Polarization controller
Conventional systems use a polarization-maintaining fiber (PMF) in order to maintain the light in the same polarization between a laser light source and an optical waveguide on a photonic integrated circuit (PIC). A polarization controller may be provided at an input port of the PIC configured for the manipulation of one or both of the TE 0 and TM 0 polarized light modes. The polarization controller may include a polarization beam splitter/rotator (PBSR), including a plurality of phase tuners and a plurality of couplers which are coupled together by waveguides, all of which are integrated in a device layer on the PIC.
1. An optical device comprising:
a light source for producing a beam of light comprising a single polarization mode;
a single mode fiber coupled at a first end to the light source, and configured to enable transmission of randomly polarized light, whereby at a second end of the single mode fiber the beam of light includes a first fundamental polarization mode and a second fundamental polarization mode; and
a photonic integrated circuit coupled to the second end of the single mode fiber comprising:
a polarization beam splitter/rotator configured to split the beam of light into a first sub-beam comprising the first fundamental polarization mode, and a second sub-beam comprising the second fundamental polarization mode, and for converting the second sub-beam from the second fundamental polarization mode to the first polarization mode;
a polarization combiner for combining the first sub-beam and the second sub-beam into a single output beam; and
an optical component configured to receive the single output beam;
wherein the polarization combiner comprises:
a first phase tuner for adjusting a phase of one of the first sub-beam or the second sub-beam;
a first coupler for combining the first sub-beam and the second sub-beam, and outputting a first combined sub-beam and a second combined sub-beam;
a second phase tuner for adjusting the phase of one of the first combined sub-beam and the second combined sub-beam;
a second coupler for combining the first combined sub-beam and the second combined sub-beam;
a third phase tuner configured for adjusting the phase of one of the first sub-beam or the second sub-beam, while the first phase tuner is being reset;
a third coupler for combining the first sub-beam and the second sub-beam, and outputting the first combined sub-beam and the second combined sub-beam;
a fourth phase tuner for adjusting the phase of one of the first combined sub-beam and the second combined sub-beam, while the second phase tuner is being reset; and
a fourth coupler for combining the first combined sub-beam and the second combined sub-beam, and outputting the single output beam.
2. The optical device according to claim 1 , further comprising a controller for adjusting the first phase tuner and the second phase tuner to maximize output power of the single output beam.
3. The optical device according to claim 2 , further comprising a monitor photo diode configured to provide an indication of the output power of the single output beam to the controller.
4. The optical device according to claim 3 , wherein the controller is configured to dither phases of the first phase tuner and the second phase tuner until the output power of the single output beam exceeds a desired threshold.
5. The optical device according to claim 1 , further comprising a controller configured for tracking polarization with the first phase tuner and the second phase tuner until a control limit in the first phase tuner and the second phase tuner is reached, and then tracking polarization with the third phase tuner and the fourth phase tuner, while the first phase tuner and the second phase tuner are concurrently reset.
6. The optical device according to claim 1 , wherein the polarization beam splitter/rotator includes a coupler comprising a primary waveguide coupled to the single mode fiber, and a secondary waveguide adjacent to the primary waveguide, wherein the coupler is configured to couple the second sub-beam off of the primary waveguide onto the secondary waveguide, and the first sub-beam remains on the primary waveguide.
7. The optical device according to claim 6 , wherein the polarization beam splitter/rotator further comprises:
a bi-layer taper configured to convert the second sub-beam to a higher-order second polarization mode than the second sub-beam; and
a bent taper mode converter configured to convert the second sub-beam to comprise the first fundamental polarization mode.
8. The optical device according to claim 1 , wherein the polarization beam splitter/rotator includes a tapered rotator and a Y-splitter optically coupled to the tapered rotator;
wherein the tapered rotator is configured to rotate the second fundamental polarization mode into a higher order mode of the first fundamental polarization mode, while leaving the first fundamental polarization mode undisturbed; and
wherein the Y-splitter splits the higher order mode of the first polarization mode and the first fundamental polarization mode, thereby producing the first sub-beam and the second sub-beam each comprising the first fundamental polarization mode.
9. The optical device according to claim 8 , further comprising a PDL tuning section between the tapered rotator and the Y-splitter configured to deform shapes of the higher order mode of the first polarization mode and the first fundamental polarization mode.
10. The optical device according to claim 9 , wherein the PDL tuning section expands to a width greater than a wide end of the tapered rotator, and/or narrows to a width less than the wide end of the tapered rotator, thereby instilling a phase delay between the higher order mode of the first polarization mode and the first fundamental polarization mode.
11. The optical device according to claim 1 , wherein the optical component comprises an optical modulator.