Parameter tolerant splitter/combiner with subdivided couplers
View Patent ↗A splitter/combiner system including directional couplers and phase shifts where some of the directional couplers are subdivided into shorter directional couplers, with 0° phase shifts between them. The system provides improved ease of design, and uniformity. The subdivided couplers also provide more accurate ratios between all the couplers in the splitter/combiner.
1. A method of increasing the tolerance to fabrication variation of an optical splitter/combiner comprising at least two directional couplers and at least one phase shift, said method comprising:
subdividing said directional couplers into at least three substantially identical couplers;
providing at least one zero-degree phase shift between at least two said substantially identical couplers.
2. The method of claim 1 , wherein said at least two directional couplers are subdivided into a lower common denominator directional coupler.
3. The method of claim 1 further comprising providing substantially identical fabrication variations of the coupling coefficients of at least two substantially identical directional couplers.
4. The method of claim 1 , wherein said splitter/combiner is fabricated in a planar waveguide system with semiconductor lithographic fabrication tools.
5. The method of claim 1 , wherein the propagation constant of at least one phase shift is tunable.
6. The method of claim 1 further comprising modifying said propagation constant using a thermo-optical method in a post-fabrication step.
7. The method of claim 1 further comprising serially connecting said directional couplers to a frequency selective element.
8. The method of claim 7 , wherein said frequency selective element comprises a grating.
9. The method of claim 8 , wherein said frequency selective element comprises a resonant filter.