Optical coherent detection is a precise and non-contact method for measurement of tiny deformation or movement of an
object. In the last century, it can only be used on the static or quasi-static measurement of deformation between two
statuses. Recently it has been applied on dynamic measurement with the help of high-speed camera. The advantage of
this technique is that it can offer a full-field measurement. However, due to the limited capturing rate of high-speed
camera, its capability in temporal domain cannot meet the requirements of many applications. In this study, several
issues in high-speed-camera-based optical interferometry are discussed. For example, introduction of carrier in temporal
and spatial domain, signal processing in temporal-frequency domain, and the introduction of dual-wavelength
interferometry in dynamic measurement. The discussion leads to a clue to select suitable technique to fulfill whole-field
dynamic measurement at different ranges.
Laser Doppler vibrometry(LDV) is a precise and non-contact optical interferometry used to measure vibrations of
structures and machine components. LDV can only provide a point-wise measurement, or a scanning measurement via
moving the laser beam rapidly onto the vibrating object which is assumed to be invariant in the scanning course.
Consequently, LDV is usually impractical to do measurement on transient events. In this paper, a new self-synchronized
multipoint LDV is proposed. The multiple laser beams are separated from one laser source, and different frequency shifts
are introduced into these beams by a combination of acousto-optic modulators. The laser beams are projected on
different points, and the reflected beams interfere with a common reference beam. The interference light intensity signal
is recorded by a single photodetector. This multipoint LDV has the flexibility to measure the vibration of different points
on various surfaces. In this study, two applications in experimental mechanics area are presented. Firstly, the proposed
system is used to measure the resonant frequencies of structure in a shock test. Secondly, The proposed multi-point LDV
is also used to measure the mode shape of a beam with an artificial crack. Compared with the original vibration mode
shape, the crack location can be identified easily.
This article presents design and development of a novel 3D micromirror for large deflection scanning application in invivo
optical coherence tomography (OCT) bio-imaging probe. Overall mirror chip size is critical to reduce the diameter of the probe; however, mirror plate itself should not be less than 500 μm as smaller size means reducing the amount of light collected after scattering for OCT imaging. In this study, mirror chip sizes of 1 × 1 mm2 and 1.5 × 1.5 mm2 were developed with respectively 400 and 500 micrometer diameter mirror plates. The design includes electro thermal excitation mechanism in the same plane as mirror plate to achieve 3D free space scanning. Larger deflection requires longer actuators, which usually increase the overall size of the chip. To accommodate longer actuators and keep overall chip size same curved beam actuators are designed and integrated for micromirror scanning. Typical length of the actuators was 800 micrometer, which provided up to 17 degrees deflection. Deep reactive ion etching (DRIE) process
module was used extensively to etch high aspect ratio structures and keep the total mirror chip size small.
In this paper, we present a non-rotatory circumferential scanning optical probe integrated with a MEMS scanner for in
vivo endoscopic optical coherence tomography (OCT). OCT is an emerging optical imaging technique that allows high
resolution cross-sectional imaging of tissue microstructure. To extend its usage to endoscopic applications, a
miniaturized optical probe based on Microelectromechanical Systems (MEMS) fabrication techniques is currently
desired. A 3D electrothermally actuated micromirror realized using micromachining single crystal silicon (SCS) process
highlights its very large angular deflection, about 45 degree, with low driving voltage for safety consideration. The
micromirror is integrated with a GRIN lens into a waterproof package which is compatible with requirements for
minimally invasive endoscopic procedures. To implement circumferential scanning substantially for diagnosis on certain
pathological conditions, such as Barret's esophagus, the micromirror is mounted on 90 degree to optical axis of GRIN
lens. 4 Bimorph actuators that are connected to the mirror on one end via supporting beams and springs are selected in
this micromirror design. When actuators of the micromirror are driven by 4 channels of sinusoidal waveforms with 90
degree phase differences, beam focused by a GRIN is redirected out of the endoscope by 45 degree tilting mirror plate
and achieve circumferential scanning pattern. This novel driving method making full use of very large angular deflection
capability of our micromirror is totally different from previously developed or developing micromotor-like rotatory
MEMS device for circumferential scanning.