Microring resonator device heater with improved reliability

Abstract

A microring resonator device includes a ring-shaped optical waveguide that has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped optical waveguide circumscribes an interior region of the microring resonator device. A ring-shaped heater is disposed within the interior region of the microring resonator device. The ring-shaped heater has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped heater circumscribes a center of the microring resonator device. The ring-shaped heater is an electrically resistive heating device. First and second electrical contacts are electrically connected to the ring-shaped heater. A heat spreader fin is disposed above a portion of the ring-shaped optical waveguide. The heat spreader fin is thermally connected to the ring- shaped heater. The heat spreader fin is electrically isolated from the ring-shaped heater and from the first and second electrical contacts.

Description

Microring Resonator Device Heater with Improved ReliabilityBackground of the Invention

[0001] 1. Field of the Invention

[0002] The present invention relates to optical data communication.

[0003] 2. Description of the Related Art

[0004] Optical data communication systems operate by modulating laser light to encode digital data patterns within optical data signals. In some embodiments, an optical modulator is used to modulate continuous wave laser light to generate the modulated laser light that conveys the encoding of digital data patterns. The modulated laser light is transmitted through an optical data network from a sending node to a receiving node. The modulated laser light having arrived at the receiving node is de-modulated to obtain the original digital data patterns from the optical data signals. In some embodiments, a photodiode is used to detect light of an optical data signal and convert the detected light into a photocurrent that can be processed through electrical circuitry to demodulate the optical data signal to obtain the original digital data pattern from the optical data signal. The transmission of light through the optical data network includes transmission of light through optical fibers and transmission of light between optical fibers and photonic integrated circuits. It is within this context that the present invention arises.Summary of the Invention

[0005] In an example embodiment, a microring resonator device is disclosed. The microring resonator device includes a ring-shaped optical waveguide that has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped optical waveguide circumscribes an interior region of the microring resonator device. The microring resonator device also includes a ring-shaped heater disposed within the interior region of the microring resonator device. The ring-shaped heater has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped heater circumscribes a center of the microring resonator device. The ring-shaped heater is an electrically resistive heating device. The microring resonator device also includes a first electrical contact disposed in electrical connection with the ring-shaped heater. The microring resonator device also includes a second electrical contact disposed in electrical connection with the ring-shaped heater. The microring resonator device also includes a heat spreader fin disposed above a portion of the ring-shaped optical waveguide. The heat spreader fin is thermally connected to the ring-shaped heater. The heat spreader fin is electrically isolated from each of the ring-shaped heater, the first electricalcontact, and the second electrical contact.

[0006] In an example embodiment, a microring resonator device is disclosed. The microring resonator device includes a ring-shaped optical waveguide that includes an outer annular region, an inner annular region, and a spatial separation region extending between the outer annular region and the inner annular region. The outer annular region is a radial section of the ringshaped optical waveguide through which a fundamental optical mode is conveyed. The inner annular region is a radial section of the ring-shaped optical waveguide configured as an embedded thermal heater. The spatial separation region is a radial section of the ring-shaped optical waveguide having a radial width sufficient to spatially separate the embedded thermal heater within the inner annular region from the optical mode within the outer annular region.

[0007] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribes an interior region of a microring resonator device. The ring-shaped optical waveguide has an outer annular region that has a first vertical thickness. The ring-shaped optical waveguide has an inner annular region that has a second vertical thickness that is less than the first vertical thickness. The electro-optical semiconductor chip also includes a first bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide, such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide. The electro- optical semiconductor chip also includes a second bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ringshaped optical waveguide, such that a second optical coupling region exists between the second bus optical waveguide and the ring-shaped optical waveguide. The electro-optical semiconductor chip also includes a plurality of metal heater wires respectively formed at a plurality of vertical levels above a top surface of the ring-shaped optical waveguide. Each of the plurality of metal heater wires is positioned a sufficient distance away from the ring-shaped optical waveguide to control optical loss within ring-shaped optical waveguide due to the plurality of metal heater wires.

[0008] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribes an interior region of a microring resonator device. The ring-shaped optical waveguide has an outer annular region that has a first vertical thickness. The ring-shaped optical waveguide has an inner annular region that has a second vertical thickness that is less than the first vertical thickness. The electro-optical semiconductor chip also includes a first bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical couplingdistance of the ring-shaped optical waveguide, such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide. The electro- optical semiconductor chip also includes a second bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ringshaped optical waveguide, such that a second optical coupling region exists between the second bus optical waveguide and the ring-shaped optical waveguide. The electro-optical semiconductor chip also includes a spiral- shaped metal heater wire that is formed at a vertical level above a top surface of the ring-shaped optical waveguide. The spiral-shaped metal heater wire is formed to extend horizontally over an outer edge of the ring-shaped optical waveguide.

[0009] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribes an interior region of a microring resonator device. The ring-shaped optical waveguide has an outer annular region that has a first vertical thickness. The ring-shaped optical waveguide has an inner annular region that has a second vertical thickness that is less than the first vertical thickness. The electro-optical semiconductor chip also includes a first double- spiral- shaped metal heater wire that is formed at a first vertical level above a top surface of the ring-shaped optical waveguide. The first double- spiral- shaped metal heater wire is formed within the interior region of the microring resonator device. The electro-optical semiconductor chip also includes a second double- spiral- shaped metal heater wire that is formed at a second vertical level above a top surface of the ring-shaped optical waveguide. The second double- spiral- shaped metal heater wire is formed within the interior region of the microring resonator device.

[0010] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribes an interior region of a microring resonator device. The ring-shaped optical waveguide has an outer annular region that has a first vertical thickness. The ring-shaped optical waveguide has an inner annular region that has a second vertical thickness that is less than the first vertical thickness. The electro-optical semiconductor chip also includes a first partial-ring-shaped metal heater wire that is formed at a first vertical level above a top surface of the ring-shaped optical waveguide. The first partial-ring-shaped metal heater wire is formed within the interior region of the microring resonator device. The electro-optical semiconductor chip also includes a second partial-ring-shaped metal heater wire that is formed at a second vertical level above a top surface of the ring-shaped optical waveguide. The second partial-ring-shaped metal heater wire is formed within the interior region of the microring resonator device.

[0011] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribesan interior region of a microring resonator device. The electro-optical semiconductor chip also includes a bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide, such that an optical coupling region exists between the bus optical waveguide and the ring-shaped optical waveguide. The electro-optical semiconductor chip also includes a first doped region that is formed within the interior region of the microring resonator device at a location adjacent to the optical coupling region. The first doped region is electrically conductive. The electro-optical semiconductor chip also includes a second doped region that is formed along a side of the bus optical waveguide that is opposite from the ring-shaped optical waveguide. The second doped region is formed at a location adjacent to the optical coupling region. The second doped region is electrically conductive. The electro-optical semiconductor chip also includes a third doped region that is formed between the first doped region and the second doped region through the optical coupling region, and through both a portion of the ring-shaped optical waveguide and a portion of the bus optical waveguide. An electrical resistance of the third doped region is higher than an electrical resistance within each of the first doped region and the second doped region. The third doped region is configured to increase in temperature when an electrical current flows between the first doped region and the second doped region through the third doped region.

[0012] In an example embodiment, an electro-optical semiconductor chip is disclosed. The electro-optical semiconductor chip includes a ring-shaped optical waveguide that circumscribes an interior region of a microring resonator device. The electro-optical semiconductor chip also includes a first bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide, such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide. The electro-optical semiconductor chip also includes a second bus optical waveguide that extends past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide, such that a second optical coupling region exists between the second bus optical waveguide and the ring-shaped optical waveguide. The second bus optical waveguide and the first bus optical waveguide are configured substantially parallel with each other on opposite sides of the ring-shaped optical waveguide. The electro-optical semiconductor chip also includes a first doped region that is formed within the interior region of the microring resonator device. The first doped region is electrically conductive. The electro-optical semiconductor chip also includes a second doped region that is formed outside of the ring-shaped optical waveguide within a region located between the first bus optical waveguide and the second bus optical waveguide. The second doped region is electrically conductive. The electro-optical semiconductor chip also includes a third dopedregion that is formed between the first doped region and the second doped region through a portion of the ring-shaped optical waveguide. The third doped region is located between the first bus optical waveguide and the second bus optical waveguide. An electrical resistance of the third doped region is higher than an electrical resistance within each of the first doped region and the second doped region. The third doped region is configured to increase in temperature when an electrical current flows between the first doped region and the second doped region through the third doped region.Brief Description of the Drawings

[0013] Figure 1 A shows a top view of a microring resonator device that implements metal heater wires disposed at locations to control optical loss, in accordance with some embodiments.

[0014] Figure IB shows a heatmap of optical mode intensity within a vertical cross-section slice through the microring resonator device of Figure 1A, referenced as View A-A in Figure 1A, in accordance with some embodiments.

[0015] Figure 2A shows a top view of a microring resonator device that implements a spiralshaped metal heater wire within a level (metal level) above and over a ring-shaped optical waveguide of the microring resonator device, in accordance with some embodiments.

[0016] Figure 2B shows the position of the spiral-shaped metal heater wire relative to the ringshaped optical waveguide within a vertical cross-section slice through the microring resonator device of Figure 2A, reference as View A-A in Figure 2A, in accordance with some embodiments.

[0017] Figure 3A shows a top view of a microring resonator device that implements multiple spiral-shaped metal heater wires in multiple respective levels (metal interconnect levels) above and over a ring-shaped optical waveguide, in accordance with some embodiments.

[0018] Figure 3B shows the position of the multiple spiral-shaped metal heater wires relative to the ring-shaped optical waveguide within a vertical cross-section slice through the microring resonator device of Figure 3A, reference as View A-A in Figure 3A, in accordance with some embodiments.

[0019] Figure 4 shows a top view of a microring resonator device that implements multiple stacked double- spiral- shaped metal heater wires in multiple respective levels (metal interconnect levels) above and over a center region circumscribed by a ring-shaped optical waveguide, in accordance with some embodiments.

[0020] Figure 5A shows a top view of a microring resonator device that implements multiple ring-shaped metal heater wires in multiple respective levels (metal interconnect levels) in close proximity to a ring-shaped optical waveguide, in accordance with some embodiments.

[0021] Figure 5B shows the position of the multiple ring-shaped metal heater wires relative tothe ring-shaped optical waveguide within a vertical cross-section slice through the microring resonator device of Figure 5A, reference as View A-A in Figure 5A, in accordance with some embodiments.

[0022] Figure 6A shows a top view of a microring resonator device that implements a heat spreader fin, in accordance with some embodiments.

[0023] Figure 6B shows a vertical cross-section view of the microring resonator device of Figure 6A, referenced as View A-A in Figure 6A, in accordance with some embodiments.

[0024] Figure 7 shows a top view of the microring resonator device of Figures 6A and 6B with a second heat spreader fin disposed opposite the center of the microring resonator device from the (first) heat spreader fin, in accordance with some embodiments.

[0025] Figure 8 shows a top view of the microring resonator device of Figures 6A and 6B with six heat spreader fins disposed in a spaced apart manner azimuthally about the center of the microring resonator device, in accordance with some embodiments.

[0026] Figure 9 shows a top view of the microring resonator device of Figure 7, with the first heat spreader fin and the second heat spreader fin azimuthally rotated about the center of the microring resonator device so that the first spacing and the second spacing between the first heat spreader fin and the second heat spreader fin occur at locations outside of an optical coupling region between the ring-shaped optical waveguide of the microring resonator device and a bus optical waveguide, in accordance with some embodiments.

[0027] Figure 10 shows a top view of a microring resonator device that implements a doped silicon heater to generate heat within a ring-shaped optical waveguide, in accordance with some embodiments.

[0028] Figure 11 shows a top view of a microring resonator device that further implements a PN junction region within the ring-shaped optical waveguide for optical modulation in combination with the doped silicon heater to generate heat within the ring-shaped optical waveguide, in accordance with some embodiments.

[0029] Figure 12 shows a top view of a microring resonator device that implements a first doped silicon heater and a second doped silicon heater to generate heat within a ring-shaped optical waveguide, in accordance with some embodiments.

[0030] Figure 13A shows a top view of a microring resonator device that implements an embedded thermal heater within a ring-shaped optical waveguide, in accordance with some embodiments.

[0031] Figure 13B shows a vertical cross-section slice through the microring resonator device of Figure 13A, referenced as View A-A in Figure 13A, in accordance with some embodiments.

[0032] Figure 14A shows a top view of a microring resonator device that implements anembedded thermal heater within a ring-shaped optical waveguide, in accordance with some embodiments.

[0033] Figure 14B shows a vertical cross-section slice through the microring resonator device of Figure 14A, referenced as View A-A in Figure 14A, in accordance with some embodiments.

[0034] Figure 15A shows a top view of a microring resonator device that implements both a first embedded thermal heater and a second embedded thermal heater on an outer wall of a ringshaped optical waveguide, in accordance with some embodiments.

[0035] Figure 15B shows a vertical cross-section slice through the microring resonator device of Figure 15A, reference as View A-A in Figure 15A, in accordance with some embodiments.

[0036] Figure 16A shows the top view of the microring resonator device of Figures 15A and 15B in which the embedded thermal heaters are implemented on the outer wall of the ring-shaped optical waveguide in combination with implementation of a modulator contact / doping region along the inner wall of the ring-shaped optical waveguide, in accordance with some embodiments.

[0037] Figure 16B shows a vertical cross-section slice through the microring resonator device of Figure 16A, referenced as View A-A in Figure 16A, in accordance with some embodiments.

[0038] Figure 17 shows a top view of a microring resonator device that implements both a first embedded thermal heater on an outer wall of a first bus / drop optical waveguide, and a second embedded thermal heater on an outer wall of a second bus / drop optical waveguide, in accordance with some embodiments.

[0039] Figure 18 shows the top view of the microring resonator device of Figure 17 in which the embedded thermal heaters are implemented on the outer walls of the bus / drop optical waveguides, respectively, in combination with implementation of a modulator contact / doping region along the inner wall of the ring-shaped optical waveguide, in accordance with some embodiments.

[0040] Figure 19 shows a top view of a microring resonator device that implements serial ring- shaped heater disposed within an interior region that is circumscribed by a ring-shaped optical waveguide, in accordance with some embodiments.

[0041] Figure 20 shows a top view of a microring resonator device that implements a parallel ring-shaped heater disposed within an interior region that is circumscribed by a ring-shaped optical waveguide, in accordance with some embodiments.

[0042] Figure 21 shows a top view of a microring resonator device that implements a parallel tapered ring-shaped heater disposed within an interior region that is circumscribed by a ring- shaped optical waveguide, in accordance with some embodiments.

[0043] Figure 22 shows a top view of a microring resonator device that implements a paralleltapered ring-shaped heater disposed within an interior region that is circumscribed by a ring- shaped optical waveguide, in accordance with some embodiments.

[0044] Figure 23 shows a top view of a microring resonator device that implements a parallel tapered ring-shaped heater disposed within an interior region that is circumscribed by a ring- shaped optical waveguide, in accordance with some embodiments.

[0045] Figure 24 shows a top view of a microring resonator device that implements a parallel tapered ring-shaped heater disposed within an interior region that is circumscribed by a ring- shaped optical waveguide, in accordance with some embodiments.Detailed Description

[0046] In the following description, numerous specific details are set forth in order to provide an understanding of the embodiments disclosed herein. It will be apparent, however, to one skilled in the art that the embodiments disclosed herein may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the disclosed embodiments.

[0047] The embodiments disclosed herein relate to optical data communication. Optical data communication systems operate by modulating laser light to encode digital data patterns within optical data signals. In some embodiments, a ring modulator is used to modulate continuous wave laser light to generate the modulated laser light that conveys the encoding of digital data patterns. In some embodiments, the ring modulator is positioned within an evanescent optically coupling distance from a bus optical waveguide and operates to modulate light that is propagating through the bus optical waveguide. The modulated laser light is transmitted through an optical data network from a sending node to a receiving node. The modulated laser light having arrived at the receiving node is de-modulated to obtain the original digital data patterns from the optical data signals. The transmission of light through the optical data network includes transmission of light through optical fibers and transmission of light between optical fibers and photonic integrated circuits. In some embodiments, a photodiode is used to detect light of an optical data signal and convert the detected light into a photocurrent that can be processed through electrical circuitry to demodulate the optical data signal to obtain the original digital data pattern from the optical data signal.

[0048] Optical cavities are used in a variety of applications in optical data communication systems, in various devices, such as lasers, optical modulators, optical splitters, optical routers, optical switches, and optical detectors, among others. In various applications and configurations, optical cavities may show strong wavelength selectivity. For this reason, optical cavities are useful in systems that rely on multiple optical data signals transmitting information at different wavelengths. In some embodiments, optical cavities are configured as ring resonators and / ordisk resonators to enable applications in which light that is coupled from an input optical waveguide into the optical cavity of the ring / disk resonator is either efficiently routed to a separate output optical waveguide, or absorbed within the optical cavity of the ring / disk resonator at specific wavelengths. Also, optical cavities, such as ring / disk resonators, are useful in sensing applications, such as in biological or chemical sensing applications in which a high concentration of optical power is needed in a small area.

[0049] In various embodiments, electrical data signals are used to drive optical modulation within an optical cavity of a ring / disc modulator. In various embodiments, electrical signal repeater / amplifier devices, such as CMOS (complementary metal oxide semiconductor) repeater / amplifier devices, are implemented within integrated circuits to mitigate / reduce electrical signal delay along an electrical signal conveyance pathway that extends from an origination point of the electrical signal to a destination point of the electrical signal. Electrical repeater / amplifier devices, such as CMOS repeater / amplifier devices, play an important role in transmitting ultra-high-speed data through electrical wires for either within chip (inter-chip) data communication and / or between chips (chip-to-chip) data communication. In some embodiments, particularly in optical data communication devices and / or systems, an electrical data signal that is used to drive optical modulation within a ring / disc modulator has to be sent along a electrical signal conveyance pathway from an origination point of the electrical data signal to the optical cavity that is used to modulate a beam of continuous wave laser light to transfer the digital data present within the electrical data signal into an optical data signal within the optical domain. In these embodiments, one or more CMOS repeater / amplifier devices are implemented along the electrical signal conveyance pathway to mitigate / reduce delay and / or mitigate / reduce signal loss associated with transmission of the electrical data signal from its origination point to the optical cavity of the ring / disc modulator.

[0050] Microring resonator device-based modulators and filters are important components in wavelength-division multiplexed (WDM) systems, since they provide compact integration. Thermal tuning of the resonant wavelengths for a microring resonator device is often required. For example, in various embodiments, thermal tuning of resonant wavelengths for a microring resonator device is implemented to compensate for ambient temperature changes, to match a light source wavelength not known at the time of fabrication, and / or to compensate for fabrication uncertainties. In various embodiments, thermal tuning of resonant wavelengths for a given microring resonator device is achieved by embedding resistive heaters in close proximity to the given microring resonator device.

[0051] It is desirable to achieve a large resonant wavelength tuning range for a given microring resonator device. For example, in various embodiments, having a larger resonant wavelengthtuning range for a given microring resonator device enables the resonant wavelength tuning of the given microring resonator device to cover a broader range of ambient temperatures and / or a broader range of source light wavelengths. In various embodiments, to achieve a larger resonant wavelength tuning range for a given microring resonator device, a heater associated with the given microring resonator device needs to operate at high electrical current and high temperature.

[0052] Microring resonator device heater failure and reliability are a major issues in designing a microring resonator device-based WDM system. The reliability of a microring resonator device heater limits the resonant wavelength tuning range available to the heater, and in turn limits the temperature range over which the WDM system can operate. Therefore, it is desirable to have microring resonator device heater designs that provide improved resilience to high temperatures and high electrical current conditions. To this end, various embodiments are disclosed herein for microring resonator device heaters that have increased reliability and increased resonant wavelength tuning range, and that provide for increased temperature range over which the WDM system can operate.

[0053] Various embodiments are disclosed herein for providing localized heating in the center of the microring modulator through the use of one or more thin film metal heater(s) formed within into the electro-optic chip. Figure 1A shows a top view of a microring resonator device 100 that implements metal heater wires 103-1 through 103-7 disposed at locations to control optical loss, in accordance with some embodiments. In some embodiments, the microring resonator device 100 is formed within an electro-optic semiconductor chip. The microring resonator device 100 includes a ring-shaped optical waveguide 105. In some embodiments, the ring-shaped optical waveguide 105 is configured as a half-rib waveguide that includes a fullthickness (vertical thickness) outer annular region 105A and a partial-thickness (vertical thickness) annular region 105B that extends from the full-thickness outer annular region 105A radially inward toward a center 107 of the ring-shaped optical waveguide 105. In some embodiments, the ring-shaped optical waveguide 105 includes interior finger-shaped features 105C that extend from the partial-thickness annular region 105B radially inward toward the center 107 of the ring-shaped optical waveguide 105. The interior finger-shaped features 105C are configured to physically and electrically connect with electrical contact structures 109A and 109B, e.g., via structures.

[0054] The electrical contact structures 109A and 109B are disposed in an alternating manner azimuthally about the center 107 of the ring-shaped optical waveguide 105. The electrical contact structures 109 A and 109B extend vertically through the semiconductor chip in which the microring resonator device 100 is formed. The electrical contact structures 109 A electrically connect with an electrical conductor 111 formed within an upper metal layer of thesemiconductor chip. Similarly, the electrical contact structures 109B electrically connect with an electrical conductor 113 formed within an upper metal layer of the semiconductor chip. The electrical conductors 111 and 113 are physically and electrically separated from each other within the semiconductor chip.

[0055] The ring-shaped optical waveguide 105 of the microring resonator device 100 is positioned next to a bus optical waveguide 115. In some embodiments, the ring-shaped optical waveguide 105 and the bus optical waveguide 115 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 118, around a location of closest approach of the bus optical waveguide 115 to the ring-shaped optical waveguide 105.

[0056] In some embodiments, the ring-shaped optical waveguide 105 of the microring resonator device 100 is positioned next to a drop optical waveguide 117. In some embodiments, the ringshaped optical waveguide 105 and the drop optical waveguide 117 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 119, around a location of closest approach of the drop optical waveguide 117 to the ring-shaped optical waveguide 105.

[0057] In some embodiments, the metal heater wires 103-1 through 103-7 are disposed / formed in various different metal layers of the semiconductor chip. The metal heater wires 103-1 through 103-7 are shaped and positioned with respect to the ring-shaped optical waveguide 105, so as to control optical loss within the ring-shaped optical waveguide 105 that is caused by the metal heater wires 103-1 through 103-7. In some embodiments, portions of the metal heater wires 103- 1 through 103-7 that run along (closest to) the ring-shaped optical waveguide 105 are formed as arcs or rings around the ring-shaped optical waveguide 105. In some embodiments, the distance between the ring-shaped optical waveguide 105 and the portion of each of the metal heater wires 103-1 through 103-7 that runs along (closest to) the ring-shaped optical waveguide 105 is substantially constant (the same) to assist with controlling the loss of optical power within the ring-shaped optical waveguide 105 caused by the proximity of the metal heater wires 103-1 through 103-7 to the optical mode of the ring-shaped optical waveguide 105.

[0058] In some embodiments, each of the metal heater wires 103-1 and 103-5 is formed in a first (Ml) metal layer of the semiconductor chip. In some embodiments, each of the metal heater wires 103-2 and 103-6 is formed in a second (M2) metal layer of the semiconductor chip. In some embodiments, each of the metal heater wires 103-3 and 103-7 is formed in a third (M3) metal layer of the semiconductor chip. In some embodiments, the metal heater wire 103-4 is formed in a fourth (M4) metal layer of the semiconductor chip.

[0059] Figure IB shows a heatmap of optical mode intensity within a vertical cross-section slice through the microring resonator device 100, referenced as View A-A in Figure 1 A, in accordancewith some embodiments. Figure IB also shows the vertical and radial locations of the metal heater wires 103-1, 103-2, 103-3, and 103-4 relative to the ring-shaped optical waveguide 105. The heat map of Figure IB shows the optical mode intensity on a decibel (db) scale. The black rectangles in Figure IB show the vertical and horizontal positions of the metal heater wires 103- 1, 103-2, 103-3, and 103-4 relative to the ring-shaped optical waveguide 105. The heatmap of Figure IB shows that the heater wires 103-1, 103-2, 103-3, and 103-4 are positioned relative to the ring-shaped optical waveguide 105 in regions of similar optical intensity.

[0060] In some embodiments, Figure 1A shows a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 105, the first bus optical waveguide 115, second bus optical waveguide 117, and the plurality of metal heater wires 103-1 to 103-7. The ring-shaped optical waveguide 105 circumscribes an interior region of the microring resonator device 100. The ring-shaped optical waveguide 105 has the outer annular region 105A that has a first vertical thickness. The ring-shaped optical waveguide has the inner annular region 105B that has a second vertical thickness that is less than the first vertical thickness. The first bus optical waveguide 115 extends past the ring-shaped optical waveguide 105 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 105, such that the first optical coupling region 118 exists between the first bus optical waveguide 115 and the ring- shaped optical waveguide 105. The second bus optical waveguide 117 extends past the ringshaped optical waveguide 105 and within an evanescent optical coupling distance of the ringshaped optical waveguide 105, such that the second optical coupling region 119 exists between the second bus optical waveguide 117 and the ring-shaped optical waveguide 105. The plurality of metal heater wires 103-1 to 103-7 are respectively formed at a plurality of vertical levels above a top surface of the ring-shaped optical waveguide 105. Each of the plurality of metal heater wires 103-1 to 103-7 is positioned a sufficient distance away from the ring-shaped optical waveguide 105 to control optical loss within ring-shaped optical waveguide 105 due to the plurality of metal heater wires 103-1 to 103-7. In some embodiments, some of the plurality of metal heater wires 103-1 to 103-7 are formed to have an arc shape that follows an arc shape of a portion of the ring-shaped optical waveguide 105 proximate to said some of the plurality of metal heater wires 103-1 to 103-7. In some embodiments, some of the plurality of metal heater wires 103-1 to 103-7 are formed to have a ring shape that follows a shape of the ring-shaped optical waveguide 105.

[0061] Figure 2A shows a top view of a microring resonator device 200 that implements a spiral-shaped metal heater wire 203 within a level (metal level) above and over a ring-shaped optical waveguide 205 of the microring resonator device 200, in accordance with some embodiments. In some embodiments, the microring resonator device 200 is formed within anelectro-optic semiconductor chip. In some embodiments, the ring-shaped optical waveguide 205 is configured as a half-rib waveguide that includes a full-thickness (vertical thickness) outer annular region 205A and a partial-thickness (vertical thickness) annular region 205B that extends from the full-thickness outer annular region 205A radially inward toward a center 207 of the ring-shaped optical waveguide 205. In some embodiments, the ring-shaped optical waveguide 205 includes interior finger-shaped features 205C that extend from the partial-thickness annular region 205B radially inward toward the center 207 of the ring-shaped optical waveguide 205. The interior finger-shaped features 205C are configured to physically and electrically connect with electrical contact structures 209A and 209B, e.g., via structures.

[0062] The electrical contact structures 209A and 209B are disposed in an alternating manner azimuthally about the center 207 of the ring-shaped optical waveguide 205. The electrical contact structures 209A and 209B extend vertically through the semiconductor chip in which the microring resonator device 200 is formed. The electrical contact structures 209A electrically connect with an electrical conductor 211 formed within an upper metal layer of the semiconductor chip. Similarly, the electrical contact structures 209B electrically connect with an electrical conductor 213 formed within an upper metal layer of the semiconductor chip. The electrical conductors 211 and 213 are physically and electrically separated from each other within the semiconductor chip.

[0063] The ring-shaped optical waveguide 205 of the microring resonator device 200 is positioned next to a bus optical waveguide 215. In some embodiments, the ring-shaped optical waveguide 205 and the bus optical waveguide 215 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 216, around a location of closest approach of the bus optical waveguide 215 to the ring-shaped optical waveguide 205.

[0064] In some embodiments, the ring-shaped optical waveguide 205 of the microring resonator device 200 is positioned next to a drop optical waveguide 217. In some embodiments, the ringshaped optical waveguide 205 and the drop optical waveguide 217 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 219, around a location of closest approach of the drop optical waveguide 217 to the ring-shaped optical waveguide 205.

[0065] The spiral- shaped metal heater wire 203 is formed to extend horizontally over the outer edge of the ring-shaped optical waveguide 205. Positioning of the spiral-shaped metal heater wire 203 over the outer edge of the ring-shaped optical waveguide 205 provides for avoidance of an abrupt change in a pattern of the spiral- shaped metal heater wire 203, where such an abrupt change in the pattern of the spiral-shaped metal heater wire 203 could lead to adverse optical reflections of light propagating within the ring-shaped optical waveguide 205.

[0066] Figure 2B shows the position of the spiral-shaped metal heater wire 203 relative to the ring-shaped optical waveguide 205 within a vertical cross-section slice through the microring resonator device 200, reference as View A-A in Figure 2A, in accordance with some embodiments. Figure 2B shows how the spiral-shaped metal heater wire 203 is positioned above the ring-shaped optical waveguide 205. Figure 2B also shows how the spiral-shaped metal heater wire 203 is configured to extend horizontally over the outer edge (outer annular region) of the ring-shaped optical waveguide 205. Also, as shown in Figure 2B, in some embodiments, the spiral-shaped metal heater wire 203 is formed within a single metal layer of the semiconductor chip within which the microring resonator device 200 is formed. In some embodiments, such as shown in Figure 2B, the various spirals of the spiral- shaped metal heater wire 203 are formed in a substantially equivalent manner with regard to shape and size. In some embodiments, such as shown in Figure 2B, adjacently positioned spirals of the spiral-shaped metal heater wire 203 are separated from each other by a substantially uniform distance as measured in the horizontal direction. In other embodiments, however, one or more of the shape, the size, and the spiral-to- spiral spacing of the various spirals of the spiral-shaped metal heater wire 203 can vary across the horizontal extent of the spiral-shaped metal heater wire 203.

[0067] In some embodiments, Figures 2A and 2B show a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 205, the first bus optical waveguide 215, the second bus optical waveguide 217, and the spiral- shaped metal heater wire 203. The ring-shaped optical waveguide 205 circumscribes an interior region of the microring resonator device 200. The ring-shaped optical waveguide 205 has an outer annular region 205A that has a first vertical thickness. The ring-shaped optical waveguide 205 has an inner annular region 205B that has a second vertical thickness that is less than the first vertical thickness. The first bus optical waveguide 215 extends past the ring-shaped optical waveguide 205 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 205, such that the first optical coupling region 216 exists between the first bus optical waveguide 215 and the ring- shaped optical waveguide 205. The second bus optical waveguide 217 extends past the ringshaped optical waveguide 205 and within an evanescent optical coupling distance of the ringshaped optical waveguide 205, such that the second optical coupling region 219 exists between the second bus optical waveguide 217 and the ring-shaped optical waveguide 205. The spiralshaped metal heater wire 203 is formed at a vertical level above a top surface of the ring-shaped optical waveguide 205. The spiral-shaped metal heater wire 203 is formed to extend horizontally over an outer edge of the ring-shaped optical waveguide 205.

[0068] Figure 3A shows a top view of a microring resonator device 300 that implements multiple spiral-shaped metal heater wires 303-1 and 303-2 in multiple respective levels (metalinterconnect levels) above and over a ring-shaped optical waveguide 305, in accordance with some embodiments. In some embodiments, the microring resonator device 300 is formed within an electro-optic semiconductor chip. In some embodiments, the ring-shaped optical waveguide 305 is configured as a half-rib waveguide that includes a full-thickness (vertical thickness) outer annular region 305A and a partial-thickness (vertical thickness) annular region 305B that extends from the full-thickness outer annular region 305A radially inward toward a center 307 of the ring-shaped optical waveguide 305. In some embodiments, the ring-shaped optical waveguide 305 includes interior finger-shaped features 305C that extend from the partial-thickness annular region 305B radially inward toward the center 307 of the ring-shaped optical waveguide 305. The interior finger-shaped features 305C are configured to physically and electrically connect with electrical contact structures 309A and 309B, e.g., via structures.

[0069] The electrical contact structures 309A and 309B are disposed in an alternating manner azimuthally about the center 307 of the ring-shaped optical waveguide 305. The electrical contact structures 309A and 309B extend vertically through the semiconductor chip in which the microring resonator device 300 is formed. The electrical contact structures 309A electrically connect with an electrical conductor 311 formed within an upper metal layer of the semiconductor chip. Similarly, the electrical contact structures 309B electrically connect with an electrical conductor 313 formed within an upper metal layer of the semiconductor chip. The electrical conductors 311 and 313 are physically and electrically separated from each other within the semiconductor chip.

[0070] The ring-shaped optical waveguide 305 of the microring resonator device 300 is positioned next to a bus optical waveguide 315. In some embodiments, the ring-shaped optical waveguide 305 and the bus optical waveguide 315 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 316, around a location of closest approach of the bus optical waveguide 315 to the ring-shaped optical waveguide 305.

[0071] In some embodiments, the ring-shaped optical waveguide 305 of the microring resonator device 300 is positioned next to a drop optical waveguide 317. In some embodiments, the ringshaped optical waveguide 305 and the drop optical waveguide 317 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 319, around a location of closest approach of the drop optical waveguide 317 to the ring-shaped optical waveguide 305.

[0072] Each of the multiple spiral-shaped metal heater wires 303-1 and 303-2 is configured and positioned to extend horizontally in a radial spiral manner over an outer radial portion and over an outer edge of the ring-shaped optical waveguide 305. The multiple spiral- shaped metal heater wires 303-1 and 303-2 are stacked vertically with respect to each other, with a layer of dielectricmaterial 321 intervening vertically between the multiple spiral-shaped metal heater wires 303-1 and 303-2. Positioning of the multiple spiral-shaped metal heater wires 303-1 and 303-2 over the outer edge of the ring-shaped optical waveguide 305 provides for avoidance of an abrupt change in a pattern of each of the spiral-shaped metal heater wires 303-1 and 303-2, where such an abrupt change in the pattern of the spiral-shaped metal heater wires 303-1 and 303-2 could lead to adverse optical reflections of light propagating within the ring-shaped optical waveguide 305.

[0073] Figure 3B shows the position of the multiple spiral-shaped metal heater wires 303-1 and 303-2 relative to the ring-shaped optical waveguide 305 within a vertical cross-section slice through the microring resonator device 300, reference as View A-A in Figure 3A, in accordance with some embodiments. Figure 3B shows how the multiple spiral-shaped metal heater wires 303-1 and 303-2 are positioned in a vertically stacked manner relative to each other above the ring-shaped optical waveguide 305. Figure 3B also shows how the multiple spiral-shaped metal heater wires 303-1 and 303-2 are configured to extend horizontally over the outer edge (outer annular region) of the ring-shaped optical waveguide 305. Also, as shown in Figure 3B, in some embodiments, each of the spiral-shaped metal heater wires 303-1 and 303-2 is respectively formed within a single metal layer of the semiconductor chip within which the microring resonator device 300 is formed.

[0074] In some embodiments, such as shown in Figure 3B, the various spirals of each of the spiral-shaped metal heater wires 303-1 and 303-2 are formed in a substantially equivalent manner with regard to shape and size. In some embodiments, such as shown in Figure 3B, adjacently positioned spirals of a given one of the multiple spiral-shaped metal heater wires 303- 1 and 303-2 are separated from each other by a substantially uniform distance as measured in the horizontal direction. In other embodiments, however, one or more of the shape, the size, and the spiral-to- spiral spacing of the various spirals of a given one of the multiple spiral-shaped metal heater wires 303-1 and 303-2 can vary across the horizontal extent of the given one of the multiple spiral-shaped metal heater wires 303-1 and 303-2. Also, while the example of Figures 3 A and 3B show two spiral-shaped metal heater wires 303-1 and 303-2, it should be understood that various embodiments of the microring resonator device 300 can include a number (N) of spiral-shaped metal heater wires 303-1 to 303-N configured in a similar manner as the spiralshaped metal heater wires 303-1 and 303-2, where the number (N) is greater than two. In these embodiments, layers of dielectric material, e.g., dielectric material 321, are formed to intervene vertically between adjacent vertically positioned ones of the number (N) of spiral-shaped metal heater wires 303-1 to 303-N.

[0075] In some embodiments, Figures 3A and 3B show a portion of an electro-opticalsemiconductor chip that includes the ring-shaped optical waveguide 205, the first bus optical waveguide 215, the second bus optical waveguide 217, and the plurality of spiral- shaped metal heater wires 303-1, 303-2. The ring-shaped optical waveguide 205 circumscribes an interior region of the microring resonator device 200. The ring-shaped optical waveguide 205 has an outer annular region 205A that has a first vertical thickness. The ring-shaped optical waveguide 205 has an inner annular region 205B that has a second vertical thickness that is less than the first vertical thickness. The first bus optical waveguide 215 extends past the ring-shaped optical waveguide 205 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 205, such that the first optical coupling region 216 exists between the first bus optical waveguide 215 and the ring-shaped optical waveguide 205. The second bus optical waveguide 217 extends past the ring-shaped optical waveguide 205 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 205, such that the second optical coupling region 219 exists between the second bus optical waveguide 217 and the ring-shaped optical waveguide 205. The plurality of spiral-shaped metal heater wires 303-1, 303-2 are respectively formed at a plurality of vertical levels above the top surface of the ring-shaped optical waveguide 305. In some embodiments, each of the plurality of spiral-shaped metal heater wires 303- 1 , 303-2 is formed to extend horizontally over the outer edge of the ring-shaped optical waveguide 305. In some embodiments, the plurality of spiral-shaped metal heater wires 303-1, 303-2 are vertically stacked with respect to each other with the layer of dielectric material 321 intervening vertically between adjacent ones of the plurality of spiral- shaped metal heater wires 303-1, 303-2.

[0076] Figure 4 shows a top view of a microring resonator device 400 that implements multiple stacked double- spiral- shaped metal heater wires 403-1 and 403-2 in multiple respective levels (metal interconnect levels) above and over a center region circumscribed by a ring-shaped optical waveguide 405, in accordance with some embodiments. In some embodiments, the microring resonator device 400 is formed within an electro-optic semiconductor chip. The microring resonator device 400 is heated from the center region by the multiple stacked double-spiral- shaped metal heater wires 403-1 and 403-2. In some embodiments, the ring-shaped optical waveguide 405 is configured as a half-rib waveguide that includes a full-thickness (vertical thickness) outer annular region 405A and a partial-thickness (vertical thickness) annular region 405B that extends from the full-thickness outer annular region 405A radially inward toward a center 407 of the ring-shaped optical waveguide 405. In some embodiments, the ring-shaped optical waveguide 405 includes interior finger-shaped features 405C that extend from the partialthickness annular region 405B radially inward toward the center 407 of the ring-shaped optical waveguide 405. The interior finger-shaped features 405C are configured to physically andelectrically connect with electrical contact structures 409A and 409B, e.g., via structures.

[0077] The electrical contact structures 409A and 409B are disposed in an alternating manner azimuthally about the center 407 of the ring-shaped optical waveguide 405. The electrical contact structures 409A and 409B extend vertically through the semiconductor chip in which the microring resonator device 400 is formed. The electrical contact structures 409A electrically connect with an electrical conductor 411 formed within an upper metal layer of the semiconductor chip. Similarly, the electrical contact structures 409B electrically connect with an electrical conductor 413 formed within an upper metal layer of the semiconductor chip. The electrical conductors 411 and 413 are physically and electrically separated from each other within the semiconductor chip.

[0078] The ring-shaped optical waveguide 405 of the microring resonator device 400 is positioned next to a bus optical waveguide 415. In some embodiments, the ring-shaped optical waveguide 405 and the bus optical waveguide 415 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 417, around a location of closest approach of the bus optical waveguide 415 to the ring-shaped optical waveguide 405.

[0079] In some embodiments, the ring-shaped optical waveguide 405 of the microring resonator device 400 is positioned next to a drop optical waveguide 417. In some embodiments, the ringshaped optical waveguide 405 and the drop optical waveguide 417 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 419, around a location of closest approach of the drop optical waveguide 417 to the ring-shaped optical waveguide 405.

[0080] Each of the multiple double- spiral- shaped metal heater wires 403-1 and 403-2 is configured and positioned to extend horizontally in a radial spiral manner over the central region of the microring resonator device 400 that is circumscribed by the ring-shaped optical waveguide 405. The multiple double- spiral- shaped metal heater wires 403-1 and 403-2 are stacked vertically with respect to each other, with a layer of dielectric material intervening vertically between the multiple double- spiral- shaped metal heater wires 403-1 and 403-2. Positioning of the multiple double-spiral-shaped metal heater wires 403-1 and 403-2 over the center region of the microring resonator device 400 provides for avoidance of an abrupt change in a pattern of each of the double-spiral-shaped metal heater wires 403-1 and 403-2, where such an abrupt change in the pattern of the double- spiral- shaped metal heater wires 403-1 and 403-2 could lead to adverse optical reflections of light propagating within the ring-shaped optical waveguide 405. While the example of Figure 4 shows two double- spiral- shaped metal heater wires 403-1 and 403-2, it should be understood that various embodiments of the microring resonator device 400 can include a number (N) of double- spiral- shaped metal heater wires 403-1 to 403-N configured ina similar manner as the double-spiral-shaped metal heater wires 403-1 and 403-2, where the number (N) is greater than two. In these embodiments, layers of dielectric material are formed to intervene vertically between adjacent vertically positioned ones of the number (N) of spiralshaped metal heater wires 403-1 to 403-N.

[0081] In some embodiments, Figure 4 shows a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 405, the first double-spiral-shaped metal heater wire 403-1, and the second double- spiral- shaped metal heater wire 403-2. The ring-shaped optical waveguide 405 circumscribes an interior region of a microring resonator device 400. The ring-shaped optical waveguide 405 has an outer annular region 405A that has a first vertical thickness. The ring-shaped optical waveguide has an inner annular region 405B that has a second vertical thickness that is less than the first vertical thickness. The first double-spiral-shaped metal heater wire 403-1 is formed at a first vertical level above a top surface of the ring-shaped optical waveguide 405. The first double-spiral-shaped metal heater wire 403-1 is formed within the interior region of the microring resonator device 400. The second double- spiral- shaped metal heater wire 403-2 is formed at a second vertical level above a top surface of the ring-shaped optical waveguide 405. The second double- spiral- shaped metal heater wire 403-2 is formed within the interior region of the microring resonator device 400.

[0082] Figure 5A shows a top view of a microring resonator device 500 that implements multiple ring-shaped metal heater wires 503-1 through 503-5 in multiple respective levels (metal interconnect levels) in close proximity to a ring-shaped optical waveguide 505, in accordance with some embodiments. In some embodiments, the microring resonator device 500 is formed within an electro-optic semiconductor chip. In some embodiments, the ring-shaped optical waveguide 505 is configured as a half-rib waveguide that includes a full-thickness (vertical thickness) outer annular region 505A and a partial-thickness (vertical thickness) annular region 505B that extends from the full-thickness outer annular region 505A radially inward toward a center 507 of the ring-shaped optical waveguide 505. In some embodiments, the ring-shaped optical waveguide 505 includes interior finger-shaped features 505C that extend from the partialthickness annular region 505B radially inward toward the center 507 of the ring-shaped optical waveguide 505. The interior finger-shaped features 505C are configured to physically and electrically connect with electrical contact structures 509A and 509B, e.g., via structures.

[0083] The electrical contact structures 509A and 509B are disposed in an alternating manner azimuthally about the center 507 of the ring-shaped optical waveguide 505. The electrical contact structures 509A and 509B extend vertically through the semiconductor chip in which the microring resonator device 500 is formed. The electrical contact structures 509A electrically connect with an electrical conductor 511 formed within an upper metal layer of thesemiconductor chip. Similarly, the electrical contact structures 509B electrically connect with an electrical conductor 513 formed within an upper metal layer of the semiconductor chip. The electrical conductors 511 and 513 are physically and electrically separated from each other within the semiconductor chip. The multiple ring-shaped metal heater wires 503-1 through 503- 5 are also positioned in close proximity to the electrical conductors 511 and 513 (the metal stack) that are used for optical signal modulation, so that the electrical conductors 511 and 513 will provide for additional heat conduction around the microring resonator device 500. In some embodiments, the ring-shaped metal heater wires 503-1 through 503-5 are positioned as close as possible to the electrical conductors 511 and 513, so that the electrical conductors 511 and 513 can assist with conduction of heat to the silicon of the ring-shaped optical waveguide 505. Additionally, the center ring-shaped metal heater wire 503-5 provides an increase in wire length and a corresponding increase in electrical resistance through the multiple ring-shaped metal heater wires 503-1 through 503-5 to enhance heating of the ring-shaped optical waveguide 505.

[0084] The ring-shaped optical waveguide 505 of the microring resonator device 500 is positioned next to a bus optical waveguide 515. In some embodiments, the ring-shaped optical waveguide 505 and the bus optical waveguide 515 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 516, around a location of closest approach of the bus optical waveguide 515 to the ring-shaped optical waveguide 505. Also, in some embodiments, the ring-shaped optical waveguide 505 of the microring resonator device 500 is positioned next to a drop optical waveguide 517. In some embodiments, the ringshaped optical waveguide 505 and the drop optical waveguide 517 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 519, around a location of closest approach of the drop optical waveguide 517 to the ring-shaped optical waveguide 505.

[0085] Figure 5B shows the position of the multiple ring-shaped metal heater wires 503-1 through 503-5 relative to the ring-shaped optical waveguide 505 within a vertical cross-section slice through the microring resonator device 500, reference as View A-A in Figure 5A, in accordance with some embodiments. Figure 5B shows how the multiple ring-shaped metal heater wires 503-1 through 503-5 are stacked vertically within various metal layers within the semiconductor chip within which the microring resonator device 500 is formed. In this manner, various layers of dielectric material are formed vertically between the multiple ring-shaped metal heater wires 503-1 through 503-5.

[0086] In some embodiments, each of the ring-shaped metal heater wires 503-1 through 503-5 is respectively formed within a single metal layer of the semiconductor chip within which the microring resonator device 500 is formed. In some embodiments, such as shown in Figure 5B,the various ring-shaped metal heater wires 503-1 and 503-5 are formed in a substantially equivalent manner with regard to vertical cross-sectional shape and size. However, in other embodiments, different ones of the various ring-shaped metal heater wires 503-1 and 503-5 are formed in a different manner with regard to vertical cross-sectional shape and / or size. Also, while the example of Figures 5A and 5B show five ring-shaped metal heater wires 503-1 and 503-5, it should be understood that various embodiments of the microring resonator device 500 can include a number (N) of ring-shaped metal heater wires 503-1 to 503-N configured in a similar manner as the ring-shaped metal heater wires 503-1 and 503-5, where the number (N) is greater than one. In these embodiments, layers of dielectric material are formed to intervene vertically between adjacent vertically positioned ones of the number (N) of ring-shaped metal heater wires 503-1 to 503-N.

[0087] In some embodiments, Figures 5A and 5B show a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 505, the first partial-ring- shaped metal heater wire 503-1, and the second partial-ring-shaped metal heater wire 503-2. The ring-shaped optical waveguide 505 circumscribes an interior region of a microring resonator device 500. The ring-shaped optical waveguide 505 has an outer annular region 505A that has a first vertical thickness. The ring-shaped optical waveguide 505 has an inner annular region 505B that has a second vertical thickness that is less than the first vertical thickness. The first partial- ring-shaped metal heater wire 503-1 is formed at a first vertical level above a top surface of the ring-shaped optical waveguide 505. The first partial-ring-shaped metal heater wire 503-1 is formed within the interior region of the microring resonator device 500. The second partial-ring- shaped metal heater wire 503-2 is formed at a second vertical level above a top surface of the ring-shaped optical waveguide 505. The second partial-ring-shaped metal heater wire 503-2 is formed within the interior region of the microring resonator device 500.

[0088] Figure 6A shows a top view of a microring resonator device 600 that implements a heat spreader fin 601, in accordance with some embodiments. In some embodiments, the microring resonator device 600 is formed within an electro-optic semiconductor chip. The heat spreader fin 601 is configured to make thermal contact with a ring-shaped heater 603 formed within the microring resonator device 600. The heat spreader fin 601 is configured and positioned to assist with uniform dissipation of the heat generated by the ring-shaped heater 603 within a ring-shaped optical waveguide 605 of the microring resonator device 600. In some embodiments, electrical current flow non-uniformity in the ring-shaped heater 603 can cause regions of high temperature and large temperature gradients ("hot spots"), which cause reliability problems. The heat spreader fin 601 is a thermally conductive structure that serves to create a more uniform temperature profile across (circuitously around) the ring-shaped heater 603 and correspondinglyaround the ring-shaped optical waveguide 605. The heat spreader fin 601 is configured to avoid electrical connection with electrical contacts 604A and 604B of the ring-shaped heater 603. In some embodiments, the heat spreader fin(s), e.g., 601, are positioned near the fundamental optical mode within the ring-shaped optical waveguide 605 so that "temperature normalizing" heat dissipation is not wasted, but is dissipated as close as possible to the fundamental optical mode within the ring-shaped optical waveguide 605. In some embodiments, a heat spreader fin, e.g., 601, is offset from an optical coupling region between the ring-shaped optical waveguide 605 and a bus / drop optical waveguide to which the ring-shaped optical waveguide 605 is evanescently optically coupled, so as to avoid impacting the optical mode within the bus / drop optical waveguide.

[0089] Figure 6B shows a vertical cross-section view of the microring resonator device 600, referenced as View A-A in Figure 6A, in accordance with some embodiments. In some embodiments, thermal contact between the heat spreader fin 601 and the ring-shaped heater 603 is made by way of a heat spreader arm 607 and heat spreader contact 609. In some embodiments, the heat spreader contact 609 is made as a stub to avoid interrupting the electrical current flow through the ring-shaped heater 603. It should be noted that no electrical current flows into the heat spreader fin 601 from the ring-shaped heater 603. In some embodiments, the heat spreader contact 609 is positioned on the inside of the ring-shaped heater 603, such that thermal contact between the heat spreader contact 609 and the inside surface (edge / sidewall) of the ring-shaped heater 603. In this manner, the heat spreader contact 609 does not disturb the electric current flow through the ring-shaped heater 603. It should be understood that one or more heat spreader contacts, e.g., 609, and associated heat spreader arms, e.g., 607, can be disposed to thermally connect the ring-shaped heater 603 to the heat spreader fin 601. In some embodiments, the heat spreader contacts, e.g., 609, are positioned at respective azimuthal positions about a center 602 of the microring resonator device 600 where thermal hot-spots occur so as to provide for maximum mitigation of non-uniformities in temperature distribution within the ring-shaped heater 603. The thermal hot-spot is a localized region within the ring-shaped heater 603 having a local temperature that exceeds an average temperature of the ring-shaped heater 603 by a threshold amount that is indicative of hot-spot designation.

[0090] In some embodiments, a lateral / horizontal overlap 611 exists between the metal heat spreader fin 601 and the optical mode of the ring-shaped optical waveguide 605, so as to bring heat as near to the optical mode of the ring-shaped optical waveguide 605 as possible. The lateral / horizontal overlap 611 exists in a radial direction relative the center 602 of the microring resonator device 600. In these embodiments, the metal heat spreader fin 601 is vertically offset from the ring-shaped optical waveguide 605, such that the optical mode of the ring-shapedoptical waveguide 605 is not disturbed by the presence of the metal heat spreader fin 601. In this manner, the metal heat spreader fin 601 is vertically separated from the ring-shaped optical waveguide 605 by an optical mode keepout region 613.

[0091] Figure 7 shows a top view of the microring resonator device 600 of Figures 6A and 6B with a second heat spreader fin 701 disposed opposite the center 602 of the microring resonator device 600 from the (first) heat spreader fin 601, in accordance with some embodiments. Like the first heat spreader fin 601 , the second heat spreader fin 701 is also configured to make thermal contact with the ring-shaped heater 603 by way of a heat spreader arm 707 and a heat spreader contact 709. The configuration and positioning of the second heat spreader fin 701, the heat spreader arm 707, and the heat spreader contact 709 relative to the ring-shaped heater 603 and the ring-shaped optical waveguide 605 is the same as that shown in Figure 6B for the first heat spreader fin 601, the heat spreader arm 607, and the heat spreader contact 609 relative to the ring-shaped heater 603 and the ring-shaped optical waveguide 605, respectively. Also, the heat spreader fins 601 and 701 are configured to avoid physical contact with each other so as to avoid creating an electrical short. More specifically, the second heat spreader fin 701 is physically separated from the first heat spreader fin 601 by a first spacing 703 and a second spacing 705.

[0092] Figure 8 shows a top view of the microring resonator device 600 of Figures 6A and 6B with six heat spreader fins 801-1 through 801-6 disposed in a spaced apart manner azimuthally about the center 602 of the microring resonator device 600, in accordance with some embodiments. Like the first heat spreader fin 601 as shown in Figures 6 A and 6B, each of the six heat spreader fins 801-1 through 801-6 is configured to make thermal contact with the ringshaped heater 603 by way of heat spreader arms 807-1 through 807-6, respectively, and a heat spreader contacts 809-1 through 809-6, respectively. The configuration and positioning of each of the heat spreader fins 801-1 through 801-6, the heat spreader arms 807-1 through 807-6, and the heat spreader contacts 809-1 through 809-6 relative to the ring-shaped heater 603 and the ring-shaped optical waveguide 605 is the same as that shown in Figure 6B for the first heat spreader fin 601, the heat spreader arm 607, and the heat spreader contact 609 relative to the ring-shaped heater 603 and the ring-shaped optical waveguide 605, respectively. Adjacently positioned ones of the heat spreader fins 801-1 through 801-6 are separated from each other by a fin-to-fin gap 802 to avoid physical contact with each other so as to avoid creating an electrical short. While the example embodiment of Figure 8 shows six heat spreader fins 801-1 through 801-6 and associated heat spreader arms 807-1 through 807-6 and heat spreader contacts 809-1 through 809-6, it should be understood that in various embodiments the number of heat spreader fins and associated heat spreader arms and heat spreader contacts can be set as needed (either more than six, or less than six) to achieve a desired thermal uniformity (optimized temperatureuniformity) along the circuitous path of ring-shaped heater 603.

[0093] Figure 9 shows a top view of the microring resonator device 600 of Figure 7, with the first heat spreader fin 601 and the second heat spreader fin 701 azimuthally rotated about the center 602 of the microring resonator device 600 so that the first spacing 703 and the second spacing 705 between the first heat spreader fin 601 and the second heat spreader fin 701 occur at locations outside of an optical coupling region 901 between the ring-shaped optical waveguide 605 of the microring resonator device 600 and a bus optical waveguide 903, in accordance with some embodiments. It should be understood that the bus optical waveguide 903 may alternatively be a drop optical waveguide. The ring-shaped optical waveguide 605 of the microring resonator device 600 is positioned next to the bus optical waveguide 903. The ringshaped optical waveguide 605 is positioned within an evanescent optical coupling distance of the bus optical waveguide 903 around a location of closest approach of the bus optical waveguide 903 to the ring-shaped optical waveguide 605.

[0094] In the configuration of Figure 9, the first heat spreader fin 601 and the second heat spreader fin 701 are angularly offset with respect to the optical coupling region 901 between the ring-shaped optical waveguide 605 and the bus optical waveguide 903. By avoiding having the first spacing 703 and the second spacing 705 within the optical coupling region 901 near the bus optical waveguide 903, a more uniform optical coupling region 901 is provided. In some embodiments, the angular offset of the first heat spreader fin 601 and the second heat spreader fin 701 with respect to the optical coupling region 901 is designed to minimize optical reflections from the first heat spreader fin 601 and / or the second heat spreader fin 701 in the bus optical waveguide 903. Additionally, in some embodiments, such as shown in Figure 9, the angular offset of the first heat spreader fin 601 and the second heat spreader fin 701 with respect to the optical coupling region 901 is decoupled from the position and number of the heat spreader contacts 609, 709 and associated heat spreader arms 607, 707. In this manner, the position and number of the heat spreader contacts 609, 709 and associated heat spreader arms 607, 707 can be optimized separately and independently from optimization of the angular offset of the first heat spreader fin 601 and the second heat spreader fin 701 with respect to the optical coupling region 901.

[0095] Figures 6 A, 6B, 7, 8, and 9 show various embodiments of the microring resonator device 600 that includes the ring-shaped optical waveguide 605 and the ring-shaped heater 603. In some embodiments, the microring resonator device 600 is formed within an electro-optic semiconductor chip. The ring-shaped optical waveguide 605 has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped optical waveguide 605 circumscribes an interior region of the microring resonator device 600. The ring-shaped heater603 is disposed within the interior region of the microring resonator device 600. More specifically, the ring-shaped heater 603 is disposed within the interior region circumscribed by the ring-shaped optical waveguide 605. The ring-shaped heater 603 has an inner radial wall, an outer radial wall, a top surface, and a bottom surface. The ring-shaped heater 603 circumscribes the center 602 of the microring resonator device 600. In some embodiments, the outer radial wall of the ring-shaped heater 603 is physically separated from inner radial wall of the ring-shaped optical waveguide 605. The ring-shaped heater 603 is an electrically resistive heating device. The microring resonator device 600 also includes the first electrical contact 604A disposed in electrical connection with the ring-shaped heater 603, and the second electrical contact 604B disposed in electrical connection with the ring-shaped heater 603. The microring resonator device 600 also includes the heat spreader fin 601 disposed above a portion of the ring-shaped optical waveguide 605. The heat spreader fin 601 is thermally connected to the ring-shaped heater 603. The heat spreader fin 601 is electrically isolated from each of the ring-shaped heater 603, the first electrical contact 604A, and the second electrical contact 604B.

[0096] The heat spreader fin 601 has an arc shape, such that the heat spreader fin 601 extends along an arc length of the portion of the ring-shaped optical waveguide 605. The heat spreader fin 601 is physically separated from the ring-shaped optical waveguide 605 by the optical mode keepout region 613 sized to prevent optical disturbance of an optical mode within the ringshaped optical waveguide 605 by the heat spreader fin 601. The heat spreader fin 601 is configured and positioned to assist with uniform dissipation of heat within the ring-shaped optical waveguide 605. The heat spreader fin 601 is positioned for dissipation of heat within a radial section of the ring-shaped optical waveguide 605 through which a fundamental optical mode is conveyed. The ring-shaped optical waveguide 605 has a radial thickness measured between the inner radial wall and the outer radial wall of the ring-shaped optical waveguide 605. The heat spreader fin 601 laterally overlaps a portion of the radial thickness of the ring-shaped optical waveguide 605.

[0097] The first electrical contact 604A and the second electrical contact 604B are positioned to electrically contact the ring-shaped heater 603 at diametrically opposed locations along the ring-shaped heater 603. The heat spreader fin 601 is positioned on one side of the microring resonator device 600 as defined by a bisection of the microring resonator device 600 along a line extending through positions at which the first electrical contact 604A and the second electrical contact 604B electrically contact the ring-shaped heater 603. The heat spreader fin 601 has an arc shape such that the heat spreader fin 601 extends along an arc length of the ring-shaped optical waveguide 605 from a first location proximate to a position of the first electrical contact 604A to a second location proximate to a position of the second electrical contact 604B.

[0098] The microring resonator device 600 also includes the heat spreader contact 609 attached in thermal communication with the ring-shaped heater 603. The microring resonator device 600 also includes the heat spreader arm 607 configured to extend from the heat spreader contact 609 to the heat spreader fin 601. The heat spreader arm 607 is attached in thermal communication with both the heat spreader contact 609 and the heat spreader fin 601. In some embodiments, the heat spreader contact 609 is attached to the inner radial wall of the ring-shaped heater 603. In some embodiments, the heat spreader arm 607 includes a vertical segment 607V that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater 603, and a horizontal segment 607H that extends in a direction substantially parallel to the top surface of the ring-shaped heater 603. The heat spreader fin 601 has a first end, a second end, and a length extending between the first end and the second end of the heat spreader fin 601. In some embodiments, the heat spreader arm 607 is physically and thermally connected to the heat spreader fin 601 at a substantially center location along the length of the heat spreader fin 601. In some embodiments, the top surface of the ring-shaped heater 603 is substantially coplanar with the top surface of the ring-shaped optical waveguide 605. In some embodiments, the heat spreader contact 609 is positioned to avoid disturbance of electric current flow through the ringshaped heater 603.

[0099] In the embodiment of Figure 7, the heat spreader fin 601 is a first heat spreader fin 601 disposed above a first portion of the ring-shaped optical waveguide 605, with the microring resonator device 600 further including the second heat spreader fin 701 disposed above a second portion of the ring-shaped optical waveguide 605. The second heat spreader fin 701 is thermally connected to the ring-shaped heater 603. The second heat spreader fin 701 is electrically isolated from each of the ring-shaped heater 603, the first electrical contact 604A, and the second electrical contact 604B. The first heat spreader fin 601 is positioned on a first side of the microring resonator device 600, and the second heat spreader fin 701 is positioned on a second side of the microring resonator device 600, where the first side and the second side of the microring resonator device 600 are defined by a bisection of the microring resonator device 600 along a line extending through positions at which the first electrical contact 604A and the second electrical contact 604B electrically contact the ring-shaped heater 603. The first heat spreader fin 601 has an arc shape such that the first heat spreader fin 601 extends along a first arc length of the ring-shaped optical waveguide 605 from a first location proximate to a position of the first electrical contact 604A to a second location proximate to a position of the second electrical contact 604B. The second heat spreader fin 701 has an arc shape such that the second heat spreader fin 701 extends along a second arc length of the ring-shaped optical waveguide 605 from a third location proximate to the position of the first electrical contact 604A to a fourth1 location proximate to the position of the second electrical contact 604B. In some embodiments, the first arc length of the first heat spreader fin 601 is substantially equal to the second arc length of the second heat spreader fin 701. The second heat spreader fin 701 is physically separated from the first heat spreader fin 601.

[0100] Also, in the embodiment of Figure 7, the first heat spreader contact 609 is attached in thermal communication with the ring-shaped heater 603. The first heat spreader arm 607 is configured to extend from the first heat spreader contact 609 to the first heat spreader fin 601. The first heat spreader arm 607 is attached in thermal communication with both the first heat spreader contact 609 and the first heat spreader fin 601. Also, in the embodiment of Figure 7, the second heat spreader contact 709 is attached in thermal communication with the ring-shaped heater 603. The second heat spreader arm 707 is configured to extend from the second heat spreader contact 709 to the second heat spreader fin 701. The second heat spreader arm 707 is attached in thermal communication with both the second heat spreader contact 709 and the second heat spreader fin 701. The first heat spreader contact 609 and the second heat spreader contact 709 are positioned to contact the ring-shaped heater 603 at diametrically opposed locations along the ring-shaped heater 603. Each of the first heat spreader contact 609 and the second heat spreader contact 709 is positioned to avoid disturbance of electric current flow through the ring-shaped heater 603. The first heat spreader contact 609 is attached to the inner radial wall of the ring-shaped heater 603, and the second heat spreader contact 709 is attached to the inner radial wall of the ring-shaped heater 603.

[0101] The first heat spreader arm 607 includes the first vertical segment 607V that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater 603, and a first horizontal segment 607H that extends in a direction substantially parallel to the top surface of the ring-shaped heater 603. Similarly, the second heat spreader arm 707 includes a second vertical segment, e.g., like 607V, that extends in the direction substantially perpendicular to the top surface of the ring-shaped heater 603, and a second horizontal segment, e.g., like 607H, that extends in the direction substantially parallel to the top surface of the ring-shaped heater 603. The first heat spreader fin 601 has a first end, a second end, and a length extending between the first end and the second end of the first heat spreader fin 601. In some embodiments, the first heat spreader arm 607 is physically and thermally connected to the first heat spreader fin 601 at a substantially center location along the length of the first heat spreader fin 601. The second heat spreader fin 701 has a first end, a second end, and a length extending between the first end and the second end of the second heat spreader fin 701. In some embodiments, the second heat spreader arm 707 is physically and thermally connected to the second heat spreader fin 701 at a substantially center location along the length of the second heat spreader fin 701. In someembodiments, such as shown in Figure 7, the top surface of the ring-shaped heater 603 is substantially coplanar with the top surface of the ring-shaped optical waveguide 605.

[0102] In the embodiment of Figure 8, the microring resonator device 600 includes a plurality of heat spreader fins 801-1 to 801-6. Each of the plurality of heat spreader fins 801-1 to 801-6 is disposed above a respective portion of the ring-shaped optical waveguide 605. Each of the plurality of heat spreader fins 801-1 to 801-6 is thermally connected to the ring-shaped heater 603. Each of the plurality of heat spreader fins 801-1 to 801-6 is physically separated from any other of the plurality of heat spreader fins 801-1 to 801-6. Each of the plurality of heat spreader fins 801-1 to 801-6 is electrically isolated from each of the ring-shaped heater 603, the first electrical contact 604A, and the second electrical contact 604B.

[0103] Also, in the embodiment of Figure 8, the microring resonator device 600 includes a plurality of heat spreader contacts 809- 1 to 809-6 attached in thermal communication with the ring-shaped heater 603. The microring resonator device 600 also includes a plurality of heat spreader arms 807-1 to 807-6. Each of the plurality of heat spreader arms 807-1 to 807-6 is configured to extend from a respective one of the plurality of heat spreader contacts 809- 1 to 809-6 to a respective one of the plurality of heat spreader fins 801-1 to 801-6. Each of the plurality of heat spreader arms 807-1 to 807-6 is attached in thermal communication with both the respective one of the plurality of heat spreader contacts 809- 1 to 809-6 and the respective one of the plurality of heat spreader fins 801-1 to 801-6. In some embodiments, the plurality of heat spreader contacts 809-1 to 809-6 are positioned at substantially equally spaced apart locations along the circumference of the ring-shaped heater 603. In some embodiments, each of the plurality of heat spreader contacts 809-1 to 809-6 is positioned to avoid disturbance of electric current flow through the ring-shaped heater 603. In some embodiments, each of the plurality of heat spreader contacts 809-1 to 809-6 is attached to the inner radial wall of the ringshaped heater 603. Each of the plurality of heat spreader arms 807-1 to 807-6 includes a respective vertical segment, e.g., 607V, that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater 603, and a respective horizontal segment, e.g., 607H, that extends in a direction substantially parallel to the top surface of the ring-shaped heater 603.

[0104] In some embodiments, each of the plurality of heat spreader fins 801-1 to 801-6 has a substantially same shape and size. In some embodiments, each of the plurality of heat spreader fins 801-1 to 801-6 is separated from each adjacently positioned one of the plurality of heat spreader fins 801-1 to 801-6 by a substantially same distance. In some embodiments, the plurality of heat spreader fins 801-1 to 801-6 is six heat spreader fins 801-1 to 801-6, and the plurality of heat spreader contacts 809-1 to 809-6 is six heat spreader contacts 809-1 to 809-6, and the plurality of heat spreader arms 807-1 to 807-6 is six heat spreader arms 807-1 to 807-6.

[0105] In the embodiment of Figure 9, the plurality of heat spreader fins is the two heat spreader fins 601, 701, and the plurality of heat spreader contacts is the two heat spreader contacts 609, 709, and the plurality of heat spreader arms is the two heat spreader arms 607, 707. In the embodiment of Figure 9, a bus optical waveguide 903 is positioned to extend past the ringshaped optical waveguide 605 and within an evanescent optical coupling distance of the ringshaped optical waveguide 605, such that an optical coupling region 901 exists between the bus optical waveguide 903 and the ring-shaped optical waveguide 605. The plurality of heat spreader fins 601, 701 are azimuthally rotated about the center 602 of the microring resonator device 600, so that each of the first spacing 703 and the second spacing 705 between the plurality of heat spreader fins 601 and 701 is located outside of the optical coupling region 901 between the bus optical waveguide 903 and the ring-shaped optical waveguide 605.

[0106] Figure 10 shows a top view of a microring resonator device 1000 that implements a doped silicon heater 1003 to generate heat within a ring-shaped optical waveguide 1005, in accordance with some embodiments. In some embodiments, the microring resonator device 1000 is formed within an electro-optic semiconductor chip. The example configuration of Figure 10 shows the microring resonator device 1000 disposed next to a first optical waveguide 1015 and next to a second optical waveguide 1017. In various embodiments, the first optical waveguide 1015 serves as either a bus optical waveguide or a drop optical waveguide. Also, in various embodiments, the second optical waveguide 1017 serves as either a bus optical waveguide or a drop optical waveguide. The ring-shaped optical waveguide 1005 and the first optical waveguide 1015 are positioned within an evanescent optical coupling distance of each other, such that an optical coupling region 1016 exists between the first optical waveguide 1015 and the ring-shaped optical waveguide 1005 around a location of closest approach of the first optical waveguide 1015 to the ring-shaped optical waveguide 1005. Similarly, the ring-shaped optical waveguide 1005 and the second optical waveguide 1017 are positioned within an evanescent optical coupling distance of each other, such that an optical coupling region 1019 exists between the second optical waveguide 1017 and the ring-shaped optical waveguide 1005 around a location of closest approach of the second optical waveguide 1017 to the ring-shaped optical waveguide 1005.

[0107] The doped silicon heater 1003 includes an inner p++ doped region 1003 A formed within the region circumscribed by the ring-shaped optical waveguide 1005 and next to the optical coupling region 1016. The doped silicon heater 1003 also includes a high-resistance p doped region 1003B formed across and through the ring-shaped optical waveguide 1005 within the optical coupling region 1016. The doped silicon heater 1003 also includes an intermediate p+ doped region 1003C formed between the inner p++ doped region 1003 A and the high-resistance p doped region 1003B so as to electrically link the inner p++ doped region 1003 A to the high-resistance p doped region 1003B. The doped silicon heater 1003 also includes an outer p++ doped region 1003D formed on an opposite side of the first optical waveguide 1015 relative to the inner p++ doped region 1003A. The doped silicon heater 1003 also includes an intermediate p+ doped region 1003E formed across and through the first optical waveguide 1015 within the optical coupling region 1016 so as to electrically link the outer p++ doped region 1003D to the high-resistance p doped region 1003B. The inner p++ doped region 1003A and the outer p++ doped region 1003D represent the lowest electrical resistance regions within the doped silicon heater 1003. The high-resistance p doped region 1003B represents the highest electrical resistance regions within the doped silicon heater 1003. The intermediate p+ doped region 1003C and the intermediate p+ doped region 1003E have an intermediate electrical resistance that is between the high electrical resistance of the high-resistance p doped region 1003B and the low electrical resistance of the inner p++ doped region 1003A and the outer P++ doped region 1003D.

[0108] The doped silicon heater 1003 also includes a number of inner electrical contacts 1021 formed to electrically contact the inner p++ doped region 1003A. The number and positions of the inner electrical contacts 1021 is determined to provide for substantially uniform electrical potential across the inner p++ doped region 1003A. The doped silicon heater 1003 also includes a number of outer electrical contacts 1023 formed to electrically contact the outer p++ doped region 1003D. The number and positions of the outer electrical contacts 1023 is determined to provide for substantially uniform electrical potential across the outer P++ doped region 1003D. During operation, a first voltage potential is applied to the inner electrical contacts 1021 and a second voltage potential is applied to the outer electrical contacts 1023. A voltage difference between the first voltage potential and the second voltage potential is controlled to cause an electrical current to flow between the inner p++ doped region 1003A and the outer P++ doped region 1003D, such that the electrical current flows through the intermediate p+ doped region 1003C, the high-resistance p doped region 1003B, and the intermediate p+ doped region 1003E. The electrical current flow through the high-resistance p doped region 1003B causes an increase in temperature within the high-resistance p doped region 1003B. For this reason, the high- resistance p doped region 1003B is formed within the optical mode of the ring-shaped optical waveguide 1005, such that operation of the doped silicon heater 1003 provides for control of the temperature of the ring-shaped optical waveguide 1005 within the optical coupling region 1016.

[0109] While the example embodiment of Figure 10 shows use of p-type semiconductor dopants to form the doped silicon heater 1003, it should be understood that in other embodiments the doped silicon heater 1003 can be formed in an equivalent manner using n-type semiconductor dopants. Also, while the example embodiment of Figure 10 shows the doped silicon heater 1003 formed primarily across the optical coupling region 1016 between the optical waveguide 1015and the ring-shaped optical waveguide 1005, it should be understood that in other embodiments the doped silicon heater 1003 can be formed over any amount of the arc length (azimuthal extent) of the ring-shaped optical waveguide 1005 and over any location along the ring-shaped optical waveguide 1005. Also, in some embodiments, multiple doped silicon heaters, e.g., 1003, are formed at respective locations along the arc length of the ring-shaped optical waveguide 1005.

[0110] In some embodiments, Figure 10 shows a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 1005, the bus optical waveguide 1015, the first doped region 1003A, the second doped region 1003D, and the third doped region 1003B. The ring-shaped optical waveguide 1005 circumscribes an interior region of the microring resonator device 1000. The bus optical waveguide 1015 extends past the ring-shaped optical waveguide 1005 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 1005, such that the optical coupling region 1016 exists between the bus optical waveguide 1015 and the ring-shaped optical waveguide 1005. The first doped region 1003A is formed within the interior region of the microring resonator device 1000 at a location adjacent to the optical coupling region 1016. The first doped region 1003A is electrically conductive. The second doped region 1003D is formed along a side of the bus optical waveguide 1015 that is opposite from the ring-shaped optical waveguide 1005. The second doped region 1003D is formed at a location adjacent to the optical coupling region 1016. The second doped region 1003D is electrically conductive. The third doped region 1003B is formed between the first doped region 1003 A and the second doped region 1003D through the optical coupling region 1016, and through both a portion of the ring-shaped optical waveguide 1005 and a portion of the bus optical waveguide 1015. An electrical resistance of the third doped region 1003B is higher than an electrical resistance within each of the first doped region 1003 A and the second doped region 1003D. The third doped region 1003B is configured to increase in temperature when an electrical current flows between the first doped region 1003A and second doped region 1003D through the third doped region 1003B.

[0111] The first plurality of electrical contacts 1021 are disposed in electrical connection with the first doped region 1003A. The second plurality of electrical contacts 1023 are disposed in electrical connection with the second doped region 1003D. The first plurality of electrical contacts 1021 and the second plurality of electrical contacts 1023 are positioned such that the electrical current flow between the first doped region 1003A and the second doped region 1003D, by way of the first plurality of electrical contacts 1021 and the second plurality of electrical contacts 1023) is substantially uniform across the third doped region 1003B. The first intermediate doped region 1003C is disposed between the first doped region 1003A and the third doped region 1003B. The first intermediate doped region 1003C is configured to electrically linkthe first doped region 1003 A and the third doped region 1003B. The second intermediate doped region 1003E is disposed between the second doped region 1003D and the third doped region 1003B. The second intermediate doped region 1003E is configured to electrically link the second doped region 1003D and third doped region 1003B. In some embodiments, each of the first doped region 1003A and the second doped region 1003D has a p++ doping, each of the first intermediate doped region 1003C and the second intermediate doped region 1003E has a p+ doping, and the third doped region 1003B has a p doping. In some embodiments, the third doped region 1003B is substantially confined within the portion of the ring-shaped optical waveguide 1005 located between the first doped region 1003A and the second doped region 1003D.

[0112] Figure 11 shows a top view of a microring resonator device 1100 that further implements a PN junction region within the ring-shaped optical waveguide 1005 for optical modulation in combination with the doped silicon heater 1003 to generate heat within the ring-shaped optical waveguide 1005, in accordance with some embodiments. The PN junction region is formed at an interface between a p++ region 1131 and an n++ region 1133 within the ring-shaped optical waveguide 1005. A number of electrical contacts 1135 are formed to electrically contact the p++ region 1131. The number and positions of the electrical contacts 1135 are determined to provide for substantially uniform electrical potential across the p++ region 1131. A number of electrical contacts 1137 are formed to electrically contact the n++ doped region 1133. The number and positions of the electrical contacts 1137 are determined to provide for substantially uniform electrical potential across the n++ doped region 1133. During operation, a temporally controlled first voltage potential is applied to the electrical contacts 1135, and a temporally controlled second voltage potential is applied to the electrical contacts 1137. The respective temporally controlled voltages that are applied to the p++ doped region 1131 and the n++ doped region 1133 provide for controlled modulation of light propagating within the ring-shaped optical waveguide 1005, by way of the PN junction region.

[0113] The PN junction region for light modulation is formed along most of the arc length of the ring-shaped optical waveguide 1005, with the balance of the ring-shaped optical waveguide 1005 used for implementation of the doped silicon heater 1003. The n-type modulator dopants (n++ doped region 1133) are located between the p-type dopants of the doped silicon heater 1003 and the p-type modulator dopants (p++ doped region 1131), which provides for electrical isolation of the doped silicon heater 1003 from the PN junction used for optical modulation. Also, while the example embodiment of Figure 11 shows use of p-type semiconductor dopants to form the doped silicon heater 1003, it should be understood that in other embodiments the doped silicon heater 1003 can be formed in an equivalent manner using n-type semiconductor dopants. In these other embodiments, the n++ doped region 1133 is instead formed as a p++doped region, and the p++ doped region 1131 is instead formed as an n++ doped region, such that the doped silicon heater 1003 is electrically isolated from the PN junction used for optical modulation.

[0114] In some embodiments, the microring resonator device 1100 of Figure 11 is a modification of the microring resonator device 1000 of Figure 10. In this manner, Figure 11 shows a portion of an electro-optical semiconductor chip that includes the features previously described with regard to Figure 10. The electro-optical semiconductor chip in which the microring resonator device 1100 is formed further includes the n++ doped region 1133 formed within the interior region of the microring resonator device 1100 along the ring-shaped optical waveguide 1005, and outside of the first doped region 1003A. The n++ doped region 1133 is formed within an inner radial portion of the ring-shaped optical waveguide 1005. The electro- optical semiconductor chip in which the microring resonator device 1100 is formed also includes the third plurality of electrical contacts 1137 disposed in electrical connection with the n+- 1- doped region 1133. The electro-optical semiconductor chip in which the microring resonator device 1100 is formed also includes the p++ doped region 1131 formed along an outside of the ring-shaped optical waveguide 1005, and outside of both the first doped region 1003A and the third doped region 1003B. The P++ doped region 1131 is formed within an outer radial portion of the ring-shaped optical waveguide 1005 such that the p++ doped region 1131 and the n++ doped region 1133 interface with each other to form a PN junction within the ring-shaped optical waveguide 1005. The electro-optical semiconductor chip in which the microring resonator device 1100 is formed also includes the fourth plurality of electrical contacts 1135 disposed in electrical connection with the p++ doped region 1131. The n++ doped region 1133 and the p++ doped region 1131 are collectively configured to control modulation of light propagating within the ring-shaped optical waveguide 1005, in accordance with application of temporally controlled voltages to the n++ doped region 1133 and the p++ doped region 1131 by way of the third plurality of electrical contacts 1137 and the fourth plurality of electrical contacts 1135, respectively.

[0115] Figure 12 shows a top view of a microring resonator device 1200 that implements a first doped silicon heater 1203 and a second doped silicon heater 1204 to generate heat within a ring- shaped optical waveguide 1205, in accordance with some embodiments. In some embodiments, the microring resonator device 1200 is formed within an electro-optic semiconductor chip. The example configuration of Figure 12 shows the microring resonator device 1200 disposed next to a first optical waveguide 1215 and next to a second optical waveguide 1217. In various embodiments, the first optical waveguide 1215 serves as either a bus optical waveguide or a drop optical waveguide. Also, in various embodiments, the second optical waveguide 1217 serves aseither a bus optical waveguide or a drop optical waveguide. The ring-shaped optical waveguide 1205 and the first optical waveguide 1215 are positioned within an evanescent optical coupling distance of each other, such that an optical coupling region 1216 exists between the first optical waveguide 1215 and the ring-shaped optical waveguide 1205 around a location of closest approach of the first optical waveguide 1215 to the ring-shaped optical waveguide 1205. Similarly, the ring-shaped optical waveguide 1205 and the second optical waveguide 1217 are positioned within an evanescent optical coupling distance of each other, such that an optical coupling region 1219 exists between the second optical waveguide 1217 and the ring-shaped optical waveguide 1205 around a location of closest approach of the second optical waveguide 1217 to the ring-shaped optical waveguide 1205. Each of the first doped silicon heater 1203 and the second doped silicon heater 1204 is configured to avoid overlapping either of the first optical waveguide 1215 and the second optical waveguide 1217. More specifically, the first doped silicon heater 1203 is formed over a left half of the ring-shaped optical waveguide 1205 within a region between the first optical waveguide 1215 and the second optical waveguide 1217. Similarly, the second doped silicon heater 1204 is formed over a right half of the ring-shaped optical waveguide 1205 within a region between the first optical waveguide 1215 and the second optical waveguide 1217.

[0116] The first doped silicon heater 1203 includes an inner p++ doped region 1203 A formed within the region circumscribed by the ring-shaped optical waveguide 1205. The first doped silicon heater 1203 also includes a high-resistance p doped region 1203B formed across and through the ring-shaped optical waveguide 1205. The first doped silicon heater 1203 also includes an intermediate p+ doped region 1203C formed between the inner p++ doped region 1203 A and the high-resistance p doped region 1203B so as to electrically link the inner p++ doped region 1203A to the high-resistance p doped region 1203B. The first doped silicon heater 1203 also includes an outer p++ doped region 1203D formed on an opposite side of the ring- shaped optical waveguide 1205 relative to the inner p++ doped region 1203A. The first doped silicon heater 1203 also includes an intermediate p+ doped region 1203E formed between the outer P++ doped region 1203D and the high-resistance p doped region 1203B so as to electrically link the outer p++ doped region 1203D to the high-resistance p doped region 1203B. The inner P++ doped region 1203 A and the outer p++ doped region 1203D represent the lowest electrical resistance regions within the first doped silicon heater 1203. The high-resistance p doped region 1203B represents the highest electrical resistance region within the first doped silicon heater 1203. The intermediate p+ doped region 1203C and the intermediate p+ doped region 1203E have an intermediate electrical resistance that is between the high electrical resistance of the high-resistance p doped region 1203B and the low electrical resistance of the inner p++ dopedregion 1203 A and the outer p++ doped region 1203D.

[0117] The first doped silicon heater 1203 also includes a number of inner electrical contacts 1221 formed to electrically contact the inner p++ doped region 1203A. The number and positions of the inner electrical contacts 1221 are determined to provide for substantially uniform electrical potential across the inner p++ doped region 1203A. The first doped silicon heater 1203 also includes a number of outer electrical contacts 1223 formed to electrically contact the outer p++ doped region 1203D. The number and positions of the outer electrical contacts 1223 are determined to provide for substantially uniform electrical potential across the outer p++ doped region 1203D. During operation, a first voltage potential is applied to the inner electrical contacts 1221 and a second voltage potential is applied to the outer electrical contacts 1223. A voltage difference between the first voltage potential and the second voltage potential is controlled to cause an electrical current to flow between the inner p++ doped region 1203A and the outer p++ doped region 1203D, such that the electrical current flows through the intermediate p+ doped region 1203C, the high-resistance p doped region 1203B, and the intermediate p+ doped region 1203E. The electrical current flow through the high-resistance p doped region 1203B causes an increase in temperature within the high-resistance p doped region 1203B. For this reason, the high-resistance p doped region 1203B is formed within the optical mode of the ring-shaped optical waveguide 1205, such that operation of the first doped silicon heater 1203 provides for control of the temperature of the left half of the ring-shaped optical waveguide 1205.

[0118] While the example embodiment of Figure 12 shows use of p-type semiconductor dopants to form the first doped silicon heater 1203, it should be understood that in other embodiments the first doped silicon heater 1203 can be formed in an equivalent manner using n-type semiconductor dopants. Also, while the example embodiment of Figure 12 shows the first doped silicon heater 1203 formed primarily across the left half of the ring-shaped optical waveguide 1205, it should be understood that in other embodiments the first doped silicon heater 1203 can be formed over another amount of the arc length (azimuthal extent) of the ring-shaped optical waveguide 1205.

[0119] The second doped silicon heater 1204 includes an inner p++ doped region 1204A formed within the region circumscribed by the ring-shaped optical waveguide 1205. The second doped silicon heater 1204 also includes a high-resistance p doped region 1204B formed across and through the ring-shaped optical waveguide 1205. The second doped silicon heater 1204 also includes an intermediate p+ doped region 1204C formed between the inner p++ doped region 1204A and the high-resistance p doped region 1204B so as to electrically link the inner p++ doped region 1204 A to the high-resistance p doped region 1204B. The second doped silicon heater 1204 also includes an outer p++ doped region 1204D formed on an opposite side of thering-shaped optical waveguide 1205 relative to the inner p++ doped region 1204A. The second doped silicon heater 1204 also includes an intermediate p+ doped region 1204E formed between the outer p++ doped region 1204D and the high-resistance p doped region 1204B so as to electrically link the outer p++ doped region 1204D to the high-resistance p doped region 1204B. The inner p++ doped region 1204A and the outer p++ doped region 1204D represent the lowest electrical resistance regions within the second doped silicon heater 1204. The high-resistance p doped region 1204B represents the highest electrical resistance region within the second doped silicon heater 1204. The intermediate p+ doped region 1204C and the intermediate p+ doped region 1204E have an intermediate electrical resistance that is between the high electrical resistance of the high-resistance p doped region 1204B and the low electrical resistance of the inner p++ doped region 1204A and the outer p++ doped region 1204D.

[0120] The second doped silicon heater 1204 also includes a number of inner electrical contacts 1225 formed to electrically contact the inner p++ doped region 1204A. The number and positions of the inner electrical contacts 1225 is determined to provide for substantially uniform electrical potential across the inner p++ doped region 1204A. The second doped silicon heater 1204 also includes a number of outer electrical contacts 1227 formed to electrically contact the outer p++ doped region 1204D. The number and positions of the outer electrical contacts 1227 is determined to provide for substantially uniform electrical potential across the outer p++ doped region 1204D. During operation, a first voltage potential is applied to the inner electrical contacts 1225 and a second voltage potential is applied to the outer electrical contacts 1227. A voltage difference between the first voltage potential and the second voltage potential is controlled to cause an electrical current to flow between the inner p++ doped region 1204A and the outer p++ doped region 1204D, such that the electrical current flows through the intermediate p+ doped region 1204C, the high-resistance p doped region 1204B, and the intermediate p+ doped region 1204E. The electrical current flow through the high-resistance p doped region 1204B causes an increase in temperature within the high-resistance p doped region 1204B. For this reason, the high-resistance p doped region 1204B is formed within the optical mode of the ring-shaped optical waveguide 1205, such that operation of the second doped silicon heater 1204 provides for control of the temperature of the right half of the ring-shaped optical waveguide 1205.

[0121] While the example embodiment of Figure 12 shows use of p-type semiconductor dopants to form the second doped silicon heater 1204, it should be understood that in other embodiments the second doped silicon heater 1204 can be formed in an equivalent manner using n-type semiconductor dopants. Also, while the example embodiment of Figure 12 shows the second doped silicon heater 1204 formed primarily across the right half of the ring-shaped optical waveguide 1205, it should be understood that in other embodiments the second doped siliconheater 1204 can be formed over another amount of the arc length (azimuthal extent) of the ringshaped optical waveguide 1205.

[0122] In some embodiments, Figure 12 shows a portion of an electro-optical semiconductor chip that includes the ring-shaped optical waveguide 1205, the first bus optical waveguide 1215, the second bus optical waveguide 1217, the first doped region 1203 A, the second doped region 1203D, and the third doped region 1203B. The ring-shaped optical waveguide 1205 circumscribes an interior region of a microring resonator device 1200. The first bus optical waveguide 1215 extends past the ring-shaped optical waveguide 1205 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 1205, such that the first optical coupling region 1216 exists between the first bus optical waveguide 1215 and the ring-shaped optical waveguide 1205. The second bus optical waveguide 1217 extends past the ring-shaped optical waveguide 1205 and within an evanescent optical coupling distance of the ring-shaped optical waveguide 1205, such that the second optical coupling region 1219 exists between the second bus optical waveguide 1217 and the ring-shaped optical waveguide 1205. The second bus optical waveguide 1217 and the first bus optical waveguide 1215 are configured substantially parallel with each other on opposite sides of the ring-shaped optical waveguide 1205. The first doped region 1203A is formed within the interior region of the microring resonator device 1200. The first doped region 1203A is electrically conductive. The second doped region 1203D is formed outside of the ring-shaped optical waveguide 1205 within a region located between the first bus optical waveguide 1215 and the second bus optical waveguide 1217. The second doped region 1203D is electrically conductive. The third doped region 1203B is formed between the first doped region 1203 A and the second doped region 1203D through a portion of the ring- shaped optical waveguide 1205. The third doped region 1203B is located between the first bus optical waveguide 1215 and the second bus optical waveguide 1217. An electrical resistance of the third doped region 1203B is higher than an electrical resistance within each of the first doped region 1203 A and the second doped region 1203D. The third doped region 1203B is configured to increase in temperature when an electrical current flows between the first doped region 1203A and the second doped region 1203D through the third doped region 1203B.

[0123] The first plurality of electrical contacts 1221 are disposed in electrical connection with the first doped region 1203A. The second plurality of electrical contacts 1223 are disposed in electrical connection with the second doped region 1203D. The first plurality of electrical contacts 1221 and the second plurality of electrical contacts 1223 are positioned such that the electrical current flow between the first doped region 1203A and the second doped region 1203D is substantially uniform across the third doped region 1203B.

[0124] In some embodiments, the first intermediate doped region 1203C is disposed betweenthe first doped region 1203 A and the third doped region 1203D. The first intermediate doped region 1203C is configured to electrically link the first doped region 1203A and the third doped region 1203B. The second intermediate doped region 1203E is disposed between the second doped region 1203D and the third doped region 1203B. The second intermediate doped region 1203E is configured to electrically link the second doped region 1203D and third doped region 1203B. In some embodiments, each of the first doped region 1203 A and the second doped region 1203D has a p++ doping, each of the first intermediate doped region 1203C and the second intermediate doped region 1203E has a p+ doping, and the third doped region 1203B has a p doping. In some embodiments, the third doped region 1203B is substantially confined within the portion of the ring-shaped optical waveguide 1205 located between the first doped region 1203A and the second doped region 1203D.

[0125] Figure 13A shows a top view of a microring resonator device 1300 that implements an embedded thermal heater 1301 within a ring-shaped optical waveguide 1305, in accordance with some embodiments. Figure 13B shows a vertical cross-section slice through the microring resonator device 1300, referenced as View A- A in Figure 13 A, in accordance with some embodiments. In some embodiments, the microring resonator device 1300 is formed within an electro-optic semiconductor chip. In some embodiments, the ring-shaped optical waveguide 1305 is formed as a single piece of silicon or other optical waveguide material that supports both an optical mode 1303 and the embedded thermal heater 1301. A portion of the silicon of the ring-shaped optical waveguide 1305 is provisioned for use as the embedded thermal heater 1301. In the example of Figures 13A and 13B, an inner annular region 1305A of the ring-shaped optical waveguide 1305 is provisioned for use as the embedded thermal heater 1301, and an outer annular region 1305B of the ring-shaped optical waveguide 1305 is provisioned for use as a waveguide for the optical mode 1303. A spatial separation region 1305C exists between the inner annular region 1305 A and the outer annular region 1305B so as to spatially separate the embedded thermal heater 1301 from the optical mode 1303. The spatial separation region 1305C is configured to ensure that the optical mode 1303 is not disturbed by the embedded thermal heater 1301.

[0126] As shown in Figure 13B, in some embodiments, the spatial separation region 1305C has a same full-thickness (vertical thickness) as the inner annular region 1305A and the outer annular region 1305B of the ring-shaped optical waveguide 1305. In these embodiments, separation of the optical mode 1303 from the embedded thermal heater 1301 is achieved by sufficient radial spacing between the inner annular region 1305 A and the outer annular region 1305B of the ring- shaped optical waveguide 1305. Having the embedded thermal heater 1301 within the same piece of silicon as the optical mode 1303 enables efficient heat transfer from the embeddedthermal heater 1301 to the outer annular region 1305B within which the optical mode 1303 is guided, which increases the thermal efficiency of the microring resonator device 1300 by keeping the temperature of the outer annular region 1305B within which the optical mode 1303 is guided as close as possible to the temperature of the embedded thermal heater 1301.

[0127] Figure 14A shows a top view of a microring resonator device 1400 that implements an embedded thermal heater 1401 within a ring-shaped optical waveguide 1405, in accordance with some embodiments. Figure 14B shows a vertical cross-section slice through the microring resonator device 1400, referenced as View A-A in Figure 14A, in accordance with some embodiments. In some embodiments, the microring resonator device 1400 is formed within an electro-optic semiconductor chip. In some embodiments, the ring-shaped optical waveguide 1405 is formed as a single piece of silicon or other optical waveguide material that supports both an optical mode 1403 and the embedded thermal heater 1401. A portion of the silicon of the ring-shaped optical waveguide 1405 is provisioned for use as the embedded thermal heater 1401. In the example of Figures 14A and 14B, a full-thickness (vertical thickness) inner annular region 1405A of the ring-shaped optical waveguide 1405 is provisioned for use as the embedded thermal heater 1401, and a full-thickness (vertical thickness) outer annular region 1405B of the ring-shaped optical waveguide 1405 is provisioned for use as a waveguide for the optical mode 1403. A partial-thickness (vertical thickness) spatial separation region 1405C exists between the inner annular region 1405A and the outer annular region 1405B so as to spatially separate the embedded thermal heater 1401 from the optical mode 1403. The spatial separation region 1405C is configured to ensure that the optical mode 1403 is not disturbed by the embedded thermal heater 1401.

[0128] As shown in Figure 14B, in some embodiments, the spatial separation region 1405C has a partial vertical thickness as compared with the full vertical thickness of each of the inner annular region 1405A and the outer annular region 1405B of the ring-shaped optical waveguide 1405. In these embodiments, separation of the optical mode 1403 from the embedded thermal heater 1401 is achieved by a combination of the partial thickness of the spatial separation region 1405C and a sufficient radial spacing between the inner annular region 1405A and the outer annular region 1405B of the ring-shaped optical waveguide 1405. Having the spatial separation region 1405C formed with partial vertical thickness allows the radial distance across the spatial separation region 1405C to be lower as compared to the radial distance across the full-thickness spatial separation region 1305C in the embodiment of Figures 13A and 13B, while ensuring that the optical mode 1403 is optically isolated from the embedded thermal heater 1401. Also, having the embedded thermal heater 1401 within the same piece of silicon as the optical mode 1403 enables efficient heat transfer from the embedded thermal heater 1401 to the outer annular region1405B within which the optical mode 1403 is guided, which increases the thermal efficiency of the microring resonator device 1400 by keeping the temperature of the outer annular region 1405B within which the optical mode 1403 is guided as close as possible to the temperature of the embedded thermal heater 1401.

[0129] In the embodiments of Figure 14A and 14B, the microring resonator device 1400 includes the ring-shaped optical waveguide 1405, which includes the outer annular region 1405B, the inner annular region 1405A, and the spatial separation region 1405C extending between the outer annular region 1405B and the inner annular region 1405 A. The outer annular region 1405B is a radial section of the ring-shaped optical waveguide 1405 through which a fundamental optical mode 1403 is conveyed. The inner annular region 1405A is a radial section of the ring-shaped optical waveguide 1405 that is configured as an embedded thermal heater 1401. The spatial separation region 1405C is a radial section of the ring-shaped optical waveguide 1405 that has a radial width sufficient to spatially separate the embedded thermal heater 1401 within the inner annular region 1405A from the optical mode 1403 within the outer annular region 1405B. In some embodiments, the outer annular region 1405B, the inner annular region 1405A, and the spatial separation region 1405C are separate portions of a single piece of optical waveguide material that forms the ring-shaped optical waveguide 1405. In some embodiments, the ring-shaped optical waveguide 1405 is formed of silicon. In some embodiments, the outer annular region 1405B has a first vertical height, the inner annular region 1405A has a second vertical height, and the spatial separation region 1405C has a third vertical height, where the third vertical height is less than each of the first vertical height and the second vertical height. In some embodiments, the second vertical height of the inner annular region 1405A is substantially equal to the first vertical height of the outer annular region 1405B. The spatial separation region 1405C is contiguously formed with both the outer annular region 1405B and the inner annular region 1405A. In some embodiments, a bottom surface of the spatial separation region 1405C is coplanar with both a bottom surface of the outer annular region 1405B and a bottom surface of the inner annular region 1405A. In some embodiments, such as shown in Figures 13A and 13B, each of the outer annular region 1405B, the inner annular region 1405A, and the spatial separation region 1405C has a same vertical height.

[0130] In some embodiments, the embedded thermal heater 1401 within the inner annular region 1405A is an electrical resistance heater. In some embodiments, the inner annular region 1405A is doped with impurities to achieve a target electrical resistance for the embedded thermal heater 1401. In some embodiments, a plurality of electrical contacts 1413A, 1413B are electrically connected to the inner annular region 1405 A. At least one of the plurality of electrical contacts 1413 A, 1413B is electrically connected to an electrical power supply, and at least oneof the plurality of electrical contacts 1413A, 1413B is electrically connected to a reference ground potential. In this manner, a controlled electrical current is made to flow through the embedded thermal heater 1401.

[0131] Figure 15A shows a top view of a microring resonator device 1500 that implements both a first embedded thermal heater 1501 and a second embedded thermal heater 1502 on an outer wall of a ring-shaped optical waveguide 1505, in accordance with some embodiments. Figure 15B shows a vertical cross-section slice through the microring resonator device 1500, reference as View A- A in Figure 15 A, in accordance with some embodiments. In some embodiments, the microring resonator device 1500 is formed within an electro-optic semiconductor chip. In some embodiments, it is desirable to have the inner region of the ring-shaped optical waveguide 1505 accessible for modulator doping and associated modulator electrical contact formation. Therefore, in these embodiments, the embedded thermal heaters of the microring resonator device 1500 should be positioned somewhere other than along the inner region of the ring-shaped optical waveguide 1505. To this end, the example embodiment of Figures 15A and 15B has the first embedded thermal heater 1501 positioned along the outer wall of the left half of the ring- shaped optical waveguide 1505, and the second embedded thermal heater 1502 positioned along the outer wall of the right half of the ring-shaped optical waveguide 1505.

[0132] The ring-shaped optical waveguide 1505 is configured as a rib-style optical waveguide by having a full-thickness (vertical thickness) annular portion 1505A, an inner partial-thickness (vertical thickness) annular portion 1505B formed along the inner edge of annular portion 1505 A, and an outer partial-thickness (vertical thickness) annular portion 1505C formed along the outer edge of annular portion 1505 A. The rib-style ring-shaped optical waveguide 1505 confines the optical mode within the full-thickness annular portion 1505A. The example of Figures 15A and 15B also show the microring resonator device 1500 positioned next to a first optical waveguide 1507 and a second optical waveguide 1509. In various embodiments, the first optical waveguide 1507 serves as either a bus optical waveguide or a drop optical waveguide. Similarly, in various embodiments, the second optical waveguide 1509 serves as either a bus optical waveguide or a drop optical waveguide.

[0133] In some embodiments, the first optical waveguide 1507 is configured as a rib-style optical waveguide by having a full-thickness (vertical thickness) central portion 1507A, a first partial-thickness (vertical thickness) side portion 1507B formed along a first side of the central portion 1507A, and a second partial-thickness (vertical thickness) side portion 1507C formed along a second side of the central portion 1507A. The first optical waveguide 1507 extends past the ring-shaped optical waveguide 1505. In some embodiments, the ring-shaped optical waveguide 1505 and the first optical waveguide 1507 are positioned within an evanescent opticalcoupling distance of each other within an optical coupling region 1511, around a location of closest approach of the first optical waveguide 1507 to the ring-shaped optical waveguide 1505. In some embodiments, the first partial-thickness side portion 1507B of the first optical waveguide 1507 is formed integrally with the outer partial-thickness annular portion 1505C of the ring-shaped optical waveguide 1505.

[0134] In some embodiments, the second optical waveguide 1509 is configured as a rib-style optical waveguide by having a full-thickness (vertical thickness) central portion 1509A, a first partial-thickness (vertical thickness) side portion 1509B formed along a first side of the central portion 1509A, and a second partial-thickness (vertical thickness) side portion 1509C formed along a second side of the central portion 1509A. The second optical waveguide 1509 extends past the ring-shaped optical waveguide 1505. In some embodiments, the ring-shaped optical waveguide 1505 and the second optical waveguide 1509 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 1513, around a location of closest approach of the second optical waveguide 1509 to the ring-shaped optical waveguide 1505. In some embodiments, the first partial-thickness side portion 1509B of the second optical waveguide 1509 is formed integrally with the outer partial-thickness annular portion 1505C of the ring-shaped optical waveguide 1505.

[0135] The first embedded thermal heater 1501 is positioned along the outer wall of the left half of the ring-shaped optical waveguide 1505 between the first optical waveguide 1507 and the second optical waveguide 1509. Similarly, the second embedded thermal heater 1502 is positioned along the outer wall of the right half of the ring-shaped optical waveguide 1505 between the first optical waveguide 1507 and the second optical waveguide 1509. The partial thickness of the annular portion 1505C along the outer edge of ring-shaped optical waveguide 1505 provides a partial thickness silicon bridging between the optical mode within the fullthickness annular portion 1505 A of the ring-shaped optical waveguide 1505 and each of the first embedded thermal heater 1501 and the second embedded thermal heater 1502. In this manner, the annular portion 1505C of the ring-shaped optical waveguide 1505 provides for efficient thermal conduction between the first embedded thermal heater 1501 and the full-thickness annular portion 1505 A of the ring-shaped optical waveguide 1505 within which the optical mode is confined, while also serving to optically isolate the optical mode from the first embedded thermal heater 1501. Similarly, the annular portion 1505C of the ring-shaped optical waveguide 1505 provides for efficient thermal conduction between the second embedded thermal heater 1502 and the full-thickness annular portion 1505A of the ring-shaped optical waveguide 1505 within which the optical mode is confined, while also serving to optically isolate the optical mode from the second embedded thermal heater 1502.

[0136] Figure 16A shows the top view of the microring resonator device 1500 of Figures 15A and 15B in which the embedded thermal heaters 1501 and 1502 are implemented on the outer wall of the ring-shaped optical waveguide 1505 in combination with implementation of a modulator contact / doping region 1601 along the inner wall of the ring-shaped optical waveguide 1505, in accordance with some embodiments. Figure 16B shows a vertical cross-section slice (corresponding to View A- A of Figure 16A) through the microring resonator device 1500, in accordance with some embodiments. In some embodiments, the modulator contact / doping region 1601 is formed as an annular- shaped region next to the inner wall of the ring-shaped optical waveguide 1505. In some embodiments, the modulator contact / doping region 1601 is formed within an inner annular region of the ring-shaped optical waveguide 1505. It should be appreciated that positioning of the arc-shaped embedded thermal heaters 1501 and 1502 outside of the ring-shaped optical waveguide 1505 frees up the inner region of ring-shaped optical waveguide 1505 to enable positioning of the modulator contact / doping region 1601 along the inner wall of the ring-shaped optical waveguide 1505.

[0137] Figure 17 shows a top view of a microring resonator device 1700 that implements both a first embedded thermal heater 1701 on an outer wall of a first bus / drop optical waveguide 1707, and a second embedded thermal heater 1702 on an outer wall of a second bus / drop optical waveguide 1709, in accordance with some embodiments. In some embodiments, the microring resonator device 1700 is formed within an electro-optic semiconductor chip. It should be understood that the first bus / drop optical waveguide 1707 can be implemented as either a bus optical waveguide or a drop optical waveguide in different embodiments. Also, it should be understood that second bus / drop optical waveguide 1709 can be implemented as either a bus optical waveguide or a drop optical waveguide in different embodiments. In some embodiments, the first embedded thermal heater 1701 is formed along an outer side wall of the first bus / drop optical waveguide 1707 relative to the microring resonator device 1700. In some embodiments, the first embedded thermal heater 1701 is embedded into (formed within) an outer portion of the first bus / drop optical waveguide 1707 relative to the microring resonator device 1700. In some embodiments, the second embedded thermal heater 1702 is formed along an outer side wall of the second bus / drop optical waveguide 1709 relative to the microring resonator device 1700. In some embodiments, the second embedded thermal heater 1702 is embedded into (formed within) an outer portion of the second bus / drop optical waveguide 1709 relative to the microring resonator device 1700.

[0138] In some embodiments, the microring resonator device 1700 includes a ring-shaped optical waveguide 1705 that is configured as a rib- style optical waveguide having a fullthickness (vertical thickness) annular portion 1705A, an inner partial-thickness (verticalthickness) annular portion 1705B formed along the inner edge of annular portion 1705A, and an outer partial-thickness (vertical thickness) annular portion 1705C formed along the outer edge of annular portion 1705A. The rib-style ring-shaped optical waveguide 1705 confines the optical mode within the full-thickness annular portion 1705A. The example of Figure 17 also shows the microring resonator device 1700 positioned next to a first bus / drop optical waveguide 1707 and a second bus / drop optical waveguide 1709.

[0139] In some embodiments, the first bus / drop optical waveguide 1707 is configured as a ribstyle optical waveguide by having a full-thickness (vertical thickness) central portion 1707 A, a first partial-thickness (vertical thickness) side portion 1707B formed along a first side of the central portion 1707A, and a second partial-thickness (vertical thickness) side portion 1707C formed along a second side of the central portion 1707A. The first bus / drop optical waveguide 1707 extends past the ring-shaped optical waveguide 1705. In some embodiments, the ring- shaped optical waveguide 1705 and the first bus / drop optical waveguide 1707 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 1711, around a location of closest approach of the first bus / drop optical waveguide 1707 to the ring-shaped optical waveguide 1705. In some embodiments, the first partial-thickness side portion 1707B of the first bus / drop optical waveguide 1707 is formed integrally with the outer partial-thickness annular portion 1705C of the ring-shaped optical waveguide 1705.

[0140] In some embodiments, the second bus / drop optical waveguide 1709 is configured as a rib-style optical waveguide by having a full-thickness (vertical thickness) central portion 1709A, a first partial-thickness (vertical thickness) side portion 1709B formed along a first side of the central portion 1709 A, and a second partial-thickness (vertical thickness) side portion 1709C formed along a second side of the central portion 1709A. The second bus / drop optical waveguide 1709 extends past the ring-shaped optical waveguide 1705. In some embodiments, the ring- shaped optical waveguide 1705 and the second bus / drop optical waveguide 1709 are positioned within an evanescent optical coupling distance of each other within an optical coupling region 1713, around a location of closest approach of the second bus / drop optical waveguide 1709 to the ring-shaped optical waveguide 1705. In some embodiments, the first partial-thickness side portion 1709B of the second bus / drop optical waveguide 1709 is formed integrally with the outer partial-thickness annular portion 1705C of the ring-shaped optical waveguide 1705.

[0141] The partial thickness of the portion 1707C along the outer side of first bus / drop optical waveguide 1707 provides a partial thickness silicon bridging between the optical mode within the full-thickness portion 1707A of the first bus / drop optical waveguide 1707 and first embedded thermal heater 1701. In this manner, the partial thickness portion 1707C of the first bus / drop optical waveguide 1707 provides for efficient thermal conduction between the first embeddedthermal heater 1701 and the microring resonator device 1700, while also serving to optically isolate the optical mode from the first embedded thermal heater 1701. Similarly, the partial thickness of the portion 1709C along the outer side of second bus / drop optical waveguide 1709 provides a partial thickness silicon bridging between the optical mode within the full-thickness portion 1709 A of the second bus / drop optical waveguide 1709 and second embedded thermal heater 1702. In this manner, the partial thickness portion 1709C of the second bus / drop optical waveguide 1709 provides for efficient thermal conduction between the second embedded thermal heater 1702 and the microring resonator device 1700, while also serving to optically isolate the optical mode from the second embedded thermal heater 1702. In some embodiments the first embedded thermal heater 1701 and the second embedded thermal heater 1702 are wired in series with each other. In some embodiments the first embedded thermal heater 1701 and the second embedded thermal heater 1702 are wired in parallel with each other.

[0142] In some embodiments, it is desirable to have the inner and outer regions of the ring- shaped optical waveguide 1705 between the first bus / drop optical waveguide 1707 and the second bus / drop optical waveguide 1709 be accessible and usable for modulator doping and associated modulator electrical contact formation. Is should be appreciated that the configuration and placements of the first bus / drop optical waveguide 1707 and the second bus / drop optical waveguide 1709 enable access and use of the inner and outer regions of the ring-shaped optical waveguide 1705 for modulator doping and associated modulator electrical contact formation. Also, the high thermal conductivity of silicon provides good thermal efficiency of the microring resonator device 1700.

[0143] Figure 18 shows the top view of the microring resonator device 1700 of Figure 17 in which the embedded thermal heaters 1701 and 1702 are implemented on the outer walls of the bus / drop optical waveguides 1707 and 1709, respectively, in combination with implementation of a modulator contact / doping region 1801 along the inner wall of the ring-shaped optical waveguide 1705, in accordance with some embodiments. In some embodiments, the modulator contact / doping region 1801 is formed as an annular- shaped region next to the inner wall of the ring-shaped optical waveguide 1705. In some embodiments, the modulator contact / doping region 1801 is formed within an inner annular region of the ring-shaped optical waveguide 1705. It should be appreciated that positioning of the first embedded thermal heater 1701 and the second embedded thermal heater 1702 outside of the first bus / drop optical waveguide 1707 and the second bus / drop optical waveguide 1709, respectively, frees up the inner region of ringshaped optical waveguide 1705 to enable positioning of the modulator contact / doping region 1801 along the inner wall of the ring-shaped optical waveguide 1705.

[0144] The example embodiment of Figure 18 also shows implementation of a counter-dopedregion 1803 between the first embedded thermal heater 1701 and the first bus / drop optical waveguide 1707. It should be understood that in various embodiments, another counter-doped region, e.g., 1803, is similarly formed between the second embedded thermal heater 1702 and the second bus / drop optical waveguide 1709. The counter-doped region 1803 serves to electrically isolate the first embedded thermal heater 1701 from the first bus / drop optical waveguide 1707 and the from the ring-shaped optical waveguide 1705. In some embodiments, the first embedded thermal heater 1701 is formed from a heavily doped silicon of a given dopant type (p-type or n-type). In these embodiments, the counter-doped region 1803 is also formed from a heavily doped silicon of a given dopant type (p-type or n-type) that is opposite of the given dopant type used to form the first embedded thermal heater 1701. Therefore, the counterdoped region 1803 and the first embedded thermal heater 1701 have opposite polarities (dopant types). In operation, a bias voltage is applied to the counter-doped region 1803 so that a PN junction formed between the counter-doped region 1803 and the first embedded thermal heater 1701 is reverse biased. In some embodiments, the doping strength within the counter-doped region 1803 is set so that the counter-doped region 1803 never becomes fully depleted. In some embodiments, the counter-doped region 1803 is designed in conjunction with the modulator doping of modulator-type rib rings, such that electrical isolation is guaranteed through reversebiasing.

[0145] With reference to the embodiments of Figures 13A-13B, 14A-14B, 15A-15B, 16A-16B, 17, and 18, it should be understood that in various embodiments a microring resonator device, e.g., 1300, 1400, 1500, 1700, can include any combination of the various disclosed embedded thermal heaters 1301, 1401, 1501, 1502, 1701, and 1702. In various embodiments, a microring resonator device can include any combination of inner embedded thermal heater(s), e.g., 1301, 1401, arc-shaped embedded thermal heater(s), e.g., 1501, 1502, and bus-embedded thermal heater(s), e.g., 1701, 1702. For example, in some embodiments, the microring resonator device includes both the arc-shaped embedded thermal heater(s), e.g., 1501, 1502, and the bus- embedded thermal heater(s), e.g., 1701, 1702. In other example embodiments, the microring resonator device includes both inner embedded thermal heater(s), e.g., 1301, 1401, and arcshaped embedded thermal heater(s), e.g., 1501, 1502. In other example embodiments, the microring resonator device includes both inner embedded thermal heater(s), e.g., 1301, 1401, and bus-embedded thermal heater(s), e.g., 1701, 1702. In other example embodiments, the microring resonator device includes each of inner embedded thermal heater(s), e.g., 1301, 1401, arc-shaped embedded thermal heater(s), e.g., 1501, 1502, and bus-embedded thermal heater(s), e.g., 1701, 1702. The electrical wiring of the various above-mentioned embedded thermal heater topologies is configured to achieve a desired electrical resistance and / or electrical current densitythrough the embedded thermal heater(s). In various embodiments, different embedded thermal heater sections can be wired in either series or parallel, as needed. In some embodiments, different embedded thermal heater sections are configured to have different electrical resistances and / or electrical current densities to enable: 1) optimal design of heat source regions in the ring- shaped optical waveguide, e.g., 1305, 1405, 1505, 1705, to achieve the highest possible thermal efficiency, and 2) optical design of heat source regions to achieve the best possible reliability.

[0146] Figure 19 shows a top view of a microring resonator device 1900 that implements serial ring-shaped heater 1901 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 1903, in accordance with some embodiments. In some embodiments, the microring resonator device 1900 is formed within an electro-optic semiconductor chip. In some embodiments, the serial ring-shaped heater 1901 includes a single resistor element 1901A with a first electrical contact 1905 at a first end 1901B and with a second electrical contact 1907 at a second end 1901C, which minimizes electrical current density for a given electrical resistance. However, in some instances, the serial ring-shaped heater 1901 can suffer reliability problems. More specifically, even with uniform electrical current distribution through the serial ringshaped heater 1901, the electrical contacts 1905 and 1907 (metal contacts) act as a heat sink, which causes a lowering of temperature near the electrical contacts 1905 and 1907. The lowering of temperature near the electrical contacts 1905 and 1907 causes a high peak temperature to occur at a location along the serial ring-shaped heater 1901 away from the electrical contacts 1905 and 1907, which it turn creates high thermal gradients across the microring resonator device 1900, leading to reliability problems. Also, because the electrical contacts 1905 and 1907 are positioned close to each other, the above-mentioned effects are magnified.

[0147] Figure 20 shows a top view of a microring resonator device 2000 that implements a parallel ring-shaped heater 2001 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 2003, in accordance with some embodiments. In some embodiments, the microring resonator device 2000 is formed within an electro-optic semiconductor chip. In contrast with the serial ring-shaped heater 1901 of Figure 19, both maximum temperature and thermal gradients are reduced along the parallel ring-shaped heater 2001. The parallel ring-shaped heater 2001 is formed as a continuous ring, whereas the serial ring-shaped heater 1901 is formed as a split-ring. The parallel ring-shaped heater 2001 is electrically contacted at diametrically opposed locations, e.g., North and South locations. In the example microring resonator device 2000, a first electrical contact 2005 is formed to electrically connect with the parallel ring-shaped heater 2001 at a first location 200 IB, and a second electrical contact 2007 is formed to electrically connect with the parallel ring-shaped heater 2001 at a second location 2001C, where the second location 2001C is diametrically opposed to thefirst location 2001B along the circular path of the parallel ring-shaped heater 2001. In this manner, the parallel ring-shaped heater 2001 effectively functions as two heaters in parallel, where a first of the two heaters is formed by a first half of the parallel ring-shaped heater 2001 that extends between the first electrical contact 2005 and the second electrical contact 2007, and where a second of the two heaters is formed by a second half of the parallel ring-shaped heater 2001 that extends between the first electrical contact 2005 and the second electrical contact 2007. In this configuration, electrical current density is reduced at each of the first electrical contact 2005 and the second electrical contact 2007. This in turn provides for a more uniform temperature distribution within the parallel ring-shaped heater 2001 as compared to the serial ring-shaped heater 1901, which corresponds to lower thermal gradients and less thermal migration across the microring resonator device 2000 as compared to the microring resonator device 1900. Additionally, the peak temperature of the parallel ring-shaped heater 2001 is lower than that of the serial ring-shaped heater 1901, which provides for a lower risk of electromigration failure of the microring resonator device 2000 as compared to the microring resonator device 1900.

[0148] In some embodiments, the electrical contacts of a resistive ring-shaped heater (e.g., the electrical contacts 1905, 1907 of the serial ring-shaped heater 1901, and the electrical contacts 2005, 2007 of the parallel ring-shaped heater 2001) act as respective heat sinks, which leads to a non-uniformity in the temperature of the ring-shaped heater, with colder regions near the electrical contacts and hotter regions located away from the electrical contacts, which results in temperature gradients across the ring-shaped heater. These temperature gradients across the ring- shaped heater introduce reliability problems, such as acceleration of electromigration in the hotter locations of the ring-shaped heater and adverse thermal diffusion. Therefore, various embodiments are disclosed in Figures 21 through 24 that implement tapered ring-shaped heaters in which portions of the tapered ring-shaped heaters that are located away from the electrical contacts are widened (increased in size) in order to reduce the electrical resistance and associated power dissipation in the hottest parts of the ring-shaped heater. The tapered ring-shaped heaters have lower maximum temperatures as compared to the non-tapered ring-shaped heaters. Also, the tapered ring-shaped heaters have a more uniform temperature distribution as compared to the non-tapered ring-shaped heaters.

[0149] Figure 21 shows a top view of a microring resonator device 2100 that implements a parallel tapered ring-shaped heater 2101 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 2103, in accordance with some embodiments. In some embodiments, the microring resonator device 2100 is formed within an electro-optic semiconductor chip. The parallel tapered ring-shaped heater 2101 has a tapered configurationthat includes a first narrow-width arc-shaped region 2101A, a first larger-width region 2101B, a second narrow-width arc-shaped region 2101C, and a second larger-width region 2101D. The first narrow-width arc-shaped region 2101A is formed as a segment of an annular-shape having an outer edge that follows along an outer circular arc of the overall parallel tapered ring-shaped heater 2101. Similarly, the second narrow-width arc-shaped region 2101C is formed as a segment of an annular-shape having an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2101. The first larger-width region 2101B has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2101. The first larger-width region 2101B also has an inner edge that is substantially straight. Similarly, the second larger-width region 2101D has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2101. The second larger- width region 2101D also has an inner edge that is substantially straight. The substantially straight inner edges of the first larger-width region 2101B and the second larger-width region 2101D are substantially parallel to each other. The parallel tapered ring-shaped heater 2101 is substantially symmetrical about a line 2105 drawn through respective center locations of the first narrowwidth arc-shaped region 2101A and the second narrow-width arc-shaped region 2101C. The substantially straight inner edge of the first larger-width region 2101B and the substantially straight inner edge of the second larger-width region 2101D reduces electrical current crowding at the inner region of the parallel tapered ring-shaped heater 2101.

[0150] A first electrical contact 2107 is electrically connected to the first narrow-width arcshaped region 2101A. A first wire 2108 is electrically connected to the first electrical contact 2107. A second electrical contact 2109 is electrically connected to the second narrow-width arcshaped region 2101C. A second wire 2110 is electrically connected to the second electrical contact 2109. During operation, a voltage difference is applied between the first electrical contact 2107 and the second electrical contact 2109, such that an electrical current flows through the parallel tapered ring-shaped heater 2101 between the first electrical contact 2107 and the second electrical contact 2109.

[0151] Figure 22 shows a top view of a microring resonator device 2200 that implements a parallel tapered ring-shaped heater 2201 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 2203, in accordance with some embodiments. In some embodiments, the microring resonator device 2200 is formed within an electro-optic semiconductor chip. The parallel tapered ring-shaped heater 2201 has a tapered configuration that includes a first narrow-width arc-shaped region 2201A, a first larger-width region 2201B, a second narrow-width arc-shaped region 2201C, and a second larger-width region 2201D. The first narrow-width arc-shaped region 2201A is formed as a segment of an annular-shape havingan outer edge that follows along an outer circular arc of the overall parallel tapered ring-shaped heater 2201. Similarly, the second narrow-width arc-shaped region 2201C is formed as a segment of an annular-shape having an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2201. The first larger- width region 220 IB has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2201. The first larger-width region 2201B also has a curved inner edge that is defined to cause a mid-region 2201B1 of the first larger-width region 2201B to be wider than each of the first narrow-width arc-shaped region 2201A and the second narrow-width arc-shaped region 2201C. Similarly, the second larger-width region 2201D has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2201. The second larger- width region 220 ID also has a curved inner edge that is defined to cause a mid-region 220 ID 1 of the second larger-width region 2201D to be wider than each of the first narrow-width arcshaped region 2201A and the second narrow-width arc-shaped region 2201C. The parallel tapered ring-shaped heater 2201 is substantially symmetrical about a line 2205 drawn through respective center locations of the first narrow-width arc-shaped region 2201A and the second narrow-width arc-shaped region 2201C. The curved inner edge of the first larger-width region 2201B and the curved inner edge of the second larger-width region 2201D reduces electrical current crowding at the inner region of the parallel tapered ring-shaped heater 2201.

[0152] A first electrical contact 2207 is electrically connected to the first narrow-width arcshaped region 2201A. A first wire 2208 is electrically connected to the first electrical contact 2207. A second electrical contact 2209 is electrically connected to the second narrow- width arcshaped region 2201C. A second wire 2210 is electrically connected to the second electrical contact 2209. During operation, a voltage difference is applied between the first electrical contact 2207 and the second electrical contact 2209, such that an electrical current flows through the parallel tapered ring-shaped heater 2201 between the first electrical contact 2207 and the second electrical contact 2209.

[0153] Figure 23 shows a top view of a microring resonator device 2300 that implements a parallel tapered ring-shaped heater 2301 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 2303, in accordance with some embodiments. In some embodiments, the microring resonator device 2300 is formed within an electro-optic semiconductor chip. The parallel tapered ring-shaped heater 2301 has a tapered configuration that includes a first arc-shaped region 2301A, a larger-width region 2301B, and a second arcshaped region 2301C. The parallel tapered ring-shaped heater 2301 is split such that a gap 2312 exists between the first arc-shaped region 2301A and the second arc-shaped region 2301C. The first arc-shaped region 2301A is formed as a segment of an annular-shape having an outer edgethat follows along an outer circular arc of the overall parallel tapered ring-shaped heater 2301. Similarly, the second arc- shaped region 2301C is formed as a segment of an annular- shape having an outer edge that follows along the outer circular arc of the overall parallel tapered ring- shaped heater 2301. The larger-width region 2301B has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2301. The larger-width region 2201B also has a substantially straight inner edge. Therefore, the width of the larger-width region 2201B increases toward a centerline 2305 of the microring resonator device 2300. The parallel tapered ring-shaped heater 2301 is substantially symmetrical about the centerline 2305. The larger-width region 230 IB reduces electrical current crowding at the inner region of the parallel tapered ring-shaped heater 2301.

[0154] A first electrical contact 2307 is electrically connected to the first arc- shaped region 2301A. A first wire 2308 is electrically connected to the first electrical contact 2307. A second electrical contact 2309 is electrically connected to the second arc-shaped region 2301C. A second wire 2310 is electrically connected to the second electrical contact 2309. During operation, a voltage difference is applied between the first electrical contact 2307 and the second electrical contact 2309, such that an electrical current flows through the parallel tapered ring- shaped heater 2301 between the first electrical contact 2307 and the second electrical contact 2309.

[0155] Figure 24 shows a top view of a microring resonator device 2400 that implements a parallel tapered ring-shaped heater 2401 disposed within an interior region that is circumscribed by a ring-shaped optical waveguide 2403, in accordance with some embodiments. In some embodiments, the microring resonator device 2400 is formed within an electro-optic semiconductor chip. The parallel tapered ring-shaped heater 2401 has a tapered configuration that includes a first arc-shaped region 2401A, a larger-width region 2401B, and a second arcshaped region 2401C. The parallel tapered ring-shaped heater 2401 is split such that a gap 2412 exists between the first arc-shaped region 2401A and the second arc-shaped region 2401C. The first arc-shaped region 2401A is formed as a segment of an annular-shape having an outer edge that follows along an outer circular arc of the overall parallel tapered ring-shaped heater 2401. Similarly, the second arc- shaped region 2401C is formed as a segment of an annular- shape having an outer edge that follows along the outer circular arc of the overall parallel tapered ring- shaped heater 2401. The larger-width region 2401B has an outer edge that follows along the outer circular arc of the overall parallel tapered ring-shaped heater 2401. The larger-width region 2401B also has a curved inner edge that is defined to cause a mid-region 2401B1 of the larger- width region 240 IB to be wider than each of the first arc- shaped region 2401 A and the second arc- shaped region 2401C. Therefore, the width of the larger-width region 240 IB increasestoward a centerline 2405 of the microring resonator device 2400. The parallel tapered ring- shaped heater 2401 is substantially symmetrical about the centerline 2405. The larger- width region 240 IB reduces electrical current crowding at the inner region of the parallel tapered ring- shaped heater 2401.

[0156] A first electrical contact 2407 is electrically connected to the first arc- shaped region 2401A. A first wire 2408 is electrically connected to the first electrical contact 2407. A second electrical contact 2409 is electrically connected to the second arc-shaped region 2401C. A second wire 2410 is electrically connected to the second electrical contact 2409. During operation, a voltage difference is applied between the first electrical contact 2407 and the second electrical contact 2409, such that an electrical current flows through the parallel tapered ring- shaped heater 2401 between the first electrical contact 2407 and the second electrical contact 2409.

[0157] The foregoing description of the embodiments has been provided for purposes of illustration and description, and is not intended to be exhaustive or limiting. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. In this manner, one or more features from one or more embodiments disclosed herein can be combined with one or more features from one or more other embodiments disclosed herein to form another embodiment that is not explicitly disclosed herein, but rather that is implicitly disclosed herein. This other embodiment may also be varied in many ways. Such embodiment variations are not to be regarded as a departure from the disclosure herein, and all such embodiment variations and modifications are intended to be included within the scope of the disclosure provided herein.

[0158] Although some method operations may be described in a specific order herein, it should be understood that other housekeeping operations may be performed in between method operations, and / or method operations may be adjusted so that they occur at slightly different times or simultaneously or may be distributed in a system which allows the occurrence of the processing operations at various intervals associated with the processing, as long as the processing of the method operations are performed in a manner that provides for successful implementation of the method.

[0159] Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications can be practiced within the scope of the appended claims. Accordingly, the embodiments disclosed herein are to be considered as illustrative and not restrictive, and are therefore not to be limited to just the details given herein, but may be modified within the scope and equivalents of theappended claims.

Claims

Claims1. A microring resonator device, comprising: a ring-shaped optical waveguide having an inner radial wall, an outer radial wall, a top surface, and a bottom surface, the ring-shaped optical waveguide circumscribing an interior region of the microring resonator device; a ring-shaped heater disposed within the interior region of the microring resonator device, the ring-shaped heater having an inner radial wall, an outer radial wall, a top surface, and a bottom surface, the ring-shaped heater circumscribing a center of the microring resonator device, wherein the ring-shaped heater is an electrically resistive heating device; a first electrical contact disposed in electrical connection with the ring-shaped heater; a second electrical contact disposed in electrical connection with the ring-shaped heater; and a heat spreader fin disposed above a portion of the ring-shaped optical waveguide, the heat spreader fin thermally connected to the ring-shaped heater, the heat spreader fin electrically isolated from each of the ring-shaped heater, the first electrical contact, and the second electrical contact.

2. The microring resonator device as recited in claim 1, wherein the heat spreader fin has an arc shape such that the heat spreader fin extends along an arc length of the portion of the ring-shaped optical waveguide.

3. The microring resonator device as recited in claim 1, wherein the heat spreader fin is physically separated from the ring-shaped optical waveguide by an optical mode keepout region sized to prevent optical disturbance of an optical mode within the ring-shaped optical waveguide by the heat spreader fin.

4. The microring resonator device as recited in claim 1, wherein the heat spreader fin is configured and positioned to assist with uniform dissipation of heat generated by the ringshaped heater within the ring-shaped optical waveguide.

5. The microring resonator device as recited in claim 1, wherein the heat spreader fin is positioned for dissipation of heat within a radial section of the ring-shaped optical waveguide through which a fundamental optical mode is conveyed.

6. The microring resonator device as recited in claim 1, wherein the ring-shaped optical waveguide has a radial thickness measured between the inner radial wall and the outer radial wall of the ring-shaped optical waveguide, wherein the heat spreader fin laterally overlaps a portion of the radial thickness of the ring-shaped optical waveguide.

7. The microring resonator device as recited in claim 1, wherein the first electrical contact and the second electrical contact are positioned to electrically contact the ring-shapedheater at diametrically opposed locations along the ring-shaped heater.

8. The microring resonator device as recited in claim 7, wherein the heat spreader fin is positioned on one side of the microring resonator device as defined by a bisection of the microring resonator device along a line extending through positions at which the first electrical contact and the second electrical contact electrically contact the ring-shaped heater.

9. The microring resonator device as recited in claim 8, wherein the heat spreader fin has an arc shape such that the heat spreader fin extends along an arc length of the ring-shaped optical waveguide from a first location proximate to a position of the first electrical contact to a second location proximate to a position of the second electrical contact.

10. The microring resonator device as recited in claim 1 , wherein the outer radial wall of the ring-shaped heater is physically separated from inner radial wall of the ring-shaped optical waveguide.

11. The microring resonator device as recited in claim 1, further comprising: a heat spreader contact attached in thermal communication with the ring-shaped heater; and a heat spreader arm configured to extend from the heat spreader contact to the heat spreader fin, the heat spreader arm attached in thermal communication with both the heat spreader contact and the heat spreader fin.

12. The microring resonator device as recited in claim 11, wherein the heat spreader contact is attached to the inner radial wall of the ring-shaped heater.

13. The microring resonator device as recited in claim 12, wherein the heat spreader arm includes a vertical segment that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater and a horizontal segment that extends in a direction substantially parallel to the top surface of the ring-shaped heater.

14. The microring resonator device as recited in claim 13, wherein the heat spreader fin has a first end, a second end, and a length extending between the first end and the second end, wherein the heat spreader arm is physically and thermally connected to the heat spreader fin at a substantially center location along the length of the heat spreader fin.

15. The microring resonator device as recited in claim 14, wherein the top surface of the ring-shaped heater is substantially coplanar with the top surface of the ring-shaped optical waveguide.

16. The microring resonator device as recited in claim 10, wherein the heat spreader contact is positioned to avoid disturbance of electric current flow through the ring-shaped heater.

17. The microring resonator device as recited in claim 1, wherein the microring resonator device is formed within an electro-optic semiconductor chip.

18. The microring resonator device as recited in claim 1, wherein the first electrical contact and the second electrical contact are positioned to electrically contact the ring-shaped heater at diametrically opposed locations along the ring-shaped heater, wherein said heat spreader fin is a first heat spreader fin disposed above a first portion of the ring-shaped optical waveguide, wherein the microring resonator device further includes a second heat spreader fin disposed above a second portion of the ring-shaped optical waveguide, the second heat spreader fin thermally connected to the ring-shaped heater, the second heat spreader fin electrically isolated from each of the ring-shaped heater, the first electrical contact, and the second electrical contact.

19. The microring resonator device as recited in claim 18, wherein the first heat spreader fin is positioned on a first side of the microring resonator device and the second heat spreader fin is positioned on a second side of the microring resonator device, wherein the first side and the second side of the microring resonator device are defined by a bisection of the microring resonator device along a line extending through positions at which the first electrical contact and the second electrical contact electrically contact the ring-shaped heater.

20. The microring resonator device as recited in claim 19, wherein the first heat spreader fin has an arc shape such that the first heat spreader fin extends along a first arc length of the ring-shaped optical waveguide from a first location proximate to a position of the first electrical contact to a second location proximate to a position of the second electrical contact, and wherein the second heat spreader fin has an arc shape such that the second heat spreader fin extends along a second arc length of the ring-shaped optical waveguide from a third location proximate to the position of the first electrical contact to a fourth location proximate to the position of the second electrical contact.

21. The microring resonator device as recited in claim 19, wherein the second heat spreader fin is physically separated from the first heat spreader fin.

22. The microring resonator device as recited in claim 21, further comprising: a first heat spreader contact attached in thermal communication with the ring-shaped heater; a first heat spreader arm configured to extend from the first heat spreader contact to the first heat spreader fin, the first heat spreader arm attached in thermal communication with both the first heat spreader contact and the first heat spreader fin; a second heat spreader contact attached in thermal communication with the ring-shaped heater; and a second heat spreader arm configured to extend from the second heat spreader contact to the second heat spreader fin, the second heat spreader arm attached in thermal communicationwith both the second heat spreader contact and the second heat spreader fin.

23. The microring resonator device as recited in claim 22, wherein the first heat spreader contact and the second heat spreader contact are positioned to contact the ring-shaped heater at diametrically opposed locations along the ring-shaped heater.

24. The microring resonator device as recited in claim 23, wherein the first heat spreader contact is attached to the inner radial wall of the ring-shaped heater, and the second heat spreader contact is attached to the inner radial wall of the ring-shaped heater.

25. The microring resonator device as recited in claim 24, wherein the first heat spreader arm includes a first vertical segment that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater and a first horizontal segment that extends in a direction substantially parallel to the top surface of the ring-shaped heater, and wherein the second heat spreader arm includes a second vertical segment that extends in the direction substantially perpendicular to the top surface of the ring-shaped heater and a second horizontal segment that extends in the direction substantially parallel to the top surface of the ring-shaped heater.

26. The microring resonator device as recited in claim 25, wherein the first heat spreader fin has a first end, a second end, and a length extending between the first end and the second end of the first heat spreader fin, wherein the first heat spreader arm is physically and thermally connected to the first heat spreader fin at a substantially center location along the length of the first heat spreader fin, and wherein the second heat spreader fin has a first end, a second end, and a length extending between the first end and the second end of the second heat spreader fin, wherein the second heat spreader arm is physically and thermally connected to the second heat spreader fin at a substantially center location along the length of the second heat spreader fin.

27. The microring resonator device as recited in claim 26, wherein the top surface of the ring-shaped heater is substantially coplanar with the top surface of the ring-shaped optical waveguide.

28. The microring resonator device as recited in claim 22, wherein each of the first heat spreader contact and the second heat spreader contact is positioned to avoid disturbance of electric current flow through the ring-shaped heater.

29. The microring resonator device as recited in claim 1, further comprising: a plurality of heat spreader fins, wherein said heat spreader fin is one of the plurality of heat spreader fins, each of the plurality of heat spreader fins disposed above a respective portion of the ring-shaped optical waveguide, each of the plurality of heat spreader fins thermally connected to the ring-shaped heater, each of the plurality of heat spreader fins physicallyseparated from any other of the plurality of heat spreader fins, each of the plurality of heat spreader fins electrically isolated from each of the ring-shaped heater, the first electrical contact, and the second electrical contact.

30. The microring resonator device as recited in claim 29, further comprising: a plurality of heat spreader contacts attached in thermal communication with the ring- shaped heater; and a plurality of heat spreader arms, each of the plurality of heat spreader arms configured to extend from a respective one of the plurality of heat spreader contacts to a respective one of the plurality of heat spreader fins, wherein each of the plurality of heat spreader arms is attached in thermal communication with both the respective one of the plurality of heat spreader contacts and the respective one of the plurality of heat spreader fins.

31. The microring resonator device as recited in claim 30, wherein the plurality of heat spreader contacts are positioned at substantially equally spaced apart locations along the circumference of the ring-shaped heater.

32. The microring resonator device as recited in claim 31, wherein each of the plurality of heat spreader contacts is positioned to avoid disturbance of electric current flow through the ring-shaped heater.

33. The microring resonator device as recited in claim 32, wherein each of the plurality of heat spreader contacts is attached to the inner radial wall of the ring-shaped heater.

34. The microring resonator device as recited in claim 31, wherein each of the plurality of heat spreader arms includes a respective vertical segment that extends in a direction substantially perpendicular to the top surface of the ring-shaped heater and a respective horizontal segment that extends in a direction substantially parallel to the top surface of the ringshaped heater.

35. The microring resonator device as recited in claim 34, wherein each of the plurality of heat spreader fins has a substantially same shape and size.

36. The microring resonator device as recited in claim 35, wherein each of the plurality of heat spreader fins is separated from each adjacently positioned one of the plurality of heat spreader fins by a substantially same distance.

37. The microring resonator device as recited in claim 36, wherein the plurality of heat spreader fins is six heat spreader fins, and the plurality of heat spreader contacts is six heat spreader contacts, and the plurality of heat spreader arms is six heat spreader arms.

38. The microring resonator device as recited in claim 36, wherein the plurality of heat spreader fins is two heat spreader fins, and the plurality of heat spreader contacts is two heat spreader contacts, and the plurality of heat spreader arms is two heat spreader arms.

39. The microring resonator device as recited in claim 38, further comprising: a bus optical waveguide positioned to extend past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that an optical coupling region exists between the bus optical waveguide and the ring-shaped optical waveguide, wherein the plurality of heat spreader fins are azimuthally rotated about the center of the microring resonator device so that each of a first spacing and a second spacing between the plurality of heat spreader fins is located outside of the optical coupling region between the bus optical waveguide and the ring-shaped optical waveguide.

40. A microring resonator device, comprising: a ring-shaped optical waveguide including an outer annular region, an inner annular region, and a spatial separation region extending between the outer annular region and the inner annular region, wherein the outer annular region is a radial section of the ring-shaped optical waveguide through which a fundamental optical mode is conveyed, wherein the inner annular region is a radial section of the ring-shaped optical waveguide configured as an embedded thermal heater, and wherein the spatial separation region is a radial section of the ring-shaped optical waveguide having a radial width sufficient to spatially separate the embedded thermal heater within the inner annular region from the optical mode within the outer annular region.

41. The microring resonator device as recited in claim 40, wherein the outer annular region, the inner annular region, and the spatial separation region are separate portions of a single piece of optical waveguide material that forms the ring-shaped optical waveguide.

42. The microring resonator device as recited in claim 41, wherein the ring-shaped optical waveguide is formed of silicon.

43. The microring resonator device as recited in claim 41, wherein the outer annular region has a first vertical height, the inner annular region has a second vertical height, and the spatial separation region has a third vertical height, wherein the third vertical height is less than each of the first vertical height and the second vertical height.

44. The microring resonator device as recited in claim 43, wherein the second vertical height is substantially equal to the first vertical height.

45. The microring resonator device as recited in claim 43, wherein the spatial separation region is contiguously formed with both the outer annular region and the inner annular region.

46. The microring resonator device as recited in claim 45, wherein a bottom surface of the spatial separation region is coplanar with both a bottom surface of the outer annular region and a bottom surface of the inner annular region.

47. The microring resonator device as recited in claim 41, wherein each of the outerannular region, the inner annular region, and the spatial separation region has a same vertical height.

48. The microring resonator device as recited in claim 40, wherein the embedded thermal heater within the inner annular region is an electrical resistance heater.

49. The microring resonator device as recited in claim 48, wherein the inner annular region is doped with impurities to achieve a target electrical resistance for the embedded thermal heater.

50. The microring resonator device as recited in claim 48, further comprising: a plurality of electrical contacts electrically connected to the inner annular region, wherein at least one of the plurality of electrical contacts is electrically connected to an electrical power supply, wherein at least one of the plurality of electrical contacts is electrically connected to a reference ground potential.

51. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device, the ring-shaped optical waveguide having an outer annular region that has a first vertical thickness, the ring-shaped optical waveguide having an inner annular region that has a second vertical thickness that is less than the first vertical thickness; a first bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide; a second bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a second optical coupling region exists between the second bus optical waveguide and the ringshaped optical waveguide; and a plurality of metal heater wires respectively formed at a plurality of vertical levels above a top surface of the ring-shaped optical waveguide, wherein each of the plurality of metal heater wires is positioned a sufficient distance away from the ring-shaped optical waveguide to control optical loss within ring-shaped optical waveguide due to the plurality of metal heater wires.

52. The electro-optical semiconductor chip as recited in claim 51, wherein some of the plurality of metal heater wires are formed to have an arc shape that follows an arc shape of a portion of the ring-shaped optical waveguide proximate to said some of the plurality of metal heater wires.

53. The electro-optical semiconductor chip as recited in claim 51, wherein some of the plurality of metal heater wires are formed to have a ring shape that follows a shape of thering-shaped optical waveguide.

54. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device, the ring-shaped optical waveguide having an outer annular region that has a first vertical thickness, the ring-shaped optical waveguide having an inner annular region that has a second vertical thickness that is less than the first vertical thickness; a first bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide; a second bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a second optical coupling region exists between the second bus optical waveguide and the ringshaped optical waveguide; and a spiral- shaped metal heater wire formed at a vertical level above a top surface of the ring-shaped optical waveguide, wherein the spiral-shaped metal heater wire is formed to extend horizontally over an outer edge of the ring-shaped optical waveguide.

55. The electro-optical semiconductor chip as recited in claim 54, further comprising: a plurality of spiral-shaped metal heater wires respectively formed at a plurality of vertical levels above the top surface of the ring-shaped optical waveguide, wherein said spiralshaped metal heater wire is one of the plurality of spiral- shaped metal heater wires.

56. The electro-optical semiconductor chip as recited in claim 55, wherein each of the plurality of spiral-shaped metal heater wires is formed to extend horizontally over the outer edge of the ring-shaped optical waveguide.

57. The electro-optical semiconductor chip as recited in claim 56, wherein the plurality of spiral-shaped metal heater wires are vertically stacked with respect to each other with a layer of dielectric material intervening vertically between adjacent ones of the plurality of spiral-shaped metal heater wires.

58. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device, the ring-shaped optical waveguide having an outer annular region that has a first vertical thickness, the ring-shaped optical waveguide having an inner annular region that has a second vertical thickness that is less than the first vertical thickness; a first double- spiral- shaped metal heater wire formed at a first vertical level above a top surface of the ring-shaped optical waveguide, wherein the first double- spiral- shaped metal heaterwire is formed within the interior region of the microring resonator device; and a second double-spiral-shaped metal heater wire formed at a second vertical level above a top surface of the ring-shaped optical waveguide, wherein the second double- spiral- shaped metal heater wire is formed within the interior region of the microring resonator device.

59. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device, the ring-shaped optical waveguide having an outer annular region that has a first vertical thickness, the ring-shaped optical waveguide having an inner annular region that has a second vertical thickness that is less than the first vertical thickness; a first partial-ring-shaped metal heater wire formed at a first vertical level above a top surface of the ring-shaped optical waveguide, wherein the first partial-ring-shaped metal heater wire is formed within the interior region of the microring resonator device; and a second partial-ring-shaped metal heater wire formed at a second vertical level above a top surface of the ring-shaped optical waveguide, wherein the second partial-ring-shaped metal heater wire is formed within the interior region of the microring resonator device.

60. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device; a bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that an optical coupling region exists between the bus optical waveguide and the ring-shaped optical waveguide; a first doped region formed within the interior region of the microring resonator device at a location adjacent to the optical coupling region, wherein the first doped region is electrically conductive; a second doped region formed along a side of the bus optical waveguide that is opposite from the ring-shaped optical waveguide, the second doped region formed at a location adjacent to the optical coupling region, wherein the second doped region is electrically conductive; a third doped region formed between the first doped region and the second doped region through the optical coupling region and through both a portion of the ring-shaped optical waveguide and a portion of the bus optical waveguide, wherein an electrical resistance of the third doped region is higher than an electrical resistance within each of the first doped region and the second doped region, wherein the third doped region is configured to increase in temperature when an electrical current flows between the first doped region and the second doped region through the third doped region.

61. The electro-optical semiconductor chip as recited in claim 60, further comprising: a first plurality of electrical contacts disposed in electrical connection with the first doped region; and a second plurality of electrical contacts disposed in electrical connection with the second doped region, wherein the first plurality of electrical contacts and the second plurality of electrical contacts are positioned such that the electrical current flow between the first doped region and the second doped region is substantially uniform across the third doped region.

62. The electro-optical semiconductor chip as recited in claim 61 , further comprising: a first intermediate doped region disposed between the first doped region and the third doped region, the first intermediate doped region configured to electrically link the first doped region and the third doped region; and a second intermediate doped region disposed between the second doped region and the third doped region, the second intermediate doped region configured to electrically link the second doped region and the third doped region.

63. The electro-optical semiconductor chip as recited in claim 62, wherein each of the first doped region and the second doped region has a p++ doping, wherein each of the first intermediate doped region and the second intermediate doped region has a p+ doping, and wherein the third doped region has a p doping.

64. The electro-optical semiconductor chip as recited in claim 63, wherein the third doped region is substantially confined within the portion of the ring-shaped optical waveguide located between the first doped region and the second doped region.

65. The electro-optical semiconductor chip as recited in claim 63, further comprising: an n++ doped region formed within the interior region of the microring resonator device along the ring-shaped optical waveguide and outside of the first doped region, the n++ doped region formed within an inner radial portion of the ring-shaped optical waveguide; a third plurality of electrical contacts disposed in electrical connection with the n++ doped region; a P++ doped region formed along an outside of the ring-shaped optical waveguide and outside of both the first doped region and the third doped region, the p++ doped region formed within an outer radial portion of the ring-shaped optical waveguide such that the p++ doped region and the n++ doped region interface with each other to form a PN junction within the ring- shaped optical waveguide; and a fourth plurality of electrical contacts disposed in electrical connection with the p++ doped region, wherein the n++ doped region and the p++ doped region are collectively configured tocontrol modulation of light propagating within the ring-shaped optical waveguide in accordance with application of temporally controlled voltages to the n++ doped region and the p++ doped region by way of the third plurality of electrical contacts and the fourth plurality of electrical contacts.

66. An electro-optical semiconductor chip, comprising: a ring-shaped optical waveguide circumscribing an interior region of a microring resonator device; a first bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a first optical coupling region exists between the first bus optical waveguide and the ring-shaped optical waveguide; a second bus optical waveguide extending past the ring-shaped optical waveguide and within an evanescent optical coupling distance of the ring-shaped optical waveguide such that a second optical coupling region exists between the second bus optical waveguide and the ringshaped optical waveguide, wherein the second bus optical waveguide and the first bus optical waveguide are configured substantially parallel with each other on opposite sides of the ring- shaped optical waveguide; and a first doped region formed within the interior region of the microring resonator device, wherein the first doped region is electrically conductive; a second doped region formed outside of the ring-shaped optical waveguide within a region located between the first bus optical waveguide and the second bus optical waveguide, wherein the second doped region is electrically conductive; and a third doped region formed between the first doped region and the second doped region through a portion of the ring-shaped optical waveguide, the third doped region located between the first bus optical waveguide and the second bus optical waveguide, wherein an electrical resistance of the third doped region is higher than an electrical resistance within each of the first doped region and the second doped region, wherein the third doped region is configured to increase in temperature when an electrical current flows between the first doped region and the second doped region through the third doped region.

67. The electro-optical semiconductor chip as recited in claim 66, further comprising: a first plurality of electrical contacts disposed in electrical connection with the first doped region; and a second plurality of electrical contacts disposed in electrical connection with the second doped region, wherein the first plurality of electrical contacts and the second plurality of electrical contacts are positioned such that the electrical current flow between the first dopedregion and the second doped region is substantially uniform across the third doped region.

68. The electro-optical semiconductor chip as recited in claim 67, further comprising: a first intermediate doped region disposed between the first doped region and the third doped region, the first intermediate doped region configured to electrically link the first doped region and the third doped region; and a second intermediate doped region disposed between the second doped region and the third doped region, the second intermediate doped region configured to electrically link the second doped region and the third doped region.

69. The electro-optical semiconductor chip as recited in claim 68, wherein each of the first doped region and the second doped region has a p++ doping, wherein each of the first intermediate doped region and the second intermediate doped region has a p+ doping, and wherein the third doped region has a p doping.

70. The electro-optical semiconductor chip as recited in claim 69, wherein the third doped region is substantially confined within the portion of the ring-shaped optical waveguide located between the first doped region and the second doped region.

Images