Glass and glass fibers formed from rare earth (RE) oxide-aluminum oxide compositions (REAlTM glasses) have properties similar to sapphire. They exhibit infrared transmission to wavelengths ~ 5000 nm; are hard and strong, thermally stable to ~ 1000°C, highly resistant to attack by aqueous solutions; and can be made into homogeneous products that contain large concentrations of optically active dopants. This paper describes the synthesis, optical properties, fluorescence lifetime measurements of Er³⁺- and Ho³⁺-doped glasses, and in-progress resaerch on materials that emit in the 2000-3000 nm wavelength range of interest for medical device applications. Effects of host glass compsition and dopant concentrations up to 32 mole% are presented.

A novel and simple noninvasive sensor techniquefor simultaneous measurement of refractinve-index and thickness of both optically transparent and non-transparent media is presented. It is a fiber-optic confocal-microscope-type sensor technique based on either a single-confocal or a combined dual-confocal fiber-optic design. The single-confocal design is a single-fiber, intensity sensing arrangement that provides precise spatial location of the backreflecting sample surfaces and bi-parameter measurements. The combined dual-confocal design includes two independent confocal channels consisting of two identical apertureless fiber-optic-type confocal microscopes constructed by use of a single 2×2 fiber coupler. This sensor arrangement provides direct measurement in absolute unites of refractive-index and thickness of optically transparent and non-transparent media.

We describe a phase sensitive optical low coherence reflectometer using polarization maintaining optical fiber with high lateral, longitudinal and phase resolution for biomedical applications. The system utilizes three sample path configurations (i.e. single beam, lateral beams, and longitudinally delayed channels) and allows investigation of various topics in biomedical research. Applications include measurement of birefringence change, intensity and phase imaging, refractive index measurements, surface analysis, and measurement of solute concentrations.

The recent development of flexible hollow waveguides for MID-IR lasers may be utilized transendoscopically to ablate selectively neoplastic, superficial tissues within body cavities. Study goals are to investigate theoretically and experimentally heat distribution and thermal response of cavity lining, during CO₂ laser Minimally Invasive Surgery (MIS), and to thermally optimize the procedure under practical conditions. Mathematical model was developed to predict temperature distribution along cavity lining during and after the irradiation. Experimental setup was built, including all the necessary components for a fully feedback-controlled MIS (CO₂ laser, hollow waveguide, suction, insufflation, electrical regulators, cavity-like phantoms, IR camera, Labview application). Thermal images of cavity lining were recorded and analyzed throughout varying conditions. Thermal gradients were obtained mathematically and experimentally. Diverse modes of heat dispersions were observed, as wel as the relative contributions of user-controlled parameters to the maximal heat of cavity lining. The software-controlled setup has demonstrated instant adaptivity to manage varying conditions, by which it automatically protects cavity lining from getting overheated. Analytical predictions and experimental measurements were highly correlated. The software-controlled systme may serve a powerful tool to control thermal side effects during MIS within body cavities.

Our goal is to produce a micro-optical scanner at the tip of an ultrathin flexible endoscope with an overall diameter of 1 mm. Using a small diameter piezoelectric tube actuator, a cantilevered optical fiber can be driven in mechanical resonance to scan a beam of light in a space-filling, spiral scan pattern. By knowing and/or controlling the fiber position and acquiring backscattered intensity with a photodetector, an image is acquired. A microfabrication process of computer-controlled acid etching is used to reduce the mass along the fiber scanner shaft to allow for high scan amplitude and frequency. A microlens (<1 mm diameter) is fabricated on the end of the optical fiber to reduce divergence of the scanned optical beam. This added mass of the microlens at the free end of the fiber causes the location of the second vibratory node to shift to near the focal length of the microlens. The result is a microlens undergoing angular rotation along two axes with minimal lateral microlens displacement. Preliminary experimental results indicate that this method of optical beam scanning can deliver laser energy over wide fields of view (>50 degrees full angle), up to video scan rates (>10 KHz), while maintaining a scanner diameter of 1 mm. A comparison can be made to bi-axial mirror scanners being fabricated as a MEMS device (micro-electro-mechanical system). Based on the opto-mechanical performance of these microlensed fiber scanners, flexible catheter scopes are possible for new microendoscopies that combine imaging with laser diagnoses.

Medical IR laser systems involving a beam delivery cable based on holow optical fibers are introduced. Two types of the systems are developed to cover a wide range of medical applications: one with a CO₂ laser which is mainly for soft tissue ablation and another wiht an Er:YAG laser for ablation of hard tissue in dental applications. The both systems which have been recently commercialized newly adopted a hollow glass fiber having inner metal and polymer films. Because of the high mechancial and chemical stability, flexibility, and the low production cost of the fibers, a reliable and easy-to-handle medical laser systems are launched at low cost. The components of the systems including the beam delivery cable and distal tips specialized for various medical applications are described in detail.

Calculi fragmentation experiments were conducted in vitro by using Er:YAG laser light. The laser light delivery system was composed of a cyclic olefin polymer (COP)-coated silver (Ag) hollow fiber and a quartz cap to seal the output end of the hollow fiber. Sealing-caps wiht various distal end goemetries were fabricated and the focusing effects for Er:YAG laser light were measured both in air and in water. Fragmentation characteristics of the sealing-caps were investigated. The deterioration of sealing-caps after calculus fragmentation was also experimentally discussed.

A fluorescence confocal microendoscope has been developed to provide high resolution, in-vivo imaging of cellular pathology. The microendoscope employs a fiber-optic imaging bundle, a miniature objective, and a miniature focusing mechanism to allow imaging in remote locations of the body. The system uses a 2mm diameter flexible catheter that is capped by a rigid opto-mechanical system measuring 3mm in diameter and 12mm in length. The small size of the confocal microendoscope was chosen so that it may be routed through the therapeutic channel of a clinical endoscope, adding microscopic functionality to conventional endoscopy procedures. The confocal nature of the microendoscope provides optical sectioning with 2 micron lateral resolution and 25 micron axial resolution. The pneumatic focusing mechanism located in the distal opto-mechanical assembly allows for imaging to a maximum depth of 200 micron in the tissue. The system is capable of providing conventional grayscale fluorescence images at 10 frames-per-second as well as spatially resolved multi-spectral fluorescence images at several seconds a frame. Preliminary in-vivo results are be presented.

Hollow glass fibers for delivery of mid-infrared lasers are drawn from a glass-tube preform to produce a long and flexible hollow fiber at low cost. To utilize the interference effect of the thin glass wall, the wall thickness is controlled by the drawing speed. A Pyrex-glass hollow fiber with an inner diameter of 280 micron and a wall thickness of 9.92 micron shows a low loss at 2.94 micron of the Er:YAG laser wavelength when coated with a silver film on the outer surface.

Since more than 2 decades, the polymer optical fiber (POF) based on PMMA is well known. A lot of applications were studied and initiated: in addition to data transmission, the automotive, lighting and sensor applications are of main interest. Due to the spectral attenuation and applications, light-sources like broadband metal-halide lamps and halogen lamps, or LEDs and laser-diodes are mainly used. Due to improvement in manufacturing of the standard step-index POF, the variations of the spectral attenuation in the blue region have been reduced. Therefore, the losses are acceptable for short-length applications in the UV-A region. Using different light-sources like high-power Xenon-lamp, deuterium-lamp or UV-LEDs, the UV-damage is an important factor. In addition to the basic attenuation, the UV-induced losses will be determined by experiment, in the interesting UV-A region. The higher flexibilty of the thick-core POF is superior in comparison to silica or glass fibers with the same outer diameter. Therefore, the bending losses in the UV-region are important, too. For special applications in the medical field, side-illuminating fibers are highly accepted. The axial and spectral dependence on the lateral radiation pattern will be described, using a very thick fiber.

During the last years we developed a flexible beam guiding system for DUV-laser radiation (λ=193 nm, 213 nm). This laser scalpel is based on hollow core waveguides and special fused silica optical fibers. We were able to demonstrate the feasibility of the laser scalpel to ablate biological tissues and technological materials. Our current interest is to develop a thinner scalpel tip which consists of 200 μm optical fibers instead of 600 μm fibers. The performance of these thin fibers was evaluated. We developed a computer controlled measurement system to study the optical fiber performance in dependence on laser fluence, laser intensity, laser repetition rate and fiber coupling conditions. We also investigated the long term behavior of the modified optical fibers for the laser scalpel.

Metal sulfide dielectric thin films have been deposited using dynamic wet chemistry processing on silver coated hollow glass waveguides (HGWs). Metal sulfides like cadmium sulfide (CdS) and lead sulfide (PbS) possess excellent optical properties in the IR and have high refractive index contrast. A linear growth regime with deposition time has been observed for CdS and PbS thin films on Ag inside silica hollow glass waveguides. The thickness of these thin films can be tailored to minimize the attenuation of the HGW at the operating wavelength. We have made single dielectric metal coated HGWs using CdS and PbS. This paper discusses the processing and characterization of the thin films and the resulting dielectric metal coated hollow glass waveguides.

Hollow silica waveguides with internal reflective coatings of silver and silver iodide were tested for optical performance after continuous exposure to 125°C for up to 1300 hours in air. The waveguides were evaluated periodically for mechanical degradation, optical spectral loss, optical loss in bending, and CO₂ laser power transmission. The waveguides were found to survive the extended high temperature exposure both mechanically and optically. Mechanically, the internal reflective coatings show no visible signs of deterioration or delamination from the silica tubing substrate. Optically, the waveguides exhibited 1dB/m increase in attenuation at both the 10.6μm and 2.9μm wavelengths for the CO₂ and Er:YAG optimized waveguides, respectively. In optical loss in bending, the CO₂ optimized waveguides exhibited a 0 -2 dB loss for one 360°, 40cm diameter bend at 10.6μm. The Er:YAG optimized waveguide exhibited higher variability in optical loss in bending and requires further study to determine the true bend loss. The CO₂ optimized waveguides were also tested for CO₂ (10.6μm) laser power transmission. The change in CO₂ laser optical loss pre to post thermal aging was (formula available in book). The post aging waveguides were also shown to transit up to 90W output of CO₂ power with no indication of degradation of the internal reflective coatings.

To date, biomedical applications of spectroscopic sensors operating in the mid-infrared spectral region are rarely reported. Among them only few refer to hollow waveguide based infrared sensor technology focusing almost exclusively on spectroscopic gas sensing applications. However, improved sensor technology and availability of compact laser light sources (e.g. quantum cascade lasers) along with suitable waveguides (e.g. hollow waveguides), leads to promising perspectives in biomedically relevant areas of application including breath analysis and gas/air monitoring. Furthermore, efficient light guiding of hollow waveguides enables flexible power delivery for surgical applications. Recently it has been demonstrated that the combination of hollow waveguide based IR sensors with membrane extraction modules extends this concept to liquid phase analysis of volatile organic compounds. Highly efficient lightguiding properties along with considerably low attenuation losses in the mid-infrared (MIR, 3-20 μm) spectral range and a high damage threshold make hollow waveguides particularly useful for these applications. The hollow core of the fiber simultaneously acts as miniature low-volume gas cell while guiding infrared radiation efficiently from the light source to the detector. By coupling radiation either from a laser light source or from a Fourier transform infrared (FT-IR) spectrometer into the waveguide and focusing the beam at the distal end of the hollow waveguide onto a detector, compact gas sensor systems can be realized. Due to the excitation (molecular vibrations and rotations) of analyte molecules present inside the hollow fiber core, intimate interaction of IR radiation with gaseous analytes for spectroscopic investigation with high molecular specificity is ensured. Using quantum cascade lasers emitting in the mid-infrared spectral region provides bright light sources enabling detection limits in the μg/L (ppb) concentration range, which is required for biomedical applications in breath analysis and air monitoring.

A new nitric oxide (NO) sensor is intended for use in assessment of airway inflammation with applications in asthma diagnosis and management as well as in other health care applications involving inflammation in the gastrointestinal tract and the urogenital organs. The sensor was designed to measure trace quantities of NO in air using the combination of hollow optical waveguides and quantum cascade lasers. The primary application intended is analysis of exhaled breath. The unique marriage of the components and the novel design provides for rapid response to concentration changes while maintaining sensitive measurement capabilities. We achieved a lower detectable limit of 58.8 ppb of NO in N2 with a 0-90% response time of 0.48 s. The QC laser was operated at room temperature in pulsed current mode near 5.4μm. The hollow waveguide used to make these measurements was 9m in length and the inside diameter was 1000μm. The waveguide was coiled with a 15cm radius of curvature and perforated on the interior walls of the coils to allow gas to flow into and out of the waveguide. The sensor can easily be converted to measure other gases in the midinfrared by selecting a QC laser whose output is coincident with the absorption line of interest.

In the DUV-region and MIR-region, the so-called Hollow-Core-Waveguide is an alternative for light-delivery systems, because flexible silica-based fibers are no lnoger useable due to the high intrinsic absorption of silica. In additionl to light-transportation, only the HCW can be used as an intrinsic sensor: due to the long path-length through the HCW with similar intensity profiles at the input and output, the spectral absorption of the gas under test can easily be monitored. Up to now, the gases are analyzed in the MIR-region, mainly. However, the UV-region offers a lot of advantages. Using commercially available components for the UV-light source and the detector-system, the whole system with UV hollow-core-waveguides has to be studied in the wavelength-region from 170 nm up to 350 nm. With this experimental system, it is obvious to observe the UV-absorption of air and carbon dioxide below 200 nm, using nitrogen as a reference gas. In addition, ozone generated by the deuterium-lamp itself and several gas mixtures (e.g. 2 ppm toluene or xylene in cabon dioxide) were studied in detail.

Prior computational investigations indicate that the origin of signals detected during fluorescence spectroscopy is highly dependent on illumination-collection geometry. The present study was undertaken to provide experimental validation of trends noted in these prior studies. Two-layered tissue phantoms were constructed using agarose gels doped with Intralipid and either Fluorescein or Rhodamine to achieve biologically relevant levels of scattering and easily measurable levels of fluorescence. The effect of fiber diameter, fiber-sample spacing, and fiber-fiber spacing were investigated using single and multi-fiber probes. Increases in diameter and fiber-sample spacing for single fiber probes resulted in improved detection of the deeper fluorophore layer, as did an increase in illumination-collection fiber spacing in multi-fiber probes. As multi-fiber probe-sample spacing was increased, an increase in relative contribution from the superficial layer, followed by a subsequent reversal of this trend, was measured. Each of these results is in qualitative agreement with prior simulations, thus providing further evidence of the utility of numerical modeling as a tool for elucidating light-tissue interactions and device design. Furthermore, the trends noted here have the potential to form the basis of systems which determine the distribution of tissue fluorophores and/or target specific tissue layers, thus leading to improvements in the efficacy of optical diagnostics.

A novel optical heterodyne surface plasmon resonance (SPR) biosensor using Zeeman laser is proposed. There are two surface plasma waves (SPWs) being excited by two correlated P polarized waves in an SPR device of Kretschmann configuration. The two reflected P waves are optically heterodyned so that the amplitude of the heterodyned signal is proportional to the multiplication of two attenuated reflected P waves. The detection sensitivity and the dynamical range based on this amplitude sensitive method are enhanced. In the experiment, the kinetics between mouse IgG and anti-mouse IgG is obtained according to the sensograms of different concentrations of anti-mouse IgG. The detection sensitivity corresponding to 0.2 nM is achieved. In addition, a concentration of 5 ng/ml of protein G interacting with mouse IgG is measured successfully.

Recent developments in fiber-optic sensor technology have demonstrated the utility of fiber-optic sensors for both medical and industrial applications. Fiber sensors based on fluorescent decay of rare earth doped materials allow rapid and accurate temperature measurement in challenging environments. Here we review the principles of operation of these sensors with a rare earth doped probe material and demonstrate why this material is an excellent choice for these types of sensors. The decay time technique allows accurate temperature determination from two measurements of the fluorescence intensity at a well-defined time interval. With this method, all instrumental and extraneous environmental effect will cancel, thus providing an accurate temperature measurement. Stability data will be presented for the fiber-optic probes. For medical applications, new breakthroughs in RF ablation technology and electro-surgical procedures are being introduced as alternative, less invasive treatment for removal of small tumors and for removal of plaque within arteries as a preventive treatment that avoids open heart surgery. The availability of small diameter temperature probes (230 microns or 450 microns in diameter) offers a whole new scope to temperature measurement. Accurate and reliable temperature monitoring during any laser treatment procedure or RF ablation at the surgical site is critical. Precise, NIST traceable reliable results are needed to prevent overheating or underheating during treatment. In addition, how interventional catheters are used in hyperthermia studies and the advantages to having flexible cables and multiple sensors are discussed. Preliminary data is given from an animal study where temperature was monitored in a pig during an RF study.

We report recent developments in the design and fabrication of molecularly self-assembled thin film materials that may be incorporated with optical fiber waveguides to form humidity and other gas sensors of use in biomedical diagnositc systems. Optical fiber distal end sensors based on this concept may be fabricated by molecularly self-assembling selected polymers and functionalized inorganic nanoclustesr into multilayered optical thin films on the cleaved and polished flat ends of singlemode optical fibers. Prior work reported at this meeting has studied the synthesis process and sensor dynamics, including sensor 10-90% risetime on the order of microseconds. This paper briefly reviews that work but then reports new developments in the synthesis of the sensor films.

For the purpose of the ophthalmology treatments a special hollow waveguide based delivery instrument was developed. It consists of a 2 m long cyclic olefin polymer coated silver hollow glass waveguide (inner diameter 700 μm) and the special cap allowing the contact of the waveguide with the wet eye tissues. The transmission characteristics for a delivery of a mid-infrared Er:YAG radiation (2.94 μm) was measured. Then the pre-clinical interaction experiments of the Er:YAG laser radiation with the eye tissue (cornea, lens, and sclera) were performed with this delivery instrument. A comparison of two types of interactions results - the action of Er:YAG free running - 40 μs long pulses and giant 450 ns long pulses were made. The human eye tissues (in vitro) were cut and samples (cornea, lens, and sclera) were gradually irradiated by the mid-infrared radiation with the energy of 7 mJ (the corresponding spot size diameter was equal ~ 700 μm). The laser energy density used in this experiment was 1.8 J/cm². From results it can be concluded that the giant pulses are more efficient in the ablation of the cornea, they are comparable with the free-running long pulses in the case of lens grinding, and they are less functioning for the sclera perforation. As concern the hollow waveguide delivery system, it has been proved that the energy delivered by this system was sufficient and suitable in both cases for delivery of long - free-running pulses, and short - giant pulses as well.

Due to increasing number of requirements dealing with the application of a high energy mid-infrared radiation in various branches of medicine (cardiology, dentistry, dermatology, urology, gastroenterology), an enough flexible and lossless delivery system is required. For a transport of this high energy pulses in a mid-infrared region special cyclic olefin polymer-coated silver (COP/Ag) hollow glass waveguides were prepared and tested. A length of the waveguides was 0.5 m and inner diameter 1 mm. As a radiation source, an Er:YAG laser was used. The system generated the energy up to 2.16 J or 2.35 J (in dependence on a repetition rate used - 3 Hz or 4 Hz, respectively). The length of transmitted pulses was measured to be from 110 up to 550 usec in dependence on output energy used. The output radiation was coupled into the COP/Ag waveguide and a throughput and losses values were measured in dependence to input radiation parameters. The transmission obtained was 91%. The maximum delivered energy was dependent on a damage threshold of the waveguide. It was found that the damage threshold is dependent on the repetition rate which shows the dependences on the heat dissipated in the waveguide wall. The value of the damage was 1.7 J and 1.5 J for 3 Hz and 4 Hz repetition rate, respectively. The safe delivered power reached the value of 5 W. The characteristics obtained make this specially constructed COP/Ag hollow glass waveguide promising for the delivery of high-energy laser pulses in medicine and also in other applications.

So far we have shown, through various preliminary imaging experiments with small-animal ankle’s and human finger’s joints both healthy and joint-diseased, that early diagnosis for joint disease such as rheumatoid arthritis (RA) is feasible using a transillumination laser CT. For a practical purpose, we have recently proposed and developed a transillumination laser CT imaging system using optical fibers based on the optical heterodyne detection method for a clinical use. In the proposed system, motion-artifact free images can be obtained because measurements can be performed with the object fixed. In addition, use of fiber-optics enables portability, and robustness against environmental changes in a room, such as variable temperature, air-flow shifts, and unexpected vibrations. The imaging system has the following sensing properties: spatial resolution of 500 μm, a dynamic range of approximately 120 dB, and a minimum-detectable-optical power of 10^-14 W as a result of the excellent properties of the heterodyne detection technique. In the present paper, we describe a prototype laser CT imaging system using optical fibers for early diagnosis of joint disease such as rheumatoid arthritis by demonstrating the first in vivo tomographic image of a volunteer’s index finger joint as well as the fundamental imaging properties.

Rare earth doped silica based fiber lasers and amplifiers have been shown to be suitable for a variety of applications in industry, science and medicine. They can yield very high power output both in the pulsed and cw regime with high efficiency, reliability and beam quality. Great progress was possible by new design concepts as non-symmetric double clads and large mode area guiding structures and by carefully tailoring the material properties. Extreme power load and complicated fiber structures make high demands on the preparation technology. Special aspects of material and technology development will be discussed in the following. Basic requirement for a successful production of defined fiber core compositions is the knowledge of the incorporation mechanism of the rare earths into the high silica matrix. Diffusion processes during the preparation steps determine refractive index distribution, geometry and numerical aperture. Strong concentration dependences of codopants and the interaction between codopants and active components must be taken into account. The optical properties of rare earths ions can be tailored by defined codopant relations according to the intended application. Some unusual basic loss contributions of certain rare earths have to be considered and controlled in order to get high laser performance. Loss effects by UV radiation play a role if UV cured coatings are used or if the fibers are provided with Bragg gratings as laser mirrors.