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{{Short description|Class of optical fiber based on the properties of photonic crystals}}
Structured optical fibres, those based on channels running along their entire length go back to Kasier and co in 1974. These include air-clad optical fibres, microstructured optical fibres sometimes called photonic crystal fibre when the arrays of holes are periodic and look like a crystal, and many other subclasses. '''Photonic-crystal fiber''' (PCF) is a new class of [[optical fiber]] based on the properties of [[photonic crystal]]s. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in [[fiber-optic communication]]s, fiber [[laser]]s, nonlinear devices, high-power transmission, highly sensitive [[gas]] sensors, and other areas. The term "photonic-crystal fiber" was coined by [[Philip Russell]] in 1995-1997 (he states (2003) that the idea dates to unpublished work in 1991), although other terms such as '''microstructured fiber''' are also used and the nomenclature in the field is not entirely consistent. More specific categories of PCF include '''photonic-bandgap fiber''' (PCFs that confine light by band gap effects), '''holey fiber''' (PCFs using air holes in their cross-sections), ''hole-assisted'' fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and '''Bragg fiber''' (photonic-bandgap fiber formed by concentric rings of multilayer film).
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}


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[[File:Photonic-crystal-fiber-from-NRL.jpg|right|thumb|350x350px|[[Scanning electron microscope|SEM]] micrographs of a photonic-crystal fiber produced at [[United States Naval Research Laboratory|US Naval Research Laboratory]]. (left) The diameter of the solid core at the center of the fiber is 5 μm, while (right) the diameter of the holes is 4 μm]]
Martelli and Canning realised that the crystal structures that have identical interstitial regions are actually not the most ideal structure for practical applications and pointed out aperiodic structured fibres, such as Fractal fibres, are a better option for low bend losses.<ref>Cicero Martelli, John Canning, Brant Gibson, and Shane Huntington, "Bend loss in structured optical fibres," Opt. Express 15, 17639-17644 (2007)</ref> Aperiodic fibres are a subclass of Fresnel fibres which describe optical propagation in analogous terms to diffraction free beams.<ref>J. Canning, Diffraction-free mode generation and propagation in optical waveguides, Optics Commun., Vol 207, (1-6), 35-39, 2002</ref> These too can be made by using air channels appropriately positioned on the virtual zones of the optical fibre.<ref>J. Canning, E. Buckley, and K. Lyytikainen, "Propagation in air by field superposition of scattered light within a Fresnel fiber," Opt. Lett. 28, 230-232 (2003) </ref>
[[File:Photonic-crystal fiber.jpg|thumb|500x500px|Diagram of a photonic crystal fiber in perspective and cross-sectional views. A solid-core fiber is shown with a periodic air hole cladding and a solid blue coating.]]
'''Photonic-crystal fiber''' ('''PCF''') is a class of [[optical fiber]] based on the properties of [[Photonic crystal|photonic crystals]]. It was first explored in 1996 at University of Bath, UK. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in [[Fiber-optic communication|fiber-optic communications]], [[Fiber laser|fiber lasers]], nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include '''photonic-bandgap fiber''' (PCFs that confine light by band gap effects), '''holey fiber''' (PCFs using air holes in their cross-sections), ''hole-assisted'' fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and '''Bragg fiber''' (photonic-bandgap fiber formed by concentric rings of multilayer film). Photonic crystal fibers may be considered a subgroup of a more general class of [[Microstructured optical fiber|microstructured optical fibers]], where light is guided by structural modifications, and not only by refractive index differences. Hollow-core fibers (HCFs) are a related type of optical fiber which bears some resemblance to holey optical fiber, but may or may not be photonic depending on the fiber.<ref>{{cite web | url=https://spie.org/news/photonics-focus/julyaug-2022/speeding-light-with-hollow-core-fibers?SSO=1 | title=Speeding light, mitigating loss: Hollow-core fibers step to the fore }}</ref><ref>https://www.rp-photonics.com/hollow_core_fibers.html</ref>


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== Description ==
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[[Image:Photonic-crystal-fiber-from-NRL.jpg|[[SEM]] micrographs of a photonic-crystal fiber produced at [[United States Naval Research Laboratory|US Naval Research Laboratory]]. (left) The diameter of the solid core at the center of the fiber is 5 µm, while (right) the diameter of the holes is 4 µm|thumb|right|350px]]
Optical fibers have evolved into many forms since the practical breakthroughs that saw their wider introduction in the 1970s as conventional step index fibers<ref>{{cite journal |last1=Kapron |first1=F. P. |year=1970 |title=Radiation Losses in Glass Optical Waveguides |journal=Applied Physics Letters |volume=17 |issue=10 |page=423 |bibcode=1970ApPhL..17..423K |doi=10.1063/1.1653255}}</ref><ref>{{cite journal |last1=Keck |first1=D.B. |year=1973 |title=On the ultimate lower limit of attenuation in glass optical waveguides |journal=Applied Physics Letters |volume=22 |issue=7 |page=307 |bibcode=1973ApPhL..22..307K |doi=10.1063/1.1654649}}</ref> and later as single material fibers where propagation was defined by an effective air cladding structure.<ref>Kaiser P.V., Astle H.W., (1974), Bell Syst. Tech. J., 53, 1021–1039</ref>


In general, regular structured fibers such as photonic crystal fibers, have a cross-section (normally uniform along the fiber length) consisting of one, two or more materials, most commonly arranged periodically over much of the cross-section. This zone is known as the "cladding" and surrounds a core (or several cores) where light is confined. For example, the fibers first demonstrated by [[Philip Russell (physicist)|Philip Russell]] consisted of a hexagonal lattice of air holes in a [[silica]] fiber, with a solid<ref>J. C. Knight, T. A. Birks, P. St. J. Russell, and D. M. Atkin, "All-silica single-mode optical fiber with photonic crystal cladding," Opt. Lett. 21, 1547-1549 (1996)</ref> or hollow<ref> {{doi|10.1126/science.282.5393.1476}}.</ref> core at the center where light is guided. Other arrangements include concentric rings of two or more materials, first proposed as "Bragg fibers" by Yeh and Yariv,<ref>P. Yeh, A. Yariv, and E. Marom, "Theory of Bragg fiber," ''J. Opt. Soc. Am.'' '''68''', 1196–1201 (1978)</ref> bow-tie, panda, and elliptical hole structures (used to achieve higher [[birefringence]] due to irregularity in the [[Refractive index#Definition|relative refractive index]]), [[spiral]]<ref>{{Cite journal |last=Agrawal |first=Arti |date=Feb 2013 |title=Stacking the Equiangular Spiral |journal=IEEE Photonics Technology Letters |volume=25 |issue=3 |pages=291–294 |doi=10.1109/LPT.2012.2236309 |bibcode=2013IPTL...25..291A |s2cid=30334079 |via=IEEE|doi-access=free }}</ref> designs which allow for better control over optical properties as individual parameters can be changed.
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==Description==
Optical fibres have evolved into many forms since the practical breakthroughs that saw their wider introduction in the 1970s as conventional step index fibres<ref> Kapron F., Keck D.B., Maurer R.D., (1970), Appl. Phys. Lett., 17, 423</ref><ref> Keck D.B., Maurer R.D., Schultz P.C., (1973), Appl. Phys. Lett., 22 (7), 307-309 </ref> and later as single material fibres where propagation was defined by an effective air cladding structure.<ref> Kaiser P.V., Astle H.W., (1974), Bell Syst. Tech. J., 53, 1021-1039 </ref> However, no matter how exotic the method of propagation, and no matter the material system, the sole driver for most that time has been the transportation of light from one point to another, whether by step-index confinement determined by simple Fresnel reflections or by coherent Fresnel reflections in bandgap fibres such as Bragg fibres.<ref> Yeh P., Yariv A., Marom E., (1978), J. Opt. Soc. Am. 68, 1196 </ref> This necessarily resulted in fibre design centred on controlling the near field of an optical mode along this distance in order to control its propagation and attempt to, in most cases, retain its properties after travel.


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(Note: PCFs and, in particular, Bragg fibers, should not be confused with [[Fiber Bragg grating|fiber Bragg gratings]], which consist of a periodic [[refractive index]] or structural variation along the fiber axis, as opposed to variations in the transverse directions as in PCF. Both PCFs and fiber Bragg gratings employ [[Bragg diffraction]] phenomena, albeit in different directions.)
Photonic crystal fibres are a variant of the microstructured fibres reported by Kaiser et al. They are an attempt to incorporate the bandgap ideas of Yeh et al. in a simple way by stacking periodically a regular array of channels and drawing into fibre form. The first such fibres did not propagate by such a bandgap but rather by an effective step index - however, the name has for historical reasons, remain unchanged although some researchers prefer to call these fibres "holey" fibres or "microstructured" optical fibers in reference to the pre-existing work from Bell Labs. The shift into the nanoscale<ref>S. Huntington, J. Katsifolis, B.C. Gibson, J. Canning, K. Lyytikainen, J. Zagari, L.W. Cahill, J.D. Love, “Retaining and Characterising nanostructure within tapered air-silica structured optical fibres”, Opt. Express 11 (2), pp.98-104, (2003) </ref> was pre-empted by the more recent label "structured" fibres. An extremely important variant was the air-clad fibre invented by DiGiovanni at Bell Labs in 1986/87 based on work by Marcatili et al. in 1984.<ref>.J. DiGiovanni, R.S. Windeler, “Article comprising an air-clad optical fiber”, US Patent 5,907,652; G02B 006/20 (1998 filed 1997); based on previous patent: E.A.J. Marcatili, “Air clad optical fiber waveguide,” US patent 3,712,705 (1973)</ref> This is perhaps the single most successful fibre design to date based on structuring the fibre design using air holes and has important applications regarding high numerical aperture and light collection especially when implemented in laser form, but with great promise in areas as diverse as biophotonics and astrophotonics.<ref> M. Aslund, J. Canning, “Air-clad fibres for astronomical instrumentation: focal-ratio degradation”, Exp. Astronomy, 24, (1-3), 1-7, (2009) </ref>


The lowest reported attenuation of solid core photonic crystal fiber is 0.37 dB/km,<ref>{{cite journal |vauthors=Tajima K, Zhou J, Nakajima K, Sato K |year=2004 |title=Ultralow Loss and Long Length Photonic Crystal Fiber" Journal of Lightwave Technology |journal=Journal of Lightwave Technology |volume=22 |issue=1 |pages=7–10 |bibcode=2004JLwT...22....7T |doi=10.1109/JLT.2003.822143|s2cid=8045306 }}</ref> and for hollow core is 1.2 dB/km.<ref>P. Roberts, F. Couny, H. Sabert, B. Mangan, D. Williams, L. Farr, M. Mason, A. Tomlinson, T. Birks, J. Knight, and P. St. J. Russell, "Ultimate low loss of hollow-core photonic crystal fibres," Opt. Express 13, 236-244 (2005) http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-1-236</ref>
In general, regular structured fibers such as photonic crystal fibers, have a cross-section (normally uniform along the fiber length) microstructured from one, two or more materials, most commonly (because its easier to make) arranged periodically over much of the cross-section, usually as a "cladding" surrounding a core (or several cores) where light is confined. For example, the fibers first demonstrated by Russell consisted of a hexagonal lattice of air holes in a [[silica]] fiber, with a solid (1996) or hollow (1998) core at the center where light is guided. Other arrangements include concentric rings of two or more materials, first proposed as "Bragg fibers" by Yeh and Yariv (1978), a variant of which was recently fabricated by Temelkuran ''et al.'' (2002) and others.


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== Construction ==
More interestingly, has been the recognition that the periodic structure is actually not the best solution for many applications. Fibres that go well beyond shaping the near field now can be deliberately designed to shape the far-field for the first time, including focusing light beyond the end of the fibre.<ref>J. Canning, Fresnel Optics Inside Optical Fibres, in Photonics Research Developments, Chapter 5, Nova Science Publishers, United States, (2008) and refs therein</ref> These Fresnel fibres use well known Fresnel optics which has long been applied to lens design, including more advanced forms used in aperiodic, fractal and irregular adaptive optics, or Fresnel/fractal zones. Many other practical design benefits include broader photonic bandgaps in diffraction based propagating waveguides and reduced bend losses, important for achieving structured optical fibres with propagation losses below that of step-index fibres.
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Generally, such fibers are constructed by the same methods as other optical fibers: first, one constructs a "[[Optical fiber#Preform|preform]]" on the scale of centimeters in size, and then heats the preform and [[Drawing (manufacturing)|draws]] it down to a much smaller diameter (often nearly as small as a human hair), shrinking the preform cross section but (usually) maintaining the same features. In this way, kilometers of fiber can be produced from a single preform. Air holes are most commonly created by gathering hollow rods into a bundle, and heating the bundle to fuse it into a single rod with ordered holes before drawing, although drilling/milling was used to produce the first aperiodic designs.<ref>{{cite journal |vauthors=Canning J, Buckley E, Lyttikainen K, Ryan T |year=2002 |title=Wavelength dependent leakage in a Fresnel-based air–silica structured optical fibre |journal=Optics Communications |volume=205 |issue=1–3 |pages=95–99 |bibcode=2002OptCo.205...95C |doi=10.1016/S0030-4018(02)01305-6}}</ref> This formed the subsequent basis for producing the first soft glass and polymer structured fibers.


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Most photonic crystal fibers have been fabricated in [[silica glass]], but other glasses have also been used to obtain particular optical properties (such as high optical non-linearity). There is also a growing interest in making them from polymer, where a wide variety of structures have been explored, including graded index structures, ring structured fibers and hollow core fibers. These polymer fibers have been termed "MPOF", short for microstructured [[Polymer optical fiber|polymer optical fibers]].<ref>Martijn A. van Eijkelenborg, Maryanne C. J. Large, Alexander Argyros, Joseph Zagari, Steven Manos, Nader A. Issa, Ian Bassett, Simon Fleming, Ross C. McPhedran, C. Martijn de Sterke, and Nicolae A.P. Nicorovici, "Microstructured polymer optical fibre," Opt. Express 9, 319-327 (2001)</ref> A combination of a polymer and a [[chalcogenide glass]] was used by Temelkuran ''et al.''<ref>{{cite journal | doi=10.1038/nature01275 | title=Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission | year=2002 | last1=Temelkuran | first1=Burak | last2=Hart | first2=Shandon D. | last3=Benoit | first3=Gilles | last4=Joannopoulos | first4=John D. | last5=Fink | first5=Yoel | journal=Nature | volume=420 | issue=6916 | pages=650–653 | pmid=12478288 | bibcode=2002Natur.420..650T | s2cid=4326376 }}</ref> in 2002 for 10.6 [[μm]] wavelengths (where silica is not transparent).
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(Note: PCFs and, in particular, Bragg fibers, should not be confused with [[fiber Bragg grating]]s, which consist of a periodic [[refractive index]] or structural variation along the fiber axis, as opposed to variations in the transverse directions as in PCF. Both PCFs and fiber Bragg gratings employ [[Bragg diffraction]] phenomena, albeit in different directions.)


== Modes of operation ==
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==Construction==
[[File:Photonic Crystal Fibers Diagram (index guide and photonic bandgap).jpg|thumb|451x451px|Diagram in cross-sectional view of two types of photonic crystal fibers: index guide (left) and photonic bandgap (right).]]
Photonic crystal fibers can be divided into two modes of operation, according to their mechanism for confinement: index guiding and photonic bandgap.


'''Index guiding''' photonic crystal fibers are characterized by a core with a higher average refractive index than that of the cladding. The simplest way to accomplish this is to maintain a solid core, surrounded by a cladding region of the same material but interspersed with air holes, as the refractive index of the air will necessarily lower the average refractive index of the cladding. These photonic crystal fibers operate on the same [[Total internal reflection|index-guiding]] principle as conventional optical fiber—however, they can have a much higher effective [[refractive index contrast]] between core and cladding, and therefore can have much stronger confinement for applications in nonlinear optical devices, [[Polarization (waves)|polarization]]-maintaining fibers. Alternatively, they can also be made with much ''lower'' effective index contrast.
⚫
Generally, such fibers are constructed by the same methods as other optical fibers: first, one constructs a "[[preform]]" on the scale of centimeters in size, and then heats the preform and draws it down to a much smaller diameter (often nearly as small as a human hair), shrinking the preform cross section but (usually) maintaining the same features. In this way, kilometers of fiber can be produced from a single preform. The most common method involves stacking although drilling/milling was used to produce the first aperiodic designs (<ref>J. Canning, E. Buckley, K. Lyytikainen, T. Ryan, “Wavelength Dependent Leakage in a Fresnel-Based Air-Silica Structured Optical Fibre”, Opt. Comm. 205 (1-3), pp. 95-99, (2002)</ref>). This formed the subsequent basis for producing the first soft glass and polymer structured fibres.


⚫
Alternatively, one can create a '''photonic bandgap''' photonic crystal fiber, in which the light is confined by a photonic bandgap created by the microstructured cladding—such a bandgap, properly designed, can confine light in a ''lower-index'' core and even a hollow (air) core. Bandgap fibers with hollow cores can potentially circumvent limits imposed by available materials, for example to create fibers that guide light in wavelengths for which transparent materials are not available (because the light is primarily in the air, not in the solid materials). Another potential advantage of a hollow core is that one can dynamically introduce materials into the core, such as a gas that is to be analyzed for the presence of some substance. PCF can also be modified by coating the holes with sol-gels of similar or different index material to enhance the transmittance of light.
⚫
Most photonic crystal fiber has been fabricated in [[silica glass]], but other glasses have also been used to obtain particular optical properties (such has high optical non-linearity). There is also a growing interest in making them from polymer, where a wide variety of structures have been explored, including graded index structures, ring structured fibres and hollow core fibers. These polymer fibers have been termed "MPOF", short for microstructured [[polymer optical fiber]]s (van Eijkelenborg, 2001). A combination of a polymer and a [[chalcogenide glass]] was used by Temelkuran ''et al.'' (2002) for 10.6 [[µm]] wavelengths (where silica is not transparent).


==Modes of operation==
== History ==
The term "photonic-crystal fiber" was coined by [[Philip Russell (physicist)|Philip Russell]] in 1995–1997 (he states (2003) that the idea dates to unpublished work in 1991).


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== See also ==
⚫
Photonic crystal fibers can be divided into two modes of operation, according to their mechanism for confinement. Those with a solid core, or a core with a higher average index than the microstructured cladding, can operate on the same [[total internal reflection|index-guiding]] principle as conventional optical fiber &mdash; however, they can have a much higher effective- [[refractive index contrast]] between core and cladding, and therefore can have much stronger confinement for applications in nonlinear optical devices, [[Polarization (waves)|polarization]]-maintaining fibers, (or they can also be made with much ''lower'' effective index contrast). Alternatively, one can create a "photonic bandgap" fiber, in which the light is confined by a photonic bandgap created by the microstructured cladding &mdash; such a bandgap, properly designed, can confine light in a ''lower-index'' core and even a hollow (air) core. Bandgap fibers with hollow cores can potentially circumvent limits imposed by available materials, for example to create fibers that guide light in wavelengths for which transparent materials are not available (because the light is primarily in the air, not in the solid materials). Another potential advantage of a hollow core is that one can dynamically introduce materials into the core, such as a gas that is to be analyzed for the presence of some substance. PCF can also be modified by coating the holes with sol-gels of similar or different index material to enhance its transmittance of light.


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* [[Fiber Bragg grating]]
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==See also==
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* [[Photonic crystal]]
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* [[Optical medium]]
* [[Fiber optics]]
* [[Fiber optics]]
* [[Gradient index optics]]
* [[Gradient index optics]]
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* [[Optical communication]]
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* [[Fiber Bragg grating]]
* [[Leaky mode]]
* [[Leaky mode]]
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* [[Optical communication]]
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* [[Optical medium]]
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* [[Photonic crystal]]
* [[Subwavelength-diameter optical fiber]]
* [[Subwavelength-diameter optical fiber]]


==References==
== References ==
<references group="" responsive="1"></references>
{{Reflist}}

{{refbegin|2}}
== Further reading ==
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* P. St. J. Russell, "Photonic crystal fibers," ''Science'' '''299''', 358-362 (2003). (Review article.)

⚫
* P. St. J. Russell, "Photonic crystal fibers", ''J. Lightwave. Technol.'', '''24''' (12), 4729-4749 (2006). (Review article.)
* T. A. Birks, P. J. Roberts, P. St. J. Russell, D. M. Atkin and T. J. Shepherd, "Full 2-D photonic bandgaps in silica/air structures" ''Electronic Letters'' '''31''', 1941-1942 (1995). (First reported PCF proposal)
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* F. Zolla, G. Renversez, A. Nicolet, B. Kuhlmey, S. Guenneau, D. Felbacq, "Foundations of Photonic Crystal Fibres" (Imperial College Press, London, 2005). ISBN 1-86094-507-4.
⚫
* P. St. J. Russell, "Photonic crystal fibers," ''Science'' '''299''', 358–362 (2003). (Review article.)
* Burak Temelkuran, Shandon D. Hart, Gilles Benoit, John D. Joannopoulos, and Yoel Fink, "Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission", ''Nature'' '''420''', 650-653 (2002).
⚫
* P. St. J. Russell, "Photonic crystal fibers", ''J. Lightwave. Technol.'', '''24''' (12), 4729–4749 (2006). (Review article.)
* J. C. Knight, J. Broeng, T. A. Birks and P. St. J. Russell, “Photonic band gap guidance in optical fibers,” Science 282, 1476-1478 (1998).
⚫
* F. Zolla, G. Renversez, A. Nicolet, B. Kuhlmey, S. Guenneau, D. Felbacq, "Foundations of Photonic Crystal Fibres" (Imperial College Press, London, 2005). {{ISBN|1-86094-507-4}}.
* J. C. Knight, T. A. Birks, P. St. J. Russell and D. M. Atkin, “All-silica single-mode fiber with photonic crystal cladding,” ''Opt. Lett.'' '''21''', 1547-1549 (1996). Erratum, ''ibid'' '''22''', 484-485 (1997).
* R. F. Cregan, B. J. Mangan, J. C. Knight, T. A. Birks, P. St.J. Russell, P. J. Roberts, and D. C. Allan, “Single-mode photonic band gap guidance of light in air,” Science, vol. 285, no. 5433, pp.&nbsp;1537–1539, Sep. 1999.
* R. F. Cregan, B. J. Mangan, J. C. Knight, T. A. Birks, P. St.J. Russell, P. J. Roberts, and D. C. Allan, "Single-mode photonic band gap guidance of light in air," Science, vol. 285, no. 5433, pp.&nbsp;1537–1539, Sep. 1999.
⚫
* A. Bjarklev, J. Broeng, and A. S. Bjarklev, "Photonic crystal fibres" (Kluwer Academic Publishers, Boston, MA, 2003). {{ISBN|1-4020-7610-X}}.
* P. J. Roberts, F. Couny, H. Sabert, B. J. Mangan, D. P. Williams, L. Farr, M. W. Mason, A. Tomlinson, T. A. Birks, J. C. Knight, and P. St.J. Russell, “Ultimate low loss of hollow-core photonic crystal fibers,” Opt. Express, vol. 13, no. 1, pp.&nbsp;236–244, 2005.
* P. Yeh, A. Yariv, and E. Marom, “Theory of Bragg fiber,” ''J. Opt. Soc. Am.'' '''68''', 1196–1201 (1978).
⚫
* A. Bjarklev, J. Broeng, and A. S. Bjarklev, "Photonic crystal fibres" (Kluwer Academic Publishers, Boston, MA, 2003). ISBN 1-4020-7610-X.
* Martijn A. van Eijkelenborg, Maryanne C. J. Large, Alexander Argyros, Joseph Zagari, Steven Manos, Nader A. Issa, Ian Bassett, Simon Fleming, Ross C. McPhedran, C. Martijn de Sterke and Nicolae A.P. Nicorovici, "Microstructured polymer optical fibre", Optics Express Vol. 9, No. 7, pp.&nbsp;319-327 (2001).
* J. M. Dudley, G. Genty, S. Coen, "Supercontinuum Generation in Photonic Crystal Fiber," Reviews of Modern Physics '''78''', 1135 (2006).
* J. M. Dudley, G. Genty, S. Coen, "Supercontinuum Generation in Photonic Crystal Fiber," Reviews of Modern Physics '''78''', 1135 (2006).
{{refend}}


==External links==
== External links ==

* Centre for Photonics and Photonic Materials (CPPM) , University of Bath [http://www.bath.ac.uk/physics/groups/cppm/]
* Group of Prof. Philip St. John Russell at the [[Max Planck Institute for the Science of Light]] in Erlangen [http://www.pcfiber.com] with some introductory material, reviews and information about current research.
* Centre for Photonics and Photonic Materials (CPPM), University of Bath [http://www.bath.ac.uk/research/centres/cppm/]
* Group of Prof. Philip St. John Russell at the [[Max Planck Institute for the Science of Light]] in Erlangen [http://www.pcfiber.com/] with some introductory material, reviews and information about current research.
* [http://www.rp-photonics.com/photonic_crystal_fibers.html Encyclopedia of Laser Physics and Technology on photonic crystal fibers], with many references
* [http://www.rp-photonics.com/photonic_crystal_fibers.html Encyclopedia of Laser Physics and Technology on photonic crystal fibers], with many references
* Steven G. Johnson, [http://ab-initio.mit.edu/photons/tutorial Photonic-crystal and microstructured fiber tutorials] (2005).
* [[Steven G. Johnson]], [http://ab-initio.mit.edu/photons/tutorial Photonic-crystal and microstructured fiber tutorials] (2005).
* [http://www.ieee.org/organizations/pubs/newsletters/leos/oct07/history.pdf Philip Russell: Photonic Crystal Fibers, Historical account in: IEEE Leo Newsletter, October 2007]
* [https://www.mpl.mpg.de/fileadmin/russel/Research_papers/2007_Russell.pdf Philip Russell: Photonic Crystal Fibers, Historical account in: IEEE LEOS Newsletter, October 2007]
* John D. Joannopoulos, Steven G. Johnson, Joshua N. Winn, and Robert D. Meade, ''[http://ab-initio.mit.edu/book Photonic Crystals: Molding the Flow of Light]'', second edition (Princeton, 2008), chapter 9. (Readable online.)
* John D. Joannopoulos, [[Steven G. Johnson]], Joshua N. Winn, and Robert D. Meade, ''[http://ab-initio.mit.edu/book Photonic Crystals: Molding the Flow of Light]'', second edition (Princeton, 2008), chapter 9. (Readable online.)
* [http://spie.org/newsroom/technical-articles/videos/pw16_plenaries-landing/pw16_plenary_russell Philip Russell plenary presentation: Emerging Applications of Photonic Crystal Fibers] SPIE Newsroom


{{DEFAULTSORT:Photonic-Crystal Fiber}}
{{DEFAULTSORT:Photonic-Crystal Fiber}}
[[Category:Photonics]]
[[Category:Photonics]]
[[Category:Optical fiber]]
[[Category:Optical fiber]]

[[es:Fibra de cristal fotónico]]
[[pl:Photonic crystal fiber]]

Latest revision as of 09:01, 20 December 2024

SEM micrographs of a photonic-crystal fiber produced at US Naval Research Laboratory. (left) The diameter of the solid core at the center of the fiber is 5 μm, while (right) the diameter of the holes is 4 μm
Diagram of a photonic crystal fiber in perspective and cross-sectional views. A solid-core fiber is shown with a periodic air hole cladding and a solid blue coating.

Photonic-crystal fiber (PCF) is a class of optical fiber based on the properties of photonic crystals. It was first explored in 1996 at University of Bath, UK. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber (PCFs that confine light by band gap effects), holey fiber (PCFs using air holes in their cross-sections), hole-assisted fiber (PCFs guiding light by a conventional higher-index core modified by the presence of air holes), and Bragg fiber (photonic-bandgap fiber formed by concentric rings of multilayer film). Photonic crystal fibers may be considered a subgroup of a more general class of microstructured optical fibers, where light is guided by structural modifications, and not only by refractive index differences. Hollow-core fibers (HCFs) are a related type of optical fiber which bears some resemblance to holey optical fiber, but may or may not be photonic depending on the fiber.[1][2]

Description

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Optical fibers have evolved into many forms since the practical breakthroughs that saw their wider introduction in the 1970s as conventional step index fibers[3][4] and later as single material fibers where propagation was defined by an effective air cladding structure.[5]

In general, regular structured fibers such as photonic crystal fibers, have a cross-section (normally uniform along the fiber length) consisting of one, two or more materials, most commonly arranged periodically over much of the cross-section. This zone is known as the "cladding" and surrounds a core (or several cores) where light is confined. For example, the fibers first demonstrated by Philip Russell consisted of a hexagonal lattice of air holes in a silica fiber, with a solid[6] or hollow[7] core at the center where light is guided. Other arrangements include concentric rings of two or more materials, first proposed as "Bragg fibers" by Yeh and Yariv,[8] bow-tie, panda, and elliptical hole structures (used to achieve higher birefringence due to irregularity in the relative refractive index), spiral[9] designs which allow for better control over optical properties as individual parameters can be changed.

(Note: PCFs and, in particular, Bragg fibers, should not be confused with fiber Bragg gratings, which consist of a periodic refractive index or structural variation along the fiber axis, as opposed to variations in the transverse directions as in PCF. Both PCFs and fiber Bragg gratings employ Bragg diffraction phenomena, albeit in different directions.)

The lowest reported attenuation of solid core photonic crystal fiber is 0.37 dB/km,[10] and for hollow core is 1.2 dB/km.[11]

Construction

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Generally, such fibers are constructed by the same methods as other optical fibers: first, one constructs a "preform" on the scale of centimeters in size, and then heats the preform and draws it down to a much smaller diameter (often nearly as small as a human hair), shrinking the preform cross section but (usually) maintaining the same features. In this way, kilometers of fiber can be produced from a single preform. Air holes are most commonly created by gathering hollow rods into a bundle, and heating the bundle to fuse it into a single rod with ordered holes before drawing, although drilling/milling was used to produce the first aperiodic designs.[12] This formed the subsequent basis for producing the first soft glass and polymer structured fibers.

Most photonic crystal fibers have been fabricated in silica glass, but other glasses have also been used to obtain particular optical properties (such as high optical non-linearity). There is also a growing interest in making them from polymer, where a wide variety of structures have been explored, including graded index structures, ring structured fibers and hollow core fibers. These polymer fibers have been termed "MPOF", short for microstructured polymer optical fibers.[13] A combination of a polymer and a chalcogenide glass was used by Temelkuran et al.[14] in 2002 for 10.6 μm wavelengths (where silica is not transparent).

Modes of operation

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Diagram in cross-sectional view of two types of photonic crystal fibers: index guide (left) and photonic bandgap (right).

Photonic crystal fibers can be divided into two modes of operation, according to their mechanism for confinement: index guiding and photonic bandgap.

Index guiding photonic crystal fibers are characterized by a core with a higher average refractive index than that of the cladding. The simplest way to accomplish this is to maintain a solid core, surrounded by a cladding region of the same material but interspersed with air holes, as the refractive index of the air will necessarily lower the average refractive index of the cladding. These photonic crystal fibers operate on the same index-guiding principle as conventional optical fiber—however, they can have a much higher effective refractive index contrast between core and cladding, and therefore can have much stronger confinement for applications in nonlinear optical devices, polarization-maintaining fibers. Alternatively, they can also be made with much lower effective index contrast.

Alternatively, one can create a photonic bandgap photonic crystal fiber, in which the light is confined by a photonic bandgap created by the microstructured cladding—such a bandgap, properly designed, can confine light in a lower-index core and even a hollow (air) core. Bandgap fibers with hollow cores can potentially circumvent limits imposed by available materials, for example to create fibers that guide light in wavelengths for which transparent materials are not available (because the light is primarily in the air, not in the solid materials). Another potential advantage of a hollow core is that one can dynamically introduce materials into the core, such as a gas that is to be analyzed for the presence of some substance. PCF can also be modified by coating the holes with sol-gels of similar or different index material to enhance the transmittance of light.

History

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The term "photonic-crystal fiber" was coined by Philip Russell in 1995–1997 (he states (2003) that the idea dates to unpublished work in 1991).

See also

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References

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  1. ^ "Speeding light, mitigating loss: Hollow-core fibers step to the fore".
  2. ^ https://www.rp-photonics.com/hollow_core_fibers.html
  3. ^ Kapron, F. P. (1970). "Radiation Losses in Glass Optical Waveguides". Applied Physics Letters. 17 (10): 423. Bibcode:1970ApPhL..17..423K. doi:10.1063/1.1653255.
  4. ^ Keck, D.B. (1973). "On the ultimate lower limit of attenuation in glass optical waveguides". Applied Physics Letters. 22 (7): 307. Bibcode:1973ApPhL..22..307K. doi:10.1063/1.1654649.
  5. ^ Kaiser P.V., Astle H.W., (1974), Bell Syst. Tech. J., 53, 1021–1039
  6. ^ J. C. Knight, T. A. Birks, P. St. J. Russell, and D. M. Atkin, "All-silica single-mode optical fiber with photonic crystal cladding," Opt. Lett. 21, 1547-1549 (1996)
  7. ^ doi:10.1126/science.282.5393.1476.
  8. ^ P. Yeh, A. Yariv, and E. Marom, "Theory of Bragg fiber," J. Opt. Soc. Am. 68, 1196–1201 (1978)
  9. ^ Agrawal, Arti (February 2013). "Stacking the Equiangular Spiral". IEEE Photonics Technology Letters. 25 (3): 291–294. Bibcode:2013IPTL...25..291A. doi:10.1109/LPT.2012.2236309. S2CID 30334079 – via IEEE.
  10. ^ Tajima K, Zhou J, Nakajima K, Sato K (2004). "Ultralow Loss and Long Length Photonic Crystal Fiber" Journal of Lightwave Technology". Journal of Lightwave Technology. 22 (1): 7–10. Bibcode:2004JLwT...22....7T. doi:10.1109/JLT.2003.822143. S2CID 8045306.
  11. ^ P. Roberts, F. Couny, H. Sabert, B. Mangan, D. Williams, L. Farr, M. Mason, A. Tomlinson, T. Birks, J. Knight, and P. St. J. Russell, "Ultimate low loss of hollow-core photonic crystal fibres," Opt. Express 13, 236-244 (2005) http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-13-1-236
  12. ^ Canning J, Buckley E, Lyttikainen K, Ryan T (2002). "Wavelength dependent leakage in a Fresnel-based air–silica structured optical fibre". Optics Communications. 205 (1–3): 95–99. Bibcode:2002OptCo.205...95C. doi:10.1016/S0030-4018(02)01305-6.
  13. ^ Martijn A. van Eijkelenborg, Maryanne C. J. Large, Alexander Argyros, Joseph Zagari, Steven Manos, Nader A. Issa, Ian Bassett, Simon Fleming, Ross C. McPhedran, C. Martijn de Sterke, and Nicolae A.P. Nicorovici, "Microstructured polymer optical fibre," Opt. Express 9, 319-327 (2001)
  14. ^ Temelkuran, Burak; Hart, Shandon D.; Benoit, Gilles; Joannopoulos, John D.; Fink, Yoel (2002). "Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission". Nature. 420 (6916): 650–653. Bibcode:2002Natur.420..650T. doi:10.1038/nature01275. PMID 12478288. S2CID 4326376.

Further reading

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  • T. A. Birks, P. J. Roberts, P. St. J. Russell, D. M. Atkin and T. J. Shepherd, "Full 2-D photonic bandgaps in silica/air structures" Electronic Letters 31, 1941-1942 (1995). (First reported PCF proposal)
  • P. St. J. Russell, "Photonic crystal fibers," Science 299, 358–362 (2003). (Review article.)
  • P. St. J. Russell, "Photonic crystal fibers", J. Lightwave. Technol., 24 (12), 4729–4749 (2006). (Review article.)
  • F. Zolla, G. Renversez, A. Nicolet, B. Kuhlmey, S. Guenneau, D. Felbacq, "Foundations of Photonic Crystal Fibres" (Imperial College Press, London, 2005). ISBN 1-86094-507-4.
  • R. F. Cregan, B. J. Mangan, J. C. Knight, T. A. Birks, P. St.J. Russell, P. J. Roberts, and D. C. Allan, "Single-mode photonic band gap guidance of light in air," Science, vol. 285, no. 5433, pp. 1537–1539, Sep. 1999.
  • A. Bjarklev, J. Broeng, and A. S. Bjarklev, "Photonic crystal fibres" (Kluwer Academic Publishers, Boston, MA, 2003). ISBN 1-4020-7610-X.
  • J. M. Dudley, G. Genty, S. Coen, "Supercontinuum Generation in Photonic Crystal Fiber," Reviews of Modern Physics 78, 1135 (2006).
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