JP2017156184A - Optical coherence tomography imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OCT device that prevents an influence due to return light to a light source occurring when generating an A-scan trigger with respect to a tomographic image without requiring an addition of components leading to increase in cost.SOLUTION: An optical coherence tomography imaging device comprises: a wavelength sweep light source that sweeps a wavelength of light to be emitted; a coherence unit that uses the light emitted from the wavelength sweep light source and within a wavelength range from a third wavelength to a fourth wavelength to make light from an inspection optical path and reference optical path interfere; an information acquisition unit that acquires information on a subject from a coherence signal created on the basis of interfered light; a wavelength filter that reflects light having a fifth wavelength; and a detection unit that detects reflection light from the wavelength filter, and creates a trigger signal. The information acquisition unit is configured to acquire the information on the subject from the coherence signal on the basis of the trigger signal. A time when light of the fourth and fifth wavelengths are emitted sets to be T4 to T5, a speed of light sets to be c, and an optical path length of an optical path connecting the wavelength sweep light source to the wavelength filter sets to be D, the optical path length D satisfies a relation of T4-T5<2D/c.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical coherence tomography apparatus.

  An apparatus using optical coherence tomography (OCT) (hereinafter referred to as an OCT apparatus) is a device that can acquire a tomographic image of a subject non-invasively with light using a technique of low coherence interference. Although the OCT apparatus is used in various fields, it is particularly useful in the medical field because the burden on the patient can be reduced because a non-invasive tomographic image of a subject can be observed.

  Particularly in the field of ophthalmology, observation of the eye to be examined from the outside is the main diagnostic method, and therefore, the OCT apparatus is rapidly spreading.

  OCT is roughly divided into two methods called time domain OCT and Fourier domain OCT. Further, among Fourier domain OCT, two methods of Spectral Domain OCT (Spectral Domain OCT: SD-OCT) and Swept Source OCT (Swept Source OCT: SS-OCT) are known.

  In an apparatus using SS-OCT (hereinafter referred to as an SS-OCT apparatus), a light source (wavelength swept light source) that changes the wavelength over a wide time band is used, and the reference light and the measurement light that has been irradiated and reflected on the subject. The light intensity of the interference light that interferes with the (probe light) is acquired at each wavelength. Then, Fourier transform is performed on the interference signal based on the interference light, and the frequency component included in the time waveform of the interference light is analyzed. Thereby, the position of the reflecting surface in the depth direction of the subject on the optical axis of the probe light is calculated, and a tomographic image of the subject is constructed based on the position of the reflecting surface.

  When performing discrete Fourier transform of an interference signal based on interference light, it is particularly required to sample the interference signal at uniform frequency intervals. As a sampling clock for sampling an interference signal at a uniform frequency interval, a signal called a k-clock signal as described in Non-Patent Document 1 is used in SS-OCT.

  As a wavelength tunable laser used in the SS-OCT apparatus, a light source that periodically and repeatedly emits a series of lights whose wavelengths change with time. This period corresponds to an A-scan period, that is, an A-scan rate, which is an operation for obtaining information on a tomographic slice in the SS-OCT apparatus. In the SS-OCT apparatus, sampling using the k-clock signal is performed on the basis of a signal indicating timing related to one cycle of A-scan.

  This reference signal is referred to as an A-scan trigger (depending on the literature, it uses a different name such as gating pulse (Non-patent document 1), trigger signal (Non-patent document 2), sweep trigger, A-trigger, etc. There is also.)

  There are two known methods for generating an A-scan trigger. One is a method in which a circuit that drives a wavelength sweeping mechanism of a wavelength swept light source (wavelength variable light source) generates and outputs a trigger signal synchronized with the drive signal. The other is based on light of a specific wavelength emitted from a wavelength swept light source using a wavelength filter mechanism such as a narrow band filter or a fiber Bragg grating (FBG) as described in Non-Patent Documents 1 and 2. This is a method for generating a trigger signal.

  Regarding the former, the operation of the wavelength sweep mechanism is often unstable with respect to an electrical signal (drive signal) that drives the wavelength sweep mechanism of the wavelength sweep light source. This is considered to be caused by a problem that the wavelength sweep operation is delayed with respect to the drive signal due to mechanical characteristics of the wavelength sweep mechanism and environmental changes. Therefore, when the A-scan trigger is generated by the method, the operation of the wavelength swept light source may be unstable even with respect to the A-scan trigger generated in synchronization with the drive signal. For this reason, the A-scan trigger generated by the method may become unstable in time with respect to light whose wavelength emitted from the light source changes.

  On the other hand, in the latter method, light having a specific wavelength is detected from the light having a different wavelength, which is emitted as a result of driving the wavelength sweeping mechanism, and an A-scan trigger is generated. Therefore, even if the drive of the wavelength sweep mechanism is unstable with respect to the drive signal, it becomes possible to generate a trigger signal stably for light of a specific wavelength.

  As a specific method of the latter method, in Non-Patent Document 1, an SS-OCT apparatus is configured using a fiber Bragg grating (FBG) that is a member that reflects light at a specific wavelength.

  In this method, light having a specific wavelength reflected by the FBG is received by a photodetector and converted into an electric signal to generate an A-scan trigger. In the method described in Non-Patent Document 1, an optical circulator is used to suppress the reflected light from the FBG from returning to the wavelength swept light source.

  As is well known, when light enters the laser light source from the outside, the intensity of the light emitted from the light source fluctuates, and the emitted light becomes a noisy laser beam. It is for suppressing.

  If an interference signal based on light with large noise is detected, a tomographic image formed by the OCT apparatus also becomes a large noise image. Therefore, it becomes impossible to describe a detailed shape in the tomographic image, and it becomes impossible to provide a tomographic image useful for medical use.

  Here, the optical circulator has only the role of suppressing the increase in the noise of the light emitted from the light source due to the reflected light from the FBG provided to generate the A-scan trigger returning to the light source. Therefore, the optical circulator is only for compensating for the disadvantages when optically generating the A-scan trigger, and does not improve the performance of the OCT apparatus itself. Therefore, the optical circulator is a component that leads to an increase in cost in the OCT apparatus, apart from an element that improves the performance of the apparatus itself.

S. Yun, G. Tearney, J. de Boer, N. Iftimia, and B. Bouma, “High-speed optical frequency-domain imaging,” Opt. Express 11, 2953-2963 (2003). B. Vakoc, S. Yun, J. de Boer, G. Tearney, and B. Bouma, “Phase-resolved optical frequency domain imaging,” Opt. Express 13, 5483-5493 (2005).

  The present invention provides an OCT apparatus that prevents the influence of return light to a light source that occurs when an A-scan trigger is generated on a tomographic image without requiring the addition of components that lead to an increase in cost.

  An optical coherence tomographic imaging apparatus according to an embodiment of the present invention includes a wavelength swept light source that sweeps the wavelength of emitted light in a wavelength range from a first wavelength to a second wavelength, An inspection optical path for irradiating the light, a reference optical path, and an interference unit for interfering light from the inspection optical path and the reference optical path, the interference of the light being emitted from the wavelength swept light source, Interference generated by using the light in the wavelength range from the third wavelength to the fourth wavelength in the wavelength range from the second wavelength to the second wavelength, and the interference generated based on the interfered light An information acquisition unit that acquires information on the subject from the signal, a wavelength filter that reflects light having a fifth wavelength in the wavelength range from the first wavelength to the second wavelength, and the wavelength swept light source Light is incident on the interference part And a dividing unit that divides the light incident on the wavelength filter, a detection unit that detects reflected light from the wavelength filter and generates a trigger signal based on the detected reflected light, and the information acquisition unit includes: Based on the trigger signal, the information of the subject is acquired from the interference signal, and the time when the wavelength swept light source emits the light of the fourth wavelength is T4, and the light of the fifth wavelength is emitted. The optical path length D satisfies the relationship of T4−T5 <2D / c, where T5 is T5, the speed of light is c, and the optical path length D of the optical path connecting the wavelength swept light source and the wavelength filter.

  The OCT apparatus according to the present invention can prevent the influence of the return light to the light source that is generated when the A-scan trigger is generated with respect to the tomographic image without requiring the addition of a component that leads to cost increase.

1 shows a schematic configuration example of an OCT apparatus according to an embodiment of the present invention. The relationship between the wavelength of the light radiate | emitted from the wavelength sweep light source in one Embodiment of this invention, and time is shown. It is a figure for demonstrating timings, such as an A-scan trigger in a OCT apparatus by Example 1 of this invention, a k-clock signal, and an interference signal. It is a figure for demonstrating timings, such as an A-scan trigger, a k-clock signal, and an interference signal, in the OCT apparatus by Example 2 of this invention. The example of schematic structure of the OCT apparatus by the modification of one Embodiment of this invention is shown.

  Hereinafter, exemplary embodiments and examples for carrying out the present invention will be described in detail with reference to the drawings. However, dimensions, materials, shapes, relative positions of components, and the like described in the following embodiments and examples 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 between the drawings to indicate the same or functionally similar elements.

  Hereinafter, an optical coherence tomography apparatus, that is, an OCT apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

  As described above, when the A-scan trigger is optically generated, the reflected light from the wavelength filter returns to the light source, so that the intensity of light emitted from the light source varies. Acquiring an OCT interference signal using light whose intensity has changed causes noise to be superimposed on the tomographic image of the subject.

  Therefore, in the present embodiment, a tomographic image is formed by the light source in one A-scan period before the reflected light from the wavelength filter (FBG) used to generate the A-scan trigger returns to the light source. The emission of light in the wavelength range to be used is terminated. Accordingly, an A-scan trigger is optically generated without requiring the addition of a component such as an optical circulator, which leads to an increase in cost, and the influence of the return light to the light source generated when the A-scan trigger is generated on the tomographic image is prevented. be able to.

  A schematic configuration of the OCT apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 shows a schematic configuration example of the OCT apparatus according to the present embodiment.

  The OCT apparatus 100 according to the present embodiment includes a wavelength swept light source 101, a dividing unit 102, an FBG 103, an OCT interferometer 104, a photodetector 105, optical fibers 106 and 107, a detector 108, an arithmetic processing unit 109, and a display unit 110. ing.

  The wavelength swept light source 101 continuously sweeps the emitted light from the short wavelength toward the long wavelength. The wavelength swept light source 101 is connected to the dividing unit 102 via the optical fiber 106, and the light emitted from the wavelength swept light source 101 enters the dividing unit 102 via the optical fiber 106. Further, the wavelength sweep light source 101 is electrically connected to the arithmetic processing unit 109. The wavelength swept light source 101 generates a k-clock signal 130 based on the emitted light and outputs it to the arithmetic processing unit 109.

  The configuration of the wavelength swept light source is not limited to the configuration of sweeping the light emitted from the short wavelength toward the long wavelength. For example, the wavelength swept light source may continuously sweep the emitted light from the long wavelength to the short wavelength, or may combine these to perform the wavelength sweep back and forth within a certain wavelength range.

  The k-clock signal may be generated based on light emitted from the wavelength swept light source by an arbitrary k-clock generating unit connected to the wavelength swept light source. The k-clock generation unit can be configured using a known circuit or the like that generates a k-clock signal, and sends the generated k-clock signal to the arithmetic processing unit 109. In this case, since the k-clock generation unit sends the k-clock signal to the arithmetic processing unit 109, the wavelength swept light source does not have to be connected to the arithmetic processing unit 109.

  The division unit 102 is an optical fiber coupler with a division ratio of 95: 5, and is connected to a wavelength swept light source 101, an FBG (fiber Bragg grating) 103, an OCT interferometer 104, and a photodetector 105 through an optical fiber. The dividing unit 102 divides the light incident from the wavelength swept light source 101, guides 95% of the incident light to the OCT interferometer 104, and guides 5% of the light to the FBG 103. Further, the dividing unit 102 divides the light incident from the FBG 103, guides 95% of the incident light to the photodetector 105, and guides 5% of the light to the wavelength swept light source 101. The dividing unit 102 may be configured using a beam splitter instead of the optical fiber coupler. Also, the split ratio is not limited to 95: 5, and an optical fiber coupler or beam splitter having an arbitrary split ratio can be used.

  The FBG 103 (wavelength filter) is connected to the dividing unit 102 via an optical fiber, and selectively reflects light in a specific wavelength band among incident light from the dividing unit 102. The light reflected by the FBG 103 is guided to the dividing unit 102 as reflected light RL. In addition, the incident light from the dividing part 102 that has not been reflected passes through the FBG 103 and is emitted from the end of the optical fiber.

  The photodetector (detection unit) 105 is connected to the division unit 102 via the optical fiber 107, and the light of 95% of the reflected light RL from the FBG 103 is guided. The photodetector 105 is electrically connected to the arithmetic processing unit 109. When the photodetector 105 detects the light (reflected light RL) guided from the dividing unit 102, the photodetector 105 generates an A-scan trigger 120 (trigger signal) and outputs it to the arithmetic processing unit 109. As the photodetector 105, an arbitrary photodetector such as a photodiode can be used. Note that the photodetector 105 can also be connected to the arithmetic processing unit 109 via a pulse shaping circuit or the like for adjusting the pulse waveform of the A-scan trigger. In this case, the detection unit that detects the reflected light and generates the A-scan trigger 120 includes the photodetector 105 and a pulse shaping circuit.

  The OCT interferometer 104 is a general Mach-Zehnder interferometer. The OCT interferometer 104 is connected to the dividing unit 102 and the detector 108 via an optical fiber. The OCT interferometer 104 generates interference light (OCT interference light) between the reflected light from the subject O (eye to be examined) and the light that has passed through the reference optical path, using the light guided from the dividing unit 102, and a detector. To 108.

  More specifically, the OCT interferometer 104 is provided with an inspection optical path 1041, a reference optical path 1042, and an interference unit 1043. The interference unit 1043 is provided with an OCT division unit 1044 and an OCT interference unit 1045. The OCT dividing unit 1044 divides the light incident from the dividing unit 102 into measurement light and reference light, and makes them enter the inspection light path 1041 and the reference light path 1042, respectively. The inspection optical path 1041 irradiates the subject O with incident light, and guides reflected light from the subject O to the interference unit 1043. The reference light path 1042 guides the light to the interference unit 1043 by irradiating the reference light with the incident light. The OCT interference unit 1045 generates OCT interference light by causing the light from the inspection optical path 1041 and the reference optical path 1042 to interfere with each other, and outputs the OCT interference light to the detector 108. As the OCT splitting unit 1044 and the OCT interfering unit 1045, an optical fiber coupler or a beam splitter having an arbitrary splitting ratio can be used.

  The OCT interferometer is not limited to a Mach-Zehnder interferometer. As the OCT interferometer, for example, a Michelson interferometer may be used, or any interferometer that can be used as an interferometer in the OCT apparatus can be used.

  The detector 108 (OCT detector) is connected to the OCT interferometer 104 and the arithmetic processing unit 109, detects the interference light output from the OCT interferometer 104, converts it into an electrical signal, and generates an interference signal (OCT interference signal). To the arithmetic processing unit 109. The detector 108 may be configured to simply detect interference light in accordance with the configuration of the OCT interferometer 104, or may detect two interference lights having different phases output from the OCT interferometer 104. In addition, it may be configured to detect the differential between the two interference lights. When the detector 108 detects the differential of the interference light, the noise based on the non-interference component of the interference light can be reduced, and the signal-to-noise ratio of information related to the subject O based on the interference signal ( S / N ratio) can be improved.

  The arithmetic processing unit 109 (information acquisition unit) is connected to the wavelength swept light source 101, the detector 108, and the photodetector 105. The arithmetic processing unit 109 samples the OCT interference signal input from the OCT interferometer 104 using the k-clock signal 130 input from the wavelength swept light source 101 as a sampling clock. In particular, the arithmetic processing unit 109 grasps the A-scan timing in the OCT apparatus 100 based on the A-scan trigger 120 input from the photodetector 105. Then, the arithmetic processing unit 109 performs sampling of the OCT interference signal using the k-clock signal 130 based on this timing. Thereafter, the arithmetic processing unit 109 forms a tomographic image of the subject based on the signal acquired by sampling, and outputs the tomographic image to the display unit 110. The arithmetic processing unit 109 may be an arithmetic unit configured inside the OCT apparatus 100 using an MPU, CPU, memory, or the like, or may be an arithmetic apparatus using a general-purpose computer separately from the OCT apparatus 100. In the following, a series of operations for generating an interference signal based on light from a light source and forming a tomographic image of a subject in the OCT apparatus is referred to as an OCT operation.

  The display unit 110 is connected to the arithmetic processing device 109 and displays a tomographic image input by the arithmetic processing device 109, information on the subject, and the like. The display unit 110 may be an arbitrary display unit provided in the OCT apparatus 100, or may be an arbitrary display apparatus as another device connected to the OCT apparatus 100.

  Hereinafter, in the OCT apparatus 100 according to the present embodiment, the operation for optically generating the A-scan trigger 120 and preventing the influence of the return light to the wavelength swept light source 101 generated when the A-scan trigger 120 is generated for the tomographic image is described. explain.

  First, in the OCT apparatus 100 having the above-described configuration, the light of 5% of the reflected light RL is returned from the dividing unit 102 to the wavelength sweep light source 101 by the FBG 103. As a result, intensity variation occurs in the light emitted from the wavelength swept light source 101.

  On the other hand, in the OCT apparatus 100, the light in the wavelength range used for forming the tomographic image by the wavelength swept light source 101 in one period of A-scan by the timing when the reflected light RL by the FBG 103 returns to the wavelength swept light source 101. Is exited. According to this operation, even if the intensity fluctuation of the emitted light from the wavelength swept light source 101 based on the return light occurs, the light in which the intensity fluctuation occurs is not used for the formation of the tomographic image. Noise to the image can be prevented. Specifically, in order to achieve such an operation, the optical path length between the wavelength sweep light source 101 and the FBG 103, the wavelength sweep range (wavelength range used for the OCT operation) of the wavelength sweep light source 101, and the time taken for the wavelength sweep. And the reflection wavelength band of the FBG 103 are adjusted.

  Hereinafter, the adjustment of these relationships will be described with reference to FIG. FIG. 2 shows an example of the emitted light emitted from the wavelength swept light source 101. In FIG. 2, the horizontal axis indicates time, and the vertical axis indicates the light intensity of the emitted light. In FIG. 2, a graph of the light intensity of the emitted light when there is no influence 201 of the return light from the wavelength swept light source 101 is indicated by a two-dot chain line.

  The wavelength sweep light source 101 used in the OCT apparatus 100 continuously sweeps the wavelength of the emitted light from a short wavelength to a long wavelength in a predetermined wavelength range. Here, the wavelength at which the wavelength sweep is started is λ1, the wavelength λ2 at which the wavelength sweep is terminated, the wavelength range used for the OCT operation is λ3 to λ4, and the center wavelength of the reflection wavelength band of the FBG 103 is λ5.

  Further, since the wavelength swept light source 101 sweeps the wavelength of the emitted light with time, the wavelength can be replaced with time. Therefore, the time when the wavelength sweep light source 101 starts the wavelength sweep is T1, the time when the wavelength sweep is finished is T2, the time when the light of wavelength λ3 used for the OCT operation is emitted is T3, and the time when the light of wavelength λ4 is emitted. T4 can be set. Similarly, the time during which the wavelength swept light source 101 emits light having the center wavelength λ5 in the reflection wavelength band of the FBG 103 can be T5. Furthermore, the interval between T5 and T4 (T4-T5) is ΔT.

In such a case, in order to prevent the return light to the wavelength swept light source 101 based on the reflected light of the FBG 103 from affecting the tomographic image, the optical path length between the wavelength swept light source 101 and the FBG 103 so as to satisfy the following formula 1. And the relationship such as the characteristics of the FBG 103 are adjusted. In Equation 1, the optical path length between the wavelength swept light source 101 and the FBG 103 is denoted by D, and the speed of light is denoted by c.
ΔT <2D / c Equation 1

  In Equation 1, 2D / c represents a time during which the light emitted from the wavelength sweep light source 101 is reflected by the FBG 103 and returns to the wavelength sweep light source 101. That is, Equation 1 shows the relationship between the time 2D / c and the time ΔT from when the light of wavelength λ5 reflected by the FBG 103 is emitted until the light of wavelength λ4 used for the OCT operation is emitted.

  When the relationship shown in Equation 1 is satisfied, the emission of light in the wavelength range λ3 to λ4 used for the OCT operation is already completed at the time when the light having the wavelength λ5 returns to the wavelength swept light source 101. There is no variation in the intensity of light used for operation.

  That is, as shown in FIG. 2, since the influence 201 of the emitted light due to the return light to the wavelength swept light source 101 based on the reflected light of the FBG 103 appears after the emission of the light of wavelength λ4, the light used for the OCT operation It is possible to prevent fluctuations in the strength of the.

  Therefore, in the present embodiment, the optical path length between the wavelength swept light source 101 and the FBG 103, the wavelength sweep range of the wavelength swept light source 101 (wavelength range used for the OCT operation), and the wavelength sweep are satisfied so as to satisfy the relationship shown in Expression 1. The relationship between the time and the reflection band of the FBG 103 is adjusted. As a result, the OCT apparatus 100 according to the present embodiment prevents the use of light superimposed with noise caused by the reflected light from the FBG 103 in the OCT operation without using an optical member such as an optical circulator, which leads to an increase in cost. A tomographic image can be obtained.

  Further, the wavelength sweep operation in the wavelength sweep light source 101 may have a time zone in which the wavelength sweep operation becomes unstable even in the time zone in which light is emitted due to the wavelength sweep mechanism. That is, the temporal wavelength change of the light emitted from the wavelength swept light source 101 may deviate from the assumed wavelength change based on the configuration of the wavelength swept light source 101. When the wavelength sweep operation of the wavelength swept light source 101 is unstable, the wavelength and frequency of the k-clock signal 130 generated from the light emitted from the wavelength swept light source 101 are also unstable. For this reason, when the A-scan trigger 120 is input to the arithmetic processing unit 109 during a time period in which the wavelength sweep operation is unstable, the range of the interference signal to be sampled is assumed due to the instability of the k-clock signal 130. It fluctuates from the signal range. For this reason, a tomographic image of the subject O based on the sampled interference signal may not be accurately formed.

Therefore, in the OCT apparatus 100, the emitted light in the time band / wavelength band in which the k-clock signal 130 is stable, that is, the wavelength sweep of the wavelength swept light source 101 is stable, is used to form a tomographic image by the OCT operation. It is desirable. Here, the wavelength range in which the wavelength sweep operation is stable is defined as wavelengths λv1 to λv2. Further, assuming that the time when the wavelength swept light source 101 emits the light with the wavelength λv1 is Tv1, and the time when the light with the wavelength λ2 is emitted is Tv2, the wavelength range λv1 to λv2 corresponds to the time zone 210 (time zone Tv1 to Tv2). . In this case, it is desirable that the time zone 220 (time zones T3 to T4) corresponding to the wavelength range λ3 to λ4 used for the OCT operation satisfy the following Expression 2.
Tv1 <= T3 <T4 <= Tv2 Equation 2

  In the present specification, the wavelength sweep of the wavelength swept light source 101 is assumed to be stable from the configuration of the wavelength swept light source 101 in terms of the temporal wavelength change of the light emitted from the wavelength swept light source 101. It means following the change in wavelength.

Also, when the A-scan trigger 120 is generated based on the emitted light in the time zone in which the wavelength sweep operation is unstable, the sampling timing reference becomes unstable. Therefore, as in the case where the k-clock signal 130 is unstable, the range of the interference signal to be sampled varies from the assumed signal range. Therefore, it is desirable that the time T5 at which the light with the wavelength λ5 for generating the A-scan trigger 120 is emitted also satisfies the following Expression 3.
Tv1 <= T5 <= Tv2 Equation 3

  When the wavelength sweep operation of the wavelength sweep light source 101 is almost stable from the start to the end of the wavelength sweep, it can be considered that Tv1 = T1 and Tv2 = T2. Therefore, in this case, the light emitted from the wavelength swept light source 101 during the time period T1 to T2 can be used for the OCT operation and also used to generate the A-scan trigger 120. Can do.

Further, when the return light of wavelength λ5 returns to the light source in the time zone 220 for emitting light in the wavelength range used for the subsequent A-scan of the OCT operation, the return light for the subsequent OCT operation of the A-scan , Noise in the tomographic image due to the influence of the return light occurs. Here, it is assumed that T is the repetition period of the wavelength sweep, that is, the period of the wavelength sweep until the wavelength sweep light source 101 emits light of wavelength λ1, and in the subsequent wavelength sweep operation, the light of wavelength λ1 is emitted again. Further, the wavelength at which the subsequent wavelength sweep is started is λ1 ′, and the wavelength at which the stable wavelength sweep is started in the subsequent wavelength sweep is λv1 ′. Further, the time for the wavelength swept light source 101 to emit light with wavelength λ1 ′ is T1 ′, and the time for the light with wavelength λv1 ′ to be emitted is Tv1 ′. In this case, it is desirable that the time 2D / c during which the light emitted from the wavelength swept light source 101 is reflected by the FBG 103 and returns to the wavelength swept light source 101 satisfies the following Expression 4.
2D / c <T− (T5−T1) + (Tv1′−T1 ′) Equation 4

Here, since the time interval Tv1′-T1 ′ of the wavelength sweep operation by the wavelength sweep light source 101 is equal to the time interval Tv1-T1, the time interval Tv1′-T1 ′ can also be regarded as the time interval Tv1-T1. Therefore, it is desirable that the time 2D / c satisfies the following formula 5.
2D / c <T− (T5−Tv1) (5)

From the above formulas 1 to 5, it is desirable that the OCT apparatus 100 satisfy the relationship represented by the following formula 6 in consideration of the time zone in which the wavelength sweep operation is unstable and the subsequent A-scan of the OCT operation. .
ΔT <2D / c <T− (T5−Tv1) Equation 6

  When the relationship shown in Expression 6 is satisfied, the OCT apparatus 100 can be configured in consideration of the time zone in which the wavelength sweep operation becomes unstable and the subsequent A-scan of the OCT operation. That is, in this case, the optical path length between the wavelength swept light source 101 and the FBG 103, the wavelength sweep range of the wavelength swept light source 101 (wavelength range used for the OCT operation), and the wavelength sweep are set so as to satisfy the relationship shown in Expression 6. The relationship between the time and the reflection band of the FBG 103 is adjusted. As a result, the OCT 100 prevents the use of light superimposed with noise caused by the reflected light from the FBG 103 in the OCT operation without using an optical member such as an optical circulator, which leads to an increase in cost. Can be obtained.

In addition, when the wavelength sweep operation of the wavelength sweep light source 101 is almost stable from the start to the end of the wavelength sweep, it can be regarded as Tv1 = T1. It is possible to fulfill the function.
ΔT <2D / c <T− (T5−T1) Equation 7

  As described above, the OCT apparatus 100 according to the present embodiment includes the wavelength swept light source 101 that sweeps the wavelength of the emitted light in the wavelength range from the first wavelength λ1 to the second wavelength λ2. The OCT apparatus 100 further includes an inspection optical path 1041 that irradiates the subject O with light from the wavelength swept light source 101, a reference optical path 1042, and an interference unit 1043 that interferes with light from the inspection optical path 1041 and the reference optical path 1042. . The light interference uses light in the wavelength range from the third wavelength λ3 to the fourth wavelength λ4 in the wavelength range from the first wavelength λ1 to the second wavelength λ2 emitted from the wavelength swept light source 101. Done. Further, the OCT apparatus 100 includes an arithmetic processing unit 109 that acquires information on the subject O from an interference signal generated based on the interfered light, and a wavelength range from the first wavelength λ1 to the second wavelength λ2. An FBG 103 that reflects light having the fifth wavelength λ5 is provided. In addition, the OCT apparatus 100 includes a dividing unit 102 that divides the light from the wavelength swept light source 101 into light incident on the interference unit 1043 and light incident on the FBG 103. Furthermore, the OCT apparatus 100 includes a detection unit that detects reflected light from the FBG 103 and generates an A-scan trigger 120 based on the detected reflected light. The arithmetic processing device 109 acquires information on the subject O from the interference signal based on the A-scan trigger 120. Here, the time when the wavelength swept light source 101 emits the light with the fourth wavelength λ4 is T4, the time when the light with the fifth wavelength λ5 is emitted is T5, the speed of light is c, and the wavelength swept light source 101 and the FBG 103 are The optical path length D of the optical path to be connected is assumed. In this case, the optical path length D satisfies the relationship of Equation 1.

  With such a configuration, in the OCT apparatus 100, it is possible to prevent the use of light superimposed with noise caused by reflected light from the FBG 103 in the OCT operation without using an optical member such as an optical circulator, which leads to an increase in cost. A tomographic image can be obtained.

  In order for the optical path length D to satisfy the relationship of Formula 1, the optical path length D between the wavelength sweep light source 101 and the FBG 103, the wavelength sweep range (wavelength range used for OCT operation) of the wavelength sweep light source 101, and the time required for wavelength sweep And the reflection band of the FBG 103 can be adjusted. With respect to this point, these relationships may be determined in advance by adjusting other optical elements, the wavelength path D may be adjusted, or the wavelength sweep range of the wavelength sweep light source 101 and the wavelength sweep time may be adjusted. , The reflection band of the FBG 103 (wavelength filter) may be adjusted.

  In the OCT apparatus 100 according to the present embodiment, the time interval from the time T5 to the time when a part of the light having the fifth wavelength λ reflected by the FBG 103 returns to the wavelength swept light source 101 is from time T4 to time T5. Longer than the time interval. That is, after the wavelength swept light source 101 finishes emitting light in the wavelength range used for the OCT operation, the light having the fifth wavelength λ5 reflected by the FBG 103 returns to the wavelength swept light source 101. Therefore, the light in the wavelength range used for the OCT operation is not affected by the light reflected by the FBG 103.

  In the wavelength range from the first wavelength λ1 to the second wavelength λ2, the wavelength range in which the wavelength swept light source 101 stably performs the wavelength sweep is defined as the sixth wavelength λv1 to the seventh wavelength λv2. Further, a time for the wavelength swept light source 101 to emit the light with the sixth wavelength λv1 is Tv1, and a time for the light with the seventh wavelength λv2 to be emitted is Tv2. At this time, the relationship between the optical path length between the wavelength sweep light source 101 and the FBG 103, the wavelength sweep range of the wavelength sweep light source 101, the time taken for the wavelength sweep, and the reflection band of the FBG 103 is adjusted so as to satisfy the expressions 1 to 6. . As a result, the OCT apparatus 100 can be configured in consideration of the time zone in which the wavelength sweep operation becomes unstable and the A-scan next to OCT.

[Example 1]
Hereinafter, an example of the OCT apparatus 100 according to the above embodiment that forms a tomographic image using an A-scan trigger will be described with reference to FIGS. 1 and 3. In addition, since each component of the OCT apparatus by a present Example is the same as that of the said embodiment, it demonstrates using the same referential mark.

  FIG. 3 shows the correlation between the light intensity of the emitted light from the wavelength swept light source 101 of this embodiment and time, and the correlation between the optical frequency and time. FIG. 3 shows a timing chart of the return light (A-scan trigger return light) returning from the A-scan trigger 120 and the FBG 103 to the wavelength sweep light source 101 and the k-clock signal 130. Further, FIG. 3 shows the correlation between the signal intensity of the OCT interference signal based on the light emitted from the wavelength swept light source 101 and time. In addition, regarding the correlation between the light intensity of the emitted light and time in FIG. Regarding the correlation between optical frequency and time, the correlation of the wavelength range used for generating the OCT interference signal is represented by a solid line, and the correlation of the wavelength range not used for generating the OCT interference signal is occupied by a two-dot chain line. . Further, regarding the correlation between the interference signal and the time, the correlation when there is no influence 321 of the return light is indicated by a two-dot chain line.

  In this embodiment, as the wavelength sweep light source 101, a light source that sweeps the wavelength of emitted light from a short wavelength to a long wavelength and that can stably sweep from a wavelength range of 1000 nm to 1100 nm is used.

  In the field of the SS-OCT apparatus, the resolution of the tomographic image obtained by the OCT operation is improved according to the wavelength bandwidth of light used for the OCT operation, and light having a wider wavelength bandwidth is used for the OCT operation. It is known that the resolution of tomographic images is improved. Therefore, the OCT apparatus 100 according to the present embodiment stabilizes the wavelength sweep operation of the wavelength sweep light source in the wavelength range of the light used for the OCT operation so that the light having the widest possible wavelength bandwidth can be used for the OCT operation. The wavelength range of 1000 nm to 1100 nm. That is, in this embodiment, the wavelength range λ3 to λ4 of light used for the OCT operation is set to the wavelength range λv1 (1000 nm) to λv2 (1100 nm) in which the wavelength sweep operation is stable. Also, from this, the time T3 for the wavelength swept light source 101 to emit the light of wavelength λ3 is equal to the time Tv1 to emit the light of wavelength λv1, and the time T4 to emit the wavelength λ4 is equal to time Tv2 to emit the wavelength λv2. .

  Therefore, in the OCT apparatus 100 according to the present embodiment, the wavelength range of light used for the OCT operation is 1000 nm to 1100 nm. The wavelength sweep light source 101 sweeps the wavelength of the emitted light from the wavelength range of 1000 nm to 1100 nm over 4.0 μsec. Wavelength sweep with a general wavelength tunable light source (wavelength swept light source) often has a nonlinear correlation between wavelength and time, and in this embodiment also time and wavelength change are correlated in the form of a quadratic function. Use a light source.

  Further, as the FBG 103, an FBG having characteristics of a reflection band center of 1098 nm, a bandwidth of 0.3 nm, and a reflectance of 95% is used. That is, in this embodiment, the center wavelength λ5 of the reflection wavelength band of the FBG 103 is 1098 nm. The wavelength sweep light source 101 sweeps the wavelength of the emitted light from the wavelength range of 1000 nm to 1098 nm over about 3.83 μsec.

  Here, assuming that T1 is a reference time (0 μsec), T4 used in Equation 1 is 4.0 μsec, T5 is 3.83 μsec, and ΔT is 0.17 μsec from the configuration of the wavelength swept light source 101 and the FBG 103. Therefore, from Equation 1, the required optical path length D between the wavelength swept light source 101 and the FBG 103 is 25.5 m or more. Therefore, in this embodiment, the optical path length between the wavelength swept light source 101 and the FBG 103 is 30 m.

  Specifically, in the configuration of the OCT apparatus 100 as shown in FIG. 1, the light emitted from the wavelength swept light source 101 is guided to the dividing unit 102 through the optical fiber 106 having a refractive index of 1.45 and a length of 18 m. . The light guided to the dividing unit 102 is guided from the dividing unit 102 to the FBG 103 via an optical fiber having a refractive index of 1.45 and a length of about 2.7 m. With this configuration, the FBG 103 is disposed at a position approximately 30 m away from the wavelength swept light source 101.

  In this case, light emitted from the wavelength swept light source 101, reflected by the FBG 103, and returned to the wavelength swept light source 101 reciprocates in the optical path length D (30 m) between the wavelength swept light source 101 and the FBG 103, and therefore is approximately from T5. After 0.20 μsec, return to the wavelength swept light source 101.

  Here, as shown in FIG. 3, in the OCT apparatus 100 of the present embodiment, the emission of light in the wavelength range λ3 to λ4 used for the OCT operation is completed at T4 after 0.17 μsec from T5. . Therefore, even if the return light reflected by the FBG 103 returns to the wavelength swept light source 101 and the emitted light from the wavelength swept light source 101 is affected by the return light 301, the emitted light is not used for the OCT operation. Therefore, in the OCT apparatus 100 according to the present embodiment, an OCT interference signal is generated using a stable A-scan trigger 120 that is optically generated with an inexpensive configuration without using an optical member such as an optical circulator that leads to an increase in cost. Can be acquired.

  In the OCT apparatus 100 according to the present embodiment, the time periods T3 to T4 in which light used for the OCT operation is emitted are equal to the time periods Tv1 to Tv2 in which the wavelength sweep operation of the wavelength sweep light source 101 is stable. Furthermore, as can be understood from the correlation between the light intensity of the emitted light and the time in FIG. 3, the influence of the return light appears before the subsequent A-scan operation. Therefore, the OCT apparatus 100 according to the present embodiment has a configuration that satisfies Expressions 1 to 6. Therefore, the OCT apparatus 100 prevents the use of light superimposed with noise caused by the reflected light from the FBG 103 in the OCT operation without using an optical member such as an optical circulator, which leads to an increase in cost. An image can be obtained.

  The light for generating the A-scan trigger 120 is reflected by the FBG 103, passes through the dividing unit 102, and then is guided to the photodetector 105 through the optical fiber 107 of about 2 m. The photodetector 105 detects the guided light and generates an electrical signal based on the detected light. The A-scan trigger 120 is generated when the generated electrical signal passes through a pulse shaping circuit (not shown) or the like. The generated A-scan trigger 120 is input to the arithmetic processing unit 109. Here, the A-scan trigger 120 reaches the arithmetic processing unit 109 in about 110 nsec from the time T5 when the light for generating the A-scan trigger 120 is emitted.

  The other light emitted from the wavelength swept light source 101 and passed through the dividing unit 102 is guided to the OCT interferometer 104. The optical path length passing through the OCT interferometer 104 is approximately 5 m immediately after the dividing unit 102. Therefore, the light emitted from the wavelength swept light source 101 reaches the detector 108, and the total optical path length from the wavelength swept light source 101 to the dividing unit 102 is about 26 m and the optical path length of the OCT interferometer 104 is about 5 m. Following the optical path, it takes about 100 nsec. Thereafter, it is converted into an electrical signal by the detector 108 and input to the arithmetic processing unit 109 as an OCT interference signal. Since it takes time to input the conversion and arithmetic processing unit 109, it takes about 110 nsec until the light emitted from the wavelength swept light source 101 is input to the arithmetic processing unit 109 as an OCT interference signal.

  The k-clock signal 130 output from the wavelength swept light source 101 is also input to the arithmetic processing unit 109. The OCT apparatus 100 uses the k-clock signal 130 as a sampling clock to acquire an OCT interference signal. Note that the k-clock signal 130 is electrically delayed using an arbitrary delay circuit or the like so as to be synchronized with the OCT interference signal input from the OCT interferometer 104 to the arithmetic processing unit 109, and then transmitted to the arithmetic processing unit 109. Entered. For this reason, the OCT interference signal and the k-clock signal based on the light emitted from the wavelength sweep light source 101 at a certain time are simultaneously input to the arithmetic processing unit 109.

  Here, regarding the time relationship when each of the OCT interference signal and the A-scan trigger 120 is input to the arithmetic processing unit 109, it is assumed that both take the same time as the time for converting the light into the electric signal. Then, as described above, the same time is required from when the light for generating the OCT interference signal and the A-scan trigger 120 is emitted until the OCT interference signal and the A-scan signal are input to the arithmetic processing unit 109. It can be regarded as such. Note that any of the signals can be electrically delayed using an arbitrary delay circuit or the like so that they are input to the arithmetic processing unit 109 in synchronization.

  Therefore, as shown in FIG. 3, in the OCT apparatus 100 according to the present embodiment, the A-scan trigger 120 is input to the arithmetic processing unit 109 in the time slot 320 (T3 + 110 nsec to T4 + 110 nsec) in which the OCT interference signal should be acquired. Will be. In FIG. 3, the timing chart of the A-scan trigger 120, the k-clock signal 130, and the interference signal indicates the timing when each signal is input to the arithmetic processing unit 109.

  Next, an operation for forming a tomographic image using the A-scan trigger 120 as a reference for the sampling timing of the OCT interference signal in the OCT apparatus 100 according to the present embodiment will be described with reference to FIG. In the timing chart of the k-clock signal in FIG. 3, the k-clock signal 130 based on the light emitted in the time period (T3 to T4) in which the wavelength sweep light source 101 can stably perform the wavelength sweep is shown. A time zone 310 input to the arithmetic processing unit 109 is shown. Further, a point added to the k-clock signal 130 in the time zone 310 is a k-clock signal 130 as a sampling clock for data used for forming a tomographic image. It shows that there is. The interference signal timing chart of FIG. 3 shows a time zone 320 in which the OCT interference signal is to be acquired, that is, a time zone 320 in which the interference signal used for the OCT operation is input to the arithmetic processing unit 109.

  As shown in FIG. 3, the A-scan trigger 120 is input to the arithmetic processing unit 109 just before the end of the time zone 320 in which the interference signal used for the OCT operation is input to the arithmetic processing unit 109. Therefore, in the arithmetic processing unit 109, after the A-scan trigger 120 is input, data is acquired retroactively.

  For this purpose, in the OCT apparatus 100 according to the present embodiment, the OCT interference signal is sampled using the k-clock signal 130 as a sampling clock, and the sampled data is stored in a memory (not shown). Then, with reference to the timing at which the A-scan trigger 120 is input to the arithmetic processing unit 109, pre-trigger sampling is performed to acquire data before the timing by a predetermined number of clocks counted from the timing. In FIG. 3, a time zone 311 for performing pre-trigger sampling is shown, and six k-clock signals 130 are shown in the time zone 311. In this embodiment, pre-trigger sampling is performed for six k-clock signals 130, but the number of k-clocks for which pre-trigger sampling is performed can be any number according to the configuration of the OCT apparatus 100. .

  Data acquisition by pre-trigger sampling can be performed by reading data stored in a memory. Note that the data can be identified by an arbitrary method when data is read by a predetermined number of clocks. For example, when storing data, a number is associated and stored, and a predetermined number of previous sampling data can be read from the input timing of the A-scan trigger 120 based on the number. In addition, the data stored in the memory may be managed using a stack, and may be appropriately read.

  Further, in the OCT apparatus 100 according to the present embodiment, after the A-scan trigger 120 is input to the arithmetic processing unit 109 and before the end of the time zone 320, the k-clock signal 130 is output from the arithmetic processing unit 109. Is input. For this reason, the OCT apparatus 100 also performs post-trigger sampling for acquiring data after a predetermined number of clocks counted from the timing based on the timing at which the A-scan trigger 120 is input to the arithmetic processing unit 109. Do. Data acquisition by post-trigger sampling can be performed in the same manner as general sampling based on the input k-clock signal 130 after the A-scan trigger 120 is input. Similarly to the pre-trigger sampling, the post-trigger sampling may be performed by reading the data after storing it in a memory (not shown).

  In FIG. 3, a time zone 312 in which post-trigger sampling is performed is shown, and two k-clock signals 130 are shown in the time zone 312. In this embodiment, post-trigger sampling is performed for two k-clock signals 130, but the number of k-clocks for which post-trigger sampling is performed should be an arbitrary number according to the configuration of the OCT apparatus 100. Can do.

  In the OCT apparatus 100 according to the present embodiment, it is possible to generate a tomographic image of the subject O by performing signal processing such as Fourier transform on the data obtained by performing pre-trigger sampling and post-trigger sampling in this way.

  As described above, in the OCT apparatus 100 according to the present embodiment, the fifth wavelength λ5 is set within the wavelength range from the third wavelength λ3 to the fourth wavelength λ4. Even in this case, by configuring the OCT apparatus 100 so as to satisfy Formula 1, the same operation as in the above embodiment can be achieved.

  In addition, the arithmetic processing unit 109 uses the time when the A-scan trigger 120 is input to the arithmetic processing unit 109 as a reference, and samples a predetermined number of times before the input time counted from the input time. The OCT interference signal is sampled according to the clock. At the same time, the arithmetic processing unit 109 uses the time when the A-scan trigger 120 is input to the arithmetic processing unit 109 as a reference, and counts from the input time by a predetermined number after the input time. The interference signal is sampled according to a sampling clock. As a result, the arithmetic processing unit 109 can acquire information on the subject O from the interference signal and form a tomographic image of the subject O.

[Example 2]
Next, the OCT apparatus 100 according to the second embodiment will be described with reference to FIGS. 1 and 4. In addition, since each component of the OCT apparatus by a present Example is the same as that of the said embodiment, it demonstrates using the same referential mark.

  FIG. 4 is a view similar to FIG. That is, FIG. 4 shows the correlation between the light intensity of the emitted light from the wavelength swept light source 101 of this embodiment and time, and the correlation between the optical frequency and time. FIG. 4 shows a timing chart of the return light (A-scan trigger return light) returning from the A-scan trigger 120 and the FBG 103 to the wavelength sweep light source 101 and the k-clock signal 130. Further, FIG. 4 shows the correlation between the signal intensity of the OCT interference signal based on the light emitted from the wavelength swept light source 101 and time. Note that the influence 401 of the return light is shown in the correlation between the light intensity of the emitted light from the wavelength swept light source 101 and time, and the influence 421 of the return light is shown in the correlation between the signal intensity of the OCT interference signal and time.

  In the present embodiment, an example in which the relationship between T3 and T4 used in the first embodiment is changed is shown. In the first embodiment, the central wavelength λ5 of the reflection wavelength band of the FBG 103 for generating the A-scan trigger 120 is in the wavelength range λ3 to λ4 of light used for the OCT operation. This is because it is necessary to generate the A-scan trigger 120 in the time zone 310 (wavelength range in which the wavelength swept light source 101 stably sweeps the wavelength) where the k-clock signal 130 is stable as described above. It is. On the other hand, in this embodiment, the wavelength range λ3 to λ4 of the light used for the OCT operation is narrowed, and the wavelength range outside the wavelength range (corresponding to after sweeping the wavelength range to be used in terms of time) The center wavelength λ5 of the reflection wavelength band is set, and the A-scan trigger 120 is generated.

  Referring again to FIG. 1 described above, the OCT apparatus 100 according to the present embodiment will be described.

  In the OCT apparatus 100 according to the present embodiment, as in the first embodiment, a light source that sweeps light stably emitted from a short wavelength to a long wavelength from 1000 nm (λv1) to 1100 nm (λv2) is used as the wavelength swept light source 101. However, in the OCT apparatus 100 according to the present embodiment, the wavelength range of light used for the OCT operation is set as narrow as 1000 to 1098 nm. That is, in this embodiment, the wavelength range λ3 to λ4 of light used for the OCT operation is set to a wavelength range of 1000 nm to 1098 nm. Also, from this, the time T3 for the wavelength swept light source 101 to emit light having the wavelength λ3 is equal to the time Tv1 for emitting the wavelength λv1.

  The wavelength sweep light source 101 sweeps the wavelength of the emitted light from the wavelength range of 1000 nm to 1098 nm over about 3.83 μsec. Also in this embodiment, a light source having a nonlinear correlation between wavelength and time is used.

  As the FBG 103, an FBG having characteristics of a reflection band center of 1100 nm, a bandwidth of 0.3 nm, and a reflectance of 95% is used. That is, in this embodiment, the center wavelength λ5 of the reflection wavelength band of the FBG 103 is 1100 nm. For this reason, the time T5 for the wavelength swept light source 101 to emit light having the wavelength λ5 is equal to the time Tv2 for emitting the wavelength λv1. The wavelength sweep light source 101 sweeps the wavelength of the emitted light from the wavelength range of 1000 nm to 1100 nm over 4.0 μsec.

  Here, when T1 is a reference time (0 μsec), T4 used in Equation 1 is 3.83 μsec, T5 is 4.0 μsec, and ΔT is −0.17 μsec from the configuration of the wavelength swept light source 101 and the FBG 103 ( (See FIG. 4). Therefore, the required optical path length D between the wavelength swept light source 101 and the FBG 103 has a negative value.

  However, in the configuration of the OCT apparatus 100 according to the present embodiment, since there is an optical fiber that guides the light emitted from the wavelength swept light source 101 to the FBG 103, the optical path length D cannot be a negative distance.

  That is, the center wavelength λ5 of the reflection wavelength band of the FBG 103 is set outside the wavelength range λ3 to λ4 of light used for the OCT operation (corresponding to after sweeping the wavelength range to be used in terms of time). In this case, Expression 1 can be satisfied without particularly considering the optical path length D between the wavelength swept light source 101 and the FBG 103. In addition, from the configuration, at the timing when the reflected light from the FBG 103 returns to the wavelength sweep light source 101, the emission of light used for the OCT operation is completed, and even if noise is superimposed on the light emitted from the wavelength sweep light source 101, OCT Noise does not enter the tomographic image due to movement.

  As described above, in the OCT apparatus 100 according to the present embodiment, the FBG 103 is in the wavelength range λv1 to λv2 in which the wavelength swept light source 101 stably sweeps the wavelength of the light and is not used for the OCT operation. The center wavelength λ5 of the reflection wavelength band is set. Therefore, in the OCT apparatus 100 according to the present embodiment, an interference signal is acquired by using a stable A-scan trigger 120 optically generated with an inexpensive configuration without using an optical member such as an optical circulator that leads to an increase in cost. can do. Thereby, the OCT apparatus 100 can provide an OCT tomographic image in which noise caused by reflected light from the FBG 103 is not superimposed.

  Further, in the OCT apparatus 100 according to the present embodiment, the wavelength sweep operation of the wavelength swept light source 101 is stable in the central wavelength λ5 of the reflection wavelength band of the time bands T3 to T4 and the FBG 103 in which the light used for the OCT operation is emitted. It is in the time zone Tv1-Tv2. Furthermore, as can be understood from the correlation between the light intensity of the emitted light and the time in FIG. 4, the influence of the return light appears before the next A-scan operation. Therefore, the OCT apparatus 100 according to the present embodiment has a configuration that satisfies Expressions 1 to 6. Therefore, the OCT apparatus 100 prevents the use of light superimposed with noise caused by the reflected light from the FBG 103 in the OCT operation without using an optical member such as an optical circulator, which leads to an increase in cost. An image can be obtained.

  In the OCT apparatus 100 according to the present embodiment, the arrangement of each component is the same as that of the OCT apparatus according to the first embodiment. Therefore, the timing at which the OCT interference signal, the A-scan trigger 120, and the k-clock signal 130 are input to the arithmetic processing unit 109 in the OCT apparatus 100 according to the present embodiment is the same as that of the OCT apparatus according to the first embodiment.

  Next, an operation for forming a tomographic image using the A-scan trigger 120 as a reference for the sampling timing of the OCT interference signal in the OCT apparatus 100 according to the present embodiment will be described with reference to FIG. In the timing chart of the k-clock signal in FIG. 4, the k-clock signal 130 based on the light emitted in the time zone (T3 to T4) in which the wavelength sweep light source 101 can stably perform the wavelength sweep is shown. A time zone 410 input to the arithmetic processing unit 109 is shown. Further, a point added to the k-clock signal 130 in the time zone 410 is a k-clock signal 130 as a sampling clock of data used for forming a tomographic image by the k-clock signal 130 to which the point is attached. It shows that there is. The interference signal timing chart of FIG. 4 shows a time period 420 in which an interference signal used for the OCT operation is input to the arithmetic processing unit 109.

  In the OCT apparatus 100 according to the present embodiment, the emission of light for use in the OCT operation ends before the light emission time T5 of the central wavelength λ5 in the reflection wavelength band of the FBG 103. Therefore, in the OCT apparatus 100 according to the present embodiment, after the A-scan trigger 120 is input to the arithmetic processing apparatus 109, the k-clock signal 130 based on the light used for the OCT operation is input to the arithmetic processing apparatus 109. There is nothing. Therefore, the OCT apparatus 100 according to the present embodiment performs only pre-trigger sampling without performing post-trigger sampling.

  The method for performing the pre-trigger sampling is the same as the method in the first embodiment, and will be omitted. In FIG. 4, a time zone 411 for performing pre-trigger sampling is shown, and six k-clock signals 130 are shown in the time zone 411. In this embodiment, pre-trigger sampling is performed for six k-clock signals 130, but the number of k-clocks for which pre-trigger sampling is performed can be any number according to the configuration of the OCT apparatus 100. .

  In the OCT apparatus 100 according to the present embodiment, it is possible to generate a tomographic image of the subject O by performing signal processing such as Fourier transform on the data acquired by performing pre-trigger sampling in this way.

  As described above, in the OCT apparatus 100 according to the present embodiment, the fifth wavelength λ5 is set outside the wavelength range from the third wavelength λ3 to the fourth wavelength λ4, and the fifth wavelength The light of λ5 is emitted from the wavelength swept light source 101 after the light of the fourth wavelength λ4. In the OCT apparatus 100 having such a configuration, Expression 1 is satisfied as long as there is an optical path from the wavelength swept light source 101 to the FBG 103, and therefore, the same operation as in the above embodiment can be achieved.

  In addition, the arithmetic processing unit 109 uses the time when the A-scan trigger 120 is input to the arithmetic processing unit 109 as a reference, and samples a predetermined number of times before the input time counted from the input time. The OCT interference signal is sampled according to the clock. As a result, the arithmetic processing unit 109 can acquire information on the subject O from the interference signal and form a tomographic image of the subject O.

[Modification]
In the OCT apparatus 100 according to the present embodiment, the k-clock signal 130 is generated by the wavelength swept light source 101 and input to the arithmetic processing unit 109. However, the configuration for generating the k-clock signal is not limited to this. For example, the k-clock signal may be generated based on the light emitted from the wavelength swept light source 101 by a k-clock signal generating unit having an arbitrary configuration connected to the wavelength swept light source via an optical fiber. Good.

  Such a modification will be described with reference to FIG. FIG. 5 shows a schematic configuration of an OCT apparatus 200 according to such a modification. In addition, about the component of the OCT apparatus 200 by this modification, the thing similar to the component of the said embodiment is demonstrated using the same referential mark.

  The OCT apparatus 200 according to this modification is provided with a wavelength swept light source 101, a first dividing unit 102, an FBG 103, an OCT interferometer 104, a photodetector 105, a detector 108, an arithmetic processing unit 109, and a display unit 110. In addition, the OCT apparatus 200 is provided with a second dividing unit 501 and a k-clock generation unit 502.

  In the OCT apparatus 200 according to this modification, a second dividing unit 501 is provided between the first dividing unit 102 and the FBG 103. The second dividing unit 501 is an optical fiber coupler having a division ratio of 50:50, and is connected to the first dividing unit 102, the FBG 103, the photodetector 105, and the k-clock generation unit 502. The second divider 501 is further divided by the first divider 102 and further divides the light incident on the FBG 103. The second splitting unit 501 guides 50% of the light incident from the first splitting unit 102 to the FBG 103 and guides the remaining 50% of the light to the k-clock generation unit 502. The second dividing unit 501 divides the light incident from the FBG 103, guides 50% of the incident light to the photodetector 105, and the remaining 50% of the light is first divided. Guide to section 102. In this case, the first dividing unit 102 guides 5% of the light incident from the second dividing unit 501 to the wavelength sweep light source 101 and emits the remaining light from the fiber end. The second dividing unit 501 may be configured using a beam splitter instead of the optical fiber coupler. Also, the division ratio is not limited to 50:50, and an arbitrary division ratio can be used.

  The k-clock generation unit 502 generates a k-clock signal 130 based on the light incident from the second division unit 501 and outputs the k-clock signal 130 to the arithmetic processing unit 109.

  As described above, the OCT apparatus 200 according to the present modified example divides the light incident on the FBG 103 from the dividing unit 102 into the light traveling toward the FBG 103 and the other light (k-clock generating unit 502). Is provided. Even in the OCT apparatus 200 having such a configuration, the same operation as that of the OCT apparatus 100 according to the above-described embodiment can be achieved by adjusting the relationship of the optical path length and the like between the wavelength swept light source 101 and the FBG 103 so as to satisfy Formula 1. it can. In the OCT apparatus 200 according to the present modification, the return light from the FBG 103 to the wavelength swept light source 101 is split and guided by the second splitting unit 501 and the first splitting unit 102, and thus the light amount of the return light Can be reduced.

  As mentioned above, although this invention was demonstrated with reference to embodiment and an Example, this invention is not limited to the said embodiment and Example. Inventions modified within the scope not departing from the spirit of the present invention and inventions equivalent to the present invention are also included in the present invention. Moreover, each above-mentioned Example and modification can be combined suitably in the range which is not contrary to the meaning of this invention.

  101: Wavelength sweep light source, 102: Division unit, 103: FBG (wavelength filter), 104: OCT interferometer (interference unit), 105: Photo detector (detection unit), 109: Arithmetic processing device (information acquisition unit), RL: Reflected light, 120: A-scan trigger (trigger signal), RL: Reflected light, O: Subject

Claims (12)

A wavelength swept light source that sweeps the wavelength of the emitted light in a wavelength range from the first wavelength to the second wavelength;
An inspection optical path for irradiating the subject with light from the wavelength-swept light source;
A reference light path;
An interference unit that interferes light from the inspection optical path and the reference optical path, and the interference of the light is emitted from the wavelength swept light source in a wavelength range from the first wavelength to the second wavelength. An interference unit that is performed using light in a wavelength range from the third wavelength to the fourth wavelength;
An information acquisition unit for acquiring information on the subject from an interference signal generated based on the interfered light;
A wavelength filter that reflects light having a fifth wavelength in a wavelength range from the first wavelength to the second wavelength;
A splitting unit that splits light from the wavelength swept light source into light incident on the interference unit and light incident on the wavelength filter;
A detector that detects reflected light from the wavelength filter and generates a trigger signal based on the detected reflected light;
With
The information acquisition unit acquires information on the subject from the interference signal based on the trigger signal,
The time that the wavelength swept light source emits the light of the fourth wavelength is T4, the time that the light of the fifth wavelength is emitted is T5,
Let the speed of light be c,
When the optical path length D of the optical path connecting the wavelength swept light source and the wavelength filter,
The optical path length D is
T4-T5 <2D / c
An optical coherence tomographic imaging apparatus that satisfies the above relationship. In the wavelength range from the first wavelength to the second wavelength, a wavelength range in which the wavelength swept light source stably performs wavelength sweep is defined as a sixth wavelength to a seventh wavelength, and the wavelength swept light source is the first wavelength. When the time for emitting light of the third wavelength is T3, the time for emitting light of the sixth wavelength is Tv1, and the time for emitting light of the seventh wavelength is Tv2,
The time T3 and the time T4 are
Tv1 <= T3 <T4 <= Tv2
The optical coherence tomography apparatus according to claim 1, wherein the relationship is satisfied. The time T5 is
Tv1 <= T5 <= Tv2
The optical coherence tomography apparatus according to claim 2, wherein the relationship is satisfied. When the wavelength sweeping period from when the wavelength swept light source emits the light of the first wavelength to the light of the first wavelength again is T, the optical path length D is
T4-T5 <2D / c <T- (T5-Tv1)
The optical coherence tomographic imaging apparatus according to claim 2 or 3, satisfying the relationship:   5. The optical coherence tomography apparatus according to claim 1, wherein the fifth wavelength is set in a wavelength range from the third wavelength to the fourth wavelength. 6.   The fifth wavelength is set outside a wavelength range from the third wavelength to the fourth wavelength, and the light of the fifth wavelength is later than the light of the fourth wavelength. The optical coherence tomographic imaging apparatus according to claim 1, which is emitted from the wavelength-swept light source.   The information acquisition unit is based on a time when the trigger signal is input to the information acquisition unit, according to a predetermined number of sampling clocks before the input time, counting from the input time. The interference signal is sampled, and the interference signal is sampled according to a predetermined number of sampling clocks counted from the input time, and the information of the subject is acquired. The optical coherence tomographic imaging apparatus according to claim 5.   The information acquisition unit is based on a time when the trigger signal is input to the information acquisition unit, according to a predetermined number of sampling clocks before the input time, counting from the input time. The optical coherence tomography apparatus according to claim 6, wherein the interference signal is sampled to acquire information on the subject. A wavelength swept light source that sweeps the wavelength of the emitted light in a wavelength range from the first wavelength to the second wavelength;
Based on the light from the wavelength swept light source, an interference unit that interferes with the light from the inspection optical path and the light from the reference optical path that irradiates the subject,
Of the interference light obtained by interfering the light from the inspection optical path and the light from the reference optical path, from the third wavelength to the fourth wavelength in the wavelength range from the first wavelength to the second wavelength. An information acquisition unit that acquires information of the subject using interference light corresponding to light in the wavelength range of
A wavelength filter that reflects light having a fifth wavelength in a wavelength range from the first wavelength to the second wavelength;
A splitting unit that splits light from the wavelength swept light source into light incident on the interference unit and light incident on the wavelength filter;
With
The time that the wavelength swept light source emits the light of the fourth wavelength is T4, the time that the light of the fifth wavelength is emitted is T5,
Let the speed of light be c,
When the optical path length D of the optical path connecting the wavelength swept light source and the wavelength filter,
T4-T5 <2D / c
An optical coherence tomographic imaging apparatus in which the wavelength filter is configured to satisfy the above relationship.   The light according to any one of claims 1 to 9, further comprising a second dividing unit that divides light incident on the wavelength filter from the dividing unit into light traveling toward the wavelength filter and other light. Coherent tomography device. A wavelength swept light source that sweeps the wavelength of the emitted light in a wavelength range from the first wavelength to the second wavelength;
A first dividing unit that divides light from the wavelength swept light source into first light and second light;
A second divider for dividing the first light into measurement light and reference light;
An interference unit that causes the return light from the subject irradiated with the measurement light to interfere with the reference light;
Of the second light, a wavelength filter that reflects light having a fifth wavelength in a wavelength range from the first wavelength to the second wavelength;
Of the interference light obtained by interfering the return light and the reference light, light in the wavelength range from the third wavelength to the fourth wavelength in the wavelength range from the first wavelength to the second wavelength. An information acquisition unit that acquires information of the subject using interference light corresponding to
With
A time interval from a time when the wavelength swept light source emits light having the fifth wavelength to a time when a part of the light having the fifth wavelength reflected by the wavelength filter returns to the wavelength swept light source However, the wavelength filter is longer than the time interval from the time when the wavelength swept light source emits light having the fourth wavelength to the time when the wavelength swept light source emits light of the fifth wavelength. An optical coherence tomography apparatus comprising:   The optical coherence tomography apparatus according to claim 1, wherein the wavelength filter is a fiber Bragg grating.

Images