Ua kom tiavfiber ntau optickev sib txuas lus, thawj qhov teeb meem yuav daws tau yog yuav ua li cas thauj cov hluav taws xob teeb liab mus rau lub teeb beam emitted los ntawm lub teeb qhov chaw, uas yuav tsum tau kho qhov muag modulation. Raws li kev sib raug zoo ntawm kev hloov kho thiab lub teeb pom kev zoo, kev hloov kho qhov muag tuaj yeem muab faib ua ob pawg loj: ncaj qha kev hloov pauv (sab hauv kev hloov kho) thiab kev hloov pauv tsis ncaj (sab nraud modulation).
Direct modulation ntawm lub teeb qhov chaw
Kev hloov pauv ncaj qha cuam tshuam ncaj qha txhaj cov teeb liab hluav taws xob rau hauv lub teeb ci, hloov cov ntaub ntawv kom xa mus rau lub zog hluav taws xob thiab txhaj rau hauv lub laser diode (LD) lossis lub teeb -emitting diode (LED) kom tau txais cov teeb liab kho qhov muag. Qhov no ua rau qhov kev siv ntawm cov zis optical carrier teeb liab sib txawv nrog cov teeb liab modulation, thiab tseem hu ua internal modulation. Txoj kev no tau hloov kho qhov kev siv luminous ntawm lub teeb ci, yog li nws yog hom kev siv kho qhov muag (IM). Daim duab qhia txog lub hauv paus ntsiab lus ntawm kev siv hluav taws xob ncaj qha digital modulation.
Indirect modulation ntawm lub teeb qhov chaw
Qhov kom zoo dua ntawm kev hloov kho sab hauv ntawm lub teeb ci yog tias lub voj voog yog qhov yooj yim thiab siv tau yooj yim. Txawm li cas los xij, siv txoj kev hloov kho no ntawm cov ntaub ntawv siab yuav ua rau qhov kev ua tau zoo ntawm lub teeb pom kev zoo, xws li kev nthuav dav cov kab dynamic spectral, nce kev sib kis thaum lub sij hawm kis tau tus mob, thiab yog li nthuav cov pulse waveform kis tau nyob rau hauv lub optical fiber, uas thaum kawg txwv qhov kis tau tus mob ntawm lub optical fiber. Yog li ntawd, nyob rau hauv siab -kev siv ceev-modulated ncaj qha- nrhiav fiber optic kev sib txuas lus systems los yog heterodyne fiber optic kev sib txuas lus systems, indirect modulation ntawm lub teeb qhov chaw yuav siv tau.
Indirect modulation tsis ncaj qha hloov kho lub teeb ci, tab sis siv cov electro-optic, magneto-optic, thiab acousto-optic thaj chaw ntawm cov siv lead ua los hloov kho qhov muag pom kev tawm los ntawm laser diode (LD). Qhov no txhais tau hais tias lub modulation voltage yog siv tom qab lub teeb tawm, ua rau lub optical carrier yuav tsum tau hloov los ntawm lub modulator. Txoj kev hloov kho no tseem hu ua kev hloov kho sab nraud. Cov qauv ntawm ib qho indirectly modulated laser yog qhia nyob rau hauv daim duab.
Tam sim no muaj cov kev hloov kho sab nraud muaj xws li electro-optic modulation, acousto-optic modulation, thiab magneto-optic modulation.
- (1) Electro-optic Modulation: Lub hauv paus ntsiab lus ua haujlwm ntawm electro-optic modulation yog linear electro-optic effect ntawm crystals. Electro- cov nyhuv optic yog hais txog qhov tshwm sim uas ua rau muaj kev hloov pauv ntawm qhov cuam tshuam ntawm cov khoom siv lead ua. Crystals uas tuaj yeem tsim cov electro-optic effect hu ua electro-optic crystals. Electro{10}}optic modulators tuaj yeem yog electro-optic siv modulators, electro-optic zaus modulators, los yog electro{13}}optic theem modulators (ie, electro{16}}optic theem modulators).
- (2) Acousto-optic Modulation: Acousto-optic modulators yog tsim los ntawm acousto-optic nyhuv ntawm qhov nruab nrab. Lawv lub hauv paus ntsiab lus ua haujlwm yog raws li hauv qab no: thaum hloov pauv hluav taws xob teeb liab hloov, lub piezoelectric siv lead ua ua rau cov neeg kho tshuab vibrations vim cov nyhuv piezoelectric, tsim ib qho ultrasonic yoj. Lub suab nthwv dej no ua rau muaj kev hloov pauv ntawm qhov ntom ntawm qhov nruab nrab, uas nyob rau hauv lem hloov lub refractive index, yog li tsim ib tug hloov grating. Vim qhov kev hloov pauv ntawm cov grating, lub teeb siv lub teeb hloov raws li, uas ua rau cov kev hloov pauv ntawm lub teeb yoj.
- (3) Magneto-optic Modulation: Magneto-optic modulation yog ib hom kev kho qhov muag sab nraud uas tau txais los ntawm Faraday effect. Cov teeb liab teeb pom kev tshwm sim dhau los ntawm polarizer, ua qhov teeb meem teeb pom kev zoo polarized. Thaum lub teeb polarized no dhau los ntawm YIG (yttrium hlau garnet) hlau nplaum, nws cov kev taw qhia polarization hloov nrog lub teeb liab modulating siv rau lub coil qhov txhab nyob ib ncig ntawm nws. Thaum cov kev taw qhia polarization yog tib yam li cov kev ntsuas tom ntej, qhov kev siv lub teeb pom kev zoo yog qhov loj heev; Thaum cov kev taw qhia polarization yog perpendicular rau cov kev taw qhia ntawm lub analyzer, cov zis lub teeb siv yog tsawg. Qhov no ua rau cov zis siv lub teeb hloov pauv nrog lub teeb liab modulating, yog li ua tiav cov kev hloov kho sab nraud ntawm lub teeb.
Cov txheej txheem sab nrauv yog qhov nyuaj, muaj qhov sib txawv ntawm qhov tsis zoo (ntau dua 13), kev nkag siab siab (feem ntau 5-6 dB), kev tsav tsheb siab (5V), nyuaj rau kev sib xyaw nrog cov teeb pom kev zoo, yog polarization-sensitive, thiab muaj kev poob siab thiab cov nqi siab; Txawm li cas los xij, lawv muaj qhov nqaim spectral linewidth thiab tuaj yeem siv rau hauv siab -ceev, muaj peev xwm kis tau tus mob ntawm lossis siab dua 2.5 Gbit / s, nrog kev sib kis ntau tshaj 300 km.
Modulation yam ntxwv
(1) Electro-optic ncua sij hawm thiab so kom txaus Oscillation Phenomena: Nyob rau hauv siab -speed mem tes modulation, lub sij hawm teb cov lus teb waveform ntawm cov zis optical mem tes ntawm lub laser yog qhia nyob rau hauv daim duab. Muaj lub sijhawm ncua sij hawm pib ntawm qhov tso zis optical pulse thiab cov mem tes tam sim no, hu ua electro-optic ncua sij hawm (td), uas feem ntau yog nyob ntawm qhov kev txiav txim ntawm nanoseconds. Tom qab cov mem tes tam sim no tau txhaj rau hauv lub laser, qhov tso zis optical mem tes yuav pom cov oscillations nrog maj mam txo qis, hu ua so oscillations. Qhov tshwm sim ntawm kev so oscillations thiab electro- optic ncua yog txwv qhov kev hloov pauv.
(2) Code Pattern Effect: Txhawm rau tsim cov qauv qauv, raws li qhia hauv daim duab, thaum lub sijhawm electro- optic ncua sij hawm yog tib qhov kev txiav txim siab raws li lub cim T / 2 ntawm cov kev hloov pauv digital, nws yuav ua rau lub mem tes dav ntawm thawj "1" me ntsis tom qab ib ntu ntawm "0" me ntsis kom nqaim thiab nws qhov amplitude yuav txo qis. Hauv qhov xwm txheej hnyav, ib qho "1" me ntsis yuav ploj. Qhov tshwm sim no yog hu ua cov qauv qauv, raws li pom hauv daim duab a thiab b. Hauv ob qhov sib law liag "1" cov khoom, ua ntej tuaj txog ntawm thawj mem tes, muaj qhov ntev ntawm "0" cov khoom. Vim lub sijhawm ntev electro- optic ncua sij hawm thiab cuam tshuam ntawm optical mem tes nce lub sij hawm, lub mem tes ua me. Thaum lub thib ob mem tes tuaj txog, vim hais tias lub electron recombination ntawm thawj mem tes tsis tau tag nrho ploj, lub electron ceev nyob rau hauv lub active cheeb tsam yog siab dua, yog li lub electro- optic ncua sij hawm luv luv, thiab cov mem tes loj dua. Cov qauv qauv tuaj yeem raug tshem tawm los ntawm kev siv qhov tsim nyog "dhau-kev hloov pauv" txoj kev them nyiaj, raws li qhia hauv daim duab c.
Tus kheej -pulsation tshwm sim
Hauv qee lub lasers, nyob rau hauv kev hloov pauv hloov pauv lossis txawm tias DC tsav tsheb, thaum qhov kev txhaj tshuaj tam sim no nce mus txog qee qhov, cov khoom siv hluav taws xob pom pom tau zoo, tsis tu ncua -amplitude siab- zaus oscillations. Qhov tshwm sim no hu ua tus kheej -pulsation, raws li pom hauv daim duab. Tus kheej-pulsation zaus tuaj yeem ncav cuag 2 GHz, uas cuam tshuam rau qhov siab -kev hloov pauv ceev ntawm laser diode (LD).
