Fiber Optic Assembly Research Articles

Monolithically integrated two-axis microgripper for polarization maintaining in optical fiber assembly.

Polarization maintaining optical fiber (PMOF) is a kind of special optical fiber that is designed to transmit the linearly polarized light. Unlike the general optical fiber, it is critical to conduct the rotational alignment between two PMOFs to guarantee the efficiency of light transmission. Until now, this alignment task still cannot be addressed with an efficient and economical way. Hence, we propose a monolithically integrated two-axis flexure-based microgripper that has the grasping and rubbing functions. To achieve a compact structure, the microgripper is designed with an asymmetric architecture. In this paper, the pseudo-rigid body model approach and finite element analysis are conducted to provide the essential guideline to accomplish the theoretical design. The prototype is fabricated by wire electrical discharge machining, with which two experiments are conducted to validate the performance of the microgripper. The experimental results demonstrate that the proposed microgripper can firmly grasp the optical fiber with the diameter of 250 μm and meanwhile can rub it more than 90° accurately and effectively, which indicate that it can satisfy the operating requirements well in the PMOF assembly.

Fourier transform optical profilometry using fiber optic Lloyd's mirrors.

A fiber optic Lloyd's mirror assembly is used to obtain various optical interference patterns for the detection of 3D rigid body shapes. Two types of fiber optic Lloyd's systems are used in this work. The first consists of a single-mode optical fiber and a highly reflecting flat mirror to produce bright and dark strips. The second is constructed by locating a single-mode optical fiber in a v-groove, which is formed by two orthogonal flat mirrors to allow the generation of square-type interference patterns for the desired applications. The structured light patterns formed by these two fiber Lloyd's techniques are projected onto 3D objects. Fringe patterns are deformed due to the object's surface topography, which are captured by a digital CCD camera and processed with a Fourier transform technique to accomplish 3D surface topography of the object. It is demonstrated that the fiber-optic Lloyd's technique proposed in this work is more compact, more stable, and easier to configure than other existing surface profilometry systems, since it does not include any high-cost optical tools such as aligners, couplers, or 3D stages. The fringe patterns are observed to be more robust against environmental disturbances such as ambient temperature and vibrations.

Interlaced photoacoustic and ultrasound imaging system with real-time coregistration for ovarian tissue characterization.

Coregistered ultrasound (US) and photoacoustic imaging are emerging techniques for mapping the echogenic anatomical structure of tissue and its corresponding optical absorption. We report a 128-channel imaging system with real-time coregistration of the two modalities, which provides up to 15 coregistered frames per second limited by the laser pulse repetition rate. In addition, the system integrates a compact transvaginal imaging probe with a custom-designed fiber optic assembly for in vivo detection and characterization of human ovarian tissue. We present the coregistered US and photoacoustic imaging system structure, the optimal design of the PC interfacing software, and the reconfigurable field programmable gate array operation and optimization. Phantom experiments of system lateral resolution and axial sensitivity evaluation, examples of the real-time scanning of a tumor-bearing mouse, and ex vivo human ovaries studies are demonstrated.

Coherent fiber bundle based integrated photoacoustic, ultrasound and fluorescence imaging (PAUSFI) for endoscopy and diagnostic bio-imaging applications

Recent research in diagnostic imaging and sensing focuses on deriving complementary information from the diagnosed site. From that perspective it is imperative to devise new imaging platforms where multiple distinct modalities are used either simultaneously or sequentially. Increased efforts have been devoted towards establishing such multi-modal imaging systems, which house and operate more than two imaging modalities within a single instrumentation set-up. In this context, we propose a novel multi-modal imaging platform using non-ionizing radiation that has been successfully conceptualized, established and experimentally demonstrated. This proposed GRIN lensed fiber-optic microscope and linear array transducer based PAUSFI (photoacoustic, ultrasound and fluorescence imaging) system makes use of non-ionizing radiation sources to map optical and acoustic heterogeneities (complementary information) along the depth of the tissue at multi-scale resolution (microscopic to mesoscopic). The fiber-optic assembly enables the system to perform minimally invasive remote light delivery and high resolution fluorescence and photoacoustic imaging of inaccessible areas of intact tissues or intra body cavities. It is expected that the proposed multi-modal imaging system could open up niches in bio-imaging research in the near future.

Reliable Measurements of UV Lamp Performance Using a Near-Field Technique

Low pressure mercury arc lamps are an effective ultraviolet light source for disinfection of water. Critical lamp operating parameters such as the decrease in UV output with time, effect of water temperature on lamp output, and the effect of lamp dimming should be determined using a lamp in water. The reliable operation of a near-field test apparatus is described that is capable of measuring these quantities. The use of a radiometer with fiber optic light collection and standard reference lamp results in the reproducible measurement of these values using the near-field system. The stability of measurement is obtained using the reference lamp, which compensates for variations in the response of the fiber optic assembly. For sample lamps, a decrease of 11% output over 12,000 hours was observed. For the same lamp type, the relative calibrated output of the lamp increases between 5 and 50°C, with a ±10% change in lamp output relative to the reference temperature of 20°C. The apparatus samples the irradiance at a local point on the lamp, but the UV output of low pressure amalgam lamps as determined by the near-field technique is shown to be uniform over the entire lamp, except for within 1 cm of the lamp filament. This is shown for both new and 12,000 hour aged lamps, so that accurate lamp aging data can be determined. The change in UV output with water temperature change was demonstrated to be similar for both new and aged lamps in this study, except for the expected decrease in peak lamp UV output noted for the aged lamp.

Optical polishing equipment

Optical grinding and polishing plays an important role when optimizing the quality of an imaging system or minimizing unwanted reflections in a fibre-optic assembly.

Remote Continuous Wave and Pulsed Laser Raman Detection of Chemical Warfare Agents Simulants and Toxic Industrial Compounds

This study describes the design, assembly, testing and comparison of two Remote Raman Spectroscopy (RRS) systems intended for standoff detection of hazardous chemical liquids. Raman spectra of Chemical Warfare Agents Simulants (CWAS) and Toxic Industrial Compounds (TIC) were measured in the laboratory at a 6.6 m source-target distance using continuous wave (CW) laser detection. Standoff distances for pulsed measurements were 35 m for dimethyl methylphosphonate (DMMP) detection and 60, 90 and 140 m for cyclohexane detection. The prototype systems consisted of a Raman spectrometer equipped with a CCD detector (for CW measurements) and an I-CCD camera with time-gated electronics (for pulsed laser measurements), a reflecting telescope, a fiber optic assembly, a single-line CW laser source (514.5, 488.0, 351.1 and 363.8 nm) and a frequency-doubled single frequency Nd:YAG 532 nm laser (5 ns pulses at 10 Hz). The telescope was coupled to the spectrograph using an optical fiber, and filters were used to reject laser radiation and Rayleigh scattering. Two quartz convex lenses were used to collimate the light from the telescope from which the telescope-focusing eyepiece was removed, and direct it to the fiber optic assembly. To test the standoff sensing system, the Raman Telescope was used in the detection of liquid TIC: benzene, chlorobenzene, toluene, carbon tetrachloride, cyclohexane and carbon disulfide. Other compounds studied were CWAS: dimethylmethyl phosphonate, 2-chloroethyl ethyl sulfide and 2-(butylamino)-ethanethiol. Relative Raman scattering cross sections of liquid CWAS were measured using single-line sources at 532.0, 488.0, 363.8 and 351.1 nm. Samples were placed in glass and quartz vials at the standoff distances from the telescope for the Remote Raman measurements. The mass of DMMP present in water solutions was also quantified as part of the system performance tests.

CCD detectors for molecular absorption spectrophotometry. A theoretical and experimental study on characteristics and performance

Uncertainty in charge-coupled devices (CCDs) as UV-vis spectrophotometric detectors is studied here considering that it highly affects the limit of detection of analytical methods. Opposite to photomultiplier-type detectors (PMDs) and diode-array detectors (DADs), where uncertainty is mainly dependent on the photonic signal (shot noise), in CCD detectors uncertainty may come from both independent and dependent effects upon the photonic signal. Shot noise is specially important for high photonic signals in the detector (those for low absorbances) while the uncertainty that is independent of the signal is specially important for low photonic signals in the detector (those for high absorbances). That is, the main source of uncertainty is different depending on the value of the experimental measurement. On the other hand, temperature does not practically affect absorbance measurements, though it is very important for emission measurements (fluorescence, Raman, scattering, etc.). Mathematical equations for uncertainty are proposed with excellent fittings to the experimental data. The equation parameters can be experimentally determined from non-linear regression analysis and used to characterize spectrometers or to test their performance. In order to help buyers and users, some recommendations are finally given considering, among others, cooling, slit, attenuator or fiber optic assemblies.

Acquiring reproducible fluorescence spectra of dissolved organic matter at very low concentrations

A method that would allow for fast and reliable measurements of dissolved organic matter (DOM), both at low and high concentration levels would be a valuable tool for online monitoring of DOM. This could have applications in a variety of areas including membrane treatment systems for drinking water applications which is of interest to our group. In this study, the feasibility of using fluorescence spectroscopy for monitoring DOM at very low concentration levels was demonstrated with an emphasis on optimizing the instrument parameters necessary to obtain reproducible fluorescence signals. Signals were acquired using a cuvette or a fibre optic probe assembly, the latter which may have applications for on-line or in-line monitoring. The instrument parameters such as photomultiplier tube (PMT) voltage, scanning rate and slit width were studied in detail to find the optimum parameter settings required. The results showed that larger excitation and emission slit widths were preferred, over larger PMT voltage or lower scanning rates, to obtain reproducible and rapid measurements when measuring very low concentration levels of DOM. However, this approach should be implemented with caution to avoid any reduction of the signal resolution.

A NADH-dependent fiber-optic biosensor for ethanol determination with a UV-LED excitation system

A fluorometric fiber-optic biosensor for ethanol determination was constructed and tested. An ultraviolet light emitting diode (UV-LED) was used as a fluorescence excitation source for nicotinamide adenine dinucleotide (NADH). The use of a UV-LED conferred the advantages of low power consumptions and the potential for portable application. The biosensor consists of a UV-LED based portable excitation system (λ=340nm), fiber optic spectrometer and an optical fiber probe with an alcohol dehydrogenase immobilized membrane. These instruments were connected using a Y-shaped optical fiber assembly. According to the experimental assessment, the power consumption was reduced to one percent of general UV light source. The measurement system was useful for 1.00–300μmolL−1 of NADH. EtOH measurement test was also carried out. The wide calibration range of the EtOH biosensor was 0.10–100.00mmolL−1, with high selectivity versus other chemical substances. The biosensing system is simplified and miniaturized by use of LED in compare with previous methods. For this advantage, the biosensing system is expected to be used for point-of-care testing applications or daily health care tests.

Focus on spectroscopy

Focus on spectroscopy

Material behavior uncertainty in the design of bonded systems – Part II: Exhaustive materials characterization and design guidelines

Uncertainties in the performance of engineering systems arise due to idealizations of geometry, material behavior, and loading history. Uncertainties in the geometry are often related to manufacturing processes, while the uncertainty in the material behavior often arises out of materials processing. In this two-part study, we analyze the effect of uncertainty in material behavior on the performance of bonded assemblies in general, but motivated by the example of a fiber-optic system. In the fiber-optic system, the motion of the surface emitting laser relative to the substrate (to which the laser is bonded) due to the viscoelsatic behavior of the bond epoxy causes a loss in the light coupled to the fiber. In the first part of the paper, we develop models to describe the shear displacement and the shear stress in bond layer of the fiber-optic assembly. In the second part, we characterize through extensive experimentation the uncertainty in the viscoelastic behavior of the bond epoxy and use it to develop guidelines for the design of the bonded system.

Material behavior uncertainty in the design of bonded systems – Part I: Shear displacement and stress prediction

Uncertainties in the performance of engineering systems arise due to idealizations of geometry, material behavior, and loading history. Uncertainties in the geometry are often related to manufacturing processes, while the uncertainty in the material behavior often arises out of materials processing. In this two-part study, we analyze the effect of uncertainty in material behavior on the performance of bonded assemblies in general, but motivated by the example of a fiber-optic system. In the fiber-optic system, the motion of the surface emitting laser relative to the substrate (to which the laser is bonded) due to the viscoelastic behavior of the bond epoxy causes a loss in the light coupled to the fiber. In the first part of the paper, we develop models to describe the shear displacement and the shear stress in bond layer of the fiber-optic assembly. In the second part, we characterize through extensive experimentation the uncertainty in the viscoelastic behavior of the bond epoxy and use it to develop guidelines for the design of the bonded system.

A microchip sensor for calcium determination

A newly designed glass-PDMS microchip-based sensor for use in the determination of Ca(2+) ions has been developed, utilizing reflectance measurements from arsenazo III (1,8-dihydroxynaphthalene-3,6-disulfonic acid-2,7-bis[(azo-2)-phenyl arsenic acid]) immobilized on the surface of polymer beads. The beads, produced from cross-linked poly(p-chloromethylstyrene) (PCMS), were covalently modified with polyethylenimine (PEI) to which the Arsenazo III could be adsorbed. The maximum amount of Arsenazo III which could be immobilized onto the PEI-attached PCMS beads was found to be 373.71 mg g(-1) polymer at pH 1. Once fabricated, the beads were utilized at the detection point of the microfluidic sensor device with a fiber optic assembly for reflectance measurements. Samples were mobilized past the detection point in the sensor where they interact with the immobilized dye. The sensor could be regenerated and re-used by rinsing with HCl solution. The pH, voltage, linear range, and the effect of interfering ions were evaluated for Ca(2+) determination using this microchip sensor. At the optimum potential, 0.8 kV, and pH 9.0, the linear range of the microchip sensor was 3.57 x 10(-5) - 5.71 x 10(-4) M Ca(2+), with a limit of detection (LOD) of 2.68 x 10(-5) M. The microchip biosensor was then applied for clinical analysis of calcium ions in serum with good results.

Monitoring some liquid cladding layer properties using LED beam transmittance coefficients through the fiber itself

We report work on the adaptation of a conventional optical fiber assembly to monitor the properties of liquid. An LED 1 1 Of the type (SY-02), retrieved from a child's toy. was used in conjunction with a home-made fiber cell fitted with glass fiber rods to monitor some of the physical properties of liquid samples. The technique discriminates between different liquids using their light transmittance ability as cladding layer to the glass fiber. Discrimination between liquids according to their transmission coefficients is partly dependant on refractive index of liquids; therefore, samples were also tested with a refractometer for comparison. Results show that the technique is superior to the refractometer in distinguishing between liquids of different indexes.

Determination of lead in environmental water by a backward light scattering technique

An optical fiber assembly developed in our laboratory, which is based on detecting backward light scattering (BLS) signals, is now applied to detect the lead content in environmental samples. Due to effectively eliminating the interference of reflected light, this BLS signals based detection assembly can be used to determine analyte directly. In HAc–NaAc buffer medium (pH 4.8), the interaction of lead and sodium tetraphenylboron (TPB) in the presence of polyethylene glycol (PEG) yields large particles of ternary complex, resulting in strong enhanced backward light scattering (BLS) signals characterized at 371 nm. By measuring the BLS signals with the homemade optical fiber assembly coupled with a common spectrofluorometer, we found that the enhanced BLS intensity is proportional to lead content over the range of 0.03–1.0 μg ml −1 with the limit of determination (LOD) of 2.6 ng ml −1. Three artificial water samples containing various coexistent substances were detected with the recovery of 90.1–107.5%. Standard addition method was used to detect the lead content in drink tap water, and found that the lead is hardly to detect due to too low content. Prior enrichment should be made in order to detect river water samples, and it was found that the content of lead in Jialing River at Bebei Dock is about 14 ng ml −1, identical to the results using inductively coupled plasma atomic emission spectrometry (ICP-AES).

High-speed high-reflectance-resolution reflectometry by synthesis of optical coherence function

A novel high-speed optical reflectometry with high-reflectance-resolution is demonstrated by synthesis of optical coherence function for diagnosis of optical fiber assembly modules. In this new scheme, the optical frequency of a laser source is modulated doubly: one in sinusoidal wave to synthesize a coherence peak scanning along the fiber under test for distributed reflection/scattering measurement, the other in linear sweep to make the wavelength domain averaging optically for high reflectance resolution. Experimental results show that a reflection-distribution profile with reflectance-resolution better than 0.1dB can be obtained within 1 minute with this method.

Laser cleaving of glass fibers and glass fiber arrays

An ultraviolet (UV)-excimer-laser-based cleaving procedure for silica fiber has been developed that enables automated cleaving for high-volume production of fiber-optic assemblies. A selective ablation of the glass in the form of a small rectangular cavity serves as a fracture initiator when the fiber is put under stress. The position of the UV-excimer-laser-induced scratch is very precise. The system provides high-quality cleaves on single-fiber and ribbon configurations. The end angle of the cleaved optical fiber is measured using a noncontact optical interferometer system and was 0.85/spl deg/ for perpendicular cleavages. Insertion loss after splicing is in the range of 0.03 dB, which is compatible with mechanical-cleaved fibers.

Photostimulator allowing independent control of rods and the three cone types

This report describes a second-generation photostimulator with four primary lights that allows independent control of the stimulation of the four receptor types in the human eye. The new design uses LEDs (with light levels controlled by eight drivers that include voltage-to-frequency converters that provide 1-micros pulses at frequencies up to 250 kHz), with four center channels being combined by use of a fiber optic assembly, and likewise for four surround channels. Four fiber optic bundles are merged into a single bundle whose output is fed into a spatial homogenizer terminated by a diffuser. An interference filter is sandwiched between each LED and the fiber optic bundle. Two camera lenses collimate light from the diffusers, one for center and one for surround. The center-surround field configuration is formed by a photometric cube with a mirrored ellipse on the hypotenuse. A field lens places images of the diffusers in the plane of an artificial pupil. The fields are highly uniform. Following alignment and calibration, the center and surround fields are indistinguishable. An observer calibration procedure, designed to compensate for prereceptoral filtering, is shown by calculation to correct also for normal observer receptoral spectral sensitivity variation. With the instrument calibrated for the individual observer, a peripherally fixated 200-ms 40% contrast rod center field pulse, highly conspicuous under dark adaptation, is invisible following light adaptation.

Lead-free universal solders for optical and electronic devices

Widely used electronic components and optical materials are made up of a variety of inorganic materials, such as nitrides, carbides, oxides, sulfides, fluorides, selenides, diamond, silicon, and GaAs. The surfaces of these materials are known to be very difficult to bond with low-melting-point solders. A direct and powerful bonding on these surfaces has been obtained in air, without using any flux, by using low-temperature solders containing rare earth (RE) alloying elements. The nature of the bonding is based on chemical reactions at the interface, and hence, strong bonds are obtained. The Sn-3.5%Ag-2.5%Lu (by weight) solder and the Au-19.5%Sn-2%Lu solder, for example, exhibit interfacial-bond strengths in excess of 6.9–13.8 MPa. They can be useful for providing direct, ohmic-electrical contacts and interconnects in a variety of electronic assemblies and for producing dimensionally stable and reliable bonding in optical fiber, laser devices, or thermal-management assemblies.