Coupled mode equations for couplers with monomodal waveguides

In the single mode case $N_{\mbox{\scriptsize b}}= N_{\mbox{\scriptsize s}} = 1$, Eq.(3.10) is given explicitely [71,34] as

$$\begin{pmatrix}{\sf {M}}_{\mbox{\scriptsize bb}} & {\sf {M}}_{\mb... ...gin{pmatrix}C_{\mbox{\scriptsize b}} \\ C_{\mbox{\scriptsize s}} \end{pmatrix},$$ (3.14)

where the mode index $p=q=1$ is omitted for simplicity.