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• A low-cost method to perform precise non-contact displacement measurement by exploiting the near-field chrematistics of fiber specklegrams. • The fiber-optic sensor achieves a resolution and repeatability of 10 nm and a detection range of 3–4 μm at 100 Hz. • Advantages (1) low-cost, (2) compact device envelope, (3) high precision, and (4) insensitivity to sample/target materials. In this paper, we present a precision non-contact displacement sensor based on the near-field property of specklegrams, achieving a precision of 10 nm and a detection range of 3–4 μm. The compact device envelope enables the application of the new fiber-optic sensor in many space-limited applications, e.g., probe-based nanofabrication and micro-/mesoscale positioning systems. In the sensor system, the laser is first coupled into a 50/50 fiber coupler; the flexible fiber transmits the laser beam to the remote sensor head that is a few micrometers away from the sample surface; the reflected light is collected by the sensor head. The interference among the different eigenmodes propagating in the multimode fiber form unique specklegram images for different sample positions in space. By recording the varying specklegrams along the scanning path, highly precise and repeatable non-contact displacement detection can be realized by comparing the recorded specklegrams with the calibrated specklegram database through imaging processing techniques. In the experiments, we demonstrate the fiber-optic sensor can perform one-axis displacement sensing with a precision of 10 nm over a range of 3–4 μm at 100 Hz, where the specklegram acquisition rate is limited only by the speed of the camera. The new fiber-optic sensor is flexible, precise, and low-cost, which may find important applications in optical metrology and nanomanufacturing. [ABSTRACT FROM AUTHOR]

This paper presents the concept, theoretical analysis, microfabrication processes and experimental characterization of a micromirror with tunable resonant frequency. For scanning applications where a large scanning angle is required, comb-drive based micromirrors are typically operated at resonance due to the limited force/energy density of electrostatic actuators. However, errors in microfabrication processes often cause natural frequencies to offset from the design value. This issue may be resolved by a frequency-tunable micromirror. In our design, the shifting of the resonant frequency is achieved by adjusting the axial stress of the micromirror’s torsion hinge via integrated chevron thermomechanical actuators. The scanning motion of the micromirror is generated by double silicon-on-insulator (SOI) wafer-based electrostatic comb-drive actuators. The experimental results show that the micromirror has achieved a frequency tuning range of approximately 3%, which is close to the analytic model. With precise frequency control, the micromirror may compensate the undesired frequency shift due to fabrication errors, which is useful for applications requiring precise scanning synchronization such as the laser scanning endomicroscope systems. [ABSTRACT FROM AUTHOR]