Reductions of UV transmission in silica-based multimode fibers, with low-OH or high-OH synthetic silica core, due to optically active UV defects will be shown using pulsed 355 nm (3rd harmonics) and, for the first time, 213 nm (5th harmonics) Nd-YAG lasers. A new experimental set-up with nearly simultaneous laser damage and spectral analysis is proposed and realized, with the main aim that the laser-induced damage can be measured for wavelengths from 190 up to 1000 nm without movement of the fiber under test. In addition, the damaging UV lasers can be easily changed and aligned. For the two wavelengths, the fibers’ UV transmission is quite different. At 355 nm, the low attenuation level lead to a nearly constant intensity along the fibers, within approx. 10 m. Therefore, the almost constant twophoton absorption is responsible for a homogeneous axial distribution of optically active UV defects, well known below 280 nm wavelengths. At 213 nm, these defects can be generated by one photon alone. However, the defect concentration depends on the axial position and is significantly higher than the wellknown values during D2-lamp irradiation.
An effort to demonstrate long term transmission stability in a high –OH synthetic fused silica step index multimode optical fiber optimized for Deep-UV operation, designated as FDP, was successfully completed at Polymicro Technologies. The development achieved significant improvement in long term stability for the 214 and 265nm absorption bands typically associated with solarization effects in fused silica. The improvements were applied to fiber core sizes from 67 to 100µm, a common size range for bundle applications used in medical and spectroscopy. Results of UV degradation measurements for the fiber with minimum 70 hour exposures are presented along with a description of the test protocols.
An effort to reduce UV-induced defect centers and improve the UV solarization resistance in a high –OH synthetic fused
silica step index multimode optical fiber, designated as FDP, was successfully completed at Polymicro
Technologies. The development achieved significant reduction in the 214 and 265nm absorption bands typically
associated with solarization effects in fused silica. The improvements were applied to fiber core diameters from 68 to
600μm. Characterization of the solarization resistance was performed with added attenuation from UV exposure
demonstrated to be less than 1dB per two meters tested for all fibers in the core size range. Results of spectral
performance and UV degradation are presented along with a description of the test protocols. Potential applications in
the medical and spectroscopy fields also will be discussed.
The current status of UV-damage in several different UV fibers due to defects in their synthetic high-OH silica core and cladding will be described. Further, steps to improve UV resistance and adequate measurement techniques based on a deuterium lamp setup are included. For the first time, the main parameters and their influences on UV induced losses are discussed in detail with an emphasis towards future standardization purposes. Applications based on two new UV light sources, a laser driven xenon plasma broad band source and a high pulse-power 355 nm Nd:YAG laser, are introduced. UV photo-darkening and -bleaching in UV fibers caused by this extremely
powerful light source is demonstrated. Finally, first results on transmission of UV light in optical fibers at cryogenic temperatures are shown.
A new silica-based fiber design has been developed which exhibits improved transmission properties over a very
wide spectral range. In the near infrared wavelength region, the attenuation of the new fiber is similar to standard
near infrared fibers having a low -OH silica core and F-doped cladding. Simultaneously, the fiber has excellent UV
transmission down to 200nm comparable to standard high -OH fibers. Additionally, the UV-defect concentrations
in this low -OH fiber have been reduced significantly, such that the solarization degradation properties are close to
UV optimized high -OH fibers with high radiation resistance.
First results of spectral performance testing are given using different light sources, including Deuterium lamp and
Tungsten-halogen lamp. In addition, the test results evaluating UV solarization are reviewed. Finally, potential
applications in the medical and industrial fiber sensing field will be discussed.
Shaped fiber tips are machined or sculpted fiber ends which are formed using the glass from the fiber with no additional glass material. The tips are fabricated through either mechanical or laser machining processes. The tips are very useful in medical and industrial applications which require high power laser delivery (material or tissue cutting), even light distribution over a broad area (tissue ablation or photodynamic therapy), modified beam divergence or spot size (materials processing and communications links), or optical power redirection from the axis of the fiber in areas with small space restrictions (tissue ablation or perforations inside the human body). Descriptions of various shaped tips are provided, with concentration on tapered tips. The tapered tip is the most commonly used. The primary objective of this study was to measure the optical loss of such tapers vs. taper length, input (launch) numerical aperture (NA), and fiber diameter. The tapers fabricated and analyzed were 2:1 tapers using 0.22 NA fibers with 200, 400, and 500 um cores. The optical loss at 633nm for fibers with a 0.22 NA was measured to be 5.9dB (25% transmission) for a fully filled input NA and 0.8 dB (83% transmission) for a 0.12 input NA. The taper loss was found to depend strongly on input NA, but be relatively independent of taper length and fiber diameter. An optical modeling ray trace program was used to analyze the taper performance and validate the actual measurements. The modeling analysis will be a useful tool in design of tapers as well as other shaped fiber tips.
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 CO<sub>2</sub> 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 CO<sub>2</sub> and Er:YAG optimized waveguides, respectively. In optical loss in bending, the CO<sub>2</sub> 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 CO<sub>2</sub> optimized waveguides were also tested for CO<sub>2</sub> (10.6μm) laser power transmission. The change in CO<sub>2</sub> 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 CO<sub>2</sub> power with no indication of degradation of the internal reflective coatings.