JP2007272121A - Optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element using a thin plate, wherein an S/N ratio of output light is improved. <P>SOLUTION: The optical element has the thin plate 1 with 20 μm or less thickness formed with a material having an electro-optic effect or with a nonlinear optical effect and an optical waveguide 4 formed on the thin plate, wherein stray light reflecting means (10, 20) to reflect stray light propagating in the thin plate and guide the reflected stray light to the outside of the thin plate are arranged in regions of the thin plate except for the optical waveguide and its vicinity. The stray light reflecting means has a chamfered portion 10 on a corner portion of the thin plate and a groove portion 20 formed on the thin plate surface and so on. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element, and more particularly, to an optical element using a thin plate formed of a material having an electro-optic effect or a nonlinear optical effect.

Conventionally, in the optical communication field and the optical measurement field, a waveguide type optical element in which an optical waveguide or a modulation electrode is formed on a substrate having an electro-optic effect has been widely used.
In particular, with the development of multimedia, the amount of information transmission is also increasing, and there is a demand for a wider optical modulation frequency. As means for realizing this, an external modulation system using an LN modulator or the like is provided. However, in order to realize a wide band of the LN modulator, it is necessary to achieve speed matching between the microwave and the light wave that are the modulation signals and to reduce the driving voltage.

As means for solving the above-described problems, it has been conventionally known that, by reducing the thickness of the substrate, the speed matching condition between the microwave and the speed of the light wave is satisfied and the driving voltage is simultaneously reduced.
In the following Patent Document 1 or 2, an optical waveguide and a modulation electrode are incorporated into a thin substrate (hereinafter referred to as “first substrate”) having a thickness of 30 μm or less, and another substrate having a lower dielectric constant than the first substrate. (Hereinafter referred to as “second substrate”), the effective refractive index with respect to the microwave is lowered, the velocity matching between the microwave and the light wave is achieved, and the mechanical strength of the substrate is maintained.
JP-A 64-18121 JP 2003-215519 A

In Patent Document 1 or 2, LiNbO ₃ (hereinafter referred to as “LN”) is mainly used for the first substrate, and a material having a lower dielectric constant than LN, such as quartz, glass, and alumina, is used for the second substrate. in use. In the combination of these materials, a temperature drift and a DC drift accompanying a temperature change occur due to a difference in linear expansion coefficient. In Patent Document 2, it is also disclosed that bonding of the first substrate and the second substrate is performed using an adhesive having a linear expansion coefficient close to that of the first substrate in order to eliminate such a problem. .

  However, when comparing a conventionally manufactured modulator using an LN substrate and a modulator having a thin LN substrate, light or incident light radiated or leaked from the optical waveguide as the substrate thickness decreases. There is a strong tendency for light incident on the substrate other than the optical waveguide (hereinafter referred to as “stray light”) to be confined in the substrate. This is because the conventional LN substrate has a thick substrate (for example, 500 to 1000 μm), so that there is a sufficient area that does not affect the waveguide (for example, a depth of several μm), and the light space is stray light. The distribution density (hereinafter referred to as “stray light density”) was lowered, and as a result, the influence of stray light was not a problem. However, if the thickness of the substrate is the same as the distance in the depth direction of the waveguide, the stray light density that propagates in the direction along the substrate surface in the substrate increases, so stray light propagates in the substrate, and the optical waveguide In such a case, the light re-enters the light beam or enters the outgoing optical fiber connected to the optical element, resulting in the deterioration of the S / N ratio of the output light.

  In addition, when a thin plate is used for the optical element, it is necessary to join the thin plate of the first substrate and the reinforcing plate of the second substrate with an adhesive or the like as described above because the mechanical strength is insufficient with only the thin plate. There is. At this time, when the refractive index of the adhesive is lower than that of the thin plate, the stray light is more confined.

  The problem to be solved by the present invention is to provide an optical element that solves the above-described problems and improves the S / N ratio of output light in an optical element using a thin plate.

  In order to solve the above-mentioned problem, in the invention according to claim 1, in an optical element having a material having an electro-optic effect or an optical waveguide formed in a thin plate having a thickness of 20 μm or less formed by a nonlinear optical effect, the thin plate The stray light reflecting means for reflecting the stray light propagating in the thin plate and guiding the reflected stray light to the outside of the thin plate is disposed in a region excluding the optical waveguide and its vicinity.

  The invention according to claim 2 is the optical element according to claim 1, wherein the stray light reflecting means has a predetermined angle with respect to the front surface or the back surface of the thin plate and is formed by a surface continuous with the outer peripheral surface of the thin plate. It is characterized by being.

  The invention according to claim 3 is the optical element according to claim 1 or 2, wherein the stray light reflecting means is formed by cutting a corner portion of the thin plate into a planar shape or a curved shape.

  The invention according to claim 4 is the optical element according to any one of claims 1 to 3, further comprising stray light absorbing means for absorbing stray light reflected by the stray light reflecting means, wherein the stray light absorbing means is the stray light reflecting means. The stray light reflected by the means is formed at a position where it is emitted from the thin plate.

  According to a fifth aspect of the present invention, there is provided the optical element according to any one of the first to third aspects, wherein the stray light that absorbs the stray light reflected by the stray light reflecting means and the reinforcing substrate joined to the thin plate via an adhesive layer. The stray light reflecting means is formed on the anti-adhesion surface of the thin plate, and the stray light absorbing means is formed on the reinforcing substrate to which the stray light reflected by the stray light reflecting means reaches. Features. The “anti-adhesion surface” means a surface that is not used for adhesion.

  The invention according to claim 6 is the optical element according to any one of claims 1 to 3, further comprising stray light emitting means for removing stray light reflected by the stray light reflecting means, wherein the stray light emitting means includes the stray light reflecting means. The stray light reflected by the means is formed at a position where it is emitted from the thin plate.

  The invention according to claim 7 is the optical element according to claim 6, wherein the stray light emitting means is provided with irregularities on the front surface or the back surface of the substrate.

  According to the first aspect of the present invention, in an optical element comprising a material having an electro-optic effect or a thin plate having a thickness of 20 μm or less formed by a nonlinear optical effect, and an optical waveguide formed on the thin plate, the optical waveguide of the thin plate And stray light reflecting means for reflecting stray light propagating in the thin plate and guiding the reflected stray light to the outside of the thin plate is disposed in a region other than the vicinity thereof, for example, along the substrate surface in the substrate. Because the propagation direction of stray light propagating in the direction can be converted to the thickness direction of the substrate, defects such as re-entering the optical waveguide or entering the outgoing optical fiber connected to the optical element can be suppressed, and as a result It is possible to provide an optical element having an improved S / N ratio of output light.

  According to the invention of claim 2, the stray light reflecting means has a predetermined angle with respect to the front or back surface of the thin plate and is formed by a surface continuous with the outer peripheral surface of the thin plate. It can be easily formed by means such as processing and etching.

  According to the invention of claim 3, since the stray light reflecting means is formed by cutting out the corners of the thin plate into a flat shape or a curved shape, the stray light reflecting means can be easily formed.

  According to the invention of claim 4, the stray light absorbing means for absorbing stray light reflected by the stray light reflecting means is provided, and the stray light absorbing means is formed at a position where the stray light reflected by the stray light reflecting means is emitted from the thin plate. Therefore, for example, the stray light deflected in the thickness direction of the substrate by the stray light reflecting means can be efficiently absorbed, reentering the optical waveguide, or entering the outgoing optical fiber connected to the optical element. As a result, it is possible to provide an optical element with an improved S / N ratio of output light.

  According to a fifth aspect of the present invention, there is provided a reinforcing substrate joined to a thin plate via an adhesive layer, and stray light absorbing means for absorbing stray light reflected by the stray light reflecting means, wherein the stray light reflecting means is anti-adhered to the thin plate. The stray light absorbing means formed on the surface is formed on the reinforcing substrate to which the stray light reflected by the stray light reflecting means reaches. For example, stray light deflected in the thickness direction of the substrate by the stray light reflecting means can be efficiently used. Can be absorbed in the optical waveguide, and can be prevented from malfunctioning due to stray light, such as incident on an optical fiber for output connected to the optical element, resulting in an improvement in the S / N ratio of the output light. Can be provided.

  According to the invention of claim 6, the stray light emitting means for removing the stray light reflected by the stray light reflecting means is provided, and the stray light emitting means is formed at a position where the stray light reflected by the stray light reflecting means is emitted from the thin plate. Therefore, for example, the stray light deflected in the thickness direction of the substrate by the stray light reflecting means can be efficiently removed, reentering the optical waveguide, or entering the outgoing optical fiber connected to the optical element. As a result, it is possible to provide an optical element with an improved S / N ratio of output light.

  According to the seventh aspect of the present invention, since the stray light radiating means is formed by providing irregularities on the front surface or the back surface of the substrate, the stray light radiating means can be easily formed.

Hereinafter, the present invention will be described in detail using preferred examples.
FIG. 1 is a perspective view of an optical element that modulates the intensity of light using a thin plate to which the present invention is applied. An optical waveguide 4 and a modulation electrode (not shown) (signal electrode, ground electrode, etc.) are formed on the thin plate 1 made of a material having an electro-optic effect, and the reinforcing substrate 3 is bonded to the thin plate 1 with an adhesive 2 or the like. It is joined. The optical waveguide can also be formed on the back surface of the thin plate.

As a method for forming the optical waveguide, it can be formed by diffusing Ti or the like on the substrate surface by a thermal diffusion method or a proton exchange method. Further, as in Patent Document 3, it is possible to form an optical waveguide by forming a ridge on the surface of the thin plate 1 in accordance with the shape of the optical waveguide.
Modulating electrodes such as signal electrodes and ground electrodes can be formed by forming a Ti / Au electrode pattern, a gold plating method, or the like. Furthermore, if necessary, a buffer layer (not shown) such as dielectric SiO ₂ may be provided on the surface of the substrate after the optical waveguide is formed, and a modulation electrode may be formed on the buffer layer.
JP-A-6-289341

  As a material having an electro-optic effect, for example, lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), quartz-based materials, and combinations thereof can be used. In particular, a lithium niobate (LN) crystal having a high electro-optic effect is preferably used.

  In the manufacturing method of the thin plate 1 including an optical element, the above-described optical waveguide is formed on a substrate having a thickness of several hundreds μm, and the back surface of the substrate is polished to produce a thin plate having a thickness of 20 μm or less. Then, a modulation electrode is formed on the surface of the thin plate. It is also possible to polish the back surface of the substrate after making the optical waveguide, the modulation electrode, and the like. In addition, there is a risk that the thin plate may be damaged when a thermal shock during the formation of the optical waveguide or a mechanical shock due to the handling of the thin film during various treatments. It is preferably performed before the substrate is polished and thinned.

  Various materials can be used as the reinforcing substrate 3. For example, in addition to using the same material as the thin plate, a material having a lower dielectric constant than the thin plate, such as quartz, glass, and alumina, can be used. It is also possible to use, or to use a material having a crystal orientation different from that of the thin plate as in Patent Document 3. However, it is preferable to select a material having a linear expansion coefficient equivalent to that of the thin plate in order to stabilize the modulation characteristics of the optical element with respect to temperature changes. If it is difficult to select an equivalent material, a material having a linear expansion coefficient equivalent to that of the thin plate is selected as an adhesive for joining the thin plate and the reinforcing plate as in Patent Document 2.

  For bonding the thin plate 1 and the reinforcing substrate 3, as the adhesive layer 2, an epoxy adhesive, a thermosetting adhesive, an ultraviolet curable adhesive, solder glass, a thermosetting, photocurable or photothickening resin It is possible to use various adhesive materials such as an adhesive sheet.

  In the optical element as shown in FIG. 1, stray light is generated in a thin plate other than the optical waveguide from the optical branching and combining part of the optical waveguide, or a junction between the optical fiber for incident and the optical element (not shown). However, when the thickness of the thin plate is thin, especially when it is set to 20 μm or less, the present inventors have a problem that the stray light propagates in the thin plate and enters the optical waveguide or the outgoing optical fiber. It has been found and has led to the present invention.

  In order to solve the above problem, the present applicant, in the following Patent Document 4, a thin plate having a thickness of 20 μm or less formed of a material having an electro-optic effect, and an optical waveguide formed on the front or back surface of the thin plate, In an optical modulator formed on the surface of the thin plate and including a modulation electrode for modulating light passing through the optical waveguide, stray light removing means is disposed in the thin plate or in proximity to the thin plate. An optical modulator characterized by this was proposed.

In particular, examples of the stray light removing means include the following.
(1) Light absorbing portion disposed in contact with the outer surface of the thin plate excluding the optical waveguide and the vicinity thereof (2) High refractive index portion disposed in contact with the outer surface of the thin plate on the optical waveguide or a part of the vicinity thereof (3) A light guide portion formed on the front or back surface of the thin plate excluding the optical waveguide. (4) A concave portion formed on the front surface or the back surface of the thin plate excluding the optical waveguide. Fill material.
Japanese Patent Application No. 2005-96447 (filing date: March 29, 2005)

However, in these methods, since the installation location of the stray light removing means is limited, it is still insufficient to remove a lot of stray light that diffuses and propagates inside the substrate. It is difficult to effectively remove a lot of stray light propagating in a direction parallel to the.
For this reason, in the present invention, in an optical element having a thin plate having a thickness of 20 μm or less formed of a material having an electro-optic effect, and an optical waveguide formed on the front or back surface of the thin plate, the optical waveguide of the thin plate Further, stray light reflecting means for reflecting stray light propagating in the thin plate and guiding the reflected stray light to the outside of the thin plate is arranged in a region other than the vicinity thereof.

As the stray light reflecting means applied to the present invention, various means can be used. In particular, the chamfer 10 at the corner of the substrate as shown in FIG. 1 or the groove 20 provided on the front surface or the back surface of the substrate is used. A recessed part etc. can be used conveniently.
FIG. 2 is a cross-sectional view taken along one-dot chain line A of the optical element shown in FIG.

In order to prevent the light wave propagating through the optical waveguide 4 formed on the thin plate 1 such as the branched optical waveguide from being reflected by the chamfer 10 which is the stray light reflecting means, the chamfer 10 avoids the optical waveguide 4 and its vicinity. Has been placed. The method for creating the stray light reflecting means is a method in which the substrate thickness is several hundred μm or more and is provided at a predetermined position by polishing or etching at the corner of the substrate, or has a thickness of 20 μm or less. There is also a method in which stray light reflecting means is provided by the above method after the thin plate is formed.
Further, the stray light reflecting means is not only chamfered at the corners of the substrate, but as shown in FIG. 3, the corners are cut into a curved surface and subjected to R processing 11, or as shown in FIG. There is also a method of providing the groove 20 on the surface.

  Furthermore, as shown in FIG. 1 to FIG. 3 as an example, as a means for removing the reflected stray light 5 and 6, the stray light absorbing means 30 or the back surface of the thin plate facing the formation portion of the stray light reflecting means provided on the substrate surface is used. 31 is disposed, and stray light in the substrate can be removed by absorbing stray light floating in the substrate and reflected by the stray light reflecting means (10, 11, 20).

The stray light absorbing means 30 and 31 are provided with a material having a light absorption coefficient larger than 0 on the back surface of the substrate facing the stray light reflecting means, and there are various methods such as vapor deposition, sputtering and plating.
In addition, when the stray light absorbing means is provided at the corner of the substrate, the stray light absorbing means is preferably provided on the back surface of the substrate facing the stray light reflecting means with a width b of 10 μm or more from the end face.

In the case where the stray light reflecting means is provided with the grooves 20 on the surface of the substrate, the stray light absorbing means 31 is provided on the back surface portion with a width c of 10 μm or more from the back surface portion of the substrate facing the stray light reflecting means to the center side of the substrate. It is preferable.
Further, since the substrate is as thin as 20 μm or less, for example, even if an optical waveguide is formed from the surface of the substrate, the light wave to be guided reaches the vicinity of the back surface, so that the stray light absorbing means 30 and 31 are formed near the waveguide. If so, even the light wave propagating through the waveguide is absorbed. Therefore, it is preferable to form the stray light absorbing means 30 and 31 at a position separated by 20 μm or more from the end portion of the optical waveguide. Therefore, the distance a from the center of the optical waveguide shown in FIG. 2 to the stray light absorbing means needs to be larger than the half of the width of the optical waveguide plus 20 μm.

When the optical element has a thin plate, a reinforcing substrate, and an adhesive layer that connects the two, the stray light absorbing means 30 and 31 are not only formed on the back surface of the thin plate, as shown in FIG. As shown in FIG. 4, it can also be formed on the adhesive layer side of the reinforcing substrate facing the stray light reflecting means.
When the stray light absorbing means 30 ′ and 31 ′ are formed on the reinforcing substrate, the formation position of the stray light absorbing means in the horizontal direction of the drawing is basically the same as that of FIG. The width b ′ from the side of the adhesive of the reinforcing substrate of the means 30 ′ toward the center of the substrate and the width c ′ from the bottom of the groove of the stray light absorbing means 31 ′ facing the groove 20 toward the center of the substrate are 20 μm or more. A width is preferred.
When the adhesive layer 2 has a lower refractive index than that of the thin plate 1, the distance a ′ between the stray light absorbing means and the optical waveguide is different from that in FIG. 2, and the stray light absorbing means 30 ′, Even if 31 'is formed, the light wave propagating through the waveguide is not absorbed because of the low refractive index adhesive layer.

  As a material for the stray light absorbing means, a metal having a high light absorption coefficient such as Al, Ti, Ta, Fe, Y, La, or the like can be suitably used. These absorb stray light floating in the substrate and reflected by the stray light reflecting means, and remove stray light in the substrate.

  Further, as a means for removing the reflected stray light different from the above, as shown in FIG. 5, as an example for removing the reflected stray light, a stray light reflecting means provided on the substrate surface is formed. Stray light radiating means 40 is arranged on the opposite thin plate back surface, and stray light in the substrate is removed by floating the inside of the substrate and radiating the stray light reflected by the stray light reflecting means to the outside of the substrate.

  The stray light radiating means is provided with unevenness on the back surface of the substrate facing the light reflecting means, and the formation method is a method of processing the back surface of the substrate by sandblasting, GC abrasive polishing, etching, or the like at a predetermined position on the back surface of the substrate. is there.

As for the formation position of the stray light radiating means, when the stray light reflecting means is provided at the corner of the substrate, the stray light radiating portion 40 is preferably provided on the back surface of the substrate with a width of 10 μm or more from the end face of the substrate as in FIG.
In the case where the stray light reflecting means is provided with a groove (not shown) on the surface of the substrate, the stray light emitting portion has a width of 10 μm or more from the back side of the substrate facing the stray light reflecting means toward the center of the substrate, as in FIG. It is preferable to provide in this back surface part.
In addition, since the substrate is as thin as 20 μm or less, for example, even if an optical waveguide is formed from the substrate surface, the guided light wave reaches the vicinity of the back surface, so the stray light emitting portion 40 is formed near the waveguide. In this case, the light wave propagating through the waveguide is removed from the substrate. Therefore, it is preferable to form the stray light emitting portion 40 at a position that is 20 μm or more away from the end portion of the optical waveguide, as in FIG.

In the above description, the optical element has been described mainly with respect to an example in which an electrode and an optical waveguide are formed on the surface of a thin plate made of a material having an electro-optic effect, but the present invention is applied to the surface of a thin plate made of a material having a nonlinear effect. The same applies to an optical element that forms an optical waveguide.
The optical element of the present invention may be one in which an optical waveguide is formed on the back surface of a thin plate. Further, the formation position of the stray light reflecting means is not limited to the surface of the thin plate, but can be formed on the back surface side. In the case where the stray light reflecting means is formed on the back surface side, the stray light absorbing means and the stray light emitting portion are formed on the surface side of the thin plate.

Next, specific examples and tests related to the optical element of the present invention will be described.
Example 1
The thin optical element uses an X-cut LN substrate having a thickness of 500 μm for the substrate, and forms a Mach-Zehnder type optical waveguide as shown in FIG. 1 on the substrate surface by Ti diffusion process or the like.
A thermoplastic resin is applied to the substrate surface, and a polishing dummy substrate is attached. The back surface of the substrate is polished by a polishing machine until the thickness of the substrate becomes 20 μm, and a modulation electrode having a height of 14 μm is formed by a plating process, thereby manufacturing a thin plate incorporating an optical element.
Chamfering is performed on the corner portion of the light guide direction on the surface of the thin plate manufactured by the above method.

(Example 2)
In Example 2, an Al film was deposited in a width of 10 μm from the end surface of the thin plate back surface facing the chamfered portion provided on the substrate surface of the LN thin plate manufactured in Example 1.

(Example 3)
In Example 3, a Ti film was deposited with a width of 20 μm from the end surface of the back surface of the thin plate facing the chamfered portion provided on the substrate surface of the LN thin plate manufactured in Example 1.

Example 4
In Example 4, etching was performed with a width of 10 μm from the end surface of the back surface of the thin plate facing the chamfered portion provided on the substrate surface of the LN thin plate manufactured in Example 1.

(Example 5)
The thin optical element uses an X-cut LN substrate having a thickness of 500 μm for the substrate, and forms a Mach-Zehnder type optical waveguide as shown in FIG. 1 on the substrate surface by Ti diffusion process or the like.
A thermoplastic resin is applied to the substrate surface, and a polishing dummy substrate is attached. The back surface of the substrate is polished by a polishing machine until the thickness of the substrate becomes 20 μm, and a modulation electrode having a height of 14 μm is formed by a plating process, thereby manufacturing a thin plate incorporating an optical element.
A V-groove (10) is provided by a slicing saw on the surface of the thin plate manufactured by the above method.

(Example 6)
In Example 6, an Al film was deposited with a width of 10 μm from the end surface of the back surface of the thin plate facing the V groove provided on the substrate surface of the LN thin plate manufactured in Example 5.

(Example 7)
In Example 7, a Ta film was deposited with a width of 20 μm from the end surface of the back surface of the thin plate facing the V groove provided on the substrate surface of the LN thin plate manufactured in Example 5.

(Example 8)
In Example 8, the etching process was performed with a width of 10 μm from the end surface of the back of the thin plate facing the V groove provided on the substrate surface of the LN thin plate manufactured in Example 5.

Example 9
In Example 9, an Al film having a width of 10 μm from the end face was deposited on the adhesive side of the reinforcing substrate facing the chamfered portion provided on the substrate surface of the LN thin plate manufactured in Example 1.

(Comparative example)
In the thin plate (thickness 20 μm) manufactured in the same manner as in Example 1, the thin plate with the optical element incorporated is not chamfered, and the substrate made of the same material as the thin plate is used as a reinforcing plate and bonded to the back surface of the thin plate. It joined through the agent.

(Test method)
Optical fibers were connected to the optical elements of Examples 1 to 9 and Comparative Example. Next, test light was incident on the incident optical fiber, the output light from the outgoing optical fiber was measured with a power meter, and the S / N ratio of the output light of each optical element was measured. The measurement results are shown in Table 1.

The quality of the extinction ratio (dB) was judged by the following evaluation.
・ For 20 dB or more, ○ (available)
-Less than 20db x (unusable)
From the results of Table 1, it is understood that the S / N ratio of the output light is improved in any of Examples 1 to 9 as compared with the comparative example.

  As described above, according to the present invention, it is possible to provide an optical element having an improved S / N ratio of output light in an optical element using a thin plate having a thickness of 20 μm or less.

It is a perspective view of the optical element of this invention. FIG. 2 shows a part of a cross-sectional view of the optical element in FIG. 1. A part of sectional drawing of the optical element which makes the corner | angular part of a thin plate into a curved surface shape as a stray light reflection means is shown. A part of sectional drawing of the optical element which has a stray light reflection means and arrange | positions a stray light absorption means on a reinforcement board | substrate is shown. A part of sectional drawing of the optical element which has a stray-light reflection means and a stray-light radiation | emission part is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thin plate 2 Adhesive layer 3 Reinforcement substrate 4 Optical waveguide 5, 6, 7 Stray light 10 Chamfer 11 Cut-off part 20 Groove part 30,30 ', 31,31' Stray light absorption means 40 Stray light radiation part

Claims (7)

A thin plate having a thickness of 20 μm or less formed of a material having an electro-optic effect or a nonlinear optical effect;
In an optical element having an optical waveguide formed on the thin plate,
An optical element characterized in that stray light reflecting means for reflecting stray light propagating in the thin plate and guiding the reflected stray light to the outside of the thin plate is disposed in a region excluding the optical waveguide of the thin plate and its vicinity. .   2. The optical element according to claim 1, wherein the stray light reflecting means has a predetermined angle with respect to the front or back surface of the thin plate and is formed by a surface continuous with the outer peripheral surface of the thin plate. Optical element.   3. The optical element according to claim 1, wherein the stray light reflecting means is formed by cutting a corner portion of the thin plate into a flat shape or a curved shape.   4. The optical element according to claim 1, further comprising stray light absorbing means for absorbing stray light reflected by the stray light reflecting means, wherein the stray light absorbing means is configured such that the stray light reflected by the stray light reflecting means is An optical element formed at a position where it is emitted from a thin plate.   The optical element according to any one of claims 1 to 3, comprising a reinforcing substrate joined to the thin plate via an adhesive layer, and stray light absorbing means for absorbing stray light reflected by the stray light reflecting means, The stray light reflecting means is formed on an anti-adhesion surface of the thin plate, and the stray light absorbing means is formed on the reinforcing substrate to which the stray light reflected by the stray light reflecting means reaches.   4. The optical element according to claim 1, further comprising: stray light emitting means for removing stray light reflected by the stray light reflecting means, wherein the stray light emitting means is configured to receive the stray light reflected by the stray light reflecting means. An optical element formed at a position where it is emitted from a thin plate. 7. The optical element according to claim 6, wherein the stray light emitting means is provided with irregularities on the front surface or the back surface of the substrate.

Images