A method for adjusting a coefficient of an equalizer, comprising: acquiring a jones matrix with coefficients Hxx(f), Hxy(f), Hyy(f), and Hyx(f) of an equalizer of a butterfly-shaped structure for polarization demultiplexing; acquiring a parameter of the jones matrix by acquiring a first parameter, a second parameter, and a third parameter by performing a mathematical operation on the jones matrix, the first parameter representing strength of a signal of X-axis polarization, the second parameter representing strength of a signal of Y-axis polarization, the third parameter being expressed by jones_val = |jones * jones - jones * jones | 2 , with _ jones 1,1 = ∑ col = 1 n Hxx 1 col , jones 1,2 = ∑ col = 1 n Hxy 1 col , jones 2,1 = ∑ col = 1 n Hyx 1 col , jones 2,2 = ∑ col = 1 n Hyy 1 col ; and in response to determining, using the third parameter of the jones matrix, that the coefficients are of singularity characteristics, adjusting a coefficient of X-axis or Y-axis polarization among the coefficients, by: in response to determining that the first parameter is greater than the second parameter, setting Hyy (1, col) = conj (Hxx(1, n+1-col)) and Hyx (1, col) = - conj (Hxy (1, n+1-col)); and in response to determining that the first parameter is less than the second parameter, setting Hxx (1, col) = conj (Hyy(1, n+1-col)) and Hxy (1, col) = - conj (Hyx (1, n+1-col)), wherein the conj represents conjugation, the n represents an order of a filter in the equalizer, and the col takes on a value of 1, 2, ..., or n. acquiring a jones matrix with coefficients Hxx(f), Hxy(f), Hyy(f), and Hyx(f) of an equalizer of a butterfly-shaped structure for polarization demultiplexing; acquiring a parameter of the jones matrix by acquiring a first parameter, a second parameter, and a third parameter by performing a mathematical operation on the jones matrix, the first parameter representing strength of a signal of X-axis polarization, the second parameter representing strength of a signal of Y-axis polarization, the third parameter being expressed by jones_val = |jones * jones - jones * jones | 2 , with _ jones 1,1 = ∑ col = 1 n Hxx 1 col , jones 1,2 = ∑ col = 1 n Hxy 1 col , jones 2,1 = ∑ col = 1 n Hyx 1 col , jones 2,2 = ∑ col = 1 n Hyy 1 col ; and in response to determining, using the third parameter of the jones matrix, that the coefficients are of singularity characteristics, adjusting a coefficient of X-axis or Y-axis polarization among the coefficients, by: in response to determining that the first parameter is greater than the second parameter, setting Hyy (1, col) = conj (Hxx(1, n+1-col)) and Hyx (1, col) = - conj (Hxy (1, n+1-col)); and in response to determining that the first parameter is less than the second parameter, setting Hxx (1, col) = conj (Hyy(1, n+1-col)) and Hxy (1, col) = - conj (Hyx (1, n+1-col)), in response to determining that the first parameter is greater than the second parameter, setting Hyy (1, col) = conj (Hxx(1, n+1-col)) and Hyx (1, col) = - conj (Hxy (1, n+1-col)); and in response to determining that the first parameter is less than the second parameter, setting Hxx (1, col) = conj (Hyy(1, n+1-col)) and Hxy (1, col) = - conj (Hyx (1, n+1-col)), wherein the conj represents conjugation, the n represents an order of a filter in the equalizer, and the col takes on a value of 1, 2, ..., or n. <EOS>