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Register a new userNonlinear filtering of an optical pulse train using dissipative Kerr solitons
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The capability to store light for extended periods of time enables optical cavities to act as narrow-band optical filters, whose linewidth corresponds to the cavitys inverse energy storage time. Here, we report on nonlinear filtering of an optical pulse train based on temporal dissipative Kerr solitons in microresonators. Our experimental results in combination with analytical and numerical modelling show that soliton dynamics enables storing information about the systems physical state longer than the cavitys energy storage time, thereby giving rise to a filter width that can be more than an order of magnitude below the cavitys intrinsic linewidth. Such nonlinear optical filtering can find immediate applications in optical metrology, low-timing jitter ultra-short optical pulse generation and potentially opens new avenues for microwave photonics.
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This chapter describes the discovery and stable generation of temporal dissipative Kerr solitons in continuous-wave (CW) laser driven optical microresonators. The experimental signatures as well as the temporal and spectral characteristics of this class of bright solitons are discussed. Moreover, analytical and numerical descriptions are presented that do not only reproduce qualitative features but can also be used to accurately model and predict the characteristics of experimental systems. Particular emphasis lies on temporal dissipative Kerr solitons with regard to optical frequency comb generation where they are of particular importance. Here, one example is spectral broadening and self-referencing enabled by the ultra-short pulsed nature of the solitons. Another example is dissipative Kerr soliton formation in integrated on-chip microresonators where the emission of a dispersive wave allows for the direct generation of unprecedentedly broadband and coherent soliton spectra with smooth spectral envelope.
Dissipative solitons are self-localised structures that can persist indefinitely in open systems characterised by continual exchange of energy and/or matter with the environment. They play a key role in photonics, underpinning technologies from mode-locked lasers to microresonator optical frequency combs. Here we report on the first experimental observations of spontaneous symmetry breaking of dissipative optical solitons. Our experiments are performed in a passive, coherently driven nonlinear optical ring resonator, where dissipative solitons arise in the form of persisting pulses of light known as Kerr cavity solitons. We engineer balance between two orthogonal polarization modes of the resonator, and show that despite perfectly symmetric operating conditions, the solitons supported by the system can spontaneously break their symmetry, giving rise to two distinct but co-existing vectorial solitons with mirror-like, asymmetric polarization states. We also show that judiciously applied perturbations allow for deterministic switching between the two symmetry-broken dissipative soliton states, thus enabling all-optical manipulation of topological bit sequences. Our experimental observations are in excellent agreement with numerical simulations and theoretical analyses. Besides delivering fundamental insights at the intersection of multi-mode nonlinear optical resonators, dissipative structures, and spontaneous symmetry breaking, our work provides new avenues for the storage, coding, and manipulation of light.
We demonstrate stable microresonator Kerr soliton frequency combs in a III-V platform (AlGaAs on SiO$_2$) through quenching of thermorefractive effects by cryogenic cooling to temperatures between 4~K and 20~K. This cooling reduces the resonators thermorefractive coefficient, whose room-temperature value is an order of magnitude larger than that of other microcomb platforms like Si$_3$N$_4$, SiO$_2$, and AlN, by more than two orders of magnitude, and makes soliton states adiabatically accessible. Realizing such phase-stable soliton operation is critical for applications that fully exploit the ultra-high effective nonlinearity and high optical quality factors exhibited by this platform.
Integrated photonics plays a central role in modern science and technology, enabling experiments from nonlinear science to quantum information, ultraprecise measurements and sensing, and advanced applications like data communication and signal processing. Optical materials with favorable properties are essential for nanofabrication of integrated-photonics devices. Here we describe a material for integrated nonlinear photonics, tantalum pentoxide (Ta$_2$O$_5$, hereafter tantala), which offers low intrinsic material stress, low optical loss, and efficient access to Kerr-nonlinear processes. We utilize >800-nm thick tantala films deposited via ion-beam sputtering on oxidized silicon wafers. The tantala films contain a low residual tensile stress of 38 MPa, and they offer a Kerr index $n_2$=6.2(23)$times10^{-19}$ m$^2$/W, which is approximately a factor of three higher than silicon nitride. We fabricate integrated nonlinear resonators and waveguides without the cracking challenges that are prevalent in stoichiometric silicon nitride. The tantala resonators feature an optical quality factor up to $3.8times10^6$, which enables us to generate ultrabroad-bandwidth Kerr-soliton frequency combs with low threshold power. Moreover, tantala waveguides enable supercontinuum generation across the near-infrared from low-energy, ultrafast seed pulses. Our work introduces a versatile material platform for integrated, low-loss nanophotonics that can be broadly applied and enable heterogeneous integration.
Dissipative solitons are self-localized structures resulting from a double balance between dispersion and nonlinearity as well as dissipation and a driving force. They occur in a wide variety of fields ranging from optics, hydrodynamics to chemistry and biology. Recently, significant interest has focused on their temporal realization in driven optical microresonators, known as dissipative Kerr solitons. They provide access to coherent, chip-scale optical frequency combs, which have already been employed in optical metrology, data communication and spectroscopy. Such Kerr resonator systems can exhibit numerous localized intracavity patterns and provide rich insights into nonlinear dynamics. A particular class of solutions consists of breathing dissipative solitons, representing pulses with oscillating amplitude and duration, for which no comprehensive understanding has been presented to date. Here, we observe and study single and multiple breathing dissipative solitons in two different microresonator platforms: crystalline $mathrm{MgF_2}$ resonator and $mathrm{Si_3N_4}$ integrated microring. We report a deterministic route to access the breathing state, which allowed for a detailed exploration of the breathing dynamics. In particular, we establish the link between the breathing frequency and two system control parameters - effective pump laser detuning and pump power. Using a fast detection, we present a direct observation of the spatiotemporal dynamics of individual solitons, revealing irregular oscillations and switching. An understanding of breathing solitons is not only of fundamental interest concerning nonlinear systems close to critical transition, but also relevant for applications to prevent breather-induced instabilities in soliton-based frequency combs.
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