Transcript Brillouin Scattering Slow Light and Secure Fiber Communication

Microwave Photonics
Applications of Stimulated
Brillouin Scattering
Dr. Avi Zadok, School of Engineering, Bar-Ilan University
+972-3-5318882
Together with:
[email protected]
www.eng.biu.ac.il/~zadoka/
Prof. Moshe Tur, Prof. Avishay Eyal, Dr. Oded Raz, Elad
Zilka, and Yair Peled, School of Electrical Engineering,
Tel-Aviv University
Outline

Broadband Stimulated Brillouin Scattering Processes in
Optical Fibers

Variable (“slow light”) group delay of waveforms

Data pulses

Analog, radar waveforms

Single-sideband modulation format

Ultra-wideband noise-based transmission
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Stimulated Brillouin Scattering
Strict phase matching conditions: p - s =  B (~211 GHz)
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Characteristics of SBS

Low threshold in standard fibers (few mW)

Simple and robust
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Detrimental effect in optical communication: restricts the
transmitted power

Gain coefficient is of Lorenzian lineshape:
g  s  
g0 Ap
2
1  j 2  s   p   B   B

g0 Ap
2
1  j 2   B

Ultra-narrow linewidth for CW pump: ~ 30 MHz only!

Objective: utilize SBS for all-optical signal
processing
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SBS with Broadened Pump
Pump
 p3
 p2
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 p1
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Signal
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SBS with Broadened Pump

Broadened Pump: Magnitude gain is proportional to
the pump spectrum

Phase response related to the magnitude gain
through the Kramers – Kronig Relations:
Img s  

2 ' Re g '
d'
2

2

' s
Calculation of SBS response for arbitrary pump
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Pump Broadening Via Direct
Modulation
Adiabatic
chirp
Thermal
chirp
Shalom et. al, JQE, Vol. 34 pp. 1816-1824, 1998
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Pump spectrum measurement
Synthesized pump
Modulation:
  t mod T 1.5 
it   i0  i 1  
   i N t 
  T  
i0  80mA
T  320ns
i  11mA
i N2 t   1.6mA
BN  20MHz
Simulation
Heterodyne measurement
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“Slow Light”

Optically-controlled, variable group delay

Sharp phase delay variations, often
associated with narrow-band gain / absorption

Control through non-linear interactions
Spectral gain
Spectral phase delay
  
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
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Pump spectrum synthesis

Sharp spectral edges of pump spectrum:
enhancement of delay–bandwidth product.
Reg   E p    B 
Img 
2
1
1.5
0.9
1
Phase response [arb.]
0.8
Relative gain
0.7
0.6
0.5
0.4
0.3
0.2
0.5
0
-0.5
-1
0.1
0
-3
-2
-1
0
1
Normalized frequency offset
2
3
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-1.5
-3
-2
-1
0
1
Normalized frequency offset
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2
3
10
Measurement of SBS gain and
phase response
Pump
EDFA
Arbitrary Waveform
Generator
Pump
Variable Attenuator
Network Analyzer
Detector
Probe
EDFA
Tunable
Laser
SSB Modulator
DSF
Isolator
Optical
BPF
Polarization
Controller
Loayssa et. al, IEE Proc. Optoelectron., Vol. 148 pp. 143-148, 2001
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SBS Slow and Fast Light
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SBS amplification accompanied by steep gradients of the
signal phase as a function of frequency – group delay
Gain [dB]
20
10
0
-3
-2
Phase [rad]
2
-1
0
1
Frequency offset [GHz]
  
0
-2
-3
2
-2
-1
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0
1
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
2
3
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Delay of Isolated Pulses

SBS amplification accompanied by steep gradients of the
signal phase as a function of frequency – group delay
A. Zadok et al., Opt. Express 14, 8498, 2006
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Delay of 5Gb/s PRBS
Output NRZ eye diagram:
Synthesized modulation, 22dBm, 120ps delay
BER for 80, 100, 120ps
delay: <10-9, 10-8, 410-6
First demonstration of high-rate PRBS delay using SBS
Zadok et. al, Opt. Express, Vol. 14 pp. 8498-8505, 2006
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5Gb/s PRBS: Delay Enhancement
140
Synthesized
Mod.
Measured PRBS delay [pS]
120
100
80
60
40
Random Mod.
20
0
6
7
8
9
10
11
12
13
PRBS signal power gain [dB]
Synthesized pump modulation: 25-40% longer delays
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True Time Delay (TTD) in phased
array antennas
D
D
D
D
D
D
D
D
True Time
Delay


Beam-stirring using variable delay between elements
Large bandwidth: group delay instead of phase delay

Low distortion necessary
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LFM “impulse response” metrics
Main lobe
width ~ 1/B
PSL
ISLR 
 hLFM  d
2
main lobe
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 hLFM  d
2
elsewhere
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Delay [ps]
Delay of LFM signals
‘+’: VNA
‘’: LFM
150
100
50
20km DSF
10
12
14
16
18
SBS power gain [dB]
20
22
Delay [ps]
300
200
3.5km HNLF:
100
10
15
20
SBS power gain [dB]
25
Zadok et. al, IEEE PTL, Vol. 19, pp. 462-464, 2007
  Nd sin     N  sin     N
c
c
f0
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50 GHz system: ~ 10 elements, 90°
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Response
[dB]
[dB]
Measured impulse response
0
T  20μs
Input pulse
0
B  1GHz
-20
-50
-40
-100
-60
-30
-150
-2
-20
-1.5
-10
-1
-0.5
0
Time0 [ns]
10
0.5
20
1
[Sec]
30
1.5
Pump power:
20dBm
2
-5
x 10
phase [rad]
1
-1
-3
-5
-500
-250
0
250
RF frequency [MHz]
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500
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Width broad: <1%
PSL: < -26dB
ISLR: > 21dB
Delay: 230ps
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SSB modulation - noise
Probe power spectral density [dB]
Heterodyne spectral measurement of LFM-modulated signal:
One side band amplified by SBS. No harmonics. NF ~ 150*.
T  2μs
-50
B  1GHz
-60
Noise
-70
Pump off
Pump on
Pump 20dBm
-80
-90
*: Olsson et. al, JLT, Vol. 5
pp. 147-153, 1987
-100
-110
-4
-3
-2
-1
0
1
2
3
4
Optical frequency Offset [GHz]
A. Zadok et al. J. Lightwave Technol. 25, 2168-2174 (2007)
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Impulse response of SSB
modulated LFM signal
Impulse response [dB]
0
Simulated noise
Ideal
Measurement
-10
-20
-30
-40
-50
-60
-40
-30
-20
-10
0
10
20
30
40
Time [ns]
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Ultra-wideband waveform
generation


UWB impulse radio: several GHz-wide, no sine-wave
carriers, low power spectral density
Applications: indoor wireless communication, imaging
systems, vehicular radar systems.
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UWB noise-based communication


Slow-rate modulation of broadband noise with carefully
controlled power spectral density
Alternative to tailored, short pulses.
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Experimental results
Brillouin pump spectrum:

Generated noise spectrum:
1.1 GHz bandwidth
Y. Peled, M. Tur and A. Zadok, Paper NTuC16, Nonlinear Photonics 2010
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Experimental results Cntd.
8 Mb/s transmission (no reference)

Correlation properties
Q = 10
Y. Peled, M. Tur and A. Zadok, Paper NTuC16, Nonlinear Photonics 2010
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Experimental results Cntd.
4 Mb/s transmission (with reference)
0.5
Decoded waveform
25
20
15
0
10
5
0
-0.5
1
2
3
4
5
-5
1
Time [micro-sec]

2
3
4
5
Time [micro-sec]
Q=5
Y. Peled, M. Tur and A. Zadok, Paper NTuC16, Nonlinear Photonics 2010
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