Abstract
Photonic radio-frequency (RF) arbitrary waveform generation (AWG) based on spectral shaping and frequency-to-time mapping has received substantial attention. This technique, however, is critically constrained by the far-field condition which imposes strict limits on the complexity of the generated waveforms. The time bandwidth product (TBWP) decreases as the inverse of the RF bandwidth which limits one from exploiting the full TBWP available from modern pulse shapers. Here we introduce a new RF-AWG technique which we call near-field frequency-to-time mapping. This approach overcomes the previous restrictions by predistorting the amplitude and phase of the spectrally shaped optical signal to achieve high fidelity waveforms with radically increased TBWP in the near field region.
Highlights
Ultrabroadband arbitrary radio-frequency (RF) waveforms with large time bandwidth product (TBWP) are relevant to a variety of applications including radar imaging and high-data rate covert wireless communications [1,2,3]
Conventional frequency-to-time mapping (FTM) is restricted to the space below the far-field limit (Eq (5)) for which good waveform fidelity is maintained, whereas Near-Field Frequency-to-Time Mapping (NF-FTM) is bounded only by the optical bandwidth (Eq (12) and (13)) and pulse shaper resolution (Eq (14)) limits
In NF-FTM the maximum achievable TBWP, which is directly proportional to the number of pulse shaping pixels resolved within the optical bandwidth, can be maintained over a wide RF bandwidth range
Summary
Ultrabroadband arbitrary radio-frequency (RF) waveforms with large time bandwidth product (TBWP) are relevant to a variety of applications including radar imaging and high-data rate covert wireless communications [1,2,3]. We predistort the amplitude and phase of the spectrally shaped optical signal to achieve high fidelity waveforms at the near field region, enabling generation of waveforms not accessible under the far-field condition In this technique, which we call Near-Field Frequency-to-Time Mapping (NF-FTM), the maximum achievable TBWP can be maintained over a wide RF bandwidth range which is quite distinct from the conventional FTM approach. We show while this signal can be generated by the NF-FTM technique with high fidelity, the conventional FTM technique results in a very badly distorted signal.
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