Abstract
Real-time electrical spectrum analysis is of great significance for applications involving radio astronomy and electronic warfare, e.g. the dynamic spectrum monitoring of outer space signal, and the instantaneous capture of frequency from other electronic systems. However, conventional electrical spectrum analyzer (ESA) has limited operation speed and observation bandwidth due to the electronic bottleneck. Therefore, a variety of photonics-assisted methods have been extensively explored due to the bandwidth advantage of the optical domain. Alternatively, we proposed and experimentally demonstrated an ultrafast ESA based on all-optical Fourier transform and temporal magnification in this paper. The radio-frequency (RF) signal under test is temporally multiplexed to the spectrum of an ultrashort pulse, thus the frequency information is converted to the time axis. Moreover, since the bandwidth of this ultrashort pulse is far beyond that of the state-of-the-art photo-detector, a temporal magnification system is applied to stretch the time axis, and capture the RF spectrum with 1-GHz resolution. The observation bandwidth of this ultrafast ESA is over 20 GHz, limited by that of the electro-optic modulator. Since all the signal processing is in the optical domain, the acquisition frame rate can be as high as 50 MHz. This ultrafast ESA scheme can be further improved with better dispersive engineering, and is promising for some ultrafast spectral information acquisition applications.
Highlights
Electrical spectrum analyzer (ESA) is a fundamental instrument widely applied in a verity of fields including the wireless communication, the radar system, and the radio astronomy [1,2,3]
The conventional ESA based on electronic technology is hard to further extend the observation bandwidth and the acquisition frame rate, which is undesirable in many applications where ultrafast analysis or large bandwidth measurement is required
The experimental setup of the ultrafast and large bandwidth ESA is illustrated in Fig. 3, and it consists of the optical Fourier transform part and the temporal magnification part
Summary
Electrical spectrum analyzer (ESA) is a fundamental instrument widely applied in a verity of fields including the wireless communication, the radar system, and the radio astronomy [1,2,3]. Photonicsassisted spectrum analysis approaches have arisen with the advanced microwave photonics, which leverages the large bandwidth in the optical domain, and multiplexes the radiofrequency (RF) to the optical field by an electro-optic modulator (EOM) [5] These RF measurement approaches are able to achieve large bandwidth or fast acquisition frame rate, based on different mechanisms, such as optical power monitoring [6,7,8,9], optical channelizing [10,11,12,13], time-domain optical processing like time stretch [14,15] and all-optical Fourier transform [16,17], and compressed sensing (CS) [18,19,20]. The ultrafast spectrum analyzer proposed here provide an alternative solution for some applications where ultrafast acquisition frame rate and large observation bandwidth are demanded simultaneous, such as the observation of dynamic frequency evolutions, the capture of instantaneous frequency, etc
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