Light-Pipes: Controlling Lightcsep.cnsi.ucsb.edu/sites/csep.cnsi.ucsb.edu/files/... · The Big Idea...
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The Big Idea • Light usually goes in a straight line, but we can control where it goes using reflections. • All our data (internet, TV etc.) is sent this way, by light pulses in optical fibers. Materials Demonstration – Reflection Tank Demonstration – Optical Fibers Jello Waveguides (per group) • Water tank with a 1-2 drops of milk/cream • Green laser pointer • Turn off lights • 2 Fiber Optic cable bundle • Laser pointer • One Laminated placemat/grid • A square piece of gelatin • Red Laser pointer • Protective goggles • Plastic knife There are enough supplies in each bin for XX groups per rotation. Supply Info: Reflection Tank Optical Fibers Jello Waves • 2 clear acrylic tubs/magazine holders, like this (water-tight): Clear Magazine Holder by US Acrylic, LLC • Fatty milk to add to reflection tank o Milk/Cream: Small amount near to day of activity • Fibers: “E1000 Simplex” fiber from here: http://www.fiberopticp roducts.com/Jacketed. htm • 100 ft ≈ $50 • 3 meters x 8 families per room • Gelatin recipe: 1/4 cup plain gelatin to 2 cups liquid. Make 6 trays of gelatin, cut each piece in half with smooth cut. o Gelatin: box o 6 trays of square/ cube silicone molds • Plastic Knifes Other Stuff Laser pointers Goggles • AAA batteries – lots (the pointers will run out!) • Garbage bags • Optional: o 2 fiber optics toys o coaxial tv cable (cut) o Telephone cable (cut) • Green Laser Pointers: 3x green, AAA batteries • Red 20x, using AAA batteries (NOT hearing- aid batteries) • http://www.miniintheb ox.com/5mw-red-light- laser- pen_p200421.html • Rosco Cinema Gel #2005 • Posterboard paper • Exacto knife to cut o Plans here: bwmag.in: anaglyph-3d-glasses Light-Pipes: Controlling Light
Transcript of Light-Pipes: Controlling Lightcsep.cnsi.ucsb.edu/sites/csep.cnsi.ucsb.edu/files/... · The Big Idea...
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TheBigIdea• Lightusuallygoesinastraightline,butwecancontrolwhereitgoesusingreflections.• Allourdata(internet,TVetc.)issentthisway,bylightpulsesinopticalfibers.
MaterialsDemonstration–ReflectionTank
Demonstration–OpticalFibers
JelloWaveguides(pergroup)
• Watertankwitha1-2dropsofmilk/cream
• Greenlaserpointer• Turnofflights
• 2FiberOpticcablebundle
• Laserpointer
• OneLaminatedplacemat/grid• Asquarepieceofgelatin• RedLaserpointer• Protectivegoggles• Plasticknife
ThereareenoughsuppliesineachbinforXXgroupsperrotation.SupplyInfo:ReflectionTank OpticalFibers JelloWaves• 2clearacrylic
tubs/magazineholders,likethis(water-tight):ClearMagazineHolderbyUSAcrylic,LLC
• Fattymilktoaddtoreflectiontanko Milk/Cream:Small
amountneartodayofactivity
• Fibers:“E1000Simplex”fiberfromhere:http://www.fiberopticproducts.com/Jacketed.htm
• 100ft≈$50• 3metersx8families
perroom
• Gelatinrecipe:1/4cupplaingelatinto2cupsliquid.Make6traysofgelatin,cuteachpieceinhalfwithsmoothcut.o Gelatin:boxo 6traysofsquare/cube
siliconemolds• PlasticKnifes
OtherStuff Laserpointers Goggles• AAAbatteries–lots(the
pointerswillrunout!)• Garbagebags• Optional:
o 2fiberopticstoyso coaxialtvcable
(cut)o Telephonecable
(cut)
• GreenLaserPointers:3xgreen,AAAbatteries
• Red20x,usingAAAbatteries(NOThearing-aidbatteries)
• http://www.miniinthebox.com/5mw-red-light-laser-pen_p200421.html
• RoscoCinemaGel#2005• Posterboardpaper• Exactoknifetocut
o Planshere:bwmag.in:anaglyph-3d-glasses
Light-Pipes:ControllingLight
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PrepWorkPreparebeforethesession:
• FibersDemoo Setupsometablesatfrontofclasswheremany/mostfamiliescangatherto
holderendsoffiberbundle• WaterTankDemo
o Fillwatertank~3/4fullo AddOneDrop(ONLY!)ofmilk/cream.o Testifgreenlaserpointercanbeclearlyseenacrosslengthoftank.
• Jello-WaveguidesActivityo Prepareplateswithmaterialstopassout:
§ Jelloblock(cubescutinhalf)§ Plasticknife§ Laserpointer§ Lasergoggles(twoorthree)
o LaminatedGraphPaperattables,andfreshpilefornextgroup• Laminatedpicturesattables,cutcablesready
ProcedureTransitionbetweengroups:
• CollectallLaserpointers(countthem!)andgoggleso Checkthattheywork–putasideanywithlowbatteries,replacewithfreshones
• Don’tcleanupjelloyet–justputasidetheusedgraphpaper+jello,andprovidefreshonesforthenextgroup.
o Cancleanitallupattheend.
Duringsession:• ASKparticipants
o Whathappenswhenyousendatext/email?(Refertoprintoutattheirtables)§ Howdoesinformationphysicallygofrommyphone/computerto
someoneelse’s?• Page1ofPrintout• Showseveredcoaxial/telephonecable
§ Allourdataissentusingpulsesoflight• Page2ofPrintout
o CellPhoneAntennas,TVCableseventuallyconnecttotheworldwidefiber-opticnetworkw/Lasers
o Whatisspecialabouta“Laser”:
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§ Howisalaserpointerdifferentthanaflashlight?• Shootlaseracrossroom• Optional:ShowSmartPhoneflashlightforcomparison
o AnswerAlaseris:VeryBright,Goesinonestraightline,Onepurecolor(whiteismanycolors!)
o Howdowecontrollightoverlongdistances?§ Thelaserpointeralwaysshootsstraight!Howwouldyoushootalaserto
England?
IMPORTANTNOTES• Keepaneyeonthetime!
o Thefirsttwodemonstrationsshouldonlytake10mintotal!• Useparentsasresponsiblelaser-wielderswhenindoubt.
o Bequicktogiveaparentsolelaser-wieldingpowerifneeded.
• ReflectionTanko Turnofflightso Shootgreenlaserintotank
§ Bounceoffbottomsuchthatlightalsobouncesoffthetop,likeinpicture.
o Wecanusereflectionstoguidethelighto ASKparticipants
§ Whatdoyounoticeaboutthelighttravellingthroughthewatertank?
• Whydoyouthinkthisishappening?§ Howisthelightfromthelaserpointerdifferentfromthatofaflashlight?
o Explanation:§ Whenlightgoesfromonematerialtoanother,thereisusuallyReflection
(bouncesoff)ANDTransmission(passesstraightthrough).§ Ifwefindananglewheremost/allisreflected,wecanmakethelightgo
wherewewantitto.
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• OpticalFiberso Assign“Audience-End”cablestofamilyrepresentativeso Holdthe“Leader”endofcables.o Explainthatamessagewillbesentthroughoneofthe
cables–whichcableisamystery.o Chooseone“LeaderEnd”andsendaMorse-codetype
signal(pulses)o Have2ndLeadernowbendthemiddleofthecable
bundleintoacurveorloopo Demonstratewithmoresignalingthrougheachcable,that
thesignalisstilldelivereddespitethebendinthecable.Thedirectionoflightismanipulated.
o Makesureeachfamilyseestheirendlightup.o Explanation:
§ SimilartotheWaterTank,lightcanbeguided/trappedinplasticfibers.
• Calleda“Waveguide”ingeneral(guidinglightwaves)
§ Canuseopticalfibertoguidelightanywhere!§ Ourinternet/dataissentusingpulsesoflight,justlike
Morsecode.• JelloWaves-----Dotheseinorder–oncematerialsarepassedout,
theywon’tlisten!o FIRST:Deliverwarningregardingsafeuseoflaserpointers
o Demonstrate/Explainhowtousethegelatinasawaveguide:§ PlacepointerFLATontablewhenusingit§ PlaceGelatinonlaminatedpaper
o Passouttraysofmaterials–COUNTthenumberofLasersgivenout!§ ObservehowlightbouncesaroundinsidetheGelatinBlock
o Challenge:Makethelightbend180degrees(backtowardsthem).§ FamiliescancutthepiecewiththeBACKofplasticknifetoexperiment
withtheprocess.MakeVertical&Smoothcuts!§ Halfway:showdesignsofsuccessfulgroups&continue§ Bonuschallenge:doitinthesmallestspacepossible
RULES1.LasersmustalwaysbeangledDOWN/horizontal–neverpointup!2.Ifthepointersareshonetowardspeople’sfaces,thepointerswillbegiventotheresponsibleparent.3.Allpointerswillbereturned–leaderswillCOUNTthenumberofpointerstheygiveout,andensureallarereturned.
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• Wrap-up
o Remember:everytimeyousendatextoremail,lasersareshootingyourdatathroughopticalfibers.
o TheJello-Waveguidesshowedushowwecanmakelightgowherewewantitto.o Fiber-Opticnetworksusespecialcomputermicrochipsthatguidelightusing
Waveguidesjustlikethesejellowaveguides–wecanguidelightinverysmallareasusingwaveguides.
SAFETY/Troubleshooting/Notes• FiberOptic:
o PositionoffiberintheLaserPointerendcanmaketheguidingturnon/off.Movethefibertiparoundinthepointer’sendwhileflashingit.
• Jello:o MakesuretheyputthepointerFLATonthetable–theyoftenholdthepointer
andshootitdownatanangle.o Makesurecutsidewallsarevertical&smooth!o IfgroupsfinishtheirJello-Challengeearly,askthemtomakeitevensmaller.(Eg.
turnthelightaroundinasmallerarea)o Evenjustasmalltrianglecanreflectthelight180°
Background• Allourinternet,phone,televisionissentaroundtheworldusingpulsesoflight.
o Theplugsinyourhousearemetal(ex.TVcoaxialcable),oryourcellphonesendsradiotoanantennasomewhere–thesethenconnecttoVerizon/Cox’sworld-widefiber-opticnetwork.
o Thelightisguidedalong“opticalfibers”–there’saworld-widenetworkofthesetosendinformationanywhere.§ Electricalsignalsgetveryweakafterlongdistances
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§ GuidedLightcangomuchfurtherwithoutlosingmuchbrightness.o MainQuestionbeingposed/answeredbytheactivity:
§ Howdowegetlighttogowherewewant?
• Totalinternalreflection(TIR)isthephenomenonthatinvolvesthereflectionofalltheincidentlightofftheboundary.TIRonlytakesplacewhenbothofthefollowingtwoconditionsaremet:
o thelightisinthemoredensemediumandapproachingthelessdensemedium.o theangleofincidenceisgreaterthantheso-calledcriticalangle.
• Totalinternalreflectionwillnottakeplaceunlesstheincidentlightistravelingwithinthemoreopticallydensemediumtowardsthelessopticallydensemedium.TIRwillhappenforlighttravelingfromwatertowardsair,butitwillnothappenforlighttravelingfromairtowardswater.TIRoccursbecausetheangleofrefractionreachesa90-degreeanglebeforetheangleofincidencereachesa90-degreeangle.
• From:http://www.physicsclassroom.com/class/refrn/Lesson-3/Total-Internal-Reflection
• Afiber-opticcableismadeupofincrediblythinstrandsofglassorplasticknownas
opticalfibers;onecablecanhaveasfewastwostrandsorasmanyasseveralhundred.Eachstrandislessthanatenthasthickasahumanhairandcancarrysomethinglike
CellPhoneAntenna(disguised) Underseafiberopticcables
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25,000telephonecalls,soanentirefiber-opticcablecaneasilycarryseveralmillioncalls.
• Fiber-opticcablescarryinformationbetweentwoplacesusingentirelyoptical(light-based)technology.Supposeyouwantedtosendinformationfromyourcomputertoafriend'shousedownthestreetusingfiberoptics.Youcouldhookyourcomputeruptoalaser,whichwouldconvertelectricalinformationfromthecomputerintoaseriesoflightpulses.Thenyou'dfirethelaserdownthefiberopticcable.Aftertravelingdownthecable,thelightbeamswouldemergeattheotherend.Yourfriendwouldneedaphotoelectriccell(light-detectingcomponent)toturnthepulsesoflightbackintoelectricalinformationhisorhercomputercouldunderstand.Sothewholeapparatuswouldbelikeareallyneat,hi-techversionofthekindoftelephoneyoucanmakeoutoftwobaked-beancansandalengthofstring!
• Lighttravelsdownafiber-opticcablebybouncingrepeatedlyoffthewalls.Eachtinyphoton(particleoflight)bouncesdownthepipelikeabobsleighgoingdownanicerun.Nowyoumightexpectabeamoflight,travelinginaclearglasspipe,simplytoleakoutoftheedges.Butiflighthitsglassatareallyshallowangle(lessthan42degrees),itreflectsbackinagain—asthoughtheglasswerereallyamirror.Thisphenomenoniscalledtotalinternalreflection.It'soneofthethingsthatkeepslightinsidethepipe.
• Artwork:Right:Totalinternalreflectionkeepslightraysbouncingdowntheinsideofafiber-opticcable.Theotherthingthatkeepslightinthepipeisthestructureofthecable,whichismadeupoftwoseparateparts.Themainpartofthecable—inthemiddle—iscalledthecoreandthat'sthebitthelighttravelsthrough.Wrappedaroundtheoutsideofthecoreisanotherlayerofglasscalledthecladding.Thecladding'sjobistokeepthelightsignalsinsidethecore.Itcandothisbecauseitismadeofadifferenttypeofglasstothecore.(Moretechnically,thecladdinghasalowerrefractiveindex.)
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• Opticalfiberscarrylightsignalsdowntheminwhatarecalledmodes.Thatsoundstechnicalbutitjustmeansdifferentwaysoftraveling:amodeissimplythepaththatalightbeamfollowsdownthefiber.Onemodeistogostraightdownthemiddleofthefiber.Anotheristobouncedownthefiberatashallowangle.Othermodesinvolvebouncingdownthefiberatotherangles,moreorlesssteep.
• Thesimplesttypeofopticalfiberiscalledsingle-mode.Ithasaverythincoreabout5-10microns(millionthsofameter)indiameter.Inasingle-modefiber,allsignalstravelstraightdownthemiddlewithoutbouncingofftheedges(redlineindiagram–yes,evenwhilebendingit).
• CableTV,Internet,andtelephonesignalsaregenerallycarriedbysinglemodefibers,wrappedtogetherintoahugebundle.Cableslikethiscansendinformationover100km(60miles).
• Anothertypeoffiber-opticcableiscalledmulti-mode.Eachopticalfiberinamulti-modecableisabout10timesbiggerthanoneinasingle-modecable.Thismeanslightbeamscantravelthroughthecorebyfollowingavarietyofdifferentpaths(purple,green,andbluelines)—inotherwords,inmultipledifferentmodes.Multi-modecablescansendinformationonlyoverrelativelyshortdistancesandareused(amongotherthings)tolinktogether.
• From:http://www.explainthatstuff.com/fiberoptics.html
