JP2004117448A - Thermo-optical phase shifter group and thermo-optical switch using the thermo-optical phase shifter group - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermo-optical phase shifter group with uniform characteristics and a thermo-optical switch using the thermo-optical phase shifter group. <P>SOLUTION: The thermo-optical switch has a plurality of the thermo-optical phase shifters and constructed by setting widths of wiring lines so as to make respective resistance values of a plurality of the wiring lines 4 identical with one another. Also the thermo-optical phase shifter is provided with an optical waveguide 2 formed on a silicon substrate 1, a thin film heater 3 arranged in the vicinity of the optical waveguide 2, the wiring lines 4 to supply electric power to the thin film heater 3 and a ground line 5. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thermo-optic phase shifter group of a waveguide type optical circuit composed of a planar optical waveguide and a thermo-optic switch using the thermo-optic phase shifter group.
[0002]
[Prior art]
With the increase in the capacity of the optical network, optical devices having various functions have been developed, and a thermo-optical switch using a silica glass optical waveguide for switching an optical signal is one of them. The principle of the thermo-optical switch will be briefly described with reference to FIGS. 3 and 4 (see Non-Patent Document 1 for details).
[0003]
FIG. 3 is a plan view showing the configuration of a 2 × 2 thermo-optical switch element.
FIG. 4 shows a cross-sectional structure of a 2 × 2 thermo-optical switch element, and is a cross-sectional view taken along line AA of FIG.
[0004]
As shown in FIGS. 3 and 4, the 2 × 2 thermo-optical switch element 6 is formed in a depth direction by forming a quartz glass clad 11 a on a flat substrate such as the Si substrate 1. In this example, a silica-based glass core 11b serving as an optical waveguide is formed. As a configuration of the 2 × 2 thermo-optical switch element 6 on a plane, two 3 dB directional couplers 9 a and 9 b are configured by part of two optical waveguides including the core 11 b being close to each other. The other optical waveguide portion is composed of two input waveguides 2a on the input side of an optical signal and two arm waveguides 2b of approximately equal length sandwiched between 3 dB directional couplers 9a and 9b. , And two output waveguides 2c on the output side of the optical signal. That is, the input waveguide 2a and the arm waveguide 2b and the arm waveguide 2b and the output waveguide 2c are connected by the 3 dB directional couplers 9a and 9b, respectively. The thin film heater 3 is formed on the surface of one arm waveguide 2b, and furthermore, a wiring 24 for supplying power to the thin film heater 3 is formed.
[0005]
Note that the portion of the arm waveguide 2b having the thin film heater 3 functions alone as a thermo-optic phase shifter by operating the thin film heater 3 by the wiring 24.
[0006]
In the 2 × 2 thermo-optical switch element 6, light incident from one input waveguide 2a is distributed by the first 3 dB directional coupler 9a to the two arm waveguides 2b by 50%. Since the two arm waveguides 2b are designed so that the optical path length difference becomes zero when no power is supplied to the thin film heater 3, the two light beams are again reduced to 50% by the second 3 dB directional coupler 9b. Binding occurs, resulting in a total of 100% binding. As a result, light is emitted from the cross port 10b.
[0007]
Next, when a current is applied to the thin film heater 3 to heat the surface of the one arm waveguide 2b, a temperature distribution 12 as shown in FIG. 4 is generated in the one arm waveguide 2b. Due to this temperature distribution, a half-wavelength optical path difference occurs between the two arm waveguides 2b. As a result, a phase difference of π occurs between the two light beams, and light is output from the through port 10a. Switching of the light output port is realized by turning on / off the power supply to the thin film heater 3.
[0008]
[Non-patent document 1]
T. Goh, Recent advices in large-Scale silica-based thermo-optic switches, Processes of APOC 2001, SPIE, Beijing, China, 12-15 Nov. 2001
[0009]
[Problems to be solved by the invention]
FIG. 5 is a logical circuit configuration diagram of the 8 × 8 thermo-optical switch.
[0010]
As shown in FIG. 5, a 2 × 2 thermo-optical switch element is provided at each intersection of eight input waveguides 2a and eight output waveguides 2b with the aforementioned 2 × 2 thermo-optical switch element 6 as a basic element. An 8 × 8 thermo-optical switch is configured by arranging 64 6s. By expanding this scale, an arbitrary N × N thermo-optical switch is realized.
[0011]
FIG. 6 is a plan view showing a waveguide layout of a 16 × 16 thermo-optical switch.
FIG. 7 is an external view showing the arrangement of the thin film heaters and wirings of the 16 × 16 thermo-optical switch.
[0012]
In FIG. 6, # 1 to # 16 represent a switch group including a plurality (16) of thermo-optic switches, and these switch groups # 1 to # 16 are connected to each other by an optical waveguide 2 on one substrate. The 16 × 16 thermo-optical switch 42 is configured by arranging 16 thermo-optical switches. A total of 256 2 × 2 thermo-optical switch elements are integrated in the 16 × 16 thermo-optical switch 42, and when a thin film heater is arranged in each of two arm waveguides, 500 or more wirings are required. For this reason, when the size of the entire substrate is 100 × 100 mm, the wiring length is short, that is, 20 mm, and that of a long wiring is 100 mm, which is a large difference in length. Usually, since the wiring widths are formed to be equal, as a result, the wiring having a short wiring length has a low wiring resistance, and the wiring having a long wiring length has a high wiring resistance. This will be described in more detail with reference to FIG.
[0013]
FIG. 8 is a plan view of a conventional thermo-optical switch.
In FIG. 8, a part of the thermo-optical switch is illustrated, and the wiring width is exaggerated for easy understanding of the wiring width.
[0014]
As shown in FIG. 8, in the thermo-optical switch, two optical waveguides 2 are formed on a Si substrate 1, and the two optical waveguides 2 constitute a 2 × 2 thermo-optical switch element 6. The thermo-optical switch has a configuration having a plurality of 2 × 2 thermo-optical switch elements 6.
[0015]
A thin film heater 3 is formed in the vicinity of the arm waveguide portion of each 2 × 2 thermo-optical switch element 6, and a wiring for supplying power to the thin film heater 3 is formed. In order to reduce the number of wires, one common ground line 5 is formed and used as one wire of all the thin film heaters 3. The wiring on the other side forms an individual wiring 34 for each thin film heater 3. An electrode pad 37 is provided at an end (peripheral portion of the chip) of the ground line 5 and the wiring 34, and power is supplied to the electrode pad 37 from a gate switch IC that controls on / off of the thin film heater 3.
[0016]
As can be seen from FIG. 8, the widths of the individual wirings 34 are formed to be equal. Then, for a plurality of 2 × 2 thermo-optical switch elements 6 arranged on the Si substrate 1, wiring is performed to the position of the thin film heater 3 of each 2 × 2 thermo-optical switch element 6 using the wiring 34 having the same wiring width. Is formed. In other words, although the wiring widths are equal to each other, the wiring lengths are different from each other. As a result, inhomogeneity occurs in that the wirings having a short wiring length have a low wiring resistance and the wirings having a long wiring length have a high wiring resistance. .
[0017]
Each 2 × 2 thermo-optical switch element 6 is driven by a common voltage source and a gate switch that controls on / off of current. Therefore, if the wiring resistance is different for each of the thin film heaters 3, the power applied to the thin film heaters 3 will vary. That is, since the wiring resistances are different, the power supplied to the thermo-optical switch elements varies, resulting in a non-uniform thermo-optical switch.
[0018]
The present invention has been made in view of the above problems, and has as its object to provide a thermo-optic phase shifter group having a uniform characteristic and a thermo-optic switch using the thermo-optic phase shifter group.
[0019]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a thermo-optical phase shifter group, comprising: an optical waveguide formed on a substrate; a heating unit disposed near the optical waveguide; and a power supply to the heating unit. And a plurality of thermo-optic phase shifters each having a wiring to be connected, and the resistances of the plurality of wirings are made equal to each other.
[0020]
According to another aspect of the present invention, there is provided a thermo-optic phase shifter group according to the second aspect of the present invention, wherein the plurality of wires having different lengths have different widths, and the plurality of wires have the same resistance. It is characterized by.
[0021]
A thermo-optical phase shifter group according to a third aspect of the present invention that solves the above-mentioned problem is characterized in that the width of each of the plurality of wirings having different widths is made uniform.
[0022]
According to a fourth aspect of the present invention, there is provided a thermo-optic phase shifter group according to the fourth aspect of the present invention, in which the widths of the plurality of wires having different lengths are locally narrowed so that the resistances of the plurality of wires are equal to each other. It is characterized by the following.
[0023]
A thermo-optical phase shifter group according to a fifth aspect of the present invention that solves the above-mentioned problem is characterized in that the width of the wiring is locally reduced so as not to affect the temperature of the heating unit.
[0024]
According to a sixth aspect of the present invention, there is provided a thermo-optical switch, comprising: two directional couplers formed by two optical waveguides formed on a substrate; and a thermoelectric switch sandwiched between the directional couplers. A thermo-optical switch element including a plurality of thermo-optical phase shifters, and any one of the thermo-optical phase shifters described above is used as the plurality of thermo-optical phase shifters.
[0025]
A thermo-optical switch according to claim 7 of the present invention for solving the above-mentioned problems, wherein the thermo-optical switch element is formed of a silica glass optical waveguide on a silicon substrate, and the heating means is formed of chromium or tantalum nitride, The wiring is mainly composed of gold.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
According to the present invention, in a wiring to a thin-film heater for driving a plurality of thermo-optic phase shifters, thermo-optic switches, and the like integrated on the same substrate, wiring resistances of a plurality of wirings having non-uniform lengths are made equal to each other. It is characteristic. Specifically, the width of each wiring to the thin-film heater was adjusted so that the wiring resistance of each wiring became equal. The specific embodiment is shown in FIGS. 1 and 2, and the embodiment of the present invention will be described in detail with reference to the drawings.
[0027]
(Example 1)
FIG. 1 is a plan view of a thermo-optical switch showing an example of an embodiment of the present invention.
Note that FIG. 1 also shows a part of the thermo-optical switch, and the wiring width is exaggerated for easy understanding of the wiring width.
[0028]
The basic configuration of the thermo-optic switch according to the present invention shown in FIG. 1 may be the same as the conventional configuration except for the configuration of the wiring 4. Specifically, as shown in FIG. 1, in the thermo-optical switch, two optical waveguides 2 are formed on a Si substrate 1, and the two optical waveguides 2 form a 2 × 2 thermo-optical switch element 6. , And the thermo-optical switch has a plurality of 2 × 2 thermo-optical switch elements 6.
[0029]
The 2 × 2 thermo-optical switch element 6 has a structure in the depth direction, in which a silica-based glass clad is formed on a flat substrate such as a Si substrate 1 and a silica-based glass core serving as the optical waveguide 2 is formed in the clad. It was formed. Further, as a configuration of the 2 × 2 thermo-optical switch element 6 on a plane, two 3 dB directional couplers 9 a and 9 b are configured by a part of two core optical waveguides 2 being close to each other. The other portion of the optical waveguide 2 is composed of two input waveguides on the input side of an optical signal and two arms of approximately equal length sandwiched between two 3 dB directional couplers 9a and 9b. It constitutes a waveguide and two output waveguides on the output side of the optical signal. The configuration is such that 3 dB directional couplers 9a and 9b are connected between the input waveguide and the arm waveguide and between the arm waveguide and the output waveguide, respectively. In the vicinity (surface) of the arm waveguide, a thin film heater 3 serving as a heating means is formed, and further, a wiring 4 for supplying power to the thin film heater 3 and a ground wiring 5 are formed. In order to reduce the number of wires, one common ground line 5 is formed and used as one wire of all the thin film heaters 3, and the other wire is connected to each thin film heater 3. , Individual wirings 34 are formed.
[0030]
The portion of the optical waveguide 2 (arm waveguide) having the thin-film heater 3 also functions as a thermo-optic phase shifter by operating the thin-film heater 3 by the wiring 4 and the ground wiring 5. It can also be said to be a configuration using a plurality of thermo-optic phase shifters, that is, a group of thermo-optic phase shifters.
[0031]
The thin film heater 3 formed on the surface of the arm waveguide portion is made of chromium or tantalum nitride, and the wiring 4 for supplying current to the thin film heater 3 and the ground wiring 5 are mainly made of gold. The wiring 4 and the ground wiring 5 are formed from each thin film heater 3 to an electrode pad 6 formed around the chip. The electrode pad 6 and the gate switch IC for controlling the ON / OFF of the current are connected by wire bonding and further connected to a common low voltage source. In this embodiment, the resistance of the thin-film heater 3 is designed to be 500Ω and the wiring resistance is designed to be 50Ω.
[0032]
In the present embodiment, the wiring width is set so that the wiring resistance of each of the wirings 4 is equal. That is, the wiring width of each wiring 4 is changed according to the wiring length, and the wiring width is made uniform over the entire length of each wiring 4, and the resistance value of each wiring 4 is designed to be equal. However, if the wiring 4 has a bent portion due to the layout of the wiring, the wiring width in the bent portion is wide (not uniform), but even in this case, the wiring width is uniform. Make the wiring equivalent to a straight line.
[0033]
The wiring length of the ground line 5 to each thin film heater 3 naturally changes depending on the position of each thin film heater 3, and the wiring length of the ground line 5 to each thin film heater 3 depends on the wiring length of each thin film heater 3. The qualitatively different resistance values of the ground line 5 are also obtained. However, since the width of the ground line 5 is sufficiently wide, this effect is quantitatively small, and the resistance value of the wiring affecting each thin film heater 3 is mainly the wiring resistance of the individual wiring 4. It depends. Therefore, here, attention is paid to the resistance value of the individual wirings 4, and the width is set so that the resistance values of the respective wirings 4 are equal.
[0034]
The wiring resistance R is given by the following equation using the wiring length L, the wiring width W, and the sheet resistivity σ.
R = σL / W
[0035]
As can be seen from the above equation, the long wiring has a large width, and the short wiring has a small width, so that the mutual wiring resistance can be made equal. Specifically, when the size of the entire substrate is 100 × 100 mm, the width of the longest 100 mm wiring is set to 200 μm, and the width of the shortest 20 mm wiring is set to 40 μm, so that all wiring resistances are set to 50Ω. . As a result, the current and power supplied to each thin-film heater became equal, and uniform switch characteristics were obtained within the chip surface.
[0036]
For comparison, a calculation was performed for a conventional thermo-optical switch, that is, a case where all the wiring widths were designed to be 200 μm (see FIG. 8). In this case, the wiring resistance is 50Ω for a wiring length of 100 mm, and 10Ω for a wiring length of 20 mm. Considering the resistance of the thin film heater at 500Ω, the power supplied to each thin film heater varies by as much as 8%. Occurred.
[0037]
On the other hand, in the configuration of the present embodiment, the variation in the power supplied to each thin film heater was only about 1%. It is considered that this variation was caused by a variation in fabrication of the thin film heater resistor. Variations in the power supplied to each thin-film heater result in variations in thermo-optical switch characteristics. That is, it can be said that the thermo-optical switch according to the present invention has an improved in-plane distribution of switch characteristics as compared with the conventional thermo-optical switch. The thermo-optical switch according to the present invention has a higher average value of the wiring resistance than the conventional thermo-optical switch, so that the power consumption of the entire thermo-optical switch is higher. However, the in-plane distribution of switch characteristics, which is an important characteristic of the thermo-optic switch, can be improved, and uniform switch characteristics can be obtained.
[0038]
(Example 2)
FIG. 2 is a plan view of a thermo-optical switch showing another example of the embodiment of the present invention.
FIG. 2 also shows a part of the thermo-optical switch, and the wiring width is exaggerated so that the wiring width can be easily understood.
[0039]
The basic configuration of the thermo-optical switch according to the present invention shown in FIG. 2 may be the same as that of the thermo-optical switch shown in FIG. Therefore, the description of the overlapping part will be omitted, and the part according to the present embodiment will be described.
[0040]
In the thermo-optical switch of Example 1, the wiring resistance was equalized by setting the width of each wiring uniformly and appropriately. However, the difference between the present embodiment and the first embodiment lies in the shape of the wiring 14, and by providing a locally narrow portion (heating region 8), the wiring resistance of each wiring 14 is appropriately set. And the wiring resistance of each other is made equal. This is because the heat generated in the wiring 14 has an adverse effect on the operation of the thermo-optical switch. Therefore, the heat-generating region 8 is provided in a portion distant from the thermo-optical switch (thin film heater 3), and heat is generated in that portion. (Thin film heater 3) is intended to be reduced. That is, the temperature of the thin film heater 3 is not affected by the heat generated by the wiring. In the present embodiment, a heat radiation fin is provided on the surface of the heat generating region 8 to improve the heat radiation efficiency, and further has no adverse effect.
[0041]
As described above, in the above-described embodiment, the description has been made using the thermo-optic switch. However, the present invention is not limited to the thermo-optic switch, but all optical circuits using the thermo-optic effect, such as an optical circuit using a plurality of phase shifters such as a transversal filter. Widely applicable to Further, the material of the optical waveguide is not limited to the silica-based glass waveguide, and a thermo-optical switch using a polymer waveguide or a semiconductor is also an object of the present invention.
[0042]
【The invention's effect】
According to the first to fourth aspects of the present invention, the thermo-optical phase shifter group includes an optical waveguide formed on a substrate, a heating unit disposed near the optical waveguide, and an electric power supplied to the heating unit. Since a plurality of thermo-optic phase shifters each having a wiring to be supplied are provided, and the resistances of the plurality of wirings are made equal to each other, variations in current and power supplied to each heating unit are reduced, and in a chip surface, A uniform phase shifter characteristic can be obtained.
[0043]
According to the invention according to claim 5, the width of the wiring is locally narrowed so as not to affect the temperature of the heating means, so that the variation in current and power supplied to each heating means is reduced. In addition, a uniform phase shifter characteristic can be obtained in the chip plane, and good characteristics can be maintained by preventing heat generation in the wiring portion from being applied to the heating means.
[0044]
According to the invention according to claim 6 or claim 7, two directional couplers constituted by two optical waveguides formed on a substrate, and a thermo-optic phase shifter sandwiched between the directional couplers Since a plurality of the thermo-optic phase shifters each having the above-described configuration are used as the plurality of thermo-optic phase shifters, the variation in the current and power supplied to each thin-film heater is reduced. In addition, uniform switch characteristics can be obtained in the chip plane, and a thermo-optical switch having good characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a plan view of a thermo-optical switch showing an example of an embodiment of the present invention.
FIG. 2 is a plan view of a thermo-optical switch showing another example of the embodiment of the present invention.
FIG. 3 is a plan view showing a configuration of a 2 × 2 thermo-optical switch element.
FIG. 4 is a sectional view taken along line AA of FIG. 3;
FIG. 5 is a logical circuit configuration diagram of the 8 × 8 thermo-optical switch.
FIG. 6 is a plan view showing a waveguide layout of a 16 × 16 thermo-optical switch module.
FIG. 7 is an external view showing an arrangement of thin film heaters and wirings of a 16 × 16 thermo-optical switch module.
FIG. 8 is a plan view of a conventional thermo-optical switch.
[Explanation of symbols]
Reference Signs List 1 Si substrate 2 Optical waveguide 3 Thin film heater 4 Wiring 5 Ground wire 6 2 × 2 thermo-optical switch element 7 Electrode pad 8 Heating area 14 Wiring 17 Electrode pad

Claims (7)

In a thermo-optic phase shifter group having a plurality of thermo-optic phase shifters each having an optical waveguide formed on a substrate, a heating unit disposed near the optical waveguide, and a wiring for supplying power to the heating unit,
A thermo-optical phase shifter group, wherein the resistances of the plurality of wirings are made equal to each other. The thermo-optic phase shifter group according to claim 1,
A group of thermo-optic phase shifters, wherein the widths of the plurality of wirings having different lengths are different from each other, and the resistances of the plurality of wirings are equal to each other. The thermo-optic phase shifter group according to claim 2,
A group of thermo-optic phase shifters, wherein the width of each of the plurality of wirings having different widths is uniform. The thermo-optic phase shifter group according to claim 1,
A group of thermo-optic phase shifters, wherein the widths of the plurality of wirings having different lengths are locally narrowed so that the resistances of the plurality of wirings are equal to each other. The thermo-optic phase shifter group according to claim 4,
A group of thermo-optic phase shifters, wherein the width of the wiring is locally reduced so as not to affect the temperature of the heating means. In a thermo-optical switch having a plurality of thermo-optical switch elements each including two directional couplers formed by two optical waveguides formed on a substrate and a thermo-optical phase shifter sandwiched between the directional couplers,
A thermo-optic switch using the thermo-optic phase shifter group according to claim 1 as a plurality of thermo-optic phase shifters. The thermo-optical switch according to claim 6,
A thermo-optical switch, wherein the thermo-optical switch element is composed of a silica-based glass optical waveguide on a silicon substrate, the heating means is composed of chromium or tantalum nitride, and the wiring is mainly composed of gold. .

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