Patent Publication Number: US-2023146862-A1

Title: Photonic waveguide structure

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application No. 63/263,595, entitled “PHOTONIC TRANSMISSION STRUCTURE,” filed on Nov. 5, 2021, the content of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     Integrated photonics is a branch of photonics in which waveguides and other photonic devices are fabricated as an integrated structure on a substrate surface. For example, a photonic integrated circuit (PIC) may use semiconductor-grade materials (e.g., silicon, indium phosphide, dielectrics such as silicon dioxide or silicon nitride, and/or the like) as a platform to integrate active and passive photonic circuits with electronic components on a single chip. As a result of integration, complex photonic circuits can process and transmit light (e.g., photons) in similar ways to how electronic integrated circuits process and transmit electrons. 
     SUMMARY 
     In some implementations, a photonic waveguide structure includes at least four photonic waveguide layers disposed in a stack configuration, wherein a first photonic waveguide layer, of the at least four photonic waveguide layers, includes a first active structure associated with a Kerr coefficient that satisfies a Kerr coefficient threshold; and a second photonic waveguide layer, of the at least four photonic waveguide layers, includes a second active structure associated with a propagation loss parameter that satisfies a propagation loss parameter threshold. 
     In some implementations, an optical device includes a photonic waveguide structure that includes at least four photonic waveguide layers disposed in a stack configuration, wherein a first photonic waveguide layer, of the at least four photonic waveguide layers, includes a first active structure associated with a Kerr coefficient that satisfies a Kerr coefficient threshold; and a second photonic waveguide layer, of the at least four photonic waveguide layers, includes a second active structure associated with a propagation loss parameter that satisfies a propagation loss parameter threshold. 
     In some implementations, a photonic waveguide structure includes at least four photonic waveguide layers disposed in a stack configuration, wherein a first photonic waveguide layer, of the at least four photonic waveguide layers, includes a first active structure associated with one or more particular nonlinear optical characteristics; and a second photonic waveguide layer, of the at least four photonic waveguide layers, includes a second active structure associated with one or more particular linear optical characteristics. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an example optical device described herein. 
         FIG.  2    shows a table of some optical characteristics of example materials of an active structure of a photonic waveguide layer described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description of example implementations refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. 
     When a PIC is formed, space (e.g., between components) is often limited. For example, components of the PIC are typically created in a single layer on a wafer, which limits a total number of components that can be created on the wafer. As another example, some components in a first layer can comprise materials that are sensitive to high temperatures (e.g., greater than 300 degrees Celsius (C)), and therefore can be damaged when a second layer disposed on the first layer requires a high temperature deposition process. Damage to components of the first layer can affect an optical behavior of the first layer and/or of the PIC. Further, designing a PIC to avoid high temperature processing issues affects an order and/or number of material combinations that can be used in the PIC. 
     Some implementations described herein provide a photonic waveguide structure (e.g., that is a type of a photonic transmission structure) that vertically integrates a plurality of photonic waveguide layers (e.g., at least a threshold number, such as four, photonic waveguide layers disposed in a stack configuration). In this way, the photonic waveguide structure may be capable of both linear optical operations and nonlinear optical operations. For example, the photonic waveguide structure may include a first photonic waveguide layer that includes a first active structure associated with one or more particular nonlinear optical characteristics (e.g., that permit the photonic waveguide structure to perform one or more nonlinear optical operations), and may include a second photonic waveguide layer that includes a second active structure associated with one or more particular linear optical characteristics (e.g., that permit the photonic waveguide structure to perform one or more linear optical operations). Vertical integration of the plurality of photonic waveguide layers in the photonic waveguide structure allows for integration of multiple materials, within the photonic transmission structure, in any order and in multiple photonic waveguide layers. This enables the photonic waveguide structure to provide linear optical operations and nonlinear optical operations that are not possible with a single-layer PIC. 
     In some implementations, various formation techniques may be used to vertically integrate materials in the photonic waveguide structure. For example, one or more sputtering processes may be used to form the plurality of photonic waveguide layers of the photonic waveguide structure. A processing temperature associated with the one or more sputtering processes may be low (e.g., less than or equal to 300 degrees Celsius (° C.)), and therefore the one or more sputtering processes are less likely to damage the plurality of photonic waveguide layers than would otherwise be possible using conventional deposition processes with high processing temperatures (e.g., greater than 300° C., and typically greater than 500° C.). In this way, a photonic waveguide structure may be formed that could not otherwise be formed using a conventional deposition process (e.g., because of high operating temperatures that would damage at least one of the plurality of photonic waveguide layers in the stack configuration). 
       FIG.  1    is a diagram of an example optical device  100  described herein. An optical device may be, for example, a PIC (e.g., that is capable of one or more linear optical operations and/or one or more nonlinear optical operations) or a similar optical device. The optical device  100  may include a photonic transmission structure, such as a photonic waveguide structure  102  shown in  FIG.  1   , disposed on a substrate  104 . As further shown in  FIG.  1   , the photonic waveguide structure  102  may include a plurality of photonic waveguide layers  106  (shown as photonic waveguide layers  106 - 1  through  106 - 4 ). While implementations described herein are directed to a photonic waveguide structure that includes photonic waveguide layers, contemplated implementations also include any photonic transmission structure that includes photonic transmission layers that can be used in association with linear optics and/or nonlinear optics. 
     The substrate  104  may include a substrate upon which other layers and/or structures shown in  FIG.  1    are formed. The substrate  104  may be a transmissive substrate, such as a glass substrate, a silicon (Si) substrate, or a germanium (Ge) substrate. In some implementations, the substrate  104  may have a refraction index that satisfies (e.g., is less than or equal to) a refraction index threshold. For example, the refraction index threshold may be less than or equal to 1.6. 
     In some implementations, the plurality of photonic waveguide layers  106  may be disposed in a stack configuration (e.g., over the substrate  104 ). For example, the photonic waveguide layer  106 - 1  may be disposed over the substrate  104 , the photonic waveguide layer  106 - 2  may be disposed over the photonic waveguide layer  106 - 1 , the photonic waveguide layer  106 - 3  may be disposed over the photonic waveguide layer  106 - 2 , the photonic waveguide layer  106 - 4  may be disposed over the photonic waveguide layer  106 - 3 , and so on. In this way, the plurality of photonic waveguide layers  106  may be said to be “vertically integrated” (e.g., vertically stacked over the substrate  104 , as shown in  FIG.  1   ). In some implementations, when a photonic waveguide layer  106  is disposed over the substrate  104  or another photonic waveguide layer  106 , the photonic waveguide layer  106  may be directly disposed on the substrate  104  or the other photonic waveguide layer  106 , or, alternatively, may be disposed on one or more other layers or structures that are disposed between the photonic waveguide layer  106  and the substrate  104  or the other photonic waveguide layer  106 . 
     In some implementations, a number (e.g., a quantity) of the plurality of photonic waveguide layers  106  may satisfy a layer number threshold. That is, the number of the plurality of photonic waveguide layers  106  (e.g., that are disposed in the stack configuration) may be greater than or equal to the layer number threshold. The layer number threshold may be greater than or equal to two, three, four, five, and/or six, among other examples. For example, as shown in  FIG.  1   , at least four of the photonic waveguide layers  106  (photonic waveguide layers  106 - 1  through  106 - 4 ) may be disposed in the stack configuration. 
     Each photonic waveguide layer  106  may include an active structure  108  and one or more cladding structures  110 . For example, as shown in  FIG.  1   , the photonic waveguide layer  106 - 1  may include the active structure  108 - 1 , the cladding structure  110 - 1 A, and the cladding structure  110 - 1 B; the photonic waveguide layer  106 - 1  may include the active structure  108 - 2 , the cladding structure  110 - 2 A, and the cladding structure  110 - 2 B; and so on. The active structure  108  may be configured to transmit light (e.g., as a waveguide). The one or more cladding structures  110  may be configured to confine light (e.g., within the active structure  108 ). 
     Within each photonic waveguide layer  106 , the active structure  108  may disposed over a cladding structure  110  of the one or more cladding structures  110 . For example, as shown in  FIG.  1   , the active structure  108 - 1  may be disposed over the cladding structure  110 - 1 A, such that the active structure  108 - 1  is disposed directly on a surface (e.g., a top surface) of the cladding structure  110 - 1 A, or, alternatively, disposed on one or more intervening layers or structures between the active structure  108 - 1  and the cladding structure  110 - 1 A. In some implementations, the active structure  108  may not be disposed over a cladding structure  110  within the photonic waveguide layer  106 . For example, the active structure  108  may be disposed on (e.g., directly on, or, alternatively, indirectly on, via one or more intervening layers or structures) the substrate  104  or another photonic waveguide layer  106  (e.g., upon which the photonic waveguide layer  106  is disposed). For example, in relation to  FIG.  1   , the active structure  108 - 1  may be disposed directly on the substrate  104  (e.g., when the cladding structure  110 - 1 A is not present) and/or the active structure  108 - 2  may be disposed directly on the photonic waveguide layer  106 - 1  (e.g., when the cladding structure  110 - 2 A is not present). 
     The active structure  108  of each photonic waveguide layer  106  may comprise a planar structure that has a width  112  (e.g., shown as widths  112 - 1  through  112 - 4  in  FIG.  1   ), which may be less than or equal to a width  114  of the substrate  104 . In some implementations, each active structure  108  may have a thickness  116  (e.g., shown as thicknesses  116 - 1  through  116 - 4 ). In some implementations, the thickness  116  may be within a thickness range from 100 nanometers (nm) to 2000 nm (e.g., greater than or equal to 100 nm and less than or equal to 2000 nm). Additionally, or alternatively, the thickness  116  may satisfy (e.g., may be greater than or equal to) a thickness threshold. For example, each of the thicknesses  116 - 1  through  116 - 4  shown in  FIG.  1    may be greater than or equal to the thickness threshold. The thickness threshold may be greater than or equal to 500 nm, 600 nm, 700 nm, 750 nm, 850 nm, and/or 1000 nm, among other examples. In some implementations, the thickness  116  may be substantially uniform. For example, the thickness  116  may vary less than a percentage threshold across a surface of the active structure  108  (e.g., a top surface of the active structure  108 ). For example, each of the thicknesses  116 - 1  through  116 - 4  shown in  FIG.  1    may vary less than the percentage threshold. The percentage threshold may be less than or equal to 1%, 2%, 3%, and/or 5%, among other examples. 
     While  FIG.  1    shows the respective widths  112  (e.g., widths  112 - 1  through  112 - 4 ) of the active structures  108  (e.g., active structures  108 - 1  through  108 - 4 ) as the same, or similar, to each other, and the respective thicknesses  116  (e.g., thicknesses  116 - 1  through  116 - 4 ) of the active structures  108 , as the same, or similar, to each other, each active structure  108  may have a particular width  112  and a particular thickness  116  (e.g., that is the same as, or different than, that of another active structure  108 ). For example, the active structure  108 - 3  may have a width  112 - 3  that is the same as (e.g., equal to, within a tolerance which may be less than or equal to 1 nm, 2 nm, 3 nm, 5 nm, and/or 10 nm) the width  112 - 4  of the active structure  108 - 4 , and different than the widths  112 - 1  and  112 - 2  of the active structures  108 - 1  and  108 - 2 . As another example, the active structure  108 - 3  may have a thickness  116 - 3  that is different than the thicknesses  116 - 1 ,  116 - 2 , and  116 - 4  of the active structures  108 - 1 ,  108 - 2 , and  108 - 4 . 
     Within each photonic waveguide layer  106 , a cladding structure  110 , of the one or more cladding structures  110 , may be disposed over the active structure  108 . For example, as shown in  FIG.  1   , the cladding structure  110 - 1 B may be disposed over the active structure  108 - 1 , such that the cladding structure  110 - 1 B is disposed directly on a surface (e.g., a top surface) of the active structure  108 - 1 , or, alternatively, disposed on one or more intervening layers or structures between the cladding structure  110 - 1 B and the active structure  108 - 1 . In some implementations, such as when the width  112  of the active structure  108  is less than the width  114  of the substrate  104 , the cladding structure  110  also may be disposed on one or more portions of a surface of another cladding structure  110  over which the active structure  108  is disposed (e.g., on one or more portions of a top surface of the other cladding structure  110 ). For example, as shown in  FIG.  1   , the cladding structure  110 - 1 B may be disposed on one or more portions of a surface of the cladding structure  110 - 1 A. Alternatively, when the photonic waveguide layer  106  does not include another cladding structure  110 , the cladding structure  110  may be disposed on one or more portions of a surface of the substrate  104  (e.g., a top surface of the substrate  104 ) or one or more portions of a surface of another photonic waveguide layer  106 . For example, in relation to  FIG.  1   , the cladding structure  110 - 1 B may be disposed directly on one or more portions of the substrate  104  (e.g., when the cladding structure  110 - 1 A is not present) and/or the cladding structure  110 - 2 B may be disposed directly on the photonic waveguide layer  106 - 1  (e.g., when the cladding structure  110 - 2 A is not present). 
     Each cladding structure  110  may comprise at least an oxide. For example, each cladding structure  110  may include an oxide material (e.g., a silicon dioxide (SiO 2 ) material) and, in some implementations, one or more other elements or materials (e.g., silicon, oxygen, and/or other materials). Additionally, or alternatively, each cladding structure  110  may comprise at least a polymer material (e.g., at least a siloxane polymer material or another polymer material) or at least an air cladding, among other examples. 
     Each active structure  108  may comprise a material  118 . For example, as shown in  FIG.  1   , the active structure  108 - 1  may comprise a material  118 - 1 , the active structure  108 - 2  may comprise a material  118 - 2 , and so on. In some implementations, each material  118  may comprise at least a non-alkali, oxide solution that includes a cation that is niobium. The non-alkali, oxide solution that includes a cation that is niobium may include at least one of a non-alkali, binary oxide solution that includes a cation that is niobium; a non-alkali, ternary oxide solution that includes a cation that is niobium; a non-alkali, quaternary oxide solution that includes a cation that is niobium; or a non-alkali, quinary oxide solution that includes a cation that is niobium (and so on). For example, the material  118  may include at least one of a niobium tantalum oxide solution, a niobium titanium oxide solution, or a niobium tantalum titanium oxide solution. As another example, the material  118  may include at least one of a niobium aluminum oxide solution, a niobium strontium oxide solution, a niobium aluminum strontium oxide solution, a niobium tantalum aluminum oxide solution, a niobium titanium aluminum oxide solution, a niobium tantalum strontium solution, a niobium titanium strontium oxide solution, a niobium titanium tantalum aluminum oxide solution, a niobium titanium tantalum strontium oxide solution, a niobium titanium aluminum strontium oxide solution, a niobium tantalum aluminum strontium oxide solution, or a niobium titanium tantalum aluminum strontium oxide solution. In some implementations, the material  118  may comprise at least one of a non-alkali, oxide solution that includes a cation that is niobium, a deuterated silicon oxynitride (SiON:D) material, a silicon nitride (Si 3 N 4 ) material, an ultra-silicon-rich nitride (USRN:Si 7 N 3 ) material, a tantalum pentoxide (Ta 2 O 5 ) material, an arsenic trisulfide (As 2 S 3 ) material, a titanium dioxide (TiO 2 ) material, an aluminum gallium arsenide (AlGaAs) material, a crystalline silicon (c-Si) material, an amorphous silicon (a-Si) material, a hydrogenated amorphous silicon (a-Si:H) material, a nitride-based material, an oxide-based material, a metal material, or a semiconductor material, among other examples. 
     As indicated by the different patterning and shading of the materials  118  shown in  FIG.  1   , each material  118  may be different than another material  118  in the photonic waveguide structure  102  (e.g., in terms of material composition). For example, the material  118 - 1  may be different than at least one of the materials  118 - 2 ,  118 - 3 ,  118 - 4 . In some implementations, a material  118  may be the same as another material  118  in the photonic waveguide structure  102  (e.g., in terms of material composition). For example, the material  118 - 1  may be the same as at least one of the materials  118 - 2 ,  118 - 3 , or  118 - 4 . 
     In some implementations, a material  118  of an active structure  108  may have a plurality of optical characteristics, such as one or more particular nonlinear optical characteristics, one or more particular linear optical characteristics, a particular refractive index, and/or a particular spectral range (e.g., that the material  118  may be configured to transmit), among other examples. As further described herein,  FIG.  2    shows a table of some optical characteristics, of the plurality of optical characteristics, of example materials  118  of an active structure  108 . 
     The one or more particular nonlinear optical characteristics of a material  118  of an active structure  108  may include, for example, a Kerr coefficient (also referred as n 2 ) that satisfies a Kerr coefficient threshold. That is, the material  118  may have a Kerr coefficient that is greater than or equal to the Kerr coefficient threshold. The Kerr coefficient threshold may be greater than or equal to 5.0×10 −19  meters squared per Watt 
     
       
         
           
             
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     among other examples. In some implementations, the material  118  may have a Kerr coefficient that is greater than or equal to 
     
       
         
           
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     Additionally, or alternatively, one or more particular nonlinear optical characteristics of the material  118  may include, for example, an effective nonlinear parameter (also referred as γ) that satisfies an effective nonlinear parameter threshold. That is, the material  118  may have an effective nonlinear parameter that is greater than or equal to the effective nonlinear parameter threshold. The effective nonlinear parameter threshold may be greater than or equal to 1 radian per Watt-meter 
     
       
         
           
             
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     among other examples. In some implementations, the material  118  may have an effective nonlinear parameter that is greater than or equal to 
     
       
         
           
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     The one or more particular linear optical characteristics of the material  118  may include, for example, a propagation loss parameter (also referred to as a) that satisfies a propagation loss parameter threshold. That is, the material  118  may have a propagation loss parameter that is less than or equal to the propagation loss parameter threshold. The propagation loss parameter threshold may be less than or equal to 0.08 decibels per centimeter 
     
       
         
           
             
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     and/or 0.55 dBcm, among other examples. A practical complexity of a photonic waveguide structure (e.g., in terms of including multiple layers that can support different linear and nonlinear optical operations) is limited when a material of an active structure of the photonic waveguide structure has a propagation loss parameter that is greater than the propagation loss parameter threshold. Accordingly, including a material  118  that has a propagation loss parameter that is less than or equal to the propagation loss parameter threshold in the active structure  108  of the photonic waveguide layer  106  enables the photonic waveguide structure  102  to have an increased practical complexity. This therefore enables the photonic waveguide structure  102  to be included in an optical device  100 , in which a photonic waveguide structure with less complexity may not be preferred. In some implementations, the material  118  may have a propagation loss parameter that is greater than or equal to 
     
       
         
           
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     and less than or equal to 
     
       
         
           
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     In some implementations, the particular refractive index (also referred to as n) of the material  118  of the active structure  108  may satisfy a refractive index threshold. That is, the material  118  may have a refractive index that is greater than or equal to the refractive index threshold. The refractive index threshold may be greater than or equal to (e.g., for light with a wavelength of 1550 nm) 1.99, 2.00, 2.02, 2.04, 2.07, 2.09, 2.12, and/or 2.17, among other examples. In some implementations, the particular spectral range of the material  118  may be a range of light wavelengths that the material  118  may transmit (e.g., the material  118  may be transparent to, or may provide a transparency window for, light associated with the spectral range). The spectral range may be associated with ultraviolet light through infrared light. For example, the spectral range may include light associated with wavelengths from 350 nm to 5000 nm, from 420 nm to 1600 nm, or another range. As another example, the spectral range may include one or more subranges of light associated with ultraviolet light through infrared light, such as one or more portions of ultraviolet light (e.g., one or more portions of light associated with wavelengths from 100 nm to 399 nm), one or more portions of visible light (e.g., one or more portions of light associated with wavelengths from 400 nm to 699 nm), and/or one or more portions of infrared light (e.g., one or more portions of light associated with wavelengths from 700 nm to 5000 nm). 
     In some implementations, the photonic waveguide structure  102  may include a first photonic waveguide layer  106 , of the plurality of photonic waveguide layers  106 , that includes a first active structure  108  associated with one or more particular nonlinear optical characteristics (e.g., a first material  118  of the first active structure  108  may have the one or more particular nonlinear optical characteristics). For example, the first active structure  108  may be associated with an effective non-linear parameter that satisfies the effective nonlinear parameter threshold (described above) and/or may be associated with a Kerr coefficient that satisfies the Kerr coefficient threshold (described above). Additionally, or alternatively, the photonic waveguide structure  102  may include a second photonic waveguide layer  106 , of the plurality of photonic waveguide layers  106 , that includes a second active structure  108  associated with one or more particular linear optical characteristics (e.g., a second material  118  of the second active structure  108  may have the one or more particular linear optical characteristics). For example, the second active structure  108  may be associated with a propagation loss parameter that satisfies the propagation loss parameter threshold (described above). Accordingly, the first material  118  may be different than the second material  118 . For example, the first material  118  may comprise at least a tantalum pentoxide material and the second material  118  may comprise at least a silicon nitride material. In this way, a material  118  that is included in the first active structure  108  may not be included in the second active structure  108  (and vice versa). Alternatively, the first material  118  may be the same as, or similar to, the second material  118 . For example, each of the first material  118  and the second material  118  may comprise at least a non-alkali, oxide solution that includes a cation that is niobium. In this way, a material  118  that is included in the first active structure  108  may be included in the second active structure  108 . 
     In some implementations, the first photonic waveguide layer  106  may be disposed over the second photonic waveguide layer  106  in the stack configuration (e.g., over the substrate  104 ). For example, the first photonic waveguide layer  106  may be the photonic waveguide layer  106 - 3  and the second photonic waveguide layer  106  may be the photonic waveguide layer  106 - 1  or the photonic waveguide layer  106 - 2 . Alternatively, the second photonic waveguide layer  106  may be disposed over the first photonic waveguide layer  106  in the stack configuration (e.g., over the substrate  104 ). For example, the first photonic waveguide layer  106  may be the photonic waveguide layer  106 - 1  and the second photonic waveguide layer  106  may be the photonic waveguide layer  106 - 2 , the photonic waveguide layer  106 - 3 , or the photonic waveguide layer  106 - 4 . 
     In some implementations, the photonic waveguide structure  102  may be formed using one or more sputtering processes, such as one or more magnetron sputtering processes, one or more ion-beam sputtering processes, one or more reactive sputtering processes, one or more alternating-current (AC) sputtering processes, and/or one or more direct-current (DC) sputtering processes. For example, the photonic waveguide layer  106 - 1  may be formed over the substrate using a first set of one or more sputtering processes, the photonic waveguide layer  106 - 2  may be formed over the substrate using a second set of one or more sputtering processes, the photonic waveguide layer  106 - 3  may be formed over the substrate using a third set of one or more sputtering processes, and so on. A processing temperature associated with the one or more sputtering processes may satisfy (e.g., may be less than or equal to) a processing temperature threshold. The processing temperature threshold may be less than or equal to 200° C., 250° C., 275° C., and/or 300° C., among other examples. In some implementations, the processing temperature threshold may be less than a temperature associated with affecting the optical characteristics of the active structures  108  of the plurality of photonic waveguide layers  106  (e.g., a temperature that may damage at least one of the active structures  108 ). In this way, the one or more sputtering processes may be considered to be “low temperature” processes. 
     Accordingly, at least one of the active structures  108  may comprise an amorphous structure (e.g., because the active structures  108  of the plurality of photonic waveguide layers  106  are formed using the one or more sputtering processes). For example, an active structure  108  may comprise a material  118  that is formed by the one or more sputtering processes to have a non-uniform and/or non-crystalline structure. This may permit the material  118  to have the one or more particular nonlinear optical characteristics described herein. 
     As indicated above,  FIG.  1    is provided as an example. Other examples may differ from what is described with regard to  FIG.  1   . 
       FIG.  2    shows a table  200  of some optical characteristics of example materials  118  of an active structure  108  of a photonic waveguide layer  106  described herein. As shown in  FIG.  2   , the table  200  includes entries for a deuterated silicon oxynitride (SiON:D) material, a silicon nitride (Si 3 N 4 ) material, an ultra-silicon-rich nitride (USRN:Si 7 N 3 ) material, a tantalum pentoxide (Ta 2 O 5 ) material, a non-alkali, oxide solution that includes a cation that is niobium (e.g., that is represented by a niobium tantalum oxide (NbTaOx) solution), an arsenic trisulfide (As 2 S 3 ) material, a titanium dioxide (TiO 2 ) material, an aluminum gallium arsenide (AlGaAs) material, a crystalline silicon (c-Si) material, and a hydrogenated amorphous silicon (a-Si:H) material. Each entry indicates a refractive index (also referred to as n, for light with a wavelength of 1550 nm), a propagation loss parameter (also referred to as α), a Kerr coefficient (also referred as n 2 ), an effective nonlinear parameter (also referred as γ), and a wavelength transparency (e.g., an indication of whether the material  118  transmits ultraviolet (UV) light, visible (VIS) light, and/or infrared (IR) light). 
     For example, a photonic waveguide layer  106  may include an active structure  108  that comprises at least a silicon nitride material that has a 1.99 refractive index, a propagation loss parameter of 
     
       
         
           
             
               0.0013 
               
                 dB 
                 cm 
               
             
             , 
           
         
       
     
     a Kerr coefficient of 
     
       
         
           
             
               2.4 
               × 
               
                 10 
                 
                   - 
                   19 
                 
               
               ⁢ 
               
                 
                   m 
                   2 
                 
                 W 
               
             
             , 
           
         
       
     
     an effective nonlinear parameter of 
     
       
         
           
             
               0.65 
               
                 1 
                 Wm 
               
             
             , 
           
         
       
     
     and a wavelength transparency for one or more portions of ultraviolet light through infrared light. As another example, a photonic waveguide layer  106  may include an active structure  108  that comprises at least a tantalum pentoxide material that has a 2.09 refractive index, a propagation loss parameter of 
     
       
         
           
             
               0.08 
               
                 dB 
                 cm 
               
             
             , 
           
         
       
     
     a Kerr coefficient of 
     
       
         
           
             
               6.2 
               × 
               
                 10 
                 
                   - 
                   19 
                 
               
               ⁢ 
               
                 
                   m 
                   2 
                 
                 W 
               
             
             , 
           
         
       
     
     an effective nonlinear parameter of 
     
       
         
           
             
               3 
               ⁢ 
               
                 1 
                 Wm 
               
             
             , 
           
         
       
     
     and a wavelength transparency for one or more portions of ultraviolet light through infrared light. In an additional example, a photonic waveguide layer  106  may include an active structure  108  that comprises at least a non-alkali, oxide solution that includes a cation that is niobium that has a 2.17 refractive index, a propagation loss parameter of 
     
       
         
           
             
               0.47 
               
                 dB 
                 cm 
               
             
             , 
           
         
       
     
     a Kerr coefficient of 
     
       
         
           
             
               1.2 
               × 
               
                 10 
                 
                   - 
                   18 
                 
               
               ⁢ 
               
                 
                   m 
                   2 
                 
                 W 
               
             
             , 
           
         
       
     
     an effective nonlinear parameter of 
     
       
         
           
             
               3.5 
               
                 1 
                 Wm 
               
             
             , 
           
         
       
     
     and a wavelength transparency for one or more portions of ultraviolet light through infrared light. 
     As indicated above,  FIG.  2    is provided as an example. Other examples may differ from what is described with regard to  FIG.  2   . 
     The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise forms disclosed. Modifications and variations may be made in light of the above disclosure or may be acquired from practice of the implementations. 
     As used herein, the term “X material” or “X solution,” where X is a chemical composition, such as silicon nitride or niobium tantalum oxide, indicates that at least a threshold percentage of X is included in the X material or X solution. The threshold percentage may be, for example, greater than or equal to 1%, 5%, 10%, 25%, 50%, 75%, 85%, 90%, 95%, and/or 99%. As used herein, when a material or solution is referred to by a specific chemical name or formula, the solution or material may include non-stoichiometric variations of the stoichiometrically exact formula identified by the chemical name. 
     As used herein, satisfying a threshold may, depending on the context, refer to a value being greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, or the like. 
     Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various implementations includes each dependent claim in combination with every other claim in the claim set. As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiple of the same item. 
     No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Further, as used herein, the article “the” is intended to include one or more items referenced in connection with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “set” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items), and may be used interchangeably with “one or more.” Where only one item is intended, the phrase “only one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Also, as used herein, the term “or” is intended to be inclusive when used in a series and may be used interchangeably with “and/or,” unless explicitly stated otherwise (e.g., if used in combination with “either” or “only one of”). Further, spatially relative terms, such as “below,” “lower,” “bottom,” “above,” “upper,” “top,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus, device, and/or element in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.