Showing papers on "Extinction ratio published in 2016"

Materials Pushing the Application Limits of Wire Grid Polarizers further into the Deep Ultraviolet Spectral Range

Abstract: Wire grid polarizers (WGPs), periodic nano-optical metasurfaces, are convenient polarizing elements for many optical applications. However, they are still inadequate in the deep ultraviolet spectral range. It is shown that to achieve high performance ultraviolet WGPs a material with large absolute value of the complex permittivity and extinction coefficient at the wavelength of interest has to be utilized. This requirement is compared to refractive index models considering intraband and interband absorption processes. It is elucidated why the extinction ratio of metallic WGPs intrinsically humble in the deep ultraviolet, whereas wide bandgap semiconductors are superior material candidates in this spectral range. To demonstrate this, the design, fabrication, and optical characterization of a titanium dioxide WGP are presented. At a wavelength of 193 nm an unprecedented extinction ratio of 384 and a transmittance of 10% is achieved.

Large-scale broadband digital silicon photonic switches with vertical adiabatic couplers

Abstract: Large-scale photonic switches are essential devices for energy- and cost-efficient optical communication networks in cloud and data-intensive computing. Silicon photonics is an attractive platform for high-density photonic integrated circuits with low manufacturing costs through the leveraging of existing advanced complementary metal-oxide-semiconductor processes. Many optical components such as lasers, modulators, splitters, and photodetectors have been successfully integrated on silicon; however, the quest for large-scale silicon photonic switches has remained elusive. Previous silicon photonic switches made of cascaded 1×2 or 2×2 building blocks have a limited port count (≤8×8) or excessive optical losses (>15 dB). Here, we present a 64×64 digital silicon photonic switch with a low on-chip insertion loss (3.7 dB) and broadband operation (300 nm). The measured switching time is 0.91 μs, and the extinction ratio is larger than 60 dB. The matrix switch with 4096 microelectromechanical-systems-actuated vertical adiabatic couplers has been integrated on a 8.6 mm×8.6 mm chip. To our knowledge this is the largest monolithic switch, and the largest silicon photonic integrated circuit, reported to date. The passive matrix architecture of our switch is fundamentally more scalable than that of multistage switches.

High-performance and linear thin-film lithium niobate Mach-Zehnder modulators on silicon up to 50 GHz.

Abstract: Compact electro-optical modulators are demonstrated on thin films of lithium niobate on silicon operating up to 50 GHz. The half-wave voltage length product of the high-performance devices is 3.1 V.cm at DC and less than 6.5 V.cm up to 50 GHz. The 3 dB electrical bandwidth is 33 GHz, with an 18 dB extinction ratio. The third-order intermodulation distortion spurious free dynamic range is 97.3 dBHz2/3 at 1 GHz and 92.6 dBHz2/3 at 10 GHz. The performance demonstrated by the thin-film modulators is on par with conventional lithium niobate modulators but with lower drive voltages, smaller device footprints, and potential compatibility for integration with large-scale silicon photonics.

Atomic Scale Plasmonic Switch

Abstract: The atom sets an ultimate scaling limit to Moore's law in the electronics industry. While electronics research already explores atomic scales devices, photonics research still deals with devices at the micrometer scale. Here we demonstrate that photonic scaling, similar to electronics, is only limited by the atom. More precisely, we introduce an electrically controlled plasmonic switch operating at the atomic scale. The switch allows for fast and reproducible switching by means of the relocation of an individual or, at most, a few atoms in a plasmonic cavity. Depending on the location of the atom either of two distinct plasmonic cavity resonance states are supported. Experimental results show reversible digital optical switching with an extinction ratio of 9.2 dB and operation at room temperature up to MHz with femtojoule (fJ) power consumption for a single switch operation. This demonstration of an integrated quantum device allowing to control photons at the atomic level opens intriguing perspectives for a fully integrated and highly scalable chip platform, a platform where optics, electronics, and memory may be controlled at the single-atom level.

High-extinction-ratio silicon polarization beam splitter with tolerance to waveguide width and coupling length variations

Abstract: We demonstrate a compact silicon polarization beam splitter (PBS) based on grating-assisted contradirectional couplers (GACCs). Over 30-dB extinction ratios and less than 1-dB insertion losses are achieved for both polarizations. The proposed PBS exhibits tolerance in width variation, and the polarization extinction ratios remain higher than 20 dB for both polarizations when the width variation is adjusted from + 10 to –10 nm. Benefiting from the enhanced coupling by the GACCs, the polarization extinction ratio can be kept higher than 15 dB and the insertion loss is lower than 2 dB for both polarizations when the coupling length varies from 30.96 to 13.76 μm.

1.89 kW all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality.

Abstract: In this manuscript, we demonstrate high power, all-fiberized and polarization-maintained amplifiers with narrow linewidth and near-diffraction-limited beam quality by simultaneously suppressing detrimental stimulated Brillouin scattering (SBS) and mode instability (MI) effects. Compared with strictly single frequency amplification, the SBS threshold is scaled up to 12 dB, 15.4 dB, and higher than 18 dB by subsequently using three-stage cascaded phase modulation systems. Output powers of 477 W, 1040 W, and 1890 W are achieved with full widths at half maximums (FWHMs) of within 6 GHz, ~18.5 GHz, and ~45 GHz, respectively. The MI threshold is increased from ~738 W to 1890 W by coiling the active fiber in the main amplifier. Both the polarization extinction ratio (PER) and beam quality (M2 factor) are maintained well during the power scaling process. To the best of our knowledge, this is the first demonstration of all-fiberized amplifiers with narrow linewidth, near linear polarization, and near-diffraction-limited beam quality at 2 kW power-level.

Efficient graphene saturable absorbers on D-shaped optical fiber for ultrashort pulse generation

Abstract: We demonstrated a method to construct high efficiency saturable absorbers based on the evanescent light field interaction of CVD monolayer graphene deposited on side-polished D-shaped optical fiber. A set of samples was fabricated with two different core-graphene distances (0 and 1 μm), covered with graphene ranging between 10 and 25 mm length. The mode-locking was achieved and the best pulse duration was 256 fs, the shortest pulse reported in the literature with CVD monolayer graphene in EDFL. As result, we find a criterion between the polarization relative extinction ratio in the samples and the pulse duration, which relates the better mode-locking performance with the higher polarization extinction ratio of the samples. This criterion also provides a better understanding of the graphene distributed saturable absorbers and their reproducible performance as optoelectronic devices for optical applications.

60 dB high-extinction auto-configured Mach-Zehnder interferometer

Abstract: Imperfections in integrated photonics manufacturing have a detrimental effect on the maximal achievable visibility in interferometric architectures. These limits have profound implications for further technological developments in photonics and in particular for quantum photonic technologies. Active optimization approaches, together with reconfigurable photonics, have been proposed as a solution to overcome this. In this Letter, we demonstrate an ultrahigh (>60 dB) extinction ratio in a silicon photonic device consisting of cascaded Mach-Zehnder interferometers, in which additional interferometers function as variable beamsplitters. The imperfections of fabricated beamsplitters are compensated using an automated progressive optimization algorithm with no requirement for pre-calibration. This work shows the possibility of integrating and accurately controlling linear-optical components for large-scale quantum information processing and other applications.

Experimental demonstration of linearly polarized 2-10 μm supercontinuum generation in a chalcogenide rib waveguide.

Abstract: This Letter reports the production of a supercontinuum extending from ≈2 μm to >10 μm generated using a chalcogenide buried rib waveguide pumped with 330 femtosecond pulses at 4.184 μm. This is, to the best of our knowledge, the broadest mid-infrared supercontinuum generated in any planar waveguide platform. Because the waveguide is birefringent, quasi-single-mode, and uses an optimized dispersion design, the supercontinuum is linearly polarized with an extinction ratio >100. Dual beam spectrophotometry is performed easily using this source.

Integrated switchable mode exchange for reconfigurable mode-multiplexing optical networks

Abstract: We propose and experimentally demonstrate an on-chip switchable mode exchange utilizing a Mach–Zehnder interferometer assisted by a phase shifter. The switchable functionality, which is essential for an advanced and reconfigurable optical network, can be realized by controlling the induced phase difference. The measured extinction ratio is ∼24 dB over the C band for OFF–ON switchover. For demonstration, open and clear-eye diagrams can be observed when processing non-return-to-zero on–off keying signals at 10 Gb/s. The bit error rate measurements indicate a reasonable power penalty of less than 1 dB for two-mode exchange. The proposed device can further promote advanced and flexible mode-multiplexing optical networks.

Realization of a compact polarization splitter-rotator on silicon

Abstract: A novel compact polarization splitter-rotator (PSR) is proposed and realized with silicon-on-insulator nanowires. The present PSR consists of an adiabatic taper, an asymmetric directional coupler (ADC), and a multimode interference (MMI) mode filter. The adiabatic taper enables an efficient mode conversion from the launched TM0 mode to the TE1 mode in a wide waveguide, which is then coupled to the TE0 mode of a narrow waveguide through the ADC. Meanwhile, the launched TE0 mode does not have mode conversion and outputs from the through port directly. The MMI mode filter is cascaded at the through port to filter out the residual power of the TE1 mode so that the extinction ratio of the PSR is improved greatly. The total length of the PSR is ∼70 μm and the fabricated PSR has an extinction ratio of ∼20 dB over a broadband ranging from 1547 to 1597 nm.

Low-loss single-mode hollow-core fiber with anisotropic anti-resonant elements

Abstract: A hollow-core fiber using anisotropic anti-resonant tubes in the cladding is proposed for low loss and effectively single-mode guidance. We show that the loss performance and higher-order mode suppression is significantly improved by using symmetrically distributed anisotropic anti-resonant tubes in the cladding, elongated in the radial direction, when compared to using isotropic, i.e. circular, anti-resonant tubes. The effective single-mode guidance of the proposed fiber is achieved by enhancing the coupling between the cladding modes and higher-order-core modes by suitably engineering the anisotropic anti-resonant elements. With a silica-based fiber design aimed at 1.06 µm, we show that the loss extinction ratio between the higher-order core modes and the fundamental core mode can be more than 1000 in the range 1.0-1.65 µm, while the leakage loss of the fundamental core mode is below 15 dB/km in the same range.

Design of practicable phase-change metadevices for near-infrared absorber and modulator applications.

Abstract: Phase-change chalcogenide alloys, such as Ge2Sb2Te5 (GST), have very different optical properties in their amorphous and crystalline phases. The fact that such alloys can be switched, optically or electrically, between such phases rapidly and repeatedly means that they have much potential for applications as tunable photonic devices. Here we incorporate chalcogenide phase-change films into a metal-dielectric-metal metamaterial electromagnetic absorber structure and design absorbers and modulators for operation at technologically important near-infrared wavelengths, specifically 1550 nm. Our design not only exhibits excellent performance (e.g. a modulation depth of ~77% and an extinction ratio of ~20 dB) but also includes a suitable means for protecting the GST layer from environmental oxidation and is well-suited, as confirmed by electro-thermal and phase-transformation simulations, to in situ electrical switching. We also present a systematic study of design optimization, including the effects of expected manufacturing tolerances on device performance and, by means of a sensitivity analysis, identify the most critical design parameters.

Polarization rotation with ultra-thin bianisotropic metasurfaces

Abstract: Controlling the polarization of light with efficient and ultra-thin devices is desirable for a myriad of optical systems. Bianisotropic metasurfaces offer a promising alternative to conventional optical components due to their ability to provide extreme wavefront and polarization control within a low profile. However, metasurfaces have typically suffered from poor efficiencies and extinction ratios due to the lack of systematic design procedures. Here, the first, to the best of our knowledge, impedance-matched polarization rotator with a subwavelength thickness that operates at optical frequencies is reported. The bianisotropic response needed for polarization rotation is systematically designed using cascaded plasmonic sheets. The metasurface is fabricated using straightforward nanolithography processes. Measurements demonstrate an efficiency of 45% and extinction ratio of 115 (20.6 dB) at the operating wavelength of 1.56 μm. This work experimentally demonstrates that a wide range of near-optimal bianisotropic responses can be designed and fabricated at optical frequencies. In the future, these surfaces could be utilized to develop high-performance, ultra-compact optical systems.

Compact and high extinction ratio polarization beam splitter using subwavelength grating couplers.

Abstract: A compact and high extinction ratio polarization beam splitter using subwavelength grating (SWG) couplers is proposed and characterized, where the SWG couplers are located between the two input/output strip waveguides, including SWG-based transitions combined at both ends. The TM mode can be confined well in the strip waveguide and transmits along it with nearly neglected coupling, while the TE mode undergoes a strong coupling and is transferred to the adjacent waveguide with the help of SWG couplers due to dissimilar modal characteristics and cutoff conditions between these two polarizations. To further enhance the performance, an additional tapered waveguide is added in the lateral end of the input SWG-based transition. Results show that a total length of 6.8 μm with an insertion loss of 0.08 (0.36) dB, extinction ratio (ER) of 32.19 (20.93) dB, and reflection loss of -34.76 (-32.59) dB for TE (TM) mode is obtained at 1.55 μm; its bandwidth can be enlarged to ∼81 nm for an ER>18 dB. In addition, fabrication tolerances and mode-field evolution are also presented.

All-optical control of microfiber resonator by graphene's photothermal effect

Abstract: We demonstrate an efficient all-optical control of microfiber resonator assisted by graphene's photothermal effect. Wrapping graphene onto a microfiber resonator, the light-graphene interaction can be strongly enhanced via the resonantly circulating light, which enables a significant modulation of the resonance with a resonant wavelength shift rate of 71 pm/mW when pumped by a 1540 nm laser. The optically controlled resonator enables the implementation of low threshold optical bistability and switching with an extinction ratio exceeding 13 dB. The thin and compact structure promises a fast response speed of the control, with a rise (fall) time of 294.7 μs (212.2 μs) following the 10%–90% rule. The proposed device, with the advantages of compact structure, all-optical control, and low power acquirement, offers great potential in the miniaturization of active in-fiber photonic devices.

High-Modulation-Efficiency, Integrated Waveguide Modulator–Laser Diode at 448 nm

Abstract: To date, solid-state lighting (SSL), visible light communication (VLC), and optical clock generation functionalities in the blue-green color regime have been demonstrated based on discrete devices, including light-emitting diodes, laser diodes, and transverse-transmission modulators. This work presents the first integrated waveguide modulator–laser diode (IWM-LD) at 448 nm, offering the advantages of small footprint, high speed, and low power consumption. A high modulation efficiency of 2.68 dB/V, deriving from a large extinction ratio of 9.4 dB and a low operating voltage range of 3.5 V, was measured. The electroabsorption characteristics revealed that the modulation effect, as observed from the red-shifting of the absorption edge, resulted from the external-field-induced quantum-confined Stark effect. A comparative analysis of the photocurrent versus wavelength spectra in semipolar- and polar-plane InGaN/GaN quantum wells (QWs) confirmed that the IWM–LD based on semipolar (2021) QWs was able to operat...

An all optical phase shifter and switch near 1550nm using tungsten disulfide (WS2) deposited tapered fiber

Abstract: Optical phase shifters and switches play an important role for various optical applications including optical signal processing, sensing and communication. In this paper, we demonstrate a fiber all optical phase shifter using few-layer 2D material tungsten disulfide (WS2) deposited on a tapered fiber. WS2 absorbs injected 980 nm pump (control light) and generates heat which changes the refractive index of the tapered fiber due to thermo-optic effect and achieves a maximum phase shift of 6.1{\pi} near 1550 nm. The device has a loss of 3.7 dB. By constructing a Mach-Zehnder interferometer with WS2 based phase shifter in one arm, an all optical switch is also obtained with an extinction ratio of 15 dB and a rise time of 7.3 ms. This all fiber low-cost and compact optical phase shifter and switch demonstrates the potential of 2D transition metal dichalcogenides for all optical signal processing devices.

Broadband high birefringence and polarizing hollow core antiresonant fibers

Abstract: We systematically study different approaches to introduce high birefringence and high polarization extinction ratio in hollow core antiresonant fibers. Having shown the ineffectiveness of elliptical cores to induce large birefringence in hollow core fibers, we focus on designing and optimizing polarization maintaining Hollow Core Nested Antiresonant Nodeless Fibers (HC-NANF). In a first approach, we create and exploit anti-crossings with glass modes at different wavelengths for the two polarizations. We show that suitable low loss high birefringence regions can be obtained by appropriately modifying the thickness of tubes along one direction while leaving the tubes in the orthogonal direction unchanged and in antiresonance. Using this concept, we propose a new birefringent NANF design providing low loss (~40dB/km) and high birefringence (>10−4) over a record bandwidth of ~550nm, and discuss how bandwidth can be traded off to further reduce the loss to a few dB/km. Finally, we propose a polarization mode-stripping technique in the birefringent NANF. As a demonstration, we propose a polarizing birefringent NANF design that can achieve orthogonal polarization loss ratios as large as 30dB over the C-band while eliminating any undesirable polarization coupling effect thereby resulting in a single polarization output in a hollow core fiber regardless of the input polarization state.

Manipulation of beat length and wavelength dependence of a polarization beam splitter using a subwavelength grating

Abstract: A polarization beam splitter assisted by a subwavelength grating (SWG) is proposed The SWG enables nearly 20-fold beat length reduction for TE, which makes the high extinction ratio (ER) possible On the other hand, the embedded SWG preferably affects the refractive index of the even mode in the coupling region and broadens the bandwidth of the splitter As a result, the ER of 287 dB (248 dB) for TE (TM) is obtained, while the insertion loss is only 010 dB (011 dB) at the wavelength of 1550 nm The ER is more than 10 dB in the wavelength range of 1450–1625 nm for TE and 1495–1610 nm for TM

Flexible terahertz wire grid polarizer with high extinction ratio and low loss.

Abstract: An aluminum-based THz wire grid polarizer is theoretically investigated and experimentally demonstrated on a sub-wavelength thin flexible and conformal foil of the cyclo-olefin Zeonor© polymer. THz time-domain spectroscopy characterization, performed on both flat and curved configurations, reveals a high extinction ratio between 40 and 45 dB in the 0.3-1 THz range and in excess of 30 dB up to 2.5 THz. The insertion losses are lower than 1 dB and are almost exclusively due to moderate Fabry-Perot reflections, which vanish at targeted frequencies. The polarizer can be easily fabricated with low-cost techniques such as roll-to-roll and/or large area electronics processes and promises to pen the way for a new class of flexible and conformal THz devices.

Tunable Fano resonances based on microring resonator with feedback coupled waveguide.

Abstract: We experimentally demonstrate a tunable Fano resonance which originates from the optical interference between two different resonant cavities using silicon micro-ring resonator with feedback coupled waveguide fabricated on silicon-on-insulator (SOI) substrate. The resonance spectrum can be periodically tuned via changing the resonant wavelengths of two resonators through the thermo-optic effect. In addition to this, we can also change the transmission loss of the feedback coupled waveguide (FCW) to tune the resonance spectrum by the injection free carriers to FCW. We also build the theoretical model and we analyze the device performance by using the scattering matrix method. The simulation results are in a good agreement with the experimental results. The measurement maximum extinction ratio of the Fano resonance is as high as 30.8dB. Therefore, the proposed device is a most promising candidate for high on/off ratio optical switching/modulating, high-sensitivity biochemical sensing.

Enhanced third harmonic generation in a silicon metasurface using trapped mode.

Abstract: We experimentally demonstrate enhanced third harmonic generation (THG) using a silicon metasurface, which is consist of symmetric spindle-shape nanoparticle array. Relying on the trapped mode supported by the high quality factor all-dielectric metasurface, the conversion efficiency of THG is about 300 times larger than that of bulk silicon slab. The maximum extinction ratio of the intensity of THG reaches about 25 dB by tuning the polarization of incident light. The simulation results agree with the experimental performances.

Metawaveguide for Asymmetric Interferometric Light-Light Switching.

Abstract: Light-light switching typically requires strong nonlinearity where intense laser fields route and direct data flows of weak power, leading to a high power consumption that limits its practical use Here we report an experimental demonstration of a metawaveguide that operates exactly in the opposite way in a linear regime, where an intense laser field is interferometrically manipulated on demand by a weak control beam with a modulation extinction ratio up to approximately 60 dB This asymmetric control results from operating near an exceptional point of the scattering matrix, which gives rise to intrinsic asymmetric reflections of the metawaveguide through delicate interplay between index and absorption The designed metawaveguide promises low-power interferometric light-light switching for the next generation of optical devices and networks

PT -symmetry-induced evolution of sharp asymmetric line shapes and high-sensitivity refractive index sensors in a three-cavity array

Abstract: It is important to control and tune the Fano-resonance spectra to achieve a large slope with, in addition, a relatively high extinction ratio for low-power optical switching and high-sensitivity sensing. Here, we explore the evolution of sharp asymmetric Fano-like line shapes in a three-cavity array with local parity-time ($\mathcal{PT}$) symmetry. In this three-cavity configuration, a single cavity is coupled to a $\mathcal{PT}$-symmetric combination of two cavities via a common waveguide. The influences of local $\mathcal{PT}$ symmetry on the asymmetric Fano-like line shapes are investigated by monitoring the output transmission spectra at various system parameters. It is found that both the slope and the extinction ratio within the sharp asymmetric line shapes can be significantly enhanced by introducing the $\mathcal{PT}$-symmetric unit, compared with the configuration of two indirectly coupled cavities. Subsequently we discuss the application of such a $\mathcal{PT}$-assisted configuration as a family of high-sensitivity refractive index sensors by numerical analysis. For practical parameters based on microring resonators, the best sensitivity of refractive index sensors is more than five orders of magnitude larger than two indirectly coupled lossy cavities. The proposed scheme can be implemented in current state-of-the-art experiments. This investigation can help us to understand the interplay between the Fano resonance and $\mathcal{PT}$ symmetry.

Silicon band-rejection and band-pass filter based on asymmetric Bragg sidewall gratings in a multimode waveguide.

Abstract: A silicon photonic wire filter based on an asymmetric sidewall Bragg grating in a multimode silicon-on-insulator strip waveguide is demonstrated. The operating principle is based on the contra-directional coupling between the transverse electric fundamental (TE0) and first-order (TE1) modes, which is enabled by the asymmetric spatially periodic refractive-index perturbations. An asymmetric Y-junction is cascaded at the input port of the filter so as to drop the Bragg reflection. Compared with conventional Bragg grating-based filters, this device eliminates the back reflection at the input port and the 6 dB inherent insertion loss at the drop port; moreover, a narrow 3 dB bandwidth can be obtained with a large critical dimension as a result of the weak coupling strength between the TE0 and TE1 modes inside the multimode waveguide. Experimental results show that a bandwidth of ∼2.8 nm is achieved by a large corrugation width of 150 nm. The insertion loss at the drop port is −2.1 dB, and the extinction ratio is −33 dB at the through port.

Graphene based widely-tunable and singly-polarized pulse generation with random fiber lasers

Abstract: Pulse generation often requires a stabilized cavity and its corresponding mode structure for initial phase-locking. Contrastingly, modeless cavity-free random lasers provide new possibilities for high quantum efficiency lasing that could potentially be widely tunable spectrally and temporally. Pulse generation in random lasers, however, has remained elusive since the discovery of modeless gain lasing. Here we report coherent pulse generation with modeless random lasers based on the unique polarization selectivity and broadband saturable absorption of monolayer graphene. Simultaneous temporal compression of cavity-free pulses are observed with such a polarization modulation, along with a broadly-tunable pulsewidth across two orders of magnitude down to 900 ps, a broadly-tunable repetition rate across three orders of magnitude up to 3 MHz, and a singly-polarized pulse train at 41 dB extinction ratio, about an order of magnitude larger than conventional pulsed fiber lasers. Moreover, our graphene-based pulse formation also demonstrates robust pulse-to-pulse stability and widewavelength operation due to the cavity-less feature. Such a graphene-based architecture not only provides a tunable pulsed random laser for fiber-optic sensing, speckle-free imaging, and laser-material processing, but also a new way for the non-random CW fiber lasers to generate widely tunable and singly-polarized pulses.

60dB high-extinction auto-configured Mach--Zehnder interferometer

Abstract: Imperfections in integrated photonics manufacturing have a detrimental effect on the maximal achievable visibility in interferometric architectures. These limits have profound implications for further photonics technological developments and in particular for quantum photonics technologies. Active optimisation approaches, together with reconfigurable photonics, have been proposed as a solution to overcome this. In this paper, we demonstrate an ultra-high (>60 dB) extinction ratio in a silicon photonic device consisting of cascaded Mach-Zehnder interferometers, in which additional interferometers function as variable beamsplitters. The imperfections of fabricated beamsplitters are compensated using an automated progressive optimization algorithm with no requirement for pre-calibration. This work shows the possibility of integrating and accurately controlling linear-optical components for large-scale quantum information processing and other applications.

Ultra-Compact Multi-Band Chiral Metamaterial Circular Polarizer Based on Triple Twisted Split-Ring Resonator

Abstract: An ultra-compact chiral metamaterial (CMM) using triple-layer twisted split-ring resonators (TSRRs) structure was proposed, which can function as a multi-band circular polarizer. This ultra-compact structure CMM can convert an incident linearly y-polarized (x-polarized) wave propagating along thez(+z) direction to the transmitted left circularly polarized (LCP) waves at 7.28 GHz, 13.22 GHz and 15.49 GHz while the right circularly polarized (RCP) waves are at 9.48 GHz simultaneously. In addition, the large polarization extinction ratio (PER) of more than 20 dB across four resonance frequencies can be achieved. The experiment results are in good agreement with the numerical simulation results. The surface current distributions of the structure are analyzed to illustrate this linear to circular polarization conversion. The unit cell structure is extremely small both in longitudinal and transverse directions. Good performances and compact design of this CMM suggest promising applications in circular polarizers that need to be integrated with other compact devices.

Monolithically integrated reconfigurable add-drop multiplexer for mode-division-multiplexing systems.

Abstract: An integrated reconfigurable optical add-drop multiplexer (ROADM) for mode-division-multiplexing systems is proposed and demonstrated for the first time, to the best of our knowledge. The present ROADM with four mode-channels is composed of a four-channel mode demultiplexer, four identical 2×2 thermo-optic Mach-Zehnder switches (MZSs), and a four-channel mode multiplexer, which are integrated monolithically on silicon. All the devices are designed for operation with TM polarization. The ROADM can add/drop any one of the mode channels freely by thermally turning on/off the corresponding MZS. For the added/dropped mode-channels, the excess loss is 1-5 dB, and the extinction ratio is 15-20 dB in the wavelength range of 1535-1565 nm.