Waveguide amplifier and waveguide amplifier manufacturing method

Abstract

The invention relates to a waveguide amplifier comprising:-at least one embedded cladding material or layer, and-at least one rare earth ion implanted silicon nitride material or layer embedded in the at least one embedded cladding material or layer, the at least one rare earth ion implanted silicon nitride material or layer defines a waveguide core enclosed by at least one embedded cladding material or layer.

Description

Technical Field

[0001] The present invention relates to a waveguide amplifier device and a method for manufacturing the waveguide amplifier, as well as a rare earth doped amplifier based on a photonic integrated circuit and a method for manufacturing the same. Background Art

[0002] Erbium-doped fiber amplifiers have revolutionized long-distance optical communications and laser technology. Erbium ions could also provide the basis for efficient light amplification in photonic integrated circuits. However, this approach has so far remained impractical due to insufficient output power.

[0003] The innovation of the erbium-doped fiber amplifier (EDFA) in the 1980s (1,2) has revolutionized long-distance optical communications and has had a profound impact on our information society. EDFAs replaced complex and bandwidth-limited electrical repeaters and enabled the realization of transatlantic fiber-based optical communications networks (3). Erbium amplifiers have many unique properties that are well suited for optical communications, such as broadband gain around 1550 nm that coincides with the band of lowest fiber propagation losses, parity-forbidden 4-f shells that lead to slow gain dynamics in multiwavelength amplification, and negligible crosstalk between channels. 4 I 15 / 2 - 4 I 13 / 2 The long ms lifetime of the transition, high temperature stability and low noise figure approaching the 3dB quantum mechanical limit of phase-insensitive amplification (4) are the key features.

[0004] Today, EDFAs provide the foundation for the development of narrow-linewidth and mode-locked lasers, which are widely used in applications such as coherent communications (3), interferometric sensing, and optical frequency metrology (5). Rare earth ion doping (6,7) can also provide the basis for compact erbium-doped waveguide amplifiers (EDWA) (8). In fact, efforts to realize EDWA based on oxide glass waveguides began as early as the 1990s (9,10). However, these approaches were limited by large waveguide background losses, large device footprint, and incompatibility with contemporary photonic integrated circuits (11), and were ultimately abandoned. Interest in EDWA has revived with the advent of Si3N4CMOS-compatible photonic integrated circuit platforms, which offer advantages over silicon, including wider transparency windows (12), no two-photon absorption in the telecom band, reduced temperature sensitivity, power handling up to tens of watts (13), and most importantly, low propagation losses of <3 dB / m over meter-scale lengths (14).

[0005] One challenge in implementing erbium amplifiers based on photonic integrated circuits is the limited gain that can be achieved due to doping concentration constraints caused by cooperative upconversion (15). This limitation requires waveguides with low propagation losses and long waveguide lengths of tens of centimeters to meters to achieve large gain and high output power, which has always been a challenge in integrated photonics. Although net gain has been shown (and it is very significant), all previous work to date using materials such as erbium-doped Al2O3(16,17) and TeO2(18) has achieved only very limited output powers, typically <1 mW. Despite high doping concentrations, past attempts using atomic layer deposited Al2O3 and Er2O3 layers(17) or single-crystalline erbium chlorosilicate nanowires(19) have only provided output powers of <<1 μW. Such output powers are far below the levels required for many applications, which are in the 10-100 mW range achieved by heterogeneous integration of III-V amplifiers onto silicon photonics(20-22). Summary of the invention

[0006] The present invention solves the above limitations by providing a photonic integrated circuit waveguide amplifier according to claim 1 and a method for manufacturing a photonic integrated circuit waveguide amplifier according to claim 48. The waveguide amplifier ensures output power required for various applications.

[0007] Further advantageous features can be found in the dependent claims.

[0008] The present disclosure demonstrates waveguide amplifiers, e.g., Erbium amplifiers based on photonic integrated circuits, that achieve 145 mW output power and over 30 dB small signal gain - comparable to commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneous integrated semiconductor amplifiers. This is achieved by applying ion implantation to Si3N4 photonic integrated circuits (e.g., ultra-low loss Si3N4 photonic integrated circuits that can, for example, have waveguides of meter-scale lengths). Devices according to the present disclosure are used, for example, to increase the output power of soliton microcombs by a factor of 100, which is required for low-noise photonic microwave generation or as a wavelength division multiplexed optical communication source.

[0009] Endowing Si3N4 photonic integrated circuits with gain could enable the miniaturization of various fiber-based devices, such as high-pulse-energy femtosecond mode-locked lasers.

[0010] An exemplary waveguide amplifier according to the present disclosure involves an Er:Si3N4 waveguide amplifier based on a photonic integrated circuit, which can provide up to 145mW on-chip output power and more than 30dB of small signal gain. The design freedom provided by the photonic integrated circuit allows the use of multi-stage configurations to optimize gain and optical signal-to-noise ratio.

[0011] Furthermore, the ion implantation technique of the disclosed waveguide amplifier fabrication method may allow other rare earth ions to be co-doped with the erbium ions, such as ytterbium (emitting at 1.1 μm) and thulium (0.8 μm, 1.45 μm and 2.0 μm), thereby providing additional gain in other wavelength regions.

[0012] The disclosed ion implantation method in Si3N4 can be used as a gain medium in various integrated laser sources, such as high-power soliton microcombs, low-noise rare-earth ion-based CW lasers, femtosecond mode-locked lasers (28), or cavity soliton lasers (29). Equally important, this active Si3N4 photonic platform is compatible with thin-film heterogeneous integration (e.g., thin-film lithium niobate), enabling the combination of high-speed electro-optic modulation and amplification on the same chip for coherent communications (27) or radio frequency distribution (30).

[0013] The above and other objects, features and advantages of the present invention and the manner in which they are accomplished will become more apparent, and the invention itself will be best understood by studying the following description with reference to the accompanying drawings, which illustrate some preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1a An exemplary waveguide amplifier of the present disclosure is shown as an integrated erbium-injected Si3N4 waveguide amplifier and an exemplary integrated active Si3N4 photonic circuit for laser and light amplification, which utilizes erbium-injected Si3N4 waveguides, ultra-low loss passive circuits, and Kerr nonlinear devices. The inset shows the light amplification process of erbium ions excited by 1480nm pump.

[0015] Figure 1b is an optical image of an exemplary 0.5 meter long Er:Si3N4 waveguide coil.

[0016] Figure 1c The erbium concentration profile calculated using SRIM simulations involving three consecutive ion implantations (dashed lines), the simulated optical transverse electric (TE) mode intensity, and the erbium concentration measured by Rutherford backscattering spectroscopy (RBS) are shown along the vertical tangent line indicated by the arrow in the inset. The inset shows a SEM image of the waveguide cross section with the simulated fundamental TE mode superimposed.

[0017] Figure 1d The measured optical losses of a Si3N4 waveguide before, during and after annealing are shown. The inset shows the background loss around 1610 nm, where erbium absorption is weak.

[0018] Figure 1eOptical image of an exemplary Er:Si3N4 chip with a waveguide butt-coupled to two optical fibers. The green emission (bottom coil) is the result of a second-order cooperative upconversion process when strongly pumped.

[0019] Figure 2a The light emission and absorption properties of an Er:Si3N4 photonic waveguide are shown, and the fluorescence emission spectrum of an exemplary 0.46 cm long Er:Si3N4 waveguide through emission transitions between energy levels shown in the inset is shown (right) when pumped at 980 nm (left).

[0020] Figure 2b The measured resonant linewidth of an exemplary Er:Si3N4 microring resonator used to characterize wavelength-dependent erbium absorption is shown. The inset illustrates two resonances at the wavelengths indicated by the arrows.

[0021] Figure 2c The emission and absorption cross sections converted from the measured fluorescence and absorption spectra are shown.

[0022] Figure 2d The experimental setup for fluorescence lifetime measurements is shown. A continuous wave 980 nm laser gated at 20 Hz with a duty cycle of 50% is used to pump the Er:Si3N4 waveguide (very weakly coupled to the microring resonator). AFG, arbitrary function generator; FPC, fiber-based polarization controller; LPF, optical low-pass filter; PD, photodetector; OSC, electronic oscilloscope.

[0023] Figure 2e Shows from 4 I 13 / 2 Fluorescence decay measured at energy levels. The inset shows gating of pump and emission.

[0024] Figure 2f The net gain per centimeter measured in an exemplary Er:Si3N4 waveguide with different erbium concentrations when pumped at 1480 nm is shown. The top shaded area indicates the on-chip net gain regime after excluding erbium absorption and waveguide losses.

[0025] Figure 3a The experimental setup for measuring light amplification in an exemplary spiral Er:Si3N4 waveguide amplifier is shown. A free-space low-pass filter is used to isolate the residual pump for amplification analysis. FPC, fiber-based polarization controller; ATT, adjustable optical attenuator; PM, power meter; LPF, optical low-pass filter; OSA, optical spectrum analyzer.

[0026] Figure 3b The measured wavelength-dependent on-chip net gain is shown. The solid line indicates the average value of the gain obtained with 0.07 mW on-chip signal input at a total on-chip pump power of 245 mW.

[0027] Figure 3c Measured (scattered dots) and simulated (solid curve) on-chip gain for a signal at 1550 nm are shown. The regions indicate the off-chip net gain region and the loss contributions from fiber-to-chip coupling losses, waveguide background losses and erbium absorption, respectively.

[0028] Figure 3d The corresponding on-chip output power at 1550 nm is shown. The inset shows the calibrated spectrum of the 145 mW signal output after amplification.

[0029] Figure 4a Broadband on-chip amplification of soliton microcombs for low-noise microwave generation and optical communication carriers, in particular, an experimental setup for broadband soliton amplification using an exemplary integrated Er:Si3N4 waveguide is shown. ECDL, external cavity diode laser; FBG, fiber Bragg grating; PM, power meter; OSA, optical spectrum analyzer; ESA, electrical spectrum analyzer.

[0030] Figure 4b This is a stitched optical image of a 19.8GHz Si3N4 racetrack microring resonator.

[0031] Figure 4c Transmission with soliton steps during laser scanning resonance is shown.

[0032] Figure 4d Amplification of a 19.8 GHz microcomb in the C-band and L-band is shown, where the top part (i) shows the generated single soliton state microcomb as input, the middle part (ii) shows the microcomb amplified by Er:Si3N4EDWA, and the bottom part (iii) shows the microcomb amplified by a commercial EDFA (Calmar Laser AMP-STY). The dashed curve indicates the input microcomb envelope. The spectral power is calibrated.

[0033] Figure 4e The corresponding single sideband (SSB) phase noise of the generated microwave signal is shown. The "staircase-like" noise characteristic is due to the analyzer noise floor shown by the dashed line.

[0034] Figure 4f The spectra of the amplified 100 GHz soliton microcomb (36 mW) and input (0.12 mW) are shown. The corresponding 24.8 dB net gain allows a maximum comb line power of > 1 mW to be achieved in the optical communication C-band.

[0035] Figure 5aA preferred exemplary waveguide amplifier manufacturing method according to the present disclosure is shown, wherein an exemplary Er:Si3N4 photonic chip manufacturing is shown. The materials shown and the details shown in the various steps are exemplary. The exemplary Er:Si3N4 (PIC) manufacturing process uses a Si3N4 photonic mosaic process (generally shown as those steps within the dashed box), and also includes ion implantation and ion (e.g., erbium) activation.

[0036] Figure 5b shows the ion implantation and post-implantation annealing before Figure 5a False color SEM image of an exemplary Si3N4 waveguide cross section produced after annealing step 6.

[0037] Figure 5c A false-color SEM image of the resulting Si3N4 waveguide after step 8 (ie, post-implantation annealing for rare-earth (erbium) activation and defect recovery at, for example, 1000°C) is shown.

[0038] Figure 5d False color SEM images of Si3N4 waveguides after different post-implantation anneals at 1200° C. These cross-section samples were briefly treated in buffered HF for ~10 seconds to create topographic contrast in the SEM.

[0039] Figure 6 Geometric representation of a Si3N4 waveguide without lateral cladding before and after erbium implantation is shown, wherein (a) is a SEM image of a cross-section of a Si3N4 ridge waveguide before ion implantation; (b) is a SEM image of a cross-section of a Si3N4 ridge waveguide after irradiation; (c) is an inclined top view SEM image of the boundary region between an irradiated waveguide section and an unirradiated section masked with a droplet of wax (Quickstick 135), where the masking wax is only partially removed in heated acetone after irradiation; (d) shows the surface morphology of (a) measured by atomic force microscopy (AFM); (e) shows the surface morphology of (b) measured by AFM; (f) shows the line profiles of (d) and (e) in a plane perpendicular to the waveguide axis.

[0040] Figure 7a shows a selective erbium-implanted Si3N4 photonic circuit, where Figure 7a Figure 1 is a dark-field optical microscope image of an exemplary selectively implanted photonic circuit. The region surrounding and containing the ring resonator is masked (not implanted), while the adjacent region with the helical coil is implanted. The total implant dose for this sample is approximately 1×10 16 cm -2 .

[0041] Figure 7b The top surface morphology of the Si3N4 portion near the boundary between the masked area and the implanted area mapped by AFM is shown.

[0042] Figure 7c Shows the perpendicular to the boundary Figure 7b Line contour.

[0043] Figure 7d shows the cross section of the implanted Si3N4 region with a width of 2 μm. Figure 7b A line outline parallel to the border.

[0044] Figures 8a to 8c shows the Rutherford backscattering spectrum measurement and analysis, where Figure 8a A portion of a measured RBS spectrum and a simulated RBS spectrum representing matrix elements is shown; Figure 8b shows the RBS spectrum highlighting the erbium signal as well as a portion of the multilayer simulation spectrum, and Figure 8c The extracted measured Er concentration profile (solid line) and the corresponding SRIM simulation of the injection profile are shown.

[0045] Figures 9a to 9e shows the Er:Si3N4 waveguide loss characterization, where Figure 9a shows the normalized transmission of a 100 GHz Si3N4 microring resonator before erbium implantation; Figure 9b The normalized transmission of a 100 GHz FSR Er:Si3N4 microring resonator after erbium activation and loss recovery annealed at 1000°C is shown. Fig.9c The intrinsic linewidth (κ0 / 2π) of the annealed Er:Si3N4 microring resonator is shown; Figure 9d shows the waveguide loss extracted from the intrinsic linewidth; and Fig.9e Shown are the waveguide losses obtained from OFDR measurements in a 0.5 m long Er:Si3N4 waveguide spiral.

[0046] Fig.10a and Fig.10b The dependence of the signal gain on the pump wavelength and the waveguide width is shown, where Fig.10a shows the measured signal enhancement per centimeter of Er:Si3N4 waveguide when pumped at 980nm and 1480nm; and Fig.10b The measured signal enhancement per centimeter for 1.8 μm, 2.1 μm, and 2.4 μm wide waveguides when pumped at 1480 nm is shown; solid dots are measurements, and lines are visual guides created by smoothing splines. The samples were doped with ∼1.35×10 20 cm -3 Peak concentration.

[0047] Fig.11a and Fig.11b The energy levels and upconversion transitions in Er:Si3N4 are shown, where Fig.11a It shows that Er in solid3+ Schematic diagram of ion energy levels and important transitions between them. Nonradiative relaxation is omitted for clarity. Transitions are labeled: (1) 980nm pump, (2) 1480nm pump, (3) excited state absorption (ESA) from 980nm pump, (4) 4 I 11 / 2 The synergistic up-conversion of 4 I 13 / 2 Synergistic upconversion, (6) green emission at 520nm / 545nm, (7) red / NIR emission at 665nm / 800nm, (8) 845nm emission, (9) 980nm emission, and (10) 1530nm emission for C-band optical amplification [134,135]. Fig.11b The measured spectrum of multilevel upconversion luminescence emitted by Er:Si3N4 helical waveguide under strong 1480nm pumping is shown (intensity uncalibrated). It is characterized by emission (6) and part (7). The weak emission at 410nm may be attributed to the higher energy level 2 H 9 / 2 Three-level up-conversion [133,134].

[0048] Figures 12a to 12c Measured and numerically fitted light amplification in an Er:Si3N4 helical waveguide is shown, where Fig.12a shows that at 1.35×10 20 cm -3 Measured (scattered points) and simulated (solid curve) on-chip net gain for a 1550 nm signal in a 50 cm long Si3N4 waveguide doped with erbium concentration. Figure 12b The corresponding on-chip output power at 1550 nm is shown, and the inset shows the calibration spectrum of 55 mW signal output at 1480 nm with a pump power of ∼120 mW; Fig.12c The on-chip net gain of two Er:Si3N4 waveguide amplifiers with different erbium concentrations at 1550 nm is shown as a function of input signal power. The shaded area indicates the regime where parasitic lasing occurs when the net gain exceeds ~26 dB.

[0049] Fig.13 Calculations of on-chip net gain for various pump powers at 1480nm and different waveguide lengths for -10dBm on-chip input signal at 1550nm are shown. Based on the experimentally extracted cross sections and fitting parameters, the on-chip net gain achievable in Er:Si3N4 with lengths varying from 5mm to 1m for on-chip forward pump powers up to 1W is calculated. The asterisk marks indicate the range that the Er:Si3N4 waveguide amplifier can approach in the presented demonstrations. The optical gain can be further improved by deploying higher pump powers or reducing coupling losses.

[0050] Figures 14a to 14d shows the reduction of Fresnel reflections and parasitic laser emissions, where Fig.14a The normalized transmission of the passive Si3N4 microring resonator side coupled to a bus waveguide with a length of 0.5 cm is shown. A pair of lensed fibers are used for optical coupling to the chip with an air gap. The calculated Fresnel reflectivity is 4.77%. Fig.14b Shown are the measured spectra and a projection of a CW signal amplified by a 0.5 m long Er:Si3N4 waveguide interfaced with a lensed fiber. Parasitic lasing is clearly observed at on-chip pump powers >10 mW. Fig.14c The normalized transmission of the passive Si3N4 microring resonator side coupled to a bus waveguide with a length of 0.5 cm is shown. A pair of UHNA fibers are in close contact with the waveguide end face for optical coupling, and the gap is filled with a refractive index matching gel. The calculated Fresnel reflection is 0.5%. Fig.14d Shown are the measured spectra and the projection of a CW signal amplified by a 0.5 cm long Er:Si3N4 waveguide coupled to a UHNA fiber to which an index matching gel is applied. Parasitic lasing is suppressed. In both cases, the input signal power is kept constant at ~-10 dBm.

[0051] Fig.15a and Fig.15b shows the noise figure characterization, where Fig.15a The measured noise figure of a 21 cm long Er:Si3N4 waveguide amplifier at 1550 nm at different on-chip pump powers and off-chip input powers is shown. The asterisk marks indicate the pump and signal conditions for the example noise figure measurements. Fig.15b Shown are the spectra of the input signal and the amplified signal after power calibration used to derive the noise figure using light source subtraction

[137] .

[0052] Fig.16 An exemplary application of Er:Si3N4 EDWA for short-distance WDM coherent communications is shown. Er:Si3N4 EDWA (co-integrated with Kerr microrings) is used to amplify low-power soliton microcombs of tens of mW output power for WDM communication transmitters, with a significantly reduced footprint compared to using desktop EDFAs. The output of the EDWA can be used for short-distance communication applications, such as intra-datacenter communications with fiber links less than 1 km. The EDWA can also be inserted at the output of the transmitter or receiver front end.

[0053] Figure 17a to Figure 17b An exemplary embodiment of an amplifier according to the present disclosure is shown. Fig.17a and Fig.17b An exemplary cross-sectional view is shown, and Fig.17c A perspective view is shown.

[0054] Fig.18 Ion implantation is shown through a covered outer surface of a silicon nitride material (eg, covered by a capping layer or material).

[0055] Figures 19a to 19d Additional exemplary embodiments of photonic integrated circuit waveguide amplifiers are shown.

[0056] Herein, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. DETAILED DESCRIPTION

[0057] Figure 1a , Figure 1b , Figure 1c , Figure 1e , Figure 5a , Figure 5c , Figures 17a to 17c and Figures 19a to 19d An exemplary amplifier or waveguide amplifier or photonic integrated circuit waveguide amplifier 1 according to the present disclosure is shown. The photonic integrated circuit waveguide amplifier 1 is, for example, an integrated photonic integrated circuit component or element.

[0058] The photonic integrated circuit waveguide amplifier 1 includes at least one cladding material or layer 3 (or embedded cladding material or layer 3) and at least one rare earth ion implanted waveguide core material or layer 5, such as silicon nitride (Si3N4) material or layer 5 embedded or enclosed in the cladding material or layer 3.

[0059] The implanted rare earth ions or atoms 7 may, for example, consist of or include erbium, ytterbium or thulium. The implanted rare earth ions 7 may, for example, include at least one of: erbium, ytterbium, thulium. Implanting different rare earth ions allows gain to be provided at other wavelengths. Implanted rare earth ions 7, such as ytterbium (emitting at 1.1 μm) and thulium (emitting at 0.8 μm, 1.45 μm and 2.0 μm), allow optical gain to be provided in these other wavelength regions.

[0060] The implanted rare earth ions 7 may, for example, include 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 allows gain (amplification) to be provided in multiple wavelength regions in the same amplifier.

[0061] The implanted rare earth ions are, for example, located at least at an intermediate distance inside at least one rare earth ion implanted silicon nitride material or layer 5. The rare earth ion implanted silicon nitride material or layer is configured or dimensioned to support, for example, a fundamental transverse electro-TE optical waveguide mode in the cross-sectional direction of the waveguide amplifier 1. The implanted rare earth ions are, for example, located in the rare earth ion implanted silicon nitride material or layer 5 to spatially overlap with the fundamental transverse electro-optical waveguide mode to ensure high optical gain or amplification. The spatial overlap is, for example, at least 25%, or at least 40%, or at least 50%, or at least 60%. At least 85%, or at least 90%, or at least 95% of the implanted rare earth ions are located in the rare earth ion implanted silicon nitride material or layer 5, interact with the light in the waveguide mode, and are optically active in the amplification of the guided light.

[0062] The rare earth ion implantation concentration in the silicon nitride material or layer 5 is, for example, 0.1×10 20 cm -3 and 3.5x10 20 cm -3 The rare earth ion implanted silicon nitride material or layer 5 carries, for example, 0.1 to 0.3 atomic % of rare earth atoms.

[0063] The rare earth ion implanted silicon nitride material or layer 5 defines or is an active material or layer of the waveguide amplifier 1. The rare earth ion implanted silicon nitride material or layer 5 defines or is, for example, an optical gain medium of the waveguide amplifier 1.

[0064] The rare earth ion implanted silicon nitride material or layer 5 defines a non-passive waveguide region or portion of the waveguide amplifier 1. The embedded cladding material or layer 3 may define an optically inactive waveguide region or portion of the waveguide amplifier 1.

[0065] The rare earth ion implanted silicon nitride material or layer 5 defines a waveguide core WC of the waveguide amplifier 1. The waveguide core WC is enclosed or embedded in a cladding material or layer 3. The cladding material or layer 3 carries the rare earth ion implanted silicon nitride material or layer 5. The cladding material or layer 3 defines a support or container CS inside which the rare earth ion implanted silicon nitride material or layer 5 is supported and / or held. The waveguide core WC is configured to propagate amplified light in an elongated (light) propagation direction PD of the waveguide amplifier 1.

[0066] The waveguide core WC and the primary cladding material or layer 3 have refractive index values ​​or refractive index contrasts that allow the waveguide core WC to guide and propagate light along the waveguide 1 in the light propagation (or guiding) direction PD or the elongated propagation direction PD. For example, the waveguide core WC has a refractive index (at the wavelength of the light to be guided) that is greater than the refractive index (at the wavelength of the light to be guided) of the cladding material or layer 3. The same is true for a material or medium located opposite or superimposed on the cladding material or layer 3, for example, which encloses or sandwiches the waveguide core WC with the cladding material or layer 3. The medium can be, for example, surrounding air or another cladding material or layer.

[0067] The waveguide amplifier 1 may comprise at least one (further) cladding / passivation material or layer FC superimposed on the embedded rare earth ion implanted silicon nitride material or layer 5 and the embedded cladding material or layer 3 .

[0068] The cladding material or layer FC may be provided or deposited on the embedded rare earth ion implanted silicon nitride material or layer 5, for example after ion implantation. Alternatively, at least one cladding material or layer FC may be provided or deposited on the embedded silicon nitride material or layer 5A, for example before rare earth ion implantation, and in such a case, the ion implantation of the silicon nitride material or layer 5A is performed by passing ions through the covering cladding material or layer FC.

[0069] For example, after rare earth ion implantation of the embedded silicon nitride material or layer 5A, at least one further cladding / passivation material or layer may be provided or deposited on the overlying cladding material or layer FC.

[0070] The further cladding material or layer and / or the at least one embedded cladding material or layer is, for example, an optically passive element or component of the waveguide amplifier 1 .

[0071] The further encapsulation / passivation material or layer and / or the embedded encapsulation material or layer may, for example, comprise silicon dioxide (SiO 2 ) or consist of silicon dioxide.

[0072] The embedded cladding material or layer 3 defines or includes, for example, first and second lateral support structures or platforms SP, which define or include lateral sidewalls SW1B, SW2B, respectively. The first and second lateral support structures SP are in contact with the upper and / or lower halves of the embedded silicon nitride waveguide core WC or the embedded silicon nitride material or layer (e.g., the upper and lower halves of the lateral sidewalls SW1A, SW2A of the embedded silicon nitride or waveguide core WC).

[0073] The first and second support structures SP extend laterally or in a planar direction away from (the upper and lower halves of) the embedded silicon nitride waveguide core WC. The distance LD from which the first and second support structures SP extend is, for example, greater than 0.1 times or 0.25 times (0.1xW or 0.25xW) the cross-sectional width W of the embedded silicon nitride waveguide core WC. This can ensure a higher optical quality waveguide and reduced optical losses. The cross-sectional width W is, for example, measured at a maximum value in a cross-sectional direction perpendicular to the light propagation direction PD.

[0074] The cladding material or layer 3 defines or comprises an elongated recess or depression 9 extending in an elongated manner in the cladding material or layer 3. The elongated recess or depression 9 extends in a planar manner or in the plane of the cladding material or layer 3, for example.

[0075] The elongated recess or depression 9 extends in the light propagation direction PD, and the rare earth ion implanted silicon nitride material or layer 5 is located inside or embedded in the elongated recess or depression 9. The rare earth ion implanted silicon nitride material or layer 5 fills or completely fills the elongated recess or depression 9. The rare earth ion implanted silicon nitride (Si3N4) material or layer 5 also extends longitudinally along the light propagation direction PD.

[0076] The rare earth ion implanted silicon nitride material or layer 5 and the recesses or depressions 9 extend in the elongation direction PD to propagate or guide light along the elongation direction PD of the waveguide amplifier 1 .

[0077] The cladding material or layer 3 may, for example, comprise or consist of a planar layer or material defining or comprising elongated recesses or depressions 9 .

[0078] The rare earth ion implanted silicon nitride (Si3N4) material or layer 5 and waveguide core WC may also for example define a planar layer or material embedded or contained within the cladding material or layer 3. The rare earth ion implanted silicon nitride material or layer 5 may for example define a substantially planar optical waveguide core WC.

[0079] The recess or depression 9 and / or the waveguide core WC of the waveguide amplifier 1 of the present disclosure may have a cross-sectional shape or profile whose width W (measured at a maximum value) is greater than its height H (measured at a maximum value). For example, the width W is between 1.5 and 5 times greater than the height H, or between 2.5 and 5 times greater than the height H. For example, the width of the waveguide core WC (measured at a maximum value) may be 2.1 μm (outer cross-sectional width W o ), the height H or thickness (measured at the maximum value) can be 0.7 μm.

[0080] The rare earth ion implanted silicon nitride material or layer 5 may, for example, define an arched or curved forward structure that is arched or curved away from the primary cladding material or layer 3 .

[0081] The rare earth ion implanted silicon nitride material or layer 5 includes an outer surface or upper / top silicon nitride surface S1, which, for example, is not in direct contact with or covered by the embedded encapsulating material or layer 3. The rare earth ion implanted silicon nitride material or layer 5 also includes an inner surface or lower / bottom surface S3 (defined by the base BS), which is located opposite the outer or upper surface S1.

[0082] The terms upper / top and lower / bottom are relative to Figure 5b to Figure 5d and Figure 17a to Figure 17b The position of the device shown in is defined.

[0083] The outward direction or position is a direction or position extending away from the supporting layer or substrate 19 supporting the embedded cladding material or layer 3 and the embedded (rare earth ion implanted) silicon nitride material or layer 5, 5A and extending in a direction toward the embedded cladding material or layer 3 and / or the embedded (rare earth ion implanted) silicon nitride material or layer 5, 5A.

[0084] As mentioned above, the outer or upper surface S1 can be, for example, directly exposed or uncovered (without material). Alternatively, as previously described, at least one (additional) cladding / passivation material or layer FC can be superimposed or provided on the embedded rare earth ion implanted silicon nitride material or layer 5 (and the outer surface S1) and the embedded cladding material or layer 3.

[0085] The outer or upper surface S1 is, for example, arched or protrudes outwardly away from the cladding material or layer 3. The embedded cladding material or layer 3 is, for example, not present on the outer surface S1, or the outer surface S1 contains no embedded cladding material.

[0086] The direction of the bow or bend is a direction perpendicular to the elongated propagation direction PD of the waveguide amplifier 1 .

[0087] The rare earth ion implanted silicon nitride material or layer 5 may define, for example, an inwardly tapered cross-sectional structure or profile in a cross-sectional direction perpendicular to the elongated propagation direction PD, which tapers to a reduced width or size in an inward direction toward the bottom of the recess or depression 9. The rare earth ion implanted silicon nitride material or layer 5 defines an inwardly tapered cross-sectional structure, which extends from the outer surface S1 and inside the cladding material or layer 3 and in a cross-sectional direction perpendicular to the light elongated propagation direction PD. The taper occurs from the outer surface S1, and the width of the rare earth ion implanted silicon nitride material or layer 5 decreases in a direction extending from the outer surface S1 and inside the cladding material or layer 3. The tapered cross-sectional structure tapers in cross-section, for example, along the entire length of the waveguide amplifier 1 extending in the elongated propagation direction PD.

[0088] The rare earth ion implanted silicon nitride material or layer 5 defines or has an inner cross-sectional width W, for example I and outer section width W o , where the inner section width W IShorter than the outer section width W o . Inner section width W I For example, measured at the lower half of the rare earth ion implanted silicon nitride material or layer 5, the outer cross-sectional width W o For example, it is measured at the upper half of the rare earth ion implanted silicon nitride material or layer 5. Alternatively, the inner cross-sectional width W I For example, the shortest measured cross-sectional width of the rare earth ion implanted silicon nitride material or layer 5, and the outer cross-sectional width W o For example, it is the maximum measured cross-sectional width of the rare earth ion implanted silicon nitride material or layer 5 .

[0089] Inner section width W I Width W of outer section o Shorter than the outer section width W by between 2.5% and 20% or o Between 5% and 15% shorter, or shorter than the outer section width W o Between 5% and 10% short.

[0090] The width ratio (in fraction W) of the embedded rare earth ion implanted silicon nitride material or layer 5 o / W I denoted by a width ratio (in fraction W) greater than the width ratio of the embedded non-ion-implanted silicon nitride material or layer 5A (without rare earth ions). o / W I ), for example, by comparing Figure 5b and Figure 5c It can be seen that the presence of implanted ions brings about this structural difference.

[0091] The rare earth ion implanted silicon nitride material or layer 5 defines or includes outwardly divergent lateral sidewalls SW1A, SW2A, and the embedded cladding material or layer 3 also defines or includes outwardly divergent lateral sidewalls SW1B, SW2B. The outward direction is a direction extending toward the external surrounding air medium, or toward the direction extending toward another cladding material or layer 3 (if any) superimposed on the rare earth ion implanted silicon nitride material or layer 5 and / or the embedded cladding material or layer 3.

[0092] The outwardly diverging lateral sidewalls SW1B, SW2B of the embedded cladding material or layer 3 mechanically support the outwardly diverging lateral sidewalls SW1A, SW2A of, for example, the rare earth ion implanted silicon nitride material or layer 5 .

[0093] The outwardly diverging lateral sidewalls SW1B, SW2B of the cladding material or layer 3 simultaneously diverge from and / or are in direct contact with the outwardly diverging lateral sidewalls SW1A, SW2A of, for example, the rare earth ion implanted silicon nitride material or layer 5 .

[0094] The first lateral sidewall SW1A and the second lateral sidewall SW2A of the rare earth ion implanted silicon nitride material or layer 5 define an inclination angle α, β respectively relative to the floor FL of the cladding material or layer 3 defining the floor of the recess 9, alternatively, relative to the surface or outer surface CS of the embedded cladding material or layer 3. The inclination angle α, β is greater than or equal to 95°. The inclination angle α, β is greater than or equal to a value x of 91°, or 92°, or 93°, or 94°, or 95°, and is less than or equal to a value y of 100°, or 101°, or 102°, or 103°, or 104°, or 105°; wherein the inclination angle α, β is greater than or equal to the value x and less than or equal to the value y.

[0095] The angle α and / or angle β of the lateral sidewalls SW1A, SW2A of the embedded rare earth ion implanted silicon nitride material or layer 5 is greater than the angle α and / or angle β of the lateral sidewalls SW1A, SW2A of the embedded non-ion implanted silicon nitride material or layer 5A (without rare earth ions), for example, by comparing Figure 5c and Figure 5c It can be seen that the presence of implanted ions brings about this structural difference.

[0096] The rare earth ion implanted silicon nitride material or layer 5 may define or include a top plate or landing area CL. The top plate or landing area CL extends between the lateral sidewalls SW1A, SW2A of the embedded ion implanted silicon nitride material or layer 5. The top plate CL is, for example, a curved top plate or a curved upper layer CL. The curved top plate or upper layer CL is bent or curved outward to define a surface extending away from the embedded encapsulating material or layer 3, or a surface extending out of the recess or depression 9, or a surface extending in the direction of the recess or depression 9. The curved top plate or upper layer CL bulges or protrudes outward or bulges or protrudes outward from the recess or depression 9.

[0097] The above cross-sectional profile of the rare earth ion implanted silicon nitride material or layer 5 and the embedded cladding material or layer 3 extends elongatedly or along the length of the waveguide amplifier and is produced by the implantation of rare earth ions inside the silicon nitride material or layer 5 and the waveguide core WC, wherein the implantation is performed directly through the directly exposed or uncovered (at least at the moment of ion implantation) outer surface S1 of the silicon nitride material or layer 5. In the case where the implantation is performed through the covered outer surface S1 (for example, covered by the cladding or material FC) Fig.18 ), a similar profile can be expected.

[0098] The floor FL and lateral side walls SW1B, SW2B of the cladding material or layer 3 define a recess or depression 9 of the cladding material or layer 3 in which the waveguide core WC is embedded. The upper layer or top plate CL of the silicon nitride material or layer is not covered by or in direct contact with the embedded cladding material or layer 3. Apart from the lateral side walls, the base BS of the silicon nitride material or layer 5A or the waveguide core WC is in (direct) contact with the floor FL of the cladding material or layer 3 before ion implantation and remains in (direct) contact after rare earth ion implantation.

[0099] The floor FL and the side walls SW1B, SW2B of the cladding material or layer 3 are in contact with and contain the silicon nitride material or layer 5A (waveguide core WC) inside the recess or depression 9. The base BS is completely contained inside the recess 9 and the lateral side walls SW1A, SW2A of the silicon nitride material or layer 5A are contained inside the recess 9. For example, at least 75% or at least 85% of the height H of the lateral side walls SW1A, SW2A of the waveguide core material or layer 5A is contained inside the recess 9. Such a constraint allows to control or limit the deformation of the silicon nitride material or layer (waveguide core WC) caused by the ion implantation and ensures that a rare earth ion implanted waveguide core material or layer 5 is obtained with a cross-sectional profile that allows efficient guiding, sufficiently low optical losses and efficient optical amplification.

[0100] The embedded silicon nitride waveguide core WC fills the recess or depression 9 of the embedded cladding material or layer 3 to define an outer surface S1 which is, for example, (substantially) located at the same level L as the outer surface S2 defined by the embedded cladding material or layer 3 (see e.g. Fig.17b ).

[0101] The bottom plate FL embedded in the cladding material or layer 3 includes or defines a support surface SS ( Fig.17b ). The embedded silicon nitride waveguide core WC extends away from the support surface SS inside the embedded cladding material or layer 3 to define an outer or upper silicon nitride surface S1 that is substantially at the same level as the outer or upper surface S2 defined by the embedded cladding material or layer 3.

[0102] The recess or depression 9 defined by the embedded cladding material or layer 3 has, for example, a recess height HR ( Fig.17b). The embedded silicon nitride waveguide core WC fills the recess or depression 9 to define an outer surface S1 of the waveguide core WC at a height level LW. The height level LW has, for example, a value between 0.8 and 1.1 times (or 0.75 to 1.2 times) the recess height value HR. For example, the outer surface S1 may be completely flush with the outer surface S2 defined by the embedded cladding material or layer 3, in which case the value of the height level LW is 1x times the recess height value HR, i.e. the same height as the recess height HR. The height value is measured from the floor FL of the recess or depression 9 defined by the embedded cladding material or layer 3.

[0103] Figures 19a to 19d Schematically illustrated is an alternative embodiment of a photonic integrated circuit waveguide amplifier 1, which is manufactured by removing and structuring, for example, a silicon nitride material or layer 5A provided on at least one supporting material or layer 19. At least one cladding material or layer 3 is provided or deposited on the silicon nitride material or layer 5A and, if necessary, removed or thinned to directly expose the silicon nitride material or layer 5A to be implanted, or thinned or removed to leave a cladding layer or material thickness covering the silicon nitride material or layer 5A through which ions can pass to ensure ion implantation into the silicon nitride material or layer 5A. Ion implantation of the silicon nitride material or layer 5A is then performed, as described in further detail below.

[0104] In this embodiment ( Figures 19a to 19d ), the embedded silicon nitride waveguide core WC extends within the embedded cladding material or layer 3 and away from the support surface SS defined by the silicon nitride material or layer or by the support material or layer 19 to define an outer or upper silicon nitride surface S1 that is substantially at the same level as the outer or upper surface S2 defined by the embedded cladding material or layer 3. The lateral sidewalls SW1A, SW2A of the rare earth ion implanted silicon nitride material or layer 5 extend in an upward or outward direction to define a top plate or contact region CL extending between the lateral sidewalls SW1A, SW2A, which includes or defines the outer or upper silicon nitride surface S1.

[0105] The embedded cladding material or layer 3 extends away from the support surface SS to define an outer or upper cladding surface S2, which is located at a cladding height CH (a cross section extending perpendicular to the light propagation direction) from the support surface SS. The embedded silicon nitride waveguide core WC, for example, extends inside the embedded cladding material or layer 3 and away from the support surface SS to define an outer or upper silicon nitride surface S1 located at a height level LW, which has a value between 0.01 and 1.0 times the cladding height CH, or between 0.1 and 1.0 times the cladding height CH, or between 0.5 and 1.0 times the cladding height CH. The height values ​​are measured from the support surface SS.

[0106] Figures 19a to 19dA non-ion implanted silicon nitride material or layer 5A is also schematically shown. The ion implanted silicon nitride material or layer 5 ensures the same characteristics or properties as described herein for the ion implanted silicon nitride material or layer 5 located in the recess 9 embedded in the cladding material or layer 3, for example.

[0107] The waveguide amplifier or device 1 may also include at least one or more passive or non-amplifying components 15 (see, for example, Fig.17c ). The passive or non-amplifying component 15 is, for example, identical to the waveguide amplifier 1 except that it comprises an embedded non-ion-implanted silicon nitride material or layer 5A (without rare earth ions), for example, Figure 5b . The passive or non-amplifying component 15 may be integrally connected to 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 continuously connected or integrated with the embedded rare earth ion implanted silicon nitride material or layer 5. The cladding material or layer 3 of the passive or non-amplifying component 15 may also be continuously connected or integrated with the cladding material or layer 3 containing the embedded rare earth ion implanted silicon nitride material or layer 5. As will be discussed later, the passive or non-amplifying component 15 may be formed using selective ion implantation.

[0108] like Figure 1a As shown, light may be coupled into a passive or non-amplifying component 15 or a waveguide amplifier or device 1 using one or more integrated couplers or integrated coupled waveguides.

[0109] The passive or non-amplifying component 15 has, for example, an embedded non-ion-implanted silicon nitride material or layer 5A with a fraction W of the thickness. o / W I denoted by a width ratio which is smaller than the width ratio of the embedded rare earth ion implanted silicon nitride material or layer 5 .

[0110] Additionally or alternatively, the angle α and / or angle β of the lateral sidewalls SW1A, SW2A of the embedded non-ion-implanted silicon nitride material or layer 5A of the passive or non-amplifying component 15 is smaller than the angle α and / or angle β of the lateral sidewalls SW1A, SW2A of the embedded rare earth ion-implanted silicon nitride material or layer 5.

[0111] The rare earth ion implanted silicon nitride material or layer 5 may include an optical input coupling interface or port 17A and / or an amplified optical output coupling interface or port 17B. The coupling interface or port may include, for example, an ion implanted and non-ion implanted material interface (which has a passive or non-amplifying component 15) or an embedded rare earth ion implanted silicon nitride material or layer 5 and / or an end face of the cladding material or layer 3, which may be formed by, for example, dicing.

[0112] The rare-earth ion-implanted silicon nitride material or layer 5 and / or the recesses 9 in the embedding cladding material or layer 3 may extend, for example, in an elongated manner along the light propagation direction PD over a distance, for example, between 0.1 m and 0.6 m.

[0113] The rare-earth ion-implanted silicon nitride material or layer 5 and the recesses 9 in the cladding material or layer 3 may extend in a substantially straight and / or curved manner (longitudinally). They may extend, for example, along the light propagation direction PD (longitudinally) to define a helical and / or coil arrangement, as, for example, Fig.17c shown.

[0114] The cladding material or layer and / or at least one embedding cladding material or layer are optical passive elements or components of the waveguide amplifier.

[0115] The waveguide amplifier 1 may further include a support layer or substrate 19 that supports the embedding cladding material or layer 3 and the embedded rare-earth ion-implanted silicon nitride material or layer 5. The support layer or substrate 19 may include, for example, silicon, MgF2 or CaF2 or consist of silicon, MgF2 or CaF2.

[0116] The embedding cladding material or layer 3 defines or includes, for example, a stress relief recess structure 21 that includes a plurality of notches or indentations 23 formed in the embedding cladding material or layer 3 ( Fig.17a ). The stress relief recess structure 21 prevents cracks from forming or propagating into the waveguide core WC or into or into the embedded rare-earth ion-implanted silicon nitride material or layer 5. The stress relief recess structure 21 encloses, for example, the waveguide recess 9.

[0117] The notch depth of the plurality of notches 23 of the stress relief recess structure 21 measured from the outer surface of the cladding material or layer 3 is, for example, substantially equal to or greater than the depth of the waveguide recess 9 measured from the outer surface of the cladding material or layer 3. The stress relief recess structure encloses at least one waveguide recess.

[0118] The notch-free region may, for example, separate the stress relief recess structure 21 and the waveguide recess 9 by a distance D, where 50 μm < D < 2 μm. The waveguide recess 9 and the stress relief recess structure 21 are, for example, located in the same plane of the cladding material or layer 3.

[0119] The plurality of notches 23 are, for example, regularly or irregularly spaced apart from each other. The plurality of notches form, for example, at least one repeating notch pattern on the cladding material or layer 3. The plurality of notches 23 form, for example, a checkerboard structure or layout on the cladding material or layer 3.

[0120] 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, an integrated amplifier based on a planar substrate.

[0121] According to another aspect, the present disclosure also relates to a system comprising a pump laser or source and at least one photonic integrated circuit waveguide amplifier 1 .

[0122] According to another aspect, the present disclosure also relates to a photonic integrated circuit PIC comprising at least one photonic integrated circuit waveguide amplifier 1. The photonic integrated circuit PIC may, for example, comprise one or more integrated silicon nitride components or devices optically coupled to the photonic integrated circuit waveguide amplifier 1 or comprise the photonic integrated circuit waveguide amplifier 1. The integrated silicon nitride components or devices may, for example, comprise or consist of a soliton microcomb generator, an electro-optic modulator or a laser source. The electro-optic modulator may, for example, comprise or consist of a lithium niobate electro-optic modulator.

[0123] According to another aspect, the present disclosure also relates to an integrated optical device or an integrated laser source, which comprises at least one photonic integrated circuit waveguide amplifier 1, wherein the photonic integrated circuit waveguide amplifier 1 serves as a gain medium of the integrated optical device or the integrated laser source. The integrated optical device or the integrated laser source may, for example, comprise or consist of a soliton microcomb, a rare earth continuous wave laser, a femtosecond mode-locked laser or a cavity soliton laser.

[0124] According to another aspect, the present disclosure relates to a waveguide amplifier manufacturing method or a photonic integrated circuit waveguide amplifier manufacturing method.

[0125] Figure 5a An exemplary photonic integrated circuit waveguide amplifier manufacturing method according to the present disclosure is shown, wherein an exemplary Er:Si3N4 waveguide amplifier manufacturing is shown. The exemplary manufacturing process uses a photonic mosaic process, as shown in FIG. Figure 5a The steps in the dashed box are shown. U.S. Patent No. 10191215 discloses the details of the damascene process, and the entire content of the patent is incorporated herein by reference. The manufacturing process also includes ion implantation and ion activation.

[0126] The waveguide amplifier manufacturing method includes: providing at least one embedded cladding material or layer 3, which includes at least one silicon nitride material or layer 5A embedded or buried inside the at least one embedded cladding material or layer 3; and performing rare earth ion implantation by ion irradiating at least one outer or upper silicon nitride surface S1A of the at least one embedded or buried silicon nitride material or layer 5A to form at least one rare earth ion implanted silicon nitride material or layer 5 embedded or buried in the at least one embedded cladding material or layer 3.

[0127] Rare earth ion implantation is performed, for example, by ion irradiating the directly exposed or uncovered surface(s) S1A of the embedded or buried silicon nitride material or layer 5A (see, for example, Figure 5a ) to form a rare earth ion implanted silicon nitride material or layer 5 embedded or buried in at least one embedded encapsulating material or layer 3.

[0128] As previously mentioned, the floor FL and the lateral side walls SW1B, SW2B of the cladding material or layer 3 are in contact with and contain the silicon nitride material or layer 5A (waveguide core WC) inside the recess or depression 9. This constraint allows the deformation of the silicon nitride material or layer (waveguide core WC) caused by the ion implantation to be controlled or limited, and allows obtaining a rare earth ion implanted waveguide core material or layer 5 having a cross-sectional profile that ensures efficient guidance, sufficiently low optical losses and efficient optical amplification.

[0129] The embedded silicon nitride waveguide material 5A fills the recess or depression 9 of the embedded cladding material or layer 3 to define an outer surface S1A, which is, for example, located at the same level or substantially the same level L1 as the level of the outer surface S2A defined by the embedded cladding material or layer 3 (see, e.g. Figure 5b ).

[0130] The recess or depression 9 defined by the embedded cladding material or layer 3 has, for example, a recess height HR ( Figure 5b ). The embedded silicon nitride waveguide core WC fills the recess or depression 9 to define an outer surface S1A of the waveguide core WC located at a height level LW1. The height level LW1 has, for example, a value between 0.8 and 1.1 times (or 0.75 to 1.2 times) the recess height value HR. For example, the outer surface S1A may be completely flush with the outer surface S2A defined by the embedded cladding material or layer 3, in which case the height level LW1 has a value of 1x times the recess height value HR, i.e. the same height as the recess height HR. The height value is measured from the floor FL of the recess or depression 9 defined by the embedded cladding material or layer 3.

[0131] Figure 5aTwo embedded silicon nitride materials or layers 5A are shown, for example, being ion implanted simultaneously. A second recess 9 is included in the embedded cladding material or layer 3, in which the second embedded silicon nitride material or layer 5A is present. The second waveguide core may, for example, be a separate element, or may, for example, be used to input electromagnetic energy into the first waveguide core and receive electromagnetic energy output therefrom. The second waveguide core may alternatively be non-ion implanted.

[0132] The stress relief recess structure 21 comprising a plurality of notches or recesses 23 encloses at least one or two recesses or recesses 9 and the silicon nitride waveguide core WC. A plurality of embedded silicon nitride materials or layers 5A may be ion implanted simultaneously, or only one of the embedded silicon nitride materials or layers 5A may be ion implanted.

[0133] Annealing is performed on at least one rare earth ion implanted silicon nitride material or layer 5 embedded or buried in at least one embedded cladding material or layer 3 to reduce implantation defect optical losses. Annealing is performed at a temperature between 800° and 1250° C., for example, at 1000° C. Annealing is performed, for example, in an oxygen environment. Annealing is performed for a duration of, for example, between 30 and 90 minutes, for example, 60 minutes.

[0134] Although Figure 5a Erbium implantation is shown, but the rare earth ions may include or consist of erbium, ytterbium or thulium. The rare earth ion implantation is performed by accelerating the rare earth ions toward at least one directly exposed surface S1A to provide an ion implantation flux to at least one directly exposed surface S1A so as to implant ions within at least one embedded or buried silicon nitride material or layer 5A.

[0135] The implantation can be performed using, for example, a Van der Graaf accelerator. Ion implantation processes are described in Polmann et al. and in reference 124 mentioned in the reference section below, the entire contents of which are incorporated herein by reference.

[0136] For example, rare earth ion implantation is performed at a plurality of different rare earth ion acceleration values ​​to define an ion implantation concentration spatial distribution that spatially overlaps an optical waveguide mode (eg, a fundamental transverse electro-optic waveguide mode) of the waveguide amplifier.

[0137] For example, rare earth ion implantation is performed at a rare earth ion acceleration value between 0.1 MeV and 2.5 MeV. For example, rare earth ion implantation is performed at a rare earth ion flux of 1.5 x 10 15 cm -2 and 5x10 15 cm -2For example, the rare earth ion implantation is performed to provide a rare earth ion acceleration value of 0.1×10 20 cm -3 and 3.5x10 20 cm -3 For example, the rare earth ion implantation is performed to provide at least one rare earth ion implanted silicon nitride material or layer carrying between 0.1 and 0.3 atomic % of rare earth atoms. The rare earth ion implantation can be performed as a wafer level implantation process.

[0138] After rare earth ion implantation, at least one encapsulating / passivation material or layer may be provided or deposited overlying the embedded rare earth ion implanted silicon nitride material or layer 5 and the embedded encapsulating material or layer 3 .

[0139] Alternatively, the rare earth ion implantation of the embedded or buried silicon nitride material or layer 5A may be performed by ion irradiating at least one cladding material or layer FC provided or deposited on at least one surface S1A of the embedded or buried silicon nitride material or layer 5A to form a rare earth ion implanted silicon nitride material or layer 5 embedded or buried in the embedded cladding material or layer 3 (see, e.g. Fig.18 ).

[0140] The cladding material or layer of the device 1 covering the upper or outer surface of the waveguide core WC may be ion implanted or may be non-ion implanted. The ions may be accelerated completely through the covering material to penetrate deep into the interior of the waveguide material without reaching the cladding material.

[0141] The cladding material or layer FC may, for example, be provided or deposited directly on the embedded or buried silicon nitride material or layer 5A (its (one or more) surfaces S1A). The thickness of the cladding material or layer FC may, for example, be between 1 nm and 500 nm, such as 200 nm. Such deposition may be Figure 5a The ion implantation step shown is performed before, for example, after, the nitride annealing step.

[0142] After the ion implantation, additional cladding materials or layers may optionally be deposited on the cladding material or layer FC.

[0143] The step of providing at least one embedded cladding material or layer 3 comprising at least one silicon nitride material or layer 5A embedded, buried or enclosed within at least one embedded cladding material or layer 3 may alternatively comprise providing a structure manufactured by a subtractive method removing and structuring, for example, a silicon nitride material or layer 5A provided on at least one supporting material or layer 19. Such an exemplary structure is as Figures 19a to 19d shown.

[0144] As described above, at least one cladding material or layer 3 is provided or deposited on the silicon nitride material or layer 5A, and if necessary, it is removed or thinned to directly expose the silicon nitride material or layer 5A to be implanted, or it is thinned or removed to leave a cladding layer or material thickness covering the silicon nitride material or layer 5A, through which ions can pass to ensure ion implantation into the silicon nitride material or layer 5A. Then, ion implantation is performed on the silicon nitride material or layer 5A.

[0145] That is, in this subtractive process, at least one waveguide core WC is defined by photolithography and vertical etching of a blanket silicon nitride film, a (oxide) cladding layer is deposited to cover the waveguide core WC and create a lateral support SP of the waveguide core WC, and the cladding layer is polished, for example, to create a (flat) top surface. During polishing, the polishing stops on the waveguide core top surface ( Fig.19a , 19b ), or stop before reaching the top surface ( Fig.19c , 19d If the removal stops before the top surface of the waveguide core, this will result in residual cladding material or layer on top of the waveguide core WC, which can be penetrated during ionization of the waveguide core WC or silicon nitride material.

[0146] Selective masking may be performed during rare earth ion implantation to form (i) at least one first portion including at least one rare earth ion implanted silicon nitride material or layer 5 embedded or buried in at least one embedded cladding material or layer 3, and (ii) at least one second portion including at least one non-implanted silicon nitride material or layer 5A embedded or buried in at least one embedded cladding material or layer 3. The silicon nitride material or layer 5 embedded or buried in the embedded cladding material or layer 3 of the first portion is, for example, optically coupled with the silicon nitride material or layer 5A embedded or buried in the embedded cladding material or layer 5A of the second portion.

[0147] Before the rare earth ion implantation is performed, annealing is performed, for example, to remove hydrogen from the embedded cladding material or layer 3 and / or the at least one silicon nitride material or layer 5A embedded in the embedded cladding material or layer 3 .

[0148] The step of providing at least one embedded cladding material or layer 3 including at least one silicon nitride material or layer 5A embedded or buried inside at least one embedded cladding material or layer 3 includes, for example, providing a cladding material or layer 25 for embedding one or more waveguide cores WC and including one or more waveguide recesses or depressions 9 and stress relief recess structures 21 for receiving silicon nitride waveguide material, and depositing silicon nitride waveguide material onto the cladding material or layer 25 and into the waveguide recesses 9 and stress relief recess structures 21 (recesses 23 thereof). The silicon nitride waveguide material completely or excessively fills the recesses 9 and the recesses of the stress relief recess structures 21.

[0149] Excess material is planarized. The deposited silicon nitride waveguide material is planarized. For example, the deposited silicon nitride waveguide material is planarized using mechanical planarization and chemical planarization.

[0150] For example, thermal energy is applied to the cladding material or layer 25 prior to depositing the silicon nitride waveguide material to allow the exposed surface of at least one waveguide recess 9 to reflow, thereby reducing optical losses in the waveguide. For example, thermal energy is applied by placing the device in a furnace or oven or by applying laser energy to the exposed surface of the waveguide recess 9.

[0151] A hard mask layer including at least one waveguide recess 9 and a stress relief recess structure is used to form at least one waveguide recess 9 and a stress relief recess structure 21 in a cladding material or layer 25 to embed the waveguide core WC and use a hard mask layer and dry plasma etching and / or wet etching. The hard mask layer includes, for example, amorphous silicon (aSi).

[0152] The cladding material or layer 25 for embedding the waveguide core WC, the embedded cladding material or layer 3 and / or the cladding material or layer FC provided or deposited on the embedded or buried silicon nitride material or layer 5A may for example comprise or consist of silicon dioxide (SiO2).

[0153] Although silicon dioxide is mentioned herein as one possible example of a coating material or layer, the coating material or layer may alternatively include or consist of an oxide material (eg, TeO 2 or Al 2 O 3 ) or one or more polymers.

[0154] As mentioned above, the waveguide core material or layer 5, 5A may include silicon nitride Si3N4, SiN x Or made of silicon nitride Si3N4, SiN x Composition; alternatively, the waveguide core material or layer 5, 5A may include tantalum oxide (TaO5, tantalum pentoxide), SiC, Hydex or lithium niobate LNOI or consist of tantalum oxide, SiC, Hydex or lithium niobate LNOI.

[0155] exist Figure 5a In the exemplary fabrication method shown, the fabrication process of rare earth ion (erbium) implanted silicon nitride Si3N4 PIC [121-123] begins by providing a (commercial 4 inch) silicon wafer having, for example, a 4 micron thick wet thermal oxide 25.

[0156] A stack of silicon oxide and silicon nitride films, or alternatively, an amorphous silicon aSi layer, is deposited by low pressure chemical vapor deposition (LPCVD) to act as a hard mask.

[0157] The waveguide structure and the filling pattern for stress relief are then defined by, for example, deep UV lithography (ASML PAS 5500 / 350C stepper, JSR M108Y photoresist and Brewer DUV-42P coating) and transferred into the thermal oxide layer by multiple steps of reactive ion etching (RIE) based on fluorine chemistry.

[0158] Thus, a preform 27 having the recess 9 for the waveguide and the filling pattern 21 is produced.

[0159] In case of a wafer using amorphous silicon aSi as hard mask, the remaining hard mask material is stripped in a concentrated KOH solution at, for example, 60°C.

[0160] A heat treatment of, for example, 1250° C. is then applied to reflow the silicon oxide and reduce the roughness caused by the RIE etching

[122] , and the preform recess 12 and the recess 23 are then filled with stoichiometric Si 3 N 4 by LPCVD.

[0161] Immediately after deposition, an etch-back process including photoresist spin coating and RIE can be performed to roughly planarize the surface and remove most of the excess Si3N4 material.

[0162] Chemical mechanical polishing (CMP) is then applied to achieve the desired waveguide thickness and create a top surface with sub-nanometer root mean square roughness. The wafer is then annealed at 1200°C to drive off hydrogen, which is known to cause optical absorption losses at technology-relevant wavelengths.

[0163] Using this fabrication process, a Si3N4 waveguide WC is created that is buried in a wet oxide cladding, but the top surface is exposed, allowing erbium to be implanted directly into the waveguide WC.

[0164] Optionally, the PIC die(s) can be separated by ultraviolet (UV) lithography, deep RIE and back grinding. This die separation process allows the creation of smooth chip end faces, resulting in high coupling efficiency to the optical fiber. This is very useful for performing measurements on a proof-of-concept device.

[0165] Perform rare earth ion implantation, such as erbium ion implantation of Si3N4 PIC or silicon nitride material or layer 5A. Implantation can be performed using a high energy ion accelerator, such as a 2MV Van de Graaff accelerator from HVEC. In this demonstration, the sample is mounted on a 2 inch silicon backing wafer and mounted perpendicular to the beam. The beam is electrostatically scanned across the wafer to ensure good uniformity, with a scan beam current of ~40 nA.

[0166] Annealing was performed to reduce optical losses caused by implantation defects. The samples that exhibited high amplification performance were those annealed in a microelectronics grade furnace at 1000°C in O2 at atmospheric pressure for 1 hour.

[0167] Subsequently, a passivation layer (e.g. of SiO2) can be selectively applied on top to enable the co-integration of other functional devices (e.g. metal microheaters and piezoelectric actuators).

[0168] Figure 5b , Figure 5c and Figure 5d Scanning electron microscope (SEM) images of cross sections of reference waveguides on the same wafer before ion implantation, after implantation and annealing (e.g., at 1000°C), and after implantation and annealing at 1200°C are compared. Figure 5c and Figure 5d The implanted waveguide shown in Figure 4 shows a clear deviation in waveguide geometry, which is believed to be caused by the volume expansion of Si3N4 during ion implantation. Despite the obvious deformation of the waveguide cross section, the impact on the waveguide background losses is still minimal according to ring resonator measurements and OFDR measurements.

[0169] When looking for the best post-implantation annealing process conditions, Figure 5d The annealing temperature of the samples shown was pushed to 1200°C. After a short buffered HF treatment, voids with a pattern size of 10-30 nm were observed on the lateral sides of the Si3N4 waveguide (but not underneath the waveguide). Such voids indicate the formation of HF-soluble erbium oxide precipitates in the SiO2 coating after annealing above 1000°C

[124] . It has been reported that the erbium ions in such precipitates are not useful for optical amplification and may lead to elevated unsaturated losses

[125] . In contrast, Figure 5c It is shown that samples annealed at 1000°C do not exhibit these voids associated with precipitation, which is consistent with observations in

[124] . Interestingly, no such voids were observed in the Si3N4 waveguide core in any of the samples examined. This provides evidence that, unlike SiO2, Si3N4 can be a good host for erbium dopants, and in the inventors' demonstration, Si3N4 can accommodate at least 0.3 at.% (atomic percentage) of erbium atoms without precipitation problems. Annealing at temperatures as high as 1250°C produced viable waveguide amplifiers.

[0170] The present disclosure also relates to a waveguide amplifier 1 produced according to the waveguide manufacturing method described herein and a device comprising the produced waveguide amplifier 1 .

[0171] Thus, the inventors have overcome the challenges of the prior art and demonstrated a waveguide amplifier based on meter-scale ultra-low-loss Si3N4 waveguides and an erbium-injected Si3N4 (Er:Si3N4) amplifier based on photonic integrated circuits.

[0172] More specific exemplary details and results provided by exemplary devices of the present disclosure are now presented, demonstrating the advantages of the devices and manufacturing methods of the present disclosure. An overview is first provided immediately below, with more specific details and determined results further provided below.

[0173] The exemplary integrated Er:Si3N4 amplifier achieves an on-chip output power of 145 mW (21.6 dBm) and a small signal gain of more than 30 dB. This result provides gain performance comparable to that of commercial EDFAs, a more than 100-fold improvement over existing photonic integrated circuit-based EDWAs (16-18), and exceeds the level achieved by state-of-the-art silicon photonic heterogeneously integrated III-V amplifiers (21) (17.5 dBm output power) (see below for details), making the technology viable for practical applications.

[0174] The exemplary device is a 0.5-meter-long densely packed Si3N4 ( Figure 1b ) Helical waveguide, cross section 0.7×2.1μm 2 , which exhibits ultra-low propagation losses of <5dB / m. The inventors do not add an upper oxide coating to the device prior to implantation. Next, the Si3N4 integrated circuit is ion implanted (6), which is a wafer-level process that benefits from much lower synergistic upconversion compared to the co-sputtered film (15). This brings gains to the Si3N4 platform, such as Figure 1a Despite the 0.5-meter-long Er:Si3N4 waveguide, a spiral coil arrangement with a gap spacing of 3 μm was achieved with a waveguide length of only 1.2 × 3.6 mm. 2 Compact footprint ( Figure 1b ). To achieve a large overlap of Γ≈50% between the embedded ions and the fundamental optical mode of the waveguide, the inventors used three consecutive implantation steps for the Si3N4 waveguide, using ion energies of 2.0, 1.416, and 0.966 MeV and corresponding ion energies of 4.50×10 15 , 3.17×10 15 and 2.34×10 15 cm -2 ion flux. Figure 1cThe concentration distribution up to a maximum depth of 400 nm in Si3N4 simulated using the Monte Carlo package "Stopping and Range of Ions in Matter" (SRIM) is shown, which agrees well with Rutherford Backscattering Spectroscopy (RBS) measurements.

[0175] After injection, the waveguide background loss was observed to increase from <5 dB / m to 100 dB / m due to injection defects, e.g. Figure 1d It was observed that after annealing at 1000°C for one hour in oxygen, the background losses outside the erbium absorption band could be significantly reduced to the same level as in the undoped waveguide. This loss was inferred from the intrinsic resonant linewidth measurements of the doped microring resonator. In addition, green luminescence ( Figure 1e ). Notably, for a 0.5 m waveguide length, such losses contribute only < 2.5 dB of background loss, significantly lower than the 30 dB passive losses of waveguides of equal length reported in previous work (16,17), which would prematurely deplete the pump and prevent efficient amplification.

[0176] Furthermore, the inventors investigated selective masking (using photoresists) during ion implantation, which could provide a basis for integrating passive and active components in Si3N4 waveguides (e.g. combining Kerr frequency combs with erbium waveguide amplifiers).

[0177] Although waveguide deformation is observed in the implanted region, the mechanical support due to the lateral oxide cladding ( Figure 1c ), the waveguide cross section can be well maintained, minimizing reflections and enabling a low-loss transition from the gain region to the passive waveguide region ( Figure 1a ). In contrast, severe deformation of the uncoated Si3N4 waveguide was observed for the same injection conditions, as detailed later.

[0178] The emission and absorption cross sections (σe(λ) and σa(λ)) are important parameters that can determine the gain characteristics of erbium. The inventors inferred σe(λ) and σa(λ) by examining the photoluminescence (PL) spectrum and the wavelength (λ)-dependent absorption loss, respectively. Figure 2a Shown is resonant pumping in a 0.46 cm long Er:Si3N4 waveguide. 4 I 11 / 2 The emission spectrum of the state (980 nm) from the first excited energy level to the ground state, from which the emission cross section ( Figure 2c ):

[0179]

[0180] Where n is the refractive index, and τ = 3.4 ms is obtained from Figure 2d and Figure 2e The PL lifetime extracted from the time measurement is shown. The wavelength-dependent erbium absorption loss α Er (in cm -1 The absorption is then converted to the erbium absorption cross section using the following equation:

[0181]

[0182] where N0 is the effective peak erbium ion concentration and Γ is the overlap factor. Figure 2b The inset shows two resonances with intrinsic dissipation rates (κ0) of ∼1000 MHz and ∼40 MHz at 1535 nm and 1600 nm. / 2π), corresponding to loss coefficients of 2 dB / cm and 0.08 dB / cm, respectively. The measured losses are calibrated by optical frequency domain reflectometry (OFDR) measurements. The absorption cross section σa(λ) is obtained by scaling its peak to the peak of the resulting σem(λ), which in turn gives 1.35×10 20 cm -3 Compared with the RBS results, almost all the added erbium ions are optically active. Different erbium concentrations in the Er:Si3N4 waveguide can be achieved by scaling the ion flux. 20 cm -3 , 1.35×10 20 cm -3 and 3.25×10 20 cm -3 In the reference Er:Si3N4 waveguide, the inventors obtained net gain coefficients of 1.0dB / cm, 1.4dB / cm and 1.9dB / cm at 1550nm respectively ( Figure 2f ), which is comparable to the theoretical gain coefficients of 0.7 dB / cm, 1.5 dB / cm, and 3.5 dB / cm given by g = Γ(σeN2-σeN1), where N2 and N1 are the populations of the first excited state and the ground state (24). The gain coefficient for 980 nm pumping and its dependence on the waveguide width were also studied.

[0183] use Figure 3a In the setup shown in the figure, the inventors used a 0.21-meter-long Er:Si3N4 waveguide (erbium concentration is about 3.25×10 20 cm -3 ) was pumped at 1480nm, demonstrating high output power and large net gain. Broadband on-chip net gain reached 30dB ( Figure 3b). Figure 3c The measured on-chip optical net gain at 1550nm and the simulation reproduced by parameter fitting are shown. For 0.07mW input, the on-chip output power reaches 60mW, resulting in a maximum net gain of 30dB and a power conversion efficiency (signal power increase divided by pump power) of about 30%. When considering the 5.8dB fiber-to-chip coupling loss on both sides, this indicates an off-chip net gain of 24dB. Figure 3d As shown in the inset, at 245 mW coupled pump power, for an increased input power of 2.61 mW, the inventors achieved an on-chip output power of 145 mW, indicating an on-chip power conversion efficiency of nearly 60%. 20 cm -3 Similar gain performance is achieved in a 0.5-meter-long Er:Si3N4 waveguide. A noise figure of approximately 7 dB is measured for a net gain >20 dB limited by coupling losses. Simulations show that higher net gain and output power can be achieved at higher pump powers without being severely affected by cooperative upconversion, which fundamentally limits the performance of EDWA using co-sputtered erbium-doped films (15). It is worth noting that the fluctuations observed in the measured net gain (yellow scattered points) are caused by the gain clamping effect when the net gain reaches approximately 26 dB, which originates from competing parasitic lasing in the optical Fabry-Perot (FP) cavity formed by the two waveguide endfaces.

[0184] As an example of one of many possible uses, the inventors applied Er:Si3N4 EDWA to soliton microcomb amplification ( Figure 4a ), and since both devices use Si3N4, they can in principle be integrated on the same chip. Soliton microcombs can provide fully coherent broadband optical frequency combs when operated in the dissipative Kerr soliton (DKS) regime (25). However, soliton microcombs exhibit low intrinsic nonlinear conversion efficiency (e.g., efficiency <1% for a 200 GHz spacing single soliton microcomb (26), so almost all applications require the use of desktop EDFAs. Here, the inventors demonstrate on-chip amplification of soliton microcombs to the 10 mW level between the C-band and L-band, suitable for microwave photon generation and wavelength division multiplexing (WDM) coherent optical communications. First, in a Si3N4 Euler bent-racetrack microresonator ( Figure 4b and Figure 4c ) generates a 19.8GHz single soliton microcomb with an output power of 0.08mW. Figure 4dCompared to -104dBc / Hz (before amplification) limited by photon shot noise, the 8.4mW off-chip power soliton amplification of the Er:Si3N4 EDWA (panel (ii)) results in a significant reduction in single sideband phase noise to <-120dBc / Hz at Fourier offset frequencies >100kHz, as shown in panel (i) of the Figure 1. Figure 4e To provide a comparison, a commercial EDFA was also deployed to amplify the same soliton microcomb to a similar power level ( Figure 4d Panel (iii) in ), gives the same performance.

[0185] As a second example, the inventors scaled up a soliton microcomb with a channel spacing of 100 GHz suitable for WDM optical communications. The inventors observed that more than 30 comb lines achieved a line power of >0.1 mW (-10 dBm) and an optical signal-to-noise ratio (OSNR) of more than 30 dB (0.05 nm resolution bandwidth), of which more than 10 comb lines exceeded 1 mW (0 dBm), such as Figure 4f The observed comb-line OSNR is assumed to be feasible for short-range coherent data transmission using soliton-based transmitter pairs with a symbol rate of 40 Gbaud per channel using 16-state quadrature amplitude modulation based on the same configuration as in past work (27).

[0186] As a result, the inventors demonstrated a waveguide amplifier, such as an erbium amplifier based on a photonic integrated circuit, that achieves an output power of 145 mW and a small-signal gain of more than 30 dB—on par with commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneous integrated semiconductor amplifiers.

[0187] The design freedom provided by photonic integrated circuits allows for multi-stage configurations to optimize gain and optical signal-to-noise ratio.

[0188] Furthermore, the ion implantation technique of the disclosed waveguide amplifier fabrication method may allow other rare earth ions such as ytterbium (emitting at 1.1 μm) and thulium (emitting at 0.8 μm, 1.45 μm and 2.0 μm) to be co-doped with erbium ions, thereby providing additional gain in other wavelength regions.

[0189] The disclosed ion implantation method in Si3N4 can be used as the gain medium for various integrated laser sources, such as high-power soliton microcombs, low-noise rare-earth ion-based CW lasers, femtosecond mode-locked lasers (28), or cavity soliton lasers (29). Equally important, this active Si3N4 photonic platform is compatible with heterogeneous integration of thin films (e.g., thin-film lithium niobate) for coherent communications (27) or RF distribution (30), enabling the combination of high-speed electro-optic modulation and amplification on the same chip.

[0190] Gain performance comparison with prior art on-chip amplifiers:

[0191] Table 1 below summarizes the prior art research results of integrated optical amplifiers, including planar amplifiers based on erbium-doped waveguide cores or coatings and heterogeneously integrated III-V semiconductor amplifiers. The inventors compared the Er:Si3N4 waveguide amplifiers presented in the present disclosure with previous studies and some commercial general-purpose erbium-doped fiber amplifiers in terms of achievable on-chip output optical power, net gain, etc. The comparison shows that the PIC-based Er:Si3N4 amplifiers of the present disclosure achieve significant improvements in output power and gain compared to the reported erbium-doped methods, achieving performance comparable to that of heterogeneously integrated III-V amplifiers of the prior art. It is also worth noting that some of the amplification performance characteristics presented in the present disclosure are comparable to or even better than the specifications of some commercial erbium-doped fiber amplifiers. It is conceivable that the presented PIC-based Er:Si3N4 amplifiers can replace such amplifiers in various applications, and the small size of the gain section can significantly reduce the size specifications.

[0192]

[0193] Table 1. Comparison with reported on-chip amplifiers and typical commercial Erbium-doped fiber amplifiers. The gain performance of the demonstrated Er:Si3N4 waveguide amplifier is compared with state-of-the-art on-chip amplifiers based on Erbium-doped gain media and heterogeneously integrated III-V semiconductors. Three typical commercial general-purpose Erbium-doped fiber amplifiers are also compared. n / a, data not available.

[0194] Injection into Si3N4 waveguide without lateral cladding:

[0195] To further investigate the deformation of Si3N4 waveguides after high-flux ion implantation, the inventors implanted Si3N4 ridge waveguides without lateral cladding 3 and characterized the geometry before and after implantation. The Si3N4 ridge waveguides used in this test were fabricated by standard UV lithography and RIE etching of 350nm thick LPCVD Si3N4 films on wet-oxidized Si wafers. The irradiation energy and flux ratio were the same as those used for the waveguides implanted with lateral cladding. The total flux was 1×10 16 cm -2 .

[0196] By comparing the SEM images of the waveguide cross section before and after injection ( Figure 6 a and Figure 6 b), the inventors noticed that the waveguide cross section changed significantly after ion implantation. Apparently, the profiles of the waveguide sidewalls and top surface were severely deformed after implantation. The implanted waveguide cross section appears to be wider and thinner than the masked waveguide, as shown in the top surface morphology mapped by AFM ( Figure 6 d and Fig. 2). This is similar to the deformation observed in a waveguide with lateral cladding injection ( Figure 5b , Figure 5c and Figure 5d ), which highlights the importance and necessity of mechanical support from lateral SiO2 encapsulation.

[0197] Selective masking of on-demand erbium implantation in complex Si3N4 photonic circuits:

[0198] As is common practice in the current microelectronics industry for semiconductor doping, regions of the PIC that are not intended to be part of the gain section can be masked prior to implantation to avoid altering the properties of the passive waveguide. Such selective implantation can maintain the desired properties, such as ultra-low loss and engineered dispersion, of passive devices such as Kerr microring resonators, microring filters, couplers, and many other passive devices. It can also avoid erbium absorption losses in the device where pump light cannot pass. This is a significant advantage over bulk doping during material growth reported in previous studies using erbium-doped lithium niobate

[111] .

[0199] The inventors demonstrated the feasibility of selective masking of erbium ion implantation using a simple photoresist masking process. In this process, the inventors defined the masking area with a 3μm thick AZ 15nXT photoresist by standard UV direct write lithography before implantation. SRIM calculations showed that a 2μm photoresist layer was sufficient to block all erbium ions at 2MeV. After erbium ion irradiation, it was noted that the photoresist showed signs of strong cross-linking and was brown in color. The inventors were able to completely remove the photoresist by ashing in a high-power oxygen plasma (15 minutes) and cleaning in an HCl solution (37%, 45°C, 15 minutes).

[0200] Although extreme ion energies and ion doses were used in the waveguide doping, i.e., the ion energies were comparable to implants used in the imaging sensor industry, and the doses were comparable to the doses used to create ohmic contacts in SiC processes

[126] , this simple masking process worked surprisingly well in the demonstration. Figure 7a As shown, after removing the photoresist, a clear contrast between the implanted and masked areas can be observed under an optical microscope, providing evidence for material property modification by ion irradiation.

[0201] For the future development scope towards more complex active Si3N4 photonic integrated circuits, it is also noted that some morphological changes may occur in the implanted area due to material volume expansion and stress accumulation. Figure 7b As shown in Figure 2, a slight local deformation of the SiO2 is observed at the boundary between the implanted and masked regions. The implanted Si3N4 core appears to expand in volume, squeezing the adjacent lateral SiO2 cladding and forming a small bulge around the waveguide with a height variation of the order of 50 nm. This observation is consistent with the geometrical variation of the cross section, as shown in Figure 2. Figure 5cand Figure 5d shown.

[0202] The inventor based Figure 5c and Figure 5d The SEM measurement geometry shown in simulates the fundamental TE optical mode field at 1550nm. Assuming that the transition between the injected and uninjected waveguide sections is abrupt, the fundamental mode to fundamental mode transmission loss at the boundary is estimated to be less than 0.018dB and the return loss is less than -45dB by calculating the mode overlap. Although the reflection and scattering caused by the "step-like" features at the boundary are quite small for many applications, methods such as introducing a grayscale mask or a tapered mask above the waveguide at the boundary can be used to design a smooth transition and further reduce reflections and scattering.

[0203] Erbium ion distribution and overlap factor calculation:

[0204] To ensure maximum overlap of erbium ion distribution and light intensity in the Si3N4 waveguide, the inventors performed a series of experiments with different energies and therefore different ion ranges. 166 Er + They optimized the overlapping implant energies and fluxes based on the Stopping and Range of Ions in Matter (SRIM) calculations

[27] . In the SRIM calculations, a stoichiometric Si3N4 of 3.17 g / cm 3 density. Monte Carlo simulations were subsequently performed using the Transport of Ions in Matter (TRIM) code to obtain a more accurate density distribution. The ion energy, ion distribution parameters from the TRIM simulations, and the injection flux are listed in Table 2. It is worth noting that some early samples received a flux 0.42 times lower than expected or even lower due to sample mounting issues. Rutherford backscattering spectroscopy (RBS) and light absorption measured in the ring resonator were used to calibrate the actual erbium concentration presented previously.

[0205]

[0206] Table 2. Parameters applied for three consecutive erbium injections into the Si3N4 waveguide.

[0207] The ion implantation method allows to achieve large overlap factors between erbium ions and optical modes, thanks to the large doping depth (comparable to the waveguide thickness) and the optimized vertical profile. Based on the parameters provided in Table 2, the overlap factor Γ between the erbium density profile and the intensity of the fundamental TE mode of interest at 1550 nm is estimated to be ~0.49 in a waveguide with lateral (cross-sectional) dimensions of 2.1 μm × 0.7 μm. It can be noted that the actual overlap factor may be higher, up to ~0.6, for thinner waveguides, taking into account the fabrication-induced variations in sample thickness.

[0208] Here, the inventors define the maximum erbium concentration normalized Γ as:

[0209]

[0210] where E(x,y) is the electric field of the fundamental TE mode, ε(x,y) is the relative permittivity of the material, and N(y) is the depth-dependent ion concentration.

[0211] Rutherford Backscattering Spectroscopy (RBS) measurement and analysis:

[0212] The erbium concentration profiles of implanted and annealed samples from the same wafer were analyzed by Rutherford backscattering spectroscopy (RBS) measurements using 2 MeV He ions. The ion beam diameter was approximately 1 mm, the backscattered ions were detected at 170° relative to the incident ion beam, and the total ion charge used to collect one spectrum was 5 μC. The measured spectra were calibrated by additional measurements of thin surface layer samples containing multiple elements ( Figure 8a ).

[0213] Since the sample consists of exposed areas of Si3N4 and SiO2, their relative coverage must first be determined. This is done by combining the simulated RBS spectra ( Figure 8a The red line in the figure is fitted to the corresponding Si, N and O signals appearing at about 1125, 730 and 625 keV, respectively. Figure 8a The result is a coverage fraction SiO2:Si3N4=0.4:0.6. Next, the ions between 1350 and 1750 keV and Figure 8b The Er signal is clearly visible in the 3D images. By assuming layers with different Er concentrations in the thickness range of 20-40 nm (which represents the depth resolution of the performed RBS measurements), a very good fit of the simulated and measured RBS spectra is obtained. Since RBS measures the density profile in thin film units, the measured Er concentration is Figure 8c The mesoscale was converted to physical depth, assuming the density of Si3N4 to be 9.65×10 22 Atom / cm 3 (3.17g / cm 3 ). The measured profile shape agrees well with that calculated by SRIM (also shown in the main manuscript), but the measured absolute erbium concentration is 0.42 times lower than expected from the nominal injection flux.

[0214] Loss characterization of erbium-implanted Er:Si3N4 waveguides.

[0215] The wavelength-dependent waveguide losses of Er:Si3N4 circuits need to be carefully characterized to infer the waveguide background losses, erbium absorption, and net gain coefficient. Here, the inventors use two methods, microring resonant linewidth characterization and optical frequency domain reflectometry (OFDR), to calibrate the waveguide losses.

[0216] The inventors first characterized the resonant linewidth of a 100 GHz Er:Si3N4 microring resonator coupled to a single bus waveguide. Figure 9a and Figure 9b The optical transmission spectra of the microrings before erbium ion implantation and after implantation and annealing are shown, respectively, using a home-made optical network analyzer with sub-MHz resolution [128,129]. Changes in the depth of the resonance dips are observed, which correlates with changes in the intrinsic linewidth Δν0 = κ0 / 2π. The intrinsic dissipation rate κ0 is inferred by fitting the measured resonances to a Lorentzian lineshape, as Fig.9c The optical loss α (in 1 / m) is converted from the intrinsic dissipation rate by the following expression:

[0217]

[0218] Among them, n eff is the effective refractive index, and c is the speed of light in a vacuum. The waveguide loss is calculated as Figure 9d As shown, the peak at 1535 nm indicates ~1.75 dB / cm.

[0219] Secondly, the inventors characterized the propagation losses in a 0.5-meter-long Er:Si3N4 waveguide by OFDR measurements. The OFDR trace records the light backreflection along the length of the waveguide, which can be converted into propagation losses by linearly fitting the distance-dependent light backreflection. By fitting the losses in various segmented spectral windows, the wavelength-dependent losses are obtained, such as Fig.9e The characterized losses from OFDR measurements are generally consistent with those inferred from intrinsic resonant linewidth measurements, but exhibit a slightly higher peak of 2.14 dB / cm at 1535 nm. This difference is attributed to possible reduced erbium absorption due to cavity-enhanced light intensity in the case of resonant linewidth measurements. In the gain calculations and simulations, we use the losses inferred from OFDR measurements.

[0220] Photoluminescence lifetime measurement:

[0221] Excited states measured from a 0.45 cm long Er:Si3N4 waveguide 4 I 13 / 2 To the ground state 4 I 15 / 2The photoluminescence (PL) lifetime τ of the transition of α was set to avoid possible erbium reabsorption in the long waveguide. The 980 nm pump laser diode was gated by a periodic square wave with a duty cycle of 50% and a duration of 50 ms. The coupled pump power was limited to <1 mW to minimize the effects from the cooperative upconversion process

[130] . ​​When the modulated pump was turned off, the spontaneous emission decayed at a rate inversely proportional to the PL lifetime τ. By exponential curve fitting, an increased lifetime τ of 3.4 ms was obtained to decay to 1 / e of the maximum value compared to 1.5 ms before annealing.

[0222] Gain coefficient analysis for different pump wavelengths and waveguide cross sections:

[0223] First, the inventors studied the gain coefficient of short (0.43–0.46 cm) Er:Si3N4 waveguides at different pump wavelengths, such as Fig.10a As shown. For 980 nm pumping, a maximum signal enhancement of 3.4 dB / cm at 1550 nm is obtained, which is higher than the peak of 2.5 dB / cm for 1480 nm pumping, because the population inversion is more complete for 980 nm pumping. By subtracting the total losses from the erbium absorption and waveguide background losses, a net gain coefficient of 2.3 dB / cm for 980 nm pumping is obtained, while the net gain coefficient for 1480 nm pumping is 1.4 dB / cm. The theoretical gain coefficient is given by g = σeΓN0 (1.7 dB / cm)

[131] . For the experiments presented in the manuscript, 1480 nm pumping was deployed due to the lower coupling losses and the cutoff wavelength (1450 nm) of the UHNA fiber for chip coupling.

[0224] Secondly, Fig.10b The optical net gain of waveguides doped with the same erbium ion flux and different widths is compared. The saturated gain of the three waveguides with widths of 1.8μm, 2.1μm and 2.4μm is the same within the measurement error. From the gain-pump power relationship, we find that the 1.8μm and 2.1μm waveguides reach saturation at the same rate, while the 2.4μm waveguide has a slightly higher pump saturation power due to its relatively large effective mode area. The gain performance can be further enhanced by adopting an increased waveguide cross-sectional size to achieve a larger mode area for higher output saturation power. This result shows that Er:Si3N4 waveguides with widths from 1.8μm to 2.4μm have similar amplification performance, which allows flexible design of waveguide geometry for optical dispersion engineering for applications such as mode-locked lasers and active cavity solitons.

[0225] In the experiment, the inventors measured the power of a 1550nm signal before and after passing through a short waveguide pumped with different optical powers. The signal enhancement was obtained, which is the difference between the maximum and minimum output signal powers. The net optical gain was then calculated by subtracting the characterized erbium absorption loss at 1550nm from the measured signal enhancement. The on-chip input signal power was set to -31dBm to avoid gain saturation and ensure that the output signal level was at least 5dB higher than the total power of the amplifier self-emission (ASE) power. The ASE level was calibrated in the absence of a signal input and then subtracted from the measured total output signal power. A wavelength division multiplexer (Thorlabs WD1450A) and free-space thin-film optical filters (Thorlabs FB1550-40 and FEL1500) were used to suppress the residual pump light by -60dBc in the output signal power measurement.

[0226] Numerical modeling of light amplification in Er:Si3N4 waveguides:

[0227] The inventors modeled the optical gain by considering erbium as a three-level system, which can generally describe the first three lower energy levels ( 4 I 15 / 2 , 4 I 13 / 2 and 4 I 11 / 2 ) in the Fig.11a The rate equation governing the population dynamics, including excited state absorption (ESA), first-order and second-order concerted upconversion (CUC) when pumped at 1480 nm, is given by [132,133] (Eq. (3)):

[0228]

[0229] Among them, N 1,2,3 Represent the first three energy levels 4 I 15 / 2 , 4 I 13 / 2 and 4 I 11 / 2 The number of particles. ij =1 / τ ij is the decay rate from energy level i to energy level j, given by the lifetime τ ij The reciprocal of is given. is the transition rate of the beam (signal, pump and self-emission) from state i to state j, where is the photon flux, σij is the hνk transition cross section, I is the light intensity, and v is the photon frequency.

[0230] R 24 Indicates that ESA 4 I 11 / 2The energy level transition rate, and C 24 and C 37 are responsible for the first and second order cooperative upconversion, respectively. These terms are included in the numerical calculations, although it has been shown that for ion-implanted substrates, C 37 May be small relative to co-sputtered doped films

[133] . N = N1 + N2 + N3 is the total ion concentration.

[0231] In a waveguide, the spatial distribution of the signal, pump, and spontaneous amplifier noise can be described by a set of propagation equations given by (Equation 4):

[0232]

[0233] where Γ is the mode-erbium overlap factor, α 0s and α 0p are the waveguide background losses of the signal and pump, respectively. 0 ASE =2Bhν ASE is the local self-emission noise power added by both polarizations within bandwidth B (~5 THz in simulations). In simulations, we include amplifier self-emission noise propagating in both directions. For the case of counter-propagating beams, such as in counter-pumping and bidirectional pumping configurations, the above equations need to be extended to include both forward and counter-propagating pumping and can be solved as an ordinal differential equation boundary value problem by, for example, the relaxation algorithm.

[0234] Fig.12a Numerical fits of the measured optical gain using simulations based on Eqs. 3 and 4 are shown to estimate the contributions from the ESA and CUC processes. The corresponding output power is given by Figure 12b The experimental results presented in the main manuscript were reproduced using the parameters listed in Table 3.

[0235]

[0236] Table 3: Parameters used in simulating the on-chip optical net gain in a 0.5 meter Si3N4 waveguide for -10 dBm input at 1550 nm.

[0237] The simulations show that due to the small C from the numerical fit of the measured results 37 Even in the range of on-chip pump powers >120 mW, the observed optical gain is not significantly affected by the second-order cooperative upconversion C 37 Although C 37 Weaker, but we observed green luminescence caused by transitions from higher energy levels when strongly pumped, e.g. Fig.11b shown. Fig.12c shows the input signal power P at 1550nmsat,s The net gain is thus changed, and the input saturation power is estimated to be about -15dBm (the small signal gain drops by 3dB), which roughly matches the theoretical value of -14dBm given by the following formula:

[0238]

[0239] Among them, A eff =1.2μm 2 is the effective area of ​​the fundamental TE mode.

[0240] The shaded area indicates the range where parasitic lasing starts when the net gain exceeds 26 dB, which causes fluctuations in the measured net gain and leads to uncertainty in the saturation input power estimate. The vertical offset between the net gains from the two samples is mainly caused by the difference in coupled pump power.

[0241] Fig.13 The simulated on-chip net gain as a function of pump power and waveguide length is presented. 20 cm -3 With the erbium concentration in the Er:Si3N4 amplifier, it was found that the optimized waveguide length is 0.5 m, which is able to provide more than 30 dB of optical net gain and 20 dBm (100 mW) on-chip output power with an on-chip pump power of about 23 dBm. Further increase in waveguide length does not contribute significantly to higher net gain because of the possible reabsorption of erbium signal in the presence of pump depletion and attenuation in longer waveguides. In experiments, Er:Si3N4 waveguide amplifiers can be operated at 100 mW due to power limitations of the laser diode and coupling losses. Fig.13 In fact, the gain can be further increased by using higher on-chip pump power of more than 23dBm, but according to simulations, it will be absorbed by the excited states (given by σ 24 In contrast, no increase in the pump level due to C was observed in simulations with pump levels >200 mW. 24 and C 37 The significant contribution from the cooperative upconversion process was determined. The fitting coefficient C of the sample based on ion implantation 24 and C 37 This is two orders of magnitude lower than that reported in sputtered Er-doped Al2O3 [104,130,133].

[0242] Experimental setup for gain and output power measurements:

[0243] The integrated waveguide amplifier is excited by pump light provided by a multi-longitudinal mode laser diode, centered at 1480 nm (with a fiber pigtail output power of 400 mW), injected into the photonic chip in both forward and reverse directions via a coupling fiber. Here, the inventors used 1480 nm pumping because of the lower fiber-to-chip coupling losses, despite the higher gain factor of 980 nm pumping. The probe signal from a frequency-tunable continuous wave (CW) laser is coupled to the chip via a fiber-based coupler (wavelength division multiplexer for 1480 / 1550 nm) in combination with the forward optical pump. A high extinction free-space low-pass filter removes the transmitted pump to ensure accurate gain characterization. The measured signal and pump power are carefully calibrated with the characterized insertion losses caused by the fiber link, optical coupler, and optical filter. The optical spectrum is calibrated using the optical power measured by a power meter. We extract the net gain by directly comparing the calibrated output and input signal powers, rather than using the subtraction between signal enhancement and total losses that may lead to an overestimation of the net gain.

[0244] Fresnel reflection on chip end face and induced parasitic laser emission:

[0245] Fresnel reflections of the waveguide input and output at the chip facets can form an optical Fabry-Perot (FP) cavity, which can lead to enhanced resonance at the resonant frequency. Fig.14a The transmission of a passive 100 GHz FSR Si3N4 microring resonator coupled to a 0.5 mm long bus waveguide is shown when a lensed fiber is used for in- and out-chip optical coupling. The laser frequency is swept over 30 GHz in 20 ms time periods. The baseline variations arise from the FP cavity fringes. Assuming the reflectivity of both facets is the same and the waveguide losses are negligible, the intensity reflection coefficient R can be inferred from the contrast K of the fringes by the expression

[136] :

[0246]

[0247] The contrast ratio is given by:

[0248]

[0249] Among them, I max and I min are the fringe maximum and minimum, respectively. This gives a calculated intensity reflection coefficient R = 4.77%, corresponding to a -13dB return loss at each end face. When the on-chip gain is sufficient to overcome the waveguide loss and return loss, parasitic lasing of the FP cavity may occur in the on-chip waveguide amplifier at wavelengths other than the input signal wavelength. This effect will limit the achievable optical gain. In a 0.5-meter-long Er:Si3N4 waveguide amplifier, parasitic lasing limits the single-pass on-chip net gain to about 16dB when considering a 3dB background loss. Fig.14b An example of parasitic lasing with a signal input of -10dBm is shown when the on-chip pump power is >10dBm. Due to the instability of the parasitic lasing, the amplified signal power will fluctuate and will not increase significantly as the pump power is increased.

[0250] In contrast, Fresnel reflections can be suppressed by reducing the refractive index mismatch caused by the air gap between the chip end face and the coupled fiber. Here, the inventors used a pair of ultra-high numerical aperture (UHNA) optical fibers, which were butt-coupled to the input and output chip end faces, respectively. The UHNA fibers were cut vertically to provide flat end faces in contact with the Er:Si3N4 chip end faces. The UHNA fiber (UHNA7, Coherent Inc.) has a small mode field diameter of 3.2 μm, which is close to the optical mode size in the inverted tapered Si3N4 waveguide. A refractive index matching gel (G608N3, Thorlabs Inc.) was applied to the air gap between the UHNA fiber and the chip end face to reduce the Fresnel reflection by an order of magnitude, from 4.77% to 0.5%, corresponding to a reflection loss of -23 dB, as Fig.14c The reduced reflection increases the threshold for parasitic lasing, which in turn allows for a net on-chip gain of up to 26 dB. In this case, no significant parasitic lasing is observed in the same Er:Si3N4 waveguide at the same input signal, as shown in Figure 2. Fig.14d shown.

[0251] When the net gain exceeds 26dB, parasitic laser emission still occurs for small input signals or increased pump power, because the waveguide can provide a high enough single-pass gain to exceed the FP cavity loss at one end, i.e., -23dB for internal Fresnel reflection and -3dB for waveguide background loss. Further reducing the end face reflection by tilting the waveguide taper and end face will help to achieve higher net gain. In the experiment, the fiber-to-chip coupling loss for 1550nm and 1480nm is 2.9dB and 3.3dB per side, respectively.

[0252] Noise figure of Er:Si3N4 amplifier:

[0253] The noise figure of the Er:Si3N4 amplifier is measured using the commonly used source subtraction method

[137] , which removes the source-source emission (SSE) noise from the total noise emitted by the erbium amplifier. In the measurement, the input laser signal and the spectrum of the amplified signal recorded by an optical spectrum analyzer (OSA) are calibrated according to the power measured by a power meter. The optical insertion loss between the amplifier output and the OSA is measured and then compensated in the calculation. The optical gain G at the optical frequency v and the input P within the optical bandwidth B0 are measured from the calibrated spectrum. SSE and output P outThe noise power at , in order to find the noise figure using the following expression:

[0254]

[0255] Fig.15a The noise figure obtained for the forward pumping scheme at different input signal powers and pump powers is shown. In the high gain range, with on-chip pump power >20dBm and off-chip signal power <-5dBm, parasitic lasing effects that limit the optical gain affect the noise figure measurement. Fig.15b The off-chip input signal is -1.9dBm ( Fig.15a Example noise figure measurement of ).

[0256] The spectral difference at the signal wavelength results in a net off-chip gain of 21 dB. The noise power P in the 0.2 nm optical bandwidth (the resolution bandwidth of the OSA) out =-27dBm and P SSE =-65dBm are interpolated from the noise floor at 3nm wavelength away from the signal peak. To avoid overestimating the noise figure, the inventors used a corrected 0.12nm resolution bandwidth instead of the displayed OSA 0.2nm resolution bandwidth. Using the above formula, the noise figure of 7.1dB is obtained, including the contribution of the input fiber to chip coupling loss and the relatively large self-emission factor n at 1480nm pumping (incomplete population inversion). sp .

[0257] On-chip amplification of soliton microcombs and microwave photon generation:

[0258] The soliton microcomb is generated by slow laser tuning and a single soliton is isolated using a back-tuning technique

[138] . The generated single soliton microcomb exhibits a characteristic squared spectral envelope under excitation with an on-chip pump power of about 100 mW, with an integrated power of 0.08 mW (the transmitted pump is removed by a fiber Bragg grating notch filter). Due to the additional optical attenuation caused by chip coupling and the fiber link loss between the coupling fiber and the photodetector, the measured soliton microcomb power is lower than the theoretical fitted power (0.3 mW). The fitted comb line power is given by the following equation

[139] :

[0259]

[0260] where μ is the number of comb modes counted away from the pump line, β2 is the group velocity dispersion coefficient, D1 / 2π = 19.8 GHz is the cavity FSR, and Δω sis the comb spectral bandwidth, the maximum line power generated is about -29dBm, and the total microcomb power is about 0.3mW. The parameters used for fitting the soliton microcomb power are extracted from the reported Si3N4 Euler curved racetrack microresonator

[140] . The group velocity dispersion β2 is -14.1fs 2 / mm, corresponding to D2 / 2π=34.9kHz. The effective nonlinear coefficient is 0.81W -1 m -1 The microcomb bandwidth is given by δω s =2 / πδτ s Given, where δτ is the maximum pump laser frequency detuning and the power in the bus waveguide is 70 mW. s About 61ps.

[0261] In the case of a generated 19.8 GHz single soliton microcomb, we achieved microwave photon generation using direct photodetection (Discovery Semiconductors, DSC40). The measured single-sideband phase noise reached a high noise plateau of -104 dBc / Hz for Fourier shift frequencies >30 kHz as measured by a phase noise analyzer (PNA, Rohde & Schwarz, FSW43). This phase noise plateau was limited by the photon shot noise due to the low incident optical power on the photodetector (0.1 mA photocurrent)

[141] .

[0262] The inventors used Er:Si3N4 EDWA to increase the soliton power to 8.4mW (6.9dBm), which corresponds to a net off-chip gain of 20.1dB. This produced a photocurrent of 3.8mA with an insertion loss of 3.5dB between the chip output and the PD. The amplified solitons were able to transmit a strong microwave signal, which reduced the phase noise at offset frequencies >10kHz to -120dBc / Hz at 100kHz and -126dBc / Hz at 1MHz, respectively. The spectral bump around the offset frequency of 4kHz is attributed to the characteristic laser phase noise (Toptica CTL), while the spectral peak between 10kHz and 100kHz originates from the laser amplitude to phase noise conversion observed in previous studies [140,142,143]. The "step-like" phase noise at offset frequencies above 100kHz is mainly determined by the phase noise analyzer floor noise (dashed dotted line). We would like to point out that the power of the amplified comb line fluctuates from 1550nm to 1650nm, which is caused by the wavelength-dependent enhanced amplification caused by the FP cavity formed on the chip end face. For the case of using a commercial erbium-doped fiber amplifier, the input soliton micro-comb is amplified to a similar output power of 6.8dBm for comparison.

[0263] Transmitter OSNR budget estimation for error-free short-distance transmission:

[0264] Fig.16 A proposed short-range (<1 km) communications application scenario, such as intra-data center communications, is shown using an integrated Er:Si3N4 EDWA to amplify the power of the soliton microcomb. The theoretical bit error rate (BER) of a 16QAM signal can be calculated using OSNR analysis and is given by the following equation

[144] :

[0265]

[0266] where erfc is the complementary error function and OSNR is the OSNR measured by an optical spectrum analyzer (OSA). ref Related, expressed as:

[0267]

[0268] Among them, B ref and B s Corresponding to the resolution bandwidth of the OSA and the effective bandwidth of the matched filter at the receiver, p = 1 (2) is related to the signal polarization multiplexing. Considering forward error correction based on 7% redundancy, the OSNR at the receiver needs to be > 20 dB to achieve less than 4.5×10 -3 The BER of the threshold (for 16 quadrature amplitude modulation (QAM) signals with a symbol rate of 40GBd) is 1.5 Mbps. This sets a minimum optical signal-to-noise ratio (OSNR) requirement for the transmitter output. For short-distance (<1km) communications with negligible fiber link losses, the output OSNR (>30dB) of the demonstrated Er:Si3N4 EDWA amplified microcomb can realistically meet the transmitter OSNR requirement, allowing for tolerance of about 10dB OSNR loss caused by additional optical amplifiers, electronic noise and nonlinear effects in the link.

[0269] Although the present invention has been disclosed with reference to certain preferred embodiments, various modifications, changes and variations may be made to the described embodiments and their equivalents without departing from the scope of the present invention. Therefore, the present invention is not limited to the described embodiments, but is given the broadest reasonable interpretation according to the language of the appended claims. The features of any of the above embodiments may be included in any other embodiment described herein.

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[0349] The entire contents of each reference are incorporated herein by reference.

Claims

1. A photonic integrated circuit waveguide amplifier (1), include: - at least one embedded encapsulating material or layer (3), and - at least one rare earth ion implanted silicon nitride material or layer (5) embedded in said at least one embedded cladding material or layer (3), said at least one rare earth ion implanted silicon nitride material or layer (5) defining a waveguide core (WC) enclosed by said at least one embedded cladding material or layer (3).

2. The photonic integrated circuit waveguide amplifier (1) according to claim 1, in, The implanted rare earth ions (7) consist of erbium, ytterbium or thulium; or include at least one of the following: erbium, ytterbium, thulium.

3. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, An embedded silicon nitride waveguide core (WC) extends within the at least one embedded cladding material or layer (3) and away from the support surface (SS) to define an outer or upper silicon nitride surface (S1) that is substantially at the same level as an outer or upper surface (S2) defined by the at least one embedded cladding material or layer (3).

4. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one embedded cladding material or layer (3) extends away from the support surface (SS) to define an outer or upper cladding surface (S2) located at a cladding height (CH) from the support surface (SS), and wherein the embedded silicon nitride waveguide core (WC) extends within the at least one embedded cladding material or layer (3) and away from the support surface (SS) to define an outer or upper silicon nitride surface (S1) located at a height level (LW) having a value between 0.01 times and 1.0 times the cladding height (CH), the height value being measured from the support surface (SS).

5. The photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims 1 to 3, in, An embedded silicon nitride waveguide core (WC) fills a recess or depression (9) of the at least one embedded cladding material or layer (3) to define an outer or upper silicon nitride surface (S1) that is substantially at the same level as an outer or upper surface (S2) defined by the at least one embedded cladding material or layer (3).

6. A photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims 1 to 3 or claim 5, in, The at least one embedded cladding material or layer (3) defines at least one recess or depression (9) having a recess height (HR), and the embedded silicon nitride waveguide core (WC) fills the at least one recess or depression (9) to define an outer or upper silicon nitride surface (S1) located at a height level (LW) having a value between 0.8 and 1.1 times the recess height (HR), the height value being measured from a floor (FL) of the recess (9).

7. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, A waveguide core (WC) enclosed by the at least one embedded cladding material or layer is configured to propagate amplified light in an elongated light propagation direction (PD) of the waveguide amplifier (1).

8. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines an active material or active layer of the waveguide amplifier (1), or an optical gain medium of the waveguide amplifier (1).

9. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) includes an outer or upper silicon nitride surface (S1) that is not in direct contact with the cladding material or layer (3), and the outer or upper silicon nitride surface is arched or protrudes outwardly away from the cladding material or layer (3).

10. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one embedded cladding material or layer (3) defines or includes at least one support structure (SP) in contact with the upper and lower halves of the embedded silicon nitride waveguide core (WC), wherein the at least one support structure (SP) extends laterally from the upper and lower halves of the embedded silicon nitride waveguide core (WC) and extends therefrom a distance (LD) greater than 0.25 times the cross-sectional width (W) of the embedded silicon nitride waveguide core (WC).

11. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines an inwardly tapered cross-sectional structure, the cross-sectional structure extending from an outer or upper silicon nitride surface (S1) and inside the cladding material or layer (3) and in a cross-sectional direction perpendicular to the light elongated propagation direction (PD), the cross-sectional structure tapering from the outer or upper silicon nitride surface (S1) to a reduced width inside the cladding material or layer (3).

12. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines an inwardly tapered cross-sectional structure along the entire length of the waveguide amplifier (1) extending in the elongated light propagation direction (PD).

13. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines an inner cross-sectional width (W I ) and outer section width (W o ), wherein the inner cross-sectional width (W I ) is shorter than the outer section width (W o ).

14. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The inner section width (W I ) is greater than the outer cross-sectional width (W o ) is between 2.5% and 20% shorter, or shorter than the outer section width (W o ) is between 5% and 15% shorter, or shorter than the outer section width (W o ) is between 5% and 10% shorter.

15. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines or includes a first outwardly diverging lateral sidewall and a second outwardly diverging lateral sidewall (SW1A, SW2A), and the at least one embedded cladding material or layer (3) defines or includes a first outwardly diverging lateral sidewall and a second outwardly diverging lateral sidewall (SW1B, SW2B), wherein the first outwardly diverging lateral sidewall and the second outwardly diverging lateral sidewall (SW1A, SW2A) of the at least one embedded cladding material or layer (3) respectively mechanically support the first outwardly diverging lateral sidewall and the second outwardly diverging lateral sidewall (SW1A, SW2A) of the at least one rare earth ion implanted silicon nitride material or layer (5).

16. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The first outwardly divergent lateral sidewall and the second outwardly divergent lateral sidewall (SW1B, SW2B) of the at least one embedded cladding material or layer (3) simultaneously diverge from and directly contact the first outwardly divergent lateral sidewall and the second outwardly divergent lateral sidewall (SW1A, SW2A) of the at least one rare earth ion implanted silicon nitride material or layer (5).

17. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines or includes at least one outwardly divergent lateral sidewall (SW1A, SW2A), and the at least one outwardly divergent lateral sidewall defines an inclination angle (α, β) relative to a bottom plate (FL) of the encapsulating material or layer (3), and the inclination angle (α, β) is greater than or equal to 92° and less than or equal to 100°.

18. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines or includes a base (BS), and the at least one embedded cladding material or layer (3) defines or includes a bottom plate (FL), and the base (BS) is in direct contact with the bottom plate (FL) of the cladding material or layer (3) to mechanically support the base (BS).

19. A photonic integrated circuit waveguide amplifier (1) according to the preceding claim, further comprising at least one passive or non-amplifying component (15) comprising an embedded non-ion-implanted silicon nitride material or layer (5A) connected to the embedded rare earth ion-implanted silicon nitride material or layer (5), the passive or non-amplifying component (15) having a fraction W denoted as the embedded non-ion-implanted silicon nitride material or layer (5A) o / W I The width ratio of the silicon nitride material or layer (5) is less than the width ratio of the embedded rare earth ion implanted silicon nitride material or layer (5).

20. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The inclination angle (α) of the lateral side walls (SW1A, SW2A) of the embedded non-ion-implanted silicon nitride material or layer (5A) of the passive or non-amplifying component (15) is smaller than the inclination angle of the lateral side walls (SW1A, SW2A) of the embedded rare earth ion-implanted silicon nitride material or layer (5), and the inclination angle (α) is measured relative to the bottom plate (FL) of the embedded cladding material or layer (3).

21. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one embedded cladding material or layer (3) defines an optically passive waveguide region or portion of the waveguide amplifier (1).

22. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The implanted rare earth ions (7) are located at least an intermediate distance inside the at least one rare earth ion implanted silicon nitride material or layer (5).

23. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) is configured or dimensioned to support a substantially transverse electric (TE) optical waveguide mode in a cross-sectional direction of the waveguide amplifier (1).

24. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The implanted rare earth ions (7) are located in the at least one rare earth ion implanted silicon nitride material or layer (5) to spatially overlap with the fundamental transverse electric (TE) optical waveguide mode.

25. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The spatial overlap is at least 25%, or at least 40%, or at least 50%, or at least 60%.

26. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, At least 85%, or at least 90%, or at least 95% of the implanted rare earth ions (7) are located in the at least one rare earth ion implanted silicon nitride material or layer (5) to be optically active in amplification.

27. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The rare earth ion implantation concentration of the at least one rare earth ion implanted silicon nitride material or layer is 0.1×10 20 cm -3 and 3.5×10 20 cm -3 between.

28. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) carries between 0.1 atomic percent and 0.3 atomic percent rare earth atoms.

29. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) and the at least one embedded cladding material or layer (3) extend longitudinally along the light propagation direction (PD) for a distance between 0.1 m and 0.6 m.

30. Photonic integrated circuit waveguide amplifier (1) according to the preceding claim, in, The at least one rare earth ion implanted silicon nitride material or layer (5) and the at least one embedded cladding material or layer (3) extend in a substantially straight and / or curved manner.

31. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) and the at least one embedded cladding material or layer (3) extend longitudinally along the light propagation direction (PD) to define a spiral and / or coil arrangement.

32. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) comprises a light input coupling interface or port (17A) and / or an amplified light output coupling interface or port (17B).

33. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) defines a substantially planar optical waveguide core.

34. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one rare earth ion implanted silicon nitride material or layer (5) and the at least one embedded cladding material or layer (3) extend in an elongated direction (PD) to propagate light along the elongated direction.

35. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one embedded cladding material or layer (3) defines or includes at least one elongated recess or depression (9) extending in the light propagation direction (PD), and the at least one rare earth ion implanted silicon nitride material or layer (5) is embedded in the elongated recess (9).

36. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one embedded cladding material or layer (3) defines or includes a stress relief recess structure (21), the stress relief recess structure including a plurality of notches (23) formed in the at least one embedded cladding material or layer (3).

37. A photonic integrated circuit waveguide amplifier (1) according to any of the preceding claims, comprising at least one cladding / passivation material or layer (FC), which is superimposed on at least one embedded rare earth ion implanted silicon nitride material or layer (5) and at least one embedded cladding material or layer (3).

38. Photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, in, The at least one cladding / passivation material or layer (FC) and / or the at least one embedded cladding material or layer (3) are optically passive elements or components of the waveguide amplifier (1).

39. The photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims 37 to 38, in, The at least one cladding / passivation material or layer (FC) and / or the at least one embedded cladding material or layer (3) comprises silicon dioxide (SiO 2 ) or consist of silicon dioxide.

40. A photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims, further comprising a support layer or substrate (19) supporting the at least one embedded cladding material or layer (3) and the at least one embedded rare earth ion implanted silicon nitride material or layer (5).

41. A photonic integrated circuit waveguide amplifier (1) according to any one of the preceding claims 1 to 36 or claim 40, in, The at least one rare earth ion implanted silicon nitride material or layer (5) comprises an outer or upper silicon nitride surface (S1) free of embedded encapsulating material.

42. A photonic integrated circuit (PIC) comprising at least one PIC waveguide amplifier (1) according to any one of the preceding claims.

43. A photonic integrated circuit (PIC) according to the preceding claim, further comprising at least one integrated silicon nitride component or device optically coupled to or comprising at least one photonic integrated circuit waveguide amplifier (1).

44. Photonic integrated circuit (PIC) according to the preceding claim, in, The at least one integrated silicon nitride component or device comprises or consists of a soliton microcomb generator, an electro-optic modulator, or a laser source.

45. Photonic integrated circuit (PIC) according to the preceding claim, in, The electro-optic modulator includes a lithium niobate electro-optic modulator or consists of a lithium niobate electro-optic modulator.

46. ​​An integrated optical device or an integrated laser source comprising at least one photonic integrated circuit waveguide amplifier (1) according to any of the preceding claims, the at least one photonic integrated circuit waveguide amplifier acting as a gain medium.

47. An integrated optical device or an integrated laser source according to the preceding claim, in, The integrated optical device or integrated laser source includes a soliton microcomb, a rare earth CW laser, a femtosecond mode-locked laser or a cavity soliton laser, or is composed of a soliton microcomb, a rare earth CW laser, a femtosecond mode-locked laser or a cavity soliton laser.

48. A method for manufacturing a photonic integrated circuit waveguide amplifier, include: - providing at least one embedded cladding material or layer (3), said embedded cladding material or layer comprising at least one silicon nitride material or layer (5A) embedded or buried within said at least one embedded cladding material or layer (3); and - performing rare earth ion implantation by ion irradiating at least one surface (S1A) of at least one embedded or buried silicon nitride material or layer (5A) to form at least one rare earth ion implanted silicon nitride material or layer (5) embedded or buried in the at least one embedded cladding material or layer (3), the at least one silicon nitride material or layer (5) defining a waveguide core (WC).

49. The method according to the preceding claim, in, Rare earth ion implantation is performed by ion irradiating at least one directly exposed or uncovered surface (S1A) of the at least one embedded or buried silicon nitride material or layer (5A) to form the at least one rare earth ion implanted silicon nitride material or layer (5) embedded or buried in the at least one embedded encapsulating material or layer (3).

50. The method according to claim 48, in, Rare earth ion implantation is performed by ion irradiating at least one coating material or layer (FC) provided or deposited on at least one surface (S1A) of the at least one embedded or buried silicon nitride material or layer (5A) to form the at least one rare earth ion implanted silicon nitride material or layer (5) embedded or buried in the at least one embedded coating material or layer (3).

51. The method according to claim 50, in, Said at least one cladding material or layer (FC) is provided or deposited directly on said at least one surface (S1A) of said at least one embedded or buried silicon nitride material or layer (5A).

52. The method according to any one of the preceding claims 48 to 51, in, The embedded silicon nitride (5A) provided is within the at least one embedded encapsulating material or layer (3) and extends away from the supporting surface (SS) to define an outer or upper silicon nitride surface (S1A), which is substantially at the same level as the outer or upper surface (S2A) defined by the at least one embedded encapsulating material or layer (3).

53. The method according to any one of the preceding claims 48 to 52, in, The at least one embedded cladding material or layer (3) extends away from the support surface (SS) to define an outer or upper cladding surface (S2A) located at a cladding height (CH) from the support surface (SS), and wherein the embedded silicon nitride (5A) extends within the at least one embedded cladding material or layer (3) and away from the support surface (SS) to define an outer or upper silicon nitride surface (S1A) located at a height level (LW) having a value between 0.01 times and 1.0 times the cladding height (CH), the height value being measured from the support surface (SS).

54. The method according to any one of the preceding claims 48 to 51, in, The embedded silicon nitride (5A) provided fills a recess or depression (9) of the at least one embedded encapsulating material or layer (3) to define an upper or outer silicon nitride surface (S1A) which is substantially at the same level as an outer or upper surface (S2A) defined by the at least one embedded encapsulating material or layer (3).

55. The method according to any one of the preceding claims 48 to 51 or claim 54, in, The at least one embedded encapsulating material or layer (3) defines at least one recess or depression (9) having a recess height (HR), and the provided embedded silicon nitride material or layer (5A) fills the at least one recess or depression (9) to define an outer or upper silicon nitride surface (S1A) located at a height level (LW1), the value of the height level (LW1) being between 0.8 times and 1.1 times the recess height (HR), the height value being measured from the floor (FL) of the recess (9).

56. The method according to any one of the preceding claims 48 to 55 further comprises annealing the at least one rare earth ion implanted silicon nitride material or layer (5) embedded or buried in the at least one embedding cladding material or layer (3) to reduce injection defect light loss.

57. The method according to the preceding claim, in, Annealing is performed at temperatures between 800° and 1250°C.

58. The method according to any one of the preceding claims 56 to 57, in, Annealing is performed in an oxygen environment.

59. The method according to any one of the preceding claims 56 to 58, in, The annealing is carried out for a duration between 30 and 90 minutes.

60. The method according to any one of claims 48 to 59, in, The rare earth ion (7) includes erbium, ytterbium or thulium, or consists of erbium, ytterbium or thulium.

61. The method according to any one of the preceding claims 48 to 60, in, The rare earth ion implantation is performed by accelerating rare earth ions (7) toward the at least one surface (S1A) to provide an ion implantation flux to the at least one surface, thereby implanting ions within at least one embedded or buried silicon nitride material or layer (5A).

62. The method according to the preceding claim, in, The rare earth ion implantation is performed under a plurality of different rare earth ion acceleration values ​​to define an ion implantation concentration spatial distribution that spatially overlaps with an optical waveguide mode of the waveguide amplifier (1).

63. The method according to any one of the preceding claims 48 to 62, in, The rare earth ion implantation is performed at rare earth ion acceleration values ​​between 0.1 MeV and 2.5 MeV.

62. The method according to any one of claims 48 to 61, wherein the rare earth ion implantation is performed while ensuring that the rare earth ion flux is 1.5×10 15 cm -2 and 5×10 15 cm -2 The experiment was carried out at rare earth ion acceleration values ​​between 20 and 25 °C.

64. The method according to any one of the preceding claims 48 to 63, in, The rare earth ion implantation is performed to provide a 0.1×10 20 cm -3 and 3.5×10 20 cm -3 The rare earth ion implantation concentration is between .

65. The method according to any one of the preceding claims 48 to 64, in, The rare earth ion implantation is performed to provide at least one rare earth ion implanted silicon nitride material or layer, the at least one rare earth ion implanted silicon nitride material or layer bearing between 0.1 atomic percent and 0.3 atomic percent rare earth atoms.

66. The method according to any one of the preceding claims 48 to 65, in, Rare earth ion implantation is performed as a wafer-level implantation process.

67. The method according to any one of the preceding claims 48 to 66, in, After rare earth ion implantation, at least one cladding / passivation material or layer (FC) is superimposed on the embedded at least one rare earth ion implanted silicon nitride material or layer (5) and the at least one embedded cladding material or layer (3).

68. A method according to any one of the preceding claims 48 to 67, comprising performing selective masking during rare earth ion implantation to form: (i) at least one first portion, the at least one first portion comprising at least one rare earth ion implanted silicon nitride material or layer (5) embedded or buried in the at least one embedded encapsulating material or layer (3), and (ii) at least one second portion, the at least one second portion comprising at least one non-implanted silicon nitride material or layer (5A) embedded or buried in the at least one embedded encapsulating material or layer (3).

69. The method according to the preceding claim, in, The silicon nitride material or layer (5) embedded or buried in the at least one embedded cladding material or layer (3) of the first portion is optically coupled with the silicon nitride material or layer (5A) embedded or buried in the at least one embedded cladding material or layer (3) of the second portion.

70. The method according to any one of the preceding claims 48 to 69, in, Prior to rare earth ion implantation, annealing is performed to remove hydrogen from the at least one embedded cladding material or layer (3) and / or the at least one silicon nitride material or layer (5A) embedded in the at least one embedded cladding material or layer (3).

71. The method according to any one of the preceding claims 48 to 70, in, The at least one embedded cladding material or layer (3) defines or includes a stress relief recessed structure (21), the stress relief recessed structure including a plurality of notches or recesses (23) formed in the at least one embedded cladding material or layer (3).

72. The method according to any one of the preceding claims 48 to 71, in, The step of providing at least one embedded cladding material or layer (3) comprising at least one silicon nitride material or layer (5A) embedded or buried in at least one embedded cladding material or layer (3) comprises: - providing at least one cladding material or layer (25) for embedding at least one waveguide core (WC) and comprising at least one waveguide recess (9) for receiving silicon nitride waveguide material and a stress relief recess structure (21), and - depositing silicon nitride waveguide material onto at least one cladding material or layer (25) and into the at least one waveguide recess (9) and the stress relief recess structure (21).

73. The method of claim 72, further comprising the step of planarizing the deposited silicon nitride waveguide material.

74. The method according to claim 72 or 73 further comprises the step of applying thermal energy to the at least one cladding material or layer (3) prior to depositing the silicon nitride waveguide material to allow reflow of the exposed surface of at least one waveguide recess, thereby reducing optical losses of the waveguide amplifier (1).

75. The method according to any one of claims 72 to 74, in, The stress relief recess structure (23) comprises a plurality of notches or depressions (23) formed in the at least one cladding material or layer (25).

76. The method according to the preceding claim, in, The depth of the recess (23) among the plurality of recesses of the stress relief recess structure (21) measured from the outer surface of the at least one cladding material or layer (25) is substantially equal to or greater than the depth of the at least one waveguide recess (9) measured from the outer surface of the at least one cladding material or layer (25).

77. The method according to any one of the preceding claims 75 to 76, in, The stress relief recess structure (21) encloses the at least one waveguide recess (9).

78. The method according to any one of claims 75 to 77, in, The at least one cladding material or layer (25) further comprises a recess-free region between the stress relief recess structure (21) and the waveguide recess (9).

79. The method according to the preceding claim, in, The non-recessed area separates the stress relief recess structure (21) and the at least one waveguide recess (9) by a distance D, wherein 50 μm <D<2μm。 80. The method according to any one of claims 75 to 79, in, The at least one waveguide recess (9) and the stress relief recess structure (21) are located in the same plane.

81. The method according to any one of claims 75 to 80, in, The plurality of recesses (23) are regularly or irregularly spaced apart from one another on the at least one covering material or layer (25).

82. The method according to any one of claims 75 to 81, in, The plurality of notches (23) form at least one repeating notch pattern on the at least one cladding material or layer (25).

83. The method according to any one of claims 75 to 82, in, The plurality of recesses (23) form a tessellated structure or layout on the at least one cladding material or layer (25).

84. The method according to any one of claims 72 to 83, further comprising: The following steps are involved: A hard mask layer including at least one waveguide recess and a stress relief recess structure is provided, and the at least one waveguide recess (9) and the stress relief recess structure (21) are formed in the at least one cladding material or layer (25) using the hard mask layer and dry plasma etching or wet etching.

85. The method according to any one of claims 73 to 84, in, Planarization of the deposited silicon nitride waveguide material is performed using mechanical planarization and chemical planarization.

86. The method according to any one of claims 48 to 85, in, At least one cladding material or layer (25) is provided or deposited on at least one embedded or buried silicon nitride material or layer (5A), at least one embedded cladding material or layer (3) and / or at least one cladding material or layer (FC) comprises silicon dioxide (SiO 2 ) or consist of silicon dioxide.

87. The method according to any one of claims 84 to 86, in, The hard mask layer includes amorphous silicon (aSi).

88. A photonic integrated circuit waveguide amplifier (1) manufactured according to the method of any one of claims 48 to 87.

89. A device comprising at least one photonic integrated circuit waveguide amplifier (1) according to the preceding claim.

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