JP2002350777A - Isolator with lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems with a polarization dependent type polarizer that the area thereof to be exclusively used is limited by the light spot diameter based in the spreading angle of a laser and the distance between lenses and there is heretofore a restriction on downsizing. SOLUTION: The isolator with the lenses is constituted by mounting the same substrate with the first polarizer which has the lenses and is subjected to antireflection coating on the light transparent surfaces and the composite element formed by optically regulating and joining a Faraday rotator and second polarizer which are respectively subjected to the antireflection coating on the respective transparent surfaces and further mounting this substrate with a magnetic material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a polarization dependent optical isolator used for preventing reflected return light generated due to a structural cause of a laser module used for transmission of optical communication or the like. The present invention relates to an isolator with a lens for realizing required reflection characteristics, miniaturization, and achieving compounding with a lens.

[0002]

2. Description of the Related Art Conventionally, an isolator used for optical communication and the like is obtained by attaching a polarizer and a Faraday rotator to a metal fitting with solder or low-melting glass, and attaching it by fusion while adjusting the rotation with a YAG laser. It is completed. When this is used, it is attached after the lens to form a collimating system or a non-collimating system, and is used by being attached at an appropriate position.

[0003] With such a configuration, the distance between the laser diode and the lens is designed in consideration of the dimensions of the lens and the dimensions of the bracket for mounting the lens. The mode field diameter is inevitably large, so that the dimensions of the polarizer and the Faraday rotator used in the isolator are increased, which is one of the cost factors of the isolator.
Had one. In addition, optical adjustments are required one by one, which further increases the processing cost.

As one of the solutions, a method has been adopted in which a non-collimating optical system is used between the laser and the pigtail, and a laminate isolator is mounted on the front of the pigtail. Therefore, when it is attached to an actual module, it is necessary to adjust the rotation to match the plane of polarization of the laser.

Further, even if a non-collimating optical system is used, the thickness of the Faraday rotator and the polarizer cannot be reduced, and the size thereof is limited by the beam shape on the surface of the front polarizer. Furthermore, since the laminate isolator has a polarizer and a Faraday rotator fixed with an adhesive, in the future, in applications where the emission intensity of the laser will increase, concerns about its reliability have not been sufficiently resolved. .

A configuration example of a conventional isolator having such a problem will be described with reference to the drawings. FIG. 8 shows a configuration example of a conventional general isolator.

As shown in the figure, a polarizer 4 is attached to a metal fitting 11 using a low melting point glass 12. Further, the Faraday rotator 3 is similarly attached to the metal fitting 11 ′ using the low melting point glass 12. After these two elements have been subjected to rotational optical adjustment, they are fixed by fusion using a YAG laser.

[0008] Another polarizer 4 is attached to the metal fitting 11 "using the low melting point glass 12. Thereafter, the metal fitting 11 '.
And 11 ″ are rotationally optically adjusted so that the two polarizers 4 are at 90 ° to each other, are fixed by fusing with a YAG laser,
An element having a function of transmitting incident laser light but absorbing reflected light is completed.

This isolator is usually used in a collimating system. Therefore, the spot diameter of the light passing through the isolator is determined by the spread angle of the laser and the focal length of the lens placed in front of the isolator. The focal length of a lens is determined by its mounting method, numerical aperture, and the like.

The spread angle of the LD is typically 30 °.
Is well known. Further, since 0.8 mm is often used as the focal length of the lens, the spot diameter of light obtained therefrom is 1 mm, and therefore, the effective range of the isolator is required to be at least 1 mm square.

FIG. 9 shows a structure adopted for the purpose of reducing the occupied area of the isolator. A laminate isolator 16 is attached to a pigtail 15.

As shown in the figure, first, plates of two polarizers 4 and one Faraday rotator 3 are rotationally optically adjusted and attached with an adhesive. Therefore, in this case, since the elements are not attached one by one, the number of processing steps is reduced. The laminate isolator 16 is obtained by cutting this into a desired size.

On the other hand, the pigtail 15 is created as follows. The ferrule 17 and the metal fitting 11 are attached by press-fitting, and the fiber 12 from which the coating 13 has been removed is the ferrule 1.
7 and fixed with an adhesive together with the coating. Thereafter, the tip of the ferrule 17 is angle-polished, and a laminate isolator is attached to the tip of the ferrule 17 with an adhesive.

Here, an isolator in which the magnetic body 5 is attached to the pigtail is completed.

Although this isolator is optically adjusted, when it is mounted on a module, the laser has polarization dependence, so it is necessary to match the directionality with this laser. In the case of mounting, it is required to mount while adjusting the rotation optical again.

FIG. 10 is disclosed in Japanese Patent Application Laid-Open No. 9-90282, in which a lens 2 is attached to a first polarizer 1, and a Faraday rotator 3 and a second polarizer 4 are further attached.
And a structure in which the magnetic body 5 is attached thereto, and the emitted light beam 22 of the laser 20 is connected to the fiber 26. In the case of such a structure, although the purpose of reducing the occupied area of the isolator has been achieved, it has various weak points described below.

[0017]

In a conventional collimating type isolator, the isolator shown in FIG. 8 is placed after a lens. In the case of a collimating type, a laser is placed at the focal length of the lens, and the distance can be set to the lens. When the isolator and the lens are configured separately, a mounting structure is required for each, and as a result, the spot diameter of the light becomes large, and therefore, the polarization component which is a component of the isolator is used. There was a problem that the size of the child and Faraday rotator could not be reduced.

In order to reduce the size of the isolator,
As shown in the figure, there is a means that employs a non-collimator system and attaches an isolator immediately before the pigtail. However, even in this case, the thickness required for the polarizer and the Faraday rotator (polarizer 0.2-0.5 m
m, Faraday rotator 0.5 mm), which naturally limits its dimensions.

Further, in the above structure, as can be seen from FIG. 9, when the metal fitting 11 is used for welding by YAG, there is no accurate mark indicating the direction on the metal fitting 11 or the isolator is accurately attached to the mark. Since it is not performed, the structure does not become clear. For this reason,
Again, optical adjustment is required, and a dedicated device for mounting is required.

Further, although the structure shown in FIG. 10 is effective for reducing the occupied area of the isolator, the structure for realizing a countermeasure against the return light and also simplifying the assembly after the countermeasure against the return light is performed. No mention. For example, a countermeasure against return light is provided by inclining the isolator. However, a structure that makes the isolator small and provides an easy mounting structure when the distance between the laser 20 and the isolator is extremely short is not disclosed.

[0021]

In view of the above, the present invention provides
A first polarizer having a lens and having a light transmission surface coated with an antireflection coating, and a composite element obtained by optically adjusting and joining a Faraday rotator and a second polarizer each having a light transmission surface coated with an antireflection coating; Are attached to the same substrate, respectively, and furthermore, a magnetic body is attached to this substrate to form an isolator with a lens, thereby providing a structure in which the lens and the isolator are integrally attached, shortening the distance between the laser and the lens, and It can be easily attached.

The lens of the first polarizer is formed integrally with the polarizer, or is formed separately and joined to form a complex of the polarizer and the lens. Further, the lens in the first polarizer is
It is also effective to form the film formed on the end face of the polarizer by etching or laser processing, or to form a low-melting glass provided on the end face of the polarizer with a mold.

Further, the end face of the first polarizer, which is not provided with a lens, is inclined at a predetermined angle from a plane perpendicular to the optical axis to prevent reflection from the back face of the first polarizer. . For the reflection from the lens surface, if an anti-reflection coating is applied, sufficient measures against return light can be taken.

The second polarizer and the Faraday rotator are provided with metal layers having different shapes in a region through which light does not pass, and are joined using the metal layers. The end face of the composite device including the second polarizer and the Faraday rotator is structured to prevent reflected return light by being inclined at a predetermined angle from a plane perpendicular to the optical axis.

These composites, the first polarizer, the Faraday rotator and the second polarizer are cut from a large substrate and
A metal layer and a solder layer are formed on the cut surface of the portion, and the metal layer and the solder layer are used to attach the substrate to the substrate.

In mounting on the substrate, the distance between the bottom surface of the substrate and the main axis of the lens is precisely controlled, so that the substrate can be easily mounted on the Si platform.

By adopting the above structure, the light is collimated at a distance where the light spot by the emitted light of the laser does not become large, and as a result, the effective diameter of the isolator is reduced by reducing the light spot. be able to. Also, by separating the lens and the first polarizer, and the Faraday rotator and the second polarizer as separate bodies, a countermeasure against returning light and simplification of assembly are achieved, and the lens is accurately formed on the first polarizer. To control the position of this lens and substrate accurately, and by using the Si platform,
By accurately setting the laser mounting position, it is easy to mount the isolator.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an isolator of the present invention. A lens 2 is formed in front of the first polarizer 1, and an end surface 1a behind the lens 2 is an inclined surface. Both surfaces of these elements are coated with an antireflection coating, and a metal layer 6a is formed on the lower surface thereof, and is attached to a substrate 7 having a metal layer 6b.

The Faraday rotator 3 is mounted on the same substrate 7.
And the second polarizer 4 are fixed, the Faraday rotator 3 tilts the plane of polarization of the incident light by 45 °, and the second polarizer 4 transmits the incident light. After being optically adjusted, these are joined together with the metal layer 6a formed on the Faraday rotator 3 and the metal layer 6d formed on the polarizer 4 to form a composite element. A metal layer 6a is formed on the lower surface of the composite device, and is attached to a substrate 7 having a metal layer 6b. Further, a magnetic body 5 for applying a magnetic field to the Faraday rotator 3 is attached to the substrate 7 to constitute an optical isolator.

The first polarizer 1 has a lens 2 as described above.
By using a lens 2 having a short focal length and a large numerical aperture, the lens 2 and the isolator can be placed in the immediate vicinity of the laser. As a result, the spot diameter of the emitted light of the laser can be suppressed small, and High coupling efficiency can be obtained.

The coupling efficiency between the return light and the laser due to the reflection characteristic from the lens will be described in detail later.
It has been confirmed that this is not a problem. Reflection at the interface between the lens 2 and the first polarizer 1 does not occur if the refractive indexes are the same. In the case of attaching by a bonding or the like, since the return light is directly coupled to the laser in the collimating system, the joining surface needs to be inclined. End face 1 behind first polarizer 1
The reflection from a is almost the same as that of a laser in the case of a collimating system.
100% will be combined. Therefore, in the present invention, the end face 1a is provided with a predetermined angle and an anti-reflection coating is applied to reduce the coupling efficiency between the return light and the laser.

However, in such a structure, when the first polarizer 1 is cut out from a large substrate as will be described in detail later, one surface of this substrate must be corrugated or saw-toothed. Not get. If a large base forming the Faraday rotator 3 and the second polarizer 4 is to be mounted on this substrate, the process will be complicated. Therefore, in the present invention, the Faraday rotator 3 and the second polarizer 4
Are separate from the first polarizer 1.

Since the Faraday rotator 3 and the second polarizer 4 can be optically adjusted for each large substrate, the dimensions to be cut and the effective area are set in advance, and each substrate is set in an area not included in the cut area. After the anti-reflection coating, the metal layers 6c and 6d are formed, and after optical adjustment, the two substrates can be bonded using the metal layers 6c and 6d. It is convenient to change the shapes of the metal layers 6c and 6d in advance so that the positional relationship when attaching the composite element can be understood.

When cutting out from a large substrate, the first polarizer and the thin film which can be selectively removed on the end faces 1a, 3a and 4a of the composite device by the Faraday rotator 3 and the second polarizer 4 such as a resist or a thin film After forming a thin film such as an organic material such as photosensitive polyimide, or an inorganic material such as a nitride film, and other metal materials, such as glass and garnet, each of the substrates is cut, and 6a is formed on a part of the cut surface. It is bonded to the substrate 7.

What is important in the present invention is that the distance from the main axis of the lens 2 to the bottom surface of the substrate 7 falls within a desired value. In order to achieve this object, the position of the lens 2 formed on a large substrate for cutting out the first polarizer 1 is formed at a precisely controlled position. Furthermore, it is cut to a correct size by the dicer. The substrate 7 is required to have an accurate flatness and an accurate thickness. For this reason, glass is optimal as a material. However, this does not mean that other materials cannot be used.

The effect that can be realized by adopting the above structure is that the lens 2 is attached to the first polarizer 1,
By using a short focal length of the lens 2 and adopting a high numerical aperture, the isolator can be made sufficiently close to the laser, and as a result, the effective area of the isolator can be reduced, thus realizing low cost. You can do it.

By combining a lens and a polarizer and forming a large number of lenses on one polarizer substrate, the cost of one lens can be reduced, and the cost for mounting the lens can be reduced. Hardware and man-hours can be reduced.

Further, since the optical adjustment of the Faraday rotator 3 and the second polarizer 4 can be performed for each large substrate, the assembly can be simplified and the cost can be reduced. The method of cutting the substrate obliquely is currently established by a dicer.

The attachment to the substrate 7 is performed by the metal layer 6a. This method is easy to control the thickness of the joint surface,
In addition, the use of the substrate 7 having an accurate thickness
, And the distance between the optical axis and the bottom surface of the substrate 7 can be easily controlled. By installing this invention by controlling this value,
The degree of freedom of attachment can be made one-dimensional, and easy attachment is realized.

In FIG. 1, when the first polarizer 1 having the lens 2, the Faraday rotator 3 and the second polarizer 4 are attached, the inclination of each element is parallel. , The rays will be tilted upward. As a structure that corrects this in the downward tilt direction, the tilt angles of the Faraday rotator 3 and the second polarizer 4 can be reversed, as shown in FIG. What is necessary is just to employ | adopt these structures suitable at the time of an assembly.

Next, the production of each optical element will be described in detail.

A substrate for separating the first polarizer 1 has a structure shown in FIG. 3, and a plurality of elements are cut out from one substrate. The angle of the cut is accurately measured, and after a thin film that can be selectively removed is coated on both sides, the cut is cut from the dotted line portion 8 in FIG. 3 by a dicer.
The first polarizer 1 is formed by forming the metal layer 6a on a part of the cut surface of the cut element and removing the selectively removable thin film. The back surface of the substrate shown in FIG. 3 has a corrugated structure that is easy to process in this example. As this structure, a directional saw-tooth structure is more accurate in order to obtain the accuracy of the position of the lens 2 from the optical axis.

One method of forming the lens 2 on the first polarizer 1 is to attach an already formed semicircular lens or lens array with an adhesive. At this time, a lens and an adhesive having the same refractive index as the polarizer are used.

When the refractive indexes of the adhesives are different, it is necessary to apply a predetermined angle (4 to 15 °) to the lens and the polarizer beforehand and bond them. Or,
After forming an antireflection coat corresponding to the refractive index of the adhesive on the lens and the first polarizer, it is necessary to bond them.

Another method of forming the lens 2 is to form an oxide film on the first polarizer 1 by low-temperature CVD, and then form a diffraction grating lens or a refractive optical lens by laser or etching.

Further, another method of forming the lens 2 is to use a low-melting glass, place the low-melting glass on the upper surface of the first polarizer 1, and mold it with a mold to form the lens 2. . The lens 2 may be formed integrally with the first polarizer 1.

A major feature of the method of forming the lens 2 is that the temperature at the time of forming the first polarizer 1 must be suppressed to at least 600 ° C. or less so as not to deteriorate the characteristics of the first polarizer 1. That is.

The composite of the second polarizer 4 and the Faraday rotator 3 is prepared as follows. As shown in FIG. 4A, first, in a region where the light spot 18 does not pass, metal layers 6 c and 6 d having shapes whose directions can be recognized are formed on one surface of the Faraday rotator 3 and the second polarizer 4. It is formed. FIG. 4B shows a state of bonding two substrates.
The optical adjustment direction of each of the substrates forming the Faraday rotator 3 and the second polarizer 4 is determined in advance as indicated by arrows 30 and 31, and fine adjustment is performed to align the two.

Thereafter, as shown in FIG. 5, the metal layers 6c and 6d are bonded together at a high temperature. The bonded substrate is provided with a thin film that can be selectively removed on both sides, and then cut along the oblique cut portion 10 indicated by a dotted line, and the cut elements are arranged with the mounting portion thereof facing upward. By forming 6a and then removing the selectively removable thin film, a composite of the polarizer 4 and the Faraday rotator 3 is formed.

The composite of the first polarizer 1, the Faraday rotator 3 and the second polarizer 4 is precisely assembled on a substrate 7 having high thickness and high flatness. 5 is attached to complete the isolator. High precision is required for the substrate 7 and the metal layers 6a and 6b, as described later, in order to reduce the degree of freedom of attachment to one dimension. As a result, an easy assembling method is realized.

The above-mentioned metal layers 6a, 6b, 6c and 6d are composed of an underlayer, an intermediate layer, an uppermost layer, and a solder layer thereon. The metal layers 6a to 6d are required to have a good adhesion of the underlayer to the glass, a middle layer to serve as a buffer layer with solder to the underlayer, a top layer to prevent oxidation of the middle layer,
And a layer that ensures the wettability of the solder layer, and is generally made of Cr / Au, Cr / Ni / Au, Ti / Pt / A
u, Ti / W / Au, etc. are suitable. As the solder layer, an Au / Sn alloy layer or a laminate is suitable.

As the above-mentioned isolator joining process, the joining of the Faraday rotator 3 and the second polarizer 4, the combination of the first polarizer 1, the composite of the Faraday rotator 3 and the second polarizer 4, and the substrate 7 are performed. It is the solder layer that joins with the solder layer. The former requires a high melting point because it must be bonded first. The following method is possible as a method of realizing the same.

One is a metal layer 6 for bonding the composite.
In this method, Au / Sn is used for c and 6d, and Ag / Sn solder is used for the metal layers 6a and 6b for bonding to the substrate 7. Another method is to change the weight ratio of Au / Sn. At a weight ratio of 7: 3, the melting point of this material is at a minimum, about 290 ° C. The joining temperature between the Faraday rotator 3 and the second polarizer 4 is reduced by changing the material cost of the alloy so that the weight ratio becomes 8: 2 or the like or changing the thickness of Au of the metal layer. Can be raised.

One of the selectively removable thin films used for separating each element is a resist or polyimide. These are removed by the developer. Also,
There is a nitride film as a hard coat. These can be selectively removed by plasma etching. In addition, in some cases, a metal that can be removed by a developer that does not attack the metal layer and the solder layer 6a can be used.

Next, an application example of the present invention is shown in FIG. Laser 20 is attached to Si platform 23 by bump 21. The substrate 7 forming the isolator of the present invention is S
The distance from the laser diode 20 is set by a cutting part 24 fixed on the i platform 23 and formed by a dicer formed on the Si platform. Since the cutting accuracy of the current dicer has been improved, it is possible to mount the laser diode 20 with an accuracy of 5 μm or less, including the mounting accuracy.

The mounting position of the isolator is S
The accuracy is determined by the height of the groove 25 formed in the i-platform 23, and the accuracy can be ± 1 μm. If the center deviation of the lens 2 is ± 1 μm, the alignment error at the time of cutting is ± 1 μm, and the control error of the metal layers 6a and 6b is ± 0.5 μm, the total error is ± 1.8.
μm, so that a sufficiently accurate mounting is possible.

With this mounting method, the lens 2
And the alignment of the laser diode 20 and the lens 2 with respect to the height direction of the optical axis are uniquely determined.
An isolator can be provided in which only the lateral direction remains as an adjusting element.

In FIG. 6, the substrate 7 of the isolator is S
Although fixed on the i platform 23, each element can be directly fixed on the Si platform 23 itself to form the isolator of the present invention.

Next, the problem of how much return light is generated due to reflection when the position of the laser diode 20 and the lens 2 are brought closer is analyzed. From the spread angle of the laser diode 20, the beam waist ω ₀ is given by ω ₀ = λ / πtan θ. Here, λ = 1.55 μm, θ = 30
When ° is included, ω ₀ = 0.8645 μm.

When calculating the reflection, the calculation may be performed assuming that a spherical reflecting mirror is present on the surface of the lens 2. Beam waist omega ₁ virtual by the spherical mirror is given by the following equation.

Ω ₁ = ω ₀ / √ [(πω ₀ ² / λ) ² · 4 / R ²
+ (1 + 2d / R) ² ] Here, the distance between the laser and the main surface of the lens is represented by R = 1
Assuming that the diameter is 00 μm and the radius of the lens is 66 μm, the distance between the laser and the lens is d = 34 μm. By substituting this, ω ₁ = 0.5086 is obtained.

The position z is given by the following equation.

Z = [(πω₁ ^Two/ Λ)^Two・ 2 / R + d (1
+ 2d / R)] / [(πω₁ ^Two/ Λ) ^Two・ 4 / R_Two+ (1+
2d / R)^TwoThis value is easily obtained, and z = 20.24 μm is obtained.
Will be.

As a result, the coupling efficiency between the return light and the laser by the mirror is given by the following equation.

Η = 4ω ₀ ² ω ₁ ² / ((ω ₀ ² + ω ₁ ² ) + λ ²
(D + z) ² / π ² ) By substituting the above parameters ω ₀ , ω ₁ , λ, d, and z into this equation, a coupling efficiency of 0.001 is obtained, that is, 30 dB, and an AR coat (typically 27 dB) is applied to the lens. When applied, a total of 57 dB is obtained, and it can be seen that there is no problem even if the lens is brought closer.

The lens 2 attached to the first polarizer 1
Is shown in FIG. In FIG. 7, (a) is a normal one,
(B) shows a lens in which the lens 2 is not exposed on a plane portion, and (c) shows a diffraction grating lens.

The lens 2 of the type shown in FIG. 7 (a) is suitable for a lens to which the already formed lens 2 is attached with an adhesive or fusion, or for a type in which a low melting glass is used and a mold is used. However, this type requires some consideration for alignment during installation.

The type shown in FIG. 7B can be mounted using a flat surface when mounting, but it is considerably difficult to make a mold or the like.

In the diffraction grating type shown in FIG. 7C, a considerably thin oxide film can be formed on the polarizer and then formed by etching or laser processing. ing.

[0070]

EXAMPLE An isolator shown in FIG. 1 was manufactured as an example according to the present invention. As shown in FIG. 3, oblique polishing is performed on the back surface of the substrate forming the first polarizer 1 at an interval of 310 μm at an angle of 8 °, and then a hemispherical ball lens of 120 μmφ is bonded to the surface with the same refractive index. Using an agent, they were fixed and arranged regularly. After that, anti-reflection coating is performed on both surfaces, and the above-mentioned substrate is covered with photosensitive polyimide.
280 μm square first polarizer 1 using a μm blade
Is cut out, and on this cut surface, an underlayer of Cr / Ni / Au,
Middle layer, top layer (500/2000/2000)
Then, a Au / Sn solder layer 2 μm was formed, a metal layer 6 a was formed, and finally the polyimide was removed to form a first polarizer 1.

The dimensions of the ball lens were calculated numerically based on the following considerations. The spread angle of the laser diode 20 is generally 30 ° in the vertical direction and 25 ° C. in the horizontal direction.

Assuming that a spherical lens is used and the distance to the main surface of the lens 2 is 100 μm, the spot diameter of the collimated light is 115 μφ. The diameter of a lens having a focal point of 100 μm is easily obtained from f = n ₂ R / 2 (n ₂ −n ₁ ), where the refractive index of the lens is 1.5, and is 66 μm. Of course, since there is a problem of aberration, such a lens design is not simply made as it is, and it is assumed that an aspherical lens is actually used. In addition, since the beam is tilted due to the deviation of the optical axis between the laser diode 20 and the lens 2, the effect needs to be considered in the effective area of the isolator.

The thickness of the Faraday rotator 3 is 0.5 mm,
Assuming that the thickness of the second polarizer 4 is 0.2 mm and the mounting space of both is 0.1 mm, a total thickness of 1 mm is required. The increase in the effective area is 105 μm.

In addition, the damage layer by the dicer was 30
Considering μm, total, 115 μm + 105 μm +
At 60 μm, 280 μm is the required size as the effective area of the isolator.

This is because the required area of the polarizer and Faraday rotator used in the conventional isolator is 1.2 mm.
This corresponds to about one-fourth of × 1.2 mm. Considering the cutting area of the dicer, the area can be greatly reduced to one-fifteenth.

At this time, the distance between the laser diode 20 and the lens 2 is 34 μm, and a sufficient distance for attachment is ensured.

Next, an anti-reflection coating is applied to the Faraday rotator 3 and the second polarizer 4, and Cr / Ni / Au (500 ° / 20) is formed on one surface of each of them as metal layers 6c and 6d.
00/2000 °), and a 3 μm solder layer Au / Sn was further formed on the Faraday rotator 3.

The second polarizer 4 and the Faraday rotator 3
After adjusting the rotational optics, the solder was melted at a high temperature and joined to form a composite. After photosensitive polyimide was formed on this substrate, it was cut with a dicer to a size of 280 × 283 μm. For cutting, one side is vertical and one side is 8
At an angle of ° and attaching the angled part, 2
The size was set to be 80 × 280 μm. next,
The metal layer 6a was formed to complete the composite.

Finally, the metal layer 6b was formed on the substrate 7, cut into a desired size, and the first polarizer 1 and the composite were attached by soldering to complete the isolator.

When this isolator was evaluated on an optical bench, a coupling efficiency of about 35% was obtained. Further, a reflectance of 35 dB or more is obtained. Of course, the insertion loss and the separation characteristic, which are the basic characteristics of the isolator, are 0.2 dB or less and 40 dB at the peak wavelength, respectively.
dB or less is obtained.

As a result, the coupling efficiency of 35% is attributable to the aberration due to the use of the spherical lens. If the original aspherical lens can be used, the coupling efficiency is 60-70%.
It is considered that the coupling efficiency of can be obtained.

Further, in the present trial production, the production was performed without considering the sufficient positioning accuracy. However, if the production is performed while the dimensions are sufficiently suppressed, it is considered that the precision can be ± 2 μm.

[0083]

As described above, according to the present invention, a first polarizer having a lens and having a light transmitting surface coated with an antireflection coating, and a Faraday rotator having a light transmitting surface each coated with an antireflection coating are provided. The composite element in which the second polarizer is optically adjusted and joined is mounted on the same substrate, and a magnetic body is mounted on the substrate to form an isolator with a lens. This makes it necessary to use a polarizer and a Faraday rotator. The area can be reduced sufficiently compared to the conventional area, and its mounting does not require adjustment of the rotation optics, and since there is no adhesive on the optical axis, high reliability is secured, In production, batch processing by substrates such as lens formation, oblique grinding, optical adjustment, and the like can be performed, so that the number of production steps can be significantly reduced. For this reason, it is possible to supply an isolator at a lower cost than in the past,
In the future, it will promote the further development of the optical communication market, which is accelerating its spread.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an isolator with a lens according to the present invention.

FIG. 2 is a sectional view showing another embodiment of the isolator with a lens of the present invention.

FIG. 3 is a cross-sectional view illustrating a method for manufacturing a first polarizer that forms the isolator with a lens according to the present invention.

FIGS. 4A and 4B are diagrams illustrating a method of manufacturing a composite of a second polarizer and a Faraday rotator that constitutes an isolator with a lens according to the present invention.

FIG. 5 is a cross-sectional view illustrating a method of manufacturing a composite of a second polarizer and a Faraday rotator that constitutes an isolator with a lens according to the present invention.

FIG. 6 is a sectional view showing an application example of the isolator with a lens of the present invention.

FIGS. 7A to 7C are cross-sectional views of a first polarizer used in the isolator with a lens according to the present invention.

FIG. 8 is a cross-sectional view showing a conventional general polarization-dependent isolator.

FIG. 9 is a sectional view showing a conventional laminate isolator mounted on a pigtail.

FIG. 10 is a sectional view of a conventional isolator with a lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st polarizer 1a end surface 2 lens 3 Faraday rotator 3a end surface 4 2nd polarizer 4a end surface 5 Magnetic body 6a-6d Metal layer 7 Substrate 8 Cutting part 9 Oblique grinding part 10 Cutting part 11 Metal fitting 11 'Metal fitting 11 "Metal fittings 12 Low melting glass 13 Fiber coating part 14 Adhesive 15 Pigtail 16 Laminating isolator 17 Ferrule 18 Light spot 20 Laser diode 21 Bump 22 Emitting light 23 Si platform 24 Cutting part 25 Groove part 30 Optical axis adjusting direction 31 Optical axis adjusting direction

Claims (9)

[Claims] An optical system comprising: a first polarizer having a lens and a light transmitting surface having an antireflection coating, a Faraday rotator having a light transmitting surface having an antireflection coating, and a second polarizer. An isolator with a lens, wherein the joined composite elements are mounted on the same substrate, and a magnetic material is mounted on the substrate. 2. The lens according to claim 1, wherein the lens of the first polarizer is formed integrally with the polarizer or formed separately and joined. With isolator. 3. The isolator with a lens according to claim 1, wherein the lens in the first polarizer is formed by etching or laser processing a film formed on an end face of the polarizer. 4. The isolator with a lens according to claim 1, wherein the lens in the first polarizer is formed by molding a low-melting glass provided on an end face of the polarizer with a mold. . 5. The isolator with a lens according to claim 1, wherein an end face of the first polarizer, which is not provided with a lens, is inclined at a predetermined angle from a plane perpendicular to an optical axis. 6. The method according to claim 1, wherein the second polarizer and the Faraday rotator each include a metal layer having a different shape in a region through which light does not pass, and are joined using the metal layer. The isolator with the lens described. 7. The isolator with a lens according to claim 1, wherein an end face of the composite element comprising the second polarizer and the Faraday rotator is inclined at a predetermined angle from a plane perpendicular to the optical axis. . 8. The method according to claim 1, wherein the first polarizer, the Faraday rotator, and the second polarizer are cut from a large substrate, and a metal layer is formed on a part of the cut surface and joined to the substrate. Item 7. The isolator with a lens according to Item 1. 9. The isolator with a lens according to claim 1, wherein the substrate is fixed on a Si platform, or the substrate is made of a Si platform.