Nonlinear Fiber Optics - 4 ed. Agrawal

11.1. Nonlinear Parameter 433
when pulse width is 100 ns), h a (t) can be replaced with a delta
function. The acoustic contribution then attains its maximum value, and the total n 2 is
close to 2.76 × 10 −20 m 2 /W.
It is clear from the preceding discussion that the largest value of n 2 is expected for
measurements performed using CW beams or long optical pulses. The XPM technique
has been used to study the frequency dependence of the electrostrictive contribution
by changing the pump-modulation frequency from 10 MHz to 3 GHz [34]. As seen in
Table 11.1, the measured value is 2.73 × 10 −20 m 2 /W at 10 MHz (pulse width 100 ns)
but is reduced to 2.23 × 10 −20 m 2 /W when the modulation frequency is increased to
2.3 GHz (pulse width