An optical modulator

Abstract

This document describes an optical modulator comprising an electro-optic (EO) material waveguide positioned between a conductively doped semiconductor thin film layer and a top electrode. The EO waveguide is configured to guide optical signals and to undergo phase modulation in response to a vertically applied electric field established between the doped semiconductor layer and the top electrode.

Description

AN OPTICAL MODULATORCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to Singapore patent application no. 10202402133Q which was filed on 18 July 2024, the contents of which are hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] This application relates to an optical modulator that utilizes an electro-optic (EO) material as a waveguide and two conductively doped semiconductor thin film layers that are vertically offset from each other and the waveguide, while being vertically aligned with the waveguide.BACKGROUND

[0003] Optical modulators serve as indispensable elements in enabling fast and reliable data communication across a broad range of applications, including telecommunications, data centers, and high-performance computing. As the global demand for data transmission continues to accelerate and emerging technologies such as the Internet of Things (loT), autonomous vehicles, and artificial intelligence (Al) gain prominence, the importance of developing high-speed, high-efficiency, and low-loss optical modulators becomes increasingly evident. On a broader scale, advanced optical modulators are instrumental in ensuring the seamless operation of these next-generation technologies, thereby empowering them to realize their full potential.

[0004] Currently, two primary classes of optical modulators are under active development. The first class comprises silicon photonic modulators that are based on the free-carrier dispersion effect and the second class comprises modulators that utilize the electro-optic (EO) effect. Both technologies have been studied extensively over several decades and present distinct advantages and limitations. Silicon photonics modulators benefit from the maturity of the Si CMOS manufacturing ecosystem, enabling cost-effective mass production and seamless integration with silicon photonic integrated circuits (PICs) and, potentially, electronic circuits. Although recent demonstrations of silicon photonics modulators have shown promisingperformance, achieving a balance among key performance metrics, such as modulation efficiency, bandwidth, and insertion loss remains a significant challenge.

[0005] Conversely, modulators based on electro-optic (EO) materials readily achieve high modulation bandwidths compared to their silicon counterparts. However, the modulation efficiency of EO modulators often falls short of expectations due to the inherent trade-off between optical loss and electrode placement. Specifically, to minimize optical loss, the lossy electrodes would have to be typically positioned at a distance from the optical waveguide, particularly in devices with longer modulation lengths. While this electrode spacing effectively reduces optical absorption losses, it concurrently diminishes the strength of the electric field across the waveguide, which is directly proportional to the modulation efficiency in EO materials.

[0006] Additionally, those skilled in the art have explored the monolithic integration of functional materials onto the mature silicon-on-insulator (SOI) platform with the aim of expanding the range of applications beyond the intrinsic limitations of silicon (Si) photonics. Due to the absence of an intrinsic EO effect in silicon, the systematic incorporation of EO materials onto the SOI backbone at the wafer scale presents significant opportunities for enhancing device capabilities.

[0007] Initially driven by efforts to enhance properties of piezoelectric materials, scandium (Sc) doped aluminum nitride (AIN) has been found to possess substantially improved optical nonlinearity. In particular, the optical nonlinear coefficient d33in Sc0 36d / 0 72 / V has been demonstrated to be approximately twice that of lithium niobatc (LN) and an order of magnitude higher than that of undoped AIN. Furthermore, it was found that when AIN was doped with scandium, the Gibbs free-energy band structure of the wurtzite AIN lattice was altered, causing the coercive field required to reverse domain polarity below the dielectric breakdown threshold to reduce. This in turn enables ferroelectric domain engineering, facilitating the development of high-efficiency nonlinear optical devices.

[0008] In particular, Sc AIN retains many of the advantageous characteristics of AIN, such as a wide bandgap exceeding 5 eV for scandium concentrations up to 25%, thereby supporting optical operations ranging from the deep ultraviolet (DUV) to the mid-infrared (MIR)spectrum. In addition, ScAlN is compatible with complementary mctal-oxidc- semiconductor (CMOS) fabrication processes, allowing seamless integration with existing foundry-scale manufacturing infrastructure.

[0009] These favorable properties have sparked growing interest in adopting ScAlN as a platform for the next generation of photonic integrated circuits. Significant efforts have been directed towards optimizing thin-film growth through methods such as single alloyed target sputtering, co-sputtcring, metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and pulsed laser deposition (PLD). Recent progress in fabrication techniques have led to substantial reductions in propagation loss in ScAlN photonic waveguides, with propagation losses below 3 dB / cm now routinely achieved. Chip-scale EO modulators based on ScAlN have been successfully demonstrated by harnessing both the r13and r33electro-optic coefficients.

[0010] As a result, those skilled in the art are constantly seeking a modulator that can leverage the advantages of both high modulation efficiency and low optical loss, while maintaining compatibility with large-scale, cost-effective fabrication processes.SUMMARY

[0011] Tn one aspect, the present application discloses optical modulator comprising a dielectric layer disposed on a substrate, a first doped semiconductor thin film layer embedded within the dielectric layer along a first horizontal plane, and an electro-optic (EO) waveguide structure embedded within the dielectric layer along a second horizontal plane. In embodiments of the disclosure, the EO waveguide structure comprises an input end for receiving an optical signal and an output end for emitting a modulated optical signal. The optical modulator further comprises a first electrode disposed on top of the dielectric layer and electrically coupled to the first dopped semiconductor thin film layer through a first conductive via, and a second electrode disposed on the dielectric layer, laterally spaced from the first electrode. In embodiments of the disclosure, the first and second horizontal planes are vertically offset from each other in the dielectric layer such that the EO waveguide structure and the first doped semiconductor layer are vertically separated by a first intermediate portion of the dielectric layer, and a portion of the EO waveguide structure is vertically aligned with a portion of the first doped semiconductor thin film layer.

[0012] In embodiments of the one aspect, a portion of the second electrode is vertically aligned with the portion of the EO waveguide structure such that an electric field is formed between the second electrode and the first doped semiconductor thin film layer when a potential difference exists between the second electrode and the first doped semiconductor thin film layer with the formed electric field intersecting the EO waveguide structure.

[0013] In embodiments of the one aspect, the optical modulator further comprises a second doped semiconductor thin film layer embedded within the dielectric layer along a third horizontal plane and electrically coupled to the second electrode through a second conductive via, wherein a portion of the second doped semiconductor thin film layer is vertically aligned with the portion of the EO waveguide structure, such that the EO waveguide structure and the second doped semiconductor layer are vertically separated by a second intermediate portion of the dielectric layer. In further embodiments, an electric field is formed between the second doped semiconductor thin film layer and the first doped semiconductor thin film layer when a potential difference exists between the first and second doped semiconductor thin film layers with the formed electric field intersecting the EO waveguide structure.

[0014] In another embodiment of the one aspect, a Mach Zehnder modulator is disclosed. The Mach Zehnder modulator comprises an input w aveguide for receiving an optical signal, a Y-branch splitter or a Multimode interferometer (MMI) for splitting the optical signal received by the input waveguide into two optical modulators, each optical modulator configured according to the optical modulator of the one aspect, a rccombincr for recombining modulated optical signals received from the two optical modulators, and an output waveguide for emitting the recombined modulated optical signal.

[0015] In another embodiment of the one aspect, a ring modulator is disclosed. The ring modulator comprises an input waveguide for receiving an optical signal, an optical modulator according to the one aspect for receiving the optical signal from the input waveguide, whereby the optical modulator is bent to form an enclosed path, and an output waveguide for receiving a modulated optical signal from the optical modulator.

[0016] In another aspect, the present application discloses a method for forming an optical modulator. The disclosed method comprises the steps of forming a first dielectric layer on asubstrate, forming a first doped semiconductor thin film layer in a first horizontal plane on the dielectric layer, depositing a second dielectric layer to encapsulate the first doped semiconductor thin film layer and exposed upper surfaces of the first dielectric layer, and forming an electro-optic (EO) waveguide structure in a second horizontal plane on the second dielectric layer. In embodiments of the disclosure, the EO waveguide structure comprises an input end for receiving an optical signal and an output end for emitting a modulated optical signal. The method then further comprises the steps of depositing a third dielectric layer to encapsulate the EO waveguide structure and exposed upper surfaces of the second dielectric layer, forming a first electrode on top of the third dielectric layer, and forming a first conductive via through the second and third dielectric layers to electrically connect the first electrode to the first doped semiconductor thin film layer, and forming a second electrode on top of the third dielectric layer, laterally spaced from the first electrode. In embodiments of the disclosure, the first and second horizontal planes are vertically offset from each other in the dielectric layer such that the EO waveguide structure and the first doped semiconductor layer are vertically separated by a first intermediate portion of the dielectric layer, and a portion of the EO waveguide structure is vertically aligned with a portion of the first doped semiconductor thin film layer.

[0017] In another embodiment of this another aspect, a portion of the second electrode is vertically aligned with the portion of the EO waveguide structure such that an electric field is formed between the second electrode and the first doped semiconductor thin film layer when a potential difference exists between the second electrode and the first doped semiconductor thin film layer with the formed electric field intersecting the EO waveguide structure.

[0018] In another embodiment of this another aspect, the method further comprises the steps of forming a second doped semiconductor thin film layer in a third horizontal plane within the third dielectric layer, forming a second conductive via through the third dielectric layer to electrically connect the second electrode to the second doped semiconductor thin film layer, wherein a portion of the second doped semiconductor thin film layer is vertically aligned with the portion of the EO waveguide structure, such that the EO waveguide structure and the second doped semiconductor layer are vertically separated by a second intermediate portion of the dielectric layer. In embodiments of the disclosure, an electric field is formed between the second doped semiconductor thin film layer and the first doped semiconductor thin film layerwhen a potential difference exists between the first and second doped semiconductor thin film layers with the formed electric field intersecting the EO waveguide structure.

[0019] In yet another embodiment of this another aspect, a method for forming a Mach Zehnder modulator is disclosed, the method comprising the steps of providing an input waveguide for receiving an optical signal, coupling a Y-branch splitter into two optical modulators, the Y-branch splitter configured to split the optical signal received by the input waveguide to the two optical modulators, wherein each optical modulator is configured according to the optical modulator of claims 16 or 20, providing a recombiner for recombining modulated optical signals received from the two optical modulators, and providing an output waveguide for emitting the recombined modulated optical signal.

[0020] In yet another embodiment of this another aspect, a method for forming a ring modulator is disclosed, the method comprising the steps of providing an input waveguide for receiving an optical signal, coupling an optical modulator according to the optical modulator of claims 16 or 20 to an output of the input waveguide for receiving the optical signal from the input waveguide, whereby the optical modulator is bent to form an enclosed path, and providing an output waveguide for receiving a modulated optical signal from the optical modulator.BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Various embodiments of the present disclosure are described below with reference to the following drawings:Figure 1 illustrates a cross-sectional view of an embodiment of an optical modulator in accordance with embodiments of the present disclosure;Figure 2 illustrates a cross-sectional view of another embodiment of an optical modulator in accordance with embodiments of the present disclosure;Figure 3 illustrates a perspective view of an embodiment of the optical modulator shown in Figure 1 in accordance with embodiments of the present disclosure;Figure 4 illustrates a perspective view of an embodiment of the optical modulator shown in Figure 2 in accordance with embodiments of the present disclosure;Figure 5 illustrates a top view of the EO waveguide structure and the first doped semiconductor thin film layer with the EO waveguide structure being coupled to a bus waveguide using a spot size converter;Figure 6 illustrates the simulated S-parameters of the optical modulator when the length of the waveguide was varied between 0.1 to 5.0 mm;Figure 7 illustrates the simulation optical mode profile in the EO waveguide modulator under TE and TM polarization;Figure 8a illustrates the simulated modulation efficiency of the optical modulator illustrated in Figure 2 when the gap between the EO waveguide and the doped semiconductor thin film layer is varied, and when the vertical dimension of the EO waveguide is varied;Figure 8b illustrates the simulated modulation efficiency of the optical modulator illustrated in Figure 2 when the gap between the EO waveguide and the doped semiconductor thin film layer is varied, and when the thickness of the doped semiconductor thin film layer is varied;Figure 9a illustrates a top view of a Mach-Zehnder modulator in accordance with embodiments of the disclosure;Figure 9b illustrates a cross-sectional view of the MZM illustrated in Figure 9a where the optical modulators of the MZM are based on optical modulator 100 in accordance with embodiments of the disclosure;Figure 9c illustrates a cross-sectional view of the MZM illustrated in Figure 9a where the optical modulators of the MZM are based on optical modulator 200 in accordance with embodiments of the disclosure;Figure 10a illustrates a top view of a ring resonator in accordance with embodiments of the disclosure;Figure 10b illustrates a cross-sectional view of the ring resonator illustrated in Figure 10a where the optical modulator of the ring modulator is based on optical modulator 100 in accordance with embodiments of the disclosure;Figure 10c illustrates a cross-sectional view of the ring resonator illustrated in Figure 10a where the optical modulator of the ring modulator is based on optical modulator 200 in accordance with embodiments of the disclosure; andFigure 11 illustrates a flowchart that sets out the process or method for forming the optical modulator in accordance with embodiments of the disclosure.DETAILED DESCRIPTION

[0022] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0023] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements. The term “and / or” includes any and all combinations of one or more of the associated listed items.

[0024] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0025] As used herein, “comprising” means including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0026] As used herein, “consisting of’ means including, and limited to, whatever follows the phrase “consisting of’. Thus, use of the phrase “consisting of’ indicates that the listed elements arc required or mandatory, and that no other elements may be present.

[0027] It should be noted that although the terms first, second and third are used herein to describe various elements, these elements should not be limited by these terms as these terms are meant to only distinguish one element from another element. Thus, the first element described herein could be termed as a second clement without departing from this disclosure.

[0028] In the context of various embodiments, the term “surround” means to enclose something completely to form a barrier around it Thus, the use of the term “surround” indicates that something is on all sides of another thing.

[0029] In the context of various embodiments, the term “disposed on" relates to the placement or deposition of one material or layer onto the surface of another and may involve one or more types of deposition techniques.

[0030] In the context of various embodiments, the tenn “around” or “adjacent” means to be in the proximity or location of something and does not necessarily mean that two objects have to be in contact.

[0031] In the context of various embodiments, the directional terms mentioned herein, such as “above” and “below” or “upper” and “lower” refer to directions as described with reference to the drawings. Therefore, the directional terms arc only used for illustration and arc not meant to limit the present disclosure.

[0032] As used herein, a “layer” refers to a material portion including a region having a particular thickness. The layer may extend over the entirety of the structure or may cover only part of the structure as defined in the description. For example, a layer may be located between two horizontal planes; may be located between, or at, a top surface and a bottom surface of the structure. The layer may also extend horizontally, vertically, and / or along the surface of the structure.

[0033] Additionally, for the sake of brevity, extensive explanations of conventional techniques of fabricating semiconductor devices and integrated circuits are not described in detail herein. The tasks and processes described herein may also be integrated into a more comprehensive procedure with extra steps of features that are not elaborated upon in this document. Specifically, certain processes of fabricating semiconductor devices arc well known to one skilled in the art hence, such processes will be omitted entirely.

[0034] An optical modulator that that utilizes an EO waveguide structure arranged between two conductively doped thin film semiconductor layers in a top-down configuration isdisclosed in this document. By employing the conductivcly doped thin film semiconductor layers, additional optical losses can be minimized even when these layers are provided near the EO waveguide structure. As a result, the optical modulator is able to achieve higher bandwidth, improved modulation efficiency, and reduced optical loss compared to conventional optical modulators known in the art.

[0035] In embodiments of the disclosure, the optical modulator may comprise a heavily doped silicon (Si) thin film layer that is embedded within a dielectric layer of the optical modulator and aluminum (Al) layers formed on an upper surface of the dielectric layer. The Si thin film layer may serve as a bottom ground electrode and the Al layers may serve as the top electrodes of the optical modulator with the Si thin film layer being conductively coupled to one of the Al layers. An EO waveguide comprising a c-axis-oriented ScAlN waveguide structure may then be arranged between the Si thin film layer and one of the Al layers. Such an arrangement enables direct exploitation of the diagonal EO coefficient (r33OApm / u) of the ScAlN material. By virtue of the strong overlap between the electrical and optical modes achieved through this configuration, the optical modulator described in this document was found to exhibit significantly enhanced performance, attaining a figure of merit, V„L (representing a product of the half-wave voltage and length of the modulator) of 119 ± 17 V ■ cm and 134 + 6 V ■ cm in the fabricated ring modulators and Mach-Zehnder modulators (MZMs), respectively, representing approximately a five-fold improvement over conventional modulator designs. Tn other embodiments of the disclosure, another heavily doped silicon (Si) thin film layer may be embedded within the dielectric layer of the optical modulator, whereby this another layer is formed between one of the top electrodes and the EO waveguide with this layer being conductively coupled to the top electrode.

[0036] Figure 1 illustrates a cross-sectional view of a first embodiment of an optical modulator in accordance with embodiments of the present disclosure. It should be noted that the phase of an optical signal propagating through the EO waveguide is modulated when an applied electric field overlaps with the optical propagation mode of the optical signal, thereby altering the effective refractive index experienced by the optical signal.

[0037] In particular, optical modulator 100 is formed on substrate 102, over which dielectric layer 104 is deposited. In embodiments of the disclosure, substrate 102 may comprise silicon(Si) while dielectric layer 104 may comprise silicon dioxide (SiCh). Embedded within dielectric layer 104 along first horizontal plane 107 (along the X-axis direction) is first doped semiconductor thin film layer 106, which serves as a bottom ground electrode for optical modulator 100. Positioned above first doped semiconductor thin film layer 106 and vertically separated from first doped semiconductor thin film layer 106 by portion 105 of the dielectric layer 104, is electro-optic (EO) waveguide structure 108 that is disposed along a second horizontal plane 109 (along the X-axis direction). EO waveguide structure 108 is configured to guide optical signals and is arranged to receive an applied electric field for phase modulation of optical signals propagating in EO waveguide structure 108.

[0038] Tn embodiments of the disclosure, EO waveguide structure 108 may have a rectangular or trapezoid shape with a width between 400 and 2000 nm and a vertical height between 200 - 1000 nm. It may also comprise a c-axis-oriented material, such as scandium- doped aluminium nitride (ScAlN), wherein the c-axis is aligned perpendicular to the substrate plane, thereby optimizing the overlap between the applied electric field and the electro-optic axis of the material. In other embodiments, EO waveguide structure may comprise, but is not limited to, a material with very high electro-optic coefficients such as lithium niobate or barium titanate. In certain embodiments, the geometric dimensions of the waveguide may be chosen to achieve single-mode operation of the optical signal propagating within EO waveguide structure 108, thereby enhancing optical confinement and minimizing modal dispersion.

[0039] As shown in Figure 1, first horizontal plane 107 is vertically offset from second horizontal plane 109 in dielectric layer 104 such that EO waveguide structure 108 and first doped semiconductor thin film layer 106 are vertically separated by an intermediate portion or a gap 105. In embodiments of the disclosure, first doped semiconductor thin film layer 106 may comprise heavily doped silicon thin film layers which are doped such that this layer gains electrical conductance. Specifically, the implantations are done sufficiently high on first doped semiconductor thin film layer 106 so that this layer may serve as a low resistance electrode. Further, first doped semiconductor thin film layer 106 may have a thickness between 20 nm and 150 nm and the gap between silicon thin film layer 106 and EO waveguide structure 108 may be between 100 - 400 nm.

[0040] Optical modulator 100 further comprises first electrode 110 and second electrode 112, both disposed on an upper surface of dielectric layer 104. As shown, first electrode 110 is electrically coupled to first doped thin film layer 106 through conductive via 111 that is formed through dielectric layer 104. As for second electrode 112, this electrode is positioned laterally adjacent to first electrode 110 and vertically aligned with a portion of EO waveguide structure 108. In embodiments of the disclosure, a gap between EO waveguide structure 108 and second electrode 112 may be between 600 - 2000 nm.

[0041] When a voltage or a potential difference is applied between first and second electrodes 110 and 112 respectively, a vertically oriented electric field (in the Y -axis direction) is formed between first doped semiconductor thin film layer 106 and second electrode 1 12, with the formed electric field intersecting EO waveguide structure 108. In operation, an optical signal propagating through EO waveguide structure 108 will undergo phase modulation resulting from changes in the effective refractive index induced by the vertical electric field intersecting EO waveguide structure 108, i.c. when a potential difference exists between the first and second electrodes. The vertical stacking of the second electrode above and first doped thin film layer 106 below EO waveguide structure 108, combined with the c-axis orientation of the EO material, enables direct exploitation of the diagonal electro-optic coefficient r33, thereby significantly enhancing the modulation efficiency of optical modulator 100.

[0042] In embodiments of the disclosure, optical modulator 100 may be formed by first heavily doping silicon slabs located in the modulation region to create first doped semiconductor thin film layer 106 that is to be positioned vertically below EO waveguide structure 108. EO waveguide structure 108 is then formed by depositing a ScAlN thin film through a sputtering process, utilizing a target with a nominal scandium doping concentration between 10% and 50%, or higher. The deposited ScAlN film may comprise a thickness of approximately 530 nm and may be oriented such that its c-axis is perpendicular to the plane of substrate 102. Thereafter, ScAlN photonic components, such as, but are not limited to, tapered waveguides, may be defined and patterned using a deep ultraviolet (DUV) lithography process.

[0043] Following the patterning of the ScAlN structures, a silicon dioxide (SiCE) cladding layer having a thickness of approximately 1 pm may be deposited over the devices using plasma-enhanced chemical vapor deposition (PECVD) to encapsulate the patterned ScAlNcomponents. Vias arc subsequently etched through the cladding layer and filled with conductive material to provide access to the underlying first doped semiconductor thin film layer 106. Aluminum (Al) layers arc then sputter deposited over the structure and patterned by etching to form first and second electrodes 110 and 112 of optical modulator 100.

[0044] Figure 2 illustrates a cross-sectional view of a second embodiment of optical modulator 200 in accordance with embodiments of the present disclosure. It should be understood that, similar to the first embodiment, the phase of an optical signal propagating through the EO waveguide structure is modulated when an applied electric field overlaps with the optical propagation mode of the optical signal, thereby altering the effective refractive index experienced by the optical signal.

[0045] In particular, optical modulator 200 is formed on substrate 102, over which dielectric layer 104 is deposited. Embedded within dielectric layer 104 along first horizontal plane 107 (extending along the X-axis direction) is first doped semiconductor thin film layer 106, which serves as a bottom ground electrode for optical modulator 200. Positioned above first doped semiconductor thin film layer 106 and vertically separated therefrom by intermediate portion 105 of dielectric layer 104 is electro-optic (EO) waveguide structure 108 disposed along a second horizontal plane 109 (along the X-axis direction). In the embodiment shown, second doped semiconductor thin film layer 202 is further provided above EO waveguide structure 108 and disposed along a third horizontal plane 204 (along the X-axis direction), vertically separated from EO waveguide structure 108 by an intermediate dielectric region. It should be noted that EO waveguide structure 108 may comprise the similar dimensions and materials as described above in relation to the first embodiment illustrated in Figure 1.

[0046] As illustrated in Figure 2, first horizontal plane 107, second horizontal plane 109, and third horizontal plane 204 are vertically spaced apart from one another within dielectric layer 104. EO waveguide structure 108 is thus provided between first doped semiconductor thin film layer 106 and second doped semiconductor thin film layer 202. In embodiments of the disclosure, the first and second doped semiconductor thin film layers 106 and 202 may comprise heavily doped silicon thin film layers, with each layer being doped to a level sufficient to achieve low electrical resistance for efficient electrode operation. The thickness of each doped semiconductor thin film layer may be between 20 nm and 150 nm, and the vertical gapsbetween EO waveguide structure 108 and each adjacent doped semiconductor thin film layer may independently be between 100 nm and 400 nm. By reducing the gap between first / second doped semiconductor thin film layer 106 / 202 and EO waveguide structure 108, this greatly enhances the modulation efficiency of the optical modulator as the distance or gap (between first doped semiconductor thin film layer 106 and EO waveguide structure 108) is inversely proportional to the electrical field strength applied to EO waveguide structure 108.

[0047] Optical modulator 200 further comprises first electrode 110 and second electrode 1 12, both disposed on an upper surface of dielectric layer 104. As shown, first electrode 1 10 is electrically connected to first doped semiconductor thin film layer 106 through conductive via 1 1 1 , and second electrode 1 12 is electrically connected to second doped semiconductor thin film layer 202 through conductive via 206. A portion of second doped semiconductor thin film layer 202 is vertically aligned with a portion of EO waveguide structure 108, such that EO waveguide structure 108 and second doped semiconductor thin film layer 202 are vertically separated by a second intermediate portion of the dielectric layer.

[0048] When a voltage is applied between first and second electrodes 110 and 112, a vertically oriented electric field (in the Y -axis direction) is formed between first and second doped semiconductor thin film layers 202 and 106, with the formed electric field intersecting EO waveguide structure 108. In operation, an optical signal propagating through EO waveguide structure 108 undergoes phase modulation resulting from changes in the effective refractive index induced by the vertical electric field intersecting EO aveguide structure 108. The arrangement of first and second doped semiconductor thin film layers 106 and 202 adjacent to EO waveguide structure 108 greatly enhances vertical electric field confinement and symmetry around the EO waveguide. Combined with the c-axis orientation of the EO material, this structure similarly enables direct exploitation of the diagonal electro-optic coefficient r33, thereby significantly improving the modulation efficiency, optical confinement, and operational stability of optical modulator 200 relative to prior designs. In embodiments of the disclosure, first and / or second doped semiconductor thin film layers 106 and 202 respectively may each have a first part with a high concentration of dopant, a second part with a median concentration of dopant relative to the first part and a third part with a low concentration of dopant relative to the first part. In embodiments of the disclosure, the first part of these dopedsemiconductor thin film layers may be the part that is conductivcly coupled to cither of first or second electrodes 110 or 112 respectively.

[0049] Figure 3 illustrates a perspective view of optical modulator 100 as illustrated in Figure 1 while Figure 4 illustrates a perspective view of optical modulator 200 as illustrated in Figure 2 in accordance with embodiments of the present disclosure. As shown in Figure 3, EO waveguide structure 108 includes a tapered input end configured to receive an optical signal with the tapered end being optically coupled to a bus waveguide 302, which serves to deliver the optical signal into the EO waveguide structure 108 for subsequent modulation. In embodiments of the disclosure, bus waveguide 302 may comprise silicon (Si) or silicon nitride (Si3N4), materials that are commonly used for low-loss optical signal transmission in photonic integrated circuits.

[0050] The tapered design of the input end of EO waveguide structure 108 facilitates efficient optical coupling between bus waveguide 302 and EO waveguide structure 108 by reducing mode mismatch and minimizing insertion loss. By gradually transitioning the optical mode from bus waveguide 302 into EO waveguide structure 108, the coupling efficiency is improved, supporting higher modulation bandwidth and lower signal degradation. This arrangement allows for the seamless integration of optical modulator 100 into larger photonic circuit architectures, ensuring that it is compatible with existing silicon or silicon nitride photonic platforms.

[0051] Figure 5 illustrates a top view of EO waveguide structure 108 and doped semiconductor thin film layers 502 and 504 with EO waveguide structure 108 being provided between doped semiconductor thin film layers 502 and 504. As shown, EO waveguide structure 108 is coupled to bus waveguide 302 using a spot size converter (SSC) 304. Bus waveguide 302 is aligned along the Z-axis direction with EO waveguide structure 108 and is configured to deliver an optical signal towards EO waveguide structure 108. Spot size converter 304 is configured to gradually transition the optical mode from the dimensions of bus waveguide 302 to match the dimensions of EO waveguide structure 108, thereby facilitating efficient optical coupling.

[0052] In embodiments of the disclosure, spot size converter 304 may operate as an evanescent coupler that tapers the width and / or thickness of the optical mode to minimize mode mismatch and coupling loss between bus waveguide 302 and EO waveguide structure 108. The gradual taper profile of spot size converter 304 enables high coupling efficiency by ensuring that the optical field expands or contracts adiabatically between the two waveguides.

[0053] In embodiments of the disclosure, SSC 304 may comprise an inter-layer mode converter. The inter-layer converter may comprise two vertically overlapping tapered waveguides, each having a length of approximately 200 pm, designed to asymptotically transfer the optical mode from the silicon waveguide to the EO waveguide structure with minimal conversion loss. In one embodiment, the silicon waveguide is tapered from a width of approximately 500 nm to 150 nm, while the EO waveguide structure is tapered from a width of approximately 1000 nm to 300 nm. This gradual tapering facilitates efficient optical mode transition between the two waveguides while minimizing optical scattering and coupling losses.

[0054] Finite Element Method (FEM) simulations were then performed based on the structure illustrated in Figure 5, with the length of EO waveguide structure 108 varied between 0.1 mm and 5 mm so that transmission losses induced by SSC 304 and the doped semiconductor thin film layers 502 and 504 (comprising a doped silicon layer) may be analysed. The resulting transmission characteristics are plotted in Figure 6. In the simulations, four different combinations of input and output optical modes were considered, denoted as TE-TE 604, TM- TM 602, TM-TE 608 and TE-TM 606. In this notation, the first mode represents the optical polarization input into the bus waveguide, and the second mode represents the optical polarization collected at the output of the EO waveguide structure.

[0055] As shown in Figure 6, TE-TM 606 and TM-TE 608 transmission plots overlap each other and they exhibit negligible power transfer, even for propagation lengths up to 5 mm, indicating minimal polarization cross-coupling within the EO waveguide structure. The TE- TE 604 plot, however, displays oscillations between approximately 30% and 75% transmission, suggesting that when the input mode is TE-polarized, undesirable coupling occurs between the silicon thin film layers and the EO waveguide structure. Such coupling can degrade the modulation efficiency and increase optical loss. In contrast, the TM-TM 602transmission plot remains consistently above 97% across the entire propagation length range, indicating a non-coupling condition between the silicon thin film layers and the EO waveguide structure when the optical signal is TM-polarizcd.

[0056] Further simulations of the optical mode behavior within the EO waveguide structure under TE and TM polarization states arc illustrated in Figure 7. As shown in plot 702, for TE polarization, excess optical modes are observed within the silicon thin film layer, indicating the occurrence of undesirable coupling between the optical field and the electrode structure. In contrast, as shown in plot 704 for TM polarization, the optical mode remains well-confined within the EO waveguide structure, with negligible interaction occurring within the silicon thin film layer.

[0057] Figures 8a and 8b illustrate the simulation results of the modulation efficiency of optical modulator 200 (as shown in Figure 2) in terms of the figure of merit V„L (i.e., VnX Length). In this context, a lower V„L value corresponds to a higher modulation efficiency of the optical modulator. Figure 8a illustrates the dependence of the modulation efficiency on the gap between the EO waveguide structure and the silicon thin film layer, as well as on the height of the EO waveguide structure. In these simulations, the gap was varied from 0 nm to 400 nm, and the height of the EO waveguide structure was varied from 200 nm to 1000 nm. It can be observed that the modulation efficiency improves (i.e., VnL decreases) as the gap becomes smaller, which aligns with the theoretical expectation that a stronger electric field overlap enhances modulation performance. However, the selection of design parameters involves a trade-off between fabrication complexity and device stability. Based on Figure 8a, it can be seen that an EO waveguide height of approximately 600 nm was identified as an optimal height, as it accommodates a wide range of gap variations while maintaining good modulation efficiency (with VnL values below 1.5) when the gap is between 0 nm and 250 nm.

[0058] Figure 8b illustrates the modulation efficiency as a function of the gap and the thickness of the silicon thin film electrode. In this simulation, the gap was varied from 0 nm to 400 nm, and the silicon thin film thickness was varied from 20 nm to 150 nm. A similar trend is observed, where smaller gap values correspond to improved modulation efficiency. However, in the lower thickness region, particularly when the gap is reduced to approximately 40-60 nm, isolated non-continuous spots appear in the plot, indicating the presence of modecompetition effects within the EO waveguide modulator. Based on these observations, a EO waveguide height greater than 80 nm may be selected to ensure stable optical mode confinement and to minimize performance degradation due to mode competition.

[0059] The simulation results show that when one or both doped Si thin film layers are brought as close as possible to the centrally positioned EO waveguide structure, this enhances the overall modulation efficiency of the optical modulator. The ability of the disclosed structure to maintain low optical coupling between the Si thin film electrode and the EO waveguide, despite their close proximity, is a key enabler of the improved performance and represents a central aspect of optical couplers 100 and 200.

[0060] Figures 9a-c and lOa-c illustrate two embodiments that utilize optical modulator 100 or 200 to form optical intensity modulators. In the embodiment shown in Figure 9a, two optical modulators are employed to form Mach-Zehnder modulator (MZM) 900, and a schematic top view of the structure is provided. A MZM operates based on a Mach-Zehnder interferometer (MZI) configuration, where input optical signal 901 is split into two separate paths. The phase difference induced between the two paths leads to constructive or destructive interference upon recombination, thereby modulating the intensity of the output optical signal.

[0061] In the embodiment illustrated in Figure 9a, optical modulators 906 and 908, may be formed by adopting the design of optical modulator 100 or 200, and by extending the adopted optical modulator continuously along the light propagation direction or discretely into several shorter segments, each segment extending over a predetermined length. Spot size converters (SSCs) 902 and 904 may then be utilized to couple the input silicon bus waveguides to optical modulators 906 and 908, respectively, for receiving the input optical signal 901, which has been split into two optical paths by a Y-branch splitter. SSCs 910 and 912 are coupled to the outputs of optical modulators 906 and 908 respectively and are configured to direct the modulated optical signals toward recombiner 913, where the two optical signals are recombined. In this embodiment, a push-pull driving configuration is adopted, wherein the two optical paths experience equal but opposite phase shifts. This configuration effectively doubles the overall modulation efficiency compared to a single-path optical modulator.

[0062] Figure 9b illustrates a cross-sectional view of MZM 900 taken along the Y-X plane along line A-A, in accordance with embodiments of the present disclosure. In this embodiment, optical modulators 906 and 908 arc constructed by embedding doped semiconductor thin film layers 921 and 923 within a dielectric layer, similar to the configurations described for optical modulators 100 or 200. EO waveguide structures 926 and 928 are then disposed above the respective doped semiconductor layers and separated by intermediate dielectric regions. Top electrodes 920, 922, and 924 are disposed on an upper surface of the dielectric layer, and vias arc formed to establish electrical connection between the top electrodes and the corresponding doped semiconductor layers where necessary. A first vertical electric field is formed across EO waveguide structure 926 when a potential difference exists between doped semiconductor thin film layer 921 and top electrode 922, and a second vertical electric field is formed across EO waveguide structure 928 when a potential difference exists between doped semiconductor thin film layer 923 and top electrode 924.

[0063] Figure 9c illustrates another cross-sectional view of MZM 900 taken along the Y-X plane along line A-A, whereby each optical modulator corresponds to the structure of optical modulator 200. In this embodiment, another doped thin film layer is introduced above each EO waveguide structure. As shown, doped semiconductor thin film layers 931 and 934 are embedded within the dielectric layer, while EO waveguide structures 938 and 940 are disposed vertically above these doped layers. Additional doped semiconductor thin film layers 932 and 935 are provided above the EO waveguide structures 938 and 940 respectively. Top electrodes 930, 932, 933, and 935 arc then disposed on the upper surface of the dielectric layer.

[0064] Vias are formed in the dielectric layer to electrically connect top electrode 930 to doped semiconductor thin film layer 931, top electrode 933 to doped semiconductor thin film layers 932 and 934, and top electrode 935 to doped semiconductor thin film layer 936, thereby enabling the application of a stronger vertical electric field across EO waveguide structures 938 and 940. This configuration corresponds to an optical modulator design based on optical modulator 200, where dual doped semiconductor thin film layers are used to further improve modulation efficiency.

[0065] Figure 10a illustrates a top view of optical micro-ring modulator (MRM) 1000 in accordance with embodiments of the present disclosure. MRM 1000 may be formed by bendingan optical modulator (either optical modulator 100 or 200) into a closed-loop path, such as a ring, thereby enabling intensity modulation through resonant optical coupling. In embodiments of the disclosure, MRM 1000 may have a diameter between 40 pm and 100 pm.

[0066] In this embodiment, an input optical signal may be delivered through silicon bus waveguide 1001, which is coupled to MRM 1000 via a spot size converter (SSC) 1002. The optical signal propagates along bus waveguide 1007, and a portion of the optical energy is coupled into MRM 1000 through evanescent coupling at a coupling region.

[0067] As can be seen, MRM 1000 comprises a top electrode 1006 which is conductively connected to a bottom silicon thin film layer (not shown) of the optical modulator structure. Another top electrode 1008 may optionally be connected to another silicon thin film layer (not shown) that is provided above EO waveguide structure 1007 of the optical modulator structure, depending on whether the optical modulator structure of MRM 1000 corresponds to optical modulator 200 (which includes a top doped thin film layer) or optical modulator 100 (which does not).

[0068] In operation, a vertical electric field is established across EO waveguide structure 1007, enabling phase modulation of the circulating optical signal. Modulation of the effective refractive index shifts the resonant condition of the micro-ring, resulting in dynamic control of the intensity of the output optical signal that is extracted at the output part of silicon bus waveguide 1003 w'hich is in turn coupled to SSC 1004. An output of SSC 1004 is then optically coupled to silicon bus waveguide 1005 such that the modulated output signal may be provided to other components of the photonic system.

[0069] Figure 10b illustrates a cross-sectional view of MRM 1000 as taken along the Y-Z plane along the B-B line, in accordance with embodiments of the present disclosure. As shown, MRM 1000 comprises doped semiconductor thin film layers 1014 and 1016 configured as a ring structure, and embedded within the dielectric layer. EO waveguide structure 1007 which is also formed as a ring resonator is formed above the doped semiconductor thin film layers and comprises discrete segments 1007a and 1007b corresponding to sections of the closed-loop optical path.

[0070] Top electrode 1006 is formed in a ring-shaped configuration and is disposed on the dielectric layer and comprises discrete segments 1006a and 1006b. A second top electrode 1008, also formed as a ring-shaped structure, is disposed concentrically within the inner perimeter of top electrode 1006 and comprises discrete segments 1008a and 1008b. Conductive vias are provided to establish electrical connections between top electrode segments 1006a and 1006b and corresponding doped semiconductor thin film layers 1014 and 1016, respectively. This arrangement enables the application of vertical electric fields across the EO waveguide structures while maintaining independent control of the electrodes positioned around the microring modulator.

[0071] Figure 10c illustrates another cross-sectional view of optical micro-ring modulator (MRM) 1000 as taken along the Y-Z plane along the B-B line, corresponding to another embodiment of the disclosure. As shown, MRM 1000 comprises doped semiconductor thin film layers 1014 and 1016 embedded within the dielectric material and configured as a ring structure. EO waveguide structure 1007 which is also formed as a ring resonator is formed above the doped semiconductor thin film layers and comprises discrete segments 1007a and 1007b corresponding to sections of the closed-loop optical path. In this embodiment, MRM 1000 also comprises doped semiconductor thin film layer 1020 embedded within the dielectric material, above EO waveguide structure and configured as a ring structure.

[0072] Top electrode 1006 is formed in a ring-shaped configuration and is disposed on the dielectric layer and comprises discrete segments 1006a and 1006b. A second top electrode 1008, also formed as a ring-shaped structure, is disposed concentrically within the inner perimeter of top electrode 1006 and comprises discrete segments 1008a and 1008b. Conductive vias are provided to establish electrical connections between top electrode segments 1006a and 1006b and corresponding doped semiconductor thin film layers 1014 and 1016, respectively, and between top electrode segments 1008a and 1008b and corresponding doped semiconductor thin film layer 1020. This arrangement enables the application of vertical electric fields across the EO waveguide structures while maintaining independent control of the electrodes positioned around the micro-ring modulator.

[0073] It should be noted that due to the directionality of the applied electric field and the polarization orientation of the EO material, conventional side-by-side arranged EO modulatorsarc unsuitable for forming such micro-ring configurations, as the modulation effects tend to cancel out over the closed loop. However, the top-down electrode configuration disclosed in Figure 10 overcomes this limitation, allowing all phase modulation effects to accumulate constructively along the closed-loop path. This enables effective intensity modulation using a micro-ring configuration without the cancellation issues associated with conventional lateral field designs.

[0074] A process for forming an optical modulator in accordance with embodiments of the disclosure is illustrated in Figure 1 1. Process 1 100 begins at step 1 102 with process 1 100 forming a first dielectric layer on a substrate. At step 1104, process 1100 then proceeds to form a first doped semiconductor thin film layer in a first horizontal plane on the dielectric layer. Process 1100 then deposits a second dielectric layer to encapsulate the first doped semiconductor thin film layer and exposed upper surfaces of the first dielectric layer. This occurs at step 1106. At step 1108, process 1100 then forms an electro-optic (EO) waveguide structure in a second horizontal plane on the second dielectric layer. The formed EO waveguide structure comprises an input end for receiving an optical signal and an output end for emitting a modulated optical signal. Process 1100 then deposits a third dielectric layer to encapsulate the EO waveguide structure and exposed upper surfaces of the second dielectric layer at step 1110. At step 1112, process 1100 then forms a first electrode on top of the third dielectric layer and forms a first conductive via through the second and third dielectric layers to electrically connect the first electrode to the first doped semiconductor thin film layer. Process 1100 then forms a second electrode on top of the third dielectric layer, the second electrode being laterally spaced from the first electrode and this occurs at step 1 1 14. Tn embodiments of the disclosure, the first and second horizontal planes are vertically offset from each other in the dielectric layer such that the EO waveguide structure and the first doped semiconductor thin film layer are vertically separated by a first intermediate portion of the dielectric layer, and a portion of the EO waveguide structure is vertically aligned with a portion of the first doped semiconductor thin film layer.

[0075] Numerous other changes, substitutions, variations, and modifications may be ascertained by the skilled in the ait and it is intended that the present application encompass all such changes, substitutions, variations, and modifications as falling within the scope of the appended claims.

Claims

CLAIMS1. An optical modulator comprising: a dielectric layer disposed on a substrate; a first doped semiconductor thin film layer embedded within the dielectric layer along a first horizontal plane; an electro-optic (EO) waveguide structure embedded within the dielectric layer along a second horizontal plane, the EO waveguide structure comprising an input end for receiving an optical signal and an output end for emitting a modulated optical signal; a first electrode disposed on top of the dielectric layer and electrically coupled to the first dopped semiconductor thin film layer through a first conductive via; a second electrode disposed on the dielectric layer, laterally spaced from the first electrode; wherein the first and second horizontal planes are vertically offset from each other in the dielectric layer such that the EO waveguide structure and the first doped semiconductor thin film layer are vertically separated by a first intermediate portion of the dielectric layer, and wherein a portion of the EO waveguide structure is vertically aligned with a portion of the first doped semiconductor thin film layer.

2. The optical modulator according to claim 1, wherein a portion of the second electrode is vertically aligned with the portion of the EO waveguide structure.

3. The optical modulator according to claim 2, wherein a vertical displacement between the second electrode and the EO waveguide structure is between 600 nm and 2000 nm.

4. The optical modulator according to claim 2, whereby an electric field is formed between the second electrode and the first doped semiconductor thin film layer when a potential difference exists between the second electrode and the first doped semiconductor thin film layer with the formed electric field intersecting the EO waveguide structure.

5. The optical modulator according to claim 1 further comprising:a second doped semiconductor thin film layer embedded within the dielectric layer along a third horizontal plane and electrically coupled to the second electrode through a second conductive via, wherein a portion of the second doped semiconductor thin film layer is vertically aligned with the portion of the EO waveguide structure, such that the EO waveguide structure and the second doped semiconductor layer are vertically separated by a second intermediate portion of the dielectric layer.

6. The optical modulator according to claim 5, whereby an electric field is formed between the second doped semiconductor thin film layer and the first doped semiconductor thin film layer when a potential difference exists between the first and second doped semiconductor thin film layers with the formed electric field intersecting the EO waveguide structure.

7. The optical modulator according to claims 5 or 6 wherein the first and second doped semiconductor thin film layers each comprise a doped silicon thin film layer or a doped polycrystalline silicon thin film layer.

8. The optical modulator according to any one of claims 5 to 7 wherein a vertical displacement between the EO waveguide structure and the second doped semiconductor thin film layer is between 100 nm and 400 nm.

9. The optical modulator according to any one of claims 5 to 8 wherein the first and second doped semiconductor thin film layers each have a thickness between 20 nm and 150 nm.

10. The optical modulator according to any one of claims 5 to 9 wherein the first and the second doped semiconductor thin film layers each have a first part with a high concentration of dopant, a second part with a median concentration of dopant and a third part with a low concentration of dopant.

11. The optical modulator according to any one of claims 1 to 10, wherein the EO waveguide structure comprises a rectangular or a trapezoidal structure having a width between 400 nm to 2000 nm, and a vertical dimension between 200 nm and 1000 nm.

12. The optical modulator according to any one of claims 1 to 11 wherein a vertical displacement between the EO waveguide structure and the first doped semiconductor thin film layer is between 100 nm and 400 nm.

13. The optical modulator according to any one of claims 1 to 12, wherein the EO waveguide structure comprises a c-axis-oriented scandium-doped aluminum nitride (SC-A1N).

14. A Mach Zehnder modulator comprising: an input waveguide for receiving an optical signal; a Y-branch splitter for splitting the optical signal received by the input waveguide into two optical modulators, each optical modulator configured according to the optical modulator of claims 2 or 5; a recombiner for recombining modulated optical signals received from the two optical modulators; and an output waveguide for emitting the recombined modulated optical signal.

15. A ring modulator comprising: an input waveguide for receiving an optical signal; an optical modulator according to the optical modulator of claims 2 or 5 for receiving the optical signal from the input waveguide, whereby the optical modulator is bent to form an enclosed path; and an output waveguide for receiving a modulated optical signal from the optical modulator.

16. A method for forming an optical modulator comprising: forming a first dielectric layer on a substrate; forming a first doped semiconductor thin film layer in a first horizontal plane on the dielectric layer; depositing a second dielectric layer to encapsulate the first doped semiconductor thin film layer and exposed upper surfaces of the first dielectric layer; forming an electro-optic (EO) waveguide structure in a second horizontal plane on the second dielectric layer, the EO waveguide structure comprising an input end for receiving an optical signal and an output end for emitting a modulated optical signal, anddepositing a third dielectric layer to encapsulate the EO waveguide structure and exposed upper surfaces of the second dielectric layer; forming a first electrode on top of the third dielectric layer, and forming a first conductive via through the second and third dielectric layers to electrically connect the first electrode to the first doped semiconductor thin film layer; forming a second electrode on top of the third dielectric layer, laterally spaced from the first electrode, wherein the first and second horizontal planes are vertically offset from each other in the dielectric layer such that the EO waveguide structure and the first doped semiconductor thin film layer are vertically separated by a first intermediate portion of the dielectric layer, and wherein a portion of the EO waveguide structure is vertically aligned with a portion of the first doped semiconductor thin film layer.

17. The method according to claim 16, wherein a portion of the second electrode is vertically aligned with the portion of the EO waveguide structure.

18. The method according to claim 17, wherein a vertical displacement between the second electrode and the EO waveguide structure is between 600 nm and 2000 nm.

19. The method according to claim 17, whereby an electric field is formed between the second electrode and the first doped semiconductor thin film layer when a potential difference exists between the second electrode and the first doped semiconductor thin film layer with the formed electric field intersecting the EO waveguide structure.

20. The method according to claim 16 further comprising: forming a second doped semiconductor thin film layer in a third horizontal plane within the third dielectric layer; forming a second conductive via through the third dielectric layer to electrically connect the second electrode to the second doped semiconductor thin film layer, wherein a portion of the second doped semiconductor thin film layer is vertically aligned with the portion of the EO waveguide structure, such that the EO waveguide structure and the second doped semiconductor layer are vertically separated by a second intermediate portion of the dielectric layer.

21. The method according to claim 20, whereby an electric field is formed between the second doped semiconductor thin film layer and the first doped semiconductor thin film layer when a potential difference exists between the first and second doped semiconductor thin film layers with the formed electric field intersecting the EO waveguide structure.

22. The method according to claims 20 or 21 wherein the first and second doped semiconductor thin film layers each comprise a doped silicon thin film layer or a doped polycrystalline silicon thin film layer.

23. The method according to any one of claims 20 to 22 wherein a vertical displacement between the EO waveguide structure and the second doped semiconductor thin film layer is between 100 nm and 400 nm.

24. The method according to any one of claims 20 to 23 wherein the first and second doped semiconductor thin film layers each have a thickness between 20 nm and 150 nm.

25. The method according to any one of claims 20 to 24 wherein the first and the second doped semiconductor thin film layers each have a first part with a high concentration of dopant, a second part with a median concentration of dopant and a third part with a low concentration of dopant.

26. The method according to any one of claims 16 to 25, wherein the EO waveguide structure comprises a rectangular or a trapezoidal structure having a width between 400 nm to 2000 nm, and a vertical dimension between 200 nm and 1000 nm27. The method according to any one of claims 16 to 26 wherein a vertical displacement between the EO waveguide structure and the first doped semiconductor thin film layer is between 100 nm and 400 nm.

28. The method according to any one of claims 16 to 27, wherein the EO waveguide structure comprises a c-axis-oriented scandium-doped aluminum nitride (SC-ATN).

29. A method for forming a Mach Zehnder modulator comprising:providing an input waveguide for receiving an optical signal; coupling a Y-branch splitter into two optical modulators, the Y-branch splitter configured to split the optical signal received by the input waveguide to the two optical modulators, wherein each optical modulator is configured according to the optical modulator of claims 16 or 20, providing a recombiner for recombining modulated optical signals received from the two optical modulators; and providing an output waveguide for emitting the recombined modulated optical signal.

30. A method for forming a ring modulator comprising: providing an input waveguide for receiving an optical signal; coupling an optical modulator according to the optical modulator of claims 16 or 20 to an output of the input waveguide for receiving the optical signal from the input waveguide, whereby the optical modulator is bent to form an enclosed path; and providing an output waveguide for receiving a modulated optical signal from the optical modulator.

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