20 GHz instantaneous bandwidth RF spectrum analyzer with high time-resolution

Abstract

We report on the experimental demonstration of a multi-gigahertz bandwidth RF spectrum analyzer exhibiting a resolution below 20 MHz, based on spectral hole burning in a rare-earth ion-doped crystal. To be compatible with demanding real-time spectrum monitoring applications, our demonstrator is designed to reach a high time resolution. For this purpose, we implemented the so-called "rainbow" architecture in which the spectral components of the incoming signal are angularly separated by the crystal, and are then acquired with a pixelated photodetector. The Tm 3+ :YAG crystal is programmed with a semiconductor DFB laser which frequency scan is servocontrolled and synchronized with the angular scan of a resonant galvanometric mirror, while a high-speed camera is used to acquire the spectra. In the perspective of future implementation within a system, the crystal is cooled below 4 K with a closedcycle cryostat. With this setup, we have been able to monitor and record the spectrum of complex microwave signals over an instantaneous bandwidth above 20 GHz, with a time resolution below 100 µs, 400 resolvable frequency components and a probability of intercept of 100 %.

Rate equation reformulation including coherent excitation: application to periodic protocols based on spectral hole-burning

“…In this section we consider a programming sequence composed of a pair of parallel linear chirps, in a Tm 3+ :YAG crystal under magnetic field. This configuration is close to the situation of the "rainbow" RF spectrum analyzer, where a wideband spectrospatial grating is burnt via a periodic sequence of frequency chirped and angularly scanned beams [18,46]. Here we simplify the excitation sequence by considering collinear programming beams, in order to be able to study the gratings in the sole frequency domain.…”