Optical Transmission Loss Research Articles

Optical rotary junction incorporating a hollow shaft DC motor for high-speed catheter-based optical coherence tomography

In intravascular optical coherence tomography (OCT), the optical rotary junction plays an important role in rotating and pulling back the catheter to generate cross-sectional coronary artery images. To meet the requirements of high-speed intravascular OCT in a clinical setting, the rotary junction should generate high torque and low vibration. In this Letter, we demonstrate an ultrahigh speed optical rotary junction incorporating a hollow shaft brushless DC servomotor to remove a pulley belt, or a gear to minimize vibration noise and transfer stable torque. To evaluate the performance of the rotary junction, the vibration noise and variation of rotation were measured as a function of motor speed. The results showed that the rotary junction rotated the catheter at 42,000 revolutions per minute, with an optical transmission loss of 1.2 dB. To assess the feasibility of the rotary junction for high-speed catheter-based OCT, OCT imaging of the cylindrical shape of a phantom made by two overlapped plastic straws was performed at a rate of 200 frames/s.

Studies on Air Exposure Effect on Polythiophene Thin Films

Abstract This article reports effect of air exposure on the vacuum evaporated Polythiophene thin films (includes vapor chopped and nonchopped) were studied for structural and surface morphological properties. The optical properties such as optical band gap and refractive index of the thin films were also investigated. The study of mechanical properties such as intrinsic stress and adhesion were measured using interferometric method and direct pull off method (DPO) respectively. The optical transmission loss was studied with prism coupling method. For the optical, mechanical and waveguiding properties 5 identical films for each thickness was used. The nonchopped and vapor chopped thin films were compared

Vapor chopped MgO thin film optical waveguide

Abstract In optoelectronic devices, optical signal transmission gets more affected due to the useof materials and their properties. Here, prepared magnesium oxide (MgO) thin films were studied for optical waveguide application by measuring their optical signal transmission loss (OSTL). Novel vapor chopping technique (VCT) was used to prepare vapor chopped (VC) MgO thin films and properties of those films were compared with as deposited or non-chopped (NC) films. Various oxidation temperatures (573, 623 and 673 K) and thin film thickness variation effect on the OSTL were studied. The VC MgO thin film waveguide showed a smaller transmission loss as compared to the NC MgO thin film waveguides. An AFM study showed that, surface roughness of VC thin films was lower than the NC MgO thin films and it increases with increase in oxidation temperatures.

A windshields surface characterization damaged by sandblasting

AbstractThe present work is part of a study of windshield glass erosion subjected to the Saharan sand particles projection. The objective is to highlight the effect of the sand grains size Ps on the degradation process of the ordinary glasses surface (damage rate Dr) and to search the visibility limit of vehicles' drivers. Various erosion tests are carried out and have led to different surface states by varying the sand mass Mp and the particles size Ps. The effect of the surface damage on root mean square roughness Rq, damage rate Dr, and optical transmission To are presented. A clear dependence between these three parameters and the particles size has been highlighted. The results show that Rq increases linearly with Ps increasing, whereas the Dr variation in function of Ps obeys a Gaussian function. In addition, a good correlation between the optical transmission loss and the damage rate is found. In terms of the driver's good vision, the damage of the windshield surface depends essentially on the parameter Dr. Therefore, the visibility limit is determined with regard to this parameter which is dependent on the sand particles size.

Radiation induced absorption of hydrogen-loaded pure silica optical fibers with carbon coating for ITER diagnostics

We present results of gamma irradiation tests of 200 μm pure silica core optical fibers with a low and high-OH concentration, with and without hydrogen loading. All the fibers were manufactured by a candidate supplier of the fiber bundles for optical plasma diagnostics in ITER. The hydrogen-loaded fibers were stored for a one year before the irradiation start. The fibers were exposed at two Co-60 gamma facilities using dose-rates of 15 and 194 mGy/s up to 15 and 70 kGy absorbed doses, respectively. The optical transmission losses of the fibers were measured in-situ in the spectral range of 450–900 nm. The results are interpreted on the basis of available data on radiation defects in silica core fibers. It is demonstrated that hydrogen loading provides a radiation hardness improvement, which allows to satisfy the ITER requirements.

Net optical parametric gain in a submicron silicon core fiber pumped in the telecom band

A silicon core fiber (SCF) has been designed and fabricated with a dispersion engineered profile to support broadband optical parametric amplification across the telecom window. The combination of low optical transmission losses and high coupling efficiency of the SCF platform has allowed for an on-off optical parametric gain up to 9 dB, without experiencing gain saturation due to nonlinear absorption, resulting in a net off-waveguide gain of ∼2 dB. The ability to splice the SCFs with conventional silica fiber systems opens a route to compact and robust all-fiber integrated optical parametric amplifiers and oscillators that could find use in telecoms systems.

Photonic micro-structures produced by selective etching of laser-crystallized amorphous silicon

We present a method for the production of polycrystalline Si (poly-Si) photonic micro-structures based on laser writing. The method consists of local laser-induced crystallization of amorphous silicon (a-Si) followed by selective etching in chemical agents that act preferentially on the a-Si material, consequently revealing the poly-Si content of the film. We have studied the characteristics of these structures as a function of the laser processing parameters and we demonstrate their potential photonic functionality by fabricating polycrystalline silicon ridge optical waveguides. Preliminary waveguide transmission performance results indicated an optical transmission loss of 9 dB/cm in these unrefined devices.

Comparative Investigation of Gamma Radiation Effects on Long Period Gratings and Optical Power in Different Optical Fibers

This work presents a comparative study regarding the effects of gamma radiation on standard and different radiation hardened optical fibers, by means of arc-induced long period gratings (LPGs) written in these fibers. In particular, the resonance wavelength shift (Δλres) of LPG attenuation bands and the attenuation in the fiber transmitted optical power (ΔP) have been comparatively explored during irradiation. Different responses were observed depending on the fiber model. The Ge-doped fiber exhibits significant changes of both resonance wavelength and optical transmission loss, whereas the pure silica core fiber is mostly insensitive to radiation (Δλres and ΔP keep almost close to zero). Surprisingly, the radiation resistant fiber, with doped core, exhibits significant resonance shift even if with trivial power losses. In addition, by combining these results with numerical modeling of LPGs, we were able to estimate the radiation effects on the optical fibers under investigation, in terms of average refractive index change. These results can be useful for the application of such devices in radiation environments, i.e., for the development of both radiation sensitive and radiation hardened sensors.

Sensitivity analysis of a multibranched light guide for real time hyperspectral imaging systems.

Hyperspectral imaging (HSI) is a spectroscopic technique which captures images at a high contrast over a wide range of wavelengths to show pixel specific composition. Traditional uses of HSI include: satellite imagery, food distribution quality control and digital archaeological reconstruction. Our lab has focused on developing applications of HSI fluorescence imaging systems to study molecule-specific detection for rapid cell signaling events or real-time endoscopic screening. Previously, we have developed a prototype spectral light source, using our modified imaging technique, excitation-scanning hyperspectral imaging (HIFEX), coupled to a commercial colonoscope for feasibility testing. The 16 wavelength LED array was combined, using a multi-branched solid light guide, to couple to the scope's optical input. The prototype acquired a spectral scan at near video-rate speeds (∼8 fps). The prototype could operate at very rapid wavelength switch speeds, limited to the on/off rates of the LEDs (∼10 μs), but imaging speed was limited due to optical transmission losses (∼98%) through the solid light guide. Here we present a continuation of our previous work in performing an in-depth analysis of the solid light guide to optimize the optical intensity throughput. The parameters evaluated include: LED intensity input, geometry (branch curvature and combination) and light propagation using outer claddings. Simulations were conducted using a Monte Carlo ray tracing software (TracePro). Results show that transmission within the branched light guide may be optimized through LED focusing lenses, bend radii and smooth tangential branch merges. Future work will test a new fabricated light guide from the optimized model framework.

真空热环境下不同涂覆层光纤传输损耗特性影响研究

真空热环境下不同涂覆层光纤传输损耗特性影响研究

Laser-irradiation-driven formation of oxygen-related defects and performance degradation in fused silica with nanosecond pulsed laser at 355 nm

Performance degradation and formation of oxygen-related defects in fused silica irradiated by large number of successive 355 nm laser pulses at low fluence were studied. Performance degradation was examined in view of optical transmission loss and decrease of laser-induced damage threshold (LIDT). When irradiated by 7200 shots at laser fluence of 4 J/cm2, ∼2% transmission loss and 25.4% decrease in LIDT were observed. What’s more, LIDT data showed an exponentially decreasing trend with the increase of laser shots number. Laser-irradiation-driven oxygen-related defects were studied by combined methods of Fourier transform infrared radiometer, laser-excited Raman and X-ray photoelectron spectroscopies. Results suggested that laser irradiation induced formation of 3 fold (Si-O)n ring structure in pre-irradiated silica, and the content of 3 fold (Si-O)n rings increased with the laser shots. Laser-irradiation induced the formation and accumulation of low valence Si3+ and NBO ions as well as POL defects in silica. Formation and accumulation of POL defects and 3-fold (Si-O)n rings were suggested to be responsible for the observed significant performance degradation of fused silica.PACS: 61. 72. Ji; 61. 80. Ba; 42. 70. Ce.

Dynamical optical response of nematic liquid crystal cells through electrically driven Fréedericksz transition: influence of the nematic layer thickness.

A dynamical optical characterization of planar nematic liquid-crystal cells electrically driven through the Fréedericksz transition is presented. Our method involves applying voltage steps with different starting voltage close to the Fréedericksz threshold. Measurements are performed on cells with various thickness, from a few microns up to 180µm, and highlight the transient molecular disorder occurring close to the Fréedericksz transition. We show that the transient disorder affects the molecular arrangement mainly in the reorientational plane of the splay motion induced by the planar cell geometry. Moreover, a disorder quantification in terms of optical transmission losses and temporal dynamics enables us to picture the Fréedericksz transition. This characterization provides the identification of the electrical driving conditions for which the effect of the reorientational disorder is minimized. When comparing cells with various thicknesses, it results that thick cells are characterized by a much smoother transition with respect to the conventional step-like Fréedericksz transition of the thin cells, hence, thick cells can be dynamically driven over a large range of voltages, even below the Fréedericksz threshold. The results are discussed in view of novel electro-optical applications of thick layers of nematics. As an example, the experimental conditions for realizing a rapid birefringence scan and the achievement of a large and tunable group delay for femtosecond pulses are presented.

Robust multimaterial chalcogenide fibers produced by a hybrid fiber-fabrication process

Double-crucible cane fabrication of highly purified chalcogenide-glass was combined with multimaterial thermal fiber drawing to produce robust low-loss 0.2 NA chalcogenide fibers. Optical transmission losses were shown to be less than 1.1 dB/m at wavelengths of 1.5, 2.0 and 4.6 μm. Fiber transmission > 97% at the 1.5 μm design wavelength was demonstrated using single-layer anti-reflection coatings that were durable under temperature, humidity and abrasion tests. Tensile-strength tests proved that the mechanical strength of the fiber was improved by a factor of 1000 compared to a jacket-free chalcogenide fiber. Multiwatt power transmission in single mode fiber was demonstrated.

Pressure-induced structural transition in chalcopyrite ZnSiP2

The pressure-dependent phase behavior of semiconducting chalcopyrite ZnSiP2 was studied up to 30 GPa using in situ X-ray diffraction and Raman spectroscopy in a diamond-anvil cell. A structural phase transition to the rock salt type structure was observed between 27 and 30 GPa, which is accompanied by soft phonon mode behavior and simultaneous loss of Raman signal and optical transmission through the sample. The high-pressure rock salt type phase possesses cationic disorder as evident from broad features in the X-ray diffraction patterns. The behavior of the low-frequency Raman modes during compression establishes a two-stage, order-disorder phase transition mechanism. The phase transition is partially reversible, and the parent chalcopyrite structure coexists with an amorphous phase upon slow decompression to ambient conditions.

Flexible and stretchable nanowire-coated fibers for optoelectronic probing of spinal cord circuits.

Studies of neural pathways that contribute to loss and recovery of function following paralyzing spinal cord injury require devices for modulating and recording electrophysiological activity in specific neurons. These devices must be sufficiently flexible to match the low elastic modulus of neural tissue and to withstand repeated strains experienced by the spinal cord during normal movement. We report flexible, stretchable probes consisting of thermally drawn polymer fibers coated with micrometer-thick conductive meshes of silver nanowires. These hybrid probes maintain low optical transmission losses in the visible range and impedance suitable for extracellular recording under strains exceeding those occurring in mammalian spinal cords. Evaluation in freely moving mice confirms the ability of these probes to record endogenous electrophysiological activity in the spinal cord. Simultaneous stimulation and recording is demonstrated in transgenic mice expressing channelrhodopsin 2, where optical excitation evokes electromyographic activity and hindlimb movement correlated to local field potentials measured in the spinal cord.

Fiber-optic arc flash sensor based on plastic optical fibers for simultaneous measurements of arc flash event position

We present an arc flash sensor that can trace the arc event position as well as intensity by utilizing conventional plastic optical fibers (POFs). In order to check the possibility as a light-receiving sensor, we experimentally confirm that the externally irradiated flash light can be coupled into the fiber core through the surface of POF without any additional treatment. After the incident light is divided in two optical paths toward opposite directions, they have the different attenuation values determined by the propagation distance. Since the optical transmission loss of a POF is constant regardless of the irradiated energy, the intensity ratio for two signals measured at both fiber ends is given as a function of position. The experimental results show that we can successfully trace the event position from this intensity ratio. In addition, it is possible to define the illuminated energy by comparing the absolute value of the intensity measured from one side. According to the experimental results, the proposed sensor has a relatively fine spatial resolution, ±10 cm, despite having a simple structure.

Glow discharge plasma polymerized nanostructured polyaniline thin film optical waveguide

In this work, glow discharge continuous wave plasma polymerization technique was used to deposit nanostructured polyaniline (PANI) thin film by varying input power. The radio frequency (RF) used for plasma polymerization was 13.56 MHz and working pressure was 0.15 mbar. It was found that, changes in the input power can be used to control the properties of the plasma polymerized PANI thin films. Highly cross-linked structure with an increase in chain length was observed from FTIR spectra with input RF power, whereas the film surface morphology was found to be highly uniform, densely packed and smooth from FE-SEM images. The surface roughness of the film was found to increase with RF power. The refractive index and adhesion of the film was found to be increased while the optical band gap and surface energy decreased with input RF power. The plasma polymerized PANI film showed outstanding optical transmission loss properties and proved itself as excellent optical waveguide.

Fabrication of photonic integrated circuits in silicon nitride using substrate conformal imprint lithography

The feasibility of nanoimprint lithography as an alternative strategy for the pattern definition of Si3N4 based PIC (photonic integrated circuit) is demonstrated in this study. The PICs were patterned by the substrate conformal imprint lithography (SCIL), a variation of UV nanoimprint lithography. The optical quality of the patterned PICs was determined by measuring the optical transmission losses of the fabricated PICs. The quality was then compared with the PICs patterned by an optical stepper. The analysis shows that the optical quality of the patterns fabricated by the SCIL process is similar to the patterns defined by an optical stepper. Our study demonstrates clearly that the SCIL is an alternative to established lithographic approaches in regards to material or pattern resolution.

Fabrication, optical and electrical properties of solvethermal reduced graphene oxide/polyimide composites by in situ polymerization

Solvothermal reduced graphene oxide (SRGO) suspensions in dimethylacetamide (DMAC) are facilely prepared by a solvothermal process. Then, SRGO/polyimide (PI) composites are efficiently prepared by in situ polymerization and finally cured at 300°C for 2h. Optical, dielectric and electrical properties are carefully evaluated by the optical transmission, dielectric constants (ε) and dielectric loss factors, conductivity, etc. The SRGO/PI composite film with 0.5wt% SRGO sheets exhibits the obvious optical absorption in region of 0.5–2.4μm and the higher emissivity in region of 6–24μm. Moreover, the dielectric constants and resistivity of SRGO/PI composites display an obvious decrease from ε=4.0 to ε=3.0 and from 1014 to 106Ωcm, respectively. This approach would supply a potential revolution to improve optical and electrical properties of SRGO/PI composites.

Pulse reference-based compensation technique for intensity-modulated optical fiber sensors

We propose a compensation technique based on pulse reference for intensity-modulated optical fiber sensors that can compensate the power fluctuation of the light source, the change of optical components transmission loss, and the coupler splitting ratio. The theoretical principle of this compensation technique is analyzed and a temperature sensor based on fiber coating-covered optical microfiber is carried out to demonstrate the compensation effect. The system noise is measured to be 0.0005 dB with the temperature sensitivity reaching ?0.063 dB/°C, and the output drift is 0.006 dB in 2 h at room temperature. The output shows a slight variation (0.0061 dB) when the light source and the common light path suffer a 3 dB attenuation fluctuation.