Optical Loss Measurements Research Articles

Branched Optical Fiber Loss Measurement Technology for End-to-end Testing in Optical Access Networks

Branched Optical Fiber Loss Measurement Technology for End-to-end Testing in Optical Access Networks

Flexible multimode polydimethyl-diphenylsiloxane optical planar waveguides

The paper reports on the fabrication and characterization of flexible optical multimode silicon-based organic elastomer planar and rectangular waveguides, where polydimethyl-diphenylsiloxane (PDMDPS) was used for the waveguide core and polydimethylsiloxane was used for the cladding and cover protection layers. We measured waveguiding properties of PDMDPS planar waveguides deposited on glass substrate using the prism coupling technique and the optical scattering losses of the waveguides by the fiber probe technique at the wavelengths region from visible to infrared. The design of the rectangular waveguides was planned for the geometric dimensions of the core 50 × 50 µm2 and the proposed shapes were realized by the doctor blade technique into a nickel mold. Insertion optical loss measurement of rectangular waveguides was done by the cut-back method and the best samples had optical losses lower than 0.35 dB cm−1 at 532, 650, 850 and 1310 nm. The main virtue of the waveguides is their flexibility, suitable in particular for optical connections in a wide range of the wavelengths.

Large core plastic planar optical splitter fabricated by 3D printing technology

We report on the design, fabrication and optical properties of large core multimode optical polymer splitter fabricated using fill up core polymer in substrate that was made by 3D printing technology. The splitter was designed by the beam propagation method intended for assembling large core waveguide fibers with 735 μm diameter. Waveguide core layers were made of optically clear liquid adhesive, and Veroclear polymer was used as substrate and cover layers. Measurement of optical losses proved that the insertion optical loss was lower than 6.8 dB in the visible spectrum.

Properties of Multimode Optical Epoxy Polymer Waveguides Deposited on Silicon and TOPAS Substrate

The paper reports on the fabrication and characterization of multimode polymer optical waveguides. Epoxy polymer EpoCore was used as the waveguide core material and EpoClad was used as a cladding and cover protection layer. The design of the waveguides was schemed for geometric dimensions of 50 mu m core and for 850 nm and 1310 nm wavelengths. Proposed shapes of the waveguides were fabricated by standard photolithography process. Optical losses of the planar waveguides were measured by the fibre probe technique at 632.8 nm and 964 nm. Propagation optical loss measurements for rectangular waveguides were done by using the cut-back method and the best samples had optical losses lower than 0.53 dB/cm at 650 nm, 850 nm and 1310 nm.

Simultaneous mapping of reflectance, transmittance and optical loss of highly reflective and anti-reflective coatings with two-channel cavity ring-down technique.

We demonstrate the use of a two-channel cavity ring-down (CRD) technique for simultaneously measuring/mapping the reflectance R, transmittance T and optical loss L (absorption plus scattering losses) of highly reflective (HR) and anti-reflective (AR) laser components. High reflectance/transmittance of HR/AR components is measured with the ring-down time of CRD signals, while the low residual transmittance/ reflectance of HR/AR components is determined by the amplitude ratio of two CRD signals, and the optical loss is then determined via L = 1-R-T. Experiments are performed to measure and map R, T, and L of HR mirrors with different transmittance levels from below 1ppm to about 70 ppm (part-per-million) and of one AR window at 635nm. For a 4 ppm-transmittance HR mirror, the measured R, T, and L at one position are 99.99821 ± 0.00004%, 4.042 ± 0.008 ppm and 13.9 ± 0.4 ppm, respectively. For the AR sample, the measured T, R, and L at one position are 99.99279 ± 0.00004%, 50.0 ± 0.7 ppm and 22.0 ± 0.4 ppm, respectively. The sub-ppm standard deviations for R, T, and L indicate the high accuracy of the two-channel CRD technique for the simultaneous measurements of reflectivity, transmittance and optical loss of HR and AR components. High-resolution mappings of R, T, and L of both HR and AR samples are demonstrated. The simultaneous measurements/mappings of reflectance, transmittance, and optical loss with sub-ppm accuracy are of great importance to the preparation of high-performance laser optics for applications such as gravitational-wave detection and laser gyroscopes.

Mechanisms for optical loss in SOI waveguides for mid-infrared wavelengths around 2 μm

We report the measurement of optical loss in submicron silicon-on-insulator waveguides at a wavelength of 2.02 μm for the fundamental TE mode. Devices were fabricated at IMEC and at A⋆STAR's Institute of Microelectronics (IME) and thus these measurements are applicable to studies which require fabrication using standard foundry technology. Propagation loss for strip and rib waveguides of 3.3 ± 0.5 and 1.9 ± 0.2 dB cm−1 were measured. Waveguide bending loss in strip and rib waveguides was measured to be 0.36 and 0.68 dB per 90° bend for a radius of 3 μm. Doped waveguide loss in rib waveguides was measured for both n-type and p-type species at two doping densities for each doping type. Measured results from propagation, bending, and free-carrier loss were found to be in good agreement with analytical or numerical models. Loss due to lattice defects introduced by ion-implantation is found to be underestimated by a previously proposed empirical model. The thermal annealing of the lattice defects is consistent with removal of the silicon divacancy.

Measurement of optical loss in nanophotonic waveguides using integrated cavities.

Measurement of optical loss in nanophotonic waveguides is necessary for monitoring the properties of integrated photonic devices. We propose a simple method of measuring the optical loss using integrated nanocavities. It is shown theoretically that weak coupling between the waveguide and cavities leads to a direct estimation of the optical loss by measuring light radiated from the cavities. In addition, we experimentally demonstrate the optical loss in a fabricated photonic crystal waveguide. Our method gives not only a degree of freedom in real-time monitoring of the optical properties of nanophotonic structures, but it also can be used for various waveguide-based applications.

Effectiveness of a TCP Conversion Coating at Inhibitiung Corrosion on AA2024-T3 during so2 Atmospheric Testing

Trivalent chromium process conversion coatings are being investigated as alternates for commonly used chromate conversion coatings on aerospace aluminum allloys. In our studies, the TCP coating is formed by immersion on a polished, degreased and deoxidized specimen. The ca. 100 nm-thick biphasic coating consists of a hydrated ZrO2 layer that is about 50 nm thick with an Al-O-F interfacial layer that is also approximately 50 nm thick. Cr(OH)3 is co-deposited within the hydrated ZrO2 layer at less than 5 at. %. There is a need to better understand the mechanisms by which these coatings inhibit corrosion on these alloys and how well the coatings perform during different accelerated degradation tests. In this presentation, we will report on the formation, chemical composition and electrochemical properties of one commercial TCP coating (Bonderite T5900) on AA2024-T3. The corrosion inhibition provided by the coating depends on the coating bath formulation as well as the physicochemical properties (roughness and elemental composition) of the aluminum alloy after degreasing and deoxidation. The coating provides both anodic and cathodic protection by serving as a barrier layer. In terms of the cathodic inhibition, the kinetics of the oxygen reduction reaction are reduced because the coating functions as a diffusional barrier and coating species chemisorb on Cu intermetallic sites to block O2 chemisorption. In this presentation, we will report on the electrochemical characterization of coated and uncoated AA2024-T3 before and after exposure to a 14-day SO2 atmospheric corrosion test (ASTM G87). SEM and EDXS, optical and stylus surface profilometry and weight loss measurements were used to assess the coating peformance. The results show that the TCP coating is stable on the alloy surface during exposure to the SO2/H2O environment and significantly reduces the corrosion damage and metal loss as compared to the uncoated controls.

Multiplexed Hard-Polymer-Clad Fiber Temperature Sensor Using An Optical Time-Domain Reflectometer

Optical fiber temperature sensing systems have incomparable advantages over traditional electrical-cable-based monitoring systems. However, the fiber optic interrogators and sensors have often been rejected as a temperature monitoring technology in real-world industrial applications because of high cost and over-specification. This study proposes a multiplexed fiber optic temperature monitoring sensor system using an economical Optical Time-Domain Reflectometer (OTDR) and Hard-Polymer-Clad Fiber (HPCF). HPCF is a special optical fiber in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An OTDR is an optical loss measurement system that provides optical loss and event distance measurement in real time. A temperature sensor array with the five sensor nodes at 10-m interval was economically and quickly made by locally stripping HPCF clad through photo-thermal and photo-chemical processes using a continuous/pulse hybrid-mode laser. The exposed cores created backscattering signals in the OTDR attenuation trace. It was demonstrated that the backscattering peaks were independently sensitive to temperature variation. Since the 1.5-mm-long exposed core showed a 5-m-wide backscattering peak, the OTDR with a spatial resolution of 40 mm allows for making a sensor node at every 5 m for independent multiplexing. The performance of the sensor node included an operating range of up to <TEX>$120^{\circ}C$</TEX>, a resolution of <TEX>$0.59^{\circ}C$</TEX>, and a temperature sensitivity of <TEX>$-0.00967dB/^{\circ}C$</TEX>. Temperature monitoring errors in the environment tests stood at <TEX>$0.76^{\circ}C$</TEX> and <TEX>$0.36^{\circ}C$</TEX> under the temperature variation of the unstrapped fiber region and the vibration of the sensor node. The small sensitivities to the environment and the economic feasibility of the highly multiplexed HPCF temperature monitoring sensor system will be important advantages for use as system-integrated temperature sensors.

Simultaneous determination of optical loss, residual reflectance and transmittance of highly anti-reflective coatings with cavity ring down technique.

Cavity ring down (CRD) technique was employed to measure optical losses (absorption and scattering losses), residual reflectance and transmittance of anti-reflectively (AR) coated laser components with transmittance higher than 99.9%. By inserting the AR coated laser component with parallel optical surfaces into the ring-down cavity and measuring the ring-down time versus the angle of incidence with respect to the surface normal, the optical loss and residual reflectance of the laser component were determined respectively at normal and out-of-normal incidences with repeatability of part-per-million level. The transmittance was also determined simultaneously. Experimental results demonstrated that CRD is a simple, inexpensive and fast technique for highly accurate measurements of optical loss, residual reflectance, and transmittance of AR coated laser components widely used in high-power laser systems.

On-Wafer Optical Loss Measurements Using Ring Resonators With Integrated Sources and Detectors

We demonstrate for the first time a fully integrated test structure dedicated to on-wafer propagation loss measurement. An integrated light source is used in combination with a resonant cavity and a full absorbing detector. It is fabricated in a multi project wafer run in an InP based foundry process. The probing of the integrated light source and detector with electrical signals avoids the reproducibility issues and time-overhead associated with high-precision optical alignment. The measurement accuracy, estimated to be ~±0.2, the compact footprint (~1.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ), and the simple and fast measurement procedure make this approach an ideal candidate for the future characterization of propagation losses in both research and manufacturing environments.

Interfacing Whispering Gallery Mode Optical Microresonator Biosensors with the Plant Defense Elicitor Chitin

The biomaterial class of chitooligosaccharides (chitin), commonly found in insects and fungi, is one of the most abundant on earth. Substantial evidence implicates chitin in mediating a diverse array of plant cellular signaling events, including the induction of plant defense mechanisms against invading pests. However, these recognition and mediation mechanisms, including the binding kinetics between chitin and their plant recognition receptors, are not fully understood. Therefore, the creation of a platform capable of both interfacing with chitin and plant cell receptors, and monitoring their interactions, would significantly advance our understanding of this plant defense elicitor. Recently, a label-free, highly sensitive biosensor platform, based on Whispering Gallery Mode optical microresonators, has been developed to study such biomolecular interactions. Here, we demonstrate how this unique platform can be interfaced with chitin using simple carbohydrate chemistry. The surface chemistry is demonstrated using X-ray photoelectron spectroscopy, fluorescence microscopy, optical profilometry, ellipsometry, and contact angle measurements. The resulting surface is uniform, with an average surface roughness of 1.25nm, and is active toward chitin recognition elements. Optical loss measurements using standard quantitative cavity analysis techniques demonstrate that the bioconjugated platforms maintain the high performance (Q>106) required to track binding interactions in this system. The platform is able to detect lectin, which binds COs, at 10μg/mL concentration. This biosensor platform's unique capabilities for label-free, high sensitivity biodetection, when properly interfaced with the biomaterials of interest, could provide the basis for a robust analytical technique to probe the binding dynamics of chitin–plant cell receptors.

A high-finesse broadband optical cavity using calcium fluoride prism retroreflectors.

A high-finesse broadband optical cavity has been developed for use in the ultraviolet and visible region using Brewster-angle calcium fluoride (CaF₂) prism retroreflectors. Prior to prism construction, optical loss measurements of CaF₂ windows were performed using cavity ring-down spectroscopy at 250 nm. Total optical loss showed high spatial correlation with crystal birefringence, which was partially mitigated by orienting the <111> crystal axis with the laser beam. Prism reflectivity was measured using cavity ring-down spectroscopy and found to be 99.77% at 250 nm and 99.96% at 500 nm, allowing for relatively high-finesse operation over hundreds of nm bandwidth with a single cavity.

Cold-cavity measurement of optical loss from oxide-confined vertical-cavity surface-emitting lasers

Microcavity laser design and performance optimization requires a quantitative knowledge of the cavity optical losses. A generalized method using sub-threshold spectral measurements matched to model calculations is demonstrated to determine optical loss in microcavity lasers. Cold-cavity spectral characteristics are used to extract the size-dependent optical loss for small diameter oxide-confined vertical-cavity surface emitting lasers. For oxide aperture diameters less than 4 μm, the oxide scattering loss can be greater than 10 cm−1, similar to the typical values of free carrier absorption loss.

Optical characterization of femtosecond laser induced active channel waveguides in lithium fluoride crystals

We successfully realized broad-band light-emitting color center waveguides buried in LiF crystals by using femtosecond laser pulses. The characterization of the waveguides was performed by optical microscopy, photoluminescence spectra, loss measurements and near-field profiling. The experimental results show that the direct-writing fabrication process induces low-index contrast active channel waveguides: their wavelength-dependent refractive index changes, estimated from 10−3 to 10−4 depending on the writing conditions, allow supporting few modes at visible and near-infrared wavelengths.

A novel fiber optic temperature monitoring sensor using hard-polymer-clad fiber and an optical time-domain reflectometer

Hard-polymer-clad fiber is a specific type of optical fiber, in which a hard polymer cladding made of fluoroacrylate acts as a protective coating for an inner silica core. An optical time-domain reflectometer is an optical loss measurement system that provides optical loss and event distance measurement in real time. This study proposes a novel fiber optic temperature monitoring sensor system using an economical optical time-domain reflectometer and hard-polymer-clad fiber. Sensor nodes were economically and quickly made by locally stripping hard-polymer-clad fiber clad through photothermal and photochemical processes using a continuous/pulse hybrid-mode laser. The core length exposed was easily controlled by adjusting the laser beam diameter, and the exposed core created a backscattering signal in the optical time-domain reflectometer attenuation trace. The backscattering peak was sensitive to the temperature variation. Since the elaborated hard-polymer-clad fiber temperature sensor was insensitive to strain applied to the sensor node and to temperature variation in the normal hard-polymer-clad fiber line, neither strain compensation nor isolation technique is required. These characteristics are important advantages for using as structure-integrated temperature sensors. The performance characteristics of the sensor nodes included an operating range of up to 120 °C, a resolution of 1.52 °C, a tensile strain resistance of 13%, and a temperature sensitivity of −0.01 dB/°C.

On the origin and formation of large defect clusters in multicrystalline silicon solar cells

Large defect clusters can represent a serious reduction of the material quality of multicrystalline silicon and the efficiency of the resulting solar cells. It is useful to find the origin of these defect-rich regions in order to understand their formations. For this work, multicrystalline silicon wafers from different positions of a compensated p-type silicon brick were processed to solar cells with a homogeneous emitter and screen-printed metallization. The solar cells from the main part of the brick showed efficiencies between 15.6% and 16.1%. The characterization for this work focuses on the positions of the three largest defect clusters by means of detailed optical, crystal orientation and electrical loss measurements. This allows the localization of the defect clusters' origins during crystallization. The locations where the observed defect clusters started to grow, show similar crystal configurations. This implies that the large clusters formed preferentially at grain boundaries between specific grain orientations. A smaller cluster disappeared at a grain boundary. The characterization showed the same crystal configuration as for the three large growing clusters.

Novel Photo-Defined Polymer-Enhanced Through-Silicon Vias for Silicon Interposers

This paper presents a silicon interposer interconnection solution featuring novel electrical and optical through-silicon vias (TSVs). The copper-based electrical TSVs include polymer-clad TSVs and polymer-embedded vias (copper vias embedded in polymer wells within a low resistivity silicon substrate). Fabrication of the novel electrical TSVs is shown along with high-frequency measurements for polymer-embedded vias. Optical TSVs are fabricated in parallel with the polymer-clad TSVs to provide chip-to-motherboard optical access at the 850-nm wavelength. Optical loss measurements are performed for the fabricated optical TSVs.

Integrated in‐plane mirror and multimode waveguide fabrication using 248 nm excimer laser ablation for optical interconnects on PCBs

PurposeThe purpose of this paper is to present the need, and a potential solution, for in‐plane routing of optical signals for optical‐enabled circuit boards.Design/methodology/approachMultimode waveguides and integrated 45° in‐plane mirror structures were made in a low loss acrylate‐based photopolymer using excimer laser ablation. The fabrication of multimode waveguides and mirrors was carried out in a single laser system which minimised alignment issues.FindingsIt was established that in‐plane mirror fabrication using laser ablation can be achieved and can potentially be used to define mirrors in waveguides made by other methods such as photolithography.Research limitations/implicationsWhile the concept (integrated in‐plane mirror) was demonstrated, the viability of its deployment will depend on the results of optical loss measurements for which further research is required.Originality/valueThe paper gives an overview of the design concept and fabrication steps for an in‐plane embedded mirror.

Electron-beam lithography for photonic waveguide fabrication: Measurement of the effect of field stitching errors on optical performance and evaluation of a new compensation method

A method for stitching error compensation in electron beam lithography by multipass writing of the pattern in the areas spanning the field boundaries is described. This method does not require reducing the write current or changing beam dwell time and was used to correct artificial stitching errors which were deliberately introduced in a layout. SOI-based photonic waveguides with intentional stitching errors of predefined amplitudes and orientation were fabricated. The number of the errors along the waveguides was chosen to produce a measurable optical effect. A corrected version of the same layout was fabricated on the same chip. The optical losses were measured for both the TE and TM polarizations and compared to the results of finite difference time domain simulations. Measurements of optical losses for the waveguides after correction show a clear improvement.