JP3083015B2 - Waveguide type optical branching coupling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical branching / coupling device in which an optical branching device and an optical coupler are integrated.

[0002]

2. Description of the Related Art In recent years, in an optical fiber communication system, a large number of optical splitters are used for distributing optical information.
Many optical couplers are used for monitoring and testing optical fiber transmission lines. As the optical branching device and the optical coupler, at present, an optical fiber itself is used as a constituent material, and a fiber coupler type configured by an optical fiber coupler formed through polishing, fusion, and stretching processes, or a flat substrate is used. A waveguide type optical waveguide formed by photolithography or etching has been developed.

In an optical fiber communication system, when monitoring and testing a large number of optical fiber transmission lines after being split by an optical splitter, conventionally, as shown in FIG. 2, a fiber coupler type or waveguide type is used. Many output fibers 2 of the optical splitter 1 and one input fiber 4 of many optical couplers 3 of the fiber coupler type or the waveguide type.
And the output fiber 5 of one of the optical couplers 3 and the optical fiber transmission lines 6 are connected to each other, and the other input fiber 7 of the optical coupler 3 is connected to the other input fiber 7 of the optical coupler 3. OTDR (Optical Time D not shown)
Omain Reflectometer) was to be connected.

[0004]

However, the above-described configuration requires a large number of components, which is expensive, and requires a circuit for processing the extra length of the optical fiber connecting the optical splitter and the optical coupler. There was a problem that the whole became very large.

In view of the above-mentioned conventional problems, the present invention provides an optical branching device for distributing optical information to a large number of optical fiber transmission lines, and a device required for monitoring and testing the optical fiber transmission line. An object of the present invention is to provide a small-sized and low-loss waveguide type optical branching / coupling element in which an optical coupler for coupling to a fiber transmission line is integrated.

[0006]

According to the present invention, in order to achieve the above object, a first optical waveguide is formed on a plane substrate, the first optical waveguide being continuous from one side of the plane substrate to the other side and branching into a plurality of paths on the way. A plurality of second optical waveguides continuous with at least one side of the planar substrate and respectively coupled to the plurality of first optical waveguides after the branch are provided on the planar substrate. The present invention proposes a waveguide-type optical branching / coupling element in which an optical coupler is formed and the plurality of second optical waveguides are arranged on one side of the flat substrate on both sides of the first optical waveguide.

[0007]

According to the present invention, there is provided an optical splitter for distributing optical information, and an optical coupler for monitoring and testing a large number of optical fiber transmission lines after splitting by the optical splitter. Can be integrally formed on one substrate.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the waveguide type optical branching / coupling device of the present invention. In FIG. 1, reference numeral 10 denotes a plane substrate, 100 denotes a first optical waveguide for distributing optical information, 201, 202,. .. 315 are optical splitters, and 401, 402,... 416 are optical couplers.

The first optical waveguide 100 has an input end on the plane substrate 10, that is, two input optical waveguides 101 and 102 are connected to one side 11 of the plane substrate 10, and optical splitters 301 to 315 are connected. The output ends branched through, that is, 16 output optical waveguides 103
To 118 are formed so as to be continuous with the other side 12 of the planar substrate 10.

Here, the optical splitter 301 is composed of two optical waveguides.
Nos. 101 and 102 are disclosed in Japanese Patent Application No. 1-26542 (Japanese Unexamined Patent Application Publication No.
No. 13829), a two-input two-output optical splitter set so that the splitting ratio is about 50% in a wide wavelength range. Each of the optical splitters 302 to 315 has an optical waveguide structure of Y
This is a well-known Y-branch type optical splitter which is formed in the shape of a letter and is set so that the splitting ratio is about 50% in a wide wavelength range. , Eight three
A total of 14 steps are arranged. The optical splitters 301 to 31
5 operates as a 2-input 16-output optical branch circuit.

The second optical waveguides 201 to 216 correspond to the flat substrate 1
0, one end thereof is continuous with one side 11 of the flat substrate 10,
The output optical waveguides 103 to 118 have optical couplers 401 to
It is formed so as to be connected via 416. Here, the optical couplers 401 to 416 are designed so that the corresponding two optical waveguides of the second optical waveguides 201 to 216 and the output optical waveguides 103 to 118 are designed in the same manner as the optical branching device 301 described above. By configuring according to the method, a coupling ratio of about 20 in a wide wavelength range is obtained.
% Is a two-input two-output optical coupler. Also, of the second optical waveguides 201 to 216, the central 2
The other ends of the optical waveguides 208 and 209 are formed so as to be continuous with the other side 12 of the flat substrate 10 so that the branch output side can be monitored and tested from the branch output side.

The second optical waveguides 201 to 216 are arranged on one side 11 of the flat substrate 10 so as to be sequentially arranged on both outer sides of the input optical waveguides 101 and 102. For this reason, the second optical waveguides 201 to 216 may intersect with the first optical waveguide 100 between the optical splitters in each stage. For example, an optical waveguide
203 crosses the optical waveguide 100 between the optical splitters 302 and 304 and 304 and 309 (501 and 502), and is connected to the optical coupler 403.

In general, when two optical waveguides intersect, if the angle of intersection is small, light propagating through one optical waveguide leaks into the other optical waveguide. A suitable bent optical waveguide is provided at a necessary portion, for example, a bent optical waveguide 119 is provided between the optical splitters 302 and 304.
Are formed.

Next, a specific configuration and operation of the waveguide type optical branching / coupling element will be described. In the following description, a quartz-based single-mode optical waveguide formed on a silicon substrate is described as an optical waveguide. This is because the silica-based single-mode optical waveguide has excellent connectivity with a single-mode optical fiber. This is because a practical waveguide-type optical branching / coupling element can be provided, and the present invention is not limited to a silica-based optical waveguide.

FIGS. 3A and 3B show an optical circuit corresponding to the optical splitter 301 in FIG. 1, wherein FIG. 3A is a plan view and FIG.
(a) It is an expanded sectional view in the AA 'line arrow direction in a middle. In the figure, 601 is a silicon substrate, 602 and 603 are silicon substrates 60
1 is a quartz optical waveguide formed on the quartz glass material.

The optical waveguides 602 and 603 form directional couplers 604 and 605 in close proximity to each other at two locations. The optical waveguides 602, 603 have a cross section of 8 μm × 8 μm embedded in a SiO ₂ glass (cladding) layer 606 having a thickness of about 50 μm.
and a refractive index of about m consists of about 0.3% higher SiO ₂ -GeO ₂ glass core than is the glass layer 606, is configured Mach-Zehnder optical interferometer circuit by a combination of the straight line pattern and the circular arc pattern I have.

Such a quartz optical waveguide can be formed by a known combination of a glass film deposition technique using a flame hydrolysis reaction of silicon tetrachloride or titanium tetrachloride and a fine processing technique by reactive ion etching. Directional coupler 604,
The coupling part of the directional coupler 605 is constructed by keeping the distance between the two optical waveguides 602 and 603 at 3 μm and 5 μm, respectively, and arranging them in parallel over a distance of 0.4 mm. The difference between the lengths of the optical waveguides in the portion connecting the 605 is set to 0.7 μm. With such a design,
An optical splitter having a splitting ratio of 50 ± 5% in a wide wavelength range of 1.25 to 1.65 μm.

Each of the optical couplers 401 to 416 in FIG. 1 has exactly the same structure as the optical circuit in FIG. 3, and simply has an optical waveguide at a coupling portion of two directional couplers formed by two optical waveguides. The difference is that the intervals between the wave paths are 4 μm and 6 μm, respectively, and the length of the parallel portion is 0.2 mm. With such a design, the coupling ratio is 20 ± 3 in a wide wavelength range of 1.25 to 1.65 μm.
% Optical coupler. Thereby, the optical waveguides 201 to 21
The optical signal incident on 6 is coupled to the output optical waveguides 103 to 118 in the wide wavelength range of 1.25 to 1.65 μm, and about 20% of the optical signal can be monitored and tested on the optical fiber transmission line using OTDR etc. Becomes The split optical signal is about 20
%, Which is radiated into the substrate at the junction, but with a loss value of about 1 dB, not so great.

As described above, when two optical waveguides cross each other, if the crossing angle is small, the amount of light that has propagated through one optical waveguide leaks into the other optical waveguide, and the amount increases. Although the radiation loss increases, increasing the crossing angle increases the size of the circuit, so the crossing angle must be set to an appropriate value.

FIG. 4 shows the result of calculating the relationship between the crossing angle of the optical waveguide and the amount of crosstalk attenuation. From FIG.
In order to reduce the crosstalk attenuation to at least -30 dB or less, it is necessary to set the crossing angle to 12 degrees or more. In this embodiment, the crossing angle is set to 13 degrees or more at least. In addition, in order to make this intersection angle in a short length, each optical waveguide has a radius of curvature as small as possible within a range in which a bending loss does not increase in a wavelength region to be used. In this embodiment, a combination of a 25 mm arc and a straight line is used. It consisted of. Further, if necessary, an appropriate bent optical waveguide, for example, the above-described bent optical waveguide 119 is formed so that the intersection angle is at least 13 degrees.

Further, in the waveguide type optical branching / coupling device of this embodiment, a total of 18 optical waveguides are provided on one side 11 of the flat substrate 10, two for optical information distribution and 16 for monitoring / testing. Each of the optical waveguides is arranged at intervals of 250 μm, and 16 optical waveguides for optical information distribution and two optical waveguides for monitoring and testing are arranged on the other side 12 at intervals of 250 μm each, and are arranged at the same pitch. A fiber array (not shown) was assembled so that it could be connected and used.

Here, the dimensions of the waveguide type optical branching / coupling element of the present embodiment will be described. The size of the substrate 10 is 70 mm in length and 7.5 mm in width. Even the size of the whole assembled circuit is 11
The size is 0 × 12 × 5 mm, and it can be made compact. An optical circuit having the same function as this can be realized by connecting and combining 31 optical fiber couplers. It can be seen that the embodiment is extremely effective for miniaturization.

FIG. 5 shows the measurement results of the branching characteristics of the waveguide type optical branching / coupling device of this embodiment. 1.31μ wavelength
m and 1.55 μm optical signals are evenly split, and the average loss is 1
It was 5.5 dB. The horizontal axis represents each output optical waveguide 103 to 1
18 is represented by numbers “1” to “16”.

FIG. 6 shows the measurement results of the wavelength characteristics of loss when an optical signal enters the optical waveguide 203 and exits from the output optical waveguide 105 in the waveguide type optical branching / coupling device of this embodiment. is there. It showed a substantially constant value of 8.5 ± 0.5 dB over a wide range of wavelengths from 1.24 to 1.69 μm. In consideration of the coupling loss between the optical fiber and the optical waveguide and various losses in the optical waveguide, this value indicates that the coupling rate of the optical coupler 403 is 19 ± 2%.
, And it can be seen that it is as designed.

The values corresponding to the two losses in a conventional optical circuit assembled by connecting a 16-branch splitter using an optical fiber coupler and an optical fiber coupler having a coupling ratio of 20% are 16 dB and 8 dB on average, respectively. Thus, it can be said that the waveguide type optical branching / coupling element of this embodiment has a sufficiently low loss.

FIG. 7 shows the measurement results of the crosstalk attenuation to the output optical waveguides 103, 104, 106 to 118 when an optical signal is incident on the optical waveguide 203 in the waveguide type optical branching / coupling device of this embodiment. Things. The crosstalk attenuation amounts are all -40 dB or less, and there is no problem in monitoring and testing the optical fiber transmission line after branching.

In the above-described embodiment, two directional couplers are connected as the optical couplers 401 to 416 to form a Mach-Zehnder optical interferometer circuit, and an optical waveguide connecting the two directional couplers is formed. The length is given a controlled small difference to reduce the wavelength dependence of the coupling ratio in the desired wavelength range. However, if the wavelength to be used is limited, one direction is used. It is also possible to configure an optical coupler with a sex coupler.

In the above embodiment, the first-stage optical splitter 30
As one, two directional couplers are connected to form a Mach-Zehnder optical interferometer circuit configuration, and a controlled small difference in the length of the optical waveguide connecting the two directional couplers is set. A two-input type branching device in which the branching ratio in the desired wavelength range is set to approximately 50% was used. Needless to say, a one-input type is also possible. Furthermore, N
The present invention can be applied to a × N star coupler.

Further, in the above embodiment, the optical waveguide is constituted by a quartz-based (SiO ₂ -GeO ₂ ) optical waveguide on a silicon substrate. However, the substrate is not limited to silicon and can be changed to a quartz glass substrate. In addition, the present invention is not limited to these silica-based optical waveguides, but can be applied to other optical waveguide material systems, such as a multi-component glass optical waveguide system, a lithium niobate optical waveguide system, and a polymer optical waveguide system. Note what you can do.

[0030]

As described above, according to the present invention, a first optical waveguide is formed on a flat substrate, which is continuous from one side of the flat substrate to the other side and is branched into a plurality of optical waveguides on the way. Forming a branching device, and providing, on the planar substrate, a plurality of second optical waveguides connected to at least one side of the planar substrate and coupled to the plurality of branched first optical waveguides, respectively; An optical branching device for distributing optical information, since the arrangement of the plurality of second optical waveguides on one side of the flat substrate is made on both sides of the first optical waveguide, An optical coupler for monitoring and testing a large number of optical fiber transmission lines after being split by the optical splitter can be integrally formed on a single substrate, so that it can be easily connected to an optical fiber array. Provide a compact, low-loss waveguide type optical branching / coupling device Door can be. Such a waveguide type optical branching / coupling element can realize an optical information distribution function and an optical fiber transmission line monitoring / testing function in an optical fiber communication system, and thus contributes to economicalization of the system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a waveguide type optical branching / coupling element of the present invention.

FIG. 2 is a configuration diagram of a conventional circuit that enables monitoring and testing of an optical fiber transmission line after branching;

FIG. 3 is a configuration diagram of an optical circuit corresponding to a first-stage optical splitter in FIG. 1;

FIG. 4 is a graph showing the relationship between the crossing angle and the crosstalk attenuation at the intersection of the optical waveguides in the waveguide type optical branching / coupling device of FIG. 1;

FIG. 5 is a graph showing optical branching characteristics of the waveguide type optical branching / coupling device of FIG. 1;

FIG. 6 is a graph showing an example of a loss wavelength characteristic of the waveguide type optical branching / coupling device of FIG. 1;

FIG. 7 is a graph showing an example of crosstalk characteristics of the waveguide-type optical branching / coupling device of FIG. 1;

[Explanation of symbols]

10: flat substrate, 11: one side, 12: other side, 100: first
Optical waveguides, 101, 102 ... input optical waveguides, 103 to 118 ...
Output optical waveguides, 201 to 216... Second optical waveguides, 301 to 31
5 ... Optical splitter, 401-416 ... Optical coupler.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Izumi Mikawa 1-6-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Hitoshi Hashimoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Japan Telegraph and Telephone Co., Ltd. (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/12-6/138

Claims (3)

(57) [Claims] An optical branching device is formed on a planar substrate by forming a first optical waveguide that is continuous from one side to the other side of the planar substrate and is branched into a plurality of optical waveguides on the way. A plurality of second optical waveguides which are continuous with at least one side of the planar substrate and are respectively coupled to the plurality of first optical waveguides after the branching, to form an optical coupler; A waveguide type optical branching / coupling device, wherein an optical waveguide is arranged on one side of the planar substrate on both outer sides of the first optical waveguide. 2. A Mach-Zehnder optical interferometer circuit configuration comprising two directional couplers connected as an optical coupler.
An optical coupler having a predetermined small difference in the length of the optical waveguide connecting the directional couplers to reduce the wavelength dependence of the coupling ratio in a desired wavelength range. 2. The waveguide type optical branching / coupling device according to 1. 3. A Mach-Zehnder optical interferometer circuit configuration comprising two directional couplers connected as an optical splitter.
2. An optical splitter having a predetermined slight difference in the length of an optical waveguide connecting two directional couplers and having a splitting ratio of approximately 50% in a desired wavelength range. The waveguide type optical branching / coupling device according to any one of the preceding claims.