JP2017044565A - Distance measurement device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement device and method that suppress an influence of a measurement error of an optical length, and can measure a correct distance, excluding an influence of an air fluctuation of a measurement environment.SOLUTION: A distance measurement method is configured to: coaxially mix white light having a first center wavelength, and white light having a second center wavelength different from the first center wavelength; divide the coaxially mixed white light into reference light to be incident upon a reference mirror and measurement light to be incident upon a length measurement target; and calculate a geometric length to a measured surface on the basis of a first optical length calculated from interference light of the first center wavelength of the interference light having respective measurement light synthesized, a second optical length calculated from interference light of the second wavelength thereof, and a correction coefficient based on a group refractive index of first air in the first center wavelength, and a group refractive index of second air in the second center wavelength.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measuring apparatus and method, and more particularly to a technique for measuring distance while eliminating the influence of a measurement environment.

  2. Description of the Related Art Conventionally, an interferometer is known in which a CW (Continuous wave) coherent laser is incident on an interferometer as a light source and the distance to a measurement object is obtained by counting formed interference fringes. Such an interferometer has a drawback that the influence of atmospheric fluctuations is strong, interference fringes occur, and the measurement error is large.

  On the other hand, Patent Document 1 calculates the geometric distance to the target by correcting the optical distances measured by the light waves of two wavelengths with the correction coefficient obtained from the refractive index at each wavelength. It is described that a length measurement error due to a change in refractive index does not occur by using a wavelength interferometer.

JP2015-75461A

  In Patent Document 1, the measurement error with respect to the geometric distance by the two-wavelength interferometer is determined by the product of the difference between the optical distances measured by the light waves of two wavelengths and the correction coefficient. Here, since the correction coefficient obtained from the refractive index of the CW coherent laser has a large value, in order to make the measurement error of the geometric distance sufficiently small, it is required to increase the measurement accuracy of the optical distance. Is done. However, it is difficult to improve measurement accuracy due to various error factors.

  The present invention has been made in view of such circumstances, and is capable of measuring an accurate distance by suppressing the influence of an optical length measurement error and eliminating the influence of air fluctuation in the measurement environment. An object is to provide an apparatus and a method thereof.

  In order to achieve the above object, one aspect of the distance measuring device includes a first light source that emits first white light having a first center wavelength, and a second center wavelength that is different from the first center wavelength. A second light source that emits the second white light, a mixing unit that mixes the first white light and the second white light, the mixed light is branched in two directions, and one reference light is The interference light that is incident on the reflection surface of the reference mirror and the other measurement light is incident on the measurement target surface of the measurement object and combines the reference reflection light reflected on the reflection surface and the measurement reflection light reflected on the measurement surface. Interference light generation means for generating, scanning means for changing the optical path length of the reference light, and interference light into a first interference light having a first center wavelength and a second interference light having a second center wavelength. Separating means for separating and a first interference signal that receives the first interference light and that corresponds to the intensity of the first interference light The first detection means for outputting, the second detection means for receiving the second interference light and outputting the second interference signal according to the intensity of the second interference light, and changing the optical path length of the reference light However, the acquisition means for acquiring the first interference signal and the second interference signal, and the first optical length to the surface to be measured based on the relationship between the optical path length of the reference light and the first interference signal An optical length calculation means for calculating the second optical length to the surface to be measured based on the relationship between the optical path length of the reference light and the second interference signal, and the group refractive index of the air A correction coefficient for calculating the geometric length to the surface to be measured excluding the influence, the group index of refraction of the first air at the first central wavelength and the second air at the second central wavelength Correction coefficient acquisition means for acquiring a correction coefficient based on the group refractive index, first optical length, second optical length, and correction coefficient A geometrical length calculating means for calculating a geometrical length based on, with a.

  According to this aspect, the first optical length measured using the first white light having the first center wavelength and the second optical length measured using the second white light having the second center wavelength. And a correction coefficient based on the first air group refractive index at the first central wavelength and the second air group refractive index at the second central wavelength. Since the geometric length of the sensor is calculated, a relatively small correction factor is used to suppress the effect of optical length measurement errors, and the effect of air fluctuations in the measurement environment is eliminated to measure the exact distance. can do.

  The correction coefficient acquisition means preferably includes storage means for storing the correction coefficient. Thereby, a correction coefficient can be acquired appropriately.

  The correction coefficient acquisition means is a reference member disposed in the optical path of the measurement light, the reference member disposed at a position where the reference surface is a known optical path length of the measurement light, and changing the optical path length of the reference light The first interference signal and the second interference signal are acquired, the third optical length to the reference plane is calculated based on the first interference signal, and the reference plane is calculated based on the second interference signal. A reference surface optical length calculation means for calculating the fourth optical length of the optical signal, a correction coefficient for calculating a correction coefficient based on the third optical length, the fourth optical length, and the known optical path length And a calculating means. Thereby, a correction coefficient can be acquired appropriately.

  An etalon disposed in the optical path of each of the first white light and the second white light, or the optical path of interference light, and a half mirror having a semi-reflective surface that reflects part of the measurement light and transmits part of the measurement light Preferably, the interference light generation unit generates interference light by combining the reference reflected light, the measurement reflected light, and the standard reflected light reflected by the semi-reflecting surface. Thereby, even when the optical path length of the measurement light becomes long, it is possible to measure an accurate distance by eliminating the influence of air fluctuation in the measurement environment.

  In order to achieve the above object, one aspect of the distance measurement method includes a first white light having a first center wavelength and a second white light having a second center wavelength different from the first center wavelength. Mixing step, and the mixed light is branched in two directions, one reference light is incident on the reflection surface of the reference mirror and the other measurement light is incident on the surface to be measured of the measurement object. An interference light generation step for generating interference light by combining the reflected reference reflected light and the measurement reflected light reflected by the surface to be measured; a first interference light having a first center wavelength; and a second center. A separation step of separating the second interference light having a wavelength, a first detection step of receiving the first interference light and outputting a first interference signal according to the intensity of the first interference light; A second detection that receives the second interference light and outputs a second interference signal according to the intensity of the second interference light. Measurement step based on the relationship between the step, the acquisition step of acquiring the first interference signal and the second interference signal while changing the optical path length of the reference light, and the optical path length of the reference light and the first interference signal An optical length for calculating the first optical length to the surface and calculating the second optical length to the surface to be measured based on the relationship between the optical path length of the reference light and the second interference signal A calculation step and a correction coefficient for calculating the geometric length to the surface to be measured, the group refractive index of the first air at the first central wavelength and the second air at the second central wavelength A correction coefficient acquiring step for acquiring a correction coefficient based on the group refractive index of the first optical length, a geometric length for calculating a geometric length based on the first optical length, the second optical length, and the correction coefficient A length calculation step.

  According to this aspect, the first optical length measured using the first white light having the first center wavelength and the second optical length measured using the second white light having the second center wavelength. And a correction coefficient based on the first air group refractive index at the first central wavelength and the second air group refractive index at the second central wavelength. Since the geometric length of the sensor is calculated, a relatively small correction factor is used to suppress the effect of optical length measurement errors, and the effect of air fluctuations in the measurement environment is eliminated to measure the exact distance. can do.

  According to the present invention, it is possible to measure an accurate distance by suppressing the influence of an optical length measurement error and eliminating the influence of air fluctuation in the measurement environment.

The block diagram which showed the whole structure of the distance measuring device which concerns on 1st Embodiment Flow chart showing distance measurement processing by the distance measuring device The figure which shows the relationship between the wavelength of the light memorize | stored in memory, and the group refractive index of air The block diagram which showed the whole structure of the distance measuring device which concerns on 2nd Embodiment. The block diagram which showed the whole structure of the distance measuring device which concerns on 3rd Embodiment. Schematic showing the internal structure of the etalon Diagram showing optical frequency components emitted from the etalon The block diagram which showed the whole structure of the distance measuring device which concerns on 4th Embodiment

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a configuration diagram showing the overall configuration of the distance measuring apparatus according to the first embodiment.

  The distance measuring device 10 is a distance measuring device using a Michelson interferometer as an interference optical system. As shown in FIG. 1, the first broad spectrum light source 12, the first collimator lens 14, the second broad spectrum light source 16, Second collimator lens 18, first dichroic beam splitter 20, beam splitter 22, scanning stage 24, reference mirror 26, second dichroic beam splitter 28, first photodetector 30, second photodetector 32, optical length A calculation unit 34, a geometric length calculation unit 36, a memory 38, and the like are provided.

  The first broad spectrum light source 12 (an example of a first light source) is a device that emits white light (an example of first white light) having a center wavelength of 0.4 [μm], and is an SLD (an example of a first light source). Super Luminescent Diode (ASE), ASE (Amplified Spontaneous Emission), SOA (Semiconductor Optical Amplifier) light source, etc. can be used.

  The second broad spectrum light source 16 (an example of the second light source) is white light (an example of the second white light) having a center wavelength of the second central wavelength 0.8 [μm] (an example of the second central wavelength). Similarly to the first broad spectrum light source 12, an SLD, ASE, SOA light source, or the like can be used.

  The first collimator lens 14 and the second collimator lens 18 are optical elements that convert incident light into parallel light.

  The first dichroic beam splitter 20 reflects light having a wavelength shorter than the cutoff wavelength (for example, 0.6 [μm]) incident from one side in the orthogonal direction and transmits light having a wavelength longer than the cutoff wavelength incident from the other side. By doing so, it is an optical element that mixes both lights coaxially. Here, the light incident on the first dichroic beam splitter 20 from the first collimator lens 14 and the light incident on the first dichroic beam splitter 20 from the second collimator lens 18 are arranged so that their optical axes are perpendicular to each other. A first collimator lens 14 and a second collimator lens 18 are disposed.

  The beam splitter 22 is an optical element that divides incident light and synthesizes each reflected light of the branched light.

The scanning stage 24 is configured to be able to scan in a direction in which the optical path length of the reference light incident on the reference mirror 26 fixed to the scanning stage 24 is increased or decreased. As a drive source for scanning the scanning stage 24, for example, a PZT (Pb (Zr1-xTix) O ₃ ) actuator can be used. The reference mirror 26 is a reflecting member having a reflecting surface 26a that reflects incident light.

  The second dichroic beam splitter 28 reflects light having a wavelength shorter than the cutoff wavelength (for example, 0.6 [μm]) in the orthogonal direction, and transmits light having a wavelength longer than the cutoff wavelength. The optical element for separating incident light.

  The first photodetector 30 and the second photodetector 32 receive the input interference light, generate an interference signal that is an electrical signal according to the intensity of the received interference light, and optically generate the generated interference signal. To the target length calculator 34.

  The optical length calculator 34 controls a drive source that scans the scanning stage 24 and changes the optical path length of the reference light. Further, each interference signal corresponding to the optical path length of the reference light is acquired from the first photodetector 30 and the second photodetector 32, and the length measurement target is obtained based on the interference signal output from the first photodetector 30. 1 (an example of an object to be measured) of the first optical length to the measured surface 1a is calculated, and the second optical distance to the measured surface 1a is calculated based on the interference signal output from the second photodetector 32. Calculate the optical length.

  The geometric length calculation unit 36 is based on the first optical length and the second optical length calculated by the optical length calculation unit 34, and the geometric length to the surface 1a to be measured. Is calculated. The geometric length calculation unit 36 includes a memory 38. The memory 38 is a non-volatile memory, and stores data necessary for calculating the geometric length in addition to a correction coefficient described later.

  FIG. 2 is a flowchart illustrating distance measurement processing (an example of a distance measurement method) performed by the distance measurement device.

  The light having the first central wavelength emitted from the first broad spectrum light source 12 is incident on the first collimator lens 14, is formed into parallel light in the first collimator lens 14, propagates in the air, and is transmitted through the first dichroic beam splitter. 20 is incident.

  On the other hand, light having a center wavelength emitted from the second broad spectrum light source 16 is incident on the second collimator lens 18, is formed into parallel light in the second collimator lens 18, propagates in the air, and travels through the first dichroic. The light enters the beam splitter 20.

  The first dichroic beam splitter 20 (an example of a mixing unit) reflects the light emitted from the first collimator lens 14 in the orthogonal direction and transmits the light emitted from the second collimator lens 18, thereby allowing the first collimator lens. The light emitted from 14 and the light emitted from the second collimator lens 18 are mixed coaxially (step S1, an example of a mixing step).

  The light mixed by the first dichroic beam splitter 20 enters the beam splitter 22.

  The beam splitter 22 splits the incident light into two directions, an orthogonal direction and a straight traveling direction, and makes the reference light, which is one of the branched lights (here, the light in the orthogonal direction), incident on the reference mirror 26, and after being branched. The measurement light, which is the other light (here, the light traveling in the straight direction), enters the length measurement target 1 (step S2).

  The reference light that has entered the reflecting surface 26a of the reference mirror 26 from the beam splitter 22 is reflected by the reflecting surface 26a and is incident on the beam splitter 22 again as reference reflected light. Further, the measurement light incident on the measurement target surface 1a of the length measurement target 1 from the beam splitter 22 is reflected by the measurement target surface 1a, and enters the beam splitter 22 again as measurement reflected light.

  The beam splitter 22 (an example of an interference light generating unit) transmits the reference reflected light in the straight direction and reflects the measurement reflected light in the orthogonal direction to synthesize the reference reflected light and the measured reflected light on the same axis, thereby causing interference. Light is generated (step S3, an example of an interference light generation process). At this time, the optical length calculator 34 scans the scanning stage 24 (an example of a scanning unit), and the optical path length of the reference light is changed (an example of a scanning process). The beam splitter 22 causes the interference light to enter the second dichroic beam splitter 28.

  The second dichroic beam splitter 28 (an example of a separating unit) separates the incident interference light into first interference light in a wavelength region including the first center wavelength and second interference light in a wavelength region including the second center wavelength. The first interference light is incident on the first photodetector 30 and the second interference light is incident on the second photodetector 32 (step S4, an example of a separation step).

  The first photodetector 30 (an example of the first detection unit) on which the first interference light is incident outputs a first interference signal corresponding to the intensity of the incident first interference light to the optical length calculation unit 34. (An example of a first detection step).

  Similarly, the second optical detector 32 (an example of the second detection unit) on which the second interference light is incident has an optical length calculation unit that generates a second interference signal corresponding to the intensity of the incident second interference light. 34 (an example of a second detection step).

The optical length calculation unit 34 (an example of an acquisition unit, an example of an optical length calculation) acquires the first interference signal and the second interference signal while changing the optical path length of the reference light (Step S5, acquisition). Example of process). Then, the relationship between the optical path length of the reference light and the first interference signal is obtained, the peak of the envelope of the first interference signal is obtained, and the first optical length L ₁ from the obtained peak to the measured surface 1a is obtained. calculate. Similarly, the relationship between the optical path length of the reference light and the second interference signal is obtained, the peak of the envelope of the second interference signal is obtained, and the second optical length L ₂ from the obtained peak to the measured surface 1a. Is calculated (step S6, an example of an optical length calculation step).

  In addition, the geometric length calculation unit 36 (an example of a correction coefficient acquisition unit) has a geometric length from the memory 38 (an example of a storage unit) to the measured surface 1a that excludes the influence of the group refractive index of air. The first group refractive index (an example of the first air group refractive index) at the first central wavelength of air and the second group refractive index (second second) at the second central wavelength. The A coefficient (an example of the correction coefficient) based on the air group refractive index) is read out (step S7, an example of the correction coefficient acquisition step).

Here, when the group refractive index of air in the light of wavelength α [μm] is _ng1 and the group refractive index of air in the light of wavelength β [μm] is _ng2 , the A coefficient is expressed by the following formula 1. The
A = (n _g1 −1) / (n _g1 −n _g2 ) (Formula 1)

FIG. 3 is a diagram showing the relationship between the wavelength of light and the group index of air. From FIG. 3, the first group refractive index n _g1 = 1.0000300 for the light having the first central wavelength of 0.4 [μm] and the second for the light having the second central wavelength of 0.8 [μm]. It can be seen that the group refractive index n _g2 = 1.000275. Therefore, the A coefficient here is from Equation 1,
A = 12.0
It can be asked. The A coefficient is stored in the memory 38 in advance.

  The relationship between the wavelength of light and the group refractive index of air shown in FIG. 3 and the above equation 1 are stored in the memory 38, and the geometric length calculation unit 36 stores the first broad spectrum light source 12. The A coefficient corresponding to the wavelength and the wavelength of the second broad spectrum light source 16 may be calculated.

Finally, geometric length calculation unit 36 calculates the geometric length D from the first optical length L ₁ to the measurement surface 1a in which the influence of the group refractive index of air (step S8 An example of a geometric length calculation step). The geometric length D is expressed by the following formula 2.
D = L ₁ −A × (L ₁ −L ₂ ) (Formula 2)

The air fluctuation in the measurement environment even when the group refractive index n _g1 of the air in the light of the first central wavelength and the group index n _g2 of the air in the light of the second center wavelength is changed, A coefficient of It is a constant value with fluctuations offset. Therefore, the geometric length D calculated by Equation 2 is not affected by the fluctuation of the group refractive index of air due to air fluctuation.

  In this way, white light mixed with a plurality of white lights having different center wavelengths is incident on the Michelson interferometer, the optical length at each center wavelength is calculated, and this optical length is calculated at each center. By correcting with the A coefficient using the group refractive index of air at the wavelength, even if there are air fluctuations in the optical path of the reference light and the optical path of the measuring light, the influence of fluctuations in the group refractive index is appropriately eliminated to be measured The geometric length to the surface can be measured accurately.

  Here, as shown in Expression 2, the accuracy of the geometric length D depends on the A coefficient, and therefore, it is preferable that the A coefficient is small. In order to reduce the A coefficient, it is necessary to increase the difference in group refractive index as shown in Equation 1, and to increase the difference in group refractive index, as shown in FIG. What is necessary is just to enlarge the difference of a wavelength. In this embodiment, as a result of using white light with a center wavelength of 0.4 [μm] and white light with a center wavelength of 0.8 [μm] as the light source, the A coefficient was 12.0. Patent Document 1 describes that the A coefficient using the phase refractive index of laser light having wavelengths of 1550 [nm] and 633 [nm] is about 83, respectively. The A coefficient can be reduced.

  In the present embodiment, since the A coefficient is 12.0, if the difference in optical length can be measured with an accuracy of 4 [nm], the geometric length can be measured with a resolution of 48 [nm]. Can be measured. Thus, since the A coefficient is relatively small, the geometric length can be obtained with high accuracy, and the group refractive index of air can be automatically corrected regardless of the measurement distance.

  Since the amount of change in the group refractive index of air with respect to the wavelength of white light is several tens [ppm] or less, the scanning amount of the reference mirror 26 in the scanning stage 24 is sufficient to be about several [mm].

<Second Embodiment>
In the first embodiment, the A coefficient stored in the memory 38 is used. However, the distance to the reference member arranged at a position where the distance (geometric length) is known in advance is measured, and the measurement result is obtained. The A coefficient calculated from the above may be used.

  FIG. 4 is a configuration diagram showing the overall configuration of the distance measuring apparatus according to the second embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the block diagram shown in FIG. 1, and the detailed description is abbreviate | omitted.

  The distance measuring device 40 is different from the distance measuring device 10 shown in FIG. 1 in that it does not include the memory 38 and includes a half mirror 42 in the optical path of the measuring light.

The half mirror 42 is a semi-reflective member having a semi-reflective surface 42a that transmits a part of incident light and reflects a part thereof. The half mirror 42 is disposed at a position where the distance (the optical path length of the measurement light) from the beam splitter 22 to the semi-reflecting surface 42a (an example of a reference surface) is a known distance. Here, the distance from the beam splitter 22 to the semi-reflecting surface 42a and _{D 0.}

In the distance measuring device 40 configured as described above, the optical length calculation unit 34 (an example of the reference surface optical length calculation unit) includes a wavelength region including the first center wavelength while changing the optical path length of the reference light. A first interference signal corresponding to the intensity of the first interference light and a second interference signal corresponding to the intensity of the second interference light in a wavelength region including the second center wavelength are obtained, and half of the first interference signal is obtained based on the first interference signal. calculating a third optical length L ₃ to the reflecting surface 42a, and calculates a fourth optical length L ₄ to the semi-reflecting surface 42a on the basis of the second interference signal.

Next, the geometric length calculation unit 36 (an example of a correction coefficient calculation unit) sets the third optical length L ₃ to L ₁ in Equation ₂ and the fourth optical length L ₄ to L _2. Substituting D ₀ into the geometric length D, the A coefficient is calculated.

Thus calculated A coefficients by air fluctuations in the measurement environment in case of the group index n _g1 of the air in the light of the first central wavelength and the group index n _g2 of the air in the light of the second center wavelength is fluctuated Even if it exists, it becomes a fixed value in which these fluctuations are offset. By performing the same processing as in the first embodiment using the A coefficient, it is possible to accurately measure the geometric length that is not affected by the variation in the group refractive index. Moreover, according to this embodiment, the non-volatile memory for memorize | storing A coefficient becomes unnecessary.

  In the present embodiment, the half mirror 42 having the semi-reflective surface 42a is used as a reference member that is arranged in advance at a position where the optical path length of the measurement light is known, but a member having a total reflection surface may be used. In this case, the A coefficient may be inserted into the optical path of the measurement light, and may be configured to retract from the optical path when measuring the geometric length D to the measured surface 1a.

<Third Embodiment>
FIG. 5 is a configuration diagram showing the overall configuration of the distance measuring apparatus according to the third embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the block diagram shown in FIG. 1, and the detailed description is abbreviate | omitted.

  As shown in FIG. 5, the distance measuring device 50 includes a first etalon 52, a second etalon 54, and a half mirror 56 in addition to the configuration of the distance measuring device 10.

  The first etalon 52 is an optical element that transmits and emits multi-wavelength (multi-frequency) light components having a constant repetition frequency interval in incident light.

  FIG. 6 is a schematic diagram showing the internal configuration of the first etalon 52. As shown in the figure, the first etalon 52 is a fiber-type Fabry-Perot interference system in which the inter-interference distance is fixed, and is a reflecting portion composed of a first reflecting plate 72A and a second reflecting plate 72B that are spaced apart from each other. 72 and a reflection region 74 between the first reflection plate 72A and the second reflection plate 72B.

  The reflection area 74 is an area where incident light repeats reflection between the first reflection plate 72A and the second reflection plate 72B, and is composed of an optical fiber. Here, the optical length of the reflection region 74 is set to about 150 [mm].

  When light is incident on the first etalon 52, the incident light is repeatedly reflected between the reflecting portions 72, a specific wavelength component (frequency component) is strengthened by the interference effect, and is transmitted through the second reflecting plate 72B to be transmitted to the first etalon 52. Emanates from.

  FIG. 7 is a diagram illustrating optical frequency components emitted from the first etalon 52, where the horizontal axis represents frequency and the vertical axis represents transmitted light intensity. As shown in the figure, the first etalon 52 outputs light having a repetition frequency Λ of 1 [GHz]. That is, the first etalon 52 functions as a pseudo optical comb having a repetition frequency of 1 [GHz]. The envelope of the optical frequency component of the first etalon 52 depends on the group refractive index of air.

  The configuration of the second etalon 54 is the same as that of the first etalon 52 shown in FIG. In this embodiment, the fiber-type Fabry-Perot etalon is used as the first etalon 52 and the second etalon 54, but a spatial-type Fabry-Perot etalon may be used.

  The half mirror 56 is a semi-reflective member having a semi-reflective surface 56a that transmits a part of incident light and reflects a part thereof. The half mirror 56 is an optical path of measurement light, and is disposed at a position where the distance from the beam splitter 22 to the semi-reflective surface 56a is a known distance.

  The operation of the distance measuring device 50 configured as described above will be described.

  The light emitted from the first broad spectrum light source 12 enters the first etalon 52, and is converted into white pulse light having the optical frequency component shown in FIG. The white pulsed light emitted from the second reflecting plate 72B of the first etalon 52 is incident on the first collimator lens 14, is formed into parallel light in the first collimator lens 14, propagates through the air, and enters the first dichroic beam splitter 20. Incident.

  Further, the light emitted from the second broad spectrum light source 16 enters the second etalon 54, and is converted into white pulse light having the optical frequency component shown in FIG. The white pulse light emitted from the second reflection plate 72B of the second etalon 54 is incident on the second collimator lens 18, is formed into parallel light in the second collimator lens 18, propagates through the air, and enters the first dichroic beam splitter 20. Incident.

  The first dichroic beam splitter 20 coaxially mixes the white pulse light emitted from the first collimator lens 14 and the white pulse light emitted from the second collimator lens 18, and emits the mixed light to the beam splitter 22.

  The beam splitter 22 branches the incident white pulse light, and makes the reference light which is one of the branched white pulse lights incident on the reflection surface 26 a of the reference mirror 26. The reference light that has entered the reflecting surface 26a is reflected by the reflecting surface 26a and enters the beam splitter 22 again as reference reflected light.

  Further, the beam splitter 22 causes the measurement light, which is the other white pulse light after branching, to enter the half mirror 56.

  The half mirror 56 causes a part of the incident measurement light to enter the measurement target surface 1 a of the length measurement target 1. The measurement light incident on the measurement target surface 1a is reflected by the measurement target surface 1a and is incident on the beam splitter 22 again as measurement reflection light. The half mirror 56 reflects a part of the incident measurement light on the semi-reflecting surface 56 a and makes the reflected reference reflected light enter the beam splitter 22.

  The beam splitter 22 combines the standard reflected light, the measurement reflected light, and the reference reflected light on the same axis to generate interference light. The beam splitter 22 causes the interference light to enter the second dichroic beam splitter 28.

  The second dichroic beam splitter 28 separates the incident interference light into first interference light in a wavelength region including the first center wavelength and second interference light in a wavelength region including the second center wavelength, and the first interference light. Is incident on the first photodetector 30 and is incident on the second photodetector 32 via the second interference light.

  The first photodetector 30 outputs a first interference signal corresponding to the intensity of the incident first interference light to the optical length calculation unit 34, and the second photodetector 32 detects the incident second interference light. The second interference signal corresponding to the intensity is output to the optical length calculator 34.

The optical length calculation unit 34 acquires the first interference signal and the second interference signal while changing the optical path length of the reference light. Then, based on the interference signal of the interference light between the reference reflected light and the reference reflected light among the first interference signals, the first optical from the interference signal of the interference light of the measurement reflected light and the reference reflected light to the surface to be measured 1a. It calculates the length _{L 1.} Similarly, based on the interference signal of the interference light between the reference reflected light and the reference reflected light among the second interference signals, the second interference signal from the interference light of the measurement reflected light and the reference reflected light to the second surface to be measured 1a. calculating the optical length L _2.

The first optical length L ₁ and the second optical length L ₂ is input geometrical length calculation unit 36, the built-in reading out the A coefficient from the memory 38, A coefficient, the first optical The length L ₁ and the second optical length L ₂ are substituted into Equation 2, and the geometric length D to the measurement target surface 1 a of the length measurement target 1 is calculated.

  In this way, a plurality of white lights each having a different center wavelength are modulated into white pulse light having a repetition frequency using an etalon, mixed coaxially, and incident on a Michelson interferometer. By calculating the length and correcting this optical length with the A coefficient using the group refractive index of air at each central wavelength, even if there are air fluctuations in the optical path of the reference light and the optical path of the measurement light, the group It is possible to accurately measure the geometric length to the surface to be measured without being affected by the change in refractive index.

  In this embodiment, by using white pulse light, it is possible to measure even when the optical path length of the measurement light is longer than the optical path length of the reference light. As the optical path length of the measurement light becomes longer, the influence of air fluctuation increases, but according to this embodiment, the distance can be accurately measured without the influence of the group refractive index of air.

  For the estimation of the refractive index of air, it is only necessary that the difference in the characteristics of the first etalon 52 and the second etalon 54 be stable and accurate, so that measurement with higher accuracy is possible.

  In the present embodiment, the A coefficient is obtained from the memory 38, but as in the second embodiment, the optical length to the semi-reflective surface 56a is measured using the semi-reflective surface 56A of the half mirror 56 as a reference surface, The A coefficient may be calculated from the measurement result.

<Fourth Embodiment>
FIG. 8 is a configuration diagram showing the overall configuration of the distance measuring apparatus according to the third embodiment. In addition, the same code | symbol is attached | subjected to the part which is common in the block diagram shown in FIG.1 and FIG.5, and the detailed description is abbreviate | omitted.

  As shown in FIG. 8, the distance measuring apparatus 60 includes a third etalon 58 in the optical path of the interference light.

  The third etalon 58 is a spatial Fabry-Perot etalon that transmits and emits multi-wavelength light components having a fixed repetition frequency interval in incident light, and the repetition frequency Λ is 1.5 [GHz]. Output light. The third etalon 58 may be a fiber type Fabry-Perot etalon.

  The interference light generated by the beam splitter 22 enters the third etalon 58. The third etalon 58 outputs the incident interference light as interference light having a repetition frequency Λ of 1.5 [GHz]. This interference light is incident on the second dichroic beam splitter 28.

  The following operations are the same as those of the distance measuring device 50 according to the third embodiment.

  As described above, even when the etalon is arranged in the optical path of the interference light, the measurement can be performed even when the optical path length of the measurement light is longer than the optical path length of the reference light. According to the present embodiment, the apparatus can be simplified because it can be configured by one etalon.

  In the embodiment of the present invention described above, the configuration requirements can be appropriately changed, added, and deleted without departing from the spirit of the present invention. The present invention is not limited to the embodiments described above, and many modifications are possible by those having ordinary knowledge in the field within the technical idea of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Measurement target, 1a ... Measuring surface, 10, 40, 50 ... Distance measuring device, 12 ... 1st broad spectrum light source, 14 ... 1st collimator lens, 16 ... 2nd broad spectrum light source, 18 ... 2nd collimator Lens 20... First dichroic beam splitter 22. Beam splitter 24. Scanning stage 26 Reference mirror 26 a Reflecting surface 28 Second dichroic beam splitter 30 First photo detector 32 Second Optical detector 34... Optical length calculator 36. Geometric length calculator 38. Memory 42 and 56 Half mirror 42 a and 56 a Semi-reflective surface 52 52 First etalon 54. 2nd etalon, 58 ... 3rd etalon

Claims (5)

A first light source that emits first white light having a first central wavelength;
A second light source that emits second white light having a second center wavelength different from the first center wavelength;
Mixing means for mixing the first white light and the second white light;
The mixed light is branched in two directions, one reference light is incident on the reflection surface of the reference mirror, the other measurement light is incident on the surface to be measured of the measurement object, and the reference reflected light reflected by the reflection surface And interference light generation means for generating interference light by combining the measurement reflected light reflected by the surface to be measured,
Scanning means for changing the optical path length of the reference light;
Separating means for separating the interference light into first interference light having the first center wavelength and second interference light having the second center wavelength;
First detection means for receiving the first interference light and outputting a first interference signal corresponding to the intensity of the first interference light;
Second detection means for receiving the second interference light and outputting a second interference signal corresponding to the intensity of the second interference light;
Obtaining means for obtaining the first interference signal and the second interference signal while changing an optical path length of the reference light;
A first optical length to the measurement surface is calculated based on a relationship between the optical path length of the reference light and the first interference signal, and the optical path length of the reference light and the second interference signal are calculated. An optical length calculating means for calculating a second optical length to the surface to be measured based on the relationship:
A correction coefficient for calculating a geometric length to the surface to be measured excluding the influence of the group refractive index of air, the first group refractive index of the first air at the first central wavelength and the first Correction coefficient acquisition means for acquiring a correction coefficient based on the group refractive index of the second air at the center wavelength of 2;
Geometric length calculation means for calculating the geometric length based on the first optical length, the second optical length, and the correction coefficient;
Distance measuring device with   The distance measuring apparatus according to claim 1, wherein the correction coefficient acquisition unit includes a storage unit that stores the correction coefficient. The correction coefficient acquisition means is
A reference member disposed in the optical path of the measurement light, the reference member disposed at a position where the reference surface is a known optical path length of the measurement light;
The first interference signal and the second interference signal are acquired while changing the optical path length of the reference light, and a third optical length to the reference plane is determined based on the first interference signal. Reference surface optical length calculation means for calculating and calculating a fourth optical length to the reference surface based on the second interference signal;
Correction coefficient calculating means for calculating the correction coefficient based on the third optical length, the fourth optical length, and the known optical path length;
The distance measuring device according to claim 1, comprising: An etalon disposed in the optical path of each of the first white light and the second white light, or the optical path of the interference light;
A half mirror having a semi-reflective surface that reflects part of the measurement light and transmits part of the measurement light;
With
4. The distance according to claim 1, wherein the interference light generation unit generates interference light obtained by combining the reference reflected light, the measurement reflected light, and a standard reflected light reflected by the semi-reflecting surface. 5. measuring device. Mixing a first white light having a first center wavelength and a second white light having a second center wavelength different from the first center wavelength;
The mixed light is branched in two directions, one reference light is incident on the reflection surface of the reference mirror, the other measurement light is incident on the surface to be measured of the measurement object, and the reference reflected light reflected by the reflection surface And an interference light generation step of generating interference light combining the measurement reflected light reflected by the measurement surface,
A separation step of separating the interference light into a first interference light having the first center wavelength and a second interference light having the second center wavelength;
A first detection step of receiving the first interference light and outputting a first interference signal corresponding to the intensity of the first interference light;
A second detection step of receiving the second interference light and outputting a second interference signal corresponding to the intensity of the second interference light;
Obtaining the first interference signal and the second interference signal while changing the optical path length of the reference light; and
A first optical length to the measurement surface is calculated based on a relationship between the optical path length of the reference light and the first interference signal, and the optical path length of the reference light and the second interference signal are calculated. An optical length calculating step for calculating a second optical length to the surface to be measured based on the relationship:
A correction coefficient for calculating a geometric length to the surface to be measured, the group index of refraction of the first air at the first central wavelength and the second air at the second central wavelength. A correction coefficient acquisition step of acquiring a correction coefficient based on the group refractive index;
A geometric length calculating step of calculating the geometric length based on the first optical length, the second optical length, and the correction factor;
Distance measuring method with

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