Chiral metamaterials have stronger optical activity than natural materials within the terahertz frequencies, so they have attracted more attention. By arranging special silicon structures at terahertz frequencies, we propose an all-silicon-based extrinsic chirality structure with high outer circular dichroism in this paper. And its circular birefringence is also better than average. The properties of our all-silicon-based metamaterials are generated due to the resonance between the circularly polarized incident wave and the special silicon structure of the surface. The circular dichroism of the device due to transmission can reach 0.54. And we obtained the maximum polarization rotation angle can achieve 50°. In addition, the chirality of the device can be dynamically changed between 0.63THz-0.79THz. Such control can be achieved merely by changing the incident tilt angle. Our research can be applied to terahertz circular polarizer and polarimeter, which has great potential in optical path construction, light detection, signal transmission and processing.
In this paper, a polarization filter based on photonic crystal fiber (PCF) with nanoscale gold film is proposed and analyzed theoretically. The cross-section of the structure is composed of four-layer air holes with a hexagonal lattice and two symmetrical air holes in the sub-internal layer are coated with gold film. We research that the PCF structure parameters affect the performances of the polarization filter through employing the finite element method. It is indicated by the numerical results that the resonance strength in y-polarization direction can reach a most value of 272.8 dB/cm at the communication wavelength of 1.55 μm. The extinction ratio can be better than 20 dB within a wavelength range from 1.45 μm to 1.75 μm when the length of the PCF is longer than 500μm. Therefore, such a length can make the communication filtering effect be realized using a shorter fiber. The calculated results can provide some references to the design of polarization micro-filter devices.
Based on the influence of surface metal materials on electric field, a terahertz metamaterial absorber with a highly symmetrical open box was designed. Aiming at the traditional square ring absorber, the absorber is made of three open square rings and a pair of symmetrical strips of silicon. Starting from the structure and material of the absorber, the absorption rate of the absorber to the three-frequency band wave is regulated by changing the size of the surface metal ring, changing the thickness of the dielectric layer, changing the dielectric constant of the dielectric layer material, and adjusting the conductivity of the silicon material after the addition of semiconductor silicon. When no semiconductor silicon is added, the absorption rate of the absorber in the low frequency band reaches 94.77% and the absorption frequency band is 0.73thz. By increasing the thickness of dielectric layer, the phenomenon of redshift is obvious, which can realize the purpose of continuous frequency band absorption. By adding the silicon strip with symmetrical structure and changing the conductivity comparison, it is found that it can close the absorption peak in the high frequency band, reducing the absorption rate to less than %, and at the same time affecting the absorption rate of the low frequency band.
Ultrasensitive near-infrared phototransistors based on Lead sulfide (PbS) quantum dots (QDs)-graphene hybrid channel are fabricated by facile solution processing. The device combines the advantages of the large light absorbance of QDs high mobility of graphene. Under light illumination, the photogenerated carriers will transfer from QDs to graphene. As result, the phototransistor exhibits fast response speed with rise time of 1.4 ms and fall time of 1.3 ms at 36 mW/cm2 illumination of 808 nm wavelength, meaning the device can follow a fast switched optical signal. The responsivity (R), effective quantum efficiency (EQE) of the device are 6 A/W and 961% under 166mW/cm2 illumination, respectively. It expected that the PbS QDs–graphene hybrid devices are promising for fast response, low-cost and easy fabrication photoelectronics
The optical responsivity of bulk-heterojunction field effect phototransistors (BH-FEpTs) based on poly [2-methoxy-5-(2´- ethylhexyloxy-p-phenylenevinylene)] (MEH-PPV) and PbS quantum dot hybrids is very low. A main reason for the low responsivity is the low carrier mobility of the blends. To overcome the shortcoming, graphene with high carrier mobility (~200,000 cm2V-1s-1) can be used for improving the responsivity of BH-FEpTs. However, the influence of monolayer graphene on the photo response of BH-FEpTs still has been not studied. In this papers, BH-FEpTs and GBH-FEpTs (single layer graphene beneath the BH layer in BH-FEpTs) were fabricated. Experimentally, the GBH-FEpTs showed ultrahigh mobility for both holes and electrons (μH and μE) of 183 and 169 cm2V−1s−1, while 11.3 and 6.2 cm2V−1s−1 in BH-FEpT. Due to the greatly promoted carrier mobility and highly ordered channels for GBH-FEpTs, higher α, μ and β are obtained for GBH-FEpTs. The responsivity of GBH-FEpTs is improved to 101 A/W, which is two orders magnitude larger than BH-FEpTs (10-1 A/W).
We fabricate and investigate the photoelectrical characterization of PbSe QDs FEpTs Field Effect photo Transistors in lateral (LQFEpT) and vertical architectures (VQFEpT) respectively. Both LQFEpT and VQFEpT apply PbSe quantum dots as active layer, with different channel length of 0.1mm and 678nm respectively. The VQFEpT apply Au/Ag nanowires (NWs) as source transparent electrode connecting with Au source electrode. The ambipolar operation of both FEpTs show low power consumption, delivering high drain current at VSD = VG = ± 4 V. The VQFEpT exhibit higher photocurrent up to 4mA, three orders magnitude higher than that in LQFEpTs (16μA), owing to the superior carrier transportion in the shorter channel. As a result, higher photo responsivity (8×104A/W), specific detectivity (2×1012Jones) and gain (1.3× 105) are achieved in VQFEpT. The all-solution processing vertical architecture provide a convenient way for IR photo detectors with high performances.
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