JP2007309881A - Wavelength sweep light source and optical tomographic imaging apparatus - Google Patents

Abstract

A wavelength swept light source that oscillates with good oscillation efficiency is realized. Light emitted from a semiconductor laser medium 211 is converted into parallel light by a collimator lens 212, reflected by a polygon mirror 213, and relay lens 217a. And 217b to enter the diffraction grating 214. Of the light dispersed by the diffraction grating 214, the return light reflected by the conjugate reflection optical system 221 is incident on the diffraction grating 214 again and returns to the semiconductor laser medium 211. Since the polygon mirror 213 rotates and the wavelength of the return light changes at a constant period with time, the light source unit 210 emits the laser light La that has been swept at a constant period. Even if the surface of the polygon mirror 213 is tilted and the direction of the light dispersed by the diffraction grating 214 is deviated in the direction of the rotation axis of the polygon mirror 213, it is reflected by the conjugate reflective optical system 221 in the direction opposite to the incident direction. Then, it returns to the semiconductor laser medium 211.
[Selection] Figure 6

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 swept type light source, an external resonator type wavelength swept light source called a Littrow type is known. This Littrow-type light source has a structure basically shown.

  The wavelength swept light source 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 103 to the semiconductor laser medium 101.

  In the wavelength swept light source having this structure, only a specific wavelength component returns to the semiconductor laser medium 101 among the wavelength components of the light emitted from the semiconductor laser medium 101 and diffracted by the diffraction grating 103. 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 swept continuously, 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 wavelength sweep light source that can repeatedly perform wavelength sweep at high speed. As shown in FIG. 2, the wavelength swept light source 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, the wavelength-swept light source 110 emits laser light L that has been wavelength-swept at a constant period.

  In addition, in the Japanese Patent Application No. 2005-374519, the present inventor has proposed a wavelength swept light source capable of sweeping a wavelength using a smaller diffraction grating. As shown in FIG. 3, the wavelength swept light source 120 includes a laser medium 111, a collimator lens 112, a polygon mirror 113, relay lenses 121a and 121b, and a diffraction grating 114. Light emitted from the end surface 111b of the semiconductor laser medium 111 is converted into parallel light by the collimator lens 112, reflected by the polygon mirror 113, relayed by the relay lenses 121a and 121b, 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) passes through the relay lenses 121b and 121a, is reflected by the polygon mirror 113, and returns to the semiconductor laser medium 111. The emission end face 111a of the semiconductor laser medium 111 and the diffraction grating 114 constitute a resonator, and the laser light La is emitted from the emission end face 111a of the semiconductor laser medium 111. At this time, the wavelength of the laser beam La 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 with respect to the optical axes of the relay lenses 121a and 121b on each reflection surface. Thereby, the angle of the light incident on the diffraction grating 114 also changes continuously. For this reason, the oscillation wavelength also changes continuously.
US2005 / 0035295 A1 US4601036

  However, in the wavelength swept light source shown in FIG. 3, since the end face 111b of the laser medium 111 and the diffraction grating 114 corresponding to the end of the resonator are not conjugated, for example, the polygon mirror 113 is tilted. In this case, the focal point of the return light on the end surface 111b of the laser medium 111 may move along the end surface 111b, and a good oscillation state may not be obtained.

  For this reason, the present inventor has a cylindrical lens 131 as shown in FIG. 4, and condenses the light in a line shape on the reflection surface of the polygon mirror 113 and the diffraction grating 114, thereby affecting the influence of the surface tilt. The wavelength swept light source 130 that can be suppressed was studied. However, in this case, on the diffraction grating 114, the light is collected only at the center of the line, and at the end of the line, it is deviated from the light collecting position. For this reason, the focus of the return light on the end surface 111b of the laser medium 111 varies in a direction perpendicular to the end surface 111b, so-called defocusing occurs, and there is a problem that a good oscillation state cannot be obtained.

  The present invention has been made in view of this problem. An optical amplifying unit, a rotary optical deflecting unit that deflects light emitted from the optical amplifying unit, and a light that disperses light deflected by the optical deflecting unit. A wavelength-swept light source including a dispersion unit and a wavelength-swept light source capable of suppressing the influence of surface tilt and also capable of suppressing defocusing on the end surface of the optical amplification unit and obtaining a good oscillation state, and the wavelength-swept light source An object of the present invention is to realize an optical tomographic imaging apparatus using a light source.

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;
Light dispersion means for wavelength-dispersing the light deflected by the light deflection means;
First optical means for causing the light deflected by the light deflecting means to enter the light dispersing means as substantially parallel light;
A wavelength swept light source having second optical means for reflecting light dispersed in a predetermined direction out of the light dispersed by the light dispersing means to the light dispersing means,
The second optical means is a conjugate reflection optical system that conjugately reflects light dispersed in the predetermined direction.

  Note that “conjugate reflection” means reflection in a direction parallel to the incident direction of light.

  Here, the “light dispersion means” is, for example, a diffraction grating, a prism, or a grism. The “light deflecting means” is, for example, a polygon mirror, a rotating mirror, a galvano or a resonant scanner, or the like.

In addition, if the light dispersion unit scatters the light deflected by the light deflection unit in a plane perpendicular to the rotation axis of the light deflection unit,
The conjugate reflection optical system may be configured such that light dispersed in the predetermined direction is light that has an angle with respect to a plane perpendicular to the rotation axis of the light deflecting means or is conjugately reflected. Good.

  The conjugate reflection optical system may include a condensing lens and a linear mirror that is disposed at a focal position of the condensing lens and extends in the rotation axis direction of the light deflecting unit. Or you may have a cylindrical lens and the mirror arrange | positioned in the focal position of this cylindrical lens. Moreover, you may have a retro reflector.

  If the light dispersion means has a plurality of light dispersion portions, it is preferable that the conjugate reflection optical system is provided corresponding to each light dispersion portion.

  The wavelength swept light source is disposed between the light deflecting unit and the light dispersing unit, deflects the light emitted from the light amplifying unit, and deflects the light in the direction of the rotation center of the light deflecting unit. There may be provided a light deflection / feedback means for returning the light deflected by the means, dispersed by the light dispersion means, and reflected by the conjugate reflection optical system to the light amplification means.

  The optical deflection / feedback means may be composed of a polarization beam splitter and a quarter wavelength phase shifter.

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 comprises light amplifying means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
A light dispersion means arranged to disperse light in a plane perpendicular to the rotation axis of the light deflection means;
First optical means for causing the light deflected by the light deflecting means to enter the light dispersing means as substantially parallel light;
A wavelength swept light source having second optical means for reflecting light dispersed in a predetermined direction out of the light dispersed by the light dispersion means, to the light dispersion means,
The second optical means is a conjugate reflection optical system that conjugately reflects light dispersed in a predetermined direction.

  The wavelength swept light source of the present invention has second optical means for reflecting light dispersed in a predetermined direction out of the light dispersed by the light dispersing means to the light dispersing means, and the second optical means comprises: Even if the light dispersed in a predetermined direction is light having an angle with respect to a plane in which the light is wavelength-dispersed by the light dispersing means when the light deflecting means is not tilted, it is conjugate. Reflected, that is, reflected in parallel to the incident direction of light, the light returns almost the same optical path as the incident optical path, and most of the return light returns to the optical amplifying means, so a stable and good oscillation state Can be obtained. Further, there will be no out-of-focus on the end face of the optical amplification means.

  The optical tomographic imaging apparatus of the present invention has a second optical means for reflecting the light dispersed in a predetermined direction out of the light dispersed by the light dispersion means to the light dispersion means. Even if the optical means disperses light in a predetermined direction, the light deflecting means is light having an angle with respect to a plane on which wavelength dispersion is performed by the light dispersing means when the light deflecting means is not tilted. Because it has a wavelength swept light source that can conjugately reflect, that is, reflect in parallel to the incident direction of light, and can obtain a stable oscillation state, it uses coherence light with a stable output. A good 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. 5 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. 5 acquires, for example, a tomographic image of a measurement target such as a living tissue or a cell in a body cavity by the above-described SS-OCT measurement, and sweeps an oscillation wavelength at a constant cycle. The light source unit 210 that emits the laser light La, the light dividing means 3 that divides the laser light La emitted from the light source unit 210 into the measuring light L1 and the reference light L2, and the reference divided by the light dividing means 3 The optical path length adjusting means 220 for adjusting the optical path length of the light L2, 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 light S1 is applied to the measuring object Sb. Sometimes, the combining means 4 for combining the reflected light L3 reflected by the measurement object Sb and the reference light L2, and the interference light detection for detecting the interference light L4 between the combined reflected light L3 and the reference light L2. Means 240 and interference light detection Based on the detection result of the step 240 has an image acquisition unit 241 for generating an optical tomographic image of the measurement object, and a display device 242 for displaying the 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. This broken image is displayed on the display device 242.

  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, and determines the light intensity S (l) of the interference light L4, thereby measuring the measurement target Sb from the measurement start position. 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.

  Details of the light source unit 210 will be described below. As shown in FIG. 6, the light source unit 210 includes a semiconductor laser medium 211, a collimating lens 212, a polygon mirror 213, a diffraction grating 214, a polarization beam splitter 215, a quarter wavelength plate 216, a relay lens. 217a and 217b, and a condensing reflection optical system 221 including a condensing lens 218 and a linear mirror 219 which is disposed at the focal position of the condensing lens 218 and extends in the rotation axis direction of the polygon mirror 213. The linear mirror 219 is held by a holder (not shown). This holder is preferably provided with an anti-reflective coating. Further, 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 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 collimator 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. The p-polarized light passes through the polarization beam splitter 215, is relayed by the relay lenses 217a and 217b, and enters the diffraction grating 214.

  Of the p-polarized light dispersed by the diffraction grating 214, the light condensed by the condenser lens 218 and reflected by the linear mirror 219 (hereinafter referred to as return light) is incident on the diffraction grating 214 again. Details of the operation of the conjugate reflection optical system 221 will be described later. The light dispersed toward the polarizing beam splitter 215 by the diffraction grating 214 is transmitted through the polarizing beam splitter 215 and further transmitted through the quarter-wave plate 216 to become circularly 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 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, from the light source unit 210, the laser light La swept at a constant cycle is emitted to the optical fiber FB1 side.

  Hereinafter, the conjugate reflection optical system 221 will be described in detail. FIG. 7A shows a top view of the conjugate reflective optical system 221 and FIG. 7B shows a side view thereof. The light dispersed by the diffraction grating 214 is collected by the condenser lens 218, but only the dispersed light reflected by the linear mirror 219 returns to the diffraction grating 214. That is, as shown in FIG. 7A, in the wavelength dispersion direction in the diffraction grating 214, the direction parallel to the optical axis direction of the condensing lens 218, which is the direction of focusing on the linear mirror 219, that is, FIG. Only the light dispersed in the X direction in (A) returns to the diffraction grating 214. This is the same as the case where a normal mirror is arranged instead of the conjugate reflection optical system 221, 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 214 may be shifted in the rotation axis direction of the polygon mirror 213, that is, the Y direction in FIG. Even when the dispersion direction is deviated in this way, as shown in FIG. 7B, the light incident on the conjugate reflection optical system 221 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. When light is incident on the linear mirror 219 with a large inclination in the Y direction, the incident light path and the reflected light path are different, but the angle of surface tilt of the polygon mirror 213 is usually small. When the light is reflected by the conjugate reflective optical system 221, most of the incident light path and the reflected light path overlap, so that most of the reflected light returns to the semiconductor laser medium 211. For this reason, even when the surface of the polygon mirror 213 is tilted, stable oscillation is possible.

  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, for example, when the reflecting surface is perpendicular to the optical axis of the incident light, the incident area of the light is substantially equal to the cross-sectional area of the light and becomes the minimum area. That is, the incident width in the rotation direction on the reflection surface of the polygon mirror 213 is smaller than the conventional light source configured so that the light always enters the polygon mirror 213 obliquely, and as a result, the rotation angle of the polygon mirror 213 is effective. The wavelength can be swept in a wide wavelength band.

  As the conjugate reflection optical system, as shown in a top view in FIG. 8A and a side view in FIG. 8B, a direction orthogonal to the Y direction (rotational axis direction of the polygon mirror 213) and the X direction. It is also possible to use a conjugate reflection optical system 253 including a cylindrical lens 251 disposed so as to collect light linearly and a mirror 252 disposed at the focal position of the cylindrical lens 251. Also in this case, as shown in FIG. 8A, the wavelength selection function works in the same way as when only the mirror 252 is arranged in the wavelength dispersion direction of the diffraction grating 214. Further, as shown in FIG. 8B, the direction of the light dispersed by the diffraction grating 214 is shifted in the rotational axis direction of the polygon mirror 213, that is, the Y direction in FIG. The light incident on the system 253 is reflected in the direction opposite to the incident direction.

  Further, as the conjugate reflection optical system, a retroreflector 254 arranged as shown in a top view in FIG. 9A and a side view in FIG. 9B can be used. Also in this case, as shown in FIG. 9A, the wavelength selection function works in the wavelength dispersion direction of the diffraction grating 214 as in the case where the mirror is arranged. As shown in FIG. 9B, the direction of the light dispersed by the diffraction grating 214 is shifted in the rotational axis direction of the polygon mirror 213, that is, the Y direction in FIG. The light incident on is reflected in the direction opposite to and parallel to the incident direction.

  As is clear from the above description, the wavelength swept light source of the present invention has a conjugate reflection optical system that selectively reflects the light dispersed by the diffraction grating 214, and this conjugate reflection optical system is formed by the diffraction grating 214. When the dispersed light is not tilted on the polygon mirror 213, even if the light has an angle with respect to the plane wavelength-dispersed by the diffraction grating 214, it is conjugately reflected, that is, the light is incident. Because the light is reflected parallel to the direction, the light reflected by the conjugate reflection optical system returns almost the same optical path as the incident optical path, and most of the return light returns to the semiconductor laser medium 211, so stable oscillation. The state can be obtained. Further, the focal blur on the end face of the semiconductor laser medium 211 does not occur.

  In addition, since the optical tomographic imaging apparatus of the present invention has a wavelength swept light source capable of obtaining a stable oscillation state, a good optical tomographic image is obtained using coherence light whose output is stable. it can.

  Further, instead of the light source unit 210, as shown in FIG. 10, a semiconductor laser medium 211, a collimator lens 212, a polygon mirror 213, relay lenses 217a and 217b, a diffraction grating 214, a conjugate reflection optical system 221, It is also possible to use a light source unit 260 provided with

  Furthermore, as shown in FIG. 11, a light source unit 270 that can perform two wavelength sweeps on one reflecting surface of the polygon mirror 213 can be used.

  The light source unit 270 includes relay lenses 271a and 271b, mirrors 272a and 272b disposed at different angles between the relay lenses 271a and 271b, and two identically shaped diffraction gratings 273a and 273b disposed at different angles. And conjugate reflection optical systems 274a and 274b that conjugately reflect even light having an angle with respect to a plane on which light is wavelength-dispersed in each diffraction grating when the polygon mirror 213 is not tilted. It has.

The conjugate reflection optical system 274a is disposed at the focal position of the condenser lens 275a and the condenser lens 275a, and with respect to a plane on which light is wavelength-dispersed in the diffraction grating 273a when the polygon mirror 213 is not tilted And a linear mirror 276a extending in a vertical direction. Similarly, the conjugate reflection optical system 274b is disposed at the focal point of the condenser lens 275b and the condenser lens 275b, and when the polygon mirror 213 is not tilted, light is wavelength-dispersed in the diffraction grating 273b. As shown in FIG. 11, the mirror 272a and the relay lens 271b are shown in the diagram of the relay lens 271a as the polygon mirror 213 rotates. The light path of the light is changed so that the light passing through the upper half in 11 enters the diffraction grating 273a. Further, the mirror 272b and the relay lens 271b change the optical path of the light so that the light passing through the lower half in FIG. 11 of the relay lens 271a enters the diffraction grating 273b. The relay lenses 271a and 271b, the mirrors 272a and 272b, and the diffraction gratings 273a and 273b are a range of incident angles where light passing through the upper half of the relay lens 271a is incident on the diffraction grating 273a and below the relay lens 271a. They are arranged so that the range of incident angles at which light passing through the half is incident on the diffraction grating 273b is equal.

  In the light source unit 270, first, as indicated by a dotted line in FIG. 11, the light emitted from the semiconductor laser medium 211 is converted into parallel light by the collimator lens 212, and branched into s-polarized light and p-polarized light by the polarization beam splitter 215, The s-polarized light is reflected by the polygon mirror 213, relayed by the relay lenses 271a and 271b, the optical path is changed by the mirror 272a, and enters the diffraction grating 273a. Of the light dispersed by the diffraction grating 273a, the return light that is reflected by the conjugate reflection optical system 274a and dispersed again by the diffraction grating 273a passes through the optical path opposite to that of the incident light to the semiconductor laser medium 211. Return. Similarly to the light source unit 210, the emission end face 211a of the semiconductor laser medium 211 and the mirror 276a constitute a resonator, and the laser light La is emitted from the emission end face 211a of the semiconductor laser medium 211. When the polygon mirror 213 rotates, the incident angle of light incident on the diffraction grating 273a changes continuously, the wavelength of the return light also changes continuously, and the wavelength of the laser light La is swept.

  When the polygon mirror 213 further rotates, the light emitted from the semiconductor laser medium 211 passes through the lower half of the relay lens 271a in FIG. 11 and enters the diffraction grating 273b. Similarly to the above, the incident angle of the light incident on the diffraction grating 273b is continuously changed, the wavelength of the return light is also continuously changed, and the wavelength of the laser light La is swept.

  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.

  Also in the light source units 260 and 270, as the conjugate reflection optical system, the conjugate reflection optical system including the cylindrical lens shown in FIG. 8 and a mirror disposed at the focal position of the cylindrical lens, or the retro reflector shown in FIG. 9 is used. be able to.

  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 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 conjugate reflective optical system Schematic configuration diagram of another conjugate reflective optical system Schematic configuration diagram of retro reflector Schematic configuration diagram of another light source unit Schematic configuration diagram of another light source unit

Explanation of symbols

3 Light splitting means
4 multiplexing means
210,260,270 Light source unit
211 Semiconductor laser medium
212 Collimating lens
213 polygon mirror
214 diffraction grating
217a, 217b Relay lens
218 condenser lens
219 linear mirror
220 Optical path length adjustment means
221,253 Conjugate reflection optics
230 Optical probe
240 Interference light detection means
241 Image acquisition means
242 display device
251 Cylindrical mirror
252 mirror
254 Retro Reflector

Claims (9)

Optical amplification means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
Light dispersion means for wavelength-dispersing the light deflected by the light deflection means;
First optical means for causing the light deflected by the light deflecting means to enter the light dispersing means as substantially parallel light;
A wavelength swept light source having second optical means for reflecting light dispersed in a predetermined direction out of the light dispersed by the light dispersing means to the light dispersing means,
2. A wavelength-swept light source, wherein the second optical means is a conjugate reflection optical system that conjugately reflects light dispersed in the predetermined direction. The light dispersion means wavelength-disperses the light deflected by the light deflection means in a plane perpendicular to the rotation axis of the light deflection means;
The conjugate reflective optical system reflects light conjugately even if the light dispersed in the predetermined direction is light having an angle with respect to a plane perpendicular to the rotation axis of the light deflector. The wavelength-swept light source according to claim 1, wherein:   The wavelength swept light source according to claim 1, wherein the conjugate reflection optical system includes a condensing lens and a linear mirror disposed at a focal position of the condensing lens.   The wavelength swept light source according to claim 1 or 2, wherein the conjugate reflection optical system includes a cylindrical lens and a mirror disposed at a focal position of the cylindrical lens.   The wavelength swept light source according to claim 1, wherein the conjugate reflection optical system includes a retroreflector.   The said light dispersion means has a some light dispersion part, and the said conjugate reflective optical system is provided corresponding to each light dispersion part, The Claim 1 characterized by the above-mentioned. Wavelength swept light source.   The light emitted from the light amplifying means disposed between the light deflecting means and the light dispersing means is deflected in the direction of the rotation center of the light deflecting means, and is deflected by the light deflecting means, 7. The wavelength sweep according to claim 1, further comprising: an optical deflection / feedback unit that feeds back the light dispersed by the light dispersion unit and reflected by the conjugate reflection optical system to the optical amplification unit. light source.   8. The wavelength swept light source according to claim 7, wherein the light deflecting / feedback means comprises a polarizing beam splitter and a quarter wavelength phase shifter. 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 comprises light amplifying means;
A rotating light deflecting means for deflecting the light emitted from the light amplifying means;
A light dispersion means for dispersing the light deflected by the light deflection means;
First optical means for causing the light deflected by the light deflecting means to enter the light dispersing means as substantially parallel light;
A wavelength swept light source having second optical means for reflecting light dispersed in a predetermined direction out of the light dispersed by the light dispersion means, to the light dispersion means,
An optical tomographic imaging apparatus characterized in that the second optical means is a conjugate reflection optical system that conjugately reflects light dispersed in a predetermined direction.

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