Amplificateur paramétrique optique

Un amplificateur paramétrique optique, abrégé OPA (pour Optical Parametric Amplfier en anglais), est une source de lumière laser qui émet de la lumière de longueur d'onde variable obtenue par un processus d'amplification paramétriquee. C'est essentiellement la même chose qu'un oscillateur paramétrique optique, mais sans la cavité optique (c'est-à-dire que les faisceaux lumineux ne traversent l'appareil qu'une ou deux fois, au lieu de plusieurs fois). Génération paramétrique optique (OPG) La génération paramétrique optique (OPG) (également appelée fluorescence paramétrique optique) précède souvent l'amplification paramétrique optique. Dans la génération paramétrique optique, une onde pompe, de fréquence ωp, est incidente dans un cristal non linéaire. Au passage de l'onde pompe dans le cristal, deux faisceaux lumineux de fréquences inférieures ωs et ωc sont générés, avec la condition ωp=ωs+ωc. Ces deux faisceaux de basse fréquence sont appelés respectivement "signal" et "comp

Integrated Gallium Phosphide Photonics

Katharina Schmeing

The integration of new materials mediating light-matter interaction in nanoscale devices is a persistent goal in nanophotonics. One of these materials is Gallium phosphide, which offers an attractive combination of a high refractive index (n=3.05 at a wavelength of 1550 nm) and a large bandgap (Eg =2.26 eV), enabling photonic devices with strongly confined light fields, not suffering from heating due to two-photon absorption at telecommunication wavelengths. Furthermore, due to its non-centrosymmetric crystal structure, it has a non-vanishing second-order susceptibility and is piezoelectric. Related to its large refractive index is a high third-order susceptibility. Prior to this work the use of GaP for photonic devices was limited to individual non-integrated components, as GaP was not available on a substrate with substantially lower refractive index equivalent to SOI-wafers for silicon. In this work a process was developed that allows the integration of GaP devices onto SiO2. It exploits direct wafer bonding of a GaP/AlxGa1-xP/GaP heterostructure onto a SiO2-on-Si wafer. After substrate removal, photonic devices are patterned by dry-etching in the top GaP device layer. The GaP devices investigated here are used to explore nonlinear optics and optomechanics. In the area of nonlinear optics, second- and third-harmonic generation are observed. The Kerr coefficient is experimentally estimated as n2[1550nm] = 1.2(5)x10^17m^2/W, for the first time in a precision measurement at telecommunication wavelengths. Four-wave mixing is used for broadband frequency comb generation, where a power threshold as low as 3 mW is obtained. The combination of four-wave mixing and second-harmonic generation leads to frequency-doubled combs. The optomechanical properties of GaP one-dimensional photonic crystal cavities are optimized by simulations and fabricated devices are characterized. Optical quality factors of Qo>10^5 and optomechanical coupling strengths of g0/2pi=400 kHz are measured. Dynamical backaction in the form of the spring effect and the parametric amplification are observed, as well as optomechanically induced transparency and absorption. A device design for a microwave-to-optical transducer is developed, relying on the piezoelectricity of GaP. It combines electromechanical and optomechanical transduction. The predicted electromechanical coupling strength is in the MHz range. Furthermore, photonic crystal cavity designs containing a slot at the center of the cavity are studied. According to simulations for slot widths below 30 nm, optomechanical coupling strengths g0/2pi>1 MHz could be achieved. Fabricated silicon photonic crystal cavities show high quality factors of Qo=8x10^4 while hosting a mechanical eigenmode with a frequency of 2.7 GHz. Because of process technology limitations, only slot widths as narrow as 40 nm can be fabricated, the achieved g0/2pi is limited to 300 kHz. The new GaP-on-insulator material platform opens the door to integrated GaP devices. Frequency combs are of interest for soliton comb formation, mid-IR frequency combs, and ultra-broadband supercontinuum generation. Microwave-to-optical transducers are on the one hand desired for quantum information processing, on the other hand they are applicable as efficient modulators or detectors for classical signals.

EPFL2019

A tunable femtosecond fiber laser source for multiphoton emission microscopy

Pierre-Marc Jean Marie Dansette

Second harmonic generation microscopy is used to image interfaces or non-centrosymmetric structures and molecules. Two-photon fluorescence microscopy can image molecules within cells without using markers. Thus those technics have lead to advances in our understanding of structure such as lipid membranes, or of the physical properties of tightly confined of water. They are also powerful tools for biological imaging, allowing to study microtubule orientation or electric potential in neurons for instance. However Multiphoton emission microscopy, as it relies on non-linear light-matter interaction, requires high intensity. Femtosecond lasers allow for such intensities while keeping fluence low enough to not cause damage to the material. Making such a laser tunable though the use of optical parametrical amplification (OPA) improves penetration in tissues and water, and allows to probe some materials at resonance. Fiber lasers should be well suited for this application, as they are cheaper than bulk lasers and less sensitive to misalignment. During this PhD we aim at building a new tunable femtosecond fiber laser. We will seek to optimise the parametrical amplification process to have high efficiency conversion from 2500 to 700nm. We expect to reach pulse duration as short as 30 fs, energy up to 200nJ and repetition rate up to 2MHz.

EPFL2021

Optical parametric gain in CMOS-compatible sub-100 mu m photonic crystal waveguides

Ezgi Sahin

Emerging compositionally engineered complementary metal-oxide-semiconductor (CMOS)-compatible platforms have been employed for high efficiencies in various on-chip applications, including optical parametric amplification and wavelength conversion. Combining the novel nonlinear optics platforms such as ultra-silicon-rich nitride (USRN: Si7N3) with periodic waveguide structures can lead to further enhancement of material nonlinearities via the slow light effect and enable ultra-compact devices. Four-wave mixing in a USRN-based, CMOS-compatible, photonic crystal waveguide (PhCWg) leading to on/off optical parametric signal gain reaching 3 dB, and a large instantaneous idler conversion efficiency of -1 dB is explored experimentally. Enhancement of Kerr nonlinearity in the presence of a sizable and near-constant group index allows the findings on an ultra-compact, 97 mu m-long PhCWg, equivalent to a large on/off gain per unit length of 333 dB/cm. (C) 2020 Author(s).

AMER INST PHYSICS2020

Integrated Gallium Phosphide Photonics

Katharina Schmeing

EPFL2019