Tolerance To Fabrication Errors Research Articles

Orbital angular momentum mode multiplexing communication in multimode fibers

Vortex beams with orbital angular momentum (OAM) have infinite mode orthogonality, which can greatly boost communication capacity through mode-division multiplexing. However, current exploration of OAM beam transmission primarily focuses on free-space or specialty fibers limited by the OAM spiral phase wavefront characteristics. Due to the mode field phase sensitivity, these methods are constrained by turbulence interference and fabrication error tolerance, restricting transmission distance of OAM beam at practical application. Herein, we propose an OAM transmission scheme using commercial multimode fiber (MMF) exploiting the eigenmodes superposition theory. Leveraging linear superposition of HE and EH vector modes with ± (π/2) phase shift over MMF, OAM excitation and transmission can be supported with low interference. Simultaneously, due to the decreased demand for fabrication precision in the gradient core structure, the tolerance for machining errors is enhanced. As a proof-of-concept, we have demonstrated a multidimensional OAM multiplexing communication with 640-channel (4 OAM modes, 80 wavelengths and 2 polarization states) over a 5 km MMF, successfully transmitting QPSK-OFDM signals at a total rate of 15 Tbit/s. The system demonstrated OAM mode purity exceeding 65% and bit error rate (BER) below the forward error correction (FEC) threshold (3.8 × 10−3). Multiplexed OAM signals can be effectively transmitted in MMF over short to medium distances with acceptable mode crosstalk, while remaining compatible with wavelength and polarization dimensions, enabling the construction of multi-dimensional multiplexing local area networks.

A sodium-based hybrid plasmonic waveguide with ultra-deep subwavelength confinement and low cross-talk

Surface plasmon photonics provides a feasible method for achieving high-density photonic integration and low-loss optical field transmission. Here we propose a sodium-based hybrid plasmonic waveguide consisting of a cylindrical sodium nanowire and a Si nano-rib waveguide located on the silica substrate at the wavelength of 1550 nm and investigate the mode properties by using the finite element method. The results indicate that ultra-deep subwavelength modal fields with the mode areas of 9.64 × 10−6A0 ∼ 9.507 × 10−4A0 (A0 = λ2/4) and propagation lengths of 8 ∼ 46.5 μm could be achieved when the thickness of the spacer is less than 4 nm. Moreover, investigations on fabrication tolerance and crosstalk show that the proposed waveguide exhibits a good fabrication error tolerance and very low cross-talk between adjacent structures with a minimum separation distance of around 300 nm, which makes it quite suitable for applications in photonic integration. These findings may have potential applications in the field of photonic devices, such as nanowaveguides, lasers, and sensors.

Finite-element modeling of a perovskite-based symmetric plasmonic waveguide with deep-subwavelength confinement and high figure of merit

The two-dimensional perovskites are emerging as an excellent material platform for various optoelectronic devices such as solar cells, lasers, and photodetectors. Here, by combining perovskite materials and plasmonic materials, a hybrid plasmonic waveguide with perovskite layers serving as the low index materials is proposed. The modal characteristics, fabrication error tolerance, and integration performance of this structure are studied by using the finite element method at the wavelength of 1550 nm. The results show that the proposed waveguide exhibits the strong field confinement ability and high figure of merit. Moreover, the proposed waveguide shows a relatively high tolerance to fabrication errors, and exhibits an extremely low crosstalk, which is quite suitable for applications in the compact photonic integration.

Coupled Tamm Phonon and Plasmon Polaritons for Designer Planar Multiresonance Absorbers.

Wavelength-selective absorbers (WS-absorbers) are of interest for various applications, including chemical sensing and light sources. Lithography-free fabrication of WS-absorbers can be realized via Tamm plasmon polaritons (TPPs) supported by distributed Bragg reflectors (DBRs) on plasmonic materials. While multifrequency and nearly arbitrary spectra can be realized with TPPs via inverse design algorithms, demanding and thick DBRs are required for high quality-factors (Q-factors) and/or multiband TPP-absorbers, increasing the cost and reducing fabrication error tolerance. Here, high Q-factor multiband absorption with limited DBR layers (3 layers) is experimentally demonstrated by Tamm hybrid polaritons (THPs) formed by coupling TPPs and Tamm phonon polaritons when modal frequencies are overlapped. Compared to the TPP component, the Q-factors of THPs are improved twofold, and the angular broadening is also reduced twofold, facilitating applications where narrow-band and nondispersive WS-absorbers are needed. Moreover, an open-source algorithm is developed to inversely design THP-absorbers consisting of anisotropic media and exemplify that the modal frequencies can be assigned to desirable positions. Furthermore, it is demonstrated that inversely designed THP-absorbers can realize same spectral resonances with fewer DBR layers than a TPP-absorber, thus reducing the fabrication complexity and enabling more cost-effective, lithography-free, wafer-scale WS-absorberss for applications such as free-space communications and gas sensing.

Design and characteristics of ellipse-assisted ring-core fiber for space division multiplexing

• Elliptical-assisted ring-core fiber with central low-refractive-index elliptical region. • 9 effectively separated spatial modes have uniform Δn eff with values greater than 3.14 × 10 −4 at 1550 nm. • The level of polarization separation is lower than 3.33 × 10 −6 . • Good scalability and fabrication error tolerance. • This fiber design could be promising candidates toward high-capacity SDM systems. We propose a novel ellipse-assisted ring-core fiber characterized by an elliptical region of low refractive index in the core. The proposed fiber proves effective in eliminating the spatial degeneracy of the LP mn mode groups and keeping the birefringence properties at a low level. This fiber, with optimized structural parameters, can guide 9 modes over the entire C-band. The simulation results show that the effective refractive index difference (Δn eff ) between adjacent modes at 1530–1565 nm falls within the scope of (3.1 ∼ 6.64) × 10 −4 . At the same time, the polarization separation level of each mode is lower than 3.23 × 10 −6 , which is 2 orders of magnitude lower than the degree of spatial mode degeneracy separation. This fiber design has good application prospects in space division multiplexing systems.

Performance analysis of 90° hybrid for InP monolithic coherent photodetector at L-band

An optical 90° hybrid monolithic with a 4-channel photodetector array is characterized and analyzed. The fabricated chip exhibits a phase error within ±10° and a common rejection ratio exceeding 13.6 dB over 40 nm range in the L-band. A taper structure is adopted at hybrid inputs and outputs to improve phase error performance by 43.8% and fabrication error tolerance is analyzed numerically to well explain the deviations from theory.

Generation of a blue-detuned optical storage ring by a metasurface and its application in optical trapping of cold molecules

A scheme for storage of cold molecules in a hollow optical ring generated by a metasurface grating is proposed. The characteristics and intensity distribution related to the ring’s structural parameters and fabrication error tolerance are theoretically studied. The optical potential and dipole force required for the ring to trap magnesium monofluoride (MgF) molecules are also calculated. The dynamic behavior of MgF molecules in the storage ring is simulated by a Monte Carlo method, which shows that a metasurface-based optical storage ring can be used to trap molecules and is an interesting platform for research into ultracold quantum gases and their quantum-state manipulation.

Robust, ultralow-loss, and broadband light-recycling for a nanophotonic delay line.

The optical delay line is a key building block for applications in photonics. It requires low loss, wide bandwidth, and small footprint. In this work, we adopt the light recycling approach based on spatial-mode multiplexing, and achieve high performance with a Mach-Zehnder interferometer (MZI)-based design, which significantly increases the fabrication error tolerance. The proposed nanophotonic delay lines allow fabrication errors of ±10 nm over the broad bandwidth of 100 nm while maintaining the excess insertion loss below 0.5 dB. It will enable power-efficient, ultralow-loss, small-footprint, and broadband optical information processing capabilities in diverse applications.

A band-pass frequency selective surface with polarization rotation

A band-pass frequency selective surface (FSS) with polarization rotation property is proposed. The proposed polarization rotating FSS (PR-FSS) is a two-dimensional periodic structure, its unit cell is an antenna-filter-antenna (AFA) module, and the polarization directions of the upper and lower antennas in each AFA module are orthogonal to each other, so the PR-FSS can achieve frequency selection and 90 degrees polarization rotation at the same time. The numerical simulation demonstrate that the anticipated frequency selection and polarization rotation are realized by the PR-FSS in the frequency band from 8.84 GHz to 10.30 GHz with a relative bandwidth of 15.26%, and the maximum insertion loss in the pass band is only 0.17 dB. Finally, one effective experiment validation is carried out, a reasonable agreement is observed between the experimental and simulated results except for a slight deviation caused by fabrication error and measurement tolerance.

An assembly-induced-emission orthogonal supramolecular network with spirobifluorene, pillararene, and tetraphenylethylene units for efficient light harvesting

An orthogonal supramolecular network has been developed as an excellent light-harvesting system with a high antenna effect. The antenna effects were over 60 with a wide range of host/guest ratios, exhibiting good fabrication error tolerance.

Graphene perfect absorber design based on an approach of mimicking a one-port system in an asymmetric single resonator.

We proposed a novel perfect absorber with an asymmetric single resonator supporting two degenerate resonant modes, whose operation concept is mimicking a one-port system by making only one of the modes experience loss while using the other for an internal 100% reflector in conjunction with the background scattering. We confirmed the operation principle and the design requirement from a theoretical study using the temporal coupled-mode theory. We also designed an example device based on the guided-mode resonances (GMRs) in a slab-waveguide grating and numerically demonstrated a high absorption of ∼ 99.95% in monolayer graphene with greatly enhanced fabrication error tolerance in comparison to the previously proposed scheme. Our proposed scheme will find various useful applications due to the intuitive design process and relatively easier fabrication, which is attributed to the one-port mimicking operation concept with a single GMR-based broadband flat-top reflector.

A reasonable tolerance multilayered polarization-insensitive grating reflector

With rigorous coupled-wave analysis (RCWA), in the study, we systematically investigate the properties of a broadband multilayered polarization-insensitive grating reflector utilized by a thin multisubpart profile. And experimental verification is carried out. Over a broadband spectrum of 1.62 ∼ 1.76 μm, the reflector experimentally demonstrates high reflectivity (R > 95%), and exists a high reflectance within 90° of the polarization angles. A qualitative explanation for the physical basis of the high reflectance is provided, and the tolerance of high reflectivity properties over fabrication errors are estimated as well. The results indicate the proposed element has a favorable tolerance of fabrication error, which is useful in the fabrication of the structure.

Fabrication-Tolerant Design for High-Power, Single-Lobe, Surface-Emitting Quantum Cascade Lasers

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) of linear geometry generally operate in an antisymmetric mode, which is undesirable due to its double-lobed far-field beam pattern. The antisymmetric mode can be suppressed by designing 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order metal/semiconductor gratings that favor symmetric-mode operation, but using such an approach requires tight tolerances in grating duty cycle that impair fabrication yields. Alternatively, the grating can be designed to favor antisymmetric-mode operation with single-lobe emission by using a central π-phaseshift. Here we show that such a design is highly fabrication tolerant. Simulations using COMSOL Multiphysics are performed followed by finite-length analysis using coupled-mode theory and the transfer-matrix method, as well as a semi-empirical QCL model for predicting CW performance. The analysis reveals a device of significantly higher tolerance for fabrication errors, operating in a single-lobe beam pattern to 0.63 W CW, although the emitted power scales less efficiently with length than for symmetric-mode operating devices.

Design of Planar Reconfigurable, Tunable, and Wide Angle Resonant Absorbers for Applications in the IR Spectrum

AbstractA hybrid resonant absorber Fabry Perot—FP tunable from a simple stack of planar layers of ultra‐thin films of phase change material is proposed, designed, and demonstrated numerically. This work shows that properly designed metal–dielectric–metal) structures comprising thin films of titanium (Ti), germanium telluride (GeTe) on a silver (Ag) substrate produce a dynamic modulation of light in the near IR with almost perfect absorption (A &gt; 93%). It is demonstrated that the resonant peaks of the hybrid absorber can be tuned in two different ways for any wavelength, with the crystallization fractions and the thickness of the dielectric. The influence of the metallic top layer thickness is also analyzed and demonstrated the fabrication error tolerance of the proposed absorber is demonstrated. Also analyzed is the influence of the thickness of the metallic top layer and tolerance to fabrication error of the proposed absorber is demonstrated. Finally, the physical mechanisms for the coupling of the electromagnetic field and the absorbed optical power in the structure proposed are presented and discussed. This study allows the beginning of the development of hybrid devices to control the absorption of light in the region of the electromagnetic spectrum used in optical communications.

Ultra-Compact Broadband In-Line Mode Converter Based on a Width-Modulated Silicon Waveguide

Mode division multiplexing (MDM) technology is becoming increasingly important for modern optical communication systems. Here, an ultra-compact broadband in-line mode converter for quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> and quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> on the silicon-on-insulator platform is proposed and demonstrated experimentally. In our device, the mode-conversion region consists of a continuously width-modulated waveguide with a footprint size as small as 1.32 × 4.52 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Its modulation profile is designed by using the particle swarm optimization algorithm. This device has a simulated conversion efficiency of about -0.174 dB and an insertion loss less than 0.153 dB within 100-nm wavelength bandwidth from 1500 nm to 1600 nm. Our design exhibits a favorable fabrication error tolerance and the fabricated device has achieved nearly the same conversion efficiency as the simulated one. Our concept can also be applied to design other high-performance mode converters, i.e., converting modes between quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> and quasi-TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> . Our work suggests a very promising path for realizing compact integrated MDM systems.

Design of an ultra-compact low-crosstalk sinusoidal silicon waveguide array for optical phased array.

In this work, an ultra-compact low-crosstalk sinusoidal silicon waveguide array is proposed and analyzed. We first design a pair of low-crosstalk sinusoidal silicon waveguides with a pitch of 695 nm, where the sinusoidal bends are the key to reduce the crosstalk between waveguides. Then, based on this idea, we propose a low-crosstalk sinusoidal silicon waveguide array with a 695 nm pitch. The simulation results show that for an array length of 100 µm, the insertion loss is as low as 0.08 dB, and the crosstalk is lower than -26 dB at 1550 nm. The 695 nm pitch waveguide array also exhibits a favorable fabrication error tolerance when taking into account the waveguide width variations in practice. Moreover, within the acceptable range of crosstalk, the center-to-center distance between adjacent waveguides of this array can be further reduced to 615 nm. Since the pitch is related to the power consumption and beam-steering range of the optical phased array, our design provides an effective method to build the emitter for an energy-efficient optical phased array with a large field of view.

Ultra-broadband solar absorbers for high-efficiency thermophotovoltaics.

Metamaterial absorbers have attracted great attention over the past few years and exhibited a promising prospect in solar energy harvesting and solar thermophotovoltaics (STPVs). In this work, we introduce a solar absorber scheme, which enables efficient solar irradiance harvesting, superb thermal robustness and high solar thermal energy conversion for STPV systems. The optimum structure demonstrates an average absorbance of 97.85% at the spectral region from 200 nm to 2980 nm, indicating the near-unity absorption in the main energy range of the solar radiance. The solar-thermal conversion efficiencies surpassing 90% are achieved over an ultra-wide temperature range (100-800 °C). Meanwhile, the analysis indicates that this metamaterial has strong tolerance for fabrication errors. By utilizing the simple two-dimensional (2D) titanium (Ti) gratings, this design is able to get beyond the limit of costly and sophisticated nanomanufacturing techniques. These impressive features can hold the system with wide applications in metamaterial and other optoelectronic devices.

Wide-Range Tunable Narrow Band-Stop Filter Based on Bilayer Graphene in the Mid-Infrared Region

In this paper, a tunable graphene-based band-stop filter in the mid-infrared region was demonstrated, which consists of periodic structure based on bilayer graphene nanoribbons. Due to the unique tunable Fermi level of graphene, the resonance wavelength of the filter can be tuned over a wide range (10020 nm–15100 nm) with the applied voltage varying from 1 V to 5 V, realizing selectivity and tunability. The results also confirm that the presented structure can realize a narrow-band selective filter with a 3 dB bandwidth of 40 nm. Furthermore, the trough transmittance of stopband is close to zero and the transmittance of passband remains above 96.7%. Moreover, this filter is quite robust to the incident angles. The stopband is still extremely narrow as the incident angle varies from 0° to 60°, realizing wide-angle filtering. In addition, the fabrication processing and fabrication error tolerance are investigated, and it has proved that the filter is quite tolerant to fabrication deviations. Hence, the work has potential applications in narrowband filters, active plasmonic switches, and sensors in the mid-infrared region.

TiO2-based compact TM-pass polarizer at visible wavelengths with ultra-low power loss

A compact transverse magnetic (TM)-pass/transverse electric (TE)-stop polarizer with ultra-low power loss at visible wavelengths is theoretically proposed on a TiO2-based platform, which is achieved via the surface plasmon polaritons effect in the hybrid plasmonic grating structure. We design the TiO2 waveguide and optimize the structural parameters of the hybrid plasmonic grating using finite element method (FEM) and 3D Finite-Difference-Time-Domain (FDTD) simulation. The proposed polarizer shows a high extinction ratio over 27 dB from the wavelength of 0.54 to 0.57 μm, a low insertion loss of 0.087 dB at 0.552 μm, a compact size of only 2.64 μm and a great fabrication error tolerance.

High polarisation extinction ratio of the TM-pass polariser with silicon carbide / graphene / silicon multilayers

We propose a compact TM-pass polariser, consisting of silicon (Si) / silicon carbide (SiC) / Si layers. Two graphene sheets are sandwiched between the Si and SiC layers as the interlayer to enhance the interaction with light. The loss characteristics have been investigated by using the finite-difference time-domain (FDTD) method. The proposed structure exhibits a low insertion loss (IL) of $$\sim $$0.25 $$\hbox {dB}$$ and a high polarisation extinction ratio (PER) of $$\sim $$57 $$\hbox {dB}$$. To verify the robustness of the proposed polariser, we analyse the fabrication tolerance of the waveguide width and the height of the Si and SiC layers. The polariser shows great fabrication error tolerance. In addition, by employing a $$100\,\mu \hbox {m}$$ long waveguide, a PER of 48.3–59.4 dB is obtained in the visible regime ranging from 400 to 600 nm.