JP2017217038A - Optical coherent tomographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize and to maintain high coupling efficiency by highly accurate alignment in an optical system which aligns an incident light beam with an end of an optical fiber while avoiding reduction in image quality due to multiple light reflection of a lens.SOLUTION: An optical coherent tomographic apparatus comprises: an incident-side waveguide part 500 for making a light beam incident to an optical system; an incident-side strong power lens 502 for collimating the incident light beam; an emission-side waveguide part end 532 for emitting a light beam from the optical system; an emission-side strong power lens 530 for collecting collimated light beams to the emission-side waveguide part end 532; and a weak power lens 531 movable in at least one direction on a plane perpendicular to the optical axis between the emission-side waveguide part end 532 and the emission-side strong power lens 530. When the coupling efficiency of the optical system is equal to or greater than a predetermined value, the weak power lens 532 is arranged such that the region around the optical axis of the weak power lens does not overlap the regions around the optical axes of the emission-side waveguide part end 532 and the emission-side strong power lens 530.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical coherence tomography apparatus, and more particularly, to an optical coherence tomography apparatus having an optical system for aligning an incident light beam to an optical fiber end.

  Currently, an imaging apparatus (hereinafter referred to as an OCT apparatus) using an optical coherence tomography (hereinafter referred to as OCT) has been developed. The OCT apparatus irradiates an object with light and causes reflected light returning from different depths of the object to interfere with reference light according to the wavelength of the irradiated light. The OCT apparatus can obtain information relating to a tomography of an object, specifically a tomographic image, by analyzing a frequency component included in a time waveform of interference light intensity (hereinafter referred to as an interference spectrum). The OCT apparatus is used, for example, for fundus examination as an ophthalmic imaging apparatus.

  In order to reduce the physical burden on the subject during the examination, an OCT apparatus using a wavelength swept light source (Swept Source OCT apparatus, hereinafter referred to as an SS-OCT apparatus) is actively used as an OCT apparatus with improved measurement speed. Has been developed. Patent Document 1 discloses an example of an SS-OCT apparatus, and exemplifies a light source using a fiber ring resonator and a wavelength selection filter as a wavelength swept light source.

  The wavelength swept light source has a dynamic characteristic that the wavelength fluctuates with time as compared with a low-coherence light source having a wide wavelength band used in SD-OCT (Spectral Domain OCT apparatus). Therefore, it is generally known that the light source has a lot of noise. Therefore, the SS-OCT apparatus generally detects the interference signal differentially in order to improve the light receiving sensitivity of the interference light.

  In an interference optical system for performing differential detection, as a method of constructing a reference optical path, there are known a method of directing light returning directly by a circulator and a method of constructing an optical path using two optical fibers. Since circulators are difficult to stabilize characteristics over a wide wavelength range and are expensive, it is common to extract the reference light separately from the input and output ends of the optical fiber of the reference optical system. is there.

  The core of the optical fiber has a relatively small diameter, and in order to efficiently couple the light beam to the output side optical fiber, alignment (alignment) of the light beam and the output side optical fiber must be performed with high accuracy. In Patent Document 2, in order to efficiently couple a light beam to an optical fiber, a lens element (hereinafter, a strong power lens) having a small absolute value of a focal length for condensing the light beam on an output side optical fiber and a focal length shorter than that. Disclosed is a method for accurately aligning a light beam with respect to an optical fiber exit end by arranging a weak lens element (hereinafter referred to as a weak power lens) having a large absolute value in a parallel light beam path and adjusting the position of the weak power lens. Yes.

JP 2012-115578 A JP 2005-222049 A

  However, when the weak power lens described in Patent Document 2 is applied to the reference optical system of the SS-OCT apparatus as it is, the light beam passes through the vicinity of the apex of the weak power lens constituting surface, so that the non-interference component is generated in the interference signal due to the multiple reflected light. (Noise component) occurs, and the image quality deteriorates. In addition, when the SS-OCT apparatus is used after alignment, the amount of light loss is caused by the positional deviation between the light beam and the exit side optical fiber due to the movement of the optical component with respect to the environmental temperature change, and the efficient coupling efficiency is maintained. It becomes a problem.

  Therefore, the present invention is a wavelength-swept optical coherence tomography apparatus having optical systems with different waveguide entrance and exit ends, while avoiding deterioration in image quality due to multiple reflected light of a weak power lens, and high accuracy between the light beam and the end of the optical fiber. Realizes high coupling efficiency through simple alignment. In addition, a reduction in coupling efficiency due to movement of optical components due to environmental temperature changes is reduced.

  In order to achieve the above object, an optical coherence tomographic imaging apparatus according to the present invention is a strong power lens for condensing the luminous flux in an optical coherence tomographic imaging apparatus having an optical system for aligning an incident luminous flux with an optical fiber end. And a weak power lens disposed between the optical fiber end and the strong power lens, wherein the weak power lens is disposed in a state of being decentered with respect to the optical axis of the light beam.

  According to the present invention, it is possible to realize high coupling efficiency by high-precision alignment between a light beam and an optical fiber end while avoiding deterioration in image quality due to multiple reflected light of a weak power lens.

The block diagram of the SS-OCT apparatus which concerns on this invention is shown. The block diagram of the reference optical system of the SS-OCT apparatus which concerns on this invention is shown. The positional relationship of the weak power lens and light beam which concern on this invention is shown. The block diagram of the light quantity adjustment optical system of the SS-OCT apparatus which concerns on this invention is shown.

  Hereinafter, an SS-OCT apparatus (wavelength swept optical coherence tomography apparatus) according to an embodiment of the present invention will be described with reference to FIGS. Although the SS-OCT apparatus according to the present invention will be described as an OCT apparatus used for examining the fundus of a subject, the SS-OCT apparatus according to the present invention can be used for applications other than fundus examination. For example, it may be used for inspection of an arbitrary object such as an organ.

  Note that the shapes described in the following embodiments, the relative positions of the components, and the like are arbitrary, and can be changed according to the configuration of the apparatus to which the present invention is applied or various conditions. Also, in the drawings, the same reference numerals are used between the drawings to indicate the same or functionally similar elements.

(First embodiment)
FIG. 1 is a configuration diagram of an SS-OCT apparatus (wavelength swept optical coherence tomography apparatus) according to a first embodiment of the present invention. The SS-OCT apparatus 1 includes a light source unit 10, a light amount adjustment optical system 20, an interference system 30, a measurement optical system 40, a reference optical system 50, a detection unit 60, an information acquisition unit 70, and a display unit. 80.

  The light source unit 10 emits light. The light amount adjustment optical system 20 adjusts the light amount of light from the light source unit 10. The interference system 30 splits the light whose light amount has been adjusted into irradiation light and reference light, and combines the reflected light from the subject Er and the reference light to generate interference light. The measurement optical system 40 irradiates the subject Er with irradiation light and emits reflected light from the subject Er to the interference system 30. The reference optical system 50 adjusts the optical path length of the reference light and emits it. The detection unit 60 detects interference light. The information acquisition unit 70 acquires fundus information of the eye that is the subject Er. The display unit 80 displays acquired information, images, and the like.

  The light source unit 10 includes a wavelength swept light source 100 that sweeps the wavelength of emitted light, light that propagates from the wavelength swept light source 100 through an optical fiber, and light that enters the light amount adjusting optical system 20 and a clock signal generation unit 102. The optical fiber coupler 101 branches into the light incident on the light. The clock generation unit 102 generates a clock signal based on the incident light from the light source and sends it to the detection unit 60. As the wavelength swept light source 100, any light source can be used as long as it can sweep the wavelength of emitted light. Therefore, the wavelength swept light source 100 may be, for example, a fiber ring resonator described in Patent Document 1 and a light source using a wavelength selection filter, or another wavelength swept laser. The optical fiber coupler 101 may use a beam splitter or the like. The same applies to the optical fiber couplers mentioned in the following configurations.

  The light amount adjusting optical system 20 branches light emitted from the optical fiber coupler light source unit 10 and propagated through the optical fiber into light incident on the interference system 30 and light incident on the light amount measuring unit 201 by the optical fiber coupler 200. . Using the light amount of the light incident on the light amount measurement unit 201 and measured, the light amount is adjusted so that the irradiation light irradiated to the subject Er becomes appropriate. Details will be described later with reference to FIG.

  The interference system 30 is provided with optical fiber couplers 300 and 301. The optical fiber coupler 300 is connected to the optical fiber couplers 200 and 301, the measurement optical system 40, and the reference optical system 50 through an optical fiber. The optical fiber coupler 300 branches the light emitted from the light quantity adjustment optical system 20 and propagated through the optical fiber into irradiation light incident on the measurement optical system 40 and reference light incident on the reference optical system 50. Irradiation light is irradiated to the subject Er via the measurement optical system 40. The reflected light reflected by the subject Er enters the optical fiber coupler 301 via the measurement optical system 40 and the optical fiber coupler 300. On the other hand, the reference light enters the optical fiber coupler 301 via the reference optical system 50. In the optical fiber coupler 301, the reflected light and the reference light interfere with each other to become interference light, and the light is branched into two light beams having different phases, one of which is inverted, and enters the detection unit 60.

  The measurement optical system 40 includes lenses 400 and 401, scanners 402 and 403, and an objective lens 404. Irradiated light that has propagated through the optical fiber from the interference system 30 and entered the measurement optical system 40 is collimated by the lens 400. The lens 401 is for focusing the irradiation light on the subject Er, and can be moved in the optical axis direction by a drive unit (not shown). By this focusing, the reflected light from the subject Er is simultaneously imaged in a spot shape on the tip of the optical fiber (ferrule). The scanner 402 and the scanner 403 are galvanometer mirrors arranged so that their rotation axes are orthogonal to each other, and can scan the irradiation light on the subject Er. The scanner 402 performs scanning in the X direction, and the scanner 403 performs scanning in the Y direction. Through the objective lens arranged opposite to the subject Er, the irradiation light is irradiated to the eye Er. The irradiation light irradiated to the subject Er is reflected as backscattered light on the fundus. Reflected light from the fundus enters the interference system 30 via the measurement optical system 40.

  The reference optical system 50 will be described later with reference to FIG.

  The detector 60 is provided with a detector 600 and an A / D converter 601. The detector 600 detects two interference lights incident from the interference system 30 and propagated through the optical fiber, and sends an interference signal based on the detected interference light to the A / D converter 601. A clock generator 102 is connected to the A / D converter 601, and the interference signal is sampled in synchronization with the clock signal sent from the clock generator 102 and converted into a digital signal. The interference signal converted into the digital signal is sent to the information acquisition unit 70.

  The information acquisition unit 70 performs frequency analysis such as Fourier transform on the digital signal received from the detection unit 60 to obtain fundus information. In addition, the information acquisition unit 70 detects the difference between the two interference signals based on the two interference lights having different phases detected by the detector 600, thereby detecting the differential of the interference signal, and the signal of the fundus information in the interference signal The ratio of the signal of the component to the non-interference component (S / N ratio) can be improved. The information acquisition unit 70 sends the obtained fundus information to the display unit 80. The information acquisition unit 70 may be configured in the SS-OCT apparatus 1 as an arbitrary information processing unit including a CPU, an MPU, or the like, or may be configured using a general-purpose computer.

  The display unit 80 displays the received information as a tomographic image. The display unit 80 may be a monitor provided in the SS-OCT apparatus 1 or may be an individual monitor connected to the SS-OCT apparatus 1.

  Through the series of operations described above, the SS-OCT apparatus 1 can acquire information related to a tomography in the depth direction at a certain point of the subject Er. Obtaining tomographic information in the depth (Z) direction of the subject Er in this way is called an A scan. By scanning this A scan in the transverse direction (X direction) of the subject Er, two-dimensional tomographic information can be acquired. This scanning is called a B scan. Three-dimensional tomographic information can be acquired by scanning the subject Er in a direction (Y direction) orthogonal to the scanning direction of both the A scan and the B scan. This scanning is called C scanning. In particular, when two-dimensional raster scanning is performed within the subject Er fundus when acquiring three-dimensional tomographic information, the direction in which scanning is performed at a high speed is B scan, and the direction in which scanning is performed at a relatively low speed is C scanning. Call. The B scan and the C scan are performed by the scanners 402 and 403 described above.

  FIG. 2 shows a configuration diagram of the reference optical system 50 of the SS-OCT apparatus according to the first embodiment of the present invention. The reference optical system 50 includes a collimator lens 502 that collimates the reference light incident on the reference optical system 50, a light amount adjustment unit 51, mirrors 503 and 504, dispersion compensation glass 505, an optical path length adjustment unit 52, A condensing unit 53 and a polarization controller 507 are provided.

  The reference light emitted from the interference system 30 is propagated to the reference optical system 50 through the optical fiber 500, and enters the reference optical system 50 from the ferrule (optical fiber end on the incident side) 501.

  The light amount adjustment unit 52 includes a variable transmittance ND filter 510 (Neutral Density), a motor 511 that rotates the variable transmittance ND filter 510, a shaft 512 that connects the motor 511 and the variable transmittance ND filter 510, The holding member 513 of the variable transmittance ND filter 510 is configured. As shown in FIG. 2, the reference light incident on the variable transmittance ND filter is refracted and transmitted to the mirror 503. On the other hand, the multiple reflected light generated by the ND filter tends to transmit more eccentrically than the reference light because the incident surface of the variable transmittance ND filter 510 is inclined with respect to the plane perpendicular to the optical axis. 513 is shielded. The motor 511 is driven so that the interference intensity of the interference light detected by the detection unit 60 is appropriate, and the light amount of the reference light is adjusted. The light amount adjustment unit may be a shielding plate connected to a motor.

  By making the reference light path in the reference optical system 50 U-shaped with the mirrors 503 and 504, the optical path length can be increased efficiently, which is effective for downsizing the apparatus. However, the present invention is not limited to this, and the path of the reference light may be a straight line, L-shaped, or S-shaped.

  The dispersion compensation glass 505 compensates the dispersion of the reference light so as to correspond to the dispersion of the reflected light from the subject Er.

  The optical path length adjustment unit 52 is provided with a prism-type retroreflector 520, and the retroreflector 520 can be moved in the direction of the arrow in FIG. 2 by a motor (not shown). Thereby, the optical path length of the reference optical system 50 can be adjusted according to the optical path length of the measurement optical system 40 through which the irradiation light and the measurement light pass and the axial length of the subject Er. Since the incident surface of the retroreflector 520 is inclined with respect to a plane perpendicular to the optical axis, the specularly reflected light of the retroreflector 520 is prevented from being returned to the wavelength sweep light source 100 and multiple reflected light is used. Can be avoided.

  The reference light returned by the mirrors 503 and 504 via the optical path length adjustment unit 52 is condensed by the condenser lens unit 53 including the strong power lens 530 and the weak power lens 531, and then ferrule (exit side). (The end of the optical fiber) is imaged in a spot shape on the core of 532. Thereafter, the polarization of the reference light is adjusted according to the measurement light by the polarization controller 507, propagates through the optical fiber 508, and enters the interference system 30.

  In such a reference optical system, in order to efficiently combine the light beams, the light condensing unit 53 takes the following adjusting means and procedure. The “weak power lens” and “strong power lens” used in this embodiment represent the strength of the relative refractive power of the lens. That is, the absolute value of the focal length is larger in the weak power lens than in the strong power lens.

  First, the XYZ3 direction alignment of the strong power lens 530 and the ferrule 532 is performed. For example, the ferrule 532 is aligned in the 2 (XY) direction of the plane perpendicular to the optical axis with respect to the optical axis center of the strong power lens 530 so that the focal length of the strong power lens 530 is appropriate with respect to the ferrule 532. Align the optical axis (Z) direction. At this time, in the weak power lens 531, the region near the optical axis center of the weak power lens 531 does not overlap the region near the optical axis center of the strong power lens 530 and the ferrule 532 (in a displaced state) between the strong power lens 530 and the ferrule 532. Is temporarily fixed. After the XYZ alignment of the strong power lens 530 and the ferrule 532 is completed, the strong power lens 530 and the ferrule 532 are permanently attached to the holding member. Known permanent attachment methods for optical components include laser welding, UV or heat-curing adhesives, soldering, etc. In any of these methods, the movement of the optical components during the attachment process. May occur. Then, the loss of coupling efficiency caused by the movement of these optical components can be compensated by moving (displacement) the weak power lens 531 temporarily fixed in the XY direction. At this time, the total focal length of the condensing lens unit may slightly vary due to the adjustment of the weak power lens, but the coupling efficiency is not greatly varied. As a result, highly accurate alignment between the light beam and the ferrule 532 is realized. Even when the weak power lens 531 is permanently attached, the weak power lens 531 may move. However, since the power of the weak power lens 531 is small, the influence on the coupling efficiency can be ignored as compared with other optical components such as the strong power lens 530 and the ferrule 532. It is desirable that the absolute value of the focal length of the strong power lens 502 and the absolute value of the composite focal length of the strong power lens 530 and the weak power lens 531 are desirable, and when the two focal lengths match, the ferrule 501 and the ferrule 532 are used. Can use the same member.

  The ferrule 532 is subjected to TEC (Thermally-diffused Expanded Core) processing and the core diameter is increased, so that an allowable deviation amount of the light beam with respect to the ferrule 532 in the XY direction can be increased. In addition, the TEC process in a present Example refers to the process which expands the core diameter of a fiber substantially by heat processing etc. As a result, the coupling efficiency can be maintained with respect to changes in the environmental temperature in which the SS-OCT apparatus is used. A more desirable configuration is one in which the focal lengths of the above-described incident and outgoing optical components are made to coincide with each other, and the FER processing is also applied to the ferrule 501. Further, the ferrule 501, the strong power lens 502, the ferrule 532, the weak power lens 531, and the strong power lens 530 are held by the same holding member, so that the relative positions of the incident side and the outgoing side with respect to the change in the environmental temperature. The amount of deviation can be reduced.

  FIG. 3 shows the positional relationship between the weak power lens 531 and the light beam. The diameter ω of the light beam on the weak power lens 531 is separated from the region D near the optical center of the weak power lens 531 by a distance R. The center of the light beam coincides with the optical axes of the strong power lens 530 and the ferrule 532. By adjusting the weak power lens 531 in the XY directions, it is necessary to determine R so that the diameter A at which the light beam can move and the optical center vicinity region D of the weak power lens 531 do not overlap. The distance required to suppress the light intensity of the multiple reflected light generated by the weak power lens 531 to 1% or less of the light intensity at the center of the light beam is 1.5 times the radius of ω, which is within the adjustment range of the weak power lens 531 in the XY direction. It should just be more than the numerical value which added one side part. In the reference optical system 50, deterioration of image quality due to multiple reflected light caused by the weak power lens 531 is avoided by decentering the optical axis of the weak power lens 531 with respect to the optical axes of the strong power lens 530 and the ferrule 532. . Furthermore, the plane perpendicular to the optical axis of the weak power lens 531 may be inclined with respect to the plane perpendicular to the optical axis of the strong power lens 530 and the ferrule 532.

(Second embodiment)
Next, a case where the light amount adjusting optical system 20 according to the second embodiment of the present invention is tilted (deflected) will be described.

  FIG. 4 is a configuration diagram of a second embodiment in which the present invention is applied to a light amount adjustment optical system disposed immediately after the light source of the SS-OCT apparatus. In addition to the optical fiber coupler 200 and the light amount measuring unit 201 described above, the light amount adjusting optical system 20 includes a strong power lens 204 that collimates light incident on the light amount adjusting optical system 20, a light amount adjusting unit 21, and a light collecting unit 22. Is provided.

  The light emitted from the light source unit 10 is propagated to the light amount adjusting optical system 20 through the optical fiber 202 and is incident on the light amount adjusting optical system 50 from the ferrule (incident end) 203. Light that is condensed by the strong power lens 220 and the weak power lens 221 via the light amount adjustment unit 21 and focused in a spot shape on the core of the ferrule 222 propagates through the optical fiber 205 to the optical fiber coupler 200. Incident. The light amount adjustment unit 21 has the same configuration as the light amount adjustment unit 51 in the reference optical system 50, and thus the description thereof is omitted.

  The condensing unit 22 has the same basic configuration as the condensing unit 53 of the reference optical system 50, but the arrangement of the weak power lens 221 is different. The weak power lens 531 of the condensing unit 53 is disposed so as not to overlap the region near the optical axis center of the weak power lens 531 and the region near the optical axis center of the strong power lens 530 and the ferrule 532. On the other hand, in the weak power lens 221 of the condensing unit 22, the plane perpendicular to the optical axis of the weak power lens 221 is inclined with respect to the plane perpendicular to the optical axes of the strong power lens 220 and the ferrule 222. Also in this configuration, at the time of alignment of the strong power lens 220 and the ferrule 222 in the XYZ3 directions, the weak power lens 221 is temporarily fixed in an inclined state (deflection state). After the strong power lens 220 and the ferrule 222 are permanently attached, the weak power lens 221 is adjusted in the XY directions to compensate for the coupling efficiency loss due to the attachment. Since the weak power lens 221 is tilted (deflected), the multiple reflected light of the weak power lens 221 is not imaged on the ferrule 222, and the image quality degradation of the SS-OCT apparatus can be avoided.

  In the above description, the reference optical system 50 and the light amount adjustment optical system 20 are both described with the configuration in which the weak power lens is arranged on the exit side (condensing unit), but the same effect can be obtained even if the weak power lens is arranged on the incident side. Can be obtained.

  By adopting the above-described configuration, it is possible to avoid degradation of the image quality of the SS-OCT apparatus due to the multiple reflected light of the weak power lens. In addition, after the step of permanently attaching the optical fiber and other optical components (such as a strong power lens) to the holding member, the highly accurate alignment of the optical components up to the output side optical fiber is optimally maintained. It becomes possible to do.

Claims (8)

In an optical coherence tomography apparatus having an optical system for aligning an incident light beam to the end of an optical fiber,
A strong power lens for condensing the luminous flux;
A weak power lens disposed between the optical fiber end and the strong power lens;
The optical coherence tomographic imaging apparatus, wherein the weak power lens is arranged in a state of being decentered with respect to the optical axis of the light beam.   The optical coherence tomographic imaging apparatus according to claim 1, wherein the weak power lens is disposed in a state of being displaced in a direction perpendicular to the optical axis.   The optical coherence tomographic imaging apparatus according to claim 1, wherein the weak power lens is arranged in a state of being deflected with respect to the optical axis.   The optical system is an optical system constituting a reference optical system, and is an optical system for causing a light beam whose optical path length has been changed by the reference optical system to be incident on the optical fiber end of an interference system. The optical coherence tomographic imaging apparatus according to claim 1.   The optical system is an optical system that constitutes an adjustment optical system that adjusts the light amount of the light beam, and an optical system for causing the light beam whose light amount has been adjusted by the adjustment optical system to enter the optical fiber end of an interference system The optical coherence tomographic imaging apparatus according to claim 1, wherein:   3. The optical coherence tomographic imaging apparatus according to claim 1, wherein the light beam that has passed through the strong power lens is condensed on the end of the optical fiber without passing through the optical axis center of the weak power lens.   4. The optical coherence tomographic imaging apparatus according to claim 1, wherein the light beam that has passed through the strong power lens is incident on an optical axis center of the weak power lens from an oblique direction and condensed on the end of the optical fiber.   The optical coherence tomographic imaging apparatus according to claim 1, wherein the light beam is a light beam emitted from a wavelength swept light source.

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