Flexible quadrature amplitude modulation with semiconductor optical amplifier and electroabsorption modulator.

Optical quadrature amplitude modulation (QAM) is experimentally demonstrated with a low-complexity modulator based on a semiconductor optical amplifier and electroabsorption modulator. Flexible amplitude/phase format transmission is achieved. The applicability of octary QAM for coherent optical access networks with sustainable 3 Gb/s per-user bandwidth is investigated for a long reach of 100 km, and its compatibility with a potentially high split is verified.

Bandpass sampling in heterodyne receivers for coherent optical access networks.

A novel digital receiver architecture for coherent heterodyne-detected optical signals is presented. It demonstrates the application of bandpass sampling in an optical communications context, to overcome the high sampling rate requirement of conventional receivers (more than twice the signal bandwidth). The concept is targeted for WDM coherent optical access networks, where applying heterodyne detection constitutes a promising approach to reducing optical hardware complexity. The validity of the concept is experimentally assessed in a 76 km WDM-PON scenario, where the developed DSP achieves a 50% ADC rate reduction with penalty-free operation.

Effects of intensity of Transcutaneous Electrical Nerve Stimulation (TENS) on pressure pain threshold and blood pressure in healthy humans: A randomized, double-blind, placebo-controlled trial.

OBJECTIVES: Transcutaneous electrical nerve stimulation (TENS) is primarily used for pain relief. However, evidence is beginning to emerge that TENS may also have a lowering effect on systemic blood pressure (BP). The purpose of this study was to investigate the comparative effects of 2 intensities on pressure pain threshold (PPT) and resting BP in healthy humans, using low-frequency stimulation applied segmentally to the pain site. METHODS: In a double-blind design, 40 volunteers, stratified by sex, were randomly allocated to 4 groups: high-intensity ("to tolerance without pain"), low-intensity ("strong but comfortable"), placebo, and control. TENS (2 Hz, 250 mu) was applied over the distribution of the superficial radial nerve of the dominant hand for 30 minutes. The outcome variables were measured at baseline and at 6 subsequent 10-minute intervals. For the PPTs, 2 measurements were taken bilaterally from the first dorsal interosseous muscle using a pressure algometer. The BP was measured in the brachial artery with an automatic monitor. Data difference scores were analyzed using repeated-measures and 1-way analyses of variance. RESULTS: The high-intensity group showed a significant rise in PPT compared with the low-intensity, placebo, and control groups for both measurement sites, which sustained 30 minutes poststimulation. TENS produced no significant effect on BP, regardless of intensity. DISCUSSION: These results affirm that high levels of intensity are of fundamental importance in effective TENS dosage. This also applies for low frequency, segmental stimulation. Resting BP seems not to be dependent on intensity.