Patent ID: 7796887

Claim:
A wavelength division multiplexing optical transmission system, comprising: a plurality of optical senders outputting signal lights with different wavelengths and filtered by a plurality of respective filters, and said filters are configured to yield filtered signal lights having respective bit rates and frequency spacing to approach a spectrum efficiency at which a product of a transmission distance and a transmission capacity of the system is maximized; an optical multiplexer multiplexing the filtered signal lights to be transmitted to an optical transmission path as a wavelength division multiplexing signal light; and an optical demultiplexer demultiplexing the wavelength division multiplexing signal light having different respective wavelengths to be received by a plurality of optical receivers, wherein the type of modulation of said signal light is an NRZ modulation type, and wherein an equation model expressing transmission characteristics of said optical multiplexer and said optical demultiplexer is expressed by the following equation in which each transmission band T(f) corresponding to each signal light is expressed by using a frequency f, where fc is a center frequency of the transmission band, and Δf is a full width at half maximum of the transmission band, as a filter order “n” T ⁡ ( f ) = 10 · log ⁡ [ exp ⁢ { - 2 · ln ⁢ 2 · (  f - fc  Δ ⁢ ⁢ f / 2 ) 2 ⁢ n } ] , ( dB ) wherein the spectrum efficiency at which the product of said transmission distance and said transmission capacity becomes the maximum value is calculated as spectrum efficiency at which a performance index PI=10·(−ΔQ/10)·B/S, which is expressed using a Q-value degradation amount ΔQ of the system, a bit rate B and frequency spacing S of the signal light, becomes a maximum value.