High efficiency distributed feedback (dfb) laser with low-duty cycle grating

Abstract

The invention provides a grating for a distributed feedback laser having decreased diffraction loss with reduced +/−1 order diffraction and scattering loss resulting from the reduced imperfections in the grating fabrication. In various embodiments, the grating has a low duty cycle wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is less than 0.5. Further, in some preferred embodiments, the invention includes a laser, the laser comprising a distributed feedback laser wherein the laser includes a grating having less diffraction and less scattering loss. In various exemplary embodiments, the grating is further a partial grating, thereby providing increased efficiency resulting from a decrease in first-order diffraction loss due to the grating being separated from the front and rear facets and in some exemplary embodiments being situated at the area of lowest electric filed.

1 . A grating for a laser wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is less than 0.5. 
     
     
         2 . The grating of  claim 1 , wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is from about 0.1 to about 0.49. 
     
     
         3 . The grating of  claim 1 , wherein the fabrication is completed by regrowth of high-index material on low-index grating layer. 
     
     
         4 . The grating of  claim 1 , wherein the fabrication is completed by regrowth of low-index material on a high-index grating or high index material on a low index grating. 
     
     
         5 . The grating of  claim 1 , wherein the grating has a high-index layer of GaAs, AlGaAs, InGaP, InGaAsP, AlInGaP, InP, GaSb, InGaSb, GaN or InGaN. 
     
     
         6 . An edge emitting distributed feedback semiconductor laser comprising:
 a front facet,   a rear facet, which defines, together with the front facet, a laser cavity;   a grating positioned within the laser cavity, wherein the ratio of the length of the low-index portion of the grating ‘a’ to the length of the pitch of the grating ‘b’ is less then 0.5.   
     
     
         7 . The laser of  claim 6 , wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is from about 0.1 to about 0.49. 
     
     
         8 . The laser of  claim 7 , wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is between from about 0.15 to about 0.45. 
     
     
         9 . The laser of  claim 6 , wherein the grating has a low-index layer of InGaP and a regrown layer of AlGaAs. 
     
     
         10 . A semiconductor laser comprising:
 a front facet,   a rear facet, which defines, together with the front facet, a laser cavity;   a grating positioned within the laser cavity, wherein the ratio of the length of the low-index portion of the grating ‘a’ to the length of the pitch of the grating ‘b’ is less then 0.5; and   wherein the grating is a partial grating and separated from the front facet and the rear facet.   
     
     
         11 . The laser of  claim 8 , wherein the grating has a ratio of the low-index portion of the grating ‘a’ to the pitch of the grating is from about 0.15 to about 0.45. 
     
     
         12 . The laser of  claim 10 , wherein the partial grating has a length that is less than about 75% of the length of the laser cavity. 
     
     
         13 . The laser of  claim 10 , wherein the partial grating is positioned in the laser cavity separated from both the front facet and the back facet. 
     
     
         14 . The laser of  claim 10 , wherein the partial grating is situated proximate to the back facet. 
     
     
         15 . The laser of  claim 10 , wherein the grating is placed in the laser cavity at the area of the lowest electric field. 
     
     
         16 . The laser of  claim 10 , wherein the edge emitting semiconductor laser is a distributed feedback laser. 
     
     
         17 . A method for fabricating a semiconductor laser having a laser cavity defined by a front facet and a rear facet, the laser comprising:
 fabricating a grating within the laser cavity wherein the ratio of the length of the low-index portion of the grating ‘a’ to the pitch of the grating ‘b’ is less than 0.5.   
     
     
         18 . The method of  claim 17 , wherein the ratio of the length of the low-index portion of the grating ‘a’ to the length of the pitch of the grating ‘b’ is from about 0.1 to about 0.5. 
     
     
         19 . The method of  claim 18 , wherein the fabrication is completed by regrowth of high-index material on a low-index grating. 
     
     
         20 . The method of  claim 18 , wherein the fabrication is completed by regrowth of low-index material on a high-index grating. 
     
     
         21 . The method of  claim 18  wherein fabrication of the grating further comprises fabricating a partial grating that is less then the length of the laser cavity. 
     
     
         22 . A composite laser having more than one semiconductor laser, wherein at least one semiconductor laser comprises:
 a front facet,   a rear facet, which defines, together with the front facet, a laser cavity;   a grating wherein the ratio of the length of the low-index portion ‘a’ to the length of the pitch of the grating ‘b’ is less than 0.5.   
     
     
         23 . The composite laser of  claim 22 , wherein at least one semiconductor laser further has a grating that is a partial grating. 
     
     
         24 . The composite laser of  claim 23 , wherein the partial grating is positioned within the laser cavity separated from the front facet and the back facet. 
     
     
         25 . The composite laser of  claim 24 , wherein the partial grating is positioned within the cavity proximate to the back facet.