CN111256846A - Method and equipment for measuring light velocity by using phase-locked amplifier - Google Patents
Method and equipment for measuring light velocity by using phase-locked amplifier Download PDFInfo
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
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Abstract
The invention provides a method and a device for measuring the speed of light by using a phase-locked amplifier, which are connected with an instrument; connecting the output end of the high-frequency signal generator to an acousto-optic frequency shifter; the synchronous output end of the signal generator is connected to the reference signal input end of the phase-locked amplifier, and the photoelectric converter is connected to the signal input end to be detected; starting an instrument, outputting a sine wave signal with the frequency of F by a signal generator, and setting a reference channel to be in a second harmonic mode; selecting preset measurement parameters; adjusting a phase shifter of the phase-locked amplifier to enable the signal output to be maximum when the reflector is at the initial position, and recording the maximum value V0; moving the reflector, and recording the output voltage V after moving and the moving distance delta s; acquiring light speed data: and an average value is taken. The acousto-optic frequency shifter is used for generating an optical beat, and the phase-locked amplifier is used for measuring the phase change generated after the optical signal moves for a distance s, so that the optical speed is measured. Compared with a beam splitting measurement method, the experimental instrument is simpler, the operation is simpler and more convenient, and the precision is higher.
Description
Technical Field
The invention relates to the technical field of light speed detection, in particular to a method and equipment for measuring light speed by using a phase-locked amplifier.
Background
The speed of light is one of the most important physical constants. The speed of light is the speed of propagation of light or electromagnetic waves in a vacuum or medium. The speed of light is the maximum speed of movement of an object in nature. Only photons with a static mass of zero are moving at the speed of light all the time. The speed of light is superimposed with any velocity, and the result is still the speed of light. The speed of light in vacuum is an important physical constant.
At present, the accurate measurement of the light speed has important physical significance and also has important practical value. The common method is to divide an optical signal into two beams to be superposed and measured on an oscilloscope, in such a test mode, a certain distance optical path needs to be configured, a large number of reflectors are needed to realize the extension of the optical path, and because a large number of reflectors are arranged, each reflector needs to be adjusted, and the optical path meets the requirement of measuring the optical path. This results in a difficult adjustment of the mirrors, which can affect the accuracy of the measurement if the mirrors are misaligned or not configured at a specified angle.
And the light velocity measuring method of the split beams is to judge by observing whether two images on the oscilloscope are superposed or not, the images on the oscilloscope are difficult to adjust to be very thin and sharp, the guide rail moves a small distance, and human eyes are difficult to observe changes.
Disclosure of Invention
In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a method for measuring the speed of light using a lock-in amplifier, the method comprising:
s11, connecting an instrument;
connecting the output end of the high-frequency signal generator to an acousto-optic frequency shifter;
the synchronous output end of the signal generator is connected to the reference signal input end of the phase-locked amplifier, and the photoelectric converter is connected to the signal input end to be detected;
s12, starting the instrument, and preheating for a preset time;
the signal generator outputs a sine wave signal with the frequency of F, and a reference channel is set to be in a second harmonic mode, namely a 2F mode is detected; selecting preset measurement parameters;
s13, adjusting a phase shifter of the phase-locked amplifier to enable the signal output to be maximum when the reflector is at the initial position, and recording the maximum value V0;
s14, moving the reflector, and recording the output voltage V after moving and the moving distance delta S;
s15, obtaining the light speed data by the following formula:
and repeating the step S14, measuring preset group data from small to large distance, and taking an average value to obtain the measured light speed data.
The present invention also provides an apparatus for measuring a speed of light using a lock-in amplifier, comprising: the device comprises a high-frequency signal generator, an acousto-optic frequency shifter, a lock-in amplifier, a photoelectric converter and a reflector;
the output end of the high-frequency signal generator is connected with the acousto-optic frequency shifter;
the synchronous output end of the high-frequency signal generator is connected with the reference signal input end of the phase-locked amplifier;
the high-frequency signal generator sends out optical signals, and the optical signals are transmitted to the photoelectric converter after passing through the acousto-optic frequency shifter and the reflector;
the input end of the photoelectric converter receives an optical signal to be measured, performs photoelectric signal conversion on the optical signal to be measured, and transmits the optical signal to the phase-locked amplifier, and the phase-locked amplifier measures the phase change generated after the optical signal moves for a distance s to measure the optical speed.
It should be further noted that the lock-in amplifier includes: the device comprises an alternating current amplifier, a band-pass filter, a phase-sensitive detector, a low-pass filter, a direct current amplifier, a display, a reference signal receiving module and a square wave driving module;
the alternating current amplifier acquires an input signal transmitted by the photoelectric converter and transmits the input signal to the phase-sensitive detector through the band-pass filter;
the phase-sensitive detector is connected with the reference signal receiving module through the square wave driving module to obtain a reference signal; the phase sensitive detector processes the input signal and the reference signal, and transmits the processed input signal and the processed reference signal to the display after passing through the low-pass filter and the direct current amplifier in sequence.
According to the technical scheme, the invention has the following advantages:
the invention relates to a method and a device for measuring light velocity by using a phase-locked amplifier. Compared with a beam splitting measurement method, the experimental instrument is simpler, the operation is simpler and more convenient, and the precision is higher.
The invention uses the principle of optical beat frequency method and phase-locked amplifier to measure the light speed, compared with the existing light speed measuring method of beam splitting, the required light path is shorter, and the light path adjustment is simpler. If the signal of 40MHzd can be provided, only about 1m of optical path change range is needed, compared with the optical path of the previous measuring method, the optical path is shorter, a large number of reflecting mirrors are reduced, and the adjusting difficulty is reduced. Light splitting is not needed, only one light path is needed, and amplitude adjustment is not needed.
The measurement precision is higher, the method of using the lock-in amplifier is a method of measuring voltage values, the precision is higher, and obvious change can be observed in the whole range of the guide rail.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of an apparatus for measuring the speed of light using a lock-in amplifier;
FIG. 2 is a schematic diagram of an optical beat frequency;
FIG. 3 is a spatial distribution plot of a light beat;
FIG. 4 is a schematic diagram of an acousto-optic frequency shifter;
fig. 5 is a schematic diagram of a lock-in amplifier.
Detailed Description
Those of ordinary skill in the art will appreciate that the elements and algorithm steps of the examples described in connection with the embodiments disclosed herein may be embodied in electronic hardware, computer software, or combinations of both, and that the components and steps of the examples have been described in a functional general in the foregoing description for the purpose of illustrating clearly the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The block diagrams shown in the figures are functional entities only and do not necessarily correspond to physically separate entities. I.e. these functional entities may be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different networks and/or processor means and/or microcontroller means.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may also be an electric, mechanical or other form of connection.
The present invention provides an apparatus for measuring the speed of light using a lock-in amplifier 3, as shown in fig. 1, comprising: a high-frequency signal generator 1, an acousto-optic frequency shifter 2, a lock-in amplifier 3, a photoelectric converter 4 and a reflector 5;
the output end of the high-frequency signal generator 1 is connected with the acousto-optic frequency shifter 2; the synchronous output end of the high-frequency signal generator 1 is connected with the reference signal input end of the phase-locked amplifier 3; the high-frequency signal generator 1 emits light signals, and the light signals are transmitted to the photoelectric converter 4 after passing through the acousto-optic frequency shifter and the reflector 5; the input end of the photoelectric converter 4 receives the optical signal to be measured, performs photoelectric signal conversion on the optical signal to be measured, and transmits the optical signal to the lock-in amplifier 3, and the lock-in amplifier 3 measures the phase change generated after the optical signal moves the path s, so as to measure the optical speed.
Those skilled in the art will appreciate that various aspects of the apparatus for measuring speed of light using lock-in amplifier 3 may be embodied as a system, method or program product. Accordingly, various aspects of the present disclosure may be embodied in the form of: an entirely hardware embodiment, an entirely software embodiment (including firmware, microcode, etc.) or an embodiment combining hardware and software aspects that may all generally be referred to herein as a "circuit," module "or" system.
The invention relates to a lock-in amplifier 3 of a device comprising: the device comprises an alternating current amplifier 11, a band-pass filter 12, a phase sensitive detector 13, a low-pass filter 16, a direct current amplifier 17, a display 18, a reference signal receiving module 14 and a square wave driving module 15; the alternating current amplifier 11 acquires an input signal transmitted by the photoelectric converter 4 and transmits the input signal to the phase sensitive detector 13 through the band-pass filter 12; the phase-sensitive detector 13 is connected with the reference signal receiving module 14 through the square wave driving module 15 to obtain a reference signal; the phase sensitive detector 13 processes the input signal and the reference signal, passes through a low pass filter 16 and a dc amplifier 17 in this order, and transmits the processed signals to a display 18 for display.
In order to realize the movement of the reflective mirror 5, the invention also comprises the following steps: the device comprises a controller, a driving motor, a bracket, a moving gear and a rack;
the reflector 5 is arranged on the bracket; the bracket is connected with the movable gear and is meshed with the rack through the movable gear; the movable gear is connected with an output shaft of a driving motor, and the driving motor is connected with a controller; the controller controls the driving motor to operate. The rack is provided with scale marks. The gear rack is matched with the rack to realize accurate movement, and the requirement on test precision is guaranteed.
The measurement mode of the device in the invention is as follows: according to the vibration superposition principle, two rows of simple harmonics which have the same speed, the same vibration surface and smaller frequency difference and are propagated in the same direction are superposed to form a beat. Let the amplitudes E be the same (for simplicity of discussion only) and the angular frequencies be ω, respectively1And ω2(frequency response is f)1And f2Frequency difference Δ f ═ f1-f2<<f1、f2) Two lines of light waves
E1＝Ecos(ω1t-k1x+φ1)
E2＝Ecos(ω2t-k2x+φ2)
In the formula k1＝2π/λ1And k2＝2π/λ2Is wave number, phi1And phi2Is the initial phase.
Two rows of light waves are superposed to obtain
The resultant wave is a traveling wave in the x-direction with an angular frequency of
Amplitude of vibration of
High frequency waves with low frequency modulation. Obviously, ESIs a function of time and space, in frequency
Periodically changing, and calling the low-frequency traveling wave as optical beat frequency, Δ f being optical beat frequency, Δ λSI.e., the beat wavelength, as shown in fig. 2.
The optical beat wave is received by a photoelectric converter (such as a photomultiplier tube) to convert the optical beat signal into an electrical signal. Photocurrent i generated by light reaction on photosensitive surface of photoelectric converter0And light intensity
Is proportional, i.e.
g is the photoelectric conversion constant of the receiver. Due to the very high frequency (f) of the light wave0>1014Hz) and the frequency response of the photosensitive surface is generally less than or equal to 108Hz, does not reflect the high light intensity variation of the frequency, so the photocurrent generated by the photoelectric converter can only be within the response time tau (1/f)<τ<1/Δ f) and integration results in
The medium-high frequency term is zero, leaving only constant and slowly varying terms, i.e.
Wherein the slow-changing term is the optical beat signal, Δ ω is the angular frequency corresponding to Δ f, and Δ φ ═ φ1-φ2Is the initial phase. The photocurrent output by the visible light-electricity converter includes two components of direct current and optical beat signal. Filtering off the direct current component gE2The photoelectric converter outputs an optical beat signal with a beat frequency of Δ f and an initial phase of Δ φ. The phase of the optical beat signal is related to the spatial position, that is, the optical beat signals output by the detectors at different positions have different phases, thereby indicating that the speed of light can be indirectly determined by comparing the spatial phases of the optical beat signals. FIG. 3 is a diagram of a light beat signal
Spatial distribution at a certain time, in the figure, Δ λSIs the beat wavelength.
Let the optical path difference between two points in space be Δ L, the phase difference of the optical beat signals of the two points be Δ φ, and should be determined according to equation (3)
As can be seen, once Δ L Δ φ is measured, the speed of light c can be determined.
The optical beat frequency wave requires that the phase-beat two optical waves have oneAnd (5) determining the frequency difference. The laser beam has a plurality of methods for generating fixed frequency shift, and the acousto-optic frequency shift device adopts an acousto-optic frequency shift method. As shown in FIG. 4, the forward wave and the reflected wave form a standing wave sound field in the acousto-optic medium, and the thickness of the medium is just an integral multiple of half wavelength of the ultrasonic wave along the propagation direction of the ultrasonic wave. I.e. an ultrasonic phase grating, through which the laser beam is diffracted. Angle frequency omega of L-th order diffraction lightL,m＝ω0+(L+2m)Ω；
Among them, L, m ± 1, ± 2, … shows that besides the frequency shift of the diffracted light waves of different orders, the diffracted light beams of the same order contain a plurality of frequency components, which is equivalent to the superposition of a plurality of laser beams of different frequencies (of course, different intensities). Therefore, the optical beat wave can be obtained only by the diffracted light of the same order without the optical path adjustment as in the traveling wave method. Normally, the first order diffracted light is selected, and two frequency components, L being 1, m being 0, -1, are superimposed to obtain an optical beat wave, Δ ω being 2 Ω.
The phase-locked amplifier adopts weak signal detection equipment based on the orthogonality principle, and can measure the amplitude and the phase of an alternating current signal with the same frequency as a reference signal. It is mainly composed of a signal channel, a reference channel, a Phase Sensitive Detector (PSD) and an output circuit, as shown in fig. 5. The voltage magnitude is shown to be related to the phase difference between the output signal and the reference signal, and the ratio of the voltage outputs is the ratio of the cosine values.
Based on the above device, the present invention further provides a method for measuring the speed of light using a lock-in amplifier, the method comprising:
s11, connecting an instrument;
connecting the output end of the high-frequency signal generator to an acousto-optic frequency shifter;
the synchronous output end of the signal generator is connected to the reference signal input end of the phase-locked amplifier, and the photoelectric converter is connected to the signal input end to be detected;
s12, starting the instrument, and preheating for a preset time; preferably for 5 to 8 minutes.
The signal generator outputs a sine wave signal with the frequency of F, and a reference channel is set to be in a second harmonic mode, namely a 2F mode is detected; selecting preset measurement parameters;
s13, adjusting a phase shifter of the phase-locked amplifier to enable the signal output to be maximum when the reflector is at the initial position, and recording the maximum value V0;
s14, moving the reflector, and recording the output voltage V after moving and the moving distance delta S;
s15, obtaining the light speed data by the following formula:
and repeating the step S14, measuring preset group data from small to large distance, and taking an average value to obtain the measured light speed data. Preferably, the distances are measured from small to large in 10 groups and averaged.
In step S15, in order to achieve higher measurement accuracy, it is required that the phase change at least from 0 to one-half pi can be covered, and the measurement instrument needs to satisfy the conditions that c is 8FL, F is the frequency that can be output by the signal generator, and L is the maximum moving range of the optical path. The measurement precision is mainly related to the measurement precision of the lock-in amplifier and the measurement precision of the optical path.
The method uses the phase-locked amplifier to measure the speed of light, uses the acousto-optic frequency shifter to generate the optical beat, and uses the phase-locked amplifier to measure the phase change generated after the optical signal moves the path s, thereby measuring the speed of light. Compared with a beam splitting measurement method, the experimental instrument is simpler, the operation is simpler and more convenient, and the precision is higher.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (6)
1. A method of measuring the speed of light using a lock-in amplifier, the method comprising:
s11, connecting an instrument;
connecting the output end of the high-frequency signal generator to an acousto-optic frequency shifter;
the synchronous output end of the signal generator is connected to the reference signal input end of the phase-locked amplifier, and the photoelectric converter is connected to the signal input end to be detected;
s12, starting the instrument, and preheating for a preset time;
the signal generator outputs a sine wave signal with the frequency of F, and a reference channel is set to be in a second harmonic mode, namely a 2F mode is detected; selecting preset measurement parameters;
s13, adjusting a phase shifter of the phase-locked amplifier to enable the signal output to be maximum when the reflector is at the initial position, and recording the maximum value V0;
s14, moving the reflector, and recording the output voltage V after moving and the moving distance delta S;
s15, obtaining the light speed data by the following formula:
and repeating the step S14, measuring preset group data from small to large distance, and taking an average value to obtain the measured light speed data.
2. The method of measuring speed of light using a lock-in amplifier according to claim 1,
in the step S15, in the step S,
covering a phase change of 0 to one-half pi, the measuring instrument satisfies that c is 8FL, F is the frequency of the output of the signal generator, and L is the maximum moving range of the optical path.
3. An apparatus for measuring speed of light using a lock-in amplifier, comprising: the device comprises a high-frequency signal generator, an acousto-optic frequency shifter, a lock-in amplifier, a photoelectric converter and a reflector;
the output end of the high-frequency signal generator is connected with the acousto-optic frequency shifter;
the synchronous output end of the high-frequency signal generator is connected with the reference signal input end of the phase-locked amplifier;
the high-frequency signal generator sends out optical signals, and the optical signals are transmitted to the photoelectric converter after passing through the acousto-optic frequency shifter and the reflector;
the input end of the photoelectric converter receives an optical signal to be measured, performs photoelectric signal conversion on the optical signal to be measured, and transmits the optical signal to the phase-locked amplifier, and the phase-locked amplifier measures the phase change generated after the optical signal moves for a distance s to measure the optical speed.
4. The apparatus for measuring speed of light using a lock-in amplifier according to claim 3,
the lock-in amplifier includes: the device comprises an alternating current amplifier, a band-pass filter, a phase-sensitive detector, a low-pass filter, a direct current amplifier, a display, a reference signal receiving module and a square wave driving module;
the alternating current amplifier acquires an input signal transmitted by the photoelectric converter and transmits the input signal to the phase-sensitive detector through the band-pass filter;
the phase-sensitive detector is connected with the reference signal receiving module through the square wave driving module to obtain a reference signal; the phase sensitive detector processes the input signal and the reference signal, and transmits the processed input signal and the processed reference signal to the display after passing through the low-pass filter and the direct current amplifier in sequence.
5. The apparatus for measuring speed of light using a lock-in amplifier according to claim 3,
further comprising: the device comprises a controller, a driving motor, a bracket, a moving gear and a rack;
the reflector is arranged on the bracket;
the bracket is connected with the movable gear and is meshed with the rack through the movable gear;
the movable gear is connected with an output shaft of a driving motor, and the driving motor is connected with a controller;
the controller controls the driving motor to operate.
6. The apparatus for measuring speed of light using a lock-in amplifier according to claim 5,
the rack is provided with scale marks.
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| CN206740251U (en) * | 2017-04-01 | 2017-12-12 | 青海民族大学 | Beat frequency method light velocity analyzer |
| CN107845317A (en) * | 2017-09-19 | 2018-03-27 | 鲁东大学 | A kind of experimental method of the single channel photo-beat phase method measurement light velocity |
| CN107919913A (en) * | 2017-10-26 | 2018-04-17 | 中国科学院上海光学精密机械研究所 | Optical phase-locked loop device and phase-lock technique based on Direct Digital Synthesizer |
| CN110531103A (en) * | 2019-09-30 | 2019-12-03 | 浙江海洋大学 | A kind of light velocity measurement method and apparatus based on Lissajou's figure |
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2020
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| GB1436314A (en) * | 1972-09-27 | 1976-05-19 | Barr R | Apparatus for measuring the speed of light |
| US5162862A (en) * | 1990-02-13 | 1992-11-10 | Optical Metrology Limited | Lightspeed-related measurement apparatus |
| CN1945245A (en) * | 2006-10-19 | 2007-04-11 | 上海大学 | Method and system for measuring light speed in short optical path using optic and electric signal phase difference |
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| CN110531103A (en) * | 2019-09-30 | 2019-12-03 | 浙江海洋大学 | A kind of light velocity measurement method and apparatus based on Lissajou's figure |
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Address after: 250101 no.2877 Kehang Road, Suncun Town, high tech Zone, Jinan City, Shandong Province Applicant after: Chaoyue Technology Co.,Ltd. Address before: 250101 no.2877 Kehang Road, Suncun Town, high tech Zone, Jinan City, Shandong Province Applicant before: SHANDONG CHAOYUE DATA CONTROL ELECTRONICS Co.,Ltd. |
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| GR01 | Patent grant | ||
| GR01 | Patent grant |