Frequency-domain light intensity spectrum analyzer based on temporal convolution.

We propose and experimentally demonstrate a new type of all-optical radio frequency (RF) spectrum analyzer based on temporal convolution and cross-phase modulation (XPM) that can be regarded as the frequency-domain counterpart of a conventional light intensity spectrum analyzer (LISA). The XPM effect converts the intensity envelope of an optical signal to the phase of the probe signal, while the temporal convolution helps to enable the RF spectrum to be temporally resolved with a high frame rate. This frequency-domain LISA (f-LISA) has experimentally demonstrated an 800-GHz observation bandwidth with 1.25-GHz resolution (1 GHz for a single frequency) and a 94-MHz frame rate. To showcase its potential applications, this analyzer has successfully characterized the dynamic RF spectrum of an ultrafast wavelength-switching signal with a 10-ns switching interval. We believe that it is promising for some ultrafast dynamic RF spectrum acquisition applications, e.g., fast tuning lasers and real-time channel monitoring.