The
plasmonic nanolaser is a class of lasers with the physical
dimensions free from the optical diffraction limit. In the past decade,
progress in performance, applications, and mechanisms of plasmonic
nanolasers has increased dramatically. We review this advance and
offer our prospectives on the remaining challenges ahead, concentrating
on the integration with nanochips. In particular, we focus on the
qualifications for electrical pumping, energy consumption, and ultrafast
modulation. At last, we evaluate the strategies for on-chip source
construction design and further threshold reduction to achieve a long-term
room-temperature electrically pumped plasmonic nanolaser, the ultimate
goal toward practical applications.
InP/GaInAsP square-resonator microlasers with an output waveguide connected to the midpoint of one side of the square are fabricated by standard photolithography and inductively-coupled-plasma etching technique. For a 20-mum-side square microlaser with a 2-mum-wide output waveguide, cw threshold current is 11 mA at room temperature, and the highest mode Q factor is 1.0x10(4) measured from the mode linewidth at the injection current of 10 mA. Multimode oscillation is observed with the lasing mode wavelength 1546 nm and the side-mode suppression ratio of 20 dB at the injection current of 15 mA.
We derive formulas for the optical confinement factor Γ from Maxwell’s equations for TE and TM modes in the slab waveguide. The numerical results show that the formulas yield correct mode gain for the modes propagating in the waveguide. We also compare the formulas with the standard definition of Γ as the ratio of power flow in the active region to the total power flow. The results show that the standard definition will underestimate the difference of optical confinement factors between TE and TM modes, and will underestimate the difference of material gains necessary for polarization insensitive semiconductor laser amplifiers. It is important to use correct optical confinement factors for designing polarization insensitive semiconductor laser amplifiers. For vertical cavity surface-emitting lasers, the numerical results show that Γ can be defined as the proportion of the product of the refractive index and the squared electric field in the active region.
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