Tailoring the interaction between light and sound has opened new possibilities in photonic integrated circuits (PICs) that range from achieving quantum control of light to high-speed information processing. However, the actuation of sound waves in Si PICs usually requires integration of a piezoelectric thin film. Lead zirconate titanate (PZT) is a promising material due to its strong piezoelectric and electromechanical coupling coefficient. Unfortunately, the traditional methods to grow PZT on silicon are detrimental for photonic applications due to the presence of an optical lossy intermediate layer. In this work, we report integration of a high quality PZT thin film on a silicon-on-insulator (SOI) photonic chip using an optically transparent buffer layer. We demonstrate acousto-optic modulation in silicon waveguides with the PZT actuated acoustic waves. We fabricate interdigital transducers (IDTs) on the PZT film with a contact photolithography and electron-beam lithography to generate the acoustic waves in MHz and GHz ranges, respectively. We obtain a V π L ∼ 3.35 V•cm at 576 MHz from a 350 nm thick gold (Au) IDT with 20 finger-pairs. After taking the effect of mass-loading and grating reflection into account, we measured a V π L ∼ 3.60 V•cm at 2 GHz from a 100 nm thick aluminum (Al) IDT consisting of only four finger-pairs. Thus, without patterning the PZT film nor suspending the device, we obtained figures-of-merit comparable to state-of-the-art modulators based on SOI, making it a promising candidate for a broadband and efficient acousto-optic modulator for future integration.
Optical isolators and circulators are critical building blocks for large-scale photonic integrated circuits. Among the several methods proposed to realize such nonreciprocal devices, including heterogeneous integration with garnet-based materials or using nonlinearities, dynamic modulation of the waveguide properties is a potentially practical and easily accessible method. However, most proposals relying on this method rely on modulators with a very large footprint, limiting their practical applicability. This paper overcomes this issue by presenting a method to achieve nonreciprocal optical transmission taking advantage of compact ring modulators. We use a cascaded system of microring modulators with a footprint as small as 15 μm × 220 μm and propose that, by tuning the relative time delay between the RF driving signals and the optical delay between the modulators, nonreciprocal transmission can be achieved. We present a detailed theoretical analysis of our design and investigate the origin of the asymmetric transmission. The modulators were designed and fabricated on IMEC's Silicon-on-Insulator platform iSiPP50G. We achieve a 16 dB difference between forward and backward optical signals at a driving voltage (V pp ) of 8 V at 6 GHz. Moreover, we analyze the impact of fabrication imperfections on the device performance. Our work leads to a significant reduction in device footprint compared to formerly explored solutions using dynamic modulation and is well suited for monolithic integration with photonic integrated circuits.
We propose and demonstrate a self-coupled micro ring resonator for resonance splitting by mutual mode coupling of cavity mode and counter-propagating mode in Silicon-on-Insulator platform The resonator is constructed with a self-coupling region that can excite counter-propagating mode. We experimentally study the effect of selfcoupling on the resonance splitting, resonance extinction, and quality-factor evolution and stability. Based on the coupling, we achieve 72% of FSR splitting for a cavity with FSR 2.1 nm with ¡ 5% variation in the cavity quality factor. The self-coupled resonance splitting shows highly robust spectral characteristic that can be exploited for sensing and optical signal processing.Advances in Silicon photonics (SiP) has provided tremendous impetus to achieve the next generation high-speed short and long reach communication. It provides the advantages of optical transparency and large-bandwidth along with CMOS compatibility to deliver compact energy-efficient circuits [1]. Moreover, improvements in the fabrication technology has enabled low-loss waveguides and highly-uniform device response that was once considered a challenge in adapting SiP for practical applications [2].Micro-Ring Resonators (MRRs) are one of the fundamental building blocks of SiP integrated circuits. Si MRRs have found applications in areas such as sensors [3], modulators [4] and filters [5]. A simple MRR consist of a ring waveguide evanescent-coupled to one or two straight waveguides. Typically, MRRs have only forward propagating cavity modes at resonant wavelengths. However, in practice, any non-ideality in the resonator can result in the generation of counter-propagating modes in the cavity. The two primary sources of such non-idealities are sidewall roughness in the waveguides and non-unidirectional coupling between the bus and the ring waveguide. The sidewall roughness act as scattering points that redistributes the energy into counter-propagating mode, while coupling region between a ring and the straight waveguide can excite contra-directional modes because of reflections caused due to mode mismatch between the straight bus waveguide and the cavity mode [6,7]. Such counterpropagating modes result in resonance splitting and are referred to as Autler-Townes splitting
We demonstrate an all-optical four-channel wavelength multicasting in a coupled Silicon microring resonator system. The scheme is based on two-photon absorption induced free carrier dispersion in Silicon. The coupled cavity facilitates resonance splitting that is utilized as individual channels for multicasting. Using the split resonances, we achieve an aggregate multicasted data rate of 48 Gbps (4×12 Gbps). Moreover, we also present a detailed analysis and performance of the multicasting architecture.
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