WO2024157322A1

WO2024157322A1 - Phase shifter and optical switch

Info

Publication number: WO2024157322A1
Application number: PCT/JP2023/001914
Authority: WO
Inventors: 慶太山口; 祥江森本; 賢哉鈴木
Original assignee: 日本電信電話株式会社
Priority date: 2023-01-23
Filing date: 2023-01-23
Publication date: 2024-08-02

Abstract

The present invention provides a phase shifter and an optical switch including the phase shifter, which are capable of maintaining a modulation state while achieving reduction in power consumption compared to the prior art. A phase shifter (200) according to the present disclosure is a waveguide phase shifter (200) comprising a core (201), a clad (202) covering the core (201), an electrode (203) extending in parallel to the optical axis direction of the core (201) and disposed in proximity to one side surface of the core (201), and electrical wirings (204a, 204b) disposed on respective side surfaces of the core (201) and the electrode (203) substantially in perpendicular to the optical axis direction of the core (201). Furthermore, the optical switch (100) according to the present disclosure includes the phase shifter (200) in at least one of an upper arm (104) and a lower arm (105).

Description

Phase shifter and optical switch

This disclosure relates to a phase shifter and an optical switch.

Waveguide-type optical switches are key devices in optical communication systems, and are widely used within optical communication networks due to their ability to realize flexible optical communication networks. A typical configuration of a waveguide-type optical switch is one that combines a Mach-Zehnder interferometer (hereinafter referred to as MZI) with a phase shifter, and waveguide-type optical switches with this configuration are being put to practical use in optical communication networks.

1 is a top view conceptually showing the structure of a waveguide-type optical switch 100 that combines an MZI and a phase shifter according to the prior art. As shown in Fig. 1, the waveguide-type optical switch 100 includes input waveguides 101a, b, output waveguides 102a, b, a coupler 103a connected to the input waveguides 101a, b, a coupler 103b connected to the output waveguides 102a, b, an upper arm 104 and a lower arm 105 connected to the couplers 103a, b, and a phase shifter 106 connected to the lower arm 105 and modulating the phase of the propagating optical signal. Although not shown here, the waveguide-type optical switch 100 also includes a substrate and a cladding formed on the substrate, and the core region through which the optical signal propagates (input side waveguides 101a, b, output side waveguides 102a, b, upper arm 104, and lower arm 105) has a structure embedded in the cladding.

The waveguide-type optical switch 100 having such a configuration can switch the output waveguide by controlling the phase difference of the optical signals passing through the upper arm 104 and the lower arm 105, which determines the interference condition in the MZI, with the phase shifter 106 (see, for example, Non-Patent Document 1). For example, when the optical path lengths of the upper arm 104 and the lower arm 105 are the same and the phase modulation amount in the phase shifter 106 is 0, the optical signal input from the input side waveguide 101a is output from the output side waveguide 102b (cross state). On the other hand, when the phase of the optical signal changes by π in the phase shifter 106, the interference state changes and the optical signal input from the input side waveguide 101a is output from the output side waveguide 102a (through state).

In general, materials used for optical waveguides can be silicon oxide (SiOx) or silicon (Si). When SiOx is used for both the core and cladding, a dopant is usually added to the SiOx used for the core to increase the refractive index of the core, thereby confining the optical signal to the core. On the other hand, when Si is used for the core, SiOx, which has a lower refractive index than Si, is generally used for the cladding.

Thermo-optic phase shifters are widely used as phase shifters for optical waveguides using SiOx or Si. Thermo-optic phase shifters use a heating mechanism such as a heater to locally heat part of the core, changing the refractive index of the heated area to change the optical path length and thus the phase of the optical signal propagating through the core. This phenomenon in which the refractive index of a material changes depending on the temperature is generally called the thermo-optic effect (in other words, a thermo-optic phase shifter is an element that uses the thermo-optic effect to change the phase of an optical signal).

As mentioned above, thermo-optic phase shifters use the change in refractive index caused by temperature, so in order to maintain the modulation state of the phase shifter, it is necessary to keep the area to be heated at a specified temperature by controlling a heater or other device. This means that the heater or other device needs to be constantly powered, which poses the problem of increased power consumption.

JP 2017-9803 A JP 2018-6915 A JP 2018-10064 A International Publication No. 2022/044101

The present disclosure has been made in consideration of the above-mentioned problems, and its purpose is to provide a phase shifter and an optical switch including the phase shifter that can maintain the modulation state while achieving reduced power consumption compared to conventional techniques.

In response to the above-mentioned problems, the present disclosure provides a phase shifter that is a waveguide type phase shifter including a core, a cladding that covers the core, an electrode that extends parallel to the optical axis direction of the core and is arranged near one side of the core, and electrical wiring that is approximately perpendicular to the optical axis direction of the core and is arranged on each of the side of the core and the side of the electrode, and an optical switch that includes the phase shifter in at least one of the upper arm and the lower arm.

FIG. 1 is a top view conceptually showing the structure of a waveguide-type optical switch 100 in which an MZI and a phase shifter are combined according to a conventional technique. 2A and 2B are diagrams conceptually illustrating a structure of a phase shifter 200 according to a first embodiment of the present disclosure, in which FIG. 2A is a top view and FIG. 2B is a cross-sectional view taken along line IIb-IIb. 2 is a diagram conceptually illustrating how a core 201 and an electrode 203 function as a parallel plate capacitor in the phase shifter 200 according to the first embodiment of the present disclosure. FIG. 4A and 4B are diagrams conceptually illustrating a structure of another form of the phase shifter 200 according to the first embodiment of the present disclosure, in which (a) is a top view and (b) is a cross-sectional view taken along the line IVb-IVb. FIG. 2 is a top view conceptually illustrating a structure of an optical switch 500 using the phase shifter 200 according to the first embodiment of the present disclosure. FIG. 13 is a diagram showing an etching region required when disposing a phase shifter 200 on the optical switch 500 according to the first embodiment of the present disclosure. 7A and 7B are diagrams conceptually illustrating a structure of a phase shifter 700 according to a second embodiment of the present disclosure, in which (a) is a top view and (b) is a cross-sectional view taken along the line VIIb-VIIb. 8A and 8B are diagrams conceptually illustrating the structure of an optical switch 800 according to a second embodiment of the present disclosure, in which (a) is a top view showing the overall structure, (b) is an enlarged view of the connection between an SSC structure 701 of a phase shifter 700 and a lower arm 105, and (c) is a cross-sectional view along the VIIIc-VIIIc cross-sectional line. 9A and 9B are conceptual diagrams showing another structure of the optical switch 800 according to the second embodiment of the present disclosure, in which (a) shows an enlarged view of the connection between the SSC structure 701 of the phase shifter 700 and the lower arm 105, and (b) shows a cross-sectional view along the IXb-IXb cross-sectional line. 10A and 10B are diagrams conceptually illustrating the structure of the connection portion between the phase shifter 700 and the lower arm 105 in another form of the optical switch 800 according to the second embodiment of the present disclosure, where (a) is a top view and (b) is a cross-sectional view along the Xb-Xb cross-sectional line. 10A and 10B are diagrams conceptually illustrating the structure of the connection portion between the phase shifter 700 and the lower arm 105 in another form of the optical switch 800 according to the second embodiment of the present disclosure, where (a) is a top view and (b) is a cross-sectional view along the XIb-XIb cross-sectional line. 10A and 10B are diagrams conceptually illustrating the structure of the connection portion between the phase shifter 700 and the lower arm 105 in another form of the optical switch 800 according to the second embodiment of the present disclosure, where (a) is a top view and (b) is a cross-sectional view along the XIIb-XIIb cross-sectional line. FIG. 13 is a top view conceptually illustrating a structure of a phase shifter 1300 according to a third embodiment of the present disclosure. FIG. 14 is a top view conceptually illustrating a structure of a phase shifter device 1400 according to a third embodiment of the present disclosure.

Various embodiments of the present disclosure will be described in detail below with reference to the drawings. The same or similar reference symbols indicate the same or similar elements, and duplicate descriptions may be omitted. Materials and numerical values are for illustrative purposes and are not intended to limit the technical scope of the present disclosure. The following description is an example, and some configurations may be omitted or modified, or additional configurations may be added, as long as they do not deviate from the gist of an embodiment of the present disclosure.

The phase shifter according to the present disclosure is a waveguide-type phase shifter having a core and a cladding, and includes an electrode extending parallel to the optical axis direction of the core and disposed near one side of the core, and electrical wiring disposed approximately perpendicular to the optical axis direction of the core and near the other side of the core and near the side of the electrode not adjacent to the core.

In the phase shifter according to the present disclosure configured in this manner, when a potential difference is generated between the core and the electrode via electrical wiring, the core and the electrode function as parallel plate capacitors, and charge is injected and accumulated in each. This injection of charge causes a plasma carrier effect, which changes the refractive index of the core. By utilizing this phenomenon, the phase shifter according to the present disclosure is able to control the phase of an optical signal.

(First embodiment)
Hereinafter, a first embodiment of the present disclosure will be described in detail with reference to the drawings. A phase shifter in this embodiment is a phase shifter disposed in a waveguide-type optical switch, and a semiconductor such as Si is used for a core other than the phase shifter of the optical switch.

(Configuration of Phase Shifter)
2 is a diagram conceptually illustrating the structure of a phase shifter 200 according to the first embodiment of the present disclosure, in which (a) is a top view and (b) is a cross-sectional view taken along the line IIb-IIb. As shown in FIG. 2, the phase shifter 200 includes a core 201, a cladding 202 surrounding the core 201, an electrode 203 extending parallel to the optical axis direction of the core 201 and disposed near one side of the core 201, and electrical wiring 204a, b disposed approximately perpendicular to the optical axis direction of the core 201 and on the side of the core 201 and the side of the electrode 203. The electrical wiring 204a, b is connected to an external power source and configured to be able to apply a voltage. Also, the cladding 202 is configured to be included between the core 201 and the electrode 203.

In the phase shifter 200 according to the present embodiment configured as described above, when a potential difference is generated between the core 201 and the electrode 203 via the electric wiring 204a, b, the core 201 and the electrode 203 function as parallel plate capacitors, and thus, as shown in FIG. 3, electric charges are injected and accumulated in each of them (in FIG. 3, "e ^- " represents electrons). On the other hand, in the phase shifter 200, if the electric field applied between the core 201 and the electrode 203 is set to 0 (constant potential), the electric charges accumulated in the core 201 return to their original state. In this way, the carrier plasma effect occurs due to the change in electron density, and the refractive index of the core 201 changes. Then, the optical path length of the optical signal propagating through the core 201 changes accordingly, and as a result, the phase shifter functions as a phase shifter that changes the phase of the optical signal. At this time, no current flows in the phase shifter 200 except during the time when the electric charges are moving, so that it is possible to significantly reduce the power required to maintain the phase shift state.

Considering the operating principle of the waveguide, the core 201 needs to have a higher refractive index than the clad 202. In addition, it is desirable that the clad 102 is a material with high insulating properties so that the charge accumulated between the core 201 and the electrode 203 does not pass. Therefore, in the phase shifter 200, for example, if the core 201 is made of Si, the above-mentioned configuration can be realized by using a material (e.g., SiOx) that has a lower refractive index than Si and has high insulating properties for the clad 202. In addition, when a semiconductor such as Si is used for the core 201, the same material as the core 201 can be applied to the electrode 203 and the electrical wiring 204a, b. In such a configuration in which the same material is used for the electrode 203, the electrical wiring 204a, b, and the core 201, it is possible to omit processes such as film formation of different materials during manufacturing. For example, by using Si for the core 201, and Si for the electrode 203 and the electrical wiring 204a, b, it is possible to simultaneously form the core 201, the electrode 203, and the electrical wiring 204a, b during manufacturing. In addition, as mentioned above, it is desirable for the electrical wiring 204a, b to have high conductivity from the viewpoint of charge injection, so the conductivity of the Si used for the electrical wiring 204a, b may be further improved by doping it with boron (B) or phosphorus (P).

In addition, by increasing the capacitance of the capacitor, it is possible to generate large variations in charge density even with a small potential difference. For this reason, the cladding 202 may be made of a material with a high dielectric constant (e.g., silicon nitride (SiN)).

2, the electrode 203 is depicted as being adjacent to the core 201 in a direction parallel to the main surface of the wafer and embedded in the clad 202, but as shown in FIG. 4, it may be adjacent to the main surface of the wafer in a direction perpendicular to the main surface of the wafer and disposed on the surface of the clad 202. The electrode 203 and the electrical wiring 204a, b may be made of a metal with low electrical resistance, etc., because of problems such as increased power consumption during charge transfer with high resistance. However, when the electrical wiring 204a, b is embedded in the clad 202 as in the core 201, it is necessary to form the clad 202 after forming the pattern of the electrical wiring 204a, b. When the phase shifter 200 is manufactured in this manner, the metal of the electrical wiring 204a, b may diffuse into the clad 202 or the core 201, which may cause loss of optical signals. In the configuration shown in FIG. 4, the electrode 203 and the electrical wiring 204a, b connected to the electrode 203 can be formed after the cladding 202 is formed, which has the effect of suppressing the loss of optical signals due to such metal diffusion.

(Configuration of optical switch)
Fig. 5 is a top view conceptually illustrating a structure of an optical switch 500 using the phase shifter 200 according to the first embodiment of the present disclosure. As shown in Fig. 5, the optical switch 500 has a configuration in which the phase shifter of the waveguide-type optical switch 100 according to the conventional technology shown in Fig. 1 is the above-mentioned phase shifter 200. Here, the

couplers

103a and 103b can be, for example, directional couplers (DC).

In the optical switch 500 having such a configuration, an optical signal input from either one of the input waveguides 101a, b is distributed by the coupler 103a to both the upper arm 104 and the lower arm 105 and propagates through each. The optical signal is then rejoined by the coupler 103b and output from the two output waveguides 102a, b. If there is a difference in the optical path length of each of the upper arm 104 and the lower arm 105, the interference state when the signals are joined at the coupler 103b changes, and the intensity ratio of the output light changes.

In the optical switch 500 according to this embodiment, the above-mentioned phase shifter 200 is disposed in at least one of the upper arm 104 or the lower arm 105. This phase shifter 200 performs phase modulation of the optical signal using the carrier plasma effect, making it possible to control the output intensity and output ratio of the optical signal output from the output side waveguides 102a, b. For example, when the optical path lengths of the upper arm 104 and the lower arm 105 are the same, if the phase modulation amount in the phase shifter 200 is 0, it becomes a cross state, and if the phase modulation amount in the phase shifter 200 is π, it changes to a through state. In other cases, it takes an intermediate state between the through state and the cross state according to the phase modulation amount in the phase shifter 200, and is distributed and output from both the output side waveguides 102a, b at a ratio corresponding to the phase modulation amount. In other words, the optical switch 500 can also function as a coupler/splitter that changes the branching ratio of the output optical signal and a variable optical attenuator (VOA) that controls the output intensity.

In FIG. 5, the phase shifter 200 is depicted as being disposed in the lower arm 105, but this is for illustrative purposes only, and the phase shifter 200 may be disposed in the upper arm 104, or in both the upper arm 104 and the lower arm 105. From the viewpoint of controlling the interference state of the optical signal, it is sufficient to dispose the phase shifter 200 in either the upper arm 104 or the lower arm 105, or to control only one of the phase shifters 200 installed in both the upper arm 104 and the lower arm 105. On the other hand, in order to achieve an effect such as suppressing the polarization characteristics so that each path has different characteristics, it is necessary to control both the upper arm 104 and the lower arm 105.

(Phase shifter arrangement method)
When forming the optical switch 500 so as to embed the optical waveguide in a dielectric film formed on a wafer, it is necessary to form a pattern in a multi-layer structure in order to make an electrical connection (connection between the electrical wiring 204a, b and an external power source outside the wafer) in a direction perpendicular to the wafer surface. However, when forming a pattern in a multi-layer structure, processing becomes difficult and the number of steps may increase, such as the need to form a pattern by etching or the like, form a film on the pattern, and further flatten the pattern. Such an increase in the number of steps leads to an increase in manufacturing costs and a longer manufacturing lead time, so it is desirable to form the electrical connection on the same plane parallel to the wafer surface.

On the other hand, since the electrical wiring 204a, b also has resistance, a voltage drop occurs when a current flows. From this perspective, in order to improve the efficiency of the above-mentioned tunnel effect, it is desirable to electrically connect the external power source and the electrical wiring 204a, b as close to the phase shifter 200 as possible. From this perspective, the arrangement of the phase shifter 200 with respect to the optical switch 500 according to this embodiment includes exposing the electrical wiring 204a, b in the same plane as the core by etching the regions 601a, b where the electrical wiring 204a, b exists and where the core (e.g., the upper arm 104 and the lower arm 105, etc.) does not exist, as shown in FIG. 6. By using such an arrangement method, it is possible to manufacture an optical switch 500 that can inject and remove charges with high efficiency while suppressing increases in manufacturing costs and prolonged manufacturing LT.

For example, as shown in FIG. 6(a), an example of a region near the phase shifter 200 and without a core is region 601a located at the center of the upper arm 104 and the lower arm 105. By forming electrical wiring 204a up to this region 601a and etching region 601a, it is possible to expose electrical wiring 204a. If region 601a is then filled with, for example, a metal, it becomes possible to electrically connect to an external power source.

Depending on the design, the area corresponding to region 601a may be narrow and etching may not be possible. In such a case, as shown in FIG. 6(b), the electrical wiring 204a may be formed across the side where the phase shifter 200 is not arranged (the upper arm 104 side in FIG. 6(b)), and the etching area may be made in region 601b located outside the upper arm 104, with the same effect being obtained. In such a case, it is desirable to minimize the effect that the electrical wiring 204a has on the optical signal propagating through the upper arm 104.

Furthermore, if the phase shifter 200 is configured as shown in FIG. 4, the electrical connection of the electrode 203 can be made on the clad 202.

Second Embodiment
Hereinafter, a first embodiment of the present disclosure will be described in detail with reference to the drawings. A phase shifter in this embodiment is a phase shifter disposed in a waveguide-type optical switch, and SiOx is used for a core other than the phase shifter of the optical switch.

(Phase shifter configuration)
In general, an optical waveguide using SiOx as a core has a characteristic that the loss in propagation and the connection loss with an optical fiber are small. However, SiOx has a high band gap energy, and in a waveguide using SiOx as a core, SiOx is often used for the cladding as well. For this reason, when SiOx is used for the core of the above-mentioned phase shifter 200, it is difficult to keep electrons in the core 201 and confine the charge. Therefore, in the optical switch 500 according to the present disclosure, even if SiOx is used for the core other than the phase shifter 200 of the optical switch 500 (for example, the upper arm 104 and the lower arm 105, etc.), it is desirable to use a material with a low band gap energy such as Si or SiN for the core 201 in the phase shifter 200.

However, in optical waveguide circuits, when the refractive index of the core is partially changed, loss due to mode coupling occurs at the boundary (transition region) where the refractive index changes. Therefore, when a different material is used only for the core 201 of the phase shifter 200 described above, the boundary between the core 201 and the core in which SiOx is used becomes a transition region accompanied by a change in refractive index. Therefore, it is desirable to configure the transition region so that the mode changes adiabatically. From this perspective, in addition to the configuration of the phase shifter 200, the phase shifter according to this embodiment further includes a spot-size converter structure (hereinafter referred to as SSC) in the part where the core 201 becomes the transition region.

FIG. 7 is a conceptual diagram showing the structure of a phase shifter 700 according to a second embodiment of the present disclosure, where (a) shows a top view and (b) shows a cross-sectional view along the VIIb-VIIb cross-sectional line. As described above and as shown in FIG. 7, in the phase shifter 700, the tip of the core 201 in the configuration of the phase shifter 200 further includes an SSC structure 701. The region in which this SSC structure 701 is formed corresponds to the transition region described above.

In general, when optical elements are connected to each other, it is important to match the mode fields of the light propagating in the optical elements in order to reduce loss at the connection point. When two optical elements are butt-connected, the coupling efficiency of the propagating optical signal is determined by the overlap integral of the mode fields of both. When the core is Si, the mode field diameter (Mode Field Diameter: hereinafter referred to as MFD) is about 300 nm, while in the case of SiOx, it is several μm, so that a large coupling loss occurs due to the mismatch of this MFD. However, in the phase shifter 700 according to this embodiment, the SSC structure 701 having a tapered structure is formed, so that the mode changes adiabatically. More specifically, it is configured so that the confinement efficiency changes with the change in diameter, and the MFD changes accordingly. Therefore, the mismatch of MFD at the connection point with the core using SiOx is eliminated, making it possible to suppress loss due to mode coupling.

In addition, in FIG. 7, the SSC structure 701 is depicted as a tapered structure in which the diameter of the core 201 changes continuously, but this is for illustrative purposes only, and the structure of the SSC structure 701 may be of any shape as long as it is a structure that changes the mode adiabatically.

(Configuration of optical switch)
8 is a diagram conceptually illustrating the structure of an optical switch 800 according to a second embodiment of the present disclosure, in which (a) is a top view showing the entire structure, (b) is an enlarged view of a connection between an SSC structure 701 of a phase shifter 700 and a lower arm 105, and (c) is a cross-sectional view taken along the line VIIIc-VIIIc. As shown in Fig. 8, the optical switch 800 has a configuration in which the phase shifter of the conventional waveguide-type optical switch 100 shown in Fig. 1 is the above-mentioned phase shifter 700. Here, for example, Si can be applied to the core 201 of the phase shifter 700, and SiOx can be applied to the lower arm 105.

In FIG. 8, the SSC structure 701 has a tapered structure in which the tip of the core 201 is tapered, and the SSC structure 701 and the tip of the lower arm 105 made of SiOx are depicted as being arranged to butt against each other. The core 201 and the lower arm 105 are covered with an undercladding layer 801 and an overcladding layer 802, and the relative refractive index difference between the lower arm 105 and each cladding layer is set to be smaller than the relative refractive index difference between the core 201 and the SSC structure 701 of the phase shifter 700 and each cladding layer. In this embodiment, the lower arm 105 is configured so that the core 201 has a larger core cross-sectional area and MFD than Si. In such a case, the optical signal propagating through the core 201 is weakly confined as it approaches the tip in the SSC structure 701, and therefore the MFD becomes larger. This eliminates the mismatch in MFD with the lower arm 105, and reduces the coupling loss.

In addition, in FIG. 8, the tips of the SSC structure 701 and the lower arm 105 are depicted as being butted together, but as shown in FIG. 9, the SSC 701 structure may be covered by the lower arm 105. In such a structure, the optical signal that is no longer able to be contained as it approaches the tip of the SSC structure 701 leaks out to the surrounding lower arm 105. The leaked optical signal adiabatically transitions to the lower arm 105, making this optical transition process adiabatic and making it possible to more efficiently suppress the loss of optical energy.

Furthermore, in the examples shown in Figures 8 and 9, the thickness of the core 201 and the thickness of the lower arm 105 are depicted as being different, and therefore the respective height centers are depicted as not coinciding. However, as shown in Figure 10, by aligning these height centers, it is possible to further suppress the coupling loss at the connection between the two.

10 is a conceptual diagram showing the structure of the connection between the phase shifter 700 and the lower arm 105 in another form of the optical switch 800 according to the second embodiment of the present disclosure, where (a) shows a top view and (b) shows a cross-sectional view along the Xb-Xb cross-sectional line. In the example shown in FIG. 10, the core 201 of the phase shifter 700 is configured to be covered with an undercladding layer 1001 and an overcladding layer 1002. Here, the same material as that of the lower arm 105 is applied to each of the undercladding layer 1001 and the overcladding layer. The core 201 and the lower arm 105 are butted together with their height centers aligned, and further, the undercladding layer 1001, the overcladding layer 1002, and the lower arm 105 are configured to be covered with the undercladding layer 801 and the overcladding layer 802. Thus, in the example shown in FIG. 10, the phase shifter 700 and the lower arm 105 have a configuration in which the waveguides having a "dual structure" are butt-connected.

In FIG. 10, the overcladding layer 1002 is depicted as covering parts of the core 201 other than the SSC structure 701, but as shown in FIG. 11, the overcladding layer 1002 may cover only the area corresponding to the SSC structure 701. In the example shown in FIG. 11, the process of forming or patterning a SiOx layer on the SSC structure 701 during manufacturing is not required, which has the advantage of reducing factors that deteriorate the circuit on the phase shifter 700 side.

Also, as shown in FIG. 12, not only the overcladding layer 1002 but also the overcladding layer 802 may be formed only in the region corresponding to the SSC structure 701. In the example shown in FIG. 12, in the portion of the core 201 that is not covered by the overcladding layer 1002 and the overcladding layer 802, air plays the role of a cladding, so that the optical signal is confined within the core 201.

The thickness of the undercladding layer 801 and the overcladding layer 802 need only be such that the mode field of the optical signal is sufficiently contained therein. For example, when the undercladding layer 801 and the overcladding layer 802 are made of SiOx, the thickness of each layer may be approximately several tens of μm.

In the phase shifter and optical switch disclosed herein, there is no upper limit to the cross-sectional size of each core, and it is also possible to make it a multi-mode optical waveguide that propagates multiple modes of light for the wavelength of the optical signal used. Also, by reducing the cross-sectional size of the core, it is possible to make it a single-mode optical waveguide that propagates only the lowest mode. Note that when the optical signal is single-mode, there are generally two methods for connecting cores together: adiabatic coupling and butt coupling. In the above explanation, the connection between the phase shifter and the optical switch has been described as being in the form of butt coupling, but this is not limited to this, and it may be adiabatic coupling or a combination of both.

Furthermore, the phase shifter and optical switch according to the present disclosure can be manufactured by techniques used in existing optical circuit manufacturing methods. For example, a deposition method such as the flame volume deposition method can be used to form the SiOx layer, and a deposition method such as the sputtering method can be used to form the Si layer.

Integration methods for optical circuits combining elements with different MFDs generally include hybrid integration, which combines separate substrates, and monolithic integration, which uses a single common substrate. In the case of hybrid integration, a process for accurately aligning the SSC structure 701 and the lower arm 105 (also called an alignment process) is required, which can increase manufacturing costs. In particular, when Si is used for the core 201, as described above, the core is very thin, measuring several hundred nm, so there is a high requirement for alignment accuracy, and there is a problem that a high-precision alignment process requires very high costs. On the other hand, monolithic integration is a manufacturing method in which different materials are integrated on the same substrate, and therefore the problems caused by such alignment processes are eliminated. From this perspective, it is desirable that the optical switch 800 according to this embodiment is formed by monolithic integration.

Third Embodiment
A third embodiment of the present disclosure will be described in detail below with reference to the drawings. An optical switch according to this embodiment has a configuration in which a phase shifter is controlled by optical power supply.

In the above examples, the

phase shifters

200, 700 according to the present disclosure are described as being configured to control the injection and removal of charge into the core 201 by an external power source, but the

phase shifters

200, 700 may also be controlled by optical power supply.

FIG. 13 is a top view conceptually illustrating the structure of a phase shifter 1300 according to a third embodiment of the present disclosure. As shown in FIG. 13, the phase shifter 1300 in this embodiment further includes an optical power supply device 1301 connected to electrical wiring 204a, b in addition to the configuration of the

phase shifters

200, 700 described above (FIG. 13 illustrates the configuration of the phase shifter 200 as an example).

The optical power supply device 1301 includes a photodiode 1302 that receives a control signal light and converts it into an electrical signal, a boost circuit 1303 that boosts the electrical signal converted by the photodiode 1302, and a capacitor 1304 connected between the anode and cathode of the photodiode 1302, and the phase shifter 1300 is configured such that the electrical wiring 204a, b of the phase shifter 200 is connected between the boost circuit 1303 and the ground line GND.

In the phase shifter 1300 according to this embodiment configured in this manner, the voltage Vc generated by storing charge in the capacitor 1304 is transmitted to the boost circuit 1003 as an electrical signal converted by the photodiode 1302. The connection point between the anode of the photodiode 1302 and the capacitor 1304 is grounded. A voltage (charging voltage) is generated by storing charge in the core 201 and electrode 203 of the phase shifter 200. The phase shifter 1300 that operates on this principle can set and maintain the phase setting in the core 201 of the phase shifter 200 using only optical power supply, eliminating the need for an external power supply.

Optical waveguides have excellent integration properties, making it possible to integrate multiple phase shifters on a single chip. When integrating multiple phase shifters 1300 according to this embodiment on a single chip, a wavelength demultiplexer 1401 can be further disposed, as in the phase shifter device 1400 shown in FIG. 14, and the control signal light can be configured to be first input to the wavelength demultiplexer. The phase shifter device 1400 having such a configuration can demultiplex multiple control signal lights having different wavelengths using the wavelength demultiplexer 1401, and input each of the demultiplexed control signal lights to a photodiode 1302 determined for each wavelength. This makes it possible to select a phase shifter according to the wavelength of the control signal light.

Note that while FIG. 14 illustrates a case where the phase shifter and the control signal light each have two wavelengths, this is not limited thereto, and three or more sets of phase shifters and control signal light wavelengths can be controlled in the same way. Also, by connecting multiple phase shifters in parallel, it is possible to control multiple phase shifters with one control signal light wavelength. In addition, it is also possible to assign multiple wavelengths of control signal light to one phase shifter by designing a wavelength demultiplexer, etc.

Furthermore, by applying an AWG (Arrayed Waveguide Grating) or the like, the wavelength demultiplexer 1401 can also be formed using a waveguide. As an integrated form, it is also possible to eliminate manufacturing costs and electrical or optical connections between devices by forming part or all of the area surrounded by the dashed line in FIG. 14 on a single chip.

As described above, the phase shifter and optical switch disclosed herein are characterized by using the carrier plasma effect to control the refractive index by injecting and removing electric charges. Phase shifters and optical switches with such characteristics do not require constant power supply, unlike conventional techniques for controlling the refractive index using heaters or the like. Therefore, they are expected to be applied to optical communication systems as phase shifters and optical switches that can reduce power consumption compared to conventional techniques.

Claims

A waveguide type phase shifter,
A core,
A cladding covering the core;
an electrode extending in a direction parallel to the optical axis direction of the core and disposed near one side surface of the core;
Electric wiring arranged substantially perpendicular to the optical axis direction of the core and on each of a side surface of the core and a side surface of the electrode;
A phase shifter comprising:
The phase shifter of claim 1, wherein the core further comprises a spot size conversion structure at its tip.
The phase shifter of claim 1, wherein the core and the electrical wiring are semiconductors and made of the same material.
Further comprising an optical power supply device connected to the electrical wiring,
The optical power supply device includes:
a photodiode that receives the control signal light and converts it into an electrical signal;
a boosting circuit that boosts the electrical signal converted by the photodiode;
a capacitor connected between the anode and cathode of the photodiode;
The phase shifter of claim 1 , comprising:
A phase shifter device comprising a plurality of phase shifters according to claim 4 arranged on a chip,
the control signal light has a plurality of wavelengths,
The phase shifter device further includes a wavelength demultiplexer that demultiplexes the control signal light having the plurality of wavelengths according to wavelength, and transmits the demultiplexed control signal light to the photodiode corresponding to each wavelength.
A Mach-Zehnder interference type optical switch, comprising a phase shifter according to claims 1 to 5 on at least one of an upper arm and a lower arm.