Page 415 - Tunable Lasers Handbook

8 Tunable External-Cavity Semiconductor Lasers 375

media or by going to tapered-stripe gain media. Recently, up to -lW output has
been obtained from an external cavity laser with a tapered-stripe gain medium
[43]. The output beam was described as diffraction-limited. The coupling effi-
ciency to optical fiber was not reported.

5. FEEDBACK MODEL

5.1 Effective Reflectance
The basic model for an extended-cavity laser is based on a 3-mirror com-
pound cavity (Fig. 11). The interior facet of the gain medium and the external
reflector foorm a compound mirror. This compound mirror together with the out-
side facet form a Fabry-Perot resonator. The effective reflectance of the extended
cavity, including multiple reflections from the inside facet, is given by [43]

In a double-ended external cavity. each extended-cavity section has its own
effective reflectance. ~e.,

where i denotes extended-cavity section 1 or 2. The various parameters are defined
in Table 4. The external feedback in a ring cavity is characterized by a wavelength-
dependent coupling strength c&) which gives the fraction of the field amplitude
from facet 1 that is coupled into facet 2. In the absence of nonreciprocal intracavity

FIGURE 1 4 Extended-cavity laser feedback model.