An interesting method for broadband arbitrary waveform generation is based on frequency upshifting of a narrowband
microwave signal. In this technique, the original microwave signal is imaged into a temporally compressed replica using
a simple and practical fiber-based system. Recently, it has been shown that the conventional limitations of this approach
(e.g. bandwidth limitations) can be overcome by exploiting a temporal self-imaging (Talbot) effect in fiber. This effect
can be used whenever the signal to be imaged is a quasi-periodic waveform (e.g. microwave tones or any arbitrary
periodic waveform). This work provides a comprehensive review of the microwave frequency upshifting technique for
broadband arbitrary waveform generation, with a special focus on the Talbot-based approach. The design specifications,
and the associated practical capabilities and constraints, of fiber-based microwave frequency upshifting systems will be
examined. The influence of higher-order effects, in particular second-order dispersion terms in the employed fibers, on
the system performance will be evaluated and some additional design rules to minimize the associated detrimental
effects will be given. Experimental evidence of our findings has been also provided. Our results show that microwave
frequencies up to a few hundreds of GHz over nanosecond temporal windows can be easily obtained with the described
technique using readily available (sub-)picosecond pulsed optical sources.
We present a method for controlling the reflection amplitude and phase of uniform fiber Bragg gratings (FBGs) during
their fabrication process. It is done by measuring the spectral interference between the reflections from the FBGs and the
fiber end by an optical spectrum analyzer and performing a fast Fourier transform. The method allows correction of the
FBGs until obtaining the needed parameters during the writing process, as well as at any time after that. We also
demonstrate the use of cascaded uniform FBGs for the generation of periodic optical pulses with arbitrary waveform. It
is a significantly simplified structure compared to complex fiber Bragg grating shapes. The pulse shaping is based on
splitting of the input pulses by low reflecting FBGs into a number of replicas and their superposition with proper
amplitude, time delay and phase shift that depend on the FBG parameters. The reflection amplitude and phase of each
grating are unambiguously determined by the needed pulse shape. This method was experimentally verified for
converting sinusoidally phase-modulated radiation of CW laser diode into a Gaussian pulse train with a pulse width of 30
ps.
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