Light source device and image acquisition device

Abstract

To provide a light source device with which it is possible to change a polarization state.SOLUTION: A light source device (100) comprises: a laser light source (10) for emitting a laser light L having a peak wavelength included in the wavelength region of light absorbed or reflected by some of regions (52B) of a subject (500) and linearly polarized; a polarization control element (12) for passing the laser light emitted from the laser light source through and changing the polarization state of the laser light; and a birefringence optical fiber (13) the cross section of which, that is orthogonal to the long axis direction in which light is propagated, includes a fast axis orthogonal to the long axis direction and a slow axis orthogonal to both the long axis and the fast axis directions.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a light source device and an image acquisition device including the light source device. [Background technology]

[0002] Laser light emitted from a laser light source is coherent light and therefore has high coherence. When laser light is scattered by a scattering medium such as a rough surface, the scattered light is given a random phase distribution, resulting in irregular interference. As a result, a high-contrast spot pattern called "speckle" is observed.

[0003] Meanwhile, a laser speckle contrast imaging (LSCI) technique has been developed that irradiates biological tissue containing blood cells, which are scattering media, with laser light and measures the movement speed of blood cells (blood flow speed) based on the speckles obtained from the biological tissue. In LSCI technology, speckles are used as a "signal" required to detect blood flow speed.

[0004] Patent Document 1 discloses an endoscope that can irradiate a predetermined part of a living body with laser light in a plurality of different polarization states, and can identifiably display tissue emerging from a diseased part or the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2012-40224 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the endoscope of Patent Document 1, there is a possibility that the polarization state of the laser light may change unintentionally as the laser light propagates through the optical fiber.

[0007] An embodiment of the present disclosure provides a light source device and an image acquisition device capable of suppressing a change in the polarization state of laser light irradiated using an optical fiber. [Means for solving the problem]

[0008] In an exemplary embodiment, the light source device of the present disclosure includes a laser light source that emits linearly polarized laser light having a peak wavelength included in the wavelength range of light absorbed or reflected by a portion of a subject, a polarization control element that transmits the laser light emitted from the laser light source and changes the polarization state of the laser light, a birefringent optical fiber whose cross section perpendicular to the long axis direction along which the light propagates includes a fast axis perpendicular to the long axis direction and a slow axis perpendicular to both the long axis direction and the fast axis, and a focusing lens that focuses the laser light transmitted through the polarization control element on an incident end of the birefringent optical fiber. The polarization control element includes a birefringent element supported rotatably around the optical axis of the laser light, and an actuator that rotates the birefringent element around the optical axis of the laser light.

[0009] In an exemplary embodiment, an image acquisition device according to the present disclosure includes the above-described light source device, an imaging device, and a control device that controls operations of the light source device and the imaging device. The control device drives the actuator in the light source device to change the polarization state of the laser light emitted from the birefringent optical fiber. Effect of the Invention

[0010] According to an embodiment of the present disclosure, there is provided a light source device capable of suppressing changes in the polarization state of laser light irradiated using an optical fiber, and an image acquisition device including such a light source device. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic view of how laser light L emitted from a laser light source 10 is reflected by a surface 55 of an object 50. As shown in FIG. [Diagram 2]FIG. 2 is a diagram showing a schematic diagram of how images of two points O1 and O2 adjacent to each other on a surface 55 are formed on an imaging plane 22S. [Diagram 3] FIG. 3 is a diagram showing an example of a speckle pattern that can be formed on the imaging surface 22S. [Figure 4] FIG. 4 is a diagram illustrating a schematic configuration example of an image acquisition device 1000 including a light source device 100 according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a graph showing the wavelength dependence of the absorption coefficient of hemoglobin contained in human blood. [Figure 6] FIG. 6 is a diagram showing a schematic example of an image in which an image of a subject 500 illuminated with white light and a speckle pattern formed by the laser light source 10 and the polarization control element 12 are superimposed. [Figure 7] FIG. 7 is a diagram showing the positions of three different types of regions 52A, 52B, and 52C in the image of FIG. [Figure 8] FIG. 8 is a diagram illustrating an example of a polarized image. [Figure 9] FIG. 9 is a diagram showing a schematic diagram of reflection of light rays constituting the laser light L. In FIG. [Figure 10] FIG. 10 is a graph showing the relationship between the angle of incidence Ψ and the reflectance when a ray of light is incident from air (refractive index is 1.0) on surface 55 of subject 500 having a refractive index N=1.5. [Figure 11A] FIG. 11A is a diagram showing the relationship between the polarization axis D1 of the laser light irradiating the subject 500 and the polarization transmission axis D2 of the polarizing filter included in the imaging device 200. FIG. [Figure 11B] FIG. 11B is a graph showing the dependence of a signal output (pixel value) of a pixel constituting an image acquired from a reflected light component transmitted through a polarizing filter on the angle Φ. [Figure 12] FIG. 12 is a diagram showing an example of the configuration of the polarization control element 12. As shown in FIG. [Figure 13] FIG. 13 is a diagram showing a schematic diagram of a birefringent element 120 supported so as to be rotatable around the optical axis of the laser light L. As shown in FIG. [Figure 14]1 is a perspective view showing how linearly polarized light having a polarization axis parallel to or inclined by 45 degrees to a fast axis 120A passes through a birefringent element 120. FIG. [Figure 15] FIG. 15 is a perspective view showing a schematic change in the polarization state inside the birefringent optical fiber 13 in this embodiment. [Figure 16] FIG. 16 is a diagram showing a schematic cross-sectional configuration example of the birefringent optical fiber 13. As shown in FIG. [Figure 17] FIG. 17 is a plan view showing a schematic relationship between part of the array of pixels 220 on imaging surface 22S of image sensor 22 and patterned polarizers 224a, 224b, 224c, and 224d placed in positions covering pixels 220. As shown in FIG. [Figure 18A] FIG. 18A is a diagram showing a part of the array of pixels 220 on the imaging surface 22S of the image sensor 22 and signals obtained from some of the pixels 220. FIG. [Figure 18B] FIG. 18B is a diagram showing a part of another array of pixels 220 on the imaging surface 22S of the image sensor 22 and signals obtained from some of the pixels 220. In FIG. [Figure 19] FIG. 19 is a diagram showing a schematic diagram of a part of the array of pixels 220 on the imaging surface 22S and an example of the range of a pixel block. [Figure 20] FIG. 20 is a diagram illustrating a schematic configuration example of a light source device 100 for an endoscope. [Figure 21] FIG. 21 is a diagram showing an example of the configuration of an image acquiring device 1000 applied to an endoscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] FIG. 1 is a diagram showing a schematic view of the state in which the laser light L emitted from the laser light source 10 is reflected by the surface 55 of the subject 50. The laser light L has high coherence. The wavelength of the laser light L in the present disclosure is, for example, in the range of visible light. The range of visible light is, for example, from 380 nm to 750 nm. A typical example of the subject 50 is biological tissue. A microscopic structure of about the wavelength of the laser light L is irregularly present on the surface 55 of the subject 50 such as biological tissue and / or on the surface region located inside from the surface 55. A part of the laser light L incident on the surface 55 of the subject 50 is reflected by the surface 55. At this time, a part of the laser light L that penetrates from the surface 55 into the surface region of the subject 50 is absorbed in the surface region of the subject 50, or returns from the surface 55 to the space on the incident side due to multiple scattering. When the subject 50 is a living tissue, even if the surface 55 itself is covered with a smooth mucous membrane, the laser light L may be scattered by cells or intracellular microparticles. Hereinafter, the surface 55 and the superficial layer region of the subject 50 may be collectively referred to as the "scattering part." The laser light L scattered in the scattering part and returned to the space on the incident side is referred to as the "scattered light." The scattered light has a spatially random phase distribution due to the minute unevenness of the surface 55 and multiple scattering, but the coherence is not lost.

[0013] The imaging device 200 includes an imaging optical system 20 including a lens, and an imaging element 22 such as an image sensor. A part of scattered light generated when the laser light L is incident on the surface 55 of the subject 50 is collected by the imaging optical system 20 of the imaging device 200 and converges on the imaging surface (observation surface) 22S of the imaging element 22. When the laser light L is incident on the subject 50, not only scattering but also specular reflection may occur. For this reason, the term "reflected light" broadly includes the return light of the light incident on the subject 50, and is not limited to scattered light.

[0014] On the imaging plane 22S, an image of the subject 50 is formed by the action of the imaging optical system 20. A bundle of light rays converging on each position on the imaging plane 22S is a superposition of light waves scattered at and near the corresponding position on the surface 55. More specifically, when a bundle of light rays emitted from each point on the surface 55 converges on the imaging plane by imaging, the image of each point on the imaging plane has a "point spread distribution" determined by the diffraction limit, aberration, and the like.

[0015] FIG. 2 is a diagram showing a schematic diagram of how images of two points O1 and O2 close to each other on the surface 55 are formed on the imaging surface 22S. The two images formed by the points O1 and O2 on the imaging surface 22S have point spread distributions P1 and P2 that partially overlap each other. The size of each of the point spread distributions P1 and P2 is determined by the numerical aperture NA of the imaging optical system 20 and the wavelength λ of the laser light L. The fact that the two point spread distributions P1 and P2 overlap means that the origins of the light rays that cause the point spread, i.e., the points O1 and O2, are within a distance equal to or less than the resolution limit of the imaging optical system 20. The length of the resolution limit is d. Such an area with the resolution limit d as a diameter may be called a "resolution area". One of the resolution areas is shown diagrammatically by a circle (diameter: d) on the surface 55 in FIG. 2.

[0016] In the area where the two point spread distributions P1 and P2 on the imaging plane 22S overlap, scattered light from within the resolution area of ​​the subject 50 interferes to form a light and dark pattern according to the phase difference. Since such a light and dark pattern depends on the unevenness of the surface 55 and the randomness of multiple scattering in the scattering part of the subject 50, it forms an irregular speckle pattern that can be evaluated by statistics.

[0017] FIG. 3 is a diagram showing an example of a speckle pattern that may be formed on the imaging surface 22S. In FIG. 3, a fine granular light and dark pattern is observed. The light intensity is relatively high in the bright areas, and the light intensity is relatively low in the dark areas. The minimum size of the speckle is about the size of the point spread distribution determined by the numerical aperture NA of the imaging optical system 20 and the wavelength λ of the laser light L.

[0018] The interference of scattered light occurs in a three-dimensional space. Therefore, the distribution of the "light intensity amplitude" that defines the speckle pattern is originally dependent on three-dimensional position coordinates. Such a speckle pattern that exists objectively in a three-dimensional space is called "objective speckle" or "non-imaging speckle". On the other hand, the speckle pattern observed by the imaging device 200 depends on the position, orientation, and numerical aperture NA of the imaging optical system 20, and is called "subjective speckle" or "imaging speckle". The speckle actually observed by the imaging device 200 is the distribution of the "intensity" of the speckle on the imaging surface 22S of the imaging element 22. Hereinafter, the "speckle pattern" in this disclosure means a two-dimensional pattern of the subjective speckle observed by the imaging device 200, unless otherwise specified.

[0019] 1, when the subject 50, the laser light source 10, and the imaging device 200 are stationary, the objective speckles and the subjective speckles are also stationary. However, when the surface 55 of the subject 50 or the cellular tissue in the superficial region of the subject 50 is moving, the phase distribution of the scattered light changes over time, so the objective speckles and the subjective speckles may also vary over time. For example, when blood vessels are present near the superficial layer of the subject 50 and red blood cells are flowing through the blood vessels, the phase distribution of the scattered light by the red blood cells changes over time, so that the speckles change over time in the region where the image of the blood vessels is formed on the imaging plane 22S.

[0020] Conventionally, for example, when a laser light source is used as a light source for an endoscope, it has been thought that speckle patterns must be removed as much as possible because they become noise in image information. For this reason, various methods have been used to reduce the coherence of the laser light emitted from the laser light source so as not to form speckle patterns.

[0021] In the light source device of the present disclosure, the reflectance of the laser light is changed by variably controlling the polarization state of the laser light having a specific wavelength, thereby forming a speckle pattern with different degrees of brightness depending on the area of ​​the subject. In this way, it becomes possible to obtain image information that could not be obtained in the past. Hereinafter, an embodiment of the light source device and the image acquisition device according to the present disclosure will be described.

[0022] <Embodiment> Hereinafter, a light source device and an image acquisition device according to an embodiment of the present disclosure will be described.

[0023] First, reference will be made to Fig. 4. Fig. 4 is a diagram that illustrates a schematic configuration example of an image acquisition device 1000 that includes a light source device 100 in this embodiment.

[0024] The illustrated image acquisition device 1000 includes a light source device 100, an imaging device 200, and a control device 300 that controls the operations of the light source device 100 and the imaging device 200. The control device 300 is connected to a display device 400. The imaging device 200, the control device 300, and the display device 400 will be described in detail later.

[0025] The light source device 100 in this embodiment includes a laser light source 10 that emits polarized laser light, a polarization control element 12 that transmits the laser light emitted from the laser light source 10 and changes the polarization state of the laser light, and a birefringent optical fiber 13. The birefringent optical fiber 13 has a cross section perpendicular to the long axis direction along which light propagates, and includes a fast axis perpendicular to the long axis direction and a slow axis perpendicular to both the long axis direction and the fast axis. Although not shown in FIG. 4, the light source device 100 also includes a converging lens that focuses the laser light transmitted through the polarization control element 12 onto the incident end of the birefringent optical fiber 13.

[0026] A typical example of the laser light source 10 is a semiconductor laser element (laser diode). The laser light source 10 emits laser light having a peak wavelength λ included in a wavelength range of light that is absorbed or reflected relatively strongly in a part of the region 52B of the subject 500 compared to the other region 52A. The laser light source 10 can form a speckle pattern having different speckle contrasts in the regions 52A and 52B of the subject 500 by emitting a coherent laser light. Here, for example, "forming a speckle pattern in the region 52A" means "forming a speckle pattern in the image of the region 52A in the image acquired by the imaging device 200". The speckle pattern formed in the image of the region 52A is based on the interference of scattered light generated in the region 52A. Therefore, when the absorption / reflection characteristics and scattering characteristics for the laser light of the peak wavelength λ differ between the regions 52A and 52B of the subject 500, it becomes possible to identify or distinguish the regions 52A and 52B based on the feature amount extracted from the speckle pattern. The peak wavelength λ may be in a wavelength range detectable by the imaging device 200. The peak wavelength λ is, for example, in the range of 410 nm or more and 660 nm or less.

[0027] FIG. 5 is a graph showing the wavelength dependency of the absorption coefficient of hemoglobin. Hemoglobin is a protein present in red blood cells found in the blood of all vertebrates including humans. In FIG. 5, the absorption coefficient of hemoglobin is shown by a solid line H. For reference, FIG. 5 also shows the scattering coefficient of human body tissue by a dashed line S. As shown in FIG. 5, in the wavelength range of about 400 nm or more and about 600 nm or less, the light absorption by hemoglobin is relatively large compared to the infrared region. In particular, at a wavelength of about 415 nm, the absorption coefficient of hemoglobin becomes specifically high and shows an absorption peak Hp. On the other hand, when the wavelength exceeds about 1350 nm, the absorption coefficient of water (not shown) increases rapidly. In the wavelength range of about 650 nm or more and about 1350 nm or less, as indicated by the white arrow with the symbol W, the absorption of light by hemoglobin or water is relatively small, and scattering is likely to occur. For this reason, light in the wavelength range W indicated by the white arrow in Fig. 5 penetrates deeper into living organisms more easily than other wavelength ranges, and this wavelength range W is called the "biological window." When it is desired to obtain information from inside human biological tissue, the biological tissue is irradiated with light in the wavelength range W. However, conventionally, incoherent light has been used for such purposes in order to prevent speckle noise.

[0028] In the embodiment of the present disclosure, the laser light source 10 emits laser light having a peak wavelength λ included in the wavelength range of light absorbed or reflected by a portion of the subject 500. This makes it possible to form a speckle pattern having different speckle contrasts according to the absorption and reflection characteristics of the subject 500. The peak wavelength λ does not need to be about 415 nm, and can be selected from the range of 410 to 420 nm, for example.

[0029] In addition, the laser light with the peak wavelength λ has a spectrum width of, for example, about several nm. The peak wavelength λ does not need to match the wavelength of light that is specifically absorbed or reflected by a part of the subject. For example, when the wavelength of light that is specifically absorbed or reflected by a part of the subject is about 415 nm, the peak wavelength λ of the laser light may be, for example, 420 nm. Even in such a case, the part of the subject may cause the absorption or reflection of the laser light. The luminosity of the human eye is highest near 555 nm. For this reason, a color pattern that is easily recognized by the human eye is observed when a speckle pattern is formed with a laser light having a peak wavelength closer to 555 nm than the wavelength of the absorption peak in the wavelength range absorbed by the part of the subject. However, the actual color of the speckle pattern (for example, purple) may be converted to a color (for example, green) of a wavelength close to the wavelength (555 nm) at which the luminosity of the human eye is high by image processing, and the speckles may be emphasized and displayed on the display device 400.

[0030] The light source device 100 according to the embodiment of the present disclosure includes a polarization control element 12 that changes the polarization state of the laser light in response to a control signal from the outside (specifically, the control device 300). As described later, the laser light whose polarization state has been changed by the polarization control element 12 is made incident on the birefringent optical fiber 13 and propagated, thereby making it possible to control the polarization state of the laser light incident on the subject 500. By changing the polarization state, the speckle pattern also changes. If the polarization state is changed at high speed, different speckle patterns are superimposed, and the contrast of the speckle pattern decreases. For this reason, it becomes possible to switch between an operation mode in which information is obtained from the speckle pattern or polarization information is obtained from the polarization component contained in the reflected light, and an operation mode in which the speckle pattern is suppressed and normal observation is performed.

[0031] In this embodiment, the light source device 100 has a white light source 14 as an illumination light source that emits illumination light. In this disclosure, "white" light broadly covers light that includes at least two wavelength components belonging to the wavelength ranges of each color of red (R), yellow (Y), green (G), and blue (B), and more preferably all colors. Here, the wavelength range of R light is, for example, 620 nm to 660 nm. The wavelength range of G light is, for example, 500 nm to 540 nm. The wavelength range of B light is, for example, 430 nm to 480 nm. The wavelength range of Y light is, for example, 550 nm to 590 nm. It is not necessary for the white light source 14 to simultaneously emit R light, G light, and B light. If R light, G light, and B light are emitted sequentially within a period of, for example, about 30 milliseconds, additive color mixing of those color components occurs in the eye, making it possible to recognize white. In addition, a phosphor may be excited with B light to emit Y light. Whitening occurs due to the mixing of B light and Y light. When an imaging element such as a CCD (Charged-Coupled Device) or a CMOS (Complementary metal-oxide-semiconductor) image sensor performs an image data read operation at 30 frames per second (=30 fps), one frame period is about 33 milliseconds. Therefore, if R light, G light, B light, etc. are emitted sequentially or simultaneously within one frame period, whitening can be achieved. Therefore, a light source that can emit R light, G light, B light, etc. sequentially or simultaneously is included in the "white light source". In this embodiment, a typical example of the white light source 14 is an LED (Light Emitting Diode) or an LD (Laser Diode). When the white light source 14 includes an LD, it is configured not to generate speckles, as described below.

[0032] The imaging device 200 can obtain an image of the subject 500 by illuminating the subject 500 with light emitted from the white light source 14. In an environment in which an endoscope is used, it is difficult to obtain a clear image of the subject 500 without an illumination light source such as the white light source 14, but the light source device 100 of the present disclosure can be used for applications other than endoscopy. For example, it can be used as a light source for observing the condition of the skin or eyes. In such applications, the subject 500 can be illuminated by other illumination devices or sunlight, so the above-mentioned white light source 14 is not essential. Note that, in an environment in which an endoscope is used, even if the subject 500 is illuminated with non-whitened light (preferably broadband light), it is possible to observe the subject 500 by image processing.

[0033] In this embodiment, an image of the subject 500 illuminated with white light can be superimposed on the speckle pattern formed by the laser light source 10 and the polarization control element 12 and displayed on the display device 400. In cases where a lesion may be overlooked with white light alone, the presence of the speckle pattern can contribute to preventing the lesion from being overlooked.

[0034] FIG. 6 is a diagram showing an example of an image (synthetic image) in which an image of a subject 500 illuminated with white light and a speckle pattern formed by a laser light source 10 and a polarization control element 12 are superimposed. FIG. 7 is a diagram showing the positions of three different types of regions 52A, 52B, and 52C in the synthetic image of FIG. 6. In FIG. 6, for simplicity, the fine structure shown in the image of the subject 500 illuminated with white light is omitted, and only the speckle pattern is shown. The regions 52A, 52B, and 52C can be distinguished from each other based on the feature amount (e.g., brightness and contrast) of the speckle pattern. In the example of FIG. 6, the region 52B is more likely to absorb the laser light of wavelength λ than the region 52A. Therefore, the brightness of the speckles in the region 52B is relatively decreased as a whole compared to the brightness of the speckles in the region 52A. In contrast, the region 52C is more likely to reflect the laser light of wavelength λ than the region 52A. Therefore, the brightness of the speckles in region 52C is relatively increased as a whole compared to the brightness of the speckles in region 52A. The discrimination of the regions based on such a speckle pattern is realized because the peak wavelength λ of the laser light emitted from laser light source 10 is included in the wavelength range of light that is specifically absorbed or reflected by some regions 52A, 52B, and 52C of subject 500, and the coherence of the laser light is maintained at a high level. On the other hand, if subject 500 is illuminated only with light emitted from white light source 14, the speckle pattern of FIG. 6 is not observed, and it may be difficult to discriminate between regions 52A, 52B, and 52C.

[0035] When the peak wavelength λ of the laser light is about 415 nm, the above-mentioned region 52B may be a region where blood components including, for example, hemoglobin are present in greater amounts than in other regions. Red blood cells containing hemoglobin can essentially scatter the laser light and contribute to the formation of a speckle pattern. However, when the laser light is strongly absorbed by hemoglobin, the intensity of the scattered light decreases, and the intensity (brightness) of the speckle also decreases. When blood containing red blood cells flows through a blood vessel, the phase of the scattered light by the red blood cells fluctuates over time. Therefore, the contrast of the speckle averaged over time decreases.

[0036] The above-mentioned region discrimination based on the speckle pattern contributes to detecting regions showing abnormalities such as lesions in biological tissue. Such detection is not limited to an example performed by a human being based on vision, but may be performed "mechanically" using information processing technology. As will be described later, various feature amounts can be extracted from the speckle pattern, so that it becomes possible to perform region division (segmentation) or classification based on these feature amounts. Region division or classification based on feature amounts can also be performed using a trained model created by machine learning such as deep learning.

[0037] With illumination by a normal white light source, there is no clear contrast difference between the lesion and the surrounding area in the biological tissue, and it may be difficult to distinguish from the image. In such a case, by using the above-mentioned speckle pattern, it is possible to prevent oversight. Therefore, the light source device in this embodiment can be particularly effective as a light source for endoscopes.

[0038] Fig. 8 is a diagram showing a schematic example of a polarized image. A polarized image is acquired by capturing an image through a polarizing filter having a polarization transmission axis in a specific direction. Changing the direction of the polarization transmission axis can change the light and dark pattern of the polarized image.

[0039] FIG. 9 is a diagram showing a schematic diagram of reflection of light rays constituting laser light L. This light ray is incident on surface 55 of object 500 at an incident angle Ψ and is reflected at a reflection angle equal to the incident angle Ψ. Here, the "incident angle Ψ" is the angle between the normal (dotted line) of surface 55 of object 500 and the incident light ray. Surface 55 of actual object 500 may not be flat, but may have undulations. For example, when object 500 is a human or animal organ, there are irregularities on the mucosal surface, so that the normal of surface 55 points in different directions depending on the position.

[0040] Fig. 10 is a graph showing the relationship between the angle of incidence Ψ and reflectance when a ray of light is incident from the air (refractive index is 1.0) on surface 55 of subject 500 with refractive index N = 1.5. The solid line shows the case when the ray of light is S-wave polarized (polarization axis perpendicular to the incident plane), and the dashed line shows the case when the ray of light is P-wave polarized (polarization axis parallel to the incident plane). The graph in Fig. 10 is calculated from Fresnel's equation.

[0041] As shown in FIG. 10, the reflectance of a light beam depends on the direction of the polarization axis of the light beam. Therefore, when the polarization axis of the laser light L irradiating the object 500 is rotated, a pixel or a group of pixels may be observed in which a noticeable difference in reflected light intensity is observed between an S-wave polarized image and a P-wave polarized image. Such a pixel or group of pixels may correspond to an inclined region on the surface 55 of the object 500 where the incident angle Ψ of the light beam is, for example, about 60°. In this way, by measuring the polarization dependency of the reflected light intensity acquired on a pixel-by-pixel basis, it is possible to acquire information on the unevenness (information in the normal direction) on the surface 55 of the object 500.

[0042] In order to obtain the polarization dependency of the reflected light intensity, it is desirable to make the polarization axis state of the laser light irradiating the subject 500 variable.

[0043] 11A is a diagram showing the relationship between the polarization axis D1 of the laser light irradiating the subject 500 and the polarization transmission axis D2 of the polarizing filter included in the imaging device 200. For simplicity, the horizontal direction of the imaging device 200 is taken as the X-axis. The polarization axis D1 of the laser light is rotated counterclockwise by an angle θ1 from the X-axis. The polarization transmission axis D2 of the polarizing filter is rotated counterclockwise by an angle θ2 from the X-axis. An angle Φ=θ1-θ2 is formed between the polarization axis D1 and the polarization transmission axis D2.

[0044] 11B is a graph showing the dependence of the signal output (pixel value) of a pixel constituting an image acquired from the component of the reflected light from the subject 500 that has passed through the polarizing filter on the angle Φ. When Φ=0°, that is, when the polarization axis D1 and the polarization transmission axis D2 coincide, the pixel value is a maximum value I maxWhen Φ=90°, that is, when the polarization axis D1 and the polarization transmission axis D2 are perpendicular to each other, the pixel value is the minimum value I min The minimum value I min is not zero. The scattered reflected component includes a component polarized in a direction different from the polarization axis D1 of the incident laser light. As a result, the pixel value will not be zero, regardless of the value of the angle Φ.

[0045] When the waveform of FIG. 11B is obtained, the degree of polarization ρ=(I max -I min ) / (I max +I min In order to obtain an accurate waveform in FIG. 11B, it is preferable to change θ continuously. However, if the pixel value I(θ) is measured at multiple values ​​of different θ, I(θ) can be calculated by data fitting. max and I min The magnitude of can be estimated.

[0046] The waveform shown in Fig. 11B may differ depending on the pixel. In other words, the characteristics of the polarization reflectance of the laser light differ depending on the part of the subject 500. The polarized image shown in Fig. 8 may show different light and dark distributions when the polarization axis of the laser light irradiating the subject 500 is rotated.

[0047] When imaging is performed through a polarizing filter having a polarization transmission axis D2 in the same direction as the polarization axis D1 of the laser light irradiating the subject 500, the image is composed of components whose polarization is not destroyed even when reflected by the subject 500. In contrast, if only the polarization axis D1 of the laser light irradiating the subject 500 is rotated by, for example, 90°, the reflected light components that can pass through the polarizing filter having the above-mentioned polarization transmission axis D2 will have their polarization direction rotated by 90° when reflected by the subject 500 and will constitute the image.

[0048] By rotating the polarization axis D1 of the laser light in this way, various polarized images can be obtained. In a polarized image, even pixels at the same position may have different reflected light intensities depending on the polarization axis D1 of the incident laser light. This is because the reflection characteristics differ depending on the location on the surface of the subject 500, and the reflected light intensity may change depending on the polarization direction of the laser light, even at the same location.

[0049] Next, with reference to FIGS. 12 to 16, an example of a configuration for rotating the polarization axis D1 of laser light in this embodiment will be described.

[0050] The polarization control element 12 is an element that can transmit the laser light L emitted from the laser light source 10 and change the polarization state of the laser light L. As shown in Fig. 12, the polarization control element 12 has a birefringent element 120 supported rotatably around the optical axis of the laser light L, and an actuator 122 that rotates the birefringent element 120 around the optical axis of the laser light L.

[0051] 13 is a schematic diagram of a birefringent element 120 supported to be rotatable around the optical axis (Z-axis) of laser light L. An arrow R in the figure indicates clockwise rotation. In the example shown, a fast axis 120A of the birefringent element 120 is tilted 45° clockwise with respect to the positive direction of the Y-axis. The angle of this tilt can be changed by the action of an actuator 122.

[0052] The fast axis 120A of the birefringent element 120 is an axis parallel to the direction in which the refractive index is highest. As shown in the upper part of Fig. 14, even if linearly polarized light having a polarization axis parallel to the fast axis 120A passes through the birefringent element 120, no rotation of the polarization axis occurs. However, for example, when the birefringent element 120 is a half-wave plate, as shown in the lower part of Fig. 14, if the fast axis 120A of the half-wave plate is inclined by 45° with respect to the polarization axis of the incident light, a rotation of 45°×2=90° occurs in the polarization axis.

[0053] Fig. 15 is a perspective view showing a schematic change in the polarization state inside the birefringent optical fiber 13 in this embodiment. Fig. 16 is a schematic view showing an example of the cross-sectional configuration of the birefringent optical fiber 13.

[0054] The birefringent optical fiber 13 in the illustrated state is an optical fiber whose cross section perpendicular to the long axis (Z axis) direction along which light propagates includes a fast axis FA perpendicular to the long axis direction and a slow axis SA perpendicular to both the long axis direction and the fast axis, as shown in FIG. 16. In order to realize such refractive index anisotropy, the birefringent optical fiber 13 has a core 13A having a relatively high refractive index and a cladding 13B located on the outer periphery of the core 13A, and a pair of stress-applying parts 13C are inserted into the cladding 13B. The stress-applying parts 13C form a stress distribution in the cladding 13B, resulting in the refractive index distribution shown in the lower part of FIG. 16. The refractive index distribution in the X-axis direction and the refractive index distribution in the Y-axis direction have different shapes, and linearly polarized light having a polarization axis in the Y-axis direction propagates faster than linearly polarized light having a polarization axis in the X-axis direction. This property is maintained even when the birefringent optical fiber 13 is bent.

[0055] The birefringent optical fiber 13 having the configuration shown in FIG. 16 is a polarization-maintaining fiber also called a "PANDA fiber." In the polarization-maintaining fiber, the core 13A receives a tensile stress in the X-axis direction and a compressive stress in the Y-axis direction due to the stress generated in the stress-applying portion 13C, and birefringence is induced by the photoelastic effect. If the propagation constant of linearly polarized light whose polarization axis is parallel to the X-axis (X-polarized mode) is βX, the propagation constant of linearly polarized light whose polarization axis is parallel to the Y-axis (Y-polarized mode) is βY, and the wave number is k, then the birefringence Δβ is (βX-βY) / k. When Δβ is greater than zero, it becomes difficult for the X-polarized mode and the Y-polarized mode to couple. Therefore, the PANDA fiber can propagate linearly polarized light in the X-polarized mode or the Y-polarized mode while maintaining its polarization state.

[0056] In this embodiment, for example, in the first operating state, linearly polarized light in the X polarization mode or the Y polarization mode is propagated. Then, in the second operating state, linearly polarized light in a polarization state in which the X polarization mode and the Y polarization mode are combined (light polarized in a direction intersecting the X axis and the Y axis at 45°) is propagated. In the second operating state, the polarization state changes periodically with a propagation distance of the "beat length" expressed by Lb=2π / Δβ. In this embodiment, when N is an integer equal to or greater than 0, the length of the birefringent optical fiber 13 is Lb×(N+1 / 2). In the example of FIG. 15, the fast axis FA of the birefringent optical fiber 13 is parallel to the fast axis 120A of the birefringent element 120 shown in the lower part of FIG. 14.

[0057] As shown in Fig. 14, by rotating the birefringent element 120, it is possible to rotate the polarization axis of the laser light incident on the birefringent optical fiber 13. By rotating the polarization axis of the laser light incident on the birefringent optical fiber 13, it is possible to control the polarization state of the laser light emitted from the birefringent optical fiber 13. Specifically, it becomes possible to switch the polarization state of the laser light emitted from the birefringent optical fiber 13 between two orthogonal directions. This makes it possible to illuminate the subject 500 by switching between S-wave polarization and P-wave polarization described with reference to Fig. 10.

[0058] Instead of changing the polarization state of the laser light inside the birefringent optical fiber 13, it is also possible to switch the polarization direction of the laser light emitted from the birefringent optical fiber 13 between two orthogonal directions by twisting the birefringent optical fiber 13 itself by 90 degrees around its axis while maintaining the polarization state.

[0059] 17 is a plan view showing a schematic relationship between a part of the array of pixels 220 on the imaging surface 22S of the imaging element 22 of the imaging device 200 and the patterned polarizers 224a, 224b, 224c, and 224d placed at positions covering the pixels 220. The patterned polarizers 224a, 224b, 224c, and 224d have polarization transmission axes that are oriented in directions different from each other by 45°. For simplicity, the optical axis of the imaging element 22 is assumed to be coaxial with the long axis direction of the birefringent optical fiber 13. The patterned polarizers 224a, 224b, 224c, and 224d have polarization transmission axes that are angled θ2=0°, 45°, 90°, and 135° with respect to the X-axis, respectively. When the subject 500 is irradiated with laser light in a certain polarization state, it is possible to obtain data corresponding to four points on the sine wave curve shown in Figure 11B based on the intensity (pixel value) of the signals output from the four pixels 220 covered by the patterned polarizers 224a, 224b, 224c, and 224d.

[0060] Based on the sine wave curve thus obtained, the polarized light reflection characteristics of each part of the subject 500 can be obtained with a resolution of four pixels.

[0061] Furthermore, when the birefringent element 120 is rotated at high speed using the actuator 122 in FIG. 12, it becomes possible to change the polarization state of the laser light irradiating the subject 500 during one frame period (for example, about 33 milliseconds) when the image sensor performs the image data readout operation. When laser light is irradiated in a plurality of different polarization states within one frame period, the coherence changes according to the polarization state, so that different speckle patterns are formed in each polarization state and are superimposed. As a result, a plurality of speckle patterns are superimposed within each frame period, and the contrast is reduced. Thus, according to this embodiment, by making the polarization state of the laser light variable, it becomes possible to control the coherence of the laser light to increase or decrease the speckle contrast.

[0062] According to the embodiment of the present disclosure, an observer of the subject can increase or decrease the speckle contrast at any time while visually checking the image displayed on the display device 400 of FIG. 4. Specifically, an observer of the subject 500 shown in FIG. 4 or an operator of the image acquisition device 1000 can operate the control device 300 using an input device (not shown) to control the operation of the polarization control element 12. For example, it is possible to first observe the image of the subject 500 without forming a speckle pattern, and then appropriately superimpose the speckle pattern on a normal subject image. In addition, by controlling the polarization state of the laser light irradiating the subject, it is possible to obtain polarization information from the subject and observe the surface state of the subject in more detail.

[0063] Next, a description will be given of an example of an image signal obtained by the imaging device 200. The imaging device 200 includes an imaging optical system 20 and an imaging element 22, as shown in FIG.

[0064] FIG. 18A is a diagram showing a part of the array of pixels 220 on the imaging surface 22S of the image sensor 22 and signals obtained from some of the pixels 220 when a subject is irradiated with laser light in a certain polarization state. Each pixel 220 has a photoelectric conversion unit that outputs an electric signal according to the amount of incident light. Each pixel 220 is connected to a readout circuit or the like via wiring (not shown). The upper part of FIG. 18A shows eight pixels 220 arranged in two rows and four columns, and a speckle 222 formed on the imaging surface 22S. The lower part of FIG. 18A shows the magnitudes of signals S11, S12, S13, and S14 output from the four pixels 220 crossed by the line B1-B1 in the upper part, represented by the height of each bar. A polarizing filter may be arranged in front of the image sensor 22. If the direction of the polarization transmission axis of this polarizing filter changes, the magnitude of the signal obtained from each pixel 220 may also change. The transmission axis of the polarizing filter may be common to all pixels 220, or may be different as shown in Fig. 17. By changing the polarization state of the laser light irradiating the subject, the speckle pattern formed on the imaging surface 22S may also change.

[0065] 18A, the pixels 220 in this example are smaller than the speckles 222. If the pixels 220 are larger than the speckles 222, it is difficult to clearly observe the speckle pattern. When the speckle pattern is stationary, the magnitude of the signal output from each pixel 220 is constant over time.

[0066] Fig. 18B shows an example in which the size and arrangement pitch of each pixel 220 are smaller than those in the example of Fig. 18A. The upper part of Fig. 18B shows 32 pixels 220 arranged in 4 rows and 8 columns, and speckles 222 formed on the imaging surface 22S. The lower part of Fig. 18B shows the magnitudes of signals S21, S22, S23, S24, S25, S26, S27, and S28 output from the eight pixels 220 intersected by the line B2-B2 in the upper part, as the height of each bar.

[0067] As is clear from FIG. 18A and FIG. 18B, the smaller the size and arrangement pitch of the pixel 220, the more precisely the speckle pattern can be observed. To observe the speckle pattern formed by the laser light with a peak wavelength λ, the pixel 220 needs to perform photoelectric conversion in response to the light with wavelength λ. When the imaging device 200 is a color image sensor, each pixel 220 shown in FIG. 18A and FIG. 18B includes, for example, an R subpixel, a G subpixel, and a B subpixel. These subpixels are arranged in, for example, a Bayer arrangement within each pixel 220. In this case, the image signal includes each of the signal components of RGB. When the peak wavelength of the laser light is, for example, about 415 nm, the bright pattern of the speckle pattern can be detected by the B subpixel.

[0068] An imaging element (image sensor) that can be used in the imaging device 200 can read out pixel signals in units of frames. When the readout rate is, for example, 30 frames per second, the period of one frame is about 33 milliseconds. In this case, pixel signals are read out about every 33 milliseconds. The pixel signal obtained from a certain pixel 220 has a magnitude according to the amount of charge that the pixel 220 accumulates by photoelectric conversion during an exposure time shorter than the period of one frame. Therefore, if the speckle moves a distance longer than the pixel size during the exposure time, it becomes difficult to clearly detect the speckle pattern. For this reason, in the mode for observing the speckle pattern, it is desirable to prevent the speckle pattern from moving at a high speed. The speckle pattern changes when the light source device 100 and the imaging device 200 move relative to the subject 500 in FIG. 4. The speckle pattern can also change if the coherence of the laser light L emitted from the light source device 100 is changed over time by, for example, rotating the birefringent element 120. Therefore, in order to make the speckle pattern still, it is desirable to make light source device 100 and imaging device 200 substantially still relative to subject 500 and to irradiate subject 500 with laser light L having high coherence from light source device 100.

[0069] The "speckle contrast" is known as a quantity (statistic) for statistically evaluating a speckle pattern. The "speckle contrast" is defined by the following formula: C=σ / J (Formula 1) Here, C is the speckle contrast, J is the spatial average value of the light intensity, and σ is the standard deviation of the light intensity.

[0070] 18A and 18B, the spatial distribution of "light intensity" on the imaging surface 22S can be measured. As a result, J and σ can be calculated.

[0071] An example of calculating the speckle contrast in units of blocks each made up of a plurality of pixels will be described with reference to Fig. 19. Fig. 19 is a diagram showing a schematic diagram of a part of the array of pixels 220 on imaging plane 22S and an example of a pixel block.

[0072] In the example of FIG. 19, the speckle contrast C of pixel (i,j) at position (i,j) on the imaging plane 22S can be determined based on pixel signals obtained from a block BL of 7×7 pixels including pixel (i,j) at its center. Specifically, C(i,j) can be obtained by calculating the average value J and standard deviation σ from the signals of all pixels in the pixel block BL. The pixel block BL is not limited to 7×7, but may be 9×9, or may have other sizes. If C(i,j) is calculated for all pixels while sliding the pixel block BL so as to shift the central pixel (i,j) of interest by one pixel at a time in the row or column direction, a two-dimensional array of C(i,j), i.e., a contrast image, can be obtained. If each pixel is sufficiently smaller than the speckle, the pixel density may be substantially reduced by adding up several adjacent pixel signals, and then C(i,j) may be calculated. Such C(i,j) can be called a local speckle contrast. The local speckle contrast can function as a feature for distinguishing a lesion from other parts. The calculation of the speckle contrast can be performed by an image processing device (arithmetic processing circuit) 32 in FIG. 4. The image processing device 32 operates together with the processor 30 to generate image data based on an image signal obtained from the imaging device 200. The image data thus generated can be displayed by the display device 400.

[0073] According to this embodiment, even when the human eye has difficulty in detecting differences in speckle patterns, detection of lesions and the like can be facilitated by performing quantitative evaluation based on the contrast image generated by the image processing device 32. In addition, by changing the polarization state of the laser light irradiating the subject, it becomes possible to obtain information on the polarization characteristics that may differ depending on the part of the subject's surface. Such polarization characteristics are effective in detecting changes in the shape of lesions and the like.

[0074] As described above, the minimum size of speckles on the imaging surface 22S depends on the numerical aperture NA of the imaging optical system 20 of the imaging device 200 and the wavelength λ of the laser light L. More precisely, the minimum size of speckles on the imaging surface 22S is expressed as 2.44×λ(1+M)×F number. M is the lateral magnification (image magnification) of the imaging optical system 20, and the F number is also called the F value and is equal to 2 / NA. (1+M)×F number is called the "effective F number." By setting the lateral magnification M to an appropriate range in consideration of the size and arrangement pitch of the pixels 220 on the imaging surface 22S, it is possible to form speckles of a size suitable for detection on the imaging surface 22S according to the type of lesion.

[0075] The feature amount of the speckle pattern is not limited to the speckle contrast, and may be a signal-to-noise ratio (SN ratio). The average size or number density of the speckles may be calculated by image processing, and may be used as the feature amount of the speckle pattern.

[0076] Next, a mode in which the light source device 100 is used as a light source for an endoscope will be described with reference to FIG.

[0077] 20 is a diagram showing a schematic configuration example of a light source device 100 for an endoscope. The light source device 100 shown in the figure has a condenser lens 126 that optically couples the laser light, the coherence of which has been controlled by the polarization control element 12, to a birefringent optical fiber 13. The specific configuration of the endoscope is arbitrary. The endoscope is not limited to a flexible endoscope, and may be a rigid endoscope.

[0078] The following describes in detail the light source device 100. The light source device 100 in FIG.

[0079] The laser light source 10 includes, for example, a blue-violet laser diode (LD) 10V with a peak wavelength λ of 415 nm. The laser light emitted from the blue-violet LD 10V is collimated by a lens 110 and then converged by a condenser lens 112 onto the birefringent element 120 of the polarization control element 12. The laser light transmitted through the birefringent element 120 is converged by a condenser lens 126 onto the incident end face of the birefringent optical fiber 13 and optically coupled to the birefringent optical fiber 13. The laser light propagating through the birefringent optical fiber 13 is eventually emitted from the tip of the endoscope and irradiates the subject, which is biological tissue. In a mode for acquiring a polarized image, the polarization state of the laser light passing through the polarization control element 12 is controlled, making it possible to irradiate the subject with laser light in a desired polarization state. On the other hand, in a mode for observing while illuminating the subject with white light, the emission of the laser light from the laser light source 10 can be stopped. In any of the above observation modes, the subject can be illuminated by white light emitted from the white light source 14.

[0080] The white light source 14 in the example of FIG. 20 has a red LD 14R, a green LD 14G, and a blue LD 14B. The laser light emitted from these LDs 14R, 14G, and 14B is collimated by the lens 142. The laser light emitted from the red LD 14R is collimated, reflected by the dichroic mirror 144R, and then passes through the dichroic mirror 144B to enter the condenser lens 146. The laser light emitted from the green LD 14G is collimated, and passes through the dichroic mirror 144R and the dichroic mirror 144B to enter the condenser lens 146. The laser light emitted from the blue LD 14B is collimated, reflected by the dichroic mirror 144B, and enters the condenser lens 146. In this way, the laser light emitted from the LDs 14R, 14G, and 14B is converged on the rotating diffusion element 148 by the condenser lens 146. The rotating diffusion element 148 reduces the coherence of the laser light to a level where speckles are not formed. The diffusion element 148 is driven by a motor so as to rotate at a speed of, for example, 3600 revolutions per minute or more. The laser light transmitted through the rotating diffusion element 148 is converged by the condenser lens 150 on the incident end face of the optical waveguide 60 such as an optical fiber, and optically coupled to the optical waveguide 60. The laser light (white light) propagating through the optical waveguide 60 is eventually emitted from the tip of the endoscope and irradiates the subject, which is a living tissue.

[0081] In the example of FIG. 20, all of the three primary color components constituting the white light are laser light emitted from an LD (laser diode), but the configuration of the white light source in the embodiment of the present disclosure is not limited to this example. A part or all of the three primary color components constituting the white light may be light emitted from an LED, or may be light emitted from a lamp such as a tungsten lamp. Since the light emitted from an LED or a lamp is incoherent, the rotating diffusion element 148 is not necessary. Alternatively, the phosphor may be excited with an excitation laser light emitted from a blue laser diode or an ultraviolet laser diode to generate white light. The fluorescence emitted by the phosphor is incoherent. Even when the phosphor is excited with an ultraviolet laser light to form white light, all of the visible light components are composed of fluorescence, so the rotating diffusion element 148 is not necessary. Also, even when the phosphor is excited with a blue laser light, the laser light is scattered in the process of passing through the phosphor and mixed with the fluorescence of the yellow component, so the rotating diffusion element 148 is not necessarily required.

[0082] Next, with reference to FIG. 21, a configuration example of an image acquisition device 1000 applied to an endoscope will be described.

[0083] The image acquisition device 1000 shown in Fig. 21 includes a light source device 100, an imaging device 200, and a control device 300 that controls the operations of the light source device 100 and the imaging device 200. The control device 300 has a processor 30 and an image processing device 32, and is connected to a display device 400. The configuration of the light source device 100 may be the same as the configuration described with reference to Fig. 20, for example. The processor 30 is typically a microcontroller equipped with a semiconductor integrated circuit. A program that controls the operation of the processor 30 is stored in a memory (not shown).

[0084] The image acquisition device 1000 of Fig. 21 includes an endoscope 600 connected to a light source device 100 and a control device 300. The endoscope 600 has a birefringent optical fiber 13 that propagates the laser light emitted from the polarization control element 12 of the light source device 100. Similarly, the endoscope 600 has an optical waveguide 60 that propagates the white light emitted from a white light source 14. The optical waveguide 60 and the birefringent optical fiber 13 are optically connected to illumination optical systems 62A and 62B, respectively. A typical example of the optical waveguide 60 is an optical fiber. The white light and the laser light are emitted toward the subject from the illumination optical systems 62A and 62B, respectively.

[0085] The endoscope 600 further includes an imaging device 200 and a signal transmission path 64 that connects the imaging device 200 to the control device 300. The imaging element of the imaging device 200 is a small image sensor that captures an image of a subject and outputs an image signal. The imaging element is provided with a polarizing filter having a polarization transmission axis in a specific direction. This polarizing filter may be, for example, a patterned polarizer shown in FIG. 17. The image signal output from the imaging element is provided to the image processing device 32 of the control device 300 through the signal transmission path 64. The image processing device 32 causes the display device 400 to display an image of the subject based on the image signal. In a mode for observing a speckle pattern, the image processing device 32 may calculate a speckle contrast and a degree of polarization, and superimpose an image that emphasizes a division of a specific area based on the calculated value.

[0086] The processor 30 of the control device 300 sends a control signal for changing the polarization state of the laser light to the polarization control element 12 according to an input by an operator. In response to this control signal, the polarization control element 12 changes the polarization state of the laser light (for example, the polarization direction of linearly polarized light).

[0087] There are various configurations for guiding the light emitted from the light source device 100 to the tip portion of the endoscope 600, and they are not limited to the illustrated example. The white light may be formed by causing the excitation light propagating through the optical waveguide in the endoscope 600 to enter a fluorescent member arranged at the tip portion of the endoscope 600. [Industrial Applicability]

[0088] The light source device of the present disclosure can be used in various applications as a light source for optically acquiring information from a subject to diagnose the condition of the subject. In particular, when the subject is biological tissue, the light source of the present disclosure is useful as a light source for an endoscope because it enables non-invasive acquisition of information from the surface or inside of the biological tissue. In addition, the light source device and image acquisition device of the present disclosure can also be used for applications for acquiring useful information from subjects other than biological tissue, such as industrial endoscopes. [Explanation of symbols]

[0089] 10 laser light source, 12 polarization control element, 14 white light source, 30 processor, 32 image processing device, 50 subject, 100 light source device, 200 imaging device, 300 control device, 400 display device, 500 subject, 600 endoscope

Claims

1. a laser light source that emits linearly polarized laser light having a peak wavelength included in a wavelength range of light that is absorbed or reflected by a portion of the subject; a polarization control element that transmits the laser light emitted from the laser light source and changes a polarization state of the laser light, and switches between an operation mode in which the contrast of a speckle pattern is relatively increased and an operation mode in which the contrast of the speckle pattern is relatively decreased for observation in response to a control signal; a birefringent optical fiber, the cross section of which is perpendicular to the long axis direction along which light propagates, and which includes a fast axis perpendicular to the long axis direction and a slow axis perpendicular to both the long axis direction and the fast axis; a focusing lens that focuses the laser light transmitted through the polarization control element onto an input end of the birefringent optical fiber; Equipped with The polarization control element comprises a birefringent element supported rotatably around the optical axis of the laser light, and an actuator that rotates the birefringent element around the optical axis of the laser light.

2. the polarization control element rotates the birefringent element by the actuator to rotate the polarization axis of the laser light incident on the birefringent optical fiber; The light source device according to claim 1 , wherein the birefringent optical fiber emits the laser light polarized in different directions depending on the rotation of the birefringent element.

3. 3. The light source device according to claim 1, wherein the length of said birefringent optical fiber is Lb×(N+1 / 2), where Lb is a beat length and N is an integer equal to or greater than 0.

4. 4. The light source device according to claim 1, wherein the peak wavelength of the laser light is in the range of 410 nm to 660 nm.

5. The light source device according to claim 1 , wherein the subject is a living tissue.

6. The illumination device further includes an illumination light source that emits illumination light, The illumination source includes: a laser diode that emits excitation laser light; A phosphor that emits fluorescence when irradiated with the excitation laser light; The light source device according to claim 1 , comprising:

7. The light source device according to claim 6 , further comprising an optical fiber for propagating the illumination light emitted from the illumination light source.

8. A light source device according to any one of claims 1 to 7, An imaging device; A control device that controls operations of the light source device and the imaging device; Equipped with The control device drives the actuator in the light source device to change the polarization state of the laser light emitted from the birefringent optical fiber.

9. The image acquisition device according to claim 8 , wherein the imaging device has a polarizing filter that transmits light from the subject.

10. 9. The image acquisition device of claim 8, wherein the imaging device comprises an image sensor provided with a plurality of patterned polarizers each having a different orientation of its polarization transmission axis.

Images