Cui X et al. (2010), Wavefront image sensor chip.

ECB-ART-41738

Opt Express 2010 Aug 02;1816:16685-701. doi: 10.1364/OE.18.016685.

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Wavefront image sensor chip.

Cui X , Ren J , Tearney GJ , Yang C .

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We report the implementation of an image sensor chip, termed wavefront image sensor chip (WIS), that can measure both intensity/amplitude and phase front variations of a light wave separately and quantitatively. By monitoring the tightly confined transmitted light spots through a circular aperture grid in a high Fresnel number regime, we can measure both intensity and phase front variations with a high sampling density (11 microm) and high sensitivity (the sensitivity of normalized phase gradient measurement is 0.1 mrad under the typical working condition). By using WIS in a standard microscope, we can collect both bright-field (transmitted light intensity) and normalized phase gradient images. Our experiments further demonstrate that the normalized phase gradient images of polystyrene microspheres, unstained and stained starfish embryos, and strongly birefringent potato starch granules are improved versions of their corresponding differential interference contrast (DIC) microscope images in that they are artifact-free and quantitative. Besides phase microscopy, WIS can benefit machine recognition, object ranging, and texture assessment for a variety of applications.

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	Fig. 1. Wavefront image sensor chip. a, Schematic of the device under a vertical plane illumination. The WIS apertures (white circles) are defined on the metal (gray) coated 2D CMOS image sensor chip (light gray grid), the transparent spacer separates the apertures away from the image sensor chip, and the aperture projections (red circles) are evenly distributed on the image sensor chip. b, Change of the transmission and shift of the aperture projections under an unknown light wave. c, Simulation of the diffraction (in SU8 resin) of a 6 μm diameter WIS aperture defined on a perfect electric conductor (PEC) layer illuminated by a halogen lamp. d, The experimental data showing the self-focusing effect of a WIS aperture on an Al coated glass cover slip. The insets are the cross-sections of the aperture diffraction perpendicular to the z axis.
	Fig. 2. Measuring the diffraction of the WIS aperture under the illumination of a halogen lamp. A 6 µm aperture was first etched on an Al coated (150 nm thick) glass cover slip (refractive index of 1.5), and then illuminated by a halogen lamp (the central wavelength was 0.6 µm and the FWHM of the spectrum was 0.2 µm). The cross-sections of the aperture diffraction at different z plane was imaged by a microscope with an oil (refractive index of 1.5) immersed 100 × objective (N.A. = 1.3) by moving the focal plane of the microscope along z axis with a micrometer with the interval of 2 µm.
	Fig. 3. Prototypes of the WIS and WM. a, Apertures with 6 μm diameter and 11 μm spacing defined on the Al coated WIS. b, Fully integrated WIS is the size of a dime. c, Converting a standard optical microscope into a WM by simply adding the WIS onto the camera port.
	Fig. 4. Calibration experiment for the normalized phase gradient measurement of the WIS. a, b, The experimental setup under a vertical illumination and a tilted illumination which imposes a specific normalized phase gradient θx or θy with respect to the WIS. c, d, the normalized phase gradient responses of the WIS in both the x and y directions. Each data point is the average normalized phase gradient measurement of the 350 apertures from the central row of our WIS; each error bar corresponds to the standard deviation among them.
	Fig. 5. Normalized intensity gradient can also induce a shift to each aperture projection spot of the WIS.
	Fig. 6. Images of polystyrene microspheres. a, b, Bright-field and DIC images. c, d, e, Intensity, normalized phase gradient images of the WM in the y and x directions. The white arrows represent the directions of the contrast enhancement.
	Fig. 8. ( Media 1) Images of an unstained starfish embryo in the late gastrula stage. a, b, Bright-field and DIC images. c, d, e, Intensity, normalized phase gradient images of the WM in the y and x directions. f, Phase-gradient-vector magnitude image. g, h, Normalized phase gradient images of the WM in the 135□ and 45□ directions. The white arrows represent the directions of the contrast enhancement. α: gastrocoel.
	Fig. 10. Images of potato starch granules. a, b, Bright-field and DIC images. c, d, e, Intensity, normalized phase gradient images of the WM in the y and x directions. The white arrows represent the directions of the contrast enhancement.
	Fig. 7. Removing the component of the normalized intensity gradient from the normalized phase gradient image of the WIS in the x direction. (a) Normalized phase gradient image measured by the WIS. (b) Normalized intensity gradient induced image. (c) Corrected normalized phase gradient image. (d) Comparison among the line profiles from the above three images.
	Fig. 9. Images of a stained starfish embryo in the early gastrula stage. a, b, Bright-field and DIC images. c, d, e, Intensity, normalized phase gradient images of the WM in the y and x directions. f, Comparison of the line profiles between the DIC image and normalized phase gradient image of the WM in the y direction. α: blastocoel, β: the background, and γ: the fertilization membrane.

References [+] :

Arnison, Linear phase imaging using differential interference contrast microscopy. 2004, Pubmed