Zbigniew Krajewski

Optimization of fiber-optic Sagnac interferometer for detection of rotational seismic events

The optimization of fiber-optic Sagnac interferometer as a sensor for the investigation of seismic rotational waves is presented in this paper. The main parameter of this optimization is maximum system sensitivity for absolute rotation in the limited range of expected velocities. The main system construction bases on the FOG minimum configuration, however the detection by system only rotational velocity without covering it on angle changes needs other approach to this system. The presented in paper theoretical and experimental investigation shows that such system can be made on base of a standard single-mode optical fiber, however needs operation on depolarized light.

Fibre Optic System for Monitoring Rotational Seismic Phenomena

We outline the development and the application in a field test of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of the seismic-origin rotations of the ground. The main advantage of AFORS is its complete insensitivity to linear motions, as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas the applied telemetric system based on the Internet allows for an AFORS remote control. The laboratory investigation of such two devices indicated that they keep an accuracy of no less than 5.1 × 10−9 to 5.5 × 10−8 rad/s in the detection frequency band from 0.83∼106.15 Hz and protect linear changes of sensitivity in the above bandpass. Some experimental results of an AFORS-1 application for a continuous monitoring of the rotational events in the Książ (Poland) seismological observatory are also presented.

Application of the FORS-II for investigation of seismic rotation waves

In the paper new results connected with application of the fiber-optic Sagnac interferometer in the area of investigation of special seismic events are discussed. The device presented in the paper is designed for investigation of rotational component existing in the earthquakes called seismic rotation waves. Generally it is a fiber-optic rotational seismometer (FORS) based on its resolution in the range of 10xE-8 rad/s which can detect the seismic rotation waves in a direct way. The paper describes the first results obtained on the base of data recorded in Ojcow standard seismic observatory. The presented discussion in paper shows a new aspect connected with physical fundamentals of the seismic rotation waves.

Possibility of fiber optic rotational seismometer design

A new area of fiber-optic Sagnac interferometer application is presented and discussed. The fiber-optic sensor described in the paper, in well-known classic fiber-optic gyro configuration, has been designed for a detection of the rotational seismic events. The basic system optimisation for a detection rotation only without conversion for angular changes distinguishes this system from the gyro application. On the other side, the detection of absolute rotation can give an advantage for this system in compare to other rotational seismometers, which calculate rotational events in indirect ways. The comparison of data from the described fiber-optic rotation seismometer and two antiparallel pendulum seismometers are also presented.

The fiber optic Sagnac interferometer application for recognition of the rotational seismic events

In the paper a new area of the fiber-optic SAgnac interferometer applications are discussed. The presented devices basing on well-known optical gyroscope configuration are optimized for detection of other special physical quantitites. Generally it is a rotational seismometer designed for calibration of the other electromechanical types of such devices, as well as a new sensor for detection of rotational seismic events. The detection of absolute rotation by the system is advantageous in comparison to the other rotational seismometers, which calculate rotational events in indirect ways. The paper desribes comparison of the data obtained from teh fiber-optic rotational seismometer and the electromechanical one. Moreover, on this base the construction of new system with resolution 10 E-8 rad/s is also presented in this paper.

Review of the Usefulness of Various Rotational Seismometers with Laboratory Results of Fibre-Optic Ones Tested for Engineering Applications

Starting with descriptions of rotational seismology, areas of interest and historical field measurements, the fundamental requirements for rotational seismometers for seismological and engineering application are formulated. On the above basis, a review of all existing rotational seismometers is presented with a description of the principles of their operation as well as possibilities to fulfill formulated requirements. This review includes mechanical, acoustical, electrochemical and optical devices and shows that the last of these types are the most promising. It is shown that optical rotational seismometer based on the ring-laser gyroscope concept is the best for seismological applications, whereas systems based on fiber-optic gyroscopes demonstrate parameters which are also required for engineering applications. Laboratory results of the Fibre-Optic System for Rotational Events & Phenomena Monitoring using a small 1-D shaking table modified to generate rotational excitations are presented. The harmonic and time-history tests demonstrate its usefulness for recording rotational motions with rates up to 0.25 rad/s.

FOSREM: Fibre-Optic System for Rotational Events and Phenomena Monitoring: Construction, Investigation and Area of Application

This paper reviews our expertise with construction, investigation and simulation of the fibre optic interferometric device named FOSREM (Fibre-Optic System for Rotational Events and Phenomena Monitoring). The presented device was designed for a direct monitoring of rotational components emitted during seismic events as well as existing in irregular and complex structures. The construction of the FOSREM utilizes the Sagnac fibre interferometer in a minimum optical gyro configuration. This approach causes that FOSREM is complete insensitivity to linear motions, and it enables to measure directly the rotational components. In order to make FOSREM mobile and autonomous device we were focused on decreasing size to the 36 × 36 × 16 cm dimension and implementing special FORS – Telemetric Server which enables to control FOSREM remotely via Internet. The laboratory investigation of our system indicated that it keeps the theoretical sensitivity equal to 2·10−8 rad/s/Hz1/2 and accuracy no less than 6·10−9–5·10−5 rad/s in a frequency band from 0 Hz to the upper frequency between 2.56 and 328.12 Hz, respectively. FOSREM protects linear changes of sensitivity in the above detection frequency bandpass and has the maximum values of rotation rate possible to record without “overshoot” equal to 10 rad/s due to an innovative electronic system.

Fiber-optic rotational seismic system for investigation of the rotational events

The paper presents a new telemetric system for direct measurement and investigation the rotational components exist in seismic events. The FORS - fiber optic rotational seismometer and seismographs constructed on the base of the Sagnac interferometer are the elements of the system. The special construction of the system protects their elements remote control in real time via internet utilize the GSP/GSM connections. The first results according application autonomous FORS (AFORS) with accuracy in the range 4.9·10-9 - 6.1·10-8 rad/s in detection bandpass 1.66 - 212.30 Hz located in Ksiαz and Warsaw, as well as older one FORS-II (mounted in Ojców) are reported.

Fibre-optic gyroscope as instrumental challenge for rotational seismology

Rotational Seismology caused highly interest in investigation of rotational movements generated by earthquake, mines and existing in engineering structures. The most oppressive aspect of research in this field is technical requirements for sensors. However, the instruments basing on the Sagnac effect seem to be the most appropriate to investigate rotational effects due to the fact that they are entirely insensitive to translational motion and are able to measure rotation rate in wide frequency and amplitude band. The paper presents a new device FOSREM which, based on FOG, possesses special solutions that makes it perfect, in author knowledge, for any rotation sensing.

Construction and laboratory test of a fibre optic sensor for rotational events recording

We present a novel and technically advanced system – Fibre-Optic System for Rotational Events & Phenomena Monitoring (FOSREM). It has been designed in order to register and monitor rotational events in seismological observatories, engineering constructions, mines and even on glaciers and in their vicinity. Its wide application field is a result of unique parameters and electronic solutions which give an opportunity to measure a component of rotation in the wide range of a signal amplitude from 10-8 rad/s to 10 rad/s, as well as a frequency from 0 Hz to the upper frequency between 2.56 Hz to 328.12 Hz. Moreover, the numerical analysis and simulations indicate that it keeps the theoretical sensitivity equal to 2·10-8 rad/s/Hz1/2. FOSREM is equipped with an advanced communication module which gives the possibility for a remote detection parameter control, as well as the recorded data receiving. It enables the sensor to assemble in any chosen place. In the paper we present laboratory investigations and tests which confirm the wide application field and practical aspects of FOSREM.