Compact sub-mW mid-infrared DFG laser source using direct-bonded QPM-LN ridge waveguide and laser diodes

Abstract

We report compact sub-mW mid-infrared (IR) laser sources based on difference frequency generation (DFG) in a quasiphase matched (QPM) LiNbO 3 (LN) waveguide directly pumped with two laser diodes (LDs). The mid-IR lasers operate in the cw mode at ambient temperatures, and can be used for the tunable diode laser absorption spectroscopy (TDLAS). To construct the mid-IR laser sources, we employed a fiber-pigtailed wavelength conversion module, which we spliced to a direct-bonded QPM-LN ridge waveguide by using the V-groove connection technique. The modules had high external conversion efficiencies of 10 and 16 %/W for 3.4 and 2.6 mm, respectively. The signal was obtained from a 1.55-mm-band distributed feedback (DFB)-LD, and the pump from a single-mode LD stabilized with a fiber-Bragg-grating (FBG). We used 1.064 and 0.976-mm pump LDs for 3.4 and 2.6-(micron)m generation, respectively. The two LDs and the wavelength converter were assembled with a polarization maintaining fiber, and then packaged in a box. We obtained high outputs of up to 0.20 mW for the 3.4-mm laser source and 0.33 mW for the 2.6-mm laser source, and detected CH 4 and H 2 O absorption lines with the 3.4 and 2.6-mm laser light sources, respectively.