Quantum confined stark effect electroabsorption modulator on a soi platform

Abstract

An electroabsorption modulator. The modulator comprising an SOI waveguide; an active region, the active region comprising a multiple quantum well (MQW) region; and a coupler for coupling the SOI waveguide to the active region. The coupler comprising: a transit waveguide coupling region; a buffer waveguide coupling region; and a taper region; wherein, the transit waveguide coupling region couples light between the SOI waveguide and the buffer waveguide coupling region; and the buffer waveguide coupling region couples light between the transit waveguide region and the active region via the taper region.

1 . An electroabsorption modulator comprising:
 an SOI waveguide;   an active region, the active region comprising a multiple quantum well (MQW) region; and   a coupler for coupling the SOI waveguide to the active region;   the coupler comprising:   a transit waveguide coupling region;   a buffer waveguide coupling region; and   a taper region;   wherein, the transit waveguide coupling region couples light between the SOI waveguide and the buffer waveguide coupling region; and the buffer waveguide coupling region couples light between the transit waveguide region and the active region via the taper region.   
     
     
         2 . The electroabsorption modulator of  claim 1 , wherein the taper region comprises a multi-segment mode expander. 
     
     
         3 . The electroabsorption modulator of  claim 1 , wherein the multiple quantum well region is a Ge/SiGe multiple quantum well region. 
     
     
         4 . The electroabsorption modulator of  claim 1 , wherein:
 the transit waveguide coupling region comprises a first portion of a transit waveguide; and   the buffer waveguide coupling region comprises a buffer waveguide located on top of a second portion of the transit waveguide.   
     
     
         5 . The electroabsorption modulator of  claim 4 , wherein:
 the transit waveguide has a refractive index bigger than that of the SOI waveguide but smaller than that of the buffer waveguide.   
     
     
         6 . The electroabsorption modulator of  claim 1 , wherein:
 the SOI waveguide is a 3 μm waveguide;   the transit waveguide has a thickness of no more than 400 nm; and   the buffer waveguide has a thickness of no more than 400 nm.   
     
     
         7 . The electroabsorption modulator of  claim 6 , wherein the transit buffer waveguide has a thickness of no more than 600 nm. 
     
     
         8 . The electroabsorption modulator of  claim 6 , wherein the transit waveguide has a thickness of no more than 800 nm. 
     
     
         9 . The electroabsorption modulator of  claim 1 , wherein each of the buffer waveguide and transit waveguide are SiGe waveguides. 
     
     
         10 . The electroabsorption modulator of  claim 4 ;
 wherein the active region comprises:
 a P-doped region between the buffer layer and the lower surface of a spacer layer underneath a multiple quantum well; and 
 an N-doped region located at the upper surface of a spacer layer on top of the multiple quantum well. 
   
     
     
         11 . The electroabsorption modulator of  claim 10 , further comprising multiple N-type doped layers with different germanium compositions and doping concentrations. 
     
     
         12 . The electroabsorption modulator of  claim 1 , wherein the waveguide slab of the P-type layer in the active region is P-doped with ion implantation followed by an RTA process. 
     
     
         13 . The electroabsorption modulator of  claim 1 , wherein the electrodes are arranged in a ground-signal (GS) configuration, where a ground electrode is located at an opposite side of the active region from the signal electrode. 
     
     
         14 . The electroabsorption modulator of  claim 1 , wherein the electrodes are arranged in a ground-signal-ground (GSG) configuration, where a first ground electrode and a second ground electrode are located at the same side of the active region as the signal electrode. 
     
     
         15 . The electroabsorption modulator of  claim 1 , wherein the multiple quantum well region includes at least 5 quantum wells. 
     
     
         16 . The electroabsorption modulator of  claim 1 , wherein the multiple quantum well region includes either 5, 7, or 10 quantum wells. 
     
     
         17 . The electroabsorption modulator of  claim 1 , wherein the multiple quantum well region is no more than 240 nm thick, and is preferably no more than 232 nm thick. 
     
     
         18 . The electroabsorption modulator of  claim 1 , wherein a spacing between respective pairs of the quantum wells is in the range of 10 nm to 20 nm. 
     
     
         19 . The electroabsorption modulator of  claim 1 , wherein each of the multiple quantum wells has a thickness in the range of 5 nm to 15 nm. 
     
     
         20 . The electroabsorption modulator of  claim 1 , further comprising a metal electrode in contact with a surface of the active region opposite to the coupler, wherein the MQW region includes at least one tapered portion of MQW material which extends into the taper region; and wherein the metal electrode extends as far as the tapered portion of MQW material. 
     
     
         21 . The electroabsorption modulator of  claim 20 , wherein the electrode has a length in the direction towards the taper region which is greater than 2.5 μm. 
     
     
         22 . The electroabsorption modulator of  claim 1 , wherein the active region includes an N-doped region located above the upper surface of a spacer layer on top of the multiple quantum well region, and wherein the N-doped region comprises Si 0.9 Ge 0.1 .