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2021 ◽  
Author(s):  
Xueke Duan ◽  
Haoxiang Chen ◽  
Yun Ma ◽  
Zhiyuan Qian ◽  
Qi Zhang ◽  
...  

Abstract Resonances in optical cavities are used to manipulate light propagation, enhance light-matter interaction, modulate quantum states, and so on. However, the index contrast between the traditional cavities and the host is generally not high, which to some extent limited their performances. By putting dielectric cavities into a host of zero-index materials, index contrast in principle can approach infinity. Here, we analytically deduced Mie resonance conditions at this extreme circumstance. Interestingly, we discovered a so-called resonance nesting effect, in which a set of cavities with different radii can possess the same type of resonance at the same wavelength. We also revealed previously unknown degeneracy between the 2l-TM (2l-TE) and 2l+1-TE (2l+1-TM) modes for " 0 ( 0) material, and the 2l-TM and 2l-TE for both " 0 and 0. Such extraordinary resonance nesting and degeneracy provide additional principles to manipulate cavity behaviors.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Timothy Lee ◽  
Qi Sun ◽  
Martynas Beresna ◽  
Gilberto Brambilla

AbstractWe introduce the fabrication and use of microcracks embedded in glass as an optical element for manipulating light propagation, in particular for enhancing waveguide performance in silica integrated optics. By using a femtosecond laser to induce a strong asymmetric stress pattern in silica, uniform cracks with set dimensions can be created within the substrate and propagated along a fixed path. The smoothness of the resulting cleave interface and large index contrast can be exploited to enhance waveguide modal confinement. As a demonstration, we tackle the longstanding high bend-loss issue in femtosecond laser written silica waveguides by using this technique to cleave the outer edge of laser written waveguide bends, to suppress radiative bend loss. The microcrack cross section is estimated to be 15 μm in height and 30 nm in width, for the 10 $$\times$$ ×  10 μm waveguides. At 1550 nm wavelength, losses down to 1 dB/cm at 10 mm bend radius were achieved, without introducing additional scattering. Both the cleave stress pattern and waveguide are fabricated with the same multiscan writing procedure, without requiring additional steps, and re-characterisation of the waveguides after 1 year confirm excellent long term performance stability.


Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7364
Author(s):  
Dario Schiavon ◽  
Robert Mroczyński ◽  
Anna Kafar ◽  
Grzegorz Kamler ◽  
Iryna Levchenko ◽  
...  

Gallium nitride (GaN) doped with germanium at a level of 1020 cm−3 is proposed as a viable material for cladding layers in blue- and green-emitting laser diodes. Spectral reflectometry and ellipsometry are used to provide evidence of a reduced index of refraction in such layers. The refractive-index contrast to undoped GaN is about 0.990, which is comparable to undoped aluminium gallium nitride (AlGaN) with an aluminium composition of 6%. Germanium-doped GaN layers are lattice-matched to native GaN substrates; therefore, they introduce no strain, cracks, and wafer bowing. Their use, in place of strained AlGaN layers, will enable significant improvements to the production process yield.


Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7127
Author(s):  
Alicia Petronela Rambu ◽  
Vasile Tiron ◽  
Eugen Oniciuc ◽  
Sorin Tascu

The α-phase waveguides directly produced in one fabrication step only are well known for preserving both the excellent nonlinear properties and the ferroelectric domains orientation of lithium niobate substrates. However, by using the piezoresponse force microscopy (PFM), we present a coherent study on ferroelectric dipoles switching induced by the fabrication process of α-phase waveguides on Z-cut congruent lithium niobate (CLN) substrates. The obtained results show that the proton exchange process induces a spontaneous polarization reversal and a reduction in the piezoelectric coefficient d33. The quantitative assessments of the impact of proton exchange on the piezoelectric coefficient d33 have been quantified for different fabrication parameters. By coupling systematic PFM investigation and optical characterizations of α-phase protonated regions and virgin CLN on ±Z surfaces of the samples, we find a very good agreement between index contrast (optical investigation) and d33 reduction (PFM investigations). We clearly show that the increase in the in-diffused proton concentration (increase in index contrast) in protonated zones decreases the piezoelectric coefficient d33 values. Furthermore, having a high interest in nonlinear performances of photonics devices based on PPLN substrates, we have also investigated how deep the spontaneous polarization reversal induced by proton exchange takes place inside the α-phase channel waveguides.


2021 ◽  
Vol 9 ◽  
Author(s):  
Pascal Freyer ◽  
Bodo D. Wilts ◽  
Doekele G. Stavenga

The iridescent plumage of many birds is structurally colored due to an orderly arrangement of melanosomes in their feather barbules. Here, we investigated the blue- to purple-colored feathers of the European starling (Sturnus vulgaris) and the blue and green feathers of the Cape starling (Lamprotornis nitens). In both cases, the barbules contain essentially a single layer of melanosomes, but in S. vulgaris they are solid and rod-shaped, and in L. nitens they are hollow and rod- as well as platelet-shaped. We analyzed the coloration of the feathers by applying imaging scatterometry, bifurcated-probe- and micro-spectrophotometry. The reflectance spectra of the feathers of the European starling showed multiple peaks and a distinct, single peak for the Cape starling feathers. Assuming that the barbules of the two starling species contain a simple multilayer, consisting locally only of a cortex plus a single layer of melanosomes, we interpret the experimental data by applying effective-medium-multilayer modeling. The optical modeling provides quantitative insight into the function of the keratin cortex thickness, being the principal factor to determine the peak wavelength of the reflectance bands; the melanosome layer only plays a minor role. The air cavity in the hollow melanosomes of the Cape starling creates a strongly enhanced refractive index contrast, thus very effectively causing a high reflectance.


Polymers ◽  
2021 ◽  
Vol 13 (21) ◽  
pp. 3843
Author(s):  
Víctor Bonal ◽  
José A. Quintana ◽  
José M. Villalvilla ◽  
Pedro G. Boj ◽  
Rafael Muñoz-Mármol ◽  
...  

The molecule N,N′-bis(3-methylphenyl)-N,N′-dyphenylbenzidine (TPD) has been widely used in optoelectronic applications, mainly for its hole-transporting properties, but also for its capability to emit blue light and amplified spontaneous emission, which is important for the development of organic lasers. Here, we report deep-blue-emitting distributed feedback (DFB) lasers based on TPD dispersed in polystyrene (PS), as active media, and dichromated gelatin layers with holographically engraved relief gratings, as laser resonators. The effect of the device architecture (with the resonator located below or on top of the active layer) is investigated with a dye (TPD) that can be doped into PS at higher rates (up to 60 wt%), than with previously used dyes (<5 wt%). This has enabled changing the index contrast between film and resonator, which has an important effect on the laser performance. With regards to thresholds, both architectures behave similarly for TPD concentrations above 20 wt%, while for lower concentrations, top-layer resonator devices show lower values (around half). Remarkably, the operational durability of top-layer resonator devices is larger (in a factor of around 2), independently of the TPD concentration. This is a consequence of the protection offered by the resonator against dye photo-oxidation when the device is illuminated with pulsed UV light.


2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Keivan Mahmoud Aghdami ◽  
Abdullah Rahnama ◽  
Erden Ertorer ◽  
Peter R. Herman

AbstractEmbedding strong photonic stopbands into traditional optical fibre that can directly access and sense the outside environment is challenging, relying on tedious nano-processing steps that result in fragile thinned fibre. Ultrashort-pulsed laser filaments have recently provided a non-contact means of opening high-aspect ratio nano-holes inside of bulk transparent glasses. This method has been extended here to optical fibre, resulting in high density arrays of laser filamented holes penetrating transversely through the silica cladding and guiding core to provide high refractive index contrast Bragg gratings in the telecommunication band. The point‐by‐point fabrication was combined with post-chemical etching to engineer strong photonic stopbands directly inside of the compact and flexible fibre. Fibre Bragg gratings with sharply resolved π-shifts are presented for high resolution refractive index sensing from $${n}_{{{{{{\rm{H}}}}}}}$$ n H  = 1 to 1.67 as the nano-holes were readily wetted and filled with various solvents and oils through an intact fibre cladding.


Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2925
Author(s):  
Daniele Eugenio Lucchetta ◽  
Riccardo Castagna ◽  
Gautam Singh ◽  
Cristiano Riminesi ◽  
Andrea Di Donato

We report on the morphological, spectral and dynamical characterization of one-dimensional transmission holographic volume phase gratings, whose refractive index contrast and nanometric pitch are dynamically controlled by an incident laser light. The grating is obtained by the photo-polymerization of a recently developed photo-mobile holographic composite polymer material. The observed changes in the refractive index contrast and grating pitch strongly suggest that the reversible all-optical real-time modulation of the obtained diffraction efficiency is induced by nano-fluidics.


2021 ◽  
Vol 16 (4) ◽  
Author(s):  
Ashutosh Patri ◽  
Kévin G. Cognée ◽  
Louis Haeberlé ◽  
Vinod Menon ◽  
Christophe Caloz ◽  
...  

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