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Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire

View Article: PubMed Central - PubMed

ABSTRACT

The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication.

No MeSH data available.


FROG trace of 810 nm pulses.(a) Measured and (b) retrieved trace. Electric field intensity (red triangle) and phase (blue square) as a function of time (c) and of wavelength (d).
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f5: FROG trace of 810 nm pulses.(a) Measured and (b) retrieved trace. Electric field intensity (red triangle) and phase (blue square) as a function of time (c) and of wavelength (d).

Mentions: From the intensity pattern in Fig. 4, we could find that with continuous movement of the delay line, the SH maximum could move in and out of the NW. For a rough estimation of pulse duration, we observed the variation of intensity at an arbitrary position of NW [i.e. right in the middle of Fig. 4(f)], and marked the displacement of the delay line between its two half-maximum, which was ~150 μm. So the full width at half maximum (FWHM) of a pulse could be calculated by ~300 μm divided by light speed, which was in the scale of picoseconds in time profile. To operate a more precise pulse characterization, we measured the auto-correlating spectra of pulses counter-propagating through the NW. With a speed of 25 μm/step, the surface emitted SH signal could be scanned out. The pulse energy was about 50 pJ/pulse and a typical spectrum was taken with 1 s exposure time. Figure 5(a) shows the spectra collection in form of a 128 × 128 grid graph, in which 128 spectra were placed in chronological order, and the intensities of spectra were represented by colormap. Notice that the temporal index was transformed from free-space optical-length displacement of delay line. Based on the results, a retrieved FROG trace could be readily obtained by a method given in ref. 18 [Fig. 5(b)]. Briefly, the method involved a solution to two-dimentional phase-retrieval problem. Two constraint sets, nonlinear-optical set and the experimental data set, are to be satisfied by alternately iteratively projecting from an initial guess. The intersection of the two constraints will lead to a solution of pulse electric field with reliable temporal and spectral information. The measured and retrieved FROG traces in Fig. 5 are in good qualitative agreement with the G error of 0.0107, which could be elevated with a higher-resolution spectrometer. The pulse intensity and phase profile are also presented in both temporal and spectral domains, as shown in Fig. 5(c,d), respectively. The intensity profile in Fig. 5(c) indicates the pulse duration of 2.8 ps, much longer than the source output. The pulse broadening mainly occurred in two parts: the ~1.1 m-length fiber, and the ~10-mm-length tapered microfiber. For a rough estimation, we can expect the dispersion as ~118 ps/nm/km for an 810-nm pulse with 22-nm width in a 1-m-long single-mode fiber (SMF-28, Corning), which leads to pulse broadening of more than 2.8 ps19. While for the fiber taper, the dispersion in the 1-μm-diameter microfiber end was estimated around 400 ps/nm/km20. Assuming that the dispersion changes linearly in the taper, the pulse width should increase for another ~100 fs. Since the length of the ZnO NW is relative short (~200 μm), the pulse broadening imposed was neglected here. Therefore, in the process the pulse change should be ~2.8 ps, almost consistent with our measurement results.


Frequency-resolved optical gating measurement of ultrashort pulses by using single nanowire
FROG trace of 810 nm pulses.(a) Measured and (b) retrieved trace. Electric field intensity (red triangle) and phase (blue square) as a function of time (c) and of wavelength (d).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC5016840&req=5

f5: FROG trace of 810 nm pulses.(a) Measured and (b) retrieved trace. Electric field intensity (red triangle) and phase (blue square) as a function of time (c) and of wavelength (d).
Mentions: From the intensity pattern in Fig. 4, we could find that with continuous movement of the delay line, the SH maximum could move in and out of the NW. For a rough estimation of pulse duration, we observed the variation of intensity at an arbitrary position of NW [i.e. right in the middle of Fig. 4(f)], and marked the displacement of the delay line between its two half-maximum, which was ~150 μm. So the full width at half maximum (FWHM) of a pulse could be calculated by ~300 μm divided by light speed, which was in the scale of picoseconds in time profile. To operate a more precise pulse characterization, we measured the auto-correlating spectra of pulses counter-propagating through the NW. With a speed of 25 μm/step, the surface emitted SH signal could be scanned out. The pulse energy was about 50 pJ/pulse and a typical spectrum was taken with 1 s exposure time. Figure 5(a) shows the spectra collection in form of a 128 × 128 grid graph, in which 128 spectra were placed in chronological order, and the intensities of spectra were represented by colormap. Notice that the temporal index was transformed from free-space optical-length displacement of delay line. Based on the results, a retrieved FROG trace could be readily obtained by a method given in ref. 18 [Fig. 5(b)]. Briefly, the method involved a solution to two-dimentional phase-retrieval problem. Two constraint sets, nonlinear-optical set and the experimental data set, are to be satisfied by alternately iteratively projecting from an initial guess. The intersection of the two constraints will lead to a solution of pulse electric field with reliable temporal and spectral information. The measured and retrieved FROG traces in Fig. 5 are in good qualitative agreement with the G error of 0.0107, which could be elevated with a higher-resolution spectrometer. The pulse intensity and phase profile are also presented in both temporal and spectral domains, as shown in Fig. 5(c,d), respectively. The intensity profile in Fig. 5(c) indicates the pulse duration of 2.8 ps, much longer than the source output. The pulse broadening mainly occurred in two parts: the ~1.1 m-length fiber, and the ~10-mm-length tapered microfiber. For a rough estimation, we can expect the dispersion as ~118 ps/nm/km for an 810-nm pulse with 22-nm width in a 1-m-long single-mode fiber (SMF-28, Corning), which leads to pulse broadening of more than 2.8 ps19. While for the fiber taper, the dispersion in the 1-μm-diameter microfiber end was estimated around 400 ps/nm/km20. Assuming that the dispersion changes linearly in the taper, the pulse width should increase for another ~100 fs. Since the length of the ZnO NW is relative short (~200 μm), the pulse broadening imposed was neglected here. Therefore, in the process the pulse change should be ~2.8 ps, almost consistent with our measurement results.

View Article: PubMed Central - PubMed

ABSTRACT

The use of ultrashort pulses for fundamental studies and applications has been increasing rapidly in the past decades. Along with the development of ultrashort lasers, exploring new pulse diagnositic approaches with higher signal-to-noise ratio have attracted great scientific and technological interests. In this work, we demonstrate a simple technique of ultrashort pulses characterization with a single semiconductor nanowire. By performing a frequency-resolved optical gating method with a ZnO nanowire coupled to tapered optical microfibers, the phase and amplitude of a pulse series are extracted. The generated signals from the transverse frequency conversion process can be spatially distinguished from the input, so the signal-to-noise ratio is improved and permits lower energy pulses to be identified. Besides, since the nanometer scale of the nonlinear medium provides relaxed phase-matching constraints, a measurement of 300-nm-wide supercontinuum pulses is achieved. This system is highly compatible with standard optical fiber systems, and shows a great potential for applications such as on-chip optical communication.

No MeSH data available.