Laser-bonded optical fibers having increased bond length from substrate penetration and corresponding substrate displacement and methods for forming the same
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-13
- Publication Date
- 2026-08-13
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Figure US2025015652_13082026_PF_FP_ABST
Abstract
Description
Attorney Docket No.: SP24-037PCT LASER-BONDED OPTICAL FIBERS HAVING INCREASED BOND LENGTH FROM SUBSTRATE PENETRATION AND CORRESPONDING SUBSTRATE DISPLACEMENT AND METHODS FOR FORMING THE SAMEFIELD
[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No. 63 / 559,539 filed February 29, 2024, the content of which is incorporated herein by reference in its entirety.
[0002] The present disclosure relates to methods for securing optical fibers to substrates. In particular, the present disclosure relates to methods for bonding optical fibers to substrates using a laser beam and assemblies comprising optical fibers bonded to substrates using a laser beam.BACKGROUND
[0003] The bonding of optical fibers to substrates for fabricating existing fiber array units (FAUs) or fiber arrays is based on introducing a swelling deformation to the contact interface between the optical fibers and the surface of the substrate. This swelling deformation can be initiated by heating the substrate surface through laser absorption via a thin metal film (e.g., pre-coated to the substrate surface). After the laser-heated substrate surface starts swelling, it begins to conform about the fiber surface for a certain length, thereby forming the (peripheral) bonding interface . At the same time, a v-groove is used to position the fiber array in such a way that the distance between each optical fiber is maintained within an acceptable tolerance for the targeted connectivity applications. Since the resultant swelling deformation is relatively small due to the low thermal expansion of the glass material of the substrate, it is difficult to increase the bonding length of the swelled substrate surface that conforms about the fiber surface.
[0004] For example, the bonding length for some applications using swelling deformation may be relative short (e.g., from about 20 pm to about 40 pm). As a result, there is still a considerable gap that is not closed between the optical fiber and substrate after the laserbonding process. To improve the durability of the integrated structure, epoxy can be applied toAttorney Docket No.: SP24-037PCT fill the gap between the optical fiber and substrate, as well as the gaps between adjacent fibers in the fiber array. However, the use of epoxy can cause risk of debonding at the bonded interface due to the inhomogeneous thermal deformation of the epoxy, especially under the case where temperature field experiences a significant change. Moreover, after the laser bonding, the swelling region cools down and shrinks. The reducing size of the substrate underneath pulls down the fiber, which can lead to a high tensile stress at the fiber surface and possible fiber cracking.
[0005] To overcome the abovementioned challenges (e.g., limited bonding length and tensile stress-induced cracking), it would be advantageous to employ a laser bonding process that uses coining deformation instead of swelling deformation.SUMMARY
[0006] One or more aspects of the disclosure are directed to an assembly for a fiber array, comprising: a substrate comprising a first surface portion and a second surface portion, the first surface portion extending across the substrate substantially within a reference plane; and an optical fiber bonded to the second surface portion along a bond interface comprising laser-melted material of the substrate that contacts the optical fiber, wherein a first portion of the bond interface is disposed below the reference plane and a second portion of the bond interface is disposed above the reference plane.
[0007] One or more aspects of the disclosure are directed to a fiber array, comprising: an assembly comprising a first surface portion and a second surface portion, the first surface portion extending across the substrate substantially within a reference plane; and an optical fiber bonded to the second surface portion along a bond interface comprising laser-melted material of the substrate that contacts the optical fiber, wherein a first portion of the bond interface is disposed below the reference plane and a second portion of the bond interface is disposed above the reference plane; a sealing layer covering the first surface portion, the second surface portion, and the optical fiber; and a second substrate disposed over the assembly in contact with the sealing layer.
[0008] One or more aspects of the disclosure are directed to a method for forming an assembly for a fiber array, comprising: pressing an optical fiber against a substrate, theAttorney Docket No.: SP24-037PCT substrate comprising a first surface portion that extends across the substrate substantially within a reference plane; and during the pressing, irradiating a lengthwise portion of the optical fiber with a laser beam to selectively melt material of the substrate adjacent the lengthwise portion and bond the optical fiber to a second surface potion of the substrate along a bond interface, wherein the bond interface comprises laser-melted material of the substrate that contacts the optical fiber, and wherein a first portion of the bond interface is disposed below the reference plane and a second portion of the bond interface is disposed above the reference plane.BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 schematically depicts a cross-section of a fiber array according to one or more embodiments;
[0010] FIG. 2 is a schematic cross-sectional view of a portion of the fiber assembly of FIG. 1 showing an assembly that comprises a circular optical fiber laser-bonded to a substrate;
[0011] FIG. 3 is a schematic cross-sectional view of a portion of the fiber assembly of FIG. 1 showing an assembly that comprises a D-shaped optical fiber laser-bonded to a substrate;
[0012] FIG. 4 is a simplified schematic depiction of a bond interface between the circular optical fiber and the substrate of the assembly shown in FIG. 2;
[0013] FIG. 5 is a simplified schematic depiction of a bond interface between the D-shaped optical fiber and the substrate of the assembly shown in FIG. 3;
[0014] FIG. 6A is a schematic side view of the assembly of FIGS. 2 and 3 showing the bond interface between the optical fiber and the substrate along a first lengthwise portion of the optical that overlaps the substrate;
[0015] FIG. 6B is a schematic side view of an assembly similar to the assembly of FIG. 6A showing the bond interface between the optical fiber and a substrate along a second lengthwise portion of the optical fiber that is shorter than the first lengthwise portion;Attorney Docket No.: SP24-037PCT
[0016] FIGS. 7A-7C are a series of cross-sectional representations that depict steps of a method for laser-bonding an optical fiber to a substrate to form an assembly for the fiber array of FIG. 1;
[0017] FIG. 8 is a schematic depiction of various elements of an optical system configured to generate a top hat, collimated laser beam for laser-bonding the optical fiber to the substrate;
[0018] FIG. 9 illustrates various simulated attributes of the laser beam generated by the optical system of FIG. 8 according to Example 1 ;
[0019] FIG. 10 depicts simulated beam propagation of the laser beam generated by the optical system of FIG. 8 through a fiber array comprising a plurality of optical fibers according to Example 2; and
[0020] FIG. 11 illustrates simulated stress response of an optical fiber laser-bonded to a substrate according to Example 3.DETAILED DESCRIPTION
[0021] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the present disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles disclosed herein as would normally occur to one skilled in the art to which this disclosure pertains.
[0022] As used herein, the term “and / or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
[0023] In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, withoutAttorney Docket No.: SP24-037PCT necessarily requiring or implying any actual such relationship or order between such entities or actions.
[0024] As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.” It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.
[0025] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range was explicitly recited. As an illustration, a numerical range of “about 1 to about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also to include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4, the sub ranges such as from 1-3, from 2-4, from 3-5, etc., as well as 1, 2, 3, 4, and 5 individually. The same principle applies to ranges reciting only one numerical value as a minimum or maximum. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described by the range.
[0026] The terms “substantial,” “substantially,” and variations thereof as used herein, unless defined elsewhere in association with specific terms or phrases, are intended to note that a described feature is equal or approximately equal to a value or description. For example, a “substantially planar” surface is intended to denote a surface that is planar or approximatelyAttorney Docket No.: SP24-037PCT planar. Moreover, “substantially” is intended to denote that two values are equal or approximately equal. In some embodiments, “substantially” may denote values within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.
[0027] Directional terms as used herein — for example up, down, right, left, front, back, top, bottom, above, below, and the like — are made only with reference to the figures as drawn and are not intended to imply absolute orientation.
[0028] As used herein the terms "the," "a," or "an," mean "at least one," and should not be limited to "only one" unless explicitly indicated to the contrary. Thus, for example, reference to "a component" includes embodiments having two or more such components unless the context clearly indicates otherwise.
[0029] FIG. 1 is a schematic cross-sectional view of a fiber array 100 according to one or more embodiments of the present disclosure. The fiber array 100 comprises an assembly 200 that includes a substrate 204 and an optical fiber 208 laser-bonded to the substrate 204. In embodiments, such as shown in FIG. 1, the assembly 200 comprises a plurality of optical fibers 208, such as 2, 4, 8, 16, 24, 32, 36, 40, 48, or more optical fibers 208, laser-bonded to the substrate 204. The fiber array 100 further comprises a second substrate 104 and a sealing layer 108. The second substrate 104 is spaced from and at least partially covers the assembly 200. The sealing layer 108 is disposed between the substrate 204 and the second substrate 104 and covers the optical fiber 208 and (exposed) surfaces of the substrate 204 so as to encapsulate the optical fiber 208 therein. In embodiments, the sealing layer 108 is an epoxy or similar encapsulant configured to fix a position of the optical fiber 208 and protect the optical fiber 208 from damage and / or deterioration.
[0030] FIGS. 2 and 3 are enlarged views of a portion of the fiber array 100 of FIG. 1 (e.g., the portion indicated by dashed box 112 in FIG. 1) showing a portion of the assembly 200. The optical fiber 208' shown in FIG. 2 has a cross-sectional shape that is circular. In embodiments, the optical fiber 208 can have a different cross-sectional shape. For example, the optical fiber 208" shown in FIG. 3 has a circular portion 212 and a flat portion 216 that define a D-shape when viewed in cross section. As described hereinbelow in connection with a method for forming the assembly 200, the optical fiber 208 has at least one curved surface configured to receive a laser beam directed towards the optical fiber 208 and focus the laser beam throughAttomey Docket No.: SP24-037PCT the optical fiber 208 at a material of the substrate 204 adjacent the optical fiber 208 to selectively melt the material of the substrate 204 for bonding to the optical fiber 208.
[0031] As shown in FIGS. 2 and 3, the substrate 204 comprises a first surface portion 220 and a second surface portion 224. The first surface portion 220 and the second surface portion 224 are disposed on the same side of the substrate 204 and collectively define the surface of the substrate 204 on one side. The first surface portion 220 is a flat or substantially flat portion of the surface of the substrate 204. In embodiments, the first surface portion 220 is unaffected in terms of surface topology by the laser irradiation and / or pressing processes that are associated the method for forming the assembly 200 such that the first surface portion 220 remains flat or substantially flat after the irradiating and the pressing, as described later in this disclosure. In embodiments, the first surface portion 220 extends across the substrate 204 substantially within a reference plane 228. As used herein, the term “substantially within a reference plane” means that most of a surface area of the first surface portion 220 (e.g., 51%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or more of the surface area) lies within the reference plane 228.
[0032] The second surface portion 224 is proximate portions of the substrate 204 along which the optical fibers 208 are disposed such that the second surface portion 224 is interposed with the first surface portion 220 . In embodiments, the second surface portion 224 is affected in terms of surface topology by the laser irradiation and / or pressing processes that are associated with the method for forming the assembly 200 such that the second surface portion 224 bulges locally about the optical fiber 208 above the reference plane 228. In embodiments, the second surface portion 224 (or each contiguous second surface portion if there are a multiple second surface portions 224) is substantially symmetrical about a mirror plane (not shown) aligned with a longitudinal axis 232 of the optical fiber 208 and oriented normal to the reference plane 228. In embodiments, the second surface portion 224 extends laterally beyond the optical fiber 208 (e.g., in a horizontal direction relative to the view of FIG. 2) when viewed in a cross-sectional plane passing through the optical fiber 208 and oriented normal to the longitudinal axis 232 of the optical fiber 208.
[0033] The optical fiber 208 is bonded to the second surface portion 224 along a bond interface 236 that comprises laser-melted material of the substrate 204 that contacts the opticalAttorney Docket No.: SP24-037PCT fiber 208. As used herein, the phrase “laser-melted” and like phrases mean that the material of the substrate is (selectively) melted via a laser beam (i.e., the laser beam heats the material of the substrate to its melting point via absorption of the laser energy) prior to and / or concurrently with the (direct) contact of the material with the optical fiber 208. The selective laser-melting of the material of the substrate 204 is described hereinbelow in connection with the method for forming the assembly 200. In embodiments in which the optical fiber is a circular optical fiber 208' (FIG. 2), a portion of the perimeter 238 (e.g., the curved surface of the perimeter) of the circular optical fiber 208' contacts the laser-melted material of the substrate 204 along the bond interface 236. In embodiments in which the optical fiber is a D-shaped optical fiber 208" (FIG. 3), the flat portion 216 of the D-shaped optical fiber 208" is oriented to contact the laser-melted material of the substrate 204 along the bond interface 236. The circular portion 212 of the D-shape optical fiber 208" can also contact the laser-melted material of the substrate 204 depending on aposition of the D-shaped optical fiber 208" below the reference plane 228 (e.g., a depth of the flat portion 216), as described hereinbelow.
[0034] As shown in FIGS. 2 and 3, the bond interface 236 has a first portion 240 disposed below the reference plane 228 and a second portion 244 disposed above the reference plane 228. In embodiments, the first portion 240 of the bond interface 236 has a depth below the reference plane 228 of at least 1% of a diameter D of the optical fiber 208 when measured in a direction normal to the reference plane 228. As used herein, the depth d is measured from the reference plane 228 to the lowest portion of the bond interface 236 below the reference plane 228. The depth d does not include material of the substrate 204 disposed or displaced above the reference plane 228 as a result of the method for forming the assembly 200.
[0035] In embodiments, the depth d of the first portion 240 of the bond interface 236 is in a range of from about 2.5% to about 60%, from about 2.5% to about 58.75%, from about 4% to about 60%, from about 2.5% to about 57.5%, from about 2.5% to about 56.25%, from about 2.5% to about 55%, from about 2.5% to about 53.75%, from about 4.5% to about 55%, from about 2.5% to about 52.5%, from about 2.5% to about 51.25%, from about 5% to about 50%, from about 5.5% to about 45%, from about 6% to about 40%, from about 6.5% to about 35%, from about 7% to about 30%, or from about 7.5% to about 25% of the diameter D of the optical fiber 208.Attorney Docket No.: SP24-037PCT
[0036] The second portion 244 of the bond interface 236 has a height h above the reference plane 228 of at least 0.5% of a diameter D of the optical fiber 208 when measured in a direction normal to the reference plane 228. As used herein, the height h is measured from the reference plane 228 to the highest portion of the bond interface 236 above the reference plane 228. The height h does not include material of the substrate 204 disposed or displaced above the reference plane 228 but not in contact with the optical fiber 208 as result of the method for forming the assembly 200. In embodiments, such as shown in FIGS. 2 and 3, the second portion 244 of the bond interface 236 can include a first sub-portion 244i on one side (e.g., the left side in the figures) of the optical fiber 208 and a second sub-portion 2442 on the other side (e.g., the right side in the figures) of the optical fiber 208. In such embodiments, the height h can be measured from the reference plane 228 to the highest portion of one or both of the first sub-portion 244i and the second sub-portion 2442. In such embodiments, the height h can be calculated as an average of the height h measured to the highest portion of the first subportion 244i and the height h measured to the highest portion of the second sub-portion 2442. In embodiments, the height h of the second portion 244 of the bond interface 236 is in a range of from about 1% to about 60% of the diameter D of the optical fiber 208.
[0037] FIGS.4 and 5 are simplified schematic depictions of the bond interface 236 between the laser-melted material of the substrate 204 and the optical fiber 208. In each of the simplified depictions, only the optical fiber 208, the second surface portion 224, the reference plane 228, and features of the bond interface 236 are shown. FIG. 4 illustrates the bond interface 236 with the circular optical fiber 208' and FIG. 5 illustrates the bond interface 236 with the D-shaped optical fiber 208". As shown in FIGS. 4 and 5, the bond interface 236 has a peripheral bond length 248c, 248D that extends about a portion of the perimeter 238 of the optical fiber 208 between opposed end points EPi, EP2 of the bond interface 236 at intersections of the optical fiber 208 and the second surface portion 224 of the substrate 204. In embodiments, the bond interface 236 extends continuously or substantially continuously about the perimeter 238 between the end points EPi, EP2 such that there are no discontinuities or substantially no discontinuities in the contact between the laser-melted material of the substrate 204 and the optical fiber 208 along the peripheral bond length 248c, 248D.
[0038] Referring now to FIG. 4, the peripheral bond length 248c of the bond interface 236 associated with the circular optical fiber 208' comprises a first length portion 250cAttorney Docket No.: SP24-037PCT corresponding to the first portion 240 of the bond interface 236 and a second length portion 252c corresponding to the second portion 244 of the bond interface 236. As shown in FIG. 4, the first length portion 250c extends along the perimeter 238 of circular the optical fiber 208' between opposed intermediate points IPi, IP2 of the bond interface 236 at intersections of the circular optical fiber 208' and the reference plane 238.
[0039] Referring still to FIG. 4, the second portion 244 of the bond interface 236 comprises the first sub-portion 244i and the second sub-portion 2442, as described previously with reference to FIG. 2. Correspondingly, the second length portion 252c comprises a first length sub-portion 252ic corresponding to the first sub-portion 244i and a second length subportion 2522c corresponding to the second sub-portion 2442. The first length sub-portion 252ic extends along the perimeter 238 of the circular optical fiber 208' between the first endpoint EPi and the first intermediate point IP2. The second length sub-portion 252ic extends along the perimeter 238 of the optical fiber 208' between the second endpoint EPi and the second intermediate point IP2.
[0040] In embodiments, the first length sub-portion 252ic and the second length subportion 2522c can be equal or approximately equal. In embodiments, the first length subportion 252ic and the second length sub-portion 2522c can differ depending on the respective heights h of the first sub-portion 244i and the second sub-portion 2442. The second length portion 252c comprises the total of the first length sub-portion 252ic and the second length sub-portion 2522c. In embodiments, the first length portion 250c is greater than the second length portion 252c.
[0041] Referring now to FIG. 5, the peripheral bond length 248D of the bond interface 236 associated with the D-shaped optical fiber 208" comprises a first length portion 250D corresponding to the flat portion 216 of the D-shaped optical fiber 208". As shown in FIG. 5, the first length portion 250D extends along the perimeter 238 of the D-shaped optical fiber 208' between opposed intermediate points IPi, IP2 of the bond interface 236 at opposed ends of the flat portion 216.
[0042] The peripheral bond length 248D of the bond interface 236 associated with the D-shaped optical fiber 208" also comprises a second length portion 252D corresponding to the portion of the circular portion 212 of the D-shaped fiber 208" that contacts the laser-meltedAttorney Docket No.: SP24-037PCT material of the substrate 204. In embodiments, such as shown in FIG. 5, the second length portion 252D can include a first length sub-portion 252ID on one side (e.g., the left side in the figure) of the D-shaped optical fiber 208" and a second length sub-portion 2522D on the other side (e.g., the right side in the figure) of the D-shaped optical fiber 208". The first length subportion 252ID extends along the perimeter 238 of the D-shaped optical fiber 208" between the first endpoint EPi and the first intermediate point IP2. The second length sub-portion 2522D extends along the perimeter 238 of the D-shaped optical fiber 208" between the second endpoint EP2 and the second intermediate point IP2.
[0043] Referring still to FIG. 5, the first length sub-portion 252ID and the second length sub-portion 2522D of the D-shaped optical fiber 208" include portions that extend above the reference plane 228 such that the first length sub-portion 252ID and the second length subportion 2522D comprise an entirety of the second portion 244 of the bond interface 236. The first length sub-portion 252ID and the second length sub-portion 2522D of the D-shaped optical fiber 208" also include portions that extend below the reference plane 228 such that the first length sub-portion 252ID and the second length sub-portion 2522D comprise a portion of the first portion 240 of the bond interface 236.
[0044] In embodiments, the first length sub-portion 252ID and the second length subportion 2522D can be equal or approximately equal. In embodiments, the first length subportion 252ID and the second length sub-portion 2522D can differ depending on one or more of the height h of the first sub-portion 244i, the height h of the second sub-portion 2442, and the depth d of the flat portion 216. The second length portion 252D comprises the total of the first length sub-portion 252ID and the second length sub-portion 2522D. In embodiments, the first length portion 250D is greater than the second length portion 252D.
[0045] Referring again to FIGS. 4 and 5, the peripheral bond length 248c, 248D of the bond interface 236 is in a range of from about 15% to about 62.5%, from about 16% to about 60%, from about 25% to about 66%, from about 17% to about 57.5%, from about 15% to about 55%, from about 25% to about 63.25%, from about 18% to about 55%, from about 30% to about 66%, from about 25% to about 60.5%, from about 19% to about 52.5%, from about 30% to about 63.25%, from about 25% to about 57.75%, from about 30% to about 60.5%, from about 20% to about 50%, from about 25% to about 55%, from about 30% to about 57.75%, fromAttorney Docket No.: SP24-037PCT about 25% to about 52.25%, from about 21% to about 47.5%, from about 30% to about 55%, from about 25% to about 49.5%, from about 22% to about 45%, from about 30% to about 52.25%, from about 25% to about 46.75%, from about 23% to about 42.5%, from about 30% to about 49.5%, from about 25% to about 44%, from about 24% to about 40%, or from about 25% to about 37.5% of the perimeter 238 of the optical fiber 208 when viewed in cross section.
[0046] FIG. 6A is a schematic side view of the portion of the assembly 200 depicted in FIGS. 2 and 3 showing the bond interface 236 between the optical fiber 208, 208', 208" and the substrate 204 along a first lengthwise portion 254, 254i of the optical fiber that overlaps the substrate 204. As shown in FIG. 6 A, the bond interface 236 has an axial bond length 256 that extends in a direction parallel to the longitudinal axis 232 of the optical fiber 208, 208', 208". In embodiments, the bond interface 236 extends continuously or substantially continuously such that there are no discontinuities or substantially no discontinuities in the contact between the laser-melted material of the substrate 204 and the optical fiber 208, 208', 208" along the axial bond length 256. In embodiments, the axial bond length 256 extends continuously or substantially continuously for at least 100% of a diameter D of the optical fiber 208, 208', 208". In embodiments, the axial bond length 256 extends continuously or substantially continuously for an entirety of an overlap of the optical fiber 208, 208', 208" with the substrate 204 along the first lengthwise portion 254, 254i as shown in FIG. 6A.
[0047] FIG. 6B is a schematic side view of an assembly 200' similar to the assembly 200 of FIG. 6A showing the bond interface 236 between the optical fiber 208, 208', 208" and a substrate 204' along a second lengthwise portion 254, 2542 of the optical fiber 208, 208', 208" that is shorter than the first lengthwise portion 254, 254i shown in FIG. 6A. As shown in FIG. 6B, the substrate 204' has a protrusion 260 and the optical fiber 208, 208', 208" is laser-bonded to a surface of the protrusion 260. Since the surface of the protrusion 260 of the substrate 204' (FIG. 6B) is smaller (e.g., in the lengthwise direction of the optical fiber) than the surface of the substrate 204 (FIG. 6A), the overlap of the optical fiber 208, 208', 208" with the substrate 204' (e.g., the second lengthwise portion 254, 2542) is shorter than the overlap of the optical fiber 208, 208', 208" with the substrate 204 (e.g., the first lengthwise portion 254, 254i). Similarly, the axial bond length 256 of the bond interface 236 between the optical fiber 208, 208', 208" and the substrate 204' (FIG. 6B) is shorter than the axial bond length 256 of the bond interface 236 between the optical fiber 208, 208', 208" and the substrate 204 (FIG. 6A).Attorney Docket No.: SP24-037PCT
[0048] Referring now to FIGS. 1-5, 6A, and 6B, the optical fiber 208 can be formed from fused silica having a first amount of hydroxide (e.g., OH") in a range of from about 0.1 ppm to about 13 ppm. The fused silica having such a low content of hydroxide can be referred to as “dry” fused silica. In embodiments, the curved portion of the optical fiber 208 can have a diameter D (e.g., cladding diameter) in a range of from about 25 pm to about 600 pm, such as from about 50 pm to about 500 pm, from about 75 pm to about 400 pm, from about 100 pm to about 300 pm, or from about 100 pm to about 200 pm. In embodiments in which the optical fiber is a circular optical fiber 208', the curved portion with the diameter D comprises an entirety of the perimeter 238, such as shown in FIG. 2. In embodiments in which the optical fiber is a D-shaped optical fiber 208", the curved portion with the diameter D comprises the circular portion 212 of the perimeter 238, such as shown in FIG. 3.
[0049] In embodiments, the substrate 204 can be formed from glass having a second amount of hydroxide (e.g., OH") that is greater than the first amount of hydroxide. For example, the second amount of hydroxide in the glass of the substrate 204 can be 2, 3, 4, 5, 6, 7, 8, 9, 10, or more times greater than the first amount of hydroxide in the fused silica of the optical fiber 208. Non-limiting glass materials can include alkaline earth boro-aluminosilicate glass (e.g., as manufactured and sold under the trade name Eagle XG® by Coming Incorporated of Coming, New York) and alkali-aluminosilicate glass (e.g., as manufactured and sold by Coming Incorporated of Corning, New York under the trade name Gorilla® Glass).
[0050] In embodiments, the optical fiber 208 has a maximum surface stress along the bond interface 236 of equal to or less than about 250 MPa, such as 225 MPa, 200 MPa, 175 MPa, 150 MPa, 125 MPa, 100 MPa, 75 MPa, 70 MPa, 65 MPa, 60 MPa, 55 MPa, 50 MPa, or less. In embodiments, the maximum surface stress along the bond interface 236 is at least 20 MPa, such as 25 MPa, 27.5 MPa, 30 MPa, 32.5 MPa, 35 MPa, 37.5 MPa, 40 MPa, 42.5 MPa, 45 MPa, 46 MPa, 47 MPa, 48 MPa, or more.
[0051] Referring again to FIG. 1, the assembly 200 can further comprise one or more additional optical fibers 208 and the second surface portion 224 can comprise one or more additional second surface portions 224 interposed with the first surface portion 220. In such embodiments, each additional optical fiber 208 is bonded to a respective additional second surface portion 224 along an additional bond interface 236 comprising laser-melted material ofAttorney Docket No.: SP24-037PCT the substrate 204 that contacts the additional optical fiber 208. In such embodiments, a first portion 240 of the additional bond interface 236 is disposed below the reference plane 228 and a second portion 244 of the additional bond interface 236 is disposed above the reference plane 228.
[0052] In embodiments, the one or more additional optical fibers are the same as or substantially similar to the optical fibers 208, 208', 208" described hereinabove with respect to FIGS. 1-5, 6A, and 6B. In embodiments, the additional bond interface is the same as or substantially similar to the bond interface 236 (e.g., in terms of depth d, height h, peripheral bond length 248c, 248D, and axial bond length 256) described hereinabove with respect to FIGS. 1-5, 6A, and 6B. In embodiments, the one or more additional optical fibers can be different than the optical fibers 208, 208', 208" described hereinabove with respect to FIGS. 1-5, 6 A, and 6B. In embodiments, the additional bond interface can be different than the bond interface 236 (e.g., in terms of depth d, height h, peripheral bond length 248c, 248D, and axial bond length 256) described hereinabove with respect to FIGS. 1-5, 6A, and 6B.
[0053] FIGS. 7A-7C and 8-10 schematically illustrate aspects of a method for forming an assembly 200 for a fiber array 100. The method is further described with reference to FIGS. 1-5, 6A, and 6B, which show various aspects of the assembly 200 with the optical fiber 208 laser-bonded to the substrate 204, as described hereinabove. Referring now to FIGS. 7A-7C, steps of the method for laser-bonding the optical fiber 208 to the substrate 204 are illustrated via a series of schematic cross-sectional representations. As shown in FIG. 7A, the method comprises positioning the optical fiber 208 against a surface 218 of the substrate 204 and pressing the optical fiber 208 against the substrate 204. During the initial positioning of the optical fiber 208, the surface 218 of the substrate 204 is flat or substantially flat and extends across the substrate 204 (e.g., substantially within the reference plane 228) since no portion of the surface 218 has been irradiated at this step of the method. Although the circular optical fiber 208' is depicted in FIGS. 7A-7C, it should be appreciated that optical fibers with different cross-sectional shapes, such as the D-shaped optical fiber 208", can be used with the method. In embodiments, prior to the positioning, the optical fiber 208 can be stripped of any jacket or outer layers to remove high coefficient of thermal expansion (CTE) material.Attorney Docket No.: SP24-037PCT
[0054] Referring still to FIG. 7A, a fixture 300 can be used for the positioning and / or the pressing of the optical fiber 208 against the substrate 204. The fixture 300 comprises a third substrate 304 with a groove 308 (e.g., a V-groove) configured to align the optical fiber 208 relative to the substrate 204 during the positioning and the pressing. In embodiments, the fixture 300 can comprise a plurality of grooves 308 configured to simultaneously align a plurality of optical fibers 208 relative to the substrate 204 during the positioning and the pressing. The plurality of grooves 308 of the fixture 308 are configured to position the plurality of optical fibers 208 at known locations on the x- and z-axis. As a non-limiting example, the precise placement of the fixture 300 on the substrate 204 can be performed by an active alignment process. Once in place, the fixture 300 can be mechanically clamped or otherwise secured to the substrate 204 to maintain the positions of the optical fibers 208 thereon.
[0055] Referring now to FIG. 7B, the method further comprises, during the pressing, irradiating a lengthwise portion 254 (FIGS. 6A and 6B) of the optical fiber 208 with a laser beam 404 to selectively melt material of the substrate 204 adjacent the lengthwise portion 254 and bond the optical fiber 208 to a second surface potion 224 of the substrate 204 along a bond interface 236. In FIG. 7B, the laser beam 404 is depicted using a dotted pattern fill so as to represent simultaneously irradiating an area that comprises an entirety of the lengthwise portion 254 of the optical fiber 208 and the second surface portion 224 of the substrate 204 as well as incidentally irradiating the first surface portion 220 of the substrate 204. As best shown in FIGS. 2 and 3, the bond interface 236 comprises laser-melted material of the substrate 204 that contacts the optical fiber 208 and, after the irradiating and the pressing, a first portion 240 of the bond interface 236 is disposed below the reference plane 228 and a second portion 244 of the bond interface 236 is disposed above the reference plane 228.
[0056] Referring again to FIGS. 2-5, 6A, and 6B, the lengthwise portion 254 of the optical fiber 208 is pressed into the selectively-melted material of the substrate 204 during the irradiating to position the first portion 240 of the bond interface 236 below the reference plane 228. During the pressing and the irradiating (e.g., while the material of the substrate 204 is selectively melted), the lengthwise portion 254 of the optical fiber 208 displaces a portion of the selectively-melted material from below the reference plane 228 to above the reference plane 228 to position the second portion 244 of the bond interface 236 above the reference plane 228.Attorney Docket No.: SP24-037PCT
[0057] Referring now to FIG. 7C, the method further comprises cooling the assembly 200 with the optical fiber 208 laser-bonded to the substrate 204 after the irradiating. In embodiments, after the irradiating, the fixture 300 can be used to maintain the position of the optical fiber 208 relative to the substrate 204 during the cooling. In embodiments, the position of the fixture 300 is fixed relative to the substrate 204 so that the optical fiber 208 is fixed in position during the cooling. As shown in FIGS. 7B and 7C, the displaced portion of the selectively-melted material of the substrate 204 corresponding to the second portion 224 of the bond interface 236 has a first height hi above the reference plane 228 during the irradiating and a second height fe above the reference plane 228 after the irradiating (e.g., during and after the cooling). The first heigh hi is greater than the second height fe. Without being bound by theory, the first height hi may be greater than the second height fe because the displaced material of the substrate 204 during pressing and the irradiating has a higher temperature than the displaced material of the substrate 204 has during and after the cooling. As such, the displaced material of the substrate 204 expands more at the higher temperature (e.g., during the irradiating) than it does at the lower temperature (e.g., during and after the cooling). After the cooling, the assembly 200 has the configuration depicted in FIGS. 2 and 4 for cylindrical optical fiber 208, 208' or the configuration depicted in FIGS. 3 and 5 for D-shaped optical fiber 208, 208".
[0058] FIG. 8 is a schematic depiction of various elements of an optical system or laser 400 configured to generate a top hat, collimated laser beam 404 for laser-bonding the optical fiber 208 to the substrate 204. The bonding of the optical fiber 208 to the substrate 204 is accomplished by selective laser bonding, which uses the laser 400 operating in the fundamental O-H (e.g., hydroxide) absorption wavelength of the material of the substrate 204. By appropriately selecting the wavelength of the laser beam 404, the laser energy can be absorbed mostly by the substrate 204 rather than the optical fiber 208, even though the laser beam 404 is configured to transmit substantially through the optical fiber 208 (e.g., without sufficient absorption to cause heating and melting of the material of the optical fiber 208) before the laser beam 404 arrives at the second surface portion 224 of the substrate 204 adjacent the optical fiber 208. Such a configuration leaves the optical fiber 208 safe, unheated, and undamaged.
[0059] In embodiments, the laser beam 404 is generated via a mid-infrared (mid-IR) laser source integrated with the optical system 400. In embodiments, the laser beam 404 has a laser wavelength in a range of from about 2.5 pm to about 10 pm though other laser wavelengthsAttorney Docket No.: SP24-037PCT outside of this range can be used in some embodiments. As discussed herein, the materials of the substrate 204 and the optical fiber 208 are chosen to enable (primarily) absorption in the material of the substrate 204 and (primarily) transmission in the material of the optical fiber 208. The optical fiber 208 can be formed from fused silica having a first amount of hydroxide (e.g., OH-) from about 0.1 ppm to about 13 ppm. The substrate 204 can be formed from glass having a second amount of hydroxide (e.g., OH-)thatis greater than the first amount of hydroxide to enable the selective heating during the irradiating. In embodiments, the third substrate 304 of the fixture 300 can be formed from fused silica having the first amount of hydroxide (e.g., OH-) so as to minimize laser absorption in the fixture 300 during the irradiating.
[0060] As described hereinabove with reference to FIG. 7B, the laser beam 404 is configured to simultaneously irradiate an area that comprises an entirety of the lengthwise portion 254 of the optical fiber 208 and the second surface portion 224 of the substrate 204. To accomplish such simultaneous irradiation in coordination with the pressing of the optical fiber 208 to accurately position the first portion 240 of the bond interface 236 below the reference plane 228, it has been discovered that uniform irradiation / heating is desired for implementing the method.
[0061] However, the intensity distribution of a typical laser source is inherently featured by a Gaussian distribution, which conflicts with the desired uniform irradiation / heating for implementing the method. Therefore, the Gaussian laser beam can be shaped into a top-hat laser, which has a uniform heating intensity. Another consideration is the refraction of the laser beam when passing through the optical fiber 208 or the plurality of optical fibers 208 of the fiber array 100 before absorption by the material of the substrate 204. If the incident angle of the top-hat laser beam varies between different optical fibers 208 in the fiber array 100, the corresponding refraction will be different, causing inconsistent heating conditions for different optical fibers 208. Therefore, the laser beam should be not only be top-hat, but also collimated when arriving at the fiber array 100.
[0062] FIG. 8 is a schematic depiction of various elements of the optical system 400 configured to generate a top hat, collimated laser beam 404 for laser-bonding the optical fiber 208 to the substrate 204. As shown in FIG. 8, a Gaussian input beam is emitted from Plane #1Attorney Docket No.: SP24-037PCT of the system 400. The optical system 400 includes a lens system with two aspherical lenses. Lens #1 of the lens system functions as the first transformer lens converting Gaussian distribution into top-hat distribution. Lens #2 of the lens system functions as the second transformer lens converting the top-hat beam into a collimated top-hat beam.
[0063] EXAMPLES
[0064] Various embodiments of the present disclosure can be better understood by reference to the following Examples which are offered by way of illustration. The present disclosure is not limited to the Examples given herein.
[0065] Example 1 -Optical System Design
[0066] The energy relationship of the optical system 400 at Plane # 1 and Plane #2 can be analyzed using ray-tracing software (e.g., ZEMAX) according to the following coordinate:
[0067] S=K*[l-exp(-2X2 / W2)]A0.5
[0068] Where S is the coordinate of each beam at Plane #2, K is the beam radius at the Plane #2, X is the coordinate of each beam at the Plane #1, and W is the beam waist. In Example 1, the beam radius K is set at 15 mm, and the beam waist W is set at 2 mm.
[0069] With this relationship and a requirement of collimation, a merit function is added into the ray-tracing software via a programming language. One part of the merit function controls each beam’s coordinate at Plane #2 (e.g., configured to achieve a top-hat feature), while the other part of the merit function controls each beam’s incident angle at Plane #3 (e.g., configured to achieve a collimation feature). Through use of the merit function, the lens system with two plane-even aspherical lens is designed, as shown in FIG. 9(A). The initial beam distribution of the input beam is Gaussian distribution with a beam waist of 2 mm at l / e2 as shown in FIG. 9(B). With Lens # 1 , the distribution is transformed into top-hat distribution with a 15 mm beam width. The uniformity of the top-hat distribution is >90% according to the intensity ratio between minimum and maximum as shown in FIG. 9(C). With Lens #2, the top-hat beam is collimated with less than 0.06° divergence angle at the final image plane, as shown in FIG. 9(D).
[0070] Example 2 - Beam Propagation through the Optical FibersAttorney Docket No.: SP24-037PCT
[0071] To further verify the beam propagation through the plurality of the optical fibers, a fiber array comprising optical fibers 208 having a diameter of 125 pm is incorporated into the optical simulation, as illustrated by FIG. 10. The collimated laser beam 404 passes through the optical fibers 208 and is focused at the bond interface 236 between the optical fibers 208 and the substrate 204. The output from this simulation confirms the proposed optical system 400 can be used to provide a desired uniform and collimated laser irradiation to selectively bond the optical fibers 208 to the substrate 204.
[0072] Example 3 - Simulated Geometry and Stress Response for Laser-Bonded Fiber
[0073] The surface stress of an optical fiber can play an important role in successful fibersubstrate bonding since a high stress can crack or otherwise degrade the surface of the optical fiber. The peripheral bonding length is another important factor because a larger bonding length enables strong cohesion and stable positioning of the optical fiber relative to the substrate. To minimize stress and increase the peripheral bonding length, the method disclosed herein utilizes coining deformation. As used herein, coining deformation comprises (1) an irradiating step in which a laser beam (e.g., operating in the mid-IR laser wavelength) is used to selectively melt a material of the substrate and (2) a concurrent pressing step in which the lengthwise portion of the optical fiber irradiated during the irradiating step is pressed into the laser-melted substrate to position a portion of the bond interface below a reference plane of the substrate and displace a portion of the laser-melted material of the substrate above the reference plane to expand the peripheral bonding length between the optical fiber and the substrate.
[0074] A finite element model has been used to demonstrate advantages of the method disclosed herein. Specifically, stress field and changes in geometrical morphology are simulated. The finite element model utilizes a single fiber due to the periodicity nature of the whole structure. Referring first to FIG. 7B, when the optical fiber 208 is irradiated, a pressing force is applied to the optical fiber 208 using a displacement control of approximately 16 pm. In embodiments, other displacement control amounts can be used. As a result, the laser-melted material of the substrate is subjected to coining deformation in which the laser-melted material is displaced from below the reference plane 228 to above the reference plane 228 on both side of the optical fiber 208. Due to the coining deformation, the second surface portion 224 of the substrate 204 is displaced (e.g., bulged locally) to a first height hi of about 13.2 pm. As a result,Attorney Docket No.: SP24-037PCT the peripheral bonding length 248c, 248D (FIGS. 4 and 5) reaches approximately 107 pm after cooling (FIG. 7C).
[0075] Moreover, the coining deformation compensates substrate shrinkage, thereby reducing the shrinkage-induced tensile stress in the surface of the optical fiber. As shown in FIG. 11, the maximum surface stress along the bond interface 236 is approximately 53 MPa with the peripheral bonding length of approximately 107 pm. These results demonstrate that the method disclosed herein can increase the peripheral bonding length and reduce the surface stress of the optical fiber.
[0076] The various embodiments of the fiber array 100, the assembly 200, and the method disclosed herein have numerous advantages. In terms of reliability, a longer bonding length by the coining-based deformation method enables a significant reduction in epoxy utilization and thus reduces debonding failure risk resulted from an unfavorable thermal deformation of the epoxy. The deep and long arc of the bonding interface formed by the coining-based deformation method forms a more reliable bonding, which has a better resistance to not only normal debonding load but also tangential debonding load, as compared to the prior swellingbased bonding. After laser heating, the substrate shrinkage in the heat affected zone tends to pull down the fiber surface, causing tensile stress at the bonding interface. This tensile stress at the bonding interface may result in fiber surface cracks. Using the method disclosed herein, the substrate shrinkage can be compensated by the coining deformation. Consequently, the tension stress at the bonding interface is significantly reduced, preventing the occurrence of the fiber surface cracking.
[0077] In terms of performance, compared to the swelling-based bonding, the coiningbased deformation method described herein forms increased bonding length. The deep and long arc of the bonding interface formed by the coining-based deformation method helps with maintaining correct optical fiber positions, thereby assuring reliable connectivity. In the swelling -based bonding, high tensile stress at the bonding interface tends to crack fiber surface. As such, effort must be taken to determine processing parameters which can achieve a tradeoff between swelling, bonding length, and tension stress. Using the method disclosed herein, less effort is needed to optimize processing parameters because coining deformation makes it easier to form longer bonding length and a minimized interface tension stress. The method disclosedAttorney Docket No.: SP24-037PCT herein not only works for single core fiber, but also for other types of fiber, such as multicore fiber, D-shaped fiber, etc. because the stress reduction mechanism from coining-based deformation is the same.
[0078] In terms of cost, high-precision glass v-groove chips account for 36.2% of the bill-of-materials for traditional FAUs. The fixture 300 with the v-groove shown in FIGS. 7A-7C is used only during the laser-bonding portion of the method disclosed herein, and the fixture 300 is reusable. As such, there is no v-groove chip in the integrated structure fabricated by the method disclosed herein, which enables a significant cost reduction by eliminating v-groove chips. Since the coining deformation of the method disclosed herein minimizes the fiber surface stress by compensating the shrinkage of the laser heated substrate, it bypasses the difficulties in selecting appropriate coefficient of thermal expansion (CTE) value for the substrate material. Therefore, the method disclosed herein can widen the material selection for the substrate glass material. For example, a less expensive glass material with a higher CTE value can work well in the method disclosed herein without exceeding tension stress limits on the fiber surface. This material flexibility further reduces the process cost. The augmented bonding length achieved by the coining deformation can help reduce the use of epoxy, which will save cost in purchasing epoxy, given that epoxy is expensive and vulnerable to irregular supply chain availability. Furthermore, since the mid-IR laser can be absorbed directly by the substrate as long as its transmission is low enough, the method disclosed herein does not rely on a metal film to absorb the laser power. Therefore, the elimination of the metal film and the associated coating process enables further cost reduction.
[0079] While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications, and further applications that come within the spirit of the disclosure are desired to be protected.
Claims
Attorney Docket No.: SP24-037PCT CLAIMSWhat is claimed is:
1. An assembly for a fiber array, comprising:a substrate comprising a first surface portion and a second surface portion, the first surface portion extending across the substrate substantially within a reference plane; and an optical fiber bonded to the second surface portion along a bond interface comprising laser-melted material of the substrate that contacts the optical fiber, wherein a first portion of the bond interface is disposed below the reference plane and a second portion of the bond interface is disposed above the reference plane.
2. The assembly of claim 1, wherein the first portion of the bond interface has a depth below the reference plane of at least 1% of a diameter of the optical fiber when measured in a direction normal to the reference plane.
3. The assembly of claim 2, wherein the depth of the first portion of the bond interface is in a range of from about 5% to about 50% of the diameter of the optical fiber.
4. The assembly of any one of claims 1-3, wherein the second portion of the bond interface has a height above the reference plane of at least 0.5% of a diameter of the optical fiber when measured in a direction normal to the reference plane.
5. The assembly of claim 4, wherein the height of the second portion of the bond interface is in a range of from about 1% to about 60% of the diameter of the optical fiber.
6. The assembly of any one of claims 1-5, wherein the bond interface has a peripheral bond length in a range of from about 15% to about 55% of a cross-sectional perimeter of the optical fiber.Attorney Docket No.: SP24-037PCT 7. The assembly of any one of claims 1-5, wherein the bond interface has a peripheral bond length in a range of from about 20% to about 50% of a cross-sectional perimeter of the optical fiber.
8. The assembly of clam 6 or claim 7, wherein the peripheral bond length comprises a first length portion corresponding to the first portion of the bond interface and a second length portion corresponding to the second portion of the bond interface, and wherein the first length portion is greater than the second length portion.
9. The assembly of any one of claims 1-8, wherein the bond interface has an axial bond length that extends continuously for at least 100% of a diameter of the optical fiber in a direction parallel to the longitudinal axis of the optical fiber.
10. The assembly claim 9, wherein the axial bond length extends continuously for an entirety of an overlap of the optical fiber with the substrate.
11. The assembly of any one of claims 1-10, wherein the optical fiber has a cross-sectional shape that is circular.
12. The assembly of any one of claims 1-10, wherein the optical fiber has a cross-sectional shape that comprises a circular portion and a flat portion, and wherein the laser-melted material contacts the flat portion of the optical fiber along the bond interface.
13. The assembly of any one of claims 1-12, wherein the optical fiber comprises fused silica having a first amount of hydroxide in a range of from about 0.1 ppm to about 13 ppm.
14. The assembly of claim 13, wherein the substrate comprises glass having a second amount of hydroxide that is at least 5 times greater than the first amount of hydroxide.Attorney Docket No.: SP24-037PCT 15. The assembly of any one of claims 1-14, wherein the second surface portion of the substrate is substantially symmetrical about a mirror plane aligned with the longitudinal axis of the optical fiber and oriented normal to the reference plane.
16. The assembly of any one of claims 1-15, wherein the second surface portion of the substrate extends laterally beyond the optical fiber when viewed in a cross-sectional plane passing through the optical fiber and oriented normal to the longitudinal axis of the optical fiber.
17. The assembly of any one of claims 1-16, wherein a maximum surface stress of the optical fiber along the bond interface is equal to or less than about 250 MPa.
18. The assembly of any one of claims 1-16, wherein a maximum surface stress of the optical fiber along the bond interface is equal to or less than about 100 MPa.
19. The assembly of any one of claims 1-18, further comprising one or more additional optical fibers, wherein the second surface portion comprises one or more additional second surface portions, each additional optical fiber bonded to a respective additional second surface portion along an additional bond interface comprising laser-melted material of the substrate that contacts the additional optical fiber, and wherein a first portion of the additional bond interface is disposed below the reference plane and a second portion of the additional bond interface is disposed above the reference plane.
20. A fiber array, comprising:the assembly of any one of claims 1-20;a sealing layer covering the first surface portion, the second surface portion, and the optical fiber; anda second substrate disposed over the assembly in contact with the sealing layer.
21. A method for forming an assembly for a fiber array, comprising:Attorney Docket No.: SP24-037PCT pressing an optical fiber against a substrate, the substrate comprising a first surface portion that extends across the substrate substantially within a reference plane; and during the pressing, irradiating a lengthwise portion of the optical fiber with a laser beam to selectively melt material of the substrate adjacent the lengthwise portion and bond the optical fiber to a second surface potion of the substrate along a bond interface, wherein the bond interface comprises laser-melted material of the substrate that contacts the optical fiber, and wherein a first portion of the bond interface is disposed below the reference plane and a second portion of the bond interface is disposed above the reference plane.
22. The method of claim 21, wherein the lengthwise portion of the optical fiber is pressed into the selectively-melted material of the substrate during the irradiating to position the first portion of the bond interface below the reference plane.
23. The method of claim 22, wherein the lengthwise portion of the optical fiber displaces a portion of the selectively-melted material from below the reference plane to above the reference plane to position the second portion of the bond interface above the reference plane.
24. The method of claim 23, wherein the displaced portion of the selectively-melted material has a first height above the reference plane during the irradiating and a second height above the reference plane after the irradiating, and wherein the first height is greater than the second height.
25. The method of any one of claims 21-24, wherein the lengthwise portion of the optical fiber extends continuously for at least 100% of a diameter of the optical fiber in a direction parallel to the longitudinal axis of the optical fiber.
26. The method of any one of claims 21-25, wherein the lengthwise portion of the optical fiber extends continuously for an entirety of an overlap of the optical fiber with the substrate.Attorney Docket No.: SP24-037PCT 27. The method of any one of claims 21-26, wherein the laser beam is configured to simultaneously irradiate an entirety of the lengthwise portion.
28. The method of any one of claims 21-27, wherein the laser beam is configured as a top-hat, collimated laser beam.
29. The method of any one of claims 21-28, wherein the laser beam has a laser wavelength in a range of from about 2.5 pm to about 10 pm.
30. The method of any one of claims 21-29, wherein, during the irradiating, the laser beam is first directed into the lengthwise portion of the optical fiber and thereafter focused by the optical fiber substantially towards the bond interface.
31. The method of any one of claims 21-30, wherein the first portion of the bond interface has a depth below the reference plane of at least 1% of a diameter of the optical fiber when measured in a direction normal to the reference plane.
32. The method of any one of claims 21-31, wherein the second portion of the bond interface has a height above the reference plane of at least 0.5% of a diameter of the optical fiber when measured in a direction normal to the reference plane.
33. The method of any one of claims 21-32, wherein the bond interface has a peripheral bond length in a range of from about 15% to about 55% of a cross-sectional perimeter of the optical fiber.
34. The method of claim 33, wherein the peripheral bond length comprises a first length portion corresponding to the first portion of the bond interface and a second length portion corresponding to the second portion of the bond interface, and wherein the first length portion is greater than the second length portion.Attorney Docket No.: SP24-037PCT 35. The method of any one of claims 21-34, wherein the bond interface has an axial bond length that extends continuously for at least 100% of a diameter of the optical fiber in a direction parallel to the longitudinal axis of the optical fiber.
36. The method of claim 35, wherein the axial bond length extends continuously for an entirety of an overlap of the optical fiber with the substrate.
37. The method of any one of claims 21-36, wherein the optical fiber has a cross-sectional profile that is circular.
38. The method of any one of claims 21-36, wherein the optical fiber has a cross-sectional profile that comprises a circular portion and a flat portion, and wherein the bond interface contacts the flat portion of the optical fiber.
39. The method of any one of claims 21-38, wherein the optical fiber comprises fused silica having a first amount of hydroxide in a range of from about 0.1 ppm to about 13 ppm.
40. The method of claim 39, wherein the substrate comprises fused silica having a second amount of hydroxide that is at least 5 times greater than the first amount of hydroxide.
41. The method of any one of claims 21-40, wherein the pressing comprises pressing the optical fiber with a fixture comprising a third substrate with a groove configured maintain a position of the optical fiber relative to the substrate during the irradiating.
42. The method of claim 41, wherein the third substrate comprises fused silica having an amount of hydroxide in a range of from about 0.1 ppm to about 13 ppm.
43. The method of any one of claims 21-42, wherein:the pressing comprises simultaneously pressing the optical fiber and an additional optical fiber against the substrate; andAttorney Docket No.: SP24-037PCT the irradiating comprises simultaneously irradiating the lengthwise portion of the optical fiber and an additional lengthwise portion of the additional optical fiber with the laser beam to selectively melt material of the substrate adjacent the additional lengthwise portion and bond the additional optical fiber to an additional second surface potion of the substrate along an additional bond interface,the additional bond interface comprises laser-melted material of the substrate that contacts the additional optical fiber, and wherein an additional first portion of the additional bond interface is disposed below the reference plane and an additional second portion of the additional bond interface is disposed above the reference plane.