OPTICAL POWER MONITOR

Abstract

An optical power monitor capable of being reduced in size even when designed as a multi-channel monitor, and having a reduced light transmission loss is disclosed. The optical power monitor has two optical fibers provided on the light transmission upstream and downstream sides and having cores, the end surfaces which are opposed to each other with the core optical axes offset from each other, and which are fusion-spliced to each other in a fusion splicing portion, a light reflection surface which faces a portion of the upstream-side optical fiber core end surface offset to protrude from the downstream-side optical fiber core end surface in the fusion splicing portion, and which is provided in the downstream-side optical fiber cladding layer, and a photo-diode positioned opposite from the light reflection surface with respect to the downstream-side optical fiber core. Third-order or fourth-order lights strengthening each other in lights leaked into the downstream-side optical fiber cladding layer from the upstream-side optical fiber core end surface are reflected by the reflection surface provided in the cladding layer and detected with the photo-diode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an optical power monitor of the present invention in a state where an upper lid is removed;

FIG. 2 is a longitudinal sectional view of the optical power monitor of the present invention;

FIG. 3A is an enlarged longitudinal sectional view for explaining a fusion splicing portion between two optical fibers and a notch in the downstream-side optical fiber, FIG. 3B a longitudinal sectional view along an offset plane for explaining the fusion splicing portion between the two optical fibers, and FIG. 3C a transverse sectional view for explaining the fusion splicing portion;

FIGS. 4A and 4B are schematic diagrams for explaining travel of light leaked into a cladding layer from the core of the fusion splicing portion;

FIG. 5 is a graph showing the relationship between the responsivity and the distance L3 (mm) between the fusion splicing portion and the light reflection surface described with respect to EXAMPLE 2;

FIG. 6 is a graph showing the relationship between the responsivity and the angle θ1 (°) of the light reflection surface described with respect to EXAMPLE 3;

FIG. 7 is a graph showing the relationship between the responsivity and the offset/the core diameter described with respect to EXAMPLE 4;

FIG. 8 is a graph showing the relationship between the transmission loss and the offset/the core diameter described with respect to EXAMPLE 4;

FIG. 9 is a graph showing the relationship between the responsivity and the surface roughness of the light reflection surface described with respect to EXAMPLE 5;

FIG. 10 is a graph showing the relationship between the responsivity and the roughness motif average length AR (nm) obtained from an envelop undulation curve of the light reflection surface, described with respect to EXAMPLE 6;

FIG. 11 is a graph showing the relationship between the responsivity and the distance d (μm) between the notch bottom and the core periphery with respect to the transmission loss;

FIG. 12A is a longitudinal sectional view of an optical power monitor according to EXAMPLE 8 of the present invention, and FIGS. 12B and 12C are perspective views of first support blocks used in the optical power monitor;

FIG. 13 is a diagram for explaining the size of the optical fibers between support blocks in EXAMPLE 8;

FIG. 14 is a graph showing the relationship between the responsivity and the curvature radius r (m) in EXAMPLE 9 of the present invention;

FIG. 15 is a longitudinal sectional view of an optical power monitor in EXAMPLE 10 of the present invention;

FIG. 16 is a longitudinal sectional view of an optical power monitor in EXAMPLE 11 of the present invention;

FIGS. 17A and 17B show a conventional optical power monitor assembly, FIG. 17A is a perspective view, and FIG. 17B is a longitudinal sectional view of one optical power monitor in the assembly; and

FIGS. 18A and 18B show a conventional planar waveguide type of optical power monitor, FIG. 18A is a plan view and FIG. 18B is a longitudinal sectional view.

Claims

1. An optical power monitor comprising: two optical fibers, each having a core in its center and a cladding layer around the core, which are disposed on an upstream side and on a downstream side of light transmission, respectively, and which end surfaces face and are fusion-spliced to each other at a fusion splicing portion with their core optical axes offset from each other;a light reflection surface disposed in the cladding layer of the downstream-side optical fiber, facing part of the end surface of the upstream-side optical fiber core, which is offset and protrudes from the end surface of the downstream-side optical fiber core at the fusion splicing portion, and being at a certain angle with the core optical axis of the downstream-side optical fiber; anda photo-diode disposed opposite to the light reflection surface with respect to the downstream-side optical fiber core to detect lights that are transmitted through the upstream-side optical fiber core, leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core offset and protruding from the end surface of the downstream-side optical fiber core, and reflected by the light reflection surface,wherein the light reflection surface is located at a position that the lights leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core interfere and strengthen each other.

2. An optical power monitor as set forth in claim 1, wherein the light reflection surface is located at a third or forth position that the lights leaked into the cladding layer of the downstream-side optical fiber from the part of the end surface of the upstream-side optical fiber core interfere and strengthen each other.

3. An optical power monitor as set forth in claim 2, wherein the light reflection surface is located at a distance of 4.5 mm to 7.5 mm downstream from the fusion splicing portion.

4. An optical power monitor as set forth in claim 1, wherein the light reflection surface is at an angle of 38° to 45° with the core optical axis of the downstream-side optical fiber.

5. An optical power monitor as set forth in claim 2, wherein the light reflection surface is a side surface of a notch on the fusion splicing portion side out perpendicularly to the core optical axis of the downstream-side optical fiber in the cladding layer of the downstream-side optical fiber.

6. An optical power monitor as set forth in claim 5, wherein a distance between a bottom of the notch and a periphery of the downstream-side optical fiber core is 0.5 μm to 8 μm.

7. An optical power monitor as set forth in claim 5, wherein a surface roughness Ra of the light reflection surface is less than 2 nm.

8. An optical power monitor as set forth in claim 5, wherein the light reflection surface is a metal film formed on the side surface on the fusion splicing portion side of the notch.

9. An optical power monitor as set forth in claim 1, wherein an offset between the core optical axes of the two optical fibers is 0.05 times to 0.32 times a core diameter of the optical fibers.

10. An optical power monitor as set forth in claim 1, further comprising a first support block holding the upstream-side optical fiber on an upstream side of the fusion splicing portion, and a second support block holding the downstream-side optical fiber on a downstream side of the light reflection surface, wherein part of the two optical fibers between the first and the second support blocks is curved in an arc-like shape to rise in a direction opposite to the photo-diode.

11. An optical power monitor as set forth in claim 10, wherein the part of the two optical fibers between the first and the second support blocks has a peak of the arc-like shape almost at a mid-point between the first and the second support blocks.

12. An optical power monitor as set forth in claim 11, wherein the part of the two optical fibers between the first and the second support blocks is supported by a third support block almost at a mid-point between the first and the second support blocks.

13. An optical power-monitor as set forth in claim 10, wherein the part of the two optical fibers curved in the arc-like shape has a curvature radius of 0.085 m to 0.111 m or 0.347 m to 2.667 m.

14. An optical power monitor as set forth in claim 10, wherein a distance between the first and the second support blocks is 4.8 mm to 14.0 mm, and distances between the first support block and the fusion splicing portion and between the light reflection surface and the second support block are 0.2 mm to 2.0 mm.