Bessel beam generator and optical scanning device using the same

Abstract

[Problem] To make it possible to improve the degree of freedom of design. [Solution] The present invention divides laser light emitted from one light source, and causes donut-shaped divergent light to be emitted toward the inside from optical fibers disposed on the same circle, thereby making it possible to realize a Bessel beam generation device that emits a disk irradiation beam focused in the vicinity of the center. The foregoing allows a disk irradiation beam to be generated without a center portion where the amount of light is high, and without decreasing the amount of light.

Description

[Technical Field]

[0001] The present invention can be suitably applied to, for example, a Bessel beam generator having a large focal depth and an optical scanning device using the same. [Background technology]

[0002] Conventionally, OCT (Optical Coherence Tomography) devices that generate Bessel beams using an axicon lens are known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2017-124055 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in an OCT device with such a configuration, because an axicon lens is used, the focal length from the axicon lens to the focal point is limited to a short length, which imposes design restrictions, such as the need to set a short distance to the object to be irradiated.

[0005] The present invention has been made to solve such problems, and an object of the present invention is to provide a Bessel beam generator that can improve the degree of freedom in design, and an optical scanning device using the same. [Means for solving the problem]

[0006] In order to solve this problem, the Bessel beam generator of the present invention comprises: a group of at least four light radiators, each of which emits light from a tip of an optical waveguide, and is arranged at equal intervals on the same circle, with the optical axis of the emitted light from each of the light radiators maintaining the same angle with respect to the diameter direction of the circle; an input section that splits a laser beam emitted from one light source and inputs the split beams to the optical waveguide sections; The optical waveguide has a function of equalizing the phase and amplitude of the light emitted from each of the light radiating portions.

[0007] The optical scanning device of the present invention further comprises: a group of at least four light radiators, each of which emits light from a tip of an optical waveguide, and is arranged at equal intervals on the same circle, with the optical axis of the emitted light from each of the light radiators maintaining the same angle with respect to the diameter direction of the circle; an input section that splits a laser beam emitted from one light source and inputs the split beams to the optical waveguide sections; an optical waveguide section having a function of making the phase and amplitude of the light emitted from each of the light radiating sections the same; a light receiving section that receives return light that is the emitted light reflected and converts the return light into an electrical signal; an analysis unit that calculates the position of a reflection point on the measurement object by analyzing the electrical signal; The present invention is characterized by having the following.

[0008] Furthermore, the Bessel beam generator of the present invention includes: a rotationally symmetric conical reflecting mirror having a generatrix that is a straight line or a curve with respect to the optical axis, which reflects the incident laser light outward from the optical axis; a reflective cover portion that is arranged to cover the conical reflector and that re-reflects the reflected waves from the conical reflector on an ellipsoidal primary mirror having the optical axis as an axis of rotational symmetry; The present invention is characterized by having the following.

[0009] The optical scanning device of the present invention comprises: a light source that emits laser light; a reflecting lens that receives the laser light and reflects the laser light outward from the optical axis; , The reflecting lens is arranged to cover the laser beam, and the laser beam traveling outward is reflected inward. By irradiating the light from the disk, the reflective cover irradiates the light. a light receiving section that receives the return light reflected from the disk irradiated light and converts it into an electrical signal; , an analysis unit that calculates the position of a reflection point on the measurement object by analyzing the electrical signal; The present invention is characterized by having the following. [Effects of the Invention]

[0010] The present invention can realize a Bessel beam generator that can improve the degree of freedom in design and an optical scanning device using the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram showing the configuration (1) of a Bessel beam generator according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a configuration (2) of the Bessel beam generator according to the first embodiment. [Figure 3] 3A and 3B are schematic diagrams illustrating laser light emitted from an optical fiber. [Figure 4] FIG. 3 is a schematic diagram showing the configuration (3) of the Bessel beam generator according to the first embodiment. [Figure 5] FIG. 2 is a schematic diagram illustrating focusing (1) of the Bessel beam generator according to the first embodiment. [Figure 6] FIG. 2 is a schematic diagram illustrating movement of a focal point of the Bessel beam generating device in a planar direction according to the first embodiment. [Figure 7] FIG. 4 is a schematic diagram illustrating focusing (2) of the Bessel beam generator according to the first embodiment. [Figure 8] 3A to 3C are schematic diagrams illustrating movement of the focal point of the Bessel beam generating device in the depth direction according to the first embodiment. [Figure 9] 1 is a schematic diagram illustrating a configuration of an OCT device according to a first embodiment. [Figure 10] 3 is a schematic diagram illustrating the configuration of a measurement unit in the first embodiment. [Figure 11] FIG. 10 is a schematic diagram illustrating the configuration of a Bessel beam generator according to a second embodiment. [Figure 12] FIG. 10 is a schematic diagram illustrating the configuration of an OCT device according to a second embodiment. [Figure 13] FIG. 10 is a schematic diagram illustrating the configuration of a Bessel beam generator according to a third embodiment. [Figure 14] FIG. 10 is a schematic diagram illustrating the configuration of a modified example of the Bessel beam generator according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Next, an embodiment of the present invention will be described with reference to the drawings.

[0013] [First embodiment] <Configuration of disk-shaped Bessel beam generator> In Fig. 1, reference numeral 10 denotes a disk-shaped Bessel beam generator. In the disk-shaped Bessel beam generator 10, as shown in Fig. 2, fiber tips 15A input split beams into optical fibers 15 arranged on the same circumference, and an irradiation beam having a doughnut-shaped cross section with the center missing from fiber tips 15A is emitted as a disk-shaped Bessel beam.

[0014] Here, we will explain the case where 32 split beams from one light source are incident on 32 optical fibers 15, but there is no limit to the number of split beams. In order to generate a uniform disk-shaped Bessel beam, it is preferable to have 8 or even 16 or more beams.

[0015] The laser light emitted from a light source (not shown) is a laser light source that emits laser light. There is no limitation on the wavelength of the laser light, and it is selected appropriately depending on the object to be irradiated. For example, when the object to be irradiated is a human body, near-infrared rays (780 nm to 2500 nm) are preferably used.

[0016] The incident section 14 is provided to adjust the diameter of the split beams so that they are efficiently incident on the optical fiber 15, and may comprise, for example, a coupling lens, a ball lens, a rod lens, or the like, either singly or in combination as appropriate.

[0017] The optical fiber 15 emits split beams from its tip, fiber tip 15A. As shown in Fig. 2, the fiber tips 15A are arranged at equal intervals on a circle (shown by the dashed line).

[0018] As shown in Fig. 3, the split beams incident on the optical fibers 15 are emitted from the fiber tips 15A as irradiation beams consisting of divergent light with a divergence angle θ corresponding to the refractive index of the optical fiber. Note that in Fig. 3, the fiber tips 15A are arranged perpendicular to the diameter of the circle, but they may also be arranged, for example, facing inward (tilted at an angle greater than 90° with respect to the diameter of the circle). This tilt angle (the angle between the optical fibers 15 and the diameter of the circle as viewed from the inside) is set to be the same for all 32 optical fibers 15.

[0019] As shown in Figure 4, a lens 16 is attached to the tip of fiber tip 15A. Lens 16 adjusts the traveling direction and divergence angle of the irradiation beam. Specifically, the divergence angle in the diameter direction of the circle is adjusted according to the focal depth; when a larger focal depth is desired, the divergence angle is set larger, and when a smaller focal depth is desired, the divergence angle is set smaller. The traveling direction of each irradiation beam is set according to the focal length; when the focal length is small, the inclination angle with respect to the diameter direction of the circle is small, and when the focal length is large, the inclination angle with respect to the diameter direction of the circle is large.

[0020] The divergence angle of the irradiation beam is adjusted by the shape of the entrance surface or exit surface, or the combination of the entrance surface and exit surface, of the lens 16. For example, if it is desired to increase the NA (numerical aperture) of the light beam emitted from the optical fiber 15, a convex lens with a convex exit surface is preferably used, and if it is desired to decrease the NA, a concave lens with a concave exit surface is preferably used.

[0021] Furthermore, lens 16 adjusts the polarization direction of the irradiation beam as necessary. Lens 16 may be a single lens, or a combination of two or more lenses. Here, the same divergence angle and inclination angle are set for all irradiation beams, so the 32 irradiation beams overlap and combine to form a single donut-shaped disk irradiation beam that diverges and travels toward the center of the circle (traveling perpendicular to the circumference).

[0022] Since split beams emitted from one light source and having the same optical path length are incident on the optical fiber 15, the focus of the disk irradiation beam coincides on the center line as shown in Figure 5. At this time, a focus (shown by the thick line) is formed according to the overlap of the disk irradiation beam, which is divergent light, on the center line, making it possible to increase the depth of focus.

[0023] It is also possible to provide a voltage application unit 21 that applies a voltage just before the tip of the optical fiber 15. By applying a voltage, the wavelength of the portion to which the voltage is applied can be temporarily changed, making it possible to speed up or slow down the wavefront. Specifically, a voltage is applied to half of the optical fiber 15 so that the voltage application unit 21 provided on the optical fiber 15 located in the direction in which you want to shift the focus has the highest voltage, and the voltage gradually decreases as you move away.

[0024] 6 shows a state in which the focal position has moved to the right side of the page by delaying the wavefront on the right side in the X direction (indicated as X(R) in the figure). That is, to shift the focal position to the right in the X direction, voltages are applied to the right side in the X direction (14A-1 to 14A-17). Specifically, the largest voltage is applied to 14A-9, which is located at the rightmost position, and the voltages applied decrease toward the left.

[0025] Also, as shown in Fig. 7, a lens driver 22 can be provided. As shown in Fig. 8, the lens driver 22 displaces the lens 16 so as to change the incident angle of the lens 16 with respect to the fiber tip 15A. This makes it possible to displace the focal position in the Z direction, which is the traveling direction of the disk irradiation beam.

[0026] <Configuration of optical scanning device> Next, a configuration when the disk-shaped Bessel beam generator 10 is used as an OCT (Optical Coherence Tomography) device, which is an optical scanning device, will be described.

[0027] 9, the OCT device 1 is connected to an external device 2 and a measurement unit 4 by a line 36. There are no restrictions on the type of line 36, and any known wired line capable of electrical communication can be used. Alternatively, a wireless network may be used instead of the line 36.

[0028] The external device 2 is configured such that a control unit 31, which is configured by an MPU (Micro Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), not shown, controls the entire external device 2.

[0029] The control unit 31 controls the display unit 33 and the measurement unit 4 in response to an operation input by the user, and displays the measurement results obtained by the measurement unit 4 on the display unit 33.

[0030] Specifically, when a request signal to start measurement is supplied from the operation input unit 32, the control unit 31 starts the measurement process and supplies a start signal to the measurement unit 4 via the external interface 34 (shown as external I / F in the figure) and line 36.

[0031] The measurement unit 4 is provided inside a housing 35 whose bottom side is exposed, and a start signal is supplied to the measurement unit 4 .

[0032] As shown in FIG. 10, the measurement unit 4 is configured such that a control unit 19, which is composed of an MPU, a ROM, and a RAM (not shown), controls the entire measurement unit 4 in an integrated manner.

[0033] When the control unit 19 receives the start signal, it causes the light source (not shown) of the light generating unit 11 to emit laser light. The light generating unit 11 converts the laser light emitted as continuous light into frequency-modulated pulsed light using an optical comb and emits the pulsed light. At this time, the light generating unit 11 may perform phase modulation or frequency conversion as necessary. Although not shown, the light generating unit 11 also supplies the signal processing unit 41 with a received light signal based on a reference light beam whose optical path length has been changed so that the optical path length of the reference light beam irradiated onto the measurement object is approximately the same as that of the return light (as long as it is within the range of the focus).

[0034] The laser light emitted from the light generating unit 11 is converted into parallel light by the collimating unit 12 and then enters the beam splitting unit 13. The beam splitting unit 13 splits the parallel light into 32 split beams with the same optical path length. The beam splitting unit 13 is composed of an optical waveguide such as an arrayed-waveguide grating (AWG) that enables optical wiring on a silicon or quartz substrate, and a combination of multiple optical elements (for example, a combination of multiple beam splitters or a combination of multiple couplers (isolators). Note that for these, a reflective element (such as a mirror) for adjusting the optical path length is used as appropriate).

[0035] The split beams are incident on the disk-shaped Bessel beam generator 10 via the optical branching unit 17. Thirty-two optical branching units 17 may be provided corresponding to each of the 32 split beams, or one may be provided for each of a plurality of split beams or for all of the split beams. The optical branching unit 17 may be an optical element that directs one of the outgoing and returning beams in a straight line and changes the direction of the other, such as a half-mirror type non-polarizing beam splitter, a polarizing beam splitter, or an isolator. When a polarizing beam splitter is used as the optical branching unit 17, a quarter-wave plate is installed between the optical branching unit 17 and the lens 16.

[0036] The disk-shaped Bessel beam generator 10 irradiates a measurement object with a disk-shaped Bessel beam as a disk irradiation beam.

[0037] Furthermore, the disk-shaped Bessel beam generator 10 causes the return light beam from the measurement object to enter the light branching unit 17. The light branching unit 17 causes the return light beam to enter the light receiving unit .

[0038] The light receiving unit 18 generates a measurement signal, which is an electrical signal corresponding to the received reference light beam and return light beam, and supplies the measurement signal to the signal processing unit 41. The signal processing unit 41 also receives the reference light beam generated from the optical comb in the light generating unit 11. The reference signal is supplied at a timing synchronized with the electrical signal generated from the return light beam from the irradiation target. The signal processing unit 41 generates a measurement composite signal by combining the measurement signal and the reference signal, and supplies the signal to the control unit 19.

[0039] The control unit 19 supplies the measurement composite signal to the external device 2 via the external interface 23. When the measurement composite signal is supplied via the line 36 and the external interface 34, the control unit 31 of the external device 2 analyzes the measurement composite signal, calculates the positions of the reflection points on the measurement object, generates image data, and displays it on the display unit 33.

[0040] Second Embodiment <Configuration of disk-shaped Bessel beam generator> Next, a second embodiment will be described with reference to Figures 11 and 12. The second embodiment differs from the first embodiment in the method of forming the irradiation beam. Reference numerals corresponding to those in the first embodiment are assigned with numbers increased by 100, and descriptions of the same parts will be omitted.

[0041] 11 denotes a disk-shaped Bessel beam generator 110. The disk-shaped Bessel beam generator 110 reflects a laser beam incident as divergent light outward, and then reflects the laser beam from the outside toward the inside, thereby emitting an irradiation beam having a doughnut-shaped cross section.

[0042] Incident unit 115 emits laser light, which is incident on lens 116. Incident unit 115 is, for example, a light source, an optical fiber, or another optical element, and refers to an element or component disposed before lens 116.

[0043] Lens 116 adjusts the divergence angle of the laser light and makes the laser light incident on the reflective cover unit 126 provided adjacent thereto. Reflective cover unit 126 has a shape, for example, with a portion cut out of a sphere or an oval sphere, and a reflective film is formed on the entire surface except for the portion that comes into contact with lens 116. Note that hereinafter, the traveling direction of the optical axis when the laser light is incident on reflective cover unit 126 is referred to as the traveling direction ZP of the laser light, and the returning direction is referred to as the return direction ZB.

[0044] The reflective cover portion 126 has an inner surface shaped like a cut-out portion of a sphere, an elliptical sphere, or a parabolic surface (a multi-dimensional curved surface), and transmits the incident laser light as is and irradiates the light onto the reflective lens 125. The reflective lens 125 has a pointed shape and a circular (e.g., conical) cross section in the XY direction. A reflective film is formed on the laser light incident side of the reflective lens 125.

[0045] The reflective lens 125 reflects the incident laser light outward (preferably at an angle of 80° to 170° with respect to the traveling direction ZP of the laser light). The reflective cover part 126 reflects the laser light inward.

[0046] Here, the laser light becomes an irradiation beam directed inward due to reflection outward by the reflecting lens 125 and reflection inward by the reflecting cover portion 126, but at this time, the light located near the optical axis before entering the reflecting lens 125 is inverted to move outward, and the light located on the outside before entering the reflecting lens 125 is inverted to move inward.

[0047] For this reason, the weaker light overlaps at a closer distance, while the stronger light overlaps at a farther distance, forming a focal point. This allows the intensity distribution of the laser light to compensate for the attenuation before the focal point.

[0048] It is also possible to adjust the irradiation direction of the disk irradiation beam by attaching the lens 116 rotatably so as to tilt it relative to the incident portion 115 .

[0049] <Configuration of optical scanning device> Next, a configuration when the disk-shaped Bessel beam generator 110 is used as an OCT (Optical Coherence Tomography) device, which is an optical scanning device, will be described.

[0050] 12, the OCT device 101 includes an external device 102, an incident part 115 which is an optical fiber, and a disk-shaped Bessel beam generator 110. The disk-shaped Bessel beam generator 110 is attached to the tip of the incident part 115 which is an optical fiber.

[0051] The external device 102 is configured such that a control unit 131, which is configured by an MPU, a ROM, and a RAM (not shown), controls the entire external device 102 in an integrated manner.

[0052] In addition to an operation input unit 132 and a display unit 133, the external device 102 has a light generating unit 111, a light branching unit 117, an incident unit 114, a light receiving unit 118, and a signal processing unit 119, which were arranged in the measurement unit 4 in the first embodiment.

[0053] Therefore, the OCT device 101 using the disk-shaped Bessel beam generator 110 has a small number of parts, so the tip portion (measuring device 104) can be made small (for example, about 1 mm square), and can be used for applications such as catheters for imaging the inside of blood vessels.

[0054] The light generating unit 111 splits the pulsed light modulated by the optical comb, adjusts the optical path length, and supplies the split light as a reference light beam to the light receiving unit 118. The light receiving unit 118 receives the return light beam and the reference light beam, and supplies them to the signal processing unit 119 as a measurement signal and a reference signal.

[0055] <Actions and effects> The following describes the features of the inventions extracted from the above-described embodiments, while indicating problems and effects as necessary. Note that, for ease of understanding, corresponding configurations in the above-described embodiments are indicated in parentheses as appropriate, but the specific configurations indicated in parentheses are not limited to these. Furthermore, the meanings and examples of terms described in each feature may also be applied as the meanings and examples of terms described in other features described in the same wording.

[0056] According to the above configuration, the Bessel beam generator of the present invention (disk-shaped Bessel beam generator 10) has the following features: an optical fiber group (32 optical fibers 15) consisting of at least four or more optical fibers (optical fibers 15) arranged with their optical fiber tips (fiber tips 15A) at equal intervals on the same circle, and with each optical fiber tip maintaining the same angle with respect to the diameter direction of the circle; an incident section (incident section 14) that causes split beams obtained by splitting laser light emitted from one light source to be incident on each of the optical fibers; a lens (lens 16) that adjusts the luminous flux of the irradiation beam emitted from each of the optical fibers, thereby emitting divergent light having a doughnut-shaped cross section with the center of the circle missing and traveling toward the inside of the circle as a disk-shaped irradiation beam emitted from the optical fiber group; The present invention is characterized by having the following.

[0057] In conventional Bessel beam generators using axicon lenses, it was difficult to adjust the focal length. In addition, in Bessel beam generators that exclude the central portion, it was necessary to exclude the central portion with the greatest light intensity, which inevitably resulted in a significant reduction in the amount of light.

[0058] The Bessel beam generator of the present invention can generate a doughnut-shaped Bessel beam with any radius and divergence angle without substantially reducing the light intensity, allowing the focal length and focal depth to be freely set. Since this Bessel beam generator can compensate for attenuation with a large light intensity, it is possible to make the irradiation beam reach a deep position from the surface of the material to be irradiated.

[0059] In the Bessel beam generating device, the lens is The irradiation beam is irradiated so that the divergence angle of the irradiation beam differs in the circumferential direction of the circle and in the diameter direction of the circle.

[0060] This allows the Bessel beam generator to freely set the distance between adjacent optical fibers (i.e., the radius of the circle), thereby improving the degree of freedom in design.

[0061] In the Bessel beam generator, the tip of the optical fiber is The arrangement is characterized in that the spheres are inclined inward with respect to the diameter direction of the circle.

[0062] This allows the focal length of a Bessel beam generator to be determined by the tilt angle of the tip of the optical fiber, and all that remains to be adjusted is the divergence angle, thereby improving the degree of freedom in designing the lens from which the irradiation beam is emitted.

[0063] In a Bessel beam generator, A voltage application device (voltage application unit 21) for moving the wavefront of the irradiation beam back and forth in time is attached to each of the optical fibers.

[0064] This allows the Bessel beam generator to move the focal position of the disk irradiation beam in a direction perpendicular to the optical axis of the disk irradiation beam.

[0065] In a Bessel beam generator, The lens driving unit 22 is characterized by having a movable part that rotatably moves the lens.

[0066] This allows the Bessel beam generator to move the focal position of the disk irradiation beam in the direction of the optical axis of the disk irradiation beam.

[0067] In the optical scanning device (OCT device 1) of the present invention, a light source (light source of the light generating unit 11) that emits laser light; a beam splitting unit (beam splitting unit 13) that generates split beams by splitting laser light emitted from one light source; an optical fiber group (32 optical fibers 15) consisting of at least four or more optical fibers (optical fibers 15) arranged with the optical fiber tips being arranged at equal intervals on the same circle, and each of the optical fiber tips (fiber tips 15A) maintaining the same angle with respect to the diameter direction of the circle; an incident section (incident section 14) that makes the split beams incident on the optical fibers; a lens (lens 16) that adjusts the luminous flux of the irradiation beam emitted from each of the optical fibers, thereby causing divergent light having a doughnut-shaped cross section with the center of the circle missing and traveling toward the inside of the circle to be emitted as a disk-shaped irradiation beam from the optical fiber group; a light receiving unit (light receiving unit 18) that receives a return light beam reflected from the disk irradiation beam and converts it into an electrical signal; The device is characterized by having an analysis unit (control unit 31) that calculates the position of the reflection point on the object to be measured by analyzing the electrical signal.

[0068] This allows the optical scanning device to have a large focal length and focal depth, making it possible to scan positions deeper from the surface, and also to check the shape of the object being irradiated over a wide range in the optical axis direction without having to move the focus.

[0069] In the Bessel beam generator (disk-shaped Bessel beam generator 110), a reflecting lens (reflecting lens 125) that reflects the incident laser light outward from the optical axis; The laser beam source is characterized by having a reflective cover portion (reflective cover portion 126) that is arranged to cover the reflective lens and that reflects the laser beam traveling outward toward the inside.

[0070] As a result, in the Bessel beam generator, by first widening the laser light and then reflecting it inward, it is possible to generate a doughnut-shaped Bessel beam with any radius and divergence angle without substantially reducing the amount of light, and therefore the focal length and focal depth can be freely set.

[0071] Furthermore, by reflecting twice, the central part of the laser beam with a large light intensity can be positioned on the outside, and the outer part of the laser beam with a small light intensity can be positioned at the center, reversing the relationship of the light intensity in the light beam and generating a donut-shaped Bessel beam in which the light intensity increases toward the outside. In this Bessel beam, the focal distance is short on the inside and long on the outside, so the light intensity increases toward the outside where the light intensity attenuates more, making it possible to make the disk-shaped irradiation light beam reach farther despite attenuation.

[0072] In a Bessel beam generator, The reflective lens is The laser beam is reflected so as to travel outside the beam of the incident laser beam.

[0073] As a result, in the Bessel beam generating device, the laser light reflected by the reflecting lens is not mixed into the return light beam, and the reduction in the amount of light can be minimized and noise mixed into the return light beam can be reduced as much as possible.

[0074] In a Bessel beam generator, The reflecting lens is characterized by having a conical shape with a 90° apex angle.

[0075] This allows the Bessel beam generator to bend the disk irradiation beam by a minimum of 90° with respect to the optical axis, preventing the laser light from being reflected in the return direction (opposite to the traveling direction) of the optical axis of the disk irradiation beam. In addition, the conical shape allows the laser light to be converted into a disk irradiation beam without any waste.

[0076] In optical scanning devices (OCT devices), a light source (light source in the light generating unit 111) that emits laser light; a reflecting lens (reflecting lens 125) that receives the laser light and reflects the laser light outward from the optical axis; a reflective cover portion (reflective cover portion 126) that is arranged to cover the reflective lens and reflects the laser light traveling outward toward the inside; It is characterized by having a light receiving unit (light receiving unit 118) that receives the return light beam reflected from the disk irradiation beam and converts it into an electrical signal, and an analysis unit (control unit 131) that calculates the position of the reflection point on the object to be measured by analyzing the electrical signal.

[0077] This allows the optical scanning device to use a disk irradiation beam that can reach long distances regardless of attenuation, making it possible to scan deep areas such as the inside of blood vessels or the inside of the human body, and to observe measurement objects that could not be observed with previous OCT devices.

[0078] <Third embodiment> Next, a third embodiment will be described with reference to Figs. 13 and 14. The third embodiment differs from the second embodiment in the configuration of the disk-type Bessel beam generator 210. Note that in the third embodiment, descriptions of the same parts as those in the second embodiment will be omitted.

[0079] 13, in a disk-shaped Bessel beam generator 210, laser light emitted from a Cassegrain antenna-type minute light source 230 having directionality is reflected by a conical generatrix 232 of a conical subreflector 231 whose axis is the optical axis 235 of the laser light. This conical subreflector 231 forms a ring-shaped virtual image light source at the first focus of the ellipse, which is an extension of the laser light that is reflected and directed toward an ellipsoidal main reflector 233.

[0080] Thereafter, the laser light reflected by the ellipsoidal main reflecting mirror 233 is collected in a ring shape at the second focal point 234 of the ellipsoidal surface of the ellipsoidal main reflecting mirror. A ring-shaped directional light source is formed on the major axis of the ellipse at the second focal point 234, and a modified Bessel beam can also be generated. That is, the ellipsoidal main reflecting mirror 233, the minute light source 230, and the conical sub-reflecting mirror 231 are configured so that the first focal point and the second focal point 234 of the ellipsoidal main reflecting mirror 233 become a virtual image light source and a directional light source, respectively.

[0081] Furthermore, by making the cone generating line 232 of the conical sub-reflector convex or concave rather than straight, the position of the virtual image light source, i.e., the position of the first focus of the ellipse, can be changed, increasing the degree of freedom in designing the ellipsoidal main reflector 231, and as a result, the effective range of the Bessel beam can be changed.

[0082] 14, in a disk-shaped Bessel beam generator 210X, if the main reflecting mirror 240 is made to have a parabolic or aspherical surface (free-form surface) instead of an ellipsoidal surface, the laser light from the main reflecting mirror 240 will become parallel rays, diverging rays that spread slightly, or rays that have a focus farther away than the range of the effective Bessel beam, and a Bessel beam similar to a Bessel beam generated by an axicon lens will be generated. Note that in Fig. 14, parts corresponding to those in Fig. 13 are indicated with an X.

[0083] According to the above configuration, in the modified Bessel beam generator of the present invention (disk-shaped Bessel beam generator 210), At least four or more light radiator groups (32 optical fibers 15) in which light radiators from which light is emitted from the tip of an optical waveguide are arranged at equal intervals on the same circle, and the optical axes of the radiated light from each of the light radiators are arranged at the same angle with respect to the diameter direction of the circle; an incident section (incident section 14) that splits a laser beam emitted from one light source and causes the split beams to enter the respective optical waveguide sections; The optical waveguide section (lens 16) has a function of making the phase and amplitude of the light emitted from each of the light emitting sections the same.

[0084] The modified Bessel beam generator is characterized in that it has an optical axis adjusting lens on the front surface of each of the light radiators for adjusting the angle between the optical axis of the radiated light, the diameter direction of the circle, and the optical axis.

[0085] In the modified Bessel beam generator, each of the optical waveguides has: It is characterized by being equipped with a phase / amplitude adjustment device for spatially or temporally changing the wavefront of the emitted light.

[0086] The modified Bessel beam generator includes a rotationally symmetric conical reflector whose generatrix is ​​a straight or curved line with respect to the optical axis, which reflects the incident laser beam outward from the optical axis; The present invention is characterized by having a reflective cover portion that is arranged to cover the conical reflector and that re-reflects the waves reflected by the conical reflector on an ellipsoidal primary mirror whose axis of rotational symmetry is the optical axis.

[0087] In the modified Bessel beam generator, the reflective cover portion is The reflected wave is re-reflected by a parabolic primary mirror whose axis of rotational symmetry is the optical axis.

[0088] <Other embodiments> Although not described in detail in the above embodiment, by frequency modulating the laser light by converting it into a PN code (Pseudo Random Noise) such as an M-sequence code, it is possible to reduce noise and improve the measurement resolution. Specifically, a coherent continuous light is generated by a light source, the continuous light is converted into a periodic optical pulse train with low interference between adjacent waveforms, the optical pulse train is binary phase modulated with a code (PN code such as an M-sequence) having an autocorrelation property and with a spatial length of the pulse width smaller than the depth range of the observation target region of the measurement object, the frequency of one of the optical pulse trains split into two is converted, and a measurement optical system is provided which irradiates one of the split optical pulse trains and sets the optical path length of the other of the split optical pulse trains to the same length as the measurement optical system. a reference optical system that changes the frequency of a backscattered wave from the object to a reference optical system, a light detection unit that receives an optical pulse train output from the reference optical system and return light input from the measurement optical system, a filter that extracts a difference signal having the shift frequency of the frequency shifter of the backscattered wave from the object to be measured based on the optical signal received by the light detection unit, a demodulator that combines and demodulates the difference signal extracted by the filter and a reference signal synchronized with the shift frequency of the frequency shifter, and an analysis unit that analyzes the signal output by the demodulator to calculate the position of the reflection point of the object to be measured. A detailed configuration is described in WO2019 / 017392.

[0089] In the first embodiment described above, the beam splitting unit 13 is configured by an arrayed waveguide grating or the like, but the present invention is not limited to this. For example, a donut-shaped beam may be formed using an inverse axicon lens having an overall conical recess with a bulging slope (i.e., fitting into a cone shape that tapers toward the apex), and the donut-shaped beam may be incident on the optical fiber 15 arranged in a donut shape. In other words, the light beam is split at the stage of incident on the optical fiber 15. In this case, the inverse axicon lens serves as both the beam splitting unit 13 and the incident unit 14.

[0090] In the second embodiment, only the disk-shaped Bessel beam generator 110 is attached to the tip of the optical fiber 105, but the present invention is not limited to this. For example, a light source and a light receiving unit may be attached together with the disk-shaped Bessel beam generator 110 as a tip device, and electrical signals may be exchanged between external devices.

[0091] Furthermore, although not specifically mentioned in the above embodiment, a travel distance measuring device such as an acceleration sensor that can measure the travel distance and a position specifying device that can specify the position of the disk-shaped Bessel beam generator can be added to the disk-shaped Bessel beam generator. This allows the position of the disk-shaped Bessel beam generator to be specified accurately, thereby improving the accuracy of image processing. Furthermore, if these devices are not available, it is possible to specify the same location in image processing or calculate a motion vector to synthesize images obtained when the disk-shaped Bessel beam generator is scanned.

[0092] Furthermore, it is possible to configure a single probe by combining and fixing a plurality of the disk-shaped Bessel beam generators according to the above-described embodiment, or to simultaneously capture images from a plurality of directions using a plurality of disk-shaped Bessel beam generators, which enables measurement of a wider range in one measurement and is expected to improve accuracy.

[0093] In the above embodiment, an optical fiber is used as the optical waveguide, but the present invention is not limited to this. For example, it is possible to realize the disk-shaped Bessel beam generator as an optical integrated circuit and use various waveguides such as silicon photonics as the optical waveguide.

[0094] A disk-shaped Bessel beam generator can also be configured by using a conical sub-reflector whose axis is the optical axis of a laser beam emitted from a Cassegrain antenna-type micro-light source to create a ring-shaped virtual image light source around the sub-reflector, and then reflecting the light from the virtual image light source with an ellipsoidal main reflector, and collecting the light in a ring shape at a real focal point formed on the major axis of the ellipsoid, thereby forming a ring-shaped directional light source and generating a modified Bessel beam.

[0095] Furthermore, the Bessel beam generator of the present invention can be configured by: generating a ring-shaped virtual image light source around a conical sub-reflector whose axis is the optical axis of the laser light, radiating and incident laser light from a Cassegrain antenna-type micro-light source; reflecting the light from the virtual image light source with a paraboloid of revolution main reflector; generating a conical wavefront with an obtuse apex angle of nearly 180 degrees generated from the ring-shaped virtual image light source; and generating a Bessel beam by phase-combining these conical wavefronts on the optical axis.

[0096] The reason why the major surface is made ellipsoidal is because a ring-shaped ring is formed at the focus of the ellipsoid. When a ring-shaped ring is formed, the side lobes around the Bessel beam due to the Fresnel zone are reduced.

[0097] In the second embodiment, the light with a large inner angle is emitted from the fiber at the periphery (strong at the center and weak at the periphery) to form a Bessel beam at the closest point, and the strong light at the center forms a distant beam. This cancels out the attenuation of light in human tissue, making it suitable for use in the human body (for example, in catheters for measuring inside blood vessels). [Industrial Applicability]

[0098] The present invention can be used in, for example, defect detection such as paint scratches, and in medical OCT devices for observing the inside of the human or animal body. [Explanation of symbols]

[0099] 1, 101:OCT device 2, 102: External device 4, 104: Measuring section 10, 110: Disk-shaped Bessel beam generator 11, 111: Light generating unit 12: Collimation part 13: Beam splitter 14, 114: Incidence part 15: Optical fiber 15A: Fiber tip 16: Lens 17: Optical branching section 18, 118: Light receiving section 19, 31, 131: Control section 21: Voltage application section 22: Lens drive unit 23: External interface 119: Signal processing section 125: Reflective lens 126: Reflective cover part 131: Control unit

Claims

1. a light source that emits laser light; an optical fiber into which the laser light emitted from the light source is incident; a lens that adjusts the light flux of the irradiation beam emitted from the optical fiber, thereby emitting divergent light having a ring-shaped cross section with a missing center and traveling toward the inside of the circle as a disk-shaped irradiation light beam emitted from the optical fiber, The lens is a reflecting lens that reflects the incident laser light outward from the optical axis; a reflective cover portion that is arranged to cover the reflective lens and that reflects the laser light traveling outward toward the inside, The reflective cover portion is The laser light traveling outward is inverted so that the light positioned inside the laser light before being reflected outward by the reflecting lens is directed outward, and the light positioned outside is directed inward. A Bessel beam generating device characterized by:

2. The reflective lens is A rotationally symmetric conical reflector whose generatrix is ​​a straight or curved line with respect to the optical axis, reflects the incident laser light outward from the optical axis, The reflective cover portion is The conical reflector is arranged to cover the conical reflector, and the reflected waves from the conical reflector are reflected again by a surface obtained by cutting out a part of a sphere, an elliptical sphere, a parabolic surface of a multi-dimensional function, or a free-form surface so that the light with a high intensity overlaps at a greater distance and forms a focus.

2. The modified Bessel beam generator according to claim 1.

3. The reflective cover portion is The reflected wave is re-reflected on a surface that is a cut-out part of an elliptical or parabolic surface that is formed by rotating an ellipse or parabola around the optical axis.

3. The modified Bessel beam generator according to claim 2.

4. a light source that emits laser light; an optical fiber into which the laser light emitted from the light source is incident; By adjusting the light flux of the irradiation beam emitted from the optical fiber, divergent light having a ring-shaped cross section with a missing center and proceeding toward the inside of the circle is emitted as a disk irradiation light beam emitted from the optical fiber, and the lens includes a reflecting lens that reflects the incident laser light toward the outside from the optical axis, and a reflecting cover portion that is arranged to cover the reflecting lens and reflects the laser light proceeding toward the inside, a light receiving section that receives the return light when the disk irradiation light is irradiated onto the measurement object and converts the return light into an electrical signal; an analysis unit that calculates the position of the reflection point of the measurement object by analyzing the electrical signal, The lens is a reflecting lens that reflects the incident laser light outward from the optical axis; a reflective cover portion that is arranged to cover the reflective lens and that reflects the laser light traveling outward toward the inside, The reflective cover portion is The laser light traveling outward is inverted so that the light positioned inside the laser light before being reflected outward by the reflecting lens is directed outward, and the light positioned outside is directed inward. An optical scanning device comprising:

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