Oscillatory trajectory of an optical beam propagating in free space.

We describe the experimental observation of nonrectilinear trajectories of a nearly Gaussian light beam propagating in free space, after reflecting from a glass-air interface near critical incidence. The angular-dependent reflection coefficients modulate the incident beam's angular spectrum, shifting the reflected beam from the rectilinear path predicted by geometrical optics. The beam trajectory shows strong dependence on the angle of incidence, changing from rectilinear to oscillatory within 0.07°. Our experimental results are in good agreement with theoretical predictions for the trajectories followed by the intensity peak of the reflected beam.

Direct measurement of the composite Goos-Hänchen shift of an optical beam.

We experimentally study the Goos-Hänchen shift of a focused Gaussian optical beam in the critical region of incidence. We directly measure the beam's shift evaluated from the displacement of the location of the beam's intensity peak and its centroid by a novel image analysis method. We verify that the evaluation method has a dramatic impact on the physics of beam shift phenomena. The influence of wavelength, beam waist, and propagation distance on the beam shift is studied. Our experimental results confirm recent theoretical predictions about the composite Goos-Hänchen shift, including the observation of negative shifts of the beam's intensity peak.

Side-lobe level reduction in bio-inspired optical phased-array antennas.

Phased arrays are expected to play a critical role in visible and infrared wireless systems. Their improved performance compared to single element antennas finds uses in communications, imaging, and sensing. However, fabrication of photonic antennas and their feeding network require long element separation, leading to the appearance of secondary radiation lobes and, consequently, crosstalk and interference. In this work, we experimentally show that by arranging the elements according to the Fermat's spiral, the side lobe level (SLL) can be reduced. This reduction is proved in a CMOS-compatible 8-element array, revealing a SLL decrement of 0.9 dB. Arrays with larger numbers of elements and inter-element spacing are demonstrated through an spatial light modulator (SLM) and an SLL drop of 6.9 dB is measured for a 64-element array. The reduced SLL, consequently, makes the proposed approach a promising candidate for applications in which antenna gain, power loss, or information security are key requirements.

Weak measurement of the composite Goos-Hänchen shift in the critical region.

By using a weak measurement technique, we investigated the interplay between the angular and the lateral Goos-Hänchen shift of a focused He-Ne laser beam for incidence near the critical angle. We verified that this interplay dramatically affects the composite Goos-Hänchen shift of the propagated beam. The experimental results confirm theoretical predictions that recently appeared in the literature.