  We first experimentally demonstrated a transverse magnetic (TM) mode laser in
a Photonic crystal (PhC) slab structure at room temperature. This study
proposes a PhC nanobeam (NB) cavity to support a high-quality-factor (Q-factor)
TM mode. For a large and complete photonic bandgap, the PhC NB structures
consist of large air holes in a thick dielectric slab. The PhC NB cavity was
optimized numerically for a high-Q-factor TM mode of over 1,000,000 by reducing
the radii of the air holes quadratically from the center to the edge of the PhC
NB. A single TM mode lasing action was observed in an InGaAsP quantum-well
(QW)-embedded optimized PhC NB cavity structure at room temperature via optical
pulse pumping, where the QW layer was lightly etched. We believe that the TM
mode lasers in PhC NB cavities with a lightly etched QW can be good candidates
for a surface plasmon excitation source or a highly sensitive optical sensor.
