System and Method for an Optical Phase Shifter

Abstract

In one embodiment, an optical phase shifter includes a first waveguide phase shifter and a second waveguide phase shifter. The optical phase shifter also includes a first polarization rotator optically coupled between the first waveguide phase shifter and the second waveguide phase shifter, where the first waveguide phase shifter, second waveguide phase shifter, and first polarization rotator are integrated on a single substrate.

What is claimed is: 
     
         1 . An optical phase shifter comprising:
 a first waveguide phase shifter;   a second waveguide phase shifter; and   a first polarization rotator optically coupled between the first waveguide phase shifter and the second waveguide phase shifter, wherein the first waveguide phase shifter, second waveguide phase shifter, and first polarization rotator are integrated on a single substrate.   
     
     
         2 . The optical phase shifter of  claim 1 , wherein the single substrate is silicon-on-insulator (SOI). 
     
     
         3 . The optical phase shifter of  claim 1 , wherein the first waveguide phase shifter is a passive phase shifter. 
     
     
         4 . The optical phase shifter of  claim 1 , wherein the first waveguide phase shifter is an active phase shifter. 
     
     
         5 . The optical phase shifter of  claim 4 , wherein the first waveguide phase shifter is a thermo-optical phase shifter. 
     
     
         6 . The optical phase shifter of  claim 4 , wherein the first waveguide phase shifter is an electro-optical phase shifter. 
     
     
         7 . The optical phase shifter of  claim 1 , wherein the first waveguide phase shifter comprises lithium niobate. 
     
     
         8 . The optical phase shifter of  claim 1 , further comprising a second polarization rotator optically coupled to the second waveguide phase shifter. 
     
     
         9 . The optical phase shifter of  claim 1 , wherein the first polarization rotator comprises an asymmetrical waveguide. 
     
     
         10 . The optical phase shifter of  claim 1 , wherein the first polarization rotator comprises lithium niobate. 
     
     
         11 . A method comprising:
 phase shifting a first optical signal to produce a first phase shifted optical signal by a phase shifter;   rotating a first polarization of the first phase shifted optical signal to produce a first rotated optical signal; and   phase shifting the first rotated optical signal to produce a second phase shifted optical signal, wherein phase shifting the first optical signal, rotating the first polarization of the first phase shifted optical signal, and phase shifting the first rotated optical signals are performed on a photonic integrated circuit (PIC).   
     
     
         12 . The method of  claim 11 , wherein rotating the first polarization of the first phase shifted optical signal comprises rotating the polarization of the first phase shifted optical signal by ninety degrees. 
     
     
         13 . The method of  claim 11 , further comprising rotating a second polarization of the second phase shifted optical signal. 
     
     
         14 . The method of  claim 11 , further comprising:
 splitting an input optical signal to produce the first optical signal and a second optical signal;   transmitting the second optical signal to produce a transmitted optical signal; and   combining the transmitted optical signal and the second phase shifted optical signal.   
     
     
         15 . The method of  claim 14 , wherein transmitting the second optical signal comprises:
 phase shifting the second optical signal to produce a third phase shifted optical signal;   rotating a second polarization of the third phase shifted optical signal to produce a second rotated optical signal; and   phase shifting the second rotated optical signal to produce the transmitted optical signal.   
     
     
         16 . A Mach-Zehnder interferometer comprising:
 a first optical coupler;   a first optical leg coupled to the first optical coupler, wherein the first optical leg comprises
 a first waveguide phase shifter, 
 a second waveguide phase shifter, and 
 a first polarization rotator coupled between the first waveguide phase shifter and the second waveguide phase shifter; 
   a second optical leg coupled to the first optical coupler; and   a second optical coupler optically coupled to the first optical leg and the second optical leg, wherein the first optical leg and the second optical leg are integrated on a single substrate.   
     
     
         17 . The Mach-Zehnder interferometer of  claim 16 , wherein the first optical leg further comprises a second polarization rotator optically coupled to the second waveguide phase shifter. 
     
     
         18 . The Mach-Zehnder interferometer of  claim 16 , wherein the second optical leg comprises:
 a third waveguide phase shifter;   a fourth waveguide phase shifter; and   a second polarization rotator coupled between the third waveguide phase shifter and the fourth waveguide phase shifter.   
     
     
         19 . The Mach-Zehnder interferometer of  claim 18 , wherein the first phase shifter is an active phase shifter and the third waveguide phase shifter is a passive phase shifter. 
     
     
         20 . The Mach-Zehnder interferometer of  claim 16 , wherein the Mach-Zehnder interferometer has a push-pull configuration.