Extraction of Elastooptic Coefficient of Thin-Film Arsenic Trisulfide Using a Mach-Zehnder Acoustooptic Modulator on Lithium Niobate

• Published in: Journal of lightwave technology 2020-04, Vol.38 (7), p.2053-2059
• Main Authors: Khan, Md Shofiqul Islam, Mahmoud, Ashraf, Cai, Lutong, Mahmoud, Mohamed, Mukherjee, Tamal, Bain, James A., Piazza, Gianluca
• Format: Article
• Language: English
• Subjects: Acousto-optic modulation; Acoustooptical devices; Arsenic trisulfide; Coefficients; elasto-optic coefficient; Finite element method; lithium niobate; Lithium niobates; Mach-Zehnder interferometers; Mathematical analysis; Optical imaging; Optical interferometry; Optical modulation; Optical waveguides; photo-elastic effect; Photonics; Q factors; Strain; Surface acoustic wave devices; Surface acoustic waves; Thin films; Waveguides
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2019.2960396

An acousto-Optic Modulator (AOM) formed by an Arsenic Trisulfide (As_2S_3) Mach-Zehnder interferometer (MZI), operating in a push-pull configuration and placed inside a surface acoustic wave (SAW) cavity on a Y-cut Lithium Niobate (LN) wafer is demonstrated. This is the first demonstration of such acousto-optic (AO) modulator in this As_2S_3-LN hybrid platform. In this approach, the high index contrast of As_2S_3 waveguides is exploited to attain a high optical confinement. Additionally, the placement of the photonic MZI inside the SAW cavity enhances the AO interaction due to the high quality factor (Q) of the SAW resonator. An analytical expression that describes such enhancement as a function of the elasto-optic (EO) coefficient of As_2S_3 is derived in conjunction with COMSOL finite element methods to describe strain in the SAW cavity. By fitting this expression to experimental data, the EO coefficient (p_{11} and p_{12}, where p_{11} \approx p_{12}) for As_2S_3 is extracted to be 0.29 at the wavelength of 1550 nm. This is the first time that the EO coefficient of thin film As_2S_3 is experimentally derived.