Jerzy Helsztynski

Fiber Bragg gratings with very smooth side slopes

The technology of fabrication of the fiber Bragg gratings with different side slopes was investigated. It was proved that confining the fiber length to about 0.3 mm causes the side slope to spread to near 2.5 nm. Such fiber Bragg gratings are very useful in sensor applications.

Multiplexed FBG strain measurement system

The idea and, design and realization of fiber Bragg grating multiplexing system is given. Special Bragg gratings with very long and linear side slopes were practically realized. They were tuned for different wavelengths distanced 9nm in each measurement channel. The system was applied for strain control. Special spectrophotometer with linear photodiode array was made. For flexible distributed multiplexing of many sensor channels fiber-optic switches were used.

Hydrogenation influence on telecom fiber Bragg gratings properties

Special photosensitive high germanium boron-codoped fibers are too expensive for every-day application in the research laboratory. To lower the running costs of the fibers high-pressure hydrogenation unit was realized in form of special piping system with pressure control, easy handling and all safety requirements fulfilled. The technology and special procedures of hydrogen loading into single-mode fibers were developed and tested. Available standard single mode fiber samples used by the telecom cable companies (lengths of 2-3m) were inserted into hydrogen for different static diffusion time periods under the pressure 100-140 bar in the room temperature. The optimal hydrogenation procedures for best quality gratings were found. The post-hydrogenation low-temperature storage conditions were also controlled and gratings spectral characteristics measured. No Bragg grating formation was seen in unloaded fibers under the same laser illumination.

Interferometric fiber Bragg gratings

The interferometric techniques of realization of fiber Bragg gratings are presented. The practically performed laboratory optical system is described. First results of Bragg gratings written by this method on hydrogenated standard telecom fibers are given.

Bragg gratings in optical fibers made by the phase mask method

A fiber Bragg grating is a very attractive passive device widely used in telecommunication networks, laser technologies, metrology and research laboratories. The Institute of Electronics Systems has recently opened the new laboratory for writing Bragg gratings directly on fiber cores. The application of a phase mask is a reasonably simple technique for material, fiber photosensitivity research and filter spectral characteristics control.

Fiber Bragg gratings: technology and measurement

At present fiber Bragg filters are widely used in telecommunication, laser technology and metrology. The new laboratory was organized in the Institute of Electronic Systems (ISE), Warsaw University of Technology for Bragg gratings writing directly on fiber cores. The first results obtained with the use of the phase mask technique are presented.

Fiber Bragg filter measurements

Narrowband fiber Bragg filters are commonly used in telecommunication, laser technology and metrology. Special techniques have to be used to achieve the sufficient resolution in the subnanometer range. The modernized standard monochromator system with the resolution of 0.16 nm is presented. Measurement results for some filter designs are presented.

Operating distance extender for photonic vibrometer

Photonic vibrometer is used for non-contact vibration measurement. Information about changes in distance between the vibrating target and the fiber bundle tip is expressed as a change in the intensity of back scattered light by the target. The optical extender accessory offers the advantage of considerably increased operating distance (from about 1mm to 40mm).

High-resolution computer-controlled monochromator system for fiber diffraction grating measurements

A simple modification of the typical wide-band monochromator based cut-back system for fiber transmission measurements is presented. To increase the spectral resolution for fiber Bragg gratings measurements the properly blazed monochromator grating was inserted, stepping motor resolution increased and mechanical chopper thoroughly redesigned to avoid signal phase fluctuations. As the result spectral resolution of 0.16nm and signal dynamic range of 30dB was achieved in the 1.5μm region.

Measurements Of Optical Waveguides By A Near-Field Scanning Technique

The transmission near-field scanning technique can be used for determining the refractive index profile, the maximum core-cladding refractive index difference and/or numerical aperture, the geometrical characteristics and the mode-field dimensions in single-mode waveguides. In the experimental apparatus presented in the paper, the near-field pattern under test is magnified onto the faceplate of a vidicon camera, the video signal is sent to a computer--controlled video digitizer with single frame buffer memory organized as 512x512x8 bits. The incoming signal is digitized in real time to 8 bit resolution. Algorithms developed to opti-mize the scanning routine and to derive waveguide parameters from the measured data are described. As measured signals are usually noisy, techniques which reduce the noice level are also presented. Futhermore, techniques applied to compensate the vidicon sensitivity nonuniformity and nonlinearity are reported. Some examples of the results of measurements of the refractive index profiles and geometrical parameters like: core and cladding diameters, core and cladding non-circularities and core/cladding concentricity errors are presented.