An active optically-controlled terahertz frequency modulation based on interference in a polymer/silicon structure was investigated. We report an interference phenomenon formed by partial-through measurements and modulation of periodic peaks in a terahertz time-domain spectroscopy system. When the terahertz beam passes through the sample edge, equally-spaced interference fringes are obtained in the frequency domain, and the interference fringes can be varied using an external continuous wave laser. This work offers the ability to observe THz-band interference fringes in the frequency domain; these interference fringes change with variations in the applied excitation light intensity, which allows an optically-controlled terahertz frequency modulator to be realized.
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