Photonic instantaneous spectrum analysis with massive frequency bins

Broadband and gap-free analysis of the time-frequency evolution of non-stationary signals is critical for emerging wireless networks and integrated sensing and communication applications. In particular, the photonic approach based on frequency-to-time mapping (FTM) has emerged as a promising solution for wideband gap-free instantaneous spectrum analysis (ISA). However, although approaches such as time-lens-based schemes have demonstrated nanosecond-scale frame rate and gigahertz-level bandwidth, they still face significant limitations, including severe bandwidth expansion before photodetection and excessive dispersion requirement, making the acquisition of massive frequency bins impractical. Here, we present a dispersion-efficient photonics scheme to overcome these limitations. By employing dual optical frequency combs (OFCs), it efficiently reduces the dispersion requirement and mitigates the output bandwidth expansion. In addition, by introducing the channelization technique, the parallel processing further extends the signal bandwidth and multiplicatively increases the number of frequency bins. In this work, we demonstrate an ISA architecture with a bandwidth of 20 GHz, a frequency resolution of 78.125 MHz, and a time resolution of 12.8 ns, yielding 256 frequency bins. In experiment, the spectrum is channelized into 16 frequency channels, with each requiring only a 2.5-GHz-bandwidth balanced photodetector (BPD). Remarkably, to achieve the demonstrated bandwidth and resolution, our architecture reduces the dispersion requirement of traditional FTM systems by a factor of 20, while avoiding the use of a 40 GHz high-speed photodetector by employing 2.5 GHz BPDs.