JP2020106514A - Optical coherence tomographic imaging device - Google Patents

Abstract

To provide an optical coherence tomographic imaging device that enables a simple configuration to properly increase a frequency of a k clock signal.SOLUTION: An optical coherence tomographic imaging device comprises: a light source unit that emits light of which an optical frequency is swept; a coherence unit that produces coherent light by measurement light, which is divided from the light which the light source unit emits and with which an analyte is irradiated, and reference light; a detection unit that detects the coherent light, and generates a coherence signal; a conversion unit that converts the coherence signal into digital data; a K clock generation unit that generates a K clock signal at equal optical frequency intervals, using the light which the light source unit emits; and a frequency doubling circuit 84 that doubles the frequency of the k clock signal. The frequency doubling circuit is configured to input a first signal 813 and second signal 814, which are generated from the k clock signal and have a phase mutually reversed, to an analog multiplier 844, and generate a frequency-doubled K clock signal 816, and the conversion unit is configured to sample the coherence signal, using the frequency-doubled K clock signal, and thereby convert a coherence signal subjected to the sampling into digital data.SELECTED DRAWING: Figure 3

Description

The present invention relates to an optical coherence tomographic imaging apparatus.

Currently, an imaging apparatus (hereinafter referred to as an OCT apparatus) using an optical coherence tomography (OCT: Optical Coherence Tomography) is being developed. The OCT device irradiates the object with light, and causes the reflected light returning from different depths of the object to interfere with the reference light according to the wavelength of the irradiation light. The OCT apparatus can obtain information about a tomographic image of an object, specifically a tomographic image, by analyzing frequency components included in a temporal waveform of the intensity of interference light (hereinafter, referred to as an interference spectrum). The OCT apparatus is used for fundus examination and the like as an imaging apparatus for ophthalmology, for example.

In the examination using the OCT apparatus, the behavior of the subject is restricted during the examination in order to obtain an accurate image. Therefore, when the measurement speed of the OCT device is low, the period during which the behavior of the subject is restricted becomes long, and the physical burden on the subject increases. Therefore, in the OCT device, it is desired to improve the measurement speed and reduce the physical burden on the subject for the examination.

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

In the SS-OCT apparatus, in order to further improve the measurement speed, it is preferable to acquire tomographic information in a wider range with a single imaging. Therefore, a method of widening the imaging range in the depth direction of the biological tissue which is the subject of the examination using the SS-OCT device has been studied. The depth direction of the biological tissue that is the subject is generally called the A-scan direction.

Here, in the SS-OCT apparatus, the number of times that the interference light (interference signal) between the reflected light from the subject and the reference light is sampled, that is, the number of times that the interference light is sampled is increased to increase the imaging range in the A-scan direction. It is known to be wider. Therefore, in order to increase the sampling number of the interference light, the frequency of the clock signal (hereinafter, referred to as k clock signal) indicating the sampling timing is increased.

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 having a long coherence length. However, since a light source with a long coherence length is expensive, when using such a light source, the cost of the SS-OCT apparatus becomes high. Therefore, a method of increasing the k clock frequency without using a light source having a long coherence length has been proposed.

Patent Document 1 discloses a method of doubling the frequency of a sample clock of an SS-OCT apparatus using a multiplier.

Japanese Patent Publication No. 2010-515919

When the k clock signal is simply divided and input to the analog multiplier, if the input signal does not include the offset voltage, the output signal of the analog multiplier is sin θ·sin θ=−cos 2θ/2+1/2, and the frequency is doubled. Be converted.

However, when the input signal includes the offset voltage a, the output signal of the analog multiplier becomes (sin θ+a)·(sin θ+a)=−cos 2θ/2+2a·sin θ+a ² +1/2, and the sin θ term of the original frequency component is The waveform is distorted because it is included. Therefore, there is a problem that the k clock signal cannot be properly doubled.

In view of the above problems, it is an object of the present invention to provide an optical coherence tomography apparatus capable of appropriately increasing the frequency of a k clock signal with a simple configuration.

An optical coherence tomographic imaging apparatus according to an embodiment of the present invention includes a light source unit that emits light whose optical frequency is swept, measurement light that is split from the light emitted by the light source unit, and is applied to a subject, and the light source. An interference section for generating interference light by reference light split from the light emitted by the section, a detection section for detecting the interference light and generating an interference signal, and a conversion section for converting the interference signal into digital data, The frequency doubling includes a k-clock generation unit that generates a k-clock signal at equal optical frequency intervals using light emitted from the light source unit, and a frequency doubling circuit that doubles the frequency of the k-clock signal. The circuit inputs a first signal and a second signal, which are generated from the k clock signal and are out of phase with each other, to an analog multiplier to generate a frequency-doubled k clock signal, The conversion unit converts the interference signal into the digital data by sampling the interference signal using the k clock signal having the frequency doubled.

According to the present invention, the frequency of the k clock signal can be appropriately increased with a simple configuration.

1 schematically shows a configuration example of an OCT apparatus according to a first embodiment. 1 schematically shows a configuration example of a k clock generation unit according to the first embodiment. 1 schematically shows a configuration example of a frequency doubling circuit according to a first embodiment. 3 shows an example of the waveform of each signal propagating in the frequency doubler circuit according to the first embodiment. 1 schematically shows a configuration example of an OCT apparatus according to a second embodiment. 2 schematically shows a configuration example of a frequency doubling circuit according to a second embodiment.

Hereinafter, exemplary embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, dimensions, materials, shapes, relative positions of constituent elements, and the like described in the following embodiments are arbitrary, and can be changed according to the configuration of the apparatus to which the present invention is applied or various conditions. Also, in the drawings, the same reference numerals are used in the drawings to denote the same or functionally similar elements.

Although the optical coherence tomographic imaging apparatus (OCT apparatus) according to the present invention is an SS-OCT apparatus using a wavelength swept light source, it will be simply referred to as an OCT apparatus below for simplification. Further, the OCT apparatus according to the present invention will be described below as an OCT apparatus used for examining the fundus of a subject. However, the OCT apparatus according to the present invention 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 or organ. At this time, the present invention can be applied to a medical device such as an endoscope in addition to the ophthalmologic apparatus.

(Example 1)
Hereinafter, an OCT apparatus according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 4E. FIG. 1 schematically shows a configuration example of the OCT apparatus according to this embodiment.

As shown in FIG. 1, the OCT apparatus 1 includes 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, and a fundus of the eye that is the subject 100. An information acquisition unit 40 for acquiring the information and a display unit 70 for displaying the acquired information are provided. Further, the OCT apparatus 1 irradiates the subject 100 with the measurement light and causes the reflected light from the subject 100 to exit to the interference unit 20 and the reference arm to interfere with the reflected light emitted from the measurement arm 50. A reference arm 60 that emits light is provided. Further, the OCT device 1 includes a k-clock generation unit 80 that generates a k-clock signal, and an optical fiber that splits the light from the light source unit 10 into light that enters the k-clock generation unit 80 and light that enters the interference unit 20. A coupler (splitting unit) 90 is provided.

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

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 an optical fiber. The optical fiber coupler 90 splits the light from the light source unit 10 into light entering the k-clock generating unit 80 and light entering the interference unit 20. A beam splitter or the like may be used instead of the optical fiber coupler 90. Further, the light division ratio may be arbitrarily set according to the desired configuration.

The k clock generation unit 80 generates a k clock signal based on the light emitted from the light source unit 10 via the optical fiber coupler 90. Further, the k clock generation unit 80 sends the generated k clock signal to the detection unit 30. The detection unit 30 detects interference light between measurement light and reference light, which will be described later, and generates a digital signal of an OCT interference signal based on the interference light in synchronization with the k clock signal received from the k clock generation unit 80.

The interference section 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 an optical fiber. The optical fiber coupler 21 splits the light emitted from the light source unit 10 that has passed through the optical fiber coupler 90 into the measurement light that is emitted to the fundus through the measurement arm 50 and the reference light that passes through the reference arm 60. .. The light division ratio may be set arbitrarily according to the desired configuration.

The measurement light is applied to 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 in the optical fiber coupler 22 and are emitted from the optical fiber coupler 22 as interference light.

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

The measurement arm 50 is provided with a polarization controller 51, a collimator 52, an X-axis scanner 53, a Y-axis scanner 54, and a focus lens 55. The polarization controller 51 is provided in the optical fiber connected from the optical fiber coupler 21 to the measurement arm 50, and adjusts the polarization state 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 emitted as the spatial light is applied to the fundus of the subject 100 via the X-axis scanner 53, the Y-axis scanner 54, and the focus lens 55.

The X-axis scanner 53 and the Y-axis scanner 54 are 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 configure 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 scans in the X-axis direction, and the Y-axis scanner 54 scans in the Y-axis direction. The X-axis direction and the Y-axis direction are directions that are orthogonal to the eye axis direction of the eye that is the subject 100, and are also directions that are orthogonal to each other.

The measurement light applied to the fundus is reflected as backscattered light (reflected light) at the fundus. The reflected light from the fundus exits the measurement arm 50 again via the focus lens 55, the Y-axis scanner 54, the X-axis scanner 53, the collimator 52, and the polarization controller 51. Then, it propagates through the optical fiber and enters the optical fiber coupler 22 via the optical fiber coupler 21.

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 adjusting optical system 64, a dispersion adjusting prism pair 65, and a collimator 66. The polarization controller 61 is provided in 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 an 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 the spatial light enters the collimator 66 via the dispersion compensation glass 63, the optical path length adjusting optical system 64, and the dispersion adjusting prism pair 65.

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 compensating glass 63 and the dispersion adjusting prism pair 65, the dispersion of the reference light can be adjusted so as to correspond to the dispersion of the reflected light of the measurement light passing through the measurement arm 50.

Further, the optical path length adjusting optical system 64 can move toward or away from the collimators 62 and 66 as shown by an arrow A1 in FIG. 1, and can adjust the optical path length of the reference arm 60. Therefore, the optical path length adjusting optical system 64 can adjust the optical path length of the reference arm 60 according to the optical path length to the fundus (subject 100) through which the measurement light passes. The reference light that has entered the collimator 66 propagates through the optical fiber that connects the collimator 66 and the optical fiber coupler 22, and enters the optical fiber coupler 22.

As described above, the measurement light and the reference light that have entered the optical fiber coupler 22 interfere with each other, and the interference light is split and emitted from the optical fiber coupler 22 into the two optical fibers for detection, respectively. It is incident on the portion 30. The non-interference light is split into two optical fibers from the optical fiber coupler 22 as light having the same phase, and is output to the detection unit 30.

The detector 30 is provided with a detector 31 and an A/D converter 32 (converter). The detector 31 is a balance detector, which removes the in-phase light of the non-interference component and detects only the light of the anti-phase which is the interference component to obtain a better signal-to-noise ratio (S/N ratio). realizable.

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. A k clock generator 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 generator 80. , Convert to 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 detects the interference light based on the measurement light and the reference light, generates the digitized OCT interference signal in synchronization with the k clock signal, and sends the OCT interference signal to the information acquisition unit 40. You can

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 fundus information. The information acquisition unit 40 detects the differential of the OCT interference signal by obtaining the difference between the OCT interference signals based on the interference lights having different phases detected by the detector 31, and based on the non-interference component of the OCT interference signal. It is possible to reduce noise. Therefore, the information acquisition unit 40 can improve the signal-to-noise ratio (S/N ratio) of fundus information based on the OCT interference signal by performing the differential detection. The information acquisition unit 40 sends the obtained fundus information to the display unit 70, and the display unit 70 displays the received information as a tomographic image.

The information acquisition unit 40 may be configured in the OCT apparatus 1 as an arbitrary information processing unit including a CPU, MPU, or the like, or may be configured using a general-purpose computer. The display unit 70 may be a monitor provided in the OCT device 1 or the information acquisition unit 40, or may be an individual monitor connected to these.

Through the series of operations described above, the OCT apparatus 1 can acquire the information regarding the tomography at a certain point of the subject 100. Acquiring the information about the tomographic slice in the depth direction of the subject 100 in this way is called A-scan. Further, in the OCT apparatus 1, information about a two-dimensional tomographic image or a three-dimensional tomographic image of the subject 100 is obtained by scanning the subject 100 with a scanning unit configured by the X-axis scanner 53 and the Y-axis scanner 54. Can be obtained.

Here, scanning the subject 100 with the measurement light in the direction in which the information on the tomographic image of the subject 100 in the direction orthogonal to the A-scan, that is, the information of the two-dimensional tomographic image is acquired is referred to as the B-scan. Further, scanning the subject 100 with the measurement light in a direction orthogonal to both the A-scan and B-scan scanning directions is called C-scan. In particular, when two-dimensional raster scanning is performed within the fundus of the subject 100 when acquiring information of a three-dimensional tomographic image, the direction in which high-speed scanning is performed is called the B-scan direction, and is orthogonal to the B-scan direction. However, the direction in which scanning is performed at low speed is called the C-scan direction.

The OCT apparatus 1 can obtain a two-dimensional tomographic image of the subject 100 by performing A-scan and B-scan, and can perform the A-scan, B-scan, and C-scan to obtain the subject 100. It is possible to obtain a three-dimensional tomographic image. The B-scan and C-scan are performed by the scanning unit configured by the X-axis scanner 53 and the Y-axis scanner 54 described above. Note that the line scanning directions such as the B-scan direction and the C-scan direction do not have to match the X-axis direction or the Y-axis direction. Therefore, the line scanning directions of B-scan and C-scan can be appropriately determined according to the two-dimensional tomographic image or the three-dimensional tomographic image to be captured.

Further, in the OCT apparatus 1, the sampling of the interference signal by the A/D converter 32 of the detection unit 30 is based on the k clock signal generated by the k clock generation unit 80 and is equal to the light from the light source unit 10. It is performed at frequency (equal wave number) intervals.

Here, since the light from the light source unit 10 of the OCT apparatus 1 is wavelength-swept, the optical frequency changes with time. On the other hand, since the k clock generation unit 80 generates the k clock signal based on the light from the light source unit 10, the k clock signal is equal to the OCT interference signal based on the interference light detected by the detection unit 30. The sampling timing at wave number intervals can be indicated.

Next, the k clock generation unit 80 will be described in more detail with reference to FIG. 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 doubling circuit 84.

The k-clock interference unit 82 splits the light from the light source unit 10 into lights that enter 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.

Light 811 from the light source unit 10 that has passed through the optical fiber coupler 90 propagates through the optical fibers connected to the optical fiber couplers 90 and 821, and enters the optical fiber coupler 821. The optical fiber coupler 821 includes a first optical path formed by the connector 822, the optical fiber 823, and the connector 824, and a second optical path formed by the connector 825, the optical fiber 826, and the connector 827. 811 is divided and made incident.

Since the optical fiber 823 and the optical fiber 826 have predetermined different 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 enters the optical fiber coupler 828 through the optical fiber from the connector 824, and the light passing through the second optical path enters the optical fiber coupler 828 through the optical fiber from the connector 827. To do. The light that has passed through the first optical path and the light that has passed through the second optical path interfere with each other in the optical fiber coupler 828, and enter the optical sensor 83 via the optical fiber as interference light.

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 doubling circuit 84.

The frequency doubling circuit 84 generates a k clock signal 816 that doubles the frequency of the interference signal 812 based on the received interference signal 812, and sends the k clock signal 816 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 whose frequency is doubled.

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 4(e). FIG. 3 schematically shows a configuration example of the frequency doubling circuit 84 that doubles the frequency of the k clock. FIGS. 4A to 4E show examples of waveforms of respective signals propagating in the frequency doubling circuit 84. In each graph in FIGS. 4A to 4E, the horizontal axis represents time and the vertical axis represents potential.

As shown in FIG. 3, the frequency doubling circuit 84 is provided with a comparator 841, a capacitor 842, a terminating resistor 843, and an analog multiplier 844 that output LVDS (Low Voltage Differential Signaling). Further, in the frequency doubling circuit 84, a high-pass filter and amplifier circuit 845 is provided at the subsequent stage of the analog multiplier 844.

The LVDS output comparator 841 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 thereof, and the comparator 841 has two signals (differential clock signals) whose phases are inverted from those of the P terminal and the N terminal. Are output respectively. The reference voltage VREF can be adjusted to a value that matches the amplitude center voltage of the interference signal 812. Further, the reference voltage VREF may be grounded according to a desired configuration.

The termination resistor 843 and the capacitor 842 form a low pass filter. Here, the output waveform of the LVDS is a substantially rectangular wave, and by using the low-pass filter formed by the terminating resistor 843 and the capacitor 842, the waveforms of the two signals output from the comparator 841 are shaped from a rectangular wave to a sine wave. can do.

The P signal 813 (positive signal, first signal) and the N signal 814 (negative signal, second signal) whose waveforms have been shaped by the low-pass filter are input to the analog multiplier 844. The analog multiplier 844 multiplies the input P signal 813 and N signal 814 and outputs an output signal 815 that is the multiplication result.

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

Hereinafter, each signal propagating in the frequency doubling circuit 84 will be described with reference to FIGS. FIG. 4A shows the waveform of the interference signal 812 output from the optical sensor 83. In FIG. 4A, the amplitude center voltage of the interference signal 812 is shown using the reference voltage VREF input to the comparator 841.

When the interference signal 812 is input to the comparator 841, the P terminal and the N terminal, which are the output terminals of the comparator 841, output the P signal and the N signal, which are differential signals whose phases are inverted. FIG. 4B shows the waveforms of the P signal and the N signal. Note that the P signal and the N signal have mutually inverted phases, but their offset voltages a are the same, and their amplitude center voltages are the same. Further, the P signal is a signal in phase with the interference signal 812, and the N signal is a signal in phase with the interference signal 812.

The P signal and the N signal are input to a low pass filter including a terminating resistor 843 and a capacitor 842, and the P signal 813 and the N signal 814 whose waveforms are shaped into a sine wave are output from the low pass filter, respectively. FIG. 4C shows the shaped P signal 813 and N signal 814.

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

Here, when the offset voltage is a, the amplitude of the signal is b, and the output signal 815 is represented by an equation, (b·sin θ+a)·(−b·sin θ+a)=b ² ·cos 2θ/2−b ² /2+a ² Becomes In this equation, there is no term of sin θ that occurs when the same signal is multiplied, that is, when the same signal is squared. Therefore, the waveform of the output signal 815 can be reduced in distortion as shown in FIG. Therefore, the output signal 815 has a frequency doubled as compared with the interference signal 812 from the optical sensor 83, and has a reduced waveform distortion.

The output signal 815 is input to the high-pass filter and amplifier circuit 845, the DC component is cut from the circuit 845, and the k clock signal 816 whose amplitude is amplified is output. FIG. 4E shows the k clock signal 816. As described above, according to the frequency doubling circuit 84 according to the present embodiment, the interference signal 812, which is the original k clock signal output from the optical sensor 83, has a frequency doubled and the waveform is distorted. K clock signal 816 can be generated.

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 can sample the OCT interference signal based on the measurement light and the reference light in synchronization with the k clock signal 816 whose frequency is appropriately doubled.

As described above, the frequency doubling circuit 84 according to the present embodiment generates the P signal and the N signal, which are differential clock signals, from the interference signal 812, which is a clock signal at equal optical frequency intervals. By inputting the generated P signal and N signal to the analog multiplier, it is possible to generate the k clock signal 816 whose distortion is reduced and whose frequency is doubled. The OCT apparatus 1 widens the imaging range in the A-scan direction (depth direction) with a simple configuration by sampling the OCT interference signal by the A/D converter 32 in synchronization with the k clock signal 816. You can

As described above, the OCT apparatus 1 according to the present embodiment includes the light source unit 10, the interference unit 20, the detection unit 30, the A/D converter 32, the k clock generation unit 80, and the frequency doubling circuit 84. With. The light source unit 10 emits light whose optical frequency is swept. The interference unit 20 generates interference light by the measurement light split from the light emitted from the light source unit 10 and applied to the subject 100 and the reference light split from the light emitted by the light source unit 10. The detector 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 uses the light emitted from the light source unit 10 to generate a k clock signal at equal optical frequency intervals. The frequency doubling circuit 84 doubles the frequency of the k clock signal.

Further, the frequency doubling circuit 84 inputs the P signal (first signal) and the N signal (second signal), which are generated from the k clock signal and whose phases are mutually inverted, to the analog multiplier 844. , K frequency doubled clock signal is generated. In the present 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 converts the OCT interference signal into digital data by sampling the OCT interference signal using the k clock signal whose frequency is doubled.

With this, in the OCT apparatus 1, the frequency of the k clock signal can be appropriately increased with a simple configuration, and the imaging range in the depth direction can be widened.

Further, in the present embodiment, in the frequency doubling circuit 84, the P signal and the N signal whose phases are mutually inverted are generated by the comparator 841 of the LVDS output. By using the LVDS output comparator 841, the P signal and the N signal can be generated at low cost and more stably than the combination of operational amplifiers. Further, the LVDS output comparator 841 can be operated only by the positive single power source, and the OCT device 1 can be prevented from increasing in size and cost.

A differential input analog multiplier can also be used as the analog multiplier 844. In this case, the P signal and the N signal may be exchanged and input to one of the input terminal groups. Specifically, in one input terminal group, the P signal is input to the X terminal, the N signal is input to the Y terminal, and in the other input terminal group, the N signal is input to the X terminal and the P signal is input to the Y terminal. You may input a signal.

Further, in this embodiment, the differential signal is generated using the LVDS output comparator 841, but other differential signal standard comparators or the like may be used. Further, the interference signal 812 output from the optical sensor 83 may be digitized and then input to the comparator 841.

Further, in the present embodiment, the P signal and the N signal having the phases different from each other by 180° are generated by using the comparator 841, but the configuration of generating the P signal and the N signal having the phases different from each other by 180° is not limited to this. For example, the interference signal 812 is divided into two signals, the phase of one signal is inverted using a phase shift circuit that shifts (inverts) the phase by 180°, and the P signal and the N signal whose phases are different from each other by 180° are generated. It may be generated. However, in this case, it should be noted that the frequencies of the P signal and the N signal generated need to be constant.

In addition, in the OCT apparatus 1 according to the present 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. Further, in the present embodiment, the frequency doubling circuit 84 is provided in the k clock generation unit 80. However, the frequency doubling circuit 84 may be provided outside the k clock generation unit 80.

Further, the configuration of the OCT device 1 other than the k clock generation unit 80 has been described based on the configuration example of the OCT device 1 illustrated in FIG. 1, but the configuration of the OCT device 1 other than the k clock generation unit 80 is not limited to this. I can't. For example, the configuration may be such that the interference light is simply detected without performing differential detection on the interference light. Further, the A/D converter 32 may be provided in the information acquisition unit 40 instead of the detection unit 30. Further, although a fiber optical system using a coupler is used as the dividing means, a spatial optical system using a collimator and a beam splitter may be used. Further, the configuration of the OCT apparatus 1 is not limited to the above configuration, and a part of the configuration included in the OCT apparatus 1 may be a configuration separate from the OCT apparatus 1.

(Example 2)
Hereinafter, an OCT apparatus according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 schematically shows a configuration example of the OCT apparatus 5 according to this embodiment. Regarding the components of the OCT apparatus 5 according to the present embodiment, those having the same functions and configurations as those of the OCT apparatus 1 according to the first embodiment are designated by the same reference numerals and description thereof will be omitted.

In the first embodiment, the k clock generation unit 80 including the frequency doubling circuit 42 is provided outside the light source unit 10. On the other hand, in this embodiment, the wavelength swept light source 11 and the k clock generation unit 580 are provided in the light source unit 510. This is a general configuration for a commercially available wavelength swept light source.

Further, the frequency doubling circuit 590 according to the present embodiment is provided outside the k clock generating unit 580. The frequency doubling circuit 590 is arranged between the k clock generating unit 580 and the A/D converter 32, and is connected so as to transmit a differential signal such as LVDS. The other components are similar to those of the first embodiment, and detailed description thereof will be omitted.

The k clock generation unit 580 is a k clock generation unit that generates a k clock signal (P signal and N signal) that is a differential signal based on the light from the wavelength swept light source 11. For example, the k-clock generation unit 580 has the same configuration as the k-clock generation unit 80, but is provided with components that generate differential signals such as an LVDS comparator instead of the frequency doubling circuit 84. Can be In this case, the k-clock generation unit 580 generates an interference signal and detects the interference signal by the optical sensor, similarly to the k-clock generation unit 80. After that, the k-clock generation unit 580 uses the comparator of the differential signal standard such as the LVDS comparator, or an arbitrary component for generating the differential signal such as the phase shift circuit, from the output signal of the optical sensor to the k-clock. Generate P and N signals for the signals. 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 that generates a differential signal regarding the k clock signal.

Next, the configuration of the frequency doubling circuit 590 will be described with reference to FIG. FIG. 6 schematically shows a configuration example of the frequency doubling circuit 590. The frequency doubling circuit 590 is provided with a capacitor 901, a terminating resistor 902, a limiting amplifier 903, an analog multiplier 904, a limiting amplifier 905, and a buffer 906 of a differential signal standard such as LVDS.

Further, AC coupling capacitors 911, 912, 914, 916 and terminating resistors 913, 915, 917 are provided between these components. In the present embodiment, the reason why the integrated circuits are connected by AC coupling is to absorb the level difference of the signal standard between the integrated circuits. Therefore, if the signal standards of the connected integrated circuits are the same, AC coupling is not necessary. Further, in the present embodiment, the terminating resistor is inserted between the P signal and the N signal, but it is necessary to perform the appropriate termination according to the level of the signal standard of the connected integrated circuit.

The signals 931 and 932 are the P signal and the N signal related to the k clock signal output from the k clock generation unit 12, respectively. The waveforms of the signals 931 and 932 can be shaped into a waveform close to a sine wave by a low-pass filter including a capacitor 901 and a terminating resistor 902. The signals 931 and 932 whose waveforms have been shaped by the low-pass filter are input to the positive and negative terminals of the differential input/output limiting amplifier 903 via the AC coupling capacitor 911.

Here, the k clock signal is a signal whose frequency changes, and generally, the higher the transmission distance, the more the high frequency attenuates. The limiting amplifier is an amplifier having a limited gain, and can limit the amplitude of the output signal to a certain voltage. By using the limiting amplifier for the k clock signal, it is possible to absorb a change in the amplitude of the signal due to a change in the frequency of the k clock signal.

The signal output from the limiting amplifier 903 passes through the AC coupling capacitor 912 and the terminating 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 the N signal is input to the XN terminal and the YP terminal.

Here, the signals input to the XP terminal, the XN terminal, the YP terminal, and the YN terminal that are the input terminals of the analog multiplier 904 are signals XP, XN, YP, and YN, respectively, and the ZP terminal and the ZN terminal that are the output terminals. The signals output from are respectively signals ZP and ZN. With respect to the input on the Y side of the analog multiplier 904, the signal input to the P terminal (positive side) and the signal input to the N terminal (negative side) are opposite to the input on the Y side. Therefore, the analog multiplier 904 outputs signals ZP and ZN that satisfy (ZP-ZN)=(XP-XN)*{-(YP-YN)}. Here, since YP=XN and YN=XP, (ZP−ZN)=(XP−XN) ² . When the P signal and the N signal are expressed by the formulas as shown in the first embodiment, (ZP−ZN)=(b·sin θ+a−(−b·sin θ+a)) ² =(2b sin θ) ² . Therefore, since there is no sin θ term that occurs when the same signal is squared, it is possible to reduce waveform distortion in the difference between output signals. Therefore, as in the first embodiment, the difference between the signals output from the analog multiplier 904 becomes a k-clock signal whose waveform distortion is reduced and which is twice the frequency of the input k-clock signal. 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.

The k clock signal output from the analog multiplier 904 passes through the AC coupling capacitor 914 and the terminating 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 fluctuate. On the other hand, the limiting amplifier 905 serves to make the amplitude of the signal as constant as possible and reduce the occurrence of jitter.

The output from the limiting amplifier 905 passes through the AC coupling capacitor 916 and the terminating 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 is a differential signal, to the A/D converter 32. The A/D converter 32 synchronizes with the k clock signal whose frequency obtained by calculating the difference between the P signal 933 and the N signal 934 is appropriately doubled, and outputs the OCT interference signal based on the measurement light and the reference light. Sampling can be done.

As described above, the analog multiplier 904 according to this embodiment has two sets of differential input terminals. The P signal is input to the XP terminal on the positive side of the differential input terminals of one set of the analog multiplier 904, and the N signal is input to the XN terminal on the negative side. On the other hand, the N signal is input to the positive side YP terminal of the other set of differential input terminals of the analog multiplier 904, and the P signal is input to the negative side YN terminal. 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 doubling circuit 590. Further, the k clock generation unit 580 is provided inside the light source unit 510, and the frequency doubling circuit 590 is provided outside the light source unit 10.

Even with such a configuration, the frequency of the k clock signal can be appropriately doubled by using the analog multiplier 904, as in the first embodiment. Therefore, in the OCT device 5, the frequency of the k clock signal can be appropriately increased with a simple configuration, and the imaging range in the depth direction can be widened.

Further, in the present embodiment, the limiting amplifiers 903 and 905 are arranged in the front stage of the input and/or the rear stage of the output of the analog multiplier 904. By providing the limiting amplifier 903 before the input of the analog multiplier 904, it is possible to reduce the change in the amplitude of the signal due to the change in the frequency of the k clock signal. Further, by providing a limiting amplifier 905 after the output of the analog multiplier 904, the amplitude of the signal is made as constant as possible, and the influence of the fluctuation of the amplitude of the output signal of the analog multiplier 904 is reduced, so that the occurrence of jitter occurs. Can be reduced.

In the present embodiment, the frequency doubling 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 doubling circuit 590 may be provided in the detection unit 30, for example. Further, the frequency doubling circuit 590 according to the second embodiment may be used depending on whether the input signal to the frequency doubling circuit and the signal to be output from the frequency doubling circuit are differential signals. Therefore, for example, even when the k clock generation unit 580 is provided outside the light source unit 510, the input signal to the frequency doubling circuit and the signal to be output from the frequency doubling circuit are differential signals. For some configurations, frequency doubling circuit 590 can be used. The input to the frequency doubling circuit 590 may be a digitized signal.

Furthermore, the configuration of the OCT device 5 other than the k clock generation unit 580 and the frequency doubling circuit 590 is not limited to the configuration example of the OCT device 5 illustrated in FIG. For example, the configuration may be such that the interference light is simply detected without performing differential detection on the interference light. Further, the A/D converter 32 may be provided in the information acquisition unit 40 instead of the detection unit 30. Further, although a fiber optical system using a coupler is used as the dividing means, a spatial optical system using a collimator and a beam splitter may be used. Further, a part of the configuration included in the OCT apparatus 5 may be a configuration separate from the OCT apparatus 5.

In the first and second embodiments, the configuration of the Mach-Zehnder interferometer 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 to this. For example, the interference optical system of the OCT devices 1 and 5 may have a Michelson interferometer configuration.

Although the present invention has been described with reference to the exemplary embodiments, the present invention is not limited to the above exemplary embodiments. Inventions modified within a range not departing from the spirit of the present invention and inventions equivalent to the present invention are also included in the present invention. Further, the above-described respective embodiments and modified examples can be appropriately combined without departing from the spirit of the present invention.

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 doubling circuit, 100: subject, 844, 904: analog multiplier

Claims (12)

A light source unit that emits light whose optical frequency is swept,
An interference section that generates interference light by the reference light divided from the light emitted by the light source section and the measurement light that is split from the light emitted by the light source section,
A detection unit that detects the interference light and generates an interference signal,
A conversion unit for converting the interference signal into digital data,
A k-clock generation unit that generates a k-clock signal at equal optical frequency intervals using the light emitted from the light source unit;
A frequency doubling circuit for doubling the frequency of the k clock signal;
Equipped with
The frequency doubling circuit inputs a first signal and a second signal, which are generated from the k clock signal and whose phases are mutually inverted, to an analog multiplier to double the frequency of the k clock signal. Produces
The optical coherence tomographic imaging apparatus, wherein the conversion unit converts the interference signal into the digital data by sampling the interference signal using the k clock signal having the frequency doubled. The optical coherence tomography apparatus according to claim 1, wherein the first signal and the second signal are generated from the k clock signal by a comparator having an LVDS output. The optical coherence tomography apparatus according to claim 1, wherein the first signal is a signal having the same phase as the k clock signal, and the second signal is a signal having a reverse phase to the k clock signal. The optical coherence tomographic imaging apparatus according to claim 1, wherein the first signal and the second signal have the same amplitude center voltage. The optical coherence tomography apparatus according to any one of claims 1 to 4, further comprising a low-pass filter that shapes the waveforms of the first signal and the second signal into a sine wave. The analog multiplier has two sets of differential input terminals,
The first signal is input to the positive side and the second signal is input to the negative side of the differential input terminals of one set of the analog multipliers,
6. The analog signal multiplier according to claim 1, wherein the second signal is input to a positive side and the first signal is input to a negative side of a differential input terminal of the other set of the analog multipliers. The optical coherence tomographic imaging apparatus described. 7. The optical coherence tomographic imaging apparatus according to claim 1, wherein a limiting amplifier is arranged at a front stage and/or a rear stage of an output of the analog multiplier. The optical coherence tomographic imaging apparatus according to claim 1, wherein the k clock signal output from the k clock generation unit is a differential signal. 9. The optical coherence tomography apparatus according to claim 1, wherein the frequency doubling circuit is provided inside the k clock generation unit. The optical coherence tomographic imaging apparatus according to claim 1, wherein the k clock generation unit is provided inside the light source unit. The optical coherence tomographic imaging apparatus according to claim 1, wherein the frequency doubling circuit is provided outside the light source unit. The k clock generation unit is provided inside the light source unit,
The optical coherence tomographic imaging apparatus according to claim 1, wherein the frequency doubling circuit is provided outside the light source unit.

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