Optical down-sampling of wide-band microwave signals

Attosecond‐precision ultrafast photonics

“…The demonstrated photonic ADC is based on optical downconversion [118] of a narrowband, high-frequency microwave signal by subsampling with a sub-10-fs-jitter optical pulse train, followed by electronic filtering and quantization of the downconverted baseband signal. Prior work on electronic subsampling downconversion (in [119] and the references therein) suffered from low SNR, mainly due to the aperture jitter of local oscillators.…”

“…The first step is convolving the optical sampling pulse train (signal a, 200.2 MHz) with the narrowband, high-frequency microwave signal (signal b, 40.04 GHz) by electro-optic sampling. The two differentially modulated outputs from the modulator result in the suppression of second-harmonic distortions and intensity noise [118]. Due to subsampling, the spectrum of the microwave signal is aliased at every harmonic of the repetition rate, including at f = 0 (baseband) in the frequency domain, as shown in the inset (part c).…”

III-V on silicon micro-photonic circuits for frequency downconversion of RF signals

“…Effectively this implies that the intensity of consecutive optical pulses at the output of the modulator is proportional to the applied RF signal (when the modulator is used in its linear regime). In other words, the RF signal is sampled by the short-pulse train, which hence, after envelope detection on a photodetector results in an RF spectrum that contains replicas of the original RF signal spectrum spaced by the repetition frequency of the modelocked laser [1]. By selecting a proper repetition rate an aliasing-free downconversion can be realized this way.…”

Simultaneous broadband microwave downconversion and programmable complex filtering by optical frequency comb shaping

“…Several optical techniques for microwave downconversion have been reported, mainly involving electro-optic mixing [7,8], optical heterodyning [9,10], or high-speed sampling [11]. The first two methods can be combined with narrowband optical filtering to achieve simultaneous downconversion and analog filtering before the detection stage [8,10].…”

“…In these techniques, however, it is difficult to implement programmable filtering, because the relatively narrow IF bandwidth with respect to the optical wavelength calls for a high-quality, fine-resolution reconfigurable optical filter. Alternatively, the high-speed sampling approach involves the use of a high-repetition-rate optical pulse train to sample the microwave signal in the temporal domain and then to perform photodetection of the modulated pulses [11]. In this method, the frequency content of the microwave signal can be as large as half the train's repetition rate.…”