Hans Juergen Schmitt

Chirp Optical Coherence Tomography of Layered Scattering Media

A new noninvasive technique that reveals cross sectional images of scattering media is presented. It is based on a continuous wave frequency modulated radar, but uses a tunable laser in the near infrared. As the full width at half maximum resolution of 16 μm is demonstrated with an external cavity laser, the chirp optical coherence tomography becomes an alternative to conventional short coherence tomography with the advantage of a simplified optical setup. The analysis of two-layer solid phantoms shows that the backscattered light gets stronger with decreasing anisotropic factor and increasing scattering coefficient, as predicted by Monte Carlo simulations. By introducing a two-phase chirp sequence, the combination of lateral resolved perfusion and depth resolved structure is shown.

Investigation of highly scattering media using near-infrared continuous wave tunable semiconductor laser

The principle of frequency modulated continuous wave radar (FMCW) has been applied to optical frequencies. By tuning the wavelength of a semiconductor laser with time, high resolution imaging in scattering media is possible. The spatial resolution depends mainly on the tuning range of the laser. Several tuning principles to be used in optical FMCW are discussed. As a coherent detection scheme with small bandwidth is used, low noise and high dynamic range are expected. The basic theory is outlined and experimental results are presented. Nonlinear tuning characteristics that degrade the resolution are discussed and interferometric methods enhancing system characteristics are proposed.

Optical coherence tomography of scattering media using frequency-modulated continuous-wave techniques with tunable near-infrared laser

A new near-infrared coherent imaging technique that can reveal scattering bodies embedded in highly scattering media is presented. Its underlying principle is extended from frequency modulated continuous wave radar systems. This technique has advantages over low coherence tomography as it does not require the reference mirror to be scanned. The tunable laser is characterized and the systems performance is demonstrated on images recorded from solid scattering phantoms. Furthermore a combination of our chirp-tomography (C-OCT) and laser Doppler perfusion imaging (LDPI) is demonstrated. The influence of moving scatterers on the tomographic images are discussed.

New highly efficient polarization converters based on hybrid supermodes

Mode coupling in strip waveguides can lead to the occurrence of hybrid supermodes. These supermodes offer the opportunity to develop highly efficient polarization converters even in isotropic materials as InP or GaAs. We present the theoretical background for the occurrence of hybrid supermodes and offer concrete design proposals for new polarization converters. >

Strong polarization conversion in periodically loaded strip waveguides

We give a comprehensive explanation for an unexpected strong polarization conversion effect in periodically loaded strip waveguides, which was detected experimentally some years ago. The effect can be put down to the occurrence of hybrid supermodes. Based on this knowledge, design proposals for new, highly efficient polarization converters can be given.

Studies of generation of ultrafine semiconductor particles in polydiacetylene Langmuir-Blodgett films accompanied with colour transition

Abstract Ultrafine semiconductor particles of cadmium sulfide were generated through exposing poly-(pentacosa-10, 12-diynoic acid) (PDA) Langmuir-Blodgett (LB) films to hydrogen sulfide gas. With the generation of ultrafine particles, the blue form of PDA multilayers was converted to the red form. UV-visible absorption spectra and ellipsometric measurements were made to study the generation of ultrafine particles and the colour phase transition of PDA LB films.

Renal Oncocytoma of the Native Kidney after Renal Transplantation

Patients with acquired cystic kidney disease (ACKD) are at an increased risk of renal neoplasms. Frequent tumors are adenomas and renal cell carcinomas. However, renal oncocytomas may occur in patients with ACKD. Little is known about oncocytomas of the native kidney following renal transplantation. By means of B scan ultrasonography, a solid and echo-inhomogeneous renal mass was incidentically observed in the right native kidney of a 28-year-old female patient with ACKD 4 years following renal transplantation. A nephrectomy was performed. The histological examination revealed a renal oncocytoma. The increased prevalence of neoplasms in the case of ACKD and following renal transplantation requires careful monitoring of the patients concerned. In very rare cases a renal oncocytoma may develop in the native kidney after renal transplantation.

In-line optical fiber polarizer and modulator coated with Langmuir-Blodgett films

In-line optical fiber polarizer and modulator were fabricated by depositing Langmuir-Blodgett (LB) films on polished fiber surface with gold layer. The thickness of LB film was adjusted by changing the number of monolayers, which then optimized the performance of the fiber polarizer. Good agreement was observed between the theoretically predicted conditions for efficient coupling and the experimentally determined conditions for high TM/TE extinction ratio of the optical field. By applying an electric field between the LB film, the polarization state of the lightwave in the optical fiber can be modulated.<<ETX>>

Optical coherent tomography with electrically tunable semiconductor laser using FMCW techniques

Imaging of highly scattering objects in scattering media can play an important part in assessing melanoma in human skin. The technique to be presented is based on frequency modulated continuous waves using a coherent tunable semiconductor laser irradiating a Michelson interferometer. The electrically tunable laser is characterized and the procedure to linearize the instantaneous frequency with time is described. The temporal point spread function of dilute milk is measured. Finally the performance of our imaging system is demonstrated on 2D-images of solid scattering phantoms and of an eye of a pig.

A new optical-fiber sensor for measuring surface pressure of Langmuir monolayers

Abstract The surface pressure of Langmuir monolayers can be measured by a Langmuir balance or Wilhelmy plate. However, both of these sensors have a long contact length with the monolayer, normally longer than 10 mm. An optical-fiber sensor has been developed for the measurement of the surface pressure of monolayers. It has a short contact length with the monolayer, less than 250 μm, while the sensitivity of this method is still very high. Thus, the new sensor presents a small disturbance to the monolayer and is very suitable for the study of inhomogeneity problems of monolayers, which are very important for the application of such layers to optical and molecular electronic devices. In the discussion, the feasibility of the application of the new optical-fiber sensor to the atomic force microscope is also analyzed.