This paper describes improvements that have been made in optical fiber biosensors based on thin films deposited onto the ends of optical fiber waveguides using molecular-level self-assembly processes. The properties of the sensor films may be varied by controlling both the chemistry and the morphology and ordering of the films during their fabrication. For example, multilayer segments of films having different indices of refraction may be deposited to form quarter wavelength stack filters whose reflection properties change as a function of concentration of target chemical that modifies the index of the outermost layer or layers. Prior work has shown that by using different chemicals in the self-assembled layers, correspondingly different target chemicals may be detected. These have included water vapor, ammonia, dichloromethane and others. Improvements have been made in the range of index of refraction that may be achieved in the individual layer segments, specifically over the range of 1.2 to 1.8 at visible and near-infrared wavelengths. This paper shows how such an improvement in index difference influences the minimum detectable chemical concentration difference detectable using this approach.

Cavity enhanced directional resonance has been experimentally observed in single optically-trapped polystyrene particles, which have a size range from 9 μm down to several hundred nm. The higher resonance peaks correspond to longitudinal modes of the directional laser oscillation in a deformed spherical resonator. The lower peaks are attributed to whispering-gallery modes. For a particle with a diameter of approximately 9 μm, the longitudinal mode numbers of the resonator that is responsible for the observed sharp emission peaks are identified using a ray optics model. It is suggested that both directional and whispering-gallery modes can exist in nanometer-scale size resonators. The potential use of such resonant optical cavities in fiber-based optical sensors for chemical diagnostics is suggested. Considerable additional work is required to completely model and measure the observation of effects briefly summarized here.

A glass capillary with inner metal coating is proposed as a high efficiency, soft x-ray optic for medical applications. Based on results of theoretical calculation, for x-ray radiated from conventional x-ray tube, nickel is chosen as a coating material. A nickel-coated capillary is fabricated by using electroless deposition and the focusing and collimating effects are observed from measurement of transmission efficiency of soft x-ray.

Quantification of calculus fragmentation by Er:YAG laser light was experimentally discussed. Er:YAG laser light was delivered to reach a calculus or a model calculus underwater by using a sealed hollow optical fiber. Fragmentation efficiency was obtained for alumina ball used as a model of calculus when sealing caps with various focusing effect were used. Three types of human calculi were analyzed and their absorption properties at the wavelength of Er:YAG laser light were obtained. The relationship among the absorption property, constituents of calculus, and the fragmentation efficiency were also discussed.

Many medical applications have been developed using light sources not only in the visible and near infra-red (NIR) regions, but also in the near ultraviolet (near UV) region of the spectrum. Hard Plastic Clad Silica (HPCS) have found much use in medical applications in general, but generally HPCS fibers are not recommended below 400 nm. Here we will describe HPCS fibers with excellent mechanical reliability and with optical losses of only 1.5 dB/m at 275 nm and less than about 0.2 dB/m at 350 nm. How this combination of properties can benefit diagnostic and surgical applications in the near UV will also be discussed.

For medical and analytical applications, thick-core fibers based on synthetic silica are widely spread. In many cases, the fibers are used as a light-guiding medium only; therefore, the coupling efficiency between the light-emitting area and the accepting fiber is of great importance described easily by the light acceptance cone related to the numerical aperture of the fiber. In the past, all-silica fibers with un-doped silica core and fluorine-doped silica cladding have been used for different applications. However, these fibers are restricted in respect to a low numerical aperture of typically 0.22. To increase the numerical aperture, different polymers can be used for cladding material. In addition to standard polymers, Teflon-AF is an attractive candidate for significantly higher NAs of approx. 0.65. In parallel, a new class of all-silica fibers was developed with high NA, the so-called “Air-clad” or microstructured fibers. Longitudinal microstructured holes, in the order of the wavelength, form the cladding-region together with the surrounding silica. The dimensions of the microstructure dictate the critical angle for light transmission in the core, rather than the refractive index of the cladding material. The light guiding properties of different fibers will be compared. Especially the optical transmission from the UV-region up to the NIR-region will be discussed. Due to the wavelength-dependent mean value of the refractive index (RI) in the cladding, the definition of numerical aperture has to be adjusted. Especially, the UV-damage within Teflon-coated fibers and the microstructured fibers will be described in detail.

A cantilevered singlemode optical fiber is base-excited to create 2D amplitude-modulated resonant motion as a basis for a scanning fiber endoscope (SFE). Over the past few years, prototype SFEs have been developed with smaller sizes of the distal rigid tip which houses the fiber scanner. Our current prototype is 2 mm in diameter with 15 mm rigid length at the tip of a highly flexible shaft. A spiral scan pattern at 40 degrees field of view generates 250 rings (500 lines) at greater than 10 frames per second with negligible distortion at 10 micron resolution. Future SFEs will use microfabrication techniques to sculpt the optical fiber cantilever to form tapered and microlensed tips for the purpose of increasing field of view without increasing electrical power. Microfabrication of complex optical fiber geometries is guided by linear and nonlinear dynamic models of the resonant motion of these fiberoptic scanners. Linear finite element analysis (FEA) is used to match low amplitude motions of tapered and notched fiber geometries, indicating that more flexible regions or hinges can be designed into future fiber scanners for increased amplitude of motion without sacrificing frequency. Nonlinear models of the fiber dynamics are developed and the results help predict the more complex behavior of microfabricated fiber scanners at wider fields of view. Thus, sophisticated fiber dynamics models are used to guide the development of more efficient scanning fiber image acquisition sensors and systems, such as ultrathin flexible SFEs and low-cost sensors.

Computer simulation was used to facilitate the design of fiber-probe geometries which enable enhanced detection of optical signals arising from specific tissue depths. Obtaining understanding of the relationship between fiber-probe design and tissue interrogation is critical when developing strategies for optical detection of epithelial pre-cancers which originate at known depths from the tissue surface. We investigated how the depth of optical interrogation may be controlled through combinations of collection angles, source-detector separations and numerical apertures. We found that increasing the obliquity of collection fibers at a given source-detector separation can effectively enhance the detection of superficially scattered signals. Fiber numerical aperture provides additional depth selectivity; however, the perturbations in sampling depth achieved through this means are modest relative to the changes generated by modifying the angle of collection and source-detection separation.

We propose a chalcogenide glass 1-D photonic bandgap (PBG) hollow fiber for the transmission of mid-IR radiation. Its structure consists of an air-core surrounded by alternating rings of high and low refractive index chalcogenide glass supported by a thick polymer coating. Theoretical calculations demonstrate the potential to achieve low transmission losses at 10.6 μm for the HE₁₁ mode. These calculations indicate that the chalcogenide glasses used in the PBG structure should have high index contrast and low extinction coefficients to minimize transmission losses. We present preliminary results of our ongoing efforts to identify a pair of chalcogenide glasses that meet this criterion. A strategy is developed for the fabrication of a drawable chalcogenide glass 1-D PBG hollow fiber preform.

Microstructured or 'air-clad' fibers, with air holes surrounding a large core, have demonstrated much wider light acceptance angles than conventional fibers. Recently, a new method employing leaky modes has been used to determine the numerical aperture in highly multimode air-clad microstructured fibers. It shows that an exceptionally high NA can only be achieved when bridge thickness is much smaller than the wavelength. The physical basis of these key results is understood in terms of the conditions for efficient excitation of bridge local modes, which radially propagate power into the outer jacket. A number of microstructured polymer optical fibers (mPOF) have been fabricated with a large core suspended by thin supporting bridges. Such mPOFs provide freedom in microstructure geometry, combined with greater mechanical flexibility. This makes them particularly suited to applications demanding high light capture efficiency from broad-beam sources with irregular shapes and in situations involving tight bends. A demonstration of the technology is presented and the measured numerical apertures of these fibres show robust agreement with theoretical calculations over a broad wavelength range.

External and implantable infusion pumps are deployed in an ever widening variety of therapies. These devices are continually driven to increasing accuracy, smaller size, and lower cost. One opportunity for advancement in infusion pump technology is the improvement of closed loop monitoring of the delivery dosage of pharmaceuticals. An optical flow sensor has been designed, developed, and demonstrated based on a non-contact thermal time of flight architecture. The device is a diffraction based sensor. An analytical theory of operation will be presented. Simulations were conducted using a computational model based on heat transfer and computational fluid dymanics combined with diffraction optics calculations. These simulations were corroborated by experimental observations. The sensor has been demonstrated on several prototype platforms, including a prototype using telecommunications devices and packaging technology at a size of 20 mm x 20 mm x 5 mm. Experimental results will be presented demonstrating monitoring of flow rates between 240 nl/sec to 800 nL/sec with accuracies of better than 1% CV.

Endoscopic Erbium laser applications have been limited by the lack of a suitable optical fiber. This study describes a hybrid germanium oxide/silica fiber for transmission of Q-switched and free-running Er:YAG and Er:YSGG laser radiation. Hybrid fibers consisted of a 1-meter-long germanium trunk fiber connected to a 1-cm-long silica fiber tip using PTFE, PET, or PTFE/FEP heat-shrink tubing. Maximum transmission of Er:YAG energy through fiber trunk/tip diameters of 250/365, 350/365, and 450/550 μm were recorded. The transmission rates through 450/550 μm fibers using Q-switched (500 ns) and free-running (300 μs) Er:YAG and Er:YSGG laser pulses were also measured. Maximum free-running Er:YAG pulse energies (fluences) measured up to 103 mJ (98 J/cm²), 112 mJ (107 J/cm²), and 233 mJ (98 J/cm²), respectively, through 250/365, 350/365, and 450/550 hybrid fibers. Free-running Er:YAG and Er:YSGG transmission averaged 56% and 65%, with an attenuation of 1.1 ± 0.1 dB/m and 0.6 ± 0.1 dB/m, respectively, after correction for Fresnel losses (n = 7). Q-switched Er:YAG and Er:YSGG laser transmission averaged 55% and 62%, with an attenuation of 1.1 ± 0.2 dB/m and 0.9 ± 0.3 dB/m, respectively. Both Q-switched lasers transmitted a maximum pulse energy of 13 mJ (n = 7). The germanium/silica fiber is promising for use with the Erbium laser in applications requiring contact laser tissue ablation through a flexible endoscope.

In this paper, a brief review on ultrasensitive fiber optic sensors and their applications, done recently at Penn State, is presented. Our discussions will mainly focus on two types of highly sensitive fiber optic sensors. One type is based on the combination of single resonant band long period gratings (LPGs) with the second refractive index matched polymer cladding layer. The other one is based on the LPGs fabricated in photonic nanostructured fibers and waveguides. It is found that a significantly increased sensitivity (two order plus) can be achieved by harnessing these approaches, which will benefit a variety of applications, in particular, low concentration chemical/biological agents detection.

Sencils (sensory cilia) are chemical sensors that are minimally invasive, disposable and easily readable to make frequent measurements of various analytes in vivo over a period of 1-3 months. A percutaneous optical fiber permits precise, reliable photonic measurement of chemical reactions in a nano-engineered polymer matrix attached to the internal end of the fiber. The first Sencils sense interstitial glucose based on measurement of fluorescence resonance energy transfer (FRET) between fluorophors bound to dextran and Concanavalin-A in a polyethylene glycol (PEG) matrix. In vitro experiments demonstrate a rapid and precise relationship between the ratio of the two fluorescent emissions and concentration of glucose in saline over the physiological range of 0-500mg/dl. Chronic implantation in pigs has demonstrated biocompatibility. The Sencil platform can be adapted to detect other analytes in interstitial fluids.

Chalcogenide glass optical fibers exhibit a large optical transparency in the mid-IR extending typically from 2 to 22 μm for the best compositions. Moreover most of these glasses possess unique thermomechanical properties that enable to shape them into optical fibers exhibiting low optical losses from 2 to about 12 μm. Due to their properties, such fibers can be used to implement remote infrared spectroscopy, known as Fiber Evanescent Wave Spectroscopy (FEWS). The glasses and ceramics Laboratory of Rennes have an active research group on this topic since about 4 years leading to interesting results in several fields of application: environment, biology, medicine ... In this contribution we would like to focus our attention mainly in the technical choices that have been done to obtain these results, for instance the glass composition, the shape of the optical fiber and the abilities of the sensor.

Since the first demonstration in 1990, two-photon fluorescence microscopy (TPFM) has made a great impact on biomedical researches. With its high penetration ability, low out-of-focus photodamage, and intrinsic three-dimensional (3D) sectioning capability, TPFM has been widely applied to various medical diagnosis and genome researches. Recently, single-mode optical fibers were introduced into the TPFM systems for remote optical pulse delivery. Fiber-based TPFM has advantages including isolating the vibration from laser and electronic devices, flexible system design, and low cross-talks. It is also the first step toward an all-fiber based two-photon endoscope. However, due to serious temporal broadening when conventional Ti:sapphire based femtosecond pulses propagate through the fiber, the two-photon excitation efficiency of the fiber-optic TPFM is much lower than the conventional one. The temporal broadening effect mainly comes from group velocity dispersion (GVD) and self-phase modulation (SPM), which also leads to significant spectral broadening. To reduce the temporal broadening effect, here we present a hollow-core photonic-bandgap fiber based TPFM. By replacing the conventional single-mode fiber with the hollow core photonic bandgap fiber, the GVD and SPM effects can be greatly reduced for high intensity, ultra-short pulse delivery. Femtosecond Ti:sapphire pulses passing through the fiber with negligible GVD and SPM effects is demonstrated in this paper. Much improvement of two-photon fluorescence excitation efficiency is thus achieved with the hollow-core photonic-bandgap fiber based TPFM.

We studied optical materials with lower refractive indices than silica, which can be used in fiber optic technology applied to medical devices. The materials were tested for biocompatibility. This paper details the experiment based on USP biocompatibility specifications, its results, and the optical properties of this material.

Patients who have had one oral cancer are at increased risk of developing a semi-malignant tumour. The detecting of oral cancer is made difficult (and is often delayed) by the unknown appearance of the early oral lesion. A technique that could reliably detect early cancers would be useful to the oral and dental health specialist. One possible technique is the use of a photosensitiser that may be preferentially taken up by cancerous cells. 5-aminolaevulinic acid (ALA) is one such drug that is converted to Protoporphyrin IX (PpIX) and fluoresces at 636nm when illuminated with light of wavelength 405nm. It has been hypothesized that cell inclined towards malignant change would have a higher metabolic rate, and thus convert more ALA into its metabolite PpIX. These drugs can then be detected using a technique called Photodynamic detection, through the analysis of their fluorescence spectra. We describe a pilot study that used a compact spectroscopic instrument designed to excite and measure fluorescence in the oral cavity. Some Inter-subject variation in PpIX time course characteristics may be evident in our volunteers, as has been reported by other researchers. The obtained data would suggest that this instrument may be a valuable tool for detecting early oral cancers. However, further studies are required, not least to ensure that these data are due to detection of ALA metabolite in cancer and not some other systemic effect.

Fluorescence- and reflectance-based imaging techniques have a strong potential to improve clinical detection of pathologies such as cervical neoplasia. However, quantitative understanding of data collected by these approaches necessitates information on tissue optical properties in vivo. At present, there is minimal in vivo data on the optical properties of many tissues in the wavelength range that is most relevant -- the ultraviolet A to visible. We report here on the development and evaluation of a second-generation diffuse reflectance system for measurement of tissue optical properties using a linear-array fiber optic probe with maximum separation distance of 2.5 mm. Improvements over the prior system include the implementation of an imaging spectrograph, a high sensitivity CCD camera and in-line neutral density filters to maximize dynamic range and signal to noise ratio. Absolute measurements of tissue reflectance were enabled through calibration of the reflectance system. Multivariate calibration models for optical property prediction were generated using a neural network algorithm and reflectance distributions calculated by a Monte Carlo model. Spatially-resolved reflectance data sets were measured in well--characterized tissue phantoms at 405 nm for absorption coefficients (μ_a) from 1 to 25 cm^-1 and reduced scattering coefficients (μ_s') from 5 to 25 cm^-1. These models were used to estimate the optical properties of tissue phantoms from reflectance measurements. By comparing predicted and known optical properties, the average percent error for μ_a and μ_s' was found to be ± 3.2% and ±5.6%, respectively. These results indicate a level of accuracy that is more than twice that of our prior approach.

The application of specially designed delivery system consisted of cyclic olefin polymer coated silver hollow glass waveguide (inner/outer diameter 700/850 μm) with protector in one side and sealed cap in the output is shown for treatment of ureter wall perforation by Er:YAG laser radiation. For this purpose Er:YAG laser system (wavelength 2.94 μm) working in free-running and Q-switched regime was utilized. The basic characteristic of the interaction of Er:YAG laser radiation with the ureter surface and its deep structures was found. Maximum interaction pulse energy and length in free-running regime were 100 mJ and 200 μs, respectively (corresponding intensity 130kW.cm^-2). Maximum interaction pulse energy and length in Q-switched regime were 30 mJ and 70 ns, respectively (corresponding intensity 111 MW.cm^-2). From the histological evaluation it follows that the application of Q-switched Er:YAG laser radiation on ureter tissue resulted in minimum tissue alteration without any influence on the deeper layers.

Hollow glass waveguide is one of a few instruments for the delivery of mid-infrared laser light favored in industrial and medical fields. The article summarizes delivery of the Er:YAG laser radiation (λ = 2.94 μm) by the cyclic olefin polymer coated silver hollow glass waveguides with different inner waveguide diameters (320 μm, 700 μm, 1 mm). For the medical applications, the so called "contact mode" in which the end of the waveguide is in contact with the soft or hard tissues is discussed. Delivery of free-running and Q-switched mid-infrared pulses was investigated.

The proposed optical fiber biosensor is used to study the qualitative and quantitative aspects of biomolecular recognition in real time. This approach is able to apply for measuring the association and dissociation rate constants of the reaction between biomolecules.

In this article a new medical application is introduced using textile production techniques to deliver a defined radiation dose. The advantage for photodynamic therapy (PDT) is that a flat luminous textile structure can homogeneously illuminate unequal body surfaces. The optical properties of this two-dimensional luminous pad are characterized with a set of bench-scale tests. In vitro investigations on petri dishes with cultivated cells and first clinical tests on animal patients are promising. In addition first measurement results are presented together with an outlook to future developments.

Chalcogenide fibers are shown to exhibit a hydrophobic surface behavior which results in detection enhancement for organic species in aqueous solutions. We use these fibers to monitor the infrared signature of human lung cells and detect the presence of toxic agents in the cell surrounding media. The signal is collected using a fiber evanescent wave spectroscopy set up with live human cells acting as a sensitizer for detection of minute quantities of toxicant. A monolayer of human alveolar epithelial cells form strong attachment at the surface of the fiber sensing zone and live in contact with the fiber while their IR spectra is collected remotely. Biochemical change in the living cells are detected during exposure to toxic agents. Variations in the spectroscopic features of the cells are observed in different spectral regions. Finally, the toxicity of Te₂As₃Se₅ fibers is investigated.