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 solitons are waveforms that preserve their shape while propagating, relying on a balance of dispersion and nonlinearity [1,2]. Soliton-based data transmission schemes were investigated in the 1980s, promising to overcome the limitations imposed by dispersion of optical fibers. These approaches, however, were eventually abandoned in favor of wavelength-division multiplexing (WDM) schemes that are easier to implement and offer improved scalability to higher data rates. Here, we show that solitons may experience a comeback in optical communications, this time not as a competitor, but as a key element of massively parallel WDM. Instead of encoding data on the soliton itself, we exploit continuously circulating dissipative Kerr solitons (DKS) in a microresonator [3,4]. DKS are generated in an integrated silicon nitride microresonator [5] by four-photon interactions mediated by Kerr nonlinearity, leading to low-noise, spectrally smooth and broadband optical frequency combs [6]. In our experiments, we use two interleaved soliton Kerr combs to trans-mit a data stream of more than 50 Tbit/s on a total of 179 individual optical carriers that span the entire telecommunication C and L bands. Equally important, we demonstrate coherent detection of a WDM data stream by using a pair of microresonator Kerr soliton combs one as a multi-wavelength light source at the transmitter, and another one as a corresponding local oscillator (LO) at the receiver. This approach exploits the scalability advantages of microresonator soliton comb sources for massively parallel optical communications both at the transmitter and receiver side. Taken together, the results prove the significant potential of these sources to replace arrays of continuous-wave lasers in high-speed communications. In combination with advanced spatial multiplexing schemes [7,8] and highly integrated silicon photonic circuits [9], DKS combs may bring chip-scale petabit/s transceivers into reach.The first observation of solitons in optical fibers [2] in 1980 was immediately followed by major research efforts to harness such waveforms for long-haul communications [1]. In these schemes, data was encoded on soliton pulses by simple amplitude modulation using on-off-keying (OOK). However, even though the viability of the approach was experimentally demonstrated by transmission over one million kilometres [10], the vision of soliton-based communications was ultimately hindered by difficulties in achieving shape-preserving propagation in real transmission systems [1] and by the fact that nonlinear interactions intrinsically prevent dense packing of soliton pulses in either the time or frequency domain. Moreover, with the advent of wavelength-division multiplexing (WDM), line rates in long-haul communication systems could be increased by rather simple parallel transmission of data streams with lower symbol rates, which are less dispersion sensitive. Consequently, soliton-based communication schemes have moved out of focus over the last two decades. More recently, frequ...

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 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.

The formation of temporal dissipative solitons in optical microresonators enables compact, high repetition rate sources of ultra-short pulses as well as low noise, broadband optical frequency combs with smooth spectral envelopes. Here we study the influence of the resonator mode spectrum on temporal soliton formation. Using frequency comb assisted diode laser spectroscopy, the measured mode structure of crystalline MgF2 resonators are correlated with temporal soliton formation. While an overal general anomalous dispersion is required, it is found that higher order dispersion can be tolerated as long as it does not dominate the resonator's mode structure. Mode coupling induced avoided crossings in the resonator mode spectrum are found to prevent soliton formation, when affecting resonator modes close to the pump laser. The experimental observations are in excellent agreement with numerical simulations based on the nonlinear coupled mode equations, which reveal the rich interplay of mode crossings and soliton formation.Temporal dissipative solitons [1][2][3] can be formed in a Kerr-nonlinear optical microresonator [4] with anomalous dispersion that is driven by a monochromatic continuous wave pump laser. These temporal solitons are sech 2 -shaped ultra-short pulses of light circulating inside the microresonator, where the temporal width of the solitons is fully determined by the resonator dispersion and nonlinearity as well as the pump power and pump laser detuning [4,5]. It has been shown that the pump laser parameters can be used to control the number of solitons circulating in the microresonator. In particular the single soliton state, where one single soliton is circulating continuously inside the resonator, is of high interest for applications. In the time domain soliton formation in microresonators allows for the generation of periodic ultrashort femto-second pulses, which in the frequency domain correspond to a frequency comb spectrum with smooth sech 2 -shaped spectral envelope. The free spectral range (FSR) of the resonator, typically in the range of tens to hundreds of GHz, determines the pulse repetition rate (equivalent to the frequency comb line spacing). Soliton formation is related to four-wave mixing based frequency comb generation in microresonators [6][7][8][9][10][11][12][13][14][15], where low and high noise operating regimes [12,16,17] have been identified. Here, techniques such as δ − ∆-matching [17], self-injection locking [18,19] or parametric seeding [20] can be used to achieve low noise operation. In contrast to these low noise four-wave mixing based combs (also termed Kerr combs), the transition to the soliton regime [17] offers a unique combination of features, such as intrinsic low noise performance, direct pulse generation in the microresonator [4,21,22], and smooth spectral envelope as shown in Figure 1. These properties are critical to applications in e.g. telecommunications [23][24][25], low phase noise microwave generation [18,26]