Nanoplasmonic solution for nonlinear optics

Nonlinear optical properties of dielectric waveguides are well known and are widely used in moderntelecommunication systems [1]. However, the fundamental law of diffraction imposes physical limitation for integration of dielectric photonics and semiconductor electronics [2]. A possible way to combine the high speed of a photonic device with the compact size of an electronic device is to produce ananoplasmonic device based on metal waveguides.

The successful solutions can be used for future sustainable technologies. In meantime, nonlinear optics of metal waveguides is not fully understood and is being under investigation in recent years [3].The purpose of our research is to study nonlinear optical properties of gold waveguides embedded intodielectric medium (silicon dioxide) using picosecond laser spectroscopy.

The work includes modeling ofoptical properties of gold waveguides, fabrication of prototype samples, and optical characterization ofsamples using a picosecond laser source.The prototype samples of gold waveguides embedded into silicon dioxide were fabricated at DTUDanchip. A silicon wafer with pre-made 6.5 μm layer of silicon dioxide was used as a substrate and goldwaveguides (films) with the thickness of 35 nm were deposited using the sputter-system (Lesker).

The waveguides have different width in the range of 1 μm to 100 μm. A cladding layer of silicon dioxide ofabout 5 μm was deposited on top of the gold waveguides using the plasma-enhanced chemical vapor deposition (PECVD) method. The quality of samples was inspected using the optical microscope, scanningelectron microscope, atomic force microscope, and ellipsometer.

The ready wafer was diced into several rectangular sliced with the fixed width of 15 mm and the different length from 2 mm to 6 mm for optical characterization in the laboratory.The samples were characterized using the picosecond laser source (NKT Photonics) with the peak wavelength of 1064 nm. The relevant spectra are shown on picture 1.

The red curve corresponds to the reference measurement of the laser spectrum. The green curve is the transmission spectrum for the silicon dioxide cladding. The blue, cyan and magenta curves correspond to the transmission spectra for the gold waveguides with the width of 10 μm and length of 2, 3, and 4 mm.The polarization of laser beam was tuned to match the transverse magnetic mode of surface plasmonpolaritons in the gold waveguides.The propagation loss per unit length and coupling loss for the gold wave guides were calculated.

The average propagation loss was 14 dB/mm and the average coupling loss was 6 dB. The obtained results showed a capability of the prototype samples to guide surface plasmon polaritons and their potential for the further investigation of nonlinear properties.