Phase-preserved optical elevator

Abstract

The unique superiority of transformation optics devices designed from coordinate transformation is their capability of recovering both ray trajectory and optical path length in light manipulation. However, very few experiments have been done so far to verify this dual-recovery property from viewpoints of both ray trajectory and optical path length simultaneously. The experimental difficulties arise from the fact that most previous optical transformation optics devices only work at the nano-scale; the lack of intercomparison between data from both optical path length and ray trajectory measurement in these experiments obscured the fact that the ray path was subject to a subwavelength lateral shift that was otherwise not easily perceivable and, instead, was pointed out theoretically [B. Zhang et al. Phys. Rev. Lett. 104, 233903, 2010]. Here, we use a simple macroscopic transformation optics device of phase-preserved optical elevator, which is a typical birefringent optical phenomenon that can virtually lift an optical image by a macroscopic distance, to demonstrate decisively the unique optical path length preservation property of transformation optics. The recovery of ray trajectory is first determined with no lateral shift in the reflected ray. The phase preservation is then verified with incoherent white-light interferometry without ambiguity and phase unwrapping.

An analogy strategy for transformation optics

“…Indeed, this is an intrinsic problem of isotropic cloaks with a truncated boundary [48]. However, the shifting effect is not significant at long wavelengths [47] and can be reduced by lowering the device physically [40] or optically [49]. Further simulations even confirmed that the performance will not be affected much if the present profile in figure 2(b) is truncated by a reasonably lower height.…”

Phase‐preserved macroscopic visible‐light carpet cloaking beyond two dimensions

“…Mirror 1 (M1) defined the reference path in air, and Mirror 2 (M2) defined the signal path where the light going through the cloak was reflected back. The coherence length of the laser source (central wavelength of ∼800 nm; spectral bandwidth of ∼20 nm) was calculated to be 14 μm , which we take as the nominal axial accuracy in the optical path length measurement. When an interference pattern was observed at the exit arm of the interferometer (such as the experimentally observed example in the inset in Fig.…”

“…To ensure high accuracy, we put the setup in air rather than in the laser liquid, whose validity has been justified in Ref. 20. As shown in Fig.…”

“…When an interference pattern was observed at the exit arm of the interferometer, precise optical path lengths of the reference path and the signal path were matched within the coherence length of the laser source. The coherence length of the laser source (central wavelength of ~800 nm; spectral bandwidth of ~20 nm) was calculated to be 14 μm [20,21], which we take as the nominal axial accuracy in the optical path length measurement. By comparing the locations of the reference mirror M1…”