Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 51175479, U1704155), the Key Scientific Research Projects of the Higher Education Institutions of Henan Province, China (Grant Nos. 16A140035, 18A140032), and the Science and Technology Innovation Team in Colleges and Universities of Henan Province, China (Grant No. 18IRTSTHN016).
Received Date:17 December 2018
Accepted Date:19 February 2019
Available Online:01 May 2019
Published Online:20 May 2019
Abstract:Incoherent digital holography (IDH) is a recently proposed technique to record three-dimensional (3D) information about the object under incoherent illumination, which breaks the limitation that the holographic recording must be illuminated by coherent light sources and thus makes it usable in white-light and fluorescence illuminating circumstance. In particular, the fresnel incoherent correlation holography (FINCH) is an exemplary method which improves the imaging resolution power and efficiency of incoherent digital holography, and it can obtain 3D distribution of objects swiftly without scanning and moving. However, compared with the conventional optical holography, the FINCH system has a very small field-of-view due to the limitation of the pixel number and size of spatial light modulator (SLM). Therefore, expanding the recording field-of-view of FINCH system is very significant for the application of IDH. In the FINCH, the SLM is used as a diffractive beam splitter so that each spherical beam, originating from each object point, is split into two spherical beams with two different curve radii. Then the interference fringes between the two beams are recorded by CCD. In this paper, the field-of-view angle recorded by the SLM is proposed and analyzed based on the physical and numerical principles of the FINCH system. The field-of-view of imaging system is improved by increasing the effective diameter of SLM through moving the center of the dual-lens optical axis mounted on the SLM to the edge in different directions respectively. An optical setup of reflection mode is constructed to verify the theoretical analysis of this study, and the sub-holograms in different field-of-views are obtained by CCD through changing the masks displayed on the SLM sequentially. Then, the complex holograms in different field-of-views are obtained by using the three-step phase-shifting method, and the reconstructed images are acquired respectively through the angular spectrum method (ASM) by using a computer. Finally, the large field-of-view image is obtained by stitching the reconstructed images in each field-of-view by utilizing the matlab program. The experimental results show that the efficient recording field-of-view of SLM can be increased by 2.77 times with our proposed method. Accordingly, the recording field-of-view of the system is improved significantly. The recording field-of-view of the FINCH system will increase further if the center of the dual-lens optical axis continues to move toward the edge. Therefore, this study provides an important support for the further application of high resolution microscopic imaging with large field-of-view. Keywords:incoherent digital holography/ spatial light modulator/ imaging field-of-view/ field-of-view splicing
图 2 FINCH大视场成像原理图 (a) SLM记录视场角; (b)四次记录光轴中心位置; (c)九次记录光轴中心位置; (d)光轴中心处于图(b)中O点时的掩模; (e)光轴中心处于图(b)中B点时的掩模; (f)光轴中心处于图(c)中C点时的掩模 Figure2. Schematic diagrams of FINCH with large field-of-view imaging: (a) The recording field-of-view angle of SLM; (b) the central position of the optical axis for recording four times; (c) central position of optical axis for recording nine times; (d) optical axis center is at point O of (b); (e) optical axis center is at point B of (b); (f) optical axis center is at point C of (c).
在整个记录过程, 将SLM上加载的双透镜掩模按照图2(b)所示方式依次更换光轴中心的位置(掩模如图3所示), 分别进行FINCH记录, 并将各视场的子图像拼接融合获得大视场图像. 结合(2)式和(3)式, 可以计算出SLM的有效记录范围增大至原来的2.25倍. 如果按照图2(c)所示方式改变掩模双透镜光轴中心的位置(如图2(f)所示), 当图2(d)中的c点移至图2(f)中的c”点时, 同理可以计算出SLM的有效记录范围增大至最初的2.77倍. 假若将SLM幅面划分得更多, 双透镜光轴中心将继续向边缘移动, 最大会移动至SLM的最边缘, 此时SLM的有效记录面积达到最大, 为原来的4倍. 但划分的区域越多, FINCH记录的次数越多, 成像速度会大大降低. 图 3 双透镜光轴中心处于四个不同位置的掩模 Figure3. The masks with the center of dual-lens optical axis in four different positions