JP2007258368A - Wavelength tunable laser apparatus and optical tomography apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the change in frequency with time linear in an external resonator type wavelength tunable laser apparatus. <P>SOLUTION: The external resonator type wavelength tunable laser apparatus 10 comprises a semiconductor laser medium 11, a diffraction optical element 13 for spatially dispersing the wavelengths of the light emitted from the semiconductor laser medium 11, and a wavelength selecting means having a reflecting surface 15a moved across the light subjected to the wavelength dispersion by the diffraction optical element 13 and selectively reflecting part of the light as return light by the reflecting surface 15a. The wavelength selecting means is so constructed that the inverse of the wavelength of the return light changes linearly with time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength tunable laser apparatus having a variable oscillation wavelength, and an optical tomographic imaging apparatus that acquires an optical tomographic image of a measurement target using the wavelength tunable laser apparatus.

  Conventionally, as a wavelength tunable laser device having a variable oscillation wavelength, for example, an external resonator type device shown in FIG. In the apparatus shown in FIG. 8, the light emitted from the low reflection surface of the semiconductor laser medium 111 is converted into parallel light by the collimator lens 112 and then incident on the diffractive surface of the diffractive optical element 113. The diffracted light is incident on the polygon mirror 125 through the two relay lenses 124a and 124b. Of the wavelength-dispersed light, only light having a specific wavelength orthogonal to the reflection surface of the polygon mirror 125 and a wavelength component in the vicinity thereof is returned to the semiconductor laser medium 111 and returned. The semiconductor laser medium 111 is guided by the light having the specific wavelength to generate a standing wave, and emits light having the specific wavelength (hereinafter referred to as an oscillation wavelength). By rotating the polygon mirror 125, the wavelength of the return light can be continuously changed, and the oscillation wavelength can be swept. In the apparatus shown in FIG. 8, the wavelength change with respect to time is proportional to sin θ (θ is an inclination angle from the optical axis) and is substantially linear.

  Further, Patent Document 1 describes the wavelength tunable laser apparatus shown in FIG. 9 having a configuration in which the lenses 124 a and 124 b and the polygon mirror 125 of the apparatus shown in FIG. 8 are replaced with a lens 134 and a rotating disk 135. In this apparatus, only light having a specific wavelength is fed back to the semiconductor laser medium 111 by a slit-like mirror 145 a linearly extending in the radial direction provided on the surface of the rotating disk 135. By rotating the rotating disk 135, the wavelength of the returning light can be continuously changed, and the oscillation wavelength can be swept. In the apparatus shown in FIG. 9, the wavelength change with respect to time is proportional to tan θ (θ is the rotation angle), and has a substantially linear sine wave shape.

  As another example of the wavelength tunable laser device, in the fiber ring resonator using the optical fiber 142 connected to both ends of the semiconductor optical amplifier 141 as shown in FIG. 10, the oscillation wavelength is changed using the tunable Fabry-Perot filter 143. A device to be selected is described in Non-Patent Document 1. In this device, the light transmission direction is regulated by the isolators 144 and 145, and the light is output from the optical coupler 146 provided in a part of the fiber ring. In the apparatus shown in FIG. 10, the wavelength change with respect to time becomes sinusoidal due to the characteristics of the tunable Fabry-Perot filter.

By the way, an optical tomographic imaging apparatus using SS-OCT (Swept source OCT) measurement is known as an important application of the laser apparatus with variable wavelength sweep as described above. The optical tomographic imaging apparatus divides the coherence light emitted from the light source into measurement light and reference light, and then combines the reflected light and the reference light when the measurement light is applied to the measurement object, and reflects the reflected light. An optical tomographic image is acquired based on the intensity of the interference light between the light and the reference light. In an optical tomographic imaging apparatus for SS-OCT measurement, interference light is detected while temporally changing the frequency of light emitted from a light source, and is emitted from the light source using a Michelson interferometer. The reflected light and the reference light are interfered with each other while changing the frequency of the laser light. Then, the reflection intensity at the depth position of the predetermined measurement target is detected from the interferogram in the optical frequency domain, and a tomographic image is generated using this.
US 2005/0035295 Specification “Amplified, frequency swept lasers for frequency domain reflectometry and OCT imaging: design and scaling principles”, OPTICS EXPRESS, 2 May 2005, Vol.13, No.9, p3513-3528

  However, in the wavelength tunable laser device shown in FIGS. 8 to 10, the wavelength change with respect to time is substantially linear or sinusoidal. In an optical tomographic imaging apparatus or the like using a wavelength tunable laser apparatus as a light source as described above, frequency analysis is often performed using Fourier transform or the like on acquired data. It is not a frequency. In the analysis, better results are obtained for data distributed at approximately equal intervals with respect to variables than with data distributed discretely with respect to variables. Therefore, considering the distribution of acquired data, there has been a demand for a wavelength tunable laser device in which the frequency change with respect to time is linear.

  In addition, there is a method of using electric signal processing so that the frequency change with time becomes linear in a pseudo manner. However, in this case, a high-speed arithmetic processing circuit is required, which increases the cost of the entire apparatus, which is not preferable.

  In view of the above problems, an object of the present invention is to provide a wavelength tunable laser device in which a frequency change with respect to time is linear, and an optical tomographic imaging apparatus including the wavelength tunable laser device.

  The wavelength tunable laser device according to the present invention is an external resonator type wavelength tunable laser device, wherein the laser medium, the dispersion means for spatially wavelength-dispersing the light emitted from the laser medium, and the wavelength dispersion by the dispersion means. A reflection surface that moves across the light, and a wavelength selection unit that selectively reflects a part of the light as return light by the reflection surface, the wavelength selection unit having a wavelength of the return light The reciprocal number is configured to change linearly with respect to time.

  As the “dispersing means”, for example, a diffractive optical element, a prism or a grism can be used. Further, “the reciprocal of the wavelength of the return light changes linearly with time” means “the frequency of the return light changes linearly with time” and “the wave number of the return light changes linearly with time”. It is synonymous with. This is derived from the fact that the wavelength λ, the frequency ν, the wave number k, and the speed of light c are in a relationship of ν = c / λ and k = 2π / λ. In the wavelength tunable laser device of the present invention, when wavelength sweeping is repeated at a predetermined period, the reciprocal of the wavelength changes linearly with respect to time within the period. The “linear change” is not limited to a strict one, and any linear change can be used.

  In the above-described wavelength tunable laser device, the reflecting surface is partially provided on a rotating body that rotates around a predetermined axis, extends substantially in the radial direction of the rotating body, and forwards in the rotational direction of the rotating body. You may comprise so that it may become the curve shape used as a concave shape.

  Further, in a plane perpendicular to the predetermined axis including the reflecting surface, the light wavelength-dispersed by the dispersing means is linearly positioned in a direction intersecting the radial direction of the rotating body, and the light from each wavelength is You may comprise so that the distance to a predetermined axis may decrease monotonously or increase monotonously in order of wavelength.

  Furthermore, the optical tomographic imaging apparatus of the present invention includes the above-described wavelength tunable laser device, light splitting means for splitting the light emitted from the wavelength tunable laser device into measurement light and reference light, and the measurement light is a measurement target. Detecting means for combining the reflected light from the measurement object and the reference light, and interference light between the reflected light combined by the combining means and the reference light. Interference light detection means and image acquisition means for acquiring a tomographic image of the measurement object from the interference light detected by the interference light detection means.

  According to the wavelength tunable laser device of the present invention, a part of the light wavelength-dispersed by the dispersion unit is selectively returned as return light by the reflection surface of the wavelength selection unit, and the wavelength of the return light is set as the oscillation wavelength. Light emitted from the wavelength tunable laser device. Since the wavelength selection means is configured so that the reciprocal of the wavelength of the return light changes linearly with respect to time, it is possible to obtain a wavelength tunable laser device in which the frequency of the emitted light changes linearly with respect to time. .

  In addition, if the reflecting surface is partially provided on a rotating body that rotates around a predetermined axis and extends in a substantially radial direction of the rotating body, the light dispersed by the dispersion means and reflected. By arranging the surface to face each other, it is possible to easily obtain a configuration in which the reflection surface crosses the wavelength-dispersed light and selectively reflects a part of the light as the rotating body rotates. Further, if the reflecting surface has a curved shape that is concave toward the front in the rotational direction, the wavelength change with respect to time is different from the device shown in FIG. 9, and the return light can be set by appropriately setting the curved shape. Can be linearly changed with respect to time.

  Further, in the above configuration, in the plane perpendicular to the predetermined axis including the reflection surface, the light wavelength-dispersed by the dispersion means is linearly positioned in a direction intersecting the radial direction of the rotating body, and each wavelength If the distance from the light to the predetermined axis is monotonously decreasing or monotonically increasing in order of wavelength, there is a one-to-one correspondence between each point that reflects light on the reflecting surface extending in the substantially radial direction and the wavelength of the return light. In order to satisfy the relationship, the shape of the reflecting surface can be designed so that the reciprocal of the wavelength changes linearly with respect to time using the coordinates of each point and the wavelength of the return light as variables.

  Since the optical tomographic imaging apparatus of the present invention acquires a tomographic image using the light emitted from the wavelength tunable laser apparatus, the frequency of the measuring light changes linearly with respect to time. For this reason, it is possible to easily acquire data so that the data distribution with respect to the frequency is almost equally spaced, and good results can be obtained in the frequency analysis at the time of image acquisition.

  Hereinafter, embodiments of a wavelength tunable laser apparatus and an optical tomographic imaging apparatus including the wavelength tunable laser apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an optical tomographic imaging apparatus according to an embodiment of the present invention. The optical tomographic imaging apparatus 1 acquires, for example, a tomographic image of a measurement target such as a living tissue or a cell in a body cavity by the above-described SS-OCT measurement. The optical tomographic imaging apparatus 1 is a laser apparatus 10 that emits light L while sweeping the oscillation wavelength at a constant period, and light that divides the light L emitted from the laser apparatus 10 into measurement light L1 and reference light L2. The dividing means 3, the optical path length adjusting means 20 for adjusting the optical path length of the reference light L2 divided by the light dividing means 3, and the probe 30 for guiding the measuring light L1 divided by the light dividing means 3 to the measuring object S And combining means 4 for combining the reflected light L3 reflected from the measuring object S and the reference light L2 when the measuring light L1 is irradiated from the probe 30 onto the measuring object S, and the combining means 4 An interference light detection means 40 for detecting the interference light L4 between the reflected light L3 and the reference light L2, and an image for obtaining a tomographic image of the measuring object S by frequency analysis of the interference light L4 detected by the interference light detection means 40 Acquisition means 50 It is.

  The laser device 10 is an external resonator type tunable laser device that emits light L while sweeping an oscillation wavelength at a constant period. As the laser medium in this example, a semiconductor laser medium used for a semiconductor laser is used. Specifically, the laser device 10 includes a semiconductor laser medium 11, a collimator lens 12, a diffractive optical element 13, a condenser lens 14, and a rotating body 15. An antireflection film (AR coating) is applied to the exit end face 11b of the semiconductor laser medium 11 on the collimator lens 12 side. An optical coupling lens 16 is disposed between the exit end face 11a opposite to the exit end face 11b of the semiconductor laser medium 11 and the external waveguide optical fiber FB0.

  The diffractive optical element 13 is a reflective element, and functions as a dispersion means for spatially wavelength-dispersing light emitted from the semiconductor laser medium 11. Diffracted light generated in the diffractive optical element 13 travels in different directions for each wavelength.

  The rotator 15 is provided with a plurality of reflecting surfaces 15a that reflect light on the surface of the disk facing the condenser lens 14, and functions as the wavelength selecting means of the present invention. The rotating body 15 has a substantially disk shape that rotates around a predetermined axis, and is rotated at a constant angular speed by a driving unit (not shown). A plurality of reflecting surfaces 15 a that reflect light are partially provided on the surface of the rotating body 15 facing the condenser lens 14. The reflecting surface 15 a has a curved shape that extends substantially in the radial direction of the rotating body 15 and is concave toward the front in the rotating direction of the rotating body 15. The detailed configuration of the reflecting surface 15a will be described later. In FIG. 1, in order to avoid complication of the drawing, the reference numerals of the reflecting surfaces 15a are typically given to only one reflecting surface, and some of the reflecting surfaces 15a are not shown.

  Non-reflective processing is applied to portions of the rotating body 15 other than the reflective surface 15a. Specifically, for example, black coating, AR (antireflection) coating, scattering treatment such as etching / sandblasting, and the like are performed. By performing such processing, the noise component is reduced, and the S / N ratio of the reflected light is improved, whereby oscillation (ripple) other than the desired wavelength can be suppressed. Note that the non-reflective treatment can be applied to a conventional apparatus using a rotating disk having a reflective part and a non-reflective part as shown in FIG.

The light emitted from the emission end face 11b of the semiconductor laser medium 11 toward the collimating lens 12 is converted into parallel light by the collimating lens 12, and then dispersed by the diffractive optical element 13 for each wavelength λ _1. , Proceed in different directions for each wavelength. The wavelength-dispersed light is condensed on the surface of the rotating body 15 by the condenser lens 14. An array of light having wavelengths λ ₁ ... Λn is formed on the board surface.

  As the rotator 15 rotates, the reflecting surface 15a moves across the wavelength-dispersed light array, and a part of the light is selectively reflected as return light. The return light passes through the reverse optical path, passes through the condenser lens 14, passes through the diffractive optical element 13, passes through the collimator lens 12, and returns to the semiconductor laser medium 11. An external resonator having both ends of the emission end face 11 a of the semiconductor laser medium 11 and the rotator 15 is configured, and light L is emitted from the emission end face 11 a of the semiconductor laser medium 11. The oscillation wavelength of the light L is the return light wavelength.

The wavelength of the return light varies with the rotation of the rotating body 15, the wavelength sweep of one cycle for one reflecting surface 15a from the wavelength lambda ₁ to wavelength λn is performed. Since the plurality of reflecting surfaces 15a are provided at predetermined intervals, this wavelength sweep is repeated at a constant period.

The wavelength sweep in the optical tomographic imaging apparatus 1 is configured such that the reciprocal of the wavelength of the return light changes linearly with respect to time. Here, since the wavelength λ, the frequency ν, and the speed of light c are in a relationship of ν = c / λ, the frequency of the return light is configured to change linearly with respect to time. 1, as shown in FIG. 2, during the sweep time T for one cycle, the wavelength sweep is performed so that the frequency ν (t) of the return light linearly changes at time t. In FIG. 2, the frequency of the return light at t = 0 when the sweep starts for one cycle is ν ₀ , and the frequency of the return light at t = T when the sweep is completed for one cycle is ν _T.

  Hereinafter, a design method of the reflection surface 15a for realizing the wavelength sweeping method will be described with reference to FIG. 3 together with the detailed configuration of the reflection surface 15a. As shown in FIG. 3, on the surface of the rotating body 15 that includes the reflecting surface 15a that reflects the return light and is perpendicular to the rotation axis, the axis position is the origin O, and the two axes orthogonal to each other through the origin O are shown in FIG. As shown, the x-axis and y-axis are used.

The reflection surface 15a has a thin curved shape that extends substantially in the radial direction of the rotating body 15 and is concave toward the front in the rotation direction of the rotating body 15. On the other hand, the array 16 of light spatially wavelength-dispersed by the diffractive optical element 13 is positioned in parallel with the y-axis in the region of the fourth quadrant (x <0, y> 0) in the order of wavelengths λ _1. The distance from the origin O to the light of each wavelength monotonously decreases or monotonically increases in order of wavelength.

  When the reflecting surface 15a and the wavelength-dispersed light array 16 cross each other, a part of the light array 16 is reflected and becomes return light, so that the position of the intersection of the reflecting surface 15a and the light array 16 is This is the return light reflection position 17. As the rotating body 15 rotates, the reflecting surface 15a moves, so the reflected light reflection position 17 also changes. The reflection position 17 is obtained by continuously scanning the light array 16 in order of wavelength. The scanning locus is the same as that of the light array 16, but the reflection position 17 and the light array 16 are different concepts. For the purpose of explanation, the reflection position 17 is conceptually represented by a set of points in FIG.

  In FIG. 3, the reflection position 17 and the light array 16 are shown to have a predetermined width, but they are not necessarily exactly the same. Since the light array 16 is obtained by condensing parallel light by the condensing lens 14, its width is equal to the beam waist diameter. Also, the width of the reflecting surface 15a is preferably equal to the beam waist diameter in order to maintain high resolution of the sweep wavelength.

Hereinafter, the design method of the reflective surface 15a will be described using equations. First, in the optical tomographic imaging apparatus 1 of the present embodiment, the frequency ν (t) of the return light is proportional to the time t, and therefore satisfies the relationship of the following expression.
ν (t) = ν ₀ + (ν _T −ν ₀ ) / (T · t)

Next, the (x, y) coordinates of the reflection position 17 of the return light are expressed as (x (t), y (t)), respectively, as a function of time t. x (t) = x ₀ , y (0) = y ₀ , and y (T) = y _T. In order to make the reflection position and the frequency of the return light have a one-to-one correspondence, y (t) is proportional to ν (t). At this time, the relationship of the following formula is satisfied.
_{y (t) = y 0 -} (y T -y 0) · (ν (t) -ν 0) / (ν T -ν 0)

Under the above conditions, the (r, θ) coordinates of the position where the return light is reflected in the reflecting surface 15a are determined as a variable of time t. The (r, θ) coordinates are a radius r and a rotation angle θ from the y-axis. When r (t) and θ (t) are respectively set, the x (t), y (t) and the rotating body Using 15 rotational angular velocities α (unit: rad / sec), it is expressed as:
r (t) = y (t) / cos θ (t)
θ (t) = tan ⁻¹ (x ₀ / y (t)) + α · t

When a plurality of, for example, N (N ≧ 2) reflecting surfaces 15a are provided, r (t) and θ (t) are expressed by the following equations.
r (t) = y (t) / cos θ (t)
θ _N (t) = θ (t) + N · α · t
FIG. 4 shows a calculation example based on the above formula. FIG. 4 shows the calculation for one reflecting surface 15a, and the parameter values marked with * in the table of FIG. 4 are input values. FIG. 5 shows the reflection surface 15a, the light array 16 and the reflection position 17 obtained by calculating the plurality of reflection surfaces in the same manner. In FIG. 5, the light array 16 and the reflection position 17 are overlapped and indicated by black lines.

  FIG. 6 shows the reflection surface 135a, the light array 116, and the reflection position 117 in the conventional apparatus shown in FIG. 6 conceptually illustrates the same as FIG. As shown in FIG. 6, in the conventional apparatus, the wavelength-dispersed light array 116 is located over the third quadrant and the fourth quadrant, and the distance from the origin O to the light of each wavelength is the wavelength. The monotonous decrease or monotonic increase does not occur in order, and as a result, the reflection position and the frequency of the return light do not correspond one to one.

  On the other hand, in the optical tomographic imaging apparatus 1 of the present embodiment, as shown in FIGS. 3 and 5, the light array 16 is in the region of the fourth quadrant (x <0, y> 0) in order of wavelength. The distance from the origin O to the light of each wavelength monotonously decreases or increases monotonically in order of wavelength, and as a result, the reflection position and the frequency of the return light have a one-to-one correspondence. The frequency of the return light can be designed to change linearly with respect to time.

  In the present example shown in FIG. 1, parallel light is incident on the diffractive optical element 13, and the distance between the condenser lens 14 and the rotating body 15 is set to be equal to the focal length of the condenser lens 14. As described above, since the rotator 15 is disposed on the focal plane that is the condensing position of the condenser lens 14, the beam diameter on the rotator 15 can be reduced. As the beam diameter is smaller, the width of the reflecting surface 15a of the rotator 15 can be reduced, and the resolution of the wavelength swept by the scanning of the reflecting surface 15a can be increased.

  In this example, the distance between the condensing lens 14 and the diffractive optical element 13 is made equal to the focal length of the condensing lens 14, and the rotating body 15 side of the condensing lens 14 is telecentric. Further, the reflecting surface 15 a of the rotator 15 is arranged perpendicular to the optical axis of the condenser lens 14. With the above configuration, the principal ray of light traveling from the condenser lens 14 toward the rotator 15 is parallel to the optical axis of the condenser lens 14, is perpendicular to the reflecting surface 15 a of the rotator 15, and is reflected by the rotator 15. , Will return through the reverse light path.

  In the laser device 10 described in detail above, the light L emitted from the emission end face 11a of the semiconductor laser medium 11 is collected by the optical coupling lens 16, and then enters the optical fiber FB0 and is guided. . Then, after passing through the optical fiber coupler 2, it is guided to the light splitting means 3 by the optical fiber FB1.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light L guided from the laser device 10 through the optical fibers FB0 and FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively, the measuring light L1 is guided by the optical fiber FB2, and the reference light L2 is guided by the optical fiber FB3. Note that the light splitting means 3 in this embodiment also functions as the multiplexing means 4.

  The probe 30 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the probe 30. The probe 30 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 31.

  The optical probe 30 includes a cylindrical probe outer cylinder 32 whose tip is closed, and one optical fiber 33 disposed in the inner space of the probe outer cylinder 32 so as to extend in the axial direction of the outer cylinder 32. And a prism mirror 34 that deflects the light L1 emitted from the tip of the optical fiber 33 in the circumferential direction of the probe outer cylinder 32, and the light L1 emitted from the tip of the optical fiber 33 is arranged on the outer circumference of the probe outer cylinder 32. A rod lens 35 that collects light so as to converge on the measurement target S as a body to be scanned and a motor 36 that rotates the prism mirror 34 about the axis of the optical fiber 33 as a rotation axis are provided.

  On the other hand, the optical path length adjusting means 20 is disposed on the side of the optical fiber FB3 where the reference light L2 is emitted. The optical path length adjusting unit 20 changes the optical path length of the reference light L2 in order to adjust the position at which tomographic image acquisition for the measurement target S is started, and the reference light L2 emitted from the optical fiber FB3 is changed. A reflection mirror 22 to be reflected, a first optical lens 21a disposed between the reflection mirror 22 and the optical fiber FB3, and a second optical lens 21b disposed between the first optical lens 21a and the reflection mirror 22. have.

  The first optical lens 21a has a function of converting the reference light L2 emitted from the core of the optical fiber FB3 into parallel light and condensing the reference light L2 reflected by the reflection mirror 22 onto the core of the optical fiber FB3. ing. Further, the second optical lens 21b condenses the reference light L2 converted into parallel light by the first optical lens 21a on the reflection mirror 22, and makes the reference light L2 reflected by the reflection mirror 22 into parallel light. have.

  Therefore, the reference light L2 emitted from the optical fiber FB3 is converted into parallel light by the first optical lens 21a, and is condensed on the reflection mirror 22 by the second optical lens 21b. Thereafter, the reference light L2 reflected by the reflection mirror 22 becomes parallel light by the second optical lens 21b, and is condensed on the core of the optical fiber FB3 by the first optical lens 21a.

  Further, the optical path length adjusting means 20 has a movable stage 23 in which the second optical lens 21b and the reflecting mirror 22 are fixed, and a mirror moving means 24 for moving the movable stage 23 in the optical axis direction of the first optical lens 21a. is doing. When the movable stage 23 moves in the arrow A direction, the optical path length of the reference light L2 is changed.

  The multiplexing means 4 is composed of a 2 × 2 optical fiber coupler as described above, and combines the reference light L2 whose optical path length has been changed by the optical path length adjusting means 20 and the reflected light L3 from the measuring object S to be light. It is configured to emit light toward the interference light detection means 40 via the fiber FB4.

  The interference light detection unit 40 detects the interference light L4 between the reflected light L3 combined by the combining unit 4 and the reference light L2. Note that the apparatus of this example has a mechanism in which the light obtained by dividing the interference light L4 by the light splitting means 3 that is an optical fiber coupler is guided to the photodetectors 40a and 40b, and the calculation means 41 performs balance detection.

  The computing means 41 is connected to an image acquisition means 50 comprising a computer system such as a personal computer, for example, and the image acquisition means 50 is connected to a display device 60 comprising a CRT or a liquid crystal display device. The image acquisition means 50 detects the intensity of the reflected light L3 at each depth position of the measurement target S by Fourier transforming the interference light L4 detected by the interference light detection means 40, and acquires a tomographic image of the measurement target S. To do. The acquired tomographic image is displayed on the display device 60.

  Here, the detection of the interference light L4 and the generation of the image in the interference light detection means 40 and the image acquisition means 50 will be briefly described. Details of this point are described in “Mitsuo Takeda,“ Optical Frequency Scanning Spectrum Interference Microscope ”, Optical Technology Contact, 2003, Vol41, No7, p426-p432”.

When the measurement light L1 is irradiated onto the measurement object S, interference fringes with respect to each optical path length difference l when the reflected light L3 and the reference light L2 from each depth of the measurement object S interfere with each other with various optical path length differences. S (l) is the light intensity I (k) detected by the interference light detection means 40.
I (k) = ∫ ₀ ^∞ S (l) [1 + cos (kl)] dl (1)
It is represented by Here, k is the wave number, and l is the optical path length difference. Formula (1) can be considered to be given as an interferogram in the optical frequency domain with the wave number k as a variable. For this reason, in the image acquisition means 50, the spectral interference fringes detected by the interference light detection means 40 are subjected to frequency analysis by Fourier transform, and the light intensity S (l) of the interference light L4 is determined, thereby measuring the measurement object S. It is possible to acquire distance information from the start position and reflection intensity information and generate a tomographic image.

  Next, an operation example of the optical tomographic imaging apparatus 1 having the above configuration will be described. First, when the movable stage 23 moves in the direction of arrow A, the optical path length is adjusted so that the measuring object S is positioned in the measurable region. Thereafter, the light L is emitted from the laser device 10, and the light L is split into the measurement light L <b> 1 and the reference light L <b> 2 by the light splitting unit 3. The measurement light L1 is guided into the body cavity by the probe 30 and irradiated to the measurement object S. Then, the reflected light L3 from the measurement object S is combined with the reference light L2 reflected by the reflection mirror 22 by the combining means 4, and the interference light L4 between the reflected light L3 and the reference light L2 is detected by the interference light detecting means 40. Is done. The detected signal of the interference light L4 is subjected to frequency analysis in the image acquisition means 50, whereby a tomographic image is acquired.

  If the probe 30 is rotated and the measurement light L1 is scanned in a one-dimensional direction with respect to the measurement target S, information in the depth direction of the measurement target S can be obtained at each portion along the scanning direction. A tomographic image of a tomographic plane including this scanning direction can be acquired. In addition, by scanning the measuring object S1 with the measurement light L1 in a second direction orthogonal to the scanning direction, a tomographic image of a tomographic plane including the second direction can be further acquired. Is possible.

  As described above, in the optical tomographic imaging apparatus 1 according to the present embodiment, the frequency of the oscillating light is configured to change linearly with respect to time, so that the data distribution is discrete during frequency analysis. In addition, it is possible to easily acquire data at equal intervals with respect to the frequency, and the accuracy of frequency analysis can be improved as compared with the conventional case. For example, when detecting an optical tomographic image signal to be measured having a depth of 2 mm, it has been reported that the linearity of frequency with respect to time is required to be 0.1%. According to 1, this condition can be easily satisfied.

  Note that the arrangement and arrangement of the arrangement of light and the shape of the reflecting surface are not limited to those shown in the above example and FIG. 5, and various modifications can be considered. For example, as shown in FIG. 7A, in the case where the absolute value of the x coordinate of the light array 216 is increased on the surface of the rotator 215, the crossing angle between the light array 216 and the reflecting surface 215a. Approaches perpendicular, and the return light becomes light having a narrow wavelength width, and the sweep wavelength resolution is increased. However, it should be noted that if the absolute value of the x coordinate is too large, the length of the light array 216 in the y direction cannot be taken sufficiently, and the wavelength resolution in the light array 216 becomes low. Further, in this case, since the curvature of the reflection surface 215a becomes tight, it is necessary to increase the interval between the adjacent reflection surfaces 215a. As a result, the sweep cycle becomes longer, the sweep speed decreases, and the surface of the rotating body 15 decreases. The number of reflective surfaces 15a that can be disposed on the surface is also reduced.

  On the other hand, as shown in FIG. 7B, when the absolute value of the x coordinate of the light arrangement 316 is arranged to be small on the surface of the rotator 315, the curvature of the reflection surface 215a becomes loose, Although the intersection angle between the light array 316 and the reflecting surface 315a is reduced and the sweep wavelength resolution is lowered, the sweep speed is improved and the number of reflecting surfaces 15a that can be disposed on the surface of the rotating body 15 is increased. it can. It is desirable that the arrangement of light and the configuration and arrangement of the reflecting surface be appropriately determined according to specifications required for the wavelength tunable laser device or the optical tomographic imaging device.

1 is a schematic configuration diagram of an optical tomographic imaging apparatus according to a first embodiment of the present invention. The figure which shows the mode of the wavelength sweep of the laser apparatus of FIG. The figure for demonstrating the structure of the wavelength selection means of the laser apparatus of FIG. The figure which shows the example of a calculation in this embodiment The figure which shows the structure and positional relationship of a reflective surface etc. based on the example of calculation of FIG. The figure for demonstrating the wavelength selection means in the conventional apparatus (A), (B) is a figure for demonstrating the structure of the wavelength selection means by the modification of the laser apparatus of this invention Schematic configuration diagram of a conventional wavelength tunable laser device Schematic configuration diagram of a conventional wavelength tunable laser device Schematic configuration diagram of a conventional wavelength tunable laser device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical tomographic imaging apparatus 2 Optical fiber coupler 3 Optical dividing means 4 Combined means 10 Laser apparatus 11 Semiconductor laser medium 11a, 11b Emission end surface 12 Collimating lens 13 Diffractive optical element 14 Condensing lens 15 Rotating body 15a Reflecting surface 16 Array 17 Reflection position 20 Optical path length adjustment means 30 Probe 40 Interference light detection means 40a, 40b Photo detector 41 Calculation means 50 Image acquisition means 60 Display device L Light L1 Measurement light L2 Reference light L3 Reflection light L4 Interference light S Measurement object

Claims (4)

In an external resonator type tunable laser device,
A laser medium;
Dispersion means for spatially wavelength-dispersing light emitted from the laser medium;
A reflection surface that moves across the light wavelength-dispersed by the dispersion means, and a wavelength selection means that selectively reflects a part of the light as return light by the reflection surface;
The wavelength tunable laser device, wherein the wavelength selection unit is configured such that the reciprocal of the wavelength of the return light changes linearly with respect to time.   The reflecting surface is partly provided on a rotating body that rotates around a predetermined axis, extends in a substantially radial direction of the rotating body, and has a curved shape that is concave toward the front in the rotational direction of the rotating body. The wavelength tunable laser device according to claim 1, wherein:   In a plane perpendicular to the predetermined axis including the reflecting surface, the light wavelength-dispersed by the dispersing means is linearly positioned in a direction intersecting the radial direction of the rotating body, and the light from each wavelength has the predetermined axis. The tunable laser device according to claim 2, wherein the distance to is monotonously decreased or monotonically increased in order of wavelength. The wavelength tunable laser device according to any one of claims 1 to 3,
Light splitting means for splitting the light emitted from the wavelength tunable laser device into measurement light and reference light;
A multiplexing means for multiplexing the reflected light from the measurement object and the reference light when the measurement light is irradiated to the measurement object;
Interference light detection means for detecting interference light between the reflected light and the reference light multiplexed by the multiplexing means;
An optical tomographic imaging apparatus comprising: an image acquisition unit configured to acquire a tomographic image of the measurement target from the interference light detected by the interference light detection unit.

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