Integrated frequency comb source based Hilbert transformer for wideband microwave photonic phase analysis

Microwave fractional Hilbert transformer implemented in a dispersion-tailored few-mode fiber

We experimentally demonstrate, for the first time to our knowledge, a microwave fractional Hilbert transformer in a few-mode fiber using a transversal filtering approach. The filter taps are provided by a tunable true-time delay line that is realized by exploiting the spatial dimension of a dispersion-engineered double-clad step-index few-mode fiber. Both the fractional order and operational bandwidth of the fractional Hilbert transformer can be continuously tuned by adjusting the tap coefficients and varying the operational optical wavelength, respectively. The magnitude and phase response for different fractional orders, ranging from 0.17 to 1.00 that correspond to phase shifts of 15° to 90°, are measured. Operational bandwidths of 7.4 to 10.6 GHz are demonstrated for a classical Hilbert transformer. Real-time temporal fractional Hilbert transform of a Gaussian-like pulse is also performed. Our results are in good agreement with theory, validating the viability of our approach for implementation of microwave fractional Hilbert transformers.

Kerr Micro-combs for Radio Frequency Photonics -INVITED

We review applications of Kerr micro-combs in RF photonic systems including fractional differentiators, Hilbert Transformers and many other functions.

Advanced RF and microwave functions based on an integrated optical frequency comb source

We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave signal processing functions for applications including radar and communication systems.

Two-octave spanning supercontinuum generation in stoichiometric silicon nitride waveguides pumped at telecom wavelengths

We demonstrate supercontinuum generation in stoichiometric silicon nitride (Si₃N₄ in SiO₂) integrated optical waveguides, pumped at telecommunication wavelengths. The pump laser is a mode-locked erbium fiber laser at a wavelength of 1.56 µm with a pulse duration of 120 fs. With a waveguide-internal pulse energy of 1.4 nJ and a waveguide with 1.0 µm × 0.9 µm cross section, designed for anomalous dispersion across the 1500 nm telecommunication range, the output spectrum extends from the visible, at around 526 nm, up to the mid-infrared, at least to 2.6 µm, the instrumental limit of our detection. This output spans more than 2.2 octaves (454 THz at the -30 dB level). The measured output spectra agree well with theoretical modeling based on the generalized nonlinear Schrödinger equation. The infrared part of the supercontinuum spectra shifts progressively towards the mid-infrared, well beyond 2.6 µm, by increasing the width of the waveguides.

Integrated line-by-line optical pulse shaper for high-fidelity and rapidly reconfigurable RF-filtering

We present a 32 channel indium phosphide integrated pulse shaper with 25 GHz channel spacing, where each channel is equipped with a semiconductor optical amplifier allowing for programmable line-by-line gain control with submicrosecond reconfigurability. We critically test the integrated pulse shaper by using it in comb-based RF-photonic filtering experiments where the precise gain control is leveraged to synthesize high-fidelity RF filters which we reconfigure on a microsecond time scale. Our on-chip pulse shaping demonstration is unmatched in its combination of speed, fidelity, and flexibility, and will likely open new avenues in the field of advanced broadband signal generation and processing.