187 research outputs found
Four-port coupled channel-guide device based on 2D photonic crystal structure
We have fabricated and measured a four-port coupled channel-waveguide device using W1 channel waveguides oriented along ΓK directions in a two-dimensional (2D) hole-based planar photonic crystal (PhC) based on silicon-on-insulator (SOI) waveguide material, at operation wavelengths around 1550 nm. 2D FDTD simulations and experimental results are shown and compared. The structure has been designed using a mode conversion approach, combined with coupled-mode concepts. The overall length of the photonic crystal structure is typically about 39 μm and the structure has been fabricated using a combination of direct-write electron-beam lithography (EBL) and dry-etch processing. Devices were measured using a tunable laser with end-fire coupling into the planar structure
Demonstration of coherent emission from high- photonic crystal nanolasers at room temperature
We report on lasing at room temperature and at telecommunications wavelength
from photonic crystal nanocavities based on InAsP/InP quantum dots. Such laser
cavities with a small modal volume and high quality factor display a high
spontaneous emission coupling factor beta. Lasing is confirmed by measuring the
second order autocorrelation function. A smooth transition from chaotic to
coherent emission is observed, and coherent emission is obtained at 8 times the
threshold power
Study of transmission properties for waveguide bends by use of a circular photonic crystal
We study the transmission properties for the waveguide bends composed by a
circular photonic crystal. Two types (Y and U type) of the waveguide bends
utilizing the circular photonic crystal are studied. It has been shown,
compared with the conventional photonic crystal waveguide bends, transmission
properties for these bends can be significantly improved. Over a 6.4%
bandwidth, less than 1-dB loss/bend are observed. U bent waveguide, i.e.,
bend, can be easily realized with low loss using the circular photonic
crystal.Comment: 9 pages, 6 figure
Strain in a silicon-on-insulator nanostructure revealed by 3D x-ray Bragg ptychography
International audienceProgresses in the design of well-defined electronic band structure and dedicated functionalities rely on the high control of complex architectural device nano-scaled structures. This includes the challenging accurate description of strain fields in crystalline structures, which requires non invasive and three-dimensional (3D) imaging methods. Here, we demonstrate in details how x-ray Bragg ptychography can be used to quantify in 3D a displacement field in a lithographically patterned silicon-on-insulator structure. The image of the crystalline properties, which results from the phase retrieval of a coherent intensity data set, is obtained from a well-controlled optimized process, for which all steps are detailed. These results confirm the promising perspectives of 3D Bragg ptychography for the investigation of complex nano-structured crystals in material science
X-ray lensless microscopy from undersampled diffraction intensities
International audienceX-ray coherent diffraction imaging including ptychography provides the nanoscale resolved three-dimensional description of matter. The combination of these approaches to the Bragg geometry case arouses a strong interest for its capability to provide information about strain state in crystals. Among the existing approaches, ptychography is particularly appealing because it allows the investigation of extended or weakly scattering samples. Coherent diffraction imaging approaches, based on redundancy in the collected diffraction intensity data set, are highly time consuming and rely on state-of-the-art mechanical setups, both being strong limitations for a general application. We show here that these can be overcome by regularization-based inversion algorithms introducing a priori structural knowledge. This method, which can be generalized to other wavelengths or beam sources, opens new possibilities for the imaging of radiation-sensitive specimens or very large samples
Room temperature spontaneous emission enhancement from quantum dots in photonic crystal slab cavities in the telecommunications C-band
We report on the control of the spontaneous emission dynamics from InAsP
self-assembled quantum dots emitting in the telecommunications C-band and
weakly coupled to the mode of a double heterostructure cavity etched on a
suspended InP membrane at room temperature. The quality factor of the cavity
mode is 44x10^3 with an ultra-low modal volume of the order of 1.2 lambda/n)^3,
inducing an enhancement of the spontaneous emission rate of up a factor of 2.8
at 300 K
Nondestructive three-dimensional imaging of crystal strain and rotations in an extended bonded semiconductor heterostructure
International audienceWe report the 3D mapping of strain and tilts of crystal planes in an extended InP nanostructured layer bonded onto silicon, measured without sample preparation. Our approach takes advantages of 3D x-ray Bragg ptychography combined to an optimized inversion process. The excellent agreement with the sample nominal structure validates the reconstruction while the evidence of spatial fluctuations hardly observable by other means, underlines the specificities of Bragg ptychography
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