Patent ID: 8472813

Claim:
A polarization-multiplexed (POLMUX) optical orthogonal frequency division multiplexing (OFDM) system with direct detection, comprising: an adaptive dual POLMUX carrier OFDM transmitter; and a block symmetric (B-S) MIMO equalizer coupled to the adaptive dual POLMUX carrier OFDM transmitter through a standard single-mode-fiber (SSMF) feedback path, wherein the B-S MIMO equalizer comprises a B-S channel estimator, wherein the B-S channel estimator first uses training sequences in determining an estimation matrix such that the received symbols on subcarriers i and N−i+1 in the polarizations X′ and Y′ can be modeled as: [ c XX ′ ⁢ a XX ′ ⁡ ( i ) c YX ′ ⁢ a YX ′ ⁡ ( i ) c YX ′ ⁢ a XX ′ ⁡ ( N - i + 1 ) c XX ′ ⁢ a YX ′ ⁡ ( N - i + 1 ) c XY ′ ⁢ a XY ′ ⁡ ( i ) c YY ′ ⁢ a YY ′ ⁡ ( i ) c YY ′ ⁢ a XY ′ ⁡ ( N - i + 1 ) c XY ′ ⁢ a YY ′ ⁡ ( N - i + 1 ) c YX ′ ⁢ a XX ′ ⁡ ( i ) c XX ′ ⁢ a YX ′ ⁡ ( i ) c XX ′ ⁢ a XX ′ ⁡ ( N - i + 1 ) c YX ′ ⁢ a YX ′ ⁡ ( N - i + 1 ) c YY ′ ⁢ a XY ′ ⁡ ( i ) c XY ′ ⁢ a YY ′ ⁡ ( i ) c XY ′ ⁢ a XY ′ ⁡ ( N - i + 1 ) c YY ′ ⁢ a YY ′ ⁡ ( N - i + 1 ) ] ︸ Channel ⁢ ⁢ Estimation ⁢ ⁢ Matrix × ⁢ [ S X , i S Y , i S X , N - i + 1 S Y , N - i + 1 ] ︸ Tx ⁢ ⁢ Signals + v = [ S X ′ , i S Y ′ , i S X ′ , N - i + 1 S Y ′ , N - i + 1 ] ︸ Re ⁢ ⁢ Signals = y where v and y denote a noise vector and a vector of received symbols, respectively and i=1, 2, . . . N, denotes the OFDM subcarrier index, and N denotes the FFT size, wherein the B-S channel estimator approximates the channel estimation matrix by a matrix of the form [ A B B A ] or a matrix of the form [ A 0 0 C ] where A and B and C are 2×2 matrices, if the error in such approximation is below an acceptable threshold.