  Single-walled carbon nanotube encapsulated in boron nitrite nanotube
(SWCNT@BNNT) is a novel nanomaterial with a one-dimensional van der Waals
(1D-vdW) heterostructure. In this paper, we demonstrated that the SWCNT@BNNT
has an enhanced optical power tolerance compared to that of the pristine SWCNT
while exhibiting an optical saturable absorption properties. Under optical
power intensity of 13kW/cm2, the lifetime of the SWCNT@BNNT is found to be
2,270 times longer than SWCNT for 1% degradation in absorbance. A short-cavity
mode-locked laser with a high repetition rate of 1 GHz has been realized using
the SWCNT@BNNT as the saturable absorber. We have shown that the technique of
fabricating nanomaterial with a 1D-vdW heterostructure can modify and enhance
the optical properties of the encapsulated nanomaterials.
