Physical and optical properties of optical fibers have improved over recent years significantly. Especially classic UV detection techniques in traditional chemistry, HPLC and dissolution testing rely more and more on fiber optic light guiding techniques to transport light to and from a sample simplifying the design of such detection techniques. An overview on the current status of UV-fiber optical properties will be given in this work. Especially, the reduction of UVdefects in the 215 nm wavelength region leading to a lower drift in the whole system, will be discussed. However, these are not the only parameters of interest in a fiber-optic system. For process control or instrumental analytics, the long-term stability including drift and noise must be determined. This requires stringent fiber test procedures similar to light-sources, connectors and complete detector systems. Further, white-light interference between optical interfaces of a fiber optic detection system due to axial movement, degradation of components and temperature often reduces system stability and must be considered. Finally, a cleaning-in-process of a fiber optic immersion probe will be introduced as a further step of system improvement.

A new tag-free photonic resonance concept occurring on subwavelength waveguide gratings is applied for rapid medical testing applications. These high-resolution sensors operate in real time while being sensitive to a wide variety of analytes, including microbials. This method does not require extensive processing steps, thus simplifying assay tests and enabling a rapid response (less than 30 minutes is possible). In this work, a sensor system that uses a single, fixed-wavelength source with a shaped input wavefront to auto-scan in angle has been developed. As binding events occur at the sensor surface, shifts in a resonance reflection peak (or a corresponding transmission minimum) are tracked as a function of incident angle. The amount of angular shift is correlated to the quantity of analyte in the test sample. Due to inherent polarization diversity, two narrow peaks shift their positions on the sensor surface when a bioreaction occurs, thereby providing cross-referenced data. The sensor system connects to portable interfaces for data acquisition and analysis by dedicated software codes. A portable guided-mode resonance sensor system prototype has been developed. Its performance for the detection of the microbial S. aureus in buffer and rat serum is presented in this paper.

A Nanoporous glass matrix is developed to encapsulate molecular probes for monitoring important biological parameters such as DO. The hydrophobic nanoporous host matrix is designed and fabricated using room temperature sol gel technique. The doped sol gel is then coated on biocompatible self adhesive patches or directly coated on the biocontainers. We demonstrate the application of this technique in non-invasive monitoring DO as well as oxygen partial pressure in a closed fermentation process as well as in a cell culture plate during bacterial growth. Dynamic response of sensor, sensitivity and accuracy is also demonstrated in this paper.

We report the fabrication and the characterization of perfluorinated cladded multimode polymer optical fibers tapers. The fibers employed was a graded-index polymer optical fibers with core and cladding diameters of 62.5/90 and 120/160 and very low refractive index (nCore = 1.356, nCladding = 1.342). The tapers were fabricated using the heat-and-pull technique. This approach permits a good prediction of the taper shape and waist dimension. Despite to the fact that taper core is not in direct contact with the external medium, these fiber tapers can be used for sensing applications. In fact, some of the guided modes are no more confined in the core region but can still be guided by the fiber in the cladding region. Therefore, there is an evanescent wave in the external medium, related to bound and tunneling rays that can pass the taper region in the cladding. In particular, the very low refractive indexes of the core-cladding perfluorinated polymers permit a strong enhancement of the power fraction in the evanescent wave in aqueous environments (n=1.33). We carried out experiments evanescent wave spectroscopy by immerging the tapered fiber water containing a dissolved organic blue dye (Methylene blue) for a concentration range 5e-8-1e-5 M.

This study aims to develop a minimal invasive photothermal imaging method to determine the oxygenation level of an internal tissue. In this method, the tissue is illuminated using an optical fiber by several wavelengths in the visible and the near IR range. The absorption of the illuminated radiation causes an increase in the tissue's temperature which is observed by a thermal camera through a coherent waveguide bundle in the mid-IR range. Analyzing the temperature rise allows estimating the tissue composition in general, and specifically the oxygenation level. This system will enable to measure the saturation on superficial tissues as well as within body cavities through a commercial endoscope. A theoretical model of this problem was implemented to help design the experimental setup and develop the experimental procedures. A curve-fitting algorithm is used to find the most suitable saturation value affecting the temperature function. The estimated saturation was calculated on different simulated model parameters and was in good agreement with the simulated saturation value.

In the present work an all-fiber optic confocal microscope with submicron depth resolution is reported. The operation of the microscope is based on the principle of back reflectance of propagated light from the target in a curve-shaped step-index multimode optical fiber. Modulation of the back-reflected light with axial displacement of the target is monitored using a photodiode (PD). The advantage of the system is its simplicity and possibility of remote monitoring. An axial displacement of minimum 0.5 μm can be detected within the focusing depth with the present work.

We present the design and fabrication of an implantable fluorescence biosensor suitable for continuously monitored, freely-moving in vivo rodent studies. The GaAs-based semiconductor sensor incorporates an un-cooled photodetector with a 670nm vertical-cavity surface-emitting laser (VCSEL) optimized for sensing fluorescent Cy5.5 dye. For filtering unwanted spectra, a combination of physical and spectral blocking layers yields OD5 excitation rejection at the detector. The sensor detects near-IR fluorescent Cy5.5 molecules in vitro at 100nM concentration (in a 100μL volume) with linear response for concentrations up to 25μM. In a preliminary study in a living mouse, subcutaneously injected dye (1μM Cy5.5 in 50μL) was detected. This technology has the potential to enable new studies of living systems in applications that require long-term, continuous fluorescence sensing.

Fiber-optic-based confocal microscopy has been extensively used as an effective imaging and sensor technology due to its submicron spatial resolution, flexible beam delivery, and scanning potential. Recent research efforts in confocal microscopy have been focused on improving the resolution, increasing the imaging speed, and adapting multi-photon modalities. Here, we present our recent research studies on various advanced confocal fiber-optic imaging and sensing approaches using the following novel confocal methods. First, we investigated an all-fiber-optic confocal interference microscope approach using a low-coherence near-infrared (1310 nm) light source. A signal-to-noise ratio (SNR) enhancement of 3.38 dB compared to a reflection-mode confocal microscope was observed. The use of a low-coherence light source reduced the interference effects between various optical components, and an all-fiber-optic, robust and compact confocal setup could be designed. Second, we experimentally investigated a single-fiber confocal microscope approach using a hollow-core photonic bandgap fiber. The single-fiber hollow-core structure reduced the back-reflection by 85% which enhanced the SNR. The measured lateral resolution was as high as or better than 0.78 μm when a 532-nm laser source was used. Third, we explored a novel upconversion confocal microscope approach utilizing a continuous-wave near-infrared (1550 nm) pump light source. An Erbium-doped glass powder was used as an upconversion phosphor medium that emits an upconverted signal at 660 nm. Using this upconversion fiber-optic confocal microscope method, high resolution images with a lateral resolution close to theoretical limits were obtained.

A hollow core waveguide (HCW) with silver nanoparticles (SNPs) coated on the inner wall has been demonstrated for molecular detection based on surface enhanced Raman scattering (SERS). With rhodamine 6G (R6G) as an analyte molecule and two types of silver nanoparticles (SNPs) as double SERS substrates, the inner wall coated HCW (IWCHCW) exhibits significantly higher sensitivity than previous fiber SERS probes with only one SERS substrate. Two kinds of HCW are used in the experiment, liquid core photonic crystal fiber (LCPCF) and hollow silica waveguide (HSW). SERS signal obtained with either an LCPCF or a HSW IWCHCW is over ten times that obtained in direct detection using a single SERS substrate. The improvement of the SERS sensitivity is attributed to the additional enhancement of the electromagnetic field by the double SERS substrate "sandwich" structure with one substrate coated on the inner wall of the HCW and the other mixed in the sample solution. Furthermore, With an LCPCF IWCHCW, the SERS signal is around 100 times as strong as that in direct detection when measured from the processed fiber tip. This is attributed to the additional R6G/SNPs solution in the fiber pit, increased coupling efficiency due to surface plasmon resonance in the SNPs in the same region, and further increased electromagnetic field in the same region due to nano-structures introduced during the collapse of the cladding holes. The simple architecture and high sensitivity of the inner wall coated HCW make it promising for molecular detection in various analytical and sensing applications.

As a continuation of our earlier study at 2.1 μm wavelength, we have investigated the laser damage to several types of step-index, large core (1500 μm) silica fibers at two new wavelengths by high power long pulsed Nd:YAG (1064 nm) and Alexandrite (755 nm) lasers. It was observed that fibers with different designs showed a significant difference in performance at these wavelengths. We will also report a correlation of damage to the fibers between the two laser wavelengths. The performance analyses of different fiber types under the given test conditions will enable optimization of fiber design for specific applications.

Transmission characteristics of infrared hollow fiber with multi- AgI and SiO₂ films are discussed. Three-dielectric-layer hollow glass fiber with SiO₂/AgI/SiO₂/Ag structure was fabricated for low-loss delivery of infrared laser light. The first SiO₂ film on the silver layer was coated by using liquid phase coating method. A semi-inorganic polymer was used as the coating material. A smooth vitreous film was formed by the treatment of a hardener at room temperature and followed by curing treatment. For the deposition of the AgI film between the two SiO₂ films, an Ag film was first plated on the SiO₂ film by silver mirror reaction method. Then the iodination process was conducted to turn the silver layer into silver iodide. The second SiO₂ layer was deposited on the AgI layer in the same way as the first SiO₂ layer. Fabrication parameters for controlling film thicknesses, such as iodination temperature, silver mirror reaction time, and solution concentration, are clarified for depositing AgI and SiO₂ films with the theoretical optimum thicknesses. By optimizing the thickness of the three dielectric layers, low-loss in the loss spectrum of SiO₂/AgI/SiO₂/Ag hollow glass waveguides can be obtained at the target infrared wavelengths. A method is proposed to evaluate the film thickness of AgI layer based on the positions of loss peaks and valleys in the loss spectra. Theoretical calculation for loss spectrum of SiO₂/AgI/SiO₂/Ag hollow glass fiber considering material dispersion of dielectric materials is also conducted. Good agreement with the measured data is demonstrated.

Advanced application of Er:YAG laser radiation in medical treatment requires a suitable, very precise delivery of this light to a target. In some cases (urology, cardiology, or endodontic treatments), thin waveguides are needed. Therefore a preliminary investigation was conducted with 250/360 μm inner/outer diameter hollow glass waveguides. The waveguide has inner coating made from cyclic olefin polymer and silver layers. All delivery systems were simple and consisted of lens, protector, and the waveguide. The laser source was the Er:YAG system working in a free-running regime and generating radiation at 2.94 μm wavelength. For testing, output laser energy up to 100 mJ with a repetition rate of 1 Hz was chosen. The output laser spatial profile was approximately TEM00 mode, so the structure changes behind the delivery system were readily detected. The energy delivery characteristics were also checked, and the transmission reached 77%. The maximum input fluence into the waveguide was 200 mJ/cm², and no significant damages to waveguides were observed after the measurements.

We have demonstrated the use of a double-clad fiber probe to conduct two-photon excited flow cytometry in vitro and in vivo. We conducted two-channel detection to measure fluorescence at two distinct wavelengths simultaneously. Because the scattering and absorption problems from whole blood were circumvented by the fiber probe, the detected signal strength from the cells were found to be similar in PBS and in whole blood. We achieved the same detection efficiency of the membrane-binding lipophilic dye DiD labeled cells in PBS and in whole blood. High detection efficiency of green fluorescent protein (GFP)-expressing cells in whole blood was demonstrated. DiD-labeled untransfected and GFP-transfected cells were injected into live mice and the circulation dynamics of the externally injected cells were monitored. The detection efficiency of GFP-expressing cells in vivo was consistent with that observed in whole blood.

In this study, we proposed a new approach to make a low-cost, high-pressure and easy-to-made fiber optic pressure sensor for human disc pressure measurement. The principle of this sensor is based on Fresnel reflection equations. The sensor is sealed in a 25G needle (500 micron outer diameter), and coated with a thin film on the tip of the sensor. The developed system is capable of measuring pressure up to 10 bar.

We hypothesize that in the presence of reduced oxygen delivery and extraction, blood flow will be redistributed in order to protect the most vital organs (e.g., brain and heart) by increasing their regional blood flow, while O₂ delivery to the less vital organs (e.g., GI tract or urethral wall) will diminish. Evaluation of mitochondrial function in vivo could be done by monitoring the oxidation reduction state of the respiratory chain. Thus, the NADH redox state of less vital organs could serve as an indicator of overall O₂ imbalance as well as an endpoint of resuscitation. We have therefore tested, in a pig model, a new medical device providing real time data on NADH redox state and tissue blood flow- TBF This device contains a modified three way Foley catheter with a fiber optic probe which connects the measurement unit to the tested tissue. Female pigs underwent graded hemorrhage (GH) or Aortic clamping (AC). The main effects of GH started when blood volume decreased by 30%. At 40% blood loss, minimal levels of TBF were correlated to the maximal NADH levels. The values of the 2 parameters returned to baseline after retransfusion of the shed blood. Aortic clamping led to significant decrease in TBF while NADH levels increased. After aortic declamping the parameters recovered to normal values. Due to the short length of the urethra in female pigs and the instable contact between the probe and the tissue, inconsistency of the responses was observed. Our preliminary results show that the CritiView may be a useful tool for the detection of body O₂ imbalance.

In practice, complete removal of the tumor during a lumpectomy is difficult; the published rates of positive margins range from 10% to 50%. A spherical lumpectomy specimen with tumor directly in the middle may improve the success rate. A light source placed within the tumor may accomplish this goal by creating a sphere surrounding the tumor that can serve as a guide for resection. In an optical phantom and a prophylactic mastectomy specimen, sinusoidally modulated light within the medium was collected by optical fiber(s) at fixed distance(s) from the source and used to measure the optical properties. These optical properties were then used to calculate the distance the light had traveled through the medium. The fiber was coupled to an 830nm diode laser that was modulated at 100, 200 and 300 MHz. A handheld optical probe collected the modulated light and a network analyzer measured the phase lag. This data was used to calculate the distance the light traveled from the emitting fiber tip to the probe. The optical properties were μ_a = 0.004mm^-1 and μ¹_s = 0.38mm^-1 in the phantom. The optical properties for the tissue were μ_a = 0.005mm^-1 and μ¹_s = 0.20mm^-1. The prediction of distance from the source was within 4mm of the actual distance at 30mm in the phantom and within 3mm of the actual distance at 25mm in the tissue. The feasibility of a frequency domain system that makes measurements of local optical properties and then extrapolates those optical properties to make measurements of distance with a separate probe was demonstrated.

Hollow fiber with internal metal and dielectric coating films is one of the promising media for THz transmission. Although the dielectric layer can effectively reduce the transmission loss, it brings additional loss due to its absorption. It has been shown in mid-infrared region that the optimum thickness of the dielectric layer becomes smaller due to absorption. For terahertz hollow fibers, the film thickness of the dielectric layer become much larger and the transmission characteristics are more dependent on the dielectric absorption. The influences of dielectric absorption on the structure parameters of the dielectric-coated metallic hollow fibers are discussed. Calculation results show that the optimum refractive index of the dielectric layer, which is 1.41 for perfect transparent dielectrics, turns out to be greater. The absorption tolerance is also investigated considering the factors of inner diameter, the refractive index, and the transmission wavelength. It is shown that absorption tolerance decreases when the inner diameter becomes smaller or when the transmission wavelength becomes larger. In extreme cases of small inner-diameter or large transmission wavelength, the absorption tolerance is not existent. Because the loss of the dielectric-coated metallic hollow fiber is larger than that of metallic hollow fiber even the dielectric layer has no absorption. The calculation results are helpful to the structure design and material selection in the fabrication of terahertz hollow fibers.

The use hollow core waveguides (HCW's) in biomedicine includes two different tasks: Power delivery in order to facilitate clinical procedures and measurement of beam parameters in order to sense the surrounding tissue and create a diagnosis. To study the interaction between light and waveguide a computer simulation of ray propagation inside a HCW was developed. The simulation is based on the statistical method of Monte Carlo repeated trials and of ray tracing optics. The simulation accounts for both meridional and skew rays, rough fiber surface, Imperfect reflection, arbitrary fiber geometry and the insertion of absorbing molecular clusters inside the fiber lumen for sensing purposes. Here we test skew rays. At first the effect of skewness on the number of wall hits and the optical distance is investigated. Then different beam profiles are tested to fulfill different tasks: Sensing and power delivery. The role of skew rays in each scenario is discussed.

We present a new fibre optic breathing/movement sensor for in-bed non-intrusive monitoring. The light is modulated through microbending effect during breathing/body movement. The sensing system consists of optical transmitter, optical receiver, a sensor sheet, and a computer. An algorithm was developed to extract body movement signals and report breathing rate and information on body movement of bedded person. The breathing rate measurement system shows an accuracy of +/-1 breath, which has been successfully demonstrated in field trial (FusionWorld).

Vitreous film based on the structural unit R₂SiO, where R is an organic group, is newly used as the reflection layer in the hollow optical fiber for CO₂ laser delivery. A smooth vitreous film is formed at room temperature by using the liquid-phase coating technique. The vitreous film-coated silver hollow optical fibers achieve low-loss property for lasers in the infrared regions by properly selecting fabrication conditions. A hollow fiber with thicker vitreous film designed for CO₂ laser light showed acceptable loss as an output tip. It is shown that the hollow tip is of high durability to withstand several cycles of autoclave sterilization.

Hard tissues are irradiated with combined beam of Er:YAG and Ho:YAG lasers to achieve highly efficient ablation with lower laser power. We controlled the delay time between pulses of the two lasers and irradiated alumina ceramic balls that are used as hard tissue samples. By optimizing the delay time, the combined laser beam provides 40% higher perforation depth compared with the result with independent radiation of Er:YAG or Ho:YAG laser. The ablation mechanism are observed and investigated by using an ultra-high-speed camera and infrared thermography camera.

The optical property of the ball lens mounted hollow optical fiber Raman probe (BHRP) is studied in the present study. Since the ball lens has rather large aberration, the focus of the BHRP is dispersed and the spatial resolution in depth direction goes low. The spatial dispersion of the focal point was evaluated using model samples. The BHRP equipped a sapphire ball lens of 500 μm diameter was employed. Layered samples consisting of a polymethyl methacrylate (PMMA) substrate and various thicknesses of polyethylene (PE) films were measured with the BHRP. The relative band intensities of the upper and the lower layers appear at different rates in the obtained spectra, reflecting the optical properties of the probe. According to the spectra, the optical dispersion of the focal point is estimated. The result suggests that the spatial dispersion of the focus point fitted to Gaussian distribution. The working distance (WD) is 53 μm and the FWHM of the fitted Gauss distribution is 64 μm.

Mitral valve regurgitation (MR) is a condition in which heart's mitral valve does not close tightly, which allows blood to leak back into the left atrium. Restoring the dimension of the mitral-valve annulus by percutaneous intervention surgery is a common choice to treat MR. Currently, this kind of open heart annuloplasty surgery is being performed through sternotomy with cardiomyopathy bypass. In order to reduce trauma to the patient and also to eliminate bypass surgery, robotic assisted minimally invasive surgery (MIS) procedure, which requires small keyhole incisions, has a great potential. To perform this surgery through MIS procedure, an accurate computer controlled catheter with wide-range force feedback capabilities is required. There are three types of tissues at the site of operation: mitral leaflet, mitral annulus and left atrium. The maximum allowable applied force to these three types of tissue is totally different. For instance, leaflet tissue is the most sensitive one with the lowest allowable force capacity. For this application, therefore, a wide-range force sensing is highly required. Most of the sensors that have been developed for use in MIS applications have a limited range of sensing. Therefore, they need to be calibrated for different types of tissue. The present work, reports on the design, modeling and simulation of a novel wide-range optical force sensor for measurement of contact pressure between catheter tip and heart tissue. The proposed sensor offers a wide input range with a high resolution and sensitivity over this range. Using Micro-Electro-Mechanical-Systems (MEMS) technology, this sensor can be microfabricated and integrated with commercially available catheters.

Large core multimode fibers (MMF) in the range of 100-1000 μm core diameter are commonly used with infrared lasers in medical, bio-photonics and other fiber optics applications. Angular misalignment of the laser source to the multimode fiber can lead to unusual angular patterns at the exit of the fiber. The angular content of the launch beam can result in under-filling, non-uniform angular filling, or over-filling of the MMF modes. Typically, the beam condition optics at the distal end of the device has a limited impact on these angular modes. The result is often loss of output power at the distal end or an uncontrolled angular and/or spatial distribution of light. We have investigated angular misalignment perturbations of various fiber and coupling optics combinations in a medical laser therapy device. We have quantified the resulting far field perturbations, as well as the resulting broadening of the fiber output numerical aperture (NA). Angular misalignment may cause the development of so called "donut modes" with highly inhomogeneous far field mode distribution, as well as a substantial NA broadening effect which may impact therapy. We have shown that in order to avoid these perturbations, tight tolerancing of fiber coupling opto-mechanics as well as a thorough alignment procedure is required.