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

C. C. Kores; N. Ismail; E. H. Bernhardi; F. Laurell; M. Pollnau

doi:10.1117/12.2514805

7 March 2019 Lasing wavelength in dielectric distributed-feedback lasers with a distributed phase shift

C. C. Kores, N. Ismail, E. H. Bernhardi, F. Laurell, M. Pollnau

Proceedings Volume 10896, Solid State Lasers XXVIII: Technology and Devices; 1089615 (2019) https://doi.org/10.1117/12.2514805
Event: SPIE LASE, 2019, San Francisco, California, United States

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.

Citation Download Citation

C. C. Kores, N. Ismail, E. H. Bernhardi, F. Laurell, and M. Pollnau "Lasing wavelength in dielectric distributed-feedback lasers with a distributed phase shift", Proc. SPIE 10896, Solid State Lasers XXVIII: Technology and Devices, 1089615 (7 March 2019); https://doi.org/10.1117/12.2514805

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KEYWORDS

Phase shifts

Resonators

Waveguides

Refractive index

Laser resonators

Optical design

Bragg gratings

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