Ultralow Noise and High-Power VECSEL for High Dynamic Range and Broadband RF/Optical Links

We describe a compact, ultralow noise, and high-power semiconductor laser implemented in a high performances wideband externally modulated optical link. The laser is based on a vertical external cavity surface emitting laser (VECSEL) designed for high-power and low-noise operation. Thanks to a specific design of the gain chip, the half-VCSEL, based on a metamorphic Bragg mirror and a report on a copper substrate, an optical power of 110 mW is obtained at 1.55 μm in the single frequency regime. For low-noise operation, the laser cavity is designed for free-relaxation-oscillations operation, i.e., in the so-called class-A regime. The Class-A VECSEL exhibits a relative intensity noise below -170 dB/Hz over a wide frequency bandwidth, from 300 MHz to 40 GHz, except at the laser free spectral range (20.4 GHz). In the low-frequency range, the laser noise, mainly due to transfer of pump noise to laser noise, goes from -110 dB/Hz at 1 kHz down to -158 dB/Hz at 10 MHz. Two externally modulated optical links are implemented and compared in terms of the RF gain and the noise figure. The first optical link is based on the ultralow noise class-A VECSEL and the second one is based on a low noise class-B DFB laser. Thanks to the outstanding noise properties of the designed VECSEL, the VECSEL-based optical link outperforms the DFB-based one, in particular for frequencies larger than 20 GHz.