JPH10186164A - Optical branching and coupling device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the dependency of the branching/coupling characteristics of light beams due to wavelengths and polarized states and also to miniaturize a device and to make a space laying optical fibers to be small. SOLUTION: The combination of a first two-fiber ferrule 12 in which two lines of coated optical fibers 10 are provided side by side and a first collimating lens 14 consisting of a homogeneous lens common to two lines of light beams by the ferrule and the combination of a similar second two-fiber ferrule 20 and a similar second collimating lens 18 are disposingly arranged so that the collimating lenses 14, 18 are positioned in inner sides and the interval between them is separated by the sum of respective focal lengths and a half mirror 16 is built up at the focal positions of them in a housing 22 in a direction in which the light beams roughly become vertical incidences. Here, for example, spherical lenses are used as the collimating lenses 14, 18. The half mirror 16 is made to be the structure in which translucent films are formed on surfaces of a parallel flat transparent substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical component capable of branching and coupling light between two two-core ferrules. More specifically, the present invention relates to a two-core ferrule having two optical fiber cores. The present invention relates to an optical branching / combining device in which a half mirror in which a light beam is substantially perpendicularly incident is provided so that the light branching / coupling characteristics do not depend on the polarization state.

[0002]

2. Description of the Related Art An optical splitter / coupler splits light guided by one optical fiber into a plurality of optical fibers, and conversely, light guided by a plurality of optical fibers. 1
An optical component having a function of coupling to an optical fiber. Although the number of input terminals and the number of output terminals of the optical branching / combining device are various, a typical example is a configuration of two input terminals and two output terminals. This type of optical splitter / coupler is roughly classified into a bulk type, a fiber type, a waveguide type, and the like.

In the bulk type, four optical fibers each having a collimating lens are radially arranged in directions different from each other by approximately 90 degrees so that the collimating lens is on the inside, and a half mirror is placed at the center position of the collimating lenses. Is provided at an angle of approximately 45 degrees. Therefore, the incident light from the optical fiber enters the half mirror at an angle of approximately 45 degrees. In this configuration, the light guided by one optical fiber is branched into two optical fibers having directions different from each other by 90 degrees by using a half mirror that transmits part of the incident light and reflects the rest. Or, conversely, it has a function of coupling light guided by two optical fibers that differ by 90 degrees into one optical fiber.

[0004] The fiber type has a structure in which the cores of two optical fibers are sufficiently close to the core diameter, and branching / coupling characteristics are obtained by utilizing the distributed coupling of light guided to each optical fiber. . The waveguide type is a structure that uses an optical waveguide and obtains the branching / coupling characteristics of light according to the same principle as that of the fiber type.

[0005]

The half mirror has the advantages of a simple structure, easy design and manufacture of a translucent film, and inexpensive manufacture. However, in the bulk type as described above, the ratio between the transmitted light and the reflected light of the half mirror may change depending on the polarization state of the incident light. It gets bigger as it deviates.

As an example, FIG. 3 is a graph showing the transmittance and reflectance of a half mirror in which a low-loss semi-transparent metal layer is attached to a plane-parallel glass substrate as a function of the angle of incidence in air. A represents the incident angle dependence of transmittance,
B represents the incident angle dependence of the reflectance. If the incident angle of the light is small (when the light is incident on the half mirror almost perpendicularly), the p-polarized component and the s-polarized component in the transmittance or the reflectance match, but as the incident angle increases, the p-polarized component becomes The transmittance or reflectance of the s-polarized light becomes unbalanced, and polarization dependence occurs and increases.

For this reason, in a conventional bulk type configuration in which four sets of optical fibers and collimating lenses are arranged radially so as to be different from each other by 90 degrees, the angle of incidence on the half mirror becomes approximately 45 degrees. Light branching depending on the condition
It is difficult to suppress changes in coupling characteristics. In the design and manufacture of a half mirror, it is technically possible to obtain a semi-transparent film with small polarization dependence at a specific incident angle of 45 degrees, but the design of the film is difficult and the manufacturing process becomes complicated, The characteristic of the half mirror that the design and manufacture of the film is easy and inexpensive is lost. In addition, since the four optical fibers are radially arranged in directions different from each other by 90 degrees, a large space for arranging the optical fibers is required, and there is a problem that the apparatus becomes large.

[0008] Further, since the fiber type or waveguide type optical branching / coupling device uses distributed coupling, the degree of coupling varies depending on the wavelength and polarization state, and it is difficult to obtain uniformity.
Therefore, the light branching / coupling characteristics depend on the wavelength and the polarization state.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical branching / combining device capable of minimizing the dependence of the light branching / coupling characteristics on the wavelength and the polarization state, miniaturizing the optical fiber, and requiring a small space for optical fiber routing. That is.

[0010]

According to the present invention, there are provided two sets of a two-core ferrule in which two optical fiber cores are juxtaposed and a collimating lens formed of a homogeneous medium lens common to the two light beams. A light splitter in which the collimating lens is located inside and the distance between the two collimating lenses is opposed to each other so as to be apart by the sum of the respective focal lengths, and the half mirrors are installed at the focal positions of the two collimating lenses so as to be almost vertically incident. -It is a coupler. The half mirror is formed by forming a translucent film on the surface of a parallel plane transparent substrate.

The distance between the two optical fiber cores incorporated in the two-core ferrule is fairly narrow, and the angle formed by the two light beams intersecting by the collimating lens falls within several degrees. Therefore, if the half mirror is installed perpendicular to the optical axis, the incident angles of all the incident light on the half mirror become almost perpendicular. When the angle of incidence on the half mirror is substantially perpendicular, the change in the ratio between the transmitted light and the reflected light due to the change in the polarization state, that is, the polarization dependence can be suppressed.

[0012]

FIG. 1 is an explanatory diagram showing an embodiment of an optical branching / combining device according to the present invention. This is a bulk type having two input terminals and two output terminals. A first two-core ferrule 12 having two optical fiber core wires 10 arranged side by side, a first collimating lens 14 composed of a homogeneous medium lens common to the two light beams thereby, a half mirror 16, and the same as described above. A second collimator lens 18 composed of a homogeneous medium lens and a second two-core ferrule 2 in which two optical fiber core wires 10 are juxtaposed.
0 are arranged in a line in that order, and the entirety is housed in the housing 22. Here, the first and second
The collimating lenses 14 and 18 are opposed to each other such that their distance is the sum of the focal lengths of the respective collimating lenses, and is fixed to the housing 22. The half mirror 16 is set at the focal position of both collimating lenses in a direction perpendicular to the optical axis (indicated by a dashed line). As a result, the incident light from the optical fiber enters the half mirror 16 almost perpendicularly.

In this embodiment, spherical lenses of the same shape and the same material are used as both collimating lenses 14 and 18. Accordingly, the half mirror 16 is located exactly at the center between the two collimating lenses 14 and 18, and is fixed to the housing 22 at that position. As the half mirror 16, a mirror having a translucent film formed on the surface of a parallel plane transparent substrate is used. Note that both ball lenses need not be of the same shape and the same material. The collimating lens is not limited to a spherical lens, but may be a spherical lens or an aspherical lens that produces a lens effect depending on its shape in a homogeneous medium.

As shown in FIG. 2, two light beams from the two-core ferrule 12 and the collimating lens 14 intersect at the focal position of the collimating lens 14. The angle θ between two intersecting light beams is represented by the following equation. θ = 2 · tan ⁻¹ (t / 2f) where f is the focal length of the collimating lens, and t is 2
This is the optical fiber core line interval of the core ferrule.

A half mirror 16 is disposed at a position (focal position) where the two light beams intersect.
By adjusting the direction of the surface, a reflected light path composed of the two light beam paths can be formed. At this time, since the angle of incidence on the half mirror is nearly perpendicular, the change in the ratio between the transmitted light and the reflected light due to the change in the polarization state is considerably small.
For example, when f = 2.5 mm and t = 0.2 mm, θ = 4.
58 °, and the angle of incidence on the half mirror is about 2.29 °
It is. With such a small incident angle, as can be seen from FIG. 3, the polarization dependence of the transmittance and the reflectance hardly occurs.

The operation of the optical splitter / combiner shown in FIG. 1 is as follows. Two optical fibers connected to the first two-core ferrule 12 are referred to as a fiber and a fiber, respectively, and two optical fibers connected to the second two-core ferrule 20 are referred to as a fiber and a fiber, respectively. Here, the fiber and the fiber are the input side, and the fiber and the fiber are the output side. First, when used as an optical splitter, a part of the light incident from the fiber passes through the half mirror 16 and is coupled to the fiber, and the remainder reflected by the half mirror 16 is coupled to the fiber. If the ratio between the transmittance and the reflectance of the half mirror 16 is set to 1: 1, the light that has propagated through the fiber can be branched and propagated half by one between the fibers. Similarly, a part of the incident light from the fiber passes through the half mirror 16 and is coupled to the fiber, and the remainder reflected by the half mirror 16 is coupled to the fiber.

When used as an optical coupler, a part of the light propagating from the fiber is
Then, the light is reflected and input to the fiber, and a part of the light transmitted from the fiber is transmitted through the half mirror 16 and input to the fiber. Thus, the fiber and the light of the fiber are coupled to the fiber. Similarly, a part of the light transmitted from the fiber passes through the half mirror 16 and enters the fiber, and a part of the light transmitted from the fiber is reflected by the half mirror 16 and enters the fiber. In this manner, the fiber and the light of the fiber are coupled to the fiber.

In the above example, since the ratio between the transmittance and the reflectance in the half mirror is set to 1: 1, the branching ratio is equal. However, if the ratio between the transmittance and the reflectance is changed by changing the design of the translucent film in the half mirror, an optical splitter / coupler having an arbitrary splitting / coupling ratio can be obtained.

In the present invention, instead of a non-homogeneous medium lens such as a distributed index lens, a homogeneous medium lens having a light condensing function depending on the lens shape is used. The spherical lens used in the above embodiment is particularly preferable because it is inexpensive, but a lens of another shape (spherical lens or aspherical lens) may be used.

[0020]

According to the present invention, as described above, the angle of incidence on the half mirror is made substantially perpendicular by the two-core ferrule and the collimating lens, so that the change in the ratio between the transmitted light and the reflected light due to the change in the polarization state is reduced. Thus, an optical branching / combining device in which the polarization dependence of the light branching / coupling characteristics is suppressed can be obtained. Further, by using the two-core ferrule, the optical fiber is only drawn out to both sides, so that the whole device can be downsized and the space for the optical fiber can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an optical branching / combining device according to the present invention.

FIG. 2 is an explanatory diagram of light rays by the two-core ferrule and a collimating lens.

FIG. 3 is a graph showing incident angle dependence in a half mirror.

[Explanation of symbols]

 Reference Signs List 10 optical fiber core wire 12 first two-core ferrule 14 first collimating lens 16 half mirror 18 second collimating lens 20 second two-core ferrule 22 housing

Claims (2)

[Claims] 1. A combination of a two-core ferrule having two optical fiber cores arranged side by side and a collimating lens composed of a homogeneous medium lens common to two light beams by the two cores, wherein the collimating lens is located inside and An optical splitter / combiner, wherein two collimating lenses are opposed to each other so as to be separated by the sum of their respective focal lengths, and a half mirror is installed at a focal position of both collimating lenses so as to be substantially perpendicularly incident. 2. The optical splitter / coupler according to claim 1, wherein the half mirror has a structure in which a semitransparent film is formed on the surface of the parallel plane transparent substrate.