Polarization-resolved linewidth-power product of a vertical-cavity semiconductor laser

We have studied the linewidth around threshold of the lasing and nonlasing polarization mode (x and y) in a TEM00 oxide-confined vertical-cavity semiconductor laser (VCSEL). We experimentally demonstrate: (i) that the nonlasing mode shows surprising behavior when the lasing mode passes through threshold, and (ii) that the polarization fluctuations in a VCSEL are limited by the same quantum noise that sets its finite Schawlow–Townes linewidth.