Dynamic Optical Systems Research Articles

Calculating non-scalar diffraction efficiently via merging Braunbek method and Bluestein method

Diffraction is an optical phenomenon that is commonly investigated for its applications in many optical systems, such as diffractive optical elements, microscopy, and coronagraphs. Current models for predicting diffraction typically suffer from either efficiency or accuracy. This paper addressed both issues by implementing techniques inspired by Braunbek method and Bluestein method. A modification to the Kirchhoffs boundary conditions is used to improve the theoretical model, and the Chirp-z transform is applied instead of the fast Fourier transform for more flexible calculations. A comparison between diffraction patterns for different models shows that the new method exceeds in accuracy. A comparison of time between numerical methods demonstrates that the chirp-z transform is faster in computation than the fast Fourier transform by about a minute. The method introduced provides many implications, such as the enhancement of dynamic optical systems and the improvement of flexibility in other realms of numerical Fourier transform.

Active metasurfaces based on phase transition material vanadium dioxide

Dynamic properties play a vital role in modern optical devices, including light detection and ranging systems, display devices, and digital cameras. Active metasurfaces provide an attractive scheme for the miniaturization and integration of dynamic optical systems compared with traditional bulk optical devices. Phase transition materials are great candidates for the design of active metasurfaces due to their high contrast refractive index and simple control characteristics. Here, we present a tunable metalens and switchable image coding metasurface in the near-infrared region through the control of the phase transition of vanadium oxide. By adjusting the phase transition of vanadium oxide, the focal intensity of the metalens is changed, and a switching effect with an intensity contrast of ∼12 times is demonstrated. In addition, the switchable imaging of two different numbers has been achieved in two different phase states. This work provides potential opportunities to realize active metasurfaces for imaging and encryption systems.

Linearization of nonlinear frequency modulated continuous wave generation using model-based reinforcement learning.

The prevalence of machine learning (ML) opens up new directions for plenty of scientific fields. The development of optics technologies also benefits from it. However, due to the complex properties of nonlinear and dynamic optical systems, optical system control with ML is still in its infancy. In this manuscript, to demonstrate the feasibility of optical system control using reinforcement learning (RL), i.e., a branch of ML, we solve the linearization problem in the frequency modulated continuous wave (FMCW) generation with the model-based RL method. The experiment results indicate an excellent improvement in the linearity of the generated FMCW, showing a sharp peak in the frequency spectrum. We confirm that the RL method learns the implicit physical characteristics very well and accomplishes the goal of the linear FMCW generation effectively, indicating that the marriage of ML and optics systems could have the potential to open a new era for the development of optical system control.

Varifocal diffractive lenses for multi-depth microscope imaging.

Flat optical elements enable the realization of ultra-thin devices able to either reproduce or overcome the functionalities of standard bulky components. The fabrication of these elements involves the structuration of material surfaces on the light wavelength scale, whose geometry has to be carefully designed to achieve the desired optical functionality. In addition to the limits imposed by lithographic design-performance compromises, their optical behavior cannot be accurately tuned afterward, making them difficult to integrate in dynamic optical systems. Here we show the realization of fully reconfigurable flat varifocal diffractive lens, which can be in-place realized, erased and reshaped directly on the surface of an azopolymer film by an all-optical holographic process. Integrating the lens in the same optical system used as standard refractive microscope, results in a hybrid microscope capable of multi-depth object imaging. Our approach demonstrates that reshapable flat optics can be a valid choice to integrate, or even substitute, modern optical systems for advanced functionalities.

Design and Analysis of a 2-D Piezoelectric Platform Based on Three-Stage Amplification and L-Shaped Guiding

In piezoelectric micro-positioning platforms, the displacement amplification mechanism can solve the small output displacement of the platform; the displacement coupling will also increase when the displacement is amplified. To solve the problem of multistage displacement amplification and displacement coupling after multistage displacement amplification, this study proposes a two-dimensional piezoelectric platform based on three-stage amplification and L-shaped guiding. First, the structure of the two-dimensional piezoelectric platform is designed and its working principle is described. Next, the two-dimensional piezoelectric platform is analyzed theoretically, and the static and dynamic characteristics of the structure are analyzed by the finite element method. Finally, a prototype of the two-dimensional piezoelectric platform is fabricated, and the theoretical and simulation results are analyzed experimentally. The experimental results reveal that the platform has a motion range of 31.8 μm × 41 μm. The multistage displacement amplification ratio is 21.8, and the displacement coupling error is less than 4.2%. The positioning error of the closed-loop control platform is less than 0.5%, and the trajectory tracking error is less than 1.6%. Compared with the traditional piezoelectric micro-positioning platform, the three-stage amplification and L-shaped guiding mechanism can effectively improve the displacement magnification and decoupling performance of the piezoelectric micro-positioning platform as well as the positioning ability and trajectory tracking ability of the platform under closed-loop control, which is expected to be utilized in fields such as multi-stage amplification micro-positioning platforms and dynamic optical systems.

Generalized phase profile design method for tunable devices using bilayer metasurfaces

Tunable devices based on bilayer metasurfaces have attracted researchers’ attention in recent years for their accurate tuning abilities and high integration. In tunable devices such as tunable beam splitters and Alvarez metalenses, opposite quadratic or cubic target phase profiles are imparted on both layers, and a varying total phase profile arises through the relatively lateral displacement between the two layers. However, there is a lack of a generalized target phase profile design method to design these tunable devices. In this study, a generalized phase profile design method named Integral of Total Phase Profile Difference (ITPD) is proposed to calculate the target phase profiles of both layers. Multiple integral equations describe the relationship between the target phase profiles and the total phase profiles. Based on this method, a tunable beam splitter and an Alvarez metalens are redesigned respectively. Moreover, a new tunable device that can be converted from a beam splitter to a metalens is designed by the ITPD method. The ITPD design method is promising for designing tunable devices with arbitrary total phase profiles in dynamic or multifunctional optical systems.

Effect of beam shape and spatial energy distribution on weld bead geometry in conduction welding

The size of a projected beam onto a workpiece and its intensity distribution profile defines the response of the material to the applied laser heat. This means that not only the processing parameters, but also the optical set-up and process tools define the process and the resulting weld profile. In high power laser delivery systems the beam propagation characteristics of the laser beam can vary during processing. A change of the focal distance, for instance, alters the spot size projected on the workpiece as well as its intensity distribution. Some dynamic optical systems can also change the shape of the projected beam. Galvo-scanners induce a small distortion to the projected beam from circular to elliptical when the mirrors deflect the beam across the working domain. This continuous change of the spatial energy distribution may affect the process stability and material response locally. This work examines the influence of changing the shape of the projected beam and its energy distribution on the weld bead profile in conduction laser welding, which is also relevant to laser cladding and additive manufacture. It has been found that for the same optical set-up and system parameters, different bead profiles can be obtained with different degree of distortion of the beam profile. In addition, different intensity distribution profiles led to different penetration depths for the same nominal beam diameter and energy density due to the difference in peak intensity.

Bi-phase emulsion droplets as dynamic fluid optical systems

Micro-scale optical components play a critical role in many applications, in particular when these components are capable of dynamically responding to different stimuli with a controlled variation of their optical behavior. Here, we discuss the potential of micro-scale bi-phase emulsion droplets as a material platform for dynamic fluid optical components. Such droplets act as liquid compound micro-lenses with dynamically tunable focal lengths. They can be reconfigured to focus or scatter light and form images. In addition, we discuss how these droplets can be used to create iridescent structural color with large angular spectral separation. Experimental demonstrations of the emulsion droplet optics are complemented by theoretical analysis and wave-optical modelling. Finally, we provide evidence of the droplets utility as fluidic optical elements in potential application scenarios.

Joint monitoring of chromatic dispersion, OSNR and inter-channel nonlinearity by LFM pilot

A novel joint monitoring method is proposed for dynamic and reconfigurable optical transmission systems to estimate chromatic dispersion (CD), optical signal-to-noise ratio (OSNR) and inter-channel nonlinearity (NL) simultaneously. This method utilizes two linear-frequency modulation (LFM) pilots with different center frequencies at two polarizations. The CD is estimated by the peak position difference of two pilots in fractional domain. Compare to previous work of CD estimation, the monitoring precision of CD is improved by zero padding at the receiver. The OSNR and the inter-channel NL are obtained in frequency and fractional domain. By verification of 9-channel 28 GBaud wavelength division multiplexing QPSK and 16QAM systems after 1000 km transmission, it proves that this method achieves stable CD (<200 ps/nm error), nonlinearity tolerant OSNR and accurate inter-channel NL (<1 dB error) monitoring.

Varifocal zoom imaging with large area focal length adjustable metalenses

Varifocal lenses are essential components of dynamic optical systems with applications in photography, mixed reality, and microscopy. Metasurface optics has strong potential for creating tunable flat optics. Existing tunable metalenses, however, typically require microelectromechanical actuators, which cannot be scaled to large area devices, or rely on high voltages to stretch a flexible substrate and achieve a sufficient tuning range. Here, we build a 1 cm aperture varifocal metalens system at 1550 nm wavelength inspired by an Alvarez lens, fabricated using high-throughput stepper photolithography. We demonstrate a nonlinear change in focal length by minimally actuating two cubic phase metasurfaces laterally, with focusing efficiency as high as 57% and a wide focal length change of more than 6 cm (> 200%). We also test a lens design at visible wavelength and conduct varifocal zoom imaging with a demonstrated 4x zoom capability without any other optical elements in the imaging path.

Recombinant reflectin‐based optical materials

AbstractReflectins are a unique group of structural proteins involved in dynamic optical systems in cephalopods that modulate incident light or bioluminescence. We describe cloning, structural characterization, and optical properties of a reflectin‐based domain, refCBA, from reflectin 1a of Hawaiian bobtail squid, Euprymna scolopes. Thin films created from the recombinant protein refCBA display interesting optical features when the recombinant protein is appropriately organized. RefCBA was cloned and expressed as a soluble protein enabling purification, with little structural organization found using Fourier transform infrared spectroscopy and circular dichroism. Single‐layer and multi‐layer thin films of refCBA were then produced by flow coating and spin coating, and displayed colors due to thin film interference. Diffraction experiments showed the assemblies were ordered enough to work as diffraction gratings to generate diffraction patterns. Nano‐spheres and lamellar microstructures of refCBA samples were observed by scanning electron microscopy and atomic force microscopy. Despite the reduced complexity of the refCBA protein compared to natural reflectins, unique biomaterials with similar properties to reflectins were generated by self‐assembled reflectin‐based refCBA molecules. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013

Coherent stitching of light in multilayered diffractive optical elements

Diffractive optical elements serve an important function in many dynamic and static optical systems. Multilayered diffractive elements offer powerful opportunity to harness both phase and amplitude modulation for benefits in diffraction efficiency and beam shaping. However, multilayered combinations have been difficult to fabricate and provide only weak diffraction for phase gratings with low refractive index contrast. Femtosecond laser writing of finely-pitched multilayer volume gratings was optimized in bulk fused silica. We identify and quantify an optimum layer-to-layer separation according to Talbot self-imaging planes and present systematic experimental validation of this new approach to enhance otherwise weakly diffracting volume gratings.

Azobenzene liquid crystal polymer-based membrane and cantilever optical systems

Optically deformable membranes and cantilevers based on azobenzene liquid crystal polymer networks (azo-LCN) are demonstrated in the context of dynamic optical systems. Large modulations in laser beam propagation direction or amplitude directed by laser-induced changes in material shape are demonstrated. These macroscopic shape changes are induced by local changes to the liquid crystalline order induced by photoisomerization processes. We demonstrate herein a number of concepts including the focusing and defocusing action of an azo-LCN membrane, laser beam steering from a bimorph azo-LCN/metal cantilever, and surface initiated bending and blocking of a parallel propagating laser beam. High speed and large angle deformations of an incident or reference beam is demonstrated when coupled into suitable optical architectures. The concepts under discussion appear to be highly practical for a number of applications due to the significant nonlinearity and photosensitivity of azo-LCN materials.

Physically constrained routing in 10-gb/s DWDM networks including fiber nonlinearities and polarization effects

Dynamic optical communication systems require fast assessment of the signal quality of the desired path through the network. This paper presents an analytical approach for describing the Q-factor due to linear (group velocity dispersion, noise, and polarization-mode dispersion) as well as the dominant nonlinear effects in 10-Gb/s nonreturn-to-zero ON-OFF keying transmission systems.

Motion capture and visualization of the hip joint with dynamic MRI and optical systems

We present a methodology for motion tracking and visualization of the hip joint by combining MR images and optical motion capture systems. MRI is typically used to capture the subject's anatomy whi...

Motion capture and visualization of the hip joint with dynamic MRI and optical systems

AbstractWe present a methodology for motion tracking and visualization of the hip joint by combining MR images and optical motion capture systems. MRI is typically used to capture the subject's anatomy while optical systems are used to capture and analyse the relative movement between adjacent bones of the joint. Reflective markers are attached to the subject's skin and their trajectories are tracked and processed. However, the skin surface deforms while in motion due to muscle contraction leading to significant errors in the estimation of trajectories. In order to reduce these errors, we use MR images to capture both the anatomy and the trajectories of the bone. Prior to the scanning, we attach skin markers to the subject in order to analyse the markers displacements relative to the bone. We reconstruct the anatomical models of the subject and we compute the markers trajectories from the images. Using these calculated trajectories, we select the best markers configuration based on the criteria of markers displacements. The optimized configuration is used for recording external movements with the optical motion capture system. The resulting animation is mapped onto the virtual body of the subject including internal bones and the joint motion is visualized. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Analysis of a widely tunable long-period grating by use of an ultrathin cladding layer and higher-order cladding mode coupling

A widely tunable long-period grating in single-mode fiber is analyzed by use of an ultrathin cladding layer and higher-order cladding mode coupling. The numerical simulation shows that a 225-nm tuning range in the newly designed ultrathin long-period grating (cladding thickness, 35 microm) with third-order cladding mode coupling can be obtained. The analyzed tuning range is seven times wider than those of the other known long-period gratings. We believe that the proposed highly sensitive long-period grating will be widely used as a gain-flattening filter for ultrawideband optical amplifiers and fast tunable filters in dynamic optical communication systems.