This paper describes the theory, modelling and design of a simple tunable l
aser with a 15-20 run quasi-continuous tuning range, 30 dB side mode suppre
ssion ratio, 400 kHz linewidth and low variation in output power. Prototype
fabrication has used focussed ion beam etching to modify standard Fabry-Pe
rot structures. The laser has four electrically isolated sections separated
by reflection/scattering sites with power reflectivity of about 1%. Tuning
is achieved by changing the currents to each section and hence altering th
e refractive indices.