In this paper, we present an experimental study of the metrological stabilization of a solid-state frequency comb for embedded metrology applications. The comb is a passively mode-locked laser diode based on InGaAs/InP Quantum-dash structure emitting optical lines into a 9 nm bandwidth centered at 1.55 $\mu$m with a repetition rate of 10.09 GHz. The frequency stabilization is achieved by optical injection locking of the comb with an external cavity laser diode referenced onto a metrological frequency standard. One observes the transfer of the spectral purity from the injection laser to the neighbouring modes of the injected one as well as the transfer of stability to the adjacent modes. The measurement of the long term stability highlights a frequency noise with random walk behavior specific of the passive mode locking process. Demonstration of sidebands of the injection laser at the repetition frequency of the comb also makes it possible to propose a transfer mechanism and to consider a complete stabilization of the frequency comb at a metrological stability level.
In this paper, we present new and encouraging results in the road towards démocratisation of optical frequency combs for metrology applications out of the laboratories. We study a compact InGaAs based Quantum-Dash Mode Locked Laser Diode (QD-MLLD) at 1.55μm generating high stable and low noise optical pulses with a repetition rate higher than 10 GHz [1]. The source is a 10.1 GHz mode spacing Fabry-Perot laser with extremely high internal correlation between modes. The spectral purity of the beat-note resulting in the beating of all the modes is lower than 50 kHz while the typical linewidth of optical modes is about 50 MHz. Thanks to injection locking with an External Cavity Laser Diode (ECLD) in one of the 125 modes, we succeed in a linewidth reduction by 500 of the MLLD optical modes, corresponding to the linewidth of the master laser.
A compact device for an optical frequency stability transfer based on a cavity referenced to a molecular transition at 1.5 μm is described. The setup is essentially fibered and uses commercial components: a tunable confocal cavity, extended cavity laser diodes, a distributed feedback laser (DFB) laser, and a H13C14N cell. The phenomena that limit the stability are carefully studied. It is shown that the short-term stability is limited by the spectral purity of sources and the long-term stability by the residual amplitude modulation inherent to our current setup. The stability transfer of the molecular reference over 7 nm is demonstrated at a level of 10−10 in relative value, limited by the detected molecular linewidth. Improvements to the device are studied, and it is shown that a stability transfer at a 10−12 level could be achieved.
Ce travail de these porte sur le developpement d’une instrumentation pour la caracterisation et la stabilisation de sources laser a 1,55 µm a verrouillage de modes pour la metrologie des frequences ou les telecommunications optiques. Deux outils de caracterisation realises a partir de composants commerciaux ont ete developpes permettant de transferer la stabilite en frequence d’une reference metrologique vers des sources largement accordables (diodes laser a cavite etendue). L’une est fondee sur une cavite Fabry Perot confocale et l’autre sur une cavite a fibre en anneau. Dans les deux cas, des transferts de stabilite sur des dizaines de nanometres ont ete demontres au niveau de 10-12. L’analyse detaillee de ces montages montre les limitations apportees par les modulations d’amplitude et de polarisation parasites dues aux dispositifs de modulation ainsi que par les fluctuations de polarisation dans les fibres. Ces dispositifs ont ete valides par la demonstration de la stabilisation d’une source a verrouillage de modes par injection optique qui a permis de reduire la largeur spectrale du mode injecte d’un facteur superieur a 1000, de transferer la stabilite du laser d’injection a l’ensemble des modes du peigne de frequences et de mesurer la stabilite a long terme des modes du laser injecte.
We present preliminary results on semiconductor frequency comb stabilization via optical injection locking with a frequency stabilized laser. An important mode linewidth reduction is observed all over the comb. A stability better than 5.10 −12 up to 30s is measured giving to this compact comb a great interest for transportable time and frequency metrology.
Using the Jones formalism, it is shown that electro-optic modulators used for phase modulation generate a modulation of the output polarization induced by the difference of phase modulation depth along the crystallographic axes of the modulator. We study two consequences of this polarization modulation in the fiber setups, limiting the performance of high sensitivity measurement devices. The first one is its partial conversion into a residual amplitude modulation (RAM) within any component presenting polarization dependent losses (PDL). The second one is a new effect that consists of the distortion of the signal detected at the output of a fiber cavity. The theoretical expressions of the detected signals are computed in each case.
