近场扫描光学显微术中,近场距离的检测和控制是需要解决的核心技术之一.本文研究了基于DDS驱动的压电传感器,在一个压电陶瓷片上,电极被分成相同的两部分,分别用于振动驱动和振幅检测.近场扫描的光纤探针固定于此压电陶瓷片上.振动驱动信号采用DDS,在样品的远场时,可以通过频率扫描得到误差在0.006 Hz以内的压电陶瓷片谐振频率驱动信号,而当光纤探针处于样品的近场距离之内时,压电陶瓷片的谐振频率偏离驱动信号频率,振幅明显减小,从而检测出近场距离.高精度振动驱动源DDS和高灵敏度压电传感器的采用提高了检测灵敏度和工作稳定性.

To detect and control the nanometer distance between the sample and the fiber tip is part of the key technology of NSOM system. Here a pizeo sensor with DDS is discussed. One of the sensor′s electrodes is separated into two like parts, one is for exciting the pizeo to shake and the other is for detecting the shake. The fiber tip is fixed on the pizeo and the pizeo is driven by a DDS. When the fiber tip is far from the sample surface, an exact resonant frequency of the fiber tip is obtained with the error of 0.006 Hz after frequency scanning, and when the tip is within the near-field of the sample, the resonant frequency of the fiber tip departures the resonant frequency in far-field, and the amplitude of the fiber tip obviously decreases because of the shear force between the fiber tip and the sample, and in this way the near-field distance is detected. The combination of high precision frequency source DDS and the pizeo sensor provides a higher sensitivity and stability of near-field detection.