Micromachined phase-shifted array-type Mirau interferometer for swept-source OCT imaging: design, microfabrication and experimental validation

Abstract

OCT instruments permit fast and non-invasive 3D optical biopsies of biological tissues. However, they are bulky and expensive, making them only affordable at the hospital and thus, not sufficiently used as an early diagnostic tool. Significant reduction of system cost and size is achieved by implementation of MOEMS technologies. We propose an active array of 4x4 Mirau microinterferometers where the reference micro-mirrors are carried by a vertical comb-drive microactuator, enabling the implementation of the phase-shifting technique that improves the sensitivity and eliminates unwanted interferometric terms. We focus on the design of the imaging system, the microfabrication and the assembly of the Mirau microinterferometer, and the swept-source OCT imaging.

MEMS Scanning Mirrors for Optical Coherence Tomography

“…Significant reduction of system cost and size can be achieved by use of opto-mechanical components, fabricated by micromachining. In 2016, an OCT microsystem including an active 4 × 4 array of spectrally tuned Mirau interferometers, including an electrostatic vertical comb-drive actuator carrying the array of reference mirrors, was proposed for dermatology applications [48]. The architecture of an active Mirau interferometer is shown schematically in Figure 11a.…”

Wire grid polarizer based in-line laser interferometer for macroscopic and microscopic phase estimation of transmissive and reflective phase samples

“…In in-line interferometer design, as the object and reference waves travel almost identical optical pathways, both the beams are identically affected by ambient fluctuations [34], resulting in a considerable reduction of noises due to external perturbations and effects due to residual aberrations of the optical components. The Mireau interference objective, representative of a common path interferometer, is well suited to white-light interferometry and provides significant environmental stability and ruggedness as compared to conventional interferometer geometries [35,36]. In spite of these obvious advantages, the Mireau objective does not have the inherent phase-shifting capability, and as such phase shifting is typically implemented by translating the objective through the use of a piezoelectric transducer which shifts the objective in relation to the sample by fractions of the wavelength.…”

Single-shot off-axis full-field optical coherence tomography

“…Furthermore, a stack of en-face images can then be retrieved, making it possible to reconstruct a three-dimensional amplitude image of biological tissues. An alternative to the full-field direct measurement of the echo time delay of light consists in performing the measurements in the frequency domain by encoding the signal in wavelength 3,4 . However, the acquisition time of the cameras must be adapted, leading to a low signal collection.…”