Planar lightwave circuit, design method for wave propagation circuit, and computer program

A computer product for automated design of a wave propagation circuit that obtains a desired output field from an input field, the computer product comprising a processor and non-transitory storage means, the computer product being programmed to:

• a) store initial values of a refractive index distribution of a propagation medium in the wave propagation circuit in the storage means;
• b) set an inlet of the wave propagation circuit as an optimized position;
• c) compute 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;
• d) store the field distribution in the storage means;
• e) compute 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;
• f) store the first field in the storage means;
• and
• g) adjust 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 forward, agree, comprising adjust, 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 adjust 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:
• increase 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
• decrease the width or height of the core of the propagation medium in the case where the phase difference determined on the boundary is negative;
• wherein steps e through g are iterated while the optimized position is being successively changed from the outlet to the inlet along a wave propagation direction.

A non-transitory computer-readable storage medium having stored thereon a computer program that, when executed by a computer, performs a method of designing a wave propagation circuit for obtaining a desired output field from an input field, the method comprising:

• a) storing initial values of a refractive index distribution of a propagation medium in the wave propagation circuit in storage means of the computer;
• b) setting an inlet of the wave propagation circuit as an optimized position;
• c) 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;
• d) storing the field distribution in the storage means of the computer;
• e) 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;
• f) storing the first field in the storage means of the computer;
• and
• g) 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 forward, agree, comprising 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 adjust, 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;
• wherein steps e through g are iterated while the optimized position is being successively changed from the outlet to the inlet along a wave propagation direction.