Bias field tailored plasmonic nano-electrode for high-power terahertz photonic devices

Abstract

Photoconductive antennas with nano-structured electrodes and which show significantly improved performances have been proposed to satisfy the demand for compact and efficient terahertz (THz) sources. Plasmonic field enhancement was previously considered the dominant mechanism accounting for the improvements in the underlying physics. However, we discovered that the role of plasmonic field enhancement is limited and near-field distribution of bias field should be considered as well. In this paper, we clearly show that the locally enhanced bias field due to the size effect is much more important than the plasmonic enhanced absorption in the nano-structured electrodes for the THz emitters. Consequently, an improved nano-electrode design is presented by tailoring bias field distribution and plasmonic enhancement. Our findings will pave the way for new perspectives in the design and analysis of plasmonic nano-structures for more efficient THz photonic devices.

Review of terahertz photoconductive antenna technology

“…66,71,72,76,140,[163][164][165][166] The key distinction here is that, in this configuration, the nanostructured regions are electrically continuous with either the anode or cathode, rather than being electrically isolated. An example of this from the work of Moon et al 167 is shown in Fig. 14 [Fig.…”

“…Here, a microscopic image of a standard dipole antenna structure is shown, along with SEM images of the various nanoplasmonic grating structures fabricated as part of the dipole electrodes. 167 Most work investigating nanostructured electrodes attempt to enhance the near-anode effect, the high output THz power that is observed when the optical pump is centered over the anode. By nanostructuring the antenna electrodes, the effective area of the near-anode region can be increased, so the full area of the incident optical pump falls on the nearanode region.…”

“…71 Plasmonic nanostructured electrodes have been studied by several other groups as well. 82,[167][168][169] Heshmat et al 168 fabricated THz PCAs on LT-GaAs with interdigitated electrodes that had 100 nm anode-cathode gaps. The emitted THz pulse peak-to-peak amplitude was found to be 2× greater than that of a commercially available conventional emitter.…”

“…FDTD simulations supported these measurements, showing that the calculated optical field enhancement matched the out THz intensity enhancement. 82 Moon et al 167 experimentally compared three different nanograting designs: nanograting electrodes with 3 μm and 200 nm anode-cathode gaps and nanograting electrodes with partially interdigitated nanogratings between the anode and cathode. All devices showed increased power output at low optical excitation power as compared to a reference, nonplasmonic PCA, as shown in the time-domain waveform and fast Fourier transform spectra in Fig.…”

An efficient terahertz detector based on an optical hybrid cavity

“…The efficiency of photoconductive (PC) THz detectors based on low temperature grown (LT) GaAs is limited by the bulk material properties: the mean free path of photo-excited carriers, and the optical absorption length. A popular method to mitigate the material limitations is to modify the photoconductive antenna to incorporate plasmonic nano-electrodes [1][2][3][4][5][6] . These electrodes support an optical plasmon resonance, which strongly localizes the generation of electron-hole pairs to the vicinity of the nano-electrodes.…”