homework anxiety disorder undergraduate dissertation structure econometrics coursework help how to write an essay in zulu personal statement help video dissertation writting with flexible payment scheme when should i start doing my homework

Quantum optics, non linear photonics and laser physics

  • Faculty P. Gallion, R. Gabet, F. Grillot, Y. Jaouën

Space quantum communications, quantum key distribution (QKD) and quantum level detection

By using the quantum coherent state model of the signal field, we have compared different quantum receiver implementations and derived the minimum signal energy required to achieve a given bit error rate, or a given bit erasure rate, in high bit rate, quantum level communications. We have implemented an optical Costas loop at 1550 nm based on polarization splitting of the laser field to detect I and Q quadratures simultaneously. We have obtained results on the performance in phase error and bit error rate and compared with the corresponding quantum limit in the quantum space communication context. Using pulse coherent detection, we have implemented an all-fiber one-way QPSK quantum key distribution system at 1550 nm using a photon counting or a balanced homodyne detection (BHD) configuration. The security issues of the BHD QKD system have also been investigated under different attack protocols. As the use of decoy states improves the security level, coping against the photon number splitting (PNS) attacks, we have generalized the standard QKD security analysis to our implemented system.

Finally, aiming at performing optical carrier recovery for weak optical signals, we implemented a receiver structure in which a sequential field quadrature measurement is achieved in association with digital Costas loop. We obtained results close to the uncertainty limit and to the standard quantum limit for low photon number reception.


Non linear fiber optics: Brillouin and Raman effects in optical fibre, assessment and application to sensing

A general formulation for the quantum macroscopic nonlinear optics has been derived for application to fibre systems. A theoretical analysis on the PMD-assisted pump-to-signal noise transfer in distributed fiber Raman amplifiers (RA) allows to account for the high frequency noise transfer which is observed experimentally. Raman amplifiers with time-division-multiplexed (TDM) pumps have been analyzed by using a computational cost-effective Fourier series approach and allows the analysis and the optimization of the pumping mechanism. An analytical approach of the forward and backward propagating configurations has allowed an explicit derivation for the Double Rayleigh Scattering (DRB) and Amplified Spontaneous Emission (ASE) noises.

Given its low power threshold, the Brillouin effect in optical fibres is one of the most promising nonlinear effects for designing new all-optical processing devices and optical sensors. A self-referenced technique for measuring the Brillouin gain in an optical fibre has been recently proposed, and the importance of the acousto-optic effective area in place of the optical effective area on the Brillouin efficiency has been confirmed for the first time. A 2 D FEM model has been proposed for accurate Brillouin gain spectrum (BGS) calculation in acoustic guiding and anti-guiding single mode optical fibres. Particularly, the influence of the geometrical structure, the doping composition profile and the internal residual draw-induced stresses on BGS properties have been investigated. An accurate determination of the strain dependence of the Brillouin frequency shift has been proposed for the first time and has been validated experimentally using different types of optical fibre.


High power lasers

Our work is carried out mainly through collaborations with external laboratories (ONERA, CEA, PhLAM) and with the Keopsys SME. We have collaborated With ONERA on the analysis of the Brillouin spectrum doping dependence of doped fibres{, as well as the combination of coherent fibre amplifiers in both continuous and pulsed regimes. Numerical space-filling designs have been proposed to analyze the sensitivity of coherent beam combination in large fibre amplifier arrays. The most critical interactions have been investigated in details. The collaboration with CEA on Laser Mégajoule focused on the spectral broadening properties through FM-AM conversion induced by non-sinusoidal phase modulation in comparison to the sinusoidal phase modulation case. The collaboration with PhLAM concerns the design of an Ytterbium-doped solid core photonic band-gap fiber for laser operation at 980 nm. In collaboration with Keopsys Company and ONERA, we are presently developing advanced architectures of pulsed fiber Thulium laser at 2 µm.


Nonlinear Photonics in Advanced Semiconductor Lasers

Investigating the field of semiconductor laser dynamic and microwave photonics, this topic investigates nonlinear dynamics and optical injection in diode oscillator especially quantum-well, quantum-dot and quantum-cascade lasers to prepare the next generation of photonic oscillators and semiconductor lasers. The applications range from mid-infrared ultra-low-noise oscillators, bandwidth enhancement for various engineering applications from optical communications up to defence and homeland security. To this end, recent studies have shown the potential of Q-Dot lasers operating under external control for free-chirp high-speed communications by linewidth enhancement factor engineering. In addition, we have theoretically reported for the first time some unique properties of optically injected Q-cascade lasers for free-space communications. It was shown that the injection-locked quantum-cascade lasers exhibit a flat modulation response at zero detuning as well as bandwidth enhancement with injection leve

Image return top of page