Optical interleaver and filter cell design with enhanced clear aperture
View Patent ↗An optical interleaver for use in a range of telecommunications applications including optical multiplexers/demultiplexers and optical routers. The optical device includes an optical processing loop which allows multi-stage performance characteristics to be achieved with a single physical filtration stage. Optical processing on the first leg and second legs of the loop is asymmetrical thereby improving the integrity of the optical signals by effecting complementary chromatic dispersion on the first and second legs. A fundamental filter cell within the interleaver filters optical signals propagating on each of the two legs of the optical loop which intersects the fundamental filter cell.
1. 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.
2. The filter cell as recited in claim 1 , wherein the first PBS and the second PBS define a first pair of delay paths including a fast delay path and a slow delay path.
3. The filter cell as recited in claim 2 , wherein the first PBS and the second PBS asymmetrically split and combine the optical signals between the fast delay path and the slow delay path of the first delay path pair depending on the optical signals' polarization.
4. The filter cell as recited in claim 3 , wherein the third PBS and the fourth PBS define a second pair of delay paths including a fast delay path and a slow delay path.
5. The filter cell as recited in claim 4 , wherein the third PBS and the fourth PBS asymmetrically split and combine the optical signals between the fast delay path and the slow delay path of the second delay path pair depending on the optical signals' polarization.
6. The filter cell as recited in claim 4 , wherein the third PBS and the fourth PBS symmetrically split and combine the optical signals between the fast delay path and the slow delay path of the second delay path pair depending on the optical signals' polarization.
7. The filter cell as recited in claim 1 , wherein the first PBS, the second PBS, the third PBS, and the fourth PBS each comprises at least one prism and a parallel plate.
8. The filter cell as recited in claim 7 , wherein at least one surface of the parallel plate is coated with a multilayer dielectric polarizing beam splitter coating.
9. The filter cell as recited in claim 1 , wherein the first PBS has two surfaces, at least one of which is tilted at an angle from normal with respect to the propagation direction of the optical signals so as to reduce chromatic dispersion ripple that would otherwise be introduced if the two surfaces were normal to the propagation direction.
10. The filter cell as recited in claim 9 , wherein the two surfaces are parallel to each other.
11. The filter cell as recited in claim 9 , wherein the two surfaces of the first PBS are coated with an antireflective coating.
12. An optical interleaver for processing optical signals including a first set of one or more optical signals and a second set of one or more optical signals, the interleaver comprising:
a filter cell mounted to a base for filtering optical signals propagating on each of two legs of an optical loop, the filter cell operating as a full waveplate to the first set of optical signals and a half waveplate to the second set of optical signals on the first leg, and as a half waveplate to the first set of optical signals and a full waveplate to the second set of optical signals on the second leg, the filter cell comprising:
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;
a retro reflector mounted to the base and optically coupled with the filter cell to reflect the optical signals from the first leg to the second leg of the optical loop; and
an optical polarization beam displacer mounted to the base and optically coupled between the filter cell and the retro reflector to split or combine the first and second sets of optical signals depending on polarization and propagation direction along the optical loop.
13. The optical interleaver as recited in claim 12 , wherein the first PBS and the second PBS define a first pair of delay paths including a fast delay path and a slow delay path, and wherein the third PBS and the fourth PBS define a second pair of delay paths including a fast delay path and a slow delay path.
14. An optical interleaver as recited in claim 13 , wherein the first PBS and the second PBS asymmetrically split and combine the optical signals between the fast delay path and the slow delay path of the first delay path pair depending on the optical signals' polarization, and wherein the third PBS and the fourth PBS asymmetrically split and combine the optical signals between the fast delay path and the slow delay path of the second delay path pair depending on the optical signals' polarization.
15. The optical interleaver as recited in claim 13 , wherein the first PBS and the second PBS symmetrically split and combine the optical signals between the fast delay path and the slow delay path of the first delay path pair depending on the optical signals' polarization, and wherein the third PBS and the fourth PBS symmetrically split and combine the optical signals between the fast delay path and the slow delay path of the second delay path pair depending on the optical signals' polarization.
16. The optical interleaver as recited in claim 12 , wherein the first PBS, the second PBS, the third PBS, and the fourth PBS each comprises at least one prism and a parallel plate.
17. The optical interleaver as recited in claim 12 , wherein the first PBS has two surfaces, at least one of which is tilted at an angle from normal with respect to the propagation direction of the optical signals so as to reduce chromatic dispersion ripple that would otherwise be introduced if the two surfaces were normal to the propagation direction.
18. The optical interleaver as recited in claim 17 , wherein the two surfaces are parallel to each other.
19. The optical interleaver as recited in claim 12 , wherein the displacer comprises a polarization beam splitter.
20. The optical interleaver as recited in claim 12 , further comprising one or more prisms to optically couple a plurality of ports to the filter cell.
21. The optical interleaver as recited in claim 20 , further comprising one or more polarization beam splitters operating as one or more optical polarization beam displacers and one or more waveplates to optically couple the one or more prisms and one or more ports to the filter cell.
22. The optical interleaver as recited in claim 12 , wherein the filter cell is a fundamental filter cell, the optical interleaver further comprising a harmonic filter cell optically coupled to the fundamental filter cell and the optical polarization beam displacer to filter the optical signals on both legs of the optical loop with a higher order harmonic.
23. The optical interleaver as recited in claim 12 , wherein the filter cell is a fundamental filter cell, the optical interleaver further comprising at least two harmonic filter cells optically coupled to the fundamental filter cell and the optical polarization beam displacer to filter the optical signals on both legs of the optical loop with higher order harmonics.
24. The optical interleaver as recited in claim 23 , further comprising a zero-order waveplate optically coupled between a first harmonic filter cell and the fundamental filter cell to rotate polarization vectors of the optical signals between the fundamental filter cell and the first harmonic filter cell in order to align the fundamental filter cell and the first harmonic filter cell with each other.
25. The optical interleaver as recited in claim 23 , further comprising a zero-order waveplate optically coupled between a first harmonic filter cell and a second harmonic filter cell to rotate polarization vectors of the optical signals between the second harmonic filter cell and the first harmonic filter cell in order to align the second harmonic filter cell and the first harmonic filter cell with each other.
26. The optical interleaver as recited in claim 23 , further comprising a zero-order waveplate optically coupled between a second harmonic filter cell and the optical polarization beam displacer and retro reflector to rotate polarization vectors of the optical signals between the second harmonic filter cell and the optical polarization beam displacer and retro reflector in order to align the second harmonic filter cell and the optical polarization beam displacer and retro reflector with each other.