Low-Cost PMD-Insensitive and Dispersion Tolerant In-Band OSNR Monitor Based on Uncorrelated Beat Noise Measurement

A polarization-mode-dispersion-insensitive and dispersion tolerant in-band optical signal-to-noise-ratio monitor based on uncorrelated beat noise measurement is proposed and demonstrated. The proposed technique uses an optical delay line interferometer in recovering symmetrical signal samples and exploits the benefits of low-speed balanced receivers and digital signal processing in measuring the uncorrelated beat noise.     

Robust Room-Temperature Ferromagnetism with Giant Anisotropy in Nd-Doped ZnO Nanowire Arrays

As an important class of spintronic material, ferromagnetic oxide semiconductors are characterized with both charge and spin degrees of freedom, but they often show weak magnetism and small coercivity, which limit their applications. In this work, we synthesized Nd-doped ZnO nanowire arrays which exhibit stable room temperature ferromagnetism with a large saturation magnetic moment of 4.1 μ(B)/Nd as well as a high coercivity of 780 Oe, indicating giant magnetic anisotropy. First-principles calculations reveal that the remarkable magnetic properties in Nd-doped ZnO nanowires can be ascribed to the intricate interplay between the spin moments and the Nd-derived orbital moments. Our complementary experimental and theoretical results suggest that these magnetic oxide nanowires obtained by the bottom-up synthesis are promising as nanoscale building blocks in spintronic devices.     

Ferroelectric Domain Wall Motion in Freestanding Single-Crystal Complex Oxide Thin Film

Ferroelectric domain walls in single-crystal complex oxide thin films are found to be orders of magnitude slower when the interfacial bonds with the heteroepitaxial substrate are broken to create a freestanding film. This drastic change in domain wall kinetics does not originate from the alteration of epitaxial strain; rather, it is correlated with the structural ripples at mesoscopic length scale and associated flexoelectric effects induced in the freestanding films. In contrast, the effects of the bond-breaking on the local static ferroelectric properties of both top and bottom layers of the freestanding films, such as domain wall width and spontaneous polarization, are modest and governed by the change in epitaxy-induced compressive strain.     

Effect of Frozen Magnetic Flux on the Electrical Transport Characteristics of Superconductor?CFerromagnet Junction

We studied electrical transport characteristics of lateral superconductor (SC)?Cferromagnet (FM)?Csuperconductor devices which were found to exhibit two strikingly different differential resistance states at zero field. The key difference between these states is that the critical current (I _c) is dramatically lower for one state (state?2) than the other (state?1). Moreover, state?2 exhibits a higher zero bias resistance than state?1. We explain this as an effect of magnetic field from the frozen flux in SC on the Andreev reflection process at the SC?CFM interface. The magnetoresistance (MR) curves at different dc current biases are nonhysteretic and symmetric with respect to zero field axis when the device is at state?1. In contrary to this, MR curves at state?2 are asymmetric and show a pronounced hysteresis at high bias current. These effects indicate a coupling between applied field and frozen flux, which affects the transport characteristics of the SC?CFM interface.     

Oxide nanowires for spintronics: materials and devices

Spintronics, or spin-based data storage and manipulation technology, is emerging as a very active research area because of both new science and potential technological applications. As the characteristic lengths of spin-related phenomena naturally fall into the nanometre regime, researchers start applying the techniques of bottom-up nanomaterial synthesis and assembly to spintronics. It is envisaged that novel physics regarding spin manipulation and domain dynamics can be realized in quantum confined nanowire-based devices. Here we review the recent breakthroughs related to the applications of oxide nanowires in spintronics from the perspectives of both material candidates and device fabrication. Oxide nanowires generally show excellent crystalline quality and tunable physical properties, but more efforts are imperative as we strive to develop novel spintronic nanowires and devices.     

Simultaneous multiplexing and demultiplexing of wavelength-interleaved channels in DWDM millimeter-wave fiber-radio networks

A simultaneous multiplexing and demultiplexing (MUX/DEMUX) scheme for wavelength-interleaved millimeter-wave 37.5-GHz-band fiber-radio channels spaced at 25 GHz has been proposed. The proposed MUX/DEMUX technique potentially realizes simple, compact, and low-cost central office and remote nodes by avoiding the use of wavelength-selective pre- and postprocessing hardware. The novel scheme incorporates an arrayed-waveguide grating with multiple loop-backs between the input and the output ports, in addition to multiple optical circulators and optical isolators. The multiplexing functionality of the proposed technology enables a carrier subtraction technique and consequently reduces the carrier-to-sideband ratios of the multiplexed channels. Multiplexing of the uplink channels generated via several methods is demonstrated experimentally. These techniques include generation of the channels by using the optical carriers that correspond to wavelengths spaced at the free spectral range (FSR) or multiples of the FSR from the downlink (DL) optical carriers and reuse of the DL optical carriers that are recovered by applying a wavelength reuse technique (/spl lambda//sub UL/=/spl lambda//sub DL//spl plusmn/n/spl times/FSR, where n=0,1,2,3,...). The demultiplexing functionality of the proposed scheme that separates the 37.5-GHz-band wavelength-interleaved DL channels spaced at 25 GHz is also demonstrated. In addition, the effect of optical crosstalk on the transmission performance of the demultiplexed channels is also characterized experimentally.     

Internetworking VCSEL-Based Hybrid Base Station Towards Simultaneous Wireless and Wired Transport for Converged Access Network

A hybrid base-station (H-BS) scheme that has the potential to establish intercommunications among neighboring access nodes without sending the signals to the edge node to simultaneously transport wireless and wireline services to integrated access nodes is proposed. As the scheme uses vertical-cavity surface-emitting lasers as the light source in the H-BS, it can potentially be realized at low cost without any temperature control.     

Investigation of Performance Enhancement of WDM Optical Interfaces for Millimeter-Wave Fiber-Radio Networks

A modified wavelength-division-multiplexed optical interface with the capability to enable optical-add-drop-multiplexing functionality as well as to deliver an uplink optical carrier to the base stations in a millimeter-wave fiber-radio system, is investigated and an optimal configuration demonstrated. The incorporation of the modification significantly enhances the performance of both uplink and downlink transmission     

Efficient Transmission Scheme for AWG-Based DWDM Millimeter-Wave Fiber-Radio Systems

We propose and demonstrate an upstream transmission scheme using a semiconductor optical amplifier (SOA) for arrayed waveguide grating (AWG)-based dense wavelength-division-multiplexed (DWDM) millimeter-wave fiber-radio systems and show improved link performance. In our scheme, unused optical carriers from the cyclic AWG in the downlink (DL) are tapped for uplink (UL) transmission. An SOA in conjunction with the AWG simultaneously amplifies the DL RF subcarriers and UL optical carrier, thus improving carrier-to-sideband ratio in the DL while also yielding an improved power budget for the UL. Our experimental results show that the proposed scheme can be a practical solution for future bidirectional wavelength interleaved DWDM transmission systems