To generate Cherenkov radiation (CR) in natural medium, the electron energy threshold is higher than hundreds of keV. Even though various approaches were adopted, the high-energy electrons as high as tens of keV is still required in experiment. Here we proposed to eliminate the threshold of electron energy to generate CR with the help of hyperbolic metamaterial (HMM). The analytical and simulation results indicate that, even though electron energy is lower than 0.1keV, the CR could be obtained in HMM in a visible and near-infrared frequency region. Further, the on-chip integrated threshold-less CR source, consisted with a planar electron emitter, Au-SiO2 multilayers HMM, and periodic metal nano-slits, has been realized. It is demonstrated that, with low-energy electrons (0.25-1.4keV), the CR is generated covering λ0=500~900nm. The electron energy generating CR experimentally is two~three orders of magnitude lower than that in natural media and artificial structures. As we know, this is the first on-chip integrated free electron light source benefiting from the threshold-less CR. Although less than 1% of the light energy could be coupled to free space, the total output light power still reaches 200nW, which is two orders of magnitude higher than free electron light source by using other nanostructures.
Optical biosensors with the high sensitivity is an important tool for environment monitoring, disease diagnosis and drug development. Integrating the biosensor could reduce the size and cost and is desirable for home and outdoor use. However, the integrated structure always results in the worsening of sensitivity and narrowing of sensing range, especially for small molecule sensing. In this work, we propose an integrated plasmonic biosensor based on the resonant structure composed of dielectric grating and metal film. With vertically incident light from the grating side, the surface plasmon polariton (SPP) mode could be excited at certain wavelength and the reflected light would vanish. Simulation results indicate that, when varying refractive index (ndet) of detection layer, the energy of reflected light changes dramatically. Assuming the resolution of the power meter is 0.01dB, the sensing resolution could be 4.37×10-6 RIU, which is very close to the bulk lens based SPP biosensor by monitoring the light intensity variation. Since antibody and antigen always have the size of tens of nanometers, it is necessary to check the sensing ability of the sensor in tens of nanometers. Fixing ndet and varying the thickness of detection layer, calculation result demonstrates that the reflected light energy is sensitive to the thickness change with one hundred nanometers. This attributes to the surface mode property of SPP mode.
Optomechanical crystal is a combination of both photonic and phononic crystal. It simultaneously confines light and mechanical motion and results in strong photon-phonon interaction, which provides a new approach to deplete phonons and realize on-chip quantum ground state. It is promising for both fundamental science and technological applications, such as mesoscopic quantum mechanics, sensing, transducing, and so on. Here high optomechanical coupling rate and efficiency are crucial, which dependents on the optical-mechanical mode-overlap and the mechanical frequency (phonon frequency), respectively. However, in the conventional optomechanical-crystal based on the same periodical structure, it is very difficult to obtain large optical-mechanical mode-overlap and high phonon frequency simultaneously. We proposed and demonstrated nanobeam cavities based on hetero optomechanical crystals with two types of periodic structure. The optical and mechanical modes can be separately confined by two types of periodic structures. Due to the design flexibility in the hetero structure, the optical field and the strain field can be designed to be concentrated inside the optomechanical cavities and resemble each other with an enhanced overlap, as well as high phonon frequency. A high optomechanical coupling rate of 1.3 MHz and a high phonon frequency of 5.9 GHz are predicted theoretically. The proposed cavities are fabricated as cantilevers on silicon-on-insulator chips. The measurement results indicate that a mechanical frequency as high as 5.66 GHz is obtained in ambient environment, which is the highest frequency demonstrated in one-dimensional optomechanical crystal structure.
Here we present investigations on utilizing two kinds of plasmonic nanoparticles (NPs) to enhance
the efficiency of dye sensitized solar cells (DSCs). The Au@PVP NPs is proposed and present the
specialty of adhesiveness to dye molecules, which could help to localize additional dye molecules near
the plasmonic NPs, hence increasing the optical absorption consequently the power conversion
efficiency (PCE) of the DSCs by 30% from 3.3% to 4.3%. Meanwhile, an irregular Au-Ag alloy
popcorn-shaped NPs (popcorn NPs) with plenty of fine structures is also proposed and realized to
enhance the light absorption of DSC. A pronounced absorption enhancement in a broadband
wavelength range is observed due to the excitation of localized surface plasmon at different
wavelengths. The PCE is enhanced by 32% from 5.94% to 7.85%.
Optical enhancement of organic solar cells with rectangular metallic gratings as the back
contact has been investigated numerically. It is demonstrated that a strongly increased light absorption
up to 37% with the plasmonic enhanced effect of metallic gratings has been obtained. In addition, we
study the light absorption enhancement at oblique incidence and also get a high absorption
enhancement within the incident angle of 30 degree.
The plasmonic enhanced absorption for thin film solar cells with silver nanoparticles (NPs) deposited on top of the
amorphous silicon film (a-Si:H) solar cells and embedded inside the active layer of organic solar cells (OSCs) has been
simulated and analyzed. Obvious optical absorption enhancement is obtained not only at vertical incidence but also at
oblique incidence. By properly adjusting the period and size of NPs, an increased absorption enhancement of about
120% and 140% is obtained for a-Si:H solar cells and OSCs, respectively.
Coupling between long range surface plasmon polariton (LRSPP) waveguide mode and dielectric waveguide (DW)
mode has been studied theoretically and experimentally. It is demonstrated that the fundamental and second-order
TM-polarized mode of dielectric waveguide could couple with LRSPP mode efficiently, respectively.
A vertical coupler composed of short range surface plasmon polariton waveguide and dielectric waveguide is studied
theoretically and experimentally. The short range surface plasmon polariton mode is excited efficiently by the dielectric
waveguide mode within tens of microns. Meanwhile, based on the hybrid coupler, a highly compact polarizer and a high
performance sensor for ultra-thin layer sensing could be achieved.
The enhanced optical absorption in solar cells using nanoscale structure and novel physical effect has received a lot of
attention in recent years. One of the promising methods is to utilize the noble metal nanoparticles with plasmonic effect
for increasing the light absorption, consequently the conversion efficiency of photovoltaic devices. While the bare metal
nanoparticles may suffer from the energy loss introduced by themselves due to the recombination of electro-hole pairs.
Here, we propose to apply the plasmonic metal-dielectric core-shell nano-particles to improve the optical absorption
efficiency of thin film solar cells. It is expected that the metal core could increase the optical absorption of thin film solar
cells due to the filed enhancement effect of localized surface plasmon (LSP), and meanwhile the dielectric shell could
avoid the metal core to become a new recombination center of the light-induced excitons. Further, varying the refractive
index of the dielectric shell could adjust the enhancement region of LSP in a large range to cover the whole wavelength
range of solar cells. Simulations are carried out by means of the finite element method in a three-dimensional model. The
results show that the absorption enhancement up to 110% could be obtained when the active layer of thin film organic
solar cells is 30nm thick. Then, some initial experiments have been done. The Au-citrate core-shell nanoparticles
synthesized by the sodium citrate reduction method are deposited on the solar cells. And the obvious photocurrent
enhancement has been observed.
Near-infrared silicon solar cell response enhanced by gold nanoparticles with core-shell structure has been studied
experimentally. The colloidal core-shell gold nanoparticles are synthesized by the standard sodium citrate
reduction method. The enhanced photocurrent response of silicon solar cell is obtained over almost the entire
silicon response spectrum, and the obvious enhancement is observed when λ0 > 800nm. The highest value 12%
near λ0=1160nm is obtained.
A hybrid coupler composed of a slot plasmonic waveguide and a dielectric waveguide is proposed and its coupling
characteristics are analyzed. The simulation results show that the ultra-small mode of the slot plasmonic waveguide can
be excited efficiently by the dielectric waveguide mode within the coupling length of just several microns, which
provides an interface between the slot plasmonic devices and dielectric devices. Meanwhile, based on this hybrid the
coupler, a highly integrated refractive index sensor could be realized.
Photometric and colorimetric parameters are important evaluations criterion of the performance of LED light sources.
Photometric and colorimetric parameters of LED were measured using PMT spectroradiometer and CCD spectrometer
respectively in this research, the result was discussed and the common method was improved. The result of experiment
indicated that temperature drift of PMT spectroradiometer was compensated effectively by introducing reference
standard light source; measurement accuracy of CCD spectrometer was improved significantly with standard LED. CCD
spectrometer suitable for the industrial application for its rapid measuring speed, PMT spectroradiometer should be used
in scientific research for its high measurement accuracy according to the experimental results.
The visibility of Liquid Crystal Display (LCD) decreasing significantly while displaying motion picture, and how to
evaluate Motion Picture Resolution of digital television has become a key concern. Motion picture resolution is a very
important parameter for the evaluation of LCD and could be evaluated with smearing time according to national
standards of PRC issued in 2006. Smearing time of LCD was measured using simulation method and SSPD pursuit
tracking system. Simulation method was improved by introducing flash spectroradiometer and color alternate patterns.
Camera pursuit tracking measurement system was established and SSPD was used instead of CCD. Results of
experiments indicate that both black white pattern and color pattern could be measured effectively using these two
improved methods and the camera pursuit tracking system's measurement resolution of smearing time could reach 0.3ms.