Bernhard Scholl

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.

In-line fiber optic polarimeter with a 99% coupler

A polarization transformer in combination with a polarization analyzer is well suited for the generation of any wanted polarization state. We describe the setup, calibration, and applications of an in-line fiber optic polarization detector (IPD) built with a fiber optic coupler of 99% coupling ratio. At the low power output port we use standard beamsplitters and polarizers to generate four different polarization dependent signals. For calibration, the polarization is measured at the high-power output port with an oft-line polarimeter (OPD). This enables the determination of the system matrix, which represents the relation between the polarization at the high-power port and the four signals at the low-power port. With this system matrix, a continuous and accurate determination of the polarization at the high-power output port is possible.

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>>

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.

Fiber-optic polarimetric temperature sensor for characterizing a 900 MHz TEM cell used in bioeffects dosimetry studies

The primary goal in the development of an exposition chamber for bioeffects dosimetry studies is the exact knowledge of the electromagnetic field components inside the biological sample. Measuring is not possible using metallic field probes. This paper describes a transversal electromagnetic (TEM) cell suitable for bioeffects dosimetry studies at 900 MHz and the design of a fiber-optic polarimetric temperature sensor which is used to measure the specific absorption rate (SAR). Using this sensor a temperature change lower than 0.003/spl deg/C is detectable. By simulating the whole TEM cell and comparing; the results with the measured SAR at certain points inside the liquid biological sample one is able to determine the electromagnetic field components.

Modulation of the polarization state in an optical fiber coated with Langmuir–Blodgett films

The optical fiber is bent in a slot and polished until one side of the fiber coating is only several micrometers thick. The hemicyanine Langmuir–Blodgett (LB) film is then deposited on the polished optical fiber surface. By applying an electric field between the LB film, the polarization state in the optical fiber has been modulated. The preparation details of the in‐line optical fiber modulator and the measurement setup are described.

Polarization analysis system for very rough surfaces

A polarimeter system has been developed to investigate the reflected light of very rough non-specular surfaces. One special application is the polarimetric analysis of road surfaces to find features for the classifications relating to type and surface condition. The reflected light of such a surface varies very much depending on the inhomogeneous surface structures. The aim was to build a measurement system which is relatively insensitive to the positioning of the surface sample, is easy to calibrate and offers a high scanning rate. These demands lead us to a polarimeter setup using a combination of a four-detector-polarimeter and a retarder-polarimeter with liquid-crystal cells as retarding elements. With the help of this laboratory system it is possible to find all polarization depended features. In a further step the setup will be simplified to measure only selected values but with higher speed. The software of the system allows the complete control of the polarization generator and of both polarimeters including the calibration,the operation in different modes, the evaluation and graphical visualization of the measuring data.

Fiber optic polarization synthesizer

Rotatable fiber loops are commonly used to change the state of polarization in fiber optic transmission systems. As an improvement of such a system we describe a feedback controlled polarization transformer which operates at its output prot as a polarization synthesizer. The whole setup allows a very efficient polarization adjustment with a stable and well known state of polarization.

Reference measurement for fiber optic polarimetric sensors

In the application of fiber optic polarimetric sensors two major problems occur: (1) the influence of the connecting fibers and (2) the influence of internal birefringence in the sensing area which has not to be constant over its whole length. In the following paper we describe a method which overcomes these problems by analyzing the polarization transfer matrix of the sensor element and we show the results for a fiber optic polarimetric current sensor.