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Professor Philip St.J. Russell, FRS

Director of the Russell Division – Photonic Crystal Fibres

Professor Philip Russell is a founding Director of the Max-Planck Institute for the Science of Light (MPL), which began operations in January 2009. Since 2005 he has also held the Krupp Chair in Experimental Physics at the University of Erlangen-Nuremberg. He obtained his D.Phil. degree in 1979 at the University of Oxford, spending three years as a Research Fellow at Oriel College, Oxford. In 1982 and 1983 he was a Humboldt Fellow at the Technical University Hamburg-Harburg (Germany), and from 1984 to 1986 he worked 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, first of all in the Optical Fibre Group and then in the Optoelectronics Research Centre. From 1996 to 2005 he was professor in the Department of Physics at the University of Bath, where he established the Centre for Photonics and Photonic Materials. His research interests currently focus on scientific applications of photonic crystal fibres and related structures. He is a Fellow of the Royal Society and The Optical Society (OSA) and has won several international 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 and the 2015 IEEE Photonics Award. He was OSA's President in 2015, the International Year of Light.

2013

Efficient optical pumping and high optical depth in a hollow-core photonic-crystal fibre for a broadband quantum memory

Michael R. Sprague, Duncan G. England, Amir Abdolvand, Joshua Nunn, Xian-Min Jin, W. Steven Kolthammer, Marco Barbieri, Bruno Rigal, Patrick S. Michelberger, et al.

NEW JOURNAL OF PHYSICS 15 055013 (2013) | Journal

The generation of large multiphoton quantum states-for applications in computing, metrology and simulation-requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realizing this goal: strong light-matter coupling at low powers, simplified alignment and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstrate, for the first time, efficient optical pumping in such a system, where 90 +/- 1% of atoms are prepared in the ground state. We measure high optical depths (3 x 10(4)) and narrow homogeneous linewidths (6 +/- 2 MHz) that do not exhibit significant transit-time broadening, showing that we can prepare a Lambda-level system in a pure state. Our results establish that kagome fibres are suitable for implementing a broadband, room-temperature quantum memory, as well as a range of nonlinear optical effects.

Measuring mechanical strain and twist using helical photonic crystal fiber

Xiaoming Xi, Gordon K. L. Wong, Thomas Weiss, Philip St J. Russell

OPTICS LETTERS 38 (24) 5401-5404 (2013) | Journal

Solid-core photonic crystal fiber (PCF) with a permanent helical twist exhibits dips in its transmission spectrum at certain wavelengths. These are associated with the formation of orbital angular momentum states in the cladding. Here we investigate the tuning of these states with mechanical torque and axial tension. The dip wavelengths are found to scale linearly with both axial strain and mechanical twist rate. Analysis shows that the tension-induced shift in resonance wavelength is determined both by the photoelastic effect and by the change in twist rate, while the torsion-induced wavelength shift depends only on the change in twist rate. Twisted PCF can act as an effective optically monitored torque-tension transducer, twist sensor, or strain gauge. (C) 2013 Optical Society of America

Photonic crystal fibres for chemical sensing and photochemistry

Ana M. Cubillas, Sarah Unterkofler, Tijmen G. Euser, Bastian J. M. Etzold, Anita C. Jones, Peter J. Sadler, Peter Wasserscheid, Philip St. J. Russell

CHEMICAL SOCIETY REVIEWS 42 (22) 8629-8648 (2013) | Journal

In this review, we introduce photonic crystal fibre as a novel optofluidic microdevice that can be employed as both a versatile chemical sensor and a highly efficient microreactor. We demonstrate that it provides an excellent platform in which light and chemical samples can strongly interact for quantitative spectroscopic analysis or photoactivation purposes. The use of photonic crystal fibre in photochemistry and sensing is discussed and recent results on gas and liquid sensing as well as on photochemical and catalytic reactions are reviewed. These developments demonstrate that the tight light confinement, enhanced light-matter interaction and reduced sample volume offered by photonic crystal fibre make it useful in a wide range of chemical applications.

Mid-infrared supercontinuum generation in As2S3-silica "nano-spike" step-index waveguide

N. Granzow, M. A. Schmidt, W. Chang, L. Wang, Q. Coulombier, J. Troles, P. Toupin, I. Hartl, K. F. Lee, et al.

OPTICS EXPRESS 21 (9) 10969-10977 (2013) | Journal

Efficient generation of a broad-band mid-infrared supercontinuum spectrum is reported in an arsenic trisulphide waveguide embedded in silica. A chalcogenide "nano-spike", designed to transform the incident light adiabatically into the fundamental mode of a 2-mm-long uniform section 1 mu m in diameter, is used to achieve high launch efficiencies. The nano-spike is fully encapsulated in a fused silica cladding, protecting it from the environment. Nano-spikes provide a convenient means of launching light into sub-wavelength scale waveguides. Ultrashort (65 fs, repetition rate 100 MHz) pulses at wavelength 2 mu m, delivered from a Tm-doped fiber laser, are launched with an efficiency similar to 12% into the sub-wavelength chalcogenide waveguide. Soliton fission and dispersive wave generation along the uniform section result in spectral broadening out to almost 4 mu m for launched energies of only 18 pJ. The spectrum generated will have immediate uses in metrology and infrared spectroscopy. (C) 2013 Optical Society of America

Low loss hollow optical-waveguide connection from atmospheric pressure to ultra-high vacuum

A. Ermolov, K. F. Mak, F. Tani, P. Hoelzer, J. C. Travers, P. St J. Russell

APPLIED PHYSICS LETTERS 103 (26) 261115 (2013) | Journal

A technique for optically accessing ultra-high vacuum environments, via a photonic-crystal fiber with a long small hollow core, is described. The small core and the long bore enable a pressure ratio of over 10(8) to be maintained between two environments, while permitting efficient and unimpeded delivery of light, including ultrashort optical pulses. This delivery can be either passive or can encompass nonlinear optical processes such as optical pulse compression, deep UV generation, supercontinuum generation, or other useful phenomena. (C) 2013 AIP Publishing LLC.

Spectrofluorimetry with attomole sensitivity in photonic crystal fibres

Gareth O. S. Williams, Tijmen G. Euser, Philip St J. Russell, Anita C. Jones

METHODS AND APPLICATIONS IN FLUORESCENCE 1 (1) (2013) | Journal

We report the use of photonic crystal fibres (PCF) as spectrofluorimetric systems in which sample solutions are excited within the microstructure of the fibre. The use of intra-fibre excitation has several advantages that combine to enable highly sensitive measurements of fluorescence spectra and lifetimes: long path-lengths are achieved by the efficient guidance of the fundamental mode; sample volumes contained within the micron-scale structure are very small, only a few nanolitres per cm of path; collection and guidance of the emitted fluorescence is efficient and the fluorescence lifetime is unperturbed. Fluorophores in bulk solution can be studied in hollow core PCF, whereas the use of PCF with a suspended, solid core enables selective excitation of molecules in close proximity to the silica surface, through interaction with the evanescent field. We demonstrate the measurement of fluorescence spectra and fluorescence lifetimes in each of these excitation regimes and report the detection of attomole quantities of fluorescein.

Chemical and (Photo)-Catalytical Transformations in Photonic Crystal Fibers

Matthias Schmidt, Ana M. Cubillas, Nicola Taccardi, Tijmen G. Euser, Till Cremer, Florian Maier, Hans-Peter Steinrueck, Philip St. J. Russell, Peter Wasserscheid, et al.

CHEMCATCHEM 5 (3) 641-650 (2013) | Journal

The concept of employing photonic crystal fibers for chemical and (photo)-catalytical transformations is presented. These optofluidic microdevices represent a versatile platform where light and fluids can interact for spectroscopic or photoactivation purposes. The use of photonic crystal fibers in chemistry and sensing is reviewed and recent applications as catalytic microreactors are presented. Results on homogeneous catalysis and the immobilization of homogeneous and heterogeneous catalysts in the fiber channels are discussed. The examples demonstrate that combining catalysis and the excellent light guidance of photonic crystal fibers provides unique features for example, for photocatalytic activation and quantitative photospectroscopic reaction analysis.

Five-ring hollow-core photonic crystal fiber with 1.8 dB/km loss

M. H. Frosz, J. Nold, T. Weiss, A. Stefani, F. Babic, S. Rammler, P. St. J. Russell

OPTICS LETTERS 38 (13) 2215-2217 (2013) | Journal

A 19-cell hollow-core photonic crystal fiber reaching 1.8 +/- 0.5 dB/km loss at 1530 nm is reported. Despite expanded corner holes in the first ring adjacent to the core, and only five cladding rings, the minimum loss is close to the previously published record of 1.7 dB/km at a comparable wavelength, achieved in a fiber with seven cladding rings. Since each additional cladding ring requires a significant increase in fabrication time and complexity, it is highly desirable to use as few as possible while still achieving low loss. Modeling results confirm that further reducing cladding deformations would yield only a small decrease in loss. This demonstrates that loss comparable to the previously demonstrated lowest-loss bandgap fibers can be achieved with fiber structures that are significantly simpler and faster to fabricate. (C) 2013 Optical Society of America

Combined soliton pulse compression and plasma-related frequency upconversion in gas-filled photonic crystal fiber

W. Chang, P. Hoelzer, J. C. Travers, P. St. J. Russell

OPTICS LETTERS 38 (16) 2984-2987 (2013) | Journal

We numerically investigate self-frequency blueshifting of a fundamental soliton in a gas-filled hollow-core photonic crystal fiber. Because of the changing underlying soliton parameters, the blueshift gives rise to adiabatic soliton compression. Based on these features, we propose a device that enables frequency shifting over an octave and pulse compression from 30 fs down to 2.3 fs. (C) 2013 Optical Society of America

Topological Zeeman effect and circular birefringence in twisted photonic crystal fibers

T. Weiss, G. K. L. Wong, F. Biancalana, S. M. Barnett, X. M. Xi, P. St. J. Russell

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 30 (11) 2921-2927 (2013) | Journal

The propagation of light guided in optical fibers is affected in different ways by bending or twisting. Here we treat the polarization properties of twisted six-fold symmetric photonic crystal fibers. Using a coordinate frame that follows the twisting structure, we show that the governing equation for the fiber modes resembles the Pauli equation for electrons in weak magnetic fields. This implies index splitting between left and right circularly polarized modes, which are degenerate in the untwisted fiber. We develop a theoretical model, based on perturbation theory and symmetry properties, to predict the observable circular birefringence (i.e., optical activity) associated with this splitting. Our overall conclusion is that optical activity requires the rotational symmetry to be broken so as to allow coupling between different total angular momentum states. (C) 2013 Optical Society of America

A gold-nanotip optical fiber for plasmon-enhanced near-field detection

P. Uebel, S. T. Bauerschmidt, M. A. Schmidt, P. St. J. Russell

APPLIED PHYSICS LETTERS 103 (2) 021101 (2013) | Journal

A wet-chemical etching and mechanical cleaving technique is used to fabricate gold nanotips attached to tapered optical fibers. Localized surface plasmon resonances (tunable from 500 to 850 nm by varying the tip dimensions) are excited at the tip, and the signal is transmitted via the fiber to an optical analyzer, making the device a plasmon-enhanced near-field probe. A simple cavity model is used to explain the resonances observed in numerical simulations. (C) 2013 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Ultrafast nonlinear dynamics of surface plasmon polaritons in gold nanowires due to the intrinsic nonlinearity of metals

A. Marini, M. Conforti, G. Della Valle, H. W. Lee, Tr X. Tran, W. Chang, M. A. Schmidt, S. Longhi, P. St J. Russell, et al.

NEW JOURNAL OF PHYSICS 15 013033 (2013) | Journal

Starting from first principles, we theoretically model the nonlinear temporal dynamics of gold-based plasmonic devices resulting from the heating of their metallic components. At optical frequencies, the gold susceptibility is determined by the interband transitions around the X, L points in the first Brillouin zone, and thermo-modulational effects ensue from Fermi smearing of the electronic energy distribution in the conduction band. As a consequence of light-induced heating of the conduction electrons, the optical susceptibility becomes nonlinear. In this paper we describe, for the first time to our knowledge, the effects of the thermo-modulational nonlinearity of gold on the propagation of surface plasmon polaritons guided on gold nanowires. We introduce a novel nonlinear Schrodinger-like equation to describe pulse propagation in such nanowires, and we predict the appearance of an intense spectral red-shift caused by the delayed thermal response.

Efficient anti-Stokes generation via intermodal stimulated Raman scattering in gas-filled hollow-core PCF

B. M. Trabold, A. Abdolvand, T. G. Euser, P. St J. Russell

OPTICS EXPRESS 21 (24) 29711-29718 (2013) | Journal

A strong anti-Stokes Raman signal, from the vibrational Q(1) transition of hydrogen, is generated in gas-filled hollow-core photonic crystal fiber. To be efficient, this process requires phase-matching, which is not automatically provided since the group velocity dispersion is typically non-zero and-inside a fiber-cannot be compensated for using a crossedbeam geometry. Phase-matching can however be arranged by exploiting the different dispersion profiles of higher-order modes. We demonstrate the generation of first and second anti-Stokes signals in higher-order modes by pumping with an appropriate mixture of fundamental and a higher-order modes, synthesized using a spatial light modulator. Conversion efficiencies as high as 5.3% are achieved from the pump to the first anti-Stokes band. (C) 2013 Optical Society of America

PHz-wide Supercontinua of Nondispersing Subcycle Pulses Generated by Extreme Modulational Instability

F. Tani, J. C. Travers, P. St. J. Russell

PHYSICAL REVIEW LETTERS 111 (3) 033902 (2013) | Journal

Modulational instability (MI) of 500 fs, 5 mu J pulses, propagating in gas-filled hollow-core kagome photonic crystal fiber, is studied numerically and experimentally. By tuning the pressure and launched energy, we control the duration of the pulses emerging as a consequence of MI and hence are able to study two regimes: the classical MI case leading to few-cycle solitons of the nonlinear Schrodinger equation; and an extreme case leading to the formation of nondispersing subcycle pulses (0.5 to 2 fs) with peak intensities of order 10(14) Wcm(-2). Insight into the two regimes is obtained using a novel statistical analysis of the soliton parameters. Numerical simulations and experimental measurements show that, when a train of these pulses is generated, strong ionization of the gas occurs. This extreme MI is used to experimentally generate a high energy (> 1 mu J) and spectrally broad supercontinuum extending from the deep ultraviolet (320 nm) to the infrared (1300 nm).

Long-distance laser propulsion and deformation-monitoring of cells in optofluidic photonic crystal fiber

Sarah Unterkofler, Martin K. Garbos, Tijmen G. Euser, Philip St. J. Russell

SI 6 (9) 743-752 (2013) | Journal

We introduce a unique method for laser-propelling individual cells over distances of 10s of cm through stationary liquid in a microfluidic channel. This is achieved by using liquid-filled hollow-core photonic crystal fiber (HC-PCF). HC-PCF provides low-loss light guidance in a well-defined single mode, resulting in highly uniform optical trapping and propulsive forces in the core which at the same time acts as a microfluidic channel. Cells are trapped laterally at the center of the core, typically several microns away from the glass interface, which eliminates adherence effects and external perturbations. During propagation, the velocity of the cells is conveniently monitored using a non-imaging Doppler velocimetry technique. Dynamic changes in velocity at constant optical powers up to 350 mW indicate stress-induced changes in the shape of the cells, which is confirmed by bright-field microscopy. Our results suggest that HC-PCF will be useful as a new tool for the study of single-cell biomechanics. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tunable vacuum-UV to visible ultrafast pulse source based on gas-filled Kagome-PCF

Ka Fai Mak, John C. Travers, Philipp Hoelzer, Nicolas Y. Joly, Philip St. J. Russell

OPTICS EXPRESS 21 (9) 10942-10953 (2013) | Journal

An efficient and tunable 176-550 nm source based on the emission of resonant dispersive radiation from ultrafast solitons at 800 nm is demonstrated in a gas-filled hollow-core photonic crystal fiber (PCF). By careful optimization and appropriate choice of gas, informed by detailed numerical simulations, we show that bright, high quality, localized bands of UV light (relative widths of a few percent) can be generated at all wavelengths across this range. Pulse energies of more than 75 nJ in the deep-UV, with relative bandwidths of similar to 3%, are generated from pump pulses of a few mu J. Excellent agreement is obtained between numerical and experimental results. The effects of positive and negative axial pressure gradients are also experimentally studied, and the coherence of the deep-UV dispersive wave radiation numerically investigated. (C) 2013 Optical Society of America

Effects of squeezed-film damping on the optomechanical nonlinearity in dual-nanoweb fiber

J. R. Koehler, A. Butsch, T. G. Euser, R. E. Noskov, P. St. J. Russell

APPLIED PHYSICS LETTERS 103 (22) 221107 (2013) | Journal

The freely-suspended glass membranes in a dual-nanoweb fiber, driven at resonance by intensity-modulated light, exhibit a giant optomechanical nonlinearity. We experimentally investigate the effect of squeezed-film damping by exploring the pressure dependence of resonant frequency and mechanical quality factor. As a consequence of the unusually narrow slot between the nanowebs (22 mu m by 550nm), the gas-spring effect causes a pressure-dependent frequency shift that is similar to 15 times greater than typically measured in micro-electro-mechanical devices. When evacuated, the dual-nanoweb fiber yields a quality factor of similar to 3 600 and a resonant optomechanical nonlinear coefficient that is similar to 60 000 times larger than the Kerr effect. (C) 2013 AIP Publishing LLC.

Raman-free nonlinear optical effects in high pressure gas-filled hollow core PCF

M. Azhar, G. K. L. Wong, W. Chang, N. Y. Joly, P. St J. Russell

OPTICS EXPRESS 21 (4) 4405-4410 (2013) | Journal

The effective Kerr nonlinearity of hollow-core kagome-style photonic crystal fiber (PCF) filled with argon gas increases to similar to 15% of that of bulk silica glass when the pressure is increased from 1 to 150 bar, while the zero dispersion wavelength shifts from 300 to 900 nm. The group velocity dispersion of the system is uniquely pressure-tunable over a wide range while avoiding Raman scattering-absent in noble gases-and having an extremely high optical damage threshold. As a result, detailed and well-controlled studies of nonlinear effects can be performed, in both normal and anomalous dispersion regimes, using only a fixed-frequency pump laser. For example, the absence of Raman scattering permits clean observation, at high powers, of the interaction between a modulational instability side-band and a soliton-created dispersive wave. Excellent agreement is obtained between numerical simulations and experimental results. The system has great potential for the realization of reconfigurable supercontinuum sources, wavelength convertors and short-pulse laser systems. (C)2013 Optical Society of America

Optical Activity in Twisted Solid-Core Photonic Crystal Fibers

X. M. Xi, T. Weiss, G. K. L. Wong, F. Biancalana, S. M. Barnett, M. J. Padgett, P. St. J. Russell

PHYSICAL REVIEW LETTERS 110 (14) 143903 (2013) | Journal

In this Letter we show that, in spectral regions where there are no orbital cladding resonances to cause transmission loss, the core mode of a continuously twisted photonic crystal fiber (PCF) exhibits optical activity, and that the magnitude of the associated circular birefringence increases linearly with twist rate and is highly reproducible. In contrast to previous work on twist-induced circular birefringence, PCF has zero linear birefringence and an on-axis core, making the appearance of circular birefringence rather unexpected. A theoretical model based on symmetry properties and perturbation theory is developed and used to show that both spin and orbital angular momentum play a role in this effect. It turns out that the degenerate left-and right-circularly polarized modes of the untwisted PCF are not 100% circularly polarized but carry a small amount of orbital angular momentum caused by the interaction between the core mode and the hollow channels. DOI:10.1103/PhysRevLett.110.143903

Mode-based microparticle conveyor belt in air-filled hollow-core photonic crystal fiber

Oliver A. Schmidt, Tijmen G. Euser, Philip St. J. Russell

OPTICS EXPRESS 21 (24) 29383-29391 (2013) | Journal

We show how microparticles can be moved over long distances and precisely positioned in a low-loss air-filled hollow-core photonic crystal fiber using a coherent superposition of two co-propagating spatial modes, balanced by a backward-propagating fundamental mode. This creates a series of trapping positions spaced by half the beat-length between the forward-propagating modes (typically a fraction of a millimeter). The system allows a trapped microparticle to be moved along the fiber by continuously tuning the relative phase between the two forward-propagating modes. This mode-based optical conveyor belt combines long-range transport of microparticles with a positional accuracy of 1 mu m. The technique also has potential uses in waveguide-based optofluidic systems. (C)2013 Optical Society of America

Nonlinear optics in Xe-filled hollow-core PCF in high pressure and supercritical regimes

M. Azhar, N. Y. Joly, J. C. Travers, P. St J. Russell

APPLIED PHYSICS B-LASERS AND OPTICS 112 (4) 457-460 (2013) | Journal

Supercritical Xe at 293 K offers a Kerr nonlinearity that can exceed that of fused silica while being free of Raman scattering. It also has a much higher optical damage threshold and a transparency window that extends from the UV to the infrared. We report the observation of nonlinear phenomena, such as self-phase modulation, in hollow-core photonic crystal fiber filled with supercritical Xe. In the subcritical regime, intermodal four-wave mixing resulted in the generation of UV light in the HE12 mode. The normal dispersion of the fiber at high pressures means that spectral broadening can be clearly obtained without influence from soliton effects or material damage.

Two techniques for temporal pulse compression in gas-filled hollow-core kagome photonic crystal fiber

K. F. Mak, J. C. Travers, N. Y. Joly, A. Abdolvand, P. St. J. Russell

OPTICS LETTERS 38 (18) 3592-3595 (2013) | Journal

We demonstrate temporal pulse compression in gas-filled kagome hollow-core photonic crystal fiber (PCF) using two different approaches: fiber-mirror compression based on self-phase modulation under normal dispersion, and soliton effect self-compression under anomalous dispersion with a decreasing pressure gradient. In the first, efficient compression to near-transform-limited pulses from 103 to 10.6 fs was achieved at output energies of 10.3 mu J. In the second, compression from 24 to 6.8 fs was achieved at output energies of 6.6 mu J, also with near-transform-limited pulse shapes. The results illustrate the potential of kagome-PCF for postprocessing the output of fiber lasers. We also show that, using a negative pressure gradient, ultrashort pulses can be delivered directly into vacuum. (C) 2013 Optical Society of America

Passive mode-locking of fiber ring laser at the 337th harmonic using gigahertz acoustic core resonances

M. S. Kang, N. Y. Joly, P. St. J. Russell

OPTICS LETTERS 38 (4) 561-563 (2013)

We report the experimental demonstration of a passively mode-locked Er-doped fiber ring laser operating at the 337th harmonic (1.80 GHz) of the cavity. The laser makes use of highly efficient Raman-like optoacoustic interactions between the guided light and gigahertz acoustic resonances trapped in the micron-sized solid glass core of a photonic crystal fiber. At sufficient pump power levels the laser output locks to a repetition rate corresponding to the acoustic frequency. A stable optical pulse train with a side-mode suppression ratio higher than 45 dB was obtained at low pump powers (similar to 60 mW). (C) 2013 Optical Society of America

Nonlinear amplification of side-modes in frequency combs

R. A. Probst, T. Steinmetz, T. Wilken, H. Hundertmark, S. P. Stark, G. K. L. Wong, P. St. J. Russell, T. W. Haensch, R. Holzwarth, et al.

OPTICS EXPRESS 21 (10) 11670-11687 (2013) | Journal

We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-Perot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors. (C) 2013 Optical Society of America

Amplification of higher-order modes by stimulated Raman scattering in H-2-filled hollow-core photonic crystal fiber

B. M. Trabold, A. Abdolvand, T. G. Euser, A. M. Walser, P. St. J. Russell

OPTICS LETTERS 38 (5) 600-602 (2013)

We report a method for amplifying higher-order guided modes, synthesized with a spatial light modulator, in a hydrogen-filled hollow-core photonic crystal fiber. The gain mechanism is intermodal stimulated Raman scattering, a pump laser source in the fundamental mode providing amplification for weak higher-order seed modes at the Stokes frequency. The gain for higher-order modes up to LP31 is calculated and verified experimentally. (C) 2013 Optical Society of America

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