Showing papers by "Jens H. Schmid published in 2023"

All‐Dielectric Huygens’ Meta‐Waveguides for Resonant Integrated Photonics

Abstract: The growing maturity of nanofabrication technology has recently enabled the deployment of high‐quality subwavelength nanostructures on photonic chips. Combining existing photonic waveguide technology with the paradigms adapted from metamaterials opens new avenues towards unprecedented control of guided light waves. However, developing new functionalities while preserving efficiencies and offering compatibility with current technology remains a major challenge in on‐chip nanophotonics. Here, a novel silicon nanophotonic waveguide comprising a chain of resonantly forward scattering nanoparticles empowered by spectrally overlapping electric and magnetic dipolar Mie‐type resonances is proposed and demonstrated. The propagation loss of the meta‐waveguides in the telecom spectral range is as low as 0.4 dB mm−1, exceeding the current record for Mie‐resonant waveguides by more than an order of magnitude. Furthermore, the meta‐waveguides support a negative group index over a broad spectral range of 60 nm and regions of vanishing and anomalous dispersion within the transmission band. Finally, it is shown that meta‐waveguide topologies can implement compact resonance‐protected waveguide bends and efficient splitters within just 320 nm propagation length. This work addresses the fundamental challenges of miniaturization, dispersion, and scattering control in integrated photonics and opens new opportunities for enhancing light–matter interactions, interfacing nanophotonic components, and developing nonlinear, ultrafast, and quantum optics resonant on‐chip devices.

Recent progress in subwavelength grating metamaterial engineered silicon photonic devices

Abstract: In this talk we present our recent advances in SWG metamaterial engineering. We will show a 1D-optical phased array composed of 112 evanescent-coupled surface emitting antennas with a length of 1.5 mm and fed by a compact distributed Bragg deflector. The measurements demonstrate a wavelength-steerable collimated beam with a far-field angular divergence of 1.8o × 0.2o. Experimental results of a bricked SWG 2×2 MMI coupler are also shown, achieving polarization agnostic performance in the 1500nm to 1560nm wavelength range. Both devices were fabricated on a standard 220-nm SOI platform using a single full-etch step process, with a minimum feature size of 80 nm, and thus compatible with immersion deep-UV lithography.

PCA-Enhanced Autoencoders for Nonlinear Dimensionality Reduction in Low Data Regimes

Abstract: Many scientific domains, such as nanophotonic design, gene expression, and materials design, are limited by high costs of acquiring data. This data is often intrinsically low-dimensional, nonlinear, and benefits from dimensionality reduction. Autoencoders (AE) provide nonlinear dimensionality reduction but are typically ineffective for low data regimes. Principal Component Analysis (PCA) is data-efficient but limited to linear dimensionality reduction. We propose a technique that harnesses the benefits of both methods by using PCA to initialize an AE. The proposed approach outperforms both PCA and standard AEs in low-data regimes and is comparable to the best of either of the two in other scenarios.

Controlling light with advanced subwavelength grating metamaterial topologies

Abstract: Subwavelength grating (SWG) structures are extremely versatile optical metamaterials that have become a fundamental design tool for the optimization of photonic devices. The importance of SWG structures arises from their capability to synthesize artificial materials with tailorable optical properties, including refractive index, dispersion, or anisotropy. In this invited talk, our advances in SWG topologies to further expand the design space of silicon photonic devices are discussed. The proposed topologies enable enhanced performance such as bandwidth broadening, polarization independency, or increased feature sizes, paving the way for the next generation of SWG-optimized devices.

Silicon-based surface gratings for efficient fiber-chip and free-space beam coupling

Abstract: Silicon photonics has established itself as a key integration platform, leveraging high-quality materials and large-scale manufacturing using mastered toolsets of complementary metal-oxide-semiconductor (CMOS) foundries. Chip-scale photonics offer unique promises for dense integration of versatile optical functions through compact and high-performance building blocks. Integrated photonics is now competing technology for many applications, spanning from telecom/datacom and interconnects up to quantum sciences and light detection and ranging (LIDAR) systems, among others. However, the lack of low-loss input/output chip interfaces can be prohibitive to successfully deploy multi-diverse device applications. Low coupling loss is essential in reducing overall power budget in photonic systems, impacting on-chip integration level. The light coupling from an off-chip environment into the planar waveguide platforms has always been a challenging research problem since the early years of integrated photonics. Optical interfaces formed on a photonic chip surface, rather than implemented on a chip edge, have been widely used to access photonic circuits with optical fibers or enabling free-space coupling of light beams. Surface gratings can be positioned at arbitrary locations and/or arranged in pre-defined patterns on the chip, facilitating wafer-scale testing and optical packaging. In this work, we present our recent progress in the development of silicon-based surface gratings for use in fiber-to-chip and free-space beam coupling. In particular, we discuss prospective design approaches to develop low-loss surface grating couplers implemented on silicon-on-insulator (SOI), silicon nitride (SiN), and hybrid silicon-silicon nitride (Si-SiN) platforms, allowing to approach a coupling loss below -1 dB. Among these, we also cover contemporary advances in compact silicon metamaterial nano-antennas for dense optical phased arrays, obtaining high a diffraction performance (> 90%) and wideband operation (> 200 nm) simultaneously.

Integrated silicon photonic optical phased arrays with large beam steering and high resolution

Abstract: Optical phased arrays in silicon photonics are an emerging technology for free-space communications and light detection and ranging (LIDAR). While traditional LIDARs with discrete components and mechanical beam steering are difficult to integrate and scale, silicon-based arrays have taken a massive leap forward in developing beam steering systems with compact footprint and high performance on a single chip. Here, we report our results in the development of chip-scale circular phased arrays. Arrays formed in a grid of concentric rings are shown to suppress the sidelobes, expand the steering range and obtain narrower beamwidths, with large spacing between optical elements.

Subwavelength metamaterial devices with optimization and machine learning

Abstract: Subwavelength metamaterials allow to synthesize tailored optical properties which enabled the demonstration of photonic devices with unprecedented performance and scale of integration. Yet, the development of metamaterial-based devices often involves a large number of interrelated parameters and figures of merit whose manual design can be impractical or lead to suboptimal solutions. In this invited talk, we will discuss the potentiality offered by multi-objective optimization and machine learning for the design of high-performance photonic devices based on metamaterials. We will present both integrated devices for on-chip photonic systems as well as recent advances in the development of devices for free-space applications and optical beam control.

Metamaterial antenna array fed by distributed Bragg deflector for beam steering on SOI platform

Abstract: The capability to radiate collimated steerable beams of light is crucial for many applications, such as remote sensing and free-space optical communications. Here we experimentally demonstrate a novel 1D-antenna array architecture that exhibits a far-field Gaussian profile with an angular divergence of 1.8° x 0.2°.

All dielectric Mie-resonant waveguides and nanophotonic structures

Abstract: We introduce a new type of silicon-based optical meta-waveguide operating in the telecom spectral range. Our waveguides comprises a chain of Mie-resonant silicon nanoresonators designed to exhibit nearly exclusively forward-scattering characteristics. This yields unique optical properties, including a large transmission gain, efficiently suppressed backscattering even in the presence of strong perturbations, a negative group index over a broad spectral range, as well as regions of almost vanishing and anomalous dispersion. This is an unprecedented combination of characteristics for any photonic system supporting guided modes, thereby unlocking completely new opportunities for fundamental research as well as future applications.

Thermally induced sideband generation in silicon-on-insulator cladding modulated Bragg notch filters.

Abstract: We investigate and experimentally demonstrate a cladding modulated Bragg grating superstructure as a dynamically tunable and reconfigurable multi-wavelength notch filter. A non-uniform heater element was implemented to periodically modulate the effective index of the grating. The Bragg grating bandwidth is controlled by judiciously positioning loading segments away from the waveguide core, resulting in a formation of periodically spaced reflection sidebands. The thermal modulation of a periodically configured heater elements modifies the waveguide effective index, where an applied current controls the number and intensity of the secondary peaks. The device was designed to operate in TM polarization near the central wavelength of 1550 nm and was fabricated on a 220-nm silicon-on-insulator platform, using titanium-tungsten heating elements and aluminum interconnects. We experimentally demonstrate that the Bragg grating self-coupling coefficient can be effectively controlled in a range from 7 mm-1 to 110 mm-1 by thermal tuning, with a measured bandgap and sideband separation of 1 nm and 3 nm, respectively. The experimental results are in excellent agreement with simulations.