Nonlinear Fiber Optics - 4 ed. Agrawal

10.3. Phase-Matching Techniques 381
Figure 10.6: Variation of FWM-generated power at the output of a 3.5-km-long fiber with (a)
input power P 3 and (b) frequency separation. (After Ref. [25]; c○1987 IEEE.)
In part (a), f 3 − f 1 = 11 GHz, f 2 − f 1 = 17.2 GHz, P 1 = 0.43 mW, P 2 = 0.14 mW, and
P 3 is varied from 0.15 to 0.60 mW. In part (b), f 3 − f 2 is varied from 10 to 25 GHz for
P 3 = 0.55 mW, while keeping all other parameters the same.
The generated power P 4 varies with P 3 linearly for the frequency component f 231
but quadratically for the frequency component f 332 . This is expected from the theory of
Section 10.2 by noting that f 231 results from nondegenerate pump waves but the pump
waves are degenerate in frequency for f 332 . More power is generated in the frequency
component f 231 because f 231 and f 321 are degenerate, and the measured power is the
sum of powers generated through two FWM processes. Finally, P 4 decreases with
increasing frequency separation because of a larger phase mismatch. A noteworthy
feature of Figure 10.6 is that up to 0.5 nW of power is generated for input powers