Fabrication Errors Research Articles

Broadband ridge waveguide to rectangular waveguide transition design in D‐band

AbstractThis article presents a D‐band (110–170 GHz) double ridge waveguide (WG) to standard rectangular WG transition with an E‐bend near the WG end. The transition incorporates metal ridge steps as impedance transformers, resulting in a compact total size of 3.53 mm × 1.95 mm × 1 mm. Fabricated using micro metal additive manufacturing with copper in a monolithic back‐to‐back configuration, the transition demonstrates a bandwidth of 50% (105–175 GHz) with an average insertion loss of 0.72 dB and return loss better than 15 dB, respectively. Measurement results align closely with simulation expectations, with deviations attributed to fabrication and assembly errors.

Enhancing multi-plane light conversion orbital angular momentum multiplexer performance via error analysis

We present what we believe to be a novel orbital angular momentum (OAM) multiplexing apparatus capable of handling topological charges ranging from l = 0 to ±3 through multi-plane light conversion (MPLC) across four phase planes. Nevertheless, the fabricating process of MPLC devices is prone to errors that cannot be avoided. Our investigation primarily delves into the repercussions of misalignment and etching inaccuracies on the device's phase, with the assistance of a spatial light modulator. The scrutiny of fabrication errors associated with the device offers valuable insights for refining the fabricating of MPLC devices. The OAM multiplexing device converts the phase of MPLC onto a glass substrate through four etching steps, corresponding to a depth of 0-775 nm. OAM multiplexing/demultiplexing crosstalk based on MPLC is less than -20 dB and -18 dB, respectively. The insertion loss of the OAM mode generated by the OAM multiplexing device coupled to the few-mode fiber is less than 7 dB. In a communication experiment, we demonstrated multiplexed three OAM channels carrying 10 Gbit/s OOK signals over a 5 km few-mode fiber using two MPLC devices. Both the bit error rate curve and constellation diagram demonstrate the excellent performance of MPLC-based OAM multiplexing devices in communication networks.

Ultra-wideband solar perfect absorber for photothermal conversion with high manufacturing error tolerance

Solar energy is a key way to solve today's energy and environmental crises, and the full collection and utilization of solar energy requires a solar absorber with a broader spectrum and higher efficiency. Here, we present a solar metamaterial absorber, consisting of a Ti substrate, a Si3N4 dielectric spacer layer, and a Ti–SiO2 patterned layer. The results of the simulation show that the average absorption of the absorber is 98.16% in the range of 200–4200 nm under normal incidence. Its high absorption is attributed to the interaction of magnetic resonance (MR), cavity resonance (CR), guided mode resonance (GMR) and surface plasmon resonance (SPR). Moreover, the total absorption of the absorber in the AM1.5 standard solar radiation spectrum is 97.8% and the total absorption of blackbody radiation at 1500 K is 98.0%. In addition, the total photothermal conversion efficiency is still 92.2% at 1000 K. The proposed metamaterial absorber is also characterized by wide-angle incidence insensitivity, polarization-independence and a high tolerance of fabrication errors, which can be practically applied in the field of solar energy harvesting.

Freeform metasurface color router for deep submicron pixel image sensors.

Advances in imaging technologies have led to a high demand for ultracompact, high-resolution image sensors. However, color filter-based image sensors, now miniaturized to deep submicron pixel sizes, face challenges such as low signal-to-noise ratio due to fewer photons per pixel and inherent efficiency limitations from color filter arrays. Here, we demonstrate a freeform metasurface color router that achieves ultracompact pixel sizes while overcoming the efficiency limitations of conventional architectures by splitting and focusing visible light instead of filtering. This development is enabled by a fully differentiable topology optimization framework to maximize the use of the design space while ensuring fabrication feasibility and robustness to fabrication errors. The metasurface can distribute an average of 85% of incident visible light according to the Bayer pattern with a pixel size of 0.6 μm. The device and design methodology enable the compact, high-sensitivity, and high-resolution image sensors for various modern technologies and pave the way for the advanced photonic device design.

Acoustic Resonance Tuning by High-Order Lorentzian Mixing.

Nanoscale mechanical resonators have attracted a great deal of attention for signal processing, sensors, and quantum applications. Recent progress in ultrahigh-Q acoustic cavities in nanostructures allows strong interactions with various physical systems and advanced functional devices. Those acoustic cavities are highly sensitive to external perturbations, and it is hard to control those resonance properties since those responses are determined by the geometry and material. In this paper, we demonstrate a novel acoustic resonance tuning method by mixing high-order Lorentzian responses in an optomechanical system. Using weakly coupled phononic-crystal acoustic cavities, we achieve coherent mixing of second- and third-order Lorentzian responses, which is capable of the fine-tunability of the bandwidth and peak frequency of the resonance with a tuning range comparable to the acoustic dissipation rate of the device. This novel resonance tuning method can be widely applied to Lorentzian-response systems and optomechanics, especially active compensation for environmental fluctuation and fabrication errors.

Nanoimprinted TiO2 Metasurfaces with Reduced Meta-Atom Aspect Ratio and Enhanced Performance for Holographic Imaging.

Metasurface holograms, with the capability to manipulate spatial light amplitudes and phases, are considered next-generation solutions for holographic imaging. However, conventional fabrication approaches for meta-atoms are heavily dependent on electron-beam lithography (EBL), a technique known for its expensive and time-consuming nature. In this paper, a polarization-insensitive metasurface hologram is proposed using a cost-effective and rapid nanoimprinting method with titanium dioxide (TiO2) nanoparticle loaded polymer (NLP). Based on a simulation, it has been found that, despite a reduction in the aspect ratio of meta-atoms of nearly 20%, which is beneficial to silicon master etching, NLP filling, and the mold release processes, imaging efficiency can go up to 54% at wavelength of 532 nm. In addition, it demonstrates acceptable imaging quality at wavelengths of 473 and 671 nm. Moreover, the influence of fabrication errors and nanoimprinting material degradation in terms of residual layer thickness, meta-atom loss or fracture, thermal-induced dimensional variation, non-uniform distribution of TiO2 particles, etc., on the performance is investigated. The simulation results indicate that the proposed device exhibits a high tolerance to these defects, proving its applicability and robustness in practice.

Monolithic deformable mirror based on lithium niobate single crystal for high-resolution X-ray adaptive microscopy

X-ray microscopy is very promising not only for nondestructive and high-spatial-resolution observation of the internal structure of a sample but also for elemental distribution and chemical state analysis. However, the spatial resolution of microscopes remains unsatisfactory owing to the fabrication error in the objective lens. To realize an ultra-high-resolution, we propose and develop a monolithic deformable mirror based on a lithium niobite single crystal and a novel adaptive imaging system based on it. An X-ray interferometer confirmed that shape modification is possible with an accuracy of 0.67 nm in peak to valley under high stability (0.17 nm over 7 h) and hysteresis-free deformation control. Introducing this adaptive mirror into an X-ray microscope based on advanced Kirkpatrick-Baez mirror optics and correcting the wavefront aberration demonstrated that the X-ray image quality could be significantly improved.

3D-Printed Conformal Meta-Lens with Multiple Beam-Shaping Functionalities for Mm-Wave Sensing Applications.

In this paper, a 3D conformal meta-lens designed for manipulating electromagnetic beams via height-to-phase control is proposed. The structure consists of a 40 × 20 array of tunable unit cells fabricated using 3D printing, enabling full 360° phase compensation. A novel automatic synthesizing method (ASM) with an integrated optimization process based on genetic algorithm (GA) is adopted here to create the meta-lens. Simulation using CST Microwave Studio and MATLAB reveals the antenna's beam deflection capability by adjusting phase compensations for each unit cell. Various beam scanning techniques are demonstrated, including single-beam, dual-beam generation, and orbital angular momentum (OAM) beam deflection at different angles of 0°, 10°, 15°, 25°, 30°, and 45°. A 3D-printed prototype of the dual-beam feature has been fabricated and measured for validation purposes, with good agreement between both simulation and measurement results, with small discrepancies due to 3D printing's low resolution and fabrication errors. This meta-lens shows promise for low-cost, high-gain beam deflection in mm-wave wireless communication systems, especially for sensing applications, with potential for wider 2D beam scanning and independent beam deflection enhancements.

Towards high-performance polarimeters with large-area uniform chiral shells: a comparative study on the polarization detection precision enabled by the Mueller matrix and deep learning algorithm

Polarization detection and imaging technologies have attracted significant attention for their extensive applications in remote sensing, biological diagnosis, and beyond. However, previously reported polarimeters heavily relied on polarization-sensitive materials and pre- established mapping relationships between the Stokes parameters and detected light intensities. This dependence, along with fabrication and detection errors, severely constrain the working waveband and detection precision. In this work, we demonstrated a highly precise, stable, and broadband full-Stokes polarimeter based on large-area uniform chiral shells and a post-established mapping relationship. By precisely controlling the geometry through the deposition of Ag on a large-area microsphere monolayer with a uniform lattice, the optical chirality and anisotropy of chiral shells can reach about 0.15 (circular dichroism, CD) and 1.7, respectively. The post-established mapping relationship between the Stokes parameters and detected light intensities is established through training a deep learning algorithm (DLA) or fitting the derived mapping-relationship formula based on the Mueller matrix theory with a large dataset collected from our home-built polarization system. For the detection precision with DLA, the mean squared errors (MSEs) at 710 nm can reach 0.10% (S1), 0.41% (S2), and 0.24% (S3), while for the Mueller matrix theory, the corresponding values are 0.14% (S1), 0.46% (S2), and 0.48% (S3). The in-depth comparative studies indicate that the DLA outperforms the Mueller matrix theory in terms of detection precision and robustness, especially for weak illumination, small optical anisotropy and chirality. The averaged MSEs over a broad waveband ranging from 500 nm to 750 nm are 0.16% (S1), 0.46% (S2), and 0.61% (S3), which are significantly smaller than those derived from the Mueller matrix theory (0.45% (S1), 1% (S2), and 39.8% (S3)). The optical properties of chiral shells, the theory and DLA enabled mapping-relationships, the combination modes of chiral shells, and the MSE spectra have been systematically investigated.

Modifying single-crystal silicon and trimming silicon microring devices by femtosecond laser irradiation

Single-crystal silicon (c-Si) is a vital component of photonic devices and has obvious advantages. Moreover, femtosecond-pulsed laser interactions with matter have been widely applied in micro/nanoscale processing. In this paper, we report the modification mechanisms of c-Si induced by a femtosecond laser (350 fs, 520 nm) at different pulse fluences, along with the mechanism of this technique to trim the phase error of c-Si-based devices. In this study, several distinct types of final micro/nanostructures, such as amorphization and ablation, were analyzed. The near-surface morphology was characterized using optical microscopy, scanning electron microscopy, and atomic force microscopy. The main physical modification processes were further analyzed using a two-temperature model. By employing Raman spectroscopy, we demonstrated that a higher laser fluence significantly contributes to the formation of more amorphous silicon components. The thickness of the amorphous layer was almost uniform (approximately 30 nm) at different induced fluences, as determined using transmission electron microscopy. From the ellipsometry measurements, we demonstrated that the refractive index increases for amorphization while the ablation decreases. In addition, we investigated the ability of the femtosecond laser to modify the effective index of c-Si microring waveguides by either amorphization or ablation. Both blue and red shifts of resonance spectra were achieved in the microring devices, resulting in double-direction trimming. Our results provide further insight into the femtosecond laser modification mechanism of c-Si and may be a practical method for dealing with the fabrication errors of c-Si-based photonic devices.

The Effect of Height Error on Performance of Propagation Phase-Based Metalens.

Metalenses, as a new type of planar optical device with flexible design, play an important role in miniaturized and integrated optical devices. Propagation phase-based metalenses, known for their low loss and extensive design flexibility, are widely utilized in optical imaging and optical communication. However, fabrication errors introduced by thin-film deposition and etching processes inevitably result in variations in the height of the metalens structure, leading to the fabricated devices not performing as expected. Here, we introduce a reflective TiO2 metalens based on the propagation phase. Then, the relationship between the height variation and the performance of the metalens is explored by using the maximum phase error. Our results reveal that the height error of the unit structure affects the phase rather than the amplitude. The focusing efficiency of our metalens exhibits robustness to structural variations, with only a 5% decrease in focusing efficiency when the height varies within ±8% of the range. The contents discussed in this paper provide theoretical guidance for the unit design of the propagation phase-based metalens and the determination of its allowable fabrication error range, which is of great significance for low-cost and high-efficiency manufacturing.

Graphene-Dielectric metasurface of asymmetric grooved disks for biosensing and surface roughness evaluation

In this paper, we propose a high-performance graphene-dielectric metasurface that is applied as an optical biosensor. The proposed metasurface is based on an array of asymmetric grooved silicon disks grown over a graphene sheet. The asymmetric silicon disks lead to the formation of a high quality factor (Q-factor) Fano resonance. In addition to the sharp resonance, the strong field confinement provided by annular grooves results in an enhanced light-analyte interaction and sensitivity of as high as 640 nm/RIU. According to the presented results, the biosensor exhibits a high linearity R2 value of 0.999 and low resolution of 1.56e-4 RIU. Furthermore, the proposed biosensor is polarization-insensitive with a figure of merit (FOM) as high as 784 RIU−1. To the best of our knowledge, this is the highest FOM ever reported for a polarization-insensitive biosensor. Such characteristics are promising for effective detection of biomolecules like hemoglobin. Finally, the effect of surface roughness on performance of the proposed biosensor is investigated where different resonance characteristics and sensitivities are obtained. It implies that the proposed structure as a multiparameter sensor could be applied for biosensing and also for evaluation of the amount of surface roughness due to fabrication errors.

Design of photonic crystal fiber supporting 190 orbital angular momentum modes with low nonlinearity coefficient

A new photonic crystal fiber is proposed for the transmission of more orbital angular momentum modes with a rectangular air hole arrangement to increase the cladding air-filling rate. The results reveal that the fiber can support 190 orbital angular momentum modes in the C+L band, with the topological charge ordering up to 48, and the effective refractive index difference between adjacent eigenmodes is above 10−3. The effective mode area of all the eigenmodes is larger than 208.02 μm2, the nonlinearity coefficient is less than 0.43 W−1∙km−1, the confinement loss reaches up to 10−12-10−8 dB/m, the dispersion is flat and the minimum dispersion change is 3.15 ps∙nm−1∙km−1, with mode purity greater than 97.4%. Compared to existing typical orbital angular momentum transmission photonic crystal fibers, this fiber can support more orbital angular momentum modes for most purposes with lower nonlinearity coefficient, higher mode purity, better propagation characteristics but simpler structure. The highest nonlinearity coefficient is reduced by at least 0.3 W−1∙km−1 compared to existing typical orbital angular momentum transmission photonic crystal fibers. The effect of fabrication errors on the transmission quality of orbital angular momentum modes is also discussed, and the results reveal that the effect on mode transmission quality is small at 1–2% variations of air holes. Therefore, this photonic crystal fiber is promising in high-capacity communication systems.

Robust optical mode converter based on topological waveguide arrays

Abstract Optical mode converters are essential for enhancing the capacity of optical communication systems. However, fabrication errors restrict the further improvement of conventional mode converters. To address this challenge, we have designed an on-chip TE0–TE1 mode converter based on topologically protected waveguide arrays. The simulation results demonstrate that the converter exhibits a mode coupling efficiency of 93.5% near 1550 nm and can tolerate a relative fabrication error of 30%. Our design approach can be extended to enhance the robustness for other integrated photonic devices, beneficial for future development of optical network systems.

On-Chip Fabrication-Tolerant Exceptional Points Based on Dual-Scatterer Engineering.

The intriguing and anomalous optical characteristics of exceptional points (EPs) in optical resonators have attracted significant attention. While EP-related phenomena have been observed by perturbing resonators with off-chip components, implementing EPs fully on-chip remains challenging due to their extreme susceptibility to fabrication errors. In this Letter, we propose a succinct and compact approach to reach EP in an on-chip integrated silicon microring resonator by manipulating the evolution of backscatterings with two nanocylinders of disparate diameters. The theoretical analysis unveils that the fabrication constraints could be significantly relieved by increasing the difference in diameters of the nanocylinders. The evolution from non-EP to EP is traced experimentally through the step-by-step tuning of the angular and radial positions of nanocylinders. The proposed method opens a pathway toward the on-chip high-density integration of non-Hermitian devices.

Global optimization of multilayer dielectric coatings for precision measurements.

We describe the design of optimized multilayer dielectric coatings for precision laser interferometry. By setting up an appropriate cost function and then using a global optimizer to find a minimum in the parameter space, we were able to realize coating designs that meet the design requirements for spectral reflectivity, thermal noise, absorption, and tolerances to coating fabrication errors. We also present application of a Markov-Chain Monte Carlo (MCMC) based parameter estimation algorithm that can infer thicknesses of dielectric layers in a coating, given a measurement of the spectral reflectivity. This technique can be a powerful diagnostic tool for both commercial coating manufacturers, and the community using dielectric mirrors for precision metrology experiments.

Efficient Structure Transformation Based on Sensitivity-Oriented Structure Adjustment for Inverse-Designed Devices

Inverse-designed devices with thousands of degrees of freedom could achieve high performance in compact footprints, but typically have complex structure topologies that contain many irregular and tiny features and sharp corners, which tend to lead to a poor robustness to fabrication errors. In order to effectively transform the structure of inverse-designed nanophotonic devices into simple structure topologies that have high robustness to fabrication errors without sacrificing device performance, in this paper, we propose a structure adjustment method that innovatively adjusts the structures of inverse-designed devices by introducing their structural sensitivity to the optical performance, extracting the device substructures with high sensitivity and eliminating those with low sensitivity, and, finally, transforming the device structures into simple structure topologies with high robustness and better performance. Two devices (90° crossing and T-junction) were designed and fabrication tolerance simulation was conducted to verify the method. The results show that the devices designed using the proposed method achieved better performance and were more robust to under/over-etched errors.

Manufacturing evaluation of seven medical device companies during the production of a 3D-printed titanium pelvic implant

Powder bed fusion (PBF) technology has become a popular manufacturing method to fabricate custom metallic implants. This trend has generated some regulatory concerns because traditional developing guidelines are not suitable for three-dimensional (3D)-printed implants. This is due to the layered microstructure of additive manufactured parts that produces mechanical properties different than those of traditionally manufactured parts. The inappropriate choice of the process parameters and postprocessing methods can lead to fabrication errors that could negatively affect mechanical properties and dimensional accuracy. The objective of the study was to perform a preliminary evaluation of the quality of manufacturing provided by the medical device industry and identify the best 3D printing practices. We designed a pelvic bone reconstructing implant and asked seven companies to manufacture it in Ti6Al4V with PBF technology. We inspected some important aspects of the manufacturing quality of the prototypes received by evaluating geometrical precision and microstructural integrity in the surface and in the matrix, including a qualitative assessment of voids and grain morphology. Results demonstrated a great difference among the implant prototypes. Two companies proved to be superior and provided defect-free implants. The other five produced evidence of some defects including: geometrical deviations (maximum values of up to 5 mm); heterogeneous acicular grain morphologies; broken sections of lattice structures; and internal and superficial voids and cracks that could potentially compromise functional and clinical performance. To our knowledge, this is the first study analyzing the production of several custom implant additive manufacturers based on a geometrical and microstructural evaluation of the same pelvic implant fabrication. The imperfections found in some prototypes produced by companies certified to commercialize personalized implants highlight the urgent need for technical standards that regulate the safe development of 3D-printed implants. Further analyses are required to determine the actual clinical and mechanical consequences of such imperfections. The results also show that when additive manufacturing is adequately managed, it can be a valid manufacturing method to fabricate defect-free implants.

All-Glass 100 mm Diameter Visible Metalens for Imaging the Cosmos.

Metasurfaces, optics made from subwavelength-scale nanostructures, have been limited to millimeter-sizes by the scaling challenge of producing vast numbers of precisely engineered elements over a large area. In this study, we demonstrate an all-glass 100 mm diameter metasurface lens (metalens) comprising 18.7 billion nanostructures that operates in the visible spectrum with a fast f-number (f/1.5, NA = 0.32) using deep-ultraviolet (DUV) projection lithography. Our work overcomes the exposure area constraints of lithography tools and demonstrates that large metasurfaces are commercially feasible. Additionally, we investigate the impact of various fabrication errors on the imaging quality of the metalens, several of which are specific to such large area metasurfaces. We demonstrate direct astronomical imaging of the Sun, the Moon, and emission nebulae at visible wavelengths and validate the robustness of such metasurfaces under extreme environmental thermal swings for space applications.

Small random library method combined with local searching in optical critical dimension measurements.

The critical dimensions (CDs) of gratings significantly influence their optical performances and require high-resolution measurements. To avoid damaging the gratings, a model-based optical critical dimension (OCD) measurement method utilizing ellipsometry or scatterometry was applied by matching the simulated and experimental values. However, online CD measurements during grating fabrication require a bulky presimulated library containing the condition points with various CDs, making it time consuming and resource intensive to build with large dimension ranges to account for grating fabrication errors. In this study, we proposed a smaller random library with an unevenly distributed resolution, offering finer resolution when the grating to be measured is close to the reference grating. This approach, validated using a home-constructed spectroscopic ellipsometer, resulted in better results. Finally, a local search algorithm based on a random library was applied to further improve the measurement accuracy. This approach extraordinarily reduced the preparation time for OCD measurements and achieved better performance, significantly improving the efficiency of grating development and fabrication inspection.