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Long working range light field microscope with fast scanning multifocal liquid crystal microlens array

Po-Yuan Hsieh, Ping-Yen Chou, Hsiu-An Lin, Chao-Yu Chu, Cheng-Ting Huang, Chun-Ho Chen, Zong Qin, Manuel Martinez Corral, Bahram Javidi, and Yi-Pai Huang

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Abstract

The light field microscope has the potential of recording the 3D information of biological specimens in real time with a conventional light source. To further extend the depth of field to broaden its applications, in this paper, we proposed a multifocal high-resistance liquid crystal microlens array instead of the fixed microlens array. The developed multifocal liquid crystal microlens array can provide high quality point spread function in multiple focal lengths. By adjusting the focal length of the liquid crystal microlens array sequentially, the total working range of the light field microscope can be much extended. Furthermore, in our proposed system, the intermediate image was placed in the virtual image space of the microlens array, where the condition of the lenslets numerical aperture was considerably smaller. Consequently, a thin-cell-gap liquid crystal microlens array with fast response time can be implemented for time-multiplexed scanning.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

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Figures (17)
Fig. 1
Fig. 1 Schematic lay out of the LFM as reported by Levoy et al.

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Fig. 2
Fig. 2 The LFM working in the plenoptic 2.0 mode. In the scheme p stands for the MLA pitch, and δ for the pixel size.

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Fig. 3
Fig. 3 The FOV of any microimage. (a) LFM working in real mode; (b) LFM working in virtual mode.

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Fig. 4
Fig. 4 Scheme for the calculation of the size of the defocused light spot.

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Fig. 5
Fig. 5 Effective resolution ratio corresponding to the host microscope and the LFM. The position z=0 is at the optimal focus plane a=−2.25 mm.

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Fig. 6
Fig. 6 The extended working range of the LFM with multifocal LC-MLA.

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Fig. 7
Fig. 7 Effective resolution ratio (ERR) and working range of the LFM (a) with the fixed MLA and (b) with the multifocal LC-MLA. The MLA plane is set at a=0. The symbol a is the depth from the intermediate image plane to the MLA plane.

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Fig. 8
Fig. 8 (a) Section view and (b) hexagonal electrode pattern of the HiR LC-MLA.

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Fig. 9
Fig. 9 R-C circuit model of an LC microlens with the HiR layer.

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Fig. 10
Fig. 10 Electric field distribution and LC molecule orientation of the (a) conventional fringe-field-controlled LC lens without the HiR layer and (b) HiR LC lens.

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Fig. 11
Fig. 11 Interference patterns of the (a) conventional fringe-field-controlled LC-MLA and (b) HiR LC-MLA.

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Fig. 12
Fig. 12 Interference patterns (IPs) and point spread functions (PSFs) of the HiR LC-MLA with different focal lengths. Microlens aperture size: ϕ ML =350 μm; LC cell gap: d LC =60 μm.

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Fig. 13
Fig. 13 Focal length of the HiR LC-MLA with different driving frequencies. Microlens aperture size: ϕ ML =350 μm; LC cell gap: d LC =60 μm; driving voltage: V=2.6 V rms .

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Fig. 14
Fig. 14 Intermediate image placed in the (a) real image space and (b) virtual image space of LC-MLA. The thickness and numerical aperture of the LC-MLA in real mode are larger than those in virtual mode.

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Fig. 15
Fig. 15 Raw light field image with f ML =3.5 mm. The partial enlarged views show that (a) the root ( a=−6.0 mm) of the wing is out-of-focus, and (b) the tip ( a=−1.4 mm ) of the wing is in-focus.

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Fig. 16
Fig. 16 Rendered images of the LFM with (a) fixed focal length MLA and (b) multifocal HiR LC-MLA that refocuses at different depth planes.

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Fig. 17
Fig. 17 Effective resolution ratio and total working range of the light field microscope with the tunable-focus HiR LC-MLA, which covers from a=−1 mm to a=−7.99 mm in the intermediate space.

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Tables (1)

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Table 1 HiR LC-MLA with a large aperture size, high N A ML , and fast response time.

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Equations (18)

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( x θ )=( − f ob / f L 0 0 − f L / f ob )( x' θ' )=( γ 0 0 M )( x' θ' ).
1 a + 1 g = 1 f ML ,
ρ''=max{ δ, s λ }.
s( z )= ϕ ML | g f ML − g a−z' −1 |= ϕ ML | g f ML − g a− M 2 z −1 |,
ρ''( z )=max{ δ, s λ ,s( z ) }.
ρ'( z )= ρ'' | M ML | = | a− M 2 z | g ρ'',
ρ( z )= ρ'( z ) | M | = f ob | a− M 2 z | f L g ρ''( z ).
ρ ' hst ( z )=max{ δ, 0.5λM NA ,2NA| zM | },
ERR( z )= ρ ' hst ( 0 ) ρ'( z ) .
ER R hst ( z )= ρ ' hst ( 0 ) ρ ' hst ( z ) .
ER R max = δ⋅ ϕ ML λ⋅| a | + δ ϕ ML ,
WR= 1 M 2 ⋅ 2δ| a | ER R min ⋅ ϕ ML ,
W R total = 1 M 2 ( | a N − a 1 |+ δ| a N + a 1 | ϕ ML ⋅ER R min ),
f ML = ϕ ML 2 8⋅Δn⋅ d LC ,
δ⋅ ϕ ML λ⋅| a | + δ ϕ ML ≥ER R min .
1 M 2 ⋅ 2δ| a | ER R min ⋅ ϕ ML ≥ d hst .
λ⋅( ER R min − δ ϕ ML ) 2δ + α' 2κ ≤N A ML ≤ δ M 2 ⋅ d hst ⋅ER R min + α' 2κ ,
α' 2κ − δ M 2 ⋅ d hst ⋅ER R min ≤N A ML ≤ α' 2κ − λ⋅( ER R min − δ ϕ ML ) 2δ .
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