Rémi Henriet

Azimuthal Turing Patterns, Bright and Dark Cavity Solitons in Kerr Combs Generated With Whispering-Gallery-Mode Resonators

We investigate the formation of cavity solitons in crystalline whispering-gallery-mode disk resonators that are pumped in different dispersion regimes. In the Fourier domain, these dissipative structures correspond to specific types of mode-locked Kerr optical frequency combs. Depending on the sign of the second-order chromatic dispersion and on the pumping conditions, we show that either bright or dark cavity solitons can emerge, and we show that these two regimes are associated with characteristic spectral signatures that can be discriminated experimentally. We use the Lugiato-Lefever spatiotemporal formalism to investigate the temporal dynamics leading to the formation of these azimuthal solitons, as well as the emergence of Turing patterns. The theoretical results are in excellent agreement with experimental measurements that are obtained using calcium and magnesium fluoride disk resonators pumped near 1550 nm.

Barium fluoride whispering-gallery-mode disk-resonator with one billion quality-factor

We demonstrate a monolithic optical whispering-gallery-mode resonator fabricated with barium fluoride (BaF₂) with an ultra-high quality (Q) factor above 10⁹ at 1550 nm, and measured with both the linewidth and cavity-ring-down methods. Vertical scanning optical profilometry shows that the root mean square surface roughness of 2 nm is achieved for our mm-size disk. To the best of our knowledge, we show for the first time that one billion Q-factor is achievable by precision polishing in relatively soft crystals with mohs hardness of 3. We show that complex thermo-optical dynamics can take place in these resonators. Beside usual applications in nonlinear optics and microwave photonics, high-energy particle scintillation detection utilizing monolithic BaF₂ resonators potentially becomes feasible.

Time-Domain Dynamics and Stability Analysis of Optoelectronic Oscillators Based on Whispering-Gallery Mode Resonators

Optoelectronic oscillators (OEOs) are microwave photonics systems intended to generate ultrastable radio-frequency signals with unprecedented phase noise performance for aerospace and communication engineering applications. They had originally been introduced in a configuration where the energy storage element was a fiber delay line. However, recent research in view of size and power consumption optimization has led to novel configurations where this fiber delay line is replaced by an ultrahigh Q whispering-gallery mode (WGM) resonator. So far, there has been no theoretical framework enabling to understand the dynamical behavior of these new architectures of OEOs. In this paper, we propose for the first time a deterministic time-domain model to investigate the dynamics of these OEOs based on WGM resonators. This model enables us to perform the stability analysis of the microwave oscillations, and to determine rigorously their range of stability as the loop gain is varied. After building the model, we perform a full stability analysis of the various stationary solutions for the microwave output. We then perform extensive numerical simulations, which are in complete agreement with the stability analysis. The theoretical analysis is also found to be in excellent agreement with our experimental measurements.

Kerr optical frequency comb generation in strontium fluoride whispering-gallery mode resonators with billion quality factor.

We report the fabrication for the first time of a strontium fluoride (SrF(2)) whispering-gallery mode resonator with quality factor in excess of 1 billion. The millimeter-size disk-resonator is polished until the surface roughness decreases down to a root-mean square value of 1.2 nm, as measured with a vertical scanning profilometer. We also demonstrate that this ultrahigh Q resonator allows for the generation of a normal-dispersion Kerr optical frequency comb at 1550 nm.

Phase noise performance comparison between optoelectronic oscillators based on optical delay lines and whispering gallery mode resonators.

We investigate the phase noise performance of optoelectronic oscillators when the optical energy storage elements are in the following three configurations: a high-Q whispering gallery mode resonator, an optical delay-line and a combination of both elements. The stability properties of these various optical elements are first characterized, and then systematically compared in the optical and in the microwave frequency domains. Subsequently, the spectral purity of the oscillator is theoretically and experimentally examined for each case. When the resonator is used as both delay and filtering element inside the delay-line based oscillator, the generated spurious modes are highly rejected. A spur rejection by more than 53 dB has been demonstrated for the first-neighboring spur.

High quality-factor optical resonators

Various resonators are investigated for microwave photonic applications. Micro-sphere, disk and fiber ring resonators were designed, realized and characterized. Obtained quality factors are as high as Q = 10^10

Barium fluoride and lithium fluoride whispering-gallery-mode resonators for photonics applications

Abstract. Crystalline whispering-gallery-mode disk resonators are finding an increasing number of applications in photonics. Their exceptional energy storage capacity is of great interest in the area of ultrastable oscillators for aerospace and communication engineerings as well as for sensing applications. Here, we investigate the physical properties of some unconventional crystalline materials. We show that these resonators can display quality factors higher than ten million at 1550 nm and we discuss their potential for various applications.

Wide-range tunability, thermal locking, and mode-crossing effects in Kerr optical frequency combs

Abstract. We theoretically and experimentally investigate some effects related to the Kerr optical frequency comb generation, using a millimeter-size magnesium fluoride ultrahigh quality disk resonator. We show that the Kerr comb tunability can be extremely wide in the Turing pattern (or primary comb) regime, with an intermodal frequency that can be tuned from 4 to 229 multiple free spectral ranges (corresponding to a frequency spacing ranging from 24 GHz to 1.35 THz). We also discuss the role played by thermal locking while pumping the resonator, as well as the effect of modal crossing when broadband combs are generated.

Experimental characterization of optoelectronic oscillators based on optical mini-resonators

The fabrication process of whispering gallery mode disk resonators is presented with different characterization techniques in order to monitor roughness and optical quality factor. This type of resonators is then used as the reference frequency element to stabilize the oscillation frequency of an optoelectronic oscillator. Experimental results are provided and demonstrate the efficiency of the method.

On the metrological performances of optoelectronic oscillators based on whispering gallery mode resonators

We investigate the phase noise performance of an optoelectronic oscillator based on a calcium fluoride high quality factor whispering gallery mode optical resonator (WGMR). In the oscillator setup, a particular attention is given to the stabilization of the laser lightwave onto an optical resonance of the WGMR. Once the laser is stabilized, different resonant optical modes are characterized in the microwave domain. Afterwards, phase noise spectra of different oscillations at different modes of the WGMR are measured. Phase noise levels below -93 dBc/Hz and around -90 dBc/Hz at 10 kHz offset frequency from 6.35 GHz and 12.7 GHz carriers are respectively obtained.