100-GHz spacing 8-channel light source integrated with external cavity lasers on planar lightwave circuit platform

We have successfully fabricated a 100-GHz spacing 8-channel light source using hybrid integration technologies based on planar lightwave circuits (PLCs). The light source was composed of UV-written Bragg gratings and laser diode (LDs) on PLC platforms. To adjust the Bragg wavelength to the ITU-T grid, we used a precise phasemask with eight different pitches. Moreover, to suppress temperature-dependent mode hopping, we tuned the longitudinal mode wavelength so that it became stable by photosensitively modifying the waveguide refractive index in the cavity, which we achieved using an ArF excimer laser, in addition to inserting silicone in the cavity. As a result, we obtained eight lasing wavelengths controlled to those of the ITU-T grids and optical powers of more than 1.5 mW at an injection current of 80 mA without any temperature dependent mode hopping in the 8-channel light source. We also confirmed direct modulation at 2.5 Gb/s in every channel and we showed that we could modulate two adjacent channels simultaneously without any interference effect. These results show that the compact PLC-type integrated light source is promising for use in WDM systems.