Sub-wavelength grating integrated VCSEL

Abstract

A vertical cavity surface emitting laser (VCSEL) is described using a sub-wavelength grating (SWG) structure that has a very broad reflection spectrum and very high reflectivity. The grating comprises segments of high and low refractive index materials with an index differential between the high and low index materials. By way of example, a SWG reflective structure is disposed over a low index cavity region and above another reflective layer (either SWG or DBR). In one embodiment, the SWG structure is movable, such as according to MEMS techniques, in relation to the opposing reflector to provide wavelength selective tuning. The SWG-VCSEL design is scalable to form the optical cavities for a range of SWG-VCSELs at different wavelengths, and wavelength ranges.

1 . A sub-wavelength grating reflector, comprising: 
 a first layer of low refractive index material;    a plurality of periodically spaced apart segments of high refractive index material on said layer of low refractive index material; and    a second layer of low refractive index material on said segments of high refractive index material.    
     
     
         2 . A grating reflector as recited in  claim 1 , wherein said second layer of low refractive index material is disposed between said segments of high index material.  
     
     
         3 . A grating reflector as recited in  claim 2 , wherein said second layer of low refractive index material comprises air.  
     
     
         4 . A grating reflector as recited in  claim 1:   wherein said second layer of low refractive index material is over said segments of high refractive index material; and    wherein said low refractive index material comprises air.    
     
     
         5 . A grating reflector as recited in  claim 1:   wherein said first layer of low refractive index material is below said segments of high refractive index material; and    wherein said first layer of low refractive index material comprises air.    
     
     
         6 . A grating reflector as recited in  claim 1 , wherein said segments of high refractive index material comprise a Group III-V compound.  
     
     
         7 . A grating reflector as recited in  claim 1 , wherein said segments of high refractive index material comprise a Group VI element.  
     
     
         8 . A grating reflector as recited in  claim 1 , wherein said segments of high refractive index material comprise a Group II-VI compound, or the use of organic polymers.  
     
     
         9 . A grating reflector as recited in  claim 1 , wherein said grating is integrated within a solar cell.  
     
     
         10 . A grating reflector as recited in  claim 1 , wherein said grating is integrated within a lens.  
     
     
         11 . A grating reflector as recited in  claim 1 , wherein said grating is within a monolithically integrated device selected from the group of devices consisting of optical emitters, optical detectors and optical filters.  
     
     
         12 . An optical resonator cavity, comprising: 
 a first sub-wavelength grating reflector configured with a plurality of periodically spaced segments of high refractive index material over a low refractive index material, the combination forming a first reflector; and    a distributed Bragg reflector retained substantially parallel to said first reflector;    wherein said distributed Bragg reflector is sufficiently separated from said first sub-wavelength grating reflector to form a cavity resonator region between said sub-wavelength grating reflector and said distributed Bragg reflector.    
     
     
         13 . An optical resonator cavity as recited in  claim 12 , further comprising: 
 a plurality of semiconductor quantum structures within an active region that forms said cavity region, said segments of high refractive index material, or a combination of said cavity region and said segments of high refractive index material.    
     
     
         14 . An optical resonator cavity as recited in  claim 13 , wherein said quantum structures comprise quantum wells, or quantum wires, or quantum dots, or any combination of quantum wells, quantum wires, and quantum dots.  
     
     
         15 . An optical resonator cavity as recited in  claim 12 , wherein said optical resonator is within a monolithically integrated vertical cavity surface emitting laser.  
     
     
         16 . An optical resonator cavity as recited in  claim 12 , wherein said optical resonator cavity is integrated within a monolitically integrated vertical external cavity surface emitting laser.  
     
     
         17 . An optical resonator cavity as recited in  claim 12 , wherein said optical resonator cavity is monolitically integrated within a light emitting diode (LED).  
     
     
         18 . An optical resonator cavity as recited in  claim 12 , wherein said optical resonator cavity is integrated within an optical detector.  
     
     
         19 . An optical resonator cavity as recited in  claim 12 , wherein said optical resonator cavity is integrated within an optical filter.  
     
     
         20 . An optical resonator cavity as recited in  claim 12:   further comprising a means for moving said first sub-wavelength grating reflector in relation to said distributed Bragg reflector; and    wherein said means for moving said first sub-wavelength grating reflector in relation to said distributed Bragg reflector comprises a micro-electro-mechanical system (MEMS).    
     
     
         21 . A surface emitting optical device cavity, comprising: 
 a first sub-wavelength grating (SWG) reflector configured with a plurality of periodically spaced segments of high refractive index material over a layer of low refractive index material; and    a distributed Bragg reflector (DBR) substantially parallel to said first reflector;    wherein said distributed Bragg reflector is separated from said first sub-wavelength grating reflector by a predetermined distance to form a resonant cavity.    
     
     
         22 . A surface emitting optical device cavity as recited in  claim 21:   further comprising a plurality of semiconductor quantum structures retained within said resonant cavity;    wherein said plurality of quantum structures are selected from the group of quantum structures consisting essentially of quantum wells, quantum wires and quantum dots.    
     
     
         23 . A surface emitting optical device cavity as recited in  claim 21 , wherein said optical resonator is within a vertical cavity surface emitting laser of an integrated circuit device.  
     
     
         24 . A surface emitting optical device cavity as recited in  claim 21 , further comprising a micro-electro-mechanical system (MEMS) for moving said first sub-wavelength grating reflector in relation to said distributed Bragg reflector.  
     
     
         25 . A surface emitting optical device cavity as recited in  claim 21 , further comprising a plurality of semiconductor quantum structures within an active region that forms said cavity region, or within said segments of high refractive index material, or within a combination of said cavity region and said segments of high refractive index material.  
     
     
         26 . A vertical-cavity surface emitting laser device, comprising: 
 a first sub-wavelength grating (SWG) reflector configured with a plurality of periodically spaced segments of high refractive index material over a layer of low refractive index material forming a first reflector;    a first distributed Bragg reflector (DBR) configured with a plurality of alternating layers of high and low refractive index materials;    said first distributed Bragg reflector retained substantially parallel to said first reflector to form a second reflector;    a resonant cavity of predetermined depth formed between said first reflector and said second reflector;    means for optical confinement between said first and second reflectors; and    means for current injection.    
     
     
         27 . A vertical-cavity surface emitting laser device as recited in  claim 26 , further comprising means for changing the distance between said first sub-wavelength grating and said first distributed Bragg reflector to form a wavelength variable vertical-cavity surface emitting laser device.  
     
     
         28 . A vertical-cavity surface emitting laser device as recited in  claim 26 , further comprising at least one reflective protective layer between said first sub-wavelength grating reflector and said resonant cavity.  
     
     
         29 . A vertical-cavity surface emitting laser device as recited in  claim 28 , wherein said reflective protective layer comprises a second distributed Bragg reflector comprising fewer layers than said first distributed Bragg reflector.  
     
     
         30 . A vertical-cavity surface emitting laser device as recited in  claim 28 , wherein said reflective protective layer comprises a second distributed Bragg reflector which is p-doped in the case of the first distributed Bragg reflector being n-doped, or n-doped in the case of the first distributed Bragg reflector being p-doped.  
     
     
         31 . A vertical-cavity surface emitting laser device as recited in  claim 26 , wherein said means for current injection comprises a first contact electrode coupled to said second distributed Bragg reflector or said first sub-wavelength grating, and a second contact electrode coupled to said first distributed Bragg reflector.  
     
     
         32 . A vertical-cavity surface emitting laser device as recited in  claim 26 , wherein said means for optical confinement comprises an in-plane aperture through a vertical portion of said resonant cavity configured to provide optical confinement.  
     
     
         33 . A vertical-cavity surface emitting laser device as recited in  claim 26 , further comprising a plurality of semiconductor quantum structures within an active region that forms said resonant cavity, or within said segments of high refractive index material, or within a combination of said resonant cavity and said segments of high refractive index material.  
     
     
         34 . A vertical-cavity surface emitting laser device as recited in  claim 33 , wherein said quantum structures are selected in any combination from the group of quantum elements consisting essentially of quantum wells, quantum wires and quantum dots.