Showing papers on "Diffraction efficiency published in 2012"
TL;DR: In this paper, a micro-lithography system with a digital micro-mirror device as dynamic mask forms arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations.
Abstract: We propose and implement a technique for arbitrary pattern fabrication in liquid crystal (LC) alignments and local polarization control for light wavefront. A micro-lithography system with a digital micro-mirror device as dynamic mask forms arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase gratings, more complex 2D patterns such as quasicrystal and checkerboard structures are demonstrated. To characterize the optical performances of the fabricated structures, the electro-optically tunable diffraction patterns and efficiencies are demonstrated in several 1D/2D phase gratings. Compared to other techniques, our method enables the arbitrary and instant manipulation of LC alignments and light polarization states, facilitating wide applications in display and photonic fields.
140 citations
TL;DR: An extension of the direct-binary-search algorithm for designing high-efficiency multi-wavelength diffractive optics that reconstruct in the Fresnel domain is presented and a fast computation method for solving the optimization problem is proposed.
Abstract: We present an extension of the direct-binary-search algorithm for designing high-efficiency multi-wavelength diffractive optics that reconstruct in the Fresnel domain. A fast computation method for solving the optimization problem is proposed. Examples of three-wavelength diffractive optics with over 90% diffraction efficiency are presented. These diffractive optical elements reconstruct three distinct image patterns when probed using the design wavelengths. Detailed parametric and sensitivity studies are conducted, which provide insight into the diffractive optic’s performance when subject to different design conditions as well as common systematic and fabrication errors.
118 citations
TL;DR: In this paper, a fast switchable grating based on ferroelectric liquid crystals and orthogonal planar alignment by means of photo alignments is presented, which provides fast response time of around 20μs, contrast of 7000:1 and high diffraction efficiency, at the electric field of 6´V/μm.
Abstract: We demonstrate a fast switchable grating based on ferroelectric liquid crystals and orthogonal planar alignment by means of photo alignments. Both 1D and 2D gratings have been constructed. The proposed diffracting element provides fast response time of around 20 μs, contrast of 7000:1 and high diffraction efficiency, at the electric field of 6 V/μm. The saturated electro-optical (EO) states up to very high frequency (≈5 kHz) are the real advantage of the proposed switchable grating, which opens several opportunities to improve the quality of existing devices and to find new applications.
96 citations
TL;DR: In this paper, a review on electron-beam lithography and accompanying technologies for high performance gratings can be found, which can be realized by different approaches, such as the one described in this paper, for the Radial Velocity Spectrometer of the GAIA-mission of the ESA.
Abstract: Gratings are essential components in different high performance optical set-ups such as spectrometers in space missions or ultrashort-pulse laser compression arrangements. Often such kinds of applications require gratings operating close to the technological accessible limits of today’s fabrication technology. Typical critical parameters are the diffraction efficiency and its polarization dependency, the wave-front error introduced by the grating, and the stray-light performance. Additionally, space applications have specific environmental requirements and laser application typically demand a high damage threshold. All these properties need to be controlled precisely on rather large grating areas. Grating sizes of 200 mm or even above are not unusual anymore. The paper provides a review on how such high performance gratings can be realized by electron-beam lithography and accompanying technologies. The approaches are demonstrated by different examples. The first example is the design and fabrication of the grating for the Radial-Velocity-Spectrometer of the GAIA-mission of the ESA. The second grating is a reflective pulse compression element with no wavelength resonances due to an optimized design. The last example shows a three level blazed grating in resonance domain with a diffraction efficiency of approximately 86 %.
81 citations
TL;DR: Unique four-state feature of the cell is obtained and their applications in optical logic devices are discussed.
Abstract: A diffraction grating is proposed by periodically defining the liquid-crystal director distribution to form alternate parallel aligned and twist nematic regions in a cell placed between two crossed polarizers. Based on the combined phase and amplitude modulation, both 1D and 2D tunable gratings are demonstrated. Low voltage ON/OFF switching of 1st order diffracted light with extinction ratio over 80 is achieved within a small voltage interval of 0.15 Vrms. Unique four-state feature of the cell is obtained and their applications in optical logic devices are discussed.
78 citations
TL;DR: This model suggests physical cross-talk between pixels and thus, filtering of addressed high spatial frequencies and can be computed a priori with any phase profile and demonstrated employing a Hamamatsu LCoS SLM X10468-02 with two-photon excitation of fluorescent Rhodamine layers.
Abstract: Pixilated spatial light modulators are efficient devices to shape the wavefront of a laser beam or to perform Fourier optical filtering When conjugated with the back focal plane of a microscope objective, they allow an efficient redistribution of laser light energy These intensity patterns are usually polluted by undesired spots so-called ghosts and zero-orders whose intensities depend on displayed patterns In this work, we propose a model to account for these discrepancies and demonstrate the possibility to efficiently reduce the intensity of the zero-order up to 95%, the intensity of the ghost up to 96% and increase diffraction efficiency up to 44% Our model suggests physical cross-talk between pixels and thus, filtering of addressed high spatial frequencies The method implementation relies on simple preliminary characterization of the SLM and can be computed a priori with any phase profile The performance of this method is demonstrated employing a Hamamatsu LCoS SLM X10468-02 with two-photon excitation of fluorescent Rhodamine layers
74 citations
TL;DR: In this paper, the polarization independence of liquid crystal gratings with alternate orthogonal aligned regions is theoritically studied and demonstrated by means of photoalignment technique, which is achieved by two-step photo exposure to guide orientations of sulfonic azo dye layers and further align the liquid crystal molecules.
Abstract: The polarization independence of liquid crystal gratings with alternate orthogonal aligned regions is theoritically studied and demonstrated by means of photoalignment technique. The different alignments in adjecent regions are achieved by two-step photo exposure to guide orientations of sulfonic azo dye layers and further align the liquid crystal molecules. Both one-dimensional and two-dimensional switchable phase gratings have been demonstrated. Such polarizer-free gratings show very high transmittance (∼92%), diffraction efficiency (over 31%), and optical contrast (over 150) including low power consumption.
68 citations
TL;DR: It is shown for the first time that this conversion into a single mode can be very efficient (i.e., ∼95% experimentally) at visible wavelengths, and the relative power between the two possible output modes is polarization-controllable from 0% to ∼100%.
Abstract: We present a novel optical element that efficiently generates orbital angular momentum
(OAM) of light and transforms light between OAM modes based on a polarization grating with a
fork-shaped singularity This forked polarization grating (FPG) is composed of liquid crystalline
materials, and can be made either static or switchable with high diffraction efficiency (ie, 100%
theoretically) into a single order By spatially varying the Pancharatnam–Berry phase, FPGs
shape the wavefront and thus control the OAM mode We demonstrate theoretically and empirically that
a charge lg FPG creates helical modes with OAM charge ±lg when a Gaussian
beam is input, and more generally, transforms the incident helical mode with OAM charge
lin into output modes with OAM charge lin±lg We also show for
the first time that this conversion into a single mode can be very efficient (ie, ∼95%
experimentally) at visible wavelengths, and the relative power between the two possible output modes
is polarization-controllable from 0% to ∼100% We developed a fabrication method that
substantially improves FPG quality and efficiency over prior work We also successfully fabricated
switchable FPGs, which can be electrically switched between an OAM generating/transforming state and
a transmissive state Our experimental results showed >92% conversion efficiency for both
configurations at 633 nm These holographically fabricated elements are compact (ie, thin
glass plates), lightweight, and easily optimized for nearly any wavelength from ultraviolet to
infrared, for a wide range of OAM charge, and for large or small clear apertures They are ideal
elements for enhanced control of OAM, eg, in optical trapping and high-capacity
information
67 citations
TL;DR: In this article, a review on the diffraction of electromagnetic waves is presented, focusing on the ways to overcome beam divergence and diffraction limit, including apodization techniques to reduce the divergence of a laser beam and increase the resolution.
Abstract: Diffraction is a natural phenomenon, which occurs when waves propagate or encounter an obstacle. Diffraction is also a fundamental aspect of modern optics: all imaging systems are diffraction systems. However, like a coin has two sides, diffraction also leads to some unfavorable effects, such as an increase in the size of a beam during propagation, and a limited minimal beam size after focusing. To overcome these disadvantages set by diffraction, many techniques have been developed by various groups, including apodization techniques to reduce the divergence of a laser beam and increase the resolution, and time reversal, STED microscopy, super lenses and optical antennas to obtain resolution down to nano-scale. This review concentrates on the diffraction of electromagnetic waves, and the ways to overcome beam divergence and the diffraction limit.
59 citations
TL;DR: A method for designing a diffractive beam splitter that enables the diffraction orders to be uniformly distributed within a required elliptic region is proposed.
Abstract: We propose a method for designing a diffractive beam splitter that enables the diffraction orders to be uniformly distributed within a required elliptic region. The performance of the designed optical element is demonstrated experimentally.
58 citations
TL;DR: In this article, a 1D/2D switchable grating based on field-induced polymer stabilized blue phase liquid crystal (PSBPLC) was proposed for 1D and 2D grating.
Abstract: We present a 1D/2D switchable grating based on field-induced polymer stabilized blue phase liquid crystal (PSBPLC). For 1D grating, the diffraction efficiency of the first order is 37.2% and the phase modulation depth of the 1D grating can achieve 2π. For 2D grating, more than 90% of light intensity is distributed to the surrounding orders of zero order and the phase modulation depth is about 3.67π. Furthermore it shows fast phase modulation and 1D/2D switching time.
TL;DR: The results in this study demonstrate the non droplet scaffolding morphology grating is characterized by a high degree of phase separation, high anisotropy, low scattering loss, and high diffraction efficiency.
Abstract: We have performed a detailed characterization of the optical properties of a holographic polymer dispersed liquid crystal (LC) transmission grating with polymer scaffolding morphology, which was fabricated with conventional high-functionality acrylate monomer under low curing intensity. Temporal evolution of the grating formation was investigated, and the amount of phase-separated LC was determined by birefringence investigation. A grating model combined with anisotropic coupled-wave theory yielded good agreement with experimental data without any fitting parameter. The results in this study demonstrate the non droplet scaffolding morphology grating is characterized by a high degree of phase separation (70%), high anisotropy, low scattering loss (<6%), and high diffraction efficiency (95%).
TL;DR: The theoretical results show that the diffraction efficiency is strongly dependent upon the angle of incident light and the pixel spacing of DMD, and DMD grating is a better choice to improve the stability and reliability of tunable fiber laser systems.
Abstract: A digital micromirror device (DMD) is a kind of widely used spatial light modulator. We apply DMD as wavelength selector in tunable fiber lasers. Based on the two-dimensional diffraction theory, the diffraction of DMD and its effect on properties of fiber laser parameters are analyzed in detail. The theoretical results show that the diffraction efficiency is strongly dependent upon the angle of incident light and the pixel spacing of DMD. Compared with the other models of DMDs, the 0.55 in. DMD grating is an approximate blazed state in our configuration, which makes most of the diffracted radiation concentrated into one order. It is therefore a better choice to improve the stability and reliability of tunable fiber laser systems.
TL;DR: In this paper, a blue-phase liquid-crystal grating was proposed by applying a vertical electric field with lateral periodic distribution, where the field-induced fast phase modulation allowed a rapid switching of diffraction orders down to the submillisecond scale.
Abstract: — A blue-phase liquid-crystal grating is proposed by applying a vertical electric field with lateral periodic distribution. Simulation on electric-field distribution was also carried out, the results of which suggest the alternation of isotropic and ordinary refractive indices in the lateral direction. Through the electrode configuration design, both 1 D and 2D gratings were demonstrated with high transmittance of ca. 85%. The diffraction efficiency of the first order reached up to 38.7% and 1 7.8% for the 1D and 2D cases, respectively. The field-induced fast phase modulation permits a rapid switching of diffraction orders down to the submillisecond scale.
TL;DR: The problem of optical image deformations caused by the phenomenon of light beam diffraction in uniaxial crystals by ultrasonic waves is considered and a general analytical expression is derived describing a dependence of spatial deformations and transmission coefficients on incidence angles as well as on parameters of the crystal and the ultrasound.
Abstract: The problem of optical image deformations caused by the phenomenon of light beam diffraction in uniaxial crystals by ultrasonic waves is considered in the paper. A general analytical expression is derived describing a dependence of spatial deformations and transmission coefficients on incidence angles as well as on parameters of the crystal and the ultrasound. The most interesting wide-angle diffraction configurations are analyzed, and all types of spatial distortions and transfer functions are described.
TL;DR: In this paper, the diffraction efficiency of a fused silica fiber containing fiber Bragg gratings (FBGs) was found to fluctuate with temperature between 2.01 −10 − 4 and 0.17 − 10 − 4 with sub-Angstrom precision.
TL;DR: Numerical simulation analyzed the reconstructed image quality and diffraction efficiency versus degree of phase compression and showed that phase compression resulted in little image degradation or power loss.
Abstract: Phase compression is used to suppress the on-axis zero-order diffracted (ZOD) beam from a pixelated phase-only spatial light modulator (SLM) by a simple modification to the computer generated hologram (CGH) loaded onto the SLM. After CGH design, the phase of each SLM element is identically compressed by multiplying by a constant scale factor and rotated on the complex unit-circle to produce a cancellation beam that destructively interferes with the ZOD beam. Experiments achieved a factor of 3 reduction of the ZOD beam using two different liquid-crystal SLMs. Numerical simulation analyzed the reconstructed image quality and diffraction efficiency versus degree of phase compression and showed that phase compression resulted in little image degradation or power loss.
TL;DR: A method to measure the optical response across the surface of a phase-only liquid crystal on silicon device using binary phase gratings is described together with a procedure to compensate its spatial optical phase variation, which reduces the residual power between zero and the minima of the first diffraction order.
Abstract: A method to measure the optical response across the surface of a phase-only liquid crystal on silicon device using binary phase gratings is described together with a procedure to compensate its spatial optical phase variation. As a result, the residual power between zero and the minima of the first diffraction order for a binary grating can be reduced by more than 10 dB, from -15.98 dB to -26.29 dB. This phase compensation method is also shown to be useful in nonbinary cases. A reduction in the worst crosstalk by 5.32 dB can be achieved when quantized blazed gratings are used.
TL;DR: It is shown that broadband unidirectional optical transmission with a total transmission maximum inside the band can be obtained for linearly polarized incident waves in the nonsymmetric photonic crystal gratings made of isotropic linear materials at a fixed nonzero or zero angle of incidence.
Abstract: We will show that broadband unidirectional optical transmission with a total transmission maximum inside the band can be obtained for linearly polarized incident waves in the nonsymmetric photonic crystal gratings made of isotropic linear materials at a fixed nonzero or zero angle of incidence. Being based on the merging of diffraction and dispersion effects, the basic physical mechanism studied exploits the transmission channels associated with higher orders, for which asymmetry in the coupling conditions at the two grating interfaces appears when spatial inversion symmetry is broken. Total transmission in one direction and zero transmission in the opposite direction can be obtained due to hybridization of Fabry-Perot type resonances with a diffraction anomaly that yields a diode-like operation regime. Single-beam deflection and two-beam splitting can be obtained, for which transmission can be (nearly) total, if the corrugated side is illuminated. In contrast to the previous studies, it is also shown that unidirectional transmission can appear only at a fixed frequency and only due to diffractions, when total transmission occurs at the noncorrugated-side illumination, being in agreement with the Lorentz Lemma.
TL;DR: An ultrasmall (<10 μm length) polarization converter in InP membrane is fabricated and characterized and is found to be broadband and tolerant to dimension variations.
Abstract: An ultrasmall ( 99% with insertion losses of <−1.2 dB at a wavelength of 1.53 μm. Furthermore, our design is found to be broadband and tolerant to dimension variations.
TL;DR: This study shows that the achievable efficiency improvement of silicon solar cells by means of backside diffraction gratings strongly depends on the proper choice of the grating parameters for a given silicon thickness.
Abstract: This numerical study investigates the influence of rectangular backside diffraction gratings on the efficiency of silicon solar cells. Backside gratings are used to diffract incident light to large propagation angles beyond the angle of total internal reflection, which can significantly increase the interaction length of long wavelength photons inside the silicon layer and thus enhance the efficiency. We investigate the influence of the silicon thickness on the optimum grating period and modulation depth by a simulation method which combines a 2D ray tracing algorithm with rigorous coupled wave analysis (RCWA) for calculating the grating diffraction efficiencies. The optimization was performed for gratings with period lengths ranging from 0.25 µm to 1.5 µm and modulation depths ranging from 25 nm to 400 nm under the assumption of normal light incidence. This study shows that the achievable efficiency improvement of silicon solar cells by means of backside diffraction gratings strongly depends on the proper choice of the grating parameters for a given silicon thickness. The relationship between the optimized grating parameters resulting in maximum photocurrent densities and the silicon thickness is determined. Moreover, the thicknesses of silicon solar cells with and without optimized backside diffraction gratings providing the same photocurrent densities are compared.
TL;DR: In this paper, the authors showed that the diffraction efficiency of phase grating is strikingly enhanced due to the existence of spontaneously generated coherence (SGC), and that the diffusion efficiency can be maintained by the application of weak coupled and relatively strong probe fields and choosing the proper length of atomic sample.
TL;DR: It turns out that the efficiency of diffraction grating is greatly improved due to the existence of the M NP, and the diffraction efficiency can be controlled by tuning the interaction strength between the SQD and the MNP.
Abstract: Photoinduced diffraction grating is theoretically investigated in a three-level ladder-type hybrid artificial molecule comprised of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP). The SQD and the MNP are coupled via the Coulomb interaction. The probe absorption vanishes under the action of a strong coupling field, indicating an effect of electromagnetically induced transparency (EIT). Based on this EIT effect, diffraction grating is achievable when a standing-wave coupling field is applied. It turns out that the efficiency of diffraction grating is greatly improved due to the existence of the MNP. Furthermore, the diffraction efficiency can be controlled by tuning the interaction strength between the SQD and the MNP. Nearly pure phase grating is obtained, showing high transmissivity and high diffraction efficiency up to 33%.
TL;DR: Quintero et al. as mentioned in this paper fabricated surface-relief diffraction gratings from the molecular spin crossover complex using the soft lithographic method described in Part 1 of this paper, where the grating geometry and optical properties were obtained from atomic force microscopy and spectroscopic ellipsometry measurements.
Abstract: Surface-relief diffraction gratings of various geometries were fabricated from the molecular spin crossover complex [FeII(hptrz)3](OTs)2 using the soft lithographic method described in Part 1 of this paper [Quintero et al., J. Mater. Chem., DOI: 10.1039/c2jm15662h]. The grating geometry and optical properties were obtained from atomic force microscopy and spectroscopic ellipsometry measurements. The grating diffraction efficiency (η) was determined as a function of the temperature at various wavelengths (400–700 nm) using a conoscopic microscopy setup. A significant effect of the molecular spin state change on η is demonstrated (ca. 3% modulation). Using scalar transmission theory the changes in the diffraction pattern were quantitatively traced back to the decrease of the real part of the refractive index (ΔnHL = –0.01) accompanying the 1A → 5T spin transition. These stimuli-responsive photonic devices exhibit useful properties for various applications. Here a proof of concept gas sensor application is demonstrated for the detection of alcohol vapor.
TL;DR: In this article, a simple-structured one-dimensional (1D) guided-mode resonance (GMR) gratings with non-polarizing resonance properties under normal incidence was presented.
Abstract: Polarization-insensitive guided-mode resonance (GMR) filters have significant role in applications such as optical communication systems. Here, we report the design and fabrication of two types of simple-structured one-dimensional (1D) GMR gratings with non-polarizing resonance properties under normal incidence. A single-layer rectangular-profile TiO2 grating is fabricated by electron beam lithography and reactive ion etching, which demonstrates, for the first time in experiment, almost perfect non-polarizing filtering effect with 1D grating under normal incidence. Then, a TiO2-coated polycarbonate 1D GMR grating is fabricated by nanoimprinting and atomic layer deposition, which also exhibits good non-polarizing property and the potential of low-cost mass replication of such functional devices.
TL;DR: In this article, a diffractive beam shaper with a cylindrical lens and a vibrating motor was used to eliminate laser speckle on the projection screen, which can achieve uniformity and contrast of 78% and 5.5% respectively, which demonstrates the feasibility and potential of the proposed scheme.
Abstract: Currently the major issues in applying the laser as an illumination source for projectors are beam shaping and laser speckle. We present a compact total solution for both issues by using a diffractive beam shaper associated with a cylindrical lens for the illumination optics and a vibrating motor attached to the beam shaper to eliminate speckle on the projection screen. The diffractive beam shaper features a double-sided microlens array with a lateral shift to each other. The illumination pattern is free of zero diffraction order mainly due to the continuous and spherical surface relief of the lenslet, which can be accurately fabricated with diamond turning and injection molding without quantizing surface relief, so that the illumination pattern on the microdisplay can match the design very well with high diffraction efficiency. In addition, the vibration of the diffractive beam shaper in the longitudinal mode has been found effective for eliminating the dot pattern in the illumination and reducing laser speckle on the projection screen. The proposed laser illuminator has been implemented on a three-panel LCoS projector engine to replace the traditional UHP lamp. The uniformity and speckle contrast are measured to be 78% and 5.5% respectively, which demonstrates the feasibility and potential of the proposed scheme.
TL;DR: In this paper, a detailed model of diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on a Kogelnik's theory of coupled waves is presented.
Abstract: A detailed model of diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on a Kogelnik’s theory of coupled waves is presented. The model describes reflecting gratings (Bragg mirrors) with arbitrary orientation in a plane-parallel plate having no material losses. It takes into account spectral width and angular
TL;DR: A theoretical analysis of asymmetrical diffraction in Raman-Nath, intermediate and Bragg diffraction regimes is presented andtic expressions for the amplitudes of the diffraction orders are derived based on rigorous multimode coupled mode equations in slowly varying amplitude approximation.
Abstract: A theoretical analysis of asymmetrical diffraction in Raman-Nath, intermediate and Bragg diffraction regimes is presented. The asymmetry is achieved by combining matched periodic modulations of the phase and of the loss/gain of the material, which enables the breakdown of optical symmetry and redirects all resulting optical energy in only positive or only negative diffraction orders, depending on the quarter period shift directions between the phase and the loss/gain modulations. Analytic expressions for the amplitudes of the diffraction orders are derived based on rigorous multimode coupled mode equations in slowly varying amplitude approximation.
TL;DR: The complete spatiotemporal characterization of the diffracted field of ultrashort pulses after passing through circularly symmetric binary phase diffraction gratings is carried out.
Abstract: The complete spatiotemporal characterization of the diffracted field of ultrashort pulses after passing through circularly symmetric binary phase diffraction gratings is carried out. The complex field is registered at different planes behind the gratings with an ultrashort-pulse measurement technique called SEA TADPOLE. Numerical simulations based on scalar diffraction theory are compared with the measurements.
TL;DR: In this article, the authors analyzed the case where the input side of the LN grating is immersed into a refractive index matching liquid (RIML) instead of a solid material and concluded that a contact grating setup using BK7 RIML is suitable for producing THz pulses even in the mJ energy range.
Abstract: According to the recent calculations, more efficient THz pulse generation is possible using relief grating on the front surface of the generating LiNbO3 (LN) crystal for tilted-pulse-front-excitation rather than imaging the pump spot on a reflection grating into the LN crystal. Very recently, it was shown that—compared to a free-standing LN surface-relief grating—significantly higher diffraction efficiency can be reached if the grating profiles are filled with fused silica. Since realisation of such a setup is technically very challenging, in the present paper, we analyse the case where the input side of the LN grating is immersed into a refractive index matching liquid (RIML) instead of a solid material. Our results showed that the diffraction efficiency remains above 90 % for a refractive index ranging 1.45–1.60 of the applied RIML, and it is as high as 99 % for using the RIML for BK7. For this case, we carried out detailed calculations for various grating parameters. We propose a practical setup applying tilted input and slightly tilted output surfaces resulting in low losses and high diffraction efficiency for the pump. We conclude that a contact grating setup using BK7 RIML is suitable for producing THz pulses even in the mJ-energy range.