On the observation of dispersion in tunable second-order nonlinearities of silicon-rich nitride thin films

Abstract

We present experimental results on second-harmonic generation in non-stoichiometric, silicon-rich nitride (SRN) films. The as-deposited film presents a second-order nonlinear coefficient, or χ (2) , as high as 8pm/V. This value can be widely tuned using the electric field induced second harmonic effect (EFISH), and a maximum value of 22.7pm/V was achieved with this technique. We further illustrate that the second-order nonlinear coefficient exhibited by these films can be highly dispersive in nature, and requires further study and analysis to evaluate their viability for inwaveguide applications at telecommunication wavelengths.

Demonstration of the DC-Kerr effect in silicon-rich nitride

“…For characterization we use a fiber coupled input, free-space output setup with a tunable Agilent 8164B CW source which has a wavelength span of 1465nm to 1575nm [5]. Electrical probes are used to contact the electrical pads (see figure 1(a)) applying voltage from a Keithly Source Meter 2400 with a maximum voltage range of +210V.…”

“…This technique can offer an alternative mechanism for employing optical phase shifters in SRN films. Furthermore, PECVD SRN is a highly tunable material which allows a designer to control its refractive index [4], thermo-optic coefficient [24], as well as second and third order nonlinear susceptibilities [3][4][5] while maintaining low loss and two photon absorption with breakdown field strengths superior to that of silicon [4]. Additionally, when processed using PECVD, a low thermal budget can be maintained using a deposition technique readily available in CMOS process flows.…”

“…It is evident that with this approach we can achieve electro-optic switching in any material platform regardless of its crystal symmetry, as long as the given material has a large enough combination of χ (3) and high electric breakdown field strength. However, in SRN the overall change in the material index is often a combination of both second and third order contributions, due to the Pockels and DC-Kerr effects respectively, even if the second order contributions are often small [5]. As such an accurate estimate of the χ (3) requires consideration for the contributions of both these terms due to the presence of a non-zero χ (2) .…”

“…For these reasons, SRN becomes a very attractive candidate. Specifically, it has been shown in literature that SRN thin films can exhibit very high third order nonlinear susceptibilities, even larger than that of silicon itself [5], have a higher breakdown field [10], while remaining a low loss dielectric waveguiding material [11,12]. It is for this reason that SRN deserves strong consideration as a candidate platform for electro-optic switching.…”

“…An attractive candidate for this is nonstoichiometric silicon nitride, and in particular Silicon-rich Nitride. A variety of deposition techniques, including but not limited to Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD), Plasma Enhanced Chemical Vapor Deposition (PECVD), and Low-Pressure Chemical Vapor Deposition (LPCVD) have all been used to demonstrate low loss SRN film with enhanced second and third order nonlinear susceptibilities (𝜒 (2) and 𝜒 (3) ) [3,4,5]. Using these deposition techniques, silicon-rich nitride (SRN) films have demonstrated efficient four-wave mixing where in the case of ultrasilicon-rich nitride 𝜒 (3) coefficients as high as 1.02 x10 -18 m 2 /v 2 have been demonstrated [4,6].…”