Showing papers on "Extinction ratio published in 2019"

The Optical to Mid-infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS, and WISE Surveys

Abstract: A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from APOGEE survey. The multiband photometric data are collected from Gaia, APASS, SDSS, Pan-STARRS1, 2MASS, and WISE surveys. For the first time, we calibrate the curvature of CERs in determining CERs E(lambda-GRP)/E(GBP-GRP) from color excess--color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (sigma < 0.015). With parallaxes from Gaia DR2, we calculate the relative extinction A_GBP/A_GRP for 5051 RC stars. By combining the CERs with the A_GBP/A_GRP, the optical--mid-IR extinction A_lambda/A_GRP has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio Rv=3.16+-0.15. Our observed extinction law supports an adjustment in parameters of the CCM Rv=3.1 curve, together with the near-IR power-law index alpha=2.07+-0.03. The relative extinction values of HST and JWST near-IR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.

Nature-inspired chiral metasurfaces for circular polarization detection and full-Stokes polarimetric measurements.

Abstract: The manipulation and characterization of light polarization states are essential for many applications in quantum communication and computing, spectroscopy, bioinspired navigation, and imaging. Chiral metamaterials and metasurfaces facilitate ultracompact devices for circularly polarized light generation, manipulation, and detection. Herein, we report bioinspired chiral metasurfaces with both strong chiral optical effects and low insertion loss. We experimentally demonstrated submicron-thick circularly polarized light filters with peak extinction ratios up to 35 and maximum transmission efficiencies close to 80% at near-infrared wavelengths (the best operational wavelengths can be engineered in the range of 1.3–1.6 µm). We also monolithically integrated the microscale circular polarization filters with linear polarization filters to perform full-Stokes polarimetric measurements of light with arbitrary polarization states. With the advantages of easy on-chip integration, ultracompact footprints, scalability, and broad wavelength coverage, our designs hold great promise for facilitating chip-integrated polarimeters and polarimetric imaging systems for quantum-based optical computing and information processing, circular dichroism spectroscopy, biomedical diagnosis, and remote sensing applications. Inspired by the polarization-sensitive vision of the compound eyes in a marine crustacean called the Mantis Shrimp, researchers from Arizona State University, US have designed a chiral metasurface for manipulating the polarization of light. The metasurface design consists of a thin nanostructured silicon layer, a dielectric spacer layer and a gold nanowire polarizer, and has a total thickness of less than 1 micrometer. This thin planar surface offers low optical loss with a transmission as high as 80% in the near-infrared wavelength range, and acts as a circular polarization filter with an extinction ratio as high as 35. The circular polarization filters, in combination with linear polarization filters, can enable chip-scale polarimeters for sensing the polarization state of light. This on-chip integrated approach could prove useful in ultra-compact devices for advanced imaging and sensing applications.

Single-Layer Dual-Band Linear-to-Circular Polarization Converter With Wide Axial Ratio Bandwidth and Different Polarization Modes

Abstract: A dual-band linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The element of the converter consists of two identical metallic layers with a combination of a connected Jerusalem cross (JC) and an “I”-type dipole for each layer. The proposed converter is designed by using an equivalent circuit model (ECM). Left-handed circularly polarized (LHCP) and right-handed circularly polarized (RHCP) beams can be, respectively, generated at ${K}$ -band and Ka -band excited by a linearly polarized (LP) wave tilted 45° relative to the ${x}$ - and ${y}$ -directions of the converter. In addition, the converter covers two operation bands for ${K}$ -/ Ka -band satellite communications with high conversion efficiency and low polarization extinction ratio (PER). After full-wave optimization, the proposed converter is fabricated and measured. The measured results show a good agreement with the simulated ones. Even though there exists a tradeoff between the angular stability and the bandwidth of the dual-band LCPCs, the measured axial ratio (AR) remains stable in the lower operation band and a slight fluctuation in the higher band with the incident angle of 20°.

Single-mode, low loss hollow-core anti-resonant fiber designs.

Abstract: In this paper, we numerically investigate various hollow-core anti-resonant (HC-AR) fibers towards low propagation and bend loss with effectively single-mode operation in the telecommunications window. We demonstrate how the propagation loss and higher-order mode modal contents are strongly influenced by the geometrical structure and the number of the anti-resonant cladding tubes. We found that 5-tube nested HC-AR fiber has a wider anti-resonant band, lower loss, and larger higher-order mode extinction ratio than designs with 6 or more anti-resonant tubes. A loss ratio between the higher-order modes and fundamental mode, as high as 12,000, is obtained in a 5-tube nested HC-AR fiber. To the best of our knowledge, this is the largest higher-order mode extinction ratio demonstrated in a hollow-core fiber at 1.55 μm. In addition, we propose a modified 5-tube nested HC-AR fiber, with propagation loss below 1 dB/km from 1330 to 1660 nm. This fiber also has a small bend loss of ~15 dB/km for a bend radius of 1 cm.

Tunable hybrid silicon nitride and thin-film lithium niobate electro-optic microresonator.

Abstract: This Letter presents, to the best of our knowledge, the first hybrid Si3N4-LiNbO3-based tunable microring resonator where the waveguide is formed by loading a Si3N4 strip on an electro-optic (EO) material of X-cut thin-film LiNbO3. The developed hybrid Si3N4-LiNbO3 microring exhibits a high intrinsic quality factor of 1.85×105, with a ring propagation loss of 0.32 dB/cm, resulting in a spectral linewidth of 13 pm, and a resonance extinction ratio of ∼27 dB within the optical C-band for the transverse electric mode. Using the EO effect of LiNbO3, a 1.78 pm/V resonance tunability near 1550 nm wavelength is demonstrated.

Tunable magneto-optical polarization device for terahertz waves based on InSb and its plasmonic structure

Abstract: The nonreciprocal circular dichroism and Faraday rotation effect for terahertz (THz) waves in longitudinally magnetized InSb were investigated by theoretical and experimental studies in the THz regime, which indicated its ability for a THz circularly polarized isolator, THz circular polarizer, tunable polarization converter, and polarization modulator by manipulation of different magnetic fields. Furthermore, we demonstrated the InSb plasmonics based on its magneto-optical effects combined with artificial microstructure. We found the magneto-optical enhancement mechanisms in this magneto-plasmonic structure, achieving broadband near-perfect orthogonal linear polarization conversion modulated by the weak magnetic field in an experiment with an extinction ratio of 33 dB. Moreover, the magneto-optical modulation with an amplitude modulation depth of 95.8% can be achieved by this device under a weak magnetic field of 150 mT. InSb and its magneto-plasmonic device have broad potential for a THz isolator, magneto-optical modulator, and polarization convertor in THz application systems.

The Optical to Mid-Infrared Extinction Law Based on the APOGEE, Gaia DR2, Pan-STARRS1, SDSS, APASS, 2MASS and WISE Surveys

Abstract: A precise interstellar dust extinction law is critically important to interpret observations. There are two indicators of extinction: the color excess ratio (CER) and the relative extinction. Compared to the CER, the wavelength-dependent relative extinction is more challenging to be determined. In this work, we combine spectroscopic, astrometric, and photometric data to derive high-precision CERs and relative extinction from optical to mid-infrared (IR) bands. A group of 61,111 red clump (RC) stars are selected as tracers by stellar parameters from APOGEE survey. The multiband photometric data are collected from Gaia, APASS, SDSS, Pan-STARRS1, 2MASS, and WISE surveys. For the first time, we calibrate the curvature of CERs in determining CERs E(lambda-GRP)/E(GBP-GRP) from color excess--color excess diagrams. Through elaborate uncertainty analysis, we conclude that the precision of our CERs is significantly improved (sigma < 0.015). With parallaxes from Gaia DR2, we calculate the relative extinction A_GBP/A_GRP for 5051 RC stars. By combining the CERs with the A_GBP/A_GRP, the optical--mid-IR extinction A_lambda/A_GRP has been determined in a total of 21 bands. Given no bias toward any specific environment, our extinction law represents the average extinction law with the total-to-selective extinction ratio Rv=3.16+-0.15. Our observed extinction law supports an adjustment in parameters of the CCM Rv=3.1 curve, together with the near-IR power-law index alpha=2.07+-0.03. The relative extinction values of HST and JWST near-IR bandpasses are predicted in 2.5% precision. As the observed reddening/extinction tracks are curved, the curvature correction needs to be considered when applying extinction correction.

High power, single-frequency, monolithic fiber amplifier for the next generation of gravitational wave detectors

Abstract: Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.

Compact polarization beam splitter with a high extinction ratio over S + C + L band

Abstract: In this paper, we experimentally demonstrate an ultra-broadband high-performance polarization beam splitter (PBS) based on silicon-on-insulator (SOI) platform. The proposed device is based on a directional coupler consisting of a 70-nm taper-etched waveguide and a slot waveguide with a compact coupling length of 11 microns, the structure of which is suitable for a commercial two-step fabrication process. Benefiting from the preferences of coupling TM mode to slot waveguide and restricting TE mode in taper-etched waveguide, the polarization extinction ratios (PER) for TE and TM polarizations can reach as high as 30 dB and 40 dB at 1550 nm based on experimental results, respectively; besides, an ultra-wide operation bandwidth with PER >20 dB is achieved as ~175 nm from 1450 nm to 1625 nm (covering S, C and L bands), or the bandwidth with PER >25 dB is over ~120 nm from 1462 nm to 1582 nm, which is the largest operation bandwidth to the best of our knowledge. At last, the insertion losses (IL) are −0.17 dB and −0.22 dB for TE and TM polarizations at 1550 nm, respectively.

Ultra-short polarization splitter based on a plasmonic dual-core photonic crystal fiber with an ultra-broad bandwidth

Abstract: A compact polarization beam splitter based on a gold-filled photonic crystal fiber with a square lattice is proposed. The full vector finite element method is used to design and characterize the proposed ultra-compact and ultra-broadband polarization splitter. The plasmonic plays an important role in order to achieve an ultra-short length of 56.33 µm with a high extinction ratio of 132.92 dB at the wavelength of 1.55 µm. It can ensure an ultra-broad bandwidth of 530 nm, from 1225 to 1755 nm, covering all the communication bands with an extinction ratio better than 20 dB. The proposed polarization splitter may be a promising candidate in communication due to its ultra-short length and ultra-broad bandwidth.

Inverse design of multifunctional plasmonic metamaterial absorbers for infrared polarimetric imaging.

Abstract: Metamaterial absorbers, consisting of assembling arrays of optical resonators with subwavelength dimensions and spacing, allow efficiently absorption electromagnetic radiation by leveraging the strong electrical and magnetic resonances. Beyond the enhanced absorption, there is a growing interest to realize multi-functional absorbers, for example, absorbers with extended bandwidth, strong polarization extinction ratio, to name a few. Traditionally, designing multi-functional absorbers require complex brute-force optimizations with sizable parameter space, which turn out to be rather inefficient. Here, using the particle swarm optimization algorithm, we design and experimentally demonstrate broadband and highly polarization selective mid-IR metal-insulator-metal absorbers, covering the technologically important 3-5 μm atmospheric transparency band. With spectrally averaged absorption exceeding 70%, a high polarization extinction ratio of 40.6 is concurrently achieved by the algorithm. We also investigate the incident angle dependence of the spectral absorption and clarify the origin of optical losses. By integrating with the growing range of mid-IR detectors and imagers, our devices can enable new applications such as mid-IR full Stokes imaging polarimetry for remote sensing.

Nano-optical Switch Based on Photonic Crystal Ring Resonator

Abstract: In recent trend, the ultra-speed nanophotonics components are highly attractive for the scientific community and next-generation high-speed optical communication systems. In this present work, a novel four-port optical switch is proposed and designed using a two-dimensional photonic crystal platform. The proposed device is composed of waveguides and ring resonator in a square lattice with gallium phosphide rods arranged in an air medium. The plane wave expansion (PWE) method is used to identify the operating wavelength of the proposed device. The functional parameters of the optical switch such as normalized output power, bit rate, response time, extinction ratio, insertion loss, and crosstalk are analyzed using the finite-difference-time-domain method (FDTD). The presented platform is designed with the ultra-fast data rate of 6.52 Tbps, very low crosstalk of − 40.45 dB, and fast response time of 153.33 femtoseconds. Hence, it is tremendously suitable for high speed photonic integrated circuits and switching application.

Demonstration of an on-chip TE-pass polarizer using a silicon hybrid plasmonic grating

Abstract: An on-chip, high extinction ratio transverse electric (TE)-pass polarizer using a silicon hybrid plasmonic grating is proposed and experimentally demonstrated. Utilizing plasmonics to manipulate the effective index and mode distribution, the transverse magnetic mode is reflected and absorbed, while the TE mode passes through with relatively low propagation loss. For a 6-μm-long device, the measurement result shows that the extinction ratio in the wavelength range of 1.52 to 1.58 μm varies from 24 to 33.7 dB and the insertion loss is 2.8–4.9 dB. Moreover, the structure exhibits large alignment tolerance and is compatible with silicon-on-insulator fabrication technology.

Coupling-enhanced dual ITO layer electro-absorption modulator in silicon photonics

Abstract: Electro-optic signal modulation provides a key functionality in modern technology and information networks. Photonic integration has enabled not only miniaturizing photonic components, but also provided performance improvements due to co-design addressing both electrical and optical device rules. However, the millimeter-to-centimeter large footprint of many foundry-ready photonic electro-optic modulators significantly limits on-chip scaling density. To address these limitations, here we experimentally demonstrate a coupling-enhanced electro-absorption modulator by heterogeneously integrating a novel dual-gated indium-tin-oxide (ITO) phase-shifting tunable absorber placed at a silicon directional coupler region. Our experimental modulator shows a 2 dB extinction ratio for a just 4 um short device at 4 volt bias. Since no material nor optical resonances are deployed, this device shows spectrally broadband operation as demonstrated here across the entire C-band. In conclusion we demonstrate a modulator utilizing strong index-change from both real and imaginary part of active material enabling compact and high-performing modulators using semiconductor foundry-near materials.

Subwavelength-grating-assisted silicon polarization rotator covering all optical communication bands

Abstract: We propose an ultra-broadband and ultra-compact polarization rotator (PR) structure on the silicon-on-insulator platform. The subwavelength gratings (SWGs) are introduced at the waveguide corner in order to excite the hybridized modes and realize the polarization rotation. The dispersion-engineered SWG can dramatically reduce the polarization conversion length deviation. High polarization extinction ratio > 20 dB and low excess loss < 1 dB can be achieved over 1.26-1.675 μm wavelength range, which covers O-, E-, S-, C-, L-, and U-bands. The total device size is as small as 4.8 × 0.34 μm2. To the best of our knowledge, the proposed structure is the first silicon PR that could cover all of the optical communication bands.

Anisotropic metamaterial-assisted all-silicon polarizer with 415-nm bandwidth

Abstract: Polarizers have been widely used in various optical systems to reduce polarization cross talk. The polarizers based on the silicon nanowire waveguide can provide chip-scale device size and a high polarization extinction ratio. However, the working bandwidth for the on-chip silicon polarizers is always limited ( 20 dB) over a >415 nm bandwidth from 1.26 to 1.675 μm, which is at least fourfold better than what has been demonstrated in all previous works. To the best of our knowledge, such a device is the first all-silicon polarizer that covers O-, E-, S-, C-, L-, and U-bands.

Total Performance of Magneto-Optical Ceramics with a Bixbyite Structure

Abstract: High-quality magneto-optical ceramics (TbxY1−x)2O3 (x = 0.5–1.0) with a Bixbyite structure were extensively investigated for the first time. The total performances of these ceramics were far superior to those of commercial TGG (Tb3Ga5O12) crystal, which is regarded as the highest class of Faraday rotator material. In particular, the Verdet constant of Tb2O3 (when x = 1.0) ceramic was the largest—495 to 154 rad·T−1·m−1 in the wavelength range of 633 to 1064 nm, respectively. It was possible to further minimize the Faraday isolator device. The insertion loss of this ceramic was equivalent to that of the commercial TGG single crystal (0.04 dB), and its extinction ratio reached more than 42 dB, which is higher than the value for TGG crystal (35 dB). The thermal lens effect (1/f) was as small as 0.40 m−1 as measured by a 50 W fiber laser. The laser damage threshold of this ceramic was 18 J/cm2, which is 1.8 times larger than that of TGG, and it was not damaged during a power handling test using a pulsed laser (pulse width 50 ps, power density 78 MW/cm2) irradiated at 2 MHz for 7000 h.

CMOS-compatible all-Si metasurface polarizing bandpass filters on 12-inch wafers.

Abstract: The implementation of polarization controlling components enables additional functionalities of short-wave infrared (SWIR) imagers. The high-performance and mass-producible polarization controller based on Si metasurface is in high demand for the next-generation SWIR imaging system. In this work, we report the first demonstration of all-Si metasurface based polarizing bandpass filters (PBFs) on 12-inch wafers. The PBF achieves a polarization extinction ratio of above 10 dB in power within the passbands. Using the complementary metal-oxide-semiconductor (CMOS) compatible 193nm ArF deep ultra-violet (DUV) immersion lithography and inductively coupled plasma (ICP) etch processing line, a device yield of 82% is achieved.

All-dielectric metasurfaces for simultaneously realizing polarization rotation and wavefront shaping of visible light.

Abstract: All-dielectric metasurfaces have shown unprecedented abilities to control light polarization and phase, yet most previous relevant studies have been mainly limited to cross-polarized schemes. This paper presents dielectric metasurfaces that incorporate distinct half-waveplate-like hydrogenated amorphous silicon nanoposts and are shown to manipulate the wavefront of transmitted visible light exhibiting controllable linear polarization angles. An anomalous beam deflector is designed, and high performances including an absolute deflection efficiency of 82%, a polarization conversion efficiency of 96%, and an extinction ratio of 37 dB are first demonstrated in the cross-polarized scheme. Furthermore, the anomalously deflected light could hold a high degree of linear polarization (>0.96), which can be continuously rotated by varying the incident polarization angle. Based on this principle, we fabricate a metalens and experimentally observe the light focusing phenomenon at the location designed for the cross-polarized light. Moreover, the rotation of the linear polarization angle corresponding to the output focused beam spot is successfully validated by tailoring the incident polarization angle. The developed metalens can therefore be treated as equivalent to the combination of a half-waveplate and focusing lens. The proposed ultra-thin dielectric metasurfaces, which do not require the alignment of multiple elements, could be used to facilitate the development of ultra-compact photonics systems.

Infrared frequency comb generation and spectroscopy with suspended silicon nanophotonic waveguides

Abstract: Nanophotonic waveguides with sub-wavelength mode confinement and engineered dispersion are an excellent platform for application-tailored nonlinear optical interactions at low pulse energies. We present fully air-clad suspended silicon waveguides for infrared frequency comb generation with optical bandwidth limited only by the silicon transparency. Precise lithographic control over the waveguide dispersion enables tailored infrared frequency comb generation across a bandwidth of 2.0–8.8 μm (1130–5000 cm−1), with the broadest simultaneous bandwidth covering 2.0–7.7 μm. Novel fork-shaped couplers provide efficient input coupling with only 1.5 dB loss. The coherence, brightness, and stability of the generated light are highlighted in a dual-frequency comb setup in which individual comb lines are resolved with 30 dB extinction ratio and 100 MHz spacing in the wavelength range of 4.9–8.8 μm (1130–2050 cm−1) using three different waveguide widths. These sources are used for broadband gas- and liquid-phase dual-comb spectroscopy with 100 MHz comb line resolution. We achieve a peak spectral signal-to-noise ratio of 10 Hz across a simultaneous bandwidth of 6.3–8.2 μm (1220–1590 cm−1) containing 112,200 comb lines. These results provide a pathway to further integration with the developing high-repetition-rate frequency comb lasers for compact sensors with applications in chip-based chemical analysis and spectroscopy.

Design of a Broadband Polarization Splitter Based on Anisotropy-Engineered Tilted Subwavelength Gratings

Abstract: Polarization management is of paramount importance in integrated optics, particularly for highly birefringent photonic platforms such as silicon-on-insulator. In this paper, we present a polarization beam splitter based on a multimode interference coupler incorporating tilted subwavelength gratings. The tilt provides accurate control of the structural anisotropy and enables independent selection of the beat length for two orthogonal polarization states. As a result, device length is reduced to less than 100 μm while simultaneously achieving broadband operation through subwavelength grating dispersion engineering. Insertion losses below 1 dB and an extinction ratio higher than 20 dB are demonstrated through three-dimensional FDTD simulation in a 131-nm bandwidth.

Ultra-Compact Tuneable Notch Filter Using Silicon Photonic Crystal Ring Resonator

Abstract: A novel ultra-compact photonic tuneable notch filter with large bandwidth, high extinction ratio, fast response, and flat stopband is modeled and designed. It consists of a silicon-based ring resonator with one-dimensional photonic crystal superimposed onto a ring portion. Engineering the defects into the photonic crystal section allows to achieve the equalization of the bottom band of the filter response. Large bandwidth ( B = 10.43 GHz) and high extinction ratio (ER = 41 dB) have been attained with a frequency response of the first-order Butterworth filter type. Continuous and wide range tunability of the central frequency (15 GHz) has been obtained by using the carrier injection technique, together with fast reconfigurability (a1 ns) and power consumption of 47 mW. The device footprint is as very small as about 150 μm2. This performance makes the proposed device suitable for several filtering applications, such as wireless networks (5G) and telecommunication reconfigurable payloads in Telecom and Space scenario, respectively.

Highly polarization-sensitive, visible-blind and self-powered ultraviolet photodetection based on two-dimensional wide bandgap semiconductors: a theoretical prediction

Abstract: Two-dimensional wide bandgap (2D-WBG) semiconductors have attracted extensive research interest in ultraviolet (UV) photodetection because of their excellent performances including ultrafast response, high responsivity and low dark current. Using quantum transport simulations, we proposed here a kind of self-powered, visible-blind and UV-polarized photodetector driven by the photogalvanic effect (PGE) based on several 2D-WBG (3.0–7.41 eV) semiconductors and their heterostructures. Such 2D-WBG semiconductors show sharp optical absorption peaks ranging from 4 eV to 8 eV, which is suitable for a variety of application fields in UV photodetection. We also designed a vertical van der Waals heterostructure (vdWh) with a type-II energy band alignment composed of 2D monolayer MgBr2 and CdCl2. Robust PGEs can be induced in the photodetectors based on this vdWh and also on monolayer ZrNY (Y = Cl and Br) due to the C3v symmetry under the illumination of both linearly and elliptically polarized light. The broadband and highly polarization-sensitive photocurrent is therefore generated at zero bias voltage, which exhibits a remarkably high extinction ratio of up to 280. These results suggest a promising mechanism for polarization-sensitive and visible-blind UV photodetection with low power consumption.

Polarization-controlled unidirectional excitation of surface plasmon polaritons utilizing catenary apertures

Abstract: Controlling the propagation direction of surface plasmon polaritons (SPPs) at will using planar structures has been investigated in recent years. However the realization of a high extinction ratio of a SPP directional launcher in a densely integrated and miniaturized way, especially at the wavelength scale, still remains a challenge. To the best of our knowledge, the maximum value of the extinction ratio of a unidirectional SPP launcher based on the planar metasurface in experiment is nearly 250, which relies on the combined effect of several gap-plasmon resonator blocks with a lateral dimension much larger than the incident wavelength. Here, we design and experimentally demonstrate a polarization-controlled unidirectional SPP launcher based on a single column catenary aperture array with a lateral dimension as small as 552 nm, which is even smaller than the working wavelength. Under the illumination of circularly polarized light, our designed SPP launcher exhibits a simulated extinction ratio reaching up to 495 at a wavelength of 618 nm and 283 in the experiment. The compact size and distinctive extinction ratio may pave a new way for the directional excitation of SPPs and can be useful in compact plasmonic circuits and other photonic integrated devices.

Angle-of-Arrival Measurement System Using Double RF Modulation Technique

Abstract: A new technique for determining the angle of arrival (AoA) of an RF signal is presented. It is based on a cascaded modulator structure, where continuous wave light from an optical source is modulated by an incoming RF signal twice. The AoA of an RF signal can be determined by the system output RF signal power. The proposed structure is capable for measuring the AoA of both narrow and broadband RF signals. This overcomes the limitation in all previously reported photonics-based AoA measurement systems, which are applicable to either a single-frequency RF signal or a broadband RF signal. It also does not involve electrical components and high extinction ratio modulators, which are required in reported structures. Experimental results are presented that show an AoA measurement range of 0° to over 65° with errors of less than 1.9° for a microwave signal at 2.65 and 12.62 GHz. Results also show that the system is capable to measure the AoA of a pseudorandom binary sequence signal at a microwave frequency.

Wide-Temperature-Range (25–80 °C) 53-Gbaud PAM4 (106-Gb/s) Operation of 1.3- μ m Directly Modulated DFB Lasers for 10-km Transmission

Abstract: A 1.3- μ m directly modulated distributed feedback laser was newly developed by adopting an asymmetric corrugation pitch modulated grating structure and an InGaAlAs multiquantum well active layer with both a high optical confinement factor and a high differential gain. A low threshold current and a large saturation current in light-current characteristics at high temperature were obtained and a high 3-dB bandwidth and a high relaxation oscillation frequency in electro-optical characteristics were also achieved over a wide temperature range. As a result, clear back-to-back eye openings were achieved for 26-Gbaud PAM4 (53-Gb/s) operation from 25 to 95 °C with large outer extinction ratio and sufficiently small transmission dispersion eye closure quaternary. Furthermore, 53-Gbaud PAM4 (106-Gb/s) operation from 25 to 80 °C was successfully demonstrated for both back-to-back and after 10-km single mode fiber transmission. These excellent characteristics make our DFB laser a promising cost-effective and compact transceiver with low power consumption for next-generation 400GbE applications.

Silicon waveguide optical modulator driven by metal-insulator transition of vanadium dioxide cladding layer.

Abstract: We have fabricated compact optical modulators consisting of a Si waveguide with a VO2 cladding layer. These devices showed a sharp decrease in transmittance at around 60 °C, which is attributable to the metal-insulator transition of the VO2 cladding layer. By systematically varying the length of the device, we evaluated the transmission losses per unit length of the device to be 1.27 dB/µm, when the VO2 cladding layer was in the insulating (ON) state and 4.55 dB/µm when it was in the metallic (OFF) state. Furthermore, we found that the device showed an additional loss in the OFF state, which is attributable to a structural effect. As a result, an 8-µm-long device showed a large extinction ratio of more than 33 dB.