Organic nonlinear optical crystal DAST growth and its device applications Original Research Article

The organic ionic salt 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) is known for its huge nonlinearity among nonlinear crystals, and has advantages such as low dielectric constants. This nonlinearity of DAST is based on the large hyperpolarizabilities β, and it causes large electro-optical (E-O) coefficients and nonlinear optical coefficients. With low dielectric constants to the high-speed devices, the large E-O coefficients generate the highly efficient E-O modulation and detection in the high-frequency region. In this paper, we report the development of the crystal growth stability and reproducibility for large and high-quality DAST by the seed crystals fixing method. In this method, large enough and crack-free crystals are grown reproducibly with reasonable growth speed. By improved cutting and polishing processes of DAST crystals, we were able to make samples for device applications. With these samples, we demonstrate 60 GHz millimeter wave-field monitoring via the large and high-speed E-O effect of DAST. This monitoring system is attractive for applications to ultra-high-speed E-O devices, such as microwave photonics.