Semiconductor lasers, in particular Quantum Cascade Lasers (QCLs) are tunable especially in the mid-IR spectral range, e.g. in wavelengths of about 3 - 14µm, by precisely controlling the laser's temperature in the vicinity of the active region. The present invention introduces a novel design for locally heating the active region, thereby allowing fast heating and thus tuning a laser. It is generally applicable for lasers across the field, e.g. to QCLs with multi-color emitters or to Vertical-Cavity Single-Emitter Lasers (VCSELs) or to Distributed Feedback (DFB) lasers. In multi-emitter lasers, a resistor can be associated with each emitter section to tune the temperature of each section and thus its emitted wavelength. Similarly, in multisection DBR lasers, with a resistor associated with each grating, the latter can be tuned and thus the associated wavelength of the optical cavity. In case of a stripe-like buried heterostructure laser diode, on a substrate (11) a stripe-like active region (12) is created by etching with an adjacent insulating burying Fe:InP layer (15). On top a cladding (13), a contact layer (17) and a Au electrode (18) are positioned. Cladding and contact layer and electrode are structured by etching resulting in a larger portion (17a,18a) above the active layer stripe providing the bias current for the LD and a portion (17b,18b) adjacent to the active stripe for providing a tuning current by locally heating via the cladding layer. The resistance of the cladding layer may be increased to result in local heating by structuring or a dopant distribution.
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