阅读说明：本技术 一种太赫兹波段频率标准、标准实现及进行量值传递方法 (Terahertz waveband frequency standard, standard realization and magnitude transmission method ) 是由 吴斌 陈坤峰 年夫顺 杨延召 刘红元 王洪超 王恒飞 应承平 靖衡 张桂鸣 程笑 于 2021-08-12 设计创作，主要内容包括：本发明提供了一种高精度太赫兹波段频率标准及量值传递方法,可产生0.1～5THz范围内任意频率的高稳定输出,并且由于溯源至微波频率标准,因此频率精度和稳定度可达10～(-11),很好地解决了太赫兹频率测量设备校准存在的可用频率点少、精度与稳定性不足的问题；并且提出了一种太赫兹频率量值传递方法,不仅可实现太赫兹频率测量设备的直接校准,还可以实现对太赫兹源输出波长的校准。(The invention provides a high-precision terahertz waveband frequency standard and magnitude transmission method, which can generate high-stability output of any frequency within the range of 0.1-5 THz, and the frequency precision and stability can reach 10 due to tracing to the microwave frequency standard ‑11 The problems of few available frequency points, insufficient precision and stability in the calibration of the terahertz frequency measuring equipment are well solved; the terahertz frequency magnitude transmission method is provided, so that direct calibration of terahertz frequency measurement equipment can be realized, and calibration of terahertz source output wavelength can also be realized.)

1. A terahertz waveband frequency standard is characterized by comprising a near-infrared tunable wavelength source, a near-infrared fixed wavelength source, a first femtosecond optical comb, a second femtosecond optical comb, a first beat frequency module, a second beat frequency module, a first servo loop, a second servo loop and a mixer;

the first femtosecond optical comb is used for providing a standard optical wavelength signal required for frequency stabilization and locking of the near-infrared tunable wavelength source; the first beat frequency module is used for realizing the beat frequency of the output wavelength of the near-infrared tunable wavelength source and the specific comb teeth of the first femtosecond optical comb, and realizing the stable control of the output wavelength of the near-infrared tunable wavelength source through an error locking electric signal obtained after the beat frequency by a first servo loop, wherein the near-infrared tunable wavelength is used for generating near-infrared light with narrow line width;

the second femtosecond optical comb is used for providing a standard optical wavelength signal required by the near-infrared fixed wavelength source for frequency stabilization and locking; the second beat frequency module is used for realizing beat frequency of the output wavelength of the near-infrared fixed wavelength source and the specific comb teeth of the second femtosecond optical comb, and stably controlling the output wavelength of the near-infrared fixed wavelength source through an error locking electric signal obtained after beat frequency by a second servo loop, wherein the near-infrared fixed wavelength source can output near-infrared light with narrow line width at a wavelength point near 1610 nm;

the frequency mixer is used for mixing the near infrared light with narrow line width generated by the near infrared tunable wavelength incident on the frequency mixer and the near infrared light with narrow line width output by the near infrared fixed wavelength source at a wavelength point near 1610nm, so that monochromatic terahertz waves are generated.

2. The terahertz waveband frequency standard of claim 1, wherein the near-infrared tunable wavelength source generates narrow-linewidth near-infrared light based on external cavity semiconductor technology, and the tuning range of the output wavelength is 1520 nm-1630 nm.

3. The thz band frequency standard according to claim 2, wherein the first femtosecond optical comb and the second femtosecond optical comb are implemented based on an erbium-doped fiber oscillator, and a repetition frequency fr and a system frequency shift f0 of the first femtosecond optical comb are locked to a microwave frequency standard, so that a wavelength value corresponding to each comb tooth of the optical comb can be accurately obtained and used for providing standard optical wavelength signals required for frequency stabilization and locking of the near-infrared tunable wavelength source and the near-infrared fixed wavelength source respectively.

4. The thz band frequency standard according to claim 3, wherein the first servo loop is configured to drive a cavity length control component inside the near-infrared tunable wavelength source, so as to control the cavity length in a stable state even in the presence of external interference, thereby achieving stable control of the output wavelength of the near-infrared tunable wavelength source.

5. The thz band frequency standard according to claim 4, wherein the second servo loop is configured to drive a cavity length control unit inside the near-infrared fixed wavelength source, and stably control the output wavelength of the fixed wavelength source.

6. The terahertz waveband frequency standard of claim 5, wherein the mixer is a nonlinear crystal or a band-biased optical switch.

7. The terahertz waveband frequency standard of claim 6, wherein the output frequency range of the mixer covers a complete terahertz waveband of 0.1THz to 10THz, and the mixer can be controlled to output the frequency of a monochromatic terahertz wave by adjusting the output wavelength of the near-infrared tunable wavelength source.

8. A thz band frequency standard implementation method as claimed in claim 1, comprising the steps of:

step 1: the method comprises the following steps of (1) dividing one path of light output from a near-infrared tunable wavelength source, enabling the light to be combined with an optical comb signal output by a first femtosecond optical comb and then to be incident to a first beat frequency module, and generating an error locking electric signal and realizing locking control on the output frequency f1 of the near-infrared tunable wavelength source through a first servo loop;

step 2: the light output from the near-infrared fixed wavelength source is divided into one path, the path is combined with an optical comb signal output by a second femtosecond optical comb, then the combined beam is incident to a second beat frequency module, and the generated error locking electric signal passes through a second servo loop to realize the locking control of the output frequency f2 of the near-infrared fixed wavelength source;

and step 3: the two beams of light with the frequencies of f1 and f2 after being locked are combined and then jointly incident into the mixer, and terahertz waves with the frequencies of f1-f2 are generated under the action of the mixer.

9. The method of claim 8, wherein step 1 and step 2 are not in sequence.

10. A method of magnitude transfer using the thz frequency standard of claim 1, comprising step a or step B:

step A: when frequency measurement equipment such as a Fourier transform terahertz spectrometer, a terahertz wavemeter and the like is calibrated, the output frequency of a terahertz source is adjusted to a frequency point needing to be calibrated, and then the frequency measurement equipment is directly calibrated;

and B: when the output frequency of a common terahertz source is calibrated, a terahertz source output signal needing to be calibrated and monochromatic terahertz waves generated by the terahertz frequency standard are subjected to beat frequency, and the calibration of the output frequency and phase noise parameters of the terahertz source to be measured is realized by reading the frequency of the beat frequency signal and calculating the standard deviation of the beat frequency signal.

Technical Field

The invention belongs to the technical field of calibration of terahertz frequency measuring equipment, and particularly relates to a terahertz waveband frequency standard, standard realization and a magnitude transmission method thereof.

Background

The terahertz waveband frequency standard is a device for generating a terahertz waveband standard frequency signal, is mainly used for calibrating terahertz spectrum instruments and frequency measuring equipment, and has important and practical significance for guaranteeing the accuracy and reliability of a terahertz frequency parameter measuring result. At present, the aspects of high-precision spectral analysis, development of high-performance terahertz sources and the like all generate clear requirements on terahertz waveband frequency standards.

Currently, a strict terahertz frequency standard is lacked, so that terahertz frequency measuring equipment such as a Fabry-Perot (F-P) interferometer and a Fourier transform spectrometer lacks of a calibration source, and the calibration of the equipment is mainly performed by depending on an etalon or a standard substance at present. For example, in calibration of a terahertz-band fourier transform spectrometer, polystyrene is generally used as a standard substance, the characteristic absorption frequency of the substance is measured by the fourier transform spectrometer, and then calibration of the spectrometer is performed based on an error between the standard value and the measured value. However, the substance has no characteristic absorption frequency in the terahertz waveband, so that the spectrometer can be calibrated only by using the characteristic absorption frequency of the substance in the far infrared waveband, namely 27.2THz, and the calibration accuracy of the terahertz waveband (generally 0.1THz to 10THz) in the true sense cannot be ensured. The prior art scheme has the following disadvantages: (1) the etalon and the standard substance generally only have discrete distributed characteristic frequencies, so that the available calibration frequency points are few; (2) the calibration precision is not enough to meet the requirements of terahertz equipment development and application development; (3) the terahertz source calibration device can only be used for calibrating terahertz frequency or spectrum measurement equipment, and cannot solve the problem of calibration of terahertz source output frequency.

Accordingly, the prior art is deficient and needs improvement.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a terahertz waveband frequency standard, a standard implementation method and a method for magnitude transmission, which can generate a terahertz waveband standard frequency signal, realize the calibration of terahertz source output frequency and the calibration of terahertz frequency measurement equipment, have important and practical significance for ensuring the accuracy and reliability of terahertz frequency parameter measurement results, and solve the problem of high-precision frequency calibration of equipment such as terahertz sources and frequency measurement.

A terahertz waveband frequency standard comprises a near-infrared tunable wavelength source, a near-infrared fixed wavelength source, a first femtosecond optical comb, a second femtosecond optical comb, a first beat frequency module, a second beat frequency module, a first servo loop, a second servo loop and a frequency mixer;

the first femtosecond optical comb is used for providing a standard optical wavelength signal required for frequency stabilization and locking of the near-infrared tunable wavelength source; the first beat frequency module is used for realizing the beat frequency of the output wavelength of the near-infrared tunable wavelength source and the specific comb teeth of the first femtosecond optical comb, and realizing the stable control of the output wavelength of the near-infrared tunable wavelength source through an error locking electric signal obtained after the beat frequency by a first servo loop, wherein the near-infrared tunable wavelength is used for generating near-infrared light with narrow line width;

the second femtosecond optical comb is used for providing a standard optical wavelength signal required by the near-infrared fixed wavelength source for frequency stabilization and locking; the second beat frequency module is used for realizing beat frequency of the output wavelength of the near-infrared fixed wavelength source and the specific comb teeth of the second femtosecond optical comb, and stably controlling the output wavelength of the near-infrared fixed wavelength source through an error locking electric signal obtained after beat frequency by a second servo loop, wherein the near-infrared fixed wavelength source can output near-infrared light with narrow line width at a wavelength point near 1610 nm;

the frequency mixer is used for mixing the near infrared light with narrow line width generated by the near infrared tunable wavelength incident on the frequency mixer and the near infrared light with narrow line width output by the near infrared fixed wavelength source at a wavelength point near 1610nm, so that monochromatic terahertz waves are generated.

In the above, the near-infrared tunable wavelength source generates a narrow-linewidth near-infrared light based on an external cavity semiconductor technology, and the tuning range of the output wavelength is 1520nm to 1630 nm.

In the above, the first femtosecond optical comb and the second femtosecond optical comb are both realized based on an erbium-doped fiber oscillator, and the repetition frequency fr and the system frequency shift f0 of the first femtosecond optical comb are locked to a microwave frequency standard, so that a wavelength value corresponding to each comb tooth in the optical comb can be accurately obtained, and the first femtosecond optical comb and the second femtosecond optical comb are respectively used for providing standard optical wavelength signals required for frequency stabilization and locking of the near-infrared tunable wavelength source and the near-infrared fixed wavelength source.

In the foregoing, the first servo loop is configured to drive a cavity length control component inside the near-infrared tunable wavelength source, and control the cavity length in a stable state even when there is interference from the outside, so as to implement stable control of the output wavelength of the near-infrared tunable wavelength source.

In the foregoing, the second servo loop is configured to drive a cavity length control component inside the near-infrared fixed wavelength source, and stably control the output wavelength of the fixed wavelength source.

In the above, the mixer is a nonlinear crystal or a biased optical switch.

In the above, the output frequency range of the mixer covers a complete terahertz wave band of 0.1THz to 10THz, and the mixer can be controlled to output the frequency of the monochromatic terahertz wave by adjusting the output wavelength of the near-infrared tunable wavelength source.

On the basis of the above content, the invention also provides a terahertz waveband frequency standard implementation method, which comprises the following steps:

step 1: the method comprises the following steps of (1) dividing one path of light output from a near-infrared tunable wavelength source, enabling the light to be combined with an optical comb signal output by a first femtosecond optical comb and then to be incident to a first beat frequency module, and generating an error locking electric signal and realizing locking control on the output frequency f1 of the near-infrared tunable wavelength source through a first servo loop;

step 2: the light output from the near-infrared fixed wavelength source is divided into one path, the path is combined with an optical comb signal output by a second femtosecond optical comb, then the combined beam is incident to a second beat frequency module, and the generated error locking electric signal passes through a second servo loop to realize the locking control of the output frequency f2 of the near-infrared fixed wavelength source;

and step 3: the two beams of light with the frequencies of f1 and f2 after being locked are combined and then jointly incident into the mixer, and terahertz waves with the frequencies of f1-f2 are generated under the action of the mixer.

In the method, the step 1 and the step 2 are not in sequence.

On the basis of the above content, the present invention also provides a method for magnitude transfer using a terahertz frequency standard, comprising step a or step B:

step A: when frequency measurement equipment such as a Fourier transform terahertz spectrometer, a terahertz wavemeter and the like is calibrated, the output frequency of a terahertz source is adjusted to a frequency point needing to be calibrated, and then the frequency measurement equipment is directly calibrated;

and B: when the output frequency of a common terahertz source is calibrated, a terahertz source output signal needing to be calibrated and monochromatic terahertz waves generated by the terahertz frequency standard are subjected to beat frequency, and the calibration of the output frequency and phase noise parameters of the terahertz source to be measured is realized by reading the frequency of the beat frequency signal and calculating the standard deviation of the beat frequency signal.

Compared with the prior art, the invention has the advantages that by adopting the scheme, the invention has the following advantages: (1) the calibration frequency can be selected randomly within the range of 0.1-10 THz; (2) the precision and stability of the output frequency are far higher than those of the prior art; (3) the terahertz source calibration method is wider in application range, not only can be used for calibrating frequency measurement equipment, but also can be used for calibrating the output frequency and phase noise of the terahertz source.

Drawings

Fig. 1 is a schematic diagram of a standard structure of a terahertz band frequency in the present invention.

Fig. 2 is a flow chart of the standard implementation of the terahertz band frequency in the present invention.

FIG. 3 is a flowchart of a method for magnitude transfer according to the terahertz wave band frequency standard of the present invention.

Detailed Description

In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

As shown in fig. 1, an embodiment of the present invention is a thz band frequency standard, which is composed of a near-infrared tunable wavelength source, a near-infrared fixed wavelength source, two femtosecond optical combs, two beat frequency modules, two servo loops, and a mixer; the femtosecond optical comb 1 is used for providing a standard optical wavelength signal required for frequency stabilization and locking of a near-infrared tunable wavelength source, the beat frequency module 1 is used for realizing beat frequency of the output wavelength of the near-infrared tunable wavelength source and a specific comb tooth of the femtosecond optical comb 1, stable control of the output wavelength of the near-infrared tunable wavelength source is realized through an error locking electric signal obtained after beat frequency through the servo loop 1, and the near-infrared tunable wavelength is used for generating near-infrared light with a narrow line width;

the femtosecond optical comb 2 is used for providing standard optical wavelength signals required by frequency stabilization and locking of a near-infrared fixed wavelength source, the beat frequency module 2 is mainly used for achieving beat frequency of output wavelengths of the near-infrared fixed wavelength source and specific comb teeth of the femtosecond optical comb 2, stable control of the output wavelengths of the near-infrared fixed wavelength source is achieved through an error locking electric signal obtained after beat frequency through the servo loop 2, and the near-infrared fixed wavelength source can output near-infrared light with narrow line width at wavelength points near 1610 nm;

the mixer is used for mixing the narrow-linewidth near infrared light generated by the near infrared tunable wavelength incident on the mixer and the narrow-linewidth near infrared light output by the near infrared fixed wavelength source at a wavelength point near 1610nm, so that monochromatic terahertz waves are generated.

The near-infrared tunable wavelength source generates near-infrared light with narrow line width based on an external cavity semiconductor technology, the tuning range of the output wavelength is 1520 nm-1630 nm, and the near-infrared tunable wavelength source has the characteristics of wide tuning range, high tuning resolution and high spectral purity. These advantages can ensure that the generated terahertz waves can realize fine tuning in a wide frequency range, and also have ultra-narrow line width.

The near infrared fixed wavelength source can output near infrared light with narrow line width at a wavelength point near 1610nm, and the tuning range is relatively fixed and is only a few nanometers.

The femtosecond optical comb 1 and the femtosecond optical comb 2 are realized based on an erbium-doped fiber oscillator, the repetition frequency fr and the system frequency shift f0 of the femtosecond optical comb are locked on a microwave frequency standard, the wavelength value corresponding to each comb tooth in the optical comb can be accurately obtained, and the wavelength values are respectively used for providing standard optical wavelength signals required for frequency stabilization and locking of a near-infrared tunable wavelength source and a near-infrared fixed wavelength source.

The beat frequency module 1 is mainly used for realizing the beat frequency of the output wavelength of the near-infrared tunable wavelength source and the specific comb teeth of the femtosecond optical comb 1, and stably controlling the output wavelength of the near-infrared tunable wavelength source by an error locking electric signal obtained after the beat frequency through the servo loop 1. By the method, the stability and the precision of the output wavelength of the near-infrared tunable wavelength source depend on the microwave frequency standard in the femtosecond optical comb. For example, if the microwave frequency standard in the femtosecond optical comb is rubidium clock, the wavelength stability and precision of the near-infrared tunable wavelength source can reach 10^-11Orders of magnitude higher than that achieved by the existing optical wavelength standards.

The beat frequency module 2 is mainly used for realizing the beat frequency of the output wavelength of the near infrared fixed wavelength source and the specific comb teeth of the femtosecond optical comb 2, and stably controlling the output wavelength of the near infrared fixed wavelength source by an error locking electric signal obtained after the beat frequency through the servo loop 2, wherein the stability and the precision can also reach the levels.

The servo loop 1 is used for driving a cavity length control component inside the near-infrared tunable wavelength source, and the cavity length is still controlled in a stable state even if interference (temperature change, vibration and the like) exists outside, so that stable control of the output wavelength of the near-infrared tunable wavelength source is realized.

The servo loop 2 is used for driving a cavity length control component inside the near-infrared fixed wavelength source, and stably controls the output wavelength of the fixed wavelength source similarly to the servo loop 1.

The mixer can be a nonlinear crystal, a biased optical switch and the like, and is mainly used for mixing two beams of narrow-linewidth near infrared light incident on the mixer, so that monochromatic terahertz waves are generated. The output frequency range of the mixer covers a complete terahertz wave band of 0.1 THz-10 THz, and the mixer can be controlled to output the frequency of monochromatic terahertz waves by adjusting the output wavelength of the near-infrared tunable wavelength source. Meanwhile, the performance of the mixer is stable, and the frequency of the generated terahertz waves is not influenced, namely the frequency of the generated terahertz waves is strictly dependent on the output characteristics of the two near-infrared wavelength sources.

As shown in fig. 2, another embodiment of the present invention based on the foregoing content is a method for implementing the thz band frequency standard, including the following steps:

step 1: the method comprises the following steps of (1) dividing one path of light output from a near-infrared tunable wavelength source, enabling the light to be combined with an optical comb signal output by a femtosecond optical comb 1 and then to be incident to a beat frequency module 1, and generating an error locking electric signal and realizing locking control on the output frequency f1 of the near-infrared tunable wavelength source through a servo loop 1;

step 2: the method comprises the following steps of (1) dividing one path of light output from a near-infrared fixed wavelength source, combining the light with an optical comb signal output by a femtosecond optical comb 2, then, irradiating the light to a beat frequency module 2, and realizing locking control on the output frequency f2 of the near-infrared fixed wavelength source through a servo loop 2 by using a generated error locking electric signal; the step 1 and the step 2 are not in sequence;

and step 3: the two beams of light with the frequencies of f1 and f2 after being locked are combined and then jointly incident into the mixer, and terahertz waves with the frequencies of f1-f2 are generated under the action of the mixer. Because both f1 and f2 are strictly locked to the optical comb, the generated terahertz output frequency has high precision and stability and can be used as a terahertz waveband frequency standard.

As shown in fig. 3, on the basis of the above, the present invention further provides a method for magnitude transmission by using the above terahertz frequency standard, which includes step a or step B:

step A: when frequency measurement equipment such as a Fourier transform terahertz spectrometer, a terahertz wavemeter and the like is calibrated, the output frequency of a terahertz source can be adjusted to a frequency point needing to be calibrated, and then the frequency measurement equipment can be directly calibrated;

and B: when the output frequency of a common terahertz source is calibrated, a terahertz source output signal needing to be calibrated and monochromatic terahertz waves generated by the terahertz frequency standard are subjected to beat frequency, and the calibration of the output frequency and phase noise parameters of the terahertz source to be measured can be realized by reading the frequency of the beat frequency signal and calculating the standard deviation of the beat frequency signal.

Specifically, the method comprises the following steps: selecting a nominal output frequency value f_QCLThe terahertz quantum cascade laser at 2.52THz is used as a terahertz source to be detected. Firstly, adjusting the output frequency f1 of a near-infrared tunable wavelength source to 1588.685nm, and generating a standard frequency of 2.5THz after beat frequency of the near-infrared tunable wavelength source and a fixed wavelength source in the frequency standard; then, the standard frequency and the output light of the terahertz quantum cascade laser are subjected to beat frequency on a beat frequency device to generate beat frequency signals with the frequency near 20GHz, and a spectrum analyzer is used for reading specific values and fluctuation data of the beat frequency signals and calculating the specific values and the fluctuation data to obtain the accurate output frequency and phase noise of the terahertz source to be detected.

Compared with the prior art, the invention has the advantages that by adopting the scheme, the invention has the following advantages: (1) the calibration frequency can be selected randomly within the range of 0.1-10 THz; (2) the precision and stability of the output frequency are far higher than those of the prior art; (3) the terahertz source calibration method is wider in application range, not only can be used for calibrating frequency measurement equipment, but also can be used for calibrating the output frequency and phase noise of the terahertz source.

The technical features mentioned above are combined with each other to form various embodiments which are not listed above, and all of them are regarded as the scope of the present invention described in the specification; also, modifications and variations may be suggested to those skilled in the art in light of the above teachings, and it is intended to cover all such modifications and variations as fall within the true spirit and scope of the invention as defined by the appended claims.