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

Abstract

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.

Microscanners for optical endomicroscopic applications

“…2a. In addition, the intrinsic off-axis misalignment of a single fiber readily causes the mechanical coupling between the vertical and horizontal axes of a single scanning fiber [9].…”

“…Compared to the spiral scanning, the Lissajous scanning also shows high uniform illumination over the full scaned area. Lissajous scanners have been demonstrated by using a MEMS based lens scanner [13] and a fiber scanner [9]. The bottom image of Fig.…”

“…The endomicroscopic microscanners mainly divide into scanning mirror, a single optical fiber scanner [7,9,[14][15][16][17][18][19][20], or a lens scanner [13,[21][22][23][24]. First, the scanning MEMS mirrors are operated by using electrostatic [25][26][27][28][29][30][31], electromagnetic [22,32], or electrothermal [33][34][35][36][37][38][39] actuation.…”

“…The Lorentz force induces attractive and repulsive actuation, which can be selectively generated by changing the direction of a current flow inside active electric coils or permalloy. However, the compulsory existence of electric coils hampers the size reduction of an endomicroscopic [7], b Raster scanning [10], and c Lissajous scanning [9]. The corresponding scanning pattern in the upper and a representative image in the bottom images package.…”

“…Lissajous scanning fiber scanners have been recently developed by operating a piezoelectric tube at two different operating frequencies for both the directions after differentiating the bi-directional spring constants of an optical fiber. For instance, Park et al have reported Lissajous fiber scanner by using an off-set fiber fragment with micromachined silicon structures to separate the two resonant frequencies [9]. The silicon structures (0.5 × 0.5 × 1 mm 3 ) were located at 3.5 mm and 13.5 mm of the 20 mm long fiber apart from the actuator.…”