JP3099854B2 - Optical passive components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication component, and more particularly to an optical passive component.

[0002]

2. Description of the Related Art Conventionally, an optical coupling device used in an optical transmission system, for example, an optical fiber amplifier is constructed by connecting respective components as shown in FIG . In FIG.
Is a wavelength multiplexer, 25 is an optical isolator, 26 to 30 are single-mode optical fibers, 31 is a connecting portion, 32 and 23 are arrows indicating the direction in which the signal light travels, and 34 is an arrow indicating the direction in which the pumping light advances. And are connected as shown in the figure.

An excitation light having a wavelength of 1480 nm incident on an optical fiber 30 from an excitation semiconductor laser (not shown) travels along an arrow 34. The excitation light from the wavelength multiplexer 24 enters the optical fiber 27. The excitation light that has passed through the connecting portion 31 and entered the optical fiber 28 enters the isolator 25. The light passing through the optical isolator 25 enters an optical fiber 29 connected to an erbium-doped optical fiber (not shown), and enters an erbium-doped optical fiber (not shown).

On the other hand, signal light having a wavelength of 1550 nm travels along the optical fiber 26 in the direction of arrow 32 and enters the optical fiber 27 via the wavelength multiplexer 24. The signal light passes through the connection point 31 and the optical fiber 28, enters the optical isolator 25, is coupled to the optical fiber 29, enters the erbium-doped optical fiber (not shown), and is amplified. Optical isolator
The reflector 25 is used to reduce reflected return light and suppress oscillation.

FIG . 5 is a diagram showing the internal configuration of the optical isolator 25 and the like. In FIG. 5 , 41 and 42 are optical fibers, 43 and 44 are lenses, 45 and 46 are birefringent crystals,
47 magneto-optical crystal 48 is half-wave plate, 49 is a magnet, is arranged as shown in Figure 5. Optical isolator
The light emitted from the optical fiber 41 is transmitted to the lens 43 by the lens 43.
Is converted into parallel rays by the birefringent crystal 45 and the magneto-optical crystal 4.
After passing through the 7, 1/2 wavelength plate 48 and the birefringent crystal 46, the light is condensed by the lens 44 and coupled to the optical fiber 42.
In this way, a configuration is adopted in which light once emitted from the optical fiber is subjected to an optical action and is then incident on the optical fiber again. In this configuration, not only the optical isolator 25 but also the wavelength multiplexer 24 has the same configuration.

[0006]

However, in the optical fiber amplifier according to the above-mentioned conventional configuration, two or more lenses are required for each optical component in order to configure each optical component. There is a problem that.

Further, since a process for fusion splicing each optical component is required, and a space for optical fiber storage after connection is required, an optical fiber is required to have a large volume as a result. There is a problem that the amplifier cannot be reduced in size.

An object of the present invention is to provide a small-sized optical fiber amplifier in consideration of such a problem of the conventional optical fiber amplifier, reducing the number of components of the optical part.

[0009]

According to the present invention, there are provided first to third aspects.
, An input / output optical fiber, a birefringent crystal, a lens that converts incident light into substantially parallel light, and a magnetic field that causes the plane of polarization of the incident light to be ｛π / 8 + Nπ / 4 (N = 0, 1,.・) A magneto-optical crystal that rotates by｝, a filter that reflects light of a specific wavelength, and a light reflector that is provided at an angle to the optical axis,
An optical passive component having a configuration arranged in this order, wherein a half-wave plate is provided between the birefringent crystal and the lens so as to partially cover an optical path.

[0010]

The light of a specific wavelength emitted from the first optical fiber passes through the half-wave plate, is reflected by the filter, and enters the third optical fiber. Similarly, light of another wavelength emitted from the second optical fiber passes through the half-wave plate, is reflected by the reflector, and enters the third optical fiber.

As described above, by using one lens and providing the reflection plate at an inclination outside the filter, the optical isolator function and the multiplexing function can be realized with a small number of parts, and the optical axis at the time of assembly is realized. Adjustment can be simplified.

[0012]

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

FIG. 1 is a front view (a) and a plan view (b) showing the configuration of an optical passive component according to a first embodiment of the present invention.
FIG. 2 is a perspective view showing the structure of a part of the optical fiber array.

In the figures, 1-3 are optical fibers, 4 is a glass plate, 5 is a birefringent crystal, 6 is a half-wave plate, 7 is a lens, 8 is a garnet crystal, 9 is a glass plate, 10 is a filter, 11 is a reflector, 12 is a magnet, and 13 to 15 are optical paths.

More specifically, in FIG. 2, the optical fibers 1, 2, and 3 are closely aligned on a glass plate 4 and aligned in a parallel (x-direction). The tip is tilted by 8 degrees in the thickness direction of the glass plate 4 (the tip surface of the optical fiber array forms an angle of 8 degrees with the xy plane),
An optical fiber array is formed by mirror polishing the tip.
By tilting the tip 8 degrees, reflected return light from the tip is removed. Optical axis of rutile crystal 5 (C
The rutile crystal 5 is adhered and fixed to the tip of the optical fiber array so that the axis is parallel to the yz plane. At this time, in the light emitted from the optical fiber, ordinary light and extraordinary light are separated in a direction (y direction) orthogonal to the alignment direction (x direction) of the optical fibers. At this time, the polarization direction of the ordinary light is in the X direction, and the polarization direction of the extraordinary light is in the YC plane. Since the refractive index of the rutile crystal 5 is large, an antireflection film is provided. In order that the light emitted from the optical fibers 2 and 3 may pass through the half-wave plate 6,
A wave plate 6 is attached to the rutile crystal 5.

The optical fiber array constructed as described above has a converging rod lens 7 as shown in FIG.
4 degrees. By tilting the optical fiber array, reflection from the end surface of the convergent rod lens 7 can be prevented, and the return loss can be set to 50 dB or more. A garnet crystal 8, a glass plate 9, and a wavelength filter 10 are bonded and fixed to the other end surface of the converging rod lens 7 in this order. Since the refractive index of the garnet crystal 8 is as large as about 2.2, an antireflection film is provided on the surface thereof. When the garnet crystal 8 and the filter surface of the wavelength filter 10 are in close contact with each other, there is a high possibility that the transmittance will decrease due to the interaction between the respective interference films. To prevent this, a garnet crystal 8
A glass plate 9 is provided between the filter and the wavelength filter 10. Further, a cylindrical magnet 12 is provided outside the garnet crystal 8 so as to transmit a magnetic field perpendicular to the garnet crystal 8. When light having a center wavelength of 1550 nm is transmitted through the garnet crystal 8, its polarization plane rotates 22.5 degrees counterclockwise. The positions of the converging rod lens 7 and the optical fiber array are adjusted so that the light emitted from the optical fiber 2 is reflected by the wavelength filter 10 and coupled to the optical fiber 1, and both are fixed. The inclination of the reflector 11 is adjusted and fixed so that the light emitted from the optical fiber 3 enters the optical fiber 1.

Next, the operation of the thus configured optical passive component will be described. The light travels in the horizontal direction of the paper, and the polarization state of the light is the normal to the light (a plane perpendicular to the paper).
Indicates the polarization direction viewed from the left, and only one polarization is described. The clockwise rotation is clockwise, and the counterclockwise rotation is counterclockwise. The behavior of the light within the converging rod lens 7 described the behavior of the center of the ray.

The wavelength 1550 n incident from the optical fiber 3
m is separated into ordinary light and extraordinary light by the rutile crystal 5, and
The polarization plane is rotated counterclockwise by 45 degrees by the half-wave plate 6.
After that, the wavelength 1550 incident on the converging rod lens 7
The light of nm is converted into parallel light while passing through the optical path 15. Light having a wavelength of 1550 nm that travels along the optical path 15 passes through the garnet crystal 8 and the glass plate 9, is reflected by the wavelength filter 10, and is collected again by the rod lens 7. When passing twice through the garnet crystal 8 to which the magnetic field is applied by the magnet 12, the polarization plane of the light having the wavelength of 1550 nm rotates counterclockwise by 45 degrees. The light reflected by the wavelength filter 10 is
Continue. The ordinary light and the extraordinary light whose polarization planes are rotated by 90 degrees by the half-wave plate 6 and the garnet crystal 8 are polarization-synthesized by the rutile crystal 5 and enter the optical fiber 1.

On the other hand, light having a wavelength of 1550 nm incident from the optical fiber 1 is separated into ordinary light and extraordinary light by the rutile crystal 5 and converted into parallel light by the convergent rod lens 7.
When the light is reflected by the wavelength filter 10 and passes through the garnet crystal 8 twice, the polarization plane rotates 45 degrees counterclockwise. The light reflected by the wavelength filter 10 travels along the optical path 15 and
Since the polarization plane is rotated clockwise by 45 degrees in the wavelength plate 6, the wavelength
In a tall, the plane of polarization does not rotate. Since the ordinary light and the extraordinary light incident on the rutile crystal 5 are not synthesized by the rutile crystal 5, both the ordinary light and the extraordinary light are hardly coupled to the optical fiber 3. With the above behavior, a function like an optical isolator can be realized.

Similarly, the wavelength 1 incident from the optical fiber 2
The 480 nm light is separated into ordinary light and extraordinary light by the rutile crystal 5, and is rotated about 48 degrees counterclockwise by the half-wave plate 6. The light is converted into parallel light by the converging rod lens 7 while passing through the optical path 14. The light transmitted through the garnet crystal 8, the glass plate 9 and the filter 10 is reflected by the reflection plate 11,
Pass 3 The polarization plane of the light that has passed through the half-wave plate 6 once and transmitted through the garnet crystal 8 twice is rotated by about 96 degrees, so that the light is polarized and synthesized by the rutile crystal 5 and is coupled to the optical fiber 1. Due to the rotation of more than one degree, some are not combined and are lost.

The wavelength 1550 n incident from the optical fiber 3
m is coupled to the optical fiber 1, and light having a wavelength of 1550 nm incident from the optical fiber 1 is coupled to the optical fibers 2 and 3.
Therefore, an optical isolator can be formed for signal light having a wavelength of 155 nm. Similarly, wavelength 1
It also has some but not complete isolator function for 480 nm light.

The use of light of two wavelengths whose wavelengths are close to each other slightly increases the insertion loss of one of them. However, an optical passive component having the functions of an optical isolator and an optical multiplexer can be formed. . Further, as described above, when the garnet crystal 8 provided with the antireflection film and the wavelength filter 10 are brought close to each other, mutual interference between the dielectric multilayer films may occur, and the loss may increase. By inserting the glass plate 9 between the two to prevent mutual interference, an effect of reducing the coupling loss is obtained.

FIG. 3 is a block diagram showing a second embodiment of the present invention. In FIG. 3, reference numeral 16 denotes a 波長 wavelength plate, and the glass plate 9 is omitted instead of the glass substrate of the filter 10. The 波長 wavelength plate 16 is arranged between the garnet crystal 8 and the reflection plate 11. The rest is almost the same as the configuration of FIG. Therefore, the light having a wavelength of 1550 nm incident from the optical fiber 3 is transmitted through the optical path 1 similarly to the first embodiment.
7, the light is reflected by the filter 10 and coupled to the optical fiber 1 through the optical path 18. On the other hand, light having a wavelength of 1480 nm emitted from the optical fiber 1 is separated into ordinary light and extraordinary light by the rutile crystal 5, and then enters the rod lens 7 to be converted into parallel light. The parallel light passes through the garnet crystal 8, the wavelength filter 10, and the quarter-wave plate 16 twice before being reflected by the reflection plate 11 and entering the rod lens 7 again.
The light having a wavelength of 1480 nm again incident on the rod lens 7 is 1
The light is rotated clockwise by about 45 degrees by the half-wave plate 6. Therefore, 1
By optimally setting the optical axis direction of the 波長 wavelength plate 16, 1
Optical path 1 of light having a wavelength of 1480 nm transmitted through half-wave plate 6
9 can be controlled so as to match the ordinary light and the extraordinary light of the rutile crystal 5. Thus, the wavelength 1480
If a quarter-wave plate 16 for nm is provided between the reflection plate 11 and the wavelength filter 10 and reciprocally passes, it can be used as a half-wave plate. Therefore, by setting the optical axis of the quarter-wave plate 16 optimally, the polarization plane of the light transmitted through the half-wave plate 6 is matched with the polarization direction of the rutile crystal 5, and ordinary light and extraordinary light are combined. As a result, optical coupling can be performed without loss. In this configuration, two lights having different wavelengths both have an isolator function regardless of the traveling direction of the light. When the traveling directions of light are different from each other, bidirectional transmission can be performed while maintaining the isolator function.

[0026]

As is apparent from the above description,
According to the present invention, since the optical isolator and the wavelength combiner can be constituted by one lens, the number of components can be reduced as compared with the prior art, and a compact optical passive component can be realized.

Further, the optical coupling can be easily performed by adjusting the optical axes of the optical fiber and the lens.

Further, by mirror-polishing the tip of the optical fiber obliquely and further providing the optical fiber at an angle to the lens, it is possible to reduce the reflected return light from the optical component.

By providing a glass plate between the two antireflection films, it is possible to prevent the transmittance from deteriorating due to the interaction between the interference films.

Also, a 1/4 distance between the reflector and the wavelength filter is provided.
By providing the wave plate, it is possible to perform bidirectional transmission while maintaining the isolator function.

Further, since the optical fiber is protruded to only one side, the routing area of the optical fiber when mounting the passive component for the optical fiber amplifier is reduced, so that the present invention contributes to the miniaturization of the optical fiber amplifier. The effect is also obtained.

[Brief description of the drawings]

FIG. 1 is a front view and a plan view showing the structure of an optical passive component according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a structure of an optical fiber array constituting the optical passive component according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a structure of an optical passive component according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a part of a connection configuration of optical components constituting a conventional optical fiber amplifier.

FIG. 5 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]

 1-3 optical fiber 4 glass plate 5 birefringent crystal 6 1/2 wavelength plate 7 lens 8 garnet crystal 9 glass plate 10 filter 11 reflector 12 magnet 13-15 optical path 16 1/4 wavelength plate 17-19 optical path

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-150524 (JP, A) JP-A-63-205636 (JP, A) JP-A-54-140813 (JP, A) JP-A 54-205 79056 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 27/28 G02B 27/10

Claims (4)

(57) [Claims] A first optical fiber for input and output and a third optical fiber for input and output;
A birefringent crystal, a lens that converts incident light into substantially parallel light,
A magneto-optical crystal that rotates the plane of polarization of the incident light by {π / 8 + Nπ / 4 (N = 0, 1,...)} Under a magnetic field, a filter that reflects light of a specific wavelength, and an optical axis A light reflector provided at an angle to the
An optical passive component, which is arranged in this order, wherein a half-wave plate is provided between the birefringent crystal and the lens so as to cover a part of an optical path. 2. An optical fiber array in which three optical fibers are arranged adjacent to each other with a flat plate interposed therebetween, and the ends thereof are obliquely mirror-polished, and the birefringent crystal is provided on the end surface of the optical fiber array. 2. The optical passive component according to claim 1, wherein a direction in which light emitted from the optical fiber is separated into ordinary light and extraordinary light by the birefringent crystal is orthogonal to an alignment direction of the optical fiber. 3. The optical passive component according to claim 1, wherein a glass plate is provided between the magneto-optical crystal and the filter. 4. The optical passive component according to claim 1, wherein a quarter-wave plate is provided between the magneto-optical crystal and the reflector.