Daniel Puerto

A one-dimensional optomechanical crystal with a complete phononic band gap

Recent years have witnessed the boom of cavity optomechanics, which exploits the confinement and coupling of optical and mechanical waves at the nanoscale. Among their physical implementations, optomechanical (OM) crystals built on semiconductor slabs enable the integration and manipulation of multiple OM elements in a single chip and provide gigahertz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and gigahertz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap, which should enable longer lifetimes, as acoustic leakage is minimized. Here we demonstrate the excitation of acoustic modes in a one-dimensional OM crystal properly designed to display a full phononic bandgap for acoustic modes at 4 GHz. The modes inside the complete bandgap are designed to have high-mechanical Q-factors, limit clamping losses and be invariant to fabrication imperfections.

Sorting linearly polarized photons with a single scatterer

Intuitively, light impinging on a spatially mirror-symmetric object will be scattered equally into mirror-symmetric directions. This intuition can fail at the nanoscale if the polarization of the incoming light is properly tailored, as long as mirror symmetry is broken in the axes perpendicular to both the incident wave vector and the remaining mirror-symmetric direction. The unidirectional excitation of plasmonic modes using circularly polarized light has been recently demonstrated. Here, we generalize this concept and show that linearly polarized photons impinging on a single spatially symmetric scatterer created in a silicon waveguide are guided into a certain direction of the waveguide depending exclusively on their polarization angle and the structure asymmetry. Our work broadens the scope of polarization-induced directionality beyond plasmonics, with applications in polarization (de)multiplexing, unidirectional coupling, directional switching, radiation polarization control, and polarization-encoded quantum information processing in photonic integrated circuits.

Universal method for the synthesis of arbitrary polarization states radiated by a nanoantenna

Optical nanoantennas efficiently convert confined optical energy into free-space radiation. The polarization of the emitted radiation depends mainly on nanoantenna shape, so it becomes extremely difficult to manipulate it unless the nanostructure is physically altered. Here, a simple way is demonstrated to synthetize the polarization of the radiation emitted by a single nanoantenna so that every point on the Poincare sphere becomes attainable. The nanoantenna consists of a single scatterer created on a dielectric waveguide and fed from its both sides so that the polarization of the emitted optical radiation is controlled by the amplitude and phase of the feeding signals. The nanoantenna is created on a silicon chip using standard top-down nanofabrication tools, but the method is universal and can be applied to other materials, wavelengths and technologies. This work will open the way towards the synthesis and control of arbitrary polarization states in nano-optics.

Honeycomb Photonic Crystal Waveguides in a Suspended Silicon Slab

We report experimental evidence of light guiding at telecommunication wavelengths along line-defect honeycomb-lattice photonic crystal waveguides created in suspended silicon slabs. Numerical results show that the guided bands correspond to modes below the cladding light line so they are inherently lossless, although the measurements show quite high losses owing to fabrication imperfections. Honeycomb photonic crystals are a suitable platform for confining light and sound in nanoscale waveguides.

Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects

We report on the modification of the optical and mechanical properties of a silicon 1D optomechanical crystal cavity due to thermo-optic effects in a high phonon/photon population regime. The cavity heats up due to light absorption in a way that shifts the optical modes towards longer wavelengths and the mechanical modes to lower frequencies. By combining the experimental optical results with finite-difference time-domain simulations, we establish a direct relation between the observed wavelength drift and the actual effective temperature increase of the cavity. By assuming that the Youngs modulus decreases accordingly to the temperature increase, we find a good agreement between the mechanical mode drift predicted using a finite element method and the experimental one.

A PhoXonic crystal: Photonic and phononic bandgaps in a 1D optomechanical crystal

Recent years have witnessed the increase of interest in cavity optomechanics, which exploits the confinement and coupling of optical waves and mechanical vibrations at the nanoscale. Amongst the different physical implementations, optomechanical (OM) crystals built on semiconductor slabs would enable the integration and manipulation of multiple OM elements in a single chip and provide GHz phonons suitable for coherent phonon manipulation. Different demonstrations of coupling of infrared photons and GHz phonons in cavities created by inserting defects on OM crystals have been performed. However, the considered structures do not show a complete phononic bandgap at the frequencies of interest, which in principle should allow longer dephasing time, since acoustic leakage is minimized. In this work we discuss the excitation of acoustic modes in a 1D OM crystal properly designed to display a full phononic bandgap for acoustic modes at about 4 GHz. The confined phonons have an OM coupling ranging from the kHz to the MHz range with contributions from moving interfaces and the photoelastic effect that add constructively for many of them. The modes inside the complete bandgap are designed to have high mechanical Q factors and invariant to fabrication imperfections, what would allow several coherent phonon manipulations at moderate cryogenic temperatures.

Resolving light spin with a silicon microdisk nanoantenna

We demonstrate a non-chiral photonic nanostructure that distinguishes the handedness of circularly polarized light. The device - a silicon microdisk coupled to two waveguides - drives photons with opposite spins towards different output waveguides with contrast ratios over 18 dB.