JPS59198408A - Waveguide type optical branching device - Google Patents

Abstract

PURPOSE:To reduce the number of constituting parts, to make them small-sized and to reduce the number of processes of polishing and sticking by inserting a multilayered interference film filter into a cut part of an optical waveguide of a substrate. CONSTITUTION:Waveguides 22a-22c are formed on a substrate 21, and multilayered interference film filters 25b and 25c are inserted into cut parts 23b and 23c. An input optical fiber 24a is connected to the waveguide 22a, and output optical fibers 24b and 24c are connected directly to waveguides 22b and 22c. A two-wavelength multiple signal light (wavelengths lambda1 and lambda2) introduced from the fiber 24a to the waveguide 22a is led to the waveguide 22c, and only the light having the wavelength lambda2 is transmitted selectively through the filter 25c and is emitted to the fiber 24c. Most of the light reflected by the filter 25c is emitted to the waveguide 22b, and only the light having the wavelength lambda1 is transmitted through the filter 25b and is led out to the fiber 24b, thus fulfilling the function of an optical branching device. A multicomponent glass produced by a macromolecule or ion diffusing method or a quartz glass consisting essentially of an SiCl4 can be used as materials of waveguides 22a-22c.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical demultiplexer used in the field of wavelength multiplexed optical communications.

In a wavelength division multiplexing transmission system in which optical signal waves with different wavelengths are transmitted through a single optical fiber, an optical demultiplexer is required to separate the optical signals with different wavelengths. Optical demultiplexers can be broadly classified into diffraction grating type and multilayer interference film filter type, but the multilayer interference film filter type tends to be mainly used from the viewpoint of wavelength separation characteristics.

Conventionally, a multilayer interference film filter type optical demultiplexer has been constructed as shown in FIG. In FIG. 1, 1 is a common substrate glass, 2a, 2b, 2c, and ZcLZe are coupling prisms, and 8
a, 8b, 8c, 8d, 8e are rod lenses, 4b, 4
Numerals c, 4d, and 4e are multilayer interference film filters, 5a is an input fiber, and 5b, 5c, 5d, and 5e are output fibers.

Wavelength multiplexed light (here, 4 wavelengths) incident from the input fiber 5a
Wave λl l 'Z lλ8. λ,) is the rod lens 8a
The light becomes a parallel beam of light, which passes through the coupling prism 2a and the common substrate glass l, and is irradiated onto the multilayer interference film filter 4b. The filter 4b selectively transmits only the signal light of wavelength λ□ and reflects the signal light of other wavelengths. The signal light having the wavelength λ□ that has passed through the filter 4b is focused by the rod lens 8b and introduced into the output fiber 5b. Similarly, filter 4e
.

4d and 4e each have a wavelength λ2. λ8. It is set to transmit only the signal light of λ, and is branched to output fibers 5c, 5d, and 5e, respectively, depending on the wavelength.

In this way, the optical demultiplexer shown in Figure 1 can perform the desired function, but its configuration is complex, requiring polishing and bonding of numerous optical blocks, and alignment of optical fibers and Rondo lenses. The major drawback was that the process required skill and a long time.

This made the finished product extremely expensive, which was one of the factors preventing the spread of wavelength multiplexing.

In order to eliminate these drawbacks, the present invention incorporates a waveguide structure into an optical demultiplexer, thereby reducing the number of required optical components and simplifying the adjustment process. The present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention. Figure 2 (a
) is a perspective view showing waveguides 22a and 22b on a substrate 21.
, 22c are formed, and a waveguide 22b.

Multilayer interference film filters 25b and 25c are inserted into the cut portions 28b and 28c of 22c. An input optical fiber 24a is connected to the waveguide 22a, and output optical fibers 24b and 24C are directly connected to the waveguide 22b22c.

2 introduced into the waveguide 22a from the input optical fiber 24a
The wavelength multiplexed signal light (wavelengths λ□, λ2) is guided to a waveguide 22c provided with a multilayer interference film filter 25c in the optical path. The filter 25c selectively transmits only the signal light having the wavelength λ2, and the signal light λ2 is guided to the output fiber 24c.

On the other hand, most of the light reflected by the filter 25c is guided to a waveguide 22k) in which a multilayer interference film filter 25b is provided in the optical path. The filter 251) selectively transmits only the signal light having the wavelength λ, and the signal light λ is guided to the output fiber 24b and can function as an optical demultiplexer.

The waveguides 22a, 22b, and 22c may be a polymer light guide, a multicomponent glass light guide made by ion diffusion, or a glass forming raw material gas mainly composed of sic e 4, such as thermal oxidation, flame hydrolysis, etc. A silica glass optical waveguide produced by a gas phase chemical reaction can be used.

FIG. 2(b) is an enlarged plan view of the cut portion 2'8b, and FIG. 2(C) is a sectional view taken along the center line 29. Next, the configuration of a specific example will be described in detail.

That is, a method centered on a flame hydrolysis reaction on a quartz glass substrate 21 (for example, Kawachi et al., Japanese Patent Application No. 56-20884)
9) A multilayer interference film filter is placed in the middle of the waveguide 22k), which is formed into an 8-dimensional pattern by photoetching and reactive sputter etching on the quartz glass film deposited using the method and apparatus for manufacturing glass optical waveguide film. 25b
is inserted. The waveguide 22b has a width of 100 μm and a height of 50 μm, and the waveguide 22b has a buffer layer 27b.
1 protective layer 28b. Waveguide 2
The glass composition of 21) is 5in2-TiO2-P2O5
-B2O3, the buffer layer 27b, and the protective layer 28b have a glass composition of 5in2-P2O5-B2O3, and the relative refractive index difference of the waveguide is 1% higher than that of the buffer layer and the protective layer.

The interval between the cut portions 28b of the waveguide 22b is 40 μm.

The multilayer interference film filter 251) is made by cutting out a double-sided polished 8i wafer with multiple layers of 5102 and TlO2 alternately formed by sputtering on one side, and removing a part of the Si substrate by selective etching. there was.

The filter holding part 26b in FIG. 2(b) is connected to the multilayer interference film 25.
I left it for support of b. This is a part of the Si substrate and is adhesively fixed to the quartz glass substrate 21.

In FIG. 2, the width of the waveguide 2Za is the same as that of the waveguides 22b and 2.
It was set to 50 μm, which is half of 2c. The input optical fiber 24a has a core diameter of 50 μm and an outer diameter of 125 μm, and the output optical fibers 24b and Z4c have a core diameter of 150 μm and an outer diameter of 2
00 μm. Optical fibers 24a, 24b, 24c
were fusion-spliced to their corresponding optical waveguides. The fusion splice is SiO□-P2O5 synthesized by flame hydrolysis reaction.
-B20B glass fine particles were applied and heated with CO2 laser light. At this time, the glass particles play the role of a binder.

The center wavelength of the multilayer interference film filter 25b is 800 nm.

The bandwidth is 20 nm, and the multilayer interference film filter 2
The center wavelength of 5c is 900 nm and the bandwidth is 22 nm.

The upper surface of the quartz glass substrate 21 equipped with the input/output optical fibers and the filter was coated with silicone resin so as to cover the waveguide. The refractive index value of the silicone resin was chosen to be the same as that of quartz glass. Therefore, in this example, the side surfaces of the optical waveguides Z2a, 22b, and 22c are directly inclined with silicone resin, but before loading the filter, a 5102 glass layer to be a cladding layer is coated several μm thick by a method such as sputtering. It is more desirable to form the above.

FIG. 8 shows the measurement results of the wavelength characteristics of the waveguide demultiplexer of the embodiment shown in FIG.
The insertion loss (I) of b and the insertion loss (ITJ) of 24c are shown.The insertion loss at center wavelengths of 800 nm and 900 nm is 2 dB and 1.5 dB, respectively.Also, the bandwidth is about 25 to 80 nm. The reason why it is slightly larger than the bandwidth of the filter itself is that the incident light angle to the filter is distributed in a range of about ±10' corresponding to the waveguide mode.Insertion loss at a center wavelength of 800 nm is larger than the insertion loss at the center wavelength of 900 nm because 8
This is because although the 00 nm light is reflected by the filter 25c and then goes to the filter 25b, some of it goes back to the waveguide 22a. The retrograde light is connected to the optical fiber 24
If the influence of such reflection is desired and is not present, the configuration shown in FIG. 4 can be used. Note that in FIG. 8, the dotted line indicates the transmission half width.

FIG. 4 shows the structure of another embodiment of the present invention, in which a) is a perspective view, and (b) is a plan view, in which 41 is a substrate, and 42a is a top view.

42b and 42c are optical waveguides, and 44a is an input optical fiber 4.
4b and 44c are output fibers. 45b is a multilayer interference film filter (transmission center wavelength: λ□), and 45c is also a multilayer interference film filter (transmission center wavelength: λ2). Waveguide 42
a, 42b form an angle of θ-75° with the filter 45c surface. Wavelength λ□ incident on input fiber 44a
The signal light propagates through the optical waveguide 42a and passes through the filter 45c.
It is totally reflected at a portion of the optical waveguide 42b, passes through a filter 45b provided in the middle of the optical waveguide 42b, and is guided to an output fiber 44b. On the other hand, the signal light of wavelength λ2 is filtered by the filter 45.
c, and the output fiber 4 via the optical waveguide 42c.
4c. In this example, the input fiber 4
Almost no light is reflected to 4a.

FIG. 5 is a block diagram of another embodiment of the present invention, and shows only a plan view. In FIG. 5, 51 is a substrate, 52
Optical waveguides a, 52b, and 52c are connected to optical fibers 54a, 54b, and 54c, respectively. 55 is a multilayer interference film filter (transmission center wavelength λ2), and 56 is a holding portion for the filter 55.

The signal light with the wavelength λ2 incident from the optical fiber 54a passes through the optical waveguide 52a, the filter 55, and the optical waveguide 5Zc,
The light is led out to an optical fiber 54c. Also, the optical fiber 54
The signal light with the wavelength λ incident from the optical waveguide 52b is totally reflected by the filter 55, and passes through the optical waveguide 52a.
The light is guided to the optical fiber 54a. The duplexer shown in FIG. 5 is effective in the field of bidirectional optical communication systems.

The configuration and operation of the waveguide optical demultiplexer of the present invention have been described above with respect to several examples. In the optical demultiplexer of the present invention, the path of the signal light is regulated by an optical waveguide precisely formed on the substrate by means such as photolithography, and there is no need for alignment of Rondo lenses, etc., and the input and output light Simply connect the fiber to the end of the optical waveguide at a fixed position (this greatly reduces assembly and adjustment effort. Especially when the optical waveguide is a silica glass waveguide, fusion splicing with optical fibers is also possible. This makes it possible to improve the long-term reliability of connections that often have problems.

Although the above embodiments have been described for two wavelengths, the present invention is also effective for optical demultiplexers for multiple wavelengths.

FIG. 6 is a perspective view showing a configuration example of a waveguide optical demultiplexer for 5-wavelength multiplexing according to the present invention, in which 61 is a substrate, 6z is an optical waveguide group, and 65 is a multilayer interference film filter group (transmission center wavelength are λ□, λ2.λ8 . counting from the input fiber 64a side.
λ6. λ5). 64b is an output fiber (other output fibers are omitted in this figure). The operation of the duplexer shown in FIG. 6 is clear from the explanation section of FIG. 3, and the description thereof will be omitted.

In the above embodiments, the output light is guided to the output optical fiber, but instead of the output optical fiber, a photodetector can be directly attached to the optical waveguide.

Furthermore, it is also possible to omit a part of the optical waveguide or path or replace it with an optical fiber, such as by bringing the optical fiber 24b directly close to the filter 25b in FIG. 2, for example.

As explained above, by using the waveguide structure of the waveguide optical demultiplexer of the present invention, the number of component parts can be significantly reduced compared to conventional types, the number of polishing and bonding steps is reduced, and assembly is possible. An optical demultiplexer with short adjustment time can be provided. Dogs have a simple structure and are suitable for miniaturization, contributing to a significant reduction in the price of optical demultiplexers.
It is expected that this will be one of the factors promoting the spread of optical communication systems in various fields including subscriber systems.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional optical demultiplexer, Figure 2 (a) is a perspective view showing the configuration of an embodiment of the present invention, and Figure 2 (b) is shown in Figure 2 (a). 2(C) is a sectional view taken along the center line 29 shown in FIG. 2(b); FIG. 8 is a wavelength characteristic diagram of the waveguide optical demultiplexer shown in FIG. 2; Figure 4 (
a) is a perspective view showing the configuration of another embodiment of the present invention, FIG. 4(b) is a plan view of the embodiment of FIG. 4(a), and FIG. 5 is a configuration of another embodiment of the present invention. FIG. 6 is a perspective view showing the configuration of a waveguide type optical demultiplexer for five-wavelength multiplexing according to the present invention. 1... Substrate glass body, Za, 2b, 2c, 2d, 2e
- Prism, 8a, 8b, 8c, 8d, 8e... o Rad lens, 4b, '4c, 4d, 4e... Multilayer interference film filter, 5 a = Input optical fiber, 5b, 5c
, 5d, 5. e=-output optical fiber, 21... substrate,
22aH22b, 22cm optical waveguide, 28b, 28c・
... Cutting section, 24a ... Input optical fiber, 24b, 2
4c... Output optical fiber, 25b, 25c... Multilayer interference film filter, 26b... Filter holding part, 27b
...Buffer layer, 28b...Protective layer, 29...Center line, 41...Substrate, 42a, 42b, 42cm optical waveguide, 44a-human powered optical fiber, 44b, 44c...Output optical fiber , 45
b, 45c...Multilayer interference film filter, 51...Substrate, 52a, 52b, 52cm optical waveguide, 54a, 54'b, 54c...Optical fiber, 55...
・Multilayer interference film filter, 56...filter holding part, 6
DESCRIPTION OF SYMBOLS 1... Substrate, 62... Optical waveguide group, 64a... Input optical fiber, 64b... Output optical fiber, 65...
・Multilayer interference film, bottom group. Patent applicant Nippon Telegraph and Telephone Public Corporation Figure 3 Liquid length (nm) Figure 4 (b)

Claims (1)

[Scope of Claims] 1. A waveguide optical demultiplexer characterized in that a part of an optical waveguide formed on a substrate is cut and a multilayer interference film filter is inserted in the cut part. (a) The waveguide type optical demultiplexer according to claim 1, wherein the optical waveguide is made of silica glass.