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

Abstract

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.

Ultrafast-nonlinear ultraviolet pulse modulation in an AlInGaN polariton waveguide operating up to room temperature

“…This technique can be enhanced when the pump pulses are resonant with electronic transition of the medium under study, which for many chemical and biological samples are in the UV 15 . CARS sources can be used with microfluidic chips 49 , and nonlinear pulse sources for CARS are being developed in silicon nitride in the IR 50 . The required bandwidth is governed by the vibrational spectrum of interest and is often of order 100 meV.…”

“…The required bandwidth is governed by the vibrational spectrum of interest and is often of order 100 meV. Required pulse energies are in the pico-Joule to nano-Joule range 15 , 49 , 50 .…”

Numerical and Experimental Demonstration of Intermodal Dispersive Wave Generation

“…As a model system for the verification of the existence of iDWG and its characterization, we used rectangular silicon nitride waveguides, featuring reliable and efficient SCG due to the high nonlinear refractive index coefficient and the tight modal confinement. [2,20,21,23,[37][38][39] Due to waveguide birefringence, as also exploited for SCG in silicon, [37] the waveguides feature two fundamental transverse modes that are distinguishable by polarization (TE 01 and TM 01 mode), that is, they can be separated by means of a polarizer and variably excited by adjusting the input polarization. This waveguide system allows for single-mode measurements in direct comparison to straightforward multi-mode measurements by launching only one or both fundamental transverse modes, respectively.…”

Optical parametric amplification in silicon nitride waveguides for coherent Raman imaging

“…Therefore, nonlinear processes such as FWM can be driven more efficiently [17][18][19][20][21], enabling operation with lower pump energies and shorter interaction lengths. Frequency conversion by spontaneous FWM was already demonstrated in Si 3 N 4 for telecommunications [22], mid-infrared generation [23], and even for broadband CARS applications [24]. Furthermore, frequency conversion was already achieved with millimeter-scale waveguide lengths and pump energies down to the picojoule regime [23].…”

“…Furthermore, frequency conversion was already achieved with millimeter-scale waveguide lengths and pump energies down to the picojoule regime [23]. However, as spontaneous FWM starts from vacuum fluctuations, the conversion efficiencies are very low, in the order of −20 dB to −30 dB [22][23][24].…”