JPS5844413A - Optical branching and coupling circuit - Google Patents

Abstract

PURPOSE:To prevent an influence upon a distribution in propagation mode even if a distribution ratio is varied, by rotating a phase difference plate and thus adjusting the branching and coupling ratio of the quantity of light. CONSTITUTION:Emitted light from an optical fiber 1 is collimated by a lens 2 and then separated by a polarizing and separating element 8 into P-polarized light and S-polarized light; the P-polarized light is reflected to change in direction by 90 deg., and is then emitted. The S-polarized light changes in direction by 90 deg. through a reflecting mirror. Then, the P-polarized light and S-polarized light are both guided to a phase difference plate 10 to rotate their planes of linear polarization by 2theta. The P-polarized light changes in direction through a reflecting mirror 11. The P-polarized light and S-polarized light both having the planes of linear polarization rotated by 2theta are caused to illuminate a polarizing and separating element 12, thereby obtaining the quantity cos<2>2theta of light at one end surface of an optical fiber 6 and the quantity 1-cos<2>2theta of light at one end surface of an optical fiber 7. Then, theta is varied by rotating the phase difference plate to vary the distribution ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical branching and coupling circuit, and for example, in an optical splitter that distributes the output light of an optical fiber for optical communication to a plurality of optical fibers, it is possible to make the distribution ratio variable. This invention relates to an optical branching and coupling circuit.

FIG. 1 is a sectional view showing a conventional optical branching and coupling circuit. In FIG. 1, a first optical fiber (1) emits light. The first lens (2) is connected to the first optical fiber (
1) converts the emitted light into parallel light beams, the focal length of which is f. ■ Letter-shaped prism (■ is the bottom surface perpendicular to the optical axis 0 where the parallel rays from the first lens (2) are incident)
301) and V-shaped reflective surfaces (302) and (303) that reflect the incident light from the bottom surface (301) in a direction perpendicular to the optical axis 0 and split it into two beams. Reflective surface (30
2), an iv-shaped reflective surface (303) installed parallel to
It is composed of reflecting surfaces (304) and (305) that reflect the light from 02) and (303) into two rays parallel to the optical axis 0, and the direction T − perpendicular to the optical axis 0. ◇The second and third lenses (Φ, (5
) are the reflective surfaces (304) of the V-shaped prism (3), respectively.
, (305) to the second and third optical fibers (
6) and (7), each having a focal length of t.

Next, we will explain this operation using a 0M1 optical fiber (1
) The emitted light from the first optical fiber (1) has a numerical aperture (
N-A) is emitted by the first lens (2) and parallel light 1i!
ll&CM will be exchanged. These parallel rays pass through a V-shaped prism (
3) enters the V-shaped prism (3) from the bottom surface (301) of the V-shaped reflective surface (302).

It is totally reflected at (303) and split into two beams, which are reflected again at one reflecting surface (304) and (305) to become two beams parallel to the optical axis 0. The second and third lights 7 eyepers (6) and (7
) To change the ratio of the amount of light coupled to the second and third optical fibers (6) and (7), align the one-character brism (3) perpendicular to the optical axis O.・It is sufficient to move the 21st and 3rd lights in the direction T-T' at an arbitrary distribution ratio depending on the amount of movement.
) can adjust the amount of light coupled to the end face of the first optical fiber The emitted light is divided into two equal parts and connected to the second and third optical fibers (6
), (7), the propagation modes of the low-order mode near the optical axis 0 and the high-order mode F at a position away from the optical axis 0 are equally distributed. However, if the V-shaped prism (3) is moved downward in FIG.
), the propagation modes of a low-order mode and a high-order mode are distributed, but the propagation mode of only the high-order mode is distributed in the third optical fiber ('7). Therefore, when the distribution ratio is other than 1:1, the second and third optical fibers (6),
(There was a drawback that the distribution of the propagation mode of η was changed, resulting in changes in propagation loss, etc.) This invention was made to eliminate the drawbacks of the conventional method as described above, and even if the distribution ratio is changed. The purpose of this invention is to provide an optical drum coupling circuit that does not affect the distribution of propagation modes.The present invention will be explained in detail with reference to the drawings below. Figure 2 shows an implementation of the optical drum coupling circuit according to the present invention. It is a configuration diagram showing an example. In the figure, the same parts as in the first gJ are given the same reference numerals. In the second WJ, the first polarization splitting element (marked is composed of a beam splitter using a dielectric multilayer film). ~The first beam made parallel by the first lens (2)
The light emitted from the optical fiber (1) is separated into P-polarized light with polarization parallel to the plane of incidence and S-polarized light with polarization perpendicular to the plane of incidence. The first reflecting mirror (9 companies' first polarization splitter ■) changes the direction of the incident light by 90 degrees and makes the S-polarized light emitted parallel to the incident light. Retardation plate (10 ) is composed of a half-wave plate, and if the angle between the vibration direction of the incident linearly polarized light and the crystal optical axis of the half-wave plate is O, then the output light is 2 times the linearly polarized light of the incident light.
It is converted into linearly polarized light rotated by 0, and the first
P polarized light transmitted through the polarization splitting element (a) and the first reflecting mirror (
0 second, where the S polarized light reflected by 9 is incident.
The reflecting mirror (11) deflects by 90 degrees the P-polarized light whose linear polarization plane has been rotated by 20 degrees by the retardation plate (10).
The second polarization separation element (12) is composed of a beam splitter using a dielectric multilayer film, and the P-polarized light and the 8-polarized light whose linear polarization planes are rotated by 2θ by the retardation plate (10) are alternately ψ. The second and third lights are incident at angles different by 90 degrees and pass through the third lenses (4) and (5). It is.

Next, this operation will be explained. The light emitted from the first optical fiber (1) is made into almost parallel light by the first lens (2), and then converted into P-polarized light with polarization parallel to the incident plane by the first polarization splitter (8). The P-polarized light is transmitted, the S-polarized light is reflected, and the oS-polarized light, which is emitted after changing its direction by 90 degrees, is polarized by 90 degrees by the first reflection 1t (9). It is converted into two parallel light beams, P-polarized light and 8-polarized light, which have mutually perpendicular polarization. ◎Then, they are input to one retardation plate (10), and both P-polarized light and 8-polarized light are converted into two parallel light beams, respectively.
The linear polarization plane is rotated by θ 〇 The P polarized light whose linear polarization plane is rotated by 20 in this way is reflected by the second reflection m (11)
The P-polarized light thus deflected by 90 degrees and the S-polarized light from the retardation plate (1α) are respectively incident on the second polarization separation element (12). Therefore, ignoring the absorption and surface reflection loss of the first, second, and third lenses e), (4), and (5) and the first and second polarization splitting elements (8) and (12), If the amount of light emitted from the first optical fiber (1) is 1, the end face of the second optical fiber (6) has 00 (2#)%, and the end face of the third optical fiber (η) has If
1-001' (2a) is coupled.

This invention is constructed as described above, and the retardation plate (10) is rotated with respect to the vibration direction of the linearly polarized light of the P-polarized light and the S-polarized light emitted from the 1st and 10th polarized light separation element (at), and the angle of the optical axis ( 2θ), the distribution ratio can be changed continuously from 0 to 1. In the above embodiment, a half-wave plate that linearly polarizes light is used as the retardation plate (10). As described above, a quarter-wave plate that performs curved and elliptical polarization may be used as the retardation plate (10).However, in this case, the range concavity that can be varied is the second optical fiber (6). 0 for K.
5-1 0.5-0 for the third optical fiber ('7)
becomes.

Further, in the above embodiment, the first and second polarization splitting elements (8)
, As for (12), a polarizing beam splitter using a dielectric multilayer film was used, but as shown in 1.3 □□□,
, a polarizing prism such as a Glan-Thompson prism may be used as the second polarization separating element (8), (12).

FIG. 3 is a configuration diagram showing another embodiment of the optical branching and coupling circuit according to the present invention. The same parts in the figure as in FIG. 2 are given the same reference numerals. In FIG. 3, polarization prisms such as Glan-Thompson prisms are used as the first and second polarization separation elements (8) and (12). In this case as well, the same effects as in the embodiment shown in FIG. According to the present invention, the splitter and coupler are collectively referred to as an optical branching and coupling circuit, and the effect is that the distribution ratio can be adjusted continuously without affecting the propagation mode distribution of the optical fiber. has.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conventional optical branching and coupling circuit. FIG. 2 is a configuration diagram showing an embodiment of the optical branching and coupling circuit according to the present invention. FIG. 3 is a block diagram showing another embodiment of the optical branching and coupling circuit according to Jin's invention. In FIG.
(4). (The groups are the first, second, and third lenses, (6), (?
) is the 21st third "light 7 eye, (, (a) is the first polarization splitting element, (9) is the first reflecting mirror, (10) is the retardation plate, , (11) is the second The reflecting mirror (12) is the second polarization separation element.The same parts in each figure are given the same reference numerals.Representative Patent Attorney Makoto Kuzuno 1986-44413 (4) Procedural amendment (spontaneous) Dear Commissioner of the Japan Patent Office ・ 1. Indication of the case Patent application No. 143588-1982 2
・Title of the invention: Optical branching/coupling circuit 3, Relationship with the case of the person making the amendment: Patent applicant 5, Detailed explanation of the invention in the specification to be amended 6, Contents of the amendment (1) Specification φ page 4 In the sixth line, "Direction Tete'" is corrected to "Direction!-!". (2) Page 8, line 9 ζ [Delete the statement that curve and elliptical polarization is performed. that's all"

Claims (1)

[Claims] 1. A first polarization separation element that separates the light emitted from the first optical fiber into two linearly polarized lights; A second polarization separation element that separates the two M-line polarized lights transmitted through the retardation plate and inputs them into a third optical fiber by 2%; An optical branching/coupling circuit characterized in that the light branching/coupling circuit is rotated so that the ratio of the amounts of light coupled to the second and third optical fibers can be set to nu. 2. The optical branching and coupling circuit according to claim 1, wherein the retardation plate is a half wavelength plate. 3. The optical branching and coupling circuit according to claim 1JJ, wherein the retardation plate is a quarter wavelength plate. 4. The optical branching and coupling circuit according to any one of claims 1 to 3, wherein each of the @1 and second polarization separation elements is a polarization beam splitter using a dielectric multilayer film. ◎ 5. 1st. Each of the second polarization splitting elements is a polarizing prism.
The optical branching and coupling circuit described in .