Page 435 - Tunable Lasers Handbook

8 Tunable External-Cavity Semiconductor Lasers 395

UNFILTERED

FIGURE 23 External view ofA0TF

7.2.2.2.3.1 Peak Wavelength The peak wavelength of the transmission
passband Ab is given by

where ua is the acoustic velocity, f, is the acoustic frequency. and An, is the
crystal birefringence. Acousto-optic filters in principle can be made that will
cover an octave of optical frequency. The practical limitation is the rf matching
network for the transducer. Tuning from 1.35 to 1.6 pm with a single device is
definitely possible.

7.2.2.2.3.2 Passband Width The passband width (often called the resolu-
tion) of an acousto-optic filter is given by

h'
s .
Ah nvHh, = -- (65)
L .An
where La is the acousto-optic interaction length. Subnanometer resolution in the
visible and a FWHM of -1 nm at around 1.3 pm have been achieved (Fig. 24)

7.2.2.2.3.3 Diffraction Efficiency The diffraction efficiency is given by