Lub teeb qhov chaw pab kom hloov dua siab tshiab los ntawm hluav taws xob teeb liab mus rauoptical teeb liabthiab yog cov tseem ceeb ntawm optical transmitters thiab fiber optic kev sib txuas lus systems. Lawv qhov kev ua tau zoo cuam tshuam ncaj qha rau kev ua tau zoo thiab qhov ntsuas tau zoo ntawm fiber ntau optic kev sib txuas lus. Tshooj lus no feem ntau qhia txog cov qauv, kev ua haujlwm, thiab cov yam ntxwv ntawm ob hom teeb pom kev zoo: laser diodes (LDs, tseem hu ua lasers) thiab lub teeb -emitting diodes (LEDs), thiab muab lawv cov kev qhia tshwj xeeb.
Muaj ntau lub tswv yim ntawm lub cev muaj feem xyuam nrog lasers
Lub tswvyim ntawm photons
Einstein lub quantum txoj kev xav ntawm lub teeb hais tias lub teeb yog tsim los ntawm photons nrog lub zoghf ua, qhov twg h=6.628 × 10⁻13J·s, hu ua Planck qhov tas li, thiab f yog qhov zaus ntawm lub teeb yoj. Cov photons no hu ua photons.
Thaum lub teeb cuam tshuam nrog cov teeb meem, lub zog ntawm photon yog absorbed los yog emissions tag nrho, tsim cov nthwv dej - particle duality txoj kev xav ntawm lub teeb.
Atomic zog theem
Hauv cov khoom siv hluav taws xob semiconductor, lub orbits ntawm electrons sab nraum lub atomic nuclei sib tshooj mus rau qhov sib txawv vim qhov sib koom ua ke ntawm cov atoms uas nyob ib sab. Raws li pom nyob rau hauv daim duab 3-1, lub zog theem nyob rau hauv lub siv lead ua tsis muaj nyob rau hauv ib qho atom; lawv tuaj yeem txav mus rau thaj tsam dav dua, txawm tias thoob plaws tag nrho cov siv lead ua. Hauv lwm lo lus, thawj qib zog tau hloov pauv mus rau hauv lub zog hluav taws xob. Lub zog band tsim los ntawm lub zog sab nraud yog hu ua conduction band, thiab lub zog sab hauv hu ua valence band. Tsis muaj electrons nyob rau hauv lub caij nyoog nruab nrab ntawm lawv; lub caij no yog hu ua band gap.
Daim duab 3-1 Lub zog muaj zog hauv cov siv lead ua
Peb hom kev sib cuam tshuam ntawm lub teeb thiab teeb meem
Kev sib cuam tshuam ntawm lub teeb thiab teeb meem tuaj yeem txo qis rau kev cuam tshuam ntawm lub teeb thiab atoms, suav nrog peb lub cev txheej txheem: txhawb kev nqus, spontaneous emission, thiab stimulated emission. Lub zog theem thiab kev hloov hluav taws xob ntawm peb hom kev sib cuam tshuam no tau qhia hauv daim duab 3-2.
Daim duab 3-2 Cov qib zog thiab kev hloov hluav taws xob hauv peb hom kev sib cuam tshuam ntawm lub teeb thiab teeb meem.
1) Raws li ib txwm muaj, electrons feem ntau yog nyob rau hauv qis zog Ea. Raws li kev cuam tshuam ntawm teeb pom kev zoo, electrons nqus lub zog ntawm photon thiab hloov mus rau qib siab E2, tsim lub photocurrent. Qhov kev hloov no yog hu ua stimulated absorption. Qhov no yog txoj hauv kev ua haujlwm ntawm photodetector.
2) Electrons nyob rau hauv lub zog siab E2tsis ruaj tsis khov. Txawm tias tsis muaj kev quab yuam sab nraud, lawv yuav hloov pauv mus rau qib qis zog Ea, recombine nrog lub qhov, thiab tso tawm lub zog hloov dua siab tshiab rau hauv photons uas yog tawg tawm sab nraud. Qhov kev hloov pauv no hu ua spontaneous emission. Qhov no yog txoj hauv kev ua haujlwm ntawm lub teeb -emitting diode (LED). Lub teeb spontaneously emitted yog incoherent teeb.
3) Thaum muaj hluav taws xob nyob rau hauv lub zog siab Eazoo siab los ntawm ib tug sab nraud photon nrog lub zog hf, nws raug yuam kom hloov mus rau qib qis zog Ea, recombine nrog lub qhov, thiab ib txhij tso ib tug photon nrog tib zaus, theem, thiab kev taw qhia raws li lub excitation teeb (hu ua ib tug zoo tib yam photon).
Txij li cov txheej txheem no yog tsim nyob rau hauv lub excitation ntawm ib tug sab nraud photon, qhov kev hloov no yog hu ua stimulated emission. Qhov no yog lub hauv paus ntsiab lus ua haujlwm ntawm laser. Stimulated emission teeb yog coherent teeb.
Population inversion thiab lub teeb amplification
Stimulated emission yog qhov tseem ceeb rau laser tiam. Cia cov particle ntom ntawm lub zog qis dua yog N, thiab qhov ntom ntom ntawm lub zog siab dua yog N². Raws li cov xwm txheej ib txwm muaj, N > N², lub ntsiab lus txhawb nqa kev nqus ib txwm dhau los txhawb kev tawm dag zog; uas yog, nyob rau hauv thermal equilibrium, teeb meem tsis tuaj yeem amplify lub teeb.
Rau qhov teeb meem kom nthuav dav lub teeb, txhawb nqa emissions yuav tsum muaj ntau tshaj qhov kev nqus nqus, txawm tias N² > N (tus naj npawb ntawm cov hluav taws xob ntawm lub zog siab dua yog ntau dua tus lej ntawm qis zog). Qhov kev faib tawm txawv txav ntawm tus lej yog hu ua pejxeem inversion.
Population inversion yog thawj yam mob rau ib yam khoom los tsim lub teeb amplification thiab emit lub teeb.
Direct bandgap thiab indirect bandgap semiconductors
Hauv kev txhawb nqa emission ntawm lub teeb, lub zog thiab lub zog yuav tsum tau khaws cia. Cov kab sib txawv ntawm cov duab muaj feem xyuam rau lub zog; Raws li qhov sib txawv band, semiconductors tuaj yeem muab faib ua qhov sib txawv ncaj qha thiab qhov sib txawv ntawm qhov sib txawv, raws li pom hauv daim duab 3-3. Nyob rau hauv ncaj qha band gap semiconductors, qhov tsawg kawg nkaus lub zog ntawm cov conduction band thiab lub siab tshaj plaws lub zog theem ntawm lub valence band muaj tib lub zog, thiab electrons hloov vertically, ua rau siab luminous efficiency, raws li qhia nyob rau hauv daim duab 3-3a. Hauv qhov sib txawv ntawm qhov sib txawv ntawm cov khoom siv hluav taws xob, lwm cov khoom yuav tsum koom nrog kom muaj kev txuag hluav taws xob rau kev hloov hluav taws xob, raws li pom hauv daim duab 3-3b. Tsuas yog cov ntaub ntawv ncaj nraim ntawm cov khoom siv semiconductor tuaj yeem siv los tsim cov khoom siv teeb pom kev zoo; Cov ntaub ntawv no suav nrog GaAs, AlGaAs, InP, thiab InGaAsP.
Daim duab 3-3 Direct bandgap thiab indirect bandgap semiconductors
Laser txoj cai
Lub semiconductor laser yog ib lub laser uas siv cov khoom siv semiconductor raws li nws cov khoom siv nruab nrab; nws tseem hu ua semiconductor laser tus kheej -oscillator.
Rau lub laser kom emit laser teeb, peb yuav tsum tau raws li nram no: yuav tsum muaj ib tug ua hauj lwm (tseem hu ua ib tug activating tshuaj) muaj peev xwm tsim lub teeb laser; yuav tsum muaj qhov excitation qhov chaw (tseem hu ua lub twj tso kua mis) muaj peev xwm muab cov khoom ua haujlwm rau hauv cov pej xeem inversion xeev; thiab yuav tsum muaj ib qho optical resonator muaj peev xwm ua tau qhov kev xaiv zaus thiab tawm tswv yim.
(1) Cov khoom ua haujlwm muaj peev xwm tsim lub teeb laser yog cov khoom siv uas tuaj yeem ua tiav cov pej xeem inversion faib. Thaum ua haujlwm, cov khoom ua haujlwm yog hu ua cov khoom ua kom muaj zog lossis nce cov khoom, thiab nws yog qhov tsim nyog rau kev tsim laser.
(2) Lub twj tso kua mis yog qhov chaw ua haujlwm sab nraud uas ua rau cov khoom siv ua haujlwm kom ua tiav qhov kev faib tawm ntawm pej xeem. Nyob rau hauv qhov kev txiav txim ntawm lub twj tso kua mis, Ni> Ni, ua rau stimulated emission ntau dua li stimulated absorption, yog li amplifying lub teeb.
(3) Optical resonator: Cov khoom siv hluav taws xob tuaj yeem ua kom pom lub teeb. Tsuas yog los ntawm kev tso cov tshuaj activating nyob rau hauv qhov kho qhov muag resonator los muab cov lus qhia tsim nyog thiab xaiv qhov zaus thiab kev taw qhia ntawm lub teeb tuaj yeem ua kom lub teeb txuas ntxiv mus thiab laser oscillation tso zis. Cov tshuaj activating thiab optical resonator yog qhov tsim nyog rau kev tsim laser oscillation.
1) Cov qauv ntawm qhov kho qhov muag resonant kab noj hniav. Cov qauv ntawm qhov kho qhov muag resonant kab noj hniav yog qhia hauv daim duab 3-4. Los ntawm kev tso ob daim iav sib luag, M1 thiab M2, nrog kev cuam tshuam coefficients r1 thiab r2 raws, ntawm qhov chaw tsim nyog ntawm ob qho kawg ntawm cov khoom siv, qhov yooj yim tshaj plaws optical resonant kab noj hniav yog tsim, kuj hu ua Fabry -Perot kab noj hniav lossis FP kab noj hniav.
Yog tias cov iav iav yog dav hlau iav, nws yog hu ua lub dav hlau kab noj hniav; yog tias cov iav yog cov iav kheej kheej, nws yog hu ua cov kab noj hniav spherical. Ntawm ob daim iav, ib qho yuav tsum muaj peev xwm cuam tshuam lub teeb tag, thiab lwm qhov yuav tsum muaj peev xwm cuam tshuam ib feem.
Daim duab 3-4 Cov qauv ntawm qhov kho qhov muag resonant kab noj hniav
2) Cov txheej txheem oscillation ntawm laser tiam nyob rau hauv ib tug resonant kab noj hniav. Daim duab schematic ntawm lub laser muaj nyob rau hauv daim duab 3-5. Thaum qhov nruab nrab ua haujlwm tiav cov pej xeem inversion nyob rau hauv qhov kev txiav txim ntawm lub twj tso kua mis, spontaneous emission generated. Yog hais tias cov kev taw qhia ntawm spontaneous emission tsis yog parallel mus rau lub axis ntawm lub optical resonant kab noj hniav, nws yog reflected tawm ntawm lub resonant kab noj hniav. Tsuas yog spontaneous emission thaum uas tig mus rau lub axis ntawm lub resonant kab noj hniav tuaj yeem muaj nyob thiab txuas ntxiv mus. Thaum nws ntsib ib tug particle ntawm lub zog siab dua, nws induces ib tug stimulated hloov, emitting ib tug zoo tib yam photon nyob rau hauv kev hloov ntawm lub zog siab dua mus rau lub zog qis zog-qhov no yog stimulated emission. Thaum lub teeb pom kev zoo emissions rov qab los ib zaug hauv lub resonant kab noj hniav, thiab cov theem hloov yog raws nraim ib tug ntau yam ntawm 2π, ob peb stimuled emission teeb propagating nyob rau hauv tib txoj kev qhia txhawb ib leeg, ua resonance. Tom qab ncav cuag ib qho kev siv zog, nws kis tau los ntawm ib feem ntawm daim iav M2, tsim ib lub teeb laser ncaj. Thaum sib npaug, lub zog nthuav dav los ntawm lub teeb pom kev zoo thaum lub sij hawm txhua qhov kev mus ncig hauv lub resonant kab noj hniav raws nraim tshem tawm lub zog noj, thaum lub sij hawm lub laser tuav ib tug ruaj khov tso zis.
Daim duab 3-5 Schematic daim duab ntawm laser
3) Resonance mob thiab resonant zaus ntawm qhov kho qhov muag resonant kab noj hniav. Cia qhov ntev ntawm qhov resonant kab noj hniav yog L, tom qab ntawd qhov tshwm sim ntawm qhov resonant kab noj hniav yog:
Hauv cov qauv, c yog qhov ceev ntawm lub teeb hauv lub tshuab nqus tsev; λ yog laser wavelength; n yog qhov refractive index ntawm cov khoom siv ua kom muaj zog; L yog kab noj hniav ntev ntawm qhov kho qhov muag resonant kab noj hniav; thiab yog tus naj npawb longitudinal,=1, 2, 3.
Lub resonant kab noj hniav muab tswv yim zoo tsuas yog rau lub wavelength ntawm lub teeb yoj txaus siab sib npaug (3-1) los yog zaus ntawm lub teeb yoj txaus siab sib npaug (3-2), ua rau lawv los txhawb ib leeg nyob rau hauv lub kab noj hniav thiab resonate rau daim laser teeb.
Txij li thaum lub teeb pom kev zoo tsuas yog tsim cov nthwv dej ntawm cov kab noj hniav (longitudinal kev taw qhia), cov no yog hu ua longitudinal hom (hom sib txawv sib haum mus rau qhov sib txawv kev faib tawm).
4) Qhov chaw pib rau oscillation. Qhov tsawg kawg nkaus kev txwv ntawm lub laser tuaj yeem tsim laser oscillation yog hu ua lub laser qhov chaw pib (F-P kab noj hniav muaj qhov poob, thiab lub teeb pom kev thiab refraction los ntawm daim iav kuj tseem noj photons). Yog tias Gu sawv cev rau qhov pib nce coefficient, ces qhov chaw pib rau oscillation yog:
Nyob rau hauv cov mis, yog qhov poob coefficient ntawm cov khoom siv nyob rau hauv qhov kho qhov muag resonant kab noj hniav; L yog kab noj hniav ntev ntawm qhov kho qhov muag resonant kab noj hniav; thiab thiab yog qhov kev xav coefficients ntawm ob daim iav ntawm lub qhov muag resonant kab noj hniav.
