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A complex problem in terahertz photonics is the need for thin emitters [1] . Traditional free-space terahertz (THz) emission crystals rely on relatively thick crystals (on the orders of millimetres), as the terahertz emission scales with the length of the crystal. Thick crystals, however, come with a number of drawbacks. One such drawback is that the emitted THz bandwidth is limited by phase-matching conditions [2] . This amounts to thicker crystals giving a lower bandwidth, making them unsuitable for broadband spectroscopy. In near-field imaging, the image resolution depends critically on how close one can approach the sample [3] : in this regime, thick crystals can quickly become unpractical as they effectively limit the achievable resolution.

Optical-Pump Terahertz (THz) Near-Field Microscopy (OP-TNFM) is a novel technique for trans- carrier hyperspectral imaging, capable of extracting recombination dynamics and the spatially distributed complex refractive index that results from thermalised carriers in semiconducting materials.

In an open nonlinear system, emergent complex structures are generally determined by a set of global parameters. Cavity-solitons are an example of such structures and, in their temporal form, have seeded the last decade of major developments in microresonator-based optical frequency combs. These optical pulses typically require complex procedures and external feedback to be induced and maintained. Recent progress has seen the microresonators directly embedded into a laser cavity [1] , [2] where it is possible to simply initiate cavity-soliton formation by increasing the laser-diode driving current [3] . Hybrid laser-microresonator schemes have been considered since 2012 [4] , and extremely efficient laser cavity-solitons have been experimentally and theoretically demonstrated in a laser microcomb [5] .

International audience; We summarize our results on the generation of temporal laser cavity-solitons in a system comprising an optical micro-cavity nested in a fiber laser. We will discuss their features, region of existence, potential and challenges ahead. Dissipative solitons are self-confined pulses which appear in driven and lossy systems when the phase dispersion is balanced by the nonlinear phase-shift. Ultrashort pulses generated by passive mode-locking lasers are a very important example of temporal dissipative solitons in optics. Temporal cavity-solitons [1,2,3] also belong to this class of pulses and have been instrumental in the development of optical frequency combs in nonlinear micro-cavities, or "micro-combs" [1]. Temporal cavity-solitons have been largely studied in a 'driven' configuration, where an external pumping source is resonantly coupled in the nonlinear micro-resonator to sustain and excite the solitary pulses. More recently, we demonstrated that it is possible to generate localised pulses in a configuration where the micro-cavity is inserted in a fiber laser loop, as described in Figure 1. In particular, we reported the observation of laser cavity-solitons [4], which have previously attracted large attention especially in spatial configurations, such as in semiconductor lasers [5]. By merging their properties with the physics of both micro-resonators and multi-mode systems, this scheme represents a fundamentally new paradigm for the generation, stabilisation and control of solitary optical pulses in micro-cavities. Fig. 1. Scheme of the nested, travelling-wave cavities configuration: a Kerr micro-resonator (green loop) is nested in an amplifying fibre-loop (black). The amplifying cavity comprises a gain fibre (erbium-ytterbium doped amplifier, EYDFA), a tuneable delay line with optical couplers (OC), polarising beam splitter (PBS), polarisation control and a band-pass filter (BPF). The output of the laser is monitored with an optical spectrum analyser (OSA), a second-harmonic non-collinear autocorrelator and an oscilloscope to measure the radio-frequency noise of the system. © 2 0 2 0 T h e Au t h o r (s)

Plasmonic metasurfaces provide a compact platform to engineer the wave-front of optical beams by tuning the material and its morphology, hence enabling advanced functionalities in ultra-thin photonic systems [1,2]. In standard metasurfaces, however, the optical response is usually static and fixed by design. An appealing possibility to achieve ultrafast dynamical tuning is given by optically-induced plasmonic systems, where the metallic response of narrow-bandgap semiconductors is driven by high-fluence illumination. Under these conditions, the surface of the semiconductor can be overflown with photo-carriers inducing a transient metallic state [3]. An intriguing question is whether the transient metallization could be employed to dynamically engineer the optical response and to control light-matter interactions on the surface.

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.

We report on 'slow' pulsing dynamics in a silica resonator-based laser system: by nesting a high-Q rod-resonator inside an amplifying fiber cavity, we demonstrate that trains of microsecond pulses can be generated with repetition rates in the hundreds of kilohertz. We show that such pulses are produced with a period equivalent to several hundreds of laser cavity roundtrips via the interaction between the gain dynamics in the fiber cavity and the thermo-optical effects in the high-Q resonator. Experiments reveal that the pulsing properties can be controlled by adjusting the amplifying fiber cavity parameters. Our results, confirmed by numerical simulations, provide useful insights on the dynamical onset of complex self-organization phenomena in resonator-based laser systems where thermo-optical effects play an active role. In addition, we show how the thermal state of the resonator can be probed and even modified by an external, counter-propagating optical field, thus hinting towards novel approaches for all-optical control and sensing applications. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

We consider the passive modulation of the surface field at a junction between semiconductors and 2D-materials. We experimentally demonstrate that this boosts the optical-to-terahertz conversion efficiency beyond that of benchmark surface emitters.

Plasmonic metamaterials enable access to extremely nonlinear regimes with remarkable full-field control. We theoretically and experimentally demonstrate a novel form of photo-induced semiconducting Time-Dependent metamaterial at THz frequencies.

We demonstrate the first fully solid-state technique for the coherent detection of ultra-broadband THz pulses (0.1-10 THz), relying on the electric-field-induced second-harmonic generation attained in integrated CMOS-compatible devices.

We experimentally investigated a novel form of photo-induced plasmonic response, in nanostructured silicon, at THz frequencies which can be employed to precisely control the full-wave properties, i.e. amplitude and phase, of the generated THz pulse.

The interest in surface terahertz emitters lies in their extremely thin active region, typically hundreds of atomic layers, and the agile surface scalability. The ultimate limit in the achievable emission is determined by the saturation of the several different mechanisms concurring to the THz frequency conversion. Although there is a very prolific debate about the contribution of each process, surface optical rectification has been highlighted as the dominant process at high excitation, but the effective limits in the conversion are largely unknown.\ud \ud The current state of the art suggests that in field-induced optical rectification a maximum limit of the emission may exist and it is ruled by the photocarrier induced neutralisation of the medium's surface field. This would represent the most important impediment to the application of surface optical rectification in high-energy THz emitters.\ud \ud We experimentally unveil novel physical insights in the THz conversion at high excitation energies mediated by the ultrafast surface optical rectification process. The main finding is that the expected total saturation of the Terahertz emission vs pump energy does not actually occur. At high energy, the surface field region contracts towards the surface. We argue that this mechanism weakens the main saturation process, re-establishing a clearly observable quadratic dependence between the emitted THz energy and the excitation. This is relevant in enabling access to intense generation at high fluences.

In this contribution, we will review our recent activities in the development of double nested cavity lasers. Several stable operating regimes can be achieved over a wide range of conditions.

The interplay between ultrafast and slow nonlinearities, like Kerr and thermo-optical nonlinearities, is well-known for generating bistability, self-pulsing and chaotic regimes in optical microcavities. These effects have been observed in different kinds of devices, such as doped silica glass optical microcavities with high refractive index [1], and numerical models have been investigated to provide a description of such dynamics, e.g. in semiconductor nanocavities [2-3]. Specifically, self-pulsing can be explored to generate all-optical stochastic sources, and it has been recently demonstrated with opto-mechanical nonlinearities [4].

We experimentally investigate the enhancement and phase change of the THz emission from photo-excited randomly structured black silicon substrates mediated by an induced metallic state of the nanostructured surface.

In this paper, we demonstrate a novel dual-pump approach to generate robust optical frequency comb with varying free spectral range (FSR) spacing in a CMOS-compatible high-Q micro-ring resonator (MRR). The frequency spacing of the comb can be tuned by an integer number FSR of the MRR freely in our dual-pump scheme. The dual pumps are self-oscillated in the laser cavity loop and their wavelengths can be tuned flexibly by programming the tunable filter embedded in the cavity. By tuning the pump wavelength, broadband OFC with the bandwidth of >180 nm and the frequency-spacing varying from 6 to 46-fold FSRs is realized at a low pump power. This approach could find potential and practical applications in many areas, such as optical metrology, optical communication and signal processing systems, for its excellent flexibility and robustness.

We demonstrate temporal measurements of sub-picosecond optical pulses via time-to-frequency conversion in a 45-cm-long CMOS compatible high-index glass spiral waveguide. The measurements are based on efficient four-wave mixing in the C-band, using around 1 W of peak pump power. We achieve a resolution of 400 fs over a time window of 100 ps, representing a time-bandwidth product >; 250.

We report on light-induced optical tuning of colloidal photonic crystals doped with gold nanoparticles (Au-nps). By resonantly exciting the Au-np surface plasmon absorption with picosecond pulses at 0.53 micron in a standard pump-probe setup, we observed permanent changes in the stop band resonance around 1.7 micron, with blue wavelength shifts as large as 30 nm and associated to a nanoparticle reshaping. Fine tuning was achieved by controlling either the pulse energy or the irradiation time.

We summarize here our recent results on high-repetition-rate laser mode-locking via microring resonators. The recent realization of multiple wavelength oscillators based on high Q-factor resonators has profoundly impacted optical frequency combs for metrology and precision measurements and other areas. The ability to mode-lock these devices is important for achieving high-precision optical clocks in a monolithic format, offering enormous benefits in performance, cost, size, and power consumption for optical waveform synthesis, high-capacity telecommunications, optical analog-to-digital conversion, and many other applications. Here, we demonstrated a mode-locked laser based on a monolithic high Q resonator. This device produces stable, self-starting transform-limited optical pulses at 200.3 GHz, with a sub-100 kHz linewidth and extremely narrow amplitude noise bandwidth of

We demonstrated coherent Terahertz characterization based on the Terahertz Field Induced Second Harmonic effect in few microns thick Silica (SiO2) samples that can be easily operated with as little as a few hundred Volts. Our sample is an infinitely long 30 μm slit written in gold. The underlying idea of our work is that of exploiting the large breakdown voltage and the high nonlinearity of glass to achieve a large signal to noise ratio detection with a very weak optical probe at moderate bias fields, thus drastically reducing the electrodes gap. Our results pave the way to a novel approach towards broadband THz detection.

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.

WOS: 000349894700001, PubMed ID: 25711343, Terahertz technologies recently emerged as outstanding candidates for a variety of applications in such sectors as security, biomedical, pharmaceutical, aero spatial, etc. Imaging the terahertz field, however, still remains a challenge, particularly when sub-wavelength resolutions are involved. Here we demonstrate an all-optical technique for the terahertz near-field imaging directly at the source plane. A thin layer (, MERST (Ministere de l'Enseignement superieur, de la Recherche et de la Science); NSERC (National Science and Engineering Research Council) in Canada; Skim Latihan Akademik IPTA (SLAI) from the Ministry of Higher Education Malaysia (MOHE); "Le Fonds Quebecois de la Recherche sur la Nature et les Technologies'' (FQRNT)FQRNT; European CommissionEuropean Commission Joint Research Centre [630833, 299522, 327627], The work has been supported by the MERST (Ministere de l'Enseignement superieur, de la Recherche et de la Science) and by the NSERC (National Science and Engineering Research Council) in Canada. Ho Sze Phing gratefully acknowledges a fellowship from the Skim Latihan Akademik IPTA (SLAI) from the Ministry of Higher Education Malaysia (MOHE). Mostafa Shalaby would like to acknowledge the financial support from "Le Fonds Quebecois de la Recherche sur la Nature et les Technologies'' (FQRNT). Marco Peccianti acknowledges the support from the FP7 Marie Curie Actions of the European Commission, via the Career-Integration Grant (contract-No 630833). Matteo Clerici acknowledges the support from the FP7 Marie Curie Actions of the European Commission, via the International-Outgoing-Fellowship (contract-No 299522). Alessia Pasquazi acknowledges the support from the FP7 Marie Curie Actions of the European Commission, via the International Incoming Fellowships (contract-No 327627).

Four-wave mixing in a thermal tunable 5th order cascaded CMOS compatible ring resonators is experimentally and numerically investigated. Flat bandwidth conversion of 3.1GHz is obtained for a range of parameter.

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 demonstrated a 1.81 μm mode-locked figure-eight laser using an integrated 11-th order microring resonator. Mode-locked train centered at 1.81 μm with repetition rate of 9.09 MHz is achieved.

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.

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.

Exploiting four-wave mixing between an optical probe and a Terahertz field in a few micrometers thick Silica sample we demonstrate broadband coherent Terahertz detection by applying a bias as low as 100 V.

Second harmonic generation is investigated in lithium niobate channels realized by proton exchange and quasi-phase-matched by surface periodic-poling. The reduction in conversion efficiency at high powers is interpreted in terms of multi-photon absorption via two-color terms, yielding an estimate of the dominating three-photon process., Comment: 2 pages, 6 figures

We demonstrate ultraviolet generation in lithium tantalate channel waveguides for frequency doubling via quasi-phase-matching. The samples, proton exchanged and nanostructured by electric-field assisted surface periodic poling with domains as deep as 40 μm, yield continuous wave light at 365.4 nm with conversion efficiencies larger than 7.5% W-1 cm-2.

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 demonstrate a range of novel functions based on a high index doped silica glass CMOS compatible platform. This platform has promise for telecommunications and onchip WDM optical interconnects for computing.

We demonstrate novel microcavity lasers in an integrated, CMOS compatible platform. This platform has promise for telecommunications and on-chip WDM optical interconnects.

We demonstrate a range of novel functions based on a high index doped silica glass CMOS compatible platform. This platform has promise for telecommunications and on-chip WDM optical interconnects for computing.

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 report a mode locked laser based on an integrated high-Q microring resonator with a highly monochromatic radiofrequency modulation thanks to the stable operation of two slightly shifted spectral optical comb replicas.

We report a mode locked laser based on an integrated high-Q microring resonator with a highly monochromatic radiofrequency modulation thanks to the stable operation of two slightly shifted spectral optical comb replicas.

We report a novel geometry for OPOs in a CMOS-compatible microring resonator. It exploits non-critical lasing of the pump inherently positioned within the resonances of the microcavity, thus counteracting the effect of thermal fluctuations.

All-optical signal processing has been demonstrated extensively in Si including demultiplexing at 160Gb/s via four-wave mixing (FWM) [1] and optical regeneration [2], as well as in chalcogenide glass (ChG) waveguides[3]. The efficiency of all-optical devices can be improved by increasing the nonlinear parameter, γ = ω n 2 / c A eff (A eff is the waveguide effective area, n 2 is the Kerr nonlinearity) as well as by using resonant structures to enhance the local field intensity. Semiconductors and ChG offer excellent optical confinement and a high n 2 that has produced γ's of 200,000 W−1 km−1 for Si nanowires [2], and 93,400 W−1 km−1 in ChG nanotapers [4]. Yet silicon suffers from a poor intrinsic nonlinear figure of merit (FOM = n 2 / (β λ), where β is the two-photon absorption coefficient) due to two-photon absorption (TPA) and the resulting free carriers [5]. Here, we report a wide range of functions in a CMOS compatible high index doped silica glass platform, including an integrated multiple wavelength source [6,7], an ultra-high repetition rate modelocked laser [8], and an all-optical integrator[9]. We achieve CW oscillation in a Q=1.2 million micro-ring resonator with a slope efficiency of 7.4% (single oscillating mode, single port), a threshold power of 54mW, and frequency spacings from 200GHz to > 6THz. We also achieve modelocking with repetition rates as high as 800GHz [9]. We also report novel functions in ultra-long (45cm) spiral waveguides, including a time-lens optical oscilloscope and parametric amplifier with > 15dB of gain [10]. The success of these devices is due to very low linear loss, negligible nonlinear loss (up to 25GW/cm2), and a high γ ≅ 233W−1km−1. The low loss, design flexibility, and CMOS compatibility of this platform will enable devices for telecommunications, computing, sensing, metrology and other areas.

We demonstrate a wide range of novel functions in integrated, CMOS compatible, devices. This platform has promise for telecommunications and on-chip WDM optical interconnects for computing.

We present a dissipative four wave mixing tunable laser based on a integrated CMOS-compatible high-Q nonlinear ring resonator, emitting subpicosecond pulses at 200GHz-repetition rate. Quasi-sinusoidal 800GHz emission regime is also demonstrated.

We present an investigation on the nonlinear dynamics of intense pulses in an AlGaAs Bragg waveguide and we report the experimental observation of an intensity dependent blue-shift of the Bragg notch spectral line.

We present a dissipative four wave mixing tunable laser based on a integrated CMOS-compatible high-Q nonlinear ring resonator, emitting subpicosecond pulses at 200GHz-repetition rate. Quasi-sinusoidal 800GHz emission regime is also demonstrated.

We present a subpicosecond, ultrahigh repetition rate, passively mode-locked laser based on four-wave mixing in an integrated CMOS-compatible high-Q nonlinear ring resonator.

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.

We present the first system penalty measurements for all-optical wavelength conversion in an integrated ring resonator. We achieve wavelength conversion over a range of 27.7 nm in the C-band at 2.5 Gb/s by exploiting four wave mixing in a CMOS compatible, high index glass ring resonator at approximately 22 dBm average pump power, obtaining0.3 dB system penalty.

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

We present a dissipative four wave mixing tunable laser based on a integrated CMOS-compatible high-Q nonlinear ring resonator, emitting subpicosecond pulses at 200GHz-repetition rate. Quasi-sinusoidal 800GHz emission regime is also demonstrated.