Photonic crystal lasers with a high-Q factor and small mode volume are
ideal light sources for on-chip nano-photonic integration. Due to the
submicron size of their active region, it is usually difficult to
achieve high output power and single-mode lasing at the same time. In
this work, we demonstrate well-selected single-mode lasing in a
line-defect photonic crystal cavity by coupling it to the high-Q modes
of a short double-heterostructure photonic crystal cavity. One of the
FP-like modes of the line-defect cavity can be selected to lase by
thermo-optically tuning the high-Q mode of the short cavity into
resonance. Six FP-like modes are successively tuned into lasing with
side mode suppression ratios all exceeding 15 dB. Furthermore, we show
a continuous wavelength tunability of about 10 nm from all the
selected modes. The coupled cavity system provides a remarkable
platform to explore the rich laser physics through the spatial
modulation of vacuum electromagnetic field at submicron scale.