We investigate the electroluminescence (EL) from light emitting diodes (LEDs) of ZnO nanowires/p-GaN structure and ZnS@ZnO core-shell nanowires/p-GaN structure. With the increase of forward bias, the emission peak of ZnO nanowires/p-GaN structure heterojunction shows a blue-shift, while the ZnS@ZnO core-shell nanowires/p-GaN structure demonstrates a changing EL emission; the ultraviolet (UV) emission at 378 nm can be observed. This discrepancy is related to the localized states introduced by ZnS particles, which results in a different carrier recombination process near the interfaces of the heterojunction. The localized states capture the carriers in ZnO nanowires and convert them to localized excitons under high forward bias. A strong UV emission due to localized excitons can be observed. Our results indicated that utilizing localized excitons should be a new route toward ZnO-based ultraviolet LEDs with high efficiency.

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MXene‐based supercapacitors are promising electrochemical energy‐storage devices due to their ultrahigh volumetric capacitance, high‐power characteristics, and excellent cyclability. However, they suffer from severe self‐discharging behavior while the underlying self‐discharging mechanism is still unclear. Here, the self‐discharge behavior of MXene‐based supercapacitors from surface electronic structure of MXenes is disclosed, and a novel method to mitigate it is proposed. A superficial engineering strategy based on bio‐thermal treatment is developed to effectively tailor surface electronic structure of Ti3C2Tx MXenes by eliminating hydroxyl terminations. With the evolution of surface electronic structure, as revealed by Kelvin probe force microscope and synchrotron radiation X‐ray absorption fine structure analysis, MXene‐based supercapacitors with common aqueous electrolytes show >20% decline in self‐discharge rate. This decline mechanism originates from the increased work function that induces higher zero‐charge potential after the removal of hydroxyl groups in MXenes. Meanwhile, the strengthened surface dipole leads to higher surface free energy between MXene and electrolytes. These two positive effects endow MXenes with weaker self‐discharge kinetics. Specifically, the activation‐controlled self‐discharge process is greatly suppressed. Illuminating the relevance between electronic structure and self‐discharge accompanying superficial engineering suppression strategy can guide to development of high‐performance energy storage devices.

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Due to its absorption properties in atmosphere, the mid-infrared (mid-IR) region has gained interest for its potential to provide high data capacity in free-space optical (FSO) communications. Here, we experimentally demonstrate wavelength-division-multiplexing (WDM) and mode-division-multiplexing (MDM) in a ~0.5 m mid-IR FSO link. We multiplex three ~3.4 μm wavelengths (3.396 μm, 3.397 μm, and 3.398 μm) on a single polarization, with each wavelength carrying two orbital-angular-momentum (OAM) beams. As each beam carries 50-Gbit/s quadrature-phase-shift-keying data, a total capacity of 300 Gbit/s is achieved. The WDM channels are generated and detected in the near-IR (C-band). They are converted to mid-IR and converted back to C-band through the difference frequency generation nonlinear processes. We estimate that the system penalties at a bit error rate near the forward error correction threshold include the following: (i) the wavelength conversions induce ~2 dB optical signal-to-noise ratio (OSNR) penalty, (ii) WDM induces ~1 dB OSNR penalty, and (iii) MDM induces ~0.5 dB OSNR penalty. These results show the potential of using multiplexing to achieve a ~30X increase in data capacity for a mid-IR FSO link.

We reported a dual-wavelength femtosecond optical parametric oscillator (OPO) based on a temperature-tuned LiB₃O₅ crystal. The OPO was synchronously pumped by a frequency-doubled, mode-locked Yb-fiber laser amplifier, providing a 520 nm pump laser with durations of 250 fs at a repetition rate of 57 MHz. High efficiency and dual-wavelength operation are obtained over the ranges of 658-846 nm and 2.45-1.35 μm. The observed dual-wavelength tuning is in agreement with the values predicted by numerical simulation. Moreover, a sum-frequency yellow laser of the longer signal and idler tunable from 555 to 623 nm with practical power is achieved. With an 8% output coupler, the maximum signal output power is 390 mW pumped at 3 W with dual-wavelength operation, while the maximum power of sum-frequency generation is 110 mW at 590 nm.

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We study, both numerically and experimentally, the relative intensity noise (RIN) and timing jitter characteristics of optical parametric generation (OPG) process in MgO-doped periodically poled LiNbO (MgO:PPLN) pumped by fiber femtosecond laser. We directly characterize the RIN, and measure timing jitter spectral density of the OPG process based on the balanced optical cross-correlator (BOC) technique for the first time as well, which are both in a fairly good agreement with numerical simulation. Both the numerical and experimental study reveals that OPG can suffer from a smaller intensity fluctuation but a lager temporal jitter when it is driven into saturation. Furthermore, we demonstrate that with a 30 mW CW diode laser injection seeding the OPG output results in superior noise performance compared to the vacuum fluctuations seeded OPG.