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.
The rapid development of photonic applications calls for scalable, miniaturized power efficient integrated circuits. Thin film lithium niobate (TFLN) now emerges as a major photonic platform for integration of advanced functionalities such as based on nonlinear optics. We report experimentally efficient second harmonic generation in periodically poled lithium niobate waveguides and design rules for nonlinear frequency conversion, including a study on tolerances on the dimensions and poling parameters. Our work aims at establishing reliable and versatile nonlinear building blocks for scalable TFLN photonic integrated circuits.
Integrated optics has shown itself very convenient for exploiting nonlinear processes as it results in high confinement factor, freedom of dispersion engineering and compactness. However, the choice of materials is crucial for the development of nonlinear systems. Ideally, one looks for a platform that offers high second and/or third order nonlinearities, low loss and ease of fabrication. Silicon nitride (Si3N4) is now proven to be a good platform for frequency conversion based on third order nonlinearity. Supercontinuum generation (SCG) was obtained in the near-IR and mid-IR regions by pumping waveguides with common fiber lasers. It resulted in broadband coherent combs extending in the mid-IR thanks to dispersive wave generation. Yet, Si3N4 does not exhibit any second order nonlinearity desirable for comb self-referencing via second-harmonic generation (SHG). On the other hand, lithium niobate (LiNbO3) is widely used in integrated photonics for second order nonlinear processes. In our work, we exploit a hybrid Si3N4-LiNbO3 photonic integrated platform that combines maturity and dispersion engineering capabilities of Si3N4 integrated photonics with second-order nonlinear properties of LiNbO3 bypassing challenging lithium niobate etching. We study numerically and experimentally the potential of SCG and SHG for frequency comb self-referencing on this platform when pumping with a fiber laser operating at 2 μm for mid-IR operation, a window useful for sensing as it contains many molecular signatures.
We report SCG over 1.4 octave(from 620nm to 1.5µm) by pumping at 1060nm on a dispersion-engineered ultra low-loss SiN integrated waveguide with femtosecond pulse of 300W as peak power. We demonstrate SCG over 2.5 octaves(from 580nm to 2.05µm) when a wider and longer waveguide being pumped at 1550nm with peak power of 800W. We also experimentally observe a 4.5 octaves(from 500nm to 2.75µm) SCG by pumping at 1550nm on the 800nm thick SiN platform. We show the versatility of CEA LETI 800nm thick ultra-low loss SiN platform to SCG,
Periodically patterning silicon with a subwavelength pitch opens new degrees of freedom to control the propagation of light and sound in silicon photonic circuits with unprecedented flexibility. In this invited presentation, we will show our most recent results on the use suspended silicon waveguides for supercontinuum generation in the near-IR and mid-IR. We will also discuss our recent demonstrations of subwavelength engineering of photons and phonons in suspended and non-suspended silicon optomechanical cavities
Silicon photonics has been largely developed as a platform to address the future challenges in several applications including datacom, sensing or optical communications, among others. However, the properties of silicon itself is not enough to overcome all limitations in terms of speed, power consumption and scalability. New strategies have then been encouraged based on the hybrid integration of new materials in the silicon photonics platform. In this paper, we will introduce the recent advances in the hybrid integration of doped crystalline-oxides on silicon and silicon nitride waveguides. Especially, Yttria-stabilized zirconia (YSZ) with a lattice parameter compatible with the silicon lattice has been considered because it exhibits promising linear and nonlinear optical properties: low propagation loss, no two photon absorption (TPA) due to its large bandgap energy, a large transparency window from the ultraviolet to the mid-infrared and a good Kerr effect. Furthermore, YSZ can be doped with many dopants to develop active photonic devices with strong second- and third-order nonlinearities and light emission. We have recently demonstrated propagation loss in YSZ waveguides as low as 2dB/cm at a wavelength of 1380 nm, a nonlinear refractive index (Kerr effect) comparable with the SiN coefficient and light amplification in Er3+ doped YSZ on SiN waveguides. The recent results are very promising to pave the way for the development of low cost and low power consumption devices.
The Si transparency (1.1 μm – 8 μm wavelength) contains the strongest absorption features of a wide range of chemical and biological substances. However, the use of SOI in the mid-IR is hampered by the large absorption of the buried oxide (BOX) for wavelengths above 4 μm. Silicon membranes have garnered great interest for their unique capability to overcome the BOX limitation while leveraging the advantages of Si photonics. On the other hand, silicon is uniquely poised for the implementation of wideband mid-IR sources based on nonlinear frequency generation.
Promising supercontinuum and frequency comb generation have already been demonstrated in Si. Still, current implementations have a limited flexibility in the engineering of phase-matching conditions and dispersion, which complicates the shaping of the nonlinear spectrum. Patterning Si with features smaller than half of the wavelength (well within the capabilities of standard large-volume fabrication processes) has proven to be a simple and powerful tool to implement metamaterials with optimally engineered properties.
Here, we present the design of nanostructured silicon membrane waveguides with ultra-wideband flat anomalous dispersion in a wavelength span exceeding 5 µm. Our three-dimensional finite difference time domain (FDTD) calculations predict flat anomalous dispersion near 50 ps/km⋅nm between 2.5 µm and 8 µm wavelength. These results illustrate the potential of subwavelength metamaterial engineering to control chromatic dispersion in Si membrane waveguides. This is a promising step towards the implementation of wideband nonlinear sources in the mid-IR for silicon photonics.
The strong evolution of silicon photonics towards very low power consumption circuits leads to the development of new strategies for photonic devices, especially for power-hungry components such as optical modulators. One strategy is to use Pockels effect in Si waveguides. However, bulk Si is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities. Nonetheless, under a strain gradient, generated by depositing a stressed layer on Si waveguides, this restriction vanishes. In our work, we experimentally demonstrated a Pockels effect based electro-optic modulation at high frequency (> 5GHz) using a strained silicon Mach-Zehnder modulator.
Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, Silicon is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities, like second harmonic generation nor the linear electro-optic effect (i.e. Pockels effect). Nonetheless, by means of strain gradients, generated by depositing a stressed layer (typically SiN) on silicon waveguides, this restriction vanishe. Hence, for years, many attempts on characterizing the second order nonlinear susceptibility tensor through Pockels effect have been performed. However, due to the semiconductor nature of silicon, its analysis has been wrongly carried out. Indeed, carriers in Si, at the Si/SiN interface and in SiN have a screening effect when performing electro-optic modulation, which have led to overestimations of the second order nonlinear susceptibility and eventually rose a controversy on the real existence of Pockels effect in strained silicon waveguides. Here, we report on unambiguous experimental characterization of Pockels effect in the microwave domain, by taking advantage of the inherent limitation of carrier effect in high frequency range. Recent results on high-speed measurements will be presented and discussed. Both charge effects and Pockels effect induced under an electric field will be also analysed.
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