Precise balancing of viscous and radiation forces on a particle in
liquid-filled photonic bandgap fiber
T. G. Euser,
M. K. Garbos,
J. S. Y. Chen,
P. St. J. Russell
OPTICS LETTERS
34
(23)
3674-3676
(2009)
A great challenge in microfluidics is the precise control of laser radiation forces acting on single particles or cells, while allowing monitoring of their optical and chemical properties. We show that, in the liquid-filled hollow core of a single-mode photonic crystal fiber, a micrometer-sized particle can be held stably against a fluidic counterflow using radiation pressure and can be moved to and fro (over tens of centimeters) by ramping the laser power up and down. Accurate studies of the microfluidic drag forces become possible, because the particle is trapped in the center of the single guided optical mode, resulting in highly reproducible radiation forces. The counterflowing liquid can be loaded with sequences of chemicals in precisely controlled concentrations and doses, making possible studies of single particles, vesicles, or cells. (C) 2009 Optical Society of America
Influence of air-filling fraction on forward Raman-like scattering by
transversely trapped acoustic resonances in photonic crystal fibers
A. Brenn,
G. S. Wiederhecker,
M. S. Kang,
H. Hundertmark,
N. Joly,
P. St. J. Russell
JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS
26
(8)
1641-1648
(2009)
Raman-like forward scattering by acoustic phonons transversely trapped in birefringent silica-air photonic crystal fibers is studied. As the air-filling fraction increases, core-confined acoustic resonances become increasingly apparent at higher frequencies (> 1.1 GHz), while the number of cladding-confined acoustic modes involved in scattering falls. Two main types of scattering are observed: intramodal (scattering to new frequencies within the same optical mode) and intermodal (frequency-shifted scattering to a different optical mode). It is shown that the twofold symmetric microstructure in a birefringent fiber causes strongly polarization-dependent intramodal scattering. Good agreement is obtained between the experimental measurements and numerical solutions of both the acoustic and electromagnetic wave equations by using a full-vectorial finite-element approach. Phononic bandgaps are found to play a significant role at higher air-filling fractions, leading to the appearance of additional bands in the scattering spectrum. (C) 2009 Optical Society of America
Tightly trapped acoustic phonons in photonic crystal fibres as highly
nonlinear artificial Raman oscillators
M. S. Kang,
A. Nazarkin,
A. Brenn,
P. St. J. Russell
Interactions between light and hypersonic waves can be enhanced by tight field confinement, as shown in periodically structured materials(1), microcavities(2), micromechanical resonators(3) and photonic crystal fibres(4-6) (PCFs). There are many examples of weak sound-light interactions, for example, guided acoustic-wave Brillouin scattering in conventional optical fibres(7). This forward-scattering effect results from the interaction of core-guided light with acoustic resonances of the entire fibre cross-section, and is viewed as a noise source in quantum-optics experiments(8). Here, we report the observation of strongly nonlinear forward scattering of laser light by gigahertz acoustic vibrations, tightly trapped together in the small core of a silica-air PCF. Bouncing to and fro across the core at close to 90 degrees to the fibre axis, the acoustic waves form optical-phonon-like modes with a flat dispersion curve and a distinct cutoff frequency Omega(a). This ensures automatic phase-matching to the guided optical mode so that, on pumping with a dual-frequency laser source tuned to Omega(a), multiple optical side bands are generated, spaced by Omega(a). The number of strong side bands in this Raman-like process increases with pump power. The results point to a new class of designable nonlinear optical device with applications in, for example, pulse synthesis, frequency comb generation for telecommunications and fibre laser mode-locking.
Solitary Pulse Generation by Backward Raman Scattering in H-2-Filled
Photonic Crystal Fibers
A. Abdolvand,
A. Nazarkin,
A. V. Chugreev,
C. F. Kaminski,
P. St. J. Russell
Using a hydrogen-filled hollow-core photonic crystal fiber as a nonlinear optical gas cell, we study amplification of ns-laser pulses by backward rotational Raman scattering. We find that the amplification process has two characteristic stages. Initially, the pulse energy grows and its duration shortens due to gain saturation at the trailing edge of the pulse. This phase is followed by formation of a symmetric pulse with a duration significantly shorter than the phase relaxation time of the Raman transition. Stabilization of the Stokes pulse profile to a solitonlike hyperbolic secant shape occurs as a result of nonlinear amplification at its front edge and nonlinear absorption at its trailing edge (caused by energy conversion back to the pump field), leading to a reshaped pulse envelope that travels at superluminal velocity.
Optimizing anti-Stokes Raman scattering in gas-filled hollow-core
photonic crystal fibers
Anti-Stokes Raman scattering in gas-filled hollow-core photonic crystal fibers is discussed. It is shown that the efficient anti-Stokes generation observed under conditions of significant wave mismatch is caused by phase locking of the interacting fields. This leads to the establishment of a phase difference that is independent of the optical path. An optimization technique, based on the adjustment of the wave mismatch along a gas-filled hollow fiber using pressure control, is proposed. Anti-Stokes conversion efficiencies close to the theoretical maximum of 50% are predicted.
All-solid bandgap guiding in tellurite-filled silica photonic crystal
fibers
Markus A. Schmidt,
Nicolai Granzow,
Ning Da,
Mingying Peng,
Lothar Wondraczek,
Philip St. J. Russell
OPTICS LETTERS
34
(13)
1946-1948
(2009)
We report all-solid bandgap-guiding fibers formed by pumping molten tellurite glass into silica-air photonic crystal fiber at high pressure. The spectral positions of the guidance bands agree well with multipole simulations and bandgap calculations. The micrometer-diameter tellurite strands are found to contain microheterogeneities (most probably originating from devitrification), which increase the fiber attenuation, although no evidence of crystallization is seen in the bulk tellurite glass. The technique offers a potential route to employing difficult-to-handle glasses, or glasses unsuitable for fiber drawing, in fiber-based amplifiers, modulators, filters, and nonlinear devices. (C) 2009 Optical Society of America
Manipulation of coherent Stokes light by transient stimulated Raman
scattering in gas filled hollow-core PCF
A. V. Chugreev,
A. Nazarkin,
A. Abdolvand,
J. Nold,
A. Podlipensky,
P. St. J. Russell
Transient stimulated Raman scattering is investigated in methane-filled hollow-core photonic crystal fiber. Using frequency-chirped ps-pulses at 1.06 mu m as pump and tunable CW-radiation as Stokes seed, the vibrational excitation of the CH4 molecules can be controlled on the sub T-2 time-scale. In this way the generated Stokes pulse can be phase-locked to the pump pulse and its spectrum manipulated. (c) 2009 Optical Society of America
Broadband sensitive pump-probe setup for ultrafast optical switching of
photonic nanostructures and semiconductors
Tijmen G. Euser,
Philip J. Harding,
Willem L. Vos
REVIEW OF SCIENTIFIC INSTRUMENTS
80
(7)
073104
(2009)
| Journal
We describe an ultrafast time resolved pump-probe spectroscopy setup aimed at studying the switching of nanophotonic structures. Both femtosecond pump and probe pulses can be independently tuned over broad frequency range between 3850 and 21 050 cm(-1). A broad pump scan range allows a large optical penetration depth, while a broad probe scan range is crucial to study strongly photonic crystals. A new data acquisition method allows for sensitive pump-probe measurements, and corrects for fluctuations in probe intensity and pump stray light. We observe a tenfold improvement of the precision of the setup compared to laser fluctuations, allowing a measurement accuracy of better than Delta R=0.07% in a 1 s measurement time. Demonstrations of the improved technique are presented for a bulk Si wafer, a three-dimensional Si inverse opal photonic bandgap crystal, and z-scan measurements of the two-photon absorption coefficient of Si, GaAs, and the three-photon absorption coefficient of GaP in the infrared wavelength range.
Octave-spanning supercontinuum generated in SF6-glass PCF by a 1060 nm
mode-locked fibre laser delivering 20 pJ per pulse
H. Hundertmark,
S. Rammler,
T. Wilken,
R. Holzwarth,
T. W. Haensch,
P. St. J. Russell
We report the generation of an octave-spanning supercontinuum in SF6-glass photonic crystal fiber using a diode-pumped passively modelocked fs Yb-fiber laser oscillating at 1060 nm. The pulses (energy up to 500 pJ and duration 60 fs) were launched into a 4 cm length of PCF (core diameter 1.7 mu m and zero-dispersion wavelength similar to 1060 nm). Less than 20 pJ of launched pulse energy was sufficient to generate a supercontinuum from 600 nm to 1450 nm, which represents the lowest energy so far reported for generation of an octave-spanning supercontinuum from a 1 mu m pump. Since the laser pulse energy scales inversely with the repetition rate, highly compact and efficient sources based on SF6-glass PCF are likely to be especially useful for efficient spectral broadening at high repetition rates (several GHz), such as those needed for the precise calibration of astronomical spectrographs, where a frequency comb spacing > 10 GHz is required for the best performance. (C) 2009 Optical Society of America
CO2 laser writing of long-period fiber grating in photonic crystal fiber
under tension
We demonstrate that the efficiency of CO2 laser writing of longperiod fiber gratings in a solid-core photonic crystal fiber (PCF) can be enhanced greatly by applying tension to the fiber during the writing process through the mechanism of frozen-in viscoelasticity. Using this mechanism, we are able to write strong gratings in PCFs with a dosage of CO2 laser radiation low enough not to cause any significant fiber structure deformation. (C) 2009 Optical Society of America
Kontakt
Bitte richten Sie forschungsbezogene Anfragen an philip.russell@mpl.mpg.de und allgemeine Anfragen an Bettina Schwender:
Max-Planck-Institut für die Physik des Lichts Staudtstr. 2 91058 Erlangen
