Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry

This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20 microns range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6 microns. We found propagation losses of about 16dB/mm, which are mainly due to the theoretical skin effect absorption in addition to the roughness of the waveguide metallic walls. The input and output coupling efficiency of our samples has been improved by adding tapers to minimize the impedance mismatch. A proper distinction between propagation losses and coupling losses is presented. Despite their elevate propagation losses, HMW show excellent spatial filtering capabilities in a spectral range where photonics technologies are only emerging.Comment: This paper was published in Optics Express and can be found at http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-26-1800

FWM-based wavelength conversion of 40 Gbaud PSK signals in a silicon germanium waveguide

We demonstrate four wave mixing (FWM) based wavelength conversion of 40 Gbaud differential phase shift keyed (DPSK) and quadrature phase shift keyed (QPSK) signals in a 2.5 cm long silicon germanium waveguide. For a 290 mW pump power, bit error ratio (BER) measurements show approximately a 2-dB power penalty in both cases of DPSK (measured at a BER of 10-9) and QPSK (at a BER of 10-3) signals that we examined

Mixed method versus full top-down microcosting for organ recovery cost assessment in a French hospital group

Background: The costing method used can change the results of economic evaluations. Choosing the appropriate method to assess the cost of organ recovery is an issue of considerable interest to health economists, hospitals, financial managers and policy makers in most developed countries. Objectives: The main objective of this study was to compare a mixed method, combining top-down microcosting and bottom-up microcosting versus full top-down microcosting to assess the cost of organ recovery in a French hospital group. The secondary objective was to describe the cost of kidney, liver and pancreas recovery from French databases using the mixed method. Methods: The resources consumed for each donor were identified and valued using the proposed mixed method and compared to the full top-down microcosting approach. Data on kidney, liver and pancreas recovery were collected from a medico-administrative French database for the years 2010 and 2011. Related cost data were recovered from the hospital cost accounting system database for 2010 and 2011. Statistical significance was evaluated at P < 0.05. Results: All the median costs for organ recovery differ significantly between the two costing methods (non-parametric test method; P < 0.01). Using the mixed method, the median cost for recovering kidneys was found to be €5155, liver recovery was €2528 and pancreas recovery was €1911. Using the full top-down microcosting method, median costs were found to be 21-36% lower than with the mixed method. Conclusion: The mixed method proposed appears to be a trade-off between feasibility and accuracy for the identification and valuation of cost components when calculating the cost of organ recovery in comparison to the full top-down microcosting approach

All-optical phase regeneration with record PSA extinction ratio in a low-birefringence silicon germanium waveguide

We report a low-power continuous wave-pumped phase sensitive amplifier (PSA)-based phase regenerator implemented in a passive silicon-based waveguide. A polarization assisted-PSA, consisting of two orthogonally-polarized pumps and a phase-locked signal copolarized to one of them, was implemented in a low-birefringence silicon germanium (SiGe) waveguide. The strong TE/TM modal symmetry of the waveguide and its large nonlinear coefficient enabled the achievement of an extremely large phase sensitive extinction ratio of approximately 29 dB for a total input power of only 21.3 dBm. This SiGe-based PSA was used to demonstrate phase regeneration on a 20 Gb/s differential phase-shift keying signal, thereby reducing its error vector magnitude and phase error by three and six times respectively and enabling a bit-error ratio improvement of up to 2 dB

VITRUV - Imaging close environments of stars and galaxies with the VLTI at milli-arcsec resolution

The VITRUV project has the objective to deliver milli-arcsecond spectro-images of the environment of compact sources like young stars, active galaxies and evolved stars to the community. This instrument of the VLTI second generation based on the integrated optics technology is able to combine from 4 to 8 beams from the VLT telescopes. Working primarily in the near infrared, it will provide intermediate to high spectral resolutions and eventually polarization analysis. This paper summarizes the result from the concept study led within the Joint Research Activity advanced instruments of the OPTICON program.Comment: In "The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd Generation VLTI Instrumentation", Allemagne (2005) in pres

Increasing the imaging capabilities of the VLTI using integrated optics

Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique

VSI: a milli-arcsec spectro-imager for the VLTI

VLTi Spectro-Imager (VSI) is a proposition for a second generation VLTI instrument which is aimed at providing the ESO community with the capability of performing image synthesis at milli-arcsecond angular resolution. VSI provides the VLTI with an instrument able to combine 4 telescopes in a baseline version and optionally up to 6 telescopes in the near-infrared spectral domain with moderate to high spectral resolution. The instrument contains its own fringe tracker in order to relax the constraints onto the VLTI infrastructure. VSI will do imaging at the milli-arcsecond scale with spectral resolution of: a) the close environments of young stars probing the initial conditions for planet formation; b) the surfaces of stars; c) the environment of evolved stars, stellar remnants and stellar winds, and d) the central region of active galactic nuclei and supermassive black holes. The science cases allowed us to specify the astrophysical requirements of the instrument and to define the necessary studies of the science group for phase A.Comment: 12 page

Increasing the imaging capabilities of the VLTI using integrated optics

Several scientific topics linked to the observation of extended structures around astrophysical sources (dust torus around AGN, disks around young stars, envelopes around AGBs) require imaging capability with milli-arcsecond spatial resolution. The current VLTI instruments, AMBER and MIDI, will provide in the coming months the required high angular resolution, yet without actual imaging. As a rule of thumb, the image quality accessible with an optical interferometer is directly related to the number of telescopes used simultaneously: the more the apertures, the better and the faster the reconstruction of the image. We propose an instrument concept to achieve interferometric combination of N telescopes (4 ≤ N ≤ 8) thanks to planar optics technology: 4 x 8-m telescopes in the short term and/or 8 x 1.8-m telescopes in the long term. The foreseen image reconstruction quality in the visible and/or in the near infrared will be equivalent to the one achieved with millimeter radio interferometers. Achievable spatial resolution will be better than the one foreseen with ALMA. This instrument would be able to acquire routinely 1 mas resolution images. A 13 to 20 magnitude sensitivity in spectral ranges from 0.6 to 2.5 μm is expected depending on the choice of the phase referencing guide source. High dynamic range, even on faint objects, is achievable thanks to the high accuracy provided by integrated optics for visibility amplitude and phase measurements. Based on recent validations of integrated optics presented here an imaging instrument concept can be proposed. The results obtained using the VLTI facilities give a demonstration of the potential of the proposed technique