Polarized Near-Field Optical Study of Cavity Modes of Lasing and Amplified Spontaneous Emissions

Abstract

To elucidate the optical coupling nature of near-field scanning optical microscope (NSOM) probes we observed by a NSOM the lasing field of commercial laser diodes (LDs) on their cleaved surface that was expected to be an ideal single TE₀₀ mode and be polarized perpendicular to the probe axis. A clear dark region was observed at the lasing active region of the LD, indicating that the optical probe coupled only the target near-field polarized parallel to the probe's long axis. Many concentric bright rings, detected in the near-field emission profile extending outside of the optical guide layer, should be polarized perpendicular to the TE₀₀ mode, and were ascribed to amplified spontaneous emissions from recombination between an electron and a light hole, based on the symmetry of radiation field. Another possibility was an optical coupling between the optical probe and the laser diode cavity, which might modify the original field distribution inside the laser diode cavity. In both cases the observation suggests that a near-field probe works as a novel tool to manipulate the cavity electromagnetic field, which is a common issue to many applications of cavities made from organic ultrathin films.

Keywords:

• cavity mode
• laser diode
• near field
• non radiating
• NSOM
• quantum well

Acknowledgments

This work was supported partly by the Academic Frontier Promotion Project of the Ministry of Education, Culture, Sports, Science and Technology and partly by the Science Research Promotion Fund of Japan Private School Promotion Foundation. We express our gratitude to Professor Wataru Susaki for the discussions on possible mode field inside the quantum wells and to Professor Hiroyuki Enomoto for assistance on the proper temperature control of the LD chip.