Waveguide dual-depletion region (ddr) photodiodes

Abstract

Consistent with the present disclosure, a DDR photodiode is provided on a substrate adjacent to a passive waveguide. In order to efficiently capture light output from the waveguide, the photodiode is coupled to the waveguide with a butt-joint. As a result, the photodiode and the waveguide abut one another such that the dominant mode of light propagating in the waveguide parallel to the substrate is supplied directly to a side of the absorber layer of the photodiode without, in one example, evanescent coupling, nor is a resonant coupler required to supply light to the photodiode. Thus, light is absorbed more efficiently in the photodiode such that the photodiode may have a shorter length. In addition, since substantially all light is input to the photodiode, nearly complete absorption and nearly ideal quantum efficiency can be achieved in a relatively short length. Further, the improved linearity associated with DDR photodiodes is preserved with the exemplary butt joint configurations disclosed herein.

1 . An optical receiver, comprising:
 a substrate;   an optical waveguide provided on a first region of the substrate; and   a photodiode provided on a second region of the substrate, such that an interface between the optical waveguide and the photodiode constitutes a butt joint, the photodiode includes:
 a first semiconductor layer having a p-conductivity type, the first semiconductor layer being a p-type cladding layer, 
 a second semiconductor layer having n-conductivity type, the second semiconductor layer being an n-type cladding layer, 
 an absorber layer provided between the p-type cladding layer and the n-type cladding layer, the absorber layer including a first undoped semiconductor layer, such that the absorber layer is aligned with the core layer of the optical waveguide to receive, via the interface, an optical signal propagating in the optical waveguide, and 
 a second undoped semiconductor layer provided between the absorber layer and the second semiconductor layer, such that, in an absence of a reverse bias applied to the photodiode, a first depletion region forms in the absorber layer and a second depletion region forms in the second undoped semiconductor layer, 
   wherein the photodiode is configured to receive an optical signal supplied by the optical waveguide, the optical signal having a propagation direction in the optical waveguide, such that the interface between the optical waveguide and the photodiode is provided at a non-orthogonal angle relative to the direction of propagation of the optical signal.   
     
     
         2 . An optical receiver in accordance with  claim 1 , wherein the absorber layer includes indium gallium arsenide. 
     
     
         3 . An optical receiver in accordance with  claim 2 , wherein the second undoped semiconductor layer includes indium phosphide. 
     
     
         4 . An optical receiver in accordance with  claim 1 , wherein the n-type cladding layer includes indium phosphide. 
     
     
         5 . An optical receiver in accordance with  claim 1 , wherein the p-type cladding layer includes indium phosphide. 
     
     
         6 . An optical receiver in accordance with  claim 1 , further including a band smoothing region provided between the p-type cladding and the absorber layer, the band smoothing region including a quaternary semiconductor alloy. 
     
     
         7 . An optical receiver in accordance with  claim 6 , wherein a composition of the quaternary semiconductor alloy changes along a thickness of the smoothing region. 
     
     
         8 . An optical receiver in accordance with  claim 6 , wherein the quaternary semiconductor alloy is indium gallium arsenic phosphide. 
     
     
         9 . An optical receiver in accordance with  claim 8 , wherein a concentration of phosphorus in the smoothing region changes along a thickness of the smoothing region. 
     
     
         10 . An optical receiver in accordance with  claim 1 , further including:
 a first band smoothing region provided between the p-type cladding and the absorber layer, the first band smoothing region including a first quaternary semiconductor alloy; and   a second band smoothing region provided between the n-type cladding and the absorber layer, the second band smoothing region including a second quaternary semiconductor alloy.   
     
     
         11 . An optical receiver in accordance with  claim 10 , wherein the first and second quaternary semiconductor alloys include indium gallium arsenic phophide. 
     
     
         12 . An optical receiver in accordance with  claim 11 , wherein a concentration of phosphorus in the first smoothing region changes along a thickness of the first smoothing region, and a concentration of phosphorus in the second smoothing region changes along a thickness of the second smoothing region. 
     
     
         13 . An optical receiver in accordance with  claim 1 , wherein the optical signal is amplitude modulated. 
     
     
         14 . An optical receiver in accordance with  claim 1 , wherein the optical signal is modulated in accordance with a m-quadrature amplitude modulation (m-QAM) modulation format, wherein m is a positive integer greater than 1. 
     
     
         15 . An optical receiver in accordance with  claim 1 , wherein the photodiode is a dual depletion region photodiode. 
     
     
         16 . An optical receiver in accordance with  claim 1 , wherein the optical signal travels in a propagation direction in the optical waveguide, and the optical signal travels in the propagation direction in the photodiode, a width of the optical waveguide transverse to the propagation direction of the optical signal being uniform along a length of the optical waveguide, and a width of the photodiode transverse to the propagation direction of the optical signal being uniform along a length of the photodiode. 
     
     
         17 . An optical receiver in accordance with  claim 1 , wherein the interface and the propagation direction define an angle, the angle having a magnitude greater than or equal to 5 degrees and less than or equal to 85 degrees. 
     
     
         18 . An optical receiver, comprising:
 a substrate;   an optical waveguide provided on a first region of the substrate;   a photodiode provided on a second region of the substrate, such that an interface between the optical waveguide and the photodiode constitutes a butt joint,   wherein the photodiode is configured to receive an optical signal supplied by the optical waveguide, the optical signal propagating in the optical waveguide in a propagation direction, and the optical signal propagating in the photodiode in the propagation direction, such that a width of the optical waveguide increases in the propagation direction.   
     
     
         19 . An optical receiver in accordance with  claim 18 , wherein a width of the photodiode transverse to the propagation direction of the optical signal is uniform along a length of the photodiode. 
     
     
         20 . An optical receiver in accordance with  claim 18 , wherein a width of the photodiode transverse to the propagation direction of the optical signal decreases along a length of the photodiode. 
     
     
         21 . An optical receiver in accordance with  claim 18 , wherein the interface is oriented at a non-orthogonal angle relative to the propagation direction of the optical signal. 
     
     
         22 . An optical receiver in accordance with  claim 21 , wherein the interface and the propagation direction define an angle, the angle having a magnitude greater than or equal to  5  degrees and less than or equal to  85  degrees. 
     
     
         23 . An optical receiver in accordance with  claim 18 , wherein, in an absence of a reverse bias applied to the photodiode, the photodiode has a first depletion region and a second depletion region. 
     
     
         24 . An optical receiver in accordance with  claim 23 , wherein the first depletion region is in a first undoped semiconductor layer and the second depletion is in a second undoped semiconductor layer. 
     
     
         25 . An optical receiver in accordance with  claim 24 , wherein the first and second undoped semiconductor layers include first and second semiconductors, respectively, the first and second semiconductors being different from one another. 
     
     
         26 . An optical receiver in accordance with  claim 25 , wherein the photodiode includes a first cladding layer and a second cladding layer, the first and second undoped semiconductor layers being provided between the first and second cladding layers. 
     
     
         27 . An optical receiver in accordance with  claim 6 , wherein the absorber layer comprises a quaternary semiconductor alloy including indium, gallium, arsenic, and phosphorus. 
     
     
         28 . An optical receiver in accordance with  claim 1 , wherein the absorber layer comprises a quaternary semiconductor alloy including of indium, gallium, arsenic, and aluminum. 
     
     
         29 . An optical receiver in accordance with  claim 1 , wherein the optical receiver includes:
 a local oscillator laser; and   an optical hybrid circuit that receives an optical output from the local oscillator laser, wherein the optical signal is supplied by the optical hybrid circuit.