  A theoretical and experimental performance analysis of a Semiconductor
Optical Amplifier - Mach-Zehnder Interferometer (SOA-MZI) photonic sampling
mixer used as a frequency up-converter is presented employing Switching and
Modulation architectures. An active mode-locked laser, generating 2 ps-width
pulses at a repetition rate equal to 10 GHz, is used as a sampling source. An
optical carrier intensity modulated by a sinusoidal signal at 1 GHz is
up-converted to 9 GHz and 39 GHz. High Conversion Gains (CGs) of about 15 dB
are demonstrated for the frequency conversion to 9 GHz using both
architectures, whereas up to 4 dB and 9 dB for the conversion to 39 GHz
employing Switching and Modulation architectures, respectively. Small-signal
equations for the up-converted signal in both architectures are formulated and
developed, which permit to quantify the CG from closed-form expressions. The
numerically calculated CG values are in very good agreement with those obtained
experimentally. The validated equations are subsequently employed to explain
the performance differences between the two architectures in terms of the CG.
Furthermore, signals modulated by QPSK and 16-QAM complex modulation formats at
different baud rates are up-converted from 750 MHz to 9.25 GHz and 39.75 GHz
and their Error Vector Magnitude is evaluated and compared. The maximum bit
rate that meets the Forward Error Correction (FEC) limit is achieved using the
Modulation architecture. It is 1 Gbps and 512 Mbps for QPSK and 16-QAM
modulations, respectively.
