Patent Application
20240200928
The present invention relates to an optical coherence tomography apparatus, an imaging method, and a non-transitory computer readable medium storing an imaging program.
As a technique for performing tomographic imaging in the vicinity of a surface of a measurement object, there is an optical coherence tomography (OCT) technique. In the OCT technique, tomographic imaging in the vicinity of a surface of a measurement target object is performed when the measurement target object is irradiated with a light beam and by utilizing interference between a scattered light beam (hereinafter also referred to as a “backscattered light beam”) from the interior of the measurement target object and a reference light beam. In recent years, the OCT technique has been increasingly applied to medical diagnosis and industrial product inspection.
The OCT technique uses interference between an object light beam radiated onto and scattered by the measurement target object and scattered therefrom and the reference light to identify the position in the optical axis direction, that is, the depth direction, of a portion of the measurement target object where the object light beam is scattered (light scattering point). Structural data spatially resolved in the depth direction of the measurement target object is thus generated. In many cases, the object light beam is not reflected by 100% only off the surface of the measurement target object, but propagates to some extent into the measurement target object and is then scattered backward. Structural data spatially resolved in the depth direction on the interior of the measurement target object can thus be generated. The OCT technique is classified into a time domain (TD-OCT) scheme and a Fourier domain (FD-OCT) scheme, and the FD-OCT scheme is more promising in terms of high speed and high sensitivity. In the FD-OCT scheme, when the object light beam interferes with the reference light beam, an interference light beam spectrum over a wide wavelength band is measured, and the spectrum is Fourier transformed into structural data in the depth direction. There are two schemes for generating an interference light beam spectrum, a spectral domain (SD-OCT) scheme using a spectrometer, and a swept source (SS-OCT) scheme using a wavelength-sweeping light source.
Furthermore, scanning the measurement target object with the object light beam in the in-plane direction perpendicular to the depth direction of the measurement target object allows generation of tomographic structural data spatially resolved in the in-plane direction and the depth direction. Three-dimensional tomographic structural data on the measurement target object can thus be generated. A galvanometric mirror or any other similar device usually sweeps the object light beam to move the radiation position of the single object light beam.
The OCT technique has been put into practical use as a fundus tomography apparatus in ophthalmological diagnosis, and the application of the OCT technique to a noninvasive tomography apparatus for a variety of biological sites is being studied.
The intensity ratio between the interference light beam R5 and the interference light beam R6 changes as the wavelength of the light emitted from the wavelength-sweeping laser light source 501 changes. The photoelectrically converted output from the balanced light receiver 507 can thus be measured as an interference light beam spectrum. Measuring and Fourier transforming the interference light beam spectrum allows generation of data representing the intensity of the backscattered light beam (object light beam) at different positions in the depth direction (direction Z) (operation of generating data representing the intensity of the backscattered light beam (object light beam) in the depth direction (direction Z) at a certain position in the measurement target object 200 is hereinafter referred to as “A scan”).
Consider now the interference between an object light beam and a reference light beam having a wavelength λ and a wave number k (=2π/λ). Let LR be the optical path length from the point where the reference light beam is split by the splitter/merger 503 to the point where the reference light beam is reflected off the reference light beam mirror 506 and returns to the splitter/merger 503, and LS=LR+z0 be the optical path length from the point where the object light beam is split by the splitter/merger 503 to the point where the object light beam is backscattered at a single light scattering point in the measurement target object 200 and returns to the splitter/merger 503, the object light beam R3 and the reference light beam R4 interfere with each other at the splitter/merger 503 with a phase difference kz0+φ therebetween. The symbol φ is a constant independent of k and z0. Let ES be the amplitude of the object light beam R3, which undergoes the interference at the splitter/merger 503, and ER be the amplitude of the reference light beam R4, the intensity difference between the interference light beam R5 and the interference light beam R6, which is expressed by the following expression, is photoelectrically converted by the balanced light receiver 507.
An optical spectrum data generation unit 508 generates interference light beam spectrum data based on information on a change in the wavelength of the light emitted from the wavelength-sweeping laser 501 and information on the intensity difference between the interference light beam R5 and the interference light beam R6 from the balanced light receiver 507. Interference light beam spectrum data I(k) generated by the measurement made from a wave number k0−Δk/2 to k0+Δk/2 shows modulation with a cycle 2π/z0. The generated interference light beam spectrum data I(k) is sent from the optical spectrum data generation unit 508 to a control unit 509. Note that k0 satisfies k0=2×π/(wavelength-sweeping light source center wavelength).
The control unit 509 performs Fourier transformation on the interference light beam spectrum data I(k). An amplitude J(z) generated as a result of the Fourier transformation of the interference light beam spectrum data I(k) is expressed by the following expression:
The amplitude J(z) represents a peak expressed as a δ function (delta function) (hereafter referred to as “δ-function-like peak”) at z=z0 (and z=−z0), which reflects a light scattering position z0. Although a mirror has one light scattering point, the object light beam radiated onto the measurement target object 200 is usually backscattered successively as the object light beam propagates to some extent into the measurement target object 200 while being attenuated, so that the light scattering points, at which the object light beam is scattered, are distributed over a range from the surface of the measurement target object 200 to a certain depth. When the light scattering points are distributed from z0−Δz to z0+Δz in the depth direction, an interference light beam spectrum shows modulation with a period 2π/(z0−Δz) to modulation with 2π/(z0+Δz), which overlap with each other.
The radiation position of the object light beam R1 is moved by the radiation optical system 505, so that the measurement target object 200 is scanned. The radiation optical system 505 repeatedly performs the A-scan operation while moving the radiation position of the object light beam R1 in a scanning line direction (direction X) and connecting the measurement results to each other, thereby generating a map of the intensities of two-dimensional backscattered light beams (object light beams) in the scanning line direction and the depth direction as the tomographic structural data (operation of repeatedly performing the A-scan operation in the scanning line direction (direction X) and connecting the measurement results to each other is hereinafter referred to as “B Scan”).
Furthermore, the radiation optical system 505 repeatedly performs the B-scan operation while moving the radiation position of the object light beam R1 not only in the scanning line direction but also in a direction (direction Y) perpendicular to the scanning line, and connects the measurement results to each other, thereby generating three-dimensional tomographic structural data (operation of repeatedly performing the B-scan operation in the direction (direction Y) perpendicular to the scanning line and connecting the measurement results to each other is hereinafter referred to as “C Scan”).
When the measurement target object is a living body, it is usually difficult to measure the living body with the living body completely immobilized. It is therefore necessary to make the measurement at high speed. When the measurement needs to be made over a wide range, it is difficult to make the measurement over the wide range at high speed simply by scanning the range with a single object light beam at high speed. The Patent Literature 1 therefore proposes a configuration in which a plurality of object light beams are radiated.
A plurality of different areas of the measurement target object 200 are simultaneously scanned with the plurality of object light beams R11 and R12, whereby high-speed measurement over a wide range is achieved. On the other hand, it is necessary to provide a plurality of reference optical paths and a plurality of photodetectors or spectrometers corresponding to the object light beams R11 and R12.
Patent Literature 2 describes a configuration in which a plurality of object light beams are radiated to achieve high spatial resolution. Also in this case, a plurality of photodetectors are required although the reference optical path corresponding to the plurality of object light beams is shared.
Patent Literature 1 Japanese Unexamined Patent Application Publication No. 2010-167253
Patent Literature 2 International Publication WO2006/054116
The aforementioned optical coherence tomography apparatus, which radiates a plurality of object light beams, requires a plurality of reference optical paths and a plurality of light receivers, resulting in an increase in size and cost as compared with the case where a single object light beam is radiated.
An object of the present invention is to provide a compact optical coherence tomography apparatus, an imaging method, and a non-transitory computer readable medium storing an imaging program each capable of wide-range, high-speed measurement at low cost.
An optical coherence tomography apparatus according to a first aspect of the present invention includes a wavelength sweeping laser light source, a first splitter unit that splits a light beam emitted from the wavelength sweeping laser light source into an object light beam and a reference light beam, a second splitter unit that splits the object light beam output from the first splitter unit into a plurality of object light beams, a radiating unit that radiates the plurality of object light beams output from the second splitter unit to different positions on a surface of a measurement target object, a merging unit that causes an object light beam to interfere with the reference light beam to generate a plurality of interference light beams, the object light beam generated by merging the plurality of object light beams obtained by radiation onto the measurement target object and then scattering by the measurement target object, with one another at the second splitter unit, a measuring unit that generates information on wavelength dependence of an intensity difference among the plurality of interference light beams output from the merging unit, and a control unit that acquires structural data in a depth direction of the measurement target object based on the information relating to wavelength dependence of an intensity difference among the plurality of interference beams and generated by the measuring unit, acquires a plurality of sets of structural data in the depth direction while controlling the radiating unit to move radiation positions of the plurality of object light beams along a direction perpendicular to the depth direction of the measurement target object, and connects the plurality of sets of acquired structural data in the depth direction to each other.
An imaging method according to a second aspect of the present invention includes causing a control unit to, after an object light beam split from a light beam emitted from a wavelength sweeping laser light source is further split into a plurality of object light beams, and the plurality of object light beams are radiated to different positions on a target object, then scattered by the measurement target object, and merged with one another into an object light beam, acquire structural data in a depth direction of a measurement target object based on information on wavelength dependence of an intensity difference among a plurality of interference light beams generated when the object light beam interferes with a reference light beam split from the light beam emitted from the wavelength sweeping laser light source, causing the control unit to acquire a plurality of sets of structural data in the depth direction while moving radiation positions of the plurality of object light beams along a direction perpendicular to the depth direction of the measurement target object, and causing the control unit to connect the plurality of sets of acquired structural data in the depth direction to each other.
A non-transitory computer readable medium storing an imaging program according to a third aspect of the present invention causes a control unit to, after an object light beam split from a light beam emitted from a wavelength sweeping laser light source is further split into a plurality of object light beams, and the plurality of object light beams are radiated to different positions on a target object, then scattered by the measurement target object, and merged with one another into an object light beam, execute a process of acquiring structural data in a depth direction of a measurement target object based on information on wavelength dependence of an intensity difference among a plurality of interference light beams generated when the object light beam interferes with a reference light beam split from the light beam emitted from the wavelength sweeping laser light source, a process of acquiring a plurality of sets of structural data in the depth direction while moving radiation positions of the plurality of object light beams along a direction perpendicular to the depth direction of the measurement target object, and a process of connecting the plurality of sets of acquired structural data in the depth direction to each other.
A compact optical coherence tomography apparatus, an imaging method, and a non-transitory computer readable medium storing an imaging program each capable of wide-range, high-speed measurement at low cost can be provided.
Example embodiments of the present invention will be described below with reference to the drawings.
The light emitted from the wavelength sweeping laser light source 101 passes through the circulator 102 and is split by the splitter/merger 103 into the object light beam R1 and the reference light beam R2. The object light beam R1 is further split by the splitter/merger 104 into the first object light beam R11 and the second object light beam R12. The first object light beam R11 and the second object light beam R12 output from the splitter/merger 104 are radiated onto the measurement target object 200 via the radiation optical system 107. Specifically, the radiation optical system 107 causes the plurality of object light beams R11 and R12 to be radiated to different positions in a plane X-Y in the measurement target object 200, so that a fixed range of the measurement target object 200 is scanned with the object light beams R11 and R12.
The object light beams R11 and R12 radiated onto the measurement target object 200 are scattered backward (in the direction opposite to the radiation direction of the object light beams R11 and R12) by the measurement target object 200. The object light (backscattered light) beams R31 and R32 scattered by the measurement target object 200 pass through the radiation optical system 107, returns to the splitter/merger 104, where the light beams R31 and R32 merge with each other and return to the splitter/merger 103.
The reference light beam R2 output from the splitter/merger 103 is reflected off the reference light beam mirror 108 and returns to the splitter/merger 103.
At the splitter/merger 103, the object light beam R3 generated as a result of the merger of the object light beams R31 and R32 and incident from the splitter/merger 104 interferes with the reference light beam R4 reflected off the reference light beam mirror 108. That is, the splitter/merger 103, at which the object light beams R31 and R32 scattered by the measurement target object 200 interfere with the reference light beam R4 reflected off the reference light beam mirror 108, generates the interference light beams R51 and R52.
The interference light beam R51 is input to the balanced light receiver 109 via the circulator 102, and the interference light beam R52 is directly input to the balanced light receiver 109. Information on the intensity difference between the interference light beams R51 and R52 is then input from the balanced light receiver 109 to the optical spectrum data generation unit 110.
The balanced light receiver 109 then photoelectrically converts an intensity difference I(k) between the interference light beams R51 and R52. The balanced light receiver 109 inputs information on the photoelectrically converted intensity difference I(k) between the interference light beams R51 and R52 to the optical spectrum data generation unit 110.
The optical spectrum data generation unit 110 generates interference light beam spectrum data based on a signal input from the wavelength sweeping laser light source 101 and a signal input from the balanced light receiver 109. Specifically, information on a change in the wavelength of the light emitted from the wavelength sweeping laser light source 101 is input from the wavelength sweeping laser light source 101 to the optical spectrum data generation unit 110. Information on the intensity difference I(k) between the interference light beams R51 and R52 is further input from the balanced light receiver 109 to the optical spectrum data generation unit 110. The optical spectrum data generation unit 110 then generates the interference light beam spectrum data (dependence of the intensity difference I(k) between the interference light beams R51 and R52 on wavelength) based on the information on a change in the wavelength of the light emitted from the wavelength-sweeping laser light source 101 and the information on the intensity difference I(k) between the interference light beams R51 and R52.
The control unit 111 acquires structural data in the depth direction (direction Z) of the measurement target object 200 based on the interference light beam spectrum data generated by the optical spectrum data generation unit 110. The control unit 111 controls the radiation optical system 107 to acquire a plurality of sets of structural data in the depth direction while moving the radiation positions of the plurality of object light beams R11 and R12 along a direction (at least one of directions X and Y) perpendicular to the depth direction (direction Z) of the measurement target object 200. In other words, the control unit 111 acquires a plurality of sets of structural data in the depth direction at different positions along at least one of the directions X and Y of the measurement target object 200. The control unit 111 then connects the plurality of sets of acquired structural data in the depth direction to each other to acquire two-dimensional or three-dimensional tomographic structural data.
The aforementioned optical coherence tomography apparatus 100 according to the present invention, in which the object light beam is split by the splitter/merger 104 into the plurality of object light beams R11 and R12, which are then radiated onto the measurement target object 200, can measure the measurement target object 200 at high speed over a wide range. The object light beams R31 and R32 backscattered by the measurement target object 200 are merged by the splitter/merger 104 to generate the object light beam R3. The splitter/merger 103, at which the object light beam R3 interferes with the reference light beam R4 reflected off the reference light beam mirror 108, generates the interference light beams R51 and R52. There is therefore no need to increase the number of optical paths for the reference light beams R2 and R4 or increase the number of balanced light receivers 109. A compact optical coherence tomography apparatus 100 capable of wide-range, high-speed measurement at low cost can thus be provided.
An optical coherence tomography apparatus 100 according to a first example embodiment of the present invention will be described.
The number of optical delayers 105 and the number of fiber collimators 106 provided in the optical coherence tomography apparatus 100 may be determined in accordance with the number of split light beams produced at the splitter/merger 104, and are each not limited to the number shown
The wavelength sweeping laser light source 101 generates wavelength-swept optical pulses. Specifically, the wavelength sweeping laser light source 101 generates optical pulses each having a wavelengths that increases from 1250 nm to 1350 nm during a duration of 10 μs. The wavelength sweeping laser light source 101 generates the optical pulse repeatedly at 50 kHz every 20 μs.
The light emitted from the wavelength sweeping laser light source 101 passes through the circulator 102 and is split by the splitter/merger 103 into the object light beam R1 and the reference light beam R2. The object light beam RI is further split by the splitter/merger 104 into the first object light beam R11 and the second object light beam R12. The first object light beam R11 and the second object light beam R12 output from the splitter/merger 104 are radiated onto the measurement target object 200 via the optical delayers 105, the fiber collimators 106, and the radiation optical system 107. Specifically, the radiation optical system 107 causes the plurality of object light beams R11 and R12 to be radiated to different positions in a plane X-Y in the measurement target object 200, so that a fixed range of the measurement target object 200 is scanned with the object light beams R11 and R12. For example, the radiation optical system 107 uses a raster scan to scan the measurement target object 200.
The object light beams R11 and R12 radiated onto the measurement target object 200 are scattered backward (in the direction opposite to the radiation direction of the object light beams R11 and R12) by the measurement target object 200. The object light (backscattered light) beams R31 and R32 scattered by the measurement target object 200 pass through the radiation optical system 107, the fiber collimators 106, and the optical delayers 105, returns to the splitter/merger 104, where the light beams R31 and R32 merge with each other and further return to the splitter/merger 103.
The reference light beam R2 output from the splitter/merger 103 is reflected off the reference light beam mirror 108 and returns to the splitter/merger 103.
At the splitter/merger 103, the object light beam R3 generated as a result of the merger of the object light beams R31 and R32 and incident from the splitter/merger 104 interferes with the reference light beam R4 reflected off the reference light beam mirror 108. That is, the splitter/merger 103, at which the object light beams R31 and R32 scattered by the measurement target object 200 interfere with the reference light beam R4 reflected off the reference light beam mirror 108, generates the interference light beams R51 and R52.
The interference light beam R51 is input to the corresponding balanced light receiver 109 via the circulator 102, and the interference light beam R52 is directly input the corresponding balanced light receiver 109. The information on the intensity difference between the interference light beams R51 and R52 is then input from the balanced light receiver 109 to the optical spectrum data generation unit 110. The balanced light receiver 109 is, for example, a light receiver in which two photodiodes are connected in series to each other, and an output (a differential output) is generated at the connected point. The band over which the balanced light receiver 109 operates is lower than or equal to 1 GHz.
Consider now the interference between the object light beams R31, R32 and the reference light beam R4 having a wavelength λ and a wave number k (=2π/λ). Let LR be the optical path length of the reference light beam R2 from the point where the reference light beam R2 is split by splitter/merger 103 to the point where the reference light beam R2 is reflected off the reference light beam mirror 108 and returns to the splitter/merger 103. On the other hand, let LS1=LR+z1 be the optical path length from the point where the first object light beam R11 is split by the splitter/merger 103 to the point where the first object light beam R11 is backscattered at a single light scattering point in the measurement target object 200 and returns to the splitter/merger 103. LS2=LR+z2 be the optical path length from the point where the second object light beam R12 is split by the splitter/merger 103 to the point where the second object light beam R12 is backscattered at a single light scattering point in the measurement target object 200 and returns to the splitter/merger 103. The relative relationship between z1 and z2 is set by adjusting the optical delayers 105A and 105B. At the splitter/merger 103, the first object light beam R31 and the reference light beam R4 are superimposed on each other with a phase difference kz1+φ1 and interfere with each other. The symbol φ1 is a constant independent of k and z1. The second object light beam R32 and the reference light beam R4 are superimposed on each other with a phase difference kz2+φ2 and interfere with each other. The symbol φ2 is a constant independent of k and z2. Furthermore, the first object light beam R31 and the second object light beam R32 are superimposed on each other with a phase difference k(z1−z2)+φ3=kz3+φ3 and interfere with each other. When 0<z2<z1 is satisfied, z3=z1−z2 and φ3 are each a constant independent of k and z3.
Let ES1 be the amplitude of the object light beam R31, which interferes at the splitter/merger 103, ES2 be the amplitude of the object light beam R32, and ER be the amplitude of the reference light beam R4, and the intensity difference between the interference light beams R51 and R52 is expressed by
The balanced light receiver 109 then photoelectrically converts an intensity difference I(k) between the interference light beams R51 and R52. The balanced light receiver 109 inputs information on the photoelectrically converted intensity difference I(k) between the interference light beams R51 and R52 to the optical spectrum data generation unit 110.
The optical spectrum data generation unit 110 generates interference light beam spectrum data based on the signal input from the wavelength sweeping laser light source 101 and the signal input from the balanced light receiver 109. Specifically, the information on a change in the wavelength of the light emitted from the wavelength sweeping laser light source 101 is input from the wavelength sweeping laser light source 101 to the optical spectrum data generation unit 110. The information on the intensity difference I(k) between the interference light beams R51 and R52 is further input from the balanced light receiver 109 to the optical spectrum data generation unit 110. The optical spectrum data generation unit 110 then generates the interference light beam spectrum data based on the information on a change in the wavelength of the light emitted from the wavelength-sweeping laser light source 101 and the information on the intensity difference I(k) between the interference light beams R51 and R52. The interference light beam spectral data I(k) generated through the measurement made from the wave number k0−Δk/2 to k0+Δk/2 shows modulations with cycles 2π/z1, 2π/z2, and 2π/z3 overlapping with each other. The optical spectrum data generation unit 110 inputs the generated interference light beam spectrum I(k) to the control unit 111. Note that k0 satisfies k0=2×π/(wavelength-sweeping light source center wavelength). In the present first example embodiment, the center wavelength of the light from the wavelength sweeping laser 101 is 1300 nm, so that k0=2π×7692 cm−1.
The control unit 111 performs Fourier transformation on the interference light beam spectrum data I(k). An amplitude P(z) generated as a result of the Fourier transformation of the interference light beam spectrum data I(k) is expressed by
The amplitude P(z) represents a peak expressed by the δ function (delta function) (hereafter referred to as “δ-function-like peak”) at z=z1 (and z=−z1), which reflects the scattering point position z1, where the first object light beam R31 is scattered, and at z=z2 (and z=−z2), which reflects the scattering point position z2, where the second object light beam R32 is scattered. At the amplitude P(z), the effect of the optical interference between the first object light beam R31 and the second object light beam R32 also appears at z=z3 (and z=−z3). However, the optical intensities of the first object light beam R31 and the second object light beam R32 are smaller than the optical intensity of the reference light beam R4, the component produced by the optical interference between the first object light beam R31 and the second object light beam R32 is small. Symbols a1, a2, and a3 are predetermined constants determined in advance under a variety of conditions.
The control unit 111 also controls each unit of the optical coherence tomography apparatus 100.
For example, the control unit 111 controls the radiation optical system 107 to cause the plurality of object light beams R11 and R12 to be radiated to different positions in a plane X-Y in the measurement target object 200. The control unit 111 further controls the cycle and speed at which the measurement target object 200 is scanned with the light from the radiation optical system 107.
The control unit 111 further controls the radiation optical system 107 to repeatedly perform the A-scan operation while moving the radiation positions of the object light beams R11 and R12 in the scanning line direction (at least one of the directions X and Y). The control unit 111 then connects a plurality of measurement results generated by repeatedly performing the A-scan operation while moving the radiation positions of the object light beams R11 and R12 in the scanning line direction. The control unit 111 thus generates two-dimensional tomographic structural data (operation of repeatedly performing the A-scan operation in the scanning line direction (at least one of the directions X and Y) and connecting the measurement results to each other is hereafter referred to as “B-scan”).
Furthermore, the control unit 111 corrects the tomographic structural data in
The control unit 111 further controls the radiation optical system 107 to repeatedly perform the B-scan operation while moving the radiation positions of the object light beams R11 and R12 are radiated not only in the scanning line direction but in a direction perpendicular to the scanning line. The control unit 111 then connects a plurality of measurement results to each other, which are generated by repeatedly performing the B-scan operation while moving the radiation positions of the object light beams R11 and R12 in the scanning line direction and the direction perpendicular to the scanning line. The control unit 111 thus generates three-dimensional tomographic structural data in the directions X, Y, and Z (operation of repeatedly performing the B-scan operation in the scanning line direction and a direction perpendicular to the scanning line and connecting the measurement results to each other is hereafter referred to as “C-scan”).
The control unit 111 executes the process of connecting a plurality of sets of three-dimensional tomographic structural data to each other, which are generated by sweeping the plurality object light beams R11 and R12.
The control unit 111 includes a CPU (central processing unit) that is not shown, a storage unit that is not shown, and other components. The CPU then executes a program stored in the storage unit to achieve all processes executed by the control unit 111.
The program stored in each storage unit of the control unit 111 contains codes executed by the CPU to achieve the corresponding process executed by the control unit 111. The storage unit includes any storage apparatus capable of, for example, storing the program and a variety pieces of information used in the process executed by the control unit 111. The storage apparatus is, for example, a memory.
The program described above can be stored by using any of a variety of types of non-transitory computer readable medium and supplied to a computer. The non-transitory computer readable medium include a variety of types of tangible storage medium. Examples of the non-transitory computer readable medium include a magnetic storage medium (floppy disk, magnetic tape, and hard disk drive, for example), a magneto-optical storage medium (magneto-optical disk, for example), a CD-ROM (read only memory), CD-R, CD-R/W, and a semiconductor memory (mask ROM, PROM (programmable ROM), an EPROM (erasable PROM), a flash ROM, a RAM (random access memory), for example). The program may instead be supplied to a computer via any of a variety of types of transitory computer readable medium. Examples of the transitory computer readable medium include an electric signal, an optical signal, and an electromagnetic wave. The transitory computer readable medium can supply the program to a computer via a wired communication path, such as an electric wire and an optical fiber, or a wireless communication path.
According to the aforementioned optical coherence tomography apparatus 100 according to the first example embodiment, in which the object light beam is split by the splitter/merger 104 into the plurality of object light beams R11 and R12, which are then radiated onto the measurement target object 200, can measure the measurement target object 200 at high-speed over a wide range. The object light beams R31 and R32 backscattered by the measurement target object 200 are merged by the splitter/merger 104 to generate the object light beam R3. The splitter/merger 103, at which the object light beam R3 interferes with the reference light beam R4 reflected off the reference light beam mirror 108, generates the interference light beams R51 and R52. There is therefore no need to increase the number of optical paths for the reference light beams R2 and R4 or increase the number of balanced light receivers 109. A compact optical coherence tomography apparatus 100, an imaging method, and a non-transitory computer readable medium storing an imaging program each capable of wide-range, high-speed measurement at low cost can thus be provided.
The control unit 111 controls the radiation optical system 107 to acquire a plurality of sets of structural data in the depth direction while moving the radiation positions of the plurality of object light beams R11 and R12 along two directions perpendicular to the depth direction (direction Z) of the measurement target object 200 and perpendicular to each other (directions X and Y). Three-dimensional tomographic structural data can therefore be acquired.
The splitter/merger 103 causes the object light beam R3, which is the merger of the object light beams R31 and R32, to interfere with the reference light beam R4 reflected off the reference light beam mirror 108 to generate the interference light beams R51 and R52. It is therefore unnecessary to add extra components that cause the object light beam R3 and the reference light beam R4 to interfere with each other.
The plurality of optical delayers 105 provided between the splitter/merger 104 and the radiation optical system 107 delay the plurality of object light beams R11 and R12 so as to have different optical path lengths from the point where the plurality of object light beams R11 and R12 are split by the splitter/merger 104 to the point where the plurality of object light beams R11 and R12 are backscattered by the measurement target object 200 and return to the splitter/merger 104. The control unit 111 then corrects the tomographic structural data based on the delays z1 and z2, created by the optical delayers 105, of the optical path lengths of the plurality of object light beams R11 and R12 split by the splitter/merger 104. The control unit 111 can thus connect the plurality of sets of structural data acquired in the depth direction to each other while moving the radiation positions of the plurality of object light beams R11 and R12.
An optical coherence tomography apparatus 300 according to a second example embodiment of the present invention will be described.
The wavelength sweeping laser light source 101, the circulator 102, the splitter/merger 103, the splitter/merger 104, the optical delayers 105, the fiber collimators 106, the radiation optical system 107, the optical spectrum data generation unit 110, and the control unit 111 provided in the optical coherence tomography apparatus 300 according to the second example embodiment have the same functions as those of the wavelength sweeping laser light source 101, the circulator 102, the splitter/merger 103, the splitter/merger 104, the optical delayers 105, the fiber collimators 106, the radiation optical system 107, the optical spectrum data generation unit 110, and the control unit 111 provided in the optical coherence tomography apparatus 100 according to the first example embodiment and therefore have the same reference characters, and the same functions will not be described.
The light emitted from the wavelength sweeping laser light source 101 is split by the splitter/merger 103 into the object light beam R1 and the reference light beam R2. The object light beam R1 passes through the circulator 102 and is further split by the splitter/merger 104 into the first object light beam R11 and the second object light beam R12. The first object light beam R11 and the second object light beam R12 output from the splitter/merger 104 are radiated onto the measurement target object 200 via the optical delayers 105, the fiber collimators 106, and the radiation optical system 107. Specifically, the radiation optical system 107 causes the plurality of object light beams R11 and R12 to be radiated to different positions in a plane X-Y in the measurement target object 200, so that a fixed range of the measurement target object 200 is scanned with the object light beams R11 and R12.
The object light beams R11 and R12 radiated onto the measurement target object 200 are scattered backward (in the direction opposite to the radiation direction of the object light beams R11 and R12) by the measurement target object 200. The object light (backscattered light) beams R31 and R32 scattered by the measurement target object 200 pass through the radiation optical system 107, the fiber collimators 106, and the optical delayers 105, returns to the splitter/merger 104, where the light beams R31 and R32 merge with each other, and the merged light beam is guided to the coherent light receiver 301 via the circulator 102.
The reference light beam R2 output from the splitter/merger 103 is guided to the coherent light receiver 301.
At the coherent light receiver 301, a first splitter 311 splits the object light beam R3 generated as a result of the merger of the object light beams R31 and R32 incident from the splitter/merger 104 into object light beams R71 and R72. The object light beams R71 and R72 from the first splitter 311 are guided to a first merger 321 and a second merger 322, respectively. A second splitter 312 splits the reference light beam R2 into the reference light beams R21 and R22. The reference light beams R21 and R22 from the second splitter 312 are guided to the first merger 321 and the second merger 322, respectively. At the first merger 321, the object light beam R71 and the reference light beam R21 interfere with each other, and at the second merger 322, the object light beam R72 and the reference light beam R22 interfere with each other. The optical path length from the second splitter 312 to the first merger 321 and the optical path length from the second splitter 312 to the second merger 322 are so set that the difference therebetween is half the wavelength (λ/2). The phase difference between the object light beam R71 and the reference light beam R21, which interfere with each other at the first merger 321, and the phase difference between the object light beam R72 and the reference light beam R22, which interfere with each other at the second merger 322, is therefore π. The first merger 321 inputs the two light beam outputs to a first balanced light receiver 331 (first measurer), and the first balanced light receiver 331 photoelectrically converts the intensity difference between the two light beams. The first balanced light receiver 331 outputs the intensity difference between the photoelectrically converted two light beams to the optical spectrum data generation unit 110. The second merger 322 inputs the two light beam outputs to a second balanced light receiver 332 (second measurer), and the second balanced light receiver 332 photoelectrically converts the intensity difference between the two light beams. The second balanced light receiver 332 outputs the intensity difference between the photoelectrically converted two light beams to the optical spectrum data generation unit 110.
Consider now the interference between the object light beams R71, R72 and the reference light beams R21, R22 having the wavelength λ and the wave number k (=2π/λ). Let LR be the optical path length of the reference light beam R2 from the point where the reference light beam R2 is split by splitter/merger 103 to the point where the reference light beam R2 propagates to the first merger 321. In this case, the optical path length of the reference light beam R2 from the point where the reference light beam R2 is split by splitter/merger 103 to the point where the reference light beam R2 propagates to the second merger 322 is LR+(λ/2). On the other hand, let LS1=LR+z1 be the optical path length from the point where the first object light beam R11 is split by the splitter/merger 103 to the point where the first object light beam R11 is backscattered at a single light scattering point in the measurement target object 200 and propagates to the first merger 321 or the second merger 322. Let LS2=LR+z2 be the optical path length from the point where the second object light beam R12 is split by the splitter/merger 103 to the point where the second object light beam R12 is backscattered at a single light scattering point in the measurement target object 200 and propagates to the first merger 321 or the second merger 322. z1 and z2 are set by adjusting the optical delayers 105A and 105B. At the first merger 321, the first object light beam R31 and the reference light beam R2 are superimposed with each other with the phase difference kz1+φ1 and interfere with each other. At the second merger 322, the first object light beam R31 and the reference light beam R2 are superimposed with each other with a phase difference kz1+φ1+π and interfere with each other. The symbol φ1 is a constant independent of k and z1. At the first merger 321, the second object light beam R32 and the reference light beam R2 are superimposed with each other with the phase difference kz2+φ2 and interfere with each other. At the second merger 322, the second object light beam R32 and the reference light beam R2 are superimposed with each other with a phase difference kz2+φ2+π/2 and interfere with each other. The symbol φ2 is a constant independent of k and z2. Furthermore, the first object light beam R31 and the second object light beam R32 are superimposed with each other at the splitter/merger 104 with the phase difference k(z1−z2)+φ3=kz3+φ3 and interfere with each other. The symbol φ3 is a constant independent of k and z3.
Using the first balanced light receiver 331 and the second balanced light receiver 332 allows detection of a state in which the object light beams R31 and R32 interfere with the reference light beam R2 with a phase difference of π/2 (quadrature phase). Under the definitions that ES1 represents the amplitude of the object light beam R31, ES2 represents the amplitude of the object light beam R32, and ER represents the amplitude of the reference light beam R2, which interfere with each other at the coherent light receiver 301, the optical spectrum data generation unit 110 generates interference light beam spectrum data expressed by
based on the information on a change in the wavelength of the light emitted from wavelength sweeping laser light source 101 and information on the interference light beam intensity difference measured by each of the first balanced light receiver 331 and the second balanced light receiver 332. The interference light beam spectral data I(k) generated through the measurement made from the wave number k0−Δk/2 to k0+Δk/2 shows modulations with the cycles 2π/z1, 2π/z2, and 2π/z3 overlapping with each other. The optical spectrum data generation unit 110 inputs the interference light beam spectrum data I(k) to the control unit 111.
The control unit 111 performs Fourier transformation on the interference light beam spectrum data I(k). The amplitude P(z) generated as a result of the Fourier transformation of the interference light beam spectrum data I(k) is expressed by
The amplitude P(z) shows the δ-function-like peak at z=z1, which reflects the scattering point position z1 of the first object light beam R31, and at z=z2, which reflects the scattering point position z2 of the second object light beam R32. At the amplitude P(z), the effect of the optical interference between the first object light beam R31 and the second object light beam R32 also appears at z=z3. However, the optical intensities of the first object light beam R31 and the second object light beam R32 are smaller than the optical intensity of the reference light beam R2, the component produced by the optical interference between the first object light beam R31 and the second object light beam R32 is small.
In the first example embodiment, performing Fourier transformation on the interference light beam spectrum at a single light scattering point provides two δ-function-like peaks at two locations symmetrical with respect to z=0, whereas in the second example embodiment using the coherent light receiver 301, the δ-function-like peak appears at only one location. Therefore, in the first example embodiment, it is necessary to adjust the optical path length of the object light beam in such a way that z1 and z2 are either positive or negative values, whereas in the second example embodiment, it is not necessary that z1 and z2 are limited to either positive or negative values. The range over which the optical path length of the object light beam can be set is thus expanded.
The control unit 111 performs filtering operation to suppress modulation in the vicinity of the cycle 2π/z3 that appears in the interference light beam spectrum I(k) and then performs Fourier transformation, as in the first example embodiment. Components in the vicinity of z3 can thus be suppressed, as shown in
The processes in the B scan and the processes in the C scan performed by the control unit 111 are also the same as those in the first example embodiment and will therefore not described.
The optical coherence tomography apparatus 300 according to the second example embodiment described above provides the same effects as those provided by the optical coherence tomography apparatus 100 according to the first example embodiment. In the coherent light receiver 301, the optical path length from the second splitter 312 to the first merger 321 and the optical path length from the second splitter 312 to the second merger 322 are so set that the difference therebetween is half the wavelength (λ/2). The phase difference between the object light beam R71 and the reference light beam R21, which interfere with each other at the first merger 321, and the phase difference between the object light beam R72 and the reference light beam R22, which interfere with each other at the second merger 322, therefore differs from each other by π/2. The amplitude P(z) produced when the control unit 111 performs Fourier transformation on the interference light beam spectrum data I(k) therefore shows the δ-function-like peak at z=z1, which reflects the scattering point position z1 of the first object light beam R31, and at z=z2, which reflects the scattering point position z2 of the second object light beam R32. That is, in the first example embodiment, performing Fourier transformation on the interference light beam spectrum at a single light scattering point provides two δ-function-like peaks at two locations symmetrical with respect to z=0, whereas in the second example embodiment, the δ-function-like peak appears at only one location. Therefore, in the first example embodiment, the optical delayers 105 need to adjust the optical path length of the object light beam in such a way that z1 and z2 are either positive or negative values, whereas in the second example embodiment, it is not necessary that z1 and z2 are limited to either positive or negative values. The range over which the optical path length of the object light beam can be set is thus expanded.
An optical coherence tomography apparatus 400 according to a third example embodiment of the present invention will be described.
The second example embodiment has been described with reference to the configuration in which the two object light beams R11 and R12 are radiated, and the number of object light beams radiated onto the measurement target object 200 is not limited to two. In fact, in the third example embodiment, the reference optical path and the first balanced light receiver 331 and the second balanced light receiver 332 are shared in a configuration in which four object light beams are radiated to different areas of the measurement target object 200, as shown in
An optical coherence tomography apparatus 700 according to a fourth example embodiment of the present invention will be described.
The wavelength sweeping laser light source 101, the circulator 102, the splitter/merger 103, the splitter/merger 104, the optical delayers 105, the fiber collimators 106, the radiation optical system 107, the optical spectrum data generation unit 110, and the control unit 111 provided in the optical coherence tomography apparatus 700 according to the fourth example embodiment have the same functions as those of the wavelength sweeping laser light source 101, the circulator 102, the splitter/merger 103, the splitter/merger 104, the optical delayers 105, the radiation optical system 107, the optical spectrum data generation unit 110, and the control unit 111 provided in the optical coherence tomography apparatus 100 according to the first example embodiment and therefore have the same reference characters, and the same functions will not be described.
The light emitted from the wavelength sweeping laser light source 101 passes through the circulator 102 and is split by the splitter/merger 103 into the object light beam R1 and the reference light beam R2. The object light beam R1 is further split by the splitter/merger 104 into the first object light beam R11 and the second object light beam R12. The first object light beam R11 and second object light beam R12 output from the splitter/merger 104 are radiated onto the measurement target object 200 via the optical delayers 105, the SMF-MCF connection unit 121, the MCF 122, the fiber collimator 123, and the radiation optical system 107. Specifically, the radiation optical system 107 causes the plurality of object light beams R11 and R12 to be radiated to different positions in a plane X-Y in the measurement target object 200, so that a fixed range of the measurement target object 200 is scanned with the object light beams R11 and R12.
The object light beams R11 and R12 radiated onto the measurement target object 200 are scattered backward (in the direction opposite to the radiation direction of the object light beams R11 and R12) by the measurement target object 200. The object light (backscattered light) beams R31 and R32 scattered by the measurement target object 200 pass through the radiation optical system 107, the fiber collimator 123, the MCF 122, the MCF-SMF connection unit 121, and the optical delayers 105, returns to the splitter/merger 104, where the light beams R31 and R32 merge with each other and return to the splitter/merger 103.
The reference light beam R2 output from the splitter/merger 103 is reflected off the reference light beam mirror 108 and returns to the splitter/merger 103.
At the splitter/merger 103, the object light beam R3 generated as a result of the merger of the object light beams R31 and R32 and incident from the splitter/merger 104 interferes with the reference light beam R4 reflected off the reference light beam mirror 108. That is, the splitter/merger 103, at which the object light beams R31 and R32 scattered by the measurement target object 200 interfere with the reference light beam R4 reflected off the reference light beam mirror 108, generates the interference light beams R51 and R52.
The interference light beam R51 is input to the corresponding balanced light receiver 109 via the circulator 102, and the interference light beam R52 is directly input the corresponding balanced light receiver 109. Information on the intensity difference between the interference light beams R51 and R52 is then input from the balanced light receiver 109 to the optical spectrum data generation unit 110.
The optical spectrum data generation unit 110 generates the interference light beam spectrum data based on the information on a change in the wavelength of the light emitted from the wavelength-sweeping laser light source 101 and the information on the intensity difference I(k) between the interference light beams R51 and R52, as in the first example embodiment. The optical spectrum data generation unit 110 then inputs the generated interference light beam spectrum to the control unit 111.
The control unit 111 performs filtering operation on the interference light beam spectrum and then performs Fourier transformation, as in the first example embodiment. According to the procedure described above, data representing the intensities of a plurality of object light beams backscattered at different positions in the depth direction (direction Z) of the measurement target object 200 are generated by interference with a common reference light beam (A scan).
The processes in the B scan and the processes in the C scan performed by the control unit 111 are also the same as those in the first example embodiment and will therefore not described.
The optical coherence tomography apparatus 700 according to the fourth example embodiment described above provides the same effects as those provided by the optical coherence tomography apparatus 100 according to the first example embodiment. In addition, the MCF 122 and the fiber collimator 123 can be used to configure a compact light radiation unit.
The present application invention has been described above with reference to the embodiments, but the invention of the present application is not limited thereto. A variety of changes can be made to the configurations and details of the invention of the present application to the extent that the changes are understandable to those skilled in the art within the scope of the invention.
A compact optical coherence tomography apparatus 100, an imaging method, and a non-transitory computer readable medium storing an imaging program each capable of wide-range, high-speed measurement at low cost can be provided.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/013050 | 3/24/2020 | WO |
