VCSELs have major applications in high-speed data- and tele-communications such as local/metro area networks, optical interconnects and free-space optical links. Even though VCSEL was invented more than three decades ago and rapidly entered into system applications, a method of mass producing monolithic, polarization stable VCSELs at industry scale is still on-demand. Unfortunately, due to the high symmetry of VCSEL along its optic (emission) axis, VCSELs do not have intrinsic polarization stability. As the injection current increases above threshold, polarization randomly switches between the two orthogonal directions and leads to relative intensity noise and degrades the bit error rates during signal transmission. Until now polarization mode in VCSELs has been stabilized by growing VCSELs on high-index and off-angled substrates; introducing single/multiple asymmetric shapes in active and current aperture layers; growing asymmetric quantum nanostructures in active layers; introducing stress externally on the top DBRs; fabricating 1D shallow surface, high-contrast sub-δ gratings and integrating with SP elements on the topmost layer of VCSEL; introducing photonic nanostructures into VCSEL cavities, and so on. Our current review not only focuses on successful demonstrations and patents in the past but also identifies suitable methods for mass production of polarization stable VCSELs for practical applications.
This paper surveys recent patents on conducted electromagnetic interference (EMI) reduction techniques for power electronic applications, i.e. switched-mode power supplies and electric drives. Most essential patents currently available are classified into three categories: switching control techniques, modifying topology techniques, and filtering techniques. Significant patented techniques are not only summarized and reported in details, but the usefulness and limitation of benchmarked techniques are also discussed. With this classification and summarization, it would be helpful for power electronic design engineers to be able to appropriately choose EMI reduction techniques with minimum hassle.
The oil and paper of power transformers gradually age and consequently their quality decreases, which has an important effect on the lifetime of the transformer. The aging rate of these two materials depends on the temperature and moisture of the environment. The presence of moisture in a transformer deteriorates transformer insulation by decreasing both its electrical and mechanical strength. Hence, silica gel is used to absorb the water from the existing air between the environment and the expansion tank.
Since the absorption capacity of silica gel decreases over time, it must be restored during the lifetime of the transformer. This paper evaluates the different effects of moisture on transformer insulation and describes a designed system: the automatic silica gel restoration machine. Applying this machine will increase the life of transformer insulation and consequently the duration of its useful life. The article presents some promising patents on life of oil immersed transformers by automatic restoration of silica gel.
In recent years, considerable attention has been devoted to the merging of Radio over Fiber (RoF) technologies with millimeter-wave-band signal distribution. This sort of systems have great potential to support secure, cost-effective, and high-capacity vehicular/mobile/wireless access for the future provisioning of broadband, interactive, and multimedia services over wireless media. Current trends in cellular networks are (1) reduction of the cell size to accommodate more users and (2) operation in the microwave/millimeter-wave (mm-wave, 26-100 GHz) frequency bands to avoid spectral congestion in lower frequency bands (2.4 or 5 GHz). The larger radio frequency (RF) propagation losses at mm-wave bands reduce the cell size covered by a single base station (BS) and allow an increased frequency reuse factor to improve the spectrum utilization efficiency. On the other hand, this type of network demands a large number of BSs to cover a service area, and cost effective BSs are the key to success in the market place. Thus, a stable and cost effective BSs should be designed with simple and effective architecture. In general, there are three possible techniques to transport the mmwave wireless signals over the optical fiber 1) RF-over-fiber, 2) Intermediate Frequency (IF)-over-fiber, and 3) Base band-over-fiber. Amongst the schemes, the RF-over-fiber transport scheme has the potential to simplify BS design. However, one of its major drawbacks is the requirement for high-speed optical components and modulation and detection techniques. This requirement has led to the development of system architectures where functions such as signal routing/processing, handover, and frequency allocation are carried out at a centralized station (CS), rather than at the BS. This paper reviews extensively recent patents related to RoF communication systems for wireless communications. It is expected that with this exhaustive review, many researchers and developers will be encouraged to investigate even further and develop newer topologies and systems for the use of RoF for broadband radio, expanding this knowledge in the advent of newer services and applications likely to be deployed in the near future.
In general, the biometric patterns of an individual are permanently bound with him/her and it is almost impossible to replace. As a result, once stolen or compromised, the biometric data are either lost forever or are very hard to recover. Thus, it is desirable to secure the original patterns and design a method to ensure their revocability when compromised, which is known as “cancelable biometrics”. In this paper, recent patents and related papers on cancelable biometrics are reviewed, including different biometrics encryption algorithms and feature transformation methods.
Recent patents and progress on all-optical wavelength converters (WCs) based on semiconductor optical amplifiers (SOAs) are reviewed. Differential schemes utilizing the nonlinear optical effects of SOAs in the configurations such as the Mach-Zehnder interferometer (MZI), the delayed-interference signal-wavelength converter (DISC), detuned narrow filter and novel turbo-switch structure are discussed and compared, which overcome the limitation of operation speed of WCs due to the SOA recovery time(~100 ps). It is shown that, by using the chirp effect or turbo-switch schemes, the WCs can be operated at the range of 160-320Gb/s, which will be good candidates for the applications in the next generation all-optical fiber networks.
A compact microstrip lowpass filter using a U-SGS, which has the same meaning as U-Defected Ground Structure (U-DGS), with compensated microstrip is proposed in the paper. The equivalent circuit for the proposed Ushaped DGS and its corresponding L-C parameters are extracted by using its Sparameters response and a simple circuit analysis method. The lowpass filter using three cascaded U-DGS provides a compact size, very good transition sharpness with low insertion loss in passband and wide rejection in the stopband. Measured results show good agreement with the theoretical results. New ideas in order to improve the compactness and the losses of the filter have been proposed. The article presents some promising patents on design of compact ultra-wide stopband lowpass filter using a U-slotted ground structure (SGS) and multilayer-technique.
This article presents recent patents and advances on the fault diagnosis for grounding grid. Electromagnetic and chemical methods are applied to the fault diagnosis for grounding grid, furthermore the new square-wave technology earns widespread respect in fault diagnosis fields. The paper presented a method of the fault diagnosis for substation grounding grid using the square-wave, based on the analysis on the frequent characteristics of soil and substation grounding grip. The method is verified in calculating simulation, simulating experiments and field experiments to satisfy the needs of power system. Since this method can diagnose the fault of grounding grid by special data mining of the surface potential measurement result, which uses the square power supply, it needs neither the detailed topological structure of the substation grounding grid nor the excavation grounding grip, which would be an obvious advantage comparing to the other fault diagnosis methods nowadays.