| Popis: |
A key element of the microwave photonic systems is the subsystem for the formation of modulated laser radiation, which provides both the transfer of the microwave signal to the optical band and the formation of a poly-harmonic optical signal with a difference frequency lying in the microwave range. For example, the latter is used for the generation of continuous microwave carriers in frequency equal to the difference after photo mixing. At the same time, for two-frequency radiation formation, as a rule, either a separate set of lasers spaced by the frequency of a microwave signal, or lasers with internal modulation or mode synchronization, or single-frequency lasers with external modulation based on electro-optical modulators with an operating frequency range up to 100 GHz of amplitude, phase and polarization types, are used. Better characteristics of the line width and the noise generation level of the microwave carriers characterize the latter. Their main disadvantage is the presence in the spectrum of parasitic spectral components, as a rule, side components of higher orders and not up to the end suppressed carrier frequency, the number and amplitudes of which grow when the conversion parameters deviate from the optimal ones. |
