Abstract
We image in near-field the transverse modes of semiconductor distributed feedback (DFB) lasers operating at λ ≈ 1.3 μm and employing metallic gratings. The active region is based on tensile-strained InGaAlAs quantum wells emitting transverse magnetic polarized light and is coupled via an extremely thin cladding to a nano-patterned gold grating integrated on the device surface. Single mode emission is achieved, which tunes with the grating periodicity. The near-field measurements confirm laser operation on the fundamental transverse mode. Furthermore--together with a laser threshold reduction observed in the DFB lasers--it suggests that the patterning of the top metal contact can be a strategy to reduce the high plasmonic losses in this kind of systems.
Highlights
Semiconductor lasers have become essential tools for fiber-optic communications, optical sensing and photonics [1, 2]
An alternative strategy – which suits lasers operating in transverse magnetic (TM) polarization - consists in patterning the device top metal electrode into a 1st-order metal grating
The laser design we have developed for this study is inspired from long mid-infrared quantum-cascade laser (QCL) devices (λ ≈7.5 μm) featuring a 1st order metal grating patterned on the top metal electrode [8,10]
Summary
Semiconductor lasers have become essential tools for fiber-optic communications, optical sensing and photonics [1, 2]. DFBs are typically realized by periodically structuring the semiconductor cladding close to the laser active region (AR) [4], or by adding a laterally coupled metallic grating [5,6,7] In the latter case, which suits well devices operating in transverse electric (TE) polarization, a metallic grating is implemented laterally to a ridge laser: it couples evanescently with the laser guided modes, yielding a complex-coupled DFB laser. In the mid-infrared, it was shown that patterning the metallic layer leads to the onset of an extremely low-loss mode The extension of this concept to the near-IR would be of importance, because it would provide a possible strategy to overcome the huge ohmic losses in plasmonic systems via metal patterning. Its field distribution analysis allows us to elucidate the action of the metallic patterning
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