JPH0766084B2 - Polarizing / splitting element composed of shaped birefringent body and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to two linearly polarized light fluxes (an ordinary ray and an anomalous ray) in which one light flux is spatially parallel and whose polarization directions are orthogonal to each other. The present invention relates to a polarization separation element that separates light beams (corresponding to light rays) or reversely combines, and particularly relates to a polarization separation element having a large polarization separation performance and a wide aperture by utilizing shape birefringence, and a manufacturing method thereof.

[Prior Art] Conventionally, one light beam is separated into two linearly polarized light beams (corresponding to ordinary ray and extraordinary ray) which are spatially parallel and whose polarization directions are orthogonal to each other, or vice versa. Crystals such as calcite and rutile are used as the polarized light separating element to be synthesized.

In this case, the birefringence of the crystal is caused by inclining the optical principal axis of the crystal with respect to the incident light beam, and is based on the function of the material itself of the crystal.

However, the polarization separation element made of crystals such as rutile and calcite has some problems as follows.

(1) Poor polarization separation performance The polarization separation angle at which one incident light beam is separated into two linearly polarized light beams in the crystal is approximately 5.7 ° for both rutile and calcite, and the two polarizations In order to obtain a predetermined separation width for the luminous flux, the thickness of rutile and calcite needs to be about 10 times the separation width, which inevitably leads to an increase in the size of the lightwave circuit and increases the optical path length. Causes an increase in the diffraction loss of.

(2) Difficult to obtain a device with a large opening Natural rutile and calcite are difficult to obtain because they are homogeneous and large, so mass production is difficult, and even for artificially obtained rutile, it is possible to grow large and homogeneous crystals. Mass production is difficult, and therefore it is not possible to enlarge the aperture and polarize and separate a large number of incident light beams at the same time.

(3) There is a limit to mining from the natural world. On the other hand, it is known that the efficiency of separating polarized light increases as the magnitude of birefringence increases. , A crystal with greater birefringence was needed. However, there is a limit in searching the natural world for a crystal having a birefringence higher than that of rutile or calcite used conventionally. At the same time, it is unlikely that such crystals will be large and stable.

(4) Difficult to handle such as processing Rutile has too high hardness, so processing such as cutting and polishing is difficult, and calcite has high solubility in water, poor environmental resistance, and mechanical properties. There is a problem of being brittle.

On the other hand, in the field of optics, it is known that a birefringent body can be artificially obtained by regularly arranging minute transparent bodies having shape anisotropy, and this is called shape birefringence.
For example, publications before the present application (“Principles of Optics”, 4th edition,
M. Born and E. Wolf, co-authored; 1970, published by Pergamon Press, pp. 705-708), in which a large number of two kinds of transparent bodies having different refractive indexes are laminated, and the direction normal to the laminated surface is the optical axis. It describes the birefringence in the case of the above, or the birefringence when an innumerable thin cylindrical transparent body is present in another transparent body having a different refractive index.

It should be noted that, in JP-A-61-87101, as a specific structural example in which a large number of the above two kinds of transparent bodies are laminated, silicon dioxide,
And those using ditantalum pentoxide or niobium pentoxide are described.

Further, regarding the analysis of the shape birefringence, a paper before the application of the present application (“shape birefringence of macromolecule”; WL Bragg and
AB Pippard, Actor Crystal 6 (1953), 865
~ 867) and the like.

[Problems to be Solved by the Invention] However, the conventional techniques relating to the above-described shape birefringence are limited to merely generating the shape birefringence and precisely controlling the size thereof, and to further expand the function and improve the performance. It did not contribute.

In addition, for example, papers before the application of the present application (S. Jacob, Y. Asahara, T. Izumitani; Applied Optics, 21 (no.
24,1982) 4526 to 4532) describes a technique for obtaining a shape birefringence by heating and stretching a porous glass containing air. However, nothing is disclosed about at least the function of separating polarized light. Not.

The present invention has been made to solve the above-mentioned problems of the prior art, has a large polarization separation performance, further has a wide opening, and has excellent environmental resistance characteristics and workability, etc. An object of the present invention is to provide a polarization separation element made of a birefringent body and a method for manufacturing the same.

[Means for Solving the Problems]

According to the invention of claim 1, a large number of two kinds of transparent thin films having different refractive indexes are alternately laminated to form a transparent laminated body having shape birefringence, and the laminated surface of the laminated body is oblique to the direction of light irradiation. And the positions of incidence and emission of light were within the oblique cross section of the stacking surface of this stack. As a result, the transparent laminate having the shape birefringence has the function of separating polarized light, and the polarization component performance can be controlled by combining the refractive indexes of two kinds of transparent thin films.

According to the invention of claim 2, one of the two kinds of thin film-shaped transparent bodies in claim 1 is made of silicon. As a result, a material having a large difference in refractive index from other transparent bodies can be easily obtained.

The invention of claim 3 is the method for manufacturing a transparent laminate having the shape birefringence of claim 1, which can be manufactured by a sputtering method, a chemical vapor deposition method, or a plasma chemical vapor deposition method.

According to a fourth aspect of the present invention, one of the two types of transparent bodies is another elongated body, the length directions thereof are aligned in a constant direction, and the transparent bodies are discretely arranged in another transparent body having a different refractive index. The whole is formed into a shape birefringent body, and the elongated body is arranged so that the lengthwise direction thereof is oblique to the incident direction of light, thereby having a polarization separating function. This structure is suitable for manufacturing a polarization separation element having a large aperture because it is not necessary to stack a large number of thin films.

The invention of claim 5 is characterized in that, in the invention of claim 4, a polarization separation element using a shape birefringent body in which elongated bubbles or transparent bodies are present in transparent glass or transparent plastic. Since air has the lowest refractive index, the difference in the refractive index with other transparent bodies becomes large, and the shape birefringence can be made large, so that the polarization separation performance becomes large.

The invention of claim 6 is the method for manufacturing a polarization beam splitting element according to the invention of claim 5, wherein an element having a wide aperture can be manufactured at low cost.

[Action]

In the structure of claim 1, as shown in FIG. 1 and FIG.
The light flux R incident on the oblique cross section 10a of the stacking surface 10c of the stack constituting the polarization separation element 10 is split into ordinary light Eo and extraordinary light Ee whose polarizations are orthogonal to each other. That is, the polarization separation element
Within 10, the ordinary light Eo is refracted in the same direction as the incident direction of the incident light beam R, and the extraordinary light Ee is refracted in the direction of the angle θ formed by the laminated surface 10c with the direction of the incident light beam R and the angle determined by the value of the shape birefringence. Since both lights are separated, they have a function as a polarization separation element. The separation angle φ of the polarized light can be controlled by adjusting the size of the shape birefringence or the angle θ formed by the incident light beam R and the laminated surface 10c. Both the lights Eo and Ee emitted from the polarization separation element 10 are emitted in the same direction as the incident light flux R.

In this case, with the structure of claim 2, a material having a large shape birefringence can be easily obtained.

According to the manufacturing method of claim 3, it is possible to easily manufacture the polarization beam splitting element having the structure shown in claim 1.

According to the structure of claim 4, as shown in FIG. 5 and FIG. 6, the transparent body 4 including a large number of transparent elongated bodies 3 obliquely oriented with respect to the incident light beam R to the polarization separation element 20 is provided. The luminous flux R emitted by a person is separated into an ordinary light Eo and an extraordinary light Ee. That is, the ordinary light Eo is in the same direction as the incident direction of the incident light beam R, and the extraordinary light Ee is the angle formed by the incident direction of the incident light beam R and the orientation direction of the transparent elongated body 3 and the angle determined by the value of the shape birefringence. Since the light is refracted in the direction of and both lights are separated, a function as a polarization separation element occurs. In this case, the size of the shape birefringence or the incident light R
By adjusting the angle formed by the alignment direction of the transparent elongated body 3, the polarization separation angle can be controlled. Both the lights Eo and Ee emitted from the polarization separation element 20 are emitted in the same direction as the incident direction of the incident light flux R.

According to the structure of claim 5, an inexpensive material such as glass or plastic can be used to easily manufacture the polarization separation element of claim 4 having a large opening.

According to the manufacturing method of claim 6, the polarization separation element having the structure shown in claim 5 can be easily manufactured by a simple process of heating and stretching a transparent body containing air.

[Embodiment] FIGS. 1 and 2 show a first embodiment of a polarization beam splitting element comprising a birefringent body according to the present invention.

The polarization splitting element 10 composed of this birefringent body is formed in a thin plate shape as a whole, and the transparent thin film 1 which is two kinds of transparent bodies,
It is formed by laminating a large number of 2 alternately. The transparent thin film 1 is made of amorphous silicon containing hydrogen, and the transparent thin film 2
Are made of quartz.

Here, hydrogen-containing amorphous silicon and quartz have refractive indices of 3.823 and 1.44, respectively, for incident light with a wavelength of 1.3 μm.
Use the one that is 6. Further, the thicknesses of the thin films 1 and 2 are set to be shorter than the wavelength of incident light.

The polarization separation element 10 according to this embodiment is structurally uniform at least in the Y direction shown in FIG.
Of the laminated surface (the direction parallel to the laminated surface is indicated by an imaginary line 10c) is the incident direction of the incident light R (oblique cross section 10 on the incident side).
It is inclined by a predetermined angle with respect to the Z direction which is the normal direction of a). In other words, the laminated surface has a predetermined crossing angle θ with the incident side oblique section 10a parallel to the X direction and the emitting side oblique section 10b parallel thereto.

It should be noted that the following steps are taken in order to manufacture such a structure. First, by high-frequency sputtering method, targeting silicon in an atmosphere of a predetermined mixture ratio of argon and hydrogen, to form a thin film of hydrogen-containing amorphous silicon on a quartz substrate with a thickness of, for example, 50 nm, followed by high-frequency sputtering method, A thin film of silicon, for example, 50 nm in an atmosphere of argon and oxygen with quartz as the target
And then deposit both thin films alternately (for example, 1000
Cycle). The laminated body obtained by this deposition is cut into a thin plate at a predetermined angle with respect to the laminated surface (angle θ formed by the incident light flux R and the laminated surface in the incident direction), and then, for example, 100
Polish to a thickness of μm.

The thin films 1 and 2 can be formed by a chemical vapor deposition method (CVD), a plasma chemical vapor deposition method (PCVD), or the like, in addition to the sputtering method.

Since the present embodiment is constructed as described above, as shown in FIG. 2, when light is incident along the predetermined direction from the left side of FIG. The R is separated into the ordinary light Eo polarized in the Y direction and the extraordinary light Ee polarized in the X direction at a predetermined polarization separation angle φ.

In the structure of the present embodiment, when the difference in refractive index between the two types of thin films 1 and 2 becomes large, the shape birefringence becomes large, and the separation angle φ becomes larger.

FIG. 3 shows the change in the refractive index n of the ordinary ray Eo and the extraordinary ray Ee using incident light with a wavelength of 1.3 μm in the occupation ratio (the ratio of the volume of hydrogen-containing amorphous silicon in quartz) Sa. It is shown to the contrary.

According to the figure, the difference in refractive index between the ordinary ray Eo and the extraordinary ray Ee is 1 or more at maximum. This is 0.258 and 0.160 respectively using conventional rutile and calcite, whereas
It is extremely large.

The both transparent bodies are not limited to those in the above-mentioned embodiment, for example, one transparent body is a thin film of amorphous titanium dioxide having a thickness of 50 nm, and the other transparent body is a quartz thin film of the same thickness. , Stack them alternately (eg 1000
The same polarization separation function as in the above-described embodiment is exhibited by the periodicity. That is, when light having a wavelength of 1.3 μm is incident, the light is separated into ordinary light Eo and extraordinary light Ee at a separation angle φ of 5 °.

In order to manufacture such a structure, the following steps are performed as in the above description.

First, a titanium target is formed by a reactive DC sputtering method, an amorphous titanium dioxide thin film is formed on a quartz substrate by a reactive DC sputtering method in an atmosphere of oxygen and argon, and then the amorphous nitric oxide film is formed by a high frequency sputtering method. A quartz thin film is formed on the titanium oxide thin film, and then both thin films are alternately deposited. The laminated body obtained by this deposition is cut into a thin plate shape at, for example, 45 ° with respect to the laminated surface, and then polished to a thickness of 100 μm, for example.

FIG. 4 shows the change in the polarization separation angle φ with respect to the inclination angle θ of the incident light with respect to the laminated surface.

That is, the curve Pa is the curve Pt in the case of the configuration shown in FIG. 1 and FIG. 2 (that is, the multilayer film structure in which the hydrogen-containing amorphous silicon thin film and the quartz thin film are laminated).
Shows a case of a multilayer film structure in which a thin film of amorphous titanium dioxide and a thin film of quartz are laminated.

The curves Pc and Pr have the conventional structure, that is, calcite,
The results in the case of using the rutile are shown for the tilt angles formed by those optical axes and the incident light. From the curve Pa of the present invention, it can be seen that the maximum width light separation angle φ of about 23 ° is obtained when the inclination angle θ is about 57 °. This value is about four times as large as that of the conventional structure shown by the curves Pc and Pr.

Next, FIGS. 5 and 6 show a polarization beam splitting element according to the second embodiment of the present invention. The polarization beam splitting element 20 composed of this shape birefringent body is formed as a thin plate as a whole. The two types of transparent bodies having different refractive indexes are a large number of elongated bodies 3 and a transparent substrate matrix 4 in which the elongated bodies 3 are discretely embedded. The elongated bodies 3 are aligned in a fixed orientation within the transparent substrate matrix 4, that is, the length direction of the elongated bodies 3 (direction indicated by an imaginary line 20c) and the incident light R form a constant angle. Are arranged as follows. Here, the elongated body 3 is
For example, the transparent substrate matrix 4 is made of bubbles, and is made of glass or transparent plastic.

Since the second embodiment is configured as described above, it is in a direction inclined with respect to the longitudinal direction of the elongated body 3, that is, from the left side in FIG. 6 to the Z direction (perpendicular to the oblique cross section 20a on the incident side). (In the direction), the incident light is the ordinary light polarized in the Y direction.
Eo and extraordinary light Ee polarized in the X direction are separated at a predetermined separation angle φ.
Emit in parallel to the direction.

FIG. 7 shows that, in the second embodiment, incident light having a wavelength of 1.3 μm is used, and glass having a refractive index of 1.5 is used as the transparent substrate matrix 4 in which a large number of bubbles are arranged.
The change in each refractive index n for e is shown with respect to the occupation ratio (the ratio of the volume occupied by the air in the glass) Sn. The difference between the refractive indices of the two lights Eo and Ee is 0.04 at maximum. Is. That is, as shown in FIG.
n _e, When n _o, a _{n e -n o = 1.27-1.23 = 0.04} .

FIG. 8 shows the change of the polarization splitting angle φ in the case of the second embodiment in which the slender angle θ of the incident light with respect to the alignment direction in the elongated body.
It can be understood that the polarization separation angle φ becomes maximum when the tilt angle θ is about 45 °. In the above description, the case where bubbles are used as the elongated body 3 which is one transparent body has been described, but the present invention is not limited to this.
For example, a transparent substance such as chalcogen glass may be used.

Further, if the combination of the elongated body 3 and the transparent substrate matrix 4 is changed and a combination having a different refractive index difference is used, as in the first embodiment, the refractive index difference may be changed according to the difference. A polarization beam splitting element having a desired polarization beam splitting angle can be obtained.

[Effects of the Invention] As described above, the present invention has the effect of separating polarized light by inclining the orientation direction of the multilayer thin film surface or a large number of elongated bodies in the shape birefringent body with respect to the direction of light irradiation. It is something that was held.

According to the first aspect of the present invention, it is possible to provide an element capable of separating polarized light by using a shaped birefringent body formed by an alternating multilayer film of two kinds of transparent thin films having different refractive indexes. Moreover, the separation angle can be controlled by a combination of two types of transparent thin films or by changing the angle formed by the alternating multilayer film surface and the human luminous flux. In particular, the combination of amorphous silicon and quartz has the effect of achieving a polarization separation performance that is four times as large as that of the conventional polarization separation element. Since amorphous silicon and quartz are both mechanically and chemically stable,
A polarized light separating element having excellent environment resistance can be obtained. Considering only the magnitude of the shape birefringence, the combination of this material is extremely large, 1.0 or more, and 0.13 is the one using quartz and ditantalum pentoxide or diniobium pentoxide, which has been reported previously. It is dramatically larger than

According to the invention of claim 2, it is possible to easily obtain a material having a large polarization separation performance by using a material such as silicon which is easily obtained.

According to the manufacturing method of claim 3, since the two kinds of transparent thin films can use the conventional techniques such as sputtering,
Easy to manufacture. Further, if manufactured by these manufacturing methods, a mechanically and chemically stable element can be manufactured.

According to the invention of claim 4, when a transparent body having a shape birefringence including a large number of oriented elongated bodies is tilted in the orientation direction of the elongated bodies with respect to a human luminous flux, polarized light is emitted. The effect of separation is obtained. This is because polarized light can be separated only by forming a large number of oriented long and narrow bodies on a substrate, so that a wide aperture polarization separating element can be obtained by using a substrate having a wide area. Further, the polarization separation angle can be controlled by changing the orientation direction of the elongated body.

According to the invention of claim 5, an inexpensive material such as glass or plastic containing bubbles can be used. Since it is made of glass or plastic, its shape can be changed freely by raising the temperature. Those made of plastic can be made flexible.

According to the manufacturing method of the sixth aspect, a wide aperture polarization separation element can be manufactured by utilizing the conventional techniques of heating and stretching.

[Brief description of drawings]

FIG. 1 is a perspective view showing the external configuration of a first embodiment of a polarization splitting element composed of a shape birefringent body according to the present invention, and FIG. 2 is a view for explaining the polarization splitting function of the element shown in FIG. A side view and FIG. 3 are graphs showing changes in the respective refractive indices for ordinary light and extraordinary light with respect to the occupation ratio (ratio of hydrogen-containing amorphous silicon in quartz), and FIG. FIG. 5 is a graph showing the change in each polarization separation angle of the polarization separation element according to the example and the conventional polarization separation element with respect to the inclination angle of the incident light with respect to the laminated surface and the optical axis, and FIG. FIG. 6 is a perspective view showing an appearance configuration of a second embodiment of a polarization separating element made of a refracting body, FIG. 6 is a side view for explaining the polarization separating function of the element shown in FIG. 5, and FIG. The change in each refractive index with respect to light is calculated as Graph showing relative), 8 is a graph showing changes in the polarization separation angle of the polarization separating element according to the second embodiment with respect to the inclination angle of the incident light with respect to the orientation direction of the long thin body. (Explanation of symbols) 1 ... Transparent thin film, 2 ... Transparent thin film, 3 ... Elongated body, 4 ...
… Transparent substrate matrix, 10, 20 …… A polarization separation element consisting of a shape birefringent body.

Claims (6)

[Claims] 1. A transparent laminated body comprising two kinds of thin film transparent bodies having different refractive indexes, and alternately laminating a large number of the transparent bodies to form a birefringent body. A polarization splitting element composed of a shape birefringent body, which is obliquely cut out and the incident and outgoing positions of light are in the obliquely cut out plane. 2. The two types of thin film transparent bodies are one of
A polarization separation element comprising a shaped birefringent body according to claim 1, wherein the kind of thin film transparent body is silicon. 3. Thin films composed of two kinds of transparent bodies having mutually different refractive indexes are alternately deposited by a sputtering method, a chemical vapor deposition method, or a plasma chemical vapor deposition method, and then the deposited thin films are deposited. 2. A polarization separation element comprising a shape birefringent body according to claim 1, wherein a cut surface having a substantially constant intersecting angle with respect to each of the laminated surfaces and having a substantially parallel plate shape is cut out from the transparent laminated body. Manufacturing method. 4. One transparent body composed of a large number of elongated bodies and another plate-shaped transparent body having a refractive index different from that of the one transparent body, wherein the elongated bodies are arranged in respective longitudinal directions. Are aligned in a substantially constant direction and are discretely arranged in the other transparent body, and each length direction is arranged so as to be oblique with respect to the incident light. A polarization separation element consisting of a body. 5. The one transparent body is a bubble or an elongated transparent substance having a refractive index different from that of the other transparent body, and the other transparent body is transparent glass or transparent plastic. A polarization separation element comprising the shape birefringent body according to claim 4. 6. A transparent glass or a transparent plastic is heated, and each air bubble discretely mixed in the transparent glass or the transparent plastic or a transparent substance having a refractive index different from that of the transparent glass or the transparent plastic is long in a certain direction. The transparent glass or transparent plastic is stretched and molded so as to extend, and thereafter, from the molded shape birefringent body, cut surfaces are substantially mixed in the longitudinal direction of each transparent substance mixed in a discrete manner. The method for manufacturing a polarization beam splitting element composed of a shape birefringent body according to claim 5, wherein a substantially parallel plate-shaped object having a constant intersection angle is cut out.