The centrosymmetric structure of stoichiometric silicon nitride inhibits the realization of second-order nonlinear processes in this low-loss, complementary-metal-oxide-semiconductor fabrication-compatible platform. Nevertheless, linear electro-optic modulation is an essential functionality desired for implementation in photonic integrated circuits. This study presents the successful achievement of electro-optical modulation in a silicon nitride microring resonator, employing thermally assisted electric-field poling. With an inscribed electric field of 100 V/μm within the silicon nitride waveguide, an effective second-order susceptibility of 0.45 pm/V is induced. Leveraging silicon nitride as the active material for electro-optic modulation, we determined the operational bandwidth of the device, constrained by the electrode design, to be 78 MHz. Furthermore, we demonstrate the capability of the device to modulate data at bitrates of up to 75 Mb/s. Our findings highlight the potential of linear electro-optical modulation in the silicon nitride integrated platform.
On-chip coherent light generation has wide-ranging applications in metrology, spectroscopy, quantum optics, etc. In this study, we demonstrate the generation of coherent light from a silicon-nitride microring resonator using cascaded nonlinear processes. This involves a telecom pump laser and its efficiently generated second harmonic through the coherent photogalvanic effect. By leveraging second- and third-order nonlinear effects such as harmonic generation, (stimulated) four-wave mixing, and optical parametric oscillation, we achieve the generation of UV, visible, and near-infrared light. This study highlights the potential of silicon nitride integrated photonics in producing broad-spectrum light sources at wavelengths beyond the capabilities of conventional lasers.
Stoichiometric silicon nitride (Si3N4) constitutes a mature platform for integrated photonics. Its pertinent properties, including wide transparency window from the visible to the mid-IR, low propagation loss, and high third-order nonlinearity, are exploited in many linear and nonlinear applications. However, due to the centrosymmetric nature of the Si3N4, the absence of the second-order susceptibility (χ(2)) impedes a realization of three-wave mixing processes as well as the linear electro-optic effect, relevant for many applications on an optical chip. Here, we implement the electric-field poling technique to induce the effective χ(2) inside a Si3N4 waveguide, thus enabling the linear electro-optic modulation. Using numerical simulations, we estimated the concentration and the diffusion coefficient of the charges responsible for the space-charge electric field formation. In addition, the DC third-order susceptibility of Si3N4 previously unknown in the literature is measured using a free-space Mach-Zehnder interferometer.
All-optical poling leads to an effective second-order nonlinearity (χ(2)) in centrosymmetric materials without the need for sophisticated fabrication techniques or material processing, through the periodic self-organization of the charges. The absence of the inherent χ(2) in prevailing silicon-based platforms can be surmounted through all-optical poling. Using the induced effective χ(2) in silicon nitride (Si3N4) waveguides, nonlinear frequency up-conversion processes, such as second-harmonic generation, were previously demonstrated on Si3N4. Here, we report near- and non-degenerate difference-frequency generation in all-optically poled Si3N4 waveguides. We show the agreement between the theory and the measurements and optimize achievable QPM bandwidth range, reaching conversion efficiency of 1 %/W.
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