Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The nonlinear directional coupler. An analytic solution   Linear and nonlinear directional couplers are currently used in fiber optics
communications. They may also play a role in multiphoton approaches to quantum
information processing if accurate control is obtained over the phases and
polarizations of the signals at the output of the coupler. With this
motivation, the constants of motion of the coupler equation are used to obtain
an explicit analytical solution for the nonlinear coupler.

7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
8
The categories of this paper are: hep-ex
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin