Spectral and mode properties of surface plasmon polariton waveguides studied by near-field excitation and leakage-mode radiation measurement
1 Research Center for Applied Sciences, Academia Sinica, 128 Academia Road, Section 2, Taipei 115, Taiwan
2 Institute of Photonics Technologies, National Tsing Hua University, 101 Kuang-Fu Road, Section 2, Hsinchu 300, Taiwan
3 Department of Optoelectronics, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan
4 Department of Mechanical and Mechatronic Engineering, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 202, Taiwan
Nanoscale Research Letters 2014, 9:430 doi:10.1186/1556-276X-9-430Published: 25 August 2014
We present a method to couple surface plasmon polariton (SPP) guiding mode into dielectric-loaded SPP waveguide (DLSPPW) devices with spectral and mode selectivity. The method combined a transmission-mode near-field spectroscopy to excite the SPP mode and a leakage radiation optical microscope for direct visualization. By using a near-field fiber tip, incident photons with different wavelengths were converted into SPPs at the metal/dielectric interface. Real-time SPP radiation images were taken through leakage radiation images. The wavelength-dependent propagation lengths for silver- and gold-based DLSPPWs were measured and compared. It confirms that silver-based SPP has a propagation length longer than a gold-based one by 1.25, 1.38, and 1.52 times for red, green, and blue photons. The resonant coupling as a function of wavelength in dual DLSPPWs was measured. The coupling lengths measured from leakage radiation images were in good agreement with finite-difference time domain simulations. In addition, the propagation profile due to multi-SPP modes interference was studied by changing position of the fiber tip. In a multimode DLSPPW, SPP was split into two branches with a gap of 2.237 μm when the tip was at the center of the waveguide. It became a zigzag profile when the SPP was excited at the corner of the waveguide.