Quantum-mechanical analysis of frequency conversion in nonlinear optics

Germano Montemezzani

Alexander S. Solntsev

This thesis encompasses a broad area of physics including linear and nonlinear optics, photonics and quantum physics. It combines the phenomena of nonlinearoptical frequency conversion with waveguiding and coupling, taking advantage of new opportunities presented by advances in fabrication technologies of micro- and nano-waveguides. In this dissertation an in-depth analysis of quantum and classical properties of light traveling in nonlinear optical waveguides, directional couplers and waveguide arrays is performed. The concepts of spatial and temporal dispersion, waveguiding in structures with subwavelength dimensions and nonlinear interactions between different frequencies of light are studied both theoretically and experimentally. Some sections of this thesis include development and implementation of novel physical ideas, while other sections are focused on comprehensive experimental and numerical analysis of advanced theoretical concepts. The results presented in this dissertation demonstrate new physical phenomena with potential applications in the areas of telecommunications and quantum information. The research performed in this thesis opens opportunities for frequency conversion with world-leading power efficiency, including operation with ultrashort pulses for a variety of wavelengths to suit a wide range of perspective application requirements. It also shows an approach for simple and energy efficient spatio-temporal optical signal control, which can find applications in next generation telecommunications networks. Furthermore, the results obtained in this dissertation demonstrate the possibility for flexible shaping of quantum statistics of photons generated in photonic waveguiding structures through spontaneous frequency conversion, contributing to the development of integrated quantum circuits. The new methods of frequency conversion in micro- and nano-scale waveguides and optical circuits have potential to advance the performance, energy efficiency, and security of future optical communication networks and computing systems.

Andrew G. White

Davıd L. Andrews, Kayn A. Forbes, Jack Ford

Issues of a fundamental quantum origin exert a significant effect on the output mode structures in optically parametric processes. An assumption that each frequency conversion event occurs in an infinitesimal volume produces uncertainty in the output wave-vector, but a rigorous, photon-based theory can provide for a finite conversion volume. It identifies the electrodynamic mechanisms operating within the corresponding region of space and time, on an optical wavelength and cycle timescale. Based on quantum electrodynamics, this theory identifies specific material parameters that determine the extent and measure of delocalized frequency conversion, and its equations deliver information on the output mode structures. The results also indicate that a system of optimally sized nanoparticles can display a substantially enhanced efficiency of frequency conversion.

Y. R. Shen

Deniz Türkpençe, Alpan Bek, Mehmet Emre Taşgın

We show that, nonlinear optical processes in a plasmonic metal nanoparticle (MNP) dimer can be controlled by the presence of a molecule or a quantum dot. (i) Frequency conversion can be suppressed if the dimer is coupled to a quantum object which is resonant to the generated frequency. This occurs simply because, EIT does not allow an excitation at the converted frequency frequency. (ii) On the contrary, a similar effect can be used to enhance the frequency conversion. Nonlinear processes can be brought to resonance without tuning the dimer modes. Path interference effect cancels the nonresonant frequency terms. Here, we consider the second harmonic generation (SHG) as an example to demonstrate the control mechanism. However, the method can be easily generalized to other nonlinear processes.