OCT measurement device and OCT measurement method

Abstract

The present application provides an OCT measuring device and an OCT measuring method. The OCT measuring device (1) comprises: a wavelength scanning light source (2) that emits light whose wavelength is scanned; an optical interferometer (9) that splits light into measurement light (18) and reference light (19), generates an optical interference intensity signal that indicates the intensity of the interference between the measurement light (18) that is irradiated to a measurement surface (21) of an object (20) to be measured and the reference light (19) that is reflected by the measurement surface (21); a phase modulation section (17) that is disposed in the optical path of the optical interferometer (9); a signal generation section (3) that derives the position of the measurement surface (21) based on the optical interference intensity signal, and generates a phase amount indication signal that indicates the phase amount of the phase modulation section (17); and a phase amount control section (6) that controls the phase amount imparted to the light that is transmitted through the phase modulation section (17) based on the phase amount indication signal.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an OCT (Optical Coherence Tomography) measurement apparatus and an OCT measurement method. BACKGROUND

[0002] In Patent Literature 1, a technique of so-called dispersion compensation that makes dispersion characteristics of a reference light path and a measurement light path coincide is disclosed in order to achieve high-quality and high-precision optical interference measurement. In the optical interference tomography apparatus of Patent Literature 1, light emitted from a light source is split into measurement light on a measurement light path fiber side and reference light on a reference light path fiber side via a fiber coupler. The measurement light on the measurement light path fiber side reaches an object to be measured via a scanning mirror, a scanning lens, and an objective lens. The reference light on the reference light path fiber side reaches a reference mirror via a first dispersion compensation material and a second dispersion compensation material. The first dispersion compensation material and the second dispersion compensation material configured in the reference light path respectively have opposite wavelength dispersion characteristics. The optical interference tomography apparatus of Patent Literature 1 combines the first dispersion compensation material and the second dispersion compensation material each set to a prescribed thickness, thereby achieving dispersion compensation of the object to be measured.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Publication No. 2013-9734 SUMMARY

[0006] An OCT measurement apparatus according to an embodiment of the present disclosure includes: a wavelength-swept light source that emits light whose wavelength is swept; an optical interferometer that splits the light into measurement light and reference light, and generates an optical interference intensity signal that indicates intensity of interference between the measurement light that is irradiated to a measurement surface of an object to be measured and the reference light that is reflected by the measurement surface; a phase modulation section that is configured in an optical path of the optical interferometer; a signal generation section that derives a position of the measurement surface based on the optical interference intensity signal, and generates a phase amount indication signal that indicates a phase amount of the phase modulation section; and a phase amount control section that controls a phase amount imparted to light transmitted through the phase modulation section based on the phase amount indication signal.

[0007] An OCT measurement method according to an embodiment of the present disclosure includes: a step of detecting an optical interference intensity signal representing an intensity of interference between measurement light irradiated to a measurement surface of an object to be measured and reference light, based on a state in which a phase modulation section in an optical path of an optical interferometer configured to generate the optical interference intensity signal representing an intensity of interference with the reference light imparts a phase to light transmitted in the optical path based on a prescribed compensation voltage control signal; a step of calculating instantaneous phase change data representing an instantaneous phase value in a wave number of light emitted from a wavelength-swept light source that emits light whose wavelength is swept, based on the optical interference intensity signal; a step of calculating linear instantaneous phase change data that linearly changes from an instantaneous phase value of leading end data in the instantaneous phase change data to an instantaneous phase value of trailing end data; a step of calculating phase compensation data by acquiring a difference between the instantaneous phase change data and the linear instantaneous phase change data; a step of calculating a compensation voltage control signal based on the phase compensation data, a phase modulation control coefficient that controls a phase modulation amount set in the phase modulation section and a phase amount control section that controls an amount of phase imparted to light transmitted through the phase modulation section; a step of saving the compensation voltage control signal to a control device; a step of imparting a phase to light transmitted in the optical path by the phase modulation section based on the compensation voltage control signal output from the control device in accordance with a wavelength-swept timing of the light emitted from the wavelength-swept light source; and a step of deriving a position of the measurement surface based on the optical interference intensity signal. BRIEF DESCRIPTION OF DRAWINGS

[0008] Figure 1 is a diagram representing a structure example of an OCT measurement device 1 in an embodiment of the present disclosure.

[0009] Figure 2 is a diagram representing an action timing at which the OCT measurement device 1 performs OCT measurement, data acquired by the OCT measurement device 1, and the like, in a case where a wave number of light emitted from the wavelength-swept light source 2 is linear with respect to a scan time.

[0010] Figure 3 is a diagram representing an action timing at which the OCT measurement device 1 performs OCT measurement, data acquired by the OCT measurement device 1, and the like, in a case where a wave number of light emitted from the wavelength-swept light source 2 is not linear with respect to a scan time.

[0011] Figure 4 is a flowchart illustrating a creation procedure of a compensation voltage control signal.

[0012] Figure 5is a graph showing the instantaneous phase change data Φ(k) with respect to each optical wave number k in the case where dispersion compensation is appropriately performed in the reference side optical path and the measurement side optical path and in the case where dispersion compensation is insufficient.

[0013] Figure 6 is a graph showing the instantaneous phase change data Φ(k) derived from the interference signal data i(k) in the case where dispersion compensation is insufficient in the reference side optical path and the measurement side optical path.

[0014] Figure 7 is a graph showing the averaged instantaneous phase change data Φ(k m ) in step S4.

[0015] Figure 8 is a graph showing the linear instantaneous phase change data ψ(k m ) corresponding to the instantaneous phase change data Φ(k m ) shown in Figure 7 .

[0016] Figure 9 is a graph for explaining a method of performing OCT measurement using a compensation voltage control signal v(k m ) for performing dispersion compensation.

[0017] Figure 10 is a graph for explaining a method of performing OCT measurement using a compensation voltage control signal v(k m ) for performing dispersion compensation.

[0018] Figure 11 is a graph showing a distribution graph of a measurement light reflection intensity distribution in a depth direction at the time of performing OCT measurement.

[0019] -Explanation of Symbols-

[0020] 1 Measurement apparatus

[0021] 2 Wavelength scanning light source

[0022] 3 Measurement processing apparatus

[0023] 4 AD conversion apparatus

[0024] 5 Photodetector

[0025] 6 Electro-optical element control apparatus

[0026] 7 Measurement optical path optical fiber end

[0027] 8 Measurement light irradiation mechanism

[0028] 9 Optical interferometer

[0029] ​​10 first coupler

[0030] 11 first circulator

[0031] 12 second coupler

[0032] 13 second circulator

[0033] 14 reference light path optical fiber end

[0034] 15 collimator

[0035] 16 reference mirror

[0036] 17 electro-optical element

[0037] 18 measurement light

[0038] 19 reference light

[0039] 20 object to be measured

[0040] 21 surface to be measured

[0041] 22 measurement light axis DETAILED DESCRIPTION

[0042] Hereinafter, a suitable embodiment of the present disclosure will be explained in detail with reference to the drawings. In addition, in the present specification and the drawings, structural elements having substantially the same function are given the same reference symbol, and repeated explanation is omitted.

[0043] (Embodiment)

[0044] First, the background leading to creation of the embodiment involved in the present disclosure will be explained. OCT is known as a method of measuring a tomogram of an object to be measured, a distance to a reflecting surface at high speed using light interference, and in recent years, is utilized in various ways in the medical field such as ophthalmology, the industrial field of measuring a melt-in depth in laser processing, and the like. OCT is known in three ways of a time domain optical coherence tomography (TD-OCT), a spectral domain optical coherence tomography (SD-OCT), and a wavelength-swept optical coherence tomography (SS-OCT) according to a method of acquiring a light interference signal.

[0045] TD-OCT uses a wideband light source for the light source, and scans the reference surface of the optical interferometer in time to scan the depth direction of the measurement section in the same principle as white light interference, and obtains the reflected light intensity distribution of the measurement light in the measurement depth direction, i.e., the measurement signal. On the other hand, SD-OCT uses a wideband light source for the light source, and uses all wavelengths at the same time, and uses a beam splitter camera in the detection of the optical interference signal. Further, SS-OCT uses a wavelength scanning light source in which the wavelength of the light source changes according to time, and acquires the signal obtained in time by the light detector as the optical interference signal. In SD-OCT and SS-OCT, the Fourier transform is performed on the obtained optical interference signal with respect to the wave number, and thus the same measurement signal as that obtained by TD-OCT is obtained. SD-OCT and SS-OCT have the characteristics that the signal-to-noise ratio is excellent and the frequency of repeated measurements is high, compared to TD-OCT. Further, SS-OCT is superior to SD-OCT in achieving measurement speedup, obtaining an optical interference signal with high light utilization efficiency and high signal-to-noise ratio, and the like.

[0046] In any of these, a plurality of wavelengths are used to perform optical interference measurement, but at this time the wavelength dispersion present in the optical system becomes a problem. In an optical interference measurement device, as an optical system that generates optical interference, a reference light path and a measurement light path that branch from light from a measurement light source have inherent wavelength dispersion characteristics, respectively. The wavelength dispersion characteristics of each light path are determined depending on the optical components (optical fibers, lenses, mirrors, etc.) that constitute the light path, and the measured object of the measurement light path, but generally, the dispersion characteristics of the reference light path and the measurement light path are not consistent with each other, in which case unintended optical interference does not occur, and the optical interference signal deteriorates. Specifically, the signal corresponding to the tomography, reflecting surface, or the like of the measured object in the measurement signal becomes weak, or blurring in the depth direction occurs, and the half-value width becomes wide, so the measurement quality decreases. Therefore, in order to achieve higher quality and higher precision optical interference measurement, so-called dispersion compensation that makes the dispersion characteristics of the reference light path and the measurement light path consistent is required.

[0047] Figure 11 is a graph that shows the profile of the measurement light reflection intensity distribution in the depth direction when OCT measurement is performed. The solid line is the measurement light reflection intensity distribution in the case where dispersion compensation is performed (in the case where dispersion compensation is present). The dotted line is the measurement light reflection intensity distribution in the case where dispersion compensation is insufficient (in the case where dispersion compensation is insufficient, no dispersion compensation, etc.). It can be seen that in the case where dispersion compensation is insufficient, the half-value width of the intensity distribution in the depth direction becomes wide compared to the case where dispersion compensation is performed, and degradation of the resolution in the depth direction, reduction of the peak value of the signal intensity, and the like occur.

[0048] In the dispersion compensation method in the existing OCT measurement apparatus, the dispersion compensation is achieved by adjusting the combination of the optical lengths of two dispersion media having different wavelength dispersion characteristics in conformity with the wavelength dispersion possessed by the measured object arranged on the measurement optical path side. Therefore, in the measurement optical path, in the case where the optical components constituting the optical path other than the measured object also become the cause of the wavelength dispersion, in addition to the dispersion compensation of the measured object having the known wavelength dispersion, the dispersion compensation for the unknown wavelength dispersion is also required, and it is difficult to properly perform the dispersion compensation. Further, if the measured object is changed, it is required to produce and replace the dispersion media having the optical length suitable for the new measured object at that time. Therefore, it is desired to implement the high-quality measurement in which the deterioration of the OCT measurement data is suppressed by compensating for the various wavelength dispersions inherent in the optical path of the OCT measurement apparatus.

[0049] In the related art, there is room for improvement in the dispersion compensation for the various wavelength dispersions inherent in the optical path such as the reference side optical path, the measurement side optical path, and the like. The non-limiting embodiments of the present disclosure provide an OCT measurement apparatus and an OCT measurement method capable of easily performing the dispersion compensation for the various wavelength dispersions inherent in the optical path.

[0050] An OCT measurement apparatus according to an embodiment of the present disclosure includes: a wavelength scanning light source that emits light whose wavelength is scanned; an optical interferometer that splits the light into measurement light and reference light, and generates an optical interference intensity signal indicating an intensity of interference of the measurement light, which is irradiated to a measured surface of a measured object and is reflected by the measured surface, and the reference light; a phase modulation section that is arranged in an optical path of the optical interferometer; a signal generation section that derives a position of the measured surface based on the optical interference intensity signal, and generates a phase amount indication signal indicating a phase amount of the phase modulation section; and a phase amount control section that controls a phase amount imparted to light transmitted through the phase modulation section based on the phase amount indication signal.

[0051] An OCT measurement method according to an embodiment of the present disclosure includes: detecting an optical interference intensity signal representing an intensity of interference between measurement light irradiated to a measurement surface of a measurement object and reference light in a state in which a phase modulation section configured to generate an optical interference intensity signal representing an intensity of interference with the reference light is not operated in an optical path of an optical interferometer configured to generate the optical interference intensity signal, calculating instantaneous phase change data representing an instantaneous phase value in a wave number of light emitted from a wavelength-swept light source which emits light whose wavelength is swept, on the basis of the optical interference intensity signal, calculating linear instantaneous phase change data which linearly changes from an instantaneous phase value of leading end data to an instantaneous phase value of trailing end data in an interval between a wave number of the leading end section in the leading end data and a wave number of the trailing end section in the trailing end data of the instantaneous phase change data, calculating phase compensation data by acquiring a difference between the instantaneous phase change data and the linear instantaneous phase change data, calculating a compensation voltage control signal on the basis of the phase compensation data, a phase modulation section, and a phase modulation control coefficient which controls a phase modulation amount set in a phase amount control section which controls a phase amount imparted to light transmitted through the phase modulation section, saving the compensation voltage control signal to a control device, imparting a phase to light transmitted through the optical path by the phase modulation section on the basis of the compensation voltage control signal output from the control device on the basis of the compensation voltage control signal in synchronization with a wavelength-swept timing of the light emitted from the wavelength-swept light source, and deriving a position of the measurement surface on the basis of the optical interference intensity signal.

[0052] According to an embodiment of the present disclosure, it is possible to construct an OCT measurement device and an OCT measurement method which can easily compensate for various wavelength dispersions inherent in an optical path.

[0053] Further advantages and effects according to an embodiment of the present disclosure are clear from the description and the drawings. The advantages and / or effects are provided by the features described in the several embodiments and the description and the drawings, respectively, and it is not necessary to provide all of them in order to obtain one or more of the same.

[0054] Hereinafter, an embodiment according to the present disclosure will be described.

[0055] <Structure of OCT measurement device 1>

[0056] Figure 1 is a diagram representing a structure example of an OCT measurement device 1 in an embodiment of the present disclosure. The OCT measurement device 1 is used to measure a distance to a measurement object 20 which is a reflector, a scatterer, or the like of light with high precision using optical interference.

[0057] The OCT measurement apparatus 1 includes an optical interferometer 9, a wavelength-swept light source 2, a measurement processing apparatus 3, an AD (Analog to Digital) conversion apparatus 4, a light detector 5, an electro-optical element control apparatus 6, a measurement light path fiber end 7, and a measurement light irradiation mechanism 8.

[0058] The optical interferometer 9 splits light emitted from the wavelength-swept light source 2 into measurement light 18 and reference light 19, and generates an optical interference intensity signal that indicates the intensity of interference between the measurement light 18 split and irradiated to the measurement surface 21 and the reference light 19 split. The wavelength-swept light source 2 is a light source that emits light whose wavelength is swept (light whose wavelength changes over time). The wavelength-swept light source 2 is, for example, a SLD (Super Luminescent Diode) light source, an ASE (Amplified Spontaneous Emission) light source, an SC (Super Continuum) light source, an SS (Swept Source) light source, or the like. The optical interference intensity signal is a signal that indicates the intensity of interference between the measurement light 18 reflected by the measurement surface 21 and the reference light 19. Hereinafter, the optical interference intensity signal is simply referred to as an optical interference signal. The optical interference signal is a signal of optical interference that occurs when the measurement light 18 and the reference light are combined.

[0059] The optical interferometer 9 includes a first coupler 10, a first circulator 11, a second coupler 12, a second circulator 13, a reference light path fiber end 14, a collimator 15, a reference mirror 16, and an electro-optical element 17. In addition, in Figure 1 In the optical interferometer 9, the solid lines connecting the respective structural components represent optical fibers.

[0060] The light detector 5 is a light sensor that inputs the optical interference signal that occurs when the measurement light 18 and the reference light 19 are combined in the second coupler 12. The AD conversion apparatus 4 converts the analog optical interference signal output from the light detector 5 into a digital signal, and outputs the converted digital signal to the measurement processing apparatus 3.

[0061] The measurement processing apparatus 3 is connected to the wavelength-swept light source 2, the AD conversion apparatus 4, and the electro-optical element control apparatus 6. The measurement processing apparatus 3 is a signal generation portion that generates a phase amount indication signal that indicates the phase amount of the electro-optical element 17 (a phase amount imparted to light transmitted through the electro-optical element 17) on the basis of the optical interference signal. The measurement processing apparatus 3 outputs the generated phase amount indication signal to the electro-optical element control apparatus 6. Details of the electro-optical element 17 are described later.

[0062] Further, the measurement processing device 3 inputs various trigger signals output from the wavelength scanning light source 2 and inputs the digital signal output from the AD conversion device 4, and calculates an OCT measurement result. The various trigger signals are a wavelength scanning start trigger signal, a sampling trigger signal, and the like. The wavelength scanning start trigger signal is a signal that serves as a trigger for the AD conversion device 4 to start reception of the optical interference signal. The sampling trigger signal is a signal that indicates the start of sampling of the analog optical interference signal input to the AD conversion device 4. The OCT measurement result is information indicating the intensity of the measurement light reflected light along the depth direction of the measurement optical axis 22, which is the optical interference signal input to the measurement processing device 3 as a digital signal, after data processing such as Fourier transform.

[0063] The electro-optical element control device 6 is connected to the electro-optical element 17. The electro-optical element control device 6 is a phase amount control section that controls the phase amount of the light imparted to the transmission electro-optical element 17, based on the phase amount indication signal. The electro-optical element control device 6 generates a compensation voltage control signal for controlling the phase amount, and outputs the generated compensation voltage control signal to the electro-optical element 17. The compensation voltage control signal is a signal for controlling the phase amount of the reference light 19 imparted to the electro-optical element 17.

[0064] The electro-optical element 17 is a phase modulation section disposed in the optical path of the optical interferometer 9. The electro-optical element 17 is an optical member that imparts a phase to the reference light 19 converted to parallel light by the collimator 15. The collimator 15 is an optical member that converts the reference light output from the reference light path fiber end 14 to parallel light. The reference light path fiber end 14 is an end portion of an optical fiber that outputs the reference light 19 input from the first circulator 11 to the collimator 15. The reference mirror 16 is an optical mirror that reflects the reference light converted to parallel light by the collimator 15.

[0065] The first coupler 10 is an optical fiber member that divides the light emitted from the wavelength scanning light source 2 into the reference light 19 and the measurement light 18, outputs the reference light to the first circulator 11, and outputs the measurement light 18 to the second circulator 13.

[0066] The first circulator 11 is an optical fiber member that transmits the input reference light 19 to the reference light path fiber end 14, and transmits the reference light 19 reflected by the reference mirror 16 and input via the reference light path fiber end 14 to the second coupler 12.

[0067] The second coupler 12 is an optical fiber member that combines the reference light 19 output from the first circulator 11 and the measurement light 18 output from the second circulator 13, and inputs the combined light to the photodetector 5 as an optical interference signal.

[0068] The second circulator 13 is an optical fiber member that transmits the measurement light 18 input from the first coupler 10 to the measurement light path optical fiber end 7, and transmits the measurement light 18 input from the measurement surface 21 of the measurement object 20, which is reflected by the measurement light irradiation mechanism 8 and the measurement light path optical fiber end 7, to the second coupler 12.

[0069] The measurement light path optical fiber end 7 is an end portion of an optical fiber that outputs the measurement light 18 split by the first coupler 10 to the outside of the optical interferometer 9.

[0070] The measurement light irradiation mechanism 8 is an optical member structure for appropriately converging the measurement light 18 output from the measurement light path optical fiber end 7 and irradiating the measurement surface 21.

[0071] In the OCT measurement apparatus 1 thus configured, the light emitted from the wavelength scanning light source 2 is split into the measurement light 18 and the reference light 19 by the first coupler 10. The measurement light 18 that passes through the second circulator 13 is output from the measurement light path optical fiber end 7, passes through the measurement light irradiation mechanism 8, and is irradiated to the measurement surface 21 of the measurement object 20 along the measurement light axis 22. The measurement light 18 reflected by the measurement surface 21 passes through the measurement light irradiation mechanism 8, the measurement light path optical fiber end 7, the second circulator 13, and the second coupler 12.

[0072] The reference light 19 that passes through the first circulator 11 is output from the reference light path optical fiber end 14, becomes parallel light by the collimator 15, transmits the electro-optical element 17, and is irradiated to the reference mirror 16. The reference light 19 reflected by the reference mirror 16 transmits the electro-optical element 17, passes through the collimator 15 and the reference light path optical fiber end 14, transmits the first circulator 11, and reaches the second coupler 12.

[0073] In the optical interferometer 9, as an optical path through which light emitted from the wavelength scanning light source 2 is guided, a measurement side optical path and a reference side optical path are formed.

[0074] The measurement side optical path is a path through which the measurement light 18 reaches the measurement surface 21 from the first coupler 10, via the second circulator 13, the measurement light path optical fiber end 7, and the measurement light irradiation mechanism 8, and reverses, and reaches the second coupler 12, via the measurement light irradiation mechanism 8, the measurement light path optical fiber end 7, and the second circulator 13.

[0075] The reference side optical path is a path through which the reference light 19 reaches the reference mirror 16 from the first coupler 10, via the first circulator 11, the reference light path optical fiber end 14, the collimator 15, and the electro-optical element 17, and reverses, and reaches the second coupler 12, via the electro-optical element 17, the collimator 15, the reference light path optical fiber end 14, and the first circulator 11.

[0076] The OCT measurement apparatus 1 is configured so that the optical path length on the measurement side and the optical path length on the reference side are substantially the same, so that the optical interference signal is maximized. The optical path length refers to an optical distance that takes into account the refractive index of optical members, glass materials, optical media, and the like.

[0077] <Function and operation of electro-optical element 17>

[0078] The electro-optical element 17 is an optical element that utilizes a change in the refractive index of a dielectric crystal when an electric field is applied to the dielectric crystal. In the electro-optical element 17, there are phase modulation type and intensity modulation type. In the present embodiment, the electro-optical element 17 of the phase modulation type is used. In the electro-optical element 17, an applied voltage required to change the phase by π is set for each wavelength used for the electro-optical element 17, and in the present embodiment, this applied voltage is set to a half-wave voltage V π . The half-wave voltage V π depends on the wavelength λ of light transmitted through the electro-optical element 17, and therefore, hereinafter, V π is denoted as V π (λ).

[0079] The phase of transmitted light when light of the wavelength λ is transmitted through the electro-optical element 17 to which the half-wave voltage V π (λ) is applied becomes a state in which the phase of transmitted light when light of the wavelength λ is transmitted through the electro-optical element 17 in a state in which the half-wave voltage V π (λ) is not applied is advanced by π / 2.

[0080] Further, the phase of transmitted light when light of the wavelength λ is transmitted through the electro-optical element 17 to which the half-wave voltage -V π (λ) is applied becomes a state in which the phase of transmitted light when light of the wavelength λ is transmitted through the electro-optical element 17 in a state in which the half-wave voltage V π (λ) is not applied is reversed by π / 2.

[0081] By thus using the electro-optical element 17, it is possible to freely advance or reverse the phase of light.

[0082] <Flow of OCT measurement>

[0083] Figure 2 A graph showing the timing of the operation of the OCT measurement apparatus 1, data acquired by the OCT measurement apparatus 1, and the like, in a case where the wave number of light emitted from the wavelength-swept light source 2 is linear with respect to the scanning time, is shown.

[0084] Figure 2In the diagram, from top to bottom, the following are represented in sequence: the wavelength scanning start trigger signal generated by wavelength scanning light source 2, the sampling trigger signal generated by wavelength scanning light source 2, the wavenumber (light wavenumber) of the light emitted from wavelength scanning light source 2, and the optical interference signal received by photodetector 5. The horizontal axis represents time t. The dashed lines extending vertically are used to indicate the relationship between data at the same time.

[0085] The wavelength scanning start trigger signal is input to the AD converter 4, and the reception of the optical interference signal begins in the AD converter 4.

[0086] The sampling trigger signal is input to the AD converter 4, where the received optical interference signal is converted into a digital signal.

[0087] exist Figure 2 In the above, the sampling times of the sampled optical interference signal are represented as t1, t2, t3, ... t, starting from the earlier time. n-1 t n n is a natural number greater than or equal to 1.

[0088] exist Figure 2 In the above, the wavenumbers corresponding to each sampling time are represented as k(t1), k(t2), k(t3), ..., k(t4). n-1 ), k(t) n n is a natural number greater than or equal to 1. The wavenumber of light is the reciprocal of the wavelength of light.

[0089] In the case of performing a typical OCT measurement, such as Figure 2 As shown in the third image above, in the OCT measurement device 1, the wavelength scanning action is a linear change in the number of light waves relative to the scanning time (time t) after the wavelength scanning start trigger signal is output.

[0090] The AD converter 4, which receives the wavelength scanning start trigger signal, samples the optical interference signal of the photodetector 5 at certain time intervals (timing) to generate interference signal data.

[0091] exist Figure 2 In the diagram, the interference signal data corresponding to each sampling time are represented as i(t1), i(t2), i(t3), ..., i(t4). n-1 ), i(t) n n is a natural number greater than or equal to 1.

[0092] The AD conversion device 4 can sample the optical interference signal of the photodetector 5 at a preset sampling frequency when it receives the wavelength scanning start trigger signal, or it can start sampling the optical interference signal of the photodetector 5 when it receives the sampling trigger signal.

[0093] Figure 3 This is a diagram showing the timing of OCT measurement by the OCT measuring device 1 and the data acquired by the OCT measuring device 1 when the wavenumber of the light emitted from the wavelength scanning light source 2 does not change linearly with respect to the scanning time.

[0094] Figure 3 In, with Figure 2 Similarly, from top to bottom, the following are represented sequentially: the wavelength scanning start trigger signal generated by wavelength scanning light source 2, the sampling trigger signal generated by wavelength scanning light source 2, the wavenumber (light wavenumber) of the light emitted from wavelength scanning light source 2, and the light interference signal received by photodetector 5. The horizontal axis represents time t. The dashed lines extending vertically are used to indicate the relationship between data at the same time.

[0095] also, Figure 3 In, with Figure 2 Similarly, it represents the sampling time t1~t n Wavenumber k(t1) ~ k(t) n n is a natural number greater than or equal to 1.

[0096] In the case of a light source where the wavenumber k of the light emitted from the wavelength scanning light source 2 does not change linearly with respect to the scanning time, a timing sampling trigger signal with a fixed wavenumber is additionally emitted from the wavelength scanning light source 2. Hereinafter, such a sampling trigger signal will be referred to as the "k clock".

[0097] like Figure 3 As shown, after the wavelength scan start trigger signal, the light wavenumber k(t) changes nonlinearly with respect to time t, and simultaneously, the k clock is output at unequal intervals with respect to time. In this case, after receiving the wavelength scan start trigger signal output from the wavelength scan light source 2, the AD conversion device 4 samples the optical interference signal of the photodetector 5 according to the timing of the k clock, thereby generating interference signal data.

[0098] Based on the above, the interference signal data i(t) generated by the AD conversion device 4 is sampled at equal wavenumber intervals. Therefore, in Figure 2 as well as Figure 3 In any of these cases, the interference signal data acquired by the AD conversion device 4 are also denoted as i(t1), i(t2), i(t3), ..., i(t4). n-1 ), i(t) n The interference signal data i(t), which is acquired as digital data by the AD conversion device 4, can be denoted as i(k1), i(k2), i(k3), ..., i(k) independently of its time interval. n-1 ), i(k n ).

[0099] <Method for obtaining compensation voltage control signal>

[0100] Next, a method for obtaining data of a compensation voltage control signal necessary for measuring wavelength dispersion inherent in the optical system of the OCT measuring apparatus 1 and for compensating the wavelength dispersion by the electro-optical element 17 will be described.

[0101] In Figure 1 the measured object 20 is assumed to be a plate-shaped metal member, the condition of the measurement light 18 reflected at the measured surface 21 of the measured object 20 is considered. The measured surface 21 is disposed near the position where the optical interference signal is maximum as described above. At this time, the optical interference signal is confirmed in advance, and the surface state of the measured surface 21 is adjusted so that the waveform of the optical interference signal is not saturated at the detection sensitivity of the photodetector 5. For example, in the case where the measured surface 21 is in a state close to a mirror surface, the photodetector 5 can easily be saturated, and therefore the measured surface 21 is preferably set to a rough surface, a pear skin surface, or the like, at which the measurement light 18 is somewhat scattered.

[0102] In addition, the measured object 20 is a member at which the measurement light 18 does not penetrate, and is not limited to a plate-shaped metal member, and for example, can be a plate-shaped ceramic or the like.

[0103] Generally, a differential photodetector is used for the photodetector 5, and the output of the photodetector 5 in this case is centered on zero output, and has a detection limit in the positive and negative directions. Therefore, it is noted that the interference waveform signal is not saturated in both the positive and negative directions.

[0104] In addition, of course, the surface state of the measured surface 21 and the bias value are preferably adjusted so that the detection sensitivity is not saturated even when a general photodetector or the like is used for the photodetector 5 and is operated with bias.

[0105] Figure 4 is a flowchart for describing the creation process of the compensation voltage control signal. In step S1, the OCT measuring apparatus 1 imports the light emitted from the wavelength-swept light source 2 in the same manner as in the general OCT measurement, and AD-converts the optical interference signal in accordance with the wavelength-swept operation of the wavelength-swept light source 2, thereby obtaining the interference signal data i(k m )(m = 1, 2, 3, ··· n-1, n). k represents the number of light waves. In the general OCT measurement, the electro-optical element 17 imparts a phase to the light passing through the reference side optical path on the basis of a prescribed compensation voltage control signal. The prescribed compensation voltage control signal is, for example, a current compensation voltage control signal or a compensation voltage control signal for correction.

[0106] In step S2, the OCT measuring device 1 uses the interference signal data i(k) acquired in step S1 as a basis. m To obtain instantaneous phase change data. For based on the interference signal data i(k) m To derive instantaneous phase change data It is possible to utilize known techniques such as the Hilbert transform. If the interference signal data i(k) is... m Let the Hilbert transform of ) be j(k) m If the instantaneous phase change data is obtained as follows:

[0107] Here, arctan{X} is the arctangent function, and the relationship X = tan{Y} holds true when Y = arctan{X}. tan{Y} is the tangent function. This is how the instantaneous phase change data is obtained. This indicates that the interference signal data i(k) has been acquired. m The wavenumbers k (k1, k2, k3, ..., k) of each light wave n-1 k n The instantaneous phase value in the interference signal data i(k). m It qualitatively represents the quantity corresponding to the instantaneous time offset in each light wavenumber k.

[0108] Figure 5 This represents the instantaneous phase change data for each light wavenumber k, indicating whether the dispersion compensation is adequate or insufficient in the reference-side and measurement-side optical paths. The graph shows the light wavenumber on the horizontal axis and the instantaneous phase on the vertical axis.

[0109] Typically, the domain of the arctan function (arctangent function) is from -π / 2 to π / 2. Therefore, when the phase value is above π / 2 or below -π / 2, the instantaneous phase change data... This results in a discontinuity of ±π. In this case, at the discontinuity points, the data is converted into continuous data by appropriately increasing ±π, a process known as "phase connection processing". Figure 5 It is data that has undergone phase-connection processing.

[0110] As mentioned earlier, instantaneous phase change data This represents the wavenumbers k (k1, k2, k3, ..., k) of the obtained interference signal data i(k). n-1 k n The instantaneous phase value in ).

[0111] With appropriate dispersion compensation performed in each of the reference-side optical path and the measurement-side optical path of the OCT measurement device 1, the phase change data... likeFigure 5 As shown by the dashed line, it changes linearly with respect to the light wavenumber k. This is because the interference signal data corresponding to the signal of the intensity of the reflected light from the measured surface 21 at a determined measurement depth position changes with a certain period relative to the light wavenumber k, and therefore the instantaneous phase also changes proportionally.

[0112] On the other hand, when the dispersion compensation in both the reference-side and measurement-side optical paths is insufficient, the instantaneous phase change data... like Figure 5 As shown by the solid line, the wavenumber changes non-linearly with respect to the light wavenumber k. This is because, since the optical path lengths of the reference side and the measurement side are inconsistent according to the wavelength, a shift in the wavenumber corresponding to the sampling timing of the optical interference signal at each moment occurs, and the change in the interference signal data is not periodic with respect to the wavenumber.

[0113] Figure 6 This represents the instantaneous phase change data derived from the interferometric signal data i(k) under the condition that dispersion compensation is insufficient in the reference-side optical path and the measurement-side optical path. The graph shows the light wavenumber on the horizontal axis and the instantaneous phase on the vertical axis.

[0114] The dots on the solid line represent the actual sampling points of the data in the AD conversion device 4. The light wavenumbers corresponding to each sampling point are k1, k2, k3, ..., k n-1 k n Derive the interference signal data i(k) from the source. m (m = 1, 2, 3...n-1, n) corresponds to the instantaneous phase change data. (m=1, 2, 3···n-1, n).

[0115] Return to Figure 4 In step S3, instantaneous phase change data cannot be obtained a specified number of times. In the case of (step S3, no), the OCT measuring device 1 repeats the processing after step S1.

[0116] Instantaneous phase change data If the required number of measurements can be obtained (step S3, yes), the OCT measuring device 1 proceeds to step S4. In step S4, the OCT measuring device 1 performs the measurement according to each light wave number k. m The process continues until step S3, where multiple instantaneous phase change data are acquired. The averaged data is then processed to obtain the averaged instantaneous phase change data Φ(k). m This process is for interfering with the signal data i(k). m The noise data contained in the data is reduced and then processed.

[0117] Here, note that if in the initial interference signal data i(k) m If the obtained time is averaged, the interference signal data waveform will be dulled due to the repeated initial phase shift based on the interference signal data waveform, and the required instantaneous phase change data cannot be obtained.

[0118] Furthermore, during OCT measurement, wavelength scanning is repeatedly performed using the wavelength scanning light source 2, ensuring sampling timing within the reproducibility range required for light emission and scanning, including semiconductors and electrical circuits. Therefore, in this embodiment, the light wavenumbers at each sampling timing are the same with sufficient and necessary accuracy (k1, k2, k3...k ... n-1 k n Data acquisition in ).

[0119] In addition, to ensure good data creation for the compensation voltage control signal, the number of times instantaneous phase change data is acquired is preferably more than 20.

[0120] In step S5, the OCT measuring device 1 calculates the instantaneous phase change data Φ(k) based on the data obtained in step S4. m ), calculate the linear instantaneous phase change data ψ(k) m Specifically, the OCT measuring device 1 calculates linear instantaneous phase change data, which is in the instantaneous phase change data Φ(k) m The front-end wavenumber and instantaneous phase change data Φ(k) in the front-end data. m The range of wavenumbers at the end of the data section changes linearly from the instantaneous phase value of the front-end data to the instantaneous phase value of the end data.

[0121] In step S6, the OCT measuring device 1 calculates the instantaneous phase change data Φ(k) based on the data obtained in step S4. m The linear instantaneous phase change data ψ(k) calculated in step S5 m ), calculate phase compensation data dψ(k m Specifically, the OCT measuring device 1 obtains the instantaneous phase change data Φ(k). m ) and linear instantaneous phase change data ψ(k m The difference is calculated as phase compensation data.

[0122] In step S7, the OCT measuring device 1 calculates the phase compensation data dψ(k) based on the data calculated in step S5. m The phase modulation control coefficients for controlling the phase modulation amount set in the electro-optic element 17 and the electro-optic element control device 6 are used to calculate the compensation voltage control signal v(k). m ).

[0123] Here, refer toFigure 7 as well as Figure 8 This section will explain the details of the data operations from step S5 to step S7.

[0124] Figure 7 It represents the averaged instantaneous phase change data Φ(k) in step S4. m The graph shows the light wavenumber on the horizontal axis and the instantaneous phase on the vertical axis. The dashed line represents the transition between the initial data Φ(k1) and the final data Φ(k) of the instantaneous phase change data. n The linear instantaneous phase change data ψ(k) is connected by a straight line.

[0125] Figure 7 The instantaneous phase change data Φ(k) shown m The data was acquired using an OCT measuring device 1 without dispersion compensation. Therefore, Figure 8 The instantaneous phase change data Φ(k) shown m The change is not linear with respect to the light wavenumber k, but with respect to equally spaced light wavenumber increments Δk. m (m=1, 2, 3, ···n-1, n), instantaneous phase increment ΔΦ(k m Unequal intervals.

[0126] Equally spaced wavenumber increments Δk m via Δk m =k m+1 -k m And to obtain the instantaneous phase increment ΔΦ(k m ) through ΔΦ(k m )=Φ(k m+1 )-Φ(k m And seek it.

[0127] Figure 7 It means Figure 8 The instantaneous phase change data Φ(k) shown m The linear instantaneous phase change data ψ(k) corresponding to ) m (The image is in...) Figure 8 For the sake of simplicity on paper, the instantaneous phase change data Φ(k) is omitted. m The diagram illustrates linear instantaneous phase change data, which can be represented as ψ(k). m )={Φ(k n )-Φ(k1)} / {k n -k1}·k.

[0128] OCT measurement device 1 obtains the linear instantaneous phase change data ψ(k) at each sampling point. m ), so that the light wavenumber k at each sampling point mThe instantaneous phase increment is constant in (m = 1, 2, 3, ..., n-1, n).

[0129] Figure 4 In, ψ(k) m ψ(k) is represented by the points at the four corners. m ) can be represented as ψ(k) m )={Φ(k n )-Φ(k1)} / {k n -k1}k m If the instantaneous phase change data Φ(k) m ) and linear instantaneous phase change data ψ(k m By comparing these values, we can see that there are differences except for the data at the beginning and end, where m=1 and m=n. Let this difference be dψ(k) = ψ(k) - Φ(k).

[0130] dψ(k) is the difference between the measured instantaneous phase value in wavenumber k and the ideal instantaneous phase. Therefore, by assigning a phase to the reference optical path side through the electro-optic element 17, the obtained interference signal data is not only linear instantaneous phase change data but also close to linear instantaneous phase change data. Therefore, dψ(k) will be discussed below. m (m = 1, 2, 3, ..., n-1, n) are called phase compensation data.

[0131] Here, the half-wavelength voltage at wavelength λ of the electro-optic element 17 is transmitted through V. π (λ) is assigned. Since there is a relationship between wavelength λ and light wavenumber k, λ = 1 / k, the half-wavelength voltage can be expressed as V. π (1 / k). Therefore, the compensation voltage control v(k) applied to the electro-optic element 17 at the light wavenumber k can use the phase compensation data dψ(k). m ), expressed as v(k)={V π (1 / k)·dψ(k)} / π. Therefore, for all light wavenumbers k from which the interference signal data is obtained... m It can set the compensation voltage control data v(k) m )={V π (1 / k m )·dψ(k m )} / π. By v(k m The compensation voltage control signal is set to compensate for the wavelength dispersion inherent in the OCT measurement device 1.

[0132] Return to Figure 9 In step S8, the compensation voltage control signal v(k) acquired during the operations up to step S7 is... mIf the signal is updated to one with less influence from the deviation (step S8, yes), the OCT measuring device 1 performs the processing of step S8-1. Without compensating the voltage control signal v(k)... m If the update is not performed (step S8, no), the OCT measuring device 1 performs the processing of step S12.

[0133] In step S8-1, the OCT measuring device 1 uses the compensation voltage control signal v(k) m If the update of the compensation voltage control signal v(km) is the first time (step S8-1, yes), proceed to step S9. If the update of the compensation voltage control signal v(km) is the second time or later (step S8-1, no), proceed to step S10.

[0134] In step S9, the OCT measuring device 1 is set to use the compensation voltage control signal v(k) calculated in step S7. m The dispersion compensation is implemented. Afterwards, the OCT measuring device 1, through repeated processing after step S1, acquires the compensation voltage control signal v(k) again. m ).

[0135] In step S10, the OCT measuring device 1 uses the compensation voltage control signal v(k) acquired in this case, obtained under the condition of compensating for wavelength dispersion. m Let v2(k) be the value of v2(k). m Based on the compensation voltage control signal, calculate v c (k m )=v(k m )+v2(k m v2(k) m Even if v(k) is performed m The dispersion compensation also failed to fully compensate for the residual wavelength dispersion. OCT measurement device 1 will then use the newly calculated v... c (k m ) is set to the latest compensation voltage control signal v(k) m Then proceed to step S11.

[0136] In step S11, if the OCT measuring device 1 repeatedly compensates for the update of the voltage control signal (step S11, yes), it performs the processing after step S1. If the OCT measuring device 1 terminates without repeatedly compensating for the update of the voltage control signal (step S11, no), it performs the processing of step S12.

[0137] Here, the data operations in steps S8 to S11 are explained in detail. Furthermore, in order to obtain a compensation voltage control signal with minimal impact from the deviation, it is preferable to use the compensation voltage control signal v(k) acquired beforehand. mTo compensate for wavelength dispersion, a series of steps are performed to acquire the compensation voltage control signal and update the current compensation voltage control signal.

[0138] The compensation voltage control data obtained under the state of compensating for wavelength dispersion is set as v2(k m When ), the new compensation voltage control signal is v c (k m )=v(k m )+v2(k m As mentioned before, v2(k) m Even if v(k) is performed m The dispersion compensation also failed to fully compensate for the residual wavelength dispersion. This v c (k m ) is reused as the compensation voltage control signal, and the same operation is repeated, then v2(k m The convergence is zero, therefore, after repeating the operation the necessary number of times, v will be... c (k m It can be used as a compensation voltage control signal.

[0139] In step S12, the OCT measuring device 1 stores the compensation voltage control signal determined in the steps up to this point as data in the control device. The "control device" can be either the electro-optic element control device 6 or the measurement processing device 3, if it can perform the operation in the dispersion-compensated OCT measurement method described later.

[0140] Furthermore, in this embodiment, assuming that shape measurements of metal surfaces, resin surfaces, etc., which do not transmit light, are not performed, the case where a metal plate is used for the object to be measured 20 will be described. In the measurement-side optical path up to the measured surface 21 of the object to be measured 20 such as the metal plate, if any light-transmitting medium is present, the OCT measuring device 1 will place the light-transmitting medium in the measurement optical path when determining the compensation voltage control signal, and acquire interference signal data.

[0141] For example, when the object being measured 20 is an eyeball, the retina, fundus, etc. of the eyeball are the measured surface 21, and the lens, cornea, etc., which are located in front of the retina, fundus, etc., are the light transmission medium in the light path on the measurement side. Furthermore, when the object being measured 20 is a structure in water, the structure in water is the measured surface 21, and the water in front of the structure is the light transmission medium in the light path on the measurement side.

[0142] <OCT measurement method with dispersion compensation>

[0143] The following is for reference Figure 9 The following explains the use of the compensation voltage control signal v(k) saved in step S12. mThis is a method for performing dispersion-compensated OCT measurements.

[0144] Figure 10 as well as Figure 9 It is used to control the signal v(k) using the compensation voltage. m The figure illustrates the method of performing dispersion-compensated OCT measurements. Figure 10 In this context, "OCT measurement device 1" refers to the timing of OCT measurement operations and the data acquired by OCT measurement device 1 when the wavenumber of light emitted from the wavelength scanning light source 2 is linear with respect to the scanning time.

[0145] Figure 2 In this context, the timing of the OCT measurement operation performed by the OCT measurement device 1 and the data acquired by the OCT measurement device 1 are described, assuming that the wavenumber of the light emitted from the wavelength scanning light source 2 does not change linearly with respect to the scanning time.

[0146] and Figure 3 as well as Figure 9 The difference is that, in Figure 10 as well as Figure 2 In addition to Figure 3 as well as Figure 9 The data shown also includes data for the compensation voltage control signal. The horizontal axis represents time t. The dashed lines extending vertically are used to show the relationship between data at the same time points.

[0147] Figure 10 as well as Figure 2 In, with Figure 3 as well as Figure 9 Similarly, the sampling times of the sampled optical interference signals are denoted as t1, t2, t3, ... t, starting from the earlier time. n-1 t n Furthermore, the wavenumbers corresponding to each sampling time are represented as k(t1), k(t2), k(t3), ..., k(t4). n-1 ), k(t) n n is a natural number greater than or equal to 1.

[0148] exist Figure 10 In the process, the wavelength scanning light source 2, in accordance with the sampling trigger signal following the emission of the wavelength scanning start trigger signal, the AD conversion device 4 processes the interference signal data i(k) m Sampling was performed as described above.

[0149] The electro-optical element control device 6 of the OCT measurement device 1 and the timing time t m Consistently, the compensation voltage control signal v(t) m )=v(k mThe output is a voltage waveform. Thus, the electro-optic element 17 imparts the previously determined phase to the reference light, achieving dispersion compensation for the OCT measurement device 1. This also applies to the case where the wavelength scanning light source 2 has characteristics that do not change linearly with respect to the scanning time.

[0150] exist ​ In the process of receiving the timing of the k clock emitted from the wavelength scanning light source 2, the AD conversion device 4 processes the interference signal data i(k) m Sampling was performed as described above.

[0151] The electro-optical element control device 6 of the OCT measurement device 1 receives a clock k and a timing time t. m Consistently, the compensation voltage control signal v(t) m )=v(k m The output is a voltage waveform. Thus, even when the light wave number k is nonlinear with respect to the scanning time, the electro-optic element 17 can impart the previously obtained phase to the reference light to achieve dispersion compensation.

[0152] By performing a Fourier transform on the interference signal data i(km) acquired through the above steps and timings, the reflected light intensity distribution of the measurement light in the depth direction is obtained; in other words, the OCT measurement signal. The resulting OCT measurement signal is a high-quality measurement result with appropriate dispersion compensation and minimal blurring in the depth direction.

[0153] <Effect>

[0154] As described above, the OCT measurement apparatus 1 according to this embodiment includes: a wavelength scanning light source 2 that emits light with a scanned wavelength; an optical interferometer 9 that splits the light into a measurement light 18 and a reference light 19, and generates an optical interference intensity signal indicating the intensity of the interference between the measurement light 18 and the reference light 19, which are irradiated by the measurement light 18 onto the measured surface 21 of the measured object 20 and reflected by the measured surface 21; an electro-optic element 17, which serves as a phase modulation unit, is disposed in the optical path of the optical interferometer 9; a measurement processing device 3, which serves as a signal generation unit, derives the position of the measured surface 21 based on the optical interference intensity signal, and generates a phase amount indication signal indicating the phase amount of the electro-optic element 17; and an electro-optic element control device 6, which serves as a phase amount control unit, controls the phase amount imparted to the light transmitted through the electro-optic element 17 based on the phase amount indication signal. With this structure, even if the optical components constituting the optical path are wavelength-dispersive, the wavelength dispersion inherent in the optical components constituting the reference-side optical path and the measurement-side optical path can be compensated by controlling the phase amount of the light transmitted through the electro-optic element 17. That is, in addition to dispersion compensation for analytes with known wavelength dispersion, dispersion compensation can also be performed for unknown wavelength dispersion. As a result, high-quality measurements can be performed that suppress the degradation of OCT measurement data.

[0155] Furthermore, by exchanging or changing the structural components of the OCT measuring device 1, particularly the optical components such as the lens and mirror of the measuring light irradiation mechanism 8 constituting the measuring side optical path, even when the wavelength dispersion characteristics change, the phase amount of the light of the transmission electro-optic element 17 can be controlled, thereby enabling easy and flexible dispersion correction without manufacturing and replacing a dispersion medium suitable for the optical length of the exchanged optical components.

[0156] Additionally, for example, understanding the following methods also falls within the technical scope of this disclosure.

[0157] (1) The phase modulation unit is an electro-optic element 17.

[0158] (2) The electro-optic element 17 is disposed in the reference optical path through which the reference light is transmitted.

[0159] (3) The OCT measurement method involved in this embodiment includes:

[0160] Without activating the phase modulation unit 17 in the optical path of the optical interferometer 9 configured to generate an optical interference intensity signal representing the intensity of interference with the reference light 19, the step is to detect the optical interference intensity signal representing the intensity of interference between the measurement light 18, which is irradiated onto the measurement surface 21 of the object to be measured 20 and reflected by the measurement surface 21, and the reference light 19, and based on the optical interference intensity signal, to calculate the instantaneous phase change data representing the instantaneous phase value of the light emitted from the wavelength scanning light source 2, which emits light with a wavelength that has been scanned.

[0161] The steps of calculating the interval between the first wave number in the first-end data and the last wave number in the last data of the instantaneous phase change data, and linear instantaneous phase change data that changes linearly from the instantaneous phase value of the first-end data to the instantaneous phase value of the last data;

[0162] The step of calculating phase compensation data by obtaining the difference between the instantaneous phase change data and the linear instantaneous phase change data;

[0163] The step of calculating the compensation voltage control signal based on the phase compensation data, the phase modulation unit 17, and the phase modulation control coefficient set in the phase amount control unit 6 that controls the phase amount imparted to the light transmitted through the phase modulation unit 17 and controls the phase modulation amount is calculated.

[0164] The step of storing the compensation voltage control signal in the control device (measurement processing device 3, electro-optic element control device 6);

[0165] In accordance with the wavelength scanning timing of the light emitted from the wavelength scanning light source 2, the phase modulation unit 17 assigns phase to the light transmitted in the optical path based on the compensation voltage control signal output from the control device according to the compensation voltage control signal; and

[0166] The step of deriving the position of the measured surface 21 based on the optical interference intensity signal.

[0167] (4) In the step of calculating the instantaneous phase change data, multiple optical interference intensity signals are obtained, the instantaneous phase change data is calculated based on each optical interference intensity signal, and the data obtained by averaging multiple instantaneous phase change data is reused as the instantaneous phase change data.

[0168] (5) In the step of giving phase to the light transmitted in the optical path, the light transmitted in the optical path that is given phase is the reference light 19.

[0169] (6) In the step of calculating the compensation voltage control signal, after calculating the compensation voltage control signal at least once, the step of using the compensation voltage control signal to give phase to the light transmitted in the optical path is performed, and a new compensation voltage control signal is calculated and the compensation voltage control signal is updated.

[0170] (7) The phase modulation unit used in the OCT measurement method of this embodiment is an electro-optic element.

[0171] Industrial availability

[0172] One embodiment of this disclosure is suitable for an OCT measurement device.

Claims

1. An OCT measurement apparatus comprising: a wavelength scanning light source that emits light whose wavelength is scanned; an optical interferometer that splits the light into measurement light and reference light, and generates an optical interference intensity signal that indicates an intensity of interference of the measurement light that is irradiated toward a measurement surface of an object to be measured and is reflected by the measurement surface, and the reference light; a phase modulation section that is disposed in an optical path of the optical interferometer; a signal generation section that derives a position of the measurement surface based on the optical interference intensity signal, and generates a phase amount indication signal that indicates a phase amount of the phase modulation section; and a phase amount control section that controls a phase amount that is imparted to light that is transmitted through the phase modulation section based on the phase amount indication signal, wherein the signal generation section calculates, based on the optical interference intensity signal, instantaneous phase change data that indicates an instantaneous phase value in a wave number of light that is emitted from the wavelength scanning light source that emits light whose wavelength is scanned, calculates an interval between a leading end wave number in leading end data of the instantaneous phase change data and a trailing end wave number in trailing end data of the instantaneous phase change data, calculates linear instantaneous phase change data that linearly changes from an instantaneous phase value of the leading end data to an instantaneous phase value of the trailing end data, calculates phase compensation data by acquiring a difference between the instantaneous phase change data and the linear instantaneous phase change data, and the phase amount control section calculates a compensation voltage control signal based on the phase compensation data, the phase modulation section, and a phase modulation control coefficient that is set in the phase amount control section that controls a phase amount that is imparted to light that is transmitted through the phase modulation section.

2. The OCT measurement apparatus according to claim 1, wherein the phase modulation section is an electro-optical element.

3. The OCT measurement apparatus according to claim 1 or 2, wherein the phase modulation section is disposed in a reference light path through which the reference light is transmitted.

4. An OCT measurement method comprising: a step of detecting, in a state in which a phase modulation section that is disposed in an optical path of an optical interferometer that generates an optical interference intensity signal that indicates an intensity of interference of measurement light that is irradiated toward a measurement surface of an object to be measured and is reflected by the measurement surface, and reference light imparts a phase to light that is transmitted in the optical path based on a prescribed compensation voltage control signal, the optical interference intensity signal that indicates the intensity of interference of the measurement light and the reference light, calculating, based on the optical interference intensity signal, instantaneous phase change data that indicates an instantaneous phase value in a wave number of light that is emitted from a wavelength scanning light source that emits light whose wavelength is scanned, a step of calculating linear instantaneous phase change data that linearly changes from an instantaneous phase value of leading end data to an instantaneous phase value of trailing end data, in an interval between a leading end wave number in the leading end data and a trailing end wave number in the trailing end data of the instantaneous phase change data, a step of calculating phase compensation data by acquiring a difference between the instantaneous phase change data and the linear instantaneous phase change data. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ calculating a compensation voltage control signal based on the phase compensation data, the phase modulation section, and a phase modulation control coefficient set in a phase amount control section that controls an amount of phase imparted to light transmitted through the phase modulation section; storing the compensation voltage control signal in a control device; the phase modulation section imparting a phase to light transmitted in the optical path based on the compensation voltage control signal output from the control device in synchronization with wavelength scanning timing of the light emitted from the wavelength scanning light source; and deriving a position of the measured surface based on the light interference intensity signal.

5. The OCT measurement method according to claim 4, wherein in the step of calculating the instantaneous phase change data, the light interference intensity signal is acquired a plurality of times, the instantaneous phase change data is calculated based on each of the light interference intensity signals, and data obtained by averaging a plurality of the instantaneous phase change data is used again as the instantaneous phase change data.

6. The OCT measurement method according to claim 5, wherein in the step of imparting a phase to light transmitted in the optical path, the light transmitted in the optical path to which a phase is imparted is the reference light.

7. The OCT measurement method according to claim 6, wherein in the step of calculating the compensation voltage control signal, after the compensation voltage control signal is calculated at least once, the step of imparting a phase to light transmitted in the optical path using the compensation voltage control signal is performed, and a new compensation voltage control signal is calculated and the compensation voltage control signal is updated.

8. The OCT measurement method according to any one of claims 4 to 7, wherein the phase modulation section is an electro-optical element.

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