Diffraction Efficiency Research Articles

High‐Contrast Switching of Light Enabled by Zero Diffraction

Diffraction allows to change the direction of light. Therefore, controlling the diffraction efficiency with high contrast enables controlling the pathway of light within optical systems. However, a high contrast requires that the diffraction efficiency is tunable close to zero. Probably the most prominent example for zero diffraction in a waveguide grating is a bound state in the continuum (BIC). Herein, zero diffraction of two plane waves under symmetric incidence to a leaky symmetric waveguide grating is found. The phenomenon not only occurs at singular spectral positions but on continuous curves in the energy–momentum space. The relative phase of the two waves enables large contrast control over diffraction in a wide spectral range. The practical meaning of this finding for local switching is demonstrated. Light is trapped into a nonlinear optical waveguide and detrapped at a desired position with electric control. A switching contrast exceeding 1000 is experimentally shown.

Self-healing properties of symmetrical power-exponent-phase vortices.

The self-healing properties of symmetrical power-exponent-phase vortices (SPEPVs) are analyzed in this paper. By placing an obstacle in the optical path of SPEPVs, we simulated the propagation of the obstructed SPEPVs and verified the self-healing of the beam theoretically. We also explored the influence of external factors (e.g.,obstacle size and position) and internal parameters (topological charge l and power exponent n) on the self-healing effect of obstructed SPEPVs. Furthermore, the energy flow density, similarity coefficient, effective self-healing distance, and diffraction efficiency of the obstructed SPEPVs were also discussed. The results demonstrated that the transverse energy flows around the obstructed region of SPEPVs will recover with the propagation distance increased, and the effective self-healing distance gradually increases linearly with the obstacle size r x increased. The self-healing characteristic gives the petal-like SPEPVs the ability to trap microparticles three-dimensionally.

Optical computation of Laplace operator using Pancharatnam-Berry lens of large focal length

We propose an optical Laplace operator consisting of a large-focal-length Pancharatnam-Berry lens placed on the Fourier plane of an optical imaging system and sandwiched with two orthogonal linear polarizers. Theoretical analysis reveals that the isotropic second-order differentiation derives from the quadratic phase attached to the left-handed and right-handed circularly polarized light. The Pancharatnam-Berry lens made of liquid crystal with high transmittance and diffraction efficiency is integrated into different imaging systems to realize edge detection for both amplitude and phase objects, and the results conform to the theory well. This work paves the way to implement Laplace operator in practical applications such as image processing and high-contrast microscopy.

New substituted pentazadienes as initiators of free-radical polymerization: synthesis, photochemical properties and perspectives for holographic media

The series of 4,4′-substituted 3-hydroxyethyl-pentaza-1,4-dienes were synthesized in the reaction of aromatic diazonium salts with an ethanol amine. Photolysis of pentaza-1,4-dienes was investigated by means of UV/Vis spectroscopy. Electron donating methyl and methoxy substituents were found to increase photosensitivity whereas electron withdrawing chloro-substituents cause higher photolytic stability. 3-hydroxyethyl-pentaza-1,4-dienes as a radical polymerization initiator has been successfully investigated in 10% methyl methacrylate solution in DMF. Gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) were used for obtained polymers characteristics evaluation. The highest values of PMMA Mn and Đ can be obtained in the case of chloro-substituted derivative. The holograms of a plane wavefront were recorded in media based on obtained PMMA doped by azo-dye by a 532 nm laser in a ∼1-μm-thick sample. The diffraction efficiency values for parallel polarized acting light increased in Cl→Me→OMe series.

Alignment‐Free Angular Momentum Detection via Spin‐Independent Astigmatic Transformation

AbstractLight beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have attracted great interest due to their great potential for high‐capacity optical communication, optical tweezers, and quantum information. However, the current detection methods suffer from the lack of robustness to misalignments in the optical system, which limits the detection accuracy and the application for off‐axis vortex array detection. Here, a high‐efficiency, broadband, and single‐layer metasurface design is proposed for alignment‐free angular momentum detection via spin‐independent astigmatic transformation (SIAT). The SAM and OAM states can be recognized from the diffraction direction and patterns, respectively. Proof‐of‐concept demonstrations are experimentally carried out on different incident beams including circular‐polarization, linear‐polarization, and vector vortex beams, as well as vortex beam arrays, showing a high diffraction efficiency of ≈81% at 1064 nm while operating within the broadband region of 900–1300 nm. The alignment‐free merit for the incident position, incident angle, and detector distance grants the device great potential for integrated quantum systems and multiparticle micromanipulation with optical tweezers.

Operating mode dependent energy transfer efficiency in a quantum well waveguide

In this paper, we delve into the intricate interplay between optical fields with varying relative phases in a closed-loop configuration semiconductor quantum well waveguide with four distinct energy levels, and how it impacts the Fraunhofer diffraction patterns obtained via four-wave mixing. By harnessing a strong control field, a standing wave driving field, and two weak probe and signal fields, we drive the waveguide to generate these patterns with maximum efficiency. To achieve this, we consider three distinct light-matter interaction scenarios, where the system is first set up in either a lower electromagnetically induced transparency or a coherent population trapping state, followed by a final state that enables electron spin coherence (ESC) induction. Our results reveal that the efficiency of Fraunhofer diffraction in the quantum well waveguide can be enhanced significantly under specific parameter regimes via the spin coherence effect. Further investigation of the light-matter interaction in the ESC zone, where only one of the control fields is a standing wave field, demonstrates that spin coherence facilitates more efficient transfer of energy from the probe light to the third and fourth orders, highlighting its crucial role in shaping the diffraction patterns.

Multi-material heterogeneous integration on a 3-D photonic-CMOS platform

Photonics has been one of the primary beneficiaries of advanced silicon manufacturing. By leveraging mature complementary metal-oxide-semiconductor (CMOS) process nodes, unprecedented device uniformity and scalability have been achieved at low costs. However, some functionalities, such as optical memory, Pockels modulation, and magnetooptical activity, are challenging or impossible to acquire on group-IV materials alone. Heterogeneous integration promises to expand the range of capabilities within silicon photonics. Existing heterogeneous integration protocols are nonetheless not compatible with active silicon processes offered at most photonic foundries. In this work, we propose a novel heterogeneous integration platform that will enable wafer-scale, multi-material integration with active silicon-based photonics, requiring zero change to the existing foundry process. Furthermore, the platform will also pave the way for a class of high-performance devices. We propose a grating coupler design with peak coupling efficiency reaching 93%, an antenna with peak diffraction efficiency in excess of 97%, and a broadband adiabatic polarization rotator with conversion efficiency exceeding 99%.

High uniformity splitter with great inhibition of ±1st orders

A transmissive double-groove grating under vertical incidence is proposed in this paper. The grating has a total of five diffraction orders, and the effect of a three-channel beam splitter is achieved by inhibiting the diffraction efficiency of ±1st orders. This is a polarization-independent micro-nano structure that achieves triple beam splitting under both TE and TM polarization. The diffraction efficiency of the 0th order and ±2nd orders for TE polarization orders can reach 32.55% and 32.72%, respectively. And the diffraction efficiency of 0th order and ±2nd orders for TM polarization can reach 32.28% and 32.59%, respectively. Both TE and TM polarization can achieve 99% uniformity. The grating performs well in terms of manufacturing tolerances and immunity to interference.

High efficiency multilayer coated laminar gratings with high line density for tender X-ray region

Driven by the demand of high efficiency and high resolution monochromators and spectrometers in the tender X-ray range, high line density multilayer coated laminar gratings (MLLG) were designed, manufactured, and analyzed. Theoretical simulations displayed that a 5000 l/mm MLLG could realize high resolution at 3 keV and 40 times higher diffraction efficiency than the single-layer coated grating. For the first demonstration of the high line density MLLGs, two 3000 l/mm laminar gratings were fabricated and coated by Cr/C multilayers with different periodic thicknesses to achieve high efficiency (HE) and high resolution (HR) performance. For MLLG-HE, a maximum efficiency of 54.5% was achieved at 4.4 keV. For MLLG-HR, relatively high efficiency of 23.1%–38.6% were demonstrated with much stronger asymmetric diffraction in 2–4 keV, which can significantly increase the energy resolution of the system.

Holographic Recording of Unslanted Volume Transmission Gratings in Acrylamide/Propargyl Acrylate Hydrogel Layers: Towards Nucleic Acids Biosensing.

The role of volume hydrogel holographic gratings as optical transducers in sensor devices for point-of-care applications is increasing due to their ability to be functionalized for achieving enhanced selectivity. The first step in the development of these transducers is the optimization of the holographic recording process. The optimization aims at achieving gratings with reproducible diffraction efficiency, which remains stable after reiterative washings, typically required when working with analytes of a biological nature or several step tests. The recording process of volume phase transmission gratings within Acrylamide/Propargyl Acrylate hydrogel layers reported in this work was successfully performed, and the obtained diffraction gratings were optically characterized. Unslanted volume transmission gratings were recorded in the hydrogel layers diffraction efficiencies; up to 80% were achieved. Additionally, the recorded gratings demonstrated stability in water after multiple washing steps. The hydrogels, after functionalization with oligonucleotide probes, yields a specific hybridization response, recognizing the complementary strand as demonstrated by fluorescence. Analyte-sensitive hydrogel layers with holographic structures are a promising candidate for the next generation of in vitro diagnostic tests.

A triple band local oscillator coupling system based on a phase grating for five-meter Dome-A terahertz explorer telescope.

For heterodyne receivers, broadband and integrated local oscillator (LO) coupling schemes are crucial. In this paper, we present a novel terahertz broadband receiver system based on a one-pixel phase grating. We designed a phase grating that can simultaneously couple the LO signals at 690, 850, and 1300GHz to a superconducting hot-electron bolometer mixer at the incident angles of 25.7°, 20.6°, and 13.3°, respectively. At these three frequencies, the measured diffraction efficiencies of the phase grating are as high as 70%, 73%, and 65%, and the total power coupling efficiencies of the LO coupling system are 22%, 23%, and 23%, in good agreement with the simulated results. This efficient and highly integrated multiband receiver system has potential applications in the proposed Five-meter Dome-A Terahertz Explorer telescope.

Impact of the multilayer dielectric design on the laser-induced damage threshold of pulse compression gratings for petawatt-class lasers.

The peak-power of petawatt-class lasers is limited by laser-induced damage to final optical components, especially on the pulse compression gratings. Multilayer dielectric (MLD) gratings are widely used in compressor systems because they exhibit a high diffraction efficiency and high damage threshold. It is now well established that the etching profile plays a key role in the electric field distribution, which influences the laser damage resistance of MLD gratings. However, less attention has been devoted to the influence of the multilayer design on the laser damage resistance of MLD gratings. In this Letter, we numerically and experimentally evidence the impact of the dielectric stack design on the electric field intensity (EFI) and the laser-induced damage threshold (LIDT). Three different MLD gratings are designed and manufactured to perform laser damage tests. On the basis of the expected EFIs and diffraction efficiencies, the measured LIDTs show how the multilayer design influences the laser resistance of the MLD gratings. This result highlights the impact of the multilayer dielectric design on the electric field distribution and shows how to further improve the laser-induced damage threshold of pulse compression gratings.

Reconfigurable Geometrical Phase Spatial Light Modulator Using Short‐Pitch Ferroelectric Liquid Crystals

AbstractThis article presents an approach to achieve a fast and analog geometrical phase modulation based on the optical axis rotation of the defect‐free Deformed Helix Ferroelectric Liquid Crystal (DHFLC) with a short pitch. This study demonstrates a Spatial Light Modulator (SLM) prototype with a feature size of 3 µm without Fringe Field Effect (FFE), having a phase depth of 1.9π, fast switching time (<250 µs) at a low operating voltage (<7 V), and high diffraction efficiency (>77%). The high phase modulation depth is achieved by developing DHFLC with a cone angle of up to 85˚, which is inherently immune to FFE. The ellipticity is minimized by using a compensation film that can suppress the changes in birefringence under the applied electric field. The proposed SLM is promising in applications such as a real‐time hologram and dynamic beam steering in Light Ranging and Detector (LiDAR).

Large aperture and defect-free liquid crystal planar optics enabled by high-throughput pulsed polarization patterning.

The liquid crystal (LC) geometrical phase optics, which is realized by the high-resolution control of the optical axis orientation in transparent micrometer-thin polymer films, is emerging as a next generation of planar optics. It features pronounced optical properties and stimuli-responsive behaviors, which could introduce appealing and new possibilities for photonic purposes. The development of fabrication techniques producing elements with large aperture sizes and arbitrarily varying molecular orientation is of significance in terms of practical utility. Here, we propose the pulsed polarization patterning technique to create large-aperture and defect-free LC geometrical phase elements. We investigated the capability of the azo photo-alignment material responding to nanosecond laser pulses and the corresponding anchoring behaviors to LCs. The threshold was reduced to one fourth of that under the continuous wave recording. The patterning resolution was found to be enhanced to around 0.71 µm, due to the ultra-fast interaction nature of the photo-alignment material with the polarized light field. We proposed the flying exposure mode to deliver high frequency modulated polarized laser pulses (8 kHz), with the precision stage moving in a uniform velocity for light-field stitching and the servo auto-focusing in the sample normal, enabling the stable and reliable polarization patterning for large aperture sizes. We further report on representative fabrication of LC polarization gratings with an aperture of 4 inch and 99.2% average diffraction efficiency.

Design of an optical illumination system for a long wave infrared scene projector based on diffraction characteristics.

This study proposes an optical illumination system design based on vector diffraction characteristics and the Scheimpflug principle to determine an optimal relationship between illumination uniformity, energy utilization, and system size in an infrared scene projector. We investigate the influence of digital micromirror device (DMD) diffraction efficiency at different incidence angles on energy utilization rate and establish a two-dimensional diffraction grating model to determine the optimal incidence angle of the DMD beam. We demonstrate that the optical illumination system of a long-wave infrared (LWIR) scene projector based on diffraction characteristics can simulate an infrared scene with a compact structure, high energy efficiency, and high uniformity.

Using high-diffraction-efficiency holographic optical elements in a full-color augmented reality display system.

Holographic optical elements (HOEs) play an important role in augmented reality (AR) systems. However, the fabrication of full-color HOEs is difficult and the diffraction efficiency is low. In this paper, we use the time-scheduled iterative exposure method to fabricate full-color HOEs with high diffraction efficiency. Through this method, a full-color HOE with an average diffraction efficiency of 73.4% was implemented in a single photopolymer, the highest rate yet reported. In addition, the AR system is simulated by the geometric optics method combining k-vector circle and ray tracing and structured by combining laser micro-drop and high diffraction efficiency HOEs. A good color blending effect was achieved in a full-color AR system by using the reconstruction wavelength consistent with the recording light. It can present clear holographic images in a full-color AR display system.

High-speed and dynamic measurement of the diffraction efficiency of a grating in a wide wavelength range

Approximate 5 min are needed to obtain diffraction efficiency of a grating in a wavelength range with 151 sampling points by the currently widely used measurement technique. The time-consuming nature restricts its usage in many dynamic measurements. To this end, we developed a fast measurement technique, and the corresponding measurement is completed in a high speed within 1 s. Meanwhile, dynamic measurement of the efficiency of a grating from 600 nm to 900 nm during a heating procedure is successfully carried out. Our technique could find applications in other circumstances where high-speed measurement is needed.

Cascaded HfO2/SiO2 microstructure for symmetrical two-port beam dispersion

A new type of double-dielectric layer two-port beam splitter grating based on sandwich structure is proposed. This grating has the characteristic of zeroth order elimination. The structural parameters of the grating are optimized by the rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SAA) to achieve the best performance of the grating. For both TE and TM polarizations, the diffraction efficiencies of ±1st orders can reach 49.34% and 49.15%, respectively. Meanwhile, the efficiency of the zeroth order is about only 0.5% for both polarizations. This novel microstructure has the significant characteristic of zeroth order elimination. Moreover, this grating has a wide incident bandwidth and excellent manufacturing tolerance. The simplified modal method (SMM) is also used to study the specific process of energy coupling in the grating.

Structural and optical properties of triple-layer for high-uniformity beam division

In this paper, a triple-layer grating beam splitter with three-port output is designed. Through the combination of rigorous coupled-wave analysis (RCWA) and simulated annealing algorithms (SAA), the calculation and optimization of each parameter of the grating is carried out to make the diffraction efficiency of the grating meet the conditions. At the incident wavelength of 800[Formula: see text]nm, the diffraction efficiencies of 0th order and ±1st order under TE polarization are 31.6% and 31.4%, respectively. The diffraction efficiencies of 0th order and ±1st order under TM polarization are 32.7% and 32.5%, respectively. It can be seen that not only the total diffraction efficiency under TE polarization and TM polarization exceeds 90%, but also the uniformity of diffraction efficiency at each order exceeds 99%. Finally, the influence of grating parameters and incident wave characteristics on diffraction efficiency is discussed.

Embedded silicon gratings for high-efficiency light-chip coupling to thin film silicon nitride waveguides.

Thin film silicon nitride (<150 nm) waveguide has emerged as a dominant ultra-low-loss platform for many loss-critical applications. While thin-film silicon nitride propagation loss is a crucial characteristic, coupling light between an optical fiber and the waveguide is still challenging. While the larger mode size of the decoupled thin waveguide offers better coupling than a highly-confined waveguide, the coupling efficiency is still sub-optimal. The poor diffraction efficiency of such thin films limits the scope of implementing standalone surface gratings. We demonstrate an efficient way to couple into thin film silicon nitride waveguides using amorphous silicon strip gratings. The high contrast gratings provide an efficient means to boost the directionality from thin films leading to an enhanced coupling performance. In addition, we incorporate a bottom reflector to further improve the coupling. We present an optimal design for uniform strip gratings with a maximum coupling efficiency of -1.7 dB/coupler. We achieved a maximum coupling efficiency of -0.28 dB/coupler by engineering the scattering strength along the grating through apodization. We have experimentally shown the highest coupling efficiency reported yet of -2.22 dB/coupler and -1.84 dB/coupler for uniform and apodized grating couplers in the C-L band. We present a detailed design strategy, simulation, fabrication and characterization data on the effect of various parameters on the coupling efficiency.