Electromagnetically induced transparency (EIT) is a quantum interference effect that reduces light absorption over a narrow spectral region. EIT gives rise to greatly enhanced nonlinear susceptibility in the spectral region of induced transparency of the medium and is associated with steep dispersion, opening great opportunities in all-optical buffering, processing, optical storage, and enhanced nonlinear optics. To overcome many of the limitations of EIT on extreme experimental conditions, bandwidth, and decoherence, its classical counterpart or equivalent phenomenon in optics, i.e., EIT-like effect, has been proposed in a variety of systems and based on different mechanisms.

Figure: Tunable EIT-like spectra controlled by the applied voltage.

We proposed an easily-integrated compact tunable filtering based on polarization-coupling process in a thin periodically poled lithium niobate (PPLN) in a reflective geometry via the transverse electro-optic (EO) effect. The half-wave voltage is reduced to below 100 V. The filtering effect can be dynamically switched on and off by a transverse electric filed. Analogy of electromagnetically induced transparency (EIT) transmission spectrum and electrically controllable group delay is experimentally observed. The mechanism features tunable center wavelength in a wide range with respect to temperature and tunable optical delay to the applied voltage, which may offer another way for optical tunable filters or delay lines.

This research was published in “Tingting Ding, Yuanlin Zheng, and Xianfeng Chen, Phase-shifted Solc-type filter based on thin periodically poled lithium niobate in a reflective geometry, Opt. Express 26(9), 12016-12021 (2018)”.