Flashcards
OCF: Q6
Cards in this deck (17)
- 1Which fiber profiles did we discuss in the lecture? Describe their characteristics, differences and advantages/disadvantagesStep 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 - 2What 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 - 3Describe 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.
- 4Write down, name and describe the different Maxwell's equations
- 5What does the material equation describe?Relates the Electrical Displacement with the Electric Field and the polarization
- 6Describe 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 - 7Discuss what is meant by EH_{mn}, HE_{mn}, TE_{0n}, TM_{0n}, and LP_{mn} fiber mode nomenclaturesEH_{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 - 8What 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
- 9Please state the Nonlinear Schrödinger Equation and explain its componentsbeta_1: group volocity
beta_2: group velocity dispersion
beta_3: dispersion slope
alpha: fiber losses
gamma_{NL}: non-linear interaction factor
- 10Explain the term group velocityGroup velocity is the velocity at which a photon moves through the fiber
- 11Explain the term group velocity dispersionVariations of the group velocity, mainly due to dispersion
- 12Explain the term dispersion slopeVariations of the Group velocity dispersion in terms of frequency
- 13Why 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.
- 14What is the origin of dispersion?Material Dispersion: n(omega)
waveguide dispersion: n_eff(omega) <- Mode changes - 15How 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 - 16What 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)
- 17Which 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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- Flashcards on OCF: Q6, created by Manuel Kohli on 14/01/2018.
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- Manuel Kohli
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