Fabrication Errors Research Articles

Continuous phase modulation technology based on grating period interval for high grating coupling coefficient and precise wavelength control.

A novel, to the best of our knowledge, grating modulation technique for distributed feedback laser arrays is proposed and demonstrated. This method modifies the initial phase within each grating period, applying a total phase shift that increments in an arithmetic progression, realizing laser arrays with channel spacings of 0.493 nm, 0.949 nm, and 1.956 nm. This method maintains a coupling coefficient comparable to traditional uniform grating structures. Furthermore, the continuous phase modulation enhances the stability of the lasing wavelength of the primary mode, reducing sensitivity to fabrication errors. This improved tolerance to manufacturing inaccuracies represents a significant technological advancement, making this approach highly promising for applications requiring precise and stable wavelength control.

Selective passive tuning of cavity resonance by mode index engineering of the partial length of a cavity

Cavities in large-scale photonic integrated circuits (PICs) often suffer from a wider distribution of resonance frequencies due to fabrication errors. It is crucial to adjust the resonances of cavities using post-processing methods to minimize the frequency distribution. We have developed a concept of passive tuning by manipulating the mode index of a portion of a microring cavity, which we named mode index engineering (MIE). Through analytical studies and numerical experiments, we have found that depositing a thin film of dielectric material on top of the cavity or etching the material enables us to fine-tune the resonances and minimize the frequency distribution. This versatile method allows for the selective tuning of each cavity’s resonance in a large set of cavities in a post-fabrication step, providing robust passive tuning in large-scale PICs. We show that the proposed method achieves a tuning resolution below 1/Q and a range of up to 103/Q for visible to near-infrared wavelengths. Furthermore, this method can be applied and explored in various integrated photonic cavities and material configurations.

Polarization-independent full-color holographic movie with a single metasurface free from crosstalk.

Metasurface holograms offer advantages, such as a wide viewing angle, compact size, and high resolution. However, projecting a full-color movie using a single hologram without polarization dependence has remained challenging. Here, we report a full-color dielectric metasurface holographic movie with a resolution of 512 × 512. Eight frames were multiplexed across blue (445 nm), green (532 nm), and red (633 nm) color channels, achieving a maximum reconstruction rate of 5.6 frames per second. The superposition of the three wavelengths was achieved by adjusting the resolution and position of each target image while maintaining a constant pitch of the meta-atoms. Additionally, we identified the positions of crosstalk images generated that occur due to fabrication errors and proposed and demonstrated conditions and corrections to ensure they do not overlap with the intended images. The superimposition of phase distributions for each wavelength was achieved using the least squares error method, based on a library of over 20,000 types of meta-atoms. These results are anticipated to advance the future development of three-dimensional metasurface holographic movies.

Design, Analysis, and Implementation of the Subdivision Interpolation Technique for the Grating Interferometric Micro-Displacement Sensor

A high-resolution grating interferometric micro-displacement sensor utilizing the subdivision interpolation technique is proposed and experimentally demonstrated. As the interference laser intensity varies sinusoidally with displacement, subdivision interpolation is a promising technique to achieve micro-displacement detection with a high resolution and linearity. However, interpolation errors occur due to the phase imbalance, offset error, and amplitude mismatch between the orthogonal signals. To address these issues, a subdivision interpolation circuit, along with 90-degree phase-shifter and high-precision DC bias-voltage techniques, converts an analog sinusoidal signal into standard incremental digital signals. This novel methodology ensures that its performance is least affected by the nonidealities induced by fabrication and assembly errors. Detailed design, analysis, and experimentation studies have been conducted to validate the proposed methodology. The experimental results demonstrate that the micro-displacement sensor based on grating interferometry achieved a displacement resolution of less than 1.9 nm, an accuracy of 99.8%, and a subdivision interpolation factor of 208. This research provides a significant guide for achieving high-precision grating interferometric displacement measurements.

Artificial Intelligence Scribe and Large Language Model Technology in Healthcare Documentation: Advantages, Limitations, and Recommendations.

Artificial intelligence (AI) scribe applications in the healthcare community are in the early adoption phase and offer unprecedented efficiency for medical documentation. They typically use an application programming interface with a large language model (LLM), for example, generative pretrained transformer 4. They use automatic speech recognition on the physician-patient interaction, generating a full medical note for the encounter, together with a draft follow-up e-mail for the patient and, often, recommendations, all within seconds or minutes. This provides physicians with increased cognitive freedom during medical encounters due to less time needed interfacing with electronic medical records. However, careful proofreading of the AI-generated language by the physician signing the note is essential. Insidious and potentially significant errors of omission, fabrication, or substitution may occur. The neural network algorithms of LLMs have unpredictable sensitivity to user input and inherent variability in their output. LLMs are unconstrained by established medical knowledge or rules. As they gain increasing levels of access to large corpora of medical records, the explosion of discovered knowledge comes with large potential risks, including to patient privacy, and potential bias in algorithms. Medical AI developers should use robust regulatory oversights, adhere to ethical guidelines, correct bias in algorithms, and improve detection and correction of deviations from the intended output.

Broadband Thermo-Optic Photonic Switch for TE and TM Modes with Adiabatic Design

Optical power switches are essential components in fiber optic communication systems, requiring minimal losses, a broad operating wavelength range, and high tolerance to fabrication errors for optimal performance. Adiabatic optical power switches inherently meet these criteria and are well suited for manufacturing processes which support large-scale production at low costs. This paper presents the design and simulation of an adiabatic switch with a flat response in the whole 1525–1625 nm wavelength range (C band and L band) for both TE and TM polarizations. The switch is based on the thermo-optic effect induced by local variations in temperature. The impacts of the design parameters, such as the device length and dissipated heat, are analyzed. The simulation results indicate that the switch achieved high efficiency and low insertion losses, highlighting the potential of adiabatic switches for reliable and scalable integration into advanced optical circuits.

Optimization and characterization of a PCF-based SPR sensor for enhanced sensitivity and reliability in diverse chemical and biological applications

This paper presents the meticulous design and characterization of a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor, analyzed using finite element method (FEM) simulations. The sensor’s superior performance is demonstrated by its exceptional sensitivity to minute changes in the refractive index (RI) of various analytes. The optimized structure reveals a peak resonance at 0.78898 µm with a maximum confinement loss of 546.34 dB/cm. Detailed investigations show resonance wavelength red shifts of up to 0.93% with a 5% increase in air hole diameter and blue shifts of up to 0.88% with a 5% decrease. Additionally, variations in the plasmonic gold layer thickness result in resonance shifts of up to 0.76% longer or 0.87% shorter wavelengths. The sensor achieves remarkable wavelength sensitivity (WS) of up to 13,000 nm/RIU and amplitude sensitivity (AS) of up to 1538.90RIU−1, underscoring its high precision in detecting analyte concentration changes. The design’s robustness against fabrication errors, evidenced by minimal variations in resonance characteristics, highlights its practical reliability. Furthermore, the use of a polynomial regression model with an R2 value near unity accurately approximates the relationship between resonance wavelength and analyte RI, ensuring precise sensing capabilities without overfitting. Comparative analysis with existing designs confirms the sensor’s superior performance, rendering it highly suitable for a wide range of applications, including biosensing of glucose, water contaminated by cholera germs, mucosa of the human intestine, important components of human blood, and detection of chemicals like acetone, ethanol, benzene, propanol, glycerol, and expired transformer oil.

Robust inverse design of digital photonic devices for photonic integrated circuits.

Digital nanophotonic devices have achieved both an ultra-compact footprint and flexibly designed functions, which hold great potential for ultradense photonic integrated circuits. However, the performance deteriorates rapidly when the size of pixels varies due to fabrication errors. In this work, we propose an inverse design method called robust adjoint method to design fabrication-tolerant digital nanophotonic devices. In the proposed method, multiple patterns with identical pixel distribution but different pixel sizes are taken into account, ensuring that the optimized designs maintain high performance when the pixels suffer diameter variations. We experimentally demonstrate a three-mode (de)multiplexer and a three-mode broadcasting photonic integrated circuit, both designed by the robust adjoint method. For the three-mode (de)multiplexer, the device achieves insertion losses < 2.0 dB, and crosstalk < -17 dB across the wavelength range of 1530-1570 nm. When it suffers ±10 nm diameter variations, the device maintains insertion losses < 2.5 dB, and crosstalk < -17 dB across the wavelength range of 1530-1570 nm. Compared with the conventional adjoint method, the average insertion losses of TE1 and TE2 modes are reduced by 3.2 dB and 2.6 dB, respectively. For the three-mode broadcasting circuit, the average insertion losses of TE1 and TE2 modes are reduced by 6.1 dB and 5.9 dB respectively under ±10 nm diameter variations, in comparison to the conventional adjoint method. The proposed robust inverse design method offers significant promise for ultradense photonic integrated circuits.

Optical metasurface fabricated using 3D nanoimprint lithography

To improve the performance of the next-generation optical metasurface device, we investigated the feasibility of practical design and fabrication processes for 3D optical metasurface. 3D nanoimprint lithography technology could duplicate the multilayer pattern of the device in a single fabrication process with high resolution, which shows the prospect of manufacturing the 3D optical metasurface. To verify the superiority of this method, we designed a novel multilayer optical metasurface 1-to-8 beam splitter, which could achieve high energy utility efficiency and light intensity distribution of the eight beams based on the principle of Dammann grating. The multilayer structure that we designed was prepared on a Si wafer. Then, the pattern could be duplicated by the 3D nanoimprint lithography. We also do the sensitivity analysis on how the fabrication errors influence the optical properties of the device. The analytical results show the fabrication process is robust. The sample we made with 3D nanoimprint lithography technology has a performance of 86.4% power efficiency and only 2.33% light intensity deviation. The high device performance and the low fabricating cost show that the 3D nanoimprint lithography technology is a solid way to manufacture the optical metasurface with complex structures.

Effects of electrolyte flow direction on height difference in electroplated Cu microstructures for fine-pitch RDL

As demand for high-performance and efficient semiconductor chips surges, advanced packaging technologies, such as heterogeneous integration and vertical stacking, are becoming increasingly significant. Among these, the redistribution layer (RDL), essential for connecting chips or packaging elements, is being designed with finer line/space dimensions to meet the growing requirements for I/O access. However, as the width of copper lines decreases to several microns, various fabrication errors arise. Notably, variation in electroplated copper height becomes a significant issue, impacting the overall process. This study analyzes the height deposition differences in copper electroplating that occur at fine-pitch lines (width: 3–11 μm) and proposes a method to mitigate height deviations by adjusting the flow direction of the electrolyte. The results indicate that the deposition height difference between the 3 μm and 11 μm width patterns was reduced from 40% to less than 10%, demonstrating improved reliability in the RDL process by enhancing the uniformity of plating heights across both wide and narrow patterns.

The Design of Highly Reflective All-Dielectric Metasurfaces Based on Diamond Resonators

All-dielectric metasurfaces offer a low-loss alternative to plasmonic metasurfaces. We proposed the configuration for high-reflectivity all-dielectric metasurfaces based on single-crystal diamond (SCD) resonators on fused silica substrate and conducted simulations to optimize and analyze such a configuration via the FDTD solver. We utilized GMR as the design principle to select the configuration and the substrate material, and analyzed the scattering properties of a single SCD resonator by multipole decomposition. Then, we demonstrated that both the cylindrical resonators in square lattice and frustum-shaped resonators in hexagonal lattice can achieve near-unity reflectivity (&gt;99.99%) and ultra-low absorption (&lt;0.001%) at 795 nm, the typical alkali-metal laser wavelength. Additionally, we demonstrated that such a design is quite tolerant of fabrication errors and further supports its potential for realistic applications. To expand the functionality of such devices across multiple wavelengths, dual-band high-reflectivity metasurfaces at 744 nm and 828 nm were also designed. Our work is quite useful for designing diamond-based highly reflective mirrors, paving the way for low-loss all-dielectric reflective metasurfaces in high-power laser applications.

Topological State in Heterostructured Gap Waveguides and Their Transitions to Classical Transmission Line

AbstractGap waveguides play a crucial role in millimeter‐wave information transmission and processing for next‐generation wireless communication and radar sensing systems. However, they suffer from challenges, such as reflection and scattering losses at sharp bends and defects. While topological photonic crystals offer innovative solutions for robust signal transmission, their localized interface states and unique electromagnetic modes pose compatibility challenges with practical circuits and systems. In this paper, a novel heterostructured gap waveguide support valley‐locked topological guided wave transport is introduced. This design ensures robust propagation against defects and bends while maintaining compatibility with classical transmission lines. Its topological characteristic reduce sensitivity to fabrication and assembly errors. More importantly, an efficient transition structure is developed to seamlessly convert quasi‐transverse electromagnetic (quasi‐TEM) modes in planar transmission lines to topological guided wave states, thereby effectively exciting topological waves. All theoretical predictions are quantitatively verified by the simulations and experiments at millimeter wave frequency. This heterostructured gap waveguide can find unique applications, such as power divider, as verified numerically. By leveraging topological principles, the proposed gap waveguide offers a significant performance boost for antennas and passive/active components in millimeter‐wave applications, including automotive radar, 5G communication, and synthetic‐aperture radar for imaging.

A fixed phase tunable directional coupler based on coupling tuning

The field of photonic integrated circuits has witnessed significant progress in recent years, with a growing demand for devices that offer high-performance reconfigurability. Due to the inability of conventional tunable directional couplers (TDCs) to maintain a fixed phase while tuning the reflectivity, Mach-Zehnder interferometers (MZIs) are employed as the primary building blocks for reflectivity tuning in constructing large-scale circuits. However, MZIs are prone to fabrication errors due to the need for perfect balanced directional couplers to achieve 0-1 reflectivity, which hinders their scalability. In this study, we introduce a design of a TDC based on coupling constant tuning in the thin film Lithium Niobate platform and present an optimized design. Our optimized TDC design enables arbitrary reflectivity tuning while ensuring a consistent phase across a wide range of operating wavelengths. Furthermore, it exhibits fewer bending sections than MZIs and is inherently resilient to fabrication errors in waveguide geometry and coupling length compared to both MZIs and conventional TDCs. Our work contributes to developing high-performance photonic integrated circuits with implications for various fields, including optical communication systems and quantum information processing.

All-optical reconfigurable optical neural network chip based on wavelength division multiplexing.

Optical computing has become an important way to achieve low power consumption and high computation speed. Optical neural network (ONN) is one of the key branches of optical computing due to its wide range of applications. However, the integrated ONN schemes proposed in previous works have some disadvantages, such as fixed network structure, complex matrix-vector multiplication (MVM) unit, and few all-optical nonlinear activation function (NAF) methods. Moreover, for the most compact MVM schemes based on wavelength division multiplexing (WDM), it is infeasible to employ intrinsic nonlinear effects to implement NAF, which brings frequent O-E-O conversion in ONN chips. Besides, it is also hard to realize a reconfigurable ONN with coherent MVMs, while it is much easier to implement in WDM schemes. We propose for the first time an all-optical silicon-based ONN chip based on WDM by adopting a new adjustment mechanism: optical gradient force (OGF). The proposed scheme is reconfigurable with tunable layers, variable neurons per layer, and adjustable NAF curves. In the task of classification of the MNIST dataset, our chip can realize an accuracy of 85.13% with 4 full-connected layers and only 50 neurons in total. In addition, we analyze the influence of the OGF-based NAF under fabrication errors and propose a calibration method. Compared to the previous works, our scheme has the two-fold advantages of compactness and reconfiguration, and it paves the way for the all-optical ONN based on WDM and opens the path to unblocking the bottleneck of integrated large-dimension ONNs.

Modeling of Fabrication Errors Caused by Operator Habits in Substrate Alignment Process

Modeling of Fabrication Errors Caused by Operator Habits in Substrate Alignment Process

Optimization of highly sensitive three-layer photonic crystal fiber sensor based on plasmonic

In this work, a photonic crystal fiber (PCF) refractive index (RI) sensor has been designed and optimized. The RIs range covered by the sensor is from 1.38 to 1.41. The proposed optical sensor has three layers of air holes with 24, 12 and 6 holes in each layer. The geometry parameters of the proposed sensor (the radius of the air holes and the thickness of the plasmonic layer) have been optimized using the Nelder-Mead algorithm and the FEM numerical with the objective of achieving the highest sensitivity. To achieve an optimized structure with minimal sensitivity to fabrication errors, the rotation angle of the hole layers has been analyzed. The results indicate that, due to the specific geometry of the proposed structure, variations in the rotation angle and displacement of the air holes have no significant impact on the outcomes. The results also indicate that the sensor’s maximum amplitude sensitivity (AS), maximum wavelength sensitivity (WS), and figure of merit (FOM) are 10000 (RIU−1), 23000 (nm/RIU) and 131 (RIU−1) respectively. The optimized design provides high sensitivity, a wide diagnostic range for the detection of the analytes’ RIs, and the advantages of a gold plasmonic layer, ensuring high stability in biological environments. This combination results in enhanced performance of the sensor for various applications particularly in biosensing and medical fields. The designed structural geometry also eliminates the effects of tolerances in manufacturing processes which makes the proposed PCF device a very efficient sensor.

Photonic crystal topological interface state modulation for nonvolatile optical switching

Phase change materials (PCMs), characterized by high optical contrast (Δn&gt;1), nonvolatility (zero static power consumption), and quick phase change speed (∼ns), provide new opportunities for building low-power and highly integrated photonic tunable devices. Optical integrated devices based on PCMs, such as optical switches and optical routers, have demonstrated significant advantages in terms of modulation energy consumption and integration. In this paper, we theoretically verify the solution for a highly integrated nonvolatile optical switch based on the modulation of the topological interface state (TIS) in the quasi-one-dimensional photonic crystal (quasi-1D PC). The TIS exciting wavelength changes with the crystalline level of the PCM. The extinction ratio (ER) of the topological optical switch is over 18 dB with a modulation length of 9 μm. Meanwhile, the insertion loss (IL) can be controlled within 2 dB. Furthermore, we have analyzed the impact of fabrication errors on the device’s performance. The obtained results show that, the topological optical switch, which changes its “on/off” state by modulating TIS, exhibits enhanced robustness to the fabrication process. We provide an interesting and highly integrated scheme for designing the on-chip nonvolatile optical switch. It offers great potential for designing highly integrated on-chip optical switch arrays and nonvolatile optical neural networks.

Design of fabrication-tolerant meta-atoms for polarization-multiplexed metasurfaces

Metasurfaces can replace bulk optical components in a more compact form factor in applications including communication systems, sensors, and manufacturing technology. However, their design and fabrication is challenging due to competing demands of selecting meta-atoms that simultaneously provide the required amplitude and phase modulation while being robust to fabrication errors. Here, we develop two design heuristics to assist with the down-selection of meta-atoms into sensitivity-informed libraries, based on either selecting meta-atoms with minimal sensitivity or minimizing the relative sensitivities between meta-atoms. We evaluate both methods on a polarization-dependent phase mask and compare the resulting phase and intensity errors.Graphical

Absolute testing of rotationally symmetric surfaces with computer-generated holograms.

Extremely high accuracy is demanded for optics working at very short wavelength. Interferometric testing of optical aspheres or freeform surfaces requires null optics, typically computer-generated holograms (CGHs), to balance the wave aberrations. The measurement uncertainty is primarily limited by the accuracy of the test wavefront, which is predominantly influenced by the CGH and the interferometer optics. Absolute testing is fundamental to achieving accuracy much higher than that of the test wavefront through error separation. This paper presents a method for absolute testing of rotationally symmetric surfaces with CGH null optics. The basic assumption is that the off-axis hologram fabricated by raster scanning beam writing has negligible error of rotationally symmetric component due to pattern error of the CGH. Consequently, the wavefront error contributed by the CGH and the transmission flat can be completely separated from the absolute surface shape by combining the N-position method and the shift-rotation method. A theoretical model for absolute testing is proposed under the assumption. Experimental cross test is then presented to validate the method with sub-nanometer uncertainty. The assumption is further confirmed by characterizing the fabrication error of the hologram structures using a white light interferometer. Finally, the effect of noise, translation error, rotation error and eccentricity of rotation on the absolute testing is analyzed.

Research on multi-resonance mechanism to achieve ultra-wideband high absorption of a metamaterial absorber in the UV to MIR range

Wideband metamaterial perfect absorbers have been extensively researched due to their excellent properties. A four-layer ultra-broadband metamaterial perfect absorber engraved with a square cavity is proposed. A clever combination of grating and square cavity allows the absorber to manifests an overall absorption of over 92 % and an average absorption rate of 97.27 % within the operational band from 280 to 5400 nm. Through analysis, it can be concluded that the coupling effects of Rayleigh anomaly (RA), magnetic resonance (MR), cavity resonance (CR), propagating surface plasmon resonance (PSPR) and local surface plasmon resonance (LSPR) result in perfect absorption. The absorber is insensitive to polarization and large angle incidence. It is worth mentioning that the average absorption rate of our structure reaches 93.32 % at a large incidence angle of 60° in TE mode, which is much higher than that of other absorbers. At 1000 K, the total photothermal conversion efficiency of our absorber is still above 90 %. The designed structure has the following advantages: high absorption, ultra-wide bandwidth, high tolerance to fabrication errors and insensitivity to large angle incidence. Thus, the absorber can be used in the solar energy harvesting and perfect stealth. Additionally, it also can be served as a reference in thermophotovoltaics, thermal imaging and infrared detection.