JP7259301B2 - Polarizer and optical isolator - Google Patents

Description

The present invention relates to polarizers and optical isolators.

An optical isolator is a magneto-optical device that propagates light in only one direction and blocks light that is reflected back. Optical isolators are used, for example, in laser oscillators used in optical communication systems, laser processing systems, and the like.

As described in Patent Document 1 below, an optical isolator has a configuration in which polarizing glass plates are attached to both surfaces of a Faraday rotator. For the purpose of preventing reflection of incident light on the polarizing glass plate, an optical functional film such as an antireflection film is sometimes formed on the surface of the polarizing glass plate.

Patent Document 2 below discloses a stress adjustment layer provided with such an optical function film. In Patent Document 2, a first dielectric multilayer film is provided on one main surface of a substrate, and a second dielectric multilayer film is provided on the other main surface of the substrate. Moreover, Patent Document 2 describes that the second dielectric multilayer film may include a stress adjustment layer. This stress adjustment layer is made of, for example, a SiO ₂ film.

JP 2016-009164 A WO2014/065373

By the way, when an antireflection film is formed on the surface of a polarizing glass plate, the polarizing glass plate may warp due to film stress. Therefore, the polarizing glass plate may be separated from the Faraday rotator.

In addition, the inventors of the present application have found that even if a stress adjustment layer made of a SiO ₂ film as in Patent Document 2 is formed, the reflection of incident light entering the Faraday rotator from the polarizing glass plate side can be sufficiently suppressed. newly found to be difficult.

An object of the present invention is to provide a polarizer and an optical isolator that can suppress the warping of the polarizer and the reflection of incident light.

A polarizer of the present invention is a polarizer for an optical isolator, comprising a polarizing glass plate having a first main surface and a second main surface facing each other, and a polarizing glass plate provided on the first main surface of the polarizing glass plate. and a warpage suppression film provided on the second main surface of the polarizing glass plate and suppressing warpage of the polarizing glass plate, wherein the warpage suppression film has a refractive index of It is characterized by being 1.47 or more and 1.55 or less.

It is preferable that the thickness of the warpage suppression film is 50 nm or more and 500 nm or less.

The first optical function film is preferably the first antireflection film.

It is preferable that the warpage suppressing film is made of silicon oxide or silicon oxynitride. Moreover, it is preferable that the warpage suppressing film is made of silicon oxide represented by SiO _{2 x} , and 1≦x<2.

An optical isolator of the present invention comprises a Faraday rotator having third and fourth principal surfaces facing each other, and directly or indirectly provided on the third principal surface of the Faraday rotator, A first polarizer and a second polarizer provided directly or indirectly on a fourth principal surface of the Faraday rotator, wherein the first polarizer and the second polarizer At least one of the polarizers is the polarizer described above.

It is preferable that a second optical function film is provided on at least one of the third principal surface and the fourth principal surface of the Faraday rotator.

ADVANTAGE OF THE INVENTION According to this invention, the polarizer and optical isolator which can suppress the curvature of a polarizer and can suppress reflection of incident light can be provided.

1 is a front cross-sectional view of an optical isolator according to one embodiment of the present invention; FIG. FIG. 2 is a front cross-sectional view of a first polarizer used in the optical isolator according to the embodiment shown in FIG. 1; FIG. 4 is a diagram showing the relationship between the value of x in SiO _x and the refractive index; FIG. 2 is a diagram showing the relationship between the value of x in SiO _x and the refractive index in the range of 1.8≦x≦2. FIG. 2 is a front cross-sectional view showing part of the optical isolator according to the embodiment shown in FIG. 1; FIG. 5 is a diagram showing the relationship between the refractive index of a warp suppressing film and the reflectance at the interface between the warp suppressing film and the Faraday rotator; FIG. 4 is a diagram showing the relationship between the refractive index of a warp suppressing film and the reflectance at the interface between the warp suppressing film and the Faraday rotator when the refractive index is 1.46 or more. It is a figure which shows the relationship between the thickness of a curvature suppression film|membrane, and the curvature amount of a 1st polarizer. 9(a) to 9(c) are front cross-sectional views for explaining an example of the method of manufacturing the optical isolator according to the embodiment shown in FIG. FIG. 10 is a diagram showing an example in which a warpage suppressing film is not formed on the base material of the polarizing glass plate; 2 is a front cross-sectional view of an optical isolator according to a modification of the embodiment shown in FIG. 1 of the present invention; FIG.

Preferred embodiments are described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. Also, in each drawing, members having substantially the same function may be referred to by the same reference numerals.

(optical isolator)
FIG. 1 is a front sectional view of an optical isolator according to one embodiment of the present invention. As shown in FIG. 1, the optical isolator 1 comprises a Faraday rotator 2, a first polarizer 3 and a second polarizer 4. Faraday rotator 2 is provided between first polarizer 3 and second polarizer 4 . The first polarizer 3 is a polarizer according to one embodiment of the invention.

2 is a front sectional view of a first polarizer used in the optical isolator according to the embodiment shown in FIG. 1. FIG. As shown in FIG. 2 , the first polarizer 3 includes a polarizing glass plate 6 , a first optical function film 7 and a warp suppressing film 8 .

The polarizing glass plate 6 has a first major surface 6a and a second major surface 6b facing each other. A first optical function film 7 is provided on the first main surface 6a. In this embodiment, the first optical function film 7 is an antireflection film. The antireflection film can be composed of, for example, a multilayer film in which a low refractive index film with a relatively low refractive index and a high refractive index film with a relatively high refractive index are alternately laminated. Note that the first optical function film 7 may be, for example, an IR cut filter or the like, and is not particularly limited.

A warp suppression film 8 is provided on the second main surface 6 b of the polarizing glass plate 6 . The warpage suppressing film 8 of the present embodiment is made of silicon oxide represented by SiO _x , where 1≦x<2. The refractive index of the warpage suppressing film 8 at a wavelength of 1550 nm is 1.47 or more and 1.55 or less. The material of the warp suppressing film 8 is not limited to silicon oxide, and may be, for example, silicon oxynitride. The refractive index of the warpage suppressing film 8 may be within the above range.

The range of x in SiO _x of the warpage suppressing film 8 is preferably 1.91≦x≦1.99. As a result, the refractive index of the warp suppressing film 8 at a wavelength of 1550 nm can more reliably be 1.47 or more and 1.55 or less.

Although the configuration of the second polarizer 4 is not particularly limited, it has the same configuration as the first polarizer 3 in this embodiment. However, at least one of the first polarizer 3 and the second polarizer 4 may be the polarizer according to the present invention. It is preferable that the first polarizer 3 on the incident side of the light A described later is the polarizer according to the present invention.

Returning to FIG. 1, the Faraday rotator 2 has a third principal surface 2a and a fourth principal surface 2b facing each other. A first polarizer 3 is provided directly on the third main surface 2 a of the Faraday rotator 2 . A second polarizer 4 is provided directly on the fourth main surface 2b. The first optical function film 7 of the first polarizer 3 is located outside the optical isolator 1, and the warpage suppressing film 8 is located on the Faraday rotator 2 side. The same applies to the second polarizer 4 as well.

As shown in FIG. 1, light A passes through the first polarizer 3 and enters the Faraday rotator 2 . The plane of polarization of light that enters the Faraday rotator 2 and passes through the Faraday rotator 2 rotates. Light emitted from the Faraday rotator 2 enters the second polarizer 4 . Light B that has passed through the second polarizer 4 is emitted from the optical isolator 1 .

Although the size of the optical isolator 1 of this embodiment is not particularly limited, it is, for example, 1 mm square when viewed from the first polarizer 3 side.

The feature of this embodiment is that the first optical function film 7 and the warp suppressing film 8 are provided on the first main surface 6a and the second main surface 6b of the polarizing glass plate 6, respectively, and the warp suppressing film This is because the film 8 has a refractive index of 1.47 or more and 1.55 or less. By providing the warp suppressing film 8 on the second principal surface 6 b of the polarizing glass plate 6 , warping of the first polarizer 3 due to the film stress of the first optical function film 7 can be suppressed. can. Therefore, the effect of the first optical function film 7 can be obtained, and the first polarizer 3 is difficult to separate from the Faraday rotator 2 . Furthermore, since the warp suppressing film 8 has a refractive index of 1.47 or more and 1.55 or less, reflection of incident light entering the Faraday rotator 2 can be suppressed. Details of the effect of suppressing reflection of incident light will be described below.

A plurality of warpage suppressing films 8 were produced by changing the value of x in SiO _x . Next, the refractive indices of the plurality of warpage suppressing films 8 were measured to determine the relationship between the value of x in SiO _x and the refractive index. The refractive index was measured using light of 1550 nm.

FIG. 3 is a diagram showing the relationship between the value of x and the refractive index in SiO _x . FIG. 4 is a diagram showing the relationship between the value of x in SiO _x and the refractive index in the range of 1.8≦x≦2. As shown in FIG. 3, it can be seen that the larger the value of x, the lower the refractive index. Specifically, as shown in FIG. 4, for example, x=2, and the refractive index is 1.46 when the warpage suppression film is an SiO ₂ film. When x=1.98, the refractive index is 1.48, when x=1.92, the refractive index is 1.54, and when x=1.9, the refractive index is 1.56.

Further, optical isolators were produced using the warpage suppressing films having the respective refractive indices produced above. The thickness of the warpage suppressing film was set to 200 nm. The refractive indices of the warp suppressing films used were 1.40, 1.42, 1.44, 1.46, 1.48, 1.50, 1.52, 1.54, 1.56, 1.48, 1.50, 1.52, 1.54, 1.56, and 1.56. 58, 1.60, 1.62, 1.64, 1.66, 1.68.

As the first optical function film, a laminated film in which SiO ₂ layers and Ta ₂ O ₅ layers were alternately laminated was used. The total number of SiO ₂ layers and Ta ₂ O ₅ layers was 4 layers. The thickness of the _SiO2 layer was 70 nm and 245 nm, and the thickness of _{the Ta2O5 layer} was 66 nm and 185 nm. On the other hand, the thickness of the polarizing glass plate was 0.2 mm. A bismuth-substituted rare earth iron garnet single crystal was used for the Faraday rotator. The refractive index of the Faraday rotator at 1550 nm is 2.34. The thickness of the Faraday rotator was 0.3 mm.

As shown in FIG. 5, part of the incident light from the first polarizer 3 side is reflected at the interface between the warpage suppressing film 8 and the Faraday rotator 2 . The reflectance at the interface of each optical isolator was measured.

FIG. 6 is a diagram showing the relationship between the refractive index of the warp suppressing film and the reflectance at the interface between the warp suppressing film and the Faraday rotator. FIG. 7 is a diagram showing the relationship between the refractive index of the warp suppressing film and the reflectance at the interface between the warp suppressing film and the Faraday rotator when the refractive index is 1.46 or more. The horizontal axis in FIGS. 6 and 7 indicates the wavelength of the light for which the reflectance was measured.

When the warpage suppression film is a SiO ₂ film, the refractive index at a wavelength of 1550 nm is 1.46, as described above. As shown in FIG. 6, when the refractive index is 1.46, the reflectance is 0.07%. Furthermore, it can be seen that the reflectance exceeds 0.05% even when the refractive index is less than 1.46. Similarly, it can be seen that the reflectance exceeds 0.05% even when the refractive index is 1.56 or more. When the refractive index is 1.46 or less, the lower the refractive index, the higher the reflectance. As shown in FIG. 7, when the refractive index is 1.56 or more, the higher the refractive index, the higher the reflectance.

On the other hand, as shown in FIG. 6, when the refractive index is higher than 1.46 and lower than 1.56, the reflectance is less than 0.05%. It can be seen that the reflection at the interface between the elements can be effectively suppressed. Thereby, reflection of incident light to the Faraday rotator can be effectively suppressed. Furthermore, in the present embodiment, the warpage suppression film has a refractive index of 1.47 or more and 1.55 or less. Thereby, reflection of incident light to the Faraday rotator can be suppressed more reliably and further.

The reflectance shown in FIGS. 6 and 7 is the reflectance at the interface between the warp suppressing film 8 and the Faraday rotator 2 shown in FIG. Reflection also occurs at the interface of 4. For example, when the warp suppressing film 8 is SiO ₂ , the sum of the reflectance at the interface between the warp suppressing film 8 and the Faraday rotator 2 and the reflectance at the interface between the Faraday rotator 2 and the second polarizer 4 is It will exceed 0.1%. In contrast, in the present embodiment, the refractive index of the warp suppressing film 8 is set to 1.47 or more and 1.55 or less, so that the total reflectance can be reduced. Furthermore, in the present embodiment, the second polarizer 4 also has a warpage suppression film similar to that of the first polarizer 3 . Therefore, the sum of the reflectance at the interface between the warp suppressing film 8 of the first polarizer 3 and the Faraday rotator 2 and the reflectance at the interface between the warp suppressing film 8 of the Faraday rotator 2 and the second polarizer 4 is further can be made smaller.

In this embodiment, the warp suppressing film 8 is made of silicon oxide represented by SiO _{2 x} , but the warp suppressing film 8 may be made of a material other than silicon oxide. For example, the warp suppressing film 8 may be made of silicon oxynitride represented _{by SiOyNz} . In silicon oxynitride, y is preferably in the range of 1.8≤y≤1.95, and z is preferably in the range of 0.05≤z≤0.2. Also in this case, warping of the first polarizer 3 can be suppressed, and reflection of incident light to the Faraday rotator 2 can be suppressed.

Here, the thickness of the warp suppression film 8 is preferably 50 nm or more and 500 nm or less, more preferably 100 nm or more and 400 nm or less. Thereby, warping of the first polarizer 3 can be suppressed more effectively. This is explained below.

A relationship between the thickness of the warp suppressing film and the amount of warp of the first polarizer was obtained. As the first optical function film in the first polarizer, a laminated film in which SiO ₂ layers and Ta ₂ O ₅ layers were alternately laminated was used. The total number of SiO ₂ layers and Ta ₂ O ₅ layers was 4 layers. The thickness of the _SiO2 layer was 70 nm and 245 nm, and the thickness of _{the Ta2O5} layer was 66 nm and 185 nm. The thickness of the polarizing glass plate was 0.3 mm. SiO _x with x=1.95 was used for the warpage suppressing film.

FIG. 8 is a diagram showing the relationship between the thickness of the warp suppressing film and the amount of warp of the first polarizer. Table 1 below shows the relationship between the thickness of the warp suppressing film and the amount of warp of the first polarizer, similar to FIG.

As shown in Table 1 and FIG. 8, when the thickness of the warpage suppressing film is 100 nm or more and 400 nm or less, the amount of warpage is close to 0 mm, which means that warpage can be effectively suppressed. It can be seen that when the thickness of the warpage suppressing film is 150 nm or more and 300 nm or less, warpage can be suppressed more effectively.

(Production method)
An example of a method for manufacturing the optical isolator 1 of this embodiment will be described below.

9(a) to 9(c) are front cross-sectional views for explaining an example of the method of manufacturing the optical isolator according to the embodiment shown in FIG. First, the base material 16 of the polarizing glass plate shown in FIG. 9A is prepared. The base material 16 of the polarizing glass plate becomes the polarizing glass plate 6 of the optical isolator 1 by being divided in a process described later.

Next, as shown in FIG. 9A, an antireflection film as the first optical function film 7 is formed on the first main surface 16a of the base material 16 of the polarizing glass plate. When forming the antireflection film, for example, a low refractive index film and a high refractive index film may be alternately laminated. The low refractive index film and the high refractive index film can each be formed by a vacuum deposition method, a sputtering method, or the like.

Next, as shown in FIG. 9(b), a warpage suppressing film 8 is formed on the second main surface 16b of the base material 16 of the polarizing glass plate. The warpage suppressing film 8 can be formed by a vacuum deposition method, a sputtering method, or the like. Thus, the base material 13 of the first polarizer is obtained. In the first polarizer base material 13 used for manufacturing the optical isolator 1 of the present embodiment, since the warp suppressing film 8 is formed, warping of the first polarizer base material 13 can be suppressed. can be done.

The warp amount of the base material 13 of the first polarizer can be adjusted by the thickness of the warp suppressing film 8, for example. It should be noted that the stress applied to the base material 16 of the polarizing glass plate can be controlled by the condition of the force with which the material constituting the warp suppressing film 8 is struck against the base material 16 of the polarizing glass plate in a vacuum deposition method, a sputtering method, or the like. , and thereby the amount of warpage can also be adjusted.

The base material 14 of the second polarizer shown in FIG. 9(c) can be obtained in the same manner as the base material 13 of the first polarizer. On the other hand, the base material 12 of the Faraday rotator is prepared. Next, as shown in FIG. 9(c), the first polarizer base material 13 is attached to the third main surface 12a of the Faraday rotator base material 12, and the first polarizer base material 12 is bonded to the third main surface 12a of the Faraday rotator base material 12. 4, the base material 14 of the second polarizer is adhered to the main surface 12b. Thus, the base material 11 of the optical isolator is obtained.

The size of the base material 11 of the optical isolator may be, for example, 10 mm square when viewed from the side of the base material 13 of the first polarizer. However, the size of the base material 11 of the optical isolator is not limited to the above.

Next, the base material 11 of the optical isolator is divided along the line II in FIG. 9(c) into individual pieces. Thereby, a plurality of optical isolators 1 can be obtained. The division of the optical isolator 1 can be performed by, for example, dicing.

By the way, as in the example shown in FIG. 10, when the warpage suppressing film 8 is not formed on the second main surface 16b of the base material 16 of the polarizing glass plate, the base material 103 of the first polarizer may be warped. There is When such a first polarizer base material 103 is used, the adhesion between the first polarizer base material 103 and the Faraday rotator base material 12 may be insufficient. Therefore, there may be a portion where the base material 103 of the first polarizer and the base material 12 of the Faraday rotator are not sufficiently bonded.

In contrast, the base material 13 of the first polarizer shown in FIG. 9(c), which is used to manufacture the optical isolator 1 of the present embodiment, is less likely to warp. Therefore, the adhesion between the base material 13 of the first polarizer and the base material 12 of the Faraday rotator can be more reliably improved. Therefore, the entire contact surfaces of the base material 13 of the first polarizer and the base material 12 of the Faraday rotator can be more securely and effectively bonded. In the base material 11 of the optical isolator, since the bonding strength can be increased over the entire surface where the base material 13 of the first polarizer and the base material 12 of the Faraday rotator are in contact, each light obtained by singulation In the isolator 1 , the first polarizer 3 is difficult to separate from the Faraday rotator 2 . Therefore, the defect rate can be reduced, and productivity can be effectively improved.

However, the method for manufacturing the optical isolator 1 of this embodiment is not limited to the above method.

(Modification)
In the first embodiment shown in FIG. 1, the first polarizer 3 is provided directly on the third main surface 2a of the Faraday rotator 2. As shown in FIG. Note that the first polarizer 3 may be indirectly provided on the third main surface 2a of the Faraday rotator 2 . An example of this is given below.

11 is a front sectional view of an optical isolator according to a modification of the embodiment shown in FIG. 1. FIG. In this modified example, a second optical function film 27 is provided on the third principal surface 2a of the Faraday rotator 2 . A first polarizer 3 is provided on the second optical function film 27 . Thus, in this modification, the first polarizer 3 is indirectly provided on the third main surface 2a of the Faraday rotator 2 via the second optical function film 27 . Similarly, a third optical function film 28 is provided on the fourth main surface 2b of the Faraday rotator 2, and a second polarizer 4 is provided on the third optical function film 28. . The second polarizer 4 is indirectly provided on the fourth main surface 2b of the Faraday rotator 2 via the third optical function film 28. As shown in FIG.

The second optical function film 27 and the third optical function film 28 are, for example, antireflection films or IR cut filters. Of the second optical function film 27 and the third optical function film 28, only the second optical function film 27 may be provided.

In this modified example, similarly to the embodiment shown in FIG. 1, warping of the first polarizer 3 can be suppressed, and reflection of incident light to the Faraday rotator 2 can be suppressed.

Reference Signs List 1 Optical isolator 2 Faraday rotator 2a Third main surface 2b Fourth main surface 3 First polarizer 4 Second polarizer 6 Polarizing glass plate 6a First main surface 6b Second main surface 7 First optical function film 8 Warp suppression film 11 Base material 12 of optical isolator Base material 12a of Faraday rotator Third main surface 12b Fourth main surface 13 First polarizer base material 14 Second polarizer base material 16 Polarizing glass plate base material 16a First main surface 16b Second main surface 27 Second optical function film 28 Third optical function film 103 . . . base material of first polarizer

Claims (7)

A polarizer for an optical isolator comprising a Faraday rotator using a bismuth-substituted rare earth iron garnet single crystal and comprising a warp suppressing film provided directly on the Faraday rotator of the optical isolator,
a polarizing glass plate having first and second main surfaces facing each other;
a first optical function film provided on the first main surface of the polarizing glass plate;
a warp suppressing film provided directly on the second main surface of the polarizing glass plate and suppressing warping of the polarizing glass plate;
with
A polarizer, wherein the warpage suppression film has a refractive index of 1.47 or more and 1.55 or less. 2. The polarizer according to claim 1, wherein the warpage suppression film has a thickness of 50 nm or more and 500 nm or less. 3. The polarizer according to claim 1, wherein said first optically functional film is an antireflection film. The polarizer according to any one of claims 1 to 3, wherein the warp suppressing film is made of silicon oxide or silicon oxynitride. 5. The polarizer according to any one of claims 1 to 4, wherein the warpage suppression film is made of silicon oxide represented by SiO 2 _x , where 1≦x<2. a Faraday rotator having third and fourth major surfaces facing each other;
a first polarizer provided directly on the third principal surface of the Faraday rotator;
a second polarizer provided directly or indirectly on the fourth principal surface of the Faraday rotator;
with
An optical isolator, wherein the first polarizer is the polarizer according to any one of claims 1-5. further comprising a second optical function film provided on the fourth main surface of the Faraday rotator ;
7. The optical isolator according to claim 6, wherein said second polarizer is indirectly provided on said fourth main surface of said Faraday rotator via said second optical functional film.

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