Polarization-independent Switching Research Articles

Simultaneous excitations of odd and even order resonances in plasmonic metasurfaces for an orthogonal terahertz probe.

Most of the compelling phenomena pertaining to plasmonic metamaterials revolve around the associated odd and even order resonances. However, excitation of odd and even order modes is polarization sensitive, particularly in the case of well-accepted split-ring resonator based terahertz (THz) plasmonic metasurfaces. Such a drawback limits the practical applications of plasmonic metasurfaces across the electromagnetic spectrum. In this context, we experimentally demonstrate multi-split-ring resonator based THz metasurfaces capable of simultaneously sustaining odd and even order resonances when the polarization of the probe beam is altered through 90°. We believe this work should be beneficial in realizing polarization-independent switches and frequency selective surfaces.

Design and Performance of Low-Power, High-Speed, Polarization-Independent and Wideband Polymer Buried-Channel Waveguide Thermo-Optic Switches

This paper analytically and experimentally investigates and compares the characteristics of two kinds of polymer buried-channel waveguide thermo-optic switches such as 1) a multimode interference (MMI) switch using a single MMI coupler and 2) a Mach–Zehnder interferometer (MZI) switch. Especially, the MZI switch experimentally exhibited low-power consumption of 3.5 mW, high-speed with a response time of less than 200 μs, polarization independence as well as in a wideband of about 80 nm. These low-power consumption, relatively high-speed, and polarization-independent switching characteristics are almost coincident with the designed ones. Furthermore, an improved MZI structure is proposed for lower switching power consumption, and it is expected below 0.5 mW with an enhanced thermal localization structure.

Optical characteristics of transparent PMNT ceramic and its application at high speed electro-optic switch

The optical characteristics of transparent lead magnesium niobate titanate (PMNT) electro-optic ceramic, including the electro-optic phase modulation, electric hysteresis property and thermo-optic coefficient, are investigated in detail. Based on this novel ceramic, a polarization independent electro-optic switch by using fiber Sagnac interferometer (FSI) structure is realized. An initial π-shift is introduced into the Sagnac loop to eliminate the effect of the polarization orientation of the incident light on the switch performance. Then an electrically controllable PMNT phase retarder is used to switch the optical signal between the reflection and transmission ports. Some theoretical analyses are given and the switch performances are also discussed, including the thermal characteristic and different switching frequency response.

Picosecond optical switching of a 1.5 μm active birefringent optical fiber loop filter using 1.3 μm control optical pulses and a 1.3 μm semiconductor optical amplifier

Less than 100ps, polarization-independent switching operation of an active birefringent optical fiber loop filter using 1.3 μm control optical pulses as well as a 1.3 μm semiconductor optical amplifier (SOA) has been demonstrated. In the proposed SOA-based active birefringent filter operating at 1.55 μm wavelength, 1.3 μm SOA is employed to control the polarization-mode dispersion in the loop part. By injecting 1.3 μm ps gain-switched optical control pulses into the SOA, 1.5 μm input signals can be switched from the transmission port to the reflection port with less than 100 ps rise time.

Techniques for Polarization-Independent Cross-Phase Modulation in Nonlinear Birefringent Fibers

We present a theoretical, numerical, and experimental investigation of the polarization dependence of cross-phase modulation in nonlinear birefringent fibers. Two new methods are described for producing a polarization-independent spectral shift through cross-phase modulation of a weak probe signal by a copropagating strong optical pulse. The birefringence of the fiber and spectral separation between the pump and probe signals are shown to play a critical role in determining the polarization dependence of the cross-phase modulation process. The methods are experimentally verified in two different highly nonlinear fibers, and are used to achieve polarization-independent optical switching at speeds of up to 160 Gb/s.

Polarization‐independent modulation for projection displays using small‐period LC polarization gratings

Abstract— Progress in the use of liquid‐crystal polarization grating (LCPG) to modulate unpolarized (and polarized) light with a grating period as small as 6.3 μm is reported. Similar to LCPGs formed at larger periods (11 μm) reported previously, polarization‐independent switching, predominantly three diffraction orders, maximum contrast ratios of ∼100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization‐independent projection display are commented upon.

<inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>2</mn><mo>×</mo><mn>2</mn></mrow></math></inline-formula>, <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>1</mn><mo>×</mo><mn>4</mn></mrow></math></inline-formula><inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mi>Ti</mi><mo>:</mo><msub><mi>LiNbO</mi><mn>3</mn></msub></mrow></math></inline-formula> digital optical switches

We propose and demonstrate a novel polarization- and wavelength-independent digital electro-optic switch in Ti:LiNbO3 with switching voltages of ±32 at 1.55 µm wavelength. This 2×2 integrated optic switch is characterized by a steplike response to the applied voltage. Switching is achieved through adiabatic mode evolution in an asymmetric waveguide junction. An average insertion loss of ~4.5 dB and polarization-independent switching with average cross talk of −12 dB are achieved. The demonstration of 1×4 polarization-independent switches with digital optical switch elements is eventually reported.

Polarization analysis and experimental implementation of PLZT electro-optical switch using fiber Sagnac interferometers

The polarization characteristics of electro-optical (EO) switches using fiber Sagnac interferometer (FSI) structures are theoretically investigated. Analytical solutions of output fields are presented when the twists and birefringence in a Sagnac loop are considered. Numerical calculations show that the twists of fiber, the orientation of the inserted phase retarder, and the splitting ratio of the coupler will influence both the output intensity and the output polarization properties of the proposed switch. A polarization-independent EO switch based on a Sagnac interferometer and a PUT bar was experimentally implemented, which showed good coincidence with the analytical results. The experiment showed a switch with 22 dB extinction ratio and less than 31.1 ns switching time. (c) 2006 Optical Society of America.

39.4: Polarization-Independent Switching With High Contrast from a Liquid Crystal Polarization Grating

We report experimental results of a liquid crystal polarization grating (LCPG) modulating unpolarized light with high contrast for the first time. Striking results are observed: nearly ideal diffraction into the first orders at > 99%, contrast ratios of up to 600:1 for monochromatic light, switching times of ∼ 2 ms for nematic LCs, and threshold voltage of 1.65 Vrms.

A polarization independent liquid crystal assisted vertical coupler switch

A novel compact cascaded structure suitable for the realization of a 2 × 2 polarization independent integrated optical switch using liquid crystal is reported. The switch consists of a vertical coupler formed by two Ag+-Na+ion-exchanged single-mode channel waveguides diffused in two BK7 glass substrates of a liquid crystal cell. The coupling properties, and thus the switching state(bar or cross), of this structure can be controlled by electrically reorienting the director of the aligned liquid crystal layer. The device was simulated and optimized atλ = 1550 nm by using a beam propagation method algorithm. Calculated crosstalk attenuation and losses of an optimized TE switch with the TE00mode propagating in the input waveguide are 42.5 dB and 0.49 dB respectively with a coupling length of 141 μm. A TM switch, with the TM00propagating mode, exhibits a crosstalk attenuation of 37.7 dB and losses of 1.42 dB with a coupling length of 127 μm. Estimated average crosstalk attenuation and losses of a polarization insensitive cascaded switch are 39.7 dB and 0.93 dB respectively. The evaluated driving voltage magnitude required for the switching operation results below 20 V.

2×2 Ti:LiNbO3 Waveguide Digital Optical Switches

We propose and demonstrate a novel polarization- and wavelength-independent digital electrooptic switch in <TEX>$Ti:LiNbO_3$</TEX> with switching voltage of <TEX>${\pm}$</TEX>32V at <TEX>$1.55{\mu}m$</TEX> wavelength. This <TEX>$2{\times}2$</TEX> integrated optic switch is characterized by a step-like response to the applied voltage. Switching is achieved through adiabatic mode evolution in an asymmetric waveguide junction. An average insertion loss of ∼4.5dB and polarization independent switching with average crosstalk of -12dB are achieved.

Tunable Fresnel lens using nanoscale polymer-dispersed liquid crystals

An electrically tunable Fresnel zone plate lens is demonstrated using nanoscale polymer-dispersed liquid crystal droplets. In the voltage-off state, the zone plate behaves like a positive lens. The measured diffraction efficiency is close to the theoretical limit and is controllable by voltage. The major advantages of such a Fresnel lens are simple fabrication, large aperture size, polarization independent, and fast switching speed, although the required operating voltage is relatively high.

Polarization-independent all-optical switching in a nonlinear GaInAsP-InP highmesa waveguide with a vertically etched Bragg reflector

We have theoretically designed and experimentally demonstrated polarization-independent all-optical switching in a nonlinear GaInAsP-InP highmesa distributed feedback (DFB) waveguide. The device, which is composed of a highmesa waveguide stripe and a vertically etched Bragg reflector, can be simply fabricated using one-step electron beam lithography and a reactive ion etching process. The device is suitable for integration with other photonic devices such as semiconductor optical amplifiers and wavelength converters. The structural birefringence of the device has a dependence on the waveguide parameters such as the refractive index and thickness of core and cladding. The structural birefringence was successfully eliminated by adjusting the width of the highmesa waveguide. The nonlinear vertical-groove DFB highmesa waveguide is attractive for a polarization-independent all-optical switch from the viewpoint of a large grating coupling coefficient, as compared with a grating-loaded DFB highmesa waveguide. The polarization dependence of the grating coupling coefficient has also been investigated experimentally. It is possible to obtain the polarization-independent grating coupling coefficient by adjusting the grating depth in the vertical-groove DFB highmesa waveguide, together with structural zero-birefringence of the device. Polarization-independent all-optical thresholding and bistable switching operations have been successfully demonstrated in the nonlinear vertical-groove DFB highmesa waveguide.

Optical switching and power control in LiNbO/sub 3/ coupled waveguide arrays

A diversity of switching and power-distribution functions in coupled multi-waveguide arrays is discussed and demonstrated. Functionality is achieved by varying the effective index in each waveguide independently by means of the electro-optic effect. The splitting and switching functions are attained by the use of a multi-variable optimization procedure. Specifically we demonstrate [1/spl times/2] and [1/spl times/5] routing and power division and [2/spl times/2] cross-connection. Polarization diversity and polarization-independent switching are attained using a special crystal orientation and electrode configuration. Single-polarization routing was measured in most cases, with crosstalk figures of the order of - 15 dB. Polarization-independent switching was achieved with crosstalk of less than - 19 dB for a three-waveguide [1/spl times/ ] switch. By addition of dummy guides, a polarization-independent [2/spl times/2] cross-connection function could be attained with crosstalk figures better than -30 dB.

Deep-ridge distributed feedback waveguide for polarisation independent all-optical switching

Structural birefringence in a deep-ridge distributed feedback (DFB) waveguide for polarisation independent all-optical switching is investigated. The coupling coefficient of the DFB structure is also polarisation independent between the TE and TM modes.

Chopped InGaAs/InP quantum wells for a polarization-independent space switch at 1.53 μm

We realized a polarization-independent Mach–Zehnder interferometric switch at 1.53 μ m using chopped quantum wells. The calculated electroabsorption and electrorefraction agree well with experiment. The window for polarization-independent switching within 0.1 V is 12 nm. A phase shifting section of 1.7 mm yields a <1dB electroabsorption unbalance and a 6 V switching voltage.

A chopped quantum-well polarization-independent interferometric switch at 1.53 /spl mu/m

We have theoretically designed and realized a phase shifter for a low-loss Mach-Zehnder interferometric switch. The phase shifter is based on 0.85% tensile strained InGaAs-InP chopped quantum-well material. We realized a Mach-Zehnder interferometric switch with polarization-independent switching voltages as low as 3.3/spl plusmn/0.05 V at 1525 nm for a switch with a 4-mm-long phase shifting section. The wavelength sensitivity of the switch is 0.036 V/nm for TE and 0.053 V/nm for TM polarization. Calculations of the electro-refraction in the -0.85% strained chopped quantum-well (QW) material based on the 4/spl times/4 Luttinger-Kohn Hamiltonian show that the electro-refraction due to the quantum-confined Stark effect (QCSE) for TM polarization is equal to the sum of the mutually comparable QCSE electro-refraction and the Pockels effect for TE polarization in waveguides along the [11~0] axis. Our first-principle model for calculating the electro refraction is an accurate design tool for predicting device performance in complicated layer structures. The shortest possible phase shifter with a <-25 dB crosstalk penalty due to electro-absorption unbalance can be as short as 2.2 mm. This compact switch is predicted to have a 6-V switching voltage and a 15-nm window for polarization-independent switching with a <-25-dB crosstalk penalty. With a slight increase of the strain, this chopped QW material can be used for polarization independent switching around 1550 nm.

2×2 fused fiber null couplers with asymmetric waist cross sections for polarization independent (&amp;gt;0.01 dB) switching

Polarization independent (<0.01 dB) switching is achieved at 1.55 /spl mu/m in a strongly guiding, fused tapered fiber null coupler acoustooptic switch. An intermediate degree of fusion of the dissimilarly sized fibers is shown experimentally to have the form birefringence required to render the mode-splitting coupler polarization insensitive. The effect of the degree of fiber fusion on the acoustic wavelength of flexural waves is studied theoretically and experimentally, and precise control over the degree of fiber fusion is obtained for coupler waist cross-sectional dimensions as small as 6 /spl mu/m.

Demonstration of ultrafast, all-optical, low control energy, single wavelength, polarization independent, cascadable, and integratable switch

A new type of ultrafast all optical switch based on a Mach–Zehnder interferometer is demonstrated with a 10 ps switching window which requires only 0.65 pJ of control pulse energy. The optical nonlinearity which is utilized is associated with the gain compression of semiconductor optical amplifiers, and the switching turnoff transition does not depend on the slow amplifier recovery time. Both data and control pulses are at the same wavelength of 1.313 μm, and are not polarized orthogonal to each other. The device configuration and the semiconductor amplifiers allow for small scale integration and data output cascadability.

Polarisation insensitive operation of ferroelectric liquid crystal devices

The accepted mode of operation of ferroelectric liquid crystal devices is to place them between crossed polarisers. The authors demonstrate that such devices may be used as diffractive modulators without polarisers. A one-to-many polarisation independent switch is presented for singlemode optical fibre networks, based on dynamic liquid crystal holograms.