JPH05313094A - Optical isolator - Google Patents

Abstract

PURPOSE:To reduce the number of parts, and simplify an optical axis adjustment by constituting a reflection type optical isolator only of a single lens. CONSTITUTION:A birefringent crystal 4 is arranged on one side of a single lens 6, and a 1/2 wave length plate 5 is arranged between this lens 6 and the birefrigent crystal 4 so as to cover an area half of the lens 6. A reflecting mirror 8 is arranged on the other side of the lens 6, and a platelike magnetooptical crystal 7 whose length is determined so that planes of polarization of incident light 11 and outgoing light 18 become different from each other by pi/8+Npi/4 (N=0, 1,...), is arranged between the lens 6 and the reflecting mirror 8. A light beam 1 incident so as to pass through the 1/2 wave length plate 5 is reflected by the reflecting mirror 8, and passes through into the 1/2 wave length plate 5, and light 18 is outputted. In this way, since the light beam is used by passing through the respective single birefringent crystal 4, lens 6 and magnetooptical crystal 7 twice, the number of parts can be reduced. Since optical fibers 1 and 2 are formed in an array structure, optical coupling can be made simply by adjusting the optical axes of an optical fiber array 3 and the lens 6.

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.

[0002]

2. Description of the Related Art A conventional polarization-independent optical isolator is shown in FIG. 5, in which 51 and 52 are optical fibers and 5 is an optical fiber.
3, 54 are lenses, 55, 56 are flat birefringent crystals, 5
Reference numeral 7 is a magneto-optical crystal, 58 is an optical rotatory crystal or birefringent crystal, and 59 is a magnet. A magnetic field is applied to the YIG crystal 57, which is a magneto-optical crystal, by the magnet 59 in parallel with the light transmitting direction. The light output from the optical fiber 51 is converted into parallel light by the lens 53. The light transmitted through the lens 53 is split into two polarizations, an ordinary ray and an extraordinary ray, by the rutile crystal 55, which is a birefringent crystal, and the optical path of the extraordinary ray moves in parallel with the optical path of the ordinary ray. When the two polarized lights that have passed through the rutile crystal 55 pass through the YIG crystal 57, their planes of polarization rotate 45 degrees counterclockwise about the optical axis. Further, the half-wave plate 58 used as the optical rotatory crystal is rotated counterclockwise by 45 degrees. YIG crystal 57 and 1/2 wave plate 5
Lights having different optical paths which are rotated 90 degrees in total at 8 are combined by the rutile crystal 56 so as to travel in one optical path, are condensed by the lens 54, and are incident on the optical fiber 52.

On the other hand, the light output from the optical fiber 52 is converted into parallel light by the lens 54, and then separated into ordinary light and extraordinary light by the rutile crystal 56, and the optical path is also divided into two. 1 /
Since the two-wave plate 58 is reversible, the plane of polarization is rotated 45 degrees clockwise. However, since the YIG crystal 57 is irreversible, the plane of polarization is rotated 45 degrees counterclockwise, and the half-wave plate 58 and YI crystal 57 are rotated.
The plane of polarization of the light that has passed through the G crystal 57 is the same as before it passed through. Therefore, the two polarized lights transmitted through the rutile crystal 55 are not combined into one optical path, and
Since the light condensed by the lens 53 is different in position, it is not coupled to the optical fiber 51. In this way, the optical fiber 5
The light emitted from 1 enters the optical fiber 52, but the light output from the optical fiber 52 does not enter the optical fiber 51, so that the light can be transmitted in only one direction.

[0004]

However, in the above-mentioned conventional structure, two lenses and two birefringent crystals necessary for optical coupling are required, and further, in order to perform optical coupling, two lenses are required.
It was necessary to adjust the positions of the optical fiber of the book and the two lenses for optical coupling.

An object of the present invention is to provide an optical isolator in which the number of constituent parts of the optical isolator is reduced and the optical axis for optical coupling can be easily adjusted.

[0006]

In order to achieve this object, the optical isolator of the present invention is provided with a birefringent crystal on one side of one lens, and a half area of the lens is provided between the lens and the birefringent crystal. A half-wave plate to cover the lens and a reflection plate on the other side of the lens, and the polarization planes of the incident light and the output light are π / 8 + Nπ / 4 (N = 0, 1,
・ ・) A magneto-optical crystal whose length is determined so as to be different from each other is provided, and the light beam incident so as to pass through the portion without the half-wave plate is reflected by the reflecting mirror and passes through the half-wave plate. It is configured to output light.

[0007]

By constructing the reflection type optical isolator with only one lens as in the above configuration, the number of parts is small and the optical axis adjustment can be simplified.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are cross-sectional views of the configuration of an optical isolator according to a first embodiment of the present invention. FIG. 1 is a diagram for explaining changes in a polarization state and an optical path when light is transmitted in a forward direction, and FIG. It is a figure explaining the change of the polarization state and the optical path at the time of transmitting light to a direction.

In FIG. 1, 1 and 2 are optical fibers, 3 is an optical fiber array, 4 is a birefringent crystal, 5 is an optical rotatory crystal or birefringent crystal, 6 is a lens, 7 is a magneto-optical crystal, and 8 is a reflecting mirror. , 9 are glass plates, 10 are magnets, 11-18 and 21-28 are light rays.

The optical fiber 1 and the optical fiber 2 are 250
A glass plate having a plate thickness of 1 mm is aligned in parallel at a distance of μm, and a glass plate having a plate thickness of 1 mm is placed on the glass plate to bond and fix it, and then the tip is mirror-polished to form an optical fiber array 3. A half-wave plate 5 having a plate thickness of 90 μm is provided on half of one side of a rutile crystal 4 which is a birefringent crystal having a plate thickness of 1.3 mm.
A glass plate 9 having a plate thickness of 90 μm is attached to the remaining half. An antireflection film is provided on both surfaces of the rutile crystal 4 so as to eliminate reflected light when adhered.

When the optical fiber array 3 and the rutile crystal 4 are adhered, the optical fiber 1 and the optical fiber 2 are placed at the center of the optical fiber 1 and the rutile crystal 4.
Positioning is performed so that the boundary between the / 2 wave plate 5 and the glass plate 9 is located so that only the light input to and output from the optical fiber 2 passes through the 1/2 wave plate 5. A Bi-substituted garnet crystal 5, which is a magneto-optical crystal having a thickness of about 120 μm, is attached to the end surface of the gradient index rod lens 6, and further, a reflecting mirror 8 is attached to the garnet crystal 7. A cylindrical magnet 10 is provided outside the garnet crystal 7 so that a magnetic field is perpendicular to the garnet crystal 7. When light with a central wavelength of 1554 nm is transmitted through the garnet crystal 7, its polarization plane rotates 22.5 degrees counterclockwise. The positions of the optical fiber array 3 and the rod lens 6 are adjusted so that the light emitted from the optical fiber 1 enters the optical fiber 2, and the half-wave plate 5 provided at the tips of the rod lens 6 and the optical fiber array 3 is adjusted. And the glass plate 9 is adhesively fixed. The operation of the optical isolator configured as above will be described. The light travels in the horizontal direction of the paper, and the polarization state of the light indicates the polarization direction viewed from the left in the normal plane of the light beam (plane perpendicular to the paper). In addition, the rotation is clockwise in the clockwise direction and counterclockwise in the counterclockwise direction. The behavior of the light in the rod lens 6 is the behavior of the center of the light ray.

The unpolarized light incident from the optical fiber 1 is separated into the ordinary ray 11 and the extraordinary ray 12 by the rutile crystal 5, and the optical path of the extraordinary ray 12 is changed. The light passing through the rutile crystal 4 has different optical paths with ordinary light and extraordinary light, but proceeds in the same way.
The right end surface of the rod lens 6 is converted into parallel rays. The light 13 and the light 14 that have passed through the rod lens 6 are 22.5 degrees counterclockwise when they pass through the garnet crystal 7, and are 2 when they pass through the garnet crystal 7 again after being reflected by the reflecting mirror 8.
Rotate to the left by 45 degrees, including 2.5 degrees. The light 13 travels in the optical path of the light 15 and the light 14 travels in the optical path of the light 16 by being reflected by the reflecting mirror 8. Light 15 transmitted through the garnet crystal 7
And 16 are incident on the ½ wavelength plate 5 while being condensed by the rod lens 6. The ½ wavelength plate 5 has a function of emitting linearly polarized light that is incident at an angle θ with its optical axis as linearly polarized light that forms an angle −θ with the optical axis of the ½ wavelength plate 5. Since the optical axis direction of the half-wave plate 5 is provided at an angle of 22.5 degrees with respect to the extraordinary light 12, the light 15
And the polarization state of the light 16 is further rotated 45 degrees to the left when transmitted through the half-wave plate 5. When the light transmitted through the half-wave plate 5 enters the rutile crystal plate 4, the light 17 which is an extraordinary light and the light 18 which is an ordinary light have the same optical path when they pass through the rutile crystal 4. Also, light 17 and light 1
Since 8 is condensed by the rod lens 6, it is efficiently coupled to the optical fiber 2 with a loss of about 0.5 dB.

On the other hand, when non-polarized light enters from the optical fiber 2, it is divided into ordinary light 21 and extraordinary light 22 by the rutile crystal 4 and travels different optical paths. After passing through the half-wave plate 5, its plane of polarization is rotated clockwise, and then converted into parallel light by the rod lens 6. Light 2 traveling through rod lens 6
Since the light 3 and the light 24 are transmitted through the garnet crystal 7 twice before and after being reflected by the reflecting mirror 8, the plane of polarization is rotated counterclockwise by 45 degrees at this time. The light 23 travels on the optical path of the light 25 and the light 24 travels on the optical path of the light 26 by being reflected by the reflecting mirror 8. The light 15 and the light 26 travel while being condensed by the rod lens 6. When the light that has passed through the glass plate 9 passes through the rutile crystal 4, the light 27 travels as ordinary light and thus goes straight.
It does not enter the optical fiber 1. Since the light 28 passes through the rutile crystal 4 as extraordinary light, the light path is deviated and does not enter the optical fiber 1. In this way, it is possible to configure the function of the optical isolator that the light incident from the optical fiber 1 is coupled to the optical fiber 2, but the light incident from the optical fiber 2 is not coupled to the optical fiber 1.

As described above, one birefringent crystal, one lens, one magneto-optical crystal, and one reflecting mirror are arranged in series, and one half of the lens is covered between the birefringent crystal and the lens.
By providing a / 2 wavelength plate and constructing an optical system that passes through a birefringent crystal, a lens, and a magneto-optical crystal twice, the number of components is reduced to about half of the conventional one. Further, since the optical fiber has an array structure, there is an effect that optical coupling can be easily performed by adjusting the optical axes of the optical fiber array and the lens.

FIG. 3 is a sectional view showing the structure of an optical isolator according to the second embodiment of the present invention. In FIG. 3, reference numeral 30 is an aspherical lens, 31 is a glass plate coated with an antireflection film on one surface, and the other parts are the same as those used in the first embodiment. Since the optical fiber 1 and the optical fiber 2 are single-mode optical fibers, their numerical aperture is 0.1 (the radiation angle of light is 5.7 degrees). The tip of the optical fiber array 3 is obliquely polished to 8 degrees, and the tip has a thickness of 1.5 m.
Paste the rutile crystal 4 of m. A ½ wavelength plate having a thickness of 90 μm is attached to the end face of the rutile crystal 4 so that only the light output from the optical fiber 2 is transmitted. Optical fiber 1
A glass plate 9 having a thickness of 90 μm is attached to a portion through which the light emitted from is transmitted. In addition, a plate thickness of 0.
A glass plate 31 of 3 mm is provided, and the surface without the antireflection film is 1
Attached to the half wave plate 5 and the glass plate 9. Therefore, the light that has passed through the optical fiber is hardly reflected by the tip of the optical fiber, and the light reflected by the tip of the optical fiber does not return to the inside of the optical fiber. When light is incident on the aspherical lens 30 provided with an antireflection film on the surface, aberration tends to be large if the incident position deviates from the central axis. The optical fiber 1 and the optical fiber 2 are provided separated by 125 μm from the central axis of the aspherical lens 30, and the numerical apertures of the optical fiber 1 and the optical fiber 2 are as small as 0.1, whereas the aspherical lens is small. Since the numerical aperture of 30 is as large as 0.2, the light output from the optical fiber 1 is converted into parallel rays with almost no aberration,
After being reflected by the reflecting mirror 8, it is condensed again by the aspherical lens 30 and efficiently coupled to the optical fiber 2. The state of rotation of the plane of polarization when passing through the half-wave plate 5, the magneto-optical crystal 7, and the rutile crystal 4 behaves the same as when light passes in the forward direction in the first embodiment.

As described above, when an aspherical lens is used as the lens, the reflected return light can be reduced by subjecting the tip of the optical fiber to oblique polishing. Furthermore, by using an aspherical lens with a numerical aperture larger than that of the optical fiber, and by setting the incident position of the light near the central axis of the aspherical lens, the characteristics of the aspherical lens with few aberrations can be used effectively. The coupling loss can be reduced.

FIG. 4 is a sectional view showing the construction of an optical component in which an optical isolator and another optical function component according to the third embodiment of the present invention are integrally incorporated. In FIG. 4, 32 is a reflection type optical isolator of the present invention, 33 and 34 are optical fibers, 3
5, 36 are rod lenses, 37 is a filter, 38-43
Is the optical path.

Wavelength 1554 incident from the optical fiber 33
The light of nm travels in the rod lens 35 along the optical path 39. Since the filter 37 has a characteristic of transmitting light having a wavelength of 1554 nm, light having a wavelength of 1554 nm is transmitted by the rod lens 3
The light travels in the optical path 6 along the optical path 40 and enters the optical isolator 32. When the optical path 43 is traveled after traveling through the optical path 42 in the rod lens 6, the light travels in the optical isolator 32 in the forward direction, so that the light passing through the optical path 43 travels through the optical paths 41 and 38. It is incident on the fiber 34. On the contrary, the wavelength 1554 incident from the optical fiber 34
The light of nm travels along an optical path 38 in the rod lens 35, an optical path 41 in the rod lens 36, and an optical path 43 in the optical isolator 32. However, since the light splits into the ordinary light and the extraordinary light in the optical isolator 32, the light travels in the rod lens 36 and the rod lens 35, but this light does not enter the optical fiber 33.

On the other hand, the wavelength 1 incident from the optical fiber 33
The light of 480 nm travels through the rod lens 35 and the optical path 39. Since the filter 37 reflects the light having the wavelength of 1480 nm, the light having the wavelength of 1480 nm is reflected and enters the optical fiber 34 through the optical path 38. On the contrary, the optical fiber 34
The light incident from the rod lens 35 travels along the optical path 38 and the optical path 39, and enters the optical fiber 33.

By thus constructing the optical component by integrating the optical isolator 32 and the filter 37 having the wavelength selecting function, the light having the wavelength of 1480 nm can pass through the inside of the optical component regardless of its direction. But wavelength 15
Since the light of 54 nm passes through the optical isolator 32, its passage direction is restricted. Therefore, it is possible to obtain the effect that the optical component having two or more functions can be constructed extremely compactly. The optical isolator 32
Although the optical functional component integrated with is the filter 37, it goes without saying that the optical functional component integrated with may be any optical component.

[0021]

As described above, according to the present invention, a birefringent crystal is provided on one side of one lens, and a half-wave plate is provided between the lens and the birefringent crystal so as to cover half the area of the lens. A reflecting mirror is provided on the other side of the lens, and the polarization planes of the incident light and the outgoing light are π / 8 + Nπ / 4 (N
= 0, 1, ...,) The plate-like magneto-optical crystal whose length is determined so as to be different is provided, and the light beam incident so as to pass through the half-wave plate is reflected by the reflecting mirror, By configuring the optical isolator so that light is output through the inside of the plate, one birefringent crystal, a lens, and a magneto-optical crystal are used by being transmitted twice. Can be halved. Further, since the optical fiber has an array structure, optical coupling can be easily performed by adjusting the optical axes of the optical fiber array and the lens. Further, since the optical fiber array is provided on only one side, the area for drawing out the optical fiber is reduced when the optical isolator is mounted, so that there is an effect that it contributes to downsizing of a device incorporating the optical isolator.

By using the aspherical lens, the coupling loss can be reduced, and the reflected return light can be reduced by providing the tip of the optical fiber array with the oblique polishing. Furthermore, the effect that multi-functionalization can be realized by incorporating an optical component is also obtained.

[Brief description of drawings]

FIG. 1 is a structural cross-sectional view of a reflective optical isolator according to a first embodiment of the present invention, showing a change in optical path and polarization of light when the light travels in a forward direction.

FIG. 2 is a cross-sectional view of the configuration of a reflective optical isolator according to the first embodiment of the present invention, showing changes in the optical path and polarization of light when the light travels in the opposite direction.

FIG. 3 is a sectional view showing the configuration of a reflective optical isolator according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing the configuration of an optical component according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional optical isolator.

[Explanation of symbols]

 1, 2 optical fibers 3 optical fiber array 4 rutile crystal 5 1/2 wavelength plate 6 rod lens 7 garnet crystal 8 reflecting mirror 9 glass plate 10 magnet 11-18 light 21-28 light 30 aspherical lens 31 anti-reflection film on one side Glass plate provided with 32 optical isolator 33, 34 optical fiber 35, 36 rod lens 37 filter 38-43 optical path

Claims (5)

[Claims] 1. A birefringent crystal, a lens for converting light transmitted through the birefringent crystal into parallel light, and a plane of polarization of the parallel light is π / 8 + Nπ / 4 (N = 0, 1 ,. .) Rotating the magneto-optical crystal, a reflector that reflects the light transmitted through the magneto-optical crystal and makes it incident on the magneto-optical crystal again, and a polarization plane of the light reflected by the reflector and transmitted through the lens. Optical isolator composed of rotating optical or birefringent crystal 2. An optical fiber array in which first and second optical fibers are aligned in parallel is provided, and the light incident on the birefringent crystal from the first optical fiber is again the second light from the birefringent crystal. The optical isolator according to claim 1, wherein a lens, a magneto-optical crystal, a reflector, and an optical rotatory crystal or a birefringent crystal are arranged so as to be incident on the fiber. 3. The optical isolator according to claim 2, wherein the lens is a gradient index rod lens or an aspherical lens having a numerical aperture larger than the numerical apertures of the first and second optical fibers. 4. The optical isolator according to claim 2, wherein the tip of the optical fiber array is obliquely polished. 5. An optical component in which the optical isolator according to claim 1 and an optical functional component are incorporated into one.