11895012
Description
Flashcards by Manuel Kohli, updated more than 1 year ago
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Created by Manuel Kohli
over 6 years ago
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| Question | Answer |
| Which fiber profiles did we discuss in the lecture? Describe their characteristics, differences and advantages/disadvantages | Step Index Profile: Cheap, easy to manifacture, optimal for short channels but high multipath distortion Graded Index: Expensive fiber, the refractive index changes gradually, less multipath distortion thus higher data rates or longer communication |
| What is described by the critical angle, the numerical aperture and the fractional index change? | Critical angle: as soon as the critical angle is exceeded, we don't have TIR anymore and light won't be guided NA: Angular light gathering ability. The higher the NA, the easier it is to couple into the fiber fractional index change: describes the the range of refr. index of the core cladding |
| Describe the characteristics of multipath dispersion? What is another name for this phenomenon? How does it limit the maximum symbol rate in an optical fiber? | Modal Dispersion: light which has a steeper angle will have a longer travelling distance than rays which travel closely to the center. Another name is multipath dispersion. |
| Write down, name and describe the different Maxwell's equations | |
| What does the material equation describe? | Relates the Electrical Displacement with the Electric Field and the polarization |
| Describe the procedure to solve the Helmholtz equation for fiber modes. How does the solution of the spatial mode distribution look like? | 1. Create Helmholtz, Insert Ansatz 2. Solve boundary conditions 3. Find non-zero field distribution of the set of linear equations by setting the determinant of the system to zero |
| Discuss what is meant by EH_{mn}, HE_{mn}, TE_{0n}, TM_{0n}, and LP_{mn} fiber mode nomenclatures | EH_{mn}: Hybrid mode with predominat E_z Field HE_{mn}: Hybrid mode with predominant H_z Field TE: transversal Electric, no Electric field in direction of propagation TM: transversal Magnetic, no Magnetic field in direction of propagation LP: linearly polarized, in weakly guided waveguides we have almost no E_z and H_z m: order of azimuthal oscillation n: order of solution |
| What does the V-parameter describe? What are the parameters one can play with to limit the number of modes propagating in a fiber? When does the fiber support only a single mode? | Normalized frequency, measure of the fiber to support different modes. The parameters to play with are the core radius and the reflactive indices of the cladding and core. V < 2.45 |
| Please state the Nonlinear Schrödinger Equation and explain its components | beta_1: group volocity beta_2: group velocity dispersion beta_3: dispersion slope alpha: fiber losses gamma_{NL}: non-linear interaction factor |
| Explain the term group velocity | Group velocity is the velocity at which a photon moves through the fiber |
| Explain the term group velocity dispersion | Variations of the group velocity, mainly due to dispersion |
| Explain the term dispersion slope | Variations of the Group velocity dispersion in terms of frequency |
| Why is the dispersion parameter D_d preferable over the group velocity dispersion and how are they related to each other? How do you interpret the dimension ps/nm/km? | It is easier in technical environments since you only have to multiply with the Bandwidth and travelled distance. It is the broadening of the pulse in ps with spectral width in nm after travelling for one km. |
| What is the origin of dispersion? | Material Dispersion: n(omega) waveguide dispersion: n_eff(omega) <- Mode changes |
| How is dispersion compensation achieved? | With special engineering fibers with a specific profile which results in a negative dispersion slope Or with digital pre or past - compensation |
| What is physical reason for polarization mode dispersion (PMD) and polad polarization dependent loss (PDL)? | Unperfect waveguides not the same dimensions in x and y - direction (birefringence for PMD) |
| Which attenuating effects limit the bandwidth of an optical fiber? | Material losses: - intrinsic losses from fused silica - extrinsic absorptions caused by impurities (most important: OH^- absorption peak strong in SiO_2 fiber) Rayleigh Scattering: local microscopic fluctuations in the density Wavieguide Imperfections - Mie Scattering: Refractive index variations on a scale larger than optical lambda |
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