Polarization filter with intermediate optical waveguide which is monomodal for one polarization and bimodal for the other

Claim 1

A polarization filter for filtering an optical signal entering via a monomodal input channel and containing both the TE and the TM polarization modes to produce an optical signal emerging via a monomodal output channel and exclusively containing, at least essentially, one of said two polarization modes, the polarization filter comprising an input section including a first incoming monomodal optical waveguide and a second incoming monomodal optical waveguide which mutually converge to within their interaction range and have a difference in propagation constant as a consequence of a mutual first asymmetry, an output section including a third, outgoing monomodal optical waveguide, and an intermediate optical waveguide, at the input of which the first optical waveguide and second optical waveguide debouch and at the output end of which the third optical waveguide is connected, characterized in that the intermediate optical waveguide is monomodal for one of said polarizations and bimodal for the other, said mutual first asymmetry between the first and second waveguide is of the same sign for both of the polarization modes, the optical waveguide having the lowest propagation constant forming said monomodal input channel, and the output section includes a fourth, outgoing monomodal optical waveguide which is connected at said output end of said intermediate optical waveguide and which mutually diverges from said third waveguide at least to a location outside the interaction range of said third and fourth waveguides, said third and fourth waveguides having a difference in propagation constant as a consequence of a mutual second asymmetry, which is of the same sign for both of the polarization modes, the optical waveguide having the lower propagation constant forming said monomodal output channel.