Catherine Lepers

Linear and nonlinear optical properties of N-4-nitrophenyl L-prolinol single crystals

Abstract N-4-nitrophenyl-(L)-prolinol (NPP), an organic molecular crystal with application in quadratic nonlinear optics, has been characterized in terms of its absorption spectrum and refractive indices. A strong birefringence, with nχ−nz as high as 0.78 at 53 2 nm, is reported. All collinear phase-matching (PM) configurations in the principal planes for second harmonic generation (SHG) are subsequently identified; three of them correspond to effective nonlinear coefficients deff larger than 50 pm V-1 for SHG at 1.06 μm, with a factor of merit reaching 834 pm V-1. The most efficient PM configurations for near infrared SHG are close to normal incidence with respect to the cleavage plane of the crystal, allowing to take full advantage of the main molecular hyper-polarizability coefficient without projection factors. A θ-noncritical configuration at 1.15 μm corresponds to a deff value of 70 pm V-1, which remains, to the best of our knowledge, unsurpassed by other organic as well as inorganic crystals in the same spectral range.

Phase-sensitive optical low-coherence reflectometry technique applied to the characterization of photonic crystal fiber properties.

Localized measurements of group-velocity dispersion and birefringence of photonic crystal fibers are achieved with a phase-sensitive optical low-coherence reflectometry technique. This technique is efficient for fiber samples no longer than 1 m. Theoretical simulations are in good agreement with experimental results. As a result, the stress-induced birefringence proves to be at most 1 order of magnitude below the geometrical-shape birefringence.

DS-OCDMA encoder/decoder performance analysis using optical low-coherence reflectometry

Direct-sequence optical code-division multiple-access (DS-OCDMA) encoder/decoder based on sampled fiber Bragg gratings (S-FBGs) is characterized using phase-sensitive optical low-coherence reflectometry (OLCR). The OLCR technique allows localized measurements of FBG wavelength and physical length inside one S-FBG. This paper shows how the discrepancies between specifications and measurements of the different FBGs have some impact on spectral and temporal pulse responses of the OCDMA encoder/decoder. The FBG physical lengths lower than the specified ones are shown to affect the mean optical power reflected by the OCDMA encoder/decoder. The FBG wavelengths that are detuned from each other induce some modulations of S-FBG reflectivity resulting in encoder/decoder sensitivity to laser wavelength drift of the OCDMA system. Finally, highlighted by this OLCR study, some solutions to overcome limitations in performance with the S-FBG technology are suggested

Spatio-temporal dynamics of a weakly multimode CO2 laser

Abstract The behavior of a slightly asymmetric weakly multimode CO 2 laser is studied experimentally and compared with that of perfectly cylindrically symmetrical lasers. It is found that in most cases, the system symmetry breaking destroys the vortices, although it appears that for a very small loss of symmetry, the behavior of the laser remains symmetrical.

Source coherence impairments in a direct detection direct sequence optical code-division multiple-access system.

We demonstrate that direct sequence optical code- division multiple-access (DS-OCDMA) encoders and decoders using sampled fiber Bragg gratings (S-FBGs) behave as multipath interferometers. In that case, chip pulses of the prime sequence codes generated by spreading in time-coherent data pulses can result from multiple reflections in the interferometers that can superimpose within a chip time duration. We show that the autocorrelation function has to be considered as the sum of complex amplitudes of the combined chip as the laser source coherence time is much greater than the integration time of the photodetector. To reduce the sensitivity of the DS-OCDMA system to the coherence time of the laser source, we analyze the use of sparse and nonperiodic quadratic congruence and extended quadratic congruence codes.

Synchronization of two strongly pulsating CO2 lasers

Abstract The response of two CO 2 lasers sharing a common saturable absorber when both lasers are strongly pulsating was studied. Both of the lasers behave as strongly nonlinear limit-cycle oscillators exhibiting different amplitudes but similar periods. Since coupling through the saturable absorber is highly nonlinear, communication between lasers occurs only during short periods of time and when they are pulsating at about the same time. Nevertheless, we show experimentally and numerically that in-phase and out-of-phase oscillations are possible modes of synchronization.

Chaotic lag synchronization and pulse-induced transient chaos in lasers coupled by saturable absorber

Abstract Two lasers coupled via a common intracavity SF 6 saturable absorber show a cooperative coupling effect, instead of the most common competitive coupling. The dynamics of the system is very rich and includes strong pulsing, which may localize the non-linear interaction in time. Two chaotic regimes are analyzed experimentally and numerically: a chaotic lag synchronization resulting from an almost continuous interaction and a transient chaos resulting from a pulsed interaction.

Nonlinear Pulse Reshaping With Highly Birefringent Photonic Crystal Fiber for OCDMA Receivers

We combine an erbium-doped fiber amplifier with a short segment of highly birefringent photonic crystal fiber to generate a nonlinear transfer function suitable for optical transmission systems based on optical code-division multiple-access (OCDMA). Such a functional element based on spectral broadening followed by an off-center narrow optical filtering provides an effective suppression of spurious signals such as multiple-access interferences in OCDMA receivers and can reduce the pulses amplitude jitter.

Spectrum fragmentation issue in flexible optical networks: analysis and good practices

Flexible grid optical networks allow an efficient utilization of spectrum resources using 12.5-GHz frequency slot multiples instead of a fixed spacing, introducing however spectrum fragmentation (SF). In the literature, SF is often assumed to be a serious problem specifically in a dynamic traffic context. It is mostly related to the bandwidth blocking ratio due to the lack of relevant comparison criteria and efficient metrics. Besides, in operator core network, traffic behavior is instead incremental and it is forecasted for short periods of time in addition to some operational constraints that make of it a specific context. In this work, we present an exhaustive analysis and an accurate evaluation for SF issue in flexible optical networks. We also propose new metric for fragmentation measurements and some approaches to address such a problem.

Upstream OCDMA-TDM passive optical network using a novel sourceless ONU

OCDMA over conventional TDM PON leads to increase access network capacity by multiplexing TDM signals with OCDMA codes. We propose a novel sourceless ONU for OCDMA-TDM PON within a centralized light source placed at OLT. Sparser and longer extended quadratic congruence (EQC) codes with good correlation properties are used as optical CDMA en/decoders. However, multiple access interference (MAI) can limit the number of simultaneous users in this system. We analyze BER performance of sourceless OCDMA-TDM PON using four different EQC codes. Finally, network scalability and throughput performance of the proposed scheme are analyzed. These analyses over OCDMA-TDM PON show an upgrade of bandwidth and network capacity with an advantage of sourceless ONUs compared to the conventional TDM PON.