Structured light, where complex optical fields are tailored in all their degrees of freedom, has become highly topical of late, advanced by a sophisticated toolkit comprising both linear and nonlinear optics. Removing undesired structure from light is far less developed, leveraging mostly on inverting the distortion, e.g., with adaptive optics or the inverse transmission matrix of a complex channel, both requiring that the distortion be fully characterized through appropriate measurement. We show that distortions in spatially structured light can be corrected through difference-frequency generation in a nonlinear crystal without any need for the distortion to be known. We demonstrate the versatility of our approach using a wide range of aberrations and structured light modes, including higher-order orbital angular momentum (OAM) beams, showing excellent recovery of the original undistorted field. To highlight the efficacy of this process, we deploy the system in a prepare-and-measure communications link with OAM, showing minimal cross talk even when the transmission channel is highly aberrated, and outline how the approach could be extended to alternative experimental modalities and nonlinear processes. Our demonstration of light-correcting light without the need for measurement opens an approach to measurement-free error correction for classical and quantum structured light, with direct applications in imaging, sensing, and communication.
When light propagates through aberrated optical systems, the resulting degradation in amplitude and phase has deleterious effects, for example, on resolution in imaging, spot sizes in focusing, and the beam quality factor of the output beam. Traditionally, this is either pre- or post-corrected by adaptive optics or phase conjugation. Here, we consider the medium as a complex channel and determine the corresponding eigenmodes which are impervious of the channel perturbation. We employ a quantum-inspired approach and apply it to the tilted lens as our example channel, a highly astigmatic system that is routinely used as a measure of orbital angular momentum. We find the eigenmodes analytically, show their robustness in a practical experiment, and outline how this approach may be extended to arbitrary astigmatic systems.
We investigate the orbital angular momentum mixing in frequency up-conversion with structured light beams. Phase and polarization vortex beams are coupled in noncollinear second harmonic generation under type-II phase matching. The spatial properties of the second harmonic beam are shaped by the combined features of the input beams. This effect creates a spin-orbit crosstalk allowing for angular momentum transfer between the two degrees of freedom. The information transfer between photonic degrees of freedom encoded on different wavelengths can be useful for connecting different physical platforms in quantum information protocols.
In this work we generate optical fields whose polarisation structures not only rotate about the propagation axis, but can be tailored to accelerate, independently from their spatial profiles. Here we will demonstrate how this can be achieved with orthogonal, scalar fields, represented by weighted superpositions of oppositely charged Bessel beams, through path interference with a beam-splitter. In addition to their creation, we investigate various aspects of these generated modes, such as their angular accelerating Stokes vectors and optical current or intensity transport between various local positions within the field. Finally, we present a digital analogy to measure such fields in order to reconstruct their state of polarisation via Stokes polarimetry. undefined In this work we generate optical fields whose polarisation structures not only rotate about the propagation axis, but can be tailored to accelerate, independently from their spatial profiles. Here we will demonstrate how this can be achieved with orthogonal, scalar fields, represented by weighted superpositions of oppositely charged Bessel beams, through path interference with a beam-splitter. In addition to their creation, we investigate various aspects of these generated modes, such as their angular accelerating Stokes vectors and optical current or intensity transport between various local positions within the field. Finally, we present a digital analogy to measure such fields in order to reconstruct their state of polarisation via Stokes polarimetry.
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