11831437
Description
Flashcards by Pascal Jud, updated more than 1 year ago
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Created by Pascal Jud
over 6 years ago
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| Question | Answer |
| 1. The three basic transmitter schemes | a) directly modulated laser b) Transmitter with external modulator c) Transmitter with external modulator and pulse shaping |
| 2. Physical parameters of an electrical signal that can be changed by modulation | frequency amplitude phase |
| 3. Necessary components for a laser | gain material for population inversion cavity (resonator) pumping mechanism |
| 4. What determines the photon rate? | confinement factor material gain no. of phontons (S) |
| 5. Describe the confinement factor & its importance for a laser. | Def: ratio between the power of the field in the active core and the total field influences the photon in-/decrease |
| 6. Charles Henry's discovery and its relevance to the laser | If the gain changes, the refractive index changes. Henry factor aka linewidth enhancement factor alpha_LE |
| 7.1 Photon-rate equation and its components | Stimulated emission - absorption + spontaneous emission |
| 7.2 Carrier rate equations and its components | injected carriers - recombination - stimulated emission |
| 8. Laser threshold condition | |
| 9. Sketch the relation of laser output power to the current applied to a laser diode. | |
| 10. Internal quantum efficiency | internal quantum efficiency n_i accounts for the fact that not all electrons generate radiating photons but only a fraction n_i |
| 11. Derivation of the frequency response of a laser. | 1. Assume small signal modulation 2. Insert I(t), S(t) & N(t) into the laser- equations 3. FT of S 4. S(w)/S(0) |
| 12. Describe the behavior. | Large signal modulation of a laser After the current is switched on, it takes a time delay td for the number of charge carriers to exceed the threshold Nth and only then the number of photons begins to increase as well. The charge carrier number increases further until the number of photons is large enough to stir up many induced emissions. Therefore, the charge carrier density depletes eventually below threshold and thus the emission of photons decreases fast. In the meantime the inversion of charge carriers is re-established by the constant injection current. |
| 13. Which characteristics of a laser are determined by the phase and amplitude fluctuations of the output optical field? | SNR is influenced by the intensity fluctuations. The spectral linewidth is limited by the phase fluctuations. |
| 14. Sketch the characteristic curves of RIN. | |
| 15. Spectral linewidth | FWHM can be reduced by having 1. a longer cavity --> Rsp down 2. Choosing a QD/QW material --> aLE down 3. increasing power --> S up |
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