Multilevel Phase Research Articles

Extended DoF and achromatic inverse imaging for lens and lensless MPM camera based on Wiener filtering of defocused OTFs

Optimal optical transfer function (OTF) is proposed for RGB inverse imaging with extended depth of field (DoF) and diminished color aberrations. This optimal OTF is derived as the Wiener filter of broadband defocused OTFs. The performance of this new inverse imaging is demonstrated for optical setups with lens and lensless with a multilevel phase mask instead of the lens. The later lensless system designed for the wavelength range (400 to 700) nm and DoF range (0.5 to 1000) m demonstrates the best performance.

Phase-Based Estimation of the Harmonic Signal Frequency

This paper examines estimating the frequency of the information signal based on the analysis of the probability characteristics of the phase fluctuations when a mix of signal and narrowband noise is observed. The new estimation algorithm is described while the shortcomings of the commonly applied methods are specified. The performance of the proposed approach is illustrated by a number of examples. In particular, it is demonstrated that the application of the introduced procedure allows high accuracy measurements of the carrier frequency of the non-modulated, the multilevel phase and quadrature keyed signals.

Should Multilevel Phase I Surgical Therapy be Recommended as Treatment for Moderate Obstructive Sleep Apnea due to Oropharyngeal and Hypopharyngeal Obstruction?

The purpose of this study was to evaluate the efficacy of multilevel phase I surgery for the treatment of moderate obstructive sleep apnea (OSA) in retrognathic patients with oropharyngeal and hypopharyngeal obstruction. This was a 10-year retrospective cohort study of patients treated by a single surgeon at the Boston University Medical Center. From 2000 to 2010, retrognathic patients with moderate OSA and verified palatal and tongue base obstruction were treated with multilevel phase I surgery that included uvulopalatopharyngoplasty, hyoid suspension, and genioglossus advancement. All patients were evaluated clinically and received polysomnographic studies at three time points: preoperatively (T1), between 6 and 12months postoperatively (T2), and a minimum of 24months postoperatively (T3). Twenty-five subjects composed the final study sample. At T2, 11 patients (44.0%) experienced a complete response, 13 (52.0%) experienced a partial response, and 1 (4.0%) experienced no response. Although phase I surgery was associated with significant changes in AHI (F(2,48)=119.3; P<.01) throughout the follow-up period, only one patient at T3 (4.0%) met the criteria for a complete response. The remaining patients were divided evenly between partial response (48.0%) and treatment failure (48.0%), of whom 4 (16.0%) patients had worsening of their obstruction. Thirteen of these patients subsequently elected to undergo maxillomandibular advancement, while 11 elected to continue using continuous positive airway pressure. Although phase I surgery was associated with AHI changes, this reduction was not sufficient to produce a long-term treatment response in over half of our patients. Treatment response was worse after 2years than at 6 to 12months. Patients with moderate OSA should understand that multilevel phase I surgery has a greater chance of failure than success and that transient improvements may not be durable.

Biomass soft sensor for a Pichia pastoris fed-batch process based on phase detection and hybrid modeling.

A common control strategy for the production of recombinant proteins in Pichia pastoris using the alcohol oxidase 1 (AOX1) promotor is to separate the bioprocess into two main phases: biomass generation on glycerol and protein production via methanol induction. This study reports the establishment of a soft sensor for the prediction of biomass concentration that adapts automatically to these distinct phases. A hybrid approach combining mechanistic (carbon balance) and data-driven modeling (multiple linear regression) is used for this purpose. The model parameters are dynamically adapted according to the current process phase using a multilevel phase detection algorithm. This algorithm is based on the online data of CO2 in the off-gas (absolute value and first derivative) and cumulative base feed. The evaluation of the model resulted in a mean relative prediction error of 5.52% and R² of .96 for the entire process. The resulting model was implemented as a soft sensor for the online monitoring of the P. pastoris bioprocess. The soft sensor can be used for quality control and as input to process control systems, for example, for methanol control.

Multilevel reversible laser-induced phase transitions in GeTe thin films

This paper presents the results of a study on the structural properties and dynamics of conductivity of thin (d ∼ 100 nm) films of germanium telluride depending on the phase states reversibly switched by nanosecond pulsed laser radiation with a «top hat» beam profile. It was determined that the threshold of laser radiation energy density at which the phase transition in GeTe thin films from the amorphous to crystalline state is in the range of E = 7.5 ÷ 47.6 mJ/cm2, and the threshold for the reverse transition from the crystalline to amorphous state starts from 47.6 mJ/cm2 and is observed up to 90 mJ/cm2 with no visible damage caused by the ablation. The full time of conductivity change associated with the phase transition between the amorphous and crystalline phases is τCA = 20.2 ns, while for the reverse crystalline to amorphous transition, the conductivity full change time it makes τAC = 52 ns.

Dispersion pre-compensation of 25.6 Tbps waveforms using an optical frequency comb synthesizer/analyzer

In this study, we propose and demonstrate a dispersion compensation system for an ultrafast 25.6 Tbps waveform using multilevel 8-ary amplitude and 32-ary phase modulation. The waveform bit period was 312.5 fs, which was controlled and compensated by a 200 GHz optical frequency comb (OFC) synthesizer with a 6.4 THz bandwidth. Dispersion spectra were measured in parallel and simultaneously (within 1 ms), based on single-shot dual-heterodyne mixing by introducing an OFC and arrayed waveguide grating to separate sidebands. An optical pulse synthesizer (OPS) can individually control the phase and amplitude spectra of the OFC. To control transmitted waveforms in a dispersed media, the OPS can be oppositely biased to feed the measured dispersion back into the source waveform when it generates an arbitrary waveform. In this study, a 25.6 Tbps dispersion-free waveform was successfully transmitted through a 10.55 km fiber.

Improved phase change properties in layered ScxIn2−xSe3 for multilevel information storage

Phase change random access memory stores information by utilizing large resistance differences between crystalline and amorphous states of phase change materials (PCM). It would be highly advantageous to realize multilevel devices with single PCM system in nanoscale to improve memory capacity and reduce power consumption. Experimental results verify the possibility of multilevel phase change in two dimensional In2Se3 thin layers with two stable single crystal phases (α and β). Here, we report, the phase change properties of layered In2Se3 can be greatly improved by substitutional doping with Sc atoms based on first-principle calculations together with semiclassical Boltzmann transport theory. The lattice thermal conductivity of both α- and β-ScxIn2−xSe3 are lower than that of the undoped models in the temperature range from 300 K to 700 K. Particularly, of β-Sc0.167In1.833Se3 at 300 K is 0.53 W m−1 K−1, which is reduced by 60% compared to β-In2Se3. The out-of-plane electrical conductivities also show a significant decrease after Sc doping. These results indicate better performance of Sc-doped In2Se3 PCM with minimized thermal crosstalk and lower RESET current. Moreover, we found the resistance difference between α and β phase can become 1–2 orders of magnitude larger in Sc0.167In1.833Se3, which is beneficial for the multilevel programming. The phase change process from α-In2Se3 to its β phase with different Sc doping sites are calculated by ab-initio molecular dynamics simulations. It is found that with the introduction of Sc atoms in tetrahedral sites, phase change speed can be significantly increased. Our studies shed light on the modification of phase change properties of layered In2Se3 with rare earth doping.

Multilevel phase supercritical lens fabricated by synergistic optical lithography

Abstract The advent of planar metalenses, including the super-oscillatory lens (SOL) and the supercritical lens (SCL) with distinctive interference properties, has profoundly impacted on the long-lasting perception of the far-field optical diffraction limit. In spite of its conspicuous success in achieving marvelously small focal spots, the planar metalens still faces tough design and fabrication challenges to realize high focusing efficiency. In this work, we demonstrated a dual-mode laser fabrication technique based on two-photon polymerization for realizing the multilevel phase SCL with focusing efficiency spiking. Synergistically controlling two types of movement trajectory, which is implemented with the piezo stage and the scanning galvo mirror, enables the fabrication of complicated structures with sub-diffraction-limit feature size. By utilizing such advantage, SCLs with discretized multilevel phase configurations are explicitly patterned. The experimental characterization results have shown that a four-level phase SCL can focus light into a sub-diffraction-limit spot with the lateral size of 0.41 λ/NA (NA is the numerical aperture), while achieve the focal spot intensity and the energy concentration ratio in the focal region 7.2 times and 3 times that of the traditional binary amplitude-type SCL with the same optimization conditions, respectively. Our results may release the application obstacles for the sub-diffraction-limit planar metalens and enable major advances in the fields from label-free optical super-resolution imaging to high precision laser fabrication.

Azimuthal multiplexing 3D diffractive optics

Diffractive optics have increasingly caught the attention of the scientific community. Classical diffractive optics are 2D diffractive optical elements (DOEs) and computer-generated holograms (CGHs), which modulate optical waves on a solitary transverse plane. However, potential capabilities are missed by the inherent two-dimensional nature of these devices. Previous work has demonstrated that extending the modulation from planar (2D) to volumetric (3D) enables new functionalities, such as generating space-variant functions, multiplexing in the spatial or spectral domain, or enhancing information capacity. Unfortunately, despite significant progress fueled by recent interest in metasurface diffraction, 3D diffractive optics still remains relatively unexplored. Here, we introduce the concept of azimuthal multiplexing. We propose, design, and demonstrate 3D diffractive optics showing this multiplexing effect. According to this new phenomenon, multiple pages of information are encoded and can be read out across independent channels by rotating one or more diffractive layers with respect to the others. We implement the concept with multilayer diffractive optical elements. An iterative projection optimization algorithm helps solve the inverse design problem. The experimental realization using photolithographically fabricated multilevel phase layers demonstrates the predicted performance. We discuss the limitations and potential of azimuthal multiplexing 3D diffractive optics.

Frequency expanded non-interferometric phase retrieval for holographic data storage

A novel frequency expanded non-interferometric phase retrieval method for holographic data storage is proposed. The limitation of twice Nyquist frequency for phase retrieval with high fidelity is broken through. Only 1 times Nyquist size frequency of the hologram is recorded, reconstructed and detected in our method which is the smallest range for complex multi-level phase retrieval in the current holographic data storage report. Required high-order frequencies for quick phase retrieval are generated artificially by expanding 1 times Nyquist frequency to high-order frequencies with utilizations of frequency periodicity. Therefore, our proposed method can increase storage density due to reducing the recording consumption of media and decreasing the recording area by 4 times compared with twice Nyquist frequency recording.

A Multilevel Fault-Tolerant Power Converter for a Switched Reluctance Machine Drive

Reliability in the electrical drives is becoming an important issue in many applications. In this context, the reliability associated to the switched reluctance machine (SRM) is also an important area of research. One of the major problems, that strongly affect its operation, are drive power semiconductors faults. Typical power converter topologies used in SRM drives cannot handle faults in their power semiconductors. So, this paper presents a power converter topology that provides fault-tolerant capabilities to the drive under a switch fault. This power converter will be used considering that a change in the direction of the current that flows in the SRM windings does not affect the behavior of the machine. Besides that, the proposed power converter will allow to generate multilevel phase voltages in order to apply different voltage levels as function of the SRM speed. A laboratory power converter was developed to test the SRM drive in normal and faulty conditions. From the obtained results it was possible to verify the fault-tolerant capability of the drive under switch faults in different devices and failure modes. It was also possible to confirm the multilevel operation of the drive.

Ultra-Low Program Current and Multilevel Phase Change Memory for High-Density Storage Achieved by a Low-Current SET Pre-Operation

We have fabricated a pillar structure phase change memory (PCM) with the prototypical phase change material Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Te <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> . Using a Low Current SET (LCS) pre-operation, the devices can operate with an ultralow RESET current density and have multilevel cell (MLC) capability, and these features both contribute to high storage density. Specifically, the RESET current density is only 4.84 MA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is lowest among all the CMOS compatible PCM devices, and this ultra-low RESET current density enables the possibility to link with a two-terminal selector for 3D cross-point application. Meanwhile LCS makes MLC operation of our PCM more stable with a low operating current. In summary, this LCS pre-operation can greatly increase the storage density both by enabling integration with selectors for 3D cross-point and by stabilizing MLC operation when maintaining the feature size of PCM devices.

Efficient mid-Infrared vortex beam generation using optical waveguides integrated with micro-spiral phase plates

Vortex beam generation from a mid-infrared photonic chip was numerically demonstrated by engineering the phase front of a waveguide mode. Multi-level micro-spiral phase plates (SPPs) consisting of N segments were patterned on the waveguide facet. The micro-SPP introduced an annular phase change by 2π that converted the Hermite–Gaussian (HG) waveguide mode into Laguerre–Gaussian (LG) mode at topological charge ∣l∣ = 1. Using a 3D finite difference time domain simulation, we resolved the near-field optical phase map next to the micro-SPP and its far-field beam profile projected from the waveguide surface. The vortex beam formation was spectrally dependent. A uniform and symmetric donut-shaped pattern corresponding to an ideal vortex beam was created at λ = 3.1–3.3 μm. In addition, the HG → LG mode conversion efficiency was improved by increasing the number of segments, N. Thus, our micro-SPP enabled present photonic circuits to create vortex beams, which is critical for the development of optical interconnection and broadband communication.

Rapid and Large‐Scale Fabrication of Full Color Woodpile Photonic Crystals via Interference from a Conformal Multilevel Phase Mask

AbstractThe practical use of photonic crystals with structural colors requires technology capable of rapidly producing large‐area, three‐dimensional (3D) periodic nanostructures. Until now, the fabrication of 3D photonic crystals has relied mainly on additive manufacturing and colloidal self‐assembly. These technologies have provided a useful academic platform based on precisely controlled 3D periodicity but have not evolved into mass production technology. Here, optical lithography for the rapid fabrication of large‐area 3D photonic crystals with structural colors is introduced. The key strategy is to incorporate two orthogonal line gratings (periodicity: 300 nm) made of an elastomer to create a conformal multilevel phase mask. When the mask is irradiated with a 355 nm laser, the five beam interference is established in the proximity region. The interlayer thickness between the two orthogonal line gratings controls the phase difference, which is closely related to the symmetry of the resulting 3D interference pattern. The interlayer thickness is designed to produce a woodpile structure with a planar periodicity of 300 nm and a vertical periodicity of 716 nm. The pattern area of the woodpile photonic crystal is expanded to 1 in2. Red, green, and blue colors are experimentally realized by controlling the vertical shrinkage of the photoresist.

SbSe/ZnSb stacked thin films with multi-level phase transition for high density phase change memory applications

As a highly integrated non-volatile memory device, phase change memory (PCM) has attracted considerable attention. In this paper, SbSe/ZnSb (SS/ZS) stacked thin films were developed for high density phase change memory applications. SS/ZS stacked thin films show two pronounced resistance steps with the increase in temperature and possess excellent thermal stability. The X-ray diffraction reveals that Sb, Sb2Se3 phases crystallize first, hexagonal ZnSb phase forms then at higher temperatures. The stacked thin films exhibit subtle variations in thickness and roughness after crystallization. Ultrafast crystallization speed (9.68 ns) in the SS(25 nm)/ZS(25 nm) thin film was validated by picosecond laser pump-probe system. Phase-change memory cells based on SS(25 nm)/ZS(25 nm) stacked thin film can realize multi-level data storage and the whole SET and RESET operations can be implemented with a 20 ns electrical pulse. Thus, SS/ZS stacked thin films have advantages for multi-level data storage capability, better thermal stability, and fast phase change speed, and are therefore good candidates for high density PCM device.

Speeding Up the Write Operation for Multi-Level Cell Phase Change Memory with Programmable Ramp-Down Current Pulses.

Multi-level cell (MLC) phase change memory (PCM) can not only effectively multiply the memory capacity while maintaining the cell area, but also has infinite potential in the application of the artificial neural network. The write and verify scheme is usually adopted to reduce the impact of device-to-device variability at the expense of a greater operation time and more power consumption. This paper proposes a novel write operation for multi-level cell phase change memory: Programmable ramp-down current pulses are utilized to program the RESET initialized memory cells to the expected resistance levels. In addition, a fully differential read circuit with an optional reference current source is employed to complete the readout operation. Eventually, a 2-bit/cell phase change memory chip is presented with a more efficient write operation of a single current pulse and a read access time of 65 ns. Some experiments are implemented to demonstrate the resistance distribution and the drift.

On Mode-Spacing Division of a Frequency Comb by Temporal Phase Modulation

Mode-spacing division of a phase-coherent optical frequency comb is numerically investigated using temporal phase modulation of a periodic optical pulse train. Different schemes, including Talbot and random phase modulations, are investigated and compared, i.e., concerning the tunability of mode-spacing division factors and the robustness to potential practical deviations on the modulation phase profiles. Talbot phase modulation provides a versatile technique for mode-spacing division of a frequency comb; however, the approach is found to be sensitive to phase deviations under certain design parameters. The results show the difficulty in obtaining experimentally the frequency shift by half mode spacing that is predicted by theory for odd division factors. In contrast, generalized random phase modulation methods, proposed here for the first time, utilize random 0-π or multilevel phase profiles to provide interesting alternative methods for implementation of mode-spacing division of a frequency comb. The use of random 0-π phase modulation simplifies the practical implementation of the scheme as it requires inducing only 0 and π phase shifts. The use of random multilevel phase modulation generalizes the approach by using multiple levels of random phase shifts. Both random phase modulation approaches enable successful mode-spacing division by any designed division factor, and they show a relatively lower sensitivity to phase deviations in the modulation functions.

CLOSED LOOP CONTROL OF MULTI LEVEL INVERTER USING REVERSE VOLTAGE TOPOLOGY

In this paper a new topology with a reversing voltage component is proposed which will improve the multilevel performance by compensating the disadvantages of increased number of components, complex pulse width modulation control method and voltage balancing problem. This topology requires fewer components compared to existing inverter topologies (particularly in higher levels) and requires fewer carrier signals and gate drives. Therefore the overall cost and complexity are greatly reduced particularly for higher output voltage levels. This paper describes the general multilevel inverter schematic and modified circuit having only seven switches for seven- level multilevel inverter using reverse voltage topology. A general method of multilevel modulation phase disposition (PD) SPWM is utilized to drive the inverter and can be extended to any number of voltage levels. The simulation of a modified seven level multilevel inverter using reverse voltage topology is also presented here.

Transferable ultra-thin multi-level micro-optics patterned by tunable photoreduction and photoablation for hybrid optics

Next-generation hybrid optics will provide superior performances over traditional optics by combining the advantages of refractive, reflective, and diffractive optics and metasurfaces. Hybrid optics have been realized by integrating diffractive optical structures to the top surface of traditional bulk refractive or reflective optics. However, high-resolution manufacturing requirement of diffractive patterns on top of free-form refractive or reflective optical surfaces have hindered the wide-spread dissemination of hybrid optics. In this paper, we demonstrate a transferable ultra-thin micro-optics having multi-level transmittance and phase profiles which are arbitrarily patterned by tunable photoreduction and photoablation of graphene oxides (GO) using femtosecond (fs) direct laser writing. A 5 × 5 array of multi-level ultra-thin micro diffractive lens having a focal length of 15 mm was exemplarily patterned with real-time laser power control; the resulting spot size was smaller than 14 μm with the suppression of diffractive side peaks by 14.9% at the first order and 10.8% at the second order ones. This laser-patterned diffractive lens array was successfully transferred to the surface of a refractive cylindrical lens via polydimethylsiloxane (PDMS) as the flexible/stretchable substrate; the resulting optical performance agrees well with the theoretical simulation result. This new fabrication method will pave a way to novel hybrid optical systems.

Performance enhancement of overall LEO/MEO intersatellite optical wireless communication systems

SummaryThis paper has deeply investigated the performance signature of modulation techniques based low earth orbit (LEO)/medium earth orbit (MEO) intersatellite optical wireless communication systems for possible communication coverage distance of 20 000 km with possible transmission bit rate of 0.5 Tb/s. These modulation techniques that are namely multilevel quadrature amplitude modulation (M‐QAM), multilevel phase shift keying (N‐PSK), multilevel pulse amplitude modulation (H‐PAM), and finally multilevel differential phase shift keying (L‐DPSK) based on different electrical pulse generators for upgrading LEO/MEO intersatellite link operation efficiency. These pulse generators that are namely Gaussian pulse generator (GPG), hyperbolic secant pulse generator (HSPG), and raised cosine pulse generator (RCPG). The variations of maximum Q‐factor, minimum bit error rate (BER), and optical signal‐to‐noise ratio in relation to number of bits/symbol for different modulation techniques can be deeply studied in the presence of vertical cavity surface emitting laser (VCSEL). This study is done with using Optiwave system simulation version 7 for different modulation techniques, and all figures are sketched with using wizard Excel sheet set up. It is observed that maximum Q‐factor and minimum BER are optimized with using GPG and 8‐PAM, as well as 4‐DPSK with both HSPG and RCPG.