CN114624007A - Difference method and device for judging resonance state of F-P cavity - Google Patents
Difference method and device for judging resonance state of F-P cavity Download PDFInfo
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Abstract
The invention discloses a difference method and a difference device for judging a resonance state of an F-P cavity, and belongs to the field of geometric precision measurement. Two beams of light with close frequency, fixed frequency difference and known frequency are generated and respectively reflected and oscillated in an F-P resonant cavity to obtain respective output light intensity curves; when the light frequency or the length of the F-P resonant cavity is changed, the obtained two output light intensity curves cannot reach a maximum value at the same time, and a phase difference exists; a small frequency difference ensures that there is overlap between the two waveforms. The characteristic that the output light intensity has phase difference is utilized, and the light intensity difference signal is used as a criterion for judging the resonance state of the F-P cavity, so that the judgment of the resonance state of the F-P cavity is realized. The invention also discloses a difference device for judging the resonance state of the F-P cavity, which mainly comprises a beam splitter prism, a reflector, an acousto-optic modulator, an F-P resonant cavity, a first photoelectric receiver and a second photoelectric receiver. The invention has simple control model and is convenient for the control system and the measurement system to judge the resonance state.
Description
Technical Field
The invention relates to a difference method and a difference device for judging a resonance state of an F-P cavity, and belongs to the field of geometric precision measurement.
Background
The F-P cavity-based resonance frequency selection technology is widely applied to the fields of laser generation, optical wave narrow-band filtering, displacement measurement by a time method and the like.
F-P cavity resonance frequency selection works according to the standing wave principle. After the input wave enters the F-P resonant cavity, the input wave is reflected back and forth, superposed and interfered between two reflecting surfaces of the resonant cavity; the output wave energy of the F-P cavity changes with the input wave frequency. When the difference between the input wave frequency and the resonant frequency of the F-P resonant cavity is large, the output wave energy is very small; as the frequency of the input wave approaches the resonant frequency of the F-P resonant cavity, the energy of the output wave has a violent rising process; when the frequency of the input wave is consistent with the resonant frequency of the F-P resonant cavity, the energy of the output wave of the resonant cavity reaches a maximum value. The process that the output wave energy changes along with the change of the input wave frequency or the length of the F-P resonant cavity is the frequency selection function of the F-P resonant cavity.
In a measuring system, the frequency selection function of an F-P resonant cavity is often utilized to realize the measurement of the frequency of an output wave or the measurement of the length of the resonant cavity.
The F-P cavity is characterized by a resonant state in which the energy of the output wave is at a maximum. How to judge the maximum value of the output wave energy on an electronic control system is the key for measuring by using an F-P resonant cavity.
The existing mature F-P resonance state judgment method is a disturbance modulation method. The method has the advantages that the micro-disturbance is applied to the F-P cavity length or the input wave frequency, the phase change of the disturbance response waveform is utilized for demodulation, the effect is equivalent to that the derivative of an output wave energy curve along with the cavity length or the input wave frequency is obtained, and the extreme point of the curve is converted into the zero crossing point of the derivative. Near the maximum value point, the derivative of the curve is a monotonic zero-crossing function, so that the measurement system can conveniently make state judgment, and the control system can also establish a linear control model. The method for judging the resonance state of the F-P cavity by the disturbance modulation method has the advantages that a mathematical model is clear, and a real extreme point can be obtained; the disadvantages are that the structure is complex, extra modulation and demodulation systems are needed, interference signals in the system are artificially increased, and the response speed is influenced by the modulation frequency.
Disclosure of Invention
The invention aims to provide a difference method and a difference device for judging the resonance state of an F-P cavity, and the judgment of the resonance state of the F-P cavity is realized by utilizing the difference method.
The purpose of the invention is realized by the following technical scheme:
the invention discloses a difference method for judging the resonance state of an F-P cavity, which is characterized in that two beams of light with close frequency, fixed frequency difference and known frequency are generated and respectively reflected and oscillated in the F-P cavity to obtain respective output light intensity curves; when the light frequency or the length of the F-P resonant cavity is changed, the obtained two output light intensity curves cannot reach a maximum value at the same time, and a phase difference exists; a small frequency difference ensures that there is overlap between the two waveforms. The characteristic that the output light intensity has phase difference is utilized, and the light intensity difference signal is taken as a criterion for judging the resonance state of the F-P cavity, so that the judgment of the resonance state of the F-P cavity is realized.
The invention also discloses a difference device for judging the resonance state of the F-P cavity, which is used for realizing the difference method for judging the resonance state of the F-P cavity.
The input laser is divided into two beams by the beam splitter prism, one beam directly enters the F-P resonant cavity, and the transmitted light is received by the first photoelectric receiver; and the other beam enters the acoustic-optical modulator after being reflected by the reflector and also enters the F-P resonant cavity, and the transmitted light is received by the second photoelectric receiver.
The frequency difference exists between the two beams of light entering the F-P resonant cavity, and the frequency difference is equal to the working frequency of the acousto-optic modulator.
After two beams of light with frequency difference pass through the F-P resonant cavity for frequency selection, output light energy of the two beams of light is converted into electric signals by the first photoelectric receiver and the second photoelectric receiver respectively.
In order to ensure that the output signals of the two photoelectric receivers are overlapped, the frequency difference of the two beams of light must be smaller than the half-gain bandwidth of the F-P resonant cavity.
The invention also discloses a working method of the differential device for judging the resonance state of the F-P cavity, which comprises the following steps:
scenario 1, the laser frequency is locked at the F-P cavity resonant frequency by controlling the laser frequency. Resonant center frequency F of F-P resonant cavity0Half gain bandwidth of 2 Δ f0(ii) a Of input lightFrequency f, the acousto-optic modulator adjusts the frequency of one beam of light to f + fAOM. When f and f + fAOMAre all out of f0±Δf0When the area is in, the outputs of the first photoelectric receiver and the second photoelectric receiver are both extremely small; with increasing f, f + fAOMFirst enter f0±Δf0In the region, the output of the second photoelectric receiver increases first, and then the first photoelectric receiver also starts to increase; f is continuously increased, then f + fAOMLeave f before f0±Δf0The second photoelectric receiver signal is reduced before the first photoelectric receiver signal, so that the output signals of the two receivers have a cross process; curve of difference between two signals as a function of f, at f0The vicinity is a monotone function which can be used as a feedback criterion for realizing closed-loop frequency locking control by a control system.
Has the advantages that:
the invention discloses a difference method and a difference device for judging the resonance state of an F-P cavity. Near the resonance point, the difference signal of the two light intensities and the change of the light frequency or the length of the resonant cavity form a monotonic zero-crossing relation, the control model is simple, and the control system and the measurement system can conveniently judge the resonance state.
Drawings
FIG. 1 is a schematic diagram of a differential method and apparatus for determining the resonant state of an F-P cavity. Wherein 1 is a beam splitter prism, 2 is a reflector, 3 is an acousto-optic modulator, 4 is an F-P resonant cavity, 5 is a first photoelectric receiver, and 6 is a second photoelectric receiver.
Fig. 2 is a graph of the variation of the transmitted light intensity and the light intensity difference signal with the frequency of the input light, where 7 is an output curve of the first photoelectric receiver, 8 is an output curve of the second photoelectric receiver, and 9 is a light intensity difference curve.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
Example 1
A slight cavity length change (slight displacement) of the F-P cavity corresponds to a change in its resonant frequency. By utilizing the sharp frequency selection characteristic of the F-P resonant cavity and locking the frequency of an external laser light source on the resonant frequency of the F-P resonant cavity through a closed-loop frequency locking control system, the micro displacement change can be converted into the change of the laser frequency, the micro displacement measurement is realized by a time (frequency) method, and thus higher displacement resolution is obtained, and the method is a typical scheme for realizing picometer displacement measurement. The key link of the process is a closed-loop frequency locking control system, how to establish a control model and realize automatic tracking frequency locking are the main difficulties of the system.
As shown in fig. 1, the difference device for determining the resonant state of the F-P cavity disclosed in this embodiment is composed of a beam splitter prism 1, a reflective mirror 2, an acousto-optic modulator 3, an F-P resonant cavity 4, a first photoelectric receiver 5, and a second photoelectric receiver 6.
The light source adopts a NewFocus 6800 tunable laser, the wavelength adjusting range is 632.5nm-640nm, and the mode-hopping-free adjusting amplitude is 120 GHz; the beam splitter prism 1 adopts a depolarization beam splitter prism with the transmission inverse ratio of 1: 1; the reflector 2 adopts a dielectric reflector; the acousto-optic modulator 3 adopts an XX acousto-optic modulator produced by Chengdu photoelectricity, and the working frequency is 10MHz-60 MHz; the F-P resonant cavity 4 adopts a double-plane mirror structure, the length of the resonant cavity is 110mm, and the half-gain bandwidth is about 20 MHz; the first photoelectric receiver 5 and the second photoelectric receiver 6 adopt 3DU5C phototriodes.
The working method of the differential device for determining the resonant state of the F-P cavity disclosed by the embodiment comprises the following steps:
and adjusting the relative positions of the laser light source, the beam splitter prism 1 and the F-P resonant cavity 4 to enable the transmission light of the beam splitter prism to enter the F-P resonant cavity 4.
The acousto-optic modulator 3 works at 10MHz, and the installation positions and angles of the reflector 2 and the acousto-optic modulator 3 are adjusted to ensure that 1-order diffraction light of the acousto-optic modulator is emitted into the F-P resonant cavity 4.
The laser frequency of the tunable laser is adjusted, and the oscilloscope can observe that the first photoelectric receiver 5 and the second photoelectric receiver 6 have obvious peak signals near the resonant frequency and have phase difference along with the change of the relative relation between the laser frequency and the resonant frequency of the F-P resonant cavity 4.
The light intensity difference signal is used as an error signal of a closed-loop frequency locking control system, so that the locking of the laser frequency and the resonant frequency of the F-P cavity is realized. The frequency locking stability can reach 50kHz, and the tracking response speed is 1 ms.
The traditional disturbance modulation method has the advantages that due to artificial disturbance and the limitation of modulation frequency, the frequency locking stability is usually 100kHz, and the tracking response speed is lower than 10 ms. Therefore, the scheme is superior to the traditional disturbance modulation scheme in the aspects of frequency locking stability and tracking response speed.
The foregoing is merely illustrative of specific embodiments of the present invention and reference should be made to apparatus and structures not specifically described herein which are understood to be embodied in the form of the common apparatus and methods known in the art.
The above detailed description is intended to illustrate the objects, aspects and advantages of the present invention, and it should be understood that the above detailed description is only exemplary of the present invention and is not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (3)
1. A difference method for judging the resonance state of an F-P cavity is characterized in that: two beams of light with close frequency, fixed frequency difference and known frequency are generated and respectively reflected and oscillated in the F-P resonant cavity to obtain respective output light intensity curves; when the light frequency or the length of the F-P resonant cavity is changed, the obtained two output light intensity curves cannot reach a maximum value at the same time, and a phase difference exists; the small frequency difference can ensure that the two waveforms are overlapped; the characteristic that the output light intensity has phase difference is utilized, and the light intensity difference signal is taken as a criterion for judging the resonance state of the F-P cavity, so that the judgment of the resonance state of the F-P cavity is realized.
2. A differentiating device for determining the resonant state of an F-P cavity, which is used for implementing the differentiating method for determining the resonant state of the F-P cavity according to claim 1, and is characterized in that: the device mainly comprises a beam splitter prism, a reflector, an acousto-optic modulator, an F-P resonant cavity, a first photoelectric receiver and a second photoelectric receiver;
the input laser is divided into two beams by the beam splitter prism, one beam directly enters the F-P resonant cavity, and the transmitted light is received by the first photoelectric receiver; the other beam enters the acoustic-optical modulator after being reflected by the reflector and also enters the F-P resonant cavity, and the transmitted light is received by the second photoelectric receiver;
the frequency difference exists between the two beams of light entering the F-P resonant cavity, and the frequency difference is equal to the working frequency of the acousto-optic modulator;
after two beams of light with frequency difference pass through the F-P resonant cavity for frequency selection, the output light energy of the two beams of light is converted into electric signals by a first photoelectric receiver and a second photoelectric receiver respectively;
in order to ensure that the output signals of the two photoelectric receivers are overlapped, the frequency difference of the two beams of light must be smaller than the half-gain bandwidth of the F-P resonant cavity.
3. The differential apparatus for determining the resonant state of an F-P cavity of claim 2, wherein:
scenario 1, laser frequency is locked on F-P cavity resonant frequency by controlling laser frequency(ii) a Resonance center frequency F of F-P resonant cavity0Half gain bandwidth of 2 Δ f0(ii) a The frequency f of input light, and the frequency of its beam splitting is adjusted to f + f by the acousto-optic modulatorAOM(ii) a When f and f + fAOMAre all out of f0±Δf0When the area is in, the outputs of the first photoelectric receiver and the second photoelectric receiver are both extremely small; with increasing f, f + fAOMFirst enter f0±Δf0In the region, the output of the second photoelectric receiver increases first, and then the first photoelectric receiver also starts to increase; f is continuously increased, then f + fAOMLeave f before f0±Δf0The second photoelectric receiver signal is reduced before the first photoelectric receiver signal, so that the output signals of the two receivers have an intersection process; curve of difference between two signals as a function of f, at f0The vicinity is a monotone function which can be used as a feedback criterion for realizing closed-loop frequency locking control by a control system;
scene 2, controlling the length of the F-P resonant cavity to enable the length F of the F-P resonant cavity0Locked to the input laser frequency f; resonant center frequency F of F-P resonant cavity0Half gain bandwidth of 2 Δ f0(ii) a The frequency f of input light, and the frequency of its beam splitting is adjusted to f + f by the acousto-optic modulatorAOM(ii) a When f and f + fAOMAre all out of f0±Δf0When the area is in, the outputs of the first photoelectric receiver and the second photoelectric receiver are both extremely small; with increasing f, f + fAOMFirst enter f0±Δf0In the region, the output of the second photoelectric receiver increases first, and then the first photoelectric receiver also starts to increase; f is continuously increased, then f + fAOMLeave f before f0±Δf0The second photoelectric receiver signal is reduced before the first photoelectric receiver signal, so that the output signals of the two receivers have a cross process; curve of difference between two signals as a function of f, at f0The vicinity is a monotone function which can be used as a feedback criterion for realizing closed-loop frequency locking control by a control system.
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| US20060050747A1 (en) * | 2004-09-08 | 2006-03-09 | Trutna William R Jr | Frequency-tunable light sources and methods of generating frequency-tunable light |
| CN104570545A (en) * | 2015-01-22 | 2015-04-29 | 上海交通大学 | All-optical tunable generation device of wide band linear frequency modulated signals |
| CN114018171A (en) * | 2021-11-11 | 2022-02-08 | 南方电网科学研究院有限责任公司 | High-resolution strain sensor based on differential optical fiber resonant cavity |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20060050747A1 (en) * | 2004-09-08 | 2006-03-09 | Trutna William R Jr | Frequency-tunable light sources and methods of generating frequency-tunable light |
| CN104570545A (en) * | 2015-01-22 | 2015-04-29 | 上海交通大学 | All-optical tunable generation device of wide band linear frequency modulated signals |
| CN114018171A (en) * | 2021-11-11 | 2022-02-08 | 南方电网科学研究院有限责任公司 | High-resolution strain sensor based on differential optical fiber resonant cavity |
Non-Patent Citations (3)
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| 杨海菁 等: "基于共焦法布里-珀罗腔的无调制激光频率锁定", 《中国激光》, vol. 33, no. 3, pages 316 - 320 * |
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