Showing papers on "Electromagnetically induced grating published in 2017"

Optical quantum memory based on electromagnetically induced transparency.

Abstract: Electromagnetically induced transparency (EIT) is a promising approach to implement quantum memory in quantum communication and quantum computing applications. In this paper, following a brief overview of the main approaches to quantum memory, we provide details of the physical principle and theory of quantum memory based specifically on EIT. We discuss the key technologies for implementing quantum memory based on EIT and review important milestones, from the first experimental demonstration to current applications in quantum information systems.

Asymmetric light diffraction of an atomic grating with PT symmetry.

Abstract: Cold atoms trapped in one-dimensional optical lattices and driven to the four-level N configuration are exploited for achieving an electromagnetically induced grating with parity-time-symmetry. This nontrivial grating exhibits unidirectional diffraction patterns, e.g., with incident probe photons diffracted into either negative or positive angles, depending on the sign relation between spatially modulated absorption and dispersion coefficients. Such asymmetric light diffraction is a result of the out-of-phase interplay of amplitude and phase modulations of transmission function and can be easily tuned via optical depth, probe detuning, pump Rabi frequencies, etc.

Polarization-independent broadband beam combining grating with over 98% measured diffraction efficiency from 1023 to 1080 nm.

Abstract: We report a grating solution for achieving broadband and polarization-independent properties that brings a laser combining system to much higher power levels The grating, with a high-refractive-index-contrast bilayer ridge, was designed and successfully fabricated based on high-power laser coatings, lithography, and ion-beam etching technology The measured −1st order non-polarized reflective diffraction efficiency of the grating exceeds 98% over the wavelength range of 1023–108 μm, and the highest value is 9915%

Holographic fabrication of an arrayed one-axis scale grating for a two-probe optical linear encoder.

Abstract: We present a method for the fabrication of an arrayed one-axis scale grating for a two-probe optical linear encoder using a dual-beam interference lithography (IL) system with a compact diode laser source. We employ a multiple-exposure stitching method to form an arrayed scale grating. This allows a scale grating with small line spacing to be achieved over a large width. This stitched scale grating integrates well with a newly developed two-probe optical encoder, allowing the measurement results to be numerically connected. Since neither the gap width nor the grating phase of the two adjacent gratings must be controlled, the fabrication process is both simplified and made more robust. This flexible and cost-effective fabrication technique can benefit many precision measurement applications. Experiments are carried out to demonstrate the feasibility of this technology.

Visibility simulation of realistic grating interferometers including grating geometries and energy spectra.

Abstract: The performance of X-ray and neutron grating interferometers is characterised by their visibility, which is a measure for the maximum achievable contrast. In this study we show how the real grating geometry in a grating interferometer with three gratings impacts the interference and self projection that leads to visibility in the first place. We quantify the individual contributions of wavelength distributions and grating shapes in terms of visibility reduction by determining the absolute as well as relative effect of each contribution. The understanding of the impact of changed geometry and wavelength distributions on the interference of neutrons/X-rays allows us to present the first fully quantitative model of a grating interferometer setup. We demonstrate the capability of the simulation framework by building a model of the neutron grating interferometer at the ICON beamline and directly comparing simulated and measured visibility values. The general nature of the model makes it possible to extend it to any given grating interferometer for both X-rays and neutrons.

Investigation of dual electromagnetically induced grating based on spatial modulation in quantum well nanostructures via biexciton coherence

Abstract: A new scheme for obtaining an electromagnetically induced grating (EIG) via biexciton coherence in quantum well nanostructures is developed. It is theoretically shown that exciton spin relaxation and biexciton binding energy have important roles in producing efficient dual electromagnetically induced phase grating. In this structure, due to biexciton coherence, the higher order diffraction intensities of the grating can be observed. Furthermore, it is shown that the efficiency of different orders in the grating patterns could be controlled by biexciton energy renormalization (ESR) and relative phase between the applied laser fields.

Beam splitter and router via an incoherent pump-assisted electromagnetically induced blazed grating.

Abstract: We propose a scheme for a beam splitter and a beam router via an electromagnetically induced blazed grating in a four-level double-Λ system driven by an intensity-modulated coupling field and an incoherent pump field. The blazed grating relies on the incoherent pump process, which helps in inducing large refractivity with suppressed absorption or even gain. Consequently, the weak probe beam can be effectively deflected with high diffraction efficiency, and, meanwhile, its energy is amplified. When using an intensity mask with two symmetric domains in the coupling field, the presented blazed grating provides the possibility of a symmetric beam splitter. The diffraction efficiency and diffraction order of the gratings are sensitive to the intensity of the coupling field, and, thus, the gratings can function as a tunable asymmetric beam splitter or a beam router, which distributes the probe field into different spatial directions. Therefore, the proposed scheme may have potential applications in optical communication and networking.

Wavelength-Selective Diffraction from Silica Thin-Film Gratings

Abstract: A reflective diffraction grating with a periodic square-wave profile will combine the effects of thin-film interference with conventional grating behavior when composed of features having a different refractive index than that of the substrate. A grating period of 700–1300 nm was modeled and compared for both silicon (Si) and silicon dioxide (SiO2) to determine the behavior of light interaction with the structures. Finite element analysis was used to study nanostructures having a multirefractive index grating and a conventional single material grating. A multimaterial grating has the same diffraction efficiency as that of a grating formed in a single material, but had the advantage of having an ordered relationship between the grating dimensions (thickness and period) and the intensity of reflected and diffracted optical wavelengths. We demonstrate a color-selective feature of the modeled SiO2 grating by fabricating samples with grating periods of 800 and 1000 nm, respectively. A high diffraction efficien...

Two-port connecting-layer-based sandwiched grating by a polarization-independent design.

Abstract: In this paper, a two-port connecting-layer-based sandwiched beam splitter grating with polarization-independent property is reported and designed. Such the grating can separate the transmission polarized light into two diffraction orders with equal energies, which can realize the nearly 50/50 output with good uniformity. For the given wavelength of 800 nm and period of 780 nm, a simplified modal method can design a optimal duty cycle and the estimation value of the grating depth can be calculated based on it. In order to obtain the precise grating parameters, a rigorous coupled-wave analysis can be employed to optimize grating parameters by seeking for the precise grating depth and the thickness of connecting layer. Based on the optimized design, a high-efficiency two-port output grating with the wideband performances can be gained. Even more important, diffraction efficiencies are calculated by using two analytical methods, which are proved to be coincided well with each other. Therefore, the grating is significant for practical optical photonic element in engineering.

Effect of partial coherence on diffraction intensity of a Gaussian Schell-model beam using two-level atomic grating

Abstract: The role of spatial coherence on diffraction intensity is investigated for a partially coherent incident Gaussian Schell-model beam which is diffracted from a two-level atomic grating. It is shown that the performance of the atomic grating is greatly influenced by the spectral coherence width of the partially coherent fields. It is observed that relatively large intensity of the diffracted light can be obtained via spatial coherence, beam width, interaction length, and mode index of partially coherent incident light. The scheme provides possibilities for the potential applications of atomic grating in lensless imaging using the partially coherent light field.

Photovoltaic absorber with different grating profiles in the near-infrared region.

Abstract: We theoretically introduce a Si-based photovoltaic absorber with different grating profiles, which demonstrates a desirable enhancement of light absorption in the near-infrared region by increasing the degree of the grating’s profile function. The mechanisms of light absorption enhancement originate from the synergetic effect of optical waveguide modes, light scattering, and Fabry–Perot resonances. Moreover, numerical results indicate that the convex grating structure is more conducive to the excitation of optical waveguide modes compared with the concave grating structure. The research findings can be utilized to guide the design of thin-film solar cells based on grating structures.

Comparing Q-factor of electromagnetically induced transparency based on different space distribution quasi-dark mode resonator

Abstract: Comparing the Q-factor of electromagnetically induced transparency based on a symmetric and asymmetric quasi-dark resonator has been numerically and experimentally demonstrated. The results show that the Q-factor of electromagnetically induced transparency based on the symmetric quasi-dark mode resonator is an order of magnitude larger than that based on the asymmetric quasi-dark mode resonator. The reason for the improved Q-factor is ascribed to the low radiative loss of the symmetric quasi-dark mode resonator. Furthermore, the proposed way holds promise to obtain a different Q-factor of electromagnetically induced transparency in the microwave, terahertz, and optical frequency range.

Nonlinear Zeeman effect, line shapes and optical pumping in electromagnetically induced transparency

Abstract: We perform Zeeman spectroscopy on a Rydberg electromagnetically induced transparency (EIT) system in a room-temperature Cs vapor cell, in magnetic fields up to 50~Gauss and for several polarization configurations. The magnetic interactions of the $\vert 6S_{1/2}, F_g=4 \rangle$ ground, $\vert 6P_{3/2}, F_e=5 \rangle$ intermediate, and $\vert 33S_{1/2} \rangle$ Rydberg states that form the ladder-type EIT system are in the linear Zeeman, quadratic Zeeman, and the deep hyperfine Paschen-Back regimes, respectively. Starting in magnetic fields of about 5~Gauss, the spectra develop an asymmetry that becomes paramount in fields $\gtrsim40$~Gauss. We use a quantum Monte Carlo wave-function approach to quantitatively model the spectra. Simulated spectra are in good agreement with experimental data. The asymmetry in the spectra is, in part, due to level shifts caused by the quadratic Zeeman effect, but it also reflects the complicated interplay between optical pumping and EIT in the magnetic field. Relevance to measurement applications is discussed. %The simulations are also used to study optical pumping in the magnetic field and to investigate the interplay between optical pumping and EIT, which reduces photon scattering and optical pumping.

Coherently induced grating in refractive index enhanced medium

Abstract: We demonstrate a scheme for coherently induced grating based on a mixture of two three-level atomic species interacting with two standing-wave fields. As a result of interaction between the absorptive and amplified Raman resonances, the refractive index of the medium can be enhanced and modulated periodically. Then a sinusoidal grating, which can diffract the probe field into high-order directions, is coherently formed in the medium. The proposed scheme is theoretically investigated in a mixture of atomic isotopes of rubidium. The results show that the diffraction efficiency depends strongly on the two two-photon detunings of the two Raman transitions and the intensities of the two driving standing-wave fields. The proposed electromagnetically induced grating scheme may be applied to the all-optical switching and beam splitting in optical networking and communication.

Electromagnetically induced grating in a thermal N-type four-level atomic system*

Abstract: The electromagnetically induced grating effect in thermal and cold atoms has been studied theoretically. Studies have shown that, by adjusting the parameters, the first-order diffraction efficiency of the probe beam in the cold atomic system and the thermal atomic system is 34% and 31%, respectively, which is very close to the ideal diffraction efficiency of the sinusoidal grating. However, it is more difficult to prepare the cold atomic system than to prepare the thermal atomic system in the practical application, so the study of the electromagnetically induced grating effect in the thermal atomic system may be helpful for practical applications.

Charged particle beam device, optical device, irradiation method, diffraction grating system, and diffraction grating

Abstract: The outer shape and size of a diffraction grating including an edge dislocation is made smaller than the irradiation areas of light waves and electromagnetic waves, by using an opener different from in the diffraction grating, the shape and size of the opening is superposed on the shape of a spiral wave that is generated by an edge dislocation diffraction grating, and the shape and size of the opening are reflected in the shape and size of the spiral wave on the diffractive surface. In addition, not only a diffraction grating system including a pair of a single opener and a single diffraction grating, but also a diffraction grating system in which plural openers and plural edge dislocation diffraction gratings are combined are used, and plural spiral waves can be generated on the diffractive surface with a higher degree of freedom.

Electromagnetically Induced Grating Without Absorption Using Incoherent Pump

Abstract: We propose a scheme for creating electromagnetically induced grating in a four-level double- Λ atomic system driven by a coupling field and an incoherent pump field. Owing to the incoherent pumping process, large refractivity accompanied with vanishing absorption or even gain across the probe field can be built up in the atoms, thus phase grating or gain-phase grating, which diffracts a probe light into different directions, can be formed with the help of a standing-wave coupling field. The diffraction efficiency of the gratings can be tuned by the coupling field intensity and the incoherent pump rate, hence the proposed gratings should be suitable for beam splitter and optical switching in optical communication and networking.

Apparatus including a bent interference grating and method for bending an interference grating for interferometric x-ray imaging

Abstract: An apparatus for interferometric x-ray imaging includes an interference grating and a frame-like holding device. The interference grating is bendable like a leaf spring and is arranged in grooves of opposing bearings of the holding device such that the interference grating has one-dimensional concave curvature or one-dimensional convex curvature.

High efficiency geometric-phase polarization fan-out grating on silicon.

Abstract: We report the design, fabrication and characterization of a 1-by-5 geometric-phase polarization fan-out grating for coherent beam combining at 1550 nm. The phase profile of the grating is accurately controlled by the local orientation of the binary subwavelength structure instead of the etching depth and profile empowering the grating to be more tolerant to fabrication errors. Deep-UV interference lithography on silicon offers an inexpensive, highly efficient and high damage threshold solution to fabricating large-area fan-out gratings than electron beam lithography (EBL) and photoalignment liquid crystals. The theoretical and experimental diffraction efficiency of the grating is 87% and 85.7% respectively. Such a fan-out grating may find application to high-power beam combining in the infrared regime.

Subwavelength interference based on light pulse storage via electromagnetically induced transparency

Abstract: By employing a light pulse storage and retrieval process based on the electromagnetically induced transparency effect, first-order subwavelength interference fringe with an effective wavelength equal to λ/n was proposed and experimentally demonstrated with n=2 and a visibility ∼80%.

The potential of diffraction grating for spatial applications

Abstract: Diffraction gratings are know, and have been fabricated for more than one century. They are now making a come back for two reasons: first, because they are now better understood which leads to the efficient exploitation of what was then called their “anomalies”; secondly, because they are now fabricable by means of the modern manufacturing potential of planar technologies. Novel grating can now perform better than conventional gratings, and address new application fields which were not expected to be theirs. This is the case of spatial applications where they can offer multiple optical functions, low size, low weight and mechanical robustness. The proposed contribution will briefly discuss the use of gratings for spatial applications. One of the most important applications is in the measurement of displacement. Usual translation and rotation sensors are bulky devices, which impose a system breakdown leading to cumbersome and heavy assemblies. We are proposing a miniaturized version of the traditional moving grating technique using submicron gratings and a specific OptoASIC which enables the measurement function to be non-obtrusively inserted into light and compact electro-mechanical systems. Nanometer resolution is possible with no compromise on the length of the measurement range. Another family of spatial application is in the field of spectrometers where new grating types allow a more flexible processing of the optical spectrum. Another family of applications addresses the question of inter-satellite communications: the introduction of gratings in laser cavities or in the laser mirrors enables the stabilization of the emitted polarization, the stabilization of the frequency as well as wide range frequency sweeping without mobile parts.