JP2016161437A - Optical interference tomographic measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical interference tomographic measurement device capable of adjusting an optical path length of a non-measurement light beam and a measurement light beam to become the same with each other even when the length of an optical fiber is changed.SOLUTION: An optical interference tomographic measurement device comprises a light source including low coherent light at least, and an interferometer including two optical paths, a measurement optical path and a non-measurement optical path, which guide low coherence light emitted from the light source. The non-measurement optical path is an optical path which only consists of an optical fiber and does not include a space propagation optical path. A reflector is formed on a tip side end face of the optical path. The measurement optical path is constituted of: a collimator lens connected to an end face of the optical fiber in order to project the low coherence light emitted from the light source onto a measurement object; projection optical means placed on the space propagation optical path of predetermined length from the end face of the optical fiber to the measurement object; and optical path length change means capable of changing the length of the space propagation optical path between the projection optical means and the collimator lens.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an optical coherence tomography measurement apparatus used when generating an optical tomographic image of a measurement object using reflected light obtained by irradiating the measurement object with low coherent light.

  OCT (Optical Coherence Tomography) technology for acquiring an optical tomographic image of an object to be measured has been put to practical use in various fields because it can detect the structure in the depth direction of the object to be measured non-invasively and with high resolution. .

  In order to collect optical tomographic images with an OCT apparatus, an optical coherence tomography measuring apparatus capable of irradiating a measured object with a light beam output from a light source called SLD (Super Luminescent Diode) and receiving the reflected light. is necessary.

  For example, in the optical coherence tomography apparatus described in Patent Document 1, incident light that exits the light source and passes through the optical fiber and enters the half mirror is separated into non-measurement light (reference light) and measurement light by the half mirror. . The separated non-measurement light passes through the optical fiber, is reflected at the end face of the optical fiber, passes through the optical fiber, and reenters the half mirror.

  On the other hand, the measurement light separated by the half mirror passes through the optical fiber, is reflected by the surface of the object to be measured, and enters the half mirror again. Each reflected light re-entering the half mirror interferes on the half mirror to generate two interference lights. One interference light goes to the photodetector, and the other interference light goes to the light source.

  In order for interference light to be generated by the half mirror, the optical path length of the return path from when the non-measurement light is reflected by the end face of the optical fiber, re-enters the half mirror through the optical fiber, and the reflected light is reflected at the surface of the object to be measured. It is necessary to make the optical path length of the return path from the reflection through the optical fiber to the half mirror reenter. In addition, the generation of interference light requires the same optical path length between the non-measurement light and the measurement light in addition to the same optical path length between the non-measurement light and the return path of the measurement light. Note that, in the case of an interferometer having different paths for the non-measurement light and the measurement light, the forward path and the return path must have the same optical path length. For this reason, the optical coherence tomography measuring device described in Patent Document 1 is provided with a piezoelectric fiber length variable device capable of changing the optical path length of each optical path.

  In this piezoelectric fiber length variable device, a long (for example, several tens of meters) optical fiber is wound around a cylindrical piezoelectric element many times, and a voltage is applied to an electrode provided on the piezoelectric element to By changing the diameter, tension is applied to the optical fiber to change the length of the optical fiber.

JP 2003-185416 A

  The optical fiber wound around the cylindrical piezoelectric element of the piezoelectric fiber length variable device is several tens of meters, but the elongation of the optical fiber is about 1 mm per 10 m. For this reason, when the optical fiber is several tens of meters, it extends only about 2 to 3 mm. In addition, when an optical fiber is long, it is likely to be affected by temperature, humidity, and vibration. Therefore, it is necessary to minimize the length of the optical fiber. Since it is necessary to maintain the distance between the interferometer and the object to be measured, the optical path lengths of the non-measurement light and the measurement light of the interferometer are preferably 10 cm or more. Therefore, assuming that the optical path length of the non-measurement light and the measurement light of the interferometer is 10 m at maximum, the optical coherence tomography apparatus including the piezoelectric fiber length variable device described in Patent Document 1 sets the optical path lengths of the non-measurement light and the measurement light. It becomes impossible to be the same.

  In view of the above circumstances, at least some embodiments of the present invention provide an optical coherence tomography measurement apparatus that can adjust the optical path lengths of non-measurement light and measurement light even when the length of the optical fiber is changed. With the goal.

An optical coherence tomography measuring apparatus according to some embodiments of the present invention includes:
A light source including at least low-coherent light, and an interferometer including two optical paths of a measurement optical path and a non-measurement optical path for guiding low-coherence light emitted from the light source. An optical coherence tomography measuring device that is an optical path that does not include a propagation optical path, and in which a reflecting mirror is formed on the end surface on the tip side of the optical path,
The measurement optical path includes a collimating lens connected to an end face of the optical fiber for projecting the low-coherence light emitted from the light source onto the object to be measured, and a spatial propagation of a predetermined length from the end face of the optical fiber to the object to be measured. An optical path length changing unit capable of changing the length of the spatial propagation optical path between the projection optical unit placed on the optical path and the collimating lens is configured.

  According to the optical coherence tomography measuring apparatus, the non-measurement optical path is an optical path composed only of an optical fiber, and the reflecting mirror is formed on the end surface on the front end side of the optical path, so that the length of the non-measurement optical path can be changed. Can not. On the other hand, since the length of the spatial propagation optical path between the projection optical means and the collimating lens placed on the spatial propagation optical path of a predetermined length from the end face of the optical fiber to the object to be measured can be changed by the optical path length changing means. By changing the optical path length of the measurement optical path according to the optical path length of the non-measurement optical path, the measurement optical path can be adjusted to the same length as the optical path length of the non-measurement optical path. Therefore, it is possible to realize an optical coherence tomography measuring apparatus that can adjust the optical path lengths of the non-measuring optical path and the measuring optical path even if the length of the optical fiber is shortened.

In some embodiments,
The optical path length changing means includes lens moving means for moving the collimating lens along a space propagation optical path having a predetermined length from the end face of the optical fiber to the object to be measured.

  In this case, since the collimating lens can be moved along the spatial propagation optical path by the lens moving means, there is no limit to the amount of movement of the collimating lens. Even if the length of the optical fiber forming the measurement optical path is shortened, the optical path length of the measurement optical path and the optical path length of the non-measurement optical path can be easily adjusted to the same length by adjusting the amount of movement of the collimating lens. it can.

In some embodiments,
The optical path length changing means is formed of a material having a refractive index different from a space through which a space propagation optical path of a predetermined length from the end face of the optical fiber to the object to be measured. And a prism moving means for moving the prism so as to be able to approach and separate from the spatial propagation optical path.

  In this case, the optical path length changing means is formed of a material having a refractive index different from that of the space through which the space propagation optical path of a predetermined length from the end face of the optical fiber to the object to be measured passes between the projection optical means and the collimating lens. Since it is configured to include a prism disposed on the spatial propagation optical path and a prism moving unit that moves the prism so as to be able to approach and leave the spatial propagation optical path, the prism is moved by the prism moving unit. The optical path length of the low coherence light passing through the prism can be easily changed.

In some embodiments,
On the space propagation optical path between the collimating lens and the projection optical means, the refractive index of the optical fiber when the low coherence light passes through the optical fiber, and the space when the low coherence light passes through the space propagation optical path. An optical dispersion compensation member for compensating for the dispersion of the low coherence light caused by the difference from the refractive index of the propagation optical path is provided.

  In this case, group velocity dispersion due to the difference in propagation velocity for each wavelength occurs depending on the material through which light passes. For this reason, conventionally, the measurement optical path and the non-measurement optical path have been configured by balancing air, optical fiber, glass and resin used for lenses and windows at the same distance, or materials with the same dispersion. There is a case where an adjustment called “dispersion compensation” is performed by a method of inserting a signal into the path. Thereby, spatial resolution (depth direction resolution) can be improved. However, since the non-measurement optical path of the embodiment of the present application has a reflecting mirror formed on the end face of the optical fiber, dispersion compensation is difficult. However, in the measurement optical path, spatial propagation between the projection optical means and the collimating lens is difficult. Since there is an optical path, “dispersion compensation” is possible. Therefore, by providing an optical dispersion compensation member on the spatial propagation optical path between the collimating lens and the projection optical means, the dispersion compensation of the light passing through the measurement optical path is performed, the change in the optical path length is canceled, and the spatial resolution (depth (Direction resolution) can be improved.

In some embodiments,
The prism is generated due to a difference between a refractive index of the optical fiber when the low coherence light passes through the optical fiber and a refractive index of the spatial propagation optical path when the low coherence light passes through the spatial propagation optical path. It is formed of a member capable of compensating for dispersion of low coherence light.

  In this case, the prism is formed of a member that can compensate for the dispersion of the low-coherence light, so that the measurement optical path length can be changed, and the dispersion compensation of the light passing through the measurement optical path is performed to obtain a spatial resolution (depth direction). Resolution) can be improved.

  According to at least some embodiments of the present invention, it is possible to provide an optical coherence tomography measurement apparatus that can adjust the optical path lengths of non-measurement light and measurement light even when the length of the optical fiber is changed.

It is a schematic block diagram of the optical coherence tomography measuring apparatus concerning one Embodiment of this invention. FIG. 4A shows a partial configuration diagram of the interferometer when a plate-shaped dispersion compensation member is provided on the space propagation optical path between the collimating lens and the objective lens, and FIG. 4B shows the collimating lens and the objective lens. FIG. 2 is a partial configuration diagram of an interferometer when a dispersion compensation member composed of two prisms is provided on a space propagation optical path between a lens and a lens. FIG. 6 is a partial configuration diagram of an interferometer when a prism having a dispersion compensation function is provided on a spatial propagation optical path between a collimating lens and an objective lens according to another embodiment of the present invention.

  Embodiments of an optical coherence tomography measuring apparatus according to the present invention will be described below with reference to FIGS. It should be noted that the materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples.

  As shown in FIG. 1, the optical coherence tomography measuring apparatus 1 includes a light source 3 and an interferometer 10 including two optical paths, a measurement optical path L1 and a non-measurement optical path L2, for guiding low-coherence light emitted from the light source 3. The interferometer 10 includes an optical branching / merging unit 11, a light intensity detector 13, a collimator lens 15, an optical scanning mirror 17, and an objective lens 19. The collimating lens 15, the optical scanning mirror 17, and the objective lens 19 are provided on the probe head 25.

  The probe head 25 has a head main body portion 26 formed in a box shape with a hollow inside, and a lens movement support portion 29 that is attached to a side wall of the head main body portion 26 and holds the collimating lens 15 movably. Become. An optical scanning mirror 17 and an objective lens 19 are provided in the head main body 26. The lens movement support portion 29 has a hole 29a into which the collimator lens 15 is movably fitted, and is formed in a cylindrical shape. A set screw 31 is screwed into the side wall portion of the lens movement support portion 29. The collimating lens 15 is movable along the measurement optical path L1 (along the axial center direction of the hole 29a) while being inserted into the hole 29a, and via a set screw 31 at an arbitrary position of the hole 29a. It is fixed to the lens movement support part 29. The lens movement support unit 29 may be provided so that the collimating lens 15 is movable with respect to the lens movement support unit 29 by using a precise feeding operation by an actuator such as a motor or a ball screw mechanism.

  The light source 3 and the optical branching / merging portion 11 are connected via an optical fiber K1. The light branching / merging unit 11 branches the light from the light source 3 and guides the respective lights to the two optical paths of the measurement optical path L1 and the non-measurement optical path L2. The non-measurement optical path L2 is an optical path that includes only the optical fiber K2 and does not include a spatial propagation optical path, and a reflecting mirror K2a is formed on the end surface of the optical fiber K2. The reflecting mirror K2a is formed with a flat polished surface obtained by polishing the end surface of the optical fiber K2 flatly in order to increase the end surface reflection at the optical fiber cut surface. The reflecting mirror K2a has a PC (Physical contact) polished surface that is spherically processed so that the end surface reflection is smaller than that of the flat polished surface, and an APC (Angled physical contact) polishing that is obliquely polished that has a smaller end surface reflection than the PC polished surface. It may be a surface. The reflecting mirror K2a may be formed by contacting or bonding the small mirror M to the optical fiber cut surface.

  The measurement optical path L1 includes an optical fiber K3 that connects the optical branching / merging portion 11 and the collimating lens 15, and a space propagation optical path L3 having a predetermined length from the end face of the optical fiber K3 to the surface of the object 40 to be measured. A collimating lens 15, an optical scanning mirror 17, and an objective lens 19 are disposed in the space propagation optical path L3.

  Here, the light emitted from the light source 3 is divided into two lights by the light branching / merging portion 11, one of the lights is irradiated to the object to be measured 40, and the other light is irradiated to the reflecting mirror K 2 a of the optical fiber K 2. The Then, the corresponding lights are reflected by the DUT 40 and the reflecting mirror K2a, and the reflected lights are merged again by the light branching / merging unit 11 and interfered. Since the collimator lens 15 is movably provided on the lens movement support portion 29 of the lens movement support portion 29, the optical path length of the measurement optical path L1 can be changed by moving the collimator lens 15.

  The position of the collimating lens 15 is moved in the optical axis direction of the reflected light from the object to be measured 40, and the reflected light from the object to be measured 40 is adjusted so that the optical path lengths of the non-measuring optical path L2 and the measuring optical path L1 are the same. By changing the optical path length, the interference waveform of the reflected light from the DUT 40 and the reflected light from the reflecting mirror K2a is measured and recorded. The light intensity can be detected by the light intensity detector 13.

  Further, since the intensity of the reflected light from the object to be measured 40 is generally weak, the objective lens 19 provided in the head main body portion 26 of the probe head 25 receives light on such a condensing portion (objective lens 19). Is set so that reflection from the object to be measured 40 occurs near the focal position. By adopting such means, the incident light is concentrated in the vicinity of the focal point, and the reflected light from the measured object 40 scattered and reflected at various angles is condensed by the objective lens 19 and used in the interferometer 10. can do. Moreover, the reflected light of the DUT 40 can be obtained from the irregular reflection surface or the inclined surface, and an interference signal can be obtained. Furthermore, by adjusting the focal point at the maximum interference point, the interference efficiency at the focal position is maximized, and the spatial resolution can be increased.

  The collimating lens 15 constitutes an optical system for producing highly accurate parallel light. Therefore, the light emitted from the optical fiber K3 can be converted into parallel light and guided to the objective lens 19 through the optical scanning mirror 17.

  The light branching / merging unit 11 branches at least light beams from the light source 3 including low-coherent light into two light beams, and examples thereof include a light beam splitter and an optical fiber coupler. The light beam splitter may be either a plate type or a cube type. In particular, the cube type is preferable from the viewpoint of easy use because there is no shift of the optical axis, and the plate type is preferable from the viewpoint of weight and price. The angle at which the light beam branches is not particularly defined, but is preferably 90 degrees.

  The light source 3 is a light source including low coherent light. For this reason, unlike Michelson light interference using a conventional single wavelength light source, a light source including low coherent light has a short coherence length (a local peak is repeated several times, and the peak value is around this point). Therefore, the absolute position can be easily measured. The low coherent light source referred to in the present invention is a light source including a wavelength band having a specific width and having a short space interference possible distance. Specific examples include SLD (Super Luminescent Diode), ultrashort pulse laser, LED, incandescent bulb, xenon lamp, and metal halide lamp. Among these, SLD is preferable because it is small and inexpensive, has high coupling efficiency to an optical fiber, and can be easily converted into a good collimated beam (collimated beam).

  As described above, the non-measurement optical path L2 of the optical coherence tomography measuring apparatus 1 is an optical path consisting only of the optical fiber K2, and the reflecting mirror K2a is formed on the end surface on the distal end side of the optical fiber K2. I can't change it. On the other hand, the spatial propagation between the objective lens 19 and the collimating lens 15 placed on the spatial propagation optical path L3 of a predetermined length from the end face of the optical fiber K3 to the surface of the device under test 40 (or a specific position inside the device under test 40). Since the length of the optical path can be changed by moving the collimating lens 15, the optical path length of the measurement optical path L1 is changed according to the optical path length of the non-measurement optical path L2, and the measurement optical path L1 is changed to the optical path length of the non-measurement optical path L2. It can be adjusted to the same length. Therefore, it is possible to realize the optical coherence tomography measuring apparatus 1 that can adjust the optical path lengths of the non-measurement optical path L2 and the measurement optical path L1 to the same even if the lengths of the optical fibers K2 and K3 are shortened.

  Further, since the collimating lens 15 is movably inserted in the head main body portion 26 of the probe head 25, if the length of the head main body portion 26 is increased, the movement amount of the collimating lens 15 can be easily increased. Therefore, there is no limit to the amount of movement of the collimating lens 15. Therefore, even if the length of the optical fiber K3 forming the measurement optical path L1 is shortened, the optical path length of the measurement optical path L1 and the optical path length of the non-measurement optical path L2 are the same by adjusting the movement amount of the collimator lens 15. It can be easily adjusted.

  As shown in FIG. 2A, a dispersion compensation member 45 may be disposed on the spatial propagation optical path L3 between the collimating lens 15 and the objective lens 19 (see FIG. 1). The dispersion compensation member 45 has low coherence caused by a difference between a refractive index of the optical fiber K3 when the low coherence light passes through the optical fiber K3 and a refractive index of the spatial propagation optical path L3 when the low coherence light passes through the spatial propagation optical path L3. The spatial resolution (depth resolution) is improved by canceling the change in the optical path length for each wavelength of the measurement optical path L1 due to the unbalance of the light dispersion. The dispersion compensation member 45 is formed in a plate shape, and the dispersion compensation member 45 having thicknesses w, w ′, w ″ corresponding to the change amount of the optical path length is used.

  Further, as shown in FIG. 2B, the dispersion compensation member 45 is disposed so as to face each other with the two prisms 46 in contact with each other on the space propagation optical path L <b> 3, and each prism 46 is interposed via the prism moving mechanism unit 50. Thus, the length of the space propagation optical path L3 passing through these prisms 46 can be changed. Therefore, as compared with the case where a plurality of dispersion compensation members 45 having different thicknesses are prepared, the change in the optical path length of the measurement optical path L1 due to the dispersion imbalance of the low coherence light can be canceled more easily. .

  Further, as shown in FIG. 3, the objective lens 19 is formed of a material having a refractive index different from that of the space A through which the space propagation optical path L3 of a predetermined length from the end face of the optical fiber K3 to the surface of the object to be measured 40 passes. The prism 49 may be disposed on the spatial propagation optical path L3 between the collimating lens 15 and the collimating lens 15. In this case, the prism 49 is configured to be able to approach and separate from the spatial propagation optical path L3 via the prism moving mechanism 51.

  By moving the prism 49 by the prism moving mechanism 51, the optical path length of the low coherence light passing through the prism 49 can be easily changed. In the present embodiment, the collimating lens 15 is fixed to the head main body portion 26. The collimating lens 15 may be provided so as to be movable with respect to the lens movement support portion 29 as described above. In this way, the amount of change in the optical path length of the measurement optical path L1 can be further increased.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the object of the present invention. For example, the various embodiments described above may be appropriately combined.

DESCRIPTION OF SYMBOLS 1 Optical coherence tomography measuring device 3 Light source 10 Interferometer 11 Optical branch and confluence part 13 Light intensity detector 15 Collimate lens 19 Objective lens (projection optical means)
25 Probe head 26 Head main body 29 Lens movement support section (optical path length changing means, lens moving means)
31 Set screw 40 DUT 45, 47 Dispersion compensation member 46, 49 Prism 50, 51 Prism moving mechanism (prism moving means)
A Space K1, K2, K3 Optical fiber K2a Reflector L1 Measurement optical path L2 Non-measurement optical path M Small mirror

Claims (5)

A light source including at least low-coherent light, and an interferometer including two optical paths of a measurement optical path and a non-measurement optical path for guiding low-coherence light emitted from the light source. An optical coherence tomography measuring device that is an optical path that does not include a propagation optical path, and in which a reflecting mirror is formed on the end surface on the tip side of the optical path,
The measurement optical path includes a collimating lens connected to an end face of the optical fiber for projecting the low-coherence light emitted from the light source onto the object to be measured, and a spatial propagation of a predetermined length from the end face of the optical fiber to the object to be measured. An optical coherence tomography measuring apparatus comprising: an optical path length changing unit capable of changing a length of a spatial propagation optical path between a projection optical unit placed on an optical path and the collimating lens. 2. The light according to claim 1, wherein the optical path length changing unit includes a lens moving unit that moves the collimating lens along a space propagation optical path having a predetermined length from an end face of the optical fiber to the object to be measured. Coherent tomography measuring device. The optical path length changing means is formed of a material having a refractive index different from a space through which a space propagation optical path of a predetermined length from the end face of the optical fiber to the object to be measured, and includes the projection optical means and the collimating lens. 2. The optical interference according to claim 1, further comprising: a prism disposed on a space propagation optical path therebetween; and a prism moving unit that moves the prism so as to approach and move away from the space propagation light path. Fault measurement device. On the space propagation optical path between the collimating lens and the projection optical means, the refractive index of the optical fiber when the low coherence light passes through the optical fiber, and the space when the low coherence light passes through the space propagation optical path. The optical coherence tomography measuring apparatus according to claim 2, further comprising an optical dispersion compensation member for compensating for the dispersion of low-coherence light caused by a difference from the refractive index of the propagation optical path. The prism is generated due to a difference between a refractive index of the optical fiber when the low coherence light passes through the optical fiber and a refractive index of the spatial propagation optical path when the low coherence light passes through the spatial propagation optical path. The optical coherence tomography measuring apparatus according to claim 3, wherein the optical coherence tomography measuring apparatus is formed of a member capable of compensating for dispersion of low coherence light.

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