A new photonic scheme for various waveforms generation has been proposed and demonstrated. In the scheme, two cascaded single-drive LiNbO Mach-Zehnder modulators serve as pulse shaper and the polarization-dependent character of the modulators is fully exploited and utilized. By arranging the polarization states of the incident light, two different spectra are achieved on two orthogonal polarization components respectively. Finally, the desired waveforms can be obtained by superimposing the photocurrents of the two orthogonal signals on a photodetector. The detailed theoretical analyses and simulations are given. In the experiment, square-shaped waveform, triangular waveform and sawtooth (or reversed-sawtooth) waveform are obtained successfully. Furthermore, an approach to smoothing the sawtooth waveform with fewer harmonics is suggested and verified.
This paper introduces a novel web‐based virtual laboratory to assist teaching of Sensitive High Resolution Ion Micro‐probe (SHRIMP) implementation, called SHRIMP VL. This virtual laboratory is especially designed to aid learning of the instrument operation procedure. SHRIMP VL was developed based on hypertext preprocessor (PHP) technology and the Browser/Server application model, combined with the Yii framework and database technology. The virtual lab includes a virtual experiment platform to simulate the experiment procedure of the actual instrument and show experiment results. It also provides an immersive and visible virtual environment with navigational hints to guide user learning of the experiment operation, as well as theory presentations. To evaluate this virtual laboratory, two questionnaires were provided to students, who reported that SHRIMP VL is effective in helping them understand and master the instrument and experimental procedures, thereby improving their learning efficiency and laying foundations for personal operation of on‐site instruments.
We propose a low-speed photonic sampling for independent high-frequency characterization of a Mach–Zehnder modulator (MZM) and a photodetector (PD) in an optical link. A low-speed mode-locked laser diode (MLLD) provides an ultra-wideband optical stimulus with scalable frequency range, working as the photonic sampling source of the link. The uneven spectrum lines of the MLLD are firstly characterized with symmetric modulation within the interesting frequency range. Then, the electro-optic modulated signals are down-converted to the first Nyquist frequency range, yielding the self-referenced extraction of modulation depth and half-wave voltage of the MZM without correcting the responsivity fluctuation of the PD in the link. Finally, the frequency responsivity of the PD is self-referenced measured under null modulation of the MZM. As frequency responses of the MZM and the PD can be independently obtained, our method allows self-referenced high-frequency measurement for a high-speed optical link. In the proof-of-concept experiment, a 96.9 MS/s MLLD is used for measuring a MZM and a PD within the frequency range up to 50 GHz. The consistency between our method and the conventional method verifies that the ultra-wideband and self-referenced high-frequency characterization of high-speed MZMs and PDs.
Promoting withdrawal from rural homesteads (WRH) is a significant way of enhancing the efficient use of homesteads, improving the living standards of farmers, and promoting new urbanization. Social networks provide farmers with necessary resources and play an important role in the practices of WRH. Based on a literature review, this paper divides farmers’ social networks into the emotional social network, the economic social network, and the political social network and analyzes the impacts of social networks on farmers’ willingness and behavior regarding WRH using the binary logistic regression model, based on the data of 299 peasant households in Sichuan Province. The following finds are established: (1) the economic social network significantly and negatively affects farmers’ willingness and behavior regarding WRH, while the political social network has a positive impact on farmers’ willingness and behavior regarding WRH; (2) the emotional social network significantly and positively affects farmers’ willingness regarding WRH, but it does not have a significant effect on farmers’ behavior regarding WRH; and (3) the economic social network and political social network exhibit opposite influences on the transition from farmers’ willingness to behavior regarding WRH. We conclude that social networks play a vital role in affecting farmers’ willingness and behavior regarding WRH. The research suggests that expanding the scope of farmers’ interactions and social networks can be helpful in implementing WRH. The employment training system and social security system should also be improved.
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