JP2001141945A - Temperature independent optical multiplexer/ demultiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature independent optical multiplexer/ demultiplexer capable of lessening addition loss and the crosstalk deterioration. SOLUTION: A channel waveguide array 3 is provided with plural channel waveguide on a substrate 1 so as to vary in lengths from each other. The plural channel waveguides of the channel waveguide array 3 have cores 13 consisting of quartz glass and clads 14 consisting of a glass material having the refractive index smaller than the refractive index of the cores 13. Boron oxide (B2O3 glass) having the temperature characteristics reverse from the temperature characteristics of the quartz glass and clad glass is added to the cores 13 and the clads 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature-independent optical multiplexer / demultiplexer, and more particularly to a temperature-independent optical multiplexer / demultiplexer using a channel waveguide array having a plurality of channel waveguides each having a core made of silica glass and having different lengths. The present invention relates to an optical multiplexer / demultiplexer.

[0002]

2. Description of the Related Art FIG. 4 shows an arrayed waveguide grating (g).
This shows a conventional optical multiplexer / demultiplexer using (rating). FIG.
Shows an aa 'cross section of FIG. On a quartz substrate 1, a plurality of cores (co) made of quartz glass having a square cross-sectional shape are provided.
re) 2 is formed in a predetermined pattern to form a channel waveguide array 3, and a cladding 4 made of pure silica glass is provided so as to cover the channel waveguide array 3. I have.
Titanium oxide (TiO ₂ ) is added to the core 2.
A channel waveguide is formed by the core 2 and the cladding 4,
Here, 22 are provided. As shown in FIG. 4, the 22 channel waveguides of the channel waveguide array 3 are set to have different lengths from each other, and are set to be longer toward the outside.

[0003] At both ends of the channel waveguide array 3, an input-side fan-shaped slab waveguide 5 (input waveguide) and an output-side fan-shaped slab waveguide 6 (output waveguide) are connected. One input channel waveguide 7 is connected to the input-side fan-shaped slab waveguide 5, and a plurality of output channel waveguides 8-1 to 8-8 are connected to the output-side fan-shaped slab waveguide 6. I have.

[0004] In the above configuration, the light including various wavelengths input to the input channel waveguide 7 is input to each of the cores 2 of the channel waveguide array 3 by the input side fan-shaped slab waveguide 5. When the light input to the channel waveguide array 3 propagates through each of the cores 2 and reaches the output-side fan-shaped slab waveguide 6, the equiphase plane is inclined depending on the wavelength. At the connection surface between the waveguide 6 and the output channel waveguides 8-1 to 8-8, the light focusing position shifts. For this reason, the output light from the output-side fan-shaped slab waveguide 6 is selectively output to the output channel waveguides 8-1 to 8-n according to the shift state of the equal phase plane, and is output from the eight waveguides. Output light of different wavelengths.

In the channel waveguide array 3, when the temperature changes, the length L of the channel waveguide changes due to thermal expansion, and the refractive index of the quartz glass constituting the core 2 changes due to the thermo-optic effect. . Therefore, the equiphase surface 9 at 0 ° C. shown in FIG. 4 changes to the position of the equiphase surface 10 at 60 ° C., for example. As a result, the light condensing position shifts according to the temperature change, and the wavelength to be demultiplexed changes.

FIG. 6 shows the details of the connection between the channel waveguide array 3 and the output fan-shaped slab waveguide 6. In the figure, d is the pitch of the channel waveguides of the channel waveguide array 3, and θ is the emission angle. Now, focusing on a certain wavelength, the following equation must be satisfied in order for the equiphase surfaces shown in FIG. 4 to be continuous. (2π / λ) N _eff · ΔL + (2π / λ) n _S dsin θ = 2πm (1) (where λ is the wavelength, m is the diffraction order (m = 1, 2, 3,
...), _ΔL is the waveguide length difference of the channel waveguide array 3, N _eff is the equivalent refractive index of the channel waveguide array 3, n
_S is the equivalent refractive index of the output fan-shaped slab waveguide 6, and ΔL is the waveguide length difference of the channel waveguide array 3. )

Since the equivalent refractive index N _eff , n _S is substantially equal to the refractive index n of the quartz glass of the core 2 constituting the channel waveguide array 3, it is approximated as n = _eff = n _S and the temperature is T T Then, the angle change Δθ of the light beam when the temperature changes by ΔT (the change in the equiphase plane) is given by the following equation based on the above equation (1). Δθ / ΔT = (1 / n) × (Δn / ΔT) × ΔL / d (2)

Here, Δn / ΔT is a change in the refractive index of the waveguide, and the effect of the linear expansion due to the temperature change is smaller than the change in the refractive index, and is ignored here. The above (2)
By using the equation, the change of the demultiplexing wavelength with respect to the temperature change is given by the following equation. Δλ / ΔT = (λ × n × d / n △ L) × (△ θ / △ T) = (λ / n) × (∂n / ∂T) (3) For example, titanium oxide ( {Λ / ΔT in quartz glass doped with TiO ₂ ) is n ≒ 1.45 and {n / ∂T}.
When 1 × 10 ⁻⁵ and λ = 1550 nm, 0.01 (nm
/ ° C). An optical component using such a channel waveguide array 3 is generally used under a temperature environment of 0 to 60 ° C.

From the above results, the temperature change is from 0 ° C. to 60 ° C.
In the case of ° C., the shift of the demultiplexing wavelength is 0.6 nm at the maximum, and therefore cannot be used in a practical system. In order to reduce the change of the center wavelength due to the temperature, conventionally, a configuration has been proposed in which a wedge-shaped groove is provided in a part of the channel waveguide array 3 and an optical resin member is inserted therein. Hereinafter, this configuration will be described.

FIG. 7 shows a conventional optical multiplexer / demultiplexer using an arrayed waveguide type grating having a structure in which an optical resin member is interposed in a wedge shape. In order to reduce the change in the center wavelength due to temperature, the value according to the above equation (2) must be smaller than the value according to the above equation (3). Therefore, as shown in FIG. 7, a wedge-shaped groove having a maximum width W is provided in a part of the channel waveguide array 3, and an optical resin member 11 is provided therein.
Insert This cancels the shift of the demultiplexing wavelength of the equiphase plane with respect to the temperature. The condition in this case is
The following equation is given by using the above equation (2).

(∂n / ∂T) △ L + (△ L '× ∂n' / ∂T) = 0 (4) Here, △ L 'is a difference between groove widths in each channel waveguide array. The values sequentially differ from those of the adjacent channel waveguides by this length. n ′ is the refractive index of the optical resin, ∂
n ′ / ΔT is a change in the refractive index temperature of the optical resin. For example, when a silicon-based resin is used for the optical resin member 11, ∂n '/ ∂T is as follows. ∂n '/ ∂T ≒ -37 × 10 ^{-5 Since} the refractive index temperature change of the quartz glass is ∂n / ∂T ≒ 1 × 10 ^-5 , △ L' / △ L is as follows. ΔL ′ / ΔL = 1/37 (5)

Generally, the waveguide length difference ΔL is about 100 μm, so that the groove width difference ΔL ′ is about 2 μm. However, the number of waveguides in the channel waveguide array 3 is 10
Since the number is about 0 to 200, the maximum width W of the optical resin member 11 is a large value of 400 μm.

[0013]

However, according to the conventional optical multiplexer / demultiplexer, in a configuration having several hundreds of waveguides, the maximum width W of the wedge-shaped groove reaches several hundred μm, so that diffraction loss is reduced. Increased, and a large additional loss of about 4 to 6 dB has been generated.

Further, in order to obtain good demultiplexing characteristics with small crosstalk, generally a high-precision groove width whose width is smoothly changed to sub-μm or less is required. When trying to form a groove, it is difficult to increase the processing accuracy, resulting in degradation of crosstalk.

Accordingly, it is an object of the present invention to provide a temperature-independent optical multiplexer / demultiplexer capable of reducing the additional loss and the deterioration of crosstalk.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to the above-mentioned object.
To achieve this, an input channel formed on one side of the board
A channel waveguide and one end is connected to the other end of the input channel waveguide.
A connected input fan-shaped slab waveguide and one end
Connected to the other end of the side fan type slab waveguide, the desired waveguide length
Multiple Channel Waveguide Arrays Sequentially Increased by Difference
And one end is connected to the other end of the plurality of channel waveguide arrays.
The output-side fan-shaped slab waveguide connected to the output-side fan-shaped slab.
Multiple output channel waveguides connected to the other end of a Love waveguide
And the plurality of channel waveguide arrays are S
iO_TwoIt is composed of quartz-based glass whose main component is glass.
Core and glass having a smaller refractive index than the core
Composed of a clad, both the core and the clad
Or one of boron oxide (B _TwoO_ThreeGlass) is added
To provide a temperature-independent optical multiplexer / demultiplexer characterized in that:
I do.

According to this configuration, for example, when boron oxide is added to the core, the boron oxide has a temperature characteristic opposite to that of the quartz glass as the main material. The refractive index of the core has no temperature dependency. Therefore, the temperature change of the demultiplexed wavelength on the equal phase plane is reduced, and the loss can be reduced. Also,
Crosstalk can be reduced.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a temperature-independent optical multiplexer / demultiplexer according to the present invention. FIG. 1 corresponds to the cross-sectional shape of one core at the aa 'portion of the channel waveguide array 3 shown in FIG. An under cladding (not shown) is formed on a substrate 12 made of quartz glass or silicon as required, and a core 13 having a square cross section is provided at a predetermined position on the under cladding. Further, a clad 14 is provided so as to cover the core 13.

The core 13 is made of quartz glass mainly composed of SiO ₂ glass, to which 15% by mass of boron oxide (B ₂ O ₃ glass) is added, and further, titanium oxide (TiO ₂ ) is added. Has been added. A glass having a smaller refractive index than the core 13 is used for the clad 14. For example, SiO ₂ glass or fluorine-processed SiO ₂ glass may be used, but it is preferable that oxygen boron is also added to the clad. Here, similarly to the core 13, 15% by mass of boron oxide is added. When the under cladding is formed, 15 mass% of boron oxide is also added to the under cladding. Thus, the core 13 is constituted by B ₂ O ₃ -TiO ₂ -SiO ₂ based glass, the cladding 14 is composed of B ₂ O ₃ -SiO ₂ -based glass.

FIG. 2 shows the relationship between boron oxide (B ₂ O) and temperature.
₃ shows changes in the refractive index of glass and quartz glass (SiO ₂ glass). As is clear from FIG. 2, the refractive index of quartz glass increases with an increase in temperature, but the refractive index of boron oxide (B ₂ O
₃ ) The refractive index of the glass decreases. Therefore, as the added amount of boron oxide is increased, there is an added amount that does not change with temperature.

FIG. 3 shows that the core 13 contains boron oxide (B ₂ O _3).
The graph shows the temperature change of the demultiplexing wavelength when 15% by mass (glass) is added and when it is not added. FIG. 3A shows the case where boron oxide is added, and FIG. 3B shows the case where boron oxide is not added. As is clear from FIG. 3, the temperature change of the demultiplexing wavelength due to the addition of boron oxide is small. Further, no change in the loss in the pass band is observed, and it can be seen that a low loss is realized. Here, the addition of boron oxide is set to 15% by mass, but it is possible to further reduce the temperature change of the demultiplexing wavelength by increasing the addition amount of boron oxide. Further, in the case where boron oxide is added only to the clad to achieve temperature independence, it is necessary to add 30% by mass of boron oxide to the clad.

[0022]

As described above, according to the temperature-independent optical multiplexer / demultiplexer of the present invention, the plurality of channel waveguides of the channel waveguide array are made of silica-based glass whose main component is SiO ₂ glass. And a clad made of glass having a lower refractive index than the core, and at least one of the core and the clad is made of boron oxide (B ₂
O ₃ glass) is added, so that loss can be reduced. Further, since it is not necessary to form a groove over a wide area unlike the related art, it is possible to reduce deterioration of crosstalk.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a temperature-independent optical multiplexer / demultiplexer according to the present invention.

FIG. 2 is a characteristic diagram showing a change in refractive index of boron oxide (B ₂ O ₃ glass) and quartz glass (SiO ₂ glass) with respect to temperature.

FIG. 3 is a characteristic diagram showing a temperature change of a demultiplexing wavelength when boron oxide (B ₂ O ₃ glass) is added to a core by 15% by mass and when boron is not added.

FIG. 4 is a plan view showing a configuration of a conventional optical multiplexer / demultiplexer.

FIG. 5 is a sectional view showing an a-a ′ section of FIG. 4;

FIG. 6 is an enlarged view showing details of a connection portion between a channel waveguide array and an output fan-shaped slab waveguide.

FIG. 7 is a plan view showing the configuration of another conventional optical multiplexer / demultiplexer.

[Explanation of symbols]

 Reference Signs List 1 substrate 3 channel waveguide array 5 input fan-shaped slab waveguide 6 output fan-shaped slab waveguide 7 input channel waveguide 8 output channel waveguide 12 substrate 13 core 14 clad

Continuing on the front page (72) Inventor Koichi Maru 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Opto-System Research Laboratory, Hitachi Cable, Ltd. (72) Inventor Hideki Nanune 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture No. 1 F-term in the Opto-System Laboratory, Hitachi Cable, Ltd. (Reference) 2H047 KA03 KA12 LA18 PA17 QA02 QA04 TA00

Claims (3)

[Claims] 1. An input channel waveguide formed on one side of a substrate, an input fan-shaped slab waveguide having one end connected to the other end of the input channel waveguide, and one end connected to the input fan. A channel waveguide array including a plurality of channel waveguides connected to the other end of the mold slab waveguide and sequentially elongated by a desired waveguide length difference, and an output having one end connected to the other end of the channel waveguide array. A side sector slab waveguide, and a plurality of output channel waveguides connected to the other end of the output side sector slab waveguide, wherein the plurality of channel waveguides of the channel waveguide array are made of SiO ₂ glass. a core which is composed of silica-based glass as a main component, the core is composed of the cladding due to small glass refractive index than, either one or both the boron oxide in the cladding and the core (B ₂ O ₃ glass ) Temperature-dependent optical demultiplexer, characterized in that is added. 2. A temperature-independent optical multiplexer / demultiplexer according to claim 1, wherein said substrate is formed of a substrate made of quartz glass or silicon. 3. The temperature-independent optical multiplexer / demultiplexer according to claim 1, wherein the core is added with titanium oxide (TiO ₂ ).