An object of this invention is to cancel a polarization dependence of a transmission
center wavelength due to the waveguide birefringence in an array waveguide and
a slab waveguide in an array waveguide diffraction grating type optical multiplexer/demultiplexer
filter applied for optical communication, particularly, wavelength split multiplexing
system. In order to achieve the object of this invention, a polarization mode convertor
converts the TE mode in a waveguide to the TM mode and the TM mode to the TE mode.
This conversion function makes it possible to cancel the polarization dependence
of the transmission center wavelength due to the waveguide birefringence in the
array waveguide and the slab waveguide in front of and behind the polarization
mode convertor.
