Low Optical Loss Research Articles

Giant Nonlinear Circular Dichroism from High Q‐Factor Asymmetric Lithium Niobate Metasurfaces

AbstractLithium niobate (LN) is a good nonlinear material with a large second‐order nonlinear polarization coefficient and low optical loss in the UV to mid‐infrared spectral regions. By combining bound states in the continuum (BICs) with chirality, a high conversion efficiency and strong second‐harmonic circular dichroism (SHG‐CD) can be achieved. The simulated results show that the SHG conversion efficiency can reach 1.35 × 10−2% for a peak‐pump intensity of ≈5.3 GW cm−2 in the near‐infrared, and the SHG‐CD can reach 0.98 by introducing a two‐layer structure. Quasi‐BICs are introduced to study nonlinear CD, which provide new insights for the further implementation of spin‐dependent nonlinear applications.

Mie-resonant mesoporous electron transport layer for highly efficient perovskite solar cells

All-dielectric nanophotonics is a powerful tool for improvement of thin-film optoelectronic devices because of low optical losses, strong light localization, and chemical robustness against such materials as halide perovskites. However, large-scale and low-cost approaches to create functional nanostructures are still not developed. In our work, we show a novel method to create mesoporous electron transport layer based on optically resonant silicon nanoparticles incorporated into TiO2 paste to be applied for perovskite (MAPbI3) solar cell. The inclusion of Mie-resonant silicon nanoparticles helps to improve light absorption by a perovskite layer without reduction of the active material. The management of Si nanoantennas concentration provides to reach a power conversion efficiency higher than 21% by increasing all main device parameters. Our multi-physical theoretical simulations of the solar cells with the resonant silicon nanoparticles provide physical understanding on the mechanisms of the device improvement as well as help to optimize the silicon nanoparticles concentration.

Continuous-wave Raman amplification in silicon core fibers pumped in the telecom band

Stimulated Raman amplification is observed for the first time in the silicon core fiber (SCF) platform. The SCFs were tapered to obtain sub-micrometer core dimensions and low optical transmission losses, facilitating efficient spontaneous scattering and stimulated Raman amplification using a continuous-wave pump source with milliwatt power levels. A maximum on–off gain of 1.1 dB was recorded at a pump power of only 48 mW with our numerical simulations, indicating that gains up to 6dB are achievable by increasing the fiber length. This work shows that the SCF platform could open a route to producing compact and robust all-fiber integrated Raman amplifiers and lasers across a broad wavelength region.

Световоды типа кварц-кварц с малыми потерями и тонкой полимерной оболочкой для ближнего ИК-спектрального диапазона.

The issues of obtaining silica optical fibers with SiO2/SiO2-F composition (where SiO2 is a core, and SiO2-F is a light-reflecting cladding) with low optical losses for the near-IR spectral range are considered. This fiber type is widely used in various fields of science and technology, including laser medicine. The study results of the dependence of the numerical aperture and fluorine concentration in silica glass of the formed fiber preforms on the Freon (C3F8) consumption in the gas phase when using a waveguide-type microwave plasmotron at the H10 wavelength, are presented. It is showed that to increase the fluorimeters sensitivity in the near-IR spectral range as probe fibers for detecting luminescence, it is promising to use quartz-quartz fibers with the “Heraeus” glass core and the reflective SiO2-F cladding with an increased fluorine content in the glass (up to 7 wt. %). In this case, the numerical aperture of such fibers will reach values up to 0.32. For laser procedures in ophthalmology, surgery, phlebology and etc., optical fibers with a standard numerical aperture 0.20-0.24 can be used (with a fluorine concentration in the glass up to 3 wt. %).

Near-IR reconfigurable 1D Ag grating Fabry-Perot absorber hybridized with phase-change material GSST.

Chalcogenide phase-change materials (PCMs) offer a unique feature that can be used to dynamically control the response of the photonic devices and achieve fast, nonvolatile, reversible, multilevel, and specific optical modulation. The phase-change material Ge2Sb2Se4Te1 (GSST) has recently received a lot of attention due to the large index contrast between its amorphous and crystalline states with significantly low optical loss in the optical to near-IR spectrum. In this paper, we propose a tunable and reconfigurable hybrid PCM plasmonic nanostructure composed of a spacer layer of GSST sandwiched between a Ag back reflector and a 1D Ag Fabry-Perot grating structure. We use the finite element method (FEM) to numerically calculate the light absorption, absorption contrast, and figure of merit of the plasmonic nanostructure for both the amorphous and crystalline state of the GSST. Our calculations show that with constant structural variation the observed multimode absorption is drastically modified when the GSST undergoes a phase change from the amorphous to the crystalline state. The absorption contrast spectrum, which is defined as the absorption difference between the amorphous and crystalline state of GSST, shows four extrema modes between 70% and 89%. The figure of merit spectrum shows two large values of 44.39 and 37.78 at the 1502 nm and 2063 nm wavelengths, respectively. We also address the observed modes in the absorption contrast spectrum through spatial representation of the enhanced electric field distribution at their corresponding wavelengths. We show how the phase change in the GSST spacer can control the coupling between the optical cavity modes and the Ag surface plasmon resonance modes in the cavities and GSST spacer strip boundaries. The findings in this paper may open new avenues toward the design of next-generation photonic systems such as thermal emission controllers, sensors, ranging holograms, modulators and optical detection devices.

FLCS-PON – A 100 Gbit/s Flexible Passive Optical Network: Concepts and Field Trial

We demonstrate concepts and results of a field trial for a flexible-rate passive optical network (FLCS-PON), which delivers bitrates up to 100 Gbit/s and allows for adaptations in the transmission method to match the users' channel conditions and optimize throughput. FLCS-PON builds on top of the hardware ecosystem that will be developed for ITU-T 50 Gbit/s PON and employs three new ingredients: optical network unit (ONU) grouping, flexible modulation format, and flexible forward error correction (FEC) code rate. Together, these techniques take advantage of the optical distribution network (ODN) statistics to realize a system capable of more than twofold throughput increase compared to the upcoming 50 Gbit/s PON, but still able to support a full array of deployed fiber edge cases, which are problematic for legacy PONs. In this paper we explain the concepts behind enabling techniques of FLCS-PON. We then report on a field trial over a deployed fiber infrastructure, using a system consisting of one FLCS-PON OLT and two ONUs. We report both pre- and post-forward-error-correction (post-FEC) performance of our system, demonstrating achievable net bitrate over an operator's fiber infrastructure. We realize a downlink transmission at double the speed of ITU-T 50 Gbit/s PON for ONUs exhibiting lower optical path loss (OPL), while simultaneously continue to support ONUs at high OPLs. We additionally realize a record-high 31.5 dB loss budget for 100 Gbit/s transmission using a direct-detection ONU with an optical preamplifier.

Ultralow-VπL Silicon Electro-Optic Directional Coupler Switch With a Liquid Crystal Cladding

An ultralow-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> L photonic switch device is demonstrated utilizing the high optical and electrical field confinement in silicon slot waveguides coupled with the strong electro-optic response of nematic liquid crystals. A silicon photonic directional coupler switch with a modulation efficiency of 0.0195 V·mm and a loss-efficiency product of 0.0624 V·dB is achieved. The 1.5 mm long device is based on two-mode interference within a single slot waveguide resulting in a V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">π</sub> of 0.013 V and an extinction ratio of ~ 9dB at 1550 nm wavelength. The power consumption of the photonic switch is estimated to be below 0.6 nW and it possesses a response time of <; 1.5 ms. A comparative performance study between the directional coupler switch and a Mach-Zehnder Interferometer (MZI) switch is performed. The directional coupler switch is projected to have a smaller footprint and lower optical loss compared to a similar design MZI switch making it a strong candidate for switch matrix designs and applications.

Integrated Si3N4 microresonator-based quantum light sources with high brightness using a subtractive wafer-scale platform.

The silicon nitride (Si3N4) platform, demonstrating a moderate third-order optical nonlinearity and a low optical loss compared with those of silicon, is suitable for integrated quantum photonic circuits. However, it is challenging to develop a crack-free, wafer-scale, thick Si3N4 platform in a single deposition run using a subtractive complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process suitable for dispersion-engineered quantum light sources. In this paper, we demonstrate our unique subtractive fabrication process by introducing a stress-release pattern prior to the single Si3N4 film deposition. Our Si3N4 platform enables 950 nm-thick and 8 μm-wide microring resonators supporting whispering-gallery modes for quantum light sources at 1550 nm wavelengths. We report a high photon-pair generation rate of ∼1.03 MHz/mW2, with a high spectral brightness of ∼5×106 pairs/s/mW2/GHz. We demonstrate the first heralded single-photon measurement on the Si3N4 platform, which exhibits a high quality of conditional self-correlation gH(2)(0) of 0.008 ± 0.003.

Electrically driven optical resonance of spherical ZnO whispering gallery mode microcavity

Spherical microcavities with low optical loss and high quality factor are attractive candidates for functional applications, including whispering gallery mode lasers, intracellular lasers, ultrasensitive biosensors, etc. In particular, electrically driven devices are beneficial for several applications such as optoelectronic integration. However, it is difficult to realize the electrically driven optoelectronic functions. In this study, the high-quality ZnO microspheres are fabricated by using a laser ablation method, and an excellent ultraviolet lasing system is achieved by optical pumping. Moreover, ultraviolet electroluminescence analysis demonstrates that ZnO microspheres are bonded to the p-GaN substrate. Furthermore, distinct resonant modes are obtained after inserting an appropriate AlN buffer layer at the n-ZnO/p-GaN interface. The optoelectronic behavior, charge carrier transportation, and recombination mechanism of the structure are systematically analyzed, and related interface modification, energy band alignment, and optical gain/loss contrast are also discussed. Overall, the results provide useful insights on further exploration of electrically pumped ZnO microsphere lasers.

Performance characteristics of low threshold current 1.25 μm type-II GaInAs/GaAsSb ‘W’-lasers for optical communications

Type-II ‘W’-lasers have made an important contribution to the development of mid-infrared laser diodes. In this paper, we show that a similar approach can yield high performance lasers in the optical communications wavelength range. (GaIn)As/Ga(AsSb) type-II ‘W’ structures emitting at 1255 nm have been realised on a GaAs substrate and exhibit low room temperature threshold current densities of 200–300 A cm−2, pulsed output powers exceeding 1 W for 100 µm wide stripes, and a characteristic temperature T 0 ≈ 90 K around room temperature. Optical gain studies indicate a high modal gain around 15–23 cm−1 at 200–300 A cm−2 and low optical losses of 8 ± 3 cm−1. Analysis of the spontaneous emission indicates that at room temperature, up to 24% of the threshold current is due to radiative recombination, with the remaining current due to other thermally activated non-radiative processes. The observed decrease in differential quantum efficiency with increasing temperature suggests that this is primarily due to a carrier leakage process. The impact of these processes is discussed in terms of the potential for further device optimisation. Our results present strong figures of merit for near-infrared type-II laser diodes and indicate significant potential for their applications in optical communications.

Titanium content influence on the optical response characteristics of TiO2/ormosils composite films doped with azobenzene.

TiO2-based organic-inorganic composite films doped with azobenzene and photosensitive groups were prepared by combining a low-temperature solgel technique and a spin-coating method. The influence of TiO2 content on the optical and structural properties of the composite films including the film thickness, the refractive index, the transmission loss, the thermal gravity analysis, and Fourier transform infrared spectroscopy spectra was studied. Photoisomerization and optical switching characteristics of the composite film were investigated under the irradiation of 365 nm ultraviolet light and 450 nm visible light. Results indicate that several micrometer thick films can be easily obtained at room temperature and there is a proportional relationship between the refractive index value and the TiO2 content. In addition, the composite films have a low optical propagation loss of about 0.1 dB/cm. The composite films with 0.2 M TiO2 content have an obvious photoisomerization and good optical switching properties. Finally, the hexagonal microlens array was fabricated in the composite films by using an ultraviolet nanoimprint technology. All these results above indicate that the as-prepared TiO2-based organic-inorganic composite film has potential applications in optical switching devices and photonic elements.

Micromechanical Fabrication of Resonator Waveguides Integrated Four‐Port Photonic Circuit from Flexible Organic Single Crystals

AbstractBy using a mechanophotonics approach, three flexible organic microcrystals of (E)‐1‐(4‐(dimethylamino)‐phenyl)iminomethyl‐2‐hydroxyl‐naphthalene (DPIN) are micromanipulated, and dual‐waveguides coupled ring resonator is fabricated. The flexibility of the DPIN crystal arises owing to its spring‐like expansion and contraction of π∙∙∙π stacked molecular chains along the (002) plane. The crystals also act as optical waveguides in straight and bent geometries with very low optical loss coefficients. The fluorescence (FL) spectra of the guided light also display Fabry‐Pérot modes. Precise mechanical manipulation of microcrystals with atomic force microscopy cantilever tip bent a straight crystal waveguide to 360° angle forming a ring‐shaped crystal resonator (diameter ≈58.6 µm). The positioning and integration of two straight parallelly oriented waveguiding crystals (bus and drop) along the opposite edge of the ring resonator forms the first of its kind all‐organic crystal‐based dual‐waveguides coupled ring resonator. The fabricated circuit with four ports selectively guides the produced input FL to through and drop ports via active, passive waveguiding and FL reabsorbance mechanisms.

Wide-range, ultra-compact, and high-sensitivity ring resonator biochemical sensor with CMOS-compatible hybrid plasmonic waveguide

A ring resonator-based biochemistry sensor with a wide range, ultra-compact footprint, and high sensitivity is proposed, which utilizes a suspended slot hybrid plasmonic (SSHP) waveguide. The waveguide consists of a suspended Si nanowire separated from a Cu metal surface by a nanoscale air gap. The hybridization of fundamental mode of a Si channel waveguide with the surface plasmon polariton (SPP) mode of Cu-Si interface achieves a strong light confinement, high waveguide sensitivity (Sw), and low optical loss, showing a great potential in integrated optical sensor. The sensitivity, the detection limit and the detection range of the SSHP waveguide-based biochemistry sensor with a miniaturized radius of 1 µm are numerically demonstrated as 458.1 nm/RIU, 3.7 × 10-5 RIU and 0.225 RIU, respectively. These superior performances as well as the fully CMOS compatibility enable the integrated optical sensing applications.

Low-loss silicon nitride strip-slot mode converter based on MMI.

Slot waveguide has attracted a lot of attention due to its ability to confine light in the low refractive index region, while strip waveguide acts as the basic component of guiding light due to its relatively low optical loss. In the multifunctional photonic integrated chips, it is critical to achieve the low loss transition between the strip waveguide and the slot waveguide. In this work, a silicon nitride strip-slot mode converter with high efficiency, large bandwidth, and large fabrication tolerance are proposed and demonstrated through the numerical investigation and experiments. The coupling efficiency of the mode converter is up to - 0.1 dB (97.7%), which enables the extremely low transition loss between the strip waveguide and the slot waveguide. Moreover, the fabrication process of silicon nitride photonic devices with high performance is introduced, which is fully compatible with the CMOS technology. Photonic devices based on silicon nitride with the characteristics of the low optical loss and the temperature insensitivity represent a new paradigm in realizing silicon-based photonic multifunctional chips.

Tantala Kerr nonlinear integrated photonics

Integrated photonics plays a central role in modern science and technology, enabling experiments from nonlinear science to quantum information, ultraprecise measurements and sensing, and advanced applications such as data communication and signal processing. Optical materials with favorable properties are essential for nanofabrication of integrated photonics devices. Here we describe a material for integrated nonlinear photonics, tantalum pentoxide ( T a 2 O 5 , hereafter tantala), which offers low intrinsic material stress, low optical loss, and efficient access to Kerr nonlinear processes. We utilize &gt; 800 n m thick tantala films deposited via ion beam sputtering on oxidized silicon wafers. The tantala films contain a low residual tensile stress of 38 MPa, and they offer a Kerr index of n 2 = 6.2 ± 2.3 × 10 − 19 m 2 / W , which is approximately a factor of 3 higher than silicon nitride. We fabricate integrated nonlinear resonators and waveguides without the cracking challenges that are prevalent in stoichiometric silicon nitride. The tantala resonators feature an optical quality factor up to 3.8 × 10 6 , which enables us to generate ultrabroad bandwidth Kerr soliton frequency combs with low threshold power. Moreover, we characterize tantala waveguides by supercontinuum generation from low-energy, ultrafast seed pulses. These demonstrations characterize future application directions with tantala integrated nonlinear photonics.

Mid-infrared single-Mode As-S-Se glass fiber and its supercontinuum generation

Two kinds of single-mode (SMF) step-index(SIF) chalcogenide fibers based on S-rich and S-poor As-S-Se glass have been fabricated successfully by an isolated extrusion method. We experimentally explored the effects of S and Se weights on the IR light transmission in the infrared area of the waveguide medium. By exploring the infrared transmission. It is found that the As-S-Se system has a transmission varied range between full S-based (As2S3) and full Se-based (As2Se3) glasses. The results show that with the addition of selenium, the red-shift is observed in both the short-wavelength absorption edge and long-wave cut-off wavelength. This phenomenon can be sourced from the varying of optical band gaps and phonon energies. Simultaneously, single-mode fibers was employed to evaluate the attenuation and supercontinuum(SC). We found that S-rich fiber shows a lower optical loss of 0.67–1.5 dB/m in 4.1–5.9 μm region, with a minimum value of 0.67 dB/m at 4.6 μm than that of S-poor fiber does. Yet, the SC results of S-poor fiber shows a flatter and broader spectrum region than that of S-rich fiber does.

Laser Thermal Processing of Group IV Semiconductors for Integrated Photonic Systems

In the quest to expand the functionality and capacity of group IV semiconductor photonic systems, new materials and production methods are constantly being explored. In particular, flexible fabrication and postprocessing approaches that are compatible with different materials and allow for tuning of the components and systems are of great interest. Within this research area, laser thermal processing has emerged as an indispensable tool that can be applied to enhance and/or modify the material, structural, electrical and optical properties of group IV elemental and compound semiconductors at various stages of the production process. Herein, the recent progress made in the application of laser processing techniques to develop integrated semiconductor systems in both fiber‐ and planar‐based platforms is evaluated. Laser processing has allowed for the production of semiconductor waveguides with high crystallinity in the core and low optical losses, as well as postfabrication trimming of device characteristics and direct writing of tunable strain and composition profiles for bandgap engineering and optical waveguiding. For each platform, the current challenges and opportunities for the future development of laser‐processed integrated semiconductor photonic systems are presented.

Geometric optimization and performance enhancement of PEDOT: PSS/GaAs NP array based heterojunction solar cells

Polymer/semiconductor nanostructure array based solar cells (SCs) exhibit extremely low optical losses, excellent light-harvesting, improved carrier lifetime, increased defect tolerance etc. and can be a new pathway for low-cost high efficiency SCs. In order to fabricate efficient heterojunction SCs, it is extremely necessary to evaluate their optimal geometric configuration theoretically. In this article, using 3D-finite difference time domain (FDTD) method, we have optimized the geometric configuration of poly (3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS) coated vertically aligned GaAs Nano pyramid (NP) array heterojunction SCs to obtain high average optical absorption and J sc of 92.2% and 41.1 mA/cm 2 , respectively. The optimized structure simulated in Lumerical Charge Solver DEVICE module, exhibit power conversion efficiency (PCE) of 15.9% despite low carrier mobility and lifetime of 1000 cm 2 v −1 s −1 and 2ns respectively. • Role of GaAs nanopyramids (NPs) in efficient light harvesting is studied. • Optimization of geometrical dimensions of the NPs is performed in terms of optical J sc . • Conformal coating of PEDOT:PSS results in absorption enhancement. • GaAs NPs/PEDOT PSS based solar cells exhibits PCE of ~13%.

Hf1-xSixO2 Nanocomposite Coatings Prepared by Ion-Assisted Co-Evaporation Process for Low-Loss and High-LIDT Optics.

Hf1−xSixO2 nanocomposites with different SiO2 doping ratios were synthesized using an ion-assisted co-evaporation process to achieve dense amorphous Hf1−xSixO2 coatings with low loss and a high laser-induced damage threshold (LIDT). The results showed that the Hf1−xSixO2 nanocomposites (x ≥ 0.20) exhibited excellent comprehensive performance with a wide band gap and a dense amorphous microstructure. High-temperature annealing was carried out to ensure better stoichiometry and lower absorption. Precipitation and regrowth of HfO2 grains were observed from 400 °C to 600 °C during annealing of the Hf0.80Si0.20O2 nanocomposites, resulting in excessive surface roughness. A phenomenological model was proposed to explain the phenomenon. The Hf1−xSixO2 nanocomposites (x = 0.3 and 0.4) maintained a dense amorphous structure with low absorption after annealing. Finally, a 1064-nm Hf0.70Si0.30O2/SiO2 high-performance reflector was prepared and achieved low optical loss (15.1 ppm) and a high LIDT (67 J/cm2).

Tuning Organic Microcrystal Morphologies through Crystal Engineering Strategies toward Anisotropic Optical Waveguide.

The construction of organic optoelectronic materials with desirable size and morphology remains a challenge now. Crystal engineering strategies (polymorphs and cocrystals) provide convenience for tailoring molecular packing and further controlling the growth morphology and photofunctionality of materials. Herein, we prepare polymorphic 2D plate crystals and 3D microhelixes by assembly of a cyanostilbene derivative (2-(3',5'-bis(trifluoromethyl)-biphenyl-4-yl)-3-(4-(pyridin-4-yl)phenyl)acrylonitrile, CF3-CN-Py). The former emits blue emission, while the latter emits green emission. Different crystallization environments contribute to the adjustable morphologies. Then, novel cocrystals are fabricated with the introduction of 1,4-diiodotetrafluorobenzene (FDIB) to CF3-CN-Py. Both molecular conformation and packing are totally changed in the cocrystal system. Such cocrystal displays a 1D sky-blue emissive rod shape on account of a long-range ordered π-stacking of molecules. In addition, the 2D plate crystal and 1D rod cocrystal are further applied to optical waveguides. In the plate crystal, a packing of transition dipole moment (μ) inclined to the upper surface leads to an anisotropic optical waveguide. In the cocrystal, owing to the nearly horizontal μ orientation, the cocrystal exhibits light propagation along the primary growth direction and a low optical loss coefficient. The present study supplies an effective way to construct materials with controlled morphology and optical waveguide.