Kenneth K. Y. Wong

Wide-band tuning of the gain spectra of one-pump fiber optical parametric amplifiers

By suitably choosing the fiber properties, and by tuning the pump wavelength near the fiber zero-dispersion wavelength, one can in principle generate a wide variety of one-pump fiber optical parametric amplifier gain spectra. These can range from a very wide single region to two symmetric narrow gain regions far away from the pump. We have experimentally verified these predictions. With a highly nonlinear fiber, we have inferred the existence of gain over a single 400-nm region and measured a maximum on-off gain of 65 dB. With a common dispersion-shifted fiber, we have obtained tunable gain regions less than 1 nm wide, up to 200 nm from the pump; we have also shifted these by several nanometers by lowering the fiber temperature to 0/spl deg/C.

Silver nanoparticles—the real “silver bullet” in clinical medicine?

The use of silver nanoparticles has become more widespread in our society. While many believe that silver can be extremely useful in clinical medicine, firm evidence is still lacking. Thus, we present here a review of their current use in clinical medicine.

Wavelength exchange in a highly nonlinear dispersion-shifted fiber: theory and experiments

With a suitable arrangement of two pumps and two signals with respect to the zero-dispersion wavelength of a fiber, simultaneous wavelength exchange between two signals can be realized by four-wave mixing in the fiber. We have demonstrated near-complete wavelength exchange between two signals at 1573.4 and 1579.9 nm with two 0.25-W pumps in a 1-km-long highly nonlinear dispersion-shifted fiber. We also have evaluated the bit-error-rate performance of wavelength exchange with a 10-Gb/s signal, and obtained a power penalty of less than 1 dB for the exchanged signal.

Polarization-independent two-pump fiber optical parametric amplifier

Fiber-optical parametric amplifiers can be rendered polarization-independent by using two pumps with orthogonal polarization states. We have analytically investigated and experimentally demonstrated, for the first time to our knowledge, a flat-gain polarization-independent continuous-wave fiber optical parametric amplifier with 15 dB of gain over a 20-nm bandwidth, by using two orthogonal pumps.

Further evidence of the anti-inflammatory effects of silver nanoparticles

The production of pure silver in nanoparticle size has opened new dimensions in the clinical use of this precious metal. We and others have demonstrated previously that silver nanoparticles (nAg) possess efficient antimicrobial activity. Herein we show they may also have significant anti‐inflammatory effects in a postoperative peritoneal adhesion model. This finding provides further insight into the biological actions of nAg as well as a potentially novel therapy for peritoneal adhesions in clinical surgery.

Silver Nanoparticles Mediate Differential Responses in Keratinocytes and Fibroblasts during Skin Wound Healing

With advances in nanotechnology, pure silver has been recently engineered into nanometer‐sized particles (diameter <100 nm) for use in the treatment of wounds. In conjunction with other studies, we previously demonstrated that the topical application of silver nanoparticles (AgNPs) can promote wound healing through the modulation of cytokines. Nonetheless, the question as to whether AgNPs can affect various skin cell types—keratinocytes and fibroblasts—during the wound‐healing process still remains. Therefore, the aim of this study was to focus on the cellular response and events of dermal contraction and epidermal re‐epithelialization during wound healing under the influence of AgNPs; for this we used a full‐thickness excisional wound model in mice. The wounds were treated with either AgNPs or control with silver sulfadiazine, and the proliferation and biological events of keratinocytes and fibroblasts during healing were studied. Our results confirm that AgNPs can increase the rate of wound closure. On one hand, this was achieved through the promotion of proliferation and migration of keratinocytes. On the other hand, AgNPs can drive the differentiation of fibroblasts into myofibroblasts, thereby promoting wound contraction. These findings further extend our current knowledge of AgNPs in biological and cellular events and also have significant implications for the treatment of wounds in the clinical setting.

Continuous-wave fiber optical parametric oscillator

We report continuous-wave operation of singly resonant fiber optical parametric oscillators. In a cavity formed by 100 m of highly nonlinear fiber and two fiber Bragg gratings, the pump power threshold was 240 mW; the output wavelength could be tuned over 80 nm by tuning of the pump. We also obtained an internal conversion efficiency of 30%, compared with the maximum theoretical value of 50%, by use of a 1-km-long cavity.

Polarization-independent one-pump fiber-optical parametric amplifier

One-pump fiber optical parametric amplifiers (OPAs) can be rendered polarization independent by using a polarization-diversity technique. We have experimentally demonstrated a fiber OPA with peak signal gain of 9 /spl plusmn/ 0.2 dB when the signal polarization angle was varied from 0/spl deg/ to 90/spl deg/. Power penalty of less than 1 dB was measured in a 10-Gb/s transmission system.

Modulation of collagen alignment by silver nanoparticles results in better mechanical properties in wound healing

UNLABELLED Our previous study has revealed that silver nanoparticles (AgNPs) have potential to promote wound healing by accelerated re-epithelization and enhanced differentiation of fibroblasts. However, the effect of AgNPs on the functionality of repaired skin is unknown. The aim of this study was to explore the tensile properties of healed skin after treatment with AgNPs. Immunohistochemical staining, quantitative assay and scanning electron microscopy (SEM) were used to detect and compare collagen deposition, and the morphology and distribution of collagen fibers. Our results showed that AgNPs improved tensile properties and led to better fibril alignments in repaired skin, with a close resemblance to normal skin. Based on our findings, we concluded that AgNPs were predominantly responsible for regulating deposition of collagen and their use resulted in excellent alignment in the wound healing process. The exact signaling pathway by which AgNPs affect collagen regeneration is yet to be investigated. FROM THE CLINICAL EDITOR The aim of this study was to explore the tensile properties of healed skin after treatment with AgNPs. These nanoparticles improved tensile properties and led to better fibril alignments in repaired skin, with a close resemblance to normal skin. The exact signaling pathway by which AgNPs affect collagen regeneration is yet to be investigated.

Automatic source camera identification using the intrinsic lens radial distortion

Source camera identification refers to the task of matching digital images with the cameras that are responsible for producing these images. This is an important task in image forensics, which in turn is a critical procedure in law enforcement. Unfortunately, few digital cameras are equipped with the capability of producing watermarks for this purpose. In this paper, we demonstrate that it is possible to achieve a high rate of accuracy in the identification by noting the intrinsic lens radial distortion of each camera. To reduce manufacturing cost, the majority of digital cameras are equipped with lenses having rather spherical surfaces, whose inherent radial distortions serve as unique fingerprints in the images. We extract, for each image, parameters from aberration measurements, which are then used to train and test a support vector machine classifier. We conduct extensive experiments to evaluate the success rate of a source camera identification with five cameras. The results show that this is a viable approach with high accuracy. Additionally, we also present results on how the error rates may change with images captured using various optical zoom levels, as zooming is commonly available in digital cameras.