638 nm narrow linewidth diode laser with a grating external cavity

In this paper, a narrow linewidth laser with an external grating cavity of 638 nm is described, wherein a reflection holographic grating was used as its external feedback element. The spectrum of the diode lasers with the grating external cavity arranged in a Littrow configuration were measured using a high-resolution monochromator and the characteristics of the threshold and tuning properties were investigated. In the experiment, reflection holographic gratings with 2400 l/mm and 1800 l/mm groove density were studied. At 120 mA injection current, the output power of the external cavity laser was 45.2 mW when the groove density was 2400 l/mm, and the threshold current of the LD was reduced from 60 mA to 51 mA and the descent rate was 11%. When the groove density was 1800 l/mm, the output power was 38.7 mW, the threshold current of the LD was reduced from 60 mA to 47 mA, and the descent rate was 24%. Furthermore, the linewidths were suppressed to within 3.5 pm, and the tuning ranges were 9.4 nm and 10.5 nm in wavelength. The experimental results showed that the performance of semiconductor lasers was improved greatly using the Littrow configuration with a reflective holographic grating.