Wideband and continuously-tunable fractional photonic Hilbert transformer based on a single high-birefringence planar Bragg grating

Abstract

We propose and experimentally demonstrate wideband and continuously tunable fractional-order photonic Hilbert transformers (FrHT). These are realized by a single apodized planar Bragg grating within a high-birefringence planar substrate. The fractional order of the FrHT is continuously tuned and precisely controlled by changing the polarization state of the input light. The experimental characterization demonstrates an operating bandwidth up to 120 GHz with amplitude ripples below 3 dB. The optical phase shift response is directly measured to verify the proposed tuning property, demonstrating transform orders of around 1, 0.7, and 0.5. This approach is simple, stable, and compact compared to other existing methods and has great potential in the fields of ultrafast all-optical signal processing.

Microwave and RF Photonic Fractional Hilbert Transformer Based on a 50 GHz Kerr Micro-Comb

“…In recent years, integrated fractional Hilbert transformers based on microring/microdisk resonators and Bragg gratings on a silicon-on-insulator (SOI) platform have been demonstrated, as well as in integrated InP-InGaAsP photonic chips, which can all provide competitive advantages such as compact device footprint, high stability, and mass-producibility [11,12,[17][18][19]. Better tunability has also been achieved by introducing thermooptic microheaters to tune the phase shift.…”

Photonic RF and microwave temporal signal processing based on optical Kerr micro-combs

“…Fractional Hilbert transforms (FHTs) that yield a variable phase shift represent a powerful extension to the standard HT, with applications to secure single sideband communications [145], hardware keys [145,146], and in forming images that are edge enhanced relative to the input object, where one can select the edges that are enhanced as well as the degree of edge enhancement [147]. Electronic fractional Hilbert transformers are limited in operation bandwidth [145,148] Bragg grating approaches [155]. In practice, the FHT of the RF and microwave signals -not the complex optical fields − is what is most desired for RF measurement and signal reshaping [156][157][158][159][160][161][162][163].…”

RF and microwave photonic temporal signal processing with Kerr micro-combs

“…Phase-shifted fibre Bragg grating based Hilbert transformers typically have bandwidths of a few 100 GHz [150][151][152][153] but only yield a precise FHT for signals with specific bandwidths, fixed fractional orders, and only operate on the complex optical field (not the actual RF signal). This also holds for integrated reconfigurable microwave processors [154] as well Bragg grating approaches [155]. In practice, the FHT of the RF and microwave signals -not the complex optical fields − is what is most desired for RF measurement and signal reshaping [156][157][158][159][160][161][162][163].…”