JP3158372B2 - Waveguide optical switch and waveguide matrix optical switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical switch and a waveguide type matrix optical switch used in the field of optical communication, and more particularly to a waveguide type switch which is resistant to fabrication errors, has an excellent extinction ratio, is small and has a small excess loss. The present invention relates to an optical switch and a waveguide type matrix optical switch.

[0002]

2. Description of the Related Art In order to further popularize optical fiber communication, in addition to increasing the performance and cost of optical fibers and light emitting / receiving elements, optical branching and coupling circuits, optical multiplexing / demultiplexing circuits, optical switches, etc. Development of various optical circuit components is indispensable. In particular, an optical switch is considered to play an important role in the near future for freely switching an optical fiber line according to demand and for securing a detour in the event of a line failure.

[0003] As a form of the optical switch, conventionally,
A bulk type and an optical waveguide type have been proposed. The bulk type is assembled by using a movable prism, a lens, and the like as components, and has an advantage that wavelength dependency is small and loss is relatively low. However, an assembly adjustment process is complicated and is not suitable for mass production and becomes expensive. Therefore, it has not been widely used. The optical waveguide type is based on an optical waveguide on a flat substrate and uses photolithography and microfabrication technology to mass produce so-called integrated optical switches in a batch. Have been. In particular, it is expected that there is no other form in which a relatively large M × N matrix optical switch having M input ports and N output ports can be actually configured in an optical waveguide type.

FIG. 8 is an example of an M × N matrix optical switch to which the present invention is applied, and is a conceptual diagram of a 4 × 4 optical switch. This 4 × 4 optical switch has a configuration in which four input optical waveguides (1a, 1b, 1c, 1d) and output optical waveguides (2a, 2b, 2c, 2d) intersect at 16 locations. , 16 intersections, a 2 × 2 optical switch element (S
00, ‥‥, S33). Such a configuration of the matrix optical switch is called a strictly non-blocking matrix optical switch, and the input optical waveguide (1
The optical paths of the four-channel signal light input to the a, 1b, 1c, and 1d) can be distributed to the output optical waveguides (2a, 2b, 2c, and 2d).

For example, when an optical signal incident on the input optical waveguide 1a is output from the output optical waveguide 2b, the optical switch elements S03, S02, S01, S11, S21, S31
To form an optical path through. At this time, the optical switch element S01
In the above, a through path is formed in which light entering from the lower left optical waveguide exits from the lower right optical waveguide, and in other optical switch elements, light entering from the lower left (or upper left) optical waveguide is converted to upper right ( Alternatively, a cross path exiting from the lower right optical waveguide is formed. To minimize the number of optical switch elements to be driven, it is necessary that a cross path is formed when the optical switch is off and a through path is formed when the switch is on. In this case, the switch S
Only 01 is on and the other switches are off.
This is the same for the other optical paths. The number of optical switch elements that are turned on to form a through path is always one regardless of the optical path, but the number of optical switch elements that are turned off to form a cross path varies from zero to six. That is, in the 4 × 4 matrix optical switch, the number of optical switch elements through which the optical signal passes is one at a minimum and seven at a maximum.

In order to construct the matrix optical switch, attempts have been made to use optical waveguides made of various materials. Among them, a thermo-optical effect utilizing a thermo-optical effect of a quartz optical waveguide on a silicon substrate has been proposed. An optical matrix optical switch is expected to be a practical matrix optical switch because it has no polarization dependence and has good matching with an optical fiber.

FIGS. 9A and 9B are schematic views for explaining the configuration of a conventional thermo-optical 4 × 4 matrix optical switch manufactured on a silicon substrate. FIG. FIG. 9B is an enlarged plan view of the optical switch element. In FIG. 9A, eight optical waveguides including four input optical waveguides (1a, 1b, 1c, 1d) constitute an input-side optical waveguide bundle 4a, and four output optical waveguides (2
Although the eight optical waveguides including a, 2b, 2c, and 2d) constitute the output-side optical waveguide bundle 4b, the actual arrangement in FIG. 9A and the conceptual configuration diagram in FIG. 8 are equivalent circuit configurations.

The optical waveguide bundles 4a and 4b are quartz optical waveguides formed on the silicon substrate 3 by a known combination of a flame hydrolysis reaction deposition method and a reactive ion etching technique. As shown in FIG. 9B, the optical switch elements (S00, ‥‥, S33) arranged at 16 locations each have a 2 × 2 Mach-Zehnder optical interferometer circuit type.
It has an optical switch configuration. That is, a part of the two optical waveguides 18 and 19 is approached to each other at two places to form the directional couplers 20a and 20b. The optical coupling rate of these directional couplers 20a and 20b is set to be 50% at the signal light wavelength. Two optical waveguides 18 connecting between the directional couplers 20a and 20b
The optical path lengths of the optical waveguides 19 and 19 are set to be equal in a state where the thermo-optic phase shifter 21 composed of a thin film heater located in the middle of the two optical waveguides 18 and 19 is not operated, that is, in an off state.

The Mach-Zehnder optical interferometer circuit type 2 ×
The switching input / output characteristics of the two-optical switch are as follows: K is the power coupling ratio of each of the directional couplers 20a and 20b, Pin is the power of the signal light input to one of the optical waveguides 18 and 19, and the output light is a through path and a cross path. Power of Pout1, Pout2, 2
Assuming that the phase difference between the two optical waveguides 18 and 19 connecting the directional couplers 20a and 20b is Δφ, the phase difference is expressed by the following equation.

[0010]

Pout1 / Pin = (1-2K) ² cos ² (Δφ / 2) + sin ² (Δφ / 2) (1)

[0011]

Pout2 / Pin = 4K (1−K) cos ² ( Δφ / 2 ) (2) In the case where the coupling ratio K = 0.5, that is, the directional coupler 20
The input / output characteristics when a and 20b are 3 dB couplers are as follows. First, in the off state (the thin-film heater non-energized state), since the phase difference Δφ = 0, the signal light passes through the optical switch element in a cross path (22a → 23b, 23a → 22b). On the other hand, the thermo-optic phase shifter 2 is arranged such that an optical path length difference near 1/2 wavelength corresponding to an optical phase of 180 degrees (π) is generated in the optical waveguide between the directional couplers 20a and 20b.
Assuming that Δφ = π by operating at least one of the elements 1 (the thin-film heater is energized) and setting Δφ = π, the signal light passes through the optical switch element through the through paths (22a → 22b, 23a → 23).
It switches to pass in b). Thus, 2
A cross / through switching operation as a × 2 optical switch element is achieved.

[0012]

However, the conventional waveguide type matrix optical switch having the above-described 2 × 2 optical switch element as a basic unit has the following manufacturing problems.

That is, in order for the Mach-Zehnder optical interferometer circuit type optical switch element of FIG. 9B to operate ideally, the coupling ratio of the directional couplers 20a and 20b, which are constituent elements, must be exactly 50 at the signal light wavelength. % Is an essential condition, but the actual optical waveguide fabrication process includes some errors, and it is difficult to set the coupling ratio to exactly 50%. This is because the directional coupler is an optical element that is extremely sensitive to deviations in structural parameters (optical waveguide width, optical waveguide interval, relative refractive index difference between the core and the clad, etc.). The coupling ratio of the directional couplers 20a and 20b is 50%
If it deviates, 100% of the signal light does not pass through the cross path in the off state, and leakage light occurs in the through path. Due to such light crosstalk, switching of the signal light is not performed clearly, and there is a serious problem that the characteristics of the matrix optical switch are deteriorated.

As a method of suppressing light crosstalk due to such a directional coupler fabrication error, an optical switch element is shown in FIG.
There is a method of making the configuration as shown in FIG.

An optical switch element shown in FIG. 10A includes a Mach-Zehnder optical interferometer circuit in which a half-wavelength optical path difference is set between two directional couplers 20a and 20b, two optical waveguides 18, It is composed of 19 plane optical waveguide intersections 24. In this optical switch element, it is already 1/2
Since the optical path length difference between the wavelengths is set, in the off state, the signal light passes through the Mach-Zehnder optical interferometer circuit through the through path. Furthermore, in the plane optical waveguide intersection 24, since the optical waveguides 18 and 19 intersect at an angle at which the light crosstalk between the optical waveguides 18 and 19 can be ignored, the signal light finally passes through the optical switch element through a cross path. Will pass through. This operation is performed by the two directional couplers 20a, 2
It is sufficient that the coupling rates of Ob are equal, and the coupling rate does not necessarily need to be 50%.

On the other hand, in the ON state, the thermo-optical phase shifter 21 provided on the optical waveguide constituting the Mach-Zehnder optical interferometer circuit is driven to cancel the optical path length difference corresponding to the half wavelength. Thereby, the plane optical waveguide intersection 2
4 can be switched to a through path.

In this configuration, the two directional couplers 20
If the coupling rates of a and 20b are equal, even if the value deviates from 50%, light crosstalk to the through path does not occur in the off state. If the coupling ratio deviates from 50%, all of the signal light cannot be switched to the through path in the ON state, and signal light crosstalk to the cross path occurs. However, in the matrix optical switch as shown in FIG. 9A, the crosstalk light is guided to the end of the dummy optical waveguide in the output side optical waveguide bundle 4b, so that the extinction ratio of the matrix optical switch does not deteriorate.

In the configuration shown in FIG. 10B, a plane optical waveguide intersection 24 is provided in the middle of connecting the two directional couplers 20a and 20b, and the interval between the two optical waveguides 18 and 19 is increased. The occupied length of the optical switch element can be reduced because the locations to be taken are combined into one location.

However, in such a configuration in which the plane optical waveguide crossing portion 24 is provided, the planar optical waveguide crossing portion 24 loses the effect of confining the optical waveguide in the lateral direction, and essentially causes diffraction loss. . When an optical waveguide having the same size as the optical fiber is used, the diffraction loss value is about 0.1 dB / point. However, in a large-scale matrix optical switch, the diffraction loss is accumulated for each optical switch element. The diffraction loss at the plane optical waveguide intersection 24 limits the loss of the entire circuit. To reduce the size and the scale of the matrix optical switch, it is promising to use a high Δ optical waveguide having a large relative refractive index difference that can reduce the radius of the bent optical waveguide. However, as the relative refractive index difference increases, the diffraction loss at the plane optical waveguide intersection 24 increases. Therefore, it has been difficult to simultaneously reduce the size and the loss of the matrix optical switch.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a waveguide type matrix optical switch which is resistant to fabrication errors, has an excellent extinction ratio, is small, and has a small excess loss. Is to provide.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0022]

Means for Solving the Problems To achieve the above object, a means (1) of the present invention is a waveguide type optical switch for switching an optical path of an input signal light, wherein the optical switch is provided on a substrate. First and second optical waveguides provided on different planes perpendicular to each other with respect to the first and second optical waveguides;
And two laminated directional couplers having the same coupling ratio, and the first optical waveguide between the two laminated directional couplers, wherein An optical path length switching means provided on at least one of the second optical waveguides; and an intersection portion for spatially intersecting the first optical waveguide and the second optical waveguide, wherein each of the laminated directional couplers is provided. The first and second optical waveguides constituting
The optical axis is parallel and the center of the first and second optical waveguides are aligned in <br/> so that to position on the same line perpendicular to the substrate, the two laminated The first optical waveguide and the second optical waveguide between the directional couplers have an effective optical path length difference corresponding to a half wavelength of the input signal light, and the optical path length switching unit includes the two optical waveguides. Wherein the effective optical path length difference between the first optical waveguide and the second optical waveguide between the stacked directional couplers is switched to an integral multiple of the wavelength of the signal light.

The means (2) of the present invention is characterized in that an optical phase shifter is used as the optical path length difference switching means.

The means (3) of the present invention is characterized in that a thermo-optic effect phase shifter comprising a thin film heater is used as the optical phase shifter.

According to a fourth aspect of the present invention, the optical phase shifter is provided on each of the first optical waveguide and the second optical waveguide between the two stacked directional couplers. It is characterized by.

The means (5) of the present invention is characterized in that the optical phase shifter is provided in an optical waveguide having a shorter effective optical path length, and the effective optical path difference is made zero in a driving state. And

In the means (6) of the present invention, the optical phase shifter is provided in an optical waveguide having a longer effective optical path length, and in a driving state, the effective optical path length difference is set to one wavelength of the signal light. It is characterized by doing so.

The means (7) of the present invention uses one of the optical phase shifters to compensate for the difference when the effective optical path length difference deviates from the half wavelength of the signal light. It is characterized by the following.

The means (8) of the present invention is characterized in that the space intersection is provided between the two stacked directional couplers.

[0030] The means (9) of the present invention is characterized in that the space intersection part is also used as one of the two stacked directional couplers.

The means (10) of the present invention is a waveguide type matrix optical switch which has a plurality of input terminals and a plurality of output terminals, and switches and outputs an input signal light, and is connected to each of the input terminals. A plurality of input optical waveguides, each connected to the output end, a direction perpendicular to the substrate
Plane different from the plane position of the input waveguide in
A plurality of output optical waveguides provided above, and a plurality of optical switch elements disposed at respective spatial intersections of the input optical waveguide and the output optical waveguide, wherein each of the optical switch elements
Are the waveguide type optical switches of the respective means.
A waveguide type matrix optical switch .

[0032] Means (11) of the present invention, the optical switch element, characterized in that connected by optical waveguide beams bent in zigzag.

[0033] Means (12) of the present invention, in the optical waveguide developing connecting the optical switch element, the position corresponding to the optical switch element, characterized in that a dummy switch.

[0034] Means (13) of the present invention has a front Symbol dummy switch, two binding rate is close to the optical waveguide which are disposed on the same plane equal two directional couplers, the 2
The two optical waveguides between the directional couplers are configured to have an effective optical path length difference corresponding to a half wavelength of the signal light.

[0035] Means (13) of the present invention, the optical waveguide, the curvature radius changes part of the portion and the curve portion of transition from straight to curved, and characterized in that to connect the optical waveguide center is offset I do.

[0036]

According to the above-mentioned means, an asymmetric Mach-Zehnder optical interferometer circuit is constituted by a laminated directional coupler using an optical waveguide having a laminated structure, and an optical waveguide intersection is constituted by a spatial intersection which does not cause diffraction loss. By doing so, it is possible to use an optical waveguide having a high relative refractive index difference (Δ), which has a disadvantage that the bending radius is small but the diffraction loss is large. A small waveguide type matrix optical switch can be realized.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 FIG. 1A shows Embodiment 1 of the present invention.
FIG. 1B is an enlarged schematic plan view for explaining the configuration of the waveguide type optical switch shown in FIG. 1A.
FIG. 1C shows the line segments AA ′, BB ′, C shown in FIG. 1B.
It is an expanded sectional schematic diagram in C ', DD'.

In FIG. 1A, FIG. 1B and FIG.
a, 1b, 1c, 1d are input optical waveguides, 2a, 2b, 2
Reference numerals c and 2d denote output optical waveguides, 3 denotes a silicon substrate, 4a denotes an input optical waveguide bundle, 4b denotes an output optical waveguide bundle, 5 denotes a lower cladding layer, 6 denotes an optical waveguide located below the laminated structure, and 7 denotes an intermediate waveguide. A cladding layer, 8 an optical waveguide located above the laminated structure, 9 an upper cladding layer, 10a and 10b laminated multilayer directional couplers for performing optical coupling in the vertical direction, 11 a thin film heater as an optical phase shifter, 12 Is a space intersection having a laminated structure. 1A and 1B, the optical waveguide 6 located on the lower side of the laminated structure is indicated by a dotted line, and the optical waveguide 8 located on the upper side is indicated by a solid line.

In the stacked directional couplers 10a and 10b,
The centers of the optical waveguides are arranged on a vertical line, and the gap between the optical waveguides and the length of the coupling portion are set so that the coupling ratio is 50%. The effective optical path length of the laminated lower optical waveguide 6 and the laminated upper optical waveguide 8 between the two laminated directional couplers 10a and 10b is smaller than that of the optical waveguide 8 in signal light.相当 of the wavelength (1.3 μm in the first embodiment), that is, 0.65 μm
The thin film heater 11 as an optical phase shifter is provided above the upper cladding layer 9 corresponding to the optical waveguide 8. Optical waveguides 6 and 8
Intersect spatially without intersecting at the spatial intersection 12.

The area between the stacked directional couplers 10a and 10b constitutes an asymmetric Mach-Zehnder optical interferometer circuit having a half-wavelength difference in optical path length. The signal light input from the input end of the waveguide 6 is output from the output end of the optical waveguide 6 as it is after passing through the laminated directional couplers 10a and 10b, and similarly the signal light input from the input end of the optical waveguide 8 Is the optical waveguide 8
Is output from the output end of After passing through the Mach-Zehnder optical interferometer circuit, the left and right positional relationship with respect to the traveling direction of the light in the optical waveguides 6 and 8 changes at the space intersection 12, so that the optical switch element as a whole is A route can be realized.

In the on state where the light passes through the thin film heater 11, the signal light input from the optical waveguide 6 is transmitted to the optical waveguide 8 by canceling out the optical path length difference of １ ／ wavelength.
Can be switched to the optical waveguide 6 and a through path can be realized.

Further, in the configuration of the optical switch element according to the first embodiment, even if the coupling ratio of the laminated directional couplers 10a and 10b deviates from 50%, as long as the coupling ratios are equal, as described above, There is no light crosstalk to the cross path in the state.

In the spatial intersection portion 12, since the optical waveguides intersect spatially without actually intersecting with each other, no diffraction loss occurs.

The multilayer matrix optical switch having such a structure is manufactured through the manufacturing process of the quartz-based waveguide circuit shown in FIG.

That is, for example, a diameter of 4 inches and a thickness of 1
First, by FHD deposition on a silicon substrate 3
The composition of the first lower cladding film 5 is SiO ₂ —P ₂ O ₅ —
A quartz glass film of B ₂ O ₃ is deposited to a thickness of 20 μm. The glass was made transparent in a mixed atmosphere of He and O _{2 at} a temperature of 1400 ° C. Next, as a core film of the first optical waveguide 6, a quartz glass having a composition of SiO ₂ —GeO ₂ was deposited by using the ECR-CVD deposition method.

In the first embodiment, ECR-CVD deposition is used. However, a core film can be formed by using CVD deposition, sputter deposition, or FHD deposition. After that, the first optical waveguide 6 is formed by reactive ion etching.

Next, the composition of the intermediate cladding layer 7 is Si
O ₂ quartz glass is deposited to a thickness of 1 μm by ECR-CVD deposition. At that time, the waveguide clad film flattening technology of Japanese Patent Application No. 1-43781, that is, while depositing by the ECR method, R
The intermediate cladding layer 7 having a flat surface was formed by using a flattening technique in which reverse bias was applied to the substrate by applying an F bias.

In the first embodiment, the flat intermediate cladding layer is formed by using the ECR-CVD deposition method. However, the CVD intermediate layer is also deposited by the sputter deposition method and the FHD deposition method.
A similar method can also be used to make the surface flat by polishing or the like.

Next, the second optical waveguide 6 is formed in the same manner as the first optical waveguide 6.
Was formed. Finally, a quartz glass film having a composition of SiO ₂ —P ₂ O ₅ —B ₂ O _{3 having} a composition of 20 μm is deposited as the upper cladding layer 9 for embedding the second optical waveguide 8 by using the FHD deposition method. Transparency of glass is 1200 ℃
In a mixed atmosphere of He and O ₂ .

Further, a thin-film heater 11 as an optical phase shifter is provided at a predetermined portion of each optical switch element on the optical waveguide produced in the above-described process.

The fabricated optical waveguides 6 and 8 had a core size of 4.5 × 4.5 μm ² and a relative refractive index difference Δ of 1.5%. The optical switch element was basically composed of a straight optical waveguide and a bent optical waveguide having a radius of 2 mm, which is an allowable bending radius.
In the conventional configuration method, the relative refractive index difference Δ of the optical waveguide cannot be increased to 0.75% or more due to the diffraction loss at the intersection, and the radius of the bent optical waveguide cannot be reduced to 4 mm or less. In this embodiment, the overall size of the matrix optical switch can be reduced by setting the radius of the bent optical waveguide to 2 mm.

The intersection angle θ of the space intersection 12 is set to 30 degrees or more so that optical coupling does not occur between the optical waveguides. The effective optical path length difference between the two stacked directional couplers 10a and 10b was accurately set to 0.65 μm, which is half the signal light wavelength of 1.3 μm, by a photolithography process. Considering that the refractive index of the optical waveguide core is about 1.47,
The actual optical waveguide length difference on the mask is 0.65 / 1.47 =
It was set to 0.44 μm. The thin film heater 11 has a thickness of 0.3 μm by a vacuum evaporation method using metal chromium as an evaporation source.
A chromium thin film having a width of 50 μm and a length of 4 mm was formed on each optical switch element by vapor deposition.

In the manufactured matrix optical switch, 4 ×
The switching operation of No. 4 was confirmed. The switch operating power is about 0.5 W, and a maximum of four thin film heaters 11 are provided.
The total power consumption in the state of operating was about 2 W. The extinction ratio of the entire matrix optical switch is
The coupling ratio of the laminated directional couplers 10a and 10b is 40 to 60
%, 20 dB or more could be secured. Further, the loss of the optical waveguide was comparable to that of a conventional matrix optical switch using a symmetric Mach-Zehnder optical interferometer circuit, and no excess loss due to the spatial intersection 12 was observed.

Embodiment 2 FIG. 3A shows Embodiment 2 of the present invention.
3B is an enlarged schematic plan view for explaining the configuration of the waveguide type optical switch shown in FIG. 3B.
It is an expanded sectional schematic diagram in CC 'and DD'. 4x4
FIG. 1A is a schematic diagram of the entire flat arrangement of the matrix optical switch.
Is the same as

3A and 3B, reference numeral 3 denotes a silicon substrate, 5 denotes a lower cladding layer, 6 denotes an optical waveguide located below the laminated structure, 7 denotes an intermediate cladding layer, and 8 denotes an upper side of the laminated structure. An optical waveguide, 9 is an upper cladding layer, 10a and 10b are stacked directional couplers for performing optical coupling in a vertical direction,
11 is a thin film heater as an optical phase shifter, and 12 is a space intersection.

In the second embodiment, the space intersection 12 is disposed between the two stacked directional couplers 10a and 10b. In the stacked directional couplers 10a and 10b, the centers of the respective optical waveguides are arranged on a vertical line, and the gap between the optical waveguides and the length of the coupling portion are such that the coupling ratio is 50%.
% Is set.

Two stacked directional couplers 10a and 10b
The effective optical path length of the laminated lower optical waveguide 6 and the laminated upper optical waveguide 8 between the optical waveguides 6 is smaller than that of the optical waveguide 8.
Is set to be equal to half of the wavelength of the signal light (1.3 μm in the second embodiment), that is, about 0.65 μm longer than that of the signal light, and is provided above the upper cladding layer 9 corresponding to the optical waveguide 8. Is provided with a thin-film heater 11 as an optical phase shifter.

The optical waveguides 6 and 8 intersect spatially without intersecting at the spatial intersection 12. The switching operation principle of the optical switch element of the second embodiment is the same as that of the first embodiment.

In the optical switch element of the second embodiment, since the space intersection 12 is located between the laminated directional couplers 10a and 10b, one place where the distance between the two optical waveguides is largely apart is one place. Therefore, there is an advantage that the optical switch element length can be slightly shorter than that of the first embodiment.

Embodiment 3 FIG. 4A shows Embodiment 3 of the present invention.
FIG. 4B is an enlarged schematic plan view for explaining the configuration of the waveguide type optical switch of FIG.
It is an expanded sectional schematic diagram in C ', DD'. FIG. 1A is a schematic plan view of the entire 4 × 4 matrix optical switch.
Is the same as

4A and 4B, reference numeral 3 denotes a silicon substrate, 5 denotes a lower cladding layer, 6 denotes an optical waveguide located below the laminated structure, 7 denotes an intermediate cladding layer, and 8 denotes an upper side of the laminated structure. An optical waveguide, 9 is an upper clad layer, 10a is a laminated directional coupler for performing optical coupling in the vertical direction, 13 is a laminated directional coupler also serving as a spatial intersection, and 11 is a thin film heater as an optical phase shifter. is there.

In the third embodiment, the space intersection part is configured to also serve as the stacked directional coupler 13. In the laminated directional couplers 10a and 13, the centers of the optical waveguides are arranged on a vertical line, and the gap between the optical waveguides and the length of the coupling portion are set such that the coupling ratio is 50%. Is set. The effective optical path lengths of the lower laminated optical waveguide 6 and the upper laminated optical waveguide 8 between the two laminated directional couplers 10a and 10 are such that the optical waveguide 6 has a smaller optical signal length than the optical waveguide 8. 1 / of the wavelength (1.3 μm in the embodiment)
The thin-film heater 11 as an optical phase shifter is provided above the upper cladding layer 9 corresponding to the optical waveguides 6 and 8. Usually, only the thin film heater 11 provided in the optical waveguide 8 having a short optical path length causes no problem. However, if the pair of thin film heaters 11 is provided, even if the optical path length difference is shifted due to a manufacturing accident. There is an advantage that the deviation of the optical path length can be compensated for by slightly applying a current to one of the thin film heaters 11.

The switching operation principle of the optical switch element of the third embodiment is the same as that of the first embodiment.

Since the optical switch element of the third embodiment has a configuration in which the spatial intersection part also serves as the laminated directional coupler 13, the optical switch element length uses a symmetric Mach-Zehnder optical interferometer circuit. It is almost the same as the conventional one that was
It is the smallest of the embodiments of the present invention.

[Embodiment 4] FIG. 5 is a schematic plan view showing the overall arrangement of a 4 × 4 matrix optical switch according to Embodiment 4 of the present invention. The arrangement of the optical switch elements in the fourth embodiment is basically the same as in the first, second, and third embodiments. However, dummy switch elements SD1 and SD2 are arranged in addition to the optical switch elements S in the optical switch group. They are different. SD1 is arranged on the upper plane of the laminated structure, and SD2 is arranged on the lower plane. Dummy optical switch element S
D1 and SD2 have the same configuration as the conventional symmetric Mach-Zehnder optical interferometer circuit-type optical switch element of FIG. 9B except that the thin film heater is omitted, and the two directional couplers have the same coupling ratio. ing. Since the optical switch intersection is not provided in the dummy switch, the signal light only passes through the dummy switch through the through path.

In the arrangement of the optical switch elements shown in FIG. 1A, the number of times that the signal light passes through the optical switch elements is from 1 to 7 due to the combination of the matrix optical switches, and the cumulative number of passage losses of the optical switch elements. Are different,
There is a possibility that a large variation occurs in the loss of the output light. However, when the dummy optical switch elements SD1 and SD2 are added as in the fourth embodiment, the signal light passes through the optical switch elements the same number of times regardless of the combination of the matrix optical switches. Variation in light loss is reduced.

Instead of the dummy switch used here,
It is needless to say that there is a mechanism that gives a loss equivalent to the passing loss of the switch element. For example, it is needless to say that a bent optical waveguide that generates a loss equivalent to the passing loss of the switch element can be used instead.

[Embodiment 5] FIG. 6 is a schematic plan view of a 4 × 4 matrix optical switch formed in a serpentine shape according to Embodiment 5 of the present invention.
a and 4b are optical waveguide bundles composed of eight stacked optical waveguides, 4a is an input-side optical waveguide bundle, and 4b is an output-side optical waveguide bundle. On the way of the optical waveguide bundles 4a and 4b, seven optical switch groups (# 1 to # 7) are arranged, and the optical switch elements in the switch groups are those shown in FIGS. 1A and 5. Is the same as

A feature of the fifth embodiment is that each optical switch element is compactly arranged on the silicon substrate 3 in a bent shape by bending an optical waveguide. In the configuration of the fifth embodiment, the radius of curvature of the bent optical waveguide determines the dimensions of the matrix optical switch. By using an optical waveguide having a high relative refractive index difference Δ, the size and the size of the matrix optical switch can be reduced. Scale can be realized.

[Embodiment 6] FIG. 7 is a schematic diagram for explaining the configuration of a laminated directional coupler having an offset structure according to Embodiment 6 of the present invention. In the first to fifth embodiments,
All the optical waveguides were connected smoothly, but in consideration of the intrinsic electric field distribution of the optical waveguide, when the radius of curvature between the linear optical waveguide and the curved optical waveguide is different, or when the radius of curvature between the curved optical waveguides is different, at the connection point. The shape and center position of the electric field distribution are also different. Therefore, when optical waveguides having different shapes are connected with the optical waveguide centers aligned, there is a problem that radiation loss occurs due to a mismatch in the intrinsic electric field distribution of each optical waveguide, and that a meandering phenomenon of propagated light occurs. Therefore, by appropriately setting the axis shift of the optical waveguide, called an offset, at the optical waveguide connection point, it is possible to make the intrinsic electric field distribution of each optical waveguide match as much as possible. In the sixth embodiment shown in FIG. 7, the offset is set at the connection points 14a to 14d and 15a to 15d between the linear optical waveguide and the curved optical waveguide of the laminated directional coupler and the inflection points 16a, 16b, 17a and 17b of the curved optical waveguide. Applied. The offset amount varies depending on the parameters of the optical waveguide, the radius of curvature, the signal wavelength, and the like, but is generally about 0.1 to 0.5 μm.

In the first to sixth embodiments, the optical phase shifter (thin film heater) is provided in the optical waveguide having the shorter optical path length,
Perform phase control so as to cancel out the half-wavelength optical path length difference,
The optical switch element was switched on.

Conversely, it is also possible to provide an optical phase shifter (thin film heater) in the optical waveguide having the longer optical path length, increase the optical path length difference by one wavelength, and switch the optical switch element to the ON state. It is. However, in this case, there is a disadvantage that the wavelength dependence in the ON state becomes strong, that is, the wavelength band in which a high extinction ratio can be obtained becomes narrow.

As described above, the present invention has been specifically described based on the embodiments. However, it is needless to say that the present invention is not limited to the above embodiments, and various changes can be made without departing from the gist of the present invention. .

[0075]

As described above, according to the present invention, an asymmetric Mach-Zehnder optical interferometer circuit is constituted by a laminated directional coupler using an optical waveguide having a laminated structure.
By forming the optical waveguide intersection with a spatial intersection that does not cause diffraction loss, it is possible to use an optical waveguide having a high relative refractive index difference Δ, which has a disadvantage that the bending radius is small but the diffraction loss is large. It is possible to realize a waveguide type matrix optical switch having an excellent ratio, a small size, and a small excess loss.

[Brief description of the drawings]

FIG. 1A is an overall schematic plan view illustrating a configuration of a 4 × 4 matrix optical switch according to a first embodiment of the present invention;

FIG. 1B is an enlarged schematic plan view illustrating the configuration of the waveguide optical switch shown in FIG. 1;

FIG. 1C shows line segments AA ′, BB ′, and C shown in FIG. 1B.
Schematic enlarged cross-sectional view at C ′, DD ′,

FIG. 2 is a schematic cross-sectional view in each manufacturing process for explaining a manufacturing process of the waveguide optical switch shown in FIG.

FIG. 3A is an enlarged schematic plan view of an optical switch element for explaining a configuration of a waveguide type optical switch according to a second embodiment of the present invention;

FIG. 3B is a diagram showing line segments AA ′, BB ′, and C shown in FIG. 3A.
Schematic enlarged cross-sectional view at C ′, DD ′,

FIG. 4A is an enlarged schematic plan view illustrating a configuration of a waveguide optical switch according to a third embodiment of the present invention;

FIG. 4B is a diagram showing line segments AA ′, BB ′, and C shown in FIG. 4A.
Schematic enlarged cross-sectional view at C ′, DD ′,

FIG. 5 is an overall schematic plan view illustrating the configuration of a 4 × 4 matrix optical switch according to a fourth embodiment of the present invention;

FIG. 6 is an overall plan view for explaining a configuration of a 4 × 4 matrix optical switch configured in a serpentine shape according to a fifth embodiment of the present invention;

FIG. 7 is a schematic diagram for explaining a configuration of a laminated directional coupler having an offset structure according to a sixth embodiment of the present invention;

FIG. 8 is a conceptual diagram showing a configuration example of a matrix optical switch according to the related art;

FIG. 9A is an overall schematic plan view showing a configuration example of a 4 × 4 matrix optical switch according to the related art;

FIG. 9B is an enlarged schematic plan view illustrating the configuration of the optical switch in FIG. 9A;

9C is an enlarged schematic cross-sectional view taken along line segments AA ′ and BB ′ shown in FIG. 9B.

FIG. 10A is an enlarged schematic plan view illustrating the configuration of a first conventional improved optical switch;

FIG. 10B is an enlarged schematic plan view illustrating the configuration of a second conventional improved optical switch.

[Explanation of symbols]

1a to 1d: input optical waveguide, 2a to 2d: output optical waveguide, 3: silicon substrate, 4a: input side optical waveguide bundle, 4b
... output side optical waveguide bundle, 5 ... lower clad layer, 6 ... laminated structure lower optical waveguide, 7 ... intermediate clad layer, 8 ... laminated structure upper optical waveguide, 9 ... upper clad layer, 10a, 10b ... laminated type direction Directional coupler, 11: thin film heater, 12: spatial intersection, 13: stacked directional coupler also serving as spatial intersection,
4a to 14d: Connection with offset between the laminated structure upper linear optical waveguide and the curved optical waveguide; 15a to 15d: Connection with offset between the laminated structure lower linear optical waveguide and the curved optical waveguide;
16a, 16b: inflection point with offset between laminated structure upper curved optical waveguides, 17a, 17b: inflection point with offset between laminated structure lower curved optical waveguides, 18, 19: conventional optical waveguide, 20a, 20b ... Conventional directional coupler,
21 ... conventional thermo-optic phase shifter (thin film heater), 22
a, 23a ... conventional optical waveguide input terminals, 22b, 23b ...
Conventional optical waveguide output end, 24... Plane optical waveguide intersection.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-B-63-22562 (JP, B2) Patent 2625312 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/313 JICST file (JOIS) WPI (DIALOG)

Claims (14)

(57) [Claims] 1. A waveguide type optical switch for switching an optical path of an input signal light, comprising: first and second optical waveguides provided on a substrate and on different planes perpendicular to the substrate. The first and second optical waveguides are arranged close to each other, and have two coupling directional couplers having the same coupling ratio; and between the two laminated directional couplers. An optical path length switching unit provided on at least one of the first optical waveguide and the second optical waveguide; and an intersection part that spatially intersects the first optical waveguide and the second optical waveguide, said first and second optical waveguide constituting each multilayer directional coupler, the optical axes are parallel, and the center of the first and second optical waveguides are the same perpendicular to the substrate
Are aligned so that to position on a line, wherein the first optical waveguide and said second optical waveguide, effective optical path length of a half wavelength of the input signal light between the two multilayer directional coupler Wherein the optical path length switching means has a difference between the effective optical path length between the first optical waveguide and the second optical waveguide between the two stacked directional couplers, and A waveguide type optical switch characterized in that the wavelength is switched to an integral multiple of the wavelength. 2. The waveguide type optical switch according to claim 1, wherein said optical path length difference switching means is an optical phase shifter. 3. The waveguide type optical switch according to claim 2, wherein said optical phase shifter is a thermo-optic effect phase shifter comprising a thin film heater. 4. The optical phase shifter according to claim 1, wherein the optical phase shifter is provided on each of the first optical waveguide and the second optical waveguide between the two stacked directional couplers. 3. The waveguide type optical switch according to item 2. 5. The waveguide according to claim 2, wherein the optical phase shifter is provided in an optical waveguide having a shorter effective optical path length, and makes the effective optical path length difference zero in a driving state. Type optical switch. 6. The optical phase shifter according to claim 1, wherein the optical phase shifter is provided in the optical waveguide having a longer effective optical path length, and in a driving state, sets the effective optical path difference to one wavelength of the signal light. 3. The waveguide type optical switch according to item 2. 7. One of the optical phase shifters, wherein the effective optical path length difference is shifted from a half wavelength of the signal light,
5. The waveguide type optical switch according to claim 4, wherein the deviation is compensated. Wherein said spatial intersections, waveguide-type optical switch according to claim 1, characterized in that provided between the two laminated type directional coupler. 9. The waveguide type optical switch according to claim 1, wherein the spatial intersection part is also used as one of the two stacked directional couplers. And a plurality of input terminals and a plurality of output terminals.
A waveguide-type matrix optical switch that switches and outputs an input signal light, a plurality of input optical waveguides connected respectively to said input terminal, respectively connected to the output terminal, perpendicular to the substrate
In such a direction different from the plane position of the input optical waveguide
A plurality of output optical waveguides provided on a flat surface, and a plurality of optical switch elements arranged at respective spatial intersections of the input optical waveguide and the output optical waveguide, wherein each of the optical switch elements is the same as described in the claim. 10. A waveguide-type matrix optical switch, which is the waveguide-type optical switch according to any one of items 1 to 9. 11. The waveguide-type matrix optical switch according to claim 10, wherein said optical switch elements are connected by an optical waveguide bundle bent in a zigzag manner. 12. A dummy switch is provided at a position corresponding to the optical switch element on an optical waveguide connecting the optical switch element.
0. The waveguide-type matrix optical switch according to 0. 13. Before SL dummy switches, two and two directional couplers equal binding rate is close to the optical waveguides are disposed on the same plane, the between the two directional couplers 2. The structure according to claim 1, wherein the two optical waveguides have an effective optical path length difference of a half wavelength of the signal light.
3. The waveguide type matrix optical switch according to item 2. 14. The optical waveguide according to claim 11, wherein the optical waveguides are connected by offsetting the center of the optical waveguide at a portion where the line transitions from a straight line to a curve and at a portion where the radius of curvature of the curved portion changes. Waveguide type matrix optical switch.