Patent ID: 7978390

Claim:
An optical modulator comprising: an input optical path; an optical splitter for splitting optical signal light input from said input optical path into N optical paths, wherein is an integer of 2 or more; one or more of K-level optical phase modulators arranged in N−1 of said N optical paths; and an optical coupler for interfering output light from said N optical paths with each other in the same polarization state to send out interfered light as an output optical signal to an output optical path, wherein one of said N optical paths has no optical phase modulator and amplitude modulated light having amplitude values which is K raised to the power of N−1 or less, or multilevel amplitude-and-phase modulated light modulated in both the amplitude and phase and having signal points which is K raised to the power of N−1 or less, is output to said output optical path, by interfering output light from the N−1 optical paths having said optical phase modulator with output light from the optical path having no optical phase modulator at the same phase or any phase angles other than ±π/2.