JP7654485B2 - Optical element and its manufacturing method, optical isolator, and optical transmission device - Google Patents

Description

The present invention relates to an optical element used in an optical isolator, and in particular to an optical element that is effective in producing a high-output optical isolator, a manufacturing method thereof, and improvements to an optical isolator and optical transmission device that use the optical element.

In optical communication systems, light emitted from a semiconductor laser is projected onto the end face of an optical fiber through a lens and transmitted, but some of the light is surface reflected by the lens and the end face of the optical fiber and returns to the semiconductor laser, becoming noise. This noise has the adverse effect of destabilizing the operation of the semiconductor laser. Therefore, optical isolators are used to remove this returning light.

In addition, in a pump laser, which is an excitation light source for an erbium-doped fiber amplifier (EDFA), it is necessary to stabilize the power of the light source and to prevent the semiconductor laser element from being damaged by strong returning light, so an optical isolator is used.
An optical isolator uses an optical element having a structure in which a Faraday rotator is integrally disposed between, for example, two polarizing glass plates (polarizers). In this case, the polarization directions of the polarizers are set to be inclined at 45 degrees to each other. When this is placed in a magnetic field, the polarization plane of the Faraday rotator rotates, and the characteristics of the light passing through one polarizer, the Faraday rotator, and the other polarizer change. Taking advantage of this characteristic, a permanent magnet for magnetically saturating the Faraday rotator is provided around the Faraday rotator, rotating the polarization plane of the Faraday rotator by 45 degrees. This makes it possible to block return light.

However, in optical isolators that use semiconductor lasers as light sources, when high-density optical power is irradiated onto the optical isolator due to the increasing power output of semiconductor lasers, localized heat generation can occur, causing the isolator to lose its function. For example, optical isolators used for pump lasers, which are the excitation light sources for EDFAs, are manufactured using glass polarizers, but when high-density optical power is irradiated onto the glass polarizer, localized heat of up to several hundred degrees Celsius occurs. If the heat generation exceeds the glass transition point of the glass polarizer, the glass polarizer itself cannot maintain its function. The glass transition temperature of glass polarizers currently available on the market for communication devices is around 500 degrees Celsius. For this reason, the optical isolator loses its function under conditions where the local temperature exceeds 500 degrees Celsius.

If the local temperature is below 500°C, the next components whose heat resistance becomes an issue are the anti-reflective coating (AR coating) applied to the surface of the polarizer and the material used to fix the polarizer. The heat resistance temperature of typical AR coating materials used when polarizers and Faraday rotators are incorporated into optical isolators is about 450°C.

Since resistance to such a temperature range is required, the techniques described in Patent Documents 1 and 2 have been adopted in conventional optical isolators.
Patent Document 1 discloses an optical isolator comprising a Faraday rotator, a polarizer, an analyzer and a holder, the holder comprising a first metal holder and a second metal holder having a coaxial shape with a through hole in the central axis, the Faraday rotator, polarizer and magnet being arranged on the central axis within a gap generated when the first metal holder and the second metal holder are combined with their central axes aligned, the analyzer being arranged on the outer central axis of the second metal holder, the polarizer, Faraday rotator and analyzer all being metallized on their outer peripheries excluding a central circular portion and adhesively fixed to the first metal holder and the second metal holder, respectively, by soldering or brazing, and the first metal holder and the second metal holder being joined by welding.
Furthermore, Patent Document 2 discloses a mode in which, in adhesively fixing each component constituting an optical isolator, a thin metal layer is formed in advance by sputtering or vapor deposition on each adhesive surface of a polarizer, a permanent magnet, and a Faraday rotator, and the adhesive surfaces between each of the component elements are adhered by soldering.
In this way, Patent Documents 1 and 2 disclose a method in which a polarizer and a Faraday rotator are arranged separately from each other, a metal film is formed on the main surface (excluding the light transmitting area) or the side surface of the polarizer or Faraday rotator, and optical elements such as the polarizer or Faraday rotator on which a thin metal layer is formed are bonded via solder or the like, or bonded to a metal holder via solder or the like to provide a heat dissipation function.

On the other hand, in the case of optical isolators for communication, which have a relatively low output, the widespread use of semiconductor lasers for communication and the demand for lower prices have led to the development of high-quality optical adhesives, as described in, for example, Patent Document 3, and in recent years, optical elements in which an organic optical adhesive is used on the optical surface and optical elements such as a polarizer and a Faraday rotator are laminated have become mainstream. Even when fixing optical elements to metal holders, organic adhesives have become mainstream instead of the above-mentioned solder, etc.
Furthermore, Patent Document 4 discloses an optical isolator in which a rectangular prism-shaped optical element consisting of a Faraday rotator, a polarizer, and an analyzer is inserted into a hole with a nearly rectangular cross section provided in a magnet, and an adhesive is filled into four gaps formed by the four faces of the optical element parallel to the optical axis and the opposing wall surfaces of the hole in the magnet, thereby fixing the magnet and the optical element.

Japanese Patent No. 2995747 (Example 1, Figure 1) Japanese Patent No. 2841210 (Example, Figure 2) Japanese Patent No. 4300790 (Example, FIG. 1) JP-A-6-265819 (Example, FIG. 1)

Optical isolators for communication, which have relatively weak optical power, are mainly made of a structure in which optical elements such as polarizers and Faraday rotators are laminated as described above. However, in recent years, optical isolators have become smaller, and the heating of the heat generating point due to the concentration of laser light places a very large load on the organic optical adhesive. The optical power generally used is several tens of mW or less. This depends on the decomposition temperature of the organic optical adhesive. The power resistance of the Faraday rotator and polarizer is about 700 mW for polarized light and about 300 mW for unpolarized light, and the organic optical adhesive, which has contributed to miniaturization and cost reduction, is now a hindrance. In other words, in a structure in which an organic optical adhesive is present on the optical surface, if the organic optical adhesive that bonds the Faraday rotator and polarizer is locally heated, the organic optical adhesive may change in quality or generate bubbles, and the limit is several hundreds of mW. In optical isolators using semiconductor lasers or the like with high output power exceeding several hundred mW, the problem of heat generation still remains. As such, conventional methods such as those shown in Patent Documents 1 and 2, in which a thin metal layer is formed on a Faraday rotator or a polarizer and bonded via solder or the like, or bonded to a metal holder via solder or the like, are used for manufacturing such isolators, resulting in high costs and preventing progress in miniaturization.
For this reason, in the field of optical isolators for use in high-output semiconductor lasers used in optical communication systems and the like, there is a strong demand for laminated optical elements that are heat resistant, can be miniaturized, and can be provided at low cost.
Incidentally, Patent Document 4 discloses a structure in which an adhesive is filled between an optical element in which optical elements such as a Faraday rotator and a polarizer are stacked, and a magnet. However, it should be noted that this adhesive is only for fixing the optical elements stacked on the magnet, and that the individual optical elements that make up the optical element are bonded together with an organic optical adhesive, and is not used to join the individual optical elements.

The technical problem that this invention aims to solve is to suppress the deterioration of optical characteristics due to the alteration of the adhesive used in the laminated optical element used in the optical isolator, even when high-power light is passed through the laminated optical element.

Therefore, in order to solve the above-mentioned technical problems, the inventors came up with the present invention from the viewpoint of eliminating the deterioration of optical properties due to the alteration of the organic optical adhesive by excluding the organic optical adhesive from the area (optical path) through which light such as a high-output semiconductor laser passes.

A first technical feature of the present invention is an optical element used in an optical isolator, comprising at least a Faraday rotator that rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements that are arranged on both sides of the Faraday rotator in the optical axis direction to polarize and guide light, and cooperate with the Faraday rotator to allow light to pass in the forward direction and block light from passing in the reverse direction, wherein these optical elements are stacked in the optical axis direction to form an optical element stack , and flat or curved chamfered portions are formed at at least a plurality of corners of side surfaces along the optical axis direction of the optical element stack, and adjacent optical elements are joined by applying an organic adhesive to the chamfered portions .
A second technical feature of the present invention is an optical element used in an optical isolator, comprising at least a Faraday rotator that rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements that are arranged on both sides of the Faraday rotator in the optical axis direction to polarize and guide light, and cooperate with the Faraday rotator to allow light to pass in the forward direction and block light from passing in the reverse direction, the optical element being characterized in that these optical elements are stacked in the optical axis direction to form an optical element stack, curved recesses are formed in at least a plurality of corners of side surfaces along the optical axis direction of the optical element stack, and adjacent optical elements are joined by applying an organic adhesive to the recesses.

A third technical feature of the present invention is an optical element having the first or second technical feature, wherein the polarization guiding element includes two polarizers whose polarization directions differ from each other by a predetermined angle, and the optical element is used as a polarization-dependent optical isolator.
A fourth technical feature of the present invention is an optical element having the first or second technical feature, wherein the polarization guide element includes a birefringent crystal on a forward light input side and a forward light output side, and the optical element is used as a polarization-independent optical isolator .

A fifth technical feature of the present invention is an optical element used in an optical isolator, the optical element including at least a Faraday rotator which rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements which are arranged on both sides of the Faraday rotator in the optical axis direction to polarize and guide light, and cooperate with the Faraday rotator to allow light to pass in a forward direction and block light from passing in a reverse direction, the optical elements being stacked in the optical axis direction to form an optical element stack, and the optical elements being stacked in the optical axis direction to bond adjacent optical elements to each other at side surfaces of the optical element stack along the optical axis direction with an organic adhesive, a manufacturing method for optical elements, the method comprising: a manufacturing step of preparing each optical element substrate of a predetermined size to constitute a body, and stacking the optical element substrates to manufacture an optical element laminated substrate; a drilling step of drilling holes in the optical element laminated substrate manufactured in the manufacturing step at least at a plurality of intersections of planned cutting locations corresponding to the size of the optical element laminate; a coating step of applying the organic adhesive to holes drilled in the optical element laminated substrate in the drilling step; and a cutting step of cutting the optical element laminated substrate to which the organic adhesive has been applied in the coating step along the planned cutting locations so as to obtain the optical element laminate.

A sixth technical feature of the present invention is an optical isolator comprising: an optical element having any one of the first to fourth technical features; and a magnet that saturates magnetization of the Faraday rotator of the optical element.
A seventh technical feature of the present invention is an optical transmission device comprising: an optical isolator having the sixth technical feature; and an optical component that inputs light to the optical isolator or receives light output from the optical isolator.

According to the first or second technical feature of the present invention, even if high-power light is passed through a laminated optical element used in an optical isolator, it is possible to suppress deterioration of optical characteristics due to deterioration of the adhesive used in the laminated optical element. In addition, compared to the case where the organic adhesive is bonded at one location, the adhesive strength to the optical element laminate can be stabilized, and further, compared to the case where the organic adhesive is bonded at a location other than the corner of the side of the optical element laminate, the distance from the optical axis center of the optical element laminate can be increased, and the effect of high-power light on the organic adhesive can be further reduced.
In particular, according to the first technical feature, the organic adhesive can be held more stably than in a case where there is no chamfered portion.
In particular, according to the second technical feature, the adhesive locations for the organic adhesive can be easily secured by perforation or the like, and the organic adhesive can be stably held.
According to a third technical feature of the present invention, even if high-power light is passed through a laminated optical element used in a polarization-dependent optical isolator, degradation of the optical characteristics due to alteration of the adhesive used in the laminated optical element can be suppressed.
According to a fourth technical feature of the present invention, even if high-power light is passed through a laminated optical element used in a polarization-independent optical isolator, degradation of the optical characteristics due to alteration of the adhesive used in the laminated optical element can be suppressed .
According to the fifth technical feature of the present invention, it is possible to provide a method for manufacturing an optical element that can suppress deterioration of optical characteristics due to deterioration of the adhesive used in the laminated optical element used in an optical isolator, even if high-power light is passed through the laminated optical element. Furthermore, in the process of manufacturing the optical element laminate, an organic adhesive can be easily applied. Also, it is possible to easily manufacture an optical element in which at least a plurality of corners of the side surface along the optical axis direction of the optical element laminate are adhesive regions of the organic adhesive.
According to the sixth technical feature of the present invention, it is possible to construct an optical isolator capable of suppressing deterioration of optical characteristics caused by alteration of adhesive used in the laminated optical element even when high-power light is passed through the laminated optical element used in the optical isolator. In addition, it is possible to provide an optical isolator that is heat-resistant, compact, and low-cost for use in a high-power semiconductor laser or the like.
According to the seventh technical feature of the present invention, it is possible to construct an optical transmission device including an optical isolator capable of suppressing deterioration of optical characteristics caused by deterioration of adhesive used in the laminated optical element even when high-power light is passed through the laminated optical element used in the optical isolator. In addition, it is possible to miniaturize the optical isolator, and therefore the optical transmission device using the optical isolator can also be miniaturized.

FIG. 1A is an explanatory diagram showing an overview of an embodiment of an optical transmission device incorporating an optical isolator using an optical element to which the present invention is applied, and FIG. 1B is a view taken from the arrow B in FIG. FIG. 2A is an explanatory diagram showing the overall configuration of an optical receptacle as an optical transmission device incorporating an optical isolator in accordance with the first embodiment, and FIG. 2B is an explanatory diagram showing the basic configuration of an optical element used in the optical isolator. 2(a) is a view taken along an arrow A of the optical element shown in FIG. 2(b), and FIG. 2(b) is a view taken along an arrow B of the optical element shown in FIG. 2(b). 5A to 5F are explanatory views showing an example of a method for manufacturing an optical element according to the first embodiment. FIG. 1A is an explanatory diagram showing an example of incorporating an optical element into a circular toric magnet, and FIG. 1B is an explanatory cross-sectional view taken along line BB in FIG. FIG. 2A is an explanatory diagram showing an optical element according to a comparative embodiment 1, and FIG. 2B is a cross-sectional explanatory diagram taken along line BB in FIG. 1A is an explanatory diagram showing the main parts of the optical element used in the optical isolator according to modification form 1-1; FIG. 1B is an explanatory diagram showing the optical isolator according to modification form 1-2; and FIG. 1C is an explanatory diagram showing the optical isolator according to modification form 1-3. 1A is an explanatory diagram showing a main part of an optical isolator according to a second embodiment, and FIG. 1B is a view taken along the arrow B in FIG. 11 is an explanatory diagram showing a main part of an optical receptacle as an optical transmission device incorporating an optical isolator according to a third embodiment. FIG. 10A is an explanatory diagram showing a main part of an optical isolator according to a fourth embodiment, and FIG. 10B is an explanatory diagram showing a modified example of the optical isolator shown in FIG.

Overview of the Embodiment FIG. 1(a) shows an overview of an embodiment of an optical transmission device incorporating an optical isolator using an optical element to which the present invention is applied.
In the figure, an optical transmission device 12 includes an optical isolator 10 and an optical component 13 that inputs light to the optical isolator 10 .
1A, the optical isolator 10 includes an optical element 1 having a predetermined structure, and a magnet 11 for forming a magnetic field that is disposed around the optical element 1. The optical component 13 is not limited to an optical component for input, but broadly includes an optical component 13 that receives light output from the optical isolator 10, and a representative example of this type of optical transmission device is an optical receptacle.

In this embodiment, the basic configuration of the optical element 1 used in the optical isolator 10 includes optical elements including at least a Faraday rotator 2 (FR: short for Faraday Rotator) that rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements 3 (specifically 3a and 3b) that are arranged on both sides of the Faraday rotator 2 in the optical axis direction to polarize and guide light, and cooperate with the Faraday rotator 2 to allow light to pass in the forward direction and block light from passing in the reverse direction. These optical elements are stacked in the optical axis direction to form an optical element stack 5, and the sides of the optical element stack 5 along the optical axis direction are bonded with an organic adhesive 6 so as to join adjacent optical elements.

In such technical means, the optical isolator 10 can be of a polarization-dependent type or a polarization-independent type, and the optical element 1 of this example can be applied to either of them. The magnet 11 of the optical isolator 10 may be arranged in contact with the optical element 1 or out of contact with it. In particular, in the case where the optical element 1 is arranged out of contact with the magnet 11, it becomes possible to design the optical element 1 and the magnet 11 separately in order to miniaturize the optical element 1, and it is sufficient to install the magnet 11 that forms a magnetic field required for the miniaturized optical element 1.
Further, the number of Faraday rotators 2 is not limited to one, but a configuration in which a plurality of Faraday rotators are used is also included.
Furthermore, as the polarization guide elements 3 (3a, 3b), in the optical element 1 used in the polarization-dependent optical isolator 10, polarizers whose polarization directions differ by a predetermined angle are used, and in the optical element 1 used in the polarization-independent optical isolator 10, birefringent crystals are used on the forward incident side and forward exit side of the light, respectively, and further, in order to adjust the polarization directions of the incident light and the exiting light, for example, a wave plate may be installed between the birefringent crystal on the incident side and the Faraday rotator 2.
Furthermore, the optical element 1 of this example may be modified in such a way that an anti-reflection film is interposed between the Faraday rotator 2 and the polarization guide element 3, or a heat dissipation element is interposed between a plurality of Faraday rotators 2, and therefore the optical element is considered to broadly include aspects that at least include a Faraday rotator 2 and a polarization guide element 3.

Furthermore, while the optical element stack 5 typically has a substantially rectangular parallelepiped shape, the location of adhesion with the organic adhesive 6 may be a flat portion or a corner portion of a side surface along the optical axis direction of the optical element stack 5. By adopting such an adhesion method, since the organic adhesive 6 is not present on the optical path surface of each optical element, there is no concern that the organic adhesive 6 will change in quality or that air bubbles will be generated even if high-power light passes through.
Furthermore, the organic adhesive 6 may be any adhesive that has heat resistance and good thermal conductivity, and transparency is not required since the adhesive is not used on the optical path surface. Here, an organic adhesive 6 with good thermal conductivity is, for example, an organic resin adhesive containing a thermally conductive filler (e.g., metal filler, etc.). For example, a thermal conductivity of 0.6 W/mK or more is preferable. When high-power light passes through the optical element 1, the optical element 1 generates heat, and if an organic adhesive 6 with good thermal conductivity is used, it is effective in diffusing the generated heat to the magnet 11 and the holder.

Next, a representative or preferred embodiment of the optical element 1 according to the present embodiment will be described.
1(a) and 1(b), a preferred embodiment of the bonding method using the organic adhesive 6 is to bond a plurality of corners 5b of the side surface 5a along the optical axis direction of the optical element laminate 5. This embodiment is preferred in that the bonding strength is stronger by bonding a plurality of bonding locations than by bonding a single location, and further, by bonding the corners 5b of the side surface 5a of the optical element laminate 5 as bonding locations, it is possible to increase the distance from the optical axis center of the optical element laminate 5 to the bonding position compared to the case where the side surface 5a other than the corners 5b is bonded, and the organic adhesive 6 is less susceptible to the effects of high-output optical power.
Another preferred embodiment of the bonding method using the organic adhesive 6 is one in which the corners 5b have flat or curved chamfered portions, and the organic adhesive 6 is applied to the chamfered portions. Here, the chamfered portions are effective as surfaces that stably hold the organic adhesive 6.
Furthermore, another preferred embodiment of the bonding method using the organic adhesive 6 is one in which the corner 5b has a curved recess, and the organic adhesive 6 is applied to the recess. Here, the recess can be easily created by drilling or the like, and is effective as a receiving portion that stably holds the organic adhesive 6.

A representative embodiment of the method for manufacturing the optical element 1 includes a manufacturing process for manufacturing the optical element 1 described above, in which each optical element substrate for constituting the optical element stack 5 is prepared in a predetermined size, and each optical element substrate is laminated to produce an optical element stack substrate; a perforation process for perforating the optical element stack substrate produced in the manufacturing process at a predetermined location among the planned cutting locations corresponding to the size of the optical element stack 5; a coating process for coating the organic adhesive 6 into the holes perforated in the optical element stack substrate in the perforation process; and a cutting process for cutting the optical element stack substrate to which the organic adhesive 6 has been applied in the coating process along the planned cutting locations to obtain the optical element stack 5.

Here, in the fabrication process, when stacking each optical element substrate, the positions may be adjusted and temporarily fixed. In addition, the drilling process may be cutting by a laser processing machine or mechanical processing such as a micro drill. In this case, holes may be drilled at any of the planned cutting locations of the optical element stack 5. Furthermore, in the application process, the organic adhesive 6 may be applied to the holes drilled in the drilling process. The amount of organic adhesive 6 applied to the holes may be appropriately selected. Furthermore, in the cutting process, a dicing device, laser cutting device, or the like may be appropriately selected.
In addition, as a preferred embodiment of the method for manufacturing the optical element 1, the perforation step may perforate all or part of the intersection of the planned cutting portion in the optical element laminate substrate. This embodiment is effective in manufacturing the optical element 1 in which the corner portion 5b of the side surface 5a along the optical axis direction of the optical element laminate 5 is the adhesion region of the organic adhesive 6.

Hereinafter, the present invention will be described in more detail based on the embodiments shown in the accompanying drawings.
First embodiment
- Overall configuration of optical receptacle -
FIG. 2A shows a basic configuration of an optical receptacle 20 serving as an optical transmission device according to the first embodiment.
In this example, the optical receptacle 20 is configured by connecting an optical fiber 21 to an optical isolator 10 via a connecting part 25, and the optical isolator 10 transmits light (laser light in this example) from the optical fiber 21 in only one direction and prevents the reflected light component from shining back toward the optical fiber 21.

<Connection parts>
Here, the connection part 25 is configured such that the optical fiber 21 protected by a jacket is inserted and attached into a through hole 27 of a ferrule 26 made of metal (e.g., stainless steel), a stepped hole 28 is formed on the outlet side of the through hole 27 of the ferrule 26, a capillary 29 made of a cylindrical small-diameter ferrule made of ceramics (e.g., zirconia) is fitted into and held in the stepped hole 28, one end of the capillary 29 is exposed so as to protrude from the stepped hole 28 of the ferrule 26, and the optical fiber bare portion 22, from which the jacket of the optical fiber 21 has been removed, is inserted and held in a through hole 30 of the capillary 29. The end face of the exposed portion of the capillary 29 is a plane perpendicular to the optical axis direction of the optical fiber bare portion 22.
<Optical isolator>
As shown in FIG. 2A, the optical isolator 10 has an annular magnet 110 (a permanent magnet in this example) disposed around the optical element 1 .

-Examples of optical element configurations-
FIG. 2B shows an example of the optical element 1 used in this embodiment.
In the figure, the optical element 1 is used in a polarization-dependent optical isolator 10, and is composed of optical elements including a rectangular Faraday rotator 2 and two rectangular polarizers 40 (specifically, 40a and 40b) arranged on both sides of the Faraday rotator 2 in the optical axis direction. In this example, the optical elements are stacked to form an optical element stack 5 having a substantially rectangular parallelepiped shape.
In this example, the Faraday rotator 2 is made of, for example, a magnetic garnet crystal film, which is a magneto-optical crystal film, and the two polarizers 40 (40a, 40b) are made of polarizing glass plates in this example, and are arranged so that the polarization directions are inclined at a predetermined angle, for example, 45°, relative to each other. The two polarizers 40 (40a, 40b) are laminated with the Faraday rotator 2 sandwiched between them via an organic adhesive 6. A magnetic field is applied to the Faraday rotator 2 by the permanent magnets 110 arranged around the optical element 1, so that the light passing through the Faraday rotator 2 is polarized.
Therefore, the polarization plane of the Faraday rotator 2 rotates, so that forward light passing through the polarizer 40a, the Faraday rotator 2, and the polarizer 40b passes through, but backward returning light is blocked.
3, an antireflection film 50 may be applied to each surface of the polarizer 40 and the Faraday rotator 2 in order to suppress reflection loss of light passing through the optical element 1. As described later, the antireflection film 50 does not use an optical adhesive on the optical path surfaces of the polarizer 40 and the Faraday rotator 2, so that there is no need to provide an antireflection film for adhesive and an antireflection film for air separately. By unifying the antireflection film for air, the productivity of the optical element 1 is also expected to be improved.

In this embodiment, the optical element stack 5 is fixed by bonding the side surface 5a along the optical axis direction of the optical element stack 5 with an organic adhesive 6, rather than the optical path surfaces of the polarizer 40 (40a, 40b) and the Faraday rotator 2. Therefore, since no organic optical adhesive is present on the optical path surfaces of the polarizer 40 and the Faraday rotator 2, even when used with a high-power semiconductor laser or the like, the organic optical adhesive does not deteriorate or generate air bubbles, and it becomes possible to maintain the optical characteristics.
Here, a specific example of a bonding method using the organic adhesive 6 will be described.
In this example, the corners 5b of the optical element stack 5 are selected as the bonding locations of the organic adhesive 6 on the optical element stack 5, and a quarter-circular arc-shaped recess 60 is formed in this corner 5b along the optical axis direction, and the organic adhesive 6 is applied to this recess 60. It is preferable to provide this recess 60 at a plurality of corners 5b, and in this example, it is provided at all four corners 5b from the standpoint of strength.

The shape of the recess 60 depends on the manufacturing method of the optical element 1 described later, and utilizes the quarter arc portion of the through hole opened in the boring process. This will be described in detail later.
Furthermore, in this example, an adhesive layer 6a is formed in the recess 60 by the organic adhesive 6, and fixes the adjacent polarizer 40 and Faraday rotator 2, respectively. The adhesive layer 6a in this example is formed in a layer shape that follows the shape of the recess 60, depending on the amount of application of the organic adhesive 6, as shown in FIG. 3(a). Here, the thickness of the adhesive layer 6a when forming the layer shape that follows the shape of the recess 60 is not particularly limited as long as it has adhesive strength. It is preferably 3 μm or more, and more preferably 10 μm to 30 μm. The adhesive strength between the polarizer 40 and the Faraday rotator 2 is sufficient to be sufficient to prevent peeling of the optical element stack 5 during the manufacture of the optical isolator 10, since the optical element 1 and the magnet 11 are fixed by the adhesive when the optical isolator 10 is finally manufactured, and it is sufficient for the adhesive layer 6a to be in a layer shape that follows the shape of the recess 60.
The shape of the adhesive layer 6a made of the organic adhesive 6 is not limited to the layered shape described above, and may be such that the organic adhesive 6 applied to the recess 60 fills the voids at the corners 5b of the optical element stack 5 so that the front shape shown in Fig. 3(a) is rectangular. However, there is no particular limitation as to whether the adhesive layer 6a is made into a layered shape that follows the shape of the recess 60, or whether the recess 60 is filled so that the front shape of the optical element stack 5 and the adhesive layer 6a, including the optical element stack 5, is rectangular as shown in Fig. 3(a) .

The organic adhesive 6 is used on the side surface 5a along the optical axis direction of the optical element laminate 5, and is not used on the optical path surface. For this reason, the organic adhesive 6 does not need to be an optically transparent adhesive, and it is important to quickly diffuse the heat generated by the polarizer 40 and the Faraday rotator 2 to the magnet 11, the holder, etc., and a thermally conductive resin adhesive with high thermal conductivity is preferable.
In general, adhesives for optical use must be organic resin adhesives that are transparent and heat resistant. For example, epoxy adhesives can be used as adhesives that are transparent and have a heat resistance of 300°C, but cannot be used when higher heat resistance is required. In contrast, thermally conductive resin adhesives are similarly organic resin adhesives, and since they do not need to be used on the optical path surface, it is preferable to use ones that are opaque and have higher thermal conductivity, and preferably contain thermally conductive fillers, such as metal fillers, and have a thermal conductivity of 0.6 W/mK or more.

-Method of manufacturing optical elements-
Next, a method for manufacturing an optical element according to the present embodiment will be described with reference to FIG.
FIG. 4(a) shows a process of preparing each optical element substrate 70 in a predetermined size for constructing the optical element laminate 5. In this example, two polarizer substrates 71 (specifically 71a and 71b) and one Faraday rotator substrate 72 are prepared as the optical element substrate 70. Here, the thickness of the Faraday rotator substrate 72 is adjusted so that the rotation angle is 45 degrees. In addition, it is preferable to prepare the polarizer substrate 71 such that the first polarizer substrate 71a has a polarization direction horizontal to one side, and the second polarizer substrate 71b has a polarization direction with a gradient of 45 degrees with respect to the first polarizer substrate 71a. In addition, the polarizer substrate 71 may have an anti-reflection film (not shown) for air on both sides of the optical path surface. For example, the anti-reflection film may be formed so that the reflectance is 0.25% or less in accordance with the refractive index of air of 1.0. In addition, the Faraday rotator substrate 72 may also have an anti-reflection film (not shown) for air on both sides of the optical path surface.
Furthermore, the sizes of the polarizer substrate 71 and the Faraday rotator substrate 72 are not particularly limited, but since they will be laminated in the next step, it is preferable that the polarizer substrate 71 and the Faraday rotator substrate 72 have the same size. For example, they can be rectangular substrates measuring 11 mm x 11 mm.
The polarization extinction ratio of the polarizer substrate 71 alone is preferably 50 dB or more. By making the polarization extinction ratio 50 dB or more, it is possible to achieve the required isolation when assembled into the optical isolator 10.

Next, FIG. 4B shows a lamination step in which the optical element substrates 70 are laminated.
In this lamination step, the first polarizer substrate 71a (71), the Faraday rotator substrate 72, and the second polarizer substrate 71b (71) are laminated in this order, their positions are adjusted, and they are temporarily fixed to form an optical element laminated substrate 73. Here, the temporary fixing is performed on the portions of the polarizer substrate 71 and the Faraday rotator substrate 72 that are not used as the optical element laminate 5. For example, the polarizer substrate 71 and the Faraday rotator substrate 72 may be bonded to four corners of their outer shapes using a small amount of adhesive. There is no particular limitation on this adhesive as long as it does not interfere with subsequent processes, and it may be a thermally conductive resin adhesive (corresponding to the organic adhesive 6) used in the bonding step described below.
4A and 4B show the steps of producing the optical element laminated substrate 73. As shown in FIG.
FIG. 4(c) shows a perforation process. This perforation process is a process of perforating a predetermined portion of the planned cutting portion corresponding to the size of the optical element stack 5 in the optical element stack substrate 73, to form a through hole 74. In this example, the perforation position is set to be a corner 5b (see FIG. 3(a)) of the optical element stack 5 by cutting to a predetermined size in the subsequent dicing process. It is preferable to perform the perforation process in common with the corner 5b of the adjacent optical element stack 5. By performing the perforation process in common with the corner 5b of the adjacent optical element stack 5, it is possible to reduce the work of the perforation process. The size of the perforation is set according to the cutting width in the subsequent dicing process, according to the recess 60 formed in the corner 5b of the optical element stack 5. Furthermore, the shape of the recess 60 in the corner 5b is determined by the size of the optical element 1 (corresponding to the size of the optical element stack 5) and the effective area (clear aperture (CA)) of the optical path of the laser used.

As shown in Fig. 3, the corners can be set to a concave shape within a range that does not overlap the clear aperture (CA) with respect to the size of the optical element 1. For example, when the size of the optical element 1 is 0.5 mm and the clear aperture (CA) is φ0.4 mm, the radius of the recesses 60 (specifically 60a to 60d) is 50 µm, when the clear aperture (CA) is φ0.3 mm, the radius of the recesses 60 is 0.1 mm, and when the clear aperture (CA) is φ0.25 mm, the radius of the recesses 60 is 0.125 mm. The cutting width is 0.05 mm to 0.2 mm, depending on the cutting method. Therefore, when the size of the optical element 1 is 0.5 mm square, the clear aperture (CA) is 0.4 mm in diameter, and the cutting width is 0.1 mm, the perforation diameter is approximately 0.2 mm in diameter, and the radius of the recesses 60 (60a to 60d) is approximately 50 μm.
There is no particular limitation on the method of drilling. Any drilling tool 80 may be used. Cutting with a laser processing machine may be used. Alternatively, machining such as a micro drill may be used.

4D shows a coating process in which the organic adhesive 6 is applied to the through-holes 74 drilled in the optical element laminated substrate 73 in the drilling process. As described above, the adhesive layer 6a is preferably made of a thermally conductive resin adhesive having a high thermal conductivity. In this example, the adhesive applicator 90 is adapted to coat the organic adhesive 6 in layers along the periphery of the through-holes 74, for example, and the organic adhesive 6 is applied so as to conform to the shape of the through-holes 74, but the through-holes 74 may be entirely filled with the organic adhesive 6. In order to adjust the state of application of the organic adhesive 6 to the through-holes 74, the amount of application of the organic adhesive 6 may be adjusted. In addition, when a curing operation is required, the organic adhesive 6 may be cured by a predetermined method. For example, in the case of a thermosetting adhesive, the adhesive is cured by heating to 80°C.
As the adhesive applicator 90, for example, an auto-dispenser manufactured by Musashi Engineering Co., Ltd. is used.

4(e) shows a dicing step. This is a cutting step in which the optical element laminate substrate 73, on which the organic adhesive 6 has been applied in the application step, is cut along the intended cutting location so as to become the optical element laminate 5. This cutting is performed so that the corners 5b of the optical element laminate 5 become part of the through holes 74. There is no particular limitation on the cutting method, and any cutting tool (not shown) may be used. As the cutting tool, a dicing device, a laser cutting device, or the like may be used.
FIG. 4(f) shows the optical element 1 (in which the corners 5b of the optical element laminate 5 are bonded with adhesive layers 6a made of an organic adhesive 6) obtained through the above-mentioned dicing step.

-Method of manufacturing optical isolator-
In this example, the optical isolator 10 is a cylindrical optical isolator in which an optical element 1 having a substantially rectangular parallelepiped shape is mounted inside a circular ring-shaped magnet 110 (a permanent magnet is used in this example), as shown in Figures 5 (a) and (b), and four corners along the optical axis direction of the optical element 1 are adhesively fixed to the inner surface facing the hollow portion of the magnet 110 via adhesive 100.
Here, it is preferable to use a thermally conductive adhesive as the adhesive 100, which can efficiently diffuse heat generated in the polarizer 40 and the Faraday rotator 2 of the optical element 1 to the magnet 110 side. In addition, as the optical element 1 is fixed to the magnet 110 by the adhesive 100, the bonding between the polarizer 40 and the Faraday rotator 2 is reinforced, and the adhesive strength is further increased.
In this example, a quarter-arc shaped recess 60 is formed at the corner along the optical axis direction of the optical element 1, and an adhesive layer 6a made of organic adhesive 6 is formed along the shape of the recess 60, so that when each corner of the optical element 1 is adhesively fixed to the inner peripheral surface of the annular magnet 110 with adhesive 100, a wide adhesive area can be ensured at each corner of the optical element 1, thereby increasing the adhesive strength of the optical element 1 to the magnet 110. In this example, all four corners of the optical element 1 are adhesively fixed, but two or three corners may be adhesively fixed.

In evaluating the performance of the optical element according to this embodiment, it is compared with the optical element according to Comparative Example 1.
Comparison form 1
6(a) and (b) show a main part of an optical element 1' according to a first comparative example.
In the figure, the optical element 1' includes a Faraday rotator 2 and two polarizers 40 (40a, 40b) arranged on both sides of the Faraday rotator 2 in the optical axis direction, and these optical elements are stacked to form an optical element stack 5' having a substantially rectangular parallelepiped shape, as in the first embodiment. Therefore, when the optical element 1' is placed in a magnetic field generated by a magnet (not shown), the polarization plane of the Faraday rotator 2 rotates, as in the first embodiment, so that forward light passing through the polarizer 40a, the Faraday rotator 2, and the polarizer 40b passes through, but backward returning light is blocked.
However, the optical elements constituting the optical element laminate 5' are laminated in the order of polarizer 40a (40), Faraday rotator 2, and polarizer 40b (40), and are fixed by applying an optical adhesive 6' to the optical path surfaces of the polarizer 40 and the Faraday rotator 2. This optical adhesive 6' is required to be transparent and heat resistant, since it bonds to the optical path surfaces of the polarizer 40 and the Faraday rotator 2. Examples of this type of optical adhesive 6' include organic resin-based transparent adhesives, such as epoxy-based adhesives.
Moreover, in order to suppress reflection loss of light passing through the optical element 1', an AR coat (anti-reflective coating) is applied to each surface of the polarizer 40 and the Faraday rotator 2 as an anti-reflection film 50. The anti-reflection film 50 is preferably provided with an anti-reflection film 50a for air on the outer surface of the polarizer 40 through which the optical axis passes, and an anti-reflection film 50b for adhesive on the surface that is bonded to the Faraday rotator 2. Moreover, it is preferably provided with an anti-reflection film 50b for adhesive on the surface of the Faraday rotator 2 that is bonded to the polarizer 40.
However, when an optical isolator using this type of optical element 1' is used with a high-output semiconductor laser or the like, the optical adhesive 6' may be locally heated, causing the adhesive 6' to change in quality or produce air bubbles, resulting in a deterioration of the optical characteristics of the optical element 1'.

The optical element 1 according to the first embodiment is not limited to the above, but may be modified and used as in the following modified embodiments 1-1 to 1-3, for example.
◎Transformation form 1-1
In the first embodiment, as shown in Fig. 3(a), a recess 60 having an arc-shaped cross section is formed in the corner 5b of the optical element stack 5, and this recess 60 serves as the bonding location of the organic adhesive 6, but as shown in Fig. 7(a), for example, a flat chamfered portion 65 may be formed in the corner 5b of the optical element stack 5, and this chamfered portion 65 may serve as the bonding location of the organic adhesive 6. It is of course also possible to use a curved chamfered portion 66, as shown by the imaginary line in Fig. 7(a).
Regarding such chamfered portions 65, 66, in the drilling process, a non-circular (rectangular or modified rectangular) through hole can be easily formed by controlling the processing position using, for example, a laser processing machine.

◎Transformation form 1-2
FIG. 7B shows the optical element 1 according to the first embodiment further reinforced.
In the figure, the optical element 1 is configured to have a reinforcing plate 150 installed on at least one side along the optical axis direction of the optical element stack 5. The material of this reinforcing plate 150 is not particularly limited as long as it does not impair the characteristics of the optical element 1, but if a material that can be cut under the same cutting conditions as the polarizer 40 and the Faraday rotator 2 is used, it is possible to obtain this type of optical element 1 by simply adding a base material that will become the reinforcing plate 150 when producing the optical element stack substrate 73, for example.
Furthermore, in the optical element 1 provided with such a reinforcing plate 150, even if the size of the optical element 1 is smaller than, for example, 0.3 mm×0.3 mm, it is possible to reinforce the bonding state between the optical elements.

◎Transformation form 1-3
In this embodiment, the optical element 1 employs a mode in which one Faraday rotator 2 is interposed between two polarizers 40 (40a, 40b), but is not limited to this, and may be, for example, an optical element laminate 5 in which five optical elements are laminated, such as a first polarizer 40a (40), a first Faraday rotator 2a (2), a heat dissipation substrate 160, a second Faraday rotator 2b (2), and a second polarizer 40b (40), as shown in Fig. 7(c). In this case, the side surface of the optical element laminate 5 along the optical axis direction may be fixed with an adhesive layer 6a made of an organic adhesive 6.

Embodiment 2
8(a) and (b) show a main part of an optical isolator according to the second embodiment.
In the figure, an optical isolator 10 is a surface-mount type optical isolator in which an optical element 1 is mounted on a plate-shaped magnet 120 (a permanent magnet in this example).
In this example, the optical element 1 has substantially the same components as those in the first embodiment, but has a cross-sectional shape different from that in the first embodiment.
In this example, there are some differences in the manufacturing method of the optical element 1 from that of embodiment 1. Specifically, in the manufacturing process of the optical element 1, in the step of applying the organic adhesive 6, all of the through holes 74 in the optical element stacked substrate 73 (see FIG. 4 ) opened by the drilling process are filled with the organic adhesive 6, and in this state, the drilling process is carried out by the dicing step.
As a result, in this embodiment, the optical element 1 is configured to have a rectangular shape when viewed from the front, as shown in Figure 8(a), including the optical element stack 5 and the adhesive layer 6a made of organic adhesive 6 that fills the recess 60 (in this example, this corresponds to the adhesive filling portion with a fan-shaped cross section that is piled on the recess 60).
In this example, adhesive 100 is applied to one side surface along the optical axis direction of optical element 1, and is adhesively fixed onto plate-shaped magnet 120. In particular, in this example, at the corners of optical element 1, adhesive layers 6a made of organic adhesive 6 are provided in recesses 60 at each corner 5b of optical element stack 5 to bond each optical element, and since adhesive layers 6a essentially constitute the corners of optical element 1 and optical element 1 has a rectangular cross-sectional shape, a larger adhesive area can be secured between optical element 1 according to embodiment 2 and plate-shaped magnet 120 compared to the case where optical element 1 shown in embodiment 1 is used, and adhesive strength can be increased accordingly.

Third embodiment
FIG. 9 shows a main part of an optical receptacle 20 as an optical transmission device according to a third embodiment.
In the figure, the basic configuration of optical receptacle 20 is substantially the same as that of embodiment 1, but unlike embodiment 1, the end face of the exposed portion of capillary 29 has an inclined surface 31 inclined at a predetermined angle θ (for example, 0<θ≦8°) with respect to a plane perpendicular to the optical axis direction of optical fiber bare wire portion 22, and optical element 1 has polarizer 40a located on the incident side directly attached to inclined surface 31 of connecting part 25 using an adhesive (not shown). Note that similar components to those in embodiment 1 are denoted by similar reference numerals and detailed description thereof will be omitted.
In this example, the optical element 1 is disposed at an angle θ with respect to the light traveling direction, so that it is possible to suppress the influence of reflected back light while maintaining the isolation function, compared to a case where the optical element 1 is not tilted.
Furthermore, in this example, the optical element 1 is not directly fixed to the annular magnet 110, so that in manufacturing the optical element 1, it is possible to pursue miniaturization of the optical element 1 without being influenced by the size of the magnet 110, etc.
In this example, the optical element 1 is mounted on the connecting part 25, but this is not limited to this. A holder (not shown) for connecting to other parts may be provided, and the optical element 1 and the magnet 110 may be mounted in the respective holders.

Fourth embodiment
FIG. 10A shows a main part of an optical isolator according to the fourth embodiment.
In the figure, an optical isolator 10 is a polarization-independent optical isolator, unlike the polarization-dependent optical isolators shown in the first to third embodiments.
Polarization-independent optical isolators are sometimes used for semiconductor optical amplifiers, in addition to being used in amplifiers such as erbium-doped fiber amplifiers (EDFAs). In this case, a cheaper product is required, and at the same time, a product with a high packaging density is also required. An optical isolator 10 useful for such applications includes, for example, an optical element 1 as shown below, and a ring-shaped magnet 110 (permanent magnet in this example) arranged around the optical element 1. The optical element 1 may be mounted on the magnet 110 as in the first embodiment, or may be mounted on a member other than the magnet 110 (for example, a connecting part 25) as shown in the third embodiment.
In this example, the optical element 1 is used in a polarization-independent optical isolator, and is configured as an optical element stack 5 by stacking a Faraday rotator 2, two birefringent crystal plates 130 (130a, 130b) arranged on both sides of the Faraday rotator 2 in the optical axis direction, and a wave plate 140 arranged between the Faraday rotator 2 and the birefringent crystal plate 130b on the output side.
Here, the birefringent crystal plate 130 (130a, 130b) is made of, for example, rutile (TiO2) crystal or YVO4 crystal, and the Faraday rotator 2 is made of a magneto-optical crystal film (for example, a magnetic garnet crystal film) as in the first embodiment.
Furthermore, in order to adjust the polarization directions of the incident light and the outgoing light, a half-wave plate is provided as a wave plate 140 between the birefringent crystal plate 130b on the outgoing side and the Faraday rotator 2. The wave plate 140 may be provided in front of the birefringent crystal plate 130b on the outgoing side, and in this example, the birefringent crystal plate 130a on the incident side, the Faraday rotator 2, the wave plate 140, and the birefringent crystal plate 130b on the outgoing side are arranged in this order, but this is not limiting.
In this embodiment, anti-reflection films are formed on the respective bonding surfaces of the Faraday rotator 2, the birefringent crystal plate 130 (130a, 130b) and the wave plate 140 as required.
In this example, adhesive layers 6 a made of an organic adhesive 6 are provided on the side surfaces of the optical element stack 5 along the optical axis direction, for example at the corners, to bond adjacent optical elements of the optical element stack 5 .

In this example, the light incident on the birefringent crystal plate 130a located on the light entrance side is split into an ordinary ray and an extraordinary ray whose polarization planes differ by 90 degrees, and these polarizations are rotated by 45 degrees by the Faraday rotator 2 and by 45 degrees by the wave plate (1/2 wave plate in this example) 140, for a total of 90 degrees, so that the ordinary ray becomes an extraordinary ray and the extraordinary ray becomes an ordinary ray again, and then they are incident on the subsequent birefringent crystal plate 130b, where they are combined and emitted with low loss.
On the other hand, as with the forward direction, the light from the reverse direction is split into an ordinary ray and an extraordinary ray when it passes through the birefringent crystal plate 130b, and passes through the wave plate 140 and the Faraday rotator 2. However, unlike the forward direction, the plane of polarization remains in its original state, so the light proceeds without being multiplexed by the birefringent crystal plate 130a located in the subsequent stage, and there is no concern that the light will be re-entered into the optical fiber.
In this embodiment, as shown in FIG. 10(b), if the optical element 1 is arranged at an angle θ (for example, 0<θ≦8°) with respect to the light propagation direction, it is possible to suppress the influence of reflected back light while maintaining the isolation function, compared to the case where the optical element is not tilted.

Examples of the present invention will now be described in detail.
Example 1
Example 1 is a tangential realization of the polarization-dependent optical isolator (see FIG. 3) shown in the first embodiment.
In this example, the polarizer substrate was a Corning polarizer having a size of 11 mm x 11 mm and a thickness of 0.2 mm, which is a commonly available size. The first polarizer substrate had a polarization direction horizontal to one side, and the second polarizer substrate had a polarization direction at an angle of 45 degrees to the first polarizer substrate.
In addition, an anti-reflection film for air, which has a refractive index of 1.0, was formed on both sides of the polarizer substrate, and the reflectance was adjusted to 0.25% or less. It was confirmed that the polarization extinction ratio of the polarizer substrate alone was 50 dB or more.
Furthermore, the Faraday rotator substrate used was manufactured by Granopt Co., Ltd. That is, a large-area Faraday rotator with a thickness of 400 μm capable of obtaining a Faraday rotation angle of 45 degrees at a wavelength of 1480 nm and 25° C. was used, and both sides of the rotator were coated with anti-reflection films for air.

The polarizer substrate and the Faraday rotator substrate were adjusted to the size of 11 mm x 11 mm according to the process shown in Figure 4, and the polarizer substrate and the Faraday rotator substrate were temporarily fixed at four corners of the outer shape using a small amount of adhesive to prepare an optical element laminate substrate. After that, a predetermined portion of the optical element laminate substrate was perforated using a processing laser (wavelength 1064 nm, beam diameter 50 microns) to form a through hole, and a thermally conductive resin adhesive was applied to the through hole using an autodispenser manufactured by Musashi Engineering. The thermally conductive resin adhesive used was an epoxy resin containing a thermally conductive filler and an adhesive with a thermal conductivity of 0.9 W/mK. After that, it was cured at 80°C, and then cut into a size with a front dimension of 0.5 mm x 0.5 mm using a dicing device to prepare an optical element for an optical isolator. The adhesive was applied in a fine manner using a nozzle with a 50-micron ceramic tip.

Next, a cylindrical optical isolator was fabricated using the optical element fabricated above, as shown in Fig. 3. First, a cylindrical magnet with an outer diameter of φ1.5 mm, an inner diameter of φ0.9 mm, and a length of 1.1 mm was prepared, so that the Faraday rotator of the optical element fabricated above would be in a saturated magnetic field. The optical element fabricated above was attached near the center of this magnet with a thermally conductive resin adhesive.
The adhesive used was an epoxy resin containing a thermally conductive filler with a thermal conductivity of 0.9 W/mK. The adhesive was applied to the four recessed corners of the optical element as shown in Figure 4. The optical element was then heated to 80°C to harden the adhesive and fixed to the magnet, completing the cylindrical optical isolator.

Next, the cylindrical optical isolator fabricated as described above was optically evaluated (input light was polarized light).
Here, the diameter of the laser (beam diameter) was φ0.2 mm. The laser output was 300 mW in Example 1-1, 500 mW in Example 1-2, and 700 mW in Example 1-3. The optical surfaces were observed at that time. The results are shown in Table 1.

Example 2
Example 2 is a concrete embodiment of the optical isolator according to the second embodiment (see FIG. 8).
In Example 2, when the thermally conductive resin adhesive was applied to the through holes of the optical element laminated substrate by an automatic dispenser, the adhesive was filled into all of the through holes. Except for this, an optical element for an optical isolator was manufactured in the same manner as in Example 1. In addition, a surface-mounted optical isolator was manufactured using the manufactured optical element as shown in FIG. 8. First, a flat magnet with a size of 1.3 mm×1.8 mm and a thickness of 1.0 mm was prepared so that the Faraday rotator of the optical element manufactured above would be saturated in magnetic field. The optical element manufactured in Example 2 was bonded near the center of this magnet with a thermally conductive resin adhesive. The adhesive used was an epoxy resin containing a thermally conductive filler and having a thermal conductivity of 0.9 W/mK. In addition, the adhesive was bonded to one side (one surface) of the optical element including the recess at the corner as shown in FIG. 8. Thereafter, the adhesive was heated to 80° C. to harden the adhesive and fix it to the magnet, thereby manufacturing a surface-mounted optical isolator.
Next, the surface mount type optical isolator produced in Example 2 was subjected to optical evaluation.
Here, the diameter of the laser (beam diameter) was φ0.2 mm. The laser output was 300 mW in Example 2-1, 500 mW in Example 2-2, and 700 mW in Example 2-3. The optical surfaces were observed at that time. The results are shown in Table 1.

Example 3
Example 3 is a concrete embodiment of the optical isolator according to the fourth embodiment (see FIG. 10B).
In the third embodiment, the optical element is structured such that instead of a polarizer, a first birefringent crystal plate that splits unpolarized light into multiple polarized lights on the light input side of the Faraday rotator and a second birefringent crystal plate on the light output side of the Faraday rotator are used, and a wave plate is interposed between the second birefringent crystal plate and the Faraday rotator. In manufacturing this optical element, the optical element laminate substrate in which the necessary optical element base materials are laminated has a size of 11 mm x 11 mm and a thickness of 0.2 mm. The rest is substantially the same as in the first embodiment, and an optical element for a polarization-independent optical isolator is manufactured.
Moreover, a cylindrical optical isolator was fabricated in substantially the same manner as in Example 1 using the optical element fabricated in Example 3.
Moreover, optical evaluation was performed in the same manner as in Example 1. The laser output was set to 500 mW in Example 3-1.

Comparative Example 1
Comparative Example 1 is an embodiment of the optical isolator according to Comparative Example 1 (see FIG. 6).
In Comparative Example 1, similarly to Example 1, two polarizer substrates and a Faraday rotator substrate were prepared, and an anti-reflection film for air was formed on the outer surface of the polarizer substrate, an anti-reflection film for adhesive was formed on the adhesive surface side, and an anti-reflection film for adhesive was formed on both sides of the Faraday rotator substrate. The first polarizer substrate, the Faraday rotator substrate, and the second polarizer substrate were bonded in this order at their optical path surfaces with an optical system adhesive to prepare an optical element laminate substrate. The adhesive used was an epoxy adhesive that was transparent and had a heat resistance of 300°C. After that, it was cured at 80°C, and then the optical element laminate substrate was cut into a size with a front dimension of 0.5 mm x 0.5 mm by a dicing device to prepare an optical element for an optical isolator.
Next, a cylindrical optical isolator was fabricated in the same manner as in Example 1 using the optical element fabricated above. Then, the surface mount optical isolator fabricated in Comparative Example 1 was subjected to optical evaluation in the same manner as in Example 1. The laser output was 300 mW in Comparative Example 1-1, 500 mW in Comparative Example 1-2, and 700 mW in Comparative Example 1-3. The optical surface was observed at that time. The results are shown in Table 1.

The results in Table 1 will be explained below.
In Examples 1-1, 1-2, and 1-3, there was no change in the appearance of the optical surface, which was good. There was no change even when the laser output was 700 mW.
In addition, in Examples 2-1, 2-2, and 2-3, there was no change in the appearance of the optical surface, which was good. No change occurred even when the laser output was 700 mW.
Thus, in the surface mount type optical isolator, similarly to the first embodiment, no change in appearance occurs even at 700 mW.
Furthermore, in Example 3-1, there was no change in the appearance of the optical surface, which was good.
In contrast, in Comparative Examples 1-1, 1-2, and 1-3, defects occurred on the optical surface at 500 mW or more. In the optical isolator according to Example 1, no change in appearance occurred even at 700 mW. This indicates that since there is no adhesive layer that receives heat on the optical path surface of the optical element, the polarizer or Faraday rotator can be used up to the limit of its heat resistance temperature. In addition, since the heat generated on the surface of the optical element can immediately escape to the heat conduction areas installed at the four corners of the optical element, it is assumed that the heat dissipation is good even when the laser is irradiated for a long time, and the effect of lowering the absolute temperature at the heat generation point is also manifested.

The optical element used in the optical isolator of the present invention is a laminated optical isolator that uses an organic adhesive, but it is possible to remove the adhesive from the optical path surface and prevent deterioration of optical characteristics due to the adhesive changing or foaming caused by heat generation. Therefore, an optical isolator using the optical element of the present invention can be used for high-power semiconductor lasers, etc., is heat resistant, can be miniaturized, and can be provided at low cost.

LIST OF SYMBOLS 1 Optical element 2 Faraday rotator 3 (3a, 3b) Polarization guide element 5 Optical element stack 5a Side 5b Corner 5' Optical element stack 6 Organic adhesive 6' Optical adhesive 6a Adhesive layer 10 Optical isolator 11 Magnet 12 Optical transmission device 13 Optical component Bm Light 20 Optical receptacle 21 Optical fiber 22 Optical fiber bare wire portion 25 Connection part 26 Ferrule 27 Through hole 28 Stepped hole portion 29 Capillary 30 Through hole 31 Inclined surface 40 (40a, 40b) Polarizer 50 (50a, 50b) Anti-reflection film 60 (60a to 60d) Recess 65 Chamfered portion 66 Chamfered portion 70 Optical element substrate 71 (71a, 71b) Polarizer substrate 72 Faraday rotator substrate 73 Optical element laminate substrate 74 Through hole 80 Drilling tool 90 Adhesive applicator 100 Adhesive 110 Magnet 120 Magnet 130 (130a, 130b) Birefringent crystal plate 140 Wave plate 150 Reinforcing plate 160 Heat dissipation substrate

Claims (7)

An optical element for use in an optical isolator,
The optical element includes at least a Faraday rotator that rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements that are arranged on both sides of the optical axis direction of the Faraday rotator to polarize and guide light, and cooperate with the Faraday rotator to allow light to pass in a forward direction and block light from passing in a reverse direction;
An optical element characterized in that these optical elements are stacked in the optical axis direction to form an optical element stack , flat or curved chamfered portions are formed at least in multiple locations on the corners of the side surfaces along the optical axis direction of the optical element stack, and adjacent optical elements are bonded by applying an organic adhesive to the chamfered portions . An optical element for use in an optical isolator,
The optical element includes at least a Faraday rotator that rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements that are arranged on both sides of the optical axis direction of the Faraday rotator to polarize and guide light, and cooperate with the Faraday rotator to allow light to pass in a forward direction and block light from passing in a reverse direction;
An optical element characterized in that these optical elements are stacked in the optical axis direction to form an optical element stack , curved recesses are formed in at least a few corners of the side surfaces along the optical axis direction of the optical element stack, and adjacent optical elements are bonded by applying an organic adhesive to the recesses . 3. The optical element according to claim 1 ,
The polarization guiding element includes two polarizers whose polarization directions differ from each other by a predetermined angle, and is an optical element used as a polarization-dependent optical isolator. 3. The optical element according to claim 1 ,
The polarization guide element includes birefringent crystals on the forward light input side and the forward light output side, and is used as a polarization-independent optical isolator. An optical element for use in an optical isolator,
In manufacturing an optical element having optical elements including at least a Faraday rotator which rotates the polarization direction of light by a predetermined angle by applying a magnetic field, and polarization guide elements which are arranged on both sides of the Faraday rotator in the optical axis direction to polarize and guide light and cooperate with the Faraday rotator to allow light to pass in the forward direction and block light from passing in the reverse direction, these optical elements are stacked in the optical axis direction to form an optical element stack, and side surfaces of the optical element stack along the optical axis direction are bonded with an organic adhesive so as to join adjacent optical elements,
a production step of preparing each optical element substrate for constituting the optical element laminate in a predetermined size, and laminating each optical element substrate to produce an optical element laminated substrate;
a perforation step of perforating at least a plurality of intersections of planned cutting locations corresponding to the size of the optical element laminate in the optical element laminate substrate produced in the production step;
a coating step of coating the organic adhesive into the holes formed in the optical element laminated substrate in the hole-forming step;
a cutting step of cutting the optical element laminate substrate onto which the organic adhesive has been applied in the application step along the intended cutting location so as to obtain the optical element laminate;
A method for manufacturing an optical element, comprising: The optical element according to claim 1 ,
a magnet for saturating the Faraday rotator of the optical element;
An optical isolator comprising: An optical isolator according to claim 6 ;
an optical component that inputs light to the optical isolator or receives light output from the optical isolator;
An optical transmission device comprising:

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