Hybrid microring resonator device

Abstract

A hybrid microring resonator (MRR) device is provided. The device has an MRR waveguide composed of a first arc portion made of a first waveguide material and a second arc portion made of a second waveguide material. The first waveguide material has at least one optical property providing a tunability of the resonant wavelength of the MRR waveguide. A pair of optical vias optically connect the first arc portion and the second arc portion. A tuning mechanism is coupled to at least the first arc portion for tuning the resonant wavelength of the MRR waveguide. Systems such as optical modulators, external cavity lasers and optical filters incorporating hybrid MRR devices are also presented.

Description

[0001] HYBRID MICRORING RESONATOR DEVICE

[0002] TECHNICAL FIELD

[0003] The technical field generally relates to microring resonator devices for use in optical modulators, external cavity lasers, and the like, and more particularly concerns a hybrid microring resonator made of material with different thermo-optic coefficients.

[0004] BACKGROUND

[0005] Microring resonators (MRRs) are compact photonic devices that use the principle of resonance to control light propagation on a chip. They typically consist of a waveguide loop or ring and one or more straight waveguides. The ring and the straight waveguide are positioned close enough that light can couple between them. When a light signal enters the straight waveguide, a portion of it is coupled into the ring. Light circulates in the ring and interacts with itself after completing each loop. This interaction allows certain wavelengths of light to interfere constructively, while others interfere destructively, leading to selective wavelength filtering. A resonant condition is achieved when the optical path length of the loop is an integer multiple of the wavelength of light, that is mres m= neffL, where m = 1,2,3,.... neffis the waveguide effective refractive index, L is the round trip length of the loop andres mis the mthresonance wavelength.

[0006] There are several types of MRRs, the most common being all-pass MRRs and add-drop MRRs. Referring to FIGs. 1A and 1B (PRIOR ART), there is shown a schematic view of an all-pass MRR and its transmission spectrum, respectively. In such a device, input light either circulates within the loop or passes through a straight waveguide without being dropped at any port. This configuration is primarily used for phase shifting, delay lines, and tuning the resonance wavelength. In an all-pass MRR, the transmission spectrum exhibits sharp dips at the resonant wavelengths (Ares), corresponding to the points in the spectrum where light is fully coupled into the MRR and interferes destructively at the output waveguide. FIGs. 2A and 2B (PRIOR ART) show the configuration and transmission spectrum of an add-drop MRR. Add-drop MRRs have a more complex configuration in which input light can be coupled into the MRR from one waveguide and dropped into another waveguide. This configuration allows specific resonant wavelengths (Ares) to be removed from the input signal and routed to a different output port, making add-drop MRRs particularly useful in applications such as wavelength-division multiplexing (WDM) systems. The add-drop configuration enables selective routing of different wavelength channels, allowing the multiplexing or demultiplexing of signals in optical networks.

[0007] Given their versatile design and precise wavelength control, MRRs are widely utilized in various applications, particularly in filtering, modulation, and external cavity lasers (ECLs). By way of example, in filtering applications, these resonators may be used to selectively pass or block specific wavelengths of light from a broader spectrum. By carefully designing the MRRs dimensions and refractive index, the device can be tuned to target particular wavelengths. In modulation applications, MRR modulators have emerged as a prominent design due to their compact size, high efficiency, and compatibility with integrated photonic circuits.

[0008] Optical MRR modulators operate based on the principles of resonance and interference within the ring-shaped waveguide of the MRR. These waveguides are typically made of silicon or other materials with high refractive indices, enabling the confinement and control of light within a small area. A typical optical MRR modulator consists of a ring-shaped waveguide that is coupled to one (all-pass MRR) or two (add-drop MRR) straight waveguides. The modulation process in optical MRR modulators hinges on the ability to control the resonance condition of the MRRs (res m= neffL / m). This control is achieved by dynamically altering or modulating the refractive index of the material of the ring-shaped waveguide, consequently modulating the effective refractive index neff. The refractive index determines how much the light is slowed down as it travels through the material, which in turn influences the wavelength of light that can resonate within the ring.

[0009] Different methods are known in the art to modulate the reflective index of the ring waveguide.

[0010] Referring to FIG. 3 (PRIOR ART), there is shown an example of an optical MRR modulator in which the refractive index modulation is achieved through the plasma dispersion effect. The plasma dispersion effect involves modulating the refractive index by changing an applied voltage 7(t), that is neff(7(t)). Through a p-n junction loaded on the MRR waveguide, the applied voltage alters the carrier concentration in the silicon or other material of the ring waveguide, which is done by injecting or depleting electrons and holes via electrical means. This method is particularly effective in silicon due to its strong interaction with free carriers.

[0011] Referring to FIG. 4 (PRIOR ART), in another modulation scheme, the refractive index modulation of optical MRR modulators may alternatively be achieved through the thermooptic effect. The thermo-optic effect leverages the relationship between temperature and refractive index neff(T). By heating or cooling the material of the ring waveguide, its refractive index can be modulated. This is typically done using micro-heaters placed in close proximity to the MRR. The thermo-optic effect is slower than the plasma dispersion effect due to the time it takes to change the temperature of the material, but it can still be useful for applications where high speed is not required.

[0012] As the refractive index changes — whether through the plasma dispersion effect or thermooptic effect — the effective optical path length (neffL) around the ring waveguide also changes. This shifts the resonance wavelength of the MRR according tores m= neffL / m. If the resonance wavelength is properly aligned with the wavelength of an incoming light, the light can be strongly coupled into the MRR, and a significant portion of it can be modulated or even dropped into the MRR. In other words, the light can either be transmitted to the output or blocked, i.e., modulated, depending on the voltage applied to the MRR and the location of the resonance wavelength.

[0013] MRRs are predominantly fabricated from Si, largely due to the excellent optical properties of silicon and its compatibility with existing semiconductor manufacturing processes. The high refractive index of silicon allows for strong light confinement within the small waveguides of typical MRRs, enabling compact device designs and efficient integration with other photonic components on a chip. However, Si MRRs face a significant challenge relative to thermal stability. The same temperature-dependent effect of the Si refractive index, i.e., nsi(T), which is beneficial for tuning the resonance of the MRR to a desired wavelength, can also negatively deviate the MRR from its intended operating wavelength due to temperature perturbations. Such undesired deviations are particularly problematic in precision applications, such as in wavelength division multiplexing (WDM) systems, where maintaining a stable and specific resonance wavelength can be a major requirement. There remains a need in the art for MRR devices that alleviates at least some of the drawbacks of prior art.

[0014] SUMMARY

[0015] In accordance with one aspect, there is provided a hybrid microring resonator (MRR) device, comprising:

[0016] an MRR waveguide having a resonant wavelength, the MRR waveguide comprising a first arc portion having a first waveguide material and a second arc portion having a second waveguide material, the first waveguide material having at least one optical property providing a tunability of the resonant wavelength of the MRR waveguide;

[0017] a pair of optical vias optically connecting the first arc portion and the second arc portion; and

[0018] a tuning mechanism coupled to at least the first arc portion for tuning the resonant wavelength of the MRR waveguide.

[0019] In some implementations, the first waveguide material has a thermo-optic coefficient higher than a thermo-optic coefficient of the second waveguide material.

[0020] In some implementations, the second waveguide material has lower propagation losses than the first waveguide material.

[0021] In some implementations, the tunability of the resonant wavelength of the MRR waveguide is based on heating. The first waveguide material may be one of Si, InP and InGaAsP, and the second waveguide material may be one of SiN, high-index doped silica glass, LN, Al2O3, AlN or a polymer having a negative TOC. The tuning mechanism may comprise a first arc portion tuning heater placed above the first arc portion. The first arc portion tuning heater may compris a metallic heat resistor extending above the first arc portion or doped silicon elements adjacent to the first arc portion.

[0022] In some implementations, the tunability of the resonant wavelength of the MRR waveguide is based on the plasma dispersion effect or electric-field-induced band-edge effects. The first waveguide material may be a doped semiconductor material, and the second waveguide material may be one of SiN, high-index doped silica glass, LN, Al2O3, AlN or a polymer having a negative TOC. The tuning mechanism may comprise a PN junction provided across the first arc portion.

[0023] In some implementations, the tunability of the resonant wavelength of the MRR waveguide is based on the electro-optic effect. The first waveguide material may be a thin-film lithium niobate (TFLN), and the second waveguide material may be one of SiN, high-index doped silica glass, LN, Al2O3, AlN or a polymer having a negative TOC. The tuning mechanism may comprise an electro-optic phase modulator coupled to the first arc portion.

[0024] In some implementations, the tuning mechanism is configured to modulate the resonant wavelength of the MRR waveguide.

[0025] In some implementations, the tuning mechanism further comprises a second arc portion tuner coupled with a segment of the second arc portion.

[0026] In some implementations, the hybrid MRR device comprises one or more bus waveguides optically coupled to the MRR waveguide to couple light in or out of the MRR waveguide.

[0027] In some implementations, the one or more bus waveguides comprise a single bus waveguide optically coupled to the MRR waveguide in an all-pass configuration. The single bus waveguide may be optically coupled to the first arc portion of the MRR waveguide or to the second arc portion of the MRR waveguide.

[0028] In some implementations, the one or more bus waveguides comprise an add bus waveguide and a drop bus waveguide optically couple to the MRR waveguide in an adddrop configuration. The add and the drop bus waveguides may be coupled to the different segments of the second arc portion of the MRR waveguide. In some variants, one of the add and drop bus waveguides is optically coupled to the first arc portion of the MRR waveguide, and another one of the add and drop bus waveguides is optically coupled to the second arc portion of the MRR waveguide.

[0029] In accordance with one aspect, there is provided an optical modulator comprising at least one hybrid MRR as described herein. In accordance with another aspect, there is provided an external cavity laser, comprising a pair of MRR devices in a Vernier configuration, at least one MRR device of said pair being a hybrid MRR device as described herein.

[0030] In accordance with yet another aspect, there is provided an MRR-based optical filter comprising at least one hybrid MRR as described herein.

[0031] Other features and advantages will be better understood upon of reading of detailed embodiments with reference to the appended drawings.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS FIGs. 1A and 1B (PRIOR ART) respectively show an all-pass MRR configuration and the associated transmission spectrum.

[0033] FIGs. 2A and 2B (PRIOR ART) respectively show an add-drop MRR configuration and the associated transmission spectra.

[0034] FIG. 3 (PRIOR ART) schematically illustrated the operation of an optical MRR modulator in which the refractive index modulation is achieved through the plasma dispersion effect.

[0035] FIG. 4 (PRIOR ART) schematically illustrated the operation of an optical MRR modulator in which the refractive index modulation is achieved through the thermo-optic effect.

[0036] FIG. 5 is schematic representation in top view of a hybrid MRR device according to one embodiment.

[0037] FIG. 6 is a schematic side elevation view in transparency of the hybrid MRR device of FIG.

[0038] 5.

[0039] FIG. 7 is a schematic side elevation view in transparency of a hybrid MRR device including an additional heater.

[0040] FIGs. 8A to 8D shown different configurations of hybrid MRR devices according to different embodiments. FIG. 9 shows a tuning mechanism including N or P -doped silicon elements.

[0041] FIG. 10 shows a tuning mechanism based on the plasma dispersion effect; FIG. 10A is an enlarged view of the PN junction of the tuning mechanism of FIG. 10.

[0042] FIGs. 11A and 11 B respectively show the through port spectra and cross port spectra of a hybrid MRR device used as a modulator.

[0043] FIG. 12 shows the thermal stability range of a hybrid MRR device made of Si and SiN; FIGs. 12A to 12C (PRIOR ART) show the simulated transmission spectra at temperatures T1 and T2 of a Si only MRR device (FIG. 12A) and the corresponding extinction ratio at temperature T1 (FIG. 12B) and temperature T2 (FIG. 12C); FIGs. 12D to 12F show the simulated transmission spectra at temperatures T1 and T2 of a hybrid MRR device (FIG.

[0044] 12D) and the corresponding extinction ratio at temperature T 1 (FIG. 12E) and temperature T2 (FIG. 12F).

[0045] FIG. 13 is a schematic representation of an ECL including a pair of hybrid MRR devices in a Vernier configuration.

[0046] FIG. 14 is a schematic representation of an MRR-based optical filter including hybrid MRR devices in a cascade configuration; FIGs. 14A and 14B show the associated transmission spectra at the through port and drop port of the filter of FIG. 14, respectively.

[0047] FIG. 15 is a schematic representation of an MRR-based optical filter including parallelly-coupled hybrid MRR devices.

[0048] FIG. 16 is a schematic representation of an MRR-based optical filter including serially-coupled hybrid MRR devices.

[0049] FIG. 17 is schematic representation in top view of a hybrid MRR device according to one embodiment having a hybrid TFNL / SiN stack in the first arc portion; FIG. 17A is crosssection view along lines A-A of FIG. 17; FIG. 17B is cross-section view along lines B-B of FIG. 17. DETAILED DESCRIPTION

[0050] It is to be understood that the phraseology and terminology employed in the present description is not to be construed as limiting and are for descriptive purposes only.

[0051] Furthermore, it is to be understood that the technology can be carried out or practiced in various ways and that it can be implemented in embodiments other than the ones outlined described herein.

[0052] Meanings of technical and scientific terms used herein are to be commonly understood as by one of ordinary skill in the art to which the invention belongs, unless otherwise defined.

[0053] In the following description, similar features in the drawings have been given similar reference numerals. In order not to unduly encumber the figures, some elements may not be indicated on some figures if they were already mentioned in preceding figures. It should also be understood herein that the elements of the drawings are not necessarily drawn to scale and that the emphasis is instead being placed upon clearly illustrating the elements and structures of the present embodiments.

[0054] The terms “a”, “an” and “one” are defined herein to mean “at least one”, that is, these terms do not exclude a plural number of items, unless stated otherwise. Terms such as “substantially”, “generally” and “about”, that modify a value, condition or characteristic of a feature of an exemplary embodiment, should be understood to mean that the value, condition or characteristic is defined within tolerances that are acceptable for the proper operation of this exemplary embodiment for its intended application.

[0055] Unless stated otherwise, the terms “connected” and “coupled”, and derivatives and variants thereof, refer herein to any structural or functional connection or coupling, either direct or indirect, between two or more elements. For example, the connection or coupling between the elements may be mechanical, optical, electrical, logical, or any combination thereof.

[0056] In the present description, the terms “light” and “optical”, and variants and derivatives thereof, are used to refer to radiation in any appropriate region of the electromagnetic spectrum. The terms “light” and “optical” are therefore not limited to visible light, but can also include, without being limited to, the infrared or ultraviolet regions of the electromagnetic spectrum. Also, the skilled person will appreciate that the definition of the ultraviolet, visible and infrared ranges in terms of spectral ranges, as well as the dividing lines between them, may vary depending on the technical field or the definitions under consideration, and are not meant to limit the scope of applications of the present techniques.

[0057] To provide a more concise description, some of the quantitative expressions given herein may be qualified with the term "about". It is understood that whether the term "about" is used explicitly or not, every quantity given herein is meant to refer to an actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including approximations due to the experimental and / or measurement conditions for such given value.

[0058] In the present description, the term “about” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e. the limitations of the measurement system. It is commonly accepted that a 10% precision measure is acceptable and encompasses the term “about”.

[0059] In the present description, when a broad range of numerical values is provided, any possible narrower range within the boundaries of the broader range is also contemplated. For example, if a broad range value of from 0 to 1000 is provided, any narrower range between 0 and 1000 is also contemplated. If a broad range value of from 0 to 1 is mentioned, any narrower range between 0 and 1, i.e. with decimal value, is also contemplated.

[0060] In accordance with some aspects, there is provided a hybrid-material microring resonator (MRR).

[0061] MRRs are predominantly fabricated from Si, largely due to the excellent optical properties of silicon and its compatibility with existing semiconductor manufacturing processes. The high refractive index of silicon allows for strong light confinement within the small waveguides of typical MRRs, enabling compact device designs and efficient integration with other photonic components on a chip. However, Si MRRs face a significant challenge relative to thermal stability. The same temperature-dependent effect of the Si refractive index, i.e., nsi(T), which is beneficial for tuning the resonance of the MRR to a desired wavelength, can also negatively deviate the MRR from its intended operating wavelength due to temperature perturbations. Such undesired deviations are particularly problematic in precision applications, such as in wavelength division multiplexing (WDM) systems, where maintaining a stable and specific resonance wavelength can be a major requirement. For example, this thermal instability can negatively impact the performance of optical filters, modulators, and other photonic devices using MRRs that rely on consistent resonance behavior. As a result, the thermal sensitivity of Si MRRs poses a challenge to their reliability and performance in high-precision optical networks and systems. Similar challenges can be encountered with other materials have a similarly high thermos-optic coefficient (TOC). On the other hand, as mentioned above, this high temperature dependency can be advantageous for intentional tuning of the resonance of a MRR. In such cases, the electrical power consumption for tuning, referring to the energy consumed in adjusting the wavelength, is relatively low for MRRs made of a high TOC material.

[0062] The temperature-dependant refractive index of Si is given by the following equation:

[0063]

[0064] nSi(T) ~ + TOCsiX ΔT,

[0065] where nsi(T0) is refractive index of Si at a reference temperature To, AT is the temperature change respect to To(AT = T - To) and TOCsi= 1.86 x 10-4is the thermo-optic coefficient of Si.

[0066] For any MRR, the shift of the spectral response with respect to the temperature variation is independent of the MRR radius and is given by:

[0067] — = — TOC [m / °C]

[0068]

[0069] dT

[0070] Hence, for a MRR made of standard strip Si waveguide (220 nm x 500 nm) with an SiO2 cladding, the resonance wavelength shift (in C-band) with respect to the temperature variation is calculated as about:

[0071] dA.

[0072] 69 pm / °C

[0073]

[0074] dT And for a rib waveguide (220 nm x 500 nm and slab of 90nm) is about:

[0075] dA.

[0076] — « 74.3 pm / °C

[0077] dT

[0078] Other examples of higher TOC materials include InP (TOCinp = ~1.9e-4), InGaAsP (TOCinGaAsP = ~2e-4), GalnP (TOCGainP =~2e’4) and GaAs (TOCGQAS =~2.4e’4).

[0079] By contrast, MRRs made of material with a lower TOC such as silicon nitride (SiN) or QXP (trademark, also referred to as high-index doped silica glass (HDSG)) can provide lower temperature variations than silicon. For example, SiN has a TOC of TOCsiN= 2.51 x 10-5. A SiN MRR thus has much better stability:

[0080] « 19 pm / °C.

[0081]

[0082] In another example, QXP has a TOC of TOCQXP= 1.4 x 10-5, resulting in a temperature variation of:

[0083] d.. „ pm

[0084] — « 13 —.

[0085] dT °C

[0086] Other examples of lower TOC materials include LN (Lithium Niobate, TOCLN = ~4e-5) AI2O3(TOCAI2O3=~ 3e-5)), AIN (TOCAIN =~ 3.5e-5) or polymers having a negative TOC (for example of the order of -6e-5).

[0087] However, a drawback of the use of lower TOC materials in MRRs is that it also leads to more complicated tuning of the resonance wavelength, which requires significantly higher electrical power for tuning than equivalent Si structures.

[0088] Other materials used for the fabrication of MRRs also have their advantages and drawbacks. For example, a ring waveguide made of TFLN (Thin-Film Lithium Niobate) could advantageously provide strong modulation capabilities through the electro-optic effect, for example for data modulation applications, as well as second-order nonlinearity X2, allowing to use spontaneous parametric down-conversion (SPDC), for example for entangled photon pairs. By comparison, SiN can provide lower propagation loss, better thermal stability and moderate third-order nonlinearity x3, allowing the use of spontaneous four-wave mixing (SFWM), for example for frequency comb generation). The use of SiN as a waveguide material could also allow for smaller footprint and low loss routing than TFLN.

[0089] In accordance with one aspect, there is provided a hybrid MRR) device, having an MRR waveguide which includes two different waveguide materials, that is, the MRR waveguide has a first arc portion made of a first waveguide material and a second arc portion made of a second waveguide material. As explained below, the first waveguide material has at least one optical property providing a tunability of the resonant wavelength of the MRR waveguide.

[0090] Referring to FIGs. 5 and 6, there is shown a hybrid MRR device 20 according to the one embodiment, also referred herein as the MRR 20. The hybrid MRR device 20 includes an MRR waveguide 21, which is a ring-shaped structure forming a closed-loop optical path of radius R,. The MRR waveguide 21 is composed of two materials, that is, it forms a hybrid-material MRR. The MRR waveguide 21 is composed of a first arc portion 22 made of a first waveguide material, and a second arc portion 24 made of a second waveguide material. Note that the MRR does not need to be perfectly circular; it can have any closed loop shape whose circumference satisfies a target radius, i.e., Li = 2TT R,. It will also be understood that the first and second arc portions may be embodied by any portion of this circumference, regardless of its shape. For example, in some embodiments (see Fig. 17), one of the arc portions 21 may be a straight segment of the MRR waveguide. A pair of optical vias 26a, 26b optically connect the first arc portion 22 and the second arc portion 24. A tuning mechanism 30 is coupled to the first arc portion 22 for tuning the resonant wavelength of the MRR waveguide 21.

[0091] In some implementations, the MRR waveguide 21 may be embodied by a strip waveguide in both waveguide materials. In other variants, the MRR waveguide may be embodied by a rib waveguide in either material, or partially strip and partially rib in both materials. By way of example, the hybrid MRR device 20 may be incorporated in a semiconductor chip 25 embodied by a SOI structure comprising several layers. In some implementations, as best seen in FIG. 6, the semiconductor chip 25 may include a substrate 60, for example made of Si, on which is provided a cladding 62, for example made of SiO2. The first arc portion 22 and second arc portion 24 may be embodied by functional layers embedded in the cladding 62 of the semiconductor chip 25 and extending generally parallel to the substrate 60. In some implementations, the first arc portion 22 and second arc portion 24 may respectively extend at different heights hi and h2 from the substrate 60.

[0092] In some implementations, the second waveguide material has a thermo-optic coefficient lower than the thermo-optic coefficient of the first waveguide material. By way of example, the first waveguide material may be Si, and the second waveguide material may be SiN. In other variants, the first waveguide material may be InP or InGaAsP, combined with SiN, QXP, LN, AI2O3, AIN, a polymer having a negative TOC or the like as the second waveguide material. The ratio between the first and second arc portions may be optimized to achieve either or both of a greater thermal stability and effective tuning. Thermal stability involves a maximization of the second arc portion, made of the material having the lower TOC, such that, for example, Lsi« LsiNor x = Lsi / Ltot« 1, where Ltot= Lst + LSIN + Ltaper- In some implementations, effective tuning is constrained by the maximum safe operating current and the temperature limit of the tuning mechanism to avoid damage to associated heater. In some embodiments, considering that heater resistance is defined by R = ps—, where LH, WHand psare the length, width, and sheetWH

[0093] resistivity of the heater, respectively, and assuming all length of the Si waveguide are covered by the heater (i.e., LH= Lsi), then, we find that Lsi min= max[LsiJmax, Lsi Tmax], where Lsi Imax=2Pzic Whis the minimum heater length due to the maximum operating njmax Ps

[0094] current I2n Imaxrequired to provide electrical power P27lneeded to induce 2n phase A

[0095] change in the MRR, and Lsi Tmax= - is the minimum heater length due to the max TOCsi

[0096] maximum allowed temperature Tmaxof the heater. Therefore, x > xmin= Lsi min / Ltot. For example, if WH= 8pm, P27l= 50mW, I2n max= 60mA, Tmax= 350° C, LsiN= 200pm, taper 60pm, TOC 1.86 X

[0097]

[0098] 10, ^Si_min mClx L i_imax9.3pm, ^si Tmax 23.8pm] = 23.8pm, resulting x > xmin= 8.4%.

[0099] The expression “optical via” may be understood to refer to any device or structure allowing the transfer of light between different waveguide segments, by analogy to the use of electrical vias in electronic chip design. In some implementations, the optical vias 26a, 26b may be embodied by a dual-layer transition such as shown in Figure 6 of Wang, Pengfei et al, “Design and fabrication of a SiN-Si optical phased array chip”, Photonic Research, Vol. 8, Issue 6, pp 912-919 (2020), the entire contents of which is incorporated herein by reference. Another embodiment of light coupling between functional layers in two different materials is for example shown in Li, Xin, et al., “Ultra-low-loss multi-layer 8x8 microring optical switch”, Photonics Research, Vol. 11, Issue 5, pp.712-723 (2023), the entire contents of which is incorporated herein by reference. It will be readily understood that the coupling of light between the different functional layers may be performed in other manners. By way of example, one or more optical edge couplers or grating couplers allowing light to travel between the first arc portion 22 and second arc portion 24 may be provided.

[0100] In typical embodiments, the hybrid MRR device 20 includes one or more bus waveguides 32 optically coupled to the MRR waveguide 21 to couple light in or out of the MRR waveguide 21. FIGs. 8A to 8D show different light coupling configurations, by way of example. In some implementations, the hybrid MRR device 20 may have an all-pass configuration in which, as explained above, input light either circulates around the MRR waveguide 21 or passes through a bus waveguide 32 without being dropped at any port. This is for example shown in FIG. 8B, wherein the bus waveguide 32 is made of Si and coupled to the Si first arc portion 22, or in FIG. 8D, wherein the bus waveguide 32 is made of Si N, QXP or other material with a low thermo-optic coefficient and coupled to the second arc portion 24 made of the same material. In other implementations, the hybrid MRR device 20 may have an add-drop configuration in which input light can be coupled into the MRR waveguide 21 from an add bus waveguide 32a and dropped into a drop bus waveguide 32b. The add or drop bus waveguides may both made of SiN, QXP or other material with a low thermo-optic coefficient and coupled to the second arc portion 24, such as shown in FIG. 8C. in another variant, illustrated in FIG. 8A, one of the add and drop bus waveguides 32a may be made of Si and coupled to the first arc portion 22, while the other is made of SiN, QXP or other material with a low thermo-optic coefficient and coupled to the second arc portion 24.

[0101] As mentioned above and referring back to FIGs. 5 and 6, the hybrid MRR device 20 further includes a tuning mechanism 30 coupled to at least the first arc portion 22.

[0102] In some implementations, the tunability of the resonant wavelength of the MRR waveguide is based on heating, and the thermo-optic (TO) effect is used for tuning and switching between adjacent and non-adjacent wavelength channels. The tuning mechanism 30 may for example include a first arc portion tuning heater 34 placed above the first arc portion 22 of the MRR waveguide. The tuning heater 34 may have an arched shape following the curvature of the first arc portion 22. As best seen on FIG. 6, in the illustrated embodiment the first arc portion tuning heater 34 may include a metallic heat resistor 36 through which a current is passed to create heat in the resistor, whose temperature modifies the index of semiconductor materials. Metals can be used as heaters which should have a higher resistivity than the Cu and Al which typically is used for routing / pads and metallization. Titanium nitride (TiN), tungsten (W) lines above the waveguide are typically used. In the illustrated implementation, the metallic heat resistor 36 is for example embodied by a TiN arch extending within the cladding 62 of the semiconductor chip 25 directly above the first arc portion 22. Metal electrodes 38 are provided over the cladding 62 and are connected to extremities of the metallic heat resistor 36. Metal vias 40 may provide the electrical connection between the electrodes 38 and the metallic heat resistor 36.

[0103] Referring to FIG. 9, in another embodiment the first arc portion tuning heater 34 may include N or P -doped silicon elements 42 as heaters to change the refractive index of the first arc portion 22 of the MRR waveguide 21. The doped silicon elements 42 may be positioned adjacent to the first arc portion 22. Having a shorter distance between the heater and the waveguide may increase the temperature of the first arc portion 22 of the MRR waveguide 21 and subsequently change its refractive index while requiring a lower electrical power than metal electrodes. Similarly to metallic heaters, Si-based heaters can be biased to create heat and cause a refractive index change in the close-by waveguide through the thermo-optic effect. The Si-doped heater may be positioned next to the MRR waveguide or in implementations, the MRR waveguide itself may act as the resistor. Other schemes using the thermo-optic effect to change the index of the MRR waveguide may also be used.

[0104] In other implementations, the tunability of the resonant wavelength of the MRR waveguide and the tuning mechanism may be based on the plasma dispersion effect or electric-field-induced band-edge effects. Referring to FIGs. 10 and 10A, there is shown an embodiment in which the first arc portion tuning heater includes a PN junction 44 provided across the first arc portion 22. Such an embodiment is of particular interest for high-speed applications of the hybrid MRR device 20. In such embodiments the first waveguide material may be a doped semiconductor material such as for example a doped Si waveguides (PN, PIN) if the free-carrier plasma dispersion effect for phase modulation, or a doped InP waveguides (PIN / NIN) if electric-field-induced band-edge effects (QCSE I Franz-Keldysh) are used. The second waveguide material may be SiN, QXP, LN, AI2O3, AIN, a polymer having a negative TOC or the like. As best seen in FIG. 10A, the PN junction 44 includes a series of doped layers 45 extending generally parallel to first arc portion 22 and forming a stack along a transverse axis. A voltage is applied to the PN junction through electrical vias which connect Cu / AI routings / pads to the doped sections with highest concentration for example P++ and N++. Applying voltage changes the carrier concentration within the silicon waveguide, which in turn alters its refractive index and absorption properties. This is achieved through carrier injection or depletion: voltage applied to a forward-biased PIN diode injects carriers, while a reverse-biased PN or PIN junction depletes carriers. The change in carrier density reduces the refractive index, enabling phase modulation of light, and can increase absorption, affecting intensity modulation.

[0105] By way of example, FIGs. 10 and 10A show such a tuning mechanism applied to a hybrid MRR device 20 in an add-drop configuration with the add and drop bus waveguides 32a and 32b coupled to opposite sections of the second arc portion 24. In this variant, CW light from the add bus waveguide 32a is coupled into the MRR waveguide 21 through the second arc portion 24. The coupled light then propagates counterclockwise through the second arc portion 24 and subsequently enters the first arc portion 22 section through a first optical via 26a. Through a strip-to-Rib taper in the Si first arc portion 22, the light is directed to the PN junction 44 in which, depending on the voltage applied to the PN junction 44 through electrical vias 46a, 46b, it accumulates a phase shift. The light is then coupled back to the first arc portion 22 and then to the second arc portion 24, through another Rib-to-Strip taper and a second optical via 26b, respectively. The light then continues to circulate counterclockwise around the MRR waveguide 21. A portion of this circulating light couples out of the MRR waveguide 21 to the drop bus waveguide 32b and appears as the output signal. Of course, a similar tuning mechanism may be used in other MRR configurations, such as the ones shown in FIGs. 8A, 8B and 8D.

[0106] In other variants, the tunability of the resonant wavelength of the MRR waveguide is based on the electro-optic effect. For example, the first waveguide material may be TFLN (Thin- Film Lithium Niobate), which provides strong modulation capabilities through the electrooptic effect, and the tuning mechanism may include an electro-optic phase modulator coupled to the first arc portion. The second waveguide material may for example be SiN, QXP, LN or the like. Referring to FIGs. 17, 17A and 17B, there in shown an example of such an embodiment. The illustrated MRR device 20 has an oblong-shaped MRR waveguide 21 with a first arc portion 22 made of a hybrid TFLN / SiN stack 22a, 22b and a second arc portion 24 made of SiN, for example. In the TFLN / SiN region 22, light is guided in hybrid modes, distributed between the TFLN waveguide 22a and the underlying SiN waveguide 22b. The width of the SiN waveguide is reduced in the optical via regions for SiN to controllably push and pull light into the TFLN region, to enable efficient EO modulation in the TFLN region. The electro-optic phase modulator includes one or more electrodes 54 proximate the TFLN region to apply EO modulation.

[0107] It will be readily understood that in the context of the present application, the expression “tuning” refers to any mean of changing the reflective index of a portion of the MRR waveguide, consequently affecting the resonant wavelength. In some embodiments the tuning mechanism may be configured to modulate the resonant wavelength of the MRR waveguide, that is, change the refractive index of the MRR waveguide in a periodic fashion, such that tuning is continuous rather than punctual. In other words, modulation of the resonant wavelength is considered herein as a form of periodic tuning.

[0108] In some variants, such as shown in FIGs. 7 and 8A to 8D, the tuning mechanism may include a second arc portion tuning heater 50 provided over a segment of the second arc portion 24 of the MRR waveguide 21 and used to fine-tune the resonant wavelength of the light circulating along the MRR waveguide. In embodiments where the additional heater operates on a section of waveguide having a lower TOC than Si, more power may be required to affect the reflective index of the second arc portion 24. The additional heater may for example have a similar configuration as the tuning heater of FIG. 6. The second arc portion tuning heater 50 may also be arc shaped and follow a portion of the curvature of the second arc portion 24. The second arc portion tuning heater 50 may have a variety of sizes and shapes, such as for example shown in FIGs. 8A to 8D. Applications

[0109] Hybrid MRR devices such as disclosed herein may provide a valuable enhancement of the thermal stability of devices and components based on MRRs, including filters, modulators, and ECLs.

[0110] The combined optical properties of first and second arc portions of different materials may be useful in a variety of contexts additional to those described above, such as, by way of example:

[0111] for telecom / data modulation applications, a more thermally stable ring resonator with fast modulation capabilities;

[0112] for quantum and nonlinear applications, versatile sources (photon or comb) with which supports both SPDC and SFWM. For example, a SiN arc portion may generate combs via x3 and a TFLN arc portion may tune the comb spacing and stabilizes the repetition rate. In another example, SPDC in TFLN may be used for entangled photon pairs and SFWM in SiN for additional photon sources;

[0113] Other uses in microwave photonics, metrology etc.

[0114] In some implementations, the MRR devices described above may be used in an intensity modulator.

[0115] Intensity modulation is a technique used in optical communication and other fields where the intensity, or power, of a light signal is varied to encode information. Intensity modulation is usually performed using either a Mach-Zehnder interferometer (MZI) or a ring resonator structure.

[0116] MZI modulators are tolerant to manufacturing errors and temperature change, but they typically consume high power, are large in size, and have nonoptimal optical loss. Ring resonator modulators, on the other hand, can be very small, highly efficient, low loss, and high speed. Typical ring resonators are however very sensitive to manufacturing errors, temperature drift, or laser wavelength change, thus they typically need dynamic and precise tuning, which may potentially require a control circuit and consume additional power. Using a hybrid MRR device such as described herein can alleviate at least some of these drawbacks. By way of example, the hybrid MRR device in the add-drop configurations of FIGs 8A, 8C or 10 may be used as an intensity modulator. With reference to FIGs. 11A and 11 B, the modulation process can be visualized as a switch that controls whether the light passes through the modulator unchanged or whether its intensity or phase is altered. As an example, first, the resonance wavelength is perfectly aligned with the incoming light wavelength for an applied voltage of V1. Then, the light can be completely coupled into the MRR waveguide and redirected to the drop port, effectively representing a "1" in digital data terms in the drop port and ”0” in the through port. Next, when the resonance wavelength is shifted with another applied voltage value of V2, the light passes through, representing a "0" in the drop port and a ”1” in the through port. This binary modulation is typically used as the foundation of data encoding in optical communication systems. The optical transmission spectrum of the add bus waveguide 32a has notches at the wavelength resonances or the MRR waveguide 21, while the transmission spectrum of the drop bus waveguide demonstrates peaks at the MRR waveguide resonances. The resonance wavelengths of the MRR waveguide 21 can be shifted by modulating voltages applied as part of the tuning mechanism. With input laser power at the input of the add bus waveguide 32a at wavelength A0, this ring resonance modulation produces an extinction ratio (ER) at the output of the drop bus waveguide 32b, as shown in FIGs. 11A and 11 B. The ring resonance is characterized by its full width at half maximum (FWHM) δλ; and the modulation is characterized by the resonance shift AA. To achieve large ER with small loss, the ratio Δλ / δλ is preferably maximized.

[0117] The spectral response shift of the multi-material optical MRRs with respect to the temperature shift quantifies the thermal stability enhancement of the proposed filter or modulator structures. An equation describing the spectral shift of the multi-material MRRs is derived and shown below:

[0118] dA. | (rOCSiLsi+ T0CsiNLsiN+ T0Csi—SiN Lsi_SiN _taper^ / pTTly

[0119]

[0120] & T YlgSi. Lsi " I" ^-gSiN^SiN + YlgSi-SiN ^Si_SiN_taper C?

[0121] Where Lsi siN taper, T0Csi siN taper, and ngsi siN_taperare the length, thermo-optic coefficient and group index of the optical vias, respectively. This equation comprises all the three sections of a multi-material MRR (here with two materials of Si and SiN) including Si and SiN sections as well as the taper region where the light is transferred from one material to another. This equation shows that the thermal stability of a multi-material MRR is found anywhere in between the stability of MRRs completely made of each material. FIG. 12 shows the thermal stability range of a hybrid MRR made of Si and SiN. A multimaterial MRR with a larger SiN portion represents a higher stability.

[0122] The ability to dynamically alter the resonance condition in real-time is what enables optical MRR modulators to encode data onto a light signal. By rapidly switching the refractive index using electric fields, the modulator can shift the resonance in and out of alignment with the input light's wavelength, modulating the light at high speeds. This rapid switching capability is crucial for modern optical communication systems, which require modulation rates in the gigahertz range to meet the demands of high-speed data transmission.

[0123] To evaluate the performance of the proposed hybrid MRR modulators, simulations were carried out using the Ansys MODE and INTERCONNECT platforms. The behaviour of an MRR modulator fully made of silicon was first examined at two temperatures separated by AT = T2 - T1 = 0.1 °C. The ring has a circumference of 300 pm, with one-third of its length (100 pm) doped. FIG. 12A (PRIOR ART) shows the corresponding transmission spectra. As expected, the temperature change induces a spectral shift, which reduces the extinction ratio of the Si MRR modulator from 19 dB (FIG. 12B - PRIOR ART) to 9.5 dB (FIG. 12C - PRIOR ART).

[0124] Next, the 200 pm undoped section of the ring is replaced with an equivalent optical length of SiN waveguide, and the same analysis is performed. Figure 12D shows the transmission spectra of this hybrid MRR modulator. Although the hybrid MRR also exhibits a thermally induced resonance shift, the magnitude of the shift is noticeably smaller. Figures 12E and 12F present the spectra at the two temperatures, where the extinction ratio decreases from 19 dB to 14 dB. In comparison, the Si MRR modulator experiences a 9.5 dB reduction in extinction ratio for the same temperature change, whereas the hybrid MRR shows only a 5 dB reduction.

[0125] In addition to binary modulation (on / off states), optical MRR modulators can also be used for more complex modulation schemes, such as phase modulation or quadrature amplitude modulation (QAM). In these schemes, the modulator is used not only to control the intensity of the light but also its phase, allowing for the transmission of more bits of information per modulation cycle. This increases the data throughput of the system without requiring higher bandwidths.

[0126] Optical MRR modulators have found widespread application in various domains, particularly in high-speed optical communication systems. Their compact size and ability to be integrated into photonic circuits make them ideal for use in data centers, telecommunications, and other environments where space and power efficiency are paramount.

[0127] Some of the key advantages of optical MRR modulators include:

[0128] • High modulation speeds: Optical MRR modulators can achieve modulation speeds in the gigahertz range, making them suitable for high-speed data transmission.

[0129] • Low power consumption: Due to their efficient design, these modulators consume less power compared to other types of optical modulators, which is crucial for large-scale deployment in data centers.

[0130] • Integration with silicon photonics: Optical MRR modulators are compatible with silicon photonics, allowing them to be fabricated using standard semiconductor manufacturing processes. This integration facilitates the development of compact, cost-effective photonic circuits.

[0131] In other implementations, such as for example illustrated in FIG. 13, the proposed hybrid MRR devices may be used in forming the external cavity of an External Cavity Laser (ECL) 100. In ECLs, optical MRR are used to provide selective feedback to the gain medium, thus determining the laser's output wavelength. The high quality-factor (Q-factor) of the ring resonator ensures that only specific wavelengths are amplified and oscillate within the laser cavity, leading to a highly coherent and stable laser output. This application is particularly important in creating tunable lasers for sensing, telecommunications, and spectroscopy.

[0132] In the illustrated example of FIG. 13, the ECL 100 includes a gain section 102 provided between a passive cavity reflector 104 and a tunable cavity reflector 106 forming a frequency selective feedback circuit. The tunable cavity reflector 106 includes a coupler 108 and a pair of hybrid MRR devices 20a and 20b cascaded and in add-drop configuration. The hybrid MRR devices may be according to any suitable variant described herein. In other implementations (not shown), the hybrid MRR devices may be placed in a loop configuration, or a separate loop mirror can be added to the end of the MRR cascade, or in a ring cavity. Broadband and / or tunable couplers are typically used to form the loop of the structure. The tunable cavity reflector 106 serves as a single wavelength filter for the ECL 100, and a phase shifter 114 positioned between the gain section 102 and tunable cavity reflector 106 is used to tune the laser cavity modes. The hybrid MRR devices 20a and 20b are designed in a Vernier configuration, whereby they have slightly different radii, giving slightly different free spectral ranges (FSRs), to obtain a Vernier effect and therefore shape the Vernier spectrum needed for wavelength tuning. The optical output of the ECL 100, whether as the main output or a monitoring output, can be extracted from various points within the laser structure. These points include the high-reflectivity (HR) mirror 104, the ports of the MRR devices 20a, 20b, and the coupler 108. For the latter, this is applicable if the coupler is non-symmetric (other than 50% / 50%) or if a tunable coupler is employed.

[0133] As understood by those skilled in the art, the so-called Vernier Effect uses two (or more) resonators at two (or more) different resonant frequencies having FSRs that are slightly different, such that they overlap perfectly only at multiples of their individual FSRs. The FSR of a given hybrid MRR device for light at a wavelength A is given by FSRt = A j, „ j. j where FSRLis the FSR of the ith

[0134]

[0135] / VngSiLSi_RingSiNLSiN_RingSi-SiNLSi_SiN_taper_Ri)

[0136] MRR device, and RLis the ithMRR of the Vernier filter. By convention, the Vernier FSR of a pair of MRR devices is determined by:

[0137] FSR1X FSR2FSRv = \FSRI — FSR2\

[0138] A2{^SiR2LsiR1) + ngSiN(LsiNR2LSINRI) + TlgSi-siN(Lsi-SiN_taper_Rl ^Si-SiN_taper_Rl

[0139]

[0140] ngSi^Si_R2 +ngSiN^SiN_R2 +ngSi-SiN ^Si_SiN_taper_R2 ~mngSi^Si_Rl +ngSiN^SiN_Rl +

[0141] ^■gSi-SiN si_SiN_taper_Rl- Assuming the optical vias are the same for both MRRs, the Vernier FSR of a pair of MRR devices is determined by: FSR. x FSR2_ _FSRV =\FSRr- FSR2\ (LSiR2-LSiR1) +ngSiN(LSiNR2~ ^ 1

[0142] (m — 1) 1n

[0143]

[0144] gSi^Si_R2 +ngSiN^SiN_R2=~ngSi^Si_Rl +ngSiN^SiN_Rl ~ ~ngSi-SiN ^Si_SiN_taper where m and m-1 are coprime integers for any m in a two MRR Vernier filter, m and m-1 numbers are known as resonant numbers of the corresponding MRR. m also quantifies the increased tuning efficiency of the Vernier MRRs in comparison to a single MRR, i.e.,

[0145] FSRV /

[0146] m

[0147]

[0148] ~ / FSRr■

[0149] In the proposed structure each MRR device of the Vernier configuration consists of a hybrid MRR device with at least two materials including an Si first arc portion 22a, 22b and SiN second arc portion 24a, 24b. The two material sections are connected using optical vias. In this structure, most of the MRR waveguide is made of SiN resulting to a more stable response thanks to the lower thermo-optic coefficient of the SiN. However, tunning of each MRR waveguide is performed through the Si first arc portion 22a, 22b which exhibits a larger thermo-optic effect, leading to lower tuning power consumption. In addition, a microheater can be placed on the top of SiN second arc portion 24a, 24b for fine tunning. Of course, other materials having high and low TOCs may be used for the first and second arc portions of the hybrid MRR devices.

[0150] In some implementations, the proposed hybrid MRR device may be used in MRR-based optical filters. MRR based optical filters exploit the resonant properties of coupled ring waveguides to achieve precise wavelength selectivity in integrated photonic circuits. Each MRR device acts as a wavelength dependent element that couples light efficiently only at discrete resonant wavelengths, determined by the condition that the optical path length around the ring equals an integer multiple of the optical wavelength. In a basic single MRR configuration, the filter exhibits a Lorentzian transmission response characterized by a narrow bandwidth and high extinction ratio. More advanced filter architectures combine multiple MRRs in various coupling topologies such as ladder, parallel-coupled, serial-coupled structures, etc to achieve higher order filtering responses. The number of rings determines the filter order, which in turn governs key spectral properties such as the bandwidth, flatness of the passband, side-lobe suppression, and roll-off steepness. Higher order MRR filters therefore enable more sophisticated spectral shaping, allowing precise control over transmission profiles essential for DWDM and signal processing applications. The operation of MRR-based filters, however, is inherently sensitive to temperature variations. The resonant wavelength of each ring depends on both its physical dimensions and the effective refractive index of the guided mode, both of which vary with temperature due to the thermo-optic effect of the constituent materials. Even minor temperature fluctuations can induce resonance shifts on the order of tens of picometers, leading to misalignment between cascaded resonators or between the filter’s designed spectral response and the target wavelength grid. In multi-ring or higher order filters, such mismatches can significantly distort the overall transmission spectrum, degrading the filter’s performance and stability. For this reason, achieving temperature-stable MRRs is desired. This can be accomplished by employing hybrid MRRs devices according to any variant above or equivalents thereto. Such stabilization ensures that the MRR-based optical filter maintains its intended resonance alignment and spectral response, thereby guaranteeing consistent performance in practical, temperature-varying environments.

[0151] FIG. 14 shows a schematic of a ladder-type MRR-based optical filter 200 having a plurality of hybrid MRR devices with identical MRRs (same waveguide structure and radii) 20a, 20b, 20c, 20d coupled in a cascaded configuration. A through bus waveguide 232a having an input port 233 and a through port 234 is coupled to a first set of the hybrid MRR devices 20a, 20b, whereas a drop bus waveguide 232b having an add port 235 and a drop port 236 is coupled to a second set of the hybrid MRR devices 20c, 20d. The MRR waveguide 21a, 21b, 21c, 21d of each hybrid MRR device 20a, 20b, 20c, 20d is coupled to both a bus waveguide 232a, 232b and the next hybrid MRR device 20a, 20b, 20c, 20d in sequence. A 7t-phase shifter 238 is provided in the through bus waveguide 232a to create a pi phase shift between the two arms. The structure is termed “ladder” because of its resemblance to an electrical ladder network, with alternating coupling sections forming rungs between two parallel optical paths. Each hybrid MRR device 20a, 20b, 20c, 20d acts as a wavelength-selective element that introduces a resonant phase shift and amplitude modification to the propagating light.

[0152] The transmission characteristics of the through port 234 and drop port 236 in such MRR-based optical filters are governed by the interference of optical fields propagating along different paths. At the through port, the transmitted signal results from the superposition of the light that propagates directly through the bus waveguide and the light that couples into the resonators, circulates, and recouples back into the bus after acquiring a wavelength dependent phase shift. Constructive or destructive interference between these two components leads to the characteristic resonant dips observed in the through-port spectrum (FIG. 14A). At the drop port 236, the output field arises from the interference of the circulating light that is coupled from the ring into the drop bus waveguide 232b, where only resonant wavelengths interfere constructively and are efficiently transmitted. This interference-based mechanism governs the spectral response of both ports and allows precise control over the filter’s shape and selectivity (FIG. 14B).

[0153] Using MRRs with reduced temperature sensitivity can significantly enhance the overall stability and reliability of the filter. When the resonant wavelengths of individual rings remain relatively invariant under thermal fluctuations, the alignment between cascaded resonators and the designed filter response is preserved. This minimizes resonance drift, suppresses spectral distortion, and maintains consistent filter characteristics such as bandwidth, extinction ratio, and passband flatness. Consequently, employing relatively thermally stable hybrid MRR devices ensures that the MRR-based optical filter operates with high precision and stability, even in environments subject to varying thermal condition.

[0154] The same hybrid MRR design can also be employed in other types of MRR-based optical filters. By way of example, FIG. 15 shows a parallel-coupled MRR-based filter 200 having a plurality of hybrid MRR-devices 20a, 20b,... 20n coupled in parallel between a through bus waveguide 232a and a drop bus waveguide 232b, whereas FIG. 16 shows a serial-coupled MRR-based filter 200 having a plurality of hybrid MRR-devices 20a, 20b,... 20n coupled serially between a through bus waveguide 232a and a drop bus waveguide 232b. These filter architectures would equally benefit from the enhanced thermal stability provided by hybrid MRR devices, as maintaining precise resonance alignment among multiple rings is essential for achieving the desired spectral response.

[0155] As will be readily understood by one skilled in the art, in some variants of systems including multiple MRR devices as for example the optical modulators, external cavity lasers and MRR-based optical filter described above, only one or a portion of the MRR device of the system may have a hybrid design as described herein, with the other MRR devices of the system have a single material waveguide design. Of course, numerous additional modifications could be made to the embodiments described above without departing from the scope of protection as defined in the appended claims.

Claims

CLAIMS1. A hybrid microring resonator (MRR) device, comprising:an MRR waveguide having a resonant wavelength, the MRR waveguide comprising a first arc portion having a first waveguide material and a second arc portion having a second waveguide material, the first waveguide material having at least one optical property providing a tunability of the resonant wavelength of the MRR waveguide;a pair of optical vias optically connecting the first arc portion and the second arc portion; anda tuning mechanism coupled to at least the first arc portion for tuning the resonant wavelength of the MRR waveguide.

2. The hybrid MRR according to claim 1, wherein the first waveguide material has a thermo-optic coefficient higher than a thermo-optic coefficient of the second waveguide material.

3. The hybrid MRR according to claim 1 or 2, wherein the second waveguide material has lower propagation losses than the first waveguide material.

4. The hybrid MRR device according to any one of claims 1 to 3, wherein the tunability of the resonant wavelength of the MRR waveguide is based on heating.

5. The hybrid MRR device according to claim 4, wherein:the first waveguide material is one of Si, InP and InGaAsP; andthe second waveguide material is one of SiN, high-index doped silica glass, LN, AI2O3, AIN or a polymer having a negative TOC.

6. The hybrid MRR device according to claim 4 or 5, wherein the tuning mechanism comprises a first arc portion tuning heater placed above the first arc portion.

7. The hybrid MRR device according to claim 6, wherein the first arc portion tuning heater comprises a metallic heat resistor extending above the first arc portion.

8. The hybrid MRR device according to claim 7, wherein the first arc portion tuning heater comprises doped silicon elements adjacent to the first arc portion.

9. The hybrid MRR device according to any one of claims 1 to 3, wherein the tunability of the resonant wavelength of the MRR waveguide is based on the plasma dispersion effect or electric-field-induced band-edge effects.

10. The hybrid MRR device according to claim 9, wherein:the first waveguide material is a doped semiconductor material; and the second waveguide material is one of SiN, high-index doped silica glass, LN, AI2O3, AIN or a polymer having a negative TOC.

11. The hybrid MRR device according to claim 9 or 10, wherein the tuning mechanism comprises a PN junction provided across the first arc portion.

12. The hybrid MRR device according to any one of claims 1 to 3, wherein the tunability of the resonant wavelength of the MRR waveguide is based on the electro-optic effect.

13. The hybrid MRR device according to claim 12, wherein:the first waveguide material is a thin-film lithium niobate (TFLN); and the second waveguide material is one of SiN, high-index doped silica glass, LN, AI2O3, AIN or a polymer having a negative TOC.

14. The hybrid MRR device according to claim 12 or 13, wherein the tuning mechanism comprises an electro-optic phase modulator coupled to the first arc portion.

15. The hybrid MRR device according to any one of claims 1 to 14, wherein the tuning mechanism is configured to modulate the resonant wavelength of the MRR waveguide.

16. The hybrid MRR device according to any one of claims 1 to 15, wherein the tuning mechanism further comprises a second arc portion tuner coupled with a segment of the second arc portion.

17. The hybrid MRR device according to any one of claims 1 to 16, comprising one or more bus waveguides optically coupled to the MRR waveguide to couple light in or out of the MRR waveguide.

18. The hybrid MRR device according to claim 17, wherein the one or more bus waveguides comprise a single bus waveguide optically coupled to the MRR waveguide in an all-pass configuration.

19. The hybrid MRR device according to claim 18, wherein the single bus waveguide is optically coupled to the first arc portion of the MRR waveguide.

20. The hybrid MRR device according to claim 18, wherein the single bus waveguide is optically coupled to the second arc portion of the MRR waveguide.

21. The hybrid MRR device according to claim 17, wherein the one or more bus waveguides comprise an add bus waveguide and a drop bus waveguide optically couple to the MRR waveguide in an add-drop configuration.

22. The hybrid MRR device according to claim 21, wherein the add and the drop bus waveguides are coupled to the different segments of the second arc portion of the MRR waveguide.

23. The hybrid MRR device according to claim 21, wherein one of the add and drop bus waveguides is optically coupled to the first arc portion of the MRR waveguide, and another one of the add and drop bus waveguides is optically coupled to the second arc portion of the MRR waveguide.

24. An optical modulator comprising at least one hybrid MRR according to any one of claims 1 to 23.

25. An external cavity laser, comprising a pair of MRR devices in a Vernier configuration, at least one MRR device of said pair being a hybrid MRR device according to any one of claims 1 to 23.

26. An MRR-based optical filter comprising at least one hybrid MRR according to any one of claims 1 to 23.

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