Page 414 - Tunable Lasers Handbook

374 Paul Zorabedian

Ucm)
FIGURE 1 3 ECL linewidth versus cavity length dependence. (Reproduced with permission
from Link and Pollock [4l]. 0 1986 IEEE.)

factors [24]. First, it depends on the composition of the gain medium: short-
wavelength (AlGaAs) lasers tend to be more stable, while lasers at 1.3 and 1.5
pm (InGaAsP) are more prone to this type of behavior. Second, it is affected by
the parameters that determine the compound external cavity: the residual facet
reflectance, the external reflectance, and the cavity mode selectivity. Third, the
mode spectrum is strongly dependent on the wavelength to which the laser is
tuned: Multimoding tends to happen at wavelengths falling within periodic
bands occurring at the positions of the residual diode cavity Fabry-Perot modes.

4.5 Output Power

The output power for an ECL at a current I above the threshold current Irh is
given by

L)

where amir the mirror loss for the appropriate external-cavity configuration.
is
Expressions for the threshold current and the mirror loss for the various extemal-
cavity configurations are given in the next section. Typically, output powers in the
range of -1-10 mW in the lowest order transverse mode can be obtained from
external-cavity lasers utilizing narrow-stripe gain media with bulk active regions.
About 30-50% of the free-space output power can be coupled into a single-mode
fiber pigtail. Higher output power can be obtained using quantum-well gain