Optical Crossover in thin silicon

Abstract

An arrangement for providing optical crossovers between waveguides formed in an SOI-based structure utilize a patterned geometry in the SOI structure that is selected to reduce the effects of crosstalk in the area where the signals overlap. Preferably, the optical signals are fixed to propagate along orthogonal directions (or are of different wavelengths) to minimize the effects of crosstalk. The geometry of the SOI structure is patterned to include predetermined tapers and/or reflecting surfaces to direct/shape the propagating optical signals. The patterned waveguide regions within the optical crossover region may be formed to include overlying polysilicon segments to further shape the propagating beams and improve the coupling efficiency of the crossover arrangement.

1 . A silicon-on-insulator (SOI)-based optical device including a surface silicon waveguiding layer disposed over an insulating layer covering a silicon substrate, the SOI-based optical device comprising: 
 a first optical waveguide for supporting the propagation of a first optical signal;    a second optical waveguide for supporting the propagation of a second optical signal; and    an optical crossover region defined by an intersection of the first optical waveguide with the second optical waveguide, the optical crossover region exhibiting a geometry defined to reduce crosstalk between the first and second optical signals in the crossover region and improve optical throughput within the optical crossover region.    
     
     
         2 . An SOI-based optical device as defined in  claim 1  wherein at least a portion of the first and second optical waveguides exhibit a sub-micron geometry and support the propagation of only a single mode optical signal.  
     
     
         3 . An SOI-based optical device as defined in  claim 1  wherein the optical crossover region geometry is defined to include beam-capturing waveguide sections at exit areas of the crossover region where the first and second optical signals continue along their associated first and second optical waveguides.  
     
     
         4 . An SOI-based optical device as defined in  claim 1  wherein the first and second optical waveguides and the optical crossover region are formed within the surface silicon layer of the SOI-based optical device.  
     
     
         5 . An SOI-based optical device as defined in  claim 1  wherein the first and second optical waveguides are formed, at least in part, as strip waveguides within the surface silicon layer.  
     
     
         6 . An SOI-based optical device as defined in  claim 1  wherein the first and second optical waveguides are formed, at least in part, as rib waveguides within the surface silicon layer.  
     
     
         7 . An SOI-based optical device as defined in  claim 1  wherein the SOI-based optical device further comprises a polysilicon layer overlying the surface silicon waveguiding layer.  
     
     
         8 . An SOI-based optical device as defined in  claim 7  wherein the first and second optical waveguides and the optical crossover region are formed in the surface silicon layer and the polysilicon layer is patterned into a set of four separate segments, a first segment disposed over an input portion of the first waveguide at the entrance to the crossover region, a second segment disposed over an output portion of the first waveguide at the exit of the crossover region, a third segment disposed over an input portion of the second waveguide at the entrance to the crossover region and a fourth segment disposed over an output portion of the second waveguide.  
     
     
         9 . An SOI-based optical device as defined in  claim 8  wherein at least the second and fourth polysilicon segments are formed to include a tapered end portion at the termination adjacent to the optical crossover region.  
     
     
         10 . An SOI-based optical device as defined in  claim 7  wherein 
 the first optical waveguide is divided into a pair of separate sections at the optical crossover region, a first separate section defined as an input waveguiding section and a second separate section defined as an output waveguiding section, with the second optical waveguide disposed through the gap created between the first and second separate sections; and    the optical crossover region geometry is defined by the polysilicon layer which is patterned to form a bridging waveguide section between the input waveguiding section and the output waveguiding section of the first optical waveguide.    
     
     
         11 . An SOI-based optical device as defined  claim 10  wherein the polysilicon bridging waveguide section is patterned to include tapered end terminations along the first and second optical waveguides.  
     
     
         12 . An SOI-based optical device as defined in  claim 1  wherein the optical crossover region comprises 
 a first pair of reflecting surfaces disposed to intercept the first optical signal propagating along the first optical waveguide, an input surface of the first pair of reflecting surfaces for providing a first redirection of the first optical signal into the optical crossover region and an output surface of the first pair of reflecting surfaces for providing a second redirection of the first optical signal out of the optical crossover region and into an output waveguiding section of the first optical waveguide; and    a second pair of reflecting surfaces disposed to intercept the second optical signal propagating along the second optical waveguide, an input surface of the second pair of reflecting surfaces for providing a first redirection of the second optical signal into the optical crossover region and an output surface of the second pair of reflecting surfaces for providing a second redirection of the second optical signal out of the optical crossover region and into an optical waveguiding section of the second optical waveguide.    
     
     
         13 . An SOI-based optical device as defined in  claim 12  wherein the first and second input surfaces are curved so as to transform an expanding input signal into a collimated redirected signal.  
     
     
         14 . As SOI-based optical device as defined in  claim 13  wherein the first and second output surfaces are curved as to transform a collimated input signal into an expanding redirected signal.  
     
     
         15 . An SOI-based optical device as defined in  claim 12  wherein each of the reflecting surfaces is formed as a 45° reflecting mirror surface.  
     
     
         16 . An SOI-based optical device as defined in  claim 12  wherein the first and second input surfaces are curved to transform a collimated input signal into a focusing redirected signal.  
     
     
         17 . An SOI-based optical device as defined in  claim 16  wherein the first and second output surfaces are curved to transform an expanding input signal into a collimated redirected signal.  
     
     
         18 . An SOI-based optical device as defined in  claim 12  wherein the first and second optical waveguides are formed to include inwardly tapering portions along their respective output waveguiding sections.  
     
     
         19 . An SOI-based optical device as defined in  claim 12  wherein the device further comprises a plurality of separate rib waveguide segments disposed over input and output sections of the first and second optical waveguides.  
     
     
         20 . An SOI-based optical device as defined in  claim 19  wherein the rib segments comprise polysilicon segments.  
     
     
         21 . An SOI-based optical device as defined in  claim 19  wherein the plurality of separate rib segments include tapered end terminations adjacent to the optical crossover region.  
     
     
         22 . An SOI-based optical device as defined in  claim 1  wherein the optical crossover region is defined as comprising a ring resonator geometry including at least a pair of wavelength-selective rings in association with a transverse optical waveguide for transferring the first optical signal from an input waveguiding section through a first ring resonator and into the transverse optical waveguide, and thereafter through a second ring resonator into an output waveguiding section.  
     
     
         23 . An SOI-based optical device as defined in  claim 1  wherein the optical crossover region is defined as comprising an evanescently coupled waveguiding geometry of a predetermined length associated with transferring the first optical signal from the first optical waveguide to the second optical waveguide and transferring the second optical signal from the second optical waveguide to the first optical waveguide.  
     
     
         24 . An SOI-based optical device as defined in  claim 1  wherein the optical crossover region is defined as comprising an optical tap geometry including an input optical tap waveguiding segment, a transverse waveguide and an output tap waveguiding segment, the first optical signal applied as an input to the input optical tap waveguiding segment and thereafter coupled into the transverse waveguide to propagate therealong and then coupled into the output optical tap.