Resolution-Enhanced Dynamic Waveform Spectral Analysis Based on the Inverse Temporal Talbot Effect

We propose and experimentally demonstrate a resolution-enhanced dynamic waveform spectral analysis scheme based on the inverse temporal Talbot effect (ITTE). In the system, a sampling and dispersion structure is adopted, and the spectral information of the RF signal is mapped to the time domain, consecutively within each of the sampling-period slots. Meanwhile, the period of the output pulses is magnified by the ITTE, where the sampling pulse train is quadratically phase-modulated prior to experiencing dispersion. Enabled by the ITTE, spectral resolution can be improved while maintaining system bandwidth. Simulations and experiments validate that real-time RF signals with bandwidths above GHz and nanosecond continuous frequency transients can be successfully captured with an improved spectral resolution.

I. Introduction

Real-time spectral analysis of dynamic waveforms is the basis of many fields, such as radar systems, cognitive radio, and electronic warfare [1]–[3]. Spectral analysis is usually carried out by detection of the waveform followed by analog-to-digital conversion (ADC) and subsequent electronic digital signal processing (DSP), involving computationally intensive fast Fourier transform (FFT) algorithms. Real-time spectral analysis based on this method is significantly limited by the performance (e.g., speed) of current DSP engines. In particular, presently available DSP-based real-time spectral analysis methods are limited to instantaneous operation bandwidths below GHz, and cannot intercept transients that are faster than a few microseconds with a 100% probability. Photonic-assisted real-time spectral analysis is considered as a promising choice due to its advantages of large bandwidth, low loss and immunity to electromagnetic interference [4]. Plenty of photonic-assisted real-time spectral analysis approaches have been proposed, such as frequency to power mapping [5], [6], photonic-assisted channelizing [7], [8] and optical real-time Fourier transform (RTFT) [9]–[14]. Frequency to power mapping scheme, transforming microwave frequency into optical power or microwave power through two complementary optical links, features large bandwidth and low latency, whereas it is only suitable for measuring single-frequency signal. Through dividing broadband signals into multiple sub-channels with small bandwidth, the photonic assisted channelization scheme can reduce the requirement of the sampling rate of ADC. Nevertheless, it still needs multi-channel digital FFT, which will introduce latency due to the enormous amount of data.