Blood flow measurement device

Abstract

Provided is a blood flow measurement device having excellent measurement accuracy. A blood flow measurement device is provided with: a light source unit that irradiates an object with near-infrared rays; and a light receiving unit that receives scattered light generated by scattering the near-infrared rays emitted from the light source unit by an object, the blood flow measurement device further comprising: a first polarization element that is disposed on the front surface of the light source unit and that includes a layer formed using a liquid crystal compound so as to change the polarization state of the near-infrared rays; and a second polarizing element that is disposed on the front surface of the light-receiving unit and includes a layer formed using a liquid crystal compound so as to change the polarization state of the near-infrared light.

Description

Technical Field

[0001] The present invention relates to a blood flow measuring device. Background Art

[0002] It is known that by measuring the blood flow in the brain, muscles, organs, etc. of a living body, it can be applied to the diagnosis of body functions, health management, information carriers between living bodies and devices, etc. In particular, regarding the brain, the following device has been proposed: a near-infrared irradiation unit and a near-infrared detection unit are provided in a cerebral blood flow measurement device called a headset, changes in blood flow on the surface of the brain are detected, and the detected data is processed by a data processing device to obtain information indicating the activity state of the brain.

[0003] For example, patent document 1 describes a blood flow measuring device comprising a first main body, a second main body and a hinge, wherein the first main body has a first frame including a first bottom surface, a light source for irradiating near-infrared rays from the first bottom surface to the outside of the first frame, and a first light receiving unit for receiving near-infrared rays from the first bottom surface side outside the first frame, the second main body has a second frame including a second bottom surface and a second light receiving unit for receiving near-infrared rays from the second bottom surface side outside the second frame, and the hinge makes the angle between the first bottom surface and the second bottom surface variable and combines the first main body and the second main body.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-054649 Summary of the invention

[0007] Technical issues to be solved by the invention

[0008] In this blood flow measurement device, for example, blood flow information is obtained by detecting near infrared rays that are absorbed by a part of the blood vessel (blood) and scattered. The near infrared rays irradiated for measurement are scattered, so the detected near infrared rays become weaker. In addition, the irradiated near infrared rays are reflected at other than the measurement part, such as the surface of the body, so that the near infrared rays reflected at other than the measurement part are detected as noise components. In the previous blood flow measurement device, since it is difficult to distinguish between the near infrared rays of the detection object and the near infrared rays of the noise component, there is a problem of low SN ratio and poor measurement accuracy.

[0009] An object of the present invention is to solve the problems of the prior art and to provide a blood flow measurement device having excellent measurement accuracy.

[0010] Means for solving technical problems

[0011] In order to solve the problem, the present invention has the following structure.

[0012] [1] A blood flow measurement device comprising: a light source unit for irradiating a target object with near infrared rays; and a light receiving unit for receiving scattered light generated when the near infrared rays emitted from the light source unit are scattered by the target object, the blood flow measurement device further comprising:

[0013] a first polarizing element disposed on the front surface of the light source section and including a layer formed using a liquid crystal compound so as to change the polarization state of near infrared light; and

[0014] The second polarizing element is disposed on the front surface of the light receiving section and includes a layer formed using a liquid crystal compound so as to change the polarization state of near infrared rays.

[0015] [2] The blood flow measurement device according to [1], wherein:

[0016] The layer formed using the liquid crystal compound included in the first polarizing element is a linear polarizer.

[0017] [3] The blood flow measurement device according to [2], wherein:

[0018] The first polarizing element further includes a λ / 4 plate.

[0019] [4] The blood flow measurement device according to [3], wherein:

[0020] The λ / 4 plate exhibits inverse wavelength dispersion.

[0021] [5] The blood flow measurement device according to [1], wherein:

[0022] The first polarizing element includes a first linear polarizer, a phase difference layer, and a second linear polarizer in this order.

[0023] At least one of the first linear polarizer and the second linear polarizer is a layer formed using a liquid crystal compound.

[0024] [6] The blood flow measurement device according to [5], wherein the phase difference plate exhibits reverse wavelength dispersion.

[0025] [7] The blood flow measurement device according to any one of [1] to [6], wherein:

[0026] The layer formed using the liquid crystal compound included in the first polarizing element has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in a plane.

[0027] [8] The blood flow measurement device according to any one of [1] to [7], wherein:

[0028] The liquid crystal compound is a rod-like liquid crystal compound or a disc-like liquid crystal compound.

[0029] Effects of the Invention

[0030] According to the present invention, it is possible to provide a blood flow measurement device having excellent measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a diagram conceptually showing an example of the blood flow measurement device of the present invention.

[0032] Figure 2 This is a conceptual diagram showing a part of an example of the blood flow measurement device of the present invention.

[0033] Figure 3 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0034] Figure 4 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0035] Figure 5 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0036] Figure 6 It is conceptually shown Figure 5 A diagram of a liquid crystal diffraction element included in the first polarizing element of the blood flow measurement device shown.

[0037] Figure 7 yes Figure 6 A top view of the liquid crystal diffraction element is shown.

[0038] Figure 8 It is used to illustrate Figure 6 A conceptual diagram showing the effect of a liquid crystal diffraction element is shown.

[0039] Fig. 9 It is used to illustrate Figure 8 A conceptual diagram showing the effect of a liquid crystal diffraction element is shown.

[0040] Fig.10 It is a schematic representation of Figure 6 FIG. 1 is a diagram showing an example of an exposure device for exposing an alignment film of a liquid crystal diffraction element shown in FIG.

[0041] Fig.11 This is a diagram conceptually showing another example of a liquid crystal diffraction element.

[0042] Fig.12 This is a diagram conceptually showing another example of a liquid crystal diffraction element. DETAILED DESCRIPTION

[0043] Hereinafter, the blood flow measurement device of the present invention will be described in detail based on the preferred embodiments shown in the drawings.

[0044] In the present specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0045] [Blood flow measurement device]

[0046] The blood flow measurement device of the present invention comprises: a light source unit for irradiating a target object with near infrared rays; and a light receiving unit for receiving scattered light generated by the near infrared rays emitted from the light source unit and scattered by the target object. The blood flow measurement device further comprises:

[0047] a first polarizing element disposed on the front surface of the light source section and including a layer formed using a liquid crystal compound so as to change the polarization state of near infrared light; and

[0048] The second polarizing element is disposed on the front surface of the light receiving section and includes a layer formed using a liquid crystal compound so as to change the polarization state of near infrared rays.

[0049] Figure 1 An example of the blood flow measurement device of the present invention is conceptually shown in FIG.

[0050] Figure 1 The blood flow measurement device 100 shown is a device that acquires information on blood flow by irradiating a living body with near-infrared rays and detecting the near-infrared rays reflected by the living body.

[0051] Figure 1 The blood flow measurement device 100 shown includes a control unit 102 , a light source unit 104 , a first polarizing element 106 , a light receiving unit 108 , a second polarizing element 110 , and a housing 112 .

[0052] <Control Department>

[0053] The control unit 102 functions as a supporting substrate for supporting the light source unit 104 and the first polarizing element 106, and the light receiving unit 108 and the second polarizing element 110, and performs measurement control and data processing in the blood flow measurement device 100. That is, the control unit 102 controls the timing and light quantity of the near infrared ray irradiation by the light source unit 104, and performs various processes on the data received by the light receiving unit 108 to calculate the blood flow change amount, pulse rate, etc. The pulse rate is equivalent to the heart rate.

[0054] The control unit 102 has a processor such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor) and a memory, and performs processing by a computer program, firmware, etc. that is executable and deployed on the memory. The control unit 102 can be a dedicated hardware circuit, FPGA (Field Programmable Gate Array), etc. that activates the light source unit 104 and the light receiving unit 108 and performs cooperative processing with each component.

[0055] like Figure 1 As shown, in the control unit 102 , the light source unit 104 and the light receiving unit 108 are arranged at a predetermined distance d apart from each other in the surface direction of the control unit 102 .

[0056] In addition, in the example shown in the figure, the control unit 102 is configured to have a structure that also serves as a supporting substrate for supporting the light source unit 104 and the first polarization element 106, and the light receiving unit 108 and the second polarization element 110, but is not limited to this. The supporting substrate for supporting the light source unit 104 and the first polarization element 106, and the light receiving unit 108 and the second polarization element 110 and the control unit 102 may also be configured as different components.

[0057] <Light source>

[0058] The light source unit 104 is used to irradiate near-infrared rays to the living body S. The light source unit 104 includes a near-infrared light source for irradiating near-infrared rays. The near-infrared light irradiated by the light source unit 104 preferably has a wavelength of 650 nm to 1400 nm.

[0059] As the near-infrared light source, for example, LED (Light Emitting Diodes), LD (Laser Diodes), etc. can be used.

[0060] The light source unit 104 basically radiates non-polarized near-infrared light. When the near-infrared light source has a linear polarizer and radiates linearly polarized near-infrared light, the linear polarizer is regarded as a linear polarizer included in the first polarizing element in the present invention.

[0061] Furthermore, the light source unit 104 can irradiate two or more near infrared rays with different wavelengths. For example, the light source unit 104 can irradiate near infrared rays with wavelengths of 780 nm and 830 nm. As such a light source unit 104, a structure having a plurality of light sources irradiating near infrared rays of different wavelengths can be provided, or a structure irradiating near infrared rays of different wavelengths by combining a light source irradiating near infrared rays of a wide band of wavelengths and a filter transmitting a specific wavelength region can be provided.

[0062] <Light receiving unit>

[0063] The light receiving unit 108 receives (detects) the near infrared rays reflected in the body of the living body S.

[0064] The light receiving unit 108 includes, for example, a photoelectric conversion element such as a photodiode or a phototransistor that outputs a current according to the amount of near-infrared light received, an amplifier circuit that amplifies the output current of the photoelectric conversion element, and an AD (Analog-to-digital) converter.

[0065] The light receiving unit 108 converts the received light into a voltage signal and outputs the voltage signal as a light detection signal.

[0066] The size of the light receiving unit 108 is not limited as long as it can receive (detect) near infrared rays reflected in the living body S, but it is preferred to increase the area and the reading angle to obtain higher detection sensitivity.

[0067] Furthermore, when the light source unit 104 irradiates near infrared rays of two or more different wavelengths, it is preferable that the light receiving unit 108 receives (detects) the near infrared rays for each wavelength. In this case, the light receiving unit 108 may be configured to include a combination of a filter and a photoelectric conversion element that transmits one wavelength region and shields another wavelength region, and a combination of a filter and a photoelectric conversion element that transmits another wavelength region and shields one wavelength region.

[0068] <First polarizing element>

[0069] The first polarizing element 106 is an element that is disposed on the front surface of the light source unit 104, that is, the irradiation surface, and changes the polarization state of the near infrared light emitted from the light source unit 104. The first polarizing element 106 includes a layer formed using a liquid crystal compound.

[0070] The first polarizing element 106 converts the polarization state of the near infrared light emitted from the light source unit 104 into linearly polarized light or circularly polarized light of a desired polarization state and makes the light incident on the body of the living body S.

[0071] The structure of the first polarizing element 106 will be described in detail later.

[0072] <Second polarizing element>

[0073] The second polarizing element 110 is disposed on the front surface, that is, the light receiving surface, of the light receiving unit 108 and changes the polarization state of near infrared light that is scattered in the body S and enters the light receiving unit 108. The second polarizing element 110 includes a layer formed using a liquid crystal compound.

[0074] The second polarization element 110 converts the polarization state of near infrared light scattered inside the living body S into linear polarized light or circular polarized light of a certain polarization state and makes the light incident on the light receiving unit 108 .

[0075] The structure of the second polarizing element 110 will be described in detail later.

[0076] In addition to the above-mentioned components, the blood flow measurement device 100 may also include a housing 112 for accommodating the components, a holding mechanism such as a belt for wearing on the head, wrist, leg, etc. of the user (living body S), etc. The blood flow measurement device 100 is worn on the head, wrist, leg, etc. of the user (living body S) by the holding mechanism, such that the near infrared light from the light source unit 104 is irradiated into the living body S with the irradiation surface facing the living body S, and the light receiving unit 110 is received near infrared light scattered in the living body S with the light receiving surface facing the living body S.

[0077] The operation of the blood flow measurement device 100 will be described.

[0078] The blood flow measurement device 100 worn on the head, wrist, leg, etc. of a living body S irradiates near infrared rays from a light source unit 104. The near infrared rays irradiated from the light source unit 104 are incident on the first polarizing element 106, and the polarization state is changed by the first polarizing element 106 and is incident on the living body S. The irradiated near infrared rays are partially absorbed and scattered, for example, near the cerebral cortex of the brain, near the blood vessels such as the wrist. A part of the scattered near infrared rays is incident on the second polarizing element 110 toward the light receiving unit 108 side. The second polarizing element 110 changes the polarization state of the incident near infrared rays and is incident on the light receiving unit 108. The light receiving unit 108 receives the near infrared rays, converts them into electrical signals and outputs them. The electrical signals (data) output from the light receiving unit 108 are sent to the control unit 102. The control unit 102 performs various processes on the received data to calculate the blood flow change amount, pulse rate, etc.

[0079] Here, for example, in the cerebral cortex of the brain, the blood flow rate changes depending on the activity state of the brain. As a result, the amount of hemoglobin bound to oxygen and the amount of hemoglobin not bound to oxygen in the blood in the cerebral cortex change according to the activity state of the brain. In addition, due to the change in the amount of hemoglobin and the change in the amount of oxygen, the absorption characteristics or scattering characteristics of near-infrared rays near the cerebral cortex change. Therefore, the amount of near-infrared light received by the light receiving unit 108 changes. Therefore, the control unit 102 can obtain information on the blood flow near the cerebral cortex, etc. (blood flow change amount, pulse rate, etc.) from the data on the amount of near-infrared light received by the light receiving unit 108.

[0080] Furthermore, changes in the absorption characteristics or scattering characteristics of near-infrared rays caused by changes in the amount of hemoglobin and changes in the amount of oxygen, etc., differ according to the wavelength. Therefore, for example, in the cerebral cortex of the brain, changes in the amount of near-infrared rays received by the light receiving unit 108 corresponding to the activity state of the brain differ for each wavelength. That is, the ratio of the amount of light of each wavelength received by the light receiving unit 108 changes according to the activity state of the brain. Therefore, as a structure in which the light source unit 104 irradiates near-infrared rays of two or more wavelengths different from each other, a structure is set in which the light receiving unit 108 receives each wavelength and obtains data on the amount of light of each wavelength, thereby being able to obtain blood flow information (blood flow change, pulse rate, etc.) from the data on the ratio of the amount of light received at two (or more than three) wavelengths.

[0081] Here, in a blood flow measurement device that irradiates near infrared rays into a living body and receives near infrared rays scattered near blood vessels to obtain blood flow information, the amount of near infrared rays received by the light receiving unit is about 1 / 100 to 1 / 1000 of the amount of near infrared rays irradiated, which becomes weak. In addition, the near infrared rays irradiated from the light source unit are also reflected in addition to the measurement parts such as the surface of the body and the interface of the organ. If the near infrared rays reflected outside the measurement part are received by the light receiving unit, it will become an unnecessary noise component. In the previous blood flow measurement device, it is difficult to distinguish between the near infrared rays of the detection object and the near infrared rays of the noise component, so there is a problem that the SN ratio becomes low and the measurement accuracy is poor.

[0082] In contrast, the blood flow measurement device 100 of the present invention has a first polarizing element 106 on the front surface of the light source section 104 that includes a layer formed using a liquid crystal compound and that changes the polarization state of the near-infrared light, and has a second polarizing element 110 on the front surface of the light receiving section 108 that includes a layer formed using a liquid crystal compound and that changes the polarization state of the near-infrared light.

[0083] The first polarizing element 106 changes the near infrared light emitted from the light source section 104 into a prescribed linear polarized light or circular polarized light. A portion of the polarized light changed by the first polarizing element 106 enters the living body S and is scattered near the blood vessels. At this time, the near infrared light of the measurement object is depolarized due to the scattering, and thus becomes a polarization state different from the prescribed polarization state, such as unpolarized light. A portion of the scattered near infrared light of the measurement object enters the second polarizing element 110. The second polarizing element 110 changes the near infrared light of the measurement object, which is unpolarized light, into a prescribed linear polarized light or circular polarized light. The polarized light changed by the second polarizing element 110, i.e., the near infrared light of the measurement object, is received by the light receiving section 108.

[0084] On the other hand, part of the polarized light changed to a predetermined polarization state by the first polarizing element 106 is reflected outside the measurement portion such as the surface of the body and the interface of the organ. Since the polarized light is not eliminated by reflection, the polarized light reflected outside the measurement portion becomes a certain polarization state. If the near infrared light reflected outside the measurement portion travels toward the light receiving unit 108, it is incident on the second polarizing element 110 disposed on the front surface of the light receiving unit 108. As described later, the second polarizing element 110 has a structure for shielding the polarized light reflected outside the measurement portion, that is, the near infrared light that becomes a noise component, so that the amount of light received in the light receiving unit 108 can be reduced.

[0085] As described above, the blood flow measurement device 100 of the present invention can distinguish the near infrared rays of the detection target from the near infrared rays of the noise component and cut off the noise component, thereby improving the SN ratio and thus improving the measurement accuracy.

[0086] Here, in the blood flow measurement device 100 of the present invention, the first polarizing element 106 and the second polarizing element 110 include a layer formed using a liquid crystal compound. In the first polarizing element 106 and the second polarizing element 110, the layer formed using a liquid crystal compound is a layer for changing the polarization state of incident near-infrared light. Specifically, as described later, the layer formed using a liquid crystal compound is a linear polarizer or a liquid crystal diffraction element. The layer formed using a liquid crystal compound can be set as a layer that efficiently changes the polarization state of near-infrared light. In addition, in the case of a linear polarizer, it can be set as an absorption type linear polarizer that does not reflect near-infrared light, thereby suppressing the generation of reflected light that may become noise.

[0087] Therefore, the blood flow measurement device 100 of the present invention is configured such that the first polarizing element 106 and the second polarizing element 110 include a layer formed using a liquid crystal compound, and can appropriately play the role of cutting off the noise component by shielding the reflected light of the near-infrared light whose polarization state is changed by the first polarizing element 106 through the second polarizing element 110.

[0088] The distance d from the light source unit 104 to the light receiving unit 108 is not particularly limited. The depth from the surface of the living body S at which blood flow information is obtained varies depending on the distance d, so the distance d may be set according to the depth at which blood flow information is to be obtained.

[0089] Hereinafter, the structures of the first polarizing element 106 and the second polarizing element 110 will be described.

[0090] Figure 2 This is a conceptual diagram showing a part of an example of the blood flow measurement device of the present invention.

[0091] Figure 2The blood flow measurement device 100a shown in the figure includes a light source unit 104, a first polarizing element 106a, a light receiving unit 108, and a second polarizing element 110a. Figure 2 In the blood flow measurement device 100a shown in FIG. 1 , the control unit and the housing are omitted. In the blood flow measurement device 100a, the light source unit 104 and the light receiving unit 108 have the same structure as in FIG. Figure 1 Since the light source unit 104 and the light receiving unit 108 are the same as those described in the blood flow measurement device 100 shown in FIG. 1 , their description is omitted. Figure 3 to Figure 5 Same.

[0092] exist Figure 2 In the blood flow measurement device 100a shown in the figure, the first polarizing element 106a has a linear polarizer 120 as a layer formed using a liquid crystal compound. And, as a preferred embodiment, the second polarizing element 110a has a linear polarizer 122 as a layer formed using a liquid crystal compound. The linear polarizer 120 of the first polarizing element 106a and the linear polarizer 122 of the second polarizing element 110a are arranged so that the transmission axes are substantially orthogonal. For example, in Figure 2 In the example shown, it is sufficient to set the transmission axis of the linear polarizer 120 possessed by the first polarization element 106a to transmit linear polarized light vibrating in the left-right direction in the figure, and the transmission axis of the linear polarizer 122 possessed by the second polarization element 110a to transmit linear polarized light vibrating in the direction perpendicular to the paper surface in the figure.

[0093] In this blood flow measurement device 100a, when near infrared light is irradiated from the light source unit 104, the linear polarizer 120 of the first polarizing element 106a changes the near infrared light into, for example, linear polarized light vibrating in the left-right direction in the figure. The near infrared light that has become linearly polarized light by the linear polarizer 120 (first polarizing element 106a) enters the living body S. The near infrared light irradiated into the living body S is partially absorbed and scattered near the blood vessels. At this time, the near infrared light is depolarized from linearly polarized light and becomes non-polarized light. A part of the scattered near infrared light enters the second polarizing element 110a toward the light receiving unit 108 side. The linear polarizer 122 of the second polarizing element 110a transmits the incident near infrared light as linearly polarized light vibrating in a direction perpendicular to the paper surface. The light receiving unit 108 receives the linearly polarized near infrared light, converts it into an electrical signal, and outputs it to the control unit. The control unit performs various processes on the received data to calculate the blood flow change amount, pulse rate, etc.

[0094] On the other hand, part of the near infrared light converted into linear polarized light by the linear polarizer 120 (first polarizing element 106a) is reflected outside the measurement part such as the surface of the body and the interface of the organ. At this time, since the polarized light is not eliminated, it enters the linear polarizer 122 (second polarizing element 110a) in the state of linear polarized light vibrating in the left and right directions in the figure. The linear polarizer 122 of the second polarizing element 110a has a transmission axis in a direction perpendicular to the paper surface, so it does not transmit but absorbs the linear polarized light vibrating in the left and right directions in the figure. As a result, the linear polarized light reflected outside the measurement part, that is, the near infrared light that becomes a noise component, can be shielded, thereby suppressing the reception of the noise component by the light receiving unit 108.

[0095] Furthermore, as described above, the linear polarizers 120 and 122 can have a high degree of polarization for near infrared light by using liquid crystal compounds. Furthermore, since the linear polarizers can be absorptive linear polarizers that do not reflect near infrared light, the generation of reflected light that may become noise can be suppressed.

[0096] There is no particular limitation on the directions of the transmission axes of the linear polarizer 120 and the linear polarizer 122 as long as the transmission axis of the linear polarizer 120 is substantially orthogonal to the transmission axis of the linear polarizer 122. The transmission axis of the linear polarizer 120 of the first polarizing element 106a is preferably set in a direction in which the transmitted linearly polarized light becomes p-polarized light with respect to the skin surface of the living body S. This can suppress reflection on the skin surface.

[0097] Furthermore, in the blood flow measurement device 100a, it is preferable that the near infrared rays emitted from the light source unit 104 are incident in an azimuth direction toward the light receiving unit 108 at an angle relative to the skin surface of the living body S. Thus, the amount of near infrared rays scattered near the blood vessels in the light receiving unit 108 can be increased, so that the SN ratio can be improved, thereby improving the measurement accuracy.

[0098] There is no particular limitation on the method of making the near infrared rays emitted from the light source unit 104 tilt relative to the skin surface of the living body S. The light source unit 104 may be arranged on the control unit 102 (the main surface of the support substrate) so that the emission direction of the light source unit 104 is tilted relative to the control unit 102 (the support substrate). Alternatively, the light source unit 104 may have a diffraction element or the like, or the first polarizing element 106a may have a diffraction element.

[0099] The linear polarizer formed using a liquid crystal compound will be described in detail later.

[0100] Figure 3 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0101] Figure 3 The blood flow measurement device 100b shown in the figure includes a light source unit 104, a first polarizing element 106b, a light receiving unit 108, and a second polarizing element 110b. Figure 3 In the blood flow measurement device 100b shown, illustration of a control unit, a housing, and the like are omitted.

[0102] exist Figure 3 In the blood flow measurement device 100b shown, the first polarizing element 106b has a linear polarizer 120 as a layer formed using a liquid crystal compound. Furthermore, the first polarizing element 106b has a λ / 4 plate 124 on the side opposite to the light source section 104 side of the linear polarizer 120. Furthermore, as a preferred embodiment, the second polarizing element 110b has a linear polarizer 122 as a layer formed using a liquid crystal compound. Furthermore, the second polarizing element 110b has a λ / 4 plate 125 on the side opposite to the light receiving section 108 of the linear polarizer 122. That is, the first polarizing element 106b and the second polarizing element 110b include a circular polarizing plate composed of a linear polarizer and a λ / 4 plate.

[0103] The λ / 4 plate 124 of the first polarizing element 106b is arranged to convert the near infrared light converted into linear polarized light by the linear polarizer 120 into circular polarized light. That is, the λ / 4 plate 124 is arranged so that the slow axis becomes approximately 45° (or -45°) with respect to the transmission axis of the linear polarizer 120. Therefore, the first polarizing element 106b converts the near infrared light emitted from the light source unit 104 into circular polarized light.

[0104] The λ / 4 plate 125 of the second polarizing element 110b converts circularly polarized light incident from the λ / 4 plate 125 side into linearly polarized light. Furthermore, the λ / 4 plate 125 is configured so that the slow axis becomes 45° (or -45°) relative to the transmission axis of the linear polarizer 122. Such a second polarizing element 110b transmits one of the right-handed circularly polarized light and the left-handed circularly polarized light, and shields the other circularly polarized light. Specifically, the second polarizing element 110b transmits circularly polarized light of the same rotation direction as the circularly polarized light emitted from the first polarizing element 106b, and shields circularly polarized light of the opposite rotation direction. Therefore, for example, the second polarizing element 110b is configured as follows: the direction of the transmission axis of the linear polarizer 122 is the same as the direction of the transmission axis of the linear polarizer 120 of the first polarizing element 106b, and the direction of the slow axis of the λ / 4 plate 125 is the same as the direction of the slow axis of the λ / 4 plate 124 of the first polarizing element 106b. Alternatively, the second polarizing element 110b is configured as follows: the direction of the transmission axis of the linear polarizer 122 is orthogonal to the direction of the transmission axis of the linear polarizer 120 of the first polarizing element 106b, and the direction of the slow axis of the λ / 4 plate 125 is orthogonal to the direction of the slow axis of the λ / 4 plate 124 of the first polarizing element 106b. Hereinafter, the configuration of the second polarizing element 110b as follows is described as an example: the direction of the transmission axis of the linear polarizer 122 is the same as the direction of the transmission axis of the linear polarizer 120 of the first polarizing element 106b, and the direction of the slow axis of the λ / 4 plate 125 is the same as the direction of the slow axis of the λ / 4 plate 124 of the first polarizing element 106b.

[0105] In this blood flow measurement device 100b, when near infrared light is irradiated from the light source section 104, the linear polarizer 120 of the first polarizing element 106b changes the near infrared light into, for example, linear polarized light vibrating in the left-right direction in the figure. The near infrared light that has become linearly polarized light by the linear polarizer 120 is incident on the λ / 4 plate 124 and is converted into circularly polarized light. For example, it is assumed that the near infrared light is converted into right-handed circularly polarized light by the λ / 4 plate 124. That is, the first polarizing element 106b converts the incident near infrared light into circularly polarized light. The near infrared light converted into right-handed circularly polarized light is incident on the living body S. The near infrared light irradiated into the living body S is partially absorbed and scattered near the blood vessels. At this time, the near infrared light is depolarized from right-handed circularly polarized light to become unpolarized light. A portion of the scattered near infrared light is incident on the second polarizing element 110b toward the light receiving section 108 side. The near infrared ray is incident on the λ / 4 plate 125 of the second polarizing element 110b, but since it is non-polarized light, it is incident on the linear polarizer 122 in a non-polarized state. The linear polarizer 122 sets the incident near infrared ray as linear polarized light vibrating in the left and right directions in the figure, for example, and transmits it. The light receiving unit 108 receives the linearly polarized near infrared ray, converts it into an electrical signal, and outputs it to the control unit. The control unit performs various processing on the received data to calculate the blood flow change amount, pulse rate, etc.

[0106] On the other hand, part of the near infrared light converted into right-handed circularly polarized light by the first polarizing element 106b (linear polarizer 120 and λ / 4 plate 124) is reflected outside the measurement part such as the surface of the body and the interface of the organ. At this time, the polarized light is not eliminated, and the circularly polarized light rotates in the opposite direction due to reflection, so it becomes left-handed circularly polarized light and enters the λ / 4 plate 125 of the second polarizing element 110b. The slow axis of the λ / 4 plate 125 is in the same direction as the slow axis of the λ / 4 plate 124 of the first polarizing element 106b, so the left-handed circularly polarized light incident on the λ / 4 plate 125 is converted into linearly polarized light vibrating in a direction perpendicular to the paper surface in the figure. This linearly polarized light enters the linear polarizer 122. The linear polarizer 122 has a transmission axis in the left-right direction in the figure, so it does not transmit but absorbs the linearly polarized light vibrating in the direction perpendicular to the paper surface. This can shield circularly polarized light reflected outside the measurement portion, that is, near infrared light that becomes a noise component, and thereby suppress the light receiving unit 108 from receiving the noise component.

[0107] In addition, circularly polarized light reflected outside the measuring part can also be shielded when the second polarization element 110b is configured as follows: the direction of the transmission axis of the linear polarizer 122 is orthogonal to the direction of the transmission axis of the linear polarizer 120 of the first polarization element 106b and the direction of the slow axis of the λ / 4 plate 125 is orthogonal to the direction of the slow axis of the λ / 4 plate 124 of the first polarization element 106b.

[0108] Specifically, a portion of the near infrared light converted into right circular polarized light by the first polarizing element 106b is reflected outside the measurement portion such as the surface of the body and the interface of the organ to become left circular polarized light, and enters the λ / 4 plate 125 of the second polarizing element 110b. The slow axis of the λ / 4 plate 125 is orthogonal to the slow axis of the λ / 4 plate 124 of the first polarizing element 106b, so the left circular polarized light incident on the λ / 4 plate 125 is converted into linear polarized light vibrating in the left-right direction in the figure. This linear polarized light enters the linear polarizer 122. In the figure, the linear polarizer 122 has a transmission axis in a direction perpendicular to the paper surface, so it does not transmit but absorbs the linear polarized light vibrating in the left-right direction. As a result, the circularly polarized light reflected outside the measurement portion, that is, the near infrared light that becomes a noise component, can be shielded, so that the noise component received by the light receiving unit 108 can be suppressed.

[0109] Here, circularly polarized light has higher biological transmittance than unpolarized light. Therefore, in the blood flow measurement device 100b, a structure using circular polarizers as the first polarizing element 106b and the second polarizing element 110b can be set to allow circularly polarized light to enter the biological body, and the amount of light scattered near the blood vessels can be further increased, so the SN ratio can be further improved.

[0110] The λ / 4 plate will be described in detail later.

[0111] exist Figure 2 and Figure 3 In the example shown, the first polarizing element and the second polarizing element have a function of changing the polarization state of the near infrared light, but may also have a function of further controlling the direction of the near infrared light.

[0112] use Figure 4-5 , an example in which the first polarizing element and the second polarizing element also have a function of controlling the direction of near-infrared rays is described.

[0113] Figure 4 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0114] Figure 4 The blood flow measurement device 100c shown in the figure includes a light source unit 104, a first polarizing element 106c, a light receiving unit 108, and a second polarizing element 110c. Figure 4 In the blood flow measurement device 100c shown, illustration of a control unit, a housing, and the like are omitted.

[0115] exist Figure 4In the blood flow measurement device 100c shown, the first polarizing element 106c includes a first linear polarizer 120a, a phase difference layer 126, and a second linear polarizer 120b in order from the light source unit 104 side. The first linear polarizer 120a and the second linear polarizer 120b correspond to the layers formed using the liquid crystal compound of the present invention. In addition, as a preferred embodiment, the second polarizing element 110c includes a first linear polarizer 122a, a phase difference layer 127, and a second linear polarizer 122b in order from the light receiving unit 108 side. The first linear polarizer 122a and the second linear polarizer 122b correspond to the layers formed using the liquid crystal compound of the present invention.

[0116] In the first polarizing element 106c, the first linear polarizer 120a and the second linear polarizer 120b are arranged so that their transmission axes are substantially orthogonal. In the following description, it is assumed that the first linear polarizer 120a has a transmission axis in the left-right direction in the figure, and the second linear polarizer 120b has a transmission axis in a direction perpendicular to the paper surface.

[0117] The retardation layer 126 is configured so that the near infrared light of the wavelength emitted from the light source unit 104, which is incident from a direction inclined at a certain angle with respect to the main surface of the retardation layer 126, functions as a λ / 2 plate. The retardation layer 126 is arranged so that the slow axis is about 45° (or -45°) with respect to the transmission axis of the first linear polarizer 120a.

[0118] Similarly, in the second polarizing element 110c, the first linear polarizer 122a and the second linear polarizer 122b are arranged so that the transmission axes are substantially orthogonal. In the following description, it is described as follows: the first linear polarizer 122a has a transmission axis in the left-right direction in the figure, and the second linear polarizer 122b has a transmission axis in a direction perpendicular to the paper surface.

[0119] The retardation layer 127 is configured to function as a λ / 2 plate for near infrared light of a wavelength emitted from the light source unit 104 incident from a direction inclined at a certain angle to the main surface of the retardation layer 127. The retardation layer 127 is arranged so that the slow axis is approximately 45° (or -45°) with respect to the transmission axis of the first linear polarizer 122a.

[0120] In this blood flow measurement device 100c, when near infrared light is irradiated from the light source unit 104, the first linear polarizer 120a of the first polarizing element 106c changes the near infrared light into, for example, linear polarized light vibrating in the left-right direction in the figure. The near infrared light that has become linear polarized light by the first linear polarizer 120a is incident on the phase difference layer 126. The phase difference layer 126 gives a phase difference to the incident linear polarized near infrared light. Here, the linear polarized light incident on the phase difference layer 126 from a direction inclined at a certain angle α is given a phase difference of λ / 2, and the vibration direction is rotated by 90°. That is, the linear polarized light incident on the phase difference layer 126 is changed into linear polarized light vibrating in a direction perpendicular to the paper surface in the figure. On the other hand, the phase difference of the linear polarized light incident from a direction inclined at an angle deviating from the angle α and from a direction perpendicular to the main surface deviates from λ / 2, so the rotation amount of the vibration direction deviates from 90°. The linear polarized light whose vibration direction is rotated in the phase difference layer 126 is incident on the second linear polarizer 120b. The second linear polarizer 120b has a transmission axis in a direction perpendicular to the paper surface, so the linear polarized light incident from the direction of the tilt angle α is transmitted through the second linear polarizer 120b, and the linear polarized light incident from the direction of the tilt angle deviating from the angle α and from the direction perpendicular to the main surface is shielded by the second linear polarizer 120b. Therefore, the traveling direction of the near infrared light that has passed through the first polarizing element 106c becomes the direction of the tilt angle α.

[0121] As described above, the first polarization element 106 c can change the polarization state of the near-infrared light emitted from the light source unit 104 and control the traveling direction of the near-infrared light.

[0122] The near infrared light converted into linear polarized light enters the living body S. The near infrared light irradiated into the living body S is partially absorbed and scattered near the blood vessels. At this time, the near infrared light is depolarized from linear polarized light to non-polarized light. A part of the scattered near infrared light enters the second polarizing element 110c toward the light receiving unit 108 side. The second linear polarizer 122b of the second polarizing element 110c converts the incident near infrared light into linear polarized light vibrating in a direction perpendicular to the paper surface. The near infrared light that becomes linear polarized light after passing through the second linear polarizer 122b enters the phase difference layer 126. The phase difference layer 126 gives a phase difference to the incident linear polarized near infrared light. Here, the linear polarized light that enters the phase difference layer 126 from a direction inclined at a certain angle β is given a phase difference of λ / 2, and the vibration direction is rotated by 90°. That is, the linear polarized light incident on the phase difference layer 126 is changed into linear polarized light vibrating in the left and right directions in the figure. On the other hand, the phase difference of the linear polarized light incident from the direction tilted from the angle β and from the direction perpendicular to the main surface deviates from λ / 2, so the rotation amount of the vibration direction deviates from 90°. The linear polarized light whose vibration direction is rotated in the phase difference layer 126 is incident on the first linear polarizer 122a. The first linear polarizer 122a has a transmission axis in the left-right direction in the figure, so the linear polarized light incident from the direction tilted from the angle β is transmitted by the first linear polarizer 122a, and the linear polarized light incident from the direction tilted from the angle β and from the direction perpendicular to the main surface is shielded by the first linear polarizer 122a. Therefore, the traveling direction of the near infrared light passing through the second polarizing element 110c becomes the direction tilted from the angle β. The near infrared light passing through the second polarizing element 110c is incident on the light receiving unit 108. The light receiving unit 108 receives the near infrared light of the linear polarized light, converts it into an electrical signal and outputs it to the control unit. The control unit performs various processes on the received data to calculate the blood flow change amount, pulse rate, etc.

[0123] On the other hand, part of the near infrared light converted into linear polarized light by the first polarizing element 106c is reflected outside the measurement part such as the surface of the body and the interface of the organ. At this time, since the polarization is not eliminated, in the figure, it is incident on the second linear polarizer 122b of the second polarizing element 110c in the state of linear polarized light vibrating in the direction perpendicular to the paper surface. The second linear polarizer 122b of the second polarizing element 110c has a transmission axis in the direction perpendicular to the paper surface, so it transmits the linear polarized light vibrating in the direction perpendicular to the paper surface. The near infrared light that becomes linear polarized light by passing through the second linear polarizer 122b is incident on the phase difference layer 126. The phase difference layer 126 gives a phase difference to the incident linear polarized near infrared light. Here, the linear polarized light incident on the phase difference layer 126 from a direction tilted at a certain angle β is given a phase difference of λ / 2, and the vibration direction is rotated by 90°, but the light reflected outside the measurement portion is incident from a direction tilted at an angle deviating from the angle β, so the phase difference based on the phase difference layer deviates from λ / 2, and the rotation amount of the vibration direction deviates from 90°. The linear polarized light whose vibration direction is rotated in the phase difference layer 126 is incident on the first linear polarizer 122a. The first linear polarizer 122a has a transmission axis in the left-right direction, so the linear polarized light incident from a direction tilted at an angle deviating from the angle β is shielded by the first linear polarizer 122a.

[0124] This can shield the linearly polarized light reflected outside the measurement portion, that is, the near infrared light that becomes a noise component, and thereby suppress the light receiving unit 108 from receiving the noise component.

[0125] The first polarization element 106c controls the traveling direction of the near-infrared light to be a direction toward the light receiving part 108 (the second polarization element 110c) which is inclined at a specified angle relative to the perpendicular line of the main surface of the first polarization element 106c. This increases the amount of near-infrared light that is irradiated into the living body S and scattered near the blood vessels and that is directed toward the light receiving part 108 (the second polarization element 110c), thereby further improving the SN ratio.

[0126] In addition, Figure 4 In the example shown, the first polarizing element 106c and the second polarizing element 110c are configured to have a first linear polarizer, a phase difference layer, and a second linear polarizer in this order, but the present invention is not limited thereto, and any one of the first polarizing element 106c and the second polarizing element 110c may be configured to have a first linear polarizer, a phase difference layer, and a second linear polarizer in this order. In this case, the other polarizing element may be configured to be, for example, a linear polarizer, and the linear polarized light reflected outside the measurement portion may be shielded by the second polarizing element.

[0127] And, in Figure 4In the example shown, in the first polarizing element 106c and the second polarizing element 110c, the first linear polarizer and the second linear polarizer are configured so that the transmission axes are orthogonal, but they may be configured so that the transmission axes are parallel. In the case where the transmission axes of the first linear polarizer and the second linear polarizer are parallel, for example, if the direction in which the refractive index of the retardation layer is 0, that is, the direction of the optical axis of the retardation layer is inclined within a range of 20 to 60 degrees relative to the main surface, the amount of light directed to the light receiving unit 108 (the second polarizing element 110c) can be increased, and thus the SN ratio can be further improved, which is preferred.

[0128] And, in Figure 4 In the example shown, in the first polarizing element 106c and / or the second polarizing element 110c, the second linear polarizer may be configured to have an absorption axis in a direction perpendicular to the surface. In this case, the absorption axes of the first linear polarizer and the second linear polarizer can be orthogonal or parallel only to near-infrared rays incident from an oblique direction. As a result, the range of angles at which oblique reflected light from the measurement portion is transmitted can be reduced, and as a result, the axis angle relationship between the polarizer and the phase difference layer can be set such that the transmitted light immediately decreases when the angle is slightly changed from the angle at which the transmission is the highest. As a result, weighted measurement can be performed using reflected light at a desired angle, so that measurement with less noise can be performed.

[0129] Figure 5 This is a conceptual diagram showing a part of another example of the blood flow measurement device of the present invention.

[0130] Figure 5 The blood flow measurement device 100d shown in the figure includes a light source unit 104, a first polarizing element 106d, a light receiving unit 108, and a second polarizing element 110d. Figure 5 In the blood flow measurement device 100d shown, illustration of a control unit, a housing, and the like are omitted.

[0131] exist Figure 5 In the blood flow measurement device 100d shown, the first polarizing element 106d includes an optically anisotropic layer as a layer formed using a liquid crystal compound, and the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane. In addition, as a preferred embodiment, the second polarizing element 110d includes an optically anisotropic layer as a layer formed using a liquid crystal compound, and the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane.

[0132] The optically anisotropic layer having a liquid crystal orientation pattern is a liquid crystal diffraction element that diffracts incident near-infrared light, and the liquid crystal orientation pattern is derived from the direction of the optical axis of the liquid crystal compound that changes while continuously rotating in at least one direction in the plane. In addition, the liquid crystal diffraction element diffracts the right-handed circularly polarized light component and the left-handed circularly polarized light component of the incident near-infrared light in different directions.

[0133] The liquid crystal diffraction element will be described in detail later.

[0134] In this blood flow measurement device 100d, when near infrared rays are irradiated from the light source unit 104, the liquid crystal diffraction element 128 of the first polarizing element 106d diffracts, for example, right-handed circularly polarized light components of the near infrared rays in a direction that is oriented toward the light receiving unit 108 (the second polarizing element 110d) in the azimuth direction and is inclined at a predetermined angle relative to the perpendicular line of the main surface of the liquid crystal diffraction element 128. The near infrared rays that have become right-handed circularly polarized light by the liquid crystal diffraction element 128 (the first polarizing element 106d) are incident on the living body S. The near infrared rays irradiated into the living body S are partially absorbed and scattered near the blood vessels. At this time, the near infrared rays are depolarized from the right-handed circularly polarized light and become non-polarized light. A portion of the scattered near infrared rays is incident on the second polarizing element 110d toward the light receiving unit 108 side. The liquid crystal diffraction element 128 of the second polarizing element 110d diffracts and transmits the right-handed circularly polarized light component or the left-handed circularly polarized light component of the near-infrared light without polarization incident from an oblique direction toward the light receiving unit 108. The light receiving unit 108 receives the near-infrared light of circular polarization, converts it into an electrical signal, and outputs it to the control unit. The control unit performs various processing on the received data to calculate the blood flow change amount, pulse rate, etc.

[0135] On the other hand, the first polarizing element 106d causes a part of the near infrared light that changes the right-handed circularly polarized light to be reflected outside the measurement part such as the surface of the body and the interface of the organ. At this time, the polarized light is not eliminated, and the circularly polarized light rotates in the opposite direction due to the reflection, so it becomes left-handed circularly polarized light and is incident on the liquid crystal diffraction element 128 of the second polarizing element 110d. The liquid crystal diffraction element 128 does not diffract the incident left-handed circularly polarized light in the direction of the light receiving unit 108, but diffracts the right-handed circularly polarized light generated as a result of depolarization in the measurement part in the direction of the light receiving unit 108. Thus, the circularly polarized light reflected outside the measurement part, that is, the near infrared light that becomes the noise component, can be shielded, so that the noise component received by the light receiving unit 108 can be suppressed.

[0136] In addition, Figure 5In the example shown, the first polarizing element 106d and the second polarizing element 110d are configured to have a liquid crystal diffraction element, but the present invention is not limited thereto, and any one of the first polarizing element 106d and the second polarizing element 110d may be configured to have a liquid crystal diffraction element. For example, when the first polarizing element is a liquid crystal diffraction element, the second polarizing element may be configured to have a circular polarizing plate (linear polarizer + λ / 4 plate), and may be configured to shield circularly polarized light reflected outside the measurement portion.

[0137] <Linear Polarizer>

[0138] The linear polarizers 120, 120a, 120b, 122, 122a, and 122b are layers formed using liquid crystal compounds and are absorption-type polarizers that absorb linearly polarized light vibrating along an absorption axis direction of incident light and transmit linearly polarized light vibrating along a transmission axis direction.

[0139] The liquid crystal compound may be a rod-like liquid crystal compound or a disc-like liquid crystal compound.

[0140] The liquid crystal compound may have a polymerizable group. Examples of the liquid crystal compound having a polymerizable group (polymerizable liquid crystal compound) include the compounds exemplified in the polymerizable liquid crystal compound described in the optically anisotropic layer described later.

[0141] The liquid crystal compound may be a thermotropic liquid crystal compound or a lyotropic liquid crystal compound. A lyotropic liquid crystal compound refers to a liquid crystal compound that exhibits a property of causing a phase transition from an isotropic phase to a liquid crystal phase by changing the temperature or concentration in a solution state dissolved in a solvent.

[0142] Examples of the lyotropic liquid crystal compound include non-coloring lyotropic liquid crystal compounds (for example, rod-shaped compounds and plate-shaped compounds) described in paragraphs

[0026] to

[0091] of International Publication No. 2021 / 200987.

[0143] The linear polarizer is preferably formed using a liquid crystal composition including a liquid crystal compound and a dichroic substance.

[0144] The liquid crystal compound included in the liquid crystal composition is as described above.

[0145] A dichroic substance refers to a compound having a property in which the absorbance in the direction of the long axis of the molecule is different from the absorbance in the direction of the short axis.

[0146] The dichroic substance preferably has a maximum absorption wavelength in the near infrared region. More specifically, the maximum absorption wavelength of the dichroic substance is preferably within the wavelength range of 700 to 1600 nm, preferably within the wavelength range of 700 to 1200 nm, and more preferably within the wavelength range of 700 to 900 nm.

[0147] That is, the dichroic substance is preferably a so-called near-infrared absorbing pigment.

[0148] A dichroic substance may or may not exhibit liquid crystallinity (eg, lyotropic liquid crystallinity).

[0149] The type of the dichroic substance is not particularly limited, but is preferably a cyanine dye, an oxonol dye, a boron complex dye, a phthalocyanine dye, a squarylium dye, a metal complex dye, a diimmonium dye, or a perylene dye.

[0150] When a linear polarizer is produced using the liquid crystal composition, there can be mentioned a method of coating the liquid crystal composition and, if necessary, subjecting the formed coating film to an alignment treatment to produce a linear polarizer.

[0151] The method for applying the liquid crystal composition is not particularly limited, and examples thereof include known methods such as spin coating and bar coating.

[0152] The substrate on which the liquid crystal composition is applied may have an alignment film on its surface. By providing the alignment film, the liquid crystal compound is aligned according to the alignment regulating force of the alignment film.

[0153] The formed coating film is subjected to an alignment treatment as necessary. As the alignment treatment, an optimal method can be used depending on the type of the liquid crystal compound used.

[0154] For example, when the liquid crystal compound is a thermotropic liquid crystal compound, when the above-mentioned alignment film is used, the liquid crystal compound can be aligned by subjecting the coating film to a heat treatment.

[0155] Furthermore, when the liquid crystal compound is a lyotropic liquid crystal compound, by adopting a coating method that applies shear to the liquid crystal composition such as wire bar coating, two processes, namely, coating and alignment of the compound, can be performed simultaneously.

[0156] The formed coating film may be subjected to a curing treatment as necessary. In particular, when the liquid crystal compound has a polymerizable group, the polymerizable groups can be polymerized by subjecting the coating film to a heating treatment or a light irradiation treatment.

[0157] By carrying out the above steps, the dichroic substance is also aligned along the alignment of the liquid crystal compound, thereby obtaining a linear polarizer having prescribed characteristics.

[0158] <λ / 4 plate>

[0159] The λ / 4 plates 124 and 125 function as λ / 4 plates with respect to the wavelength of the incident light, and can convert linear polarized light into circular polarized light, and convert circular polarized light into linear polarized light. The λ / 4 plates are not particularly limited as long as they can convert incident linear polarized light into circular polarized light, and convert incident circular polarized light into linear polarized light, and any conventionally known λ / 4 plates can be used.

[0160] In the present invention, from the viewpoint of wide-angle characteristics and wide wavelength dispersion, the λ / 4 plate is preferably a layer formed using a liquid crystal compound.

[0161] The wide-angle characteristic means that a phase difference of λ / 4 can be imparted when near infrared light is incident on the λ / 4 plate from an oblique direction, that is, the range of angles (angle of the incident light with respect to the perpendicular line of the main surface of the λ / 4 plate) at which the λ / 4 plate functions.

[0162] From the viewpoint of being able to function as a λ / 4 plate in a wider angle range, the λ / 4 plate is preferably a laminate of a layer formed using a rod-like liquid crystal compound (e.g., a layer formed by fixing a horizontally oriented rod-like compound) and a layer formed using a disc-like liquid crystal compound (e.g., a layer formed by fixing a vertically oriented disc-like liquid crystal compound). Examples of the layers constituting such a laminate include those described in Japanese Patent Nos. 6975074 and 6640847.

[0163] Alternatively, the λ / 4 plate is preferably a laminate of a layer in which a rod-like liquid crystal compound is horizontally oriented (e.g., a layer in which a horizontally oriented rod-like compound is fixed) and a layer in which a rod-like liquid crystal compound is vertically oriented (e.g., a layer in which a vertically oriented rod-like compound is fixed). As each layer constituting such a laminate, for example, the layers described in International Publication No. 2019 / 159960 can be cited.

[0164] Wavelength dispersion is a wavelength range showing a 1 / 4 wavelength characteristic. As described above, in the blood flow measurement device of the present invention, it is preferable to use a structure of near-infrared rays of two or more different wavelengths. In this case, the λ / 4 plate preferably shows a 1 / 4 wavelength characteristic for any wavelength, and preferably shows so-called reverse wavelength dispersion (a characteristic in which the in-plane delay increases as the measurement wavelength increases).

[0165] From the viewpoint of wavelength dispersibility, the λ / 4 plate is preferably a layer formed using a reverse dispersed liquid crystal compound. As a layer formed using a reverse dispersed liquid crystal compound, for example, a layer described in International Publication No. 2019 / 159960 can be cited.

[0166] Furthermore, the λ / 4 plate may be a laminate of a λ / 4 plate and a λ / 2 plate. Examples of the layers constituting such a laminate include layers described in Japanese Patent Nos. 6975074 and 6640847.

[0167] Furthermore, the λ / 4 plate may be in the form of a layer including a liquid crystal compound fixed in a twisted orientation along a helical axis extending in the thickness direction. As a form of a layer including a liquid crystal compound fixed in a twisted orientation along a helical axis extending in the thickness direction, for example, a layer described in International Publication No. 2021 / 033631 can be cited.

[0168] As described above, the λ / 4 plate can be formed using a liquid crystal compound.

[0169] The liquid crystal compound may be a rod-like liquid crystal compound or a disc-like liquid crystal compound.

[0170] The liquid crystal compound may have a polymerizable group. Examples of the liquid crystal compound having a polymerizable group (polymerizable liquid crystal compound) include the compounds exemplified in the polymerizable liquid crystal compound described in the optically anisotropic layer described later.

[0171] Furthermore, as described above, the liquid crystal compound may have positive wavelength dispersion or may have reverse wavelength dispersion.

[0172] There is no particular limitation on the method for manufacturing a λ / 4 plate formed using a liquid crystal compound, and a known method can be used. For example, the following method can be used: a liquid crystal composition including a liquid crystal compound is coated on a substrate having an alignment film, and the coating film is subjected to an alignment treatment (for example, a heating treatment), and further subjected to a curing treatment as required.

[0173] <Phase difference layer>

[0174] The retardation layer adds a phase difference (optical path difference) to two orthogonal polarized light components to convert the state of incident polarized light. In the present invention, the retardation layer is a layer in which a material having birefringence such as a liquid crystal compound is arranged in the same direction.

[0175] like Figure 4 As described in the foregoing, from the viewpoint of transmitting near infrared rays in a direction inclined at a certain angle, the phase difference layer used in the polarizing element for controlling the direction of near infrared rays is preferably a layer that functions as a λ / 2 plate with respect to near infrared rays incident in a direction inclined at a certain angle. From this point of view, the phase difference layer preferably orients the liquid crystal compound in an inclined manner relative to the main surface.

[0176] As described above, the blood flow measurement device of the present invention preferably uses two or more different near-infrared wavelengths. In this case, the phase difference layer preferably exhibits a predetermined phase difference for any wavelength, and preferably exhibits so-called reverse wavelength dispersion.

[0177] The phase difference layer can be formed using a liquid crystal compound.

[0178] The liquid crystal compound may be a rod-like liquid crystal compound or a disc-like liquid crystal compound.

[0179] The liquid crystal compound may have a polymerizable group. Examples of the liquid crystal compound having a polymerizable group (polymerizable liquid crystal compound) include the compounds exemplified in the polymerizable liquid crystal compound described in the optically anisotropic layer described later.

[0180] The method for manufacturing the phase difference layer formed by using the liquid crystal compound is not particularly limited, and a known method can be used. For example, the following method can be cited: coating a liquid crystal composition including the liquid crystal compound on a substrate having an orientation film, and subjecting the coating film to an orientation treatment (e.g., a heat treatment), and further subjecting the coating film to a curing treatment as needed.

[0181] <Liquid crystal diffraction element>

[0182] The liquid crystal diffraction element has an optically anisotropic layer in which a liquid crystal compound is oriented in a predetermined arrangement, and bends near-infrared rays by diffraction.

[0183] use Figure 6 and Figure 7 , the optically anisotropic layer of the liquid crystal diffraction element is described.

[0184] Figure 6 and Figure 7 The optically anisotropic layer described above is a layer in which a liquid crystal phase of a liquid crystal compound is fixed and has a liquid crystal alignment pattern in which the direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in a plane.

[0185] As in Figure 6 2 conceptually shows that, in the optically anisotropic layer, the liquid crystal compound 40 is not twisted in a spiral shape in the thickness direction, and the liquid crystal compound 40 located at the same position in the plane direction is oriented so that the optical axis 40A is oriented in the same direction.

[0186] <<Liquid crystal orientation pattern of optically anisotropic layer>>

[0187] The optically anisotropic layer has a liquid crystal alignment pattern in which the direction of the optical axis 40A derived from the liquid crystal compound 40 changes while continuously rotating in one direction within the plane of the optically anisotropic layer.

[0188] In addition, the optical axis 40A derived from the liquid crystal compound 40 is an axis having the highest refractive index in the liquid crystal compound 40, which is a so-called slow axis. For example, when the liquid crystal compound 40 is a rod-shaped liquid crystal compound, the optical axis 40A is along the long axis direction of the rod shape. In the following description, the optical axis 40A derived from the liquid crystal compound 40 is also referred to as "optical axis 40A of the liquid crystal compound 40" or "optical axis 40A".

[0189] Figure 7 2 is a conceptual top view of an optically anisotropic layer.

[0190] In addition, the top view refers to Figure 6 The figure in which the optically anisotropic layer is observed from above is a figure in which the optically anisotropic layer is observed from the thickness direction (=the lamination direction of each layer (film)).

[0191] And, in Figure 7 In FIG. 1 , in order to clearly show the structure of the optically anisotropic layer, only the surface of the liquid crystal compound 40 is shown.

[0192] like Figure 7 As shown, on the surface, the liquid crystal compound 40 constituting the optical anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis 40A changes while continuously rotating in a predetermined direction indicated by an arrow D (hereinafter referred to as the arrangement axis D) in the plane of the optical anisotropic layer. In the example shown in the figure, the liquid crystal orientation pattern has a liquid crystal compound 40 having an optical axis 40A that changes while continuously rotating in a clockwise direction along the arrangement axis D direction.

[0193] The liquid crystal compound 40 constituting the optically anisotropic layer is in a state of being two-dimensionally aligned in the alignment axis D and in a direction orthogonal to the one direction (the alignment axis D direction).

[0194] In the following description, for convenience, the direction perpendicular to the arrangement axis D direction is referred to as the Y direction. That is, the arrow Y direction is a direction perpendicular to a direction in which the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating within the plane of the optical anisotropic layer. Figure 8-Figure 9 In the figure, the Y direction is perpendicular to the paper surface.

[0195] The orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating along the arrangement axis D direction (a predetermined direction). Specifically, it means that the angle formed by the optical axis 40A of the liquid crystal compound 40 arranged along the arrangement axis D direction and the arrangement axis D direction is different depending on the position in the arrangement axis D direction. Along the arrangement axis D direction, the angle formed by the optical axis 40A and the arrangement axis D direction changes from θ to θ+180° or θ-180° in sequence.

[0196] The difference in angle between the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the arrangement axis D direction is preferably 45° or less, more preferably 15° or less, and still more preferably a smaller angle.

[0197] Furthermore, in the present invention, it is assumed that the rotation direction of the optical axis 40A of the liquid crystal compound in the direction of the arrangement axis D is the direction in which the liquid crystal compound 40 (optical axis 40A) rotates in a direction in which the angle formed by the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of the arrangement axis D becomes smaller. Figure 6 and Figure 7 In the optically anisotropic layer shown, the optical axis 40A of the liquid crystal compound 40 rotates rightward (clockwise) along the arrow direction of the alignment axis D.

[0198] On the other hand, the liquid crystal compound 40 forming the optically anisotropic layer is oriented in the same direction as the optical axis 40A in the Y direction orthogonal to the arrangement axis D direction (ie, the Y direction orthogonal to one direction in which the optical axis 40A rotates continuously).

[0199] In other words, in the Y direction of the liquid crystal compound 40 forming the optically anisotropic layer, the angles formed between the optical axis 40A of the liquid crystal compound 40 and the direction of the alignment axis D are equal.

[0200] In the optically anisotropic layer, the angles formed by the optical axis 40A and the direction of the arrangement axis D (a direction in which the direction of the optical axis of the liquid crystal compound 40 is rotated) of the liquid crystal compound arranged in the Y direction are equal. The region in which the liquid crystal compound 40 in the Y direction, in which the angles formed by the optical axis 40A and the direction of the arrangement axis D are equal, is defined as region R.

[0201] In this case, it is preferable that the value of the in-plane retardation (Re) in each region R is half a wavelength, that is, λ / 2. These in-plane retardations are calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of the region R and the thickness of the optical anisotropic layer. Among them, the refractive index difference associated with the refractive index anisotropy of the region R in the optical anisotropic layer is a refractive index difference defined by the difference between the refractive index in the direction of the slow axis in the plane of the region R and the refractive index in the direction orthogonal to the direction of the slow axis. That is, the refractive index difference Δn associated with the refractive index anisotropy of the region R is equal to the difference between the refractive index of the liquid crystal compound 40 in the direction of the optical axis 40A and the refractive index of the liquid crystal compound 40 in the direction perpendicular to the optical axis 40A in the plane of the region R. That is, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound 40.

[0202] In the optically anisotropic layer, in the liquid crystal orientation pattern of this liquid crystal compound 40, in the direction of the arrangement axis D where the in-plane optical axis 40A continuously rotates and changes, the length (distance) of rotating the optical axis 40A of the liquid crystal compound 40 by 180° is set as the length Λ of one period in the liquid crystal orientation pattern.

[0203] That is, the distance between the centers of the two liquid crystal compounds 40 in the direction of the arrangement axis D, which have the same angle with respect to the direction of the arrangement axis D, is set to the length Λ of one period. Figure 7 As shown, the distance between the centers of the two liquid crystal compounds 40 whose arrangement axis D direction coincides with the direction of the optical axis 40A is defined as the length of one period Λ. In the following description, the length of one period Λ is also referred to as "one period Λ".

[0204] The liquid crystal alignment pattern of the optically anisotropic layer repeats this one period Λ in the direction of the arrangement axis D (that is, one direction in which the orientation of the optical axis 40A changes by continuous rotation).

[0205] If circularly polarized light is incident on such an optically anisotropic layer, the light is refracted and the direction of the circularly polarized light is converted.

[0206] exist Figure 8 and Fig. 9 This effect is conceptually shown in . In the optically anisotropic layer, the value of the product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer is set to λ / 2.

[0207] like Figure 8 As shown, when the value of the product of the refractive index difference of the liquid crystal compound of the optical anisotropic layer and the thickness of the optical anisotropic layer is λ / 2, if the incident light L1 as left-handed circularly polarized light is incident on the optical anisotropic layer, the incident light L1 is given a phase difference of 180° by the optical anisotropic layer, so that the transmitted light L2 is converted into right-handed circularly polarized light.

[0208] Furthermore, the liquid crystal orientation pattern formed on the optical anisotropic layer is a periodic pattern in the direction of the arrangement axis D, so the transmitted light L2 travels in a direction different from the direction of the incident light L1. In this way, the incident light L1 of left-handed circular polarization is converted into the transmitted light L2 of right-handed circular polarization that is tilted by a predetermined angle in the direction of the arrangement axis D relative to the incident direction. Figure 8 In the example shown, the transmitted light L2 is diffracted to travel in the lower right direction.

[0209] On the other hand, Fig. 9As shown, when the value of the product of the refractive index difference of the liquid crystal compound of the optical anisotropic layer and the thickness of the optical anisotropic layer is λ / 2, if the incident light L4 of right-handed circularly polarized light is incident on the optical anisotropic layer, the incident light L4 is given a phase difference of 180° by the optical anisotropic layer, and is thereby converted into transmitted light L5 of left-handed circularly polarized light.

[0210] Furthermore, the liquid crystal orientation pattern formed on the optically anisotropic layer is a periodic pattern in the direction of the arrangement axis D, so the transmitted light L5 travels in a direction different from the direction of the incident light L4. At this time, the transmitted light L5 travels in a direction different from the transmitted light L2, that is, in a direction opposite to the arrow direction of the arrangement axis D relative to the incident direction. In this way, the incident light L4 is converted into the transmitted light L5 of left-handed circularly polarized light that is tilted by only a specified angle in the direction opposite to the arrangement axis D direction relative to the incident direction. Fig. 9 In the example shown, the transmitted light L5 is diffracted to travel in the lower left direction.

[0211] As described above, the optical anisotropic layer can adjust the refraction angle of the transmitted light L2 and L5 according to the length of one period Λ of the formed liquid crystal orientation pattern. Specifically, with respect to the optical anisotropic layer, the shorter one period Λ of the liquid crystal orientation pattern is, the stronger the interference between the lights passing through the adjacent liquid crystal compounds 40 is, so the transmitted light L2 and L5 can be refracted more.

[0212] Furthermore, by setting the rotation direction of the optical axis 40A of the liquid crystal compound 40 rotating along the arrangement axis D to the opposite direction, the azimuth direction of the refraction of the transmitted light can be set to the opposite direction. Figure 8-Figure 9 In the example shown, the rotation direction of the optical axis 40A toward the arrangement axis D is clockwise, but by setting the rotation direction to counterclockwise, the azimuth direction of the refraction of the transmitted light can be set to the opposite direction. Figure 8 and Fig. 9 In the figure, when the rotation direction of the optical axis 40A toward the arrangement axis D is counterclockwise, the left-handed circularly polarized light incident on the optical anisotropic layer from the upper side in the figure is converted into right-handed circularly polarized light by the optical anisotropic layer, and diffracted to travel in the lower left direction in the figure. Also, the right-handed circularly polarized light incident on the optical anisotropic layer from the upper side in the figure is converted into left-handed circularly polarized light by the optical anisotropic layer, and diffracted to travel in the lower right direction in the figure.

[0213] <<Method for forming optically anisotropic layer>>

[0214] The method for forming the optically anisotropic layer includes, for example, the steps of applying a liquid crystal composition including the prepared liquid crystal compound on an alignment film and curing the applied liquid crystal composition.

[0215] The preparation of the liquid crystal composition can be carried out by a conventionally known method. In addition, the coating of the liquid crystal composition can be carried out by various known methods used in the coating of liquids such as inkjet and roll printing, and spin coating, rod coating, gravure coating, and spray coating. In addition, the coating thickness (film thickness) of the liquid crystal composition can be appropriately set according to the composition of the liquid crystal composition, etc. to obtain the coating thickness of the optically anisotropic layer of the target thickness.

[0216] Here, as described later, since an alignment pattern is formed on the alignment film, the liquid crystal compound of the liquid crystal composition applied on the alignment film is aligned along the alignment pattern (anisotropic periodic pattern) of the alignment film.

[0217] The liquid crystal composition is dried and / or heated as required, and then cured. The curing of the liquid crystal composition can be carried out by a known method such as photopolymerization, thermal polymerization, etc. Regarding polymerization, photopolymerization is preferred. Ultraviolet rays are preferably used for light irradiation. The irradiation energy is preferably 20 mJ / cm 2 ~50J / cm 2 , more preferably 50 to 1500 mJ / cm 2 In order to promote the photopolymerization reaction, light irradiation may be performed under heating conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet rays to be irradiated is preferably 250 to 430 nm. When heating is performed, the heating temperature is preferably 200° C. or less, and more preferably 130° C. or less.

[0218] By curing the liquid crystal composition, the liquid crystal compound in the liquid crystal composition is fixed in a state of being oriented along the orientation pattern of the orientation film (liquid crystal orientation pattern), thereby forming an optically anisotropic layer having a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound changes while continuously rotating in at least one direction in the plane.

[0219] In addition, at the time when the optically anisotropic layer is completed, the liquid crystal compound may not exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may lose its liquid crystallinity due to the increase in molecular weight through a curing reaction.

[0220] Furthermore, the optically anisotropic layer can be formed by coating a liquid crystal composition on an alignment film in multiple layers. Multilayer coating refers to a method in which the first layer of liquid crystal composition is first coated on the alignment film, and then heated, cooled, and UV-cured to form a liquid crystal fixing layer, and then the second layer and the subsequent layers are overlapped and coated on the liquid crystal fixing layer, and then heated, cooled, and UV-cured, and the process is repeated until the desired thickness is reached to form an optically anisotropic layer. Forming by multilayer coating can make the total thickness of the liquid crystal layer thicker. Furthermore, even when the total thickness of the liquid crystal layer becomes thicker, the orientation direction of the alignment film extends from the lower surface to the upper surface of the liquid crystal layer.

[0221] <Liquid crystal composition for forming an optically anisotropic layer>

[0222] As a material for forming the optically anisotropic layer, a liquid crystal composition containing a liquid crystal compound can be given as an example. The liquid crystal compound is preferably a polymerizable liquid crystal compound.

[0223] Furthermore, the liquid crystal composition used in forming the liquid crystal layer may further contain a surfactant and a chiral agent.

[0224] --Polymerizable Liquid Crystalline Compounds--

[0225] The polymerizable liquid crystal compound may be a rod-like liquid crystal compound or a disc-like liquid crystal compound.

[0226] Examples of rod-shaped polymerizable liquid crystal compounds include rod-shaped nematic liquid crystal compounds. As rod-shaped nematic liquid crystal compounds, preferably used are azomethines, azoxyls, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans, and alkenylcyclohexylbenzonitriles. Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

[0227] A polymerizable liquid crystal compound can be obtained by introducing a polymerizable group into a liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridine group, preferably an unsaturated polymerizable group, and more preferably an ethylenically unsaturated polymerizable group. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups possessed by the polymerizable liquid crystal compound is preferably 1 to 6, and more preferably 1 to 3.

[0228] Examples of polymerizable liquid crystal compounds include compounds described in Makromol.Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Pat. No. 4,683,327, U.S. Pat. No. 5,622,648, U.S. Pat. No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Application Publication No. 1-272551, Japanese Patent Application Publication No. 6-16616, Japanese Patent Application Publication No. 7-110469, Japanese Patent Application Publication No. 11-80081 and Japanese Patent Application Publication No. 2001-328973. Two or more polymerizable liquid crystal compounds may be used simultaneously. When two or more polymerizable liquid crystal compounds are used simultaneously, the alignment temperature can be lowered.

[0229] As the exceptional polymerizable liquid crystal compound, the cyclic organopolysiloxane compound disclosed in Japanese Patent Publication No. 57-165480 can be used. In addition, as the polymer liquid crystal compound, a polymer having a mesogen group showing liquid crystal introduced into the main chain, the side chain, or both the main chain and the side chain, a polymer cholesteric liquid crystal having a cholesteric group introduced into the side chain, a liquid crystal polymer disclosed in Japanese Patent Publication No. 9-133810, and a liquid crystal polymer disclosed in Japanese Patent Publication No. 11-293252 can be used.

[0230] --Disc-like Liquid Crystalline Compounds--

[0231] As the discotic liquid crystal compound, for example, the discotic liquid crystal compounds described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used.

[0232] The amount of the polymerizable liquid crystal compound added to the liquid crystal composition is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, and even more preferably 85 to 90% by mass, relative to the solid content mass of the liquid crystal composition (mass excluding the solvent).

[0233] --Surfactant--

[0234] The liquid crystal composition used when forming the liquid crystal layer may contain a surfactant.

[0235] The surfactant is preferably a compound that can function as an alignment control agent that helps the liquid crystal compound 40 in the liquid crystal layer 102 to be oriented stably or quickly. Examples of the surfactant include silicone surfactants and fluorine surfactants, and preferably fluorine surfactants are used.

[0236] Specific examples of surfactants include compounds described in paragraphs

[0082] to

[0090] of JP-A-2014-119605, compounds described in paragraphs

[0031] to

[0034] of JP-A-2012-203237, compounds exemplified in paragraphs

[0092] and

[0093] of JP-A-2005-99248, compounds exemplified in paragraphs

[0076] to

[0078] and

[0082] to

[0085] of JP-A-2002-129162, and fluoro(meth)acrylate polymers described in paragraphs

[0018] to

[0043] of JP-A-2007-272185, etc.

[0237] The surfactant may be used alone or in combination of two or more.

[0238] As the fluorine-based surfactant, compounds described in paragraphs

[0082] to

[0090] of JP-A-2014-119605 are preferred.

[0239] The amount of the surfactant added in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.02 to 1% by mass, relative to the total mass of the liquid crystal compound.

[0240] --Polymerization Initiator--

[0241] When the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is carried out by ultraviolet irradiation, the polymerization initiator used is preferably a photopolymerization initiator that can initiate the polymerization reaction by ultraviolet irradiation.

[0242] Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Pat. No. 2,367,661 and U.S. Pat. No. 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Pat. No. 2,722,512), polynuclear quinone compounds (described in U.S. Pat. No. 3,046,127 and U.S. Pat. No. 2,951,758), a combination of a triaryl imidazole dimer and p-aminophenyl ketone (described in U.S. Pat. No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Application Laid-Open No. 60-105667 and U.S. Pat. No. 4,239,850), and oxadiazole compounds (described in U.S. Pat. No. 4,212,970).

[0243] The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, relative to the content of the liquid crystal compound.

[0244] --Crosslinking agent--

[0245] The liquid crystal composition may contain a crosslinking agent to increase the film strength after curing and improve durability. As the crosslinking agent, a crosslinking agent that is cured by ultraviolet rays, heat, moisture, etc. can be preferably used.

[0246] There is no particular limitation on the crosslinking agent, and it can be appropriately selected according to the purpose. For example, multifunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate can be cited; epoxy compounds such as (meth)acrylate glycidyl and ethylene glycol diglycidyl ether; 2,2-bishydroxymethylbutanol-tri[3-(1-aziridine)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane and other aziridine compounds; isocyanate compounds such as hexamethylene diisocyanate and biuret type isocyanate; polyoxazoline compounds having an oxazoline group on the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. In addition, a known catalyst can be used according to the reactivity of the crosslinking agent, so that in addition to improving the film strength and durability, the productivity can also be improved. These may be used alone or in combination of two or more.

[0247] The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass relative to the solid content of the liquid crystal composition. As long as the content of the crosslinking agent is within the above range, the effect of increasing the crosslinking density is easily obtained, thereby further improving the stability of the liquid crystal phase.

[0248] --Other additives--

[0249] A polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, metal oxide fine particles, and the like may be added to the liquid crystal composition as necessary within a range not to deteriorate optical properties.

[0250] A liquid crystal composition is preferably used as the liquid when forming the optically anisotropic layer.

[0251] The liquid crystal composition may contain a solvent. The solvent is not limited and can be appropriately selected according to the purpose, but is preferably an organic solvent.

[0252] The organic solvent is not limited and can be appropriately selected according to the purpose. For example, ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters and ethers can be mentioned. These can be used alone or in combination of two or more. Among these, ketones are preferred when the burden on the environment is taken into consideration.

[0253] Furthermore, the liquid crystal diffraction element may have layers other than the optically anisotropic layer, such as a support and an alignment film.

[0254] (Support)

[0255] As a support for supporting the alignment film and the optically anisotropic layer, various sheet-like objects (films, plates) can be used as long as they can support the alignment film and the optically anisotropic layer.

[0256] The support preferably has a transmittance of 50% or more, more preferably 70% or more, and even more preferably 85% or more, to diffracted light (near infrared light).

[0257] The thickness of the support is not limited, and may be appropriately set to a thickness capable of supporting the alignment film and the optically anisotropic layer, depending on the application of the liquid crystal diffraction element and the material forming the support.

[0258] The thickness of the support is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and further preferably 5 to 150 μm.

[0259] The support may be a single layer or a multi-layer.

[0260] As a single-layer support, there can be exemplified a support made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic acid, polyolefin, etc. As an example of a multi-layer support, there can be exemplified a support including any of the above-mentioned single-layer supports as a substrate, and a support having other layers disposed on the surface of the substrate.

[0261] (Oriented Film)

[0262] An alignment film is formed on the surface of the support.

[0263] The alignment film is an alignment film for aligning the liquid crystal compound 40 in a predetermined liquid crystal alignment pattern when forming the optically anisotropic layer.

[0264] As described above, in the present invention, the optically anisotropic layer has an optical axis 40A derived from the liquid crystal compound 40 (refer to Figure 7 ) is a liquid crystal orientation pattern in which the orientation of the liquid crystal changes while continuously rotating in one direction in the plane. Therefore, the orientation film is formed so that the optically anisotropic layer can form the liquid crystal orientation pattern.

[0265] In the following description, “the rotation of the direction of the optical axis 40A” is also simply referred to as “the rotation of the optical axis 40A”.

[0266] As the alignment film, various known alignment films can be used.

[0267] For example, friction-treated films composed of organic compounds such as polymers, oblique vapor-deposited films of inorganic compounds, films having microgrooves, and films in which LB (Langmuir-Blodgett) films based on the Langmuir-Blodgett method are accumulated using organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate.

[0268] The alignment film based on the rubbing treatment can be formed by rubbing the surface of the polymer layer with paper or cloth several times in a predetermined direction.

[0269] Preferred materials for the alignment film include polyimide, polyvinyl alcohol, polymers having polymerizable groups described in Japanese Patent Application Laid-Open No. 9-152509, and materials used for forming the alignment film 32 described in Japanese Patent Application Laid-Open Nos. 2005-97377, 2005-99228, and 2005-128503.

[0270] The alignment film is preferably a so-called photo-alignment film formed by irradiating a photo-alignment material with polarized light or non-polarized light. That is, the alignment film is preferably a photo-alignment film formed by coating a photo-alignment material on a support.

[0271] Irradiation with polarized light can be performed from a vertical direction or an oblique direction with respect to the photo-alignment film, and irradiation with unpolarized light can be performed from an oblique direction with respect to the photo-alignment film.

[0272] Examples of the photo-alignment material that can be used in the alignment film of the present invention include Japanese Patent Application Publication No. 2006-285197, Japanese Patent Application Publication No. 2007-76839, Japanese Patent Application Publication No. 2007-138138, Japanese Patent Application Publication No. 2007-94071, Japanese Patent Application Publication No. 2007-121721, Japanese Patent Application Publication No. 2007-140465, Japanese Patent Application Publication No. 2007-15643 Azo compounds described in Japanese Patent Publication No. 9, Japanese Patent Publication No. 2007-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, and aromatic ester compounds described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013. Maleimide and / or alkenyl-substituted nadic imide compounds having photo-alignment units, photo-crosslinkable silane derivatives described in Japanese Patent Nos. 4205195 and 4205198, photo-crosslinkable polyimides, photo-crosslinkable polyamides and photo-crosslinkable polyesters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850 Preferred examples include compounds capable of photodimerization described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, International Publication No. 2010 / 150748, JP-A-2013-177561, and JP-A-2014-12823, in particular cinnamate compounds, chalcone compounds, and coumarin compounds.

[0273] Among them, azo compounds, photo-crosslinkable polyimides, photo-crosslinkable polyamides, photo-crosslinkable polyesters, cinnamate compounds, and chalcone compounds can be preferably used.

[0274] The thickness of the alignment film is not limited, and may be appropriately set according to the material forming the alignment film so as to obtain a desired alignment function.

[0275] The thickness of the alignment film is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

[0276] The method for forming the alignment film is not limited, and various known methods corresponding to the materials for forming the alignment film can be used. As an example, a method of forming an alignment pattern by coating the alignment film on the surface of a support and drying it, and then exposing the alignment film with a laser beam can be exemplified.

[0277] Fig.10An example of an exposure device for exposing an alignment film to form an alignment pattern is conceptually shown in FIG.

[0278] Fig.10 The exposure device 60 shown comprises: a light source 64 having a laser 62; a λ / 2 plate 65 for changing the polarization direction of the laser beam M emitted by the laser 62; a beam splitter 68 for separating the laser beam M emitted by the laser 62 into two light beams MA and MB; reflectors 70A and 70B respectively arranged on the optical paths of the two separated light beams MA and MB; and λ / 4 plates 72A and 72B.

[0279] The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (light beam MA) into right-handed circularly polarized light P R , the λ / 4 plate 72B converts the linear polarized light P0 (light MB) into left-handed circularly polarized light P L .

[0280] The support 30 having the alignment film 32 before the alignment pattern is formed is placed in the exposure section, and two light beams MA and MB are made to intersect and interfere with each other on the alignment film 32, and the interference light is irradiated onto the alignment film 32 for exposure.

[0281] Due to the interference at this time, the polarization state of the light irradiated on the alignment film 32 changes periodically in the form of interference fringes. Thus, an alignment film having an alignment pattern in which the alignment state changes periodically (hereinafter also referred to as a pattern alignment film) can be obtained.

[0282] In the exposure device 60, the period of the alignment pattern can be adjusted by changing the cross angle α of the two light beams MA and MB. That is, in the exposure device 60, by adjusting the cross angle α, in the alignment pattern in which the optical axis 40A originating from the liquid crystal compound 40 continuously rotates in one direction, the length of one period in which the optical axis 40A is rotated 180° in one direction can be adjusted.

[0283] By forming an optically anisotropic layer on the alignment film 32 having such an alignment pattern in which the alignment state changes periodically, it is possible to form an optically anisotropic layer having a liquid crystal alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 continuously rotates in one direction.

[0284] Furthermore, the rotation direction of the optical axis 40A can be reversed by rotating the optical axes of the λ / 4 plates 72A and 72B by 90° respectively.

[0285] As described above, the patterned orientation film has an orientation pattern as follows: the liquid crystal compound is oriented so as to form a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound in the optically anisotropic layer formed on the patterned orientation film changes while continuously rotating along at least one direction in the plane. It can be said that if the axis of the patterned orientation film along the direction in which the liquid crystal compound is oriented is set as the orientation axis, the patterned orientation film has an orientation pattern in which the direction of the orientation axis changes while continuously rotating along at least one direction in the plane. The orientation axis of the patterned orientation film can be detected by measuring the absorption anisotropy. For example, when linearly polarized light is irradiated onto the patterned orientation film while rotating and the amount of light transmitted through the patterned orientation film is measured, it is observed that the direction in which the amount of light becomes maximum or minimum gradually changes along one direction in the plane.

[0286] In the present invention, the alignment film is provided in a preferred embodiment and is not an essential constituent element.

[0287] For example, an orientation pattern can be formed on the support by rubbing the support, processing the support with a laser beam, etc., so that the optically anisotropic layer can have a structure in which the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in at least one direction in the plane. That is, in the present invention, the support can also function as an orientation film.

[0288] Here, in Figure 6 and Figure 7 In the optically anisotropic layer shown in FIG. 1 , the optical axes of the liquid crystal compounds arranged in the thickness direction are aligned in the same direction, but the present invention is not limited thereto. Fig.11 As shown in the optical anisotropic layer 36b, the optical axis of the liquid crystal compound may be twisted in the thickness direction. In this case, the twist angle of the region twisted in the thickness direction is 10° to 360° over the entire thickness direction.

[0289] In this way, if the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of the optical axis 40A changes while continuously rotating along the arrangement axis D in the plane, and the liquid crystal compound 40 has a twisted structure in the thickness direction, then in a cross section parallel to the arrangement axis D, the optically anisotropic layer has a structure in which a line segment connecting the liquid crystal compound 40 oriented in the same direction in the thickness direction is inclined relative to the main surface of the optically anisotropic layer, and in an image of a cross section obtained by cutting the optically anisotropic layer in the thickness direction along the arrangement axis D observed with a scanning electron microscope (SEM), the optically anisotropic layer has a structure in which the observed stripe pattern of the bright and dark parts is inclined relative to the main surface. Thus, the diffraction efficiency of the diffraction element can be improved.

[0290] In order to make the optically anisotropic layer have a structure in which the liquid crystal compound is twisted and aligned in the thickness direction, a chiral agent may be contained in the liquid crystal composition for forming the optically anisotropic layer.

[0291] --Chiral Reagents (Optically Active Compounds)--

[0292] Chiral agents have the function of inducing a helical structure of a liquid crystal phase. Since the twisting direction and helical twisting power (HTP) of the helix induced by the compound are different, the chiral agent can be selected according to the purpose.

[0293] There are no particular restrictions on the chiral agent, and known compounds (for example, those recorded in Handbook of Liquid Crystal Devices, Chapter 3, Item 4-3, TN (twisted nematic), STN (Super Twisted Nematic) Chiral Agents, page 199, compiled by the 142nd Committee of the Japan Society for the Promotion of Science, recorded in 1989), isosorbide and isomannide derivatives, etc. can be used.

[0294] Chiral agents usually contain asymmetric carbon atoms, but axially asymmetric compounds or surface asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral agents. Examples of axially asymmetric compounds or surface asymmetric compounds include binaphthyl, helicene, paracyclophane and their derivatives. Chiral agents can also have polymerizable groups. In the case where both the chiral agent and the liquid crystal compound have polymerizable groups, a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent can be formed by polymerization reaction of the polymerizable chiral agent and the polymerizable liquid crystal compound. In this manner, the polymerizable group possessed by the polymerizable chiral agent is preferably a group of the same type as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridine group, more preferably an unsaturated polymerizable group, and further preferably an olefinic unsaturated polymerizable group.

[0295] Furthermore, the chiral agent may also be a liquid crystal compound.

[0296] When the chiral agent has a photoisomerizable group, it is preferred because the desired twisted orientation corresponding to the emission wavelength can be formed by irradiating a photomask with activating light or the like after coating and orientation. The photoisomerizable group is preferably an isomerization site of a compound showing photochromic properties, an azo group, an oxyazolyl group, or a cinnamoyl group. As specific compounds, compounds described in JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, and JP-A-2003-313292 can be used.

[0297] The content of the chiral agent in the liquid crystal composition is preferably 0.01 to 200 mol %, more preferably 1 to 30 mol %, relative to the molar amount of the liquid crystal compound.

[0298] Furthermore, the optically anisotropic layer may have a structure having regions with different twist states (twist angles and twist directions) in the thickness direction. In the case of such a structure, in the optically anisotropic layer, in an image of a cross section cut in the thickness direction in a direction in which the orientation of the optical axis of the liquid crystal compound changes while continuously rotating, a bright portion and a dark portion extending from one main surface to the other main surface are observed using a scanning electron microscope, and the dark portion has one or more angle inflection points.

[0299] exist Fig.12 An example of such an optically anisotropic layer is shown in FIG. Fig.12 In the figure, the bright part 42 and the dark part 44 are overlapped with the cross section of the optical anisotropic layer 36c. In the following description, an image of a cross section cut in the thickness direction along one direction rotated along the optical axis observed by SEM is also referred to as a "cross-sectional SEM image".

[0300] Fig.12 In the cross-sectional SEM image of the optically anisotropic layer 36c shown, the dark portion 44 has two inflection points of angle change. That is, the optically anisotropic layer 36c can be said to have three regions, namely, the region 37a, the region 37b, and the region 37c, in the thickness direction according to the inflection points of the dark portion 44.

[0301] The optically anisotropic layer 36c has a liquid crystal orientation pattern at any position in the thickness direction, wherein the optical axis derived from the liquid crystal compound 40 rotates clockwise toward the left in the figure when viewed from above in the in-plane direction, and one period of the liquid crystal orientation pattern is constant in the thickness direction.

[0302] And, if Fig.12 As shown, the liquid crystal compound 40 is twistedly aligned in the lower region 37 a in the thickness direction so as to be twisted into a spiral shape clockwise (right-handed) from the upper side to the lower side in the figure in the thickness direction.

[0303] In the middle region 37b in the thickness direction, the liquid crystal compound 40 is not twisted in the thickness direction, and the optical axes of the liquid crystal compounds 40 stacked in the thickness direction are oriented in the same direction. That is, the optical axes of the liquid crystal compounds 40 at the same position in the in-plane direction are oriented in the same direction.

[0304] In the upper region 37 c in the thickness direction, the liquid crystal compound 40 is twistedly aligned so as to be twisted in a spiral shape counterclockwise (left-handed) from the upper side toward the lower side in the figure in the thickness direction.

[0305] That is, in Fig.12 The regions 37 a , 37 b , and 37 c of the optically anisotropic layer 36 c shown have different states of twisting of the liquid crystal compound 40 in the thickness direction.

[0306] In an optically anisotropic layer having a liquid crystal alignment pattern in which the optical axis of the liquid crystal compound rotates continuously in one direction, it is observed that the bright and dark parts in the cross-sectional SEM image of the optically anisotropic layer connect the liquid crystal compounds in the same direction.

[0307] As an example, in Fig.12 In FIG. 1 , a dark portion 44 is observed to be connected to a liquid crystal compound 40 whose optical axis is oriented in a direction perpendicular to the paper surface.

[0308] In the lowermost region 37a in the thickness direction, the dark portion 44 is inclined toward the upper left in the figure. In the middle region 37b, the dark portion 44 extends in the thickness direction. In the uppermost region 37c, the dark portion 44 is inclined toward the upper right in the figure.

[0309] Right now, Fig.12 The optically anisotropic layer 36c shown has two angle inflection points where the angle of the dark portion 44 changes. In the uppermost region 37c, the dark portion 44 is inclined toward the upper right, and in the lowermost region 37b, the dark portion 44 is inclined toward the upper left. That is, the dark portion 44 has different inclination directions in the region 37c and the region 37a.

[0310] also, Fig.12 In the optically anisotropic layer 36 c shown, the dark portion 44 has one inflection point where the inclined direction turns back in the opposite direction.

[0311] Specifically, the dark portion 44 of the optically anisotropic layer 36c has an inclination direction in the region 37c that is opposite to the inclination direction in the region 37b. Therefore, the inflection point located at the interface between the region 37c and the region 37b is an inflection point where the inclination direction turns back in the opposite direction. That is, the optically anisotropic layer 36c has one inflection point where the inclination direction turns back in the opposite direction.

[0312] As an example, the thickness of the region 37c and the region 37a of the optically anisotropic layer 36c are equal, and as described above, the twisted states of the liquid crystal compound 40 in the thickness direction are different. Figure 1 As shown, the bright portion 42 and the dark portion 44 in the cross-sectional SEM image are substantially C-shaped.

[0313] Therefore, in the optically anisotropic layer 36 c , the shape of the dark portion 44 is symmetrical with respect to the center line in the thickness direction.

[0314] In the optically anisotropic layer 36c, i.e., in the cross-sectional SEM image, the optically anisotropic layer 36c has a bright portion 42 and a dark portion 44 extending from one surface to the other surface, and the dark portion 44 has one or more angle inflection points, and can reduce the wavelength dependence of the diffraction efficiency and diffract light with the same diffraction efficiency regardless of the wavelength. In addition, the wide-angle characteristics of the optically anisotropic layer 36c are improved, and light can be diffracted with the same diffraction efficiency regardless of the incident angle.

[0315] In addition, Fig.12 In the example shown, the dark portion 44 is configured to have two angle inflection points, but the present invention is not limited thereto. The dark portion 44 may have one angle inflection point or three or more angle inflection points. For example, when the dark portion 44 of the optically anisotropic layer has one angle inflection point, Fig.12 Alternatively, for example, when the dark portion 44 of the optically anisotropic layer has a structure having three angle inflection points, two of the dark portions 44 may be alternately provided. Fig.12 The structures of the regions 37c and 37a shown in the figure may be used.

[0316] The period Λ in the optical anisotropic layer can be appropriately set according to the refraction angle of the transmitted light. The period Λ is preferably about 1 to 3 times the wavelength of the near infrared light emitted from the light source. By setting the period Λ within this range, the refraction angle can be made as follows: Figure 1 The incident and emitted angles are inclined as shown in α and β.

[0317] As mentioned above, the blood flow measurement device of the present invention has been described in detail, but the present invention is not limited to the above-mentioned example, and it is a matter of course that various improvements and changes can be made without departing from the scope of the present invention.

[0318] Explanation of symbols

[0319] 30-support, 32-orientation film, 36, 36b~36c-liquid crystal diffraction element (optical anisotropic layer), 37a~37c-area, 60-exposure device, 62-laser, 64-light source, 65-λ / 2 plate, 68-beam splitter, 70A, 70B-reflecting mirror, 72A, 72B-λ / 4 plate, 100, 100a~100d-blood flow measurement device, 102-control unit, 104-light source unit, 106, 106a~106d-first polarization element, 108-light Receiving unit, 110, 110a~106d-second polarizing element, 112-frame, 120, 122-linear polarizer, 120a, 122a-first linear polarizer, 120b, 122b-second linear polarizer, 124, 125-λ / 4 plate, 126, 127-phase difference layer, 128-liquid crystal diffraction element, S-living body, R-region, Λ-1 period, D-arrangement axis, L1, L4-incident light, L2, L5-transmitted light, M-laser beam, MA, MB-light, P O -Linearly polarized light, P R -Right-handed circularly polarized light, P L -Left-hand circularly polarized light, α-crossing angle.

Claims

1. A blood flow measurement device comprising: a light source unit for irradiating a target object with near infrared rays; and a light receiving unit for receiving scattered light generated by the near infrared rays emitted from the light source unit and scattered by the target object, the blood flow measurement device further comprising: a first polarizing element disposed on the front surface of the light source unit and including a layer formed using a liquid crystal compound to change the polarization state of near infrared light; and The second polarizing element is disposed on the front surface of the light receiving unit and includes a layer formed using a liquid crystal compound, and changes the polarization state of near infrared light.

2. The blood flow measurement device according to claim 1, wherein: The layer formed using the liquid crystal compound included in the first polarizing element is a linear polarizer.

3. The blood flow measurement device according to claim 2, wherein: The first polarizing element further includes a λ / 4 plate.

4. The blood flow measurement device according to claim 3, wherein: The λ / 4 plate exhibits inverse wavelength dispersion.

5. The blood flow measurement device according to claim 1, wherein: The first polarizing element comprises a first linear polarizer, a phase difference layer and a second linear polarizer in this order. At least one of the first linear polarizer and the second linear polarizer is a layer formed using the liquid crystal compound.

6. The blood flow measurement device according to claim 5, wherein: The phase difference plate exhibits reverse wavelength dispersion.

7. The blood flow measurement device according to claim 1, wherein: The layer formed using the liquid crystal compound included in the first polarizing element has a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in a plane.

8. The blood flow measurement device according to claim 1, wherein: The liquid crystal compound is a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound.

Images