Detection Of Optical Vortices Research Articles

Generation and Detection of Optical Vortices with Multiple Cascaded Spiral Phase Plates

Spiral phase plate (SPP) is the widely used method in the generation of vortex beam (VB) with fixed topological charges (TCs) for specific wavelength. Although VB with large TCs can be directly generated by using the SPP with high vortex order. The fabrication of high-quality SPPs with high vortex orders usually requires complex manufacturing process and high machining accuracy. An alternative method to generate VBs with large TCs is cascaded multiple SPPs with low order. In this study, we numerically calculate the transmitted light field of cascaded multiple SPPs according to the Huygens–Fresnel diffraction integral, and perform the experimental verifications. Based on cascading 6 SPPs (3 SPPs with TCs of 2, and 3 SPPs with TCs 4, respectively), an VB with TCs as high as 18 is generated. Furthermore, The TCs of the generated VB are detected by coaxial and off-axis interfering with fundamental Gaussian beam or its conjugate beam, respectively. The generated fork and spiral patterns allow us to distinguish the value and sign of TCs carried by the VB. The experimental results coincide well with the theoretical simulations. The fork pattern shows better resolution than the spiral one, and the petal pattern with small spiral allows us to distinguish large TCs with a higher resolution.

Detection of the orbital angular momentum state of light using sinusoidally shaped phase grating

We demonstrate a method based on a unique sinusoidally shaped phased grating for efficient and nearly alignment free detection of both signs and modulus of the orbital angular momentum (OAM) of light. OAM detection efficiency is almost the same over the whole grating area. The capability and robustness of this method are demonstrated by detection of optical vortices with OAM topological charge up to 150 using a reflective phase-only liquid crystal on a silicon spatial light modulator.

Optical vortices in nanophotonics

In the last two decades, optical vortices carried by twisted light wavefronts have attracted a great deal of interest, providing not only new physical insights into light-matter interactions, but also a transformative platform for boosting optical information capacity. Meanwhile, advances in nanoscience and nanotechnology lead to the emerging field of nanophotonics, offering an unprecedented level of light manipulation via nanostructured materials and devices. Many exciting ideas and concepts come up when optical vortices meet nanophotonic devices. Here, we provide a mini review on recent achievements made in nanophotonics for the generation and detection of optical vortices and some of their applications.

Optical vortices in nanophotonics

In the last two decades, optical vortices carried by twisted light wavefronts have attracted a great deal of interest, providing not only new physical insights into light-matter interactions, but also a transformative platform for boosting optical information capacity. Meanwhile, advances in nanoscience and nanotechnology lead to the emerging field of nanophotonics, offering an unprecedented level of light manipulation via nanostructured materials and devices. Many exciting ideas and concepts come up when optical vortices meet nanophotonic devices. Here, we provide a mini review on recent achievements made in nanophotonics for the generation and detection of optical vortices and some of their applications.

Application of a binary curved fork grating for the generation and detection of optical vortices outside the focal plane

In this paper, we consider using a binary curved fork grating not only for the simultaneous formation of several Bessel vortex beams but also for detecting the presence of angular harmonics (optical vortices) in an analyzed beam outside the focal plane. In this case, we use the effect of a longitudinal shift of focus (or correlation peak) when the lens is supplemented with an axicon. The combination of a lens and an axicon provides, in the focal plane, the generation of narrow light rings whose radii do not depend on the vortex phase component. Thus, the detection of an optical vortex cannot be carried out in the focal plane, but only at a certain distance from it, which provides additional security for information transmission. In addition, the use of these gratings makes it possible to simultaneously manipulate microparticles in various planes, and they can be used for fabricating complex three-dimensional metastructures as well as the single-shot pulse laser processing of transparent materials or polymers.

Generation and detection of optical vortices using all fiber-optic system

We demonstrate simultaneous generation, propagation and detection of optical vortices using all fiber-optic system. A fiber-optic Y-coupler was used for generating spherical and doughnut beams, simultaneously. Gaussian (TEM 00) beam emitted from CW red He–Ne laser is coupled into the fiber coupler and is converted into vortex beam via second arm of fiber which propagates with azimuthal phase dependence having well defined orbital angular momentum. The phase structure of vortex beam was detected by interfering both the beams using simple fiber-optic interferometer. The present all fiber-optic system might find application for detecting, sensing physical parameters and is simple and cost effective for generating and detecting optical vortices.

Detection of phase singularity using a lateral shear interferometer

We demonstrate use of lateral shear interferometry for the detection of phase singularities in optical fields. Existing interferometric methods of vortex detection entail a separate reference wave front, either plane or spherical, to yield fork or spiral fringes as vortex signatures. The method of vortex detection reported here is a self-referencing technique, as the reference wave front required to form interference fringes is drawn from the test wave front itself. The technique is simple, robust and vibration insensitive. Isolated vortices as well as randomly distributed vortices in a speckle field are detected using this technique. It is shown that detection of optical vortices is possible even with an ordinary glass plate acting as the shear plate.

Shearograms of an optical phase singularity

Shearograms are known to represent phase gradients but when vortices are present in the optical field, these do not represent true phase gradients. Phase gradients of an optical phase singularity are presented. A lateral shear interferometer is used for obtaining shearograms of optical fields with vortices. A diffractive phase element is used to generate vortices. It is shown that shearograms can be used in the detection of optical vortices. Shearogram of speckle field is also presented.