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Most of the environmental gases like H2S, C2H2, CH4, CO(2), N2O and H2O have strong absorption lines within 2-3 µm wavelength range. Detection of these gases requires a spectrally broad, compact, efficient, cost-effective, and high output power light source. Such choice of parameters can be offered by high brightness and broadband superluminescent diodes (SLD). Here we report the development of GaSb-based high power broadband superluminescent diodes (SLDs) emitting around 2.55 μm. The active region consists of two GaInAsSb/GaSb quantum wells. To enable high gain and high output power we adopted a long ridge waveguide (RWG) geometry, i.e. 2.5 mm. The width (5µm) and etching depth (1800 nm) of waveguide was chosen to operate device in single transverse mode. Lasing inside the cavity was suppressed by tilting the waveguide 8° with respect to cavity facets. Recently developed cavity suppression element [1] was employed to further suppress the spectral modulations and smoothen out the spectrum. For operation at long wavelengths, we employed a pulsed driving scheme with sub-µs pulse injection to address temperature dependent non-radiative Auger recombination.
Devices have demonstrated an average output power of more than 3 mW and peak power over 15 mW at room temperature (RT). The maximum full-width at half-maximum (FWHM) of spectrum was ~124 nm, corresponding to 1200 mA drive current. This is the highest power reported to date for 2.55 µm SLDs. For comparison, SLD at 1.90µm emitted a continuous wave (CW) output power up to 60 mW and FWHM of ~ 60 nm [1]. Integration of this high brightness, broadband light sources with SOI-waveguides enables realization of a compact multiple gas sensor in this wavelength range [2].
[1] N. Zia, J. Viheriälä, R. Koskinen, A. Aho, S. Suomalainen, and M. Guina, “High power (60 mW) GaSb-based 1.9 μm superluminescent diode with cavity suppression element,” Appl. Phys. Lett., vol. 109, no. 23, p. 231102, 2016.
[2] P. Karioja, T. Alajoki et al, “Multi-wavelength mid-IR light source for gas sensing”, Proc. SPIE 10110, 2017.
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