JPH1184317A - Optical isolating element and optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical isolator whose optical characteristic is improved by suppressing nonuniformity in the boundary part of a central part in a light transmission area and reducing or vanishing diffracted light, reflected light and scattered light. SOLUTION: An optical isolating element in which a Faraday rotator 6 which is in parallel with a surface perpendicular to the transmission direction of light and plates in which one half wave plates 3, 4 and Faraday rotators 5, 7 are joined, are respectively arrayed on the surfaces of both sides of the rotator 6, the rotators 5, 7 are integrated into one body with the Faraday rotator 6 in the up-and-directions and are constituted of a magneto-optical material and the surfaces of them including the one half wave plates 3, 4 on which light is made incident and from which the light is emitted, forms one flat plane on which differences in level are not present and is inclined with respect to the advancing direc-tion of the light. Then, optical waveguides 1, 2 and optical elements having lens functions are arrayed in front of and behind the optical isolating element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an optical isolator used as an optical passive component mainly for preventing return light of laser light in the field of optical communication.

[0002]

2. Description of the Related Art In recent years, in optical communication systems, optical fiber amplifiers for directly amplifying optical signals without replacing optical signals with electric signals have been used. In this case, an erbium (Er) -doped optical fiber having a specific length is provided in the amplifier, and the amplified signal light and pump light are transmitted therethrough to obtain amplified light.

[0003] In order to prevent oscillation, an optical fiber amplifier transmits only light transmitted in the forward direction with low loss, and
The use of an optical isolator to block return light in the opposite direction has become indispensable. The optical isolator includes a polarization-dependent type that transmits only a specific polarization component of the transmitted light in the forward direction and a polarization-independent type that transmits all components of the transmitted light.

In an optical communication system, both polarization-dependent and polarization-independent optical isolators are used. The polarization-dependent type is located immediately near a laser for a light source, and the polarization-independent type is located between an optical fiber through which signal light passes. Often used properly.

[0005] Of these, a polarization-independent optical isolator having a relatively complicated structure has conventionally been of the type using a birefringent parallel flat plate (JP-A-54-159245) and the type using a tapered birefringent plate (Japanese Patent Application Laid-Open No. 54-159245). Kosho 61-5880
Several structures such as 9) have been proposed.

The polarization independent optical isolator shown in FIG. 6 was proposed by Shintaku et al. (1997. Spring. IEICE General Conference. C-3-98. P283. An optical fiber having one Faraday rotator 59 made of magnetic garnet, two half-wave plates 57 and 58, and two aspheric lenses 55 and 56, and optical fibers 53 and 54 at both ends. It is an isolator.

In this example of the optical isolator, the light is separated into lights of the same intensity in which the polarization components are mixed. The separated two types of separated lights each include the same amount of the same polarization component, and in the case of forward transmission light, the light is transmitted through the aspheric lens 56 on the emission side and then combined again at the end face of the optical fiber 54.

In this case, the two separated lights to be combined are in a mutually reinforcing relationship, so that the transmitted light passes through the optical isolator without being attenuated.
It is desirable that the light transmitted through the Faraday rotator 59 between the two aspheric lenses 55 and 56 and the half-wave plates 57 and 58 be parallel light.

On the other hand, in this optical isolator, in the case of transmitted light in the opposite direction, light exiting the end of the optical fiber 54 on the incident side is separated at the end face of the half-wave plate 58, and When they are combined at the 53 end, they are in a mutually canceling relationship. Therefore, the transmitted light in the backward direction does not pass through the optical fiber, and it is understood that the optical device functions as an optical isolator.

[0010]

However, in the optical isolator having such a configuration, it is difficult to manufacture an optical isolator having excellent optical characteristics because it is difficult to perform precise alignment during assembly. Diffraction, scattering, and the like caused by light passing through two paths in the same element.
Due to the reflection, it becomes difficult to produce an optical isolator having excellent characteristics. The reason will be described below.

In the polarization independent optical isolator shown in FIG. 6, the two separated lights do not follow completely different paths apart from each other. It is considered that each half of the transmitted light according to it becomes half.

In other words, it is described that two kinds of transmitted light are separated into two light beams after being transmitted through different optical elements and then combined into one light again. , The boundary between the two separated lights is continuous, on the contrary,
Because this boundary is located in the center of the light transmission area,
The light intensity of the transmitted light is generally considered to be the maximum region.

[0013] Scattering and reflection due to diffraction and non-uniformity at the boundary in this region significantly deteriorate the insertion loss and isolation characteristics of the optical isolator.

In the case of this conventional optical isolator, even when perfect parallel light is incident, the edge 6
Diffraction and scattering occur at 1, 62, deteriorating the characteristics. In the transmission path of the two-separated light, since the installation position of the half-wave plate is structurally different, the end faces of the optical element of the two-separated light at the time of incidence are not aligned, and the stepped region is diffracted. , Causing reflection and scattering.

An object of the present invention is to provide an isolator having improved optical characteristics by suppressing non-uniformity at a central boundary portion of a light transmitting region and reducing or eliminating diffraction, reflection, and scattered light.

[0016]

The present invention employs the following method in order to prevent the optical characteristics of the optical isolator from deteriorating due to the above reasons. Light emitted from an optical waveguide such as an optical fiber is guided to a Faraday rotator or the like as completely parallel light as possible. For this purpose, an element in which an optical waveguide and a lens mechanism are integrated is used. Assemble so that the upper and lower joints of the optical isolator element at the center of the light transmitting part of the optical isolator element part are reduced as much as possible, and the light incident / exit surface forms one continuous plane without any steps. . The transmitted light is divided into two parts in advance by an optical coupler, and each part is independently combined after being transmitted through an optical element. By implementing these three methods alone or in combination, an optical isolator that avoids a decrease in the optical characteristics of the optical isolator.

In the above method, the transmitted light is close to the parallel light, and the optical adjustment between the lens and the optical waveguide such as an optical fiber is not required at the time of assembling, so that the adjustment after assembling becomes easy. In addition, since a structure for separately holding the lens mechanism is not required, there is an advantage that a very small element is sufficient and the total length of the optical isolator is shortened.

This is a method proposed in claim 6 of the present invention, wherein a method of using an optical waveguide having a TEC structure (core expanded fiber optical waveguide) according to claim 7 as an optical waveguide with a lens mechanism, And a method of using the optical waveguide with a spherical lens described in claim 8, and P
A method using an optical waveguide having an LC structure (planar optical waveguide) has been proposed.

The use of these optical waveguides with a lens mechanism not only improves the optical characteristics of the optical isolator, but also simplifies the assembly and optical alignment steps, shortens the overall length of the optical isolator, and reduces its size. As a result, there is an advantage that the required area of the optical element is reduced and cost reduction is expected.

In addition, in the above-mentioned method, the amount of reflection and scattering can be reduced by generally minimizing the amount of the step between the elements on the input / output surface, and the Faraday rotator and the half-wave plate can be used. If a rod-shaped (deep) element is prepared by bonding it to a plate made of an optically isotropic material, it is cut into two pieces, and if a construction method is used in which the elements are stacked, two types of upper and lower optical elements are used. Since the thicknesses of the elements can be made practically the same, it is possible to further reduce the level difference between the end faces of the joints of the two. In addition, the number of joints of the optical element at the center of the element where the light density is maximum can be reduced, and the insertion loss can be further reduced.

Further, according to the above-mentioned method, since the transmitted light is two kinds of independent separated lights separated from each other by the optical splitter, the reflection and reflection due to the step structure at the end of the optical element.
There is no need to consider scattering. However, if the incident light is not perfectly parallel light, reflection scattering may occur at the upper and lower junctions of the optical element.

With this structure, an optical isolator having excellent optical characteristics can be constructed which is superior to the above case.
Since this optical waveguide and two optical multiplexers / demultiplexers are used, the configuration becomes slightly larger, and it is necessary to sufficiently manage the entire length of the optical waveguide and the junction area so that the optical path length difference of the two separated light does not occur. There will be.

In order to prevent the optical path length difference from occurring, a method using a PLC structure in which an optical waveguide is formed on a glass substrate, or a method using a glass substrate, a Si substrate, etc. A method of fixing and processing the optical fiber is effective.

As a method of embodying this method, when an optical waveguide having a PLC structure performs the function of an optical multiplexer / demultiplexer, the optical waveguide is connected to a Faraday rotator by a half.
Instead of being installed at the center of the wave plate, it is installed with a slight offset.

FIG. 3 shows an embodiment in that case.
In both the left and right optical waveguides on the substrate, the transmitted light is linearly incident on the half-wave plate side, and is incident so as to wrap around the magnetic garnet (Faraday rotator).

By appropriately designing the shape and the area of the optical waveguide, the incident light can be divided into two separated lights having the same light intensity. It is possible to do. However, the phase of one of the separated lights is delayed by 90 °. By forming such an optical waveguide on a substrate, an optical multiplexer / demultiplexer according to the above method can be easily formed.

That is, according to the present invention, a member in which a Faraday rotator having the same thickness as a half-wave plate having a slow axis of 22.5 ° is bonded to both surfaces of the Faraday rotator symmetrically to form a light input port. An optical isolator element in which the surface including the half-wave plate that emits light forms a continuous plane without any step.

Further, the present invention provides a method in which a member obtained by joining a plate having optical isotropy having the same thickness as a half-wave plate having a slow axis of 22.5 ° is joined symmetrically to both surfaces of a Faraday rotator. An optical isolator element in which a surface including the half-wave plate from which light enters and exits forms a continuous single plane without a step.

Further, according to the present invention, the Faraday rotator at the center of the optical isolator element has
This is an optical isolator element having a structure divided into two parts before and after.

Further, the present invention is an optical isolator in which the above-mentioned optical isolator element is inclined with respect to the traveling direction of light, and an optical element having an optical waveguide and a lens function is disposed before and after the optical isolator element.

Further, according to the present invention, the optical waveguide has an optical splitter, and the optical splitter divides the light path into two, and the light transmitted through one of the paths is divided by 1/1/2 of the one. The light transmitted through the two-wavelength plate and transmitted through the other path is the above-described optical isolator provided with a light path so as to transmit through the other half-wavelength plate.

Further, the present invention is the above-mentioned optical isolator, wherein the optical element is an optical element integrating an optical waveguide and a lens function.

Further, the present invention is the above-mentioned optical isolator, wherein the optical element integrating the optical waveguide and the lens function is constituted by an optical waveguide having a TEC structure.

Further, the present invention is the above-mentioned optical isolator, wherein the optical element integrating the optical waveguide and the lens function is constituted by an optical waveguide with a spherical lens.

Further, the present invention is the above-mentioned optical isolator, wherein the optical element integrating the optical waveguide and the lens function is constituted by an optical waveguide having a PLC.

[0036]

Embodiments of the present invention will be described with reference to the drawings.

First, a first embodiment of the present invention will be described.

FIG. 1 is an explanatory view of an optical isolator according to a first embodiment of the present invention. The optical waveguides 1 and 2 having a TEC structure as means for guiding transmitted light to an optical isolator element.
It is shown about the case where is used. Also, this TE
In addition to the optical waveguides 1 and 2 having the C structure, an optical waveguide with a spherical lens or another optical waveguide may be used as long as it can guide the transmitted light with low loss.

FIG. 1A is a perspective view of the optical isolator of the present invention, and FIG. 1B is an exploded view of the optical isolator element. FIG. 1C is a configuration diagram of the optical isolator of the present invention in which the optical isolator elements are obliquely arranged.

As shown in FIG. 1, when the angle of the slow axis is 2
Quarter-wave half-wave plate of 2.5 ° or −22.5 °,
4 and the Faraday rotators 5 and 7 having the same thickness as the half-wave plates 3 and 4, and the thickness thereof was adjusted so as to rotate the polarization plane by 45 ° together with the Faraday rotators 5 or 7. The optical isolator element 100 is configured by combining the Faraday rotator 6.

A magnetic garnet is often used for the Faraday rotator 6, and in this embodiment, a GdBi-substituted garnet is used. Also, by using two magnetic garnets in each of the upper and lower stages, the thickness of each magnetic garnet can be reduced, and the boundary at the center can be reduced, and the same as the conventional configuration shown in FIG. About the same size.

In addition to the above-mentioned optical isolator element 100, the optical waveguide structure includes an optical waveguide having a TEC structure as an optical element integrating an optical waveguide and a lens function.
2 is used. For this, a permanent magnet (magnet) 10 is used as an external magnetic field applying means. As shown in FIG. 1A, a V-shaped groove 9 is formed on a glass substrate 8,
The optical waveguides 1 and 2 having a TEC structure were embedded therein and used.

In FIG. 1C, the direction of the magnetic field is applied from left to right in the figure. In this case, the magnetic garnet is designed such that the polarization plane of the light rotates clockwise by 45 °, and the optical isolator element 10 shown in FIG.
At 0, the angle of the optical axis of the half-wave plate 3 at the front of the stage is −22.5 °, and the angle of the optical axis of the half-wave plate 4 at the rear of the stage is 22.5 °. And

In the first embodiment, the light incident from the optical waveguide 1 on the left side of FIG. 1A, the light transmitted through the upper and lower paths, the polarization plane in the same direction as the incident light, Since they have the same phase, they are coupled and transmitted by the optical waveguide.

The light incident from the optical waveguide 2 on the right side of FIG. 1A passes through each optical path and then has the same polarization plane and a phase difference of 180 °. Light is not coupled to the waveguide 1 and light does not pass through the optical waveguide. This operation is basically the same in the following embodiments.

Next, a second embodiment of the present invention will be described.

FIG. 2 is an explanatory view of an optical isolator according to a second embodiment of the present invention, which is an optical isolator having a waveguide structure composed of an optical waveguide with a spherical lens.

In FIG. 2, the angle of the slow axis is 22.
A half-wave plate 13 made of quartz of 5 ° or −22.5 °,
The optical isolator element 100 is formed by adhering a glass 16, 16 having the same thickness as the half-wave plates 13 and 14, and a Faraday rotator 15 having a thickness adjusted so that the polarization plane is rotated by 45 °. And

The optical isolator shown in FIG. 2 has the same thickness as the half-wave plates 13 and 14 in addition to the conventional configuration shown in FIG.
In addition, the dummy 16 and 17 made of an optically isotropic material having substantially the same refractive index are connected by an adhesive having the same refractive index.

Thus, the influence of the edges 61 and 62 of the half-wave plate shown in FIG. 6 can be suppressed. Further, since there is no boundary at the center of the magnetic garnet, insertion loss can be suppressed. In addition, when a dummy made of a material having optical isotropy is made of glass, it is possible to improve the characteristics with a slight increase in price.

In addition to the above-described optical isolator element 100, the optical waveguide structure is an optical element having an optical waveguide and a lens function integrated therein.
2 is used. This was buried in a V-shaped groove 19 formed on a glass substrate 18 to simplify the adjustment, and a permanent magnet was used as an external magnetic field applying means.

Next, a third embodiment of the present invention will be described.

FIG. 3 is an explanatory view of an optical isolator according to a third embodiment of the present invention, which is an optical isolator constituted by optical waveguides 21 and 22 having a PLC structure.

The optical isolator shown in FIG. 3 is an embodiment realized by an element manufactured by combining two plates cut out from the same substrate, and combines a half-wave plate 23 and two magnetic garnets 25 and 26. Device
It is cut out so that the Slow axis becomes 22.5 ° or −22.5 °, and two of them are combined to form the optical isolator element 100. According to this embodiment, element assembly is greatly simplified.

In addition to the above-described optical isolator element 100, in order to suppress the coupling loss between the optical isolator element and the optical waveguide structure, the transmitted light must be parallel light or light equivalent thereto. Optical waveguides 21 and 22 having a PLC structure are used as optical elements having an integrated lens function. By embedding this on the glass substrate 20, the fabrication is further facilitated. For this, a permanent magnet 29 is used as an external magnetic field applying means.

Next, a fourth embodiment of the present invention will be described.

FIG. 4 is an explanatory view of an optical isolator according to a fourth embodiment of the present invention, which is an optical isolator realized by an optical isolator element formed by combining two plates cut from the same substrate.

In FIG. 4, an element was prepared by combining one half-wave plate, one glass, and one magnetic garnet, and the Slow axis was 22.5 ° or −22.
An optical isolator element 100 is formed by cutting the magnetic garnets 36 and 37 so as to face each other at an angle of 5 °. According to this embodiment, the assembly of the optical isolator element is greatly simplified.

Further, in addition to the optical isolator element 100 described above, aspheric lenses 32 and 33 are used as optical elements having optical waveguides 30 and 31 and a lens function. For this, a permanent magnet 40 is used as an external magnetic field applying means.

Next, a fifth embodiment of the present invention will be described.

FIG. 5 is a configuration diagram of an optical isolator according to a fifth embodiment of the present invention.

In FIG. 5, the optical isolator 100
In addition to (the same configuration as that already described in the first embodiment), optical couplers 41 and 42 are provided in the optical waveguide to divide the light path into two and transmit light through the boundary of the optical element. This is an embodiment in which a light path is provided so as not to prevent it.

The optical waveguides 43 and 4 having the TEC structure
By using 4, 45, 46, parallel light can be obtained, and diffraction, scattering, and reflection at the boundary can be suppressed. Here, the same applies to the case where an optical waveguide with a spherical lens is used instead of the optical waveguide having the TEC structure.

By using an optical element or an optical waveguide in which an optical waveguide and an element having a lens function are integrated, and an element having a lens function, it is possible to obtain parallel light. By using an optical element in which the elements are integrated, the optical characteristics of the optical isolator are improved. In addition, since the lens mechanism is not independent, the steps of assembly and optical alignment are facilitated. Further, since the entire length of the optical isolator is shortened and miniaturized, there is an advantage that the required area of the optical isolator element is reduced and cost reduction is expected.

As described above, in the first to third embodiments of the present invention, one case is described as satisfying the requirements of the present invention, but it goes without saying that the same effect can be obtained in any combination. . As a result, 1550 nm
In the case of an optical isolator for use in the related art, the insertion loss of about 2 dB in the conventional example becomes about 0.7 dB in the present invention.

In the configuration of each of the above figures, in each embodiment of the optical isolator, the optical path lengths of the two upper and lower light transmission paths in each figure are different between the two optical couplers. In each region, it is equal to or a multiple of the wavelength of the transmitted light.

[0067]

As described above, according to the present invention, in an optical isolator used as a constituent device in an optical amplifier or the like, transmitted light is not impaired on the input / output surface of the optical element, and reflection is not affected. It can transmit less. Also in the fabrication of the optical isolator element portion, by using the second and third aspects, high precision and simplification can be achieved, and the cost can be reduced. Further, when used in combination with claim 5, the characteristics can be further improved, the optical adjustment at the time of assembling becomes easy, and the cost can be reduced by downsizing the optical element of the waveguide system. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical isolator according to a first embodiment of the present invention. FIG. 1A is a perspective view of one configuration example of an optical isolator according to a first embodiment of the present invention. FIG. 1 (b)
Is an exploded view of the optical isolator element of the present embodiment;
The figure which shows a / 2 wavelength plate and a Faraday rotator. FIG.
(C) is a configuration diagram of the present embodiment.

FIG. 2 is an explanatory diagram of an optical isolator according to a second embodiment of the present invention. FIG. 2A is a perspective view of one configuration example of an optical isolator according to a second embodiment of the present invention. FIG. 2 (b)
Is an exploded view of the optical isolator element of the present embodiment;
The figure which shows the structure of a / 2 wavelength plate, a Faraday rotator, and glass. FIG. 2C is a configuration diagram of the present embodiment.

FIG. 3 is an explanatory diagram of an optical isolator according to a third embodiment of the present invention. FIG. 3A is a configuration diagram of an optical isolator according to a third embodiment of the present invention. FIG. 3B is an exploded view of the optical isolator element according to the present embodiment, showing a configuration of a half-wave plate and a magnetic garnet. FIG. 3 (c)
FIG. 2 is a perspective view of the embodiment.

FIG. 4 is an explanatory diagram of an optical isolator according to a fourth embodiment of the present invention. FIG. 4A is a configuration diagram of an optical isolator according to a fourth embodiment of the present invention. FIG. 4B is an exploded view of the optical isolator element according to the present embodiment, showing a configuration of a half-wave plate, a magnetic garnet, and glass.

FIG. 5 is a diagram showing one configuration of an optical isolator according to a fifth embodiment of the present invention.

FIG. 6 is a schematic diagram of a configuration of a conventional optical isolator.

[Explanation of symbols]

1, 2 Optical waveguide (having TEC structure) 3, 4 1/2 wavelength plate 5, 6, 7 Faraday rotator 8 Substrate 9 V-shaped groove 10 Permanent magnet (magnet) 11, 12 Optical waveguide with forward spherical lens 13 , 14 1/2 wavelength plate 15 Faraday rotator 16, 17 glass (dummy) 18 substrate 19 V-shaped groove 20 substrate 21, 22, optical waveguide having PLC structure 23, 24 1/2 wavelength plate 25, 26, 27, 28 Magnetic Garnet 29 Permanent Magnet (Magnet) 30, 31 Optical Fiber (Optical Waveguide) 32, 33 Aspheric Lens 34, 35 1/2 Wavelength Plate 36, 37 Magnetic Garnet 38, 39 Glass 40 Permanent Magnet 41, 42 Optical Coupler 43,44,45,46 Optical waveguide having TEC structure 47,48 1/2 wave plate 49,50,51 Magnetic garnet 52 Permanent magnet 53,54 Optical fiber 55,56 Aspheric lens 57,58 1/2 wavelength plate 59 Faraday rotator 60 Permanent magnet 61,62 Edge portion of 1/2 wavelength plate 100 Optical isolator element

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Haruhiko Tsuchiya 6-7-1, Koriyama, Taishiro-ku, Sendai-shi, Miyagi-ken Tokin Co., Ltd.

Claims (9)

[Claims] 1. A member in which a Faraday rotator having the same thickness as a half-wave plate having a slow axis of 22.5 ° is bonded to both sides of a Faraday rotator symmetrically, and the first and second members for inputting and outputting light are provided. An optical isolator element, wherein a surface including a half-wave plate forms one continuous plane without a step. 2. A member in which a plate member having optical isotropy and having the same thickness as a half-wave plate having a slow axis of 22.5 ° is bonded to both surfaces of a Faraday rotator symmetrically, An optical isolator element, wherein a surface including the half-wave plate for inputting and outputting is formed as one continuous flat surface having no step. 3. The optical isolator element according to claim 1, wherein the Faraday rotator at the center of the optical isolator element has a structure that is divided into two parts in front and rear with respect to the traveling direction of light. 4. The optical isolator element according to claim 1, wherein the optical isolator element is inclined with respect to the traveling direction of light, and an optical waveguide and an optical element having a lens function are disposed before and after the optical isolator element. Optical isolator. 5. The optical waveguide has an optical splitter, and the optical splitter divides a light path into two parts, and light transmitted through one path is transmitted through the one half-wave plate. 5. The optical isolator according to claim 4, wherein a light path is provided so that the light transmitted and transmitted through the other path is transmitted through the other half-wave plate. 6. The optical isolator according to claim 4, wherein said optical element is an optical element in which an optical waveguide and a lens function are integrated. 7. The optical isolator according to claim 6, wherein the optical element integrating the optical waveguide and the lens function is constituted by an optical waveguide having a TEC structure. 8. The optical isolator according to claim 6, wherein the optical element integrating the optical waveguide and the lens function comprises an optical waveguide with a spherical lens. 9. The optical isolator according to claim 6, wherein the optical element integrating the optical waveguide and the lens function is constituted by an optical waveguide having a PLC.