INTEGRATED PHOTONIC NANOWIRES-BASED WAVEGUIDE

Abstract

A novel waveguide with excellent optical properties can be easily produced. The photonic nanowires based waveguide has a) a plurality of nanowires; each nanowire having a ridge shape; b) the nanowires are supported by a support substrate or partially or totally free standing; c) the support substrate further supports interfacing waveguides disposed on both sides of the plurality of nanowires. The special concept of present invention allows to align a number of ridge-shaped nanowire that enables to control the amount of light being outside the solid waveguide in the evanescence field. Further, the design is compatible with solid waveguides and offers the possibility to confine (guide the light) within a multiple waveguide arrangement.

Claims

1-12. (canceled)

13. A photonic nanowire-based waveguide, comprising: a) a plurality of nanowires, each of said nanowires having a ridge shape; b) said nanowires being supported by a support substrate or partially or completely free standing; c) interfacing waveguides supported on said support substrate, said interfacing waveguides being disposed on both sides of said plurality of nanowires.

14. The waveguide according to claim 13, wherein an aspect ratio of said nanowires is at least 2:1.

15. The waveguide according to claim 13, wherein at least one dimension of said nanowires other than a propagation dimension is smaller than a coupled light wavelength.

16. The waveguide according to claim 15, wherein both dimensions of said nanowires, other than the propagation dimension, are smaller than the coupled light wavelength.

17. The waveguide according to claim 13, wherein said plurality of nanowires are disposed according to at least one of the following design options: array, ordered, regular and disordered, semi-random, random, variable period or thickness as an array of nanowires.

18. The waveguide according to claim 13, wherein said nanowires are formed according to one or more design options selected from the group consisting of: perforated ridges, short interruptions, stabilization posts, roughness, and draft angle.

19. The waveguide according to claim 13, wherein said nanowires are bent and/or hollow.

20. The waveguide according to claim 13, wherein a ridge of said nanowires is formed with at least one of the following: a thickness variation, a partial or complete coating, a single material, or different materials.

21. The waveguide according to claim 13, wherein said support substrate is selected from the group consisting of silicon, glass, polymer, metal, and multilayer structures.

22. The waveguide according to claim 21, wherein said support substrate is formed with anti-resonant reflecting layers to form an ARROW waveguide or a Fabry-Perot waveguide .

23. The waveguide according to claim 13, wherein said plurality of nanowires are produced by a method selected from the group consisting of an additive fabrication method, a subtractive fabrication method, and a molding fabrication method.

24. The waveguide according to claims 23, wherein the fabrication method is selected from different techniques that include one or more of the following: a) etching, photolithography, two-photon polymerization, direct writing by laser or electron beam, electron beam lithography; b) spincoated films, non-supported films, release from surface, sacrificial layers, selective etching; c) embedded design, also applicable if one or two sides are attached to the support substrate or covered by the same or another support substrate; d) molding, inclusive of vertical sidewalls and/or draft angle and/or thickness variations; e) made from block copolymers, blocks with different refractive indices and/or different etching behavior.

25. The waveguide according to claim 23, wherein a material for said nanowires is selected from one or more of the following materials: polymers, doped polymers, sol-gels, insulators, semiconductors, hybrid organic-inorganic materials, hydro-gels, a combination of such materials, and any coated version of such materials, formed with metallic or insulating coatings.

Description

[0027] Preferred embodiments of the present invention are hereinafter described with reference to the attached drawings which depict in:

[0028] FIG. 1 (a) a schematic representation of an Integrated Photonic Nanowire array-based waveguide connected to interfacing classical waveguides as an example of auxiliary photonic elements; numerical simulations of the effective refractive index n.sub.eff (b) and the percentage of light intensity propagating in the environment (P.sub.e) versus the number of photonic nanowires for different nanowires widths (c);

[0029] FIG. 2 (a) a schematic representations of a standard optical waveguide 5×5 μm.sup.2 with a core refractive index (n.sub.c) of 1.55, the numerically simulated light distribution into the fundamental mode and the EF of such waveguide and (b) a schematic representations of proposed integrated photonic nanowires composed waveguide with total cross-section dimensions of 5×5 μm2 segmented into 10 nanowires with a n.sub.c of 1.55, the numerically simulated light distribution into the fundamental mode and the EF of such segmented waveguide; and

[0030] FIG. 3 a SEM picture of (a) an integrated photonic nanowires array composed waveguide with a height of 12 μm and (b) increased magnification of the same structure showing the integrated photonic nanowires with a width of 265 nm, resulting in an aspect ratio of ˜45 and (c) an optical image of the coupling of light into such segmented waveguide and the out-coupling light.

[0031] FIG. 4 a schematic representation of possible cross-section distributions of nanowires with 2 dimensions smaller than the working wavelength. The representation shows increasing number of combined equidistant nanowires. The distribution can be organized or randomized and equidistant or non-equidistant in one or both direction.

[0032] FIG. 5 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength. The representation shows increasing number of combined nanowires. The distribution can be organized or randomized and equidistant or non-equidistant.

[0033] FIG. 6 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength placed on a substrate that can be on the bottom or top.

[0034] FIG. 7 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength placed on a combined top and bottom substrates.

[0035] FIG. 8 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength placed on an intermediate substrate.

[0036] FIG. 9 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength fully embedded on a medium. Such configuration is also compatible with the substrate configurations presented in FIGS. 6, 7 and 8. The nanowires can be also partially embedded. This option is also compatible with the 2D nanowires.

[0037] FIG. 10 a schematic representation of possible cross-section distributions of nanowires with 1 dimension smaller than the working wavelength fully coated by another material. Such configuration is also compatible with the substrate configurations presented in FIGS. 6, 7 and 8 and they can be further embedded in another material as shown in FIG. 9. This option is also compatible with the 2D nanowires.

[0038] FIG. 11 schematic representation of possible cross-sections of 1D and 2D nanowires. FIGS. 1-10 shows rectangular like nanowires, but the shape can be arbitrary as shown this examples.

[0039] Hereinafter the concept of an Integrated photonic nanowires-based waveguide 2 is described and shown in FIG. 1. Presently, thin wires (1D) or fences (2D) 4 directly aligned in a substrate 6 in isolated or in an array configuration to couple the light. The array of such nanowires 4 behaves equivalently to a standard waveguide but with an extremely large amount of light, coupled, propagating, and interacting in and with the surrounding medium. Each of this wires (fibers) (2D) or fences 4 (lamellae, 1D) has at least one lateral dimension smaller than the coupled light's wavelength. The smaller this nanometric dimension is the larger will be the formed evanescent field. The index contrast between the integrated photonic wires (I-PNW) and the surrounding medium (polymer and air or water, respectively, but also other like Si, hybrid organic-inorganic materials, sol-gels, hydrogels and other mediums, like buffered solutions, biological mediums, cell-growth mediums) will also affect the evanescent field that is formed. The fences 4—the term “ridges” could also be used—are normally characterized by their aspect ratio; wires usually by their diameter. FIGS. 4 and 5, represent schematically possible but not limiting distributions of 1D and 2D nanowires, respectively. Since such structures can be fabricated into a complex substrate they can be easily integrated with other optical components or fluidic systems. Possible substrate configurations are presented in FIG. 6 (top or bottom substrate), FIG. 7 (top and bottom substrate enclosing the wires), and FIG. 8 an intermediate substrate with wires on both sides.

[0040] The light is typical coupled and outcoupled from the waveguide (classical or integrated photonic nanowires based) via focusing optics, via solid (larger) integrated waveguides, via fibers (standard waveguides attached to light emission elements or to semiconductor-based detectors) or Bragg-gratings as this is also exemplarily shown in FIG. 3.

[0041] As mentioned before, the plurality of multiple integrated photonic nanowires 4 are assembled in an array. This is one of the main breakthrough and novelties in the present invention since an isolated, difficult to handle photonic nanowire (which has been the strategy so far) is not considered but rather the monolithic fabrication of integrated photonic nanowires in array configuration as it can be seen in FIG. 1a, other possible examples of configurations are schematized in FIGS. 4 and 5 for different number of nanowires of 2D and 1D nanowires. In this frame, considering the ubiquitous confined light profile, the evanescent field of an arbitrarily number of I-PNW will be coupled from one individual PNW to its neighbors behaving as a single photonic entity. Thus, the resulting light profile at the I-PNW can be envisaged as a supermode (a light intensity distribution over several ridges which resembles a light distribution over one single waveguide) where the evanescent field will be highly enhanced, with the here called ultra-evanescent field (UEF). Hence the UEF will be partially propagating in the environment medium which can be a gas, a liquid, a solid or a combination of such. It is also possible to embed or coat the wires, as shown in FIGS. 9 and 10, respectively, to enhance or control this effect.

[0042] Numerical simulations (see FIGS. 1b and 1c) show that the coupling efficiency, represented by means of the effective refractive index (n.sub.eff), increases as a function of the number of I-PNW. Conversely, the interaction between light and the surrounding media, represented as the percentage of light intensity propagating in the environment or surrounding medium (P.sub.e), is initially stable or even increases slightly, until the density of PNW is so high that it starts to resemble a solid waveguide. This behavior anticipates that I-PNW arrays will enable strong coupling and interaction with the medium, even for low photonic nanowires density and no technologically critical configurations. The light coupled into such arrays, if they are dense enough, behaves as it would be in a standard waveguide with dimensions similar to the one of the array, while a large amount of the total waveguide area is from by surrounding medium and not core material. This is a new physical principle. Preliminary optical simulations of such system demonstrate that such integrated photonic nanowire-based waveguides will have a behavior equivalent to the one observed in a standard waveguide, but with an increase of light interacting with the medium (Pe) from around 0.005% to up to >95%.

[0043] FIG. 2 shows a comparison of the light distribution once it is coupled to a standard waveguide (FIG. 2a) and to an integrated photonic nanowires array waveguide with total equivalent dimensions (FIG. 2b). This results in the formation of the UEF maintaining the coupling and modal behavior of the waveguide. Hence, the amount of the light in the UEF is extremely enlarged compared to the one observed in classical total internal refraction waveguides, and can be used for sensing purposes, to fabricated classical integrated optical components with increased technological tolerances or even new components.

[0044] FIG. 2 shows in (a) a schematic representations of a standard optical waveguide with 5×5 μm.sup.2 cross-section with a core refractive index (n.sub.c) of 1.55, the numerically simulated light distribution into the fundamental mode and the EF of such waveguide. FIG. 2b shows a schematic representation of the invented integrated photonic nanowires composed waveguide 2 with total dimensions of 5×5 μm.sup.2 segmented into 10 nanowires with a n.sub.c of 1.55, the numerically simulated light distribution into the fundamental mode and the EF of such segmented waveguide. This is the proof that the “segmented waveguide” works as an entire waveguide (=“equivalence”), but with air (or another medium with different refractive index) inside.

[0045] An example of nanowire fences 4 were fabricated using a technology combining photolithography and 3D two-photon polymerization, in which aspect ratios up to ˜45 have been achieved as shown in FIGS. 3(a) and (b), and coupling of light into such non-functionalized PDEs have been demonstrated, as this can be seen in FIG. 3(c), respectively. These results demonstrate the viability of the proposed I-PNW-based waveguide 2.

[0046] Although up to now the wires shown have rectangular or circular/elliptic shapes, there is no real limit on the shape of the wires as far as they have one or two lateral dimensions smaller than the working wavelength. FIG. 11 shows some non-limiting examples of possible cross-sections shapes that the nanowires can have.

[0047] The design of the nanowire fences 4 can have the one or more of the following options:

[0048] Ridge waveguides: aspect ratio 2:1 and larger

[0049] One lateral dimension (not the propagation one) smaller than the coupled light wavelength

[0050] Perforated ridges, short interruptions, slits, stabilization posts, roughness, draft angle

[0051] Bent waveguides

[0052] Hollow waveguides

[0053] Arrays, ordered, regular and disordered, semi-random, random, variable period or thickness

[0054] With thickness variation in the lateral direction (grating, taper, depressions, expansions, dots)

[0055] With coating (e.g. metal film , dots or particles of a different material) covering the entire ridge array, single ridges or part of them (gratings, tapers, ordered or random dots)

[0056] Arbitrary substrate: Silicon, glass, polymer, metal, multilayer structures (i.e. anti-resonant reflecting layers to from an ARROW waveguide or a Fabry-Perot).

[0057] With varying period (tapering of the entire array), stopping of single ridges, adding of new ridges along the direction of propagation

[0058] The proposed fabrication methods for the 1D or 2D nanowires are one or more of the following:

[0059] Etching, photolithography, two-photon polymerization, direct writing (i.e. laser, electron beam, and/or focused ion beam), electron beam lithography, etc;

[0060] Spincoated films, non-supported films, release from surface, sacrificial layers (selective etching);

[0061] embedded design, also applicable if one or two sides are attached to the support substrate or covered by the same or another support substrate;

[0062] Molding, incl. vertical sidewalls and/or draft angle and/or thickness variations;

[0063] Made from block copolymers such as blocks with different refractive indices and/or different etching behavior.

[0064] Made from grafting from patterned substrates (directed growth of polymer brushes)

[0065] Extruded through nozzles with the shape of the waveguide cross-section

[0066] Mechanical removal by scribing (combined cutting and moulding)

[0067] Also if one or two sides (the smaller ones are attached to a substrate or covered by another substrate)-embedded design

[0068] Molding: vertical sidewalls, draft angle, thickness variation

[0069] Materials: polymers, doped polymers, sol-gels, insulators, and any coated version of such materials (i.e. metallic or electrically insulating coatings)

[0070] Made from block copolymers (blocks with different refractive indices or etching behavior)

[0071] Examples for the application of the integrated nanowire based waveguide 2 are the following:

Ridge Waveguides

[0072] Absorption detection [0073] Phase detection [0074] Fluorescent detection [0075] Coupling between waveguides [0076] Reflection (mirror, U-turn) [0077] Focusing element [0078] Beam widening and focusing, tapering, gradients [0079] In-and outcoupling [0080] Mode-shaping [0081] Splitting and uniting [0082] Ring resonators [0083] Match-Zehnder interferometers [0084] Bio-sensors [0085] Optical distribution and shaping [0086] . . .

REFERENCES

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