LASER-TO-OPTICAL-FIBER CONNECTION

Abstract

An article of manufacture including a fiber optic termination of a small core optical fiber for use with a surgical laser (characterized by a high M.sup.2 factor) or other high-power or high-energy pulse laser is configured for safe and efficient coupling of light at a large laser focal point and/or to enable the process of coupling of radiant intensities exceeding the silica fiber damage thresholds and/or those ionizing the air if fully focused therein. The termination includes a glass cylinder structured to include a core region and a glass cladding region the ratio of dimensions of which is substantially equal to the ratio of respectively-corresponding dimensions of the employed optical fiber. A method of coupling laser light characterized by an M.sup.2 factor of 25 or higher into an optical fiber with the use of same.

Claims

1. A method for coupling light into an optical fiber that has a fiber glass core and a fiber glass cladding, the method comprising: directing an input beam of laser light having an M.sup.2 factor of 25 or higher in air to a front surface of an optical termination element cooperated with an input facet of the optical fiber, wherein the optical termination element has a termination glass core and a termination glass cladding dimensioned such that a first ratio of a termination glass core diameter to a termination glass cladding diameter is substantially equal to a second ratio of the fiber glass core diameter to the fiber glass cladding diameter; upon transmitting said input beam through the front surface, spatially concentrating said input beam inside the optical termination element to form a converging beam while propagating said converging beam towards the input surface; and coupling light from said converging beam into the optical fiber through the input surface.

2. A method according to claim 1, wherein said coupling includes forming a waist of the converging beam in a glass material.

3. A method according to claim 1, wherein said spatially concentrating is devoid of total internal reflection of the laser light at a boundary between the termination glass core and termination glass cladding.

4. A method according to claim 1, wherein said transmitting the input beam through the front surface of the optical termination element includes transmitting said beam through a surface of a lens.

5. A method according to claim 4, wherein the front surface of the optical termination element is said surface of a lens.

6. A method according to claim 4, wherein said lens in a gradient index lens.

7. A method according to claim 1, comprising one of the following: (7a) directly coupling said input beam from air to the optical termination element through said front surface that separates air from a material of the optical termination element; and (7b) coupling said input beam from air to an auxiliary glass element that is in contact with the optical termination element at the front surface thereof.

8. A method according to claim 1, wherein said spatially concentrating the input beam inside the optical termination element includes converging the input beam inside the optical termination element with the termination glass cladding diameter of at least 0.5 mm.

9. A method according to claim 1, wherein said transmitting the input beam through the front surface of the optical termination element includes transmitting at least 90% of a power carried by the input beam through the front surface of the optical termination element.

10. A method according to claim 1, wherein the spatially concentrating said input beam inside the optical termination element is devoid of propagating light from said input beam through an optical taper.

11. A method according claim 1, wherein the termination glass core and the fiber glass core are both made from a first material, and wherein the termination glass cladding and the fiber glass cladding are both made from a second material.

12. A method according to claim 3, wherein said transmitting the input beam through the front surface of the optical termination element includes transmitting said beam through a surface of a lens.

13. A method according to claim 12, wherein the front surface of the optical termination element is said surface of a lens.

14. A method according to claim 12, comprising one of the following: (14a) directly coupling said input beam from air to the optical termination element through said front surface that separates air from a material of the optical termination element; and (14b) coupling said input beam from air to an auxiliary glass element that is in contact with the optical termination element at the front surface thereof.

15. A method according to claim 14, wherein the spatially concentrating said input beam inside the optical termination element does not include propagating light from said input beam through an optical taper.

16. An article of manufacture, comprising: an optical fiber having a fiber core and a fiber cladding, and an optical termination element in contact with an input surface of the optical fiber, the optical termination element having a front surface, a termination core, and a termination cladding, wherein a first ratio of a termination core diameter to a termination cladding diameter is substantially equal to a second ratio of a fiber core diameter to the fiber cladding diameter.

17. An article of manufacture according to claim 16, wherein the optical termination element has a length along which the first ratio is substantially constant.

18. An article of manufacture according to claim 16, wherein at least one of the following conditions is satisfied: (18a) the optical termination element contains an optical lens component; (18b) the front surface of the optical termination element is a surface of said optical lens component; (18c) the article further comprises an auxiliary optical element affixed to the front surface of the optical termination element; and (18d) the front surface is a curved surface.

19. An article of manufacture according to claim 16, wherein, at the input surface of the optical fiber, the termination core and a fiber core are co-axially merged with one another in a tangentially-parallel fashion, and the termination cladding and a fiber cladding are co-axially merged with one another in a tangentially-parallel fashion.

20. An article of manufacture according to claim 16, configured to satisfy one or more of the following multiple conditions: (20a) to accept a beam of light at the front surface and transmit said beam of light through the front surface into the optical termination element while changing a degree of convergence of the beam upon transmitting thereof through the front surface; and (20b) to converge the beam of light, received at the front surface of the optical termination element, internally within the optical termination element such as to focus said beam at the input surface of the optical fiber; and (20c) to transmit the beam of light through an optical lens, wherein the optical lens is a part of the optical termination element and is separated from the optical fiber by a portion of the optical termination element containing said termination core and termination cladding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawing figures, of which:

[0024] FIG. 1A and FIG. 1B illustrate schematically two typical causes of excitation of cladding modes in surgical fibers used with holmium lasers (˜the holmium laser fibers), both resulting from defects in fiber termination defects often found in related art;

[0025] FIG. 2A and FIG. 2B illustrate schematically the effect of ‘blooming” of the output beam generated by a typical holmium laser, and its effect on coupling into a surgical optical fiber;

[0026] FIG. 3 presents a cross-section of a tapered segment of an optical fiber, showing the transformation of a high-order modes upon coupling to a fiber through such tapered segment;

[0027] FIG. 4 presents the combination of the same taper input section (as that depicted in FIG. 3) but with a re-structured input facet, the operation of which affects propagation of a high order laser mode through the taper section such as to avoid the conversion to modes propagating at higher angles with respect to the optical axis (see, for example, U.S. Pat. No. 7,488,116);

[0028] FIG. 5 illustrates a quartz ferrule sleeved optical fiber termination with integral beam scattering elements (per Brown in U.S. Pat. No. 7,090,411);

[0029] FIG. 6 depicts critical elements of a fiber optic termination discussed in U.S. Pat. Nos. 9,122,009 and 9,223,089;

[0030] FIG. 7 illustrates one embodiment of the optical fiber termination;

[0031] FIG. 8 depicts a related embodiment of the optical fiber termination;

[0032] FIG. 9 depicts yet another related embodiment of the optical fiber termination.

[0033] Generally, the sizes and relative scales of elements in Drawings may be set to be different from actual ones to appropriately facilitate simplicity, clarity, and understanding of the Drawings. For the same reason, not all elements present in one Drawing may necessarily be shown in another. While specific embodiments are illustrated in the figures with the understanding that the disclosure is intended to be illustrative, these specific embodiments are not intended to limit the scope of invention implementations of which are described and illustrated herein.

DETAILED DESCRIPTION

[0034] The disclosure of each patent document and/or publication referred to in this application is incorporated herein by reference.

[0035] Embodiments of the present invention solve a persisting problem of inability of the systems of related art to effectively couple laser light where sufficiently-focused light either exceeds the damage threshold of the fiber and/or exceeds the ionization breakdown threshold of the medium (such as air, in one example) in which the process of coupling occurs. Notably, while rate of air ionization may depend on the wavelength of used light and/or a pulse duration, the thresholds for breakdown (for ˜2 ns pulses in clean dry air at atmospheric pressure) were found to be in the power density range of 6*10.sup.11 W/cm.sup.2 at 1064 nm; about 3*10.sup.11 W/cm.sup.2 at 532 nm; and about 2*10.sup.12 W/cm.sup.2 at 355 nm, which data provide a good assessment of the required levels for a single laser pulse. While repetition of pulses may lower the threshold, the laser damage thresholds are lower as well—and depending on a preparation of a surface the laser damage threshold may be as low as 104 W/cm.sup.2.

[0036] Specifically, embodiments of the invention described here minimize technical uncertainties and variations in some prior art parameters while eliminating other uncertainties altogether, thereby permitting reproducible efficiency that has not been demonstrated so far. Specifically, in reference to the related art solutions outlined in reference to FIGS. 3 and 6, for example, longer fiber tapers are inherently superior for guiding overfill energy into the original fiber core and NA, while shorter tapers are preferable for targeting the original core position with the input lens. Formation, and positioning of tapers in ferrules for fusion are inherently variable, as is angular position of the taper within the ferrule bore, forcing compromise in lens parameters.

[0037] A skilled artisan will readily appreciate that—as used in this disclosure and the appended claims—the term “cladding modes” refers to light propagating within the optical fiber that is not guided within the space defined by the glass-core boundary and the -glass-cladding boundary (that is, the light guided within the bounds of the glass cladding layer of the optical fiber) but, instead, is guided within a space defined between the boundary of the glass body of the optical fiber and the boundary of the polymer cladding of the fiber, regardless of the source of light. Multimode fibers that are used in holmium-laser-based surgery procedures are typically step-index and “doubly clad” fibers, in which the glass cladding layer is coated with a fluoropolymer coating having a refractive index lower than that of the fluorine-doped (F-doped) silica glass cladding of the fiber. A secondary numerical aperture (NA) of such fibers—of approximately 0.30 to 0.45—is thus formed by such polymer coating (polymer cladding, often referred to as “secondary cladding”). These fibers may be additionally buffered (or “jacketed”) with a relatively thick layer of a polymer, typically ethylene tetrafluoroethylene (ETFE) copolymer (refractive index of about 1.4 @ 633 nm) that is dyed blue or green to form what is often referred to as a “jacket layer” (or jacket, for short) with enhanced visibility, which is important in the surgical field.

[0038] As shown schematically in FIG. 7, which represents an embodiment of the invention, a laser's collimated light output 725 is shown to be converged, 730, by a single optic (which is typical in the art of surgical lasers; shown here as a lens 700) and focused onto an input curved facet of an optical fiber system 734, which materially and optically combines the conventional surgical fiber 710 with an optical head region (the region of OF termination) 708. The optical head section is, substantially, a cylindrical body exhibiting substantially the same material structure as the fiber 710. Specifically, the head 708 has the axial core region and the co-axial glass cladding region (which could be imagined in a cross-sectional view) just like the optical fiber 710 with the exception that, in the optical head 708, both the dimension of the core and that of the glass cladding are proportionately expanded (increased, as compared to those of the fiber 710) to such values that the front/input surface of the head 708 could support the concave refracting surface 715 that, in turn, is dimensioned to substantially completely accept laser light in the focal spot formed by the converging beam 730 and to focus such light (upon refraction through the surface 715 into the optical head 708) onto the cross-sectional surface 725 of the structure 734, where the regions of spatially-expanded core and the spatially-expanded glass cladding of the head 708 end and the core and the glass cladding of the regular fiber 710 begin. The so-defined surface 725—that is, the surface beyond which, as seen from the head 708, the dimension(s) of the glass core region of the structure 734 and the dimension(s) of the glass cladding region of the structure 734 are substantially equal to those of the fiber 710—is defined as an input surface or facet of the fiber 710, at least for the purposes of the appended claims.

[0039] In at least one implementation—for example in the case when the head 708 is made from a preform from which the fiber 710 is drawn—the ratio of a thickness of the glass cladding region of the optical head 708 to the diameter of the core region of the optical head 708 is substantially equal to that of the fiber 710.

[0040] The lensing surface 715 is judiciously dimensioned to change—and, in this example—to reduce the rate of convergence of laser light upon traversing the surface 715. In the example of FIG. 7, the adiabatic merging between the optical head 708 and the conventional fiber 710 is shown to be carried out in a transition region or section 720 (which may optionally be considered to be a part of the head 708). Throughout such transition region 720, both the diameter of the core portion of the head 708 (which is maintained to be substantially constant along at least a larger portion 705 of the head 708) and the diameter of the glass cladding of the head 708 (which is maintained to be substantially constant along at least the same portion 705) are gradually reduced toward the values of the diameter of the core and the diameter of the glass cladding of the fiber 710. At the surface 725, the core and glass cladding regions of the head 708 are seamlessly merged into, respectively, the core and glass claddings of the fiber 710, in a substantially tangentially-parallel fashion. (In other words, at the input surface of the fiber 710, a tangent to the surface of the core of the fiber and a tangent to the surface of the core of the transition region 710, both drawn in a plane containing the optical fiber axis are substantially co-incident with one another, while a tangent to the surface of the cladding of the fiber and a tangent to the surface of the cladding of the transition region 710, both drawn in the same plane containing the optical fiber axis, are also substantially co-incident with one another.)

[0041] Optionally, and in a related implementation, the cylindrical portion of the head 708 may be merged with the cylindrical body of the fiber 710 without a transition section—in a step-like fashion (in which case, understandably, there will be a spatial disconnect between the corresponding core regions and/or corresponding glass cladding regions of the portions 708 and 710 of the structure 734). In any case, the portion of the structure 734 preceding the fiber section 710 is configured such that, all the way throughout the axial extent of the structure 734 between the lensing surface 715 and the surface 725 (at which the body of the conventional fiber 710 begins), laser light coupled into the structure 734 through the surface 715 is continually and uninterruptingly converging. At the surface 725, the rate (or angle) of such convergence is configured to correspond to the accepting NA of the fiber 710. Optionally, such convergence may be effectuated at a substantially constant rate throughout the head 708.

[0042] Due to the fact that the materials of the core region and the glass cladding region—and, therefore, the indices of refraction of the core region and the glass cladding region—of the head 708 (with or without the transition section 720) are the same as those of the core and glass cladding regions of the fiber 710, there is no internal reflection of laser light coupled into and propagating through the structure 734.

[0043] A skilled artisan will readily appreciate that FIG. 7 depicts a construct configured such that various critical dimensions may be precisely maintained (as compared with inability of related art to do so) and—in particular—the absolute axial starting position, 725, of the core of the conventional, substantially-constant diameter and the axial position of the input surface 715. In practice, the dimensions of the head 708 (with or without the transition region 720) are easily maintained with high precision and compatible with focal lengths of the lens formed by the surface 715 that may be produced in the available glass materials, thereby—as compared with the embodiments similar to those of FIG. 3 and FIG. 4, for example—obviating the need for a tapered wall and, therefore, the need in a tapered section completely. Furthermore—and in comparison with an embodiment similar to that of FIG. 6—the contraption 734 does not require an accessory quartz ferrule (685, as in FIG. 6, that is fused 690 about the taper 695 to produce a larger surface upon which to form a functional lens).

[0044] FIG. 8 illustrates an embodiment related to that of FIG. 7. Specifically, FIG. 8 depicts an embodiment of the optical fiber structure 834 containing an OF termination (section 808) configured to couple laser light, into a conventional surgical fiber 880, at a power level that would otherwise damage the input surface of the fiber 880 is such laser light were focused on the input surface directly; or at a power level that would otherwise ionize the air around the fiber 880 if focused sufficiently to be coupled directly into the fiber 880. In this example, collimated laser beam 725 is acquired by the OF termination (head) portion 808 through its front surface (facing the laser source of light) that is dimensioned to define a convex lens element at such front surface and, having traversed the lensing surface 855, propagates through the body of the section 808 while converging towards the fiber section 880. (The skilled person will appreciate that the embodiment 834 is also configured to ensure that a degree of convergence of light, received and accepted at the front surface of the OF termination 808, is changed upon transmission through such front surface.)

[0045] The material configuration/structure of the head 808 at least in one case may be substantially similar to that of the head 708 (of FIG. 7). For example, at least along a larger portion 865 of the length of the section 808, the section 808 may be structured as a spatially-expanded version of the fiber 880 and dimensioned such that the waist of the spatially-converging (internally to the head 808) beam 860 that contains highest density of radiant power occurs within the body of the glass material (for example, at or near the diameter transition section 875. The transition section 875, if and when present, is preferably structured in a fashion similar to that discussed in reference to FIG. 7. The head region 808 is materially and optically merged with the fiber 880 at a surface 825 which, as was already alluded to above in reference to the surface 725 of FIG. 7,—is the input surface of the fiber 880, that is a surface beyond which, as seen from the head 808, the dimension(s) of the glass core region of the structure 834 and the dimension(s) of the glass cladding region of the structure 834 are substantially equal to those of the fiber 880. In at least in one specific implementation, the structure 834 is dimensioned such that, at the input surface of the optical fiber, the core of the termination element 808 and a core of the fiber 880 are co-axially merged with one another in a tangentially-parallel fashion, while the cladding of the termination element 808 and that of the fiber 880 cladding are also co-axially merged with one another in a tangentially-parallel fashion.

[0046] A related implementation of the system 934, schematically illustrated in FIG. 9, provides an OF termination (to the surgical optical fiber 925) structured to include two main portions: a head 908 (having a core region and a glass cladding region, and fabricated in the same fashion the fiber 925 is fabricated, and structured as discussed above in reference to heads 708, 808 of FIGS. 7, 8) and a front bulk glass cylinder 910 configured as an accessory lens, in this case a Gradient Index lens (or GRIN lens), in ˜¼ pitch length, fused with the head 908. The head 908 generally may or may not have a transition region at region of attachment to the fiber 910 and in the example of FIG. 9 such transition region is present, depicted as 975, and structured by analogy of transition regions 720, 875 described in reference to FIGS. 7, 8.

[0047] As shown, the input and substantially collimated light 725 is an output from the surgical laser (such as a holmium laser) with an M.sup.2 factor on the order of about 25 or higher, which is accepted by the bulk lens 910 and converged through the head 908 into a beam waist 915. The gradient index lens portion is dimensioned to ensure that the waist 915 of the converging beam 905 is located at or near the diameter transition region 975 (when present) or at an input surface 940 of the optical fiber 925.

[0048] In at least in one specific implementation, the structure 934 is dimensioned such that, at the input surface 940 of the optical fiber, the core of the head 908 and a core of the fiber 880 are co-axially merged with one another in a tangentially-parallel fashion, while the cladding of the head 908 and that of the fiber 880 cladding are also co-axially merged with one another in a tangentially-parallel fashion.

[0049] In at least one implementation of an embodiment of any of FIGS. 7, 8, and 9, the length of the head portion 708, 808, 908 of the optical fiber termination may be about 1.5 mm to about 5 mm in length (preferably, about 1.5 to about 3 mm in length) with an outer diameter of about 1 mm to about 2 mm (and the core diameter being about 80%, about 90%, or about 95% of the value of the outer diameter of the head, depending on the specifics of a particular implementation). The so-dimensioned optical termination facilitates the situation when laser light (during the process of converging inside the bulk of the head portion) substantially avoids interaction with a boundary between the glass core and glass cladding regions of the head portion—for example, no total internal reflection on such boundary occurs.

[0050] In one related embodiment, a fiber termination contraption includes an optical fiber having a terminus, adjacent to the terminus a clad fiber and distal from the terminus and adjacent to the clad fiber a polymeric-coated fiber. The clad fiber includes a silica core and an F-doped silica cladding and the polymeric-coating fiber includes the clad fiber carrying one or more polymeric coatings. The fiber termination also includes an expanded core section proximal to the unaltered fiber core, and clad. The transition from expanded core to unaltered core is abrupt such that modes entering the expanded core at angles unsupported by the fiber core-cladding NA are not guided, but leak in a generally distal direction.

[0051] In another related embodiment, a method for manufacturing an optical fiber termination includes providing an optical fiber with a denuded portion adjacent to a terminus; then forming an expanded section by controlled heating of the denuded glass fiber. The process may additionally include positioning overfill glass tube on denuded fiber section prior to expanding the core and cladding.

[0052] In yet another related embodiment, a method for manufacturing an optical fiber termination includes fusing a silica tube to a terminus of a clad fiber; and forming one or more furrows in an exterior surface of the silica tube.

[0053] References throughout this specification to “one embodiment,” “an embodiment,” “a related embodiment,” or similar language mean that a particular feature, structure, or characteristic described in connection with the referred to “embodiment” is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. It is to be understood that no portion of disclosure, taken on its own and in possible connection with a figure, is intended to provide a complete description of all features of the invention.

[0054] For the purposes of this disclosure and the appended claims, the use of the terms “substantially”, “approximately”, “about” and similar terms in reference to a descriptor of a value, element, property or characteristic at hand is intended to emphasize that the value, element, property, or characteristic referred to, while not necessarily being exactly as stated, would nevertheless be considered, for practical purposes, as stated by a person of skill in the art. These terms, as applied to a specified characteristic or quality descriptor means “mostly”, “mainly”, “considerably”, “by and large”, “essentially”, “to great or significant extent”, “largely but not necessarily wholly the same” such as to reasonably denote language of approximation and describe the specified characteristic or descriptor so that its scope would be understood by a person of ordinary skill in the art. In one specific case, the terms “approximately”, “substantially”, and “about”, when used in reference to a numerical value, represent a range of plus or minus 20% with respect to the specified value, more preferably plus or minus 10%, even more preferably plus or minus 5%, most preferably plus or minus 2% with respect to the specified value. As a non-limiting example, two values being “substantially equal” to one another implies that the difference between the two values may be within the range of +/−20% of the value itself, preferably within the +/−10% range of the value itself, more preferably within the range of +/−5% of the value itself, and even more preferably within the range of +/−2% or less of the value itself. The use of these terms in describing a chosen characteristic or concept neither implies nor provides any basis for indefiniteness and for adding a numerical limitation to the specified characteristic or descriptor. As understood by a skilled artisan, the practical deviation of the exact value or characteristic of such value, element, or property from that stated falls and may vary within a numerical range defined by an experimental measurement error that is typical when using a measurement method accepted in the art for such purposes.

[0055] The use of these terms in describing a chosen characteristic or concept neither implies nor provides any basis for indefiniteness and for adding a numerical limitation to the specified characteristic or descriptor. As understood by a skilled artisan, the practical deviation of the exact value or characteristic of such value, element, or property from that stated falls and may vary within a numerical range defined by an experimental measurement error that is typical when using a measurement method accepted in the art for such purposes.

[0056] While the invention is described through the above-described exemplary embodiments, it will be understood by those of ordinary skill in the art that modifications to, and variations of, the illustrated embodiments may be made without departing from the inventive concepts disclosed herein. Disclosed aspects, or portions of these aspects, may be combined in ways not listed above. Accordingly, the invention should not be viewed as being limited to the disclosed embodiment(s).