Second-harmonic distortion in vertical-cavity surface-emitting lasers with lateral loss effects

The influence of lateral loss effects on the second-harmonic distortion (SHD) of vertical-cavity surface-emitting lasers is investigated theoretically. Two parameters, differential confinement factor and differential cavity loss, are defined for the consideration of self-focusing and diffraction loss. It is found that SHD increases at low modulation frequencies due to the presence of differential cavity loss, especially for lasers with small core radius.published_or_final_versio

Lateral loss effects on modulation bandwidth in VCSELs

Intensity noise and chromatic fiber dispersion in analog optical communication systems are attributed to harmonic and inter-modulation distortion in the amplitude modulation of semiconductor lasers. In addition, maximum usable bandwidth of the communication systems is limited by harmonic distortion. Due to the use of Fabry Perot type resonator, second harmonic distortion exists in both edge-emitting devices and VCSELs. However the distortion caused by lateral loss may be more so in VCSELs because of its smaller core size. Two factors, namely, the lateral field confinement factor and the lateral loss due to diffraction, are considered for their effect on harmonic distortion when the laser device is under small signal modulation.published_or_final_versio

P53 tumour-suppressor gene mutations are mainly localised on exon 7 in human primary and metastatic prostate cancer.

Mutations in the p53 tumour-suppressor gene are among the most common genetic alterations in human cancers. In the present study we analysed the mutations in the p53 tumor-suppressor gene in 25 primary and 20 metastatic human prostate cancer specimens. DNA extracted from the paraffin-embedded sections was amplified by hot-start polymerase chain reaction, and p53 gene mutations in the conserved mid-region (exons 4-9) were examined using single-strand conformation polymorphism (SSCP) analysis and immunohistochemistry. In the present study, we used a novel hot-start PCR-SSCP technique using DNA Taq polymerase antibody, which eliminates primer-dimers and non-specific products. Because of this new technique, the results of PCR-SSCP showed very high resolution. Polymerase chain reaction products were sequenced directly for point mutations for the p53 gene. Mutations were found in 2 out of 25 primary prostate cancers (8%) and 4 out of 20 metastatic cancers (20%). Mutations were observed exclusively in exon 7 and not in exons 4, 5, 6, 8 or 9. Nuclear accumulation of p53 protein, determined by immunohistochemistry, correlated with the degree of metastasis in prostatic cancer

Widely-tunable continuous-wave single-longitudinal-mode fiber optical parametric oscillator

A continuous-wave fiber optical parametric oscillator with a tunability of 114 nm, a wavelength span of 143 nm and single-longitudinal-mode oscillation is demonstrated. The short-term linewidth of the output is as narrow as 1.5 kHz. © 2011 Optical Society of America.published_or_final_versio

Comparison on crosstalk tolerance of RZ-DPSK and RZ-OOK modulation format in fiber optical parametric amplifier

We investigated crosstalk tolerance of RZ-DPSK and RZ-OOK modulation format in OPA with 100GHz channel spacing. Results show an average of 2.4dB improvement in Q factor by using RZ-DPSK format over RZOOK format.published_or_final_versio

Multiwavelength Single-Longitudinal-Mode Ytterbium-Doped Fiber Laser

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A comprehensive study on crosstalk suppression techniques in fiber optical parametric amplifier by modulation format

With the presence of multiple-WDM input signals, ON-OFF keying (OOK)-modulated signals suffer from crosstalk in fiber optical parametric amplifier (OPA) due to cross-gain modulation (XGM) and four-wave mixing (FWM) effects. We demonstrated substantial crosstalk suppression in one-pump OPA by using return-zero differential phase-shift keying (RZ-DPSK) modulation format, which with its pattern-independent amplitude and subunity duty cycle would be effective in reducing the XGM and FWM effects significantly. By using the RZ-DPSK format, the power penalty was improved by at least 0.8 dB over RZ-OOK, non-RZ (NRZ)-DPSK, and NRZ-OOK formats with four 10 Gb/s channels, separated by 200 GHz spacing. With eight 10 Gb/s channels separated by 100 GHz spacing, a Q -factor penalty of the RZ-DPSK signal was reduced by 2.4 dB compared to RZ-OOK counterparts. © 2008 IEEE.published_or_final_versio

All-optical tunable delay with NRZ-to-RZ format conversion capability based on optical Kerr switch and pulse pre-chirping

All-optical tunable delay plays an important role for enabling high-throughput optical routing, such as buffer for contention resolution and timing synchronization. We proposed and demonstrated a widely tunable optical delay using optical Kerr-switch-based wavelength converter and pulse pre-chirping for compensating chromatic dispersion in fiber delay. With wideband operation provided by a Kerr-switch wavelength converter, a tunable delay range up to 8.56 ns was achieved. Meanwhile, pulse pre-chirping helped to alleviate group-velocity dispersion (GVD)-induced penalty, and provided simultaneous nonreturn-zero (NRZ)-to-RZ format conversion functionality. © 2008 IEEE.published_or_final_versio

High-sensitivity polarization gating frequency-resolved optical gating (PG-FROG) using highly-nonlinear dispersion-shifted fiber

We experimentally demonstrate a frequency-resolved optical gating (FROG) system in pulse characterization at 1.55 μm by using cross-phase modulation (XPM) in highly nonlinear dispersion-shifted fiber (HNL-DSF), with over 6-times sensitivity improvement. © 2011 National Sun Yat-Sen Univ.published_or_final_versio

Comparison of the state-of-art phase modulators and parametric mixers in time-lens applications under different repetition rates

Ever since the discovery of space-time duality, several methods have been developed to perform temporal imaging, and there are two major categories: the quadratic signal onto the phase modulator and the parametric mixer with a linear chirped pump. The features of each mechanism have been thoroughly and quantitatively explored and optimized for certain kinds of applications, but a comparison of some key parameters, especially in the aspect of the repetition rate, is required. In this paper, we will first review the theoretical models and existing performance of these two mechanisms and, consequently, compare them quantitatively in different aspects: the focal group delay dispersion, the pupil size, the effective duty ratio, and the temporal numerical aperture. All these fundamental parameters are related to the repetition rate. The results obtained in this study would provide some important guidelines for the time-lens design, so as to be optimized in different kinds of applications with different repetition rate requirements, such as ultrafast optical communication and real-time bio-imaging systems.published_or_final_versio