Optical receiving apparatus and optical receiving method using changing coefficient values for fast fourier transform

1 . An optical reception apparatus comprising:

at least one wavelength dispersion compensation unit configured to perform wavelength dispersion compensation for each subcarrier contained in a reception signal obtained by interfering a received optical signal and a local light emission; and

a plurality of delay compensation units configured to compensate for a delay between reception signals at different subcarriers among the reception signals at subcarriers obtained by the wavelength dispersion compensation, wherein

the at least one wavelength dispersion compensation unit comprises a plurality of wavelength dispersion compensation units, and

each of the plurality of wavelength dispersion compensation units delimits a reception signal of the reception signals input into blocks each having a specific length such that an overlapping portion having a predetermined length between adjacent blocks is generated, outputs the blocks delimited, performs a Fourier transform for each of the blocks, holds the blocks that are temporally consecutive after the Fourier transform, applies a coefficients defined according to a wavelength dispersion compensation amount in accordance with a frequency position and a delay amount in accordance with the frequency position and a time position to each of the blocks held, generates a coefficients applied block by adding up a coefficients applied frequency component value for each frequency position, performs an inverse Fourier transform on the coefficient-applied block generated, and removes the overlapping portion from the coefficient-applied block after the inverse Fourier transform,

wherein the coefficients are a different value for each time position and are different for each frequency position.

2 . The optical reception apparatus according to claim 1 further comprising:

one or more adaptive equalization units configured to compensate for distortion generated in a waveform of an optical signal in an optical transmission path;

one or more frequency/phase compensation units configured to compensate for a frequency offset and a phase offset for a signal on which the adaptive equalization processing has been executed by the one or more adaptive equalization units; and

one or more error correction units configured to perform error correction on an input signal, wherein

the plurality of delay compensation units are provided in any of a later stage of one or more error correction units, a position between the at least one wavelength dispersion compensation unit and the one or more adaptive equalization units, a position between the one or more frequency/phase compensation units and the one or more error correction units, and a position between combinations of the one or more adaptive equalization units and the one or more frequency/phase compensation units, the combinations being provided before and after the plurality of delay compensation units.

3 . The optical reception apparatus according to claim 1 , wherein

each of the plurality of wavelength dispersion compensation units calculates the coefficients aforementioned coefficient based on the following Equation (1),

H l ( k )= B l (ω)×exp( j/ 2β 2 ω 2 −jlβ 1 ω)  (1)

In equation (1), l=1 to L, Bl (ω) is a window function, β2 is a wavelength dispersion parameter, w is expressed by equation (2), and β 1 is expressed by equation (3),

ω=2πΔ f ( k− 1)  (2)

β 1 =Δt×N ( M− 1)/ M   (3).

4 . An optical reception method comprising:

performing wavelength dispersion compensation for each subcarrier contained in a reception signal obtained by interfering a received optical signal and a local light emission; and

compensating for a delay between reception signals at different subcarriers among the reception signals at subcarriers obtained by the wavelength dispersion compensation, delimiting, by each of the plurality of wavelength dispersion compensation units, a reception signal of the reception signals input into blocks each having a specific length such that an overlapping portion having a predetermined length between adjacent blocks is generated,

outputting, by each of the plurality of wavelength dispersion compensation units, the blocks delimited,

performing, by each of the plurality of wavelength dispersion compensation units, a Fourier transform for each of the blocks,

holding, by each of the plurality of wavelength dispersion compensation units, the blocks that are temporally consecutive after the Fourier transform,

applying, by each of the plurality of wavelength dispersion compensation units, coefficients defined according to a wavelength dispersion compensation amount in accordance with a frequency position and a delay amount in accordance with the frequency position and a time position to each of the blocks held,

generating, by each of the plurality of wavelength dispersion compensation units, a coefficients applied block by adding up a coefficients applied frequency component value for each frequency position,

performing, by each of the plurality of wavelength dispersion compensation units, an inverse Fourier transform on the coefficient-applied block generated, and removing, by each of the plurality of wavelength dispersion compensation units, the overlapping portion from the coefficient-applied block after the inverse Fourier transform,

wherein the coefficients are a different value for each time position and are different for each frequency position.