Txoj Cai Qhia Txog Optical Fiber

Lub teeb yog electromagnetic yoj uas muaj zaus heev, thiaboptical fiber ntaunws tus kheej yog dielectric waveguide; Yog li ntawd, txoj kev xav ntawm lub teeb propagation nyob rau hauv optical fibers yog heev complex. Kev nkag siab zoo yuav tsum muaj kev paub txog electromagnetic field theory, wave optics theory, thiab txawm tias quantum field theory.

Txhawm rau kom nkag siab, phau ntawv no tham txog lub teeb -cov ntsiab lus ntawm kev kho qhov muag fibers los ntawm qhov kev xav ntawm geometric optics, uas yog qhov yooj yim dua, pom, thiab nkag siab yooj yim dua. Ntxiv mus, rau multimode optical fibers, txij li thaum lawv qhov ntev geometric loj dua lub wavelength ntawm lub teeb, lub teeb nthwv dej tuaj yeem kho tau raws li ib qho hluav taws xob, uas yog qhov tseem ceeb pib taw tes rau geometric optics.

The Guiding Principle of Optical Fiber

"Thaum lub teeb nthuav dav hauv qhov nruab nrab tsis sib xws, nws mus rau hauv txoj kab ncaj nraim, tab sis thaum nws mus txog qhov sib cuam tshuam ntawm ob qhov kev tshaj tawm sib txawv, qhov tshwm sim ntawm kev xav thiab kev cuam tshuam tshwm sim.

Raws li txoj cai ntawm kev xav, lub kaum sab xis ntawm kev xav sib npaug ntawm lub kaum sab xis ntawm qhov xwm txheej; raws li txoj cai ntawm refraction, n₁sinθ₁=n₂sinθ₂. Qhov twg n₁ yog qhov refractive index ntawm cov tub ntxhais fiber ntau; n₂ yog qhov refractive index ntawm cladding.

Obviously, yog n₁> n₂, ces θ₂> θ₁. Yog hais tias qhov piv ntawm n₁ rau n₂ nce mus rau ib qho twg, lub kaum sab xis refraction θ₂ Ntau dua lossis sib npaug li 90 degree, thiab lub teeb refracted yuav tsis nkag mus rau hauv cladding, tab sis yuav refracted raws qhov sib cuam tshuam ntawm cov tub ntxhais fiber ntau thiab cladding (thaum θ₂=90 degree) rov qab mus rau hauv cov tub ntxhais fiber ntau, los yog rov qab rau hauv cov tub ntxhais. > 90 degree). Qhov tshwm sim no yog hu ua tag nrho sab hauv kev xav ntawm lub teeb. Raws li pom hauv daim duab 2-5. "

The Guiding Principle of Optical Fiber

Lub kaum sab xis ntawm qhov xwm txheej sib raug rau lub kaum sab xis refraction θ₂=90℃hu ua lub kaum sab xis (θ₀), uas tuaj yeem tau yooj yim.

Nws yog ib qho yooj yim to taub tias thaum tag nrho cov kev xav sab hauv tshwm sim nyob rau hauv ib qho kev kho qhov muag fiber ntau, vim hais tias yuav luag tag nrho cov teeb propagates nyob rau hauv lub fiber core, thiab tsis muaj lub teeb tawm mus rau hauv lub cladding, lub fiber ntau attenuation yog heev txo. Cov kauj ruam thaum ntxov-index optical fibers tau tsim raws li lub tswv yim no.

(1) Kev nthuav tawm ntawm Lub Teeb Rays hauv Optical Fibers Txhawm rau kom nkag siab, peb yuav xub siv txoj kev xav ntawm txoj kab hluav taws xob los muab cov lus piav qhia yooj yim ntawm kev nthuav tawm ntawm lub teeb tsis nyob hauv cov fibers optical. Thaum lub teeb pom kev sib txuas ua ke rau hauv cov khoom siv kho qhov muag los ntawm lub ntsej muag kawg, tej zaum yuav muaj ntau hom teeb pom kev zoo hauv fiber ntau: meridional rays thiab oblique rays. Daim duab 2-6a qhia ib txoj kab hluav taws xob uas ib txwm nthuav tawm hauv lub dav hlau uas muaj lub hauv paus axis 00' ntawm cov khoom siv kho qhov muag, thiab cuam tshuam lub hauv paus axis ob zaug hauv ib lub voj voog kev nthuav tawm. Hom kab hluav taws xob no hu ua meridional ray, thiab lub dav hlau uas muaj qhov nruab nrab ntawm cov kab hluav taws xob kho qhov muag hu ua meridional dav hlau. Daim duab 2-6a qhia lub dav hlau meridional MN. Lwm hom yog qhov chaw ntawm lub teeb rays thaum lub sij hawm propagation tsis nyob rau hauv tib lub dav hlau thiab tsis cuam tshuam lub central axis ntawm lub optical fiber. Hom kab hluav taws xob no hu ua oblique ray, raws li pom hauv daim duab 2-6b. Kev tsom xam ntawm oblique rays yog qhov nyuaj heev txawm tias siv txoj kab hluav taws xob txoj kev xav. Qhov no yog vim hais tias kev nthuav tawm ntawm oblique rays tsis yog nyob rau hauv ib lub dav hlau zoo li meridional rays, tab sis nyob rau hauv ib tug kauv qauv nyob rau hauv ib tug peb-dimensional qhov chaw, raws li qhia nyob rau hauv daim duab 2-6b. Kev tshuaj xyuas yuav tsum tau siv cov kev tswj peb-dimensional, uas yog ib qho kev paub daws teeb meem, tab sis nws cov ntsiab lus tseem ceeb ntawm lub teeb pom kev zoo yog tib yam li txoj kev meridian, yog li tsis muaj kev ntsuam xyuas ntxaws.

(2) Meridian propagation nyob rau hauv kauj ruam -index fiber Kev nthuav tawm ntawm meridian nyob rau hauv ib kauj ruam-index fiber yog qhia nyob rau hauv daim duab 2-7. Ib kauj ruam-index fiber muaj ib tug tub ntxhais nrog ib tug refractive index ntawm n₂thiab cladding nrog ib tug refractive index ntawm n₁,qha n₁thiab n₂yog cov tsis tu ncua, thiab n₁> n₂.

"Thaum lub teeb O nkag los ntawm huab cua (n_₀= 1) mus rau hauv qhov chaw kho qhov muag fiber ntau ntawm lub kaum sab xis φ₁, ib feem ntawm lub teeb yuav nkag mus rau qhov muag fiber ntau. Lub sijhawm no, raws li Snell txoj cai lij choj n₀sinφ₁=n₁sinθ₁, thiab txij li cov tub ntxhais fiber ntau refractive index n_₁> n_₀(air refractive index), lub kaum sab xis refraction θ₁ < φ₁, thiab lub teeb txuas ntxiv mus rau propagation, xwm txheej ntawm lub kaum sab xis θᵢ=90℃- θ₁ mus rau qhov sib cuam tshuam ntawm cov tub ntxhais fiber ntau thiab cladding. Yog hais tias θᵢ me dua lub kaum sab xis tseem ceeb θc=arcsin (n₂ / n₁) ntawm cov tub ntxhais fiber ntau thiab cladding interface, ces ib feem ntawm lub teeb yuav refracted rau hauv cladding thiab ploj, thaum lwm qhov kev xav rov qab mus rau hauv cov tub ntxhais fiber ntau. Nyob rau hauv no txoj kev, tom qab ob peb reflections thiab refractions, lub teeb rays yuav sai sai no attenuated. Yog φ₁ txo mus rau φ₀ (raws li nyob rau hauv lub teeb rays ②), ces θᵢ kuj txo, thaum θᵢ=90℃- θ₁ nce. Yog tias φ₁ nce siab tshaj qhov tseem ceeb ntawm lub kaum sab xis θc, lub teeb hluav taws xob no yuav ua rau muaj kev cuam tshuam sab hauv ntawm cov tub ntxhais fiber ntau thiab cladding interface, nrog rau tag nrho lub zog rov qab los rau hauv cov tub ntxhais fiber ntau. Thaum nws txuas ntxiv nthuav tawm thiab ntsib cov tub ntxhais fiber ntau thiab cladding interface dua, tag nrho cov kev xav sab hauv yuav tshwm sim dua. Rov ua cov txheej txheem no, lub teeb tuaj yeem kis tau los ntawm ib kawg ntawm txoj kev zigzag mus rau lwm qhov kawg.

Cia peb tsom xam seb qhov me me φ₁ yuav tsum yog li cas kom xa lub teeb los ntawm ib qho kawg ntawm qhov kho qhov muag mus rau lwm qhov kawg.

Piv txwv tias φ₁=φ₀, ces θc=θc₀, θᵢ=θc, n₀=1, peb muaj: n₀sinφ₀=sinφ₀=n₁sin - θc)=n₁cosθc

Yog li peb muaj: sinφ₀=n₁cosθc=n₁√(1 - sin²θc)=n₁√({4}} (n₂/n₁)²)=n₁√(2Δ) {{7})²}

Hauv kab zauv, Δ yog qhov txheeb ze refractive index sib txawv ntawm optical fiber, Δ=(n₁² - n₂²)/(2n₁²) ≈ (n₁ - n₂)/n₁.

Los ntawm qhov no nws tuaj yeem pom tias ntev npaum li qhov xwm txheej kaum φ₁ Tsawg dua lossis sib npaug ntawm φ₀ ntawm qhov chaw kho qhov muag fiber ntau, lub teeb tuaj yeem xa mus los ntawm tag nrho cov kev xav sab hauv hauv cov tub ntxhais fiber ntau. φ₀ yog hu ua qhov teeb meem siab tshaj plaws ntawm qhov chaw kho qhov muag fiber ntau, thiab 2φ₀ yog qhov siab tshaj plaws txais lub kaum sab xis ntawm cov khoom siv fiber ntau rau lub teeb.

The Guiding Principle of Optical Fiber

(Daim duab 2-7 Meridian propagation nyob rau hauv ib kauj ruam-index optical fiber)

"(3) Numerical Aperture: Txij li qhov sib txawv ntawm n₁ thiab n₂ yog qhov me me, qhov sine ntawm qhov xwm txheej siab tshaj plaws ntawm qhov chaw kho qhov muag fiber ntau thaum tag nrho cov kev xav sab hauv tshwm sim hauv cov khoom siv fiber ntau yog sinφ₀ ≈ φ₀, uas yog hu ua tus lej aperture ntawm optical fiber, feem ntau denoted li Aperture: NA (N.

NA=sinφ₀=n₁√2Δ=√(n₁² - n₂²)

Qhov kev sib npaug no qhia txog lub teeb - sib sau ua ke ntawm cov fiber ntau optical. Txhua qhov teeb meem teeb pom kev zoo nrog lub kaum sab xis me dua li φ₀ tuaj yeem ua tiav tag nrho cov kev xav hauv nruab nrab thiab yuav raug kaw nyob rau hauv cov tub ntxhais fiber ntau kom nthuav tawm raws cov kev taw qhia axial. Nws tuaj yeem pom tias tus lej aperture ntawm optical fiber yog ncaj qha proportional rau lub hauv paus square ntawm tus txheeb ze refractive index sib txawv. Hauv lwm lo lus, qhov ntau dua qhov refractive Performance index sib txawv ntawm cov tub ntxhais fiber ntau thiab cladding, qhov loj ntawm cov zauv aperture ntawm optical fiber ntau, thiab nws lub teeb muaj zog dua - sib sau ua ke. "

The Guiding Principle of Optical Fiber

Lub refractive index ntawm cov tub ntxhais ntawm ib tug graded -index fiber tsis tas li; nws maj mam txo nrog nce fiber ntau lub vojvoog kom txog rau thaum nws sib npaug ntawm qhov refractive index ntawm cladding, raws li qhia hauv daim duab 2-8. Txhawm rau txheeb xyuas qhov kev nthuav tawm ntawm lub teeb nyob rau hauv cov qhab-nees fiber ntau, ib txoj hauv kev zoo ib yam li "kev txhais lus" hauv lej tuaj yeem siv. Ua ntej, cov tub ntxhais fiber ntau tau muab faib ua ntau concentric nyias cylindrical txheej. Txhua txheej yog nyias heev, thiab nws cov refractive index yog kwv yees li nyob rau hauv txhua txheej. Muaj qhov sib txawv me me hauv qhov ntsuas qhov ntsuas ntawm qhov nyob ib sab.

Lub dav hlau meridional thiab txheej txheej ntawm qib -index optical fiber ntau tau pom hauv daim duab 2-8. Cov refractive indices ntawm txhua txheej ua rau muaj kev sib raug zoo hauv qab no: n(r_O) > n(r₁)>n(r₂)>n(r₄)>…>n(r), Thaum lub teeb pom kev zoo tshwm sim los ntawm qhov kawg ntawm lub ntsej muag ntawm ib qho khoom siv kho qhov muag ntawm lub kaum sab xis nruab nrab, nws qhov kev nthuav tawm hauv cov fiber ntau optical fiber ntau nrog ntau qhov sib txawv refractive indexes qhia hauv daim duab 2-8. Thaum cov kab hluav taws xob tawm tsam qhov cuam tshuam ntawm cov khaubncaws sab nraud povtseg 1 thiab 2 ntawm qhov xwm txheej ntawm lub kaum sab xis ntawm θ, txij li cov kab hluav taws xob mus los ntawm qhov nruab nrab denser mus rau qhov nruab nrab ntom ntom, nws lub kaum sab xis ntawm refraction θ yuav loj dua θ. Raws li pom nyob rau hauv daim duab, cov duab hluav taws xob no yuav rov qab los ntawm qhov sib cuam tshuam ntawm cov khaubncaws sab nraud povtseg 2 thiab 3 nrog qhov xwm txheej tshiab ntawm θ, thiab lwm yam. Txij li thaum lub teeb ib txwm propagates los ntawm ib tug denser nruab nrab mus rau ib tug tsawg ntom nruab nrab, nws lub kaum sab xis ntawm qhov tshwm sim maj mam nce, piv txwv li, θ<><><><θ5", until="" at="" a="" certain="" interface="" (interface="" u="" in="" the="" diagram),="" the="" angle="" of="" incidence="" exceeds="" the="" critical="" angle,="" at="" which="" point="" total="" internal="" reflection="" occurs.="" afterward,="" the="" light="" travels="" along="" a="" perfectly="" symmetrical="" trajectory,="" layer="" by="" layer,="" from="" less="" dense="" to="" denser,="" towards="" the="" central="" axis.="" at="" this="" point,="" the="" angle="" of="" incidence="" decreases="" as="" the="" light="" propagates="" towards="" the="" center="" due="" to="" the="" increasing="" refractive="" index="" of="" each="" layer,="" and="" the="" light="" crosses="" the="" central="" axis.="" since="" the="" refractive="" index="" distribution="" below="" the="" central="" axis="" is="" exactly="" the="" same="" as="" above,="" after="" passing="" the="" central="" axis,="" the="" light="" is="" essentially="" propagating="" from="" a="" denser="" medium="" to="" a="" less="" dense="" medium="" again,="" and="" its="" angle="" of="" incidence="" gradually="" increases,="" subsequently="" undergoing="" total="" internal="" reflection="" and="" returning="" to="" the="" central="" axis.="" then,="" it="" again="" enters="" the="" interface="" of="" layers="" 1="" and="" 2="" at="" an="" angle="" θ,="" and="" the="" cycle="" repeats.="" in="" this="" way,="" light="" can="" be="" transmitted="" from="" one="" end="" to="" the="">

The Guiding Principle of Optical Fiber