JP2004233566A - Laser beam coupling optical fiber, optical fiber and optical fiber module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser beam coupling optical fiber that can increase an optical coupling efficiency with a laser diode, and also to provide an optical fiber and an optical fiber module. <P>SOLUTION: This is a laser beam coupling optical fiber 33 having a core 35 on which a laser beam with an elliptical optical spot from a laser diode 31 is made incident. The optical fiber is characterized in that the core shape at the end face where the laser beam enters has an elliptical shape corresponding to the elliptical optical spot from the laser diode 31 and that the core 35 is formed into a circular shape gradually from the end face toward the transmitting direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical fiber for coupling laser light, an optical fiber, and an optical fiber module.
[0002]
[Prior art]
As a light emitting source for optical communication, a laser diode, a light emitting diode, or the like is used. The pattern of the light emitted from the short-wavelength laser diode is not a circular Gaussian distribution but an elliptical Gaussian distribution that differs in the vertical and horizontal directions. In particular, a radius at which the intensity becomes 1 / e (base of natural logarithm) with respect to the peak value is called a spot size. The position where the spot size becomes minimum is called beam waist. A typical 980 nm laser diode has a pattern of emitted light (elliptical spot shape) having an aspect ratio between 2.5: 1 and 4: 1. Conventionally, a wedge-shaped wedge fiber is used for coupling.
[0003]
In a conventional wedge-shaped wedge fiber, the coupling efficiency changes depending on the spot size of the laser diode, and thus the angle of the inclined surface of the tip and the radius of curvature of the tip are selected according to each spot size. For example, the conventional wedge fiber 10 shown in FIG. 3 includes a lens 11 composed of a pair of inclined surfaces 11a that are symmetric with respect to the core axis 12 of the optical fiber and form a sharp ridge at the tip of the optical fiber.
[0004]
Further, the two-stage wedge-shaped wedge fiber 10 shown in FIG. 4 has a pair of inclined surfaces 11a that are symmetric with respect to the core axis 12 of the optical fiber and form a sharp ridge at the fiber tip, and are continuous in the inclined direction of the inclined surfaces 11a. There is provided a lens 11 including a pair of inclined surfaces 11b provided at an angle smaller than the inclined surface 11a with respect to the core axis of the optical fiber (for example, see Patent Document 1).
[0005]
For the same purpose as the wedge fiber 10 shown in FIG. 4, the wedge fiber 20 shown in FIG. 5 has a pair of inclined surfaces 21 symmetrical with respect to the core axis 23 of the optical fiber and has a wedge shape. A lens is formed continuously with a semi-cylindrical curved surface 22 (for example, see Patent Document 2).
[0006]
The wedge fiber 30 shown in FIG. 6 includes two inclined surfaces 31 symmetrical with respect to a core axis 33 and a flat portion 32 perpendicular to the core axis at the tip of the optical fiber. A lens having an angle θ of 10 ° to 70 ° with respect to a plane portion perpendicular to the axis is formed (for example, see Patent Document 3).
[0007]
[Patent Document 1]
JP-A-8-5865 [Patent Document 2]
Japanese Patent Application Laid-Open No. 8-86923 [Patent Document 3]
JP-A-10-307230
[Problems to be solved by the invention]
However, each of the above-mentioned conventional wedge fibers has a problem that the optical coupling characteristics are low. That is, the wedge fiber 10 shown in FIG. 3 has a sharp point, so that the optical coupling efficiency with the laser diode is very poor, and the tip of the optical fiber is sharpened by polishing using a grindstone or the like. However, it is very difficult to form a ridge line since chipping or the like is likely to occur at the tip ridge line portion. Chipping at the ridge of the optical fiber tip causes a loss, and there is a problem that the optical coupling characteristics are significantly reduced.
[0009]
Further, in the conventional wedge fiber 10 shown in FIG. 4, although the optical coupling efficiency is better than that in FIG. 3, the wedge angle does not change smoothly at the boundary between the clad and the core. Efficiency was poor. Also, as in FIG. 3, the tip of the optical fiber needs to be processed into a sharp ridge by polishing using a grindstone or the like. There is a problem that the temperature is significantly reduced.
[0010]
Further, in the conventional wedge fiber 20 shown in FIG. 5, the angle θ of the inclined surface 21 to the plane perpendicular to the core axis is 25 ° to 65 °, the radius of curvature of the curved surface 22 is 3.0 to 8.0 μm, and the laser If the combination with the spot size of the diode is not appropriate, the optical coupling efficiency is poor, and it takes time to assemble with the laser diode and the yield is poor. In addition, when the combination is bad, there is a disadvantage that the range in which high optical coupling efficiency can be obtained when assembling with the laser diode is limited.
[0011]
Furthermore, in the conventional wedge fiber 30 shown in FIG. 6, the tip is flat and the normal to the surface is in the direction of the optical axis, so that the optical coupling efficiency with the laser diode is extremely poor. In addition, since it is necessary to process the optical fiber tip into a sharp ridge by polishing using a grindstone or the like, chipping of the optical fiber tip ridge portion causes a loss, as described above, and significantly degrades optical coupling characteristics. There was a problem.
[0012]
That is, there has been a problem that any of the conventional wedge fibers cannot provide a satisfactory optical coupling efficiency in coupling with a laser diode.
[0013]
SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber for laser light coupling, an optical fiber, and an optical fiber module that can increase the efficiency of light coupling with a laser diode.
[0014]
[Means for Solving the Problems]
The laser light coupling optical fiber of the present invention is a laser light coupling optical fiber having a core into which laser light having an elliptical light spot shape from a laser diode is incident, and the core shape of an end face on which the laser light is incident. Is an elliptical shape corresponding to the elliptical light spot shape of the laser diode, and the core is gradually formed in a circular shape from the end face in the transmission direction.
[0015]
In such an optical fiber for coupling laser light, since the core shape of the end face on which the laser light is incident is elliptical and is gradually formed in a circular shape from the end face toward the light transmission direction, the ellipse from the laser diode is formed. Since the laser beam having the light spot shape is incident on the elliptical core and is transmitted through the gradually becoming circular core, and since no polishing or the like is required and there is no sharp portion, the loss is reduced. Becomes very small, and the optical coupling efficiency with the laser diode can be increased.
[0016]
In the optical fiber for coupling laser light of the present invention, the spot size determined from the core size of the end face on which the laser light is incident is substantially equal to the spot size of the laser diode. In such a laser light coupling optical fiber, the mismatch between the fiber core shape and the laser spot size does not contribute to reflection, so that the optical coupling efficiency can be further increased.
[0017]
Further, the optical fiber for coupling laser light of the present invention is characterized in that the spot size determined from the core size of the end face on which the laser light is incident substantially matches the spot size at the beam waist of the laser diode. In such an optical fiber for coupling laser light, the laser light immediately after being emitted enters the optical fiber for coupling laser light, and furthermore, approximately matches the spot size at the beam waist of the laser diode. can do.
[0018]
Further, in the laser light coupling optical fiber of the present invention, the shape of the end face on which the laser light is incident is an elliptical shape corresponding to the core, and the cross-sectional shape is gradually formed in a circular shape from the end face in the transmission direction. It is characterized by having. In such an optical fiber for coupling laser light, the shape of the end face on which the laser light is incident is an elliptical shape corresponding to the core, and the cross-sectional shape gradually changes from the elliptical shape to a circular shape. Then, in a general manufacturing method in which the material is stretched into a circular cross section, the material can be easily formed by stretching the material in a slightly deformed state by pressing the front end portion therebetween.
[0019]
Further, an optical fiber according to the present invention is characterized by comprising the optical fiber for coupling laser light and an optical fiber main body connected to the optical fiber for coupling laser light and having a circular core. In such an optical fiber, the optical coupling efficiency with the laser diode can be increased, and the optical signal can be efficiently propagated.
[0020]
Further, the optical fiber module according to the present invention includes a laser diode that emits laser light having an elliptical light spot shape, the laser light coupling optical fiber that receives laser light from the laser diode, and the laser light coupling light. An optical fiber body connected to the fiber and having a circular core.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an optical fiber module according to the present invention. The optical fiber module comprises a laser diode 31 for emitting a laser beam having an elliptical spot shape and a laser beam coupling for receiving the laser beam from the laser diode 31. And an optical fiber main body 34 connected to the laser light coupling optical fiber 33. An optical fiber is constituted by the optical fiber 33 for laser light coupling and the optical fiber main body 34.
[0022]
The laser diode 31 emits laser light having an elliptical light spot shape as shown in FIG. 2A, and the laser light is incident on the laser light coupling optical fiber 33.
[0023]
The laser light coupling optical fiber 33 has a core 35 into which the laser light from the laser diode 31 is incident. In the optical fiber for coupling laser light of the present invention, the shape of the core 35 on the end face on which the laser light is incident has an elliptical shape corresponding to the elliptical light spot shape of the laser diode 31 as shown in FIG. The core 35 is formed in a circular shape gradually from the end face toward the transmission direction X.
[0024]
It is desirable that the spot size determined from the core size of the end face on which the laser light is incident substantially coincides with the spot size of the laser diode 31. Further, it is desirable that the spot size determined from the core size of the end face on which the laser light is incident substantially coincides with the spot size at the beam waist of the laser diode. In this case, the emitting portion of the laser diode 31 and the end face of the optical fiber for coupling laser light are almost in contact with each other.
[0025]
The cross-sectional shape (outer shape) of the laser light coupling optical fiber 33 is such that the shape of the end face on which the laser light is incident is an elliptical shape corresponding to the core size, and is gradually formed in a circular shape from the end face in the transmission direction X. Have been. Such an optical fiber 33 for laser beam coupling can be easily manufactured by using a general optical fiber manufacturing process.
[0026]
That is, in a general manufacturing method in which an optical fiber material is melted and the material is stretched to have a circular cross section, the fiber can be easily formed by pressing the tip end portion and stretching it in a slightly deformed state.
[0027]
The optical fibers 33 and 34 are for excitation light, and the single mode optical fiber (optical fiber main body 34) is composed of a core 35 having a circular cross section in which light is confined and a clad 37 surrounding the core 35 concentrically. In the coupling optical fiber 33, both the core 35 and the clad 37 are elliptical. The length of the laser light coupling optical fiber 33 in the transmission direction X is desirably 1 mm or more.
[0028]
In the optical fiber for laser light coupling configured as described above, the core shape of the end face is elliptical and is gradually formed in a circular shape from the end face toward the light transmission direction X. Since the laser light having the light spot shape is incident on the elliptical core 35 and is transmitted through the gradually increasing circular core 35, and since there is no need for polishing or the like, there is no sharp portion, The loss is very small, and the optical coupling efficiency with the laser diode 31 can be increased.
[0029]
【Example】
The case where the spot size at the beam waist of the laser diode is w1x = 2.550 μm and w1y = 0.720 μm, and the spot size of the coupling optical fiber is w2x = w2y = 2.95 μm is taken as an example.
[0030]
It is known that the electromagnetic field from a laser diode and the electromagnetic field in a single-mode fiber can be well approximated as a Gaussian beam, so that the coupling efficiency is calculated using Gaussian beam approximation below. When the coupling efficiency in the air is C,
C = 2 / (w1x / w2x + w2x / w1x)
* 2 / (w1y / w2y + w2y / w1y)
It becomes. w1x, w1y and w2x, w2y are spot sizes in two directions perpendicular to each other in a plane perpendicular to the beam propagation direction (for example, “Basic and application of an optical coupling system for an optical device (Kono, Hyundai Engineering Co., Ltd.) Company))).
Therefore, if a fiber is directly coupled to this laser diode, C = 0.456
It becomes. In addition, the transmittance T of the penetration of the plane wave from the air into the SiO ₂ constituting the fiber is shown.
T = 1 − ((1−n) / (1 + n)) ＾ 2
Consider. Here, ＾ 2 means the square. Substituting the refractive index n = 1.457 of SiO ₂ , T = 0.965.
Therefore, the final coupling efficiency is CT = 0.44.
It becomes.
[0031]
On the other hand, when the single mode spot size near the end face in the fiber matches that of the laser diode, w2x = 2.550 μm, w2y = 0.720 μm, and C = 1, so that the coupling efficiency is CT = 0. 965.
[0032]
This greatly exceeds the theoretical coupling efficiency of 0.8 units realized by a conventional method such as a lens fiber or a wedge fiber.
[0033]
【The invention's effect】
According to the present invention, the single-mode spot size in the vicinity of the end face in the optical fiber is elliptical such that it is equal to that of the laser diode, and is gradually deformed into a perfect circular shape in the longitudinal direction from the end face. An excellent optical fiber for laser light coupling having high light coupling efficiency can be provided.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an optical fiber module of the present invention.
2A is a cross-sectional view (laser light) taken along the line AA in FIG. 1, FIG. 2B is a side view taken along the line BB showing the shape of the end face of the optical fiber for coupling laser light, (C) is a cross-sectional view along the line CC.
FIG. 3 is a side view of a first conventional wedge fiber.
FIG. 4 is a side view of a second conventional wedge fiber.
FIG. 5 is a side view of a third conventional wedge fiber.
FIG. 6 is a side view of a fourth conventional wedge fiber.
[Explanation of symbols]
31 laser diode 35 core 33 optical fiber 34 for coupling laser light optical fiber body

Claims (6)

A laser light coupling optical fiber having a core on which laser light having an elliptical light spot shape from a laser diode is incident, wherein the core shape of the end face on which the laser light is incident has an elliptical light spot shape of the laser diode. An optical fiber for laser light coupling, having a corresponding elliptical shape, wherein the core is gradually formed in a circular shape from an end face in a transmission direction. 2. The optical fiber for coupling laser light according to claim 1, wherein a spot size determined from a core size of the end face on which the laser light is incident substantially coincides with a spot size of the laser diode. The optical fiber for coupling laser light according to claim 1, wherein a spot size determined from a core size of an end face on which the laser light is incident substantially coincides with a spot size at a beam waist of the laser diode. 4. An end face on which laser light is incident has an elliptical shape corresponding to the core, and a cross-sectional shape is gradually formed in a circular shape from the end face in a transmission direction. The optical fiber for coupling laser light according to any one of the above. An optical fiber, comprising: the optical fiber for laser light coupling according to any one of claims 1 to 4; and an optical fiber body connected to the optical fiber for laser light coupling and having a circular core. 5. A laser diode for emitting laser light having an elliptical light spot shape, a laser light coupling optical fiber according to claim 1, wherein the laser light from the laser diode is incident, and a laser light coupling optical fiber for laser light coupling. An optical fiber module, comprising: an optical fiber body connected to the optical fiber and having a circular core.

Images