JP2016090280A - Optical tomographic imaging apparatus and imaging method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an SS-OCT device of high resolving power and high resolution.SOLUTION: An optical tomography imaging device according to the present invention comprises: a wavelength variable laser light source that is composed of a plurality of continuous wavelength swept laser different in an oscillation wavelength region; a wavelength multiplexer that multiplexes laser light from the plurality of wavelength swept laser; an interferometer that is composed of a Mach-Zehnder type interferometer having a reference optical path and a sample optical path to which light from the wavelength multiplexer is input, respectively; a wavelength demultiplexer that demultiplexes interference laser light from the interferometer for each oscillation wavelength of the plurality of wavelength swept laser; and a plurality of balance type optical detectors that converts the interference laser light from the interferometer to respective electric signals.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an optical tomographic imaging apparatus and an imaging method using the same, and more particularly to an optical tomographic imaging apparatus using a wavelength sweep laser and an imaging method using the same.

  Optical coherence tomography (OCT) is a tomographic imaging apparatus using optical interference. For OCT, near infrared light having a wavelength band of 0.7 to 1.3 μm is mainly used. The photon energy in the near-infrared wavelength band is about 1 eV, and the energy is lower than that of diagnostic X-rays. Moreover, since this near-infrared wavelength band is often used for optical communications and the like, many basic technologies have been developed. Therefore, the OCT technology has been rapidly developed and put into practical use.

  Hereinafter, the principle of OCT will be described first. FIG. 1 is a configuration diagram showing a conventional OCT 100. The OCT 100 is a tomographic imaging apparatus called a time domain type OCT (TD-OCT). The TD-OCT 100 includes a light source 101 and a beam splitter 102 that branches the light from the light source 101. Further, the TD-OCT 100 is movable in the optical axis direction, the reference light mirror 103 that reflects the branched light from the beam splitter 102, the biological sample 104 that is a sample to be measured, the reflected light from the reference light mirror 103, and the biological body And a photodetector 105 that detects interference light with reflected light from the sample 104.

As the light source 101, a low coherence light source is used. The low-coherence light f ₀ from the light source 101 is branched in two directions by the beam splitter 102, one of which is reflected by the reference light mirror 103 and returns to the beam splitter 102 as reference light f ₀ + f _D. The other is reflected on the surface and inside of the biological sample 104 to be measured, and becomes countless signal light f ₀ and returns to the beam splitter 102. The reference light and the signal light are combined and interfered by the beam splitter 102 and detected by the photodetector 105.

The low coherence light has low coherence reference beam reflected optical path length from the mirror 103 L _R reflected light from a biological sample (signal light) when the optical path length L _S is matched only photodetecting The interfering light signal is detected in the device 105. Therefore, the TD-OCT 100 detects the reflected light (signal light) intensity distribution in the optical axis direction of the sample to be measured by moving the reference light mirror 103 in the optical axis direction, and obtains a tomographic image of the biological sample 104. Can do.

  FIG. 2 is a diagram showing the reflected light intensity when the reference light mirror 103 is moved in the optical axis direction. When the reference light mirror is moved at the speed v, the reflected light intensity distribution in the optical axis direction of the living tissue 104 can be detected. Furthermore, the reflected light intensity distribution in the cross section of the biological sample 104 can be measured and imaged by scanning the incident light on the sample to be measured (biological sample 104).

The spatial resolution (Δz) in the optical axis direction, that is, the depth direction of the sample at this time is given by the coherence distance (coherence length) 1 _C of the low coherence light source, that is, the wavelength spectrum width (Δλ). That is, when the spectrum shape can be regarded as Gaussian, l _C = 4ln (2) · λ _C ² / (π · Δλ), and Δz = l _C / 2,

It is.

The TD-OCT 100 that moves by scanning the reference light mirror 103 has a limit in the mechanical moving speed of the reference light mirror 103, and the number of images that can be captured is only a few in one second.
However, in the medical application and practical application of OCT including retinal diagnosis, since a dynamic measurement object is an object, higher-speed imaging is required. Further, high speed imaging is an important factor from the viewpoint of reducing the burden on the subject.

OCT, which is currently being put into practical use, is a system that uses a wavelength tunable laser light source and Fourier-transforms the signal obtained by detecting the interference light obtained by changing the oscillation wavelength to obtain a reflected light intensity distribution. This is called wavelength-swept OCT (Swept-Source OCT; SS-OCT). In SS-OCT, a laser beam whose oscillation wavelength is changed with time is interfered and converted into an electric signal, and the converted electric signal is Fourier-transformed to obtain a wavelength intensity distribution. Therefore, as in TD-OCT, a reference mirror is used. Even without moving in the direction of the optical axis, the reflected light intensity distribution in the depth direction of the biological sample as the sample can be obtained. In addition, this method is a method in which a high SN is expected because there is little principle loss in the amount of light because no spectroscopy is performed. Here, the spatial resolution Δz in the depth direction of the sample in SS-OCT can be expressed by the equation (1) as the center wavelength λ _c and the wavelength sweep width Δλ of the wavelength tunable laser, and therefore the wavelength sweep width Δλ is The wider the area, the higher (higher) the spatial resolution Δz. In the case of SS-OCT, the wavelength sweep speed of the wavelength tunable laser is an important factor that determines the imaging speed. Therefore, in order to enable high-speed imaging with high resolution, it is required that the wavelength tunable laser has a wide sweep width and can be swept at high speed.

From this point of view, many tunable lasers (= optical frequency sweep lasers) capable of high-speed wavelength sweep are being developed. In a high _- speed wavelength sweep laser using an electro-optic (EO) optical deflector using an electro-optic crystal such as KTN (KTa _1-x Nb _x O ₃ ), which is an example of a wavelength tunable laser capable of high-speed wavelength sweep, A sweep speed of 200 Hz, a wavelength sweep width (= wavelength spectrum width) of 100 nm, and a center wavelength of 1.3 μm are realized (see Non-Patent Document 2). The spatial resolution Δz at this time is about 7.5 μm from the equation (1).

  FIG. 3 is a configuration diagram showing a conventional SS-OCT 300 (see Non-Patent Document 3). The SS-OCT 300 includes a light source 301, an optical fiber coupler 302 that branches the laser light from the light source 301, a reference optical path 310 to which one laser light from the optical fiber coupler 302 is input, and the other from the optical fiber coupler 302. And a sample optical path 320 to which the light of the above is input. Further, the SS-OCT 300 detects an interference laser beam by the optical fiber coupler 331 that combines, interferes with, and further branches the reflected light from the reference optical path 310 and the reflected light from the sample optical path 320. And a balanced photodetector 332.

  The interferometer of SS-OCT300 is configured as a Mach-Zehnder type in which a reference optical path (Reference arm) and a sample optical path (Sample arm) are separated. As the light source 301, a 1.3 μm band KTN wavelength sweep laser is used. The light source 301 and the optical fiber coupler 302 are connected by an optical fiber, and the optical fiber coupler 302 branches the laser light from the light source 301 at 10:90. Further, the optical fiber coupler 331 and the balance type photodetector 332 are connected by an optical fiber, and the optical fiber coupler 331 receives the combined and interfered laser light from the reference optical path 310 and the sample optical path 320 by 50: The laser beam 50 is branched into two laser beams whose phases are different by 180 degrees. A reference light mirror 313 is disposed at one end of the reference light path 310, and a biological sample 325 is disposed at one end of the sample light path 320.

  The reference optical path 310 is collimated by a collimating lens 311 for converting laser light from the light source 301 into parallel light, a condensing lens 312 for condensing the parallel light converted by the collimating lens 311, and collected by the condensing lens 312. A reference light mirror 313 that reflects light. The reference optical path 310 is connected to the optical fiber coupler 302 by an optical fiber, and a circulator 314 for extracting reflected light from the reference light mirror 313, and an optical fiber type polarization connected between the circulator 314 and the optical fiber coupler 331. And a controller 315.

  The sample optical path 320 reflects a collimating lens 321 that converts light from the light source 301 into parallel light, a galvano mirror 322 that reflects the parallel light converted by the collimating lens 321, and irradiates the biological sample 325, and reflection by the galvano mirror 322. And a condensing lens 323 for condensing light. The sample optical path 320 is connected to the optical fiber coupler 302 by an optical fiber, and a circulator 324 for extracting reflected light from the biological sample 325, and an optical fiber type polarization controller connected between the circulator 324 and the optical fiber coupler 331. 326.

  In addition, the SS-OCT 300 is connected to the light source 301 and the balanced photodetector 332, and samples a signal of interference light detected by the balanced photodetector 332 and a digital ac interference (DAQ) board 341. And a PC 342 for performing discrete Fourier transform on the optical signal. The SS-OCT 300 is connected to the DAQ board 341, and is connected to the function generator 343 that converts the synchronization signal from the light source 301 into an external device synchronization signal. The SS-OCT 300 is connected to the function generator 343, and is based on the synchronization signal from the light source 301. And a driver 344 for controlling the mirror 322.

  The laser light from the light source 301 is branched 10 to 90 by the optical fiber coupler 302. 10% of the laser beam branched by the optical fiber coupler 302 is input to the reference optical path 310, and 90% of the laser light is input to the sample optical path 320.

  The laser light input to the reference optical path 310 passes through the circulator 314 and is converted into parallel light by the collimator lens 311. The laser light converted into parallel light is condensed by the condensing lens 312, imaged on the reference light mirror 313, and reflected. The reflected laser light again passes through the condenser lens 312 and the collimator lens 311 and is separated by the circulator 314. The laser light separated by the circulator 314 passes through the polarization controller 315 and is input to the optical fiber coupler 331.

  The laser light incident on the sample optical path 320 passes through the circulator 324 and is converted into parallel light by the collimator lens 321. The laser light converted into parallel light is reflected by the galvanometer mirror 322, and the reflected laser light is collected by the condenser lens 323, and is imaged and reflected on the surface of the biological sample 325 and each layer. The laser beam reflected by the surface and each layer of the biological sample 325 passes through the condenser lens 323, the galvano mirror 322, and the collimator lens 321 again and is separated by the circulator 324. The laser light separated by the circulator 324 passes through the polarization controller 326 and is input to the optical fiber coupler 331.

  In the optical fiber coupler 331, the reflected laser light from the reference optical path 310 and the reflected laser light from the sample optical path 320 are combined and interfered. The interference light is again separated into 50 to 50 and is converted into an electric signal by the balanced photodetector 332. When the laser light from the reference optical path and the sample optical path is branched by 50:50 in the optical fiber coupler 332 and detected by the balanced photodetector 332, the direct current component of the light is canceled and only the interference signal is output. . The interference signal detected by the balanced photodetector 332 is digitally converted by the DAQ board 341, and when a discrete Fourier transform is performed by the PC 342, one-dimensional information in the depth direction of the biological sample is obtained (A scan).

  Here, the laser beam irradiated to the biological sample 325 input to the sample optical path 320 can be scanned on the biological sample 325 by the galvanometer mirror 322 (B scan). The detection of one-dimensional information in the depth direction (A scan) is repeated one after another while scanning the irradiation direction of the laser light to the biological sample 325 in the lateral direction with respect to the optical axis using the galvano mirror 322 (B scan). Each interference signal obtained by scanning the galvanometer mirror 322 is also digitally converted by the DAQ board 341 and the reflection intensity obtained by the discrete Fourier transform by the PC 342 is grayscale on the plane in the depth direction and the lateral direction. Alternatively, if it is converted into a color code and drawn as a color map, a tomographic image of the biological sample 325 can be obtained.

  A trigger signal synchronized with the sweep frequency is output from the light source 301, and this is used as a synchronization signal (raster trigger) for acquiring one-dimensional information in the depth direction of the biological sample 325 (A scan). Furthermore, the raster trigger is converted into an external device synchronization signal by the function generator 343 and transmitted to the driver 344 to synchronize the operation (B scan) of the galvano mirror 322 for acquiring two-dimensional information for changing the light in the horizontal direction. Used. One tomographic image of the biological sample 325 is constructed by sequentially acquiring and arranging one-dimensional information (A line data) acquired by the A scan in the horizontal direction by the B scan.

Masamitsu Haruna, “Optical Coherence Tomography (OCT)”, Journal of the Institute of Image Information and Television Engineers / Vol.65 / No.1 / pp. 67-71 / 2011 S. Yagi, et al, “Improvement of Coherence Length in a 200-kHz Swept Light Source equipped with a KTN deflector”, Proc. Of SPIE Vol. 8213, pp. 821333-1-6. Koji Obayashi, “Optical Frequency Sweep Coherence Tomography”, Laser Research July 2006, Vol. 34, No. 7, pp. 483-487

  In SS-OCT, in order to further improve the spatial resolution Δz to achieve higher resolution and higher resolution, it is necessary to increase the wavelength sweep width. Here, in the SS-OCT of FIG. 3, one 1.3 μm band KTN optical wavelength sweep laser is used as a light source. However, when the wavelength sweep speed of a single wavelength sweep laser is kept as it is and the wavelength sweep width is expanded and used as an SS-OCT light source, the number of sweeps per unit time decreases and the imaging speed decreases. . For this reason, there exists a possibility of giving a burden to a dynamic to-be-measured object. In addition, increasing the sweep speed causes a decrease in laser light quality, such as a reduction in the coherence length of the laser light and a decrease in the stability of the laser light intensity, resulting in a decrease in the OCT measurable area (depth) and a decrease in image quality. It happens. It is technically difficult to increase the wavelength sweep speed of the laser while having a high coherence length and high laser beam intensity stability. As described above, in SS-OCT using only one wavelength sweep laser, it is difficult to further increase the wavelength sweep speed and further expand the wavelength sweep width to improve the spatial resolution Δz. .

  The present invention has been made in view of such a problem. The object of the present invention is to easily expand the wavelength sweep width of SS-OCT without increasing the characteristics of the wavelength sweep laser and to measure the time ( It is to provide a high-resolution and high-resolution SS-OCT apparatus by shortening (imaging time).

  In order to achieve such an object, a first embodiment of the present invention is an optical tomographic imaging apparatus, which is a wavelength tunable laser composed of a plurality of wavelength swept lasers having different oscillation wavelength ranges and continuous. A Mach-Zehnder type having a light source, a wavelength multiplexer that multiplexes laser beams from the plurality of wavelength swept lasers, a reference optical path to which light from the wavelength multiplexer is input, and a sample optical path, respectively. An interferometer, a wavelength demultiplexer that demultiplexes the interference laser light from the interferometer for each oscillation wavelength of the plurality of wavelength swept lasers, and the interference laser light from the wavelength demultiplexer is converted into an electrical signal, respectively. And a plurality of balanced photodetectors.

  According to a second embodiment of the present invention, there is provided the optical tomographic imaging apparatus according to the first embodiment, wherein the plurality of wavelength swept lasers are controlled so as to operate in synchronization with each other. .

  A third embodiment of the present invention is the optical tomographic imaging apparatus according to the first or second embodiment, wherein the oscillation wavelengths of the plurality of wavelength sweep lasers are controlled so as not to be the same at the same time. It is characterized by that.

  According to a fourth embodiment of the present invention, there is provided a wavelength tunable laser light source composed of a plurality of wavelength swept lasers, a wavelength combiner for combining laser light from the plurality of wavelength swept lasers, and the wavelength combiner. An interferometer having a Mach-Zehnder type having a reference optical path and a sample optical path to which light from the wave separator is input, a wavelength demultiplexer for demultiplexing the interference laser light from the interferometer, and the wavelength demultiplexing A method for obtaining one-dimensional information in the depth direction of a sample for cross-sectional imaging of the sample in an optical tomographic imaging apparatus comprising a plurality of balanced photodetectors that convert interference laser light from the detector into electrical signals A step of oscillating laser light while performing wavelength sweeping in each oscillation wavelength region from each of the plurality of wavelength sweeping lasers, wherein each of the plurality of wavelength sweeping lasers has a different oscillation wavelength region. A continuous step, a step of combining the laser light and inputting it to the interferometer, and a step of demultiplexing the interference laser light from the interferometer for each oscillation wavelength of the wavelength sweep laser by the wavelength demultiplexer. And a step of converting the interference laser light from the wavelength demultiplexer into an electric signal in each of a plurality of balanced photodetectors.

  The fifth embodiment of the present invention is the method of the fourth embodiment, characterized in that the sweeps of the plurality of wavelength swept lasers are controlled to operate synchronously.

  A sixth embodiment of the present invention is the method of the fourth or fifth embodiment, wherein the oscillation wavelengths of the plurality of wavelength swept lasers are controlled so as not to be the same at the same time. Features.

  In the present invention, by using a plurality of wavelength sweep lasers, the wavelength sweep width of SS-OCT can be easily expanded without improving the characteristics of the wavelength sweep laser. Further, by simultaneously sweeping the wavelength of the wavelength sweep laser, the measurement time (imaging time) can be shortened, and as a result, a high-resolution and high-resolution SS-OCT apparatus can be provided. Furthermore, by reducing the examination time for the subject, it is possible to contribute to reducing the burden on the subject.

It is a block diagram which shows the conventional TD-OCT. It is a figure which shows the mode of the reflected light intensity at the time of moving the reference light mirror of TD-OCT of FIG. 1 to an optical axis direction. It is a block diagram which shows the conventional SS-OCT. It is a block diagram which shows SS-OCT concerning one Embodiment of this invention. It is a figure which shows the mode of the wavelength of two light sources. (A) is a figure which shows the relationship between the wavelength of each oscillation laser beam of two light sources, and light intensity, (b) is a figure which shows the motion of each wavelength sweep of two light sources. It is a figure which shows the tomographic structure figure of the sample used as a measuring object, and the tomographic image of the sample measured by SS-OCT. (A) is a tomographic structure diagram of a sample to be measured, (b) is a tomographic image captured only with a light source having a wavelength sweep width of 90 nm, and (c) is a diagram showing a tomographic image using both two light sources. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 4 is a block diagram showing an SS-OCT 400 that is an optical tomographic imaging apparatus according to an embodiment of the present invention. The SS-OCT 400 includes two light sources 401 and 402, a wavelength combiner 403 that combines the laser beams from the two light sources 401 and 402, and an optical fiber coupler 404 that branches the laser beams from the wavelength combiner 403. With. The SS-OCT 400 includes a reference optical path 410 to which one light from the optical fiber coupler 404 is input and a sample optical path 420 to which the other light from the optical fiber coupler 404 is input. Further, the SS-OCT 400 combines an optical fiber coupler 431 that combines, interferes with, and branches the reflected laser light from the reference optical path 410 and the reflected laser light from the sample optical path 420, and the interference laser light from the optical fiber coupler 431, respectively. Wavelength demultiplexers 432 and 433 for demultiplexing, and balanced photodetectors 434 and 435 for detecting demultiplexed light from the wavelength demultiplexers 432 and 433, respectively.

  The interferometer of SS-OCT400 is configured as a Mach-Zehnder type in which a reference optical path (Reference arm) and a sample optical path (Sample arm) are separated. The light sources 401 and 402 are wavelength swept lasers whose oscillation wavelength ranges are continuous and are not the same. As the light source 401, a KTN wavelength sweep laser (LASER1) having a center wavelength of 1270 nm and a wavelength sweep width of 90 nm is used. As the light source 402, a KTN wavelength sweep laser (LASER2) having a center wavelength of 1350 nm and a wavelength sweep width of 90 nm is used. Both wavelength sweep speeds are 200 kHz, and both LASER1 and LASER2 are controlled to simultaneously perform a sweep operation from a short wavelength to a long wavelength. Further, LASER1 and LASER2 are controlled so as not to have the same wavelength at the same time. Specifically, when LASER1 oscillates at 1225 nm, LASER2 oscillates at 1305 nm, and when LASER1 oscillates at 1315 nm, LASER2 is controlled to oscillate at 1395 nm. The sweep wavelength width of LASER 1 is set so as to be within the transmission band determined by the wavelength multiplexer 403 + wavelength demultiplexer 432, and the sweep wavelength width of LASER 2 is the transmission band determined by the wavelength multiplexer 403 + wavelength demultiplexer 433. Set to fit inside.

  The light sources 401 and 402 and the wavelength multiplexer 403 are connected by an optical fiber. The wavelength multiplexer 403 and the optical fiber coupler 404 are connected by an optical fiber, and the optical fiber coupler 404 branches the combined laser light from the light sources 401 and 402 into 10:90. The optical fiber coupler 431 and the wavelength demultiplexers 432 and 433 are connected by an optical fiber. The optical fiber coupler 431 branches the combined and interfered laser beams from the reference beam path 410 and the sample beam path 420 into two laser beams having a 50:50 phase difference of 180 degrees. A reference light mirror 413 is disposed at one end of the reference light path 410, and a biological sample 425 is disposed at one end of the sample light path 420.

  Further, the two outputs of the wavelength demultiplexer 432 are connected to the balanced optical detectors 434 and 435 through optical fibers, respectively, and the two outputs of the wavelength demultiplexer 433 are connected to the balanced optical detectors 434 and 435, respectively. Connected with optical fiber.

  The reference light path 410 includes a collimating lens 411 that converts laser light from the light sources 401 and 402 into parallel light, a condensing lens 412 that condenses the parallel light converted by the collimating lens 411, and condensing by the condensing lens 412. And a reference light mirror 413 for reflecting the laser beam. The reference optical path 410 includes a circulator 414 that is connected to the optical fiber couplers 404 and 431 through an optical fiber and extracts reflected light from the reference light mirror 413.

  The sample optical path 420 includes a collimator lens 421 that converts light from the light sources 401 and 402 into parallel light, a galvano mirror 422 that reflects the parallel light converted by the collimator lens 421, and irradiates the biological sample 425, and a galvano mirror 422. And a condensing lens 423 that condenses the reflected light. The sample optical path 420 includes a circulator 424 that is connected to the optical fiber couplers 404 and 432 through an optical fiber and extracts reflected light from the biological sample 425.

  The SS-OCT 400 is connected to the light sources 401 and 402 and the balanced photodetectors 434 and 435, and a DAQ board 441 for sampling the interference light signal detected by the balanced photodetectors 434 and 435, and a digital conversion PC442 for performing discrete Fourier transform on the signal of the interference light. The SS-OCT 400 is connected to the DAQ board 441 and is connected to the function generator 443 that converts the synchronization signal from the light sources 401 and 402 into an external device synchronization signal, and the function generator 443, and the synchronization signal from the light sources 401 and 402. And a driver 444 for controlling the galvanometer mirror 422 based on the above.

  The laser beams from the light sources 401 and 402 combined by the wavelength multiplexer 403 are branched into 10 to 90 by the optical fiber coupler 404. 10% of the laser beam branched by the optical fiber coupler 404 is input to the reference optical path 410, and 90% of the laser light is input to the sample optical path 420.

  The laser light input to the reference light path 410 passes through the circulator 414 and is converted into parallel light by the collimator lens 411. The laser light converted into parallel light is condensed by the condensing lens 412, imaged on the reference light mirror 413, and reflected. The reflected laser light again passes through the condenser lens 412 and the collimating lens 411 and is separated by the circulator 414. The laser beam separated by the circulator 414 is input to the optical fiber coupler 431.

  The laser light input to the sample optical path 420 passes through the circulator 424 and is converted into parallel light by the collimator lens 421. The laser light converted into parallel light is reflected by the galvanometer mirror 422, and the reflected laser light is collected by the condenser lens 423, imaged on the surface of the biological sample 425, and reflected. The reflected laser light again passes through the condenser lens 423, is reflected by the galvanometer mirror 422, passes through the collimator lens 421, and is separated by the circulator 424. The laser beam separated by the circulator 424 is input to the optical fiber coupler 431.

  In the optical fiber coupler 431, the reflected laser light from the reference optical path 410 and the reflected laser light from the sample optical path 420 are combined and interfered. The interference light is again split 50 to 50 and input to the wavelength demultiplexers 432 and 433, respectively. In the wavelength demultiplexer 432, the interference laser light is separated into wavelengths corresponding to the light source 401 and the light source 402, and one (laser light from the light source 401) is sent to the balanced photodetector 434, and the other (from the light source 402). Laser beam) is input to the balanced photodetector 435. Further, in the wavelength demultiplexer 432, the interference laser light is separated into wavelengths corresponding to LASER 1 and LASER 2, one (laser light from the light source 401) being sent to the balanced photodetector 434 and the other (from the light source 402 being taken). Laser beam) is input to the balanced photodetector 435.

  The respective interference laser beams input to the balanced photodetectors 434 and 435 are converted into electric signals. When the laser light from the reference optical path 410 and the sample optical path 420 is branched by the optical fiber coupler 431 and detected by the balanced photodetectors 434 and 435, the direct current component of the light is canceled and only the interference signal is output. . The interference signals detected by the balanced photodetectors 434 and 435 are digitally converted by the DAQ board 441, and when a discrete Fourier transform is performed by the PC 442, one-dimensional information in the depth direction of the biological sample is obtained (A scan). .

  Here, the laser light irradiated to the biological sample 425 input to the sample optical path 420 can be scanned on the biological sample 425 by the galvanometer mirror 422 (B scan). The detection of one-dimensional information in the depth direction (A scan) is repeated one after another while scanning the irradiation direction of the laser light to the biological sample 425 in the direction transverse to the optical axis using the galvano mirror 422 (B scan). For each interference signal obtained by scanning the galvanometer mirror 422, the reflection intensity obtained by digital conversion by the DAQ board 441 and discrete Fourier transform by the PC 442 is grayscale on the plane in the depth direction and the horizontal direction. Alternatively, a tomographic image of the biological sample 425 can be obtained by converting it into a color code and drawing it as a color map.

  A trigger signal synchronized with the sweep frequency is output from the light sources 401 (LASER1) and 402 (LASER2), and this is a synchronization signal (raster) for acquiring one-dimensional information in the depth direction of the biological sample 425 (A scan). Used as a trigger). Further, the raster trigger is converted into an external device synchronization signal by the function generator 443 and transmitted to the driver 444 to synchronize the operation (B scan) of the galvano mirror 422 for acquiring two-dimensional information for changing the light in the horizontal direction. Used. One tomographic image of the biological sample 425 is constructed by sequentially acquiring and arranging one-dimensional information (A line data) acquired by the A scan in the horizontal direction by the B scan.

  FIG. 5 is a diagram showing the state of the wavelengths of the light source 401 and the light source 402. FIG. 5A is a diagram illustrating the relationship between the wavelength and the light intensity of the oscillation laser light of each of the light source 401 and the light source 402, and FIG. 5B is a diagram illustrating the wavelength sweep of each of the light source 401 and the light source 402. It is a figure which shows a motion.

  As shown in FIG. 5A, the light source 401 and the light source 402 oscillate simultaneously and are swept from a short wavelength to a long wavelength. The light source 401 is a KTN wavelength sweep laser having a center wavelength of 1270 nm and a wavelength sweep width of 90 nm, and the sweep wavelength is in a transmission band determined by the wavelength multiplexer 403 + wavelength demultiplexer 432. The light source 402 is a KTN wavelength sweep laser having a center wavelength of 1350 nm and a wavelength sweep width of 90 nm, and the sweep wavelength is in a transmission band determined by the wavelength multiplexer 403 + wavelength demultiplexer 433. As shown in FIG. 5A, by combining the light source 401 and the light source 402, the wavelength sweep width of the wavelength sweep laser can be set to 170 nm in a pseudo manner. As shown in FIG. 5B, the light source 401 (LASER1) and the light source 402 (LASER2) oscillate simultaneously (operate synchronously) and are swept from a short wavelength to a long wavelength. The light source 401 and the light source 402 can provide a wavelength sweep laser having a wavelength sweep width of 170 nm in a pseudo manner.

[Example]
In order to verify the improvement in resolution by SS-OCT400, a sample in which three layers of resin films having different refractive indices were formed on a quartz substrate was prepared, and tomographic imaging was attempted. FIG. 6 is a diagram showing a tomographic structure diagram of a sample to be measured and a tomographic image of the sample measured by SS-OCT. 6A is a tomographic structure diagram of a sample to be measured, FIG. 6B is a tomographic image captured only by the light source 401 (wavelength sweep width 90 nm), and FIG. 6C is both the light source 401 and the light source 402. It is a figure which shows the tomographic image using. The resin layer is laminated with the first layer, the second layer, and the third layer from the substrate surface, and the thickness is 50 μm for the first layer, 5 μm for the second layer, and 50 μm for the third layer. (C) shows the resolution dependency for the second layer having a thickness of 5 μm. As apparent from the equation (1), the spatial resolution with respect to the wavelength sweep width of 90 nm (using only one laser) is 8.3 μm, while the two lasers of the light source 401 and the light source 402 are substantially used. When the wavelength sweep width is 170 nm, the spatial resolution is 4.4 μm. Also in the imaging result, the imaging in FIG. 6C is clearer than that in FIG. 6B.

  As described above, as a result of imaging an optical tomographic image having a resolution equivalent to 200 kHz and a wavelength sweep width of 170 nm by SS-OCT according to the present invention, the wavelength sweep speed nm / s is increased in a pseudo manner, It was found that high-resolution imaging is possible.

  As described above, the SS-OCT apparatus of the present invention enables high-resolution and high-resolution optical tomographic imaging without increasing the sweep characteristics of the wavelength sweep laser. Further, since the imaging time is shortened, it contributes to reducing the burden on the subject.

  Although an example using two lasers of the light source 401 and the light source 402 has been described above, higher resolution and higher resolution can be obtained by using more lasers.

100 TD-OCT
101, 301, 401, 402 Light source 102 Beam splitter 103, 313 Reference light mirror 104, 325, 425 Biological sample 105 Photo detector 300, 400 SS-OCT
302, 331, 404, 431 Optical fiber couplers 310, 410 Reference optical paths 311, 321, 411, 421 Collimating lenses 312, 323, 412, 423 Condensing lenses 314, 324, 414, 424 Circulators 315, 326 Optical fiber polarization Controller 320, 420 Sample optical path 322, 422 Galvano mirror 332, 434, 435 Balanced photodetector 341, 441 DAQ board 342, 442 PC
343, 443 Function generator 344, 444 Driver 403 Wavelength multiplexer 432, 433 Wavelength demultiplexer

Claims (6)

A tunable laser light source composed of a plurality of wavelength swept lasers having different oscillation wavelength ranges and continuous,
A wavelength multiplexer for multiplexing laser beams from the plurality of wavelength swept lasers;
An interferometer composed of a Mach-Zehnder type having a reference optical path and a sample optical path to which light from the wavelength multiplexer is respectively input;
A wavelength demultiplexer for demultiplexing the interference laser light from the interferometer for each oscillation wavelength of the plurality of wavelength swept lasers;
An optical tomographic imaging apparatus comprising: a plurality of balanced photodetectors that respectively convert interference laser light from the wavelength demultiplexer into electrical signals.   2. The optical tomographic imaging apparatus according to claim 1, wherein sweeps of the plurality of wavelength sweep lasers are controlled to operate in synchronization with each other.   The optical tomographic imaging apparatus according to claim 1, wherein the oscillation wavelengths of the plurality of wavelength swept lasers are controlled so as not to be the same. A tunable laser light source composed of a plurality of wavelength-swept lasers;
A wavelength multiplexer for multiplexing laser beams from the plurality of wavelength swept lasers;
An interferometer composed of a Mach-Zehnder type having a reference optical path and a sample optical path to which light from the wavelength multiplexer is respectively input;
A wavelength demultiplexer for demultiplexing the interference laser light from the interferometer;
In an optical tomographic imaging apparatus comprising a plurality of balanced photodetectors that convert interference laser light from the wavelength demultiplexer into an electrical signal, one-dimensional information in the depth direction of the sample is obtained for cross-sectional imaging of the sample. A method for obtaining
A step of oscillating laser light while performing wavelength sweeping in each oscillation wavelength region from each of the plurality of wavelength sweeping lasers, wherein the plurality of wavelength sweeping lasers have different oscillation wavelength regions and are continuous. When,
Combining the laser light and inputting it to an interferometer;
Demultiplexing the interference laser light from the interferometer for each oscillation wavelength of the wavelength swept laser by the wavelength demultiplexer;
Converting the interference laser light from the wavelength demultiplexer into an electric signal in each of a plurality of balanced photodetectors.   5. The method of claim 4, wherein sweeps of the plurality of wavelength swept lasers are controlled to operate synchronously.   6. The method according to claim 4, wherein the oscillation wavelengths of the plurality of wavelength swept lasers are controlled so as not to be the same at the same time.