Ultra-low Loss Research Articles

Rutile (In0.5Ta0.5)0.1Ti0.87O1.88F0.12 ceramics with excellent dielectric performance and thermal stability sintered at 1220 °C

TiO2-based colossal dielectric ceramics have emerged as a prominent research focus in recent years. However, their further applications have been constrained by several key limitations, including the requirement of high sintering temperature (>1400 °C), relatively high dielectric loss (>0.05, 1 kHz), and temperature stability (<200 °C). This study reports rutile (In0.5Ta0.5)0.1Ti0.87O1.88F0.12 ceramics at 1220 °C sintering using 12 % InF3 as the acceptor In3+ source, which exhibits a colossal dielectric constant (1.1 × 105) and an ultra-low dielectric loss (0.0071) at 1 kHz and room temperature, even loss values below 0.04 (20 Hz - 100 kHz). Notably, the thermal stabilities (10 kHz, 100 kHz) simultaneously satisfy X9E (Δεr/ε25 °C ≤ ±4.7 %) above 300 °C. F− not only supplies electrons to enhance the semiconductivity of grains, but also decreases the oxygen vacancy and average grain size (270 ± 12.53 nm) to improve grain boundaries resistances, which reduces dielectric loss and enhances frequency and temperature stabilities. As a result, the dielectric mechanism is mainly related to internal barrier layer capacitor (IBLC) and high grain boundary resistance. Therefore, this strategy provides a creative design for developing TiO2-based ceramics.

Switching in microseconds: design of a 5 × 5 non-blocking free space optical switch at 1550nm with a piezo-actuator and beam-steering lens system

Modern data center networks (DCNs) require optical switches with ultra-low loss, ultra-fast reconfiguration speed, high throughput, and high extinction ratio performances. In this work, we propose the design of a 5 × 5 optical switch at 1550 nm based on a piezo-actuator serving as a translating input optical source, and a beam-steering system built of spherical lenses to complete the switching behaviour. An ultra-fast actuator switching speed is estimated as 1.55 μs latency for a single connection with a demo circuit. We further simulate the beam-steering system end-to-end in a commercial optical design software CODE V and demonstrate a theoretical 2.16 dB insertion loss for a single connection in the switch at optimum alignment.

Broadband terahertz modulation in symmetric gate-controlled graphene photonic crystals

Innovative research in terahertz (THz) communications is urgently needed to meet the evolving demands of the industry. In the past, the absence of optoelectronic devices made it difficult to control THz waves effectively. In this study, a symmetric gate-controlled graphene photonic crystal (PC) is proposed, which achieves a modulation depth (MD) of more than 99 %, an ultralow insertion loss (IL) of 0.08, and a wide operation bandwidth (BW) simultaneously. Additionally, even in graphene samples with low carrier mobilities, the high-performance MD can be achieved with acceptable IL in the broadband THz range. Furthermore, our proposed one-dimensional graphene PC system enhances manufacturing convenience. Through the adoption of the proposed symmetric structure, highly efficient THz communications can be achieved through photonic systems that utilize graphene.

Ultra-low loss Rayleigh scattering enhancement via light recycling in fiber cladding

Rayleigh backscattering enhancement (RSE) of optical fibers is an effective means to improve the performance of distributed optical fiber sensing. Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE. However, in-core modulation loses more transmission light, thus limiting the sensing distance. In this work, a cladding-type RSE (cl-RSE) structure is proposed, where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core. The refractive-index modulation structure redistributes the light in the cladding, and the backward scattered light is recovered, which enhances the Rayleigh backscattered signal with almost no effect on the core light. Experimentally, it was demonstrated that in an effectual cl-RSE structure, the insertion loss was reduced to 0.00001 dB per scatterer, corresponding to the lowest value for a point scatterer to date. The cl-RSE structure accomplished measurements up to 800°C. In particular, the temperature measurement fluctuation of the cl-RSE fiber portion is only 0.00273°C after annealing. These results show that the cl-RSE structure has effective scattering enhancement, ultra-low loss, and excellent high-temperature characteristics, and has great potential for application in Rayleigh scattering-enhanced distributed fiber sensing.

Ultra-low core loss and high permeability Fe-based amorphous soft magnetic composites with ultra-fine FeNi additives

Ultra-low core loss and high permeability Fe-based amorphous soft magnetic composites with ultra-fine FeNi additives

Near-infrared Sb2S3 metasurface with giant and tunable circular dichroism

Tunable circular dichroism (CD) is crucial for the development of chiral imaging, biosensing, and optical communication etc Herein, by employing the ultralow loss reversible phase-change materials Sb2S3, we achieved the giant and tunable CD signal in a chiral double-L array. Numerical results show that CD strength of the Sb2S3 metasurface can be over 0.9 in both amorphous and crystalline states. Strikingly, the resonant wavelength shift induced by the phase change of Sb2S3 reaches 93 nm, proving that the proposed metasurface possesses excellent tunability. In addition, the physical mechanism of the giant CD response is explained via multipole analysis. The proposed Sb2S3 metasurface capable of giant and tunable CD effect will facilitate the design of tunable dichroic devices.

Design of hollow-core anti-resonant optical fiber based on bragg elements with low-loss and wide bandwidth

A type of anti-resonant hollow-core optical fiber consisting of Bragg elements is proposed. The confinement and bending losses are numerically simulated using the finite element method. It is found that the introduction of concentric rings to form anti-resonant structure can reduce the mode transmission loss by 2 ∼ 4 orders of magnitude compared with the anti-resonant element composed of only one dielectric layer, therefore it can achieve ultra-low loss optical transmission. The influence of the structural parameters on the confinement loss was investigated. Furthermore, it is demonstrated that each dielectric layer independently contributes to the confinement of the core modes. It is also found that the Bragg reflection structure can effectively suppress the coupling between core and cladding modes, and achieve broadband low-loss optical transmission under small bending radius. In particular, it can achieve a low transmission loss of less than 0.1 dB km−1 over a wide wavelength range of 600 nm at the bending radius of 3 cm.

Highly efficient hybrid-structured photonic crystal fiber with ultra-low loss and near-zero flat dispersion for terahertz waveguiding

Highly efficient hybrid-structured photonic crystal fiber with ultra-low loss and near-zero flat dispersion for terahertz waveguiding

Preparation of polyimide films with ultralow dielectric loss at high frequency by reducing intermolecular friction

Due to the rapid development of high frequency and high rate communication technology, polyimide (PI) films with ultra-low dielectric loss (Df) at high frequency, excellent thermal and mechanical properties are urgently needed. A series of PI films with ultra-low Df were prepared by introducing different mesogen units. Among them, one novel PI film with biphenyl liquid-crystal-like units (BAHQ-TFMB) achieve a recorded low Df of 0.00169 (10 GHz) which surpasses previous studies on pure PI bulk films. Importantly, the high degree of collinearity of the friction work (Wf) and Df of PI films (Pearson's r = 0.992) was confirmed, which indicate that Wf among PI macromolecules plays an important role in determining Df of PI films. To reveal underlying reason for reducing the Wf and Df of PI films, the contribution of the degree of orientation and crystallinity of PI films with or without liquid-crystal-like structures were comparative studied. Through a two-dimensional orientation determinant, it is found that increasing the crystallinity of liquid-crystal-like PI films is the main contribution to reducing Wf and corresponding Df of PI films while the orientation of PI films seems to have weak effect. Moreover, BAHQ-TFMB PI film exhibits excellent mechanical properties. The tensile strengths is 145.5 ± 12.0 MPa and Young's moduli is 4.76 ± 0.28 GPa.

Twenty-nine million intrinsic Q-factor monolithic microresonators on thin-film lithium niobate

The recent emergence of thin-film lithium niobate (TFLN) has extended the landscape of integrated photonics. This has been enabled by the commercialization of TFLN wafers and advanced nanofabrication of TFLN such as high-quality dry etching. However, fabrication imperfections still limit the propagation loss to a few dB/m, restricting the impact of this platform. Here, we demonstrate TFLN microresonators with a record-high intrinsic quality (Q) factor of twenty-nine million, corresponding to an ultra-low propagation loss of 1.3 dB/m. We present spectral analysis and the statistical distribution of Q factors across different resonator geometries. Our work pushes the fabrication limits of TFLN photonics to achieve a Q factor within 1 order of magnitude of the material limit.

Heterogeneous quantum dot lasers on low-confinement silicon nitride with reduced-bending architecture.

Low-confinement silicon nitride (SiN) waveguides offer ultra-low losses but require wide bend radii to avoid radiative losses. To realize the benefits of silicon nitride in a heterogeneous laser while maintaining a small footprint, we employ metal-coated etched facets and transversely coupled Fabry-Perot resonators as mirrors. Heterogeneous quantum dot lasers are fabricated using an on-chip facet plus adiabatic taper coupler, and Fabry-Perot cavities are defined by metal mirrors and post-grating-distributed Bragg reflectors (DBRs). Threshold current densities below 250 A/cm2 are observed, and a power >15 mW is measured in an integrating sphere. A laser linewidth of <5 MHz is measured by tuning two lasers to about 50 MHz apart and measuring their beatnote on a photodiode. The total device footprint is <1 mm2.

Wafer-scale fabrication of single-crystalline calcium fluoride thin-film on insulator by ion-cutting

Developing bulk materials into thin-films not only enables multiple physical fields to interact strongly within a smaller volume but also enhances the stability, scalability, and integrability of the system. This transformation has been witnessed to lead to significant improvements in the performance of devices utilizing diverse materials across various fields. Calcium Fluoride (CaF2), with remarkable optical properties such as ultralow optical loss and strong nonlinear features, is a preferable material for building ultra-high-Q resonators and stimulating light-matter interaction with low threshold. However, the integration of CaF2 material has remained elusive due to its low hardness and high thermal expansion, which plagues the large-scale fabrication of CaF2 thin film. Here, an optimized ion-cutting technique is proposed for engineering CaF2 thin films theoretically and experimentally. Taking the thermal expansion into consideration, we employ the Lithium niobate (LN) as substrate, and utilize accessible ion implantation, wafer bonding and precisely designed annealing process to attain the CaF2-LN and the CaF2-on-insulator (CaFOI) with high film thickness uniformity and maintained crystalline quality. The perspectives of our work are also illustrated by numerical simulation for further verifying the potential of integrated photonic applications, which could be extended to monolithic optical network by means of large-scale manufacturing method.

Anneal-free ultra-low loss silicon nitride integrated photonics

Heterogeneous and monolithic integration of the versatile low-loss silicon nitride platform with low-temperature materials such as silicon electronics and photonics, III–V compound semiconductors, lithium niobate, organics, and glasses has been inhibited by the need for high-temperature annealing as well as the need for different process flows for thin and thick waveguides. New techniques are needed to maintain the state-of-the-art losses, nonlinear properties, and CMOS-compatible processes while enabling this next generation of 3D silicon nitride integration. We report a significant advance in silicon nitride integrated photonics, demonstrating the lowest losses to date for an anneal-free process at a maximum temperature 250 °C, with the same deuterated silane based fabrication flow, for nitride and oxide, for an order of magnitude range in nitride thickness without requiring stress mitigation or polishing. We report record low anneal-free losses for both nitride core and oxide cladding, enabling 1.77 dB m-1 loss and 14.9 million Q for 80 nm nitride core waveguides, more than half an order magnitude lower loss than previously reported sub 300 °C process. For 800 nm-thick nitride, we achieve as good as 8.66 dB m−1 loss and 4.03 million Q, the highest reported Q for a low temperature processed resonator with equivalent device area, with a median of loss and Q of 13.9 dB m−1 and 2.59 million each respectively. We demonstrate laser stabilization with over 4 orders of magnitude frequency noise reduction using a thin nitride reference cavity, and using a thick nitride micro-resonator we demonstrate OPO, over two octave supercontinuum generation, and four-wave mixing and parametric gain with the lowest reported optical parametric oscillation threshold per unit resonator length. These results represent a significant step towards a uniform ultra-low loss silicon nitride homogeneous and heterogeneous platform for both thin and thick waveguides capable of linear and nonlinear photonic circuits and integration with low-temperature materials and processes.

Interdiffusion mechanism of hybrid interfacial layers for enhanced electrical resistivity and ultralow loss in Fe-based nanocrystalline soft magnetic composites

Soft magnetic composites (SMCs) composed of ferromagnetic particles and insulating binder are highly desired in energy-saving and high-efficiency devices for their high electrical resistivity and softer saturation characteristics. However, traditional insulation coatings are facing thermal instability, inhomogeneous distribution, and magnetic dilution, presenting a major challenge for the trade-off relationship between power loss and permeability. Here, the phosphate-coated FeSiBCuNb/SiO2 SMC is successfully fabricated by a unique interdiffusion effect in hybrid interfacial layers, which shows a combination of ultralow power loss of 135.8 kW/m3 (50 kHz/100 mT), high effective permeability of 80.6, and good temperature stability. The interdiffusion behavior between Si/O and Fe/P/O elements promotes the formation of ultrathin, uniform, and multilayer interface structure, which alleviates the magnetic dilution. Penetrating oxidation at the edge interface and elements interdiffusion effect contribute to a higher electrical resistivity induced by hot isostatic pressing with rapid quenching, leading to a low eddy current loss. Synergistic effect of isostatic pressures and rapid quenching facilitates the formation of high-density Cu clusters corresponding to ultrafine microstructure, which is beneficial for low coercivity and low hysteresis loss. This study involves the interdiffusion mechanism of hybrid interfacial layers and nanocrystalline behavior, providing a new strategy for the next-generation of high-performance SMCs.

Application of Multi-Vinyl Silicon-Containing Cross-Linkers in Free-Radical Cross-Linked Thermosets with Ultra-Low Dielectric Loss

Application of Multi-Vinyl Silicon-Containing Cross-Linkers in Free-Radical Cross-Linked Thermosets with Ultra-Low Dielectric Loss

Ultra-low dielectric loss and high thermal conductivity of PTFE composites improved by schistose and globular alumina

Polytetrafluoroethylene (PTFE) based microwave dielectric composite has been widely used because of its adjustable dielectric constant and low dielectric loss, but its low thermal conductivity can not meet the heat dissipation requirements of high-power microwave devices. Therefore, it is of great significance to develop microwave dielectric composites with high thermal conductivity and low loss. In order to obtain microwave composite materials with high thermal conductivity and low losses, schistose Al2O3/PTFE (S-A/PTFE) composites and globular Al2O3/PTFE (G-A/PTFE) composites were successfully prepared. It is compared whether S-A can combine with PTFE more fully than G-A, which can promote the dielectric properties and thermal conductivity of Al2O3/PTFE composites. Surprisingly, the S-A/PTFE composites demonstrate higher thermal conductivity, lower thermal expansion and hygroscopic properties. The S-A/PTFE composites can deliver a high thermal conductivity of 0.986 W/m K. Composite substrates with 53 wt% S-A filler exhibits excellent performance, which specifically show credible dielectric constant (εr = 4.01) and admissible dielectric loss (tanδ = 0.0014 at 10 GHz). Furthermore, the composite substrate shows a similar thermal expansion coefficient to copper, and lower water absorption rate (0.05 %). The relationship between dielectric constant of composite and filler was predicted by different theoretical modeling methods.

Improving performances of PZT-PMS-PMT ceramics through rational tuning of Al3+-ion doping

Heat dissipation and ultra-low mechanical loss are important characteristics of advanced miniaturized and intelligent electronic devices. Herein, novel 0.86PZT-0.05PMS-0.09PMT + x mol%Al2O3 piezoelectric ceramics were prepared by solid-phase sintering method. The properties and structural variations of the resulting ceramics were systematically investigated by various analytical techniques. The results suggested excellent comprehensive performances of ceramics obtained at x = 0.6 mol%, with d33 = 340 pC/N, kp = 0.507, Qm = 2117, TC = 249.8 °C, and εr = 1473. The properties of the ceramics can be optimized by different defect dipoles induced by different Al3+ ion contents occupying the A-site and B-site. In addition, the promotion of domain changes within the lattice and the introduction of polar nano-regions by doping ions, decreased the lowering and redistribution of energy barriers. Overall, the excellent performance and ultra-high Qm of the proposed ceramics look promising for future construction of miniaturized devices.

Production of dense forsterite with ultra low dielectric loss using ZrO2 additive

Forsterite was synthesized with MgCO3 and SiO2 powders using a solid-state method at 1200–1300°C. The ceramic specimen with the highest forsterite phase content was sintered with the ZrO2 sintering aid at mass fractions of 0.5, 1.0, and 1.5 wt% at 1400°C for 4 h. The dielectric constant and loss tangent were also measured via the waveguide method at 8–12 GHz. The formation of enstatite and cristobalite was minimized through precise synthesis temperature control. Phase measurement by the Rietveld method showed that specimen F28 contained more than 99.8% forsterite. It was found that ZrO2 reduced the pore volume percent and increased the density even at low mass fractions. A liquid phase on the grain boundaries was demonstrated. The solid ceramic specimen F28-15Z showed a dielectric constant of 6.5 and high quality factor of 189000.

Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method

In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.

Microstructure and magnetic properties of the FeSiBCuNb nanocrystalline soft magnetic composites coated with oil-phase single Fe3O4 nanoparticles by thermal decomposition method

Here, the core-shell structured FeSiBCuNb/Fe3O4 soft magnetic composites (SMCs) were successfully designed and fabricated by coating Fe3O4 magnetic nanoparticles on the surface of phosphorylated FeSiBCuNb powder. The effects of Fe3O4 and Polyvinylpyrrolidone (PVP) contents on the micromorphology, interface structure, and soft magnetic properties of SMCs were systematically investigated. The results demonstrate that the Fe3O4 magnetic nanoparticles are uniformly distributed on the surface of magnetic powders, which fill up the air gap in-between the magnetic powder and increase the resistivity. It shows that the permeability gradually decreases with the increase of Fe3O4 from 0 wt% to 1 wt%, while the loss decreases first and then increases. The loss separation of SMCs indicates that the Fe3O4 nanoparticles effectively reduce the hysteresis loss and eddy current loss. Furthermore, the FeSiBCuNb/Fe3O4 SMCs with the addition of PVP as a binder enhance the binding force between Fe3O4 nanoparticles and the powder matrix, which facilitates the formation of a uniform and dense interface structure. When adding 0.3 wt% PVP + Fe3O4 nanoparticles, the FeSiBCuNb/Fe3O4 SMCs exhibit excellent soft magnetic properties with ultra-low loss of 138.5 kW/m3 (100 mT/50 kHz), high permeability of 54, and good frequency stability. The presented results provide a new strategy for synthesizing ultra-low core loss and frequency stability of core-shell structured SMCs, which has great potential for applications at high frequencies.