Patent ID: 6975781
Filing Date: 2005-12-13
Classification: G02B

Abstract:
1. An adjustment method of characteristics of a multistage Mach-Zehnder interferometer type optical circuit that includes: a first input/output optical waveguide pair; a second input/output optical waveguide pair; M directional couplers disposed between said first and second input/output optical waveguide pairs, where M is an integer equal to or greater than two; and (M−1) phase control means, each of which is disposed between two adjacent directional couplers of said M directional couplers, is attached to at least one of two optical waveguides of the optical waveguide pair placed between said adjacent directional couplers, and controls relative phase of light beams passing through a first optical waveguide and a second optical waveguide of said optical waveguide pair in response to a phase control signal, wherein said adjacent directional couplers, said phase control means disposed between said adjacent directional couplers, and said optical waveguide pairs that are disposed between said directional couplers and have same optical path lengths constitute symmetrical Mach-Zehnder type optical interferometers, whereas said adjacent directional couplers, said phase control means disposed between said adjacent directional couplers, and said optical waveguide pairs that are disposed between said directional couplers and have different optical path lengths constitute asymmetrical Mach-Zehnder type optical interferometers, and (M−1) Mach-Zehnder type optical interferometers are connected in cascade to construct said multistage Mach-Zehnder interferometer type optical circuit, said adjustment method of the characteristics of the multistage Mach-Zehnder interferometer type optical circuit comprising: a first step of sequentially carrying out, for each of said symmetrical Mach-Zehnder interferometers, setting of the phase control signal based on a correlation between the phase control signal of said phase control means disposed in said symmetrical Mach-Zehnder interferometer and optical intensity output from a first optical waveguide of said second input/output optical waveguide pair disposed in an output side of said multistage Mach-Zehnder interferometer type optical circuit, after inputting low coherence light, which has a coherence length shorter than a minimum optical path length difference between said asymmetrical Mach-Zehnder interferometers, from a first optical waveguide of said first input/output optical waveguide pair disposed at an input side of said multistage Mach-Zehnder interferometer type optical circuit; a second step of sequentially carrying out, for each of said asymmetrical Mach-Zehnder interferometers, setting of the phase control signal based on a correlation between the phase control signal of said phase control means disposed in said asymmetrical Mach-Zehnder interferometer and optical intensity output from one of first and second optical waveguides of said second input/output optical waveguide pair disposed in the output side of said multistage Mach-Zehnder interferometer type optical circuit, after inputting wavelength tunable coherent light from one of first and second optical waveguides of said first input/output optical waveguide pair disposed at the input side of said multistage Mach-Zehnder interferometer type optical circuit; and a third step of optimizing the individual phase control signals of said phase control means to achieve a desired characteristic of the output light from said multistage Mach-Zehnder interferometer type optical circuit based on the correlations between the phase control signals and output light intensity obtained at the first step and the second step.