Low Propagation Loss Research Articles

Optical integrated reconfigurable mode generator-multiplexer for radio-frequency orbital angular momentum.

Radio-frequency orbital angular momentum (RF-OAM) mode multiplexing has received increasing attention in next-generation (6G) wireless communication as a new spatial multiplexing dimension to further extend data capacity. In particular, the circular antenna array (CAA) based RF-OAM generation using photonic methods is a promising approach due to its flexible reconfigurability, low propagation loss, high operating bandwidth, and high pattern quality. However, most current reports focus either on the bulk optics-based implementations or on band-limited delay line-based approaches. In this paper, we present a novel phased array-based integrated photonic RF-OAM generator-multiplexer for a four-antenna CAA system supporting three RF-OAM modes at 16 GHz for both fast mode switching and mode multiplexing. It consists of a specially designed interleaved optical filter and a four-element phased array based on cascaded phase shifters. By changing the pair of wavelengths used, the output RF-OAM modes can be quickly switched between fundamental mode and ±1 modes. A bandwidth of 1 GHz was experimentally demonstrated. Mode multiplexing can be achieved when all three wavelength pairs are loaded.

Topological Edge State Ring Resonator for Mid-Infrared(MI) Refractive Indices Biosensor for detection of Brain Tumors

The unique properties of light underlie the perspectives of quantum photonic technologies, optical interconnects, and a wide range of new sensors.Some of the most dangerous and deadly diseases are tumors, cancers, and brain lesions, which are expensive to detect and treat. Therefore, a low-cost and accurate method to diagnose them can prevent and treat the progress of this disease. In this work, we used the precise topological valley photonic crystal (TVPC) method for detection. TVPC is an important method for transmitting and controlling light in the optical device. The valley-spin locking in the topology state provides robust transfer and low propagation loss at the desired path.In order to design, by finding the edge band within the first bulk band gap of 146.4 THz–155.9 THz, the model and design of the topological ring resonator (TRS)were realized. We proposed a topological biosensorbyusing the hexagonal lattice air holes in the silicon slab with a compact size of 22.95 μm × 10 μm. the quality factor and sensitivity at best value are 2.905 × 104 and 9021 nm RIU−1 respectively. This design can be implemented on the Complementary Metal-Oxide-Semiconductor (CMOS) technology as a high-sensitivity optical device.

Low-Loss Buried InGaAs/InP Integrated Waveguides in the Long-Wave Infrared.

In this work, we present a photonic integrated platform based on buried InGaAs waveguides with InP cladding that operates over a large mid-infrared (mid-IR) spectral range. Thanks to wet-etch fabrication patterning and Fe doping, low propagation losses below 1.2 dB/cm (0.3 cm-1 loss coefficient) have been obtained between 4.6 and 11.2 μm wavelengths (890-1960 cm-1 wavenumber), in both transverse electric (TE) and transverse magnetic (TM) polarization modes. The possibility of monolithically integrating such waveguides with mid-IR sources offers promising perspectives for developing broadband, homogeneously integrated systems.

Silicon nanocrystal slab optical waveguide by multi-energy ion implantation: Linear and nonlinear optical properties

Silicon nanocrystals (Si-nc) have gained attention in optics and photonics research areas in recent years due to their advanced optical nonlinear properties. However, a nonlinear integrated optical platform that allows the fabrication of photonic devices with different Si-nc composition is yet under investigation. In this work, we experimentally demonstrated a nonlinear optical waveguide based on ion implantation that offers advantages in terms of material composition, low propagation losses, and enhanced nonlinear optical properties, such as a high nonlinear refractive index. In this work we present the fabrication of Si-nc containing waveguiding structures, and a study of their linear and nonlinear optical properties. Our nonlinear integrated optical platform presents a two-photon absorption coefficient β = 3.17 × 10−6 cm W−1 and a nonlinear refractive index n2 = 1.19 × 10−10 cm2 W−1, which shows potential applications in all-optical signal processing devices, such as single-photon sources.

Engineering topological interface states in metal-wire waveguides for broadband terahertz signal processing.

Innovative terahertz waveguides are in high demand to serve as a versatile platform for transporting and manipulating terahertz signals for the full deployment of future six-generation (6G) communication systems. Metal-wire waveguides have emerged as promising candidates, offering the crucial advantage of sustaining low-loss and low-dispersion propagation of broadband terahertz pulses. Recent advances have opened up new avenues for implementing signal-processing functionalities within metal-wire waveguides by directly engraving grooves along the wire surfaces. However, the challenge remains to design novel groove structures to unlock unprecedented signal-processing functionalities. In this study, we report a plasmonic signal processor by engineering topological interface states within a terahertz two-wire waveguide. We construct the interface by connecting two multiscale groove structures with distinct topological invariants, i.e., featuring a π-shift difference in the Zak phases. The existence of this topological interface within the waveguide is experimentally validated by investigating the transmission spectrum, revealing a prominent transmission peak in the center of the topological bandgap. Remarkably, we show that this resonance is highly robust against structural disorders, and its quality factor can be flexibly controlled. This unique feature not only facilitates essential functions such as band filtering and isolating but also promises to serve as a linear differential equation solver. Our approach paves the way for the development of new-generation all-optical analog signal processors tailored for future terahertz networks, featuring remarkable structural simplicity, ultrafast processing speeds, as well as highly reliable performance.

Hybrid plasmonic valley-Hall topological insulators

Abstract The emerging field of photonic topological insulators offers promising platforms for high-performance optical communication, computing, and sensing. However, conventional photonic topological insulator designs typically operate within the diffraction limit due to their dielectric nature. This limitation imposes constraints on device miniaturization, reduces light–matter interaction, and decreases overall device sensitivity. Introducing a new valley-Hall hybrid plasmonic topological insulator, we overcome this limitation by exploiting the coupling of surface plasmon oscillations with the optical modes of a dielectric photonic crystal, allowing for sub-diffraction vertical confinement of light. Deep-subwavelength chiral edge states can, therefore, be generated and robustly guided along disordered Z-shaped topological boundaries with much lower propagation loss compared to purely plasmonic platforms. Such extreme manipulation of light on an integrated chip platform maximizes light–matter interaction and opens the door for truly compact and efficient optical modulators, molecular sensors, and next-generation nanophotonic and quantum devices.

Low-kappa DBR grating filters on an InP generic photonic integration foundry platform

We demonstrate narrow-bandwidth, low-kappa, distributed Bragg reflector (DBR) grating filters on an indium phosphide (InP) generic foundry platform. With the varying corrugation widths of the DBR grating, we achieve flexibility in the design of the coupling coefficients from 10 to 50cm−1, which correspond to grating bandwidths of 0.68 nm to 1.28 nm, respectively. These values are experimentally observed and agree well with the theoretical analysis. The DBR grating is based on periodic rectangular grooves in quaternary material that is placed between the waveguide core and cladding region. Such configurations of the DBR grating provide a low propagation loss of ∼2dB/cm near the telecom band around 1550 nm.

Ultra-broadband MMI power splitter from 1.26 to 1.67 μm with photonic bound states in the continuum

Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO3) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO3), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO3 film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM0 mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.

GeAsSeTe/GeAsSe Pedestal Waveguides for Long-Wave Infrared Tunable on-Chip Spectroscopy

A dry-etched pedestal chalcogenide waveguide platform, designed for use in long-wave IR spectrometer applications, is demonstrated, fabricated and optically characterized. The optical layers were deposited on pre-patterned dry-etched silicon pedestals. An exceptionally low waveguide propagation loss was measured, at around 0.1 dB/cm at λ = 10 μm. The modal thermo-optic coefficient of the waveguide was experimentally estimated to be approximately 1.1 × 10−4 C−1 at λ = 1.63 μm, which is comparable to that of Si and GaAs. Waveguide spiral interferometers were fabricated, proving the potential for realization of more complex, chalcogenide-based, integrated photonic circuits. The combination of low propagation losses and a strong thermo-optic coefficient makes this platform an ideal candidate for utilization in on-chip tunable spectrometers in the long-wave IR wavelength band.

Porous core fiber with hybrid cladding for ultra-flattened dispersion and low loss propagation of terahertz waves

This work proposes a design of a porous-core photonic crystal fiber (PC-PCF) made of a cyclic olefin copolymer, Zeonex, with a hybrid cladding for low-loss terahertz (THz) wave transmission. A combination of circular and elliptical air holes is employed, resulting in a very low material absorption loss of 0.045 cm-1 at Dcore = 450 µm and f = 1 THz. A flat dispersion of 0.73 ± 0.13 ps/THz/cm is obtained for a broad frequency range of 0.5–1.4 THz. Core diameter and frequency response of other key features such as normalized frequency (V-parameter), confinement loss, effective area, nonlinearity and the percentage of the power flow through different sections of the proposed PC-PCF are also analyzed. Comparing to state-of-the-art, our design is superior in terms of loss, dispersion and power fraction. Our proposed design can be manufactured using the established extrusion process and be used for long distance low-loss Terahertz (THz) communication.

Waveguide Eavesdropping Threat for Terahertz Wireless Communications

As wireless communications move to higher frequency band for 5G networks and beyond, resiliency against eavesdropping and other security threats is still one of the key system-design considerations. Compared to data transmissions by lower frequencies, terahertz links are inherently more robust against eavesdropping attacks due to their propagation characteristics (such as high free-space path loss) and aligned link path by high-gain antennas. However, it does not indicate that eavesdropping is always impossible. Line-of-sight terahertz links have proven to be vulnerable to active/passive eavesdroppers by placing scatters in the path of data transmission, or by collecting side-lobe leakages. Here, we demonstrate a waveguide-based approach for signal eavesdropping which can be operated much more feasibly with several advantages, such as lower propagation loss and reliable data interception. Our method relies on a 3D printed rectangular dielectric waveguide and can overcome spatial limitations caused by directional modulation or near-field modulation. We demonstrate successful eavesdropping attacks for a 16 quadrature amplitude modulated (16-QAM) data link at rates up to 5 gigabits per second. Our work highlights the importance of system designs in resisting waveguide-based eavesdropping strategies and identifies aspects where

Manipulating hyperbolic transient plasmons in a layered semiconductor

Anisotropic materials with oppositely signed dielectric tensors support hyperbolic polaritons, displaying enhanced electromagnetic localization and directional energy flow. However, the most reported hyperbolic phonon polaritons are difficult to apply for active electro-optical modulations and optoelectronic devices. Here, we report a dynamic topological plasmonic dispersion transition in black phosphorus via photo-induced carrier injection, i.e., transforming the iso-frequency contour from a pristine ellipsoid to a non-equilibrium hyperboloid. Our work also demonstrates the peculiar transient plasmonic properties of the studied layered semiconductor, such as the ultrafast transition, low propagation losses, efficient optical emission from the black phosphorus’s edges, and the characterization of different transient plasmon modes. Our results may be relevant for the development of future optoelectronic applications.

Boosting the Downconversion Luminescence of Tm3+-Doped Nanoparticles for S-Band Polymer Waveguide Amplifier.

Polymer waveguide devices have attracted increasing interest in several rapidly developing areas of broadband communications since they are easily adaptable to on-chip integration and promise low propagation losses. As a key member of the waveguide gain medium, lanthanide doped nanoparticles have been intensively studied to improve the downconversion luminescence. However, current research efforts are almost confined to erbium-doped nanoparticles and amplifiers operating at the C-band; boosting the downconversion luminescence of Tm3+ for S-band optical amplification still remains a challenge. Here we report a Tb3+-induced deactivation control to enhance Tm3+ downconversion luminescence in a stoichiometric Yb lattice without suffering from concentration quenching. We also demonstrate their potential application in an S-band waveguide amplifier and record a maximum optical gain of 18 dB at 1464 nm. Our findings provide valuable insights into the fundamental understanding of deactivation-controlled luminescence enhancement and open up a new avenue toward the development of an S-band polymer waveguide amplifier with high gain.

Self-channeling of a multi-Joule 10 µm picosecond pulse train through long distances in air.

In the long-wave infrared (LWIR) range, where, due to wavelength scaling, the critical power of Kerr self-focusing Pcr in air increases to 300-400 GW, we demonstrate that without external focusing a train of picosecond CO2 laser pulses can propagate in the form of a single several-centimeter diameter channel over hundreds of meters. The train of 10 µm pulses, for which the total energy ≥20 J is distributed over several near-terawatt picosecond pulses with a maximum power ≤2Pcr, is generated naturally during short pulse amplification in a CO2 laser. It is observed that the high-power 10 µm beam forms a large diameter "hot gas" channel in the ambient air with a ≥ 50 ms lifetime. Simulations of the experiment show that such filamentation-free self-channeling regime has low propagation losses and can deliver multi-Joule/TW-power LWIR pulses over km-scale distances.

Silicon nitride electric-field poled microresonator modulator

Stoichiometric silicon nitride is a highly regarded platform for its favorable attributes, such as low propagation loss and compatibility with complementary metal-oxide-semiconductor technology, making it a prominent choice for various linear and nonlinear applications on a chip. However, due to its amorphous structure, silicon nitride lacks second-order nonlinearity; hence, the platform misses the key functionality of linear electro-optical modulation for photonic integrated circuits. Several approaches have been explored to address this problem, including integration with electro-optic active materials, piezoelectric tuning, and utilization of the thermo-optic effect. In this work, we demonstrate electro-optical modulation in a silicon nitride microring resonator enabled by electric-field poling, eliminating the complexities associated with material integration and providing data modulation speeds up to 75 Mb/s, currently only limited by the electrode design. With an estimated inscribed electric field of 100 V/μm, we achieve an effective second-order susceptibility of 0.45 pm/V. In addition, we derive and confirm the value of the material’s third-order susceptibility, which is responsible for the emergence of second-order nonlinearity. These findings broaden the functionality of silicon nitride as a platform for electro-optic modulation.

Comprehensive FR1(C) and FR3 Lower and Upper Mid-Band Propagation and Material Penetration Loss Measurements and Channel Models in Indoor Environment for 5G and 6G

Comprehensive FR1(C) and FR3 Lower and Upper Mid-Band Propagation and Material Penetration Loss Measurements and Channel Models in Indoor Environment for 5G and 6G

Bragg gratings with novel waveguide models fabricated in bulk glass via fs-laser writing and their slow-light effects.

We present the experimental realization of an innovative parallel partially overlapping waveguides (PO-WGs) model grounded in the thermal accumulated regime and fabricated using femtosecond (fs) laser direct-writing within low-iron bulk glass. The 75mm long novel PO-WGs model was made by partially overlapping the shell parts of two core-shell types of waveguides via a back-and-forth single pass fs-laser inscription. The detailed evolution of the PO-WGs model from inception to completion was offered, accompanying by a thorough characterization, which unveils a substantial refractive index (RI) change, on the order of 10-3, alongside low propagation loss (0.2 dB/cm) and distinctive features associated with the single mode and shell-guided light. Notably, the unsaturated performance of PO-WGs model after the primary inscription paves the way for potential applications in the successful creation of two distinctive types of Bragg gratings: first-order dot-Bragg grating and second-order line-Bragg grating. The 75 mm long dot-Bragg grating was written by a periodic dot array with a height of 6 µm atop the PO-WGs, and the birefringence was measured of 1.5 × 10-5 with a 16 pm birefringence-induced wavelength difference. The line-Bragg grating, which was inscribed with dual PO-WGs extending the line grating part to 40 mm in length along its period for increasing the transmission dip, exhibits a pronounced polarization dependence showcasing an effective birefringence of 4.2 × 10-4 at the birefringence-induced wavelength difference of 0.45 nm. We delved into the slow-light effects of the two Bragg gratings thoroughly, which the theoretical analysis revealed an effective group delay of 0.58 ns (group index 2.3) for the dot-Bragg grating. Similarly, the line-Bragg grating exhibited an effective group delay of 0.3 ns (group index 2.3), in good agreement with experimental measurements. These findings underscore the exciting potential of our gratings for creating optical slow-wave structures, particularly for future on-chip applications.

X-Cut Lithium Niobate Optical Waveguide with High-Index Contrast and Low Loss Fabricated by Vapor Proton Exchange

Highly integrated and stable devices are appealing in optical communication and sensing. This appeal arises from the presence of high refractive index contrast and high-quality waveguides. In this study, we improved the vapor proton exchange (VPE) process, enabling large-scale waveguide fabrication and addressing the issue of liquid exchange during cooling. Additionally, we have prepared and characterized planar waveguides on X-cut lithium niobate (LN) crystals. The exchanged samples exhibit α and k1 phases, refractive index contrasts as high as 0.082, and exceptional refractive index uniformity. Furthermore, we utilized the same process to fabricate channel waveguides and Y-branch waveguides. We achieved low propagation losses in channel waveguides, accompanied by small mode sizes, and low-loss Y-branch waveguides with a highly uniform beam splitting ratio. All waveguides exhibited consistent performance across multiple preparations and tests, remaining free from aging effects for three months. Our results underscore the promising potential of VPE for creating Y-branch splitters and modulators in LN crystals.

Guided spiraling phonon polaritons in rolled one-dimensional MoO3 nanotubes.

Polaritons in reduced-dimensional materials, such as nanowire, nanoribbon and rolled nanotube, usually provide novel avenues for manipulating electromagnetic fields at the nanoscale. Here, we theoretically propose and study hyperbolic phonon polaritons (HPhPs) with rolled one-dimensional molybdenum trioxide (MoO3) nanotube structure. We find that the HPhPs in rolled MoO3 nanotubes exhibit low propagation losses and tunable electromagnetic confinement along the rolled direction. By rolling the twisted bilayer MoO3, we successfully achieve a canalized phonon polaritons mode in the rolled nanotube, enabling their propagation in a spiraling manner along the nanotube. Our findings demonstrate the considerable potential of the rolled MoO3 nanotubes as promising platforms for various applications in light manipulation and nanophotonics circuits, including negative refraction, waveguiding and routing at the ultimate scale.

Highlighting the role of 3C–SiC in the performance optimization of (Al,Ga)N‒based High‒Electron mobility transistors

AlN nucleation layer is the key issue for the performance of GaN high frequency telecommunication and power switching systems fabricated after heteroepitaxy on Silicon or Silicon Carbide. In this work, we demonstrate and explain both the low level and the origin of propagation losses in GaN/3C–SiC/Si High Electron Mobility Transistors (HEMTs) at microwaves frequencies, in view of providing efficient circuits. First, it is shown that the use of 3C–SiC as an intermediate layer between the Si substrate and the GaN epitaxial layer drastically decreases RF propagation losses. Using Secondary Ion Mass Spectroscopy (SIMS) measurements, we demonstrate that dopant in-diffusion (both Al and Ga) into the 3C–SiC pseudo-substrate remains confined beneath the interface. Furthermore, by combining scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM), the 2D profile shows the presence of a slightly conductive zone beneath the AlN/3C–SiC interface that is highly limited (less than 50 nm) whatever the growth conditions of the (Al, Ga)N layers on 3C–SiC explaining the low propagation losses obtained for such devices. This behavior differs from the one previously observed for GaN growth on Si substrate. This work demonstrates the importance and efficiency of the 3C–SiC intermediate layer when used as a pseudo-substrate increasing not only the crystalline quality of the subsequent (Al, Ga)N layers but also permits to achieve high potential GaN power devices as it is crucial.