A. Brenn

Coherent control of ultra-high frequency acoustic resonances in photonic crystal fibers

Acoustic resonances trapped within the glass core (1 mum diameter) of a photonic crystal fibre are excited electrostrictively using laser pulses. Using pulse sequences they can be coherently controlled leading to a 100-fold increase in their amplitude.

Optical excitation and characterization of gigahertz acoustic resonances in optical fiber tapers

Transverse acoustic resonances at gigahertz frequencies are excited by electrostriction in the few-micrometer-thick waists of low-loss optical fiber tapers of up to 40 cm long. A pump-probe technique is used in which the resonances are excited by a train of optical pulses and probed in a Sagnac interferometer. Strong radially symmetric acoustic resonances are observed and the dependence of their frequencies on taper thickness is investigated. Such easily reconfigurable acousto-optic interactions may have applications in the high-frequency mode locking of fiber lasers.

Influence of air-filling fraction on forward Raman-like scattering by transversely trapped acoustic resonances in photonic crystal fibers

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.

Sound, light and particles in photonic crystal fibres

Keeping light tightly guided, over metre-long distances, in both nanoscale solid glass cores and hollow cores allows enhanced and highly reproducible control of linear and nonlinear interactions between light, acoustic vibrations and trapped particles.

Optical control of transverse acoustic resonances in PCF core by multi-frequency laser light

Coherent control of forward Raman-like scattering by transverse acoustic resonances (ARs) has recently been demonstrated in small-core photonic crystal fibres (PCFs) with large air-filling fractions [1]. A sequence of precisely timed short pulses, duration less than half the AR period, is launched into the PCF. Electrostriction leads to the excitation of an AR, the duration and amplitude of which can be controlled by adjusting the pulse sequence. Strong confinement of both optical waves and ARs in the tiny PCF core enhances the efficiency of this interaction. Since the AR frequency is independent of the optical frequency, the AR can be controlled with multi-frequency laser light. Here we demonstrate two new methods of optical control of the scattering process.

Microwave sound-light interactions in nanostructured photonic crystal fibres

The interaction between light and microwave sound can be strongly enhanced by tight confinement within the wavelength-scale core of a nano-structured photonic crystal fibre. A new family of efficient acousto-optical and nonlinear-optical devices is emerging.

Forward Brillouin scattering in tapered optical fibers

We experimentally study forward Brillouin scattering in tapered fibers. Circularly symmetric acoustic phonons resonant in fibers are observed by using a novel photoacoustic measurement technique. Strong acousto-optic interaction can take place in highly tapered fibers.

Forward-Brillouin Scattering of Light at Acoustic Resonances in SF6 Glass PCF

Using a polarization-spectroscopy technique, we observe spontaneous forward Brillouin scattering of light in birefringent lead-silicate PCF. The higher stress-optical coefficient of the glass means that signals can be detected even in short lengths of fiber.

Influence of air-filling fraction on forward Brillouin scattering in highly birefringent PCF

In this paper, we report on the influence of cladding air-filling fraction on the spontaneous forward Brillouin spectrum in birefringent PCFs. We focused our investigation on a range of birefringent fibers drawn from the same fiber perform and showing roughly the same structure, but with different cladding air-filling fractions. To measure the spontaneous forward Brillouin scattering spectrum we launched light from a linearly polarized CW laser at 45deg with respect to the birefringence axis into 10 m long fibers. The polarization modulation induced by thermally excited phonons was measured using a polarization spectroscopy technique In addition to the experiments, we modelled the optical and acoustic modes of such fibers using a full-vectorial finite element approach. The ability to engineer the forward scattering spectrum by altering the cladding structure is important for the design of efficient acousto-optic devices and in reducing low frequency noise in quantum optics experiments.

Controlling Acousto-Optic Interactions in Photonic Crystal Fiber with Sub-Wavelength Core-Hole

The quasi-Raman interaction between confined acoustic phonons and light in PCF is strongly altered by the introduction of a sub-wavelength hole running axially through the core. Coupling calculations and forward scattering spectra illustrate the effect.