JPH0667118A - Optical coupler - Google Patents

Abstract

PURPOSE:To provide the optical isolator of a small size which is half the number of parts of the conventional coupler and is simple in optical axis adjustment. CONSTITUTION:The multiplexer is provided with 4 pieces of optical fiber arrays 31-34, a double refraction crystal 4 provided on one side of one piece of lens 6, a halfwave plate 5 which exists between this lens 6 and the double refraction crystal 4 and covers half the area of the lens 6, a filter 36 which exists on the other one side of the lens 6 and reflects the light of a wavelength lambda1, a flat planar magneto-optical crystal 7 determined in length in such a manner that the planes of polarization of incident light and exit light are varied by about (pi/8+Npi/4 (N=0, 1,...) by the magnetization on the other end face of the filter 36 and a reflection plate 37. The multiplexer is so constituted that incident light lambda1 on the double refraction crystal 4 from the first optical fiber of the optical fiber array is reflected by the filter 36 and is made incident on the second optical fiber. The reflection plate 37 is so inclined that the incident light lambda2 of the wavelength on the double refraction crystal 4 from the first optical fiber passes the halfwave plate 5 and is made incident on the third optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical coupling device, and more particularly to an optical coupling device having an optical isolator function.

[0002]

2. Description of the Related Art Conventionally, an optical coupling device used in an optical processing system, for example, an optical fiber amplifier has been constructed by connecting optical components as shown in FIG. In FIG. 5, 51
Is a multiplexer, 52 is an optical isolator, 53 is a polarization combiner,
Reference numeral 54 is an erbium-doped optical fiber, 55-60 is a single-mode optical fiber, 61 and 62 are polarization-maintaining optical fibers, 63-65 are fusion spliced portions, 66 is an arrow indicating the direction in which excitation light travels, and 67 is output light. Is an arrow that indicates the direction of travel, and is connected as shown in the figure.

The light from the semiconductor laser (not shown) incident on each of the polarization plane optical fibers 61 and 62 from the two pumping semiconductor lasers (not shown) is combined by the polarization combiner 53 to the optical fiber 60. Incident. The excitation light enters the optical fiber 65 fusion-spliced to the optical fiber 60,
The light is output to the optical fiber 55 by the multiplexer 51 and is incident on the erbium-doped optical fiber 54 fusion-spliced to the optical fiber 55.
On the other hand, the light amplified by the erbium-doped optical fiber 54 enters the optical fiber 57 fusion-spliced with the optical fiber 56 via the multiplexer 51, passes through the optical isolator 52, and is directed from the optical fiber 58 in the direction of arrow 67. Output. In this way, the lights output from the two pumping semiconductor lasers are combined by the polarization combiner 53, input to the combiner 51 and the erbium-doped optical fiber 54, and the erbium optical fiber 54
An optical fiber amplifier can be constructed by extracting the light amplified by the multiplexer 51. Therefore, at least the multiplexer 5 is required to form the optical fiber amplifier.
1. The polarization combiner 53 and the optical isolator 52 are required, and the optical components are fusion-spliced to form an optical amplifier.

FIG. 6 is a diagram showing the structure of the optical isolator 52 in these optical components. In FIG. 6, 71,
Reference numeral 72 is an optical fiber, 73 and 74 are lenses, 75 and 76 are flat birefringent crystals, 77 is a magneto-optical crystal, 78 is an optical rotatory crystal or birefringent crystal, and 79 is a magnet. It is set up. In the optical isolator 52, the light output from the optical fiber 71 is converted into parallel rays by the lens 73, transmitted through the birefringent crystals 75, 76, the magneto-optical crystal 77, and the optical rotatory crystal 78, and then condensed by the lens 74. It is incident on 52. In this way, the light once emitted from the optical fiber is subjected to an optical action and is made incident on the optical fiber again. This configuration is an optical isolator 5
Not only 2 but also a multiplexer and a polarization combiner have the same configuration.

[0005]

However, it is said that the optical fiber amplifier having the above-mentioned conventional configuration has many components such as one optical component requiring two or more lenses in order to configure each optical component. There are challenges. Also,
There is a problem that the optical fiber amplifier occupies a large volume as a result of requiring the step of fusion splicing the respective optical components and the storage processing space of the optical fiber after the connection.

An object of the present invention is to provide a small-sized optical coupling device in which the components of the optical component are reduced and the optical axis can be easily adjusted in consideration of the problems of the conventional optical fiber amplifier. .

[0007]

The present invention includes the first to fourth aspects.
, An optical fiber for input and output, a birefringent crystal, a first lens for converting incident light into substantially parallel light, a filter for reflecting light of a specific wavelength, and a polarization plane of π for incident light by receiving a magnetic field. / 8
A magneto-optical crystal that rotates by + Nπ / 4 (N = 0, 1, ...) And a light reflection plate that is tilted with respect to the optical axis are arranged in this order. In the optical coupling device, a half-wave plate is provided between the refraction crystal and the first lens so as to cover a part of the optical path.

[0008]

The linearly polarized lights of specific wavelengths emitted from the first and second optical fibers and having orthogonal polarization planes are reflected by the filter, and then combined on the same optical axis by the birefringent crystal to form the third optical fiber. Inject the third optical fiber (or the fourth optical fiber)
Of the other wavelength emitted from the optical fiber of (1), is reflected by the light reflection plate, passes through the ½ wavelength plate, and enters the fourth optical fiber (or the third optical fiber).

As described above, by using one lens and tilting the reflector outside the filter, the optical isolator function and the demultiplexer function can be realized with a small number of parts, and the optical axis can be adjusted during assembly. Can be simplified.

[0010]

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

1 and 2 are cross-sectional views for explaining the function of the optical isolator in the first embodiment of the optical coupling device of the present invention. FIG. 1 shows the polarization when light is transmitted in the forward direction. FIG. 2 is a diagram for explaining changes in states and optical paths, and FIG. 2 is a diagram for explaining changes in polarization states and optical paths when light is transmitted in the opposite direction. FIG. 3 is a sectional view showing a configuration having both an optical isolator and an optical demultiplexer according to the first embodiment of the present invention. First, the operation of the optical isolator will be described.

1 and 2, basically, 1,
2 is an optical fiber, 3 is an optical fiber array, 4 is a birefringent crystal (rutile crystal), 5 is an optical rotatory crystal or birefringent crystal (quartz), 6 is a lens, 7 is a magneto-optical crystal (garnet crystal), 8 Is a reflector, 9 is a glass plate, 10 is a magnet, 1
1 to 18 and 21 to 28 are light rays.

More specifically, in FIG. 1, the optical fiber 1 and the optical fiber 2 are aligned in parallel on a glass plate having a thickness of 1 mm at a distance of 250 μm, and a glass plate having a thickness of 1 mm is placed on the glass plate. After the adhesive fixing, the tip is mirror-polished to form the optical fiber array 3. Thickness 1.3
A half-wave plate 5 having a plate thickness of 90 μm is attached to one half of one side of a rutile crystal 4 which is a birefringent crystal of mm, and a glass plate 9 having a plate thickness of 90 μm is attached to the other half. An antireflection film is provided on both surfaces of the rutile crystal 4 so that reflected light disappears when adhered. When the optical fiber array 3 and the rutile crystal 4 are bonded, the optical fiber 1 and the optical fiber 2 are aligned such that the boundary between the half-wave plate 5 and the glass plate 9 is located at the center of the optical fiber 1 and the optical fiber 2, and the optical fiber 2 is inserted into the optical fiber 2. Only the output light passes through the half-wave plate 5. A garnet crystal 7, which is a magneto-optical crystal having a thickness of about 170 μm, is attached to the end surface of the gradient index rod lens 6, and a reflector 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 transmitted perpendicularly to the garnet crystal 7. When light with a central wavelength of 1554 nm passes 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.
The two-wave plate 5 and the glass plate 9 are bonded and fixed.

Next, the operation of the optical isolator constructed as described 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 (a plane perpendicular to the paper). Also,
Rotation is clockwise clockwise and counterclockwise counterclockwise.
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 light 11 and the extraordinary light 12 by the rutile crystal 4, and the optical path of the extraordinary light 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 are reflected by the reflector 8 and again pass through the garnet crystal 7.
Combined with 2.5 degrees, it rotates 45 degrees to the left. By being reflected by the reflector 8, 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. Light 15 transmitted through the garnet crystal 7
And 16 are incident on the half-wave plate 5 while being condensed by the rod lens 6. The ½ wavelength plate 5 has a function of emitting linearly polarized light incident at an angle θ with the optical axis thereof as linearly polarized light forming an angle of −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 polarization states of the light 15 and the light 16 are different when they pass through the half-wave plate 5. The polarized light rotates further 45 degrees to the left. Since 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, in FIG. 2, 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. 1/2 wave plate 5
When the plane of polarization rotates clockwise when passing through,
It is converted into parallel light by the rod lens 6. Rod lens 6
The light 23 and the light 24 traveling inside are transmitted through the garnet crystal 7 twice before and after being reflected by the reflection plate 8, so that the polarization plane is rotated counterclockwise by 45 degrees at this time. By being reflected by the reflector 8, the light 23 is in the optical path of the light 25, and the light 24 is the light 26.
Follow the optical path. Further, the light 25 and the light 26 travel while being condensed by the rod lens 6. When the light transmitted through the glass plate 9 passes through the rutile crystal 4, the light 27 travels as ordinary light and thus goes straight, and is not incident on 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.

As described above, it is possible to obtain 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.

Next, an embodiment in which the functions of the optical isolator and the demultiplexer are combined will be described with reference to FIG. The upper diagram of FIG. 3 is a diagram in the xz direction, and the lower diagram is y.
It is a figure of-z direction. In FIG. 3, the basic configuration is described as follows: 31 and 32 are optical fibers, 33 and 34 are polarization-maintaining optical fibers, 35 is a spacer, 36 is a filter, 37
Is a half mirror, 38 is a lens, 39 is a light-absorbing part, 40-
Reference numeral 46 is light, 47 is a light receiving element, and the others are the same as those described above.

The optical fibers 33 and 34 are polarization-maintaining fibers and are commonly called PANDA fibers. Linearly polarized light is incident on the optical fiber 33 and the optical fiber 34 from a semiconductor laser for excitation (not shown). The optical fibers 33 and 34 are arranged so that the light output from the optical fiber 33 becomes ordinary light in the rutile crystal 4 and the light output from the optical fiber 34 becomes extraordinary light in the rutile crystal 4. Since the optical path of extraordinary light is tilted in the rutile crystal 4,
The light 40 emitted from the optical fiber 33 and the light 41 emitted from the optical fiber 34 pass through the rutile crystal 4 and travel in the rod lens 6 along the optical paths 42a and 42b, respectively. Since the light output from the optical fibers 33 and 34 has a wavelength of 1480 nm, the lights 42a and 42b converted into parallel rays by the rod lens 6 have a wavelength of 1480n.
It is reflected by the filter 36 that reflects the light of m. Since the filter 36 is adhered to the spacer prism 35 which is inclined by 3 degrees, the light reflected by the filter 36 is reflected in the optical path 4 respectively.
When passing through the rutile crystal 4 again through the optical path 3a and the optical path 43b, they overlap with each other and enter the optical fiber 32. The optical fiber 32 is connected to an erbium-doped optical fiber (not shown).

The light with a wavelength of 1554 nm amplified by the erbium-doped optical fiber enters the rod lens 6 from the optical fiber 32, passes through the optical path 44, passes through the filter 36 that transmits the light with a wavelength of 1554 nm, and passes through the garnet crystal 7. pass. Most of the light that has passed through the garnet crystal 7 is reflected by the half mirror 37 that reflects 99%, passes through the garnet crystal 7, the filter 36, and the spacer prism 35 again, and is then condensed by the rod lens 6 to obtain the optical path 4.
5, and enters the optical fiber 31 through the half-wave plate 5 and the rutile crystal 4. The coupling from the optical fiber 32 to the optical fiber 31 is the forward coupling of the optical isolator. Therefore, the light emitted from the optical fiber 31 does not enter the optical fiber 32.

The remaining 1% of the light transmitted through the half mirror 37 enters the light receiving element 47 through the rod lens 38 and the optical path 46a. Since 1% of the light 46b that has entered the rod lens 6 from the optical fiber 31 travels to the rod lens 38, the black light-shielding portion 39 is connected to the rod lens 38 so that this light does not enter the light receiving element 47. It is provided in the section.

Since the four optical fibers 31 to 34 form an optical fiber array, the optical coupling between the optical fibers may be performed by positioning the optical fiber array with respect to the rod lens 6 or by performing half-mapping. This can be easily performed by adjusting the inclination of the mirror 37 or the filter 36.

Further, in order to reduce the reflected return light from the end faces of the optical fibers 31 and 32, the tip of the optical fiber is set to 8 mm.
The end surface of the rod lens 6 on the side to be connected to the optical fiber is also inclined by 8 degrees while being inclined and polished. The tilt direction of the end surface of the rod lens 6 and the tilt direction of the spacer prism 35 have a twisted relationship with each other, and reflection between both surfaces is eliminated.

When a polarization combiner is not required, the specification can be easily changed by changing the number of PANDA fibers used on the input side to one without changing the basic structure.

FIG. 4 is a sectional view showing the construction of an optical coupling device according to the second embodiment of the present invention. In FIG. 4, the basic structure is described. 48 is an oblique cut portion of the lens, 49 is a reflector,
Others are the same as the embodiment of FIG. The light having a wavelength of 1554 nm output from the optical fiber 32 is converted into parallel light by the rod lens 6, and then passes through the spacer prism 35 and the filter 36. Half mirror 37 that transmits 1% of light
The light that has passed through is condensed by the rod lens 38 and enters the light receiving element 47. On the other hand, the light output from the optical fiber 31 and having a wavelength of 1554 nm that has passed through the inner half mirror 37 is condensed by the rod lens 38. This light is received by the light receiving element 4
In order to prevent 7 incidents, a part of the end surface of the rod lens 38 is obliquely cut to provide a reflection plate 49 so that the condensed light is reflected and does not enter the light receiving element 47.

[0026]

As is apparent from the above description,
The present invention can reduce the number of components as compared with the conventional one.

Optical adjustment can be easily performed by adjusting the optical axes of the optical fiber and the lens.

Further, a polarization combiner using one lens,
When the multiplexer and the optical isolator are configured and the light receiving element is provided on the other end surface of the lens, it is possible to realize a multi-function that a monitor function can be added without increasing the number of parts.

Further, since the optical fiber is provided on only one side, the area around which the optical fiber for the optical fiber amplifier is laid out is reduced when mounting the optical part for the optical fiber amplifier. The present invention also has an effect of contributing.

[Brief description of drawings]

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

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

FIG. 3 is a configuration cross-sectional view of an optical coupling device according to a first embodiment of the present invention.

FIG. 4 is a sectional view showing the configuration of an optical coupling device according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a part of a connection configuration of optical components constituting a conventional optical fiber amplifier.

FIG. 6 is a diagram showing a configuration of an optical isolator which is one of optical components constituting a conventional optical fiber amplifier.

[Explanation of symbols]

 1 Optical Fiber 2 Optical Fiber 3 Optical Fiber Array 4 Rutile Crystal 5 1/2 Wave Plate 6 Rod Lens 7 Garnet Crystal 8 Reflector 9 Glass Plate 10 Magnet 11-18 Light 21-28 Light 31, 32 Optical Fiber 33, 34 Polarization Surface preserving optical fiber 35 Spacer prism 36 Filter 37 Half mirror 38 Rod lens 39 Light-shielding portion 40 to 46 light 47 Light receiving element 48 Diagonal cut portion of lens 49 Reflector plate

Claims (6)

[Claims] 1. First to fourth optical fibers for input and output,
A birefringent crystal, a first lens that converts incident light into substantially parallel light, a filter that reflects light of a specific wavelength, and a polarization plane of incident light that receives a magnetic field to be π / 8 + Nπ / 4 (N = 0, 1, ...
.) And a light reflection plate tilted with respect to the optical axis are arranged in this order, and the birefringent crystal and the first lens are combined. An optical coupling device, characterized in that a half-wave plate is provided so as to cover a part of the optical path therebetween. 2. A first to a fourth optical fiber for input and output,
A birefringent crystal, a first lens that converts incident light into substantially parallel light, a filter that reflects light of a specific wavelength, and a polarization plane of incident light that receives a magnetic field to be π / 8 + Nπ / 4 (N = 0, 1, ...
A magneto-optical crystal that rotates only by ()), a half mirror that is inclined with respect to the optical axis, a second lens that converges parallel light that has passed through the half mirror, and a light receiving element that detects this converged light. , Having a configuration arranged in this order,
An optical coupling device, wherein a half-wave plate is provided between the birefringent crystal and the first lens so as to cover a part of an optical path. 3. The linearly polarized lights having specific wavelengths emitted from the first and second optical fibers and having orthogonal polarization planes orthogonal to each other are reflected by the filter, and then are combined on the same optical axis by the birefringent crystal. The light having another wavelength which is incident on the optical fiber No. 3 and is emitted from the third optical fiber (or the fourth optical fiber) is reflected by the light reflection plate or the half mirror to be the half-wave plate. The first to fourth optical fibers for entrance / exit are arranged so as to pass through and enter the fourth optical fiber (or the third optical fiber). Item 2. The optical coupling device according to item 2. 4. A polarization-maintaining optical fiber as the first and second optical fibers, and an optical fiber array in which the tips of the first to fourth optical fibers are aligned integrally. Item 3. The optical coupling device according to item 3. 5. Outgoing from the third and fourth optical fibers,
A shielding member is provided between the second lens and the light receiving element so as to shield either one of the light that has passed through the half mirror and converged by the second lens. The optical coupling device according to claim 2. 6. The second lens comprises a converging rod lens in which a part of a surface facing the light receiving element is obliquely cut so as to shield a part of light incident on the light receiving element. The optical coupling device according to claim 2, which is characterized in that.