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Microcavity-based frequency combs, or ‘microcombs’1,2, have enabled many fundamental breakthroughs3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21 through the discovery of temporal cavity-solitons. These self-localized waves, described by the Lugiato–Lefever equation22, are sustained by a background of radiation usually containing 95% of the total power23. Simple methods for their efficient generation and control are currently being investigated to finally establish microcombs as out-of-the-lab tools24. Here, we demonstrate microcomb laser cavity-solitons. Laser cavity-solitons are intrinsically background-free and have underpinned key breakthroughs in semiconductor lasers22,25,26,27,28. By merging their properties with the physics of multimode systems29, we provide a new paradigm for soliton generation and control in microcavities. We demonstrate 50-nm-wide bright soliton combs induced at average powers more than one order of magnitude lower than the Lugiato–Lefever soliton power threshold22, measuring a mode efficiency of 75% versus the theoretical limit of 5% for bright Lugiato–Lefever solitons23. Finally, we can tune the repetition rate by well over a megahertz without any active feedback.

Microcombs are optical frequency combs based on microcavity resonators [1] . They find multiple applications, including metrology, spectroscopy, frequency synthesis, and optical communications. Temporal cavity solitons (TCS), the temporal counterpart of spatial cavity solitons [2] , have been shown to produce microcombs with optimal spectral features [1] and are well modeled by the Lugiato-Lefever equation in passive systems. High contrast TCS can be also obtained in active systems inclusive of laser gain [3] .

Novel metamaterial platforms exhibiting time-dependent electromagnetic properties enable the investigation of previously unexplored light-matter interactions [1] - [2] . A variation in the dielectric function on a timescale shorter than the electric field period is perceived as an ultrafast temporal boundary [3] , thus resulting in a time-dependent "Snell’s law" which connects the polarisation field frequency before and after the transition [4] , [5] . The onset of a frequency shift therefore enables the engineering of exotic nonlinear phenomena such as time refraction and photon acceleration [5] - [7] , with key fundamental and practical implications [8] . In one scheme, a temporal boundary is induced via photoexcitation of semiconducting metamaterials excited by ultrashort optical pulses. Above-bandgap photons drive an ultrafast transition from a dielectric to a metallic state. Temporal-boundaries-mediated nonlinearities become relevant for transition times shorter than the wave-period timescale, a challenging regime in optics. This condition is achieved in a hybrid approach, exploiting the interaction of terahertz (THz) fields and ultrafast photo-excited transients. The peculiar advantage of THz Time-Domain-Spectroscopy techniques is that they allow the agile reconstruction of full-field dynamics with sub-wave-period resolution. In addition, in all the considered schemes, terahertz waves impinge from vacuum onto a positionally static transient, in other words a large velocity mismatch always exists. An unexplored physical scenario is then when the transient is applied directly to a source where the transient exists in the same positional reference as the THz wave.

Controlling the propagation of waves in random scattering media is a recurring challenge in several physical settings. Multiple scattering has a ubiquitous impact in wave domains like sound and mechanical [1] , and electromagnetic [2] . A fundamental limitation in the study of random wave propagation is the limited experimental access to the time-resolved oscillations of the electric field. At optical frequencies, in particular, the instantaneous electric field of optical wave-packets is, in general, not a directly measurable quantity, although particular settings, e.g., in the domain of optical frequency combs, allows for indirect reconstruction [3] . Conversely, full-wave characterization is quite mature in the state of the art of ultrafast terahertz (THz) photonics. The possibility of field-sensitive detection raises the important question of whether operating on the time-space domain of the electric field could provide insight on random wave propagate on typically not accessible in the optical domain. Indeed, this scenario recalls, in some fashion, the way random wave propagation is handled in the microwave and ultrasound domains, where multiple-path and scattering modelling allows specific deterministic approaches (e.g., time-reversal). A quite apt example is how the scattering matrix of a complex sample can be retrieved at optical frequency through measurements of the transmitted intensity profile [2] . This approach typically leads to a massive loss of information since scattering operates simultaneously in time and space [4] . However, it is conceivable that a more direct approach can be cast in a domain like THz, where the field is measurable in space and time. This ability would not only have a profound impact on THz imaging as a whole [5] , [6] , but it could also define novel approaches to the imaging of objects hidden behind scattering media while preserving their spectral fingerprint.

In photonics, the study of wave propagation in scattering media is limited by the inherent challenges in detecting the time-varying electric field oscillations, as detectors and cameras are only sensitive to the optical intensity. In the Terahertz (THz) domain, however, Time-Domain Spectroscopy (TDS) is an established technique capable of directly measuring the electric field and provide full-wave characterisation (amplitude and optical delay) in time. The combination of THz time-resolved measurements with the theory of wave propagation in scattering media is a rapidly emerging subject. It opens a promising route to gain coherent control over multiple-scattering phenomena in ways not previously accessible in optics [1] . Besides, the combination of broadband excitation and coherent, field-sensitive detection could allow investigating the transmission properties of a scattering medium in unprecedented detail and retrieve its coherent transfer-matrix representation, a task out-of-reach at optical frequencies. In this work, we theoretically demonstrate spatiotemporal refocusing of THz waves following a direct measurement of the transfer matrix of the scattering medium. Our approach combines the advantages offered by field-sensitive detection with the nonlinear wavefront shaping of THz waves. Wavefront shaping represents the state-of-the-art in the control of complex wave propagation at optical frequencies, as it allows to sequentially retrieve the transfer matrix elements of the scatterer [2] . To overcome the limited availability of THz Spatial Light Modulator (SLM) devices, we employ a recently proposed technique based on the nonlinear conversion of structured optical beams to THz patterns [3] . Specifically, we take inspiration from nonlinear Ghost-Imaging techniques and project a complete set of orthogonal Hadamard patterns on the scatterer [4] . This technique allows us to retrieve the complex-valued elements of the transfer matrix by numerical inversion ( Fig. 1a,b ). We apply the direct knowledge of the transfer matrix elements to identify the optimal focusing pattern in a deterministic fashion ( Fig. 1c,d ). Unlike iterative optimisation techniques [2] , our deterministic approach takes advantage of the full amount of spatiotemporal information encoded in the transfer matrix elements. Under this view, the task of identifying the optimal input wavefront is rewritten into an inverse problem that can be solved via constraint least-square optimisation methods. An exemplary result is shown in Fig. 1c,d , where our technique is employed to achieve spatiotemporal refocusing (i.e., focusing in space and compression in time) of a single cycle THz pulse.

Solitary waves — solitons — occur in a wide range of physical systems with a broad array of attributes and applications. Carefully engineered light–matter interactions have now produced an optomechanical dissipative soliton with promising properties.

We theoretically present a design of self-starting operation of microcombs based on laser-cavity solitons in a system composed of a micro-resonator nested in and coupled to an amplifying laser cavity. We demonstrate that it is possible to engineer the modulational-instability gain of the system's zero state to allow the start-up with a well-defined number of robust solitons. The approach can be implemented by using the system parameters, such as the cavity length mismatch and the gain shape, to control the number and repetition rate of the generated solitons. Because the setting does not require saturation of the gain, the results offer an alternative to standard techniques that provide laser mode-locking., Comment: To be published in Optics Express

We present a theoretical investigation of broadband, spatio-temporal control of THz light in random media. We consider the refocusing and compression of a THz pulse by optimising the spatiotemporal features of the transmitted field.

A cartographical study is conducted within the parameter space of a microresonator- filtered fiber laser. We identify a region in which solitons are spontaneously formed and maintained, and we investigate the effects which govern their emergence.

We provide the first demonstration of two-color optical rectification from semiconductors in an extreme absorption regime. The THz generation is free from phase-matching constraints due to the confinement of the interaction within a 25-atomic-layer region.

Microcombs based on Turing patterns have been extensively studied in configurations that can be modelled by the Lugiato-Lefever equation. Typically, such schemes are implemented experimentally by resonant coupling of a continuous wave laser to a Kerr microcavity in order to generate highly coherent and robust waves. Here, we study the formation of such patterns in a system composed of a microresonator nested in an amplifying laser cavity, a scheme recently used to demonstrate laser cavity solitons with high optical efficiency and easy repetition rate control. Utilizing this concept, we study different regimes of Turing patterns, unveiling their formation dynamics and demonstrating their controllability and robustness. By conducting a comprehensive modulational instability study with a mean-field model of the system, we explain the pattern formation in terms of its evolution from background noise, paving the way towards complete self-starting operation. Our theoretical and experimental paper provides a clear pathway for repetition rate control of these waves over both fine (Megahertz) and large (Gigahertz) scales, featuring a fractional frequency nonuniformity better than 7 × 10−14 with a 100-ms time gate and without the need for active stabilization.

We theoretically analyze and experimentally demonstrate optical bi-stability and multi-stability in an integrated nonlinear high-order microring resonator filter based on high-index contrast doped silica glass. We use a nonlinear model accounting for both the Kerr and thermal effects to analyze the instability behavior of the coupled-resonator based filter. The model also accurately predicts the multi-stable behavior of the filter when the input frequency is slightly detuned. To understand the role of the intracavity power distribution, we investigate the detuning of the individual rings of the filter from the optical response with a pump–probe experiment. Such a measurement is performed scanning the filter with a low-power probe beam tuned a few free spectral ranges away from the resonance where the pump is coupled. A comprehensive understanding of the relationship between the nonlinear behavior and the intracavity power distribution for the high-order microring resonator filter will help the design and implementation of future all-optical switching systems using this type of filter.

The stability of laser temporal cavity solitons in micro-ring cavities nested in an externally pumped fibre loop with gain is investigated. The crucial roles of group velocity mismatch and gain dispersion are identified.

Micro-resonator-based frequency combs, or micro-combs, have gained considerable interest in recent years due to their many potential applications such as high-speed communication systems, spectroscopy and ultrafast optical clocks [1]. Most micro-combs systems are based on laser pumped optical parametric oscillation and are typically non-self-starting, requiring a well-defined warm-up strategy involving smart control [2]. An alternative approach to micro-combs is represented by the Filter-Driven Four-Wave Mixing (FD-FWM) laser [3–5], based on a nonlinear micro-resonator nested in a main amplifying fibre cavity. Although this system has demonstrated self-starting regimes, stable operation typically imposes a strict relation between the minimum free-spectral range (FSR) of the main-cavity and the Q-factor of the micro-resonator. The use of longer main-cavity fibre lengths (highly desirable for several positive features, such as a larger gain) results in unrecoverable unstable regimes, i.e. in super-mode instability, which arises from the existence of many oscillating main-cavity modes within each micro-resonator resonance.

One of the major challenges in photonics is the full-wave reconstruction of arbitrary field distributions. Indeed, measuring both the amplitude and the optical delay (or optical phase) entails achieving breakthroughs in a wide range of scenarios, spanning from bio-imaging to material characterisation [1]. Time-Domain Spectroscopy (TDS) is routinely employed to perform field-sensitive measurements at terahertz (THz) frequencies. THz has been widely employed in developing advanced spectroscopy applications, thanks to its non-ionizing nature and to the fact that several materials possess a distinctive THz signature. All these features allow to precisely determine the composition of complex samples with critical implications in several fields, such as in-vivo biological imaging, medical diagnosis, security scanners and manufacturing control [2–3]. Despite the large body of research, however, the limited availability of high-resolution, full-wave imaging devices (i.e. field-sensitive THz cameras) poses a critical technological limit in this promising field.

Nonlinear optics in sub-wavelength structures plays a crucial role in the development of integrated photonics platforms and devices [1]. Surfaces, nanostructures and two-dimensional media are inherently free from longitudinal phase matching constraints and constitute an attractive framework to engineer complex forms of lightmatter interactions [2–3]. Most recent efforts in this area have focused on the generation of frequencies in the optical and infrared regions, e.g., second or third harmonic generation. An open question, however, is whether the broadband frequency conversion enabled by nanoscale nonlinear media could lead to the generation of long-wavelength radiation in a process known as Optical Rectification (OR). To date, OR of ultrafast optical pulses in nonlinear media has been subject of intense research, since it provides a robust and versatile approach to generate and manipulate broadband Terahertz (THz) fields. Using non-centrosymmetric crystals such as ZnTe and LiNbO 3 , large bandwidth THz pulses limited mainly by longitudinal phase-matching constraints, could be achieved [4]. Highly nonlinear Quasi-2D structures represent an intriguing alternative to this popular approach.

The quest towards the integration of ultra-fast, high-precision optical clocks is reflected in the large number of high-impact papers on the topic published in the last few years. This interest has been catalysed by the impact that high-precision optical frequency combs (OFCs) have had on metrology and spectroscopy in the last decade [ [1] , [2] , [3] , [4] , [5] ]. OFCs are often referred to as optical rulers: their spectra consist of a precise sequence of discrete and equally-spaced spectral lines that represent precise marks in frequency. Their importance was recognised worldwide with the 2005 Nobel Prize being awarded to T.W. Hansch and J. Hall for their breakthrough in OFC science [ 5 ]. They demonstrated that a coherent OFC source with a large spectrum – covering at least one octave – can be stabilised with a self-referenced approach, where the frequency and the phase do not vary and are completely determined by the source physical parameters. These fully stabilised OFCs solved the challenge of directly measuring optical frequencies and are now exploited as the most accurate time references available, ready to replace the current standard for time. Very recent advancements in the fabrication technology of optical micro-cavities [ 6 ] are contributing to the development of OFC sources. These efforts may open up the way to realise ultra-fast and stable optical clocks and pulsed sources with extremely high repetition-rates, in the form of compact and integrated devices. Indeed, the fabrication of high-quality factor (high-Q) micro-resonators, capable of dramatically amplifying the optical field, can be considered a photonics breakthrough that has boosted not only the scientific investigation of OFC sources [ [8] , [13] , [11] , [12] , [10] , [7] , [9] ] but also of optical sensors and compact light modulators [ [14] , [6] ]. In this framework, the demonstration of planar high-Q resonators, compatible with silicon technology [ [14] , [13] , [11] , [12] , [10] ], has opened up a unique opportunity for these devices to provide entirely new capabilities for photonic-integrated technologies. Indeed, it is well acknowledged by the electronics industry that future generations of computer processing chips will inevitably require an extremely high density of copper-based interconnections, significantly increasing the chip power dissipation to beyond practical levels [ [15] , [16] , [17] ]; hence, conventional approaches to chip design must undergo radical changes. On-chip optical networks, or optical interconnects, can offer high speed and low energy per-transferred-bit, and micro-resonators are widely seen as a key component to interface the electronic world with photonics. Many information technology industries have recently focused on the development of integrated ring resonators to be employed for electrically-controlled light modulators [ [14] , [15] , [16] , [17] ], greatly advancing the maturity of micro-resonator technology as a whole. Recently [ [13] , [11] , [12] ], the demonstration of OFC sources in micro-resonators fabricated in electronic (i.e. in complementary metal oxide semiconductor (CMOS)) compatible platforms has given micro-cavities an additional appeal, with the possibility of exploiting them as light sources in microchips. This scenario is creating fierce competition in developing highly efficient OFC generators based on micro-cavities which can radically change the nature of information transport and processing. Even in telecommunications, perhaps a more conventional environment for optical technologies, novel time-division multiplexed optical systems will require extremely stable optical clocks at ultra-high pulse repetition-rates towards the THz scale. Furthermore, arbitrary pulse generators based on OFC [ [18] , [19] ] are seen as one of the most promising solutions for this next generation of high-capacity optical coherent communication systems. This review will summarise the recent exciting achievements in the field of micro-combs, namely optical frequency combs based on high-Q micro-resonators, with a perspective on both the potential of this technology, as well as the open questions and challenges that remain.

We experimentally demonstrate the generation of highly coherent Type-II micro-combs based on a microresonator nested in a fiber cavity loop, known as the filter-driven four wave mixing (FD-FWM) laser scheme. In this system, the frequency spacing of the comb can be adjusted to integer multiples of the free-spectral range (FSR) of the nested micro-resonator by properly tuning the fiber cavity length. Sub-comb lines with single FSR spacing around the primary comb lines can be generated. Such a spectral emission is known as a “Type-II comb.” Our system achieves a fully coherent output. This behavior is verified by numerical simulations. This study represents an important step forward in controlling and manipulating the dynamics of an FD-FWM laser.

Surface-Terahertz generation at high excitation is dominated by both the nonlinear response and surface field dynamics. Our experimental characterization sheds light on this synergy revealing that no hard saturated limit for the THz emission exists.

We propose a scheme for bifurcation control in micro-cavities based on the interplay between the ultrafast Kerr effect and a slow nonlinearity, such as thermo-optical, free-carriers-induced, or opto-mechanical one. We demonstrate that Hopf bifurcations can be efficiently controlled with a low energy signal via four-wave mixing. Our results show that new strategies are possible for designing efficient micro-cavity-based oscillators and sensors. Moreover, they provide new understanding of the effect of coherent wave mixing in the thermal stability regions of optical micro-cavities, fundamental for micro-resonator-based applications in communications, sensing, and metrology, including optical micro-combs.

In this work, we study the nonlinear dynamics of micro-resonators in the presence of a thermo-optic effect, showing that four-wave mixing can trigger and control periodic thermal instabilities and chaotic regimes.

Recent developments in quantum photonics have initiated the process of bringing photonic-quantumbased systems out-of-the-lab and into real-world applications. As an example, devices to enable the exchange of a cryptographic key secured by the laws of quantum mechanics are already commercially available. In order to further boost this process, the next step is to transfer the results achieved by means of bulky and expensive setups into miniaturized and affordable devices. Integrated quantum photonics is exactly addressing this issue. In this paper, we briefly review the most recent advancements in the generation of quantum states of light on-chip. In particular, we focus on optical microcavities, as they can offer a solution to the problem of low efficiency that is characteristic of the materials typically used in integrated platforms. In addition, we show that specifically designed microcavities can also offer further advantages, such as compatibility with telecom standards (for exploiting existing fibre networks) and quantum memories (necessary to extend the communication distance), as well as giving a longitudinal multimode character for larger information transfer and processing. This last property (i.e., the increased dimensionality of the photon quantum state) is achieved through the ability to generate multiple photon pairs on a frequency comb, corresponding to the microcavity resonances. Further achievements include the possibility of fully exploiting the polarization degree of freedom, even for integrated devices. These results pave the way for the generation of integrated quantum frequency combs that, in turn, may find important applications toward the realization of a compact quantum-computing platform.

Passive fiber mode-locked lasers enable the excitation of multiple pulses per round trip representing a potential solutions for the increasing demand of practical optical sources with repetition rates of hundreds of GHz or higher. The control of such high repetition rate regimes is however a challenge. To this purpose, linear filters have been used in an "intracavity" configuration to force the repetition rate of the laser. This design is known as dissipative four wave mixing (DFWM) but it is usually unstable and hence marginally suitable for practical applications. We explore the use of nonlinear intracavity filters, such as integrated micro-ring resonators, capable of “driving” the FWM interaction in the laser. We term this approach as Filter-Driven FWM. With a proper choice of the filter properties in terms of free spectral range (FSR) and Q factor, we could observe stable regimes over a wide range of operating conditions, from high repetition rate oscillation at a 200GHz to the formation of two stable spectral comb replicas separated by the FSR of the main cavity (65MHz). High order filters, moreover, allow achieving nonlinear operation over large passbands. With an 11th order filter we achieve low-frequency mode-locking between the main cavity modes that oscillate within each resonance of the filter, producing burst pulsed operation. A stable mode-locked pulse train at 655GHz with an envelope of 42ps at 6.45MHz is achieved.

In this talk, the physics of microring resonators is discussed in the classical and quantum regimes, in the context of the exploitation of chi-3 effects in these cavities as done by our group. Through the implementation of a novel microring pumping scheme and a quantum reinterpretation of the frequency comb, we present an integrated platform for the generation of quantum optical states spread over multiple optical modes. The scheme allows for highly stable and potentially fullyintegrable quantum light sources. Following the demonstration of a multiplexed heralded photon source, the scheme also enabled the first demonstration of a new nonlinear process on the integrated platform (type II spontaneous four-wave mixing) allowing the first direct generation of polarization-diverse photon pairs, where the first time two ring modes can be pumped in a stable configuration.

The spatial features of a sub-wavelength terahertz source are not accessible using time-integrated knife-edge techniques due to the non-separable space-time nature of the radiated field and to systematic modifications induced by the blade itself. We show that combining knife-edge with a time resolved electro-optical sampling, the space-time coupling can be addressed and the source field profile can be exactly reconstructed.

We demonstrate a novel bi-chromatically pumped OPO operating on orthogonal polarizations in a CMOS compatible micro-ring resonator. Below threshold the device operates in the quantum regime and cross-polarized heralded photons are directly generated.

We observe second harmonic generation via random quasi-phase-matching in a 2.0 micron periodically poled, 1-cm-long, z-cut lithium tantalate. Away from resonance, the harmonic output profiles exhibit a characteristic pattern stemming from a stochastic domain distribution and a quadratic growth with the fundamental excitation, as well as a broadband spectral response. The results are in good agreement with a simple model and numerical simulations in the undepleted regime, assuming an anisotropic spread of the random nonlinear component. (C) 2010 Optical Society of America

We investigate the interaction of two coherent 2D+1 solitary beams in a high index glass.

We demonstrated broadband second-harmonic generation via random Quasi-Phase-Matching in periodically poled Lithium Tantalate.

Nonlinear optical processes are one of the most important tools in modern optics with a broad spectrum of applications in, for example, frequency conversion, spectroscopy, signal processing and quantum optics. For practical and ultimately widespread implementation, on-chip devices compatible with electronic integrated circuit technology offer great advantages in terms of low cost, small footprint, high performance and low energy consumption. While many on-chip key components have been realized, to date polarization has not been fully exploited as a degree of freedom for integrated nonlinear devices. In particular, frequency conversion based on orthogonally polarized beams has not yet been demonstrated on chip. Here we show frequency mixing between orthogonal polarization modes in a compact integrated microring resonator and demonstrate a bi-chromatically pumped optical parametric oscillator. Operating the device above and below threshold, we directly generate orthogonally polarized beams, as well as photon pairs, respectively, that can find applications, for example, in optical communication and quantum optics., On-chip nonlinear optics devices find a number of applications in modern optics from spectroscopy to communications. Here, the authors increase the degrees of freedom for frequency mixing by demonstrating the nonlinear interaction of perpendicularly-polarized modes in an integrated microring resonator.

We report an integrated, CMOS-compatible source of multiplexed heralded photons, distributed over several wavelengths at standard communication channels and compatible with quantum memories. Our system operates in a self-locked mode without an external pump laser.

By suppressing stimulated processes, we directly generate orthogonally polarized photon pairs on a chip via spontaneous non-degenerate FWM between orthogonally polarized pumps. Photon coincidences and optical parametric oscillation are measured.

We demonstrated coherent Terahertz characterization based on Terahertz Field Induced Second Harmonic effect in a Silica samples, operated with 10-100 V sources. Our sample is an infinitely long 30 μm slit written in gold. Our results pave the way to a novel approach towards broadband THz detection.

6 pags. ; 9 figs., We investigate beam propagation in a heavy-metal-oxide glass of the group Nb2O5 –PbO–GeO2 using picosecond pulses in the near infrared. We observe a wavelength-dependent self-focusing, with beam collapse and modulation instability in the Kerr regime at 1.064 m and stable spatial solitons at 820 nm where multiphoton absorption is present. We report near-infrared beam self-confinement and solitons, filamentation, interactions, and conical emission in the ps regime and discuss them with the aid of a numerical model., This work was funded by the Italian Ministry for University and Research through an “Italy-Spain Integrated Action” Grant No. IT1890/HI2006-0095,A.F.2007 and by the Spanish Ministry of Education and Science Grants No. MAT2005-06508-C02-01 and No. TEC2005-00074/MIC .

We demonstrate spatial solitons via twin-beam second-harmonic generation in hexagonal lattices realized by poling lithium niobate planar waveguides. These simultons can be steered by acting on power, direction, and wavelength of the fundamental frequency input.

Spatial solitary waves induced by quadratic nonlinearities have been the subject of many theoretical and experimental investigations in the last decade, with extensive studies being devoted to soliton formation in 1D nonlinear photonic crystals (NPC) such as PPLN (periodically poled LiNbO3). Here we present results on a new class of (1 + 1)D spatial solitary waves, the first examples of quadratic self-confinement in a 2D NPC.

We report on the first observation of spatial solitons in a 2D nonlinear photonic crystal. The experiments were performed in an hexagonally poled LiNbO3 waveguide designed for second harmonic generation from ~1.55 micron.

We present a theoretical and experimental investigation of soliton dynamics associated to twin-beam second harmonic generation in a purely nonlinear two-dimensional planar photonic lattice in LiNbO3.

We present theoretical and experimental investigations on the soliton dynamics associated to multiple second harmonic generation resonances in two-dimensional nonlinear photonic crystals, highlighting a wealth of new possibilities for soliton management in such structures.

We present a novel extraction algorithm for spectral phase interferometry for direct field reconstruction (SPIDER) for the so-called X-SPIDER configuration. Our approach largely extends the measurable time windows of pulses without requiring any modification to the experimental X-SPIDER set-up.

Ultrashort pulsed lasers, operating through the phenomenon of mode-locking, have had a significant role in many facets of our society for 50 years, for example, in the way we exchange information, measure and diagnose diseases, process materials, and in many other applications. Recently, high-quality resonators have been exploited to demonstrate optical combs. The ability to phase-lock their modes would allow mode-locked lasers to benefit from their high optical spectral quality, helping to realize novel sources such as precision optical clocks for applications in metrology, telecommunication, microchip-computing, and many other areas. Here we demonstrate the first mode-locked laser based on a microcavity resonator. It operates via a new mode-locking method, which we term filter-driven four-wave mixing, and is based on a CMOS-compatible high quality factor microring resonator. It achieves stable self-starting oscillation with negligible amplitude noise at ultrahigh repetition rates, and spectral linewidths well below 130 kHz., Stable, ultrahigh repetition rate optical clocks are critical for applications in high-speed communications, metrology and microchip computing. Peccianti et al. present a mode-locked laser based on an integrated microcavity, with repetition rate exceeding 200 GHz and narrow linewidth pulses.

We develop a method capable of characterizing both the amplitude and phase of ultrafast optical pulses with the aid of a synchronized incoherently-related clock pulse based on a novel variation of SPIDER. It exploits degenerate four-wave-mixing and its design is amenable for full ?on chip? signal characterization. By implementing our method in a CMOS compatible waveguide, we measure pulses with 1THz, and up to 100ps pulsewidths. Our novel reconstruction algorithm that we call Fresnel-Limited Extraction Procedure (FLEA), yields a time-bandwidth product (TBP)>100. Full Text: PDF References R. Trebino, "Frequency Resolved Optical Gating: the Measurement of Ultrashort Optical Pulses", (Kluwer Academic, 2002) [CrossRef] I. A. Walmsley and C. Dorrer, "Characterization of ultrashort electromagnetic pulses", Adv. Opt. Photon. 1, 308-437 (2009) [CrossRef] Nature Photonics Workshop on the future of optical communication,Tokyo, Oct. 2007. M. A. Foster et al.,"Silicon-chip-based ultrafast optical oscilloscope", Nature 456, 81-84 (2008) [CrossRef] E. K. Tien, X. Z. Sang, F. Qing, Q. Song, and O. Boyraz., "Ultrafast pulse characterization using cross phase modulation in silicon", Appl. Phys. Lett. 95, 051101 (2009) [CrossRef] A. Pasquazi et al.,"Sub-picosecond phase-sensitive optical pulse characterization on a chip", [CrossRef] C. Iaconis and I.A. Walmsley,"Spectral phase interferometry for direct electric-field reconstruction of ultrashort optical pulses", Opt. Lett., 23, 792-794 (1998) [CrossRef] L. Gallmann et al.,"Characterization of sub-6-fs optical pulses with spectral phase interferometry for direct electric-field reconstruction", Opt. Lett., 24, 1314-1316 (1999) [CrossRef] C. Dorrer et al.,"Single-shot real-time characterization of chirped-pulse amplification systems by spectral phase interferometry for direct electric-field reconstruction", Opt. Lett., 24, 1644-1646 (1999) [CrossRef] D. Keusters et al.,"Relative-phase ambiguities in measurements of ultrashort pulses with well-separated multiple frequency components", J. Opt. Soc. Am. B, 20, 2226-2237 (2003) [CrossRef] M. Hirasawa et al.,"Sensitivity improvement of spectral phase interferometry for direct electric-field reconstruction for the characterization of low-intensity femtosecond pulses", Appl. Phys. B, 74, S225-S229 (2002) [CrossRef] J. Wemans, G. Figueira, N. Lopes and L. Cardoso,"Self-referencing spectral phase interferometry for direct electric-field reconstruction with chirped pulses", Opt. Lett., 31, 2217-2219 (2006)Self-referencing spectral phase interferometry for direct electric-field reconstruction with chirped pulses [CrossRef] M. Peccianti et al.,"Subpicosecond optical pulse compression via an integrated nonlinear chirper", Opt. Express, 18, 7625-7633 (2010) [CrossRef] A. Pasquazi et al.,"All-optical wavelength conversion in an integrated ring resonator", Opt. Express 18, 3858-3863 (2010) [CrossRef]

We introduce an innovative geometry for OPOs in a CMOS-compatible microring resonator that is robust against the effect of thermal fluctuations. It exploits lasing of the pump inherently positioned within the resonances of the microcavity.

We demonstrate a stable passively mode locked soliton laser that extends the Dissipative-FWM concept, in a highly nonlinear, CMOS compatible integrated micro-ring resonator. Operation at 200GHz, free of supermode instability, is demonstrated.

We present a subpicosecond, 200GHz-repetition rate, passively mode-locked laser based on the dissipative four-wave mixing scheme exploiting a integrated CMOS-compatible high-Q nonlinear ring resonator.