Communications system employing single-mode lasers and multimode optical fibers

Abstract

An optical transmission system having a single mode laser that generates an optical signal that is carried by a multimode optical fiber to a receiver is disclosed. The single mode laser has an emitting aperture from which the optical signal is routed to the input end of the multimode optical fiber. The receiver receives light from the output end of the optical fiber. The receiver includes an equalizer that corrects the received light for modal dispersion introduced by the multimode optical fiber. Light leaving the emitting aperture of the laser is introduced into the multimode optical fiber in a pattern that excites a subset of the plurality of optical transmission modes thereby reducing the modal dispersion introduced into the light signal and stabilizing the dispersion in time. The improved dispersion enables further correction of the dispersion through the utilization of equalization techniques.

1 . An optical transmission system comprising: 
 a single mode laser having an emitting aperture;    a multimode optical fiber having an input end and an output end and a plurality of optical transmission modes; and    a receiver that receives light from said output end, said receiver comprising an equalizer that corrects said received light for modal dispersion introduced by said multimode optical fiber, wherein light leaving said emitting aperture of said laser is introduced into said multimode optical fiber in a pattern that excites a subset of said plurality of optical transmission modes.    
     
     
         2 . The optical transmission system of  claim 1  further comprising an optical element that couples light from said emitting aperture to said input end.  
     
     
         3 . The optical transmission system of  claim 2  wherein said optical element comprises a diffractive optical element that generates a non-uniform illumination pattern on said input end.  
     
     
         4 . The optical transmission system of  claim 2  wherein said optical element comprises a patch cord that connects said emitting aperture to said input end such that said emitting aperture illuminates an off-center spot on said input end.  
     
     
         5 . The optical transmission system of  claim 1  wherein said emitting aperture is positioned relative to said input end such that light from said emitting aperture illuminates an off-center spot on said input end.  
     
     
         6 . The optical transmission system of  claim 1  wherein said equalizer is an adaptive equalizer.  
     
     
         7 . The optical transmission system of  claim 1  wherein said laser comprises a VCSEL.  
     
     
         8 . The optical transmission system of  claim 1  wherein said laser comprises a Fabry-Perot laser.  
     
     
         9 . The optical transmission system of  claim 1  wherein said laser comprises an edge-emitting laser.  
     
     
         10 . The optical transmission system of  claim 1  wherein said laser comprises an externally-modulated laser.  
     
     
         11 . A method for transmitting a signal over a MMF optical link having an input end and an output end, said method comprising: 
 modulating a light signal from a single laser;    coupling said modulated signal to said input end in a manner that excites a restricted subset of optical modes of said MMF; and    receiving a light signal from said output end and correcting said received signal for dispersion in said MMF to create an output signal.    
     
     
         12 . The method of  claim 11  wherein said modulated signal is coupled to said input end utilizing an optical element that couples light from an emitting aperture of said laser to said input end to provide a non-uniform illumination pattern.  
     
     
         13 . The method of  claim 12  wherein said optical element comprises a diffractive optical element.  
     
     
         14 . The method of  claim 12  wherein said optical element comprises a patch cord that connects said emitting aperture to said input end such that said emitting aperture illuminates an off-center spot on said input end.  
     
     
         15 . The method of  claim 11  wherein said emitting aperture is positioned relative to said input end such that light from said emitting aperture illuminates an off-center spot on said input end.  
     
     
         16 . The method of  claim 11  wherein said correction of said received signal comprises adaptive equalization.