Abstract
We present a photonic approach for generating low phase noise, arbitrary chirped microwave waveforms based on heterodyne beating between high order correlated comb lines extracted from frequency-agile optical frequency comb. Using the dual heterodyne phase transfer scheme, extrinsic phase noises induced by the separate optical paths are efficiently suppressed by 42-dB at 1-Hz offset frequency. Linearly chirped microwave waveforms are achieved within 30-ms temporal duration, contributing to a large time-bandwidth product. The linearity measurement leads to less than 90 kHz RMS frequency error during the entire chirp duration, exhibiting excellent linearity for the microwave and sub-THz waveforms. The capability of generating arbitrary waveforms up to sub-THz band with flexible temporal duration, long repetition period, broad bandwidth, and large time-bandwidth product is investigated and discussed.
Highlights
The generation of broad bandwidth linearly or arbitrarily chirped microwave (MW) and subTHz signals has attracted extensive research interest for a wide range of applications such as frequency-modulated continuous-wave (FMCW) radar [1,2,3], ultra-wideband sensing [4, 5], bio-medical imaging [6], physical chemistry [7], noncontact sensing and non-destructive diagnosis [1, 8, 9]
We have demonstrated a dual-heterodyne phase error transfer (DHPT) method [24] for detecting and suppressing the phase noises induced by the separate optical paths in photonic generation of stable RF signals at fixed frequencies
We experimentally demonstrate photonic generation of linearly chirped MW waveforms based on heterodyne beating between two correlated frequency-chirped optical comb lines which are extracted from our specially designed frequency-agile optical frequency comb (OFC) [25]
Summary
The generation of broad bandwidth linearly or arbitrarily chirped microwave (MW) and subTHz signals has attracted extensive research interest for a wide range of applications such as frequency-modulated continuous-wave (FMCW) radar [1,2,3], ultra-wideband sensing [4, 5], bio-medical imaging [6], physical chemistry [7], noncontact sensing and non-destructive diagnosis [1, 8, 9]. Thereby, phase correlated carriers with flexible chirp features are of significant interest These heterodyne-based approaches suffer from phase noise deterioration ascribing to the separated optic paths before beating [22, 23]. We experimentally demonstrate photonic generation of linearly chirped MW waveforms based on heterodyne beating between two correlated frequency-chirped optical comb lines which are extracted from our specially designed frequency-agile optical frequency comb (OFC) [25]. Such OFC offers arbitrary continuous sweep capability of the comb spacing, providing phase correlated, arbitrary chirped high order frequency-agile comb lines. The arbitrary characteristics of the generated signals such as flexible temporal duration, repetition period and large TBWP, which potentially make our approach applicable for photonic arbitrary waveforms generation, are investigated and discussed
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