Yeong-Hyeon Seo

Lissajous fiber scanning for forward viewing optical endomicroscopy using asymmetric stiffness modulation

We report a fully packaged and compact forward viewing endomicroscope by using a resonant fiber scanner with two dimensional Lissajous trajectories. The fiber scanner comprises a single mode fiber with additional microstructures mounted inside a piezoelectric tube with quartered electrodes. The mechanical cross-coupling between the transverse axes of a resonant fiber with a circular cross-section was completely eliminated by asymmetrically modulating the stiffness of the fiber cantilever with silicon microstructures and an off-set fiber fragment. The Lissajous fiber scanner was fully packaged as endomicroscopic catheter passing through the accessory channel of a clinical endoscope and combined with spectral domain optical coherence tomography (SD-OCT). Ex-vivo 3D OCT images were successfully reconstructed along Lissajous trajectory. The preview imaging capability of the Lissajous scanning enables rapid 3D imaging with high temporal resolution. This endoscopic catheter provides many opportunities for on-demand and non-invasive optical biopsy inside a gastrointestinal endoscope.

Electrothermal MEMS fiber scanner for optical endomicroscopy.

We report a novel MEMS fiber scanner with an electrothermal silicon microactuator and a directly mounted optical fiber. The microactuator comprises double hot arm and cold arm structures with a linking bridge and an optical fiber is aligned along a silicon fiber groove. The unique feature induces separation of resonant scanning frequencies of a single optical fiber in lateral and vertical directions, which realizes Lissajous scanning during the resonant motion. The footprint dimension of microactuator is 1.28 x 7 x 0.44 mm3. The resonant scanning frequencies of a 20 mm long optical fiber are 239.4 Hz and 218.4 Hz in lateral and vertical directions, respectively. The full scanned area indicates 451 μm x 558 μm under a 16 Vpp pulse train. This novel laser scanner can provide many opportunities for laser scanning endomicroscopic applications.

High resolution and high frame rate Lissajous scanning using MEMS fiber scanner

We present a high resolution and high frame rate (HRHF) Lissajous scanning. The Lissajous scanning was achieved by the selection rule of scanning frequencies, i.e., optimizing the greatest common divisor of transverse driving frequencies and the sum of transverse driving frequency ratios. HRHF Lissajous fiber scanner provides 10 fps with 89.5 % fill factor at driving frequencies of 1000 Hz and 1210 Hz, unlike conventional Lissajous scanners. This new method offers the highest fill factor during the shortest period to provide a new direction for real-time high resolution laser scanning. HRHF MEMS Lissajous scanners can be applied for an endomicroscopy and a pico projector.

Electrothermal MEMS parallel plate rotation for single-imager stereoscopic endoscopes

This work reports electrothermal MEMS parallel plate-rotation (PPR) for a single-imager based stereoscopic endoscope. A thin optical plate was directly connected to an electrothermal MEMS microactuator with bimorph structures of thin silicon and aluminum layers. The fabricated MEMS PPR device precisely rotates an transparent optical plate up to 37° prior to an endoscopic camera and creates the binocular disparities, comparable to those from binocular cameras with a baseline distance over 100 μm. The anaglyph 3D images and disparity maps were successfully achieved by extracting the local binocular disparities from two optical images captured at the relative positions. The physical volume of MEMS PPR is well fit in 3.4 mm x 3.3 mm x 1 mm. This method provides a new direction for compact stereoscopic 3D endoscopic imaging systems.

Frequency selection rule for high definition and high frame rate Lissajous scanning

Lissajous microscanners are very attractive in compact laser scanning applications such as endomicroscopy or pro-projection display owing to high mechanical stability and low operating voltages. The scanning frequency serves as a critical factor for determining the scanning imaging quality. Here we report the selection rule of scanning frequencies that can realize high definition and high frame-rate (HDHF) full-repeated Lissajous scanning imaging. The fill factor (FF) monotonically increases with the total lobe number of a Lissajous curve, i.e., the sum of scanning frequencies divided by the great common divisor (GCD) of bi-axial scanning frequencies. The frames per second (FPS), called the pattern repeated rate or the frame rate, linearly increases with GCD. HDHF Lissajous scanning is achieved at the bi-axial scanning frequencies, where the GCD has the maximum value among various sets of the scanning frequencies satisfying the total lobe number for a target FF. Based on this selection rule, the experimental results clearly demonstrate that conventional Lissajous scanners substantially increase both FF and FPS by slightly modulating the scanning frequencies at near the resonance within the resonance bandwidth of a Lissajous scanner. This selection rule provides a new guideline for HDHF Lissajous scanning in compact laser scanning systems.

Forward-viewing endoscopic OCT catheter using asymmetrically resonant fiber scanner

This work presents a forward viewing endoscopic OCT catheter based on a resonant fiber scanning. Two-dimensional optical scanning in a Lissajous pattern was realized by a piezoelectric tube with quartered electrodes and asymmetrically resonant fiber cantilever. Asymmetrically resonant fiber cantilever was assembled by additional fiber fragment and silicon supporting structure to avoid mechanical coupling effect at resonance. The endoscopic catheter of 3.2 mm diameter was assembled and combined with SD-OCT system. Three dimensional images were directly reconstructed by mapping the A-line data sets along non-repeating Lissajous trajectories with high temporal resolution.

Fully packaged confocal endomicroscopic system using Lissajous fiber scanner for indocyanine green in-vivo imaging

This work presents a fully packaged confocal endomicroscopic system using Lissajous fiber scanner for in-vivo imaging. The confocal endomicroscopic system consists of a scanning probe part, an optical part, and an electrical part. The scanning probe uses resonant Lissajous fiber scanner based on a piezoelectric tube. The scanner successfully achieves 10 frame rate with ~ 1 kHz scanning frequencies. The probe was fully packaged for waterproofing and disinfection of medical instruments into the outer diameter of 3.4 mm. The endomicroscopic system and successfully obtained 2D reflectance imaging results, human ex-vivo imaging results and a real-time in-vivo imaging results.

Fully packaged video-rate confocal laser scanning endomicroscope using Lissajous fiber scanner

This paper reports a fully packaged confocal endomicroscope high resolution and high frame-rate (HRHF) Lissajous fiber scanning. The confocal endomicroscope features a resonant scanning fiber with ∼1kHz actuated by a piezoelectric tube (PZT). The Lissajous scanning with high resolution and high frame rate has been successfully achieved by using the selection rule of scanning frequency, i.e., strong correlation between the total lobe number of Lissajous images and the greatest common divisor (GCD) between two scanning frequencies. Our main results clearly demonstrate exceptional fill factor of 85 % at 10 Hz in frame rate. Besides, this fully packaged endomicroscopic catheter was further combined with a portable confocal microscopic system to obtain video-rate 2D reflectance as well as in-vivo mouse vascular imaging.

Mouse tissue imaging using real-time Lissajous confocal endomicroscopic system

We present mouse tissue imaging using real-time Lissajous confocal endomicroscopic system. The system consists of endomicroscopic catheter, confocal imaging system, and image processing module. The system obtained 2D fluorescence ex-vivo imaging results of mouse tissue.

Electrothermal MEMS fiber scanner with lissajous patterns for endomicroscopic applications

We report an electrothermal MEMS fiber scanner with Lissajous patterns for endomicroscopic applications. The MEMS fiber scanner consists of a double hot arm structure, and a directly mounted optical fiber. The mounted single mode optical fiber moves to angled direction due to both lateral and vertical force of MEMS fiber scanner due to Joule heating. Besides, top silicon structure makes resonance separation of the single mode fiber in lateral, and vertical directions. Resonance frequency separation allows two-dimensional Lissajous scanning without any additional structures, and Lissajous patterns were successfully obtained within 16 Vpp. This scanner can give a new direction for compact and cost-effective endomicroscopic catheter.