  Comb-based optical arbitrary waveform measurement (OAWM) techniques can
overcome the bandwidth limitations of conventional coherent detection schemes
and may have disruptive impact on a wide range of scientific and industrial
applications. Over the previous years, different OAWM schemes have been
demonstrated, showing the performance and the application potential of the
concept in laboratory experiments. However, these demonstrations still relied
on discrete fiber-optic components or on combinations of discrete coherent
receivers with integrated optical slicing filters that require complex tuning
procedures to achieve the desired performance. In this paper, we demonstrate
the first wavelength-agnostic OAWM front-end that is integrated on a compact
silicon photonic chip and that neither requires slicing filters nor active
controls. Our OAWM system comprises four IQ receivers, which are accurately
calibrated using a femtosecond mode-locked laser and which offer a total
acquisition bandwidth of 170 GHz. Using sinusoidal test signals, we measure a
signal-to-noise-and-distortion ratio (SINAD) of 30 dB for the reconstructed
signal, which corresponds to an effective number of bits (ENOB) of 4.7 bit,
where the underlying electronic analog-to-digital converters (ADC) turn out to
be the main limitation. The performance of the OAWM system is further
demonstrated by receiving 64QAM data signals at symbol rates of up to 100 GBd,
achieving constellation signal-to-noise ratios (CSNR) that are on par with
those obtained for conventional coherent receivers. In a theoretical
scalability analysis, we show that increasing the channel count of non-sliced
OAWM systems can improve both the acquisition bandwidth and the signal quality.
We believe that our work represents a key step towards out-of-lab use of highly
compact OAWM systems that rely on chip-scale integrated optical front-ends.
