Kaiyu Cui

Broadband light absorption enhancement in dye-sensitized solar cells with Au-Ag alloy popcorn nanoparticles.

In this paper, we present an investigation on the use of Au-Ag alloy popcorn-shaped nanoparticles (NPs) to realise the broadband optical absorption enhancement of dye-sensitized solar cells (DSCs). Both simulation and experimental results indicate that compared with regular plasmonic NPs, such as nano-spheres, irregular popcorn-shaped alloy NPs exhibit absorption enhancement over a broad wavelength range due to the excitation of localized surface plasmons (LSPs) at different wavelengths. The power conversion efficiency (PCE) of DSCs is enhanced by 16% from 5.26% to 6.09% by incorporating 2.38 wt% Au-Ag alloy popcorn NPs. Moreover, by adding a scattering layer on the exterior of the counter electrode, the popcorn NPs demonstrate an even stronger ability to increase the PCE by 32% from 5.94% to 7.85%, which results from the more efficient excitation of the LSP mode on the popcorn NPs.

Aluminum plasmonic nanoparticles enhanced dye sensitized solar cells

We present an investigation on utilizing plasmonic aluminium (Al) nanoparticles (NPs) to enhance the optical absorption of dye-sensitized solar cells (DSCs). The Al NPs exhibit not only the light absorption enhancement in solar cells with localized surface plasmon (LSP) effect but also the chemical stability to iodide/triiodide electrolyte. Besides, the lower work function (~4.06 eV), compared with that of TiO₂ (~4.6 eV), may suppress the quenching processes, such as charge transfer to metal NPs, to reduce the loss. Thus, high concentration of Al NPs could be incorporated into the TiO₂ anodes, and the power conversion efficiency (PCE) of DSCs is improved by nearly 13%. Moreover, electrochemical impedance spectroscopy (EIS) characterization also indicates that the plasmonic DSCs with Al NPs present better electrochemical performance than regular ones, which contributes to the improvement of PCE of the device.

Thermo-optic switch based on transmission-dip shifting in a double-slot photonic crystal waveguide

Optical switch based on an ultra-compact double-slot photonic crystal waveguide (DS-PCWG) with a titanium/aluminum microheater is demonstrated. The operating principle relies on shifting a transmission-dip caused by the defect mode coupling in photonic band gap (PBG). Based on the unique mode coupling in PBG, low switching power of 9.2 mW and high extinction ratio of 17 dB are achieved experimentally while the length of DS-PCWG is only 16 μm.

Temperature dependence of ministop band in double-slots photonic crystal waveguides

We proposed and fabricated a double-slots photonic crystal waveguides (PCWGs) structure formed by introducing two slots into PCWGs with air-bridge structure on silicon-on-insulator substrate. The mode characteristics of double-slots PCWGs were investigated theoretically and experimentally. The transmission spectra present a sharp and deep dip (22 dB with bandwidth of 6 nm) caused by ministop band in the proposed structure, which is 15 dB deeper than that in the W3 PCWG. Additionally, dependence of the dip on temperature in the double-slots PCWG was measured and a temperature coefficient 0.159 nm/°C can be concluded.

Generating optical superimposed vortex beam with tunable orbital angular momentum using integrated devices.

An integrated device, which consists of a variable amplitude splitter and an orbital angular momentum (OAM) emitter, is proposed for the superposition of optical vortex beams. With fixed wavelength and power of incident beam, the OAM of the radiated optical superimposed vortex beam can be dynamically tuned. To verify the operating principle, the proposed device has been fabricated on the SOI substrate and experimentally measured. The experimental results confirm the tunability of superimposed vortex beams. Moreover, the ability of independently varying the OAM flux and the geometric distribution of intensity is illustrated and discussed with numerical simulation. We believe that this work would be promising in various applications.

Tunable and Reconfigurable Bandstop Microwave Photonic Filter Based on Integrated Microrings and Mach–Zehnder Interferometer

A bandstop microwave photonic filter is experimentally demonstrated with integrated optical processor fabricated on silicon-on-insulator substrate. The optical processor consists of microrings and a Mach-Zehnder interferometer so that two bandstop responses are produced for processing two sidebands separately. With such a structure, tunable and reconfigurable bandstop MPFs can be easily realized by thermally tuning the resonant wavelength of microrings. According to the experimental results, the operating frequency and 10-dB bandwidth can be tuned within the range of 7-34 GHz and 1.85-4.55 GHz, respectively.

Strong Optomechanical Coupling in Nanobeam Cavities based on Hetero Optomechanical Crystals

A hetero optomechanical crystal nanobeam cavity with high mechanical frequency of 5.88 GHz is proposed. By enhancing the overlap between optical and strain field, an optomechanical coupling rate as high as 1.31 MHz is achieved.

Two-surface-plasmon-polariton-absorption based nanolithography

We propose and demonstrate the two-surface-plasmon-polariton-absorption (TSPPA), which is a nonlinear effect by absorbing two surface-plasmon-polaritons (SPPs), as well as a nanolithography technique based on TSPPA. The TSPPA effect is verified with the plasmonic interference structure to exclude the possibility of two photon absorption. Benefiting from the short wavelength and the field enhancement of SPP as well as the selective transfer of plasmonic patterns into photoresist induced by TSPPA, resist strips with the linewidth of ∼λ0/11 are achieved by a single illumination on the plasmonic mask with the femtosecond laser for only 15 s, which shows great potential for future large-area nanolithography.

Broadband switching functionality based on defect mode coupling in W2 photonic crystal waveguide

Broadband switching functionality realized by an ultra-compact W2 photonic crystal waveguide (PCW) is demonstrated with an integrated titanium/aluminum microheater on its surface. Due to the enhanced coupling between the defect modes in W2 PCW, switching functionality with bandwidth up to 24 nm is achieved by the PCW with footprint of only 8 μm × 17.6 μm, while the extinction ratio is in excess of 15 dB over the entire bandwidth. Moreover, the switching speed is measured by alternating current modulation. Response time for this thermo-optic switch is 11.0 ± 3.0 μs for rise time and 40.3 ± 5.3 μs for fall time, respectively.

Optomechanical crystal nanobeam cavity with high optomechanical coupling rate

An optomechanical crystal nanobeam cavity, only by increasing the radius of air holes in the defect region, is proposed and optimized for a high optomechanical coupling rate. In our proposed cavity, the photonic and phononic defect modes are simultaneously confined by each corresponding bandgap, and the overlap of the optical and mechanical modes can be improved simply by adjusting the radius of the air holes. Accordingly, an optomechanical coupling rate (g) as high as 1.16 MHz is obtained, which is the highest coupling rate among the reported optomechanical crystal cavities. What’s more, the proposed cavity also exhibits a high mechanical frequency of 4.01 GHz and a small effective mass of 85 fg for the fundamental mechanical mode.