Multi-pulse spectral interference optical frequency comb distance measuring device and method

Abstract

The invention relates to a multi-pulse spectral interference optical frequency comb distance measuring device and method, and the device comprises two Michelson interferometers, light emitted by an optical frequency comb is divided into two beams through a beam splitter, and the reflected light is reflected by a reference reflector through the beam splitter to serve as reference light; and the light transmitted by the beam splitter is reflected by the semi-transparent and semi-reflective mirror and the measurement reflector in sequence to serve as two pieces of measurement light. The reference light and the two measuring light can interfere with each other, a generated multi-pulse spectrum interference signal is detected and received by a spectrograph, the group refractive index and the distance measurement result in a measuring light path are synchronously determined by using phase information in the multi-pulse spectrum interference signal, the distance measurement result is compensated by using the group refractive index measured in real time, and the distance measurement result is obtained. The distance measurement precision of nanometer magnitude is ensured, and the measured distance can be expanded to any length from the non-fuzzy range of spectral interference distance measurement through fine tuning of the repetition frequency and differential calculation. The method is simple and reliable, and can realize wide-range high-precision absolute distance measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical frequency comb ranging, and in particular to an optical frequency comb ranging device and method of multi-pulse spectral interference. Background Art

[0002] The optical frequency comb is an ultrashort pulse of light with a pulse width of femtoseconds in the time domain, and millions of spectral lines with equal frequency intervals in the frequency domain. Every optical frequency it contains can be traced back to an atomic clock, giving the optical frequency comb a huge advantage in the field of absolute distance measurement and the potential to achieve large-scale and high-precision absolute distance measurement.

[0003] Although the measurement resolution of spectral interferometry is in the nanometer range, its unambiguous range is generally in the millimeter range. It needs to cooperate with multiple ranging technologies such as time-of-flight method and synthetic wavelength method to expand the ranging range, and the system is relatively complex.

[0004] The research on large-scale high-precision distance measurement technology is applied to the geometric value transfer and traceability system on the one hand, and to the actual industrial site, aerospace industry and other occasions on the other hand. Different from the high requirements of cleanliness, temperature and humidity in optical laboratories, the temperature, humidity, atmospheric pressure and other environmental conditions in outdoor environments or industrial sites are generally relatively harsh, resulting in drastic changes in the atmospheric refractive index. Taking multi-wavelength distance measurement technology as an example, for a measured distance of 1m, the fluctuation of the atmospheric refractive index will cause the distance measurement value to change by 10 -6 ~10 -7 Therefore, even if the ranging resolution reaches the nanometer level, the final ranging accuracy cannot be guaranteed. In order to be applicable to industrial sites or outdoor environments, it is of great research value and application prospect to study a simple system, large range, and high-precision arbitrary length absolute ranging technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and propose an optical frequency comb ranging device and method of multi-pulse spectral interference, which includes two equivalent Michelson interferometers, and uses the measurement light of the two Michelson interferometers to simultaneously perform multi-pulse spectral interference with the reference light, and can synchronously determine the group refractive index and ranging results in the measurement light path through the pseudo time domain. By fine-tuning the repetition frequency and differential calculation, the measured distance can be extended from the unambiguous range of traditional spectral interference ranging to any length.

[0006] The present invention solves the technical problem by adopting the following technical solutions: The invention discloses an optical frequency comb ranging device of multi-pulse spectral interference, comprising an optical frequency comb FC, a beam splitter BS, a reference reflector MR, a semi-transparent and semi-reflective mirror HM, a measuring reflector MT, a shading plate S1, a shading plate S2, a shading plate S3 and a spectrometer; the reference reflector MR, the beam splitter BS, the semi-transparent and semi-reflective mirror HM and the measuring reflector MT constitute two Michelson interferometers, the reference reflector MR, the beam splitter BS and the semi-transparent and semi-reflective mirror HM constitute a Michelson interferometer A, the reference reflector MR, the beam splitter BS and the measuring reflector MT constitute a Michelson interferometer B, the optical frequency comb FC, the beam splitter BS, the semi-transparent and semi-reflective mirror HM and the measuring reflector MT are arranged in sequence on the same horizontal plane, the reference reflector MR is arranged above the beam splitter BS, the spectrometer is arranged below the beam splitter BS, the shading plate S1 is arranged between the reference reflector MR and the beam splitter BS, the shading plate S2 is arranged between the semi-transparent and semi-reflective mirror HM and the beam splitter BS, and the shading plate S3 is arranged between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT.

[0007] Moreover, the spectrometer is also connected to a data processing computer. The spectrometer detects and receives a multi-pulse spectral interference signal generated after the reference light reflected by the reference mirror MR, the measurement light 1 reflected by the semi-transparent and semi-reflective mirror HM, and the measurement light 2 reflected by the measurement mirror MT are combined by the beam splitter BS. The spectrometer sends the measured signal to the data processing computer for processing.

[0008] A distance measurement method of an optical frequency comb distance measurement device using multi-pulse spectral interference, comprising the following steps: Step 1: Place the measuring reflector MT so that the distance difference between the two arms of the Michelson interferometer B is the distance to be measured. L ; Step 2: Calibrate the distance between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT to obtain the reference spacing. d ; Step 3: Open the shading plate S1, close the shading plate S2, and record the intensity of the light reflected by the reference reflector MR. ; Close the shading plate S1, open the shading plate S2, close the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM ; Close the shading plate S1, open the shading plate S2, open the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM and the measuring reflector MT ,Depend on and The intensity of the light reflected by the measuring reflector MT is calculated by the difference between ; Step 4: Calculate the time delay between measurement light 1 and measurement light 2 in the pseudo-time domain according to the light intensity obtained in step 3. , and the time delay of the two measurement beams relative to the reference beam and ; Step 5: Calculate the group refractive index based on the delay data obtained in step 4 ; Step 6: Calculate the measured distance based on the group refractive index obtained in step 5 L .

[0009] Moreover, in the step 1, the reference reflector MR and the beam splitter BS of the Michelson interferometer B form a reference arm, and the measuring reflector MT and the beam splitter BS form a measuring arm. The length difference between the measuring arm and the reference arm is the distance to be measured. L .

[0010] Moreover, the specific calculation method of step 4 is: ;

[0011] Moreover, the specific calculation method of step 5 is: according to the reference spacing between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT d With non-ambiguous range The numerical relationship between the two determines the actual time delay of the measurement light 2 relative to the measurement light 1 ; ; Where, is the actual time delay of measurement light 2 relative to measurement light 1, m is a natural number, is the unambiguous range of spectral interferometry, is the optical distance between adjacent pulses of the optical frequency comb, c is the speed of light in vacuum, is the repetition frequency of the optical frequency comb, To measure the group refractive index in the optical path; By calibrating the reference distance d Determine the time delay of measurement light 2 relative to measurement light 1 in vacuum ,contrast and Calculate the group refractive index of the actual measurement optical path ; .

[0012] Moreover, the specific calculation method of step 6 is: ； N is an integer multiple of the measured distance and the unambiguous range; is the pseudo time domain ranging result, , Determined by the peak position in the pseudo-time domain; Integer NBy fine-tuning the repetition rate of the optical frequency comb becomes Indicates that when N When is an even number, the measured distance is expressed as: ; Calculate the integer by difference N : ; when N When it is an odd number, the integer N The expression is ; Delay in determining time , group refractive index and integers N Then calculate the measured distance L The unique value of completes the absolute distance measurement.

[0013] The advantages and positive effects of the present invention are: The present invention comprises two equivalent Michelson interferometers, and the measurement light of the two Michelson interferometers is used to simultaneously generate multi-pulse spectral interference with the reference light, and the group refractive index and the distance measurement result in the measurement light path can be synchronously determined through the pseudo time domain. By fine-tuning the repetition frequency and differential calculation, the distance measurement range can be extended from the non-ambiguous range of traditional spectral interference distance measurement to any length. The present invention uses the group refractive index in the measurement light path calculated quickly to correct the distance measurement result in real time, and can ensure the distance measurement accuracy at the nanometer level. At the same time, the present invention uses the repetition frequency and differential calculation of the fine-tuning optical frequency comb to extend the measurement range from the non-ambiguous range of traditional spectral interference distance measurement to any length, thereby realizing large-size and high-precision distance measurement. The distance measurement method of the present invention is simple and reliable, has the characteristics of large size and high precision, and can be applied to absolute distance measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a structural principle diagram of an optical frequency comb ranging device of multi-pulse spectral interference according to the present invention; Figure 2 It is a schematic diagram of extracting three time delays using the pseudo time domain according to the present invention. DETAILED DESCRIPTION

[0015] The present invention is further described in detail below with reference to the accompanying drawings.

[0016] An optical frequency comb ranging device based on multi-pulse spectral interference, such as Figure 1As shown, it includes an optical frequency comb FC, a beam splitter BS, a reference mirror MR, a semi-transparent mirror HM, a measuring mirror MT, a shading plate S1, a shading plate S2, a shading plate S3 and a spectrometer; the reference mirror MR, the beam splitter BS, the semi-transparent mirror HM and the measuring mirror MT constitute two Michelson interferometers, the reference mirror MR, the beam splitter BS, the semi-transparent mirror HM constitute a Michelson interferometer A, the reference mirror MR, the beam splitter BS, the measuring mirror MT constitute a Michelson interferometer B, the optical frequency comb FC, the beam splitter BS, the semi-transparent mirror HM and the measuring mirror MT are arranged in sequence on the same horizontal plane, the reference mirror MR is arranged above the beam splitter BS, the spectrometer is arranged below the beam splitter BS, the shading plate S1 is arranged between the reference mirror MR and the beam splitter BS, the shading plate S2 is arranged between the semi-transparent mirror HM and the beam splitter BS, and the shading plate S3 is arranged between the semi-transparent mirror HM and the measuring mirror MT.

[0017] Moreover, the spectrometer is also connected to a data processing computer. The spectrometer detects and receives a multi-pulse spectral interference signal generated after the reference light reflected by the reference mirror MR, the measurement light 1 reflected by the semi-transparent and semi-reflective mirror HM, and the measurement light 2 reflected by the measurement mirror MT are combined by the beam splitter BS. The spectrometer sends the measured signal to the data processing computer for processing.

[0018] A distance measurement method of an optical frequency comb distance measurement device using multi-pulse spectral interference, comprising the following steps: Step 1: Place the measuring reflector MT so that the distance difference between the two arms of the Michelson interferometer B is the distance to be measured. L .

[0019] The reference reflector MR and beam splitter BS of Michelson interferometer B form a reference arm, and the measuring reflector MT and beam splitter BS form a measuring arm. The length difference between the measuring arm and the reference arm is the distance to be measured. L .

[0020] Step 2: Calibrate the distance between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT to obtain the reference spacing. d .

[0021] Step 3: Open the shading plate S1, close the shading plate S2, and record the intensity of the light reflected by the reference reflector MR. ; Close the shading plate S1, open the shading plate S2, close the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM ; Close the shading plate S1, open the shading plate S2, open the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM and the measuring reflector MT ,Depend on and The intensity of the light reflected by the measuring reflector MT is calculated by the difference between ; Step 4: Calculate the time delay between measurement light 1 and measurement light 2 in the pseudo-time domain according to the light intensity obtained in step 3. , and the time delay of the two measurement beams relative to the reference beam and , the pseudo time domain spectrum can be obtained by Fourier transforming the multi-pulse spectral interference signal; ; like Figure 2 As shown, the right side in the pseudo-time domain (i.e., when t>0) contains three pulses, corresponding to , and , and their strengths are , and , just ensure , which can be distinguished by the peak size , , The specific location.

[0022] Step 5: Calculate the group refractive index based on the delay data obtained in step 4 .

[0023] According to the reference distance d between the half-transparent mirror HM and the measuring mirror MT and the unambiguous range The numerical relationship between the two determines the actual time delay of the measurement light 2 relative to the measurement light 1 ; ; In the formula, is the actual time delay of measuring light 2 relative to measuring light 1, m is a natural number, is the unambiguous range of spectral interferometry, The optical distance between adjacent pulses of the optical frequency comb, c is the speed of light in vacuum, is the repetition frequency of the optical frequency comb, To measure the group refractive index in the optical path; By calibrating the reference distance d Determine the time delay of measurement light 2 relative to measurement light 1 in vacuum ,contrast and Calculate the group refractive index of the actual measurement optical path ; .

[0024] Step 6: Calculate the measured distance based on the group refractive index obtained in step 5L。

[0025] ； N is an integer multiple of the measured distance and the unambiguous range; is the pseudo time domain ranging result, , Determined by the peak position in the pseudo-time domain; integer N By fine-tuning the repetition rate of the optical frequency comb becomes Indicates that when N When is an even number, the measured distance is expressed as: ; Calculate the integer by difference N : ;when N When it is an odd number, the integer N The expression is ; Delay in determining time , group refractive index and integers N Then calculate the measured distance L The unique value of completes the absolute distance measurement.

Claims

1. An optical frequency comb ranging device based on multi-pulse spectral interference, characterized in that: It includes an optical frequency comb FC, a beam splitter BS, a reference mirror MR, a semi-transparent mirror HM, a measuring mirror MT, a shading plate S1, a shading plate S2, a shading plate S3 and a spectrometer; the reference mirror MR, the beam splitter BS, the semi-transparent mirror HM and the measuring mirror MT constitute two Michelson interferometers, the reference mirror MR, the beam splitter BS, the semi-transparent mirror HM and the measuring mirror MT constitute a Michelson interferometer A, the reference mirror MR, the beam splitter BS, and the measuring mirror MT constitute a Michelson interferometer B, the optical frequency comb FC, the beam splitter BS, the semi-transparent mirror HM and the measuring mirror MT are arranged in sequence on the same horizontal plane, the reference mirror MR is arranged above the beam splitter BS, the spectrometer is arranged below the beam splitter BS, the shading plate S1 is arranged between the reference mirror MR and the beam splitter BS, the shading plate S2 is arranged between the semi-transparent mirror HM and the beam splitter BS, and the shading plate S3 is arranged between the semi-transparent mirror HM and the measuring mirror MT.

2. The optical frequency comb ranging device of multi-pulse spectral interference according to claim 1, characterized in that: The spectrometer is also connected to a data processing computer. The spectrometer detects and receives a multi-pulse spectral interference signal generated after the reference light reflected by the reference mirror MR, the measurement light 1 reflected by the semi-transparent and semi-reflective mirror HM, and the measurement light 2 reflected by the measurement mirror MT are combined by the beam splitter BS. The spectrometer sends the measured signal to the data processing computer for processing.

3. A distance measurement method of the optical frequency comb distance measurement device of multi-pulse spectral interference according to any one of claims 1 to 2, characterized in that: The following steps are involved: Step 1: Place the measuring reflector MT so that the distance difference between the two arms of the Michelson interferometer B is the distance to be measured. L ; Step 2: Calibrate the distance between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT to obtain the reference spacing. d ; Step 3: Open the shading plate S1, close the shading plate S2, and record the intensity of the light reflected by the reference reflector MR. ; Close the shading plate S1, open the shading plate S2, close the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM ; Close the shading plate S1, open the shading plate S2, open the shading plate S3, and record the light intensity reflected by the semi-transparent and semi-reflective mirror HM and the measuring reflector MT ,Depend on and The intensity of the light reflected by the measuring reflector MT is calculated by the difference between ; Step 4: Calculate the time delay between measurement light 1 and measurement light 2 in the pseudo-time domain according to the light intensity obtained in step 3. , and the time delay of the two measurement beams relative to the reference beam and ; Step 5: Calculate the group refractive index based on the delay data obtained in step 4 ; Step 6: Calculate the measured distance based on the group refractive index obtained in step 5 L .

4. The distance measurement method of the optical frequency comb distance measurement device with multi-pulse spectroscopy according to claim 3 is characterized in that: In the step 1, the reference reflector MR and the beam splitter BS of the Michelson interferometer B form a reference arm, and the measuring reflector MT and the beam splitter BS form a measuring arm. The length difference between the measuring arm and the reference arm is the distance to be measured. L .

5. The distance measurement method of the optical frequency comb distance measurement device of multi-pulse spectral interference according to claim 3 is characterized in that: The specific calculation method of step 4 is: 。 6. The distance measurement method of the optical frequency comb distance measurement device of multi-pulse spectral interference according to claim 3 is characterized in that: The specific calculation method of step 5 is: based on the reference spacing between the semi-transparent and semi-reflective mirror HM and the measuring reflector MT d With non-ambiguous range The numerical relationship between them determines the actual time delay of the measurement light 2 relative to the measurement light 1 ; ； Where, is the actual time delay of measurement light 2 relative to measurement light 1, m is a natural number, is the unambiguous range of spectral interferometry, is the optical distance between adjacent pulses of the optical frequency comb, c is the speed of light in vacuum, is the repetition frequency of the optical frequency comb, To measure the group refractive index in the optical path; By calibrating the reference distance d Determine the time delay of measurement light 2 relative to measurement light 1 in vacuum ,contrast and Calculate the group refractive index of the actual measurement optical path ; .

7. The distance measurement method of the optical frequency comb distance measurement device of multi-pulse spectral interference according to claim 3 is characterized in that: The specific calculation method of step 6 is: ； N is an integer multiple of the measured distance and the unambiguous range; is the pseudo time domain ranging result, , Determined by the peak position in the pseudo-time domain; Integer N By fine-tuning the repetition rate of the optical frequency comb becomes Indicates that when N When is an even number, the measured distance is expressed as: ； Calculate the integer by difference N : ； when N When it is an odd number, the integer N The expression is ； Delay in determining time , group refractive index and integers N Then calculate the measured distance L The unique value of completes the absolute distance measurement.

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