Fresnel-Reflection-Free Self-Aligning Nanospike Interface between a Step-Index Fiber and a Hollow-Core Photonic-Crystal-Fiber Gas Cell


High power laser delivery, telecommunication and fiber sensing technologies have been boosted by the development of the low loss hollow-core photonic crystal fibers (HC PCFs).  The HC PCFs guide light in a hollow region with minor optic power propagated in the glass. Filling the hollow core with gases or liquids has enabled intense light-matter interaction over distances that are thousands of times longer than the Rayleigh length. This has caused advancements in quantum optics, atomic physics and gas spectroscopy. Usually, these experimental setups require gas cells in which laser light is launched in the system through windows and using standard optical components. The dimensions of the system are therefore limited to the size of the gas cells and hence scaling is challenging.

A remedy for this limitation was the direct fusion splicing of a solid-core single-mode fiber (SMF) to the HC PCF. However, efficient optical coupling was obtained only for HC PCF with mode field diameter (MFD) comparable to the one of standard SMF (about 10 μm). Furthermore the gas-air interface can be a problem at high power because of back reflections.

Researchers led by Professor Philip Russell at Max Planck Institute for the Science of Light in Germany reported a new technique for launching light from a SMF to a HC PCF. A nanospike, or in simple words a silica tip, obtained by thermally tapering a SMF, is inserted to the core of the HC PCF. Proper taper design ensures efficient adiabatic transmission from the nanospike into the hollow core without Fresnel reflections and a correct choice of the nanospike diameter permits coupling to HC PCFs of any core size. Nanospikes with smaller tip diameters are necessary for larger HC PCF cores. In addition an optomechanical backaction between the nanospike and the HC PCF allows optical trapping of the nanospike at the core center. Pennetta et al. exploit this idea to realize an integrated all fiber device that can operate as a compact gas cell, only a few centimeters long. To demonstrate its perfomances, the author use the proposed device to observe Raman scattering and molecular modulation of hydrogen.

Fresnel-Reflection-Free Self-Aligning Nanospike Interface between a Step-Index Fiber and a Hollow-Core Photonic-Crystal-Fiber Gas Cell. Advances in Engineering

About the author

Riccardo Pennetta is currently a PhD in the group of Philip Russell at the Max Planck Institute for the Science of Light in Erlangen, Germany. He received his Master degrees in Physics from University of Bari, Italy in 2014. His current research interests include optomechanicas, tapered fibres and photonic crystal fibres.

About the author

Shangran Xie received his B.E and Ph.D. degrees from Department of Electronics Engineering, Tsinghua University (P. R. China) in 2007 and 2013 respectively. From 2010 to 2011, he joined Fiber Optics Group in University of Ottawa in Canada as a joint Ph.D. student, working on long-distance distributed temperature, strain and birefringence sensing using Brillouin scattering in optical fibers. From 2013, he was appointed as a postdoctoral fellow in Russell Division, Max Planck Institute for the Science of Light in Germany, working on mid-IR supercontinuum generation, optical tweezers and optomechanics based on custom-designed specialty fibers, including hybrid waveguides, tapered waveguides and photonic crystal fibers.

He is currently the group leader for the optomechanics team in Russell Division. His research interests cover fiber-based optical tweezers and optomechanics, mid-IR supercontinuum generation and fiber sensing.

About the author

Manoj Mridha is currently pursuing his PhD degree at the Max Planck Institute for the science of light, in Erlangen, Germany, under the supervision of Prof. Philip Russell. He received his Master’s of Science degree from Institute National de la Reserche Scientifique-Énergie, Matériaux et Télécommunications, Varennes, Canada in 2014. His Master’s Thesis was based on developing Two-Wire waveguides for broadband dispersionless propagation of THz (0.1-2 THz) radiation. His current research focuses on developing narrowband high-spectral density UV light sources based on stimulated Raman scattering in gas-filled hollow-core phtonic crystal fibres.

About the author

David Novoa (Spain, 1983) obtained his bachelor degree in Physics and master degree in Photonics and Laser Technologies at the university of Vigo (Spain). After that, in 2011 he obtained his PhD degree at the same university for his work on novel soliton dynamics in coherent optical and matter systems. In 2012 he moved to the Centre for Ultrashort Ultraintense Pulsed Lasers in Salamanca (Spain) as a postdoctoral researcher. In 2013, he got a postdoctoral position in the Russell division of the Max-Planck Institute for the Science of Light in Erlangen (Germany), where he is nowadays research group leader.

His main research interests deal with the study of strong light-matter interactions in gas-filled hollow-core photonic crystal fibers. Additionally, he is also interested in other areas of photonics as singular optics, optomechanics and quantum vacuum polarization.

About the author

Professor Philip Russell is a Director at the Max-Planck Institute for the Science of Light (MPL), a position he has held since January 2009 when MPL was founded. Since 2005 he has held the Krupp chair in experimental physics at the University of Erlangen-Nuremberg.  He obtained his D.Phil. (1979) degree at the University of Oxford, spending three years as a Research Fellow at Oriel College, Oxford. At that time his interests were in the propagation of light in three-dimensional periodic structures, in particular the behaviour of photonic Bloch waves. From 1982 to 1983 he was a Humboldt Fellow at the Technical University Hamburg-Harburg (Germany), where he carried out a series of experiments exploring the propagation of photonic Bloch waves in periodic planar waveguides, observing such phenomena as negative refractive and diffraction and Bloch wave interference. From 1984 to 1986 he further developed his interests in photonic Bloch waves while working at the University of Nice (France) and the IBM TJ Watson Research Center in Yorktown Heights, New York. From 1986 to 1996 he was based mainly at the University of Southampton in the Optical Fibre Group, which later became part of the Optoelectronics Research Centre. During this period he worked on photosensitivity, second harmonic generation, fibre Bragg gratings and rocking filter formation in optical fibres. He also carried out theoretical studies on nonlinear holography and the interaction of light and sound in tapered optical fibre couplers and dual-mode optical fibres. From 1996 to 2005 he was professor in the Department of Physics at the University of Bath, where the main focus was on photonic crystal fibres—a new kind of optical fibre that he proposed in 1991.

His research interests currently focus on scientific applications of these fibres and related structures. He is a Fellow of the Royal Society and The Optical Society (OSA) and has won several awards for his research including the 2000 OSA Joseph Fraunhofer Award/Robert M. Burley Prize, the 2005 Thomas Young Prize of the Institute for Physics (UK), the 2005 Körber Prize for European Science, the 2013 EPS Prize for Research into the Science of Light, the 2014 Berthold Leibinger Zukunftspreis, the 2015 IEEE Photonics Award and the 2018 Rank Prize for Optoelectronics. He was OSA’s President in 2015, the International Year of Light. In June 2016 he received an honorary doctorate from the Universidad Internacional Menéndez Pelayo in Santander, Spain.


Pennetta R., Xie S., Lenahan F., Mridha M., Novoa D., Russell P. St. J. Fresnel-Reflection-Free Self-Aligning Nanospike Interface between a Step-Index Fiber and a Hollow-Core Photonic-Crystal-Fiber Gas Cell. Physical Review Applied. 2017 Jul 14; 8(1):014014.


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