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At λ = 1.3; 1.55 µm: InGaAsP-InP light sources, Ge or InGaAs-InP detectors.
Light emitting diodes (LEDs):
• non-coherent light sources
• wide spectrum oscillations
• wide radiation angle
Laser diodes (LDs):
• coherent light sources
• small radiation angle
• small width of radiation spectrum
• great power from small area
• higher modulation frequency
Light is emitted as a result of direct radiative recombination of excess electrons and holes.
A parameter that needs to be made as large as possible in an optical source is the internal quantum efficiency . It is defined as the ratio of the number of photons generated to the number of carriers crossing the junction.
Semiconductors such as silicon, germanium and gallium phosphide have indirect band-gap. This means that an electron in an energy state near the bottom of the conduction band has a momentum in the crystal that is quite different from that of an electron in an energy state near to the top of the valence band. Excess momentum must change (must be absorbed) during the recombination in an indirect-band gap semiconductor. But probability of two events simultaneously (producing a phonon as well as a photon) is small. As a result non-irradiative processes tend to dominate in indirect band-gap semiconductors and the internal quantum efficiency is very small.Galium arsenide and other semiconductor materials have direct band-gap. An electron can jump from the conduction band to the valence band and a photon can be emitted. Then the internal quantum efficiency in LEDs can be to 0.5.
Light is emitted as a result of direct radiative recombination of excess electrons and holes.
A parameter that needs to be made as large as possible in an optical source is the internal quantum efficiency . It is defined as the ratio of the number of photons generated to the number of carriers crossing the junction.
Semiconductors such as silicon, germanium and gallium phosphide have indirect band-gap. This means that an electron in an energy state near the bottom of the conduction band has a momentum in the crystal that is quite different from that of an electron in an energy state near to the top of the valence band. Excess momentum must change (must be absorbed) during the recombination in an indirect-band gap semiconductor. But probability of two events simultaneously (producing a phonon as well as a photon) is small. As a result non-irradiative processes tend to dominate in indirect band-gap semiconductors and the internal quantum efficiency is very small.Galium arsenide and other semiconductor materials have direct band-gap. An electron can jump from the conduction band to the valence band and a photon can be emitted. Then the internal quantum efficiency in LEDs can be to 0.5.
The distribution of the photon energy and wavelength can be found taking into account the distribution of electrons in the conduction band and the distribution of holes in the valence band.
Researchers intensively work on the problem of silicon laser diodes...
Silicio šviesos šaltinių veikimas pagrįstas šiais principais:
1. Silicio nanokristalai silicio diokside veikia kaip kvantiniai narvai. Kuo mažesnis nanokristalas, tuo platesnė draudžiamoji juosta. Be to kvantiniai narvai leidžia spręsti momentų problemą ir padidinti spindulinės rekombinacijos tikimybę.
2. Į silicį įterpti retųjų žemės elementų (lantanidų nuo 58 (cerio) iki 71 (lutecio)) jonai spinduliuoja šviesą.
Įtaisas spinduliuoja šviesą normalioje temperatūroje. Jo kvantinis efektyvumas gali būti iki 10 % nuo kvantinio efektyvumo, gaunamo panaudojant III-V grupių medžiagas ir šiuolaikiškas technologijas.
Šviesos spalva priklauso tik nuo panaudoto lantanido. Samaris skleidžia raudonos, terbis – žalios, ceris – mėlynos spalvos šviesą, erbis – infraraudonuosius spindulius, taikomus telekomunikacijose.
… pakeisti varinį laidininką optine skaidula, vietoje elektronų naudoti fotonus.
Slicio fotonikos perspektyva – visur taikyti optinių ryšių principus. Gamintojai galės sudaryti optoelektroninius elementus taikydami silicio integrinių grandynų gamybos technologiją. Fotonikos elementų savikaina labai sumažėtų.
… integruotas silicio luste imtuvas-siųstuvas galėtų priimti ir siųsti duomenis 10 ir net 100 gigabitų per sekunde sparta.
Light is emitted in all directions. Only light emitted in the direction of the semiconductor-air surface is useful.
There is absorption between the point of generation and the emitting surface.Only light reaching the emitting surface at an angle of incidence less than the
critical angle is transmitted through it. Part of this light is reflected at the semiconductor-air surface.
The cross section area of a fiber core is very small. For this reason, the LED-to-fiber efficiency is also very small – about 0.0005.
LEDs
Combined spectral curves for blue, yellow-green, and high brightness red solid-state semiconductor LEDs. FWHMspectral bandwidth is approximately 24-27 nanometres for all three colors.
Due to the resonator … the emission spectrum width of a laser diode is
much less than that of a LED.
The thickness of the active layer is small. Only photons that move along the active region stimulate recombination. For this reason amplified light is emitted in the direction of the active region (in the direction perpendicular to a mirror). .
The phase balance condition is satisfied at the same phase angles of incident wave and wave that appears after the second reflection.
The length of the active region (the distance between mirrors) must equal the integer number of half wave.
Zarlink launches a new line of long-wavelength laser diodes with the industry’s highest level of customization. The ZL60401 laser diodes can be tailored for a broad range of industrial and commercial equipment, as well as telecom and datacom applications.
Change of the drive current causes the frequency to vary, as well as the output power. This is normally referred to as chirp.
Amplitude, phase and frequency modulation is used in coherent systems.
The emitted power is proportional to the diode current. This property is used for amplitude modulation of light. The modulation bandwidth can be to 10 GHz. Usually the diode is biased beyond the threshold.
ENCODING PHOTONS WITH DATA: An optical modulator encodes 1s and 0s by first splitting a laser beam in two and then applying an electric field to the beams, so that one beam is delayed by half a wavelength relative to the other. When the beams recombine, both beams will be out of phase, and they will cancel out.When no voltage is applied, on the other hand, the beams remain in phase when recombined. Encoding the beam with 1s and 0s, then, means making the beams interfere (0) or keeping them in phase (1).
The key to Intel's continuous silicon laser—the world's first—is a PIN (p-type–intrinsic–n-type) diode placed on either side of the light beam. The diode sweeps free electrons from the path of the light. Without it, the electrons build up and absorb some of the light, killing the amplification.
1. Šviesos diodui panaudotas galio arsenidas, kurio draudžiamosios juostos plotis ∆W = 1,42 eV. Raskime šviesos diodo intensyviausiai spinduliuojamos šviesos bangos ilgį ir šviesos spektrinės linijos santykinįplotį 0 0C ir 100 0C temperatūrose. Palyginkime šviesos bangos ilgio santykinį pokytį ir šviesos spektrinės linijos santykinį plotį. Įvertinkime maksimalaus intensyvumo virpesių dažnio absoliutinį pokytį.
2. Sudarykime dvigubos GaAlAs-GaAs-GaAlAs NpP heterosandūrosenergijos lygmenų diagramą, kai neveikia išorinė įtampa. Kokio poliarumo įtampa šiai dvigubai heterosandūrai būtų tiesioginė? Kaip pasikeistųheterosandūros energinė diagrama veikiant tiesioginei įtampai?
3. Dvigubos heterosandūros aktyviojo sluoksnio storis – 0,5 µm, spindulinės rekombinacijos laiko pastovioji – 10 ns, nespindulinės rekombinacijos laiko pastovioji – 30 ns, rekombinacijos greitis heterosandūroje – 10 m/s. Raskime heterosandūros kvantinį našumą ir moduliacijos dažnių juostos viršutinį dažnį.
4. Šviesos diodo sandūra atvaizduota 2.10 paveiksle, a. Virš aktyviojo sluoksnio yra puslaidininkis, kurio lūžio rodiklis – 3,7. Diodo vidinis kvantinis našumas – 0,7. Raskime diodo išorinį kvantinįnašumą.
5. Šviesos diodo ir skaidulos sąsaja atvaizduota 2.10 paveiksle, b. Skaidulos NA = 0,1. Raskime šaltinio-skaidulos kvantinį našumą.
6. Šviesos diodui panaudota dviguba NpP heterosandūra, kurios storis 0,5 µm. Medžiagų parametrai duoti lentelėje. Kai diodo tiesioginėįtampa 2 V ir per jį teka 100 mA srovė, diodas spinduliuoja 2 mWoptinę galią. Koks diodo, kaip energijos keitiklio, naudingumo koeficientas?