Geometric thiab optical zog ntawm optical fibers
Geometric khoom
Cov yam ntxwv geometric ntawmoptical fibersmuaj feem cuam tshuam nrog kev tsim kho thiab qis- kev sib txuas tsis zoo. Cov yam ntxwv geometric no suav nrog txoj kab uas hla, qhov ntev cladding, fiber ntau concentricity, thiab tsis yog -circularity.
(1) Core Diameter: Core txoj kab uas hla yog qhov yuav tsum tau ua rau cov fiber ntau optical fibers. ITU-T qhia cov tub ntxhais txoj kab uas hla ntawm multimode optical fibers li (50 ± 3) μm.
(2) Sab nraud txoj kab uas hla: Sab nraud txoj kab uas hla ntawm optical fiber yog hais txog txoj kab uas hla ntawm cov liab qab fiber ntau. Txawm hais tias nws yog multimode lossis ib zaug -mode fiber ntau, ITU-T qhia txog cov kab uas hla ntawm optical fibers siv rau kev sib txuas lus li (125 + 3) μm.
(3) Fiber Concentricity thiab Out- ntawm -Circularity: Concentricity yog qhov sib piv ntawm qhov kev ncua deb ntawm lub hauv paus nruab nrab thiab lub cladding center mus rau lub core txoj kab uas hla. Tawm - ntawm - ncig lub voj voog suav nrog qhov tawm - ntawm - ncig ntawm lub hauv paus thiab cov cladding, thiab tuaj yeem hais los ntawm cov qauv hauv qab no:
Hauv cov qauv, Dmaxthiab Dminyog qhov siab tshaj plaws thiab qhov tsawg kawg nkaus diameters ntawm cov tub ntxhais (cladding); Dcoyog tus qauv txoj kab uas hla ntawm cov tub ntxhais (cladding).
ITU-T qhia meej tias: qhov yuam kev concentricity ntawm multimode fiber ntau yuav tsum tsawg dua 6%; cov tub ntxhais uas tsis yog-circularity yuav tsum tsawg dua 6% (xws li ib leeg- hom); lub cladding tsis yog -circularity yuav tsum tsawg dua 2%; thiab qhov yuam kev concentricity ntawm ib zaug - hom fiber ntau yuav tsum yog 1μm.
Optical zog
Cov khoom siv kho qhov muag ntawm optical fibers yog qhov tseem ceeb tshaj plaws los txiav txim siab lawv qhov kev sib kis.
(1) Refractive Index Distribution: Lub refractive index faib ntawm multimode fibers txiav txim lub fiber bandwidth thiab kev twb kev txuas poob; qhov refractive index faib ntawm ib zaug - hom fibers txiav txim siab xaiv ntawm kev khiav hauj lwm wavelength. Cov qauv dav dav rau qhov refractive index ntawm optical fibers yog:
Nyob rau hauv cov mis, yog qhov kev ncua deb ntawm lub fiber axis; n(0) yog qhov refractive index ntawm cov tub ntxhais fiber ntau thaum r=0; g yog qhov refractive index faib index, uas muaj qhov sib txawv ntawm qhov sib txawv refractive index distributions, raws li qhia hauv daim duab 2-2; yog fiber core radius (μm); thiab △ yog qhov txheeb ze refractive index sib txawv.
Core refractive index: thaum r < ,n(r)=n(0)[1-2△(r/a)g]1/2
Cladding refractive index: thaum r Ntau dua lossis sib npaug rau ,n=n(r)=n(0)[1-2△]1/2
(2) Tus naj npawb aperture (NA) ntawm optical fiber yog ze ze rau lub teeb qhov chaw coupling efficiency, fiber ntau rhiab heev rau microbending, thiab bandwidth. Ib tug lej aperture loj dua pab txhawb kev sib txuas, txo cov microbending rhiab heev, thiab ua rau lub bandwidth nqaim. Qhov siab tshaj plaws theoretical numerical aperture yog txhais raws li hauv qab no:
Nyob rau hauv cov mis, n yog lub refractive Performance index ntawm lub uniform tseem ceeb ntawm cov kauj ruam -index fiber (lub refractive index n(0) ntawm lub core centre ntawm lub graded -index fiber); ng yog lub refractive index ntawm lub uniform cladding.
(3) Hom teb txoj kab uas hla Lub hom teb txoj kab uas hla tuaj yeem txhais tau los ntawm kev hloov pauv kev ua haujlwm ntawm lub hauv paus hom teb Ea, uas yog, qhov dav ntawm ob 1 / é cov ntsiab lus ntawm qhov nkhaus ntawm kev sib raug zoo ntawm kev hloov pauv kev ua haujlwm ntawm lub hauv paus hom teb Ea thiab radial r yog hom teb txoj kab uas hla.
Kev kwv yees ntawm pwm teb txoj kab uas hla: 2S.=2入/(πn√△)
Hauv ib qho - hom fiber ntau, hom kab kab uas hla yog siv los ntawm cov tub ntxhais txoj kab uas hla. Qhov laj thawj yog vim li cas fibers nrog tib txoj kab uas hla yuav muaj ntau hom kev faib tawm raws li qhov sib txawv refractive index distributions, thiab kev sib kis ntawm fiber ntau nyob ntawm hom kev faib tawm.
Rau kev tsim kho, yog hais tias lub hom teb txoj kab uas hla yog mismatched nyob rau hauv lub fiber kev twb kev txuas, ib tug loj deviation yuav ua rau kom qhov kev twb kev txuas poob. ITU-T qhia txog hom kab kab uas hla li (9-10) ± 1 μm.
(4) Cutoff Wavelength (Ib zaug-Mode Transmission Condition) Qhov kev txiav tawm wavelength yog qhov xwm txheej rau ib zaug - hom fiber ntau los lav ib qho - hom kis tau tus mob. Tshaj li qhov wavelength no, qhov thib ob - xaj LP hom tsis tawm lawm. Lub cutoff wavelength txawv ntawm lwm yam tsis nyob rau hauv uas nws tsis tas li tab sis hloov nrog ntev. Qhov no yuav tsum tau txiav tawm wavelength ntawm ib qho - hom fiber ntau kom tsawg dua qhov kev khiav hauj lwm wavelength ntawm optical kev sib txuas lus system. Tam sim no, qhov kev txiav tawm wavelength ntawm ib qho - hom fiber ntau yog 1.10 ~ 1.28µm, txiav txim siab los ntawm tus txheeb ze refractive index sib txawv Δ thiab tus ntoo khaub lig-sectional shape.
Nonlinear teebmeem ntawm optical fibers
Nyob rau niaj hnub no cov ntom ntom wavelength division multiplexing (DWDM) siab -muaj peev xwm, siab-kev sib txuas lus fiber ntau ceev nrog erbium-doped fiber ntau amplifiers, cov fibers optical fibers kis tau ntau lub wavelengths thiab siab zog. Lub hwj chim kho qhov muag siab no tuaj yeem ua rau muaj ntau yam tsis zoo vim muaj kev cuam tshuam ntawm cov teeb liab thiab fiber ntau. Yog tias cov teebmeem nonlinear no tsis raug txwv kom raug, lawv tuaj yeem cuam tshuam kev ua haujlwm ntawm lub cev thiab txwv qhov kev ncua deb ntawm qhov rov ua dua. Linearity los yog nonlinearity yog hais txog cov khoom ntawm lub teeb nyob rau hauv cov kis nruab nrab, tsis yog cov khoom ntawm lub teeb nws tus kheej. Txawm li cas los xij, lub xub ntiag ntawm qhov chaw kho qhov muag hloov cov khoom ntawm qhov nruab nrab. Thaum qhov nruab nrab raug rau qhov chaw kho qhov muag muaj zog, cov khoom siv hluav taws xob hauv cov atoms lossis cov molecules uas ua rau nruab nrab hloov lossis vibrate, ua rau polarization. Dipole nthwv dej tshwm nyob rau hauv nruab nrab polarized, thiab cov dipoles radiate electromagnetic nthwv dej ntawm tib zaus, uas yog superimposed nyob rau hauv thawj qhov teeb meem teb, dhau los ua tag nrho optical teb nyob rau hauv nruab nrab. Qhov no qhia tau hais tias kev hloov hauv nruab nrab cov khoom, nyob rau hauv lem, muaj feem xyuam rau lub optical teb.
Cov teebmeem nonlinear ntawm optical fibers tuaj yeem muab faib ua ob pawg: stimulated scattering thiab refractive index perturbation.
◇ Kev tawm tsam tshwm sim tshwm sim hauv cov tshuab hloov pauv uas cov teeb liab kho qhov muag cuam tshuam nrog acoustic nthwv dej lossis qhov system vibrations hauv optical fibers; uas yog, qhov chaw kho qhov muag hloov qee lub zog mus rau qhov nruab nrab nonlinear. Stimulated Raman scattering thiab stimulated Brillouin tawg yog nyob rau hauv pawg no.
Stimulated Raman scattering (SRS) yog tshwm sim los ntawm kev hloov pauv (kev sib cuam tshuam) ntawm molecular vibrations nyob rau hauv nruab nrab ntawm teeb meem teeb meem (hu ua lub teeb lub teeb), uas ua rau tawg ntawm qhov teeb meem teeb meem. Cia qhov zaus ntawm qhov teeb meem tshwm sim, thiab qhov zaus ntawm qhov nruab nrab molecular vibrations yog ν, ces qhov zaus ntawm lub teeb tawg yog ∞=∞∞ thiab ν=∞, +∞. Qhov no tshwm sim yog hu ua stimulated Raman tawg. Lub teeb tawg nrog qhov zaus ntawm ∞ hu ua Stokes nthwv dej; lub teeb tawg nrog qhov zaus ntawm ν yog hu ua anti-Stokes nthwv dej.
◇ Nyob rau hauv lub hwj chim kho qhov muag tsis tshua muaj, qhov refractive index ntawm silica iav fiber tseem nyob tas li vim refractive index perturbation. Txawm li cas los xij, thaum siv lub tshuab hluav taws xob ballasted kom tau txais lub zog kho qhov muag siab, hloov qhov kev siv ntawm cov teeb liab kis tau tuaj yeem ua rau muaj kev hloov pauv ntawm cov fiber ntau refractive index. Peb qhov kev cuam tshuam tsis zoo tshwm sim los ntawm kev cuam tshuam qhov ntsuas qhov cuam tshuam yog tus kheej - theem kev hloov pauv (SPM), hla - theem hloov kho (CPM), thiab plaub- nthwv dej sib xyaw.
Tus kheej-phase modulation (SPM) yog hais txog qhov tshwm sim uas theem ntawm cov pulse optical hloov thaum lub sij hawm kis tau tus mob, ua rau mem tes spectral broaden. SPM yog ze ze rau tus kheej - tsom; Yog tias hnyav heev, nyob rau hauv qhov ntom ntom wavelength division multiplexing (DWDM), spectral broadening tuaj yeem sib tshooj rau hauv cov kab uas nyob ib sab.
Mechanical thiab kub khoom ntawm optical fibers
Mechanical zog ntawm optical fibers
Cov khoom siv kho qhov muag ntawm optical fibers yog qhov tseem ceeb. Quartz optical fibers siv nyob rau hauv kev sib txuas lus yog nyias iav filaments nrog ib tug txheej txoj kab uas hla ntawm kwv yees li 125 μm. Cov iav yog ib qho nyuaj heev, tsis yog- cov khoom siv tawv, thiab cov khoom nkig. Nws lub zog txwv yog txiav txim siab los ntawm kev sib koom ua ke ntawm Si-O daim ntawv cog lus hauv nws cov qauv. Raws li kev xav, qhov kev ntxhov siab yuav tsum tau ua txhaum Si-O atomic bonds yog kwv yees li ntawm 19600-24500 N / mm², yog li ntawd, fiber ntau optical nrog ib txoj kab uas hla ntawm 125 μm tuaj yeem tiv taus lub zog tensile ntawm 294 N. Txawm li cas los xij, cov kab nrib pleb inevitably muaj nyob ntawm qhov chaw lossis sab hauv ntawm cov khoom siv kho qhov muag. Thaum cov fiber ntau raug rau sab nraud, txawm tias me me heev - tawg tuaj yeem nthuav dav thiab nthuav tawm, ua rau muaj kev puas tsuaj loj heev, uas txo cov fiber ntau lub zog (kwv yees li 1/4 ntawm tus nqi theoretical). Yog li ntawd, los ntawm txoj kev loj hlob mus rau qhov loj -tej daim ntawv thov ntawm optical fibers, kev siv zog loj, peev txheej, thiab nyiaj txiag tau nqis peev pab rau kev kov yeej cov teeb meem no. Tam sim no, kev tshawb fawb, kev tsim khoom, cabling, thiab kev tsim kho vaj tse tau tshawb xyuas ntxiv yuav ua li cas txhawm rau txhim kho lub zog tensile thiab kev pab cuam lub neej ntawm optical fibers.
Lub zog tensile ntawm kev lag luam muaj fiber ntau yuav tsum tsis pub tsawg tshaj 2.35 N ntawm tensile quab yuam. Tam sim no, lub zog tensile ntawm kev lag luam muaj fiber ntau tau mus txog 0.5% strain, lossis 432 g ntawm tensile quab yuam. Hauv tsev siv optical fibers rau engineering tej yaam num feem ntau muaj lub zog tensile ntau dua 400 g ntawm tensile quab yuam. Qhov zoo tshaj plaws txawv teb chaws optical fibers muaj tensile zog tshaj 700 g ntawm tensile quab yuam, thiab fibers siv rau submarine cables yuav tsum tau txawm ntau zog. Cov kev cai no rau lub zog tensile ntawm optical fibers yog ua tiav los ntawm kev soj ntsuam txoj kev thaum lub sij hawm tsim fiber ntau txheej txheem.
Lub lifespan ntawm optical fiber feem ntau hu ua nws cov kev pab cuam lub neej. Los ntawm kev xav txog kev ua haujlwm ntawm kev ua haujlwm, kev pabcuam lub neej yog hais txog nws lub neej tawg. Nyob rau hauv kev tsim thiab engineering ntawm optical fibers thiab cables, ib tug 20-xyoo kev pab cuam lub neej yog feem ntau tsim. Txawm li cas los xij, lub neej ua haujlwm tiag tiag ntawm cov fibers optical tsis zoo ib yam vim muaj kev cuam tshuam ntawm qhov chaw ua haujlwm (xws li kub, av noo, thiab zoo li qub thiab qaug zog). Kev kwv yees tam sim no qhia tias cov fibers kho qhov muag tsim los rau 20-xyoo lub neej yuav kav ntev li 30 txog 40 xyoo.
Cov yam ntxwv kub ntawm optical fibers
Cov yam ntxwv ntawm qhov kub thiab txias ntawm optical fiber yog hais txog qhov cuam tshuam ntawm qhov kub thiab txias ntawm fiber ntau poob, feem ntau ua rau poob ntau ntxiv. Fiber poob nce nyob rau hauv ob qho tib si kub thiab tsis kub kub vim hais tias cov ntaub ntawv siv nyob rau hauv lub fiber txheej thiab cladding yog organic resins thiab yas, uas muaj ntau coefficients loj ntawm contraction thiab expansion tshaj quartz. Yog li ntawd, ntawm qhov kub thiab txias, cov fiber ntau ntsib axial compressive force, ua rau micro-bending, thaum nyob rau ntawm qhov kub thiab txias, nws muaj axial elongation quab yuam, ua rau muaj kev ntxhov siab thiab ua rau poob ntau ntxiv. Cov yam ntxwv ntawm qhov kub thiab txias ntawm cov khoom siv fiber ntau pom tau tias thaum qhov kub thiab txias poob, fiber ntau poob kuj nce. Thaum qhov kub thiab txias poob rau ib ncig ntawm -55 degree, qhov poob nce ntau, ua rau lub cev siv tsis tau. Tam sim no, qhov qis-kub yam ntxwv ntawm optical fibers tau mus txog qib zoo; Feem ntau, ntawm -20 degree, qhov poob nce yog tsawg dua 0.1dB / km, thiab rau cov fibers zoo, nws yog tsawg dua 0.05dB / km.
Qhov qis- qhov kub thiab txias ua haujlwm ntawm optical fibers yog qhov tseem ceeb. Rau cov kab hluav taws xob siv hluav taws xob thiab cov kab hluav taws xob nyob rau sab qaum teb, qhov tsis zoo - qhov kub thiab txias yuav cuam tshuam rau kev sib txuas lus zoo. Yog li ntawd, thaum lub sij hawm tsim kho qhov muag fiber ntau, nws yog ib qho tseem ceeb los xaiv cov txheej txheem tsim nyog thiab cov ntaub ntawv cladding thiab txhim kho cov txheej txheem. Hauv kev tsim engineering, nws yog qhov tsim nyog los xaiv cov fibers optical nrog cov yam ntxwv zoo heev.
