Compact and high-performance vortex mode sorter for multi-dimensional multiplexed fiber communication systems

With the amplitude, time, wavelength/frequency, phase, and polarization/spin parameter dimensions of the light wave/photon almost fully utilized in both classical and quantum photonic information systems, orbital angular momentum (OAM) carried by optical vortex modes is regarded as a new modal parameter dimension for further boosting the capacity and performance of the systems. To exploit the OAM mode space for such systems, stringent performance requirements on a pair of OAM mode multiplexer and demultiplexer (also known as mode sorters) must be met. In this work, we implement a newly discovered optical spiral transformation to achieve a low-cross-Talk, wide-opticalbandwidth, polarization-insensitive, compact, and robust OAM mode sorter that realizes the desired bidirectional conversion between seven co-Axial OAM modes carried by a ring-core fiber and seven linearly displaced Gaussian-like modes in parallel single-mode fiber channels. We further apply the device to successfully demonstrate high-spectralefficiency and high-capacity data transmission in a 50-km OAM fiber communication link for the first time, in which a multi-dimensional multiplexing scheme multiplexes eight orbital-spin vortex mode channels with each mode channel simultaneously carrying 10 wavelength-division multiplexing channels, demonstrating the promising potential of both the OAM mode sorter and the multi-dimensional multiplexed OAM fiber systems enabled by the device. Our results pave the way for futureOAM-based multi-dimensional communication systems

A multisensing setup for the intelligent tire monitoring

The present paper offers the chance to experimentally measure, for the first time, the internal tire strain by optical fiber sensors during the tire rolling in real operating conditions. The phenomena that take place during the tire rolling are in fact far from being completely understood. Despite several models available in the technical literature, there is not a correspondently large set of experimental observations. The paper includes the detailed description of the new multi-sensing technology for an ongoing vehicle measurement, which the research group has developed in the context of the project OPTYRE. The experimental apparatus is mainly based on the use of optical fibers with embedded Fiber Bragg Gratings sensors for the acquisition of the circumferential tire strain. Other sensors are also installed on the tire, such as a phonic wheel, a uniaxial accelerometer, and a dynamic temperature sensor. The acquired information is used as input variables in dedicated algorithms that allow the identification of key parameters, such as the dynamic contact patch, instantaneous dissipation and instantaneous grip. The OPTYRE project brings a contribution into the field of experimental grip monitoring of wheeled vehicles, with implications both on passive and active safety characteristics of cars and motorbikes

Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Centrifuge Modelling With Transparent Soil and Laser Aided Imaging

Transparent synthetic soils have been developed as a soil surrogate to enable internal visualization of geotechnical processes in physical models. While significant developments have been made to enhance the methodology and capabilities of transparent soil modelling, the technique is not yet exploited to its fullest potential. Tests are typically conducted at 1 g in small bench size models, which invokes concerns about the impact of scale and stress level observed in previously reported work. This paper recognized this limitation and outlines the development of improved testing methodology whereby the transparent soil and laser aided imaging technique are translated to the centrifuge environment. This has a considerable benefit such that increased stresses are provided, which better reflect the prototype condition. The paper describes the technical challenges associated with implementing this revised experimental methodology, summarizes the test equipment/systems developed, and presents initial experimental results to validate and confirm the successful implementation and scaling of transparent soil testing to the high gravity centrifuge test environment. A 0.6 m wide prototype strip foundation was tested at two scales using the principle of “modelling of models,” in which similar performance was observed. The scientific developments discussed have the potential to provide a step change in transparent soil modelling methodology, crucially providing more representative stress conditions that reflect prototype conditions, while making a broader positive contribution to physical modelling capabilities to assess complex soil–structure boundary problems

Low-cost, stand-off, 2D+3D face imaging for biometric identification using Fourier transform profilometry

EDU meets the goals for the 2D+3D face imager of Class 1M eye-safe operation, 2D+3D face capture at \u3e20-m stand-off distance, ~1-mm lateral resolution, ~1-mm rang

Low-cost,stand-off, 2D+3D face imaging for biometric identification using Fourier transform profilometry –Update

Lockheed Martin Coherent Technologies is developing laser-based technologies for stand-off 2D+3D face imaging for biometric identification. Among other potential industrial, commercial, and governmental users, the Department of Homeland Security (DHS) and the Department of Defense (DoD) desire the ability to capture biometric data from minimally cooperative subjects with a minimally invasive system at stand-off distances. The initial applications are fixed installations for relatively large volume access points such as security check points and transportation gateways for which minimal cooperation, stand-off operation, and real-time operation are desired so that the biometric identification process will have little impact on traffic flow. Last year we presented a paper on the development and testing of a 2D+3D face imager breadboard based on th

Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit

High-dispersion coronagraphy (HDC) optimally combines high contrast imaging techniques such as adaptive optics/wavefront control plus coronagraphy to high spectral resolution spectroscopy. HDC is a critical pathway towards fully characterizing exoplanet atmospheres across a broad range of masses from giant gaseous planets down to Earth-like planets. In addition to determining the molecular composition of exoplanet atmospheres, HDC also enables Doppler mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as precise measurements of exoplanet rotational velocities. Here, we demonstrate an innovative concept for injecting the directly-imaged planet light into a single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). Our laboratory demonstration includes three key milestones: close-to-theoretical injection efficiency, accurate pointing and tracking, on-fiber coherent modulation and speckle nulling of spurious starlight signal coupling into the fiber. Using the extreme modal selectivity of single-mode fibers, we also demonstrated speckle suppression gains that outperform conventional image-based speckle nulling by at least two orders of magnitude.Comment: 10 pages, 7 figures, accepted by Ap

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial

Manufacturing Metrology

Metrology is the science of measurement, which can be divided into three overlapping activities: (1) the definition of units of measurement, (2) the realization of units of measurement, and (3) the traceability of measurement units. Manufacturing metrology originally implicates the measurement of components and inputs for a manufacturing process to assure they are within specification requirements. It can also be extended to indicate the performance measurement of manufacturing equipment. This Special Issue covers papers revealing novel measurement methodologies and instrumentations for manufacturing metrology from the conventional industry to the frontier of the advanced hi-tech industry. Twenty-five papers are included in this Special Issue. These published papers can be categorized into four main groups, as follows: Length measurement: covering new designs, from micro/nanogap measurement with laser triangulation sensors and laser interferometers to very-long-distance, newly developed mode-locked femtosecond lasers. Surface profile and form measurements: covering technologies with new confocal sensors and imagine sensors: in situ and on-machine measurements. Angle measurements: these include a new 2D precision level design, a review of angle measurement with mode-locked femtosecond lasers, and multi-axis machine tool squareness measurement. Other laboratory systems: these include a water cooling temperature control system and a computer-aided inspection framework for CMM performance evaluation

3D printed components for quantum devices

Since the first demonstrations of laser cooling of atomic vapors in the late 1970s, the field of ultracold atoms has seen rapid advancements in the preparation, control and measurement of atomic gases. Ultra-cold atomic systems, either as individual atoms or in larger ensembles, provide a powerful tool for experimenters. Their large deBroglie wavelengths make them particularly useful for interferometric applications, and their isotropic properties when unperturbed make them ideal candidates for frequency standards. A recent drive has seen experimenters looking to develop scalable, portable and robust atomic systems as a metrological tool outside of the typical laboratory environment. This could see unprecedented sensitivities made available for areas as diverse as GPS-free navigation, biomedical imaging and non-invasive underground mapping. Over the course of this thesis we explore additive manufacturing (3D printing) as a production technique for quantum technology. 3D-printing offers unrivalled design freedom and rapid prototyping, allowing us to develop a number of printed structures to test the viability of selective laser melting as a technique to produce metallic components that survive within, and also hold, the ultra-high vacuum environment necessary for ultracold physics. The technique has the potential to improve the efficiency and compactness of devices. We begin first by printing an Al-Si-Mg vacuum flange, which is then solution heat treated in post processing and milled to have a standard vacuum-sealing knife edge on its surface. By installing the flange on a test vacuum set-up, baking out over a week at 200­­­°C and pumping down, a pressure of 10⁻¹¹ mbar is achieved. In the same material, a conductive structure called the cylinder trap is printed as a proof of concept ultracold atom source producing the fields necessary for a magneto-optical trap. A complete cold atom experiment is constructed to test the device, including a simple microcontroller-based control system. Dissipating as little as 20mW electrical power, the atom trap generates 10⁸ atoms with an average temperature on the order of (20.1 ± 0.2)μK, whilst having no measurable effect on the vacuum pressure, measured as < 10⁻¹⁰ mbar. A next-generation device is then investigated, building on the work of the cylinder trap and consideration of contemporary work on cold-atom sources. This device would output an even colder source of atoms, with a tapered design to both act as a differential pump and for atom compression for transport to a secondary trap. With calculations on optimal trapping regimes, an Ioffe-Pritchard style magnetic trap layout is created to efficiently capture atoms from the magnetooptical trap. Atoms would then be transported through a three-dimensional funnel structure into a secondary magnetic trap where fast, evaporative cooling could occur. Simultaneously the next thermal cloud can be captured to improve the average cycle time. Encouraged by collaborative work on a additively manufactured chamber, called the coral trap, a prototype design is developed and presented consisting of the funnel structure split across a multi-chamber printed architecture