Clemens Krückel

Linear and nonlinear characterization of low-stress high-confinement silicon-rich nitride waveguides

In this paper we introduce a low-stress silicon enriched nitride platform that has potential for nonlinear and highly integrated optics. The manufacturing process of this platform is CMOS compatible and the increased silicon content allows tensile stress reduction and crack free layer growth of 700 nm. Additional benefits of the silicon enriched nitride is a measured nonlinear Kerr coefficient n(2) of 1.4·10(-18) m(2)/W (5 times higher than stoichiometric silicon nitride) and a refractive index of 2.1 at 1550 nm that enables high optical field confinement allowing high intensity nonlinear optics and light guidance even with small bending radii. We analyze the waveguide loss (∼1 dB/cm) in a spectrally resolved fashion and include scattering loss simulations based on waveguide surface roughness measurements. Detailed simulations show the possibility for fine dispersion and nonlinear engineering. In nonlinear experiments we present continuous-wave wavelength conversion and demonstrate that the material does not show nonlinear absorption effects. Finally, we demonstrate microfabrication of resonators with high Q-factors (∼10(5)).

Continuous wave-pumped wavelength conversion in low-loss silicon nitride waveguides

In this Letter we introduce a complementary metal-oxide semiconductor (CMOS)-compatible low-loss Si3N4 waveguide platform for nonlinear integrated optics. The waveguide has a moderate nonlinear coefficient of 285  W/km, but the achieved propagation loss of only 0.06  dB/cm and the ability to handle high optical power facilitate an optimal waveguide length for wavelength conversion. We observe a constant quadratic dependence of the four-wave mixing (FWM) process on the continuous-wave (CW) pump when operating in the C-band, which indicates that the waveguide has negligible high-power constraints owing to nonlinear losses. We achieve a conversion efficiency of -26.1  dB and idler power generation of -19.6  dBm. With these characteristics, we present for the first time, to the best of our knowledge, CW-pumped data conversion in a non-resonant Si3N4 waveguide.

Octave-spanning supercontinuum generation in a silicon-rich nitride waveguide

We generate supercontinuum (817-2250 nm at -30dB) in a dispersion-engineered silicon-rich nitride waveguide by pumping fs pulses with 82 pJ from an erbium-fiber oscillator. Spectral broadening mechanisms include soliton fission and dispersive wave generation.

Triply resonant coherent four-wave mixing in silicon nitride microresonators

Generation of multiple tones using four-wave mixing (FWM) has been exploited for many applications, ranging from wavelength conversion to frequency comb generation. FWM is a coherent process, meaning that its dynamics strongly depend on the relative phase among the waves involved. The coherent nature of FWM has been exploited for phase-sensitive processing in different waveguide structures, but it has never been studied in integrated microresonators. Waveguides arranged in a resonant way allow for an effective increase in the wavelength conversion efficiency (at the expense of a reduction in the operational bandwidth). In this Letter, we show that phase shaping of a three-wave pump provides an extra degree of freedom for controlling the FWM dynamics in microresonators. We present experimental results in single-mode, normal-dispersion high-Q silicon nitride resonators, and numerical calculations of systems operating in the anomalous dispersion regime. Our results indicate that the wavelength conversion efficiency and modulation instability gain in microcavities pumped by multiple waves can be significantly modified with the aid of simple lossless coherent control techniques.

Hybrid dielectric waveguide spectroscopy of individual plasmonic nanoparticles

© 2017 Author(s). Plasmonics is a mature scientific discipline which is now entering the realm of practical applications. Recently, significant attention has been devoted to on-chip hybrid devices where plasmonic nanoantennas are integrated in standard Si 3 N 4 photonic waveguides. Light in these systems is usually coupled at the waveguide apexes by using multiple objectives and/or tapered optical fibers, rendering the analysis of spectroscopic signals a complicated task. Here, we show how by using a grating coupler and a low NA objective, quantitative spectroscopic information similar to standard dark-field spectroscopy can be obtained at the single-nanoparticle level. This technology may be useful for enabling single-nanoparticle studies in non-linear excitation regimes and/or in complex experimental environments, thus enriching the toolbox of nanophotonic methods.

Optical bandgap engineering in nonlinear silicon nitride waveguides

Silicon nitride is a well-established material for photonic devices and integrated circuits. It displays a broad transparency window spanning from the visible to the mid-IR and waveguides can be manufactured with low losses. An absence of nonlinear multi-photon absorption in the erbium lightwave communications band has enabled various nonlinear optic applications in the past decade. Silicon nitride is a dielectric material whose optical and mechanical properties strongly depend on the deposition conditions. In particular, the optical bandgap can be modified with the gas flow ratio during low-pressure chemical vapor deposition (LPCVD). Here we show that this parameter can be controlled in a highly reproducible manner, providing an approach to synthesize the nonlinear Kerr coefficient of the material. This holistic empirical study provides relevant guidelines to optimize the properties of LPCVD silicon nitride waveguides for nonlinear optics applications that rely on the Kerr effect.

All-optical radio frequency spectrum analyzer based on cross-phase modulation in a silicon-rich nitride waveguide

We report RF-spectrum analysis of optical signals based on cross-phase-modulation in a silicon-rich nitride waveguide. Measurements show a bandwidth of at least 560 GHz for our RF-spectrum analyzer. RF-spectra measurements for pulse trains at rates from ~ 10 GHz to ~ 160 GHz are demonstrated.

Bandgap engineering in nonlinear silicon nitride waveguides

We show that controlling the bandgap of SiN provides an additional degree of freedom for engineering waveguides for nonlinear optics. We show an optimized structure with γ· max L<inf>eff</inf> = 0.17 rad/W and absence of nonlinear loss.

Towards on-chip net-gain in CMOS-compatible waveguides

On-chip optical parametric gain was first demonstrated in a silicon waveguide using a pulsed pump source [1]. However, the realization of optical net-gain with a continuous-wave (CW) pump remains a challenge in integrated platforms. Highly nonlinear fibers can provide parametric gain with CW pump [2]. The key advantage of this low-loss platform is its long effective length Leff, which results in a huge nonlinear phase shift, ΘNL = γPLeff using moderate power levels, P, in spite of the relatively low nonlinear parameter γ. The question we address in this contribution is: How far are we from obtaining net gain in a CMOS-compatible platform under CW pumping?

Silicon-rich nitride waveguides for broadband nonlinear signal processing

Silicon nitride waveguides are among the most promising platforms for nonlinear optical processing applications. In this invited contribution we will highlight how the dispersion and Kerr coefficient (n2) can be tuned by precisely controlling the stoichiometry of the waveguides core material.