Improvements in GaInNAs/GaAs quantum-well lasers using focused ion beam post-processing

At the present time, there is a considerable demand for long wavelength (1.3μm-1.5μm) laser diodes for low cost data-communication applications capable of operating at high speed and at high ambient temperatures without the need for thermoelectric coolers. First proposed in 1995 by M. Kondow, the GaInNAs/GaAs material system has attracted a great deal of interest as it promises good temperature performance. The broad gain observed in GaInNAs/GaAs QW samples suggests that wavelength tuning should be possible by the application of gratings to select an optical mode. In addition, splitting the contact has been shown to improve modulation speed in other materials. These two methods should be able to be used jointly and processed together. The use of split-contact lasers has the advantage of that no change is made in the processing steps, since there is only need for a new metal mask to define a new top p-contact. Despite the bandwidth enhancement of two-contact lasers compared to the single contact case is well known, to the authors' knowledge, so far it has not being applied to GaInNAs/GaAs lasers. The use of Bragg-gratings on the ridge waveguide of the laser will generate a periodic modulation inducing an interaction between the forward and backward travelling modes. The effect of this interaction is the one of a band pass filter on the gain shape of the laser, allowing filtering out the actual lasing wavelength, and tuning the lasing wavelength in the range of wavelengths with substantial optical gain. Therefore, this method can be used optimally in lasers with broad gain, as is the case of GaInNAs/GaAs. In this paper, we reveal experimental investigations in how to apply these two post-processing methods to 600m-long 1.25μm-Ga0.66In0.34N0.01As0.0.99/GaAs 6nm single quantum-well ridge waveguide lasers.