Optical Fiber Waveguides Research Articles

High-efficiency broadband out-of-plane fiber-to-polymer waveguide grating coupler

Polymer photonics is receiving significant attention due to its potential for a wide range of integrated photonic applications and wide wavelength transparency. Wafer-scale testing is challenging due to low-index contrast in polymer waveguides. In this Letter, we demonstrate an amorphous silicon based out-of-plane polymer waveguide grating coupler. Simulations predict a maximum efficiency of −1.13 dB, with a 1 dB bandwidth of 95 nm over the C–L-band. Experimentally measured peak coupling efficiency between a single-mode optical fiber and polymer waveguide is −2.15 dB per coupler with a 1 and 3 dB bandwidth of 49 and 89 nm, respectively.

Exciton Dissociation and Recombination Afford Narrowband Organic Afterglow Through Efficient FRET.

Organic afterglow with long-persistent luminescence (LPL) after photoexcitation is highly attractive, but the realization of narrowband afterglow with small full-width at half-maximum (FWHM) is a huge challenge since it is intrinsically contradictory to the triplet- and solid-state emission nature of organic afterglow. Here, narrow-band, long-lived, and full-color organic LPL is realized by isolating multi-resonant thermally activated delayed fluorescent (MR-TADF) fluorophores in a glassy steroid-type host through a facile melt-cooling treatment. Such prepared host becomes capable of exciton dissociation and recombination (EDR) upon photoirradiation for both long-lived fluorescence and phosphorescence; and, the efficient Förster resonance energy transfer (FRET) from the host to various MR-TADF emitters leads to high-performance LPL, exhibiting small FWHM of 33nm, long persistent time over 10s, and facile color-tuning in a wide range from deep-blue to orange (414-600nm). Moreover, with the extraordinary narrowband LPL and easy processability of the material, centimeter-scale flexible optical waveguide fibers and integrated FWHM/color/lifetime-resolved multilevel encryption/decryption devices have been designed and fabricated. This novel EDR and singlet/triplet-to-singlet FRET strategy to achieve excellent LPL performances illustrates a promising way for constructing flexible organic afterglow with easy preparation methods, shedding valuable scientific insights into the design of narrow-band emission in organic afterglow.

A temperature sensor based on multi-beam capture and interference

In this study, we proposed and validated a temperature fiber sensor based on optical signal capture Mach-Zehnder Interferometer (OSC-MZI) with high-precision temperature measurement capabilities. By creating three air cavities on a continuously offset-spliced no-core fiber (NCF), the optical signal experiences reflection and divergence within these cavities, which enhances the optical path of propagating light. Gradually, filling these NCF cavities with polymethyl methacrylate (PMMA) microspheres to increase the light coupling efficiency and as a sensing unit. Due to the directly contact between the optical fiber waveguide and PMMA, the state of incident lights is easily influenced by the refractive index (RI) variations of PMMA. When the environmental temperature changes, RI of the PMMA with high thermal-optic coefficient shows marked change, which finally leads to the obvious wavelength shift of interference dips in the transmission spectrum. Experimental results show that MZI coated with the polymer materials achieves a temperature sensitivity of up to 2.04 nm/°C within the temperature range of 25–50 °C. Furthermore, as an interference-based MZI sensor, its total length is only 4.75 mm. The proposed OSC-MZI provides a new approach for combining optical fiber sensors with polymer materials.

Design of uncomplicated triangular core PCF for enhanced non-linearity applications

An innovative design of Photonic Crystal Fibre (PCF) for enhanced non-linearity applications using simulation with the Finite Element Method (FEM) is presented. The PCF is a kind of fibre optic waveguide that has air-holes along the entire length of the optical fibre, which exploits its exclusive features of being continuously single-moded and having a modifiable spot-size and dispersion properties for various linear and non-linear applications. This proposed triangular core PCF is made of silica material with a refractive index of 1.445 and features three large air-holes placed 120° apart in the core, each with a refractive index of 1.00. The air-holes have a pitch length of 6.03 μm and a radius of 2.86 μm, and the wavelength of operation is 1.55 μm. The proposed PCF design has a large diameter to pitch ratio (d/Λ) of up to 0.95, resulting in a reduced spot-size of just above 1.00 μm2. This indicates that the proposed triangular core PCF design could be used to enhance non-linearity applications. This study introduces a novel structure that simplifies construction by employing three strategically positioned large air-holes in the cladding, thus achieving the necessary properties for guiding light through the core. This streamlined approach overcomes complexities associated with previous designs from the literature, hence, offering a practical solution for effective light guidance while minimising construction difficulties. This inventive proposed PCF design can be fabricated using the Stack and Draw process or the slurry casting method.

Mirrorless MEMS imaging: a nonlinear vibrational approach utilizing aerosol-jetted PZT-actuated fiber MEMS scanner for microscale illumination.

This study introduces a novel image capture and lighting techniques using a cutting-edge hybrid MEMS scanner system designed for compact microscopic imaging. The scanner comprises a tapered optical fiber waveguide and innovative aerosol-jet printed PZT (lead zirconate titanate) bimorph push-pull actuators on a stainless-steel substrate, effectively addressing issues that are commonly associated with PZT on silicon substrates such as fracture and layer separation. By leveraging nonlinear vibration, the scanner achieves a spiral scan pattern from a single signal input, in addition to the expected two-dimensional scanning and target illumination from two phase-shifted inputs. This capability is further enhanced by a novel process to taper the optical fiber, which reduces illumination scattering and tunes the fiber to the resonant frequencies of the scanner. The precisely tapered tip enables large fields of view while maintaining independent 2-axis scanning through one-degree-of-freedom actuation. Experimental validation showcases the successful generation of a spiral scan pattern with a 60 μm diameter scan area and a 10 Hz frame rate, effectively reconstructing scanned images of 5 μm lines, cross patterns (15 μm in length with a 5 μm gap), and structures of a Psychodidae wing.

Improving the mathematical model of a fiber-optic inclinometer for vibration diagnostics of elements in the propulsion system with sliding bearings

The operational capacity of a vessel’s propulsion system (VPS) has an exceptionally large impact on the safety of the ship and shipping as a whole. This requires constant long-term technical diagnostics of VPS elements in order to determine their real resource. First of all, this refers to the bearing units of VPS. The practical use of the concept of continuous diagnostics requires the introduction of the latest means of monitoring the technical condition of VPS, which can significantly increase the reliability of the measurement results. That is why solving the scientific problem of creating diagnostic tools invariant to operating conditions and adapted for continuous, long-term, and reliable monitoring, namely fiber-optic inclinometers (FOI), is relevant. In order to solve the problem, the object of research has been determined – fiber-optic measuring devices for monitoring changes in the geometric position or damping conditions of oscillations in bearing units of VPS elements. The task to improve fiber-optic means was to increase the accuracy of measurement results. The results are in the form of an improved mathematical model of FOI. The difference of the model is the calculation of actual properties of each material layer of the multilayer structure of real fiber-optic waveguides. A distinctive feature of the proposed solution is that the description of the optical-mechanical process in FOI using an improved mathematical model is more accurate and closer to the parameters of the actual process, which are determined experimentally. The results of the research belong to the field of systems and means of technical diagnosis of VPS elements and can be applied primarily on ships, submarines, and vessels of large displacement

Al2O3/GeO2/P2O5/F-Doped Silica Large-Mode-Area Optical Fibers for High-Power Single-Frequency Radiation Delivery

A new design of a passive optical fiber waveguide with a large mode area (LMA) and strong stimulated Brillouin scattering (SBS) suppression is proposed. The fiber core consists of two parts: a central one, doped with Al2O3 and GeO2, and a peripheral one, doped with P2O5 and F. The doping profiles form a gradient-increasing profile of the acoustic refractive index, which effectively implements the acoustic multimode SBS suppression method. Measurements of the SBS gain spectrum and SBS threshold power were carried out, showing an increase in the SBS threshold of no less than 11 dB compared to a conventional uniformly doped passive LMA fiber.

An extendable optical fibre probe survey meter for naturally occurring radioactive material (NORM) and other weak emitters

We have developed a radioluminescence-based survey meter for use in industries in which there is involvement in naturally occurring radioactive material (NORM), also in support of those needing to detect other weak emitters of radiation. The functionality of the system confronts particular shortcomings of the handheld survey meters that are currently being made use of. The device couples a LYSO:Ce scintillator with a photodetector via a polymer optical fibre waveguide, allowing for "intrinsically safe" inspection within pipework, separators, valves and other such component pieces. The small-diameter optical fibre probe is electrically passive, immune to electromagnetic interference, and chemically inert. The readout circuit is entirely incorporated within a handheld casing housing a silicon photomultiplier (SiPM) detection circuit and a microprocessor circuit connected to an LCD display. A 15 m long flexible PMMA optical fibre waveguide is butt coupled to an ABS plastic probe that retains the LYSO:Ce scintillator. Initial tests have included the use of lab-based mixed gamma-ray sources, measurements being made in concert with a reference conventional GM survey-meter. Characterization, via NORM sources at a decontamination facility, has shown useful sensitivity, covering the dose-rate range 0.10- to 28 µSv h−1 (R-squared 0.966), extending to 80 µSv/h as demonstrated in use of a Cs-137 source. The system is shown to provide an effective tool for detection of radioactivity within hard to access locations, in particular for sources emitting at low radiation levels, down to values that approach background.

An Optical-Fiber-Based Key for Remote Authentication of Users and Optical Fiber Lines.

We have shown the opportunity to use the unique inhomogeneities of the internal structure of an optical fiber waveguide for remote authentication of users or an optic fiber line. Optical time domain reflectometry (OTDR) is demonstrated to be applicable to observing unclonable backscattered signal patterns at distances of tens of kilometers. The physical nature of the detected patterns was explained, and their characteristic spatial periods were investigated. The patterns are due to the refractive index fluctuations of a standard telecommunication fiber. We have experimentally verified that the patterns are an example of a physically unclonable function (PUF). The uniqueness and reproducibility of the patterns have been demonstrated and an outline of authentication protocol has been proposed.

Accelerating the solar-thermal energy storage via inner-light supplying with optical waveguide

Solar-thermal storage with phase-change material (PCM) plays an important role in solar energy utilization. However, most PCMs own low thermal conductivity which restricts the thermal charging rate in bulk samples and leads to low solar-thermal conversion efficiency. Here, we propose to regulate the solar-thermal conversion interface in spatial dimension by transmitting the sunlight into the paraffin-graphene composite with side-glowing optical waveguide fiber. This inner-light-supply mode avoids the overheating surface of the PCM, accelerates the charging rate by 123% than that of the traditional surface irradiation mode and increases the solar thermal efficiency to ~94.85%. Additionally, the large-scale device with inner-light-supply mode works efficiently outdoors, indicating the potential of this heat localization strategy in practical application.

Laser Doppler vibrometry measurements of acoustic attenuation in optical fiber waveguides.

Fiber Bragg grating (FBG) sensors have been widely applied for structural health monitoring applications. In some applications, remote bonding of the optical fiber is applied, where ultrasonic waves are coupled from the structure to the optical fiber and propagated along the fiber to the FBG sensor. The distance that this signal can propagate along the optical fiber without decaying below a threshold value can be critical to the area of the structure that can be monitored per sensor. In this paper, we develop a method to measure the acoustic mode attenuation of fiber waveguides based on laser Doppler vibrometry (LDV) that is independent of the fiber type. In order to validate the method, we compare attenuation measurements on single-mode optical fibers using both the LDV and FBG sensor methods. Once the method is validated, experimental measurements of different coated and uncoated optical fibers are performed to quantify the role of the fiber diameter on the attenuation coefficient. As the radius of the waveguide decreases, the signal attenuation increases exponentially.

Advances in Fiber-Optic Extrinsic Fabry–Perot Interferometric Physical and Mechanical Sensors: A Review

Fabry–Perot interferometers (FPIs) have found a multitude of scientific and industrial applications ranging from gravitational wave detection, high-resolution spectroscopy, and optical filters to quantum optomechanics. Integrated with optical fiber waveguide technology, the fiber-optic FPIs have emerged as a unique candidate for high-sensitivity sensing and have undergone tremendous growth and advancement in the past two decades with their successful applications in an expansive range of fields. The extrinsic cavity-based devices, i.e., the fiber-optic extrinsic FPIs (EFPIs), enable great flexibility in the design of the sensitive Fabry–Perot cavity combined with state-of-the-art micromachining and conventional mechanical fabrication, leading to the development of a diverse array of EFPI sensors targeting at different physical quantities. Here, we summarize the recent progress of fiber-optic EFPI sensors, providing an overview of different physical and mechanical sensors based on the FPI principle, with a special focus on displacement-related quantities, such as strain, force, tilt, vibration and acceleration, pressure, and acoustic. The working principle and signal demodulation methods are shown in brief. Perspectives on further advancement of EFPI sensing technologies are also discussed.

In Situ Mineralizing Spinning of Strong and Tough Silk Fibers for Optical Waveguides.

Biopolymer-based optical waveguides with low-loss light guiding performance and good biocompatibility are highly desired for applications in biomedical photonic devices. Herein, we report the preparation of silk optical fiber waveguides through bioinspired in situ mineralizing spinning, which possess excellent mechanical properties and low light loss. Natural silk fibroin was used as the main precursor for the wet spinning of the regenerated silk fibroin (RSF) fibers. Calcium carbonate nanocrystals (CaCO3 NCs) were in situ grown in the RSF network and served as nucleation templates for mineralization during the spinning, leading to the formation of strong and tough fibers. CaCO3 NCs can guide the structure transformation of silk fibroin from random coils to β-sheets, contributing to enhanced mechanical properties. The tensile strength and toughness of the obtained fibers are up to 0.83 ± 0.15 GPa and 181.98 ± 52.42 MJ·m-3, obviously higher than those of natural silkworm silks and even comparable to spider silks. We further investigated the performance of the fibers as optical waveguides and observed a low light loss of 0.46 dB·cm-1, which is much lower than natural silk fibers. We believed that these silk-based fibers with excellent mechanical and light propagation properties are promising for applications in biomedical light imaging and therapy.

Elimination of Side Lobe Ghost Peak Using Wiener Deconvolution Filter in OFDR

Ghost peaks refer to these peaks on backscattering trace measured by a reflectometer similar to Fresnel reflection peaks appearing at the position of non-reflection events in optical fiber or optical waveguide networks testing, which will cause ambiguity in the interpretation of reflection events on backscattering trace. We present a simple and effective method to eliminate side lobe ghost peaks in optical frequency domain reflectometry (OFDR) using a Wiener deconvolution filter. An OFDR system usually contains a main interferometer that is used to measure backscattering trace of fiber umber test (FUT) and an auxiliary interferometer that is used to measure the phase of tunable laser source (TLS) to compensate tuning nonlinearity. Multi-peaks in the spectrum of TLS and reflections in the auxiliary interferometer will generate side lobes on point spread function (PSF) of OFDR system, which will cause ghost peaks on FUT trace. By performing a Wiener deconvolution filtering on the auxiliary interferometer, we can obtain the PSF of an auxiliary interferometer, which is used as a convolution kernel to perform a Wiener deconvolution filtering on FUT trace from the main interferometer. Comparing the main interferometer spatial signal before and after deconvolution filtering, the peak amplitude whose reduction higher than threshold is identified to a ghost peak and is eliminated. By this ghost peak elimination method, we can acquire a pure FUT trace by an OFDR using a low-cost distributed feedback (DFB) TLS with a 26 m test length and an mm level spatial resolution.

A 60 μm-Long Fiber-to-Chip Edge Coupler Assisted by Subwavelength Grating Structure with Ultralow Loss and Large Bandwidth

Efficient fiber-to-chip coupling is a key issue in the field of integrated optics and photonics due to the lack of on-chip silicon light source at present. Here, we propose a silicon-based fiber-to-chip edge coupler by use of subwavelength grating (SWG)-assisted structure. The key conversion region is composed of a trident-shaped SWG in the center and two matched strip waveguides on both sides. To achieve high mode match between fiber mode and silicon waveguide mode and to realize low-loss transmission on-chip, we have divided the conversion region into three parts and determined their optimum dimensions. From results, the total device length is only 60 μm from input fiber to output silicon waveguide, and the insertion loss (IL) is as low as 0.23 dB at the wavelength of 1.55 μm. For the working bandwidth, its value can be enlarged to 240 nm (or 390 nm) by keeping IL < 1 dB (or 1.5 dB), which is quite promising for on-chip broadband devices. Based upon these advantages, we hope such a device could be applied in light coupling between optical fiber and on-chip silicon waveguide.

A fibre-based 2D-slit homogenizer concept for high-precision space-based spectrometer missions

The measurement accuracy of recent and future space-based imaging spectrometers with a high spectral and spatial resolution suffer from the inhomogeneity of the radiances of the observed Earth scene. The Instrument Spectral Response Function (ISRF) is distorted due to the inhomogeneous illumination from scene heterogeneity. This gives rise to a pseudo-random error on the measured spectra. In order to assess the spectral stability of the spectrograph, stringent requirements are typically defined on the ISRF such as shape knowledge and the stability of the centroid position of the spectral sample. The high level of spectral accuracy is particularly crucial for missions quantifying small variations in the total column of well-mixed trace gases like hbox {CO}_{2}. In the framework of the hbox {CO}_{2} Monitoring Mission (CO2M) industrial feasibility study (Phase A/B1 study), we investigated a new slit design called 2D-Slit Homogenizer (2DSH). This new concept aims to reduce the Earth scene contrast entering the instrument. The 2DSH is based on optical fibre waveguides assembled in a bundle, which scramble the light in across-track (ACT) and along-track (ALT) direction. A single fibre core dimension in ALT defines the spectral extent of the slit and the dimension in ACT represents the spatial sample of the instrument. The full swath is given by the total size of the adjoined fibres in ACT direction. In this work, we provide experimental measurement data on the stability of representative rectangular core shaped fibre as well as a preliminary pre-development of a 2DSH fibre bundle. In our study, the slit concept has demonstrated significant performance gains in the stability of the ISRF for several extreme high-contrast Earth scenes, achieving a shape stability of <0.5{%} and a centroid stability of <0.25 text {pm} (NIR). Given this unprecedented ISRF stabilization, we conclude that the 2DSH concept efficiently desensitizes the instrument for radiometric and spectral errors with respect to the heterogeneity of the Earth scene radiance.

A Review: Surface Plasmon Resonance-Based Biosensor for Early Screening of SARS-CoV2 Infection

Rapid viral diagnosis is essential to contain the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) in the community and ensure effective patient management. However, the current gold standard for diagnosis of viral disease depends on the time-consuming molecular technique. Surface plasmon resonance (SPR) phenomenon has been widely applied in the analysis of biomolecular interactions and analytes detection, which is currently being investigated as a quick diagnostic method of numerous viral infections. In this regard, researchers have performed experimental studies dedicated to enhancing the sensitivity and specificity of the SPR sensor performance for utilization in the medical diagnostic field. In this review, we summarized various SPR application including the recent advancements and advantages of different types of SPR-based biosensor such prism-based, localized surface plasmon resonance (LSPR), fiber optic, optical grating, and optical waveguide for the detection of SARS-CoV2. We proposed various technical recommendations to improve the sensitivity, accuracy, time response, and cost-saving means of the SPR sensor. A special focus was set for sensitivity enhancement aspects in terms of the type of prism, nanomaterials, support layer with type and shape of optical fibers for early, swift, and ultra-sensitive detection of viral infection. With the highlighted impacts of SPR application, this review frames the current potential and challenges of SPR in comparison to the current gold standard of viral infection diagnostic strategy.

Polarization-maintaining and radiation resistant optical fiber with germanosilicate elliptical core

This paper aims to consider fabrication of single-mode polarization-maintaining (PM) optical fibers with elliptical core, doped with 20 mol. % GeO2 and to study their optical properties and radiation resistance. The optical fiber preform was fabricated by chemical vapor deposition method. The low-oxygen central piece of the core in the preform was removed by high-temperature chemical gas-phase etching. The single-mode optical fibers 125 µm in diameter, with 65 µm thick polymer protection coating were drawn. The results of measurements of the optical properties at a wavelength of 1.3–1.55 μm confirmed that the highly-doped GeO2 optical fiber waveguides have a low optical loss and high radiation resistance owing to gas phase etching. Polarization-maintaining factor (h-parameter) of ≈ 8∙10-6 m−1 was achieved. As to the radiation resistance, our single-mode PM optical fiber with elliptical core appears to be quite competitive to the known PANDA PM optical fibers with a core made of pure silica glass.

Surface Plasmonic Sensors: Sensing Mechanism and Recent Applications.

Surface plasmonic sensors have been widely used in biology, chemistry, and environment monitoring. These sensors exhibit extraordinary sensitivity based on surface plasmon resonance (SPR) or localized surface plasmon resonance (LSPR) effects, and they have found commercial applications. In this review, we present recent progress in the field of surface plasmonic sensors, mainly in the configurations of planar metastructures and optical-fiber waveguides. In the metastructure platform, the optical sensors based on LSPR, hyperbolic dispersion, Fano resonance, and two-dimensional (2D) materials integration are introduced. The optical-fiber sensors integrated with LSPR/SPR structures and 2D materials are summarized. We also introduce the recent advances in quantum plasmonic sensing beyond the classical shot noise limit. The challenges and opportunities in this field are discussed.

Subwavelength-Structured High-Efficiency Nanophotonic Coupler for Air Top-Cladded Silicon Waveguide

Efficient coupling between an optical fiber and silicon waveguide has been a major practical challenge for silicon photonics since the first day due to the huge mode size mismatch between them. In this paper, we propose a subwavelength structured edge coupler for efficient coupling light into/out from air top-cladded silicon waveguides. Through refractive index engineering, we demonstrate a single-step patterned coupler with a coupling loss of ~2.5 dB for the wavelength range from 1.5 μm to 1.65 μm.