Philippe Giaccari

Graph colouring approaches for a satellite range scheduling problem

A goal of this paper is to efficiently adapt the best ingredients of the graph colouring techniques to an NP-hard satellite range scheduling problem, called MuRRSP. We propose two new heuristics for the MuRRSP, where as many jobs as possible have to be scheduled on several resources, while respecting time and capacity constraints. In the permutation solution space, which is widely used by other researchers, a solution is represented by a permutation of the jobs, and a schedule builder is needed to generate and evaluate a feasible schedule from the permutation. On the contrary, our heuristics are based on the solution space which contains all the feasible schedules. Based on the similarities between the graph colouring problem and the MuRRSP, we show that the latter solution space has significant advantages. A tabu search and an adaptive memory algorithms are designed to tackle the MuRRSP. These heuristics are derived from efficient graph colouring methods. Numerical experiments, performed on large, realistic, and challenging instances, showed that our heuristics are very competitive, robust, and outperform algorithms based on the permutation solution space.

Active Fourier-transform spectroscopy combining the direct RF beating of two fiber-based mode-locked lasers with a novel referencing method.

A new approach is described to compensate the variations induced by laser frequency instabilities in the recently demonstrated Fourier transform spectroscopy that is based on the RF beating spectra of two frequency combs generated by mode-locked lasers. The proposed method extracts the mutual fluctuations of the lasers by monitoring the beating signal for two known optical frequencies. From this information, a phase correction and a new time grid are determined that allow the full correction of the measured interferograms. A complete mathematical description of the new active spectroscopy method is provided. An implementation with fiberbased mode-locked lasers is also demonstrated and combined with the correction method a resolution of 0.067 cm(-1) (2 GHz) is reported. The ability to use slightly varying and inexpensive frequency comb sources is a significant improvement compared to previous systems that were limited to controlled environment and showed reduced spectral resolution. The fast measurement rate inherent to the RF beating principle and the ease of use brought by the correction method opens the venue to many applications.

All-fiber comb filter with tunable free spectral range

We demonstrate a new class of all-fiber frequency comb filter that exhibits unprecedented capabilities for tuning the combs free spectral range (FSR). The filter exploits a spectral Talbot-like effect in a sampled chirped fiber Bragg grating. The FSR is tailored by application of a linear strain gradient to modify the relative phase between the samples. The FSR can be tuned in discrete steps that correspond to the nominal value of the FSR of the sampled unchirped grating divided by integer factors. In this demonstration the FSR is varied from 51 to 3.9 GHz.

Hybrid sampling approach for imaging Fourier-transform spectrometry

A new approach to interferogram sampling is demonstrated for Fourier-transform spectrometry. Sampling of the infrared channel is triggered at equidistant optical path differences while samples are time-referenced with a high-resolution digital clock. This hybrid method exploits the advantages of both time and position-sampling techniques. It minimizes the dataload while allowing a postcorrection scheme to remove sampling errors. It is therefore highly adapted to imaging spectrometers designed for massively parallel spatial sampling. Also, this technique is particularly interesting for spectrometers equipped with an integrating detector, such as a CCD camera, since it can account for the inevitable delay caused by camera integration.

Erbium Amplifier Dynamics in Wireless Analog Optical Links With Modulator Bias Optimization

Modulator bias optimization is a technique used to improve the transmitted radio-frequency power of amplified analog optical links. However, when bias optimization is used, the mean optical power at the modulator output is dependent on the amplitude of the modulation signal. In this letter, we show how fluctuations of the modulation signal power, in conjunction with the dynamic behavior of the erbium optical amplifier, can deteriorate the transmission of data frames compliant to the 802.11 a/g IEEE protocol. Optical and electrical compensating methods, based on mean power clamping at the modulator output, are proposed, and their efficiency in restoring a high-quality transmission is demonstrated

Lippmann waveguide spectrometer with enhanced throughput and bandwidth for space and commercial applications

This article presents an innovative high spectral resolution waveguide spectrometer, from the concept to the prototype demonstration and the test results. The main goal is to build the smallest possible Fourier transform spectrometer (FTS) with state of the art technology. This waveguide FTS takes advantage of a customized pattern of nano-samplers fabricated on the surface of a planar waveguide that allows the increase of the measurement points necessary for increasing the spectral bandwidth of the FTS in a fully static way. The use of a planar waveguide on the other hand allows enhancing the throughput in a waveguide spectrometer compared to the conventional devices made of single-mode waveguides. A prototype is made in silicon oxynitride/silicon dioxide technology and characterized in the visible range. This waveguide spectrometer shows a nominal bandwidth of 256~nm at a central wavelength of 633~nm thanks to a custom pattern of nanodisks providing a μm sampling interval. The implementation of this innovative waveguide FTS for a real-case scenario is explored and further development of such device for the imaging FTS application is discussed.

Micrometer-Scale Measurement of the Local Bragg Wavelength of Fiber Bragg Gratings

The Bragg wavelength distribution inside fiber Bragg gratings is determined with 5 mum -spatial resolution using optical low coherence reflectometry. Chirp distributions are observed along 20 mum long gratings written with UV beams of varying divergence