Transcript Performance of the Coherent Optical Binary Polarization

X. Tang1, Z. Ghassemlooy1, S. Rajbhandari1, W. O. Popoola1 and C. G. Lee2
1: Optical Communications Research Group, NCRLab, Northumbria University, Newcastle
upon Tyne, UK
2: Department of Electronic Engineering, Chosun University, S. Korea
Email: [email protected]
I.
FSO INTRODUCTION



II.
III.
LOGNORMAL TURBULENCE MODEL
SYSTEM DESCRIPTION


IV.
V.
VI.
Features
Applications
Challenges
Transmitter
Receiver
BIT ERROR PROBABILITY ANALYSIS
RESULTS AND DISCUSSIONS
CONCLUSION
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FSO Networks
FSO transmission systems loose some of their energy from signal scattering,
absorption and scintillation.
 Scattering: light signals are redirected as they pass through water particles.
 Absorption: some optical energy is converted to heat as it strikes particles
(such as smog).
 Scintillation: when heated (such as from smokestacks) air cause a bending
of the optical beam.
The atmosphere behaves like prism
of different sizes and refractive indices
Phase and irradiance
fluctuation
Result in deep
signal fades that
lasts for ~1-100 μs
DEPENDS ON:
• Altitude, Pressure, Wind speed
• Temperature and relative beam size
Eddies of different sizes
and refractive indices
Model
Comments
Log Normal
Simple; tractable
Weak regime only
I-K
Weak to strong
turbulence regime
K
Strong regime only
Rayleigh/Negative
Exponential
Saturation regime only
Gamma-Gamma
All regimes
The limitation of
the log-normal
model is defined
by the Ryotov
variance rage
Irradiance PDF
I:
p( I ) 
 ln( I / I )   2 / 2) 2 
1
no


l
exp 
 I 0
2
I
2 l
2l




1
The received irradiance at the
receiver
Ino: The received irradiance without
scintillation.
σl: Log irradiance variance
(turbulence strength indicator)
Vmatch applied to the
3 dB coupler is
used for wavelength
matching
The PolSK modulator is based on the
LiNbO3 device of which the
operating wavelength is 1550 nm [1].
LD: laser diode
PBS: polarizing beam splitter
Va controls the
amount of light
launched in x and y
polarizations
Vb controls the
relative phase of
the two
polarizations
x and y are the axes
of polarization used
to represent digital
symbol ‘0’ and ‘1’,
respectively.
[1] S. Benedetto, A. Djupsjobacka, B. Lagerstrom, R. Paoletti, P. Poggiolini, and G. Mijic, IEEE Photonics Technology Letters, vol. 6, pp. 949951, August 1994.
LO: local oscillator;
DC: directional coupler;
BPF: bandpass filter;
LPF: lowpass filter.
Pr,lo : signal power
ωr.lo: angular frequencies
Фr,lo : phase noises
m(t): the binary information
The 2PolSK modulation is based on the definition of the Stokes
parameters S0, S1, S2 and S3 [1]:
{ni(t)}i=0,1,2,3 : the noise contribution
which are independent of the
received SOP and have the same
variance.
Note that the proposed 2PolSK
refers only to the parameter S1. A
digital symbol ‘0’ is assumed to
have been received if S1 is above
the threshold zero and ‘1’
otherwise.
[1] E. Collett, "The stokes polarization parameters," in Polarized light: fundamentals and applications New York: Marcel Dekker, Inc., 1993, pp.
33-66.
[1] M. Nazarathy and E. Simony, "Error probability performance of equi-energy combined transmission of differential phase, amplitude, and
polarization," Journal of Lightwave Technology, vol. 25, pp. 249-260, January 2007.
[2] M. N.-A.-S. Bhuiyan, M. Matsuura, H. N. Tan, and N. Kishi, "Polarization insensitive wavelength conversion for polarization shift keying
signal based on four wave mixing in highly non-linear fiber " 14th OECC 2009, pp. 1-2, 13-17 July 2009.
[3] X. Zhao, Y. Yao, Y. Sun, and C. Liu, "Circle polarization shift keying with direct detection for free-space optical communication " Optical
Communications and Networking, , vol. 1, pp. 307-312, September 2009.
The conditional BER of the received irradiance:
The unconditional probability Pe is obtained by averaging Pec over
the log normal irradiance fluctuation statistics:
This result is same as the BER expression of FSK. As regards
the system sensitivity, PolSK and FSK techniques have complete
equivalence [1].
[1] R. Calvani, R. Caponi, F. Delpiano, and G. Marone, "An experiment of optical heterodyne transmission with polarization
modulation at 140 Mbit/s bitrate and 1550 nm wavelength " GLOBECOM '91, vol. 3, pp. 1587-1591, 2-5 December 1991
The simulated and calculated BERs performance against the SNR in an
AWGN channel without turbulence
0
10
-2
BER
10
-4
10
-6
10
simulation
theory
-8
10
0
5
10
15
SNR (dB)
Both simulated and theoretical curves match very closely which confirms the
validity of the simulation.
The fading penalty against turbulence variances for a range of BERs
Fading Penalty (dB)
20
BER=10-9
BER=10-6
15
BER=10-3
10
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Turbulence Variance
For a fixed BER, the fading penalty increases with the turbulence variance
Fading penalty is higher for lower values of BER at the same turbulence level
The BER performances of 2ASK, 2PolSK and 2PSK against the SNR in the
AWGN channel with various turbulence variances
0
10
-3
 l2=0
 l2=0.9
BER
10
7.1 dB
-6
10
ASK
PSK
PolSK
10
-9
0
5
10
3 dB
3 dB
15
SNR (dB)
20
25
30