Variable Splitting Ratio Research Articles

The Design and Characterization of an Ultra-Compact Asymmetrical Multimode Interference Splitter on Lithium Niobate Thin Film

We propose and demonstrate a high-performance asymmetrical multimode interference splitter on X-cut lithium niobate on insulator (LNOI) with an ultra-compact size of 5.8 μm × (26.4–35.6) μm. A rectangle with a small region is removed from the upper left corner of the multimode interference (MMI) coupler to achieve a variable splitting ratio. Here, we design and characterize MMIs in six different distribution ratios ranging from 50:50 to 95:5 on a 600 nm thick LNOI. Based on the cascade structure, the linear fitting method accurately shows the device loss (~0.1–0.9 dB). Our fabricated devices demonstrate robustness across a 30 nm optical bandwidth (1535–1565 nm). In addition, we numerically simulate the Z-cut LNOI, showing that the structure corresponding to the TM mode can also achieve a good variable splitting ratio.

Effects of split diesel injection strategies on combustion, knocking, cyclic variations and emissions of a natural gas-diesel dual fuel medium speed engine

Accelerated by the harms and depletion risk of fossil fuels, transition to low-carbon or renewable fuels have become an urgent need for combustion engines to decarbonize transport sectors. Natural gas-diesel dual-fuel combustion is a promising method to achieve these goals by allowing the usage of natural gas in diesel engines. However, this concept has drawbacks of low combustion efficiency, high unburned hydrocarbon (HC) emissions and high cyclic variations at low engine loads. These drawbacks hinder the benefits of dual-fuel such as low NOx and soot emissions. To find solutions to these drawbacks, split diesel injections with variable injection timings and mass split ratios (ratio of first injection diesel mass to total diesel mass) were investigated experimentally and numerically on a medium speed marine engine at low load using constant natural gas and diesel amounts.Experimental results of the split injection were compared to single injection dual-fuel and conventional diesel operation. Single injection case resulted in slightly lower HC emissions and cyclic variations and higher NOx emissions than split cases in a narrow injection timing interval. Apart from that, split injections increased combustion efficiency and decreased cyclic variations in a broader timing interval. For split cases, early first injection timing prevented high premixed heat release peak, suppressed NOx emissions and knocking. Especially, using 70% split ratio with retarded second injections increased combustion efficiency, decreased knocking level and provided simultaneous reduction of HC and NOx emissions compared to lower split ratio cases. In short, despite not giving the minimum values at all conditions, split injection showed potential to find a remedy to high HC emissions and cyclic variations issues by keeping robust operation in a wider injection timing interval.The numerical results support the experiments in which better combustion and decreased HC emissions are attained using sufficiently early diesel injections. Simulations show that, compared to late single injection, early single injection dual-fuel case enables more homogeneous temperature distribution and better oxidization of methane near the cylinder wall and central region above the piston crown. Besides, split injection shows improved methane oxidation near the cylinder wall and inside top-land crevice volume.

Protection of Noise Squeezing in a Quantum Interferometer with Optimal Resource Allocation.

Interferometers are crucial for precision measurements, including gravitational waves, laser ranging, radar, and imaging. The phase sensitivity, the core parameter, can be quantum-enhanced to break the standard quantum limit (SQL) using quantum states. However, quantum states are highly fragile and quickly degrade with losses. We design and demonstrate a quantum interferometer utilizing a beam splitter with a variable splitting ratio to protect the quantum resource against environmental impacts. The optimal phase sensitivity can reach the quantum Cramér-Rao bound of the system. This quantum interferometer can greatly reduce the quantum source requirements in quantum measurements. In theory, with a 66.6% loss rate, the sensitivity can break the SQL using only a 6.0dB squeezed quantum resource with the current interferometer rather than a 24dB squeezed quantum resource with a conventional squeezing-vacuum-injected Mach-Zehnder interferometer. In experiments, when using a 2.0dB squeezed vacuum state, the sensitivity enhancement remains at ∼1.6 dB via optimizing the first splitting ratio when the loss rate changes from 0% to 90%, indicating that the quantum resource is excellently protected with the existence of losses in practical applications. This strategy could open a way to retain quantum advantages for quantum information processing and quantum precision measurement in lossy environments.

Ultra-compact low-loss variable-ratio 1×2 power splitter with ultra-low phase deviation based on asymmetric ladder-shaped multimode interference coupler.

We propose a novel optical 1×2 power splitter based on an asymmetric ladder-shaped multimode interference (MMI) coupler in silicon-on-insulator (SOI) which has an ultra-compact size of 3.3 µm×2.4 µm. A trapezoid with a small region is removed from the bottom left corner of the MMI coupler to achieve variable splitting ratio. The comparison with the asymmetric rectangular 1×2 splitter is numerically analyzed. By carefully optimizing the width of input taper, the proposed splitter shows a low phase deviation for the two output ports while keeping both of a low-loss performance and feasible splitting ratio. The simulated results show that the splitter can operate with an insertion loss less than 0.67 dB, a large range of splitting ratio from 50:50 to 11:89 and an ultra-low phase deviation less than 2.8° among the C band spectra.

Video Compression Using Generalized Binary Partitioning, Trellis Coded Quantization, Perceptually Optimized Encoding, and Advanced Prediction and Transform Coding

In this paper, we describe a video coding design that enables a higher coding efficiency than the HEVC standard. The proposed video codec follows the design of block-based hybrid video coding, but includes a number of advanced coding tools. A part of the incorporated advanced concepts was developed by the Joint Video Exploration Team, while others are newly proposed. The key aspects of these newly proposed tools are the following. A video frame is subdivided into rectangles of variable size using a binary partitioning with variable split ratios. Three new approaches for generating spatial intra prediction signals are supported: A line-wise application of conventional intra prediction modes, coupled with a mode-dependent processing order, a region-based template matching prediction method and intra prediction modes based on neural networks. For motion-compensated prediction, a multi-hypothesis mode with more than two motion hypotheses can be used. In transform coding, mode dependent combinations of primary and secondary transforms are applied. Moreover, scalar quantization is replaced by trellis-coded quantization and the entropy coding of the quantized transform coefficients is improved. The intra and inter prediction signals can be filtered using an edge-preserving diffusion filter or a non-linear DCT-based thresholding operation. The video codec includes an adaptive in-loop filter for which one of three classifiers can be chosen on a picture basis. We also incorporated an optional encoder control, which adjusts the quantization parameters based on a perceptually motivated distortion measure. In a random access scenario, our proposed video codec achieves luma BD-rate savings between 32.5% for HDR HLG UHD and 39.6% for SDR UHD over the HEVC (HM software) anchor for different categories of test sequences.

Tailorable and Broadband On-Chip Optical Power Splitter

An on-chip optical power splitter is a key component of photonic signal processing and quantum integrated circuits and requires compactness, wideband, low insertion loss, and variable splitting ratio. However, designing an on-chip splitter with both customizable splitting ratio and wavelength independence is a big challenge. Here, we propose a tailorable and broadband optical power splitter over 100 nm with low insertion loss less than 0.3%, as well as a compact footprint, based on 1×2 interleaved tapered waveguides. The proposed scheme can design the output power ratio of transverse electric modes, lithographically, and a selection equation of a power splitting ratio is extracted to obtain the desired power ratio. Our splitter scheme is close to an impeccable on-chip optical power splitter for classical and quantum integrated photonic circuits.

Ultracompact Optical Comparator for 4-bit QPSK-Modulated Signal Based on Silicon Photonic Waveguide

Optical comparators have the potential to improve the operational speed and power consumption of optical communication systems, as they directly perform the required operations in the optical domain to avoid any optic-electro conversions. Various comparators are optically implemented; however, most studies have been confined to an on-off keying modulation. Although there is a comparator available for the phase-shift keying (PSK) modulation, the device has a limitation that requires integration into an actual system. In this paper, the author provides an optical comparator based on a silicon waveguide for a quadrature PSK (QPSK) signal. The proposed comparator is a simple 2.0 × 0.1 mm 2 rectangle, which is approximately 1/7500 the size of comparators from previous studies, and the device mainly comprises a delay line interferometer, a variable splitting ratio optical coupler, and a phase shifter. The performance of the comparator designed for 00 00 and 11 00 codewords was experimentally evaluated. The comparator generates the coupled symbol with the comparison result between the target code and the input signal. The paper demonstrates the feasibility of the ultracompact optical comparator for a 4-bit QPSK-modulated signal at 10 Gbaud.

A Numerical Solution for Broadband PLC Splitter with Variable Splitting Ratio Based on Asymmetric Three Waveguide Structures

A numerical solution for the broadband planar-lightwave-circuit (PLC) splitter with a variable splitting ratio based on asymmetric three waveguides weighted by the Blackman weighting function is designed for passive optical network applications with wavelengths between 1.53 and 1.57 µm. The performance of the proposed splitter is verified using the beam propagation method (BPM). It was found that a polynomial function of the splitting ratios accompanying a geometrical shift can be derived from the proposed splitter. The splitting ratio can be changed from 50:50 to 90:10 with this geometrical shift. The excess loss, crosstalk, polarization dependent loss, and splitting ratio variations against wavelength of the proposed splitter with wavelengths between 1.53 and 1.57 µm are better than 0.139 dB, −22.75 dB, 0.006 dB, and 0.335%, respectively. Obviously, the proposed splitter with variable splitting ratio retains the advantages of the symmetric design, such as low excess loss, low crosstalk, polarization insensitivity, broadband, and wavelength insensitivity.

Entanglement generation using a controlled-phase gate for time-bin qubits

Quantum logic gates are important for quantum computation and quantum information processing in numerous physical systems. Although time-bin qubits are suitable for quantum communication over optical fiber, many essential quantum logic gates for them have not yet been realized. Here, we demonstrated a controlled-phase (C-Phase) gate for time-bin qubits that uses a 2 × 2 optical switch based on an electro-optic modulator. A Hong–Ou–Mandel interference measurement showed that the switch could work as a time-dependent beam splitter with a variable splitting ratio. We confirmed that two independent time-bin qubits were entangled as a result of C-Phase gate operation with the switch.

Broadband 1 × 3 Couplers With Variable Splitting Ratio Using Cascaded Step-Size MMI

In this paper, we propose and fabricated a novel scheme of SOI-based 1 × 3 coupler with variable splitting ratio. The coupler consists of two cascaded MMI with different sizes, and a wide range of splitting ratios from 1:0.1:1 to 1:18:1 can be achieved by modifying the size of the first-step MMI. Using the structure of cascaded step-size MMI, this kind of device has a compact footprint of below 15 μm × 15 μm and simple fabrication process. Meanwhile, the simulation analyses prove that the proposed couplers have a large operation bandwidth above 60 nm and be robust to the fabrication errors. Couplers with several splitting ratios were fabricated and well measured. Based on the measurement results, the splitting ratios of fabricated couplers from 1:0.67:1 to 1:18:1 can be achieved, and stable performance with the transmission efficiencies above 80% can be maintained over 50 nm wavelength range, which is the largest operation bandwidth to the best of our knowledge.

Tolerable performance of silicon photonic optical-serial-to-parallel converter with variable power splitter.

We have proposed and investigated the tolerable performance of an optical serial-to-parallel converter with phase operation (OSPC) with lower power consumption than the conventional scheme for the purpose of achieving reduction of both the processing load and the processing latency of the high-speed packet switching systems in the data center. The target OSPC consists of Mach-Zehnder delay interferometers (MZDIs) and balanced photodetectors with silicon (Si) photonic technology. However, we have confirmed that the performance becomes degraded due to optical propagation losses of the delay lines in MZDIs. To solve this issue, unbalanced splitting ratio of a multi-mode interferometer (MMI)-type couplers in the MZDIs has been investigated, but we have found the necessity of improving the tolerance of the splitting ratio deviation. In this paper, we will analytically and experimentally demonstrate the improvement of the characteristics by using an OSPC with variable splitting ratio optical coupler (VSOC) consisting of a symmetric Mach-Zehnder interferometer (MZI). By observing the transmission spectra of the device with various applied voltage to the heater, controllability of peak-to-valley ratios of transmission spectra was observed. In addition, splitting ratio of the output symmetric MMI almost matches well with that of the optimized peak-to-valley ratios of transmission spectra by using short-optical pulse injection. We have confirmed the tolerable performance of the Si-photonic OSPC by using VSOC with the symmetric MZI.

Silicon nitride tri-layer vertical Y-junction and 3D couplers with arbitrary splitting ratio for photonic integrated circuits.

We designed and demonstrated a tri-layer Si3N4/SiO2 photonic integrated circuit capable of vertical interlayer coupling with arbitrary splitting ratios. Based on this multilayer photonic integrated circuit platform with each layer thicknesses of 150 nm, 50 nm, and 150 nm, we designed and simulated the vertical Y-junctions and 3D couplers with arbitrary power splitting ratios between 1:10 and 10:1 and with negligible(< -50 dB) reflection. Based on the design, we fabricated and demonstrated tri-layer vertical Y-junctions with the splitting ratios of 1:1 and 3:2 with excess optical losses of 0.230 dB. Further, we fabricated and demonstrated the 1 × 3 3D couplers with the splitting ratio of 1:1:4 for symmetric structures and variable splitting ratio for asymmetric structures.

Ultra-compact polarization beam splitter utilizing a graphene-based asymmetrical directional coupler

A novel ultra-compact polarization beam splitter (PBS) utilizing an asymmetrical directional coupler with a combination of a silicon waveguide (SW) and a graphene multilayer embedded silicon waveguide (GMESW) has been proposed and investigated. The modal characteristics of the GMESW for the TM mode varies significantly, whereas that for the TE mode changes slightly with respect to the SW, inducing the launched TM mode to directly pass through the SW with little influence from the GMESW, while the TE mode undergoes a strong coupling and is transferred to the GMESW. A designed PBS with an 8.3 μm-long coupler and 200 nm-wide gap separation offers high extinction ratios (18.2 and 21.2 dB) and low insertion losses (0.16 and 0.36 dB) for the thru and cross ports, respectively. The presented PBS also presents the ability to work with variable splitting ratio power for the TM mode by varying the chemical potential of graphene, implying various applications in signal processing on a chip.

Laser oscillation in Yb:YAG waveguide beam-splitters with variable splitting ratio.

In this Letter, we report on laser emission from Yb:YAG beam-splitters fabricated by direct femtosecond-laser inscription. These devices consist of two adjacent mirrored s-curved waveguides merged into a section allowing for multi-mode interference (MMI) and a straight waveguide. Nine-millimeter-long one-to-two beam-splitters with radii of curvature between 10 and 80mm have been fabricated resulting in separations between the two arms of up to 0.65mm. Due to the MMI-section, the splitting ratio was variable by slightly changing the incoupling conditions. Maximum laser output powers of 2.29W and slope efficiencies of 52% were achieved with the best beam-splitter waveguide laser. For all radii of curvature exceeding 10mm, similar efficiencies were demonstrated.

1×N wavelength selective adaptive optical power splitter for wavelength-division-multiplexed passive optical networks

Abstract In this paper, a 1× N wavelength selective adaptive optical power splitter (WS-AOPS) suitable for wavelength-division-multiplexed passive optical network (WDM-PON) systems is proposed and experimentally demonstrated based on the use of an Opto-VLSI processor. The input signals with different wavelengths can be split and coupled into N output ports with variable splitting ratios. A proof-of-principle 1×2 WS-AOPS structure driven by optimized multicasting phase holograms uploaded onto the Opto-VLSI processor is developed, demonstrating an arbitrary splitting ratio for each input wavelength channel over C-band.

Broadband directional coupling in aluminum nitride nanophotonic circuits

Aluminum nitride (AlN)-on-insulator has emerged as a promising platform for the realization of linear and non-linear integrated photonic circuits. In order to efficiently route optical signals on-chip, precise control over the interaction and polarization of evanescently coupled waveguide modes is required. Here we employ nanophotonic AlN waveguides to realize directional couplers with a broad coupling bandwidth and low insertion loss. We achieve uniform splitting of incoming modes, confirmed by high extinction-ratio exceeding 33dB in integrated Mach-Zehnder Interferometers. Optimized three-waveguide couplers furthermore allow for extending the coupling bandwidth over traditional side-coupled devices by almost an order of magnitude, with variable splitting ratio. Our work illustrates the potential of AlN circuits for coupled waveguide optics, DWDM applications and integrated polarization diversity schemes.

Theory and practice of a variable dome splitter for gas chromatography-olfactometry

For olfactometric measurements in combination with gas chromatography a device is needed to split the GC effluent between the detector and the sniffing port. Fixed split ratios are obtained by simple flow splitters with appropriate restrictions towards the two outlets. Variable split ratios are possible with additional control flows. One such device is a dome splitter with one input flow (the GC effluent), two output flows (to the two outlets) and two control inputs. Preliminary experiments revealed deviations from the expected split ratios of such a device. The dimensioning of the flow restrictors at only one working point was not sufficient to obtain the expected split ratios over the whole temperature range of a GC run. Therefore a physical model of the flow system has been developed, taking into account the temperature dependence of the restrictors and the internal pressure in the dome. This included the solution of the flow (respectively the mass) balance under the condition of a compressible, isothermal and laminar flow regime. The measurements are in good agreement with theoretical calculations. The model can therefore be used to optimise the dimensions of the restrictions and to calculate the effective split ratio at a given temperature during the GC run.

Continuously variable, electrically addressed beam splitter based on vanadium dioxide

Vanadium dioxide (VO(2)) is used to implement an electrically addressable beam splitter with continuously variable splitting ratios. The electrical control of temperature in a thin VO(2) layer is used to vary its transmission/reflection behavior. The technique is characterized for various incidence angles, s- and p-polarizations, and the wavelength range of 400-2000 nm. Splitting ratios continuously tunable over four orders of magnitude are reported.

Sub-μm^2 power splitters by using silicon hybrid plasmonic waveguides

Nano-scale power splitters based on Si hybrid plasmonic waveguides are designed by utilizing the multimode interference (MMI) effect as well as Y-branch structure. A three-dimensional finite-difference time-domain method is used for simulating the light propagation and optimizing the structural parameters. The designed 1 × 2 50:50 MMI power splitter has a nano-scale size of only 650 nm × 530 nm. The designed Y-branch power splitter is also very small, i.e., about 900 nm × 600 nm. The fabrication tolerance is also analyzed and it is shown that the tolerance of the waveguide width is much larger than±50 nm. The power splitter has a very broad band of over 500 nm. In order to achieve a variable power splitting ratio, a 2×2 two-mode interference coupler and an asymmetric Y-branch are used and the corresponding power splitting ratio can be tuned in the range of 97.1%:2.9%-1.7%:98.3% and 84%:16%-16%:84%, respectively. Finally a 1×4 power splitter with a device footprint of 1.9 μm × 2.6 μm is also presented using cascaded Y-branches.

Nano-scale Power Splitters by using Plasmonic Multimode Interference Couplers

Nano-scale power splitter based on Si plasmonic waveguides are designed by utilizing the multimode interference (MMI) coupler. Effective dielectric method and longitudinal modal transmission-line theory are used for simulating the light propagation and optimizing the structural parameters at 3-D guiding geometry. The designed 50:50 MMI power splitter has a nano-scale size of only . In order to achieve a variable power splitting ratio, a MMI coupler is designed and the corresponding power splitting ratio can be tuned in the range of 78.5%:15.5%~5.5%:86.6%. Also, it is shown that it has a large bandwidth of . In this range, the transmission is over 0.8.