Self-stabilization of the beat-note of monolithic DFB lasers for microwave signal generation

Aurélien Thorette (1) , Peppino Primiani (1, 2) , Marco Romanelli (1) , Mehdi Alouini (1) , Frederic van Dijk (2) , Marc Vallet (1)

1 FOTON - Institut des Fonctions Optiques pour les Technologies de l'informatiON
2 III-V Lab - Alcatel-Thalès III-V lab

We report an opto-RF source based on the beating between two integrated DFB lasers, and discuss several schemes for self-stabilization (i.e. without an external reference oscillator) of the output beat-note. These schemes are based on a hybrid opto-electronic feedback loop, combining optical cross-injection locking and delayed optoelectronic feedback. We demonstrate the generation of a dual-frequency output signal with a good spectral purity. This stabilization mechanism has also been integrated on a single chip as a standalone opto-RF generator, showing good performances up to 20 GHz. Such a scheme should be scalable up to 100GHz. At high frequencies, RF signals become harder to generate and to carry by electronic means, and optical solutions are often considered. Such so-called opto-RF signals can be generated by various schemes, for instance using an opto-electronic oscillator (OEO), and then carried over long distances through conventional fiber links. However, as the RF signal is embedded in sidebands around the optical carrier, it is sensitive to chromatic dispersion along the fiber link, which can lead to a dramatic reduction of the modulation depth. Alternatively, if the signal is generated by a heterodyne method, i.e. by mixing two optical frequencies, it will feature almost 100% modulation depth and be insensitive to dispersion. This can be done by using the beat-note between two laser sources, which also allows for a more convenient and wider tuning range of the RF frequency. As a drawback, the frequency difference between the two lasers has to be stabilized. Here we present a hybrid stabilization method, which merges passive optical injection locking and an opto-electronic loop based on an optical delay line. This scheme benefits of standard phase stabilization methods used in OEO technology. This setup can be further integrated into a semiconductor photonic device. Figure 1: Two samples of monolithic dual DFB lasers used as heterodyne source. (a) 2 DFB lasers coupled to a microlensed fiber. (b) PIC containing 2 DFBs, semiconductor optical amplifiers, electroabsorption modulators, and UTC photodiodes. Instead of using two separate lasers, we consider a specially-designed photonic integrated circuit (PIC) that contains two quantum dash InGaAsP DFB lasers, whose outputs are coupled (as shown on Fig. 1). Other elements, such as amplifiers, modulators and photodiodes can be added on our PICs, allowing for a great versatility [1]. Having the two lasers to share the same wafer allows them to experience correlated thermal and acoustic noises, so that their output beat-note does not drift significantly. By tuning the bias current of one of the lasers, RF frequencies up to 100GHz can be obtained [2].

Domaines: Optique [physics.optics]

Aurélien Thorette, Peppino Primiani, Marco Romanelli, Mehdi Alouini, Frederic van Dijk, et al.. Self-stabilization of the beat-note of monolithic DFB lasers for microwave signal generation. International Symposium on Physics and Applications of Laser Dynamics 2017 (IS-PALD 2017), Nov 2017, Paris, France. ⟨hal-01708260⟩