JP6723835B2 - Optical coherence tomography device - Google Patents

Description

The present invention relates to an optical coherence tomographic imaging apparatus, and more particularly to an optical coherence tomographic imaging apparatus having an optical system that aligns an incident light beam with an optical fiber end.

At present, an imaging device (hereinafter, referred to as OCT device) using an optical coherence tomography method (optical coherence tomography, hereinafter referred to as OCT) is being developed. The OCT device irradiates the object with light, and causes the reflected light returning from different depths of the object to interfere with the reference light according to the wavelength of the irradiation light. The OCT apparatus can obtain information about a tomographic image of an object, specifically a tomographic image, by analyzing frequency components included in a temporal waveform of the intensity of interference light (hereinafter, referred to as an interference spectrum). The OCT apparatus is used for fundus examination and the like as an imaging apparatus for ophthalmology, for example.

In order to reduce the physical burden on the subject at the time of inspection, an OCT device using a wavelength swept light source (Sweep Source OCT device, hereinafter referred to as SS-OCT device) is actively used as an OCT device with improved measurement speed. Being developed. Patent Document 1 discloses an example of an SS-OCT device, 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 changes 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, in the SS-OCT device, it is general to differentially detect the interference signal 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 it is difficult and stable to stabilize the characteristics of a circulator in a wide band wavelength, it is common to extract the reference light by separating the incident end and the emitting end 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 emission side optical fiber, the light beam and the emission side optical fiber must be aligned with high accuracy. Patent Document 2 discloses a lens element (hereinafter, a powerful power lens) having a small absolute value of a focal length for condensing a light beam on an emission side optical fiber in order to efficiently couple the light beam to an optical fiber, and a focal length longer than that. Disclosed is a method of arranging a weak lens element having a large absolute value of (hereinafter, a weak power lens) in a parallel light beam path and adjusting the position of the weak power lens to accurately align the light beam with respect to the optical fiber emission end. There is.

JP 2012-115578 A JP, 2005-222049, A

However, if the weak power lens described in Patent Document 2 is directly applied to the reference optical system of the SS-OCT apparatus, the light beam passes near the apex of the weak power lens constituent surface, and thus the non-interference component is generated in the interference signal by the multiple reflected light. (Noise component) occurs and the image quality deteriorates. Further, when the SS-OCT device is used after the alignment, a light amount loss occurs due to the positional deviation between the light flux and the emission-side optical fiber due to the movement of the optical components with respect to the environmental temperature change, and the efficient coupling efficiency can be maintained. It becomes an issue.

In view of this, the present invention provides a wavelength-swept optical coherence tomographic imaging apparatus having optical systems with different entrance and exit ends of a waveguide section, while avoiding deterioration of image quality due to multiple reflection light of a weak power lens, and high accuracy of a light beam and an end of an optical fiber. Achieves high coupling efficiency through precise alignment. Further, the reduction of the coupling efficiency due to the movement of the optical components due to the environmental temperature change is reduced.

In order to achieve the above object, the optical coherence tomographic imaging apparatus of the present invention is an optical coherence tomographic imaging apparatus having an optical system that aligns an incident light beam with an optical fiber end, and a strong power lens for condensing the light beam. And a weak power lens arranged between the optical fiber end and the strong power lens, wherein the weak power lens is arranged 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 highly accurate alignment of a light beam and an optical fiber end while avoiding deterioration of image quality due to multiple reflection 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. 4 shows a positional relationship between a weak power lens and a light beam according to the present invention. The block diagram of the light amount adjustment optical system of the SS-OCT apparatus which concerns on this invention is shown.

An SS-OCT apparatus (wavelength swept optical coherence tomography apparatus) according to an embodiment of the present invention will be described below with reference to FIGS. Although the SS-OCT device according to the present invention will be described as an OCT device used for examining the fundus of a subject, the SS-OCT device 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.

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 device to which the present invention is applied or various conditions. Also, in the drawings, the same reference numerals are used in the drawings to denote 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 device 1 includes a light source unit 10, a light amount adjusting optical system 20, an interference system 30, a measuring optical system 40, a reference optical system 50, a detecting unit 60, an information acquiring unit 70, and a display unit. And 80.

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

The light source unit 10 has a wavelength swept light source 100 that sweeps the wavelength of emitted light, and light that propagates the light from the wavelength swept light source 100 through an optical fiber and enters the light amount adjustment optical system 20 and a clock signal generation unit 102. It has an optical fiber coupler 101 that splits the light to be incident on the. 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 sweeping light source 100, any light source can be used as long as it is a light source capable of sweeping the wavelength of emitted light. Therefore, the wavelength swept light source 100 may be, for example, a light source using a fiber ring resonator described in Patent Document 1 and a wavelength selection filter, or may be another wavelength swept laser or the like. Further, 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 adjustment optical system 20 branches the light emitted from the optical fiber coupler light source unit 10 and propagated through the optical fiber into light entering the interference system 30 and light entering the light amount measuring unit 201 by the optical fiber coupler 200. .. Using the light amount of the light that is incident on and measured by the light amount measuring unit 201, the light amount is adjusted so that the irradiation light with which the subject Er is irradiated is 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 via an optical fiber. The optical fiber coupler 300 splits the light emitted from the light amount adjusting optical system 20 and propagated through the optical fiber into irradiation light that enters the measurement optical system 40 and reference light that enters the reference optical system 50. The irradiation light is applied 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 one light is branched into two lights having different phases and incident on the detection unit 60.

The measurement optical system 40 is provided with lenses 400 and 401, scanners 402 and 403, and an objective lens 404. The irradiation light that has propagated through the optical fiber from the interference system 30 and has 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 is movable in the optical axis direction by a driving unit (not shown). By this focusing, the reflected light from the subject Er is simultaneously imaged in a spot shape on the tip (ferrule) of the optical fiber. The scanner 402 and the scanner 403 are galvanomirrors arranged such that their rotation axes are orthogonal to each other, and can scan the irradiation light on the subject Er. The scanner 402 scans in the X direction, and the scanner 403 scans in the Y direction. Irradiation light is emitted to the eye Er to be inspected through the objective lens arranged to face the subject Er. The irradiation light applied to the subject Er is reflected by the fundus as backscattered light. The 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 each of the 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 lights to the A/D converter 601. The clock generation unit 102 is connected to the A/D converter 601, and the interference signal is sampled and converted into a digital signal in synchronization with the clock signal sent from the clock generation unit 102. 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 differential of the interference signals by obtaining the difference between the two interference signals based on the two interference lights having different phases detected by the detector 600, and the signal of the fundus information in the interference signals. It is possible to improve the signal ratio (S/N ratio) of the component to the non-interference component. 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, 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 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 regarding a tomographic slice in the depth direction at one point of the subject Er. Acquiring the tomographic information in the depth (Z) direction of the subject Er in this manner is called A scan. Two-dimensional tomographic information can be acquired by scanning this A-scan in the transverse direction (X direction) of the subject Er. This scan is called a B scan. By scanning the subject Er in the direction (Y direction) orthogonal to the scanning direction of both the A scan and the B scan, it is possible to acquire three-dimensional tomographic information. This scan is called a C scan. In particular, when two-dimensional raster scanning is performed on the inside of the fundus Er of the subject Er when acquiring three-dimensional tomographic information, the direction in which high-speed scanning is performed is B scan, and the direction in which relatively low-speed scanning is performed is C scan. Call. The B scan and the C scan are performed by the scanners 402 and 403 described above.

FIG. 2 is a block 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 for collimating the reference light incident on the reference optical system 50, a light amount adjusting unit 51, mirrors 503 and 504, a dispersion compensating glass 505, and an optical path length adjusting 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 by 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 adjusting unit 52 includes a variable transmittance ND filter 510 (Neutral Density), a motor 511 for rotating the variable transmittance ND filter 510, a shaft 512 connecting the motor 511 and the variable transmittance ND filter 510, The holding member 513 of the variable transmittance ND filter 510 is used. As shown in FIG. 2, the reference light that has entered the variable transmittance ND filter is refracted and transmitted to the mirror 503. On the other hand, since the incident surface of the variable transmittance ND filter 510 is inclined with respect to the plane perpendicular to the optical axis, the multiple reflection light generated by the ND filter tries to be transmitted eccentrically from the reference light, but the pressing member Shielded by 513. The motor 511 is driven so that the interference intensity of the interference light detected by the detector 60 becomes appropriate, and the light amount of the reference light is adjusted. The light quantity adjusting unit may be a shield plate connected to the motor.

By making the path of the reference light in the reference optical system 50 into a U shape by the mirrors 503 and 504, the optical path length can be efficiently obtained, which is effective for downsizing of the device. 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 adjusting unit 52 is provided with a prism type retro-reflector 520, and the retro-reflector 520 can be moved in the arrow direction of FIG. 2 by a motor (not shown). Accordingly, the optical path length of the reference optical system 50 can be adjusted according to the irradiation light, the optical path length of the measurement optical system 40 through which the measurement light passes, and the axial length of the subject Er. Since the incident surface of the retro-reflector 520 is inclined with respect to the plane perpendicular to the optical axis, the specularly reflected light of the retro-reflector 520 is prevented from returning to the wavelength swept light source 100 and the multiple-reflected light is prevented. Can be prevented from being combined.

The reference light reflected by the mirrors 503 and 504 via the optical path length adjusting unit 52 is condensed by the condensing lens unit 53 configured by the strong power lens 530 and the weak power lens 531 and the ferrule (emission side). An image is formed in a spot shape on the core of the optical fiber end) 532. Then, the polarization of the reference light is adjusted by the polarization controller 507 according to the measurement light, 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 fluxes, the condensing unit 53 employs the following adjusting means and procedure. The “weak power lens” and the “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 of the weak power lens is larger than that of the strong power lens.

First, the strong power lens 530 and the ferrule 532 are aligned in the XYZ3 directions. 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, and the focal length of the strong power lens strong power lens 530 is appropriate for the ferrule 532. Align the optical axis (Z) direction. At this time, the weak power lens 531 is arranged such that the area near the optical axis center of the weak power lens 531 does not overlap the area near the optical axis center of the strong power lens 530 and the ferrule 532 between the strong power lens 530 and the ferrule 532. Is temporarily fixed to. 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, ultraviolet or heat-curable adhesives, soldering, and the like. May occur. Therefore, after that, the temporarily fixed weak power lens 531 is moved (displaced) in the XY directions, whereby the loss of the coupling efficiency caused by the movement of these optical components can be compensated. At this time, the total focal length of the condenser lens unit may be slightly changed by adjusting the weak power lens, but the coupling efficiency is not greatly changed. As a result, highly accurate alignment between the light flux and the ferrule 532 is realized. The weak power lens 531 may move even when the weak power lens 531 is permanently attached. However, since the power of the weak power lens 531 is small, the influence on the coupling efficiency can be neglected 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 match, and if the two focal lengths match, the ferrule 501 and the ferrule 532. Can use the same members.

The ferrule 532 is subjected to TEC (Thermally-diffused Expanded Core) processing and the core diameter is increased to increase the allowable deviation amount of the light flux in the XY directions with respect to the ferrule 532. The TEC processing in the present embodiment refers to processing for substantially expanding the core diameter of the fiber by heat treatment or the like. This makes it possible to maintain the coupling efficiency with respect to changes in the ambient temperature in which the SS-OCT device is used. As a more desirable configuration, the focal lengths of the above-mentioned incident and outgoing optical components are matched, and the ferrule 501 is also subjected to TEC processing. Further, the ferrule 501 and the strong power lens 502, and 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 of 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 flux. The diameter ω of the light beam on the weak power lens 531 is separated by a distance R from the region D near the optical center of the weak power lens 531. The center of the light flux 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 does not overlap the optical center vicinity region D of the weak power lens 531. The distance required to suppress the light intensity of the multiple reflection light generated by the weak power lens 531 to 1% or less of the light intensity at the center of the light flux is 1.5 times the radius of ω within the adjustment range of the weak power lens 531 in the XY directions. It is sufficient if it is equal to or greater than the value obtained by adding one side. 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. .. Further, the plane perpendicular to the optical axis of the strong power lens 530 and the ferrule 532 may be inclined to the plane perpendicular to the optical axis of the weak power lens 531.

(Second embodiment)
Next, the 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 arranged immediately after the light source of the SS-OCT apparatus. In addition to the above-described optical fiber coupler 200 and light amount measuring unit 201, the light amount adjusting optical system 20 includes a strong power lens 204 for collimating the light incident on the light amount adjusting optical system 20, a light amount adjusting unit 21, and a condensing unit 22. It is provided.

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

The condensing unit 22 has the same basic configuration as the condensing unit 53 of the reference optical system 50, but the arrangement state of the weak power lens 221 is different. The weak power lens 531 of the light condensing unit 53 is arranged so as not to overlap the optical axis center area of the weak power lens 531 and the optical axis center area 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, the weak power lens 221 is temporarily fixed in an inclined state (deflected state) at the time of alignment of the strong power lens 220 and the ferrule 222 in the XYZ3 directions. After the permanent attachment of the strong power lens 220 and the ferrule 222, the weak power lens 221 is adjusted in the XY directions to compensate for the loss of coupling efficiency due to the attachment. Since the weak power lens 221 is inclined (deflected), the multiple reflection light of the weak power lens 221 is not imaged on the ferrule 222, and the deterioration of the image quality of the SS-OCT apparatus can be avoided.

In the above description, both the reference optical system 50 and the light amount adjusting optical system 20 have been described with the configuration in which the weak power lens is arranged on the emission side (condensing portion), but the same effect can be obtained even if the weak power lens is arranged on the incident side. You can get it.

With the above-mentioned configuration, it is possible to avoid the deterioration of the image quality of the SS-OCT apparatus due to the multiple reflection light of the weak power lens. Furthermore, even after the step of permanently attaching the optical fiber and other optical components (such as a strong power lens) to the holding member, it is possible to optimally maintain the highly accurate alignment state of the optical components up to the emission side optical fiber. It becomes possible to do.

Claims (8)

In an optical coherence tomographic imaging apparatus having an optical system for aligning the incident light flux to the optical fiber end,
A strong power lens for collecting the light flux,
A weak power lens disposed between the optical fiber end and the strong power lens,
An optical coherence tomography apparatus, wherein the weak power lens is arranged in a state of being decentered with respect to the optical axis of the light flux. The optical coherence tomography apparatus according to claim 1, wherein the weak power lens is arranged in a state of being displaced in a direction perpendicular to the optical axis. The optical coherence tomography 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 that constitutes a reference optical system, and is an optical system for causing a light beam whose optical path length is changed by the reference optical system to be incident on the optical fiber end of the interference system. The optical coherence tomographic imaging apparatus according to claim 1. The optical system is an optical system that constitutes an adjusting optical system that adjusts the light amount of the light flux, and an optical system that causes the light flux whose light amount is adjusted by the adjusting optical system to enter the optical fiber end of the interference system. The optical coherence tomographic imaging apparatus according to claim 1, wherein The optical coherence tomographic imaging apparatus according to claim 1, wherein the light flux passing through the strong power lens is focused on the optical fiber end without passing through the optical axis center of the weak power lens. The optical coherence tomographic imaging apparatus according to claim 1, wherein the light flux passing through the strong power lens is obliquely incident on the optical axis center of the weak power lens and is condensed at the optical fiber end. 8. The optical coherence tomographic imaging apparatus according to claim 1, wherein the light flux is a light flux emitted from a wavelength swept light source.

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