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Signal processing procedure and the experimental results. (a) Digitized frequency-shifted spectral slices. (b) Spectral slices after compensating for the time-invariant transfer functions. The dotted lines indicate the used overlap regions for estimating the frequency-independent complex factors. (c) Reconstructed spectrum of a 100-GBd 16QAM signal, obtained through merging the signal tributaries by maximal-ratio combing (MRC). (d, e) Comparison of 100-GBd signal data signals with different modulation formats, obtained by OAWM-based detection (top row) and by single-slice single-polarization intradyne coherent receiver (Intradyne Rx, bottom row). For OAWM reception, we observe less than 1 dB SNR penalty for 100-GBd 64QAM and negligible penalty for 100-GBd QPSK and 16QAM, while the ADC bandwidth requirements are greatly reduced.
Source publication
We demonstrate optical arbitrary waveform measurement (OAWM) using a silicon photonic spectral slicer. Exploiting maximal-ratio combining (MRC), we demonstrate the viability of the scheme by reconstructing 100-GBd 64QAM signals with high quality.
Contexts in source publication
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... of the comb lines and of the fibers and can thus be assumed constant during a single signal recording. With the complete complex transfer functions at hand, the incoming waveform can then be reconstructed by offline DSP. To this end, the digitized signal slices are first frequency-shifted according to the spacing of the LO comb tones, see Fig. 2 (a). Figure 2 (b) shows the corresponding data after compensating for the time-invariant transfer functions of the various signal paths. The dotted lines indicate the position of the 500 MHz-wide overlap regions that are used to estimate the frequency-independent complex factors associated with neighboring slices. Note that the ...
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... this end, the digitized signal slices are first frequency-shifted according to the spacing of the LO comb tones, see Fig. 2 (a). Figure 2 (b) shows the corresponding data after compensating for the time-invariant transfer functions of the various signal paths. The dotted lines indicate the position of the 500 MHz-wide overlap regions that are used to estimate the frequency-independent complex factors associated with neighboring slices. ...
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... of these regions is defined by the crossing points of the slightly non-uniform CROW transfer functions, which are not strictly equidistant. For merging the signal tributaries, we consider our receiver as a single-input multiple-output (SIMO) system and use maximal-ratio combing (MRC) [9] to maximize the SNR of the reconstructed waveform, see Fig. 2 (c) for the reconstructed spectrum of a 100 GBd Experimental setup of our proof-of-concept demonstration. For testing, we use a 100-GBd 64QAM signal, generated by a lithium-niobate IQ modulator that is driven by a benchtop-type arbitrary-waveform generator (AWG, Keysight M9536 A). The test signal and is spectrally sliced by an array of ...
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... test signal. In the example shown in Fig. 2 (a-c), the spectral widths of the four signal slices amounts to 46.5 GHz, 29.4 GHz, 31.9 GHz, and 32.2 GHz, leading to an overall bandwidth of 140 GHz. Note that the bandwidth of our heterodyne receivers amounts to approximately 50 GHz and thus exceeds both the comb line spacing of 30 GHz and the width of the CROW passband, which amounts to ...
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... leading to an overall bandwidth of 140 GHz. Note that the bandwidth of our heterodyne receivers amounts to approximately 50 GHz and thus exceeds both the comb line spacing of 30 GHz and the width of the CROW passband, which amounts to approximately 40 GHz. As a consequence, the spectral slices in our experiment exhibit significant overlap, see Fig. 2 (a) and (b). We find that reducing this overlap by omitting parts of the digital spectra does not have any detrimental impact on the quality of the stitched waveform. The scheme could hence have implemented with reduced electronic acquisition ...
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... estimate the performance of our OAWM scheme, we analyze the quality of received data signals with different modulation formats and compare it to single-polarization single-slice intradyne coherent reception, see Fig. 2 (d) and (e). For a fair comparison, we use identical DSP algorithms in both cases, and we extract the constellation signalto-noise ratio (SNR), which is related to the error-vector magnitude (EVM). For OAWM reception, we observe less than 1 dB SNR penalty for 100-GBd 64QAM and negligible penalty for 100-GBd QPSK and 16QAM, while the ADC ...
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... After converting individually each slice with reduced-bandwidth electrical ADCs featuring a high ENOB, the original RF signal can be retrieved by stitching together the signal slices in a downstream DSP. The low jitter of high-grade comb sources is also essential here, as it results in narrow RF linewidths and a high degree of correlation between the phase noise of the individual comb lines, that greatly facilitates the implementation of spectral stitching [34]- [36]. ...
... In the following, the presented optical detection concept is experimentally demonstrated by spectrally sliced reception of high-speed optical data signals using the CROW filter bank from the ePIC [36]. While in this experiment, electrooptic conversion was still implemented off-chip, the demonstration may still serve to validate key aspects of the integrability of this system architecture, as the impact of the exact spectral shape of the filters onto the signal stitching and reconstruction algorithm was one of the fundamental aspects that needed to be assessed. ...
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Comb-based optical arbitrary waveform measurement (OAWM) techniques can overcome the bandwidth limitations of conventional coherent detection schemes, thereby enabling ultra-broadband signal acquisition in a wide range of scientific and industrial applications. For efficient and robust implementation of such OAWM systems, miniaturization into chip-scale form factors is key. In this paper, we propose and demonstrate an OAWM scheme that exploits chip-scale Kerr soliton combs as compact and highly scalable multi-wavelength local oscillators (LO) and that does not require optical slicing filters, thus lending itself to efficient implementation on state-of-the-art high-index-contrast integration platforms such as silicon photonics. The scheme allows for measuring truly arbitrary waveforms with high accuracy based on a dedicated system model that is calibrated by means of a femtosecond laser with a known pulse shape. We demonstrate the viability of our approach in a proof-of-concept experiment by capturing optical waveforms with multiple 16QAM and 64QAM wavelength-division multiplexed (WDM) data signals, reaching overall line rates of up to 1.92 Tbit/s within an optical acquisition bandwidth of 610 GHz. To the best of our knowledge, this is the highest bandwidth that has so far been demonstrated in an OAWM experiment. Our work opens a path towards efficient implementation of OAWM systems, offering THz acquisition bandwidths in highly compact and robust assemblies that can rely on chip-scale frequency-comb generators and simple filter-less detector circuits.
