使用液晶元件於高解析度與延展景深之光場顯微鏡

Resolution and Depth-of-field Enhanced Light Field Microscope with Liquid Crystal Devices

謝博元(Po-Yuan Hsieh)

指導教授 ： 黃乙白

國立交通大學/電機學院/光電工程系所/博士(2018年)

摘要

光場顯微鏡可以提供重新對焦、三維立體重建、立體視角等功能，是一種極具有潛力的立體顯微鏡系統。藉由在數位顯微鏡的成像面前插入一組微透鏡陣列，顯微鏡樣品的空間與角度資訊會被單獨分離，並記錄在二維影像中的不同位置(稱為光場影像)。然而，光場顯微鏡受限於自身過低的影像解析度，以及有限的景深範圍，目前還難以取代現有的立體顯微鏡系統(如共焦顯微鏡)。
本研究提出利用可電壓調變之液晶元件，搭配時間多工拍攝的方式，提升光場顯微鏡的橫向解析度並擴大景深範圍，使其有更廣泛的應用。首先，我們將楔形液晶盒放置在光場顯微鏡的光軸上，使得顯微鏡的中繼影像在微透鏡陣列上產生半個孔徑距離的位移。藉由時序性切換楔形液晶盒的折射率，可以提升光場顯微鏡的擷取頻率，從16 lp/mm提升至32 lp/mm，使得影像解析度提高。其次，我們發展出可電壓/頻率調變焦距的微型液晶透鏡陣列，藉由時序性切換液晶透鏡的焦平面位置，並且拍攝多組聚焦在不同深度的光場影像，可以有效延展光場顯微鏡的景深範圍，從原本的62.5 μm增加至436.8 μm。同時，藉由將中繼影像移動至微透鏡陣列的虛像空間，我們將液晶盒厚度縮小為一般液晶透鏡的六分之一，使得其反應時間縮短至80毫秒，更適合時間多工的應用需求。

關鍵字

液晶透鏡 ； 高阻值微型液晶透鏡陣列 ； 光場顯微鏡 ； 提高解析度 ； 延展景深

並列摘要

The light field microscope is a potential equipment for 3D microscope applications. It can produce the focal stacks and the perspective views of the 3D specimen with a single photograph. By inserting a microlens array in front of the digital sensor, each elemental image underneath the microlens stores a portion of spatial and angular information of micro specimens. Those elemental images compose the light field image, which records the 4D (two spatial-axes and two angular-axes) light field information of object space respectively. However, the light field microscope has two issues such as the low resolution and limited working range, which limit the light field microscope applications.
In this dissertation, we proposed the resolution and working range enhanced light field microscope with the tunable LC devices and the time-multiplexed method. First, we used the LC wedge to shift the intermediate images along the perpendicular direction and increase the spatial sampling density; thus the image resolution would be enhanced. The cut-off frequency of light field images was increased from 16 lp/mm to 32 lp/mm. Then, we developed the tunable focus high-resistance LC microlens array to replace the fixed MLA in the light field microscope. By capturing multiple light field image with different depth-of-focus ranges, the total working range of the proposed light field microscope was much extended from 62.5 μm to 436.8 μm, for observing the thick 3D specimens. Furthermore, the intermediate image was placed into the virtual image space of the microlens array, so that the conditions of the LC microlens array can be reduced, and the response time of the LC devices can be much faster for the time-multiplexed method.

並列關鍵字

Liquid Crystal Lens ； High-resistance Liquid Crystal Micro-lens Array ； Light Field Microscope ； Resolution Enhancement ； Extended Depth-of-Field

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