研究目的
To develop and demonstrate a high-frame-rate single-shot spectrum measurement technique for ultrafast optical pulses with high repetition rates and improved spectral resolution, enabling the capture of non-repetitive and rare phenomena in substances.
研究成果
The TS-DFT technique combined with W-DEMUX enables pulse-by-pulse single-shot spectrum measurement at 1 GHz repetition rate with a spectral resolution of less than 67 pm, representing a threefold improvement over conventional methods, facilitating the capture of ultrafast optical phenomena.
研究不足
The spectral resolution and capturable pulse-repetition-rate are limited by pulse overlap if chromatic dispersion is not properly selected; the number of acquired frames is constrained by the oscilloscope's memory size (e.g., 39,997 frames in this case).
1：Experimental Design and Method Selection:
The study employs the time stretch dispersive Fourier Transform (TS-DFT) technique using fiber chromatic dispersion to map spectral information to temporal waveforms, with a wavelength demultiplexing (W-DEMUX) technique using a wavelength selective switch (WSS) to avoid pulse overlap and improve resolution.
2：Sample Selection and Data Sources:
Optical pulses are generated from a 10 GHz semiconductor mode-locked laser diode (MLLD) with a pulse width of
3：6 ps and center wavelength of 1550 nm, down-converted to 1 GHz repetition rate. List of Experimental Equipment and Materials:
Includes MLLD, lithium niobate intensity modulator (LN-MOD), pulse pattern generator (PPG), optical fibers with specific chromatic dispersion (-100 ps/nm and -300 ps/nm), 3 dB coupler, wavelength selective switch (WSS), high-speed real-time digital oscilloscope (16 GHz bandwidth, 50 Gsample/s), and computer for data processing.
4：Experimental Procedures and Operational Workflow:
Optical pulses are chirped using dispersive fibers, divided into wavebands via WSS, received by the oscilloscope, and waveforms are synthesized and corrected on a computer to recover spectra.
5：Data Analysis Methods:
Temporal waveforms are mapped to frequency axes using software, with waveform synthesis and correction for spectral narrowing and detector ripple.
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semiconductor mode-locked laser diode
MLLD
Generates 10 GHz repetition-rate optical pulse train with 1.6 ps pulse width and 1550 nm center wavelength.
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lithium niobate intensity modulator
LN-MOD
Down-converts the optical pulse repetition rate from 10 GHz to 1 GHz.
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pulse pattern generator
PPG
Controls the lithium niobate intensity modulator for down-conversion.
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optical fiber
Provides chromatic dispersion (-100 ps/nm and -300 ps/nm) to chirp optical pulses.
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3 dB coupler
Copies the chirped optical pulse train for reference and W-DEMUX processing.
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wavelength selective switch
WSS
Divides chirped optical pulses into wavebands (e.g., 1547.66 – 1549.96 nm and 1550.06 – 1552.37 nm) to avoid overlap.
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real-time digital oscilloscope
Receives and digitizes the chirped optical pulses for spectrum measurement.
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computer
Processes the waveforms, performs mapping to frequency axis, synthesis, and correction.
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