Dissipative solitons can emerge in a wide variety of dissipative nonlinear systems throughout the fields of optics, medicine or biology. Dissipative solitons can also exist in Kerr-nonlinear optical resonators and rely on the double balance between parametric gain and resonator loss on the one hand and nonlinearity and diffraction or dispersion on the other hand. Mathematically these solitons are solution to the Lugiato-Lefever equation and exist on top of a continuous wave (cw) background. Here we report the observation of temporal dissipative solitons in a high-Q optical microresonator. The solitons are spontaneously generated when the pump laser is tuned through the effective zero detuning point of a high-Q resonance, leading to an effective red-detuned pumping. Red-detuned pumping marks a fundamentally new operating regime in nonlinear microresonators. While usually unstablethis regime acquires unique stability in the presence of solitons without any active feedback on the system. The number of solitons in the resonator can be controlled via the pump laser detuning and transitions to and between soliton states are associated with discontinuous steps in the resonator transmission. Beyond enabling to study soliton physics such as soliton crystals our observations open the route towards compact, high repetition-rate femto-second sources, where the operating wavelength is not bound to the availability of broadband laser gain media. The single soliton states correspond in the frequency domain to low-noise optical frequency combs with smooth spectral envelopes, critical to applications in broadband spectroscopy, telecommunications, astronomy and low phase-noise microwave generation.Comment: Includes Supplementary Informatio

Optical frequency combs [1,2] provide a series of equidistant laser lines and have revolutionized the field of frequency metrology within the last decade. Originally developed to achieve absolute optical frequency measurements, optical frequency combs have enabled advances in other areas [3] such as molecular fingerprinting [4,5], astronomy [6], range finding [7] or the synthesis of low noise microwave signals [8]. Discovered in 2007[9, 10], microresonator (Kerr) frequency combs have emerged as an alternative and widely investigated method to synthesize optical frequency combs offering compact form factor, chipscale integration, multi-gigahertz repetition rates, broad spectral bandwidth and high power per frequency comb line. Since their discovery there has been substantial progress in fundamental understanding [11][12][13], theoretical modeling [14][15][16], on-chip planar integration [17,18] and resulting applications [19][20][21]. Yet, in no demonstration could two key properties of optical frequency combs, broad spectral bandwidth and coherence, be achieved simultaneously. Here we overcome this challenge by accessing, for the first time, soliton induced Cherenkov radiation [22,23] in an optical microresonator. By continuous wave pumping of a dispersion engineered, planar silicon nitride microresonator [17,18], continuously circulating, sub-30 fs short temporal dissipative Kerr solitons [24][25][26] are generated, that correspond to pulses of 6 optical cycles and constitute a coherent optical frequency comb in the spectral domain. Emission of soliton induced Cherenkov radiation caused by higher order dispersion broadens the spectral bandwidth to 2/3 of an octave, sufficient for self referencing [1,2], in excellent agreement with recent theoretical predictions [16] and the broadest coherent microresonator frequency comb generated to date. Once generated it is shown that the soliton induced Cherenkov radiation based frequency comb can be fully phase stabilized. The overall relative accuracy of the generated comb with respect to a reference fiber laser frequency comb is measured to be 3 · 10 −15 . The ability to preserve coherence over a broad spectral bandwidth using soliton induced Cherenkov radiation marks a critical milestone in the development of planar optical frequency combs, enabling on one hand application in e.g. coherent communications [19], broadband dual comb spectroscopy [27] and Raman spectral imaging [28], while on the other hand significantly relaxing dispersion requirements for broadband microresonator frequency combs [29] and providing a path for their generation in the visible and UV. Our results underscore the utility and effectiveness of planar microresonator frequency comb technology, that offers the potential to make frequency metrology accessible beyond specialized laboratories.Optical solitons are propagating pulses of light that retain their shape due to a balance of nonlinearity and dispersion [24][25][26]30]. In the presence of higher order dispersion optical solitons can emit solito...

Optical frequency combs allow for the precise measurement of optical frequencies and are used in a growing number of applications. The new class of Kerr-frequency comb sources, based on parametric frequency conversion in optical microresonators, can complement conventional systems in applications requiring high repetition rates such as direct comb spectroscopy, spectrometer calibration, arbitrary optical waveform generation and advanced telecommunications. However, a severe limitation in experiments working towards practical systems is phase noise, observed in the form of linewidth broadening, multiple repetition-rate beat notes and loss of temporal coherence. These phenomena are not explained by the current theory of Kerr comb formation, yet understanding this is crucial to the maturation of Kerr comb technology. Here, based on observations in crystalline MgF 2 and planar Si 3 N 4 microresonators, we reveal the universal, platformindependent dynamics of Kerr comb formation, allowing the explanation of a wide range of phenomena not previously understood, as well as identifying the condition for, and transition to, low-phase-noise performance.O ptical frequency combs [1][2][3][4] have revolutionized the field of frequency metrology and spectroscopy and are enabling components in a range of applications 5 . Recently, a novel class of frequency comb generators has been discovered 6 by coupling a continuous-wave (c.w.) laser to a high-finesse fused silica microcavity, where the Kerr nonlinearity enables (cascaded) fourwave-mixing (FWM), resulting in an optical frequency comb. These Kerr combs could complement conventional frequency combs in applications where high power per comb line (typically .100 mW) and high repetition rate (.10 GHz spacing between the comb lines) are desirable 7 , such as in astronomical spectrometer calibration [8][9][10] , direct comb spectroscopy 11 , arbitrary optical waveform generation 12,13 and advanced telecommunications. The creation of Kerr combs using microresonators has been demonstrated in crystalline CaF 2 (refs 14,15) and MgF 2 (refs 16-18) resonators, fused-silica microspheres 19 , planar high-index silica 20 and Si 3 N 4 ring resonators 21,22 , and compact fibre cavities 23 . Over recent years, a significant advance in Kerr comb technology has been achieved by demonstrating a single and well-defined radiofrequency (RF) beat note between adjacent comb lines (corresponding to the equidistant comb spacing and required for stabilizing the comb) 6,14,24 , a fully phase-stabilized Kerr comb 24 , the generation of octave-spanning spectra (required for self-referencing the comb using the f-2f scheme) 25,26 , the detection and shaping of pulses 13 , and extension of spectral coverage towards the visible 27 and midinfrared spectral regimes 18 . In addition to these experimental advances, theoretical work 28,29 has also enabled an explanation of the power distribution of Kerr combs, particularly the first comb modes appearing not necessarily adjacent to the pump. Despite these advances,...

Optical frequency combs have the potential to revolutionize terabit communications1. Generation of Kerr combs in nonlinear microresonators2 represents a particularly promising option3 enabling line spacings of tens of GHz. However, such combs may exhibit strong phase noise4-6, which has made high-speed data transmission impossible up to now. Here we demonstrate that systematic adjustment of pump conditions for low phase noise4,7-9 enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit/s on a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment demonstrates feedback-stabilization of the comb and transmission of a 1.44 Tbit/s data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive solution towards chip-scale terabit/s transceivers.

Optical frequency combs [1,2,3] have revolutionized the field of frequency metrology within the last decade and have become enabling tools for atomic clocks [4], gas sensing [5,6] and astrophysical spectrometer calibration [7,8]. The rapidly increasing number of applications has heightened interest in more compact comb generators. Optical microresonator based comb generators bear promise in this regard. allow deriving an optical frequency comb directly from a continuous wave laser source and have been demonstrated in a number of optical microresonator geometries [9,10,11,12,13,14,15]. Critical to their future use as 'frequency markers', is however the absolute frequency stabilization of the optical comb spectrum [16]. A powerful technique for this stabilization is self-referencing [16,17], which requires a spectrum that spans a full octave, i.e. a factor of two in frequency. In the case of mode locked lasers, overcoming the limited bandwidth has become possible only with the advent of photonic crystal fibres for supercontinuum generation [18,19]. Here, we report for the first time the generation of an octave-spanning frequency comb directly from a toroidal microresonator on a silicon chip. The comb spectrum covers the wavelength range from 990 nm to 2170 nm and is retrieved from a continuous wave laser interacting with the modes of an ultra high Q microresonator, without relying on external broadening. Full tunability of the generated frequency comb over a bandwidth exceeding an entire free spectral range is demonstrated. This allows positioning of a frequency comb mode to any desired frequency within the comb bandwidth. The ability to derive octave spanning spectra from microresonator comb generators represents a key step towards achieving a radio-frequency to optical link on a chip, which could unify the fields of metrology with micro-and nano-photonics and enable entirely new devices that bring frequency metrology into a chip scale setting for compact applications such as space based optical clocks.In addition to the advantage of compact integration, microresonator based frequency combs have high power per comb line, which is a result of the smaller resonator size and the correspondingly higher repetition rate. This high power per comb line enables direct comb spectroscopy [20] and is advantageous for many applications, and critical for high capacity telecommunication. On the other hand, the high repetition rate of micro-combs results in a smaller peak power of the optical pulses that are underlying the generated frequency comb. This renders spectral broadening using nonlinear fibres [1,18] inefficient. Spectral broadening is a method which allowed for the first broadening of mode locked lasers to octave spanning combs ten years ago [19], leading to a breakthrough of the optical frequency comb technology.Here we show that the high power enhancement in a microresonator itself is sufficient for direct octave spanning frequency comb synthesis without the need for any additional spectral broadening. Optical freq...