JPS60214336A - Optical collimator - Google Patents

Abstract

PURPOSE:To align projection parallel luminous flux with the optical axis of a distributed index cylindrical lens by slanting the parallel luminous flux projection end surface of the distributed-index cylindrical lens to the optical axis of the cylindrical lens, and setting an end surface of an incidence optical fiber at a specific position. CONSTITUTION:The end surface 5 of the incidence optical fiber 4 is joined with the vertical end surface 3 of the distributed-index cylindrical lens which has a slanting end surface 2 as a projection terminal and the vertical end surface 3 as an incidence terminal. A light beam 12 incident on the cylindrical lens 1 from the end surface 5 of the incidence optical fiber 4 which is S away from the optical axis center 11 of the vertical end surface 3 onto the plane containing the normal line 10 of the slanting end surface 2 and an optical axis 9 is passed through the lens and then slants by an angle theta0 to the optical axis 9. When the focal length and maximum refractive index of the distributed- index denoted as (f) and (n) and the core diameter of the optical fiber 1 is denoted as (d), the projection end surface of the cylindrical lens 1 is slanted to the optical axis 9 by an angle theta1 determined by theta1>d/2f and the optical axis center of the incidence optical fiber 4 is set (n0-1)ftheta1 away from the optical axis center 9 of the lens 1 on the surface containing the normal line of the projection end surface and the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical collimator with less reflected return light.

[Background of the invention]

An optical collimator converts diffused light emitted from an optical fiber into parallel light beams when configuring optical multiplexers/demultiplexers, optical switches, lens-type optical connectors, etc. A distributed index cylindrical lens is often used as the lens. It is being However, since the conventional optical collimator uses a distributed index cylindrical lens having a vertical end face, there is a drawback that the reflected light from the end face of the distributed index cylindrical lens returns to the incident optical fiber. In order to solve this drawback, it has been proposed to apply an anti-reflection coating to the end face of the distributed index cylindrical lens, but it is difficult to form an anti-reflection coating over a wide wavelength band. In addition, a structure has been proposed in which the end face of the distributed index cylindrical lens is polished obliquely to prevent the reflected light from returning to the input optical fiber, but in this case, the output parallel light beam from the distributed index cylindrical lens Since the direction of the gradient index cylindrical lens does not coincide with the optical axis of the gradient index cylindrical lens, it has the disadvantage that it must be used under strict angular conditions with respect to the rotation of the gradient index cylindrical lens.

[Purpose of the invention]

In order to eliminate the above-mentioned drawbacks, the present invention tilts the parallel light beam output end face of the distributed index cylindrical lens with respect to the optical axis of the cylindrical lens, and sets the end face of the input optical fiber at a predetermined position. , the purpose is to make the emitted parallel light beam coincide with the optical axis of the distributed index cylindrical lens.

[Summary of the invention]

In order to achieve the above object, an optical collimator according to the present invention is an optical collimator in which an end of an optical fiber is arranged at a focal position of a distributed index cylindrical lens, and the focal length of the distributed index cylindrical lens is set to f, a maximum. When the refractive index is n and the core diameter of the optical fiber is d, the output end face of the distributed index cylindrical lens is tilted with respect to the optical axis by an angle θ1 determined by θ1>d/2f, and the optical axis of the input optical fiber is By setting the center at a position away from the optical axis center of the distributed index cylindrical lens by (no-1) fθ1 on a plane including the normal to the output end face and the optical axis, the output parallelism of the distributed index cylindrical lens can be adjusted. The light beam is made to coincide with the optical axis of the cylindrical lens.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view showing one embodiment of the optical collimator according to the present invention, FIG. 2 is an explanatory diagram showing the operating principle of the above embodiment, and FIG. 3 is a cross-sectional view showing another embodiment of the optical collimator according to the present invention. It is a diagram. In the embodiment shown in FIG. 1, the distributed index cylindrical lens 1 has a pitch of 0.25, a maximum refractive index of 1.55,
It has a focal length of 2.8 m, and has an inclined end face 2 at the output end and a vertical end face 3 at the input end. The end face 5 of the input optical fiber 4 with a core diameter of 50 I1 m is held by a fiber holder 6 and joined to the vertical end face 3 of the cylindrical lens 1, and is housed together with the cylindrical lens 1 in the lens holder 7, and the end face 5 is bonded with an adhesive 8. is fixed at a fixed position on the vertical end surface 3. In the optical collimator with the above configuration, the light incident from the input optical fiber 4 is guided into the distributed index cylindrical lens 1 from the end face 5, and is converted into a parallel light beam when passing through the 0.25 pitch cylindrical lens 1. Then, the light is emitted from the inclined end face 2 into free space. In this embodiment, the end face 5 of the input optical fiber 4 is located at a distance of 28I1 m from the center of the optical axis of the cylindrical lens 1 on a plane including the normal line of the inclined end face 2 and the optical axis, and the angle of the inclined end face 2 is Since the angle is set to 1.02°, the output parallel light beam coincides with the optical axis of the cylindrical lens 1. Further, the light reflected by the inclined end face 2 is converged while traveling backwards inside the cylindrical lens 1, and does not form an image on the end face 5 of the input optical fiber 4 and become returned light.

The operating principle of the embodiment shown in FIG. 1 will be explained below with reference to FIG. 2. In Figure 2, the output end is set to the inclined end face 2.
, an end face 5 of an input optical fiber 4 is bonded to a vertical end face 3 of a distributed index cylindrical lens 1 whose input end is a vertical end face 3 . In the figure, 9 indicates the optical axis of the cylindrical lens 1, 10 indicates the normal line to the optical axis center of the inclined end surface 2, and 11 indicates the optical axis center on the vertical end surface 3. A light ray 12 that enters the cylindrical lens 1 from the end face 5 of the input optical fiber 4, which is spaced by S from the optical axis center 11 of the vertical end face 3 on a plane including the normal 10 of the inclined end face 2 and the optical axis 9, is 0. After passing through a 25-pitch lens, the angle θ with respect to the optical axis 9 is expressed by the following formula. tilt high.

Here n. is the maximum refractive index of the distributed index cylinder Mens 1, f
is the focal length. If the inclination angle of the inclined end face 2 is θ, then the angle θ2 that the incident light ray 12 makes with respect to the normal 10 of the inclined end face 2 is expressed by the following equation.

θ2=01−〇〇 (2) The angle that the emitted light 13 makes with respect to the normal 10 is 5 in-' (no sun θz) #no θ2 according to Snell's law. Therefore, the direction of the emitted light 13 is the same as that of the cylindrical lens 1.
In order to coincide with the optical axis 9 of , the following equation (3) must hold true.

no θ2=θ□ (3) From the above equations (1) to (3), the following relationship of equation (4) is obtained.

A part of the incident light ray 12 is reflected by the inclined end face 2 and becomes a reflected light ray 14.
At that time, since the angle difference between the incident light 12 and the reflected light 14 is 2θ2, the input optical fiber 4 on the vertical end face 3
The center of the end surface 5 and the center of the image 15 formed by the reflected light 14 are separated by a distance W given by the following equation (5).

In order for no return light to occur, w>d must be satisfied.

Here, d is the core diameter of the input optical fiber.

From this, the inclination angle θ1 of the inclined end face 2 must satisfy the following condition.

θ,>d/2f (6) In the embodiment shown in FIG. 1, the core diameter of the input optical fiber 4 is 50-, the maximum refractive index is 1.55, and the focal length is 2.
Since an 8 nm cylindrical lens 1 is used, the minimum inclined end face angle is 0.51° and the axis deviation of the input optical fiber 4 is 14- from equation (6), but the angle setting error and alignment error are They are estimated to be 1.02" and zaIlm, respectively.

Another embodiment of the present invention shown in FIG.
The input optical fibers 17a, 17
b, and these input optical fibers 17a, 1
The fiber holders 18a and 18b holding the lens 7b are attached together with the cylindrical lenses 16a and 16b to the lens holder 19a,
19b, and these lens holders 19a
, 19b are supported within a centering sleeve 20 that covers almost the entire length of the cylindrical lenses 16a, 16b with their inclined end faces facing each other. In this embodiment, the optical collimators shown in FIG. 1 are inserted from both ends of the alignment sleeve 20 to obtain optical coupling, so that an optical connector with an extremely large allowable displacement in the optical axis direction can be obtained. Since the reflected light from the lens end face of the other collimator is inclined with respect to the optical axis, the second
If the above-mentioned conditions shown in the figure are satisfied, in principle, there will be no return light. However, in order to avoid fluctuations in loss due to interference of multiple reflected light between the inclined end surfaces, it is necessary to align the inclined end surfaces of the distributed index cylindrical lenses 16a and 16b with respect to the plane perpendicular to the optical axis, as shown in FIG. It is desirable to arrange them so that they are mirrored. For this purpose, the alignment sleeve 20
A known technique for preventing the lens holders 19a and 19b from rotating can be applied.

〔Effect of the invention〕

As described above, the optical collimator according to the present invention is an optical collimator in which the end of an optical fiber is arranged at the focal length position of a distributed index cylindrical lens, where the focal length of the distributed index cylindrical lens is f, and the maximum refractive index is f. n, and when the core diameter of the optical fiber is d, the output end face of the distributed index cylindrical lens is tilted with respect to the optical axis by an angle θ□ determined by θ□>d/2f, and the optical axis center of the input optical fiber is By providing (no 1) fθ away from the optical axis center of the distributed index cylindrical lens on the plane that includes the normal to the output end face and the optical axis, the reflected return light due to reflection from the output end face can be prevented. Moreover, since the direction of the emitted parallel light beam coincides with the optical axis of the distributed index cylindrical lens, it is possible to obtain an optical collimator with extremely small characteristic fluctuations with respect to rotation around the optical axis.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the optical collimator according to the present invention, FIG. 2 is an explanatory diagram showing the operating principle of the above embodiment, and FIG. 3 is a cross-sectional view showing another embodiment of the optical collimator according to the present invention. It is a diagram. 1... Distributed refractive index cylindrical lens 2... Output end face (slanted end face) 4... Optical fiber 5... Optical fiber end 9... Optical axis 10... Normal line patent at the output end face Applicant: Junnosuke Nakamura, Patent Attorney, Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] In an optical collimator in which an optical fiber end is placed at the focal point of a distributed index cylindrical lens, where f is the focal length of the distributed index cylindrical lens, n is the maximum refractive index, and d is the core diameter of the optical fiber. , the angle θ of the output end face of the distributed index cylindrical lens with respect to the optical axis determined by O>d/2f,
At the same time, the optical axis center of the input optical fiber is set at a position far away from the optical axis center of the distributed index cylindrical lens by (no-1) fθ on a plane that includes the normal to the output end face and the optical axis. An optical collimator characterized by: