Semiconductor UV Photonics|6 Article(s)
Switchable dual-wavelength Q-switched fiber laser using multilayer black phosphorus as a saturable absorber
Junmin Liu, Yu Chen, Ying Li, Han Zhang, Shuiqin Zheng, and Shixiang Xu
Black phosphorus (BP), with thickness-dependent direct energy bandgaps (0.3–2 eV), shows an enhanced nonlinear optical response at near- and mid-infrared wavelengths. In this paper, we present experimentally multilayer BP flakes coated on microfiber (BCM) as a saturable absorber with a modulation depth of 16% and a saturable intensity of 6.8 MW/cm2. After inserting BCM into an Er-doped fiber ring laser, a stable dual-wavelength Q-switched state with central wavelengths of 1542.4 nm and 1543.2 nm (with wavelength spacing as small as 0.8 nm) is obtained with the aid of two cascaded fiber Bragg gratings as a coarse wavelength selector. Moreover, single-wavelength Q-switched operation at 1542.4 nm or 1543.2 nm is also realized, which can be switched between the two wavelengths flexibly just by adjusting the intracavity birefringence. These results suggest that BP combined with the cascaded fiber gratings can provide a simple and feasible candidate for a multiwavelength fiber laser. Our fiber laser may have potential applications in terahertz generation, laser radar, and so on.
Photonics Research
  • Publication Date: Feb. 27, 2018
  • Vol. 6, Issue 3, 03000198 (2018)
Fano resonances with a high figure of merit in silver oligomer systems
Hong-Jin Hu, Fan-Wei Zhang, Guo-Zhou Li, Jun-Yi Chen, Qiang Li, and Li-Jun Wu
A silver quadrumer consisting of four parallel aligned rectangular nanobars, with three at the bottom and one at the top, is proposed to provide two Fano resonances. These two resonances can be adjusted either simultaneously or independently simply by tuning the geometrical parameters. Due to the formation of the two resonances in a relatively short wavelength range, one of them can be spectrally squeezed to be very narrow, which induces a very high figure of merit (FoM=45). By decomposing the scattering spectrum into bright modes and dark modes, the double Fano resonances are found to be originated from grouping the unit cells into two different groups. The evolution of the scattering spectrum with the central dimer position along the polarization direction suggests that the symmetry reducing induces the second Fano resonance and improves the FoM of the first one. By introducing one more nanobar into the quadrumer system, the FoM can approach the material’s limit, although the dip is relatively shallow. The ultrahigh FoM of the Fano resonance in the proposed quadrumer can provide ultra-sensitive refractive index sensing. Furthermore, the method for providing multiple independently tunable Fano resonances can offer new solutions to designing plasmonic-related nanolasers, photocatalysis, and biochemical sensors, etc.
Photonics Research
  • Publication Date: Feb. 28, 2018
  • Vol. 6, Issue 3, 03000204 (2018)
Visible- and solar-blind photodetectors using AlGaN high electron mobility transistors with nanodot-based floating gate
Andrew M. Armstrong, Brianna A. Klein, Andrew A. Allerman, Albert G. Baca, Mary H. Crawford, Jacob Podkaminer, Carlos R. Perez, Michael P. Siegal, Erica A. Douglas, Vincent M. Abate, and Francois Leonard
AlGaN-channel high electron mobility transistors (HEMTs) were operated as visible- and solar-blind photodetectors by using GaN nanodots as an optically active floating gate. The effect of the floating gate was large enough to switch an HEMT from the off-state in the dark to an on-state under illumination. This opto-electronic response achieved responsivity >108??A/W at room temperature while allowing HEMTs to be electrically biased in the off-state for low dark current and low DC power dissipation. The influence of GaN nanodot distance from the HEMT channel on the dynamic range of the photodetector was investigated, along with the responsivity and temporal response of the floating gate HEMT as a function of optical intensity. The absorption threshold was shown to be controlled by the AlN mole fraction of the HEMT channel layer, thus enabling the same device design to be tuned for either visible- or solar-blind detection.
Photonics Research
  • Publication Date: May. 17, 2019
  • Vol. 7, Issue 6, 06000B24 (2019)
Increasing the hole energy by grading the alloy composition of the p-type electron blocking layer for very high-performance deep ultraviolet light-emitting diodes
Zi-Hui Zhang, Jianquan Kou, Sung-Wen Huang Chen, Hua Shao, Jiamang Che, Chunshuang Chu, Kangkai Tian, Yonghui Zhang, Wengang Bi, and Hao-Chung Kuo
It is well known that the p-type AlGaN electron blocking layer (p-EBL) can block hole injection for deep ultraviolet light-emitting diodes (DUV LEDs). The polarization induced electric field in the p-EBL for [0001] oriented DUV LEDs makes the holes less mobile and thus further decreases the hole injection capability. Fortunately, enhanced hole injection is doable by making holes lose less energy, and this is enabled by a specifically designed p-EBL structure that has a graded AlN composition. The proposed p-EBL can screen the polarization induced electric field in the p-EBL. As a result, holes will lose less energy after going through the proposed p-EBL, which correspondingly leads to the enhanced hole injection. Thus, an external quantum efficiency of 7.6% for the 275 nm DUV LED structure is obtained.
Photonics Research
  • Publication Date: Apr. 11, 2019
  • Vol. 7, Issue 4, 040000B1 (2019)
High-speed and high-performance polarization-based quantum key distribution system without side channel effects caused by multiple lasers|On the Cover
Heasin Ko, Byung-Seok Choi, Joong-Seon Choe, Kap-Joong Kim, Jong-Hoi Kim, and Chun Ju Youn
Side channel effects such as temporal disparity and intensity fluctuation of the photon pulses caused by random bit generation with multiple laser diodes in high-speed polarization-based BB84 quantum key distribution (QKD) systems can be eliminated by increasing the DC bias current condition. However, background photons caused by the spontaneous emission process under high DC bias current degrade the performance of QKD systems. In this study, we investigated the effects of spontaneously emitted photons on the system performance in a high-speed QKD system at a clock rate of 400 MHz. Also, we show further improvements in the system performance without side channel effects by utilizing the temporal filtering technique with real-time field-programmable gate array signal processing.
Photonics Research
  • Publication Date: Feb. 28, 2018
  • Vol. 6, Issue 3, 03000214 (2018)