X. Tang 1, Z. Ghassemlooy 1, S. Rajbhandari 1, W. O. Popoola 1 and C. G. Lee 2 1: Optical Communications Research Group, NCRLab, Northumbria University, Newcastle upon Tyne, UK 2: Department of Electronic Engineering, Chosun University, S. Korea

I.FSO I NTRODUCTION  Features  Applications  Challenges II.L OGNORMAL T URBULENCE M ODEL III.S YSTEM D ESCRIPTION  Transmitter  Receiver IV.B IT E RROR P ROBABILITY A NALYSIS V.R ESULTS AND D ISCUSSIONS VI.C ONCLUSION

Benefits include  Ultra High Wireless Bandwidth  Most Secure Wireless Transmission  License free operation  Versatile Protocol  Safe to Use All  Major Cost Savings  Reliable Communication  High MTBF (Mean Time Between Failures) The world's first 10 Gig point-to-point deployment - Hollywood California by System Support Solutions, Inc.

Typical Free-Space Optics deployments pictured above include point-to-point, multiple point-to-point, and mesh.

The above chart displays the approximate costs for full duplex 10BaseT, FastE and GigE links at distances from 10 meters to 6000 meters. You will observe that GigE is the real bargain with FSO technology (compared to FastE, 10x throughput for little more cost).

FSO has been participated in over 400 link deployments including every continent in USA.

 Multi-campus University LightPointe's optical wireless products

 Last-mile Connectivity

 Clear Mesh Combines FSO Mesh for Metro Nets ClearMesh Networks, a start-up based in Pasadena, California, unveiled a wireless optical mesh networking solution capable of delivering business-class services at Mbps without requiring licensed spectrum.  Ship-to-shore FSO Under a Phase II SBIR program sponsored by NAVSEA, LSA has developed a Free Space Optical Ship to Shore Communication System to address development of a Low Probability of Intercept/ Detection (LPI/LPD) communication capability for the littoral environment.

 FSO Networks  Indoor FSO ENTERPRISE APPLICATIONS  Enterprise Connectivity Health Care Engineering & Design Voice & Data Video Telco Bypass Security Disaster Recovery MOBILE CARRIER APPLICATIONS BTS Backhaul Connectivity

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.

DEPENDS ON: Altitude, Pressure, Wind speed Temperature and relative beam size Eddies of different sizes and refractive indices 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

I: The received irradiance at the receiver I no : The received irradiance without scintillation. σ l: Log irradiance variance (turbulence strength indicator) I: The received irradiance at the receiver I no : The received irradiance without scintillation. σ l: Log irradiance variance (turbulence strength indicator) ModelComments Log NormalSimple; tractable Weak regime only I-KWeak to strong turbulence regime KStrong regime only Rayleigh/Negative Exponential Saturation regime only Gamma-GammaAll regimes Irradiance PDF The limitation of the log-normal model is defined by the Ryotov variance rage

The PolSK modulator is based on the LiNbO 3 device of which the operating wavelength is 1550 nm [1]. LD: laser diode PBS: polarizing beam splitter V b controls the relative phase of the two polarizations V a controls the amount of light launched in x and y polarizations V match applied to the 3 dB coupler is used for wavelength matching 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 , August 1994.

LO: local oscillator; DC: directional coupler; BPF: bandpass filter; LPF: lowpass filter. P r,lo : signal power ω r.lo : angular frequencies Ф r,lo : phase noises m(t): the binary information

The 2PolSK modulation is based on the definition of the Stokes parameters S 0, S 1, S 2 and S 3 [1]: {n i (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 S 1. A digital symbol ‘0’ is assumed to have been received if S 1 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

[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 , January [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, July [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 , September 2009.

The conditional BER of the received irradiance: The unconditional probability P e is obtained by averaging P ec 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 , 2-5 December 1991

Both simulated and theoretical curves match very closely which confirms the validity of the simulation. The simulated and calculated BERs performance against the SNR in an AWGN channel without turbulence

 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 fading penalty against turbulence variances for a range of BERs

The BER performances of 2ASK, 2PolSK and 2PSK against the SNR in the AWGN channel with various turbulence variances 3 dB 7.1 dB