JP2011196693A - Optical coherence tomographic system and method for taking tomographic image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OCT system for forming tomographic imageS by means of Fourier transformation, using a single photodetector unit.SOLUTION: The rear stage of the interferometer constituting the OCT system is provided with a light pulse time sharing multiplication unit which delays a second binding light pulse (interference light pulse) by a predetermined delay time behind a first binding light pulse (inference light pulse), and subsequently allowing the first binding light pulse to merge with the second binding light pulse to alternately emit the first binding light pulse and the second binding light pulse.

Description

  The present invention relates to an optical coherence tomography apparatus and a tomographic imaging method.

  Optical coherence tomography (OCT) is a tomographic technique that utilizes the interference phenomenon of light, and is applied to tomographic imaging of the retina.

  There are various types of OCT, but the method of constructing a tomographic image by Fourier transforming the intensity of interference light based on the backscattered light to be measured is excellent in terms of high speed and high resolution.

JP 2006-201087 A

  However, this method requires two photodetectors that operate at high speed, which contributes to the complexity of an OCT apparatus that constructs a tomographic image by Fourier transform (hereinafter simply referred to as an OCT apparatus).

  Accordingly, an object of the present invention is to provide an OCT apparatus that can capture a tomographic image with only one light detection.

  In order to achieve the above object, according to a first aspect of the present invention, an optical pulse generating unit that sequentially generates a plurality of optical pulses having different wave numbers, and a reference optical pulse and a measuring light for each of the optical pulses. Branching into pulses, irradiating the object to be measured with the measurement light pulse to generate a backscattered light pulse, and combining the backscattered light pulse and the reference light pulse to form a first combined light pulse and a second combined light An interferometer unit that generates a pulse, and after delaying the second combined light pulse by a predetermined delay time with respect to the first combined light pulse, the first combined light pulse and the second combined light pulse Are combined, and the first combined light pulse and the second combined light pulse are alternately emitted, and the optical pulse time division multiplexing unit alternately emits the first light pulse time division multiplexing unit. The combined light pulse and the first An optical pulse intensity measuring unit for sequentially measuring the intensity of the combined optical pulse, and the difference between the intensity of the first combined optical pulse and the intensity of the second combined optical pulse measured by the optical pulse intensity measuring unit is Fourier transformed. An optical coherence tomography apparatus having a tomogram deriving unit for converting and deriving a tomogram of the measurement object is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the Fourier-transform OCT apparatus which can image | photograph a tomogram with only one photodetector can be provided.

It is the schematic explaining the structure of a 2 detector type | mold OCT apparatus. It is a figure explaining the time change of the wave number (= 2 (pi) / wavelength) of the laser beam which a variable wavelength light source produces | generates. It is a figure explaining the relationship between the intensity | strength of 1st coupling light and 2nd coupling light, and a wave number. It is a figure explaining the structure of the OCT apparatus of embodiment. It is a figure explaining the time change of the intensity | strength of the optical pulse which an optical pulse generation unit produces | generates. It is a figure explaining the time change of the wave number of the optical pulse which an optical pulse generation unit produces | generates. It is a figure explaining the time change of the intensity | strength of the optical pulse which an optical pulse time division multiplexing unit radiate | emits. It is a figure explaining the time change of the wave number of the optical pulse which an optical pulse time division multiplexing unit produces | generates.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof. It should be noted that even if the drawings are different, corresponding parts are denoted by the same reference numerals, and description thereof is omitted.

  First, the intensity of interference light based on the backscattered light to be measured is measured by two photodetectors, and the OCT apparatus that constructs a tomographic image by Fourier transforming the interference light intensity (hereinafter referred to as a two-detector type OCT). ). FIG. 1 is a schematic diagram illustrating the configuration of a two-detector OCT apparatus 2. In order to simplify the description, a case where a one-dimensional tomographic image is captured will be described.

  As shown in FIG. 1, the OCT apparatus 2 includes a variable wavelength light source 4 and an interferometer unit 6 on which light generated by the variable wavelength light source 4 enters. In addition, the OCT apparatus 2 performs an Fourier transform of the interference light intensity measurement unit 8 that measures the intensity of the interference light generated by the interferometer unit 6 and the interference light intensity measured by the interference light intensity measurement unit 8, and It has a tomographic image deriving unit 10 for constructing a tomographic image.

  FIG. 2 is a diagram for explaining the time change of the wave number (= 2π / wavelength) of the laser light generated by the variable wavelength light source 4. The horizontal axis in FIG. 2 is time. The vertical axis in FIG. 2 is the wave number. As shown in FIG. 2, the wave number of the laser light generated by the variable wavelength light source 4 increases (or decreases) at a predetermined wave number interval Δk.

  As shown in FIG. 1, the interferometer unit 6 includes an optical splitter 18 (for example, a directional coupler) that branches the laser beam 12 generated by the variable wavelength light source 4 into the measuring beam 14 and the reference beam 16. Yes. Further, the interferometer unit 6 includes a light irradiation / supplementation unit 25 that irradiates the measurement light 16 onto the measurement object 20 and supplements the backscattered light 22 generated by the measurement light 16 being backscattered by the measurement object 20. Yes. In addition, the interferometer unit 6 combines the reference light 14 and the backscattered light 22 to emit the first combined light 24 and the second combined light 26 (for example, the branching ratio is 1: 1). A directional coupler).

  The first combined light 24 and the second combined light 26 emitted from the optical coupler 28 are interference light in which the backscattered light 22 and the reference light 14 are combined. As described later, the phases of the intensity changes of the first coupled light 24 and the second coupled light 26 are shifted by π.

  The optical pulse intensity measurement unit 8 includes a first photodetector 32 (eg, a pin photoresist diode) that outputs a signal (eg, photocurrent) corresponding to the intensity of the first coupled light 24, and a second coupling. A second photodetector 34 (for example, a pin photoresist diode) that outputs a signal (for example, a photocurrent) corresponding to the intensity of the light 26; The optical pulse intensity measuring unit 8 has a differential amplifier 36 that amplifies the difference between the output of the first photodetector 32 and the output of the second photodetector 34. The optical pulse intensity measurement unit 8 includes an AD converter 38 that performs analog-digital conversion on the output of the differential amplifier 36. As described above, the optical pulse intensity measurement unit 8 measures the difference in intensity between the first combined light 24 and the second combined light 26.

  The tomographic image deriving unit 10 (for example, a personal computer loaded with a program for operating the OCT apparatus 2) has the intensity of the first combined light 24 and the second combined light 26 measured by the optical pulse intensity measuring unit 8. The difference is Fourier transformed with respect to the wave number, and its absolute value (or its square) is calculated. This absolute value is a function of position coordinates, and represents a depth direction distribution of the intensity of backscattered light to be measured, that is, a one-dimensional tomographic image.

  As described above, the two-detector-type OCT apparatus measures the intensity difference between two interference lights whose phases are shifted by π with the two light detections 32 and 34, and constructs a tomographic image by Fourier transforming the intensity difference. To do. Thus, the S / N ratio (signal to noise ratio) of the tomographic image can be improved by Fourier-transforming the intensity difference between the two interference lights whose phases are shifted by π.

  Each optical member is connected by an optical fiber indicated by a solid line in FIG. Further, the optical fiber through which the measurement light 16 propagates and the optical fiber through which the backscattered light 22 propagates are connected to the optical path to the measurement target 20 by the optical circulator 30 of the light irradiation / supplementation unit 25.

  Hereinafter, the reason why the S / N ratio of the tomographic image is improved by Fourier transforming the intensity difference of the interference light whose phase is shifted by π will be described. For simplicity of explanation, it is assumed that the measuring object 20 has only one light reflecting surface (or back scattering surface).

  FIG. 3 is a diagram for explaining the relationship between the intensity and the wave number of the first coupled light 24 and the second coupled light 26. The vertical axis represents the intensity (power) of the first combined light 24 and the second combined light 26. The horizontal axis represents the wave numbers of the first coupled light 24 and the second coupled light 26. As described above, the wave number of the laser light generated by the variable wavelength light source 4 increases (or decreases) by a predetermined wave number interval Δk. This wave number interval Δk is sufficiently narrower than the wave number scanning range. Therefore, the intensity of each coupled light changes substantially continuously as shown in FIG.

  As shown in FIG. 3, the light intensity 40 of the first coupled light 24 and the intensity 42 of the second coupled light 26 have a vibration component and a direct current component that change as a cosine function with respect to the wave number. Here, the vibration component 44 of the first coupled light 24 and the vibration component 46 of the second coupled light 26 are shifted in phase by π. On the other hand, the direct current component of the first coupled light and the direct current component of the second coupled light are equal. Accordingly, when the intensity 42 of the second coupled light 26 is subtracted from the intensity 40 of the first coupled light 24, the DC component is removed and the vibration component is doubled. As a result, noise associated with the DC component is removed, while the vibration component, that is, the signal intensity is doubled, so that the S / N ratio (signal to noise ratio) of the tomographic image is improved.

  The square root of the intensity of the vibration components 44 and 46 of the interference light is proportional to the intensity of the backscattered light. Further, the period of the vibration components 44 and 46 of the interference light is the depth from the surface of the measurement target 20 (more precisely, the difference between the sum of the optical path lengths of the measurement light 16 and the backscattered light 22 and the optical path length of the reference light 14). ) In inverse proportion. Therefore, the distribution of the backscattering intensity in the depth direction of the measuring object 20 can be obtained by Fourier transforming the vibration components 44 and 46 with respect to the wave number and deriving the absolute value thereof (Patent Document 1).

(1) Device Configuration FIG. 4 is a diagram for explaining the configuration of the OCT device 48 of the present embodiment.

  As shown in FIG. 4, the OCT apparatus 48 of the present embodiment includes an optical pulse generation unit 50, an interferometer unit 52, an optical pulse time division multiplexing unit 54, an optical pulse intensity measurement unit 56, and a tomographic image. A derivation unit 58 is provided. Each optical member in FIG. 4 (including the optical pulse generation unit 50 and the optical pulse intensity measurement unit 56) is connected by an optical fiber indicated by a solid line.

(i) Optical Pulse Generation Unit The optical pulse generation unit 50 is an apparatus having, for example, an SSG-DBR laser (Super Structure Grating-Distributed Bragg Reflector Laser) and a drive unit thereof. The optical pulse generation unit 50 drives this SSG-DBR laser in response to the command 60 of the tomographic image deriving unit 58 to generate an optical pulse.

  FIG. 5 is a diagram for explaining the temporal change in the intensity of the optical pulse generated by the optical pulse generation unit 50. The horizontal axis is time. The vertical axis represents the light intensity (power). FIG. 6 is a diagram for explaining the time change of the wave number of the optical pulse generated by the optical pulse generation unit 50. The horizontal axis is time. The vertical axis is the wave number.

  As shown in FIGS. 5 and 6, the optical pulse generation unit 50 generates an optical pulse 62 in which the wave number increases (or decreases) by a predetermined wave number interval Δk every time a predetermined time Tp elapses. That is, the optical pulse generation unit 50 sequentially generates a plurality of optical pulses having a predetermined wave number interval Δk with a predetermined time Tp (hereinafter referred to as an optical pulse time interval). Here, the time interval Tp of the optical pulse 62 is, for example, twice the time width PW of the optical pulse (full width at half maximum; hereinafter referred to as the optical pulse time width).

  When the scanning of the predetermined wave number range is completed, the optical pulse generation unit 50 resumes the wave number scanning in accordance with the command 60 of the tomogram deriving unit 58. One wave number scanning is repeated each time the irradiation position of the measurement light pulse moves little by little, as will be described later.

  Here, the intensity of the optical pulse 62 is preferably constant regardless of the wave number. The time interval Tp of the optical pulse 62 is most preferably twice the optical pulse time width PW. This is because in this case, the optical pulse train multiplexed by the optical pulse time division multiplexing unit 54 is the densest. However, the time interval Tp of the optical pulse 62 may be twice or more the optical pulse time width PW. In this case, the time interval Tp of the optical pulse 62 is preferably within 3 times the optical pulse time width PW. This is to prevent the multiplexed light pulses from becoming too sparse.

  The wave number scanning range is, for example, 1570 nm to 1610 nm in terms of wavelength. Δk is, for example, 0.01 nm in terms of wavelength. The time interval Tp of the optical pulse is 1.0 μs, for example. The optical pulse time width PW is, for example, 0.5 μs.

  In the present embodiment, the wave number interval Δk of the optical pulse 62 is constant. However, a tomographic image can be constructed even if the wave number interval Δk varies somewhat. Alternatively, a tomographic image can be constructed even if the wave number is missing. The OCT apparatus 48 can also be configured by an optical pulse generation unit that sequentially generates such optical pulses. However, if the wave number fluctuates or falls out, the tomographic image becomes unclear.

(ii) Interferometer unit The interferometer unit 52 includes an optical splitter 68 (optical splitter) that branches the optical pulse 62 into a measurement optical pulse 64 and a reference optical pulse 66, as shown in FIG. Further, the interferometer unit 52 irradiates the measurement light pulse 64 to the measurement object 20 (for example, the retina, the anterior eye part, the built-in inner wall, etc.) and the backscattering generated by the measurement light pulse being backscattered by the measurement object 20. A light pulse irradiation / capture unit 72 for supplementing the light pulse 70 is included. The interferometer unit 52 has an optical delay unit 88 that adjusts the optical length of the optical path through which the reference light pulse 66 propagates. Further, the interferometer unit 52 combines the reference light pulse 66 a whose optical length is adjusted by the delay unit 88 and the backscattered light pulse 70 to generate the first combined light pulse 95 and the second combined light pulse 97. A first optical coupler 69 is included.

-Optical splitter-
The optical splitter 68 is, for example, a directional coupler. The branching ratio of the optical splitter 68 is, for example, 90% (measurement light pulse side) and 10% (reference light pulse side).

―Light irradiation / supplementary unit―
As shown in FIG. 4, the light irradiation / supplementing unit 72 includes a first optical circulator 80 that emits the measurement light pulse 64 branched by the light splitter 68 and incident on the light incident port 81a from the light incident / exit port 81b. Have.

  Further, the light irradiation / supplementation unit 72 has a collimator lens 82 for converting the measurement light pulse emitted from the light incident / exit port 81b of the first circulator 80 into a parallel light beam. Further, the light irradiation / supplementing unit 72 has a galvanometer mirror 84 that deflects the parallel light beam and a focusing lens 86 that collects the deflected parallel light beam and irradiates the measurement target 20.

  In response to a command from the tomographic image deriving unit 58, the galvanometer mirror 84 moves the irradiation position of the collected parallel light beam (measurement light pulse) along a straight line on the measurement target 20. The galvanometer mirror 84 does not move the irradiation position while the optical pulse generation unit 50 scans a predetermined wave number range. Then, every time wave number scanning is completed, the irradiation position is slightly moved in one direction along the straight line. That is, the galvanometer mirror 84 scans the irradiation position of the measurement light pulse.

  A part of the measurement light pulse irradiated to the measurement object 20 is backscattered to become a backscattered light pulse. The backscattered light pulse enters the focusing lens 86, then travels backward in the optical path along which the measurement light pulse has traveled, and enters the light incident / exit port 81 b of the first optical circulator 80. The light exits from 80 light exit ports 81c.

  With the above configuration, the light irradiation / supplementing unit 72 irradiates the measurement light pulse 64 to the measurement object 20 (for example, the retina, the anterior eye portion, the built-in inner wall, etc.), and the measurement light pulse is backscattered by the measurement object 20. The backscattered light pulse 70 generated in this way is supplemented. The light irradiation / supplementing unit 72 repeats this operation along a straight line on the surface of the measurement target 20.

―Optical delay unit―
As shown in FIG. 4, the optical delay unit 88 includes a second optical circulator 90 that emits the reference light pulse 66 branched by the optical splitter 68 and incident on the light incident port 91a from the light incident / exit port 91b. ing. The optical delay unit 88 also has a collimator lens 82a that converts the reference light pulse 66 emitted from the light incident / exit port 91b of the second circulator 90 into a parallel light beam. Further, the optical delay unit 88 has a focusing lens 86 a that collects the parallel light beam (reference light pulse) and irradiates the reference mirror 92. Here, the reference mirror 92 is a movable mirror that can move back and forth in the traveling direction of the parallel light beam (reference light pulse).

  The reference light pulse applied to the reference mirror 92 is reflected by the reference mirror 92, reverses the traveling direction, and reenters the focusing lens 86a. Thereafter, the reference light pulse travels backward along the traveling optical path, enters the light incident / exit port 91b of the second optical circulator 90, and exits from the light exit port 91c of the second optical circulator 90.

  Therefore, the optical length of the optical path of the reference light pulse 66 (hereinafter referred to as the reference optical path) can be adjusted to a desired length by moving the reference mirror 92 along the traveling direction of the parallel light. In the present embodiment, the reference mirror 92 is configured such that the optical length of the reference optical path is substantially equal to the optical length of the optical path (hereinafter referred to as the measurement optical path) that combines the optical path of the measurement light pulse 64 and the optical path of the backscattered light pulse 70. Adjust the position. In addition, the optical delay unit 88 can be omitted by adjusting the length of the optical fiber constituting the reference optical path in advance (see FIG. 1).

―Optical coupler―
The first optical coupler 69 is, for example, a directional coupler. The branching ratio of this directional coupler is 50:50. Therefore, the difference in intensity between the first combined light pulse 95 and the second combined light pulse 97 is similar to the optical length of the reference optical path and the measurement optical path as in the two-detector type OCT apparatus 2 described with reference to FIG. It is proportional to the cosine function of the product of the difference and the wave number (Patent Document 1).

  With the above configuration, the interferometer unit 52 branches each light pulse 62 into a reference light pulse 66 and a measurement light pulse 64, and irradiates the measurement light pulse 20 to the measurement object 20 to generate a backscattered light pulse 70. Further, the interferometer unit 52 combines the backscattered light 70 and the reference light pulse 66 a to generate a first combined light pulse 95 and a second combined light pulse 97.

  In the present embodiment, directional couplers are used as the optical splitter 68 and the first optical coupler 69. However, as the optical splitter 68 and the first optical coupler 69, for example, another optical branch coupler such as a multi-mode interference waveguide may be used.

(Iii) Optical Pulse Time Division Multiplexing Unit As shown in FIG. 4, the optical pulse time division multiplexing unit 54 includes a first optical path 94 for propagating the first combined optical pulse 95, and a second combined optical pulse. Has a second optical path 96 for propagating 97. Further, the optical pulse time division multiplexing unit 54 combines the first combined light pulse 95 propagated through the first optical path 94 and the second combined light pulse 97 propagated through the second optical path 96. An optical coupler 98 is provided.

  Here, the optical length of the second optical path 96 is longer than the optical length of the first optical path 94. Therefore, the second optical path 96 delays the second combined light 97 with respect to the first combined light 95 by a delay time corresponding to the difference ΔL in optical length between the second optical path 96 and the first optical path 94. In the present embodiment, this delay time (the delay time of the second combined light pulse 97) is the light pulse time width PW of the light pulse 62 (= the light pulse time width of the first combined light pulse 95). It is equal to the optical pulse time width of the combined optical pulse 97.

  FIG. 7 is a diagram for explaining the temporal change of the intensity of the optical pulse emitted from the optical pulse time division multiplexing unit 54. The horizontal axis is time. The vertical axis represents the light intensity (power).

  As described above, the time interval Tp of the optical pulse 62 is twice the optical pulse time width PW of the optical pulse 62. In addition, the delay time Δt of the second combined light pulse 97 is equal to the light pulse time width PW of the light pulse 62 as described above. Therefore, the optical pulse time division multiplexing unit 54 alternately emits the first combined light pulse 95 and the second combined light pulse 97 as shown in FIG.

  FIG. 8 is a diagram for explaining the time change of the wave number of the optical pulse generated by the optical pulse time division multiplexing unit 54. The horizontal axis is time. The vertical axis is the wave number. A solid line 100 in FIG. 8 represents the wave number of the first combined light pulse 95. The wavy line 102 in FIG. 8 is the wave number of the second combined light pulse 97. As shown in FIG. 8, the optical pulse time division multiplexing unit 54 emits the first combined optical pulse 95 and the second combined optical pulse 97 having the same wave number in this order, and then has the next wave number. The first combined light pulse 95 and the second combined light pulse 97 are emitted again in this order.

  As described above, the optical pulse time division multiplexing unit 54 delays the second combined optical pulse 97 with respect to the first combined optical pulse 95 by a predetermined delay time Δt, The second combined light pulse 97 is merged, and the first combined light pulse 95 and the second combined light pulse 97 are emitted alternately.

  In the above example, the optical pulse time interval Tp is twice the optical pulse time width PW, and the delay time Δt of the second combined optical pulse 97 is equal to the optical pulse time PW of the optical pulse 62. However, the delay time Δt may be not less than the optical pulse time width PW of the optical pulse 62 and the sum of the delay time Δt and the optical pulse time width PW may be not more than the time interval Tp of the optical pulse 62. Even in such a case, the first combined light pulse 95 and the second combined light pulse 97 combined by the second optical coupler 98 do not overlap each other, and the second coupler 98 is alternately switched. Exit.

(Iv) Optical Pulse Intensity Measurement Unit As shown in FIG. 4, the optical pulse intensity measurement unit 56 converts one optical detector 104 (for example, a pin photodiode) and the output of the optical detector 104 into an analog-digital converter ( A high-speed analog-to-digital conversion unit 106 (hereinafter referred to as a high-speed AD conversion unit) for recording by recording (hereinafter referred to as AD conversion) is provided.

  Here, the high-speed AD conversion unit 106 is an analog-digital converter (hereinafter referred to as an AD converter) 108 for AD-converting the output of the photodetector 104, and a digital signal converted by the AD converter 108. A memory unit 110 (for example, Random Access Memory) for recording is included.

  With the above configuration, the optical pulse intensity measurement unit 56 sequentially measures and records the intensities of the first combined light pulse 95 and the second combined light pulse 97 emitted alternately by the optical pulse time division multiplexing unit 54.

(V) Tomographic image deriving unit The tomographic image deriving unit 58 is a computer 59, and as shown in FIG. 4, a CPU (Central Processing Unit) 112, a main storage device (for example, Random Access Memory) 114, and an OCT It has an auxiliary storage device 116 (such as a magnetic disk) in which a program for operating the device 48 (hereinafter referred to as a measurement program) is recorded.

  In order to operate the tomographic image deriving unit 58, first, a measurement program is loaded from the auxiliary storage device 116 to the main storage device 114. As a result, the computer 59 causes the CPU 112 to respond to an instruction of the measurement program in the main storage device 114 (that is, by executing the measurement program in the main storage device 110), and to another device (optical pulse generation unit). 50, etc.) and a calculation control device for deriving a tomographic image based on the measurement data.

  The computer 59 controls the light pulse unit 50 and the galvanometer mirror 84 to scan the irradiation position of the measurement light pulse 64 along the straight line on the surface of the measurement object 20 while repeating the wave number scanning of the light pulse 62. Here, the computer 59 does not move the irradiation position of the measurement light pulse 64 during the wave number scanning. Then, each time the wave number scanning is completed, the computer 59 slightly moves the irradiation position in one direction along the straight line and restarts the wave number scanning.

  During this time, the light pulse intensity measuring unit 56 measures the intensity of the first combined light pulse 95 and the second combined light pulse 97 sequentially with the photodetector 104 and records each intensity corresponding to its wave number.

  When the position scanning of the measurement light pulse 64 is completed, the computer 59 Fourier-transforms the intensity of the first combined light pulse 95 and the second combined light pulse 97 with respect to the wave number, and calculates the absolute value (or the square thereof). calculate. Thereby, the distribution of the backscattered light intensity of the measurement target 20 in the depth direction (more precisely, the traveling direction of the measurement light pulse) is obtained. The computer 59 constructs a two-dimensional tomographic image of the measurement target 20 by associating the distribution of the backscattered light intensity with the irradiation position of the measurement light pulse 64.

  As described above, the tomographic image deriving unit 58 performs Fourier transform on the difference between the intensity of the first combined light pulse 95 and the intensity of the second combined light pulse 97 measured by the optical pulse intensity measuring unit 56 to measure the difference. A tomographic image of the object 20 is derived.

  As is apparent from the above description, in the present OCT apparatus 48, as shown in FIG. 7, the first combined light pulse 95 and the second combined light pulse 97 merge to form one optical pulse train. The intensity of one combined light pulse 95 and the intensity of the second combined light pulse 97 can be detected by a single photodetector 104. Therefore, according to the present OCT apparatus 48, the number of photodetectors and their driving devices can be reduced one by one. Furthermore, a differential amplifier is not necessary. Therefore, the configuration of the OCT apparatus is simplified.

(2) Usage Next, the usage of this OCT apparatus 48 is demonstrated.

  First, the optical pulse generating unit 50, the optical pulse intensity measuring unit 56, and the tomographic image deriving unit 58 are activated. Next, the measuring object 20 is arranged at the light pulse irradiation position of the light pulse irradiation / supplementation unit 72. Next, the position of the reference mirror 92 of the optical delay unit 88 is adjusted so that the optical path lengths of the reference optical path and the measurement optical path are substantially matched. Thereafter, the computer 59 is operated in accordance with the measurement program to take a tomographic image.

(3) Tomographic imaging method Next, a tomographic imaging method according to the present embodiment will be described.

  First, the measuring object 20 is arranged at a predetermined position. Next, the optical path lengths of the reference optical path and the measurement optical path are substantially matched.

  Next, a plurality of optical pulses 62 having a predetermined wave number interval Δk are sequentially generated (see FIGS. 5 and 6).

  Next, each light pulse 62 is branched into a reference light pulse 66 and a measurement light pulse 64, and the measurement light pulse 64 is applied to the measurement object 20 to generate a backscattered light pulse. Next, the backscattered light pulse 70 and the reference light pulse 66 are combined to generate a first combined light pulse 95 and a second combined light pulse 97.

  Next, after delaying the second combined light pulse 97 by a predetermined delay time Δt with respect to the first combined light pulse 95, the first combined light pulse 95 and the second combined light pulse 97 are merged, The first combined light pulse 95 and the second combined light pulse 95 are alternately arranged (see FIG. 7).

  Next, the first combined light pulse 95 and the second combined light pulse 95 that are alternately arranged are received by one photodetector, and the respective intensities are sequentially measured.

  Next, the difference between the measured intensity of the first combined light pulse 95 and the intensity of the second combined light pulse 97 is Fourier transformed to derive a tomographic image of the measurement object 20.

  In the above example, a two-dimensional tomographic image is taken by moving the irradiation position of the measurement light pulse along a straight line. However, the irradiation position of the measurement light pulse may be fixed and a one-dimensional tomographic image may be taken. Alternatively, a three-dimensional tomographic image may be captured by two-dimensionally scanning the measurement light pulse irradiation position.

  In the above example, the variable wavelength light source is used as the optical pulse generation unit. However, a device that can be used as an optical pulse generation unit is not limited to a variable wavelength light source. For example, a broadband light source such as an SLD (Super Luminescent Diode) is modulated to generate a broadband optical pulse, and the broadband optical pulse is dispersed to generate a plurality of optical pulses. Next, the plurality of optical pulses may be combined after being delayed for a predetermined time in accordance with each wave number, and a plurality of optical pulses having slightly different wave numbers may be sequentially generated.

  In the above example, the interferometer unit 52 is a Mach-Zender interferometer. However, the interferometer unit 52 may be composed of another interferometer, for example, a Michelson interferometer.

48 ... OCT device 50 ... optical pulse generation unit 52 ... interferometer unit 54 ... optical pulse time division multiplexing unit 56 ... optical pulse intensity measurement unit 58 ... tomographic image deriving unit 62 ... optical pulse 64 ... measurement optical pulse 66 ... reference optical pulse 68 ... optical splitter 69 ... first optical coupler 70 ... backscattered light pulse 72 ... optical pulse Irradiation / supplementing unit 88 ... optical delay unit 94 ... first optical path 95 ... first combined light pulse 96 ... second optical path 97 ... second combined light pulse 98 ...・ Second optical coupler

Claims (5)

An optical pulse generation unit that sequentially generates a plurality of optical pulses having different wave numbers;
Branching each of the light pulses into a reference light pulse and a measurement light pulse, irradiating the measurement light pulse onto a measurement object to generate a backscattered light pulse, and combining the backscattered light pulse and the reference light pulse An interferometer unit that generates a first combined light pulse and a second combined light pulse;
After delaying the second combined light pulse by a predetermined delay time with respect to the first combined light pulse, the first combined light pulse and the second combined light pulse are merged, and the first combined light pulse is combined. An optical pulse time division multiplexing unit that alternately emits a combined optical pulse and the second combined optical pulse;
An optical pulse intensity measuring unit for sequentially measuring the intensity of the first combined optical pulse and the second combined optical pulse emitted alternately by the optical pulse time division multiplexing unit;
A tomographic image deriving unit for deriving a tomographic image to be measured by Fourier transforming the difference between the intensity of the first combined optical pulse and the intensity of the second combined optical pulse measured by the optical pulse intensity measuring unit. An optical coherence tomography device. The optical coherence tomography device of claim 1,
The delay time is equal to or greater than a pulse time width of the optical pulse;
The sum of the optical pulse time width and the delay time is within the time interval of the optical pulse,
Features optical coherence tomography equipment. The optical coherence tomography device according to claim 1 or 2,
The optical pulse time division multiplexing unit is:
A first optical path for propagating the first combined light pulse;
A second optical path having an optical path length longer than the first optical path and propagating the second combined optical pulse;
An optical coupler that combines the first combined light pulse propagated through the first optical path and the second combined light pulse propagated through the second optical path;
Features optical coherence tomography equipment. The optical coherence tomography device according to any one of claims 1 to 3,
The interferometer unit is
An optical branching device for branching the optical pulse into the measurement light pulse and the reference light pulse, and backscattered light generated by irradiating the measurement light pulse onto the measurement object and the measurement light pulse being backscattered by the measurement object A light pulse irradiation / capturing unit for capturing a pulse; and an optical coupler for combining the reference light pulse and the backscattered light pulse to generate a first combined light pulse and a second combined light pulse. ,
Features optical coherence tomography equipment. A light pulse generating step for sequentially generating a plurality of light pulses having different wave numbers;
Branching each of the light pulses into a reference light pulse and a measurement light pulse, irradiating the measurement light pulse onto a measurement object to generate a backscattered light pulse, and combining the backscattered light pulse and the reference light pulse An interference step for generating a first combined light pulse and a second combined light pulse;
After delaying the second combined light pulse by a predetermined delay time with respect to the first combined light pulse, the first combined light pulse and the second combined light pulse are merged, and the first combined light pulse is combined. An optical pulse time division multiplexing step of alternately arranging combined optical pulses and the second combined optical pulses;
An optical pulse intensity measuring step for measuring the intensities of the first combined optical pulse and the second combined optical pulse, which are alternately arranged, sequentially with a photodetector;
A tomographic image deriving step for deriving a tomographic image of the measurement object by Fourier-transforming the difference between the intensity of the first combined optical pulse and the intensity of the second combined optical pulse measured in the optical pulse intensity measuring step A method for taking a tomographic image.

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