Patent ID: 7173763

Claim:
A filter cell for filtering optical signals propagating on each of two legs of an optical loop which intersects the filter cell, the filter cell operating as a full waveplate to a first set of one or more optical signals and a half waveplate to a second set of one or more optical signals on a selected one of the two legs and as a half waveplate to the first set of one or more optical signals and a full waveplate to the second set of one or more optical signals on a remaining one of the two legs, the filter cell comprising: a base; a first polarization beam splitter (PBS) pair, comprising: a first PBS horizontally mounted to the base and oriented to split or combine the first and second sets of one or more optical signals depending on polarization and propagation direction along the optical loop; and a second PBS horizontally mounted to the base and optically coupled to the first PBS to split or combine the first and second sets of one or more optical signals depending on polarization and propagation direction along the optical loop, wherein the second PBS is oriented to split when the first PBS is oriented to combine, and wherein the second PBS is oriented to combine when the first PBS is oriented to split; a second PBS pair, comprising: a third PBS horizontally mounted to the base and oriented as the first PBS, the third PBS being affixed to the second PBS; and a fourth PBS horizontally mounted to the base and oriented as the second PBS, the fourth PBS being affixed to the first PBS; and one or more optical components mounted to the base, and optically coupled and shared by the first and second PBS pair.