1,721,954 research outputs found
Silicon photonic mode multiplexers based on subwavelength metamaterials and on-chip beam forming
No full textIntegration of photonic circuits on silicon offers a unique opportunity to address the scaling of inter- and intra-chip communications in an energy-efficient and cost-effective manner. Mode-division multiplexing (MDM) is deemed as one of the most promising technologies to increase aggregated data bandwidth and avoid a communication capacity crunch. In this invited talk, we review our latest advances on integrated silicon mode multiplexers, including new topologies based on subwavelength grating (SWG) metamaterials for extended broadband operation and higher-order mode support. Specifically, we report on an ultra-broadband multiplexer based on a phase shifter and a multimode interference (MMI) coupler both engineered with subwavelength metamaterials. Experimental measurements of a complete multiplexer-demultiplexer link show losses lower than 2 dB and crosstalk below -17 dB over a bandwidth of 245 nm (1427 – 1672 nm).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QN/Groeblacher La
MOEMS Fabry-Pérot interferometers with ALD TiO2 anti-stiction coating for pull-in failure prevention
No full textIn metallic mirror Micro-opto-electro-mechanical system (MOEMS) Fabry Pérot interferometer (FPI) chips, sticking and non-reversible pull-in of the two mirrors is lowering the lifetime of the component. Adding 10 nm of atomic layer deposited (ALD) of semiconducting titanium dioxide (TiO2) coating over the cavity of the mirror decreased the static charge inside the mirror cavity preventing sticking of the mirrors and the mirrors survived actuated to pull-in for more than 1000 times. As too thick layers can optically lower the performance of the mirror and overly thin layers would not decrease the static charge, we studied three different TiO2 thicknesses of 3 nm, 5 nm, and 10 nm. In conclusion, 10 nm TiO2 layer does not optically interfere in the FPI´s performance and it has the best conductivity of all tested TiO2 film thicknesses.</p
Modeling of low- and high-order harmonic generation in ultrashort laser-excited resonant semiconductor nanostructures
No full textUltrashort laser-excited semiconductor nanostructures, supporting individual Mie or collective resonances, can serve as efficient miniaturized sources for low- and high-order harmonic generation. Upon laser excitation, multiple nonlinearities come into interplay on subwavelength spatial and ultrafast temporal scales, including surface and bulk effects, contributions from bound electrons and photo-excited carriers. In turn, transient optical properties affect the structure and the amplitude of the transmitted laser pulse. Computational approaches, coupling ultrashort pulse propagation with semiconductor nonlinear optical response, compatible with the considered spatial and temporal scales, are urgently needed to provide new strategies for efficient light modulation and manipulation, for instance, in order to enhance the nonlinear conversion efficiency. Nonlinear dynamics in ultrashort laser-excited nanostructures will be discussed from the perspective of classical perturbative, semi-classical, and microscopic non-perturbative models based on semiconductor Bloch equations, considering electronic multi-band structure of the material and involved intra- and inter-band transitions. As an example, an enhanced harmonic generation will be shown from a single nanoparticle or periodic array of nanoparticles, supporting Mie and collective lattice resonances, and a subwavelength resonator supporting quasi-bound states in the continuum. Ultrafast processes involved in nonlinear pulse propagation such as spectrum broadening and plasma blue-shift, frequency mixing and saturation in the harmonic yield, as well as the restrictions due to carrier absorption and heating of the sample, will be discussed within the framework of a classical model. Perspectives of applying self-consistent nonlinear Maxwell-based approaches to large-scale problems in nonlinear meta-photonics as well as their current limitations will be finally outlined
Autocorrective interferometers for photonic integrated circuits:Invited paper
No full textExtensive literature has shown that finite impulse response (FIR) interferometers can be engineered to be insensitive under variations of different physical parameters, e.g., to ensure flat-top response and/or tolerance to fabrication errors. In this context, I will show how the Bloch sphere representation can be a very powerful design tool providing superior physical insight into the working principle of autocorrective devices like broadband 50:50 splitters or flat-top interleavers, that can be therefore designed through simple analytical formulas. I will eventually review the recent progress in practical implementation of the autocorrective designs in the micron-scale silicon photonics platform of VTT
Silicon photonics based laser doppler vibrometer for non-contact photoacoustic sensing
No full textNon-contact detection of photoacoustic signals is important for various applications, particularly in medical sensing and imaging, where contact methods can be uncomfortable or risky for the patient. Techniques using optical detection of vibrations, such as laser doppler vibrometers (LDVs), have been proven to be a key component for enabling non-contact photoacoustic sensing. However, most LDV systems rely on fiber-based or free-space optics, which can be unwieldy and expensive, especially for multiple location sensing. In this work, we present a compact, photonic integrated circuit (PIC)-based homodyne LDV system for the detection of photoacoustic signals. The system is fabricated on a silicon-on-insulator platform, which has the potential to be low-cost in case of medium or large volume production. To generate the photoacoustic signals, we used a 532 nm pulsed laser directed towards a target embedded in a silicone phantom designed to mimic the acoustic properties of human tissue. The target consists of an ink-solution-filled channel, which absorbs the excitation light and generates acoustical signals within the phantom through the photoacoustic effect. After performing a series of measurements with different ink concentrations, we found a good correlation between the photoacoustic signals detected by the on-chip detectors and the absorption of the target. Our system was able to detect ink solutions with absorption values as low as 5 cm−1, an order of magnitude lower than the typical absorption of whole blood at 532 nm. These results demonstrate that PIC-based LDVs can be used to realize compact and low-cost non-contact detection for photoacoustic biomedical sensing applications
Terahertz nanodevices for photonic integrated circuits
No full textOver the past decades, Terahertz (THz) systems development has taken a major step forward together with laser-based technologies for the generation and detection of THz signals. Optoelectronic generation of continuous-wave THz signals relies on mixing two optical signals oscillating in a high-speed photoconductive antenna, for which the photocurrent depends on the incident optical power. The capability to operate THz fields in passive devices can be combined smoothly with photonic integrated circuit (PIC) technologies to enable photonic chips with enhanced THz efficiency. There are still many open questions about implementation and improvement to reduce equipment size, noise, alignment efforts, electrical and optical power consumption, and to increase the system flexibility. In this manuscript, we introduce a new THz system platform based on photonic integrated circuits and micro-structured photoconductive antennas that will increase the integration by reducing the footprint of THz spectrometers by more than 3 orders of magnitude. Additionally, a new integrated lens-antenna consisting of a Fresnel zone plate is designed and implemented for a nanocontact based THz photomixer. The new design replaces the standard conventional bulky silicon lens, which normally no THz photomixer can avoid. THz measurements showed a comparable behavior with the Fresnel zone plate to that of the conventional bulky silicon lens, demonstrating its readiness for photonic integrated circuits-based THz systems. This integration platform will represent a technological jump from currently bulky equipment and devices to extremely flexible, portable, and energy efficient THz systems-on-chip, at much lower costs.</p
Nonlinear crystals for imaging and detection of mid-IR radiation
No full textThe mid-IR wavelength range, i.e. 2-25 μm, houses the vibrational spectra of most gaßes and large molecules found in complex structures such as tißue, plastics or food. When designing an upconversion system for imaging or mid-IR detection, several aspects should be considered. Upconversion has several advantageous features which makes it an interesting option to consider for many mid-IR applications. Main advantages include, low-noise detection even at elevated temperatures, an almost instantaneous response time, phase preservation, and the ability to perform upconversion imaging. The χ(2) crystal properties impact the performance of the system significantly. Design aspects related to the choice of crystal as well as different applications is presented.</p
Integrated Metasurfaces for Advanced Solid-State-Lighting
Get PDFLight-Emitting Diodes (LEDs) exhibit a typical Lambertian emission, usually requiring reshaping by means of secondary optics. We review the potential of various integrated photonic architectures to address the demand for system miniaturization and high efficiency in emerging applications. Photonic structures that can be potentially integrated in LED devices include metalenses, photonic crystals and reflective metasurfaces. We embed periodic nanoantennas in InGaN/GaN multi-quantum well (MQW) LEDs to control their far-field emission directionality and enhance collection efficiency. We propose exploiting mechanisms such as surface lattice resonances, which rely on the near-field coupling between the quantum wells and the nanoantenna array. Multiple experimental and modeling studies demonstrate the benefits and challenges of optimized integrated metasurfaces to enable efficient SSL sources without the need of bulky secondary optics for directional beam control.</p
- …
