ABSTRACT
We report on the design of cavity-resonator integrated grating couplers for second-harmonic generation. The key point is that the base pattern of our grating coupler (GC) is made of two ridges with different widths (bi-atom). Thus, we reach extremely high Q-factors (above 105) with structures whose fabrication is not challenging, since the bi-atom base pattern is close to that of the surrounded distributed Bragg reflectors (DBR). Yet, the parameters of the structure have to be chosen cautiously to reduce the transition losses between each section (GC, DBR). We numerically demonstrate conversion efficiencies η of several tenths per Watt, even doubled when we include a phase-matching grating within the structuration. Such efficiencies are comparable to those obtained with waveguides and nano-resonators.
ABSTRACT
It has been shown both experimentally and numerically that the phenomenon of extraordinary transmission through subwavelength hole arrays is generally associated with a drop in transmission located very close to it. Paradoxically, this antiresonant drop occurs at the wavelength that, at first glance, should provoke a resonant excitation of a surface plasmon propagating along the metallic surface of the screen. The present paper gives a theoretical demonstration of this phenomenon, which dispels the paradox. Our theory is supported by numerical calculations.
ABSTRACT
The spatial and spectral properties of three-dimensional photonic jets are studied in a framework employing rigorous Lorentz-Mie theory. The contributions to the field from each spectral component are studied quantitatively and highlight the distinctive features of photonic jets. In particular, the role of evanescent field in photonic jets generated by small spheres is investigated. Secondary lobes in the propagative frequency distribution are also singled out as a distinctive property of photonic jets. It is shown that these differences lead to angular openings of photonic jets at least twice as small as those in comparable 'Gaussian' beams.
Subject(s)
Light , Models, Theoretical , Spectrum Analysis , Computer Simulation , Scattering, RadiationABSTRACT
We report the direct experimental observation of photonic nanojets created by single latex microspheres illuminated by a plane wave at a wavelength of 520 nm. Measurements are performed with a fast scanning confocal microscope in detection mode, where the detection pinhole defines a diffraction-limited observation volume that is scanned in three dimensions over the microsphere vicinity. From the collected stack of images, we reconstruct the full 3 dimensional photonic nanojet beam. Observations are conducted for polystyrene spheres of 1, 3 and 5 microm diameter deposited on a glass substrate, the upper medium being air or water. Experimental results are compared to calculations performed using the Mie theory. We measure nanojet sizes as small as 270 nm FWHM for a 3 microm sphere at a wavelength lambda of 520 nm. The beam keeps a subwavelength FWHM over a propagation distance of more than 3 lambda, displaying all the specificities of a photonic nanojet.
Subject(s)
Nanoparticles/chemistry , Nanotechnology/methods , Air , Equipment Design , Image Enhancement/methods , Image Processing, Computer-Assisted/methods , Lasers , Microscopy, Confocal/methods , Microspheres , Models, Theoretical , Optics and Photonics , Photons , Polystyrenes/chemistry , Scattering, Radiation , Water/chemistryABSTRACT
Fluorescence Correlation Spectroscopy is used to investigate fluorescent molecules in solution diffusing in subwavelength rectangular apertures milled in Aluminium films. This rectangular shape allows to switch between a propagating and an evanescent excitation field within the aperture, leading to a significant tunability of the observation volume. Due to the vicinity of the metal surface, the fluorophore's molecular lifetime inside the aperture appears to be dramatically reduced whatever the excitation field is set to. However, for a properly tailored evanescent excitation field within the nanoaperture, the detected fluorescence rate per molecule is significantly enhanced as compared to open solution. This suggests that the observed molecular fluorescence enhancement is mainly due to the excitation near field within the subwavelength aperture.
