AFORS -Autonomous Fibre- Optic Rotational Seismograph Design...

AFORS AFORS -- Autonomous FibreAutonomous Fibre--Optic Rotational Seismograph Optic Rotational Seismograph

Design and ApplicationDesign and Application

L.R. Jaroszewicz, Z. Krajewski

Institute of Applied Physics, Military University of Technology2 Gen Sylwestra Kaliskiego Street, 00-908 Warsaw, Poland

FACULTY OF ADVANCED TECHNOLOGIES AND CHEMISTRY

2nd IWGoRS, Prague, 102nd IWGoRS, Prague, 10--13 October 201013 October 2010

• Way Fibre-Optic Gyroscope as RS ?• FORS – Fibre-Optic Rotational Seismometer

– principle of operation• AFORS – Autonomous FORS (seismograph):

- optic and electronic parts optimization,- calibration & accuracy estimation,- remote control.

• Example of events recording in Książ• Conclusions


Outline Outline


2nd IW Go RS, Prague, 102nd IW Go RS, Prague, 10--13 October 201013 October 2010


FORS-->FORS-->

TAPS-->TAPS-->

srad/108.9 6min

Recorded digital data smoothing by the spline function[L. Solarz, et all, Acta Geophys. Pol., 52, (2004), 198]

26.5 27 27.5 28 28.5 29t@sD- 2

- 1

0

1

2

edutilpmA

@ler.nu.D

Rotation - TAPS , FORS - I

26.5 27 27.5 28 28.5 29t@sD

- 1.5

- 1

- 0.5

0

0.5

1

1.5

2

edutilpmA

@ler.nuD

Translation - TAPS

FORS -> a direct quantity from physical effect

TAPS -> ucalibration problem,

sensitivity on linear motionFOG -> ∫ dtdrift phenomenon,

dynamic range problem

Way FibreWay Fibre--Optic Gyroscope as RS ?Optic Gyroscope as RS ?


FORS FORS –– principle of operationprinciple of operationFORS – Fiber-Optic Rotational Seismometer

– FOSI optimized for RSE detection

oc

RLS14

System optimization:1.Optical unit increase sensitivity as well as minimization external influences2.Electronic unit proper signal processing for long time operation as well as remote control



2

0

1000/10/10/20

2

10/1

1000/10/min 411010

81

1084.11024

4 AL

LA

L

L

IRTkXPSe

RV

PJSLRc

B

Ωmin in quantum noise limitation [Ostrzyżek, 1989]:

where: B - detection bandpass, c- light speed in vacuum, - optical wavelenght, R – sensor loop radius, L – fibre lenght, - fibre attenuation in dB/km, total loss in optical part (without loss of used fibre in sensor loop), PL – optical power of used source, S – sensitivity of used photodiode, VA, IA – dark voltage and current of photodiode, R0 – photodiode impedance, e - electron charge, k – Boltzmann constant, T –temperature.

Conclusions:1.Sensitivity increase with the bandpass B narrowing,2.Sesnitivity is linear function of bandpass,3.The higher sensitivity is for shorter wavelenght but fibre attenuation growing)4.Sensitivity increase with source power PL, 5.Sensitivity increase with radius of sensor loop R,6.The total loss of system should be minimized for better sensitivity,7.Increase the total lenght of fiber in sensor loop L increase sensitivity (but - fibre attenuation in dB/km).

Optical unit:Optical unit:



Influence of SMF-28 fibre lenght on system sensitivity for constructed AFORS



AFORS optimized parameters:• L= 15 000 [m], 15 layers, double quadropole winded,• =0.436 [dB/km], • loop R=0.34 [m] contains permaloy particles, • d• cascade polarizers (46 and 55 [dB]), • depolarizer with 0.02 [dB] extinction ratio, • nm], nm], PL =20 [mW], • S=0.99 [ A/W], IA =0.06 [nA], R0 =163 [k.

min =1.93 10-9 [rad/sHz1/2]

Output SOP from loop - simulation:



Application of the synchronic detection unit [Krajewski, 2005]:

Electronic unit:Electronic unit:

)sin()( 0 tt mm

112

120

00

]')12sin[()(2)sin(

)'2cos()(2)()cos(1)()(cos1)(

nmen

nmene

mm

tnJ

tnJJPttPtI

where: t’=t+/2e=20 sin(m/2), 2P0 – output optical power - time for light passing throughout sensor loop.



For proper choose of the m – as correlated with (AFORS 6.8 kHz), only first two harmonic of output signal are important:

2

1

2

1

1

2 )(,)(arctanarctanAAtutuS

AA

JJ

ee

e

)(arctan tuSS eo

AFORS communication scheme:


AFORS AFORS –– calibrationcalibration


)(arctan tuSS eo

”

N

Warsaw W-E E =0.00 o/h N-S E =9.18 o/h

E o /h

tan)()()(

2

1

2

1

e

e

JJ

AAtuASPU: hence

tan1

2

AASe

Based on well defined Earth rotation and data from 7280 DSP lock-in amplifier:

)()(;

1

2

1

2

2

1

e

ewwe J

JZZEAEA

LALAS

63199.1

22)(

0

20|2 ee P

AJ

Se = 0,0144, So = 0,00433



AFORS AFORS –– accuracyaccuracy


AFORS directed in W-E and measurement with modulation switch off

2

1021 tan),(

AASArcSAA e

2

22

2

11

AA

re

21 , are mean values of noises recorded for amplitude A1, A2 in given detection bandpass


Accuracy B= 1.66 [Hz] 21.2 [Hz] 106.15 [Hz]

5.1 10-9 [rad/s] 1.7 10-8 [rad/s] 3.9 10-8 [rad/s]



Remote controlRemote control


Acronyms:

1. Fiber-Optic Rotational Seismometer FORS

2. Fiber-Optic Rotational Seismograph FORS-II

3. Autonomous Fiber-Optic Rotational Seismograph AFORS

4. Two AFORS AFORS-two and AFORSAFORS--oneone


ConclusionConclusionThis work has been made under financial support the Polish Ministry of the Science and Higher Education grant No N N525 2166 33 as well as Key Project POIG.01.03.01-14-016/08-04 „New photonic materials

and their advanced application”.


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