Self-mode-locking in a high-power hybrid silicon nitride integrated laser.

Integrated mode-locked lasers are useful tools in microwave photonic applications as a local oscillator. In particular, hybrid integrated lasers could easily be integrated with passive processing circuits. In this Letter, we report on the self-mode-locking of a hybrid integrated laser comprising two indium phosphide gain sections and a silicon nitride feedback circuit that filters light using two ring resonators. The hybrid laser is shown to mode-lock and to have a mostly frequency-modulated field in the cavity using a stepped-heterodyne optical complex spectrum analysis. A mostly frequency modulated field output is good for high powers per line due to a more continuous emission, compared with mode-locked lasers using a saturable absorber; additionally, the filter limits the bandwidth of the comb, condensing the power to the fewer comb lines.

Spontaneous four-wave mixing in silicon nitride waveguides for broadband coherent anti-Stokes Raman scattering spectroscopy.

We present a light source for coherent anti-Stokes Raman scattering (CARS) based on broadband spontaneous four-wave mixing, with the potential to be further integrated. By using 7 mm long silicon nitride waveguides, which offer tight mode confinement and a high nonlinear refractive index coefficient, broadband signal and idler pulses were generated with 4 nJ of input pulse energy. In comparison to fiber-based experiments, the input energy and the waveguide length were reduced by two orders of magnitude, respectively. The idler and residual pump pulses were used for CARS measurements, enabling chemically selective and label-free spectroscopy over the entire fingerprint region, with an ultrafast fiber-based pump source at 1033 nm wavelength. The presented simple light source paves the path towards cost-effective, integrated lab-on-a-chip CARS applications.

Low-power broadband all-optical switching via intermodal cross-phase modulation in integrated optical waveguides.

We demonstrate the potential of all-optical switches in integrated waveguides based on intermodal cross-phase modulation between transverse modes. For this purpose, the differential phase between two transverse modes of a probe beam was altered by cross-phase modulation with a control beam propagating only in the fundamental mode. A switching behavior was accomplished by spatially filtering the resulting multimode interference of the probe modes, which changed depending on the control beam power. All-optical switching with a contrast of 82% at 1280 nm over a frequency range of 4.4 THz at 1.6 nJ was achieved, representing an improvement of the product of necessary power and waveguide length by a factor of nearly 2000 compared to similar experiments in graded-index fibers. Additionally, we show that the center wavelength of the switch can be tailored by changing the cross-sectional geometry of the waveguide or the involved probe modes.

Two-octave spanning supercontinuum generation in stoichiometric silicon nitride waveguides pumped at telecom wavelengths.

We demonstrate supercontinuum generation in stoichiometric silicon nitride (Si3N4 in SiO2) integrated optical waveguides, pumped at telecommunication wavelengths. The pump laser is a mode-locked erbium fiber laser at a wavelength of 1.56 µm with a pulse duration of 120 fs. With a waveguide-internal pulse energy of 1.4 nJ and a waveguide with 1.0 µm × 0.9 µm cross section, designed for anomalous dispersion across the 1500 nm telecommunication range, the output spectrum extends from the visible, at around 526 nm, up to the mid-infrared, at least to 2.6 µm, the instrumental limit of our detection. This output spans more than 2.2 octaves (454 THz at the -30 dB level). The measured output spectra agree well with theoretical modeling based on the generalized nonlinear Schrödinger equation. The infrared part of the supercontinuum spectra shifts progressively towards the mid-infrared, well beyond 2.6 µm, by increasing the width of the waveguides.

Ultrafast, low-power, all-optical switching via birefringent phase-matched transverse mode conversion in integrated waveguides.

We demonstrate the potential of birefringence-based, all-optical, ultrafast conversion between the transverse modes in integrated optical waveguides by modelling the conversion process by numerically solving the multi-mode coupled nonlinear Schroedinger equations. The observed conversion is induced by a control beam and due to the Kerr effect, resulting in a transient index grating which coherently scatters probe light from one transverse waveguide mode into another. We introduce birefringent phase matching to enable efficient all-optically induced mode conversion at different wavelengths of the control and probe beam. It is shown that tailoring the waveguide geometry can be exploited to explicitly minimize intermodal group delay as well as to maximize the nonlinear coefficient, under the constraint of a phase matching condition. The waveguide geometries investigated here, allow for mode conversion with over two orders of magnitude reduced control pulse energy compared to previous schemes and thereby promise nonlinear mode switching exceeding efficiencies of 90% at switching energies below 1 nJ.

High confinement, high yield Si(3)N(4) waveguides for nonlinear optical applications.

In this paper we present a novel fabrication technique for silicon nitride (Si(3)N(4)) waveguides with a thickness of up to 900 nm, which are suitable for nonlinear optical applications. The fabrication method is based on etching trenches in thermally oxidized silicon and filling the trenches with Si(3)N(4). Using this technique no stress-induced cracks in the Si(3)N(4) layer were observed resulting in a high yield of devices on the wafer. The propagation losses of the obtained waveguides were measured to be as low as 0.4 dB/cm at a wavelength of around 1550 nm.

On-chip visible-to-infrared supercontinuum generation with more than 495 THz spectral bandwidth.

We report ultra-broadband supercontinuum generation in high-confinement Si3N4 integrated optical waveguides. The spectrum extends through the visible (from 470 nm) to the infrared spectral range (2130 nm) comprising a spectral bandwidth wider than 495 THz, which is the widest supercontinuum spectrum generated on a chip.

Integrated CARS source based on seeded four-wave mixing in silicon nitride.

We present a theoretical investigation of an integrated nonlinear light source for coherent anti-Stokes Raman scattering (CARS) based on silicon nitride waveguides. Wavelength tunable and temporally synchronized signal and idler pulses are obtained by using seeded four-wave mixing. We find that the calculated input pump power needed for nonlinear wavelength generation is more than one order of magnitude lower than in previously reported approaches based on optical fibers. The tuning range of the wavelength conversion was calculated to be 1418 nm to 1518 nm (idler) and 788 nm to 857 nm (signal), which corresponds to a coverage of vibrational transitions from 2350 cm-1 to 2810 cm-1. A maximum conversion efficiency of 19.1% at a peak pump power of 300 W is predicted.