Due to its non-invasive, high-resolution, and real-time imaging capabilities, optical scanning microscopy has been widely applied in biomedicine, physical chemistry, and materials science to realize three-dimensional imaging detection of cells, tissue analysis, and microstructure samples. Beam scanning systems play an important role in optical microscopy. When scanners are leveraged for scanning and imaging, it is necessary to add a relay system composed of a scan lens and tube lens between the scanner and the objective lens. As a result, the beam does not deviate from the rear pupil of the objective lens to ensure the imaging quality. However, traditional relay systems adopt lenses design, and their inherent defects can cause optical aberration, which affects the resolution of optical microscopy imaging systems. Commercial scan lens and tube lens are optimized to suppress aberrations, but they feature high price, large volume, and long focal length, making them unsuitable for miniaturized design occasions. The relay system composed of doublet lenses can be miniaturized according to requirements, but it is difficult to effectively suppress aberrations, especially under large beam scanning angles. The utilization of parabolic reflectors to form a relay system can effectively eliminate the chromatic aberration, but the coma aberration of the reflection system is difficult to eliminate. This is the same as the lens relay system, which requires a one-to-one correspondence of the focal position and high installation accuracy. Therefore, how to design aberration-free beam scanning systems with miniaturization and simple structures is still an important problem facing optical microscopy imaging technology.

Aiming at the large size, large aberration, and high alignment accuracy of the relay systems in existing beam scanning systems, we propose a dual two-dimensional (2D) MEMS mirror beam scanning method. This method adopts two 2D MEMS mirrors to realize beam telecentric scanning. One mirror replaces the scan lens and tube lens in the traditional relay system to avoid the introduction of aberrations, reduce the system size, and finally design an aberration-free beam scanning system with miniaturization and simple structures. There is a one-to-one correspondence between the scanning angle of the scanning beam and the tilt angle of the MEMS mirrors. By controlling two MEMS mirrors to cooperate with different tilt angles, this method can make the excitation beam arrive the rear pupil of the objective lens at different angles to complete the 2D lateral scanning.

To obtain the relationship between the angle of the scanning beam and the deflection angle of the two MEMS mirrors, we build a mathematical model of the dual 2D MEMS mirror scanning system, and analyze it in detail. First, the relationship between the tilt angle of the MEMS mirror and the beam scanning angle is analyzed. Under different d/l ratios (with dbeing the distance between two MEMS mirrors,and l being the distance between the second MEMS mirror and the rear pupil of the objective), the tilt angle of the MEMS mirror and the beam scanning angle have different relations. It is found that the dual 2D MEMS mirror scanning system can achieve a large angle beam scanning by adjusting the d/lvalue when the deflection angle of the first MEMS mirror is constant (Fig. 4). Additionally, the values of d and l can be selected arbitrarily, which is flexible in design and convenient for system miniaturization. Then, the aberrations of the traditional relay system and the dual 2D MEMS mirror scanning system are analyzed by Zemax optical design software, and their performances are compared. According to the simulation results, the dual 2D MEMS mirror scanning system avoids the introduction of aberrations and has better imaging quality than the traditional relay system (Figs. 6-7). Meanwhile, the system structure is simple, easier to adjust, and can avoid the influence of installation error on the system (Fig. 10). Finally, based on this method, a miniaturized confocal scanning microscope is constructed, and the step sample is utilized to obtain the height and period information of the sample (Fig. 13), which verifies the feasibility of the method.

We propose a dual 2D MEMS mirror beam scanning method, which leverages a 2D MEMS mirror instead of the traditional relay system to design an aberration-free beam scanning system. In addition, the dual 2D MEMS mirror structure has no requirements for the focus position, making it convenient for miniaturization design and installation. A dual 2D MEMS mirror scanning confocal microscope is constructed based on this method, and the feasibility of this method is verified by testing standard step samples. This method provides a new beam scanning approach for optical microscopy, which is of great significance for optical microscopic systems with strict aberration requirements such as confocal microscopes, two-photon microscopes, optical coherence scanning microscopes, and chromatic confocal microscopes.