ORCID Identifier(s)


Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Electrical Engineering


Electrical Engineering

First Advisor

Michael Vasilyev


We investigate spatial-mode-selective frequency up-converters in ?(2) multimode waveguides for classical and quantum communication. For the classical application, our method works as spatial-mode de-multiplexer for mode-division-multiplexing (MDM) communication system. For the quantum application, mode-selective quantum frequency conversion (QFC) enables multidimensional quantum encoding (qudits rather than qubits) which could eventually contribute to higher capacity of quantum communication links (higher QKD rates). First, we numerically investigate mode-selective up-conversion in a slab waveguide (2D free space) and periodically-polled KTP (PPKTP) waveguide. A 2D slab waveguide model is proposed based on non-collinear sum frequency generation (SFG). This model enables the calculation of conversion efficiencies of various spatial modes of the 2D slab waveguide by performing singular value decomposition (SVD) of Green’s function. Next, the PPKTP waveguide is investigated to achieve mode-selective up-conversion. By proper tailoring of waveguide dimensions and quasiphase-matching (QPM) period, we found two interesting scenarios. First scenario has application in image up-conversion, where a single pump mode simultaneously up-convert many signal modes. At the second scenario, a pump mode up-converts only a specific signal mode without disturbing the rest of the modes, while simultaneously another pump mode up-converts another signal mode. The second scenario can be used for spatial-mode de-multiplexing, where any superposition of two signal modes can be selectively up-converted by the corresponding superposition of pump modes, while leaving the orthogonal signal superposition unperturbed. Then, we implement the second scenario in periodically-poled lithium niobate (PPLN) waveguides, custom-made for us by Dr. Carsten Langrock in Prof. Martin Fejer’s group at Stanford. Using these PPLN waveguides, we demonstrate four proof-of-concept experiments with different types of signals. The different signal types used for our experiments are continuous-wave (CW) classical (medium-power) and single-photon-level signals, 10-GHz data-modulated signal, and two-mode signal transmitted through a few-mode-fiber (FMF). To prove whether our method is suitable for the quantum application, we first demonstrate mode-selective up-conversion with CW classical signal and extend it to single-photon-level signal. For classical signals, we have observed conversion efficiency > 70% and crosstalk < –16 dB. For single-photon-level signals, we have observed conversion efficiency > 74%, crosstalk < –12 dB, and background noise at least 100 times lower than the signal. To prove that our method is suitable for the classical application in MDM communication system, we demonstrate mode-selective up-conversion with 10-GHz data-modulated two-mode signal, yielding < 2.5 dB crosstalk penalty at the 10–9 bit error rate level, as well as with a two-mode signal transmitted through an FMF, yielding > 46% conversion efficiency and < –14 dB crosstalk. Our mode selection is performed by choosing the pump spatial profile and can be reconfigured at ~50 Hz rate. With several QPM gratings, the mode-selective up-conversion can be extended to a larger mode space and used for dynamically reconfigurable mode de-multiplexing.


sum frequency generation, quantum frequency conversion (QFC), PPLN, nonlinear waveguide, mode-division-multiplexing, spatial light modulator (SLM), parametric interaction.


Electrical and Computer Engineering | Engineering


Degree granted by The University of Texas at Arlington