Waveguide mode stripper for integrated optical components
Through the introduction of an imaging multimode interference device in an integrated optical circuit, such performance degradations as lateral waveguide field oscillations and backreflections may be suppressed. The suppression of lateral waveguide field oscillations (that may occur due to misaligned optical coupling), in particular, can significantly reduce variations in the power splitting ratio of an optical power splitting structure, such as those employed by a Mach-Zehnder modulator.
1. An integrated optical circuit comprising:
an input waveguide;
an imaging multimode interference device adapted to substantially remove all modes but a fundamental mode of an optical signal received from said input waveguide; and
an optical power splitter structure in optical communication with said imaging multimode interference device;
wherein said multimode interference device includes a primary output in optical communication with said optical power splitter structure and a secondary output in optical communication with a dump port.
2. The optical circuit of claim 1 , wherein said multimode interference device includes two said secondary output, of which is in optical communication with a respective said dump port.
3. A method for suppressing propagating lateral waveguide field oscillations at the input of an optical power splitter structure comprising,
fabricating an imaging multimode interference device in optical communication with said optical power splitter structure, wherein said multimode interference device includes a primary output in optical communication with said optical power splitter structure and a secondary output in optical communication with a dump port; and
receiving an error signal from said dump port and monitoring said error signal for a substantial change.
4. The method of claim 3 wherein said optical power splitter structure is a component of a interferometric modulator.
5. The method of claim 4 wherein said interferometric modulator is a Mach-Zehnder modulator.
6. The method of claim 3 , wherein said multimode interference device includes two said secondary output, each of which is in optical communication with a respective said dump port, said method further comprising receiving an error signal from each of said dump ports and monitoring said error signal for a substantial change.
7. An integrated optical circuit comprising:
a waveguide device;
an angle output, the angle of which is non-perpendicular with respect to the direction of optical propagation;
an imaging multimode interference device between said waveguide device and said angle output; and
an angled input, the angle of which is non-perpendicular with respect to the direction of multimode interference device and said integrated optical circuit further comprises a second imaging multimode interference device between said wave guide device and said angled input, the first and second imaging multimode interference device adapted to substantially remove all modes but a fundamental mode of an optical signal received by the devices.
8. The integrated optical circuit of claim 7 wherein the waveguide device comprises a semiconductor optical amplifier.