Study On Grating External-Cavity Semiconductor Lasers

The article is about external cavity semicinductor laser (ECSL) . Based on the principle of semiconductor laser and the characteristics of threshold current, space model,and spectral line width, the rate equation under the condition of strong feedback and the oscillations of the grating external cavity semiconductor laser are studied. And then the characteristics of mode selection,linewidth reduction,and wavelength tuning are discussed. The semiconductor laser, collimating len and blazed grating are also selected,and the ECSL's driving circuit, temperature control circuit and the principle of F-P cavity spectrum analyzer are briefly introduced. The Littrow-type grating external cavity semiconductor laser is set up, and realizes the laser output. At the highest working current of 80mA, the output power can reach 2.5mW,and divergence angle is 4.2×10^-2 mrad. The threshold current of ECSL is compared with that of the original semiconductor lasers. After the external cavity's feedback, the threshold current decline to 27.5 mA. Rotating of the blazed grating's angle can greatly reduce the line width, and realize the wavelength tuning.