Fabrication Errors Research Articles

Theoretical research of chalcogenide waveguide CH4 sensor based on lift‐off method

AbstractChalcogenide (ChG) waveguide gas sensor with good application prospect at mid‐infrared band can be fabricated by the lift‐off method with a simple process. However, the inclined sidewalls of the core layer caused by lift‐off are unavoidable. The TE and TM mode ChG rectangular waveguides were optimized and the influence of inclined angle on the sensing performance was studied. The performance of TE mode ChG waveguide is more affected by the fabrication error of the inclined angle. The relative variation of the external confinement factor and limit of detection of the TM mode waveguide are 10 and 23 times smaller than that of the TE mode waveguide. This work provides guidance for the design, fabrication, and application of the ChG waveguide gas sensors fabricated by the lift‐off method.

The Effect of Fabrication Error on the Performance of Mid-Infrared Metalens with Large Field-of-View.

Mid-infrared large field-of-view (FOV) imaging optics play a vital role in infrared imaging and detection. The metalens, which is composed of subwavelength-arrayed structures, provides a new possibility for the miniaturization of large FOV imaging systems. However, the inaccuracy during fabrication is the main obstacle to developing practical uses for metalenses. Here, we introduce the principle and method of designing a large FOV doublet metalens at the mid-infrared band. Then, the quantitative relationship between the fabrication error and the performance of the doublet metalens with a large FOV from four different fabrication errors is explored by using the finite-difference time-domain method. The simulation results show that the inclined sidewall error has the greatest impact on the focusing performance, and the interlayer alignment error deforms the focusing beam and affects the focusing performance, while the spacer thickness error has almost no impact on the performance. The contents discussed in this paper can help manufacturers determine the allowable processing error range of the large FOV doublet metalens and the priority level for optimizing the process, which is of significance.

Optimization of bulk sensitivity for strip, slot, and subwavelength grating-based waveguides for dual-polarization operation.

We propose a dual-polarization optimization method for the bulk sensitivity of silicon-on-insulator (SOI) waveguides by defining a multi-objective function that accounts for the substrate leakage losses. The proposed optimization method was used to design micro-ring resonator bulk sensors with strip, slot, subwavelength grating, and subwavelength grating slot waveguides. The subwavelength grating slot waveguide has a bulk sensitivity of 520 nm/RIU and 325 nm/RIU for the TE and TM modes, respectively, both of which are higher than the bulk sensitivities of strip, slot, and subwavelength grating waveguides. Moreover, our Monte Carlo analysis shows that the subwavelength grating slot waveguide has the highest immunity to fabrication errors.

Fabrication error detection in diffraction gratings with high dynamic range Fourier plane imaging and spatial filtering

We summarize our development of a low-cost instrument for the detection of fabrication errors in diffraction gratings. Our instrument applies a low-cost digital camera and high dynamic range (HDR) imaging in the focal plane of a lens to analyze light reflected by a diffraction grating. A dynamic range close to 1010 is achieved for a spatial frequency range that is relevant for types of errors that occur in the lithographic fabrication of gratings. We also describe a modification of the instrument in which a spatial filter is used to block the large fraction of light that does not carry information on fabrication errors. This “coronagraph” modification reduces measurement times by about an order of magnitude. A unique pseudologarithmic transformation is described for the visualization of wide range data that include zero or negative values, such as HDR images.

A self-similar sine–cosine fractal architecture for multiport interferometers

Abstract Multiport interferometers based on integrated beamsplitter meshes have recently captured interest as a platform for many emerging technologies. In this paper, we present a novel architecture for multiport interferometers based on the sine–cosine fractal decomposition of a unitary matrix. Our architecture is unique in that it is self-similar, enabling the construction of modular multi-chiplet devices. Due to this modularity, our design enjoys improved resilience to hardware imperfections as compared to conventional multiport interferometers. Additionally, the structure of our circuit enables systematic truncation, which is key in reducing the hardware footprint of the chip as well as compute time in training optical neural networks, while maintaining full connectivity. Numerical simulations show that truncation of these meshes gives robust performance even under large fabrication errors. This design is a step forward in the construction of large-scale programmable photonics, removing a major hurdle in scaling up to practical machine learning and quantum computing applications.

Fabrication of biconvex spherical and aspherical lenses using 3D printing.

In this work, we present the methods of fabrication and characterization of biconvex spherical and aspherical lenses with 25 and 50 mm diameters that have been created via additive technology using a Formlabs Form 3 stereolithography 3D printer. After the prototypes are postprocessed, fabrication errors ≤2.47% for the radius of curvature, the optical power, and the focal length are obtained. We show eye fundus images captured with an indirect ophthalmoscope using the printed biconvex aspherical prototypes, proving the functionality of both the fabricated lenses and the proposed method, which is fast and low-cost.

Non-Destructive Evaluation of Preload Loss of Bolted Spherical Joints Based on Time Reversal Acoustics: A Numerical Simulation

Bolted spherical joints are widely used in space grid structures. However, the preload loss, which may arise from fabrication error, insufficient twist of the screw and some other unknown reasons can undermine the structural integrity and even lead to the collapse of the whole structure. Therefore, a method for evaluating the preload status of bolted spherical joints is vital to the structural health monitoring of the space grid structures. To this end, a non-destructive evaluation of the preload loss of bolted spherical joints based on time reversal acoustics (TRA) is presented. In this method, an excited signal generated by a lead zirconate titanate (PZT) patch at the bolted sphere is reconstructed after the signal recorded by another PZT patch at the bar is time-reversed and re-emitted. The deviation of the reconstructed signal from the initial signal allows identification of preload loss of the bolted spherical joint. This method is demonstrated to be effective by a finite element simulation. Furthermore, the effect of preload loss of the bolted spherical joint on its ultimate flexural capacity is studied, which highlights the necessity for the non-destructive evaluation.

Design and analysis of a compact micro-ring resonator signal emitter to reduce the uniformity-induced phase distortion and crosstalk in orbital angular momentum (OAM) division multiplexing.

To improve the transmission capacity of an optical system, different multiplexing schemes have been proposed, such as optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), polarization division multiplexing (PolDM), spatial division multiplexing (SDM), etc. One kind of SDM technique to boost the capacity is through modifying the spatial phase structure of an optical beam, which is known as the orbital angular momentum (OAM) division multiplexing. Moreover, the OAM signal emitter can be produced by using mature and high-yield silicon photonic (SiPh) technology, without the need of using bulky optical components or expensive spatial light modulator (SLM). The SiPh-based micro-ring resonator is one of the promising OAM signal emitter candidates, since it is simple, compact and easy to fabricate. However, the device performance is highly subjected to the structural design, and the uniformity-induced phase distortion will significantly degrade the purities of OAM beams; hence, introducing severe OAM signal crosstalk during the OAM division multiplexing. In this work, a compact SiPh-based micro-ring resonator type OAM signal emitter with detailed design parameters is presented and the output signal uniformity issue is comprehensively investigated. Two kinds of the structural optimization are performed by adjusting the angular grating width as well as the grating height. The results indicate that a significant improvement in output OAM beam uniformity can be achieved, with the attenuation factor being improved over 88% at the price of acceptable 4 ∼ 5% coupling efficiency reduction. The variations of the transmission and the uniformity induced by the fabrication error are also analyzed.

Polarization independent Bragg gratings using tilted subwavelength grating waveguide Bragg gratings.

We propose and experimentally demonstrate a polarization independent subwavelength grating (SWG) waveguide Bragg grating (WBG) by using an SWG waveguide with tilted segments. By optimizing the tilting angle and other geometry parameters, such as the width and the length of the loading segments used to create the BG, we can obtain a zero birefringence tilted SWG waveguide and consequently, a polarization independent SWG WBG. In our simulations, the optimal tilting angle is ∼ 58°, whereas the optimal angle obtained in fabrication is ∼ 46°. This deviation is mainly due to fabrication errors, e.g., on the sidewall angle of the silicon segments. For the optimal tilting angle of 46°, the characterized Bragg wavelengths of the TE and TM modes are both ∼ 1517 nm. We believe that the proposed device can have applications in optical communications and interconnections.

Fabrication error analysis of nonperiodic-multilayer-dielectric gratings

We analyzed fabrication errors of nonperiodic-multilayer-dielectric gratings that were designed to have a high reflective diffraction efficiency for one wavelength and a high transmittance for another wavelength at the same time. Significant deviations were found between the measured and calculated efficiency values although the groove profile parameters were very closed to the design values. The source of error was attributed to coating errors of the film stack. To explain the deviation well, we estimated the parameters of actual coating stack by reverse calculations and using scanning electron microscope. We recalculated the diffraction efficiencies and the results showed that the actual film stack parameters were inverted well. This provided a foundation for us to reoptimize grating groove parameters on the basis of actual coating stack.

Real-Valued Optical Matrix Computing with Simplified MZI Mesh

The Mach–Zehnder interferometer (MZI) mesh, a mainstream structure for optical matrix-vector multiplication (MVM), has been widely employed in recently developed optical neural networks (ONNs) and combination optimization problem solvers. The conventional MZI mesh was designed specifically for complex-valued optical MVM. The network includes 2 N 2 phase shifters, and coherent detection is indispensable for retrieving the output complex-valued vectors. Nonetheless, the majority of applications, including ONNs, merely require real-valued optical matrices with N 2 degrees of freedom (DOFs). The DOF gap between the 2 types of matrices results in a severe redundancy in the number of phase shifters when the conventional MZI mesh is applied to implement real-valued optical MVM. In this study, we propose a simplified MZI mesh for performing real-valued incoherent optical MVM. It has N 2 phase shifters and an optical depth of N + 1, and it outperforms the conventional MZI mesh. Furthermore, we constructed an ONN with the proposed MZI mesh and successfully performed the iris classification task via in situ training of particle swarm optimization. More importantly, we introduced a matched on-chip nonlinear activation function, so the proposed MZI mesh can be cascaded onto a single chip. Overall, the proposed real-valued MZI mesh and in situ training method are space efficient, energy efficient, scalable, and robust to fabrication errors. Therefore, they are suitable for large-scale ONNs.

Technology for developing a high-aperture four-mirror lens with aspherical mirrors

Subject of study: Methods for optimizing the design, assembly, and alignment of a high-aperture wide-angle four-mirror axisymmetric lens are presented. Aim of study: The aim is the development of a high-tech lens design considering the relationship between the calculated tolerances for the decentering of mirrors and the technological capabilities of their fabrication, assembly, and alignment. Method: The methods include selection of an image quality criterion and calculation of its permissible decrease, distribution of the fabrication errors between the decentering errors and surface shape errors, and calculation of the tolerances based on the obtained ratios. Moreover, the motivation for choosing a lens design with a minimum number of adjustment stages based on the optimization of the calculated permissible decentering is provided considering the technological tolerances for positioning the optical elements. In addition, the possibilities of the scheme to compensate for the residual aberrations resulting from the fabrication and positioning of the mirrors are investigated. At the final stage, the method of reducing the evaluation function for the final adjustment of the optical elements in the lens is used. Main results: The design and technological solutions enabling the optimization of the requirements for the tolerances for deviation of the surface shape of the mirrors from their calculated profile, as well as decentering of the optical elements considering the technological capabilities of production, are examined. The criteria for the distribution of tolerances for permissible deviations of optical system parameters affecting the image quality are formulated. The possibility of designing a high-tech drop-in structure of a high-aperture four-mirror lens comprising a case of two blocks and a single linear adjustment stage of the second mirror to compensate for residual aberrations is demonstrated using the proposed method. Practical significance: The proposed technical solutions were tested by designing a high-resolution lens comprising four aspherical mirrors. The positive results of fabricating a lens with a high aperture and resolution allow the proposed solutions to be used for the design of multimirror axisymmetric lenses.

Development and Performance Evaluation of a Mix-Kneader for Drying Soap

Soap is a salt of fatty acids obtained worldwide from mainly agricultural products and by-products such as plant (vegetable) oils (Yahaya et al., 2012). Drying neat soap is one of the key steps in the process of manufacturing bar soap. Currently, small and medium-scale local processors in Uganda rely entirely on tarpaulins and buckets to dry neat soap. These methods are labor intensive and take a lot of time (about 24 hours) to dry soap from 29-35% (w.b.) to the required moisture content of 15% – 21% (w.b.). Therefore, the aim of this research was to develop a Mix-kneader for drying soap in order to boost local production of bar soap. First, the different parts of the machine were designed and sized with the help of Solid Edge ST9 mechanical computer-based software. Fabrication of the component parts was done and finally, performance evaluation of the machine was carried out. At ‘No’ load test, the results indicated that the machine can run freely without too much noise and there were no visual breakdowns. At ‘Full’ load test, the Mix-kneader was able to dry 180 kg of neat soap in an average time of 15.5 minutes. The average machine capacity was approximately 560 kg/hr with a drying efficiency of 83.4%. The drying rate of the machine was calculated as 2.13 kg of water per minute. The material wastage was calculated as 1.31% which can be attributed to the fabrication errors. The developed Mix-kneader is affordable to processors and can be fabricated from any workshop within the country since it was developed from locally available materials.

Harnessing Dynamical Encircling of an Exceptional Point in Anti-PT-Symmetric Integrated Photonic Systems.

Dynamically encircling an exceptional point in a non-Hermitian system can lead to chiral behaviors, but this process is difficult for on-chip PT-symmetric devices which require accurate control of gain and loss rates. Here, we experimentally demonstrated encircling an exceptional point with a fixed loss rate in a compact anti-PT-symmetric integrated photonic system, where chiral mode switching was achieved within a length that is an order of magnitude shorter than that of a PT-symmetric system. Based on the experimental demonstration, we proposed a topologically protected mode (de)multiplexer that is robust against fabrication errors with a wide operating wavelength range. With the advantages of simplified fabrication and characterization processes, the demonstrated system can be used for studying higher-order exceptional points and for exotic light manipulation.

A novel S-shaped frequency and pattern reconfigurable patch antenna for 4G LTE, WLAN/Wi-Max application

PurposeIn wireless communication system, use of multiple antennas for different requirements of system will increase the system complexity. However, reconfigurable antenna is maximizing the connectivity to cover different wireless services that operate different frequency range. Pattern reconfigurable antenna can improve security, avoid noise and save energy. Due to their compactness and better performance at different applications, reconfigurable antennas are very popular among the researchers. The purpose of this work, is to propose a novel design of S-shaped antenna with frequency and pattern diversity. The pattern and frequency reconfiguration are controlled via ON/OFF states of the PIN diode.Design/methodology/approachThe geometrical structure of the proposed antenna dimension is 18 × 18 × 0.787 mm3 with εr = 2.2 dielectric constant. Three S-shaped patches are connected to a ring patch through PIN diodes. The approximate circumference of ring patch is 18.84 mm and length of patch is 5 mm, so approximate length of radiating patch is 14.42 mm and effective dielectric constant is 1.93. Conductor backed coplanar waveguide (CPW) is used for feeding. The proposed antenna is designed and simulated on CST microwave studio and fabricated using photolithography process. Measurements have been done in anechoic chamber.FindingsAntenna shows the dual band operation at 2.1 and 3.4 GHz frequency. The first band remains constant at 2.1 GHz resonant frequency and 200–400 MHz impedance bandwidth. Second band is switched at seven different resonant frequencies as 3.14, 3.45, 3.46, 3.68, 3.69, 3.83 and 3.86 GHz with switching of the diodes. The −10 dB bandwidth is more than 1.4 GHz.Research limitations/implicationsPattern reconfigurability can be achieved using mechanical movement of antenna easily but it is not a reliable approach for planar antennas. Electronic switching method is used in proposed antenna. Antenna size is very small so fabrication is very crucial task. Measured results are deviated from simulation results due to fabrication error and effect of leads of diodes, connecting wires and battery.Practical implicationsThe reconfiguration of the proposed antenna is controlled via ON/OFF states of the three PIN diodes. The lower band of 2.1 GHz is fixed, while second band is switched at five different resonant frequencies as 3.27, 3.41, 3.45, 3.55 and 3.88 GHz, with switching of the PIN diodes with all state of diodes and exhibit pattern reconfigurability at 2.1 GHz frequency. At second band center frequency is significantly changed with state of diodes and at 3.4 GHz pattern is also changed with state of diodes, hence antenna exhibits frequency and pattern reconfigurability.Originality/valueA novel design of pattern and frequency reconfigurable antenna is proposed. Here, work is divided into two parts: first is frequency reconfiguration and second is radiation pattern reconfiguration. PIN diodes as switch are used to select the frequency band and reconfigure the radiation pattern. This proposed antenna design is novel dual band frequency and pattern reconfigurable antenna. It resonates at two distinct frequencies, i.e. 2.1 and 3.4 GHz, and has a pattern tilt from 0° to 355°. The conductor backed CPW feed technique is used for impedance matching.

A Demultiplexing Filter With Box-Like Response and Large FSR Based on LNOI Second-Order Micro-Ring Resonators

We propose and experimentally demonstrate a high-performance micro-ring resonator (MRR) with a large free-spectral range (FSR) on the lithium niobate-on-insulator (LNOI) platform. Mode crosstalk happens in LNOI waveguide bends because more than one mode is generated from the anisotropy of lithium niobate, which limits the minimum bending radius of MRRs. Mode properties of ridge waveguides on X-cut LNOI with different bend radii and wavelengths have been analyzed to remove the effect of mode hybridization and reduce the mode crosstalk. On this basis, a small radius MRR with large FSR and 3dB bandwidth is achieved. Further, to deal with the wavelength shift caused by fabrication error, a second-order micro-ring resonators (2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order MRRs) filter with a box-like response and a high out-of-band rejection ratio is realized. Besides, a multichannel demultiplexing filter is realized based on 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order MRRs with low crosstalk (<−13 dB) at a channel spacing of 1.16 nm. The demonstration of the demultiplexing filter with a box-like response paves an important step for high-density photonic integration on the LNOI platform.

Troubleshooting in complete denture fabrication.

In countries with a high amount of geriatric patients, it is mandatory for a dental clinician to have working knowledge on complete denture (CD) procedures. The aim of this study was to troubleshoot the errors in denture fabrication by assessing the difficulties in clinical procedures. A questionnaire was distributed among dental undergraduates across the country in the present study. A total of 26 questions were included in the study. An online sharing medium was used for distribution and a total of 140 responses were received. SPSS for windows, version 20 was used for data tabulation. Descriptive statistics and Chi-square test were done. The results of this study revealed that jaw relation was the most difficult procedure followed by border molding. Multiple problems arise from the practitioner's end due to the lack of knowledge. One of the causes for these problems could be inability to learn the principles and procedures during the undergraduate program. This must be addressed at the base level so that better care can be given to patients.

Robust Directional Couplers for State Manipulation in Silicon Photonic-Integrated Circuits

Photonic integrated circuits play a central role in current and future applications such as communications, sensing, ranging, and information processing. Photonic quantum computing will also likely require an integrated optics architecture for improved stability, scalability, and performance. Fault-tolerant quantum computing mandates very accurate and robust quantum gates. In this work, we demonstrate high-fidelity directional couplers for single-qubit gates in photonic integrated waveguides, utilizing a novel scheme of detuning-modulated composite segments. Specific designs for reduced sensitivity to wavelength variations and real-world geometrical fabrication errors in waveguides width and depth are presented. Enhanced wavelength tolerance is demonstrated experimentally. The concept shows great promise for scaling high fidelity gates as part of integrated quantum optics architectures.

Influencing Effects of Fabrication Errors on Performances of the Dielectric Metalens.

Despite continuous developments of manufacturing technology for micro-devices and nano-devices, fabrication errors still exist during the manufacturing process. To reduce manufacturing costs and save time, it is necessary to analyze the effects of fabrication errors on the performances of micro-/nano-devices, such as the dielectric metasurface-based metalens. Here, we mainly analyzed the influences of fabrication errors in dielectric metasurface-based metalens, including geometric size and shape of the unit element, on the focusing efficiency and the full width at half maximum (FWHM) values. Simulation results demonstrated that the performance of the metasurface was robust to fabrication errors within a certain range, which provides a theoretical guide for the concrete fabrication processes of dielectric metasurfaces.

Optical design of a null test for off-axis three-mirror system based on refractive-diffractive zoom hybrid compensator

In general, the reflectors of off-axis three-mirror system have large apertures and large differences in surface shape, which means it is difficult to use one set of null compensators to test all the aspheric mirrors in the off-axis three-mirror system because of the limitation of the dynamic range of the testing equipment. In this paper, we propose a surface shape test method that combines a refractive-zoom lens group and a Spatial Light Modulator (SLM) as a null compensator to test all the aspheric surfaces of one off-axis three-mirror system. The proposed method is verified by simulating the null test process of three aspheric mirrors of one off-axis three-mirror system, with the consideration of the fabrication and alignment errors. Simulation results show that the probability that residual wave aberration is within 0.1λ RMS is 50% for the primary mirror and 40% for the secondary mirror and 80% for the tertiary mirror.