FACULTY OF ADVANCED TECHNOLOGIES AND CHEMISTRY
AFORS - Autonomous FibreOptic Rotational Seismograph
Design and Application
L.R. Jaroszewicz, Z. Krajewski
Institute of Applied Physics, Military University of Technology
2 Gen Sylwestra Kaliskiego Street, 00-908 Warsaw, Poland
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Outline
• 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
2nd IWGoRS, Prague, 10-13 October 2010
WayOFFibre
-OpticTECHNOLOGIES
Gyroscope as
?
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FORS-->
FORS-->
Recorded digital
data smoothing by
the spline function
TAPS-->
TAPS-->
[L. Solarz, et all, Acta
Geophys. Pol., 52, (2004), 198]
min  9.8106 rad/ s
Amplitude rel. un.
@D
Rotation - TAPS , FORS - I
2
1
FORS ->  
0
a direct quantity from physical effect
TAPS -> u
-1
@
D
-2
@D
26.5
2
27 Translation
27.5 - TAPS 28
t s
Amplitude rel. un
1.5
28.5
29
calibration problem,
sensitivity on linear motion
FOG ->  ∫ dt
1
drift phenomenon,
dynamic range problem
0.5
0
- 0.5
-1
- 1.5
26.5
27
@
D
27.5
t s
28
28.5
29
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FORS – principle of operation
FORS – Fiber-Optic Rotational Seismometer
– FOSI optimized for RSE detection

1
  4RL  

c
So
System optimization:
1.Optical unit  increase sensitivity as well as minimization external influences
2.Electronic unit  proper signal processing for long time operation as well as remote
control
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Optical unit:
Ωmin in quantum noise limitation [Ostrzyżek, 1989]:
 min
 c
4  2 10 /10L /1000
VA2 1
4  k T
 / 10
 / 10L / 1000





e

S

P

10

10

1

X


 I A2
L
 / 10
2
R0 8
R0
B 4  R  L S  J1 1.84  PL 10
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).
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Influence of SMF-28 fibre lenght on system sensitivity for constructed AFORS
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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.
Output SOP from loop - simulation:
min =1.93 10-9 [rad/sHz1/2]
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Electronic unit:
Application of the synchronic detection unit [Krajewski, 2005]:
m (t )  0 sin( mt )



 
1

cos(


)
J
(

)

2
J
(

)
cos(
2
n

t
'
)


2n
e
m
 0 e
 


n 1
 
I (t )  P0 1  cos   m (t )   m (t   )  P0 


sin( )2 J ( ) sin[(2n  1) t ' ]


2 n 1
e
m




 n 1



where: t’=t+/2e=20 sin(m/2), 2P0 – output optical power - time for light passing throughout sensor loop.
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For proper choose of the m – as correlated with  (AFORS  6.8 kHz), only first two harmonic
of output signal are important:
 J   A 
  arctan 2 e  1   arctanS e  u (t ),
 J 1 e  A2 
u (t ) 
A1
A2
  So arctanSe  u (t )
AFORS communication scheme:
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  So arctanSe  u (t )
AFORS – calibration
o

/h
E
ASPU: u (t ) 
N-S E=9.18 o/h
N
Warsaw
o
W-E E=0.00 /h
A1 J1 (e )

tan 
A2 J 2 (e )
hence S e 
A2
tan 
A1
Based on well defined Earth rotation and data from
7280 DSP lock-in amplifier:
 LA EA 
J ( )
2 A2
S e   1  2   Z w ; Z w  2 e J 2 (e ) |  0 
 e  1.63199
J1 (e )
2 P0
 LA2 EA1 


”
Se = 0,0144,
So = 0,00433
2nd IWGoRS, Prague, 10-13 October 2010
re
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AFORS – accuracy
AFORS directed in W-E and measurement with modulation switch off
 A 
( A1 , A2 )  S 0 Arc tan  S e 1 
 A2 
 1 ,  2
2
 
  

  
  1   
  2 
 A1
  A2

are mean values of noises recorded for amplitude A1, A2 in given detection bandpass
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2
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B=
1.66 [Hz]
5.1 10-9 [rad/s]
Accuracy
21.2 [Hz]
1.7 10-8 [rad/s]
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106.15 [Hz]
3.9 10-8 [rad/s]
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Remote control
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Conclusion
This 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”.
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 AFORS-one
2nd IWGoRS, Prague, 10-13 October 2010
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2nd IW Go RS, Prague, 10-13 October 2010