Di Gaetano, Eugenio

McBrearty, Euan

Paul, Douglas

Sorel, Marc

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Chirped DFB grating for narrow linewidth lasers Eugenio Di Gaetano, Euan McBrearty, Douglas Paul, Marc SorelUniversity of GlasgowLaser Linewidth DFB Laser DesignChirped GratingChirped Grating Simulations Linewidth ResultsTheoretical laser linewidth in semiconductor lasers:Real laser linewidthLine broadening due to the 𝛼𝐻 linewidth enhancement factor which takes into account nonlinear effects, i.e. Longitudinal Spatial Hole Burning (LSHB), at high power.Tuning of the two chirp parameters allows to shape the electrical field distribution inside the grating cavity.The configuration giving the most uniform distribution, i.e. closer to no phase shift grating, is the best for the narrow linewidth at high-power.Under the same fabrication conditions narrower linewidth for chirped device, as narrow as 109𝑘𝐻𝑧 at high-power operation.Δ𝜈 =Γ𝑎𝑐𝑡𝑖𝑣𝑒𝑅𝑠𝑝𝑜𝑛𝑡ℎ𝜈 𝛼𝑖 + 𝛼𝑚 𝛼𝑚 1 + 𝛼𝐻2 𝜈𝑔28𝜋𝑃𝑜𝑢𝑡Sidewall Bragg Grating to generate the laser feedback; side mode suppression ratio (SMSR) exceeding 60𝑑𝐵.Phase shift layer to solve mode degeneracy and allow single mode operation.Longitudinal Spatial Hole BurningLarge fabrication tolerances for the chirp of the grating waveguide (i.e. 10 − 100 𝑛𝑚).Constant average effective index in the chirp region.Critical parameters: chirp length 𝐿𝑐ℎ𝑖𝑟𝑝 and depth 𝜅𝑚𝑖𝑛Phase shift layer modifies the electric field distribution, i.e. field peaked at the phase shift position.Enhanced field non-uniformity which leads to LSHB and linewidth broadening.E. Di Gaetano, M. Sorel, Optics Letters, Vol. 44, No. 7, pp. 1642-1645 (2019)(1993)]

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Chirped DFB Grating for Narrow Linewidth Lasers

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Chirped DFB Grating for Narrow Linewidth Lasers

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