Signal processing device, OCT device, signal processing method, and program

Abstract

To extract, more easily than before, signals at a plurality of positions to be measured from signals obtained in one measurement in an FD-OCT.SOLUTION: A signal processor includes: an acquisition part which acquires an output signal outputted by a single light receiving part receiving a plurality of interference lights where light outputted by a single light source and tracing a measurement optical path heading for an object to be measured and light outputted by the light source and tracing a reference light path different from the measurement optical path which differ in wavelength dispersion characteristics between the measurement optical path traced by the interfering lights and the reference light path vary respectively; and an extraction part which extracts an extraction signal to be a signal every interference light on the basis of the output signal acquired by the acquisition part and a correction signal in which wavelength dispersion correction processing is applied to the output signal.SELECTED DRAWING: Figure 11

Description

【Technical Field】 【0001】 The present invention relates to a signal processing device, an OCT device, a signal processing method, and a program. 【Background Art】 【0002】 As a technique for measuring the position of a measurement target by utilizing the interference property of light, there is OCT (Optical Coherence Tomography). OCT has a method called Fourier domain FD-OCT (Fourier Domain-OCT). In FD-OCT, there is a technique for extracting signals at a plurality of positions of a measurement target from a signal obtained by a single measurement. Patent Document 1 discloses an OCT system for imaging a plurality of depth positions. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Translation of PCT International Publication No. 2018-514251 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In the prior art, it is necessary to adjust the dispersion characteristics of each of a plurality of optical paths traveled by the reference light to match the dispersion characteristics of the optical path traveled by the corresponding measurement light, which is troublesome. The present invention has been made in view of such problems, and an object thereof is to extract signals at a plurality of positions of a measurement target from a signal obtained by a single measurement in FD-OCT more simply than in the prior art. 【Means for Solving the Problems】 【0005】 To achieve the above objective, the signal processing device includes: an acquisition unit that acquires an output signal output from a single light receiving unit that receives multiple interference lights, each having a different difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path followed by the interfering light; and an extraction unit that extracts an extracted signal, which is a signal for each of the interference lights, based on the output signal acquired by the acquisition unit and a corrected signal obtained by applying wavelength dispersion correction processing to the output signal. 【0006】 In other words, the signal processing device extracts a signal for each interfering light from an output signal, which is the signal of multiple interfering lights with different wavelength dispersions, and a corrected signal that has undergone wavelength dispersion correction processing, by utilizing the characteristics of the changes that occur in the signal due to the correction of wavelength dispersion. This makes it possible to measure multiple locations simultaneously more easily without the trouble of matching the wavelength dispersion characteristics of the corresponding measurement optical path and the reference optical path. [Brief explanation of the drawing] 【0007】 [Figure 1] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 2] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 3] This diagram illustrates the correction of wavelength dispersion. [Figure 4] This diagram illustrates the correction of wavelength dispersion. [Figure 5] This figure shows an example of a measurement signal and a correction signal. [Figure 6] This figure shows an example of a measurement signal and a correction signal. [Figure 7] This figure shows an example of a measurement signal and a correction signal. [Figure 8] This figure shows an example of a measurement signal and a correction signal. [Figure 9] This figure shows an example of a measurement signal and a correction signal. [Figure 10]This is a diagram illustrating an example of how an image is displayed. [Figure 11] This is a flowchart illustrating an example of the extraction process. [Figure 12] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 13] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 14] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 15] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 16] This figure shows the configuration of an FD-OCT device according to one embodiment of the present invention. [Figure 17] This figure shows an example of a correction signal. [Modes for carrying out the invention] 【0008】 Here, an example of an embodiment of the present invention will be described in the following order. (1) First embodiment: (1-1) Configuration of the FD-OCT device: (1-2) Extraction process: (2) Second embodiment: (3) Third embodiment: (4) Fourth embodiment: (5) Other embodiments: 【0009】 (1) Configuration of the FD-OCT device: The following describes the FD-OCT device 1 according to this embodiment. The FD-OCT device 1 is an example of a signal processing device. The FD-OCT device 1 of this embodiment measures multiple positions on the subject's eyeball (hereinafter referred to as the eye under examination) using the FD-OCT method (in this embodiment, the SD (Spectral-domain)-OCT method). In this embodiment, the FD-OCT device 1 measures multiple positions on the eye under examination (in this embodiment, the cornea and retina, but other positions may also be used). Figures 1 and 2 are schematic diagrams showing the configuration of the FD-OCT device 1 of this embodiment. The FD-OCT device 1 includes a control unit 10, an adjustment mechanism 11, mirrors 12 (mirror 12a, mirror 12b), an alignment mechanism 13, a light source 14, a light receiving unit 15, and a display unit 16. Furthermore, the FD-OCT device 1 includes optical elements (branching section 30, transmission sections 41, 42, 43, 44, half mirror 45, wavelength dispersion member 46, diffraction grating 47) that form the optical path of the light output from the light source 14. In this embodiment, the FD-OCT device 1 generates interference light from the light output from the light source 14 using a Michelson interferometer. 【0010】 The control unit 10 includes a processor, RAM, ROM, etc., and controls the FD-OCT device 1 by executing a program recorded in the ROM, etc. The adjustment mechanism 11 is a mechanism that can move mirrors 12a and 12b in a linear direction along the optical path. In this embodiment, the adjustment mechanism 11 is assumed to be a ball screw mechanism for moving mirrors 12a and 12b, but it may be other mechanisms such as a slider-crank mechanism or a power transmission mechanism such as a cam. Mirrors 12a and 12b each reflect incident light. The control unit 10 adjusts the positions of mirrors 12a and 12b via the adjustment mechanism 11. The alignment mechanism 13 is a mechanism used to adjust the positional relationship between the FD-OCT device 1 and the object to be measured. Before measuring the object to be measured by FD-OCT, the control unit 10 detects the position of the corneal apex of the subject's eye via the alignment mechanism 13, and adjusts the position of the FD-OCT device 1 so that the detected corneal apex position and the FD-OCT device 1 are in a predetermined positional relationship. The light source 14 outputs light within a predetermined wavelength band in response to instructions from the control unit 10. The light receiving unit 15 consists of multiple light-receiving elements arranged in a straight line. 【0011】 The branching section 30 is an optical component that branches the light output from the light source 14 into a reference light that follows a reference optical path and a measurement light that is irradiated onto the object to be measured. For example, it is a filter coupler. Hereinafter, the optical path of the reference light will be referred to as the reference optical path. Hereinafter, the optical path of the measurement light will be referred to as the measurement optical path. The transmission section 41 is an optical fiber that transmits light from the light source 14 to the branching section 30 in this embodiment. The transmission section 42 is an optical fiber used to form the optical path of the reference light branched from the branching section 30. The reference light branched by the branching section 30 passes through the transmission section 42 and heads toward the half mirror 45. The half mirror 45 branches the incoming reference light into light that goes toward mirror 12a via the wavelength dispersion member 46 and light that goes toward mirror 12b. Hereinafter, the optical path of the reference light that goes toward mirror 12a will be referred to as reference optical path A. Hereinafter, the optical path of the reference light that goes toward mirror 12b will be referred to as reference optical path B. Furthermore, in the following, the reference light following reference optical paths A and B will be referred to as reference light A and B, respectively. Reference optical paths A and B are examples of the first and second optical paths, respectively. The wavelength dispersion member 46 is a dispersion medium or a pulse stretcher, etc. Thus, in this embodiment, multiple (two) reference optical paths with different wavelength dispersion characteristics are configured. In this embodiment, reference optical path A has a longer optical path length than reference optical path B. That is, reference light A is used to measure the position of the object to be measured in the back direction more than reference light B. Here, the back direction is the direction in which the measurement light travels when incident on the object to be measured. The opposite direction of the back direction is the front direction. In this embodiment, the control unit 10 adjusts the optical path lengths of reference optical paths A and B by moving the mirrors 12a and 12b via the adjustment mechanism 11. Here, the optical path length is the length of the distance that light travels through the vacuum during the period in which it passes through the optical path in the corresponding medium. For example, the optical path length of an optical path 1 m long in a medium with a refractive index of 1.2 is the refractive index of the medium (1.2) × the length of the medium (1 m) = 1.2 m. The reference light that passes through the wavelength-dispersing member 46 and is reflected by the mirror 12a passes through the wavelength-dispersing member 46 and the half-mirror 45, follows the transmission section 42, and heads towards the branching section 30. The reference light that is reflected by the mirror 12b heads towards the half-mirror 45, has its direction changed by the half-mirror 45, follows the transmission section 42, and heads towards the branching section 30.Furthermore, the transmission unit 43 is an optical fiber used to form an optical path through which the measurement light branched by the branching unit 30 travels toward the object to be measured. A portion of the measurement light directed toward the object to be measured goes toward the cornea of ​​the object, where a portion is reflected and scattered, and returns in the direction from which it came. Another portion of the measurement light directed toward the object to be measured goes toward the retina of the object, where a portion is reflected and scattered, and returns in the direction from which it came. Hereafter, the optical path of the measurement light toward the retina will be referred to as measurement optical path A. Also below, the measurement light following measurement optical path A will be referred to as measurement light A. Also below, the optical path of the measurement light toward the cornea will be referred to as measurement optical path B. Also below, the measurement light following measurement optical path B will be referred to as measurement light B. In this embodiment, measurement optical paths A and B coincide until they enter the eye under examination. Therefore, measurement light A and B reach the eye under examination along the same optical axis. The measurement light A and B that have returned from the object to be measured pass through the transmission unit 43 and head toward the branching unit 30. Zero points A and B in the measurement optical path in Figure 2 are the zero points of reference optical paths A and B, respectively. A zero point is a position on the measurement optical path where the optical path length of the measurement light, when reflected in the opposite direction at that position and returning, is the same as the optical path length of the reference optical path. Zero point B is adjusted to be in front of the cornea of ​​the eye being measured (on the anterior side from the perspective of the eye being measured). 【0012】 At the branching section 30, interference light between reference light A and measurement light A, interference light between reference light B and measurement light B, and interference light between reference light A and reference light B are generated. Hereafter, the interference light between reference light A and measurement light A will be referred to as interference light A. Similarly, the interference light between reference light B and measurement light B will be referred to as interference light B. In this embodiment, because a wavelength-dispersing member 46 is present, the difference in wavelength dispersion characteristics between the corresponding measurement optical path and reference optical path is different for interference light A and interference light B. That is, the difference in wavelength dispersion characteristics between the reference optical path A and measurement optical path A corresponding to interference light A is different from the difference in wavelength dispersion characteristics between the reference optical path B and measurement optical path B corresponding to interference light B. Also below, the interference light between reference light A and reference light B will be referred to as interference light C. Interference light C is an example of an interference reference light. The transmission section 44 is an optical fiber that forms the optical path of light including each of the interference lights generated at the branching section 30. The light, including each interference light generated at the branching section 30, passes through the transmission section 44 and heads toward the diffraction grating 47. The diffraction grating 47 disperses the incoming light. The dispersed light then reaches a lens (not shown) positioned between the diffraction grating 47 and the light-receiving section 15. This lens focuses the light dispersed by the diffraction grating 47 onto each light-receiving element of the light-receiving section 15, according to its wavelength component (wavenumber component). In other words, each light-receiving element of the light-receiving section 15 receives light with different wavenumbers. 【0013】 Light traveling through the transmission unit 44 is dispersed by the diffraction grating 47, separating into wavelength components (wavenumber components) and focusing onto the light receiving unit 15. This allows the control unit 10 to detect signal currents corresponding to the intensity of each wavelength component (wavenumber component) of the received light via the multiple light-receiving elements of the light receiving unit 15. However, the wavenumbers of the light received by the multiple light-receiving elements of the light receiving unit 15 are not equally spaced. Therefore, the control unit 10 performs interpolation based on the detected signal currents to obtain signal currents corresponding to multiple equally spaced wavenumbers. Hereafter, these signal currents corresponding to multiple equally spaced wavenumbers will be referred to as the measured current signal. The control unit 10 converts the measured current signal from a signal in wavenumber-current space (hereinafter referred to as K-space) to a signal in frequency-signal intensity space (hereinafter referred to as Z-space) by performing a discrete Fourier transform. Hereafter, the signal converted here will be referred to as the measured signal. 【0014】 Here, we will explain the signals obtained with conventional FD-OCT. Conventionally, FD-OCT could not distinguish signals from samples with symmetrical optical path length differences with respect to the zero point. That is, the interference light of the measurement light and reference light returned from a sample at a predetermined distance behind the zero point (behind the eye being examined) is indistinguishable from the interference light of the measurement light and reference light returned from a sample at a predetermined distance in front of the zero point (in front of the eye being examined). In this case, when the current signal with respect to wavenumber obtained via the light-receiving unit is performed using a discrete Fourier transform, a signal that is symmetrical on both the positive and negative sides of the frequency is obtained. The dashed graph in Figure 3A shows an example of a signal obtained with conventional FD-OCT. In Figure 3A, it can be seen that peaks corresponding to the sample are symmetrically placed on both the positive and negative sides of the frequency. In this way, a signal that appears in a frequency band with the opposite positive and negative sign to the original signal is called a mirror signal. In such cases, for example, the zero point is adjusted to be clearly in front of or behind the sample, and the signal in the direction where the sample does not exist is ignored to measure the sample. Therefore, only one side of the zero point—either the front or the back—can be measured. 【0015】 Therefore, there is a technique called full-range OCT that distinguishes between positive and negative frequency signals, thereby acquiring signals on both the positive and negative sides (full range) (signals on both sides of the zero point). Full-range OCT can measure both sides of the zero point simultaneously. One method of full-range OCT is DEFR (Dispersion Encoded Full Range). For example, by providing a wavelength-dispersing element as shown in wavelength-dispersing element 46 in Figure 2, the wavelength dispersion characteristics of the reference light and the measurement light can be made different. In this case, due to the difference in wavelength dispersion between the reference light and the measurement light, the signal in Z space obtained by receiving the interference light of the reference light and the measurement light at the light-receiving element becomes broader. That is, the width of the signal peak widens, and the signal intensity decreases. The solid line graph in Figure 3A shows the signal when a wavelength-dispersing element is provided. It can be seen that the signal is broadened by making the wavelength dispersion characteristics of the reference light and the measurement light different. 【0016】 Here, by performing a process of correcting the influence of wavelength dispersion on the measurement current signal obtained through the light receiving unit, in the Z space after discrete Fourier transform, the peak portion corresponding to the sample becomes sharp (the width becomes narrow and the signal intensity becomes strong), and the other peak portions become broad. This will be explained in more detail. 【0017】 In the interferometer of OCT, the measurement current signal I obtained by interpolating the signal current output from the light receiving element when the interfering measurement light and reference light are received by the light receiving element is expressed by the following formula 1. 【0018】 【Number】 【0019】 u with a bar written above formula 1 sample (Hereinafter, it will be described as u - sample ), u reference (Hereinafter, it will be described as u - reference ) is the energy of each of the two interfering lights. η is the quantum efficiency of the light receiving unit (the ratio of the incident photons that are converted into electrons as signals). h is Planck's constant. q is the elementary charge. λ is the wavelength of light. k is the wave number of light (the reciprocal of the wavelength λ). Δz is the optical path length difference between the two interfering lights (measurement light, reference light). The influence of light interference appears in the third term of formula 1. Here, assuming that a wavelength dispersion member is arranged on the reference optical path, Δz is expressed by the following formula 2. 【0020】 【Number】 【0021】 In formula 2, z sample is the optical path length of the measurement optical path. z reference is the optical path length of the reference optical path. z zero-dispersionis the optical path length of the optical path that can be considered to have approximately no wavelength dispersion characteristics in the reference optical path (the optical path length of the portion excluding the wavelength dispersion member). L is the length of the wavelength dispersion member in the optical path provided in the measurement optical path. n(k) is the refractive index of light with wavenumber k in the wavelength dispersion member. The phase φ of the measured current signal I is expressed as a function of wavenumber k in the following equation 3, using the argument of cos in the third term of equation 1. 【0022】 【number】 【0023】 Furthermore, if we perform a Taylor expansion of n(k) in equation 3 with respect to wavenumber k, using a predetermined wavenumber k0 as the base, we obtain the following equation 4. 【0024】 【number】 【0025】 Substituting equation 4 into equation 3 yields the following equation 5. 【0026】 【number】 【0027】 In equation 5, φ0 is expressed by the following equation 6. 【0028】 【number】 【0029】 Furthermore, Δz0 in Equation 5 is expressed by the following Equation 7. 【0030】 【number】 【0031】 In Equation 5, the first term (φ0) and the second term (Δz0(k-k0)) of the phase φ are a component proportional to k and a constant, respectively. Therefore, if the phase φ consists only of the first and second terms, the measured current signal I will have a sinusoidal shape as a function of wavenumber k, and the peak signal will not be distorted when the measured current signal I is subjected to a discrete Fourier transform. In contrast, the third term of the phase φ in Equation 5 indicates the effect of the difference in dispersion characteristics between the reference optical path and the measurement optical path. The presence of this third term causes the measured current signal I to cease being a sinusoidal wave. As a result, when the measured current signal I is subjected to a discrete Fourier transform, the peak signal becomes broad. 【0032】 Once φ in equation 5 is found, the found φ can be expressed as a polynomial Σ j=0 (a j (k-k0) j By approximating with ), we can obtain the approximate formula for Equation 5. Then, by subtracting the zeroth and first-degree terms from this polynomial, we can obtain the information for the third term of Equation 5. Here, a j This indicates the coefficient of the j-th degree term. Also, φ in equation 5 is a polynomial Σ j=0 (a j (k-k0) j Alternatively, we can approximate it as follows and consider the quadratic and subsequent components as information for the third term of Equation 5. The third term of Equation 5 is a dimensionless value φ that indicates the magnitude of wavelength dispersion. dispersion Far away. φ dispersion This is expressed by the following equation 8. 【0033】 【number】 【0034】 The measured current signal I is φ dispersion The following equation 9 is used to express this. The first and second terms of equation 9 are constant terms. The third term represents the interference signal between the measurement light that reaches the sample and returns from the sample and the reference light. The fourth term represents the complex conjugate component (mirror signal) of the third term, and is a signal in a frequency band with the opposite sign to the third term. 【0035】 【number】 【0036】 The measured current signal I is given by exp(-iφ) dispersion By multiplying by exp(-iφ), the effect of wavelength dispersion can be corrected. dispersion Multiplying by ) results in the following equation 10. 【0037】 【number】 【0038】 The first and second terms of Equation 10 are constant terms resulting from the measurement light and reference light, and are therefore ignored in the signal after the Discrete Fourier Transform. Looking at the third term of Equation 10, we see that the φ that was present in the third term of Equation 9 is absent. dispersion It can be seen that it has disappeared. In other words, in the third term, it can be seen that the effect of wavelength dispersion has been corrected. In contrast, in the fourth term of Equation 10, φ dispersion This is twice as large as the fourth term in Equation 9, indicating that the effect of wavelength dispersion has become greater. 【0039】 exp(-iφ dispersionWhen I multiplied by ) is subjected to a Discrete Fourier Transform, in Z space, a signal related to the third term of Equation 10 and a signal related to the fourth term are generated in the frequency band opposite in sign to the signal related to the third term. The signal related to the third term becomes sharper as the effect of wavelength dispersion is reduced. The signal related to the third term becomes broader as the effect of wavelength dispersion is increased. That is, the interference signal related to the measurement light from the sample becomes sharp, and the mirror signal becomes broad. Using these characteristics, it is possible to distinguish between the sample signal and the mirror signal which appears symmetrically in Z space. Figure 3B shows the signal when wavelength dispersion correction is applied to the signal represented by the solid line graph in Figure 3A. Compared to Figure 3A, it can be seen that the peak on the positive frequency side is sharper, and the peak on the negative frequency side is broader. From this, it can be seen that the signal on the positive frequency side is the signal corresponding to the sample, and the signal on the negative frequency side is the mirror signal. In this way, by distinguishing between the real signal and the mirror signal, full-range OCT is realized. In this embodiment, the FD-OCT device 1 performs full-range measurements (measurements on both sides of zero point A) when using interference light A. 【0040】 If the measured current signal I is not affected by the difference in wavelength dispersion characteristics in the optical path, then exp(-iφ) dispersion When wavelength dispersion correction is applied, the signal after the discrete Fourier transform becomes broad on both the positive and negative frequency sides. The measured current signal I of interference light from light following the same optical path with the same wavelength dispersion characteristics is expressed by the following equation 11. 【0041】 【number】 【0042】 To this measurement current signal, exp(-iφ) dispersion When the wavelength dispersion correction is applied by ), the following equation 12 is obtained. 【0043】 【number】 【0044】 Looking at the third and fourth terms of Equation 12, we see that φ is different from the third and fourth terms of Equation 11. dispersion It can be seen that the effect of φ is occurring. Therefore, when a chromatic dispersion correction is applied to the measured current signal I of interference light between two optical paths with the same chromatic dispersion characteristics, the signal in Z space becomes broad. The graph in Figure 4A shows an example of a signal obtained with FD-OCT using interference light that is unaffected by chromatic dispersion. It can be seen that the signal is sharp in both the positive and negative frequency bands. Also, Figure 4B shows the effect of chromatic dispersion φ on the signal in Figure 4A. dispersion The corrected signal is shown. It can be seen that the signal is broadened in both the positive and negative frequency bands. 【0045】 In this embodiment, the control unit 10 uses these features to extract signals related to each interference light from the measurement signal. The functions and processing details of the FD-OCT device 1 will be described below. 【0046】 The control unit 10 functions as the acquisition unit 101, extraction unit 102, derivation unit 103, and display control unit 104 by executing the signal processing program 100 stored in ROM. Therefore, in the following, processes that refer to each functional component as the subject are actually processes performed by the control unit 10. 【0047】 The acquisition unit 101 acquires an output signal output from a single light receiving unit 15 that receives multiple interference lights, which are formed when a measurement light output from a single light source 14 and following a measurement optical path interferes with a reference light output from the light source 14 and following a reference optical path, and where the difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path taken by the interfering light is different for each interference light. The details of the processing of the acquisition unit 101 will be described below. 【0048】 The acquisition unit 101 detects the position of the corneal apex of the subject's eye being examined, which is located at a predetermined position, via the alignment mechanism 13, and adjusts the position of the FD-OCT device 1 so that the detected corneal apex position and the FD-OCT device 1 are in a predetermined positional relationship. The acquisition unit 101 causes the light source 14 to output light. In response to the light output from the light source 14, the light receiving unit 15 receives the light, including interference light A to C, for each wavenumber component. The acquisition unit 101 acquires the signal current output from each light receiving element of the light receiving unit 15 that has received the light, including interference light A to C. Then, the control unit 10 performs interpolation processing based on the detected signal current to obtain signal currents corresponding to multiple equally spaced wavenumber values ​​as measurement current signals. The control unit 10 obtains the measurement signal by performing a discrete Fourier transform on the measurement current signal. The measurement current signal and measurement signal output from the light receiving unit 15 and processed are examples of output signals. 【0049】 In addition, in this embodiment, the acquisition unit 101 also performs the following processing. The acquisition unit 101 acquires a signal obtained by discrete Fourier transforming the measured current signal, which is interpolated from the signal current output from the light receiving unit 15 that receives interference light A (interference light between reference light A and the measured light returned from the mirror), with the half mirror 45 removed and a mirror placed in place of the object to be measured to reflect the incident light in the opposite direction (a state in which reference light B, interference light B, and interference light C do not exist). The acquisition unit 101 replaces all values ​​of the signals in the negative frequency band of the signal after the discrete Fourier transform with 0. The acquisition unit 101 obtains a complex number signal in K space by performing an inverse Fourier transform on the substituted signal. For each value of k, the acquisition unit 101 finds the phase φ of this measured current signal by finding the arctangent of the value obtained by dividing the imaginary component by the real component. The acquisition unit 101 then expresses the obtained φ as a polynomial Σ j=0 (a j (k-k0) j The approximation is performed using φ. The acquisition unit 101 removes the first and second terms from the approximated polynomial to obtain a value φ that indicates the magnitude of the difference in wavelength dispersion (influence of the wavelength dispersion member 46) between the reference optical path A and the measurement optical path A caused by the wavelength dispersion member 46. dispersion An approximate value of is obtained. However, the acquisition unit 101 sums the 3rd term to the mth (a natural number greater than or equal to 3) term of the approximated polynomial, and calculates φdispersion You can also find an approximate value. 【0050】 Also, φ dispersion This may be determined by other methods. For example, the acquisition unit 101 acquires a measurement current signal by interpolating the signal current output from the light receiving unit 15, which receives interference light A, with the half mirror 45 removed and a mirror placed in place of the object to be measured to reflect the incident light in the opposite direction (a state in which reference light B and interference light B do not exist). In addition, the acquisition unit 101 also acquires φ dispersion Set this to the default initial value, and apply exp(-iφ) to this measurement current signal. dispersion The wavelength dispersion is corrected by applying φ, and the corrected measured current signal is obtained by performing a discrete Fourier transform. Next, the acquisition unit 101 performs φ dispersion The value of is varied, and the same process is performed to obtain the signal after the discrete Fourier transform (signal in Z space). The acquisition unit 101 repeats this process, φ dispersion For each value of φ, the signal in Z space is obtained. dispersion Among the signals corrected while varying the value of , the signal with the most corrected chromatic dispersion will have the strongest signal intensity. Therefore, the acquisition unit 101 identifies the signal in which the highest peak (strongest signal intensity) exists, and the φ corresponding to the identified signal dispersion The value of φ dispersion This can also be used as the determined value. 【0051】 The acquisition unit 101 obtains the φ dispersion Using this, a corrected signal is obtained in which wavelength dispersion correction processing has been applied to correct the effect of wavelength dispersion on the measurement signal. More specifically, the acquisition unit 101 applies exp(-iφ) to the measurement current signal. dispersion The two signals are multiplied together to obtain a corrected current signal in which the effects of wavelength dispersion have been corrected. The acquisition unit 101 then obtains the signal obtained by discrete Fourier transform of the acquired corrected current signal as a corrected signal in which the measurement signal has been subjected to wavelength dispersion correction processing. 【0052】 The extraction unit 102 extracts the extracted signals, which are the signals for each interference light A to C, based on the measurement signal acquired by the acquisition unit 101 and the correction signal. The details of the processing of the extraction unit 102 are described below. In this embodiment, the zero point B is located in front of the cornea. Therefore, the signals in the negative frequency band of the measurement signal are mirror signals of the signals in the positive frequency band. Accordingly, in this embodiment, the extraction unit 102 ignores the signals in the negative frequency band of the measurement signal and extracts the signals for each interference light from the signals in the positive frequency band and the correction signal. 【0053】 The extraction unit 102 extracts the signal with the highest signal intensity from the measurement signal and the correction signal, which is the peak signal, representing the signal with the largest peak. The peak signal is an example of an extracted signal. Figure 5 shows an example of the measurement signal and the correction signal. In the example in Figure 5, signal p1 is the signal with the highest signal intensity. 【0054】 Wavelength dispersion correction processing (exp(-iφ) applied to the measured current signal) dispersion The signal corrected for wavelength dispersion by the process of applying φ becomes narrower in width and stronger in intensity than the original signal. For signals that were not corrected by the wavelength dispersion correction process, φ dispersion The effect of the wavelength dispersion component 46 becomes larger, resulting in a broader signal (wider width and weaker intensity) compared to the original signal. Therefore, if the signal with the highest signal intensity is present in the corrected signal, this signal is the signal corrected for wavelength dispersion by the wavelength dispersion component 46 (i.e., the signals related to interference light A and interference light C that were originally affected by the wavelength dispersion component 46). Also, if the signal with the highest signal intensity is present in the measured signal, this signal is the signal related to interference light B that was originally not affected by the wavelength dispersion component 46. 【0055】 If the extracted peak signal is included in the correction signal, the extraction unit 102 stores it in RAM as a signal related to interference light A and C. Here, if we let the coordinates of the peak signal in Z-space be (frequency fr, signal intensity str, phase θ), then the peak signal can be expressed as str × F[exp(i fr·k+i θ)]. Here, F is the operator representing the Discrete Fourier Transform. The calculation of the F operator is F[(f(x)]=Σ y=0 N-1 It is defined as f(x)exp(-2πixy / N). 【0056】 If the peak signal is included in the correction signal, the extraction unit 102 calculates the mirror signal of the peak signal in the correction signal based on the peak signal. Hereinafter, the mirror signal of the peak signal in the correction signal will be referred to as the mirror peak signal. More specifically, the extraction unit 102 calculates the peak signal (str × F[exp(i fr·k)+i θ]) as (F[exp(2i φ dispersion The convolution is performed using )] / N). Here, N represents the number of data points in the Discrete Fourier Transform. That is, the extraction unit 102 is str×F[exp(i fr·k+i θ)])*(F[exp(2i φ dispersion We calculate () / N). Here, * is the operator representing convolution. Convolution of a function f(x) with a function g(x) is defined as follows: That is, f(x)*g(x)=Σ y=0 N-1 It is defined as (f(y) × g(xy)). Then, the extraction unit 102 finds the value obtained by inverting the sign of the dependent variable k in the convolution result. The extraction unit 102 acquires the signal of the complex conjugate of the obtained value as a mirror peak signal. 【0057】 Furthermore, if the peak signal is included in the correction signal, the extraction unit 102 determines the signal corresponding to the peak signal in the measurement signal (the peak signal before correction for the effect of wavelength dispersion) based on the peak signal. In the following, the signal corresponding to the peak signal in the measurement signal will be referred to as the pre-correction peak signal. More specifically, if the peak signal exists in the positive frequency band as shown in P1 of Figure 5, the extraction unit 102 calculates the peak signal as (F[exp(i φ dispersionThe uncorrected peak signal is obtained by convolution with () / N). Furthermore, if the peak signal exists in the negative frequency band, the extraction unit 102 converts the peak signal (str×F[exp(i fr·k+i θ)]) to (F[exp(i φ dispersion The convolution is performed using ) / N). Then, the extraction unit 102 obtains the value of the dependent variable k in the convolution result with the sign reversed, and obtains the uncorrected peak signal by calculating the complex conjugate of the obtained value. The extraction unit 102 then removes the pre-correction peak signal from the measurement signal. The extraction unit 102 also removes the peak signal and the Miller peak signal from the corrected signal. Figure 6 shows an example in Figure 5 where the peak signal P1, the pre-correction peak signal, and the Miller peak signal have been removed. The dashed lines in Figure 6 indicate the removed signals. This removes the signal corresponding to the peak signal from both the measurement signal and the corrected signal. 【0058】 Furthermore, if the extracted peak signal is included in the measurement signal, the extraction unit 102 stores it in RAM as a signal related to interference light B. If the measurement signal and the correction signal are the signals shown by the solid lines in Figure 6, the extraction unit 102 extracts signal p2 as the peak signal. If the peak signal is included in the measurement signal, the extraction unit 102 determines, based on the peak signal, the signal corresponding to the peak signal in the correction signal (the peak signal after correction for the effect of wavelength dispersion by the wavelength dispersion member 46) and the mirror signal of that signal. In the following, the signal corresponding to the peak signal in the correction signal will be referred to as the corrected peak signal. More specifically, the extraction unit 102 calculates the peak signal as (F[exp(-i φ dispersion The corrected peak signal is obtained by convolution with (F[exp(i φ)). The extraction unit 102 also extracts the peak signal using (F[exp(i φ) dispersion The convolution is performed using ) / N) and the value obtained by inverting the sign of the dependent variable k in the convolution result is obtained. The extraction unit 102 obtains the mirror signal of the corrected peak signal by calculating the complex conjugate of the obtained value. The extraction unit 102 then removes the peak signal from the measurement signal. Figure 7 shows how the signal corresponding to signal p2 has been removed from the measurement signal and the correction signal in the example of Figure 6. The dashed line in Figure 7 indicates the removed signal. The extraction unit 102 also removes the corrected peak signal and the mirror signal of the corrected peak signal from the correction signal. As a result, the signal corresponding to the peak signal is removed from the measurement signal and the correction signal. 【0059】 The extraction unit 102 repeats the above process (extracting and storing the peak signal from the measurement signal and the correction signal, and deleting the signal corresponding to the peak signal from the measurement signal and the correction signal) until there are no more signals with a signal intensity above a predetermined threshold in the measurement signal and the correction signal. Figure 8 shows the measurement signal and the correction signal when this process is repeated until there are no more signals with a signal intensity above a predetermined threshold in the example of Figure 5. 【0060】 The extraction unit 102 combines the corrected signal, from which the signal corresponding to the extracted peak signal has been removed, with the peak signals related to interference light A and C stored in RAM. In this way, the extraction unit 102 extracts the signal measured using interference light A and C. The extraction unit 102 also combines the measurement signal, from which the signal corresponding to the extracted peak signal has been removed, with the peak signal related to interference light B stored in RAM. As a result, the extraction unit 102 extracts the signal measured using interference light B. Figure 9 shows the signals related to interference light A and C and the signal related to interference light B extracted in the example of Figure 5. In this way, the extraction unit 102 extracts signals related to each of the interference lights from the measurement signal. 【0061】 In this embodiment, the extraction unit 102 generates an image of the target to be measured from the signals extracted for each interference light using a known method. More specifically, the extraction unit 102 uses the signals measured using interference lights A and C to generate an image of the vicinity of the retina (image A) measured using interference light A. The extraction unit 102 also uses the signal measured using interference light B to generate an image of the vicinity of the cornea (image B) measured using interference light B. 【0062】 The derivation unit 103 derives the difference between reference optical path A and reference optical path B based on the extracted signal corresponding to interference light C, which is the interference light of reference optical path A traveling along reference optical path A and reference optical path B traveling along reference optical path B, from the extracted signals extracted by the extraction unit 102. The details of the processing of the derivation unit 103 are described below. The signals related to interference light A and C extracted by the extraction unit 102 include the signal related to interference light C. This signal appears in Z space as a peak at a frequency corresponding to the distance between zero point A and zero point B. In this embodiment, the range in which zero point B can exist relative to zero point A is predetermined. The derivation unit 103 identifies the peak included in the frequency band corresponding to this range in the signals related to interference light A and C extracted by the extraction unit 102 as the signal related to interference light C. The derivation unit 103 derives the distance between zero point A and zero point B (the difference between reference optical path A and reference optical path B) from the frequency of the identified signal. In this way, the derivation unit 103 can determine the distance between the zero points. 【0063】 The display control unit 104 displays multiple images generated for each interference light based on the extraction signals extracted by the extraction unit 102 on the display unit 16. The details of the processing of the display control unit 104 will be explained below. 【0064】 The display control unit 104 displays each of the multiple images generated by the extraction unit 102 on the display unit 16 so that their positional relationships correspond to the positional relationships of the subjects. That is, the display control unit 104 displays images B and A so that the cornea in image B and the retina in image A are the same as the actual positional relationship of the cornea and retina at the scale of the images. More specifically, the display control unit 104 identifies the position of zero point B in image B and the position of zero point A in image A. The display control unit 104 also identifies the position of zero point B in image A based on the difference between the reference optical path A and the reference optical path B (the distance between zero point A and zero point B) derived by the derivation unit 103. The display control unit 104 displays images B and A so that the position of zero point B in image B and the position of zero point B in image A overlap. Furthermore, if images B and A partially overlap, the display control unit 104 overlays images B and A on top of each other for the overlapping portion. More specifically, the display control unit 104 displays an image created by combining image B and image A at 50% each for the overlapping portion. However, the display control unit 104 may display either image B or image A for the overlapping portion. Figure 10 shows an example of superimposed images B and A. This allows the display control unit 104 to present images of multiple measurement targets to the user in the same positional relationship as the actual positional relationship. Furthermore, by superimposing images A and B for the overlapping portion, the display control unit 104 can present images A and B to the user as a single unit. 【0065】 The display control unit 104 does not need to determine the position of zero point B in both image B and image A. For example, the display control unit 104 may detect the same object (e.g., a lens) from both image A and image B, and display image B and image A in such a way that the detected object is superimposed. 【0066】 However, the display control unit 104 may display image B and image A in other display modes. For example, the display control unit 104 may display image B and image A in other display modes if the direction of the retina as seen from the cornea is the same as the direction of the retina in image A as seen from the cornea in image B. For example, the display control unit 104 may display image B and image A so that they do not overlap. 【0067】 As described above, with the configuration of this embodiment, the FD-OCT device 1 acquires measurement signals, which are signals related to interference lights A and B, where the difference in wavelength dispersion characteristics between the corresponding measurement optical path and the reference optical path is different. The acquired measurement signals are then subjected to a wavelength dispersion correction process for interference light A to acquire a corrected signal. The FD-OCT device 1 then utilizes the characteristics of the signal change corresponding to the wavelength dispersion correction process to extract the signal of the retina of the eye being examined, measured using interference light A, and the signal of the cornea of ​​the eye being examined, measured using interference light B, from the measurement signal and the corrected signal. In this way, the FD-OCT device 1 can extract signals from multiple locations more easily than conventional methods without the effort required to make the wavelength dispersion characteristics of the measurement optical path and the reference optical path the same. 【0068】 (1-2) Extraction process: The axial length measurement process performed by the FD-OCT device 1 of this embodiment will be explained using Figure 11. After the subject's eye to be examined is positioned in a predetermined location, the control unit 10 starts the process shown in Figure 11 at a specified timing. 【0069】 In step S100, the acquisition unit 101 detects the position of the corneal apex of the subject's eye being examined, which is located in a predetermined position, via the alignment mechanism 13, and adjusts the position of the FD-OCT device 1 so that the detected corneal apex position and the FD-OCT device 1 are in a predetermined positional relationship. After the completion of the process in step S100, the acquisition unit 101 proceeds to step S105. 【0070】 In step S105, the acquisition unit 101 outputs light from the light source 14 and acquires a measurement current signal by interpolating the signal current output from the light receiving unit 15 with respect to wavenumber k. After completing the process in step S105, the acquisition unit 101 proceeds to step S110. 【0071】 In step S110, the acquisition unit 101 determines the magnitude of the difference in wavelength dispersion characteristics between the reference optical path A and the measurement optical path φ dispersion Obtain the following. Then, the measured current signal obtained in step S105 is converted to exp(-i φ). dispersion The wavelength dispersion is corrected by applying a function (S105), and the corrected signal is obtained by performing a discrete Fourier transform on the corrected signal. After the processing in step S110 is completed, the acquisition unit 101 proceeds to step S115. The processing in steps S105 to S110 is an example of the acquisition steps. 【0072】 In step S115, the extraction unit 102 performs the following processing: It extracts the maximum peak as the peak signal from the measurement signal acquired in step S105 and the correction signal acquired in step S110. If the peak signal is included in the correction signal, the extraction unit 102 stores the peak signal in RAM as a signal related to interference light A and C. Then, the extraction unit 102 determines the Miller peak signal and the pre-correction peak signal based on the peak signal. The extraction unit 102 removes the peak signal and the Miller signal from the correction signal and removes the pre-correction peak signal from the measurement signal. Also, if the peak signal is included in the measurement signal, the extraction unit 102 stores the peak signal in RAM as a signal related to interference light B. Then, the extraction unit 102 determines the corrected peak signal and the Miller signal of the corrected peak signal based on the peak signal. The extraction unit 102 removes the corrected peak signal and the Miller signal of the corrected peak signal from the correction signal and removes the peak signal from the measurement signal. The extraction unit 102 repeats the above process until there are no signals with a signal intensity above a predetermined threshold in the measurement signal and correction signal. 【0073】 The extraction unit 102 extracts the signal related to interference light B by combining the peak signal and the pre-correction peak signal, which have been removed from the measurement signal, with the peak signal related to interference light B stored in RAM. The extraction unit 102 also extracts the signals related to interference lights A and C by combining the peak signal, the mirror peak signal, the corrected peak signal, and the mirror signal of the corrected peak signal, which have been removed from the correction signal, with the peak signals related to interference lights A and C, which have been stored in RAM. Based on the extracted signal related to interference light B, the extraction unit 102 generates an image of the vicinity of the cornea. The extraction unit 102 also generates an image of the vicinity of the retina based on the extracted signals related to interference lights A and C. After the processing in step S115 is completed, the extraction unit 102 proceeds to step S120. The processing in step S115 is an example of an extraction step. 【0074】 In step S120, the derivation unit 103 derives the distance between zero point A and zero point B based on the signal related to the interference light C extracted in step S115. After completing the process in step S120, the derivation unit 103 proceeds to step S125. In step S125, the display control unit 104 identifies the position of zero point B in the corneal vicinity image generated in step S115. The display control unit 104 also identifies the position of zero point B in the retinal vicinity image generated in step S115 based on the distance derived in step S120. The display control unit 104 then displays the corneal vicinity image and the retinal vicinity image on the display unit 16 so as to align the position of zero point B in the images. 【0075】 (2) Second embodiment: In the first embodiment, a case was described in which multiple reference optical paths with different wavelength dispersion characteristics are provided. In this embodiment, a case is described in which multiple measurement optical paths with different wavelength dispersion characteristics are provided. Figure 12 shows the configuration of the FD-OCT device 1 of this embodiment. In Figure 12, components with the same reference numerals as in Figure 2 are the same as those in Figure 2. The differences in the configuration of the FD-OCT device 1 of this embodiment compared to the first embodiment will now be explained. In this embodiment, the FD-OCT apparatus 1 does not include a mirror 12b, a half-mirror 45, or a wavelength-dispersing member 46, and has only one reference optical path. The FD-OCT apparatus 1 also includes an optical system (polarizing beam splitters 48, 51, mirrors 49, 50, wavelength-dispersing member 52, lenses 53a, 53b) for forming multiple measurement optical paths with different wavelength-dispersion characteristics. 【0076】 In the FD-OCT apparatus 1 of this embodiment, the measurement light path followed by the measurement light will be described. The measurement light branched at the branching section 30 goes toward the polarizing beam splitter 48. At the polarizing beam splitter 48, the measurement light is branched into light going toward mirror 49 and light going toward mirror 50. In this embodiment, the light going toward mirror 50 is the measurement light used to measure the retina of the eye under examination. Hereinafter, the measurement light used to measure the retina of the eye under examination will be referred to as measurement light A. The light path followed by measurement light A will be referred to as measurement light path A. The light going toward mirror 49 is the measurement light used to measure the cornea of ​​the eye under examination. Hereinafter, the measurement light used to measure the cornea of ​​the eye under examination will be referred to as measurement light B. The light path followed by measurement light B will be referred to as measurement light path B. 【0077】 The measurement light A, which is split by the polarizing beam splitter 48 and reaches the mirror 50, is reflected by the mirror 50, passes through the wavelength-dispersing member 52 and lens 53a, and heads towards the polarizing beam splitter 51. Lens 53a is a lens that focuses (forms a focal point) near the position of the object to be measured using the measurement light A. However, in this embodiment, the object to be measured using the measurement light A is the retina, and it is conceivable that the measurement light A is focused near the retina by the cornea and lens of the eye being measured. Therefore, lens 53a may be omitted. The measurement light A then passes through the polarizing beam splitter 51 and heads towards the retina of the eye being measured. The measurement light A is reflected and scattered by the retina, and a portion returns in the opposite direction to the incident direction. The measurement light A returns to the branching section 30 via the polarizing beam splitter 51, lens 53a, wavelength-dispersing member 52, mirror 50, and polarizing beam splitter 48. 【0078】 The measurement light B, split by the polarizing beam splitter 48, passes through lens 53b and heads towards mirror 49. Lens 53b is located at a different position from lens 53a and is a lens that focuses near the cornea being measured using the measurement light B. In this way, by providing a lens that focuses near the object to be measured in the measurement light path, the FD-OCT device 1 can perform more accurate measurements. The measurement light B is reflected by mirror 49 and heads towards polarizing beam splitter 51, where its direction is changed, and it is reflected and scattered by the cornea of ​​the eye being examined, with some of it returning in the opposite direction to the incident direction. The measurement light B returns to the branching section 30 via polarizing beam splitter 51, mirror 49, lens 53b, and polarizing beam splitter 48. 【0079】 At the branching section 30, interference light (hereinafter referred to as interference light A) is generated between the measurement light A and the reference light (light that travels toward the mirror 12a and returns from the mirror 12a), and interference light (hereinafter referred to as interference light B) is generated between the measurement light B and the reference light. The generated interference lights A and B are received by the light receiving section 15 for each wavenumber component via the transmission section 44 and the diffraction grating 47. Interference light A is chromatically dispersed due to the influence of the wavelength dispersion member 52. Interference light B is not affected by the wavelength dispersion member 52. 【0080】 The processing of the FD-OCT device 1 in this embodiment will be described. The processing of the acquisition unit 101 in this embodiment is the same as in the first embodiment. That is, the acquisition unit 101 interpolates the signal current output from the light receiving unit 15 that has received the interference light A to C with respect to wavenumber k, and acquires a measurement current signal. Then, the acquisition unit 101 performs a discrete Fourier transform on the acquired measurement current signal and acquires a measurement signal. 【0081】 Furthermore, the acquisition unit 101 detects the magnitude of wavelength dispersion φ due to the influence of the wavelength dispersion member 52 in the interference light A. dispersion The acquisition unit 101 obtains φ in the same manner as in the first embodiment. dispersionThe acquisition unit 101 calculates an approximate value of φdispersion based on the measurement current signal obtained by interpolating the signal current output from the light receiving unit 15, which receives interference light A when the lens 53b is shielded (when measurement light B and interference light B are absent). 【0082】 The acquisition unit 101 obtains the φ dispersion Using this method, a corrected signal is obtained in which wavelength dispersion correction processing is applied to correct the effect of wavelength dispersion on the measurement signal, in the same manner as in the first embodiment. 【0083】 The extraction unit 102 extracts extraction signals for each interference light A and B based on the measurement signal acquired by the acquisition unit 101 and the correction signal. In this embodiment, the zero point B in the measurement optical path B is located in front of the cornea. Therefore, the signal in the negative frequency band of the measurement signal is a mirror signal of the positive signal. Accordingly, in this embodiment, the extraction unit 102 ignores the signal in the negative frequency band of the measurement signal and extracts the extraction signal for each interference light from the signal in the positive frequency band of the measurement signal and the correction signal. 【0084】 The extraction unit 102 extracts the signal related to interference light A and the signal related to interference light B from the measurement signal and the correction signal by performing the same processing as in the first embodiment. That is, the extraction unit 102 extracts the signal with the greatest signal intensity from the measurement signal and the correction signal as the peak signal, which is the signal with the largest peak. If the extracted peak signal is included in the correction signal, the extraction unit 102 stores the peak signal in RAM as a signal related to interference light A. The extraction unit 102 also acquires the mirror peak signal and the pre-correction peak signal based on the peak signal. The extraction unit 102 then removes the uncorrected peak signal from the measurement signal. Furthermore, the extraction unit 102 removes the peak signal and the Miller peak signal from the corrected signal. As a result, the signal corresponding to the peak signal is removed from both the measurement signal and the corrected signal. 【0085】 Furthermore, if the extracted peak signal is included in the measurement signal, the extraction unit 102 stores it in RAM as a signal related to interference light B. The extraction unit 102 also acquires a corrected peak signal and a mirror signal of the corrected peak signal based on the peak signal. The extraction unit 102 then removes the peak signal from the measurement signal. Furthermore, the extraction unit 102 removes the corrected peak signal and the mirror signal of the corrected peak signal from the correction signal. As a result, the signal corresponding to the peak signal is removed from both the measurement signal and the correction signal. 【0086】 The extraction unit 102 repeats the above process until there are no longer any signals with a signal intensity above a predetermined threshold in either the measurement signal or the correction signal. 【0087】 The extraction unit 102 combines the corrected signal, from which the signal corresponding to the extracted peak signal has been removed, with the peak signal related to interference light A stored in RAM. This allows the extraction unit 102 to extract the signal measured using interference light A. Furthermore, the extraction unit 102 combines the peak signal related to interference light B, stored in RAM, with the measurement signal from which the signal corresponding to the extracted peak signal has been removed. This allows the extraction unit 102 to extract the signal measured using interference light B. In this way, the extraction unit 102 extracts signals related to each of the interference lights from the measurement signal. 【0088】 In this embodiment, the extraction unit 102 generates an image of the target to be measured from the signals extracted for each interference light using a known method. More specifically, the extraction unit 102 uses the signal measured using interference light A to generate an image of the vicinity of the retina (image A) measured using interference light A. The extraction unit 102 also uses the signal measured using interference light B to generate an image of the vicinity of the cornea (image B) measured using interference light B. 【0089】 The processing of the display control unit 104 is the same as in the first embodiment. 【0090】 As described above, with the configuration of this embodiment, the FD-OCT device 1 can measure multiple positions simultaneously more easily than conventional methods, even when multiple measurement optical paths exist. 【0091】 Furthermore, the measurement optical paths A and B may be configured so that measurement light A and measurement light B are directed toward different measurement targets. For example, as shown in Figure 13, measurement light A may travel along a different optical axis than measurement light B and be directed toward a different measurement target than the one measured by measurement light B. Alternatively, as shown in Figure 14, the measurement optical paths A and B may be configured so that measurement light A and measurement light B are directed toward different locations on the same measurement target along different optical axes. This allows the FD-OCT device 1 to simultaneously measure multiple locations located on different optical axes. 【0092】 (3) Third embodiment: In this embodiment, we will describe the case where each interference light used to measure the object to be measured is an interference light that follows a different measurement optical path and a reference light that follows a different reference optical path. That is, we will describe the case where each interference light used for measurement has a different reference optical path and a different measurement optical path. Figure 15 shows the configuration of the FD-OCT device 1 of this embodiment. Components with the same symbols as in Figure 2 are the same as in Figure 2. The FD-OCT device 1 of this embodiment differs from the first embodiment in that it separately provides a transmission and branching section for forming the reference optical path A and the measurement optical path A, from the transmission and branching section for forming the reference optical path B and the measurement optical path B. 【0093】 In this embodiment, the FD-OCT device 1 is equipped with two sets corresponding to the transmission sections 41-44 and branch section 30 in Figure 2 (transmission sections 41a-44a and branch section 30a, and transmission sections 41b-44b and branch section 30b). The transmission sections 41a-44a and branch section 30a are used to form the reference optical path (reference optical path A) followed by the reference light (reference light A) heading toward the mirror 12a and the measurement optical path (measurement optical path A) followed by the measurement light (measurement light A). The transmission sections 41b-44b and branch section 30b are used to form the reference optical path (reference optical path B) followed by the reference light (reference light B) heading toward the mirror 12b and the measurement optical path (measurement optical path B) followed by the measurement light (measurement light B). 【0094】 The measurement light A output from the transmission unit 43a passes through the polarizing beam splitter 54 and heads toward the object to be measured, and returns from the object to the transmission unit 43a via the polarizing beam splitter 54. At the branching unit 30a, the returned measurement light A and the reference light A are combined to generate interference light A. The interference light A passes through the transmission unit 44a, the polarizing beam splitter 56, and the diffraction grating 47 and heads toward the light receiving unit 15. Similarly, the measurement light A output from the transmission unit 43b passes through the mirror 55 and the polarizing beam splitter 54 and heads toward the object to be measured, and returns from the object to the transmission unit 43b via the polarizing beam splitter 54 and the mirror 55. At the branching unit 30b, the returned measurement light B and the reference light B are combined to generate interference light B. The interference light B passes through the transmission unit 44b, the polarizing beam splitter 56, and the diffraction grating 47 and heads toward the light receiving unit 15. The processing of the FD-OCT device 1 in this embodiment is the same as in the first embodiment. 【0095】 As described above, with the configuration of this embodiment, the FD-OCT device 1 can measure multiple positions simultaneously more easily than conventional methods, even when different reference optical paths and different measurement optical paths exist for each interference light used for measurement. 【0096】 (4) Fourth embodiment: In the first embodiment, there were two measurement locations. This embodiment describes the case where there are three or more measurement locations. Figure 16 shows the configuration of the FD-OCT device 1 of this embodiment. Components with the same reference numerals as in Figure 2 are the same as in Figure 2. The differences between the configuration of the FD-OCT device 1 of this embodiment and the first embodiment will be explained. The FD-OCT device 1 of this embodiment is equipped with X pairs of half-mirrors and mirrors for forming X (an integer of 3 or more) reference optical paths. In this embodiment, the half-mirror and mirror for forming the nth set of reference optical paths (hereinafter referred to as reference optical path (n)) are expressed as half-mirror 45(n) and mirror 12(n). Furthermore, for n of 2 or more, wavelength-dispersing members 46(n) with different wavelength-dispersing characteristics are arranged between the half-mirror 45(n) and mirror 12(n). 【0097】 The reference light (n) output from the transmission unit 42 passes through the half mirrors (1) to (n) and the wavelength-dispersing member 46(n), reaches the mirror 12(n), is reflected, passes through the wavelength-dispersing member 46(n), the half mirrors (n) to (1), and the transmission unit 42, and reaches the branching unit 30. 【0098】 At the branching section 30, interference light is generated between each of the reference lights (1) to (X) and the measurement light. Hereinafter, the interference light between the reference light (n) and the measurement light will be referred to as interference light (n). The light containing interference light (1) to (X) is directed toward the light receiving section 15 and received. In this embodiment, due to the influence of the wavelength dispersion members 46(2) to (X), the difference in wavelength dispersion characteristics between the reference light path and the measurement light path followed by the interfering reference light and measurement light is different for each of the interference light (1) to (X). That is, the difference in wavelength dispersion characteristics between the reference light and the measurement light path followed by the reference light and measurement light path included in interference light (n) is different from the difference in wavelength dispersion characteristics between the reference light and the measurement light path followed by the reference light and measurement light path included in interference light (m) (m≠n). 【0099】 The processing of the FD-OCT device 1 in this embodiment will be described. The acquisition unit 101 interpolates the signal current output from the light receiving unit 15 with respect to wavenumber k to obtain a measurement current signal. Then, the acquisition unit 101 obtains a measurement signal by performing a discrete Fourier transform on the acquired measurement current signal. The acquisition unit 101 approximates the obtained φ with the polynomial Σj=0(aj(k-k0)j). The acquisition unit 101 obtains an approximate value of φdispersion, which represents the magnitude of the difference in wavelength dispersion between the reference optical path A and the measurement optical path A due to the wavelength dispersion member 46 (influence of the wavelength dispersion member 46), by deleting the first and second terms from the approximated polynomial. However, the acquisition unit 101 may also obtain an approximate value of φdispersion by summing the third to the mth (a natural number greater than or equal to 3) terms of the approximated polynomial. 【0100】 The acquisition unit 101 determines the magnitude of wavelength dispersion φ due to the influence of each of the wavelength dispersion members 46(2) to 46(X) in each of the interference light (2) to (X). dispersion_2 ~φ dispersion_XThe acquisition unit 101 obtains φ in the same manner as in the first embodiment. dispersion_n The following is done to determine n (for each of n from 1 to X). Specifically, the acquisition unit 101 acquires a signal obtained by performing a discrete Fourier transform on the measured current signal, which is an interpolated signal of the signal current output from the light receiving unit 15 when the interference light (n) is received in a state where no reference light other than the reference light (n) exists (for example, a state where all half mirrors except half mirror 45(n) are excluded from half mirrors 45(1) to 45(X)). The acquisition unit 101 replaces all values ​​of the signals in the negative frequency band of the discrete Fourier transform signal with 0. The acquisition unit 101 obtains a complex number signal in K space by performing an inverse Fourier transform on the substituted signal. For each value of k, the acquisition unit 101 finds the phase φ of this measured current signal by finding the arctangent of the value obtained by dividing the imaginary component by the real component. The acquisition unit 101 then uses the obtained φ as a polynomial Σ j=0 (a j (k-k0) j The approximation is performed using φ. The acquisition unit 101 removes the first and second terms from the approximated polynomial to obtain a value φ that indicates the magnitude of the difference in wavelength dispersion (influence of the wavelength dispersion member 46(n)) between the reference optical path and the measurement optical path A caused by the wavelength dispersion member 52. dispersion_n An approximate value of is obtained. However, the acquisition unit 101 sums the 3rd term to the mth (a natural number greater than or equal to 3) term of the approximated polynomial, and calculates φ dispersion_n An approximate value of φ may be obtained. In addition, the acquisition unit 101 determines the magnitude of wavelength dispersion φ in the interference light (1). dispersion_1 The acquisition unit 101 acquires the wavelength dispersion magnitude φ in the interference light (1). In this embodiment, since no wavelength dispersion member is placed in the reference optical path (1), the acquisition unit 101 acquires the wavelength dispersion magnitude φ in the interference light (1). dispersion_1 Let this value be 0. 【0101】 Also, φ dispersion_n This may be determined by other methods. For example, the acquisition unit 101 acquires a measured current signal by interpolating the signal current output from the light receiving unit 15, which receives light including interference light (n), in the absence of any reference light other than the reference light (n). In addition, the acquisition unit 101 also determines φ dispersion_n Set this to the default initial value, and apply exp(-iφ) to this measurement current signal. dispersion_nThe wavelength dispersion is corrected by applying φ, and the corrected measured current signal is obtained by performing a discrete Fourier transform. Next, the acquisition unit 101 performs φ dispersion_n The value of is varied, and the same process is performed to obtain the signal after the discrete Fourier transform (signal in Z space). The acquisition unit 101 repeats this process, φ dispersion_n For each value of φ, the signal in Z space is obtained. dispersion_n Among the signals corrected while varying the value of , the signal with the most corrected chromatic dispersion will have the strongest signal intensity. Therefore, the acquisition unit 101 identifies the signal in which the highest peak (strongest signal intensity) exists, and the φ corresponding to the identified signal dispersion_n The value of φ dispersion_n This can also be used as the determined value. Furthermore, the acquisition unit 101 measures the magnitude of wavelength dispersion φ in the interference light (1). dispersion_1 This is obtained as 0. In this embodiment, since no wavelength-dispersing member is placed in the reference optical path (1), the magnitude of wavelength dispersion in the interference light (1) φ dispersion_1 Let this value be 0. 【0102】 The acquisition unit 101 is φ dispersion_1 ~φ dispersion_X of φ dispersion_n For each, the measured current signal is given exp(-i φ dispersion_n By applying a correction factor to correct the wavelength dispersion and performing a discrete Fourier transform, a corrected signal (n) with corrected wavelength dispersion in the interfering light (n) is obtained. Furthermore, in the following, the acquisition unit 101 treats the measurement signal as the corrected signal (1). In this embodiment, the zero point of the reference optical path (1) in the measurement optical path is adjusted to be in front of the object to be measured. Therefore, signals in the negative frequency band of the corrected signal (1) are ignored. 【0103】 The extraction unit 102 extracts the signal with the highest signal intensity from the correction signals (1) to (n) as the peak signal, which is the signal with the largest peak. Figure 17 shows an example of the measurement signal and the correction signals. In the example in Figure 17, signal pn is the signal with the highest signal intensity. 【0104】 If the extracted peak signal is included in the correction signal (n), the extraction unit 102 stores it in RAM as a signal relating to the interference light (n) (or the interference light between the reference light (n) and the reference light (1)). The extraction unit 102, if the peak signal is included in the correction signal (n), calculates the mirror signal (mirror peak signal) of the peak signal in the correction signal (n) based on the peak signal. More specifically, the extraction unit 102 calculates the peak signal (str × F[exp(i fr·k+i θ)]) as (F[exp(2i φ dispersion_n The convolution is performed using ) / N). Then, the extraction unit 102 obtains the value of the dependent variable k in the convolution result with the sign reversed. The extraction unit 102 acquires the signal of the complex conjugate of the obtained value as a mirror peak signal. 【0105】 Furthermore, if the peak signal is included in the correction signal (n), the extraction unit 102 determines the signal corresponding to the peak signal in other correction signals based on the peak signal. More specifically, the extraction unit 102 determines the signal corresponding to the peak signal in the correction signal (m) (m≠n) and the mirror signal of this signal as follows. In the following, the signal corresponding to the peak signal in the correction signal (m) will be referred to as the corresponding signal (m). That is, the extraction unit 102 determines the peak signal as (F[exp(iφ dispersion_n -iφ dispersion_m The corresponding signal (m) is obtained by convolution with (F[exp(iφ) / N). The extraction unit 102 also extracts the peak signal, (F[exp(iφ) dispersion_n i's φ dispersion_m Convolution is performed using ) / N). Then, the extraction unit 102 inverts the sign of the dependent variable k in the convolution result and takes the complex conjugate to obtain the mirror signal of the corresponding signal (m). However, when m=1, the extraction unit 102 does not need to obtain the corresponding signal (m) and the mirror signal of the corresponding signal (m) that exist in the negative frequency band. In Figure 17, the corresponding signal (m) and the mirror signal of the corresponding signal (m) of the peak signal pn present in the corrected signal (n) are shown by dashed lines. 【0106】 The extraction unit 102 removes the peak signal and the mirror peak signal from the correction signal (n). The extraction unit 102 also removes the corresponding signal (m) and the mirror signal of the corresponding signal (m) from each of the other correction signals (m). However, when m=1, the extraction unit 102 removes the corresponding signal (m) and the mirror signal of the corresponding signal (m) that exist in the positive frequency band. 【0107】 The extraction unit 102 repeats the above process (extracting and storing peak signals from the correction signals (1) to (X), and deleting signals corresponding to the peak signals from the correction signals (1) to (X)) until there are no signals with a signal intensity above a predetermined threshold from the correction signals (1) to (X). 【0108】 The extraction unit 102 combines, for each correction signal, the correction signal (n) from which the signal corresponding to the extracted peak signal has been removed, with the peak signal related to the interference light (n) (or the interference light between reference light (1) and reference light (n)) stored in RAM. This allows the extraction unit 102 to extract the signal measured using the interference light (n). In this way, the extraction unit 102 extracts signals related to each of the interference lights from the measurement signal. 【0109】 In this embodiment, the extraction unit 102 generates an image of the object to be measured from the signal extracted for each interference light using a known method. 【0110】 In this embodiment, the derivation unit 103 determines the difference between the reference optical path (1) and the reference optical path (n) (the distance between the zero point of the reference optical path (1) and the zero point of the reference optical path (n) in the measurement optical path) based on the signal measured using the interference light (n) extracted by the extraction unit 102, in the same manner as in the first embodiment. 【0111】 In this embodiment, the display control unit 104 displays the image generated by the extraction unit 102 on the display unit 16 in a positional relationship corresponding to the positional relationship of the subjects, similar to the first embodiment. 【0112】 As described above, with the configuration of this embodiment, the FD-OCT device 1 has different φ for each interference light.dispersion_n By using dispersion_n , signals related to each of the interference lights can be extracted, and three or more different positions can be measured together. 【0113】 In this embodiment, for three or more reference optical paths, by making the wavelength dispersion characteristics different, for each of the interference lights (1) to (X), the difference in the wavelength dispersion characteristics between the corresponding reference optical path and the measurement optical path is made different. However, it is also possible to configure three or more measurement optical paths and make the wavelength dispersion characteristics different for each of the measurement optical paths, so that for each of the interference lights (1) to (X), the difference in the wavelength dispersion characteristics between the corresponding reference optical path and the measurement optical path is made different. 【0114】 (5) Other embodiments: The above embodiments are examples for implementing the present invention, and various other embodiments can also be adopted. Therefore, at least some of the configurations of the above embodiments may be omitted, replaced, or configured differently. Also, configurations in which the above embodiments are appropriately combined may be used. Further, at least some of the functions of the acquisition unit 101, the extraction unit 102, the derivation unit 103, and the display control unit 104 may be implemented in a signal processing device different from the FD-OCT device 1 (for example, a computer incorporated in the FD-OCT device 1, a computer connected to the FD-OCT device 1, etc.). 【0115】 In each of the above embodiments, for the optical path in which the wavelength dispersion characteristics are not made different between the measurement optical path and the reference optical path, a wavelength dispersion member is not provided and wavelength dispersion is not caused. However, for the optical path in which the wavelength dispersion characteristics are not made different between the measurement optical path and the reference optical path, wavelength dispersion (hereinafter, the magnitude of this wavelength dispersion is φ d is used) may be caused. In this case, the FD-OCT device 1 does not have to ignore either the positive frequency band or the negative frequency band of the measurement signal. The extraction unit 102 corrects the wavelength dispersion of φ d for the signal related to the extracted interference light B (in the fourth embodiment, interference light (1)), and excludes the mirror signal in the same manner as DEFR based on the signals before and after correction, so that the interference light B (interference light (1)) can also be measured in full range. 【0116】 Furthermore, in the above-described embodiment 2, a lens is provided that focuses near the position of the object to be measured, corresponding to each measurement optical path. However, in any embodiment, a lens that focuses near the position of the object to be measured may be provided in at least a portion of the measurement optical path. 【0117】 Furthermore, in each of the embodiments described above, one of the optical paths, the measurement optical path and the reference optical path, which has different wavelength dispersion characteristics, is not provided with a wavelength dispersion member to prevent wavelength dispersion. However, wavelength dispersion can be prevented by providing a wavelength dispersion member in this optical path as well (hereinafter, the magnitude of this wavelength dispersion is φ). dis This may cause (to be the case). In this case, the FD-OCT device 1 does not need to ignore either the positive frequency band or the negative frequency band of the measurement signal. With respect to the signal related to the interference light B (in the fourth embodiment, interference light (1)) extracted by the extraction unit 102, φ dis By correcting the wavelength dispersion and removing the mirror signal in the same way as DEFR based on the signals before and after correction, full-range measurements can be performed for interference light B (interference light (1)). 【0118】 Furthermore, in each of the embodiments described above, a wavelength-dispersing member is provided in either the reference optical path or the measurement optical path to make the difference in wavelength dispersion characteristics between the corresponding reference optical path and the measurement optical path different for each of the multiple interference rays involved in the measurement. However, other embodiments may be adopted as long as it is possible to make the difference in wavelength dispersion characteristics between the corresponding reference optical path and the measurement optical path different for each of the multiple interference rays involved in the measurement. For example, wavelength-dispersing members may be provided in both the reference optical path and the measurement optical path. 【0119】 Furthermore, in the above embodiment, the FD-OCT device 1 was assumed to perform measurements using the SD-OCT method. However, the FD-OCT device 1 may be a device that performs measurements using other FD-OCT methods, such as the SS (Swept source)-OCT method. 【0120】 Furthermore, in the above-described embodiment, the measurement targets were the cornea and retina of the eye being examined. However, the measurement targets may also be other locations of the eye being examined (a part of the cornea other than the corneal apex, the iris, conjunctiva, etc.). Furthermore, in the above-described embodiment, the FD-OCT device 1 is configured as a Michelson interferometer to generate interference light. However, the FD-OCT device 1 may be configured as other interferometers such as a balanced Michelson interferometer or a Mach-Zehnder interferometer. 【0121】 Furthermore, the present invention is also applicable as a program or method. For example, it is possible to provide a method or program implemented with the above-described apparatus. Moreover, it can be modified as appropriate, such as having part be software and part be hardware. Furthermore, the invention also works as a recording medium for programs. Of course, the recording medium for the software may be a magnetic recording medium, a semiconductor memory, or any recording medium developed in the future. [Explanation of symbols] 【0122】 1…FD-OCT device, 10…Control unit, 11…Adjustment mechanism, 12…Mirror, 13…Alignment mechanism, 14…Light source, 15…Light receiving unit, 16…Display unit, 100…Signal processing program, 101…Acquisition unit, 102…Extraction unit, 103…Derivation unit, 104…Display control unit, 30…Branching unit, 41…Transmission unit, 42…Transmission unit, 43…Transmission unit, 44…Transmission unit, 45…Half mirror, 46…Wavelength dispersive member, 47…Diffraction grating, 48…Polarizing beam splitter, 49…Mirror, 50…Mirror, 51…Polarizing beam splitter, 52…Wavelength dispersive member, 53…Lens, 54…Polarizing beam splitter, 55…Mirror, 56…Polarizing beam splitter

Claims

[Claim 1] An acquisition unit that acquires an output signal output from a single light receiving unit that receives multiple interference lights, each having a different difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path, which are emitted from a single light source and travel toward the object to be measured, and multiple interference lights, each having a different difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path, respectively. An extraction unit extracts an extracted signal, which is a signal for each of the interference rays, based on the output signal acquired by the acquisition unit and the corrected signal obtained by applying wavelength dispersion correction processing to the output signal. A signal processing device equipped with the following features. [Claim 2] The signal processing apparatus according to claim 1, wherein the plurality of interference lights are lights resulting from the interference of a plurality of lights following the plurality of optical paths which are the reference optical path and a light following the measurement optical path. [Claim 3] The signal processing apparatus according to claim 1, wherein the plurality of interference lights are lights resulting from the interference of a plurality of lights following the plurality of optical paths which are the measurement optical paths and a light following the reference optical path. [Claim 4] The signal processing apparatus according to claim 1, wherein the plurality of interference lights are light obtained by the interference of light following different measurement optical paths and light following different reference optical paths. [Claim 5] The acquisition unit acquires the output signal output from a single light receiving unit that receives a plurality of interference lights and interference reference light in which light following a first optical path among the reference optical paths and light following a second optical path different from the first optical path among the reference optical paths interfere. The extraction unit further extracts the signal of the interference reference light based on the output signal and the correction signal. The signal processing apparatus according to claim 2, further comprising a derivation unit for deriving the difference between the first optical path and the second optical path based on the signal of the interference reference light. [Claim 6] The signal processing apparatus according to any one of claims 1, 3, or 4, wherein each of the multiple light beams traveling along each of the multiple optical paths that constitute the measurement optical path is focused at a different position. [Claim 7] The signal processing apparatus according to any one of claims 1, 3, or 4, wherein each of the multiple light beams following each of the multiple optical paths that constitute the measurement optical path is directed toward the object to be measured via a different optical axis. [Claim 8] The signal processing apparatus according to any one of claims 1 to 5, wherein the extraction unit extracts the maximum peak signal from the output signal and the correction signal, repeatedly processes the removal of a signal corresponding to the peak signal extracted from the output signal and the correction signal, and extracts, as the extracted signal for each interference light, a signal obtained by combining one or more of the peak signals extracted from the output signal and a signal obtained by combining one or more of the peak signals extracted from the correction signal. [Claim 9] The signal processing apparatus according to any one of claims 1 to 5, further comprising a display control unit that causes a plurality of images generated for each interference light based on the extracted signal extracted for each interference light by the extraction unit to be displayed on a display unit. [Claim 10] The signal processing apparatus according to claim 9, wherein the display control unit causes each of the plurality of images to be displayed on the display unit in a positional relationship corresponding to the positional relationship of the subjects of each of the plurality of images. [Claim 11] The signal processing apparatus according to claim 10, wherein the display control unit, when there is overlap in a plurality of images, displays the overlapping images overlaid on the overlapping portion. [Claim 12] The system further includes a display control unit that causes a display unit to display multiple images generated for each interference light based on the extracted signal extracted for each interference light by the extraction unit, The signal processing apparatus according to claim 5, wherein the display control unit displays the image corresponding to the interference light including light following the first optical path and the image corresponding to the interference light including light following the second optical path, such that they are separated by a distance corresponding to the difference, and if there is overlap among the multiple images, the overlapping images are superimposed and displayed in the overlapping portion. [Claim 13] Light source and Light receiving section, An optical system comprising: a measurement optical path, which is an optical path from the light source toward the object to be measured and from the object to be measured toward the light receiving unit; and a reference optical path, which is an optical path different from the measurement optical path, wherein the light output from the light source toward the light receiving unit; Control unit and Equipped with The control unit acquires an output signal output from a single light receiving unit that receives a plurality of interference lights, which are formed when light output from a single light source and following the measurement optical path and light output from the light source and following the reference optical path interfere with each other, wherein the difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path taken by the interfering lights is different for each of the plurality of interference lights, and extracts a signal for each of the interference lights based on the output signal and a correction signal obtained by applying wavelength dispersion correction processing to the output signal. [Claim 14] A signal processing method performed by a signal processing device, An acquisition step of acquiring an output signal output from a single light receiving unit that receives multiple interference lights, which are multiple interference lights resulting from the interference of light emitted from a single light source and traveling along a measurement optical path toward the object to be measured, and light emitted from the same light source and traveling along a reference optical path different from the measurement optical path, wherein the difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path taken by the interfering lights is different for each of the multiple interference lights, An extraction step in which an extracted signal, which is a signal for each of the interference rays, is extracted based on the output signal acquired in the acquisition step and the corrected signal obtained by applying wavelength dispersion correction processing to the output signal. A signal processing method that includes this. [Claim 15] On the computer, An acquisition step of acquiring an output signal output from a single light receiving unit that receives multiple interference lights, which are formed when light emitted from a single light source and traveling along a measurement optical path toward the object to be measured, and light emitted from the light source and traveling along a reference optical path different from the measurement optical path, wherein the difference in wavelength dispersion characteristics between the measurement optical path and the reference optical path taken by the interfering light is different for each of the multiple interference lights. An extraction step in which an extracted signal, which is a signal for each of the interference spectroscopy, is extracted based on the output signal acquired in the acquisition step and the corrected signal obtained by applying wavelength dispersion correction processing to the output signal. A program to execute.

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