Vertically-coupled surface-etched grating dfb laser

Abstract

A VCSEG-DFB laser, fully compatible with MGVI design and manufacturing methodologies, for single growth monolithic integration in multi-functional PICs is presented. It comprises a laser PIN structure, in mesa form, etched from upper emitter layer top surface through the active, presumably MQW, gain region, down to the top surface of the lower emitter. Lower electrical contacts sit adjacent the mesa disposed on the lower emitter layer with upper strip contacts disposed atop the upper emitter layer on the mesa top. An SEG is defined/etched from mesa top surface, between the upper strip contacts, through upper emitter layer down to or into the SCH layers. Vertical confinement is provided by the SCH structure and the lateral profile in the bottom portion of the mesa provides lateral confinement. The guided mode interacts with the SEG by the vertical tail penetrating the SEG and evanescent field coupling to the SEG.

1 . A device comprising:
 a mesa formed within a semiconductor structure grown on a semiconductor substrate in one growth process supporting a fundamental optical mode and comprising a plurality of semiconductor layers, an undercut formed within a first predetermined layer of the plurality of semiconductor layers and a surface etched grating vertically coupled to the fundamental optical mode, wherein the undercut in conjunction with the mesa provides confinement of the fundamental optical mode and current injected into the mesa.   
     
     
         2 . The device according to  claim 1  wherein,
 the surface grating provides for manipulation of the sign of the imaginary part of the coupling coefficient between the surface grating and fundamental optical mode to establish either “gain-type” or “loss-type” coupling. 
 
     
     
         3 . The device according to  claim 1  wherein,
 the mesa further comprises a pair of separate confined hetero structures and an active layer such that the fundamental optical mode experiences optical gain in dependence upon the injected current. 
 
     
     
         4 . The device according to  claim 1  wherein,
 the surface etched grating is etched to a predetermined depth into the uppermost layer of the plurality of semiconductor layers. 
 
     
     
         5 . The device according to  claim 1  further comprising;
 a first electrical contact disposed atop the mesa adjacent the surface etched grating, 
 a second electrical contact disposed atop a semiconductor layer below the plurality of semiconductor layers and adjacent the mesa. 
 
     
     
         6 . A method comprising:
 providing a mesa formed within a semiconductor structure grown on a semiconductor substrate in one growth process supporting a fundamental optical mode and comprising a plurality of semiconductor layers, an undercut formed within a first predetermined layer of the plurality of semiconductor layers and a surface etched grating vertically coupled to the fundamental optical mode, wherein the undercut in conjunction with the mesa provides confinement of the fundamental optical mode and current injected into the mesa.   
     
     
         7 . The method according to  claim 6  wherein,
 providing the surface grating comprises establishing the sign of the imaginary part of the coupling coefficient between the surface grating and fundamental optical mode to a predetermined value to establish either “gain-type” or “loss-type” coupling. 
 
     
     
         8 . The method according to  claim 6  wherein,
 providing the mesa further comprises providing a pair of separate confined heterostructures and an active layer such that the fundamental optical mode experiences optical gain in dependence upon the injected current. 
 
     
     
         9 . The method according to  claim 6  wherein,
 providing the surface etched grating comprises etching to a predetermined depth the uppermost layer of the plurality of semiconductor layers. 
 
     
     
         10 . The device according to  claim 6  further comprising;
 providing a first electrical contact disposed atop the mesa adjacent the surface etched grating; and 
 providing a second electrical contact disposed atop a semiconductor layer below the plurality of semiconductor layers and adjacent the mesa. 
 
     
     
         11 . A device comprising:
 an epitaxial semiconductor structure comprising a plurality of semiconductor layers grown on a semiconductor substrate in one growth process; and   an optical emitter by processing the epitaxial semiconductor structure, the optical emitter comprising;
 a mesa formed by etching from an upper emitter layer sequentially down through a separate confined hetero structure, an active layer, and an undercut layer to the upper surface of a lower emitter layer; 
 an undercut formed by etching a predetermined amount of a layer within the mesa; and 
 a surface grating formed over a predetermined central portion of the upper emitter layer, wherein 
   the mesa and undercut act to provide vertical and lateral confinement of an optical mode propagating within the optical emitter.   
     
     
         12 . The device according to  claim 11  wherein,
 the layer within the mesa is the undercut layer or the active layer. 
 
     
     
         13 . The device according to  claim 11  wherein,
 forming an undercut within a layer of the mesa further comprises etching the each of the other layers within the mesa a predetermined amount, the predetermined amount being different for each other layer. 
 
     
     
         14 . The device according to  claim 11  further comprising;
 a vertical coupler for vertically coupling the emitted optical mode of the optical emitter to a passive waveguide formed within the semiconductor structure, the passive waveguide vertically disposed below the optical emitter and characterized by a bandgap lower than the bandgap of the active layer. 
 
     
     
         15 . The device according to  claim 11  wherein,
 the optical emitter operates in at least one of a DFB and a DBR configuration. 
 
     
     
         16 . The device according to  claim 11  wherein,
 the surface grating is formed by etching a single series of periodic structures in the upper emitter layer of the epitaxial semiconductor structure to a predetermined depth into at least one of the upper emitter layer and the separate confined hetero structure. 
 
     
     
         17 . The device according to  claim 1  further comprising;
 a first electrical contact formed atop the upper emitter layer; and 
 a second electrical contact formed atop the lower emitter layer and disposed adjacent the mesa.