11859357
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 |
| What is the difference between the pulse carver of a RZ format and a CSRZ format? | The MZM is biased at pi and the repetition rate is 1/2 of the symbol rate |
| How big is the bandwidth advantage of CSRZ over RZ (for amplitude modulation)? | There is no advantage |
| Discuss the advantages and disadvantages of CSRZ-ASK over NRZ-OOK and RZ-OOK | Advantage: In RZ and NRZ we have strong nonlinear interactions when long sequences propagate ( due to high spikes in Power). In CSRZ the nonlinear tolerances are relaxed. Disadvantage: ? |
| What is the difference between single sideband (SSB) and vestigial sideband (VSB)? | In SSB one sideband is completely suppressed while in VSB only a vestige of the sideband is suppressed and the rest is kept. |
| In optical communication, the VSB filtering is done at the receiver. Why? | Because if a sideband was suppressed at the transmitter, it would quickly deconstruct itself upon non-linear fiber propagation |
| How is |S| minimized in VSB transmission? | The |S| is minimized with an effective spectral detuning equal to one quarter of the bit rate. |
| What is SSB and what are its advantages? | SSB (single sideband modulation) eliminates all components of one sideband from an amplitude-modulated wave. Advantage: more information is transmitted for the same power since the final RF amplification is concentrated in a single sideband. It uses less bandwidth. |
| What methods can be used to create SSB? | 1. Filter (removing one sideband) 2. Hilbert Transform 3. Hartley Method |
| How do we generate Duobinary and Alternate Mark Inversion with a single MZI | Duobinary: Add a delay to the data and add it with the original data. Feed it to the MZI with one arm having the inverted signal. (not really sure about the invertion) Alternate Mark: Same as for duobinary, but use a substraction instead of addition. |
| How is information encoded on an optical carrier when using binary differential phase-shift keying (DPSK)? | Use a continuously oscillating laser followed by one or two external modulators. The first is used to encode phase-shift keying and a second for pulse carver (RZ-DPSK). Two techniques: first one uses an external straight-line phase modulator for encoding. Second one uses MZI for phase modulation, biased at its transmission null in push-pull operation mode. |
| How can DPSK be detected? | It cannot be directly detected. Thus an optical delay interferometer is inserted in the optical path at the receiver to convert the differential phase modulation into amplitude modulation. |
| What is the influence of polarization multiplexed modulation compared to single polarization with respect to transmitted symbols M? | Switching the polarization adds an additional degree of freedom. The available bits changes from m to m+1 thus doubling the available symbols M. |
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