Two-dimensional Optical System Research Articles

Evaluation of a novel physically cross-linked fricke-xylenol orange-polyvinyl alcohol radio-chromic gel dosimeter for radiotherapy

In this work, a novel sensitive composition of Fricke radio-chromic gel dosimeter based on polyvinyl alcohol (PVA), xylenol orange (XO), and physical cross-linking agent gellan gum (GG) is presented and evaluated with two optically detection methods. The Fricke dosimeter was irradiated up to 30Gy using medical linear accelerator and analyzed optically using ultraviolet visible (UV–Vis) spectrophotometry technique at wavelengths of 585 nm (i.e., within the visible range) and two-dimensional optical imaging system of charge-coupled-device (CCD) camera with a uniform red light-emitting-diode (LED) array source. The Fricke dosimeter demonstrated important properties including independence of beam energy and dose rate over the range studied. In addition, these dosimeters have high sensitivity in the range of 0–10Gy, and significant low diffusion coefficient of 0.070 mm2 h−1. In addition, the composition shows a lower diffusion coefficient with respect to those reported so far for a Fricke dosimeter. The total uncertainty of the estimated doses for the Fricke dosimeter was 3.96% at 95% confidence level.

Optimizing the feasibility of polyvinyl alcohol-potassium iodine gel for medical dosimeter

This work aims to improve the post stabilty of reusable potassium iodide hydrogel dosimter. A reusable and low-cost radiochromic dosimeter containing a gel matrix of polyvinyl alcohol, potassium iodide dye, froctose as reducing agent and glutaraldehyde as cross-linking agent was developed for dose calibration in radiotherapy. The gel samples were exposed to different absorbed doses using a medical linear acceleration. UV–vis Spectrophotometry was utilized to investigate the changes in optical-properties of irradiated gels with regard to peak wavelength of 353 nm. The stability of the gel (one of the most limitation of using this dosimeter) was improved significantly by the addition of certain concentrations of dimethyl sulfoxide. The two-dimensional optical imaging system of charge-coupled-device (CCD) camera with a uniform RGB light-emitting-diode (LED) array source was used for diffusion coefficient purpose using two dimensional gel template. The value of diffusion coefficient reported is significant and highly reduced compared with other dosimeters reported in the literatures. Moreover, heating the improved gels to certain temperatures results in resetting their optical properties, which makes it possible to reuse for multiple times.

Mutual optical intensity propagation through non-ideal two-dimensional mirrors.

The mutual optical intensity (MOI) model is a partially coherent radiation propagation tool that can sequentially simulate beamline optics and provide beam intensity, local degree of coherence and phase distribution at any location along a beamline. This paper extends the MOI model to non-ideal two-dimensional (2D) optical systems, such as ellipsoidal and toroidal mirrors with 2D figure errors. Simulation results show that one can tune the trade-off between calculation efficiency and accuracy by varying the number of wavefront elements. The focal spot size of an ellipsoidal mirror calculated with 100 × 100 elements gives less than 0.4% deviation from that with 250 × 250 elements, and the computation speed is nearly two orders of magnitude faster. Effects of figure errors on 2D focusing are also demonstrated for a non-ideal ellipsoidal mirror and by comparing the toroidal and ellipsoidal mirrors. Finally, the MOI model is benchmarked against the multi-electron Synchrotron Radiation Workshop (SRW) code showing the model's high accuracy.

Generation of Bloch surface beams with arbitrarily designed phases.

We proposed a new manipulation method for Bloch surface waves that can almost arbitrarily modulate the lateral phase through in-plane wave-vector matching. The Bloch surface beam is generated by a laser beam from a glass substrate incident on a carefully designed nanoarray structure, which can provide the missing momentum between the two beams and set the required initial phase of the Bloch surface beam. An internal mode was used as a channel between the incident and surface beams to improve the excitation efficiency. Using this method, we successfully realized and demonstrated the properties of various Bloch surface beams, including subwavelength-focused, self-accelerating Airy, and diffraction-free collimated beams. This manipulation method, along with the generated Bloch surface beams, will facilitate the development of two-dimensional optical systems and benefit potential applications of lab-on-chip photonic integrations.

Aberration compensation in two-dimensional reflective optical systems

We present a novel approach to minimize aberrations in imaging systems. The energy distributions at the source and target of an optical system play a crucial role in designing freeform surfaces through illumination optics methodologies. We quantify the on-axis and off-axis aberrations using a merit function that depends on the energy distributions. The minimization of the merit function yields optimal energy distributions, which subsequently enable us to design freeform reflector surfaces that cause the least aberrations. We validate our method by testing it for two configurations, a single-reflector system with a parallel source to a near-field target, and a double-reflector system with a parallel source to a point target.

Rogue waves in nonlinear optics

Understanding the phenomenon of rogue wave formation, often called extreme waves, in diverse branches of nonlinear science has become one of the most attractive domains. Given the great richness of the new results and the increasing number of disciplines involved, we are focusing here on two pioneering fields: hydrodynamics and nonlinear optics. This tutorial aims to provide basic background and the recent developments on the formation of rogue waves in various systems in nonlinear optics, including laser physics and fiber optics. For this purpose we first discuss their formation in conservative systems, because most of the theoretical and analytical results have been realized in this context. By using a multiple space–time scale analysis, we review the derivation of the nonlinear Schrödinger equation from Maxwell’s equations supplemented by constitutive equations for Kerr materials. This fundamental equation describes the evolution of a slowly varying envelope of dispersive waves. This approximation has been widely used in the majority of systems, including plasma physics, fluid mechanics, and nonlinear fiber optics. The basic property of this generic model that governs the dynamics of many conservative systems is its integrability. In particular, we concentrate on a nonlinear regime where classical prototypes of rogue wave solutions, such as Akhmediev breathers, Peregrine, and Ma solitons are discussed as well as their experimental evidence in optics and hydrodynamics. The second part focuses on the generation of rogue waves in one- and two-dimensional dissipative optical systems. Specifically, we consider Kerr-based resonators for which we present a detailed derivation of the Lugiato–Lefever equation, assuming that the resonator length is shorter than the space scales of diffraction (or the time scale of the dispersion) and the nonlinearity. In addition, the system possesses a large Fresnel number, i.e., a large aspect ratio so that the resonator boundary conditions do not alter the central part of the beam. Dissipative structures such as solitons and modulational instability and their relation to frequency comb generation are discussed. The formation of rogue waves and the control employing time-delayed feedback are presented for both Kerr and semiconductor-based devices. The last part presents future perspectives on rogue waves to three-dimensional dispersive and diffractive nonlinear resonators.

Scattering by a collection of [formula omitted]-function point and parallel line defects in two dimensions

Interaction of waves with point and line defects is usually described by δ-function potentials supported on points or lines. In two dimensions, the scattering problem for a finite collection of point defects or parallel line defects is exactly solvable. This is not true when both point and parallel line defects are present. We offer a detailed treatment of the scattering problem for finite collections of point and parallel line defects in two dimensions. In particular, we perform the necessary renormalization of the coupling constants of the point defects, introduce an approximation scheme which allows for an analytic calculation of the scattering amplitude and Green’s function for the corresponding singular potential, investigate the consequences of perturbing this potential, and comment on the application of our results in the study of the geometric scattering of a particle moving on a curved surface containing point and line defects. Our results provide a basic framework for the study of spectral singularities and the corresponding lasing and antilasing phenomena in effectively two-dimensional optical systems involving lossy and/or active thin wires and parallel thin plates.

Fast spatial orthogonal frequency‐division multiplexing based on two‐dimensional discrete cosine transform for a pixelated optical wireless communication system

Pixelated two-dimensional (2-D) optical wireless communication systems, with intensity-modulation and direct-detection (IM/DD), are capable to transmit data at high data rates by modulating the data into image intensities at the transmitter. Frequency division modulation (FDM) and space-domain modulation (SDM) are two common modulation schemes in a 2-D pixelated system. Generally, FDM is preferred because FDM benefits from the capability of controlling the spectrum of transmitting signals so that the output signal could be shaped according to the characteristics of a particular optical channel. However, the computational complexity of FDM is relatively high and complex computation is needed at both the transmitter and the receiver. In this work, a fast orthogonal frequency-division multiplexing (FOFDM) modulation which employs 2-D inverse discrete cosine transform (IDCT2) instead of 2-D inverse Fourier transform (IFFT2) is presented. As the image intensities must be real and positive, two schemes are hereby introduced to generate unipolar image intensities. The proposed FOFDM is simulated and discussed in terms of key characterisations including the signal spectrum, spectral efficiency, peak to average power ratio (PAPR), bit error ratio (BER) and computational complexity. Compared with traditional spatial orthogonal frequency-division multiplexing (OFDM) based on IFFT2, the proposed FOFDM has similar BER performance, twice the spatial efficiency for the same constellation size, lower computational complexity and a much simpler structure in the transmitter.

Design of a large field-of-view two-dimensional geometrical waveguide

Geometrical waveguide has great advantages over conventional imaging systems, like larger field of view, larger exit pupil area, lower thickness and lighter weight. Two-dimensional (2D) geometrical waveguide can expand the vertical and horizontal pupil simultaneously, thus becoming a mainstream solution for commercial applications. The transmission path of two-dimensional optical system is more complicated and therefore the stray light in two-dimensional geometrical waveguide is more complex compared with one-dimensional waveguide. In this paper, the causes of stray light in 2D geometrical waveguide are discussed based on the non-sequential ray-tracing with detailed numerical analysis and the targeted solutions are developed to effectively improve the imaging quality. Consequently, a stray-light-free design of geometrical waveguide is proposed having the field of view reaching 49° × 56° with 22.6 mm × 26 mm eye box at 20 mm eye relief.

Inverse ray mapping in phase space for two-dimensional reflective optical systems

A new method to compute the target photometric variables of non-imaging optical systems is presented. The method is based on the phase space representation of each surface that forms the optical system. All surfaces can be modeled as detectors of the incident light and emitters of the reflected light. Moreover, we assume that the source can only emit light and the target can only receive light. Therefore, one phase space is taken into account for the source and one for the target. For the other surfaces both the source and target phase spaces are considered. The output intensity is computed from the rays that leave the source and hit the target. We implement the method for two-dimensional optical systems, and we compare the new method with Monte Carlo (MC) ray tracing. This paper is a proof of principle. Therefore, we present the results for systems formed by straight lines which are all located in the same medium. Numerical results show that the intensity found with the ray mapping method equals the exact intensity. Accuracy and speed advantages of several orders are observed with the new method.

"Short circuit" of power flux of light in near-zero refractive index metamaterials.

An interesting phenomenon of "short circuit" of the power flux of light arising from the electromagnetic decoupling has been discovered in a composite structure composed of epsilon-mu-near-zero medium (EMNZ) and epsilon-near-zero (ENZ). In the composite structure, the power flux of light goes around the ENZ components with any shapes and sizes and perfectly passes through the composite structure via the EMNZ until the connection of the EMNZ is broken. The ENZ components can freely manipulate the power flux of light flowing along arbitrary paths inside the EMNZ without reflection. In addition, we discover that the embedded ENZ components enhance the stability of transmission property of impure EMNZ effectively. The arbitrarily-shaped non-ENZ dopants of EMNZ are able to be well hidden by coating an ENZ cladding with moderate thickness, which is demonstrated through an actual structure composed of photonic crystals. In the area of transmission and processing of optical signal in two-dimensional integrated optical systems, the EMNZ-ENZ composite structure we construct employs potential application prospects.

Interference Solutions for the Deployed 2D Optical Coding PON Link Health Detection System With Massive Densely Distributed Customers

To process the complex link state signals and obtain the accurate failure decision criterion in the deployment of two-dimensional optical coding link health detection system to an actual PON system with massive densely distributed customers, we develop a customer distribution model which divide interference customers into two categories: sparse and dense distribution, and propose a code allocation rule by changing the connection between the output ports of encoder and access customers. Simulation results show that in 128-customer system with 2km2 coverage, customer interference probability is reduced by 0.129. The customer distribution model and the code allocation rule are demonstrated by experiment, and the results show that customer interference is significantly mitigated by using code allocation.

Higher-order topological states in a three-dimensional acoustic metamaterial

Topologically gapless edge states, characterized by topological invariants and Berry’s phases of bulk energy bands, provide amazing techniques to robustly control the reflectionless propagation of electrons, photons and phonons. Recently, a new family of topological phases, dictated by the bulk polarization, has been observed, leading to the discovery of the higher-order topological insulators. The higher-order topological states located on the “boundaries of boundaries” can be used to limit and control the transmission of optical waves, acoustic waves and elastic waves. So far, the higher-order topological states have been demonstrated in two-dimensional mechanical, electromagnetic, optical, acoustic and elastic systems. However, the study of higher-order topological states in three-dimensional acoustic systems, which can increase the possibility of topological metamaterial design, is rarely reported. In this letter, we propose a three-dimensional acoustic metamaterial supporting topologically protected second-order hinge states along with topologically protected first-order surface states within the same bandgap. Only the nearest neighbor couplings are considered in this metamaterial, and the coupling strengths can be adjusted by changing the diameters of the connection pipes. The intra-cell coupling strength t 1 is proportional to the diameters of the intra-cell connection pipes d 1, and the inter-cell coupling strength t 2 is proportional to the diameters of the inter-cell connecting pipes d 2. The band structure of the unit cell of three-dimensional acoustic metamaterial with the same intra-cell and inter-cell coupling strengths can form a two-fold nodal line along the K-H direction of its Brillouin zone. When intra-cell and inter-cell coupling strengths are different, the two-fold nodal line is lifted to form a complete bandgap, yielding two different kinds of acoustic metamaterials, that are, trivial and topological non-trivial metamaterials. The numerical results of band structures and eigenfrequencies indicate that: When the intra-cell coupling strength t 1 is less than the inter-cell coupling strength t 2, the acoustic metamaterial has 3 second-order hinge bands, 12 first-order surface bands and 18 second-order hinge eigenfrequencies, 72 first-order surface eigenfrequencies in the complete bandgap range respectively; when the inter-cell coupling strength t 2 is less than the intra-cell coupling strength t 1, there is neither any energy bands nor any eigenfrequencies in the complete bandgap range. The second-order hinge states and first-order surface states have great immunity against defects, favorably evidencing the strong robustness of the topological states. The numerical results of the transmission spectra furtherly verify the above phenomena. When t 1 2, the transmission spectrum of the second-order hinge reaches its peak at 4670 Hz. For the first-order surface transmission spectrum, a high peak, located in the bandgap, is observed around 4555 Hz. When t 1 >t 2, the surface and hinge transmission spectra are very low within the complete bandgap, the acoustic energy is concentrated only at the excitation cylinder, showing that the acoustic wave will not propagate in any part of the acoustic metamaterial in the complete bandgap range and the acoustic metamaterial is trivial. The realization of the higher-order topological states in three-dimensional acoustic metamaterial breaks through the limitation of that in two-dimensional system, realizes the topologically transform of acoustic energy among bulk, surface and hinge states and has the potential application prospect in acoustic energy recovery and high-precision acoustic sensor.

Crosstalk-Mitigated AWGR-Based Two-Dimensional IR Beam-Steered Indoor Optical Wireless Communication System With a High Spatial Resolution

In this paper, a crosstalk-mitigated transmission scheme in arrayed waveguide grating router (AWGR) based two dimensional infrared beam-steered optical wireless communication (OWC) system is proposed for indoor applications. By creating polarization orthogonality between the odd and even AWGR channels, high crosstalk tolerance between spectrally overlapping AWGR channels is realized experimentally. Because two signals with orthogonal polarization states will not beat with each other in a photodiode. The optical crosstalk on the orthogonal polarization state will not generate a beat note upon detection and thus crosstalk in the electrical domain can be largely reduced. Reduced crosstalk leads to a reduction in the required spectral guard band and/or an improved tolerance to spectral overlap, which allows higher spectral efficiency. Moreover, the port number of an AWGR can be increased by simply shortening the spatial gap between adjacent output waveguides on a chip. The higher port number can support the high spatial resolution of the steered OWC system. This technique can also tolerate the wavelength misalignment between AWGRs and lasers, which relaxes the design of low crosstalk AWGRs and high wavelength stable lasers. A 20 Gbit/s data rate, four-level pulse amplitude modulation OWC transmission has been experimentally demonstrated over 1.2-m free-space link. The experimental results show that the proposed scheme can maintain stable, low crosstalk impact with an apparent improvement of the responsivity.

Topological states in amorphous magnetic photonic lattices

Since the discovery of topological phases in optical systems, most of the efforts have been focused on the periodic and quasiperiodic optical structures which have both long-range and short-range orders. In this paper, we construct a kind of two-dimensional aperiodic optical systems, named the amorphous magnetic photonic lattices (AMPLs), which only have short-range orders, and investigate the topological states in these AMPLs. By using the supercell method, we build supercell magnetic photonic crystals as approximate equivalents of the AMPLs. Based on the band structure calculation and full wave simulation, we demonstrate the existence of single-mode and multimode topological edge states in these AMPLs. Through calculating the gapless edge states in reciprocal space, our research gives an intuitive understanding of the topology underlying aperiodic optical systems. Our system provides a platform to explore the relationship between short-range orders and topology and also paves an easy way to fabricate topological optical devices in application.

Quantification of Cerenkov Luminescence Imaging (CLI) Comparable With 3-D PET Standard Measurements.

Cerenkov luminescence imaging (CLI) is commonly performed using two-dimensional (2-D) conventional optical imaging systems for its cost-effective solution. However, quantification of CLI comparable to conventional three-dimensional positron emission tomography (PET) is challenging using these systems due to both the high attenuation of Cerenkov radiation (CR) on mouse tissue and nonexisting depth resolution of CLI using 2-D imaging systems (2-D CLI). In this study, we developed a model that estimates effective tissue attenuation coefficient and corrects the tissue attenuation of CLI signal intensity independent of tissue depth and size. To evaluate this model, we used several thin slices of ham as a phantom and placed a radionuclide (89Zr and 64Cu) inside the phantom at different tissue depths and sizes (2, 7, and 12 mm). We performed 2-D CLI and MicroPET/CT (Combined small animal PET and Computed Tomography (CT)) imaging of the phantom and in vivo mouse model after administration of 89Zr tracer. Estimates of the effective tissue attenuation coefficient (μeff) for 89Zr and 64Cu were ∼2.4 and ∼2.6 cm−1, respectively. The computed unit conversion factor to %ID/g from 2-D CLI signal was 2.74 × 10−3 μCi/radiance estimated from phantom study. After applying tissue attenuation correction and unit conversion to the in vivo animal study, an average quantification difference of 10% for spleen and 35% for liver was obtained compared to PET measurements. The proposed model provides comparable quantification accuracy to standard PET system independent of deep tissue CLI signal attenuation.

Ultra-thin Bloch-surface-wave-based reflector at telecommunication wavelength

We experimentally demonstrate the optical properties of gratings engraved in a single-mode waveguide fabricated on top of a dielectric multilayer platform. The structure can be approached as a reflector for Bloch-surface-wave-based two-dimensional optical systems. The gratings have been fabricated on a thin (∼λ/25) titanium dioxide layer with a thickness of a few tens of nanometers deposited on the top of a multilayer platform. The optical properties of the gratings have been characterized in the near field with the aid of multi-heterodyne scanning near-field optical microscopy. We investigate the surface wave’s interference pattern, produced by incident and reflected light in front of the gratings. The presented gratings behave as an efficient Bloch-surface–wave-based reflector at telecommunication wavelength.

Phase Space Ray Tracing for a Two-dimensional Parabolic Reflector

Ray tracing is a technique used in geometric optics for calculating the light distribution at the target of an optical system. Monte Carlo (MC) ray tracing is very common in non-imaging optics. We propose a new ray tracing method that employs the phase space of the source and the target of the system. The new method gives a more accurate target distribution than classical MC ray tracing and requires less computational time. It is tested for two-dimensional optical systems. The results for the paraboloid reflector are provided.

Bose-Einstein-condensed cold atoms in a lattice system with k -space Berry curvature

In this paper we study the properties of cold bosons in a two-dimensional optical lattice system where Bose-condensation occurs at a momentum point k with non-zero k-space Berry curvature. By combining results from both analytic and numerical approaches, we show that the boson system carries non-universal, temperature dependent equilibrium angular momentum and edge current at low temperatures.

Two-Dimensional Optical CDMA System Parameters Limitations for Wavelength Hopping/Time-Spreading Scheme based on Simulation Experiment

Abstract A new family of two-dimensional optical hybrid code which employs zero cross-correlation (ZCC) codes, constructed by the balanced incomplete block design BIBD, as both time-spreading and wavelength hopping patterns are used in this paper. The obtained codes have both off-peak autocorrelation and cross-correlation values respectively equal to zero and unity. The work in this paper is a computer experiment performed using Optisystem 9.0 software program as a simulator to determine the wavelength hopping/time spreading (WH/TS) OCDMA system performances limitations. Five system parameters were considered in this work: the optical fiber length (transmission distance), the bitrate, the chip spacing and the transmitted power. This paper shows for what sufficient system performance parameters (BER≤10−9, Q≥6) the system can stand for.