We present a high-transmittivity non-periodic sub-wavelength high-contrast grating （HCG） with large-angle beam-steering ability for transmitted light. The phase front profile of transmitted light is a decisive factor to the beam-steering property of the HCG. By designing the structural parameters of the HCG, both beam steering and high transmittivity can be achieved. The properties of the beam steering and transmission are numerically studied with the finite element method. The results show that the transmittivity is up to 0.91 and the steering angle is 27.42° which is consistent with the theoretical 30°.
A robust design for a photonic crystal fiber （PCF） based on pure silica with small normal dispersion and high nonlinear coefficient for its dual concentric core structure is, presented. This design is suitable for flat broadband supercontinuum （SC） generation in the 1.55-μm region. The numerical results show that the nonlinear coefficient of the proposed eight-ring PCF is 33.8 W^-1·km^-1 at 1550 nm. Ultraflat dispersion with a value between -1.65 and -0.335 ps/（nm·km） is obtained ranging from 1375 to 1625 nm. The 3-dB bandwidth of the SC is 125 nm （1496-1621 nm）, with a fiber length of 80 m and a corresponding input peak power of 43.8 W. The amplitude noise is considered to be related to SC generation. For practical fabrication, the influence of the random imperfections of airhole diameters on dispersion and nonlinearity is discussed to verify the robustness of our design.
采用有限元法分析了基于金纳米层的新型微结构光纤表面等离子体共振传感器的相关特性。在数值仿真中,使用精确的德鲁德-洛伦兹(Drude-Lorentz)模型来描述金属介电常数。计算结果表明,随待测样品折射率的增加,表面等离子体共振峰波长向长波长方向漂移。该微结构光纤表面等离子体共振传感器的探测灵敏度可达1200 nm/RIU(refractive index unit),探测极限可达8.33×10-5RIU。
We report on the Au-assisted vapour-liquid-solid （VLS） growth of GaAs/InxGal xAs/GaAs （0.2 ≤ x ≤1） axial double-heterostructure nanowires on GaAs （ 111 ） B substrates via the metal-organic chemical vapor deposition （MOCVD） technique. The influence of the indium （In） content in an Au particle on the morphology of nanowires is investigated systematically. A short period of pre-introduced In precursor before the growth of InxGal xAs segment, coupled with a group III precursor interruption, is conducive to obtaining symmetrical heterointerfaces as well as the desired In/Ga ratio in the InxGa1-xAs section. The nanowire morphology, such as kinking and tapering, are thought to be related to the In composition in the catalyst alloy as well as the VLS growth mechanism.
A top-illuminated circular mesa uni-traveling-carrier photodetector（UTC-PD） is proposed in this paper. By employing Gaussian graded doping in In Ga As absorption layer and In P depleted layer, the responsivity and high speed response characteristics of the device are optimized simultaneously. The responsivity up to 1.071 A/W（the external quantum efficiency of 86%） is obtained at 1550 nm with a 40-μm diameter device under 10-V reverse bias condition. Meanwhile, the dark current of 7.874 n A and the 3-d B bandwidth of 11 GHz are obtained with the same device at a reverse bias voltage of3 V.
Vertical InAs/GaAs nanowire （NW） heterostructures with a straight InAs segment have been successfully fabricated on Si （111） substrate by using AlGaAs/GaAs buffer layers coupled with a composition grading InGaAs segment. Both the GaAs and InAs segments are not limited by the misfit strain induced critical diameter. The low growth rate of InAs NWs is attributed to the AlGaAs/GaAs buffer layers which dramatically decrease the adatom diffusion contribution to the InAs NW growth. The crystal structure of InAs NW can be tuned from zincblende to wurtzite by controlling its diameter as well as the length of GaAs NWs. This work helps to open up a road for the integration of high-quality III-V NW heterostructures with Si.
The fabrication of self-catalyzed InP nanowires(NWs)is investigated under different growth conditions.Indium droplets induced by surface reconstruction act as nucleation sites for NW growth.Vertical standing NWs with uniform cross sections are obtained under optimized conditions.It is confirmed that the growth rate of NWs is strongly affected by the surface diffusion adatoms while contributions from the direct impingement of vapor species onto the In droplets can be negligible.The results indicate that the droplet acts as an adatom collector rather than a catalyst.Moreover,the diffusion flow rate of adatoms increases with time at the beginning of growth and stabilizes as the growth proceeds.
Vertical p-type gallium arsenide （GaAs） nanowires with pure zinc blende structure were grown on GaAs （111） B substrate by metal-organic chemical vapor deposition via a Au-catalyst vapor-liquid-solid mechanism. The p-type doping was investigated by additional diethyl zinc （DEZn）. In the high Ⅱ/Ⅲ ratio range （Ⅱ/Ⅲ〉9.1%）, there exists a critical length beyond which kinking takes place. Two possible reasons are discussed. Zn occurrence in the nanowires was verified by energy dispersive X-ray （EDX） analysis. Corresponding to Ⅱ/Ⅲ = 0.2%, the doping concentration is about 8 × 10^18 cm^-3.
