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Research

Photonic Device Modelling

We investigate scattering processes within semiconductor lasers in order to achieve narrow linewidths while minimizing noise. A ridge waveguide with a partially-slotted, high-order grating has been shown to achieve linewidths less than 500 kHz with SMSR values above 50 dB while being ideal for integrating additional photonic devices [1-3]. Utilizing slot dimensions on the order of a micron, we aim for robustness in the laser’s spectral characteristics beginning with the reflectivity and transmission power of the grating. In principle, this robustness will allow fabrication via photolithography. Analysis is undertaken using scattering matrix calculations and subsequently deriving key parameters for implementation within the rate equations or the coupled wave equations in order to accurately predict the spectral and spatial dynamics within the laser cavity.

3D image and 2D schematic utilized for simulations consisting of a slotted section adjacent to a uniform section without slots.

Scattering matrix results for reflectivity as a function of slot spacing and width showing a region of consistent reflectivity.

A sample emission spectrum utilizing a 37th order grating and 24 slots along with the coefficient of photon-carrier noise coupling {3}.

Linewidth for the same grating as a function of slot depth.

References

  1. Q. Y. Lu, W. H. Guo, D. Byrne, and J. F. Donegan, "Analysis of slot characteristics in slotted single-mode semiconductor lasers using the 2-D scattering matrix method," IEEE Photon. Technol. Lett., vol. 18, pp. 2605-2607 (2006).
  2. A. Abdullaev, Q. Lu, W. Guo, M. Nawrocka, F. Bello, J. O’Callaghan, and J. F. Donegan, "Linewidth characterization of integrable slotted, single-mode lasers," IEEE Photon. Technol. Lett., vol. 26, pp. 2225-2228, (2014).
  3. F. Bello, Q. Lu, A. Abdullaev, M. Nawrocka, and J. F. Donegan, “Linewidth and noise characterization for a partially-slotted, single mode laser,” IEEE J. Quantum Electron. vol. 50, 755-759, Sept. 2014.



  4. Nonlinear Optics in Bode-Einstein Condensate Systems

    An investigation of Bose-Einstein condensates (BECs) is undertaken and the conditions under which they exhibit self-trapping phenomena in driven-dissipative systems. Using a modified Gross-Pitaevskii treatment we take advantage of symmetric double wells undergoing asymmetric pumping in order to better control the Josephson current and therefore population distribution. Dissipative effects are known to demonstrate nonlinear phenomena while reducing constraints previously placed on well potential and tunneling strengths. Effective manipulation of BECs is pertinent towards building long-range coherent systems as well as ultrafast optical switches.

    Schematic representing a symmetric, on-resonance double well consisting of a population limit for either well which may be surpassed as the system moves into a self-trapping regime controlled by asymmetrically driven and dissipative methods.

    State maps of normalized well populations showing three stable states of the system as a function of right well decay (γ), left well pumping (g), and tunneling (J). One state exists where the wells are on-resonance considering the blueshift (Son) with equal populations, off-resonance with respect to the blueshift (Soff), or no condensate exists (S0). A region with 2 stable solutions are derived (Son-off) within which self-trapping can occur as a function of initial state conditions while independent on the interaction strength of polaritons.

    References

    1. P. R. Eastham, "Mode locking and mode competition in a nonequilibrium solid-state condensate," Phys. Rev. B, vol. 78, 053319, (2008).
    2. F. Bello and P. R. Eastham, “Dissipative self-trapping in asymmetrically driven Bose-Einstein condensates,” to be published (2015).