JP2006218193A - Optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element being suitable for a new endoscope system, which enables the accurate specification of a lesion and the highly precise analysis of the lesion during an endoscopic observation while maintaining the diameter reduction and the miniaturization of a flexible tube. <P>SOLUTION: This optical element is used for an endoscope system equipped with a spectral means which performs a spectral process regarding a biological tissue in a body cavity by emitting terahertz light through the flexible tube. The optical element has a first optical member, an abutment region which abuts on the biological tissue, a second optical member, and a proximity arranging region. In this case, the first optical member is arranged on the distal end of the flexible tube, and has a slope which tilts to a surface on the incidence side of the optical element where the terahertz light enters. The second optical member has an end surface located on the opposite side from the abutment region. In the proximity arranging region, the slope and the end surface are proximately arranged across an optical membrane having a predetermined thickness and a refractive index which is smaller than those of respective optical members. The optical element is constituted in such a manner that a bonding region transmits an S component only from the entered terahertz light, and the abutment region deflects the S component of the terahertz light, and an evanescent wave may be generated by the incidence of the S component. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element used in an endoscope system for observing a living tissue in a body cavity.

  2. Description of the Related Art Conventionally, so-called endoscopic observation is widely used in which visible light or near infrared light is irradiated into a body cavity using an endoscope, and a biological tissue illuminated by each light is observed through a monitor or the like. While performing endoscopic observation, a surgeon such as a doctor collects a lesioned part and an obscured part using a forceps probe or the like to make a sample for pathological examination or remove it.

  In the pathological examination, in recent years, analysis using terahertz light as described in Non-Patent Document 1 below is being put into practical use.

Tera View ltd., [Online] [searched May 26, 2004], Internet <http://www.teraview.co.uk/ap_oncology.asp>

  Terahertz light is light having a frequency in the range of 0.3 to 3 THz (wavelength in the range of 100 μm to 1000 μm), and has both characteristics as light (for example, straightness) and characteristics as radio waves (substance permeability). . Further, it is known that the absorption characteristics of a substance relating to terahertz light differ depending on the molecular structure of each substance. Non-Patent Document 1 discloses a technique for performing spectroscopic analysis on a sample using terahertz light based on the above characteristics and analyzing whether or not a lesion (cancer cell part) is included based on the spectroscopic result. is doing.

  Here, under visible light or near-infrared light, accurate judgment and analysis of the composition of the biological tissue currently being observed, and more specifically, where the lesion is located in the body cavity It is very difficult to obtain information on the living tissue for performing the operation. This is not much of a problem if the biological tissue is collected on the premise of a pathological examination capable of obtaining a more accurate analysis result. It is in a state where it must be relied on, and it may impose an excessive burden on the surgeon.

  Further, even if the analysis can be performed by the pathological examination as described above, the pathological examination is often performed in a temporally and spatially separated manner from the endoscopic observation. For this reason, it has been pointed out that inefficiency is likely to hinder rapid diagnosis and treatment.

  Therefore, in recent years, there has been a demand for realization of a new endoscope system including spectroscopic means that enables accurate identification of a lesioned part and high-accuracy analysis of the lesioned part during endoscopic observation. Here, the endoscope system performs endoscopic observation by inserting a long and flexible tube (flexible tube) into the body cavity of the subject. For this reason, the new endoscope system can maintain the reduction in diameter and size of the flexible tube in order to alleviate the physical and mental pain of the subject even if it is equipped with the above-described analysis means. It is required to be.

  Therefore, in view of the above circumstances, the present invention provides a new endoscope system that enables accurate identification of a lesion and accurate analysis of the lesion during endoscopic observation. An object of the present invention is to provide an optical element suitable for achieving miniaturization.

  In order to solve the above-described problem, the optical element according to claim 1 irradiates a living tissue in the body cavity with terahertz light via a flexible tube inserted into the body cavity, and reflects light from the living tissue. An optical element in an endoscope system including a spectroscopic unit that performs spectroscopy on the living tissue using the illuminating element, and is disposed at the distal end of the flexible tube, and the incident side surface of the optical element on which the terahertz light is incident A first optical member having an inclined surface inclined with respect to the living body tissue, a second optical member having an end surface located on the opposite side of the corresponding contact region, a predetermined thickness, Sandwiching an optical film having a refractive index smaller than that of each optical member, the slope and the end face are close to each other, and the joining region transmits only the S component of the incident terahertz light, The contact area deflects the S component of the terahertz light. Moni, the S component is characterized by being configured to evanescent wave is generated by the incident.

  As described above, the optical element according to the present invention has a function of irradiating the living tissue in the body cavity with the terahertz light used for the spectroscopy and simultaneously returning the reflected light from the living tissue to the spectroscopic means. Therefore, the number of members disposed inside the flexible tube can be reduced by applying the optical element according to the present invention to an endoscope system (new endoscope system) including a spectroscopic unit. Therefore, the new endoscope system enables highly accurate analysis of living tissue in a body cavity using the spectroscopic means, and at the same time, the diameter and size of the flexible tube can be reduced.

  According to the optical element of the second aspect, it is desirable that the optical path of the terahertz light incident on the optical element is substantially parallel to the optical path of the S component deflected by the contact area. Thereby, the diameter of the flexible tube can be further reduced.

  In order for the optical path of the terahertz light incident on the optical element and the optical path of the S component deflected by the contact area to be substantially parallel, the contact area is composed of at least two surfaces that are adjacent to each other at right angles. The at least two surfaces may be arranged such that the S component of the terahertz light is incident while satisfying the total reflection condition.

  For example, according to the invention described in claim 4, the contact region can be configured as three surfaces formed in a corner cube shape.

  According to the fifth aspect of the present invention, the junction region reflects the P component of the incident terahertz light at the first interface between the inclined surface of the first optical member and the optical film, and reflects the incident terahertz light. The S component is irradiated as an evanescent wave, and at the second interface between the optical film and the end face, the evanescent wave irradiated from the first interface is transmitted as the S component of the terahertz light.

  According to the sixth aspect of the present invention, the predetermined thickness is a thickness that reaches the second optical member before the evanescent wave is completely attenuated. According to the seventh aspect of the present invention, an air layer can be used as an alternative to the optical film. Furthermore, according to the invention described in claim 8, the first optical member and the second optical member may be made of the same material.

  From another viewpoint, the optical element according to claim 9 irradiates the biological tissue in the body cavity with terahertz light via a flexible tube inserted into the body cavity, and uses the reflected light from the biological tissue. An optical element in an endoscope system including a spectroscopic unit that performs spectroscopy on the living tissue, the optical branching unit being disposed at the distal end of the flexible tube and transmitting only the S component of the incident terahertz light; A retroreflecting unit configured to contact the living tissue and retroreflect the S component of the terahertz light emitted from the optical branching unit, and to generate an evanescent wave when the S component is incident It is characterized by that.

  As described above, according to the present invention, an optical element having a function of irradiating a living tissue in a body cavity with terahertz light used for spectroscopy and simultaneously returning reflected light from the living tissue to the spectroscopic means is provided. By applying the optical element having the above function to a new endoscope system having a spectroscopic means, it is possible to effectively contribute to reducing the diameter and size of the flexible tube of the system. That is, the optical element according to the present invention can be said to be an optical element suitable for a new endoscope system.

  Hereinafter, an embodiment of an endoscope system having an optical element according to the present invention will be described. FIG. 1 is a diagram illustrating a schematic configuration of an endoscope system 500 of the present embodiment. The endoscope system 500 includes an endoscope 100, a processor 200, and a monitor 300. The endoscope 100 includes a flexible tube 101, a forceps insertion port 102, and a main body 103. The main body portion 103 is provided with an operation member. The processor 200 includes a first light source 210 that emits predetermined pulsed light, a second light source 220 that emits visible light, and an image processing unit 230.

  A flexible tube 101 formed in the endoscope 100 is a long tube that is inserted into a body cavity, and has flexibility. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the distal end portion of the flexible tube 101. As shown in FIG. 2, the endoscope 100 includes a first optical unit 50 and a second optical unit 60 for observing a living tissue C in the body cavity. More specifically, the distal end portion of the flexible tube 101 has two openings (cavities). The optical units 50 and 60 are disposed in the cavities without gaps.

  The first optical unit 50 converts predetermined pulsed light emitted from the first light source 210 into terahertz light. And it is a unit for performing the highly accurate analysis regarding the molecular composition of the biological tissue C using this terahertz light. In addition, the 1st light source 210 of this embodiment irradiates a femtosecond laser as predetermined pulse light. The processing using the first optical unit 50 will be described in detail below.

  FIG. 3 is a diagram mainly showing a configuration of the first optical unit 50 of the first embodiment. As shown in FIG. 3, the femtosecond laser emitted from the first light source 210 enters the half mirror 1 in the first optical unit 50 through a light guide (not shown). The femtosecond laser transmitted through the first half mirror 1 enters the first optical antenna 2. Note that the femtosecond laser deflected by the first half mirror 1 goes to a delay optical system 17 to be described later.

  FIG. 4 is an enlarged view showing the first optical antenna 2. The first optical antenna 2 has a substrate 2A. On the substrate 2A, two T-shaped electrodes 2B and 2C are arranged such that the convex portions thereof face each other and a predetermined gap is formed between the convex portions. Each electrode 2B, 2C is connected to a DC power source, and a DC bias voltage is applied in advance. When the femtosecond laser enters the gap of the first antenna 2, terahertz light is generated. Since the terahertz light is generated in almost all directions of the first optical antenna 2, the terahertz light is collected by the first silicon lens 3 and emitted from the lens 3 forward, that is, toward the flexible tube 101.

  The terahertz light emitted from the first silicon lens 3 enters the first optical fiber 5 via the first lens 4. The first lens 4 is disposed to narrow the light flux so that the terahertz light is preferably incident on the core of the first optical fiber 5. In the present embodiment, the terahertz light emitted from the first lens 4 is parallel light. That is, the first lens 4 of this embodiment functions as a collimating lens.

  As the 1st optical fiber 5, the thing of the structure which can propagate terahertz light, for example, a hollow fiber, a photonic crystal fiber, etc. is used. The same applies to the second optical fiber 12 described later.

  The terahertz light emitted from the first optical fiber 5 is incident on an optical element (hereinafter referred to as a tip element for convenience of description) 90 disposed at the tip of the flexible tube 101 via the second lens 7.

  FIG. 5 is an enlarged view of the tip element 90. The tip element 90 has a first prism portion 91, a second prism portion 92, and an optical film 93. The prism portions 91 and 92 are bonded to each other with the surfaces 91 </ b> A and 92 </ b> C through the optical film 93. In other words, the inclined surfaces 91A and 92C are arranged close to each other with the optical film 93 interposed therebetween.

  As shown in FIG. 3, the first prism unit 91 has a right-angled triangular cross-section on the surface including the optical axis of the first optical unit 50 (a surface parallel to the paper surface), and has an inclined surface 91A. The slope 91A is inclined with respect to the surface on which the terahertz light is incident. The second prism portion 92 has at least two total reflection surfaces whose adjacent surfaces are in contact with each other at a right angle, and an end surface located on the opposite side of the total reflection surface. The second prism portion 92 of this embodiment has two total reflection surfaces 92A and 92B that are in contact with each other at right angles, and an end surface 92C that is located on the opposite side of each of the total reflection surfaces 92A and 92B and has substantially the same shape as the inclined surface 91A.

  In the present embodiment, each of the total reflection surfaces 92A and 92B is formed by making the end of the second prism portion 92 opposite to the end surface 92C into a right-angle prism shape, as shown in FIG. The total reflection surfaces 92A and 92B are in contact with the living tissue C as shown in FIG. That is, each of the total reflection surfaces 92A and 92B functions as a contact surface that contacts the living tissue C.

  In the tip element 90, each of the members 91 to 93 transmits the S component of the terahertz light incident on the element 90 as an evanescent wave through the interface between the first prism part 91 and the optical film 93 and enters the second prism part 93. The P component is totally reflected at the interface. In addition, the tip element 90 is configured such that the S component of the terahertz light incident on the second prism portion 93 is totally reflected by the two total reflection surfaces 92A and 92B of the second prism portion 93.

More specifically, assuming that the refractive index of the first prism portion 91 is n1, the refractive index of the optical film 93 is n2, the refractive index of the second prism portion 92 is n3, and the refractive index of the living tissue C is nc, n1> The relations n2, n3> n2, n1> nc, and n3> nc are established. The tip element 90 has an incident angle θ1 in the optical film 93 of terahertz light satisfying the following condition (1),
θ1 ≧ arcsin (n2 / n1) (1)
Configured to meet. Further, the incident angle θ2 at the two total reflection surfaces 92A and 92B of the S component of the terahertz light is the above condition (2),
θ2> arcsin (nc / n3) (2)
Configured to meet.

The first prism portion 91 and the second prism portion 92 can be made of the same material (n1 = n3). The optical film 93 may be a single layer or a multilayer, and may be an air layer (n2 = 1.0). However, the film thickness of the optical film 93 (that is, the distance between the prism portions 91 and 92) is determined so that the evanescent wave generated at the interface between the first prism portion 91 and the optical film 93 is completely attenuated. It is set to a very small value so as to enter the portion 92 as the S component of the terahertz light.

  From the terahertz light incident on the tip element 90 configured as described above, only the S component is extracted at the interface between the first prism portion 91 and the optical film 93. Then, the S component of the terahertz light is totally totally reflected by the two total reflection surfaces 92A and 92B of the second prism portion 92 sequentially. When total reflection is performed, evanescent waves are applied to the living tissue C from the total reflection surfaces 92A and 92B.

  Here, the evanescent wave absorption rate is different depending on the molecular structure of the biological tissue C. Therefore, for example, the absorption rate of the evanescent wave differs between the healthy part and the affected part. That is, the S component of the terahertz light totally reflected by each of the total reflection surfaces 92A and 92B is attenuated corresponding to the absorption rate of the molecular structure of the biological tissue C irradiated with the evanescent wave. In addition, by repeating total reflection on a plurality of reflection surfaces (total reflection surfaces 92A and 92B) as in the present embodiment, the component irradiated to and absorbed by the sample (that is, the biological tissue C) is amplified and measurement sensitivity is improved. Can be made.

  Each of the total reflection surfaces 92 </ b> A and 92 </ b> B returns the S component of the terahertz light to the direction in which the terahertz light is incident on the tip element 90. In the present embodiment, the optical path of light incident on the tip element 90 and the optical path of light emitted from the tip element 90 are in a substantially parallel relationship. Thus, the total reflection surfaces 92A and 92B in the tip element 90 not only function as contact surfaces with the living tissue C, but also return the optical path of the S component of the incident terahertz light to the incident direction (this embodiment). Then, it also functions as a deflection means for retroreflecting.

  The S component (total reflection attenuation wave) of the terahertz light emitted from the tip element 90 is incident on the second optical fiber 12 by the third lens 11 designed in the same manner as the second lens 7. The attenuated total reflection wave emitted from the second optical fiber 12 enters the second optical antenna 15 via the fourth lens 13 and the second silicon lens 14. The fourth lens 13 has the same design as the first lens 4 and the second silicon lens 14 has the same design as the first silicon lens 3.

  The second optical antenna 15 has substantially the same shape as the first optical antenna 2 shown in FIG. However, in the first optical antenna 2, the electrodes 2B and 2C are connected to a DC power supply, whereas in the second optical antenna 15, the electrodes 15B and 15C are connected to the image processing unit 230 of the processor 200 via an amplifier. Is different.

  In the second optical antenna 15, the side opposite to the side where the total reflection attenuation wave is incident (here, the electrode arrangement side) is branched by the half mirror 1, and is femtosecond via the delay optical system 17 and the third mirror 16. Laser enters. In the second optical antenna 15, a current proportional to the intensity of the attenuated total reflection wave is generated between the electrodes 15 </ b> B and 15 </ b> C when the incidence of the femtosecond laser is triggered. The current is amplified as a current signal by an amplifier and transmitted to the image processing unit 230 of the processor 200. Here, the total reflection attenuation wave incident on the second optical antenna 15 through the same part of the living tissue C is always a pulse having substantially the same waveform. Therefore, by shifting the timing of the femtosecond laser incident on the second optical antenna 15 by the delay optical system 17, the pulse waveform of the total reflection attenuation wave can be sampled sequentially. Therefore, the pulse waveform can be reproduced by sequentially developing the level of the current signal along the time axis.

  The image processing unit 230 reproduces the pulse waveform of the attenuated total reflection wave based on the sequentially transmitted current signal, and performs the spectroscopy of the living tissue C using the pulse waveform. The spectral result is displayed on the monitor 300. The surgeon looks at the spectroscopic result displayed on the monitor 300, and does not collect the living tissue C during endoscopic observation, but performs high-precision analysis on the living tissue C to accurately identify the lesioned part. Can do.

  Further, by operating the flexible tube 101 while performing the above operation and sliding the total reflection surface 9B in a plane substantially orthogonal to the optical axis of the first optical unit 50, the above pulse waveforms relating to different parts are obtained. It is done. The image processing unit 230 can also generate a two-dimensional image of the living tissue C based on a plurality of sequentially obtained pulse waveforms.

  In this embodiment, as shown in FIG. 3, the members closer to the tip element 9 than the first lens 4 and the fourth lens 13 are accommodated in the flexible tube 101, and the optical antennas 2, 15 and the like are flexible tubes. 101 (in this case, inside the main body 103). Thus, only the minimum necessary optical members are arranged inside the flexible tube 101. Further, as shown in FIG. 3, each member inside the flexible tube 101 is arranged so that the optical path of the light incident on the tip element 9 and the optical path of the light reflected by the tip element 9 are parallel. By configuring as described above, the flexible tube 101 can be reduced in diameter.

  In the present embodiment, the polarizing beam splitter 6 can be disposed immediately after the first silicon lens 3 if the configuration of the distal end of the flexible tube 101 is simplified.

  The second optical unit 60 is a so-called normal observation optical unit that images and observes the inside of the body cavity using visible light that is emitted from the second light source 220 and illuminates the inside of the body cavity via a light guide (not shown). . More specifically, the second optical unit 60 includes an objective optical system 61 and an image sensor (not shown). Then, the visible light reflected by the site in the body cavity enters the image sensor via the objective optical system, and the image sensor captures an observation image. Data (image data) related to the image captured by the image sensor is output to the image processing unit 230 of the processor 200. The image processing unit 230 performs predetermined processing on the image data and causes the monitor 300 to display an image.

  When performing an endoscopic observation using the endoscope system 500, the surgeon performs the above-described analysis using the terahertz light while referring to an image captured by the second optical unit 60 and displayed on the monitor 300. FIG. 6 is a diagram illustrating an example of an image captured by the second optical unit 60 and displayed on the monitor 300. Here, as shown in FIG. 2, the first optical unit 50 has a tip (more precisely, the total reflection surfaces 92 </ b> A and 92 </ b> B shown in FIG. 3) by a predetermined distance D from the tip surface of the second optical unit 60. It is in a protruding state. Moreover, the imaging range in the second optical unit 60 is indicated by a one-dot chain line in FIG. As shown in FIG. 2, the second optical unit 60 has a wide field of view including the tip of the first optical unit 50. Accordingly, as shown in FIG. 6A, a part of the tip of the first optical unit 50 is displayed in the image captured by the second optical unit 60. The surgeon operates the flexible tube 101 of the endoscope so that the tip of the unit 50 overlaps the living tissue C to be analyzed (contacts in the actual body cavity) in the image. An image in a state where the tip of the first optical unit 50 overlaps the living tissue C is shown in FIG.

  The predetermined distance D will be further described. As described above, the predetermined distance D is set to a predetermined length or more so that a part of the tip of the first optical unit 50 is displayed in the image captured by the second optical unit 60. However, if the predetermined distance D is set too long, the ratio of the tip of the first optical unit 50 in the normal observation image captured by the second optical unit 60 becomes too large, and the required body cavity It becomes difficult to see the state inside. Therefore, in the present embodiment, as shown in FIG. 6A, when an image captured by the second optical unit 60 is divided into four areas by a virtual cross line that intersects at the center of the image, The predetermined distance D is set to a length that allows the tip of the first optical unit 50 to be within one area.

  The above is the description of the embodiment of the present invention. According to this embodiment, since the members disposed at the distal end portion of the flexible tube can be collected, the diameter of the distal end portion can be further reduced. The present invention is not limited to these embodiments and can be modified in various ranges.

  It should be noted that the shape of the region (contact region) including the total reflection surfaces 92A and 92B functioning as the contact surfaces in the tip element 90 is not necessarily limited to the rectangular prism shape as shown in FIGS. . The shape of the contact area in the tip element 90 may be a shape having at least two surfaces in which adjacent surfaces contact each other at a right angle. 7 and 8 are diagrams showing a modification of the tip element 90. FIG.

  The tip element 90α shown in FIG. 7 is formed in a quadrangular pyramid shape with two pairs of a pair of surfaces orthogonal to each other. The tip element 90α can use a set of surfaces in the quadrangular pyramid shape as a total reflection surface (contact surface). Further, the tip element 90β shown in FIG. 8 is formed in a shape having three surfaces orthogonal to each other, that is, a corner cube shape. The tip element 90β can use the above three surfaces as a total reflection surface (contact surface).

  In the above embodiment, the first optical unit 50 for performing analysis using terahertz light and the endoscope 100 provided with the second optical unit 60 for normal observation are used. The endoscope system on which the optical element according to the invention is mounted is not limited to this configuration. For example, the structure which uses the endoscope 100 with which the 1st optical unit 50 was mounted independently may be sufficient.

  Further, in the above-described embodiment, the members closer to the tip element 90 than the first lens 4 and the fourth lens 13 are accommodated in the flexible tube 101, and the optical antennas 2, 15 and the like are outside the flexible tube 101 (here, the main body portion). 103). However, this is merely an example, and which tip element is accommodated in the flexible tube 191 can be changed as appropriate in relation to other components and signal lines provided in the endoscope 100. is there.

  In each of the above embodiments, the evanescent wave is generated by totally reflecting the S component of the terahertz light by the total reflection surface that is a contact surface with the living tissue. However, as an evanescent wave generation method, Is not limited to this. For example, an evanescent wave can be generated by forming a diffractive structure on the contact surface.

It is a figure showing a schematic structure of an endoscope system of an embodiment of the present invention. It is sectional drawing which expands and shows the front-end | tip part vicinity of a flexible tube. It is a figure which mainly shows the structure of the 1st optical unit of this embodiment. It is a figure which expands and shows a 1st optical antenna. It is a figure which shows the optical element (tip element) of embodiment of this invention. It is a figure which shows an example of the image imaged with the 2nd optical unit and displayed on the monitor. It is a figure which shows the modification of an optical element (tip element). It is a figure which shows the modification of an optical element (tip element).

Explanation of symbols

2, 15 Optical antenna 5, 12, 19 Optical fiber 6 Polarizing beam splitter 90 Optical element (tip element)
50 First Optical Unit 100 Endoscope 101 Flexible Tube 200 Processor 210 First Light Source 230 Image Processing Unit

Claims (11)

Internally provided with spectroscopic means for irradiating a living tissue in the body cavity with terahertz light through a flexible tube inserted into the body cavity and using the reflected light from the living tissue to perform spectroscopy on the living tissue. An optical element in an endoscope system,
Disposed at the distal end of the flexible tube;
A first optical member having a slope inclined with respect to a surface on the incident side of the optical element on which the terahertz light is incident;
A second optical member having an abutting area that abuts against the living tissue, and an end face located on the opposite side of the corresponding contacting area;
With an optical film having a predetermined thickness and a refractive index smaller than each of the optical members, the slope and the proximity arrangement region where the end face is arranged in proximity,
The junction region transmits only the S component of the incident terahertz light,
The abutting region is configured to deflect an S component of the terahertz light and to generate an evanescent wave when the S component is incident. The optical element according to claim 1,
An optical element, wherein an optical path of the terahertz light incident on the optical element and an optical path of the S component deflected by the contact region are substantially parallel. The optical element according to claim 1 or 2,
The contact area is at least two surfaces where adjacent surfaces contact each other at right angles,
The optical element is characterized in that each of the at least two surfaces is disposed so that an S component of the terahertz light is incident while satisfying a total reflection condition. The optical element according to any one of claims 1 to 3,
The contact area has three surfaces formed in a corner cube shape. The optical element according to any one of claims 1 to 4,
The junction region irradiates the S component of the incident terahertz light as an evanescent wave by totally reflecting the P component of the incident terahertz light at the first interface between the inclined surface and the optical film, An optical element that transmits the evanescent wave irradiated from the first interface as an S component of terahertz light at a second interface between the first end face and the end face. The optical element according to claim 5, wherein
The predetermined thickness is an optical element that reaches the second optical member before the evanescent wave is completely attenuated. The optical element according to any one of claims 1 to 6,
An optical element using an air layer as an alternative to the optical film. The optical element according to any one of claims 1 to 7,
The optical element, wherein the first optical member and the second optical member are made of the same material. Internally provided with spectroscopic means for irradiating a living tissue in the body cavity with terahertz light through a flexible tube inserted into the body cavity and using the reflected light from the living tissue to perform spectroscopy on the living tissue. An optical element in an endoscope system,
Disposed at the distal end of the flexible tube;
A light branch that transmits only the S component of the incident terahertz light;
A retroreflecting unit configured to contact the biological tissue and retroreflect the S component of the terahertz light emitted from the optical branching unit and generate an evanescent wave when the S component is incident; And an optical element. A first optical member having a slope inclined with respect to a surface on the incident side of the optical element on which the terahertz light is incident;
A second optical member having an end face on the opposite side of the retroreflective portion and the retroreflective portion;
With the optical film in between, the slope and the joining area where the end face is joined,
The optical element according to claim 9, wherein the light branching portion is the bonding region. The optical element according to claim 10, wherein
The retroreflective portion is at least two surfaces where adjacent surfaces contact each other at right angles,
The optical element is characterized in that each of the at least two surfaces is disposed so that an S component of the terahertz light is incident while satisfying a total reflection condition.

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