JP2003344808A - Polarization independent optical isolator and optical circulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical isolator and an optical circulator which has simpler constitution and lower price than before. <P>SOLUTION: The polarization independent optical isolator is constituted by combining a reflection type polarization splitting element 6 which is formed on a base plate 5 and uses photonic crystal having polarization dependence different with places, 1st and 2nd Faraday rotating elements 1 and 2 with a 22.5° angle of rotation, a transparent plate 8, and 1st and 2nd total reflecting mirrors 3 and 4, and polarization splitting element parts 7a and 7b of the reflection type polarization splitting element as parts having different characteristics deviate by 45° in direction of transmitted polarized light; and the reflection type polarization splitting element 6 is disposed between the 1st and 2nd Faraday rotating elements 1 and 2, the transparent plate 8 is disposed between the reflection type polarization splitting element 6 and 2nd Faraday rotating element 2, and the 1st and 2nd Faraday rotating elements 1 and 2 are arranged between the 1st and 2nd total reflecting mirrors 3 and 4. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-independent optical isolator and an optical circulator which are used in optical communication equipment, optical information processing equipment and the like and transmit light only in a specific direction.

[0002]

2. Description of the Related Art A polarization-independent optical isolator that has been widely used in the past is a combination of a polarization separation element that separates light into components having polarization directions different from each other by 90 degrees and a Faraday rotation element that rotates the polarization direction by 45 degrees. It is realized with the basic configuration. As the polarization separation element, a parallel plate birefringent optical crystal, a wedge-shaped birefringent optical crystal, a combination of prisms of a birefringent optical crystal, a polarization beam splitter composed of a dielectric and a metal multilayer film (hereinafter referred to as " PBS ”)) and so on.

[0003]

It is difficult to obtain a high extinction ratio, and PBS is rarely used in optical isolators that require high performance. Further, while the one using the birefringent optical crystal can obtain a high-performance one, it is expensive because the optical crystal takes a long time to grow and requires high-precision cutting and polishing, and the entire optical isolator is also expensive. It is expensive. An object of the present invention is to provide an optical isolator and an optical circulator that are simpler in structure and lower in cost than conventional ones.

[0004]

A polarization-independent optical isolator according to the present invention comprises a reflection-type polarization separation element having a plurality of regions having different polarization characteristics, and first and second Faraday having a rotation degree of 22.5 degrees. It is provided with a rotating element and first and second total reflection mirrors. The reflective polarization separation element is arranged between the first and second Faraday rotation elements, and the first and second Faraday rotation elements are arranged between the first and second total reflection mirrors. The first total reflection mirror is capable of reflecting light, which is transmitted through the second Faraday rotator element and is incident, to the second Faraday rotator side, and the second total reflection mirror is transmitted through the first Faraday rotator element and is incident. The reflected light can be reflected to the first Faraday rotator element side. The reflective polarization separation element using a polymer multilayer film,
Those using a photonic crystal are included. In order to have a simple structure and reduce the cost, it is good to select a reflection type polarization separation element using a photonic crystal as the polarization separation element, and this kind of reflection type polarization separation element is different on the substrate. If only the first and second reflective polarization separation element portions, which are a plurality of regions having polarization characteristics, are formed, then one polarizer will be enough. The optical circulator of the present invention is the optical isolator provided with the third port or the third and fourth ports.

[0005]

According to the polarization-independent optical isolator of the present invention, it is possible to use an inexpensive and high-performance reflective polarization separation element that is realized by a multi-layer film deposition process that does not use an optical crystal and does not require polishing. It is possible to realize an inexpensive optical isolator.
According to the polarization-independent optical isolator of the present invention, the polarization separation element itself has a plurality of regions having different polarization characteristics, and since it also has the functions of a plurality of polarizers, the polarizer can be composed of a plurality of members. Since it does not need to be configured and the rotation angle required for the Faraday rotation element is 22.5 degrees, which is half of the conventional one,
It requires only half the thickness of conventional Faraday rotator elements, but the number of required Faraday rotator elements will double, but since it is only half the thickness, it can reduce the crystal growth time and improve the yield. It is possible that the price of the rotating element will be less than half that of conventional products, and as a result, an inexpensive isolator can be provided compared to existing optical isolators. In the polarization-independent optical circulator of the present invention,
Using the basic configuration of the polarization independent optical isolator,
An element operating as an optical circulator can be realized only by providing the third and fourth input / output ports in this basic configuration.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The basic configuration of the polarization independent optical isolator of the present invention shown in FIG. 1 is such that first and second Faraday rotators 1 and 2 having a rotation angle of 22.5 degrees, and first and second Faraday rotators. It includes total reflection mirrors 3 and 4, a substrate 5, a polarization separation element 6 having first and second polarization separation element portions 7a and 7b, and a transparent plate 8. The polarization separation element 6 has a plurality of regions having different polarization characteristics, and the first polarization separation element portion 7a and the second polarization separation element portion 7b, which are the respective regions, transmit specific polarized light and are perpendicular to it. Polarized light in different directions is reflected. The first polarization separation element portion 7a transmits the polarized light in the x direction and reflects the polarized light in the y direction. Polarization separation element section 7b
Transmits polarized light in a direction rotated 45 degrees clockwise from the y-axis when viewed in the z direction, and reflects polarized light perpendicular thereto. The polarization separation element 6 is divided into two areas 9 and 10 as shown in FIG. 2, and the polarization directions of the light transmitted through the respective areas are different from each other by 45 degrees. In the illustrated example,
The region 9 corresponds to the first polarization separation element portion 7a, and is a polarization separation element that transmits polarized light in the x direction and reflects polarized light in the y direction. The region 10 corresponds to the second polarization separation element portion 7b, and is a polarization separation element in which polarized light in a direction rotated clockwise by 45 degrees from the y axis when viewed in the z direction is transmitted and polarized light perpendicular thereto is reflected. The Faraday rotators 1 and 2 are adjusted so that the rotation angle of the polarization direction is 22.5 degrees, and the light reciprocates through the Faraday rotation elements 1 and 2 to realize the rotation of the polarization direction of 45 degrees. The first and second Faraday rotation elements 1 and 2 are arranged so as to face each other with the polarization separation element 6 and the transparent plate 8 which are adjacent to each other interposed therebetween. The first and second total reflection mirrors 3 and 4 are installed outside the Faraday rotators 1 and 2 so as to face each other.

The polarization separation element 6 is composed of a reflection type polarization separation element. As this reflective polarization separation element, one using a polymer multilayer film, for example, JP-A-2000-5 is used.
One using the photonic crystal described in JP-A-6133, page 2, column 2, line 38 to page 5, column 7, line 8 is considered. When a polymer multilayer film is used, in order to realize different polarization characteristics depending on the location, it is necessary to stick two polarizing elements in a mutually offset form.
On the other hand, in the case of a polarization element using a photonic crystal, it is possible to fabricate a polarization element having polarization characteristics in any direction on any one substrate by patterning the substrate. Such a polarizing element can be easily realized on the substrate. Other reflective polarization separation elements include a prism type such as PBS in which a dielectric multi-layer film is sandwiched by 45-degree wedge-shaped glass plates or Glan-Thompson prism in which prisms of two birefringent optical crystals are bonded with their crystal axes orthogonal to each other. There are polarization separation elements of the above, but when they are used, the angle for separating each polarization is 90 degrees or less, and it is impossible to realize the configuration of the optical isolator shown in FIG. .

Therefore, according to the present invention, a photonic crystal having a plurality of regions, on each of which a plurality of polarized lights of different directions are reflected, that is, the first and second polarization separation element portions 7a and 7b are provided on one substrate 5. Of the Faraday rotator, and the first and second Faraday rotators 1 and 2 and the first and second total reflection mirrors 3 and 4 are provided on both sides thereof. A polarization-independent optical isolator that offers a rotation angle of 22.5 degrees, which is half that of conventional products, is provided.

[0009]

(Embodiment 1) In the optical isolator shown in FIG. 1, the polarization separation element 6 is integrally formed on the outer surface (right surface in the drawing) of the substrate 5. The photonic crystal polarization separation element used for the polarization separation element 6 will be described in detail. A two-dimensional or three-dimensional refractive index periodicity whose period is in the order of wavelength is called a "photonic crystal", and its optical characteristics are the refractive index of the material used, the period of the structure,
It depends on the periodic arrangement and its direction. To give an example of the optical characteristics to be realized, multiple reflections of light in each cycle cause Bragg cutoff, and a phenomenon occurs in which light is cut off in a specific wavelength band. Further, such optical characteristics can be provided with structural anisotropy.

A major feature of the photonic crystal is that it is an artificial structure, so that the optical characteristics can be designed by designing the structure. Therefore, it becomes possible to realize a specific optical characteristic at a specific place.

For example, two-dimensional photonic crystal parts 11 and 2 in which two two-dimensional periodic structures as shown in FIG. 3 are combined.
Consider a structure including the three-dimensional photonic crystal portion 12. The two-dimensional photonic crystal portion 11 has a uniform structure in the x direction. The two-dimensional photonic crystal portion 12 has a uniform structure in the direction rotated by 45 degrees from the x axis. In such an artificial periodic structure composed of a high-refractive index medium and a low-refractive index medium, two polarization components orthogonal to each other have independent dispersion relations (relationship between frequency and wave vector). ing. Between the polarization components parallel to and perpendicular to the columns shown,
The band gap, that is, the wavelength range in which light is blocked is also different.
That is, in a certain wavelength range, one polarization mode may be blocked and the other polarization mode may propagate. In this wavelength range, this periodic structure can operate as a polarizer that reflects or diffracts one polarized light and transmits the other polarized light. In addition, the extinction ratio is theoretically high enough (Tetsuko Hamano, Masayuki Izutsu, Hideki Hirayama, "Possibility of Polarizers Using Two-dimensional Photonic Crystals", Proceedings of the 58th Response Period Cycle, paper 2a. -W-7, 1997, Akira Sato, Masahiro Takebe, "Optically anisotropic multilayer film by structural birefringence", Optics Japan'97, Proceedings of lectures,
paper 30pDO1, 1997). By forming a structure in which the two-dimensional photonic crystal portion 12 is rotated 45 degrees in the xy plane with respect to the two-dimensional photonic crystal portion 11, the two-dimensional photonic crystal portion 12 is different from the two-dimensional photonic crystal portion 11. It is possible to realize a characteristic that polarized light in a direction shifted by 45 degrees is reflected and polarized light in a direction perpendicular to the reflected light is transmitted.

The characteristics of transmission and reflection can be changed by design depending on the required function, and the angle between the two-dimensional photonic crystal portion 11 and the two-dimensional photonic crystal portion 12 need not be 45 degrees. There may be a plurality of regions having different angles.

As a method for producing a photonic crystal, for example, the autocloning method described in JP-A-10-335758 can be mentioned. This reflects the pattern of the substrate by depositing an alternate multilayer film on the substrate on which the concavo-convex pattern is formed by using a film formation method that uses diffused incidence of deposited particles represented by bias sputtering and sputter etching. This is a method of stacking while preserving the uneven shape. This mechanism has the following three effects, (1) the effect of slowing the deposition rate of the recessed portion that becomes a shadow due to diffused incidence of deposited particles, and (2) the etching rate on a surface with an inclination angle of about 50 to 60 degrees due to sputter etching. It can be explained that it is a superposition at an appropriate ratio of the maximum effect, and the effect that particles scraped by sputter etching on the (3) surface reattach to another place on the substrate (Shinjiro Kawakami, Hisashi Sato, Takayuki Kawashima, "Mechanism of formation of 3D periodic nanostructures produced by bias sputtering", IEICE Journal C-1, vol. J81-C-1, n
o. 2, pp. 108-109, February 1998).

In the above self-cloning method, since the concavo-convex pattern on the substrate is formed by lithography and etching, it is possible to form an arbitrary pattern that differs depending on the location, and the photonic crystal formed on it can also be patterned. Reflecting the above, a photonic crystal that differs depending on the location is realized.

The fact that a polarizer having high performance has been realized in the two-dimensional periodic structure produced by this self-cloning method is described in the above-mentioned JP-A-2000-561.
No. 33 published patent gazette.

A photonic crystal structure as shown in FIG. 5 can be realized by preparing a substrate 13 as shown in FIG. 4 and depositing a multi-layered film on it by a self-cloning method. In such a structure, like the photonic crystal shown in FIG. 3,
It is possible to give different polarization dependence between the two-dimensional photonic crystal portion 16 and the two-dimensional photonic crystal portion 17. The two-dimensional photonic crystal 16 is produced by the self-cloning method and has a uniform structure in the y direction. The two-dimensional photonic crystal 17 has a uniform structure formed by the self-cloning method in a direction rotated by 45 degrees from the y direction. In the substrate 13 shown in FIG. 4, 14 is an antireflection coating layer, and 15 is a periodic groove portion.

A method of manufacturing the photonic crystal polarization separation element 6 using the above-mentioned self-cloning method in the present invention will be described in detail with reference to the two-dimensional photonic crystal portion 16 shown in FIG. In FIG. 5, the cycle Lx in the x-axis direction is 0.5 μm, and the cycle Lz in the z-axis direction is 0.57 μm. The SiO ₂ layer (amorphous SiO ₂ layer) 18 and the Si layer (amorphous Si layer) 19 have a shape that is periodically bent along the x-axis direction while slightly changing the thickness. Two-dimensional photonic crystal part 16
The two-dimensional photonic crystal portion 17 has a structure rotated by 45 degrees. Reference numeral 20 is a substrate molding layer.

First, a periodic resist pattern is formed on the substrate 13 by the electron beam lithography technique. Figure 4
A schematic view of the substrate 13 is shown in FIG. 9, in which the groove portion 15 has a width of 0.25 μm, a depth of 0.2 μm, and a lateral period of 0.5 μm. Generally, the antireflection coating layer 14 and the groove portion 15 are selected from materials different from those of the substrate 13 depending on the selection of the dimensions of the periodic structure, but it is also possible to form the grooves on the same material as the substrate. In the example shown in FIG. 5, a target of SiO ₂ and Si is used on the quartz substrate 13 by a bias sputtering method to form SiO 2.
_Two layers 18 and Si layers 19 were alternately laminated. At that time, each S
It is important to perform film formation while preserving the shape of the periodic unevenness of the iO ₂ layer 18 and the Si layer 19 in the x-axis direction. The conditions were as follows. A for the deposition of SiO ₂
r gas pressure 2 Pa, target high-frequency power 800 W, substrate high-frequency power 20 W: Ar gas pressure 0.
The target high frequency power was 400 W at 15 Pa. S
10 layers of the iO ₂ layer 18 and 10 layers of the Si layer 19 were laminated. The laminated thickness is about 6 μm.

The periodic groove portions 15 on the substrate 13
In order to prevent reflection between the multilayer film and the multilayer film, and between the multilayer film and the air, in order to prevent reflection caused by the difference in refractive index between the multilayer film and the air, the multilayer film and the substrate or the air are inserted. It is matched with and reduces reflection. This time, air is used as the top of the multilayer film, but another substance can be used.

FIG. 6 shows the results of measuring the transmittance for each polarized wave when light is vertically incident on the fabricated structure while changing the wavelength. In the figure, the horizontal axis represents wavelength [μm] and the vertical axis represents transmittance [%]. Here, the polarized wave parallel to the groove is referred to as TE wave, and the polarized wave perpendicular to the groove is referred to as TM wave. Reference numeral 21
TM polarized light is transmitted around the wavelength of 1.5 μm
TE polarization is blocked. The blocked TE polarized light is reflected as reflected light. Further, as a result of introducing the non-reflective layer into the stacking start part and the stacking end part, the transmittance of the TM polarized wave shows a high value in the vicinity of the wavelength of 1.5 μm, and at the interface between the multilayer film and the substrate and between the multilayer film and the air. Due to the effect of multiple reflections that occur, flat characteristics are obtained without changing the transmittance with changes in wavelength.

(Embodiment 2) An embodiment of the optical isolator of the present invention shown in FIGS. 7 and 8 will be described. First and second Faraday rotation elements 22 and 2 in the optical isolator
3, the first and second total reflection mirrors 24 and 25, the substrate 26, the polarization separation element 27 having the first and second polarization separation element parts 28a and 28b, and the transparent plate 29 are the Faraday rotations of the optical isolator shown in FIG. Elements 1 and 2, first and second total reflection mirrors 3 and 4, substrate 5, first and second polarization separation element sections 7a and 7b
Corresponding to the polarization separation element 6 and the transparent plate 8. It is assumed that the first and second Faraday rotator elements 22 and 23 have the same magnetic charge by an appropriate external or internal magnetic field, and that the polarization directions of the two Faraday rotator elements are the same. Here, in the z-axis, the positive direction is the forward direction and the opposite direction is the reverse direction, and an optical path diagram of the forward direction is shown in FIG.
FIG. 8 shows a reverse optical path diagram. The first and second polarization separation element portions 28a and 28b in the polarization separation element 27 are formed on the quartz substrate 26 having a refractive index of 1.5 and a thickness of 500 μ (micron), and the transparent plate 29 also has a refractive index of 1.5. 50 thickness
It is 0 μ (micron). First and second total reflection mirror 2
4, 25 are formed on a part of the surfaces of the first and second Faraday rotation elements 22, 23 by vapor deposition or the like. The first and second Faraday rotator elements 22 and 23 are adjusted to have a thickness of about 225 μ (micron) that gives a rotation of 22.5 degrees in the polarization direction, and have a refractive index of about 2.5. The first polarization splitting element portion 28a of the polarization splitting element 27 transmits the polarized light in the x direction and reflects the polarized light in the y direction. Second polarization separation element section 28
As for b, polarized light in a direction rotated 45 degrees clockwise from the y axis when viewed in the z direction is transmitted, and polarized light perpendicular thereto is reflected.

The forward operation of the optical isolator will be described. As shown in FIG. 7, the light emitted from the first port 30 first passes through the first Faraday rotator element 22, but here, it is considered that an arbitrary polarized light is incident, so that the polarized light Rotation doesn't make sense. The light that has entered the first polarization separation element section 28a of the polarization separation element 27 is separated into polarized light that passes through this polarization separation element section and polarized light that reflects it. The transmitted polarized light passes through the second Faraday rotator element 23 and passes through the first total reflection mirror 24.
And is passed through the second Faraday rotation element 23 again. At this time, due to the non-reciprocity of the second Faraday rotation element 23, the polarization direction is uniquely determined by the direction of the magnetic field applied from the outside regardless of the traveling direction. Therefore,
The polarization direction is rotated 45 degrees by reciprocating in the second Faraday rotator 23. By further obliquely entering the second Faraday rotator element 23, the light can be emitted to a position displaced from the position of incidence on the second Faraday rotator 23.

First for the first Faraday rotator 22
When the light emitted from the port 30 enters at an incident angle of 18 degrees, it travels through the Faraday rotator at an angle of about 7 degrees. Further, the substrate 26 of the polarization separation element portions 28a and 28b
Inside, it advances at an angle of 11 degrees and enters the polarization separation element portion 28a. It has been proved that the polarization separation element portion 28a has sufficient polarization characteristics even at this incident angle. That is, when the light travels at the above angle, the point of passing through the polarization separation element portion 28a and the point of being reflected back by the first total reflection mirror 24 are displaced by 250 μm. This distance is sufficient to realize a photonic crystal polarization separation element having different polarization characteristics, and the light returning to the polarization separation element section 28b impinges on the polarization separation element section 28a to generate unnecessary stray light. There is nothing to do. The light returning to the polarization separation element unit 28b has a polarization direction that is reflected by the polarization separation element unit 28b due to the rotation of the polarization direction by 45 degrees, and thus is reflected and goes to the second port 31.

On the other hand, the polarized light reflected by the first polarization separation element portion 28a passes through the first Faraday rotator element 22,
The light is reflected by the total reflection mirror 25, and thus reciprocates in the first Faraday rotation element 22. As a result, the polarization direction is rotated by 45 degrees and enters the second polarization separation element section 28b. The amount of positional deviation when entering the second polarization separation element portion 28b is shifted by the same amount (250 μm) as the amount studied in the above paragraph [0023]. At this time, the polarization direction is the direction through which the second polarized light separating element portion 28b is transmitted, and therefore the light is transmitted to the second port 31.

Both the light transmitted through the first polarization separation element portion 28a and the reflected light are reflected by the first and second Faraday rotation elements 22 and 2.
It is transmitted again through 3, but the rotation of the polarization direction here does not make sense. It is also clear that by adjusting the size of the second Faraday rotator element 23, light can be extracted without passing through the second Faraday rotator element 23.

The operation in the reverse direction shown in FIG. 8 will be described. The light that has entered the polarization separation element section 28b from the second port 31 is separated into a transmitted polarization and a reflected polarization. At this time, the light beam passes through the second Faraday rotation element 23 between the second port 31 and the polarization separation element portion 28b, but the rotation of the polarization direction here does not make sense.

The light reflected by the second polarization separation element section 28b reciprocates through the second Faraday rotation element 23, so that the polarization direction is rotated by 45 degrees and is incident on the first polarization separation element section 28a. The positional shift amount here is as discussed in the above paragraph [0023]. Since the polarization direction at this time is the direction reflected by the second polarization separation element portion 28b, it is reflected and does not couple to the first port 30.

On the other hand, the polarized light transmitted through the second polarization separation element portion 28b reciprocates in the first Faraday rotation element 22 and the polarization direction is rotated by 45 degrees. Then, the first polarization separation element section 28
The incident light is incident on a, but the polarization direction is such that it is transmitted through the first polarization separation element portion 28a. Therefore, the light is transmitted through the first polarization separation element portion 28a and is not coupled to the first port 30. Thus, the optical isolator shown in FIGS. 7 and 8 functions as a polarization-independent optical isolator.

In the optical isolator shown in FIG. 7, by using the transparent plate 29 having the same refractive index and thickness as the substrate 26 on which the polarization separation element 27 is formed, the polarization dispersion is theoretically zero. it can. In the optical isolator of the present invention, the first
The distance between the position of incidence on the polarization separation element section 28a and the position of incidence on the second polarization separation element section 28b greatly affects the characteristics.

(Embodiment 3) An embodiment of the optical isolator of the present invention shown in FIG. 9 will be described. The structure of the optical isolator in this embodiment is based on that of the optical isolator shown in FIG. 7, and by adding the transparent plates 50 and 51, it is possible to increase the distance of the incident position described in the previous section. It is a thing. In this optical isolator, the first and second Faraday rotation elements 42 and 43, the first and second total reflection mirrors 44 and 45, the substrate 46, and the polarization separation element 47 having the first and second polarization separation element sections 48a and 48b,
The transparent plate 49 is the first and second optical isolator shown in FIG.
Faraday rotation elements 22 and 23, first and second total reflection mirrors 24 and 25, substrate 26, first and second polarization separation element section 2
They correspond to the polarization separation element 27 having 8a and 28b and the transparent plate 29, respectively. For example, by inserting the transparent plate 50 between the first Faraday rotation element 42 and the second total reflection mirror 45, and the transparent plate 51 between the second Faraday rotation element 43 and the first total reflection mirror 44, respectively, You can increase the distance. The transparent plates 50 and 51 may be substrates of the first and second total reflection mirrors 44 and 45. In this case,
The transparent plates 50 and 51 are composed of two Faraday rotation elements 42 and 4, respectively.
Although the optical path lengths are to be set outside the respective No. 3, it is necessary that the optical path lengths are the same in order to make the polarization dispersion zero. The first polarization separation element portion 48a of the polarization separation element 47 is x
The polarized light in the direction is transmitted and the polarized light in the y direction is reflected. The second polarized light separating element portion 48b transmits polarized light in a direction rotated 45 degrees clockwise from the y axis when viewed in the z direction, and reflects polarized light perpendicular thereto.

(Embodiment 4) An embodiment of the optical isolator of the present invention shown in FIG. 10 will be described. In the self-cloning method described above, various substances can be used for the substrate, and for example, a Faraday rotation element can be used for the substrate of the polarizer. In this case, in this example, the first and second
Since the photonic crystal polarization separation element 56 is formed directly on the surface of the Faraday rotation elements 52 and 53, the first and second Faraday rotation elements 5 are substantially formed as shown in the figure.
An optical isolator can be realized only with a thickness of 2,53. First polarization separation element section 57 in polarization separation element 56
If the distance between the position of incidence on a and the position of incidence on the second polarization separation element portion 57b is not so large, the above paragraph [0
030], the first and second total reflection mirrors 54,
By inserting a transparent plate between 55 and the Faraday rotator elements 52, 53, a distance can be provided. The first polarization separation element portion 57a transmits polarized light in the x direction and reflects polarized light in the y direction. The second polarized light separating element portion 57b transmits the polarized light in the direction rotated by 45 degrees clockwise from the y axis when viewed in the z direction, and reflects the polarized light perpendicular thereto.

FIG. 11 shows the optical circulator of the present invention.
And FIG. 12 will be described. The configuration of the main body of the optical circulator of the present invention shown in FIG. 11 includes first and second Faraday rotation elements 32 and 33 having a rotation angle of 22.5 degrees, and first and second Faraday rotation elements.
A polarization splitting element 37 having total reflection mirrors 34 and 35, a substrate 36, and first and second polarization splitting element portions 38a and 38b.
And a transparent plate 39, and a second port 40 and a third port 41 are provided on the same outer side (right side in the drawing) of the main body. The main structure of the optical circulator of the present invention is the same as that of the optical isolator shown in FIG. 1, and includes the first and second Faraday rotation elements 32 and 33, total reflection mirrors 34 and 35, and
The substrate 36, the polarization separation element 37 having the first and second polarization separation element portions 38a and 38b, and the transparent plate 39 are the Faraday rotation elements 1 and 2, the total reflection mirrors 3 and 4, the substrate 5, the first and second polarizations. A polarization separation element 6 having separation element portions 7a and 7b,
Each corresponds to the transparent plate 8. As is apparent from the above configuration, by providing the third port 41 that captures the light incident from the second port 40, the optical isolator of the present invention is configured so that the light incident from the first port (not shown) is It operates as an optical circulator that is emitted to the second port and the light incident from the second port is emitted to the third port. The basic configuration is the same as the case of operating as an optical isolator, and the function of the optical isolator and the function of the optical circulator are selected depending on whether the light emitted to the third port 41 is incident on an optical fiber or the like and used. be able to.

The structure of the main body of the optical circulator of the present invention shown in FIG. 12 is the same as that of the optical circulator shown in FIG. 11, and the first and second Faraday rotation elements 58 and 59 having a rotation angle of 22.5 degrees are provided. The first and second total reflection mirrors 60,
61, a substrate 62, and first and second polarization separation element sections 64
The polarization separating element 63 having a and 64b and the transparent plate 65 both constitute the main body of the optical circulator shown in FIG. 11, and the first and second Faraday rotating elements 32 and 33 having a rotation angle of 22.5 degrees. And the first and second total reflection mirrors 34, 3
5, the substrate 36, the first and second polarization separation element portions 38a,
They correspond to the polarization separation element 37 having 38b and the transparent plate 39, respectively. However, the optical circulator of the present invention is provided with the third port 41 in that the third and fourth ports 66 and 67 are provided, but is different from the optical circulator shown in FIG. 11 which does not have the fourth port. is doing. As is apparent from the above configuration, by providing the fourth port 67 that captures the light emitted from the third port 66, the optical isolator of the present invention allows the light incident from the first port 68 to be emitted to the second port 69. The light incident on the second port is emitted to the third port, and the light incident on the third port is emitted to the fourth port, thereby operating as an optical circulator. The basic configuration is the same as the case of operating as an optical isolator, and the function of the optical isolator and the function of the optical circulator are selected depending on whether or not the light emitted to the fourth port 67 is used by being incident on an optical fiber or the like. be able to. As described above, the optical circulator shown in FIGS. 11 and 12 can easily realize different functions with the same configuration as the optical isolator, which greatly contributes to the rationalization of the production process.

[0034]

According to the present invention, the reflection type polarized light separating element having different polarization directions to be transmitted is used, and the reflection type polarization separating element is used with the first and second Faraday rotation elements having half the thickness conventionally required. By installing with the separation element sandwiched between them, an optical isolator having a simple structure which is cheaper than the conventional example can be realized. When a photonic crystal is used as the reflection type polarization separation element of the present invention, it becomes easy to simultaneously manufacture polarization separation elements having different directivities on one substrate. This photonic crystal polarization separation element does not require processing such as polishing, is excellent in mass productivity, and has performance comparable to that of existing high-performance polarization separation elements. By forming the photonic crystal reflection type polarization separation element on the substrate, only one polarization separation element, which was required in the past, is needed, and the Faraday rotation element can be half the thickness.
It is possible to provide an isolator that is less expensive than existing optical isolators. Further, since it can function as an optical circulator simply by adding ports with the same component structure as that of the optical isolator of the present invention, a simple structure and efficient production are possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic structure of an optical isolator in a first embodiment of the present invention.

FIG. 2 is a diagram showing a polarizer having different polarization dependence depending on a place used in the present invention.

FIG. 3 is a perspective view showing a concept of a photonic crystal having polarization dependence on location.

FIG. 4 is a perspective view showing a substrate required to realize the photonic crystal corresponding to FIG. 3 by a self-cloning method.

5 is a perspective view showing a structure in which the photonic crystal corresponding to FIG. 3 is realized by a self-cloning method.

FIG. 6 is a graph showing the relationship between wavelength and transmittance of the photonic crystal polarization separation element used in the present invention.

FIG. 7 is a diagram showing an optical path in a forward direction of an optical isolator in a second embodiment of the present invention.

FIG. 8 is a diagram showing an optical path in the opposite direction of the optical isolator in the second embodiment of the present invention.

FIG. 9 is a diagram showing a basic structure of an optical isolator in a third embodiment of the present invention.

FIG. 10 is a diagram showing a basic structure of an optical isolator according to a fourth embodiment of the present invention.

FIG. 11 is a diagram showing a basic structure of an optical circulator having a third port according to the present invention.

FIG. 12 is a diagram showing a basic structure of an optical circulator having third and fourth ports according to the present invention.

[Explanation of symbols]

1 1st Faraday rotation element 2 2nd Faraday rotation element 3 1st total reflection mirror 4 2nd total reflection mirror 5 substrate 6 of polarization separation element 7 polarization separation element 7a first polarization separation element section (region) 7b second polarization separation element Part (region) 8 Transparent plate 11 Two-dimensional photonic crystal portion 12 Two-dimensional photonic crystal portion 13 Substrate 14 Antireflection coating layer 15 Periodic groove portion 16 Two-dimensional photonic crystal portion 17 Two-dimensional photonic crystal portion 18 SiO ₂ layer 19 Si layer 20 Substrate molding layer 21 One of wavelength bands acting as a polarizer for transmitting TM waves 22 First Faraday rotator 23 Second Faraday rotator 24 First total reflection mirror 25 Second total reflection mirror 26 Substrate of Polarization Separation Element 27 Polarization Separation Element 28a First Polarization Separation Element Section (Region) 28b Second Polarization Separation Element Section (Region) 9 Transparent plate 30 1st port 31 2nd port 32 1st Faraday rotation element 33 2nd Faraday rotation element 34 1st total reflection mirror 35 2nd total reflection mirror 36 Substrate of polarization splitting element 37 Polarization splitting element 38a First polarization splitting Element part (area) 38b Second polarized light separating element part (area) 39 Transparent plate 40 Second port 41 Third port 42 First Faraday rotation element 43 Second Faraday rotation element 44 First total reflection mirror 45 Second total reflection mirror 46 Substrate of Polarization Separation Element 47 Polarization Separation Element 48a First Polarization Separation Element Section (Region) 48b Second Polarization Separation Element Section (Region) 49 Transparent Plate 50 Transparent Plate 51 Transparent Plate 52 First Faraday Rotation Element 53 Second Faraday Rotation Element 54 First total reflection mirror 55 Second total reflection mirror 56 Polarization separation element 57a First polarization separation element section (region) 57b Polarization separation element part (area) 58 First Faraday rotation element 59 Second Faraday rotation element 60 First total reflection mirror 61 Second total reflection mirror 62 Substrate of polarization separation element 63 Polarization separation element 64a First polarization separation element part (area) ) 64b Second polarization separation element section (region) 65 Transparent plate 66 Third port 67 Fourth port

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shojiro Kawakami             Atago Bridge, 236 Tohigai, Wakabayashi Ward, Sendai City, Miyagi Prefecture             Mansion Pharaoh C-09 (72) Inventor Takayuki Kawashima             3-21-11 Minamikoizumi, Wakabayashi-ku, Sendai City, Miyagi Prefecture               Grace coat S102 (72) Inventor Osamu Ishikawa             2-21-21 Shiomidainan, Shichigahama-cho, Miyagi-gun, Miyagi Prefecture             No. 8 (72) Inventor Nao Sato             1-2-5 Tomizawaminami, Taihaku-ku, Sendai City, Miyagi Prefecture               Bonard Tomizawa No. 302 (72) Inventor Jun Iwashita             2-4-1 Kosugaya, Sakae-ku, Yokohama-shi, Kanagawa             No. Shinmitsu Co., Ltd. F-term (reference) 2H038 AA21 BA35                 2H042 AA04 AA30 DA08                 2H049 BA05 BA08 BA45 BB03 BC06                       BC25                 2H099 AA01 BA02 BA06 CA05 DA00

Claims (24)

[Claims] 1. A reflection type polarization separation element having a plurality of regions having different polarization characteristics, and first and second rotation degrees of 22.5 degrees.
A Faraday rotator and first and second total reflection mirrors are provided, and the reflection-type polarization separation element is arranged between the first and second Faraday rotators, and the first and second Faraday rotators are provided. The element is arranged between the first and second total reflection mirrors, and the first total reflection mirror is capable of reflecting the light transmitted through the second Faraday rotation element and incident to the second Faraday rotation element side, The polarization independent optical isolator, wherein the second total reflection mirror is capable of reflecting the light that has passed through the first Faraday rotator and is incident on the side of the first Faraday rotator. 2. The polarization-independent optical isolator according to claim 1, wherein the reflection-type polarization separation element uses a photonic crystal. 3. The reflection-type polarization separation element uses a photonic crystal, and a first and second reflection-type polarization separation element portions, which are a plurality of regions having different polarization characteristics, are formed on a substrate. The polarization-independent optical isolator according to claim 1, wherein 4. The polarization-independent light according to claim 1, wherein a transparent plate is arranged between the reflective polarization separation element and the second Faraday rotator. Isolators. 5. The reflection-type polarization separation element uses a photonic crystal, and first and second reflection-type polarization separation element portions, which are a plurality of regions having different polarization characteristics, are formed on a substrate. The transparent plate is disposed between the reflective polarization separation element and the second Faraday rotator, and the transparent plate has the same refractive index and thickness as the substrate. Polarization independent optical isolator. 6. A transparent plate is disposed between the reflective polarization separation element and the second Faraday rotation element, and adjacent first and second reflection polarization separation elements and first and second total reflection mirrors are provided. A polarization-independent optical isolator according to any one of claims 1 to 3, characterized in that a transparent plate is arranged between the respective opposing surfaces. 7. The reflection-type polarization beam splitting element uses a photonic crystal and is directly formed on at least one of the first and second Faraday rotator elements. Item 3. The polarization-independent optical isolator according to Item 1. 8. The polarization independent optical isolator according to claim 1, wherein the total reflection mirror is a reflection type polarizer. 9. An optical circulator, wherein the polarization independent optical isolator according to claim 1 is provided with a third port. 10. An optical circulator, wherein the polarization-independent optical isolator according to claim 1 is provided with third and fourth ports. 11. An optical circulator, wherein the polarization independent optical isolator according to claim 2 is provided with a third port. 12. An optical circulator, wherein the polarization independent optical isolator according to claim 2 is provided with third and fourth ports. 13. An optical circulator, wherein the polarization independent optical isolator according to claim 3 is provided with a third port. 14. An optical circulator, wherein the polarization independent optical isolator according to claim 3 is provided with third and fourth ports. 15. An optical circulator, wherein the polarization independent optical isolator according to claim 4 is provided with a third port. 16. An optical circulator, wherein the polarization independent optical isolator according to claim 4 is provided with third and fourth ports. 17. An optical circulator, wherein the polarization independent optical isolator according to claim 5 is provided with a third port. 18. An optical circulator, wherein the polarization independent optical isolator according to claim 5 is provided with third and fourth ports. 19. An optical circulator, wherein the polarization independent optical isolator according to claim 6 is provided with a third port. 20. An optical circulator, wherein the polarization-independent optical isolator according to claim 6 is provided with third and fourth ports. 21. An optical circulator, wherein the polarization independent optical isolator according to claim 7 is provided with a third port. 22. An optical circulator, wherein the polarization independent optical isolator according to claim 7 is provided with third and fourth ports. 23. An optical circulator, wherein the polarization independent optical isolator according to claim 8 is provided with a third port. 24. An optical circulator, wherein the polarization independent optical isolator according to claim 8 is provided with third and fourth ports.