Mid-Infrared External-Cavity Two-Segment Quantum-Cascade Laser

An external-cavity mid-infrared quantum-cascade laser allows broad and continuous wavelength tuning and modulation when controlled with a combination of grating position and cavity phase on a two-segment optical amplifier chip. The electrically controlled phase segment allows fine wavelength tuning to complement the coarse grating tuning. The 4.8-mum laser was tested with CO gas absorption and wavelength modulation spectroscopy, showing a spectral resolution limited by the laser linewidth of similar to550 MHz, but also allowing sublinewidth modulation of less than or equal to200 MHz. The tuning range from 4.855 to 4.9 mum (0.57 THz) was limited by the device intrinsic gain. (C) 2003 American Institute of Physics.