Stephan Lvovich Logunov

Cavity ringdown detection of losses in thin films in the telecommunication wavelength window.

The method of cavity ringdown spectroscopy (when a tunable pulsed optical parametric oscillator was used) was extended for the loss evaluation in thin films (2-20-microm thickness). The technique was applied in two key telecommunication wavelength ranges of 1260-1330 and 1480-1650 nm. The measurement sensitivity was determined to be 50 ppm (5 x 10(-5)). The results for polymer films are in close correlation with conventional spectrophotometric data and propagation loss for planar waveguides. Films of greater thickness and better optical quality are expected to provide an even higher loss resolution.

Extraordinary laser-induced swelling of oxide glasses

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, which 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. The hypothetical mechanism includes laser heating of glass, glass melting, and directional flow. We review several potential applications of such glass swelling.

Experimental and theoretical study of bulk light scattering in CaF2 monocrystals

A variety of different types of light scattering (Rayleigh, Brillouin, Raman, and Mie scatterings), which may contribute to the transmission losses in the bulk of high-quality CaF2 monocrystals, have been investigated experimentally and theoretically. The angular distribution of Rayleigh and Mie scatterings in the visible spectral range has been measured using an imaging technique. An effective technique for scattering measurements in the uv spectral range has also been implemented. Measurement of Raman scattering has shown that its contribution to the total scattering loss is negligible. In order to estimate the scattering from thermal fluctuations versus that from crystalline defects, a measurement of the temperature dependence of the scattering at the scattering angle of 90° has been performed. It has been shown that scatterings from thermal fluctuations and defects are of the same order of magnitude. Taking into account the dependence of the Brillouin scattering on the direction of the incident beam r...

Analysis of excess scattering in optical fibers

We have systematically analyzed the excess scattering in a relatively large index optical fiber operating in the single mode regime. A mathematical model based on the theory of scattering of plane waves from a randomly perturbed core-clad interface is presented that predicts excess scattering confined within a small angle in the forward direction. An experimental system is developed that can measure the angular distribution of the scattering over ∼0°–180°. Excellent agreement between computed and measured scattering distribution is observed over multiple wavelengths and wide angular range. The spectral and angular distribution of the excess scattering and its response to the perturbation parameters are analyzed.

Photothermal behavior of an optical path adhesive used for photonics applications at 1550 nm

A theoretical and experimental study of photothermal behavior in a commercially available optical path adhesive is described. Photothermal effects were examined for cw and pulsed laser radiation (approximately 1 micros) at 1550 nm. A fiber-optic backreflection technique was used to measure the thermo-optic glass transition temperature of the adhesive. This transition temperature was then used to calibrate fiber-optic photothermal blooming and backreflection pump-probe experiments. Simple thermal models predict DT at 300 mW (cw) to be 65 degrees C and 53 degrees C at 100 W (pulsed). Experimental results are in reasonable agreement with theoretical predictions. The characteristic photothermal relaxation time after a 1-mus pulse for optical path adhesives is found to be 166 micros at the end of a fiber where the mode field diameter is 10.5 micron. Photothermally induced temperatures were found to be below the thermal degradation temperature of the adhesive even at powers as high as 1 W (cw) or 100 W (pulse).

Scattering losses in fused silica and CaF2 for DUV applications

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/λ4, and scattering loss at 193 nm was found to be (0.65±0.08)x10-3/ cm absorption units or (0.15±0.02)% transmission per cm. CaF2 measurements were completed in the visible wavelength range. The experimental approach for DUV wavelength measurements for CaF2 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 CaF2 indicate deviation from Rayleigh-type scatter.

Laser texturing of doped borosilicate glasses

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.

Nano-engineered optical fibers and applications1

Abstract The paper reviews optical fibers with nano-engineered features and methods to fabricate them. These optical fibers have nano-engineered regions comprising of randomly distributed voids which provide unique properties for designing next generation of fibers. Discussion of impact of void morphology on fiber optical properties is presented, along with the methods to control the void characteristics. Use of nano-engineered fibers for different applications (ultra-low bend loss single mode fiber, quasi-single mode bend loss fiber, endless single-mode fiber, light diffusing fibers) is discussed and the unique optical attributes of the fibers in these applications is highlighted.

Light diffusing optical fiber for Illumination

We describe the design of thin, ~ 100-180 micron diameter, optical silica fibers for illumination. The fiber has a silica core with specially engineered scattering centers to scatter light through walls of the fiber across a wide wavelength range

Nano-engineered optical fibers and applications

This paper reviews a technology for making nano-engineered optical fibers. Key features and advantages of nano-enginneered glass fibers are discussed. Fiber designs and their applications are presented.