Polarization Couplers: Rocking Filters 1 0.8 Transmission A 0.6 0.4 0.2 0 ­0.02 B C Tx (kL = pi/2, 2L) C Tx (kL = pi, L) B Tx (kL = pi/2,L) A 145 ­0.01 0.00 0.01 0.02 Normalized detuning, ( l B - l )/l B Figure 4.9 Cross-coupled transmission for codirectional coupling. The data shown is for coupling constants of p/2 with a grating length of L (curve A) and length 2L (curve C). The bandwidth is halved for the longer grating. Also shown is data for kL ¼ p and grating length L (curve B). Note that the grating overcouples at zero detuning. The transmission spec- tra of LPGs are identical to that shown above for each of the cladding modes to which the guided mode couples. The difference between reflection as in contradirectional coupling and codirec-