Study of frequency-dependent plasmonic enhancement of a circular disk nano-optical antenna array using a femtosecond laser frequency comb

• Published in: Journal of physics. D, Applied physics Applied physics, 2019-09, Vol.52 (38), p.385104
• Main Authors: Kemsri, Thitikorn, Gu, Guiru, Schnitzer, Cheryl, Sullivan, Michaela, Xiang, Boyang, GhafaryAghdam, Ainaz, Li, Lin, Lu, Xuejun
• Format: Article
• Language: English
• Subjects: frequency-resovled enhancement; fs laser frequency comb; nano-optical antenna; plasmonic enhancement
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/1361-6463/ab2ab8

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 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.