3.0-μm wavelength-tunable compact light source with 805/1064-nm differential frequency generation using intracavity photon reuse and spectrum shaping techniques

Mid-infrared (mid-IR) light sources operating in the 3-μm waveband are useful photonic devices for the spectroscopic detection of trace gases and biomaterials. In order to achieve efficient mid-IR light emissions with a small footprint, we propose an attractive technique for developing a compact intracavity system that enables the reuse of the photons emitted by the pump source. Periodically poled congruent LiNbO₃(PPCLN) and Nd-YVO ₄crystals were both set in the intracavity. An 805-nm waveband GaAs-based laser diode was used as the signal and pump light sources for differential frequency generation (DFG), since GaAs-based device technology enables the construction of high-power, highefficiency lasers operating in this waveband. We have successfully demonstrated that a 3-μm wavelength-tunable light source using the photon reuse technique is the most effective and compact intracavity system; it possesses useful broadband wavelength tunability characteristics up to approximately 90 nm and offers a small footprint (15 × 30 cm). We obtained high output power of the order of a few milliwatts from the developed light source. In addition, since the optical spectrum shape of the mid-IR light is also important, we propose a useful spectrum shaping technique using a Fabry-Perot (FP) etalon filter included in the intracavity system; we obtained a fine single-peak spectrum in the 3-μm waveband. The developed wavelength-tunable compact intracavity mid-IR light source using the photon reuse and spectrum shaping techniques is attractive for optical communications and biomedical applications.