Microcomb-Based Photonic RF Signal Processing

Abstract

Microcombs are powerful tools as sources of multiple wavelength channels for photonic RF signal processing. They offer a compact device footprint, large numbers of wavelengths, and wide Nyquist bands. Here, we review recent progress on microcomb-based photonic RF signal processors, including true time delays, reconfigurable filters, Hilbert transformers, differentiators, and channelizers. The strong potential of optical micro-combs for RF photonics applications in terms of functions and integrability is also discussed.Index Terms-Microwave photonics, micro-ring resonators. I. INTRODUCTIONHOTONIC RF techniques have attracted great interest during the past two decades since they offer ultra-high RF bandwidths, low transmission loss and strong immunity to electromagnetic interference. They have found wide applications ranging from radar systems to communications [1-5]. Among the many useful photonic RF techniques, optical frequency combs are one of the most fundamental and powerful tools due to their ability to provide multiple wavelength channels that can greatly increase the capacity of communications systems and allow the broadcast of RF spectra for advanced signal processing functions. However, traditional approaches for frequency comb generation, including those based on discrete laser arrays or electro-optic (EO) modulation, [6-9] all face limitations, such as their bulky size and large cost brought about by laser arrays and RF sources, or a limited free spectral range (FSR) of the comb lines that in turn yields a limited Nyquist zone for the RF system.Kerr optical frequency combs [10-22], or "microcombs", that originated from the optical parametric oscillation in monolithic micro-ring resonators (MRRs), offer distinct advantages over traditional multi-wavelength sources for RF applications, such as the potential to provide a much higher number of wavelengths, an ultra-large FSR, as well as greatly reduced footprint and complexity. In particular, for RF transversal functions, the number of wavelengths dictates the available channel number of RF time delays, and thus with microcombs, the performance of RF beamforming systems and filters can be greatly enhanced in terms of the angular resolution and quality factor, respectively. In addition, for photonic RF channelizers, with a given bandwidth for each wavelength channel, the total operation bandwidth (i.e., the maximum bandwidth of the input RF signal that can be processed) will depend on the number of wavelengths, and thus can be greatly enhanced with microcombs. Based on these advantages, a wide range of RF applications have been demonstrated, such as optical true time delays [23][24][25], transversal filters [25][26][27], signal processors [28,29], channelizers [30,31] and others [32][33][34]. Here, we review the recent advances of RF signal processing functions made possible through the use of microcombs, highlighting their potential and future possibilities.

Photonic RF fractional Hilbert transformers and spectral filters based on 49GHz FSR soliton crystal microcombs

“…We have demonstrated photonic RF signal processors based on soliton crystal microcombs. This approach offers a greatly reduced footprint, lower complexity, and potentially lower cost, representing a solid step towards the miniaturization of high performance photonic RF systems [16][17][18][19][20][21][22][23][24][25].…”

BiOBr nanoflakes with strong Kerr nonlinearity towards hybrid integrated photonic devices

“…Featuring broad operation bandwidths, low power consumption, and potentially reduced cost, all-optical signal processing based on nonlinear photonic devices has provided a competitive solution to realize ultrafast signal processing. [1][2][3][4][5][6][7] As the key building blocks for implementing nonlinear photonic devices, advanced optical materials with superior nonlinear properties have been widely investigated. Recently, two-dimensional (2D) layered materials such as graphene [8,9], graphene oxide (GO) [10][11][12][13][14], transition metal dichalcogenides (TMDCs) [15][16][17], and black phosphorus (BP) [18][19][20] have attracted significant interest with their remarkable optical properties, such as ultrahigh Kerr optical nonlinearities, strong nonlinear absorption, significant material anisotropy, and layer-dependent material properties.…”

Photonic RF channelizer based on 49GHz soliton crystal microcombs

“…Recently, microcombs [27][28][29][30][31], particularly those based on CMOS-compatible platforms [32][33][34][35][36][37][38][39][40], came into focus since they offer a large number of coherent wavelength channels in a mm 2 -size footprint, and have enabled a wide range of RF applications [41,42], such as RF true time delays [43,44], transversal signal processors [45][46][47][48][49][50], frequency conversion [51], phase-encoded signal generators [52], and RF channelizers [53,54]. Previously [54], we reported an RF channelizer based on a microcomb that achieved high performance in a compact footprint.…”