In this paper, we report the study of the frequency-dependent plasmonic enhancement of a circular disk nano-optical antenna array and the photo-response of the optical antenna enhanced photodetector at different frequencies using a femtosecond (fs) laser frequency comb. A fs-laser frequency comb can provide hundreds of evenly spaced harmonic frequencies and thus allows simultaneous measurement of the plasmonic optical antenna enhancement effect at these harmonic frequencies. This offers a highly efficient frequency-dependent measurement approach compared to the conventional method of modulating of a c.w. laser, which measures the frequency response at each frequency. The impulse response of the circular disk nano-optical antenna array and the electric-field (E-field) distribution profile are simulated under a fs laser illumination. The light intensity spectrum is simulated and verified to have uniform intensities on the harmonic frequencies within the ±5 GHz frequency range. The photocurrent densities in different regions of a GaAs p-i-n photodetector are analyzed together with their frequency dependence at the harmonic frequencies of the fs laser frequency comb with a repetition rate of f 0 = 94.2 MHz. A circular disk nano-optical antenna array enhanced GaAs p-i-n photodetector was fabricated and measured using a fs laser frequency comb with the same repetition rate. The nano-optical antenna can provide ~20 dB enhancement for the harmonic frequencies and extend the detector cut-off frequency from 2.4 GHz to 4.2 GHz.

In this paper, we present the analysis of the evanescent waveguide modes in a 2D subwavelength hole array (2DSHA) plasmonic structure and their relationship with the excited surface plasmonic resonance (SPR). It is found that when the metal film thickness is larger than 0.0625 µm, the excited SPRs have a linear dependence on the evanescent waveguide modes, whereas when the metal film is thin, the linear relationship does not hold, primarily due to the coupling of the SPRs on the asymmetric interfaces of the metal film. The linear dependence is also verified by curve-fitting the Fano transmission profiles of the 2DSHA structures. 2DSHA enhanced quantum dot infrared photodetectors with various metal film thicknesses were fabricated and tested. The measured plasmonic enhancement ratios agree well with the analysis.

No abstract

No abstract

No abstract