Phase shifter and wavelength selector

Abstract

To provide a phase shifter capable of stabilizing the amount of phase shift associated with a variation in the value of resistance of a heat generating element, and to provide a wavelength selector.SOLUTION: A phase shifter according to an embodiment comprises a substrate, an optical waveguide provided vertically with respect to the substrate, first and second temperature measurement elements provided horizontally with respect to the optical waveguide to sandwich the optical waveguide between the first and second temperature measurement elements, and a heat generating element provided vertically with respect to the optical waveguide and first and second temperature measurement elements.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to phase shifters and wavelength selectors. [Background technology]

[0002] Patent Document 1 describes a wavelength selector. The wavelength selector includes a ring resonator, a temperature sensor, and a heater. The temperature sensor is disposed inside a semiconductor substrate, which is a silicon substrate. The ring resonator and heater are disposed inside an insulating layer made of silicon dioxide. The heater, ring resonator, and temperature sensor are aligned in the vertical direction. The ring resonator is disposed between the heater and the temperature sensor in the vertical direction. In a plan view of the wavelength selector, the heater, ring resonator, and temperature sensor have an annular shape. The temperature sensor is formed by a PN junction. The wavelength selector has a groove located inside the heater in a plan view of the wavelength selector.

[0003] Patent Document 2 describes a thermo-optic phase shifter. The thermo-optic phase shifter includes a Si substrate, a sacrificial layer, a lower cladding layer, an upper cladding layer, and a heater. An optical waveguide core layer is provided in the upper cladding. In a plan view of the thermo-optic phase shifter, the heater and the upper cladding layer are arc-shaped. The thermo-optic phase shifter has a groove on the outer side of the heater in a plan view. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 1,155,6020 [Patent Document 2] International Publication No. 2008 / 111407 Summary of the Invention [Problem to be solved by the invention]

[0005] In optical integrated circuits using silicon photonics technology, a heater or other heat-generating element can heat an optical waveguide, thereby shifting the phase of an optical signal propagating through the waveguide. This optical circuit, which shifts the phase of an optical signal, is called a phase shifter. In a phase shifter, the amount of phase shift (amount of phase change) is changed by adjusting the power supplied to the heat-generating element. For example, when controlling the wavelength of an optical signal, it may be necessary to continuously supply a relatively large amount of power to the heat-generating element for a long period of time. However, the resistance of the heat-generating element may change over time, for example. If the resistance of the heat-generating element changes, the amount of phase shift relative to the supplied power may deviate from the desired value. Therefore, it is necessary to stabilize the amount of phase shift relative to changes in the resistance of the heat-generating element.

[0006] An object of the present disclosure is to provide a phase shifter and a wavelength selector that can stabilize the amount of phase shift in response to changes in the resistance value of a heating element. [Means for solving the problem]

[0007] The phase shifter according to the present disclosure comprises a substrate, an optical waveguide arranged perpendicular to the substrate, a first temperature measuring element and a second temperature measuring element arranged horizontally to the optical waveguide and sandwiching the optical waveguide therebetween, and a heat generating element arranged perpendicular to the optical waveguide, the first temperature measuring element, and the second temperature measuring element. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to stabilize the amount of phase shift relative to changes in the resistance value of the heating element. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view showing a phase shifter according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line BB in FIG. [Figure 4] FIG. 4 is a cross-sectional view showing a phase shifter according to a first modification. [Figure 5] FIG. 5 is a plan view showing a phase shifter according to a second modification. [Figure 6] FIG. 6 is a cross-sectional view taken along line CC in FIG. [Figure 7] FIG. 7 is a plan view showing a wavelength selector according to an embodiment. [Figure 8] FIG. 8 is a cross-sectional view taken along line DD in FIG. [Figure 9] FIG. 9 is a cross-sectional view showing a phase shifter according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Description of the embodiment of the present invention] First, the contents of the embodiments of the present disclosure will be listed and described. (1) A phase shifter according to one embodiment includes a substrate, an optical waveguide arranged perpendicular to the substrate, a first temperature measuring element and a second temperature measuring element arranged horizontally to the optical waveguide so as to sandwich the optical waveguide therebetween, and a heat generating element arranged perpendicular to the optical waveguide, the first temperature measuring element, and the second temperature measuring element.

[0011] In this phase shifter, an optical waveguide is disposed perpendicular to the substrate. The phase shifter includes an optical waveguide and first and second temperature measuring elements disposed on either side of the optical waveguide. The heating element is disposed perpendicular to the optical waveguide, the first and second temperature measuring elements. The heating element is disposed perpendicular to the optical waveguide, the first and second temperature measuring elements, and the optical waveguide is disposed between the first and second temperature measuring elements. The first and second temperature measuring elements, located on both horizontal sides of the optical waveguide, monitor the temperature of the optical waveguide. By controlling the power to the heating element so that the monitored temperature reaches a predetermined value, the temperature of the optical waveguide can be stabilized at the predetermined value. Therefore, even if the resistance value of the heating element changes due to aging or other reasons, the power to the heating element can be controlled according to the monitored temperature, thereby suppressing deviations in the amount of phase shift and stabilizing the amount of phase shift.

[0012] (2) In (1) above, in a plan view along the vertical direction, the heating element may have a portion overlapping the optical waveguide and a portion overlapping with at least one of the first temperature measuring element and the second temperature measuring element. In this case, by having the heating element have a portion overlapping with the optical waveguide and a portion overlapping with at least one of the first temperature measuring element and the second temperature measuring element, the temperature of the optical waveguide and the temperature of at least one of the first temperature measuring element and the second temperature measuring element can be made closer to uniform. Therefore, the temperature of the optical waveguide can be monitored with higher accuracy by at least one of the first temperature measuring element and the second temperature measuring element, and the amount of phase shift can be made more stable.

[0013] (3) In the above (1) or (2), the optical waveguide may be made of silicon, and the first and second temperature measuring elements may be made of salicide. The temperature coefficient of resistance of salicide is about five times that of titanium nitride (TiN). Therefore, when the first and second temperature measuring elements are made of salicide, the sensitivity of the first and second temperature measuring elements to temperature changes can be increased. As a result, the temperature of the optical waveguide can be monitored with higher accuracy, thereby further stabilizing the amount of phase shift.

[0014] (4) In any of (1) to (3) above, one end of the first temperature measuring element may be connected to one end of the second temperature measuring element. In this case, the first temperature measuring element is connected in series to the second temperature measuring element. By connecting the first temperature measuring element in series to the second temperature measuring element, the resistance values of the first temperature measuring element and the second temperature measuring element can be increased. Therefore, the accuracy of temperature detection by the first temperature measuring element and the second temperature measuring element can be further improved.

[0015] (5) A wavelength selector according to one embodiment includes any one of the phase shifters described above in (1) to (4). Therefore, in this wavelength selector, like the phase shifters described above, the power to the heating element can be controlled according to the monitored temperature, thereby stabilizing the amount of phase shift.

[0016] [Details of the embodiments of the present disclosure] Specific examples of phase shifters and wavelength selectors according to embodiments of the present disclosure will be described with reference to the drawings. The present invention is not limited to the following examples, but is set forth in the claims and includes all modifications within the scope of equivalents to the claims. In the description of the drawings, identical or corresponding elements are denoted by the same reference numerals, and redundant description will be omitted as appropriate. For ease of understanding, some parts of the drawings may be simplified or exaggerated, and dimensional ratios and the like are not limited to those shown in the drawings.

[0017] FIG. 1 is a plan view showing a phase shifter 1 according to a first embodiment. FIG. 2 is a cross-sectional view showing the phase shifter 1 taken along line AA. The phase shifter 1 is used, for example, in a Mach-Zehnder interferometer or a ring resonator to control the wavelength characteristics of an optical signal. As shown in FIGS. 1 and 2, the phase shifter 1 includes a substrate 2, a silicon dioxide (SiO2) layer 3 laminated on the substrate 2, and an optical waveguide 4 formed within the SiO2 layer 3. For ease of illustration, each component is indicated by a solid line in FIG. 1. An optical signal propagates through the optical waveguide 4. The phase shifter 1 includes a heating element 5 disposed in a direction D1 perpendicular to the optical waveguide 4. The optical waveguide 4 is disposed between the substrate 2 and the heating element 5 in the vertical direction D1. The optical waveguide 4 has a width in a horizontal direction D2 intersecting (e.g., perpendicular to) the vertical direction D1 and extends along an extension direction D3 intersecting both the vertical direction D1 and the horizontal direction D2.

[0018] In this embodiment, the "vertical direction" refers to the direction in which the optical waveguide 4 is located when viewed from the substrate 2. In the following description, the vertical direction may be referred to as "upper," "upper side," or "upper," and the direction opposite to the vertical direction may be referred to as "lower," "lower side," or "lower." In this embodiment, the "horizontal direction" refers to the width direction of the optical waveguide 4, and the "extension direction" refers to the direction in which the optical waveguide 4 extends. However, these directions are used for convenience of description and do not limit the placement position or direction of components, etc.

[0019] The substrate 2 is made of silicon (Si). The substrate 2 has a rectangular parallelepiped shape. For example, the length of the substrate 2 in the vertical direction D1 is shorter than the length of the substrate 2 in the horizontal direction D2. The length of the substrate 2 in the horizontal direction D2 is shorter than the length of the substrate 2 in the extending direction D3. The length of the substrate 2 in the horizontal direction D2 corresponds to the width of the substrate 2, and the length of the substrate 2 in the vertical direction D1 corresponds to the thickness of the substrate 2. The substrate 2 has a first side surface 2b extending along both the vertical direction D1 and the extending direction D3, an upper surface 2c and a lower surface 2d extending along both the horizontal direction D2 and the extending direction D3, and a second side surface 2f extending along both the vertical direction D1 and the horizontal direction D2. The substrate 2 has a pair of first side surfaces 2b aligned along the horizontal direction D2; for example, the pair of first side surfaces 2b extend parallel to each other. The upper surface 2c is in contact with the SiO2 layer 3. For example, the upper surface 2c and the lower surface 2d extend parallel to each other. The substrate 2 has a pair of second side surfaces 2f aligned along the extension direction D3, and for example, the pair of second side surfaces 2f extend parallel to each other.

[0020] The SiO2 layer 3 has a rectangular parallelepiped shape. The length of the SiO2 layer 3 in the vertical direction D1 is shorter than the length of the SiO2 layer 3 in the horizontal direction D2. The length of the SiO2 layer 3 in the horizontal direction D2 is shorter than the length of the SiO2 layer 3 in the extending direction D3. The length of the SiO2 layer 3 in the horizontal direction D2 corresponds to the width of the SiO2 layer 3, and the length of the SiO2 layer 3 in the vertical direction D1 corresponds to the thickness of the SiO2 layer 3. The SiO2 layer 3 has a first side surface 3b extending along both the vertical direction D1 and the extending direction D3, an upper surface 3c and a lower surface 3d extending along both the horizontal direction D2 and the extending direction D3, and a second side surface 3f extending along both the vertical direction D1 and the horizontal direction D2.

[0021] The SiO2 layer 3 has a pair of first side surfaces 3b aligned along the horizontal direction D2, for example, the pair of first side surfaces 3b extending parallel to each other. The bottom surface 3d is in contact with the top surface 2c of the substrate 2. For example, the top surface 3c and the bottom surface 3d extend parallel to each other. The SiO2 layer 3 has a pair of second side surfaces 3f aligned along the extension direction D3, for example, the pair of second side surfaces 3f extend parallel to each other.

[0022] The phase shifter 1 may be formed as part of an optical integrated circuit on a silicon chip. In this case, the substrate 2 and the SiO2 layer 3 are continuous with other parts of the optical integrated circuit in the horizontal direction D2 and the extension direction D3, and the first side surfaces 2b, 3b and the second side surfaces 2f, 3f do not exist. Therefore, the first side surfaces 2b, 3b and the second side surfaces 2f, 3f are regarded as conveniently representing the boundary surfaces of the phase shifter 1 with the other parts.

[0023] The optical waveguide 4 is made of, for example, silicon (Si). However, the optical waveguide 4 may also be made of silicon nitride (SiN) or Si. The optical waveguide 4 may also be a Si slot waveguide that confines light between a pair of parallel thin wires. As such, the material and configuration of the optical waveguide 4 are not particularly limited. The optical waveguide 4 is arranged in a direction D1 perpendicular to the substrate 2. The phase shifter 1 has an electrode 6 that supplies power to the heating element 5, a first temperature measuring element 7 and a second temperature measuring element 8 that are arranged in a horizontal direction D2 relative to the optical waveguide 4, and an electrode 10 that is electrically connected to the first temperature measuring element 7 and the second temperature measuring element 8. The optical waveguide 4, the heating element 5, the electrode 6, the first temperature measuring element 7, the second temperature measuring element 8, and the electrode 10 are provided inside the SiO2 layer 3. For example, the distance from the substrate 2 to the first temperature measuring element 7 and the distance from the substrate 2 to the second temperature measuring element 8 are the same as the distance from the substrate 2 to the optical waveguide 4.

[0024] The optical waveguide 4 extends, for example, along the extension direction D3 at the center of the horizontal direction D2 of the phase shifter 1. Ends of the optical waveguide 4 in the extension direction D3 are exposed from each second side surface 3f of the SiO2 layer 3. A cross section of the optical waveguide 4 cut by a plane extending in both the vertical direction D1 and the horizontal direction D2 has a rectangular shape having a first side extending along the vertical direction D1 and a second side extending along the horizontal direction D2. For example, the length of the optical waveguide 4 in the extension direction D3 is 100 μm or more and several mm or less, and the length (width) of the second side of the optical waveguide 4 is 0.2 μm or more and 1 μm or less. The length (thickness) of the first side of the optical waveguide 4 is, for example, 0.4 μm or more and 0.5 μm or less.

[0025] The heating element 5 is located above the optical waveguide 4. The heating element 5 has, for example, a flat plate shape extending in both the horizontal direction D2 and the extension direction D3 and having a thickness in the vertical direction D1. The length of the heating element 5 in the vertical direction D1 is shorter than the length of the heating element 5 in the horizontal direction D2. The length of the heating element 5 in the horizontal direction D2 is shorter than the length of the heating element 5 in the extension direction D3. In a cross section cut along a plane extending in both the vertical direction D1 and the horizontal direction D2, the heating element 5 has a rectangular shape having a first side extending along the vertical direction D1 and a second side extending along the horizontal direction D2. For example, the length of the heating element 5 in the extension direction D3 is 100 μm or more and several mm or less, and the length (width) of the second side of the heating element 5 is several μm or more and several tens of μm or less. The length (thickness) of the first side of the heating element 5 is, for example, 0.1 μm or more and several μm or less.

[0026] The heating element 5 is disposed in the vertical direction D1 relative to the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8. The optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8 are disposed between the substrate 2 and the heating element 5 in the vertical direction D1. In a plan view along the vertical direction D1, the heating element 5 has a portion 5b that overlaps with the optical waveguide 4 and a portion 5c that overlaps with at least one of the first temperature measuring element 7 and the second temperature measuring element 8. In the example of FIG. 2, the heating element 5 has a pair of portions 5c aligned along the horizontal direction D2. In a plan view along the vertical direction D1, the pair of portions 5c are a portion 5c that overlaps with the first temperature measuring element 7 and a portion 5c that overlaps with the second temperature measuring element 8. The heating element 5 extends along the horizontal direction D2 above the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8.

[0027] FIG. 3 is a cross-sectional view taken along line BB in FIG. 1. As shown in FIGS. 1, 2, and 3, the phase shifter 1 has electrodes 6 electrically connected to the ends of the heating element 5 in the extension direction D3. For example, one electrode 6 is disposed on a first end of the heating element 5 in the extension direction D3, and another electrode 6 is disposed on a second end of the heating element 5 in the extension direction D3. The phase shifter 1 further has electrodes 10 electrically connected to the first temperature measuring element 7 and the second temperature measuring element 8. The electrodes 10 include a first electrode 10b located at the ends of the first temperature measuring element 7 and the second temperature measuring element 8 in the extension direction D3, and a second electrode 10c connecting the first temperature measuring element 7 and the second temperature measuring element 8 to each other. The first electrode 10b protrudes upward from each of the first temperature measuring element 7 and the second temperature measuring element 8. The first electrode 10b is disposed at a first end in the extension direction D3 of the first temperature measuring element 7 and at a first end in the extension direction D3 of the second temperature measuring element 8. The second electrode 10c is disposed on a second end in the extension direction D3 of the first temperature measuring element 7 and at a second end in the extension direction D3 of the second temperature measuring element 8.

[0028] In a plan view along the vertical direction D1, the second electrode 10c has a rectangular shape with a first side extending along the horizontal direction D2 and a second side extending along the extension direction D3. The second electrode 10c is disposed above the first temperature measuring element 7 and the second temperature measuring element 8 so as to straddle the optical waveguide 4. The second electrode 10c electrically connects the second end of the first temperature measuring element 7 to the second end of the second temperature measuring element 8. The electrode 6 includes a pair of electrodes 6c arranged along the extension direction D3. In a plan view along the vertical direction D1, the electrode 6c is located more inward (closer to the center) in the extension direction D3 than the first electrode 10b and the second electrode 10c. That is, the electrode 6c is located between the first electrode 10b and the second electrode 10c in the extension direction D3.

[0029] In the phase shifter 1, power is supplied to the heating element 5 via the electrode 6. When power is supplied to the heating element 5, the heating element 5 generates heat, which in turn heats the optical waveguide 4. The heated optical waveguide 4 changes the refractive index due to its thermo-optic effect, thereby changing the phase of the optical signal propagating through the optical waveguide 4. In the phase shifter 1, the temperature of the optical waveguide 4 changes due to the power supplied to the heating element 5, and the temperature change of the optical waveguide 4 adjusts the amount of phase shift (amount of phase change) of the optical signal propagating through the optical waveguide 4. For example, the temperature range ΔT of the optical waveguide 4 used for adjustment is 100°C or less, and the corresponding amount of phase shift is π or more and nπ or less (n is a natural number greater than or equal to 2).

[0030] FIG. 9 is a cross-sectional view of a phase shifter 100 according to a comparative example. The phase shifter 100 includes a substrate 2, a SiO2 layer 3 disposed on the substrate 2, an optical waveguide 4 disposed within the SiO2 layer 3, and a heating element 5 disposed above the optical waveguide 4 within the SiO2 layer 3. The phase shifter 100 does not include a first temperature measuring element 7 or a second temperature measuring element 8. The heating element 5 may operate for a long time while receiving a large amount of power, for example, 50 mW or more and several hundred mW or less. The resistance of the heating element 5 may be, for example, 100 Ω or more and several hundred Ω or less. The resistance of the heating element 5 may change due to aging or other reasons, such as deterioration over time after long-term use. In this case, the amount of heat generated by the heating element 5 relative to the power supplied to the heating element 5 may change. This change in the amount of heat generated by the heating element 5 also changes the temperature of the optical waveguide 4, potentially resulting in a shift in the phase shift of the optical signal propagating through the optical waveguide 4.

[0031] In this embodiment, as shown in FIGS. 1, 2, and 3, the first temperature measuring element 7 and the second temperature measuring element 8 are disposed on either side of the optical waveguide 4 in the horizontal direction D2 below the heating element 5, thereby compensating for the deviation in the amount of phase shift. The first temperature measuring element 7 and the second temperature measuring element 8 are disposed in the horizontal direction D2, sandwiching the optical waveguide 4 therebetween. The first temperature measuring element 7 and the second temperature measuring element 8 are disposed along the optical waveguide 4 and the heating element 5 (for example, along the same direction as the optical waveguide 4 and the heating element 5). The first temperature measuring element 7 and the second temperature measuring element 8 are disposed below the heating element 5, spaced apart from the optical waveguide 4 so as not to be coupled with the optical signal propagating through the optical waveguide 4. For example, in a plan view along the vertical direction D1, the first temperature measuring element 7 and the second temperature measuring element 8 each overlap the end of the heating element 5 in the horizontal direction D2.

[0032] For example, the length of the first temperature measuring element 7 in the extension direction D3 is 100 μm or more and several mm or less, and the length (width) of the first temperature measuring element 7 in the horizontal direction D2 is 0.5 μm or more and several μm or less. The length (thickness) of the first temperature measuring element 7 in the vertical direction D1 is, for example, 0.4 μm or more and 0.5 μm or less. For example, the length of the second temperature measuring element 8 in the extension direction D3, the length of the second temperature measuring element 8 in the horizontal direction D2, and the length of the second temperature measuring element 8 in the vertical direction D1 are the same as above.

[0033] For example, the first temperature measuring element 7 and the second temperature measuring element 8 are made of salicide. That is, the first temperature measuring element 7 and the second temperature measuring element 8 include a salicide layer (salicide resistor). For example, the first temperature measuring element 7 has a silicon layer 7b and a salicide layer 7c located above the silicon layer 7b. Similarly, the second temperature measuring element 8 has a silicon layer 8b and a salicide layer 8c located above the silicon layer 8b.

[0034] The resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 change with temperature. In this embodiment, the first temperature measuring element 7 and the second temperature measuring element 8 are temperature monitors. The temperature of the optical waveguide 4 can be detected based on changes in the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8. The phase shifter 1 monitors the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 that change with temperature, and controls the power supplied to the heating element 5 so that the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 become predetermined values. This allows the heat generation amount of the heating element 5 and the temperature of the optical waveguide 4 to be appropriate even if the resistance value of the heating element 5 changes due to aging or other reasons, thereby preventing deviations in the phase shift amount of the optical signal propagating through the optical waveguide 4.

[0035] When the first temperature measuring element 7 and the second temperature measuring element 8 are made of salicide, the temperature coefficient of resistivity of the first temperature measuring element 7 and the second temperature measuring element 8 is five times or more that of materials (e.g., titanium nitride (TiN)) typically used as heaters. Therefore, because the first temperature measuring element 7 and the second temperature measuring element 8 are made of a material with a higher temperature coefficient than TiN or the like, they can detect temperature changes with higher accuracy and are suitable as temperature monitors.

[0036] For example, in the phase shifter 1, a current is supplied to the first temperature measuring element 7, and the resistance value of the first temperature measuring element 7 is monitored by measuring the potential difference between the first end and the second end of the first temperature measuring element 7 while the current is being supplied. The resistance value of the second temperature measuring element 8 is monitored in the same manner. If the first temperature measuring element 7 and the second temperature measuring element 8 are made of salicide, a small, constant current (for example, a current of 100 μA or less) can be used as the current. In this case, the possibility that the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 will change due to aging or other reasons can be reduced.

[0037] For example, the second end of the first temperature measuring element 7 may be connected to the second end of the second temperature measuring element 8. As an example, the second end of the first temperature measuring element 7 may be electrically connected to the second end of the second temperature measuring element 8 via the second electrode 10c. In this case, the first temperature measuring element 7 and the second temperature measuring element 8 may be used as a single monitor resistor. The series resistance of the first temperature measuring element 7 and the second temperature measuring element 8 may be monitored by measuring the potential difference between the first end of the first temperature measuring element 7 and the first end of the second temperature measuring element 8. Note that instead of the second electrode 10c, the second end of the first temperature measuring element 7 may be electrically connected to one first electrode 10b, and the second end of the second temperature measuring element 8 may be electrically connected to another first electrode 10b, and these two first electrodes 10b may be electrically connected to each other by wiring.

[0038] The first temperature measuring element 7 and the second temperature measuring element 8 are arranged along the heating element 5. That is, the first temperature measuring element 7 and the second temperature measuring element 8 are arranged adjacent to the heating element 5 in the vertical direction D1 so as to extend in the same direction as the heating element 5 (extension direction D3). Therefore, the first temperature measuring element 7 and the second temperature measuring element 8 can monitor the average temperature of the entire heating element 5. The first temperature measuring element 7 and the second temperature measuring element 8 are arranged on either side of the optical waveguide 4 in the horizontal direction D2. Because heat from the heating element 5 is conducted through the SiO2 layer 3 and the substrate 2 and dissipates to the surroundings, by placing the optical waveguide 4 inside the first temperature measuring element 7 and the second temperature measuring element 8, the error between the monitored temperature and the actual temperature of the optical waveguide 4 can be reduced.

[0039] The phase shifter 1 has a groove 9 on each side of the heating element 5 in the horizontal direction D2. The phase shifter 1 has a pair of grooves 9 aligned along the horizontal direction D2. For example, the groove 9 has a rectangular shape. In a plan view along the vertical direction D1, the groove 9 has a rectangular shape with a first side extending along the extension direction D3 and a second side extending along the horizontal direction D2. For example, the length of the second side of the groove 9 is shorter than the length of the groove 9 in the vertical direction D1. For example, the length of the groove 9 in the vertical direction D1 is shorter than the length of the first side of the groove 9.

[0040] The length of the groove 9 in the extension direction D3 is, for example, shorter than the length of the first temperature measuring element 7 in the extension direction D3 and shorter than the length of the second temperature measuring element 8 in the extension direction D3. The length of the optical waveguide 4 in the extension direction D3 is longer than the length of the first temperature measuring element 7 in the extension direction D3 and longer than the length of the second temperature measuring element 8 in the extension direction D3. By forming grooves 9 on both sides of the optical waveguide 4 in the horizontal direction D2, the grooves 9 block the thermal conduction of heat generated by the heating element 5 in the horizontal direction D2. Therefore, the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8 can be heated efficiently with little power.

[0041] Furthermore, by blocking heat conduction in the horizontal direction D2, the temperature distribution in the SiO2 layer 3 sandwiched between the pair of grooves 9 can be made uniform in a plan view along the vertical direction D1, thereby improving the accuracy of temperature monitoring by the first temperature measuring element 7 and the second temperature measuring element 8. As described above, in the case of the phase shifter 1 having the grooves 9, the power consumption required to obtain the same amount of phase shift can be reduced by 35% compared to a phase shifter without grooves 9 due to the effect of increased thermal resistance. Therefore, the power efficiency of the heating element 5 can be improved by approximately 54%.

[0042] Next, the effects obtained from the phase shifter 1 according to this embodiment will be described in more detail. In the phase shifter 1, the optical waveguide 4 is disposed in the vertical direction D1 relative to the substrate 2. The phase shifter 1 includes the optical waveguide 4 and a first temperature measuring element 7 and a second temperature measuring element 8 disposed so as to sandwich the optical waveguide 4 therebetween. The heating element 5 is disposed in the vertical direction D1 relative to the first temperature measuring element 7 and the second temperature measuring element 8. The heating element 5 is disposed in the vertical direction D1 relative to the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8, and the optical waveguide 4 is disposed between the first temperature measuring element 7 and the second temperature measuring element 8. The first temperature measuring element 7 and the second temperature measuring element 8, located on both sides of the optical waveguide 4 in the horizontal direction D2, monitor the temperature of the optical waveguide 4. By controlling the power to the heating element 5 so that the monitored temperature reaches a predetermined value, the temperature of the optical waveguide 4 can be stabilized at the predetermined value. Therefore, even if the resistance value of the heating element 5 changes due to aging or other reasons, the power to the heating element 5 can be controlled according to the monitored temperature, so that the deviation in the amount of phase shift due to the change in resistance value can be compensated for, and the amount of phase shift can be stabilized.

[0043] As described above, in a plan view along the vertical direction D1, the heating element 5 may have a portion 5b overlapping with the optical waveguide 4 and a portion 5c overlapping with at least one of the first temperature measuring element 7 and the second temperature measuring element 8. In this case, by having the heating element 5 have the portion 5b overlapping with the optical waveguide 4 and the portion 5c overlapping with at least one of the first temperature measuring element 7 and the second temperature measuring element 8, at least one of the first temperature measuring element 7 and the second temperature measuring element 8 is heated by the heating element 5 in the same manner as the optical waveguide 4, and the temperature of the optical waveguide 4 and at least one of the first temperature measuring element 7 and the second temperature measuring element 8 can be made closer to uniform. Therefore, the temperature of the optical waveguide 4 can be monitored with higher accuracy by at least one of the first temperature measuring element 7 and the second temperature measuring element 8, and the amount of phase shift can be made more stable.

[0044] As described above, the optical waveguide 4 may be made of silicon, and the first temperature measuring element 7 and the second temperature measuring element 8 may be made of salicide. The temperature coefficient of the resistance of salicide is about five times the temperature coefficient of the resistance of titanium nitride (TiN). Therefore, when the first temperature measuring element 7 and the second temperature measuring element 8 are made of salicide, the sensitivity of the first temperature measuring element 7 and the second temperature measuring element 8 to temperature changes can be increased. As a result, the temperature of the optical waveguide 4 can be monitored with higher accuracy, and the amount of phase shift can be further stabilized.

[0045] As described above, one end of the first temperature measuring element 7 may be connected to one end of the second temperature measuring element 8. In this case, the first temperature measuring element 7 is connected in series to the second temperature measuring element 8. By connecting the first temperature measuring element 7 in series to the second temperature measuring element 8, the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 can be increased. Therefore, the accuracy of temperature detection based on changes in the resistance values of the first temperature measuring element 7 and the second temperature measuring element 8 can be further improved.

[0046] Next, various modified examples of the phase shifter according to the present disclosure will be described. A portion of the configuration of the phase shifter according to each modified example described below is the same as a portion of the configuration of the phase shifter 1 described above. Therefore, in the following description, the description of parts that overlap with the configuration of the phase shifter 1 will be omitted as appropriate by assigning the same reference numerals.

[0047] FIG. 4 is a cross-sectional view showing a phase shifter 11 according to a first modification. The phase shifter 11 has a ridge-type optical waveguide 14, a first temperature measuring element 17, and a second temperature measuring element 18. The phase shifter 11 has a ridge-type optical waveguide 14 instead of the optical waveguide 4 described above. For example, the optical waveguide 14 is located between the first temperature measuring element 17 and the second temperature measuring element 18 in the horizontal direction D2. The optical waveguide 14 has a silicon layer 14b that constitutes the optical waveguide 14. The first temperature measuring element 17 has a silicon layer 14b and a salicide layer 7c located above the silicon layer 14b. The second temperature measuring element 18 has a silicon layer 14b and a salicide layer 8c located above the silicon layer 14b.

[0048] That is, the silicon layer 14b extends along the horizontal direction D2 from the first temperature measuring element 17 to the second temperature measuring element 18, and the first temperature measuring element 17 and the second temperature measuring element 18 are formed on the silicon layer 14b. As described above, in the phase shifter 11, the optical waveguide 14, the first temperature measuring element 17, and the second temperature measuring element 18 are connected to one another by the common silicon layer 14b. Connecting the first temperature measuring element 17 and the second temperature measuring element 18 to the optical waveguide 14 by the silicon layer 14b reduces the difference in temperature between the first temperature measuring element 17 and the second temperature measuring element 18 and the temperature of the optical waveguide 14. This provides the effect of further reducing temperature measurement errors. Note that the portion (connection portion) of the silicon layer 14b connecting the first temperature measuring element 17 and the second temperature measuring element 18 to the optical waveguide 14 has a length (thickness) that is smaller than the length (thickness) of the silicon layer 14b of the optical waveguide 14 in the vertical direction D1. This reduces the influence of the connection portion on the propagation of the optical signal through the optical waveguide 14.

[0049] FIG. 5 is a plan view showing a phase shifter 21 according to a second modified example. FIG. 6 is a cross-sectional view taken along line CC in FIG. 5. As shown in FIGS. 5 and 6, the phase shifter 21 has a space 29 below the SiO2 layer 3 (the optical waveguide 4, the heating element 5, the first temperature measuring element 7, and the second temperature measuring element 8). The space 29 is a hollow portion surrounded by the substrate 2 and the SiO2 layer 3 in the vertical direction D1 and the extension direction D3. For example, the space 29 has a rectangular parallelepiped shape. The phase shifter 21 has a plurality of spaces 29, which are arranged along the extension direction D3.

[0050] The phase shifter 21 has, for example, a substrate 22 having a shape different from that of the substrate 2 described above. The substrate 22 has a first upper surface 22b in contact with the lower surface 3d of the SiO2 layer 3 and a second upper surface 22c spaced downward from the lower surface 3d of the SiO2 layer 3. A space 29 is formed between the lower surface 3d of the SiO2 layer 3 and the second upper surface 22c. The space 29 is formed in the substrate 22 by, for example, etching.

[0051] The phase shifter 21 has a support portion 28 that supports the SiO2 layer 3. The support portion 28 is disposed between two spaces 29 aligned along the extension direction D3. The support portion 28 is a portion where the first upper surface 22b of the substrate 22 contacts the lower surface 3d of the SiO2 layer 3. FIG. 5 shows an example in which three spaces 29 aligned along the extension direction D3 and two support portions 28 aligned along the extension direction D3 are formed. However, the number and arrangement of the spaces 29 and the support portions 28 are not particularly limited.

[0052] As described above, in the phase shifter 21, a space 29 is formed between the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8 and the substrate 22. The space 29 reduces the thermal conduction of heat generated by the heating element 5 to the substrate 2, thereby improving the thermal insulation of the optical waveguide 4, the first temperature measuring element 7, and the second temperature measuring element 8. This improves the accuracy of temperature measurement by the first temperature measuring element 7 and the second temperature measuring element 8, and also improves the power efficiency of temperature control of the optical waveguide 4 by the heating element 5.

[0053] Next, a wavelength selector 31 according to a second embodiment will be described with reference to FIGS. 7 and 8. FIG. 7 is a plan view showing the wavelength selector 31 as viewed along the vertical direction D1. FIG. 8 is a cross-sectional view taken along line DD in FIG. 7. In FIG. 7, each component is indicated by a solid line for ease of understanding. As shown in FIGS. 7 and 8, the wavelength selector 31 is a ring resonator. The wavelength selector 31 includes a phase shifter 41. A portion of the configuration and function of the phase shifter 41 is the same as the configuration and function of the phase shifter 1 described above. Therefore, a description of the configuration and function of the phase shifter 41 that is the same as the configuration and function of the phase shifter 1 described above will be omitted.

[0054] In a plan view along the vertical direction D1, the wavelength selector 31 has a pair of first sides 31b extending along a first direction A1 perpendicular to the vertical direction D1 and a pair of second sides 31c extending along a second direction A2 perpendicular to both the vertical direction D1 and the first direction A1. The pair of first sides 31b are aligned along the second direction A2, and the pair of second sides 31c are aligned along the first direction A1.

[0055] Incidentally, the wavelength selector 31 can be formed as part of an optical integrated circuit on a silicon chip, similar to the aforementioned phase shifter 21. In this case, the substrate 42 and the SiO2 layer 43 are continuous with other parts of the optical integrated circuit in the first direction A1 and the second direction A2, and the first side 31b and the second side 31c do not exist. Therefore, for the sake of convenience, the first side 31b and the second side 31c are regarded as representing the boundaries of the wavelength selector 31 with the other parts.

[0056] The phase shifter 41 includes a substrate 42, a SiO2 layer 43, an optical waveguide 44, a heating element 45, an electrode 46, a first temperature measuring element 47, a second temperature measuring element 48, and a groove 49. The optical waveguide 44 includes a pair of first optical waveguides 44b extending along a first direction A1 and a second optical waveguide 44c having a circular shape centered at a fixed point O between the pair of first optical waveguides 44b. The fixed point O is located between the pair of first optical waveguides 44b along the second direction A2. The optical waveguide 44 forms a ring resonator. In a plan view along the vertical direction D1, the second optical waveguide 44c and the heating element 45 have a circular shape centered at the fixed point O.

[0057] The heating element 45 is located above the second optical waveguide 44c, the first temperature measuring element 47, and the second temperature measuring element 48. In a plan view along the vertical direction D1, the heating element 45 has an arc shape of a circle centered at the fixed point O. The heating element 45 is formed so that a current flows in the circumferential direction of the arc, and electrodes 46a are disposed on both ends. The electrodes 46a are electrically connected to the heating element 45. When a current flows from the first electrode 46a to the second electrode 46a, the heating element 45 generates Joule heat. In a plan view along the vertical direction D1, the first temperature measuring element 47 has an arc shape of a circle centered at the fixed point O. The phase shifter 41 has a pair of second temperature measuring elements 48 aligned along the first direction A1. The second temperature measuring elements 48 have an arc shape of a circle centered at the fixed point O. In a plan view along the vertical direction D1, the second temperature measuring element 48 is provided outside the first temperature measuring element 47 with respect to the fixed point O. In other words, the distance from the fixed point O of the second temperature measuring element 48 is greater than the distance from the fixed point O of the first temperature measuring element 47. An electrode 46b is provided at each end of the first temperature measuring element 47, and an electrode 46c is provided at each end of the second temperature measuring element 48. Wiring (not shown) is connected to the electrodes 46b and 46c. For example, the first temperature measuring element 47 and the second temperature measuring element 48 may be connected in series with each other.

[0058] The phase shifter 41 has multiple grooves 49. The multiple grooves 49 include first grooves 49b located inside the heating element 45 in a plan view along the vertical direction D1 and second grooves 49c located outside the heating element 45 in a plan view along the vertical direction D1. For example, the distance from the fixed point O of the first groove 49b is shorter than the distance from the fixed point O of the second groove 49c. The phase shifter 41 has a pair of first grooves 49b aligned along the first direction A1. The pair of first grooves 49b are positioned to sandwich the electrode 46 in the first direction A1. The phase shifter 41 has multiple second grooves 49c. The multiple second grooves 49c are aligned along both the first direction A1 and the second direction A2. For example, the multiple second grooves 49c are aligned so as to surround the heating element 45 from the inside in a plan view along the vertical direction D1. In a plan view along the vertical direction D1, the phase shifter 41 has a region 49d located between the pair of first grooves 49b and a region 49f located between the plurality of second grooves 49c. The pair of first grooves 49b are separated by the region 49d. The plurality of second grooves 49c are separated by the region 49f. At least one of the region 49d and the region 49f is a region in which wiring or the like can be arranged in the SiO2 layer 43.

[0059] As described above, the wavelength selector 31 according to the second embodiment includes a phase shifter 41, and the phase shifter 41 provides the same effects as the phase shifter 1 described above. In the wavelength selector 31, similar to the phase shifter 1, the temperature of the second optical waveguide 44c can be monitored by the first temperature measuring element 47 located inside the second optical waveguide 44c with respect to the fixed point O and the second temperature measuring element 48 located outside the second optical waveguide 44c with respect to the fixed point O. Furthermore, the power to the heating element 45 is controlled so that the monitored temperature becomes a predetermined value. Therefore, the temperature of the second optical waveguide 44c can be stabilized at the predetermined value. Therefore, even if the resistance value of the heating element 45 changes due to aging or other reasons, the power to the heating element 45 can be controlled according to the monitored temperature, thereby compensating for any deviation in the amount of phase shift and stabilizing the amount of phase shift.

[0060] Various embodiments and modifications of the phase shifter and wavelength selector according to the present disclosure have been described above. However, the present invention is not limited to the above-described embodiments or modifications, and may be further modified within the scope of the gist described in the claims. In other words, the configuration, shape, size, material, number, and arrangement of each part of the phase shifter and wavelength selector may be changed as appropriate within the scope of the above-described gist. For example, the wavelength selector according to the present disclosure may be a combination of any of the phase shifter 1, phase shifter 11, and phase shifter 21 described above. [Explanation of symbols]

[0061] 1...Phase shifter 2...Substrate 2b…first side 2c…Top surface 2d…Bottom surface 2f…Second side 3...SiO2 layer 3b…1st side 3c…Top surface 3d…Bottom surface 3f…Second side 4...Optical waveguide 5...heating element 5b,5c…part 6...Electrode 6c...Electrode 7…First temperature measuring element 7b...Silicone layer 7c...Salicide layer 8…Second temperature measuring element 8b...Si layer 8c...Salicide layer 9…Groove 10...Electrode 10b...1st electrode 10c…Second electrode 11...Phase shifter 14...Optical waveguide 14b...Si layer 17…First temperature measurement element 18…Second temperature measuring element 21...Phase shifter 22... Circuit board 22b...first top surface 22c…Second top surface 28...Support part 29…Space part 31...Wavelength selector 31b...First side 31c...Second side 41...Phase shifter 42... Circuit board 43...SiO2 layer 44...Optical waveguide 44b...first optical waveguide 44c...Second optical waveguide 45...heating element 46...Electrode 46a...electrode 46b...Electrode 46c…electrode 47…First temperature measuring element 48…Second temperature measuring element 49...Groove 49b...First groove 49c…Second groove 49d,49f…area

Claims

1. A substrate; an optical waveguide disposed perpendicular to the substrate; a first temperature measuring element and a second temperature measuring element that are arranged horizontally with respect to the optical waveguide and sandwich the optical waveguide therebetween; a heat generating element disposed in the perpendicular direction relative to the optical waveguide, the first temperature measuring element, and the second temperature measuring element; Equipped with Phase shifter.

2. When viewed in a plan view along the vertical direction, the heat generating element has a portion overlapping with the optical waveguide and a portion overlapping with at least one of the first temperature measuring element and the second temperature measuring element.

2. The phase shifter of claim 1.

3. the optical waveguide is made of silicon, the first temperature measuring element and the second temperature measuring element are made of salicide; 3. The phase shifter according to claim 1.

4. One end of the first temperature measuring element is connected to one end of the second temperature measuring element.

3. The phase shifter according to claim 1.

5. A wavelength selector comprising the phase shifter according to claim 1 or 2.

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