Patent ID: 8554040

Claim:
A method of designing a wave propagation circuit for obtaining a desired output field from an input field, the method comprising: a refractive-index-distribution initialization step of storing initial values of a refractive index distribution of a propagation medium in the wave propagation circuit, in storage means of a computer; a step of setting an inlet of the wave propagation circuit as an optimized position; a backward-propagation output-field-distribution computation step, performed by the computer, of computing a field distribution in a case where the output field has propagated backward from an outlet of the wave propagation circuit to the input thereof, and storing the field distribution in the storage means of the computer; a forward-propagation optimized-position input-field computation step, performed by the computer, of computing a first field, in a case where the input field has propagated forward from the inlet of the wave propagation circuit to the optimized position, and storing the first field in the storage means of the computer; and a refractive-index-distribution alteration step, performed by the computer, of adjusting the refractive index distribution at the optimized position so that wavefronts of the first field and a second field, in the case where the desired output field has propagated backward, agree; said forward-propagation optimized-position input-field computation step and said refractive-index-distribution alteration step being iterated while the optimized position is being successively changed from the inlet to the outlet along a wave propagation direction, wherein adjusting the refractive index distribution at the optimized position comprises adjusting, at two points on a boundary between a core and a clad in the propagation medium, the refractive index distribution at the optimized position based on a phase difference between a forward propagation field and a backward propagation field, the forward propagation field being a field when the input field is propagated forward from the inlet of the propagation medium to the optimized position, and the backward propagation field being a field when the desired output field is propagated backward from the outlet of the propagation medium to the optimized position, wherein adjusting, at two points on the boundary between the core and the clad in the propagation medium, the refractive index distribution at the optimized position based on the phase difference comprises: increasing the width or height of the core of the propagation medium in the case where the phase difference determined on the boundary is positive; and decreasing the width or height of the core of the propagation medium in the case where the phase difference determined on the boundary is negative.