Laser dynamics study from eigenmode decomposition – LASAGNE

Time or frequency reference sources are essential technologies in both fundamental and applied science, their applications spanning from atomic clock and quantum metrology to GPS, telecommunication systems, radars and electronic warfare systems. The most promising architectures are nowadays based on lasers, either directly, using optical frequency combs, or indirectly for radio-frequency signals generation. Photonic technologies are attractive because of their large operating bandwidth, stability, versatility and high signal to noise ratio. The objective of the LASAGNE project is to improve the performances of photonics oscillators thanks to a more detailed and exhaustive understanding of their noise properties. This project mixes fundamental developments on laser theory with practical implementations of optical and opto-electronic oscillators (OEO). It is built around a novel approach to noise analysis, imported from quantum optics, based on eigenmode decomposition.

The fact that the noise of laser light sources can be decomposed into time/frequency uncorrelated eigenmodes is not a new concept. However, so far, there are very few experimental evidences due to the difficulty to measure frequency dependent noises and correlations, in both amplitude and phase. We propose to develop a fully multimode real-time detection system able to recover the whole noise covariance matrix, spanning from electric sidebands frequencies to optical frequencies. Such an approach yields an exhaustive vision of the system noise, without any a priori assumptions about its origin or about its characteristics. The diagonalization of this matrix permits to extract uncorrelated noise modes. The properties of such principal noise modes will enable us to get a precise physical insight into all the specific independent noise sources. We will be then able to identify the different independent “knobs” to act on in order to correct for such a noise, for example using servo-loops.

The project is organized along three main tasks. The first one is related to detector developments both at 800nm and 1.5µm wavelength, for optical and electric sideband frequency characterization and correlations measurements. The second one will tackle solid-state and fiber based optical frequency combs. It will provide new insight to both external and internal noise transfer to laser light physical parameters (Carrier Envelope Offset (CEO) phase, timing jitter, intensity noise, etc.). In particular, pump noise transfer will be thoroughly studied and noise cancellation strategies developed. The third one will consider single and dual wavelength semiconductor lasers and OEO and Coupled OEO, transferring the optical wavelength know-how to sideband frequencies (MHz range). Noise sources such as thermal and amplifier noise will be considered along with their influence on RF frequencies generation.

The project gathers competences from three complementary research groups. Laboratoire Kastler Brossel (LKB), specialist in multimode measurement with shot noise sensitivity, Thales Research and Technology France (Thales), specialist in low-noise lasers and optoelectronic oscillators and their applications, and Laboratoire Aimé Cotton (LAC), specialist in laser dynamics and dual frequency laser RF sources. It is based on pioneering work from LKB on optical frequency comb covariance matrix characterization, LAC optical sideband frequency noise transfer from laser pump noise studies and Thales recent developments on optoelectronics oscillators.

The system and competences developed during the project will not only benefit to the identified applications, but should also benefit to a wide range of developments. Indeed, efficient and normalized modal decomposition of laser noise can be applied to any laser source, and ultimately made available as a very general benchmark on laser quality. It is one of the goals of LASAGNE to prove the efficiency and applicability of these concepts.