Grating Beam Splitter Research Articles

Trapezoidal dual-function splitter under second Bragg incidence

In this paper, a reflective trapezoidal dual-functional beam splitter grating is proposed, which performs two independent functions at 1550 nm. For TE polarization, the grating can achieve a uniform three-port output with efficiencies of 32.85%, 32.89%, and 32.75% for 0th, -1st, and -2nd orders respectively. For TM polarization, the grating can achieve a highly-efficient single-channel output of order -2nd with an efficiency of 93.27%. HfO2 is chosen as the material of grating ridge layer, the structural parameters of the grating are studied by using rigorous coupled-wave analysis (RCWA) and simulated annealing algorithm (SAA), and the results are verified by using finite element method (FEM). In addition, the influence of structure and incident error on grating efficiency was also analyzed, the results indicate that the grating has good incident bandwidth and manufacturing tolerance with excellent performance.

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.

High-efficiency multi-port beam control device based on periodic nanodisk arrays

In this article, a multi-port two-dimensional (2D) reflective grating by a nanodisk array is proposed, which can be used for high-efficiency four-port ((0, ±1) and (±1, 0) orders) and five-port ((0, 0), (0, ±1) and (±1, 0) orders) optical control at a communication wavelength. Finite element method provides fast and effective optimization and analysis of the proposed 2D grating, while the 3D finite-difference time-domain provides strong support for the data in this paper. The four-port grating beam splitter has an efficiency of nearly 24% for all main diffraction orders with uniformity and polarization-dependent losses (PDL) of 0.8% and 0.08 dB, respectively. Meanwhile, the five-port grating beam splitter achieves an efficiency of over 19% for each diffraction order and in excess of 96% overall, with a uniformity and PDL of 0.4% and 0.06 dB, respectively. In addition, the detailed analysis of bandwidth performance and manufacturing tolerances shows the advantages of the proposed 2D nano-grating in practical applications and manufacturing. These findings have positive implications for future research on 2D nano-gratings, and the proposed 2D nano-grating has promising applications in the fields of sensor networks, grating measurements, photonic crystals, etc.

Diffraction-grating beam splitter, interferometric-lithography nanopatterning with a multilongitudinal-mode diode laser

Large-area, oblique-incidence interferometric nanopatterning using a low-cost multilongitudinal-mode diode laser as the source and a spin-on-glass based diffraction-phase-mask grating beam splitter is demonstrated. The phase mask is engineered to have only two equal intensity orders (0th and −1st), dramatically simplifying the optical arrangement and decreasing the propagation distance between the beam splitter and the sample. The low-cost, high-power (150 mW) TEM00 405-nm diode laser operates with a large number of longitudinal modes, resulting in an impractical mask-to-sample-gap proximity requirement. A dual-grating-mask, achromatic interferometric scheme is introduced to extend this gap dimension to easily accessible scales. Uniform nanopatterns with a periodicity of 600 nm were fabricated over a 1 cm diameter area using this multimode diode laser. This technique is scalable and has the potential for large-area nanopatterning applications.

Generation of highly mutually coherent hard-x-ray pulse pairs with an amplitude-splitting delay line

Beam splitters and delay lines are among the key building blocks of modern-day optical laser technologies. Progress in x-ray free electron laser source development and applications over the past decade is calling for their counter part operating in the Angstrom wavelength regime. Recent efforts in x-ray optics development have demonstrated relatively stable delay lines that most often adopted the division of wavefront approach for the beam splitting and recombination configuration. However, the two recombined beams have yet to achieve sufficient mutual coherence to enable applications such as interferometry, correlation spectroscopy, and nonlinear spectroscopy. We present the first experimental realization of the generation of highly mutually coherent pulse pairs using an amplitude-split delay line design based on transmission grating beam splitters and channel-cut crystal optic delay lines. The performance of the prototype system was analyzed in the context of x-ray coherent scattering and correlation spectroscopy, where we obtained nearly identical high-contrast speckle patterns from both branches. We show in addition the high level of dynamical stability during continuous delay scans, a capability essential for high sensitivity ultra-fast measurements.

Compact silica-based equal nine-channel generated by triple-layer arrays

In order to achieve the demands of multi-beam splitting in the optical communication system, a compact high-efficiency silica-based nine-channel beam splitter grating (BSG) at infrared wavelength is proposed based on a three-layer array structure. The grating profile parameters are investigated by the rigorous coupled-wave analysis (RCWA) and the finite-element method (FEM). The total efficiency of the nine-channel beam splitter reaches 96.98%, and the error of uniformity is reduced to 2.98%. The results show that the theoretical values of the two optimization methods are in good agreement. Moreover, the presented grating has a good performance against fabrication tolerances. The modal method is used for detailed physical explanation of the energy exchange and propagation modes inside the grating. The proposed high-efficiency nine-channel beam separation by three-layer arrays should be helpful for developing the multi-beam splitting of the optical system of the lithography machine and the new ultra-precision optical devices.

A single-chip multi-beam steering optical phased array: design rules and simulations.

A waveguide-based multi-beam steering device is proposed for light detection and ranging (LIDAR). The device integrates binary gratings with an optical phased array (OPA), thus enabling a single-chip LIDAR system. The device can provide an N×M beam array that covers a wide angular range while phase shifters help realize steering over a narrow angle range between the beams. The antenna structure for 1D beam splitting is realized by combining the design of a grating coupler and a beam splitter grating, and a uniform beam splitting is achieved along the other dimension using non-uniformly distributed antennas. To illustrate the design, an OPA with an 11×11 beam array is designed at a wavelength of 905 nm. The OPA achieves a wide total field of view (FOV) of 68.8° × 77° with a narrow beam-array-steering angle of 6.5°, enabling a wide-FOV 3D sensing with a high frame rate.

Shot noise limited soft x-ray absorption spectroscopy in solution at a SASE-FEL using a transmission grating beam splitter.

X-ray absorption near-edge structure (XANES) spectroscopy provides element specificity and is a powerful experimental method to probe local unoccupied electronic structures. In the soft x-ray regime, it is especially well suited for the study of 3d-metals and light elements such as nitrogen. Recent developments in vacuum-compatible liquid flat jets have facilitated soft x-ray transmission spectroscopy on molecules in solution, providing information on valence charge distributions of heteroatoms and metal centers. Here, we demonstrate XANES spectroscopy of molecules in solution at the nitrogen K-edge, performed at FLASH, the Free-Electron Laser (FEL) in Hamburg. A split-beam referencing scheme optimally characterizes the strong shot-to-shot fluctuations intrinsic to the process of self-amplified spontaneous emission on which most FELs are based. Due to this normalization, a sensitivity of 1% relative transmission change is achieved, limited by fundamental photon shot noise. The effective FEL bandwidth is increased by streaking the electron energy over the FEL pulse train to measure a wider spectral window without changing FEL parameters. We propose modifications to the experimental setup with the potential of improving the instrument sensitivity by two orders of magnitude, thereby exploiting the high peak fluence of FELs to enable unprecedented sensitivity for femtosecond XANES spectroscopy on liquids in the soft x-ray spectral region.

Parallel Broadband Femtosecond Reflection Spectroscopy at a Soft X-Ray Free-Electron Laser

X-ray absorption spectroscopy (XAS) and the directly linked X-ray reflectivity near absorption edges yield a wealth of specific information on the electronic structure around the resonantly addressed element. Observing the dynamic response of complex materials to optical excitations in pump–probe experiments requires high sensitivity to small changes in the spectra which in turn necessitates the brilliance of free electron laser (FEL) pulses. However, due to the fluctuating spectral content of pulses generated by self-amplified spontaneous emission (SASE), FEL experiments often struggle to reach the full sensitivity and time-resolution that FELs can in principle enable. Here, we implement a setup which solves two common challenges in this type of spectroscopy using FELs: First, we achieve a high spectral resolution by using a spectrometer downstream of the sample instead of a monochromator upstream of the sample. Thus, the full FEL bandwidth contributes to the measurement at the same time, and the FEL pulse duration is not elongated by a monochromator. Second, the FEL beam is divided into identical copies by a transmission grating beam splitter so that two spectra from separate spots on the sample (or from the sample and known reference) can be recorded in-parallel with the same spectrometer, enabling a spectrally resolved intensity normalization of pulse fluctuations in pump–probe scenarios. We analyze the capabilities of this setup around the oxygen K- and nickel L-edges recorded with third harmonic radiation of the free electron laser in Hamburg (FLASH), demonstrating the capability for pump–probe measurements with sensitivity to reflectivity changes on the per mill level.

Contrast analysis in two-beam laser interference lithography

Interference lithography enables large area, sub-µm, periodic patterning without photomasks or projection lithography tools. We show that optical contrast, which is the fundamental design variable of interference lithography, enforces coupled constraints on source coherence, beam pointing stability, field size, polarization state, and the intensity balance between beams. The analysis enables selection and alignment tolerance of components to meet a specific design requirement. In particular, the analysis reveals that grating beam splitters are significantly less sensitive to beam pointing and polarization misalignment than plate beam splitters.

Polarization-Independent Two-Layer Grating With Five-Port Splitting Output Under Normal Incidence

In this paper, we report a two-layer five-port diffraction grating by a polarization-independent design under normal incidence. To be different from conventional five-port gratings, initially, we design a novel two-layer grating with operation in transmission. Next, we firstly design a polarization-independent grating with five-port splitting output. On the one hand, the accurate grating vector parameters are optimized using rigorous coupled-wave analysis (RCWA) approach. On the other hand, the inherent coupling mechanism happened in the grating region can be well explained by employing simplified modal method (SMM). More importantly, all reported conventional five-port beam splitter gratings were designed based on polarization dependent. Although they could obtain high diffraction efficiency for TE or TM polarization, it requires more complicated and time-consuming fabrication processes in practical grating applications. Thus, this work can open up a possible thought for designing polarization-independent multi-port beam splitter diffraction gratings.

Wavefront preserving and high efficiency diamond grating beam splitter for x-ray free electron laser.

X-ray free electron lasers (XFELs) provide femtosecond high-power x-ray beams with high spatial coherence, resulting in numerous influential discoveries. Diffractive optics allow for the easy manipulation and measurement of an x-ray beam's wavefront and enable the realization of complex designed properties and specifications. For example, phase gratings can be used as x-ray beam splitters to enable beam sharing by multiple end stations or in-situ beam monitoring, including spectrum and wavefront measurements. Wavefront preservation and high efficiency and survivability under high power are requirements for such beam splitters. Diamond is the most suitable choice for phase grating fabrication, due to its high thermal conductivity that enables it to survive high average power XFEL beams. We have fabricated a large area (2×2 mm2) high aspect ratio (13:1) diamond grating on a diamond plate. Testing was performed at 9.5 keV and resulted in a high splitting efficiency (30%). Tunable efficiency was obtained via tilting the grating with respect to the x-ray beam. Wavefront fidelity of the split beams were measured to less than λ/100 using a Talbot wavefront sensor.

Flat transmitted serrated-phase high-contrast-index subwavelength grating beam splitter

We proposed a method to form a flat transmitted serrated-phase (SP) high-contrast-index subwavelength grating (HCG) beam splitter (HBS) for all dielectric materials, which is to alternately arrange two kinds of grating bars with a phase difference of π. Compared to the typical linear-phase (LP) HBS, which consists of two symmetrical deflecting gratings, the SP-HBS is extensible in size, and can achieve excellent splitting ability regardless of normal incidence or small-angle oblique incidence with large deflection angles, higher diffraction efficiency, lower energy loss, and higher tolerance of fabrication accuracy. Furthermore, the incident light can be split in half at any part of the SP-HBS, and the output beams of light maintain the original shape. In this Letter, we designed an SP-HBS with a 44.8° deflection angle and a 90.28% transmissivity.

Generation of three-port splitter by double-layer grating in second-order Littrow configuration

In this paper, a novel double-layer three-port grating is described. The incident grating structure is in the second-order Littrow configuration. The grating region is composed of fused silica and Ta2O5. The designed grating beam splitter has high efficiency under TE polarization and TM polarization, respectively. The efficiency of two polarizations is more than 90%. In addition, compared with a single-layer three-port grating, this new beam splitter has good fabrication tolerance and incident bandwidth. Therefore, the optimized structure has a good application value.

Formation of 1 × 3 splitting by embedded double-layer reflective grating under second Bragg illumination

In order to obtain a [Formula: see text] grating with high performance, we designed a double-layer reflective grating beam splitter with a covering layer at a wavelength of 1550 nm. We obtain a better grating structure by modal analysis and rigorous coupled-wave method. The reflectivity of the three diffraction orders for the grating is close to 33.3%. The optimized data show that the grating beam splitter has a large period process tolerance for TE polarization. The grating performance has high incident performance and uniform splitting effect.

Embedded dual-layered dielectric slit arrays under second Bragg incidence for 1×3 splitting field propagation

Embedded double-layer transmission grating beam splitter under the second Bragg incidence is presented in this paper. With a given duty cycle of 0.5 and a period of 940 nm, we use rigorous coupled-wave analysis method to investigate this beam splitter. The grating parameters are optimized for high-efficiency output. Each efficiency of the three orders under polarizations of TE and TM is close to 33.3 % respectively. Compared with the single-layer fused-silica grating, the three-port double-layer grating is flexible with complex structure and stable in performance. The field distribution modal method are given, which can well explain the propagation process and coupling mechanism.

Elimination of error induced by a beam splitter substrate for a dispersion-compensated polarization Sagnac interferometer.

A wire grating beam splitter (WGBS) substrate in a dispersion-compensated polarization Sagnac interferometer (DCPSI) may introduce an additional shear distance in the shear distance generated by the DCPSI, thereby causing poor adaptability of the DCPSI to white light. This work applies a compensation scheme of an optical flat with the same material and thickness as the WGBS and parallel to the WGBS introduced in the other arm of the DCPSI. Theoretically, this method can decrease the additional shear distance approaching 0. The ideal shear distance in the simulation experiment is 5.86mm, and the shear distance before and after compensation is 5.40 and 5.86mm, respectively. The theoretical value of the additional shear distance in this experiment is -0.6625 mm, and the average compensation value is 0.66mm. Overall, experiment and simulation results indicate that the above method can effectively eliminate the additional shear distance.

Si waveguide polarisation rotation chirped Bragg grating

Polarisation independent silicon waveguide wavelength filter using Bragg grating with chirped period is reported. The polarisation rotation and filter peak with wide flat top response is obtained. An antisymmetric grating structure and rib waveguide is used. We experimentally obtained polarisation independent flat-top band-pass filter consisting of polarisation beam splitter (PBS) and Bragg grating.

Analysis and Optimization of the Sandwiched Metal-Dielectric Polarizing Beam Splitter Grating

A reflective sandwiched polarizing beam splitter (PBS) grating with a connecting layer in Littrow mounting is described and designed in this paper. By using two-beam-interference theory for a modal method, a duty cycle and a period of grating can be calculated, where the first order is well suppressed for transverse magnetic (TM) polarization. In addition, the grating groove depth can be roughly evaluated, in which the zeroth order is well restrained for transverse electric (TE) polarization. By using numerical optimization for rigorous coupled-wave analysis, some of exact parameters of grating are obtained. On the basis of the precise numerical results, the diffraction efficiencies in the first order and in the zeroth order for TE polarization and TM polarization are enhanced, respectively. Most importantly, compared to the reported surface-relief reflective PBS gratings, the grating extinction ratio and incident spectrum band width can be improved greatly. Therefore, this highly efficient PBS wideband grating with high extinction ratio would become excellent optical diffraction device.

Investigation on multilayer microstructure grating for three-port splitting

A new structure of microstructure reflection three-port beam splitter grating is described in this paper. The grating includes two dielectric layers and a metal slab on the substrate, where incident waves are reflected into the zeroth-order and the ± first-order with polarization-independent property. With the optimized grating profile, reflection efficiencies’ ratios between the first-order and the zeroth-order can reach 0.998 and 1.001 for TE and TM polarizations, respectively. Especially, the reflection grating can diffract efficiencies more than 30% into the ± first-order and the zeroth-order with the incident angular bandwidth of −1.9–1.9[Formula: see text] for TM polarization, which can have merits compared with single-layer transmission grating.