Measured Propagation Loss Research Articles

Measurement of radiation induced attenuation in irradiated active fibers using optical frequency domain reflectometry

Radiation induced attenuation (RIA) is a major factor affecting the performance of fiber laser systems operated in adverse environments. To investigate the output characteristics of lasers with irradiated active fibers, measurement of detailed RIA profiles is required. Here, a novel method is proposed to explore the attenuation characteristics of irradiated active fibers using optical frequency domain reflectometry (OFDR), which enables propagation loss measurement by acquiring the spatial-resolved backscattered optical signals. With this technique, the RIA data of Yb-doped fibers (YDFs) under uniform radiation is derived by linear fitting of the OFDR traces. And, conventional optical transmission (OT) method is also exploited for comparison. Analysis show that the measured results of the two approaches are consistent. Then, the capability of OFDR is further verified for non-uniform RIA profile measurement of YDFs. For a pump bleached YDF, an upward parabolic RIA profile is attained by taking derivative of the smoothed polynomial fitting of the OFDR trace. Finally, the impacts of RIA profile on the output characteristics of Yb-doped fiber lasers are examined theoretically with a multiphysics thermal model, further validating the necessity of RIA profile measurement.

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

Low-loss operation of silicon-on-insulator integrated components at 2.6-2.7 µm.

Development of mid-infrared photonics is gaining attention, driven by a multitude of sensing applications requiring increasingly compact and cost-effective photonics systems. To this end, low-loss operation of µm-scale silicon-on-insulator photonic integration elements is demonstrated for the 2.6-2.7 µm wavelength region. The platform utilizes the 3 µm thick silicon core layer technology enabling demonstration of low-loss and low birefringence waveguides. Measurements of record low single mode waveguide propagation losses of 0.56 ± 0.09 dB/cm and bend losses <0.08 dB for various miniaturized bend geometries are presented and validated by simulation. Furthermore, a wavelength filter based on echelle grating that allows to select several operating channels within the 2.64-2.7 µm band, with a linewidth of ∼1.56 nm for each channel is presented.

Studying the influence of cold-core mesoscale ocean eddies on sound propagation based on the parabolic equation method

Mesoscale vorticity is an important factor that affects the non-uniform horizontal and vertical distribution of hydrologic elements in the ocean. In this paper, temperature and salinity data from measured mesoscale cold-core eddies during a voyage within a certain sea area are studied, and a synchronous sound field test was conducted on the mesoscale vorticity. Based on the temperature and salinity data, the parabolic equation (PE) method was selected to predict the acoustic field, and the results were compared with the measured propagation loss data of the acoustic field to verify the accuracy and effectiveness of the PE model. The underwater sound propagation characteristics in the mesoscale cold-core eddy environment were then analyzed using the temperature and salinity data retrieved from the voyage. It was found that the convergence area of the acoustic field gradually dispersed with an increase in the depth of the sound source. In a mesoscale eddy environment, when sound waves propagate from inside to outside the eddy, the presence of a cold-core eddy causes the convergence area to shift toward the edge of the eddy, and the deviation gradually decreases with an increase in the depth of the sound source.

Deep-sea explosion sound signal propagation loss measurement and model verification

This paper researched the low-frequency sound field propagation characteristics in the continental slope sea area, the sound field propagation loss is calculated by using the radiated sound field data of the deep-fixed explosive sound sources with 50 m and 200 m depth in the continental slope sea area, and the experimental results are verified by combining with the Kraken normal wave model. The model verification results are in good agreement with the experimental measurement data.

An Ab Initio, Fully Coherent, Semi-Analytical Model of Surface-Roughness-Induced Scattering

Integrated optics and silicon photonics is a rapidly maturing technology and is progressing in telecom, computation, and sensing. Surface-roughness-induced scattering is the primary source of optical loss in most photonic integrated circuits, and as such, ultimately limits the performance of their applications. However, a closed-form description for arbitrary refractive index profiles remains lacking, even though such a one is essential to enable an objective-oriented design of the waveguide platform. We present an ab initio, fully coherent, analytical model based on the volume current method that uses the surface roughness' autocorrelation function and the unperturbed mode's electromagnetic fields to predict the loss coefficient in closed form. An improved expression for the perturbation facilitates the application also to high-index-contrast systems. Hence, it is flexible concerning wavelength, materials, fabrication process, geometry and mode. Consequently, our model may be seamlessly integrated into electromagnetic simulation software suites, once the surface roughness is known for the utilized fabrication process. To verify our model, we compare the calculated scattering losses to measured propagation losses and established models for a wide range of waveguide systems in literature. We find that the previously neglected correlation along the waveguide height significantly impacts the scattering, which necessitates the holistic statistical analysis of the surface roughness. We believe these comprehensive prediction capabilities to be a useful tool for the optimization of silicon photonics design and fabrication, especially for low-confinement applications like sensors.

Low Loss Vertical TiO2/Polymer Hybrid Nano-Waveguides.

This article proposes a novel demonstration of a low-loss polymer channel hybridized with a titania core leading to a nano-waveguide elongated in the normal direction to the substrate. It is aimed at using the quasi-transverse magnetic (TM) mode as the predominant mode in compact photonic circuitry. A detailed design analysis shows how a thin layer of a higher-refractive index material in a trench within the core of the waveguide can increase the confinement and reduce the propagation losses. This thin layer, produced by atomic layer deposition, covers the entire polymer structure in a conformal manner, ensuring both a reduction of the surface roughness and a stronger field confinement. The trench can be made at any place within the polymer channel and therefore its position can be tuned to obtain asymmetric modal distribution. The waveguide is demonstrated at telecom wavelengths, although the material's properties enable operation over a large part of the electromagnetic spectrum. We measured propagation losses as low as 1.75 ± 0.32 dB/cm in a 200 nm × 900 nm section of the waveguide core. All processes being mass-production compatible, this study opens a path towards easier integrated-component manufacture.

Method for the simultaneous measurement of waveguide propagation loss and bending loss

Abstract: The propagation loss of waveguide is a key indicator to evaluate the performance of an integrated optical platform. The commonly used cut-back method to measure the propagation requires the introduction of the Spiral test structure. In order to remove the effect of bending loss, the bending radius is usually designed to be large enough, taking up a lot of foot print. In this paper, we suggested a method to measure the propagation loss and bending loss of waveguide simultaneously with cut-back structure. The bending loss can be exponentially fitted with the bending radius according to simulation, which can be further simplified as linear fitting between the natural logarithm of the bending loss and the bending radius. A genetic algorithm was used to fit the insertion loss curve of the cutback structure and calculate the propagation loss and bending loss. With this method, we measured a cut-back structure of lithium niobate waveguide and got the propagation loss of 0.558dB/cm and bending

Effect of CO2 laser annealing with different laser frequencies on Ge core fiber

The germanium (Ge) core fibers via molten core drawing (MCD) method were annealed by CO2 lasers of 30 kHz, 50 kHz and 70 kHz frequencies respectively under the same laser output power condition. The effect of different laser frequencies on the Ge fiber was mainly investigated using Raman frequency maps, propagation loss measurement and Energy dispersive X-ray spectroscopy (EDS). Raman frequency maps show that the optimization effect of 50 kHz laser annealing on Ge core properties is significantly better than that of 30 kHz and 70 kHz lasers. For the samples annealed by 30 kHz, 50 kHz and 70 kHz lasers, the lowest propagation loss obtained in each laser frequency is 4.598 dB/cm, 2.102 dB/cm, and 2.873 dB/cm respectively, which were measured using a quantum cascade laser with the wavelength range from 4.7 to 4.9 μm. The results of this study indicate that the laser frequency had a significant impact on the properties of Ge core during the process of CO2 laser annealing.

Near-field probing of image phonon-polaritons in hexagonal boron nitride on gold crystals.

Near-field mapping has been widely used to study hyperbolic phonon-polaritons in van der Waals crystals. However, an accurate measurement of the polaritonic loss remains challenging because of the inherent complexity of the near-field signal and the substrate-mediated loss. Here we demonstrate that large-area monocrystalline gold flakes, an atomically flat low-loss substrate for image polaritons, provide a platform for precise near-field measurement of the complex propagation constant of polaritons in van der Waals crystals. As a topical example, we measure propagation loss of the image phonon-polaritons in hexagonal boron nitride, revealing that their normalized propagation length exhibits a parabolic spectral dependency. Furthermore, we show that image phonon-polaritons exhibit up to a twice longer normalized propagation length, while being 2.4 times more compressed compared to the case of the dielectric substrate. We conclude that the monocrystalline gold flakes provide a unique nanophotonic platform for probing and exploitation of the image modes in low-dimensional materials.

Precise laser-cutting of single silver nanowires for direct measurement of SPPs propagation losses

This work presents an alternative experimental approach to directly measure propagation losses of surface plasmon polaritons (SPPs) in a single silver nanowire (AgNW). The methodology synergistically combines several techniques, including single nanowire optical shaping, accurate triggering of SPPs by upconversion nanocrystals (NCs), and precise deposition of sub-micrometer-size droplets with emitters. Indeed, a femtoliter volume of colloidal NCs deposited at one end of the nanowire and excited with a laser through an objective provides a stable source of polaritons, which propagate in the nanowire. The intensity of radiation released by the SPPs scattered out at the opposite AgNW end is a direct measure of propagation losses. This is enabled through a method of precise laser cutting of the nanowire, where the length of the nanowire can be gradually reduced by an optically controlled melting process. At the same time, both the length and diameter of the nanowire are constantly monitored using optical imaging of the complex interaction between the nanowire and polarized Gaussian beam. The optical cutting technique, implemented in this experiment, shows great potential for advanced and inexpensive shaping of the metallic nanostructures for nanophotonic applications.

Evaluation of COAMPS Boundary Layer Refractivity Forecast Accuracy for 2–40 GHz Electromagnetic Wave Propagation

AbstractIn this paper, the performance of the Coupled Ocean‐Atmosphere Mesoscale Prediction System (COAMPS®) electromagnetic (EM) propagation forecast is assessed using numerous metrics such as forecast lengths, frequencies, ranges, and spatial resolutions. The modeled PL (Propagation Loss) for 2–40 GHz based on the COAMPS ®predicted refractivity profiles is evaluated by 1 month of range‐dependent measurements, which were collected during Coupled Air‐Sea Processes and Electromagnetic ducting Research (CASPER) East Campaign. PL data were collected using a shore‐to‐ship radio link, near the coast of Duck, NC. Mesoscale atmospheric refractivity predictions for the CASPER East operational area are provided by COAMPS®. Propagation loss predictions are computed from these refractivity profiles via a parabolic wave equation propagation code. The results show a good agreement between the COAMPS®‐predicted and the measured propagation loss for the northwest Atlantic region. The analyses show that the prediction error varies from 3 to 8 dB as the frequency increases from 2 to 40 GHz. In addition, COAMPS® successfully tracked the changes in the refractivity field even when the forecast length increased from 0 to 48 hr, with only a marginal degradation in EM prediction accuracy within the first 12 hr. Higher horizontal range resolution does not result in significant improvement in EM predictions as long as there are at least 2 M‐profiles that allows the EM propagation code to capture the first order horizontal variation. Low‐resolution, high order nested COAMPS® fields still produce good EM forecasts for this particular geometry.

Mid-infrared Fourier-transform spectrometer based on metamaterial lateral cladding suspended silicon waveguides.

Integrated mid-infrared micro-spectrometers have a great potential for applications in environmental monitoring and space exploration. Silicon-on-insulator (SOI) is a promising platform to tackle this integration challenge, owing to its unique capability for large volume and low-cost production of ultra-compact photonic circuits. However, the use of SOI in the mid-infrared is restricted by the strong absorption of the buried oxide layer for wavelengths beyond 4 µm. Here, we overcome this limitation by utilizing metamaterial-cladded suspended silicon waveguides to implement a spatial heterodyne Fourier-transform (SHFT) spectrometer operating at wavelengths near 5.5 µm. The metamaterial-cladded geometry allows removal of the buried oxide layer, yielding measured propagation loss below 2 dB/cm at wavelengths between 5.3 and 5.7 µm. The SHFT spectrometer comprises 19 Mach-Zehnder interferometers with a maximum arm length imbalance of 200 µm, achieving a measured spectral resolution of 13 cm-1 and a free spectral range of 100 cm-1 at wavelengths near 5.5 µm.

Frequency Diversity in Electromagnetic Remote Sensing of Lower Atmospheric Refractivity

This article explores the effects of system frequency on electromagnetic (EM) remote sensing of atmospheric refractivity. A frequency range of 2–40 GHz covering S- to Ka-bands is analyzed. A multifrequency inversion algorithm is developed to estimate the evaporation duct heights using a parabolic wave equation propagation model. The capabilities of a theoretical multifrequency system are explored for high and low signal-to-noise ratios for varying numbers of frequencies and bands. Experimental data were collected using the lower atmospheric propagation ultrawideband (LATPROP-UWB) system deployed during the Coupled Air-Sea Processes and EM Ducting Research (CASPER) East Campaign. Range-dependent propagation loss measurements at 53 frequencies ranging from 2 to 40 GHz were made. The evaporation duct refractivity profiles estimated from the multifrequency LATPROP-UWB data were compared to the profiles inferred from the concurrent meteorological and oceanographic measurements. Inversion results show that the optimal refractivity retrieval can be achieved using ten frequencies and results in a fourfold reduction in the estimation RMSE compared to a single-frequency inversion.

Ultralow-loss compact silicon photonic waveguide spirals and delay lines

Low-loss and compact optical waveguides are key for realizing various photonic integrated circuits with long on-chip delay lines, such as tunable optical delay lines, optical coherence tomography, and optical gyroscopes. In this paper, a low-loss and compact silicon photonic waveguide spiral is proposed by introducing broadened Archimedean spiral waveguides with a tapered Euler S-bend. A 100-cm-long waveguide spiral is realized with a minimal bending radius as small as 10 μm by using a standard 220-nm-thick silicon-on-insulator foundry process, and the measured propagation loss is as low as 0.28 dB/cm. Furthermore, the present waveguide spirals are used to realize a 10-bit tunable optical delay line, which has a footprint as small as 2.2 mm × 5.9 mm and a dynamic range of 5120 ps with a fine resolution of 10 ps.

Terrain-based adaption of propagation model loss parameters using non-linear square regression

Reliable and real-time propagation loss modeling play a significant role in the efficient planning, development, and optimization of macrocellular communication networks in a given terrain. Thus, the need to adapt or tune an existing model to enhance its signal prediction accuracy in a specified terrain becomes imperative. In this paper, we proposed and applied a non-linear square regression method based on the Levenberg-Marquart (LM) algorithm to adapt and improve the empirical propagation loss estimation accuracy of the Egli model for two major cities in Nigeria. A comprehensive propagation loss measurement acquired over Long Term Evolution (LTE) mobile broadband networks operating at 2630 MHz for four different cities was collected using TEMS investigation tools to achieve the Egli model adaption. Results indicate that the adapted Egli model displays a high estimation accuracy over the Gauss-Newton (GN) algorithm leveraging the non-linear regression method employed to benchmark the propagation loss estimation. Using six standard statistical indicators, the adapted Egli model displayed lower estimation errors than the classical Egli model across the tested locations in the two cities investigated. Finally, the LM-adapted Egli model was compared with extensive measurements from another eNodeB in Port Harcourt different from the initial four eNodeBs investigated. The results indicate that the adapted model is suitable for deployment in related macrocellular environments.

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave (CW), direct pulse, frequency domain using a vector network analyzer (VNA), correlation-based, and swept-time delay cross-correlator. Each of these has unique advantages and disadvantages. CW systems have a larger dynamic range than other systems with a signal that can propagate further into the environment. As the audio sampling rates allow smaller file sizes than other systems, data collection can be continuous and last for several hours. This article discusses a CW-channel sounder system, which has been used to make numerous propagation loss measurements in various cities in the United States of America. Such propagation measurements should be accurate, reproducible, and free of artifacts or biases. This article shows how to set up the measurement, how to validate and verify that the system is making reliable measurements, and finally, it shows results from some of the measurement campaigns such as repeatability measurements, clutter loss measurements (where clutter loss is defined as the excess loss from free-space transmission loss), and reciprocity measurements.

Continuous-Wave Propagation Channel-Sounding Measurement System - Testing, Verification, and Measurements.

Channel sounders are used to measure channel characteristics for radio systems. There are several types of channel sounders used today: continuous-wave (CW), direct pulse, frequency domain using a vector network analyzer (VNA), correlation-based, and swept-time delay cross-correlator. Each of these has unique advantages and disadvantages. CW systems have a larger dynamic range than other systems with a signal that can propagate further into the environment. As the audio sampling rates allow smaller file sizes than other systems, data collection can be continuous and last for several hours. This article discusses a CW-channel sounder system, which has been used to make numerous propagation loss measurements in various cities in the United States of America. Such propagation measurements should be accurate, reproducible, and free of artifacts or biases. This article shows how to set up the measurement, how to validate and verify that the system is making reliable measurements, and finally, it shows results from some of the measurement campaigns such as repeatability measurements, clutter loss measurements (where clutter loss is defined as the excess loss from free-space transmission loss), and reciprocity measurements.

Germanium-on-silicon waveguides for long-wave integrated photonics: ring resonance and thermo-optics.

Germanium-on-silicon (GOS) represents the leading platform for foundry-based long-wave infrared photonic integrated circuits (LWIR PICs), due to its CMOS compatibility and absence of oxides. We describe ring resonance (Q-factors between 2×103 and 1×104) and thermo-optic tunability in germanium-on-silicon waveguides throughout the long-wave-infrared. The ring resonances are characterized by Q-factors and couplings that agree with measurements of propagation loss (as low as 6 dB/cm) and simulations and are enabled by broadband edge coupling (12dB/facet over a 3 dB bandwidth of over 4 microns). We demonstrate the furthest into the infrared that ring resonators have been measured and show the potential of this platform for photonic integration and waveguide spectroscopy at wavelengths from 7 microns to beyond 11 microns.

Femtosecond laser direct inscription of 3D photonic devices in Er/Yb-doped oxyfluoride nano-glass ceramics

The fabrication of optical waveguides by direct femtosecond laser irradiation in Er3+/Yb3+ oxyfluoride nano-glass ceramics is investigated. Following the strategy of single line irradiation, a wide range of laser parameters can be used to obtain single-mode waveguides with nearly-gaussian modal profiles, in the visible and near-infrared. Measured propagation loss is 1.6 dB/cm for the optimum parameters (0.34 μJ/pulse and 20 μm/s scanning velocity), with no annealing after irradiation, and the induced refractive index contrast is Δn∼0.006 (at 800 nm). The multi-scan technique is used to gain control of the refractive index profiles thus producing multimodal structures. The active behavior of the waveguides is induced under ∼800 nm seeding and the co-propagating guidance of the erbium emission is demonstrated. The integration of photonic elements such as Y-splitters, both in 2D and 3D, as well as Mach-Zehnder interferometers, is also shown. Results demonstrate the optimum behavior of Er3+/Yb3+ oxyfluoride nano-glass ceramics as a host material for the integration of complex active photonic devices by femtosecond laser irradiation in the low repetition rate regime.