Tunable laser diodes exploiting the free-carrier plasma-effect are renown for their large tuning range. To control the emission wavelength, carriers are injected into a tuning region inducing a refractive index change. Typically, the material system GaInAsP/InP is used for tuning regions. Since this material shows strong recombination, a large current has to be applied while tuning. Unfortunately, the tuning current causes a parasitic temperature
increase of the device acting negatively in a twofold way. Firstly, the index change due to the temperature increase works directly against the index change that is brought about by the plasma-effect. Secondly, many parameters of the laser device depend critically on temperature. Therefore, a reduction of the current consumption would
instantly improve all relevant device parameters. In this paper we propose a type-II superlattice consisting of Al0.30Ga0.17In0.53As/Al0.50Ga0.50As0.56Sb0.44 as a tuning region. The staggered band alignment leads to a spatial separation of the electrons and holes. As a result, the recombination rate can be significantly reduced by over one order of magnitude, which in turn leads to an increase of the carrier density as a function of the
current. An analysis shows that type-II superlattices can provide an equal tuning range with a reduced current consumption by a factor of six compared to conventional heterostructures.
Tunable filters are indispensable elements for tunable laser diodes, which provide an electronic control of the emission
wavelength by exploiting the free-carrier plasma effect. A tunable filter consists of a combination of tuning region that
forms a waveguide core and a Bragg grating for the wavelength-selective feedback. By injection of carriers into the
tuning region, the refractive index and, thus, the Bragg wavelength can be decreased. Thereby, it is obvious that the
maximum tuning range depends on the achievable carrier density in the tuning region. In this paper, a type-II diode is
presented, which shows an improved carrier density-current characteristic. This is achieved by spatial separation of
electrons and holes, which in turn leads to a suppression of carrier recombination. Since high carrier densities can be
achieved at comparatively low injection currents, type-II superlattices are particularly well suited for application as
tuning region in tunable filters. They have the potential to double the tuning range that is presently achievable using
bulk tuning layers.