Ultrahigh Extinction Ratio Research Articles

Ultra-Broadband TE-Pass Polarizer Using a Cascade of Multiple Few-Layer Graphene Embedded Silicon Waveguides

Considering that the variation of the modal characteristics for the TM mode is significantly larger than that for the TE mode when graphene is involved in a silicon-based waveguide, a silicon waveguide TE-pass polarizer with few-layer graphene embedded is proposed and demonstrated. Such a polarizer shows the performance merits including ultrahigh extinction ratio, low insertion loss for the TE mode, ultracompact footprint, and tunable bandwidth by dynamically varying the chemical potential of graphene with gate voltage. We further reveal that the operation bandwidth can be significantly enlarged by cascading multiple polarizers, each of which consists of a silicon waveguide embedded with few-layer graphene and is biased at different gate voltages. We numerically demonstrate that using a cascade of seven polarizers, it is capable of achieving 20-dB extinction ratio and ultralow insertion loss for the TE mode (<0.13 dB) with bandwidth over 120 nm at telecommunication wavelengths.

Compact high extinction ratio asymmetric polarization beam splitter of periodic rods waveguide.

A compact high extinction ratio polarization beam splitter based on an asymmetric directional coupler was proposed and theoretically investigated. The asymmetric directional coupler consists of a silicon wire waveguide and a 1D periodic silicon rods waveguide, which results in an ultracompact polarization splitting length. By using the plane wave expansion method, a minimum coupling length of 3.43 μm was obtained, and the length was then confirmed by finite-difference time-domain simulation. Moreover, for 1550 nm wavelength, high extinction ratios of about 28 and 18 dB were also observed for TE and TM polarizations, respectively. The ultrahigh extinction ratio for TE polarization is mainly arising from the appearance of TM bandgap in the periodic rods waveguide. In addition, for both polarizations, the extinction ratios are all above 10 dB covering a 180 nm bandwidth, and it was also demonstrated that the device has a high transmission for TM polarization.

Variable optical attenuator based on a reflective Mach–Zehnder interferometer

A low power-consuming variable optical attenuator (VOA) on silicon is demonstrated by using a reflective Mach–Zehnder interferometer (MZI), which consists of broadband highly-efficient Bragg-grating reflectors at the ends of the MZI arms. The present reflective-MZI VOA enables an ultra-high extinction ratio intrinsically even when the 2×2 3dB coupler is not balanced perfectly, which make it very robust to realize a VOA array. The power consumption is reduced by half in comparison with the regular MZI-type VOA. For the fabricated reflective MZI-type VOA with 125μm-long heaters, the power consumption is only about 10.8mW for a high attenuation of 35.5dB.

Efficiently Unidirectional Coupling of Surface Plasmons Based on Asymmetric Cascaded Nanoslits

A compact unidirectional plasmonic coupler based on asymmetric cascaded nanoslits is proposed and theoretically analyzed. The incident photons illuminated on the structure are unidirectionally coupled into the metal–insulator–metal waveguide. The operation principle is clarified and a universal theoretical model based on coupled-mode equations is developed to facilitate structure design. Proof-of-principle demonstrations show that an ultrahigh extinction ratio ER $= 43.8$ dB at a specific wavelength and broadband of 160 nm covering a wide angular range from −20° to 15° with ER ≥ 10 dB are achieved.

Design of short polarization splitter based on dual-core photonic crystal fiber with ultra-high extinction ratio

A novel (to our knowledge) type of dual-core photonic crystal fiber (PCF) based polarization splitter is proposed. The effects of the geometrical parameters on the performances of the polarization splitter are studied numerically based on full vector finite element method (FEM). Finally, an optimal design based on the proposed dual-core PCF with a length of 0.401mm is achieved, the extinction ratio (ER) of the splitter can reach 110.1dB at the wavelength of 1.55µm, and the bandwidth of ER over 20dB and 10dB can be as wide as 140nm and 200nm, respectively. This polarization splitter proposed in this paper provides a new structure for designing a splitter with short length, high ER and wide bandwidth simultaneously.

Ultrahigh extinction ratio of polarization beam splitter based on hybrid photonic crystal waveguide structures

A novel heterogeneous structure of two-dimensional photonic crystal polarization beam splitter is proposed, which is similar to the structure of graphene. Research and analysis in this paper are combined with the FDTD method. The results show that, the extinction ratio of the TE and TM output ports can reach over 95dB and 60dB respectively. The transmission efficiency for multiple normalized frequencies in the range from 0.3904 ωa/2πc to 0.4199 ωa/2πc are within −3dB. When the normalized frequency is 0.4112 ωa/2πc, the transmission efficiency is −0.13dB and the extinction ratio is 31.76dB at the TM output port, the transmission efficiency is −0.04dB and the extinction ratio is 80.54dB at the TE output port. This polarization beam splitter has not only high transmission efficiency, but also ultrahigh extinction ratio. These features have important application prospects in integrated optical circuit, optical communication and other fields.

短长度超高消光比双芯光子晶体光纤偏振分束器

短长度超高消光比双芯光子晶体光纤偏振分束器

Compact Plasmonic Unidirectional Coupler With High Performance Based on an Asymmetric Slit-Groove Structure

A new scheme for unidirectional coupling of surface plasmon polaritons (SPPs) from freely propagating light into a metal-insulator-metal waveguide is proposed, which is composed of an asymmetric double-slit of different widths sandwiched by symmetric grooves. A theoretical model based on coupled-mode equations is developed to facilitate structure design and elucidate the underlying physical mechanism. With the model, the asymmetric double-slit with different widths is designed for unidirectional launching of SPPs with an ultrahigh extinction ratio of 44.8 dB at the wavelength 800 nm. A method of stepwise design is proposed for simplicity of design and convenience of analysis. Proof-of-principle demonstrations show that an ultrahigh extinction ratio of 37.1 dB and significant field enhancement for the proposed whole structure are obtained. In addition, an ultracompact plasmonic dichroic splitter based on the asymmetric double-slit with high extinction ratios of 24.2 and $-$ 21.8 dB at splitting wavelengths of 800 and 900 nm is achieved, and the lateral dimension of the plasmonic dichroic splitter is only 760 nm.

Ultra-High Extinction Ratio and Low Cross Talk Characteristics of 4-Array Integrated SOA Module with Novel Wavelength-Insensitive Parallel Optical Coupling Scheme

Ultra-High Extinction Ratio and Low Cross Talk Characteristics of 4-Array Integrated SOA Module with Novel Wavelength-Insensitive Parallel Optical Coupling Scheme

Ultra-high extinction ratio micropolarizers using plasmonic lenses

The design of a new type of plasmonic ultra-high extinction ratio micropolarizing transmission filter is presented along with an experimental demonstration. A pair of dielectric coated metal gratings couple incident TM polarized light into surface plasmons, which are fed into a central metal-insulator-metal (MIM) waveguide, followed by transmission through a sub-wavelength aperture. Extinction ratios exceeding 10¹¹ are predicted by finite element simulation. Good absolute agreement for both the spectral and polarization response is obtained between measurement and simulations using measured geometric parameters. The filters can be easily fabricated and sized to match the pixel pitch of current focal plane arrays.

High-Speed Control of Lightwave Amplitude, Phase, and Frequency by Use of Electrooptic Effect

High-speed control of lightwave using electrooptic (EO) effect is investigated in this paper. Agile optical frequency shift can be achieved by optical single-sideband (SSB) and frequency-shift-keying (FSK) modulators, where high-speed optical phase-shift-keying (PSK) signals can also be generated by using FSK/SSB modulators. We also describe ultrahigh extinction ratio optical intensity modulation (IM) technique for two-tone lightwave signals with high spurious suppression, which is useful for photonic microwave and millimeter-wave generation. In addition, we investigated high-order optical sideband generation techniques: quadruple dual-sideband suppressed carrier (QDSB-SC) modulation and reciprocating optical modulation (ROM). Sub-tetrahertz signals can be obtained from lightwaves with high-order sidebands

Electro-optic cutoff modulator using a Ti-indiffused LiNbO_3 channel waveguide with asymmetric strip electrodes

A new type of cutoff light modulator, which consists of a single-mode channel waveguide and strip electrodes placed asymmetrically on either side of the guide, is proposed. When a voltage is applied to the electrodes, this device exhibits an asymmetric refractive-index profile along a direction parallel to the crystal surface through the electrooptic effect. This produces a strong condition for cutoff of the fundamental mode of the guide. An ultrahigh extinction ratio of greater than 56 dB has been achieved by using a Ti-indiffused Y-cut LiNbO(3) cutoff modulator with a 165-V drive at a wavelength of 0.6328 microm.