Integration of mode-hop-free tunable laser array and a semiconductor optical amplifier is most reliable approach to
realize widely tunable lasers. We have developed two types of tunable lasers, one is a thermally tunable DFB laser array
for DWDM tunable transponders, which has shown high power and wide tunability covering Cband or L-band, housing
in compact butterfly packages with robust wavelength locker. Another is a short-cavity DBR laser array for optical burst
switching, whose lasing frequency can be monotonously tuned and locked on the ITU grid within 5 microseconds. Both
lasers have demonstrated superior performances in system experiments.
We have developed highly reliable widely tunable module, whose performances were comparable with fixed-wavelength DFB laser module. To realize wide tunability, 12 l/4-shifted DFB laser array, S-bend waveguides, MMI coupler and an SOA were integrated on a chip. We could achieve 37nm tunability by controlling each chip temperature in the range of 5 to 45°C. High output fiber coupled power of 30mW and very uniform L-I curves out of 12 DFB lasers were achieved even at 50°C. Good quality of lasing spectrum was obtained. Side mode suppression ratio (SMSR) > 45dB. The well-suppressed reflection at chip front facet contributed to the lower noise characteristics, such as RIN < -140dB/Hz and linewidth < 4MHz. The shift of locked frequency was less than 0.4GHz as the case temperature varied from -5 to 75°C. Very small frequency shift was realized by controlling the temperature of locker part, independently. By optimizing TEC design, we could achieve low TEC power consumption less than 4W under Tcase=75°C and the end of life condition of SOA current. The new function by incorporating SOA was VOA. By changing the operating SOA current, we could vary output power from 1mW to 20mW, maintaining SMSR > 40dB, RIN < -135dB/Hz, linewidth < 4MHz. We also performed optical blocking > 40dB, when SOA current was turned off. We examined modules reliability under high temperature storage of 85°C. The change of output power was < ± 10%, and the shift of locked frequency was < ± 5pm after 2000 hours.
A novel approach of on-wafer wavelength control for vertical cavity surface emitting lasers (VCSELs) is proposed using nonplanar metalorganic chemical vapor deposition. The resonant wavelength of 980nm VCSELs grown on a patterned substrate can be controlled in the wavelength range over 45nm by changing the size of circular patterns. We have fabricated linear and 2D multiwavelength vertical surface emitting laser (VCSEL) arrays fabricated by using this technique. The threshold of multi-wavelength VCSELs formed on the patterned substrate is as low as 3 mA. A possibility of an extremely large wavelength span for multi- wavelength arrays will be discussed. The proposed method will be useful for multi-wavelength VCSEL arrays as well as for the cancellation of wavelength nonuniformity across a wafer.