1. Tunable lasers The tunable laser could be set to any desired wavelength either in the factory or in the field by a software command. The performance parameters are:  Power  Spurious mode suppression  Wavelength stability  Life time

2. Development of monolithic tunable diode lasers Significant effort to develop DBR laser marks the develop ment of todays monolithic diode lasers. DBR laser incorporates separate active and passive grating reflector regions.

3. Some works included vertically integrated twin guide structures to separate active and passive DBR regions, but it has inherent limitations. Earlier works were not inteneted for wide tunability but to develop DBR lasers that could be integrated with passive waveguides for monolithic coupling to other integrated optical components.  First concentrated effort to develop monolithic tunable lasers was carried out at Bell Labs. Two and three section tunable DBR laser It provides a tuning range of 5 to 10 nm.

5. New application and the invention of internet demanded more band width and this led to the development of VCSELs and widely tunable lasers. Various configurations employed for thw development of widely tunable lasers are;  Configurations employing two multielement mirrors and vernier tuning enhancement structure  Y-branch configurations SGDBR laser It is the first monolithic device to tune over a wavelength region of 30nm or more.

6. The laser operates at a wave length where a reflection peak from each mirror coincide. Since the peak spacing are different only one pair of peaks can line up at a time. The peaks are spaced by: