Optical fiber apparatus and optical fiber-chip coupling arrangement for efficient vertical edge coupling

Abstract

The present disclosure relates to an integrated photonic device, specifically an efficient fiber-chip coupling structure or arrangement in which an optical fiber has at least two facet cuts that are made or configured to efficiently transmit an optical field from / to an optical chip. The efficient fiber-chip coupling arrangement may be part of an optical coupling setup used in, for example, optical wafer level testing applications. The optical fiber may optionally include an additional facet cut that is made or configured to provide improved visualisation of an optical alignment edge of the optical fiber during alignment with the optical chip or other elements.

Description

[0001] OPTICAL FIBER APPARATUS AND OPTICAL FIBER-CHIP COUPLING ARRANGEMENT FOR EFFICIENT VERTICAL EDGE COUPLING

[0002] FIELD

[0003]

[0001] The present disclosure relates to the field of integrated optics, wafer level testing, and optical couplers, and more particularly to an optical fiber apparatus and an optical fiber-chip coupling arrangement in which the optical fiber includes two or more facet cuts which facet angles are defined such that the facet cuts optimise an incident optical signal transmission from the optical fiber to an optical chip.

[0004] BACKGROUND

[0005]

[0002] Optical fiber-to-chip coupling approaches have been implemented to transfer optical signals between an optical fiber and an optical chip. To couple light onto and from optical chip, optical coupling structures are typically designed on the optical chip. Two conventional structures are typically adopted: grating couplers and edge couplers. While edge coupling structures are convenient for optical chip testing, they require vertical optical fiber coupling (i.e., optical axis of the optical fiber is relatively perpendicular to a structural surface of the optical chip) for wafer level testing.

[0006]

[0003] It is important to have a wafer level testing-compatible optical coupler to expedite mass production testing. In wafer level testing, optoelectronic measurements are performed on the wafer without having to dice the wafer into individual chips. Such testing requires vertical optical coupling methods. Grating couplers have been typically used for wafer level testing as optical coupling structures.

[0007]

[0004] Although grating couplers are convenient for wafer level testing, signal transmission using grating couplers suffer from low spectral bandwidth, and can require complex grating designs to enhance optical coupling efficiency. In contrast, edge couplers have the advantage of high spectral bandwidth and can be structurally straightforward to design - typically using inverse tapers.

[0005] In recent years, there have been efforts to realize vertical edge coupling for wafer level testing by using faceted optical fibers, i.e., fibers with polished end-faces that are angled. The facets on the fiber are angled such that optical signal from the fiber can be reflected to be coupled onto the optical chip. Conventional facet angles result in inefficient vertical edge coupling, and designing facet angles that enable efficient vertical edge coupling is complex.

[0008]

[0006] Accordingly, optical fibers with improved facet angles and / or structures that overcome the above shortcomings are highly desirable.

[0009] SUMMARY OF THE INVENTION

[0010]

[0007] According to an aspect, an optical fiber apparatus is provided which comprises:

[0011] at least one optical fiber having a waveguide core, a cladding coaxially surrounding the waveguide core, and a coating coaxially surrounding the cladding, wherein a plurality of angled-cleaved facets are formed in the cladding and include a first facet and a second facet,

[0012] wherein the first facet is located at an end of the optical fiber and defines a first cut inward angle a being relative to an optical axis of the optical fiber,

[0013] wherein the second facet defines a second cut inward angle b located at the end of the optical fiber, or a second cut outward angle c located at a non-end region of the optical fiber, the second cut inward angle b and the second cut outward angle c being relative to the optical axis of the optical fiber,

[0014] wherein

[0015]

[0016] < < 90°

[0017]

[0018] b = 90°

[0019] c — —90 "

[0020]

[0021] wherein nxis a refractive index of the waveguide core, n2is a refractive index of the cladding, and n3is a refractive index of the coating.

[0022]

[0008] In some embodiments, the angled-cleaved facets include a third facet which is located at a non-end region of the optical fiber.

[0009] In some embodiments, the third facet is provided by a notch cut into the cladding. In some embodiments, an angle at a notch tip of the notch cut is between -85° to 85°.

[0023]

[0010] In some embodiments, the third facet is arranged at an azimuthal angle which is between 0° to 360° relative to a cross-section of the optical fiber.

[0024]

[0011] In some embodiments, the waveguide core is selected from the group consisting of: a total internal reflection-based waveguide, a slot waveguide, a surface plasmon polariton waveguide, an in-plane scattering waveguide.

[0025]

[0012] In some embodiments, the waveguide core includes at least a material selected from the group consisting of: Si, SiC>2, BaTiOs, LisNbOs, InP, a lll-V compound, a ll-VI compound, and a polymer.

[0026]

[0013] In some embodiments, the coating is air.

[0027]

[0014] In an aspect, a fiber-chip coupling arrangement is provided which comprises:

[0028] an optical chip; and

[0029] an optical coupling structure arranged on the optical chip, wherein the optical coupling structure includes an on-chip coupler and optical components coupled thereto,

[0030] wherein the optical coupling structure is coupled to the optical fiber apparatus of any one of the above embodiments to allow optical signal transmission between the optical chip and the optical fiber.

[0031]

[0015] In some embodiments, the optical fiber is arranged at a tilt of 0° to about 75° relative to a vertical direction, or preferably 0° to about 45° relative to the vertical direction, wherein the vertical direction is orthogonal to an optical waveguide of the optical chip.

[0032]

[0016] In some embodiments, the optical coupling structure comprises phase masks which include a material selected from the group consisting of silicon (Si), polysilicon,silicon nitride (SisIXk), silicon dioxide, germanium (Ge), lithium niobate (LisNbOs), a polymer, a lll-V compound, and a ll-VI compound.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034]

[0017] Figure 1 shows a schematic block diagram of a fiber-chip coupling structure or arrangement;

[0035]

[0018] Figure 2 shows schematic side views of various fiber-chip coupling structures or arrangements corresponding to optical fiber apparatuses having different facet designs;

[0036]

[0019] Figure 3 shows isometric views of some arrangements of Figure 2;

[0037]

[0020] Figure 4A shows simulated plots having optical field incidence angle against reflectance at an interface between an optical fiber core and a coating of an optical fiber and also at an interface between an optical fiber cladding and the coating of the optical fiber;

[0038]

[0021] Figure 4B shows locations A, B, and C, as referred to in Figure 4A, in context some of the arrangements of Figure 2;

[0039]

[0022] Figure 5 shows a table having simulated resulting electric field (|E|) profiles of optical field of various optical fibers having different face angles or designs;

[0040]

[0023] Figure 6 shows a table having simulated resulting electric field (|E|) profiles and transmission of optical field from an optical fiber to an optical chip, of various optical fibers which are separated from the optical chips by 5 pm gap;

[0041]

[0024] Figure 7 shows a table having simulated resulting electric field (|E|) profiles and transmission of optical field from an optical fiber to an optical chip, of various optical fibers which are separated from the optical chips by 20 pm gap; and

[0042]

[0025] It should be understood that the drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of thefeatures of the present disclosure. The specific design features of the optical fiber as disclosed here, including, for example, the specific dimensions of the optical fiber, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to help provide clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration.

[0043] DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

[0044]

[0026] In the following description, numerous specific details are set forth in order to provide a thorough understanding of various illustrative and non-limiting embodiments. It will be understood, however, to one skilled in the art, that embodiments of the invention may be practiced without some or all these specific details. It is understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the invention. In the drawings, like reference labels or numerals, refer to same or similar functionalities or features throughout the several views.

[0045]

[0027] It should be understood that the articles "a", "an" and "the" as used with regard to a feature or element include a reference to one or more of the features or elements. The term "and / or" includes any and all combinations of one or more of the associated feature or element. The terms "comprising", "including", "having", and any of their related terms, as used in description and claims, are intended to be open-ended and mean that there may be additional features or elements other than the listed ones. Identifiers such as "first", "second", "third", and so on, are used merely as labels, and are not intended to impose numerical requirements on their objects, nor construed in a manner imposing any relative position or time sequence between limitations. The term “to” may include a reference to “configured to”, "adapted to", and "constructed and arranged to" which may be used interchangeably. Furthermore, terms such as “top”, “bottom”, “upper”, “lower”, “under”, “over”, “on” and their related terms used herein are merely for ease of description and may refer to the orientation of the features or elements as shown in the figures. It should be understood that any orientation of the features described herein is within the scope of the invention.

[0028] The term “coupled” may be used to include a reference to operational sense and may also include, but not necessarily limited to, a physical, optical, and / or electrical connection or coupling which may be direct or indirect. Thus, for example, two devices may be coupled directly, or indirectly via one or more intermediary devices. Based on the present disclosure, a person of ordinary skill in the art will appreciate a variety of ways in which coupling exists in accordance with the aforementioned definition.

[0046]

[0029] The present disclosure relates to an integrated photonic device, specifically an efficient fiber-chip coupling structure or arrangement in which an optical fiber has at least two facet cuts that are made or configured to efficiently transmit an optical field from / to an optical chip. The efficient fiber-chip coupling arrangement may be part of an optical coupling setup used in, for example, optical wafer level testing applications. The optical fiber may optionally include an additional facet cut that is made or configured to provide improved visualisation of an optical alignment edge of the optical fiber during alignment with the optical chip or other elements.

[0047]

[0030] The efficient fiber-chip coupling arrangement includes at least the following features: an optical fiber having at least two facets; and an optical chip optically coupled to the optical fiber. The optical fiber serves to deliver or receive optical signals to or from an optical chip. The optical fiber may be relatively vertically tilted for optical coupling lateral spatial constraints such as for wafer level testing.

[0048]

[0031] For optical coupling from an optical fiber to an optical chip, the fiber facets are configured such that a first facet is configured to reflect the optical field that propagates in the optical fiber core, and a second facet is configured to efficiently transmit the optical field to the optical chip. For optical coupling from an optical chip to an optical fiber, the fiber facets are configured such that a second facet is configured to efficiently transmit the optical field it receives, from the optical chip, into the optical fiber core, and a first facet is configured to efficiently reflect the optical field transmitted from to the second facet such that an optical field propagation direction is relatively aligned with the optical axis of the optical fiber.

[0032] The at least two facets may optionally include a third facet configured to reduce a vertical cladding height between the third facet and an optical alignment edge of the optical fiber. The third facet may be provided by a notch cut into the optical fiber. In other words, the optical fiber cladding between third facet and the optical alignment edge of the optical fiber is thinned down such that visualising the optical alignment edge during optical alignment purpose, e.g., alignment with the optical chip, is easier or improved as compared to an optical fiber without such third facet or thinned down optical fiber cladding.

[0049]

[0033] Embodiments of the efficient fiber-chip coupling arrangement is described in greater detail below in conjunction with the accompanying figures.

[0050]

[0034] Figure 1 shows a schematic block diagram of a fiber-chip coupling structure or arrangement 100, according to embodiments of the present disclosure, which includes an optical fibre apparatus having an optical fiber 110, and an optical coupling structure 120 on an optical chip 130 which is positioned in close proximity with the optical fiber 110 to allow optical signal transmission between the optical chip 130 and the optical fiber 110. The arrangement may include a plurality of optical fibers. The or each optical fiber 110 includes angle-cleaved end-face and, optionally, additional cleaved edge(s) which are advantageous in optically coupling optical signals efficiently between the optical fiber 110 and the optical chip 130.

[0051]

[0035] The optical fiber 110 is arranged to relatively vertically couple optical signals between the optical fiber 110 and optical chip 130, via an optical coupling structure 120. Particularly, the optical axis of the optical fiber 110 is arranged at a tilt angle, 0, from a vertical direction which may range from 0° to about 75°, or preferably 0° to about 45°. Ideally, the optical axis of the optical fiber 110 is exactly 90° to an optical axis of an optical waveguide of the optical chip 130, angle 0 is 0°. Hence, a vertical direction is taken as a direction orthogonal to the optical axis of the optical waveguide of the optical chip 130. This follows that the phrase “vertically couple” or its related phrase refers an arrangement in which the optical axis of the optical fiber 110 is orthogonal to an optical axis of an optical waveguide of the optical chip 130. That said, embodiments of the present disclosure may include arrangements where the optical axis of the optical fiber 110 is tilted, within the above-described or other prescribedworkable angle ranges, to an optical axis of an optical waveguide of the optical chip 130. Hence, the phrase “relatively vertically couple” or its related phrase refers an arrangement in which the optical axis of the optical fiber 110 is orthogonal or relatively orthogonal, i.e., within prescribed workable angle ranges, to the optical axis of the optical waveguide of the optical chip 130. In Figures 2 and 3, the vertical direction 50 is denoted by three round dots.

[0052]

[0036] The optical coupling structure 120 (optical chip waveguide structures) comprises an on-chip coupler (edge coupler) 121 and other optical components 122 coupled thereto. The optical coupling structure 120 is arranged on the optical chip 130 (see Figures 2 and 3). The optical coupling structure 120 may be realised by phase masks fabricated from, for example, any of silicon (Si), polysilicon, silicon nitride (SialS ), silicon dioxide, germanium (Ge), lithium niobate (LisNbOa), a polymer, a lll-V compound, i.e., an alloy containing elements from Groups III and V in the Periodic Table, and a ll-VI compound, i.e., an alloy containing elements from Groups II and VI in the Periodic Table.

[0053]

[0037] The optical fiber 110 comprises a waveguide core 111 , a cladding 112, and a coating 113 (optional). The waveguide core 111 is elongate and includes an optical axis which defines an optical signal propagation direction. The optical axis generally corresponds to a longitudinal direction of the waveguide core 111. The waveguide core 111 which is configured to be coupled to an on-chip coupler 121 of an optical chip 130 may be any type of waveguide. For example, the waveguide core 111 may be a total internal reflection-based waveguide, a slot waveguide, or a surface plasmon polariton waveguide. Alternatively, an in-plane scattering waveguide may be used, such as waveguide formed from photonic crystals which also use total internal reflection, and metamaterials. A composition of each of the plurality of waveguide cores may be, for example, one or more of the following: Si, SiO2, BaTiOs, LisNbOs, InP, a lll-V compound, a ll-VI compound, and a polymer. The waveguide core 111 may support any of the optical waveguide modes, for example, Transverse Electric mode and Transverse Magnetic mode. The waveguide core 111 has a refractive index, m, which may be in the range of 1.45-1.48.

[0038] The cladding 112 surrounds, and is disposed in contact with, the waveguide core 111 along the optical signal propagation or longitudinal direction. Thus, the waveguide core 111 and the cladding 112 are in a coaxial arrangement. A composition of the cladding may be, for example, one or more of the following: SiO2, and a polymer. The cladding has a refractive index, / ?2, which is lower than the refractive index, m, of the waveguide core 111. The refractive index, ri2, may be in the range of 1.40 to 1.45.

[0054]

[0039] The coating 113 surrounds, and is disposed in contact with, the cladding 112 along the optical signation propagation or longitudinal direction. The coating 113 may be a polymer, a metallic sheath, or air in an environment surrounding the optical fiber 110. The coating has a refractive index, r?3, which may be in the range of 1.38 to 1.42. If the coating is air, the refractive index, m, is 1. These values of m, rte, and na conform to the general rule: m > 02 to ensure total internal reflection occurs in the optical fiber. These values can vary depending on the specific type of optical fiber and its intended use, e.g., single-mode fiber vs. multimode fiber.

[0055]

[0040] The optical fiber 100 includes two opposite ends and a non-end region therebetween. At one of the two opposite ends (hereinafter “the faceted end”), multiple angled-cleaved facets are formed to provide end-faces. This faceted end includes an alignment surface or edge which is to be aligned to the optical chip 130 for in-coupling of optical signals from the optical chip 130 and / or out-coupling of optical signals to the optical chip 130. Accordingly, the alignment surface or edge provides optical coupling from the optical fiber 110 to the optical chip 130, and vice versa. Optical signal propagation during the in-coupling generally defines an in-coupling direction while optical signal propagation during the out-coupling defines an out- coupling direction. Various embodiments are described in the following paragraphs.

[0056]

[0041] Figure 2 provides schematic side views of various fiber facet designs or embodiments 210, 220, 230, 240, 2401 (equivalent to 240), 2402, 2403, 2404, 2405, 2406. For illustrative purpose, only the faceted ends and part of non-end regions of the optical fibers are shown. Prior art design 210 (single facet design) includes a single facet defining a conventional facet cut inward angle, e.g., angle a is 45°. In Embodiments 220, 230, 240, 2401 (equivalent to 240), 2402, 2403, 2404, 2405, 2406. each embodiment includes a plurality of angle-cleaved facets according to the presentdisclosure. Figure 3 provides isometric views of Embodiments 210, 220, 230, 240 of Figure 2.

[0057]

[0042] In Embodiment 220, the angle-cleaved facets are located at an end of the optical fiber 110, and includes a first facet and a second facet. The first facet defines a first cut inward angle, a, relative to the optical axis of the optical fiber 110, while the second facet defines a second cut inward angle, b, relative to the optical axis of the optical fiber 110. In Embodiment 220, the first facet and the second facet traverse or cut two non-intersecting portions of an end of the optical fiber 110 such that the resulting two end-faces are non-intersecting. Thus, the first facet and the second facet at the faceted end of the optical fiber 110 are non-intersecting. An “inward angle’’ refers to an angle in which a combination of its vertex and two arms generally points towards the in-coupling direction. Accordingly, an “outward angle” refers to an angle in which a combination of its vertex and two arms generally points to the out-coupling direction.

[0058]

[0043] Embodiment 230 is similar to Embodiment 220 except that the second facet defines a second cut outward angle, c, relative to the optical axis of the optical fiber 110 instead of the second cut inward angle, b. In Embodiment 230, the first facet and the second facet traverse or cut two non-intersecting portions of an end of the optical fiber 110 such that the resulting two end-faces are non-intersecting. Thus, the first facet and the second facet at the faceted end of the optical fiber 110 are nonintersecting.

[0059]

[0044] It is to be appreciated that variations to Embodiment 220 and 230 may be envisaged. For example, the first facet and the second facet may traverse or cut two intersecting portions of an end of the optical fiber 110. Thus, the first facet and the second facet may be intersecting.

[0060]

[0045] In embodiments of the present disclosure, the values of a, b, c are determined by the following equations:

[0061] < <

[0062]

[0063] Equation (3)

[0064]

[0065] wherein

[0066]

[0067] is a refractive index of the waveguide core, n2is a refractive index of the cladding, and n3is a refractive index of the coating surrounding the cladding.

[0068]

[0046] Embodiment 240 includes the above-described features, including the first facet and the second facet, of Embodiment 220. In addition, the angle-cleaved facets of Embodiment 240 additionally include a third facet located at the non-end region of the optical fiber 110. The third facet is located more distal or further from the faceted end of the optical fiber 110 than the first facet and / or the second facet. The third facet may be provided by or a part of a notch cut into the cladding 112 of the optical fiber 110. The notch may be a V-shape, L-shape or other shape having straight edges, and defines an angle at the notch tip, i.e., intersection of edges of the notch. The vertical angle at the notch tip may be between -85° to 85°, and is limited by the angle at which optical signal transmission through the waveguide core 111 is obstructed. A vertical angle of 0° indicates that the notch cut is exactly 90° (orthogonal) to the optical axis of the optical fiber 110.

[0069]

[0047] While the first facet and the second facet are designed for optimal optical transmission, the third facet is designed to thin down or reduce a vertical cladding height between the third facet and an optical alignment surface or edge of the optical fiber 110. This vertical height is taken along the vertical direction and may be denoted by h as shown in Figure 2.

[0070]

[0048] For fiber to chip alignment, an alignment indicator may be added for visibility. The alignment indicator may be deposited on the third facet. Non-limiting examples of alignment indicator include colored buffer coatings such as polymer materials, e.g., acrylate, PVC, polyurethane, marker dyes or ink, reflective coatings such as microbeads or metallic films, protective coatings such as acrylic, silicone or polymer materials, marker beads or spots such as glass, plastic or silicon or permanent markers or patterns laser etched into glass itself.

[0049] It is to be appreciated that variations to the above embodiments may be envisaged in other embodiments. For example, the optical fiber 110 may have at most two facets or three facets. For example, the optical fiber 110 may have at least two facets or at least three facets. For example, the third facet may be configured to be arranged at any azimuthal angle which is between 0° to 360° on a cross-section of the optical fiber 110. For example, the notch cut may alternatively be a hollow traversing the cladding or a crater having curved edges.

[0071]

[0050] Figure 4A illustrates a simulated plot of optical field incidence angle against reflectance at an interface between an optical fiber core and a coating of an optical fiber according to the present disclosure, and also at an interface between an optical fiber cladding and the coating of the optical fiber. In the example of Figure 4, the numerically simulated optical fiber has the following parameters: core diameter of 8.3 pm, cladding diameter of 125 pm and an air coating. There are three main points or locations A, B, C which are used for the analysis. In order to ensure enhanced transmission through the optical fiber which is an objective of the present disclosure, reflectance R is preferably as low as possible for all three locations A, B, and C. The plot shows the various values or ranges or incident angles, at which the reflectance is low, which would assist in determining the cut angles for the first facet and the second facet. Figure 4B shows possible locations of A, B, and C, in context of Embodiments 220 and 230. In particular, location A is on or along a first facet of the optical fiber 110; location B is on or along a waveguide core 111 of the optical fiber 110; location C is on or along the second facet of the optical fiber 110.

[0072]

[0051] Figure 5 illustrates estimated resulting electric field (| E\) profiles of optical field of embodiments of facet cut designs 510 and 520 in an optical fiber 110. In the example of Figure 5, the numerically simulated optical fiber has same parameters as the example of Figure 4. Prior art design 510 does not conform to the angle range prescribed by Equations 1 to 3. Conventionally, facet angle (a, b) = (40°, 10°) is adopted. Embodiments 520, 530, 540 conform to the angle range described in Equations 1 to 3. In particular, Embodiment 520 (Design I) provides for facet angle (a, b) = (34.9°, 55.1°), Embodiment 530 (Design II) provides for facet angle (a,b) = (25°, 74.8°), and Embodiment 540 (Design III) provides for facet angle (a,c) = (40°,24.8°). The embodiments 520, 530, 540 are three example designs which conform to the angle range prescribed by Equations 1 to 3.

[0073]

[0052] Figure 6 is a table showing simulated resulting electric field (| E |) profiles and transmission of optical field from an optical fiber 110 to an optical chip 130, which are separated by a 5 pm gap, of the prior art design 510 of Figure 5 that does not conform to the angle range prescribed by Equations 1 to 3, and Embodiment 520 (referring to Design I of Figure 5) that conforms to the angle range prescribed by Equations 1 to 3. As shown by Figure 6, Embodiment 520 has a higher transmission efficiency than prior art design 510. In the example of Figure 6, the numerically simulated optical fiber has the following defined parameters: diameter core of 8.3 pm, diameter cladding of 125 pm. The numerically simulated edge coupler has the following parameters: width tip of 0.2 pm which transitioned to waveguide width of 0.5 pm within a length of 200 pm.

[0074]

[0053] Figure 7 is a table showing estimated resulting electric field (|E |) profiles and transmission of optical field from an optical fiber 110 to an optical chip 130, which are separated by a 20 pm gap, of the prior art design 510 of Figure 5 that does not conform to the angle range prescribed by Equations 1 to 3, and Embodiment 540 (referring to Design III of Figure 5) that conforms to the angle range prescribed by Equations 1 to 3. As shown by Figure 7, Embodiment 540 has a higher transmission efficiency than the prior art design 510 of Figure 5.

[0075]

[0054] Embodiments of the present disclosure are advantageous at least as follows.

[0076]

[0055] Compared to conventional design, embodiments herein provide low loss optical transmission, and with broad optical bandwidth, between a relatively vertical optical fiber and an optical chip coupled thereto. This prevents loss of signal information across a broad spectral wavelength, which would otherwise exist due to non-optimal optical reflection and optical transmission between the optical fiber and the optical chip.

[0077]

[0056] Furthermore, the third facet provided at a non-end region of the optical fiber provides a reduced or thinned down vertical cladding height between the third facet and an optical alignment edge such that visualising the optical alignment edge duringoptical alignment purpose, e.g., alignment with the optical chip, is easier or improved as compared to an optical fiber without such third facet or vertically thinned down optical fiber cladding.

[0078]

[0057] From the foregoing disclosure and detailed description of certain embodiments, it will be apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope of the invention of the present disclosure. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

CLAIMS1. An optical fiber apparatus comprising:at least one optical fiber having a waveguide core, a cladding coaxially surrounding the waveguide core, and a coating coaxially surrounding the cladding, wherein a plurality of angled-cleaved facets are formed in the cladding and include a first facet and a second facet,wherein the first facet is located at an end of the optical fiber and defines a first cut inward angle a being relative to an optical axis of the optical fiber,wherein the second facet defines a second cut inward angle b located at the end of the optical fiber, or a second cut outward angle c located at a non-end region of the optical fiber, the second cut inward angle b and the second cut outward angle c being relative to the optical axis of the optical fiber,. .wherein < <b = 90°C = -90°whereinis a refractive index of the waveguide core, n2is a refractive index of the cladding, and n3is a refractive index of the coating.

2. The optical fiber apparatus of claim 1, wherein the angled-cleaved facets include a third facet which is located at a non-end region of the optical fiber.

3. The optical fiber apparatus of claim 2, wherein the third facet is provided by a notch cut into the cladding.

4. The optical fiber apparatus of claim 3, wherein an angle at a notch tip of the notch cut is between -85° to 85°.

5. The optical fiber apparatus of claim 2, wherein the third facet is arranged at an azimuthal angle which is between 0° to 360° relative to a cross-section of the optical fiber.

6. The optical fiber apparatus of any one of claim 1 to claim 5, wherein the waveguide core is selected from the group consisting of: a total internal reflectionbased waveguide, a slot waveguide, a surface plasmon polariton waveguide, an inplane scattering waveguide.

7. The optical fiber apparatus of any one of claim 1 to claim 6, wherein the waveguide core includes at least a material selected from the group consisting of: Si, SiO2, BaTiOa, LigNbOa, InP, a lll-V compound, a ll-VI compound, and a polymer.

8. The optical fiber apparatus of any one of claim 1 to claim 7, wherein the coating is air.

9. A fiber-chip coupling arrangement comprising:an optical chip; andan optical coupling structure arranged on the optical chip, wherein the optical coupling structure includes an on-chip coupler and optical components coupled thereto,wherein the optical coupling structure is coupled to the optical fiber apparatus of any one of claim 1 to claim 8 to allow optical signal transmission between the optical chip and the optical fiber.

10. The fiber-chip coupling arrangement of claim 9, wherein the optical fiber is arranged at a tilt of 0° to about 75° relative to a vertical direction, or preferably 0° to about 45° relative to the vertical direction, wherein the vertical direction is orthogonal to an optical waveguide of the optical chip.

11. The fiber-chip coupling arrangement of claim 9, wherein the optical coupling structure comprises phase masks which include a material selected from the group consisting of silicon (Si), polysilicon, silicon nitride (SiaN4), silicon dioxide, germanium (Ge), lithium niobate (LisNbOs), a polymer, a lll-V compound, and a ll-VI compound.

Images