Hossein Taheri

Soliton Formation in Whispering-Gallery-Mode Resonators via Input Phase Modulation

We propose a systematic method for soliton formation in whispering-gallery-mode (WGM) resonators through input phase modulation. Our numerical simulations of a variant of the Lugiato-Lefever equation (LLE) suggest that modulating the input phase at a frequency equal to the resonator free spectral range and at modest modulation depths provides a deterministic route toward soliton formation in WGM resonators without undergoing a chaotic phase. We show that the generated solitonic state is sustained when the modulation is turned off adiabatically. Our results support parametric seeding as a powerful means of control, in addition to input pump power and pump-resonance detuning, over frequency comb generation in WGM resonators. Our findings also help pave the way toward ultrashort pulse formation on a chip.

Self-synchronization phenomena in the Lugiato-Lefever equation

The damped driven nonlinear Schrodinger equation (NLSE) has been used to understand a range of physical phenomena in diverse systems. Studying this equation in the context of optical hyper-parametric oscillators in anomalous-dispersion dissipative cavities, where NLSE is usually referred to as the Lugiato-Lefever equation (LLE), we are led to a new, reduced nonlinear oscillator model which uncovers the essence of the spontaneous creation of sharply peaked pulses in optical resonators. We identify attracting solutions for this model which correspond to stable cavity solitons and Turing patterns, and study their degree of stability. The reduced model embodies the fundamental connection between mode synchronization and spatiotemporal pattern formation, and represents a novel class of self-synchronization processes in which coupling between nonlinear oscillators is governed by energy and momentum conservation.

Extending chip-based Kerr-comb to visible spectrum by dispersive wave engineering

Anomalous group velocity dispersion is a key parameter for generating bright solitons, and thus wideband Kerr frequency combs. Extension of the frequency combs spectrum to visible wavelengths has been a major challenge because of the strong normal dispersion of conventional photonic materials at these wavelengths. In this paper, we numerically demonstrate a wideband frequency comb extending from near-infrared to visible wavelengths (∼1200 nm to 650 nm). The proposed frequency comb micro-resonator takes advantage of a wideband blue-shifted anomalous dispersion, achieved in an optimized over-etched silicon nitride waveguide and strong power transfer to shorter wavelengths through radiative dispersive waves, achieved by modulating the dispersion in a coupled resonator architecture. We show the possibility of obtaining a close to visible dispersive Cherenkov radiation peak that is only 10 dB below the overall comb peak and can be tuned by adjusting the coupling structure in the coupled resonator architecture.

Anatomy of Phase Locking in Hyperparametric Oscillations Based on Kerr Nonlinearity

We investigate the dynamical origin of synchronization and phase locking of hyperparametric oscillations in Kerr-nonlinear media. These oscillations occur in the presence of parametric gain and, although arising from modulational instability of random vacuum fluctuations with arbitrary phases, lead to phase-locked states in the form of pulse trains. Using few-mode approximations of the Lugiato–Lefever equation (LLE), we find that the pumped mode injection-locks to the driving laser pump following the Adler equation. Based on experimentally motivated assumptions, we derive analytical expressions, which reveal the essence of phase locking in frequency combs and confirm them through numerical integration of the LLE. Clear understanding of the phenomenon of phase locking in optical microresonators can lead to devising novel techniques for achieving phase-locked states or improving the coherence properties of frequency combs. Our results are mathematically generic and apply to other systems described by an externally driven damped nonlinear Schödinger equation.

Anatomy of Phase Locking in Parametric Frequency Combs

We investigate the dynamical origin of phase locking of optical frequency combs in Kerr-nonlinear media using few-mode approximations of the Lugiato-Lefever equation. We find analytical expressions which reveal the essence of phase locking.

Large enhancement of second harmonic emission using lattice plasmon polaritons

We demonstrate a bilayer nanostructure, supporting lattice plasmon polaritons and vertically confined localized plasmonic modes. Fano-type resonance increases the net absorption cross-section of the nanostructure, resulting in a significant enhancement in the second harmonic intensity.

Polarization cross-coupling between microring and bus waveguide in double-layer SOI

We investigate polarization cross-coupling between modes of microring resonators and waveguides due to structural asymmetries. We experimentally demonstrate the coupling between a double-layer SOI waveguide fundamental TM mode and microring higher-order radial TE modes.