P. F. Jarschel

Brillouin scattering self-cancellation

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it.

Effects of Ga+ milling on InGaAsP quantum well laser with mirrors milled by focused ion beam

InGaAsP/InP quantum well ridge waveguide lasers were fabricated for the evaluation of Ga+ focused ion beam milling of mirrors. Electrical and optical properties were investigated. A 7% increment in the threshold current, a 17% reduction in the external quantum efficiency, and a 15 nm blueshift in the emission spectrum were observed after milling as compared to the as-cleaved facet result. Annealing in inert atmosphere partially reverts these effects, resulting in a 4% increment in the threshold current, an 11% reduction in the external efficiency, and a 13 nm blueshift with the as-cleaved result. The current-voltage behavior after milling and annealing shows a very small increase in leakage current, indicating that optical damage is the main effect of the milling process.

Silicon technology compatible photonic molecules for compact optical signal processing

Photonic molecules (PMs) based on multiple inner coupled microring resonators allow to surpass the fundamental constraint between the total quality factor (QT), free spectral range (FSR), and resonator size. In this work, we use a PM that presents doublets and triplets resonance splitting, all with high QT. We demonstrate the use of the doublet splitting for 34.2 GHz signal extraction by filtering the sidebands of a modulated optical signal. We also demonstrate that very compact optical modulators operating 2.75 times beyond its resonator linewidth limit may be obtained using the PM triplet splitting, with separation of ∼55 GHz.

a-SiO x active photonic crystal resonator membrane fabricated by focused Ga + ion beam

We have fabricated thin erbium-doped amorphous silicon sub-oxide (a-SiOx) photonic crystal membrane using focused gallium ion beam (FIB). The photonic crystal is composed of a hexagonal lattice with a H1 defect supporting two quasi-doubly degenerate second order dipole states. 2-D simulation was used for the design of the structure and full 3-D FDTD (Finite-Difference Time-Domain) numerical simulations were performed for a complete analysis of the structure. The simulation predicted a quality factor for the structure of Q = 350 with a spontaneous emission enhancement of 7. Micro photoluminescence measurements showed an integrated emission intensity enhancement of ~2 times with a Q = 130. We show that the discrepancy between simulation and measurement is due to the conical shape of the photonic crystal holes and the optical losses induced by FIB milling.

Fiber taper diameter characterization using forward Brillouin scattering

We propose a fast and non-destructive method to characterize the absolute diameter and uniformity of micrometer-scale fiber tapers using a pump and probe forward Brillouin scattering setup. The fundamental torsional-radial acoustic mode supported by the wire is excited using a pulsed pump laser and oscillates at a frequency that is inversely proportional to the taper waist diameter. This standing time-varying torsional-radial wave induces polarization modulation on a probe signal, whose spectrum structure reveals the sample diameter and its non-uniformity. By comparing our results with measurements using scanning-electron microscopy, a relative deviation of 1% or less was demonstrated, and diameter non-uniformity of less than 0.5% could be detected.

Theory and Observation of the Brillouin Scattering Self-Cancellation

The Brillouin scattering self-cancellation effect arising from the interplay between the photo-elastic and moving-boundary effects is reviewed. Our recent demonstration of this effect for the fundamental Rayleigh acoustic mode in silica nanowires is also discussed.

Continuous and Pulsed THz generation with molecular gas lasers and photoconductive antennas gated by femtosecond pulses

We report THz generation based on two systems: 1) continuous‐wave (cw) laser generation in molecular gas lasers, and 2) short pulse generation in photoconductive antennas, gated by femtosecond near‐infrared Ti:sapphire lasers. With the first system, we have generated tens of monochromatic cw laser lines over the last years, extending roughly from 40 microns to several hundred microns. This is done by optical pumping of gas lasers based on polar molecules such as methanol and its isotopes. In the second system, under development, pulsed THz radiation is generated by a photoconductive antenna built in a semi‐insulating GaAs substrate excited by femtosecond pulses from a near‐infrared (800 nm) Ti:sapphire laser.