Yovanny A. V. Espinel

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.

Photonic-crystal fiber-based pressure sensor for dual environment monitoring.

In this paper the development of a side-hole photonic-crystal fiber (SH-PCF) pressure sensor for dual environment monitoring is reported. SH-PCF properties (phase and group birefringence, sensitivity to pressure variations) are measured and compared to simulated data. In order to probe two environments, two sections of the SH-PCF with different lengths are spliced and set in a Solc filter-like configuration. This setup allows obtaining the individual responses of the first and second fiber independently, which is useful for a space-multiplexed measurement. As the employed fiber is sensitive to pressure variations, we report the use of this configuration for dual environment pressure sensing.

Brillouin Optomechanics in Coupled Silicon Microcavities

The simultaneous control of optical and mechanical waves has enabled a range of fundamental and technological breakthroughs, from the demonstration of ultra-stable frequency reference devices, to the exploration of the quantum-classical boundaries in optomechanical laser-cooling experiments. More recently, such an optomechanical interaction has been observed in integrated nano-waveguides and microcavities in the Brillouin regime, where short-wavelength mechanical modes scatter light at several GHz. Here we engineer coupled optical microcavities to enable a low threshold excitation of mechanical travelling-wave modes through backward stimulated Brillouin scattering. Exploring the backward scattering we propose silicon microcavity designs based on laterally coupled single and double-layer cavities, the proposed structures enable optomechanical coupling with very high frequency modes (11 to 25 GHz) and large optomechanical coupling rates (g0/2π) from 50 kHz to 90 kHz.

Tunable Single-Polarization Single-Mode Microstructured Polymer Optical Fiber

A new procedure to obtain single-polarization single-mode polymeric optical fibers is reported. The selective polarization confinement loss mechanism is obtained by applying external hydrostatic pressure in a specially designed side-hole microstructured polymer optical fiber. It is shown that, at λ = 588 nm, pressure around 380 bar allows inducing confinement loss as high as 35 dB/m for one polarization state while the other is guided with low loss (3 ×10-3 dB/m). The loss mechanism is shown to be related to coupling between the fundamental core modes and the cladding modes of the pressurized fiber. Finally, the possibility of tuning the single-polarization single-mode state with the input wavelength with fixed pressure or by introducing small changes in the inner ring of holes of the fiber cross section is presented.

Efficient anchor loss suppression in coupled near-field optomechanical resonators

Elastic dissipation through radiation towards the substrate is a major loss channel in micro- and nanomechanical resonators. Engineering the coupling of these resonators with optical cavities further complicates and constrains the design of low-loss optomechanical devices. In this work we rely on the coherent cancellation of mechanical radiation to demonstrate material and surface absorption limited silicon near-field optomechanical resonators oscillating at tens of MHz. The effectiveness of our dissipation suppression scheme is investigated at room and cryogenic temperatures. While at room temperature we can reach a maximum quality factor of 7.61k (fQ-product of the order of 1011 Hz), at 22 K the quality factor increases to 37k, resulting in a fQ-product of 2 × 1012 Hz.

Pressure Induced Single-Polarization Single-Mode Microstructured Polymer Optical Fiber

We report a new procedure to obtain single-polarization single-mode polymeric optical fibers. The state is induced by applying hydrostatic pressure and is shown to be related with coupling between core and cladding modes.

Side-hole photonic crystal fibers

A new class of photonic crystal fiber, namely side-hole PCF, is analyzed and demonstrated. The presence of massive holes surrounding a microstructured cladding allows the realization of devices based on PCFs with integrated electrodes and fibers with high pressure sensitivity. The side holes can also be used to produce ultrahigh birefringence fibers based on squeezed-lattice structures and tunable single-polarization single-mode polymeric microstructured fibers.

Hybrid Confinement Of Optical And Mechanical Modes In A Bullseye Optomechanical Resonator

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and applied aspects of the interaction between mechanical and optical waves. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Simulations foresee an optomechanical coupling rate g0 reaching 2π × 100 kHz for mechanical frequencies around 5 GHz as well as anchor loss suppression of 60 dB. Our device design is not limited by unique material properties and could be easily adapted to allow for large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our devices were fabricated in a commercial silicon photonics facility, demonstrating g0/2π = 23 kHz for mechanical modes with frequencies around 2 GHz and mechanical Q-factors as high as 2300 at room temperature, also showing that our approach can be easily scalable and useful as a new platform for multimode optomechanics.

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.

Brillouin Scattering in Silicon Slot Waveguides

Here we numerically investigate Brillouin scattering (BS) in a silicon slot waveguide. We show that BS is strongly influenced by the boundary effects, instead of the usual photo-elastic effect leading to the interaction with distinct mechanical modes.