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Lasing wavelength in dielectric distributed-feedback lasers with a distributed phase shift
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Paper Abstract

Distributed-feedback waveguide lasers based on Bragg-grating resonators generate ultranarrow-linewidth emission. Oscillation at the center of the reflection band ensures maximum reflectivity, hence minimum laser linewidth. The required μ/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates, thereby placing the resonance and laser emission at a position with lower reflectivity inside the reflection band. This effect is usually incorrectly attributed to fabrication errors. Here we show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in a distributed-feedback channel-waveguide resonator in amorphous Al2O3 on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin2 function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides the desired performance.

Paper Details

Date Published: 7 March 2019
PDF: 6 pages
Proc. SPIE 10896, Solid State Lasers XXVIII: Technology and Devices, 1089615 (7 March 2019); doi: 10.1117/12.2514805
Show Author Affiliations
C. C. Kores, KTH Royal Institute of Technology (Sweden)
N. Ismail, KTH Royal Institute of Technology (Sweden)
E. H. Bernhardi, KTH Royal Institute of Technology (Sweden)
F. Laurell, KTH Royal Institute of Technology (Sweden)
M. Pollnau, Univ. of Surrey (United Kingdom)
KTH Royal Institute of Technology (Sweden)

Published in SPIE Proceedings Vol. 10896:
Solid State Lasers XXVIII: Technology and Devices
W. Andrew Clarkson; Ramesh K. Shori, Editor(s)

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