Integrated on-chip polarizer

A waveguide polarizer, comprising:

• an input optical waveguide capable of supporting a first mode and a second mode;
• an output optical waveguide for outputting the first mode;
• and
• a mode-selective expander (MSE), extending between the input and output optical waveguides, comprising:
• a mode separating section for separating the first mode from the second mode;
• and
• an output filter section for preventing the second mode from entering the output optical waveguide;
• wherein the mode separating section comprises:
• a ridge waveguiding region disposed to receive light of the first and second modes from the input optical waveguide, and
• an outer slab waveguiding region disposed alongside the ridge waveguiding region in optical communication therewith;
• wherein the ridge waveguiding region and the outer slab waveguiding region are configured to expand the light of the second mode from the ridge waveguiding region into the outer slab waveguiding region, and to propagate the first mode along the ridge waveguiding region for coupling into the output optical waveguide, so that the outer slab waveguiding region remains substantially absent of the first mode;
• and
• wherein the MSE comprises an input taper section in which the outer slab waveguiding region gradually widens in a direction of light propagation, and the ridge waveguiding region gradually narrows in the direction of light propagation.

A waveguide polarizer, comprising:

• an input optical waveguide capable of supporting a first mode and a second mode;
• an output optical waveguide for outputting the first mode;
• a mode-selective expander (MSE), extending between the input and output optical waveguides, comprising:
• a mode separating section for separating the first mode from the second mode;
• and
• an output filter section for preventing the second mode from entering the output optical waveguide;
• and
• wherein the mode separating section comprises:
• a ridge waveguiding region disposed to receive light of the first and second modes from the input optical waveguide, and
• an outer slab waveguiding region disposed alongside the ridge waveguiding region in optical communication therewith;
• wherein the ridge waveguiding region and the outer slab waveguiding region are configured to expand the light of the second mode from the ridge waveguiding region into the outer slab waveguiding region, and to propagate the first mode along the ridge waveguiding region for coupling into the output optical waveguide, so that the outer slab waveguiding region remains substantially absent of the first mode;
• and
• a light absorber configured to selectively absorb light propagating in the outer slab waveguiding region;
• wherein the light absorber comprises at least one of:
• a metal layer coupled to the outer slab waveguiding region, a layer of light-absorbing semiconductor material coupled to the outer slab waveguiding region, and a doped region of a semiconductor layer forming the outer slab waveguiding region.

A waveguide polarizer, comprising:

• an input optical waveguide capable of supporting a first mode and a second mode;
• an output optical waveguide for outputting the first mode;
• a mode-selective expander (MSE), extending between the input and output optical waveguides, comprising:
• a mode separating section for separating the first mode from the second mode;
• and
• an output filter section for preventing the second mode from entering the output optical waveguide;
• and
• wherein the mode separating section comprises:
• a ridge waveguiding region disposed to receive light of the first and second modes from the input optical waveguide, and
• an outer slab waveguiding region disposed alongside the ridge waveguiding region in optical communication therewith;
• and
• wherein the ridge waveguiding region and the outer slab waveguiding region are configured to expand the light of the second mode from the ridge waveguiding region into the outer slab waveguiding region, and to propagate the first mode along the ridge waveguiding region for coupling into the output optical waveguide, so that the outer slab waveguiding region remains substantially absent of the first mode;
• and
• a light redirecting element configured to selectively re-direct light propagating in the outer slab waveguiding region thereof away from the output optical waveguide.