Medical treatments benefit from increased sharpness of radiation emission or detection. Noncircular core silica/silica optical fibers have benefits of better control of irradiation of diseased tissue and more uniform irradiations. Description of tested fiber structures and others available are presented Data will be presented on mechanical reliability of such fibers, primarily, medium-to-long term static fatigue experiments as well as shorter term strength experiments. Spectral behavior will also be presented. The loss of radial symmetry provides for more uniform output across the core face. These fibers have mechanical properties remarkably as good as standard circular core fibers, with high dynamic strengths and very good Static Fatigue Parameters.
Hard Plastic Clad Silica (HPCS) optical fibers with pure silica cores have been
developed which are robust and have NA(Numerical Aperture)>0.50. Improved clad only
HPCS fibers have been produced for both new 'standard' and 'high' NA versions. Based on
new cladding formulations, the 'standard' NA fiber has an NA of 0.41, while the new ultrahigh
NA fiber has an NA of 0.54. Mechanical strength and preliminary fatigue data are
presented along with spectral characterization data. For the first time significant results were
obtained for clad only high NA fibers, The fibers are useful for diagnostic and surgical
applications.
Short to medium length time to failure results, indicate that the static fatigue
parameters of the new high numerical aperture (NA) optical fibers are at least as good as
those for former standard NA (0.37) HPCS fibers, which is an advance from previous results on the older formulation high NA fibers.
KEYWORDS: Optical fibers, Silica, Semiconductor lasers, Failure analysis, Reliability, Cladding, High power lasers, Laser systems engineering, Optics manufacturing, Laser energy
The high power diode laser systems with their laser diode bars and arrays not only require
special fibers to couple directly to the diode emitters, but also require special fibers to couple from
the laser to the application sites. These power delivery fibers are much larger than the internal
fibers, but must be flexible, and have not only good strength but also good fatigue behavior. This is
particularly important for industrial systems using robotic arms or robots to apply the high power
laser energy to the treatment site. The optical properties of hard plastic clad silica (HPCS) fibers
are well suited for the needs of delivery of high power from diode laser bars and arrays to an
application site. New formulations for HPCS fibers have been developed which have demonstrated
fibers with good mechanical strength in preliminary tests. A systematic study has been undertaken
to determine the strength and fatigue behavior of three 'new' HPCS fibers and to compare them with
results for earlier HPCS fibers. Benefits of stronger median dynamic strengths and tighter flaw
distributions have been found. Short to medium length time to failure results, indicate that the static
fatigue parameters of the new high numerical aperture (NA) optical fibers are at least as good as
those for standard NA HPCS fibers, which is an advance from previous results on the older
formulation clad fibers.
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.
Typically, output from high power, diode lasers and arrays must be transported to a final application/treatment site, whether the application is industrial, military or medical. Many demands are placed on optical fibers to couple the laser output into their structures and to transmit the power to the application site. All silica fibers become much more expensive as the diameter of the fiber increases to handle larger spot sizes and higher NA beams, especially from diode arrays. High strength, low fatigue Hard Plastic Clad Silica fibers provide benefits of larger Numerical Aperture (NA), more flexibility and less strain at the core-clad interface. Fibers with these characteristics and available in both high OH and low OH versions for UV and NIR spectral regions are described. Short and long term strength, and spectral properties are presented. Results for a new high NA version are also presented.
A number of spectroscopic techniques make use of UV absorbance and luminescence measurements e.g. to characterize materials, for use in medical/pharmaceutical applications, for forensic and sensor applications, etc. Remote detection or monitoring, especially for hazardous environments, benefit from the use of optical fibers. Furthermore many high power applications in medicine and industry are looking to use UV wavelengths. All silica compositions are better able to provide transmission of uv wavelengths, however there have been limitations on their use. Numerical aperture and solarization of the fibers are main concerns. Fibers have been recently developed which can be used for extended periods of time at wavelengths from 193 to 400 nm without serious degradation of their transmission properties (non-solarizing) and with significant broader numerical apertures,[NA] of 0.26-0.30 allowing sampling of larger areas and greater collection of transmitted or reflected beams from materials under test. Mechanical and spectral properties for these new fibers will be presented and compared with the standard all silica fibers. This will include reliability test results at selected UV wavelengths. Possible application areas which would particularly benefit from these high NA, UV non-solarizing optical fibers will be suggested.
An important feature of achieving low coupling losses in systems with small dimensions is the availabilty of optical fibers with larger numerical apertures while retaining the excellent loss characteristics of synthetic silica. Larger acceptance angles permit more efficient pick up of signals in smaller diameter optical fibers. Likewise broader angles can benefit illumination systems, providing larger areas of coverage with smaller components. Examples where one or both aspects are valuable include remote spectroscopic sampling and hands-free fiber optic illumination systems for hazardous environments. Optical fibers with doped synthetic silica cores are described which have numerical apertures of over 0.50 for power delivery and effective NAs approaching 0.60 for illumination, sensing or other 'low power' applications. Spectral and optical properties of these fivers are presented along with how they allow improved low loss coupling of optical components in photonic and microelectronic systems.
For most Photodynamic Therapy (PDT) applications a diffuse, broad and uniform source of irradiation is needed to obtain the most effective and consistent treatment. Since many treatments are within the patient's body, an effective compact fiber optic delivery system is needed for the activation of the photsensitizer drub at the site of the tissue to be treated. High Numerical Aperture (NA) optical fibers have benefits for PDT treatments but possibly even more so for PDT diagnostic applications These are summarized and new optical fibers with high and ultra high NAs are described. Properties of these fibers are presented as well as advantages they have over other fibers for delivering light in various PDT applications. Silica fibers with enhanced effective NAs approaching 0.6 are described.
Many medical applications have need of 'broad' irradiation patterns, but benefit from small diameter fibers to provide minimal invasive surgery. These applications also benefit from using the low intrinsic loss character of silica based core material as well as the power capability of a silica/silica construction. Pure silica core, all silica optical fibers are now available with an NA of 0.30 ± 0.02. Variations include fibers with non-solarizing ultraviolet transmissions as well as fibers with transmission through the near infrared [IR] region of the electromagnetic spectrum. Additionally ultra high NA fibers with silica cores and silica/silica structures are now available for use in the visible and near IR regions with effective NAs higher than 0.6. Properties of these fibers are presented and the advantages over other fibers and potential medical applications are also discussed.
A major problem with coupling high power diode lasers into optical fibers is the counter effects of requiring a synthetic silica core for its energy carrying capacity but needing also high numerical aperture and/or core size to capture the highly diverging fast axis light. Coupling the output of diode arrays efficiently and for maximum brightness retention involves additional problems, some of which are discussed. A possible solution to these probelms is having the availability of higher numerical aperture [NA] fibers based primarily on a silica core and silica cladding. New deposition techniques have permitted the formation of preforms leading to fibers with pure silica cores which have an NA of 0.30 versus the standard 0.22 value. Further new structures and approaches to the problem have lead to optical fibers with a doped silica core having an NA above 0.50. Properties of these fibers are presented along with advantages they have for improving coupling high power diode lasers and also some newer concepts for improving retention of high brightness output from such laser systems.
Diode laser arrays present challenges to delivering maximum brightness laser energy to remote sites. Coupling with optical fibers is key to achieving this goal. Fiber core diameters are chosen to capture all the energy from the slow axis, with fiber placement and/or lensing to assure capture output from the fast axis. Multiple fibers are then bundled as tightly as possible and their output focused into a single output fiber. The optimum brightness is achieved by using as small as possible bundle dimensions before reduction to the output fiber's dimensions. A major aim is thus to minimize jacketing and cladding thickness. Data and analysis of the effects of cladding thickness on the spectral transmission of optical fibers having core diameters between about 100 micrometers to about 300 micrometers are presented. Particularly below a 200 micrometers core, cladding thickness can significantly alter the transmission of laser energy in the visible and near infrared spectral regions, especially between 600nm and 1700 nm. Data primarily deals with low-OH, 'water-free' fibers having cladding thicknesses between 5 to 20micrometers . Especially for fibers having cladding/core ratios below 1.2, care must be taken to either use core sizes approaching 200 micrometers or work in the UV or lower visible wavelength region. Further guidelines are given below.
Key to many laser and sensor applications, in the medical area, is the desire to maintain high core to clad ratios for minimum penetration and maximum flexibility. The transmission of laser beams through optical fibers in a stable, uniform manner is a critical need and assumption for many surgical and sensing medical applications. Cladding thickness has been found to affect the transmission of signals across the electromagnetic spectrum in an uneven manner, especially when typical jacketing materials are used to protect the optical fibers against mechanical/environmental degradation. Experimental data and analysis of the effect of cladding thickness of the spectral transmission of optical fibers having core diameters below 300 micrometers are presented. Particularly for fibers with below 100 micrometers core diameters, fibers with cladding/core ratios below 1.2 are shown to have altered transmission spectra at wavelengths above 600 nm. The sensitivity is more pronounced for 'water-free,' low-OH optical fibers, which have significant transmission through the near infrared [NIR] region.
A new type of optical fiber has been developed with all pure silica in both core and cladding. The cladding is a nano porous silica produced on line from an oligimeric organo-silicate by a modified sol-gel technology. Characteristics, mainly mechanical properties, are described. The strength and fatigue of these optical fibers are very good, even without additional protective jackets. The nano porous silica is also being evaluated as an outer coating on all silica optical fibers. Unjacketed fibers have mean Weibull strengths in bending of 6.5 to 7.6 GPa with Weibull slopes in the 40 to 60 range. Strength decrease with decreasing strain rate is similar for both jacketed and unjacketed fibers. Static fatigue results using mandrel wrap tests are also presented. Dynamic and static fatigue parameters appear to be essentially the same with values around 20. A thin polyimide jacket does improve some of the mechanical properties. Results for nano porous silica ‘buffer’ over a silica/fluorosilica core clad structure are also presented. Effects of water and dry environments are presented, including results of short to intermediate term aging in boiling water. Possible mechanisms to explain the strength and fatigue behavior are discussed in light of these fibers’ unique structure.
Optical fibers and fiber bundles have been developed for UV applications in general but have specific benefits for UV applications within medicine such as excimer angioplasty and UV perforation of the heart wall in heart bypass operations. Optical fibers have been tested for transmission changes at 193 nm, 214 nm, 253 nm and 365 nm. Whereas standard synthetic silica optical fibers developed color centers within 10,000 pulses of 193 nm energy, the new CeramOptec fibers were observed to experience only minimal changes in attenuation after 100,000 pulses. Similarly under constant irradiation by a high power deuterium lamp only minor changes in the attenuation at both 214 nm and 253 nm were observed for the 'non-solarizing' UV fibers after 121 hours, whereas standard UV fibers lost up to 50% after only 24 hours of exposure. Fiber bundles have been produced which can stand up to the elevated temperatures experienced at the source end when strong UV sources are needed for specific applications. Test results and information on the testing as well as some information on the fibers tested is given below.
A new type of optical fiber has been developed. It is made with all pure silica in both the core and cladding. This is possible because the cladding is a micro porous silica produced by a modified sol-gel technology. The formation and characteristics of this new optical fiber type are described. In particular the optical and mechanical properties are illustrated and described. The strength and fatigue of these optical fibers are very good, even without additional protective jackets. Unjacketed fibers have mean Weibull strengths in bending of 6.5 to 7.6 GPa with Weibull slopes in the 40 to 60 range. Fatigue results for fibers tested in ambient air, ambient water and boiling water are presented. The dynamic and static fatigue parameters are around 20. The micro porous structure of the sol-gel cladding provides sites for attaching different moieties which could activate biochemical reactions or be useful as sensing sites. Based on preliminary experiments, some possibilities are presented. In general this new structure can provide opportunities for as yet unidentified applications where chemicals and or light must be brought in close contact with body tissue to effect beneficial reactions there.
Recent development of specialty silica and non-silica fibers in a synergy with an innovated design of fiber catheters, bundles and probes promote the growth of various fiber applications. There are three main areas of fibers usage: telecommunications, fiber sensing and laser power delivery, -- but we review briefly only the exiting area of fiber applications in remote spectroscopy.
Hard Plastic Clad Silica (HPCS) optical fibers were invented about a decade ago to improve on the original Plastic Clad Silica (PCS) optical fibers. Details of the invention/innovation process are reviewed along with the development of this new type of optical fiber structure. A compilation of the several types now offered in the USA, Japan and Europe is presented. The advantages and limitations of these fibers for a wide range of medical applications are reviewed. Finally a description of future developments and expanded products are suggested.
In developing a better understanding of the requirements on optical fibers to make them more useful for medical and other applications where UV light/lasers are the preferred source, previous papers have dealt with all silica optical fibers. Here we describe the UV transmission of all the available fiber types; illustrating, for commercially available fibers, the effects of fiber type, core diameter, cladding thickness, and core OH level on this transmission. We also describe our first efforts to fabricate a new, modified hard plastic clad silica fiber with enhanced UV performance. Finally some of the remaining problems and concerns are identified and reviewed.
As the lead paper for the session describing new results in the application of fiber optic
systems to invasive treatments and surgery, this paper presents an overview of the basic
properties of optical fibers and the advantages of using them in such applicaticns along with
the challenges and problems which need to be addressed in designing the systems.
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