Integrated Nonlinear Optics
There is nothing truly linear about this world. After all, linearity is usually only approximately true within a tiny region of parameter space. For example, light matter interaction at low light intensities is typically described as linear. However, there exists rich nonlinear optical processes that are usually less prominent due to the difficulty in observing them. Nevertheless, there are materials and conditions under which these nonlinear light-matter interactions can be significantly enhanced. Here at QTE, we seek to enhance these nonlinear interactions that are widely used in lasers, spectroscopy, imaging, and quantum optics.
High light intensity is a key requirement for obtaining significant light-matter interaction. This can be achieved by confining light into a small area, which we accomplish by developing structures that have transverse dimensions of the order of a few hundred nanometers (nm), which is roughly one-hundredth times the size of a human hair (you can have hundred such devices inside your hair!), and lengths of a few millimeters. These structures are designed and fabricated by us to have both high coupling and waveguiding efficiencies with minimal losses, and to sustain efficient nonlinear light-matter interaction that grows along the length of the structure. Achieving these three properties simultaneously is non-trivial, and we have pushed the limits of physics and engineering over the last few years to demonstrate some of the highest efficiencies and performances in these devices. This research has been done collaboratively with the Institute of High-Performance Computing, A*STAR.
We also work with a type of flat-optic metasurface that is only hundreds of nm thick and about a hundred micrometer wide. In these structures, high quality factor resonances are responsible for creating high light intensity. Since light is hardly propagating through these structures, only one parameter needs to be optimized – the quality factor of the resonance. In general, increasing the light intensity results in more efficient nonlinear interactions. We have to date demonstrated one of the highest nonlinear conversion efficiencies in such metasurfaces. These thin metasurfaces are very attractive for a wide array of optical applications since they can be easily integrated with or even replace existing bulk lenses and optics. For this work, we collaborate with our colleagues in the Advanced Optical Technologies department at the Institute of Materials Research and Engineering, A*STAR.