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We report the observation of Brillouin backscattering in a 50-cm long spiral high-index doped silica chip waveguide and measured a Brillouin frequency shift of 16 GHz which is in very good agreement with theoretical predictions and numerical simulations based on the elastodynamics equation., Comment: 5 pages, 6 figures

Photonic integrated circuits (PICs) are a key component [1] for future telecommunication networks, where demands for greater bandwidth, network flexibility, low energy consumption and cost must all be met. The quest for all optical components has naturally targeted materials with extremely large nonlinearity, including chalcogenide glasses (ChG) [2] and semiconductors, such as silicon [3] and AlGaAs [4]. Yet issues such as immature fabrication technologies for ChG, and high linear and nonlinear losses for semiconductors, motivate the search for other materials. Here we present the first demonstration of nonlinear optics in integrated silica based glass waveguides using continuous wave (CW) light. We demonstrate four wave mixing (FWM), with low (7mW) CW pump power at a wavelength of 1550nm, in high index doped silica glass ring resonators capable of performing in photonic telecommunications networks as linear filters [5]. The high reliability, design flexibility, and manufacturability of our device raises the possibility of a new platform for future low cost nonlinear all optical PICs., Comment: 15 pages, 5 figures, 32 references

Ultrashort high-energy pulses at wavelengths longer than 1 $\mu$m are nowadays desired for a vast variety of applications in ultrafast and strong-field physics. To date, the main answer to the wavelength tunability for energetic, broadband pulses still relies on optical parametric amplification (OPA), which often requires multiple and complex stages, may feature imperfect beam quality and has limited conversion efficiency into one of the amplified waves. In this work, we present a completely different strategy to realize an energy-efficient and scalable laser frequency shifter. This relies on the continuous red shift provided by stimulated Raman scattering (SRS) over a long propagation distance in nitrogen-filled hollow core fibers (HCF). We show a continuous tunability of the laser wavelength from 1030 nm up to 1730 nm with conversion efficiency higher than 70% and high beam quality. The highly asymmetric spectral broadening, arising from the spatiotemporal nonlinear interplay between high-order modes of the HCF, can be readily employed to generate pulses (~20 fs) significantly shorter than the pump ones (~200 fs) with high beam quality, and the pulse energy can further be scaled up to tens of millijoules. We envision that this technique, coupled with the emerging high-power Yb laser technology, has the potential to answer the increasing demand for energetic multi-TW few-cycle sources tunable in the near-IR.

We demonstrate a photonic radio frequency (RF) transversal filter based on an integrated optical micro-comb source featuring a record low free spectral range of 49 GHz yielding 80 micro-comb lines across the C-band. This record-high number of taps, or wavelengths for the transversal filter results in significantly increased performance including a QRF factor more than four times higher than previous results. Further, by employing both positive and negative taps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using Gaussian apodization, together with a tunable centre frequency covering the RF spectra range, with a widely tunable 3-dB bandwidth and versatile dynamically adjustable filter shapes. Our experimental results match well with theory, showing that our transversal filter is a competitive solution to implement advanced adaptive RF filters with broad operational bandwidths, high frequency selectivity, high reconfigurability, and potentially reduced cost and footprint. This approach is promising for applications in modern radar and communications systems., Comment: 19 pages, 12 figures, 107 references, Winner IEEE JLT 2019 Paper of the Year Revised - references updated and links to award websites added

The goal of this report is to study the conditions for efficient THz generation using Frequency Difference Generation principle. In particular, two CW IR beams are used together with a periodically poled lithium niobate crystal in order to generate a continuous THz wave. As a source of the IR pump beams we consider a 30W (CW) IPG Er-doped fiber-amplifier which currently is the most powerful commercial amplifier on the market. The work is motivated by application of CW sources of THz waves in high bit wireless communication applications. The amplifier will allow to mix two optically modulated IR beams and to generate modulated THz signal.

We demonstrate efficient, low power, continuous-wave four-wave mixing in the C-band, using a high index doped silica glass micro ring resonator having a Q-factor of 1.2 million. A record high conversion efficiency for this kind of device is achieved over a bandwidth of 20nm. We show theoretically that the characteristic low dispersion enables phase-matching over a bandwidth > 160nm., Comment: 7 pages, 5 figures, 24 references

We demonstrate sub-picosecond wavelength conversion in the C-band via four wave mixing in a 45cm long high index doped silica spiral waveguide. We achieve an on/off conversion efficiency (signal to idler) of +16.5dB as well as a parametric gain of +15dB for a peak pump power of 38W over a wavelength range of 100nm. Furthermore, we demonstrated a minimum gain of +5dB over a wavelength range as large as 200nm., Comment: 8 pages, 4 figures, 30 references

Nonlinear photonic chips have succeeded in generating and processing signals all-optically with performance far superior to that possible electronically - particularly with respect to speed. Although silicon-on-insulator has been the leading platform for nonlinear optics, its high two-photon absorption at telecommunications wavelengths poses a fundamental limitation. This paper reviews some of the recent achievements in CMOS-compatible platforms for nonlinear optics, focusing on amorphous silicon and Hydex glass, highlighting their potential future impact as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement., Comment: 8 pages, 10 figures 80 references. arXiv admin note: substantial text overlap with arXiv:1404.5610

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., Comment: 6 pages, 7 figures, 67 references, 1 table. arXiv admin note: text overlap with arXiv:1404.5361

Ultrashort pulsed lasers, operating through the phenomenon of mode-locking, have played 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. The ability to phase-lock the modes of the high-quality resonators recently exploited to demonstrate optical combs, would allow mode-locked lasers to benefit from their high optical spectral quality in order to realize novel sources such as precision optical clocks for applications to metrology, telecommunications, microchip-computing, and many other areas. We demonstrate the first mode-locked laser based on a micro-cavity resonator. It operates via a new mode-locking method we termed Filter-Driven (FD) Four-Wave-Mixing, and is based on a CMOS-compatible high quality factor micro-ring resonator. It achieves stable self-starting oscillation with negligible amplitude noise at ultrahigh repetition rates, and spectral linewidths well below 130 kHz., Comment: 16 pages, 32 references, 5 figures

The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is principally investigated as a means for the detection of radiation in the hardly accessible THz spectral region. Most studies have targeted second-order nonlinear processes, given their higher efficiencies, and only a limited number have addressed third-order nonlinear interactions, mainly investigating four-wave mixing in air for broadband THz detection. We have studied the nonlinear interaction between THz and NIR pulses in solid-state media (specifically diamond), and we show how the former can be frequency-shifted up to UV frequencies by the scattering from the nonlinear polarisation induced by the latter. Such UV emission differs from the well-known electric-field-induced second harmonic (EFISH) one, as it is generated via a phase-insensitive scattering, rather than a sum- or difference-frequency four-wave-mixing process.

When light waves propagate through disordered photonic lattices, they can eventually become localized due to multiple scattering effects. Here we show experimentally that while the evolution and localization of the photon density distribution is similar in the two cases of diagonal and off-diagonal disorder, the density-density correlation carries a distinct signature of the type of disorder. We show that these differences reflect a symmetry in the spectrum and eigenmodes that exists in off-diagonally disordered lattices but is absent in lattices with diagonal disorder., Comment: 4 pages, 3 figures, comments welcome

The anisotropic effective mass of electrons is directly measured using time-resolved THz- pump/THz-probe techniques in a n-doped InGaAs semiconductor thin film. A microscopic theory is used to attribute this anisotropy in the THz probe transmission to the nonparabolicity of the conduction band. Self-consistent light-matter coupling is shown to contribute significantly to the THz response.

We use an open-aperture Z-scan technique to show how intense few-cycle terahertz pulses can experience a nonlinear bleaching of absorption in an n-doped semiconductor due to terahertz-electric-field-driven intervalley scattering of electrons in the conduction band. Coherent detection of the transmitted terahertz pulse waveform also allows the nonlinear conductivity dynamics to be followed with sub-picosecond time resolution. Both the Z-scan and time-domain results are found to be in agreement with our theoretical analysis., Comment: Submitted to Physical Review B, 16 pages, 3 figures, 1 table

We study quantum and classical Hanbury Brown-Twiss correlations in waveguide lattices. We develop a theory for the propagation of photon pairs in the lattice, predicting the emergence of nontrivial quantum interferences unique to lattice systems. Experimentally, we observe the classical counterpart of these interferences using intensity correlation measurements. We discuss the correspondence between the classical and quantum correlations, and consider path-entangled input states which do not have a classical analogue. Our results demonstrate that waveguide lattices can be used as a robust and highly controllable tool for manipulating quantum states, and offer new ways of studying the quantum properties of light., Comment: Comments are welcome

The localization of waves in non-periodic media is a universal phenomenon, occurring in a variety of different quantum and classical systems, including condensed-matter, Bose-Einstein condensates in optical lattices, quantum chaotic systems, sound waves and light. A localization phase transition is expected to occur in three dimensional disordered systems as the strength of disorder crosses a critical value. Recently, a crossover from an extended to a localized phase has been observed in low-dimensional photonic lattices and Bose-Einstein condensates. Other experiments studied the critical behaviour near the transition in three dimensions via transmission measurements. However, no direct observation of a localization transition for light has been reported. In 1979 Aubry and Andre predicted that for a certain class of quasi-periodic potentials, a localization phase transition can occur already in one-dimension. This strongly correlated potential is markedly different from the disordered case were the potential is uncorrelated. Here we report an experiment that realizes the Aubry-Andre model in quasi-periodic photonic lattices. We observe the signature of a localization phase transition by directly measuring the expansion rates of initially narrow wave packets propagating in the lattice. Below the transition point, all the modes of the system are extended and therefore an initially narrow wave-packet eventually spreads across the entire lattice. Above the critical point, all modes are localized and expansion is suppressed. In addition, we study the effect of weak nonlinear interactions on light propagation below and above the transition., Comment: Comments welcome

We study experimentally and numerically the nonlinear scattering of wave packets by local multi-site guiding centers embedded in a continuous dielectric medium, as a function of the input power and angle of incidence. The extent of trapping into the linear modes of different sites is manipulated as a function of both the input power and incidence angle, demonstrating power-controlled switching of nonlinear trapping by local photonic potentials., Comment: Submitted to Optics Letters

We study experimentally the interactions between normal solitons and tilted beams in glass waveguide arrays. We find that as a tilted beam, traversing away from a normally propagating soliton, coincides with the self-defocusing regime of the array, it can be refocused and routed back into any of the intermediate sites due to the interaction, as a function of the initial phase difference. Numerically, distinct parameter regimes exhibiting this behavior of the interaction are identified., Comment: Physical Review Letters, in press