A bidirectional guided optical router comprising an evanescent-field optical coupler having three input ports (Pa, Pe, Pf), three output ports (Pb, Pc, Pd), a first central single-mode waveguide connecting the first input port (Pa) and the first output port (Pb), a second lateral single-mode waveguide connecting the second input port (Pe) and the second output port (Pc), and a third lateral single-mode waveguide connecting the third input port (Pf) and the third output port (Pd), said optical coupler comprising an evanescent-field optical coupling zone in which said first, second and third waveguides (31, 32, 33) are arranged parallel to each other, said second and third lateral waveguides (32, 33) being arranged symmetrically with respect to the first central waveguide, and the distance d between, on the one hand, the first central waveguide and any one of the second and third lateral waveguides being lower that a predetermined distance to allow an evanescent-field coupling between the first central waveguide and any one of the second and third lateral waveguides (32, 33) in the optical coupling zone, characterized in that: the evanescent-field optical coupling zone of the evanescent-field optical coupler has a coupling length L comprised between 1.3154 x L eq and 2 x L eq, where L eq represents the length of equidistributed-power coupling for a reference evanescent-field optical coupler with three input ports and three output ports, having the same distances between waveguides and in the same conditions of beam wavelengths and of temperature, in such a way that, for said coupling length L, an optical beam coupled at the first input port (Pa) having a power p and propagating in the first central waveguide in the forward direction is split into a first secondary beam having a power higher than or equal to 90 % of p/2 at the second output port (Pc) and another secondary beam having a power higher than or equal to 90 % of p/2 at the third output port (Pd), and in that said first, second and third waveguides (31, 32, 33) go away from each other outside the optical coupling zone between each of the input ports (Pa, Pe, Pf) and the optical coupling zone and, respectively, between the optical coupling zone and each of the output ports (Pb, Pc, Pd), said first, second and third waveguides (31, 32, 33) being adapted to collect and guide in separated waveguides (31, 32, 33) optical beams in symmetric mode and anti-symmetric mode propagating in the forward direction between the optical coupling zone and each of the output ports (Pb, Pc, Pd) and, respectively, to collect and guide in separated waveguides (31, 32, 33) optical beams in symmetric mode and anti-symmetric mode propagating in the reverse direction between the optical coupling zone and each of the output ports (Pa, Pe, Pf). the evanescent-field optical coupling zone of the evanescent-field optical coupler has a coupling length L comprised between 1.3154 x L eq and 2 x L eq, where L eq represents the length of equidistributed-power coupling for a reference evanescent-field optical coupler with three input ports and three output ports, having the same distances between waveguides and in the same conditions of beam wavelengths and of temperature, in such a way that, for said coupling length L, an optical beam coupled at the first input port (Pa) having a power p and propagating in the first central waveguide in the forward direction is split into a first secondary beam having a power higher than or equal to 90 % of p/2 at the second output port (Pc) and another secondary beam having a power higher than or equal to 90 % of p/2 at the third output port (Pd), and in that said first, second and third waveguides (31, 32, 33) go away from each other outside the optical coupling zone between each of the input ports (Pa, Pe, Pf) and the optical coupling zone and, respectively, between the optical coupling zone and each of the output ports (Pb, Pc, Pd), said first, second and third waveguides (31, 32, 33) being adapted to collect and guide in separated waveguides (31, 32, 33) optical beams in symmetric mode and anti-symmetric mode propagating in the forward direction between the optical coupling zone and each of the output ports (Pb, Pc, Pd) and, respectively, to collect and guide in separated waveguides (31, 32, 33) optical beams in symmetric mode and anti-symmetric mode propagating in the reverse direction between the optical coupling zone and each of the output ports (Pa, Pe, Pf).