Waveguide amplifier fabrication method and waveguide amplifier

Abstract

Photonic integrated circuit waveguide amplifier fabrication method comprising providing at least one support cladding material or layer supporting at least one silicon nitride material or layer and / or at least one embedding cladding material or layer comprising the at least one silicon nitride material or layer embedded inside the at least one embedding cladding material or layer; wherein the at least one silicon nitride material or layer (has a material or layer thickness that is less than or equal to 400nm and greater than or equal to 40nm; and carrying out rare-earth ion implantation, at rare-earth ion acceleration values between 0.01 MeV and 0.5 MeV, by ion irradiation of at least one surface of the at least one supported and / or embedded silicon nitride material or layer, the at least one rare-earth ion implanted silicon nitride material or layer defining a waveguide core of the waveguide amplifier.

Description

[0001] WAVEGUIDE AMPLIFIER FABRICATION METHOD AND WAVEGUIDE AMPLIFIER

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] The present application claims priority to European patent application number EP24165703.0 filed on March 22nd 2024, the entire contents thereof being herewith incorporated by reference.

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to a rare earth doped waveguide amplifier fabrication method and a rare earth doped waveguide amplifier device, as well as a rare earth doped photonic integrated circuit fabrication method and a rare earth doped photonic integrated circuit.

[0006] BACKGROUND

[0007] Erbium-doped fiber amplifiers have revolutionized long-haul optical communications and laser technology. Erbium ions could equally provide a basis for efficient optical amplification in photonic integrated circuits (PICs) for operation, for example, in the optical C-band.

[0008] Pioneering efforts in the 1990s have been made to implement erbium-doped waveguide amplifiers (EDWAs) based on oxide glass waveguides, yet ultimately abandoned due to limitation by large waveguide background losses, incompatibility with contemporary PICs and insufficient output power.

[0009] Interest in EDWAs re-emerged with the SisN4 CMOS-compatible photonic integrated circuit platform, with advantages over silicon including its record low propagation losses of only <3 dB / m that can be maintained over meter-scale lengths. EDWAs based on silicon nitride PICs have demonstrated large output power and intense net-gain up to 30 dB, as disclosed in international PCT application WO2023 / 180788, the entire contents of which are incorporated herein by reference.

[0010] In the fabrication of the above-mentioned EDWAs based on silicon nitride, the Inventors observed that after rare earth ion implantation of the waveguide, the waveguide can deform significantly sometimes despite the lateral supporting structures. Figure 1A is a SEM image showing the waveguide cross-section prior to rare earth ion implantation of the waveguide. Figures 1 B and 1C (Figure 1 C being annotated) are SEM images showing the waveguide cross-section after rare earth ion implantation. The initially substantially straight waveguide sidewalls (Figure 1A) are replaced by undulated deformed waveguide sidewalls (Figures 1 B and 1C) after implantation despite the lateral support.

[0011] As a result, the precise control of optical parameters such as the effective refractive index or the dispersion of the waveguides becomes more difficult.

[0012] The resulting structural lateral deformations can cause undercuts which complicate the cladding deposition process and introduce additional scattering losses. Furthermore, the undercuts alter the waveguide’s dispersion properties, which can degrade the optical performance of the waveguide.

[0013] The Inventors also believe, without limitation to this particular theory, that an intermixing of silicon nitride and silicon oxide may be present at the waveguide sidewall where the silicon nitride core is in contact with the silicon oxide support. Such intermixed material can have more disorder resulting in a higher optical loss and an unknown / unpredictable refractive index for the material of these principal elements of the optical device.

[0014] The article entitled “Low-energy erbium implanted Si3N4 / SiO2 / Si waveguides by Lumholt et al, published in Electronic Letters, Volume 28, No.24, November 19th1992 pages 2242 to 2243, ISSN:0013-5194 discloses a slab device consisting of a plurality of superposed slabs including an outer Er-doped silicon nitride slab.

[0015] SUMMARY OF THE INVENTION

[0016] The present invention addresses the above-mentioned limitations by providing a photonic integrated circuit waveguide amplifier fabrication method according to claim 1 , and a photonic integrated circuit waveguide amplifier according to claim 22.

[0017] Other advantageous features can be found in the dependent claims.

[0018] The Inventors surprising found that a silicon nitride waveguide core of low thickness allows the silicon nitride waveguide core side-wall deformation to be significantly reduced. Even more surprisingly, the Inventors found that this is also achieved in the absence of supporting lateral sidewalls of the cladding layer or material. This is particularly non-intuitive given that previous experimental results (as presented in Figure 6 of international PCT application WO2023 / 180788) produced by the Inventors indicated that reducing the silicon nitride thickness of a protruding silicon nitride structure also produced undulated deformed waveguide sidewalls resulting in such a silicon nitride waveguide not being integrated into a waveguide amplifier device, as well as no longer being considered for use in a waveguide amplifier device.

[0019] Moreover, reducing the thickness of the waveguide core of low thickness is generally not envisaged due the resulting reduced overlap factor between ion density and optical mode due to the weaker optical mode confinement.

[0020] Figure 2 shows the waveguide cross-section of a rare earth doped silicon nitride waveguide core produced by the method of the present disclosure. The silicon nitride waveguide core side-wall deformation is significantly reduced, and the waveguide sidewalls only show a moderate deformation.

[0021] This not only enhances the efficiency and reliability of the rare earth doped photonic integrated circuits and devices but also allows a more streamlined and less-complex fabrication process.

[0022] Figure 6A shows a PIC containing a plurality of rare earth doped waveguide amplifiers having the lower silicon nitride waveguide core thickness of the present disclosure. Figure 7 shows the measured optical gain provided by theses rare earth doped waveguide amplifiers.

[0023] The above and other objects, features, and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description with reference to the attached drawings showing some preferred embodiments of the invention.

[0024] A BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0025] These and / or other aspects, features, and / or advantages will become apparent and more readily appreciated from the following description of various example embodiments, taken in conjunction with the accompanying drawings. Thicknesses of layers / elements, and sizes of components / elements, are not necessarily drawn to scale or in actual proportion to one another, but rather are shown as example representations. Like reference numerals may refer to like parts throughout the several views. Each embodiment herein may be used in combination with any other embodiment(s) described herein. Figure 1A is a scanning electron microscopy SEM image showing a waveguide cross-section prior to rare earth ion implantation of the waveguide.

[0026] Figures 1 B is a scanning electron microscopy SEM image showing the waveguide crosssection after rare earth ion implantation. Figures 1 C is the SEM image of Figure 1 B annotated.

[0027] Figure 2 is a scanning electron microscopy SEM image showing a waveguide cross-section of a rare earth doped silicon nitride waveguide core of the present disclosure.

[0028] Figures 3 is schematic cross-sectional representation of an exemplary waveguide amplifier of the present disclosure.

[0029] Figure 4 shows a preferred exemplary waveguide amplifier fabrication method according to the present disclosure where an exemplary Er:Si3N4photonic chip fabrication is shown. The materials indicated and details indicated in the various steps are exemplary. Not all steps are necessarily required. The exemplary Er:Si3N4(PIC) fabrication process uses a subtractive fabrication process, and furthermore comprises ion implantation and ion (e.g. erbium) activation.

[0030] Figure 5 shows another exemplary waveguide amplifier fabrication method according to the present disclosure where an exemplary Er:Si3N4photonic chip fabrication is shown. The materials indicated and details indicated in the various steps are exemplary. Not all steps are necessarily required. The exemplary Er:Si3N4(PIC) fabrication process uses a subtractive fabrication process, and furthermore comprises ion implantation and ion (e.g. erbium) activation.

[0031] Figures 6(a) to 6(d) show an exemplary PIC of the present disclosure comprising an exemplary multiple-lane PIC device or four-lane Er-doped waveguide amplifiers. Figure 6(a) shows a layout of the Er:SisN4PIC chip. Figure 6(b) is a photo of the hybrid coupled four-lane amplifier under test. Figure 6(c) is a scanning electron microscopy image of the Er:SisN4waveguide, overlaid with a simulated optical mode. Figure 6(d) left: is a zoomed-in view of the coupling between the Er:SisN4chip and a fiber array for signal input and output, and Figure 6(d) right is a zoomed in view of the coupling with the hybrid-integrated four-channel pump laser diode.

[0032] Figures 7(a) to 7(d) show the multilane-EDWA performance characterization of the exemplary PIC device of Figure 6. Figure 7(a) shows the device characterization setup. For simplicity, only two channels are shown. Figure 7(b) shows measured on-chip net gain at different 1550 nm signal power level, where off-chip pump power is around 242 mW. Figure 7(c) shows On- chip net gain at different diode pump power, measured at -19.9 dBm on-chip signal power. Figure 7(d) shows On-chip output power at different Off-chip pump power, measured at 5.4 dBm on-chip signal power, the inset shows the output optical spectrum.

[0033] Figure 8 shows a schematic cross-sectional representation of an exemplary waveguide amplifier of the present disclosure during fabrication thereof.

[0034] Herein, identical reference numerals are used, where possible, to designate identical elements that are common to the Figures.

[0035] DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0036] The following detailed structural and / or functional description(s) is / are provided as examples only, and various alterations and modifications may be made. The example embodiments herein do not limit the disclosure and should be understood to include all changes, equivalents, and replacements within ideas and the technical scope herein. Hereinafter, certain examples will be described in detail with reference to the accompanying drawings. When describing various example embodiments with reference to the accompanying drawings, like reference numerals may refer to like components and a repeated description related thereto may be omitted.

[0037] The present disclosure concerns a waveguide amplifier fabrication method or photonic integrated circuit waveguide amplifier fabrication method.

[0038] Figures 4 and 5 show exemplary photonic integrated circuit waveguide amplifier fabrication methods according to the present disclosure where an exemplary Er:Si3N4waveguide amplifier fabrication is shown. The exemplary fabrication processes use an exemplary subtractive process.

[0039] The method includes providing at least one support cladding material or layer 3A supporting at least one (or a plurality thereof) waveguide core (or waveguide structure) material or layer 5A, for example, at least one silicon nitride material or layer 5A, or at least one silicon nitride waveguide core (structure) material or layer 5A (see, for example, Figure 4(iv) or Figure 5(vii)). It is noted that some illustrated features are shown with a white colored outline in Figures, while others are shown with a black colored outline to visually aid in distinguishing the features for comprehension reasons.

[0040] The waveguide core material or layer 5, 5A may, for example, comprise of consist of silicon nitride SisNzi, SiNx; alternatively, the waveguide core material or layer 5, 5A may comprise of consist of, for example, Tantala (TaOs, tantalum penoxide), SiC, Hydex, silicon oxynitride (SiOxNy), or Litium Niobate LNOLThe supported waveguide core (or waveguide structure) material or layer 5A or the supported silicon nitride 5A defines or includes, for example, exposed first and second lateral side walls SW1 A, SW2A (or elongated side walls) extending outside the supporting cladding material or layer 3A and away from a support surface SS of the supporting cladding material or layer 3A that the silicon nitride material or layer 5A (directly or indirectly) contacts, for example, at a base BS of the waveguide core material or layer 5A or silicon nitride material or layer 5A (see, for example, Figure 4(iii) and Figure 4(iv)).

[0041] The first and second lateral side walls SW1A, SW2A extend outside the supporting cladding material or layer 3A and away from the support surface SS (from the base BS) to an outer or upper surface S1 A of the material or layer 5A, for example a silicon nitride surface S1 A or to define an outer or upper surface SIA for example silicon nitride surface S1A to receive or be exposed to receive ion irradiation during rare-earth ion implantation during ion implantation of the silicon nitride material or layer 5A.

[0042] The waveguide core (or waveguide structure) material or layer 5A is structured to define an optical waveguide to laterally confine light in a lateral direction (for example, the x-direction) and propagate the light in the elongated light guiding direction PG across the waveguide device or support substrate 15.

[0043] The supported waveguide core (or waveguide structure) material or layer 5A forms or defines, for example, a ridge structure or an elongated ridge structure protruding from the supporting cladding material or layer 3A and flanked by surfaces 3A1 of the supporting cladding material or layer 3A located on either side of the ridge structure. The surfaces 3A1 faces outwards in a direction that is, for example, the same as the outer or upper surface S1 A of the supported waveguide core (or waveguide structure) material or layer 5A, and / or the surfaces 3A1 extend in a direction, for example, that is different to the surface of the outer lateral side walls LS1 , LS2 of the supporting cladding material or layer 3A. The first and second lateral side walls SW1A, SW2A (or surfaces thereof) are, for example, located displaced from or at a distance from the (at least one) outer lateral side walls LS1 , LS2 of the supporting cladding material or layer 3A, and / or (at least one) outer lateral side walls of the support layer or substrate 15.

[0044] The supported waveguide core (or waveguide structure) material or layer 5A protrudes from the supporting cladding material or layer 3A. The supported waveguide core (or waveguide structure) material or layer 5A protrudes from the supporting cladding material or layer 3A, and the cladding material or layer flanks the supported waveguide core (or waveguide structure) material or layer 5A or the first and second lateral side walls SW1 A, SW2A thereof, or is located laterally to each of the first and second lateral side walls SW1 A, SW2A thereof.

[0045] The outer or upper surface S1A of the supported waveguide core (or waveguide structure) material or layer 5A is located at a different or offset level (for example, a higher level) to that of the support surface SS of the supporting cladding material or layer 3A that the waveguide core (or waveguide structure) material or layer 5A contacts or protrudes from. The first and second lateral side walls SW1A, SW2A extend away from the different or offset location (for, example downwards) towards or to the supporting cladding material or layer 3A, or towards / to the support surface SS thereof, located for example a lower-level location.

[0046] The waveguide core (or waveguide structure) material or layer 5A includes or defines the base BS, a deck or landing DK located opposite the base BS, the deck or landing DK including or defining surface S1A. The first and second lateral side walls SW1A, SW2A extend, for example, from the base BS to the deck DK.

[0047] The waveguide core (or waveguide structure) material or layer 5A extends in an elongated manner in a light propagation direction or light guiding direction, for example, on and / or across at least one supporting layer or substrate 15. The waveguide core (or waveguide structure) material or layer 5A forms, for example, a stripe or band extending in an elongated manner across and / or laterally on the supporting layer or substrate 15.

[0048] The first and second lateral side walls SW1A, SW2A (and surfaces ES1 , ES2) also extend in an elongated manner in a light propagation direction or light guiding direction PD (for example, Z-direction in Figures 4 and 5), for example, on and / or across at least one supporting layer or substrate 15. The waveguide core (or waveguide structure) material or layer 5A defines or has a cross- sectional shape or form that may for example be an elongated cross-sectional shape or form. The cross-sectional plane (for example, the X-Y plane) is, for example, (substantially) perpendicular to the light propagation direction or light guiding direction PD (for example, the Z-direction).

[0049] For example, a distance or width W (for example, axial / x-axis) between the first and second lateral side walls SW1 A, SW2A (and surfaces thereof) may be equal or greater that a distance or thickness t (for example, axial / y-axis) between the base BS and the deck DK of the waveguide core (or waveguide structure) material or layer 5A. The width W and the thickness t are, for example, cross-sectionally measured, for example in the previously mention cross- sectional plane. The width W and the thickness t measured value is, for example, that which is the largest width W and the thickness t cross-sectionally measured, for example in the previously mention cross-sectional plane.

[0050] The thickness t and the width W of the waveguide core (or waveguide structure) material or layer 5A extend, for example, in directions that are (substantially) perpendicular to the elongated direction of extension in the light guiding direction PD (for example, Z-direction in Figures 4 and 5).

[0051] The first and second lateral side walls SW1A, SW2A define or include, for example, exposed surfaces ES1 , ES2. A clearance or spacing CL is, for example, located facing or opposite the first and second lateral side walls SW1A, SW2A, or facing or opposite the exposed surface of first and second lateral side walls SW1 A, SW2A (see, for example, Figure 4(iv)).

[0052] For example, the clearance or spacing CL is devoid of material / solid material, and / or incudes at least one gas.

[0053] The first and second lateral side walls SW1A, SW2A extend in an elongated or longitudinal direction, for example, in a plane (substantially) perpendicular to the plane defined by the supporting layer or substrate 15, in the X-Z directions (Z-direction being into the page direction in Figure 3).

[0054] Alternatively, the method includes providing at least one embedding cladding material or layer 3A, 3B comprising the waveguide core (or waveguide structure) material or layer 5A (or for example the at least one silicon nitride material or layer 5A) embedded (or buried) inside the at least one embedding cladding material or layer 3A, 3B (see, for example, Figure 5(vii)). In the exemplary embodiment of Figure 5, the waveguide core (or waveguide structure) material or layer 5A or the silicon nitride material or layer 5A is laterally embedded or laterally buried inside the embedding cladding material or layer 3B.

[0055] The cladding material or layer 3A,3B supports for example the waveguide core (or waveguide structure) material or layer 5A, as in the exemplary embodiment of Figure 4, and also provides a lateral embedding or lateral support for the first and second lateral side walls SW1 A, SW2A the waveguide core (or waveguide structure) material or layer 5A.

[0056] The embedded waveguide core (or waveguide structure) material or layer 5A or embedded silicon nitride 5A extends inside the embedding cladding material or layer 3B and away from the support surface SS to define the outer or upper silicon nitride surface S1 A to receive or be exposed to receive ion irradiation during rare-earth ion implantation. The silicon nitride material or layer 5A defines or includes the first and second lateral side walls SW1 A, SW2A that are in (for example, direct or indirect) contact with the embedding cladding material or layer 3B. The embedding cladding material or layer 3 defines or includes first and second lateral side walls SW1 B, SW2B. The first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3 respectively mechanically support and contact (directly or indirectly) the first and second lateral side walls SW1A, SW2A of the silicon nitride material or layer 5A.

[0057] The first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3 include or define outer surfaces that may contact (directly or indirectly) outer surfaces of the first and second lateral side walls SW1 A, SW2A of the embedded waveguide core (or waveguide structure) material or layer 5A.

[0058] The first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3 (and / or the outer surfaces thereof) extend for example in an elongated manner in the light guiding direction PD. The first and second lateral side walls SW1 B, SW2B extend, for example, along (partially or fully) the first and second lateral side walls SW1A, SW2A of the embedded waveguide core (or waveguide structure) material or layer 5A, for example, partially or fully between the base BS and the deck DK of the waveguide core (or waveguide structure) material or layer 5A

[0059] The first and second lateral side walls SW1 B, SW2B and / or he first and second lateral side walls SW1 A, SW2A are, for example, located displaced from or at a distance from the (at least one) outer lateral side walls LS1 , LS2 of the supporting cladding material or layer 3A, and / or (at least one) outer lateral side walls of the support layer or substrate 15. The supported waveguide core (or waveguide structure) material or layer 5A forms or defines, for example, an embedded ridge structure or an elongated and embedded ridge structure protruding from the supporting cladding material or layer 3A and flanked by first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3 located on either side of the ridge structure. Outer surfaces OS of the embedding cladding material or layer 3 faces outwards, for example, in a direction that is the same as the outer or upper surface S1 A of the supported waveguide core (or waveguide structure) material or layer 5A, and / or the outer surfaces OS extend, for example, in a direction that is different to the surface of the outer lateral side walls LS1 , LS2 of the supporting cladding material or layer 3A.

[0060] The waveguide core (or waveguide structure) material or layer 5A or the at least one silicon nitride material or layer 5A comprises or defines an elongated waveguide core or non-doped elongated waveguide core. A plurality of silicon nitride material stripes / bands or layers 5A may be present and each one or the plurality may comprise or define an elongated waveguide core or non-doped elongated waveguide core. One or more of which may subsequently be rare- earth ion implanted or doped.

[0061] The cladding material or layer 3A, 3B and / or the silicon nitride material or layer 5A may, for example, comprise or consist of a planar layer or material. The cladding material or layer 3A, 3B and / or the silicon nitride material or layer 5A may, for example, extend in planar directions or directions defining the plane (X-direction, Z-direction, Figure 3).

[0062] In another embodiment, a further material or layer or cladding material or layer (not shown) may in addition be provided or deposited on the waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A (and optionally on the embedding cladding material or layer 3B) on an opposite side to that of the supporting and / or embedding cladding layer or material 3A, the first and second lateral side walls extending there-between. As a result, the silicon nitride material or layer 5A can be both laterally embedded or laterally buried inside the embedding cladding material or layer 3B, and vertically embedded or buried inside the embedding cladding materials or layers, the vertical direction (Y-direction, see for example, Figure 3) being orthogonal to a plane of the extension (for example, plane defined by X-direction and Z-direction, see for example, Figure 3) of the silicon nitride material or layer 5A and / or the embedding cladding layer or material 3A, 3B. The waveguide core 5A or the silicon nitride material or layer 5A extends, for example, in a plane (for example, a plane defined by X-direction and Z-direction) and / or in the elongated direction of extension in the light guiding direction PD (for example, Z-direction).

[0063] Advantageously, the waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A has a material or layer thickness t, where thickness t is less than or equal to (<) 400nm and greater than or equal to (>) 10nm or 40nm or 100nm, or preferably <300nm and >1 OOnm or 40nm or 10nm, or more preferably <250nm and >1 OOnm or 40nm or 10nm, or even more preferably <200nm and >1 OOnm or 40nm or 10nm, in a direction (vertical direction, Y-direction Figure 3) perpendicular to for example the light guiding direction PD or the plane in which the silicon nitride material or layer 5A extends (plane defined by X-direction and Z-direction). The thickness t, is for example, measured as the maximum thickness value in the vertical (thickness) direction.

[0064] The thickness direction or the direction of the thickness t is, for example, a direction perpendicular or substantially perpendicular to the surface of the supporting substrate or layer 15.

[0065] As previously mentioned, the thickness t can, for example, be cross-sectionally measured, for example in the previously mention cross-sectional plane (the X-Y plane for example). The the thickness t measured value is, for example, that which is the largest thickness t cross- sectionally measured, for example in the previously mention cross-sectional plane, for example, in the Y-direction indicated in the exemplary embodiments of Figures 3 to 5. The thickness t extends, for example, in a direction that is (substantially) perpendicular to the elongated direction of extension in the light guiding direction PD (for example, the Z-direction in Figures 3 to 5).

[0066] The above lower thickness values t of the waveguide core assure that light is still guided or propagated in a propagation, longitudinal or elongated direction of the waveguide core. Such low thickness values are capable of weakly guiding light in the waveguide core (see, for example, Puckett, M.W., Liu, K., Chauhan, N. et al. 422 Million intrinsic quality factor planar integrated all-waveguide resonator with sub-MHz linewidth. Nat Commun 12, 934 (2021 ). https: / / doi.org / 10.1038 / s41467-021-21205-4, the entire contents of which is incorporated herein by reference). Amplification by doped cladding portions FR (see, for example, Figure 4(vi) and Figure 5(ix)) contribute to a larger extent to light amplification when the thickness value t is closer to these lower extremity values. The upper thickness values assure the provision of a waveguide core structure having reduced or significantly reduced structural deformation and / or reduced or significantly reduced waveguide core side-wall deformation.

[0067] The method further includes carrying out rare-earth ion implantation. Implantation can be carried out using, for example, a Van der Graaf accelerator. The ion implantation process is described in the article by Polmann et al (Polman, A., Jacobson, D. C., Eaglesham, D. J., Kistler, R. C. & Poate, J. M. Optical doping of waveguide materials by MeV Er implantation. Journal of Applied Physics 70, 3778-3784 (1991 ). URL http: / / aip.scitation.org / doi / 10.1063 / 1.349234), the entire contents of which are incorporated herein by reference.

[0068] Implantation can be carried out using, for example, a high-energy ion accelerator, for example, a 2 MV Van der Graaf accelerator from the HVEC company. The samples can be, for example, mounted on to a 2-inch silicon backing wafer and mounted perpendicular to the beam.

[0069] The rare-earth ion implantation can, for example, be carried out at rare-earth ion acceleration values between 0.01 MeV and 2MeV, (extremity values included).

[0070] The rare-earth ion implantation is preferably carried out at rare-earth ion acceleration values between (i) 0.01 MeV or 0.05MeV and (ii) 1 MeV (extremity range values included) or more preferably between (i) 0.01 MeV or 0.05MeV and (ii) 0.5 MeV (extremity range values included). For example, at 0.35MeV. The rare-earth ion implantation is carried out by ion irradiation of the surface S1A of the supported or embedded silicon nitride material or layer 5A (see, for example, Figures 4(iv) and 5(vii)) to form at least one rare-earth ion implanted silicon nitride material or layer 5 supported on the supporting cladding material or layer 3A and / or embedded in the embedding cladding material or layer 3B.

[0071] The rare-earth ion implantation is, for example, carried out by ion irradiation of, for example, the directly exposed or uncovered surface S1A of the supported or embedded waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A to form the rare-earth ion implanted waveguide core (or waveguide structure) material or layer 5 or rare- earth ion implanted silicon nitride material or layer 5 supported on the cladding material or layer 3A and / or embedded in the embedding cladding material or layer 3B.

[0072] The rare-earth ion implantation may alternatively be, for example, carried out by ion irradiation through the cladding material or layer provided or deposited on the surface S1A of the embedded silicon nitride material or layer 5A. In addition to the supported and / or embedded waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A being rare-earth ion implanted, (elongated) enclosing / surrounding portion or portions FR of the supporting cladding material or layer 3A and / or the embedding cladding material or layer 3B may be rare-earth ion implanted or doped with the same rare earth ion 7 type as that of the silicon nitride material or layer 5A.

[0073] Portions extending laterally away (x-direction) from the base BS on either or both sides of the waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A, and away from the first and second lateral side walls SW1A, SW2A are rare earth ion implanted to provide rare earth ion implanted supporting cladding material or layer portions FR (see for example, Figure 4(vi)). The portions FR may, for example, extend parallel with the waveguide core (or waveguide structure) material or layer 5A in the elongated direction of extension of the light guiding direction PD.

[0074] Alternatively, or additionally, embedded portions of the embedding cladding material or layer including respectively the first and second lateral side walls SW1 B, SW2B extending laterally away (x-direction) from the first and second lateral side walls SW1A, SW2A of layer or material 5A,5 may be rare earth ion implanted to provide rare earth ion implanted embedded cladding material or layer portions FR (see for example, Figure 5(ix)).

[0075] The selective mask SM is provided to select the portions FR directly adjacent or neighboring the silicon nitride material or layer 5A for ion implantation. The or each portion FR may, for example, extend a (lateral) width WFR that is between 5% and 100% of the width W of the silicon nitride material or layer 5A.

[0076] The portions FR can, for example, also contribute to light amplification. They can, for example, contribute or compensate amplification lost due to the relatively thinner waveguide core material (the silicon nitride material or layer 5A).

[0077] The rare-earth ion implantation is carried out by accelerating the rare-earth ions 7 towards the surface S1A to provide an ion implantation fluence of between 5 x 1014cm’2and 5 x 1016cm'2, and preferably between 1 x 1015cm’2and 2 x 1016cm’2to the surface for ion implantation inside the supported and / or embedded silicon nitride material or layer 5A.

[0078] This provides, for example, a peak rare-earth ion implanted concentration in the rare-earth ion implanted silicon nitride material or layer 5 between 0.1 x 1O20cm’3and 1 .0 x 1021cm’3. The rare-earth ion implanted silicon nitride material or layer 5 defines or is an active material or active layer or optical gain medium or waveguide core of the waveguide amplifier.

[0079] The implanted rare-earth ions or atoms 7 may, for example, consist of or comprise Erbium, Ytterbium, or Thulium. The implanted rare-earth ions 7 may, for example, comprise at least one of: Erbium, Ytterbium, Thulium. Implanting different rare-earth ions or co-doping with different rare-earth ions permits to provide gain at other wavelengths. Implanted rare-earth ions 7 such as ytterbium (emission at 1.1 pm) and thulium (0.8 pm, 1 .45 pm and 2.0 pm) permit to provide optical gain in these other wavelength regions.

[0080] The implanted rare-earth ions 7 may, for example, comprise or consist of (i) Erbium and Ytterbium, or (ii) Erbium and Thulium, or (iii) Erbium, Ytterbium and Thulium. Co-doping with other rare-earth ions permit to providing gain (amplification) in multiple wavelength regions in the same amplifier.

[0081] The rare-earth ion implantation energy performed at rare-earth ion acceleration values between (i) 0.01 MeV or 0.05 MeV or 0.1 MeV and (ii) 0.5 MeV advantageously allows to achieve a satisfactory doping of the waveguide core 5, while maintaining a satisfactorily operational overlap between Erbium ions and the silicon nitride waveguide mode.

[0082] In the exemplary embodiments shown in Figures 4 and 5, Erbium ion implantation was carried out at with maximum beam energy of 350 keV and a total implantation dose of 2.4 * 1015cm’2.

[0083] The rare-earth ion implanted waveguide core (or waveguide structure) material or layer 5 or implanted silicon nitride material or layer 5 defines an elongated waveguide core WC or rare- earth ion implanted waveguide core WC. The elongated waveguide core WC may, for example, include one or more elongated rare-earth ion implanted waveguide core sections and one or more elongated rare-earth ion non-implanted waveguide core sections.

[0084] The rare-earth ion implanted waveguide core 5A or the rare-earth ion implanted silicon nitride material or layer 5 extends in the light guiding direction PD or a plane (plane defined by X- direction and Z-direction). The rare-earth ion implanted silicon nitride material or layer 5 has a material or layer thickness t1 , where thickness t1 is less than or equal to (<) 400nm and greater than or equal to (>) 10Onm or 40nm or 10nm, or preferably <300nm and >1 OOnm or 40nm or 10nm, or more preferably <250nm and >100nm or 40nm or 10nm, or even more preferably <200nm and >100nm or 40nm or 10nm, in a direction (vertical direction, Y-direction Figure 3) perpendicular to the plane in which the silicon nitride material or layer 5A extends (plane defined by X-direction and Z-direction). The thickness t1 , is for example, measured as the maximum thickness value in the vertical (thickness) direction.

[0085] The thickness direction or the direction of the thickness t1 is, for example, a direction perpendicular to the surface of the supporting substrate or layer 15.

[0086] The thickness t1 is for example measured in the same manner as the thickness t discussed previously above.

[0087] As mentioned, this thickness t results in a lower propagation loss thanks to the reduction in waveguide core side-wall deformation or the silicon nitride waveguide core side-wall deformation. Additionally, this thickness t results in an expansion of the waveguide mode area assuring an increase in the saturation power for rare-earth ion gain waveguides. Furthermore, this enables the amplification of larger power signals.

[0088] The silicon nitride material or layer 5A and / or the rare-earth ion implanted silicon nitride material or layer 5 also extends longitudinally along the light propagation direction PD (Z- direction, Figure 3). The silicon nitride material or layer 5A and / or rare-earth ion implanted silicon nitride material or layer 5 and waveguide core WC may also, for example, define a planer layer or material supported on and / or embedded / contained inside the cladding material or layer 3B. The rare-earth ion implanted silicon nitride material or layer 5 may, for example, define a substantially planar optical waveguide core WC.

[0089] The silicon nitride material or layer 5A and / or the rare-earth ion implanted silicon nitride material or layer 5 may have a cross-section shape or profile whose width W (measured at maximum value) is greater that its thickness t (measured at maximum value). For example, the width W is between 2.5 and 200 times greater than the thickness t, or between 5 and 150 times greater than the thickness t. For example, a width W (measured at maximum value) of 2pm (outer cross-sectional width W) and a thickness t (measured at maximum value) of 0.2pm.

[0090] As previously mentioned, the width W can, for example, be cross-sectionally measured, for example in the previously mention cross-sectional plane (the X-Y plane for example). The width W measured value is, for example, that which is the largest width W cross-sectionally measured, for example in the previously mention cross-sectional plane, for example, in the X- direction indicated in the exemplary embodiments of Figures 3 to 5. The width W extends, for example, in a direction that is (substantially) perpendicular to the elongated direction of extension in the light guiding direction PD (for example, the Z-direction in Figures 3 to 5), and / or that is (substantially) perpendicular to the direction of extension of the thickness t.

[0091] The method may, for example, include carrying out selective masking during rare-earth ion implantation (see, for example, Figure 4(iv) and Figure 5(vii)). This forms (i) at least one first portion P1 or elongated portion P1 of rare-earth ion implanted waveguide core (or waveguide structure) material or layer 5 or silicon nitride material or layer 5 supported on and / or embedded in the cladding material or layer 3A, 3B, and (ii) at least one second portion P2 or elongated portion P2 of non-implanted waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A supported on or embedded in the cladding material or layer 3A, 3B. The rare-earth ion implanted first portion P1 can be, for example, optically coupled to the rare-earth ion non-implanted second portion P2 or located relatively to the rare-earth ion non-implanted second portion P2 to be optically evanescently coupled thereto.

[0092] The rare-earth ion implanted first portion P1 and the rare-earth ion non-implanted second portion P2 each define, for example, a waveguide core identical to the above-described waveguide core or waveguide structure for light propagation as part of a waveguide, amplifier device or photonic circuit.

[0093] Selective masking during ion implantation can provide a basis for integrating both passive and active components. Selective masking also permits to avoid modifying the property of passive waveguide cores or elements of the waveguide device or photonic circuit.

[0094] Selective masking may, for example, be used to mask ion implantation along a longitudinal direction of extension of the waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A in the light propagation direction PD (Z-direction, Figure 3). This provides a waveguide core 5 or rare-earth ion implanted silicon nitride material or layer 5 including elongated sections that are rare-earth ion implanted and rare-earth ion nonimplanted.

[0095] While the exemplary embodiments of Figures 4 and 5 show implantation of one silicon nitride material / layer 5A or one elongated waveguide core / non-doped elongated waveguide core, a plurality of silicon nitride materials / layers 5A or elongated waveguide cores / non-doped elongated waveguide cores may be present to be simultaneously or serially implanted with rare earth ions 7.

[0096] The selective mask SM is provided or deposited prior to carrying out ion implantation of the target surface of the material or layer. The selective mask can be formed using photoresist or patterned photoresist.

[0097] Selective masking for erbium ion implantation, for example, can be achieved using a simple photoresist masking process. The masked area can be defined by the standard UV direct- write lithography with 3 pm thick AZ 15nXT photoresist before the implantation. Complete removal of the photoresist can be done, for example, by ashing in high power oxygen plasma (15 min) and washing in HCI solution (37%, 45°C, 15 min).

[0098] In an exemplary embodiment, the provision of the at least one support cladding material or layer 3A supporting at least one silicon nitride material or layer 5A comprises, for example, providing at least one cladding material or layer 3A and at least one silicon nitride material or layer 5A provided or deposited on the supporting at least one cladding material or layer 3A.

[0099] The at least one silicon nitride material or layer 5A can be provided thereon including at least one recess or depression 9 or cladding recess or depression 9, or a first recess 9A or cladding recess 9A and a second recess 9B or cladding recess 9B for receiving (embedding) cladding material 11 (see, for example, Figure 4(ii) & (iii) and Figure 5(ii) & (iii)).

[0100] The first cladding recess 9A and the second cladding recess 9B surrounds or encloses, for example laterally, the at least one portion P1 (or elongated portion P1 ) of the at least one (non- rare earth ion implanted) silicon nitride material or layer 5A or the waveguide core material 5A provided or deposited on the supporting cladding material or layer 3A. A plurality of portions P1 (or elongated portions P1 ) of the (non-rare earth ion implanted) silicon nitride material or layer 5A or the waveguide core material 5A may be present, each surrounded or enclosed, for example laterally, by at least one cladding recess 9, or a first cladding recess 9A and a second cladding recess 9B. The rare-earth ion implantation is, for example, carried out on the portion P1 of the silicon nitride material or layer 5A surrounded by the cladding recesses 9, 9A, 9B.

[0101] The recess 9, 9A, 9B is, for example, an elongated recess extending longitudinally with or parallel to or in the same plane as the silicon nitride material or layer 5A or the waveguide core material 5A. The side walls SW1A, SW2A of the silicon nitride material or layer 5A, for example, may delimit or define the recesses 9, 9A, 9B. According to exemplary embodiments, the at least one silicon nitride material or layer 5A supported on the cladding material or layer 3A is, for example, obtained or provided as now described (and in each of the fabrication methods of the exemplary methods of Figures 4 and 5).

[0102] The cladding material or layer 3A can be provided (directly or indirectly) on at least one supporting layer or substrate 15 or deposited (directly or indirectly) on at least one supporting layer or substrate 15. The supporting layer or substrate 15 may, for example, comprise or consist of silicon (as shown in the exemplary embodiments shown in Figures 4 and 5), or MgF2 or CaF2 or sapphire (AI2O3) or silicon oxide SiC>2 (quartz or fused silica).

[0103] The cladding material or layer 3A may, for example, be superposed on the supporting layer or substrate 15. The supporting layer or substrate 15 defines, for example, a surface supporting and / or contacting the cladding material or layer 3A. The surface may for example extend to define a planar surface non-laterally surrounding the cladding material or layer 3A and / or the waveguide core (or waveguide structure) material or layer 5A or waveguide core WC supported by or on the supporting layer or substrate 15.

[0104] The supporting layer or substrate 15 may, for example, comprise or consist of silicon such as a (commercial 4-inch) silicon wafer with, for example, a (4-micron thick) wet thermal oxide, the wet thermal oxide forming the silicon oxide cladding material or layer 3A.

[0105] Alternatively, silicon oxide may be deposited onto the substrate to form the cladding material or layer 3A comprising or consisting of silicon dioxide (SiC ). Deposition may be carried out, for example, by low-pressure chemical vapor deposition (LPCVD) to deposit, for example, 3 microns of SiC>2 onto the supporting layer or substrate 15.

[0106] The silicon oxide SiC>2 cladding material or layer 3A may be deposited at low pressure, for example, based on the LPCVD TEOS (tetraethyl orthosilicate Si(OC2Hs)4)) process. It employs the dissociation of TEOS at low pressure, e.g. 250 mTorr, and at a temperature exceeding 600°C. The deposition can be expressed as: Si(OC2Hs)4 — > SiO2 + 2C2H4 + H2O.

[0107] The waveguide core material or layer CM is then provided or deposited (directly or indirectly) on the cladding material or layer 3A. For example, a silicon nitride SisN4 material or layer is deposited (see, for example, Figures 4(i) and 5(i)), for example, by low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced low-pressure chemical vapor deposition as known to the skilled person (see, for example, Jaeger, Richard C. (2001 ), “Thermal Oxidation of Silicon”. Introduction to Microelectronic Fabrication, Upper Saddle River: Prentice Hall, ISBN 978-0-201-44494-0, the entire contents of which are incorporated herein by reference).

[0108] A hard mask 17 is provided or formed on the (SisNzi) waveguide core material or layer CM. The hard mask 17 includes at least one or a plurality of recesses or depressions 19 defining or delimiting a mask pattern (see, for example Figure 4(ii) and Figure 5(ii)). The pattern allows to form, in the deposited waveguide core material or layer CM, one or more waveguide core materials or layers, or one or more structures comprising the waveguide core material or layer that will subsequently be implanted with rare earth ions 7. The hard mask 17 includes, for example, at least one first hard mask recess or depression 19A and at least one second hard mask recess or depression 19B (see, for example Figure 4(ii) and Figure 5(ii)).

[0109] A hard mask layer 21 comprising or consisting of, for example, amorphous silicon aSi (see, for example Figures 4(i) and 5(i)) may for example be provided or deposited, and used to form the hard mask 17. The amorphous silicon aSi layer 21 (of for example 300nm thickness) may, for example, be deposited by low-pressure chemical vapor deposition (LPCVD) onto the waveguide core material or layer CM. Amorphous silicon aSi is provided as an exemplary material for forming the hard mask 17. The hard mask layer 21 may alternatively comprise or consist of, for example, silicon oxide SiO?, or diamond-like carbon (DLC).

[0110] The hard mask 17 and the waveguide structure (or recesses) are then formed or defined in the hard mask layer 21 , for example, using photolithography for example deep ultra-violet photolithography (ASML PAS 5500 / 350C stepper, JSR M108Y resist, and Brewer DUV-42P coating).

[0111] The waveguide structure pattern(s) is defined using DUV lithography into a resist coating 23 (see, for example Figure 4(i) and Figure 5(i)). The resist coating 23 is, for example, provided or deposited on the hard mask layer 21 that is to be patterned (see, for example Figures 4(i) and 5(i)).

[0112] Photolithography or UV lithography can used to transfer a (geometric) pattern or structure from a photomask or optical mask PM to the deposited hard mask layer or material 21. Deep ultraviolet (DUV) photolithography using, for example, light of wavelength <400nm, for example, in the range 193nm-254nm illuminates the photomask PM to define an exposure pattern on and in the deposited hard mask layer or material 21 such that the resulting pattern formed on the hard mask layer or material 21 can then be transferred into the underlying waveguide core material or layer CM.

[0113] For example, the exposed resist of the resist coating 23 is removed. For example, by development as is well known to the skilled person in the art. This can, for example, be done using a TMAH photoresist developer, which for example, is commercially available from the company JSR. The resulting waveguide structure pattern(s) is then transferred into the underlying and exposed aSi hardmask layer 21 using a silicon dry etch (for example based on SFe and C4F8) to form the hard mask 17 (see, for example Figures 4(ii) and 5(ii)). The resist mask is subsequently stripped off. Such resist stripping is well known to the skilled person in the art.

[0114] The exposed and / or underlying waveguide core material or layer CM is then removed. The (geometric) pattern or structure of the hard mask 17 is transferred from the hard mask 17 to the exposed and / or underlying waveguide core material or layer CM (see, for example Figures 4(ii) and 5(ii)). This is done, for example, by dry or wet etching.

[0115] Dry etching, or reactive ion etching or plasma etching of the waveguide core material or layer CM to form the one or more silicon nitride elongated waveguide cores 5A (see for examples Figures 4(ii) and 5(ii)) may comprise, for example, carrying out anisotropic dry etching carried out using, for example, CxFy-based chemical substances. Oxygen, may, for example, be added in order to remove CF polymers created as an etching by-product. Etching can, for example, be carried out with CHF3 and SFe, and with O2 also, serving to remove the etching by-product from chemical reactions between SisN4 and CHF3 / SF6.

[0116] Alternatively, a wet etch may be carried out.

[0117] As seen in Figures 4(ii) and 5(ii), this forms the first recess 9A or first cladding recess 9A and the second recess 9B or second cladding recess 9B in the silicon nitride material or layer 5A. Etching is, for example, performed to remove the silicon nitride material to form the recess or recesses and to expose a surface 3A1 that will receive cladding material. Etching is, for example, performed to remove the silicon nitride material to expose the surface 3A1 of the underlying supporting cladding material or layer 3A.

[0118] In the case of amorphous silicon aSi as the hard-mask 17, the remaining hard-mask material is stripped in concentrated KOH solution at, for example, 60°C (see, for example, Figures 4(iii) and 5(iii)). This exposes the surface of the silicon nitride material or layer 5A or the surface of the silicon nitride material or layer portion 1 for subsequent rare earth ion implantation.

[0119] Prior to carrying out rare-earth ion implantation, annealing may be carried out to, for example, reduce optical or absorption losses in the waveguide device (see, for example, Figures 4(iii) and 5(iii)).

[0120] For example, annealing can, for example, be performed to remove Hydrogen from the supporting and / or embedding cladding material or layer 3A, 3B, and / or the silicon nitride material or layer 5A supported on or embedded therein. Annealing can, for example, be performed in an oven or furnace, for example, in a controlled atmosphere, for example, a nitrogen atmosphere. Annealing can be carried out, for example, for 11 hours at a temperature of 1200°C.

[0121] Rare earth ion implantation of the exposed silicon nitride material or layer 5A delimiting or defining the recesses 9, 9A, 9B, and supported on the cladding material or layer 3A (see for example Figure 4(iv)) may now be performed.

[0122] As mentioned above, a selective mask SM may be provided or deposited prior to carrying out ion implantation of the target surface of the silicon nitride material or layer 5A.

[0123] Providing the embedding cladding material or layer 3B comprising the waveguide core (or waveguide structure) material or layer 5A or silicon nitride material or layer 5A embedded or laterally embedded inside the embedding cladding material or layer 3B may be done in different ways. Figure 5 schematically shows one exemplary embodiment.

[0124] In the exemplary embodiment shown in Figure 5, prior to carrying out rare-earth ion implantation, and to provide supporting side walls for the waveguide core (structure) material or layer 5A, at least one embedding material or layer 11 is, for example, provided or deposited on the etched or patterned waveguide core material or layer 5A and onto the exposed surface or surfaces 3A1 of, for example, the cladding material or layer 3A, to fill the recesses 9, 9B, 9B that are provided to receive the embedding material or layer 11 .

[0125] This permits to provide the embedding cladding material or layer 3B comprising the silicon nitride material or layer 5A embedded or laterally embedded inside the embedding cladding material or layer 3B. The cladding material 11 is, for example, deposited onto the cladding material or layer 3A and onto the silicon nitride material or layer 5A and into both the first (cladding) recess 9A and the second (cladding) recess 9B for receiving cladding or embedding material 11 (see, for example, Figure 5(iv)).

[0126] For example, silicon oxide (SiO?) cladding material or layer 11 may also be deposited at low pressure, for example, based on the LPCVD TEOS (tetraethyl orthosilicate Si(OC2Hs)4)) process. It employs the dissociation of TEOS at low pressure, e.g. 250 mTorr, and at a temperature exceeding 600°C. The deposition can be expressed as: Si(OC2Hs)4 — > SiO2 + 2C2H4+ H2O.

[0127] The deposited cladding material 11 is then structured and / or processed to provide the embedding cladding material or layer 3B comprising the at least one silicon nitride material or layer 5A embedded or laterally embedded inside the embedding cladding material or layer 3B, and to provide at least one silicon nitride material or layer 5A ready to be implanted through the surface S1A thereof.

[0128] For example, cladding material can be removed and / or structured to reduce the cladding material amount or level. For example, reduction may be to or to about the same thickness t as the silicon nitride material or layer 5A.

[0129] For example, wet and / or dry etching may be used to remove and structure the deposited cladding material 11 .

[0130] For example, as shown in the illustrated example of Figure 5, planarization and / or thinning down of the deposited cladding material 11 may be carried out to provide the embedding cladding material or layer 3A comprising the silicon nitride material or layer 5A laterally embedded inside the embedding cladding material or layer 3B (see, for example, Figure 5(v)).

[0131] The excess material can be removed, for example, by a planarization of the deposited material 11. Planarization is carried out, for example, using mechanical planarization and chemical planarization.

[0132] Immediately after the deposition of material 11 , an etchback process comprising photoresist spin-coating and RIE may optionally be performed to roughly planarize the surface and remove most of the excess material 11 . Chemical mechanical polishing (CMP) can, for example, then be applied to reach the desired embedding cladding thickness of the material 11 , and for example create a top surface with sub-nanometer root-mean-square roughness.

[0133] Optionally, etch trimming may be carried out using a Hydrofluoric acid HF wet etch. This, for example, allows to enhance control of the material removal depth (see, for example, Figure 6(vi).

[0134] Cladding material 11 is, for example, removed to re-expose the surface S1A of the (SisNzi) waveguide core structure 5A, and / or to have, for example, an outer surface OS of the embedding material or layer 3B (substantially) flush with the surface S1A of the (SisNzi) waveguide core structure 5A.

[0135] The recesses or recesses 9A, 9B contain or include lateral cladding bodies 11A that fill the recesses or recesses 9A, 9B. The lateral cladding bodies 11 A comprise or consist of cladding material.

[0136] Using this process, the (SisNzi) waveguide core structure 5A is formed buried or embedded in a cladding but with the top or outer surface S1 A of the waveguide core structure 5A exposed, allowing for direct rare earth ion implantation directly into the waveguide core structure 5A, as previously explained. As mentioned, a selective mask SM may be provided or deposited prior to carrying out ion implantation of the target surface of the silicon nitride material or layer 5A.

[0137] As a result, first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3B respectively mechanically support and contact (directly or indirectly) the first and second lateral side walls SW1 A, SW2A of the waveguide core structure 5A or silicon nitride material or layer 5A. Surfaces of the first and second lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3B may respectively contact (directly or indirectly) surfaces of the first and second lateral side walls SW1A, SW2A of the waveguide core structure 5A or silicon nitride material or layer 5A.

[0138] Following rare earth ion implantation, annealing of the rare-earth ion implanted silicon nitride material or layer 5 supported or embedded in the embedding cladding material or layer 3A, 3B can or may be carried out to reduce implantation defect optical losses (see, for example, Figures 4(v) and 5(viii). Annealing may be carried out at a temperature between 800° and 1250°C, for example, at 1000°C. Annealing is, for example, carried out at in an oxygen environment. Annealing is carried out, for example, for a duration between 30 and 90 minutes, for example 60 minutes.

[0139] Following ion implantation and a possible post-ion implantation anneal, at least one cladding / passivation material or layer 25 is provided or deposited on the rare-earth ion implanted waveguide core structure 5 or silicon nitride material or layer 5 (See, for example, Figures 4(vi) and 5(ix)). The cladding / passivation material or layer 25 may, for example, have a thickness between 1 pm and 4pm, for example, 2pm. The at least one cladding / passivation material or layer 25 may also be provided or deposited on the non-implanted waveguide core structure or structure 5A (see, for example, Figures 4(vi) and 5(ix)).

[0140] In the exemplary embodiment of Figure 4, the provision or deposition of the cladding / passivation material is, for example, onto the exposed surface or surfaces 3A1 of, for example, the cladding material or layer 3A.

[0141] In the exemplary embodiment of Figure 4, the provision of the cladding / passivation material or layer 25 provides lateral cladding bodies 25A that fill the recesses or depressions 9, 9A, 9B of the waveguide core material or layer 5 or the silicon nitride material or layer 5 to laterally embed the waveguide core material or layer 5 or the silicon nitride material or layer 5 in a cladding material 25. The provision embeds the waveguide core material or layer 5 or the silicon nitride material or layer 5 in, for example, the vertical direction (Y-direction) in both the case of the exemplary embodiment of Figure 4 and Figure 5.

[0142] As a result, the rare-earth ion implanted waveguide core structure 5 or silicon nitride material or layer 5 is both laterally embedded or laterally buried inside the embedding cladding material or layer 3B, and vertically embedded or buried inside the embedding cladding materials or layers 3A, 25 located on opposing sides of the rare-earth ion implanted waveguide core structure 5 or silicon nitride material or layer 5. The rare-earth ion implanted waveguide core structure 5 or silicon nitride material or layer 5 is, for example, top-embedded by the embedding cladding materials or layers 25, the top side being located on the opposite side of the waveguide core structure 5, 5A to that of the support layer or substrate 15.

[0143] The cladding / passivation material or layer 25 may comprise or consist of silicon oxide (SiO?). The deposition may, for example, be based on the LPCVD TEOS, as previously mentioned. Alternatively, deposition may be carried out by inductively coupled plasma chemical vapor deposition ICPCVD or ICP-PECVD inductively coupled plasma plasma-enhanced chemical vapor deposition ICP-PECVD. This allows the cladding material to deposited at a relatively lower deposition temperature.

[0144] At least one silicon dioxide (SiO?) layer or material 25 is, for example, deposited by plasma- enhanced chemical vapor deposition PECVD using precursors comprising, for example, silicon tetrachloride SiCk and an oxidizer, for example, oxygen O2 and / or nitrous oxide N2O. Argon (Ar) gas may, for example, also be used during deposition. The plasma is an inductively coupled plasma ICP. An ICP power source generates a plasma or high-density plasma through inductive coupling between a radio frequency (RF) antenna and the plasma. An induction coil is excited or powered by an RF power source or voltage generator, and the plasma is generated by coupling energy to the plasma through the generation of a magnetic field by the RF power source passing a high frequency current through the induction coil. The bias radiofrequency power is between 180W and 400W. The ICP excitation power is greater than or equal to 1600W. The silicon dioxide (SiC ) layer or material 25 is deposited by inductively coupled plasma plasma-enhanced chemical vapor deposition ICP-PECVD using a plasma-enhanced chemical vapor deposition ICP-PECVD tool or reactor (see for example, Zheru Qiu, et al., “Low-temperature and hydrogen-free silicon dioxide cladding for integrated photonics,” in CLEO 2023, Technical Digest Series (Optica Publishing Group, 2023), paper SM2H.2, the entire contents of which are fully incorporated herein by reference). The silicon dioxide (SiO2) layer or material 25 may, for example, have a thickness between 1 pm and 4pm.

[0145] According to another embodiment, the cladding / passivation material or layer 25 is absent and the present disclosure also concerns a device or waveguide amplifier in which the cladding / passivation material or layer 25 is absent.

[0146] While silicon dioxide has been mentioned herein as one possible example of the cladding material or layer, alternatively, the cladding material or layer may comprise or consist of oxide materials such as TeC>2 or AI2O3, or one or more polymers.

[0147] An exemplary fabricated device is shown in cross-section in Figure 2 (fabricated using the exemplary method of Figure 4), and schematically shown in Figure 3. The present disclosure also concerns a waveguide amplifier 27, a photonic integrated circuit waveguide amplifier 27, or a photonic integrated circuit 127 including at least one or more waveguide amplifiers 27 produced according to the fabrication methods of the present disclosure.

[0148] One or more stress release structures SR may, for example, also be optionally included in any of the embodiment disclosed herein. The stress release structures SR may be formed in the cladding material or layer 3A and can be, for example, located or arranged to enclose the waveguide core (or waveguide structure) material or layer 5A (see, for example, the exemplary embodiment of Figure 8). A plurality of waveguide core (or waveguide structure) material or layer 5A may, for example, be located or enclosed between the stress release structures SR.

[0149] The stress release structures SR are, for example, formed in the cladding material or layer 3A after the provision or deposition of the cladding material or layer 3A and prior to the provision or deposition of the waveguide core material or layer CM on the cladding material or layer 3A.

[0150] The stress release structures or stress release trench structures SR comprise at least one or a plurality of indentations or depressions 33 formed in the cladding material or layer 3A (see exemplary embodiment of Figure 8). The plurality of indentations or depressions 33 define or delimit one or more cladding material pillars or supports 35. The plurality of indentations or depressions 33 are filled with the waveguide core material, for example, silicon nitride material 37 when this material is deposited onto the cladding material or layer 3A. The stress release trench structure SR can prevent cracks forming or propagating to or into the waveguide core WC or waveguide device.

[0151] A depth of the indentations 33 measured from an outer surface of the cladding material or layer 3A and extending into the cladding material or layer 3A may, for example, be (substantially) equal to or greater than the thickness t of the waveguide core (or waveguide structure) material or layer 5A. A depth of the indentation 33 may, for example, be between 1.5 microns and 5 microns, for example 2.5 microns. A depth of the indentation 33 may, for example, be >3 microns, for example, >3 microns and <5 microns, or >3 microns and <10 microns, for example 3.5 microns. This can prevent cracks forming or extending through or across the optical waveguide or waveguide core 3, and / or also reduce impurity contamination diffusion to the waveguide core (or waveguide structure) material or layer 5A or waveguide core WC from the support substrate or layer 15. The depth direction being in a direction towards a plane or surface of extension defined by the support substrate or layer 15, for example, perpendicular to the plane or surface of extension defined by the substrate 15, or perpendicular to the elongated guiding direction or propagation direction PD of light in the waveguide core WC.

[0152] A further aspect of the present disclosure concerns a waveguide amplifier 27, or a photonic integrated circuit waveguide amplifier 27, or a photonic integrated circuit 127 including at least one or more waveguide amplifiers 27. An example of such a device or structure is schematically shown in Figure 3 and in Figure 6a. An example of such a device or structure is schematically shown in Figures 4(vi) and 5(ix).

[0153] The waveguide amplifier 27, or the photonic integrated circuit waveguide amplifier 27, or the photonic integrated circuit 127 may include, for example, the structural and / or functional features previously described above in the context of the fabrication method.

[0154] The waveguide amplifier 27 includes embedding cladding material(s) or layer(s), or the at least one embedding cladding material or layer 3A, 3B, 25, and includes at least one rare-earth ion implanted waveguide core 5 or rare-earth ion implanted waveguide core 5 comprising a rare- earth ion implanted silicon nitride material or layer 5 extending in a plane (for example, X-Z directions) or a plane of the device, or in the elongated direction of extension in the light guiding direction PD (for example, Z-direction). The rare-earth ion implanted waveguide core 5 or rare- earth ion implanted silicon nitride material or layer 5 is embedded in the embedding cladding material or layer 3B, or the embedding cladding materials or layers 3A, 25. The rare-earth ion implanted silicon nitride material or layer 5 defines a waveguide core enclosed by the embedding cladding material(s) or layer (s).

[0155] The implanted rare-earth ions 7 comprise or consist of Erbium, Ytterbium, or Thulium.

[0156] The embedded waveguide core 5 or rare-earth ion implanted silicon nitride material or layer 5 has a material or layer thickness t1 , where thickness t1 is less than or equal to (<) 400nm and greater than or equal to (>) 100nm or 40nm or 10nm, or preferably <300nm and >100nm or 40nm or 10nm, or more preferably <250nm and >100nm or 40nm or 10nm, or even more preferably <200nm and >1 OOnm or 40nm or 10nm, in a direction (vertical direction, Y-direction Figure 3) perpendicular to the plane in which the waveguide core 5 or silicon nitride material or layer 5 extends (plane defined by X-direction and Z-direction). The thickness t1 , is for example, measured as the maximum thickness value in the vertical (thickness) direction.

[0157] First and second lateral side walls (or surfaces thereof) SW1 B, SW2B of the embedding cladding material(s) or layer(s) 3B respectively mechanically support and contact (directly or indirectly) the first and second lateral side walls SW1A, SW2A of the rare earth doped waveguide core structure 5 or silicon nitride material or layer 5.

[0158] The rare-earth ion implanted silicon nitride material or layer 5 is, for example, structured in the plane in which the rare-earth ion implanted silicon nitride material or layer 5 extends, or in the plane of the device in or inside which the rare-earth ion implanted silicon nitride material or layer 5 extends.

[0159] The waveguide amplifier 27 includes, for example, the supporting cladding material or layer 3A, and the rare-earth ion implanted silicon nitride material or layer 5 extending in a plane of the waveguide amplifier 27. The rare-earth ion implanted silicon nitride material or layer 5 is supported by the supporting cladding material or layer 3A. The rare-earth ion implanted silicon nitride material or layer 5 extends to define the elongated waveguide core WC.

[0160] As mentioned, the waveguide amplifier 27 includes, the embedding cladding material(s) or layer(s) 3B extending, for example, from the supporting cladding material or layer 3A. The first and second elongated lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3B enclose, for example, the elongated waveguide core WC defined by the rare-earth ion implanted silicon nitride material or layer 5. The first and second elongated lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3B extend, for example, away from the supporting cladding material or layer 3A to laterally enclose the elongated waveguide core WC.

[0161] The first and second elongated lateral side walls SW1 B, SW2B of the embedding cladding material or layer 3B may respectively mechanically support and contact the first and second elongated lateral side walls SW1A, SW2A of the rare-earth ion implanted silicon nitride material or layer 5.

[0162] The rare-earth ion implanted silicon nitride material or layer 5, for example, forms or defines an embedded and elongated ridge structure protruding from the supporting cladding material or layer 3A, and flanked by the first and second elongated lateral side walls SW1 B, SW2B of the at least one embedding cladding material or layer 3B.

[0163] Surfaces of the first and second lateral side walls SW1A, SW2A of the rare-earth ion implanted silicon nitride material or layer 5 are, for example, located laterally displaced from or at a distance from at least one or first and second outer lateral side walls LS1 , LS2 of the supporting cladding material or layer 3A, and / or from at least one or first and second outer lateral side walls of a support substrate 15.

[0164] The upper surface S1A of the rare-earth ion implanted silicon nitride material or layer 5 is located offset to that of the support surface SS of the supporting cladding material or layer 3A. The first and second lateral side walls SW1A, SW2A of the rare-earth ion implanted silicon nitride material or layer 5 extend away from the offset location towards the support surface SS of the supporting cladding material or layer 3A. The first and second elongated lateral side walls SW1 B, SW2B of the at least one embedding cladding material or layer 3B can be, for example, supported on the second surfaces 3A1 of the supporting cladding material or layer 3A. The second surfaces 3A1 extend laterally away from the support surface SS.

[0165] The rare-earth ion implanted silicon nitride material or layer 5 may, for example, include at least one elongated rare-earth ion implanted portion and at least one elongated non-rare-earth ion implanted portion.

[0166] The waveguide amplifier 27 may, for example, include at least one further rare-earth ion implanted silicon nitride material or layer 5 or a non-rare-earth ion implanted silicon nitride material or layer 5A extending to define a further elongated waveguide core. The further elongated waveguide core is located relatively to the rare-earth ion implanted silicon nitride material or layer 5 to be optically coupled thereto or to be evanescently optically coupled thereto.

[0167] The photonic integrated circuit 27 may include a plurality of waveguide amplifiers and one or more non-implanted waveguide cores 5A that are part of a passive waveguide device PWD.

[0168] The rare-earth ion implanted silicon nitride material or layer 5 defines or is an active material or active layer of the waveguide amplifier 27. The rare-earth ion implanted silicon nitride material or layer 5 defines or is, for example, an optical gain medium of the waveguide amplifier 27.

[0169] The rare-earth ion implanted silicon nitride material or layer 5 defines a waveguide core of the waveguide amplifier 27. The waveguide core WC is enclosed or embedded in the cladding material(s) or layer(s). The cladding material(s) or layer(s) hosts the rare-earth ion implanted silicon nitride material or layer 5. The cladding material(s) or layer(s) defines a support or container inside which the rare-earth ion implanted silicon nitride material or layer 5 is supported and / or held. The waveguide core is configured to propagate amplified light in the elongated (light) propagation direction PD of the waveguide amplifier 27.

[0170] The waveguide core WC and the host cladding material(s) or layer(s) have refractive index values or a refractive index contrast permitting the waveguide core to guide and propagate light along the waveguide 27 in a light propagation (or guiding) direction PD or elongated propagation direction PD. The waveguide core has, for example, a refractive index (at the wavelength of light to be guided) that is greater that the refractive index (at the wavelength of light to be guided) of the cladding material or layer. This is also true for the material or medium located or superposed opposite the cladding material or layer 3, for example, that encloses or sandwiches the waveguide core with the cladding material or layer. This medium may, for example, be the surrounding air or a further cladding material or layer.

[0171] The cladding material or layer 25 may, for example, be provided or deposited on the embedded rare-earth ion implanted silicon nitride material or layer 5 after ion implantation. Alternatively, the at least one cladding material or layer 25 may, for example, be provided or deposited on the embedded silicon nitride material or layer 5A prior to rare-earth ion implantation and, in such a case, ion implantation of the silicon nitride material or layer 5A is carried out by passing the ions through the covering cladding material or layer 25.

[0172] The cladding or passivation material or layer 25 is, for example, provided on the rare-earth ion implanted waveguide core structure 5 and on the embedding cladding material or layer 3B.

[0173] At least one further cladding / passivation material or layer may, for example, be provided or deposited on the covering cladding material or layer 25 after rare-earth ion implantation of the embedded silicon nitride material or layer 5A.

[0174] The further cladding material or layer and / or the at least one embedding cladding material or layer are, for example, optically passive elements or components of the waveguide amplifier 27.

[0175] The further cladding / passivation material or layer and / or the embedding cladding material or layer may, for example, comprise or consist of silicon dioxide (SiO?).

[0176] The recesses or depressions 9 are for example elongated recesses or depressions 9 extending in an elongated manner in the waveguide core material or layer 5A. The elongated recess or depression 9 extends, for example, in a planar manner or in the plane of the waveguide core material or layer 5A.

[0177] The elongated recesses or depressions 9 extends in the light propagation direction PD. The rare-earth ion implanted silicon nitride (SisNzi) material or layer 5 also extends longitudinally along the light propagation direction PD. The rare-earth ion implanted silicon nitride material or layer 5 and the cladding material or layers extend in the elongated direction PD to propagate or guide light along the elongated direction PD of the waveguide amplifier 27.

[0178] The cladding material(s) or layer (s) may, for example, comprise or consist of a planar layer or material.

[0179] The rare-earth ion implanted silicon nitride (SisNzi) material or layer 5 and waveguide core WC may also, for example, define a planer layer or material embedded or contained inside the cladding material or layer. The rare-earth ion implanted silicon nitride material or layer 5 may, for example, define a substantially planar optical waveguide core.

[0180] The PIC device 27 may also include at least one or a plurality of passive or non-amplification components PWD. The passive or non-amplification component PWD is, for example, identical to the waveguide amplifier 27 except that it includes an embedded non-ion implanted silicon nitride material or layer 5A (absence of rare earth ions), as can be seen for example in Figure 3. The passive or non-amplification component may be integrally connected with the embedded rare-earth ion implanted silicon nitride material or layer 5. The embedded non-ion implanted silicon nitride material or layer 5A may be continually connected or integrated with the embedded rare-earth ion implanted silicon nitride material or layer 5. The cladding material or layer of the passive or non-amplification component 15 may also be continually connected or integrated with the cladding material or layer containing the embedded rare-earth ion implanted silicon nitride material or layer 5. The passive or non-amplification component may be formed using selective ion implantation, as discussed earlier. The passive or non- amplification component may be optically coupled with the embedded rare-earth ion implanted silicon nitride material or layer 5, or located relative to the embedded rare-earth ion implanted silicon nitride material or layer 5 to be evanescently optically coupled with the embedded rare- earth ion implanted silicon nitride material or layer 5.

[0181] Light may be coupled into the passive or non-amplification component or the waveguide amplifier or device using one or more integrated couplers or integrated coupling waveguides.

[0182] The rare-earth ion implanted silicon nitride material or layer 5 may include a light input coupling interface or port, and / or an amplified light output coupling interface or port. The coupling interface or port may, for example, comprise the ion-implanted and non-ion implanted material interface with a passive or non-amplification component, or a facet of the embedded rare- earth ion implanted silicon nitride material or layer 5 and / or cladding material or layer, that may be formed, for example, by dicing. The rare-earth ion implanted silicon nitride material or layer 5 may extend, for example, in an elongated manner along the light propagation direction PD over a distance, for example, between 0.1 m and 0.6m.

[0183] The rare-earth ion implanted silicon nitride material or layer 5 may (longitudinally) extend in a substantially straight and / or curved manner. They may, for example, extend (longitudinally) along the light propagation direction PD to define a spiral and / or coil arrangement, as for example shown in Figure 6a.

[0184] The cladding material or layer and / or the at least one embedding cladding material or layer may be optically passive elements or components of the waveguide amplifier.

[0185] The waveguide amplifier 1 is, for example, a photonic circuit integrated waveguide amplifier, or a chip-based (or photonic chip-based) waveguide amplifier. The waveguide amplifier 1 is, for example, a photonic integrated circuit component or a planar lightwave circuit component. The waveguide amplifier 1 is, for example, a planar substrate-based integrated amplifier.

[0186] According to another aspect, the present disclosure also concerns a system including a pump laser or source and at least one photonic integrated circuit waveguide amplifier.

[0187] According to another aspect, the present disclosure also concerns a photonic integrated circuit PIC including at least one photonic integrated circuit waveguide amplifier. The photonic integrated circuit PIC may, for example, include one or more integrated silicon nitride component or device optically coupled to the photonic integrated circuit waveguide amplifier, or comprising the photonic integrated circuit waveguide amplifier. The integrated silicon nitride component or device may, for example, comprise or consist of a soliton microcomb generator, or an electro-optical modulator, or a laser source. The electro-optical modulator may, for example, comprise or consist of a lithium niobate electro-optical modulator.

[0188] According to another aspect, the present disclosure further concerns an integrated optical device or integrated laser source including at least one photonic integrated circuit waveguide amplifier 1 , where the photonic integrated circuit waveguide amplifier serves as a gain medium of the integrated optical device or integrated laser source. The integrated optical device or integrated laser source may, for example, comprise or consist of a soliton microcomb, a rare- earth CW laser, a femtosecond mode-locked laser or a cavity soliton laser. Figures 6(a) shows an exemplary hybrid-integrated waveguide amplifier module 127 that integrates four independent Erbium-doped waveguide amplifiers 27 on a single SisN4 PIC chip, achieved by 4-inch wafer-scale thin-SisN4 PIC fabrication and ion-implantation. The adoption of 200-nm SisN4 waveguides allows to increase amplifier saturation power. The Inventors demonstrate an on-chip net gain of up to 15 dB and an output power of 22 mW for individual EDWA lanes / amplifiers.

[0189] Figure 6(a) shows the layout of an exemplary four-lane Er:Si3N4 waveguide optical amplifier chip that accommodates four individual EDWAs, each of which consists of a 17-cm-long Archimedean spiral gain section and an on-chip WDM coupler for pump injection. This amplifier device is implemented using 200nm thick, 5pm wide SisN4 strip waveguides. The outer diameter of each gain spiral is ~ 2.6 mm (< 30 mm2area) with a > 2.5 pm waveguide section in the S-bend to strip higher order optical modes. The Inventors design the on-chip WDMs based on directional couplers to combine the optical signal near 1550 nm and hybrid- integrated 1480 nm pump sources. The input and output ports of all the EDWAs are arranged in an arrayed fashion with a pitch of 250pm along one chip edge, while the Input ports of the pump light are located at the other side of the chip (Figure 6(b)). The thin and wide waveguide enables a large mode area of >10pm2, beneficial for higher saturation power and reduced nonlinearity-induced impairment, which is demanded by high power waveguide amplifiers, compared to those using thick waveguides with tight optical confinement. The hybrid integration of the multi-lane amplifier device is implemented using with an optical fiber array (PHIX) (Figure 6(c)) and a multi-lane pump laser diode chip (Seminex) (Figure 6(d)). The pump diodes are single transverse mode Fabre -Perot diodes delivering up to 400 mW.

[0190] The use of 200 nm waveguides, compared to the 700nm previously used, leads to a lower gain coefficient (in dB / m), as the overlap factor between ion density and optical mode is reduced due to the weaker optical mode confinement.

[0191] The waveguides were fabricated by low-pressure chemical vapor deposition, deep ultra-violet lithography, and dry etching / reactive ion etching. The passive sections were masked by 3 pm- thick photoresist. Erbium ion implantation was carried out with maximum beam energy of 350 keV and total implantation dose of 2.4 x 1015cm’2. After implantation, the Inventors annealed the samples at 1000 degrees Celsius (1 h, in O2) and deposited a 3 pm SiO? cladding by plasma-enhanced chemical vapor deposition with SiCk as precursor. The background loss of the annealed waveguides ranges from 5 dB / m to 10 dB / m at 1.3 pm (outside the erbium absorption bands). Figure 7(a) shows the experimental setup for characterization of the multi-lane EDWA. The signal input and output were coupled with a 250-pm pitch fiber array with twelve UHNA7 fibers that have matched optical mode area with the waveguide tapers. The coupling loss was characterized to be ~ 4.9dB per facet, which is subject to further optimization. An 1550 nm external cavity diode laser (Toptica) is used as input signal after attenuation (ATT) and polarization controller (FPC). Signal output is measured with a power meter (PM) and an optical spectrum analyzer (OSA) after a 1500 nm low-pass filter (LPF) to reject the residual pump.

[0192] Figure 7(b) shows the small signal on-chip net gain of two channels, both channels have comparable maximum gain of 13 dB to 15 dB. The achieved gain is so far constrained by the estimated ~20% overlap factor, which leads to a limited gain coefficient. This can be overcome by increasing the overlap factor. The saturation input power was increased to around -5 dBm (Figure 7 (c)). Figure 7(d) shows the on-chip output power in typical large signal operation. An output power of up to 22 mW is achieved at 278 mW off-chip pump power. This corresponds to a 12% on-chip power conversion efficiency considering a pump coupling loss of 2.5 dB. Both channels show comparable gain performance in characterization. The Inventors operated the EDWA lanes individually, considering thermal management in this proof-of- concept demonstration.

[0193] The Inventors demonstrate 200nm four-channel erbium-doped waveguide amplifiers with a hybrid integrated pump laser diode array. The four gain spirals and the WDMs are integrated within a 6.5 mm x13 mm chip. The amplifier lanes achieved maximum 15 dB on-chip gain and up to 22 mW on-chip output power. Such high-density multi-channel amplifiers have potential for applications requiring scalability such as compact, pluggable optical line systems for interdatacenter communications, integrated microwave photonics, phased array systems, spacedivision multiplexing transmission, and submarine optical cables.

[0194] It is to be understood that a singular form of a noun corresponding to an item may include one or more of the things, unless the relevant context clearly indicates otherwise. Terms such as “first”, “second”, or “first” or “second” may simply be used to distinguish the component from other components in question, and do not limit the components in other aspects (e.g., importance or order). Terms, such as “first”, “second”, and the like, may be used herein to describe various components. Each of these terminologies is not used to define an essence, order or sequence of a corresponding component but used merely to distinguish the corresponding component from other component(s). For example, a "first" component may be referred to as a "second" component, and similarly, the "second" component may be referred to as the "first" component.

[0195] It will be further understood that the terms "comprises / comprising" and / or "includes / including" when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or populations thereof.

[0196] The word “about” as used herein means the identified value plus / minus 5%.

[0197] Each embodiment herein may be used in combination with any other embodiment(s) described herein.

[0198] While the invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments, and equivalents thereof, are possible without departing from the sphere and scope of the invention. Accordingly, it is intended that the invention not be limited to the described embodiments and be given the broadest reasonable interpretation in accordance with the language of the appended claims. The features of any one of the above described embodiments may be included in any other embodiment described herein.

Claims

CLAIMS1. Photonic integrated circuit waveguide amplifier fabrication method comprising:- providing at least one support cladding material or layer (3A) supporting at least one silicon nitride material or layer (5A), or at least one embedding cladding material or layer (3B) comprising the at least one silicon nitride material or layer (5A) embedded inside the at least one embedding cladding material or layer (3B) and at least one support cladding material or layer (3A) supporting the at least one silicon nitride material or layer (5A) and the at least one embedding cladding material or layer (3B); wherein the at least one silicon nitride material or layer (5A) is a structured silicon nitride material or layer (5A) and defines or includes first and second lateral side walls (SW1 A, SW2A) for laterally confining light, the first and second lateral side walls (SW1A, SW2A) extending outside the at least one supporting cladding material or layer (3A) and away from a support surface (SS) of the at least one supporting cladding material or layer (3A), and extending to at least one outer or upper surface (S1 A) of the at least one silicon nitride material or layer (5A) for receiving ion irradiation during rare-earth ion implantation; wherein the at least one silicon nitride material or layer (5A) extends in a plane, and the at least one silicon nitride material or layer (5A) has a material or layer thickness (t) that is less than or equal to 400nm and greater than or equal to 40nm in a direction perpendicular to the plane in which the at least one silicon nitride material or layer (5A) extends; and- carrying out rare-earth ion (7) implantation, at rare-earth ion (7) acceleration values between 0.01 MeV and 0.5 MeV, by ion irradiation of the at least one outer or upper surface (S1A) of the at least one supported silicon nitride material or layer (5A) or embedded and supported silicon nitride material or layer (5A) to form at least one rare-earth ion implanted silicon nitride material or layer (5) supported on the at least one supporting cladding material or layer (3A) or embedded in the at least one embedding cladding material or layer (3B) and supported on the at least one supporting cladding material or layer (3A), the at least one rare-earth ion implanted silicon nitride material or layer (5) defining a waveguide core (WC) of the waveguide amplifier.

2. Method according to claim 1 , wherein the at least one silicon nitride material or layer (5A) has a material or layer thickness (t) that is less than or equal to 200nm and greater than or equal to 40nm.

3. Method according to claim 1 or 2, wherein the at least one silicon nitride material or layer (5A) is at least laterally embedded inside the at least one embedding cladding material or layer (3B).

4. Method according to any one of the previous claims, wherein the at least one silicon nitride material or layer (5A) forms or defines an elongated ridge structure.

5. Method according to any one of the previous claims, wherein rare-earth ion implantation is carried out by ion irradiation of at least one directly exposed surface (S1 A) of the at least one supported and / or embedded silicon nitride material or layer (5A) to form the at least one rare- earth ion implanted silicon nitride material or layer (5) supported on the at least one cladding material or layer (3A) or embedded in the at least one embedding cladding material or layer (3B) and supported on the at least one cladding material or layer (3A).

6. Method according to anyone of the previous claims, wherein the provided embedded at least one silicon nitride material or layer (5A) extends inside the at least one embedding cladding material or layer (3B) and away from the support surface (SS) of the at least one supporting cladding material or layer (3A) to define the outer or upper silicon nitride surface (S1A) to receive ion irradiation during rare-earth ion implantation, and the at least one silicon nitride material or layer (5A) defines or includes the first and second lateral side walls (SW1 A, SW2A), and the at least one embedding cladding material or layer (3B) defines or includes first and second lateral side walls (SW1 B, SW2B), wherein the first and second lateral side walls (SW1 B, SW2B) of the at least one embedding cladding material or layer (3B) respectively mechanically support and contact the first and second lateral side walls (SW1A, SW2A) of the at least one silicon nitride material or layer (5A).

7. Method according to anyone of the previous claims 1 to 5, wherein the provided supported at least one silicon nitride material or layer (5A) defines or includes exposed first and second lateral side walls (SW1A, SW2A) extending outside the at least one supporting cladding material or layer (3A) and away from the support surface (SS) of the at least one supporting cladding material or layer (3A) to define exposed outer surfaces (ES1 , ES2), and extend to the outer or upper silicon nitride surface (S1A) that receives ion irradiation during rare-earth ion implantation.

8. Method according to any one of the previous claims, further including annealing the at least one rare-earth ion implanted silicon nitride material or layer (5) to reduce implantation defect optical losses.

9. Method according to anyone of the previous claims, wherein the rare-earth ions (7) comprise or consist of Erbium, Ytterbium, or Thulium.

10. Method according to anyone of the previous claims, wherein the rare-earth ion implantation is carried out by accelerating rare-earth ions (7) towards the at least one surface (S1A) toprovide an ion implantation fluence to the at least one surface for ion implantation inside the at least one embedded or buried silicon nitride material or layer (5A).

11. Method according to anyone of the previous claims, wherein the rare-earth ion implantation is carried out into elongated surrounding portions (FR) of the at least one supporting cladding material or layer (3A), or the at least one embedding cladding material or layer (3B) and the at least one supporting cladding material or layer (3A) to provide rare earth ion implanted cladding material to amplify light guided or propagated by the waveguide core (WC) of the waveguide amplifier, the elongated surrounding portions (FR) surrounding the at least one silicon nitride material or layer (5A).

12. Method according to anyone of the previous claims, including carrying out selective masking during rare-earth ion implantation to form (i) at least one first portion (P1 ) comprising at least one rare-earth ion implanted silicon nitride material or layer (5) supported on the at least one support cladding material or layer (3A), and (ii) at least one second portion (P2) comprising at least one non-implanted silicon nitride material or layer (5A) supported on the at least one support cladding material or layer (3A), wherein the silicon nitride material or layer (5) supported on the at least one support cladding material or layer (3A) of the first portion (P1 ) is optically evanescently coupled to the silicon nitride material or layer (5A) supported on the at least one support cladding material or layer (3A) of the second portion (P2).

13. Method according to anyone of the previous claims, wherein, prior to carrying out rare- earth ion implantation, annealing is carried out to remove Hydrogen from the at least one silicon nitride material or layer (5A) and the at least one supporting cladding material or layer (3A), or from the at least one silicon nitride material or layer (5A), the at least one embedding cladding material or layer (3B), and the at least one supporting cladding material or layer (3A).

14. Method according to anyone of the previous claims, wherein the step of providing at least one support cladding material or layer (3A) supporting at least one silicon nitride material or layer (5A) comprises:- providing at least one cladding material or layer (3A) for supporting at least one waveguide core and at least one silicon nitride material or layer (5A) provided or deposited on the supporting at least one cladding material or layer (3A), the at least one silicon nitride material or layer (5A) provided or deposited thereon including at least a first recess (9A) and at least a second recess (9B) for receiving cladding material, the first recess (9A) and the second recess (9B) surrounding at least one portion (P1 ) of the at least one silicon nitride material or layer (5A) provided or deposited on the supporting at least one cladding material or layer (3A).

15. Method according to the previous claim, wherein the rare-earth ion implantation is carried out on the at least one portion (P1 ) of the at least one silicon nitride material or layer (5A) surrounded by the first cladding recess (9A) and the second cladding recess (9B).

16. Method according to anyone of the previous claims 1 to 13, wherein the step of providing at least one embedding cladding material or layer (3B) comprising the at least one silicon nitride material or layer (5A) embedded inside the at least one embedding cladding material or layer (3B) and the at least one support cladding material or layer (3A) supporting the at least one silicon nitride material or layer (5A) and the at least one embedding cladding material or layer (3B) comprises:- providing at least one cladding material or layer (3A) for supporting at least one waveguide core and at least one silicon nitride material or layer (5A) provided or deposited on the supporting at least one cladding material or layer (3A), the at least one silicon nitride material or layer (5A) provided or deposited thereon including at least a first cladding recess (9A) and at least a second cladding recess (9B) for receiving cladding material,- depositing cladding material (11 ) onto the at least one silicon nitride material or layer (5A) and into both the first cladding recess (9A) and the second cladding recess (9B).

17. Method according to the previous claim, including:- carrying out at least a thinning down of the deposited cladding material (11 ) to provide at least one embedding cladding material or layer (3B) laterally embedding the at least one silicon nitride material or layer (5A) inside the at least one embedding cladding material or layer (3B).

18. Method according to the previous claim 16 or 17, including:- carrying out at least planarization of the deposited cladding material (11 ) to provide at least one embedding cladding material or layer (3B) laterally embedding the at least one silicon nitride material or layer (5A) inside the at least one embedding cladding material or layer (3B).

19. Method according to the previous claim, wherein the rare-earth ion implantation is carried out on the at least one silicon nitride material or layer (5A) laterally embedded inside the at least one embedding cladding material or layer (3B).

20. Method according to anyone of claims further including the step of providing a hard mask (17) including at least first and second hard mask recesses (19A, 19B), and forming the first cladding recess (9) and the second cladding recess (9B) in the at least one silicon nitride material or layer (5A) using said hard mask (17) and a dry plasma etch or a wet etch.

21. Method according to anyone of the previous claims, wherein at least one cladding / passivation material or layer (25) is provided or deposited on the at least one rare- earth ion implanted silicon nitride material or layer (5) after rare-earth ion implantation.

22. Photonic integrated circuit waveguide amplifier (27) comprising:- at least one supporting cladding material or layer (3A), and- at least one rare-earth ion implanted silicon nitride material or layer (5) extending in a plane of the photonic integrated circuit waveguide amplifier (27),the at least one rare-earth ion implanted silicon nitride material or layer (5) being supported by the at least one supporting cladding material or layer (3A), the at least one rare-earth ion implanted silicon nitride material or layer (5) extending to define an elongated waveguide core (WC), wherein the implanted rare-earth ions (7) consist of Erbium, Ytterbium, or Thulium, and wherein the at least one supported rare-earth ion implanted silicon nitride material or layer (5) has a material or layer thickness (t) that is less than or equal to 400nm and greater than or equal to 40nm in a direction perpendicular to the plane in which the at least one rare-earth ion implanted silicon nitride material or layer (5) extends; and wherein the photonic integrated circuit waveguide amplifier (27) comprises:- at least one embedding cladding material or layer (3B) extending from the at least one supporting cladding material or layer (3A), the at least one embedding cladding material or layer (3B) including first and second elongated lateral side walls (SW1 B, SW2B) enclosing the elongated waveguide core (WC) defined by at least one rare-earth ion implanted silicon nitride material or layer (5), and wherein the at least one rare-earth ion implanted silicon nitride material or layer (5) includes first and second elongated lateral side walls (SW1A, SW2A), and the first and second elongated lateral side walls (SW1 B, SW2B) of the at least one embedding cladding material or layer (3B) respectively mechanically support and contact the first and second elongated lateral side walls (SW1A, SW2A) of the at least one rare-earth ion implanted silicon nitride material or layer (5).

23. Photonic integrated circuit waveguide amplifier (27) according to the previous claim, wherein the at least one supported rare-earth ion implanted silicon nitride material or layer (5) has a material or layer thickness (t) that is less than or equal to 200nm and greater than or equal to 40nm.

24. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 23, wherein the first and second elongated lateral side walls (SW1 B, SW2B) of the at least one embedding cladding material or layer (3B) extend away from the at least one supporting cladding material or layer (3A) to laterally enclose the elongated waveguide core (WC) defined by at least one rare-earth ion implanted silicon nitride material or layer (5).

25. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 24, wherein the at least one rare-earth ion implanted silicon nitride material or layer (5) forms or defines an embedded and elongated ridge structure protruding from the supporting cladding material or layer 3A and flanked by the first and second elongated lateral side walls (SW1 B, SW2B) of the at least one embedding cladding material or layer (3B).

26. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 25, wherein surfaces of the first and second lateral side walls (SW1 A, SW2A) of the at least one rare-earth ion implanted silicon nitride material or layer (5) are located laterally displaced from or at a distance from at least one outer lateral side wall (LS1 , LS2) of the supporting cladding material or layer (3A), and / or from at least one outer lateral side wall of a support substrate (15) of the photonic integrated circuit waveguide amplifier (27).

27. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 26, wherein an upper surface (S1 A) of the at least one rare-earth ion implanted silicon nitride material or layer (5) is located offset to that of a first support surface (SS) of the at least one supporting cladding material or layer (3A), and the first and second lateral side walls (SW1A, SW2A) of the at least one rare-earth ion implanted silicon nitride material or layer (5) extend away from the offset location towards the first support surface (SS) of the at least one supporting cladding material or layer (3A), and the first and second elongated lateral side walls (SW1 B, SW2B) of the at least one embedding cladding material or layer (3B) are supported on second surfaces (3A1 ) of the at least one supporting cladding material or layer (3A) that extend laterally away from the first support surface (SS).

28. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 27, including at least one cladding or passivation material or layer (25) provided on the at least rare-earth ion implanted waveguide core structure (5) and the at least one embedding cladding material or layer (3B).

29. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 28, wherein the at least one rare-earth ion implanted silicon nitride material or layer (5) includes at least one elongated rare-earth ion implanted portion and at least one elongated non-rare-earth ion implanted portion.

30. Photonic integrated circuit waveguide amplifier (27) according to any one of the previous claims 22 to 29, including at least one further rare-earth ion implanted or non-rare-earth ion implanted silicon nitride material or layer (5) extending to define a further elongated waveguide core, wherein the further elongated waveguide core is located relatively to the at least one rare-earth ion implanted silicon nitride material or layer (5) to be optically evanescently coupled thereto.

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