I. Introduction
Wavelength-tunable semiconductor lasers are important devices in many coherent optical systems, such as optical communication systems, low-noise coherent sensor and optical high spectral resolution LIDAR. Several widely tunable semiconductor lasers, including the sampled grating distributed Bragg reflector (SG-DBR) laser, the modulated grating Y-branch (MGY) laser, and the digital super-mode distribute Bragg grating (DS-DBR) laser, have been successfully demonstrated, with wide tuning range (>40 nm), high side mode suppression ratio (SMSR> 35dB), and large output power (>10dBm) [1]. New structures have been developed as well [2]. For practical applications, reliability characterization for these lasers is very important.