Page 386 - Fiber Bragg Gratings

8.2 Static and dynamic properties ofFGLs 363

Figure 8.5: L-I characteristics (up and down) of large-spot angled facet laser
at 20°C with index-matched gel between laser facet and cleaved fiber end. (Cour-
tesy M. C. Brierley, BT Laboratories.)

is heated along with the laser. Mode hopping may be observed as the
temperature is increased, as shown in Fig. 8.6. The cavity length deter-
mines the magnitude of the wavelength hop, and for this laser, it is —0.16
nm. Note that the overall change in the lasing wavelength is approxi-
mately 0.4 nm for a 25°C change in temperature. With an unheated
grating, the drift in the wavelength is made almost insignificant. The
increased stability of a short-cavity semiconductor laser in an external
long passive cavity has also been demonstrated [11].
5
With an AR-coated front facet reflectivity of 5 X 10~ and a grating
reflectivity of 28%, it has been shown that this type of laser may be

Figure 8.6: Wavelength vs temperature characteristics of the large mode-
field FGL with index-gel. The grating is heated along with the laser chip. (Courtesy
M. C. Brierley, BT Laboratories.)