[OPTICAL REVIEW Vol. 8, No. 6 (2001) 451-458]
Wavelength Tuning Characteristics of a Fabry-Perot Semiconductor Laser with an External Short Cavity
Masakatsu OKADA1,*, Bijan GHAFARY1,2 and Hiroo UKITA1
1Department of Photonics, Ritsumeikan University, 1-1-1, Noji-Higashi, Kusatsu, Shiga, 525-8577 Japan
(Received April 19, 2001; Accepted July 25, 2001)
Wavelength tuning characteristics of a Fabry-Perot semiconductor laser with an external short cavity are analyzed, in which the oscillation wavelength can be changed by slightly altering the external cavity length. Analysis is based on rate equations for an optical power and carrier density. It is shown that the wavelength tuning range is dominated by a change of carrier density through the effect of carrier-induced refractive index change in the active layer of a laser diode. This depends on effective coupling coefficients of the optical field iteratively reflected back to the laser diode by the external mirror, and on reflection coefficients of an anti-reflection coated laser facet and the external mirror which compose the external cavity. The effective coupling coefficient is also derived using the waveguide theory and Kirchhoff's theory. Finally, an unstable condition which may limit a stable wavelength tuning range is shown by results of a linear stability analysis of rate equations.
Key words : tunable laser diode, short coupled cavity, coupling coefficient of reflected optical field, tuning range, carrier-induced refractive index change, stability analysis