Enhanced Optical Coupling Structure Based On Surface Plasmons

Superconducting nanowire single-photon detectors (SNSPD) have many applications in quantum communication, fundamental research of quantum optics and other regions. The SNSPDs have many advantages such as low dark count rate, high timing resolution and broad spectral response. But the systems efficiency of SNSPDs is usually not very good.First, the absorption spectrum of Au nanoparticle are studied for improving the light coupling to supercoducting nanowires and system efficiency of SNSPD in the visible light range. We simulate respectively the absorbance of single Au nanoparticle, single- and double-layer Au nanoparticles by COMPUTER SIMULATION TECHNOLOGY(CST). The simulation results agreed with experimental measurement which confirms the correctness of our model used in CST. Then, we investigate the relations between several factors, such as the size of Au nanoparticle, the distance between nanoparticles and the dielectric constant of coating materials, with the absorption and the resonance frequency of surface plasmon. Finally, Au nanoparticle array is placed on the top of superconducting nanowire single photon detectors and observe a substantial change of the critical current caused by surface plasmon resonance of Au nanoparticles. We give a reasonable explanation to our experiment.We also study the absorption of a hybrid plasmonic-photonic microstructure for near-infrared SNSPD since Au nanoparticle array can not resonate in the near-infrared region. By choosing the proper parameters the dual-band absorption is observed. Particularly, we use a revised model in CST and get broadband absorption in 1310-1550nm by tuning the size of the colloidal particles.