The paper will describe application of Brilluoin spectroscopy to obtain Young modulus, stress, and thermal history of different glass parts as well as mechanical properties of polymer coating on optical fibers. We demonstrate that use of empirical relationships between Brilluoin frequency and stress and thermal history in glass can provide useful information about different glass products like optical fibers, ion-exchanged glass and others. In addition, similar approach for polymers can serve as a tool to obtain degree of cure or Young modulus for multilayered products such optical fiber.
Fiber-based cylindrical light diffusers are often used in photodynamic therapy to illuminate a luminal organ, such as the esophagus. The diffusers are often made of plastic and suffer from short diffusion lengths and low transmission efficiencies over a broad spectrum. We have developed Fibrance<sup>TM</sup>, a glass-based fiber optic cylindrical diffuser which can illuminate a fiber from 0.5 cm to 10 meters over a broad wavelength range. With these longer illumination lengths, a variety of other medical applications are possible beyond photodynamic therapy. We present a number of applications for Fibrance ranging from in situ controllable illumination for Photodynamic Therapy to light guided anatomy highlighting for minimally invasive surgery to mitigating hospital acquired infections and more.
We describe a novel process of laser-assisted fabrication of surface structures on doped oxide glasses with heights
reaching 10 - 13% of the glass thickness. This effect manifests itself as a swelling of the irradiated portion of the glass,
and occurs in a wide range of glass compositions. The extent of such swelling depends on the glass base composition.
Doping with Fe, Ti, Co, Ce, and other transition metals allows for adjusting the absorption of the glass and maximizing
the feature size. In the case of bumps grown on borosilicate glasses, we observe reversible glass swelling and the bump
height can increase or decrease depending on whether the consecutive laser pulse has higher or lower energy compared
with the previous one. To understand the hypothetical mechanism, which includes laser heating of glass, glass melting,
and directional flow, we explored density, refractive index, fictive temperature, and phase separation dynamics.
Laser writing of waveguides in bulk glasses opens the opportunity for creating three-dimensional photonic devices. In
order to become practical, the numerical aperture (NA) of these waveguides should be significantly higher than currently
achievable of 0.1 - 0.15. One reason is that with higher NAs one can decrease the bending radii of the embedded
photonic devices without significant loss penalty and make them compact. Thus, femtosecond-laser-written waveguides
in glasses do not allow bending radii smaller than 15 - 20 mm. In order to overcome this limitation, we propose to
fabricate waveguides in phase-separable and leachable glass where the index contrast is determined by the difference
between the refractive indices of the unprocessed glass and of the leached porous glass. We show that we can achieve
the NA = 0.25 prior to optimization. Surface and sub-surface treatment with a nanosecond ultraviolet (UV) laser
produces a similar effect with even higher NA = 0.35. Applications may include a range of tightly packed embedded and
three-dimensional photonic devices in bulk glass like directional couplers, splitters, interferometers, etc.
Optical fiber networks are being developed that require higher optical power levels. Examples include long haul communication with Raman amplification and fiber to the premises. Previous studies indicate that tightly bent optical fiber can mechanically fail when exposed to high optical power levels. In an extreme case where fiber is sharply bent and subjected to a power level of 1 to 2 W in the near-infrared wavelength window, optical fiber can fail in minutes. It also has been shown that time to failure decreases with increasing bend stress and optical power. This study is a further investigation of the physical events leading to failure. Previously we demonstrated that the optical signal that escapes the core of bent fiber passes into the coating, where a small amount is absorbed and converted to heat. As a result the coating can be heated to significant temperatures resulting in degradation over time. This paper focuses on several key aspects of the failure kinetics associated with bent fiber under high power. As a result of bending, optical power leaked from the core is distributed in the glass cladding and polymer coating. We have modeled this power distribution and compared it with measured temperature profiles in the coating. The results show that this redistribution of the power is key to establishing the distribution of temperature in the coating and ensuing degradation. This understanding is used to design glass and coating solutions for inhibiting this potential failure mode.
In this paper we present the result of a sensitive experimental technique used to provide information about the limitations of using organic polymers for fiber-optic high power applications. Optical path adhesives are commonly used in fiber optics assemblies due to their mechanical and optical properties. However, their use in high power applications creates certain concerns about short-term and long-term stability of the adhesive material. We developed an approach for evaluating the effects of high power in optical path adhesives used in applications for fiber-optic devices. We extended far field experimental technique for analysis on a thin polymer layer placed on the tip of an optical fiber exposed to a wide range of optical powers. We found that this technique can be used for both thermo-optical effects evaluation and electronic non-linear contributions to the refractive index of the material. We show how this method permits separation of these two effects, and long term behavior of polymer materials in such applications. This approach could be used for evaluation of wide range polymer materials in photonics.
The failure of tightly bent optical fiber under high optical power is observed dynamically with fine time resolution and explained in terms of the behavior of the polymer coating and underlying glass. An abrupt rise in coating temperature stimulates the viscoelastic deformation of the glass. The abrupt bending of the glass is explained by the ability of highly quenched silica to deform at low temperatures. There is no evidence of thermal runaway of the glass core. Coating decomposition is self limiting with no visible flame.
Scattering losses for fused silica were measured over a wide wavelength range (193-800 nm) using different laser sources. The data indicate that scattering centers are smaller than ~ 12 nm, and scattering is consistent with Rayleigh type even at 193 nm. Scattering losses scale with wavelength as 1/λ<sup>4</sup>, and scattering loss at 193 nm was found to be (0.65±0.08)x10<sup>-3</sup>/ cm absorption units or (0.15±0.02)% transmission per cm. CaF<sub>2</sub> measurements were completed in the visible wavelength range. The experimental approach for DUV wavelength measurements for CaF<sub>2</sub> is described. Estimated scattering losses at 193 nm are ~0.003% transmission per cm and ~0.006% transmission per cm at 157 nm. Data for CaF<sub>2</sub> indicate deviation from Rayleigh-type scatter.