The TeX glass fibers, with high flexibility and relatively low losses, have been developed for many applications especially carbon-dioxide laser power transmission and radiometry. The use of TeX glass fibers to transmit thermal radiation of an object to a remote detector allows temperature measurements, without contact, in inaccessible and hostile environments. The TeX glass fiber sensor can detect temperatures in a wide range [minus 20, 200 degrees Celsius] with a resolution estimated better than 0.2 degrees Celsius at high temperature (200 degrees Celsius) and close to 1 degree Celsius at room temperature. The transmission of carbon-dioxide laser beam through a TeX glass fiber has been performed. More than 2.6 W have been obtained through a 1 meter long fiber by injecting the maximum input power of 6 W at the wavelength of 9.3 micrometer. TeX glass fibers are very promising for biomedical applications such as welding which require an energy transfer through the fiber and a temperature monitoring by another fiber.
AMI is engaged in a number of programs to produce infrared transmitting fiber and lenses using AMTIRR materials, for commercial and military purposes. Through adaptation of Computer Engineering Services (author's prior company) conventional silicate glass extrusion technology, it is possible to fabricate fire polished rods and tubes of virtually any cross-sectional geometry. Diameters between about 3 mm and 75 mm and lengths as great as 1000 mm have been achieved. Extrusion is similar in many respects to fiber optic draw technology and requires precise control of feed and draw parameters, via the use of microprocessor systems. Internal homogeneity of the starting material is completely retained. This paper discusses the effort to date and describes product applications.
During the last 15 years, numerous programs have been carried out in the U.S., UK, France, Japan, Israel and Russia aimed at providing a flexible chalcogenide glass fiber suited for delivery of power from a carbon dioxide laser emitting at 10.6 micrometer. The success of these programs has been modest at best with output power limited to 10 watts or less. The purpose of this paper is to examine chalcogenide glasses used for fiber from a thermal lensing standpoint.
A new type of flexible hollow waveguide made of polyimide was developed. Mechanical bending and flexibility of the polyimide was changed and brought to be similar to that of Teflon hollow waveguide using a plastic sleeve. The optical characteristics of this new waveguide were studied and it was shown that high power (up to 25) Watts of carbon-dioxide laser radiation can be delivered. The delivered power remained constant for more than 150 seconds, which shows that the polyimide waveguides may be suitable for applications in medicine, where the requested maximum delivered power is about 20 Watts. Transmission (T) as a function of bending (1/R), where R is the radius of curvature, has shown that very strong bending may be obtained (R greater than or equal to 4 mm) without damage to the waveguide. Also demonstrated was the importance of angle, in addition to the radius of bending. The measurements of divergence of delivered beam was small (approximately 10-3), which is comparable with those obtained for core fibers. Beam profile measurements have shown that the shape and mode distribution of the delivered radiation from waveguide are similar to that delivered by the coupled carbon-dioxide radiation. The measured value of maximum accepted incident angle of the beam on the internal wall of the waveguide was about 12 degrees which is larger than of silica and Teflon waveguides.
We report transmission properties of two kinds of robust bent hollow stainless steel (St) waveguides whose inner surface is coated by the thin silver (Ag) and fluorocarbon- polymer (FCP) layers. The bore size of the waveguides is 700 micrometer and all types of waveguides have been fabricated based on the liquid phase process, i.e., the process of silver mirror reaction for the silver layer and liquid flow- coating method for the fluorocarbon polymer layer. Measurements have been conducted for the fixed bent FCP- coated Ag hollow St waveguides with the length of 3 cm and the bending angles of 20 and 70 degrees, respectively for Er:YAG laser light. It turned out that the losses of 0.8 dB and 0.7 dB have been attained for the above 20 degree and 70 degree structures, respectively. As the St tube itself has the very robust structure and high heat conductivity compared with the corresponding glass hollow waveguide, the waveguide devices proposed in this paper will open a new application in medicine.
Hollow waveguides have been well characterized for their optical properties, but many applications require long-term reliability as well as short-term performance. The average strength and the strength distribution of hollow glass waveguides (HGWs) have been evaluated. In addition, the effects of processing on waveguide strength have been assessed. In limited life-test data, waveguides up to one- year old have shown no measurable change in their transmission losses.
A launching coupler for hollow fibers consisting of a convex lens and a tapered hollow-guide piece is proposed. We fabricated the coupler which has a conical-tapered, Pyrex glass tube as the tapered section. The bore size of the taper-guide's input end is 3 mm and the output end is 0.7 mm which is the same as the size of coupled hollow fibers. The results of preliminary experiments show that the launching system has a large tolerance for the coupling condition between laser light and hollow fibers.
The transmission and input end heating of hollow-glass waveguides are greatly affected by the launch conditions of the input laser energy. A theoretical discussion is given on the effect of coupling conditions from a carbon-dioxide laser and its effect on waveguide performance. It is shown that the optimum coupling for maximum transmission is not necessarily equivalent to optimum coupling to the lowest- order HE11 mode. It is also shown that the input end heating of these waveguides can be reduced substantially with minimal effect on transmission if the waveguide bore size is large.
The spectral transmittance of mixed silver-halide polycrystalline fibers was measured while they were undergoing repeated bending leading to mechanical fatigue. Microscopic mechanical defects were detected through their influence on the optical losses, without interfering with the deformation. Optical and mechanical lifetimes of the fibers were found to depend on the composition and to be larger for highly mixed compositions. Scanning electron microscope observations of fatigued fibers revealed strong influence of the fiber composition on the fatigue damage. This dependence on the composition was explained using a theoretical model of solid-solution strengthening.
The relation between microscopic scattering and absorption properties, and the measurable macroscopic transmission properties of silver halide infrared fibers were investigated. Four mechanisms were considered, both by numerical simulation and far-field measurements: core scattering, surface scattering, absorption, and surface losses. The dominant mechanism in changing the angular distribution of the transmitted light was found to be the core scattering. Microscopic scattering and absorption properties were derived by fitting the experimental results.
Unconventional designs of silica-core optical fibers providing efficient lateral emission through the cylindrical side surface have been developed and manufactured. A physical model of the side-glowing fibers, available experimental data and potential clinical applications of this type of lightguides are discussed. Promising, clinical applications can be expected in the following areas: (1) Phototherapy, including photo-dynamic therapy, soft-laser therapy and visible/UV broadband irradiation therapy. (2) Single-fiber laser Doppler flowmetry. (3) Laser-tissue dosimetry. (4) Linear and planar 'cold light' illumination. (5) Optical sensing of mechanical pressure.
A sensor for measuring chest circumference by means of an optical fiber has been developed. The method is based on the measurement of light transmitted through a bent optical fiber, which is connected to an elastic band, wrapped around the chest, and whose radius of curvature changes due to the respiratory act. The amount of transmitted light is related to the radius of curvature of the fiber which depends on the chest circumference. The output of the respiratory sensor was checked qualitatively by changing the respiration depth. The changes in breathing effort were clearly demonstrated in the sensor output recording. The respiratory effort was also correlated with the heart rate, measured by photoplethysmography. Statistically significant correlation was found between the lungs' volume and the heart rate, but the correlation coefficient was not high. The magnitude of the breathing depth and the height of the corresponding respiratory changes of the heart cycle period were not correlated.
Silica based optical fibers are in operation for light- guidance in many applications, with wavelengths ranging from 230 nm to 2.2 micrometer. At shorter wavelengths, UV- improved fibers (UVI) can be used, which overcome the significant generation of UV-defects and associated loss in throughput using broadband deuterium-lamps or UV-lasers with fixed wavelengths such as excimer-lasers and quadrupled Nd:YAG lasers. Alternatively, many spectroscopic applications need a tunable and powerful UV-light to carry out remote-measurements, in-situ. In addition, specialized fiber-optics probe may be useful. We report for the first time on the transmission properties of the UVI-fibers with high-power pulsed lasers with wavelengths in the vicinity of the dominant UV-defect at 215 nm using a frequency-doubled dye-laser, tunable from 206 to 245 nm. Due to the high intensity of this pulsed laser system, especially near the fiber frontface, two-photon absorption plays a major role with decreasing wavelength. Therefore, properties such as starting transmission and UV-induced loss were measured as a function of the wavelength and input pulse energy. The envelope of the wavelength-dependent induced losses is comparable with results taken from tests with low-power broadband deuterium-lamps. However, the temporal behavior during recovery is quite different.
The interactions of UV laser beams and biotissues have been studied. The cutting quality of an ArF laser was the best sharp for hard biotissues (e.g. a bone, a tooth). From the current experiments, we found that the KrF laser beam has the highest incision ability for biological lipid of excimer lasers. For example, suet was cut off sharply by the KrF laser beam. On the other hand, the ArF laser incision has no thermal damage on suet even for the high repetition rate and the high energy fluence. However the conventional optical quartz fiber can not be available for an excimer laser beam (far-UV). So we have been investigating about UV laser power beam delivery systems. In the case of the hollow light guide with the aluminum-phosphor bronze reflector, we have obtained 56 and 75%/m transmittance of the ArF and KrF laser in straight state, respectively. Its delivery energy was 45 and 110 mJ/pulse of the ArF and KrF laser, respectively. The ArF laser transmittance has been tried in various atmosphere such as air, nitrogen, oxygen and helium. Finally, the medium of the laser delivery of the hollow light guide had better use the helium gas instead of the air. And the ArF laser transmittance and delivery energy were obtained 71%/m and 50 mJ/pulse, respectively. We have also tried the quartz fiber with OH ion doped core. The effects of a lightly doped clad with B and F on the transmittance have been investigated. In the one pulse operation, the ArF laser transmittance of B and F doped clad fiber was obtained 82%/m, which was better than that of only F doped clad fiber. The hollow light guide is suitable for the delivery system of UV laser scalpels, and the UV fiber is the useful delivery system of UV laser endoscopes.
A low-temperature fiber optic two-color infrared thermometer has been developed. Radiation from a target is collected via a single 700 micrometer-bore hollow glass optical fiber coated with a metallic/dielectric layer on the inner surface, simultaneously split into two paths and modulated by a gold-coated reflective chopper, and focused onto two thermoelectrically cooled mid-infrared HgCdZnTe photoconductors by 128.8 mm-radius gold-coated spherical mirrors. The photoconductors have spectral bandpasses of 2 - 6 micrometer and 2 - 12 micrometer, respectively. The modulated detector signals are recovered using lock-in amplification. The two signals are calibrated using a blackbody (emissivity equal to 1) of known temperature, and exponential fits are applied to the two resulting voltage versus temperature curves. Using the two calibration equations, a computer algorithm calculates the temperature and emissivity of a target in real time, taking into account reflection of the background radiation field from the target surface.
The gradient-index rod lenses have been conventionally used as the objective lens of the ultrathin medical fiberscope. In this paper, we propose to apply the new hemispherical fiber lens for the ultrathin fiberscopes. The lens can be fabricated by attaching a silica rod to imagefiber and heating the free end of the rod in arc charge. As the result of our investigation, it has been known that the radius of the hemispherical lens can be controlled by the discharge time. The imagefiber with the hemispherical lens had a diameter of 0.2 mm, 1600 pixels, a working distance of 3 mm and the angle of view of 40 degrees. It has been found by evaluating its image quality that it has the sufficient feature for the practical medical usage. In addition, it has been shown that the end of the imagefiber itself can be transformed to the hemispherical objective lens, and its optical characteristics as a lens can be controlled by changing the elongating length and the preheating condition.
For the research aim in the fields of the ship industry, the ocean engineering, the navigation and the navy, it is necessary to measure the ship water pressure (SWP) from the deep. In this paper we present a deep water optical fiber sensor to measure the SWP of moving ship. The advantages of this sensor are the automatic compensation for large static water pressure in the deep water, high sensitivity for SWP, and less sensitive to humidity. In our experiment in field, we successfully got the SWP-time curve by this optical fiber sensor underwater 40 - 50 M deep when the ship went through.
A theoretical study of the longitudinal vibration response of a bent fiber used as an active element of a medical applicator for laser ultrasound surgical therapy (LUST) is presented. An important problem concerns taking into account fiber bending which may appear due to applications in endoscopy. NIR laser radiation and low frequency ultrasound (20 - 50 kHz) with amplitudes of up to 100 micrometers can be transmitted by silica glass fibers. The fiber cross- section is much smaller than the longitudinal wavelength. Wave propagation in the bent fiber is described by the governing second-order equations of motion which neglect the flexure effect. In contest to numerous works on bent rods, the case of an arbitrary continuous curvative distribution along the fiber is investigated. A simple analytical formula for the transfer function (the ratio of displacements at the working end of the fiber divided by those at the driven end) is obtained. The transfer function depends on frequency, fiber length, output impedance, loss factor, and the mean- square curvative of the fiber. The behavior of this function is investigated applied to some fibers whose lengths are of the order 1 m. If the displacement at the driven end of the fiber is known, the acoustical power output of the applicator can be found from the known values of the tissue impedance and the transfer function.
Fused silica capillaries proved to be a suitable cladding material for liquid core lightguides. They have small diameters, a good mechanical stability and a high flexibility. Due to these properties such lightguides can be used for applications in minimally invasive surgery for endoscopical treatments. Filled with carbontetrachloride (CCl4), the optical properties were investigated spectrometrically and with various lasers. The transmission measurements of straight and 180 degree bent fibers were performed with a free-running Er:YAG, Er:YSGG, Ho:YAG, and Nd:YAG laser. Due to an overlap of the refractive indices of CCl4 and fused silica between 500 nm and 1 micrometer, laser wavelengths in this spectral range, e.g., of the Nd:YAG and the HeNe laser, cannot be transmitted in this lightguide. If the core liquid is a mixture of CCl4 and tetrachloroethylene (C2Cl4) the lightguide is transparent from the near UV (380 nm) up to the NIR (3 micrometer) and consequently, it is suitable also for the Nd:YAG laser. With the CCl4-filled fused silica capillaries distal energy densities up to 30 J/cm2 were achieved and thus the ablation threshold of soft tissue is exceeded.
Due to the high absorption coefficient of water in biological tissues at 3 micrometer, the Er:YAG (2.94 micrometer) and the Er:YSGG laser (2.79 micrometer) are very effective tools for medical applications. A widespread use of these lasers is prevented by the lack of a lightguide which satisfies the demands of medical practice, e.g. flexibility, low bending radius and unbreakability. If teflon (FEP) tubes filled with carbontetrachloride (CCl4) are used for high laser energies, absorbing and scattering particles in the liquid core are responsible for the decreasing transmission and damaging of the lightguide. A system was developed therefore to purify the liquid continuously even during laser irradiation. Two concentric FEP tubes are used to realize a circulation system. Different inner diameters of cladding tubes (1.6 mm and 0.5 mm) were tested with an Er:YAG and a Ho:YAG laser. A theoretical model of the different intrinsic attenuation losses in those lightguides was developed, which is in good agreement with the experimental results. Distal energy densities of 88 J/cm2 (Er:YAG) up to 220 J/cm2 (Ho:YAG) could be achieved with the small cladding tubes. These values were only limited by the output power of our laser devices. This waveguide setup has a better flexibility than those with a solid core. Due to the high numerical aperture (NA equals 0.54) the bending losses are negligible down to a bending radius of 15 mm. The high flexibility and transmittable power of the presented circulation system is particularly attractive for medical laser treatments.