JP2006064771A - Optical multiplexer / demultiplexer - Google Patents

Abstract

An object of the present invention is to enable efficient switching with a small number of parts by extending a switching function by having a fusion extending portion which is easy to make a high-density parallel multi-channel with little coupling loss and does not require assembly cost.
A first divided member and a second divided member formed by cutting a plurality of optical fibers A and B fused and stretched at a fusion stretched portion M to form a cut portion C, and the first divided member. And an optical filter F provided so as to be freely inserted and removed between the opposed surfaces of the member and the second divided member. The optical fiber has wavelength selection characteristics. AR coating was applied to the opposite end faces of the cut part.
[Selection] Figure 1

Description

  The present invention relates to an optical multiplexer / demultiplexer in which a plurality of optical fibers are fused and stretched.

  The optical switch transmits and blocks light. Conventionally, for example, Patent Documents 1 to 3 disclose the optical switch. Among these, in Patent Document 1, two end faces of four optical fibers are opposed to each other so as to cross each other, and a mirror that forms 45 degrees with respect to the end faces can be taken in and out using the micromachining technology. The technology which comprises the 2 * 2 optical switch which has the structure arrange | positioned in this and is equipped with the mirror driven with an electrostatic force and changes an optical path is disclosed. Patent Documents 2 and 3 disclose an optical switch having a structure in which an optical filter can be inserted and removed in the middle of a fiber for switching an optical signal.

On the other hand, as another optical fiber switching technique, there is an optical multiplexer / demultiplexer having an optical fiber coupler structure in which two optical fibers are fused and stretched. This optical multiplexer / demultiplexer transmits through the same fiber (referred to as “through”) depending on the manufacturing conditions and structure of the fused and stretched part, or a part of or all of the light passes through different fibers (referred to as “cross”). Have This optical multiplexer / demultiplexer is typically used as a switch for branching from a healthy line when a line failure occurs in an optical communication network, or as an optical communication multiplexer (OADM; Optical Add / Drop Multiplexer). A x2 optical switch is constructed.
JP 11-119129 A Japanese Patent Laid-Open No. 8-94944 JP-A-8-15620

However, in the above optical multiplexer / demultiplexer, it is possible to perform through or cross switching, but it is possible to perform efficient switching with fewer parts by expanding the switching function by using more ports. It is very preferable in various respects that the fields of use are widened such as increasing the number of uses.
On the other hand, in Patent Documents 1 to 3 disclosed as the above-described optical switches, in Patent Document 1, a mirror is disposed between the end faces of the optical fiber because of the structure. Must be large. In addition, since the optical fibers are individually mounted and the end face of the optical fiber and the mirror are not vertical, positioning and routing of the optical fiber is complicated and troublesome, and this makes it difficult to achieve high-density parallel multi-channel. . In addition, assembling the four optical fibers individually increases the assembly cost.

On the other hand, Patent Documents 2 and 3 are single optical fiber switching structures, and wavelength separation or the like is not possible as in the optical multiplexer / demultiplexer described above.
The present invention has been invented in view of the above-mentioned problems, and has optical splicing / demultiplexing having a fusion-stretching part that has a low coupling loss and a high-density parallel multi-channel, and that does not require assembling costs. It is an object of the present invention to provide an optical multiplexer / demultiplexer that can perform efficient switching with a reduced number of parts by expanding the switching function.

  The present invention that achieves the above-mentioned object includes a first divided member and a second divided member formed by cutting a plurality of optical fibers fused and stretched at the fusion stretched portion, the first divided member, And an optical filter provided so as to be freely put in and out between the opposed surfaces of each of the second divided members.

  According to the present invention, the optical filter can be inserted into and removed from the fusion stretched portion, which has a structure in which the coupling loss is small and the high-density parallel multi-channel is easy and the assembly cost is not required. By expanding the switching function, it is possible to perform efficient switching with a small number of components, and furthermore, it has a very effective division multiplexing function as a wavelength division multiplexing switch.

Now, an embodiment of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 shows an optical multiplexer / demultiplexer according to the first embodiment, which has a 2 × 2 fiber coupler structure. This fiber coupler structure is formed by heating and adhering to two optical fibers while applying tension, so-called fusion drawing, and by continuously changing the coupling coefficient for the light traveling inside the fiber. Yes. In the state in which the two optical fibers A and B are fused and stretched, for example, the light input from the port 1 becomes a through through the wavelength and is output to the port 3, and the port that passes through the optical fiber B is crossed by the cross. 4 or 3 and 4 depending on the coupling coefficient.

In the fusion-stretched portion M in which the distance between the two cores is smaller than the diameter of the two clads of the optical fiber due to fusion-stretching, the cut portion is cut perpendicularly to the longitudinal direction at the central portion in the longitudinal direction. C is formed. The end surface of the cut portion C is subjected to an AR coating (Anti Reflection Coating). In this disconnected state, the optical multiplexer / demultiplexer is divided into a first divided member on the left side in the figure having ports 1 and 2 and a second divided member on the right side in the figure having ports 3 and 4.
The optical filter F is perpendicular to the optical paths of the optical fibers A and B between the opposed end surfaces of the cut portions C of the first divided member and the second divided member on which the AR coating is applied. Thus, it is arranged so that it can be taken in and out. The optical filter F insertion / removal structure is manufactured using a micromachining technique, and can be formed by, for example, a double-supported beam structure, a cantilever beam structure, or a structure in which the filter support rigid body is approached / separated. Here, the optical filter F has a filtering function having so-called wavelength selectivity for discriminating the wavelength of light by reflection and transmission, and also has a function of totally reflecting light with a reflectance of 100% (reflection mirror). Is also included as a filter. Therefore, for example, when light is input to the port 1 in a state where the optical filter F is not inserted in the optical path, light of the same wavelength is branched at a certain ratio between the port 3 and the port 4, or different wavelengths. Can be designed such that the light from the port 3 is branched at a certain ratio between the port 3 and the port 4, and the light from the port 1 is transferred (shifted) to the cross port 4 by approximately 100%. Also for reverse multiplexing, the degree of crossing or through can be adjusted depending on the wavelength, and can be used properly as described above.

  In a state where the optical filter F is inserted in the optical path, when light is input to the port 1 of the optical filter F, a filtering function or a reflection function by the optical filter F is further added to enable further light discrimination. It becomes. For example, the light input from the port 1 is reflected and transmitted by the optical filter F with the same wavelength, and oozes into the optical fiber B due to the coupling coefficient. As a result, the light is output from all other ports 2, 3, 4. Is done. Alternatively, light having different wavelengths is output from all other ports 2, 3, 4 due to reflection and transmission of the optical filter F, and light leakage due to fusion stretching, or the optical filter F In the case of a reflection mirror (a filter having a reflectance of 100%), light can be output only to port 2. Also, with respect to the reverse multiplexing when the shining filter F is inserted, the degree of cross or through can be adjusted depending on the wavelength, and can be used properly as described above.

  In manufacturing such an optical switch, the following steps are taken. First, a 2 × 2 fiber coupler is formed by fusion drawing. Regarding the formation of the fusion extension portion of the 2 × 2 fiber coupler, for example, light input from one of the two input ports 1 or 2 crosses one of the two output ports 4 or 3 to have a desired coupling coefficient. For example, it is designed so as to shift approximately 100%. Next, cutting is performed perpendicularly to the longitudinal direction (to the optical path) at the central portion along the longitudinal direction of the fusion stretched portion M by dicing or the like. Thereafter, the cut end face is polished if necessary, and, for example, dirt is removed to improve the end face state. Next, AR coating is applied to the cut end face by sputtering or the like. An optical filter F is arranged between the end surfaces to which the AR coating is applied so as to be put in and out using a micromachining technique. In this case, the optical filter F is configured such that it can be inserted / removed along the cut surface (perpendicular to the optical path).

  An example of the light traveling operation in the manufactured optical switch will be described. Now, light that needs to be changed is input to port 1. Here, when a reflection mirror that reflects a certain frequency band as the optical filter F is inserted between cut surfaces (between optical paths), light in a certain frequency band from the port 1 is reflected by the reflection mirror and output to the port 2. Then, light in other frequency bands is transmitted and becomes output light to the through port 3 or the cross port 4. Here, when the light reflected by the reflecting mirror is also light that crosses at the fusion extension part M, for example, when the light from the port 1 is designed to move to the port 4 approximately 100%. In other words, the light oozing state at the cut longitudinal center of the fusion stretched part M is an energy state equally divided into the port 1 side and the port 2 side. Therefore, in the process in which the light from the port 1 is reflected by the reflecting mirror and propagates to the port 2, the light in an equal energy state at the central portion in the longitudinal direction is completely transferred to the port 2. Therefore, all light in a certain frequency band from port 1 is output to port 2. At this time, the free space propagation distance between the cut surface and the reflecting mirror is extremely small, and mode transition hardly occurs in this free space propagation.

  On the other hand, when the reflecting mirror is not inserted between the cut planes (between the optical paths), when the light from the port 1 is designed to transfer to the port 4 approximately 100%, the light from the port 1 remains as it is. Go straight and output to cross port 4. In this case, in the fusion stretched part M, the light is output to the port 4 in a state where the light is completely transferred. At this time, since the free space propagation distance of the reflecting mirror is extremely short, mode transition hardly occurs. Thus, in this example, the light from the port 1 can be switched between the port 2 and the port 4 by inserting and removing the reflecting mirror between the cut surfaces.

Here, the insertion loss, which is a characteristic of the optical switch, is calculated by substituting the thickness of the optical filter F actually created and the gap between the fiber end face and the filter. The main insertion loss is a mode coupling loss received when light emitted from the optical fiber propagates through free space and reenters the optical fiber, and is obtained by the following equation of coupling efficiency η.
η = 2 (4 + λZ ² / (π ² ω ⁴ )) ^−1/2
Here, λ is the wavelength, Z is the free space propagation distance, and ω is the mode radius at the fiber exit end.

Based on this equation, the coupling efficiency with a long free propagation distance from port 1 to port 3 is calculated. In this case, λ = 1.55 μm, Z = 30 μm (optical fiber end face and reflecting mirror gap 10 μm × 2 and reflecting mirror thickness 10 μm), and ω = 7 μm (multi-mode average in the vertical and horizontal directions) are substituted. As a result, η = 99.3% (loss conversion 0.03 dB), and the insertion loss value sufficiently satisfies the usable level as an optical switch.
[Second Embodiment]
FIG. 2 shows a second embodiment of an optical multiplexer / demultiplexer having a fiber coupler structure. Here, as an example, an optical module for PON (Passive Optical Network; technology for drawing from a fiber optic network to a subscriber by a branching device) in FTTH (Fiber To The Home; optical fiber network) is formed.
This optical module has a 2 × 2 fiber coupler structure, and a WDM (Wavelength Division Multiplexing) filter is inserted perpendicularly in the longitudinal direction (optical path) at the longitudinal center of the fusion stretched portion. . In this case, the WDM filter F has a characteristic of reflecting light having a wavelength of 1.55 μm or more, and even light having a wavelength of 1.55 or less is divided into through light or cross light depending on the wavelength. In the example of FIG. 2, when 1.49 μm and 1.55 μm light is input to port 1, 1.55 μm cross light is output to port 2 due to reflection, and 1.49 μm through light is output to port 3. Is output, and 1.31 μm cross light is output to port 1 when 1.31 μm light is input to port 4.

As described above, since the WDM filter F is interposed in the fusion extending portion M of the optical switch having the fiber coupler structure, light that has been wavelength-divided is output from the three ports with respect to the input light.
In the example shown in FIG. 2, the optical filter F is interposed and fixed between the opposed surfaces of the first divided member and the second divided member, but the optical filter F can be taken in and out as in the first embodiment. Thus, the reflection and transmission characteristics due to this insertion and removal can be taken into consideration.
In the above description, the 2 × 2 fiber coupler structure has been described. However, as shown in FIG. 3, a structure in which three optical fibers A, B, and C are fused and stretched, or a fusion stretched portion M is used. The present invention can also be applied to three or more optical fibers such as a cut structure.

It is a disassembled block diagram of 1st Embodiment. It is a block diagram of 2nd Embodiment. It is a block diagram of another example.

Claims (4)

A first split member and a second split member formed by cutting a plurality of optical fibers fused and stretched with each other at the melt stretch portion;
An optical multiplexer / demultiplexer comprising: an optical filter provided so as to be freely inserted and removed between opposed surfaces of the first divided member and the second divided member.   2. The optical multiplexer / demultiplexer according to claim 1, wherein the optical filter has a wavelength selection characteristic.   3. The optical multiplexer / demultiplexer according to claim 1, wherein an AR coating is applied to the cut opposing surface. A first split member and a second split member formed by cutting a plurality of optical fibers fused and stretched at the fusion stretch portion;
An optical multiplexer / demultiplexer comprising: an optical filter having a wavelength selection characteristic that is interposed and fixed between the opposed surfaces of the first divided member and the second divided member.

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