Lee Yongbeom, Lee Keekeun
Depart. of Electrical & Computer Eng., Ajou Univ., Suwon, Geonggi-do 16449, Korea.
Sensors (Basel). 2020 Feb 23;20(4):1218. doi: 10.3390/s20041218.
An acousto-optic (AO) holographic display unit based on a suspended waveguide membrane was developed. The AO unit consists of a wide bandwidth chirp interdigital transducer (IDT) on a 20 µm thick suspended crystalline 128° YX LiNbO membrane, a light blocker with a 20 µm hole near the entrance, and an active lens near the exit. The 20 µm thickness of the floating membrane significantly enhanced surface acoustic wave (SAW) confinement. The light blocker was installed in front of the AO unit to enhance the coupling efficiency of the incident light to the waveguide membrane and to remove perturbations to the photodetector during measurement at the exit region. The active lens was vertically attached to the waveguide sidewall to collect the diffracted beam without loss and to modulate the focal length in free space through the applied voltage. As SAWs were radiated from the IDT, a Bragg grating with periodic refractive indexes was formed along the waveguide membrane. The grating diffracted incident light. The deflection angle and phase, and the intensity of the light beam were controlled by the SAW frequency and input power, respectively. The maximum diffraction efficiency achieved was approximately 90% for a 400 MHz SAW. COMSOL simulation and coupling of mode modeling were performed to optimize design parameters and predict device performance.
研制了一种基于悬浮波导薄膜的声光（AO）全息显示单元。该AO单元由一个位于20μm厚的悬浮晶体128°YX LiNbO薄膜上的宽带啁啾叉指换能器（IDT）、一个在入口附近有20μm孔的光阑以及一个在出口附近的有源透镜组成。20μm厚的浮动薄膜显著增强了表面声波（SAW）的限制。光阑安装在AO单元前面，以提高入射光与波导薄膜的耦合效率，并在出口区域测量期间消除对光电探测器的干扰。有源透镜垂直附着在波导侧壁上，以无损耗地收集衍射光束，并通过施加电压在自由空间中调制焦距。当SAW从IDT辐射时，沿波导薄膜形成了具有周期性折射率的布拉格光栅。该光栅使入射光发生衍射。光束的偏转角和相位以及强度分别由SAW频率和输入功率控制。对于400MHz的SAW，实现的最大衍射效率约为90%。进行了COMSOL模拟和模式耦合建模，以优化设计参数并预测器件性能。
