Philippe Hamel

Time-Wavelength Reflectance Maps of Photonic Crystal Waveguides: A New View on Disorder-Induced Scattering

We investigate the impact of disorder on the propagation of photonic crystal waveguide modes using phase-sensitive optical low-coherence reflectometry.Combined with a suitable numerical processing, this technique reveals a considerable amount of information that we cast as time-wavelength reflectance maps. By comparing measurements on different samples, we easily identify inter-mode scattering and propagation losses mediated by slow leaky modes. We also characterize the dispersive behaviour of point defects. Our results verify previous theoretical predictions about the general group velocity scaling of losses and the dominant role of backscattering.

Optical low-coherence reflectometry for complete chromatic dispersion characterization of few-mode fibers

A phase-sensitive optical low-coherence reflectometry (OLCR) technique is demonstrated to simultaneously measure the absolute chromatic dispersion values of each guided LP mode of a few-mode fiber. We show that the OLCR technique requires only short samples of fiber (<1 m) and has no need for high-ratio mode converters to reach an accurate wavelength-dependent group delay evolution of every mode. As an example we present for the first time to our knowledge a direct and complete analysis of few-mode fibers with high, low, positive, and negative modal dispersion values, leading to chromatic dispersion parameters in good agreement with theoretical predictions.

Investigation of group delay, loss, and disorder in a photonic crystal waveguide by low-coherence reflectometry

The authors propose highly resolved optical low-coherence reflectometry for investigating low-loss photonic crystal slab waveguides. This technique allows a fast, reliable, and straightforward measurement of the group delay and propagation losses for both TE and TM polarizations. The agreement with theory is very good. These measurements reveal effects related to structural disorder. The versatility and deep physical insight of this measurement technique will play a key role in the study of slow-light devices such as photonic crystal waveguides.

Time-Frequency Analysis for an Efficient Detection and Localization of Side-Coupled Cavities in Real Photonic Crystals

We propose and demonstrate here the high efficiency of concurrent time and frequency analysis to detect and unambiguously identify the coupled cavities in real photonic crystals containing imperfections and/or process-induced disorder. This procedure when applied to reflectograms recorded using phase-sensitive optical low-coherence reflectometry allows a straightforward and complete assessment of cavities (spectral and spatial localization in addition to photon lifetime) over a wide spectral range. Considering such a reflectogram (recorded in ~ 2 s), we show that this procedure greatly eases the evaluation of cavities under guiding conditions in real photonic crystals by discriminating their signature from the in-plane scattering induced by disorder.

Investigation of group delay and disorder in a Photonic Crystal Waveguide using Low-Coherence Reflectometry

The optical low-coherence reflectometry technique is proposed for investigating photonic crystal slab waveguides. We show its ability of providing a direct measurement of the group delay and highlight the structural disorder resulting into TE/TM scattering.

Chromatic dispersion measurements of few-mode fibres using OLCR technique

We present a complete dispersion characterization of few-mode fibres using low-coherence reflectometry. Several LP modes with highly different propagation properties are characterized simultaneously in a single measurement without the need for spatial mode transformation.

Structural disorder induced polarization and mode scrambling in Photonic Crystals

The authors investigates the impact of structural disorder in line-defect photonic crystal waveguides through optical low-coherence reflectometry (OLCR). The potential of photonic crystal waveguides for dispersion engineering and, in particular, controlling the propagation delay was realised very early, however, the practical implementation of this beautiful concept had been hampered by severe technological and also theoretical difficulties, leading to unacceptable propagation losses. More recently, the proper design of line-defect waveguides on 2D Photonic Crystal slabs allowed an impressive reduction of propagation loss down to less than 10dB/cm, thus opening new perspectives in the field of optical processing. However, fabrication defects and, in particular, structural disorder and roughness still have a strong impact on propagation as the group velocity is decreased. Therefore, understanding disorder appears as a critical task in view of implementation of slow-light with photonic crystal technology.

Modal Analysis and Spatial Dispersion Evolution in PCF Fibres

We report spatial evolution of chromatic dispersion along a full span of microstructured fibre. For the first time, dispersion characterization of different guided modes in good agreement with modelling is reported, thanks to the OLCR technique.