Optical interference tomographic imaging apparatus, control method of optical interference tomographic imaging apparatus and program

Abstract

To reduce a ghost that occurs in a tomographic image.SOLUTION: An optical interference tomographic imaging apparatus according to the present disclosure comprises: a light source unit that emits light in which an optical frequency is swept; a k-clock generation unit that generates a first k-clock signal using light emitted by the light source unit; a frequency duplication unit that generates a first signal and second signal which have a mutually inverted phase using the first k-clock signal, and generates a second k-clock signal having higher frequency than the first k-clock signal using the first signal and the second signal; and a voltage control unit that corrects non-periodicity of the second k-clock signal by changing at least one voltage of a first offset signal applied to the first signal or a second offset signal applied to the second signal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an optical coherence tomography device, a control method for an optical coherence tomography device, and a program.

Background Art

[0002] Currently, an imaging device using optical coherence tomography (OCT) (hereinafter referred to as an OCT device) has been developed. The OCT device irradiates light onto an object and causes reflected light returning from different depths of the object to interfere with reference light according to the wavelength of the irradiated light. The OCT device can obtain information regarding a tomogram of the object, specifically a tomogram, by analyzing frequency components included in the temporal waveform of the intensity of the interference light (hereinafter referred to as an interference spectrum). The OCT device is used, for example, as an ophthalmic imaging device for fundus examinations and the like.

[0003] In an examination using an OCT device, in order to obtain an accurate image, the behavior of the subject is restricted during the examination. Therefore, if the measurement speed of the OCT device is slow, the period during which the behavior of the subject is restricted becomes long, increasing the physical burden on the subject. For this reason, in an OCT device, it is desired to improve the measurement speed and reduce the physical burden on the subject during the examination.

[0004] Therefore, as an OCT device with an improved measurement speed, an OCT device using a wavelength-sweeping light source (Swept Source OCT device, hereinafter referred to as an SS-OCT device) has been actively developed.

[0005] In an SS-OCT device, in order to further improve the measurement speed, it is preferable to acquire tomographic information over a wider range in a single shot. Therefore, techniques for widening the imaging range in the depth direction of a biological tissue that is a subject of an examination using an SS-OCT device have been studied. Note that the depth direction of the biological tissue that is the subject is generally referred to as the A-scan direction.

[0006] Here, in an SS-OCT device, it is known that by increasing the number of times the interference light (interference signal) between the reflected light from the subject and the reference light is sampled, that is, the sampling number of the interference light, the imaging range in the A-scan direction can be made wider. For this reason, in order to increase the sampling number of the interference light, the frequency of a clock signal (hereinafter referred to as the k clock signal) indicating the sampling timing is increased.

[0007] Generally, in order to generate a high-frequency k clock signal using light from a light source, it is necessary to use a light source with a long coherence length. However, since a light source with a long coherence length is expensive, the cost of the SS-OCT device increases when such a light source is used. Therefore, a method of increasing the k clock frequency without using a light source with a long coherence length has been proposed.

[0008] Here, Patent Document 1 discloses a method of increasing the frequency of the k clock signal by inputting signals (differential signals) whose phases are inverted with respect to each other, which are generated from the k clock signal, into an analog multiplier.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Here, it is ideal that the duty ratio of the k clock signal generated using the light from the light source is 50:50. However, in reality, the duty ratio of the k clock signal may not be 50:50. When the frequency is increased using a k clock signal with a duty ratio other than 50:50, for example, the k clock signal with the increased frequency may have non-periodicity. Specifically, non-periodicity means a state where the period for each cycle is shifted (the period for each cycle is not constant). When sampling the interference signal using a k clock signal with non-periodicity, for example, ghosts may occur in the captured tomographic image.

[0011] Therefore, an object of the present disclosure is to reduce ghosts occurring in the tomographic image.

Means for Solving the Problem

[0012] The optical coherence tomography apparatus of the present disclosure includes a light source unit that emits light with a swept optical frequency, a k clock generation unit that generates a first k clock signal using the light emitted by the light source unit, a frequency multiplication unit that generates a first signal and a second signal whose phases are inverted from each other using the first k clock signal, and generates a second k clock signal with a higher frequency than the first k clock signal using the first signal and the second signal, and a voltage control unit that corrects the non-periodicity of the second k clock signal by changing at least one voltage of a first offset signal applied to the first signal or a second offset signal applied to the second signal.

Effect of the Invention

[0013] According to the present disclosure, ghosts occurring in the tomographic image can be reduced.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments for carrying out the present disclosure will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions of the components, etc. described in the following embodiments are arbitrary and can be changed according to the configuration of the apparatus to which the present disclosure is applied or various conditions. Also, in the drawings, the same reference numerals are used between the drawings to indicate elements that are the same or functionally similar.

[0016] Note that the optical coherence tomography (OCT) device in the present disclosure is an SS-OCT device using a wavelength-swept light source, but will be simply referred to as an OCT device hereinafter for simplicity. Further, hereinafter, the OCT device in the present disclosure will be described as an OCT device used for examining the fundus of an eye of a subject. However, the OCT device in the present disclosure can be used for applications other than fundus examination, and may be used, for example, for examining any object such as the anterior segment of the eye to be examined or an organ. At this time, the present disclosure can be applied to medical devices such as endoscopes in addition to ophthalmic devices.

[0017] (Embodiment 1) Hereinafter, with reference to FIGS. 1 to 8, the OCT device according to Embodiment 1 of the present disclosure will be described. FIG. 1 schematically shows a configuration example of the OCT device according to the present embodiment.

[0018] As shown in FIG. 1, the OCT device 1 is provided with a light source unit 10 that emits light, an interference unit 20 that generates interference light, a detection unit 30 that detects the interference light, an information acquisition unit 40 that acquires information on the fundus of the eye as the subject 100, and a display unit 70 that displays the acquired information. Further, the OCT device 1 is provided with a measurement arm 50 that irradiates the subject 100 with measurement light and emits the reflected light from the subject 100 to the interference unit 20, and a reference arm 60 that emits reference light that interferes with the reflected light emitted from the measurement arm 50. In addition, the OCT device 1 is provided with a k-clock generation unit 80 that generates a k-clock signal, and an optical fiber coupler (splitting unit) 90 that splits the light from the light source unit 10 into the light incident on the k-clock generation unit 80 and the light incident on the interference unit 20.

[0019] The light source unit 10 includes a wavelength-sweeping light source 11 that sweeps the wavelength of the emitted light and sweeps the optical frequency. As the wavelength-sweeping light source 11, any light source can be used as long as it can sweep the wavelength of the emitted light and sweep the optical frequency. Therefore, the wavelength-sweeping light source 11 may be, for example, a light source using a fiber ring resonator and a wavelength selection filter, or other commercially available wavelength-sweeping lasers or the like. The light source unit 10 is connected to an optical fiber coupler 90 via an optical fiber. Note that the wavelength-sweeping light source 11 is an example of a light source unit that emits light with a swept optical frequency.

[0020] The optical fiber coupler 90 is connected to the light source unit 10, the interference unit 20, and the k-clock generation unit 80 via optical fibers. The optical fiber coupler 90 divides the light from the light source unit 10 into light incident on the k-clock generation unit 80 and light incident on the interference unit 20. Note that a beam splitter or the like may be used instead of the optical fiber coupler 90. Also, the light splitting ratio may be arbitrarily set according to the desired configuration.

[0021] The k-clock generation unit 80 generates a k-clock signal based on the light emitted from the light source unit 10 that has passed through the optical fiber coupler 90. Also, the k-clock generation unit 80 sends the generated k-clock signal to the detection unit 30. The detection unit 30 detects the interference light between the measurement light and the reference light described later, and generates a digital signal of the OCT interference signal based on the interference light in synchronization with the k-clock signal received from the k-clock generation unit 80.

[0022] The interference unit 20 is provided with optical fiber couplers 21 and 22. The optical fiber coupler 21 is connected to the optical fiber couplers 90 and 22, the measurement arm 50, and the reference arm 60 via optical fibers. The optical fiber coupler 21 divides the light emitted from the light source unit 10 that has passed through the optical fiber coupler 90 into measurement light that is irradiated onto the fundus via the measurement arm 50 and reference light that passes through the reference arm 60. Note that the light splitting ratio may be arbitrarily set according to the desired configuration.

[0023] The measurement light is irradiated onto the subject 100 via the measurement arm 50, and enters the optical fiber coupler 22 as reflected light reflected by the subject 100 via the measurement arm 50 and the optical fiber coupler 21. On the other hand, the reference light enters the optical fiber coupler 22 via the reference arm 60. The reflected light of the measurement light and the reference light interfere with each other at the optical fiber coupler 22, and are emitted from the optical fiber coupler 22 as interference light.

[0024] The optical fiber coupler 22 is connected to the detection unit 30 via two optical fibers. Note that the interference unit 20 may be configured using a beam splitter or the like instead of the optical fiber coupler.

[0025] The measurement arm 50 is provided with a polarization controller 51, a collimator 52, a focus lens (not shown), an X-axis scanner 53, a Y-axis scanner 54, and an objective lens 55. The polarization controller 51 is provided on the optical fiber connected from the optical fiber coupler 21 to the measurement arm 50, and adjusts the polarization states of the measurement light passing through the measurement arm 50 and the reflected light of the measurement light. The collimator 52 is connected to the optical fiber coupler 21 via an optical fiber, and irradiates the measurement light whose polarization state has been adjusted by the polarization controller 51 as spatial light. The measurement light irradiated as spatial light is irradiated onto the fundus of the subject 100 via the focus lens, the X-axis scanner 53, the Y-axis scanner 54, and the objective lens 55.

[0026] The X-axis scanner 53 and the Y-axis scanner 54 are each composed of deflection mirrors arranged such that their rotation axes are orthogonal to each other. The X-axis scanner 53 and the Y-axis scanner 54 constitute a scanning unit having a function of scanning the fundus with the measurement light, and can change the irradiation position of the measurement light on the fundus. Here, the X-axis scanner 53 performs scanning in the X-axis direction, and the Y-axis scanner 54 performs scanning in the Y-axis direction. Note that each of the X-axis direction and the Y-axis direction is a direction orthogonal to the eye axis direction of the eye which is the subject 100, and is also a direction orthogonal to each other.

[0027] The measurement light irradiated onto the fundus is reflected as backward scattered light (reflected light) on the fundus. The reflected light from the fundus exits the measurement arm 50 via the objective lens 55, Y-axis scanner 54, X-axis scanner 53, focus lens, collimator 52, and polarization controller 51 again. Then, it propagates through the optical fiber and enters the optical fiber coupler 22 via the optical fiber coupler 21.

[0028] On the other hand, the reference arm 60 is provided with a polarization controller 61, a collimator 62, a dispersion compensation glass 63, an optical path length adjustment optical system 64, a dispersion adjustment prism pair 65, and a collimator 66. The polarization controller 61 is provided on the optical fiber connected from the optical fiber coupler 21 to the reference arm 60, and adjusts the polarization state of the reference light passing through the reference arm 60. The collimator 62 is connected to the optical fiber coupler 21 via the optical fiber, and emits the reference light whose polarization state has been adjusted by the polarization controller 61 as spatial light. The reference light emitted as spatial light enters the collimator 66 via the dispersion compensation glass 63, the optical path length adjustment optical system 64, and the dispersion adjustment prism pair 65.

[0029] The dispersion compensation glass 63 and the dispersion adjustment prism pair 65 can adjust the dispersion of the reference light. Therefore, by using the dispersion compensation glass 63 and the dispersion adjustment prism pair 65, the dispersion of the reference light can be adjusted to correspond to the dispersion of the reflected light of the measurement light passing through the measurement arm 50.

[0030] Also, as shown by the arrow A1 in FIG. 1, the optical path length adjustment optical system 64 can move in a direction approaching or moving away from the collimators 62 and 66, and can adjust the optical path length of the reference arm 60. Therefore, the optical path length of the reference arm 60 can be adjusted according to the optical path length to the fundus (subject 100) through which the measurement light passes by the optical path length adjustment optical system 64. The reference light incident on the collimator 66 propagates through the optical fiber connecting the collimator 66 and the optical fiber coupler 22, and enters the optical fiber coupler 22.

[0031] As described above, the measurement light and the reference light incident on the optical fiber coupler 22 interfere with each other, and the interference light is split and emitted from the optical fiber coupler 22 into two optical fibers as light with opposite phases, and the non-interference light is light with the same phase, and enters the detection unit 30.

[0032] The detection unit 30 is provided with a detector 31 and an A / D converter 32 (conversion unit). The detector 31 is a balance detector, and by reducing the in-phase light of the non-interference component and detecting only the light with the opposite phase that is the interference component, a better signal-to-noise ratio (S / N ratio) can be realized.

[0033] The detector 31 sends an interference signal (OCT interference signal) based on the detected interference light to the A / D converter 32, and the A / D converter 32 converts the received OCT interference signal into a digital signal. Note that a k clock generation unit 80 is connected to the A / D converter 32, and the A / D converter 32 samples the interference signal in synchronization with the k clock signal sent from the k clock generation unit 80 and converts it into a digital signal. The A / D converter 32 sends the interference signal converted into a digital signal to the information acquisition unit 40. Therefore, the detection unit 30 can detect the interference light based on the measurement light and the reference light, generate an OCT interference signal digitized in synchronization with the k clock signal, and send the OCT interference signal to the information acquisition unit 40.

[0034] The information acquisition unit 40 performs frequency analysis such as Fourier transform on the digital signal of the OCT interference signal received from the detection unit 30 to obtain information on the fundus of the eye. Note that the information acquisition unit 40 can detect the differential of the OCT interference signal by taking the difference between OCT interference signals based on interference light with different phases detected by the detector 31, and reduce the noise based on the non-interference component of the OCT interference signal. Therefore, the information acquisition unit 40 can improve the signal-to-noise ratio (S / N ratio) of the information on the fundus of the eye based on the OCT interference signal by performing the differential detection. The information acquisition unit 40 sends the obtained information on the fundus of the eye to the display unit 70, and the display unit 70 displays the received information as a tomographic image.

[0035] Note that the information acquisition unit 40 may be configured in the OCT apparatus 1 as an arbitrary information processing unit including a CPU, an MPU, or the like, or may be configured using a general-purpose computer. Further, the display unit 70 may be a monitor provided in the OCT apparatus 1 or the information acquisition unit 40, or may be an individual monitor connected thereto.

[0036] By the above-described series of operations, the OCT apparatus 1 can acquire information regarding a tomogram at a certain point of the subject 100. Thus, acquiring information regarding a tomogram in the depth direction of the subject 100 is called an A-scan. Further, in the OCT apparatus 1, by scanning the subject 100 with a scanning unit including the X-axis scanner 53 and the Y-axis scanner 54, information on a two-dimensional tomogram or a three-dimensional tomogram of the subject 100 can be acquired.

[0037] Here, scanning the subject 100 with measurement light in a direction for acquiring information regarding a tomogram of the subject 100 in a direction orthogonal to the A-scan, that is, information on a two-dimensional tomogram, is called a B-scan. Further, scanning the subject 100 with measurement light in a direction orthogonal to both the scanning directions of the A-scan and the B-scan is called a C-scan. In particular, when performing two-dimensional raster scanning within the fundus of the eye of the subject 100 when acquiring information on a three-dimensional tomogram, the direction in which scanning is performed at high speed is called the B-scan direction, and the direction orthogonal to the B-scan direction and in which scanning is performed at low speed is called the C-scan direction.

[0038] The OCT device 1 can obtain a two-dimensional tomographic image of the subject 100 by performing A-scan and B-scan, and can obtain a three-dimensional tomographic image of the subject 100 by performing A-scan, B-scan, and C-scan. The B-scan and C-scan are performed by a scanning unit constituted by the above-described X-axis scanner 53 and Y-axis scanner 54. Note that the line scanning directions such as the B-scan direction and the C-scan direction do not have to coincide with the X-axis direction or the Y-axis direction. Therefore, the line scanning directions of the B-scan and the C-scan can be appropriately determined according to the two-dimensional tomographic image or the three-dimensional tomographic image to be photographed.

[0039] Further, in the OCT device 1, sampling of the interference signal by the A / D converter 32 of the detection unit 30 is performed at an equal optical frequency (equal wave number) interval with respect to the light from the light source unit 10 based on the k-clock signal generated by the k-clock generation unit 80.

[0040] Here, since the light from the light source unit 10 of the OCT device 1 is wavelength-swept, the optical frequency changes according to time. On the other hand, since the k-clock generation unit 80 generates a k-clock signal based on the light from the light source unit 10, the k-clock signal can give sampling timing at an equal wave number interval with respect to the OCT interference signal based on the interference light detected by the detection unit 30.

[0041] Next, with reference to FIG. 2, the k-clock generation unit 80 will be described in more detail. FIG. 2 schematically shows a configuration example of the k-clock generation unit 80. As shown in FIG. 2, the k-clock generation unit 80 is provided with a k-clock interference unit 82 (clock interference unit), an optical sensor 83 (clock detection unit), and a frequency multiplication circuit 84.

[0042] The k-clock interference unit 82 divides the light from the light source unit 10 into light incident on two optical paths having different optical path lengths, and generates clock interference light by the light emitted from the two optical paths. The k-clock interference unit 82 is provided with optical fiber couplers 821 and 828, connectors 822, 824, 825, and 827, and optical fibers 823 and 826.

[0043] The light 811 from the light source unit 10 passing through the optical fiber coupler 90 propagates through the optical fibers connected to the optical fiber couplers 90 and 821 and is incident on the optical fiber coupler 821. The optical fiber coupler 821 divides and makes the light 811 from the light source unit 10 incident on a first optical path constituted by a connector 822, an optical fiber 823, and a connector 824 and a second optical path constituted by a connector 825, an optical fiber 826, and a connector 827.

[0044] Since the optical fiber 823 and the optical fiber 826 have different predetermined optical path lengths, the first optical path and the second optical path have different optical path lengths. The light passing through the first optical path is incident on the optical fiber coupler 828 via the connector 824 and the optical fiber, and the light passing through the second optical path is incident on the optical fiber coupler 828 via the connector 827 and the optical fiber. The light passing through the first optical path and the light passing through the second optical path interfere with each other at the optical fiber coupler 828 and enter the optical sensor 83 as interference light via the optical fiber.

[0045] The optical sensor 83 detects the incident interference light and generates an interference signal 812 (k clock signal). The optical sensor 83 sends the generated interference signal 812 to the frequency multiplication circuit 84. Note that the interference signal 812 is an example of a first k clock signal. Also, the optical sensor 83 is an example of a k clock generation unit.

[0046] Based on the received interference signal 812, the frequency multiplication circuit 84 generates a k clock signal 816 with the frequency of the interference signal 812 doubled and sends it to the A / D converter 32 of the OCT apparatus 1. Thereby, the A / D converter 32 can sample the OCT interference signal based on the measurement light and the reference light in synchronization with the k clock signal 816 with the frequency doubled. Note that the k clock signal 816 with the frequency of the interference signal 812 doubled is an example of a second k clock signal. Also, the frequency multiplication circuit 84 is an example of a frequency multiplication unit.

[0047] Next, the frequency doubling circuit 84 in the OCT apparatus 1 according to the present embodiment will be described with reference to FIGS. 3 to 6. FIG. 3 schematically shows a configuration example of the frequency doubling circuit 84 that doubles the frequency of the k clock. Note that the horizontal axis in each graph represents time, and the vertical axis represents potential.

[0048] As shown in FIG. 3, the frequency doubling circuit 84 is provided with a comparator 841 with an LVDS (Low Voltage Differential Signaling) output, a low-pass filter 842, a termination resistor 843, and an analog multiplier 844. D / A converters 846 and 847 are connected to the P signal 813 (a positive signal and an example of the first signal) and the N signal 814 (a negative signal and an example of the second signal) output from the low-pass filter 842 via resistors, and an offset signal can be applied. In the frequency doubling circuit 84, a circuit 845 of a high-pass filter and an amplifier is provided at the subsequent stage of the analog multiplier 844. Note that the offset signal applied by the D / A converter 846 is an example of the first offset signal. The offset signal applied by the D / A converter 847 is an example of the second offset signal. The D / A converters 846 and 847 are an example of a voltage control unit.

[0049] The comparator 841 with an LVDS output is provided with a positive terminal and a negative terminal as input terminals, and a P terminal and an N terminal as output terminals. The interference signal 812 is input to the positive terminal of the comparator 841, the reference voltage VREF is input to the negative terminal, and the comparator 841 outputs two signals (differential clock signals) with inverted phases from the P terminal and the N terminal, respectively. Note that the reference voltage VREF can be adjusted to a value corresponding to the amplitude center voltage of the interference signal 812. The reference voltage VREF may be grounded according to a desired configuration.

[0050] Here, the output waveform of the LVDS is approximately a rectangular wave. By passing through the low-pass filter 842, the two signals output from the comparator 841 can be shaped from a rectangular wave into a waveform close to a sine wave.

[0051] The analog multiplier 844 receives the P signal 813 (positive signal, first signal) and the N signal 814 (negative signal, second signal) whose waveforms are shaped by the low-pass filter. The analog multiplier 844 multiplies the input P signal 813 and N signal 814 and outputs the output signal 815 which is the multiplication result.

[0052] The output signal 815 of the analog multiplier 844 is input to the high-pass filter and amplifier circuit 845. The circuit 845 cuts the DC component of the output signal 815 and amplifies the output signal 815.

[0053] FIG. 4 is an example of the waveforms of each signal when the duty ratio of the interference signal 812 (k clock signal) is 50:50. FIG. 5 is an example of the waveforms of each signal when the duty ratio of the interference signal 812 (k clock signal) deviates from 50:50. Note that the outputs of the D / A converters 846 and 847 are in the off state.

[0054] Hereinafter, with reference to FIGS. 4 and 5, each signal propagating within the frequency multiplier circuit 84 will be described. FIGS. 4(A) and 5(A) show the waveforms of the interference signal 812 output from the optical sensor 83. In FIG. 4(A), the amplitude center voltage of the interference signal 812 is shown using the reference voltage VREF1 input to the comparator 841. Also, in FIG. 5(A), a voltage slightly deviated from the amplitude center of the interference signal 812 is shown using the reference voltage VREF2 input to the comparator 841.

[0055] First, the signals shown in FIG. 4 will be described.

[0056] When the interference signal 812 is input to the comparator 841, P signals and N signals, which are differential signals with inverted phases, are respectively output from the P terminal and the N terminal, which are the output terminals of the comparator 841. Fig. 4(B) shows the waveforms of the P signal and the N signal. Note that although the phases of the P signal and the N signal are inverted with respect to each other, their respective amplitude center voltages (VCM) a are the same, and their respective amplitude center voltages are the same. Also, the P signal is a signal with the same phase as the interference signal 812, and the N signal is a signal with the opposite phase to the interference signal 812. At this time, the Hi period Th and the Low period Tl of the P signal are the same time. That is, it is a signal in a state where the duty ratio is 50:50.

[0057] The P signal and the N signal are input to the low-pass filter 842, and the P signal 813 and the N signal 814, which are shaped into waveforms close to sine waves, are respectively output from the low-pass filter 842. Fig. 4(C) shows the shaped P signal 813 and N signal 814.

[0058] The shaped P signal 813 and N signal 814 are respectively input to the X terminal and the Y terminal, which are the input terminals of the analog multiplier 844. Here, the P signal 813 input to the X terminal is defined as signal X, the N signal input to the Y terminal is defined as signal Y, and the signal output from the Z terminal, which is the output terminal of the analog multiplier 844, is defined as signal Z. The analog multiplier 844 multiplies signals X and Y and outputs signal Z = X·Y as the output signal 815. Fig. 4(D) shows the output signal 815.

[0059] Here, when the amplitude center voltage is a and the amplitude of the signal is b, the output signal 815 is expressed by the formula: (b·sinθ + a)·(-b·sinθ + a) = b 2 ·cos2θ / 2 - b 2 / 2 + a 2 This formula is for the multiplication of the same signal, that is, when the same signal is squared (b·sinθ + a) 2There is no term of sinθ generated therein. Therefore, as shown in FIG. 4(D), the waveform of the output signal 815 can have its distortion reduced. For this reason, the output signal 815 becomes a signal with its frequency doubled and its waveform distortion reduced as compared with the interference signal 812 from the optical sensor 83.

[0060] The output signal 815 is input to a circuit 845 of a high-pass filter and an amplifier. From the circuit 845, a DC component is cut off and a k clock signal 816 with its amplitude amplified is output. FIG. 4(E) shows the k clock signal 816. Thus, when the duty ratios of the P signal and the N signal are 50:50 as shown in FIG. 4(B), the k clock signal 816 can be generated which has a frequency twice that of the interference signal 812 which is the original k clock signal output from the optical sensor 83 and in which the periods T1 and T2 of each cycle are the same.

[0061] Next, the signal shown in FIG. 5 will be described.

[0062] When the reference voltage input to the comparator 841 is deviated from the amplitude center voltage of the interference signal 812 like VREF2 as shown in FIG. 5(A) or when the output of the optical sensor 83 is distorted, the output signal of the comparator 841 is such that the Hi period Th and the Low period Tl of the P signal are different times as shown in FIG. 5(B). That is, it is a signal in a state where the duty of the signal is deviated from 50:50.

[0063] The P signal and the N signal are input to the low-pass filter 842, and the P signal 813 and the N signal 814 shaped into waveforms close to sine waves are output from the low-pass filter 842 respectively. FIG. 5(C) shows the shaped P signal 813 and N signal 814.

[0064] The shaped P signal 813 and N signal 814 are input to the X terminal and Y terminal which are the input terminals of the analog multiplier 844 respectively. Here, let the P signal 813 input to the X terminal be signal X, the N signal input to the Y terminal be signal Y, and the signal output from the Z terminal which is the output terminal of the analog multiplier 844 be signal Z. The analog multiplier 844 multiplies signals X and Y and outputs, as output signal 815, signal Z = X·Y. Fig. 5(D) shows the output signal 815. The output signal 815 is input to the circuit 845 of a high-pass filter and an amplifier, and a k clock signal 816 with its DC component cut and its amplitude amplified is output from the circuit 845. Fig. 5(E) shows the k clock signal 816. The doubled k clock signal 816 at this time has non-periodicity. Specifically, the periods T1 and T2 per cycle are different.

[0065] Taking a tomographic image using such a k clock with different periods per cycle will cause ghosting.

[0066] Next, a method for correcting the non-periodicity (cycle shift per cycle) of the doubled k clock will be described using the signals shown in Fig. 6.

[0067] Fig. 6(B) is a signal in a state where the duty is shifted from 50:50 as in Fig. 5.

[0068] Fig. 6(C) is a waveform in which an offset voltage larger than the electrical amplitude center voltage (VCM) a is applied from the D / A converter 846 to the P signal 813, and an offset voltage smaller than the electrical amplitude center voltage (VCM) a is applied from the D / A converter 847 to the N signal 814. Taking the P signal as X, the N signal as Y, and the offset voltage as c, then as output signal 815, signal Z = (X + c)·(Y - c) is output.

[0069] Taking the amplitude center voltage as a and the amplitude of the signal as b, when expressing the output signal 815 by an equation, (b·sinθ + a + c)·(-b·sinθ + a - c) = b 2 ·cos2θ / 2 - b 2 / 2 - 2bc·sinθ + a 2+c 2 This results in the appearance of the sinθ term, which is the cause of the distortion of the k clock signal. If the duty ratio of the k clock signal before frequency doubling deviates from 50:50, the waveform is distorted by the sinθ term, making the distortion greater than that of the waveform in FIG. 5(D). However, as shown in FIG. 6(D), the cycle deviation for each cycle of the frequency-doubled k clock signal 816 can be corrected. In other words, the periods T1 and T2 can be made closer to the same time.

[0070] The k clock signal 816 output from the frequency doubling circuit 84 is sent to the A / D converter 32. The A / D converter 32 samples the OCT interference signal based on the measurement light and the reference light in synchronization with the k clock signal 816 whose frequency has been doubled and the cycle for each cycle has been corrected.

[0071] As described above, the OCT apparatus 1 according to the present embodiment includes a light source unit 10, an interference unit 20, a detection unit 30, an A / D converter 32, a k clock generation unit 80, and a frequency doubling circuit 84. The light source unit 10 emits light whose optical frequency is swept. The interference unit 20 generates interference light by the measurement light divided from the light emitted by the light source unit 10 and irradiated to the subject 100 and the reference light divided from the light emitted by the light source unit 10. The detection unit 30 detects the interference light and generates an OCT interference signal. The A / D converter 32 converts the OCT interference signal into digital data. The k clock generation unit 80 generates a k clock signal at equal optical frequency intervals using the light emitted by the light source unit 10. The frequency doubling circuit 84 doubles the frequency of the k clock signal.

[0072] Furthermore, the frequency doubling circuit 84 applies offset voltages to the P signal (first signal) and the N signal (second signal) that are generated from the k clock signal and have inverted phases with respect to each other by the D / A converters 846 and 847, and then inputs them to the analog multiplier 844 to generate a k clock signal with doubled frequency and corrected cycle shift for each cycle. In this embodiment, the frequency doubling circuit 84 is provided inside the k clock generation unit 80 and generates the P signal and the N signal from the k clock signal. Further, the A / D converter 32 samples the OCT interference signal using the k clock signal with doubled frequency to convert the OCT interference signal into digital data.

[0073] Next, a method for correcting the period of the k clock signal after doubling by applying offset voltages to the P signal and the N signal using the D / A converters 846 and 847 will be described with reference to the flowchart of FIG. 7.

[0074] In step S1, initial settings are made. Specifically, a test object for adjustment is placed at a predetermined position in front of the objective lens 55, and the optical axes of the X-axis scanner 53 and the Y-axis scanner 54 and the position of the optical path length adjustment optical system 64 are adjusted to prepare for obtaining an OCT interference signal from the test object for adjustment.

[0075] In step S2, the A / D converter 32 samples the OCT interference signal using the k clock signal with doubled frequency, and the information acquisition unit 40 performs frequency analysis such as Fourier transform to obtain an A-scan image. A waveform as shown in FIG. 8(a) is displayed on the display unit 70. The first large peak is the signal from the test object for adjustment. The second peak is noise generated due to the cycle shift for each cycle of the doubled k clock signal and occurs at a position a predetermined distance away from the first peak.

[0076] In step S3, the noise level is determined. If the noise level (for example, the peak value) is greater than the allowable level, the process proceeds to step S4, and the information acquisition unit 40 changes the offset voltage applied to the P signal and the N signal via the D / A converters 846 and 847 and returns to step S2. When the peak value of the signal from the subject is set to 0 dB, the allowable level may be -30 dB or less. That is, the peak value of the noise may be -30 dB or less than the peak value of the signal from the subject.

[0077] The loops of steps S2, S3, and S4 are repeated. When it is determined in step S3 that the noise level (for example, the peak value) is equal to or less than the allowable level as shown in FIG. 8(b), the process proceeds to step S5, and the offset voltages set in the D / A converters 846 and 847 are stored in a non-volatile memory or the like, and the correction of the cycle of the k clock signal is completed.

[0078] The stored offset voltages are set in the D / A converters 846 and 847 at an arbitrary timing before the start of tomographic image acquisition, such as at the start of the OCT apparatus 1.

[0079] Thereby, in the OCT apparatus 1, the cycle of each cycle of the frequency-multiplied k clock signal can be corrected with a simple configuration, and the generation of ghosts due to the cycle deviation of the k clock signal can be reduced.

[0080] Also, in the present embodiment, in the frequency multiplier circuit 84, the LVDS output comparator 841 generates P signals and N signals whose phases are inverted from each other. By using the LVDS output comparator 841, P signals and N signals can be generated at low cost and stably compared with a combination of operational amplifiers. Further, the LVDS output comparator 841 can be operated with only a positive single power supply, and an increase in the size and cost of the OCT apparatus 1 can be suppressed.

[0081] Note that in this embodiment, an offset voltage is applied to both the P signal and the N signal, but the offset voltage may be applied to either the P signal or the Y signal instead.

[0082] Note that in the OCT device 1 in this embodiment, the k-clock generation unit 80 and the optical fiber coupler 90 are provided outside the light source unit 10. However, the k-clock generation unit 80 and the optical fiber coupler 90 may be provided inside the light source unit 10. Also, in this embodiment, the frequency doubling circuit 84 is provided inside the k-clock generation unit 80. However, the frequency doubling circuit 84 may be provided outside the k-clock generation unit 80.

[0083] Furthermore, regarding the configuration of the OCT device 1 other than the k-clock generation unit 80, although it has been described based on the configuration example of the OCT device 1 shown in FIG. 1, the configuration of the OCT device 1 other than the k-clock generation unit 80 is not limited to this. For example, it may be configured to simply detect the interference light without performing differential detection on the interference light. Also, the A / D converter 32 may be provided in the information acquisition unit 40 instead of the detection unit 30. Furthermore, although a fiber optic system using a coupler as the splitting means is used, a spatial optic system using a collimator and a beam splitter may also be used. Also, the configuration of the OCT device 1 is not limited to the above configuration, and a part of the configuration included in the OCT device 1 may be configured as a separate body from the OCT device 1.

[0084] (Embodiment 2) Hereinafter, with reference to FIG. 9, the OCT device in Embodiment 2 of the present disclosure will be described centering on the differences from Embodiment 1. FIG. 9 schematically shows a configuration example of the OCT device 5 according to this embodiment. Note that for the components of the OCT device 5 according to this embodiment that have the same functions and configurations as those of the OCT device 1 according to Embodiment 1, the same reference numerals are given and the description thereof is omitted.

[0085] In Embodiment 1, the k-clock generation unit 80 including the frequency multiplication circuit 42 was provided outside the light source unit 10. In contrast, in the present embodiment, a wavelength-swept light source 11 and a k-clock generation unit 580 are provided inside the light source unit 510. This is a common configuration for commercially available wavelength-swept light sources.

[0086] Also, the frequency multiplication circuit 590 according to the present embodiment is provided outside the k-clock generation unit 580. The frequency multiplication circuit 590 is arranged between the k-clock generation unit 580 and the A / D converter 32 and is connected to transmit differential signals such as LVDS. Since the other components are the same as those in Embodiment 1, detailed description thereof will be omitted.

[0087] The k-clock generation unit 580 is a k-clock generation unit that generates a k-clock signal (P signal and N signal), which is a differential signal, based on the light from the wavelength-swept light source 11. For example, the k-clock generation unit 580 can have the same configuration as the k-clock generation unit 80, and instead of the frequency multiplication circuit 84, a component for generating a differential signal such as an LVDS comparator can be provided. In this case, similar to the k-clock generation unit 80, the k-clock generation unit 580 generates an interference signal and detects the interference signal with an optical sensor. Then, the k-clock generation unit 580 uses a comparator with a differential signal standard such as an LVDS comparator or any component for generating a differential signal such as a phase shift circuit to generate a P signal and an N signal related to the k-clock signal from the output signal of the optical sensor. Note that the configuration of the k-clock generation unit 580 is an example, and the k-clock generation unit 580 may have any configuration for generating a differential signal related to the k-clock signal.

[0088] Next, the configuration of the frequency multiplication circuit 590 will be described with reference to FIG. 10. FIG. 10 schematically shows a configuration example of the frequency multiplication circuit 590. The frequency multiplication circuit 590 is provided with a low-pass filter 901, a termination resistor 902, a limiting amplifier 903, an analog multiplier 904, a limiting amplifier 905, and a buffer 906 with a differential signal standard such as LVDS.

[0089] Also, between these components, AC coupling capacitors 911, 912, 914, 916, and termination resistors 913, 915, 917 are provided. In this embodiment, the reason for connecting the integrated circuits by AC coupling is to absorb the level difference of the signal standards between the integrated circuits. Therefore, if the levels of the signal standards of the connected integrated circuits are the same, the connection by AC coupling is unnecessary. Also, in this embodiment, the termination resistors are placed between the P signal and the N signal, but it is necessary to perform appropriate termination according to the level of the signal standard of the connected integrated circuit.

[0090] Signals 931, 932 are the P signal and the N signal regarding the k clock signal output from the k clock generation unit 12, respectively. The waveforms of signals 931, 932 can be shaped into waveforms close to sine waves by the low-pass filter 901. The signals 931, 932 whose waveforms are shaped by the low-pass filter are input to the positive terminal and the negative terminal of the differential input / output limiting amplifier 903 via the AC coupling capacitor 911, respectively.

[0091] Here, the k clock signal is a signal whose frequency changes, and generally, the higher the frequency, the more it attenuates as the transmission distance becomes longer. The limiting amplifier is an amplifier with a gain limit, and it can limit the amplitude of the output signal to a certain voltage. By using the limiting amplifier for the k clock signal, the change in the amplitude of the signal due to the frequency change of the k clock signal can be absorbed.

[0092] The signal output from the limiting amplifier 903 passes through the AC coupling capacitor 912 and the termination resistor 913 and is input to the differential input / output analog multiplier 904. At this time, the P signal output from the limiting amplifier 903 is input to the XP terminal and the YN terminal of the analog multiplier 904, and further, the D / A converter 921 is connected via a resistor and an offset voltage can be applied. The N signal is input to the XN terminal and the YP terminal.

[0093] Here, let the signals input to the XP terminal, XN terminal, YP terminal, and YN terminal, which are the input terminals of the analog multiplier 904, be signals XP, XN, YP, and YN respectively, and let the signals output from the ZP terminal and ZN terminal, which are the output terminals, be signals ZP and ZN respectively. For the X-side input of the analog multiplier 904, the signals input to the P terminal (positive side) and the N terminal (negative side) on the Y side are reversed. Therefore, signals ZP and ZN such that (ZP - ZN) = (XP - XN) × (YP - YN) are output from the analog multiplier 904. Here, since YP = XN and YN = XP, (ZP - ZN) = -(XP - XN). 2 When the P signal and the N signal are expressed by equations as shown in Embodiment 1, (ZP - ZN) = -(b·sinθ + a - (-b·sinθ + a)). 2 = 2b 2 cos2θ - 2b 2 Thus, since there is no term of sinθ that occurs when the same signal is squared, the distortion of the waveform in the difference of the output signals can be reduced. Therefore, similar to Embodiment 1, the difference of the signals output from the analog multiplier 904 has reduced waveform distortion and becomes a k-clock signal with a frequency twice that of the input k-clock signal.

[0094] Next, at this time, when an offset voltage c is applied to the signal XP by the output from the D / A converter 921, (ZP - ZN) = {(XP + c) - XN} × {YP - (YN + c)}. Here, since YP = XN and YN = XP, (ZP - ZN) = -(XP - XN + c). 2 When the P signal and the N signal are expressed by equations as shown in Embodiment 1, (ZP - ZN) = -(b·sinθ + a - (-b·sinθ + a) + c). 2 = -(2b·sinθ + c). 2 = 2b 2 cos2θ - 4bsin2θ - 2b 2 - c 2As a result, a sinθ term that causes distortion of the k clock signal appears as in the first embodiment. However, when the duty ratio of the k clock signal before multiplication deviates from 50:50, the period for each cycle of the multiplied k clock signal can be corrected by distorting the waveform due to the sinθ term.

[0095] Note that the N signal may be input to the XP terminal and the YN terminal of the analog multiplier 904, and the P signal may be input to the XN terminal and the YP terminal.

[0096] The k clock signal output from the analog multiplier 904 passes through the AC coupling capacitor 914 and the termination resistor 915 and is input to the limiting amplifier 905. Since the output of the analog multiplier 904 is proportional to the square of the amplitude of the input signal, the amplitude of the output signal may vary. In contrast, the limiting amplifier 905 serves to make the amplitude of the signal as constant as possible and reduce the generation of jitter.

[0097] The output from the limiting amplifier 905 passes through the AC coupling capacitor 916 and the termination resistor 917 and is input to the buffer 906. The buffer 906 is a buffer of a differential signal standard such as LVDS that matches the standard of the clock input of the A / D converter 32. The buffer 906 outputs the P signal 933 and the N signal 934 of the k clock signal, which are differential signals, to the A / D converter 32. The A / D converter 32 can sample the OCT interference signal based on the measurement light and the reference light in synchronization with the k clock signal in which the cycle deviation of the frequency obtained by calculating the difference between the P signal 933 and the N signal 934 is corrected for each multiplied cycle.

[0098] As described above, the analog multiplier 904 according to the present embodiment has two sets of differential input terminals.

[0099] The P signal is input to the XP terminal, which is the positive side of one set of differential input terminals of the analog multiplier 904, and the N signal is input to the XN terminal, which is the negative side. On the other hand, the N signal is input to the YP terminal, which is the positive side of the other set of differential input terminals of the analog multiplier 904, and the P signal is input to the YN terminal, which is the negative side. Note that the output from the k clock generation unit 580 is a differential signal, and the differential signal output from the k clock generation unit 580 is input to the frequency multiplication circuit 590. Also, the k clock generation unit 580 is provided inside the light source unit 510, and the frequency multiplication circuit 590 is provided outside the light source unit 10.

[0100] Even with such a configuration, similar to Embodiment 1, by applying an offset voltage to the P signal or the N signal by the D / A converter 921, it is possible to correct the cycle deviation for each cycle of the k clock signal after frequency multiplication. Therefore, in the OCT apparatus 5, it is possible to correct the cycle for each cycle of the k clock signal after frequency multiplication with a simple configuration, and it is possible to reduce the occurrence of ghosts caused by the cycle deviation of the k clock signal.

[0101] Also, in this embodiment, an offset voltage is applied from the D / A converter to either the P signal or the N signal, but an offset voltage may be applied from different D / A converters to each signal.

[0102] In this embodiment, the frequency multiplication circuit 590 is arranged between the k clock generation unit 580 of the light source unit 510 and the A / D converter 32 of the detection unit 30. On the other hand, the frequency multiplication circuit 590 may be provided, for example, inside the detection unit 30. Also, the frequency multiplication circuit 590 according to Embodiment 2 may be used according to whether the input signal to the frequency multiplication circuit and the signal to be output from the frequency multiplication circuit are differential signals. Therefore, for example, even when the k clock generation unit 580 is provided outside the light source unit 510, in the case of a configuration where the input signal to the frequency multiplication circuit and the signal to be output from the frequency multiplication circuit are differential signals, the frequency multiplication circuit 590 can be used. Note that the input to the frequency multiplication circuit 590 may be a digitized signal.

[0103] Furthermore, the configuration of the OCT device 5 other than the k clock generation unit 580 and the frequency multiplication circuit 590 is not limited to the configuration example of the OCT device 5 described in FIG. 5. For example, a configuration may be adopted in which differential detection of the interference light is not performed and the interference light is simply detected. Further, the A / D converter 32 may be provided in the information acquisition unit 40 instead of the detection unit 30. Furthermore, although a fiber optical system using a coupler as the splitting means is used, a spatial optical system using a collimator and a beam splitter may be used. Also, a part of the configuration included in the OCT device 5 may be configured separately from the OCT device 5.

[0104] In the above-described Embodiments 1 and 2, the Mach-Zehnder interferometer configuration is used as the interference optical system of the OCT devices 1 and 5, but the configuration of the interference optical system is not limited thereto. For example, the interference optical system of the OCT devices 1 and 5 may have a Michelson interferometer configuration.

[0105] (Other Embodiments) The disclosed technology can also be realized by executing the following processing. That is, the disclosed technology supplies software (program) that realizes one or more functions of the various embodiments described above to a system or device via a network or a storage medium, and a computer (or CPU, MPU, etc.) of the system or device reads and executes the program. A computer may have one or more processors or circuits and may include a network of multiple separate computers or multiple separate processors or circuits for reading and executing computer-executable instructions. At this time, the processor or circuit may include a central processing unit (CPU), a microprocessing unit (MPU), a graphics processing unit (GPU), an application-specific integrated circuit (ASIC), or a field programmable gate array (FPGA). Also, the processor or circuit may include a digital signal processor (DSP), a data flow processor (DFP), or a neural processing unit (NPU).

[0106] Although the present disclosure has been described with reference to the embodiments above, the present disclosure is not limited to the above embodiments. Disclosures modified within the scope not contrary to the gist of the present disclosure, and disclosures equivalent to the present disclosure are also included in the present disclosure. Further, each of the above-described embodiments and modified forms can be appropriately combined within the scope not contrary to the gist of the present disclosure.

[0107] The disclosure of the present embodiment includes the following configurations, methods, and programs.

[0108] (Configuration 1) A light source unit that emits light with a swept optical frequency, A k-clock generation unit that generates a first k-clock signal using the light emitted by the light source unit, Using the first k-clock signal, a first signal and a second signal with inverted phases are generated, and using the first signal and the second signal, a second k-clock signal having a higher frequency than the first k-clock signal is generated. A frequency multiplier, A voltage control unit that corrects the non-periodicity of the second k-clock signal by changing at least one voltage of a first offset signal applied to the first signal or a second offset signal applied to the second signal, An optical coherence tomography imaging device comprising:

[0109] (Configuration 2) The optical coherence tomography imaging device according to Configuration 1, wherein the frequency multiplier generates a second k-clock signal by multiplying the first signal and the second signal.

[0110] (Configuration 3) The optical coherence tomography imaging device according to any one of Configuration 1 or 2, wherein the frequency multiplier generates a second k-clock signal obtained by multiplying the first signal and the second signal by inputting the first signal and the second signal to an analog multiplier.

[0111] (Configuration 4) The analog multiplier has two sets of differential input terminals, The first signal is input to the positive side of one set of differential input terminals of the analog multiplier, and the second signal is input to the negative side, The optical coherence tomography apparatus according to Configuration 3, wherein the second signal is input to the positive side of the other set of differential input terminals of the analog multiplier, and the first signal is input to the negative side.

[0112] (Configuration 5) An interference unit that generates interference light between the measurement light that is split from the light emitted by the light source unit and irradiated to the subject and the reference light that is split from the light emitted by the light source unit, An acquisition unit that acquires a tomographic image of the subject by sampling the interference signal obtained by detecting the interference light using the second k clock signal, The optical coherence tomography apparatus according to any one of Configurations 1 to 4, further comprising:

[0113] (Configuration 6) The optical coherence tomography apparatus according to Configuration 5, wherein the voltage control unit changes at least one of the voltages of the first offset signal or the second offset signal so that the peak value of the frequency corresponding to the second k clock signal obtained by analyzing the frequency of the sampled interference signal is below the allowable level.

[0114] (Configuration 7) The optical coherence tomography apparatus according to Configuration 6, wherein the allowable level is -30 dB or less of the peak value of the frequency corresponding to the subject obtained by analyzing the frequency of the sampled interference signal.

[0115] (Configuration 8) The optical coherence tomography apparatus further includes storage means for storing at least one of information regarding the voltage of the first offset signal or information regarding the voltage of the second offset signal. The voltage control unit corrects the aperiodicity of the second k clock signal by changing the voltage of at least one of the first offset signal or the second offset signal using the information stored in the storage means, the optical coherence tomography apparatus according to any one of Configurations 1 to 7.

[0116] (Method 1) A light source unit that emits light with a swept optical frequency, A k clock generation unit that generates a first k clock signal using the light emitted by the light source unit, Using the first k clock signal, a first signal and a second signal with inverted phases are generated, and using the first signal and the second signal, a second k clock signal with a higher frequency than the first k clock signal is generated. A frequency multiplication unit, A control method for an optical coherence tomography apparatus comprising: A control method for an optical coherence tomography apparatus having a voltage control step of correcting the aperiodicity of the second k clock signal by changing the voltage of at least one of the first offset signal applied to the first signal or the second offset signal applied to the second signal.

[0117] (Program 1) A program that causes a computer to execute the control method described in Method 1.

Explanation of Signs

[0118] 10 Light source unit 20 Interference unit 30 Detection unit 32 A / D converter (conversion unit) 80,580 k clock generation unit 84,590 Frequency multiplication circuit 100 Subject 844,904 Analog multiplier 846, 847, 921 D / A converters

Claims

1. A light source unit that emits light with a swept optical frequency, A k-clock generation unit that generates a first k-clock signal using the light emitted by the light source unit, Using the first k-clock signal, a first signal and a second signal with inverted phases are generated, and using the first signal and the second signal, a second k-clock signal with a higher frequency than the first k-clock signal is generated. A frequency multiplier, A voltage control unit that corrects the non-periodicity of the second k-clock signal by changing at least one of the voltage of a first offset signal applied to the first signal or a second offset signal applied to the second signal, An optical coherence tomography imaging device comprising:

2. The optical coherence tomography imaging device according to claim 1, wherein the frequency multiplier generates a second k-clock signal by multiplying the first signal and the second signal.

3. The optical coherence tomography imaging device according to claim 1, wherein the frequency multiplier generates a second k-clock signal obtained by multiplying the first signal and the second signal by inputting the first signal and the second signal to an analog multiplier.

4. The analog multiplier has two sets of differential input terminals, The first signal is input to the positive side of one set of differential input terminals of the analog multiplier, and the second signal is input to the negative side, The second signal is input to the positive side of the other set of differential input terminals of the analog multiplier, and the first signal is input to the negative side. The optical coherence tomography imaging device according to claim 3.

5. An interference unit that generates interference light between measurement light divided from the light emitted by the light source unit and irradiated to the subject and reference light divided from the light emitted by the light source unit, An acquisition unit that acquires a tomographic image of the subject by sampling an interference signal obtained by detecting the interference light using the second k clock signal; The optical coherence tomography apparatus according to claim 1, further comprising . **Claim 6** The optical coherence tomography apparatus according to claim 5, wherein the voltage control unit changes at least one of the voltages of the first offset signal or the second offset signal so that a peak value of a frequency corresponding to the second k clock signal obtained by analyzing the frequency of the sampled interference signal is equal to or lower than an allowable level. **Claim 7** The optical coherence tomography apparatus according to claim 6, wherein the allowable level is -30 dB or less of a peak value of a frequency corresponding to the subject obtained by analyzing the frequency of the sampled interference signal. **Claim 8** The apparatus further comprises storage means for storing at least one of information regarding the voltage of the first offset signal or information regarding the voltage of the second offset signal, and the voltage control unit corrects the non-periodicity of the second k clock signal by changing at least one of the voltages of the first offset signal or the second offset signal using the information stored in the storage means before starting imaging of the subject. The optical coherence tomography apparatus according to claim 1. **Claim 9** A light source unit that emits light with a swept optical frequency; A k clock generation unit that generates a first k clock signal using the light emitted by the light source unit; Using the first k clock signal, a first signal and a second signal with inverted phases are generated, and using the first signal and the second signal, a second k clock signal with a higher frequency than the first k clock signal is generated. A control method for an optical coherence tomography apparatus, comprising: ​A control method for an optical coherence tomography apparatus having a voltage control step of correcting the aperiodicity of the second k clock signal by changing the voltage of at least one of a first offset signal applied to the first signal and a second offset signal applied to the second signal.

10. A program for causing a computer to execute the control method according to claim 9.

Images