Abstract
An exact theory describing the intensity PSD of photonic signal processors
based on modulated thermal sources with smooth spectrum, first-order dispersion
and intensity-noise-limited direct detection is presented. The theory is applied
to the evaluation of the signal-to-noise ratio (SNR) of Microwave Photonic
Filters (MPF) and of systems based on Incoherent Frequency-to-Time Mapping
(IFTM) and Time-Spectrum Convolution (TSC) driven by thermal carriers whose
optical spectra (continuous or sliced) is smooth at microwave scales. It is
shown that the noise PSD of MPF based on low-index amplitude modulation coincides
with the white-noise PSD of unmodulated, continuous wave (cw) polarized thermal
light. In turn, both IFTM and TSC show modulation-dependent noise PSDs resulting
in an SNR not better than cw, which decreases with pulse spreading. For IFTM
the SNR is poor, with typical values of a few dB, whereas the SNR of TSC interpolates
between the cw SNR and that of IFTM, thus showing a range of parameters where
the SNR of IFTM is outperformed.
© 2012 IEEE
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