Recently, the method of multipoint interferometer (MI) was proposed to detect the orbital angular momentum (OAM), which could be used for measuring OAM of light from astronomical sources. However, this method is limit to low topological charge, because the interference pattern can repeat periodically. In order to solve this problem, we proposed an improved multipoint interferometer method (IMI) capable of measuring the OAM of optical vortex with arbitrary topological charge. However, the method of IMI is limited by complex interference patterns detection difficult. To overcome these disadvantages of MI and IMI, we proposed a method called DRI using screen plate with a binary ring slit and two pinholes. This method is demonstrated viability theoretically
Hitherto, methods to generate optical vortex beams have been widely researched, ranging from mode conversion to diffractive optical elements. However, bulky-sized traditional methods are unsuitable for nanophotonic systems, metasurface has become an alternative option for generating optical vortices. In this paper, a metasurface combining dynamic and geometric phases is proposed. Under the incidence of circular polarized light, optical vortices with different topological charges can be generated simultaneously by a single metasurface. The dynamic phase makes the topological charge of the vortex light vary with distance. The intensity distribution and relative distance of the focused vortices can be manipulated with different focal length of the metasurface. This method provides a new design to generate different vortices in a single device and has potential applications in particle capture and integrated optical systems.
Optical beam carrying orbital angular momentum(OAM) exhibits profound potential in optical communications, micromanipulation and other related fields due to its helical wavefront. However, complex configuration of manipulating optical vortices have hindered the realization of nanophotonic systems. Recently, owing to the ultrathin structure, plasmonic metasurfaces based on abrupt phase shift have aroused appreciable interest. In this paper, we introduce a multifunctional device that integrates a focusing apparatus and an orbital angular momentum generator by the use of the plasmonic metasurfaces. This metasurface combining Archimedean spirals and spatially variant nanoslits achieves plasmonic focusing and an optical needle in the near- and far-field, respectively. Moreover, generation of optical vortex beams is shown in the far- and near-field simultaneously, where light field can be arbitrarily manipulated. We expect this work to have further applications in integrated photonic systems.
Due to the spin-orbit Hall effect of light, the intensity distribution of the reflected light is related to the incident angle, spin-orbital angular momentum and the refractive index of the reflective surface. In this paper, we research the spin-orbit Hall effect in the reflection with incident vortex lights carrying spin and orbital angular momentum. Then, the orbital angular momentum (OAM) spectrum of the reflected light are calculated. Subsequently, owing to the fact that the light field is redistributed after reflection, we propose a method for measuring the refractive index of optical materials based on the OAM spectrum of the reflected light. This measurement technique has the advantage of high sensitivity and strong anti-interference ability. We expect this work to contribute to other fields of precise measurements.
The atmospheric turbulence can cause wavefront distortion when vortex beam carrying orbital angular momentum (OAM) propagates in free space. This brings challenges to the recognition of OAM modes. To realize effective recognition of multichannel vortex beams in atmospheric turbulence, a hybrid interference-convolutional neural network (CNN) scheme is proposed. Here, we compare two different approaches to identify the topological charges under different turbulence levels: the first is based on CNN only and the second is the hybrid scheme of interference and CNN. The simulation shows that the recognition performance of multiple vortex beams under different turbulence levels is improved by our hybrid scheme. Compared with the traditional CNN-based method, the interference-CNN scheme can further identify the sign of topological charge. Moreover, we generalize its feasibility through different kinds of vortex beams with a radial index of p ≠ 0. This provides a versatile tool for large-capacity optical communication based on OAM modes.
We introduce a method for detecting the topological charge of power-exponential-phase vortex beam(PEPVB) and its power-exponent parameter by using a Laguerre-Gaussian beam that interferes with a PEPVB. The intensity shows a unique flower pattern after interference. According to the number of petals l-l0 and the topological charge of LG light l0 , we can obtain the topological charge of the PEPVB 𝑙. One of the most significant characteristics of PEPVB is the petals in the interference pattern become narrower clockwise. Moreover, the angle of the largest petal Δφ gradually decreases with an increasing power-exponent parameter. By measuring the angle φ1, φ2, the value of the power-exponent parameter 𝑛 can be calculated.
Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer. In the case of 3D trapping with a single beam, this is termed optical tweezers. Optical tweezers are a powerful and noninvasive tool for manipulating small objects, and have become indispensable in many fields, including physics, biology, soft condensed matter, among others. In the early days, optical trapping was typically accomplished with a single Gaussian beam. In recent years, we have witnessed rapid progress in the use of structured light beams with customized phase, amplitude, and polarization in optical trapping. Unusual beam properties, such as phase singularities on-axis and propagation invariant nature, have opened up novel capabilities to the study of micromanipulation in liquid, air, and vacuum. We summarize the recent advances in the field of optical trapping using structured light beams.
A new 4×4 point to point router is investigated with the transfer matrix method. Its routing paths and low loss of power are successfully demonstrated. The proposed design is easily integrated to a larger scale with less microring resonators, and the power loss from the input port to the output port is demonstrated to be lower than 10%. All of the microrings designed here have the identical radii of 6.98 μm, and they are all in resonance at a wavelength of 1550 nm. Both the gap between the microring and the bus waveguide and the gap between two neighbouring rings are 100 nm. The width of bus waveguide as well as the microrings is designed to be 200 nm. Free spectral range (FSR) is supposed to be around 17 nm based on the parameters above. A large extinction ratio (ER) is also achieved, which shows the high coupling efficiency to a certain extent. Thermal tuning is employed to make the microrings be in resonance or not, not including the two microring resonators in the middle. In other words, the two microrings are always in resonance and transport signals when the input signals pass by them. Hence, only two microrings are needed to deal with if one wants to route a signal. Although this architecture is blocking and not available for multicasting and multiplexing, it is a valuable effort that could be available for some optical experiments on-chip, such as optical interconnection, optical router.
Based on the vectorial Raleigh-Sommerfeld diffraction integral, an analytical propagation equation of vectorial nonparaxial hollow Gaussian beams (HGBs) through an annular aperture is derived. The corresponding closed-forms for a circular aperture, a circular black screen, and unapertured case are given as special cases of the general results. The typical numerical examples are given to illustrate our analytical results. It is shown that the f parameter plays an important role in determining the nonparaxiality of vectorial apertured HGBs.
The anomalous spectral behaviors of a chirped Gaussian pulsed beam diffracted by an annular aperture in the turbulent atmosphere are studied. On the basis of the extended Huygens-Fresnel principle and by introducing a hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression for the spectral intensity of chirped Gaussian pulses diffracted by an annular aperture in the turbulent atmosphere is derived. The corresponding expressions for a circular aperture, a circular black screen, and the unapertured case are given as special cases of the general results. The relative spectral shift of diffracted chirped Gaussian pulses in the turbulent atmosphere versus the different values of the radius of the annular aperture and the different values of the position parameter are also studied and illustrated with numerical calculations. The results of this work have potential applications in information encoding and transmission in a turbulent atmosphere.
The far-field spectral characteristics of a space-time-dependent Gaussian pulsed beam passing through an annular aperture are studied. Based on the expansion of a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, some analytical expressions for the spectral distribution of the diffraction field are derived. The expressions for a circular black screen and a circular aperture are given as special cases of the general results. The red and blue shifts of the spectral intensity maximum and the spectral intensity shape distortion and distribution are studied and illustrated with numerical calculations.
The near-field-intensity distributions of diffusion-cooled axisymmetric folded-combined CO2 lasers are investigated. Formulas representing the near-field distributions for some typical kinds of folded-combined CO2 lasers are suggested, and the near-field-intensity profiles are calculated numerically and simulated. For several centimeters from the output mirror along the direction of the symmetric axis, the intensity in the output beam is very high and its radius (or width) is very small (approximately double waist radius). The frequency differences between different cavities would induce fluctuations of the intensity distribution, but the fluctuations are not distinctive. The near-field beam can be used directly in some industrial material processing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.