Abstract
We investigate the far-field pattern generation for a micro-lens array (MLA) illuminated under different conditions. Plane wave and Gaussian beam illumination are considered for an MLA with a small diameter of 27 microns and 30 microns period. At these dimensions, the optical effects are governed by diffraction and refraction and sometimes the regime is called the refraction limit. For Gaussian beam illumination, a high contrast dot pattern can be obtained in the far field according to the self-imaging theory for point source illumination and it is investigated in the simulation part. Also, we designed an interference microscopy setup to record both the phase and intensity in near field behind the MLA and also in the far field. The new instrument allows us to change illumination conditions from plane wave to point source. We then experimentally compare the near-field phase modulation and resulting far-field intensity for different conditions. For plane wave illumination, a high contrast pattern is observed in the far field. For the Gaussian beam illumination, the contrast of the far-field pattern depends on the distance of the source and MLA resulting in high contrast and a larger field of view only for particular distances depending on the interference of the Gaussian beam curved phase front and the MLA.
Highlights
Arbitrary light pattern generation has various applications including imaging, sensing, and microscopy [1, 2]
By employing periodic microoptical elements in the refraction diffraction regime, a structured pattern is generated that can be engineered by the optical element surface profile [9–12]
The near-field phase modulation shows the effect of the Gaussian beam wave-front in comparison to the uniform wave-front of plane wave illumination
Summary
Arbitrary light pattern generation has various applications including imaging, sensing, and microscopy [1, 2]. In many sensing and imaging applications, generating large numbers of points with a wide field of view and uniform intensity distribution over peaks is desired For this purpose, employing diffractive or micro-optical elements from thin to thick can be accomplished [3–5]. Designing the binary diffractive optical elements by applying optimization techniques, results in a structured pattern with a certain functionality [6, 7] Applying this technique is limited; for example, the fabrication errors can tend to unwanted energy in zero-order and outside the desired field of view [8]. In another scenario, by employing periodic microoptical elements in the refraction diffraction regime, a structured pattern is generated that can be engineered by the optical element surface profile [9–12]. We numerically and experimentally demonstrate that for certain values of the distance D, a high contrast pattern with a larger field of view compared to plane wave illumination can be generated in the far field
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