Microwave Photonic Signal Processing

Abstract

The full exploitation of the advantages that radio frequency, microwave and millimetre-wave technologies bring to broadband telecommunications and other related applications requires a coordinated effort in the development of signal processing techniques suitable for them. This is especially important as novel applications demand the use of increasingly higher-frequency carriers and broadband signals.The traditional approach towards radio frequency (RF) signal processing is illustrated in the upper part of Figure 8.1. Here an RF signal originating from an RF source or coming from an antenna is fed to an RF circuit that performs the signal processing tasks either at the RF signal or at an intermediate frequency band after a down-conversion operation. In any case, the RF circuit is capable of performing the signal processing tasks for which it has been designed only within a specified (often reduced) spectral band. This approach results in poor flexibility since changing the band of the signals to be processed requires the design of a novel RF circuit and possibly the use of different hardware technology. Furthermore, even if the RF carrier is not changed, the nature of the modulating signal might be, thus requiring more bandwidth or sampling speed from the processor. This is especially true in the case where discrete time signal processing has to be carried over the RF signal. This set of drawbacks is often termed in the optical communications technology literature as the electronic bottleneck. Although important it is by no means the only source of degradation, since electromagnetic interference (EMI) and frequency dependent losses can also be sources of major impairments.An interesting approach to overcome the above limitations involves the use of photonics technology and especially fibre and integrated optics devices and circuits to perform the Microwave Photonics: Devices and Applications Edited by Stavros Iezekiel

Microwave Signal Processing over Multicore Fiber

“…As appreciated from the optical spectra in reflection gathered in Figure 6b, all the FBGs present similar levels of strength with a maximum difference of 3 dB. The performance of this multicavity delay line device was evaluated in the context of microwave signal filtering [36]. To achieve the filtering effect, we combined and photodetected all the delayed RF signal samples coming from the MCF device output.…”

“…The performance of this multicavity delay line device was evaluated in the context of microwave signal filtering [36]. To achieve the filtering effect, we combined and photodetected all the delayed RF signal samples coming from the MCF device output.…”

“…These experimental results are actually in very good agreement with the theoretical ones, with small discrepancies in the basic differential delays that may be caused by discrepancies between the theoretical and actual values of the core refractive indices and small imbalances in the reflectivity strength of the FBGs. The performance of this multicavity delay line device was evaluated in the context of microwave signal filtering [36]. To achieve the filtering effect, we combined and photodetected all the delayed RF signal samples coming from the MCF device output.…”

“…Even though MCFs were initially envisioned in the context of core and metro optical networks, they can also be applied to a wide range of application fields including radio access networks and multiple antenna connectivity [6,33,34], multi-parameter optical fiber sensing [35] and radiofrequency (RF) signal processing [36][37][38][39]. For instance, Diamandi et al have recently demonstrated that opto-mechanical intercore crosstalk in MCFs can be very useful for applications such as multicore fiber lasers, parametric amplification in SDM networks for MCFs, sensing or optoelectronic oscillators (OEOs) [15].…”

“…This leads to what we call "fiber-distributed signal processing", a concept with great potential regarding converged fiber-wireless telecommunications scenarios, as those envisioned for 5G systems and the Internet of Things. A true time delay line (TTDL) can be considered the key building block of radiofrequency signal processing [36][37][38][39][40][41][42][43][44][45][46][47]. This photonic subsystem provides a frequency independent and tunable group delay for the RF signal within a given frequency range.…”