Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

Abstract

We report on the first experimental demonstration of terahertz (THz) whispering-gallery modes (WGMs) with an ultra high quality (Q) factor of 1.5 × 10 4 at 0.62 THz. The WGMs are observed in a high resistivity float zone silicon (HRFZ-Si) spherical resonator coupled to a sub-wavelength silica waveguide. A detailed analysis of the coherent continuous wave (CW) THz spectroscopy measurements combined with a numerical model based on Mie-Debye-Aden-Kerker (MDAK) theory allows to unambiguously identify the observed higher order radial THz WGMs.

Terahertz Gas-Phase Spectroscopy Using a Sub-Wavelength Thick Ultrahigh-Q Microresonator

“…As mentioned above, a low-loss resonator substrate is essential as even with a thickness of λ 0 /8 about 50 % of the total energy remain in the disc's substrate. Here, the disc microresonator is made of high resistivity float-zone grown silicon (HRFZ-Si) with a resisitivity of >10 kΩcm, as this is one of the lowest loss materials known in the THz domain [29]. Fabrication of the discs is achieved by thinning a standard 100 µm thick, 2 inch diameter wafer and subsequent laser micro-machining.…”

“…While such monolithic resonators have been extensively studied at optical frequencies [15][16][17][18][19][20][21][22], they remain largely unexplored in the THz domain. It is only very recently that this concept has been translated into the THz domain [23][24][25][26][27][28][29][30][31], achieving unprecedented Q-factors more than two orders of magnitude higher compared to previous systems [29]. Unfortunately, while the demonstrated devices highlight the potential of monolithic THz resonators, their characteristics are still insufficient for demanding gas-phase spectroscopy applications.…”

Industrial Applications of Terahertz Sensing: State of Play

“…Figure 3 illustrates the sequence of steps in an FDS measurement; the sample is a silicon sphere resonator with a whispering-gallery-mode (WGM) resonance [25]. Akin to TDS, a reference measurement is recorded, followed (or preceded) by a measurement of the sample (Figure 3a blue and grey).…”

Whispering Gallery Modes at THz

“…Earliest work on WGMs covered visible to near‐infrared and microwave regions where the source and detectors are widely available. Some of the pioneering works on WGMs are single molecule detection, high quality factors, sensors, notch filters, nonlinear phenomena, and laser cavity selectors . High quality factor ( Q ) and small mode volume ( V ) WGMs are utilized in low threshold solid state lasing, dye doped capillaries, spherical droplets, and doped microspheres .…”