Contents 1. Introduction
Optical arbitrary waveform measurement (OAWM) based on frequency combs [1]–[3] has the potential to unlock a wide variety of applications, ranging from reception of high-speed data signals [2]–[5] and elastic optical networking [6] to investigation of ultra-short events and photonic-electronic analog-to-digital conversion (ADC) [7]–[8]. Previous demonstrations of OAWM relied on spectrally sliced coherent detection [1]–[3], where optical filters are used to decompose a broadband signal into several spectral slices, that are individually detected by an array of in-phase/quadrature receivers (IQR) using a frequency comb as multi-wavelength local oscillator (LO). The reconstruction of the optical waveform then relies on precise stitching of the spectral slices through digital signal processing (DSP). Based on this concept, OAWM of a 228 GHz-wide signal was demonstrated using discrete components [2], and further work demonstrated a 320 GHz photonic-electronic ADC that combines spectrally sliced OAWM with high-speed electro-optic modulators [7]. However, all these schemes crucially rely on high-quality optical filters for spectral slicing of the optical signal and for separating the comb tones. These filters lead to additional insertion loss and render the overall schemes difficult to miniaturize, in particular when relying on high index-contrast integration platforms such as indium phosphide (InP) or silicon photonics. Therefore, integrated OAWM systems had to either rely on phase-error-correction of the underlying arrayed waveguide gratings (AWG) [9] or on thermally tunable ring filters in a coupled-resonator optical waveguide (CROW) structure [3], both requiring sophisticated control schemes.
