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Showing papers on "Optical polarization published in 2020"


Journal ArticleDOI
Xiang Zhou1, Ryohei Urata1, Hong Liu1
TL;DR: A comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution, with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.
Abstract: We discuss technology options and challenges for scaling intra-datacenter interconnects beyond 1 Tb/s bandwidths, with focus on two possible approaches: pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate sampled coherent technology. In our studies, we compare the performance of various orders of PAM modulation (PAM4 to 8). In addition to these fixed PAM signaling options, a flexible PAM (FlexPAM) technique leveraging granularity in spectral efficiency (SE) is proposed to maximize link margin. For baud-rate sampled coherent technology, we propose a simplified digital signal processing (DSP) architecture to bring down power consumption of the coherent approach closer to that of IM-DD PAM. We also propose two new phase noise tolerant 2D coherent modulation formats to relax the laser linewidth requirement. In closing, a comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution (200 Gb/s per dimension), with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.

142 citations


Journal ArticleDOI
TL;DR: In this article, the authors comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications.
Abstract: 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.

138 citations


Journal ArticleDOI
TL;DR: This study demonstrates the significant advantages resulting from the use of machine learning-based protocols for the construction and characterization of high-dimensional resources for quantum protocols.
Abstract: Structured light is attracting significant attention for its diverse applications in both classical and quantum optics. The so-called vector vortex beams display peculiar properties in both contexts due to the nontrivial correlations between optical polarization and orbital angular momentum. Here we demonstrate a new, flexible experimental approach to the classification of vortex vector beams. We first describe a platform for generating arbitrary complex vector vortex beams inspired to photonic quantum walks. We then exploit recent machine learning methods-namely, convolutional neural networks and principal component analysis-to recognize and classify specific polarization patterns. Our study demonstrates the significant advantages resulting from the use of machine learning-based protocols for the construction and characterization of high-dimensional resources for quantum protocols.

85 citations


Journal ArticleDOI
TL;DR: This work introduces the recent and ongoing activities demonstrating controllable excitation of spiking signals in optical neurons based upon vertical-cavity surface emitting lasers (VCSEL-Neurons), and reports on ultrafast artificial laser neurons and their potentials for future neuromorphic (brainlike) photonic information processing systems.
Abstract: We report on ultrafast artificial laser neurons and on their potentials for future neuromorphic (brainlike) photonic information processing systems. We introduce our recent and ongoing activities demonstrating controllable excitation of spiking signals in optical neurons based upon vertical-cavity surface emitting lasers (VCSEL-Neurons). These spiking regimes are analogous to those exhibited by biological neurons, but at sub-nanosecond speeds (>7 orders of magnitude faster). We also describe diverse approaches, based on optical or electronic excitation techniques, for the activation/inhibition of sub-ns spiking signals in VCSEL-Neurons. We report our work demonstrating the communication of spiking patterns between VCSEL-Neurons toward future implementations of optical neuromorphic networks. Furthermore, new findings show that VCSEL-Neurons can perform multiple neuro-inspired spike processing tasks. We experimentally demonstrate photonic spiking memory modules using single and mutually coupled VCSEL-Neurons. Additionally, the ultrafast emulation of neuronal circuits in the retina using VCSEL-Neuron systems is demonstrated experimentally for the first time to our knowledge. Our results are obtained with off-the-shelf VCSELs operating at the telecom wavelengths of 1310 and 1550 nm. This makes our approach fully compatible with current optical network and data center technologies, hence offering great potentials for future ultrafast neuromorphic laser-neuron networks for new paradigms in brain-inspired computing and artificial intelligence.

75 citations


Journal ArticleDOI
TL;DR: A comprehensive review of the available ML-based techniques for MFI, OPM, and joint MFI/OPM, describing their performance, advantages, and limitations and some lessons learned are presented to help the reader identify the gaps, weaknesses, and strengths.
Abstract: The trade-off between more user bandwidth and quality of service requirements introduces unprecedented challenges to the next generation smart optical networks. In this regard, the use of optical performance monitoring (OPM) and modulation format identification (MFI) techniques becomes a common need to enable the development of next-generation autonomous optical networks, with ultra-low latency and self-adaptability. Recently, machine learning (ML)-based techniques have emerged as a vital solution to many challenging aspects of OPM and MFI in terms of reliability, quality, and implementation efficiency. This article surveys ML-based OPM and MFI techniques proposed in the literature. First, we address the key advantages of employing ML algorithms in optical networks. Then, we review the main optical impairments and modulation formats being monitored and classified, respectively, using ML algorithms. Additionally, we discuss the current status of optical networks in terms of MFI and OPM. This includes standards, monitoring parameters, and the available commercial products with their limitations. Second, we provide a comprehensive review of the available ML-based techniques for MFI, OPM, and joint MFI/OPM, describing their performance, advantages, and limitations. Third, we give an overview of the exiting ML-based OPM and MFI techniques for the emerging optical networks such as the new fiber-based networks that use future space division multiplexing techniques (e.g., few-mode fiber), the hybrid radio-over-fiber networks, and the free space optical networks. Finally, we discuss the open issues, potential future research directions, and recommendations for the potential implementation of ML-based OPM and MFI techniques. Some lessons learned are presented after each section throughout the paper to help the reader identifying the gaps, weaknesses, and strengths in this field.

62 citations


Journal ArticleDOI
TL;DR: In this article, the authors demonstrate optical wireless transmission with two-dimensional (2D) beam-steering using an optical phased array (OPA) consisting of 64-elements of electro-optic p-i-n phase shifters and tunable n-i n grating radiators, employed for 2D beam-stacking in the transversal and longitudinal directions.
Abstract: We demonstrate optical wireless transmission with two-dimensional (2D) beam-steering using an optical phased array (OPA). The OPA consists of 64-elements of electro-optic p-i-n phase shifters and thermo-optic tunable n-i-n grating radiators, employed for 2D beam-steering in the transversal and longitudinal directions. The design of the transmitter and receiver device parameters allowed the error-free transmission of 32 Gbps data over a distance of 3 m. The beam-steering range covered 46.0°/10.2° in the transversal/longitudinal direction with a beam divergence of 0.7°/0.9°. When compared with a transmission over fiber, it was confirmed that free-space transmission through the OPA did not degrade the quality of the tens of Gbps signals.

57 citations


Journal ArticleDOI
TL;DR: The results shown in this review reflect the significance and maturity of the state-of-the-art photonic fabrication technology and contribute to the implementation of high-capacity, general-purpose optical signal processing functionalities on the chip scale.
Abstract: Integrated optical signal processors, in combination with conventional electrical signal processors, are envisioned to open a path to a new generation of signal processing hardware platform that allows for significant improvement in processing bandwidth, latency, and power efficiency. With its well-known features and potential, silicon photonics is considered as a favorable candidate for the device implementation, particularly with high circuit complexity, and hence has been the focus of the study. As an outlook from the previous discussions on such processors, we are considering new building blocks in the silicon photonics platform for further extending the processor capabilities and adding practical features, particularly the miniaturized devices that enable ultra-dense integration of complex circuits into such processor chips. As enlightening examples, we review here our recent contribution together with representative works from other groups of compact designs of silicon photonics devices that enrich functionalities of processor building blocks such as multiplexing, polarization handling, and optical I/Os. The results shown in this review reflect the significance and maturity of the state-of-the-art photonic fabrication technology and contribute to the implementation of high-capacity, general-purpose optical signal processing functionalities on the chip scale.

50 citations


Journal ArticleDOI
TL;DR: In this article, a hybrid THz photonic-wireless transmission based on a THz orthogonal polarization dual-antenna scheme is presented, achieving a potential total system throughput of 612.65 Gbit/s with an average net spectral efficiency of 4.445 bit/s/Hz per antenna.
Abstract: The proliferation of wireless broadband services have significantly raised the demand for high data rates. Due to the limited bandwidth of radio frequency (RF) bands that are currently in use for communication purposes, the choice of the ‘Terahertz (THz) frequency region’ (0.3–10 THz) is getting favored thanks to its merits of bringing together wireless and optical communications with photonics technologies. We report on an experimental demonstration of a hybrid THz photonic-wireless transmission based on a THz orthogonal polarization dual-antenna scheme. Probabilistic shaped 64-ary quadrature amplitude modulation based orthogonal frequency division multiplexing (64QAM-OFDM) modulation format is used to realize high transmission rate. A potential total system throughput of 612.65 Gbit/s (around 2 × 300 Gbit/s line rate) with an average net spectral efficiency of 4.445 bit/s/Hz per antenna is successfully achieved.

48 citations


Journal ArticleDOI
TL;DR: In this article, an improved polarization-insensitive design based on silicon-nanocylinders on silica substrates is presented, which can tune the focal length of a metalens doublet by varying the relative angle between the two metalenses.
Abstract: Metasurface-based lenses (metalenses) offer specific conceptual advantages compared to ordinary refractive lenses. For example, it is possible to tune the focal length of a metalens doublet by varying the relative angle between the two metalenses while fixing their distance, leading to an extremely compact zoom lens. An improved polarization-insensitive design based on silicon-nanocylinders on silica substrates is presented. This design is realized and characterized experimentally at 1550 nm wavelength. By varying the relative angle between the metalenses in steps of 10 degrees, tuning of the doublet focal length is demonstrated from -54 mm to -+3 mm to +54 mm. This results in a zoom factor of an imaging system varying between 1 and 18. For positive focal lengths, the doublet focusing efficiency has a minimum of 34% and a maximum of 83%. Experiment and theory are in very good agreement.

44 citations


Journal ArticleDOI
22 May 2020
TL;DR: In this paper, the spatial features and the polarization structure of vectorial optical vortexes propagating in scattering media with different concentrations were investigated and a sudden swift decrease in contrast ratio for Gaussian, OAM, and VVB modes for concentrations of the adopted scattering media exceeding 0.09%.
Abstract: Scattering phenomena affect light propagation through any kind of medium from free space to biological tissues. Finding appropriate strategies to increase the robustness to scattering is the common requirement in developing both communication protocols and imaging systems. Recently, structured light has attracted attention due to its seeming scattering resistance in terms of transmissivity and spatial behavior. Moreover, correlation between optical polarization and orbital angular momentum (OAM), which characterizes the so-called vector vortex beam (VVB) states, seems to allow for the preservation of the polarization pattern. We extend the analysis by investigating both the spatial features and the polarization structure of vectorial optical vortexes propagating in scattering media with different concentrations. Among the observed features, we find a sudden swift decrease in contrast ratio for Gaussian, OAM, and VVB modes for concentrations of the adopted scattering media exceeding 0.09%. Our analysis provides a more general and complete study on the propagation of structured light in dispersive and scattering media.

44 citations


Journal ArticleDOI
Yong Zhang1, Ruihuan Zhang1, Qingming Zhu1, Yuan Yuan1, Yikai Su1 
TL;DR: This paper discusses the general architecture of integrated silicon photonic switches by exploiting multi-dimensions in wavelength, polarization, and mode, and proposes a design of a mode-polarization-wavelength selective switch by leveraging three physical dimensions.
Abstract: Switching can be performed with multiple physical dimensions of an optical signal. Previously optical switching was mainly focused in the wavelength domain. In this paper we discuss the general architecture of integrated silicon photonic switches by exploiting multi-dimensions in wavelength, polarization, and mode. To route a data channel from one input port to an arbitrary output port in a network node, three basic functions are required: de-multiplexing, switching, and multiplexing. The multiplexing and de-multiplexing processes can be realized in any one physical dimension. The capacity of a switch can be effectively scaled by using joint physical dimensions. As two examples, we first present a wavelength switch based on dual-nanobeam cavities with high quality factors, a low power consumption, and a compact footprint. We then propose a design of a mode-polarization-wavelength selective switch by leveraging three physical dimensions, and experimentally demonstrate the building blocks and key functionalities.

Proceedings ArticleDOI
19 Jul 2020
TL;DR: In this paper, disaggregated network elements and subsystems can be abstracted to manage and control propagation of WDM optical data transport, enabling the application of the software-defined paradigm down to the physical layer, with optical transport fully summarized by a quality of transmission estimator.
Abstract: Transparent optical networks operated by WDM coherent optical technologies for data transport are moving-on towards the implementation of the openness paradigm. In such a context, disaggregated network elements and subsystems can be abstracted to manage and control propagation of WDM optical data transport. It enables the application of the software-defined paradigm down to the physical layer, with optical transport fully summarized by a quality of transmission estimator.

Journal ArticleDOI
30 May 2020
TL;DR: The effects of parity-time (PT) symmetry breaking in active-lossy plasmonic arrays are demonstrated: the emergence of exceptional points, nontrivial topology of photonic bands, diverging effective unit-cell polarizability, and spin polarization in the PT-broken phase.
Abstract: Periodic lattices of strongly scattering objects coupled to active media are of central importance in applied nanophotonics, serving as light-emitting metasurfaces of tailored emission properties and promising an attractive platform for testing novel physical concepts and realization of unprecedented light-shaping functions. We provide an overview of the semianalytical Green function method with Ewald lattice summation applied to the investigation of surface lattice resonances in periodic arrays of resonant nanoscatterers with gain and loss. This theory is meant as a minimal model for plasmonic lattices and metasurfaces with gain: minimal in complexity, yet sufficiently rich to be a self-consistent, fully retarded multiple scattering model. It enables to include the electromagnetic interactions between electric and/or magnetic point dipoles of arbitrary orientation and arrangement, taking into account retardation and tensorial nature of these interactions and including radiation damping. It gives access to the far-field observables (reflection/transmission), as well as to the photonic band structure of guided modes. At the same time, it does not violate the optical theorem, as opposed to the commonly used tight-binding or quasi-static models. After extending the lattice Green function formalism to include gain and loss in the unit cell, we demonstrate the effects of parity-time (PT) symmetry breaking in active-lossy plasmonic arrays: the emergence of exceptional points, nontrivial topology of photonic bands, diverging effective unit-cell polarizability, and spin polarization in the PT-broken phase.

Journal ArticleDOI
TL;DR: This work introduces the experimental realization of structures known as framed knots within optical polarization fields and develops a protocol in which the topological properties of framed knots are used in conjunction with prime factorization to encode information.
Abstract: Modern beam shaping techniques have enabled the generation of optical fields displaying a wealth of structural features, which include three-dimensional topologies such as Mobius, ribbon strips and knots. However, unlike simpler types of structured light, the topological properties of these optical fields have hitherto remained more of a fundamental curiosity as opposed to a feature that can be applied in modern technologies. Due to their robustness against external perturbations, topological invariants in physical systems are increasingly being considered as a means to encode information. Hence, structured light with topological properties could potentially be used for such purposes. Here, we introduce the experimental realization of structures known as framed knots within optical polarization fields. We further develop a protocol in which the topological properties of framed knots are used in conjunction with prime factorization to encode information. Beam shaping methods can generate optical fields with nontrivial topologies, which are invariant against perturbations and thus interesting for information encoding. Here, the authors introduce the realization of framed optical knots to encode programs with the conjoined use of prime factorization.

Journal ArticleDOI
TL;DR: This article discusses the concept of a "THz-wireless fiber extender" in more detail and reports on the recent demonstration of a real-time, short-range THz- wireless Fiber extender with 100 Gb/s net capacity, and analyzes the effect of weather conditions on the transmission performance and determines the maximum physical layer net data rate.
Abstract: Using the concept of a "THz-wireless fiber extender," we can combine the flexibility of wireless networks with the high capacity of fiber optic communication. The availability of a large, contiguous bandwidth in the frequency band around 300 GHz creates the opportunity to seamlessly interconnect coherent THz-wireless and fiber optic transceiver frontends using a transparent, analog baseband interface. In this article, we discuss this concept in more detail and report on the recent demonstration of a real-time, short-range THz-wireless fiber extender with 100 Gb/s net capacity. This combined fiber optic/THz-wireless transmission system is operated by a high-speed fiber optic real-time modem, which is capable of compensating the channel impairments of both the optical and THz-wireless links. In addition, we discuss the potential of THz-wireless links to achieve long-range transmission distances by reporting on the operation of a 500-m-long line-of-sight THz-wireless outdoor link in Berlin, Germany. We analyze the effect of weather conditions on the transmission performance and determine the maximum physical layer net data rate of the system by means of various modulation formats and symbol rates. Finally, we summarize all of our recent high-capacity experiments using THz-wireless transmission, including a field trial with a 1-km-long link, and compare our results to theoretical limits and achieved data rates in the laboratory.

Journal ArticleDOI
TL;DR: In this article, a polarization diversity architecture is proposed to realize UWB-SOA modules, which have been successfully used to demonstrate 100+ Tb/s transmission over 100 km distance.
Abstract: We report on the use of semiconductor optical amplifiers (SOAs) to extend the optical bandwidth of next generation optical systems to 100 nm and beyond. After discussing the technological progress and the motivation for rekindling the interest in SOAs for line amplification, we describe the innovative approach developed for the realization of ultra-wideband (UWB) SOAs. Leveraging custom design of singly polarized SOAs to provide gain over 100+ nm bandwidth, we developed a polarization diversity architecture to realize UWB-SOA modules. Embedded in a compact package, the UWB amplifier modules have been successfully used to demonstrate 100+ Tb/s transmissions. We subsequently review recent experimental transmission results based on such novel 100+ nm wide semiconductor optical amplifiers, including our first demonstration of 100+Tb/s transmission over 100 km distance, our field trial using real-time traffic, and finally the transmission of 107 Tb/s throughput over three spans of standard single mode fiber (SSMF) using hybrid UWB Raman/SOA amplification technique.

Journal ArticleDOI
TL;DR: A silicon-photonic Mach–Zehnder modulator-based optical TX on an Silicon-on-Insulator (SOI) process, and linear, high-swing SiGe drivers on 130-nm BiCMOS process are presented.
Abstract: Coherent optical links improve spectral efficiency over their intensity-modulation direct-detect (IM-DD) counterparts using advanced modulation schemes such as quadrature phase shift keying (QPSK) and quadrature amplitude modulation (QAM), and by utilizing dual polarization (DP) of light. This increase in spectral efficiency also leads to stringent requirements for the link components. The transmitter (TX) must simultaneously achieve high bandwidth (BW), linearity, output swing, and reliability. In this article, we present a silicon-photonic Mach–Zehnder modulator-based optical TX on an Silicon-on-Insulator (SOI) process, and linear, high-swing SiGe drivers on 130-nm BiCMOS process. The output stage of the driver uses a voltage breakdown enhancement technique to ensure the reliability of the TX. A resistor-based capacitor splitting technique is introduced, and aided by other methods such as zero-peaking and degeneration, the targeted gain, BW, swing, and linearity for the driver are realized. The driver achieves a differential swing of 6 V peak-to-peak, a total harmonic distortion (THD) of 3.6%, and more than 40 GHz of electrical BW. Co-designed and co-packaged with the silicon-photonic modulators, the TX achieves 272 Gb/s/wavelength with DP-16 QAM at 6-V peak-to-peak driver swing and exceeds 0.5 Tb/s/wavelength data rates with DP-16 QAM at 2.4-V peak-to-peak driver swing. The low-cost, compact, and all-Si/SiGe design matches the required optical SNR performance of LiNbO3 modulators with III–V drivers at 34 Gbaud.

Journal ArticleDOI
TL;DR: Polarization remote sensing can be used to obtain polarization data for a given target as discussed by the authors, which can acquire not only radiation data, as also measured by conventional remote sensing, but also to quantitatively measure quantitatively the polarization of a target.
Abstract: Polarization remote sensing can be used to obtain polarization data for a given target. It can be acquire not only radiation data, as also measured by conventional remote sensing, but also to quant...

Journal ArticleDOI
TL;DR: In this article, multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters are reported.
Abstract: We report multicolor optical imaging and polarimetry observations of the afterglow of the first TeV-detected gamma-ray burst (GRB), GRB 190114C, using the RINGO3 and MASTER II polarimeters. Observations begin 31 s after the onset of the GRB and continue until ~7000 s postburst. The light curves reveal a chromatic break at ~400–500 s, with initial temporal decay α = 1.669 ± 0.013 flattening to α ~ 1 postbreak, which we model as a combination of reverse and forward shock components with magnetization parameter R B ~ 70. The observed polarization degree decreases from 7.7% ± 1.1% to 2%–4% 52–109 s postburst and remains steady at this level for the subsequent ~2000 s at a constant position angle. Broadband spectral energy distribution modeling of the afterglow confirms that GRB 190114C is highly obscured (A v,HG = 1.49 ± 0.12 mag; ${N}_{{\rm{H}},\mathrm{HG}}=(9.0\pm 0.03)\,\times {10}^{22}\,$ cm−2). We interpret the measured afterglow polarization as intrinsically low and dominated by dust —in contrast to the P > 10% measured previously for other GRB reverse shocks—with a small contribution from polarized prompt photons in the first minute. We test whether first- and higher-order inverse Compton scattering in a magnetized reverse shock can explain the low optical polarization and subteraelectronvolt emission but conclude that neither is explained in the reverse shock inverse Compton model. Instead, the unexpectedly low intrinsic polarization degree in GRB 190114C can be explained if large-scale jet magnetic fields are distorted on timescales prior to reverse shock emission.

Journal ArticleDOI
TL;DR: This paper considers the recently proposed learned digital backpropagation (LDBP) approach, where the linear steps in the split-step method are re-interpreted as general linear functions, similar to the weight matrices in a deep neural network, and shows how LDBP can be integrated into a coherent receiver DSP chain and successfully trained in the presence of various hardware impairments.
Abstract: Efficient nonlinearity compensation in fiber-optic communication systems is considered a key element to go beyond the “capacity crunch”. One guiding principle for previous work on the design of practical nonlinearity compensation schemes is that fewer steps lead to better systems. In this paper, we challenge this assumption and show how to carefully design multi-step approaches that provide better performance–complexity trade-offs than their few-step counterparts. We consider the recently proposed learned digital backpropagation (LDBP) approach, where the linear steps in the split-step method are re-interpreted as general linear functions, similar to the weight matrices in a deep neural network. Our main contribution lies in an experimental demonstration of this approach for a 25 Gbaud single-channel optical transmission system. It is shown how LDBP can be integrated into a coherent receiver DSP chain and successfully trained in the presence of various hardware impairments. Our results show that LDBP with limited complexity can achieve better performance than standard DBP by using very short, but jointly optimized, finite-impulse response filters in each step. This paper also provides an overview of recently proposed extensions of LDBP and we comment on potentially interesting avenues for future work.

Journal ArticleDOI
TL;DR: A coherent optical transmitter front-end module compactly integrating two AMUX-Driver ICs and an InP-based optical in-phase quadrature (IQ) modulator achieves an electro-optic bandwidth higher than 80 GHz at the 6-dB point.
Abstract: This article presents an optical transmitter front-end based on 2:1 analog multiplexer (AMUX) for beyond-1-Tb/s/carrier coherent optical communications systems. An AMUX is monolithically integrated with an optical modulator driver to realize an AMUX-Driver IC that can directly drive an optical modulator. The AMUX-Driver IC fabricated by using our in-house 250-nm InP double heterojunction bipolar transistors (DHBTs), which have a peak cutoff frequency ( $f_{\mathrm {T}}$ ) and maximum oscillation frequency ( $f_{\mathrm {max}}$ ) of 460 and 480 GHz, respectively, achieves a record bandwidth of 110 GHz and a 1.5- $\text{V}_{\mathrm {ppd}}$ linear differential output range with a <3% total harmonic distortion (THD). A coherent optical transmitter front-end module compactly integrating two AMUX-Driver ICs and an InP-based optical in-phase quadrature (IQ) modulator achieves an electro-optic (EO) bandwidth higher than 80 GHz at the 6-dB point. Beyond-1-Tb/s/carrier optical modulation based on 168-GBaud polarization-division-multiplexed (PDM) 16-ary quadrature-amplitude-modulation (16QAM) was successfully demonstrated by using this integrated module.

Journal ArticleDOI
TL;DR: The results indicate that optimally designed MZMs and their associated control methods can increase the information capacity of short-reach multimode optical fiber links.
Abstract: A Mach–Zehnder mesh (MZM), which is comprised of a network of tunable $2\times 2$ Mach–Zehnder interferometers and embedded photodetectors (PDs), can be used to perform arbitrary unitary matrix multiplications in the optical domain and compensate modal crosstalk in short-reach mode-division-multiplexed (MDM) links that use direct detection (DD). MZMs can be adapted using a self-configuration method, proposed by Miller, where multiple low-speed and low-power code sequences are superimposed on parallel high-speed information streams. We show that self-configuration in its original form is a sub-optimal equalization method for high-speed data transmission because adaptation based on detected code strengths is adversely impacted by low measurement signal-to-noise ratios and interference from the high-speed information streams. These impairments prevent the method from accurately tracking the millisecond-timescale modal dynamics of short-reach DD-MDM channels. We propose small modifications to the self-configuration method that can enable the MZM to track up to $10^8$ -fold faster channel dynamics. In particular, we show that replacing continuous equalization of low-power code sequences by periodic equalization of full-power training signals and using special optimization methods can yield faster MZM tuning. We also discuss the tradeoffs between MZM architectures that embed PDs inside the mesh and those that have PDs at the output ports only. Our results indicate that optimally designed MZMs and their associated control methods can increase the information capacity of short-reach multimode optical fiber links.

Journal ArticleDOI
TL;DR: In this paper, the authors present simultaneous data and power transmission systems using a double-clad fiber (DCF), which consists of a singlemode (SM) core and an inner cladding that surrounds the SM core.
Abstract: This article presents simultaneous data and power transmission systems using a double-clad fiber (DCF). In future radio-over-fiber (RoF) networks, a large number of remote antenna units (RAUs) will be required to provide various kinds of mobile communication services. Power-over-fiber (PWoF), which delivers electrical power to drive the RAUs in optical fibers, is an attractive technique that offers cost-effective installation, operation, and maintenance of RAUs, and achieves the power savings across the entire RoF networks. In particular, the use of double-clad fibers (DCFs), which consist of a single-mode (SM) core and an inner cladding that surrounds the SM core, are useful for much higher power transmission than conventional PWoF techniques. Along the DCF link, optical data signals are transmitted into the SM core, whereas high-power feed light for optical powering is transmitted into the inner cladding, which has a core area that is approximately 240 times larger core area than that of conventional SM cores. In this article, we experimentally demonstrate a PWoF feed with up to 150-W of power using a 1-km DCF. To show the feasibility of the PWoF system, we investigate the bend performance and temperature characteristics of the DCF link. We also evaluate data and power transmission performance under the 150-W PWoF feed in the DCF link.

Journal ArticleDOI
01 May 2020
TL;DR: Two-dimensional layered semiconductors have attracted a great deal of attention recently from many fields of science and technology, and the major progress from the perspective of light-emission properties and related device applications of such 2-D materials is overviews.
Abstract: Two-dimensional layered semiconductors have attracted a great deal of attention recently from many fields of science and technology. This article overviews the major progress from the perspective of light-emission properties and related device applications of such 2-D materials. We begin with the overview of basic optical properties, including emission features of various excitonic complexes, many-body effects, light-emission enhancement due to plasmonic coupling, and mechanisms of optical gain. This is followed by discussions of coupling of 2-D materials with an optical cavity, including cavity-enhanced emission due to the Purcell effect, strong and weak coupling, as well as lasing behavior. We then discuss the design and the fabrication of various heterostructures by stacking layers of different 2-D materials for the purpose of confining and injecting charge carriers. Such structures are indispensable for light-emitting devices under electrical injection, the ultimate goal of any semiconductor-based light-emitting diode (LED) or lasers. The progress in electrical injection devices is reviewed next, where LEDs under lateral and vertical electrical injection schemes are discussed. The review is concluded with an outlook and future perspectives.

Journal ArticleDOI
TL;DR: In this paper, an all-digital approach that enables a rapid measure of all four intensities without any moving components is presented. But it is not suitable for real-time polarimetry.
Abstract: Stokes polarimetry is widely used to extract the polarization structure of optical fields, typically from six measurements, although it can be extracted from only four. To measure the required intensities, most approaches are based on optical polarization components. In this work, we present an all-digital approach that enables a rapid measure of all four intensities without any moving components. Our method employs a polarization grating (PG) to simultaneously project the incoming mode into left- and right-circular polarized states, followed by a polarization-insensitive digital micromirror device (DMD), which digitally introduces a phase retardance for the acquisition of the remaining two polarization states. We demonstrate how this technique can be applied to measuring the SoP, vectorness, and intramodal phase of optical fields, without any moving components, and shows excellent agreement with theory, illustrating fast, real-time polarimetry.

Journal ArticleDOI
TL;DR: In this paper, the authors predict linear polarization for a radioactively powered kilonova following the merger of a black hole and a neutron star, and perform 3D Monte Carlo radiative transfer simulations for two different models, both featuring a lanthanide-rich dynamical ejecta component from numerical-relativity simulations.
Abstract: We predict linear polarization for a radioactively powered kilonova following the merger of a black hole and a neutron star. Specifically, we perform 3D Monte Carlo radiative transfer simulations for two different models, both featuring a lanthanide-rich dynamical ejecta component from numerical-relativity simulations while only one including an additional lanthanide-free disc-wind component. We calculate polarization spectra for nine different orientations at 1.5, 2.5, and 3.5 d after the merger and in the 0.1−2μm wavelength range. We find that both models are polarized at a detectable level 1.5 d after the merger while show negligible levels thereafter. The polarization spectra of the two models are significantly different. The model lacking a disc wind shows no polarization in the optical, while a signal increasing at longer wavelengths and reaching ∼1−6 per cent at 2μm depending on the orientation. The model with a disc-wind component, instead, features a characteristic ‘double-peak’ polarization spectrum with one peak in the optical and the other in the infrared. Polarimetric observations of future events will shed light on the debated neutron richness of the disc-wind component. The detection of optical polarization would unambiguously reveal the presence of a lanthanide-free disc-wind component, while polarization increasing from zero in the optical to a peak in the infrared would suggest a lanthanide-rich composition for the whole ejecta. Future polarimetric campaigns should prioritize observations in the first ∼48 h and in the 0.5−2μm range, where polarization is strongest, but also explore shorter wavelengths/later times where no signal is expected from the kilonova and the interstellar polarization can be safely estimated.

Journal ArticleDOI
TL;DR: In this paper, Kislat and Krawczynski presented an improved constraint on anisotropic Lorentz invariance and charge-parity time violation by searching for astrophysical signals of cosmic vacuum birefringence with broadband optical polarimetry of high redshift astronomical sources, including active galactic nuclei and gamma-ray burst afterglows.
Abstract: In the framework of the Standard Model extension (SME), we present improved constraints on anisotropic Lorentz invariance and charge-parity-time ($CPT$) violation by searching for astrophysical signals of cosmic vacuum birefringence with broadband optical polarimetry of high redshift astronomical sources, including active galactic nuclei and gamma-ray burst afterglows. We generalize the reference [F. Kislat, Symmetry 10, 596 (2018)], which studied the SME mass dimension $d=4$ case, to the arbitrary mass dimension for both the $CPT$-even and the $CPT$-odd cases. We then present constraints on all 10, 16, and 42 anisotropic birefringent SME coefficients for dimension $d=4$, $d=5$, and $d=6$ models, respectively, using 7554 observations for odd $d$ and 7376 observations for even $d$ of 1278 unique sources on the sky, which, to our knowledge, comprises the most complete catalog of optical polarization from extragalactic sources in the literature to date. Compared to the smaller sample of 44 and 45 broadband optical polarimetry observations analyzed in Kislat [Symmetry 10, 596 (2018)] and Kislat and Krawczynski [Phys. Rev. D 95, 083013 (2017)], our dimension $d=4$ and $d=5$ average constraints are more sensitive by factors of 35 and 10, corresponding to a reduction in allowed SME parameter space volume for these studies of 15 and 16 orders of magnitude, respectively. Constraints from individual lines of sight can be significantly stronger using spectropolarimetry, due to the steep energy dependence of birefringence effects at increasing mass dimension. Nevertheless, due to the increased number of observations and lines of sight in our catalog, our average $d=4$ and $d=5$ broadband constraints are within factors of 2 and 12 of previous constraints using spectropolarimetry from Kislat [Symmetry 10, 596 (2018)] and Kislat and Krawczynski [Phys. Rev. D 95, 083013 (2017)], respectively, using an independent dataset and an improved analysis method. By contrast, our anisotropic constraints on all 42 birefringent SME coefficients for $d=6$ are the first to be presented in the literature.

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TL;DR: In this article, the authors present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV.
Abstract: Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by VLBA at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.

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TL;DR: In this paper, a carrierless coherent detection technique using a two-dimensional (2D) photodetector array (PDA) is proposed based on the idea of phase retrieval (PR).
Abstract: To achieve an ultra-compact and flexible coherent transceiver solution, a carrier-less coherent detection technique using a two-dimensional (2-D) photodetector array (PDA) is proposed based on the idea of phase retrieval (PR). In the proposed PR-based coherent receiver, the optical phase information is digitally reconstructed from multiple intensity-only measurements acquired by arrayed photodetectors; neither local light sources, optical hybrids, nor spatial demultiplexers are needed. We develop a robust and low-complexity PR algorithm, which exploits prior knowledge on the optical modulation format, for the proposed PR receiver. As a proof-of-concept, the coherent detection of 10-Gbaud optical phase-modulated signals, including QPSK, 16-QAM, coherent optical OFDM, and polarization-multiplexed QPSK signals, using only a 2-D PDA is demonstrated experimentally.

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Yang Jing Wen, An Li, Qing Guo, Yan Cui, Yusheng Bai 
TL;DR: Investigation of the self-homodyne detection system with orthogonal polarization between pilot and signal (oSHD) through optical polarization demultiplexing of carrier and signal at receiver shows that the oSHD system is very tolerant to crosstalk, with a negligible penalty for crosStalk up to -22dB.
Abstract: This paper investigates the self-homodyne detection system with orthogonal polarization between pilot and signal (oSHD) through optical polarization demultiplexing of carrier and signal at receiver. Compared to digital demultiplexing, optical demultiplexing provides around a 0.9dB benefit in receiver sensitivity. The impact of crosstalk due to optical demultiplexing has been investigated in terms of carrier-to-signal power ratio, and delay between signal and carrier. Results show that the oSHD system is very tolerant to crosstalk, with a negligible penalty for crosstalk up to -22dB. Experiments were carried out to evaluate the system performance, including polarization tracking performance, long term stability, bit error rate performance, and tolerance to laser linewidth and delay between signal and pilot. 41Gbaud 64QAM oSHD with 200Gb/s net data rate has been realized by using the scheme with receiver sensitivity better than -4dBm, providing a promising candidate solution for 800Gb/s Ethernet.