Renaud Gabet

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.

Self-referenced and single-ended method to measure Brillouin gain in monomode optical fibers

We present a new self-referenced and single-ended method to measure the Brillouin-gain coefficient in monomode optical fibers accurately with high reliability. Our comparative measurements on several different fibers show that a fiber with a smaller optical effective mode area can nevertheless have a higher Brillouin threshold, thus confirming the significance of acousto-optic effective mode area.

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.

Importance of residual stresses in the Brillouin gain spectrum of single mode optical fibers

Residual stresses inside optical fibers can impact significantly on Brillouin gain spectrum. Based on a 2D-FEM modeling, theoretical results are compared with Brillouin gain measurements for fibers from a same preform with different draw tensions.

All-Optical Packet-Switching Decoder Design and Demonstration at 10 Gb/s

A 3 times 8 all-optical decoder based on cross-polarization modulation in semiconductor optical amplifiers is demonstrated for the first time to our knowledge. The design requires a single active optical device per output. Experimental results are shown for return-to-zero modulated 10-Gb/s signals. Applications include label processing in optical packet switched optical networks

Complete Dispersion Characterization of Few Mode Fibers by OLCI Technique

Few-mode optical fibers (FMFs) are useful for many applications such as space-division-multiplexing (SDM), high laser power generation and transport, dispersion compensation, etc. The emergence of SDM induces considerable requirements in terms of FMF characterization (chromatic dispersion, birefringence, modal content, bending losses). All LP modes of an FMF can be simultaneously characterized using phase-sensitive optical low-coherence interferometry. The differential modal group delay and absolute chromatic dispersion values of each mode are retrieved from a single measurement without spatial mode transformers.

Performance analysis of quadratic congruence codes using superstructured fiber Bragg gratings for a flexible data rate coherent DS-OCDMA system

The performance of a coherent direct sequence optical code division multiple access (DS-OCDMA) system using quadratic congruence codes implemented with superstructured fiber Bragg gratings is experimentally analyzed. We point out that nonperiodic and sparse quadratic congruence codes reduce multipath beat noise and intersymbol interference, respectively. These two properties of the structure of the quadratic congruence codes are shown to improve the bit-error-rate (BER) performance of the coherent system. As a result, we demonstrate that the performance enhancement of the coherent DS-OCDMA system allows the data bit rate of the system to be varied from 1 Gbit/sto2.5 Gbits/s and the receiver bandwidth to be decreased from 15 GHzto5 GHz respecting the low-cost requirement of the optical access network. These data bit rate and receiver bandwidth performances are achieved with moderate BER penalty.

Pulsed laser source coherence time impairments in a direct detection DS-OCDMA system

We investigate the impact of laser source coherence time on bit error rate (BER) and autocorrelation function performances of a direct sequence OCDMA system. Congruence codes are suggested to reduce the observed coherence effects.

Microbending behavior of large-effective-area Bragg fibers

We use a phase-sensitive optical low-coherence interferometry technique and camera imaging to identify microbend-induced mode couplings in Bragg fibers. Results show the importance of the quality of fabrication of Bragg fibers on their modal content when they are subject to microbends. Design strategies to improve the microbending robustness are identified.