So called “twisted light” has been in the spotlight for the past years in the field of optical communication for the potential to aid in the demand for increased information capacity. This twisted light is attributed to the property of orbital angular momentum (OAM) which, unlike its limited counterpart spin angular momentum (SAM), is unbounded. Higher-Order Poincaré (HOP) spheres have been used to geometrically describe the angular momentum of laser beams that are generated through linear combinations of  two SAM and OAM locked states.  Although this has theoretically been promising, issues have lied in the actual implementation, integration, flexible generation and detection.

FengLab is at the forefront of this research and in 2016 successfully integrated the OAM microlaser on a chip. Research since then has been focused on promoting the design by new physics for scalability and tunability. Phase and amplitude are the two fundamental parameters for the control of any coherent emissions from a laser. It is simple to control these two parameters by bulk optics such as phase plates and attenuators, however, challenging in the micro/nano regime directly at OAM laser sources.  Rather, FengLab strategized a way to generate arbitrary states on a HOPS with desired phase and amplitude through full optical control.

In addition to creating and strategizing the apparatus, characterization of the generated emissions is critical for verification and optimization of the laser design. Given the measurement process and set up has its own set of challenges and limitations, we focused on this aspect of research to attempt to aid in improving the accuracy of the optical measurement setup and methodology. 

Throughout the summer, we used MATLAB to process images of the intensity patterns from a HOPS microlaser to retrieve associated phase and amplitude information. We tested two measurement approaches in order to find the optimal method to accurately acquire the phase difference and power ratios between two spin-OAM locked states. The first approach relied on the tracing of interference maxima and minima to retrieve the phase and amplitude information. The second approach applied Stoke’s polarimetry, a known method to determine the phase difference and power ratio.