Showing papers on "Optical polarization published in 2019"

Advanced Adaptive Photonic RF Filters with 80 Taps Based on an Integrated Optical Micro-Comb Source

Abstract: We demonstrate a photonic radio frequency (RF) transversal filter based on an integrated optical micro-comb source featuring a record low free spectral range of 49 GHz, yielding 80 micro-comb lines across the C -band. This record high number of taps, or wavelengths for the transversal filter results in significantly increased performance including a Q RF factor more than four times higher than previous results. Furthermore, by employing both positive and negative taps, an improved out-of-band rejection of up to 48.9 dB is demonstrated using a Gaussian apodization, together with a tunable center frequency covering the RF spectra range, with a widely tunable 3-dB bandwidth and versatile dynamically adjustable filter shapes. Our experimental results match well with theory, showing that our transversal filter is a competitive solution to implement advanced adaptive RF filters with broad operational bandwidth, high frequency selectivity, high reconfigurability, and potentially reduced cost and footprint. This approach is promising for applications in modern radar and communications systems.

Communicating Using Spatial Mode Multiplexing: Potentials, Challenges, and Perspectives

Abstract: Time, polarization, and wavelength multiplexing schemes have been used to satisfy the growing need of transmission capacity. Using space as a new dimension for communication systems has been recently suggested as a versatile technique to address future bandwidth issues. We review the potentials of harnessing the space as an additional degree of freedom for communication applications including free space optics, optical fiber installation, underwater wireless optical links, on-chip interconnects, data center indoor connections, radio frequency, and acoustic communications. We focus on the orbital angular momentum (OAM) modes and equally identify the challenges related to each of the applications of spatial modes and the particular OAM modes in communication. We further discuss the perspectives of this emerging technology. Finally, we provide the open research directions and discuss the practical deployment of OAM communication links for different applications.

Mueller Matrix Polarimetry—An Emerging New Tool for Characterizing the Microstructural Feature of Complex Biological Specimen

Abstract: Recently, with the emergence of new light sources, polarization devices, and detectors, together with a prominent increase in data processing capability, polarization techniques find more and more applications in various areas, one of which is biomedicine. For probing the characteristic features of complex biomedical specimen, Mueller matrix polarimetry has demonstrated distinctive advantages. Mueller matrix polarimetry can be achieved on other optical techniques by adding the polarization state generator and analyzer to their existing optical paths appropriately. Common biomedical optical equipment, such as microscopes and endoscopes, can be upgraded to fulfill Mueller matrix imaging and measurement abilities. Compared with traditional non-polarization optical methods, Mueller matrix polarimetry can provide far more information to characterize the samples, including the anisotropic optical properties, such as birefringence and diattenuation, as well as the distinctive features of various scattering particles and microstructures. Also, Mueller matrix polarimetry is more sensitive to scattering by sub-wavelength microstructures. As a label-free and non-invasive tool, Mueller matrix polarimetry has broad application prospects in biomedical studies and clinical diagnosis. In this review, we provide an introduction to the Mueller matrix methodology, including the Stokes–Mueller formalism, and also the decomposition and transformation methods to derive new parameters. We also summarize the status of the Mueller matrix polarimetric field, including recent improvements, both in instrumentation and data analysis. The current and future applications of Mueller matrix polarimetry in biomedicine are provided and discussed.

Polarization-Independent Perfect Optical Metamaterial Absorber as a Glucose Sensor in Food Industry Applications

Abstract: Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. In all the reported absorbers, the absorption occurs only at a single wavelength or dual/multi-band wavelengths where plasmon resonances are ex-cited in the nanostructure. Here we not only show a single-band perfect absorber but also demonstrate that our proposed design has the ability to be multi-band absorber at the same structure. Furthermore, we numerically demonstrate the proposed POMMA can be utilized as a glucose sensor for refractive index sensing which has more than 225 nm/RIU sensitivity at the infrared frequency regime which is good value. Its polarization-independent absorbance is about 100% at normal incidence for both TE and TM polarization modes. The proposed optical glucose sensor offers great potential to maintain the performance of localized surface plasmon (LSP) sensors in nanostructures in food industry applications.

Knotting fractional-order knots with the polarization state of light

Abstract: The fundamental polarization singularities of monochromatic light are normally associated with invariance under coordinated rotations: symmetry operations that rotate the spatial dependence of an electromagnetic field by an angle θ and its polarization by a multiple γθ of that angle. These symmetries are generated by mixed angular momenta of the form Jγ = L + γS, and they generally induce Mobius-strip topologies, with the coordination parameter γ restricted to integer and half-integer values. In this work we construct beams of light that are invariant under coordinated rotations for arbitrary rational γ, by exploiting the higher internal symmetry of ‘bicircular’ superpositions of counter-rotating circularly polarized beams at different frequencies. We show that these beams have the topology of a torus knot, which reflects the subgroup generated by the torus-knot angular momentum Jγ, and we characterize the resulting optical polarization singularity using third- and higher-order field moment tensors, which we experimentally observe using nonlinear polarization tomography. The polarization structure around polarization singularities can exhibit arbitrary fractional rotations when tracing around the singularity, due to an underlying topology of a torus knot imprinted by the chosen ratio of frequencies contained in the light beam.

Application of Machine Learning in Fiber Nonlinearity Modeling and Monitoring for Elastic Optical Networks

Abstract: Fiber nonlinear interference (NLI) modeling and monitoring are the key building blocks to support elastic optical networks. In the past, they were normally developed and investigated separately. Moreover, the accuracy of the previously proposed methods still needs to be improved for heterogenous dynamic optical networks. In this paper, we present the application of machine learning (ML) in NLI modeling and monitoring. In particular, we first propose to use ML approaches to calibrate the errors of current fiber nonlinearity models. The Gaussian-noise model is used as an illustrative example, and significant improvement is demonstrated with the aid of an artificial neural network. Further, we propose to use ML to combine the modeling and monitoring schemes for a better estimation of NLI variance. Extensive simulations with 2411 links are conducted to evaluate and analyze the performance of various schemes, and the superior performance of the ML-aided combination of modeling and monitoring is demonstrated.

Photonics-Assisted Technologies for Extreme Broadband 5G Wireless Communications

Abstract: We summarize the enabling technologies for photonics-assisted broadband millimeter-wave (mm-wave) communication, which is a promising candidate for the enhanced mobile broadband (eMBB) communications, one of the three main typical application scenarios of 5G wireless networks. These enabling technologies, mainly focusing on the improvement of the system structure, include broadband mm-wave signal generation with simple and cost-effective schemes, multiple-input multiple-output architecture with polarization-multiplexing optical mm-wave signal, advanced multilevel modulation, optical or electrical multicarrier modulation, antenna polarization multiplexing and the employment of the high-gain mm-wave antenna, multi-band multiplexing, and broadband mm-wave signal detection. We also review the advanced digital signal processing (DSP) for heterodyne coherent detection, which can be applied into the photonics-assisted mm-wave communication systems, to further enhance the system performance for a given system structure and certain available devices. Based on these enabling technologies and advanced DSP, we have realized over 1 Tb/s wireless signal transmission at D-band and over 2.5 km wireless transmission with a bit rate up to 54 Gb/s at W-band. Our work verifies the photonics-assisted broadband mm-wave communication can meet the high-data-rate demand of eMBB.

120 Gb/s Wireless Terahertz-Wave Signal Delivery by 375 GHz-500 GHz Multi-Carrier in a 2 × 2 MIMO System

Abstract: We propose and experimentally demonstrate a photonics-aided 2 × 2 multiple-input multiple-output (MIMO) wireless Terahertz-wave (THz-wave) signal transmission system, which realizes 6 × 20-Gb/s six-channel polarization division multiplexing quadrature-phase-shift-keying THz-wave signal delivery over 10-km wireline single-mode fiber- link and 142-cm wireless 2 × 2 MIMO link with a bit-error ratio under the hard-decision forward-error-correction threshold of 3.8 × 10−3. Our employed multi-carrier frequencies are located within the range of 375 GHz to 500 GHz. To the best of our knowledge, this is the first experimental demonstration of 2 × 2 MIMO wireless transmission of multi-channel THz-wave signal. Here, it is worth noting that our wireless 2 × 2 MIMO link, which offers point-to-point straight transmission and brings neither interference nor gain, is different from the traditional MIMO link defined in the field of wireless communications.

Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding

Abstract: Optical isolators and circulators are fundamental building block in photonic integrated circuits to block undesired reflections and routing light according to a prescribed direction. In silicon photonics, heterogeneous integration of magneto-optic garnet bonded on a pre-patterned silicon layer has been demonstrated to be an effective solution for manufacturing optical isolators and circulators for TM polarized light. However, most integrated semiconductor lasers emit TE polarized light, which indicates the need to find a reliable solution for this polarization. In this paper, we demonstrated broadband optical isolators and circulators for TE polarized light based on heterogeneous bonding on the silicon photonics platform. To achieve this goal, an integrated adiabatic coupler and a broadband polarization rotator are designed and optimized. The nonreciprocal behavior is induced through an energy-efficient integrated electromagnet with a minimum power consumption of 3 mW. Two isolators/circulators are fabricated with small and large free spectral range, respectively. In the former case, an optical isolation ratio as large as 30 dB is measured at 1555 nm with an insertion loss of 18 dB, while for the broadband circulator, an optical isolation larger than 15 dB is guaranteed over more than 14 nm (1.75 THz) for all port combinations with an insertion loss between 14 and 18 dB at 1560 nm. Finally, it has been theoretically shown that the insertion loss can be reduced below 6 dB with design and fabrication improvements. To the best of the authors’ knowledge, the proposed integrated TE optical circulator is the first experimental demonstration of this device in silicon photonics.

Advanced Modulation Techniques for Flexible Optical Transceivers: The Rate/Reach Tradeoff

Abstract: This tutorial paper reviews advanced modulation techniques that have been proposed in the literature for the implementation of flexible (or reconfigurable) transceivers, which are fundamental building blocks of next-generation software-defined optical networks. Using a common reference multi-span propagation system scenario, the performance of transceivers employing standard quadrature amplitude modulation with variable-rate forward error correction, probabilistic constellation-shaping, and time-domain hybrid formats is assessed, highlighting the achievable flexibility in terms of continuous tradeoff between transmission rate and distance. The combination of these techniques with sub-carrier multiplexing, which enables an increase of the fiber nonlinearity tolerance thanks to the optimization of the symbol rate per sub-carrier, is also discussed.

Dual-Polarization Non-Linear Frequency-Division Multiplexed Transmission With $b$ -Modulation

Abstract: There has been much interest in the non-linear frequency-division multiplexing (NFDM) transmission scheme in the optical fiber communication system. Up to date, most of the demonstrated NFDM schemes have employed only single polarization for data transmission. Employing both polarizations can potentially double the data rate of NFDM systems. We investigate in simulation a dual-polarization NFDM transmission with data modulation on the $b$ -coefficient. First, a transformation that facilitates the dual-polarization $b$ -modulation was built upon an existing transformation in [M. Yousefi and X. Yangzhang, “Linear and nonlinear frequency-division multiplexing,” in Proc. Eur. Conf. Opt. Commun. , Dusseldorf, Germany, Sep. 2016, pp. 342-344]. Second, the $q_c$ - and $b$ -modulation for dual polarization were compared in terms of Q -factor, spectral efficiency (SE), and correlation of sub-carriers. The correlation is quantified via information theoretic metrics, joint and individual entropy. The polarization-multiplexed $b$ -modulation system shows 1-dB Q -factor improvement over $q_c$ -modulation system due to a weaker correlation of sub-carriers and less effective noise. Finally, the $b$ -modulation system was optimized for high data rate, achieving a record net data rate of 400 Gb/s (SE of 7.2 b/s/Hz) over $12\times 80$ km of standard single-mode fiber with erbium-doped fiber amplifiers. Based on the aforementioned simulation results, we further point out the drawbacks of our current system and quantify the error introduced by the transceiver algorithms and non-integrability of the channel

Imaging antiferromagnetic domains in nickel oxide thin films by optical birefringence effect

Abstract: Recent demonstrations of electrical detection and manipulation of antiferromagnets (AFMs) have opened new opportunities toward robust and ultrafast spintronics devices. However, it is difficult to establish the connection between the spin-transport behavior and the microscopic AFM domain states in thin films due to the lack of a real-time imaging technique under the electric field. Here we report a large magneto-optical birefringence effect with polarization rotation up to 60 millidegrees in thin NiO(001) films at room temperature. Such large optical polarization rotation allows us to directly observe AFM domains in thin-film NiO by utilizing a wide-field optical microscope. Complementary x-ray magnetic linear dichroism--photoemission electron microscopy measurement further confirms that the optical contrast is related to the NiO AFM domain. We examine the domain pattern evolution at a wide range of temperatures and with the application of external magnetic field. Comparing to large-scale-facility techniques such as x-ray photoemission electron microscopy, using a wide-field, tabletop optical imaging method in reflection geometry enables straightforward access to domain configurations of single-layer AFMs.

Learning life cycle to speed up autonomic optical transmission and networking adoption

Abstract: Autonomic optical transmission and networking requires machine learning (ML) models to be trained with large datasets. However, the availability of enough real data to produce accurate ML models is rarely ensured since new optical equipment and techniques are continuously being deployed in the network. One option is to generate data from simulations and lab experiments, but such data could not cover the whole features space and would translate into inaccuracies in the ML models. In this paper, we propose an ML-based algorithm life cycle to facilitate ML deployment in real operator networks. The dataset for ML training can be initially populated based on the results from simulations and lab experiments. Once ML models are generated, ML retraining can be performed after inaccuracies are detected to improve their precision. Illustrative numerical results show the benefits of the proposed learning cycle for general use cases. In addition, two specific use cases are proposed and demonstrated that implement different learning strategies: (i) a two-phase strategy performing out-of-field training using data from simulations and lab experiments with generic equipment, followed by an in-field adaptation to support heterogeneous equipment (the accuracy of this strategy is shown for a use case of failure detection and identification), and (ii) in-field retraining, where ML models are retrained after detecting model inaccuracies. Different approaches are analyzed and evaluated for a use case of autonomic transmission, where results show the significant benefits of collective learning.

Near-Unity Anisotropic Infrared Absorption in Monolayer Black Phosphorus With/Without Subwavelength Patterning Design

Abstract: As an emerging anisotropic two-dimensional (2-D) material, few-atomic-layer black phosphorus (BP) has shown some promising potentials for infrared optoelectronics. Engineering and enhancing its light-matter interaction is significant for many advanced photonic devices. In view of this, we aim to achieve extremely high infrared absorption in monolayer BP with/without subwavelength patterning. By optimizing the polarization and angle of the incident light, the dielectric thickness, and the n -type doping concentration, respectively, infrared radiation can be sufficiently coupled to optical absorption of the monolayer BP in a multiscale photonic structure. The anisotropic infrared absorbance ratios of the unpatterned monolayer BP are enhanced up to 98.2% and 96%, respectively, in inequivalent crystal directions. Moreover, monolayer BP with a design of metasurface and optimized doping can reach near-unity anisotropic infrared absorption under a smaller incident angle. This paper provides a simple and efficient scheme to trap infrared light for developing promising optoelectronic devices based on monolayer BP and potentially other anisotropic 2-D materials.

Study of efficient semipolar (11-22) InGaN green micro-light-emitting diodes on high-quality (11-22) GaN/sapphire template

Abstract: We investigated the electrical and optical performances of semipolar (11-22) InGaN green µLEDs with a size ranging from 20 × 20 µm2 to 100 × 100 µm2, grown on a low defect density and large area (11-22) GaN template on patterned sapphire substrate. Atom probe tomography (APT) gave insights on quantum wells (QWs) thickness and indium composition and indicated that no indium clusters were observed in the QWs. The µLEDs showed a small wavelength blueshift of 5 nm, as the current density increased from 5 to 90 A/cm2 and exhibited a size-independent EQE of 2% by sidewall passivation using atomic-layer deposition, followed by an extremely low leakage current of ~0.1 nA at -5 V. Moreover, optical polarization behavior with a polarization ratio of 40% was observed. This work demonstrated long-wavelength µLEDs fabricated on semipolar GaN grown on foreign substrate, which are applicable for a variety of display applications at a low cost.

Switchable 0.612-nm-Spaced Dual-Wavelength Fiber Laser With Sub-kHz Linewidth, Ultra-High OSNR, Ultra-Low RIN, and Orthogonal Polarization Outputs

Abstract: A high-performance switchable 0.612-nm-spaced dual-wavelength erbium-doped fiber (EDF) laser is proposed and experimentally demonstrated. For the first time, we combine a compound-cavity structure (CCS) and an enhanced polarization hole burning (PHB) effect in laser cavity to obtain stable dual-wavelength lasing ( λ 1 and λ 2) and single-longitudinal-mode (SLM) operation at each wavelength without mode hopping. In the CCS, a high-quality triple-ring passive resonator is employed to achieve SLM lasing and a high-birefringence fiber Bragg grating combined with a three-loop polarization controller made with a length of EDF is used to establish a strong PHB effect. Easy switch between dual- and single-wavelength lasing modes is achieved. At a pump power of 150 mW, we obtain dual-wavelength lasing with optical signal-to-noise ratios (OSNRs) of >84 dB for both wavelengths and linewidths of 663 Hz for λ 1 and 768 Hz for λ 2, respectively; we also obtain single-wavelength lasing at λ 1 with an OSNR of >86 dB and a linewidth of 687 Hz or at λ 2 with an OSNR of >88 dB and a linewidth of 678 Hz. For both dual- and single-wavelength operations, the two lasing wavelengths are orthogonally polarized, with a degree of polarization of ∼100%, and their relative intensity noises are <−155 dB/Hz at frequencies over 3 MHz. In addition, the dependence of wavelength, OSNR, and linewidth on pump power and wavelength-tunability on temperature for the proposed fiber laser are also investigated in detail.

Polarization of changing-look quasars

Abstract: If the disappearance of the broad emission lines observed in changing-look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions.

Optical light polarization and light extraction efficiency of AlGaN-based LEDs emitting between 264 and 220 nm

Abstract: The influence of aluminum mole fraction of Al x Ga1-x N/Al y Ga1-y N multiple quantum wells (MQWs) on the optical polarization, light extraction efficiency (LEE) and external quantum efficiency (EQE) of deep ultra violet light emitting diodes in the wavelength range between 264 and 220 nm is investigated. The on-wafer EQE decreases from 0.6% to 0.00013% in this wavelength range. Polarization resolved photoluminescence and electroluminescence measurements show a change from dominant transverse-electric to dominant transverse-magnetic polarized light emission with increasing aluminum mole fraction in the MQW. The quantitative agreement with kp calculations allow to ascribe this shift to a change of the characteristic of the Γ7+ valance band. Ray tracing simulations predict a reduction of the on-wafer LEE from 4% to 1.5%. Therefore the dramatic drop of the EQE in this wavelength range cannot be attributed to a drop in LEE and is most likely dominated by charge carrier injection and radiative recombination efficiency.

Dual-Polarization NFDM Transmission With Continuous and Discrete Spectral Modulation

Abstract: Nonlinear distortion experienced by signals during their propagation through optical fibers strongly limits the throughput of optical communication systems. Recently, a strong research focus has been dedicated to nonlinearity mitigation and compensation techniques. At the same time, a more disruptive approach, the nonlinear Fourier transform, aims at designing signaling schemes more suited to the nonlinear fiber channel. In a short period, impressive results have been reported by modulating either the continuous spectrum or the discrete spectrum. Additionally, very recent works further introduced the opportunity to modulate both spectra for single polarization transmission. Here, we extend the joint modulation scheme to dual-polarization transmission by introducing the framework to construct a dual-polarization optical signal with the desired continuous and discrete spectra. After a brief analysis of the numerical algorithms used to implement the proposed scheme, the first experimental demonstration of dual-polarization joint nonlinear frequency division multiplexing modulation is reported for up to 3200 km of low-loss transmission fiber. The proposed dual-polarization joint modulation schemes enables to exploit all the degrees of freedom for modulation (both polarizations and both spectra) provided by a single-mode fiber.

Polarization-Ring-Switching for Nonlinearity-Tolerant Geometrically Shaped Four-Dimensional Formats Maximizing Generalized Mutual Information

Abstract: In this paper, a new four-dimensional 64-ary polarization ring switching (4D-64PRS) modulation format with a spectral efficiency of 6 bit/4D-sym is introduced. The format is designed by maximizing the generalized mutual information (GMI) and by imposing a constant modulus on the 4D structure. The proposed format yields an improved performance with respect to state-of-the-art geometrically shaped modulation formats for bit-interleaved coded modulation systems at the same spectral efficiency. Unlike previously published results, the coordinates of the constellation points and the binary labeling of the constellation are jointly optimized. When compared with polarization-multiplexed 8-ary quadrature-amplitude modulation (PM-8QAM), gains of up to 0.7 dB in signal-to-noise ratio are observed in the additive white Gaussian noise channel. For a long-haul nonlinear optical fiber system of 8,000 km, gains of up to 0.27 bit/4D-sym ( $\text{5.5}$ % data capacity increase) are observed. These gains translate into a reach increase of approximately 16% (1,100 km). The proposed modulation format is also shown to be more tolerant to nonlinearities than PM-8QAM. Results with low-density parity-check codes are also presented, which confirm the gains predicted by the GMI.

Optical Field Recovery in Stokes Space

Abstract: Coherent detection empowers optical receivers the capability of recovering the optical field propagating through the fiber. Field recovery not only increases the degree of freedom for optical modulations, but also enables the digital compensation of fiber dispersion that avoids the sophisticated optical dispersion management. Compared with coherent detection, direct detection (DD) owns a natural advantage—the simplicity, but lacks the capability of field recovery. To increase the modulation dimension for DD, the recent development of Stokes vector receiver takes the advantage of polarization diversity and extends the modulation dimension up to three-dimension with reference to the four-dimensional coherent detection (i.e., dual-polarization intensity and phase). However, a Stokes vector receiver is not inherently capable of field recovery because the second-order signal representation in Stokes space nonlinearizes the first-order linear field information, making it infeasible to digitally compensate the chromatic dispersion. In this paper, we provide a comprehensive review of Stokes-space field recovery (SSFR) that completely or partially recovers the optical field by DD. We analyze the degree of freedom for a variety of Stokes-space modulations compatible with SSFR, and reveal their tradeoff between optical spectral efficiency (that determines fiber capacity) and electrical spectral efficiency (that determines transceiver cost per bit). We review the Stokes-space polarization recovery methods and generalize a novel concept as analog polarization identification to simplify the DSP of SSFR. Furthermore, we compare the OSNR sensitivity among various common direct detection schemes to provide reliable predictions of their transmission performance. With its high spectral efficiency and capability of digital dispersion compensation, SSFR is very promising for future high-capacity short-reach applications over single- or multispan fiber transmission.

108-km Distributed Acoustic Sensor With 220-p $\varepsilon /\surd$ Hz Strain Resolution and 5-m Spatial Resolution

Abstract: The measurement distance is one of the most important parameters for distributed acoustic sensor (DAS). In this paper, we report a long-distance and high-sensitivity DAS system based on time-gated digital optical frequency domain reflectometry. The bi-directional distributed Raman amplification is adopted to realize long measurement distance. The shape of optical pulse is pre-distorted to be a standard Hanning window, which provides a theoretical peak-side lobe ratio of 46 dB to suppress the crosstalk. The interference fading and polarization fading are well suppressed, and hence phase-demodulation method is adopted, instead of intensity demodulation method. As a result, the sensitivity is enhanced and the full information (amplitude, phase, and frequency) of the vibration can be obtained. In experiments, the fiber length is about 108 km, whereas the spatial resolution is 5 m. A weak vibration with peak–peak amplitude of 14.7 n $\varepsilon$ is correctly located at the distance of 98 km with a high SNR of 30 dB. It is the first time that 220-p $\varepsilon /\surd$ Hz strain sensitivity is realized over 100-km-level fiber and the vibration waveform is retrieved linearly without harmonics.

Light Attenuation Display: Subtractive See-Through Near-Eye Display via Spatial Color Filtering

Abstract: We present a display for optical see-through near-eye displays based on light attenuation, a new paradigm that forms images by spatially subtracting colors of light Existing optical see-through head-mounted displays (OST-HMDs) form virtual images in an additive manner—they optically combine the light from an embedded light source such as a microdisplay into the users' field of view (FoV) Instead, our light attenuation display filters the color of the real background light pixel-wise in the users' see-through view, resulting in an image as a spatial color filter Our image formation is complementary to existing light-additive OST-HMDs The core optical component in our system is a phase-only spatial light modulator (PSLM), a liquid crystal module that can control the phase of the light in each pixel By combining PSLMs with polarization optics, our system realizes a spatially programmable color filter In this paper, we introduce our optics design, evaluate the spatial color filter, consider applications including image rendering and FoV color control, and discuss the limitations of the current prototype

A Tunable Compact Polarizer in a Circular Waveguide

Abstract: The possibility to design a tunable polarization plane (PP) rotator in waveguides with circular symmetry is proven. The appearance of artificial “optical activity” in the interaction of a pair of conjugated planar chiral irises by the fringing fields is used. The rotator can be reconfigured by rotating the irises relative to each other providing the rotation of the PP up to cross-one. Being relatively narrowband, the rotator has a longitudinal dimension $\lambda _{0}/50$ – $\lambda _{0}/10$ .

Near-Infrared Lasing at 1 μm from a Dilute-Nitride-Based Multishell Nanowire

Abstract: A coherent photon source emitting at near-infrared (NIR) wavelengths is at the heart of a wide variety of applications ranging from telecommunications and optical gas sensing to biological imaging and metrology. NIR-emitting semiconductor nanowires (NWs), acting both as a miniaturized optical resonator and as a photonic gain medium, are among the best-suited nanomaterials to achieve such goals. In this study, we demonstrate the NIR lasing at 1 μm from GaAs/GaNAs/GaAs core/shell/cap dilute nitride nanowires with only 2.5% nitrogen. The achieved lasing is characterized by an S-shape pump-power dependence and narrowing of the emission line width. Through examining the lasing performance from a set of different single NWs, a threshold gain, gth, of 4100-4800 cm-1, was derived with a spontaneous emission coupling factor, β, up to 0.8, which demonstrates the great potential of such nanophotonic material. The lasing mode was found to arise from the fundamental HE11a mode of the Fabry-Perot cavity from a single NW, exhibiting optical polarization along the NW axis. Based on temperature dependence of the lasing emission, a high characteristic temperature, T0, of 160 (±10) K is estimated. Our results, therefore, demonstrate a promising alternative route to achieve room-temperature NIR NW lasers thanks to the excellent alloy tunability and superior optical performance of such dilute nitride materials.

Electrically Controlled Neuron-Like Spiking Regimes in Vertical-Cavity Surface-Emitting Lasers at Ultrafast Rates

Abstract: We report experimentally on the electrically controlled, tunable, and repeatable neuron-like spiking regimes generated in an optically injected vertical-cavity surface-emitting laser (VCSEL) operating at the telecom wavelength of 1300 nm. These fast spiking dynamics (obtained at sub-nanosecond speed rates) demonstrate different behaviors observed in biological neurons such as thresholding, phasic and tonic spiking, and spike rate and spike latency coding. The spiking regimes are activated in response to external stimuli (with controlled strengths and temporal duration) encoded in the bias current applied to a VCSEL subject to continuous wave optical injection. These results reveal the prospect for fast (>7 orders of magnitude faster than neurons), novel, electrically controlled spiking photonic modules for future neuromorphic computing platforms.

Real-Time 10 Gbps Polarization Independent Quasicoherent Receiver for NG-PON2 Access Networks

Abstract: In this paper, we propose and test experimentally a real-time 10 Gbps polarization independent quasicoherent receiver for NG-PON2 access networks. The proposed 10 Gbps quasicoherent receiver exhibits a sensitivity of −35.2 dBm after 40 km standard single mode fiber (SSMF) transmission with a commercial generic EML as transmitter. This sensitivity means a 14.9 dB improvement over a direct detection scheme with a photodiode after 40 km SSMF transmission. Therefore, the use of the proposed 10 Gbps quasicoherent receiver with the tested EML will provide a power budget of 35.64 dB (class E2) and a splitting ratio of 128 after the 40 km SSMF transmission. Finally, the proposed 10 Gbps quasicoherent receiver allows a colorless and optical filterless operation because wavelength selection is done by tuning the local oscillator wavelength and using electrical intermediate frequency filtering.

VENUS: A Vertical-Cavity Surface-Emitting Laser Electro-Opto-Thermal NUmerical Simulator

Abstract: The properties of vertical-cavity surface-emitting lasers (VCSELs) are investigated by means of a multiphysical Vcsel Electro-opto-thermal NUmerical Simulator (VENUS). VENUS includes a three-dimensional vectorial electromagnetic code, a description of the quantum well optical response, a heat equation solver, and a quantum-corrected drift-diffusion simulator. The proposed suite includes coupling mechanisms often overlooked in VCSEL simulation and allows to reassess the impact of parameters, which can be critically dependent on implementation details inaccessible in commercial codes. The agreement with experimental results holds the promise of the application of this framework to the computer-aided design of innovative VCSEL concepts.

Nonlinearity Mitigation in WDM Systems: Models, Strategies, and Achievable Rates

Abstract: After reviewing models and mitigation strategies for interchannel nonlinear interference (NLI), we study its characteristics and coherence properties. Based on this study, we devise an NLI mitigation strategy, which exploits the synergic effect of phase and polarization noise (PPN) compensation and subcarrier multiplexing with symbol-rate optimization. This synergy persists even for high-order modulation alphabets and Gaussian symbols. A particle method for the computation of the resulting achievable information rate and spectral efficiency (SE) is presented and employed to lower-bound the channel capacity. The dependence of the SE on the link length, amplifier spacing, and presence or absence of in-line dispersion compensation is studied. Single-polarization and dual-polarization scenarios with either independent or joint processing of the two polarizations are considered. Numerical results show that, in links with ideal distributed amplification, an SE gain of about 1 bit/s/Hz/polarization can be obtained (or, in alternative, the system reach can be doubled at a given SE) with respect to single-carrier systems without PPN mitigation. The gain is lower with lumped amplification, increases with the number of spans, decreases with the span length, and is further reduced by in-line dispersion compensation. For instance, considering a dispersion-unmanaged link with lumped amplification and an amplifier spacing of 60 km, the SE after 80 spans can be be increased from 4.5 to 4.8 bit/s/Hz/polarization, or the reach raised up to 100 spans (+25%) for a fixed SE.

An Optically Transparent Dual-Polarized Stacked Patch Antenna With Metal-Mesh Films

Abstract: A wideband dual-polarized stacked patch antenna with optical transparency is proposed in this letter. The traditional metal plates are replaced by transparent conductive films made by printing metal meshes with sheet resistance of 0.5 Ω/sq to single side of polyethylene terephthalate. The planar conductive layers are separated by substrates made by transparent polymethyl methacrylate plates. The majority of the antenna area has a high optical transparency. A wide impedance bandwidth is realized by applying stacked round microstrip patches. The disk probes provide good impedance matching as well as a small occlusion area. Measurement results show the antenna exhibits an impedance bandwidth of 19% (2.4–2.9 GHz, ${{\bf VSWR}} ) for both ports. The radiation efficiency is around 75%. The optical transparency is nearly 70% throughout the visible spectrum for the majority of the antenna. The antenna has a stable unidirectional radiation pattern with low cross polarization $({ and low back-radiation level across the operating frequency band.