Through investigation of mode-coupling in VECSELs: towards robust dual-frequency operation of a single-axis laser

International audience; The coupling constant C, as defined by Lamb, is an important physical parameter in multimode lasers as it governs the dynamics of coupled modes. In dual-mode lasers, C rules the stability condition as well as the robustness of dual-mode operation. As far as semiconductor disks are considered, a slight spatial separation between the two modes is usually introduced in order to reduce C leading to stringent shaping of the pump. Single axis laser is thus highly desired provided that the coupling constant is reduced or at least its spectral dependence is mastered. In this framework, the use of QD active media is expected to be a way forward as recently predicted theoretically. More recently, we performed the first direct measurement of C and its wavelength dependence in InGaAlAs-QW active medium by embedding the experiment within the laser oscillator itself. Thus, the wavelengths of the two modes can be tuned independently while simultaneous oscillation and perfect spatial overlap of the two modes are maintained. C is found to be significantly high, i.e., C = 0.84±0.02. More importantly, while the cross-to-self-saturation coefficients evolve with respect to wavelength, C is proven to remain constant for mode-frequency-differences ranging from 45 GHz up to 1.35 THz. This major result proves that the coupling constant, originally introduced by Lamb for gas lasers, is still a relevant physical parameter in semiconductor lasers. The reduction of C using lower dimensionality gain structures such as Quantum-Dash and Quantum-Dot active media is under investigation experimentally.