Counter-rotating cavity solitons in a silicon nitride microresonator

Abstract

We demonstrate the generation of counter-rotating cavity solitons in a silicon nitride microresonator using a fixed, single-frequency laser. We demonstrate a dual 3-soliton state with a difference in the repetition rates of the soliton trains that can be tuned by varying the ratio of pump powers in the two directions. Such a system enables a highly compact, tunable dual comb source that can be used for applications such as spectroscopy and distance ranging.Advancements in optical frequency comb technology over the past two decades have enabled applications in a wide range of fields including precision spectroscopy [1], frequency metrology [2], optical clockwork [3,4], astronomical spectrograph calibration [5,6], and microwave signal synthesis [7]. Applications benefit from the high precision of the frequencies of the comb lines and require low noise, stable operation [8]. Stabilized low-noise comb sources were first demonstrated using mode-locked solid state lasers and fiber lasers [9,10]. Over the last decade, on-chip optical frequency comb generation using microresonators has seen significant progress and has been demonstrated in several materials including silica [11][12][13][14] [13, 14, 17, 20-22, 27, 29] by sweeping the relative detuning between the laser and cavity resonance from the blue-to the red-detuned [17,30]. The dynamics of mode-locking have been studied using various approaches to control the effective detuning, including laser frequency tuning [17,22,29], power kick [13,14,21], and resonance frequency tuning using integrated heaters [20] or free-carrier lifetime control [27].Recently, there has been interest in studying the nonlinear dynamics of bidirectionally pumped microresonators [31,32]. For the case in which the pumps have unequal powers, the counter-rotating fields experience different nonlinear phase shifts that leads to unequal * Corresponding author: chaitanya.joshi@columbia.edu detuning from the cavity resonances for the clockwise (CW) and counter-clockwise (CCW) directions. Such behavior can lead to bistability [31] and can be exploited to create a gyroscope with enhanced sensitivity to rotation [33,34]. For the case in which such a system can be mode-locked it would result in the generation of two soliton trains with different repetition rates in a single microresonator and thus be used as a dual-comb source in a number of applications [35][36][37][38][39][40][41][42]. Recently counterpropagating solitons were generated in silica microresonators using a single laser, frequency shifted using two acousto-optic modulators (AOM's) pumping a single microresonator [32]. The difference in effective detuning was controlled using the two AOM's and leads to a difference in repetition rate for the solitons. While there have also been recent demonstrations of bidirectional modelocked solid state [43] and fiber [44,45] laser cavities, a microresonator-based system could be highly compact and fully integrated onto a chip.In this Letter, we present a novel approach to generating counter-rotating...

Dissipative Kerr solitons in optical microresonators

“…Counterpropagating solitons and spatial multiplexing WGM microresonators support both counterpropagating traveling modes, which allows simultaneous excitation of DKS in both clockwise and counterpropagating directions (112,113). The two combs, however, have been observed to lock to each other, an effect likely associated with Rayleigh backscattering.…”

Modulational instability and frequency combs in whispering-gallery-mode microresonators with backscattering

“…Also frequency comb generation at normal group velocity dispersion (GVD) was demonstrated in case of the coupling between different co-propagating spatial or polarizational mode families existing simultaneously in the microresonators [22][23][24]. Recently a number of results on the impact of the linear and nonlinear couplings between the counter-propagating waves has been reported [25,26] including generation of DKS [27][28][29]. However, the absence of the consistency and transparent justification of the applied models call for a revision of this problem in * noxobar@mail.ru the view of its persistent importance for practical applications.…”

Synchronization of coupled optical microresonators

“…Such a frequency-locking regime is similar to that reported in the context of counter-propagating solitons in a single microresonator. 45,46 This range of heater voltage corresponds to 400 MHz resonance shift relative to the pump (see Methods for calibration). This result also shows that the allowed comb spacing mismatch between the two combs for this particular coupling strength is approximately 2.6 MHz or 1.7 MHz, depending on the sign of the mismatch (whether the spacing of the slave comb is larger or smaller than the master resonator).…”