JP2002107671A - Waveguide type optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compact a means for applying a magnetic field to a Faraday rotation element regarding a waveguide type optical isolator having the Faraday rotation and to highly accurately and simply produce the optical isolator. SOLUTION: The Faraday rotation element 2 arranged between both polarization control elements 9, 9 has fiber type constitution consisting of a core 21 having a non-reciprocal effect and a clad 23 formed on the outer periphery of the core 21 and a coat layer 10 consisting of a magnetic material for applying a magnetic field to the element 2 is formed on the outer periphery of the element 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field of a waveguide type optical isolator used in an optical transmitter or an optical amplifier and transmitting light in only one direction.

[0002]

2. Description of the Related Art Conventionally, there has been known a waveguide type optical isolator in which a crystal such as YIG (yttrium / iron / garnet, Y ₃ Fe ₅ O ₁₂ ) is applied to a Faraday rotator having a nonreciprocal effect. . In order for the Faraday rotation element to rotate the polarization direction of the signal light, a magnetic field in the same direction as the propagation direction of the signal light is required. Therefore, a ring-shaped permanent element for applying a magnetic field around the Faraday rotation element is required. It is also known to provide a magnet.

It is necessary to reduce the size of such a waveguide type optical isolator for the purpose of improving the space efficiency and the like. Therefore, the thickness of the Faraday rotator in the signal light passing direction must be reduced. Is valid. That is, since the Faraday rotation element applied to the optical isolator has a Faraday rotation angle of usually 45 °, the Faraday rotation element is made of a material having a large rotation angle per unit thickness (Faraday rotation capability) to reduce the thickness. The thickness can be reduced, which is advantageous for miniaturization.

On the other hand, the permanent magnet provided around the Faraday rotator substantially determines the size of the waveguide-type optical isolator, which is a major factor preventing miniaturization.

Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 7-36000, a nonmagnetic GGG (gadolinium gallium garnet, Gd ₃ Ga ₅ O ₁₂ ) single crystal substrate is formed on a YIG single crystal substrate. By forming a wave path and an optical anti-reflection film to form a Faraday rotation element, furthermore, disposing a thin plate type polarizing element on both end faces of the Faraday rotation element, and bonding a plate-like permanent magnet in an in-plane direction,
It has been proposed to construct a waveguide type optical isolator by reducing the size of a permanent magnet.

[0006]

However, in the above-mentioned proposal, a permanent magnet is provided separately from the Faraday rotation element, which makes it difficult to reduce the size in the direction perpendicular to the axial direction. is there.

In addition, since the Faraday rotator has a crystal structure, a high-precision alignment by an optical system is required to connect to another polarization control element or an optical fiber, which increases the manufacturing cost. There was also.

The present invention has been made in view of the above points, and an object of the present invention is to provide a means for applying a magnetic field to a Faraday rotation element by improving the structure of a waveguide type optical isolator. It is an object of the present invention to reduce the size and to make it easy to manufacture with high precision.

[0009]

In order to achieve the above object, in the present invention, the reciprocal effect element is constituted by an optical fiber coated with a coating layer, and the coating layer has magnetism.

Specifically, according to the first aspect of the present invention, there is provided a fiber type non-reciprocal effect element comprising a core having a non-reciprocal effect, a clad provided on the outer periphery of the core, and a non-reciprocal effect element. And a coating layer made of a magnetic material for applying a magnetic field to the non-reciprocal effect element.

According to the above configuration, the coating layer covering the optical fiber, which is the Faraday rotation element, is made of a magnetic material, and there is no need to provide a permanent magnet separately from the Faraday rotation element. The size of the isolator can be reduced.

According to the second aspect of the present invention, a grooved magnetic structure having a groove and made of a magnetic material for generating a magnetic field, a core disposed in the groove and having a nonreciprocal effect, and the core And a fiber type non-reciprocal effect element composed of a clad provided on the outer periphery of the optical fiber.

With this configuration, the same effect as that of the waveguide type optical isolator of the first aspect can be obtained, and the configuration can be easily manufactured.

According to a third aspect of the present invention, in the waveguide type optical isolator of the first or second aspect, a fiber type polarization control element for controlling the polarization direction of light is bonded to both sides of the nonreciprocal effect element. It is characterized by being.

According to the above configuration, the non-reciprocal effect element and the polarization control element are interconnected between optical fibers, so that accurate alignment is not required, and each element can be easily and accurately joined. You can do it.

According to a fourth aspect of the present invention, in the waveguide type optical isolator of the third aspect, a condensing element for condensing the signal light is joined to the polarization control element.

According to a fifth aspect of the present invention, in the waveguide type optical isolator of the third aspect, an optical fiber for transmitting signal light is bonded to the polarization control element. This makes it easy to join with other optical components.

According to a sixth aspect of the present invention, in the waveguide type optical isolator of the fourth aspect, the light condensing element is a fiber type element. As a result, the light-collecting system element can be easily and accurately formed because the optical fiber is bonded to another element at the junction with the other element.

According to a seventh aspect of the present invention, in the waveguide type optical isolator of the fifth or sixth aspect, each element is integrally joined to a flat sheet substrate.

With the above configuration, even if the Faraday rotation element is relatively long, it can be fixed in a relatively small size if it is curved and attached to a flat sheet substrate.

[0021]

(Embodiment 1) Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a waveguide type optical isolator 1 according to the present embodiment, together with an optical fiber amplifier 60 and a gain equalizer 70.

That is, an optical isolator 1, an optical fiber amplifier 60, an optical isolator 1, a gain equalizer 70, and an optical isolator 1 are arranged on an optical fiber 15 as an optical waveguide extending in the left-right direction of FIG. Connected, and signal light (wavelength is, for example, 1538 to 1564n)
m) is guided from the left side to the right side in FIG.

The optical fiber amplifier 60 includes an erbium-doped optical fiber 61, an excitation light source 62 for exciting the erbium-doped optical fiber 61, and an optical coupler 63. The excitation light source 62 is, for example, an excitation light (pu) having a wavelength of 1.48 μm or 0.98 μm.
mp light), which is an optical fiber 64
Are connected to the optical coupler 63 via the. Further, one end of an erbium-doped optical fiber core 61 is connected to the optical coupler 63 to constitute an optical fiber amplifier 60.

Although the intensity of the signal light is amplified by the optical fiber amplifier 60, usually, the gain of the optical fiber amplifier depends on the wavelength and has gain characteristics in which the gain becomes a peak at a plurality of wavelengths. Large variations occur in the intensity of the signal light. In order to compensate for such light intensity variations, a gain equalizer 70 is provided downstream of the optical fiber amplifier 60 in the signal light propagation direction.

The gain equalizer 70 comprises an optical fiber having a long-period fiber grating (LPG) formed in a core, and a plurality of loss filters having a loss peak wavelength corresponding to the gain peak are connected in series. It is configured.

Then, two optical isolators 1 and 1 are disposed on the optical fiber 15 with the optical fiber amplifier 60 and the gain equalizer 70 interposed therebetween.

As described above, the signal light guided through the optical fiber 15 from the left side of FIG. 1 is input to the optical coupler 63 via the optical isolator 1, while the excitation light from the excitation light source 62 is also an optical fiber. The light is input to the optical coupler 63 via the optical coupler 64. In the optical coupler 63, the signal light and the pump light are combined and output to the erbium-doped optical fiber core 61. Then, the intensity of the signal light is amplified in the erbium-doped optical fiber core 61. The gain variation is filtered by the gain equalizer 70 so as to compensate for the variation in the intensity of the signal light thus amplified. Thereafter, the signal light whose gain has been equalized is output via the optical isolator 1. In the present embodiment, this optical isolator has a waveguide type structure.

Hereinafter, the waveguide type optical isolator 1 according to the present embodiment will be described in detail. As shown in FIG.
The waveguide type optical isolator 1 includes a Faraday rotator 2
And a coating layer 10 for covering the Faraday rotation element 2.
And two polarization control elements 9, 9 connected to both ends of the Faraday rotation element 2, respectively. The waveguide type optical isolator 1 is connected to optical fibers 15 at both ends.

As shown in FIGS. 2 and 3, the Faraday rotator 2 includes a core 21 having a non-reciprocal effect by doping quartz glass with, for example, lead (Pb), and a cladding 22 provided on the outer periphery of the core 21. And a fiber type non-reciprocal effect element.

Further, a coating layer 10 is provided on the outer peripheral surface of the Faraday rotating element 2, and the coating layer 10
For example, it is made of a magnetic material in which a powder of a magnetic material is mixed in a resin such as polyethylene, urethane, epoxy, and nylon. By applying a magnetic field to the Faraday rotator 2 in the same direction as the signal light propagation direction (A direction indicated by an arrow in FIG. 2), the Faraday rotator 2 exhibits the Faraday effect.

That is, when a signal light having a predetermined polarization direction passes through the Faraday rotation element 2, the predetermined polarization direction rotates in a predetermined rotation direction. When this rotation angle is used for an optical isolator, the rotation angle is normally set to a constant value of 45 °.

On both sides of the Faraday rotation element 2, fiber-type polarization control elements 9 for controlling the polarization direction of the signal light are joined. This polarization control element 9
As shown in FIG. 2, a polarization plane preserving element 4 for passing only signal light in a predetermined polarization direction and preserving the polarization direction is provided.

FIG. 4 shows a cross section of the polarization-maintaining element 4. As shown in FIG. 1, the polarization-maintaining element 4 includes a coating layer 11 made of, for example, polyethylene, an optical fiber 6 having a core 23 and a cladding 24 provided at the center of the coating layer 11, and an optical fiber 6 And two stress applying rods 8, 8 provided symmetrically with respect to the position of. That is, the stress applying rods 8 and 8 and the optical fiber 6 are arranged at predetermined intervals in the cross section of the coating layer 11 so as to be arranged on the straight line L.

Each of the stress applying rods 8 and 8 is
A stress is applied to the optical fiber 6 through the optical fiber 1. At this time, by making the magnitudes of the stresses applied by the two stress applying rods 8 and 8 different from each other, the state of the stress applied to the core 23 is made different along the straight line L, and a predetermined polarization Only the signal light in the direction passes through the core 23.

Further, the polarization control element 9 includes, in addition to the polarization plane preserving element 4, the filter element 3 upstream of the polarization plane preserving element 4 in the signal light propagation direction (hereinafter abbreviated as “upstream side”). I have to.

That is, the filter element 3 is shown in FIGS.
As shown in the figure, a core 25 whose refractive index is modulated so as to pass only a signal light having a predetermined polarization direction which is the same as the polarization direction by the polarization plane preserving element 4, and a clad 26 provided on the outer periphery thereof. And a covering portion 13 made of, for example, polyethylene. Thus, the performance of the polarization control element 9 to polarize the signal light is improved.

The signal light from the optical fiber 15 on the upstream side (ie, the left side in FIG. 2) is first propagated to the polarization control element 9 on the upstream side and is polarized in a predetermined polarization direction. The polarized signal light is subsequently propagated to the Faraday rotator 2 and its polarization direction is changed to 45 degrees in a predetermined rotation direction.
° rotated.

The polarization control element 9 on the downstream side in the signal light propagation direction (hereinafter abbreviated as “downstream side”) is a Faraday rotation element 2.
Is configured to pass only light having the same polarization direction as the polarization direction of the signal light that has passed through the signal light, so that the signal light passes through the polarization control element 9 on the downstream side and passes through the light on the further downstream side. Propagated to fiber 15. Thus, the desired signal light passes through the optical isolator.

On the other hand, when light is reflected somewhere on the downstream side of the optical isolator 1 and propagates from the right side of FIG. 2 and returns, the light passes through the polarization control element 9 on the downstream side. Since the polarization direction of the light is further rotated by 45 ° in the Faraday rotation element 2, the upstream polarization control element 9
Can not pass through. In other words, the light flowing backward to the optical isolator 1 and passing through the polarization control element 9 and the Faraday rotation element 2 on the downstream side is converted into the polarization control element 9 on the upstream side.
For a given polarization direction of light that can pass through
Since it has a polarization direction rotated by 90 °, it cannot pass through the polarization control element 9 on the upstream side. As a result, the waveguide type optical isolator 1 prevents backflow of light.

At this time, since the coating layer 10 covering the optical fiber 2 as the Faraday rotator is made of a magnetic material, there is no need to provide a permanent magnet separately from the Faraday rotator. The size can be reduced.

The Faraday rotation element 2 and the polarization control element 9 are formed by making the polarization control element 9 a fiber type.
Can be used as a joint between optical fibers, so there is no need for accurate alignment at the time of joining.
Each element can be easily and accurately joined.

In this embodiment, the quartz glass is doped with Pb as the Faraday rotator. However, the present invention is not limited to this, and other materials such as Ge, Sn, Pb, and Tb may be used.
At least one of e, Yb, Bi, Er, Nd, Al and the like may be doped.

Although the polarization control element 9 is configured by joining the polarization plane preserving element 4 and the filter element 3 to each other, other configurations for polarizing the signal light may be employed.

(Embodiment 2) FIGS. 6 and 7 show Embodiment 2 of the present invention (in the following embodiments, the same parts as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. This is a modification of the mode of the coating layer of the Faraday rotator 2 in the first embodiment.

That is, the waveguide type optical isolator 1 according to this embodiment has a groove 32, a grooved magnetic structure 31 made of a magnetic material that generates a magnetic field, and is disposed in the groove 32. , A core 21 having a non-reciprocal effect, and the core 2
1 is provided with a fiber type non-reciprocal effect element (Faraday rotator) 2 composed of a clad 22 provided on the outer periphery of the first clad 22 and a protective coating layer 11 coated on the outer periphery of the clad 22.

The grooved magnetic structure 31 can be manufactured by, for example, putting powder of a magnetic material in a plastic or rubber-based material, stirring the mixture, and then extruding it. Subsequently, the formed grooved magnetic structure 31
By inserting the fiber core 2 'including the Faraday rotation element 2 into the concave portion 32, the waveguide type optical isolator 1 can be manufactured. When the protective coating layer 11 is a glass body in which the clad 22 is exposed,
There is a risk of damage at the time of insertion into the device 2, and therefore it is provided for the purpose of preventing this.

At this time, the same effects as those of the waveguide type optical isolator of the first embodiment can be obtained, and the structure can be easily manufactured. Further, the replacement of the magnetic structure 31 is easy, and furthermore, it is possible to avoid thermal and stress disturbances when the magnetic structure 31 is covered.

The grooved magnetic structure does not necessarily need to be continuously magnetized in its length direction, but may be magnetized locally.

(Embodiment 3) FIG. 8 shows Embodiment 3 of the present invention.
In this example, a light-collecting device and an optical fiber are further connected to the waveguide-type optical isolator of the first embodiment.

That is, as shown in FIGS. 8 and 9, a fiber-type light condensing element 30 for condensing signal light is joined to the polarization control element 9 on the upstream side. The collective element 30 includes a core 33 configured to collect signal light input from the upstream side, a clad 34 provided on the outer periphery thereof, and a polyethylene or the like provided on the outer peripheral surface of the clad 34. And a covering layer 32 made of a waveguide.

On the other hand, an optical fiber 40 for transmitting signal light is joined to the downstream side of the polarization control element 9 on the downstream side. The waveguide-type optical isolator 1 according to the present embodiment includes the light-collecting system element 30, the polarization control elements 9, 9, the Faraday rotation element 2, the coating layer 10, and the optical fiber 40.

At this time, the joining with other optical components, elements, optical fibers, and the like can be made by mutual joining of the optical fibers, so that the joining can be made easily and with high precision.

In the present embodiment, the light condensing element 3 is provided on the upstream side.
Although the optical fiber 40 is provided on the downstream side while the optical fiber 40 is provided on the downstream side, the optical fiber 40 may be provided only on the upstream side without being limited thereto, and the optical fiber 40 may be provided on at least one of the upstream and downstream sides. 40 may be provided.
Further, the light collecting system element 30 may have another configuration that is not a fiber type.

Then, the Faraday rotator 2 is coated with the coating layer 1.
Instead of being covered with zero, the grooved magnetic structure 31 shown in the second embodiment may be provided.

Fourth Embodiment FIG. 10 shows a fourth embodiment of the present invention, in which the waveguide type optical isolator 1 shown in the first embodiment is joined to a flat sheet substrate.

That is, the substrate 50 is formed of an adhesive layer (not shown).
Each element constituting the waveguide type optical isolator is adhered to this adhesive layer, so that the substrate 50
Is fixed against

As the substrate 50, it is preferable to use a substrate which is strong against vibration so that the wired optical isolator hardly bends. As a material for forming the substrate 50, for example, a polyimide resin, a polyethylene terephthalate resin, a polyethylene naphthalate resin, or the like can be used.

The adhesive layer may be any layer having tackiness or adhesiveness, as long as it can securely fix the optical isolator. Therefore, it can be formed using a known pressure-sensitive adhesive or adhesive (for example, silicone adhesive).

At this time, even if the Faraday rotation element 2 is relatively long in order to improve the Faraday rotation capability, it can be fixed to a relatively small size if it is bent and attached to the substrate 50. At this time, since the core 21 of the Faraday rotation element 2 is doped with lead or the like, even if the Faraday rotation element 2 is curved, the core 2
The magnitude of the refractive index of 1 does not change.

The structure of the optical isolator to be attached to the substrate 50 may be the same as that described in the second and third embodiments, regardless of the structure of the present embodiment.

[0061]

As described above, according to the first aspect of the present invention, there is provided a fiber type non-reciprocal effect element including a core having a non-reciprocal effect and a clad provided on the outer periphery of the core. Provided on the outer peripheral surface of the non-reciprocal effect element,
By providing the non-reciprocal effect element with a coating layer made of a magnetic material for applying a magnetic field, the size of the device can be reduced as compared with the case where the permanent magnet is provided separately from the Faraday rotation element. it can.

According to the second aspect of the present invention, a grooved magnetic structure having a groove and made of a magnetic material for generating a magnetic field, a core provided in the groove and having a nonreciprocal effect, By providing a fiber type non-reciprocal effect element composed of a cladding provided on the outer periphery of the device, the same effect as the invention of the above-mentioned claim 1 can be obtained, and a configuration that is easier to manufacture can be obtained. can do.

According to the third aspect of the present invention, fiber-type polarization control elements for controlling the polarization direction of light are respectively joined to both sides of the nonreciprocal effect element, so that each element can be easily and accurately joined. Can be done.

According to the fifth aspect of the present invention, by joining the optical fiber for transmitting the signal light to the polarization control element, the joining with other optical components can be facilitated.

According to the sixth aspect of the present invention, since the light-collecting element is a fiber-type element, the light-collecting element can be easily and highly accurately formed.

According to the seventh aspect of the present invention, even if the Faraday rotation element is relatively long, it can be curved and affixed to the flat sheet substrate by integrally joining the elements to the flat sheet substrate. It can be fixed relatively small.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a waveguide type optical isolator together with an optical fiber amplifier and a gain equalizer.

FIG. 2 is a perspective view schematically showing the waveguide type optical isolator according to the first embodiment.

FIG. 3 is a cross-sectional view of the Faraday rotation element according to the first embodiment.

FIG. 4 is a sectional view of the polarization maintaining element according to the first embodiment.

FIG. 5 is a cross-sectional view of the filter element according to the first embodiment.

FIG. 6 is a perspective view schematically showing a waveguide type optical isolator according to a second embodiment.

FIG. 7 is a cross-sectional view of the grooved magnetic structure according to the second embodiment.

FIG. 8 is a perspective view schematically showing a waveguide type optical isolator according to a third embodiment.

FIG. 9 is a cross-sectional view of a light-collecting device according to a third embodiment.

FIG. 10 is a plan view schematically showing a waveguide type optical isolator according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveguide type optical isolator 2 Faraday rotation element (non-reciprocal effect element) 2 'Faraday rotation element with a coating layer (non-reciprocal effect element) 3 Filter element (polarization control element) 4 Polarization preserving element (polarization control element) REFERENCE SIGNS LIST 9 polarization control element 10 coating layer 11 protective coating layer 21 core 22 clad 30 light condensing element 31 grooved magnetic structure 32 concave groove 40 optical fiber 50 substrate (flat sheet substrate)

Claims (7)

[Claims] 1. A fiber type non-reciprocal effect element comprising a core having a non-reciprocal effect, and a clad provided on the outer periphery of the core, and a non-reciprocal effect element provided on an outer peripheral surface of the non-reciprocal effect element. A waveguide type optical isolator, comprising: a coating layer made of a magnetic material for applying a magnetic field to the reciprocal effect element. 2. A grooved magnetic structure having a concave groove and made of a magnetic material for generating a magnetic field, a core disposed in the concave groove and having a non-reciprocal effect, and provided on an outer periphery of the core. And a fiber type non-reciprocal effect element comprising a clad and a cladding. 3. The waveguide type optical isolator according to claim 1, wherein a fiber type polarization control element for controlling the polarization direction of light is bonded to both sides of the non-reciprocal effect element. Waveguide type optical isolator. 4. The waveguide type optical isolator according to claim 3, wherein a condensing element for condensing the signal light is joined to the polarization control element. 5. The waveguide type optical isolator according to claim 3, wherein an optical fiber for transmitting signal light is bonded to the polarization control element. 6. The waveguide type optical isolator according to claim 4, wherein the light condensing element is a fiber type element. 7. The waveguide type optical isolator according to claim 5, wherein each element is integrally joined to a flat sheet substrate.