A genetic algorithm is developed with a view to optimizing surface-etched grating tunable lasers over a large optimization space comprised of several variables. Using this approach, a new iteration of slotted lasers arrays are optimized showing significant improvements over previous designs. Output power, lower grating order, fabrication tolerance and performance at high temperatures are among key parameters improved. The new designs feature a much lower grating order (24-29) than used previously (37). The biggest improvement is a near doubling to slope efficiency to 0.1-0.13 mW/mA, with wavelengths from the array covering the C-band . The designs show a reduced sensitivity to etch depth variations. Designs with linewidths down to 100 kHz are also simulated. This algorithm can be readily applied to different wafer materials to efficiently generate slotted lasers designs at new wavelengths.

Athermalisation is a procedure in which the wavelength of a semiconductor laser remains unchanged even as the temperature is altered. This is achieved by altering the currents that flow through the laser so as to maintain the wavelength and avoid mode hops. In this study, we demonstrate that lasers operating with a large red-shift with respect to the gain peak yield the best performance in terms of the highest temperature operation and also in terms of the widest athermal operating range. In particular, a device with red detuning of approximately 25 nm yields the best results. This device is athermalised continuously (without mode hops) from 5 to 106 o C, and discontinuously to 115 o C while maintaining wavelength stability of ± 0.4 GHz/0.003 nm and side mode suppression ratio of above 40 dB in most of the continuous range and above 30 dB in the discontinuous regime. Operating in this manner will enable semiconductor lasers to be used without a thermoelectric cooler in applications where the temperature changes substantially.

We incorporate thermal effects for injection currents ranging up to 150 mA in order to model the tuning behavior of a two-section, all-active distributed-Bragg-reflector (DBR), ridge-waveguide semiconductor laser utilized for a single-mode operation. In particular, we investigate wavelength tuning as a function of injected currents within the grating and phase/gain sections of the laser cavity and examine how any athermal lasing conditions may arise. The effect of thermal drift on the resonant wavelength due to a change in refractive index as well as thermal expansion of the laser cavity is included within a traveling wave analysis (TWA). From the TWA, the spatial distribution of gain along the active region of the laser is also derived in order to help describe the tuning behavior for a high-order (37th) grating previously optimized to minimize linewidth. A comparative analysis with a single mirrored, active-passive DBR laser is also included. Results show a good agreement with reported experimental data and compare well with the wavelength stability of other laser devices.

Two twelve-channel arrays based on surface-etched slot gratings, one with non-uniformly spaced slots and another with uniformly spaced slots are presented for laser operation in the O-band. A wavelength tuning range greater than 40 nm, with a side-mode suppression ratio (SMSR) > 40 dB over much of this range and output power greater than 20 mW, was obtained for the array with non-uniform slots over a temperature range of 15 °C - 60 °C. The introduction of multiple slot periods, chosen such that there is minimal overlap among the side reflection peaks, is employed to suppress modes lasing one free spectral range (FSR) from the intended wavelength. The tuning range of the array with uniformly spaced slots, on the other hand, was found to be discontinuous due to mode-hopping to modes one FSR away from the intended lasing mode which are not adequately suppressed. Spectral linewidth was found to vary across devices with the lowest measured linewidths in the range of 2 MHz to 4 MHz.