JP7221433B1 - Optical element and method for manufacturing optical element - Google Patents

Abstract

Kind Code: A1 An optical element in which occurrence of anisotropic strain is reduced even when optical members are joined by optical contact is provided.
A Fresnel rhomb 1 (optical element) includes a first rhombohedron 10 (first optical member), a second rhombohedron 20 (second optical member), and a disk-shaped member 30 (third optical member). member) and The first rhombohedron and the second rhombohedron are made of the first isotropic material, and have quadrangular (polygonal) surfaces through which light rays pass. The disk-shaped member is a plate-shaped member made of a second isotropic material. The outer periphery of the disk-shaped member is circular (curved) less than the outer periphery of the quadrangle. A disk-shaped member is joined between the first rhombohedron and the second rhombohedron by an optical contact OC with the first rhombohedron and the second rhombohedron.
[Selection drawing] Fig. 2

Description

The present invention relates to an optical element and a method for manufacturing the optical element, and more particularly to an optical element in which optical members are joined by optical contact and a method for manufacturing the optical element.

One method of joining optical members is optical contact. Optical contact is a technique for bonding polished flat surfaces of an optical member (for example, a prism) in close contact without using an adhesive.

An advantage of the optical contact is that it does not impair the transmission wavelength band and transmittance of the material constituting the optical member, and it does not impair the transmission wavefront precision, because no adhesive is used. Therefore, optical contacts are used for joining optical members in the ultraviolet light region and infrared light region, and for joining optical components that require high transmitted wavefront accuracy.

Patent Document 1 describes a Fresnel rhomb comprising a first parallelogram rhombohedron and a second rhombohedron made of an isotropic material, and a technique in which the two rhombohedrons are joined by optical contact.

Japanese Patent No. 6876188

Optical parts include members with a circular outer shape like lenses and members with rectangular outer shapes like prisms. In particular, the present inventor found a problem that anisotropic strain occurs when angular members are joined by optical contact. Anisotropic strain occurs particularly remarkably when the materials of the members to be joined are isotropic materials.

When anisotropic strain occurs, the polarization state of transmitted light changes. As a result, the parts and devices that control the polarization are affected, and instrumental polarization is likely to occur, which poses a problem for precision optical measuring instruments and the like.

The present invention has been made in view of the above problems, and an object of the present invention is to control polarized light with reduced occurrence of anisotropic distortion even when optical members are joined by optical contact. An object of the present invention is to provide an optical element and a method for manufacturing an optical element that controls polarization .

As a result of intensive research to solve the above problems, the present inventors have found that by sandwiching a plate-shaped optical member with a curved outer periphery between two optical members and joining them by optical contact, an anisotropic The inventors have found that the distortion can be reduced, and have completed the present invention.

According to the optical element of the present invention, the above object is provided with a first optical member, a second optical member, and a third optical member, and the first optical member and the second optical member is formed of a first isotropic material and has a polygonal surface through which light rays pass; the third optical member is a plate-shaped member formed of a second isotropic material ; wherein the third optical member is joined to the first optical member and the second optical member by optical contact between the first optical member and the second optical member; The outer circumference of the third optical member on the surface joined by the optical contact is arranged inside the outer circumference of the polygon and has a curved shape or a shape with an obtuse angle, The bonded surface is a surface through which the light beam is transmitted, and the optical element that controls the polarization changes the polarization state of the light beam transmitted through the surface bonded by the optical contact and is emitted. be.
At this time, the optical element is preferably a Fresnel Rhomb.
At this time, the first isotropic material and the second isotropic material are preferably the same material.
At this time, the third optical member is preferably disc-shaped.

Further, according to the method for manufacturing an optical element of the present invention, the first optical member and the second optical member are formed of a first isotropic material and have a polygonal surface through which light rays are transmitted. a step of preparing a third optical member which is a plate-like member formed of a second isotropic material; and a step of combining the third optical member with the first optical member and the a step of joining the first optical member and the second optical member by optical contact between the second optical member, and the third optical member on the surface joined by the optical contact; The outer periphery of the member is arranged inside the outer periphery of the polygon and has a curved shape or a shape with an obtuse angle, and the surface joined by the optical contact is the surface through which the light beam is transmitted . 2. A method for manufacturing an optical element for controlling polarization, in which the light transmitted through the surfaces joined by the optical contact is emitted with a changed polarization state.
At this time, the optical element is preferably a Fresnel Rhomb.
At this time, the first isotropic material and the second isotropic material are preferably the same material.
At this time, the third optical member is preferably disc-shaped.

According to the present invention, it is possible to provide an optical element in which the occurrence of anisotropic strain is reduced even when optical members are joined by optical contact.

FIG. 4 is a schematic diagram showing a state of joining with an optical contact in a normal Fresnel ROM; FIG. 4 is a schematic diagram showing how Fresnel rhombs are joined in an optical contact according to the present embodiment. It is a schematic diagram of a Fresnel Rhomb. It is a shape diagram of a comparative sample. It is the measurement result of the distortion of the conventional Fresnel rhomb joined by the optical contact. 1 is a schematic diagram of a Fresnel lom according to one embodiment of the present invention; FIG. It is a shape diagram of a fresnel rom according to one embodiment of the present invention. FIG. 10 is a strain measurement result of a fresnel lom joined by optical contact through a disc according to an embodiment of the present invention; FIG. 4 is a photograph showing the state of distortion of Fresnel rhombs joined by a normal optical contact. 4 is a photograph showing distortion of Fresnel roms joined by optical contact through a disc according to an embodiment of the present invention.

An optical element and a method for manufacturing an optical element according to an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described below with reference to FIGS. 1 to 10. FIG. The optical element according to this embodiment is an optical element that performs polarization control with reduced occurrence of anisotropic distortion.

In the present specification, ◯ to Δ mean ◯ or more and Δ or less.
As used herein, "optical contact" means that a pair of adjacent optical members are in direct contact with each other without an adhesive agent or an air layer interposed therebetween.

Observing the anisotropic strain that occurs when square optical members are joined together by optical contact, it was found that the anisotropic strain occurs particularly at the square corners of the surfaces through which light rays pass. In addition, anisotropic strain is less likely to occur between optical members having round surfaces through which light rays pass. Therefore, the present inventors have found a method of reducing the anisotropic strain by joining angular optical members with optical contacts via disc-shaped members.

The configuration of the optical element according to this embodiment will be described in comparison with a conventional optical element. In the following description, a Fresnel Rhomb is used as an example of an optical element, but the optical element is not limited to a Fresnel Rhomb. The technical idea of the present invention can be applied to the case of joining optical members having a rectangular joint surface by optical contact, and can reduce anisotropic strain.

FIG. 1 shows the structure of a typical Fresnel ROM. A general roof-type Fresnel rom has a structure in which two parallelogram blocks B made of an isotropic material are joined at a joint surface P. As shown in FIG. When the bonding surface P is an air gap or when bonding is performed with an adhesive selected so as not to generate anisotropic strain, no anisotropic strain is generated by bonding. When joining, anisotropic strain occurs. Anisotropic strain is mainly generated from the four corners of the joint surface P in the case of FIG.

FIG. 2 shows the configuration of the Fresnel ROM according to this embodiment. It is a structure in which a disk C is sandwiched between parallelogram blocks B of a general Fresnel rhomb. Both sides of the disc C are optically polished, as are the parallelogram blocks. Also, the disk C is made of an isotropic material. The size of the disk C should be equal to or smaller than the joint surface P of the parallelogram block B.

In the structure of the Fresnel rom according to the present embodiment, since there are no corners on the joint surface, distortion occurring during joining is reduced. The disk C is preferably made of the same material as the parallelogram block B, but is not limited to this. When the disk C and the parallelogram block B are made of the same material, there is an effect that deterioration of reliability due to expansion and contraction due to temperature change as an element and deterioration of performance due to reflection on the joint surface are reduced. Moreover, there is also an advantage that temperature control of each member before joining by the optical contact OC becomes easy. The size of the disk C is made equal to or smaller than the joint surface P of the parallelogram block B so as not to form a corner (corner) on the surface that is optically contacted OC.

As shown in FIG. 3, the normal Fresnel ROM 1 has a structure (roof-shaped Fresnel ROM) in which two parallelogram-shaped prism elements are combined. Specifically, the Fresnel rhomb 1 has a parallelogram-shaped first rhombohedron 10 and A second rhombohedron 20 is provided. The first rhombohedron 10 and the second rhombohedron 20 have the same shape and are made of an isotropic material.

As shown in FIG. 3 , the first rhombohedron 10 includes a first incident end face 11 , a first exit end face 12 arranged parallel to the first incident end face 11 , the first incident end face 11 and the first exit end face 12 . and a second total reflection surface 14 arranged parallel to the first total reflection surface 13 .

In the first rhombohedron 10, the first entrance end face 11 and the first exit end face 12 are parallel to each other, and the first total reflection surface 13 and the second total reflection surface 14 are parallel to each other. Further, in the first rhombohedron 10, the angles between the first incident end surface 11 and the first total reflection surface 13 and between the first exit end surface 12 and the second total reflection surface 14 are less than 90 degrees each other. They intersect at an angle (wedge angle α). Further, in the first rhombohedron 10, the angles between the first incident end surface 11 and the second total reflection surface 14 and between the first output end surface 12 and the first total reflection surface 13 are greater than 90 degrees to each other. intersect at an angle.

The second rhombohedron 20 has a second incident end face 21, a second exit end face 22 arranged parallel to the second incident end face 21, and a third total reflection surface intersecting the second incident end face 21 and the second exit end face 22. 23 and a fourth total reflection surface 24 arranged parallel to the third total reflection surface 23 .

In the second rhombohedron 20, the second entrance end face 21 and the second exit end face 22 are parallel to each other, and the third total reflection surface 23 and the fourth total reflection surface 24 are parallel to each other. Further, in the second rhombohedron 20, the angles between the second incident end surface 21 and the third total reflection surface 23 and between the second exit end surface 22 and the fourth total reflection surface 24 are less than 90 degrees to each other. They intersect at an angle (wedge angle α). Further, in the second rhombohedron 20, the angles between the second incident end surface 21 and the fourth total reflection surface 24 and between the second exit end surface 22 and the third total reflection surface 23 are greater than 90 degrees. intersect at an angle.

The first rhombohedron 10 and the second rhombohedron 20 are arranged to face each other such that the first emission end face 12 of the first rhombohedron 10 and the second incident end face 21 of the second rhombohedron 20 are parallel to each other. ing. The first emission facet 12 and the second incidence facet 21 are directly joined by optical contact.

As described above, the first incident end surface 11 and the first total reflection surface 13 (the first output end surface 12 and the second total reflection surface 14) of the first rhombohedron 10 form a wedge angle α. The second entrance end surface 21 and the third total reflection surface 23 (the second exit end surface 22 and the fourth total reflection surface 24) of the rhombohedron 20 also form a wedge angle α. Here, the wedge angle α can be appropriately set according to the type of isotropic material forming the first rhombohedron 10 and the second rhombohedron 20 .

As described above, the Fresnel rhomb is made of an isotropic material that does not have birefringence, but is a phase shifter that utilizes the phase difference between the p-wave and s-wave generated during total internal reflection. Total internal reflection is a phenomenon that occurs when light is incident from a high refractive material to a low refractive material at an angle equal to or greater than the critical angle.

Fresnel roms are formed from an isotropic material. The isotropic material may be any material that transmits a wavelength region from vacuum ultraviolet to near infrared. It is preferable to use at least one material selected from the group consisting of CaF ₂ (refractive index n=1.44@546 nm) and lithium fluoride (LiF: refractive index n=1.39@600 nm). As for the isotropic material to be used, it is also important that there are no material defects or distortions that deteriorate the phase difference, and it is preferable to use quartz (fused quartz) rather than CaF ₂ .

<Description of Fresnel Rhom of the present embodiment>
The Fresnel rhomb 1 (optical element) of the present embodiment includes a first rhombohedron 10 (first optical member), a second rhombohedron 20 (second optical member), and a disk-shaped member 30 (third optical member). member) and The first rhombohedron 10 and the second rhombohedron 20 are made of a first isotropic material. The first incident end face 11, the first exit end face 12, the second incident end face 21, and the second exit end face 22, which are surfaces through which light rays pass, are squares (polygons).

The disk-shaped member 30 (third optical member) is a plate-shaped member made of a second isotropic material. The outer periphery of the third optical member has a circular shape (curved shape) or a shape with an obtuse angle that is less than the rectangular outer periphery of the first entrance end face 11, the first exit end face 12, the second entrance end face 21, and the second exit end face 22. be. In other words, that the outer circumference of the disk-shaped member 30 (the third optical member) is curved means that there is no acute-angled portion in the shape of the outer circumference. Since the disk-shaped member 30 is disk-shaped, it is easy to process.

Between the first rhombohedron 10 and the second rhombohedron 20, the disk-shaped member 30 is joined to the first rhombohedron 10 and the second rhombohedron 20 by the optical contact OC. More specifically, the incident plane 31 of the disk-shaped member 30 is joined to the first output end face 12 of the first rhombohedron 10 by optical contact OC, and the output plane 32 of the disk-shaped member 30 is connected to the first output end face 12 of the first rhombohedron. It is joined to the second incident end face 21 of the dihedral body 20 by the optical contact OC.

The size of the disk-shaped member 30 is preferably smaller than or less than the joint surface in order to eliminate "corners" on the surface of the optical contact OC. In other words, the outer periphery of the incident plane 31 of the disk-shaped member 30 fits inside the outer periphery of the first output end face 12 of the first rhombohedron 10, and the outer periphery of the output plane 32 of the disk-shaped member 30 fits within the second rhombus. It fits inside the outer circumference of the second incident end face 21 of the facepiece 20 . In the Fresnel ROM 1 of this embodiment, the anisotropic distortion can be reduced by eliminating the "corner" on the surface of the optical contact OC.

Preferably, the first isotropic material and the second isotropic material are the same material. When the disk-shaped member 30 is made of the same material as the first rhombohedron 10 and the second rhombohedron 20, the reliability of the optical element deteriorates due to expansion and contraction due to temperature changes, and the reflection at the joint surface causes deterioration in reliability. Less performance degradation. Also, temperature control of each member before joining by the optical contact OC becomes easy.

(Multilayer film M)
The Fresnel ROM 1 preferably has a multilayer film M formed on at least one or more total reflection surfaces. Specifically, the first total reflection surface 13, the second total reflection surface 14 of the first rhombohedron 10, the third total reflection surface 23, and the fourth total reflection surface 24 of the second rhombohedron 20 have , the isotropic material forming the first rhombohedron 10 and the second rhombohedron 20 is preferably coated with a multilayer film M having a refractive index different from that of the isotropic material.

Here, the multilayer film M includes a high refractive index film _MH formed of a high refractive index material having a higher refractive index than the isotropic material forming the first rhombohedron 10 and the second rhombohedron 20; Low refractive index films _ML formed of a low refractive index material having a lower refractive index than the isotropic material forming the rhombohedron 10 and the second rhombohedron 20 are alternately laminated. The order of lamination of the high refractive index film _MH and the low refractive index film _ML is even if the high refractive index film _MH and the low refractive index film _ML are laminated in this order on the isotropic material serving as the substrate. Alternatively, a low refractive index film M _L and a high refractive index film M _H may be laminated in this order on an isotropic material that serves as a substrate.

The incident light I is totally reflected by each total reflection surface, and at the same time a phase difference occurs between the p-polarized light and the s-polarized light. Generally, the phase difference caused by total reflection increases as the wavelength becomes shorter. Therefore, a high refractive index film MH having a higher refractive index than the isotropic material ₍ quartz or CaF ₂ ) constituting the first rhombohedron 10 and the second rhombohedron 20 and a low refractive index film _ML having a smaller refractive index A multilayer film M in which two types of film materials are alternately laminated may be applied to the total reflection surface.

As high refractive index materials constituting the high refractive index film _MH , gadolinium fluoride (GdF ₃ : refractive index n = 1.59 @ 550 nm), lanthanum fluoride (LaF ₃ : refractive index n = 1.59 @ 550 nm ) and neodymium fluoride (NdF ₃ : 1.61@550 nm), but are not limited to these materials. Further, magnesium fluoride (MgF ₂ : refractive index n=1.38 to 1.40 @ 550 nm) is exemplified as a low refractive index material constituting the low refractive index film _ML , but is limited to this. not a thing

The high refractive index film _MH and the low refractive index film _ML can be formed by methods such as vacuum deposition, CVD, and sputtering. The thickness of the high refractive index film _MH and the low refractive index film _ML depends on the type of material, and may be, for example, 100 Å or more and 650 Å or less, but is not limited to this range.

<Method for Manufacturing Optical Element>
The method for manufacturing an optical element according to the present embodiment includes a step of preparing a first optical member and a second optical member which are formed of a first isotropic material and have polygonal surfaces through which light rays pass (Step 1 ), and a step of preparing a third optical member which is a plate-like member made of a second isotropic material and whose outer circumference is curved or has an obtuse angle less than the outer circumference of the polygon (Step 2 ), and a step of joining the third optical member to the first optical member and the second optical member by optical contact between the first optical member and the second optical member ( Step 3) and are performed.

In step 1, a first optical member (first rhombohedron 10) and a second optical member (second rhombohedron 20) formed of a first isotropic material and having polygonal surfaces through which light rays pass prepare.

In step 2, a third optical member (disk-shaped member 30 ) is prepared.

In step 3, the third optical member (disk-shaped member 30) is interposed between the first optical member (first rhombohedron 10) and the second optical member (second rhombohedron 20) to form the first The optical member and the second optical member are joined with the optical contact OC.

<Application example of the optical element of the present embodiment>
Application examples of the optical element of this embodiment are shown below. The optical element of this embodiment can be applied to a measuring device. Here, the "measurement device" includes various measurement devices, analysis devices, inspection devices, and observation devices.

The semiconductor inspection apparatus is an apparatus for inspecting a fine area, and since it actively uses ultraviolet light, the broadband circular polarizer of this embodiment that can be used in the wavelength range from vacuum ultraviolet to near infrared (phase difference 90 ° Fresnel rhombus) is preferably used. The broadband circular polarizer of this embodiment can be used for semiconductor inspection equipment that utilizes polarized white light.

A spectroscopic ellipsometer is exemplified as a specific target device to which the optical element of this embodiment is applied. Specifically, a broadband circular polarizer (Fresnel rhomb with a phase difference of 90°) can be used as a compensating element of the spectroscopic ellipsometer.

Also, the optical element of this embodiment can be applied to an observation device for observing a minute area. Contrast can sometimes be improved by controlling polarization. In order to observe finer details, it is necessary to use short wavelengths as well, so there is an advantage in using the broadband circular polarizer (Fresnel rhomb with a phase difference of 90°) of this embodiment.

Furthermore, in order to detect foreign matter, an observation device or an inspection device that utilizes the characteristic that the polarization state of the scattered light from the foreign matter is different from that of the normal portion is used. Specifically, the polarization state of the wiring pattern on the semiconductor wafer is observed. The broadband circular polarizer (Fresnel rhomb with a phase difference of 90°) of this embodiment can be applied to a device for detecting foreign matter. The method of using polarized light differs depending on the device, but when discovering an abnormality (defect) occurring in each semiconductor process from polarization information, the optical element (Fresnel rhomb with a phase difference of 90°) according to this embodiment is used with a phase difference of 180°. Combining with a (λ/2) phase shifter enables various polarization measurements. Further, the phase shifter with a phase difference of 180° (λ/2) may be a Fresnel rhomb with a phase difference of 180° using the present invention.

Also, the optical element of this embodiment can be applied to a film thickness meter. Film thickness gauges are mainly used for inspection during semiconductor processes, but they are also used for inspection of other film-like objects, such as measuring film thickness, coating thickness, and the like. There are various measurement principles of film thickness meters, but there are devices that measure film thickness by ellipsometry similar to ellipsometers.

Additionally, the optical element of the present embodiments can be used in place of a depolarizing element to reduce instrument polarization. In a reflective optical system, since the reflectances of p-polarized light and s-polarized light are different, when the polarization state of incident light is different or fluctuates, the transmittance also differs or fluctuates. In order to prevent this, the polarization state of the incident light may be made constant, or the polarization state of the outgoing light from the optical system may be made constant. In the case of a device for precise measurement, it is necessary to keep the polarization state of the incident light beam and the outgoing light beam constant. By combining the optical element (Fresnel rhomb with a phase difference of 90°) of this embodiment with a phase shifter with a phase difference of 180° (λ/2), any polarization state can be created, so the polarization state of the incident light beam and the outgoing light beam can be made constant. Further, the phase shifter with a phase difference of 180° (λ/2) may be a Fresnel rhomb with a phase difference of 180° using the present invention.

Methods for analyzing the three-dimensional structure of macromolecules such as proteins, pharmaceuticals, and foods include optical rotatory dispersion measurement (ORD) and circular dichroism (CD) spectrometry for investigating optical isomers of macromolecules. These measurements are methods of measuring the difference in refractive index and absorption between left and right circularly polarized light, and are measurements for which a circular polarizer with high accuracy and a wide wavelength band is desired. The optical element of the present embodiment meets such demands, and can improve the accuracy of optical rotatory dispersion measurement and circular dichroism spectrometry.

EXAMPLES The optical element of the present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

The effect of the present invention is particularly high in Fresnel rhombs, which are polarization control elements made using isotropic materials. Therefore, the effects of the present invention will be shown here using the roof-type Fresnel rom 1 as an example. The roof-shaped Fresnel rhomb 1 is a retarder shaped as shown in FIG. A ray incident from the incident end surface (first incident end surface 11) is totally reflected by the first total reflection surface 13, the second total reflection surface 14, the third total reflection surface 23, and the fourth total reflection surface 24 (slants 1 to 4). The light is reflected and emitted from the emission end face (second emission end face 22). The Fresnel rhomb 1 is a broadband phase shifter that utilizes the fact that a phase difference occurs between the p-wave and the s-wave when the light is totally reflected on the slopes 1-4. Since the phase difference generated by total reflection varies depending on the incident angle, the material of the element and the total reflection angle may be appropriately set in order to obtain the desired phase difference.

As shown in FIG. 3, the roof-shaped Fresnel rom 1 is composed of two parallelogram-shaped members (a first rhombohedron 10 and a second rhombohedron 20) made of glass, crystal, or the like. The two parallelogram members must either be joined by a method such as gluing or optical contact, or placed side by side without joining with an air gap. If the wavelength band used is ultraviolet light or infrared light, there is no adhesive that is transparent in this wavelength range, so it is necessary to join them by optical contact or arrange them in an arrangement with an air gap. If an air gap is provided, the number of planes of incidence and emission increases, resulting in an increase in loss due to reflection and a disadvantage that the phase performance deteriorates due to multiple reflections.

Conventionally, however, when isotropic materials with angular shapes as shown in FIG. 3 are brought into optical contact with each other, distortion occurs. FIG. 5 shows the result of actually measuring the state of distortion when the Fresnel roms having the shape shown in FIG. 3 are joined by optical contact. In order to quantify the state of distortion, the extinction ratio of linearly polarized light of p-wave linearly polarized light emitted from the Fresnel rhomb is used as an index. The extinction ratio is a quantity indicating the degree of linear polarization and is defined by the following formula.
Extinction ratio [dB] = -10 x log (Is/Ip)
Here, Is is the amount of s-wave light, and Ip is the amount of p-wave light. A higher extinction ratio indicates better linearly polarized light, and a change of 10 dB indicates that the ratio between Is and Ip differs by one order of magnitude.

Sample measurements are made with incident linearly polarized light with a wavelength λ=633 nm and an extinction ratio of about 65 dB. In addition, the measurement was performed by moving the incident light beam at intervals of 1 (mm) vertically and horizontally with a beam diameter of about Φ1 (mm). The size of the plane of incidence (bonded surface) of the Fresnel rhomb of the sample is 10×10 (mm). Details of the samples are shown in FIG.

If the extinction ratio is 50 dB or more, it can be said that the influence of distortion is very small. From the measurement results shown in FIG. 5, it can also be seen that there are many portions where the extinction ratio is less than 50 dB, and there are portions where the extinction ratio is very poor at 30 to 40 dB.

Next, measurement results of the Fresnel ROM 1 of this embodiment are shown. The shape of the manufactured Fresnel rom is shown in FIGS. 6 and 7. FIG. A disk-shaped member 30 is arranged between the incidence-side ROM (first rhombohedron 10) and the emission-side ROM (second rhombohedron 20) of the Fresnel ROM 1 in FIG. They are joined by contacts OC. The disk-shaped member 30 is made smaller than the bonding surfaces of the ROM (the first exit end surface 12 and the second entrance end surface 21), and has no contact point on the outer circumference. The disk-shaped member 30 was made of the same material as the first rhombohedron 10 and the second rhombohedron 20, and the sample was made of quartz. Details of the Fresnel ROM 1 (sample) of this embodiment are shown in FIGS.

FIG. 8 shows the measurement results of the in-plane distribution of the extinction ratio. At the low extinction ratio, it is about 45 dB, but it can be seen that the very bad portion of 30 to 40 dB has disappeared.

In order to visually show the state of distortion, similarly to the above measurement, linearly polarized light was incident on the sample, and the output light was observed through an analyzer arranged in a direction that does not transmit the incident light. The results are shown in FIGS. shown. A white light source is used as the light source. By observing the transmitted light in such an arrangement, the portion where the anisotropic strain occurred appeared white, and the state of the anisotropic strain could be observed.

FIG. 9 shows the distortion of the sample in which the ROMs shown in FIG. 3 are directly connected by optical contact, and FIG. 10 shows the distortion of the sample in which optical contact is made through the disk of the present invention shown in FIG. , respectively, are the results of visual observation.

From FIGS. 9 and 10, it was found that direct optical contact between the ROMs causes anisotropic strain around the corners of the joined square surfaces. It was also found that no significant anisotropic strain was generated by joining with the optical contact OC via the disk-shaped member 30 .

1 Fresnel rhomb 10 First rhombohedron (first optical member)
REFERENCE SIGNS LIST 11 first incident facet 12 first outgoing facet 13 first total reflection facet 14 second total reflection facet 20 second rhombohedron (second optical member)
21 second incident end face 22 second outgoing end face 23 third total reflection surface 24 fourth total reflection surface 30 disk-shaped member (third optical member)
31 incident plane 32 exit plane OC optical contact C disk (third optical member)
B Parallelogram block (first optical member, second optical member)
P Joint surface M Multilayer film α Wedge angle I Incident light E Output light

Claims (8)

comprising a first optical member, a second optical member, and a third optical member;
the first optical member and the second optical member are formed of a first isotropic material, and have polygonal surfaces through which light rays are transmitted;
The third optical member is a plate member made of a second isotropic material,
wherein the third optical member is joined to the first optical member and the second optical member by optical contact between the first optical member and the second optical member;
The outer periphery of the third optical member on the surface joined by the optical contact is arranged inside the outer periphery of the polygon and has a curved shape or an obtuse angle,
the surface joined by the optical contact is a surface through which the light beam is transmitted;
An optical element for controlling polarization, in which the light beam transmitted through the surfaces joined by the optical contact is emitted with a changed polarization state. 2. The optical element according to claim 1, which is a Fresnel rhomb. 3. The optical element according to claim 1, wherein the first isotropic material and the second isotropic material are the same material. 4. The optical element according to any one of claims 1 to 3, wherein the third optical member has a disk shape. a step of preparing a first optical member and a second optical member which are formed of a first isotropic material and have polygonal surfaces through which light rays pass;
preparing a third optical member, which is a plate-like member made of a second isotropic material;
bonding the third optical member to the first optical member and the second optical member by optical contact between the first optical member and the second optical member; ,
The outer periphery of the third optical member on the surface joined by the optical contact is arranged inside the outer periphery of the polygon and has a curved shape or an obtuse angle,
the surface joined by the optical contact is a surface through which the light beam is transmitted;
A method for manufacturing an optical element that controls polarization, wherein the light beam transmitted through the surfaces joined by the optical contact is emitted with a changed polarization state. 6. The method for manufacturing an optical element according to claim 5, wherein the optical element is a Fresnel rhomb. 7. The method of manufacturing an optical element according to claim 5, wherein the first isotropic material and the second isotropic material are the same material. 8. The method for manufacturing an optical element according to claim 5, wherein the third optical member is disc-shaped.

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