Design analysis of a fiber-bundle-based mobile free-space optical link with wavelength diversity.

This paper reports on a simulation-based investigation of a wavelength diverse free-space optical link with an emphasis on identifying design choices that optimize the performance of the system under different operating scenarios. The simulation incorporates experimental data into the theoretical calculations for optical propagation to better describe the performance of the physical designs. The performance is evaluated in terms of the coverage area at the receiver, which is a measure of misalignment tolerance and is dependent not only on wavelength but on other key parameters, such as link length, transmitted power, the pattern of transmitters, beam divergence, and the receiver construction. The investigation finds that the coverage area of the receiver can be optimized for a given wavelength by proper choices of these parameters, and that parameter choices exist that minimize the change in performance when switching between wavelengths or for variations in link parameters. The interrelationships among key parameters and their impact on the potential system performance are investigated. The results provide guidance on the further development of the overall system.

Switched diversity approach for multireceiving optical wireless systems.

A number of existing spatial diversity schemes have been shown to improve the performance of optical wireless communication systems in diversity-rich environments. Among all, switched diversity has low complexity and is simple to implement. In this paper, an innovative spatial diversity scheme based on switched diversity is proposed. The scheme, namely switch-to-dominant combining, contributes to a higher bit error rate (BER) performance when compared to conventional switched diversity schemes, including switch-and-stay and switch-and-examine diversity. The optical multireceiver wireless system operates in a spatially correlated and lognormally distributed fading channel. Analytical analyses are conducted to demonstrate BER and processing load performance offered by the new scheme and compare them to available schemes, i.e., conventional switched combining and selection combining.

Differential strain measurement using multiplexed fiber Bragg grating sensors.

We investigate differential measurement of strain using fiber Bragg gratings and spatial demultiplexing methods. Differential measurement is shown to improve strain resolution in the presence of noise by an average of 34% compared to absolute measurements of the Bragg wavelengths. Spatial demultiplexing of the gratings provides potentially high-resolution sensing without calculating the sensor wavelengths. The differential method is still temperature dependent. We apply the differential technique to the problem of oil-water boundary detection in production columns, with promising preliminary results.

Wavelength and intensity dependence of retinal evoked responses using in vivo optic nerve recording.

We use a whole-animal model and wavelength-selective optical stimulation to investigate relationships between optical stimulus characteristics and neural signaling. Light-emitting diodes are used to selectively stimulate rod and cone pathways in Rana pipiens. A suction electrode is used to make in vivo measurements of the compound action potential from the optic nerve as the wavelength and intensity of the stimulus is varied. Our results demonstrate that the cone and rod pathways can be separately stimulated and analyzed with our method and, thus, provide a means to model the response of such pathways to more complex stimuli.