Silicon Nitride Slot Waveguides Research Articles

Multiple coherent dispersive waves generation in silicon nitride slot waveguide

A method to generate multiple dispersive waves (DWs) with pumping in a normal dispersion regime is proposed. We show flexibility of producing four DWs in a silicon nitride (Si3N4) slot waveguide and explain the underlying dynamics of a four DWs generation process in detail, i.e., DWs emission via the optical wave-breaking phenomenon in an anomalous dispersion regime. Compression of the first anomalous DW results in the subsequent cascade DW generation. Combined with the soliton induced blue-shifted dispersive wave and red-shifted dispersive wave, the spectrum spans from visible to mid-IR with high coherence. The four DWs generation process has agreement with prediction of the phase-matching condition. Overall, this multiple DWs generation method in a Si3N4 waveguide provides the possibility for having an efficient, compact, and coherent mid-IR light source.

Silicon-nitride microring resonators for nonlinear optical and biosensing applications.

We discuss the design, fabrication, and characterization of silicon-nitride microring resonators for nonlinear-photonic and biosensing device applications. The first part presents new theoretical and experimental results that overcome highly normal dispersion of silicon-nitride microresonators by adding a dispersive coupler. The latter parts review our work on highly efficient second-order nonlinear interaction in a hybrid silicon-nitride slot waveguide with nonlinear polymer cladding and silicon-nitride microring application as a biosensor for human stress indicator neuropeptide Y at the nanomolar level.

Designs of Silicon Nitride Slot Waveguide Modulators With Electro-Optic Polymer and the Effect of Induced Charges in Si-Substrate on Their Performance

Dimensional parameters are optimized comparing stoichiometric and Si-rich silicon nitride-based push-pull modulators using a slot waveguide structure, electro-optic polymer cladding, and in-plane ground-signal-ground electrode. An optical power confinement in slot spacing is examined for choosing the optimal device parameters for wavelength of 1550 nm. The electrical simulations are set to calculate an asymmetric spatial distribution of poling efficiency and modulating refractive index change in polymer. The influence of carrier charge in Si-substrate is also considered. The voltage-length products as well as the poling efficiency of Si-rich SiN are calculated as 1.47 V·cm and 0.74 respectively for a polymer with a γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33,bulk</sub> of 100 pm/V. For the selected polymer the calculated efficiency comparable to standard silicon based plasma dispersion depletion modulators. The efficiency can be increased more than two times for demonstrated polymers with a γ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">33,bulk</sub> of ~230. Low metal absorption loss of ~ 1dB/cm can be achieved from the optimal designed device. Comparing to the conventional simulation method without Si-substrate effect, a more accurate simulation method is also presented in this work.

Ultra-sensitive slot-waveguide-enhanced Raman spectroscopy for aqueous solutions of non-polar compounds using a functionalized silicon nitride photonic integrated circuit.

We demonstrate an ultra-sensitive waveguide-enhanced Raman sensor for low concentration organic compounds dissolved in water. The spectra are obtained using silicon nitride slot waveguides coated with a thin film of hexamethyldisilazane-modified mesoporous silica. Enriched locally by 600-fold within the coating, a micromolar level of cyclohexanone is probed. The sensor is also capable of simultaneous quantification of multiple analytes, and the adsorbed analytes can be completely released from the coating. These properties make this on-chip Raman sensor promising for diverse applications, especially for the monitoring of non-polar organics and biomolecules in aqueous environments.

Design of Partially Suspended Silicon Nitride Slot Waveguides for Efficient Forward Stimulated Brillouin Scattering

We design a partially suspended silicon nitride (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) slot waveguide on silica to realize efficient on-chip forward stimulated Brillouin scattering (FSBS). The slot waveguide can intensify radiation pressure close to the slot and simultaneously confine both optical and acoustic modes, resulting in an enhanced FSBS gain on the order of 300 W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . The acoustic radiation loss is significantly suppressed due to the strong acoustic coupling in the narrow slot waveguides. We analyze the impacts of structural parameters on the SBS properties, which produces the optimal parameters for maximum SBS gain. Based on the nonlinear coupled-mode equations, we compare the performance of Stokes amplification between the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> slot waveguides and the silicon nanowires. Simulation results indicate that the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> slot waveguides with low linear loss can offer a larger net Stokes amplification than silicon waveguides under moderate pump power. Such approach enables efficient on-chip SBS devices in CMOS-compatible Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> platform.

Ultraflat and low dispersion in a horizontal silicon nitride slot waveguide at near-infrared wavelengths

A strip/slot hybrid horizontal silicon nitride slot waveguide is designed to provide an ultraflat and low dispersion. By optimizing the height and width of the structure, an ultraflat and low dispersion of ∼0±7 ps/nm/km over 812 nm wavelength range (from 1137 to 1949 nm) can be achieved. The waveguide with a 20-nm conformal overlayer has chromatic dispersion within ±1 ps/nm/km over 682-nm bandwidth. So the flatness is 0.0015, which is the lowest flatness in near-infrared regime of this kind of waveguide to our knowledge. The influence of the waveguide sidewall to dispersion is also discussed.

Highly sensitive Mach–Zehnder interferometer biosensor based on silicon nitride slot waveguide

We demonstrate a highly sensitive label-free Mach–Zehnder interferometer (MZI) biosensor based on silicon nitride slot waveguide. Unlike the conventional MZI sensors, the sensing arm of the sensor consists of a slot waveguide while the reference arm consists of a strip waveguide. Thanks to the slot waveguide's property to provide high optical intensity in a subwavelength-size low refractive index region (slot region), which allows high light–analyte interaction, higher sensitivity can be obtained as compared to conventional waveguides using the slot waveguide as sensing region. The bulk refractive index sensitivity of the slot waveguide MZI sensor was found to be 1864π/RIU (refractive index unit) with 7mm long slot waveguide sensing arm, which shows higher sensitivity compared to the conventional MZI device based on silicon nitride. The biosensing capability of the developed slot waveguide MZI was investigated using biotin–streptavidin binding as a model system. The sensitivity of the system was demonstrated down to 18.9fM or 1pg/ml of streptavidin solution and to the best of our knowledge, it is the best reported experimental value for the limit of detection of a MZI sensor. Furthermore, we investigated the specific detection and quantification of the methylation of DAPK (Death-associated protein kinase) gene, which is a widely used biomarker for human cancers. We have shown that methylation sequences of DAPK gene of various methylation densities (100%, 50%, and 0% of methylation sites) can be quantified and discriminated even at a concentration as low as 1fmol/μl or 1nM.

Thermal independent Silicon-Nitride slot waveguide biosensor with high sensitivity

As the sensitivity and detection limit of photonic refractive index (RI) biosensor increases, the temperature dependence becomes a major challenge. In this paper, we present a Mach-Zehnder Interferometer (MZI) biosensor based on silicon nitride slot waveguides. The biosensor is designed for minimal temperature dependence without compromising the performance in terms of sensitivity and detection limit. With air cladding, the measured surface sensitivity and detection limit of MZI biosensor reach 7.16 nm/(ng mm(-2)) and 1.30 (pg mm(-2)), while achieving a low temperature dependence is 5.0 pm/° C. With water cladding, the measured bulk sensitivity and detection limit reach 1730(2π)/RIU and 1.29 × 10(-5) RIU respectively. By utilizing Vernier effect through cascaded MZI structures, the measured sensitivity enhancement factor is 8.38, which results in a surface detection limit of 0.155 (pg mm(-2)).

Tunable optical coupler controlled by optical gradient forces

We demonstrate optical gradient force-tunable directional couplers in free-standing silicon nitride slot waveguides. Utilizing device geometries optimized for strong optomechanical interactions allows us to control the optical transmission without the aid of a cavity. Static, wideband tuning as well as low-power optical modulation is achieved.

On-chip two-octave supercontinuum generation by enhancing self-steepening of optical pulses

Dramatic advances in supercontinuum generation have been made recently using photonic crystal fibers, but it is quite challenging to obtain an octave-spanning supercontinuum on a chip, partially because of strong dispersion in high-index-contrast nonlinear integrated waveguides. We show by simulation that extremely flat and low dispersion can be achieved in silicon nitride slot waveguides over a wavelength band of 500 nm. Different from most of previously reported supercontinua that were generated either by higher-order soliton fission in anomalous dispersion regime or by self-phase modulation in normal dispersion regime, a two-octave supercontinuum from 630 to 2650 nm (360 THz in total) can be generated by enhancing self-steepening in pulse propagation in nearly zero dispersion regime, when an optical shock as short as 3 fs is formed.