JP2007309882A - Wavelength sweeping light source, and optical tomographic imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength sweeping light source capable of sweeping a wavelength with a high repetition cycle. <P>SOLUTION: Light emitted from a semiconductor laser medium 211 is converted into a parallel beam by a collimator lens 212, is reflected by a polygon mirror 213, and gets incident into a wavelength selecting means 214. Return light of light dispersed to an incident direction out of the light dispersed by the wavelength selecting means 214 is reflected by the polygon mirror 213 to be fed back to the semiconductor laser medium 211. A laser beam La is emitted from an emission end face 211a of the semiconductor laser medium 211. A wavelength of the return light is varied when the polygon mirror 213 is rotated. The wavelength selecting means 214 is constituted of compact diffraction gratings 261a, 261b of same shape. The diffraction gratings 261a, 261b are arranged with different angles with respect to a reflecting face of the polygon mirror 213 to change the wavelength in the same wavelength band. Twice wavelength sweepings are thereby attained in the one reflecting face of the polygon mirror 213. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength swept light source in which an oscillation wavelength changes and an optical tomographic imaging apparatus that acquires an optical tomographic image of a measurement target using the wavelength swept light source.

  Conventionally, as a wavelength sweep type light source, an external resonator type wavelength sweep type laser device called a Littrow type is known. This Littrow type laser apparatus has a structure basically shown.

  The laser apparatus shown in FIG. 1 converts the light emitted from the low reflection surface of the semiconductor laser medium 101 into parallel light by the collimator lens 102 and enters the diffraction surface of the diffraction grating 103 that diffracts the light. The oscillation wavelength is selected by returning the diffracted light diffracted by the above to the semiconductor laser medium 101.

  In the laser device having this structure, only a specific wavelength component of the wavelength components of the light emitted from the semiconductor laser medium 101 and diffracted by the diffraction grating 103 returns to the semiconductor laser medium 101. The semiconductor laser medium 101 generates a standing wave by being guided by the returned light having a specific wavelength, and emits light having the specific wavelength (hereinafter referred to as an oscillation wavelength).

  This oscillation wavelength is defined by both the angle between the optical axis of the light emitted from the semiconductor laser medium 101 and the diffraction grating 103 and the grating period of the diffraction grating 103. By rotating 103, the oscillation wavelength can be continuously changed, that is, the oscillation wavelength can be swept.

  On the other hand, as one method for acquiring a tomographic image of a measurement target such as a biological tissue, the measurement light is irradiated when the measurement light is irradiated after the coherence light emitted from the light source is divided into the measurement light and the reference light. A method is known in which reflected light and reference light are combined and an optical tomographic image is acquired based on the intensity of interference light between the reflected light and the reference light. As one of the methods, there has been proposed an OCT apparatus that detects interference light while temporally changing the frequency of light emitted from a light source (see, for example, Patent Document 1). In this OCT apparatus, a Michelson interferometer is used to cause interference between reflected light and reference light while temporally changing the frequency of laser light emitted from a light source. 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. In order to acquire an optical tomographic image with such an OCT apparatus, it is necessary to repeat wavelength sweeping at a light source at high speed.

  Patent Document 2 also describes a laser device that can repeatedly perform wavelength sweeping at high speed. As shown in FIG. 2, the wavelength sweep laser apparatus 110 includes a laser medium 111, a collimator lens 112, a polygon mirror 113, and a diffraction grating 114. Light emitted from the laser medium 111 is converted into parallel light by the collimator lens 112, reflected by the polygon mirror 113, and incident on the diffraction grating 114. Of the light dispersed by the diffraction grating 114, the light dispersed in the incident direction (hereinafter referred to as return light) is reflected by the polygon mirror 113 and returns to the laser medium 111. A resonator is constituted by the emission end face 111a of the laser medium 111 and the diffraction grating 114, and the laser light L is emitted from the emission end face 111a of the laser medium 111. At this time, the wavelength of the laser light L is the wavelength of the return light.

  Here, the polygon mirror 113 is rotated in the direction of the arrow R1, and the reflection angle continuously changes on each reflection surface. As a result, the angle of light incident on the diffraction grating 114 changes continuously, and the oscillation wavelength also changes continuously.

Further, when the polygon mirror 113 rotates at a constant speed in the direction of the arrow R1, the wavelength of the return light changes with a constant period as time passes. For this reason, laser light that has been wavelength-swept at a constant cycle is emitted from the laser device 110.
US2005 / 0035295 A1 US4601036

  However, in the wavelength swept light source shown in FIG. 2, the wavelength sweep period is determined by the number of polygon mirrors and the number of rotations, and if the repetition frequency is increased without increasing the size of the apparatus, the number of polygon mirrors is increased. It is necessary to increase the rotation speed or the rotation speed. However, the polygon mirror has an invalid rotation angle that cannot be used for sweeping before and after the effective rotation angle that can actually be used for wavelength sweeping. If the number of mirror surfaces is increased, the invalid rotation angle for this effective rotation angle is increased. There is a problem in that a good wavelength sweep cannot be established. There is also a problem that increasing the number of rotations is not easy due to the structure of a motor or the like.

  The present invention has been made in view of these problems. A wavelength swept light source capable of sweeping a wavelength at a high repetition period by using a conventional rotary deflection means, and an optical tomographic image using the wavelength swept light source The purpose of this is to realize a conversion apparatus.

The wavelength swept light source of the present invention comprises an optical amplification means,
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
In a wavelength swept light source having wavelength selection means for changing the wavelength of light returning to the incident direction by changing the incident angle or the incident position of the light deflected by the light deflecting means,
The wavelength selection unit includes a plurality of wavelength selection units in which wavelengths of light returning to the incident direction change in substantially the same wavelength band.

  The rotating light deflecting means may be a polygon mirror (rotating polygon mirror). Alternatively, a rotating mirror, a galvano, a resonant scanner, or the like may be used.

    The wavelength selection unit may include a light dispersion unit that wavelength-disperses the light. Here, the “light dispersion portion” is, for example, a diffraction grating, a prism, or a grism.

An optical system in which the light dispersion unit has a wavelength of return light that returns to the light incident direction in accordance with an incident angle of the light, and the light deflected by the light deflecting unit is incident on the light dispersion unit. If you have the means,
The light deflection unit and the optical unit may change an incident angle of light incident on the light dispersion unit.

An optical system in which the light dispersion portion has a wavelength of return light that returns to the light incidence direction according to the light incident position, and the light deflected by the light deflection means is incident on the light dispersion portion. If you have the means,
The light deflecting unit and the optical unit may change an incident position of light incident on the light dispersing unit.

An optical tomographic imaging apparatus of the present invention includes a light source that emits laser light while sweeping a wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the light source 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 the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light combined by the multiplexing means; ,
In an optical tomographic imaging apparatus comprising: an image acquisition unit configured to acquire a tomographic image of the measurement target using the intensity of the interference light at each depth position detected by the interference light detection unit;
The light source comprises light amplifying means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
A wavelength swept light source having wavelength selection means for changing the wavelength of light returning to the incident direction by changing the incident angle or the incident position of the light deflected by the light deflecting means,
The wavelength selection unit includes a plurality of wavelength selection units in which wavelengths of light returning to the incident direction change in substantially the same wavelength band.

  The wavelength swept light source of the present invention has wavelength selection means for changing the wavelength of light that is emitted from the light amplification means and returned to the incident direction by changing the incident angle or the incident position of the light deflected by the light deflection means, Since this wavelength selection unit has a plurality of wavelength selection units in which the wavelengths of light returning to the incident direction change in substantially the same wavelength band, a plurality of wavelength sweeps are performed by scanning at once by the light deflection unit. The wavelength can be swept with a high repetition period without changing the light deflecting means.

  In addition, the optical tomographic imaging apparatus of the present invention includes a wavelength swept light source that can sweep the wavelength at a high repetition period, so that it is possible to shorten the time required to acquire one optical tomographic image. it can.

  The optical tomographic imaging apparatus according to the first embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a schematic configuration diagram of the optical tomographic imaging apparatus according to the first embodiment of the present invention. An optical tomographic imaging apparatus 200 shown in FIG. 3 acquires 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, and sweeps an oscillation wavelength at a constant cycle. A light source unit 210 that functions as a wavelength swept laser device that emits the laser light La, a light splitting means 3 that splits the laser light La emitted from the light source unit 210 into measurement light L1 and reference light L2, and light splitting The optical path length adjusting means 220 for adjusting the optical path length of the reference light L2 divided by the means 3, the optical probe 230 for irradiating the measuring object Sb with the measuring light L1 divided by the light dividing means 3, and thus the measuring object Sb. Multiplexing means 4 for multiplexing the reflected light L3 reflected by the measurement object Sb and the reference light L2 when irradiated with the measuring light L1, and interference light between the combined reflected light L3 and the reference light L2 Detect L4 The interference light detection means 240, an image acquisition unit 241 that generates an optical tomographic image to be measured based on the detection result of the interference light detection means 240, and a display device 242 that displays the optical tomography image Yes.

  The light source unit 210 is a wavelength sweep laser device that emits laser light La while sweeping the oscillation wavelength at a constant period so that the oscillation wavelength λc is in the range of 950 nm to 1150 nm. The semiconductor laser medium used in the above is used. Details of the light source unit 210 will be described later.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light La guided from the light source unit 210 through the optical fiber 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 measurement light L1 is guided through the optical fiber FB2, and the reference light L2 is guided through the optical fiber FB3. The light splitting means 3 in this example also functions as the multiplexing means 4.

  An optical probe 230 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 230. The optical probe 230 is inserted into a body cavity from a forceps opening through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 31.

  The optical probe 230 includes a cylindrical probe outer cylinder 15 having a closed tip, and one optical fiber 13 disposed in an inner space of the probe outer cylinder 15 so as to extend in the axial direction of the outer cylinder 15. And a prism mirror 17 that deflects the light L emitted from the tip of the optical fiber 13 in the circumferential direction of the probe outer cylinder 15 and the light L1 emitted from the tip of the optical fiber 13 are arranged on the outer circumference of the probe outer cylinder 15. A rod lens 18 that condenses light to converge on the measurement target Sb as a scanned body, and a motor 14 that rotates the optical fiber 13 about the optical axis of the optical fiber 13 as a rotation axis. The rod lens 18 and the prism mirror 17 are disposed so as to rotate together with the optical fiber 13.

  On the other hand, optical path length adjusting means 220 is arranged on the side of the optical fiber FB3 from which the reference light L2 is emitted. The optical path length adjusting unit 220 changes the optical path length of the reference light L2 in order to adjust the position where the tomographic image acquisition is started, and reflects the reference light L2 emitted from the optical fiber FB3. 22, a first optical lens 21 a disposed between the reflection mirror 22 and the optical fiber FB 3, and a second optical lens 21 b disposed between the first optical lens 21 a and the reflection mirror 22. Yes.

  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. 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 also converts the reference light L2 reflected by the reflection mirror 22 into parallel light. have. That is, the first optical lens 21a and the second optical lens 21b form a confocal optical system.

  Accordingly, 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 reflecting 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 220 has a base 23 on which the second optical lens 21b and the reflecting mirror 22 are fixed, and a mirror moving means 24 for moving the base 23 in the optical axis direction of the first optical lens 21a. is doing. When the base 23 moves in the direction of arrow A, the optical path length of the reference light L2 can be 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 220 and the reflected light L3 from the measuring object Sb. The light is emitted to the interference light detection means 240 side through the optical fiber FB4.

  The interference light detection unit 240 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 light obtained by dividing the interference light L4 into two by the optical fiber coupler 3 is guided to the photodetectors 40a and 40b, and the calculation means 41 performs balance detection.

  The image acquisition unit 241 detects the intensity of the reflected light L3 at each depth position of the measurement target Sb by performing Fourier transform on the interference light L4 detected by the interference light detection unit 240, and obtains a tomographic image of the measurement target Sb. get.

  The operation of the optical tomographic imaging apparatus 200 having the above configuration will be described below. When acquiring a tomographic image, the optical path length is adjusted so that the measurement target Sb is positioned within the measurable region by first moving the base 23 in the direction of arrow A. Thereafter, light La is emitted from the light source unit 210, and this light La is split by the light splitting means 3 into the measurement light L1 and the reference light L2. The measurement light L1 is emitted from the optical probe 230 toward the body cavity and irradiated on the measurement target Sb. At this time, the measurement light L1 emitted from the optical probe 230 operating as described above scans the measurement target Sb in one dimension. Then, the reflected light L3 from the measuring object Sb is combined with the reference light L2 reflected by the reflecting mirror 22, and the interference light L4 between the reflected light L3 and the reference light L2 is detected by the interference light detection means 240.

  Here, the detection of the interference light L4 and the generation of the image in the interference light detection means 240 and the image acquisition means 241 will be briefly described. Details of this point are described in “Mitsuo Takeda,“ Optical Frequency Scanning Spectrum Interference Microscope ”, Optical Technology Contact, 2003, Vol. 41, No. 7, p426-p432”.

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 Sb interfere with each other with various optical path length differences when the measurement object Lb is irradiated with the measurement light S1. S (l) is the light intensity I (k) detected by the interference light detection means 240,
I (k) = ∫ ₀ ^∞ S (l) [1 + cos (kl)] dl
It is represented by Here, k is the wave number, and l is the optical path length difference. It can be considered that the above equation is given as an interferogram in the optical frequency domain with the wave number k = ω / c as a variable. For this reason, the image acquisition unit 241 performs Fourier transform on the spectral interference fringes detected by the interference light detection unit 240 to determine the light intensity S (l) of the interference light L4, thereby determining the measurement start position of the measurement target Sb. Distance information and reflection intensity information can be acquired, and a tomographic image can be generated. This tomographic image is displayed on the display device 242.

  Hereinafter, a detailed description of the light source unit 210 will be described. A top view of the light source unit 210 is shown in FIG. 4 (A), and a side view thereof is shown in FIG. 4 (B). The light source unit 210 includes a semiconductor laser medium 211, a collimator lens 212, a polygon mirror 213, a wavelength selection unit 214, a polarization beam splitter 215, and a quarter wavelength plate 216. Instead of the quarter wavelength plate 216, a Faraday rotator whose polarization changes by a quarter wavelength can be used.

  The semiconductor laser medium 211 emits linearly polarized laser light, and is arranged so that the light emitted from the semiconductor laser medium 211 enters the polarization beam splitter 215 as s-polarized light.

  The polarization beam splitter 215 and the quarter wavelength plate 216 are disposed between the polygon mirror 213 and the diffraction grating 214. The polarization beam splitter 215 transmits p-polarized light and reflects s-polarized light at a right angle. The light emitted from the semiconductor laser medium 211 and converted into parallel light by the collimator lens 212 is incident on the polarization beam splitter 215 at an angle parallel to the rotation axis of the polygon mirror 213 and is reflected by the polarization beam splitter 215 at a right angle. The semiconductor laser medium 211, the collimating lens 212, the polarization beam splitter 215, and the polygon mirror 213 are arranged so that the s-polarized light is incident on the polygon mirror 213 in the direction of the rotation center.

  The wavelength selection means 214 is composed of small and identical diffraction gratings 261a and 261b. The diffraction grating 261a and the diffraction grating 261b are arranged at different angles with respect to the reflection surface of the polygon mirror 213 so that the wavelength changes in the same wavelength band. In this way, by using a plurality of diffraction gratings in combination, a plurality of wavelength sweeps can be performed on one reflecting surface of the polygon mirror 213.

  First, light emitted from the semiconductor laser medium 211 is converted into parallel light by the collimator lens 212 and is incident on the surface 215 a of the polarization beam splitter 215. In the polarization beam splitter 215, p-polarized light is transmitted among the incident light, and s-polarized light is reflected at a right angle and is emitted from the surface 215b. This s-polarized light passes through the quarter-wave plate 216 and becomes circularly polarized light. This circularly polarized light is incident on the polygon mirror 213 toward the center of rotation. The light reflected by the polygon mirror 213 passes through the quarter wavelength plate 216 again and becomes p-polarized light. This p-polarized light passes through the polarization beam splitter 215 and enters the diffraction grating 214. Of the p-polarized light dispersed by the diffraction grating 214, the light dispersed in the incident direction (hereinafter referred to as return light) is transmitted through the polarization beam splitter 215 and further transmitted through the quarter-wave plate 216 to be circularly polarized. It becomes. This circularly polarized light is reflected by the polygon mirror 213, passes through the quarter wavelength plate 216 again, and becomes s-polarized light. The s-polarized light enters the surface 215b of the polarization beam splitter 215, is reflected at a right angle, is emitted from the surface 215a, and returns to the semiconductor laser medium 211. The emission end face 211a of the semiconductor laser medium 211 and the diffraction grating 214 constitute a resonator, and the laser light La is emitted from the emission end face 211a of the semiconductor laser medium 211. At this time, the wavelength of the laser beam La is the wavelength of the return light.

  Here, the polygon mirror 213 rotates in the direction of the arrow R1, and the reflection angle continuously changes on each reflection surface. As a result, the angle of light incident on the diffraction grating 214 also changes continuously. When the wavelength of the return light returning to the incident direction of the dispersed light is λ, the groove period of the diffraction grating is G, and the incident angle of the incident light to the diffraction grating 214 is θ, the return light is the first-order diffracted light. These relationships can be expressed by the following equation.

2Sinθ = λ / G (1)
Therefore, when the incident angle θ of the incident light on the diffraction grating 214 changes continuously, the oscillation wavelength also changes continuously.

  Further, when the polygon mirror 213 rotates at a constant speed in the direction of the arrow R1, the wavelength of the return light changes at a constant period with the passage of time. Therefore, the wavelength-swept laser light La is emitted from the light source unit 210 to the optical fiber FB1 side at a constant period.

  In the light source 210, the light emitted from the semiconductor laser medium 211 is deflected by the polarization beam splitter 215 and is incident toward the rotation center of the polygon mirror 213. For this reason, the incident area of the light incident on the reflecting surface of the polygon mirror 213 is substantially equal to the cross-sectional area of the light and becomes the minimum area. That is, the incident width in the light rotation direction on the reflecting surface of the polygon mirror 213 is smaller than the conventional light source configured so that light is always incident obliquely on the polygon mirror. As a result, the rotation angle of the polygon mirror 213 is reduced. Can be used effectively, and the wavelength can be swept in a wide wavelength band.

  Further, as apparent from the above description, in the present optical tomographic imaging apparatus 200, the light source unit 210 can sweep the wavelength with a high repetition period by using the polygon mirror 213 conventionally used. .

  In addition, since the optical tomographic imaging apparatus according to the present embodiment uses the light source unit 210 having a high repetition cycle, the time required to acquire one optical tomographic image can be shortened.

  In the light source unit 210, light emitted from the semiconductor laser medium 211 and converted into parallel light by the collimator lens 212 enters the polarization beam splitter 215 at an angle parallel to the rotation axis of the polygon mirror 213, and the polarization beam The semiconductor laser medium 211, the collimator lens 212, the polarization beam splitter 215, and the polygon mirror 213 are arranged so that the s-polarized light reflected by the splitter 215 at a right angle enters the polygon mirror 213 in the direction of the rotation center. The arrangement of the polarizing beam splitter 215, the semiconductor laser medium 211, and the collimating lens 212 can be rotated at an arbitrary angle around the polarizing beam splitter 215 in a plane perpendicular to the paper surface in FIG. Therefore, for example, a light source unit 250 in which the polarization beam splitter 215, the semiconductor laser medium 211, and the collimator lens 212 are arranged in a plane perpendicular to the rotation axis of the polygon mirror 213 as shown in FIG. it can.

  In addition, as shown in FIG. 6, a light source unit 260 including a prism 202 that shifts the optical path of light emitted from the semiconductor laser medium 211 and incident on the polygon mirror 213 so as to follow the rotation direction of the polygon mirror 213 is provided. It can also be used. As shown in FIG. 7, when the laser beam La is incident on the point A of the prism 202 at a predetermined angle, if the wavelength is short, it is emitted from the point B in FIG. 7, for example, and the wavelength of the laser beam La becomes long. Are sequentially ejected from the point B to the point C and D in FIG. That is, the prism 202 is formed and arranged so that the optical path of the laser beam La is shifted by the wavelength of the laser beam La incident on the prism 202. The optical path shift amount differs depending on the refractive index, shape and arrangement angle of the prism 202, and the wavelength and incident angle of the incident light, so that a desired optical path shift amount is obtained in a desired wavelength band in advance. It is necessary to form a prism having an appropriate shape and refractive index and arrange it at an appropriate position and angle.

  By arranging such a prism 202, for example, when the laser beam La is swept in a wavelength band of 0.95 μm to 1.15 μm, first, as shown in FIG. 8, the laser beam La of wavelength 0.95 μm is used. Is emitted from the point B of the prism 202, reflected by the polygon mirror 213, further dispersed by the diffraction grating 214, and the return light (wavelength 0.95 μm) is reflected again by the polygon mirror 213 and enters the point B of the prism 202. And return to the semiconductor laser medium 211.

  When the polygon mirror 213 rotates in the R1 direction and the wavelength becomes longer, for example, 1.05 μm, the laser light La having a wavelength of 1.15 μm is emitted from the point C of the prism 202 as shown in FIG. The reflected light is further dispersed by the diffraction grating 214, the return light (wavelength 1.05 μm) is reflected again by the polygon mirror 213, enters the point C of the prism 202, and returns to the semiconductor laser medium 211.

  Further, when the polygon mirror 213 rotates in the R1 direction and the wavelength becomes longer, for example, 1.15 μm, as shown in FIG. 10, the laser light La having a wavelength of 1.15 μm is emitted from the point D of the prism 202, and the polygon Reflected by the mirror 213, further dispersed by the diffraction grating 214, the return light (wavelength 1.05 μm) is reflected again by the polygon mirror 213, enters the D point of the prism 202, and returns to the semiconductor laser medium 211.

  8 to 10, when the prism 202 is arranged, the rotation angle of the polygon mirror 213 can be used more effectively than in the conventional case where the prism 202 is not arranged. Can be swept.

  Next, an optical tomographic imaging apparatus that is a specific second embodiment of the present invention will be described with reference to FIG. In the optical tomographic imaging apparatus according to the second embodiment, the light source unit 310 is different from the light source unit 210 used in the optical tomographic imaging apparatus shown in FIG. 3, but the other configurations are the same. Therefore, only the light source unit 310 is illustrated, and the description of other configurations is omitted. FIG. 11A shows a top view of the light source unit 310, and FIG. 11B shows a side view.

  The light source unit 310 is a wavelength sweep laser device that emits laser light La while sweeping the oscillation wavelength at a constant period so that the oscillation wavelength λc is in the range of 950 nm to 1150 nm. The laser medium is a semiconductor laser medium. 211 is used.

  Further, the incident position of the light incident on the wavelength selection means 315 is changed by the polygon mirror 213 as the light deflection means and the telecentric lens 314 as the optical system. Note that the wavelength selection means 315 is composed of the same-shaped radiation type diffraction gratings 316a, 316b and 316c. Each of the radial diffraction gratings is a diffraction grating in which grooves are formed in a radial pattern, and the groove intervals are equal in the direction orthogonal to the extending direction of the grooves arranged at the center of the radial diffraction grating 321. Has been created.

  The light emitted from the semiconductor laser medium 211 is condensed by the condenser lens 312a and the cylindrical lens 312b. Note that the condensing lens 312a and the cylindrical lens 312b are configured such that light is collected in a line shape in a direction perpendicular to the paper surface of FIG. 11B on the reflecting surface of the polygon mirror 213. Each radial diffraction grating is arranged so that the extending direction of the groove disposed at the center of the radial diffraction grating is orthogonal to the direction in which the light extends in a line.

  Of the light emitted from the semiconductor laser medium 211 and incident on the polarization beam splitter 215, p-polarized light is transmitted, and s-polarized light is reflected at right angles to the direction of the polygon mirror 213 and emitted from the surface 215b. This s-polarized light passes through the quarter-wave plate 216 and becomes circularly polarized light. This circularly polarized light is incident on the polygon mirror 213 toward the center of rotation. The light reflected by the polygon mirror 213 passes through the quarter wavelength plate 216 again and becomes p-polarized light. This p-polarized light passes through the polarization beam splitter 215 and enters the wavelength selection means 315. Of the p-polarized light dispersed by the wavelength selection means 315, the light dispersed in the incident direction (hereinafter referred to as return light) is transmitted through the polarization beam splitter 215 and further transmitted through the quarter-wave plate 216 to obtain a circle. It becomes polarized light. This circularly polarized light is reflected by the polygon mirror 213, passes through the quarter wavelength plate 216 again, and becomes s-polarized light. The s-polarized light is reflected at a right angle by the polarization beam splitter 215 and returned to the semiconductor laser medium 211. The emission end face 211a of the semiconductor laser medium 211 and the diffraction grating 315 constitute a resonator, and the laser light La is emitted from the emission end face 211a of the semiconductor laser medium 211. At this time, the wavelength of the laser beam La is the wavelength of the return light.

  The light reflected by the polygon mirror 213 is incident on the telecentric lens 314 at predetermined positions of the radiation diffraction gratings 316a, 316b, and 316c according to the angle of the light incident on the telecentric lens 314. As described above, each radiation type diffraction grating is arranged such that the extending direction of the groove disposed at the center of the radiation type diffraction grating is orthogonal to the direction in which the light extends in a line shape.

  FIGS. 12A, 12B, and 12C are diagrams for explaining the incident states of light at points A, B, and C in each of the radiation type diffraction gratings 316a, 316b, and 316c. It is the schematic in the cross section perpendicular | vertical with respect to the paper surface of A). Thus, when the incident position of light on the radiation type diffraction grating is different, the groove period of the diffraction grating is different. As shown in Equation (1), the wavelength λ of the return light returning to the incident direction among the dispersed light is determined by the groove period and the incident angle. For this reason, if the groove period is different according to the incident position of light, the wavelength of the return light is also different. For this reason, the wavelength of the return light returning in the light incident direction varies depending on the incident position of the light incident on the radiation type diffraction grating 321, so the incident position of the light incident on each of the radiation type diffraction gratings 316a, 316b and 316c is When it changes continuously, the oscillation wavelength also changes continuously.

  Of the light dispersed by the wavelength selection means 315, the light dispersed in the incident direction passes through the telecentric lens 314, is reflected by the polygon mirror 213, and returns to the semiconductor laser medium 211.

  Here, the polygon mirror 213 rotates in the direction of the arrow R1, and the reflection angle continuously changes with respect to the optical axis of the telecentric lens 314 on each reflection surface. Thereby, the position of the light incident on the wavelength selecting means 315 also changes continuously. As described above, the wavelength of the return light returning in the light incident direction varies depending on the incident position of the light incident on the wavelength selecting unit 315. That is, when the polygon mirror 213 rotates at a constant speed in the direction of the arrow R1, the wavelength of the return light changes with a constant period as time passes. Therefore, the wavelength-swept laser light La is emitted from the light source unit 310 to the optical fiber FB1 side at a constant period. In addition, since the wavelength selection means 315 in which the radiation diffraction gratings 316a to 316c having the same shape are arranged is used, a plurality of wavelength sweeps can be performed on one reflection surface of the polygon mirror 213.

  Further, instead of the radiation type diffraction gratings 316a to 316c as shown in FIG. 13, the light passes through the multilayer optical filters 322a to 322c having different transmission wavelengths when the light incident positions are different, and the multilayer optical filters 322a to 322c. It is also possible to use a light source unit 320 using wavelength selection means 321 comprising a reflection mirror 323 that reflects the reflected light vertically. Each multilayer optical filter 322a to 322c is created so that the transmission wavelength increases or decreases when the incident position changes in a certain direction, and is arranged so that the increase / decrease direction of the transmission wavelength coincides with the light scanning direction. ing. Accordingly, the wavelength of the return light that is transmitted through each of the multilayer optical filters 322a to 322c, reflected by the reflection mirror 323, and transmitted through each of the multilayer optical filters 322a to 322c again differs depending on the light incident position. Therefore, similarly to the optical unit 310, the wavelength of the return light returning in the light incident direction varies depending on the incident position of the light incident on the multilayer optical filters 322a to 322c. When the incident position of light on 322c changes continuously, the oscillation wavelength also changes continuously.

  Each of the multilayer optical filters 322a to 322c has the same light transmission characteristics (the transmission wavelength is different when the light incident position is different). Also in the light source unit 320, a plurality of wavelength sweeps can be performed on one reflecting surface of the polygon mirror 213.

  Next, an optical tomographic imaging apparatus according to a third embodiment of the present invention will be described with reference to FIGS. In the optical tomographic imaging apparatus according to the third embodiment, the light source unit 410 is different from the light source unit 210 used in the optical tomographic imaging apparatus shown in FIG. 3, but the other configurations are the same. Therefore, only the light source unit 410 is illustrated, and the description of other configurations is omitted.

  As shown in FIG. 14 and FIG. 15, the light source unit 410 has a different angle from a mirror set 415 consisting of relay lenses 411a and 411b and mirrors 414a and 414b arranged at different angles between the relay lenses 411a and 411b. Wavelength selection means 412 comprising two diffraction gratings 413a and 413b having the same shape and arranged in the above. As shown in FIG. 14, the mirror 414a and the relay lens 411b are configured so that the light passing through the upper half in FIG. 14A of the relay lens 411a enters the diffraction grating 413a as the polygon mirror 213 rotates. It changes the optical path of light. As shown in FIG. 15, the mirror 414b and the relay lens 411b change the optical path of light so that light passing through the lower half of the relay lens 411 in FIG. 15A enters the diffraction grating 413b. . The relay lenses 411a and 411b, the mirrors 414a and 414b, and the diffraction gratings 413a and 413b are a range of incident angles at which light passing through the upper half of the relay lens 411a is incident on the diffraction grating 413a and below the relay lens 411a. It arrange | positions so that the range of the incident angle which the light which passes half may enter into the diffraction grating 413b may become equal.

  In the light source unit 410, first, as shown in FIG. 14, the light emitted from the semiconductor laser medium 211 is converted into parallel light by the collimator lens 212, branched into s-polarized light and p-polarized light by the polarization beam splitter 215, and s-polarized light. Is reflected by the polygon mirror 213, relayed by the relay lenses 411a and 411b, the optical path is changed by the mirror 414a, and enters the diffraction grating 413a. Of the light dispersed by the diffraction grating 413a, the return light, which is the light dispersed in the incident direction, returns to the semiconductor laser medium 211 through an optical path opposite to that of the incident light. Similar to the light source unit 210, the emission end face 211a of the semiconductor laser medium 211 and the diffraction grating 413a constitute a resonator, and the laser light La is emitted from the emission end face 211a of the semiconductor laser medium 211. While the polygon mirror 213 rotates from the state indicated by the solid line to the state indicated by the dotted line, the incident angle of the light incident on the diffraction grating 413a continuously changes, and the wavelength of the return light also changes continuously.

  When the polygon mirror 213 further rotates, the state changes from the state indicated by the dotted line in FIG. 14 to the state indicated by the dotted line in FIG. While the polygon mirror 213 rotates from the state indicated by the dotted line to the state indicated by the solid line, the incident angle of the light incident on the diffraction grating 413b changes continuously, and the wavelength of the return light also changes continuously.

  For this reason, the wavelength can be swept twice with respect to one reflecting surface of the polygon mirror 213, and the wavelength can be swept with a high repetition period by using the polygon mirror 213 conventionally used.

  It should be noted that instead of the wavelength selection means 412, the light having an angle with respect to the plane in which the light is wavelength-dispersed in each diffraction grating when the polygon mirror 213 is not tilted as shown in FIG. Alternatively, wavelength selection means 421 including conjugate reflection optical systems 423a and 423b that reflect conjugately and diffraction gratings 422a and 422b arranged in a Littman arrangement can be used.

  The conjugate reflection optical system 423a is disposed at the focal position of the condenser lens 424a and the condenser lens 424a, and with respect to a plane on which light is wavelength-dispersed in each diffraction grating when the polygon mirror 213 is not tilted. And a linear mirror 425a extending in the vertical direction.

  Hereinafter, the conjugate reflection optical system 423a will be described. A top view of the conjugate reflective optical system 423a is shown in FIG. 117 (A), and a side view thereof is shown in FIG. 17 (B). The light dispersed by the diffraction grating 422a is collected by the condenser lens 424a, but only the dispersed light reflected by the linear mirror 425a returns to the diffraction grating 422a. That is, as shown in FIG. 17A, in the wavelength dispersion direction in the diffraction grating 422a, the direction parallel to the optical axis direction of 424a, which is the direction of focusing on the linear mirror 425a, that is, FIG. Only the light dispersed in the X direction at is returned to the diffraction grating 422a. This is the same as the case where a normal mirror is arranged instead of the conjugate reflection optical system 423a, and the wavelength selection function works.

  On the other hand, when the surface of the polygon mirror 213 is tilted, the direction of the light dispersed by the diffraction grating 422a may be shifted in the Y direction in FIG. 17B, for example. Even when the dispersion direction is deviated in this way, as shown in FIG. 17B, the light incident on the conjugate reflective optical system 423a is reflected in the direction opposite to and parallel to the incident direction. For this reason, this light returns to the semiconductor laser medium 211 by following the almost same optical path as the incident optical path. For this reason, it becomes difficult to be affected by the surface tilt of the polygon mirror 213.

  Note that the conjugate reflection optical system 423b is the same as the conjugate reflection optical system 423a, and a description thereof will be omitted.

  As the conjugate reflection optical system, a cylindrical lens 431 arranged as shown in a top view in FIG. 18A and a side view in FIG. 18B, and a mirror arranged at the focal position of the cylindrical lens 431 are shown. A conjugate reflective optical system 433 made of 432 can also be used. Also in this case, as shown in FIG. 18A, the wavelength selection function works in the same way as when only the mirror 432 is arranged in the wavelength dispersion direction of the diffraction grating 422a. Further, as shown in FIG. 18B, even when the direction of the light dispersed by the diffraction grating 422a is shifted in the Y direction in FIG. 18B, the light incident on the conjugate reflective optical system 433 is Reflected in the direction opposite to the incident direction.

  Further, as the conjugate reflection optical system, a retroreflector 441 arranged as shown in a top view in FIG. 19A and a side view in FIG. 19B can be used. Also in this case, as shown in FIG. 19A, the wavelength selection function works in the wavelength dispersion direction of the diffraction grating 422a as in the case where the mirror is arranged. Further, as shown in FIG. 19B, even if the direction of the light dispersed by the diffraction grating 422a is shifted in the Y direction in FIG. And reflected in the opposite direction.

  In each embodiment, the semiconductor laser medium 211 is used as the optical amplifying unit. However, the optical amplifying unit may be any unit as long as it has an optical amplifying function. Or a fiber constituting a fiber laser.

Schematic diagram of a conventional wavelength swept light source Schematic diagram of a conventional wavelength swept light source 1 is a schematic configuration diagram of an optical tomographic imaging apparatus according to a first embodiment of the present invention. Schematic configuration diagram of the light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit Illustration of prism Illustration of the optical path in the light source unit Illustration of the optical path in the light source unit Illustration of the optical path in the light source unit The schematic block diagram of the light source unit used for the optical tomographic imaging apparatus which is the 2nd Embodiment of this invention. Explanatory diagram of the relationship between the incident position of incident light and the grating plane of the radial diffraction grating Schematic configuration diagram of another light source unit The schematic block diagram of the light source unit used for the optical tomographic imaging apparatus which is the 3rd Embodiment of this invention. Schematic configuration diagram of the light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of conjugate reflective optical system Schematic configuration diagram of conjugate reflective optical system Schematic configuration diagram of conjugate reflective optical system

Explanation of symbols

3 Light splitting means
4 multiplexing means
210,310,410 Light source unit
211 Semiconductor laser medium
212 Collimating lens
213 polygon mirror
214a, 214b Relay lens
214 diffraction grating
220 Optical path length adjustment means
230 Optical probe
240 Interference light detection means
241 Image acquisition means
242 display device
415 Radiation diffraction grating
416 Radiation diffraction grating set

Claims (6)

Optical amplification means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
In a wavelength swept light source having wavelength selection means for changing the wavelength of light returning to the incident direction by changing the incident angle or the incident position of the light deflected by the light deflecting means,
The wavelength sweeping light source, wherein the wavelength selection unit includes a plurality of wavelength selection units in which wavelengths of light returning to the incident direction change in substantially the same wavelength band.   2. A wavelength-swept light source according to claim 1, wherein the rotary light deflecting means is a polygon mirror.   The wavelength sweeping light source according to claim 1, wherein the wavelength selection unit has a light dispersion unit that wavelength-disperses the light. The wavelength of the return light that returns to the incident direction of the light is different according to the incident angle of the light, the light dispersion unit,
Comprising optical means for causing the light deflected by the light deflecting means to enter the light dispersing section;
4. The wavelength swept light source according to claim 3, wherein the light deflecting unit and the optical unit change an incident angle of light incident on the light dispersing unit. The light dispersive part has a different wavelength of return light returning to the light incident direction according to the light incident position,
Comprising optical means for causing the light deflected by the light deflecting means to enter the light dispersing section;
4. The wavelength swept light source according to claim 3, wherein the light deflecting means and the optical means change an incident position of light incident on the light dispersing means. A light source that emits laser light while sweeping the wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the light source 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 the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light combined by the multiplexing means; ,
In an optical tomographic imaging apparatus comprising: an image acquisition unit configured to acquire a tomographic image of the measurement target using the intensity of the interference light at each depth position detected by the interference light detection unit;
The light source comprises light amplifying means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
A wavelength swept light source having wavelength selection means for changing the wavelength of light returning to the incident direction by changing the incident angle or the incident position of the light deflected by the light deflecting means,
The optical tomography apparatus according to claim 1, wherein the wavelength selection unit includes a plurality of wavelength selection units in which wavelengths of light returning to the incident direction change in substantially the same wavelength band.

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