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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30EE 566 EE 566 Optical CommunicationOptical CommunicationMing LiMing Liminglimingli@[email protected] Space Optic (FSO)Why choose this topic?Why still choose this topic?September 11, 2001, New YorkEvery thing was destroyed Every thing was destroyed including normal fiber linkincluding normal fiber linkWall street stock market was closed because the communication was destroyedTwo of these units were used Two of these units were used between building to re-establish a between building to re-establish a high speed communication link.high speed communication link.FSO communication between Merrill Lynch FSO communication between Merrill Lynch Brokerage and Wall Street in New York Brokerage and Wall Street in New York following the terrorist attack that destroyed following the terrorist attack that destroyed normal fiber optic linknormal fiber optic linkHistory of Free Space OpticsHistory of Free Space OpticsThe transmission of information using The transmission of information using light is actually not a new idea.light is actually not a new idea. Great WallIn the late nineteenth century, Alexander In the late nineteenth century, Alexander Bell expanded his "phone-phone" Bell expanded his "phone-phone" communication which modulated by communication which modulated by sunlight.sunlight.In the mid-1960's In the mid-1960's NASA initiated NASA initiated experiments to experiments to utilize the laser as a utilize the laser as a means of means of communication communication between the ground between the ground and space.and space. Gemini-7Birth of Laser FSO CommunicationsSpace-to-Ground Lasercom LinkSpace-to-Ground Lasercom Link2000 km Link Distance2000 km Link Distance1 Gbps Transmission Rate1 Gbps Transmission RateSatellite Laser CommunicationChinese First Maned SpaceshipAir ForceAir Force Its potential for low Its potential for low electromagnetic electromagnetic emanation when emanation when transferring sensitive transferring sensitive datadataNavyNavySecure Secure communication communication with submerged with submerged submarines. submarines. Military Application of FSOTechnology from Space LasercomAdvantage of FSOAdvantage of FSOWireless communicate from A to BWireless communicate from A to BLow costs ($10K to $20K)Low costs ($10K to $20K)High bit rate (10 Mbps to 2.5 Gbps)High bit rate (10 Mbps to 2.5 Gbps)Set up a link in a few daysSet up a link in a few daysThe lasers used are eye safe, so The lasers used are eye safe, so even a butterfly can fly unscathed even a butterfly can fly unscathed through a beamthrough a beamApplication of FSOApplication of FSOConnectivity Solutions Connectivity Solutions 'Last-Mile' Network Solutions'Last-Mile' Network SolutionsTemporary Network ProvisionTemporary Network ProvisionCable Free Connectivity in the Cable Free Connectivity in the Finance SectorFinance SectorCCTV Security ApplicationsCCTV Security ApplicationsGSM Microcell ConnectivityGSM Microcell ConnectivityIndustrial estates, Science parks and university Industrial estates, Science parks and university campus environments typically exhibit a common campus environments typically exhibit a common problem – a number of separate buildings, separated problem – a number of separate buildings, separated by roads or other obstacles, between which by roads or other obstacles, between which communications links are frequently in demandcommunications links are frequently in demand..Cable digging, increasingly unpopular in cities, is Cable digging, increasingly unpopular in cities, is regulated by the local authority who may restrict re-regulated by the local authority who may restrict re-digging frequency of roads - and the cost may be digging frequency of roads - and the cost may be prohibitive in any case, especially if a river or railway is in prohibitive in any case, especially if a river or railway is in the way.the way.FSO vs RFFSO vs RF RF 2.4 GHz systems were typically running at 2-4 Mbps due to interference issues in the unlicensed frequency ranges FSO provided 10 Mbps of throughput for less than unlicensed RFFSO was less cost, more secure, and seemed simplerChallenge of FSOChallenge of FSOChallenge #1—hitting the Challenge #1—hitting the targettarget  Challenge #2—interrupted Challenge #2—interrupted signals signalsHitting the targetHitting the targetGetting a laser beam to hit the mark in Getting a laser beam to hit the mark in a laboratory setting is easy, but in the a laboratory setting is easy, but in the real world it is much harder. real world it is much harder. 1)Atmospheric turbulence1)Atmospheric turbulence2)Fog2)Fog3)Building movement3)Building movementAtmospheric Atmospheric attenuation and attenuation and scatterscatter6.5 dB/km 150 dB/km 225 dB/km300m distance to tall buildingSolution Solution Active beam steering (sometimes Active beam steering (sometimes involving MEMS), involving MEMS), Multiple laser beams, Multiple laser beams, Automated power control, and Automated power control, and calculated laser beam divergence. calculated laser beam divergence. Pulsed laser beams start out just Pulsed laser beams start out just centimeters wide and can diverge to 1 centimeters wide and can diverge to 1 meter or more over typical link meter or more over typical link distances—like using a really big bullet distances—like using a really big bullet to hit a small target. to hit a small target.Challenge #2—Challenge #2—interrupted signalsinterrupted signalsAn email is beaming across the An email is beaming across the FSO connection just as a bird flies FSO connection just as a bird flies through, blocking the signal. through, blocking the signal.Solution #2—no lost Solution #2—no lost datadata No fear. FSO linkheads essentially "talk" to No fear. FSO linkheads essentially "talk" to one another, and just as people repeat words one another, and just as people repeat words in conversation, data can be retransmitted in in conversation, data can be retransmitted in the event of a temporary beam blockage. the event of a temporary beam blockage. Several companies even have redundant


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UB EE 566 - Free Space Optic

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