Optical coherence tomography apparatus and optical coherence tomography method

Abstract

Provided is an optical coherence tomography device and an optical coherence tomography method using the same. The optical coherence tomography device is difficult to cause a shift in a tomographic image even when it is portable, and is capable of simultaneously performing tomography on a wide range. The optical coherence tomography device includes an objective lens that condenses light from a light source on a sample, and performs tomography of the sample based on interference between sample light that is reflected light from the sample and reference light that is reflected light from a reference surface provided between the objective lens and the sample, both of the sample light and the reference light passing through the objective lens, the objective lens being an Fθ lens.

Description

Technical Field

[0001] This disclosure relates to an optical coherence tomography apparatus and an optical coherence tomography method. Background Technology

[0002] Optical coherence tomography (OCT) is mainly used in the medical field for tomographic imaging of biological organs such as the eye.

[0003] As an optical coherence tomography apparatus, it is generally used to split the light from the light source by a beam splitter or the like, and to irradiate the sample and the reference mirror respectively to obtain reflected light. Tomography is then performed by using the interference of these reflected lights that have passed through different optical paths (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2011-104127 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The purpose of this invention is to provide an optical coherence tomography apparatus and an optical coherence tomography method using the optical coherence tomography apparatus, which is less prone to tomographic image shift even when portable, and is capable of simultaneously performing tomographic imaging over a wide range.

[0009] Methods for solving problems

[0010] This disclosure relates to an optical coherence tomography apparatus comprising an objective lens that focuses light from a light source onto a sample, and performs tomographic imaging of the sample based on interference between sample light, which is reflected light from the sample, and reference light, which is reflected light from a reference surface disposed between the objective lens and the sample, wherein both the sample light and the reference light pass through the objective lens, which is an Fθ lens.

[0011] Preferably, the optical coherence tomography apparatus is configured to perform tomography by setting the distance between the reference plane and the sample to 0 cm to 3 cm.

[0012] Preferably, the reference surface comprises a plane of at least one reference component selected from the group consisting of MgF2, CaF2, quartz and sapphire.

[0013] Preferably, both the sample light and the reference light are generated by light from the light source that has passed through the objective lens.

[0014] Preferably, the interference is a Fizeau-type interference.

[0015] Preferably, the optical coherence tomography apparatus further includes a circulator that outputs light from the light source to the objective lens side and outputs the sample light and reference light that have passed through the objective lens to the detector side that detects the sample light and reference light.

[0016] Preferably, the optical coherence tomography apparatus further includes a coupler that splits the light from the light source into split light 1 for generating the sample light and the reference light and split light 2 for removing the DC component of the interference signal, wherein the intensity ratio of split light 1 to split light 2 is 90:10 to 99:1.

[0017] Preferably, the optical coherence tomography apparatus is configured such that a user can carry the portion equipped with the objective lens to perform the tomography.

[0018] Preferably, the portion carrying the objective lens and the portion not carrying the objective lens are connected via an optical fiber, and the light from the light source, as well as the sample light and the reference light, are transmitted through the optical fiber.

[0019] Preferably, when the length of the optical fiber is 3m or more and the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is 1°C or more, the offset of the obtained optical coherence tomography image is 100μm or less.

[0020] The present invention also relates to an optical coherence tomography method using any of the aforementioned optical coherence tomography apparatuses.

[0021] Invention Effects

[0022] According to the present invention, an optical coherence tomography apparatus and an optical coherence tomography method using the optical coherence tomography apparatus are provided. The optical coherence tomography apparatus is not prone to tomographic image shift even when it is portable, and can simultaneously perform tomographic imaging over a wide range. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating an example of an existing optical coherence tomography (OCT) device.

[0024] Figure 2 This is a schematic diagram illustrating an example of the OCT device of the present invention.

[0025] Figure 3 This is a schematic diagram illustrating another example of the OCT device of the present invention.

[0026] Figure 4 This is a diagram showing the OCT image obtained in Example 1.

[0027] Figure 5 This is a diagram showing the OCT image obtained in Comparative Example 1.

[0028] Figure 6 This is a diagram showing the OCT image obtained in Comparative Example 2.

[0029] Figure 7 This is a diagram representing the OCT image obtained in Reference Example 1. Detailed Implementation

[0030] In the medical field, commonly used methods include... Figure 1 The optical coherence tomography (OCT) setup shown uses a Michelson interferometer. Figure 1 In the OCT device 10, the light output from the light source 11 is split by the coupler 12 to generate a reference light that passes through an optical path including a circulator 13 and a reference mirror 14, and a sample light that passes through an optical path including a circulator 15 and a sample 16. The reference light and the sample light are coupled through the coupler 17, and an interference signal is detected by the photodetector 18.

[0031] In the medical field, the probe with the sample optical path and the main body (casing) of the OCT device with the reference optical path are usually set close together and used in the same room.

[0032] In contrast, in industrial applications, it is sometimes necessary to carry a probe to photograph objects located outdoors, far from the main body (casing) of the OCT device. In such cases, the sample light and reference light travel through different optical paths. Figure 1 The Michelson-type OCT device has the following problem: the environment (temperature, etc.) of the sample optical path (probe) and the reference optical path (body) are prone to difference. Due to the change in the optical path length, the offset (drift) of the obtained tomographic image becomes larger.

[0033] In addition, OCT devices used in the medical field are designed to perform high-precision tomography on extremely narrow areas such as the eyeball, which makes them difficult to apply to fields that require simultaneous tomography on a wide area.

[0034] The inventors conducted in-depth research and found that by passing both the sample light and the reference light through the objective lens and using an Fθ (F lens) as the objective lens, the above-mentioned problems can be eliminated, thus completing the OCT device of the present invention.

[0035] The present invention will now be described in detail.

[0036] The present invention relates to an optical coherence tomography (OCT) apparatus comprising an objective lens that focuses light from a light source onto a sample, and performing tomographic imaging of the sample based on the interference between sample light, which is reflected light from the sample, and reference light, which is reflected light from a reference surface disposed between the objective lens and the sample, wherein both the sample light and the reference light pass through the objective lens, which is an Fθ lens.

[0037] In the OCT apparatus of the present invention, both the sample light, which is reflected light from the sample being photographed, and the reference light, which is reflected light from a reference surface, pass through the objective lens. According to this structure, even when the part equipped with the objective lens (e.g., the probe) is portable, there is no difference in the environment between the sample light path and the reference light path, thus resulting in minimal shift in the obtained tomographic image.

[0038] In addition, the sample light and the reference light are incident from the sample side of the objective lens and emitted towards the light source side.

[0039] The sample light and reference light are generated from light from a light source. The light from the light source is focused onto the sample by the objective lens of the OCT device of the present invention. The reflected light from the sample becomes the sample light. In addition, a portion of the light from the light source is reflected by a reference surface disposed between the objective lens and the sample to become the reference light.

[0040] Preferably, both the sample light and the reference light are generated from light from the light source that has passed through the objective lens. Compared to conventional Michelson-type OCT devices, where the sample light and reference light are generated separately from light that has been split before passing through the objective lens, this reduces the environmental differences between the sample light path and the reference light path, and further reduces the shift in the obtained tomographic images.

[0041] The objective lens of the OCT device of the present invention is an Fθ lens. Based on this structure, it is possible to simultaneously perform tomographic imaging over a wide range.

[0042] The Fθ lens is a lens in which light incident at an angle θ relative to the optical axis of the lens exits at the focal point from the optical axis of the plane perpendicular to the optical axis at a position fθ when the focal length of the lens is set to f.

[0043] The Fθ lens can be a telecentric Fθ lens or a non-telecentric Fθ lens.

[0044] A telecentric Fθ lens is an Fθ lens designed so that the principal ray is parallel to the optical axis of the lens. It is preferred because it can obtain high-precision tomographic images even when the distance between the lens and the sample changes.

[0045] In the OCT apparatus of the present invention, the light passing through the objective lens may not necessarily be incident on the sample at a telecentric position, but from the viewpoint of obtaining a more accurate tomographic image, it is preferable to configure the objective lens so that it is incident as close to the telecentric position as possible.

[0046] Preferably, the reference surface is disposed perpendicular to the optical axis of the objective lens between the objective lens and the sample.

[0047] The reference surface can be any surface that reflects at least a portion of the light from the light source, but it is preferable that it allows a portion of the light from the light source to pass through and a portion to be reflected, so that the sample light and the reference light can easily pass through a common optical path. In this manner, the light transmitted through the reference surface is focused onto the sample to generate sample light, while the light reflected by the reference surface becomes the reference light.

[0048] The reference surface is preferably a plane of the reference component, and more preferably the surface of the reference component on the sample side.

[0049] Preferably, the reference component allows a portion of the light from the light source to pass through while reflecting a portion.

[0050] Examples of materials constituting the reference component include crystalline materials, preferably those suitable for optical windows. Specifically, examples include MgF2, quartz (SiO2), sapphire (Al2O3), CaF2, BaF2, LiF, and ZnSe. From the perspective of excellent chemical resistance, at least one material selected from the group consisting of MgF2, CaF2, quartz, and sapphire is preferred.

[0051] One preferred approach is that the reference surface is a plane comprising at least one of a reference component selected from the group consisting of MgF2, CaF2, quartz and sapphire.

[0052] The reference component is preferably uncoated (e.g., with a coating for adjusting reflection).

[0053] The reference component can be any planar shape, such as plate, cylinder, or prism, but is preferably cylindrical. Even if it is cylindrical, it does not necessarily have to be a perfect cylinder. Furthermore, if the reference component also has a plane other than the reference surface, the reference surface does not necessarily have to be parallel to other planes.

[0054] The thickness of the reference component (thickness in the optical axis direction) is preferably 1 mm to 50 mm, and more preferably 10 mm to 30 mm.

[0055] Furthermore, when the thickness of the reference component is not constant, it is preferable that the thicknesses of both the thinnest and thickest parts are within the specified range.

[0056] The reference component preferably satisfies the following relationship (1).

[0057] nd≧Z max (1)

[0058] (In the formula, nd represents the optical thickness of the reference component, Z) max (Indicates the measurable distance.)

[0059] Optical thickness is the product of the refractive index of the reference component and its actual (geometric) thickness.

[0060] The measurable distance is represented by the following relationship (2).

[0061] Z max =c / (4δf) (2)

[0062] (In the formula, c represents the speed of light, and δf represents the frequency interval of the OCT interference signal sampling.)

[0063] When a reference component satisfying relation (1) is used, the signal based on the rear reflection from the rear base surface (the surface opposite to the reference surface) of the reference component will not appear in the tomographic image (as with a depth greater than 0 and less than Z). max Within the corresponding range, higher precision tomographic images can be obtained.

[0064] The reference component more preferably satisfies the following relationship (3).

[0065] n×WD>nd>n×Z max (3)

[0066] (In the formula, n represents the refractive index of the reference component, WD represents the working distance of the OCT device, and nd and Z) max As stated above.

[0067] The working distance is the distance from the frontmost point of the objective lens on the sample side to the sample when focusing.

[0068] If a reference component that satisfies relation (3) is used, the intensity of the ghost image based on the rear reflection from the rear base surface (the surface opposite to the reference surface) of the reference component can be reduced, and a higher precision tomographic image can be obtained.

[0069] In order to further reduce the intensity of the ghosting image based on the rear reflection, the thickness of the reference component is preferably relatively thick within the range that satisfies relation (3). In addition, it is preferable that the rear base surface of the reference component is inclined relative to the reference surface.

[0070] The effect is particularly noticeable when the anti-aliasing filter (low-pass filter) described later is set.

[0071] The reference component is particularly preferably satisfied with the following relation (4).

[0072] nd = m × Z max (4)

[0073] (where nd and Z are in the formula) max As mentioned above, m represents an integer greater than or equal to 1.

[0074] m is preferably an integer greater than or equal to 1 and less than 20, and is also preferably an integer greater than or equal to 1 and less than 10.

[0075] When a reference component satisfying relation (4) is used, the signal reflected from the rear base surface (the surface opposite to the reference surface) of the reference component is compared with the end of the tomographic image (with depth 0 or Z). max The corresponding positions overlap, so the impact on the tomographic image is small, and a higher precision tomographic image can be obtained.

[0076] The OCT device of the present invention may include the reference surface (reference component).

[0077] The OCT apparatus of the present invention is preferably configured to perform tomography at a distance of 0 to 3 cm between the reference plane and the sample. This close proximity of the reference plane and the sample results in a shorter working distance, lower noise, and higher resolution. Furthermore, the focus can be aligned to the depths of the sample, allowing for clear tomographic images even at greater depths, which is preferable. The OCT apparatus of the present invention uses an Fθ lens as the objective lens; therefore, as described above, high-precision tomography can be performed even when the distance between the reference plane and the sample is relatively close.

[0078] Of course, tomography can also be performed with the distance between the reference surface and the sample greater than the specified distance.

[0079] The light source can be a low-coherence light source, preferably a frequency scanning light source that performs scanning by changing the frequency (wavelength) over time.

[0080] As the frequency scanning light source, wavelength scanning lasers, FDML lasers, MEMS wavelength scanning light sources (MEMS VCSELs, external resonator type MEMS Fabry-Perot lasers, etc.) that use wavelength scanning filters (based on multi-faceted mirror driving, current mirror driving, etc.) and SGDBR lasers can be used.

[0081] Examples of light emitted from the light source include visible light and infrared light, with near-infrared (NIR) light being preferred. Light with wavelengths between 800 nm and 2000 nm is preferably used. From the perspective of light source stability and sensor reliability, light with center wavelengths of 940±50 nm, 1100±50 nm, 1310±50 nm, 1550±100 nm, or 1750±100 nm is more preferred.

[0082] The OCT device of the present invention may include the light source.

[0083] The OCT device of the present invention performs tomographic imaging of the sample based on the interference between the sample light and the reference light. The interference only needs to be an interference that allows both the sample light and the reference light to pass through the objective lens, but is preferably a Fizeau interference or a Mohr interference, and more preferably a Fizeau interference.

[0084] Examples of OCT types that can be used in the OCT device of the present invention include Time Domain OCT (TD-OCT) and Fourier Domain OCT (FD-OCT). Examples of FD-OCT include Spectral Domain OCT (SD-OCT) and Swept Source OCT (SS-OCT). Among these, SS-OCT is preferred from the viewpoint of high sensitivity and deep measurement depth.

[0085] The OCT device of the present invention preferably further includes a collimator that converts light from the light source into parallel light. The collimator is preferably disposed in the optical path between the light source and the objective lens.

[0086] Preferably, the OCT device of the present invention further includes a scanning mirror that scans the light from the light source focused on the sample. The scanning mirror is preferably disposed in the optical path between the light source and the objective lens, and more preferably disposed in the optical path between the collimator and the objective lens.

[0087] Examples of scanning mirrors include current mirrors, polygon mirrors, and MEMS mirrors. Among these, current mirrors are preferred, 1-axis or 2-axis current mirrors are more preferred, and 2-axis current mirrors are even more preferred.

[0088] Preferably, the OCT device of the present invention further includes a driving device for driving the scanning mirror.

[0089] Preferably, the OCT device of the present invention further includes a circulator that outputs light from the light source to the objective lens side, and outputs the sample light and reference light that have passed through the objective lens to the detector side for detecting the sample light and reference light. In this manner, the sample light and reference light can be transmitted through a single circulator. With such a structure, it is comparable to... Figure 1 Compared to the case shown where separate circulators are set up to allow the sample light and reference light to pass through, the device can be miniaturized and the cost can be reduced.

[0090] The circulator preferably has three or more ports, more preferably three ports.

[0091] Preferably, the circulator is disposed in the optical path between the light source and the objective lens, and more preferably, it is disposed in the optical path between the light source and the collimator.

[0092] In the case of a three-port circulator, light from the light source enters from the first port located on the light source side and exits from the second port located on the objective lens side. The sample light and reference light passing through the objective lens enter from the second port and exit from the third port located on the detector side.

[0093] Preferably, the OCT device of the present invention further includes a detector (also called detector (1)) for detecting the sample light and the reference light. Preferably, the detector (1) detects the interference signal based on the sample light and the reference light.

[0094] The detector (1) is preferably a differential optical detector. The detector (1) may also have the function of amplifying the signal. Alternatively, an amplifier may be provided separately.

[0095] Preferably, the OCT device of the present invention further includes a coupler (also called coupler (1)) that splits the light from the light source into split light 1 for generating the sample light and the reference light and split light 2 for removing the DC component of the interference signal. The coupler (1) is preferably disposed in the optical path between the light source and the objective lens, and more preferably disposed in the optical path between the light source and the circulator.

[0096] When the coupler (1) is provided, the intensity ratio of the split light 1 to the split light 2 is preferably 90:10 to 99:1, more preferably 92:8 to 98:2. By splitting the light into such an intensity ratio, the DC component can be effectively removed from the interference signal.

[0097] Preferably, the OCT device of the present invention further includes a detector (also called detector (2)) for detecting the split light 2. Detector (2) may be the same as the detector (1) or a different detector.

[0098] Preferably, the OCT device of the present invention further includes an attenuator for attenuating the split light 2. A variable optical attenuator (VOA) is preferred as the attenuator. The attenuator is preferably disposed in the optical path between the coupler (1) and the detector (2) that detects the split light 2.

[0099] Preferably, the OCT device of the present invention further includes a data acquisition (DAQ) device that collects interference signals based on the sample light and the reference light. Preferably, the DAQ device includes an A / D converter. Preferably, the DAQ device converts the collected interference signals into digital data.

[0100] Preferably, the OCT device of the present invention further comprises the capability to exceed the measurable distance (Z). max An anti-aliasing filter (also known as a low-pass filter) that attenuates unwanted frequency components. The anti-aliasing filter is preferably located in the optical path between the detector (1) and the DAQ device.

[0101] Preferably, the OCT device of the present invention further includes a computing unit that generates an optical coherence tomography image based on the interference signal of the sample light and the reference light. The computing unit visualizes the interference signal according to characteristics such as intensity, thereby generating the optical coherence tomography image.

[0102] Preferably, the OCT device of the present invention further includes a display device for displaying the obtained optical coherence tomography image. The display device can be fixed or portable; a portable device allows for image confirmation at the shooting location, which is therefore preferred. Furthermore, the connection to the computing device can be wired or wireless. There can be one or more display devices.

[0103] exist Figure 2 An example of the OCT device of the present invention is shown, but the OCT device of the present invention is not limited thereto.

[0104] exist Figure 2 In the OCT device 100, a frequency scanning light source 101 outputs light for OCT. The frequency scanning light source 101 outputs a trigger signal each time a frequency scan begins. Additionally, a Mach-Zehnder interferometer is used to detect the light and output a K-clock signal for frequency-interval sampling.

[0105] The light output from the frequency scanning light source 101 is split in the coupler 102 at an intensity ratio of 95:5 into split beam 1 for generating sample light and reference light, and split beam 2 for removing the DC component of the interference signal. Split beam 1 is input to port 1 of the circulator 103, output from port 2, and transmitted to the probe 104 through an optical fiber several meters long.

[0106] In probe 104, the split light 1 is converted into parallel light by collimator 105, then reflected by current mirror 106 and incident on objective lens 107, which serves as an Fθ lens. Current mirror 106 is driven by current mirror driver 111 to scan the parallel light in the XY direction perpendicular to the optical axis. The parallel light incident on objective lens 107 is focused onto the sample 110, which is the object of photography, by reference member 108, and reflected on the sample surface to become sample light incident on objective lens 107. In addition, a portion of the parallel light incident on objective lens 107 is reflected on reference surface 109 of reference member 108 and becomes reference light incident on objective lens 107.

[0107] The sample light and reference light incident on the objective lens 107 pass through the current mirror 106 and collimator 105, and are then input to port 2 of the circulator 103 via optical fiber. They are output from port 3 and then input to the differential optical detection amplifier 113. The differential optical detection amplifier 113 detects and amplifies the interference signal based on the interference of the sample light and the reference light.

[0108] The split beam 2, separated in coupler 102, is attenuated by variable optical attenuator 112 and then input to differential optical detection amplifier 113. Differential optical detection amplifier 113 uses the signal of split beam 2 to remove the DC component contained in the interference signal.

[0109] The interference signal, after the DC component is removed and amplified by the differential optical detection amplifier 113, is collected by the DAQ device (A / D converter) of PC114 and converted into digital data. The collection of the interference signal begins according to the trigger signal emitted by the frequency scanning light source 101 and is synchronized with the K clock signal.

[0110] Additionally, a distance exceeding the measurable distance (Z) is provided between the differential optical detection amplifier 113 and the DAQ device. max An anti-aliasing filter (not shown) that attenuates unwanted frequency components.

[0111] The computing device of PC114 generates an optical coherence tomography image of sample 110 based on the interference signal converted by the DAQ device and displays it on the mobile display 115.

[0112] The OCT device of the present invention is preferably configured such that the tomographic imaging can be performed by a user carrying the part equipped with the objective lens. In the OCT device of the present invention, even when the part equipped with the objective lens is portable, there is no environmental difference between the sample optical path and the reference optical path, therefore, the obtained tomographic image has small offset.

[0113] Preferably, the portion having the objective lens also includes the reference surface (or reference component), the collimator, and the scanning mirror.

[0114] The part containing the objective lens is preferably a probe of an OCT device.

[0115] The OCT device of the present invention is preferably configured such that the user can hold the part with the objective lens to perform the tomography, and more preferably configured such that the user can hold the part with the objective lens with one hand to perform the tomography.

[0116] In addition to the objective lens portion, the OCT device of the present invention may also include a portion that can be carried by the user during tomography. Examples of this portion include, for instance, a drive device for driving the scanning mirror and the display device.

[0117] In the OCT apparatus of the present invention, preferably, the portion equipped with the objective lens and the portion not equipped are connected via an optical fiber, and light from the light source, as well as the sample light and reference light, are transmitted through the optical fiber. In this manner, even when the subject is located far from the unequipped portion, by adjusting the length of the optical fiber, the portion equipped with the objective lens can be positioned near the subject for tomographic imaging. Since light from the light source, as well as the sample light and reference light, are all transmitted through the optical fiber, even when the optical fiber is lengthened, there is no environmental difference between the sample light path and the reference light path, resulting in a small shift in the obtained tomographic image. Furthermore, because it is a wired method using the optical fiber, high-resolution OCT measurements can be performed even for subjects located far from the unequipped portion.

[0118] The length of the optical fiber is not particularly limited and can be determined according to the location of the photographed object. For example, it can be more than 1m, preferably more than 3m, more preferably more than 5m, and even more preferably more than 10m. Alternatively, it can be less than 100m or less than 50m.

[0119] The uncarried portion preferably includes, for example, the light source, the circulator, the detector, the DAQ device, the computing device, etc.

[0120] The uncarried portion is preferably the main body (casing) of the OCT device.

[0121] In the case where there is a carried portion other than the portion with the objective lens, the connection between the carried portion and the portion with the objective lens or the portion not carried is not necessarily limited to an optical fiber-based connection; for example, it can also be a wire-based connection.

[0122] In the OCT apparatus of the present invention, it is preferable that the offset of the obtained optical coherence tomography image is 100 μm or less when the length of the optical fiber is 3 m or more and the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is 1 °C or more.

[0123] In industrial applications and other settings, the subject of the photograph is sometimes located far from the OCT device body (housing), outdoors, or in facilities with high or low temperatures. In such cases, due to the significant difference in environment (temperature) between the probe and the OCT device body, a large offset occurs in the obtained tomographic image in OCT devices where the sample optical path is located on the probe side and the reference optical path is located on the body side, due to the environmental difference between the sample optical path and the reference optical path. In contrast, the OCT device of the present invention does not produce an environmental difference between the sample optical path and the reference optical path even in such situations, and therefore the offset of the obtained tomographic image is small.

[0124] The length of the optical fiber in the described method is preferably 3m or more, more preferably 5m or more, and even more preferably 10m or more. Alternatively, it can be less than 100m or less than 50m.

[0125] The temperature difference of the atmosphere in the described method is preferably 1°C or more, more preferably 5°C or more, and even more preferably 10°C or more. Furthermore, the temperature difference is preferably 50°C or less.

[0126] The offset of the optical coherence tomography image is preferably less than 100 μm, more preferably less than 50 μm, and particularly preferably less than 30 μm.

[0127] The offset (ΔZ) is defined by the following equation (A):

[0128] ΔZ(μm)=dn / dT(1 / ℃)×L(m)×10 6 ×2×Δt(℃)(A)

[0129] (In the formula, dn / dT represents the temperature coefficient of the refractive index of the optical fiber material (1 / ℃), L represents the length of the optical fiber (m), and Δt represents the temperature difference between the sample optical path and the reference optical path (℃).)

[0130] ΔZ is the offset of the optical distance.

[0131] When the optical fiber is made of quartz glass, the wavelength of light is 1.3 μm, and the temperature is near room temperature, dn / dT is approximately 1.9 × 10⁻⁶. -5 (1 / ℃).

[0132] In an OCT device where the sample optical path is located on the probe side and the reference optical path is located on the main body side, the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is almost directly reflected in the temperature difference Δt of the optical path, resulting in a large offset ΔZ in the obtained tomographic image. In contrast, in the OCT device of the present invention, even when the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is large, the temperature difference Δt of the optical path is extremely small, and therefore ΔZ is also extremely small.

[0133] Figure 3 Another example of the OCT device of the present invention is shown (the part with the objective lens is a portable example), but the OCT device of the present invention is not limited thereto.

[0134] exist Figure 3 In the diagram, the user 201 carries the OCT device probe 202 with one hand and a current mirror driver 205 at their waist to drive the current mirror built into the probe 202. The probe 202 is connected to the OCT device housing 206 via an optical fiber 203. The current mirror driver 205 is connected to the probe 202 and the housing 206 via a wire 204.

[0135] The housing 206 contains a light source, a detector, a DAQ device, a computing device, etc.

[0136] The OCT device of the present invention is preferably configured such that, each time tomographic imaging is performed using the light source described below, the area in the planar direction that can be imaged at a resolution of 10 μm or higher is within a range of 0.1 mm to 14 mm in length and 0.1 mm to 14 mm in width. Therefore, (even when using other light sources) it is possible to simultaneously perform tomographic imaging of a large area with high precision.

[0137] (light source)

[0138] AXSUN high-speed wavelength scanning light source (center wavelength: 1310nm, scan width: 100nm, A-scan rate: 50kHz, output: 25mW, coherence length: 12mm)

[0139] The OCT apparatus of the present invention can be used to perform optical coherence tomography on samples. The present invention also relates to an optical coherence tomography method using the OCT apparatus of the present invention.

[0140] In the optical coherence tomography method of the present invention, even when the user carries a part equipped with the objective lens (e.g., a probe) while performing tomography, there is no environmental difference between the sample optical path and the reference optical path, thus the obtained tomographic image has small deviation. In addition, it is possible to perform tomography on a wide range simultaneously.

[0141] The OCT device and optical coherence tomography method of the present invention are applicable to all optical coherence tomography, regardless of the field. As described above, even when part of the OCT device is made portable, it is not easy to produce tomographic image shift. In addition, it is possible to perform tomography on a wide range simultaneously, and therefore, it is particularly suitable for use in industrial fields.

[0142] Example

[0143] Next, embodiments will be listed to illustrate the present invention in more detail, but the present invention is not limited to these embodiments.

[0144] Example 1

[0145] Use with Figure 2 The OCT apparatus shown depicts an OCT image taken from the PFA layer side of a 7.8 mm thick, 25 mm long and 25 mm wide fluoropolymer sheet, which is formed by sequentially stacking a 3.1 mm thick polytetrafluoroethylene (PTFE) layer, a 0.4 mm thick tetrafluoroethylene / hexafluoropropylene copolymer (FEP) layer, and a 4.3 mm thick tetrafluoroethylene / perfluoro(alkyl vinyl ether) copolymer (PFA) layer. The resulting tomographic image (8 mm long × 8 mm wide) is shown below. Figure 4 .

[0146] The following details the OCT equipment used and the photographic conditions.

[0147] OCT scanning laser source: Center wavelength: 1310nm, Scan width: 100nm, A-scan rate: 50kHz, Output: 25mW, Coherence length: 12mm

[0148] Objective lens: Fθ lens (trade name: Thorlabs LSM04), effective wavelength range (1250nm~1380nm), effective focal length (54mm)

[0149] Reference component: made of quartz glass, cylindrical shape, diameter 20mm in length

[0150] Optical fiber: made of quartz glass, 10m in length

[0151] Photography temperature: 26℃

[0152] Distance between reference surface and sample: 0cm

[0153] Other shooting conditions: Brightness 100, Contrast 30

[0154] Comparative Example 1

[0155] Except for changing the objective lens to an achromatic lens (trade name: Thorlabs AC254-050-C, effective wavelength range: 1050nm~1700nm, effective focal length: 50mm) instead of an Fθ lens, OCT imaging was performed in the same manner as in Example 1. The resulting tomographic images (8mm x 8mm) are shown below. Figure 5 .

[0156] exist Figure 4 In the middle, the fault images are clear and uniform overall; in contrast, in Figure 5 In the middle section, except for the area surrounded by dotted lines, there is a lot of noise and the effective field of view is narrow (making it impossible to perform large-scale tomography).

[0157] Comparative Example 2

[0158] Use with Figure 1 The OCT apparatus shown was used, and OCT imaging was performed on a fluoropolymer tube with an outer diameter of 12 mm and an inner diameter of 8 mm by heating only the optical fiber of the sample arm to 40°C using a dryer. The resulting tomographic images are shown below. Figure 6 .

[0159] The following details the OCT equipment used and the photographic conditions.

[0160] OCT scanning laser source: Center wavelength: 1310nm, Scan width: 100nm, A-scan rate: 50kHz, Output: 25mW, Coherence length: 12mm

[0161] Objective lens: Fθ lens (trade name: Thorlabs LSM03), effective wavelength range (1250nm~1380nm), effective focal length (36mm)

[0162] Fiber optic cable (sample arm, reference arm): made of quartz glass, 4m in length, shooting temperature: 26℃

[0163] Other shooting conditions: Brightness 100, Contrast 30

[0164] Reference Example 1

[0165] Except for not heating the optical fiber of the sample arm, OCT imaging was performed in the same manner as in Comparative Example 2. The resulting tomographic images are shown below. Figure 7 .

[0166] A temperature difference is generated between the arms. Figure 6 In, with Figure 7 In contrast, the tomographic image of the tube drifts upwards in the depth direction by more than 2 mm, with the portion corresponding to the tube's surface extending beyond the image frame. Additionally, in Figure 6 Artifacts were also observed as reflection noise (images of inverted circular arcs at the top of the image).

[0167] Explanation of reference numerals in the attached figures

[0168] 10: OCT device; 11: Light source; 12, 17: Coupler; 13, 15: Circulator; 14: Reference mirror; 16: Sample; 18: Photodetector; 100: OCT device; 101: Frequency scanning light source; 102: Coupler; 103: Circulator; 104: Probe; 105: Collimator; 106: Current mirror; 107: Objective lens; 108: Reference component; 109: Reference surface; 110: Sample; 111: Current mirror driver; 112: Variable optical attenuator; 113: Differential optical detection amplifier; 114: PC; 115: Mobile display; 201: User; 202: Probe; 203: Fiber optic cable; 204: Wire; 205: Current mirror driver; 206: Housing.

Claims

1. An optical coherence tomography (OCT) apparatus, comprising an objective lens that focuses light from a light source onto a sample, and performing tomographic imaging of the sample based on interference between sample light (reflected light from the sample) and reference light (reflected light from a reference surface disposed between the objective lens and the sample), wherein... Both the sample light and the reference light pass through the objective lens. The objective lens is an Fθ lens. The reference surface is a plane possessed by a reference component that satisfies the following relationship (3), and is the surface of the reference component on the sample side. n×WD>nd>n×Z max (3) In the formula, n represents the refractive index of the reference component, WD represents the working distance of the OCT device, which is the distance from the frontmost point of the objective lens on the sample side to the sample during focusing, nd represents the optical thickness of the reference component, and Z... max The measurable distance is expressed by the following relation (2). Z max =c / (4δf) (2) In the formula, c represents the speed of light, and δf represents the frequency interval of OCT interference signal sampling.

2. The optical coherence tomography apparatus according to claim 1, wherein, The optical coherence tomography apparatus is configured to perform tomography by setting the distance between the reference plane and the sample to 0-3 cm.

3. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The reference surface is a plane comprising at least one of a reference component selected from the group consisting of MgF2, CaF2, quartz, and sapphire.

4. The optical coherence tomography apparatus according to claim 1 or 2, wherein, Both the sample light and the reference light are generated by light from the light source that has passed through the objective lens.

5. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The interference is a Fizeau-type interference.

6. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The optical coherence tomography apparatus also includes a circulator that outputs light from the light source to the objective lens side and outputs the sample light and reference light that have passed through the objective lens to the detector side that detects the sample light and reference light.

7. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The optical coherence tomography apparatus also includes a coupler that splits the light from the light source into split light 1 for generating the sample light and the reference light and split light 2 for removing the DC component of the interference signal, wherein the intensity ratio of split light 1 to split light 2 is 90:10 to 99:

1.

8. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The optical coherence tomography apparatus is configured to allow a user to carry a portion equipped with the objective lens and perform the tomography.

9. The optical coherence tomography apparatus according to claim 8, wherein, The portion equipped with the objective lens that is being carried is connected to the portion that is not being carried via an optical fiber. The light from the light source, as well as the sample light and the reference light, are transmitted through the optical fiber.

10. The optical coherence tomography apparatus according to claim 9, wherein, The optical fiber is 3m or longer, and when the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is 1°C or more, the offset of the obtained optical coherence tomography image is less than 100μm.

11. The optical coherence tomography apparatus according to claim 1 or 2, wherein, The optical coherence tomography apparatus also includes a scanning mirror that scans the light from the light source focused on the sample. The light from the light source is light with a center wavelength of 1100±50nm, 1310±50nm, or 1550±100nm. The OCT mentioned is frequency scanning OCT. The OCT is configured to allow a user to perform tomographic imaging by carrying a portion equipped with the objective lens. The portion equipped with the objective lens that is being carried is connected to the portion that is not being carried via an optical fiber. The light from the light source, as well as the sample light and the reference light, are transmitted through the optical fiber. The length of the optical fiber is 10m to 100m. When the temperature difference between the ambient atmosphere of the portion carrying the objective lens and the ambient atmosphere of the portion not carrying the objective lens is 1°C or more and 50°C or less, the offset of the obtained optical coherence tomography image is 100 μm or less.

12. An optical coherence tomography method, which uses the optical coherence tomography apparatus according to any one of claims 1 to 11.

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