质子交换铌酸锂（LiNbO₃）波导中从共线导波到漏波的声光相互作用

Matteo A M, Tsai C S, Do N

CSELT, Centro Studi e Laboratori Telecomunicazioni, via Reiss Romoli 274, 1478 Torino, Italy.

IEEE Trans Ultrason Ferroelectr Freq Control. 2000;47(1):16-28. doi: 10.1109/58.818745.

The results of a detailed theoretical study on collinear guided wave to leaky wave acoustooptic (AO) interactions in proton-exchanged LiNbO(3) (PE:LiNbO(3)) planar waveguides are presented. The guided-to-leaky mode conversion for an input optical beam at the wavelength of 632.8 nm by the induced diffraction grating from a collinear surface acoustic wave (SAW) is analyzed using a generalized multimode formulation of the coupled mode theory. Mode conversion efficiency and AO bandwidth have been calculated as functions of acoustic frequency, interaction length, guiding layer thickness, and acoustic drive power density for three cuts of the LiNbO(3) substrate. High performance configurations that are desirable for application to demultiplexing and switching in optical communication systems are identified, and the corresponding channel capacity and frequency resolution are determined. For example, it was shown that the X-cut configuration features the highest mode conversion efficiency. However, a relatively small AO bandwidth is associated with this configuration. Both high mode conversion efficiency and large AO bandwidth can be accomplished at the guiding layer thickness of 1.0 microm. A TM(o)-->TE(nu) mode conversion efficiency as high as 42% together with an AO bandwidth of approximately 70 MHz can be achieved in the Z-cut waveguide at the guiding layer thickness of 1.0 microm, acoustic drive power density of 50 mW/mm, interaction length of 40 mm, and acoustic frequency of 460 MHz. The corresponding channel capacity and frequency resolution are 745 and 0.09 MHz, respectively. Measured mode conversion efficiencies as high as 90 and 78% obtained at the acoustic frequencies of 107 and 367 MHz using the X-cut substrate and the Y-propagation SAW have verified the theoretical prediction on the mode conversion efficiencies.

本文给出了质子交换铌酸锂（PE:LiNbO₃）平面波导中，共线导波到漏波光声光（AO）相互作用的详细理论研究结果。利用耦合模理论的广义多模公式，分析了由共线表面声波（SAW）产生的诱导衍射光栅，对波长为632.8 nm的输入光束的导模到漏模转换。对于铌酸锂衬底的三种切割方式，计算了模式转换效率和声光带宽与声频、相互作用长度、波导层厚度以及声驱动功率密度的函数关系。确定了适用于光通信系统中解复用和开关应用的高性能配置，并确定了相应的信道容量和频率分辨率。例如，结果表明X切割配置具有最高的模式转换效率。然而，该配置的声光带宽相对较小。在波导层厚度为1.0微米时，可以实现高模式转换效率和大声光带宽。在Z切割波导中，当波导层厚度为1.0微米、声驱动功率密度为50 mW/mm、相互作用长度为40 mm、声频为460 MHz时，TM(o)→TE(ν)模式转换效率高达42%，声光带宽约为70 MHz。相应的信道容量和频率分辨率分别为745和0.09 MHz。使用X切割衬底和Y传播SAW，在107和367 MHz声频下测得的模式转换效率高达90%和78%，验证了模式转换效率的理论预测。