Halide perovskite is a promising candidate for high-performance and ultra-compact light emitters which are the core of the next-gen display technology. Despite various µ-Perovskite-LED array design availability, achieving finely controlled emission patterns, by implementing nanopatterns on the active media (metasurfaces), is a key challenge. In this work, we demonstrate a design and fabrication procedure for perovskite metasurface LED whose optical properties are controlled by nanopatterning. The obtained results pave the way for radiation control in perovskite LEDs and micro-LEDs.
We report on the design, fabrication, and characterization of the first photonic crystal (PhC)-based red multiple-quantum-well (MQW) color converters fully optimized for augmented reality (AR) microdisplays through a quasi-3D light harnessing principle. This principle leverages an aluminum (Al) bottom reflector and a silicon dioxide (SiO2) gap to harness the bottom-emitted light, along with copper (Cu) lateral mirrors and a silicon nitride (SiN) phase-matcher for Bloch-mode replication. These structures were designed using 3D-FDTD simulations. As a proof-of-principle, we fabricated corresponding devices that exhibit promising characteristics, including record light extraction efficiencies over 40% for 4µm pixels and emission patterns with high directionality. Time-resolved photoluminescence (TRPL) analyses, along with a four-wave intensity model developed in this work, indicate that there is still room for improvement. We believe that the guidelines established in this study could pave the way for the use of MQW color converters in the next generation of very bright, high-resolution RGB microdisplays for AR glasses and beyond.
While state-of-the-art RGB microdisplays rely on quantum-dot color-converters (CC), the next generation of very bright and high-resolution AR microdisplays could be based on MQW CC due to their better photostability and higher blue-light absorption. However, their practical implementation is still hindered by their low light extraction efficiency (LEE), their Lambertian-like emission patterns, as well as the challenges related to their integration on on-Silicon blue µLED arrays (transfer and pixelization). In this work, we use photonic-crystals (PhCs) as light extractors and investigate all the challenges related to the design, integration & fabrication as well as testing of novel MQW based CC.
Photovoltaic (PV) solar cells are designed to efficiently absorb solar photons but convert only a limited proportion of them into electricity. The remaining energy is converted into heat, which in turn, heats the entire solar modules up to 50-60 °C under real operating conditions. This is detrimental to both their power conversion efficiency and lifetime. Recently, there has been a growing interest in the so-called radiative sky cooling (RSC) strategy. This approach consists in optimizing the thermal radiation of cells or modules - with the help of photonic structures - by taking advantage of the atmospheric transparency in the 8-13 μm range. Although some basic studies predict cooling of more than 10°C on silicon devices, they remain insufficient to assess the potential of this technique for various PV technologies directly from their material properties. Using COMSOL Multiphysics, we are working on a fully coupled model of silicon solar cells in order to predict their opto-electro-thermal behaviour from the bottom-up (i.e. using only material properties as an input). This enables us to study various photonic pathways for enhanced radiative sky cooling. Our work also shows the importance of moving towards fully coupled models to accurately predict the temperature and electrical output under real conditions.
State-of-the-art RGB microdisplays use quantum-dot color converters (CC), which suffer from photostability issues and low blue-light absorption. Inorganic MQW based CC offer higher blue-light absorption and better photostability. However, their practical use for microdisplays has not been implemented yet because of their low light extraction efficiency (LEE) inherent to their high refractive indices. In this paper, we investigate the use of photonic crystals (PhC) with different optogeometrical parameters to fully optimize AlGaInP/InGaP MQW CC for blue-to-red and green-to-red color conversions in microdisplays. A 600nm-thick CC was successfully bonded on a transparent substrate using oxide-mediated molecular bonding. By using optimized photonic-crystal designs, we obtained a large LEE enhancement (x 9) within ultra-short extraction lengths (~2μm), which shows quasi-perfect light outcoupling and compatibility with pixel lateral sizes under 5μm. Experimental results are in agreement with 3D-FDTD simulations, showing that those unique characteristics are paired with highly directional emission. A phenomenological model derived from the standard coupled-mode theory has been proposed and used to determine the mean coupling strengths between the guided Bloch modes and radiated modes. We believe that the design guidelines set in this work could pave the way for the use of inorganic MQW CC to achieve monolithic integration for full-color microdisplay applications.
In this communication, we present the potentialities offered by 2D photonic crystals to trap and absorb photons in thin silicon layers. We will specifically focus on the impact of the photonic crystal unit cells symmetry, and the possibility to increase light absorption and generated photocurrent using multi-periodic and pseudo-disordered photonic nanostructures.
In silicon-based solar cells, a substantial part of the energy losses is related to the charge carriers thermalization in the UV-blue range and the week carriers collection at these wavelenghts. To avoid this issue, we introduce a new concept which combines a rare-earths doped thin layer with a photonic crystal (PC) layer, allowing an efficient conversion from UV-blue photons to near-IR photons. We report on the feasibility of such a nanostructured down-converter module using an active rare-earth doped CaYAlO4 thin layer and a silicon nitride PC on top. By means of optical numerical simulations, the promising potentialities of the concept are demonstrated.
In order to achieve high efficiency photovoltaic devices and sensors, we propose to implement photonic crystals on thin
absorbing layers in such a way to generate two Bloch mode resonances with opposite symmetries. Through FDTD and
RCWA simulations, we track and adjust the characteristics of these modes so as to reach their degeneracy. Design and
simulations were carried out considering a hydrogenated amorphous silicon layer. We demonstrate that up to 92%
absorption can be achieved, far above the 50% limit corresponding to the critical coupling condition between an incident
wave and an optical resonance. Moreover, the robustness of the absorption peak was tested by varying both the
topographical parameters of the PhC membrane and the angle of incidence. Finally, some guidelines are provided to
generalize our approach for the design of broadband absorbers.
KEYWORDS: Absorption, Solar cells, Photonic crystals, Silicon, Optical lithography, Aluminum, Silicon films, Reactive ion etching, Holography, Thin film solar cells
In this paper, we present the integration of an absorbing photonic crystal within a monocrystalline silicon thin film solar
cell stack. Optical simulations performed on a complete solar cell revealed that patterning the epitaxial monocrystalline
silicon active layer as a 1D and 2D photonic crystal enabled to increase its integrated absorption by 38%rel and 50%rel in
the whole 300-1100 nm range, compared to a similar but unpatterned stack. In order to fabricate such promising cells, a
specific fabrication process based on holographic lithography, inductively coupled plasma etching and reactive ion
etching has been developed and implemented to obtain such photonic crystal patterned solar cells. Optical measurements
performed on the patterned stacks highlight the significant absorption enhancement, as expected by simulation. A more
advanced structuration combining a front and a rear 1D binary photonic patterning with different periods is designed,
enabling a 60%abs larger absorption in silicon.
KEYWORDS: Absorption, Solar cells, Photonic crystals, Holography, Etching, Lithography, Reactive ion etching, Silicon, Thin film solar cells, Optical lithography
In this paper, we present the integration of an absorbing photonic crystal within a thin film photovoltaic solar cell.
Optical simulations performed on a complete solar cell revealed that patterning the epitaxial crystalline silicon
active layer as a 1D and 2D photonic crystal enabled to increase its integrated absorption by 37%abs and 68%absbetween 300 nm and 1100 nm, compared to a similar but unpatterned stack. In order to fabricate such promising
cells, a specific fabrication processes based on holographic lithography, inductively coupled plasma etching and
reactive ion etching has been developed and implemented to obtain ultrathin patterned solar cells.
A modeling method for passive photonic components such as add-drop filters is presented, which allows for fast and
accurate system-level ONoC simulation in an electrical EDA simulation environment. This method can be used for
design verification of electronic / photonic heterogeneous system, and allows for considerable acceleration of the system
simulation.
We present the integration of an absorbing planar photonic crystal within a thin film photovoltaic cell. The devices are
based on a stack including a hydrogenated amorphous silicon P-i-N junction surrounded by TCO layers, with a back
metallic contact. Optical simulations exhibit a significant increase of the integrated absorption in the 300-720nm
wavelength range. The global electro-optical characteristics of such a new solar cell, and the impact of surface
passivation, are also discussed. Carrier generation rate maps calculated by optical simulations are introduced as input
data in a commercial electrical simulation software. The fabrication of such a device is finally addressed, with a specific
focus on the use of low cost nanopatterning processes compatible with large areas.
The absorption of thin hydrogenated amorphous silicon layers can be efficiently enhanced through a controlled periodic
patterning. Light is trapped through coupling with photonic Bloch modes of the periodic structures, which act as an
absorbing planar photonic crystal. We theoretically demonstrate this absorption enhancement through one or two
dimensional patterning, and show the experimental feasibility through large area holographic patterning. Numerical
simulations show over 50% absorption enhancement over the part of the solar spectrum comprised between 380 and
750nm. It is experimentally confirmed by optical measurements performed on planar photonic crystals fabricated by
laser holography and reactive ion etching.
A design is proposed to significantly increase the absorption of a thin layer of absorbing material such as amorphous
silicon. This is achieved by patterning a one-dimensional photonic crystal (1DPC) in this layer. Indeed, by coupling the
incident light into slow Bloch modes of the 1DPC, we can control the photon lifetime and then, enhance the absorption
integrated over the whole solar spectrum. Optimal parameters of the 1DPC maximize the integrated absorption in the
wavelength range of interest, up to 45% in both S and P polarization states instead of 33% for the unpatterned, 100 nm
thick amorphous silicon layer. Moreover, the absorption is tolerant with respect to fabrication errors, and remains
relatively stable if the angle of incidence is changed.
We analyze a highly compact optical add-drop filter topology based on a pair of microdisk resonators and a bus waveguide intersection. The filter is further assessed on an integrated optical 4×4 network for optical on-chip communication. The proposed network structure, as compact as 50×50 µm, is fabricated in a CMOS-compatible process on a silicon-on-insulator (SOI) substrate. Finally, the experimental results demonstrate the proper operation of the fabricated devices.
We report on enhancement of thin layer absorption through photonic band-engineering of a photonic crystal
structure. We realized amorphous silicon (aSi) photonic crystals, where slow light modes improve absorption
efficiency. We show through simulation that an increase of the absorption by a factor of 1.5 is expected for a
model film of 100nm of aSi. The proposal is then validated by an experimental demonstration, showing a 50%
increase of the absorption of a demonstrator layer of 1μm thick aSi over a spectral range of 0.32 0.76μm.
This shows new possibilities of increasing the efficiency of thin film photovoltaic cells. Photonic crystal based
architecture are proposed and discussed.
A new concept of ultra-thin film photovoltaic solar cell including a planar photonic crystal is proposed. The goal is to
couple the incident light into broad resonances guided in the absorbing layer. To achieve this, a periodic lattice is
patterned within the active layer, for example made of holes in amorphous silicon. By adjusting the pattern dimensions,
the spectral position and quality factor of these resonances can be controlled so as to optimise the global absorption.
Design details will be discussed in this communication.
We present a compact passive optical add-drop filter which incorporates two microring resonators and a waveguide intersection in silicon-on-insulator (SOI) technology. Such a filter is a key element for designing simple layouts of highly integrated complex optical networks-on-chip. The filter occupies an area smaller than 10μm×10μm and exhibits relatively high quality factors (up to 4000) and efficient signal dropping capabilities. In the present work, the influence of filter parameters such as the microring-resonators radii and the coupling section shape are analyzed theoretically and experimentally
A low loss refractive waveguided mode can be efficiently coupled to Bloch modes in two dimensional array of
nanopillars, in a two-level high index membrane structure, according to a numerical study. More specifically, when using
a slow Bloch mode above the light line, a wavelength selective, directional extraction can occur from the waveguide to
the free space. The main conditions to be achieved, such as phase matching, strength of the coupling, photon lifetime in
the photonic crystal, influence of embedding... will be discussed.
Sol-gel ZrO2 thin films deposited by dip-coating on various substrates are characterized. The film thickness, the refractive index and the thermo-optic coefficient (δn/δT) are measured using the prism coupler technique. The thickness of the uniform and good quality sol-gel films ranges between 100nm and 130nm, while the refractive index ranges between 1.9 and 2.1 at 25°C, depending on the substrate material and surface quality, and depending on some process parameters. The δn/δT measurements of the sol-gel ZrO2 thin films deposited on several substrates show that the TM refractive index always exhibits much higher dependence with respect to temperature than the TE refractive index. Such variations had not previously been reported and will require much attention and future study due to the importance of δn/δT for advanced optical telecommunications devices.
We present a new, one-dimensional, transfer matrix formalism for describing the spectral properties of a quasi-periodic integrated waveguide filter (reflection R, transmission T, overall losses L = 1 - R - T), where losses (essentially due to the modal mismatch between adjacent sections) are modeled as localized, Dirac-like singularities of the (complex) dielectric permittivity. As far as losses appear periodic, the coupling constant between propagating and contra-propagating waves is complex: such a distribution leads to a specific spectral response for L, different from that provided by homogeneous absorption. Besides, the transfer matrix of a unit cell (made of two quarter-wave sections of high and low indices) can be expressed rigorously in the frame of usual coupled-wave equations, even for arbitrary high index contrast. As a result, any periodic section can be represented by one transfer matrix only, whatever the number of unit cells. This can dramatically reduce the computational time by comparison with more accurate simulation tools such as Film Mode Matching (FMM) method.
The I3O technology based on Titanium ion implantation in silica is proposed for the fabrication of passive compact PLC devices. It is demonstrated that the guided field can be easily tailored to fit standard fibers or can be compatible with the use of bent waveguides having a small radius of curvature.
Optical and electro-optical properties of pulse laser deposited PLZT thin films are measured using the m-lines technique. Sample preparation is described. Correlation between the deposition process and optical and electro-optical properties is presented.
We numerically demonstrate that the classical thin film computation method (Abeles Computation Method) may be used to obtain reflectance or transmittance of integrated optics filters with a good approximation. Radiative losses are simulated by absorption losses. Results agree well with Film Mode Matching computed optical properties and the computation time can be divided by a factor of 104. Synthesis of integrated Bragg reflectors, narrow band pass filters, high pass filters is presented. Integrated optics filters with non-periodic structures such as gain flattening filters can be easily designed using the Abeles Computation Method. Thus, classical thin film synthesis softwares are useful to design integrated components with arbitrary guided mode spectral reflectance or transmittance. This leads to prospects of new integrated optics functionalities of a great importance such as broadband dispersion compensation for WDM systems or high - order dispersion compensation with non linearly chirped integrated Bragg reflectors.
Thanks to progresses in photolithography techniques optical materials can now be structured to a scale of a few tens of a nanometer. This has opened a wide field of new applications. When concerned with a scale of some tens of a micron down to a few microns, microlens and integrated optic components can be made. When the material is structured with a scale in the order of the wavelength of light, different filtering functions can be made. This concerns Bragg mirrors or more generally Photonic Crystals. A structuration in a scale small in front of the wavelength is also of a great interest. In this case the material does not diffract the light anymore an dit behaves like a homogeneous one. The calculated transmittance of a laser mirror is used to determine the effective index of the single layer equivalent to the multilayer stack. The artificial anisotropy of thin films structured with a one-dimension sub wavelength grating made by holography is measured. The limitation of the first order homogenization theory is given for two different grating steps. Polarizing coatings or polarization rotators are designed to work in normal incidence by inserting anisotropic films in simple multilayer structures.
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