Direction Of Light Propagation Research Articles

Просветляющие покрытия на основе ZnO, полученные методом электронно-лучевого испарения

In this work, research was carried out to analyze the possibility to fabricate nanostructured antireflection coatings based on ZnO. The dependence of structural features of the film on the substrate heating temperature during deposition of an aluminum-doped zinc oxide (AZO) has been studied. It is shown that it is impossible to obtain the required structural properties of the film by changing one parameter, the substrate temperature during deposition of the material, in the range of 20 – 600 °C. For this purpose, an approach has been suggested, which consists in preliminary deposition of a nanometer-thick Sn layer with subsequent substrate heating up to the temperature of deposition of the main material layer. The optimization of coating deposition conditions led to the fabrication of a medium consisting of many whiskers with transverse dimensions of tens of nanometers and a length of hundreds of nanometers, which are oriented mainly perpendicular to the substrate. It is shown that the gradient nature of a change in the material density, and, hence, in the effective refractive index in the direction perpendicular to the substrate plane, provides antireflection properties of the coating over a wide range of wavelengths as well as in different directions of light propagation.

Intelligent design of large angle deflection beam splitter based on method of moving asymptotes

Photonic chip is a kind of integrated device that uses light as a carrier for information transportation and processing. Owing to its advantages of small size, lightweight, and low power consumption, photonic chip has become the most popular research topic nowadays. The beam splitter is a vital part of on-chip integration. For conventional beam splitting elements, Y-type and tree-branch output are the main elements, which are usually realized by interference principles. However, it is appropriate only for simple conventional beam splitter because the propagation direction of light cannot achieve large angle deflection. In the case of relay loading, optical amplification, pumping, and frequency upconversion, the vertical loading is often required without affecting the main optical path. To complete the large-angle deflection beam splitting, one needs to add a mirror to realize it or use a right-angle mirror structure for geometric double-sided reflection and splitting in traditional ways, but these structures are relatively complicated and difficult to complete on-chip integration. Based on previous work on inversely designed multi-channel wavelength routers and wide spectrum efficient focusing devices by using the intelligent algorithm, and combining the years of research on the coherent superposition theory of multi-scattering of the disordered medium, a large angle beam splitter that can realize from the near-infrared band is designed through using the intelligent algorithm. The beam splitter structure is based on AMTIR-1 glass, the part to be etched is air. The composition of AMTIR-1 is Ge<sub>33</sub>As<sub>12</sub>Se<sub>55</sub>. And the size of the structure is only 1 μm × 2 μm. The beam splitter can achieve 180° linear separation of beams in a range from 800 nm to 1100 nm, the beam splitting ratio of the entire waveband is approximately 1∶1, and the gross beam splitting efficiency is stable between 85% and 92%. Compared with several conventional structures with the same size, the efficiency of the beam splitter designed by this algorithm is higher. At the same time, the algorithm has the advantages of fast computation speed and small computation amount, and it can be completed only by ordinary personal computers without the support of hardware such as workstations. This intelligent algorithm can also be applied to the design of various passive photonic devices such as optical polarization splitters, routers, optical isolators, etc., providing an idea and reference for the design of integrated micro-nano photonic devices on high-density sheets.

T-matrix calculations of spin-dependent optical forces in optically trapped nanowires

We present computational results associated with the onset of a spin-dependent optical force component occurring on zinc oxide nanowires trapped in optical tweezers with circularly polarized light. This type of non-conservative force appears directed perpendicularly with respect to the propagation direction of the incident light on the nanowires both for plane wave illumination and for optical tweezers. We show how this transverse optical force component is also shape dependent and connected with the imaginary part of the local Poynting vector and the local spin density.

On-chip optical non-reciprocity through a synthetic Hall effect for photons

We demonstrate a synthetic Hall effect for light, using an acousto-optically modulated nanophotonic resonator chain. To produce this effect, we simultaneously generate the required synthetic electric field using temporal modulation and the required synthetic magnetic field using spatial modulation of the resonator chain. We show how the combination of these synthetic fields transverse to the direction of light propagation can be used to produce non-reciprocal optical transmission, as a basis for new photonic and topological devices.

The Size of a Photon

This paper begins by exploring a useful and neglected detail of a photon—its physical size perpendicular to the direction of propagation in the same way as an atom or neutron has a physical size. Such a photon size would be quite separate from the cross-section of a photonic interaction, which depends on the material interacting. Such a perpendicular dimension of a photon will be invariant under Lorentz transform parallel to the light propagation direction and will thus be the same for all frequencies of light. This study also leads to new details about how a photon interacts, offering an explanation for the familiar physics where light slightly above and below the mean frequency of an excited state can still excite the same state without violation of conservation of energy—a mystery explored thoroughly in a previous paper without finding the solution offered here. As usual, a better elucidation of the details of light interaction also leads to new insights—especially about the vacuum field. The Appendix summarizes some previous research relevant to this discussion

Real-time viewpoint generation-based 3D display with high-resolution, low-crosstalk, and wide view range

A real-time viewpoint generation-based 3D display with low crosstalk and high resolution is proposed. The proposed 3D display consists of a pattern image display (PID), a lenticular lens, and a transparent liquid crystal display (LCD) panel. For each eye of the observer, the PID can provide a pattern image with stripes that have a calculated pitch and displacement according to the eye position. The light from the stripes can be concentrated 3D display eye tracking by the lenticular lens and generate a viewpoint at the eye position. The transparent LCD panel is used to provide parallax images. This transparent LCD panel will not change the direction of light propagation and the location of the generated viewpoints. Then the whole parallax image on the transparent LCD panel can be projected by the PID and the lenticular lens to the viewpoint, so the resolution will not suffer like that in the convention 3D displays. Because the viewpoints are real-time generated according to the position of the observer’s eyes, the observer’s eyes will completely coincide with the position of the generated viewpoint. So crosstalk can be limited at a low level, and the viewing range is almost unlimited.

Transversally travelling ultrasound for light guiding deep into scattering media

The application of optical methods for tissue diagnosis, activation, and treatment suffers dramatically from the low accessible depths due to strong light scattering in tissues. Here we demonstrate a method to address this issue by utilizing transient ultrasound waves, travelling transversally to the light propagation direction, to guide light into deeper tissue regions. We study the formation of the ultrasound-induced refractive index structures and waveguides using simple ultrasound field configurations and analyze their effects on the propagation of short light pulses. As a proof of concept, we demonstrate using 5 ns pulses of 532 nm light and Intralipid-20%-based phantoms with mu _{mathrm{s}}^prime up to 4.5 cm−1 a waveguide supported light intensity increase up to the depths of at least 90 mean free paths.

Light Switching with a Metal-Free Chiral-Sensitive Metasurface at Telecommunication Wavelengths

Controlling the direction of light propagation, or light switching, enables the addressing of individual optical elements in high-density and complex photonic integrated devices. Light switching is...

Waveguide Logic Gates for Magnetooptical Qubits

Results of studying properties of magnetooptical waveguide logic gates are presented. Simple logical operations can be implemented by changing photon states in a substance under the action of a modulating magnetic field. Varying the amplitude and orientation of the magnetic field relative to the light propagation direction, choosing the orientation of the polarizer and analyzer and appropriate configuration of the waveguide, one can design logic gates, including ones for qubit models. In doing this, the time barrier of low coherence peculiar to optical qubits is passed.

Three-dimensional Measurement of Specular Surfaces Based on the Light Field

As an important branch of computational optics, the light field can simultaneously record the spatial intensity and propagation direction of light, which provides a new way to realize three-dimensional (3D) measurement. Although light field measuring system (LFMS) can quickly detect nontransparent surfaces, specular light affects the overall measurement result. In this paper, an LFMS based on a diffuse light source and polarization technology is proposed to eliminate specular light and obtain a more accurate 3D reconstruction result in one exposure. During the measurement, a series of images corresponding to continuously varying polarization angle are captured, in which the value(V)-channel value distribution is used as the criterion of specular light removal efficiency, and hence, the image at the optimal polarization angle is obtained, in which the influence of specular light is removed. The depth map and specular light removal efficiency are experimentally compared with those of the traditional LFMS. The experimental results show that the depth map error can be greatly reduced, which further verifies the feasibility of the proposed method and system. The present study can be extended to the traditional optical system or other machine vision measurement methods involving specular light.

High-sensitivity dual-direction weak magnetic field sensor based on structural modulated ultralong period microfiber grating

A high-sensitivity optical fiber dual-direction weak magnetic field sensor based on a structural modulated ultralong period microfiber grating (SULPMG) is proposed. The SULPMG was fabricated by an electric arc discharge and flame-heating drawing method, and the sensor was fabricated by cascading the SULPMG with a core offset section. By tuning the direction of an applied magnetic field, the refractive index of a magnetic fluid (MF) can be tuned accordingly. The transmission spectral response of the proposed sensor was measured and analyzed. For the weak magnetic field intensity range from 0 mT to 7 mT, the obtained magnetic field sensitivity is −1.759 nm/mT and 1.082 nm/mT when the magnetic field is perpendicular or parallel to the light propagation direction, respectively. Theoretical analysis shows that reducing the waist diameter can further improve the sensitivity of the sensor. The proposed sensor is expected to be applied to weak magnetic field measurements in the aviation, vehicle detection and biomedical fields.

Tailoring the gradient and scattering forces for longitudinal sorting of generic-size chiral particles.

Based on the concepts of conservative and non-conservative optical forces (COF and NCOF), we analyze the physical mechanism of longitudinal chirality sorting along the direction of light propagation in some simple optical fields. It is demonstrated, both numerically and analytically for particle of arbitrary size, that the sorting relies solely on the NCOF, which switches its direction when particle chirality is reversed. For particles larger than half of the optical wavelength λ, the NCOF far surpasses its counterpart COF, enabling the longitudinal chirality sorting. When the particle is much smaller than λ, however, the COF outweighs the NCOF, destroying the sorting mechanism. A scenario is thus proposed that totally eliminates the COF while leaving the sorting NCOF unchanged, extending the applicability of longitudinal chirality sorting to small particles.

Phase-sensitive nuclear target spectroscopy

M\"ossbauer nuclei feature exceptionally narrow resonances at hard x-ray energies, which render them ideal probes for structure and dynamics in condensed-matter systems, and a promising platform for x-ray quantum optics and fundamental tests. However, a direct spectroscopy at modern x-ray sources such as synchrotrons or x-ray free electron lasers is challenging, because of the broad spectral bandwidth of the delivered x-ray pulses, and because of a limited spectral resolution offered by x-ray optics and detectors. To overcome these challenges, here, we propose a spectroscopy technique based on a spectrally narrow reference absorber that is rapidly oscillating along the propagation direction of the x-ray light. The motion induces sidebands to the response of the absorber, which we scan across the spectrum of the unknown target to gain spectral information. The oscillation further introduces a dependence of the detected light on the motional phase at the time of x-ray excitation as an additional controllable degree of freedom. We show how a Fourier analysis with respect to this phase enables one to selectively extract parts of the recorded intensity after the actual experiment, throughout the data analysis. This allows one to improve the spectral recovery by removing unwanted signal contributions. Our method is capable of gaining spectral information from the entire measured intensity, and not only from the intensity at late times after the excitation, such that a significantly higher part of the signal photons can be used. Furthermore, it not only enables one to measure the amplitude of the spectral response, but also its phase.

Effect of a local nonlinearity on the light dynamics around an exceptional point: A quantitative analysis

This paper investigates the effect of local nonlinearity on exceptional points-aided asymmetric modal dynamics using the framework of a dual-mode optical waveguide and reports on a non-chiral asymmetric mode conversion scheme, where depending on only the type of nonlinearities, the waveguide can deliver different dominating mode, irrespective of input and also the direction of light propagation.

Optical generation and detection of gigahertz shear acoustic waves in solids assisted by a metallic diffraction grating

Absorption of ultrashort laser pulses in a metallic grating deposited on a transparent sample launches in the material both compression/dilatation (longitudinal) and shear coherent acoustic pulses in directions of different orders of acoustic diffraction. The propagation of the emitted acoustic pulses can be monitored by measuring the variation of the optical reflectivity of the time-delayed ultrashort probe laser pulses. The direction of probe light incidence and its polarization relative to the sample surface as well as the orientation of the metallic grating should be specifically chosen for efficient Brillouin scattering of the probe light from shear phonons propagating in the elastically isotropic materials. As theoretically predicted, the obtained experimental data contain multiple frequency components which are due to a variety of possible Brillouin scattering angles for both shear and compression/dilatation coherent acoustic waves. All these different frequency components are explained through multiplexing the propagation directions of probe light and coherent sound by the metallic diffraction grating. Our experimental scheme of time-domain Brillouin scattering with metallic gratings operating in reflection mode provides access to monitoring the shear acoustic waves launched in the direction of the first diffraction order by backward Brillouin scattering process. Applications include simultaneous determination of several different acoustic mode velocities and optical refractive index and, potentially, measurements of the acoustic dispersion of samples with a single direction of possible optical access.

Observation of Photoion Backward Emission in Photoionization of He and N_{2}.

We experimentally investigate the effects of the linear photon momentum on the momentum distributions of photoions and photoelectrons generated in one-photon ionization in an energy range of 300 eV≤E_{γ}≤40 keV. Our results show that for each ionization event the photon momentum is imparted onto the photoion, which is essentially the system's center of mass. Nevertheless, the mean value of the ion momentum distribution along the light propagation direction is backward-directed by -3/5 times the photon momentum. These results experimentally confirm a 90-year-old prediction.

Long-distance optical pulling of nanoparticle in a low index cavity using a single plane wave.

Optical pulling force (OPF) can make a nanoparticle (NP) move against the propagation direction of the incident light. Long-distance optical pulling is highly desired for nano-object manipulation, but its realization remains challenging. We propose an NP-in-cavity structure that can be pulled by a single plane wave to travel long distances when the spherical cavity wrapping the NP has a refractive index lower than the medium. An electromagnetic multipole analysis shows that NPs made of many common materials can receive the OPF inside a lower index cavity. Using a silica-Au core-shell NP that is encapsulated by a plasmonic nanobubble, we experimentally demonstrate that a single laser can pull the Au NP-in-nanobubble structure for ~0.1 mm. These results may lead to practical applications that can use the optical pulling of NP, such as optically driven nanostructure assembly and nanoswimmers.

Interferometric Optical Isolator with Si Guiding Layer Operated in Unidirectional Magnetic Field

INTRODUCTIONIn optical communication systems, an optical isolator is indispensable in protecting active photonic devices from unwanted reflected light. An optical isolator with a Si guiding layer is a significant device for silicon photonic integrated circuits. In this paper, the authors report on an interferometric optical isolator with a Si guiding layer which can be operated in unidirectional magnetic field.DEVICE STRUCTUREFigure 1 shows an interferometric optical isolator with a Si guiding layer employing a nonreciprocal phase shift [1]. The nonreciprocal phase shift occurs in transverse-magnetic (TM) modes that travel in magneto-optic waveguides in which magnetization is aligned transverse to the light propagation direction in the film plane. The optical isolator employing the nonreciprocal phase shift is attractive because the device utilizes TM modes only so that there is no need for phase matching. The optical isolator includes an optical interferometer that consists of two coupling devices, a nonreciprocal phase shifter and a reciprocal phase shifter. In Fig. 1, one arm in the optical interferometer has a magnetic garnet cladding layer. When the interferometer has distinct layer structures, the optical isolator can be operated in a unidirectional magnetic field. The optical isolator employing the nonreciprocal phase shift was designed at 1.55 μm. The nonreciprocal phase shifts in the magneto-optic waveguides with a magnetic-garnet/Si/SiO2 structure were calculated. The multimode interference (MMI) coupler and the reciprocal phase shifter were also designed. As a preliminary experiment, deposition of the magnetic garnet crystals were investigated on various substrates.ACKNOWLEDGMENTThis work was partially supported by the SIT Research Center for Green Innovation.REFERENCES1. H. Yokoi, T. Mizumoto and Y. Shoji, Appl. Opt., 42, 6605 (2003). Figure 1

Chiral quantum optics in photonic sawtooth lattices

Chiral quantum optics has become a burgeoning field due to its potential applications in quantum networks or quantum simulation of many-body physics. Current implementations are based on the interplay between local polarization and propagation direction of light in nanophotonic structures. In this manuscript, we propose an alternative platform based on coupling quantum emitters to a photonic \emph{sawtooth} lattice, a one-dimensional model with an effective flux per plaquette introduced by complex tunnelings. We study the dynamics emerging from such structured photonic bath and find the conditions to obtain quasi-perfect directional emission when the emitters are resonant with the band. In addition, we find that the photons in this bath can also mediate complex emitter-emitter interactions tunable in range and phase when the emitters transition frequencies lie within a band-gap. Since these effects do not rely on polarization they can be observed in platforms beyond nanophotonics such as matter-waves or circuit QED ones, of which we discuss a possible implementation.

Modeling and simulation of optimized photonic crystal waveguide for slow-light enhancement

We present a novel type of slow-light photonic crystal waveguide prepared by changing only the position of the second rows of holes in the direction of light propagation of a line-defect photonic crystal waveguide. A nearly constant group index is achieved of 30, 31 and 32 over wavelength ranges of 10.4 nm, 13.5 nm and 14.5 nm, respectively. In addition, a large normalized-delay-bandwidth product ranging from 0.201 to 0.300 is obtained at the operation wavelength of 1550 nm.