CDMA Techniques in Optical Fiber LANs

Optical detection of optical code division multiple access

“…An F 3 T interleaver is made up of three cascaded directional couplers as shown in with AL being the physical length difference of the differential delays that is associated with the phase of power spectrum 0. n is the refractive index, A the wavelength of the incident light signal, K, (i = 1, 2,3) is respectively the power coupling ratio of the i-th directional coupler that can be expressed in another form given by c* which is the bar-state coupling ratio and Sj is the cross-state coupling ratio. Note that P x3 (9) and Pu (9) are all periodical with respect to 0 or the incident wavelength A, and they satisfy Pn(0) + Pn(B) = 1 (6.36) which is usually referred to as the energy conservative condition.…”

“…Given an unflatness level, the interleaver design problem is reduced to find those coupling ratios to maximize the channel isolation, that is, max{P 13 (0)-P 13 (7r/2)} (6.55) It is obvious that P\ 3 {92) = 1 and ^13(^3) = 1, which means P\ 3 (9) reaches its maximum at 9 = 0 2 and 9 = 9 3 . It is concluded in turn that P\ 3 {9) has a minimum at 9 = 0, otherwise Pu(&) would be flat over [^2,^3] because P\$ (9) has only three stationary points in [-TT/2,TT/2). Therefore, ^P > 0, which completes the proof that o > 0.…”

“…The fact that a > 0 can also be understood as below. Note that the first order derivative of Pn (9) is always zero at 9 = 0 which means Pu (9) has an either convex or concave peak at 9 = 0. The convexity is determined by the second order derivauve dff2 .…”