1And the frequency f of the second frequency stabilized laserr2To control the power and wavelength of the pumping light signal of the microcavity optical comb module to make the repetition frequency f of the newly generated optical frequency comb signalrepLocking to frequency fr1And frequency fr2The difference between the first comb tooth frequency and the second comb tooth frequency is used for realizing the microwave frequency output of the optical frequency atomic clock, wherein the nth comb tooth frequency fn＝fceo+nfrepFor the nearest frequency f in the optical frequency comb signalr1The mth comb frequency fm＝fceo+mfrepFor the nearest frequency f in the optical frequency comb signalr2N and m are positive integers respectively.
2. The optical frequency atomic clock according to claim 1, wherein the microcavity optical comb module comprises a pump light source and an optical microcavity, wherein a pump light signal output end optical path of the pump light source is connected to an optical signal input end of the optical microcavity, and an optical signal output end of the optical microcavity is configured to output the optical frequency comb signal.
3. The optical-frequency atomic clock of claim 2, wherein the optical microcavity is fabricated from a silicon nitride, silicon dioxide, aluminum nitride, lithium niobate, fused silica, or fluoride material and is capable of generating the repetition frequency frepMicro-cavity structures from GHz to THz scale.
4. The optical frequency atomic clock of claim 1, wherein the first frequency stabilized laser and the second frequency stabilized laser are generated from the same physical system.
5. The optical-frequency atomic clock according to claim 1, wherein the frequency-stabilized laser source module employs a laser source that excites a frequency-stabilized laser based on an atomic transition line, a molecular transition line, or an ionic transition line.
6. The optical-frequency atomic clock according to claim 5, wherein the atomic transition line includes a hydrogen atomic transition line, a potassium atomic transition line, a rubidium atomic transition line, or a cesium atomic transition line.
7. The optical frequency atomic clock according to claim 5, wherein said molecular transition line comprises an ammonia molecular transition line and a hydrogen cyanide molecular transition line.
8. The optical-frequency atomic clock according to claim 5, wherein the ion transition line includes a calcium ion transition line, a mercury ion transition line, and an aluminum ion transition line.
9. The optical-frequency atomic clock of claim 1, wherein said phase-locked loop module comprises a first phase-locked loop and a second phase-locked loop;
the first phase-locked loop is used for carrying out frequency f according to the nth comb toothn＝fceo+nfrepAnd the frequency f of the first frequency stabilized laserr1To control the pump light signal power of the microcavity optical comb module to make the nth comb frequency f of the optical frequency comb signal generated newlyn＝fceo+nfrepLocking to frequency fr1To obtain fr1＝fn+frep/a＝fceo+(n+1/a)frepWherein a is a preset constant;
the second phase-locked loop is used for carrying out frequency f according to the mth comb toothm＝fceo+mfrepAnd the frequency f of the second frequency stabilized laserr2To control the wavelength of the pump light signal of the microcavity optical comb module to make the mth comb frequency f of the optical frequency comb signal generated newlym＝fceo+mfrepLocking to frequency fr2To obtain fr2＝fm+frep/b＝fceo+(m+1/b)frepWherein b is a preset constant.
10. The optical frequency atomic clock of claim 9, further comprising a first photodetector, a second photodetector, and a third photodetector;
the output end of the first photoelectric detector is in communication connection with the first phase-locked loop and is used for detecting the nth comb frequency fn＝fceo+nfrepWith said frequency fr1The frequency difference therebetween;
the output end of the second photoelectric detector is in communication connection with the second phase-locked loop and is used for detecting the mth comb frequency fm＝fceo+mfrepWith said frequency fr2The frequency difference therebetween;
the output end of the third photoelectric detector is respectively in communication connection with the first phase-locked loop and the second phase-locked loop and is used for detecting the repetition frequency frepThe numerical value of (c).
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