Magneto-optical Switches Research Articles

The Design and Analysis of Pulse Generator Electronic Circuits Based on Avalanche Transistor

Avalanche transistor is a ideal device which can provide quick response and high peak power simultaneously, and this device is cheap. A pulse generator based on avalanche transistor is designed in this paper; this generator can generate transient current pulse. This generator can be easily triggered, what is more, the performance of this generator is stable and it has a well-behaved load capacity. Therefore, this generator is suitable for using as the magneto-optical switch in the all-optical communication network. Future work will focus on further shorten the duration and rising time of the pulse.

Magnetic pulse generation for high-speed magneto-optic switching

In this article, the magnetic pulse characteristics needed to achieve high-speed magneto-optic (MO) switching are investigated. A fiber-based, MO, low-voltage optical switch capable of 200 ns switching is presented, along with the special circuit characteristics for magnetic field generation for high-speed switching. The switch consists of the optical system, the MO material (bismuth substituted iron garnet [(Bi1.1Tb1.9)(Fe4.25Ga0.75)O12]), and a high-speed magnetic field driving circuit. A Faraday rotator is placed within the interferometric loop of a fiber-optic Sagnac interferometer, and interference at the output ports is controlled by the applied field. The fast switching speed is accomplished via the special design of the magnetic pulse generation circuitry. The applied magnetic field overshoots the field necessary to achieve the desired Faraday rotation and then settles to a steady state field. If the duration of the overshoot is less than the time it takes the material to saturate, a fast optical switching time can be achieved without saturating the material. The effects of the overshoot amplitude and duration and steady-state amplitude on optical rise time (determined by domain wall velocity) are studied and experimental results are presented.

Electro- and magneto-optical switching of defect modes in one- dimensional photonic crystals

The transmission spectra of polarized light waves in a photonic crystal/liquid crystal (PC/LC) cell placed between crossed polarizers and controlled by an electric or magnetic field have been studied experimentally and theoretically. Electro- and magneto-optical switching based on the interference of polarized defect modes has been demonstrated. The transmission spectra of the PC/LC cell have been calculated as a function of the voltage applied to the LC layer and the magnetic field strength. The results of the calculations agree well with the experimental data.

Magneto-optical switching and routing via coherently induced photonic band gaps in a driven Fe = 0↔Fg = 1 transition

In an Fe = 0↔Fg = 1 transition interacting with a weak π-polarized probe and a strong σ-polarized standing-wave coupling, we obtain single or double photonic band gaps depending on the applied magnetic field. Moreover, the coherently induced two-photonic-band gap structure can be tuned by the magnitude of the magnetic field. Such a magnetic-field-dependent feature is exploited to devise magneto-optical switching and routing of two light pulses. The efficient magneto-optical control of light propagation may have applications in an optical network and optical information processing.

Novel photonic approach to microwave frequency measurement using tunable group delay line

A photonic approach for measuring microwave frequency over a wide bandwidth is proposed. An optic group delay line composed of several magneto-optical switches and a 1.6-km single-mode fiber is used as a tunable dispersive medium in the measurement setup. A minimum frequency accuracy of 80 MHz in the range of 1-20 GHz is achieved experimentally.

基于可调光延迟线的光子学微波频率测量

A photonic approach for microwave frequency measurement is proposed.A phase difference of the two microwave signals carried on two optical wavelengths is induced by a tunable dispersion medium.The interference microwave power is tuned periodically by changing dispersion value.The frequency of the microwave signal can be extracted from the period.In the proposed approach,a 7-bit optic delay line composed by 8 magneto-optical switches and 1.6 km single-mode fiber(SMF) is utilized as the tunable dispersion medium.The measurement accuracy remains within ±40 MHz over a range of 1～20 GHz.The minimum measureable power can reach to-20 dBm and the dynamic range is 45 dB.

Quantum memory and all-optical switching in positive charged quantum dots via Zeemancoherent oscillations

Linear and nonlinear properties in an ensemble of single-hole spin InGaAs/GaAs quantum dots aretheoretically studied. The application of a DC magnetic field in the semiconductor growth planeinduces a Zeeman splitting of the hole levels which can be modeled like a four-level atom in theX-type configuration. All-optical and magneto-optical switching of a weak probe field areshown to be feasible in this system either by changing the Rabi frequency of an auxiliarycontrol field or by changing the magnitude of the external magnetic field. We analyze thefeasibility to store and release a weak pulse from the medium resulting from Zeemancoherent oscillations, thus the system is expected to be useful to develop a variablesemiconductor optical buffer.

Geometrical confinement effects on the magnetization and polarization response in resonant magneto-optic rotator waveguides

Control of magnetization is central to the performance of magneto-optical switches and isolators. Photonic crystal technology on these devices can yield significant improvements in polarization rotation efficiency and an overall reduction in device dimensions. The optical response and field reversal characteristics of resonant magneto-optic polarization rotators fabricated on chip are presented herein and analyzed by micromagnetic simulation. By introducing domain-strip structures into the resonant cavity of Bragg gratings formed on magnetic garnet films, a bi-stable magnetic state is demonstrated and the enhancement of characteristic saturation field is studied. Domain closure loops between the strips affect the hysteresis response in the resonant cavity. Large magneto-optic rotations exceeding 45° are produced near resonance between 1500 and 1580 nm in the stop-bands, although the presence of linear birefringence in these gyrotropic waveguides strongly suppresses the Faraday rotation outside the stop-bands and degrades the linearity of the output polarization.

Magnetoexcitons in electron-hole bilayer nanotubes made of rolled-up type-II band aligned quantum wells

A new Aharonov–Bohm (AB) system based on spatially separated electron-hole bilayer nanotubes made of rolled-up type-II band aligned AlAs/GaAs quantum wells for observation of the so-called excitonic AB-effect is theoretically investigated. Our results explain how the AB oscillations are manifested in both the spectrum and optical intensity of the exciton through angular momentum transitions from zero to successive nonzero values and persistent fluctuations, respectively. We attribute the former regular transitions and later undamped oscillations to the radial and axial charge separation appeared in the electron-hole Coulomb attraction, respectively. The impact of the magnetic field on the binding energy, magnetization, and energy-shift in the magnetoexciton is examined as well. Such study lead to the proposal that electron-hole bilayer nanotubes of type-II could be utilized as magneto-optical switching devices based on the AB-effect which may have potential applications in quantum information systems.

Propagation of twin light pulses under magneto-optical switching operations in a four-level inverted-Y atomic medium

Propagation dynamics of twin laser pulses through a cold four-level inverted-Y atomic medium is investigated theoretically via switching on and off an external magnetic field under the application of a strong driving field. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously on a spacetime grid, our spatio-temporal results clearly show that dynamic control of twin-pulse propagation and magneto-optic dual switching operation are possible in such an inverted-Y system. The proposed scheme may be used for the design of magneto-optic switching and magneto-optic storage devices.

First-principles calculation of monitoring spin states of small magnetic nanostructures with IR spectrum of CO

A fully ab initio controlled ultrafast magnetooptical switching mechanism in small magnetic clusters is achieved through exploiting spin-orbit-coupling enabled Λ processes. The idea is that in the magnetic molecules a fast transition between two almost degenerate states with different spins can be triggered by a laser pulse, which leads to an electron excitation from one of the degenerate states to a highly spin-mixed state and a deexcitation to the state of opposite spin. In this paper a CO molecule is attached to one magnetic center of the clusters, which serves as an experimental marker to map the laser-induced spin manipulation to the IR spectrum of CO. The predicted spin-state-dependent CO frequencies can facilitate experimental monitoring of the processes. We show that spin flip in magnetic atoms can be achieved in structurally optimized magnetic clusters in a subpicosecond regime with linearly polarized light.

A 5 bit fiber delay line based on magneto-optic switch

In order to fulfill the reliability requirements in field application, the high reliability magneto-optic (MO) switches are used to realize an optical true time delay (OTTD) line. This paper first analyzes the characteristics of MO switch, then the topologies of OTTD are analyzed. Latter, two key supporting aspects are put forward, including measuring method and integrated structure design. In this article, we present and demonstrate a 5 bit optical fiber delay line (FDL) based on MO switches and fiber. The FDL exhibits the maximal delay error of 2.98 ps in 32 states.

High speed magneto-optical valve: Rapid control of the optical transmittance of aqueous solutions by magnetically induced self-assembly of superparamagnetic particle chains

Magneto-optical effects of magnetorheological fluids are of interest for applications including magnetic field sensors and optical modulators. Here, we describe the rapid control of the optical transmittance of a magnetorheological fluids by rotating columnar arrays of self-assembled superparamagnetic bead (SPB) chains by applying an external field using a permanent magnet. The columnar arrays of chains of magnetic beads acted as optical valves exhibiting distinct “on” and “off” states. For a given magnetic field, the maxima/minima of transmittance occurred when the applied field was parallel/perpendicular to light path and the intensity of light at the maxima varied with the strength of the applied field. Importantly, the response time for rotating the columnar arrays of magnetic chains was very rapid, and in the millisecond range. Our procedure provides a simple means for producing fast, magneto-optical switches that does not require cumbersome and power consuming electromagnetic coils and related peripheral equipment.

Sagnac interferometric switch utilizing Faraday rotation

In this paper, a novel fiber-based, magneto-optic switch based on a Sagnac interferometer is presented. Experimental results at 1550nm are reported and device performance such as extinction ratio for both single-mode and multi-mode fiber is presented. The performance is modeled using an analytical model which includes reflections at magneto-optic interfaces. The paper examines ways to improve the extinction ratio and the performance of the Sagnac configuration.

Field Coil for Magneto-Optic Switching: Capacitance Considerations

A tractable method for accurately predicting the parasitic capacitance of a field coil as part of an all-fiber Mach-Zehnder interferometric switch based on Faraday rotation is reported. The effects of the wire insulation layer, inter-turn air gap as well as capacitive coupling to the four nearest adjacent turns are considered in predicting the effective parasitic capacitance for single-layer coils. The complex distributed capacitance network that results is resolved using Kron reduction to yield the equivalent shunt capacitance. Several coil configurations were designed and compared to experimental results. This new approach can be used in conjunction with existing expressions for inductance and loss to enable the complete and accurate a priori design of field generating coils.

First-principles study of ultrafast magneto-optical switching in NiO

We present a fully ab initio ultrafast magneto-optical switching mechanism in NiO. All intragap $d$ states of the bulk and the (001) surface are obtained with highly correlational quantum chemistry and propagated in time under the influence of a static magnetic field and a laser pulse. We find that demagnetization and switching can be best achieved in a subpicosecond regime with linearly rather than circularly polarized light. Going beyond the electric dipole approximation is mandatory for the bulk and greatly enhances the process even for the surface, where it is not required by symmetry.

Magnetically Controlled Switches for Optoelectronics Networking: The Problem, Available Technology, New Implementations

This paper introduces some physical layer requirements of electro-optical as well as all optical networking. Due to the huge volume of data that is transmitted on these networks, there is a need for high-speed switching with effective switching in the nanosecond regime or better. While such switches exist for electronic media, they have been challenging for optical applications. Taking the recent developments in magneto-optical switches into consideration, there is a pressing need for fast switching of highly inductive loads. The state-of-the-art as well as the trends and needs for high speed switching in optical networks are presented. Some of the newest developments in the small-scale high-speed switching for electro-optical and all optical light path applications will also be presented. Experimental results of the newly developed switches at our program are presented and discussed. Based on the results, system requirements are identified and some shortcomings of the initial system are addressed. Possible improvements to the overall light-trail system are proposed and discussed

Faraday rotation in femtosecond laser micromachined waveguides

We demonstrate magneto-optic switching in femtosecond-laser micromachined waveguides written inside bulk terbium-doped Faraday glass. By measuring the polarization phase shift of the light as a function of the applied magnetic field, we find that there is a slight reduction in the effective Verdet constant of the waveguide compared to that of bulk Faraday glass. Electron Paramagnetic Resonance (EPR) measurements confirm that the micromachining leaves the concentration of the terbium ions that are responsible for the Faraday effect virtually unchanged.

Magneto-Optic-Based Fiber Switch for Optical Communications

Magneto-optical switching using Faraday rotation is investigated for optical fiber networks. Nonlinearity of the Faraday rotation was measured, and the optical switch was designed accordingly. The device was implemented experimentally with promising results

High-speed and highly repeatable polarization-state analyzer for 40-gb/s system performance monitoring

We demonstrate a fast (<1 ms), all solid-state, highly repeatable, and accurate polarization-state analyzer based on magnetooptic polarization switches. The module is further used for optical signal-to-noise-ratio performance monitoring in a 14times40-Gb/s wavelength-division-multiplexing system