Efficient coupling of complex light fields to multi-mode waveguide chips

Abstract

Photonics is a promising area to solve challenges in telecommunications. In photonics modes can act as communication channels.The aim of this bachelor's thesis is to create an interface between free-space modes and waveguide eigenmodes. We want to couple the generated waveguide modes into multimode waveguide chips form VTT. We study how well the generated modes match the calculated eigenmodes of the waveguides and how well the modes couple to the multimode waveguides.

At first we discuss the theory of the modes for both free-space and waveguides starting from the Helmholtz equation. We consider the free-space solutions Laguerre-Gaussian and Hermite-Gaussian modes and discuss the how to numerically calculate the eigenmodes of waveguides. In the second half of theoretical background we discuss the methods to implement an interface between free space modes and waveguide modes. In this part we introduce spatial light modulators and multi-plane light conversion.

The experiments are performed with an optical setup using multi-plane light conversion to transform the free-space modes to the eigenmodes of the waveguide. To conduct multi-plane light conversion, we are using a spatial light modulator. The alignment of the setup requires a lot of precision and, hence, the important aspects of the alignment will be described in detail.

The results are obtained by processing the recorded camera images using MATLAB. From the measured results we can notice significant coupling of the generated modes to the eigenmodes of the waveguide. We can see also clear correlations between how well the eigenmodes couple compared with how well the modes are created.