4. Conclusion

In this chapter an overview in the current state of the art in mid-IR single mode lasers was presented and a low cost laser technology platform based on the InP material system for the manufacture of single mode laser diodes in the near to mid-IR wavelength range introduced. These DM lasers, are ridge waveguide Fabry Perot lasers whose emission spectra have been modified to produce a single mode operation. This modification is achieved during wafer processing by etching surface features into the ridge of an otherwise conventional ridge waveguide laser diode structure and therefore avoiding the need for grating overgrowth [35].

The basic principles underlying DM laser operation and their fabrication have been described. Basic static characteristics of the devices have been discussed and operation in the 1.6–2.1 μm spectral window demonstrated. The results demonstrate that InP-based light sources provide a promising concept for mid-infrared semiconductor diode lasers and are suitable for a range of sensor and other applications.

InP based diode lasers covering the 1.8–2.1 μm range have already reached a considerable level of maturity, as evidenced by the low threshold currents and good spectral performance as highlighted in Section 3. Thus current R&D focuses on the optimization of these lasers towards longer wavelengths >2.3 μm where specific application are in high demand.
