Showing papers on "Optical polarization published in 2018"

Digital Signal Processing for Short-Reach Optical Communications: A Review of Current Technologies and Future Trends

Abstract: Driven primarily by cloud service and data-center applications, short-reach optical communication has become a key market segment and growing research area in recent years. Short-reach systems are characterized by direct detection-based receiver configurations and other low-cost and small form factor components that induce transmission impairments unforeseen in their coherent counterparts. Innovative signaling and digital signal processing (DSP) play a pivotal role in enabling these components to realize their ultimate potentials and meet data rate requirements in cost-effective manners. This paper presents an overview of recent DSP developments for short-reach communications systems and discusses future trends.

Creation and Detection of Vector Vortex Modes for Classical and Quantum Communication

Abstract: Vector vortex beams are structured states of light that are nonseparable in their polarisation and spatial mode, they are eigenmodes of free-space and many fiber systems, and have the capacity to be used as information carriers for both classical and quantum communication. Here, we outline recent progress in our understanding of these modes, from their creation to their characterization and detection. We then use these tools to study their propagation behavior in free-space and optical fiber and show that modal cross-talk results in a decay of vector states into separable scalar modes, with a concomitant loss of information. We present a comparison between probabilistic and deterministic detection schemes showing that the former, while ubiquitous, negates the very benefit of increased dimensionality in quantum communication while reducing signal in classical communication links. This work provides a useful introduction to the field as well as presenting new findings and perspectives to advance it further.

Terahertz Technologies to Deliver Optical Network Quality of Experience in Wireless Systems Beyond 5G

Abstract: This article discusses the basic system architecture for THz wireless links with bandwidths of more than 50 GHz into optical networks. New design principles and breakthrough technologies are required in order to demonstrate terabit- per-second data rates at near zero latency using the proposed system concept. Specifically, we present the concept of designing the baseband signal processing for both the optical and wireless links and using an E2E error correction approach for the combined link. We provide two possible electro-optical baseband interface architectures, namely transparent optical-link and digital- link architectures, which are currently under investigation. THz wireless link requirements are given as well as the main principles and research directions for the development of a new generation of transceiver front-ends that will be capable of operating at ultra-high spectral efficiency by employing higher-order modulation schemes. Moreover, we discuss the need for developing a novel THz network information theory framework, which will take into account the channel characteristics and the nature of interference in the THz band. Finally, we highlight the role of PBF, which is required in order to overcome the propagation losses, as well as the physical layer and medium access control challenges.

Passively Q-Switched and Mode-Locked Fiber Laser Based on an ReS2 Saturable Absorber

Abstract: Transition metal dichalcogenides, a family of two-dimensional material with unusual electronic, optical, mechanical, and electrochemical properties, have received much research attention in recent years. Here we demonstrate that, another type of few-layer transition metal dichalcogenides, rhenium disulfide (ReS2) nanosheets display saturable absorption property at 1.55 μm. By incorporating the ReS2 nanosheets with the polyvinyl alcohol (PVA), a film-type ReS2-PVA saturable absorber is fabricated to realize Q-switching and mode locking of erbium-doped fiber lasers. The repetition rate of the Q-switched laser pulses varies from 12.6 to 19 KHz while the duration changes from 23 to 5.496 μs by tuning the pump from 45 to 120 mW. By optimizing the polarization state, the mode-locked operation is also obtained, emitting a train of pulses centered at 1558.6 nm with the duration of 1.6 ps and the fundamental repetition rate of 5.48 MHz. It is demonstrated that ReS2 nanosheets have the similar saturable absorption property as that of MoS2 and WS2, and may find potential applications in pulsed laser, optical modulators, and sensors.

Reconstructing the topology of optical polarization knots

Abstract: Knots are topological structures describing how a looped thread can be arranged in space. Although most familiar as knotted material filaments, it is also possible to create knots in singular structures within three-dimensional physical fields such as fluid vortices1 and the nulls of optical fields2–4. Here we produce, in the transverse polarization profile of optical beams, knotted lines of circular transverse polarization. We generate and observe both simple torus knots and links as well as the topologically more complicated figure-eight knot. The presence of these knotted polarization singularities endows a nontrivial topological structure on the entire three-dimensional propagating wavefield. In particular, the contours of constant polarization azimuth form Seifert surfaces of high genus5, which we are able to resolve experimentally in a process we call seifertometry. This analysis reveals a level of topological complexity, present in all experimentally generated polarization fields, that goes beyond the conventional reconstruction of polarization singularity lines. Knotted lines representing torus knot and figure-eight knot are produced in the polarization profile of optical beams, leading to a topological characterization of the structure of the polarization field.

MEMS-tunable dielectric metasurface lens

Abstract: We report a micro-electromechanically tunable metasurface doublet composed of a moving metasurface on a membrane and a stationary one. The doublet provides more than 180 diopters change in the optical power.

Orthogonally Polarized RF Optical Single Sideband Generation and Dual-Channel Equalization Based on an Integrated Microring Resonator

Abstract: We demonstrate narrowband orthogonally polarized optical radio frequency (RF) single sideband generation as well as dual-channel equalization based on an integrated dual-polarization-mode high- Q microring resonator. The device operates in the optical communications band and enables narrowband RF operation at either 16.6 or 32.2 GHz, determined by the free spectral range and TE/TM mode interval in the resonator. We achieve a very large dynamic tuning range of over 55 dB for both the optical carrier-to-sideband ratio and the dual-channel RF equalization.

Optical time reversal from time-dependent Epsilon-Near-Zero media

Abstract: We provide an efficient surface time-reversal of the incident electric field in an ENZ material producing both phase-conjugated and negative refracted beams. The results obtained exploiting degenerate four-wave mixing show an efficiency conversion over 200%.

Robust optical polarization of nuclear spin baths using Hamiltonian engineering of nitrogen-vacancy center quantum dynamics

Abstract: Dynamic nuclear polarization (DNP) is an important technique that uses polarization transfer from electron to nuclear spins to achieve nuclear hyperpolarization. Combining efficient DNP with optically polarized nitrogen-vacancy (NV) centers offers promising opportunities for novel technological applications, including nanoscale nuclear magnetic resonance spectroscopy of liquids, hyperpolarized nanodiamonds as magnetic resonance imaging contrast agents, and the initialization of nuclear spin–based diamond quantum simulators. However, none of the current realizations of polarization transfer are simultaneously robust and sufficiently efficient, making the realization of the applications extremely challenging. We introduce the concept of systematically designing polarization sequences by Hamiltonian engineering, resulting in polarization sequences that are robust and fast. We theoretically derive sequences and experimentally demonstrate that they are capable of efficient polarization transfer from optically polarized NV centers in diamond to the surrounding 13C nuclear spin bath even in the presence of control errors, making the abovementioned novel applications possible.

Silicon Photonics in Optical Coherent Systems

Abstract: Optical coherent systems, which employ the interference of a received optical signal with a local laser to achieve high signal-to-electrical-noise ratio and capture the magnitude, phase, and polarization of the signal, have grown dramatically in the last decade due to improvements in digital signal processors. The optics of both the transmitter and receiver have grown in complexity, and its deployment has benefitted greatly from the integration offered by silicon photonics. Today’s coherent systems range from 1.2-Tb/s fiber-optic communication transceivers to optical coherence tomography medical instruments. This paper will give an overview of optical coherent systems, present the state-of-the-art in silicon photonic components shipping today, and discuss where silicon photonics is going in this field.

RoboPol: connection between optical polarization plane rotations and gamma-ray flares in blazars

Abstract: We use results of our 3 yr polarimetric monitoring programme to investigate the previously suggested connection between rotations of the polarization plane in the optical emission of blazars and their gamma-ray flares in the GeV band. The homogeneous set of 40 rotation events in 24 sources detected by RoboPol is analysed together with the gamma-ray data provided by Fermi-LAT. We confirm that polarization plane rotations are indeed related to the closest gamma-ray flares in blazars and the time lags between these events are consistent with zero. Amplitudes of the rotations are anticorrelated with amplitudes of the gamma-ray flares. This is presumably caused by higher relativistic boosting (higher Doppler factors) in blazars that exhibit smaller amplitude polarization plane rotations. Moreover, the time-scales of rotations and flares are marginally correlated.

Design of a High Extinction Ratio Tunable Graphene on White Graphene Polarizer

Abstract: A thermally/electrically tunable graphene on white graphene polarizer is proposed, in which the resonant coupling between the plasmonic surface modes of the structure and the transverse electric (TE) [or transverse magnetic (TM)] polarized incident wave is used to absorb this polarization, while the TM (or TE) polarized incident wave is totally reflected. It is then shown that the thermal and electrical tunability of surface conductivity of graphene can be used to control the optical properties of the proposed polarizer, including the selection of the desired polarization, and adjusting the amplitude of the reflected (desired) polarization. The application of the hexagonal boron-nitride (white graphene) as the substrate of graphene increases the propagation of the surface waves of the structure, which in turn results in the very high polarization extinction ratio of 75 dB. Moreover, the ultra-small insertion loss of 0.022 dB and relatively large bandwidth of ~ 60 nm are calculated for the proposed polarizer.

Controlling optical polarization conversion with Ge2Sb2Te5-based phase-change dielectric metamaterials

Abstract: Recent progress in the metamaterial-based polarization manipulation of light highlights the promise of novel polarization-dependent optical components and systems. To overcome the limited frequency bandwidth of metamaterials resulting from their resonant nature, it is desirable to incorporate tunability into metamaterial-based polarization manipulations. Here, we propose a dielectric metamaterial for controlling linear polarization conversion using the phase-change characteristic of Ge2Sb2Te5 (GST), whose refractive index changes significantly when transforming from the amorphous phase to the crystalline phase under external stimuli. The polarization conversion phenomena are systematically studied using different arrangements of GST in this metamaterial. The performance of linear polarization conversion and the tunability are also analyzed and compared in three different designs. It is found that phase-change materials such as GST can be employed in dielectric materials for tunable and switchable linear polarization conversion in the telecom band. The conversion efficiency can be significantly modulated during the phase transition. Our results provide useful insights for incorporating phase-change materials with metamaterials for tunable polarization manipulation.

Polymer Waveguides Enabling Scalable Low-Loss Adiabatic Optical Coupling for Silicon Photonics

Abstract: Optically transparent polymer waveguides are employed for interfacing silicon photonics devices to fibers. The highly confined optical mode in the nanophotonic silicon waveguide is transferred to a fiber-matched polymer waveguide through adiabatic optical coupling by tapering the silicon waveguide. The polymer waveguides are either processed onto the silicon photonics wafer or bonded to individual chips. Fibers are interfaced to the polymer waveguides through butt-coupling. We show polarization and wavelength-tolerant fiber-to-chip coupling loss of less than 3.5 dB across the O-band. The polymer waveguide-to-silicon-chip alignment tolerance is 2 μ m for a loss increase of only 1 dB. Reflection losses are well below −45 dB and the scalability to large numbers of channels is demonstrated. These results open a path to broadband and polarization-tolerant optical packaging of silicon photonics devices for ultrahigh bandwidth applications employing wavelength division multiplexing across multiple channels as envisioned for future data-center interconnects.

Theory of the optical spin-polarization loop of the nitrogen-vacancy center in diamond

Abstract: The nitrogen-vacancy (NV) center in diamond is of high importance in quantum information processing applications. The operation of the NV center relies on the efficient optical polarization of its electron spin. However, the full optical spin-polarization process, which involves the intersystem crossing between the shelving singlet state and the ground-state triplet, is not understood. Here we develop a detailed theory of this process which involves a combination of pseudo- and dynamic Jahn-Teller interactions together with spin-orbit interaction. Our theory provides an explanation for the asymmetry between the observed emission and absorption spectra of the singlet states. We apply density functional theory to calculate the intersystem crossing rates and the optical spectra of the singlets, and we obtain a good agreement with the experimental data. Since the NV center serves as a template for other solid-state-defect quantum bit systems, our theory provides a toolkit to study them that might help optimize their quantum bit operation.

Advanced Passive Silicon Photonic Devices With Asymmetric Waveguide Structures

Abstract: Various passive photonic integrated devices have been developed successfully with silicon-on-insulator (SOI) nanowires in the past decade. It is well known that SOI-nanowire waveguides have ultrahigh index contrast ( $\Delta $ ) and ultrahigh birefringence. As a result, the structures and the design rules of a silicon photonic device are probably very different from the conventional case of using low- $\Delta $ optical waveguides. For example, some asymmetric waveguide structures have been used often to realize many silicon photonic devices developed recently. Furthermore, higher order modes have been involved in some of these silicon photonic devices. This paper discusses the special mode properties of silicon nanophotonic waveguides, including birefringence, mode dispersion, and mode hybridness. A review is then given on recent progress of these advanced passive silicon photonic devices with structural asymmetry, including on-chip polarization-handling devices, mode converters/(de)multiplexers, microring-resonator optical filters/switches, and Mach..Zehnder interferometer optical switches. Silicon photonic integrated circuits with these building blocks are also reviewed, including hybrid (de)multiplexers and reconfigurable optical add..drop multiplexers.

Chip-Integrated Geometric Metasurface As a Novel Platform for Directional Coupling and Polarization Sorting by Spin–Orbit Interaction

Abstract: The focus of the research in metasurfaces has mainly been on the manipulation of the electromagnetic waves in free space during the past few years, which generally require thousands of subwavelength meta-atoms or even more. In this paper, we propose a conceptually new approach that chip-integrated metasurface can behave as a promising compact platform to control the propagation of guided waves when it is integrated with optical waveguide. As a proof of the concept, geometric metasurfaces consisting of only seven rotating anisotropic antennas, both metallic and dielectric, are integrated with silicon-on-insulator waveguide. Benefiting from the geometric phase shift stemming from spin–orbit interaction in metasurfaces, linearly gradient wavefront is generated along the waveguide, which is equivalent to introduce a unidirectional effective wavevector and thus leads to directional coupling. Inspired by the spin dependent gradient wavefront, opposite light flow is excited in the integrated waveguide by switching the handedness of incidence, which may provide a potential pathway to integrated polarization sorters and switchers.

Large-amplitude Blazar Polarization Angle Swing as a Signature of Magnetic Reconnection

Abstract: Relativistic magnetic reconnection events may exist in magnetized plasmas in astrophysical systems. During this process, oppositely directed magnetic field lines reconnect and release magnetic energy, efficiently accelerating nonthermal particles. However, so far there is little clear observational signatures of relativistic magnetic reconnection events in astrophysical systems. Blazars are relativistic magnetized plasma outflows from supermassive black holes. Their multi-wavelength flares may be powered by relativistic magnetic reconnection. The highly variable radiation and polarization signatures are well covered by multi-wavelength observation campaigns, making them ideal targets to examine the magnetic reconnection model. Recent observations have found that several blazar flares are accompanied by optical polarization angle swings that may have an amplitude as large as >180°, challenging existing theoretical models. In this Letter, we present integrated particle-in-cell and polarized radiation transfer simulations of magnetic reconnection events. We find that plasmoid coalescences in the reconnection layer can give rise to highly variable light curves, low and fluctuating polarization degree, and rotating polarization angle. In particular, large-amplitude polarization angle swings, similar to those observed during blazar flares, can be a unique signature of relativistic magnetic reconnection events.

Kirigami metamaterials for reconfigurable toroidal circular dichroism

Abstract: The ancient paper craft of kirigami has recently emerged as a potential tool for the design of functional materials. Inspired by the kirigami concept, we propose a class of kirigami-based metamaterials whose electromagnetic functionalities can be switched between nonchiral and chiral states by stretching the predesigned split-ring resonator array. Single-band, dual-band, and broadband circular polarizers with reconfigurable performance are experimentally demonstrated with maximum circular dichroism of 0.88, 0.94, and 0.92, respectively. The underlying mechanism is explained and calculated via detailed analysis of the excited multipoles, including the electric, magnetic, and toroidal dipoles and quadrupole. Our approach enables tailoring the electromagnetic functionalities in kirigami patterns and provides an alternate avenue for reconfigurable optical metadevices with exceptional mechanical properties. A new twist on the Japanese art of origami has helped researchers achieve dynamic optical polarization switching for applications including lasers and biosensors. Metamaterials, substances engineered to manipulate radiation in non-natural ways—bending light around objects to make them appear invisible, for example—are normally impossible to re-configure after being fabricated. Liqiao Jing from Zhejiang University in Hangzhou, China, and colleagues have overcome this limitation by depositing periodic arrays of copper rings onto thin, foldable polymer sheets. By introducing small cuts and then stretching the sheets, the team created buckled, 3D surfaces with different symmetries to the original flat film. The rearranged atoms in the new structures enabled filtering of circularly polarized light, an effect which could be expanded to broadband frequencies by stacking two folded films on top of one another. An approach towards kirigami metamaterials with reconfigurable toroidal circular dichroism is presented. Inspired by the kirigami concept, kirigami-based chiral metamaterials are proposed to switch the electromagnetic performance between non-chiral and chiral states. When transforming the 2D metasurface to 3D kirigami patterns, the resonant modes exhibit gradually enhanced chiroptical response, from single-band, dual-band to broad-band functionalities.

Comparison of Low Complexity Coherent Receivers for UDWDM-PONs ( $\lambda$ -to-the-User)

Abstract: It is predicted that demand in future optical access networks will reach multigigabit/s per user. However, the limited performance of the direct detection receiver technology currently used in the optical network units at the customers’ premises restricts data rates per user. Therefore, the concept of coherent-enabled access networks has attracted attention in recent years, as this technology offers high receiver sensitivity, inherent frequency selectivity, and linear field detection enabling the full compensation of linear channel impairments. However, the complexity of conventional (dual-polarization digital) coherent receivers has so far prevented their introduction into access networks. Thus, to exploit the benefits of coherent technology in access networks, low complexity coherent receivers, suitable for implementation in ONUs, are needed. In this paper, the recently proposed low complexity coherent (i.e., polarization-independent Alamouti-coding heterodyne) receiver is, for the first time, compared in terms of its minimum receiver sensitivity with five previously reported receiver designs, including a detailed discussion on their advantages and limitations. It is shown that, of all the configurations considered, the Alamouti-coding based receiver approach allows the lowest number of photons per bit (PPB) transmitted (with a lower bound of 15.5 PPB in an ideal implementation of the system), while requiring the lowest optical receiver hardware complexity (in terms of the optical component count). It also exhibits comparable complexity to the currently deployed direct-detection receivers, which typically require over 1000 PPB. Finally, a comparison of experimentally achieved receiver sensitivities and transmission distances using these receivers is presented. The highest spectral efficiency and longest transmission distance at the highest bit rate (10 Gb/s) was reported using the Alamouti-coding receiver, which is also the only one, to date, to have been demonstrated in a full system bidirectional transmission.

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 $\theta$ and its polarization by a multiple $\gamma\theta$ of that angle. These symmetries are generated by mixed angular momenta of the form $J_\gamma = L + \gamma S$ and they generally induce Mobius-strip topologies, with the coordination parameter $\gamma$ restricted to integer and half-integer values. In this work we construct beams of light that are invariant under coordinated rotations for arbitrary $\gamma$, 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 $J_\gamma$, and we characterize the resulting optical polarization singularity using third-and higher-order field moment tensors, which we experimentally observe using nonlinear polarization tomography.

Generation of Linear Frequency-Modulated Waveforms by a Frequency-Sweeping Optoelectronic Oscillator

Abstract: In this paper, a simple scheme for linear frequency-modulated (LFM) waveform generation based on a frequency-sweeping optoelectronic oscillator is proposed and demonstrated. The OEO is built up with an optically injected semiconductor laser and the oscillation frequency can be tuned by adjusting the optical injection strength. By applying an injection strength controller in the OEO for rapid frequency sweeping, an LFM microwave waveform can be generated. When the sweep period of the output frequency matches with the round-trip time of the OEO cavity, signal quality of the generated LFM waveform can be significantly enhanced by the high Q optoelectronic oscillation. In the experiment, an LFM signal with a bandwidth as large as 7 GHz, a chirp rate reaching 0.18 GHz/ns, and a time-bandwidth product (TBWP) up to 2804.2 is generated. The corresponding electrical spectrum is a frequency comb with a contrast as high as 47 dB. Based on this system, an improved scheme for extending the frequency and bandwidth of the generated LFM signal is proposed by employing a polarization modulator to implement microwave photonic frequency multiplication. With this method, an LFM waveform with a TBWP as large as 13839.1 (bandwidth 15.6 GHz; temporal period 887.12 ns) is obtained.

Titanium Selenide Saturable Absorber Mirror for Passive Q-Switched Er-Doped Fiber Laser

Abstract: Titanium selenide saturable absorber mirror (TiSe2-SAM) is fabricated by a combination of magnetron sputtering method and chemical vapor deposition method. With the optical circulator, the TiSe2-SAM is flexibly injected in the experimental cavity as the saturated absorber, and a steady Q-switched Er-doped fiber (EDF) laser is established. The modulation depth of TiSe2-SAM is measured to be 25.92%. Through appropriately adjusting the polarization states and changing the pump power, the shortest pulse duration and maximum output power of the passive Q-switched EDF laser are 1.126 μ s and 11.54 mW, respectively. The adjustable range of the repetition rate is 70–154 kHz, and the signal to noise ratio is greater than 62 dB. To our best knowledge, there is no report on Q-switched EDF lasers based on TiSe2 up to now, and our new attempt on TiSe2-based Q-switched EDF laser proves that TiSe2 as a powerful candidate is promising in ultrafast optical generation for the characteristics of high modulation depth and high stability.

Photonic Generation of Neuron-Like Dynamics Using VCSELs Subject to Double Polarized Optical Injection

Abstract: We propose to generate excitatory and inhibitory neuron-like dynamics in vertical-cavity surface-emitting lasers (VCSELs) by applying simultaneously the orthogonally-polarized CW optical injection (OPCWOI) and parallelly-polarized pulse optical injection stimulus. Based on the spin flip model, excitatory and inhibitory neuron-like dynamics accompanying with reverse polarization switching is numerically investigated. It is found that, due to the injection locking effect or beating effect between two injected fields, the excitatory phasic and tonic spiking dynamics can be obtained in the originally dominated polarization mode. Moreover, the unwanted relaxation oscillation followed by the excitatory spiking dynamics at the end of the stimulus pulse, which is present in previous reported photonic neuron based on the VCSELs subject to a single orthogonally-polarized optical pulse injection, can be completely suppressed. In addition, the inhibition of tonic spiking dynamics can also be achieved, and the transition from tonic spiking dynamics to phasic bursting dynamics can be obtained, when the two injected fields have the same frequency. These results are interesting and valuable for the ultrafast photonic neuromorphic systems and neuron-inspired photonic information processing.

10 Tb/s PM-64QAM Self-Homodyne Comb-Based Superchannel Transmission With 4% Shared Pilot Tone Overhead

Abstract: We demonstrate transmission of a comb-based 10 Tb/s 50 $\times$ 20 Gbaud PM-64QAM superchannel using frequency comb regeneration to reduce carrier offsets and allow for self-homodyne detection. The regeneration is enabled by transmitting two optical pilot tones which are filtered and recovered in the receiver using optical injection locking and an electrical phase-locked loop. We show that by utilizing frequency combs together with optical pilot tones, self-homodyne detection similar to systems using one pilot tone per wavelength channel, can be achieved. Sharing the overhead for pilot tones reduces the complexity and limits the overhead to 4%. This enabled a total superchannel spectral efficiency of 7.7 b/s/Hz. To evaluate the performance, we perform both back-to-back measurements and transmission over 80 km of standard single-mode fiber. Successful self-homodyne detection of all 50 data channels in the 10-nm-wide superchannel demonstrates that the spectral coherence from frequency combs, combined with the use of optical pilots, can overcome limitations arising from frequency offset and phase noise in high-order QAM transmission while keeping the pilot overhead low.

Ultrahigh Degree of Optical Polarization above 80% in AlGaN-Based Deep-Ultraviolet LED with Moth-Eye Microstructure

Abstract: For the first time, an ultrahigh degree of optical polarization (DOP) of 81.8% in AlGaN-based deep ultraviolet LED (DUV-LED) operated at 286 nm has been experimentally demonstrated. The very high DOP was obtained by introducing the novel moth-eye microstructure fabricated on the backside of a sapphire substrate. Compared with conventional DUV-LED with a DOP of 64.7%, a significant 1.26-fold enhancement was obtained. It was worth mentioning that the DOP was accurately measured via self-built full spatial transverse electric (TE) and transverse magnetic (TM) mode light intensity test system, which was mainly composed of angle resolution bracket, Glan-Taylor prism, and spectrometer. For both TE and TM mode light, the extraction angle inside the semiconductor was extended from conventional (−26°, 26°), (−52°, −41°), (41°, 52°) to (−52°, 52°). Combined with finite difference time domain simulation, it was further confirmed that the novel moth-eye microstructure could notably weaken the total internal reflectio...

Coherent Optical RF Channelizer With Large Instantaneous Bandwidth and Large In-Band Interference Suppression

Abstract: RF channelization is regarded as one of the most effective approaches to relieve the difficulty of processing wideband signals in microwave and millimeter-wave receivers. In this paper, a novel coherent optical RF channelizer with broad instantaneous bandwidth and large in-band interference suppression is proposed and demonstrated based on a multichannel photonic image-reject mixer (IRM). A Ku-band RF signal with an instantaneous bandwidth of 5 GHz is sliced into five consecutive subchannels with 1-GHz instantaneous bandwidth by the proposed channelizer. The in-band interference suppression, which relies on the image-rejection ratios of the IRM, is about 25 dB. To the best of our knowledge, the proposed channelizer achieves the highest in-band interference suppression in such wide instantaneous bandwidth.

Heterogeneous Thin-Film Lithium Niobate Integrated Photonics for Electrooptics and Nonlinear Optics

Abstract: Ion-sliced thin-film lithium niobate (LN) compact waveguide technology has facilitated the resurgence of integrated photonics based on the material. The thin-film waveguides offer over an order of magnitude improvement in optical confinement and bending radius compared to conventional LN waveguides. The thin-film technology can also be implemented on versatile silicon substrates. Harnessing the improved confinement, a variety of miniaturized and efficient photonic devices has been realized. The state of the art of thin-film LN integrated photonics is reviewed, focusing on heterogeneous integration, electrooptic modulation, and nonlinear frequency conversion. The potential applications and associated challenges of next-generation LN-based integrated photonics are discussed.

Waveguide Engineering of Graphene Optoelectronics—Modulators and Polarizers

Abstract: The concept of incorporating graphene into nanophotonic waveguides has pullulated into massive broadband optoelectronic applications with compact footprint. We theoretically demonstrate that by solely altering the dimension design of graphene-laminated silicon waveguides, the phase, amplitude, and polarization of the fundamental propagating modes can all be effectively tailored under different bias voltages. Different device functionalities, including optical amplitude/phase modulators and polarizers, are ascribed into the devising of the effective mode index. A comprehensive analysis and unified design scenarios upon waveguide geometries are summarized, with fabrication robustness and moderate process complexity. Moreover, design examples are manifested. We report a TM-mode-based phase modulator, achieving a π phase shift within an active length of 49.2 μm with dual graphene layers. A feasible polarization-independent amplitude modulator is also demonstrated, where the discrepancy of the imaginary parts of the effective mode index between the two fundamental modes is kept at an order of 10−5 over a broad wavelength range from 1.35 to 1.65 μm.

Image Translation Between Sar and Optical Imagery with Generative Adversarial Nets

Abstract: In this paper, we propose a method for the translation from Synthetic Aperture Radar (SAR) to optical images using conditional Generative Adversarial Networks (cGANs). Satellite images have been widely utilized for various purposes, such as natural environment monitoring (pollution, forest or rivers), transportation improvement and prompt emergency response to disasters. However, the obscurity caused by clouds leads to unstable monitoring of the ground situation while using the optical camera. Images captured by a longer wavelength are introduced to reduce the effects of clouds. In particular, SAR images are known to be nearly unaffected by clouds and are often used for stably observing the ground situation. On the other hand, SAR images have lower spatial resolution and visibility than optical images. Therefore, we propose a deep neural network that generates optical images from SAR images. Finally, we confirm the feasibility of the proposed network on a dataset consisting of optical images and the corresponding SAR images.