Optical waveguide assemblies

Abstract

An optical waveguide assembly includes a substrate having a coupling surface and an interface surface transverse to the coupling surface. The optical waveguide assembly further includes a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface. The waveguide may be configured to receive light at the coupling surface and transmit the light therethrough. The optical waveguide assembly further includes a gradient layer extending along the interface surface and overlapping the waveguide. The gradient layer includes a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

Description

OPTICAL WAVEGUIDE ASSEMBLIESRELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 63 / 763,589 filed on February 26, 2025, the content of which is relied upon and incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] Embodiments of the present disclosure relate to optical waveguide assemblies for use in optical coupler systems and, more specifically, optical waveguide assemblies that provide a refractive index transition.BACKGROUND

[0003] The use of waveguides in glass allows for the integration of electronic and photonic components in computing and switching applications (e.g., copackaged optics). This allows the integration of optics into substrates for opto-electronic chips, where previously only electronic conducting paths were possible on printed circuit boards.

[0004] The glass substrates allow the attachment of optical fibers and electronic connectors at the edge of the substrate with waveguides for the optical signals and conducting lines for the electronic signals to the appropriate positions (e.g., electronic chips, photonic integrated circuits (PICs), or electro-optic chips) on the substrate.

[0005] While the electrical connections do not require anything beyond physical contact, the optical connection between the optical fibers and the waveguides requires precise alignment between and matching of the optical mode fields at the coupling interface. If the mode fields are not ideally matched, signal losses are incurred. The waveguides in the glass substrates are only a few pm underneath the surface and have a somewhat elliptical cross-section, which leads to a non-circular mode field. This is caused by the substrate-air interface above the waveguide that confines the mode field strongly at the top while allowing expansion into the substrate material surrounding the waveguide. The mode field of the optical fibers, however, is circularly symmetric due to the geometry of the fiber. Accordingly, even when the dimensions of the mode fields of the optical fibers and the waveguides are matched, signal losses are incurred due to the mismatched symmetry.

[0006] Accordingly, a need exists for alternative optical waveguide assemblies to reduce losses resulting from signal transition between optical fibers and waveguides.SUMMARY

[0007] In one embodiment, an optical waveguide assembly may include a substrate having a coupling surface and an interface surface transverse to the coupling surface. The optical waveguide assembly may further include a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface. The waveguide may be configured to receive light at the coupling surface and transmit the light therethrough. The optical waveguide assembly may further include a gradient layer extending along the interface surface and overlapping the waveguide. The gradient layer includes a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

[0008] In another embodiment, an optical waveguide assembly may include a substrate having a coupling surface and an interface surface transverse to the coupling surface. The optical waveguide assembly further includes a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface. The waveguide is configured to receive light at the coupling surface and transmit the light therethrough. The optical waveguide assembly may further include a cover extending along the interface surface and overlapping the waveguide and a gradient layer disposed between and contacting each of the cover and the substrate. The gradient layer may include at least one structural portion and defining at least one space. A volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction.

[0009] In yet another embodiment, an optical coupler system may include a body, an optical fiber disposed within the body and configured to transmit light therethrough, and a substrate having a coupling surface abutting the body and an interface surface transverse to the coupling surface. The optical coupler system may further include a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface. The waveguide is aligned with the optical fiber and configured to receive the light from the optical fiber at the coupling surface and transmit the light therethrough. The optical coupler system may further include a cover extending along the interface surface and overlapping thewaveguide and a gradient layer disposed between and contacting each of the cover and the substrate.

[0010] Additional features and advantages of the embodiments described herein will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description that follows, the claims, as well as the appended drawings.

[0011] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0013] FIG. 1 schematically depicts a perspective view of an optical coupler system, according to one or more embodiments shown and described herein;

[0014] FIG. 2 schematically depicts a cross-sectional view of the optical coupler system of FIG. 1 taken along line 2-2, according to one or more embodiments shown and described herein;

[0015] FIG. 3 schematically depicts a cross-sectional view of the optical coupler system of FIG. 1 taken along line 3-3, according to one or more embodiments shown and described herein;

[0016] FIG. 4 schematically depicts a cross-sectional view of a portion of the optical coupler system of FIG. 1, according to one or more embodiments shown and described herein;

[0017] FIG. 5 schematically depicts a bottom plan view of an embodiment of a metamaterial of the optical coupler system, according to one or more embodiments shown and described herein;

[0018] FIG. 6 schematically depicts a bottom plan view of another embodiment of a metamaterial of the optical coupler system, according to one or more embodiments shown and described herein;

[0019] FIG. 7 schematically depicts a mode field plot of light transmitting through an optical fiber of an optical coupler system, according to one or more embodiments shown and described herein;

[0020] FIG. 8 schematically depicts a mode field plot of light transmitting through a waveguide of an optical coupler system without the use of a gradient layer, according to one or more embodiments shown and described herein; and

[0021] FIG. 9 schematically depicts a mode field plot of light transmitting through a waveguide of an optical coupler system with the use of a gradient layer, according to one or more embodiments shown and described herein.DETAILED DESCRIPTION

[0022] FIG. 1 generally depicts an embodiment of an optical coupler system that provides a connection between optical transmission components by aligning light transmitted therethrough. The optical coupler system as illustrated generally includes an optical fiber assembly having a plurality of optical fibers. The optical coupler system further includes an optical waveguide assembly including a substrate having a plurality of waveguides extending through the substrate and aligned with the optical fibers. The optical waveguide assembly includes a gradient layer that extends along an interface surface and overlaps the waveguides. The gradient layer has a refractive index that varies along the waveguide.

[0023] Previous optical coupler systems that utilize waveguides incur optical losses caused by a substrate-air interface above the waveguide. The embodiments described herein overcome these limitations by utilizing a gradient layer that extends along the substrate and overlaps the waveguides and has a refractive index that varies along the waveguide. The gradient layer provides for a graduated transition for the optical mode from the refractive index of the substrate to that of the air above the waveguides, resulting in lower signal losses. Variousembodiments and benefits of the optical coupler system, and the operation of the optical coupler system, will be described in more detail herein.

[0024] Reference will now be made in greater detail to various embodiments, some embodiments of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts.

[0025] Before describing several exemplary embodiments, it is to be understood that the present disclosure is not limited to the details of construction or process steps set forth in the present disclosure. The disclosure provided herein is capable of other embodiments and of being practiced or being carried out in various ways.

[0026] Reference throughout this specification to “one embodiment,” “certain embodiments,” “various embodiments,” “one or more embodiments” or “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. Thus, the appearances of the phrases such as “in one or more embodiments,” “in certain embodiments,” “in various embodiments,” “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment, or to only one embodiment. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

[0027] In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures. It is also understood that, unless otherwise specified, terms such as “top,” “bottom,” “outward,” “inward,” and the like are words of convenience and are not to be construed as limiting terms. In addition, whenever a group is described as comprising at least one of a group of elements and combinations thereof, it is understood that the group may comprise, consist essentially of, or consist of any number of those elements recited, either individually or in combination with each other. Similarly, whenever a group is described as consisting of at least one of a group of elements or combinations thereof, it is understood that the group may consist of any number of those elements recited, either individually or in combination with each other. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range as well as any ranges therebetween.

[0028] As used herein, the indefinite articles “a,” “an,” and the corresponding definite article “the” mean “at least one” or “one or more,” unless otherwise specified. It also is understood that the various features disclosed in the specification and the drawings can be used in any and all combinations.

[0029] It is noted that the terms "substantially" and "about" may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.

[0030] Referring now to FIG. 1, an optical coupler system 20 in accordance with one or more embodiments of the present disclosure is shown. The optical coupler system 20 provides a connection between optical transmission components by aligning light transmitted therethrough. For example, the optical transmission components may include electronic chips, photonic integrated circuits (PICs), electro-optic chips, or the like.

[0031] The optical coupler system 20 may include a first coupler portion 22 and a second coupler portion 24. The first coupler portion 22 and the second coupler portion 24 are configured to be selectively mechanically connected to one another. Said differently, the first coupler portion 22 and the second coupler portion 24 may be non-permanently or removably coupled to one another. When mechanically connected, the first coupler portion 22 and the second coupler portion 24 define an optical pathway therethrough for transmission of optical signals.

[0032] Still referring to FIG. 1, the first coupler portion 22 may include an optical fiber assembly (OF A) 26. The OFA 26 may include a body 28 and an optical fiber disposed within the body 28 and configured to transmit light therethrough. In the example shown in FIG. 1, the OFA 26 includes a plurality of optical fibers 30 extending substantially parallel to one another. The plurality of optical fibers 30 may be formed of glass, a polymer, or any other material configured to transmit light therethrough. The plurality of optical fibers 30 transmit the light by total internal reflection of the light therein, which allows the light to move longitudinally through the optical fibers 30. The OFA 26 may be a fiber array unit, a multifiber ferrule, or any other optical coupling device.

[0033] The plurality of optical fibers 30 may be positionally fixed within the body 28. The body 28 includes an abutment surface 32, with the plurality of optical fibers 30 extending toand truncating at or adjacent the abutment surface 32. The body 28 may be formed of metal, polymer, glass, or any other material or combination of materials suitable to retain the plurality of optical fibers 30.

[0034] With reference to FIG. 1, the second coupler portion 24 may include an optical waveguide assembly (OWA) 34. The OWA 34 may include a substrate 36 having a coupling surface 38 abutting the body 28, when mounted thereto, and an interface surface 40 transverse to the coupling surface 38. More specifically, the coupling surface 38 of the substrate 36 contacts the abutment surface 32 of the body 28 of the OFA 26. The interface surface 40 serves as an interface to an enveloping medium. The enveloping medium may encompass material that abuts the interface surface 40, including air. Furthermore, the enveloping medium may vary along the interface surface 40, as will be described in greater detail below.

[0035] The OFA 26 and the OWA 34 may be mechanically coupled to one another. FIGS.1 and 2 show an example of a mechanical coupling between the OFA 26 and the OWA 34. The OWA 34 includes a clamp portion 42 that extends along the interface surface 40 of the substrate 36. The clamp portion 42 may be adhered, bonded, or otherwise affixed to the substrate 36. Moreover, in other examples the clamp and the substrate 36 may be formed of a unitary, monolithic construction. As shown in FIGS. 1 and 2, the substrate 36 and the clamp portion 42 may collectively define a pair of passages 44 spaced from one another. The OFA 26 may include a corresponding pair of pins 46 fixed to the body 28. The pair of pins 46 are spaced from one another and align with the pair of passages 44 of the OWA 34. The pair of pins 46 and the pair of passages 44 may be sized to form an interference fit therebetween, such that insertion of the pair of pins 46 into the pair of passages 44 retains the OFA 26 relative to the OWA 34. It is to be appreciated that the OFA 26 and the OWA 34 may be mechanically coupled to one another in any suitable fashion.

[0036] The OWA 34 may further include a waveguide. In the embodiment shown in FIG.1, the OWA 34 includes a plurality of waveguides 48 extending in a longitudinal direction L through the substrate 36 along the interface surface 40 to the coupling surface 38. In embodiments, the OWA 34 and the OFA 26 may have the same number of waveguides 48 and optical fibers 30, respectively. The waveguides 48 are aligned with the optical fibers 30 and configured to receive the light from the optical fibers 30 (or send the light to the optical fibers 30) at the coupling surface 38 and transmit the light therethrough. More specifically, with the coupling surface 38 of the substrate 36 in contact with the abutment surface 32 of the body 28 of the OFA 26, the plurality of waveguides 48 are configured to align individually with theplurality of optical fibers 30 (e.g., one waveguide 48 per one optical fiber 30). The alignment of the waveguides 48 with the optical fibers 30 allow the light transmitting through the optical fibers 30 to transmit from the abutment surface 32 of the OF A 26 to the coupling surface 38 of the OWA 34 and into the waveguides 48.

[0037] In some embodiments, both the substrate 36 and the waveguides 48 are formed of glass. More specifically, the substrate 36 and the waveguides 48 may be formed of a single piece of glass, with the waveguides 48 formed in the glass by ion exchange. Ion exchange in glass involves the local substitution of relatively mobile ions (e.g., Na + ions) originally in the glass with other ions having different size and polarizability, causing a change in the refractive index in selected regions. In some embodiments, the substrate 36 and the waveguides 48 may be dissimilar glass materials such that the substrate 36 and the waveguides 48 have different refractive indices. In other embodiments, the substrate 36 and / or the waveguides 48 may be formed of a polymer. In any of the above embodiments, both the substrate 36 and the waveguides 48 are transparent at a wavelength of interest. The wavelength of interest may include light in the visible spectrum (e.g., white light). On the other hand, the wavelength of interest may include light in the non-visible spectrum (e.g., infrared light). For example, in one embodiment, the material may be transparent to light having a wavelength in the non-visible spectrum and therefore would appear opaque to humans (e.g., silicon, which is transparent in the near infrared, but not in the visible light spectrum). It is to be appreciated, that the substrate 36 and the waveguides 48 may be transparent within any range of wavelength of light.

[0038] In one embodiment, the optical fibers 30 and the waveguides 48 are formed of the same material such that the optical fibers 30 and the waveguides 48 have a similar refractive index to reduce losses in the transmission of the light therebetween. In another embodiment, the optical fibers 30 and the waveguides 48 are formed of dissimilar materials but having similar refractive indices. The OFA 26 and the OWA 34 are shown to have planar configurations along the abutment surface 32 and the coupling surface 38, respectively, in FIGS. 1 and 2. However, slight variations in the abutment surface 32 and / or the coupling surface 38 may result in air being disposed between the optical fibers 30 the waveguides 48. As air has different refractive index than glass, polymer, etc., losses may occur between the OFA 26 and the OWA 34. Accordingly, an index matching material (such as a gel, coating, etc.) may be positioned between the abutment surface 32 and the coupling surface 38 and mayhave a refractive index similar to the optical fibers 30 and / or the waveguides 48 to reduce losses therebetween.

[0039] As described above, the plurality of waveguides 48 extend in the longitudinal direction L through the substrate 36 along the interface surface 40 to the coupling surface 38. More specifically, in the example shown in FIGS. 1 and 2, the waveguides 48 may be positioned just below the interface surface 40 and extend parallel to the interface surface 40. However, in other examples the waveguides 48 may be flush with the interface surface 40 or positioned further from the interface surface 40 within the substrate 36. Moreover, the waveguides 48 may be transverse to the interface surface 40 while extending along the interface surface 40 (e.g., non-parallel). Furthermore, in other embodiments, the waveguides 48 may protrude outwardly from the substrate 36 along the interface surface 40.

[0040] Since the substrate 36 is transparent at the wavelength of interest and the waveguides 48 are positioned along the interface surface 40, additional losses may occur due to the substrate-air interface at the interface surface 40 (which is described in greater detail below). To reduce such losses, the OWA 34 may include a gradient layer 50, as shown in FIGS. 2 and 3. The gradient layer 50 extends along the interface surface 40 and overlaps the waveguides 48. The gradient layer 50 has a refractive index that varies along the waveguides 48 in the longitudinal direction L. More specifically, the refractive index of the gradient material transitions from a value similar to the refractive index of the substrate 36 (e.g., approximately 1.5) to a value similar to the refractive index of the air (e.g., approximately 1.0). The reduction in losses due to the gradient layer 50 will be better understood in view of the description below.

[0041] As shown in FIGS. 1-3, the OWA 34 may include a cover 52 extending along the interface surface 40 and overlapping the waveguides 48. The cover 52 is configured as a support upon which the gradient layer 50 may coated, formed, mounted, or otherwise disposed upon. In turn, the cover 52 is mounted to the substrate 36 to dispose the gradient layer 50 along the interface surface 40 of the substrate 36. It is to be appreciated that the gradient layer 50 may be independently disposed along and coupled to the interface surface 40 of the substrate 36 (e.g., without the cover 52). The cover 52 may be formed of a polymer, glass, metal, or any other material suitable for supporting the gradient layer 50.

[0042] As shown in FIGS. 2-4, the gradient layer 50 may be disposed between and contact each of the cover 52 and the substrate 36. The gradient layer 50 and the cover 52 extend along the substrate 36 in the longitudinal direction L to the coupling surface 38. By extending fromthe coupling surface 38, the gradient layer 50 prevents the waveguides 48 from incurring the refractive index of air and corresponding losses at the junction between the OFA 26 and the OWA 34 due to the mismatch of the mode fields of the optical fibers 30 and the waveguides 48. The gradient layer 50 and the cover 52 overlap a portion of the waveguides 48 in the longitudinal direction L. As shown in FIG. 1, the portion of waveguides 48 that is overlapped by the gradient layer 50 and the cover 52 in the longitudinal direction L is less than half of a length of the waveguides 48. This is for exemplary purposes. It is to be appreciated that the portion of waveguides 48 that is overlapped by the gradient layer 50 and the cover 52 in the longitudinal direction L may be any length suitable to provide a desired transition in the refractive index of the gradient layer 50, including up to an entire length of the waveguides 48 in the longitudinal direction L.

[0043] The cover 52 has an engagement surface 54 facing the substrate 36 and contacting the gradient layer 50, with the engagement surface 54 of the cover 52 and the interface surface 40 of the substrate 36 both having planar configurations that are positioned parallel to one another. Accordingly, the gradient layer 50 may have a uniform or substantially uniform thickness across the interface surface 40. However, in other examples, the thickness of the interface surface 40 may vary to provide different characteristics (e.g., changes in the refractive index of the gradient layer 50, or the like).

[0044] The OWA 34 may further include an adhesive 56 disposed between and contacting each of the cover 52 and the substrate 36, adjacent the gradient layer 50, to bond together the cover 52 and the substrate 36. As shown in FIG. 2, the adhesive 56 may have a thickness similar to the thickness of the gradient layer 50 to ensure contact of the gradient layer 50 with the interface surface 40 of the substrate 36, to prevent air from being disposed therebetween and corresponding losses. Moreover, the adhesive 56 may be laterally spaced from the waveguides 48 along the interface surface 40 to prevent the adhesive 56 from altering the refractive index of the gradient layer 50 along the interface surface 40 adjacent the waveguides 48. The adhesive may be an optical adhesive or any commercially available adhesive, such as epoxy, acrylic, or resin adhesives.

[0045] The gradient layer 50 may include or be formed of a metamaterial 58 having a refractive index that varies along the waveguides 48 in the longitudinal direction L. More specifically, the refractive index of the metamaterial 58 of the gradient layer 50 decreases along the waveguides 48 in the longitudinal direction L away from the coupling surface 38, as described above in order to transition from the refractive index of the substrate 36 to therefractive index of air along the waveguides 48. More specifically, and with reference to FIG.4, the metamaterial 58 of the gradient layer 50 includes at least one structural portion 60 and defines at least one space 62 (e.g., opening, aperture, discontinuity, void, or the like). The at least one structural portion 60 of the metamaterial 58 of the gradient layer 50 may be transparent and may have a refractive index similar to the refractive index of the substrate 36 in order to mimic the refractive index of the substrate 36. A volumetric ratio of the at least one space 62 to the at least one structural portion 60 increases along the waveguides 48 in the longitudinal direction L away from the coupling surface 38, as shown in FIG. 4. The at least one space 62 may have air disposed therein. As such, more air is disposed within the metamaterial 58 of the gradient layer 50 further away from the coupling surface 38. Accordingly, the refractive index of the metamaterial 58 of the gradient layer 50 progressively decreases away from the coupling surface 38 as the gradient layer 50 incorporates more air therein. In other embodiments, the at least one space 62 may be filled with a material. The material within the at least one space 62 may differ from the material of the at least one structural portion 60, resulting in the material with the at least one space 62 having a refractive index that is different than the refractive index of the at least one structural portion 60. In yet another embodiment, the at least one space 62 of any material (e.g., a vacuum), having a refractive index of 1.0. It is to be appreciated that that the at least one space 62 may encompass any of the above conditions in any suitable manner to produce a desired change in the refractive index of the metamaterial 58 of the gradient layer 50 progressively away from the coupling surface 38 (e.g., decreasing or increasing). Moreover, while the volumetric ratio of the at least one space 62 is shown to increases along the waveguides 48 in the longitudinal direction L away from the coupling surface 38 in FIG. 4, in other embodiments the opposite may true. More specifically, the volumetric ratio of the at least one space 62 may decrease along the waveguides 48 in the longitudinal direction L away from the coupling surface 38.

[0046] In one example, the gradient layer 50 is a coating formed along the cover 52. However, the gradient layer 50 may be formed by additive manufacturing, machining, etching, or any other suitable manner for forming the at least one structural portion 60 and the at least one space 62. It is also to be appreciated that the gradient layer 50 may be formed along the interface surface 40 of the substrate 36 or formed independent of both the cover 52 and the substrate 36 and then applied to the cover 52 or the substrate 36. The gradient layer 50 may include a polymer, a glass, or any other suitable material having a refractive index substantially equal to that of the substrate 36.

[0047] FIG. 5 shows one example of the metamaterial 58, in which the at least one structural portion 60 includes a plurality of pillars 64 spaced from one another and extending between the substrate 36 and the cover 52, with the at least one space 62 disposed between and around the pillars 64. The plurality of pillars 64 may become progressively spaced apart and / or progressively smaller in size further away from the coupling surface 38 to dispose more air in the metamaterial 58. The pillars 64 are shown in FIG. 5 as having cylindrical configurations. However, the pillars 64 may have any shape and configuration that allows for the at least one space 62 to be disposed between and around the pillars 64.

[0048] FIG. 6 shows another example of the metamaterial 58, in which the at least one structural portion 60 is configured as a lattice 66 that defines of a plurality of the spaces 62 spaced from one another and extending between the substrate 36 and the cover 52. The lattice 66 of the structural portion 60 may vary in configuration such that the plurality of spaces 62 become progressively closer together and / or progressively larger in size further away from the coupling surface 38 to dispose more air in the metamaterial 58. The spaces 62 shown in FIG.6 as having cylindrical configurations. However, the spaces 62 may have any shape and configuration that allows for the formation of the lattice 66 of the at least one structural portion 60. It is to be appreciated that the at least one structural portion 60 and the at least one space 62 may have any suitable shape and configuration for allowing the metamaterial 58 to decrease in refractive index away from the coupling surface 38, including combinations of the configurations described above.

[0049] FIGS. 7-9 show comparisons of optical mode field shapes in various scenarios in order make known the advantages of the optical coupler system 20 contemplated herein. More specifically, FIG. 7 shows a mode field plot of light transmitting through one of the plurality of optical fibers 30, which is circular and centered due to the circular cross-section of the optical fiber 30. On the other hand, FIG. 8 shows a mode field plot of light transmitting through one of the plurality of waveguides 48 within the substrate 36, but without the use of the gradient layer 50. The mode field of the waveguide 48 may be squashed as shown in FIG. 8. More specifically, the substrate / air interface may squash the mode field from the original round shape of the optical fiber 30, leading to the non-circular mode as shown in FIG. 8. The mode field of the optical fiber 30 is circularly symmetric due to the geometry of the fiber, as shown in FIG.7. Even when the dimensions of the mode fields of the optical fiber 30 and the waveguide 48 are matched, losses are incurred due to the broken symmetry (see comparison of FIGS. 7 and 8). Moreover, the substrate-air interface above the interface surface 40 of substrate 36 confinesthe mode field strongly at the top while it can expand freely into the substrate 36 surrounding the waveguide 48.

[0050] FIG. 9 shows a mode field plot of light transmitting through one of the plurality of waveguides 48 within the substrate 36 of the OWA 34 described herein, utilizing the gradient layer 50. The gradient layer 50 having the refractive index at the coupling surface 38 of the substrate 36 that is similar to the refractive index of the substrate 36 reduces the coupling loss between the waveguide 48 and the optical fiber 30, with the remaining coupling loss due to the shape mismatch between the optical fiber 30 and waveguide 48 modes as shown in FIG. 9. Moreover, the decrease in the refractive index of the gradient layer 50 along the waveguide 48 in the longitudinal direction L causes the mode field to change slowly along the waveguide 48, leading to little or no losses. More specifically, in one example, the signal loss at waveguide 48 without the gradient layer 50 (FIG. 8) may be about 0.34 dB while the signal loss at the waveguide 48 that has the gradient layer 50 (FIG. 9) may be about 0.14 dB. Accordingly, the gradient layer 50 may result in a 0.2 dB reduction in signal loss and an approximately 60% improvement in signal loss, overall. It is to be appreciated that the reduction in signal loss may be further improved by further developments to the design and processing of the OWA 34.

[0051] Embodiments of the present disclosure may be further described with respect to the following numbered clauses:

[0052] 1. An optical waveguide assembly, the optical waveguide assembly comprising: a substrate having an coupling surface and an interface surface transverse to the coupling surface; a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, the waveguide configured to receive light at the coupling surface and transmit the light therethrough; and a gradient layer extending along the interface surface and overlapping the waveguide, the gradient layer comprised of a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

[0053] 2. The optical waveguide assembly of clause 1, wherein the refractive index of the gradient layer decreases along the waveguide in the longitudinal direction away from the coupling surface.

[0054] 3. The optical waveguide assembly of any one of clauses 1 or 2, wherein the gradient layer extends along the substrate in the longitudinal direction to the coupling surface.

[0055] 4. The optical waveguide assembly of clause 3, wherein the gradient layer overlaps a portion of the waveguide in the longitudinal direction.

[0056] 5. The optical waveguide assembly of any one of clauses 1-3, further comprising a cover extending along the interface surface and overlapping the waveguide, wherein the gradient layer is disposed between and contacts each of the cover and the substrate.

[0057] 6. The optical waveguide assembly of clause 5, wherein the cover has an engagement surface facing the substrate and contacting the gradient layer, with the engagement surface of the cover and the interface surface of the substrate both having planar configurations that are positioned parallel to one another.

[0058] 7. The optical waveguide assembly of clause 5, further comprising an adhesive disposed between and contacting each of the cover and the substrate, adjacent the gradient layer, to bond together the cover and the substrate.

[0059] 8. The optical waveguide assembly of clause 5, wherein the gradient layer is a coating formed along the cover.

[0060] 9. The optical waveguide assembly of any one of clauses 1-8, wherein the gradient layer comprises a polymer.

[0061] 10. The optical waveguide assembly of any one of clauses 1-9, wherein the gradient layer is transparent.

[0062] 11. The optical waveguide assembly of any one of clauses 1-10, wherein the gradient layer comprises at least one structural portion and defines at least one space.

[0063] 12. An optical waveguide assembly, the optical waveguide assembly comprising: a substrate having an coupling surface and an interface surface transverse to the coupling surface; a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, the waveguide configured to receive light at the coupling surface and transmit the light therethrough; a cover extending along the interface surface and overlapping the waveguide; and a gradient layer disposed between and contacting each of the cover and the substrate, the gradient layer comprising at least one structural portion and defining at least one space, wherein a volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction.

[0064] 13. The optical waveguide of clause 12, wherein the volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction away from the coupling surface.

[0065] 14. The optical waveguide of any one of clauses 12 or 13, wherein the at least one structural portion comprises a plurality of pillars spaced from one another and extending between the substrate and the cover, with the at least one space disposed between and around the pillars.

[0066] 15. The optical waveguide of any one of clauses 12-14, wherein the at least one structural portion is configured as a lattice that defines of a plurality of the spaces spaced from one another and extending between the substrate and the cover.

[0067] 16. The optical waveguide of any one of clauses 12-15, wherein the gradient layer and the cover extend along the substrate in the longitudinal direction to the coupling surface.

[0068] 17. The optical waveguide of clause 16, wherein the gradient layer and the cover overlap a portion of the waveguide in the longitudinal direction.

[0069] 18. The optical waveguide of any one of clauses 12-17, further comprising an adhesive disposed between and contacting each of the cover and the substrate, adjacent the gradient layer, to bond together the cover and the substrate.

[0070] 19. The optical waveguide assembly of any one of clauses 12-18, wherein the cover has an engagement surface facing the substrate and contacting the gradient layer, with the engagement surface of the cover and the interface surface of the substrate both having planar configurations that are positioned parallel to one another.

[0071] 20. An optical coupler system, the optical coupler system comprising: a body; an optical fiber disposed within the body and configured to transmit light therethrough; a substrate having an coupling surface abutting the body and an interface surface transverse to the coupling surface; a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, wherein the waveguide is aligned with the optical fiber and configured to receive the light from the optical fiber at the coupling surface and transmit the light therethrough; a cover extending along the interface surface and overlapping the waveguide; and a gradient layer disposed between and contacting each of the cover and the substrate.

[0072] 21. The optical coupler system of clause 20, wherein the gradient layer is comprised of a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

[0073] 22. The optical coupler system of any one of clauses 20 or 21, wherein the gradient layer comprises at least one structural portion and defines at least one space, wherein a volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction.

[0074] It should now be understood that embodiments of the present disclosure are directed to an optical coupler system that includes an optical fiber assembly having a plurality of optical fibers. The optical coupler system further includes an optical waveguide assembly including a substrate having a plurality of waveguides extending through the substrate and aligned with the optical fibers. The optical waveguide assembly includes a gradient layer that extends along the interface surface and overlaps the waveguides. The gradient layer has a refractive index that varies along the waveguide. The gradient layer provides for a graduated transition for the optical mode field from the refractive index of the substrate to that of the air above the waveguides, resulting in lower signal losses compared to previous optical coupler systems utilizing waveguides that incur optical losses caused by the substrate-air interface above the waveguide.

[0075] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. An optical waveguide assembly comprising:a substrate having a coupling surface and an interface surface transverse to the coupling surface;a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, the waveguide configured to receive light at the coupling surface and transmit the light therethrough; anda gradient layer extending along the interface surface and overlapping the waveguide, the gradient layer comprised of a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

2. The optical waveguide assembly of claim 1, wherein the refractive index of the gradient layer decreases along the waveguide in the longitudinal direction away from the coupling surface.

3. The optical waveguide assembly of claim 1, wherein the gradient layer extends along the substrate in the longitudinal direction to the coupling surface.

4. The optical waveguide assembly of claim 3, wherein the gradient layer overlaps a portion of the waveguide in the longitudinal direction.

5. The optical waveguide assembly of claim 1, further comprising a cover extending along the interface surface and overlapping the waveguide, wherein the gradient layer is disposed between and contacts each of the cover and the substrate.

6. The optical waveguide assembly of claim 5, wherein the cover has an engagement surface facing the substrate and contacting the gradient layer, with the engagement surface of the cover and the interface surface of the substrate both having planar configurations that are positioned parallel to one another.

7. The optical waveguide assembly of claim 5, further comprising an adhesive disposed between and contacting each of the cover and the substrate, adjacent the gradient layer, to bond together the cover and the substrate.

8. The optical waveguide assembly of claim 5, wherein the gradient layer is a coating formed along the cover.

9. The optical waveguide assembly of claim 1, wherein the gradient layer comprises a polymer.

10. The optical waveguide assembly of claim 1, wherein the gradient layer is transparent.

11. The optical waveguide assembly of claim 1, wherein the gradient layer comprises at least one structural portion and defines at least one space.

12. An optical waveguide assembly comprising:a substrate having a coupling surface and an interface surface transverse to the coupling surface;a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, the waveguide configured to receive light at the coupling surface and transmit the light therethrough;a cover extending along the interface surface and overlapping the waveguide; and a gradient layer disposed between and contacting each of the cover and the substrate, the gradient layer comprising at least one structural portion and defining at least one space, wherein a volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction.

13. The optical waveguide assembly of claim 12, wherein the volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction away from the coupling surface.

14. The optical waveguide assembly of claim 12, wherein the at least one structural portion comprises a plurality of pillars spaced from one another and extending between the substrate and the cover, with the at least one space disposed between and around the pillars.

15. The optical waveguide assembly of claim 12, wherein the at least one structural portion is configured as a lattice that defines of a plurality of the spaces spaced from one another and extending between the substrate and the cover.

16. The optical waveguide assembly of claim 12, wherein the gradient layer and the cover extend along the substrate in the longitudinal direction to the coupling surface.

17. The optical waveguide assembly of claim 16, wherein the gradient layer and the cover overlap a portion of the waveguide in the longitudinal direction.

18. The optical waveguide assembly of claim 12, further comprising an adhesive disposed between and contacting each of the cover and the substrate, adjacent the gradient layer, to bond together the cover and the substrate.

19. The optical waveguide assembly of claim 12, wherein the cover has an engagement surface facing the substrate and contacting the gradient layer, with the engagement surface of the cover and the interface surface of the substrate both having planar configurations that are positioned parallel to one another.

20. An optical coupler system comprising:a body;an optical fiber disposed within the body and configured to transmit light therethrough; a substrate having a coupling surface abutting the body and an interface surface transverse to the coupling surface;a waveguide extending in a longitudinal direction through the substrate along the interface surface to the coupling surface, wherein the waveguide is aligned with the optical fiber and configured to receive the light from the optical fiber at the coupling surface and transmit the light therethrough;a cover extending along the interface surface and overlapping the waveguide; and a gradient layer disposed between and contacting each of the cover and the substrate.

21. The optical coupler system of claim 20, wherein the gradient layer is comprised of a metamaterial having a refractive index that varies along the waveguide in the longitudinal direction.

22. The optical coupler system of claim 20, wherein the gradient layer comprises at least one structural portion and defines at least one space, wherein a volumetric ratio of the at least one space to the at least one structural portion increases along the waveguide in the longitudinal direction.

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