Ultra-low threshold and spontaneous emission control in semiconductor microdisk lasers

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We obtained the following achievements on microdisk lasers :1. Ultra-small cavity : The injection lasing was obtained in 2-μm-diameter and 0.2-μm-thickness GaInAsP microdisk. The cavity volume is 0.4 μm^3. Although this value is larger than that achieved in a single defect photonic crystal laser, it is still the smallest for injection lasers. Such a small cavity provides various evidences of the spontaneous emission control.2. Ultra-low threshold : I_<th>=40μA was achieved under cw condition, the lowest record for GaInAsP lasers. The effective J_<th> is 320 A/cm_2 (80 A/cm_2 per QW). Key issues for lower threshold are the reduction in scattering loss caused by the roughness in the microdisk, and the balance between the carrier diffusion and the scattering loss at post edges. A threshold less than 10 μA and internal efficiency higher than 50 % will be possible by the engineering of whispering gallery modes, free carrier absorption, strain relaxation in QWs, etc.3. Fragileness : This wil … More l be a problem in future applications. To satisfy both the mechanical strength and optical confinement, a microdisk buried by the selectively oxidized AlInAs claddings was proposed. The depth and the optical absorption in the oxidized claddings are key issues to be investigated.4. Strong optical confinement : The low threshold is obtained by the total internal reflection at microdisk boundaries, which is unsuitable for light extraction. The evanescent coupling of microdisk elements was investigated by the FDTD simulation. Over 60 % extraction efficiency is expected by the <0.3 μm space between the microdisk elements.5. Evanescent field spreading around the microdisk : This feature can be used in a near field probe sensor. The lasing characteristic is modulated by the surface profile of an object put close to the microdisk. A spatial resolution of 〜λ/10 were expected theoretically and experimentally. The scanning microscopy against metal and dielectric objects was demonstrated by the use of this active probe. Less