Tolerance analysis of the pulse signal of a novel lateral deformable optical NEMS grating transducer

摘要

This paper discusses the pulse signal of a novel opto-mechanical zeroth-order grating transducer based on an anomalous diffraction phenomenon, Wood's type anomaly and its corresponding tolerance analysis. In this device, tiny changes in the displacement of the nanostructured grating elements lead to a dramatic increase or decrease of the optical reflection amplitude. With this special feature, this structure is ideal to measure very small displacement. Unexpectedly, the original sinusoidal signal of the device develops into a new signal form, i.e. pulse signal with the decrease of the air gap between two layers of gratings. Thus the sensitivity of the structure is improved 8 times higher, as the slope of the pulse signal, namely 2.5%m, i.e. 0.65dBm, is 8 times higher than that of the original signal form, namely 0.3%m, i.e. 0.03dBm. However, this device is very sensitive to parameters including wavelength, period, duty ratio, air gap as well as thickness of the gratings. Thus, in this paper the performance of the structures with different parameter settings is analyzed and optimized through rigorous coupled wavelength analysis (RCWA) and 3-D finite difference time domain (FDTD) method. All the calculated data enables us to apply the structure into fields required for different sensitivities with different values of grating parameters and thus broadens the further usage of such novel structure. In addition, a synthetic tolerance analysis of the pulse signal is conducted and indicates the possibility of achieving an actual device with the highest slope superior to 0.5%m is close to 85% and the possibility that the highest slope of an actual device falls in the interval ranging from 1.0%m to 2.0%m is 64%. All the simulated data enables us to get a better understanding of the tolerance of the pulse signal and a guidance of successful realization of an actual device.