Objective The developments in adaptive optics, image stabilization, fast laser scanning, and optical communications have resulted in the increasing demand for high-performance fast steering mirrors (FSMs). In some optical systems, such as laser metrology, projection system, and inter-satellite optical communication, FSM size is crucial. In integrated optical systems, there is an urgent application demand for portable FSM systems. However, the existing FSM design does not consider the volume, especially height size, which is not conducive to miniaturization of optical systems. To meet the requirements of a portable FSM system for small-size FSMs, a compact piezoelectric driven FSM structure was designed. We expect the FSM not only to be portable but also to have excellent performance.
Methods There are two types of FSM driving actuators: voice coil actuator and piezoelectric ceramic stack actuator (PCSA). Voice coil actuator is a direct drive motor based on Lorentz force, its size is generally larger than PCSA, and its environmental adaptability is also poor. For the miniaturization of FSM, we chose a PCSA with a height of only 17 mm. Because the displacement of the PCSA is small, we set a lever displacement amplification mechanism in the FSM structure. In the structural design of FSM, a decoupled flexure hinge was parallel to the PCSA. Through a reasonable layout of driving elements, displacement amplification mechanism, and decoupling support of the mirror, the overall dimension of the FSM, especially the height dimension, can be significantly reduced. We established a theoretical model for FSM and analyzed its angular stroke and resonance frequency. The theoretical results show that the angular stroke and resonance frequency of FSM reach 4.714 mrad and 707 Hz, respectively, which are consistent with our expected performance.
Results and Discussions The overall dimension of the mechanical structure of 75-mm diameter transparent mirror is 90 mm×90 mm×33 mm. We tested the angular stroke and resonant frequency of the FSM. The experiment results show that the angular stroke of the compact FSM is 4.2 mrad (Fig. 6). There is an error of 12.23% between the experiment and theory results; the main reason for this error is that the deformation of the flexure hinge in the theoretical model is considered a pure rotation, but there is a small lateral displacement in practice. The mechanical resonance frequency is 671 Hz (Fig. 7), the error between the theoretical value and the measured value of resonance frequency is 5.36%. The main causes of the errors are machining errors and PCSA stiffness errors. The experiment results show that the FSM has a good performance and can meet the application requirements of a portable FSM system.
Conclusions We design a compact FSM that is portable and has high performance based on the application requirements of portable FSM for small-size and integrated optical systems. We choose PCSA with small stroke and height and use a one-stage amplification mechanism in the FSM structure. PCSAs and decoupling support hinges are in parallel position. This design is the first example in FSM with a lever amplification mechanism. Through reasonable structure design, the size of FSM is significantly reduced. In this article, a theoretical model for FSM is established, and the angular stroke and resonant frequency of FSM are derived. The experiment results are consistent with the theoretical results. Finally, based on the experiment, the established FSM is not only portable but also exhibits excellent performance. Compared with the same caliber product S-340 of PI company, the compact FSM has similar performance, smaller volume, and good engineering application value.
