JPH07281054A - Optical fiber terminal - Google Patents

Abstract

PURPOSE:To restrain a reflection attenuating quantity, eliminate a polarization change, and facilitate assembling and adjustment by inclining an end surface on the opposite side of an optical fiber connecting end surface of coreless fiber at a specific angle to a surface vertical to the optical axis. CONSTITUTION:The tip of optical fiber is fused on and connected to one end surface S of coreless fiber 8 composed of a transparent body whose refractive index distribution is flat and which has a refractive index equal to an optical fiber core A, and an end surface T on the opposite side of the optical fiber connecting end surface S of the coreless fiber 8 is inclined within theta=0 to 6 degrees to a surface vertical to the optical axis. Since beams (arrows E) emitted from the optical fiber core A spread in the careless fiber 8 and advance while leaking, the return light to an optical fiber core A part is cut off. Thereby, even if a forward inclination of an emitting end surface T of the coreless fiber 8 is within 6 degrees and very small to the surface vertical to the optical axis, interference of the return light can be prevented, and a reflection attenuating quantity becomes 6.0 dB or more. A beam of light is not dislocated from the central axis of the optical fiber.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention can be applied to a wide range of optical fields such as optical communication devices and optical measuring devices, and is used for returning reflection from a lens surface when converting light emitted from an optical fiber into parallel light. The present invention relates to an optical fiber terminal that prevents light interference.

[0002]

2. Description of the Related Art With the development of optical communication, miniaturization of optical devices, optical components, etc. used is desired, and miniaturization of optical isolators, optical circulators, optical multiplexers / demultiplexers, etc., in a state of coupling with an optical fiber. There is a demand for streamlining and simplification of the structure. Further, in recent years, high-speed and high-density systems for optical communication are sensitive to back reflection and use a distributed feedback laser with an extremely narrow spectral line width, so the end of the optical fiber has high return loss. It has become required to have it.

Generally, in the case of a pigtail type optical isolator having optical fibers at both ends, the light emitted from the optical fiber 1 is incident on the optical device 4 as parallel light by the spherical lens 2 or the gradient index lens 3 as shown in FIG. Then, after the light is emitted, the light is similarly focused on the optical fiber 1 to perform optical coupling.

However, in the conventional optical coupling system as shown in FIG. 7, there is a problem that the optical axis positions of the optical fiber and the lens have to be adjusted in the submicron range, the assembling apparatus is expensive, and the optical fiber collimator is used. It was expensive as a product or an optical system product including an optical fiber coupling system.

Further, in the conventional structure, as shown in FIG. 8, the refractive index matching agent 5 made of an organic material is used to prevent reflection, so that there is a defect in weather resistance and heat resistance. In addition, from the viewpoint of miniaturization of optical devices, the luminous flux is sufficiently thin, for example, 20
Collimator light of 0 μm or less is required, but in the prior art, the coupling loss is large, so that only a thin collimator light of about 300 μm is practical.

Further, as shown in FIG. 9, there is also a method in which the return light is cut at an angle to the tip of the fiber and a parallel light beam is taken out by combining with a gradient index lens. And the lens surface is parallel and will pick up the reflected light. As described above, the optical system of the conventional optical fiber collimator always has parallel end faces, and the return loss can be obtained only up to about -27 dB.

In order to solve the above-mentioned drawbacks of the conventional optical coupling system, attempts have recently been made to form a minute fiber collimator light. Journal of Lightwave Technol
In ogyVol. LT-5 No. 9 (1987), a single mode fiber (hereinafter referred to as SMF) by William L. Emkey, etc. was fused with a multimode gradient index fiber (hereinafter referred to as GIF),
We have proposed the coupling of minute fiber collimator light up to 40 μm parallel rays, and reported that optical coupling can be obtained with a coupling loss of 0.1 to 1.6 dB in a space of about 3 mm.

However, in the structure using SMF + GIF,
The expansion width of the luminous flux is theoretically impossible beyond the core diameter of the GIF, and the maximum limit is 50 to 62.5 μm, and it cannot be made larger than this, and significant coupling loss deterioration occurs at a distance of 3 mm or more. There is no degree of freedom in distance, and the manufacturing process must be performed while individually measuring the refractive index distribution state of the GIF and the adjustment of the wavelength pitch, which is expensive and unsuitable for mass production.

On the other hand, in Japanese Patent Laid-Open No. 61-264304,
Kevin John Warbrick proposes SMF + undoped silica fiber lens optics. But,
In this case as well, the curvature of the lens portion is limited to 62.5 μm due to the reason of diffraction loss, so the obtained light flux is about 60 μm, and structurally the maximum is about 80% of the silica fiber diameter. Yes, it is too narrow to insert an optical device. That is, a luminous flux of about 60 μm is too thin to be suitable for coupling Gaussian beams. Therefore, how to realize a light beam of 60 to 200 μm is a practical issue.

As a means for solving the above-mentioned drawbacks, the present inventor has proposed an optical fiber terminal for optical coupling, which is substantially composed of SMF + non-doped silica fiber beam expanding portion + undoped silica spherical lens (Japanese Patent Application No. Hei 3). -17022
issue). The specific structure is such that the first optical fiber and the second optical fiber having the same outer diameter and having the same refractive index of the core portion are joined.

The second optical fiber has a spherical lens having a diameter R larger than its outer diameter formed at the tip,
The function of expanding the light flux to at least half the optical fiber diameter (62.5 μm), preferably 80 μm or more at the stage of passing through the spherical lens part, and converting it from the curved surface of the spherical lens into parallel light flux or light with an emission angle according to the application To indicate
We have established an optical fiber terminal with a condensing function, which has a radius of curvature of at least 200 μm.

However, since the quartz portion at the tip is actually formed into a spherical shape by melting, the sphere has many variations in shape and curvature, and there is a drawback that a desired microlens cannot be obtained at the tip.

The present invention has been made in view of the above-mentioned circumstances, and improves the conventional defects and reduces the return loss.
The objective is to provide an optical fiber terminal that is suppressed to 60 dB or more, has no polarization fluctuation, and is easy to assemble and adjust.

[0014]

The present invention has been made to solve the above-mentioned problems of the prior art. The optical fiber terminal according to the present invention will be described with reference to FIGS. 1 to 6 corresponding to the embodiments. Coreless fiber 8 made of a transparent material having a flat index distribution and a refractive index equal to that of the optical fiber core A
The tip end of the optical fiber is fusion-spliced to one end face S of the one end, and the end face T of the coreless fiber 8 opposite to the optical fiber connecting end face S is inclined within θ = 0 to 6 degrees with respect to the plane perpendicular to the optical axis. It was made.

In the above optical fiber terminal, a collimator lens 9 such as a focusing rod lens is arranged on the end surface T of the coreless fiber 8 opposite to the optical fiber connecting end surface S.

Further, in the optical fiber terminal, an AR coating is applied to an end surface T of the coreless fiber 8 opposite to the optical fiber connecting end surface S to prevent return light interference.

In the above optical fiber terminal, the length L of the coreless fiber 8 in the optical axis direction is within 1 to 4 mm.

[0018]

In the optical fiber terminal according to the present invention, the coreless fiber 8 having a flat refractive index distribution and a refractive index equal to that of the optical fiber core A and having no waveguide structure is fusion-spliced at the tip of the optical fiber 1 to form an optical fiber core. The beam arrow E emitted from A spreads in the coreless fiber 8 and travels while leaking, so that the return light to the optical fiber core A portion is blocked, and the coreless fiber 8
Even if the angle of divergence of the exit end face T of is less than 6 degrees with respect to the plane perpendicular to the optical axis, return light interference can be prevented and the return loss is 60
It is above dB.

Further, the exit end surface T of the coreless fiber 8 is
Since the angle of inclination is θ = 0 to 6 degrees or less with respect to the plane perpendicular to the optical axis, there is no polarization fluctuation due to inclination, and the beam light incident on the collimator lens is Only the adjustment in the direction of the arrow G is required without any deviation from the central axis, the assembly and adjustment are easy, and the alignment is good.

Further, in the above-mentioned optical fiber terminal, by applying an AR coat to the end surface T of the coreless fiber 8 opposite to the optical fiber connecting end surface S, the return loss can be further reduced and the bevel angle can be further reduced. Since the length of the optical axis 8 can be shortened, the cost of parts can be reduced, and the optical performance and alignment can be improved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a configuration of an optical fiber terminal and a collimator lens showing an embodiment of the present invention.
FIG. 2 is a sectional view for explaining the configuration of a flat type optical fiber terminal showing an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating the configuration of a tip-end type optical fiber terminal showing an embodiment of the present invention. 4, FIG. 5, and FIG. 6 are graphs showing the relationship between the length L of the coreless fiber 8 in the optical axis direction and the return loss (dB) when the optical fiber terminal of the present invention is used.

As shown in FIGS. 1, 2 and 3, the optical fiber terminal of the present invention is an optical fiber 1 having a core diameter of 10 μm.
A coreless fiber 8 made of lot-shaped quartz having a diameter of 125 μm and having a flat refractive index distribution and a refractive index equal to that of the optical fiber core A and having no refractive index structure is fusion-spliced to the tip of the optical fiber 1 of the coreless fiber 8. The end surface T on the opposite side of the connection end surface S of and is inclined within θ = 0 to 6 degrees with respect to the surface perpendicular to the optical axis.

Next, a collimator lens 9 such as a focusing rod lens is arranged on the end surface T of the coreless fiber 8 opposite to the end surface S for connecting the optical fiber, so that collimated light can be emitted.

With the above-described structure, the beam arrow E emitted from the optical fiber core A spreads in the coreless fiber 8 and advances while leaking, so that the return light to the optical fiber core A portion is blocked and the coreless fiber. Even if the angle of inclination of the exit end face T of 8 is within 6 degrees with respect to the plane perpendicular to the optical axis, the return light interference can be prevented and the return loss becomes 60 dB or more.

Further, the exit end surface T of the coreless fiber 8 is
The angle of inclination is small within the range of θ = 0 to 6 degrees with respect to the plane perpendicular to the optical axis. Therefore, there is no polarization fluctuation due to the inclination, and the beam light incident on the collimator lens 9 is an optical fiber. It is only necessary to adjust in the direction of the arrow G without shifting from the central axis of, the assembly and adjustment are easy, and the alignment is good.

Further, in the above-mentioned optical fiber terminal, by applying an AR coat to the end surface T of the coreless fiber 8 opposite to the optical fiber connecting end surface S, the return loss can be further reduced and the bevel angle can be further reduced. Since the length of the optical axis 8 can be shortened, the cost of parts can be reduced, and the optical performance and alignment can be improved.

5 (a), 5 (b) and 6, the optical fiber terminal of the present invention was used without AR coating, and the angle of inclination was θ = 0 °, θ = 3 ° and θ = 4 °, respectively. At this time, the relationship between the length L of the coreless fiber 8 in the optical axis direction and the return loss (dB) is shown. Even if the AR coating is not provided, if the angle of inclination θ = 4 °, the length of the coreless fiber 8 in the optical axis direction is shown. With L = about 3 mm, we were able to achieve return loss of 60 dB or more.

4 (a) and 4 (b), the coreless fiber 8 is obtained when the optical fiber terminal of the present invention is used in which the AR coating is provided and the inclination angles are θ = 0 ° and θ = 3 °, respectively. The relationship between the length L in the optical axis direction and the return loss (dB) is shown. With the AR coating, the return loss is about 2 mm in the optical axis direction of the coreless fiber 8 even if the angle θ is 0 °. Amount of 60 dB or more was achieved. Also, when the tip angle θ = 3 °,
A return loss of 60 dB or more was achieved when the length L of the coreless fiber 8 in the optical axis direction was about 1 mm.

[0029]

As described in detail above, according to the present invention, the returning light to the optical fiber core A portion is blocked, and the angle of inclination of the emitting end face T of the coreless fiber 8 is within 6 degrees with respect to the optical axis. However, return light interference can be prevented, and the return loss is 60 dB or more.

The exit end surface T of the coreless fiber 8 is
Since the tip inclination angle of is small, there is no polarization fluctuation due to inclination,
The light beam incident on the collimator lens 9 does not deviate from the center axis of the optical fiber, and the assembly and adjustment are easy,
Good alignment.

Further, by applying the AR coating, the return loss can be further reduced, the bevel angle can be further reduced, and the length of the coreless fiber 8 in the optical axis direction can be shortened, so that the cost of parts can be reduced and the optical performance, Good alignment.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an optical fiber terminal and a collimator lens showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the configuration of a flat type optical fiber terminal showing an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating the configuration of a beveled optical fiber terminal showing an embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the length L of the coreless fiber 8 in the optical axis direction and the return loss (dB) when the optical fiber terminal with AR coat of the present invention is used.

FIG. 5 shows the length L of the coreless fiber 8 in the optical axis direction when the AR-coated optical fiber terminal of the present invention is used.
And a graph showing the return loss (dB).

FIG. 6 shows the length L of the coreless fiber 8 in the optical axis direction when the AR-coated optical fiber terminal of the present invention is used.
And a graph showing the return loss (dB).

FIG. 7 is a schematic view of a conventional optical fiber optical system.

FIG. 8 is a sectional view of a conventional optical collimator fiber.

FIG. 9 is a sectional view of a conventional optical collimator fiber.

[Explanation of symbols]

 1 optical fiber 2 spherical lens 3 gradient index lens 4 optical device 5 refractive index matching agent 6 entrance / exit surface 8 coreless fiber 9 collimator lens A optical fiber core S, T end face L coreless fiber length E beam

Claims (4)

[Claims] 1. A tip of an optical fiber is fusion-spliced to one end face of a coreless fiber made of a transparent material having a flat refractive index distribution and a refractive index equal to that of the optical fiber core, and the opposite side of the coreless fiber from the optical fiber connecting end face. An optical fiber terminal characterized in that the end face of is inclined within 0 to 6 degrees with respect to a plane perpendicular to the optical axis. 2. The optical fiber terminal according to claim 1, wherein a focusing rod lens or a collimator lens is arranged on the end surface of the coreless fiber opposite to the optical fiber connection end surface. 3. The optical fiber terminal according to claim 1, wherein an end surface of the coreless fiber opposite to an optical fiber connection end surface is AR-coated. 4. The optical fiber terminal according to claim 3, wherein the length of the coreless fiber in the optical axis direction is 1 to 4
An optical fiber terminal characterized by being within mm.