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(a) Schematics of the magnetic field distribution ( component) of the two waveguided modes: (i) the dielectric mode confined in the AR and (ii) the SPP mode at the metal-semiconductor interface. (b) The two modes on the same ridge. They are not coupled since the thick ( ) upper cladding prevents the coupling. (c) A thin cladding enables mode coupling, yielding two hybrid modes (one symmetric and one anti-symmetric). They both present a “plasmonic” and a “dielectric” component. The electric field is traditionally employed to describe the laser modes. We plot here the magnetic field instead in order to highlight the symmetric/anti-symmetric character of the modes.
(a) Mode dispersion curves for a real structure with a 250-nm-thick cladding, calculated using a finite elements 1D simulation. The gold index dispersion is taken from Ref. 7 . The dispersions of the uncoupled modes do not cross: the mode coupling induces only slight perturbation, which is best visible in the inset. The advantage is the onset of a hybrid, relatively low-loss mode, which is highlighted by a green point in the inset. (b) Finite elements simulation of the low-loss hybrid waveguided mode for a laser with a 250-nm-thick cladding ( ). The electric field squared modulus is plotted and a 1D cross-section is shown on the left. The maximum of the “plasmonic” component is about 30% of the mode maximum. The propagation loss is .
LJ curves, in pulsed regime (DC = 1%—10 kHz repetition rate, 100 ns pulses), for three ridges with different cladding thicknesses: (green curve), (red curve), and (black curve). Reducing the cladding thickness brings the metal closer to the AR, hence increasing optical losses and laser thresholds. The JV characteristic (dashed black line) is also shown for a device with . (b) Typical laser spectrum (black line) of a device with at an injection current density of . Luminescence spectrum (red line) of a device with at .
(a)–(c): SEM images and NSOM measurement of the facets for threedifferent laser types: (a) , (b) , and (c) . The lasing mode can be clearly identified and positioned with respect to the facet. (d)–(f): Integrated NSOM signal (red lines, integration performed along the y-direction) and square of the electric field (black line) obtained from 2D finite element simulations. The origin of the x coordinate is taken at the metal-semiconductor interface and the curves are normalized. The agreement between experiment and theory is good, taking into account a tip-induced broadening of the NSOM data, which prevents the system from detecting the extremely sharp decrease in field at the metal-semiconductor interface. See also note in Ref. 23 .
Detailed description of the structure, with material, thickness, doping, and optical index of each layer. The AR is grown by metal-organic chemical vapor deposition (MOCVD), while the upper cladding is grown by MBE.
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