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(a) Spectral-domain representation. The ultrafast optical data signal (fs ) mixes with the broadband pulsed pump (Δfp = fp 1 − fp 2) via theFWM process. (b) Time-domain representation. At each time instant along the signal, a wavelength of the pre-chirped broadband pump mixes with the signal at that time instant; creating a chirped modulated idler. The idler is then time-stretched to reduce the analog bandwidth of the optical data signal.
Detailed schematic of the experimental setup for demonstrating the all-optical time-stretch pre-processor based on four-wave mixing process. BW: bandwidth; EDFA: erbium-doped fiber amplifier; VOA: variable optical attenuator; PC: polarization controller; WDM: wavelength division multiplexer; HNLF: highly nonlinear fiber; OSA: optical spectrum analyzer; PD: photo-detector; ADC: analog-to-digital converter. Inset: spectrum of pump, signal, and idler at the output of the HNLF.
Detailed schematic of the 40-Gb/s NRZ OOK signal transmitter. This unit was implemented to evaluate the performance of the all-optical time-stretch pre-processor. CW: continuous wave; PC: polarization controller; EDFA: erbium-doped fiber amplifier; VOA: variable optical attenuator; PRBS: pseudo-random bit stream source.
40-Gb/s NRZ OOK data. (a) Two real-time segments of 40-Gb/s data captured at an effective sampling rate of 1.25 TS/s. (b) Eye-diagram of 40-Gb/s constructed from real-time segments in equivalent-time mode.
Dispersion penalty in an all-optical time-stretch digitizer with an initial dispersion of −150 ps/nm. Note that we intentionally increased the initial dispersion to shift the bandwidth roll-off into the measurable range of our equipment. When DSB modulation is used, the measured penalty (blue curve) that is in good agreement with theoretical prediction (green solid curve). By employing single-sideband technique, the dispersion penalty is completely mitigated (red curve). Single-sideband modulation is implemented by suppressing one of the sidebands of the optical data signal. An optical bandpass filter can be used for this purpose.
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