Journal: Light, Science & Applications

Article Title: Optical arbitrary waveform generation (OAWG) using actively phase-stabilized spectral stitching

doi: 10.1038/s41377-025-01937-4

Figure Lengend Snippet: The transmitter comb (Tx comb, Point Ⓐ) is generated by modulating a CW tone emitted by an external-cavity laser (ECL). The resulting Tx comb is amplified by an erbium-doped fiber amplifier (EDFA), and individual tones \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$f_{1}, \,f_{2}, \,f_{3},\, f_{4}$$\end{document} f 1 , f 2 , f 3 , f 4 are selected by a wavelength-selective switch (WSS) to serve as carriers for IQ modulation. The drive signals for the IQ modulators (IQM1,..., IQM4) are calculated by offline digital signal processing (DSP) and generated by a DAC array (Keysight M8194A) that is RF-synchronized to the Tx comb generator. A phase-stabilizing signal-combining tree (SCT) combines all tributaries, Point Ⓑ, thus forming the output waveform \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\underline{a}}_{{\rm{S}}}(t)$$\end{document} a _ S ( t ) , Point Ⓒ. The generated waveform is measured by a two-channel non-sliced OAWM receiver—either directly (upper position of switches S1 and S2) or after transmission through an 87 km-long fiber link (lower switch positions). The OAWM system uses two IQ receivers (IQRs) that are fed by the received waveform and by time-delayed copies of the Rx comb, comprising two tones (LO1, LO2, Inset Ⓓ) derived from a dissipative Kerr soliton (DKS) comb. The photocurrents of the IQRs are digitized by an ADC array (Keysight UXR series oscilloscope) and are used to reconstruct the received waveform via the OAWM DSP, Point Ⓔ. The reconstructed waveform is then demodulated (Demod. DSP) to retrieve the transmitted data, Point Ⓕ. Inset Ⓐ: Optical spectrum of Tx comb. Note that the displayed spectral width of the individual comb-tones is dictated by the rather large resolution bandwidth (RBW) of the spectrum analyzer that was used for the measurement (RBW = 2.48 GHz). Inset Ⓑ: High-resolution (RBW = 100 MHz) optical spectra of individual the tributary signals. Inset Ⓒ: High-resolution (RBW = 100 MHz) optical spectrum of 320 GBd 16QAM signal. Inset Ⓓ: Optical spectrum of the Rx comb (RBW = 2.48 GHz) that is used for OAWM. Inset Ⓔ: Spectrum of reconstructed 320 GBd 16QAM waveform obtained from the OAWM receiver in the optical back-to-back configuration (RBW = 100 MHz). Inset Ⓕ: Constellation diagram and constellation signal-to-noise ratio (CSNR) for an exemplary 320 GBd 32QAM signal measured in back-to-back configuration

Article Snippet: The drive signals for the IQ modulators (IQM1,..., IQM4) are calculated by offline digital signal processing (DSP) and generated by a DAC array (Keysight M8194A) that is RF-synchronized to the Tx comb generator.

Techniques: Generated, Amplification, Transmission Assay, Derivative Assay

Journal: Light, Science & Applications

Article Title: Optical arbitrary waveform generation (OAWG) using actively phase-stabilized spectral stitching

doi: 10.1038/s41377-025-01937-4

Figure Lengend Snippet: a Optical spectra of 16QAM signals with symbol rates ranging from 80 GBd to 320 GBd generated using spectrally sliced OAWG and measured using a high-resolution optical spectrum analyzer (AP2060, Apex Technologies, Marcoussis, France, resolution bandwidth 100 MHz). For better comparison, all spectra are normalized to the out-of-band amplified spontaneous emission (ASE) noise level. We indicate the frequencies \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$f_{1}, \;f_{2}, \;f_{3}, f_{4}$$\end{document} f 1 , f 2 , f 3 , f 4 of the Tx comb, for which a constant free spectral range (FSR) is maintained throughout the experiment. b Constellation signal-to-noise ratio (CSNR) as a function of the symbol rate for 16QAM (blue dots and solid blue line) and 32QAM signals (red dots and red dashed line)—measured in an optical back-to-back (ob2b) configuration and after transmission over 87 km of single-mode fiber (blue and red cross, see inset). The results are compared to other high-symbol-rate optical signaling experiments that rely on single digital-to-analog converters (DACs) , , , or photonic-electronic , , (circular markers) or purely electronic – , – (square markers) multiplexing techniques. References , , demonstrate pulse-amplitude modulation (PAM) signaling, whereas the other publications show QAM signals. References – and – use the commercially available signal generators Keysight M8199A and M8199B, respectively, which rely two time-interleaved DAC channels. Insets: Exemplary constellation diagrams for 16QAM and 32QAM 320 GBd signals and measured bit-error ratio (BER) obtained for the optical back-to-back configuration

Article Snippet: The drive signals for the IQ modulators (IQM1,..., IQM4) are calculated by offline digital signal processing (DSP) and generated by a DAC array (Keysight M8194A) that is RF-synchronized to the Tx comb generator.

Techniques: Generated, Comparison, Amplification, Transmission Assay, Multiplexing

Journal: Nature Communications

Article Title: Photonic-electronic arbitrary-waveform generation using quadrature multiplexing and active optical-phase stabilization

doi: 10.1038/s41467-025-61564-w

Figure Lengend Snippet: As a performance metric, we use the SNDR estimated from received PAM symbols (SNDR PAM ). a SNDR PAM penalty as a function of the LO-to-signal power ratio (LOSPR). The penalty is measured with respect to the optimum LOSPR of 14.5 dB and initially decreases with increasing LOSPR, because the residual signal-signal beat interference (SSBI) decreases. b Peak-to-peak voltage swing measured at the PE-AWG output as a function of the LOSPR. Since the electrical output power grows with decreasing LOSPR, a trade-off between output voltage swing and signal quality needs to be made. The yellow stars in Subfigures ( a ) and ( b ) correspond to the levels used in the subsequent measurements shown in Subfigures ( d ) and ( e ). c Simulated SNDR PAM penalty for BPD skews between 0 and 2 ps and for different LOSPR levels as indicated by the different colors. We find a SNDR PAM penalty of 0.9 dB for a LOSPR of 8 dB and a skew of 0.7 ps as specified for the BPD used in our experiments. We hence conclude that the skew results mainly from a path-length mismatch between the two fiber pigtails connected to the BPD, such that future integration of the PE-AWG can improve the SNDR PAM . d SNDR PAM levels achieved for generating PAM waveforms at various symbol rates with the PE-AWG and with several other waveform generators, comprising both commercially available AWGs , , as well as other research-type waveform generators , – . Square markers refer to results obtained in electrical back-to-back measurements, whereas circular markers represent optical back-to-back experiments. In case of the PE-AWG, we compare the SNDR PAM for the case without and with an adaptive equalizer ( L = 100 taps) used to remove residual inter-symbol interference, see the associated square markers with white filling and colored filling, respectively. The PE-AWG relies on Keysight’s AWG model M8194A (red star) and offers a signal quality that is on par with that offered by some commercially available waveform generators such as the Keysight M8199A or the Micram DAC5, while featuring a much higher usable bandwidth than these devices. At symbol rates beyond 140 GBd, the PE-AWG is only outperformed by Keysight’s most recent AWG model M8199B (green markers), which was not available as a signal source for our experiments at the time they were conducted. e Average voltage swing observed at the PE-AWG output for RRC pulses with a spectral roll-off of ρ = 0.05. We achieve decent voltage swings between 250 and 300 mV pp irrespective of the symbol rate.

Article Snippet: Overall, we find that the signal quality (SNDR PAM ) of our PE-AWG can well compete with that of several commercially available electronic waveform generators such as the underlying CMOS-based Keysight AWG model M8194A itself , the Micram DAC5 , or the Keysight M8199A, while offering symbol rates that are clearly above the 140 GBd achieved by the Keysight M8199A.

Techniques: