Patent ID: 12210185

DETAILED DESCRIPTION

Various implementations described herein provide improved wavelength division multiplexers for space division multiplexing (SDM-WDM devices) such as wavelength division multiplexing fanout devices and pump-signal combiners for multicore fibers (MCFs). Various implementations described herein provide improved space division multiplexing (SDM). Some components can include adapters between multicore fibers (MCFs) with different core patterns. Some examples can include add-drop multiplexers for MCFs. Some designs can include multiplexers with pattern adaptation and channel add-drop.

In some instances, improved cross sectional (or transverse) positioning of waveguides is desirable in many multichannel optical coupler arrays. In the present disclosure, some embodiments of the housing structure (e.g., a common single coupler housing structure in some cases) can allow for self-aligning waveguide arrangement at a close proximity to a first end (e.g., hexagonal close packed arrangement in a housing structure having circular (as shown inFIG.8) or hexagonal inner cross section) and improved (precise or near precise in some cases) cross sectional positioning of the waveguides at a second end.

Packaging of photonic integrated circuits (PICs) with low vertical profile (perpendicular to the PIC plane) can also be desirable for a variety of applications, including optical communications and sensing. While this is easily achievable for edge couplers, surface couplers may require substantial vertical length.

Accordingly, it may be advantageous to provide various embodiments of a pitch reducing optical fiber array (PROFA)-based flexible optical fiber array component that may be configured and possibly optimized to comprise a structure that maintains all channels discretely with sufficiently low crosstalk, while providing enough flexibility to accommodate low profile packaging. It may further be desirable to provide a PROFA-based flexible optical fiber array component comprising a flexible portion to provide mechanical isolation of a “PROFA-PIC interface” from the rest of the PROFA, resulting in increased stability with respect to environmental fluctuations, including temperature variations and mechanical shock and vibration. It may be additionally desirable to provide a PROFA-based flexible optical fiber array comprising multiple coupling arrays, each having multiple optical channels, combined together to form an optical multi-port input/output (IO) interface.

Certain embodiments are directed to an optical fiber coupler array capable of providing a low-loss, high-coupling coefficient interface with high accuracy and easy alignment between a plurality of optical fibers (or other optical devices) with a first channel-to-channel spacing, and an optical device having a plurality of waveguide interfaces with a second, smaller channel-to-channel spacing. Advantageously, in various embodiments, each of a larger size end and a smaller size end of the optical fiber coupler array is configurable to have a correspondingly different (i.e., larger vs. smaller) channel-to-channel spacing, where the respective channel-to-channel spacing at each of the optical coupler array's larger and smaller ends may be readily matched to a corresponding respective first channel-to-channel spacing of the plural optical fibers at the larger optical coupler array end, and to a second channel-to-channel spacing of the optical device plural waveguide interfaces at the smaller optical coupler array end.

In various embodiments thereof, the optical coupler array includes a plurality of waveguides (at least one of which may optionally be polarization maintaining), that comprises at least one gradually reduced “vanishing core fiber”, at least in part embedded within a common housing structure. Alternatively, in various additional embodiments thereof, the coupler array may be configured for utilization with at least one of an optical fiber amplifier and an optical fiber laser.

Each of the various embodiments of the optical coupler array advantageously comprises at least one “vanishing core” (VC) fiber waveguide, described, for example, below in connection with a VC waveguide30A of the optical coupler array10A ofFIG.1A.

It should also be noted that the term “optical device” as generally used herein, applies to virtually any single channel or multi-channel optical device, or to any type of optical fiber, including, but not being limited to, standard/conventional optical fibers. For example, optical devices with which the coupler array may advantageously couple may include, but are not limited to, one or more of the following:a free-space-based optical device,an optical circuit having at least one input/output edge coupling port,an optical circuit having at least one optical port comprising vertical coupling elements,a multi-mode (MM) optical fiber,a double-clad optical fiber,a multi-core (MC) optical fiber,a large mode area (LMA) fiber,a double-clad multi-core optical fiber,a standard/conventional optical fiber,a custom optical fiber, and/oran additional optical coupler array.

In addition, while the term “fusion splice” is utilized in the various descriptions of the example embodiments of the coupler array provided below, in reference to interconnections between various optical coupler array components, and connections between various optical coupler array components and optical device(s), it should be noted, that any other form of waveguide or other coupler array component connectivity technique or methodology may be readily selected and utilized as a matter of design choice or necessity, without departing from the spirit of the invention, including but not limited to mechanical connections.

Referring now toFIG.1A, a first example embodiment of an optical fiber coupler array is shown as an optical coupler array10A, which comprises a common housing structure14A (described below), at least one VC waveguide, shown inFIG.1Aby way of example, as a single VC waveguide30A, and at least one Non-VC waveguide, shown inFIG.1Aby way of example, as a pair of Non-VC waveguides32A-1,32A-2, each positioned symmetrically proximally to one of the sides of the example single VC waveguide30A, wherein the section of the VC waveguide30A, located between positions B and D ofFIG.1Ais embedded in the common housing structure14A.

Before describing the coupler array10A and its components in greater detail, it would be useful to provide a detailed overview of the VC waveguide30A, the example embodiments and alternative embodiments of which, are advantageously utilized in each of the various embodiments of the coupler arrays ofFIGS.1A to5.

The VC waveguide30A has a larger end (proximal to position B shown inFIG.1A), and a tapered, smaller end (proximal to position C shown inFIG.1A), and comprises an inner core20A (comprising a material with an effective refractive index of N-1), an outer core22A (comprising a material with an effective refractive index of N-2, smaller than N-1), and a cladding24A (comprising a material with an effective refractive index of N-3, smaller than N-2).

Advantageously, the outer core22A serves as the effective cladding at the VC waveguide30A large end at which the VC waveguide30A supports “M1” spatial propagating modes within the inner core20A, where M1 is larger than 0. The indices of refraction N-1 and N-2, are preferably chosen so that the numerical aperture (NA) at the VC waveguide30A large end matches the NA of an optical device (e.g. an optical fiber) to which it is connected (such as an optical device34A-1, for example, comprising a standard/conventional optical fiber connected to the VC waveguide30A at a connection position36A-1(e.g., by a fusion splice, a mechanical connection, or by other fiber connection designs), while the dimensions of the inner and outer cores (20A,22A), are preferably chosen so that the connected optical device (e.g., the optical device34A-1), has substantially the same mode field dimensions (MFD). Here and below we use mode field dimensions instead of commonly used mode field diameter (also MFD) due to the case that the cross section of the VC or Non-VC waveguides may not be circular, resulting in a non-circular mode profile. Thus, the mode field dimensions include both the mode size and the mode shape and equal to the mode field diameter in the case of a circularly symmetrical mode.

During fabrication of the coupler array10A from an appropriately configured preform (comprising the VC waveguide30A preform having the corresponding inner and outer cores20A,22A, and cladding24A), as the coupler array10A preform is tapered in accordance with at least one predetermined reduction profile, the inner core20A becomes too small to support all M1 modes. The number of spatial modes, supported by the inner core at the second (tapered) end is M2, where M2<M1. In the case of a single mode waveguide, where M1=1 (corresponding to 2 polarization modes), M2=0, meaning that inner core is too small to support light propagation. The VC waveguide30A then acts as if comprised a fiber with a single core of an effective refractive index close to N-2, surrounded by a cladding of lower index N-3.

During fabrication of the coupler array10A, a channel-to-channel spacing S-1 at the coupler array10A larger end (at position B,FIG.1A), decreases in value to a channel-to-channel spacing S-2 at the coupler array10A smaller end (at position C,FIG.1A), in proportion to a draw ratio selected for fabrication, while the MFD value (or the inversed NA value of the VC waveguide30A) can be either reduced, increased or preserved depending on a selected differences in refractive indices, (N-1-N-2) and (N-2-N-3), which depends upon the desired application for the optical coupler array10A, as described below.

The capability of independently controlling the channel-to-channel spacing and the MFD values at each end of the optical coupler array is a highly advantageous feature of certain embodiments. Additionally, the capability to match MFD and NA values through a corresponding selection of the sizes and shapes of inner20A and outer22A cores and values of N-1, N-2, and N-3, makes it possible to utilize the optical coupler array to couple to various waveguides without the need to use a lens.

In various embodiments thereof, the property of the VC waveguide permitting light to continue to propagate through the waveguide core along the length thereof when its diameter is significantly reduced, advantageously, reduces optical loss from interfacial imperfection or contamination, and allows the use of a wide range of materials for a medium28A of the common housing structure14A (described below), including, but not limited to:(a) non-optical materials (since the light is concentrated inside the waveguide core),(b) absorbing or scattering materials or materials with refractive index larger than the refractive index of standard/conventional fibers for reducing or increasing the crosstalk between the channels, and(c) pure-silica (e.g., the same material as is used in most standard/conventional fiber claddings, to facilitate splicing to multi-core, double-clad, or multi-mode fiber.

Preferably, in accordance with certain embodiments, the desired relative values of NA-1 and NA-2 (each at a corresponding end of the coupler array10A, for example, NA-1 corresponding to the coupler array10A large end, and NA-2 corresponding to the coupler array10A small end), and, optionally, the desired value of each of NA-1 and NA-2), may be determined by selecting the values of the refractive indices N1, N2, and N3 of the coupler array10A, and configuring them in accordance with at least one of the following relationships, selected based on the desired relative numerical aperture magnitudes at each end of the coupler array10A:

Desired NA-1/NA-2Corresponding RelationshipRelative Magnitudebet. N1, N2, N3NA-1 (lrg. end) > NA-2 (sm. end)(N1 − N2 > N2 − N3)NA-1 (lrg. end) = NA-2 (sm. end)(N1 − N2 = N2 − N3)NA-1 (lrg. end) < NA-2 (sm. end)(N1 − N2 < N2 − N3)

Commonly the NA of any type of fiber is determined by the following expression:
NA=√{square root over (ncore2−nclad2)};where ncoreand ncladare the refractive indices of fiber core and cladding respectively.

It should be noted that when the above expression is used, the connection between the NA and the acceptance angle of the fiber is only an approximation. In particular, fiber manufacturers often quote “NA” for single-mode (SM) fibers based on the above expression, even though the acceptance angle for a single-mode fiber is quite different and cannot be determined from the indices of refraction alone.

In accordance with certain embodiments, as used herein, the various NA values are preferably determined utilizing effective indices of refraction for both ncoreand ncladding, because the effective indices determine the light propagation and are more meaningful in the case of structured waveguides utilized in various embodiments. Also, a transverse refractive index profile inside a waveguide may not be flat, but rather varying around the value N1, N2, N3, or N4. In addition, the transition between regions having refractive indices N1, N2, N3, and N4 may not be as sharp as a step function due to dopant diffusion or some other intentional or non-intentional factors, and may be a smooth function, connecting the values of N1, N2, N3, and N4. Coupling design or optimization may involve changing both the values of N1, N2, N3, and N4 and the sizes and shapes of the regions having respective indices.

Returning now toFIG.1A, the common coupling structure14A, comprises the medium28A, in which the section of the VC waveguide30A located between positions B and D ofFIG.1Ais embedded, and which may include, but is not limited to, at least one of the following materials:a material, having properties prohibiting propagation of light therethrough,a material having light-absorbing optical properties,a material having light scattering optical properties,a material having optical properties selected such that said fourth refractive index (N-4) is greater than said third refractive index (N-3), and/ora material having optical properties selected such that said fourth refractive index (N-4) is substantially equal to said third refractive index (N-3).

At the optical coupler array10A large end (proximally to position B inFIG.1A), the VC waveguide30A is spliced, at a particular splice location36A-1(shown by way of example as positioned inside the common housing structure14A), to a corresponding respective elongated optical device34A-1(for example, such as an optical fiber), at least a portion of which extends outside the common housing structure14A by a predetermined length12A, while the Non-VC waveguides32A-1,32A-2are spliced, at particular splice locations36A-2,36A-3, respectively (disposed outside of the common housing structure14A), to corresponding respective elongated optical devices34A-2,34A-3(such as optical fibers), and extending outside the common housing structure14A by a predetermined length12A.

Optionally, the coupler array10A may also include a substantially uniform diameter tip16A (shown between positions C and D inFIG.1A) for coupling, at an array interface18A with the interface42A of an optical waveguide device40A. The uniform diameter tip16A may be useful in certain interface applications, such as for example shown inFIGS.1D,4and5. Alternatively, the coupler array10A may be fabricated without the tip16A (or have the tip16A removed after fabrication), such that coupling with the optical device interface42A, occurs at a coupler array10A interface at position C ofFIG.1A.

In an alternative embodiment, if the optical device40A comprises a double-clad fiber, when the small end of the coupler array10A is coupled (for example, fusion spliced) to the optical device interface42A, at least a portion of the common housing structure14A proximal to the splice position (such as at least a portion of the tip16A), may be coated with a low index medium (not shown), extending over the splice position and up to the double-clad fiber optical device40A outer cladding (and optionally extending over a portion of the double-clad fiber optical device40A outer cladding that is proximal to the splice position).

Referring now toFIG.1B, a second example embodiment of the optical fiber coupler array, is shown as a coupler array10B. The coupler array10B comprises a common housing structure14B, at least one VC waveguide, shown inFIG.1Bby way of example, as a single VC waveguide30B, and at least one Non-VC waveguide, shown inFIG.1Bby way of example, as a single Non-VC waveguide32B, disposed in parallel proximity to the VC waveguide30B, where a portion of the optical coupler array10B, has been configured to comprise a larger channel-to-channel spacing value S2′ at its small end, than the corresponding channel-to-channel spacing value S2 at the small end of the optical coupler array10A, ofFIG.1A. This configuration may be readily implemented by transversely cutting the optical fiber array10A at a position C′, thus producing the common housing structure14B that is shorter than the common housing structure14A and resulting in a new, larger diameter array interface18B, having the larger channel-to-channel spacing value S2′.

Referring now toFIG.1C, a third example embodiment of the optical fiber coupler array, is shown as a coupler array10C. The coupler array10C comprises a plurality of VC waveguides, shown inFIG.1Cas VC waveguides30C-1, and30C-2, and a plurality of Non-VC waveguides, shown inFIG.1Cas Non-VC waveguides32C-1,32C-2, and32C-a, all disposed longitudinally and asymmetrically to one another, wherein at least a portion of the plural Non-VC waveguides are of different types and/or different characteristics (such as single mode or multimode or polarization maintaining etc.)—for example, Non-VC waveguides32C-1,32C-2are of a different type, or comprise different characteristics from the Non-VC waveguide32C-a. Additionally, any of the VC or Non-VC waveguides (such as, for example, the Non-VC waveguide32C-a) can readily extend beyond the coupler array10C common housing structure by any desired length, and need to be spliced to an optical device proximally thereto.

Referring now toFIG.1D, a fourth example embodiment of the optical fiber coupler array that is configured for multi-core fan-in and fan-out connectivity, and shown as a coupler array50. The coupler array50comprises a pair of optical fiber coupler array components (10D-1and10D-2), with a multi-core optical fiber element52connected (e.g., by fusion splicing at positions54-1and54-2) between the second (smaller sized) ends of the two optical fiber coupler array components (10D-1,10D-2). Preferably, at least one of the VC waveguides in each of the coupler array components (10D-1,10D-2) is configured to increase or maximize optical coupling to a corresponding selected core of the multi-core optical fiber element52, while decreasing or minimizing optical coupling to all other cores thereof.

Referring now toFIG.2A, a fifth example embodiment of the optical fiber coupler array, is shown as a coupler array100A. The coupler array100A comprises a plurality of longitudinally proximal VC waveguides at least partially embedded in a single common housing structure104A, shown by way of example only, as plural VC waveguides130A-1,130A-2. Each plural VC waveguide130A-1,130A-2is spliced, at a particular splice location132A-1,132A-2, respectively, to a corresponding respective elongated optical device134A-1,134A-2(such as an optical fiber), at least a portion of which extends outside the common housing structure104A by a predetermined length102A, and wherein each particular splice location132A-1,132A-2is disposed within the common housing structure104A.

Referring now toFIG.2B, a sixth example embodiment of the optical fiber coupler array, is shown as a coupler array100B.

The coupler array100B comprises a plurality of longitudinally proximal VC waveguides at least partially embedded in a single common housing structure104B, shown by way of example only, as plural VC waveguides130B-1,130B-2. Each plural VC waveguide130B-1,130B-2is spliced, at a particular splice location132B-1,132B-2, respectively, to a corresponding respective elongated optical device134B-1,134B-2(such as an optical fiber), at least a portion of which extends outside the common housing structure104B by a predetermined length102B, and wherein each particular splice location132B-1,132B-2is disposed at an outer cross-sectional boundary region of the common housing structure104B.

Referring now toFIG.2C, a seventh example embodiment of the optical fiber coupler array, is shown as a coupler array100C.

The coupler array100C comprises a plurality of longitudinally proximal VC waveguides at least partially embedded in a single common housing structure104C, shown by way of example only, as plural VC waveguides130C-1,130C-2. Each plural VC waveguide130C-1,130C-2is spliced, at a particular splice location132C-1,132C-2, respectively, to a corresponding respective elongated optical device134C-1,134C-2(such as an optical fiber), at least a portion of which extends outside the common housing structure104C by a predetermined length102C, and wherein each particular splice location132C-1,132C-2is disposed outside of the common housing structure104C.

Referring now toFIG.2D, an alternative embodiment of the optical fiber coupler array, is shown as a coupler array150. The coupler array150comprises a plurality of longitudinally proximal VC waveguides at least partially embedded in a single common housing structure, that is configured at its second end, to increase or optimize optical coupling to a free-space-based optical device152. The free-space-based optical device152may comprise a lens154followed by an additional optical device component156, which may comprise, by way of example, a MEMS mirror or volume Bragg grating. The combination of the coupler and the free-space-based optical device152may be used as an optical switch or WDM device for spectral combining or splitting of light signals160b(representative of the light coupler array150output light signals160aafter they have passed through the lens154.) In this case, one of the fibers may be used as an input and all others for an output or vice versa. In another embodiment, a free-space-based device152can be fusion spliceable to the second coupler's end. This device may be a coreless glass element, which can serve as an end cup for power density redaction at the glass-air interface. In another modification, the coreless element can serve as a Talbot mirror for phase synchronization of coupler's waveguides in a Talbot cavity geometry

Prior to describing the various embodiments shown inFIGS.3A to3Lin greater detail, it should be understood that whenever a “plurality” or “at least one” coupler component/element is indicated below, the specific quantity of such coupler components/elements that may be provided in the corresponding embodiment of the coupler array, may be selected as a matter of necessity, or design choice (for example, based on the intended industrial application of the coupler array), without departing from the spirit of the present invention. Accordingly, in the variousFIGS.3A to3L, single or individual coupler array components/elements are identified by a single reference number, while each plurality of the coupler component/elements is identified by a reference number followed by a “(1. . .n)” designation, with “n” being a desired number of plural coupler elements/components (and which may have a different value in any particular coupler array embodiment described below).

Also, all the waveguides VC and Non-VC are shown with a circular cross-section of the inner and outer core and cladding only by example. Other shapes of the cross-sections of the inner and outer core and cladding (for example, hexagonal, rectangular or squared) may be utilized without departure from the current invention. The specific choice of shape is based on various requirements, such as channel shape of the optical device, channel positional geometry (for example, hexagonal, rectangular or square lattice), or axial polarization alignment mode.

Similarly, unless otherwise indicated below, as long as various relationships set forth below (for example, the relative volume relationship set forth below with respect to optical coupler arrays200C and200D ofFIGS.3C and3D, respectively, and the feature, set forth below in connection with the coupler array200H ofFIG.3H, that the PM VC waveguide204H is positioned longitudinally off-centered transversely from the coupler array200H central longitudinal axis), are adhered to, the sizes, relative sizes, relative positions and choices of composition materials, are not limited to the example sizes, relative sizes, relative positions and choices of composition materials, indicated below in connection with the detailed descriptions of the coupler array embodiments ofFIGS.3A to3L, but rather they may be selected by one skilled in the art as a matter of convenience or design choice, without departing from the spirit of the present invention.

Finally, it should be noted that each of the various single common housing structure components202A to202L, of the various coupler arrays200A to200L ofFIGS.3A to3L, respectively, may be composed of a medium having the refractive index N-4 value in accordance with an applicable one of the above-described relationships with the values of other coupler array component refractive indices N-1, N-2, and N-3, and having properties and characteristics selected from the various contemplated example medium composition parameters described above in connection with medium28A ofFIG.1A.

Referring now toFIG.3A, a first alternative embodiment of the optical fiber coupler array embodiments ofFIGS.1D to2D, is shown as a coupler array200A in which all waveguides are VC waveguides. The coupler array200A comprises a single common housing202A, and plurality of VC waveguides204A-(1. . .n), with n being equal to 19 by way of example only, disposed centrally along the central longitudinal axis of the housing202A. The coupler array200A may also comprise an optional at least one fiducial element210A, operable to provide one or more useful properties to the coupler array, including, but not limited to:enabling visual identification (at at least one of the coupler array's ends) of the coupler array waveguide arrangement; andfacilitating passive alignment of at least one of the coupler array ends to at least one optical device.

Furthermore, when deployed in optical coupler array embodiments that comprise at least one polarization maintaining VC waveguide (such as the optical coupler array embodiments described below in connection withFIGS.3H-3L), a fiducial element is further operable to:enable visual identification of the optical coupler array's particular polarization axes alignment mode (such as described below in connection withFIGS.3H-3L); andserve as a geometrically positioned reference point for alignment thereto, of one or more polarization axis of PM waveguides in a particular optical coupler array.

The fiducial element210A may comprise any of the various types of fiducial elements known in the art, selected as a matter of design choice or convenience without departing from the spirit of the invention—for example, it may be a dedicated elongated element positioned longitudinally within the common housing structure202A in one of various cross-sectional positions (such as positions X or Y, shown inFIG.3A. Alternatively, the fiducial element210A may comprise a dedicated channel not used for non-fiducial purposes, for example, replacing one of the waveguides204A-(1. . .n), shown by way of example only at position Z inFIG.3A.

Referring now toFIG.3B, a first alternative embodiment of the optical fiber coupler array10A ofFIG.1A, above, is shown as a coupler array200B, that comprises a single housing structure202B, and at least one VC waveguide, shown inFIG.3Bby way of example as a VC waveguide204B, and a plurality of Non-VC waveguides206B-(1. . .n), with n being equal to 18 by way of example only. The VC waveguide204B is positioned along a central longitudinal axis of the common housing structure202B, and circumferentially and symmetrically surrounded by proximal parallel plural Non-VC waveguides206B-(1. . .n).

Referring now toFIG.3C, a first alternative embodiment of the optical fiber coupler array200B ofFIG.3B, above, is shown as a coupler array200C that comprises a single housing structure202C, a VC waveguide204C, and a plurality of Non-VC waveguides206C-(1. . .n), with n being equal to 18 by way of example only. The VC waveguide204C is positioned along a central longitudinal axis of the common housing structure202C, and circumferentially and symmetrically surrounded by proximal parallel plural Non-VC waveguides206C-(1. . .n). The coupler array200C is configured such that a volume of the common housing structure202C medium, surrounding the sections of all of the waveguides embedded therein (i.e., the VC waveguide204C and the plural Non-VC waveguides206C-(1. . .n)), exceeds a total volume of the inner and outer cores of the section of the VC waveguide204C that is embedded within the single common housing structure202C.

Referring now toFIG.3D, a first alternative embodiment of the optical fiber coupler array200C ofFIG.3C, above, is shown as a coupler array200D that comprises a single housing structure202D, a plurality of VC waveguides204D-(1. . . N), with N being equal to 7 by way of example only, and a plurality of Non-VC waveguides206D-(1. . .n), with n being equal to 12 by way of example only. The plural VC waveguides204D-(1. . . N) are positioned along a central longitudinal axis of the common housing structure202D, and circumferentially and symmetrically surrounded by proximal parallel plural Non-VC waveguides206D-(1. . .n). The coupler array200D is configured such that a volume of the common housing structure202D medium, surrounding the sections of all of the waveguides embedded therein (e.g., the plural VC waveguides204D-(1. . . N), and the plural Non-VC waveguides206D-(1. . .n)), exceeds a total volume of the inner and outer cores of the section of the plural VC waveguides204D-(1. . . N) that are embedded within the single common housing structure202D.

Referring now toFIG.3E, a first alternative embodiment of the optical fiber coupler array200D ofFIG.3D, above, is shown as a coupler array200E, that comprises a single housing structure202E, a plurality of VC waveguides204E-(1. . . N), with N being equal to 6 by way of example only, a plurality of Non-VC waveguides206E-(1. . .n), with n being equal to 12 by way of example only, and a separate single Non-VC waveguide206E′. The Non-VC waveguide206E′, is preferably operable to provide optical pumping functionality therethrough, and is positioned along a central longitudinal axis of the common housing structure202E and circumferentially and symmetrically surrounded by proximal parallel plural VC waveguides204E-(1. . . N), that are in turn circumferentially and symmetrically surrounded by proximal parallel plural Non-VC waveguides206E-(1. . .n).

Referring now toFIG.3F, a second alternative embodiment of the optical fiber coupler array200B ofFIG.3B, above, is shown as a coupler array200F, that comprises a single housing structure202F, a plurality of VC waveguides204F-(1. . . N), with N being equal to 6 by way of example only, a separate single VC waveguide204F′, and a plurality of Non-VC waveguides206F-(1. . .n), with n being equal to 12 by way of example only, that preferably each comprise enlarged inner cores of sufficient diameter to increase or optimize optical coupling to different types of optical pump channels of various optical devices, to which the coupler array200F may be advantageously coupled. The VC waveguide204F′, is positioned along a central longitudinal axis of the common housing structure202F, and circumferentially and symmetrically surrounded by proximal parallel plural VC waveguides204F-(1. . . N), that are in turn circumferentially and symmetrically surrounded by proximal parallel plural Non-VC waveguides206F-(1. . .n).

Referring now toFIG.3G, a third alternative embodiment of the optical fiber coupler array200B ofFIG.3B, above, is shown as a coupler array200G, that comprises a single housing structure202G, and at least one VC waveguide, shown inFIG.3Gby way of example as a VC waveguide204G, and a plurality of Non-VC waveguides206G-(1. . .n), with n being equal to 18 by way of example only. The VC waveguide204G is positioned as a side-channel, off-set from the central longitudinal axis of the single common housing structure202G, such that optical fiber coupler array200G may be readily used as a fiber optical amplifier and or a laser, when spliced to a double-clad optical fiber (not shown) having a non-concentric core for improved optical pumping efficiency. It should be noted that because a double-clad fiber is a fiber in which both the core and the inner cladding have light guiding properties, most optical fiber types, such as SM, MM, LMA, or MC (multi-core), whether polarization maintaining or not, and even standard (e.g., conventional) single mode optical fibers, can be converted into a double-clad fiber by coating (or recoating) the fiber with a low index medium (forming the outer cladding).

Optionally, when the second end of the coupler array200G is spliced to a double-clad fiber (not shown), at least a portion of the common housing structure202G proximal to the splice point with the double-clad fiber (not-shown), may be coated with a low index medium extending over the splice point and up to the double-clad fiber's outer cladding (and optionally extending over a portion of the outer cladding that is proximal to the splice point).

Referring now toFIGS.3H to3L, in various alternative example embodiments of the optical coupler, at least one of the VC waveguides utilized therein, and, in certain embodiments, optionally at least one of the Non-VC waveguides, may comprise a polarization maintaining (PM) property. By way of example, the PM property of a VC waveguide may result from a pair of longitudinal stress rods disposed within the VC waveguide outside of its inner core and either inside, or outside, of the outer core (or through other stress elements), or the PM property may result from a noncircular inner or outer core shape, or from other PM-inducing optical fiber configurations (such as in bow-tie or elliptically clad PM fibers). In various embodiments of the optical fiber in which at least one PM waveguide (VC and/or Non-VC) is utilized, an axial alignment of the PM waveguides (or waveguide), in accordance with a particular polarization axes alignment mode may be involved.

In accordance with certain embodiments, a polarization axes alignment mode may comprise, but is not limited to, at least one of the following:axial alignment of a PM waveguide's polarization axis to the polarization axes of other PM waveguides in the optical coupler; when a PM waveguide is positioned off-center: axial alignment of a PM waveguide's polarization axis to its transverse cross-sectional (geometric) position within the optical coupler;when the single common housing structure of the optical coupler comprises a non-circular geometric shape (such as shown by way of example inFIG.3L): axial alignment of a PM waveguide's polarization axis to a geometric feature of the common housing structure outer shape;in optical coupler embodiments comprising one or more waveguide arrangement indicators, described below, in connection withFIGS.3J-3L: axial alignment of a PM waveguide's polarization axis to at least one geometric characteristic thereof;in optical coupler embodiments comprising at least one fiducial element210A, as described above in connection withFIG.3A: axial alignment of a PM waveguide's polarization axis to a geometric position of the at least one fiducial element210A;

The selection of a specific type of polarization axes alignment mode for the various embodiments of the optical coupler is preferably governed by at least one axes alignment criterion, which may include, but which is not limited to: alignment of PM waveguides' polarization axes in a geometric arrangement that increases or maximizes PM properties thereof; and/or satisfying at least one requirement of one or more intended industrial application for the coupler array.

Referring now toFIG.3H, a first alternative embodiment of the optical fiber coupler array200G ofFIG.3G, above, is shown as a coupler array200H, that comprises a single housing structure202H, and at least one VC waveguide, shown inFIG.3Hby way of example as a PM VC waveguide204H having polarization maintaining properties, and a plurality of Non-VC waveguides206H-(1. . .n), with n being equal to 18 by way of example only. The PM VC waveguide204H is positioned as a side-channel, off-set from the central longitudinal axis of the single common housing structure202H, and comprises a polarization axis that is aligned, by way of example, with respect to the transverse off-center location of the PM VC waveguide204H.

Referring now toFIG.3I, a fourth alternative embodiment of the optical fiber coupler array200B ofFIG.3B, above, is shown as a coupler array200I, that comprises a single housing structure202I, and at least one VC waveguide, shown inFIG.3Iby way of example as a PM VC waveguide204I having polarization maintaining properties, and a plurality of PM Non-VC waveguides206I-(1. . .n), with n being equal to 18 by way of example only, each also having polarization maintaining properties. The PM VC waveguide204I is positioned along a central longitudinal axis of the common housing structure202I, and circumferentially and symmetrically surrounded by proximal parallel plural PM Non-VC waveguides206I-(1. . .n). By way of example, the coupler array200I comprises a polarization axes alignment mode in which the polarization axes of each of the PM VC waveguide204I and of the plural PM Non-VC waveguides206I-(1. . .n) are aligned to one another. The PM properties of the PM VC waveguide204I and of the plural PM Non-VC waveguides206I-(1. . .n) are shown, by way of example only, as being induced by rod stress members (and which may readily and alternately be induced by various other stress, or equivalent designs)).

Referring now toFIG.3J, a first alternative embodiment of the optical fiber coupler array200I ofFIG.3I, above, is shown as a coupler array200J, that comprises a single housing structure202J, and at least one VC waveguide, shown inFIG.3Jby way of example as a PM VC waveguide204J having polarization maintaining properties, and a plurality of PM Non-VC waveguides206J-(1. . .n), with n being equal to 18 by way of example only, each also having polarization maintaining properties. The PM VC waveguide204J is positioned along a central longitudinal axis of the common housing structure202J, and circumferentially and symmetrically surrounded by proximal parallel plural PM Non-VC waveguides206J-(1. . .n). The PM properties of the PM VC waveguide204J and of the plural PM Non-VC waveguides206J-(1. . .n) are shown, by way of example only, as resulting only from a non-circular cross-sectional shape (shown by way of example only as being at least in part elliptical), of each plural PM Non-VC waveguide206J-(1. . .n) core (and from a non-circular cross-sectional shape of the outer core of the PM VC waveguide204J).

The coupler array200J optionally comprises at least one waveguide arrangement indication element208J, positioned on an outer region of the common housing structure202J, that is representative of the particular cross-sectional geometric arrangement of the optical coupler array200J waveguides (i.e., of the PM VC waveguide204J and of the plural PM Non-VC waveguides206J-(1. . .n)), such that a particular cross-sectional geometric waveguide arrangement may be readily identified from at least one of a visual and physical inspection of the common coupler housing structure202J that is sufficient to examine the waveguide arrangement indication element208J. Preferably, the waveguide arrangement indication element208J may be configured to be further operable to facilitate passive alignment of a second end of the optical coupler array200J to at least one optical device (not shown).

The waveguide arrangement indication element208J, may comprise, but is not limited to, one or more of the following, applied to the common housing structure202J outer surface: a color marking, and/or a physical indicia (such as an groove or other modification of the common housing structure202J outer surface, or an element or other member positioned thereon). Alternatively, the waveguide arrangement indication element208J may actually comprise a specific modification to, or definition of, the cross-sectional geometric shape of the common housing structure202J (for example, such as a hexagonal shape of a common housing structure202L ofFIG.3L, below, or another geometric shape).

By way of example, the coupler array200J may comprise a polarization axes alignment mode in which the polarization axes of each of the PM VC waveguide204J and of the plural PM Non-VC waveguides206J-(1. . .n) are aligned to one another, or to the waveguide arrangement indication element208J.

Referring now toFIG.3K, a fifth alternative embodiment of the optical fiber coupler array200B ofFIG.3B, above, is shown as a coupler array200K, that comprises a single housing structure202K, and at least one VC waveguide, shown inFIG.3Kby way of example as a PM VC waveguide204K having polarization maintaining properties, and a plurality of Non-VC waveguides206K-(1. . .n), with n being equal to 18 by way of example only. The PM VC waveguide204K is positioned along a central longitudinal axis of the common housing structure202K, and circumferentially and symmetrically surrounded by proximal parallel plural PM Non-VC waveguides206K-(1. . .n). The PM properties of the PM VC waveguide204K are shown, by way of example only, as being induced by rod stress members (and which may readily and alternately be induced by various other stress, or equivalent approaches)). The coupler array200K, may optionally comprise a plurality of waveguide arrangement indication elements—shown by way of example only, as waveguide arrangement indication elements208K-a and208K-b, which may each be of the same, or of a different type, as described above, in connection with the waveguide arrangement indication element208J ofFIG.3J.

Referring now toFIG.3L, a second alternative embodiment of the optical fiber coupler array200I ofFIG.3I, above, is shown as a coupler array200L, that comprises a single housing structure202L comprising a cross section having a non-circular geometric shape (shown by way of example as a hexagon), and at least one VC waveguide, shown inFIG.3Lby way of example as a PM VC waveguide204L having polarization maintaining properties, and a plurality of PM Non-VC waveguides206L-(1. . .n), with n being equal to 18 by way of example only, each also having polarization maintaining properties. The PM VC waveguide204L is positioned along a central longitudinal axis of the common housing structure202L, and circumferentially and symmetrically surrounded by proximal parallel plural PM Non-VC waveguides206L-(1. . .n).

By way of example, the coupler array200L comprises a polarization axes alignment mode in which the polarization axes of each of the PM VC waveguide204L and of the plural PM Non-VC waveguides206L-(1. . .n) are aligned to one another, and to the common housing structure202L cross-sectional geometric shape. The PM properties of the PM VC waveguide204L and of the plural PM Non-VC waveguides206L-(1. . .n) are shown, by way of example only, as being induced by rod stress members (and which may readily and alternately be induced by various other stress, or equivalent designs)). The coupler array200K, may optionally comprise a waveguide arrangement indication element208L-a which may comprise any of the configurations described above, in connection with the waveguide arrangement indication element208J ofFIG.3J.

Referring now toFIG.4, a second end302(i.e. “tip”) of the optical fiber coupler array is shown, by way of example, as being in the process of connecting to plural vertical coupling elements306of an optical device304in a proximal open air optical coupling alignment configuration, that may be readily shifted into a butt-coupled configuration through full physical contact of the optical fiber coupler array second end302and the vertical coupling elements306.

Referring now toFIG.5a second end322(i.e. “tip”) of the optical fiber coupler array is shown, by way of example, as being in the process of connecting to plural edge coupling elements326of an optical device324in a butt-coupled configuration, that may be readily shifted into one of several alternative coupling configuration, including a proximal open air optical coupling alignment configuration, and or an angled alignment coupling configuration.

In at least one alternative embodiment, the optical coupler array (i.e., such as optical coupler arrays200D to200L ofFIGS.3C to3L) may be readily configured to pump optical fiber lasers, and/or optical fiber amplifiers (or equivalent devices). In a preferred embodiment thereof, a pumping-enabled coupler array comprises a central channel (i.e., waveguide), configured to transmit a signal (i.e., serving as a “signal channel”) which will thereafter be amplified or utilized to generate lasing, and further comprises at least one additional channel (i.e., waveguide), configured to provide optical pumping functionality (i.e., each serving as a “pump channel”). In various example alternative embodiments thereof, the pumping-enabled coupler array may comprise the following in any desired combination thereof:at least one of the following signal channels: a single mode signal channel configured for increased or optimum coupling to a single mode amplifying fiber at at least one predetermined signal or lasing wavelength, a multimode signal channel configured for increased or optimum coupling to a multimode amplifying fiber at at least one predetermined signal or lasing wavelength, andat least one of the following pumping channels: a single mode pumping channel configured for increased or optimum coupling to a single mode pump source at at least one predetermined pumping wavelength, a multimode pumping channel configured for increased or optimum coupling to a multimode pump source at at least one predetermined pumping wavelength.

Optionally, to increase or maximize pumping efficiency, the pumping-enabled coupler array may be configured to selectively utilize less than all the available pumping channels. It should also be noted that, as a matter of design choice, and without departing from the spirit of the invention, the pumping-enabled coupler array may be configured to comprise:a. At least one signal channel, each disposed in a predetermined desired position in the coupler array structure;b. At least one pumping channel, each disposed in a predetermined desired position in the coupler array structure; andc. Optionally—at least one additional waveguide for at least one additional purpose other than signal transmission or pumping (e.g., such as a fiducial marker for alignment, for fault detection, for data transmission, etc.)

Advantageously, the pump channels could be positioned in any transverse position within the coupler, including along the central longitudinal axis. The pump channels may also comprise, but are not limited to, at least one of any of the following optical fiber types: SM, MM, LMA, or VC waveguides. Optionally, any of the optical fiber(s) being utilized as an optical pump channel (regardless of the fiber type) in the coupler may comprise polarization maintaining properties.

In yet another example embodiment, the pumping-enabled coupler array may be configured to be optimized for coupling to a double-clad fiber—in this case, the signal channel of the coupler array would be configured or optimized for coupling to the signal channel of the double-clad fiber, while each of the at least one pumping channels would be configured or optimized to couple to the inner cladding of the double-clad fiber.

In essence, the optical coupler arrays, shown by way of example in various embodiments, may also be readily implemented as high density, multi-channel, optical input/output (I/O) for fiber-to-chip and fiber-to-optical waveguides. The optical fiber couplers may readily comprise at least the following features:Dramatically reduced channel spacing and device footprint (as compared to previously known solutions)Scalable channel countAll-glass optical pathReadily butt-coupled or spliced at their high density face without the need of a lens, air gap, or a beam spreading mediumMay be fabricated through a semi-automated production processBroad range of customizable parameters: wavelength, mode field size, channel spacing, array configuration, fiber type.

The optical fiber couplers may be advantageously utilized for at least the following applications, as a matter of design choice or convenience, without departing from the spirit of the invention:Coupling to waveguides:PIC or PCB-based (single-mode or multimode)Multicore fibersChip edge (1D) or chip face (2D) couplingNA optimized for the application, factoring in:Packaging alignment needsChip processing needs/waveguide up-taperingPolarization maintaining properties may be readily configuredCoupling to chip-based devices: e.g. VCSELs, photodiodes, vertically coupled gratingsLaser diode couplingHigh density equipment Input/Output (I/O)

Accordingly, when implemented, the various example embodiments of the optical fiber couplers comprise at least the following advantages, as compared to currently available competitive solutions:Unprecedented densityLow-loss coupling (<0.5 dB)Operational stabilityForm factor supportBroad spectral rangeMatching NAScalable channel countPolarization maintenance

Referring now toFIG.7, at least one example embodiment of a flexible optical coupler array is shown as a flexible pitch reducing optical fiber array (PROFA) coupler450. Although various features of the example PROFA coupler may be described with respect toFIG.7, any feature described above can be implemented in any combination with a flexible PROFA coupler. For example, any of the features described with respect toFIGS.1A-5may be utilized in a flexible PROFA coupler. Further, any feature described with respect toFIGS.1A-5may be combined with any feature described with respect toFIG.7.

With continued reference toFIG.7, the example flexible PROFA coupler450shown inFIG.7can be configured for use in applications where interconnections with low crosstalk and sufficient flexibility to accommodate low profile packaging are desired. The vanishing core approach, described herein and in U.S. Patent Application Publication No. 2013/0216184, entitled “CONFIGURABLE PITCH REDUCING OPTICAL FIBER ARRAY”, which is hereby incorporated herein in its entirety, allows for the creation of a pitch reducing optical fiber array (PROFA) coupler/interconnect operable to optically couple, for example, a plurality of optical fibers to an optical device (e.g., a PIC), which can be butt-coupled to an array of vertical grating couplers (VGCs). If the cross sectional structure of the coupler450has an additional layer of refractive index, N-2A, even lower than N2, as described herein and in U.S. Patent Application Publication No. 2013/0216184, the vanishing core approach can be utilized once more to reduce the outside diameter further without substantially compromising the channel crosstalk. This further reduction can advantageously provide certain embodiments with a flexible region which has a reduced cross section between a first and second end.

In some preferred embodiments, the difference (N-2A minus N-3) is larger than the differences (N-2 minus N-2A) or (N-1 minus N-2), resulting in a high NA, bend insensitive waveguide, when the light is guided by the additional layer having refractive index N-2A. Also, in some preferred embodiments, after the outside diameter of the coupler450is reduced along a longitudinal length from one end to form the flexible region, the outer diameter can then be expanded along the longitudinal length toward the second end, resulting in a lower NA waveguide with larger coupling surface area at the second end.

For example, as illustrated inFIG.7, certain embodiments of an optical coupler array450can comprise an elongated optical element1000having a first end1010, a second end1020, and a flexible portion1050therebetween. The optical element1000can include a coupler housing structure1060and a plurality of longitudinal waveguides1100embedded in the housing structure1060. The waveguides1100can be arranged with respect to one another in a cross-sectional geometric waveguide arrangement. InFIG.7, the example cross-sectional geometric waveguide arrangements of the waveguides1100for the first end1010, the second end1020, and at a location within the flexible portion1050are shown. The cross-sectional geometric waveguide arrangement of the waveguides1100for an intermediate location1040between the first end1010and the flexible portion1050is also shown. As illustrated by the shaded regions within the cross sections and as will be described herein, light can be guided through the optical element1000from the first end1010to the second end1020through the flexible portion1050. As also shown inFIG.7, this can result in a structure, which maintains all channels discretely with sufficiently low crosstalk, while providing enough flexibility (e.g., with the flexible portion1050) to accommodate low profile packaging.

The level of crosstalk and/or flexibility can depend on the application of the array. For example, in some embodiments, a low crosstalk can be considered within a range from −45 dB to −35 dB, while in other embodiments, a low crosstalk can be considered within a range from −15 dB to −5 dB. Accordingly, the level of crosstalk is not particularly limited. In some embodiments, the crosstalk can be less than or equal to −55 dB, −50 dB, −45 dB, −40 dB, −35 dB, −30 dB, −25 dB, −20 dB, −15 dB, −10 dB, 0 dB, or any values therebetween (e.g., less than or equal to −37 dB, −27 dB, −17 dB, −5 dB, etc.) In some embodiments, the crosstalk can be within a range from −50 dB to −40 dB, from −40 dB to −30 dB, from −30 dB to −20 dB, from −20 dB to −10 dB, from −10 dB to 0 dB, from −45 dB to −35 dB, from −35 dB to −25 dB, from −25 dB to −15 dB, from −15 dB to −5 dB, from −10 dB to 0 dB, any combinations of these ranges, or any ranges formed from any values from −55 dB to 0 dB (e.g., from −52 dB to −37 dB, from −48 dB to −32 dB, etc.).

The flexibility can also depend on the application of the array. For example, in some embodiments, good flexibility of the flexible portion1050can comprise bending of at least 90 degrees, while in other embodiments, a bending of at least 50 degrees may be acceptable. Accordingly, the flexibility is not particularly limited. In some embodiments, the flexibility can be at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, 120 degrees, or at least any value therebetween. In some embodiments, the flexible portion1050can bend in a range formed by any of these values, e.g., from 45 to 55 degrees, from 50 to 60 degrees, from 60 to 70 degrees, from 70 to 80 degrees, from 80 to 90 degrees, from 90 to 100 degrees, from 100 to 110 degrees, from 110 to 120 degrees, or any combinations of these ranges, or any ranges formed by any values within these ranges (e.g., from 50 to 65 degrees, from 50 to 85 degrees, from 65 to 90 degrees, etc.) In other embodiments, the flexible portion1050can bend more or less than these values. Bending can typically be associated with light scattering. However, various embodiments can be configured to bend as described herein (e.g., in one of the ranges described above) and achieve relatively low crosstalk as described herein (e.g., in one of the ranges described above).

In various applications, the flexible portion1050might not bend in use, however the flexibility can be desired for decoupling the first1010or second1020end from other parts of the coupler array450. For example, the flexible portion1050of the flexible PROFA coupler450can provide mechanical isolation of the first end1010(e.g., a PROFA-PIC interface) from the rest of the PROFA, which results in increased stability with respect to environmental fluctuations, including temperature variations and mechanical shock and vibration.

In the example shown inFIG.7, the coupler array450can be operable to optically couple with a plurality of optical fibers2000and/or with an optical device3000. The optical fibers2000and optical device3000can include any of those described herein. The coupler array450can couple with the optical fibers2000via the plurality of waveguides1100at the first end1010. In addition, the coupler array450can couple with the optical device3000via the plurality of waveguides1100at the second end1020. As described herein, the plurality of waveguides1100can include at least one VC waveguide1101.FIG.7illustrates all of the waveguides1100as VC waveguides. However, one or more Non-VC waveguides may also be used. In addition,FIG.7illustrates 7 VC waveguides, yet any number of VC and/or Non-VC waveguides can be used.

As also shown in the cross sections, each of the waveguides1100can be disposed at an individual corresponding cross-sectional geometric position, relative to other waveguides of the plurality of waveguides1100. AlthoughFIG.7shows a waveguide surrounded by 6 other waveguides, the cross-sectional geometric waveguide arrangement is not limited and can include any arrangement known in the art or yet to be developed including any of those shown inFIGS.3A-3L.

As described herein, the VC waveguide1101can include an inner core (e.g., an inner vanishing core)1110, an outer core1120, and an outer cladding1130with refractive indices N-1, N-2, and N-3 respectively. As shown inFIG.7, the VC waveguide1101can also include a secondary outer core1122(e.g., between the outer core1120and the outer cladding1130) having refractive index N-2A. As the outer core1120can longitudinally surround the inner core1110, the secondary outer core1122can longitudinally surround the outer core1120with the outer cladding1130longitudinally surrounding the secondary outer core1122. In various embodiments, the relationship between the refractive indices of the inner core1110, outer core1120, secondary outer core1122, and outer cladding1130can advantageously be N-1>N-2>N2-A>N-3. With such a relationship, each surrounding layer can serve as an effective cladding to the layers within it (e.g., the outer core1120can serve as an effective cladding to the inner core1110, and the secondary outer core1122can serve as an effective cladding to the outer core1120). Hence, the use of the secondary outer core1122can provide an additional set of core and cladding.

By including the secondary outer core1122with a refractive index N-2A, certain embodiments can achieve a higher NA (e.g., compared to without the secondary outer core1122). In various embodiments, the difference (N-2A minus N-3) can be larger than the differences (N-2 minus N-2A) or (N-1 minus N-2) to result in a relatively high NA. Increasing NA can reduce the MFD, allowing for the channels (e.g., waveguides1100) to be closer to each other (e.g., closer spacing between the waveguides1100) without compromising crosstalk. Accordingly, the coupler array450can be reduced further in cross section (e.g., compared to without the secondary outer core1122) to provide a reduced region when light is guided by the secondary outer core1122. By providing a reduced region between the first end1010and the second end1020, certain embodiments can include a flexible portion1050which can be more flexible than the regions proximal to the first end1010and the second end1020.

For example, the inner core1110size, the outer core1120size, and the spacing between the waveguides1100can reduce (e.g., simultaneously and gradually in some instances) along the optical element1000from the first end1010to the intermediate location1040such that at the intermediate location1040, the inner core1110size is insufficient to guide light therethrough and the outer core1120size is sufficient to guide at least one optical mode. In certain embodiments, each waveguide1100can have a capacity for at least one optical mode (e.g., single mode or multi-mode). For example, at the first end1010, the VC waveguide1101can support a number of spatial modes (M1) within the inner core1110. At the intermediate location1040, in various embodiments, the inner core1110may no longer be able to support all the M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the intermediate location1040, the outer core1120can be able to support all the M1 modes (and in some cases, able to support additional modes). In this example, light traveling within the inner core1110from the first end1010to the intermediate location1040can escape from the inner core1110into the outer core1120such that light can propagate within both the inner core1110and outer core1120.

In addition, the outer core1120size, the secondary outer core1122size, and the spacing between the waveguides1100can reduce (e.g., simultaneously and gradually in some instances) along said optical element1000, for example, from the intermediate location1040to the flexible portion1050such that at the flexible portion1050, the outer core1120size is insufficient to guide light therethrough and the secondary outer core1122size is sufficient to guide at least one optical mode therethrough. In certain embodiments, at the intermediate location1040, the VC waveguide1101can support all the M1 modes within the outer core1120. At the flexible portion1050, in various embodiments, the outer core1120may be no longer able to support all the M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the flexible portion1050, the secondary outer core1122can be able to support all the M1 modes (and in some cases, able to support additional modes). In this example, light traveling within the outer core1120from the intermediate location1040to the flexible portion1050can escape from the outer core1120into the secondary outer core1122such that light can propagate within the inner core1110, the outer core1120, and secondary outer core1122.

Furthermore, the outer core1120size, the secondary outer core1122size, and the spacing between the waveguides1100can expand (e.g., simultaneously and gradually in some instances) along the optical element1000from the flexible portion1050to the second end1020such that at the second end1020, the secondary outer core1122size is insufficient to guide light therethrough and the outer core1120size is sufficient to guide at least one optical mode therethrough. In certain embodiments, at the second end1020, in various embodiments, the secondary outer core1122may no longer be able to support all the M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the second end1020, the outer core1120can be able to support all the M1 modes (and in some cases, able to support additional modes). In this example, light traveling within the secondary outer core1122from the flexible portion1050to the second end1020can return and propagate only within the inner core1110and the outer core1120.

It would be appreciated that light travelling from the second end1020to the first end1010can behave in the reverse manner. For example, the outer core1120size, the secondary outer core1122size, and spacing between the waveguides1100can reduce (e.g., simultaneously and gradually in some instances) along the optical element1000from the second end1020to the flexible portion1050such that at the flexible portion1050, the outer core1120size is insufficient to guide light therethrough and the secondary outer core1122size is sufficient to guide at least one optical mode therethrough.

The reduction in cross-sectional core and cladding sizes can advantageously provide rigidity and flexibility in a coupler array450. Since optical fibers2000and/or an optical device3000can be fused to the ends1010,1020of the coupler array450, rigidity at the first1010and second1020ends can be desirable. However, it can also be desirable for coupler arrays to be flexible so that they can bend to connect with low profile integrated circuits. In certain embodiments, the flexible portion1050between the first1010and second1020ends can allow the first1010and second1020ends to be relatively rigid, while providing the flexible portion1050therebetween. The flexible portion can extend over a length of the optical element1000and can mechanically isolate the first1010and second1020ends. For example, the flexible portion1050can mechanically isolate the first end1010from a region between the flexible portion1050and the second end1020. As another example, the flexible portion1050can mechanically isolate the second end1020from a region between the first end1010and the flexible portion1050. Such mechanical isolation can provide stability to the first1010and second1020ends, e.g., with respect to environmental fluctuations, including temperature variations and mechanical shock and vibration. The length of the flexible portion1050is not particularly limited and can depend on the application. In some examples, the length can be in a range from 2 to 7 mm, from 3 to 8 mm, from 5 to 10 mm, from 7 to 12 mm, from 8 to 15 mm, any combination of these ranges, or any range formed from any values from 2 to 20 mm (e.g., 3 to 13 mm, 4 to 14 mm, 5 to 17 mm, etc.). In other examples, the length of the flexible portion1050can be shorter or longer.

At the same time, the flexible portion1050can provide flexibility. In many instances, the flexible portion1050can have a substantially similar cross-sectional size (e.g., the cross-sectional size of the waveguides1100) extending over the length of the flexible portion1050. In certain embodiments, the cross-section size at the flexible portion1050can comprise a smaller cross-sectional size than the cross-sectional size at the first1010and second1020ends. Having a smaller cross-sectional size, this flexible portion1050can be more flexible than a region proximal to the first1010and second1020ends. The smaller cross-sectional size can result from the reduction in core and cladding sizes. An optional etching post-process may be desirable to further reduce the diameter of the flexible length of the flexible PROFA coupler450.

In some embodiments, the flexible portion1050can be more flexible than a standard SMF 28 fiber. In some embodiments, the flexible portion1050can bend at least 45 degrees, 50 degrees, 55 degrees, 60 degrees, 65 degrees, 70 degrees, 75 degrees, 80 degrees, 90 degrees, 100 degrees, 110 degrees, 120 degrees, or at least any value therebetween. In some embodiments, the flexible portion1050can bend in a range formed by any of these values, e.g., from 45 to 55 degrees, from 50 to 60 degrees, from 60 to 70 degrees, from 70 to 80 degrees, from 80 to 90 degrees, from 90 to 100 degrees, from 100 to 110 degrees, from 110 to 120 degrees, or any combinations of these ranges, or any ranges formed by any values within these ranges (e.g., from 50 to 65 degrees, from 50 to 85 degrees, from 65 to 90 degrees, etc.) In other embodiments, the flexible portion1050can bend more or less than these values. As described herein, in various applications, the flexible portion1050might not bend in use, however the flexibility can be desired for decoupling the first1010or second1020end from other parts of the coupler array450.

The coupler array450can include a coupler housing structure1060. For example, the coupler housing structure1060can include a common single coupler housing structure. In certain embodiments, the coupler housing structure1060can include a medium1140(e.g., having a refractive index N-4) surrounding the waveguides1100. In some instances, N-4 is greater than N-3. In other examples, N-4 is equal to N-3. The medium1140can include any medium as described herein (e.g., pure-silica). The medium can also include glass such that the coupler array450can be an all-glass coupler array. The waveguides1100can be embedded within the medium1040of the housing structure1060. In some examples, a total volume of the medium1140of the coupler housing structure1060can be greater than a total volume of all the inner and outer cores1110,1120,1122of the VC waveguides confined within the coupler housing structure1060.

In some embodiments, each waveguide can couple to the optical fibers2000and/or optical device3000at a location inside, outside, or at a boundary region of the coupler housing structure1060, e.g., as shown inFIGS.1A to2D. Because the optical fibers2000and optical device3000can be different at each end, the first end1010and the second end1020can each be configured for the optical fibers2000or optical device3000with which it is coupled. For example, the MFD of the VC waveguide at the first1010and/or second1020ends can be configured (e.g., using the sizes of the cores) to match or substantially match the MFD of the optical fiber2000or optical device3000with which it is coupled. In addition, the NA of the VC waveguide at the first1010and/or second1020ends can be configured (e.g., using the refractive indices) to match or substantially match the NA of the optical fiber2000or optical device3000with which it is coupled. The refractive indices can be modified in any way known in the art (e.g., doping the waveguide glass) or yet to be developed. In various embodiments, as described herein, the difference (N-1 minus N-2) can be greater than the difference (N-2 minus N-2A) such that the NA at the first end1010is greater than the NA at the second end1020. In other embodiments, the difference (N-1 minus N-2) can be less than the difference (N-2 minus N-2A) such that the NA at the first end1010is less than the NA at the second end1020. In yet other embodiments, the difference (N-1 minus N-2) can be equal to (N-2 minus N-2A) such that the NA at the first end1010is equal to the NA at the second end1020. The VC waveguide can include any of the fiber types described herein including but not limited to a single mode fiber, a multi-mode fiber, and/or a polarization maintaining fiber.

The core and cladding (1110,1120,1122,1130) sizes (e.g., outer cross-sectional diameters if circular or outer cross-sectional dimensions if not circular) are not particularly limited. In some embodiments, the inner1110and/or outer1120core sizes can be in a range from 1 to 3 microns, from 2 to 5 microns, from 4 to 8 microns, from 5 to 10 microns, any combination of these ranges, or any range formed from any values from 1 to 10 microns (e.g., 2 to 8 microns, 3 to 9 microns, etc.). However, the sizes can be greater or less. For example, the inner1110and/or outer1120core sizes can range from submicrons to many microns, to tens of microns, to hundreds of microns depending, for example, on the wavelength and/or number of modes desired.

In addition, the difference in the refractive indices (e.g., between N-1 and N-2, between N-2 and N-2A, and/or between N-2A and N-3) is not particularly limited. In some examples, the index difference can be in a range from 1.5×10−3to 2.5×10−3, from 1.7×10−3to 2.3×10−3, from 1.8×10−3to 2.2×10−3, from 1.9×10−3to 2.1×10−3, from 1.5×10−3to 1.7×10−3, from 1.7×10−3to 1.9×10−3, from 1.9×10−3to 2.1×10−3, from 2.1×10−3to 2.3×10−3, from 2.3×10−3to 2.5×10−3, any combination of these ranges, or any range formed from any values from 1.5×10−3to 2.5×10−3. In other examples, the index difference can be greater or less.

As described herein, the optical device3000can include a PIC. The PIC can include an array of VGCs. Also, as described in U.S. Patent Application Publication 2012/0257857, entitled “HIGH DENSITY OPTICAL PACKAGING HEADER APPARATUS”, which is hereby incorporated herein in its entirety, multiple flexible PROFA couplers (such as the coupler450), each having multiple optical channels, can be combined together to advantageously form an optical multi-port input/output (IO) interface. As such, an optical multi-port10interface can include a plurality of optical coupler arrays, at least one of the optical coupler arrays can include an optical coupler array450as described herein.

With reference now toFIG.8andFIG.9, example cross sectional views of the housing structure at a proximity to a first end of a multichannel optical coupler array are shown. The cross-sectional view is orthogonal to the longitudinal direction or length of the optical coupler array. Some such configurations may have improved cross sectional or transverse (or lateral) positioning of waveguides at the first end allowing for self-aligning waveguide arrangement at a close proximity to a first end (e.g., hexagonal close packed arrangement in a housing structure having circular (as shown inFIG.8) or hexagonal inner cross section) and improved (precise or near precise in some cases) cross sectional positioning of the waveguides at a second end. Such configurations may also provide alignment during manufacturing such that the cross sectional positioning of the waveguides at a second end may be more precisely disposed as desired.

Although various features of the example optical coupler arrays may be described with respect toFIGS.8and9, any feature described above (for example, in connection with any of the figures or embodiments describe above) can be implemented in any combination with a multichannel optical coupler array. For example, any of the features described with respect toFIGS.1A-5and7may be utilized in a multichannel optical coupler array and may be combined with any feature described with respect toFIGS.8and9.

For example, referring to the example embodiments shown inFIGS.1A-2D, there are two ends of the coupler array: a first (larger) end, and a second (smaller) end. The two ends are spaced apart in the longitudinal direction (along the z direction). For example, inFIG.1A, the first end is proximate to position B and the second end is proximate to positions C and D.

In certain embodiments, one of the functions of the first end (proximate to position B) is to encapsulate the waveguides30A,32A-1,32A-2with increased or approximate positioning accuracy. For example, the coupler housing structure14A at a proximity to the first end (proximate to position B) may encapsulate, e.g., circumferentially surround a portion of the length of the waveguides30A,32A-1,32A-2, but not necessarily completely enclose the ends of the waveguides30A,32A-1,32A-2. In some such instances, the waveguides30A,32A-1,32A-2may or may not extend (e.g., longitudinally) outside the coupler housing structure14A. InFIG.1A, proximate the first end, the end of waveguide30A is disposed within the coupler housing structure14A, but the ends of waveguides32A-1and32A-2extend, e.g., longitudinally (in a direction parallel to the z-direction) outside of the coupler housing structure14A. InFIG.2B, proximate the first end, the ends of waveguides130B-1,130B-2are disposed at an outer cross sectional boundary region of the coupler housing structure14A and do not extend, e.g., longitudinally (in a direction parallel to the z-direction) outside of the coupler housing structure14A.

In various embodiments, one of the functions of the second end (proximate to positions C and D) is to have the waveguides30A,32A-1,32A-2embedded in a housing structure (e.g., a common housing structure in some instances) with improved (precise or near precise in some cases) cross sectional positioning. For example, the waveguides30A,32A-1,32A-2at a proximity to the second end (proximate to positions C and D) may be embedded, e.g., be circumferentially surrounded by the contiguous coupler housing structure14A. InFIG.1A, proximate the second end, the ends of waveguides30A,32A-1,32A-2are longitudinally disposed at an outer cross sectional boundary region of the coupler housing structure14A. In some embodiments, proximate the second end, one or more ends of the waveguides may be disposed within or may longitudinally extend outside the coupler housing structure14A.

To achieve improved positioning, some embodiments can include the example cross sectional configuration of the housing structure shown inFIG.8at a proximity to the first end. The cross section is orthogonal to the longitudinal direction or length of the optical coupler array. As shown inFIG.8, the coupler array800can include a housing structure801having a transverse (or lateral) configuration of a ring surrounding the plurality of longitudinal waveguides805at a close longitudinal proximity to the first end. A gap, such as an air gap, may separate the plurality of longitudinal waveguides805from the surrounding ring. Some such configurations may allow for self-aligning waveguide arrangement at a close proximity to a first end (e.g., hexagonal close packed arrangement in a housing structure having circular (as shown inFIG.8) or hexagonal inner cross section)

In an example configuration shown inFIG.8, the waveguides805are in a hexagonal arrangement. Other arrangements are possible, e.g., square, rectangular, etc.

The ring may have an inner cross section801a(in the transverse direction, i.e., orthogonal to the longitudinal direction or length of the optical coupler array) that is circular or non-circular. For example, the inner cross section801amay be circular, elliptical, D-shaped, square, rectangular, hexagonal, pentagonal, octagonal, other polygonal shape, etc. The inner cross section801adoes not necessarily follow the arrangement of the waveguides805. For example, four waveguides arranged in a square arrangement can be confined in an inner circular cross section. As another example, as shown inFIG.8, the inner cross section801ais circular, while the waveguides805are hexagonally arranged. In some embodiments, a circular inner cross section, as shown inFIG.8, may be a preferred shape, which can allow for a close-pack hexagonal arrangement. Also, other inner cross sectional shapes may also be used, such as square or rectangular, which can allow for non-hexagonal waveguide arrangements. In some instances, the inner cross section801amay be similar as the arrangement of the waveguides805to reduce empty space. For example, for waveguides805in a hexagonal arrangement, the inner cross section801aof the ring may be hexagonal to reduce empty space between the inner cross section801aand the waveguides805.

The outer cross section801b(in the transverse direction, e.g., orthogonal to the longitudinal direction or length of the optical coupler array) may be circular or non-circular. For example, the outer cross section801bmay be circular, elliptical, hexagonal, D-shaped (e.g., to provide for passive axial alignment of the coupler since the flat surface allow for an easy rotational alignment), square, rectangular, pentagonal, octagonal, other polygonal shape, etc. InFIG.8, the outer cross section801b(e.g., circular) follows the shape of the inner cross section801a(e.g., circular). However, in some embodiments, the outer cross section801bneed not be similar as the inner cross section801a. One of the functions of the inner cross sectional shape is to allow for an improvement in the transverse positional accuracy at the proximity to the second end, while one of the functions of the outer cross sectional shape is to allow for a passive axial alignment of the coupler (e.g., the alignment can be done without launching light into the coupler). In some configurations it may be preferred to substantially preserve the outer cross sectional shape from the first end to the second end to facilitate the passive alignment at one of the ends or at both ends of the coupler array.

FIG.9shows another example cross sectional configuration of the housing structure at a proximity to the first end. As shown inFIG.9, the coupler array850can include a housing structure851having a configuration of a structure (e.g., a contiguous structure in some cases) with a plurality of holes852. At least one of the holes852may contain at least one of the longitudinal waveguides855. A gap, such as an air gap, may separate the plurality of longitudinal waveguides855from the surrounding housing structure851. Similarly to the description related to the example shown inFIG.8, the outer cross section may be circular, elliptical, hexagonal, D-shaped, square, rectangular, pentagonal, octagonal, other polygonal shape, etc. Some of such configurations may allow for passive alignment at one of the ends or at both ends of the coupler array. While the example configuration shown inFIG.8may allow for simpler fabrication in some cases, the example configuration shown inFIG.9may allow for arbitrary transverse waveguide positioning.

FIG.9shows an example configuration with six holes852, yet other number of holes is possible. The holes852in this example configuration may be isolated or some or even all holes852may be connected. For example, as shown inFIG.9, a first hole852-1is isolated from a second hole852-2. However, in some configurations, the first hole852-1may be connected to at least one second hole852-2. The arrangement of the holes852is shown as a 3×2 array, yet other arrangements are possible. For example, the hole arrangement pattern may be hexagonal, square, rectangular, or defined by an XY array defining positions of the holes in the transverse plane.

FIG.9shows all the holes852with a waveguide855illustrated as a vanishing core (VC) waveguide. However, while at least one of the waveguide in this example is a VC waveguide, one or more of the holes852may include a non-vanishing core (Non-VC) waveguide. The VC or Non-VC waveguide855can include any of the waveguides described herein, e.g., single mode fiber, multi-mode fiber, polarization maintaining fiber, etc. In some embodiments, one or more of the holes852may be empty, or populated with the other (e.g., non-waveguide) material, e.g., to serve as fiducial marks. One or more of the holes852may be populated with a single waveguide855(in some preferred configurations) as shown inFIG.9or with multiple waveguides855. Depending on the design, one or more of the holes852may be identical or different than another hole852to accommodate, for example, waveguides855of different shapes and dimensions (e.g., cross sectional shapes, diameters, major/minor elliptical dimensions, etc.). The cross sections of the holes852may be circular or non-circular. For example, the cross section may be circular, elliptical, hexagonal or D-shaped (e.g., to provide for passive axial alignment of polarization maintaining (PM) channels), square, rectangular, pentagonal, octagonal, other polygonal shape, etc. As illustrated, in many cases, the cross section of the hole852at close proximity to the first end is larger than the cross section of the waveguides855such that a gap is disposed between an inner surface851aof the coupler housing structure851and the waveguide855.

The coupler housing structure (e.g.,801inFIG.8or851inFIG.9) can include a medium from a wide range of materials as described herein. As also described herein, the medium of the coupler housing structure801,851can have refractive index (N-4). The medium can be a transversely contiguous medium. This can allow for a robust housing structure with improved transverse positioning accuracy in some embodiments. In some embodiments, the total volume of the medium of the coupler housing structure801,851can be greater than a total volume of all the inner and outer cores of the VC waveguides confined within the coupler housing structure801,851to provide that in some embodiments, all VC waveguides are reliably embedded in the housing structure allowing for stable performance).

In certain embodiments, the example configurations shown inFIG.8andFIG.9may allow for improved manufacturability of the devices with improved cross sectional (transverse) positioning of the waveguides e.g., at the second end. This transverse position, may for example, be defined in the x and/or y directions, while z is the direction along the length coupler array (e.g., from the first end to the second end). In various fabrication approaches, the assembly, comprising the waveguides (e.g.,805inFIGS.8and855inFIG.9) and coupler housing structure (e.g.,801inFIG.8or851inFIG.9), may be heated and drawn to form a second end as shown in the lateral cross sectional views shown inFIGS.3A-3L. Referring toFIG.8, the waveguides805can be inserted into the coupler housing structure801having a configuration of a ring (in the cross section orthogonal to the longitudinal direction or length of the optical coupler array, e.g., in the x-y plane shown). As described above, a gap such as an air gap can be disposed between the coupler housing structure801and the waveguide805to permit lateral movement (in x and/or y directions) of the waveguide with respect to the coupler housing structure801. Referring toFIG.9, one or more waveguides855can be inserted into the coupler housing structure851having a plurality of holes852(e.g., as seen in the cross section orthogonal to the longitudinal direction or length of the optical coupler array, e.g., in the x-y plane shown) where the waveguides855can be passively aligned within the housing structure851. A gap such as an air gap can be disposed between the coupler housing structure851and the waveguide855to permit transverse movement (in x and/or y directions) of the waveguide with respect to the coupler housing structure851. In the case of close packed waveguide arrangement (e.g., hexagonal), this ability to move can result in more precise cross sectional positioning at the second end after manufacturing.

Referring toFIG.1A, the coupler array can include a plurality of longitudinal waveguides30A,32A-1,32A-2with at least one VC waveguide30A having an inner core20A and an outer core22A. The inner core20A, the outer core22A, and the spacing between the plurality of waveguides30A,32A-1,32A-2can reduce (e.g., simultaneously and gradually in some cases) from the first end (proximate to position B) to the second end (proximate to positions C and D), e.g., from S-1 to S-2. In various embodiments, the cross sectional configuration at the first end (proximate position B) is shown as inFIG.8orFIG.9, while the cross sectional configuration at the second end (proximate positions C and D) can be shown inFIGS.3A-3LorFIG.7. In some embodiments, proximate to the second end, there is substantially no gap between the coupler housing structure and the waveguides, some gaps being filled by housing material and some gaps being filled by waveguide cladding material. As a result of the described cross sectional configuration at the first end, the cross sectional or transverse positioning of the waveguides at the second end can be improved. The waveguides at the second end can thus be properly aligned in the transverse direction (e.g., x and/or y direction) with an optical device.

With reference now toFIG.10andFIG.11, further example embodiments of optical coupler arrays4000,5000are shown. The coupler arrays4000,5000can be configured to couple to and from a plurality of optical fibers, such as to and from optical fibers with different mode fields and/or core sizes. In some instances, the coupler arrays4000,5000can be configured to provide coupling between a set of individual isolated optical fibers2000and an optical device3000having at least one optical channel allowing for propagation of more than one optical mode. In some preferred embodiments, all isolated optical fibers2000can be identical (or some different in some instances) and the optical device3000can include at least one few-mode fiber, multimode fiber, multicore single mode fiber, multicore few-mode fiber, and/or multicore multimode fiber. Compared to certain embodiments described herein with respect toFIGS.1A-5, various embodiments4000,5000can include a further reduction of the taper diameter, which can allow light to escape the outer core4120,5120and propagate in a combined waveguide4150,5150, formed by at least two neighboring cores. Accordingly, various embodiments described herein can be configured to optically couple between fibers with dissimilar mode fields and/or core shapes or sizes. Advantageously, some embodiments of the coupler arrays can improve and/or optimize optical coupling between one or more of single mode fibers, few-mode fibers, multimode fibers, multicore single mode fibers, multicore few-mode fibers, and/or multicore multimode fibers.

Although various features of the example coupler arrays will now be described with respect toFIGS.10and11, any described feature can be implemented in any combination with the coupler arrays described with respect toFIGS.1A-5and7. Further, any feature described with respect toFIGS.1A-5and7may be combined with any feature described with respect toFIGS.10and11. For instance, the example coupler arrays4000,5000are illustrated utilizing housing structures4060,5060similar to the housing structures801,851shown inFIGS.8-9. In these examples, the cross sectional configuration of the housing structure4060,5060may include a structure with a plurality of holes (e.g., multi-hole) as shown inFIG.10, or may include one hole (e.g., single-hole surrounded by a ring), as shown inFIG.11. However, other housing structures can also be used. For example, the housing structures described with respect toFIGS.1A-5and7may be used.

Referring toFIG.10, certain embodiments of a multichannel optical coupler array4000can include an elongated optical element4001having a first end4010, an intermediate location or cross section4050, and a second end4020. The optical element4001can include a coupler housing structure4060and a plurality of longitudinal waveguides4100disposed in the housing structure4060. The waveguides4100can be arranged with respect to one another in a cross-sectional geometric waveguide arrangement. InFIG.10, the example cross-sectional geometric waveguide arrangements of the waveguides4100for the first end4010, the intermediate cross section4050, and the second end4020are shown. As illustrated by the shaded regions within the cross sections and as will be described herein, light can be guided through the optical element4001from the first end4010, through the intermediate cross section4050, and to the second end4020.

As shown inFIG.10, proximally (e.g. proximately) to the first end4010, the housing structure4060(e.g., a common single coupler housing structure in some cases) can have a cross sectional configuration of a structure (e.g., transversely contiguous structure in some cases) with a plurality of holes4062.FIG.10shows an example configuration with three circular holes4062-1,4062-2,4062-3. However, the shape of the holes, number of holes, and/or arrangement of the holes are not particularly limited and can include any other shape, number, and/or arrangement including those described with respect toFIG.9. At least one of the holes4062may contain at least one of the longitudinal waveguides4100. A gap, such as an air gap, may separate the plurality of longitudinal waveguides4100from the surrounding housing structure4060proximally to the first end4010. In some embodiments, there may be substantially no gap between the coupler housing structure4060and the waveguides4100at the intermediate location4050and/or at the second end4020. For example, one or more gaps may be filled by housing material and/or waveguide cladding material. As described herein, in some embodiments, proximate to the first end4010, there may be a gap between the coupler housing structure4060and the waveguides4100, but proximate to the second end4020, there may be substantially no gap between the coupler housing structure4060and the waveguides4100(or vice versa). In some embodiments, there may be substantially no gap between the coupler housing structure4060and the waveguides4100proximate the first end4010, the intermediate location4050, and/or at the second end4020.

As described herein, the coupler array4000can be operable to optically couple with a plurality of optical fibers2000and/or with an optical device3000. The coupler array4000can couple with the optical fibers2000via the plurality of waveguides4100proximate the first end4010(e.g., via a fusion splice2001), and/or with the optical device3000via the plurality of waveguides4100proximate the second end4020(e.g., via a fusion splice not shown). InFIG.10, three waveguides4100are shown in each of the three holes4062-1,4062-2,4062-3. However, any number of waveguides4100for each of the holes4062can be used. In some embodiments, the number of waveguides4100may equal the number of optical fibers2000(e.g., 9 waveguides to couple with 9 optical fibers). In some other embodiments, the number of waveguides4100in at least one hole may equal the number of optical modes supported by a corresponding few-mode or multi-mode waveguide of the device3000(e.g. 3 waveguides in each of 3 holes to couple with three 3-mode cores of a multicore fiber). In various embodiments, the waveguides4100can be positioned within each hole4062at a spacing (e.g., predetermined in some instances) from one another. In some preferred embodiments of the multi-hole configuration, the individual holes4062-1,4062-2,4062-3may contain all the waveguides (e.g., fibers) intended to couple to at least one particular core of a few-mode, multimode and/or multicore fiber of an optical device. In some other embodiments, one or more additional fibers and/or dummy fibers (e.g., which might not guide light) may be utilized to create a particular geometrical arrangement of the active, light-guiding fiber waveguides.

In various embodiments, the plurality of waveguides4100can have a capacity for at least one optical mode (e.g., a predetermined mode field profile in some cases). The plurality of waveguides4100can include at least one vanishing core (VC) waveguide4101.FIG.10illustrates all of the waveguides4100as VC waveguides. However, one or more Non-VC waveguides may also be used. As described herein, the VC waveguide4101can include an inner core (e.g., an inner vanishing core)4110, an outer core4120, and an outer cladding4130with refractive indices N-1, N-2, and N-3 respectively. The outer core4120can longitudinally surround the inner core4110, and the outer cladding4130can longitudinally surrounding the outer core4120. As described herein, the relative magnitude relationship between the refractive indices of the inner core4110, outer core4120, and the outer cladding4130can advantageously be N-1>N-2>N-3.

In various embodiments, the housing structure4060can surround the waveguides4100. The coupler housing structure4060can include a medium4140having an index of refraction N-4. The medium4140can include any of those described herein. In some instances, a total volume of the medium4140of the coupler housing structure4060can be greater than a total volume of all the inner and outer cores4110,4120of the VC waveguides confined within the coupler housing structure4060. In some examples, the waveguides4100may be embedded in the housing structure4060(e.g., proximate the second end4020).

In certain embodiments, the inner core4110waveguide dimensions, the outer core4120waveguide dimensions, refractive indices, and/or numerical apertures (NAs) are selected to increase and/or optimize coupling to the individual fibers2000. In various embodiments, the outer core4120waveguide dimensions, refractive indices, NAs, and/or the cladding4130dimensions are selected to increase and/or optimize coupling to the optical device3000. Various embodiments described herein can also include reflection reduction features of the pitch-reducing optical fiber array described in U.S. application Ser. No. 14/677,810, entitled “OPTIMIZED CONFIGURABLE PITCH REDUCING OPTICAL FIBER COUPLER ARRAY”, which is incorporated herein in its entirety. For polarization control, some of the outer cores4120can be made with a non-circular cross section (e.g., elliptical as shown inFIG.10) and a particular orientation of the outer cores4120can be used to increase and/or optimize optical coupling. Various embodiments described herein can also include features of any of the optical polarization mode couplers described in U.S. application Ser. No. 15/617,684, entitled “CONFIGURABLE POLARIZATION MODE COUPLER”, which is incorporated herein in its entirety.

In some embodiments, the inner core4110size, the outer core4120size, the cladding4130size, and/or the spacing between the waveguides4100can reduce (e.g., simultaneously and gradually in some instances) along the optical element4001from the first end4010to an intermediate location or cross section4050. In some embodiments, a predetermined reduction profile may be used. In the example shown inFIG.10, at the intermediate location4050, the inner core4110may be insufficient to guide light therethrough and the outer core4120may be sufficient to guide at least one optical mode (e.g., spatial mode).

In some embodiments, each core of a waveguide4100can have a capacity for at least one optical mode (e.g., single mode, few-mode, or multi-mode). For example, at the first end4010, the VC waveguide4101can support a number of spatial modes (M1) within the inner core4110. At the intermediate location4050, in various embodiments, the inner core4110may no longer be able to support all the M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the intermediate location4050, the outer core4120can be able to support all the M1 modes (and in some cases, able to support additional modes). In this example, light traveling within the inner core4110from the first end4010to the intermediate location4050can escape from the inner core4110into the outer core4120such that light can propagate within the outer core4120.

In some embodiments, the inner core4110size, the outer core4120size, the cladding4130size, and/or the spacing between the waveguides4100can be further reduced (e.g., simultaneously and gradually in some instances) along the optical element4001from the intermediate location4050to the second end4020. In the example shown inFIG.10, at the second end4020, the outer core4120may be insufficient to guide light therethrough.

In certain embodiments, at the intermediate location4050, the VC waveguide4101can support all the M1 modes within the outer core4120. At the second end4020, the outer core4120may be no longer able to support all the M1 modes (e.g., cannot support light propagation). However, in some such embodiments, at the second end4020, a combined core4150of at least two cores may be able to support all the M1 modes of all waveguides4101combined (and in some cases, able to support additional modes). In this example, light traveling within the outer core4120from the intermediate location4050to the second end4020can escape from the outer core4120into a combined waveguide4150formed by at least two outer cores (e.g., two or more neighboring cores) such that light can propagate within the combined cores. In the example shown inFIG.10, each of the combined waveguides4150is formed by three outer cores. However, in some embodiments, the combined waveguides4150may be formed with another number of outer cores.

It would be appreciated that light travelling from the second end4020to the first end4010can behave in the reverse manner. For example, in some embodiments, light can move from the combined waveguide4150formed by at least two neighboring outer cores into the at least one outer core4120proximally to the intermediate cross section4050, and can move from the outer core4120into corresponding inner core4110proximally to the first end4010. In the example shown inFIG.10, each of the combined waveguides4150can support three propagation modes. Travelling from the second end4020to the first end4010, each propagation mode can be coupled to a corresponding outer core4120proximally to the intermediate cross section4050and move from the outer core4120into a corresponding inner core4110proximally to the first end4010.

Referring now toFIG.11, the example embodiment5000includes similar features as the example embodiment4000shown inFIG.10. One difference is that the cross sectional configuration of the housing structure5060includes a structure with a single hole5062instead of a plurality of holes4062. Similar to the example embodiment4000shown inFIG.10, the optical element5001can include a coupler housing structure5060(e.g., including a medium5140) and a plurality of longitudinal waveguides5100disposed in the housing structure5060. The waveguides5100can be arranged with respect to one another in a cross-sectional geometric waveguide arrangement within the hole5062. As illustrated, light can be guided through the optical element5001from the first end5010, through the intermediate cross section5050, and to the second end5020.

As described herein, a gap may separate the plurality of longitudinal waveguides5100from the surrounding housing structure5060. In some embodiments, there may be substantially no gap between the coupler housing structure5060and the waveguides5100proximate the intermediate location5050and/or the second end5020. For example, inFIG.11, although a gap is shown proximate the second end5020, in preferred embodiments, there may be substantially no gap between the coupler housing structure5060and the waveguides5100. In some embodiments, there may be substantially no gap between the coupler housing structure5060and the waveguides5100proximate the first end5010, the intermediate location5050, and/or the second end5020.

In various embodiments, the plurality of waveguides5100can include at least one VC waveguide5101.FIG.11illustrates all thirty seven of the waveguides5100as VC waveguides5101in a hexagonal arrangement. However, any arrangement may be used. In addition, any number of VC waveguides, Non-VC waveguides, and/or dummy fibers may be used. As described herein, one or more dummy fibers may be utilized to create a particular geometrical arrangement of the active, light-guiding fiber waveguides. As described herein, the VC waveguide5101can include an inner vanishing core5110, an outer core5120, and an outer cladding5130.

In certain embodiments, the inner core5110waveguide dimensions, the outer core5120waveguide dimensions, the cladding5130dimensions, refractive indices, and/or the numerical apertures (NAs) can be selected to increase and/or optimize coupling to the individual fibers2000and/or optical device3000. In some embodiments, the inner core5110size, the outer core5120size, the cladding5130size, and/or the spacing between the waveguides5100can reduce along the optical element5001from the first end5010to the second end5020. In the example shown inFIG.11, at the intermediate location5050, the inner core5110of certain waveguides5100may be insufficient to guide light therethrough and the outer core5120of certain waveguides5100may be sufficient to guide at least one optical mode (e.g., spatial mode). In this example, proximate the second end5020, the outer core5120may be insufficient to guide light therethrough. Accordingly, in some embodiments, light traveling within the outer core5120from the intermediate location5050to the second end5020can escape from the outer core5120into a combined waveguide5150formed by at least two outer cores (e.g., two or more neighboring cores) such that light can propagate within the combined cores. In the example shown inFIG.11, although each of the combined waveguides5150is formed by three outer cores, the combined waveguides5150may be formed by another number of outer cores. The remaining cores (e.g., cores of waveguides or dummy fibers) may or may not guide light. Light travelling from the second end5020to the first end5010can behave in the reverse manner.

Space division multiplexing (SDM) can be used to overcome single fiber capacity limits. To allow deployment of multicore fiber (MCF), as one of the possible SDM implementations, development of fiber optic components providing access to the individual cores of the MCFs is desirable. The present application addresses some such components: adaptors between MCFs with different core patterns and/or add-drop multiplexers for MCFs.

As shown inFIGS.12A-12C, both functions, combined or separately, may be achieved with two individual fan-in/fan-out devices with the pigtail fiber spliced together as indicated by the stars.FIG.12Ashows single channel add-drop;FIG.12Bshows pattern adaptation; andFIG.12Cshows combined pattern adaptation and channel add-drop. Some considerations, however, are (1) high insertion loss, which can include a sum of two fan-out devices, (2) large size of the combined component, and (3) high cost of the assembly.

To address these factors, in the present disclosure, in various implementations, space division multiplexers can comprise a double-tapered elongated optical element in which the pass-through-channels do not include splices and can provide low-loss connections between two similar or dissimilar MCFs or other multichannel optical devices.FIG.13is a schematic diagram of an example double-tapered elongated optical coupler array. The coupler array6000can include a housing structure6005, a first end6010, a middle portion6015, and a second end6020. The coupler array6000can include a first tapered portion6030and a second tapered portion6040. The first tapered portion6030can be located between the first end6010and the middle portion6015, and the second tapered portion6040can be located between the second end6020and the middle portion6015. In various designs, the housing structure6005can include the first and second tapered portions6030,6040and a connecting sleeve therebetween6035. InFIG.13, the outer diameter of the coupler array6000is tapered up from the first end6010to the middle portion6015, and is tapered down from the middle portion6015to the second end6020. The coupler array6000can include a plurality of spatial optical channels6050. For example, the pass-through-channels may comprise vanishing core waveguides (e.g., as described herein), or enlarged core waveguides (e.g., waveguides with core sizes larger than for standard optical fiber), or other type waveguides allowing for up and down tapering with light propagation preservation. The spatial optical channels6050(e.g., via one or more through-channels) can be configured to optically couple a first optical device6070to a second optical device6080. For example, at least one through-channel can be operable to couple (e.g., directly couple) at least one optical channel of the first optical device6070with at least one optical channel of the second optical device6080. In various instances, the through-channel can be embedded in the housing structure6005at the first and/or second ends6010,6020. In various designs, individual ones of the spatial optical channels6050(e.g., through-channels) do not include splices within the housing structure6005.

The first optical device6070and/or the second optical device6080can include a MCF or other multichannel optical device. The transverse channel patterns of the optical devices6070,6080may be arbitrarily configured as desired, for example, by an application. In some instances, the transverse channel patterns of the optical devices6070,6080may be similar. In other instances, the transverse channel patterns of the optical devices6070,6080may be dissimilar. For example, as shown inFIG.13, the transverse channel pattern can include two rows of channels in one device6070and a circumferential channel pattern in the other one6080, and the pattern adaptation (e.g., converting one spatial pattern of channels to another different spatial pattern of channels) can be achieved. In some such designs, the spatial optical channels6050disposed within the housing6005can form transverse channel patterns at the first and second ends6010,6020, which can be similar to the transverse channel patterns of the first and second optical devices6070,6080respectively. For example, the first tapered portion6030can have a transverse channel pattern similar to the transverse channel pattern of the first optical device6070and the second tapered portion6040can have a transverse channel pattern similar to the transverse channel pattern of the second optical device6080.

In various implementations, the first tapered portion6030and/or the second tapered portion6040can include a tapered housing structure and a plurality of longitudinal waveguides (e.g., a portion of the spatial optical channels6050). Individual ones of the longitudinal waveguides can be positioned at a spacing (e.g., predetermined in some cases) from one another, can have a capacity for at least one optical mode (e.g., of a predetermined mode field profile), and can be embedded in the tapered housing structure proximally to the corresponding first or second end6010,6020. At least one of the longitudinal waveguides can be the through-channel common for both the first and second tapered portions6030,6040.

In some implementations, at least one through-channel can include a vanishing core waveguide, e.g., as described herein. In some implementations, at least one through-channel can include an enlarged core waveguide, such as a waveguide with a core size larger than that of a standard optical fiber. In some instances, the enlarged core waveguide can include an enlarged core having a core refractive index (NCO). The enlarged core can have a first enlarged core size (ECS-1) at the first end6010, a second enlarged core size (ECS-2) at the second end6020, and an intermediate enlarged core size (ECS-IN) at the middle portion6015therebetween. The enlarged core waveguide can also include an outer cladding longitudinally surrounding the enlarged core. The outer cladding can have a cladding refractive index (NCL). A relative magnitude relationship between the refractive indices can include the following magnitude relationship: (NCO>NCL). In some instances, the first enlarged core size (ECS-1) can be gradually increased from the first end6010to the middle portion6015and gradually reduced from the middle portion6015to the second end6020, e.g., in accordance with a predetermined profile along the housing structure6005. In some instances, the first and second enlarged core sizes (ECS-1 and ECS-2, respectively) and the refractive indices NCO and NCL can match (e.g., selected to substantially match in some cases) waveguide properties of at least one channel of the first and/or second optical devices,6070,6080respectively. In some instances, the intermediate enlarged core size (ECS-IN) can have (e.g., selected to have in some cases) larger mode volume than at least one channel of the first and second optical devices6070,6080, such that light traveling from the first end6010to the middle portion6015then from middle portion6015to the second end6020keeps propagating in at least one lowest order mode.

FIGS.14-15are schematic diagrams of other example double-tapered elongated optical coupler arrays configured to optically couple a first optical device to a second optical device. In some implementations, the coupler array can be configured to provide access (e.g., direct access) to at least one optical channel of the first and/or second optical device. Similar to the example coupler array6000inFIG.13, each of the optical coupler arrays7000,8000inFIGS.14-15can include a housing structure7005,8005; a first end7010,8010; a middle portion7015,8015; a second end7020,8020; a first tapered portion7030,8030; and a second tapered portion7040,8040. In some designs, the housing structure7005,8005can be a single monolithic coupler housing structure comprising the first tapered portion7030,8030; the middle portion7015,8015; and the second tapered portion7040,8040. The spatial optical channels7050,8050(e.g., via one or more through-channels) can be configured to optically couple a first optical device7070,8070to a second optical device7080,8080.

As shown inFIGS.14-15, an access region7016,8016in the middle portion7015,8015can allow the creation of an add-drop multiplexer, where one or two access channels (e.g., direct access channels)7051,7052inFIGS.14and8051,8052inFIG.15(e.g., any type of waveguide such as standard optical fiber, a vanishing core waveguide, an enlarged core waveguide, etc.) can be coupled (e.g., directly) to the optical devices7070,7080inFIGS.14and8070,8080inFIG.15at the first and/or second ends of those access channels. For example, one or more optical waveguides can pass through the access region7016,8016from outside space into the housing structure7005,8005operable to provide access to at least one optical channel of the first optical device7070,8070or second optical device7080,8080. The optical waveguide (e.g., an optical fiber)7051,7052,8051,8052can have a first end disposed within the housing structure7005,8005and a second end disposed outside the housing structure7005,8005. For example, the first end of the optical waveguide7051,7052,8051,8052can be disposed at the first end7010or second end7020of the housing structure7005,8005. The optical waveguide7051,7052,8051,8052can exit the housing structure7005,8005through the middle portion7015,8015of the housing structure7005,8005.

As shown inFIGS.14-15, an access channel7051,8051can be coupled to the first optical device7070,8070at the first end7010,8010of the coupler array7000,8000and access channel7052,8052can be coupled to the second optical device7080,8080at the second end7020,8020of the coupler array7000,8000. In some implementations, one channel7051,8051can serve as a “drop” channel to extract an optical signal from an SDM transmission line and another one7052,8052can serve as an “add” channel to substitute the dropped signal with a new one. This add-drop functionality may be achieved without pattern adaptation, as shown inFIG.14(e.g., optical devices7070,7080having similar transverse channel patterns), or with a pattern adaptation, e.g., if an access region8016is created in the connecting sleeve, as shown inFIG.15(e.g., optical devices8070,8080having dissimilar transverse channel patterns). AlthoughFIGS.14-15show examples with one “add” channel and one “drop” channel, some optical coupler arrays can be configured to provide more than one “add” and/or “drop” channels. In addition, some optical coupler arrays can be configured to provide only one or more “add” channels or only one or more “drop” channels.

In various implementations, at least one access optical channel7051,7052,8051,8052can be a vanishing core waveguide. For example, at least one access optical channel7051,7052,8051,8052may be operable to provide access to at least one optical channel of the first optical device7070,8070and/or the second optical device7080,8080can be a vanishing core waveguide. In some such instances, at least one access channel7051,7052,8051,8052can also include a standard optical fiber fusion spliced to the access vanishing core waveguide with the splice location outside the housing structure7005,8005in such a way that the access vanishing core waveguide passes through the access region7015,8015from outside space into the housing structure7005,8005. In some instances, the splice location can be inside the housing structure7005,8005in such a way that the standard optical fiber passes through the access region7015,8015from outside space into the housing structure7005,8005.

Another application of the present disclosure can include fiber optic gyroscopes, where access to a single channel of the looped MCF is desired. In some designs, two ends of the same span of MCF can be coupled to the first and second ends of the device shown inFIG.14(e.g., forming a fiber loop in the fiber optic gyroscope). In various implementations, the MCF can have a circumferential core arrangement pattern, for example, numbered along the circumference: core number 1 or channel 1, core number 2 or channel 2, . . . core number N or channel N. A connection orientation at the first end7010can provide coupling of at least one access channel7051to core number 1, and a connection orientation at the second end7020can provide coupling of core number 1 via at least one through-channel to core number 2 at the first end7010. Core number 2 can couple to core number 3, until core number N-1 is coupled to core number N, which can be coupled to a second access channel7052at the second end7020. For example, the MCF can be axially twisted, such that a light signal from the “drop” channel7051can be coupled to channel 1 of the MCF7070at the first end7010. At the second end7020, the light signal can be coupled to a through-channel of the spatial optical channels7050, and, then the signal can be coupled to channel 2 of the MCF7070at the first end7010. In this same manner, core number 2 can couple to core number 3 and so on, until core number N-1 can be coupled to core number N, which can be finally coupled to the “add” channel7052at the second end7020.

In various implementations, the housing structure may be glass, metal, or polymer, e.g., as desired by an application. The channels can be embedded in a portion of the housing structure. For example, the channels can be embedding in the housing structure closer to the tapered end(s). In some instances, the channels can be embedded in 40%, 45%, 50%, 55%, 60%, etc. (or any ranges formed by such values) of the tapered length. In some designs, the channels can be embedded throughout the housing structure. In some instances, there may be gaps (e.g., air or filled with a filling material, or a combination of both) in the middle portion, for example, where the diameter is larger. The housing structure can be substantially straight (e.g., straight or from 175° to 185°).FIG.16is a schematic diagram of an optical coupler array9000configured to optically couple a first optical device9070to a second optical device9080. The coupler array9000can comprise a first end9010, a second end9020, a first tapered portion9030, and a second tapered portion9040. The coupler array9000can include a plurality of spatial optical channels9050such as through-channels. As shown inFIG.16, the housing structure9005(e.g., a middle portion) may be bent. In some instances, the housing structure9005may include a flexible portion that allows bending. In some instances, the housing structure9005may include a rigidly bent portion. In various examples, the housing structure9005may be bent at 90°, 100°, 110°, 120°, 130°, 140°, 150°, 160°, 170°, etc. or any ranges formed by such values (e.g., 90° to 170°, 90° to 150°, 90° to 130°, etc.). The bending may be 90 degrees as shown or 180 degrees as desired by an application.FIG.16shows an example illustrating pattern adaptation. Also, add-drop multiplexing or a combination of the pattern adaptation and add-drop multiplexing may be desired in either straight or bent configurations.

In some implementations, an optical coupler array can be configured to couple with at least one optical device having at least one multimode optical channel. As an example, the multimode optical channel can be an inner cladding (e.g., for pump delivery) of a double-clad multicore fiber. In some instances, direct access can be provided to at least one optical mode of the multimode optical channel.FIG.17shows one such example of an optical coupler array9100coupling a first optical device9170(e.g., single-clad MCF) at the first end9110to a second optical device9180(e.g., double-clad MCF comprising an inner cladding9181and outer cladding9182) at the second end9120. Both of the coupled multichannel optical devices9170,9180can comprise multicore fibers with the cores coupled via spatial optical channels9150such as through-channels (e.g., signal channels) and at least one access (e.g., direct access) optical channel9152can comprise a multimode fiber coupled to at least one cladding mode of an inner cladding9181of the double-clad multicore fiber9180.

InFIG.17, signal channels can be the pass-through channels of the spatial optical channels9150from the cores of the single-clad MCF9170at the first end9110to the cores of the double-clad MCF9180at the second end9120. The cores of the double-clad MCF9180can be single mode, few mode, or multimode. The spatial optical channels9150(e.g., through channels) can be multimode or vanishing core waveguides. When drawn, the cores of the optical coupler array9100at the second end9120can be configured to match (e.g., substantially match) the cores of the double-clad MCF9180. For example, in some implementations, the through channels can be vanishing core channels with single mode cores at the second end9120to match (e.g., substantially match) single mode cores of the double-clad MCF9180. In some instances, when the through channels are drawn, both ends (e.g., both tapered ends) may match the cores of the double-clad MCF9180. For example, both ends of the through channels may be single mode (or few mode or multimode) to match the single mode (or few mode or multimode) cores of the double-clad MCF9180. An access channel9152through the access region9116can be coupled to the cladding modes. As illustrated inFIG.17, at least one access channel9152can comprise a pump channel coupled to cladding modes (e.g., to the inner cladding9181) of the double-clad MCF9180at the second end9120. The double-clad MCF9180may be an active fiber, where one or more cores are doped with erbium or other active elements which are capable to amplify light when pumped by another light wave. As illustrated, some implementations can have access to at least one pump channel at the access region9116(only one add channel shown) and the signal channels can be the pass-through channels9150. There may be a drop channel for at least one pump channel, which can be useful for pump recycling at the other end of the double-clad MCF9180. Add/drop pump channel(s) can be coupled to the cladding of the MCF and the cross-sectional location(s) need not match any MCF cores (e.g., coupled to the inner cladding of a double-clad multicore fiber). Similarly toFIG.3E, pump channels may be conventional single core multimode pump delivery fibers, not vanishing core fibers. In some instances, the pump channels may be vanishing core fibers. The number of the pump channels may be one or more. There may be combinations of pump and signal add functionality, pump and signal drop functionality, and/or pattern adaptation in one device.

To allow deployment of multicore fiber (MCF), as one of the possible SDM implementations, development of fiber optic components providing access to the individual cores of the MCFs at two wavelengths (e.g., pump and signal wavelengths) can be desirable. The present application addresses some such components: a wavelength division-multiplexing (WDM) fanout device and a pump-signal combiner for MCFs.

As shown inFIGS.18A-18B, both functions, may be achieved with a combination of WDM device(s) with a fan-out (or fan-in) device and by combining WDM device(s) with two fan-in/fan-out devices with the pigtail fiber spliced together as indicated by the stars.FIG.18Ashows a WDM-fanout device1810, andFIG.18Bshows an MCF-WDM device1820. InFIG.18A, the WDM-fanout device1810includes a WDM device1811, a fan-out (or fan-in) device1812, and a splice1815therebetween. The WDM device1811can be, for example, a wavelength combiner (e.g., a 980/1550 combiner) which combines light at a first wavelength (Wavelength-1 or W-1) with light at a second wavelength (Wavelength-2 or W-2). Light at the first wavelength can include signal light at 1550 nm and light at the second wavelength can include pump light at 980 nm (or vice versa). Other examples are possible. The light at the first wavelength and the light at the second wavelength can be combined into one of the cores1816of an output MCF1817. In some instances, the MCF1817can include Er-doped fiber. InFIG.18B, the MCF-WDM device1820includes a WDM device1821combined with two fan-in/fan-out devices1822,1824with splices1825therebetween. The MCF-WDM1820can include an input MCF1826and an output MCF1827. In some instances, the input MCF1826can include a transmission MCF. In some instances, the output MCF1827can include Er-doped fiber.

Some considerations, however, are (1) high insertion loss, which can include a sum of the WDM component and one or two fan-out devices, (2) the large size of the combined components, and (3) the high cost of the assembly.

To address these factors, in the present disclosure, in various implementations, the WDM function can be integrated into the space division multiplexer.FIG.19Ashows a cross section of an example WDM-fanout device (e.g., a combined SDM-WDM)1910. Light at one wavelength W-1 can be combined with light at another wavelength W-2 in a core of a MCF (e.g., into a core of a MCF coupled with the WDM-fanout device1910). For example, a signal (e.g., 1550 nm) or multiple signals (e.g., signals within the 1520-1570 nm C-band) and pump light (e.g., 980 nm) can be combined in a core of a MCF. As another example, two signals (e.g., 1550 nm and 1310 nm) can be combined in a core of a MCF. In the example shown inFIG.19A, 1550 nm signal light can be combined with 980 nm pump light in each core of a 4-core MCF. For example, inFIG.19A, the WDM-fanout device1910includes 4 WDMs1911A,1911B,1911C,1911D represented by 4 pairs of adjacent waveguides. Each pair1911A,1911B,1911C,1911D of adjacent waveguides includes a first waveguide for light at a first wavelength (W-1) and second waveguide for light at a second wavelength (W-2). The light at W-1 and the light at W-2 from each of the WDMs1911A,1911B,1911C,1911D can be combined into each core of a 4-core MCF coupled with the WDM-fanout device1910. Other designs can have more or less WDMs and/or can be coupled to an MCF with more or less cores. The number of WDMs and/or cores is not particularly limited.FIGS.19B-19Fshow side views of various examples of the WDM-fanout tapered device1910. InFIG.19B, at the tapered end a composite waveguide1913formed by outer cores of the signal and pump channels guides the light at both wavelengths and is coupled to a corresponding core1916of the MCF1917. In some embodiments, the signal light can be coupled into a lowest order mode of the MCF core and the pump light can be coupled into a set of modes with corresponding coupling coefficients. The wavelength combining is this case can be broadband, but the two wavelengths can be coupled to a set of modes with corresponding coupling coefficients in the MCF core. For example, the signal light can be coupled into the lowest order mode of the output waveguide, and the pump light can be coupled into a higher order mode (e.g., the 2ndorder mode) of the output waveguide.

In various implementations, light of different wavelengths from different input waveguides (e.g., from the lowest order modes of the input waveguides) can be combined into the same (e.g., lowest order) mode of the output waveguide. In the examples shown inFIG.19C,FIG.19D,FIG.19E, andFIG.19F, no composite waveguide formed at the MCF interface, but instead the MCF core1926,1936,1946,1956is coupled only with one of the input waveguides1923,1933,1943,1953. In the examples shown inFIG.19CandFIG.19D, the wavelength combining can be achieved by creating a neck (e.g. neck coupling section)1928,1938and in the examples shown inFIG.19EandFIG.19F, the wavelength combining can be achieved by a small waveguide separation section (e.g. substantially straight coupling section)1948,1958at close proximity to the second end. Over these coupling sections1928,1938, the two wavelengths can be combined either in one (e.g.,FIG.19C) or the other (e.g.,FIG.19D) waveguide, which in turn, can be coupled to a corresponding MCF core1926,1936. Similarly, the examples shown inFIG.19EandFIG.19Fmay be configured to couple MCF cores to the inner (e.g., as shown inFIG.19F) or outer cores (e.g., as shown inFIG.19E) at the tapered end. In various designs of the neck and substantially straight coupling section, the waveguides can be close together such that the light at one wavelength (e.g., W-1 or W-2) can remain in its waveguide, while the light at the other wavelength can be coupled to the other waveguide. Both light signals at W-1 and W-2 can propagate in the same output waveguide. Design parameters can include waveguide separation and coupling section length. In various instances, the coupling distance between waveguides can be configured to couple light at one wavelength (e.g., W-1 or W-2) of at least one core mode of the waveguide with at least one core mode of another waveguide while continuing or preserving the propagation of light at the other wavelength (e.g., W-2 or W-1) of the other waveguide.

In various instances, the neck1928,1938can be fabricated similar to some embodiments shown inFIG.7. For example, in some instances, the first inner vanishing core size (ICS-1), the first outer core size (OCS-1), and the spacing between the plurality of longitudinal waveguides can be simultaneously and gradually reduced between the first end and the second end along the optical element to an intermediate location (e.g., the neck coupling section), and simultaneously and gradually increased from said intermediate location to the second end until the second inner vanishing core size (ICS-2) and the second outer core size (OCS-2) are reached. Some embodiments may be flexible, while some embodiments may not be flexible.

To accomplish the function of an MCF-WDM device, one of the example embodiments of the combined SDM-WDM devices described above may be fusion spliced to a fanout device. To fabricate a single device with reduced number of splices, one or more channel(s) (e.g., the pump channel(s)) may be introduced via an access region of the modified MCF add-drop multiplexer as shown inFIG.14orFIG.15. Either one or both of “direct access channels” may be used to introduce pump channels for co- and/or for counter-propagating pumping. In this case, the cross section of the access region may be modified from the add-drop multiplexer design as shown inFIG.20(e.g., side-polished region for accessing the fiber). In this example, the cross-section1950shows a side-polished region1951configured to provide an accessing hole for the fiber carrying light at W-2 (e.g., pump light at 980 nm), which is adjacent the fiber carrying light at W-1 (e.g., signal light at 1550 nm). The cross section of the “middle portion” may also be modified from the add-drop multiplexer design and is shown inFIG.19Aafter the fiber carrying light at W-2 is installed.

Various implementations described herein can be modified from the examples shown. For example, the number of WDMs in the WDM-fanout device and/or the number of cores of the MCF can be different than those shown and described. For example, the number of WDMs in the WDM-fanouot device is not limited to the number of WDMs shown in the figures. As another example, the number of cores of the MCF is not limited to the number of cores shown in the figures. In addition, the number of WDMs in the WDM-fanout device and the number of cores of the MCF can be different from each other. For example, the number of WDMs in the WDM-fanout device does not necessarily have to equal the number of cores of the MCF to which the WDM-fanout device is coupled.

FIG.19Ashows 4 WDMs1911A,1911B,1911C,1911D in the WDM-fanout device1910represented by 4 pairs of adjacent waveguides. Each pair of adjacent waveguides includes a first waveguide for light at a first wavelength (e.g., Wavelength-1 or W-1) and second waveguide for light at a second wavelength (e.g., Wavelength-2 or W-2). For example, W-1 can be signal light at 1550 nm and W-2 can be pump light at 980 nm. In other examples, W-1 can be pump light and W-2 can be signal light. Other wavelengths are also possible.

As set forth herein, the light propagating in the adjacent first and second waveguides of the WDM-fanout device1910can be coupled into a core1916,1926,1936,1946, or1956of a MCF1917,1927,1937,1947, or1957as shown inFIGS.19B-19F. While the number of WDMs in the WDM-fanout device1910can equal the number of cores of the MCF (e.g., 4 WDMs for a 4-core MCF), the number of WDMs in the WDM-fanout device1910can be less than the number of cores of the MCF.FIG.21Ais a schematic diagram of a cross-sectional view of such an example combined SDM-WDM device1960. InFIG.21A, the cross-sectional view of the example SDM-WDM device1960has a combination of 2 WDMs1961A,1961D (e.g., 2 pairs of adjacent W-1/W-2 waveguides) and 2 single waveguides1961B,1961C (e.g., 2 waveguides without adjacent waveguides) that can be configured to be coupled to a 4-core MCF.

A first WDM1961A is represented by a pair of adjacent waveguides in the upper left of the cross-sectional view and a second WDM1961D is represented by another pair of adjacent waveguides in the lower right of the cross-sectional view. Each of the other 2 waveguides1961B,1961C in the upper right and lower left of the cross-sectional view can be a single waveguide. For example, the single waveguide1961B,1961C can be configured to not couple light with another waveguide of the SDM-WDM device1960.

Some such examples can be utilized for co-propagating and counter-propagating light. For instance, the SDM-WDM device1960shown inFIG.21Acan be a WDM-fanout device D1 that can be configured to be coupled to a 4-core MCF 1, where diagonal cores of the MCF 1 can transmit co-propagating light (e.g., two diagonal cores can transmit light in the same direction as each other and the two other diagonal cores can transmit light in the same direction as each other) and the neighboring cores can transmit counter-propagating light (e.g., in two neighboring cores, light can propagate in the opposite directions). The MCF 1 can be a transmission MCF or an Erbium-doped fiber (EDF), namely an Erbium-doped MCF. In some implementations, the device can be used in an amplifier. In some instances, the MCF 1 can be a submarine SDM link which provides a communication link below a body of water such as a sea or ocean.

As shown within the dotted lines inFIG.21B, the SDM-WDM device1960shown inFIG.21A(e.g., WDM-fanout device D1) can be coupled (e.g., with splices1965) with fanout device D2 having single waveguides (e.g., without adjacent pairs of waveguides or WDMs). Device D2 can be any non-WDM fanout device known in the art or yet to be developed. AlthoughFIG.21Bschematically illustrates device D1 and device D2 as triangular in shape, device D1 and/or device D2 can include a tapered region and optical fibers extending from the tapered region (e.g., D1 and/or D2 can include portions of the fibers which are shown outside of the triangular shapes). Each of the two WDMs of device D1 can couple light at W-1 and light at W-2 into a respective core of MCF 1. InFIGS.21A-21B, W-1 can be signal light at 1550 nm and W-2 can be pump light at 980 nm. In other examples, W-1 can be pump light and W-2 can be signal light. In other examples, other wavelengths are possible.FIG.21Bshows the pump light entering an input waveguide of device D1. In some examples, D1 and D2 may by combined in one device similarly to the device shown inFIG.14and the pump light can enter combined device D1 via a direct access channel of device D1 such as described with respect toFIG.20.

Light at W-1 can be transmitted from MCF 2 (e.g., a transmission MCF) via device D2 and light at W-2 can be transmitted from a pump (e.g., a 980 nm pump). Device D1 can combine the light at W-1 and W-2 and couple the combined light into two respective diagonal cores of MCF 1 (e.g., a 4-core Erbium-doped MCF) transmitting light from MCF 2 to MCF 1. Any of the coupling configurations shown inFIGS.19B-19Fcan be used. The other two diagonal waveguides of device D1 can transmit light received from MCF 1 (e.g., a transmission MCF) to MCF 2 (e.g., an Erbium-doped MCF) via device D2.

In various examples, mode size adaptation and/or pattern adaptation functions may be utilized if the Erbium-doped fiber and transmission fibers have different mode field diameters and/or core patterns. Splice protectors may or may not be used. All components within the dotted lines inFIG.21Bcan be co-packaged as a single compact MCF-WDM device1970.

FIG.22is a schematic diagram of another example configuration1980utilizing the device1960inFIG.21A(e.g., WDM-fanout device D1) coupled with fanout device D2 without WDMs, e.g., as shown in the dotted lines. The configuration can mimic a single-core fiber amplifier pair used to amplify light in a counter-propagating pair of optical fibers. In various implementations, an amplifier1980can include two of the MCF-WDMs1970(e.g., shown inFIG.21B) and a gain medium therebetween MCF 1. For example, inFIG.22, device D1 and device D2 within the dotted lines can be similar to the configuration1970shown inFIG.21B. For example, signal light from MCF 2 (e.g., a transmission 4-core MCF) can be transmitted via device D2 and coupled with pump light via device D1 into MCF 1 (e.g., an Erbium-doped MCF). This approach can provide co-propagating pumping (e.g., light at W-1 and light at W-2 propagate in the same direction) for all four cores of the Erbium-doped 4C-MCF 1, 2 from one end and 2 from the other end, as demonstrated inFIG.22. An Erbium-doped fiber amplifier (EDFA) is shown, but other implementations can apply to other amplifiers, e.g., amplifiers using gain mediums other than Erbium-doped fiber.

As described with respect toFIG.22, various implementations can include a pair of the MCF-WDMs1970as described herein with a gain medium MCF 1 therebetween. The gain medium can be an active MCF. The active MCF can have at least one pair of nearest-neighbor cores and at least two pairs of next-nearest-neighbor cores. The next-nearest-neighbor cores can be configured to transmit light in a same direction and the nearest-neighbor cores can be configured to transmit light in the opposite direction. One of the two MCF-WDMs1970can be configured to couple pump light into at least one pair of the two pairs of next-nearest-neighbor cores at one end of the active MCF 1, and a second of the two MCF-WDMs1970can be configured to couple pump light into another pair of the at least two next-nearest neighbor cores at the other end of the active MCF 1. Although the example amplifier1980shown utilizes a 4-core MCF 1, the number of cores is not limited to 4, e.g., the number of cores can be less or more than 4. In addition, the array of cores can form a square pattern. In other implementations, non-square core patterns can also be used.

Any of the coupling configurations shown inFIGS.19B-19Fcan be used. Additional devices (e.g., one or more gain flattening filters1984and/or one or more isolators1985) can also be used. Mode size adaptation can be integrated into devices D1 and/or D2, e.g., if MCF 1 and MCF 2 are dissimilar. In addition, core pattern adaptation may also be achieved using devices D1 and D2 with different core patterns and/or spacing matching that of MCF 1 and MCF 2, respectively. Splice protectors may or may not be used. All components within the dotted lines inFIG.22can be co-packaged as a single compact MCF-WDM device1970. In the opposite direction, light from MCF 1 (e.g., Erbium-doped MCF) can be transmitted to MCF 2 via devices D1 and D2.

FIG.23is a schematic diagram of another example configuration1990utilizing the device1960shown inFIG.21A. (e.g., WDM fanout device D1) coupled with fanout device D2 without WDMs. The configuration is similar toFIG.22and includes a monitoring channel (e.g., a high loss loopback1989). As shown, additional devices (e.g., one or more gain flattening filters1984, one or more isolators1985, one or more couplers1986, one or more line buildout (LBO) attenuators1987, and/or one or more fiber Bragg gratings1988) can also be used. Mode size adaptation and/or pattern adaptation may also be utilized. Splice protectors may or may not be used. All components within the dotted lines inFIG.23can be co-packaged as a single compact MCF-WDM device1970. Various implementations can be used with presently available components, but in a more compact and efficient form.

Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices and methods illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.