Patent Description:
A nested anti-resonant nodeless hollow core fiber (NANF) is an optical fiber such that light is confined and guided within a hollow region of space defined using a glass structure. The hollow region can be a vacuum or filled with air. A light beam transmitted in the hollow region has only very weak interactions with the glass defining the optical fiber, and so the light beam can propagate with low loss. In some instances, a NANF can achieve transmission losses below <NUM>% across multi-kilometer propagation. The physical principle for light confinement and guiding is optical anti-resonance, instead of total internal reflection.

As shown in <FIG>, a NANF of the prior art, such as described in <CIT>, has a first tubular, cladding element <NUM> which defines an internal cladding surface <NUM>. A plurality of second tubular elements <NUM> are also included which are arranged in a spaced symmetrical relation at the cladding surface <NUM> and together define a core <NUM> with a radius R from the center C of the NANF. A further plurality of third tubular elements <NUM> are each nested within a respective one of the second tubular elements <NUM>. The nested ones of the second and third tubular elements <NUM>, <NUM> provide nested tubular arrangements 11a-11f. In the prior art, the core radius R is typically less than <NUM>. Other parameters and dimensions of the NANF include a wall thickness t of each of the tubular elements <NUM>, <NUM>, a gap distance d between tubular elements <NUM>, and a distance z between the portions of the tubular elements <NUM>, <NUM> closest to the center C of the NANF. <CIT> discloses an anti-resonant hollow-core fiber comprising a first tubular, cladding element which defines an internal cladding surface, a plurality of second tubular elements which are attached to the cladding surface and together define a core with an effective radius, the second tubular elements being arranged in spaced relation and adjacent ones of the second tubular elements having a spacing therebetween, and a plurality of third tubular elements, each nested within a respective one of the second tubular elements to provide nested tubular arrangements.

NANFs of the prior art form a core surrounded with a negative curvature, such that nodes are pushed further away from an air-guided mode of the optical fiber. Such NANFs have been applied to optical data communications, low latency data transmission, radiation hardness, high power delivery, mid-IR gas spectroscopy, biomedical applications, and gyroscopes and temperature-insensitive fibers for delivery of precise frequency/time information.

According to the invention, an optical fiber according to claim <NUM> and a method according to claim <NUM> are disclosed.

It is noted that the drawings are illustrative and are not necessarily to scale.

Example embodiments consistent with the teachings included in the present disclosure are directed to a nested anti-resonant nodeless hollow core optical fiber (NANF) and a subsurface system and method using such a NANF. Referring to the cross-sectional view in <FIG>, an optical fiber <NUM> is configured as a NANF. The optical fiber <NUM> comprises a first tubular member <NUM>. The first tubular member <NUM> can be a cladding element composed of glass. The first tubular member <NUM> has an internal surface <NUM> and an outer surface <NUM> with a first wall thickness t<NUM>. In one example embodiment, the thickness t<NUM> is between <NUM> and <NUM>. In another example embodiment, the thickness t<NUM> is between <NUM> and <NUM>. In a further example embodiment, the thickness t<NUM> is <NUM> ± <NUM>.

As shown in <FIG>, the first tubular member <NUM> has an outer diameter D. The outer diameter D is greater than <NUM>. In another example embodiment, the outer diameter D can be at least <NUM>. In a further example embodiment, the outer diameter D is between <NUM> and <NUM>.

The optical fiber <NUM> can be surrounded by coatings disposed on the outer surface <NUM>. In an example embodiment, coatings with a low Young's modulus are used. The coatings can include materials commercially available from LUVANTIX. Alternatively, the coatings can include materials commercially available from FOSPIA. The coatings are employed to minimize micro-bending loss. A low-index coating has a first, soft layer with a low Young's Modulus and a low glass transition temperature Tg. The low-index coating has a second, hard layer with a high Young's Modulus. In an example embodiment, both of the first and second layers have a refractive index lower than about <NUM>.

The optical fiber <NUM> includes a plurality of second tubular members <NUM> which extend through the first tubular member <NUM> and are spaced apart about the inner periphery of the internal surface <NUM>. Each second tubular member has a second wall thickness t<NUM>. The second wall thickness t<NUM> can be in the range from <NUM> to <NUM>,<NUM>. A gap <NUM> with a minimum spacing d is between adjacent second tubular members <NUM>. In one example embodiment, the minimum spacing d can be as small as <NUM>, but up to <NUM> gap spacing can be used. In another example embodiment, the minimum spacing d is a gap of 4t<NUM> ± 2t<NUM>. The second tubular members <NUM> define a core region <NUM> within the interior of the first tubular member <NUM>. The core region <NUM> is hollow. In an embodiment, the core region <NUM> is filled with air. In another embodiment, the core region <NUM> is a vacuum.

The core region <NUM> is centered about the longitudinal axis C of the first tubular member <NUM>. The core region <NUM> has a core radius R extending from the longitudinal axis C to a point <NUM> on each second tubular member <NUM> which is closest to the longitudinal axis C. According to the claimed invention, the core radius R is in the range from <NUM> to <NUM>, depending on the outer diameter D of the fiber <NUM> and on the coating used to reduced microbending.

The optical fiber <NUM> also includes a plurality of third tubular members <NUM>, with each third tubular member <NUM> nested in and extending through a respective second tubular member <NUM>. Each third tubular member <NUM> has a third wall thickness t<NUM> which can be in the range from <NUM> to <NUM>,<NUM>. In an example embodiment, the wall thicknesses t<NUM>, t<NUM> can be equal. Referring again to <FIG>, a distance z is measured between the portions of the tubular elements <NUM>, <NUM> closest to the longitudinal axis C of the optical fiber <NUM>. In an example embodiment, the distance z is. <NUM> times the core radius R, such that the ratio z/R is. <NUM> for the optical fiber <NUM>. Accordingly, for the optical fiber <NUM>, z is in the range of <NUM> to <NUM>.

Such an arrangement of tubular members <NUM>, <NUM>, <NUM> defines a NANF configured to confine and guide light for transmission through the core region <NUM> by optical anti-resonance. The light has a wavelength in the range between <NUM>,<NUM> and <NUM>,<NUM>, and when the optical fiber <NUM> has the dimensions described herein, the optical fiber <NUM> has a signal loss of <NUM>. The low signal loss of <NUM>. 3dB/km is due, in part, to the outer diameter D being greater than <NUM> while the core radius R is in the range from <NUM> to <NUM>, and the gap <NUM> is maintained with a minimum spacing d of <NUM>. Accordingly, the tubular members <NUM>, <NUM>, <NUM> are configured and dimensioned to conform to these values of the outer diameter D, core radius R, and minimum spacing d. The dimensions of the optical fiber <NUM> provide a core surrounded with a negative curvature, such that nodes are pushed further away from or entirely eliminated from an air-guided mode of the optical fiber <NUM>. By pushing away or eliminating the nodes that might form at the contact point between tubes, the microstructured region <NUM> becomes nodeless. The absence of glass nodes around the core region <NUM> helps decreasing the optical loss of the fiber <NUM>, and therefore allows for high energy light beams greater than 1kW and low signal loss of <NUM>. 3dB/km to be transmitted by the optical fiber <NUM>.

The low signal loss of <NUM>. 3dB/km of the optical fiber <NUM>, acting as a NANF, can be utilized in long distance applications. For example, a system <NUM> shown in <FIG> comprises a laser <NUM> emitting light <NUM> to in-coupling optics <NUM>. The in-coupling optics <NUM> couple the laser <NUM> to an optical fiber <NUM> as described above in connection with the optical fiber <NUM> in <FIG>. The light <NUM> transmitted through the optical fiber <NUM> is conveyed to out-coupling optics <NUM> which couple the optical fiber <NUM> to a receiving assembly <NUM>. Thus, the system <NUM> is configured to transmit the light <NUM> from the laser <NUM> to the receiving assembly <NUM>. The receiving assembly <NUM> can have a subsurface depth greater than <NUM>,<NUM> ft. In particular, the receiving assembly <NUM> can be a subsystem requiring high power laser beams with low loss delivery for subsurface oil and gas applications, such as in the petroleum industry. The laser <NUM> in the system <NUM> can provide a beam of light <NUM> with high output power, for example, greater than 1kW. With such low losses of <NUM>. 3dB/km provided by the NANF of <FIG>, the high output power is conveyed efficiently by a high power laser beam to such subsurface applications.

In addition, the system <NUM> can include a downhole cabling assembly, at least one additional fiber, an opto-mechanical bottom hole assembly (oBHA), and at least one sensor, with the system <NUM> configured to perform various applications of a beam of light <NUM> from the laser <NUM>. The applications of the beam of light <NUM> can include perforation, spallating, melting, evaporating, and heating subsurface matter. The applications of the beam of light <NUM> can also include welding, cutting, heating, evaporating, and melting metallic or non-metallic materials in the subsurface environment. The downhole cabling assembly protects the optical fiber <NUM> from the subsurface environment. The downhole cabling assembly can include a hollow tube of carbon, T-<NUM> steel, Hastelloy, or other composites that are resistant to corrosion. The at least one additional fiber can include few-mode, multi-mode, and single-mode fibers configured to perform distributed temperature sensing, strain sensing, shape-sensing, and acoustic sensing fiber assembly provides information about macro-bending of the downhole optical fiber cable. The distributed temperature fiber provides information about the temperature of the environment. The distributed acoustic fiber is used to acquire information about the flow of material around the optical cable.

The oBHA can include at least one of refractive and diffractive optics or optomechanics configured to control the beam of light <NUM>, to modify the transversal beam profile, to focus or de-focus the beam, and to stir the beam to a desired target in the subsurface environment. The plurality of sensors can be included in the oBHA to characterize the beam profile, to measure its spectral content and distribution, and to measure the overall power of the beam. The system <NUM> can also include a beam splitter. The beam splitter can be a <NUM>/<NUM> beam splitter in combination with at least one filter to achieve beam sampling of the beam of light <NUM>.

In another embodiment, a method comprises providing an optical fiber having a first tubular member having an internal surface, a first wall thickness t<NUM>, and an outer diameter D. The method also includes providing a plurality of second tubular members extending through the first tubular member and spaced apart about the internal surface, with a minimum spacing d between adjacent second tubular members, with the second tubular members defining a core region having a radius R, and each second tubular member having a second wall thickness t<NUM>. The method further includes providing a plurality of third tubular members, with each third tubular member nested in and extending through a respective second tubular member, and each third tubular member having a third wall thickness t<NUM>, with the arrangement of tubular members defining a Nested Anti-resonant Nodeless hollow core Fiber (NANF) configured to confine and guide light for transmission through the core region by optical anti-resonance. Accordingly, the method includes transmitting the light through the core region using the optical anti-resonance.

Portions of the methods described herein can be performed by software or firmware in machine readable form on a tangible (e.g., non-transitory) storage medium. For example, the software or firmware can be in the form of a computer program including computer program code adapted to cause the system to perform various actions described herein when the program is run on a computer or suitable hardware device, and where the computer program can be embodied on a computer readable medium. Examples of tangible storage media include computer storage devices having computer-readable media such as disks, thumb drives, flash memory, and the like, and do not include propagated signals. Propagated signals can be present in a tangible storage media. The software can be suitable for execution on a parallel processor or a serial processor such that various actions described herein can be carried out in any suitable order, or simultaneously.

It is to be further understood that like or similar numerals in the drawings represent like or similar elements through the several figures, and that not all components or steps described and illustrated with reference to the figures are required for all embodiments or arrangements.

It will be further understood that the terms "contains", "containing", "includes", "including," "comprises", and/or "comprising," and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Terms of orientation are used herein merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third) is for distinction and not counting. For example, the use of "third" does not imply there is a corresponding "first" or "second. " Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," "having," "containing," "involving," and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Claim 1:
An optical fiber (<NUM>), comprising:
a first tubular member (<NUM>) having an internal surface (<NUM>), a first wall thickness (t<NUM>), and an outer diameter (D) greater than <NUM>;
a plurality of second tubular members (<NUM>) extending through the first tubular member (<NUM>) and spaced apart about the internal surface (<NUM>), with a minimum spacing (d) of <NUM> between adjacent second tubular members (<NUM>), with the second tubular members (<NUM>) defining a core region (<NUM>) having a radius (R) in the range of <NUM> to <NUM>, and each second tubular member (<NUM>) having a second wall thickness (t<NUM>); and
a plurality of third tubular members (<NUM>), with each third tubular member (<NUM>) nested in and extending through a respective second tubular member (<NUM>), and each third tubular member (<NUM>) having a third wall thickness (t<NUM>),
wherein the arrangement of the tubular members (<NUM>, <NUM>, <NUM>) defines a Nested Anti-resonant Nodeless hollow core Fiber, NANF, configured to confine and guide light in the range between <NUM> and <NUM> for transmission through the core region (<NUM>) with a loss of <NUM>.3dB/km from optical anti-resonance in the arrangement of the tubular members (<NUM>, <NUM>, <NUM>).