Zugl.: Zürich, Techn. Hochsch., Diss., 2009

Hannover, Universiẗat, Diss., 2003.

The demand for efficient and cost-effective transmission and distribution of RF signal is increasing with the rapid development of wireless communication. This thesis studies the effect of using cost-effective vertical cavity surface emitting laser (VCSEL) to distribute ultra wide band (UWB) RF signal. Properties of multimode and single mode VCSEL are studied and simulated using commercial optical design suite. One of the biggest drawbacks of Orthogonal Frequency Division Multiplexing (OFDM) used by UWB is high peak to average power ratio (PAPR). Signal pre-distortion method is proposed to mitigate nonlinear effect from VCSEL optical system. Software connector is implemented to interconnect the Optical and Wireless design suite. Integrated VCSEL optical link and UWB simulation is carried out for the performance of the radio-on-fiber (RoF) system. The RoF system with optimized single mode VCSEL and proposed pre-distortion method is found to be capable of distributing UWB RF signal.

The demand for efficient and cost-effective transmission and distribution of RF signal is increasing with the rapid development of wireless communication. This thesis studies the effect of using cost-effective vertical cavity surface emitting laser (VCSEL) to distribute ultra wide band (UWB) RF signal. Properties of multimode and single mode VCSEL are studied and simulated using commercial optical design suite. One of the biggest drawbacks of Orthogonal Frequency Division Multiplexing (OFDM) used by UWB is high peak to average power ratio (PAPR). Signal pre-distortion method is proposed to mitigate nonlinear effect from VCSEL optical system. Software connector is implemented to interconnect the Optical and Wireless design suite. Integrated VCSEL optical link and UWB simulation is carried out for the performance of the radio-on-fiber (RoF) system. The RoF system with optimized single mode VCSEL and proposed pre-distortion method is found to be capable of distributing UWB RF signal.

The thermal stresses, residual stresses distributions in a vertical cavity surface emitting laser (VCSEL) are investigated in this thesis. The post-weld shifts of the laser light sources in the VCSEL under the re-flow, temperature cycling test and high temperature aging test have also been simulated and studied. The creeping effects of the 63Sn/37Pb solder on the stresses distributions and post-weld shifts are compared and discussed. The finite element package MARC is used for the stresses and deformation simulations of a VCSEL under different load cases. The heat transfer, the non-linear couple elastic-plastic increment and the creep models are employed in the numerical simulations. The temperature dependent material properties of the 63Sn/37Pb and 96.5Sn/3.5Ag solder are used for the temperature cycling and aging test. The effect of the circle and square solder pad designs on the stresses distributions in a VCSEL is also studied in this thesis. Numerical results indicate that the residual stresses introduced in the solidification is significant in stress and post-weld analyses of a VCSEL.

A microelectromechanical systems (MEMS) optical microphone that measures the interference of light resulting from its passage through a diffraction grating and reflection from a vibrating diaphragm (JASA, v. 122, no. 4, 2007) is described. In the present embodiment, both the diffractive optical element and the sensing diaphragm are micromachined on silicon. Additional system components include a semiconductor laser, photodiodes, and required readout electronics. Advantages of this optical detection technique have been demonstrated with both omni-directional microphones and biologically inspired directional microphones. In efforts to commercialize this technology for hearing-aids and other applications, a goal has been set to achieve a microphone contained in a small surface mount package (occupying 2mm x 2mm x 1mm volume), with ultra-low noise (20 dBA), and broad frequency response (20Hz–20kHz). Such a microphone would be consistent in size with the smallest MEMS microphones available today, but would have noise performance characteristic of professional-audio microphones significantly larger in size and more expensive to produce. This paper will present several unique challenges in our effort to develop the first surface mount packaged optical MEMS microphone. The package must accommodate both optical and acoustical design considerations. Dynamic models used for simulating frequency response and noise spectra of fully packaged microphones are presented and compared with measurements performed on prototypes. / text

Optical brain imaging is proven to be useful to understand brain function and morphology at cellular and network level. Different optical imaging modalities were developed over the years, with our group developing multi-modal simultaneous imaging using Vertical Cavity Surface Emitting Lasers (VCSELs). This thesis improves and demonstrates the applicability of the imaging system and adapts it to portable imaging. Specifically, it was found that using multiple exposures provide better flow measurements when compared to tracking measurements. An intrinsic parameter to monitor the state of the Blood Brain Barrier (BBB) was also discovered, proving more practical than previous fluorescence methods. We finally demonstrate initial results of imaging flow velocities and fluorescence in awake and moving rodents using VCSELs, achromatic doublets and a CMOS camera. Future work involves developing new prototypes of the portable system for imaging of disease states in awake animals and minimizing movement artefacts for oxygenation measurements.

No description available.

Optical brain imaging is proven to be useful to understand brain function and morphology at cellular and network level. Different optical imaging modalities were developed over the years, with our group developing multi-modal simultaneous imaging using Vertical Cavity Surface Emitting Lasers (VCSELs). This thesis improves and demonstrates the applicability of the imaging system and adapts it to portable imaging. Specifically, it was found that using multiple exposures provide better flow measurements when compared to tracking measurements. An intrinsic parameter to monitor the state of the Blood Brain Barrier (BBB) was also discovered, proving more practical than previous fluorescence methods. We finally demonstrate initial results of imaging flow velocities and fluorescence in awake and moving rodents using VCSELs, achromatic doublets and a CMOS camera. Future work involves developing new prototypes of the portable system for imaging of disease states in awake animals and minimizing movement artefacts for oxygenation measurements.

There is a great deal of interest in monitoring atmospheric greenhouse gases such as methane. Although distributed feedback edge-emitting lasers are often used for atmospheric detection, the development of the vertical cavity surface-emitting laser (VCSEL) has allowed for an alternative source. The VCSEL exhibits several advantages over distributed feedback (DFB), edge-emitting lasers, especially in terms of power requirements and tuning capabilities. A second harmonic spectroscopy system based on a VCSEL laser is presented. Battery operation of the driver, temperature control and receiver is achieved. The system is used to detect methane gas in open path situations, as well as in gas cylinders. Temperature and current scanning are compared as methods for laser wavelength modulation. Mathematical methods for characterizing and filtering absorption signals are investigated. The receiver system is also used with a DFB laser to compare performance with the VCSEL. A software receiver using LabVIEW is implemented, and its performance is compared with the hardware designs. A minimum detectable limit of 1.4 ppmm of methane for the hardware receiver is reported. / Photonics and Plasmas