Patent ID: 6987904

Claim:
A variable-optical-delay apparatus comprising: an optical input section; an optical output section; a first optical filter disposed on an optical path between the optical input section and the optical output section; and a unidirectional wavelength shifter disposed on an optical path between the optical input section and the optical filter and configured to adjust an amount by which a wavelength of an input optical signal is shifted in one frequency direction, wherein the input optical signal is repeatedly shifted in wavelength with each pass through the wavelength shifter to produce a shifted input optical signal until the shifted input optical signal has a wavelength that will pass the first optical filter and, after passing the first optical filter, the shifted input optical signal is output from the optical output section as a delayed input optical signal, and a delay time of the delayed input optical signal is determined by an amount the input optical signal is shifted in wavelength by each pass through the wavelength shifter.