We experimentally demonstrate, for the first time to our knowledge, a phase-sensitive amplifier based on frequency nondegenerate parametric amplification in optical fiber, where the input signal-idler pair is prepared all-optically. Using two fiber-optic parametric amplifier sections separated by a fiber-based wavelength-dependent phase shifter, we observe and investigate phase-sensitive gain profile in the 1550 nm region both experimentally and theoretically. The realized scheme automatically generates gain-defining phase that is environmentally stable, making it advantageous for building phase-sensitive transmission links.
We demonstrate a novel, self-starting optoelectronic oscillator based on an electro-absorption modulator in a fiber-extended cavity for generating an optical pulse stream with high-rate and ultra-low jitter capabilities. Optical pulses at 10GHz repetition rate are demonstrated with >90dBc/Hz side-mode suppression and the lowest timing jitter (42fs in the 100Hz-1MHz range) reported to date for a self-starting source. Along with the optical pulse stream, the oscillator also generates a 10GHz electrical signal with ultra-low phase noise.
We demonstrate phase-sensitive amplification of multiple wavelength-division-multiplexed continuous-wave (CW) signals by frequency nondegenerate four-wave-mixing process in optical fiber. By fine-tuning the optical wavelengths of the CW signals, simultaneous phase-sensitive in-line amplification of three signal channels is realized. This indicates the possibility of amplifying multiple data channels by an in-line phase-sensitive fiber parametric amplifier. We also discuss a potential system architecture employing such amplifiers.
Objective
To determine whether applying a mediolateral corrective force to the pelvis during treadmill walking would enhance muscle activity of the paretic leg and improve gait symmetry in individuals with post-stroke hemiparesis
Methods
Fifteen subjects with post-stroke hemiparesis participated in this study. A customized cable-driven robotic system based over a treadmill generated a mediolateral corrective force to the pelvis toward the paretic side during early stance phase. Three different amounts of corrective force were applied. Electromyographic (EMG) activity of the paretic leg, spatiotemporal gait parameters and pelvis lateral displacement were collected.
Results
Significant increases in integrated EMG of hip abductor, medial hamstrings, soleus, rectus femoris, vastus medialis and tibialis anterior were observed when pelvic corrective force was applied, with pelvic corrective force at 9% of body weight inducing greater muscle activity than 3% or 6% of body weight. Pelvis lateral displacement was more symmetric with pelvic corrective force at 9% of body weight.
Conclusions
Applying a mediolateral pelvic corrective force toward the paretic side may enhance muscle activity of the paretic leg and improve pelvis displacement symmetry in individuals post-stroke.
Significance
Forceful weight shift to the paretic side could potentially force additional use of the paretic leg and improve the walking pattern.
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