臺大光電所所訊

Development of mesoscopic nonlinear imaging system with record-dense sampling capability

Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所孫啟光教授

Nonlinear imaging [1] of volumetric biological specimens can reveal its three-dimensional (3D) structural details with ultra-high spatial resolution, in terms of depth-resolved cross-sectional views with a better penetration capability due to the use of near-infrared (NIR) excitation spectrum and excitation localization of nonlinear optical absorption, in comparison to single-photon based imaging modalities. To facilitate high-speed, but aliasing-free laser-scanning of a centimeter-scale volumetric sample, an ultra-large field of view (FOV) is mandatory, which must be digitized with an ultra-fast sampling rate in order to fulfil the Nyquist Criterion, being a fundamental limitation to all the state-of-the-art mesoscopic imaging systems to date [2].

Our group has developed a nonlinear optical mesoscope (NLOM) with an extended FOV of up-to 1.6×1.6 mm² while preserving a smallest resolvable spacing of 0.48 μm. We further introduced a one-pulse-per-voxel extreme-synchronized-sampling for the first time in an NLOM with a FOV/ resolution ratio over 3000. Our record acquisition system holds the capability of simultaneously sampling 4 channels at up-to 125 MSps sampling-rate, reaching a record single-frame pixel number of 15720×16000 for each of the 4 channels, leading to a total of ~1 Gigapixels per frame, while maintaining ~0.5 fps; including real-time calibration, preview and storage of the acquired data in 16-bit format with 14-bit resolution.

Fig. 1(a) 3D view of coronal sections from medulla of a Nav1.8-tdTomato mouse; (b), (c) zoomed views of ROI R1 in (a). Red, green & cyan axes are X, Y & Z axes, respectively. Scale bars: (a) 0.2 mm, (b) 0.1 mm, (c) 0.05 mm.

Reference:

1. W. R. Zipfel, R. M. Williams, W. W. Webb, Nonlinear magic: multiphoton microscopy in the biosciences. Nature biotechnology, 21,1369–1377 (2003).

2. M. Balu, H. Mikami, J. Hou, E. O. Potma, B. J. Tromberg, Rapid mesoscale multiphoton microscopy of human skin. Biomedical Opt. Express 7, 4375-4387 (2016).

Study on the Design Parameters for Curved-Type Parallax-Barrier Dual-View Display

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所林晃巖教授

The 3D stereoscopic display makes both eyes to see the left and right image information separately, and recombine them to create stereoscopic vision. The dual-view display distributes the left and right images to each viewing zone, which can be realized through spatial multiplexing methods. The image information can be divided into different position by adding the parallax-barrier or lenticular-lens structures on the display system. The difference between the dual-view and 3D stereoscopic displays is that the viewing position is changed from the distance between both eyes of a person to the double viewing zones which can be designed by yourself. It becomes a technology that can provide at least two users on a single display at the same time. In recent years, the advancement of flexible substrate technology has brought attention to the issue of curved display. Curved displays provide screen-enlarged perception and immersive vision experience.

For the dual-view display, viewing position and the range nearby strongly affect image quality. Viewing zone describes the spatial range in front of the display where a viewer could move around while experiencing the corresponding image information. Regarding a curved dual-view display, radius and viewing angle of the screen determine the relative degrees of bending, by which the spatial light distribution can be determined. In addition, this is a key factor influencing image quality, especially for the display which directs the views for left and right viewing zones based on different image information. By using geometric optics and ray-tracing software, the viewing zone can be calculated and depicted, and discussed as given different curvature radius or viewing angle of the screen with refractive index substrate. Considering crosstalk and uniformity, we present a method to control the viewing zones by shifting parallax barrier in this study.

A curved-type parallax barrier dual-view display was constructed and shown as in Fig. 1(a). P_D and P_B are the pitches of the sub-pixel on display and the barrier aperture, respectively. A distance from the display to barrier is defined as f, a distance from barrier to a viewer is defined as Z_DEP, and the dual people distance (DPD) is marked as P_E. The geometric relationship is similar to our preview study for 3D stereoscopic displays. First, we take the emitting light rays through the sub-pixel edge to intersect in front of the display. Considering the radius of curvature, the design viewing positions on the left and right must be rotated into a plane parallel to the sub-pixels. The line of intersection point is the barrier, and the opening position of it can be calculated from the period of the barrier. By connecting the edge sub-pixels with the opening position of the parallax barrier, the right viewing zone, corresponding points STUV, can be calculated and depicted. ∆x and ∆z are the width and depth of the viewing zone, respectively. The left viewing zone can calculated an depicted in the same way.

Considering crosstalk and uniformity, it is defined that the crosstalk value must be less than 10%. Under the condition, the received image information will not be blurred or distorted. The uniformity value must be greater than 60%. Human eyes face the entire screen so that there is no uneven brightness problem. Spatial luminance distribution of the right viewing zone is shown as Fig. 2, (a) without considering crosstalk and uniformity, and (b) with crosstalk and uniformity situation.

Fig. 1. Construction of curved type parallax barrier dual-view display

Fig. 2. Spatial luminance distribution of the right viewing zone

Reference:

Yen-Wen Lin, Wei-Chen Chen, Hoang Yan Lin, Study on the Design Parameters for Curved-Type Parallax-Barrier Dual-View Display, submitted to OPTIC 2020.