Narrowing the linewidth to a desired value with a reflecting volume-Bragg-grating (RVBG) for high-powered LDs

In recent years, reflecting volume-Bragg-gratings (RVBGs) have been considered as the perfect elements to narrow the spectrum with highly adjustable parameters. In fact, the effects of narrowing the linewidth of high-powered LDs are determined by the parameters such as the grating thickness, refractive index modulation, and grating spatial frequency. By use of the theoretical regime, the relationships between the effective diffraction efficiency and these parameters of a RVBG have been systematically investigated to narrow the linewidth to a desired value. Although the results reveal that a higher effective diffraction efficiency may be achieved by adopting three parameters mentioned above with higher values, by considering the difficulties and confinement in production process of a RVBG, the characteristic parameters should be carefully selected as some appropriate values. From the evaluation, one also understands that the narrow linewidth of a RVBG-coupled LD and the high effective diffraction efficiency cannot be arbitrarily realized at the same time for a real case. The conclusions are thought to be valuable in construction of a practical narrow linewidth LD system.