Ph.D. Defense: Oscar Herrera

    Monday, November 24, 2014 - 9:30am
    Franken Conference Room (Meinel 821)

    "Nonlinear Photonics in Waveguides for Telecommunications"


    Bandwidth demands in global telecommunication infrastructures continue to rise, and new optical techniques are needed to deal with massive data flows. Generating high-bandwidth signals (greater than 40 gigahertz) using conventional modulation techniques is hindered by material limitations and fabrication complexities. Similarly, controlling such high bandwidths in both the temporal and spectral domain becomes more problematic using conventional electronic processes. Advances in electro-optic organic materials, fibers/micro-fluidics integration and nonlinear optics have significant potential for higher bandwidth modulation and temporal-spectral control. The work presented in this dissertation demonstrates the use of various nonlinear optical effects in new photonic device and system designs towards the generation and manipulation of high-speed optical pulses.

    First, an all-fiber-based system utilizing an integrated carbon disulfide-filled liquidcore optical fiber (i-LCOF) and copropagating pulses of comparable temporal lengths is presented. The slow light effect was observed in one meter of i-LCOF, where 18-picosecond pulses were delayed up to 34 picoseconds through the use of stimulated Raman scattering. Delays greater than a pulse width indicate a potential application as an ultrafast controllable delay line for time division multiplexing in multi-gigabit-per-second telecommunication systems. Similarly, an optically tunable frequency shift was observed using this system. Pulses experienced a full spectral bandwidth shift at low peak pump powers when utilizing the Raman-induced frequency shift and slow light effects. Numerical simulations of the pulse-propagation equations agree well with the observed shifts. Included in our simulations are the contributions of both the Raman cross-frequency shift and slow light effects to the overall frequency shift. These results make the system suitable for numerous applications including low-power wavelength converters.

    Second, a silica/electro-optic-polymer phase modulator with an embedded bowtie antenna is proposed for use as a microwave radiation receiver. The detection of high-frequency electromagnetic fields has been heavily studied for wireless data transfer. Recently there has been growing interest in the field of microwave photonics. We present the design and optimization of a waveguide with an EO polymer core and silica/sol-gel cladding. The effect of electrodes on the insertion losses and poling efficiency are also analyzed, and conditions for low-loss and high poling efficiency are established. Experimental results for a fabricated device with microwave-response between 10 and 14 gigahertz are presented.

    Finally, we present the design for a fast optical switch incorporating silicon as the passive waveguide structure and EO polymer as the active material. The design uses a simple directional coupler with coplanar electrodes and promises to have low cross-talk and high switching speed (on the order of nanoseconds). An initial design for a 1 X 2 switch is fabricated and tested, and future optimization processes are also presented.