COUPLED WAVEGUIDE STRUCTURE

摘要

PROBLEM TO BE SOLVED: To provide the coupled waveguide structure which has no polarization dependence and is easier to manufacture. SOLUTION: On a InP substrate 10, two InGaAsP rectangular waveguides 12 and 14 are formed across a gap (d). Over both the waveguides 12 and 13, a diffraction grating 16 having cyclesΛare formed to a necessary distance L. The cyclesΛof the diffraction grating 16 are so set as to meet phase matching conditions:|β1(TE)+β2(TE)|=K|β1(TM)+β2(TM)|=K where K(=2π/Λ) is the wave number of the diffraction grating 16,β1(TE) andβ2(TM) are the propagation constants of the TE mode and TM mode of the waveguide 12. For the purpose, a1=b2 and b1=a2 ideally hold for the width a1 and thickness b1 of the waveguide and the width a2 and thickness b2 of the waveguide 14.