Integrated quantum optics

Resource efficient single photon source based on active frequency multiplexing

We propose a new, to the best of our knowledge, single photon source based on the principle of active multiplexing of heralded single photons, which, unlike previously reported architecture, requires a limited amount of physical resources. We discuss both its feasibility and the purity and indistinguishability of single photons as a function of the key parameters of a possible implementation.

Microscopy and spectroscopy

Gold-induced photothermal background in on-chip surface enhanced stimulated Raman spectroscopy

Surface enhanced Raman spectroscopy (SERS) and stimu- lated Raman spectroscopy (SRS) are well established techniques capable of boosting the strength of Raman scattering. The combination of both techniques (surface enhanced stimulated Raman spectroscopy, or SE-SRS) has been reported using plasmonic nanoparticles. In parallel, waveguide enhanced Raman spectroscopy has been devel- oped using nanophotonic and nanoplasmonic waveguides. Here, we explore SE-SRS in nanoplasmonic waveguides. We demonstrate that a combined photothermal and thermo- optic effect in the gold material induces a strong background signal that limits the detection limit for the analyte. The experimental results are in line with theoretical estimates. We propose several methods to reduce or counteract this background.

Integrated quantum optics

Nondegenerate two-photon absorption in GaAs/AlGaAs multiple quantum well waveguides

We present femtosecond pump-probe measurements of the nondegenerate (1960nm excitation and 1176–1326nm probe) two-photon absorption spectra quantum well waveguides. Experiments were performed with light pulses copolarized normal and tangential to the quantum well plane. The results are compared to perturbative calculations of transition rates between states determined by the k.p method with an 8- or 14-band basis. We find excellent agreement between theory and experiment for normal polarization, then use the model to support predictions of orders-of-magnitude enhancement of nondegenerate two-photon absorption as one constituent photon energy nears an intersubband resonance.

N. Cox, J. Wei, H. Pattanaik, T. Tabbakh, S.-P. Gorza, D. Hagan, and E. W. Van Stryland, Phys. Rev. Research 2, 013376 (2020). DOI

Nonlinear interaction in nanowaveguides

Heterogeneous III-V on silicon nitride amplifiers and lasers via microtransfer printing

The development of ultralow-loss silicon-nitride-based waveguide platforms has enabled the realization of integrated optical filters with unprecedented performance. Such passive circuits, when combined with phase modulators and low-noise lasers, have the potential to improve the current state of the art of the most critical components in coherent communications, beam steering, and microwave photonics applications. However, the large refractive index difference between silicon nitride and common III-V gain materials in the telecom wavelength range hampers the integration of electrically pumped III-V semiconductor lasers on a silicon nitride waveguide chip. Here, we present an approach to overcome this refractive index mismatch by using an intermediate layer of hydrogenated amorphous silicon, followed by the microtransfer printing of a prefabricated III-V semiconductor optical amplifier. Following this approach, we demonstrate a heterogeneously integrated semiconductor optical amplifier on a silicon nitride waveguide circuit with up to 14 dB gain and a saturation power of 8 mW. We further demonstrate a heterogeneously integrated ring laser on a silicon nitride circuit operating around 1550 nm. This heterogeneous integration approach would not be limited to silicon-nitride-based platforms: it can be used advantageously for any waveguide platform with low-refractive-index waveguide materials such as lithium niobate.

Camiel Op de Beeck, Bahawal Haq, Lukas Elsinger, Agnieszka Gocalinska, Emanuele Pelucchi, Brian Corbett, Günther Roelkens, and Bart Kuyken, "Heterogeneous III-V on silicon nitride amplifiers and lasers via microtransfer printing," Optica 7, 386-393 (2020). DOI

Pattern formation in optical resonators

Parametric localized patterns and breathers in dispersive quadratic cavities

We study the formation of localized patterns arising in doubly resonant dispersive optical parametric oscillators. They form through the locking of fronts connecting a continuous-wave and a Turing pattern state. This type of localized state can be seen as a slug of the pattern embedded in a homogeneous surrounding. They are organized in terms of a homoclinic snaking bifurcation structure, which is preserved under the modification of the control parameters of the system. We show that, in the presence of phase mismatch, localized patterns can undergo oscillatory instabilities which make them breathe in a complex manner.


P. Parra-Rivas, C. Mas-Arabí, and F. Leo, Phys. Rev. A 101, 063817 (2020). DOI

Nonlinear interaction in nanowaveguides

Octave-spanning coherent supercontinuum generation in an AlGaAs-on-insulator waveguide

We demonstrate supercontinuum generation over an octave spaning from 1055 to 2155 nm on the highly nonlinear alu- minum gallium arsenide (AlGaAs)-on-insulator platform. This is enabled by the generation of two dispersive waves in a 3-mm-long dispersion-engineered nano-waveguide. The waveguide is pumped at telecom wavelengths (1555 nm) with 3.6 pJ femtosecond pulses. We experimentally validate the coherence of the generated supercontinuum around the pump wavelength (1450–1750 nm), and our numerical simulation shows a high degree of coherence over the full spectrum.


B. Kuyken, M. Billet, F. Leo, K. Yvind, and M. Pu, Opt. Lett., 45, 603 (2020). DOI

Nonlinear interaction in nanowaveguides

Modeling of quasi-phase-matched cavity-enhanced second-harmonic generation

We propose a mean-field model to describe second-harmonic generation in a resonator made of a material with zinc-blende crystalline structure. The model is obtained through an averaging of the propagation equations and boundary conditions. It considers the phase-mismatched terms, which act as an effective Kerr effect. We analyze the impact of the different terms on the steady state solutions, highlighting the competition between nonlinearities.

C. Mas Arabí, P. Parra-Rivas, C. Ciret, S. P. Gorza, and F. Leo, Phys. Rev. A 101, 043818 (2020). DOI

Integrated quantum optics

Strong Nonlinear Coupling in a Si3N4 Ring Resonator

We report a nonlinear strong coupling between to weak fields containing a few photons inside a cavity. This strong coupling is the result of an effective second order nonlinearity induced by strong pump field in a Kerr cavity. The strong coupling regime is evidenced by Rabi splitting of the cavity resonance.

REFERENCE: Ramelow, S, Farsi, A, Verno, Z, S. Clemmen, Ji, X, Sipe, J, Liscidini, M, Lipson, M, Gaeta, A, Strong Nonlinear Coupling in a Si3N4 Ring Resonator, Physical Review Letters, 122, p.153906 (2019) DOI

Nonlinear interaction in nanowaveguides

Integrated silicon nitride electro-optic modulators with atomic layer deposited overlays

We present an integrated electro-optics modulator. Existing SiN waveguides have been enriched by a cladding of ZnO presenting a second order nonlinearity. We report phase modulation using this hybrid SiN waveguide.

REFERENCE: A. Hermans, M. Van Daele, J. Dendooven, S. Clemmen, C. Detavernier, R. Baets, Integrated silicon nitride electro-optic modulators with atomic layer deposited overlays, Optics Letters, 44(5), p.1112-1115  (2019) DOI

Microscopy and spectroscopy

Surface-enhanced Raman spectroscopy based on plasmonic slot waveguides with free-space oblique illumination

In our quest to demonstrate an all-on-a-chip Raman spectrometer, we are reporting a configuration that strongly suppresses background noise typical of the SiN photonics waveguides. We use an excitation of a plasmonic waveguide that is oblique so that the molecules within the plasmic waveguides are Raman excited but the pump light is not properly coupled to the waveguide but only slightly scattered. As only scattered light is coupled to the collecting SiN waveguide, the pump-induced background photon noise is highly suppressed. Moreover, the plasmonic structure and the incidence angles are engineered so that there is a resonant enhancement thus boosting further the field of the pump beam.

REFERENCE: Y. Li, H. Zhao, A. Raza, S. Clemmen, R. Baets, Surface-enhanced Raman spectroscopy based on plasmonic slot waveguides with free-space oblique illumination, Journal of Quantum Electronics, 56(1), p.paper 7200108 (2020) DOI