Distributed feedback laser with differential grating

Abstract

This disclosure concerns distributed feedback (“DFB”) lasers. In one example, a DFB laser includes a body that has first and second end facets. The DFB laser is implemented in a stack configuration that includes an active region interposed between a first top layer and a substrate. A second top layer is disposed on the first top layer and has an index of refraction different from that of the first top layer. Additionally, a grating is defined in one of the top layers and extends from the first end facet to the second end facet. The grating includes a tooth/gap structure whose configuration varies between the first end facet and the second end facet. Finally, an antireflective (AR) coating is disposed on the first end facet and on the second end facet.

1 . A distributed feedback (DFB) laser, comprising: 
 a body having a first end facet and a second end facet, and comprising: 
 a substrate;  
 first and second top layers stacked together, the first top layer having an index of refraction that is different from an index of refraction of the second top layer;  
 an active region interposed between the first top layer and the substrate; and  
 a grating defined in one of the top layers, the grating extending from the first end facet to the second end facet and the grating including a tooth/gap structure whose configuration varies between the first end facet and the second end facet; and  
   an antireflective (AR) coating disposed on the first end facet and on the second end facet.    
   
   
       2 . The DFB laser as recited in  claim 1 , wherein the substrate is n-doped and the first and second top layers are p-doped.  
   
   
       3 . The DFB laser as recited in  claim 1 , wherein the substrate is p-doped and the first and second top layers are n-doped.  
   
   
       4 . The DFB laser as recited in  claim 1 , wherein the first and second top layers are in substantially continuous contact with each other.  
   
   
       5 . The DFB laser as recited in  claim 1 , wherein the active region includes a plurality of quantum wells.  
   
   
       6 . The DFB laser as recited in  claim 1 , wherein the grating is defined in the first top layer.  
   
   
       7 . The DFB laser as recited in  claim 1 , wherein the grating is configured to have a first value of reflectivity “κ” proximate the first end facet and a second value of reflectivity “κ” proximate the second end facet, the first value of reflectivity “κ” being different from the second value of reflectivity “κ.” 
   
   
       8 . The DFB laser as recited in  claim 1 , wherein the grating comprises first and second portions and is implemented such that a configuration of the tooth/gap structure in the first portion is different from a configuration of the tooth/gap structure in the second portion.  
   
   
       9 . The DFB laser as recited in  claim 8 , wherein the first portion of the grating extends approximately from the first end facet to a midpoint of the grating, and the second portion of the grating extends approximately from the midpoint of the grating to the second end facet.  
   
   
       10 . The DFB laser as recited in  claim 1 , wherein one portion of the grating differs from another portion of the grating with regard to one or more of the following parameters: tooth geometry; and, tooth spacing.  
   
   
       11 . The DFB laser as recited in  claim 1 , wherein a transition between differing portions of the grating occurs relatively abruptly.  
   
   
       12 . The DFB laser as recited in  claim 1 , wherein a transition between differing portions of the grating occurs relatively gradually.  
   
   
       13 . The DFB laser as recited in  claim 1 , wherein the tooth/gap structure of the grating is substantially symmetric with respect to a reference point.  
   
   
       14 . The DFB laser as recited in  claim 1 , wherein the tooth/gap structure of the grating is substantially asymmetric with respect to a reference point.  
   
   
       15 . The DFB laser as recited in  claim 1 , wherein at least one parameter of the grating structure varies substantially continuously between the first end facet and the second end facet.  
   
   
       16 . A distributed feedback (DFB) laser, comprising: 
 a body having a first end facet and a second end facet, and comprising: 
 a doped substrate;  
 top and bottom confinement layers, the bottom confinement layer being disposed on the doped substrate;  
 an active layer interposed between the top and bottom confinement layers;  
 first and second top layers stacked together and the first top layer being disposed on the top confinement layer, each of the top layers being doped and the first top layer having an index of refraction that is different from an index of refraction of the second top layer; and  
 a grating defined in the first top layer, the grating extending from the first end facet to the second end facet and the grating including a tooth/gap structure whose configuration varies between the first end facet and the second end facet;  
   a contact layer disposed on the second top layer; and    an antireflective (AR) coating disposed on the first end facet and on the second end facet.    
   
   
       17 . The DFB laser as recited in  claim 16 , wherein a width of each tooth in at least a portion of the grating is substantially equal to one-quarter the wavelength of the light waves emitted by the DFB laser.  
   
   
       18 . The DFB laser as recited in  claim 16 , wherein teeth of the tooth/gap structure have a substantially square cross-section.  
   
   
       19 . The DFB laser as recited in  claim 16 , wherein teeth of the tooth/gap structure have a substantially rectangular cross-section.  
   
   
       20 . The DFB laser as recited in  claim 16 , wherein the first and second top layers are in substantially continuous contact with each other.  
   
   
       21 . The DFB laser as recited in  claim 16 , wherein the active region includes a plurality of quantum wells.  
   
   
       22 . The DFB laser as recited in  claim 1 , wherein the grating is configured to have a first value of reflectivity “κ” proximate the first end facet and a second value of reflectivity “κ” proximate the second end facet, the first value of reflectivity “κ” being different from the second value of reflectivity “κ.” 
   
   
       23 . The DFB laser as recited in  claim 16 , wherein the grating comprises first and second portions and is implemented such that a configuration of the tooth/gap structure in the first portion is different from a configuration of the tooth/gap structure in the second portion.  
   
   
       24 . The DFB laser as recited in  claim 23 , wherein the first portion of the grating extends approximately from the first end facet to a midpoint of the grating, and the second portion of the grating extends approximately from the midpoint of the grating to the second end facet.  
   
   
       25 . The DFB laser as recited in  claim 16 , wherein one portion of the grating differs from another portion of the grating with regard to one or more of the following parameters: tooth geometry; and, tooth spacing.  
   
   
       26 . The DFB laser as recited in  claim 16 , wherein a transition between differing portions of the grating occurs relatively abruptly.  
   
   
       27 . The DFB laser as recited in  claim 16 , wherein a transition between differing portions of the grating occurs relatively gradually.  
   
   
       28 . The DFB laser as recited in  claim 16 , wherein the tooth/gap structure of the grating is substantially symmetric with respect to a reference point.  
   
   
       29 . The DFB laser as recited in  claim 16 , wherein the tooth/gap structure of the grating is substantially asymmetric with respect to a reference point.  
   
   
       30 . The DFB laser as recited in  claim 16 , wherein at least one parameter of the grating structure varies substantially continuously between the first end facet and the second end facet.  
   
   
       31 . The DFB laser as recited in  claim 30 , wherein the at least one parameter of the grating structure comprises a tooth period.  
   
   
       32 . The DFB laser as recited in  claim 16 , further comprising at least one phase shifting tooth portion disposed in the grating.  
   
   
       33 . The DFB laser as recited in  claim 32 , wherein the at least one phase shifting tooth portion is disposed proximate one of the first and second end facets.