JP2000241635A - Optical wavelength multiplexer/demultiplexer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously realize reliability improvement for a long-time and productivity improvement and lower cost in a manufacturing process, by providing at least upper clad with a specific material as a main dorpant and the same extent of thermal expansion coefficient as a plane substance. SOLUTION: A lower clad 2 is formed on a plane substrate 1. A core 4 for propagating a light signal is formed on this lower clad 2. In addition, an upper clad 3 is formed on the lower clad 2 and the core 4 so as to cover this core 4. Material of the plane substrate 1 is Si, and material of the lower clad 2, the upper clad 3, and the core 4 is quartz-based glass. The upper clad 3 and the core 4 contain GeO2 as a main dopant. Especially, contents of GeO2 of the upper clad 3 is adjusted so as to have the same extent of thermal expansion coefficient as the substrate 1. The contents of GeO2 is at most 50 mol%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide circuit used in fields such as optical communication, optical signal processing and optical measurement, and more particularly to the use of interference of optical signals passing through waveguides having different optical path lengths. And an optical wavelength multiplexer / demultiplexer that performs optical signal demultiplexing.

[0002]

2. Description of the Related Art An optical waveguide circuit mainly composed of a silica glass manufactured on a flat substrate such as Si or quartz is used for optical communication,
R & D is progressing as a promising practical optical device in fields such as optical information processing and optical measurement (Kawach
i et al., J. Quantum Electron. 22 (1990) 391.). Among these optical circuits, a circuit having a wavelength multiplexing / demultiplexing function of light has been increasing in importance as the demand for constructing a wavelength division multiplexing optical communication system has increased in recent years. Along with this, not only have high performance such as low crosstalk and polarization independence, but also guarantee high long-term reliability,
There is also a strong demand for improved productivity and reduced manufacturing costs.

FIG. 8 shows a conventional arrayed waveguide grating which is an example of this type of optical wavelength multiplexer / demultiplexer.
1 is a perspective view showing a configuration of an (ing: AWG) type optical wavelength multiplexer / demultiplexer. The AWG type optical wavelength multiplexer / demultiplexer includes an input channel waveguide 111, an input fan-shaped slab waveguide 112, a channel waveguide array 113, and an output fan-shaped slab waveguide 1.
14 and an output channel waveguide 115. The input sector slab waveguide 112 is disposed between the input channel waveguide 111 and the channel waveguide array 113, and the output sector slab waveguide 114 is disposed between the channel waveguide array 113 and the output channel waveguide 115. Are located in The channel waveguide array 113 includes a plurality of channel waveguides 113a having different optical path lengths. A plurality of output channel waveguides 115 are prepared for each wavelength to be demultiplexed. Further, a plurality of input channel waveguides 111 may be provided.

In such a configuration, wavelength multiplexing (λ ₁ , λ ₂ ,...,
λ _n ) is input, the optical signal is diffused by the input-side sector slab waveguide 112, and each channel waveguide 113 a constituting the channel waveguide array 113 is provided.
Will be introduced. The phase of the optical signal when it reaches the output-side fan-shaped slab waveguide 114 through the channel waveguide 113a differs for each wavelength included in the optical signal. That is, since the inclination of the wavefront when input to the output-side fan-shaped slab waveguide 114 varies depending on the wavelength, the optical signal is collected by the output-side fan-shaped slab waveguide 114 at an angle corresponding to the wavelength.

[0005] The optical path length of each channel waveguide 113a constituting the channel waveguide array 113 is such that an optical signal condensed after passing through each channel waveguide 113a has a different position for each wavelength (output side fan-shaped slab waveguide). (The position of the output end of the wave path 114). Since each output channel waveguide 115 is arranged at a position where the desired wavelength (λ ₁ , λ ₂ ,..., Λ _n ) is strengthened, it is separated from each output channel waveguide 115 by wavelength. An optical signal can be extracted.

FIG. 9 is a cross-sectional view of the channel waveguide array 113 in FIG. 8 taken along the line IX-IX '. A lower clad 102 is formed on a flat substrate 101. On this lower cladding 102, a core 1 for transmitting an optical signal
04 is formed. Further, an upper clad 103 is formed on the lower clad 102 and the core 104 so as to cover the core 104. Lower cladding 10
2, the upper clad 103 and the core 104 together
This is called an optical waveguide layer 105.

Here, the refractive index of the lower cladding 102 is n
₀ , the refractive index of the upper cladding 103 is n ₁ , and the refractive index of the core 104 is n ₂ . Further, the relative refractive index difference between the upper cladding 103 and the lower cladding 102 is Δn ₁ (= (n ₁ −n
₀ ) / n ₁ ), and the relative refractive index difference between the core 104 and the upper cladding 103 is Δn ₂ (= (n ₂ −n ₁ ) / n ₂ ).
In this case, in the conventional AWG type optical wavelength multiplexer / demultiplexer,
The design is such that Δn ₁ = 0 and Δn ₂ > 0. That is, the lower and upper clads 102 and 103 have the same refractive index, and the core 104 has a higher refractive index.

[0008] Since an optical signal propagating through an optical network is non-polarized light, the characteristics of an AWG type optical wavelength multiplexer / demultiplexer are required to be polarization independent from the viewpoint of high performance. However, the material of the substrate 101 and the optical waveguide layer 1
It is known that when the material of the optical fiber 05 is different from the material of the optical fiber 05, polarization dependence is caused in the optical multiplexing / demultiplexing characteristic of the optical signal propagating through the core 104 due to a photoelastic effect caused by a difference in thermal expansion coefficient. That is, although the optical wavelength multiplexer / demultiplexer is manufactured at a high temperature, if the substrate 101 and the optical waveguide layer 105 have different coefficients of thermal expansion,
There is a difference in the degree of shrinkage between the two during cooling. As a result, the optical waveguide layer 105 is distorted, and polarization dependence occurs in the optical multiplexing / demultiplexing characteristics.

For example, the material of the substrate 101 is Si, the lower clad 102, the upper clad 103, and the core 104.
When the material is quartz glass, the thermal expansion coefficient of the conventional quartz glass having a small amount of dopant is smaller than that of Si, so that a compressive stress is applied to the optical waveguide layer 105, and the optical multiplexing / demultiplexing characteristics are reduced. Polarization dependence occurs. FIG.
It is a graph which shows an example of such polarization dependence of an optical demultiplexing characteristic. However, the AWG type optical wavelength multiplexer / demultiplexer used for the measurement has a channel interval of 100 GHz and 32 channels. The lower clad 102 has a thickness of 20 μm, the upper clad 103 has a thickness of 30 μm, and the core 104 has a sectional size of 6 μm.
μm × 6 μm, and the relative refractive index difference Δn ₂ between the core 104 and the upper cladding 103 is 0.75%.

The horizontal axis of the graph indicates the wavelength, and the vertical axis indicates the transmittance at the center port of the output channel waveguide 115 (the ratio of the intensity of the output light to the intensity of the input light). From FIG. 10, it can be seen that the peaks of the split optical signal are separated between the TM mode (solid line) and the TE mode (dotted line). If the optical multiplexing / demultiplexing characteristic has polarization dependence as described above, the width of the wavelength extracted from the output channel waveguide 115 is widened, so that accurate demultiplexing cannot be performed.

As means for eliminating the polarization dependence of an AWG type optical wavelength multiplexer / demultiplexer using a Si substrate, an optical waveguide layer 10 is used.
A method of adding a dopant such as B ₂ O ₃ or P ₂ O ₅ to the quartz glass at the time of fabrication to increase the coefficient of thermal expansion of the optical waveguide layer 105 to be equal to the coefficient of thermal expansion of the Si substrate ( Suzuki et al., Electronics Letter
s 33 (1997) 1173., Ojha et al., Electronics Letters 3
4 (1998) 78.), a method of forming a groove in the optical waveguide layer 105 along the line VIII-VIII 'shown in FIG. 8, and inserting a wave plate into this groove (Takahashi et al., Optics Letters 17 (1992) ) 49
9.), has been proposed.

[0012]

SUMMARY OF THE INVENTION Among these means,
The method of increasing the dopant such as B ₂ O ₃ and P ₂ O ₅ merely adjusts the raw material components at the time of depositing the waveguide material, so that polarization independence can be achieved without complicating the conventional manufacturing process. is there. However, a large amount of B ₂ O ₃ , P ₂ O ₅
Is high in hygroscopicity and chemically unstable in ordinary air, so that the long-term reliability of the AWG type optical wavelength multiplexer / demultiplexer remains a problem.

The method of inserting a wave plate is such that a completed AWG type optical wavelength multiplexer / demultiplexer is grooved and then the wave plate is inserted. You have to do extra work. Therefore, the purchase of the wave plate, the work of inserting the wave plate, the inspection before and after the wave plate is inserted, and the like directly lead to the prolongation of the manufacturing period and the increase in cost. That is, from the viewpoint of productivity and manufacturing cost, it is inevitable that the method is more disadvantageous than the above-described method of increasing the dopant.

[0014] A method of realizing the polarization independence of an AWG type optical wavelength multiplexer / demultiplexer using a quartz substrate instead of the Si substrate has also been proposed (Suzuki et al., Electronics Lecture).
tters30 (1994) 158.). However, since the quartz substrate is hard, chipping easily occurs during processing such as cutting. Also,
Since it is necessary to add a dopant to the optical waveguide layer 105 for manufacturing reasons, the thermal expansion coefficient of the optical waveguide layer 105 becomes larger than that of the substrate 101. For this reason, a tensile stress is applied to the optical waveguide layer 105 at the time of completion, and there is a disadvantage that the optical waveguide layer 105 is easily cracked.

As described above, the polarization-independent optical wavelength multiplexer / demultiplexer proposed so far is insufficient in long-term reliability, productivity, and cost. As the importance of key devices in wavelength-division multiplexing optical communication systems has increased in recent years, polarization-independent optical wavelength multiplexer / demultiplexers have high performance, high long-term reliability, and high productivity. Immediate improvements are sought for improvements and reductions in manufacturing costs.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and it is an object of the present invention to improve the long-term reliability of a polarization independent optical wavelength multiplexer / demultiplexer and to improve the productivity in a manufacturing process. It is to realize cost reduction at the same time.

[0017]

In order to achieve the above object, an optical wavelength multiplexer / demultiplexer according to the present invention comprises a waveguide having a lower clad formed on a flat substrate and a lower clad formed on the lower clad. A formed core, comprising an upper clad formed on the lower clad so as to cover the core, the lower clad, the core and the upper clad are made of quartz glass,
At least the upper cladding is 50
It is characterized by containing less than mol% GeO ₂ and having a thermal expansion coefficient comparable to that of a flat substrate.
In this case, the contact area between the upper clad and the core is preferably larger than the contact area between the lower clad and the core. In the above-described optical wavelength multiplexer / demultiplexer, the core may include GeO ₂ of 50 mol% or less as a main dopant and have a thermal expansion coefficient similar to that of a flat substrate. Further, in the above-described optical wavelength multiplexer / demultiplexer, the lower cladding may contain GeO ₂ of 50 mol% or less as a main dopant and have a thermal expansion coefficient similar to that of a flat substrate. As described above, by using GeO ₂ as a main dopant for adjusting the thermal expansion coefficient, the contents of B ₂ O ₃ and P ₂ O ₅ conventionally used for adjusting the thermal expansion coefficient can be reduced.

In the above-mentioned optical wavelength multiplexer / demultiplexer, the refractive index of the lower cladding may be lower than that of the upper cladding. Thereby, the thickness of the lower cladding layer can be made smaller than before.

In the above-described configuration example of the optical wavelength multiplexer / demultiplexer, the optical path length of each waveguide is set so that an optical signal passing through each waveguide is strengthened by interference at a different position for each wavelength. An output means is provided at a position where a predetermined wavelength is strengthened and extracts this wavelength. That is, the present invention can be applied to an AWG type optical wavelength multiplexer / demultiplexer.

In another configuration example of the optical wavelength multiplexer / demultiplexer described above, the optical path length of each waveguide is such that a branching means for branching an input optical signal into two waveguides, Interference means for interfering with the transmitted optical signal, and two output means for extracting the frequency component of the optical signal enhanced by the interference are provided, and the optical path length difference between the two waveguides is such that the frequency component of the optical signal is a predetermined value. Are set so as to be alternately output from the two output units at the frequency interval of. That is, the present invention provides an asymmetric Mach-Zehnder interferom.
eter: Applicable to MZI) type optical wavelength multiplexer / demultiplexer.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) First, an embodiment in which the present invention is applied to an AWG type optical wavelength multiplexer / demultiplexer will be described. FIG. 1 is a perspective view showing the configuration of an AWG type optical wavelength multiplexer / demultiplexer to which the present invention is applied.

This AWG type optical wavelength multiplexer / demultiplexer has an input channel waveguide 11, an input fan-shaped slab waveguide 12,
It comprises a channel waveguide array 13, an output fan-shaped slab waveguide 14, and an output channel waveguide (output means) 15. The input sector slab waveguide 12 is disposed between the input channel waveguide 11 and the channel waveguide array 13, and the output sector slab waveguide 14 is disposed between the channel waveguide array 13 and the output channel waveguide 15. Are located in The channel waveguide array 13 includes a plurality of channel waveguides 13a having different optical path lengths. A plurality of output channel waveguides 15 are prepared for each wavelength to be demultiplexed. Further, a plurality of input channel waveguides 11 may be provided.

In such a configuration, wavelength multiplexing (λ ₁ , λ ₂ ,..., Λ _n ) is performed from the input channel waveguide 11.
When the input optical signal is input, the optical signal is diffused by the input-side fan-shaped slab waveguide 12 and introduced into each channel waveguide 13 a constituting the channel waveguide array 13. The phase of the optical signal when it reaches the output-side fan-shaped slab waveguide 14 through the channel waveguide 13a differs for each wavelength included in the optical signal. That is, since the inclination of the wavefront when input to the output-side fan-shaped slab waveguide 14 varies depending on the wavelength, the optical signal is collected by the output-side fan-shaped slab waveguide 14 at an angle corresponding to the wavelength.

The optical path length of each channel waveguide 13a constituting the channel waveguide array 13 is
It is set so that the optical signal condensed after passing through a is strengthened by interference at a different position for each wavelength (the position of the output end of the output-side fan-shaped slab waveguide 14). Each output channel waveguide 15 has a desired wavelength (λ ₁ , λ ₂ ,
.., Λ _n ) can be taken out, so that an optical signal separated for each wavelength from each of the output channel waveguides 15 can be extracted.

Here, the case where the optical signal is demultiplexed for each wavelength has been described. However, it is also possible to multiplex the optical signal based on the same principle from the viewpoint of reversibility. In this case, optical signals separately input for each wavelength from each output channel waveguide 15 are multiplexed via the output slab waveguide 14, the channel waveguide array 13, and the input slab waveguide 12, and It is taken out from one input channel waveguide 11.

FIG. 2 is a sectional view showing a section taken along line II-II 'of the channel waveguide array 13 in FIG. A lower clad 2 is formed on a flat substrate 1. On this lower cladding 2, a core 4 for transmitting an optical signal is formed. Further, the lower clad 2 is covered so as to cover the core 4.
The upper clad 3 is formed on the core 4. The lower clad 2, the upper clad 3, and the core 4 are collectively referred to as an optical waveguide layer 5.

The material of the planar substrate 1 is Si, and the material of the lower clad 2, the upper clad 3 and the core 4 is quartz glass. However, the upper clad 3 and core 4
Contains GeO ₂ as a main dopant. In particular, the content of GeO ₂ is adjusted so that the upper clad 3 has the same thermal expansion coefficient as the substrate 1. However, considering the stability of the quartz glass, the content of GeO ₂ is set to 50 mol% or less.

Further, the refractive index of the lower clad 2 is n ₀ , the refractive index of the upper clad 3 is n ₁ , the refractive index of the core 4 is n ₂ , and the relative refractive index difference between the upper clad 3 and the lower clad 2 is Δn ₁ (= (n ₁ −n ₀ ) / n ₁ ), and the relative refractive index difference between the core 4 and the upper cladding 3 is Δn ₂ (= (n ₂ −n
₁ ) / n ₂ ), the AWG type optical wavelength multiplexer / demultiplexer shown in FIG. 1 satisfies Δn ₁ > 0 and Δn ₂ > 0. That is, the refractive index n ₂ of the core 4 and the refractive index n of the upper clad 3
The relationship with ₁ is the same as the conventional _one , but the refractive index n ₀ of the lower cladding 2 is further lower than the refractive index n ₁ of the upper cladding 3.

As described above, in the AWG type optical wavelength multiplexer / demultiplexer shown in FIG. 1, GeO ₂ is used as a main dopant for adjusting the thermal expansion coefficient. For this reason, B ₂ O ₃ , which has been conventionally used to adjust the coefficient of thermal expansion,
The content of P ₂ O ₅ can be reduced. Therefore, since the hygroscopicity of the quartz glass can be suppressed as compared with the related art, the long-term reliability of the optical wavelength multiplexer / demultiplexer can be improved.

GeO ₂ is a dopant that increases the coefficient of thermal expansion and also a dopant that increases the refractive index.
Accordingly, the refractive index n ₂ of the refractive index n ₁ and the core 4 of the upper cladding 3 is adjusted by GeO ₂ in principle. However, the refractive indices n ₁ and n ₂ may be adjusted by B ₂ O ₃ and P ₂ O ₅ in some cases. The lower clad 2, the method of manufacturing the optical waveguide layer 5 of the upper cladding 3 and core 4, there is a case where B ₂ O _3, not help adding P ₂ O _5. However, by using GeO _{2 as} the main dopant for adjusting the thermal expansion coefficient, B ₂ O ₃ , P
The content of ₂ O ₅ can be minimized.

Further, in the AWG optical multiplexer / demultiplexer shown in FIG. 1, the upper clad 3 has the same thermal expansion coefficient as the substrate 1. Of course, the core 4 may have the same thermal expansion coefficient as the substrate 1. Further, GeO ₂ may be used as a main dopant in the lower cladding 2 to have a thermal expansion coefficient similar to that of the substrate 1. When the thermal expansion coefficient of the entire optical waveguide layer 5 is made the same as that of the substrate 1, the distortion of the optical waveguide layer 5 which is generated during the manufacturing process of the optical wavelength multiplexer / demultiplexer can be eliminated, and the polarization-independent optical wavelength coupling / demultiplexing can be achieved. A wave device can be realized.

However, even if the thermal expansion coefficients of the lower cladding 2 and the core 4 are not necessarily the same as those of the substrate 1, a polarization independent optical wavelength multiplexer / demultiplexer can be realized. The reason is that the influence on the polarization dependence of the optical wavelength multiplexer / demultiplexer is due to the upper cladding 3
Is dominant, and the influence of the lower cladding 2 and the core 4 is small. That is, by making the thermal expansion coefficient of the upper clad 3 the same as that of the substrate 1, the lower clad 2 is sandwiched between members having the same thermal expansion coefficient (that is, the substrate 1 and the upper clad 3). Distortion can be suppressed. Further, at this time, the core 4 is surrounded on three sides by a member having the same thermal expansion coefficient as the substrate 1, so that the lower clad in contact with only one side of the core 4 has a small influence on the core directly. Therefore, by making at least the thermal expansion coefficient of the upper cladding 3 approximately equal to that of the substrate 1, a polarization-independent optical wavelength multiplexer / demultiplexer can be realized.

In the AWG optical wavelength division multiplexer shown in FIG. 1, Δn ₁ > 0 and Δn ₂ > 0. By adjusting such a refractive index, productivity improvement and cost reduction can be realized by the following principle. The production of the optical waveguide layer 5 formed on the planar substrate 1 includes four steps of lower clad layer deposition, core layer deposition, core processing, and upper clad layer deposition, as described later. In order to improve productivity and reduce costs, it is necessary to minimize the thicknesses of the lower cladding layer, the core layer, and the upper cladding layer. However, if the core size is simply reduced, the loss in the bending waveguide and the connection loss with the single mode optical fiber increase. Therefore, by making the clad layer thinner without making the core size smaller than the conventional design,
It is necessary to improve productivity and reduce costs.

On the other hand, in the optical waveguide, light seeps from the core 4 to the claddings 2 and 3. When the thickness of the clad layer is reduced, if the refractive index is Δn ₁ = 0 and Δn ₂ > 0 (that is, n ₀ = n ₁ and n ₁ <n ₂ ), the core 4
Light leaking from the substrate leaks into the substrate 1 below the lower cladding 2 and the air layer above the upper cladding 3, thereby increasing the loss.

Therefore, the design is such that Δn ₁ > 0 and Δn ₂ > 0 (that is, n ₀ <n ₁ and n ₁ <n ₂ ).
The difference between the refractive index n _{2 of the} core and the refractive index n ₀ of the lower clad 2 is made larger than the conventional design value. Thereby, the core 4
Bleeding of light into the lower cladding 2 from
It is possible to reduce the thickness of the lower cladding layer. Also, by setting the value of the relative refractive index difference Δn ₂ between the core 4 and the upper clad 3 to the same value as the conventional design value, it is possible to prevent a remarkable increase in bending loss and connection loss. in this way,
By setting Δn ₁ > 0 and Δn ₂ > 0, the thickness of the lower cladding layer can be reduced as compared with the conventional AWG type optical wavelength multiplexer / demultiplexer. This leads to a reduction in the time required for depositing the lower cladding layer and at the same time to save raw materials.
It is possible to simultaneously improve the productivity and reduce the cost of the AWG type optical wavelength multiplexer / demultiplexer.

As described above, GeO ₂ is also a dopant that increases the refractive index. Therefore, the refractive index n ₀ of the lower clad 2 can be reduced by lowering the GeO ₂ content in the lower clad 2 or by not adding GeO ₂ to the lower clad 2, so that Δn ₁ > 0 and Δn ₂ > 0 can be easily realized. In this case, since the dopant content of the lower cladding 2 decreases, the effect of increasing the stability of the glass constituting the lower cladding 2 can also be obtained.

Next, a method of manufacturing the AWG type optical wavelength multiplexer / demultiplexer shown in FIG. 1 will be described. The present invention is based on the selection of the main dopant, GeO ₂ , and Δn ₁ > 0 and Δn ₂
Since the invention is characterized by a refractive index structure of> 0, the invention is not limited to the manufacturing method. That is, an AW having a quartz glass as a main component, such as a flame deposition method, a sputtering method, and a CVD method.
All methods for producing a G-type optical wavelength multiplexer / demultiplexer can be applied. Here, as an example, a manufacturing method using a flame deposition method will be described.

FIG. 3 is a sectional view showing main steps in manufacturing the AWG type optical wavelength multiplexer / demultiplexer shown in FIG. First, as shown in FIG. 3A, a lower cladding layer 2a mainly composed of SiO ₂ is deposited on a flat substrate 1 which is an Si substrate by a flame deposition method. GeO ₂ is added to the lower cladding layer 2a as necessary. Subsequently, the lower clad layer 2a is turned into a transparent glass by heating in an electric furnace. The lower vitrified lower cladding layer 2a is
Call.

Next, as shown in FIG. 3B, a core layer 4 mainly composed of SiO ₂ doped with GeO ₂ as a main dopant is formed on the lower clad 2 by a flame deposition method.
a is deposited. Subsequently, the core layer 4a is heated in an electric furnace.
Into a transparent glass. Thereafter, the core 4 is formed by etching the core layer 4a.

Next, as shown in FIG. 3C, Ge is again deposited on the lower clad 2 and the core 4 by a flame deposition method.
An upper cladding layer 3a mainly composed of SiO ₂ to which O ₂ is added as a main dopant is deposited. Subsequently, the upper clad layer 3a is made transparent and vitrified by heating in an electric furnace to form the upper clad 3, thereby completing the optical wavelength multiplexer / demultiplexer as shown in FIG. 3 (D).

The dimensions of the AWG type optical wavelength multiplexer / demultiplexer shown in FIG. 3D are as follows: the lower cladding 2 has a thickness of 7 μm, the upper cladding 3 has a thickness of 30 μm, and the core 4 has a cross-sectional dimension of 6 μm × 6 μm.
m, relative refractive index difference Δn between upper clad 3 and lower clad 2
₁ (= (n ₁ −n ₀ ) / n ₁ ) = 0.4%, relative refractive index difference Δn ₂ between core 4 and upper clad 3 (= (n ₂ −n ₁ ) /
n ₂ ) = 0.75%. Here, Δn ₁ = 0.4%
By doing so, the thickness of the lower clad 2 was set to 7 μm. This is because the thickness of the conventional lower cladding 102 is 20 μm.
About one third of the thickness. Therefore, not only the cost can be reduced by reducing the glass raw material to about one third, but also the productivity can be improved because the deposition time can be reduced to about one third.

FIG. 4 shows an AW manufactured by the method shown in FIG.
It is a graph which shows the optical wavelength demultiplexing characteristic of a G type optical wavelength multiplexer / demultiplexer. However, this AWG type optical wavelength multiplexer / demultiplexer has a channel interval of 100 GHz and 32 channels. GeO ₂ is not added to the lower cladding 2. The horizontal axis of the graph indicates the wavelength, and the vertical axis indicates the transmittance (the ratio of the intensity of the output light to the intensity of the input light) at the center port of the output channel waveguide 15. From FIG.
The demultiplexed optical signals are almost completely coincident between the TM mode (solid line) and the TE mode (dotted line), indicating that polarization independence is actually achieved.

As described above, by using GeO ₂ at least as a main dopant for the upper cladding 3,
Since the contents of B ₂ O ₃ and P ₂ O ₅ can be reduced, the long-term reliability of the polarization independent optical wavelength multiplexer / demultiplexer can be improved. According to this method, since only the adjustment of the raw material components is performed at the time of depositing the optical waveguide layer 5, it is possible to make the polarization independent without complicating the manufacturing process of the AWG type optical wavelength multiplexer / demultiplexer. Therefore, productivity improvement and cost reduction can be realized as compared with the related art in which the polarization dependence is eliminated by inserting a wave plate.

(Second Embodiment) Next, the present invention relates to an MZ.
An embodiment applied to an I-type optical wavelength multiplexer / demultiplexer will be described. FIG. 5 is a plan view showing the configuration of an MZI optical wavelength multiplexer / demultiplexer to which the present invention is applied. This MZI type optical wavelength multiplexer / demultiplexer has two input waveguides 31a and 31b, two arm waveguides 33a and 33b, and two output waveguides 3a and 3b.
5a, 35b and two 3dB directional couplers 32, 34
It is composed of The 3 dB directional coupler 32 includes input waveguides 31 a and 31 b and arm waveguides 33 a and 33.
b, and the 3 dB directional coupler 34 is disposed between the arm waveguides 33a, 33b and the output waveguides 35a, 35b.

In such a configuration, for example, an optical signal in which frequency components (ν ₁ , ν ₂ ,..., Ν _n ) at predetermined frequency intervals (Δν) are multiplexed is input from the input waveguide 31 a. And This optical signal is branched by the 3 dB directional coupler (branching means) 32 into each of the arm waveguides 33a and 33b. The arm waveguides 33a and 33b have a difference in optical path length, and each of the arm waveguides 33a and 33b
The optical signal passing through the optical signal interferes with the 3 dB directional coupler (interference means) 34, and the odd-numbered frequency component (ν
_{1, ν 3,} ···) is outputted from one of the output waveguides 35a, even-numbered frequency component of the optical signal (ν _2, ν _4,
...) Are output from the other output waveguide 35b.

In other words, the optical path length difference between the arm waveguides 33a and 33b is set so that the frequency components of the optical signal are alternately extracted from the output waveguides (output means) 35a and 35b. When the above optical signal is input from the input waveguide 31b, it is similarly separated.

FIG. 6 shows the arm waveguide 33 in FIG.
It is sectional drawing which shows the VI-VI 'cross section of 33a, 33b. FIG.
The MZI type optical wavelength multiplexer / demultiplexer shown in FIG.
It has the same features as the G-type optical wavelength multiplexer / demultiplexer.

That is, the material of the planar substrate 21 is Si, and the lower clad 22, the upper clad 23 and the core 2
The material of No. 4 is quartz glass. However, the upper cladding 23 and the core 24 are made of Ge as a main dopant.
Contains O ₂ . In particular, the upper cladding 23 is
The content of GeO ₂ is adjusted so as to have the same thermal expansion coefficient as 1. Further, if the relative refractive index difference between the upper cladding 23 and the lower cladding 22 is Δn ₁ and the relative refractive index difference between the core 24 and the upper cladding 23 is Δn ₂ , then Δn
₁ > 0 and Δn ₂ > 0 are satisfied.

FIG. 7 is a graph showing optical wavelength demultiplexing characteristics of a conventional MZI optical wavelength multiplexer / demultiplexer and the MZI optical wavelength multiplexer / demultiplexer to which the present invention is applied. The horizontal axis of the graph indicates frequency, and the vertical axis indicates transmittance. FIG. 7A shows an optical demultiplexing characteristic of a conventional MZI optical wavelength multiplexer / demultiplexer. The optical wavelength multiplexer / demultiplexer used for the measurement was prepared under the same conditions as those of the measurement target in FIG. That is, if the material of the substrate is S
i, and the material of the lower clad, the upper clad, and the core is SiO ₂ with a small amount of dopant. In the optical demultiplexing characteristic of the MZI optical wavelength multiplexer / demultiplexer, the peak of the demultiplexed optical signal is separated between the TM mode (solid line) and the TE mode (dotted line).

FIG. 7B shows an MZI to which the present invention is applied.
Optical demultiplexing characteristics of a type optical wavelength multiplexer / demultiplexer. The optical wavelength multiplexer / demultiplexer used for the measurement was prepared under the same conditions as those of the measurement target in FIG. That is, the material of the substrate 21 is Si,
The main components of the lower cladding 22, the upper cladding 23, and the core 24 are SiO ₂ . Although the upper clad 23 and core 24 GeO ₂ is added as the main dopant, GeO ₂ is not added in the lower clad 22. The optical demultiplexing characteristics of the MZI type optical wavelength multiplexer / demultiplexer show that the demultiplexed optical signal almost completely coincides between the TM mode (solid line) and the TE mode (dotted line). It can be seen that dependency has been achieved.

[0051]

As described above, according to the present invention, GeO _{2 is used} as a main dopant at least in the upper cladding.
The content of B ₂ O ₃ and P ₂ O ₅ can be reduced by adopting. Accordingly, since the hygroscopicity of the quartz glass can be suppressed as compared with the related art, the long-term reliability of the polarization independent optical wavelength multiplexer / demultiplexer can be improved. Further, since a polarization independent optical wavelength multiplexer / demultiplexer can be realized without using a wave plate, productivity can be improved and cost can be reduced.

By making the refractive index of the lower cladding lower than that of the upper cladding, the thickness of the lower cladding layer can be made thinner than before. This leads to a reduction in the time required for depositing the lower cladding layer and, at the same time, to save the material, so that it is possible to simultaneously improve the productivity and reduce the cost of the optical wavelength multiplexer / demultiplexer.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an AWG type optical wavelength multiplexer / demultiplexer to which the present invention is applied.

FIG. 2 shows II-I of the channel waveguide array in FIG.
It is sectional drawing which shows the I 'line cross section.

FIG. 3 is a cross-sectional view showing main steps in manufacturing the AWG type optical wavelength multiplexer / demultiplexer shown in FIG.

FIG. 4 is a graph showing optical wavelength demultiplexing characteristics of an AWG type optical wavelength multiplexer / demultiplexer manufactured by the method shown in FIG.

FIG. 5 is a plan view showing a configuration of an MZI type optical wavelength multiplexer / demultiplexer to which the present invention is applied.

FIG. 6 is a sectional view showing a section taken along line VI-VI ′ of the arm waveguide in FIG. 5;

FIG. 7 is a graph showing optical wavelength demultiplexing characteristics of a conventional MZI optical wavelength multiplexer / demultiplexer and an MZI optical wavelength multiplexer / demultiplexer to which the present invention is applied.

FIG. 8 is a perspective view showing a configuration of a conventional AWG type optical wavelength multiplexer / demultiplexer.

9 is IX-I of the channel waveguide array in FIG.
It is sectional drawing which shows the X 'line cross section.

10 is a graph showing the optical wavelength demultiplexing characteristics of the AWG type optical wavelength multiplexer / demultiplexer shown in FIG.

[Explanation of symbols]

1, 21 ... substrate, 2, 22 ... lower clad, 2a ... lower clad layer, 3, 23 ... upper clad, 3a ... upper clad layer, 4, 24 ... core, 4a ... core layer, 5 ... optical waveguide layer, 11 ... input channel waveguide, 12 ... input-side sector slab waveguide, 13 ... channel waveguide array, 13a ... channel waveguide, 14 ... output-side sector slab waveguide, 15 ...
Output channel waveguides, 31a, 31b ... input waveguides, 32, 34 ... 3 dB directional couplers, 33a, 33b
... arm waveguides, 35a and 35b ... output waveguides.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akio Sugita 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Hisaaki Okazaki 3-192 Nishishinjuku, Shinjuku-ku, Tokyo No. F-term in Nippon Telegraph and Telephone Corporation (reference) 2H047 KA02 KA04 KA12 LA01 LA19 PA01 PA24 QA04 TA00 TA41

Claims (7)

[Claims] An optical waveguide circuit formed on a planar substrate made of Si, wherein at least two optical waveguide circuits having different optical path lengths are provided.
In an optical wavelength multiplexer / demultiplexer that branches an optical signal into each of the waveguides and interferes with an optical signal that has passed through these waveguides to demultiplex the optical signal for each predetermined wavelength, the waveguide is formed on the planar substrate. A lower clad, a core formed on the lower clad, and an upper clad formed on the lower clad so as to cover the core, wherein the lower clad, the core and the upper clad are made of quartz. An optical wavelength multiplexer / demultiplexer comprising a base glass, wherein at least the upper cladding contains GeO ₂ of 50 mol% or less as a main dopant and has a thermal expansion coefficient similar to that of the planar substrate. 2. The optical wavelength demultiplexer according to claim 1, wherein a contact area between the upper clad and the core is larger than a contact area between the lower clad and the core. 3. The optical wavelength combining device according to claim 1, wherein the core contains GeO ₂ of 50 mol% or less as a main dopant and has a thermal expansion coefficient similar to that of the planar substrate. Waver. 4. The semiconductor device according to claim 1, wherein the lower clad is 50 mo as a main dopant.
An optical wavelength multiplexer / demultiplexer comprising 1% or less of GeO ₂ and having a thermal expansion coefficient similar to that of the flat substrate. 5. The optical wavelength multiplexer / demultiplexer according to claim 1, wherein a refractive index of the lower cladding is lower than a refractive index of the upper cladding. 6. The optical path according to claim 1, wherein an optical path length of each of the waveguides is set such that an optical signal passing through each of the waveguides is strengthened by interference at a different position for each wavelength. An optical wavelength multiplexer / demultiplexer, which is provided at a position where a predetermined wavelength is strengthened and includes output means for extracting the wavelength. 7. The branching unit according to claim 1, wherein the branching unit branches an input optical signal into two waveguides, and the interference unit interferes with an optical signal passing through each of the waveguides. To extract the frequency component of the optical signal enhanced by the interference 2
The output means of the two waveguides, wherein the optical path length difference between the two waveguides is set so that frequency components of the optical signal are alternately output from the two output means at predetermined frequency intervals. An optical wavelength multiplexer / demultiplexer characterized in that: