CN112945108B - A precision displacement measurement method and device based on electro-optical modulation sidebands - Google Patents

Abstract

The invention belongs to the technical field of precision displacement measurement, and provides a precision displacement measurement method and device based on electro-optical modulation sidebands. The method obtains the first cavity length of the interferometer by adjusting the sideband frequency of the electro-optic modulator and the resonance of the interferometer. The corresponding first free spectral range Δν ₁ and the second free spectral range Δν ₂ corresponding to the second cavity length; the displacement ΔL of the interferometer is calculated according to the first free spectral range Δν ₁ and the second free spectral range Δν ₂ . The invention converts the displacement measurement of the interferometer into the measurement of microwave resonant frequency by locking the sideband frequency of the electro-optic modulator to resonate with the free spectrum range of the interferometer, thereby improving the accuracy of displacement measurement.

Description

A precision displacement measurement method and device based on electro-optical modulation sidebands

technical field

The invention relates to the technical field of precision displacement measurement, in particular to a precision displacement measurement method and device based on electro-optical modulation sidebands.

Background technique

Precision displacement measurement plays an important role in precision manufacturing, advanced sensing, and metrology. The commonly used precision displacement measurement method is mainly based on the laser interferometer method, and the precise measurement of displacement is realized by counting and subdividing the interferometer fringes. The traditional method uses two laser beams to simultaneously lock the Fabry-Perot (Fabry-Perot resonator) interferometer, which has high complexity and low measurement accuracy.

Contents of the invention

Aiming at the technical problems existing in the above-mentioned prior art, the present invention provides a precise displacement measurement method and device based on electro-optic modulation sidebands, mainly by locking the sideband frequency of the electro-optic modulator to resonate with the free spectral range of the interferometer, and the The displacement measurement of the interferometer is converted into the measurement of microwave resonance frequency, which improves the accuracy of displacement measurement.

Specifically, it is mainly realized through the following technical solutions:

A precise displacement measurement method based on electro-optical modulation sidebands, comprising the following steps:

By adjusting the sideband frequency of the electro-optic modulator to resonate with the interferometer, the first free spectral range Δν ₁ corresponding to the first cavity length of the interferometer, and the second free spectral range Δν ₂ corresponding to the second cavity length are obtained;

The displacement ΔL of the interferometer is calculated according to the first free spectral range Δν ₁ and the second free spectral range Δν ₂ .

Preferably, the displacement ΔL of the interferometer is calculated according to the first free spectral range _Δν1 and the second free spectral range _Δν2 , specifically including:

The displacement ΔL of the interferometer is calculated by the following formula:

Among them, Δν ₁ is the first free spectral range, Δν ₂ is the second free spectral range, c is the vacuum light velocity constant, and n is the refractive index.

Preferably, adjusting the sideband frequency of the electro-optic modulator to resonate with the interferometer specifically includes:

The electro-optic modulator comprises a first electro-optic modulator and a second electro-optic modulator, and the laser beam output by the laser emitter passes through the first electro-optic modulator and the second electro-optic modulator in sequence to generate the first sideband with a frequency of ω ₁ and a frequency of the second sideband of ω ₂ ;

The photoelectric receiver generates a microwave signal according to the received laser beam comprising the first sideband and the second sideband, and the microwave signal comprises a first microwave signal with a frequency of _ω1 and a second microwave signal with a frequency of _ω2 ;

The frequency division processing unit separates the first microwave signal and the second microwave signal, and inputs the first microwave signal to the laser frequency locker, and inputs the second microwave signal to the electro-optic sideband locker;

The laser frequency locker compares the phase difference between the third microwave signal and the first microwave signal, generates an error signal for locking the laser and the interferometer, and feeds the error signal back to the laser transmitter;

The electro-optic sideband locker adjusts the frequency ω ₂ of the fourth microwave signal to resonate with the interferometer through the output voltage signal;

The frequency counter records the frequency ω ₂ of the fourth microwave signal when it resonates with the interferometer, so as to obtain the free spectral range corresponding to different cavity lengths of the interferometer according to the recorded frequency;

The third microwave signal is a microwave signal with a frequency of _ω1 that the microwave signal generator inputs to the first electro-optic modulator, and is used to drive the first electro-optic modulator to generate a first sideband with a frequency of _ω1 , and the fourth The microwave signal is a microwave signal with a frequency of _ω2 that is input to the second electro-optic modulator by the voltage-controlled oscillator, and is used to drive the second electro-optic modulator to generate a second sideband with a frequency of _ω2 .

Preferably, the first free spectral range Δν ₁ corresponding to the first cavity length of the interferometer and the second free spectral range Δν ₂ corresponding to the second cavity length are obtained, specifically including:

Move the plane reflector of the interferometer to the first position, the cavity length of the interferometer is the first cavity length, then the electro-optic sideband locker adjusts the frequency _ω of the fourth microwave signal to resonate with the interferometer through the output voltage signal, at this time The frequency ω ₂ is recorded as ω ₂₁ , then the first free spectral range Δν ₁ = ω ₂₁ corresponding to the first cavity length of the interferometer;

Move the flat reflector of the interferometer to the second position, and the cavity length of the interferometer is the second cavity length, then the electro-optic sideband locker adjusts the frequency _ω of the fourth microwave signal to resonate with the interferometer through the output voltage signal, and at this time The frequency ω ₂ is denoted as ω ₂₂ , then the second free spectral range Δν ₂ =ω ₂₂ corresponding to the second cavity length of the interferometer.

A precision displacement measurement device based on electro-optical modulation sidebands, including a laser transmitter, a first electro-optic modulator, a second electro-optic modulator, a polarization beam splitter, a quarter-wave plate, a coupling lens, and an interferometer arranged in sequence , the interferometer includes a concave mirror and a movable plane mirror;

The first electro-optic modulator is also connected with a microwave signal generator, and the microwave signal generator is connected with a laser frequency locker, and the laser frequency locker is respectively connected with the laser transmitter and the frequency division processing unit, and the The frequency division processing unit is respectively connected with the photoelectric receiver and the electro-optic sideband locker, and the electro-optic sideband locker is respectively connected with the frequency counter and the voltage-controlled oscillator, and the voltage-controlled oscillator is connected with the second electro-optic modulator, so The photoelectric receiver is connected with the polarization beam splitting prism.

Compared with the prior art, the present invention has the following beneficial effects:

1. By locking the sideband frequency of the electro-optic modulator to resonate with the free spectral range of the interferometer, the displacement measurement of the interferometer is converted into the measurement of microwave resonance frequency, which is conducive to improving the accuracy of displacement measurement;

2. Utilizing the characteristics of high frequency response of electro-optical modulation sidebands and easy control by voltage-controlled oscillators, the locking of electro-optic modulation sideband frequencies and the free spectral range of the interferometer is realized, and the displacement of the interferometer is measured in real time;

3. It overcomes the problem of high complexity and low measurement accuracy in the traditional method of simultaneously locking the interferometer with two laser beams.

Description of drawings

1. Figure 1 is a schematic structural view of a precision displacement measuring device based on electro-optic modulation sidebands provided by the present invention;

Reference signs:

Single-frequency narrow-linewidth laser-1, first electro-optic modulator-2, second electro-optic modulator-3, polarization beamsplitter prism-4, quarter-wave plate-5, coupling lens-6, Fabry-Perot interferometer The concave mirror of the Fabry-Perot interferometer-7, the plane mirror of the Fabry-Perot interferometer-8, the voltage-controlled oscillator-9, the microwave signal generator-10, the laser frequency locker-11, the frequency division processing unit-12, the electro-optic sideband Locker-13, Frequency Counter-14 and Photoelectric Receiver-15.

Detailed ways

In order to make those skilled in the art understand the core idea of the present invention more clearly, it will be described in detail below with reference to the accompanying drawings.

The embodiment of the present invention provides a precision displacement measurement device based on electro-optical modulation sidebands, as shown in Figure 1, which specifically includes a single-frequency narrow-linewidth laser 1, a first electro-optic modulator 2, a second electro-optic modulator Device 3, polarization beam splitter prism 4, quarter wave plate 5, coupling lens 6, concave mirror 7 of Fabry-Perot interferometer and plane mirror 8 of Fabry-Perot interferometer, plane mirror 8 can move left and right.

The first electro-optic modulator 2 is also connected to a microwave signal generator 10, and the microwave signal generator 10 is connected to a laser frequency locker 11, and the laser frequency locker 11 is connected to the single-frequency narrow linewidth laser 1 respectively. It is connected with the frequency division processing unit 12, and the frequency division processing unit 12 is connected with the photoelectric receiver 15 and the electro-optic sideband locker 13 respectively, and the electro-optic sideband locker 13 is connected with the frequency counter 14 and the voltage-controlled oscillator 9 respectively, so The voltage-controlled oscillator 9 is connected to the second electro-optic modulator 3 , and the photoelectric receiver 15 is connected to the polarization beam splitter prism 4 .

A precise displacement measurement method based on electro-optical modulation sidebands according to an embodiment of the present invention will be described below in conjunction with accompanying drawing 1, including:

First move the plane reflector 8 of the Fabry-Perot interferometer to the first position, at this time the cavity length of the Fabry-Perot interferometer is recorded as the first cavity length L ₁ , and the first free spectral range corresponding to the first cavity length of the interferometer Denoted as Δν ₁ .

The laser beam emitted by the single-frequency narrow-linewidth laser 1 passes through the first electro-optic modulator 2 and the second electro-optic modulator 3 in sequence, generating a first sideband with a frequency of _ω1 and a second sideband with a frequency of _ω2 , respectively.

The laser beam including the first sideband and the second sideband passes through the polarization splitter prism 4, the quarter-wave plate 5 and the coupling lens 6 in turn, and enters the Fabry-Perot interferometer, and enters the Fabry-Perot interferometer The laser beam includes two parts, the first laser beam and the second laser beam. The concave mirror 7 in the Fabry-Perot interferometer reflects a part of the first laser beam to the coupling lens 6, and then passes through the quarter-wave plate in turn. 5 and the polarization beam splitter prism 4, it is incident on the photoelectric receiver 15, and the other part, namely the second laser beam, is incident on the flat mirror 8 of the Fabry-Perot interferometer through the concave mirror 7 of the Fabry-Perot interferometer.

The photoelectric receiver 15 generates a microwave signal according to the received laser beam containing the first sideband and the second sideband, and the microwave signal includes a first microwave signal with a frequency of _ω1 and a second microwave signal with a frequency of _ω2 .

The frequency division processing unit 12 separates the first microwave signal and the second microwave signal, and inputs the first microwave signal to the laser frequency locker 11 , and inputs the second microwave signal to the electro-optic sideband locker 13 .

The laser frequency locker 11 compares the phase difference between the third microwave signal and the first microwave signal, generates an error signal for locking the laser and the Fabry-Perot interferometer, and feeds the error signal back to the single-frequency narrow-linewidth laser 1, The third microwave signal is a microwave signal with a frequency of _ω1 that is input to the first electro-optic modulator 2 by the microwave signal generator 10, and is used to drive the first electro-optic modulator 2 to generate a first sideband with a frequency of _ω1 .

The electro-optic sideband locker 13 adjusts the frequency ω ₂ of the fourth microwave signal to resonate with the Fabry-Perot interferometer through the output voltage signal, and the frequency ω ₂ of the fourth microwave signal at this time is denoted as ω ₂₁ , therefore, the Fabry-Perot interferometer The first free spectral range Δν ₁ corresponding to the first cavity length L ₁ is: Δν ₁ = ω ₂₁ , the above fourth microwave signal is a microwave signal with a frequency of ω ₂ input by the voltage-controlled oscillator 9 to the second electro-optic modulator 3 , used to drive the second electro-optic modulator 3 to generate the second sideband with frequency ω ₂ .

Use a frequency counter to record the frequency ω ₂ of the fourth microwave signal when it resonates with the interferometer, that is, ω ₂₁ .

Then, move the plane reflector 8 of the Fabry-Perot interferometer to the second position. At this time, the cavity length of the Fabry-Perot interferometer is recorded as the second cavity length L ₂ , and the second free space corresponding to the second cavity length of the interferometer The spectral range is noted as Δν ₂ .

In the same way, the electro-optic sideband locker 13 adjusts the frequency _ω of the fourth microwave signal to resonate with the Fabry-Perot interferometer through the output voltage signal, and the frequency _ω of the fourth microwave signal at this time is denoted as ω ₂₂ , therefore, Fabry- The second free spectral range Δν ₂ corresponding to the second cavity length L ₂ of the Perot interferometer is: Δν ₂ =ω ₂₂ .

Use a frequency counter to record again the frequency ω ₂ of the fourth microwave signal when resonating with the interferometer, ie ω ₂₂ .

Therefore, it can be seen from the above that the displacement ΔL of the Fabry-Perot interferometer is:

ΔL=L ₂ -L ₁ (1)

The free spectral range Δν of the Fabry-Perot interferometer is calculated according to the following formula (2):

Among them, c is the vacuum light velocity constant, n is the refractive index, and L is the cavity length of the Fabry-Perot interferometer.

Therefore, according to formulas (1) and (2), the displacement ΔL of the Fabry-Perot interferometer can be expressed as:

In summary, it can be known from formula (3) that only by measuring the first free spectrum range Δν ₁ corresponding to the first cavity length of the Fabry-Perot interferometer and the second free spectrum corresponding to the second cavity length of the Fabry-Perot interferometer The range Δν ₂ can realize the displacement measurement of the Fabry-Perot interferometer.

However, there are Δν ₁ = ω ₂₁ and Δν ₂ = ω ₂₂ above. Therefore, the present invention converts the displacement measurement of the interferometer into the measurement of the microwave resonance frequency by locking the sideband frequency of the electro-optic modulator to resonate with the free spectral range of the interferometer , which is conducive to improving the accuracy of displacement measurement. At the same time, using the characteristics of high frequency response of electro-optical modulation sidebands and easy control by voltage-controlled oscillators, the locking of electro-optic modulation sideband frequency and the free spectral range of the interferometer is realized, and the interferometer can be measured in real time. It solves the problem of high complexity and low measurement accuracy in the traditional method of simultaneously locking the interferometer with two laser beams.

The embodiments of the present invention have been described in detail above, and specific examples have been used in this paper to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only used to help understand the core idea of the present invention; at the same time, for those in the art Ordinary technicians, according to the idea of the present invention, will have changes in the specific implementation and application range. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims (4)

1. A precision displacement measurement device based on electro-optic modulation sideband, characterized in that it comprises a laser transmitter, a first electro-optic modulator, a second electro-optic modulator, a polarization beam splitter, and a quarter wave plate arranged in sequence , a coupling lens and an interferometer, the interferometer includes a concave mirror and a movable plane mirror; The first electro-optic modulator is also connected with a microwave signal generator, and the microwave signal generator is connected with a laser frequency locker, and the laser frequency locker is respectively connected with the laser transmitter and the frequency division processing unit, and the The frequency division processing unit is respectively connected with the photoelectric receiver and the electro-optic sideband locker, and the electro-optic sideband locker is respectively connected with the frequency counter and the voltage-controlled oscillator, and the voltage-controlled oscillator is connected with the second electro-optic modulator, so The photoelectric receiver is connected with the polarization beam splitter; The photoelectric receiver produces a microwave signal according to the received laser beam comprising the first sideband and the second sideband, and the microwave signal comprises a first microwave signal with a frequency of _ω1 and a second microwave signal with a frequency of _ω2 ; The frequency division processing unit separates the first microwave signal and the second microwave signal, and inputs the first microwave signal to the laser frequency locker, and inputs the second microwave signal to the electro-optic sideband locker; the laser frequency locker Comparing the phase difference between the third microwave signal and the first microwave signal to generate an error signal for locking the laser and the interferometer, and feeding the error signal back to the laser transmitter, the third microwave signal is the input of the microwave signal generator The microwave signal that the frequency to the first electro-optic modulator is ω ₁ is used to drive the first electro-optic modulator to generate the first sideband with a frequency of ω ₁ ; the electro-optic sideband locker adjusts the frequency of the fourth microwave signal through the output voltage signal ω ₂ resonates with the interferometer, and the frequency ω ₂ of the fourth microwave signal at this time is recorded as ω ₂₁ , therefore, the first free spectral range Δν ₁ corresponding to the first cavity length L ₁ of the interferometer is: Δν ₁ = ω ₂₁ , Above-mentioned 4th microwave signal is the microwave signal that the frequency that the voltage-controlled oscillator inputs to the second electro-optic modulator 3 is ω ₂ , is used to drive the second electro-optic modulator 3 to produce the second sideband that frequency is ω ₂ ; Utilize frequency counter Record the frequency ω ₂ of the fourth microwave signal when it resonates with the interferometer, that is ω ₂₁ ; the laser beam emitted by the laser transmitter passes through the first electro-optic modulator and the second electro-optic modulator in turn, respectively generating the first frequency of ω ₁ sideband and a second sideband at frequency _ω2 . 2. A precision displacement measurement method based on electro-optic modulation sideband, is characterized in that, utilizes displacement measuring device as claimed in claim 1 to measure, comprising: By adjusting the sideband frequency of the electro-optic modulator to resonate with the interferometer, the electro-optic modulator includes a first electro-optic modulator and a second electro-optic modulator, and the laser beam output by the laser transmitter passes through the first electro-optic modulator and the second electro-optic modulator in sequence After the modulator, the first sideband with a frequency of _ω1 and the second sideband with a frequency of _ω2 are produced; the photoelectric receiver produces a microwave signal according to the received laser beam that contains the first sideband and the second sideband, and the microwave The signal includes a first microwave signal with a frequency of ω ₁ and a second microwave signal with a frequency of ω ₂ ; the frequency division processing unit separates the first microwave signal and the second microwave signal, and inputs the first microwave signal to the laser frequency locking device, and input the second microwave signal to the electro-optical sideband locker; the laser frequency locker compares the phase difference between the third microwave signal and the first microwave signal, generates an error signal for locking the laser and the interferometer, and sends the The error signal is fed back to the laser transmitter; the electro-optical sideband locker adjusts the frequency ω ₂ of the fourth microwave signal to resonate with the interferometer through the output voltage signal; the frequency counter records the frequency ω ₂ of the fourth microwave signal when it resonates with the interferometer, so that Obtain the free spectral range corresponding to the different cavity lengths of the interferometer according to the recorded frequency; the third microwave signal is a microwave signal that the microwave signal generator inputs to the first electro-optic modulator at a frequency of _ω1 , and is used to drive the first electro-optic The modulator generates the first sideband with a frequency of _ω1 , and the fourth microwave signal is a microwave signal with a frequency of _ω2 that is input to the second electro-optic modulator by the voltage-controlled oscillator, and is used to drive the second electro-optic modulator to generate a frequency is the second sideband of ω ₂ ; obtaining the first free spectral range Δν ₁ corresponding to the first cavity length of the interferometer, and the second free spectral range Δν ₂ corresponding to the second cavity length; The displacement ΔL of the interferometer is calculated according to the first free spectral range Δν ₁ and the second free spectral range Δν ₂ . 3. a kind of precision displacement measurement method based on electro-optic modulation sideband as claimed in claim 2, is characterized in that, calculates the displacement ΔL of interferometer according to the first free spectral range Δν ₁ and the second free spectral range Δν ₂ , Specifically include: The displacement ΔL of the interferometer is calculated by the following formula:

Among them, Δν ₁ is the first free spectral range, Δν ₂ is the second free spectral range, c is the vacuum light velocity constant, and n is the refractive index. 4. A kind of precision displacement measurement method based on electro-optical modulation sideband as claimed in claim 3, it is characterized in that, obtain the first free spectral range Δν ₁ corresponding to the first cavity length of the interferometer, and the corresponding Δν 1 of the second cavity length The second free spectral range Δν ₂ specifically includes: Move the plane reflector of the interferometer to the first position, the cavity length of the interferometer is the first cavity length, then the electro-optic sideband locker adjusts the frequency _ω of the fourth microwave signal to resonate with the interferometer through the output voltage signal, at this time The frequency ω ₂ is recorded as ω ₂₁ , then the first free spectral range Δν ₁ = ω ₂₁ corresponding to the first cavity length of the interferometer; Move the flat reflector of the interferometer to the second position, and the cavity length of the interferometer is the second cavity length, then the electro-optic sideband locker adjusts the frequency _ω of the fourth microwave signal to resonate with the interferometer through the output voltage signal, and at this time The frequency ω ₂ is denoted as ω ₂₂ , then the second free spectral range Δν ₂ =ω ₂₂ corresponding to the second cavity length of the interferometer.

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