Optical waveguide terminators with doped waveguides
Disclosed herein are methods, structures, apparatus and devices for the termination of unused waveguide ports in planar photonic integrated circuits with doped waveguides such that free-carrier absorption therein may advantageously absorb any undesired optical power resulting in a significant reduction of stray light and resulting reflections.
1. A photonic integrated circuit comprising: a Mach-Zehnder optical interferometer having: a first waveguide arm and a second waveguide arm, the first waveguide arm having a first port and a second port at opposite ends of the first waveguide arm, and the second waveguide arm having a third port and a fourth port at opposite ends of the second waveguide arm; wherein the third port is an unused waveguide port, wherein a portion of the third port is doped with a dopant configured to induce optical absorption and optically terminate the third port.
2. The photonic integrated circuit of claim 1 , wherein the Mach-Zehnder optical interferometer further comprises a first 2×2 optical coupler between the third port and the fourth port.
3. The photonic integrated circuit of claim 2 , wherein the first 2×2 optical coupler is also between the first port and the second port.
4. The photonic integrated circuit of claim 1 , wherein the Mach-Zehnder optical interferometer is configured to be operated as a modulator.
5. The photonic integrated circuit of claim 2 , wherein the Mach-Zehnder optical interferometer further comprises a second 2×2 optical coupler between the third port and the fourth port.
6. The photonic integrated circuit of claim 1 , wherein the Mach-Zehnder optical interferometer is disposed on a silicon substrate.
7. The photonic integrated circuit of claim 1 , wherein the portion of the third port is p-doped.
8. The photonic integrated circuit of claim 1 , wherein the portion of the third port is n-doped.
9. The photonic integrated circuit of claim 1 , wherein the portion of the third port comprises an electron concentration of 10 20 cm −3 .
10. The photonic integrated circuit of claim 1 , wherein the dopant is configured to optically terminate the third port through free-carrier absorption.