Physics Commons^™

Design And Characterization Of An Affordable Laser Communication System, Andrea Tellez

Theses and Dissertations

Over the last decades, an exponential growth in communication demand has been observed. Radio Frequency (RF) band has been one of the most used bandwidths for data transmission in the world. Given the influence and the continuous growth of communication technology, the RF spectrum is overpopulated. More efficient systems are necessary to meet the communication needs of this generation. A change to optical bandwidth is the most practical alternative to deal with the congestion of radio frequency.

The aim of this thesis is to present the features of Free Space Optical links with off-the-shelf components. A description of how these …

Diffusion Of Rubidium Vapor Through Hollow-Core Fibers For Gas-Phase Fiber Lasers, Eric M. Guild

Theses and Dissertations

This work examines the diffusion of rubidium through a small diameter tube alone and in the presence of noble gases. A fluid dynamics analysis is investigated to aid in choosing a method for transferring atomic rubidium vapor that is reliable and efficient. Solutions to the time dependant ordinary differential equation describing the experimental flow properties of the system reveal more precise outcomes than previously practiced routines. Resolved viscosities and Poiseuille flow theory velocity profile distributions are characterized for noble gas carriers of the rubidium vapor. Applying Reynolds Numbers to the flow experiments provides pressure differential boundaries that are employed in …

Q-Switched And Mode Locked Short Pulses From A Diode Pumped, Yb-Doped Fiber Laser, Seth M. Swift

Theses and Dissertations

A diode-pumped, ytterbium (Yb)-doped fiber laser system was designed and demonstrated to operate in continuous wave (cw), passively Q-switched and possibly passively mode locked operation. To our knowledge, this was the first fiber laser oscillator built at the Air Force Institute of Technology. A Cr⁴⁺:YAG (Chromium: Ytterbium Aluminum Garnett) crystal was used as a saturable absorber to generate Q-switched pulses. Attempts to mode lock the laser were performed using a semiconductor saturable absorber mirror (SESAM) and through nonlinear polarization rotation (NPR). The best output power result was 5 Watts (W) while pumping at 8.3 W, yielding 60% efficiency …

Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey

Theses and Dissertations

The objective of this research effort was to demonstrate the path to continuous wave, coherent beam combination through stimulated Brillouin scattering phase conjugation in optical fiber. This work experimentally determined the fiber parameters necessary for phase conjugation in step-index optical fiber. Continuous wave phase conjugation using stimulated Brillouin scattering in step-index fibers was achieved for the first time with a fidelity of 0.8 and a threshold power of 16 W in a 15-m fiber with 0.13 NA. A fidelity of 0.8 was also achieved using 40 m of fiber with 0.06-NA and a threshold power of 15 W. The fidelity …

Modeling Of Sbs Phase Conjugation In Multimode Step Index Fibers, Justin B. Spring

Theses and Dissertations

Stimulated Brillouin scattering in a multimode step-index fiber can be used to generate a counter-propagating, phase-conjugate beam that would prove useful in many applications, such as near diffraction limited, double-pass high-power amplifiers or coherent beam combination. Relatively little modeling of such a fiber-based phase conjugator has been done, making design decisions regarding type and length of fiber largely guesswork. A numerical model was constructed with the aim of providing educated predictions about the phase conjugate fidelity that could be expected from a given pump intensity input coupled into a specific fiber. A numerical perturbation algorithm was constructed to search for …

Collision Broadening Using Alkali-Filled, Hollow Core Fibers, Luke P. Rodgers

Theses and Dissertations

The goal of this research was to demonstrate the possibility of collision broadening in a cesium-filled, hollow-core fiber as an alternative to the proven technique of pressure broadening. Theoretically, alkali electrons should relax from the ²P_3/2 to the ²P_1/2 level and the absorption spectrum should collisionally broaden due to the presence of fiber walls, as opposed to the more common pressure broadening method. An absorption dip located at 852.34nm was recorded in a pressure broadened comparison leg. This data was used as a baseline during analysis of the fiber leg's data. While the fiber was successfully …

Direct Diode Pumped Raman Amplifier Based On A Multimode Graded Index Fiberr, Charles James Baird

Theses and Dissertations

The direct pumping of a Raman fiber amplifier (RFA) was attempted using an array of four 25W, fiber pigtailed diodes at 936nm, combined via a 7 channel fiber beam combiner. The initial attempt was conducted using a 1.8 km, 100 micron core, GRIN fiber with an NA of .29 and attenuation 3.6 dB/km at 936nm. While amplification was not achieved, over 200mW of conversion was shown, with 10.4W of pump power and 3.5W of seed. This corresponds to an average conversion efficiency of 2.2%. The subsequent effort utilized a 2km long, 200 micron core, GRIN fiber, with NA of .27 …

Phasing A Dual Optical Path System Using An Optical Fiber As A Phase Conjugate Mirror, Shawn M. Willis

Theses and Dissertations

Phase conjugation properties of stimulated Brillouin scattering (SBS) in a short multimode fiber have been investigated with an eye towards its application for a multi-channel double pass master oscillator power amplifier (MOPA) system. In particular, properties of the SBS beam to compensate for the axial and transverse phase distortion between individual channels in a multi-channel amplifier system were studied. Two optical paths were created by covering half of the laser beam with a microscope slide, and also by spatially splitting the wavefronts with a 4 prism set-up. The Stokes beams that traversed the same optical paths as the pump beams …

Laser Beam Combining And Cleanup Via Stimulated Brillouin Scattering In Multi-Mode Optical Fibers, Blake C. Rodgers

Theses and Dissertations

The main objective of this thesis was to demonstrate the feasibility of combining and cleaning up multiple laser beams via Stimulated Brillouin Scattering (SBS) in a multi-mode optical fiber. Beam combining via SBS in an optical fiber is of interest because of the low SBS threshold power in an optical fiber allowing low power diode laser beams to be combined into one high power beam. SBS theory and some of the important historical results are described briefly. The experimental results clearly indicate that SBS in multi-mode optical fiber can indeed combine laser beams and clean up the beams at the …