Light measuring device

Abstract

This light measurement device is provided with: a wavelength scanning light source (1) that outputs scanning light having a wavelength continuously varying with respect to time; an irradiation optical system (3) that emits measurement output light formed by the scanning light from the wavelength scanning light source (1) as measurement light to a space toward an object to be measured (8), receives reflected light obtained by reflecting the measurement light by the object to be measured (8), and outputs the received reflected light as measurement reflected light; a surrounding light path (4) that has a loop section in which reference output light formed from the scanning light from the wavelength scanning light source (1) surrounds N (an integer of 0 or more) turns, and outputs surrounding reference light for each turn; and a measurement signal acquisition unit (5) that multiplexes the measurement reflected light from the irradiation optical system (3) and the surrounding reference light from the surrounding light path (4), outputs a fine measurement signal obtained by photoelectrically converting the multiplexed interference light, and outputs a plurality of coarse measurement signals composed of electrical signals, the plurality of coarse measurement signals being composed of a plurality of coarse measurement light beams, the plurality of coarse measurement light beams being formed on the basis of the scanning light. A plurality of turns of measurement light having different refractive index dependencies with respect to the optical path; and a signal processing unit (7) that obtains an optical path length difference between the reflected light for measurement and the surrounding reference light from the fine measurement signal from the measurement signal acquisition unit (5), and obtains an optical path length difference between the reflected light for measurement and the surrounding reference light from the plurality of coarse measurement signals from the measurement signal acquisition unit (5). The number of turns of the surrounding reference light in the surrounding light path (4), the number of turns of the surrounding reference light having the optical path length difference between the reflected light for measurement and the surrounding reference light being obtained.

Description

Technical Field

[0001] The present invention relates to a light measuring device. Background Art

[0002] As a method of measuring the distance from a light source to an object using light emitted from a light source, a pulse propagation method, a triangulation distance measurement method, a confocal method, a white interference method, a wavelength scanning interference method, and the like are known.

[0003] Among such methods, Patent Document 1 discloses a measuring device that uses a wavelength scanning interferometry method and can expand the measuring range without being limited by the coherence specific to the light source.

[0004] The measuring device shown in Patent Document 1 configures a surround reference optical system consisting of a 2×2 fiber coupler, optical fibers, and an optical path delay / selector between a 1×2 fiber directional coupler (coupler) and a 1×2 fiber coupler for interference, and has a measuring light path and a reference light path. In the measuring light path, the measuring light output reaches the spectrometer from the coupler, and the measuring light reflected by the measuring object reaches the 1×2 fiber coupler for interference from the spectrometer. In the reference light path, the reference light output reaches the surround reference optical system from the coupler, and the surround reference light reaches the 1×2 fiber coupler for interference.

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-41706 Summary of the invention

[0006] With regard to the measuring device shown in Patent Document 1, since the refractive index of the optical fiber is temperature-dependent, the speed of light in the optical fiber varies by tens of μm / min depending on the ambient temperature, and the optical path lengths of the measuring optical path and the reference optical path are susceptible to variation. In particular, since the reference optical path is provided with a surround reference optical system, the optical path length per turn is susceptible to variation, and the measurement accuracy is susceptible to temperature changes.

[0007] The present invention has been proposed in view of the above-mentioned problems, and its purpose is to obtain an optical measuring device of wavelength scanning interference method, which can expand the measurement range and suppress the resistance to temperature changes, that is, it is not easily affected by environmental temperature changes and can perform high-precision measurements.

[0008] The optical measurement device of the present invention comprises: a wavelength scanning light source that outputs scanning light whose wavelength changes continuously with respect to time; an irradiation optical system that emits measurement output light formed by the scanning light from the wavelength scanning light source as measurement light toward a measurement object into space, receives reflected light obtained by the measurement object reflecting the measurement light, and outputs the reflected light as measurement reflected light; a surrounding light path that has a loop portion, in which reference output light formed by the scanning light from the wavelength scanning light source circulates N times in the loop portion, and outputs surrounding reference light for each circumference, wherein N is an integer greater than or equal to 0; and a measurement signal acquisition unit that receives the measurement reflected light from the irradiation optical system. and a surround reference light from a surround light path, outputs a precise measurement signal after photoelectric conversion of the combined interference light, and outputs a plurality of coarse measurement signals composed of electrical signals, wherein the plurality of coarse measurement signals are obtained based on scanning light using a plurality of turns of measurement light having different refractive index dependencies with respect to the optical path; and a signal processing unit, which obtains the optical path length difference between the measurement reflected light and the surround reference light through the precise measurement signal from the measurement signal acquisition unit, and identifies the number of turns of the surround reference light in the surround light path from which the optical path length difference between the measurement reflected light and the surround reference light is obtained through the plurality of coarse measurement signals from the measurement signal acquisition unit.

[0009] Effects of the Invention

[0010] According to the present invention, even when a low-coherence light source having a narrow measurement range is used, the measurement range can be expanded, and the distance to the measurement object can be measured with high accuracy without being easily affected by changes in ambient temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 1 is a diagram showing the structure of a light measuring device according to the first embodiment.

[0012] Figure 2 It is a schematic diagram showing a spectrum formed by the reflected light for measurement and a spectrum formed by the reflected light from the end face.

[0013] Figure 3 This is a schematic diagram showing the optical path length formed by the reflected light for measurement, the optical path length formed by the surround reference light in the first wavelength region, and the optical path length formed by the surround reference light in the second wavelength region in the optical measurement device according to the first embodiment.

[0014] Figure 4 This is a schematic diagram showing a spectrum formed by the surround reference light in the first wavelength region and a spectrum formed by the surround reference light in the second wavelength region in the optical measurement device according to the first embodiment.

[0015] Figure 5This is a schematic diagram showing the light intensity of a part of the scanning light before passing through the optical filter in the light measuring device according to the first embodiment.

[0016] Figure 6 This is a schematic diagram showing light intensity obtained by dividing a part of scanning light that has passed through the optical filter into k in the light measuring device according to the first embodiment.

[0017] Figure 7 This is a schematic diagram showing a spectrum obtained by precise measurement in the light measuring device according to the first embodiment.

[0018] Figure 8 This is a schematic diagram showing a spectrum obtained by rough measurement in the light measuring device according to the first embodiment.

[0019] Fig. 9 This is a schematic diagram showing how the slope of frequency with respect to time changes due to chromatic dispersion per loop of the loop reference light in the loop unit in the optical measurement device according to the first embodiment.

[0020] Fig.10 This is a schematic diagram showing, as another example, how the slope of the frequency with respect to time changes due to wavelength dispersion per turn of the loop of the measurement reflected light in the loop section in the light measurement device according to the first embodiment.

[0021] Fig.11 This is a diagram showing the structure of a light measuring device according to the second embodiment.

[0022] Fig.12 1 is a diagram showing the configuration of a rough measurement signal acquisition unit in the light measurement device according to the second embodiment.

[0023] Fig.13 This is a schematic diagram showing the optical path length formed by the reflected light for measurement, the optical path length formed by the surround reference light of the P wave, and the optical path length formed by the surround reference light of the S wave in the optical measurement device according to the second embodiment.

[0024] Fig.14 This is a schematic diagram showing a spectrum formed by P-wave surround reference light and a spectrum formed by S-wave surround reference light in the optical measurement device according to the second embodiment.

[0025] Fig.15 It is a diagram showing the structure of a light measuring device according to the third embodiment.

[0026] Fig.16 It is a diagram showing the structure of a light measuring device according to a fourth embodiment. DETAILED DESCRIPTION

[0027] Implementation Method 1

[0028] use Figures 1 to 10 The light measuring device according to Embodiment 1 will be described.

[0029] The optical measurement device according to the first embodiment is an optical measurement device of a wavelength scanning interferometry method using a wavelength scanning optical interferometry tomography (SS-OCT: SweptSource-OCT).

[0030] The light measuring device according to the first embodiment is a light measuring device that uses a low-coherence light source (hereinafter referred to as a wavelength-swept light source) having a short coherence length, for example, a coherence length of about 10 mm.

[0031] Low coherence light sources are cheap but have a narrow measurement range.

[0032] The optical measurement device according to the first embodiment achieves an expansion of the measurement range by arranging a surround light path in the reference light path.

[0033] The optical measurement device involved in embodiment 1 identifies the number of turns of the surround light path of the reference output light based on the scanning light from the wavelength scanning light source using a plurality of rough measurement signals composed of electrical signals. The plurality of rough measurement signals are obtained using a plurality of turn measurement lights having different refractive index dependencies with respect to the optical path.

[0034] The optical measurement device according to Embodiment 1 obtains a plurality of rough measurement signals using the wavelength dependence of the refractive index caused by the light propagation medium in the reference light path, namely the so-called wavelength dispersion, and uses the obtained plurality of rough measurement signals to identify the number of turns of the reference output light around the light path.

[0035] The optical measurement device involved in embodiment 1 utilizes the fact that the shift amount of the beat frequency relative to each light of different frequencies is proportional to the number of turns of the surround light path and the wavelength dependence of the refractive index, generates multiple rough measurement signals, and uses the generated multiple rough measurement signals to identify the number of turns of the surround light path of the reference output light.

[0036] The optical measurement device involved in embodiment 1 generates a plurality of rough measurement signals, and uses the generated plurality of rough measurement signals to identify the number of turns of the surround light path of the reference output light. The plurality of rough measurement signals use a beat frequency formed by the turn measurement light of different wavelength regions within the scanning range of the scanning light from the wavelength scanning light source 1.

[0037] Furthermore, the optical path length is proportional to the product of the length and the refractive index of the light propagation medium, the beat frequency is proportional to the optical path length, and the difference in optical path lengths with different wavelength dependencies of the refractive index is proportional to the number of turns around the light path.

[0038] like Figure 1 As shown, the light measurement device according to Embodiment 1 includes a wavelength scanning light source 1 , a light distribution unit 2 , an irradiation optical system 3 , a surround light path 4 , a measurement signal acquisition unit 5 , a measurement position correction signal generation unit 6 , and a signal processing unit 7 .

[0039] In order to facilitate the description of the embodiment, the measurement position correction signal generating unit 6 is shown as a component different from the measurement signal acquiring unit 5 , but the measurement position correction signal generating unit 6 is one component of the measurement signal acquiring unit 5 .

[0040] The wavelength-swept light source 1 includes a laser light source and a scanning unit that continuously changes the wavelength of laser light of a single frequency from the laser light source with respect to time and outputs (emits) wavelength-swept laser light, that is, scanning light.

[0041] The wavelength scanning by the scanning unit may use a method of scanning a plurality of wavelengths simultaneously, such as TROSA used in optical information communication.

[0042] The scanning light preferably scans in a first-order linear manner with respect to time, and the time and wavelength are preferably in a 1:1 relationship.

[0043] However, even if the scanning light is nonlinear with respect to time, the nonlinearity may be compensated by the measurement signal acquisition unit 5 and the signal processing unit 7. As a technique for compensating for the nonlinearity, a generally known technique may be used.

[0044] If the scanning light emitted from the scanning unit is emitted in a cycle of multiple turns (N turns), the light is emitted in units of one cycle, and the emission time is longer than the time between turns and shorter than the time for two turns.

[0045] The wavelength-sweeping light source 1 is a light source with a short coherence length, for example, a coherence length of about 10 mm.

[0046] The wavelength scanning light source 1 continuously changes the wavelength with respect to time within a scanning range, and emits wavelength-scanned laser light, that is, scanning light having a central wavelength of 1550 nm and a scanning range of 100 nm with a wide scanning bandwidth, for example.

[0047] In addition, as a wavelength scanning light source 1, the wavelength region can be continuously changed relative to a plurality of different wavelength regions in a time-division multiplexing manner through a scanning unit within a scanning range, and a laser that is a light scanned into a plurality of wavelength regions, i.e., a scanning light, can be emitted. For example, 20 scanning lights with a wavelength shifted by 5nm each time centered at 1550nm can be scanned in a time-division multiplexing manner, and scanning light with a central wavelength of 1550nm and a scanning range of 100nm having a large scanning bandwidth can be emitted.

[0048] The scanned light from the wavelength scanned light source 1 is input to the light distribution unit 2 via the optical fiber and distributed into the measurement output light and the reference output light. The distribution ratio of the measurement output light and the reference output light is set according to various conditions, but it is preferable to set a larger distribution ratio for the measurement output light so that even if the measurement object 8 is an object with low reflectivity, it can be measured.

[0049] The optical distribution unit 2 is a coupler which is a 1×2 optical fiber directional coupler.

[0050] The optical fiber is a commonly used single-mode optical fiber. The optical fiber connecting the components described below is also a single-mode optical fiber.

[0051] The measurement output light from the light distribution unit 2 is input to the irradiation optical system 3 via the optical fiber, emitted into space toward the measurement object 8 as measurement light, and the reflected light obtained by the measurement object 8 is received and output as measurement reflected light.

[0052] The irradiation optical system 3 includes an optical circulator, a condenser lens, and a connector.

[0053] The optical circulator outputs the measurement output light from the light distribution unit 2 to the condenser lens as measurement light, receives reflected light from the measurement target 8 , and outputs it to the measurement signal acquisition unit 5 as measurement reflected light.

[0054] The optical circulator and the optical distribution unit 2 , and the optical circulator and the measurement signal acquisition unit 5 are connected via optical fibers.

[0055] The measurement light from the optical circulator is guided to the condenser lens through the optical fiber, and the measurement light condensed by the condenser lens is emitted toward the space of the measurement object 8 from the end face of the connector at one end of the optical fiber through the optical fiber.

[0056] The reflected light obtained by reflecting the measurement light from the measurement target 8 is incident on the end face of the connector, passes through the optical circulator, and is output as the measurement reflected light to the measurement signal acquisition unit 5 via the optical fiber.

[0057] In order to obtain sufficient light intensity of the reflected light from the measurement object 8, it is preferable that the measurement object 8 is located near the focal point of the condenser lens.

[0058] Alternatively, light may be spatially scanned by an electrically controlled mirror or the like.

[0059] In the surround light path 4 , the reference output light from the light distribution unit 2 surrounds N (an integer greater than or equal to 0) circles, and surround reference light is output for each circle.

[0060] The surrounding light path 4 has a coupler 41 and a loop portion 42 formed of an optical fiber.

[0061] The coupler 41 is a fiber coupler having two input ports and two output ports.

[0062] The reference output light from the optical distribution unit 2 input to one input port of the coupler 41 is branched to two output ports, one output port being used as surround reference light that is looped around 0, and the other output port being used as surround light to the loop unit 42.

[0063] The surround light from the loop unit 42 input to the other input port of the coupler 41 is branched to two output ports, one of which is used as surround reference light that travels N times, and the other is used as surround light to the loop unit 42 .

[0064] That is, the coupler 41 outputs, from one output port, the surround reference light that directly passes the reference output light and each of the surround reference light that is looped 1 to N times by the loop unit 42 to the measurement signal acquisition unit 5 .

[0065] The loop section 42 is an optical fiber that connects the other output port and the other input port of the coupler 41 .

[0066] The optical fiber constituting the loop portion 42 is a single-mode optical fiber.

[0067] The length of the optical fiber constituting the loop section 42 is set to 1.0 m, for example, with respect to the length of 0.5 m of the reference light path from the wavelength-swept light source 1 to the measurement signal acquisition section 5 excluding the loop section.

[0068] Furthermore, a dispersion-shifted optical fiber may be used as the optical fiber constituting the loop portion 42. By using a dispersion-shifted optical fiber, the slope of the frequency with respect to time can be increased in units of the number of turns.

[0069] In addition, the optical fiber constituting the loop portion 42 may be covered with a heat insulating material. By covering the optical fiber constituting the loop portion 42 with a heat insulating material, the influence of the temperature change of the loop portion 42 can be further suppressed.

[0070] The measurement signal acquisition unit 5 combines the measurement reflected light from the irradiation optical system 3 and the surround reference light from the surround light path 4 , and outputs a precise measurement signal obtained by photoelectrically converting the combined interference light.

[0071] Precision measurement is implemented in the signal processing unit 7, that is, a high-speed Fourier transform (FFT) is performed on the precision measurement signal to obtain the peak position of the spectrum of the interference light of the measurement reflected light and the surrounding reference light in the wavelength region of the scanning range of the scanning light, and the difference in optical path length formed by the measurement reflected light and the surrounding reference light.

[0072] The measurement signal acquisition unit 5 outputs a plurality of rough measurement signals composed of electrical signals based on the scanning light, the plurality of rough measurement signals being obtained by using a plurality of turns measurement lights having different refractive index dependencies on the optical path.

[0073] Rough measurement is performed in the signal processing unit 7, that is, a plurality of rough measurement signals are subjected to fast Fourier transform, and the number of turns in the loop unit 42 is determined using the optical path length difference formed by the plurality of turn measurement lights based on the peak positions of the spectra of the plurality of turn measurement lights.

[0074] The plurality of turns measurement lights having different refractive index dependencies with respect to the optical path, that is, the reference light path, are lights having a plurality of wavelength time dependencies based on the scanning light.

[0075] Specifically, the multiple-turn measurement light is a measurement position correction signal obtained by converting light of multiple different wavelengths within a scanning range of the scanning light into an electrical signal, the correction reference light of different wavelengths obtained by dividing the surround reference light, and the correction reflected light of different wavelengths obtained by dividing the measurement reflected light.

[0076] Each of the plurality of rough measurement signals is a signal obtained by combining correction reference light and correction reflected light of corresponding wavelengths and performing photoelectric conversion on the combined interference light.

[0077] As an example in embodiment 1, when using scanning light with a central wavelength of 1550nm and a scanning range of 100nm, the correction reference light and the correction reflected light are respectively set to light in the first wavelength region of the 1500nm to 1550nm band and light in the second wavelength region of the 1550nm to 1600nm band.

[0078] In addition, the light in the first wavelength region and the light in the second wavelength region are divided into two with the central wavelength of 1550nm as the center, but for example, the light in the first wavelength region can be set to 1500nm to 1560nm, the light in the second wavelength region can be set to 1540nm to 1600nm, and the light in the first wavelength region and the light in the second wavelength region can be partially overlapped. It can also be light in a wavelength region where the light in the first wavelength region is set to 1500nm to 1540nm, the light in the second wavelength region is set to 1560nm to 1600nm, and the light in the first wavelength region and the light in the second wavelength region are separated.

[0079] Alternatively, the light in the scanning range from 1500 nm to 1600 nm may be shifted to light in 20 wavelength regions of 5 nm band.

[0080] The light in the first wavelength region and the light in the second wavelength region based on the scanning light can be divided into the light in the first wavelength region and the light in the second wavelength region by the measurement signal acquisition unit 5 when using a wavelength scanning light source 1 that emits scanning light with a central wavelength of 1550nm and a scanning range of 100nm with a wide scanning bandwidth.

[0081] In addition, when using a wavelength scanning light source 1, it is sufficient to use light of different wavelength regions that is divided into light of a first wavelength region and light of a second wavelength region in the emission stage from the wavelength scanning light source 1. The wavelength scanning light source 1 emits scanning light of different wavelength regions centered on 1550nm, for example, 20 scanning lights with wavelengths shifted by 5nm are scanned in a time division multiplexing manner, which is essentially scanning light with a central wavelength of 1550nm and a scanning range of 100nm.

[0082] In implementation mode 1, multiple rough measurement signals are obtained by combining correction reference light in the first wavelength region and correction reflected light in the first wavelength region, performing photoelectric conversion on the combined interference light, combining correction reference light in the second wavelength region and correction reflected light in the second wavelength region, and obtaining the second rough measurement signal after photoelectric conversion on the combined interference light.

[0083] When using the wavelength scanning light source 1 that continuously changes the wavelength with respect to time within a scanning range and outputs wavelength-scanned laser light, i.e., scanning light, the measurement signal acquisition unit 5 includes a multiplexing unit, a photoelectric conversion unit, and a measurement position correction signal generation unit 6.

[0084] The combining unit combines the measurement reflected light from the irradiation optical system 3 and the surround reference light from the surround light path 4, and outputs the combined light, that is, interference light. The combining unit is a commonly known combining unit that combines two lights to obtain interference light.

[0085] The photoelectric conversion unit converts the interference light from the combining unit into an electric signal, and outputs a measurement signal.

[0086] Furthermore, it is preferable to use a polarization-maintaining optical fiber that maintains two orthogonal polarization states as the optical fiber used in the measurement light path from the optical distribution unit 2 to the photoelectric conversion unit of the measurement signal acquisition unit 5. By using the polarization-maintaining optical fiber, the influence of the delay caused by factors other than the inside of the measurement object 8 is less likely to occur, and the measurement can be performed under the condition that the delay variation in the air layer from the irradiation optical system 3 to the measurement object 8 is small.

[0087] Figure 2The spectrum M formed by the reflected light for measurement indicated by the dark black hill shape and the spectrum S0 to S1 formed by the end surface reflected light as so-called Fresnel reflection reflected by the end surface of the connector of the irradiation optical system 3 indicated by the light black hill shape are shown. N .exist Figure 2 In the equation, C represents the coherence length.

[0088] The spectrum M formed by the reflected measurement light is a spectrum obtained by the signal processing unit 7 performing fast Fourier transform on the measurement signal obtained by converting the beat frequency of the reflected measurement light obtained by the multiplexing unit of the measurement signal acquisition unit 5 into an electrical signal.

[0089] In addition, the spectrum S0~S formed by the end face reflected light N This is a spectrum obtained by fast Fourier transforming a measurement signal obtained by converting the beat frequency of the measurement reflected light obtained by the multiplexing unit of the measurement signal acquisition unit 5 into an electrical signal by the signal processing unit 7 .

[0090] By performing a fast Fourier transform on the electric signal formed by the interference light from the measurement signal acquisition unit 5 , a frequency corresponding to the reflection position is obtained. The stronger the reflected light intensity is, the higher the peak value is.

[0091] When the coherence length is short, the beat frequency S0~S N In general, the longer the reference light path is, that is, the more turns the loop portion 42 has, the lower the peak value of the beat frequency is.

[0092] Figure 3 The optical path length (beat frequency) formed by the measurement reflected light formed by the combining section of the measurement signal acquisition section 5, the optical path length (beat frequency) formed by the surround reference light in the first wavelength region (1500nm to 1550nm band), and the optical path length (beat frequency) formed by the surround reference light in the second wavelength region (1550nm to 1600nm band) are shown.

[0093] The optical path length formed by the surround reference light in the first wavelength region corresponds to the optical path length formed by the first turn measurement light, and the optical path length formed by the surround reference light in the second wavelength region corresponds to the optical path length formed by the second turn measurement light.

[0094] exist Figure 3 In the figure, the vertical axis represents the number of turns of the surround light path, the horizontal axis represents the optical path length (beat frequency), the solid line represents the optical path length formed by the reflected light for measurement, the dotted line represents the optical path length formed by the surround reference light in the first wavelength region, and the single-dot chain line represents the optical path length formed by the surround reference light in the second wavelength region.

[0095] In addition, Figure 3It is shown that the reflected light for measurement is received between the kth and (k+1)th turns. Figure 3 This is a diagram showing a case where the beat frequency fb1 of the k-th surround reference light and the reflected light for measurement is greater than the beat frequency fb2 of the (k+1)-th surround reference light and the reflected light for measurement.

[0096] like Figure 3 As shown, since the optical path length is proportional to the refractive index of the light propagation medium at the wavelength, the optical path length formed by the surrounding reference light in the first wavelength region propagating along the same reference light path is shorter than the optical path length formed by the surrounding reference light in the second wavelength region.

[0097] In a common single-mode optical fiber, the slope of the refractive index / wavelength is about -0.001 / 100nm. For example, the optical path length measured at a wavelength of 1500nm is different from the optical path length measured at a wavelength of 1600nm, and the optical path length becomes shorter as the wavelength increases. When the loop length of the loop portion 42 is set to 1m, if the wavelength increases from 1500nm to 1600nm, the difference in the shortening of the optical path length is 1000μm, which is shifted in the negative direction.

[0098] In addition, with each turn of the loop portion 42, the optical path length formed by the surrounding reference light in the first wavelength region and the optical path length formed by the surrounding reference light in the second wavelength region become longer, and the slope of the optical path length formed by the surrounding reference light in the first wavelength region with respect to the number of turns is greater than the slope of the optical path length formed by the surrounding reference light in the second wavelength region with respect to the number of turns.

[0099] Therefore, the difference between the optical path length formed by the surround reference light in the first wavelength region and the optical path length formed by the surround reference light in the second wavelength region per turn, that is, the shift amount, is proportional to the number of turns.

[0100] Figure 4 The spectrum shown is obtained by fast Fourier transforming the measurement signal obtained by converting the beat frequency obtained by the multiplexing unit of the measurement signal acquisition unit 5 into an electrical signal for each of the surround reference light in the first wavelength region and the surround reference light in the second wavelength region by the signal processing unit 7 .

[0101] exist Figure 4 In FIG. 1 , a spectrum fbλ1 formed by the surrounding reference light in the first wavelength region is represented by a dark black mountain shape, and a spectrum fbλ2 formed by the surrounding reference light in the second wavelength region is represented by a light black mountain shape. Figure 4 This is a diagram for a case where the beat frequency fb1 is greater than the beat frequency fb2.

[0102] exist Figure 4 In the figure, the horizontal axis represents the number of circles, that is, the measured distance, and the vertical axis represents the intensity of the spectrum.

[0103] exist Figure 4 In the figure, spectrum fbλ11 and spectrum fbλ21 located on the left side of the figure represent the spectra when the number of turns is 0, and the interval between the peak position of spectrum fbλ11 and the peak position of spectrum fbλ21 represents the shift amount, in other words, the difference in optical path length when the number of turns is 0.

[0104] In addition, located Figure 4 The spectrum fbλ12 and the spectrum fbλ22 on the right side of the figure represent the spectra when the number of turns is N. The interval between the peak positions of the spectrum fbλ12 and the peak positions of the spectrum fbλ22 represents the shift amount, in other words, the difference in the optical path length when the number of turns is N.

[0105] Therefore, since the amount of displacement is proportional to the number of turns, the timing (Timing) of receiving the reflected light for measurement, in other words, the number of turns, can be determined by knowing the amount of displacement.

[0106] The optical measurement device according to embodiment 1 implements a rough measurement of the number of turns of the loop portion 42 by using the difference between the optical path length formed by the surround reference light in the first wavelength region and the optical path length formed by the surround reference light in the second wavelength region, by making a space exist between the end face of the connector of the irradiating optical system 3 and the measurement object 8 in the measurement light path, thereby utilizing the difference between the wavelength dispersion characteristics of the measurement light path and the wavelength dispersion characteristics of the reference light path.

[0107] The measurement position correction signal generating unit 6 (hereinafter simply referred to as the correction signal generating unit) generates a measurement position correction signal (hereinafter simply referred to as the correction signal) for use in cutting out a plurality of wavelengths in rough measurement for each cycle based on the scanning light of each cycle.

[0108] In this example, the correction signal generating unit 6 generates a correction signal for cutting out each of the first wavelength region and the second wavelength region from the surround reference light and the reflected light for measurement.

[0109] The scanning light emitted from the wavelength scanning light source 1 includes a linear variation (jitter) in the time axis direction, that is, with respect to time, in each cycle, that is, in each scanning.

[0110] The correction signal is a signal for accurately cutting out a plurality of wavelengths even when there is a variation due to jitter in the scanning light.

[0111] The correction signal generating section 6 includes an optical filter 61 and a photodetector 62 .

[0112] A part of the scanned light emitted from the wavelength scanned light source 1 via the light distribution unit 2 is input to the optical filter 61 , and the position correction light in the first wavelength region and the position correction light in the second wavelength region are cut out.

[0113] Input to filter 61 Figure 6 A portion of the scanning light having a central wavelength of 1550 nm and a scanning range of 100 nm is shown, and position correction light in a first wavelength region of 1500 nm to 1500 nm and position correction light in a second wavelength region of 1550 nm to 1600 nm are cut out.

[0114] In addition, if Figure 6 As shown in the figure, the position correction light is to divide the scanning range of the scanning light into 1 / k (k is an integer greater than or equal to 2), λ1 to λ k These k positions can be corrected using light.

[0115] For example, the filter 61 may have k set to 20 and cut out the position correction light from the first wavelength region λ1 to the twentieth wavelength region λ20 having a bandwidth of 5 nm from the frequency band of 1500 nm to 1600 nm.

[0116] By increasing the amount of position correction light, the accuracy of determining the number of turns is improved.

[0117] The optical filter 61 uses an air cell which is a component that transmits only a specific wavelength.

[0118] As the optical filter 61, a component that can obtain an absorption spectrum corresponding to the vibration mode of a molecule, such as an HCN (hydrogen cyanide) gas cell, or a component that allows only a specific wavelength to pass using a Mach-Zehnder (MZ) interferometer, such as an etalon, can be used.

[0119] The photodetector (PD) 62 converts the position correction light in the first wavelength region and the position correction light in the second wavelength region from the optical filter 61 into electrical signals and outputs the first correction signal and the second correction signal to the measurement signal acquisition unit 5 .

[0120] Furthermore, when the 20 position correction lights are cut out by the optical filter 61 , the position correction lights are converted into electrical signals, and the first correction signal to the second correction signal are output to the measurement signal acquisition unit 5 .

[0121] The correction signal generating unit 6 obtains a correction signal using a portion of the scanning light emitted from the wavelength scanning light source 1 input via the optical distribution unit 2, but as the correction signal, it is sufficient to obtain the scanning characteristics of the wavelength scanning light source, so the correction signal can also be obtained by using a surround reference light that surrounds the reference output light from the surround light path 4 by 0 circles (not surrounded).

[0122] In the measurement signal acquisition unit 5, the first correction signal and the second correction signal from the correction signal generation unit 6 are synchronized with the scanning light emitted from the wavelength scanning light source 1, and correction reference light for the first wavelength region and correction reference light for the second wavelength region are cut out from the surround reference light from the surround light path 4 as turn number measurement light, and correction reflected light for the first wavelength region and correction reflected light for the second wavelength region are cut out from the measurement reflected light from the irradiation optical system 3.

[0123] The measurement signal acquisition unit 5 outputs the first rough measurement signal and the second rough measurement signal to the signal processing unit 7. The first rough measurement signal is obtained by combining the correction reference light in the first wavelength region and the correction reflected light in the first wavelength region, and performing photoelectric conversion on the combined interference light. The second rough measurement signal is obtained by combining the correction reference light in the second wavelength region and the correction reflected light in the second wavelength region, and performing photoelectric conversion on the combined interference light.

[0124] In addition, as a wavelength scanning light source 1, when 20 scanning lights with wavelengths shifted by 5 nm are scanned in a time-division multiplexing manner with 1550 nm as the center, and scanning light with a central wavelength of 1550 nm and a scanning range of 100 nm with a large scanning bandwidth is actually emitted, when a precise measurement signal is obtained, the measurement reflected light from the irradiation optical system 3 and the surround reference light from the surround light path 4 actually use a central wavelength of 1550 nm and a scanning range of 100 nm with a large scanning bandwidth.

[0125] When obtaining rough measurement signals in the first and second wavelength regions, 10 measurement reflected lights from the irradiation optical system 3 and surround reference lights from the surround light path 4 may be used after the wavelength is divided into two equal parts, among the 20 scanning lights.

[0126] At this time, the scanning light in the first wavelength region output from the wavelength scanning light source 1 is synchronized with the correction reference light in the first wavelength region input to the measurement signal acquisition unit 5 and the correction reflected light in the first wavelength region, and the scanning light in the second wavelength region output from the wavelength scanning light source 1 is synchronized with the correction reference light in the second wavelength region input to the measurement signal acquisition unit 5 and the correction reflected light in the second wavelength region.

[0127] In this case, the correction signal generating unit 6 is unnecessary.

[0128] The signal processing unit 7 implements precise measurement, that is, in the measurement signal acquisition unit 5, a high-speed Fourier transform is performed on the precise measurement signal composed of the electric signal to obtain the peak position of the spectrum of the interference light of the measurement reflected light and the surrounding reference light in the wavelength region of the scanning range of the scanning light, and the optical path length difference formed by the measurement reflected light and the surrounding reference light. The precise measurement signal is obtained by combining the measurement reflected light from the irradiation optical system 3 and the surrounding reference light from the surrounding light path 4, which have the same frequency band as the scanning range of the scanning light emitted from the wavelength scanning light source 1.

[0129] In precise measurement, the signal processing unit 7 obtains the beat frequency by using the measurement reflected light and the surrounding reference light in the wavelength range with the same frequency band as the scanning range of the scanning light and with a large bandwidth. Therefore, although the half-width of the beat frequency is inversely proportional to the wavelength used for the high-speed Fourier transform, high-precision precise measurement can be performed.

[0130] For example, when the central wavelength is 1550 nm and the scanning range is 100 nm, the half-width of the obtained beat frequency is about 10 um, so that the distance measurement with a sufficiently high accuracy of about 1 μm can be performed.

[0131] Figure 7 Graph 2 shows a spectrum obtained by precise measurement by the signal processing unit 7. Figure 7 In the case of the reflected light used for measurement, Figure 3 When the number of circles shown is the kth circle and the (k+1)th circle, the spectrum on the left side represents the surrounding reference light side of the kth circle, and the spectrum on the right side represents the surrounding reference light side of the (k+1)th circle.

[0132] That is, the optical path length difference between the measurement reflected light and the ambient reference light, that is, the distance, can be measured based on the peak position of the spectrum of interference light of the measurement reflected light and the ambient reference light in the wavelength range scanned by the scanning light.

[0133] However, the number k of turns of the reference light cannot be determined by precise measurement alone.

[0134] For example, it is assumed that the length of the reference light path from the wavelength swept light source 1 to the measurement signal acquisition unit 5 excluding the loop portion 42 is 0.5 m, the loop length of the loop portion 42 is 1.0 m, and the measurement light path passing through the measurement target 8 is 1.8 m.

[0135] The result obtained by the accurate measurement by the signal processing unit 7 is 0.3 m (=1.8-1.5), which is the difference in the optical path length between the measurement reflected light and the surrounding reference light.

[0136] The signal processing unit 7 performs a high-speed Fourier transform in the measurement signal acquisition unit 5 on the first coarse measurement signal that is synchronized with the scanning light emitted from the wavelength scanning light source 1 through the first correction signal from the correction signal generation unit 6, and obtains the optical path length difference in the first wavelength region based on the peak position of the spectrum of the interference light formed by the correction reference light in the first wavelength region.

[0137] The signal processing unit 7 performs a high-speed Fourier transform in the measurement signal acquisition unit 5 on the second coarse measurement signal obtained by synchronizing the second correction signal from the correction signal generation unit 6 with the scanning light emitted from the wavelength scanning light source 1, and obtains the optical path length difference in the second wavelength region based on the peak position of the spectrum of the interference light formed by the correction reference light in the second wavelength region.

[0138] Figure 8 Spectra obtained by fast Fourier transforming the first rough measurement signal and the second rough measurement signal by the signal processing unit 7 are shown.

[0139] like Figure 8 As shown, the peak interval between the spectrum formed by the optical path length difference in the first wavelength region and the spectrum formed by the optical path length difference in the second wavelength region, that is, the shift amount is proportional to the number of turns.

[0140] Therefore, the relationship between the number of turns and the shift amount is stored in advance in a table, or the linear relationship between the number of turns and the shift amount is stored in advance.

[0141] Furthermore, in cases where the slope of wavelength versus temperature of the light propagating medium in the reference light path is not linear, the effect of temperature changes is accounted for in the table or linear relationship.

[0142] Figure 8 is with Figure 4 The same picture, in Figure 8 The spectrum fbλ11 formed by the optical path length difference in the first wavelength region and the spectrum fbλ21 formed by the optical path length difference in the second wavelength region located on the left side of the figure represent the spectra when the number of turns is 0, and the interval between the peak position of the spectrum fbλ11 and the peak position of the spectrum fbλ21 represents the shift amount, in other words, represents the optical path length difference when the number of turns is 0.

[0143] In addition, located Figure 8 The spectrum fbλ12 and the spectrum fbλ22 on the right side of the figure represent the spectra when the number of turns is N. The interval between the peak positions of the spectrum fbλ12 and the peak positions of the spectrum fbλ22 represents the shift amount, in other words, the optical path length difference when the number of turns is N.

[0144] If the first rough measurement signal is a rough measurement signal composed of an electrical signal obtained by combining the measurement reflected light (correction reflected light) from the irradiation optical system 3 in the first wavelength region and the surround reference light (correction reference light) from the surround light path 4, and the second rough measurement signal is a rough measurement signal composed of an electrical signal obtained by combining the measurement reflected light (correction reflected light) from the irradiation optical system 3 in the second wavelength region and the surround reference light (correction reference light) from the surround light path 4, then the optical path length difference in the first wavelength region formed by the correction reflected light and the correction reference light and the optical path length difference in the second wavelength region formed by the correction reflected light and the correction reference light are obtained.

[0145] The shift amount formed by the optical path length difference in the first wavelength region and the optical path length difference in the second wavelength region is obtained, and the number of turns corresponding to the obtained shift amount is obtained based on the obtained shift amount and the relationship between the number of turns and the shift amount stored as a table or the linear relationship between the stored number of turns and the shift amount.

[0146] The signal processing unit 7 performs rough measurement using the first rough measurement signal and the second rough measurement signal from the measurement signal acquisition unit 5 , and acquires the number of turns of the measurement reflected light obtained from the irradiation optical system 3 .

[0147] For example, similar to the above example, assume that the length of the reference light path from the wavelength scanning light source 1 to the measurement signal acquisition unit 5 excluding the loop portion 42 is 0.5 m, the length of the loop portion 42 is 1.0 m, and the measurement light path passing through the measurement object 8 is 1.8 m.

[0148] In the rough measurement performed by the signal processing unit 7, based on the shift amount formed by the optical path length difference in the first wavelength region and the optical path length difference in the second wavelength region and the relationship between the number of turns and the shift amount in the table, it is determined that the number of turns exists between turn number 1 (optical path length of the surrounding reference light is 1.5m) and turn number 2 (optical path length of the surrounding reference light is 2.5m) and is located on the turn number 1 side.

[0149] As a result, it is possible to perform distance measurement of 1.8 m, which is the sum of 0.3 m obtained by precise measurement and 1.5 m, which is the number of turns 1 obtained by rough measurement.

[0150] The signal processing unit 7 performs fast Fourier transform of the precise measurement signal in the precise measurement and fast Fourier transform of each of the first rough measurement signal and the second rough measurement signal in the rough measurement in parallel, thereby achieving high speed.

[0151] The optical measurement device according to the first embodiment uses the difference between the wavelength dispersion characteristics of the measurement light path and the wavelength dispersion characteristics of the reference light path by providing a space between the end face of the connector of the irradiation optical system 3 and the measurement object 8 in the measurement light path. Fig. 9 As shown, the slope of the frequency with respect to time changes according to the wavelength dispersion with each turn of the loop portion 42 surrounding the reference light as a unit, and thus the number of turns can be identified by rough measurement.

[0152] Furthermore, the optical fiber constituting the loop portion 42 may be different from the single-mode optical fiber used in other paths. For example, by using dispersion-shifted optical fiber to increase the slope with respect to the number of turns, the accuracy of identifying the number of turns may be further improved.

[0153] In addition, if Fig.10 As shown, the fact that the thickness of the air layer between the object 8 and the end face of the connector of the irradiating optical system 3 and the object 8 is proportional to the distance to the object 8 can be utilized, and the slope of the frequency with respect to time changes according to the wavelength dispersion per turn of the loop in the loop portion 42 for measuring the reflected light, thereby identifying the number of turns by rough measurement.

[0154] Next, the operations of fine measurement and rough measurement in the light measurement device according to Embodiment 1 will be described.

[0155] First, the operation of the precise measurement will be described.

[0156] If the measurement reflected light is input to the measurement signal acquisition unit 5, the measurement signal acquisition unit 5 combines the input measurement reflected light and the surround reference light before and after the input time point of the measurement reflected light, and outputs the precise measurement signal converted into an electrical signal to the signal processing unit 7.

[0157] The signal processing unit 7 performs a high-speed Fourier transform on the measurement signal, obtains the optical path difference between the measurement reflected light and the surrounding reference light based on the peak position of the spectrum of the interference light of the measurement reflected light and the surrounding reference light in the wavelength region of the scanning range of the scanning light, and obtains the distance formed by the measurement reflected light and the surrounding reference light.

[0158] On the other hand, in the rough measurement, if the measurement reflected light is input to the measurement signal acquisition unit 5, the measurement reflected light of the first wavelength region in the input measurement reflected light, i.e., the correction reflected light, which is synchronized with the first wavelength region of the scanning light emitted from the wavelength scanning light source 1, is obtained by the first correction signal from the correction signal generating unit 6 and the first wavelength region of the scanning light emitted from the wavelength scanning light source 1, and the surrounding reference light of the first wavelength region in the surrounding reference light before and after the input time point of the measurement reflected light, i.e., the correction reference light, are synthesized, and the first rough measurement signal converted into an electrical signal is output to the signal processing unit 7.

[0159] In addition, the measurement signal acquisition unit 5 obtains the measurement reflected light of the second wavelength region in the input measurement reflected light synchronized with the second wavelength region of the scanning light emitted from the wavelength scanning light source 1 through the second correction signal from the correction signal generation unit 6, i.e., the correction reflected light, and the ambient reference light of the second wavelength region in the ambient reference light before and after the input time point of the measurement reflected light, i.e., the correction reference light, and converts the converted second coarse measurement signal into an electrical signal, which is output to the signal processing unit 7.

[0160] In addition, in the case of using a wavelength scanning light source 1 that outputs scanning lights that perform wavelength scanning in the first wavelength region and the second wavelength region that are different from each other in the scanning range by a scanning unit in a time-division multiplexing manner, each of the measurement reflected lights, i.e., correction reflected lights, input synchronously with the scanning lights of the first wavelength region and the second wavelength region emitted from the wavelength scanning light source 1 and each of the surround reference lights, i.e., correction reference lights, of the first wavelength region and the second wavelength region before and after the input time point of the measurement reflected lights of the first wavelength region and the second wavelength region are combined from the measurement signal acquisition unit 5, and the first wavelength region and the second rough measurement signals converted into electrical signals are output to the signal processing unit 7.

[0161] The reflected light for correction and the reference light for correction constitute the light for measuring the number of turns.

[0162] The signal processing unit 7 performs a high-speed Fourier transform on the first rough measurement signal to obtain an optical path length difference in the first wavelength region between the reflected light for measurement in the first wavelength region and the surrounding reference light based on the peak position of the spectrum of the interference light formed by the surrounding reference light in the first wavelength region, and performs a high-speed Fourier transform on the second rough measurement signal to obtain an optical path length difference in the second wavelength region between the reflected light for measurement in the second wavelength region and the surrounding reference light based on the peak position of the spectrum of the interference light formed by the surrounding reference light in the second wavelength region.

[0163] The signal processing unit 7 calculates the shift amount between the optical path length difference in the first wavelength region and the optical path length difference in the second wavelength region, and obtains the number of turns corresponding to the obtained shift amount based on the calculated shift amount, the relationship between the number of turns and the shift amount stored as a table, or the linear relationship between the stored number of turns and the shift amount.

[0164] The signal processing unit 7 obtains the distance to the measurement object 8 based on the distance formed by the measurement reflected light and the surrounding reference light obtained by the precise measurement and the number of turns obtained by the rough measurement, and outputs the obtained distance.

[0165] As described above, in the precise measurement, the measurement reflected light and the surrounding reference light of the same frequency band as the wide scanning range from the wavelength scanning light source 1 are used, and the entire wide frequency band is used for the fast Fourier transform, thereby Figure 7 The peak position shown does not change, and the distance measurement can be maintained with high accuracy.

[0166] In the rough measurement, the high-speed Fourier transform is performed by using the reflected light for measurement and the surrounding reference light in a frequency band with a narrower scanning range than the rough measurement, so that Figure 8 As shown, although the width of the spectrum is increased, the information on the shift amount can be accurately obtained.

[0167] Since the optical measurement device according to the first embodiment has a surround light path having a loop portion, even if a low-coherence light source having a narrow measurement range is used as the wavelength swept light source 1 , the measurement range can be expanded.

[0168] Furthermore, the present invention comprises: a measurement signal acquisition unit 5, which outputs a plurality of rough measurement signals composed of electrical signals based on the scanning light, and the plurality of rough measurement signals are obtained by using a plurality of turns of measurement light having different refractive index dependencies with respect to the optical path; and a signal processing unit 7, which identifies the number of turns of the surround reference light in the surround light path 4 for obtaining the optical path length difference between the measurement reflected light and the surround reference light through the plurality of rough measurement signals from the measurement signal acquisition unit 5, thereby being less susceptible to changes in the ambient temperature and being able to measure the distance to the measurement object with high precision.

[0169] In addition, the light measuring device involved in embodiment 1 obtains multiple coarse measurement signals for identifying the number of turns by using the measurement reflected light and surrounding reference light in wavelength regions corresponding to the wavelength regions obtained by dividing the scanning range of the scanning light from the wavelength scanning light source 1 into a plurality of obtained wavelength regions, thereby not reducing the time resolution of the measurement and not increasing the complexity of the hardware structure of the light measuring device.

[0170] Implementation Method 2

[0171] use Figures 11 to 14The light measuring device according to the second embodiment will be described.

[0172] The light measuring device involved in embodiment 1 obtains the first number of turns measurement light and the second number of turns measurement light having different refractive index dependencies on the optical path for obtaining the first rough measurement signal and the second rough measurement signal by using measurement reflected light and surrounding reference light in wavelength regions corresponding to wavelength regions obtained by dividing the scanning range of the scanning light from the wavelength scanning light source 1 into a plurality of obtained wavelength regions. On the other hand, the light measuring device involved in embodiment 2 obtains the first rough measurement signal and the second rough measurement signal by using correction reflected light and correction reference light obtained by separating the measurement reflected light and the surrounding reference light into two orthogonal polarized lights, respectively. This point is different from embodiment 1, and other aspects are the same or identical.

[0173] exist Figures 11 to 14 in Figures 1 to 10 The same reference numerals as those used in the drawings represent the same or corresponding parts.

[0174] The optical measurement device involved in embodiment 2 utilizes the polarization dependence of the refractive index of the light propagation medium on the two polarizations of light, namely, light of polarization mode P and light of polarization mode S orthogonal to polarization mode P. In other words, it utilizes the so-called birefringence to obtain the first rough measurement signal and the second rough measurement signal to identify the number of turns of the surrounding light path.

[0175] The optical measurement device involved in embodiment 2 utilizes the fact that the difference between the beat frequency (optical path length) of light of polarization mode P and the beat frequency (optical path length) of light of polarization mode S, i.e., the so-called shift amount, is proportional to the number of turns of the surround light path and the birefringence, to obtain the first rough measurement signal and the second rough measurement signal, and uses the obtained first rough measurement signal and the second rough measurement signal to identify the number of turns of the surround light path of the reference output light.

[0176] Furthermore, the optical path length is proportional to the product of the length and the refractive index of the light propagation medium, the beat frequency is proportional to the optical path length, and the difference in optical path lengths with different birefringence is proportional to the number of turns around the light path.

[0177] like Fig.11 As shown, the optical measurement device according to the second embodiment includes a wavelength scanning light source 1 , a light distribution unit 2 , an irradiation optical system 3 , a surround light path 4 , a measurement signal acquisition unit 5 , and a signal processing unit 7 .

[0178] The measurement signal acquisition unit 5 has Fig.12 The rough measurement signal acquisition unit 9 is shown.

[0179] Next, the light measurement device according to the second embodiment will be described focusing on the measurement signal acquisition unit 5 , particularly the rough measurement signal acquisition unit 9 , in the light measurement device according to the first embodiment.

[0180] The description of the wavelength scanning light source 1 , the light distribution unit 2 , the irradiation optical system 3 , and the surround light path, which have the same configuration as the light measurement device according to the first embodiment, will be omitted as much as possible.

[0181] In addition, it is preferable that polarization-maintaining fibers be used as optical fibers used for the measurement optical path and the reference optical path. By using polarization-maintaining fibers, birefringence is temporally and spatially stable over the entire length of the polarization-maintaining fibers.

[0182] The measurement signal acquisition unit 5 combines the measurement reflected light from the irradiation optical system 3 and the surround reference light from the surround light path 4 , and outputs a precise measurement signal obtained by photoelectrically converting the combined interference light.

[0183] like Fig.12 As shown, the rough measurement signal acquisition unit 9 includes a reflected light spectrometer 91 , a reference light spectrometer 92 , a P wave multiplexing unit 93 , an S wave multiplexing unit 94 , a P wave balanced detector 95 , and an S wave balanced detector 96 .

[0184] The measurement signal acquisition unit 5 uses an integrated coherent receiver (ICR: Integrated Coherent Receiver), which is an optical integrated device generally used in a receiver in the field of optical information communication.

[0185] The reflected light spectrometer 91 splits the measurement reflected light from the irradiation optical system 3 into measurement reflected light of polarization mode P (hereinafter referred to as P wave), i.e., correction reflected light of P wave, and measurement reflected light of polarization mode S (hereinafter referred to as S wave), i.e., correction reflected light of S wave.

[0186] The reference light spectrometer 92 splits the surround reference light from the surround light path 4 into P-wave surround reference light, that is, P-wave correction reference light, and S-wave surround reference light, that is, P-wave correction reference light.

[0187] The P-wave combining unit 93 combines the P-wave measurement reflected light from the reflected light spectrometer 91 and the P-wave surround reference light from the reference light spectrometer 92, and outputs the combined light, i.e., interference light of the P-wave having a beat frequency.

[0188] The S wave combining unit 94 combines the S wave measurement reflected light from the reflected light spectrometer 91 and the S wave surround reference light from the reference light spectrometer 92 to output the combined light as S wave interference light having a beat frequency.

[0189] The P-wave balanced detector 95 converts the interference light of the P-wave from the P-wave combining unit 93 into an electric signal, and outputs a first measurement signal (P-wave).

[0190] The S wave balanced detector 96 converts the interference light of the S wave from the S wave combining unit 94 into an electric signal, and outputs a second measurement signal (S wave).

[0191] The P-wave balanced detector 95 and the S-wave balanced detector 96 are composed of balanced photodiodes (BPDs), and convert interference light of the P wave and interference light of the S wave into electrical signals.

[0192] Fig.13 The optical path length (beat frequency) formed by the surrounding reference light of the P wave and the optical path length (beat frequency) formed by the surrounding reference light of the S wave are shown.

[0193] exist Fig.13 In the figure, the vertical axis represents the number of turns of the surround light path, the horizontal axis represents the optical path length (beat frequency), the solid line represents the optical path length formed by the reflected light for measurement, the dotted line represents the optical path length formed by the surround reference light of the P wave, and the single-dot chain line represents the optical path length formed by the surround reference light of the S wave.

[0194] In addition, Fig.13 It is shown that the reflected light for measurement is received between the kth and (k+1)th turns. Fig.13 This is a diagram showing a case where the beat frequency fb1 of the k-th surround reference light and the reflected light for measurement is greater than the beat frequency fb2 of the (k+1)-th surround reference light and the reflected light for measurement.

[0195] The optical path length formed by the surrounding reference light of the P wave is shorter than the optical path length formed by the surrounding reference light of the S wave.

[0196] The optical path length formed by the surround reference light of the P wave and the optical path length formed by the surround reference light of the S wave become longer each time they circle the loop portion 42, and the slope of the optical path length formed by the surround reference light of the P wave with respect to the number of circles is greater than the slope of the optical path length formed by the surround reference light of the S wave with respect to the number of circles.

[0197] Therefore, the difference between the optical path length formed by the P-wave surround reference light and the optical path length formed by the S-wave surround reference light per turn, that is, the shift amount, is proportional to the number of turns.

[0198] Fig.14 The spectrum obtained by performing fast Fourier transform by the signal processing unit 7 on each of the first (P wave) measurement signal and the second (S wave) measurement signal is shown.

[0199] exist Fig.14In the figure, the dark black mountain represents the spectrum fbP formed by the surrounding reference light of the P wave, and the light black mountain represents the spectrum fbS formed by the surrounding reference light of the S wave. Fig.14 This is a diagram for a case where the beat frequency fb1 is greater than the beat frequency fb2.

[0200] exist Fig.14 In the figure, the horizontal axis represents the number of circles, that is, the measured distance, and the vertical axis represents the intensity of the spectrum.

[0201] exist Fig.14 , the spectrum fbP1 and the spectrum fbS1 on the left side of the figure represent the spectra when the number of turns is 0, and the interval between the peak position of the spectrum fbP1 and the peak position of the spectrum fbS1 represents the shift amount, in other words, the difference in the optical path length when the number of turns is 0.

[0202] In addition, located Fig.14 Spectra fbP2 and fbS2 on the right side of the figure represent spectra when the number of turns is N. The interval between the peak positions of spectrum fbP2 and spectrum fbS2 represents the shift amount, in other words, the difference in optical path length when the number of turns is N.

[0203] Therefore, since the amount of displacement is proportional to the number of turns, the timing at which the reflected light for measurement is received, in other words, the number of turns, can be determined by knowing the amount of displacement.

[0204] according to Fig.13 and Fig.14 It can be seen that birefringence is determined by the light propagation medium in the measurement light path and the reference light path, and the shift amount is proportional to the number of turns. Therefore, the relationship between the shift amount and the number of turns is obtained in advance and the relationship between the number of turns and the shift amount is stored in advance in a table.

[0205] Next, the operations of fine measurement and rough measurement in the light measurement device according to the second embodiment will be described.

[0206] First, the operation of the precise measurement will be described.

[0207] If the measurement reflected light is input to the measurement signal acquisition unit 5, the measurement signal acquisition unit 5 combines the input measurement reflected light and the surround reference light before and after the input time point of the measurement reflected light, and outputs the precise measurement signal converted into an electrical signal to the signal processing unit 7.

[0208] The signal processing unit 7 performs a high-speed Fourier transform on the precise measurement signal, obtains the optical path length difference between the measurement reflected light and the surrounding reference light based on the peak position of the spectrum of the interference light of the measurement reflected light and the surrounding reference light in the wavelength region of the scanning range of the scanning light, and obtains the distance formed by the measurement reflected light and the surrounding reference light.

[0209] On the other hand, in the rough measurement, if the measurement reflected light is input to the measurement signal acquisition unit 5, the measurement reflected light of the P wave in the input measurement reflected light and the surround reference light of the P wave in the surround reference light before and after the input time point of the measurement reflected light are synthesized by the rough measurement signal acquisition unit 9 in the measurement signal acquisition unit 5, and the first rough measurement signal converted into an electrical signal is output to the signal processing unit 7.

[0210] In addition, the measurement signal acquisition unit 5 combines the measurement reflected light of the S wave in the input measurement reflected light and the surround reference light of the S wave in the surround reference light before and after the input time point of the measurement reflected light, and outputs the second coarse measurement signal converted into an electrical signal to the signal processing unit 7.

[0211] The signal processing unit 7 performs a high-speed Fourier transform on the first rough measurement signal to obtain the optical path length difference of the P wave between the P-wave measurement reflected light and the P-wave surrounding reference light based on the peak position of the spectrum of the interference light formed by the P-wave surrounding reference light, and performs a high-speed Fourier transform on the second rough measurement signal to obtain the optical path length difference of the S wave between the S-wave measurement reflected light and the S-wave surrounding reference light based on the peak position of the spectrum of the interference light formed by the S-wave surrounding reference light.

[0212] The signal processing unit 7 obtains the shift amount between the optical path length difference of the P wave and the optical path length difference of the S wave, and obtains the number of turns corresponding to the obtained shift amount based on the obtained shift amount and the relationship between the number of turns and the shift amount stored as a table.

[0213] The signal processing unit 7 obtains the distance to the measurement object 8 based on the distance formed by the measurement reflected light and the surrounding reference light obtained by the precise measurement and the number of turns obtained by the rough measurement, and outputs the obtained distance.

[0214] As described above, in precise measurement, the same frequency band as the wide scanning range of the wavelength scanning light source 1 is used for the measurement reflected light and the surrounding reference light. The entire wide frequency band is used for the fast Fourier transform, so that the peak position does not change and the distance measurement can be maintained with high accuracy.

[0215] In the rough measurement, relative to the rough measurement, the reflected light for measurement of the P wave and the surround reference light of the P wave, the reflected light for measurement of the S wave and the surround reference light of the S wave are used, and the first rough measurement signal formed by the P wave and the second rough measurement signal formed by the S wave are subjected to high-speed Fourier transform, thereby accurately obtaining information on the shift amount.

[0216] Since the optical measurement device according to the second embodiment has a surround light path having a loop portion, even if a low-coherence light source having a narrow measurement range is used as the wavelength swept light source 1 , the measurement range can be expanded.

[0217] Furthermore, the device comprises: a measurement signal acquisition unit 5, which utilizes the dependence of different refractive indices with respect to the optical path, that is, utilizes the polarization dependence of the refractive index of the light propagation medium with respect to two polarized lights of light, namely, light of polarization mode P and light of polarization mode S, in other words, utilizes the so-called double refraction, and outputs each of a first rough measurement signal formed by a P wave and a second rough measurement signal formed by an S wave, which are composed of electrical signals, through each of the P-wave surrounding reference light and the S-wave surrounding reference light; and a signal processing unit 7, which identifies the number of turns of the surrounding reference light in the surrounding light path 4, which obtains the optical path length difference between the measurement reflected light and the surrounding reference light, through the P-wave rough measurement signal and the S-wave rough measurement signal from the measurement signal acquisition unit 5, and thus is not easily affected by changes in the ambient temperature and can measure the distance to the measurement object with high accuracy.

[0218] In addition, the optical measuring device involved in embodiment 2 obtains the first coarse measurement signal and the second coarse measurement signal for identifying the number of turns by using the P wave and the S wave in the measurement reflected light and the surrounding reference light respectively, thereby not reducing the time resolution of the measurement and not increasing the complexity of the hardware structure of the optical measuring device.

[0219] Implementation 3

[0220] use Fig.15 A light measuring device according to Embodiment 3 will be described.

[0221] The light measurement device according to the third embodiment is different from the light measurement device according to the first embodiment in that a common optical path interference system is used, and the other aspects are the same or identical.

[0222] exist Fig.15 in Figures 1 to 10 The same reference numerals as those used in the drawings represent the same or corresponding parts.

[0223] In the optical measurement device involved in embodiment 1, the measurement output light is emitted from the light distribution unit 2 toward the measurement object 8 as measurement light through the irradiation optical system 3, the emitted measurement light is reflected by the measurement object 8, and reaches the measurement signal acquisition unit 5 as measurement reflected light through the irradiation optical system 3. The optical fiber used in the measurement light path is different from the optical fiber used in the reference light path for the reference output light to reach the measurement signal acquisition unit 5 as surround reference light from the light distribution unit 2 via the surround light path 4.

[0224] On the other hand, the optical measurement device according to the third embodiment uses a common optical path interference system to make the measurement optical path and the reference optical path a common optical fiber.

[0225] In addition, Fig.15In the figure, the reflected light for measurement and the surrounding reference light are shown separately, but this is only for the convenience of explanation and they are common optical fibers.

[0226] like Fig.15 As shown, the light measuring device involved in embodiment 3 has a wavelength scanning light source 1, a light distribution unit 2, an irradiation optical system 3, a surround light path 4, a measurement signal acquisition unit 5 having a measurement position correction signal generation unit 6, and a signal processing unit 7, just like the light measuring device involved in embodiment 1.

[0227] As described above, the light measurement device according to the third embodiment is different from the light measurement device according to the first embodiment in that a common optical path interference system is used, and therefore the description will focus on the measurement optical path and the reference optical path.

[0228] The measurement light path will be described.

[0229] The scanned light from the wavelength scanned light source 1 is distributed by the light distribution unit 2, and the scanned output light obtained is input to the coupler 41 of the surround light path 4 via the common optical fiber. The scanned output light input to the coupler 41 is directly input to the irradiation optical system 3 as the output light for measurement via the common optical fiber.

[0230] The measurement output light input to the irradiation optical system 3 is emitted as measurement light to the space toward the measurement object 8. The irradiation optical system 3 receives the reflected light obtained by the measurement object 8, and outputs it from the irradiation optical system 3 to the measurement signal acquisition unit 5 as measurement reflected light via a common optical fiber.

[0231] The reference light path will be described.

[0232] The scanned light from the wavelength scanned light source 1 is distributed by the light distribution unit 2, and the scanned output light obtained is input to the coupler 41 of the surround light path 4 via the common optical fiber. The scanned output light input to the coupler 41 is directly input to the irradiation optical system 3 as the surround reference light of the surround 0 circle via the common optical fiber.

[0233] The scan output light input to the coupler 41 is looped in the loop section 42 , and is input to the irradiation optical system 3 via a common optical fiber as respective loop reference lights that have looped the loop section 42 once to N times.

[0234] The surround reference light of each of the 0th to Nth turns from the surround light path 4 passes through the irradiation optical system 3 and is then output to the measurement signal acquisition unit 5 through a common optical fiber.

[0235] The scan output light from the light distribution unit 2 is input to the measurement signal acquisition unit 5 as the measurement reflected light and the surround reference light via the common optical path interference system as described above.

[0236] The measurement signal acquisition unit 5 operates in the same manner as the measurement signal acquisition unit 5 in embodiment 1 by inputting the measurement reflected light and the surrounding reference light, and outputs a precise measurement signal, a first (first wavelength region) coarse measurement signal, and a second (second wavelength region) coarse measurement signal.

[0237] The signal processing unit 7 which has received the precise measurement signal from the measurement signal acquisition unit 5 performs precise measurement operations similar to the signal processing unit 7 in the first embodiment, and obtains the distance formed by the measurement reflected light and the surround reference light.

[0238] The signal processing unit 7 which has received the first rough measurement signal and the second rough measurement signal from the measurement signal acquisition unit 5 performs a rough measurement operation similar to the signal processing unit 7 in the first embodiment, and obtains the number of turns.

[0239] The signal processing unit 7 obtains the distance to the measurement object 8 based on the distance formed by the measurement reflected light and the surrounding reference light obtained by the precise measurement and the number of turns obtained by the rough measurement, and outputs the obtained distance.

[0240] The optical measuring device involved in embodiment 3 has the same effect as the optical measuring device involved in embodiment 1. In addition, since the measuring optical path and the reference optical path are formed by a common optical path interference system, the influence of the temperature change of the common optical fiber on the measurement of the distance to the measuring object 8 can be suppressed.

[0241] Implementation 4

[0242] use Fig.16 A light measuring device according to Embodiment 4 will be described.

[0243] The light measurement device according to the fourth embodiment is different from the light measurement device according to the second embodiment in that a common optical path interference system is used, and the other aspects are the same or identical.

[0244] exist Fig.16 in Fig.11 The same reference numerals as those used in the drawings represent the same or corresponding parts.

[0245] In the optical measurement device involved in embodiment 2, the measurement output light is emitted from the light distribution unit 2 toward the measurement object 8 as measurement light through the irradiation optical system 3, the emitted measurement light is reflected by the measurement object 8, and reaches the measurement signal acquisition unit 5 as measurement reflected light through the irradiation optical system 3. The optical fiber used in the measurement light path is different from the optical fiber used in the reference light path for the reference output light to reach the measurement signal acquisition unit 5 as surround reference light from the light distribution unit 2 via the surround light path 4.

[0246] On the other hand, the optical measurement device according to the fourth embodiment uses a common optical path interference system to make the measurement optical path and the reference optical path a common optical fiber.

[0247] In addition, Fig.16 In the figure, the reflected light for measurement and the surrounding reference light are shown separately, but this is only for the convenience of explanation and they are common optical fibers.

[0248] like Fig.16 As shown, the optical measurement device according to the fourth embodiment includes a wavelength scanning light source 1, an irradiation optical system 3, a surround light path 4, a measurement signal acquisition unit 5 having a rough measurement signal acquisition unit 9, and a signal processing unit 7, similarly to the optical measurement device according to the second embodiment.

[0249] As described above, the optical measurement device according to the fourth embodiment is different from the optical measurement device according to the second embodiment in that a common optical path interference system is used, and therefore the description will focus on the measurement optical path and the reference optical path.

[0250] The measurement light path will be described.

[0251] The scanning light from the wavelength scanning light source 1 is input to the coupler 41 of the surround light path 4 via a common optical fiber. The scanning light input to the coupler 41 is directly input to the irradiation optical system 3 as output light for measurement via a common optical fiber.

[0252] The measurement output light input to the irradiation optical system 3 is emitted as measurement light to the space toward the measurement object 8. The irradiation optical system 3 receives the reflected light obtained by the measurement object 8, and outputs it from the irradiation optical system 3 to the measurement signal acquisition unit 5 as measurement reflected light via a common optical fiber.

[0253] The reference light path will be described.

[0254] The scanning light from the wavelength scanning light source 1 is input to the coupler 41 of the surround light path 4 via the common optical fiber. The scanning light input to the coupler 41 is directly input to the irradiation optical system 3 as surround reference light of the surround 0 circle via the common optical fiber.

[0255] The scanning light input to the coupler 41 is looped in the loop section 42 , and is input to the irradiation optical system 3 via a common optical fiber as respective loop reference lights that have looped the loop section 42 from 1 to N times.

[0256] The surround reference light of each of the 0th to Nth turns from the surround light path 4 passes through the irradiation optical system 3 and is output to the measurement signal acquisition unit 5 through a common optical fiber.

[0257] The scanned light from the wavelength scanned light source 1 is input to the measurement signal acquisition unit 5 as the measurement reflected light and the surround reference light via the common optical path interference system as described above.

[0258] The measurement signal acquisition unit 5 operates similarly to the measurement signal acquisition unit 5 in Embodiment 2 based on the input measurement reflected light and surround reference light, and outputs a precise measurement signal, a first (P wave) rough measurement signal, and a second (S wave) rough measurement signal.

[0259] The signal processing unit 7 which has received the precise measurement signal from the measurement signal acquisition unit 5 performs precise measurement operations similar to the signal processing unit 7 in the second embodiment, and obtains the distance by measuring the reflected light and the surrounding reference light.

[0260] The signal processing unit 7 for the first rough measurement signal and the second rough measurement signal from the measurement signal acquisition unit 5 performs a rough measurement operation similar to the signal processing unit 7 in the second embodiment, and obtains the number of turns.

[0261] The signal processing unit 7 obtains the distance to the measurement object 8 based on the distance formed by the measurement reflected light and the surrounding reference light obtained by the precise measurement and the number of turns obtained by the rough measurement, and outputs the obtained distance.

[0262] The optical measuring device involved in embodiment 4 has the same effect as the optical measuring device involved in embodiment 2. In addition, since the measuring optical path and the reference optical path are formed by a common optical path interference system, the influence of the temperature change of the common optical fiber on the measurement of the distance to the measuring object 8 can be suppressed.

[0263] Furthermore, it is possible to freely combine the various embodiments, to modify any constituent element in the various embodiments, or to omit any constituent element in the various embodiments.

[0264] Industrial Applicability

[0265] The light measuring device according to the present invention is suitable as a light measuring device for measuring the distance to a measurement object in a processing device or a semiconductor inspection device.

[0266] Description of the label

[0267] 1 wavelength scanning light source, 2 light distribution unit, 3 irradiation optical system, 4 surround light path, 5 measurement signal acquisition unit, 6 measurement position correction signal generation unit, 7 signal processing unit, 8 measurement object, 9 rough measurement signal acquisition unit.

Claims

1. A light measuring device, comprising: A wavelength scanning light source, which outputs scanning light whose wavelength varies continuously with respect to time; an irradiation optical system that emits measurement output light formed by scanning light from the wavelength scanning light source as measurement light toward a measurement object in space, receives reflected light obtained by reflecting the measurement light from the measurement object, and outputs the reflected light as measurement reflected light; A surrounding light path having a loop portion, wherein the reference output light formed by the scanning light from the wavelength scanning light source circles around N times in the loop portion, and the surrounding reference light is output for each circle, wherein: N is an integer greater than or equal to 0; a measurement signal acquisition unit that combines the measurement reflected light from the irradiation optical system and the surround reference light from the surround light path, outputs a precise measurement signal obtained by photoelectrically converting the combined interference light, and outputs a plurality of rough measurement signals composed of electrical signals, the plurality of rough measurement signals being obtained based on the scanning light using a plurality of turn measurement lights having different refractive index dependencies with respect to the optical path; as well as A signal processing unit obtains the optical path length difference between the measurement reflected light and the surrounding reference light through the precise measurement signal from the measurement signal acquisition unit, and identifies the number of turns of the surrounding reference light in the surrounding light path for obtaining the optical path length difference between the measurement reflected light and the surrounding reference light through a plurality of rough measurement signals from the measurement signal acquisition unit.

2. The light measuring device according to claim 1, wherein: The plurality of turns measurement lights having different refractive index dependencies with respect to the optical path are lights having a plurality of wavelength time dependencies based on the scanning light.

3. The light measuring device according to claim 1, wherein The plurality of turn measurement lights having different refractive index dependencies with respect to the optical path are measurement position correction signals obtained by converting the lights divided into a plurality of different wavelengths within the scanning range of the scanning light into electrical signals, correction reference lights of different wavelengths obtained by dividing the surround reference light, and correction reflected lights of different wavelengths obtained by dividing the measurement reflected light. Each of the plurality of rough measurement signals is a signal obtained by combining the correction reference light and the correction reflected light of corresponding wavelengths and performing photoelectric conversion on the combined interference light.

4. The light measuring device according to claim 1, wherein The plurality of turn measurement lights having different refractive index dependencies with respect to the optical path are obtained by converting lights of a plurality of different wavelengths within a scanning range of a surround reference light divided into 0 turns from the surround light path into a measurement position correction signal after being converted into an electrical signal, correction reference lights of different wavelengths for each of the surround reference lights, correction reflected lights of different wavelengths for each of the measurement reflected lights, Each of the plurality of rough measurement signals is a signal obtained by combining the correction reference light and the correction reflected light of corresponding wavelengths and performing photoelectric conversion on the combined interference light.

5. The light measuring device according to claim 1, wherein The scanning light whose wavelength changes continuously with respect to time outputted from the wavelength scanning light source is a laser beam that is a light having a wavelength scanned into a plurality of wavelength regions, i.e., scanning light, in which the wavelength region is continuously changed with respect to a plurality of wavelength regions respectively different in a time division multiplexing manner within the scanning range. The plurality of turn measurement lights having different refractive index dependencies with respect to the optical path are correction reference lights having different wavelengths formed by surround reference lights for each of the lights in the plurality of wavelength regions output from the wavelength scanning light source, and correction reflected lights having different wavelengths formed by measurement reflected lights for each of the lights in the plurality of wavelength regions, Each of the plurality of rough measurement signals is a signal obtained by combining the correction reference light and the correction reflected light of corresponding wavelengths and performing photoelectric conversion on the combined interference light.

6. The light measuring device according to claim 1, wherein The plurality of turn measurement lights having different refractive index dependencies with respect to the optical path are correction reflected light and correction reference light obtained by separating the measurement reflected light and the surrounding reference light into two orthogonal polarized lights, respectively. Each of the plurality of rough measurement signals is a signal obtained by combining the correction reference light and the correction reflected light of corresponding polarized light and performing photoelectric conversion on the combined interference light.

7. The light measuring device according to any one of claims 1 to 6, wherein: The optical path of the measurement output light is a common optical path with the reference output light and the surrounding reference light to the irradiation optical system, and the optical path of the measurement reflected light is a common optical path with the surrounding reference light from the irradiation optical system.

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