Patent ID: 7555216

Claim:
An optical communications system using optical codes, characterized by: an optical transmitter which: emits from a light source an optical signal having an optical frequency width FSR contained in an optical frequency range from a predetermined optical frequency Fst to a predetermined optical frequency Fla; and provides said optical signal to an encoder formed by at least one of filter means whose optical filtering characteristic is a function Ci(f) or its complementary function (1−Ci(f)) both corresponding to an i-th code at least in said optical frequency range from the predetermined optical frequency Fst to the predetermined optical frequency Fla; and generates by and transmits from said encoder an optical code signal whose optical intensity-frequency characteristic is at least one of said function Ci(f) and its complementary function (1−Ci(f)) of said i-th code corresponding to the value of each piece of data of said i-th binary data sequence, at least in the optical frequency width FSR constained in said optical frequency range from the predetermined optical frequency Fst to the predetermined optical frequency Fla; wherein: said function Ci(f) is a periodic function with an optical frequency f as a variable, expressed as Ci(f)=Ci(f+PFRi); the optical frequency width FSR is an optical frequency width which is a common multiple of a repetition period PFRi of a function forming each code in an optical frequency range from a predetermined optical frequency Fst to a predetermined optical frequency Fla; the complementary function of said function Ci(f) is a function obtained by subtracting the function Ci(f) from 1; said function Ci(f) and said complementary function (1−Ci(f)) bear the following relation: ∫ Ci ( f )· Ci ( f ) df>∫Ci ( f )·(1 −Ci ( f )) df where ∫df is a definite integral with respect to f for an arbitrary interval corresponding to said optical frequency width FSR constained in said optical frequency range from the optical frequency Fst to the optical frequency Fla; and the function Ci(f), a function Cj(f) of an arbitrary j-th code other than the i-th code and the complementary function (1−Cj(f)) of said function Cj(f) bear the following relation: ∫ Ci ( f )· Cj ( f ) df=∫Ci ( f )·(1 −Cj ( f )) df ; and an optical receiver which includes: at least optical filter means and an intensity detector for detecting the optical intensity of a received optical signal; and which: generates from said received optical signal a first difference signal corresponding to the difference between a first intensity signal corresponding to the optical intensity of an optical signal whose optical intensity-frequency characteristic is Ci(f) based on said function Ci(f) and a second intensity signal corresponding to the optical intensity of an optical signal whose optical intensity-frequency characteristic is (1−Ci(f)) based on the complementary function (1−Ci(f)); and regenerates said data sequence from said first difference signal.