Complete Crossing of Fano Resonances in an Optical Microcavity via Nonlinear Tuning

M. Bernard; F. Ramiro-Manzano; L. Pavesi; G. Pucker; I. Carusotto; M. Ghulinyan

doi:10.1364/PRJ.5.000168

Research · Publication & note

Complete Crossing of Fano Resonances in an Optical Microcavity via Nonlinear Tuning

Journal article

M. Bernard, F. Ramiro-Manzano, L. Pavesi, G. Pucker, I. Carusotto and M. Ghulinyan

Photonics Research Volume 5 Issue 3 168–175 2017

Abstract

We report on the modeling, simulation, and experimental demonstration of complete mode crossings of Fano resonances within chip-integrated microresonators. The continuous reshaping of resonant lineshapes is achieved via nonlinear thermo-optical tuning when the cavity-coupled optical pump is partially absorbed by the material. The locally generated heat then produces a thermal field, which influences the spatially overlapping optical modes, allowing us to alter the relative spectral separation of resonances. Furthermore, we exploit such tunability to continuously probe the coupling between different families of quasi-degenerate modes that exhibit asymmetric Fano interactions. As a particular case, we demonstrate a complete disappearance of one of the modal features in the transmission spectrum as predicted by Fano [Phys. Rev. 124, 1866 (1961)]. The phenomenon is modeled as a third-order nonlinearity with a spatial distribution that depends on the stored optical field and thermal diffusion within the resonator. The performed nonlinear numerical simulations are in excellent agreement with the experimental results, which confirm the validity of the developed theory.

How to cite

Initials first

M. Bernard, F. Ramiro-Manzano, L. Pavesi, G. Pucker, I. Carusotto and M. Ghulinyan. Complete crossing of Fano resonances in an optical microcavity via nonlinear tuning. Photonics Research 5(3), 168–175 (2017). DOI: 10.1364/PRJ.5.000168.

Family name first

Bernard, M., Ramiro-Manzano, F., Pavesi, L., Pucker, G., Carusotto, I., & Ghulinyan, M. (2017). Complete crossing of Fano resonances in an optical microcavity via nonlinear tuning. Photonics Research, 5(3), 168–175. https://doi.org/10.1364/PRJ.5.000168

Article access and reuse

The Version of Record is openly available from the journal. The Photonics Research copyright transfer agreement permits authors to reuse all or part of the work, including the publisher-formatted version, on their personal web homepage when the Chinese Laser Press copyright notice is retained. The figures below are the complete original compositions extracted from the article PDF and are reproduced with that notice.

Figures

Figure 1 from Complete Crossing of Fano Resonances — **Figure 1.** Schematic representation of the mode-crossing possibilities. (a) Azimuthal modes of two radial families progressively shift at each increment of the azimuthal number due to the difference in FSR, possibly going through a crossing. (b) Continuous tuning of a doublet of resonances may be obtained via nonlinearities, such as a localized thermo-optic effect.

Figure 2 from Complete Crossing of Fano Resonances — **Figure 2.** Simulated thermal distribution generated by (a) the first and (b) the second optical radial family modes. The contour lines show the modes’ electric field profiles.

Figure 3 from Complete Crossing of Fano Resonances — **Figure 3.** Resonant line shape modification under a sweeping pump in the presence of optical nonlinearity. The cold cavity spectrum (dashed line) is obtained with a weak probe. When sweeping the spectrum using a high-power laser (solid line), the resonance shifts progressively due to the increasing nonlinear effect, resulting in a spectrum with an apparent discontinuity, where the cavity mode de-locks from the pump laser.

Figure 4 from Complete Crossing of Fano Resonances — **Figure 4.** Experimental setup. A tunable laser amplified with an EDFA is mixed with the broadband signal of a BOA and shone into the sample with a taper fiber. The output also is collected with a taper fiber, split, and fed to an OSA and a broadband germanium detector.

Figure 5 from Complete Crossing of Fano Resonances — **Figure 5.** Experimental cold cavity spectrum of the resonator. Three azimuthal modes are present for the families R₁, R₂, and R₃. The relative position of the R₁–R₂ doublet peaks transforms across the spectrum due to the difference in the respective FSRs.

Figure 6 from Complete Crossing of Fano Resonances — **Figure 6.** Results of the pump and probe experiment. Panel (a) shows the cold (dashed) and hot (solid) cavity transmission spectra of the device around the strongly pumped resonance doublet. The thermo-optic nonlinearity, induced by the pumped doublet, also affects the other resonances (b), allowing for a relative detuning of the peaks as shown by the transmission color map. (c) Selected transmission spectra show the transformation of the Fano resonance in the vicinity of the critical phase point, where a complete disappearance of the Rˢ₁ peak feature takes place (panel C). The probe spectrum time-evolution, together with the pump dynamic transmission is represented in Visualization 1.

Figure 7 from Complete Crossing of Fano Resonances — **Figure 7.** Pump and probe experiments demonstrating a complete crossing of the modes. Panels (a), (b), and (c) represent the same experiment under different input power conditions of 0.5, 1, and 2 W, respectively. (d) The selected spectra, under 2 W pump, demonstrate three cases of the relative detuning, which changes from positive (A) to negative (C) passing through the δω₁₂⁰ = 0 condition (B). The probe spectrum time evolution, together with the pump dynamic transmission with input power 2.0 W is represented in Visualization 2.

Figure 8 from Complete Crossing of Fano Resonances — **Figure 8.** Experimental and simulated data of the pump and probe experiment. (a) Experimental pump transmission spectrum of the loaded cavity (black line) is simulated (dashed red) by inserting the cold cavity fit parameters into Eq. (15). (b) Experimental transmission map as a function of both pump and probe wavelength is shown. (c) Relative coupling η₁ among the two radial family modes to the waveguide, extracted from results in panel (b). Successively, η₁ is used to compute the Γ and Δ matrices of Eq. (10) to also take into account the changes in the coupling induced by the thermally induced δn(r). Panel (d) shows the transmission map as a function of both pump and probe wavelength using the simulated in (a) pump excitation for Eq. (16).