To incorporate vertical-cavity surface-emitting lasers (VCSELs) into polarization-sensitive systems such as magneto-optic disks or coherent detection systems, VCSELs with a single preferential polarization are desirable. Most VCSELs without intentional polarization selectivity show orthogonal polarization states at and above the threshold and unstable polarization switching with increased current. Although researchers have produced a single dominant polarization mode using features such as anisotropic transverse cavities, and even non [001] gallium arsenide (GaAs) structures, changing the dominant polarization mode was impossible once the device was fabricated.
Researchers at the Korea Advanced Institute of Science and Technology and the Electronics and Telecommunications Research Institute (both in Taejon, Korea), working with a colleague at the University of California, Berkeley (Berkeley, CA), have developed a polarization-control method for VCSELs based on a [001] GaAs substrate using electro-optic birefringence. Birefringence was induced at the top distributed Bragg reflector by applying an electric field along the [001] direction. The cavity resonance of the polarized light along the [110] and [110] directions shifted to shorter and longer wavelengths, depending on the direction of the applied field. By varying the direction and strength of the electric field, the scientists actively controlled VCSEL polarization, with the dominant mode in the [110] direction for a negative field and in the [110] direction for a positive field. Contact Byung Tae Ahn at [email protected].