WO2017081808A1

WO2017081808A1 - Measurement method and device

Info

Publication number: WO2017081808A1
Application number: PCT/JP2015/081956
Authority: WO
Inventors: 達雄針山; 渡辺　正浩; 敦史谷口; 啓晃笠井
Original assignee: 株式会社日立製作所
Priority date: 2015-11-13
Filing date: 2015-11-13
Publication date: 2017-05-18
Also published as: JPWO2017081808A1; JP6303026B2

Abstract

The present invention provides a plurality of means for addressing the problem, one example of these means being a measurement device, wherein the measurement device is characterized by including: a light source for emitting light; a first optical system provided with a separation unit for separating the light into reference light and measurement light, and an object-of-measurement-installation unit, the first optical system emitting the reference light and the reflected light, which is reflected by the object of measurement; a second optical system provided with a separation unit for separating the light into reference light and measurement light, and a plurality of reflection units of which the positions are established in advance, the second optical system emitting the reference light and the reflected light, which is reflected by each of the reflection units; an optical system selection unit for selecting either the first optical system or the second optical system; a reception unit for receiving the plurality of rays of light emitted by the first optical system or the second optical system; a distance calculation unit for analyzing the light rays received by the reception unit and calculating the distance to the object of measurement or to the reflection units; a correction value calculation unit for calculating a correction value by using the distance to the reflection units as calculated by the distance calculation unit; and a correction unit for correcting the distance to the object of measurement by using the correction value.

Description

Measuring method and apparatus

The present invention relates to a distance measurement method and a distance measurement device for measuring a distance to a measurement object in a non-contact manner.

FMCW (Frequency Modulated Continuous Waves) method is known as a method for measuring the distance to the measurement object in a non-contact manner.

The technique described in Patent Document 1 is an example of distance measurement using the FMCW method. In Patent Literature 1, a calibration optical system is provided in addition to the measurement optical system, thereby correcting a distance error due to a change with time of the semiconductor laser.

JP2013-180111A

First, FIG. 2 shows a configuration example of the FMCW system. When a triangular wave current is injected from the oscillator 102 to the semiconductor laser 101 and the drive current is modulated, FM light that is temporally frequency swept at a constant modulation speed is generated. The FM light is divided by the beam splitter 202, a part of the output light is irradiated onto the measurement object 114, and a part is reflected by the reference mirror 201. The return light from the measurement object and the interference light of the reference light are detected by the light receiver 203, and the detected beat signal is analyzed by the PC 119 and displayed on the screen 120.

FIG. 3 shows the beat signal 301 observed by the light receiver. The horizontal axis of the graph is the observed beat frequency, and the vertical axis is the signal intensity. FIG. 4 shows the principle of distance measurement. The time change of the optical frequency in the light receiver of the reference light 401 and the measuring light 402 is shown, the horizontal axis of the graph is time, and the vertical axis is the optical frequency. It can be seen that the beat frequency fb, the difference Δt in the arrival time of the reference beam 401 and the measuring beam 402 at the light receiver Δt, the frequency sweep width Δν, and the modulation period T have the following relationship.

Therefore, the distance L to the measurement object can be calculated as follows using the light velocity c in the atmosphere.

In order to accurately measure the distance L from Equation (2), the beat frequency fb needs to be constant during the modulation period T. However, as a characteristic of the semiconductor laser, since the change amount of the optical frequency is nonlinear with respect to the change amount of the injection current, there is a problem that the measurement accuracy is deteriorated.

In the FMCW method, the distance error when the change in the optical frequency sweep becomes nonlinear will be described with reference to FIG. The description will be made assuming that the non-linearity is second-order (actually, it may be a high-order non-linearity, but for the sake of explanation, it is assumed that it is second-order). The optical frequency of the reference light 501 is expressed by the following equation.

Where a is a secondary coefficient of time t, and b is a primary coefficient. Similarly, the optical frequency of the measuring light 502 is expressed by the following equation.

The interference beat frequency generated when the reference light 501 and the measurement light 502 are received by the light receiver is represented by the following equation.

When the optical frequency is swept linearly from equation (5), only the third term is obtained, and the beat frequency is proportional to Δt, that is, proportional to the distance to the measurement object. It becomes possible. However, in the case of non-linear sweeping, the first and second terms are generated, and therefore the distance cannot be obtained accurately from the beat frequency. Therefore, generally, a method is adopted in which the injection current of the semiconductor laser is made into a non-linear waveform and the sweep frequency is adjusted to be linear. However, the characteristics of the semiconductor laser with respect to the injection current change with time. When it changes over time, the coefficients a and b in Equation (5) fluctuate, so the distance cannot be determined accurately from the beat frequency.

For such a problem, Patent Document 1 corrects the influence of the semiconductor laser over time by providing an optical system for calibration in addition to the optical system for measuring the target.

Referring to FIG. 1 of Patent Document 1 for explanation, it is shown in FIG. The light emitted from the semiconductor laser light source passes through a beam splitter and then passes through another beam splitter. The second beam splitter measures the distance to the reflecting surface whose distance is accurately known at the same time as the object to be measured. A beat signal detected in FIG. 4 of Patent Document 1 is shown. In Patent Document 1, since the reflected light from the object and the reflected light from the reflecting surface are detected at the same time, it is necessary to increase the distance of the reflecting surface from the distance to the object so that the beat frequencies do not overlap. In the case of this method, calibration is possible if the coefficient b in Equation (5) fluctuates due to the change of the semiconductor laser with time and the frequency fluctuates linearly. However, if the coefficient a in Equation (5) fluctuates and the frequency fluctuates nonlinearly, there is no information on the beat frequency for calibration during the distance to the target, so calibration cannot be performed with high accuracy.

In order to solve the above problems, for example, the configuration described in the claims is adopted. The present application includes a plurality of means for solving the above problems. To give an example, a measuring device is a light source that emits light, a separation unit that separates light into reference light and measurement light, and measurement. A measurement target installation unit for installing a target, a first optical system that emits reference light and reflected light reflected by the measurement target, a separation unit that separates the light into reference light and measurement light, and a position previously determined A second optical system that emits the reference light and the reflected light reflected by the respective reflective units, and the first optical system and the second optical system are selected. An optical system selection unit, a light receiving unit that receives a plurality of light beams emitted from the first optical system or the second optical system, and an analysis of the light received by the light receiving unit to determine the distance to the measurement target or the reflection unit Using the distance calculation unit to calculate and the distance to the reflection unit calculated by the distance calculation unit A correction value calculation unit for calculating a correction value, and having a correction unit for correcting the distance to the measurement object by using the correction value.

Alternatively, in the measurement method, when the optical system selection unit selects the optical path of the light emitted from the light source, and when the optical system selection unit selects the first optical system, the light is the first reference light. And the first measurement light, the second step of emitting the first reflected light and the first reference light reflected by the first measurement light on the measurement target to the light receiving unit, and the optical system selection unit is the second optical When a system is selected, the second reference light and the second reference light are separated from the second reference light and the second measurement light, and the second reflected light and the second reference light are reflected by the plurality of reflection portions whose positions are known in advance. A third step for emitting light to the light receiving unit, a fourth step for analyzing the light received by the light receiving unit, calculating a distance to the measurement object or the reflecting unit, and a step for calculating the distance to the reflecting unit calculated in the fourth step. The fifth step of calculating the correction value using the distance and the distance to the measurement object are corrected using the correction value. A sixth step of, characterized by having a.

According to the present invention, the distance can be measured with high accuracy.

It is the figure which showed the structure of the distance measuring device in a 1st Example. It is the figure which showed the structure of the FMCW system. It is the figure which showed the beat signal which generate | occur | produces with a light receiver. It is a figure explaining the principle of FMCW system. It is a figure explaining the cause which a distance error produces in a FMCW system. FIG. 3 is a diagram illustrating a configuration of a control unit in the first embodiment. It is a figure which quotes and demonstrates patent document 2. FIG. It is the figure which showed the reflective surface of the fiber in a 1st Example. It is the figure which showed the beat signal which generate | occur | produces with the light receiver in a 1st Example. It is a figure showing the first calibration method in the 1st example. It is the figure which showed the calibration method for every measurement in a 1st Example. It is the figure which showed the structure of the distance measuring device in a 2nd Example. It is the figure which showed the structure of the distance measuring device in a 3rd Example. It is the figure which showed the structure of the distance measuring device in a 4th Example. It is the figure which showed the structure of the distance measuring device in a 5th Example. It is the figure which showed the structure of the distance measuring device in a 6th Example. It is the figure which showed the structure of the distance measuring device in a 7th Example. It is the figure which showed the structure of the distance measuring device in an 8th Example. It is the figure which showed the structure of the distance measuring device in a 9th Example. It is the figure which showed the structure of the distance measuring device in a 10th Example. It is the figure which showed the structure of the distance measuring device in an 11th Example.

Hereinafter, examples will be described with reference to the drawings.

The surface shape measuring method and apparatus in Example 1 will be described with reference to FIG. A sweep waveform signal is transmitted from the control unit 119 to the arbitrary signal generator 102. The optical signal is swept by modulating the drive current of the semiconductor laser 101 by the arbitrary signal generator 102. A part of the light emitted from the semiconductor laser is guided to the reference optical system 132 by the fiber coupler 103. In the reference optical system, the laser beam is further branched into two by the fiber coupler 104, provided with a certain optical path difference by the optical fiber 105, and then combined again by the fiber coupler 106 and received by the light receiver 107. Yes. This has the structure of a Mach-Zehnder interferometer, and the light receiver 107 generates a constant beat signal proportional to the optical path difference. The beat frequency generated by the light receiver 107 is as follows.

Here, Δt ₀ is the time during which light propagates through the optical path difference of the reference optical system.

On the other hand, the light that has not been guided to the reference optical system passes through the circulator 108 and is selectively transmitted to the measurement optical system (first optical system) 131 and the calibration optical system (second optical system) 130 by the optical switch 110. Led. When guided to the measurement optical system 131, it is branched by the fiber coupler 111, part of it is reflected by the reference mirror 112 and becomes reference light, and most of the rest is irradiated to the space by the collimator lens 113, and the measurement target installation unit 133 The object 114 installed in The measurement object installation unit 133 can move the object installation position 133 within a certain range.

The light reflected from the object 114 passes through the collimator lens 113 again, merges with the reference light from the reference mirror 112 at the fiber coupler 111 portion, passes through the optical switch 110, and reaches the light receiver 109 by the circulator 108. The light is guided and a beat signal is generated by the interference between the reference light and the measurement light. The beat signal received by the light receiver 109 is expressed by Equation (5). Here, when sampling is performed with the beat signal received by the light receiver 107, the following equation is obtained.

If the distance to the measurement target is close to the optical path difference of the reference optical system from Equation (7), the second term becomes zero, so the beat frequency when measuring the target and the beat frequency generated by the reference optical system It is possible to calculate the distance from the ratio. However, if the distance to the measurement object is away from the optical path difference of the reference optical system, the second term cannot be ignored, resulting in a distance error. Therefore, by making the current waveform applied to the semiconductor laser non-linear and making the sweep frequency as linear as possible, the coefficient a in equation (7) is reduced and the influence of the second term is suppressed. However, since the current characteristics of the semiconductor laser change with time, the value of a may fluctuate and a distance error may occur. Therefore, a calibration optical system is provided separately.

The light guided to the calibration optical system 130 by the optical switch 110 is branched by the fiber coupler 115, part of the light is reflected by the reference mirror 116 and becomes reference light, and most of the rest is engraved with a reflecting surface at equal intervals. It passes through the optical fiber 117. In the optical fiber 117, reflecting surfaces are engraved at equal intervals, a part of the light is reflected at each point, and most of the light is transmitted. As a result, light is reflected at a plurality of points. The distance to each reflecting surface in the calibration optical system 130 is known, and the distance measured by the measurement optical system 131 is calibrated using this value. Details of the calibration method will be described later. At this time, the position of the reflection surface closest to the light source among the plurality of reflection surfaces is closer to the light source than the end of the movable range of the measurement target installation unit 133 on the light source side. In addition, the position of the reflective surface farthest from the light source among the reflective surfaces is farther from the light source than the end of the movable range of the measurement target installation unit 133 that is far from the light source. With this configuration, the distance to the plurality of reflecting surfaces is always included in the same distance as the distance to the measurement target installation unit, and calibration can be performed in an appropriate range.

A fiber attenuator 118 is installed at the end of the fiber 117 (the end far from the light source) so that light is absorbed and not reflected at the end. The light reflected at each point merges with the reference light from the reference mirror 116 at the fiber coupler 115, passes through the optical switch 110, is guided to the light receiver 109 by the circulator 108, and the reference light and the measurement light A beat signal is generated by the interference. The beat signal received by the light receiver 109 is sampled with the beat signal received by the light receiver 107.

FIG. 9 shows a beat signal 901 generated by light reflected at each point of the fiber 117. Multiple beat signals are generated according to the distance. The beat signal 902 obtained when the fiber switch 110 is switched and the target is irradiated with light is also shown in FIG. Here, the length of the fiber 117 is determined so that the maximum distance to the object is within the length of the fiber 117. As a result, even when the semiconductor laser changes with time, the coefficient a in Equation (5) fluctuates, and the frequency fluctuates nonlinearly, there is a lot of information on the beat frequency for calibration between the distance to the target. It can be calibrated well.

The calibration method will be described with reference to FIG. First, it is necessary to accurately obtain the distance of each reflection carved in the fiber 117. As an example, a fiber switch is used to guide light to the measurement optical system, and a mirror mounted on a positioning stage with higher accuracy than that required for FMCW measurement is used as a measurement target to drive the stage and measure the distance to the mirror. . At this time, the injection current of the semiconductor laser is adjusted so that the distance measurement result by FMCW becomes equal to the moving distance of the stage.

Next, light is guided to the calibration optical system 130 by the fiber switch, and the distance of each reflection point is obtained from the beat frequency of each reflection point of the fiber 117 and recorded in the memory of the PC. This method only needs to be performed once after the device is manufactured.

Next, the calibration method for each measurement will be described with reference to FIG. Before measuring the target, the calibration optical system 130 is measured by the fiber switch 110, and the distance calculation unit 601 calculates the distance to each reflection point. 1001 indicates the distance obtained in FIG. 10, and 1101 indicates the distance measured before the measurement. If the distance between 1001 and 1101 is not shifted, calibration is not necessary. However, if 1001 and 1101 are misaligned, calibration is required. The calibration method will be described with reference to FIG. A distance calculation unit 601 calculates the distance to each reflection of the calibration optical system. Next, the correction value calculation unit 602 obtains the difference or ratio between the distance data recorded in the memory of the PC at the time of the first calibration and the distance data calculated by the distance calculation unit 601. A correction value is calculated from the obtained difference or ratio. As the correction value, for example, data of an area where no reflection point exists is calculated using polynomial approximation or the like. Next, the object is measured by the fiber switch 110, and the correction value obtained by the correction value calculation unit 602 is corrected by the distance correction unit 603 with respect to the distance obtained by the distance calculation unit 601.

Alternatively, a method of correcting by changing the injection current of the semiconductor laser is also possible. By using multiple points for calibration at this time, it is possible to calibrate even higher-order nonlinearities.

FIG. 8 shows an example of carving a reflection surface on the fiber 117. For example, there is a method of processing into a fiber by irradiating ultraviolet rays. This method is a method used when manufacturing FBG (Fiber Bragg Grating) fiber, and is a general method.

Based on the above, the measurement apparatus described in the present embodiment includes a light source 101 that emits light, a separation unit 111 that separates light into reference light and measurement light, and a measurement target installation unit. And a first optical system 131 that emits reflected light reflected by the measurement object, a separation unit 111 that separates the light into reference light and measurement light, and a plurality of reflection units 117 whose positions are known in advance, A second optical system 130 that emits the reference light and the reflected light reflected by the respective reflecting units; an optical system selecting unit 110 that selects one of the first optical system 131 and the second optical system 130; A light receiving unit 109 that receives a plurality of lights emitted from one optical system or the second optical system, and a distance calculation unit 601 that analyzes the light received by the light receiving unit and calculates the distance to the measurement target or the reflection unit. And a correction value calculation unit 6 that calculates a correction value using the distance to the reflection unit calculated by the distance calculation unit 02 and a correction unit 603 that corrects the distance to the measurement object using the correction value.

In addition, the measurement method described in the present embodiment includes a first step in which the optical system selection unit 110 selects the optical path of light emitted from the light source 101, and the optical system selection unit 110 selects the first optical system 131. In this case, the light is separated into the first reference light and the first measurement light, and the first reflected light and the first reference light reflected by the measurement object 114 are emitted to the light receiving unit 109. And when the optical system selection unit 110 selects the second optical system 130, the light is separated into the second reference light and the second measurement light, and a plurality of reflection units 117 whose positions are known in advance are used. The third step of emitting the second reflected light and the second reference light reflected by the second measurement light to the light receiving unit 109, analyzing the light received by the light receiving unit 109, and determining the distance to the measurement object or the reflection unit Fourth step 601 to calculate, and fifth step 6 to calculate the correction value using the distance to the reflection part calculated in the fourth step 6 02 and a sixth step 603 for correcting the distance to the measurement object using the correction value. With these configurations, by switching between two optical systems that always include the same distance as the distance to the measurement target installation unit within the distance to the plurality of reflecting surfaces, the optical system selection unit switches between the distances to the measurement target. Thus, information on the beat frequency for calibration can be obtained, and the distance can be constructed with high accuracy.

The distance measuring method and apparatus in Example 2 will be described with reference to FIG. The difference from the first embodiment described in FIG. 1 is the position of the reference mirror 116. By attaching the reference mirror 116 to the tip of the calibration fiber 117, the light reflected at each point and the light transmitted through the fiber and reflected by the reference mirror 116 interfere to generate a beat signal. . In this case, since the fiber coupler 115 and the optical attenuator 118 described with reference to FIG. 1 are not necessary, the configuration is simpler than that of the first embodiment, and the measurement apparatus can be easily manufactured.

A distance measuring method and apparatus in Example 3 will be described with reference to FIG. The difference from the first embodiment described with reference to FIG. 1 is that, in FIG. 1, the distance between the reflection points of the fiber 117 is uniform, but in FIG. 13, the distance between the reflection points of the fiber 1401 is non-uniform. . When the intervals are uniform in the wavelength order, the structure is similar to that of the FBG, so that a certain wavelength band within the sweep wavelength is reflected by the fiber 117 with high intensity, and there is a possibility that the reference mirror is not irradiated. In this case, no beat signal is generated, and the distance cannot be measured. Therefore, by making the intervals between the reflecting surfaces non-uniform so that the intervals are not uniform in the wavelength order, the possibility that a beat signal is not generated and the calibration accuracy is reduced is reduced.

The distance measurement method and apparatus in Example 4 will be described with reference to FIG. In the fourth embodiment, a polarization beam splitter 1501 is used in place of the switch 110 between the measurement optical system and the calibration optical system. The light irradiated from the semiconductor laser is set to a polarization state in which S polarization and P polarization are mixed. The polarization beam splitter 1501 introduces the S polarization component into the measurement optical system, and introduces the P polarization component into the calibration optical system. Alternatively, the P-polarized component is introduced into the measurement optical system, and the S-polarized component is introduced into the calibration optical system.

The light introduced into the measurement optical system passes through the circulator 108 and is branched by the fiber coupler 111. A part of the light is reflected by the reference mirror 112 to become reference light, and most of the rest is irradiated to the space by the collimator lens 113. The object 114 is irradiated. The light reflected from the object 114 passes through the collimator lens 113 again and merges with the reference light from the reference mirror 112 at the fiber coupler 111 portion, and then guided to the light receiver 109 by the circulator 108 to be measured with the reference light. A beat signal is generated by light interference.

On the other hand, the light introduced into the calibration optical system passes through the circulator 1502 and is branched by the fiber coupler 115. A part of the light is reflected by the reference mirror 116 to become reference light, and most of the rest is engraved with a reflecting surface at equal intervals. It passes through the optical fiber 117. In the optical fiber 117, reflecting surfaces are engraved at equal intervals, a part of the light is reflected at each point, and most of the light is transmitted.

Thus, light is reflected at a plurality of points, and a fiber attenuator 118 is installed at the end of the fiber 117, and the light is absorbed. The light reflected at each point is merged with the reference light from the reference mirror 116 at the fiber coupler 115 portion, and then guided to the light receiver 1503 by the circulator 1502 to generate a beat signal due to interference between the reference light and the measurement light. .

In the control PC 119, the signals of the

light receivers

109 and 1503 can be switched. The 109 signal can be selected during the target measurement, and the 1503 signal can be selected during calibration.

Also, the polarization beam splitter 1501 may be a fiber coupler.

A distance measuring method and apparatus in Example 5 will be described with reference to FIG. The difference from the first embodiment described in FIG. 1 is that the position of the optical switch 110 is arranged after the fiber coupler 115. By doing so, the reference mirror 116 can be shared by the measurement optical system and the calibration optical system to be one. This has the advantage that the number of parts can be reduced. However, it is conceivable that the distance between the reference mirror and the measurement target may be increased, causing a variation in the distance, and the reflected light generated by the optical switch 110 may be noise.

A distance measuring method and apparatus in Example 6 will be described with reference to FIG. The difference from the first embodiment described in FIG. 1 is a calibration fiber. In the sixth embodiment, the light guided to the calibration optical system by the optical switch 110 is branched by the fiber coupler 115, part of the light is reflected by the reference mirror 116 and becomes reference light, and most of the remaining part is further the fiber coupler 1701. Are reflected by the reflecting

surfaces

1705, 1706 and 1707 after passing through the

fibers

1702, 1703 and 1704 having different lengths. This makes it possible to form reflecting surfaces with different distances.

The light reflected at each point merges with the reference light from the reference mirror 116 at the fiber coupler 115, passes through the optical switch 110, is guided to the light receiver 109 by the circulator 108, and the reference light and the measurement light A beat signal is generated by the interference.

A distance measuring method and apparatus in Example 7 will be described with reference to FIG. The difference from the first embodiment described in FIG. 1 is a calibration fiber. In the seventh embodiment, the light guided to the calibration optical system by the optical switch 110 is branched by the fiber coupler 115, part of the light is reflected by the reference mirror 116 and becomes reference light, and most of the rest is by the fiber coupler 1801. Loop through the resonator.

A reflecting surface 1802 is provided in the resonator, and a plurality of reflecting surfaces having different distances can be formed by looping the resonator a plurality of times. The light reflected at each point merges with the reference light from the reference mirror 116 at the fiber coupler 115, passes through the optical switch 110, is guided to the light receiver 109 by the circulator 108, and the reference light and the measurement light A beat signal is generated by the interference.

A distance measuring method and apparatus in Example 8 will be described with reference to FIG. The difference from the first embodiment described in FIG. 1 is that the

temperature control boxes

1901 and 1902 are provided in the eighth embodiment. In the present invention, the standard of distance is a calibration fiber and a reference fiber. Therefore, if the fiber length changes with temperature, a distance error occurs.

Therefore, the fiber coupler 104, the fiber 105, and the fiber coupler 106 are put in the temperature control box 1902 to keep the temperature constant, and the fiber coupler 115, the reference mirror 116, the fiber 117, and the fiber attenuator 118 are put in the temperature control box 1901. To keep the temperature constant. Instead of keeping the temperature constant, the actual fiber length may be calculated and the distance calculated by accurately measuring the fiber temperature and taking into account the thermal effect of the fiber from the temperature change.

The surface shape measuring method and apparatus in Example 9 will be described with reference to FIG. The difference from the first embodiment described with reference to FIG. 1 is that the ninth embodiment is configured without a reference clock generating optical system. Even if there is no reference clock, the beat signal obtained by the equation (5) and the beat signal obtained by the reflection surface of the fiber 117 can be compared to obtain the distance.

The surface shape measuring method and apparatus in Example 10 will be described with reference to FIG. A part of the light emitted from the semiconductor laser is guided to the reference optical system by the fiber coupler 103. In the reference optical system, the laser beam is branched into two by the fiber coupler 104 and is further selectively guided to the

optical fibers

2103 and 2104 having different lengths by the optical switch 2101 to provide a certain optical path difference, and then the optical switch 2101. The optical fiber is selected by the optical switch 2102 so that the same optical fiber as the optical fiber selected in (1) is selected, multiplexed by the fiber coupler 105, and received by the light receiver 107. This has the structure of a Mach-Zehnder interferometer, and the light receiver 107 generates a constant beat signal proportional to the optical path difference.

On the other hand, the light that has not been guided to the reference optical system passes through the circulator 108 and is branched by the fiber coupler 111, part of the light is reflected by the reference mirror 112 and becomes the reference light, and most of the rest is made into space by the collimator lens 113. The target 114 is irradiated. The light reflected from the object 114 passes through the collimator lens 113 again and merges with the reference light from the reference mirror 112 at the fiber coupler 111 portion, and then guided to the light receiver 109 by the circulator 108 to be measured with the reference light. A beat signal is generated by light interference. The beat signal received by the light receiver 109 is sampled with the beat signal received by the light receiver 107. At this time, the

optical fiber

2103 or 2104 of the reference optical system selects a fiber that is close to the distance to the object by the optical switch. As a result, the second term of Equation (7) is reduced, and the non-linear influence can be suppressed. Although the number of optical fibers is two in FIG. 20, a plurality of optical fibers may be provided according to the measurement distance.

The surface shape measuring method and apparatus in Example 11 will be described with reference to FIG. In the eleventh embodiment, the distance measuring unit 2201 of any of the first to tenth embodiments is held, and the stage 2203 on which the focus lens 2202 is mounted is driven to adjust the focus on the target, and the galvanometer mirrors 2204 and 2205 are shaken. Thus, it is possible to measure the shape of the object by scanning in two dimensions.

As an example of beam scanning, a galvanometer mirror is used. However, a method of scanning by rotating a mirror mounted on a rotary motor or a method of scanning by a polygon mirror may be used.

DESCRIPTION OF SYMBOLS 101 ... Semiconductor laser, 102 ... Signal generator, 103 ... Fiber coupler, 104 ... Fiber coupler, 105 ... Fiber, 106 ... Fiber coupler, 107 ... Light receiver, 108 ... Circulator, 109 ... Light receiver, 110 ... Fiber switch, DESCRIPTION OF SYMBOLS 111 ... Fiber coupler, 112 ... Reference mirror, 113 ... Fiber collimator, 114 ... Measurement object, 115 ... Fiber coupler, 116 ... Reference mirror, 117 ... Calibration fiber, 118 ... Attenuator, 119 ... PC, 120 ... Monitor , 201 ... reference mirror, 202 ... beam splitter, 203 ... light receiver, 301 ... beat signal, 401 ... optical frequency of reference light, 402 ... optical frequency of measurement light, 501 ... reference light when the sweep frequency is nonlinear Optical frequency, 502 ... Measurement light when sweep frequency is non-linear Optical frequency, 601 ... Fiber coupler, 602 ... Fiber, 603 ... Fiber coupler, 604 ... Light receiver, 701 ... Beam splitter, 702 ... Reference mirror, 801 ... Beat signal to be measured, 802 ... Beat of reflection point for calibration 901... Beat signal of each reflection point of calibration fiber, 902... Beat signal to be measured, 1001... Reflection point position of calibration fiber at the time of initial calibration, 1101. Point position, 1201 ... Fiber processing method, 1401 ... Calibration fiber with different reflection point intervals, 1501 ... Polarizing beam splitter, 1502 ... Circulator, 1503 ... Light receiver, 1701 ... Fiber coupler, 1702 ... Calibration fiber, 1703 ... Calibration Fiber 1704 ... Calibration fiber 1705 ... Reflective surface, 1706 ... reflective surface, 1707 ... reflective surface, 1801 ... fiber coupler, 1802 ... reflection point, 1901 ... temperature control box, 1902 ... temperature control box, 2101 ... fiber switch, 2102 ... fiber switch, 2103 ... see 2104. Reference fiber, 2201. Distance measuring unit, 2202. Focus lens, 2203 Focus lens, 2204 Galvanometer mirror, 2205 Galvanometer mirror.

Claims

A light source that emits light;
A first optical system that includes a separation unit that separates the light into reference light and measurement light, and a measurement target installation unit that sets a measurement target, and emits the reference light and reflected light reflected by the measurement target;
A second optical system that includes a separation unit that separates the light into reference light and measurement light and a plurality of reflection units whose positions are known in advance, and that emits the reference light and the reflected light reflected by the respective reflection units When,
An optical system selector that selects one of the first optical system and the second optical system;
A light receiving unit that receives a plurality of lights emitted from the first optical system or the second optical system, and a distance that analyzes the light received by the light receiving unit and calculates a distance to the measurement object or the reflecting unit A calculation unit;
A correction value calculation unit that calculates a correction value using the distance to the reflection unit calculated by the distance calculation unit;
And a correction unit that corrects the distance to the measurement target using the correction value.
In claim 1,
The measurement object installation part has a movable range of a predetermined distance,
The distance from the light source to the light source at a position farthest from the light source in the movable range is equal to the distance from the light source to the light source at the farthest reflection portion among the plurality of reflection units.
In claim 1,
The measuring apparatus, wherein the intervals between the plurality of reflecting portions are non-uniform.
In claim 1,
The measuring apparatus according to claim 1, wherein the plurality of reflecting units are a plurality of fibers having a reflecting surface at an end far from the light source and having different distances to the reflecting surface.
In claim 1,
The measuring apparatus further comprising an attenuator at a position farther from the light source than the reflecting portion.
In claim 1,
The first optical system further includes a calibration interferometer.
In claim 1,
The optical system selector is a fiber switch or a polarization beam splitter.
In claim 1,
The second optical system further includes a temperature sensor.
A first step of selecting an optical path of light emitted from the light source by an optical system selection unit;
When the optical system selection unit selects the first optical system, the light is separated into first reference light and first measurement light, and the first reflected light reflected by the first measurement light on the measurement object A second step of emitting the first reference light to the light receiving unit;
When the optical system selection unit selects the second optical system, the light is separated into the second reference light and the second measurement light, and the second measurement is performed by a plurality of reflection units whose positions are known in advance. A third step of emitting the second reflected light reflected by the light and the second reference light to the light receiving unit;
A fourth step of analyzing the light received by the light receiving unit and calculating a distance to the measurement object or the reflection unit;
A fifth step of calculating a correction value using the distance to the reflecting portion calculated in the fourth step;
And a sixth step of correcting the distance to the measurement object using the correction value.
In claim 9,
The measuring method characterized in that intervals between the plurality of reflecting portions are non-uniform.
In claim 9,
The measurement method, wherein the optical system selection unit is a fiber switch or a polarization beam splitter.