JP2007309880A - Wavelength sweeping light source, and optical tomographic imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the effective use of a rotation angle in a rotary type light deflection means, and to sweep a wavelength over a wide wavelength band. <P>SOLUTION: Light emitted from a semiconductor laser medium 211 gets incident into a polarization beam splitter 215, p-polarized light is transmitted, and s-polarized light is reflected at right angle to be emitted from a face 215b. The s-polarized light is transmitted through a 1/4-wavelength plate 216 to be brought into circularly polarized light, and gets incident into a polygon mirror 213 along a rotation center direction. Reflected light on the polygon mirror 213 is transmitted again through the 1/4-wavelength plate 216 to be brought into the p-polarized light, and is transmitted through the polarization beam splitter 215 to get incident into a diffraction grating 214. Return light dispersed to an incident direction by the diffraction grating 214 is reflected by the polygon mirror 213, and is reflected at a right angle in the polarization beam splitter 215 to be fed back to the semiconductor laser medium 211. A laser beam La wavelength-swept at a fixed period is emitted from a light source unit 210, because the polygon mirror 213 is rotated to change a wavelength of the return light at the fixed period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength swept light source in which an oscillation wavelength is swept 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 device shown in FIG. 1A converts the emitted light 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, By returning the diffracted light diffracted by the diffraction grating 104 to the semiconductor laser medium 101, the oscillation wavelength is selected.

  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. The oscillation wavelength can be continuously changed by rotating 103, 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. 1B, the wavelength sweep laser apparatus 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, this laser device emits laser light that is wavelength-swept at a constant period.
US2005 / 0035295 A1 US4601036

  However, in the wavelength swept light source shown in FIG. 1B, the light emitted from the laser medium is always incident obliquely on the reflecting surface of the polygon mirror, so that the incident width in the rotation direction becomes large. As a result, there is a problem that the rotation angle of the polygon mirror that can be used for the wavelength sweep is reduced, and the wavelength sweep width is reduced.

  The present invention has been made in view of this problem, a wavelength swept light source capable of effectively utilizing the rotation angle of the rotating light deflecting means and sweeping a wavelength in a wide wavelength band, and optical tomographic imaging using the wavelength swept light source The object is to realize an 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;
A wavelength selecting unit that changes a wavelength of light that returns to the incident direction when the incident angle or the incident position of the light deflected by the light deflecting unit changes, and the optical deflecting unit is optically coupled to the optical amplifying unit. And a wavelength swept light source arranged between the wavelength selecting means and
The light emitted from the optical amplifying means disposed between the optical deflecting means and the wavelength selecting means is deflected in the direction of the rotation center of the optical deflecting means, and is deflected by the optical deflecting means to An optical deflecting / feedback means for returning the light incident on the wavelength selecting means and returning to the optical amplifying means is provided.

  Note that “the direction of the rotation center of the light deflecting means” includes a direction that can be substantially regarded as the direction of the rotation center even if it is slightly deviated from the complete rotation center in addition to the direction of the complete rotation center. It is a waste. That is, if the incident width in the rotation direction of the light incident on the light deflecting means is within a range that can be regarded as substantially the same width as the minimum width, that is, within 1.1 times the minimum width, It is included in “the direction of the rotation center”.

  The light deflection / feedback means may be constituted by a mirror, a half mirror, a polarization beam splitter, and a quarter wavelength phase shifter.

  As the quarter wavelength phase shifter, a normal quarter wavelength plate made of a birefringent element or the like, or a Faraday rotator set so that the phase is shifted by a quarter wavelength can be used.

  The light amplification means may emit linearly polarized light.

  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 element. Here, the “light dispersion element” is, for example, a diffraction grating, a prism, or a grism.

If the light dispersion element has a different wavelength of light returning to the incident direction depending on the incident position of the light,
The light deflecting unit and the optical unit disposed between the light deflecting unit and the light dispersing element may change the incident position of the light incident on the light dispersing unit.

  The optical means may be a telecentric optical system. Further, the light dispersion element may be a diffraction grating in which the grating surface is continuously twisted about the extending direction of the groove or a diffraction grating in which the grooves are formed radially.

  The wavelength selection unit may include a plurality of wavelength selection units capable of selecting wavelengths in substantially the same wavelength band.

An optical tomographic imaging apparatus of the present invention includes a light source that emits coherent light while sweeping a wavelength at a constant period;
Light splitting means for splitting the coherent 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 includes a light amplifying means, a rotating light deflecting means for deflecting light emitted from the light amplifying means, and an incident direction or an incident position of the light deflected by the light deflecting means is changed. And a wavelength sweeping light source optically disposed between the light amplification means and the wavelength selection means,
The light emitted from the light amplifying means is deflected in the direction of the rotation center of the light deflecting means, and the light deflected by the light deflecting means and incident on the wavelength selecting means is returned to the light amplifying means. An optical deflection / feedback means for returning is provided.

  In the wavelength swept light source of the present invention, the light emitted from the light amplifying means is deflected by the light deflecting / feedback means toward the rotation center of the rotary light deflecting means and further deflected by the light deflecting means. The area of light incident on the deflecting surface of the light deflecting means becomes small, and the rotation angle of the light deflecting means can be used effectively.

  In addition, the optical tomographic imaging apparatus of the present invention can effectively use the rotation angle of the light deflecting means in the wavelength swept light source used, and can sweep the wavelength in a wide wavelength band. High optical tomographic image can be acquired.

  The optical tomographic imaging apparatus according to the first embodiment of the present invention will be described below with reference to FIG. FIG. 2 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. 2 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 Interference to detect L4 Based on a detection result of the light detection means 240, the detection result of the interference light detection means 240, an image acquisition unit 241 that generates an optical tomographic image to be measured, and a display device 242 that displays the optical tomographic image. .

  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 measurement light L1 and 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. 3A, and a side view thereof is shown in FIG. The light source unit 210 includes a semiconductor laser medium 211, a collimator lens 212, a polygon mirror 213, a diffraction grating 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.

  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 optical tomographic imaging apparatus 200, the rotation angle of the polygon mirror 213 can be used effectively in the light source unit 210, and the wavelength is swept in a wide wavelength band. Therefore, an optical tomographic image with high measurement resolution can be acquired. When high measurement resolution is not required, the number of polygon mirrors 213 can be increased, and the acquisition time required for acquiring one optical tomographic image can be reduced.

  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 at right angles by the splitter 215 is incident on 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 FIG. 3, the polarizing beam splitter 215 and the quarter wavelength plate 216 are arranged between the polygon mirror 213 and the diffraction grating 214, but moved in the vertical direction on the paper surface of FIG. It may be arranged at a position. In this case, it is necessary to arrange the polarizing beam splitter 215, the polygon mirror 213, and the diffraction grating 214 at appropriate angles. If the optical path between the polarizing beam splitter 215 and the polygon mirror 213 and the optical path between the polygon mirror 213 and the diffraction grating 214 do not overlap, a mirror 217 is used instead of the polarizing beam splitter 215 as shown in FIG. May be used. Alternatively, the semiconductor laser medium 211 may be arranged so that light emitted from the semiconductor laser medium 211 is directly incident on the polygon mirror 213.

  Further, as shown in FIG. 6, instead of the diffraction grating 214, a light source unit 260 in which two small and identical diffraction gratings 261a and 261b are arranged along the scanning direction of light by the polygon mirror 213 is used. You can also 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. By using a plurality of diffraction gratings in combination in this way, a plurality of wavelength sweeps can be performed on one reflecting surface of the polygon mirror 213, and a faster wavelength sweep is possible.

  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. 2, 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. 7A shows a top view of the light source unit 310, and FIG. 7B 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. 211 is used.

  Further, the incident position of the light incident on the twisted diffraction grating 315 as the dispersion means is changed by the polygon mirror 213 as the light deflection means and the telecentric lens 314 as the optical system. The twisted diffraction grating 315 is a diffraction grating in which the grating surface is continuously twisted about the direction in which the groove extends, and the wavelength of the return light returning to the light incident direction depends on the light incident position. Is different.

  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. 7B on the reflection surface of the polygon mirror 213.

  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 diffraction grating 315. Of the p-polarized light dispersed by the diffraction grating 315, 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 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 a predetermined position of the twisted diffraction grating 315 by the telecentric lens 314 in accordance with the angle of the light incident on the telecentric lens 314. The twisted diffraction grating 315 is disposed so that the extending direction of the grooves is orthogonal to the direction in which the light extends in a line shape.

  FIG. 8 is a diagram for explaining the incident state of light on the twisted diffraction grating 315 at points A, B, and C in FIG. 7, and is a schematic diagram in a cross section perpendicular to the paper surface of FIG. . The incident angle is exaggerated. As described above, when the incident position of light on the twisted diffraction grating 315 is different, the angle formed between the incident light and the grating surface is different. For this reason, the wavelength of the return light returning in the light incident direction varies depending on the light incident position. Of the light dispersed by the twisted diffraction grating 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. As a result, the position of the light incident on the twisted diffraction grating 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 twisted diffraction grating 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 the light source unit 310, the twisted diffraction grating 315 in which the grating surface is continuously twisted about the direction in which the groove extends is used, so that a desired wavelength sweep width can be obtained depending on the degree of twist. Further, since the polygon mirror 213 and the telecentric lens 314 are used, the incident position of the light to the twisted diffraction grating 315 can be continuously changed with a simple configuration, and the wavelength can be swept.

  Further, instead of the twisted diffraction grating 315 as shown in FIG. 9, a light source unit 320 using a radiation type diffraction grating 321 can be used. The radial diffraction grating 321 is a diffraction grating in which grooves are formed in a radial pattern so that the groove intervals are equal in the direction perpendicular to the extending direction of the grooves arranged at the center of the radial diffraction grating 321. Has been created. The radial diffraction grating 321 is arranged such that the extending direction of the groove disposed at the center of the radial diffraction grating 321 is orthogonal to the direction in which the light extends in a line shape.

  FIG. 10 is a diagram for explaining the incident state of light on the radial diffraction grating 321 at points A, B, and C in FIG. 9, and is a schematic view in a cross section perpendicular to the paper surface of FIG. Note that the groove period is exaggerated. As described above, when the incident position of light on the radiation type diffraction grating 321 is different, the groove period 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, as with the light source unit 310, the wavelength of the return light that returns to the incident direction of light varies depending on the incident position of the light incident on the radiation type diffraction grating 321, so the light incident position on the radiation type diffraction grating 321 is also different. When is continuously changed, the oscillation wavelength is also continuously changed.

  Further, as shown in FIG. 11, a light source unit 330 is used in which a radiation type diffraction grating set 332 in which small-sized radiation diffraction gratings 331a to 331c having the same shape are arranged in place of the radiation type diffraction grating 321 is used. In addition, it is possible to easily obtain a light source capable of sweeping the wavelength with a high repetition period.

  Further, instead of the twisted diffraction grating 315 as shown in FIG. 12, the multilayer optical filter 341 having a different transmission wavelength when the incident position of the light is different, and the reflection that vertically reflects the light transmitted through the multilayer optical filter 341 A light source unit 340 using a mirror 342 can also be used. The multilayer optical filter 341 is formed 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. Therefore, the wavelength of the return light that is transmitted through the multilayer optical filter 341, reflected by the reflection mirror 341, and transmitted through the multilayer optical filter 341 again differs according to the incident position of light. Therefore, similarly to the light source 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 filter 341. Therefore, the incident position of the light on the multilayer optical filter 341 When is continuously changed, the oscillation wavelength is also continuously changed.

  Further, as shown in FIG. 13, a light source using a multilayer filter set 352 in which multilayer optical filters 351a to 351c having a small size and the same transmission characteristics (the transmission wavelengths differ depending on the incident position of light) are arranged. The unit 350 can also be used, and it is possible to easily obtain a light source whose wavelength can be swept with a high repetition period.

  Next, an optical tomographic imaging apparatus according to a third embodiment of the present invention will be described with reference to FIG. 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. 2, 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, the light source unit 410 includes relay lenses 411a and 411b. In the light source unit 410, 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 the s-polarized light is reflected by the polygon mirror 213 and relayed. Relayed by the lenses 411 a and 411 b and enters the diffraction grating 412. Of the light dispersed by the diffraction grating 412, the return light that is dispersed in the incident direction passes through the relay lenses 411b and 411a, is reflected by the polygon mirror 213, and returns to the semiconductor laser medium 211. Similar to the light source unit 210, the emission end face 211a of the semiconductor laser medium 211 and the diffraction grating 412 constitute a resonator, and the laser light La is emitted from the emission end face 211a of the semiconductor laser medium 211. Since the polygon mirror 213 rotates and the wavelength of the return light changes with a constant period as time elapses, the wavelength-swept laser light La is emitted from the light source unit 410 at the optical fiber FB1 side at a constant period. Is injected into. Since substantially the same part is used in the diffraction grating 412, a small diffraction grating can be used as the diffraction grating 412, and the light source unit 410 can be downsized. The polarization beam splitter 215 and the quarter wavelength plate 216 may be disposed between the relay lenses 411a and 411b or between the relay lens 411b and the diffraction grating 412.

  Further, the arrangement of the polarizing beam splitter 215, the semiconductor laser medium 211, the collimating lens 212, and the polarizing beam splitter 215 can be rotated at an arbitrary angle around the polarizing beam splitter 215 in a plane perpendicular to the paper surface in FIG. is there.

  Further, instead of the light source unit 410, a light source unit 420 capable of performing two wavelength sweeps on one reflecting surface of the polygon mirror 213 can be used. As shown in FIGS. 15 and 16, the light source unit 420 includes relay lenses 421a and 421b, mirrors 424a and 424b arranged at different angles between the relay lenses 421a and 421b, and 2 arranged at different angles. The diffraction gratings 423a and 423b having the same shape are provided. As shown in FIG. 14, the mirror 424a and the relay lens 421b are arranged so that the light passing through the upper half in FIG. 14A of the relay lens 421a enters the diffraction grating 423a as the polygon mirror 213 rotates. It changes the optical path of light. As shown in FIG. 15, the mirror 424b and the relay lens 421b change the optical path of light so that light passing through the lower half of the relay lens 421 in FIG. 15A enters the diffraction grating 423b. . The relay lenses 421a and 421b, the mirrors 424a and 424b, and the diffraction gratings 423a and 423b are a range of incident angles at which light passing through the upper half of the relay lens 421a is incident on the diffraction grating 423a and below the relay lens 421a. It arrange | positions so that the range of the incident angle which the light which passes half may enter into the diffraction grating 423b may become equal.

  In the light source unit 420, first, as shown in FIG. 15, 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 421a and 421b, the optical path is changed by the mirror 424a, and enters the diffraction grating 423a. Of the light dispersed by the diffraction grating 423a, 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. Similarly to the light source unit 210, a resonator is constituted by the emission end face 211a of the semiconductor laser medium 211 and the diffraction grating 423a, and the laser beam 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 423a continuously changes, and the wavelength of the return light also continuously changes.

  When the polygon mirror 213 further rotates, the state changes from the state indicated by the dotted line in FIG. 15 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 423b continuously changes, 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.

  Further, instead of the diffraction grating 412, even if the polygon mirror 213 is not tilted as shown in FIG. 17, it may be light having an angle with respect to a plane in which light is wavelength-dispersed in each diffraction grating. Alternatively, a light source unit 430 having a conjugate reflection optical system 431 that conjugately reflects and a diffraction grating 434 arranged in a Littman arrangement can be used.

  The conjugate reflection optical system 431 is disposed at the focal point of the condenser lens 432 and the condenser lens 432, and with respect to the plane on which the light is wavelength-dispersed in the diffraction grating 434 when the polygon mirror 213 is not tilted. And a linear mirror 433 extending in a vertical direction. In the present embodiment, diffraction grating 434 is arranged so as to disperse light in a plane perpendicular to the rotation axis of polygon mirror 213 when polygon mirror 213 is not tilted. The linear mirror 433 extends in the rotation axis direction of the polygon mirror 213.

  Hereinafter, the conjugate reflection optical system 431 will be described. FIG. 18A shows a top view of the conjugate reflective optical system 431a, and FIG. 18B shows a side view thereof. The light dispersed by the diffraction grating 434 is collected by the condenser lens 432, but only the dispersed light reflected by the linear mirror 433 returns to the diffraction grating 434. That is, as shown in FIG. 16A, in the wavelength dispersion direction in the diffraction grating 434, the direction parallel to the optical axis direction of 432, which is the direction of focusing on the linear mirror 433, that is, FIG. Only the light dispersed in the X direction at is returned to the diffraction grating 434. This is the same as the case where a normal mirror is arranged instead of the conjugate reflection optical system 431, 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 434 may shift in the Y direction in FIG. 18B, for example. Even in such a case where the dispersion direction is deviated, as shown in FIG. 18B, the light incident on the conjugate reflective optical system 431 is reflected in the direction opposite to and parallel to the incident direction. The reflected light returns to the semiconductor laser medium 211 by following the substantially 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.

  As the conjugate reflection optical system, a cylindrical lens 435 arranged as shown in a top view in FIG. 19A and a side view in FIG. 19B, and a mirror arranged at the focal position of the cylindrical lens 435 are shown. A conjugate reflection optical system 437 made of 436 can also be used. Also in this case, as shown in FIG. 17A, the wavelength selection function works in the same manner as when only the mirror 436 is arranged in the wavelength dispersion direction of the diffraction grating 434. Further, as shown in FIG. 19B, even when the direction of the light dispersed from the diffraction grating 434 is shifted in the Y direction in FIG. 19B, the light incident on the conjugate reflective optical system 437 is Reflected in the direction opposite to the incident direction.

  Further, as the conjugate reflection optical system, a retroreflector 438 arranged as shown in a top view in FIG. 20A and a side view in FIG. 20B can be used. Also in this case, as shown in FIG. 20A, the wavelength selection function works in the wavelength dispersion direction of the diffraction grating 438 as in the case where the mirror is arranged. As shown in FIG. 20B, even when the direction of the light dispersed by the diffraction grating 438 is shifted in the Y direction in FIG. And reflected in the opposite direction.

  Further, the light source unit 440 shown in FIG. 21 that has both the function of the light source unit 420 and the function of the light source unit 430 can be used. The light source unit 440 is a conjugate reflection optical system that conjugately reflects light having an angle with respect to a plane in which light is wavelength-dispersed in each diffraction grating when the polygon mirror 213 is not tilted. 441a and 441b, and diffraction gratings 442a and 442b arranged in a Littman arrangement.

  The conjugate reflection optical system 441a is arranged at the focal position of the condenser lens 443a and the condenser lens 443a, and with respect to the plane on which the light is wavelength-dispersed in the diffraction grating 442a when the polygon mirror 213 is not tilted. And a linear mirror 444a extending in a vertical direction.

  Similarly, the conjugate reflection optical system 441b is disposed at the focal point of the condenser lens 443b and the condenser lens 443b, and when the polygon mirror 213 is not tilted, the light is wavelength-dispersed in the diffraction grating 442b. And a linear mirror 444b extending in a direction perpendicular to the flat surface.

  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 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 the light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit Explanatory diagram of the relationship between the incident position of incident light and the grating plane of the torsional diffraction grating Schematic configuration diagram of another light source unit 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 the light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of the light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit Schematic configuration diagram of conjugate reflected light optical system Schematic configuration diagram of conjugate reflected light optical system Schematic configuration diagram of conjugate reflected light optical system Schematic configuration diagram of another light source unit

Explanation of symbols

3 Light splitting means
4 multiplexing means
210,250,260,310,320,330,340,350,410,420,430, light source unit
211, semiconductor laser medium
212 Collimating lens
213 polygon mirror
214a, 214b, 411a, 411b Relay lens
214,434 diffraction grating
215 Polarizing beam splitter
216 1/4 wave plate
217 mirror
220 Optical path length adjustment means
230 Optical probe
240 Interference light detection means
241 Image acquisition means
242 display device
314 Telecentric lens
315 Twisted diffraction grating
321 Radiation diffraction grating
341 Multilayer optical filter
342 Mirror
431,437 Conjugate reflective optical system

Claims (9)

Optical amplification means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
A wavelength selecting unit that changes a wavelength of light that returns to the incident direction when the incident angle or the incident position of the light deflected by the light deflecting unit changes, and the optical deflecting unit is optically coupled to the optical amplifying unit. And a wavelength swept light source arranged between the wavelength selecting means and
The light emitted from the light amplifying means is deflected in the direction of the rotation center of the light deflecting means, and the light deflected by the light deflecting means and incident on the wavelength selecting means is returned to the light amplifying means. A wavelength swept light source comprising an optical deflection / feedback means for returning.   2. The wavelength swept light source according to claim 1, wherein the light deflecting / feedback means is disposed between the light deflecting means and the wavelength selecting means.   3. The wavelength swept light source according to claim 1, wherein the light deflecting / feedback means comprises a polarizing beam splitter and a quarter wavelength phase shifter.   4. The wavelength swept light source according to claim 3, wherein the light amplifying means emits linearly polarized light.   The wavelength-swept light source according to any one of claims 1 to 4, wherein the rotary light deflecting means is a polygon mirror.   6. The wavelength swept light source according to claim 1, wherein the wavelength selection means has a light dispersion element. The light dispersion element has a different wavelength of light returning to the incident direction according to the incident position of the light,
Optical means is disposed between the light deflecting means and the light dispersing element,
The wavelength swept light source according to claim 6, wherein the light deflecting unit and the optical unit change an incident position of light incident on the light dispersing unit.     The wavelength-swept light source according to any one of claims 1 to 7, wherein the wavelength selection unit includes a plurality of wavelength selection units capable of selecting wavelengths in substantially the same wavelength band. A light source that emits coherent light while sweeping the wavelength at a constant period;
Light splitting means for splitting the coherent 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 includes a light amplifying means, a rotating light deflecting means for deflecting light emitted from the light amplifying means, and an incident direction or an incident position of the light deflected by the light deflecting means is changed. And a wavelength sweeping light source optically disposed between the light amplification means and the wavelength selection means,
The light emitted from the light amplifying means is deflected in the direction of the rotation center of the light deflecting means, and the light deflected by the light deflecting means and incident on the wavelength selecting means is returned to the light amplifying means. An optical tomographic imaging apparatus comprising optical deflection / feedback means for returning.

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