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(Color online) Conceptual diagram of the optical preprocessor. An ultrafast electrical signal is modulated onto the envelope of a chirped optical pulse which is further chirped and photodetected. As a result, the output electrical signal is time stretched, and therefore compressed in bandwidth, to within the Nyquist limit of a real-time oscilloscope.
(Color online) Experimental setup of the optical preprocessor with a 250 times bandwidth compression factor. A distributed Raman amplification scheme is employed to overcome of insertion loss in the dispersive element. Below, a conceptual diagram shows the advantage of distributed amplification (sinusoidal curve) over discrete amplification (sawtooth curve), e.g., a chain of EDFAs, in avoiding undesirable regions of high noise and optical nonlinearities. The dashed lines show the propagation of the bidirectional Raman pump lasers. DCF: dispersion compensating fiber; EDFA: erbium-doped fiber amplifier; MZM: Mach-Zehnder modulator; FM: Faraday mirror.
A klystron tone is digitized in real time at .
A single-shot electrical impulse digitized at sampling intervals. The real-time single-shot waveform (shown in black) is filtered over and compared to a repetitive version recorded by a sampling oscilloscope (shown in gray).
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