FDTD analysis of probe-fed cylindrical dielectric resonator antennaoperating in fundamental broadside mode

An analysis of a cylindrical dielectric resonator antenna operating at the fundamental broadside mode using the finite-difference time-domain (FDTD) method is presented. Good agreement between theoretical and experimental results on the input impedance of the DR antenna is obtained. The effects of the probe length, feed position and the dielectric constant on the input impedance are presented     

Photoreflectance study of GaAs and GaAs/GaAlAs single quantum wells grown on (001) Si substrates

The optical features associated with biaxially strained bulk GaAs and three GaAs/GaAlAs quantum wells (QWs), with widths of 52 Å, 120 Å and 200 Å, grown on (001) Si have been studied using photoreflectance at 300 K and 77 K. The ordering and/or separation of the light- and heavy-hole quantum transitions in the QWs can be tuned by altering the width of the well.     

Combining shape and physical modelsfor online cursive handwriting synthesis

This paper proposes a novel learning-based approach to synthesizing cursive handwriting of a user's personal handwriting style by combining shape and physical models. In the training process, some sample paragraphs written by a user are collected and these cursive handwriting samples are segmented into individual characters by using a two-level writer-independent segmentation algorithm. Samples for each letter are then aligned and trained using shape models. In the synthesis process, a delta log-normal model based conditional sampling algorithm is proposed to produce smooth and natural cursive handwriting of the user's style from models. Received: 26 April 2003, Accepted: 27 September 2004, Published online: 29 November 2004 Correspondence to: Jue Wang Jue Wang and Chenyu Wu completed this work while interns at Microsoft Research Asia.     

Polarization Maintaining Air-Core Bandgap Fibers for Terahertz Wave Guiding

A polarization-maintaining air-core bandgap polymer fiber is proposed for low-loss terahertz (THz) wave guiding. The polarized guided modes are confined in an asymmetric core by a bandgap of periodic arrangement of square holes with round corners in the cladding. The guiding properties, including transmission bandwidth, numerical aperture, phase-index birefringence, modal absorption loss, and bend loss, are systematically investigated. The influence of background polymers on guiding properties is demonstrated in detail. Numerical simulations reveal that, while maintaining a relatively high phase-index birefringence (of the order of 10^-3 ), the THz fiber shows a significant suppression of absorption loss of the background polymers (by a factor of more than 25) due to the bandgap effect that repels the modal power from the absorbent polymers. The proposed THz fiber has potential for guiding intense THz waves for polarization-sensitive applications.     

All-Fiber Q-Switched Erbium-Doped Fiber Ring Laser Using Phase-Shifted Fiber Bragg Grating

We propose a unique all-fiber Q-switched erbium-doped fiber ring laser. It consists of a phase-shifted fiber Bragg grating (FBG) and an apodized FBG reflector. By using the piezoelectric transducer (PZT) to periodically stretch the apodized FBG and detune it with the phases-shifted FBG, the cavity loss of the fiber ring laser is switched between high and low states to achieve Q-switching. This Q-switched fiber laser has advantages of narrow spectral bandwidth, stable oscillation wavelength, and the repetition rate of the Q-switched pulses can be double of the PZT modulation frequency. A numerical model is developed and presented to simulate and analyze this FBGs-based Q-switched fiber ring laser with consideration of the dynamic response of FBGs during Q-switching. We experimentally demonstrate 10 and 20 kHz Q-switching operation with 10 kHz PZT modulation frequency. The experimental result is similar to the simulation result.     

Experimental Demonstration of Multipoint Temperature Warning Sensor Using a Multichannel Matched Fiber Bragg Grating

A novel time-division-multiplexing fiber Bragg grating (FBG) sensor for multipoint temperature warning sensor is proposed and demonstrated. A multiwavelength pulsed laser based on a multichannel matched FBG is employed. The sensor array consists of multiple uniform FBGs at different positions and with different nominal wavelengths. When the temperature exceeds the threshold at a certain position, the light at the corresponding time slot and wavelength can be detected. The sensor provides a simple and flexible solution to locate the abnormal temperature increase with different tolerable thresholds at different locations.     

Single-Longitudinal-Mode Erbium-Doped Fiber Ring Laser Based on High Finesse Fiber Bragg Grating Fabry–PÉrot Etalon

We present a simple and stable single-longitudinal-mode (SLM) erbium-doped fiber laser. It consists of an apodized fiber Bragg grating (FBG) and a high finesse FBG-based Fabry-Perot (FP) etalon in the ring cavity. The apodized FBG acts as a wavelength discriminative component selecting a few oscillation modes while the FP etalon serves as narrow bandwidth bandpass filter to further discriminate and select SLM efficiently. Stable SLM laser output at 1.55 m with linewidth about 2.5 kHz is acquired. Furthermore, continuous wavelength tuning over 8 nm is achieved by simultaneously applying strain to the FBG and the FP etalon.     

Photonic Monocycle Pulse Frequency Up-Conversion for Ultrawideband-Over-Fiber Applications

We demonstrate a photonic monocycle pulse frequency up-conversion scheme for ultrawideband (UWB)-over-fiber applications using nonlinear polarization rotation arising in a semiconductor optical amplifier. For the first time, we have successfully realized the photonic up-conversion of UWB monocycle pulses with an optical local oscillator signal at 24 GHz in the whole -band. The up-converted UWB monocycle pulse at 24 GHz exhibits a power spectrum density fitting the UWB emission mask. After electrical down-conversion, the UWB monocycle pulse has shown low distortion induced by the optical mixing process.     

Droplet and Microchamber‐Based Digital Loop‐Mediated Isothermal Amplification (dLAMP)

Digital loop‐mediated isothermal amplification (dLAMP) refers to compartmentalizing nucleic acids and LAMP reagents into a large number of individual partitions, such as microchambers and droplets. This compartmentalization enables dLAMP to be an excellent platform to quantify the absolute number of the target nucleic acids. Owing to its low requirement for instrumentation complexity, high specificity, and strong tolerance to inhibitors in the nucleic acid samples, dLAMP has been recognized as a simple and accurate technique to quantify pathogenic nucleic acid. Herein, the general process of dLAMP techniques is summarized, the current dLAMP techniques are categorized, and a comprehensive discussion on different types of dLAMP techniques is presented. Also, the challenges of the current dLAMP are illustrated together with the possible strategies to address these challenges. In the end, the future directions of the dLAMP developments, including multitarget detection, multisample detection, and processing nucleic acid extraction are outlined. With recently significant advances in dLAMP, this technology has the potential to see more widespread use beyond the laboratory in the future.