WO2004111695A1 - Articles comprenant des fibres microstructurees a ame creuse et leurs procedes d'epissage, de connexion et d'utilisation - Google Patents

Articles comprenant des fibres microstructurees a ame creuse et leurs procedes d'epissage, de connexion et d'utilisation Download PDF

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Publication number
WO2004111695A1
WO2004111695A1 PCT/DK2004/000439 DK2004000439W WO2004111695A1 WO 2004111695 A1 WO2004111695 A1 WO 2004111695A1 DK 2004000439 W DK2004000439 W DK 2004000439W WO 2004111695 A1 WO2004111695 A1 WO 2004111695A1
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WIPO (PCT)
Prior art keywords
optical
fibre
optical fibre
structured
micro
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PCT/DK2004/000439
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English (en)
Inventor
Peter M. W. Skovgaard
Jacob Riis Folkenberg
Theis Peter Hansen
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Crystal Fibre A/S
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Publication of WO2004111695A1 publication Critical patent/WO2004111695A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/06708—Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/255—Splicing of light guides, e.g. by fusion or bonding
    • G02B6/2551—Splicing of light guides, e.g. by fusion or bonding using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/262—Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/023—Microstructured optical fibre having different index layers arranged around the core for guiding light by reflection, i.e. 1D crystal, e.g. omniguide
    • G02B6/02304—Core having lower refractive index than cladding, e.g. air filled, hollow core
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02295—Microstructured optical fibre
    • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
    • G02B6/02319—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by core or core-cladding interface features
    • G02B6/02323—Core having lower refractive index than cladding, e.g. photonic band gap guiding
    • G02B6/02328—Hollow or gas filled core
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/032—Optical fibres with cladding with or without a coating with non solid core or cladding
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/32—Optical coupling means having lens focusing means positioned between opposed fibre ends
    • G02B6/327—Optical coupling means having lens focusing means positioned between opposed fibre ends with angled interfaces to reduce reflections
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/22—Gases

Definitions

  • the present invention relates to articles and assemblies comprising micro- structured, hollow-core fibres, and methods of their manufacturing.
  • the invention further relates to methods of splicing a hollow-core fibre to other micro-structured, hollow-core or non-micro-structured optical fibres. It further relates to a fibre laser or amplifier comprising an article according to the invention.
  • the invention further relates to use of such articles or optical fibre assemblies or fibre lasers or amplifiers in various applications.
  • Optical Time Domain Reflectometry typically works by sending a short optical pulse down through an optical fibre and measures the time delay and the intensity of the reflected pulses. In this way, e.g. point scat- terers, fibre defects, and reflections from splice interfaces can be measured. A reflection from a glass-air interface typically creates a very intense reflection that will bleach out or saturate the fast photo detector, thus making the measurement impossible.
  • Optical communication systems are typically very sensitive to reflections as they can travel backward through the optical path and degrade the performance of the system. Even a reflection (return loss) as little as -30 dB (0.1%) can have detrimental consequences.
  • Pigtailing of lasers typically have to be done very carefully to avoid feedback.
  • Many lasers e.g. gas lasers or semiconductor lasers
  • Single-pass fibre amplifiers are spliced or free space coupled with a fibre laser.
  • the output coupler of the laser is a low reflectivity mirror defined by Bragg gratings written into the fibre laser. Again in this case, reflected light can induce instability of the laser. Also, even small levels of reflections within an amplifier can induce lasing, which will severely degrade amplifier performance.
  • micro-structured optical fibre' or 'photonic crystal fibre' is in the present application taken to mean an optical fibre comprising a multitude of longitudinally extending elements dispersed in a back ground material.
  • the term 'a multitude of longitudinally extending elements' is in the present context taken to mean more than 2, such as more than 4, such as more than 6, such as more than 8, such as more than 12 longitudinally extending elements in a given cross section perpendicular to a longitudinal direction of the optical fibre.
  • the longitudinally extending elements may be distributed in a periodic or non-periodic pattern when viewed in a cross section perpendicular to a longitudinal direction of the optical fibre.
  • a micro- structured, hollow-core optical fibre is taken to mean a micro-structured optical fibre comprising a hollow core for guiding light.
  • An article comprising a micro-structured, hollow-core optical fibre:
  • an article comprising a micro-structured, hollow-core optical fibre for propagating a light beam comprising light of a wavelength ⁇ in a longitudinal direction of the optical fibre and an optical window made of an optical material of refractive index n ow , the optical fibre having an even end face forming an angle ⁇ with a plane perpendicular to a longitudinal direction of the optical fibre, the optical window being of length l ow in said longitudinal direction and having a first face parallel to and contacting said end face of said optical fibre, wherein said angle ⁇ is different from 0°.
  • ⁇ is larger than Tsuch as larger than 2°, such as larger than 5°.
  • the refractive index n ow , and the angle ⁇ are adapted to prevent a majority of the reflected light from being coupled back into the hollow core of the micro-structured optical fibre.
  • the term 'a majority of the reflected light' is in the present context taken to mean more than 50%, such as more than 80%, such as more than 95% of the intensity of the reflected light.
  • the angle ⁇ is adapted to the numerical aperture of the optical fibre and/or to the mode field diameter of the light beam of the optical fibre.
  • the angle ⁇ is adapted to the numerical aperture of the optical fibre and/or to the mode field diameter of the light beam to reduce the back reflection from the end face of the optical fibre.
  • the back reflection is reduced to levels below -30 db, such as below -40 db, such as below -50 db.
  • the refractive index n ow , the angle ⁇ and the length l ow are adapted to control the spatial displacement d disp of the light beam in the optical window from a centre line of the hollow core. This has the advantage of providing design freedom with respect to the location of the light beam at the second face of the optical window.
  • the location of the centre line of the hollow core is displaced relative to a centreline of the optical fibre (as determined by its outer boundary).
  • the refractive index n ow , the angle ⁇ and the length l ow are adapted to facilitate the coupling of the light beam into the core region of another optical fibre.
  • the refractive index n ow , the angle ⁇ and the length l ow are adapted to provide the light beam to be centrally located at the second face of the optical window.
  • the optical window comprises a Bragg grating. This has the advantage of providing the possibility to select a wavelength to be reflected by the optical window, e.g. in connection with a laser, e.g. a fibre laser.
  • the first and/or the second faces of the optical window comprise an antireflective (AR) coating or a high-reflection (HR) coating.
  • AR antireflective
  • HR high-reflection
  • the article further comprises an (external) optically reflective element.
  • This may be optically coupled to the optical window via a free space region and/or via an optical lens. This may be useful in connection with the use of the article in a laser arrangement, e.g. in a fibre laser.
  • Optically coupled' is in the present context taken to mean either, physically integrated with, directly butt-coupled to, joined to by any appropriate method including glue, splicing, index-matching material, etc., coupled to via a free space region (e.g. air), possibly via an optical component such as a lens.
  • Optically coupled' means a low loss coupling, e.g. a splice or a butt-coupling of carefully aligned faces, e.g. in an optical connector.
  • the optical window is made of silica. This has the advantage of being an appropriate material for a large number of commonly used optical fibres (micro-structured as well as non-micro-structured). In general, the physical properties of the optical window should preferably be adapted to those of the hollow-core micro structured fibre and to a possible second optical fibre to which the article is to be coupled.
  • the micro-structured, hollow-core optical fibre is a silica based optical fibre.
  • the micro-structured, hollow-core optical fibre is a hollow core PCF from BlazePhotonics (Bath, Great Britain), e.g. the HC-1550-02 fibre or an air guiding fibre from Crystal Fibre A/S (Birker ⁇ d, Denmark), e.g. the Al R-10-1550 fibre.
  • the micro-structured, hollow-core optical fibre and the optical window are spliced together.
  • the optical window is constituted by a length of a non- micro-structured optical fibre. This has the advantage of providing an article that comprises an optical coupling between a micro-structured, hollow-core optical fibre and a non-micro-structured optical fibre.
  • the micro-structured, hollow-core optical fibre and a non-micro-structured optical fibre are optically coupled via a connector or spliced together (cf. FIG. 4).
  • a fibre laser or amplifier is a fibre laser or amplifier
  • a fibre laser or amplifier comprising an article according to any one of the embodiments described above under the heading "An article comprising a micro-structured, hollow- core optical fibre” or in the corresponding claims wherein the micro- structured, hollow-core fibre comprises an optically active material such as a rare-earth ion (e.g. Er and/or Yb).
  • a rare-earth ion e.g. Er and/or Yb
  • the hollow-core of the optical fibre comprises an optically active material in fluid form, such as a gas.
  • an optically active material in fluid form, such as a gas.
  • the angle ⁇ is substantially equal to Brewster's angle. This has the advantage of facilitating the discrimination of TM and TE polarised light, thereby enabling single frequency operation of the laser.
  • ⁇ is within 10° of Brewster's angle, such as within 5°, such as within 1°.
  • An optical fibre assembly comprising two optically coupled hollow-core optical fibres:
  • an optical fibre assembly comprising first and second articles as described above under the heading "An article comprising a micro-structured, hollow-core optical fibre” or in the corresponding claims, the articles being optically coupled to each other via the second faces of the optical windows wherein the angle ⁇ is substantially identical for both the first and second articles.
  • This has the advantage of providing a scheme for optically coupling two micro-structured, hollow-core optical fibres to each other with a relatively low return loss.
  • angles ⁇ of the first and second articles are within 5% of each other, such as within 2%, such as within 1%.
  • the centre lines of the hollow cores of the micro- structured fibres are displaced in opposite radial directions from a centre line of the joined optical fibre assembly (as illustrated schematically in FIG. 5c).
  • This has the advantage of enabling a low loss coupling (e.g. via an optical connector or a splice) of two micro-structured hollow-core optical fibres.
  • the determination of an appropriate radial displacement in dependence of the angle ⁇ , the refractive index n ow and the length l ow of the optical window is outlined below.
  • an optical fibre assembly comprising a hollow-core optical fibre optically coupled to a non-micro-structured optical fibre I:
  • an optical fibre assembly comprising first and second articles as described above under the heading "An article comprising a micro-structured, hollow-core optical fibre” or in the corresponding claims, wherein - in the second article - the micro-structured, hollow-core optical fibre is substituted by a non-micro-structured optical fibre, and the first and second articles are optically coupled to each other via the second faces of the optical windows wherein the angles ⁇ of the end faces are substantially identical.
  • This has the advantage of providing a scheme for optically coupling a micro-structured, hollow-core optical fibre to a non-micro- structured optical fibre with a relatively low return loss (e.g. via an optical connector or a splice).
  • the second faces of the optical windows of the first and second articles are joined via an optical connector or a splice.
  • the non-micro-structured optical fibre is a silica fibre, e.g. a single mode fibre, such as a SMF28 fibre.
  • a method of manufacturing an article comprising a micro-structured, hollow- core optical fibre :
  • One or more objects of the invention are fulfilled by a method of manufacturing an article comprising a micro-structured, hollow-core optical fibre, the method comprising the steps of a) providing the optical fibre with an even end face forming an angle ⁇ with a plane perpendicular to a longitudinal direction of the optical fibre wherein the angle ⁇ is different from 0°; b) providing an optical window made of an optical material of refractive index n ow and having a length l ow in the longitudinal direction; c) providing the optical window with a first face parallel to the end face of the optical fibre; d) providing that the end face of the fibre and the first face of the optical window are joined.
  • the refractive index n 0WI and the angle ⁇ are adapted to prevent a majority of the reflected light from being coupled back into the hollow core of the optical fibre.
  • step a) the end face of the optical fibre is formed by cleaving and/or polishing or laser cutting.
  • step d) the end face of the fibre and the first face of the optical window are joined by abutment, by splicing or by means of an adhesive material or an index matching material.
  • step a) the optical window is provided with a second face substantially parallel to the first face.
  • a method of splicing a micro-structured, hollow-core optical fibre to another optical fibre :
  • a method of splicing a micro-structured, hollow-core optical fibre to a second optical fibre comprising the steps of a) providing a fist article comprising a micro-structured, hollow-core optical fibre by a method described above under the heading "A method of manufacturing an article comprising a micro-structured, hollow-core optical fibre” and in the corresponding claims; b) providing a second article comprising a second optical fibre, the method comprising the sub-steps of; b1) providing the second optical fibre with an even end face forming an angle ⁇ 2 with a plane perpendicular to a longitudinal direction of the second optical fibre wherein the angle Q 2 is different from 0°; b2) providing an optical window made of an optical material of refractive index n ow2 and having a length l ow2 in the longitudinal direction; b3) providing the optical window with first and second faces substantially parallel to the end face of the second optical fibre; b4) providing that the end face of the
  • the micro-structured, hollow-core optical fibre of the first article is an air guiding fibre from Crystal Fibre A/S (Birker ⁇ d, Denmark), e.g. the Al R-10-1550 fibre.
  • the other optical fibre is a micro-structured fibre.
  • the other optical fibre is a micro-structured fibre, e.g. a double clad fibre, e.g. a DC-150-28-Yb fibre or an LMA-15 fibre from Crystal Fibre A/S, (Birker ⁇ d, Denmark).
  • a micro-structured fibre e.g. a double clad fibre, e.g. a DC-150-28-Yb fibre or an LMA-15 fibre from Crystal Fibre A/S, (Birker ⁇ d, Denmark).
  • the other optical fibre is a non-micro-structured fibre, such as an SMF28 fibre from Corning Inc.
  • One or more objects of the invention are fulfilled by a method of splicing a micro-structured, hollow-core optical fibre to a non-micro-structured optical fibre, the method comprising the steps of a) providing a first micro-structured, hollow-core optical fibre; b) providing a second non-micro-structured optical fibre; c) providing each of the first and second optical fibres with an even end face forming an angle ⁇ with a plane perpendicular to a longitudinal direction of the optical fibres wherein the angle ⁇ is different from 0°; d) axially aligning the first and second optical fibres to allow optical coupling of light between the optical fibres ensuring that the angled end faces are parallel; and e) splicing the optical fibres together.
  • a non-micro-structured optical fibre e.g. a standard SMF28-fibre
  • the angle ⁇ is in the range from 1 ° to 25°, such as in the range 5° to 15°, such as in the range 8° to 12°.
  • optical fibre assembly comprising a hollow-core optical fibre optically coupled to a non-micro-structured optical fibre II:
  • an optical fibre assembly comprising a) a first micro-structured, hollow-core optical fibre; b) a second non-micro-structured optical fibre; c) the first and second optical fibres each having an even end face forming an angle ⁇ with a plane perpendicular to a longitudinal direction of the respective optical fibre wherein the angle ⁇ is different from 0°; d) the first and second optical fibres being axially aligned to allow optical coupling of light between the optical fibres ensuring that the angled end faces are parallel;
  • a micro-structured, hollow-core optical fibre e.g. a standard SMF28-fibre
  • the angle ⁇ is in the range from 1 ° to 25°, such as in the range 5° to 15°, such as in the range 8° to 12°.
  • the end faces of the first and second optical fibres are joined by splicing or by an optical connector.
  • One or more objects of the invention are fulfilled by the use of an article as described above under the heading "An article comprising a micro- structured, hollow-core optical fibre” and in the corresponding claims, or of a fibre laser or amplifier as described above under the heading “A fibre laser or amplifier” and in the corresponding claims, or of an optical fibre assembly as described above under the heading “An optical fibre assembly comprising two optically coupled hollow-core optical fibres” and in the corresponding claims, or of an optical fibre assembly as described above under the heading "An optical fibre assembly comprising an hollow-core optical fibre optically coupled to a non-micro-structured optical fibre-l” and in the corresponding claims, or of an optical fibre assembly as described above under the heading "An optical fibre assembly comprising an hollow-core optical fibre optically coupled to a non-micro-structured optical fibre-M” and in the corresponding claims.
  • FIG. 1 shows an OTDR measurement of 100 m air core PBG fibre (solid). Also shown in the figure is the measured response when no fibre is connected (dash-dot).
  • FIG. 2a shows a photo of angle cleaved photonic crystal fibre according to the present invention (left) aligned to SMF28 (right), cleaved at 10.5 degrees;
  • FIG. 2b shows a photo of angle cleaved photonic crystal fibre according to the present invention (left) aligned to SMF28 (right), cleaved at 8.1 degrees;
  • FIG. 2c shows a photo of the above angle cleaved photonic crystal fibre according to the present invention (left) spliced to SMF28 (right);
  • FIG. 3 shows a schematic illustration of angle cleaved fibre according to the present invention
  • FIG. 4 shows a schematic illustration of angle cleaved fibres, spliced according to the present invention
  • FIG. 5a shows a schematic illustration of angle cleaved fibre connectorized according to the present invention
  • FIG. 5b shows a schematic illustration of an angle cleaved micro-structured fibre with a radially displaced hollow core connectorized according to the present invention
  • FIG. 5c shows a schematic illustration of angle cleaved fibre-to-fibre connection according to the present invention
  • FIG. 6 shows a schematic illustration of an output coupler of a PBG fibre gas laser according to the present invention with Brewster window.
  • Brewster angle: ⁇ ⁇ 56°.
  • Refracted angle: G 2 34°.
  • the Brewster angle is indicated;
  • FIG. 8 shows a calculation of power in reflected light coupled back into the core
  • FIG. 9 shows a calculation of minimum connector angle vs. NA for a desired Return Loss (RL) of -50 dB.
  • PBG photonic bandgap
  • air-core or hollow-core fibres are also denoted air-core or hollow-core fibres.
  • these reflections can be a particular problem. If the fibre end is spliced or butt coupled to a silica core fibre (solid or micro structured), the light propagating down the fibre experiences a large index change at the splice interface. Since the core material changes from air to silica, the refractive index changes from 1 to ⁇ 1.45, which will cause a Fresnel reflection of 4% (-14 dB) for normal incidence.
  • FIG. 1 shows an OTDR measurement of 100 m air core PBG fibre 11 (solid). Also shown in the figure is the measured response 12 when no fibre is connected (dash-dot). This corresponds to the case where no reduction of the back reflection is performed. The large reflection 121 is seen to bleach out the response from the connected fibre, thereby destroying the measurement.
  • the present invention solves this by preventing the reflected light to be guided backwards in the fibre system.
  • they should preferably be cleaved or cut at substantially the same angle (see FIGs. 2 and 3).
  • the fibres 41 , 42 for the splice should preferably be rotated relative to each other so that the angled facets are parallel.
  • the splice interface 43 defines an angle being substantially identical to the cleaved or cut angle ⁇ (see FIG. 4).
  • FIG. 2a shows a photo of an angle cleaved photonic crystal fibre, here a hollow-core optical fibre 21 according to the present invention (left) aligned to a non-micro-structured optical fibre, here an SMF28 fibre 22 (right).
  • the end faces 211 and 221 of the respective optical fibres 21 , 22 are both cleaved at 10.5°. This represents an appropriate angle for a silica non-micro-structured optical fibre 22 to avoid back reflection from its end facet 221 into the core of the micro-structured, hollow-core optical fibre 21.
  • the fibres 21 , 22 are axially aligned in preparation to a connectorization or a splicing.
  • FIG. 2b shows a photo corresponding to that of FIG. 2a with the only difference that the cleaving angles of the end faces 211 , 221 of the optical fibres 21 , 22 are 8.1° instead of 10.5°.
  • FIG. 2c illustrates a splice 23 of the optical fibres 21 , 22 of FIG. 2b, the end faces 211 , 221 of the optical fibres being cleaved at an angle of 8.1°, axially aligned (ensuring that the two end faces 211 , 221 are parallel) and subsequently spliced using a conventional cleaving and splicing apparatus.
  • the air-core fibres can be connectorized with much reduced return loss.
  • Equipment for performing these steps may be bought commercially through the company Vytran (Vytran Corporation, Morganville, NJ 07751 , USA).
  • a suitable exemplary equipment is the Vytran FFS 2000 splicing and cleaving machine.
  • Appropriate setting of cleaving and splicing parameters of the equipment e.g. temperature, time, etc.
  • Fig. 5b comprising a the centre line 591 (shown dotted) of the hollow-core 59 of the non-micro-structured optical fibre 53 is radially displaced relative to the centre line 531 (shown dotted) of the optical fibre to achieve that the light beam 54 is leaving the second face 552 of the optical window (stud) 55 substantially following the centre line 531 of the optical fibre (assuming that the hollow-core and the environment 'outside' the article comprise materials having substantially identical refractive indices (e.g. consist of air)).
  • the direction of light may be out of as well as into the article (stud).
  • Such a displacement is enough to significantly reduce the coupling from one fibre 56 to the other 57 if the fibre core is situated in the centre of the fibre.
  • the PBG fibre 57 can be designed to have the core 58 placed a few microns away from the centre.
  • the length of the stud can then be defined to make sure that the beam is centralised at the facet.
  • This technique can also be used to couple light from one air-core fibre 56 to another 57, cf. FIG. 5c.
  • angle cleaving fibres The technology for angle cleaving fibres is well developed and applies to most phonic crystal fibres.
  • the typical approach to make an angle cleave is to apply torque as well as tension in the fibre at the same time as scorching the side of the fibre with a blade. Due the torque, the stress lines will cause cleaving to occur at an angle.
  • a Vytran FFS 2000 splicing and cleaving machine may be used.
  • an angled fibre end can also be achieved using e.g. a CO 2 laser to cut the fibre.
  • an air-core PBG fibre is filled with gas (or have a portion of the glass rare-earth doped) and used in a fibre-based laser or amplifier.
  • the fibre core is filled with gas, and a hermetic sealing is needed to keep the gas inside the fibre. This can be done by splicing a stud 61 like the one described in FIG. 6 onto the fibre 62.
  • the "internal" angle G 1 could now be made so large that it will be close to or preferably equal to the Brewster angle. In this case the reflection coefficient for the two states of linearly polarised light will be very different and thus the roundtrip loss different for TM and TE polarised light.
  • n v n 2 are the refractive indices of the two materials, and ⁇ v ⁇ 2 is the incident and refracted angle, respectively. To calculate the reflected power these coefficients should be squared. The Brewster angle is calculated:
  • the reflection at both sides of the laser cavity can now be defined in the solid glass stud.
  • a Bragg reflector can be written into the stud, thus providing well-defined reflection back into the laser cavity.
  • the outer facet of the stud can be coated with an AR or HR coating. In either case, there are no moving parts in the laser cavity, and one is left with the task of coupling pump light into the fibre and capturing the emitted laser light.
  • the glass stud acts as the Brewster window commonly used in traditional gas lasers.
  • a polarising beam splitter For coupling pump light into the fibre, a polarising beam splitter can be used. Most laser gain media may be pumped with the polarization orthogonal to the laser light. Also, since the laser light is emitted in a single linearised polarisation, such beam splitter will add no extra loss to the system.
  • the angle needs to be large enough to prevent the majority of the reflected light to be coupled back into the core.
  • two fibre-to-fibre connectors are mounted face to face.
  • the light has to travel across a glass-air interface and the reflections are thus larger.
  • NA Numerical Aperture
  • FF Far Field
  • the APC standard is to polish the connector end to an angle of 8.0°, which means that the reflected light is diverted by 16°. This is enough to reduce the back reflection levels to below -50 dB.
  • the necessary connector angle depends on the NA and acceptance angle.
  • the NA can be as small as 0.03 or smaller.
  • the connector angle can be chosen to be just a few degrees and still maintain the same low level of back reflection.
  • FIG. 8 the level of reflected light coupled into the fibre is theoretically calculated.
  • the following equations are used (see e.g. ref: Introduction to Fibre Optics, A. Ghatak and K. Thyagarajan, Cambridge University Press, 1998, p. 168):
  • ⁇ is the connector angle and ⁇ is the wavelength in free space.
  • the - 14 dB comes from the fact that at perpendicular incidence only Fresnel reflection (4%) is reflected from the glass-air interface (note that a certain connector angle gives twice the angle in the reflected light).
  • the MFD is typically 10 ⁇ m and the NA thus 0.12.
  • the calculated RL is shown as full line in FIG. 8. Also in the same figure, two fibres with high NA (dashed) and low NA (dotted) are shown.
  • the needed connector angle vs. NA can be calculated. If we fix the allowed RL, then the minimum connector angle in degrees is given as:
  • this curve is given for an allowed RL of -50 dB.

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  • Optical Couplings Of Light Guides (AREA)

Abstract

La présente invention concerne des articles comprenant des fibres microstructurées à âme creuse ainsi que leurs procédés d'épissage et de connexion. Un objet de l'invention vise à l'obtention d'un système de couplage optique d'un article comprenant une fibre optique microstructurée à âme creuse à d'autres fibres optiques ou composants ayant une perte de retour relativement faible. L'objectif est atteint en ce qu'un article comprenant une fibre optique microstructurée à âme creuse est doté d'une fenêtre optique en matériau optique à indice de réfraction now, la fibre optique ayant une face terminale régulière formant un angle υ avec un plan perpendiculaire à un sens longitudinal de la fibre optique, la fenêtre optique ayant une longueur Iow dans le sens longitudinal et ayant une première face parallèle et au contact de la face terminale de la fibre optique, l'angle υ étant différent de 0°. L'invention concerne également des procédés de couplage optique d'une fibre à âme creuse à d'autres fibres optiques microstructurées à âme creuse ou non microstructurées au moyen d'un connecteur optique ou d'un épissage, et un laser ou un amplificateur à fibres comprenant un article selon l'invention. L'invention peut être utilisée dans toutes les applications de fibres optiques à âme creuse dans lesquelles la perte de retour n'a pas d'importance, par exemple dans des systèmes de communications optiques.
PCT/DK2004/000439 2003-06-19 2004-06-21 Articles comprenant des fibres microstructurees a ame creuse et leurs procedes d'epissage, de connexion et d'utilisation WO2004111695A1 (fr)

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WO2007140960A1 (fr) * 2006-06-05 2007-12-13 Trumpf, Inc. Laser à fibre creuse
US7787729B2 (en) 2005-05-20 2010-08-31 Imra America, Inc. Single mode propagation in fibers and rods with large leakage channels
EP2309609A3 (fr) * 2005-01-24 2011-07-27 The University of Bath Ensemble et procédé optique
US8422024B2 (en) 2011-06-01 2013-04-16 Honeywell International Inc. High performance hollow-core optical-fiber filter for optical rotation sensing
US8995051B2 (en) 2007-09-26 2015-03-31 Imra America, Inc. Glass large-core optical fibers
US9252559B2 (en) 2012-07-10 2016-02-02 Honeywell International Inc. Narrow bandwidth reflectors for reducing stimulated Brillouin scattering in optical cavities
US10197727B2 (en) 2004-01-16 2019-02-05 Imra America, Inc. Large core holey fibers
US10260881B2 (en) 2017-05-30 2019-04-16 Northrop Grumman Systems Corporation Hollow core fiber pigtail system and method
WO2020070487A1 (fr) * 2018-10-03 2020-04-09 Lumenisity Limited Ensemble adaptateur de guide d'ondes optiques
JP2023507373A (ja) * 2019-12-16 2023-02-22 オーエフエス ファイテル，エルエルシー 低レイテンシパッチコードのための光コネクタアセンブリ
EP4018234A4 (fr) * 2019-08-21 2023-08-30 Ofs Fitel Llc Réduction de perte de couplage entre des fibres optiques
EP4206762A4 (fr) * 2020-08-25 2024-01-24 Yokowo Seisakusho Kk Structure de terminaison de fibre optique, composant de connexion optique et fibre optique à coeur creux
WO2024102291A1 (fr) * 2022-11-07 2024-05-16 Panduit Corp. Connecteur à entrefer à fibre à âme creuse

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Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10197727B2 (en) 2004-01-16 2019-02-05 Imra America, Inc. Large core holey fibers
EP2309609A3 (fr) * 2005-01-24 2011-07-27 The University of Bath Ensemble et procédé optique
US10067289B2 (en) 2005-05-20 2018-09-04 Imra America, Inc. Single mode propagation in fibers and rods with large leakage channels
US7787729B2 (en) 2005-05-20 2010-08-31 Imra America, Inc. Single mode propagation in fibers and rods with large leakage channels
WO2007140960A1 (fr) * 2006-06-05 2007-12-13 Trumpf, Inc. Laser à fibre creuse
US8995051B2 (en) 2007-09-26 2015-03-31 Imra America, Inc. Glass large-core optical fibers
US9632243B2 (en) 2007-09-26 2017-04-25 Imra America, Inc. Glass large-core optical fibers
US10353144B2 (en) 2007-09-26 2019-07-16 Imra America, Inc. Glass large-core optical fibers
US8422024B2 (en) 2011-06-01 2013-04-16 Honeywell International Inc. High performance hollow-core optical-fiber filter for optical rotation sensing
US9252559B2 (en) 2012-07-10 2016-02-02 Honeywell International Inc. Narrow bandwidth reflectors for reducing stimulated Brillouin scattering in optical cavities
US10260881B2 (en) 2017-05-30 2019-04-16 Northrop Grumman Systems Corporation Hollow core fiber pigtail system and method
JP2022502716A (ja) * 2018-10-03 2022-01-11 ルメニシティ・リミテッド 光導波路アダプタ組立体
WO2020070487A1 (fr) * 2018-10-03 2020-04-09 Lumenisity Limited Ensemble adaptateur de guide d'ondes optiques
JP7371828B2 (ja) 2018-10-03 2023-10-31 マイクロソフト テクノロジー ライセンシング，エルエルシー 光導波路アダプタ組立体
US11960119B2 (en) 2018-10-03 2024-04-16 Microsoft Technology Licensing, Llc Optical waveguide adapter assembly
EP4018234A4 (fr) * 2019-08-21 2023-08-30 Ofs Fitel Llc Réduction de perte de couplage entre des fibres optiques
JP2023507373A (ja) * 2019-12-16 2023-02-22 オーエフエス ファイテル，エルエルシー 低レイテンシパッチコードのための光コネクタアセンブリ
EP4206762A4 (fr) * 2020-08-25 2024-01-24 Yokowo Seisakusho Kk Structure de terminaison de fibre optique, composant de connexion optique et fibre optique à coeur creux
WO2024102291A1 (fr) * 2022-11-07 2024-05-16 Panduit Corp. Connecteur à entrefer à fibre à âme creuse

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