The far-field imaging properties of a high index microsphere lens spatially separated from the object are experimentally studied. Our experimental results show that, for a Blu-ray disk whose spacing is 300 nm, the high index microsphere lens also can discern the patterns of the object sample when the distance between the lens and the object is up to 5.4 μm. When the distance is increased from 0 to 5.4 μm, for the microsphere lens with a diameter of 24 μm, the lateral magnification increases from 3.5× to 5.5×, while the field of view decreases from 5.1 to 3.0 μm. By varying the distance between the lens and the object, the optical image can be optimized. We also indicate that the far-field imaging capability of a high index microsphere lens is dependent on the electromagnetic field intensity profile of the photonic nanojet under different positions of the microsphere lens.
In this reported work, three types of microlenses, the whole microsphere solid lens (W-SL), the melted microsphere solid lens (M-SL) and the microsphere solid lens semi-immersed in SU-8 resist (S-SL), have been fabricated from mircospheres with a diameter of 2.87 µm. Their imaging properties on the nanosphere arrays with diameters of 280-600 nm were experimentally studied. It was found that the shape of the microlens plays an important role in the imaging properties. The imaging resolution of the S-SL is the best as more high Fourier components of the object can be coupled into the lens, while the magnification (∼2.0×) of the M-SL is the largest.
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