JP5467343B2 - Optical coherence tomography apparatus and tomographic imaging method - Google Patents

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.

  In recent years, the imaging speed of OCT has been dramatically improved. In particular, according to a recently developed method of performing spectroscopy after interference with broadband light, it is also possible to capture a moving image of a three-dimensional tomographic image.

International Publication WO2008 / 090599 JP 2005-156540 A

  However, to implement this method, hundreds of photodetectors are required, and the tomography apparatus becomes large and complicated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an OCT apparatus that enables high-speed imaging of tomographic images with only a small number of photodetectors.

  In order to achieve the above object, according to a first aspect of the present invention, a broadband optical pulse having a predetermined wavelength band is demultiplexed from a broadband optical pulse generation unit, and the broadband optical pulse is demultiplexed. Generates a plurality of narrow-band optical pulses narrower than the predetermined wavelength band, combines each of the narrow-band optical pulses after being delayed for different times, and generates an optical pulse train composed of a plurality of optical pulses having different center wavelengths. An optical pulse demultiplexing / demultiplexing unit, an optical branching device for branching the optical pulse train into a measurement optical pulse train and a reference optical pulse train, and irradiating the measurement optical pulse train on the measurement target, and the measurement optical pulse train is the measurement target An optical pulse irradiation / supplementing unit that supplements the backscattered light pulse train generated by backscattering by the light source, and the reference light pulse train and the backscattered light pulse train are combined to form a combined light pulse train An optical coupler, an optical pulse intensity measurement unit for measuring the optical intensity of each optical pulse of the combined optical pulse train, and a Fourier transform of the measurement data corresponding to the intensity according to the wave number of each optical pulse of the combined optical pulse train. An OCT apparatus having a tomographic image deriving unit for deriving the tomographic image of the measurement object based on the Fourier transformed measurement data is provided.

  According to the second aspect of the present invention, after splitting an optical pulse train composed of a plurality of optical pulses having different center wavelengths to form a measurement optical pulse train, the measurement target is irradiated with the measurement optical pulse train, and the measurement target A light source used in an optical coherence tomography device for deriving a tomographic image of a broadband optical pulse generating unit that generates a broadband optical pulse having a predetermined wavelength band, and demultiplexing the broadband optical pulse to obtain a wavelength An optical pulse demultiplexing delay multiplexer that generates a plurality of narrowband optical pulses having a narrower band than the predetermined wavelength band, and combines the narrowband optical pulses after delaying the narrowband optical pulses by different times. A light source for an optical coherence tomography device having a wave unit is provided.

  According to a third aspect of the present invention, a broadband optical pulse generating step for generating a broadband optical pulse having a predetermined wavelength band, and the broadband optical pulse is demultiplexed so that the wavelength band is narrower than the predetermined wavelength band. An optical pulse demultiplexing delay multiplexer that generates a plurality of narrowband optical pulses, combines the narrowband optical pulses after delaying them for different times, and generates an optical pulse train composed of a plurality of optical pulses having different center wavelengths. A wave step, an optical branching step for branching the optical pulse train into a measurement optical pulse train and a reference optical pulse train, and irradiating the measurement optical pulse train on a measurement target, and the measurement optical pulse train is generated by being backscattered by the measurement target An optical pulse irradiation / capturing step for supplementing the backscattered light pulse train, and an optical coupling step for forming the combined light pulse train by combining the reference light pulse train and the backscattered light pulse train. And a Fourier transform of the measurement data corresponding to the measured light intensity according to the optical intensity measurement step of measuring the light intensity of each light pulse of the combined light pulse train, and the wave number of each light pulse of the combined light pulse train. And a tomographic image deriving step for deriving a tomographic image of the measurement object based on the Fourier-transformed measurement data and the irradiation position.

  According to a fourth aspect of the present invention, after branching an optical pulse train composed of a plurality of optical pulses having different center wavelengths to form a measurement optical pulse train, the measurement target is irradiated with the measurement optical pulse train, and the measurement target A method for generating an optical pulse train used in a tomographic imaging method for deriving a tomographic image of the optical system, comprising: generating a broadband optical pulse having a predetermined wavelength band; and demultiplexing the broadband optical pulse An optical pulse for generating the optical pulse train by generating a plurality of narrow-band optical pulses whose wavelength band is narrower than the predetermined wavelength band, delaying each of the narrow-band optical pulses for a different time, and then combining them A method for generating an optical pulse train for tomographic imaging having a demultiplexing delay multiplexing step is provided.

  According to the present invention, it is possible to provide an OCT apparatus that enables tomographic imaging at high speed only by providing a small number of photodetectors.

It is a block diagram of the OCT apparatus of embodiment. It is a figure explaining the time change of the optical intensity of a broadband optical pulse. It is a figure explaining the instantaneous optical spectrum of the broadband optical pulse in the period corresponding to optical pulse width (DELTA) t. It is a time-resolved light spectrum of a broadband light pulse. It is the schematic explaining the structure of the optical delay device of embodiment. It is a time-resolved spectrum of a narrow-band optical pulse train. It is a figure explaining the structure of the light source for OCT of embodiment.

  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.

(1) Configuration (i) Broadband Optical Pulse Generation Unit FIG. 1 is a configuration diagram of the OCT apparatus 2 of the present embodiment. Although not specifically described below, the following optical devices are optically connected by optical fibers indicated by solid lines.

  As shown in FIG. 1, the OCT apparatus 2 includes a broadband optical pulse generation unit 4 that repeatedly generates a broadband optical pulse 5 in response to a trigger generated by a tomogram deriving unit 60 described later. Have. The broadband optical pulse generation unit 4 includes, for example, an SLD 6 (Super Luminescent Diode; SLD) and a voltage pulse generator 8 (Pulse Generator; PG) 8 that is driven by applying a voltage pulse to the SLD 6.

  FIG. 2 is a diagram for explaining the temporal change of the light intensity (optical power) of the broadband optical pulse 5. The horizontal axis is time. The vertical axis represents the light intensity (instantaneous value of light intensity, the same applies hereinafter).

As shown in FIG. 2, the broadband optical pulse generation unit 4 repeatedly generates the broadband optical pulse 5. The time interval T of the broadband optical pulse 5 is, for example, 128 ns to 5120 ns. Further, the full width at half maximum of the duration time of the broadband optical pulse 5 (the time during which the light intensity becomes 1/2 or more of the maximum value P _max ), that is, the optical pulse width Δt is, for example, 0.5 ns to 5 ns.

  FIG. 3 is a diagram for explaining the instantaneous optical spectrum (optical spectrum at one time) of the broadband optical pulse 5 within a period corresponding to the optical pulse width Δt (hereinafter referred to as an optical pulse duration). The horizontal axis is the wavelength. The vertical axis represents the optical power density (light intensity per unit wavelength).

  A wavelength range wr illustrated in FIG. 3 indicates a wavelength range in which the optical power density of the broadband optical pulse 5 is 1/2 or more of the maximum value (hereinafter referred to as an optical pulse wavelength range). The optical pulse wavelength range wr is preferably constant within the optical pulse duration, but generally varies slightly with time. In the present embodiment, the wavelength range common to each optical pulse wavelength range wr at all times within the optical pulse duration (that is, the wavelength band of the optical pulse) is a predetermined wavelength range (for example, 1525 nm to 1575 nm). Thus, the SLD 6 and its driving condition are selected.

  FIG. 4 is a time-resolved light spectrum 16 of the broadband light pulse 5. As shown in FIG. 4, the time-resolved light spectrum 16 includes a time axis 10 corresponding to time, a wavelength axis 12 corresponding to wavelength, and an optical power density axis 14 corresponding to optical power density (light intensity per unit wavelength). have.

  As shown in FIG. 4, the broadband optical pulse 5 of the present embodiment has a predetermined optical pulse width Δt (for example, 0.5 ns to 5.0 ns), and a substantially constant time interval T (for example, 128 ns to 5120 ns). The broadband optical pulse 5 has a sufficiently wide predetermined wavelength band WR (for example, 1525 nm to 1575 nm).

(Ii) Optical Pulse Demultiplexing / Demultiplexing Unit The OCT apparatus 2 generates an optical pulse train composed of optical pulses having different center wavelengths from the broadband optical pulse 5 generated by the broadband optical pulse generation unit 4. A demultiplexing / demultiplexing unit 18 is provided.

  As shown in FIG. 1, the optical pulse demultiplexing / demultiplexing unit 18 of the present embodiment is a first unit that emits the broadband optical pulse 5 generated by the SLD 6 and incident on the light incident port 24 from the light incident / exit port 26. The optical circulator 27 is provided. Here, the light incident port 24 belongs to the first optical circulator 27.

  The present optical pulse demultiplexing delay multiplexing unit 18 demultiplexes the broadband optical pulse 5 emitted from the light incident / exit port 26 of the first circulator 27 and incident on the broadband light incident / exit port 28, An optical multiplexer / demultiplexer 32 that generates a narrow band optical pulse and emits each of the generated narrow band optical pulses from a corresponding narrow band light incident / exit port 30 is provided. The optical multiplexer / demultiplexer 32 of this embodiment is an arrayed waveguide grating (AWG), as shown in FIG. The number of channels of this AWG is, for example, 256 to 1024. Here, the broadband light incident / exit port 28 and the narrowband light incident / exit port 30 belong to the optical multiplexer / demultiplexer 32.

  The optical pulse demultiplexing / demultiplexing unit 18 delays each narrowband light pulse emitted from the narrowband light incident / exit port 30 of the optical multiplexer / demultiplexer 32 for a different time, and then narrows the light in the narrowband light. A plurality of optical delay devices 34 to be incident on the mouth 30 are provided.

  FIG. 5 is a schematic diagram illustrating the configuration of the optical delay device 34 according to the present embodiment. As shown in FIG. 5, the optical delay device 34 of the present embodiment is an optical fiber 36 in which a reflecting mirror 35 made of, for example, a gold deposition film is formed at one end. The other end of the optical fiber 36 is connected to the narrowband light incident / exit port 30 of the AWG 32. Here, the length of the optical fiber 36 is 1 time, 2 times, 3 times,... A predetermined length (for example, approximately 7.5 cm to 75 cm) in order from the shortest. The length 15 cm of the optical fiber 36 corresponds to a delay time of 1 ns.

  The optical multiplexer / demultiplexer 32 on which the delayed narrow-band optical pulse 22 is incident multiplexes the narrow-band optical pulse to generate an optical pulse train (hereinafter referred to as a narrow-band optical pulse train), and the generated narrow-band optical pulse train Is emitted from the broadband light incident / exit port 28.

  Next, the narrow-band optical pulse train 20 emitted from the broadband light incident / exit port 28 enters the light incident / exit port 26 of the first optical circulator 27 and exits from the light exit port 37 of the first optical circulator 27.

FIG. 6 is a time-resolved light spectrum of the narrow-band optical pulse train 20. As shown in FIG. 6, each narrow-band optical pulse 22 of the narrow-band optical pulse train 20 of the present embodiment has a substantially constant optical pulse width Δt _nb (for example, 0.5 ns to 5.0 ns) and a substantially constant. It has a wavelength band WR _nb (for example, 0.05 to 0.20 nm).

As described above, the narrow-band optical pulse 22 is formed by demultiplexing the broadband optical pulse 5 by the AWG 32. Therefore, the optical pulse width Δt _nb of the narrow-band optical pulse 22 is a predetermined value that is substantially the same as the optical pulse width Δt of the broadband optical pulse 5. Further, the optical pulse wavelength band WR _nb of the narrow band optical pulse 22 is a predetermined value that is substantially the same as the channel width of the AWG 32.

Each narrow-band light pulse 22 formed by the AWG 32 exits the narrow-band light entrance / exit 30 of the AWG 32 substantially simultaneously, and is delayed by different times D1, D2, D3,. Thereafter, each narrow-band light pulse 22 enters the narrow-band light entrance / exit 30 of the AWG 32 and is then combined into a narrow-band light pulse train 20 as shown in FIG. Here, the delay times D1, D2, D3,... Of each narrowband optical pulse 22 are the times when the narrowband optical pulses 22 are not overlapped (more precisely, the optical pulse duration of each narrowband optical pulse 22 It is preferable that the delay time is not to overlap. That is, it is preferable that the interval (= D2-D1, D3-D2...) Of each narrow-band light pulse 22 is equal to or larger than the light pulse width Δt _nb of the narrow-band light pulse 22. Although only five optical pulses are shown in FIG. 6, the number of optical pulses in the narrow-band optical pulse train 20 usually reaches several hundreds.

  As described above, the optical pulse demultiplexing delay multiplexing unit 18 generates a plurality of narrowband optical pulses 22 whose wavelength band is narrower than the wavelength band (predetermined wavelength band) of the wideband optical pulse, and each narrowband light. An optical pulse train 20 composed of a plurality of optical pulses having different center wavelengths is generated by multiplexing the pulses 22 after being delayed for different times.

(Iii) Optical splitter The present OCT apparatus 2 has an optical splitter 42 that branches the narrow-band optical pulse train 20 into a measurement optical pulse train 38 and a reference optical pulse train 40. Here, the optical splitter 42 is, for example, a directional coupler. The branching ratio of the optical splitter 42 is, for example, 90% (measurement light pulse train side) and 10% (reference light pulse train side).

(Iv) Light Irradiation / Supplement Unit The OCT apparatus 2 also includes a light irradiation / supplementation unit 50 that supplements the backscattered light pulse train 48 generated by the measurement light pulse train 38 being backscattered by the measurement object 46. . The measurement object 46 is, for example, a retina, an anterior eye portion, a built-in inner wall, or the like.

  Here, as shown in FIG. 1, the light irradiation / supplementation unit 50 is configured to emit a measurement light pulse train 38 that is branched by the optical branching device 42 and incident on the light incident port 24a from the light incident / exit port 26a. It has an optical circulator 27a.

  The light irradiation / supplementation unit 50 also has a collimator lens 52 that converts the measurement light pulse train 38 emitted from the light incident / exit port 26a of the second circulator 27a into a parallel light beam 56. Further, the light irradiation / supplementation unit 50 has a galvanometer mirror 54 that deflects the parallel light beam 56 (measurement light pulse train), and a focusing lens 58 that collects the deflected parallel light beam 56 and irradiates the measurement object 46. Yes. Here, the galvanometer mirror 54 responds to a command from the computer 62 of the tomographic image deriving unit 60 described later, and immediately before each time point when the SLD 6 repeatedly generates the broadband light pulse 5, This is a device that moves the irradiation position of the optical pulse train) along a straight line on the measurement object 46.

  The measurement light pulse train applied to the measurement object 46 is applied to the measurement object 46, and a part of the measurement light pulse train is backscattered to form a backscattered light pulse train 48. The backscattered light pulse train 48 is incident on the focusing lens 58, then travels backward in the optical path along which the measurement light pulse train has traveled, and enters the light incident / exit port 26a of the second optical circulator 27a. The light exits from the light exit 37a of the circulator 27a.

  As described above, the main irradiation / supplementing unit 50 irradiates the measurement light pulse train 38 to the measurement object 46 and supplements the backscattered light pulse train 48 generated by the measurement light pulse train 38 being backscattered by the measurement object 46. The irradiation position of the measurement light pulse train is moved before each time point at which the broadband light pulse 5 is repeatedly generated.

(V) Optical Delay Unit The OCT apparatus 2 has an optical delay unit 64 that adjusts the optical length of the optical path of the reference light pulse train 40.

  As shown in FIG. 1, the optical delay unit 64 has a third optical circulator 27b that emits the reference light pulse train 40 branched to the optical splitter 42 and incident on the light incident port 24b from the light incident / exit port 26b. doing. The optical delay unit 64 has a collimator lens 52b that converts the reference light pulse train emitted from the light incident / exit port 26b of the third circulator 27b into a parallel light beam 56b. Further, the optical delay unit 64 has a focusing lens 58 b that collects the parallel light beam (reference light pulse train) 56 b and irradiates the reference mirror 66. Here, the reference mirror 66 is movable in the traveling direction of the reference light pulse train.

  The reference light pulse train irradiated on the reference mirror 66 is reflected by the reference mirror 66, reverses the traveling direction, and enters the focusing lens 58b. Thereafter, the reference light pulse train travels backward along the traveling optical path, enters the light incident / exit port 26b of the third optical circulator 27b, and exits from the light exit port 37b of the third optical circulator 27b.

  Here, the reference mirror 66 has a function of moving in the traveling direction of the parallel light 56b and adjusting the optical length of the optical path of the reference optical pulse train 40 (hereinafter referred to as the reference optical path) to a desired length. Yes. In the present embodiment, the optical length of the optical path of the reference light pulse train 40 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 train 38 and the optical path of the backscattered light pulse train 48. Then, the position of the reference mirror 66 is adjusted.

(Vi) Optical Coupler The OCT apparatus 2 further includes an optical coupler 70 that combines the reference light pulse train 40 and the backscattered light pulse train 48 to form combined light pulse trains 68a and 68b. Yes. Here, the optical coupler 70 is a directional coupler, for example, and the branching ratio is 50% to 50%.

  The optical coupler 70 emits a first combined optical pulse train 68a from the first exit port, and emits a second combined optical pulse train 68b from the second exit port. Both the first combined light pulse train 68 a and the second combined light pulse train 68 b are interference light beams of the reference light pulse train 40 and the backscattered light pulse train 48. However, in the first combined optical pulse train 68a and the second combined optical pulse train 68b, the phase of the light intensity of each optical pulse that periodically changes with respect to the wavelength is shifted by π.

  That is, when the intensity of each optical pulse of the reference optical pulse train 40 and the backscattered optical pulse train 48 is constant and each optical pulse reaches the optical coupler 70 in the order of the size of the center wavelength, the first combined optical pulse train The intensity of each optical pulse in 68a and the second combined optical pulse train 68b is a trigonometric function with the generation order as a variable. The phase of this trigonometric function is shifted by π between the first combined optical pulse train 68a and the second combined optical pulse train 68b.

  The optical branching device 42, the light irradiation / supplementing unit 50, the optical delay unit 64, the optical coupler 70, and the optical fiber connecting these optical devices form a Matsender interferometer. Since the reference optical path and the measurement optical path are substantially equal as described above, the optical pulse of the reference optical pulse train and the optical pulse of the backscattered optical pulse train derived from the same narrowband optical pulse 22 are overlapped by the optical coupler 70. have a finger in the pie.

(Vii) Optical Pulse Intensity Measurement Unit The present OCT apparatus 2 has an optical pulse intensity measurement unit 72 that measures the optical intensity of each optical pulse in the combined optical pulse trains 68a and 68b. The optical pulse intensity measurement unit 72 of the present embodiment includes a first photodetector 74a (for example, a pin photodiode), a second photodetector 74b (for example, a pin photodiode), and these photodetectors 74a. , 74b, a differential amplifier 76 is connected.

  Here, the first photodetector 74 a detects the light intensity of the first combined optical pulse train 68 a and supplies the output signal to the positive input terminal of the differential amplifier 76. On the other hand, the second photodetector 74 b detects the light intensity of the second combined optical pulse train 68 b and supplies the output signal to the negative input terminal of the differential amplifier 76.

  As described above, the phases of the optical pulses in the combined optical pulse trains 68a and 68b are shifted by π. Therefore, the differential amplifier 76 removes the direct current component included in each optical pulse, amplifies only the vibration component, and transmits the optical pulse intensity signal 94 to the high-speed analog-digital conversion unit 78 described below. The vibration component is an interference signal generated by interference between the optical pulse of the first combined optical pulse train 68a and the optical pulse of the second combined optical pulse train 68b.

(Viii) Tomographic image deriving unit
The OCT apparatus 2 further includes a tomographic image deriving unit 60 for deriving a tomographic image of the measurement object 46 based on the light intensity of each light pulse of the combined light pulse train and the irradiation position 44 of the measurement light pulse train.

  The tomographic image deriving unit 60 performs high-speed analog-digital conversion unit 78 (hereinafter referred to as “AD conversion”) and records the output signal (hereinafter referred to as “light pulse intensity signal 94”) of the light pulse intensity measurement unit 72 after analog-digital conversion. (Hereinafter referred to as a high-speed AD conversion unit).

  Here, the high-speed AD conversion unit 78 includes an analog / digital converter (hereinafter referred to as an AD converter) 80 that performs AD conversion on the output of the optical pulse intensity measurement unit 72, and a digital signal converted by the AD converter 80. A memory unit 82 (for example, Random Access Memory) for recording signals is included.

  The tomogram deriving unit 60 controls the operation of the voltage pulse generator 8, the galvanometer mirror 54, the high-speed AD conversion unit 78, and the like, and processes the digital signal converted by the high-speed AD conversion unit 78 to measure the object. A computer 62 for deriving 46 tomographic images is provided.

  The computer 62 includes a CPU (Central Processing Unit) 84, a main storage device (for example, Random Access Memory) 86, and an auxiliary storage device 88 (such as a magnetic disk) in which a control program for the OCT device 2 is recorded. Yes.

  In order for the computer 62 to realize the above functions, the computer 62 is started and a control program is loaded from the auxiliary storage device 88 to the main storage device 86. After that, the CPU 84 responds to the command of the control program in the main storage device 86 (that is, by executing the control program in the main storage device 86), thereby controlling other devices (such as the high-speed AD conversion unit 78). In addition, an arithmetic control device for deriving a tomographic image is obtained.

  With the above configuration, the tomographic image deriving unit 78 performs Fourier transform on the measurement data corresponding to the light intensity of the light pulse based on the wave number of each light pulse in the combined light pulse trains 68a and 68b, and the Fourier transformed measurement data and measurement light pulse train. Based on the 38 irradiation positions 44, a tomographic image of the measurement object 46 is derived (see “(2) Operation” below).

(2) Operation Next, the operation of the OCT apparatus 2 will be described.

―Operation of electronic devices―
First, the operation of each electronic device forming the OCT apparatus 2 will be described.

  The CPU 84 of the tomographic image deriving unit 60 receives a command from the control program in the main storage device 86, and sends a command 96 to a drive device (not shown) of the galvano mirror 54 of the light irradiation / supplementation unit 50 to measure light. The irradiation position 44 of the pulse train 38 is set to a desired position on the measurement target.

  Next, the CPU 84 receives a command of a control program in the main storage device 86 and transmits a trigger 90 to the voltage pulse generator 8. In response to the trigger 90, the voltage pulse generator 8 transmits the trigger 92 to the high-speed AD conversion unit 78 and applies one voltage pulse to the SLD 6. The SLD 6 to which the voltage pulse is applied generates the broadband light pulse 5.

  On the other hand, the AD converter 80 of the high-speed AD conversion unit 78 starts AD conversion of the optical pulse intensity signal 94 output from the optical pulse intensity measurement unit 72 in response to the trigger 92. As described above, AD conversion is started in synchronization with the optical pulse intensity signal 94 corresponding to the first optical pulse of the combined optical pulse trains 68a and 68b.

  In the present embodiment, the AD conversion cycle is set to substantially coincide with the time interval of each optical pulse of the combined optical pulse trains 68a and 68b. Further, the AD converter 80 repeats the AD conversion at least as many times as the number of optical pulses in the combined optical pulse trains 68a and 68b.

  With the above procedure, the AD converter 80 AD converts the optical pulse intensity signal 94 in synchronization with the optical pulses of the combined optical pulse trains 68a and 68b. Then, the high-speed AD conversion unit 78 sequentially records the AD converted optical pulse intensity signal 94 in the memory unit 82.

  After completion of the above series of operations, the CPU 84 receives a command from the control program in the main storage device 86 and transmits a command 96 to a drive device (not shown) of the galvano mirror 54. In response to this command 96, the driving device controls the attitude of the galvanometer mirror 54 to slightly move the irradiation position 44 of the measurement light pulse train 38 along a straight line on the measurement target.

  Next, the CPU 84 receives a command of the control program in the main storage device 86 and transmits the trigger 90 to the voltage pulse generator 8 again. In response to the trigger 90, the voltage pulse generator 8 transmits the trigger 92 to the high-speed AD conversion unit 78 again and applies a voltage pulse to the SLD 6. The SLD 6 to which the voltage pulse has been applied generates the broadband light pulse 5 again. Further, the high-speed analog-digital converter 78 restarts AD conversion in response to the trigger 92 and sequentially records the digitized optical pulse intensity signal 94 in the memory unit 82.

  The electronic device of the present OCT apparatus 2 performs the above-described movement of the irradiation position 44, generation of the broadband optical pulse 5, AD conversion and recording of the optical pulse intensity signal 94 along a straight line on the measurement target, for example, Repeat several tens to several thousand times.

  Next, the CPU 84 receives an instruction of a control program in the main storage device 86, receives the measurement data (digitized optical pulse intensity signal) in the memory unit 82 at once, and records it in the main storage device 86.

  Next, the CPU 84 receives an instruction of a control program in the main storage device 86, reads out the measurement data recorded in the main storage device 86, and Fourier transforms the received measurement data by the center wave number of each optical pulse of the combined optical pulse train. To do. The center wave number of the optical pulse is a wave number (= 2π / wavelength) corresponding to the center wavelength of the wavelength band of the optical pulse.

  Next, the computer 62 receives a command from the control program in the main storage device 86 and derives a tomographic image of the measurement object 46 based on the square of the absolute value of the measurement data subjected to Fourier transform and the irradiation position of the measurement light pulse train. To do. This calculation process is substantially the same as the tomographic image derivation process disclosed in Patent Document 1 and the like.

  By the way, the pulse width Δt of the narrow-band light pulse 22 is, for example, 0.5 ns to 5 ns. Further, the number of narrowband optical pulses 22 included in the narrowband optical pulse train 20 is, for example, 256 to 1012. Therefore, the time required to irradiate the measurement light pulse train 38 to one irradiation position 44 is 128 ns to 5 μs.

In order to form a two-dimensional tomographic image, it is preferable to irradiate at least about 100 irradiation positions 44 with the measurement light pulse train. The time required for irradiation of such a measurement light pulse train is as follows:
12 μs (= 128 ns × 100 points) to 5 ms (= 5 μs × 100 points). That is, according to the present OCT apparatus 2, data used for deriving a two-dimensional tomographic image can be obtained in a very short time. Despite such high-speed measurement, the present OCT apparatus 2 has only two photodetectors. As described above, according to the present embodiment, it is possible to capture a tomographic image at high speed by using an OCT apparatus including a small number of photodetectors.

In the present embodiment, the optical pulse intensity of the first combined optical pulse train 68a (the optical intensity of the optical pulse) and the optical pulse intensity of the second combined optical pulse train 68b are differentially amplified, and the differentially amplified optical pulse The intensity is Fourier transformed. However, only the optical pulse intensity of the first combined optical pulse train 68a (or the optical pulse intensity of the second combined optical pulse train 68b) is measured with one photodetector and then amplified, and the measured and amplified optical pulse intensity is measured. May be directly Fourier transformed. Further, the wave number of each optical pulse of the combined optical pulse train used for Fourier transform is not necessarily the center wave number. However, the wave number used for the Fourier transform is preferably the wave number corresponding to the wavelength in the wavelength band WR _nb of each optical pulse.

―Operation of optical device―
Next, the operation of each optical device forming the OCT apparatus 2 will be described.

  First, the SLD 6 of the broadband optical pulse generation unit 4 generates the broadband optical pulse 5 having a predetermined wavelength band in response to the trigger 90 transmitted by the CPU 62.

  The broadband optical pulse 5 generated by the SLD 6 enters the light incident port 24 of the first optical circulator 27 and exits from the light incident / exit port 26.

  Next, the broadband optical pulse 5 emitted from the light incident / exit port 26 is incident on the broadband light incident / exit port 28 of the optical multiplexer / demultiplexer (AWG) 32 and is demultiplexed into a plurality of narrowband optical pulses 22 to cope with them. The light is emitted from the narrow-band light incident / exit port 30.

  Each narrow-band light pulse 22 is incident on an optical delay device (optical fiber) 34 connected to the emitted narrow-band light incident / exit port 30. The narrow-band light pulse 22 that has entered the optical delay device 34 is reflected by a reflecting mirror 35 formed at the end of the optical delay device 34, and enters the optical multiplexer / demultiplexer (AWG) 32 from the narrow-band light input / output port 30. To do. At this time, since the optical lengths of the respective optical delay devices (optical fibers) 34 are different, the narrow-band optical pulse 22 is delayed by different times and then enters the optical multiplexer / demultiplexer (AWG) 32.

  The narrow-band optical pulse 22 incident on the optical multiplexer / demultiplexer (AWG) 32 is combined to form a narrow-band optical pulse train 20 and is emitted from the broadband light incident / exit port 28. Thereafter, the narrow-band optical pulse train enters the light incident / exit port 26 of the first optical circulator 27 and then exits from the light output port 37 of the first optical circulator 27.

  Next, the narrow-band optical pulse train 20 enters the optical branching device 42 and is branched into the measuring optical pulse train 38 and the reference optical pulse train 40.

  The measurement light pulse train 38 enters the light incident port 24a of the second optical circulator 27a of the light irradiation / supplementation unit 50, and exits from the light incident / exit port 26a. Next, the measurement light pulse train 38 enters the collimator lens 52 and is converted into a parallel light beam 56.

  The parallel light beam 56 (measurement light pulse train 38) is deflected by the galvanometer mirror 54. Thereafter, the parallel light beam 56 is collected by the focusing lens 58 and irradiated onto the measurement object 46.

  A part of the measurement light pulse train 38 irradiated to the measurement object 46 is backscattered inside the measurement object 46 to become a backscattered light pulse train 48. The backscattered light pulse train 48 is incident on the focusing lens 58, and then travels back along the optical path through which the measurement light pulse train 38 travels, and then enters the light incident / exit port 26a of the second optical circulator 27a. The light exits from the light exit 37a of the second optical circulator 27a.

  On the other hand, the reference light pulse train 40 enters the light incident port 24b of the third optical circulator 27b of the optical delay unit 64, and then exits from the light incident / exit port 26b. Next, the reference light pulse train 40 enters the collimator lens 52b and is converted into a parallel light beam 56b. The parallel light beam 56b (reference light pulse train 40) is collected by the focusing lens 58b and applied to the reference mirror 66.

  The reference light pulse train 40 irradiated on the reference mirror 66 is reflected by the reference mirror 66, and its traveling direction is reversed, and then enters the focusing lens 58b. Thereafter, the reference light pulse train 40 travels backward through the traveling optical path, enters the light incident / exit port 26b of the third optical circulator 27b, and exits from the light exit port 37b of the third optical circulator 27b. Here, the position of the reference mirror 66 is adjusted such that the sum of the optical path length of the measurement light pulse train 38 and the optical path length of the backscattered light pulse train 48 is substantially equal to the optical path length of the reference light pulse train 40.

  Thereafter, the measurement light pulse train 38 and the reference light pulse train 40 are incident on the first light entrance and the second light entrance of the optical coupler 70, respectively. Thereafter, the measurement light pulse train 38 and the reference light pulse train 40 are combined by the optical coupler 70 and then emitted from the first light exit port and the second light exit port of the optical coupler 70. Here, the first coupled light pulse train 68 a is emitted from the first light exit of the optical coupler 70. On the other hand, a second combined light pulse train 68b having a phase different from that of the first combined light pulse train 68a by the second light output port of the optical coupler 70 is emitted.

  Next, the first combined optical pulse train 68a and the second combined optical pulse train 68b are incident on the first photodetector 74a and the second photodetector 74b of the optical pulse intensity measurement unit 72, respectively. The photodetectors 74 a and 74 b generate the light intensity signal 94 corresponding to the light intensity of each light pulse in the combined light pulse trains 68 a and 68 b, and transmit the light intensity signal 94 to the AD converter 80. Subsequent signal processing is as described above.

(3) Tomographic imaging method Next, a tomographic imaging method of the present embodiment will be described. Initially, the interference data acquisition process repeated by the tomography method of this Embodiment is demonstrated.

  First, a broadband optical pulse 5 having a predetermined wavelength band is generated (see FIG. 1).

  Next, the broadband optical pulse 5 is demultiplexed to generate a plurality of narrow-band optical pulses whose wavelength band is narrower than the predetermined wavelength band, and the respective narrow-band optical pulses are delayed for different times and then combined. Thus, a narrow-band optical pulse train 20 composed of a plurality of optical pulses having different center wavelengths is generated.

  Next, the narrow-band optical pulse train 22 is branched into a measurement optical pulse train 38 and a reference optical pulse train 40. Thereafter, the measurement light pulse train 38 is irradiated onto the measurement object 46, and the backscattered light pulse train 48 generated by the backscattering of the measurement light pulse train 38 by the measurement object 46 is supplemented.

  Next, the reference light pulse train 40 and the backscattered light pulse train 48 are combined to form combined light pulse trains 68a and 68b.

  Next, the light intensity of each light pulse in the combined light pulse trains 68a and 68b is measured. Here, the intensity measurement of the optical pulse can be performed by two photodetectors as described in the above “(2) Operation”. Thus, the interference data acquisition process is completed.

  In the present embodiment, after slightly moving the irradiation position 44 of the measurement light pulse train along the straight line on the measurement pair, the step of performing the interference data acquisition step is repeatedly performed.

  Thereafter, the measurement data (digitized optical pulse intensity signal 94) corresponding to the light intensity of the combined optical pulse trains 68a and 68b is subjected to Fourier transform according to the wave number of each optical pulse of the combined optical pulse trains 68a and 68b, and the Fourier transform is performed. Based on the data and the irradiation position 44, a tomographic image of the measurement object 46 is derived. Thereafter, the derived tomographic image is output to an output device (for example, a display device) of the computer 62.

  As is clear from the above description, only one or two photodetectors are used in the tomographic layer imaging method. Therefore, according to the tomographic layer imaging method, a tomographic image can be captured at high speed with a small number of photodetectors.

(4) OCT Light Source and Optical Pulse Train Generation Method FIG. 7 is a diagram illustrating the configuration of the OCT light source 100 of the present embodiment. In the above example, as shown in FIG. 1, the broadband optical pulse generation unit 4 and the optical pulse demultiplexing / demultiplexing unit 18 are integrated with other parts (hereinafter referred to as the OCT main body part) such as the optical branching unit 42. It has become. However, as shown in FIG. 7, the broadband optical pulse generation unit 4 and the optical pulse demultiplexing / demultiplexing unit 18 may be separated from the OCT main body portion to form the OCT light source 100 including these units.

  As shown in FIG. 7, the OCT light source 100 includes the broadband optical pulse generation unit 4 and the optical pulse demultiplexing delay multiplexing unit 18 described above. Further, the OCT light source 100 has an optical connector 102 into which the narrow-band optical pulse train 20 emitted from the light emission port 37 of the first optical circulator 27 enters. Further, the OCT light source 100 is generated by the voltage pulse generator 8 in response to the first electrical connector 104 to which the first trigger 90 supplied to the voltage pulse generator 8 is input and the first trigger 90. It has a second electrical connector 106 that outputs a second trigger 92.

  With the above configuration, the OCT light source 100 of the present embodiment responds to the first trigger 90 input to the first electrical connector 104 to generate a tomographic image pulse train (narrowband optical pulse train 20). Generate. This optical pulse train for tomographic imaging is supplied to the optical branching device 42 of the OCT main body through an optical fiber optically connected to the optical connector 102. The first trigger 90 is supplied from the tomographic image deriving unit 60 of the OCT main body through an electric cable electrically connected to the first electric connector 104. Further, the second trigger 92 is supplied to the tomographic image deriving unit 60 of the OCT main body through an electric cable electrically connected to the second electric connector 106.

  Here, the operation of the OCT light source 100 includes the operation of the broadband optical pulse generation unit 4 and the operation of the optical pulse demultiplexing / demultiplexing unit 18 in the OCT apparatus 2. Further, the generation method of the optical pulse train for tomographic imaging performed in the OCT light source 100 is the step of generating the broadband optical pulse 5 and the narrow-band optical pulse train 20 described in “(3) Tomographic imaging method”. Comprises the steps of generating Therefore, detailed description thereof will be omitted.

  According to the present OCT light source, the performance of the OCT apparatus can be changed by changing the specifications of the OCT light source 100 connected to the OCT main body. For example, the resolution of the tomographic image and the measurement range can be changed by using the OCT light source 100 in which the wavelength band of the SLD 6 and the number of channels of the AWG 32 are different.

  In the above embodiment, the optical pulse demultiplexing delay multiplexing unit 18 is formed by the optical circulator 27, the AWG 32, and the optical fiber delay unit 34. However, the optical pulse demultiplexing delay multiplexing unit may be formed by other optical members, for example, an optical circulator, a diffraction grating, and a reflecting mirror.

  In the above example, a directional coupler is used as the optical branching device. However, other optical members such as a Y-branch waveguide or a multimode interference waveguide may be used as the optical branching device.

  In the above example, the measurement light pulse train is scanned by the galvanometer mirror. However, the scanning of the measurement light pulse train may be executed by another light deflection unit such as a polygon scanner. Further, by using a combination of a polygon scanner and a galvanometer mirror, high-speed two-dimensional scanning of the measurement light pulse train is possible. Thereby, high-speed imaging of a three-dimensional tomographic image becomes possible.

  In the above example, data for deriving a two-dimensional tomographic image is acquired by repeatedly generating a broadband light pulse and moving the irradiation position 44 of the measurement light pulse train. However, a one-dimensional tomographic image may be taken from data obtained by generating a broadband light pulse only once and irradiating a point on the measurement target with a measurement light pulse train. In this case, the generation of the broadband optical pulse is not repeated. Further, the irradiation position 44 of the measurement light pulse train is not moved in accordance with the generation of the broadband light pulse.

  In the above example, the broadband optical pulse generation unit 4 is formed by the SLD 6 and the voltage pulse generator 8. However, the broadband optical pulse generation unit 4 may be formed by another configuration, a mode-locked laser and the voltage pulse generator 8.

DESCRIPTION OF SYMBOLS 2 ... OCT apparatus 4 ... Broadband optical pulse generation unit 5 ... Broadband optical pulse 18 ... Delay multiplexing unit 22 ... Narrow band optical pulse 32 ... Optical multiplexer / demultiplexer 34 ... Optical delay unit 38 ... Measurement optical pulse train 40 ... Reference optical pulse train 42 ... Optical splitter 48 ... Back scattered light pulse train 50 ... Light irradiation / supplementing unit 60 ... Tomographic image deriving unit 64 ... Optical delay units 68a, 68b ... Combined optical pulse train 70 ... Optical coupler 72 ... Optical pulse intensity measuring unit 78 ... High-speed analog-digital conversion unit

Claims (5)

A broadband optical pulse generating unit for generating a broadband optical pulse having a predetermined wavelength band; and
The broadband optical pulse is demultiplexed to generate a plurality of narrowband optical pulses whose wavelength band is narrower than the predetermined wavelength band, and each of the narrowband optical pulses is delayed for a different time, and then multiplexed. An optical pulse demultiplexing delay multiplexing unit for generating an optical pulse train composed of a plurality of optical pulses having different wavelengths;
An optical splitter that branches the optical pulse train into a measurement optical pulse train and a reference optical pulse train;
A light pulse irradiation / supplementation unit that irradiates the measurement light pulse train to the measurement object and supplements the backscattered light pulse train generated by the measurement light pulse train being backscattered by the measurement object;
An optical coupler that combines the reference light pulse train and the backscattered light pulse train to form a combined light pulse train;
An optical pulse intensity measurement unit for measuring the optical intensity of each optical pulse of the combined optical pulse train;
The wave number of the light pulse of the combined optical pulse train, the measurement data corresponding to the light intensity Fourier transform, on the basis of the measurement data obtained by performing Fourier transform, have a tomogram derivation unit for deriving a tomographic image of the measurement target And
The optical pulse demultiplexing delay multiplexing unit is:
An optical circulator for emitting the broadband optical pulse incident on the light incident port from the light incident / exit port;
The broadband optical pulse emitted from the light incident / exit port and incident on the broadband light incident / exit port is demultiplexed to generate a plurality of the narrowband optical pulses, and each of the generated narrowband optical pulses is associated with the corresponding narrowband optical pulse. An optical multiplexer / demultiplexer that emits light from the band light incident / exit port;
Each of the narrow-band light pulses emitted from the narrow-band light incident / exit port is delayed by different times, and then is incident on the narrow-band light incident / exit port from which each of the narrow-band light pulses is emitted. An optical delay device,
The optical multiplexer / demultiplexer generates the optical pulse train by combining the narrow-band optical pulses incident from the narrow-band optical input / exit port, and causes the generated optical pulse train to be output from the broadband optical input / output port,
The optical pulse train emitted from the broadband light entrance / exit is incident on the light entrance / exit, and exits from the exit of the optical circulator.
Optical coherence tomography device. The optical coherence tomography device according to claim 1 ,
The optical multiplexer / demultiplexer is an array optical waveguide grating;
The optical delay device is an optical fiber having one end connected to the narrow-band light input / output port of the arrayed waveguide grating and a reflecting mirror formed at the other end.
Features optical coherence tomography equipment. Optical coherence tomography for deriving a tomographic image of the measurement object by irradiating the measurement object with the measurement light pulse train after branching an optical pulse train composed of a plurality of optical pulses having different center wavelengths A light source used in the apparatus,
A broadband optical pulse generating unit for generating a broadband optical pulse having a predetermined wavelength band; and
The broadband optical pulse is demultiplexed to generate a plurality of narrowband optical pulses having a wavelength band narrower than the predetermined wavelength band, and after the respective narrowband optical pulses are delayed for different times, An optical pulse demultiplexing / demultiplexing unit for generating an optical pulse train ,
The optical pulse demultiplexing delay multiplexing unit is:
An optical circulator for emitting the broadband optical pulse incident on the light incident port from the light incident / exit port;
The broadband optical pulse emitted from the light incident / exit port and incident on the broadband light incident / exit port is demultiplexed to generate a plurality of the narrowband optical pulses, and each of the generated narrowband optical pulses is associated with the corresponding narrowband optical pulse. An optical multiplexer / demultiplexer that emits light from the band light incident / exit port;
Each of the narrow-band light pulses emitted from the narrow-band light incident / exit port is delayed by different times, and then is incident on the narrow-band light incident / exit port from which each of the narrow-band light pulses is emitted. An optical delay device,
The optical multiplexer / demultiplexer generates the optical pulse train by combining the narrow-band optical pulses incident from the narrow-band optical input / exit port, and causes the generated optical pulse train to be output from the broadband optical input / output port,
The optical pulse train emitted from the broadband light entrance / exit is incident on the light entrance / exit, and exits from the exit of the optical circulator.
Light source for optical coherence tomography equipment. A broadband optical pulse generating unit for generating a broadband optical pulse having a predetermined wavelength band; and
The broadband optical pulse is demultiplexed to generate a plurality of narrowband optical pulses whose wavelength band is narrower than the predetermined wavelength band, and each of the narrowband optical pulses is delayed for a different time, and then multiplexed. An optical pulse demultiplexing delay multiplexing unit for generating an optical pulse train composed of a plurality of optical pulses having different wavelengths;
An optical splitter that branches the optical pulse train into a measurement optical pulse train and a reference optical pulse train;
A light pulse irradiation / supplementation unit that irradiates the measurement light pulse train to the measurement object and supplements the backscattered light pulse train generated by the measurement light pulse train being backscattered by the measurement object;
An optical coupler that combines the reference light pulse train and the backscattered light pulse train to form a combined light pulse train;
An optical pulse intensity measurement unit for measuring the optical intensity of each optical pulse of the combined optical pulse train;
A measurement image corresponding to the light intensity is Fourier-transformed according to the wave number of each optical pulse in the combined optical pulse train, and a tomographic image deriving unit for deriving the tomographic image of the measurement object based on the Fourier-transformed measurement data. And
The optical pulse demultiplexing delay multiplexing unit,
An optical circulator for emitting the broadband optical pulse incident on the light incident port from the light incident / exit port;
The broadband optical pulse emitted from the light incident / exit port and incident on the broadband light incident / exit port is demultiplexed to generate a plurality of the narrowband optical pulses, and each of the generated narrowband optical pulses is associated with the corresponding narrowband optical pulse. An optical multiplexer / demultiplexer composed of an arrayed optical waveguide grating that emits light from a band light incident / exit port;
It consists of an optical fiber having one end connected to the narrowband light incident / exit port and a reflecting mirror formed at the other end, and each of the narrowband light pulses emitted from the narrowband light incident / exit port is delayed for different times. And a plurality of optical delay devices that enter the narrow-band light incident / exit port,
The optical multiplexer / demultiplexer generates the optical pulse train by combining the narrow-band light pulses incident from the narrow-band light input / exit port, and causes the generated optical pulse train to be output from the broadband light input / output port,
The optical pulse train emitted from the broadband light entrance / exit is incident on the light entrance / exit, and exits from the exit of the optical circulator.
Optical coherence tomography device. Optical coherence tomography for deriving a tomographic image of the measurement object by irradiating the measurement object with the measurement light pulse train after branching an optical pulse train composed of a plurality of optical pulses having different center wavelengths A light source used in the apparatus,
A broadband optical pulse generating unit for generating a broadband optical pulse having a predetermined wavelength band; and
The broadband optical pulse is demultiplexed to generate a plurality of narrowband optical pulses having a wavelength band narrower than the predetermined wavelength band, and after the respective narrowband optical pulses are delayed for different times, An optical pulse demultiplexing / demultiplexing unit for generating an optical pulse train,
The optical pulse demultiplexing delay multiplexing unit,
An optical circulator for emitting the broadband optical pulse incident on the light incident port from the light incident / exit port;
The broadband optical pulse emitted from the light incident / exit port and incident on the broadband light incident / exit port is demultiplexed to generate a plurality of the narrowband optical pulses, and each of the generated narrowband optical pulses is associated with the corresponding narrowband optical pulse. An optical multiplexer / demultiplexer composed of an arrayed optical waveguide grating that emits light from a band light incident / exit port;
It consists of an optical fiber having one end connected to the narrowband light incident / exit port and a reflecting mirror formed at the other end, and each of the narrowband light pulses emitted from the narrowband light incident / exit port is delayed for different times. And a plurality of optical delay devices that enter the narrow-band light incident / exit port,
The optical multiplexer / demultiplexer generates the optical pulse train by combining the narrow-band light pulses incident from the narrow-band light input / exit port, and causes the generated optical pulse train to be output from the broadband light input / output port,
The optical pulse train emitted from the broadband light entrance / exit is incident on the light entrance / exit, and exits from the exit of the optical circulator.
Light source for optical coherence tomography equipment.

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