JP6628030B2 - Distance measuring device and method - Google Patents

Description

  The present invention relates to a distance measuring apparatus and method, and more particularly to a distance measuring apparatus and method for measuring an absolute distance using a plurality of lights having different free spectral ranges.

  2. Description of the Related Art A length measuring device using laser interference such as a He-Ne (helium-neon) laser is known. This length measuring device has a measurable range of the absolute distance of about half a wavelength of the laser used. Therefore, when measuring a long distance, the absolute distance to the object to be measured is calculated by integrating the displacement of the half wavelength or less. Need to ask. Therefore, if the laser is interrupted during the measurement, the integration result up to that point becomes useless, and it is necessary to return to the origin where the integration of the displacement amount was started and repeat the measurement, which is very inconvenient.

  On the other hand, Patent Literature 1 discloses an apparatus for measuring an absolute distance using a plurality of types of optical combs having different repetition frequencies. According to the device of Patent Document 1, it is not necessary to integrate displacements of a half wavelength or less, and it is possible to measure a distance at high speed.

JP 2015-155822 A

  However, Patent Document 1 has a disadvantage that an optical comb light source to be used is expensive. In addition, it is necessary to adjust the free spectral range of the etalon for measurement light and the etalon for reference light to the repetition frequency of the optical comb, so that there is a disadvantage that it is difficult to manufacture the etalon. Further, there is another problem that it is difficult to measure the length in an arbitrary wavelength region.

  The present invention has been made in view of such circumstances, and provides a distance measuring device and a method for measuring an absolute distance at high speed and with high accuracy using an arbitrary wavelength region with a simple configuration. With the goal.

  One embodiment of the distance measuring device for achieving the above object is a light source that emits white light, and a branching unit that branches white light in two directions, wherein one of the branched reference lights is reflected by a reference mirror. A branching means for making the other measurement light incident on the surface to be measured of the object to be measured while the light is incident on the surface, and disposed between the branching means and the object to be measured, partially reflecting the incident light and transmitting partly A half mirror having a semi-reflective surface to be reflected, a reference light reflected by the reflective surface, a measuring light reflected by the surface to be measured, and an interference light generating means for generating interference light by combining the measuring light reflected by the semi-reflective surface, Scanning means for changing the optical path length of the reference light, and optical comb generating means arranged on the optical path of the white light or the interference light, wherein the first free spectral range and a second free spectral range different from the first free spectral range. Free Spectral Les An optical comb generating means having a pass band as a passband, and a first interference signal receiving a first interference light having a first free spectral range and outputting a first interference signal corresponding to the intensity of the first interference light. Detection means, second detection means for receiving a second interference light having a second free spectral range and outputting a second interference signal corresponding to the intensity of the second interference light, and an optical path of the reference light Acquisition means for acquiring the first interference signal and the second interference signal while changing the length, an optical path length of the reference light having a peak of the first interference signal, and a reference light having a peak of the second interference signal. An interference order determining means for determining the interference order of the first interference signal from the difference between the optical path length of the first interference signal and the interference order, based on the optical path length and the interference order of the reference light at which the first interference signal has a peak. Distance calculating means for calculating the distance of the object.

  According to this aspect, the white light is divided into the reference light and the interference light to generate the interference light between the reference light and the interference light, and the second light having the first free spectral range 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 having a second free spectral range are acquired, and the optical path length of the reference light at which the first interference signal has a peak and the second interference signal are obtained. The interference order between the peak of the first interference signal and the peak of the second interference signal is determined from the difference between the optical path length of the reference light and the peak of the first interference signal, and the reference light having the peak of the first interference signal is determined. Since the distance to the surface to be measured is calculated based on the optical path length and the interference order, it is possible to measure the absolute distance at high speed and with high accuracy using a simple wavelength range with a simple configuration. Can be.

  The optical comb generating means is an etalon having a pair of reflecting portions facing each other, and it is preferable to change the pass band by changing the distance between the reflecting portions. Thus, one etalon can output light having a plurality of free spectral ranges.

  It is preferable that the optical comb generating means is arranged in the optical path of white light. Thus, light having a free spectral range can be used as the reference light and the measurement light.

  The optical comb generating means includes a first etalon having a pass band in the first free spectral range and a second etalon having a pass band in the second free spectral range. And an interference light splitting unit that causes one of the split beams to enter the first etalon and the other to enter the second etalon. Thus, an etalon having a simple configuration can be used.

  In order to achieve the above object, one embodiment of a distance measuring method is to use a branching unit that branches white light emitted from a light source in two directions so that one of the branched reference lights is made incident on a reflection surface of a reference mirror and the other is split into two. A branching step of causing the measurement light of the measurement target to be incident on the surface to be measured, the reference light reflected by the reflection surface, the measurement light reflected by the surface to be measured, and the branching means disposed between the branching means and the measurement target; Light generation process for generating interference light that combines measurement light reflected from the semi-reflection surface of a half mirror that has a semi-reflection surface that reflects and partially transmits the reflected light, and changes the optical path length of the reference light And the optical comb generating means having a pass band of the first free spectral range and a second free spectral range different from the first free spectral range are arranged on the optical path of white light or interference light. Placement step; a first detection step of receiving a first interference light having a first free spectral range and outputting a first interference signal corresponding to the intensity of the first interference light; A second detection step of receiving a second interference light having a spectral range and outputting a second interference signal according to the intensity of the second interference light; and a first detection step while changing an optical path length of the reference light. An obtaining step of obtaining an interference signal and a second interference signal; and obtaining an interference signal based on a difference between an optical path length of the reference light at which the first interference signal has a peak and an optical path length of the reference light at which the second interference signal has a peak. An interference order determining step of determining an interference order of the first interference signal, and a distance calculating step of calculating a distance to a surface to be measured based on an optical path length and an interference order of the reference light at which the first interference signal has a peak. And with.

  According to this aspect, the white light is divided into the reference light and the interference light to generate the interference light between the reference light and the interference light, and the second light having the first free spectral range 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 having a second free spectral range are acquired, and the optical path length of the reference light at which the first interference signal has a peak and the second interference signal are obtained. The interference order between the peak of the first interference signal and the peak of the second interference signal is determined from the difference between the optical path length of the reference light and the peak of the first interference signal, and the reference light having the peak of the first interference signal is determined. Since the distance to the surface to be measured is calculated based on the optical path length and the interference order, it is possible to measure the absolute distance at high speed and with high accuracy using a simple wavelength range with a simple configuration. Can be.

  According to the present invention, the absolute distance can be measured at high speed and with high accuracy using an arbitrary wavelength region with a simple configuration.

Configuration diagram showing overall configuration of length measuring device Diagram to explain pseudo optical comb generation by etalon The figure which shows the relationship between the scanning amount of a scanning stage, and the peak of interference light Diagram showing the free spectral range of pseudo optical comb The figure which shows the difference of the peak of two interference light Flow chart showing each step of the absolute length measurement method Diagram showing peak of two interference lights and stage search range Schematic diagram showing an example of the internal configuration of the etalon Diagram showing changes in free spectral range of emitted light from etalon Configuration diagram showing the overall configuration of a length measuring device according to another embodiment

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

[Configuration of distance measuring device]
FIG. 1 is a configuration diagram illustrating an overall configuration of a length measuring device 10 (an example of a distance measuring device) according to the present embodiment. The length measuring device 10 is a distance measuring device using a Michelson interferometer as an interference optical system, and as shown in FIG. It includes a cube mirror 36, a scanning stage 38, a reference mirror 40, a collimator lens 42, a half mirror 44, a photodetector 46, a signal processing circuit 48, a control unit 50, and the like.

  The broad spectrum light source 12 is a device that emits white light (broad spectrum light) having a center wavelength of about 0.8 [μm], and includes SLD (Super Luminescent Diode), ASE (Amplified Spontaneous Emission), and SOA (Semiconductor Optical Amplifier). ) A light source or the like can be used. The light emitted from the broad spectrum light source 12 enters the etalon 14.

  The etalon 14 (an example of an optical comb generating means) has a pass band of a constant repetition frequency (free spectral range) of the incident light, and transmits and emits light of a pass band component (pseudo optical comb). Optical element. Light emitted from the etalon 14 enters the circulator 30.

  The circulator 30 has a first terminal 30a, a second terminal 30b, and a third terminal 30c. The circulator 30 emits light incident from the first terminal 30a from the second terminal 30b, and emits light incident from the second terminal 30b to the third terminal 30b. It is an optical element emitted from the terminal 30c. Light emitted from the etalon 14 and incident on the first terminal 30a of the circulator 30 exits from the second terminal 30b and enters the beam splitter 32.

  The beam splitter 32 (an example of a branching unit) is an optical element that branches incident light into two directions, and transmits a part of the incident light in a straight traveling direction and reflects a part in an orthogonal direction. The beam splitter 32 divides the light incident from the circulator 30, causes the reference light, which is one of the divided lights, to enter the collimator lens 34, and causes the measurement light, which is the other divided light, to enter the collimator lens 42. .

  The collimator lens 34 is an optical element that converts incident light into parallel light and emits the light. The collimator lens 34 converts the incident reference light into parallel light and causes the light to enter the corner cube mirror 36.

  The corner cube mirror 36 is an optical element that reflects incident light and changes the traveling direction. The corner cube mirror 36 makes the incident reference light incident on the reference mirror 40.

  The reference mirror 40 is a reflection member having a reflection surface 40a that reflects incident light. The reference light incident on the reference mirror 40 is reflected on the reflection surface 40a, and is incident on the beam splitter 32 via the corner cube mirror 36 and the collimator lens 34.

  Here, the corner cube mirror 36 is mounted on a scanning stage 38, and the scanning stage 38 (an example of a scanning unit) is configured to be able to scan in a direction perpendicular to the optical path of the reference light. Therefore, by scanning the scanning stage 38, the optical path length of the reference light can be changed. For example, when the scanning stage 38 is scanned by the distance d, the optical path length of the reference light changes by the distance 2 × d.

In the scanning stage 38, the optical path length of the reference light from the beam splitter 32 to the reflection surface 40a of the reference mirror 40 is the same as the optical path length of the measurement light from the beam splitter 32 to the semi-reflection surface 44a of the half mirror 44 described later. the position P ₀ where the distance is scanned as a reference.

  The collimator lens 42 is an optical element that converts incident light into parallel light and emits the same as the collimator lens 34. The collimator lens 42 converts the light incident from the beam splitter 32 into parallel light and causes the light to enter the half mirror 44.

  The half mirror 44 is a semi-reflective member having a semi-reflective surface 44a that transmits part of incident light and reflects part of the light. The half mirror 44 is disposed at a position (reference position) where the distance from the beam splitter 32 to the semi-reflective surface 44a is a known distance. Part of the measurement light incident on the half mirror 44 is reflected on the semi-reflection surface 44a, and is incident on the beam splitter 32 via the collimator lens 42. In addition, a part of the measurement light that has entered the half mirror 44 transmits through the semi-reflection surface 44a, and enters the length measurement target 1 (an example of a measurement target).

  The measurement light incident on the length measurement target 1 is reflected on the surface (measurement surface) 1a of the length measurement target 1 and is incident on the beam splitter 32 via the half mirror 44 and the collimator lens 42.

  The beam splitter 32 (an example of interference light generation means) reflects the reference light (reference light reflected by the reflection surface 40a) incident from the collimator lens 34 in the orthogonal direction, and measures the measurement light (semi-reflection surface) incident from the collimator lens 42. The reference light reflected by the reflecting surface 40a, the measuring light reflected by the semi-reflecting surface 44a, and the measured surface 1a are transmitted by transmitting the measuring light reflected by the reflecting surface 44a and the measuring light reflected by the measured surface 1a in the straight traveling direction. The measurement light reflected by the light source is coaxially combined to generate interference light. This interference light enters the second terminal 30b of the circulator 30, exits from the third terminal 30c, and enters the photodetector 46.

  The light detector 46 is a photoelectric conversion element that converts incident light into an electric signal corresponding to the intensity of the light. The photodetector 46 outputs an interference signal corresponding to the intensity of the incident interference light to the signal processing circuit 48.

  The signal processing circuit 48 calculates an absolute distance from the input interference signal to the measured surface 1a of the length measurement target 1.

  The control unit 50 controls the length measuring device 10 as a whole. In the present embodiment, in particular, the free spectral range of the etalon 14 and the optical path length of the reference light by the scanning stage 38 are controlled.

[Principle of absolute distance measurement (absolute length measurement)]
FIG. 2A is a diagram illustrating an example of a broad spectrum of the broad spectrum light source 12 and a transmission spectrum (pass band) of the etalon 14, and FIG. FIG. 4 is a diagram showing a spectrum of a pseudo optical comb which is light emitted from the etalon 14 when the light is made incident on the etalon 14. Free spectral range lambda ₁ of the pseudo-optical comb shown in FIG. 2 (b) is a 15 [GHz].

When the free spectral range _１1 is 15 [GHz], assuming that the speed of light in vacuum is c = 299792458 m / s and the refractive index n of air is 1, the repetition distance D ₁ in the optical path length direction is
D ₁ = c / (n × Λ ₁ ) = 19.986 [mm]
It is. Because half of the repeat distance D ₁ is the geometrical length Michelson interferometer, the measurement optical path length each time changed by D ₁ /2=9.993[mm], low coherence interference fringes are formed. Therefore, when the optical path length of the reference light scans D _1/2 or more, the peak of the interference light (pulse) is formed in an arbitrary measurement optical path length.

  FIG. 3 is a diagram showing a scanning amount of the scanning stage 38 and an obtained interference signal when the length measuring device 10 shown in FIG. 1 scans the optical path length of the reference light by about 24 [mm]. The 0 position signal shown in the figure is a pulse signal based on the peak of the interference light due to the measurement light reflected by the semi-reflective surface 44a of the half mirror 44, and is a signal that always appears at a fixed position. The length measurement signal is a pulse signal based on the peak of the interference light due to the measurement light reflected by the measurement target surface 1a of the length measurement target 1, and a signal whose position appears according to the distance to the measurement target surface 1a changes. is there.

  In FIG. 3, the scanning stage 38 scans the length measurement signal based on the eleventh (interference order = 11) interference light peak and the twelfth (interference order = 12) interference light peak from the reference position. Signals. The interference order corresponds to the number of light pulses of the pseudo optical comb emitted into the space from the reference position (semi-reflective surface 44a) to the measurement position (measured surface 1a).

When using one pseudo optical comb by etalon 14, the 0 position signal and the measurement signal each time the scanning distance D ₁ repeatedly scanning stage 38 is repeated, what number (the number order of interference) measurement It is unknown whether the signal is a long signal and the absolute distance cannot be measured.

Therefore, in this embodiment, a pseudo optical comb _{C 1} shown in FIG. 4 (a) free spectral range Λ ₁ = 15 [GHz] as shown in (an example of the first free spectral range), free shown in FIG. 4 (b) A pseudo optical comb C ₂ having a spectral range Λ ₂ = 14.9 [GHz] (an example of a second free spectral range) is output from the etalon 14, and an absolute distance is obtained using the _two pseudo optical combs C ₁ and C _2. Is measured.

Here, when the free spectral range Λ ₂ is 14.9 [GHz], the repetition distance D ₂ in the optical path length direction is
D ₂ = c / (n × Λ ₁ ) = 20.120 [mm] Therefore, when the optical path length of the reference light is scanned by D ₂ /2=1.060 [mm] or more, a peak of the interference light is formed at an arbitrary measurement optical path length.

As described above, the peak of the interference light in the free spectral range # ₁ occurs every time the measurement optical path length changes by 9.993 [mm], and the peak of the interference light in the free spectral range # ₂ has the measurement optical path length of 10 mm. 0.060 [mm]. Therefore, the difference between the peak positions of the two interference lights in the optical path length of the reference light is an integral multiple of 10.060 [mm] -9.993 [mm] = 67 [μm] according to the distance to be measured. Here, this integer is called an interference order.

  For example, as shown in FIG. 5, when the interference order = 1, the difference between the peak positions of the two interference lights is 67 [μm], and when the interference order = 15, the difference between the peak positions of the two interference lights is 67 [μm] × 15 = 1.005 [mm]. As described above, the difference between the peak positions of the two interference lights (the optical path length difference of the reference light) and the interference order have a correlation, and the length measuring device 10 measures the absolute distance using the interference order. I do.

[Absolute length measurement method]
An absolute length measuring method (an example of a distance measuring method) using the length measuring device 10 will be described. FIG. 6 is a flowchart showing each step of the absolute length measuring method.

  First, under the control of the control unit 50, the broad spectrum light source 12 is turned on (step S1), and the measurement stage 1 is irradiated with measurement light while scanning (scanning) the scanning stage 38 at a constant speed (step S2). (Step S3).

  As described above, the light of the broad spectrum light source 12 is formed on the pseudo optical comb by the etalon 14 arranged in the optical path (an example of an arrangement process), and then enters the beam splitter 32 via the circulator 30 to be split by the beam splitter 32. At 32, the light is branched into measurement light and reference light (an example of a branching step). The branched measurement light irradiates the half mirror 44 and the length measurement target 1, and the reference light irradiates the reference mirror 40. The beam splitter 32 coaxially combines the reference light reflected by the reflection surface 40a, the measurement light reflected by the semi-reflection surface 44a, and the measurement light reflected by the measured surface 1a to generate interference light (interference). Example of light generation step).

Here, etalon 14, the output control of the control unit 50 (see FIG. 1), for each time-divided output (e.g. 256 [.mu.s] and a pseudo optical comb _{C 1} and the pseudo optical comb _{C 2} by the number [kHz] Order ). Thus, the beam splitter 32, the free spectral range lambda ₁ of the interference light and the free spectral range lambda ₂ of the interference light is generated by time division.

(An example of the first detection means, an example of a second detection means) optical detector 46, free spectral range lambda ₁ of the interference light (first example of the interference light) and the free spectral range lambda ₂ of the interference light ( And an interference signal (an example of a first interference signal and an example of a second interference signal) corresponding to the intensity of each interference light (first detection). Example of step and second detection step).

The signal processing circuit 48 (an example of an acquiring unit) acquires an interference signal from the photodetector 46 while scanning the scanning stage 38 under the control of the control unit 50 to change the optical path length of the reference light (an example of an acquiring step). ). At this time, a pulse signal is detected from the interference signal in the free spectral range # ₁ (step S4), and a pulse signal is detected from the interference signal in the free spectral range # ₂ (step S5). The pulse signal detected here includes a zero position signal based on the measurement light reflected on the semi-reflection surface 44a of the half mirror 44 and a length measurement signal based on the measurement light reflected on the measured surface 1a of the length measurement target 1.

Here, the scanning stage 38 scans the optical path length of the reference light within the range of the distance S × 2 by moving the corner cube mirror 36 within the range of the distance S (an example of a scanning step). Distance S × 2 is half of the repetition distance D ₂ (D _2/2) greater than, here by moving the corner cube mirror 36 in a range of a distance S = 7 [mm], the reference light optical path of the The length is scanned in a range of 14 [mm].

Then, the signal processing circuit 48 (an example of the interference order determining means), a time difference between when the pulse signal of the free spectral range lambda ₁ and the free spectral range lambda ₂ of the interfering signal is detected, the free spectral range lambda ₁ interference The interference order N of the signal is determined (Step S6, an example of the interference order determination step).

In the present embodiment, since the scanning stage 38 scans at a constant speed, the time when the pulse signal of the interference signal of the free spectral range # ₁ is detected and the pulse signal of the interference signal of the free spectral range # ₂ are detected. from the time difference at the time of the free spectral range lambda ₁ of the interference signal of the scanning stage pulse signals of the position P ₁ and the free spectral range lambda ₂ of the interference signal of the scanning stage 38 a pulse signal is detected has been detected 38 (P ₂ −P ₁ ) from the position P ₂ can be obtained. The position _{P 1} and the position _{P 2} of the scanning stage 38, the distance from the position _{P 0} [Unit: m] expressed as.

The interference order N corresponds to the number of optical pulses of the pseudo optical comb from the reference position, and there is a correlation between the position difference (P ₂ −P ₁ ) and the interference order N. Here, as shown in FIG. 7, the difference between 1/2 of the 1/2 and repeat distance of the pseudo-optical comb _{C 2} of the repeating distance of the pseudo-optical comb _{C 1 (D 1/2-} D 2/2) is Since it is 67 [μm], the value obtained by dividing the difference (P ₂ −P ₁ ) of the position of the scanning stage 38 by 67 [μm] is the interference order N to be obtained. For example, the difference _(P 2 -P ₁₎ is 134 [[mu] m] order of interference N = 2 if the difference _(P 2 -P ₁₎ be obtained with the interference order N = 15 if 1.005 [mm] Can be.

Subsequently, the pulse signal of the free spectral range lambda ₁ of the interference signal to detect the position P ₁ of the scanning stage 38 upon which is detected (step S7). Free pulse signal spectral range lambda ₂ of the interference signal may detect the position P ₂ of the scanning stage 38 when detected. Then, in the signal processing circuit 48 (an example of a distance calculating unit), the length measurement is performed based on the interference order N obtained in step S6 and the position P ₁ of the scanning stage 38 obtained in step S7 (an example of the optical path length of the reference light). The distance D to the target is calculated (step S8, an example of a distance calculation step). The distance D [unit: m] can be obtained by the following equation 1.

D = c / n ₁ / Λ ₁ × N + P ₁ (Equation 1)
Here, n ₁ is a refractive index with respect to the center wavelength of the pseudo optical comb C ₁ . The obtained distance D may be displayed on a display unit (not shown) or may be stored in a storage unit (not shown).

  Finally, it is determined whether or not to terminate the length measurement process (step S9). If not, the process returns to step S4 to perform the same process.

The free spectral range lambda ₁ = 15 pseudo optical comb _{C 1} of [GHz], the case of using the pseudo-optical comb _{C 2} free spectral range Λ ₂ = 14.9 [GHz] is the principle of combined frequency, The interference order can be specified up to a geometric length of 1500 [mm] and the absolute length can be measured (L / 2 = D ₁ × D ₂ / (D ₂ −D ₁ ) / 2 = 1500 [mm]). .

If the positional relationship between the reference position and the measurement position is unknown up to 1500 [mm], the range of the absolute length measurement is up to 750 [mm]. In this case, by using a pseudo optical comb having a free spectral range different from the free spectral ranges # ₁ and # ₂ , the range of the absolute length measurement can be expanded. For example, using the free spectral range lambda ₃ = 15.1 pseudo optical comb _{C 3} of [GHz], since the reuse distance of a pseudo optical comb _{C 3} is _D 3 = 19.854 [mm], the geometrical length Absolute length measurement is possible up to 7.5 [m].

  As described above, according to the length measuring device 10, an arbitrary absolute distance can be measured. In addition, light in an arbitrary wavelength region can be used as the broad spectrum light.

[Structure of etalon]
It explained free spectral range lambda ₁ of the pseudo-optical comb C ₁ and the free spectral range lambda ₂ of the etalon for outputting a pseudo optical comb C _2. FIG. 8 is a schematic diagram illustrating an example of the internal configuration of the etalon 14. As shown in the figure, the etalon 14 is a fiber-type Fabry-Perot interference system in which the distance between the interferences is variable, and a pair of incident portions 16 into which light from the broad spectrum light source 12 is incident and a pair of opposed portions arranged opposite to each other. The width of the reflecting area 20 including the first reflecting plate 20A and the second reflecting plate 20B, the width of the reflecting area 22 between the first reflecting plate 20A and the second reflecting plate 20B, and the width of the reflecting area 22 are reduced. It has a PZT (Pb (Zr1-xTix) O ₃ ) actuator 26 that is displaced in the increasing and decreasing directions, and an emission unit 28 that emits an optical frequency component transmitted through the second reflection plate 20B to the circulator 30.

  The reflection area 22 is an area in which incident light is repeatedly reflected between the first reflection plate 20A and the second reflection plate 20B, and the optical fiber 24 is disposed therein. A gap 25 of 15 [μm] is formed between the optical fiber 24 and the second reflection plate 20B.

  The PZT actuator 26 increases the distance between the first reflection plate 20A and the second reflection plate 20B (interference distance) by 10 [in accordance with the rectangular wave signal applied by the control unit 50 (see FIG. 1). μm]. When the PZT actuator 26 is displaced between the gaps 25, the interference distance is set to one of (10 [mm] -15 [μm]) and (10 [mm] -5 [μm]). can do. The free spectral range of the light (pseudo optical comb) emitted from the etalon 14 is the first free spectral range 15 [15] when the inter-interference distance is the first distance (10 [mm] -15 [μm]). GHz], and when the inter-interference distance is the second distance (10 [mm] -5 [μm]), the second free spectral range is (15 [GHz] -15 [MHz]).

  By configuring the etalon 14 in this way, a pseudo optical comb having a free spectral range of several [MHz] to several hundred [GHz] can be generated. Further, length measurement in a wavelength region according to a user's request becomes possible. The optical fiber has a small loss even if there is a gap of about 15 [μm], and does not hinder the distance measurement.

  FIG. 9 is a diagram showing a change in the free spectral range of the light emitted from the etalon 14. The etalon 14 receives 15 [GHz] and (15 [GHz] -15 [MHz] as shown in FIG. 9 by applying a rectangular wave modulation signal to the PZT actuator 26 by the control unit 50 (see FIG. 1). ) Are emitted in a time-division manner.

  Here, by setting the frequency of the rectangular wave modulation signal higher than the scanning speed of the scanning stage 38 (see FIG. 1), a low coherence interference fringe equivalent to the case where two etalons are used can be formed. it can.

  Thus, according to the etalon 14, the free spectral range can be arbitrarily changed. Accordingly, a plurality of pseudo optical combs can be generated by one etalon 14.

  If the inter-interference distance of the etalon 14 is modulated and phase detection is performed by a lock-in amplifier or the like, highly sensitive absolute measurement can be performed. Therefore, even if the measured surface 1a of the length measuring target 1 is a rough surface, measurement becomes possible.

[Other embodiments of distance measuring device]
FIG. 10 is a configuration diagram showing an overall configuration of a length measuring device according to another embodiment. Note that the same reference numerals are given to processes common to the configuration diagram shown in FIG. 1 and detailed description thereof is omitted. As shown in FIG. 10, the length measuring device 60 does not include the etalon 14 as compared with the configuration of the length measuring device 10, but includes a beam splitter 52, etalons 54a and 54b, and photodetectors 46a and 46b.

  Light emitted from the broad spectrum light source 12 enters the first terminal 30 a of the circulator 30, exits from the second terminal 30 b, and enters the beam splitter 32. The beam splitter 32 divides the incident light, causes the reference light, which is one of the divided lights, to enter the collimator lens 34, and causes the measurement light, which is the other light after the division, to enter the collimator lens 42.

  The reference light that has entered the collimator lens 34 enters the reference mirror 40 via the corner cube mirror 36, is reflected on the reflection surface 40a, and returns to the beam splitter 32 via the corner cube mirror 36 and the collimator lens 34.

  On the other hand, the measurement light that has entered the collimator lens 42 enters the half mirror 44. The measurement light transmitted through the semi-reflective surface 44a is reflected on the measured surface 1a of the length measuring target, and returns to the beam splitter 32 via the half mirror 44 and the collimator lens 42. The measurement light reflected on the semi-reflective surface 44a returns to the beam splitter 32 via the collimator lens 42.

  The beam splitter 32 coaxially combines the reference light reflected by the reflection surface 40a, the measurement light reflected by the semi-reflection surface 44a, and the measurement light reflected by the measured surface 1a, and generates interference light. This interference light enters the second terminal 30b of the circulator 30, exits from the third terminal 30c, and enters the beam splitter 52.

  The beam splitter 52 (an example of an interference light splitting unit) is an optical element that splits incident light, like the beam splitter 32. The beam splitter 52 divides the incident interference light and causes one of the divided lights to enter the etalon 54a and the other of the divided lights to enter the etalon 54b. An optical isolator that allows light to pass only in a single direction may be arranged between the beam splitter 52 and the etalon 54a and between the beam splitter 52 and the etalon 54b.

The etalon 54a (an example of the first etalon) and the etalon 54b (an example of the second etalon), like the etalon 14, are optical elements that transmit through a pseudo optical comb having a fixed free spectral range in the incident light. Element. The etalon 54a and the etalon 54b have different free spectral ranges. Here, the free spectral range of the etalon 54a is Λ ₁ , and the free spectral range of the etalon 54b is Λ ₂ (Λ ₁ ≠ Λ ₂ ). Interference light pseudo optical comb C ₁ emitted from the etalon 54a is incident on the photodetector 46a, the interference light of the quasi-optical comb C ₂ emitted from the etalon 54b is incident on the light detector 46b.

Each of the photodetectors 46a and 46b is a photoelectric conversion element that converts incident light into an electric signal corresponding to its intensity, similarly to the photodetector 46. Photodetectors 46a, 46b outputs an interference signal corresponding to the intensity of the interference light pseudo optical comb C _1, C ₂ that is incident on the signal processing circuit 48.

Signal processing circuit 48 of the measuring apparatus 60 having such a configuration, similarly to the signal processing circuit 48 of the measuring device 10, the pulse signal by the interference light of the quasi-optical comb C _1, due to the interference light of the quasi-optical comb C ₂ pulse signal, and the position P ₂ position P ₁ and the scanning stage 38 of the pulse signal by the interference light of the quasi-optical comb C ₂ is detected in the scanning stage 38 to a pulse signal by the interference light of the quasi-optical comb C ₁ is detected The difference (P ₂ −P ₁ ) and the position P ₁ of the scanning stage 38 when the pulse signal due to the interference light of the pseudo optical comb C ₁ is detected are input. Therefore, the distance D to the length measurement target can be measured in the same manner as the length measurement device 10.

Incidentally, in the case of obtaining the distance D using the equation 1, the position P ₂ of the scanning stage 38 when the pulse signal by the interference light of the quasi-optical comb C ₂ is detected, only necessary to determine the interference orders Since it is information, the required measurement accuracy may be on the order of [mm].

  As described above, the etalons 54a and 54b may be arranged after the Michelson interferometer. Thus, the absolute distance can be measured without being affected by the accuracy of the etalons 54a and 54b.

  In the embodiment of the present invention described above, constituent elements can be appropriately changed, added, or deleted without departing from the spirit of the present invention. The present invention is not limited to the embodiments described above, and many modifications can be made by those having ordinary knowledge in the art within the technical spirit of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Length measuring target, 1a ... Measurement surface, 10 ... Length measuring device, 12 ... Broad spectrum light source, 14,54a, 54b ... Etalon, 16 ... Injection part, 20 ... Reflection part, 22 ... Reflection area, 24 ... Light Fiber, 25 gap, 26 PZT actuator, 28 emission part, 30 circulator, 32, 52 beam splitter, 34, 42 collimator lens, 36 corner cube mirror, 38 scanning stage, 40 reference mirror, 42 collimator lens, 44 half mirror, 46, 46a, 46b photodetector, 48 signal processing circuit, 50 control unit

Claims (4)

A light source that emits white light;
An etalon that is arranged on the optical path of the white light, has a pair of reflecting portions facing each other, and changes a pass band by changing a distance between the reflecting portions, and includes a first free spectral range and the first free spectral range. An etalon having a passband of a second free spectral range different from the first free spectral range;
A branching means for branching the light output from the etalon in two directions, wherein one of the branched reference lights is made incident on a reflection surface of a reference mirror, and the other measurement light is made incident on a surface to be measured of a measurement object. Branching means for causing
A half mirror having a semi-reflective surface disposed between the branching unit and the object to be measured and reflecting part of incident light and transmitting part of the light.
Reference light reflected by the reflection surface, measurement light reflected by the surface to be measured, and interference light generation means for generating interference light by combining the measurement light reflected by the semi-reflection surface,
Scanning means for changing the optical path length of the reference light ,
First detection means for receiving the first interference light having the first free spectral range and outputting a first interference signal according to the intensity of the first interference light;
Second detection means for receiving the second interference light having the second free spectral range and outputting a second interference signal according to the intensity of the second interference light;
Acquisition means for acquiring the first interference signal and the second interference signal while changing the optical path length of the reference light;
Interference for determining an interference order of the first interference signal from a difference between an optical path length of the reference light at which the first interference signal has a peak and an optical path length of the reference light at which the second interference signal has a peak. Order determining means;
Distance calculating means for calculating a distance to the measured surface based on the optical path length of the reference light and the interference order at which the first interference signal has a peak,
Distance measuring device equipped with. A light source that emits white light;
A branching unit that branches the white light in two directions, and a branching unit that causes one of the branched reference lights to enter the reflection surface of the reference mirror and causes the other measurement light to enter the surface to be measured of the measurement target; ,
A half mirror having a semi-reflective surface disposed between the branching unit and the object to be measured and reflecting part of incident light and transmitting part of the light.
Reference light reflected by the reflection surface, measurement light reflected by the surface to be measured, and interference light generation means for generating interference light by combining the measurement light reflected by the semi-reflection surface,
Scanning means for changing the optical path length of the reference light,
Interference light splitting means for splitting the interference light in two directions;
A first etalon that is disposed on the optical path of the one of the branched interference lights and has a first free spectral range as a pass band;
A second etalon that is disposed on the optical path of the other of the branched interference lights and has a second free spectral range different from the first free spectral range as a pass band;
First detection means for receiving the first interference light having the first free spectral range and outputting a first interference signal according to the intensity of the first interference light;
Second detection means for receiving the second interference light having the second free spectral range and outputting a second interference signal according to the intensity of the second interference light;
Acquisition means for acquiring the first interference signal and the second interference signal while changing the optical path length of the reference light;
Interference for determining an interference order of the first interference signal from a difference between an optical path length of the reference light at which the first interference signal has a peak and an optical path length of the reference light at which the second interference signal has a peak. Order determining means;
Distance calculating means for calculating a distance to the measured surface based on the optical path length of the reference light and the interference order at which the first interference signal has a peak,
Distance measuring device equipped with. An etalon having a pair of reflecting portions facing each other and changing a pass band by changing a distance between the reflecting portions, which is different from the first free spectral range and the first free spectral range. Causing white light emitted from the light source to enter an etalon having a pass band in the second free spectral range ;
A branching unit that branches the light emitted from the etalon in two directions so that one of the branched reference lights 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. Process and
The reference light reflected on the reflection surface, the measurement light reflected on the surface to be measured, and a half that is disposed between the branching unit and the object to be measured and reflects part of incident light and transmits part of the light. An interference light generation step of generating interference light that combines measurement light reflected on the semi-reflection surface of the half mirror having a reflection surface,
A scanning step of changing the optical path length of the reference light ,
A first detection step of receiving a first interference light having the first free spectral range and outputting a first interference signal according to the intensity of the first interference light;
A second detection step of receiving a second interference light having the second free spectral range and outputting a second interference signal according to the intensity of the second interference light;
An acquisition step of acquiring the first interference signal and the second interference signal while changing an optical path length of the reference light;
Interference for determining an interference order of the first interference signal from a difference between an optical path length of the reference light at which the first interference signal has a peak and an optical path length of the reference light at which the second interference signal has a peak. An order determining step;
A distance calculating step of calculating a distance to the surface to be measured based on the optical path length and the interference order of the reference light at which the first interference signal has a peak,
Distance measuring method provided with. A branching step of causing one of the branched reference lights to be incident on the reflection surface of the reference mirror and the other of the measurement light to be incident on the surface to be measured of the measurement object by the branching means for branching the white light emitted from the light source in two directions. When,
The reference light reflected on the reflection surface, the measurement light reflected on the surface to be measured, and a half that is disposed between the branching unit and the object to be measured and reflects part of incident light and transmits part of the light. An interference light generation step of generating interference light that combines measurement light reflected on the semi-reflection surface of the half mirror having a reflection surface,
A scanning step of changing the optical path length of the reference light,
The interference light is branched in two directions, one of the branched lights is made incident on a first etalon having a first free spectral range as a pass band, and the other is separated into a second free etalon different from the first free spectral range. An interference light branching step of entering a second etalon having a pass band in a spectral range,
A first detection step of receiving a first interference light having the first free spectral range and outputting a first interference signal according to the intensity of the first interference light;
A second detection step of receiving a second interference light having the second free spectral range and outputting a second interference signal according to the intensity of the second interference light;
An acquisition step of acquiring the first interference signal and the second interference signal while changing an optical path length of the reference light;
Interference for determining an interference order of the first interference signal from a difference between an optical path length of the reference light at which the first interference signal has a peak and an optical path length of the reference light at which the second interference signal has a peak. An order determining step;
A distance calculating step of calculating a distance to the surface to be measured based on the optical path length and the interference order of the reference light at which the first interference signal has a peak,
Distance measuring method provided with.

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