Injection locking of mid-infrared quantum cascade laser at 14 GHz, by direct microwave modulation

TLDR: In this paper, an injection locking of the roundtrip frequency of a QCL emitting at 9 μm is reported, where the inter modes laser fre- quency separation is stabilized and controlled by an external microwave source.

Abstract: Compact laser sources operating in mid infrared spectral region with stable emission are important for appli- cations in spectroscopy and wireless communication. Quantum cascade lasers (QCL) are unique semiconductor sources cover- ing mid infrared frequency range. Based on intersubband tran- sitions, the carrier lifetime of these sources is in the ps range. For this reason their frequency response to direct modulation is expected to overcome the limits of standard semiconductor lasers. In this work injection locking of the roundtrip frequency of a QCL emitting at 9 μm is reported. Inter modes laser fre- quency separation is stabilized and controlled by an external microwave source. Designing an optical waveguide embedded in a microstrip line a flat frequency response to direct modu- lation up to 14 GHz is presented. Injection locking over MHz frequency range at 13.7 GHz is demonstrated. Numerical so- lutions of injection locking theory are discussed and presented as tool to describe experimental results.