JP2002277691A - Optical fiber with lens, its assembling method, and optical fiber with optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a miniaturized and inexpensive optical fiber 10 with lens capable of preventing reflected return light from being made incident on an LD. SOLUTION: In the optical fiber with lens forming a wedge-like inclined face in the end part of the optical fiber and forming a semi-cylindrical curve or a plane or an acute angle in the tip part of the inclined face, an optical isolator consisting of at least one Faraday rotor and at least one polarizer is fixed to the tip part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber with a lens used for optical coupling between a light emitting source used for optical communication and an optical fiber, and an assembling method thereof.

[0002]

2. Description of the Related Art As a light emitting source for optical communication, a laser diode (hereinafter referred to as an LD) or a light emitting diode is used. The pattern of the light emitted from the LD has an elliptical beam shape in which the light distribution is not a Gaussian distribution in a circular shape but is different in the vertical and horizontal directions. A typical LD having a wavelength of 980 nm has a pattern of emitted light having an aspect ratio of 2.5 to 4: 1. LD with such a large aspect ratio
Since the optical fiber with a lens used for coupling between the optical fiber and the optical fiber is an optical fiber with a wedge lens, the optical fiber with a wedge lens will be described below.

As shown in FIG. 6, a conventional optical fiber with a wedge-shaped lens is provided with a pair of inclined surfaces 11 symmetrical with respect to a core axis 12 of the optical fiber to form a wedge shape. 13 was provided with a semi-cylindrical curved surface (see JP-A-8-86923).

Further, as shown in FIG. 7, there is an optical fiber with lens 10 in which a tip portion 13 of a wedge-shaped lens is processed into a plane inclined at an angle δ with respect to a plane perpendicular to the core axis 12. The optical fiber with lens 10 has a core axis 12 of the optical fiber as in FIG.
(See Japanese Patent Application Laid-Open No. 2000-347048).

Further, as shown in FIG. 8, in a structure in which light emitted from the LD 50 passes through the lens 41 and is condensed to enter the core of the optical fiber 45, the optical fiber 45 is held and fixed to the ferrule 43. The end surface 44 is a flat surface inclined at a fixed angle with respect to the core axis 12, and the surface thereof has an optical isolator 4 composed of at least one Faraday rotator and at least one polarizer.
2 was fixed (see JP-A-6-88926).

[0006]

However, in the above-mentioned conventional optical fiber with lens 10 shown in FIG.
The light emitted from the LD 50 is reflected by the tip portion 13 and
Reflected light returning from the end of the optical fiber line and entering the LD 50,
However, there is a problem that the noise emitted from the laser beam becomes unstable and becomes unstable, and eventually the LD 50 itself is destroyed.

[0007] In the conventional optical fiber with lens 10 shown in FIG. 7, in order to solve the problem of FIG.
3 is formed at a plane inclined by an angle δ with respect to the core axis 12, the light emitted from the LD 50 does not return to the LD 50 even if reflected by the plane of the tip portion 13, but from the end of the optical fiber line. The returned reflected light enters the LD 50, which causes noise on the light emitted from the LD 50, and has a problem that only unstable light can be emitted as in FIG.

Further, in the conventional method shown in FIG.
The light emitted from 0 does not return to the LD 50 even if it is reflected at the end face of the optical isolator 42, and the reflected return light returned from the end of the optical fiber line is blocked by the optical isolator 42 and enters the LD 50. However, the use of the lens 41 and the ferrule 43 increases the size of an LD module using the same, and the use of an LD 50 having a high aspect ratio results in a single lens 4.
With only one, a light beam having an elliptical cross-sectional shape cannot be corrected to a circular shape in order to efficiently enter the core of the optical fiber, and a plurality of lenses 41 must be used, and the LD module using the same becomes even larger. The problem had arisen.

Further, in the device shown in FIG. 8, since the optical isolator 42 made of an expensive material has a larger area than the end face of the optical fiber, there is a problem that the cost cannot be reduced.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned conventional problems, the present invention provides an optical fiber with a lens having a wedge-shaped inclined surface formed at the end of the optical fiber. An optical isolator comprising at least one Faraday rotator and at least one polarizer is fixed.

The ridgeline of the tip is inclined with respect to a plane perpendicular to the core axis of the optical fiber.

Further, a magnet is arranged on the outer periphery of the Faraday rotator.

A wedge-shaped inclined surface is formed at an end of the optical fiber, and an optical isolator including at least one Faraday rotator and at least one polarizer is assembled in advance. The fiber is fixed to the tip of the inclined surface using an adhesive matched with the refractive index of the core.

Further, in an optical fiber with an optical isolator having an end portion whose coating is removed and an optical isolator fixed to the end portion, when viewed from the optical fiber end side, the outer peripheral portion of the optical isolator is the outer peripheral portion of the optical fiber. It is characterized by being more inside.

[0015]

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

FIGS. 1A and 1B are a plan view and a side view showing an optical fiber with lens 10 according to an embodiment of the present invention. As is well known, an optical fiber includes a core portion having a circular cross section in which light is confined, and a cladding portion which concentrically surrounds the core portion.

At the end of the optical fiber with lens 10, there is provided a pair of wedge-shaped inclined surfaces 11, and a front end of a planar shape inclined at an angle δ with respect to a surface perpendicular to the core axis 12 at the end of the inclined surface 11. An optical isolator 20 having a polarizer 21, a Faraday rotator 22, and a polarizer 23 adhered and fixed in this order is fixed to the tip 13.

Since the optical isolator 20 is fixed to the optical fiber with lens 10, the light emitted from the LD is inclined at an angle δ with respect to the plane perpendicular to the core axis 12 at the end face of the optical isolator 20. LD even if reflected
The reflected return light returned from the end of the optical fiber line is not blocked by the optical isolator 20 and does not enter the LD.

Furthermore, there is no need to use a lens or a ferrule, and the LD module using the optical isolator with a lens of the present invention can be reduced in size, thereby realizing a lower cost.

The angle δ is preferably in the range of 4 to 12 °, and if it is less than 4 °, light reflected on the surface will return to the LD. If it exceeds 12 °, the insertion loss will be extremely large. It is preferable to be within the above-mentioned range, because it deteriorates. Still more preferably, it is desirable to be within the range of 6 to 10 °.

The angle θ of the inclined surface 11 is an angle with respect to a surface perpendicular to the inclined surface 11 and the core axis 12 of the optical fiber.
It is desirable that the angle is in the range of <70 <70. This is because the optical coupling efficiency is extremely deteriorated when the angle θ is out of this range.

Since the angle δ of the tip 13 and the angle θ of the inclined surface 11 are greatly affected by the characteristics of the LD used, it is necessary to set a narrower tolerance within the above range depending on the type of LD. is necessary.

The optical fiber with lens 10 of the present invention is mainly applied to a single mode optical fiber, but can also be applied to a multimode optical fiber. The present invention can also be applied to a plurality of parallel processing optical fibers.

The core portion of the optical fiber with lens 10 of the present invention is a lens whose optical coupling efficiency is further improved by using a so-called core-enlarged optical fiber whose core portion is enlarged in advance at its distal end portion 13. The attached optical fiber 10 can be obtained.

Next, in the optical isolator 20 used in the present invention, a flat Faraday rotator 22 is disposed between two polarizers 21 and 23 as optical components, and each is attached with a light transmitting adhesive. I'm matching.

The Faraday rotator 22 is a self-biased Faraday rotator to which a saturation magnetic field has been applied in advance, and has a thickness for rotating the polarization plane of light having a predetermined wavelength by 45 ° at the saturation magnetic field intensity. It is set to have.

The two polarizers 21 and 23 are absorption polarizers or birefringent crystals. In the case of using an absorption polarizer, the transmission directions of the two polarizers 21 and 23 are adjusted so as to be shifted in the 45 ° rotation direction. Also,
In order to efficiently couple the light emitted from the LD to the optical fiber, the optical isolator 20 is cut into a rectangle, and the long side thereof is configured to be parallel to the ridge direction of the tip portion 13. Further, the transmission polarization direction of the incident side polarizer 21 of the optical isolator 20 is configured to be parallel to the tilt direction.

The optical isolator 20 is manufactured by a process of performing optical adjustment with a large-sized optical element and then cutting out a large number of pieces into a desired size. Here, if an attempt is made to construct the optical isolator 20 at lower cost, the number of optical isolators 20 to be cut out is necessarily larger and smaller.

As for the method of joining the optical isolator 20 and the optical fiber with lens 10, it is desirable to use a light-transmitting adhesive 30 having substantially the same refractive index as the core of the optical fiber. Since the refractive index of the optical fiber core is set near 1.470, the refractive index of the light transmitting adhesive 30 is 1.35.
It is desirably within the range of 1.60 to 1.60. Within this range, the reflectance from the end face of the optical fiber is sufficiently small, within 0.1%, so that the optical coupling efficiency does not decrease.

Here, it is desirable to use an epoxy-based adhesive or an ultraviolet-curable adhesive in consideration of the reliability of the bonding surface as the light-transmitting adhesive 30, and further use an ultraviolet-curable adhesive from the viewpoint of bonding workability. It is more preferable to use.

Next, a side view as another embodiment of the present invention is shown in FIGS.

FIG. 2 (a) shows that the tip 13 of the optical fiber with a lens has an acute angle, and the tip of the optical isolator 2
Numeral 0 is bonded and fixed with the light transmitting adhesive 30.

FIG. 2 (b) shows an inclined surface 11b further provided with an inclined surface 11b on the distal end side, and a distal end portion 13 having a semi-cylindrical curved surface.
Are bonded and fixed with a light-transmitting adhesive 30.

Further, in FIG. 2 (c), the inclined surface 11 has a curved surface at the end portion 13, and an optical isolator 20 is bonded and fixed to the end of the inclined surface 11 with a light transmitting adhesive 30.

FIG. 2D shows the tip 1 of the inclined surface 11.
3 has a flat surface, and an optical isolator 20 is adhered and fixed to the end of the optical isolator 20 with a light transmitting adhesive 30.

Next, FIGS. 3A to 3C are plan views showing another embodiment of the present invention.

In FIG. 3A, a curved or flat chamfer 17 is formed at the boundary 16 between the tip 13 and the outer periphery 15, and an optical isolator 20 is bonded to the tip with a light-transmitting adhesive 30. It is fixed.

In FIG. 3B, the tip 13 is inclined at an angle φ with respect to the perpendicular to the core shaft 12, and the optical isolator 20 is bonded and fixed to the tip with a light transmitting adhesive 30.

In FIG. 3C, the tip portion 13 has a curved surface shape, and the optical isolator 20 is bonded and fixed to the tip end thereof with a light transmitting adhesive 30.

Next, various embodiments of the optical isolator 20 of the present invention will be described with reference to FIGS.

FIG. 4A shows a case where only the Faraday rotator 22 and the polarizer 23 are used in the optical isolator 20, and if the polarization direction of the LD to be used is known in advance, the first polarized light is used. The child 21 can be omitted.

FIG. 4B shows a configuration in which a magnet 24 is arranged on the outer periphery of the Faraday rotator 22 of the optical isolator 20. At this time, a general bismuth-substituted garnet can be used for the Faraday rotator 22. If the magnet 24 is directly attached to the optical fiber, the load of the magnet 24 is relatively large, so that the optical fiber having low bending strength may be broken. Therefore, it is desirable to fix the optical fiber to the main body of the LD module without directly attaching it to the optical fiber.

The various shapes of the distal end portion 13 of the optical fiber shown in FIGS. 2 to 4 are merely examples, and the effects of the present invention can be exerted by combinations other than the shapes described above.

Next, various embodiments of the optical isolator 20 of the present invention will be described with reference to FIGS.

FIGS. 5A to 5D are end views showing various shapes of the optical isolator 20 viewed from the end of the optical fiber.

In FIG. 5A, the optical isolator 20 fixed to the tip 13 of the inclined surface 11 has a square shape, and the outer peripheral portion of the optical isolator 20 is located inside the outer peripheral surface 15 of the optical fiber. . By doing so, an excessive load is not applied to the optical fiber having a small allowable bending strength due to the small optical isolator, and the optical isolator 20 is not attached to the optical fiber with lens 10 because it does not protrude from the optical fiber outer peripheral surface 15. Even if it is incorporated in advance, it can be incorporated into the optical fiber insertion hole of the optical package.

Next, as shown in FIG. 5B, the same effect can be obtained by making the optical isolator 20 circular.

Furthermore, as shown in FIGS. 5C and 5D, the area of the optical isolator 20 can be further reduced by making it rectangular or elliptical, and expensive optical elements can be used efficiently. It becomes possible.

Since the optical fiber with lens 10 uses an LD having a high aspect ratio and a wavelength of 980 nm, the light incident on the optical fiber has an elliptical shape. More desirably, the major axis direction is made to coincide with the ridge direction of the tip portion 13.

In this case, the major axis A along the ridge direction of the optical isolator 20 is desirably 30 to 125 μm, and the minor axis B in the perpendicular direction is desirably 10 to 125 μm. This is because if the major axis A is less than 30 μm or the minor axis B is less than 10 μm, light cannot efficiently enter the core of the optical fiber.

In the present invention, the optical fiber with lens 1
Although the optical isolator 20 is attached to the distal end of the optical fiber 10, the optical isolator 20 is not limited to the optical fiber with lens 10, and the optical isolator with the conventional optical isolator shown in FIG. Can be made inside the outer circumference of the optical fiber.

The method for processing the optical fiber with lens 10 according to the present invention is as follows. First, at least one Faraday rotator 2
The optical isolator 20 in the form of a wafer composed of two and at least one polarizer 21 and 23 is bonded by performing optical adjustment, and then cut into a predetermined size using a laser. Here, since cutting is performed using a laser, several tens μm
It can be made as small as possible.

Then, the tip of the optical fiber with lens 10 is subjected to wedge-shaped processing, and is bonded and fixed using a light-transmitting adhesive 30 that is substantially matched with the refractive index of the core of the optical fiber.

[0054]

EXAMPLE Here, an experiment was conducted by the following method.

As an embodiment of the present invention, an optical fiber with lens 10 having an optical isolator 20 shown in FIG.
As a comparative example, the end face 4 of the conventional ferrule 43 shown in FIG.
A pigtail 10 with an optical isolator having the optical isolator 42 fixed to 4 was prototyped, and 20 sets were assembled in each LD module.

In the optical fiber with lens 10 of the present invention, first, the coating of the optical fiber is removed, the inclined surface 11 is formed by polishing, and the tip 13 is further polished to the perpendicular of the core shaft 12. A plane was formed at an angle δ. An optical isolator 20 previously assembled in the order of a polarizer, a Faraday rotator, and a polarizer was bonded and fixed to the tip using a light transmitting adhesive 30. On the other hand, in the conventional example shown in FIG. 8, an optical fiber 45 is inserted and fixed in the through hole of the ferrule 43, and the end face 44 is polished to a mirror surface.
1. The optical isolator 20 assembled in the order of the Faraday rotator 22 and the polarizer 23 was bonded and fixed using a light transmitting adhesive 30.

The light-transmitting adhesive 30 used together is a UV-curable adhesive having a refractive index of 1.556, and is set near the refractive index 1.470 of the optical fiber core. When receiving the light emitted from the LD, the incident light does not cause irregular reflection or unstable behavior at the end face of the optical fiber.
The coupling efficiency to the optical fiber is not reduced.

The pigtail 10 with an optical isolator according to the present invention and the conventional example is packaged in a package designed with optimal dimensions by using an LD.
Then, an LD module was assembled with other components, and the manufacturing cost required for the trial production and the total length of the LD module package were compared.

Table 1 shows the results. In the table, the ratio of the present invention is expressed by assuming that the manufacturing price and the total length of the conventional LD module are 100.

The production cost and the total length of the conventional LD module shown in FIG. 8 are 100, while the LD module using the optical fiber with lens 10 of the present invention has a production price of 62 and a total length of 76, which is a good result. was gotten.

That is, since the lens is unnecessary, the optical isolator is reduced in size, and the structure is simplified, the cost of members and assembly is reduced, and the size of the member can be reduced. The package itself of the LD module incorporating the fiber could also be reduced in size.

[0062]

[Table 1]

[0063]

According to the present invention, there is provided an optical fiber with a lens in which a wedge-shaped inclined surface is formed at the end of the optical fiber and a semi-cylindrical curved surface, flat surface or an acute angle is formed at the tip of the inclined surface. By fixing an optical isolator comprising at least one Faraday rotator and at least one polarizer at the tip, a small and inexpensive optical fiber with a lens can be obtained without reflected return light being incident on an LD. Can be done.

[Brief description of the drawings]

FIG. 1A is a plan view showing a fiber with a lens of the present invention, and FIG. 1B is a side view of the same.

FIGS. 2A to 2D are side views showing another embodiment of the present invention.

FIGS. 3A to 3C are plan views showing another embodiment of the present invention.

FIGS. 4A and 4B are plan views showing another embodiment of the present invention.

5 (a) to 5 (d) are end views showing another embodiment of the present invention.

FIG. 6 is a side view showing a conventional optical fiber with lens and LD.

FIG. 7 is a side view showing a conventional optical fiber with a lens and an LD.

FIG. 8 is a side view showing a conventional optical fiber with a lens and an LD.

[Explanation of symbols]

 Reference Signs List 10 optical fiber with lens 11 inclined surface 11a inclined surface 11b inclined surface 12 core axis 13 tip 15 optical fiber outer peripheral surface 16 boundary 17 chamfer 20 optical isolator 21 polarizer 22 Faraday rotator 23 polarizer 24 magnet 30 adhesive 31 fixed Tool 41 Lens 42 Optical isolator 43 Ferrule 44 End face 45 Optical fiber θ angle φ angle δ angle A major axis B minor axis

Claims (5)

[Claims] 1. An optical fiber with a lens, wherein a wedge-shaped inclined surface is formed at an end of an optical fiber, wherein at least one Faraday rotator and at least one polarizer are provided at the tip of the inclined surface. An optical fiber with a lens, wherein an optical isolator is fixed. 2. The optical fiber with a lens according to claim 1, wherein a ridgeline of the tip is inclined with respect to a plane perpendicular to a core axis of the optical fiber. 3. The optical fiber with a lens according to claim 1, wherein a magnet is arranged on an outer periphery of the Faraday rotator. 4. A wedge-shaped inclined surface is formed at an end of an optical fiber, and an optical isolator comprising at least one Faraday rotator and at least one polarizer is previously assembled. A method for assembling an optical fiber with a lens, characterized in that the optical fiber with a lens is fixed to an end portion of an inclined surface of the fiber using an adhesive matching the refractive index of a core. 5. An optical fiber with an optical isolator having an end covered with an optical isolator and an optical isolator fixed to the end of the optical fiber when viewed from the end of the optical fiber. An optical fiber with an optical isolator, which is located further inside.