Comb-based radiofrequency photonic filters with rapid tunability and high selectivity

Abstract

Photonic technologies have received considerable attention for enhancement of radio-frequency (RF) electrical systems, including high-frequency analog signal transmission, control of phased arrays, analog-to-digital conversion, and signal processing. Although the potential of radio-frequency photonics for implementation of tunable electrical filters over broad RF bandwidths has been much discussed, realization of programmable filters with highly selective filter lineshapes and rapid reconfigurability has faced significant challenges. A new approach for RF photonic filters based on frequency combs offers a potential route to simultaneous high stopband attenuation, fast tunability, and bandwidth reconfiguration. In one configuration tuning of the RF passband frequency is demonstrated with unprecedented (~40 ns) speed by controlling the optical delay between combs. In a second, fixed filter configuration, cascaded four-wave mixing simultaneously broadens and smoothes comb spectra, resulting in Gaussian RF filter lineshapes exhibiting extremely high (>60 dB) main lobe to sidelobe suppression ratio and (>70 dB) stopband attenuation.Optical frequency combs, generated via self-referenced and stabilized mode-locked lasers, have enabled revolutionary progress in precision optical frequency synthesis and metrology 1-4 . Optical combs are also of tremendous interest for other applications 5 , such as multi-wavelength coherent lightwave communications 6-8 , optical arbitrary waveform generation 9-11 , generation of low-phasenoise 12 or agile ultrabroadband microwaves 13 , and signal processing 6,14 . For these purposes, in which higher pulse repetition rates are desired and only moderate frequency stability is required, comb sources based on strong electro-optic modulation of a continuous-wave laser have seen substantial attention [15][16] . Here we report significant advances in RF photonic filters enabled by the ability to rapidly tune the timing of the comb and shape its power spectrum.

Integrable microwave filter based on a photonic crystal delay line

“…Equivalent configurations use dispersive optical fibre links (DOFL), with lengths up to 20 km (ref. 38), or dispersion-compensating fibres (DCFs) 23 .…”

“…The salient features include: notch and band-pass operation; a footprint reduced by several orders of magnitude compared to filters based on FBG or fibre delay lines; broadband operation up to 50 GHz; and tunable free spectral ranges over 70 GHz. In addition, there is clear potential for the improvement of the selectivity, the main to secondary side-lobe (MSSL) ratio and the Q factor, thereby leading to highperformance MWP filtering owing to compatibility with sources of optical frequency combs 23 .…”

Microwave Photonic Filter: A Systematic Literature Review

“…Once, the time delay line if fabricated in FBGs tuning will be difficult. so tuning can be performed by tuning wavelength spacing .The tuning speed in laser array is in microsecond , faster tuning speed in the range of nanosecond can be achieve using optical comb , demonstration at speed of 40ns was reported [3]. It is observed that delay line microwave photonic filter operating incoherent regime with all positive coefficients operates as a low pass filter.…”

Reconfigurable Filter-free Sinc-shaped RF Photonic Filters Based on Rectangular Optical Frequency Comb

“…Radio frequency (RF) filters based on optical frequency comb and dispersive propagation enable RF signal processing in the photonic domain [1,2]. Compared to its electrical counterpart, this approach is favored due to the broad bandwidth and low losses rendered by optical fibers, as well as arbitrary RF filter shape empowered by lineby-line shaping of the optical frequency comb [2,3].…”

“…Compared to its electrical counterpart, this approach is favored due to the broad bandwidth and low losses rendered by optical fibers, as well as arbitrary RF filter shape empowered by lineby-line shaping of the optical frequency comb [2,3]. For instance, highly selective rectangular RF filter shape has been demonstrated using programmable pulse shapers to tailor optical frequency comb [4] or slice ASE source [5].…”