Apparatus and method for polarization mode dispersion emulation and compensation

A polarization mode dispersion emulator comprising:

• a first optical network exhibiting the transfer matrix R + 1 ⁡ ( ω ) = [ cos ⁡ ( k ⁢ ⁢ ω ) + sin ⁡ ( k ⁢ ⁢ ω ) - sin ⁡ ( k ⁢ ⁢ ω ) cos ⁡ ( k ⁢ ⁢ ω ) ]
• a second optical network connected to receive the output of the first optical network and exhibiting the transfer matrix D ⁡ ( ω ) = [ d ⁡ ( ω ) 0 0 d * ⁡ ( ω ) ] ;
• and
• a third optical network connected to receive the output of the second optical network and exhibiting the transfer matrix R - 1 ⁡ ( ω ) = [ cos ⁡ ( k ⁢ ⁢ ω ) - sin ⁡ ( k ⁢ ⁢ ω ) + sin ⁡ ( k ⁢ ⁢ ω ) cos ⁡ ( k ⁢ ⁢ ω ) ]
• where:
• d(ω)=exp(j(Δτ0ω+(1/2)Δτ1ω2)/2).

A method of compensating for polarization mode dispersion (PMD) imparted to an optical signal by a device characterized by a transfer function U, said method comprising the steps of:

• (A) in a first mode mapper, mapping the polarization modes of a randomly polarized optical signal by dividing the signal into orthogonally polarized component signals and routing each of the component signals into a separate path, with one of the separate paths configured to rotate the polarization state of one of the component signals until it is parallel to the polarization of the other component signal;
• (B) passing the mode-mapped component signals from the first mode mapper through a lossless two by two filter network connected to receive the component signals from the first mode mapper, the filter network being characterized by a transfer function U−1 that is the inverse of the transfer function of the device which imparts polarization mode dispersion to the optical signal;
• and
• (C) in a second mode mapper, mapping the polarization modes of the filtered component optical signals received from the filter network by rotating one of the filtered component signals to a polarization state orthogonal to that of the other filtered component signal and combining the component signals in a polarization beam combiner.

A method of emulating polarization mode dispersion comprising the steps of:

• (A) rotating an optical signal in an optical network characterized by a frequency dependent rotatation matrix R + 1 ⁡ ( ω ) = [ cos ⁡ ( k ⁢ ⁢ ω ) + sin ⁡ ( k ⁢ ⁢ ω ) - sin ⁡ ( k ⁢ ⁢ ω ) cos ⁡ ( k ⁢ ⁢ ω ) ]
• (B) delaying the principle states of polarization of the signal in an optical network characterized by a frequency dependent rotation matrix D ⁡ ( ω ) = [ d ⁡ ( ω ) 0 0 d * ⁡ ( ω ) ] ;
• and
• (C) rotating an optical signal in an optical network characterized by a frequency dependent rotatation matrix R - 1 ⁡ ( ω ) = [ cos ⁡ ( k ⁢ ⁢ ω ) - sin ⁡ ( k ⁢ ⁢ ω ) + sin ⁡ ( k ⁢ ⁢ ω ) cos ⁡ ( k ⁢ ⁢ ω ) ]
• where:
• d(ω)=exp(j(Δτ0ω+(1/2)Δτ1ω2)/2).