We report on the wavelength tuning and spectral properties of distributed feedback (DFB) diode lasers operated with a plane external cavity (XC) mirror positioned as close as possible to the diode-laser front facet. These lasers generate single-frequency near IR radiation at wavelengths of 1392, 1580, 1602, and 1653 nm. A piezoelectric variation of the XC length provided continuous single-frequency tuning to as high as 19 GHz. A further benefit of XC DFB lasers is a residual amplitude modulation per gigahertz tuning of less than 10-3. The XC feedback also suppresses residual side-mode oscillations to less than 60 dB. The laser’s total intensity noise is close to the shot noise limit. The laser linewidth (measured in a beat note experiment) is less than 90 kHz within an acquisition time of 40 ms. The advantageous properties of XC DFB lasers for molecular spectroscopy are demonstrated by recording R(3) 2ν3 overtone spectra of methane by single-scan single-pass absorption or frequency-modulation spectroscopy.
© 2001 Optical Society of America
Original Manuscript: August 31, 2000
Revised Manuscript: January 26, 2001
Published: June 20, 2001
Christian K. Laue, Ralf Knappe, Klaus-Jochen Boller, and Richard Wallenstein, "Wavelength tuning and spectral properties of distributed feedback diode lasers with a short external optical cavity," Appl. Opt. 40, 3051-3059 (2001)