Tunable Distributed Amplification (TDA-) DFB Laser with Asymmetric Structure

The wavelengths of tunable distributed amplification (TDA) distributed feedback (DFB) lasers consisting of multiple units including an active region and a tuning region can be changed without mode hopping. To expand the tuning range of TDA-DFB lasers, an asymmetric periodic structure is proposed where the units in the cavity have different lengths. It is shown theoretically that the asymmetric periodic structure is effective for expanding the mode-hop-free tuning range. In addition, a tunable laser array was fabricated consisting of six TDA-DFB lasers with an asymmetric periodic structure. A total wavelength tuning range of 44 nm was successfully obtained by expanding the tuning range of each laser, which corresponded to 110 channels with a 50-GHz grid. Moreover, the channel switching speed was investigated in relation to thermal drift. A switching time of less than 40 μs with a frequency deviation of less than 1 GHz was achieved with a thermal drift suppression technique that used the tuning regions of non-lasing lasers as heaters for temperature compensation.