3.9 THz spatial filter based on a back-to-back Si-lens system

Yuner Gan, Behnam Mirzaei, Sebastiaan Van Der Poel, Jose R.G. Silva, Matvey Finkel, Martin Eggens, Marcel Ridder, Ali Khalatpour, Jian Rong Gao, More Authors

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Abstract

We present a terahertz spatial filter consisting of two back-to-back (B2B) mounted elliptical silicon lenses and an opening aperture defined on a thin gold layer between the lenses. The beam filtering efficiency of the B2B lens system is investigated by simulation and experiment. Using a unidirectional antenna coupled 3rd-order distributed feedback (DFB) quantum cascade laser (QCL) at 3.86 THz as the source, the B2B lens system shows 72% transmissivity experimentally with a fundamental Gaussian mode as the input, in reasonably good agreement with the simulated value of 80%. With a proper aperture size, the B2B lens system is capable of filtering the non-Gaussian beam from the QCL to a nearly fundamental Gaussian beam, where Gaussicity increases from 74% to 99%, and achieves a transmissivity larger than 30%. Thus, this approach is proven to be an effective beam shaping technique for QCLs, making them to be suitable local oscillators in the terahertz range with a Gaussian beam. Besides, the B2B lens system is applicable to a wide frequency range if the wavelength dependent part is properly scaled.

Original languageEnglish
Pages (from-to)32693-32708
JournalOptics Express
Volume28
Issue number22
DOIs
Publication statusPublished - 2020

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