Extended source transmitter for free space optical communication systems

Abstract

An apparatus for transmission of free space optical communication system signals employing a spatially-extended light source and method of using the same. A laser beam source directs an optical signal into a free end of a segment of multimode fiber. As the optical signal passes through the segment of multimode fiber, the optical signal is converted into a mode-scrambled optical signal. This mode-scrambled signal may then be used as a spatially-extended light source that is directed outward as an optical beam through the use of a collimating lens.

What is claimed is: 
     
       1. A free-space optical communication system (FSOCS) transmitter An apparatus, comprising:
 a spatially-extended light source including comprising: 
 a laser; and 
 to generate a mode-scrambled optical signal, the spatially extended light source further including a segment of multimode fiber having a first end positioned to receive a laser optical signal produced by the laser and a second end from which a mode-scrambled optical signal is emitted and, wherein a portion of the segment of multimode fiber is configured in a series of alternating loops; 
 a power controller, operatively coupled to drive the laserand 
 output optics, optically coupled configured to receive the mode-scrambled optical signal from the spatially-extended light source and direct the mode-scrambled optical signal outward from the FSOCS transmitter apparatus as an optical beam having a controlled divergence; 
 wherein the multimode fiber comprises two or more separate pieces of multimode fiber segments that are joined together to be a continuous single strand. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first end of the segment of multimode fiber is operatively coupled to the laser so as to produce an offset-launched optical signal. 
     
     
       3. The apparatus of  claim 1 , wherein the segment of multimode fiber consists of two or more separate pieces of multimode fiber that are joined together to be a continuous single strand. 
     
     
       4. The apparatus of claim  3  1, wherein there are two joined segments the two or more separate pieces of multimode fiber wherein the segments comprise a first segment piece of multimode fiber comprises segment having a 62.5 micron graded-index core, and the a second segment piece of multimode fiber comprises segment having a 200 micron step-index core. 
     
     
       5. The apparatus of claim  3  1, wherein the two or more segments separate pieces of multimode fibers fiber segments are operatively coupled together using one or more fusion splices. 
     
     
       6. The apparatus of  claim 1 , wherein a laser beam carrying the laser optical signal converges or diverges at an angle that substantially matches a numerical aperture of the multimode fiber. 
     
     
       7. The apparatus of  claim 1 , wherein the mode-scrambled optical signal beam has a power intensity distribution that has a shape substantially similar to a top hat. 
     
     
       8. The apparatus of  claim 1 , wherein an output of the spatially-extended light source is located coincident with in or adjacent a focal plane of a collimating lens comprising the output optics. 
     
     
       9. The apparatus of  claim 1 , further comprising a data modulator operatively coupled to the spatially-extended light source, wherein the data modulator is configured to modulate the optical beam. 
     
     
       10. The apparatus of  claim 1 , wherein the optical beam has a wavelength from in a range of about 400 to 1400 nanometers. 
     
     
       11. A method for generating a free space optical communication system (FSOCS) spatially-extended light signal, comprising:
 producing a mode-scrambled modulated optical signal with a spatially-extended light source by: 
 operatively coupling a segment of multimode fiber configured in a series of alternating loops; and 
 directing an optical signal a laser beam produced by a laser to the a first end of the segment of a multimode fiber to generate a launched optical signal that is received by the first segment of multimode fiber;, wherein the multimode fiber is configured in a series of alternating loops, 
 wherein, as the launched optical signal laser beam passes through the segment of multimode fiber, it is converted into a the spatially-extended light signal that is mode-scrambled optical signal that serves as a spatially extended light source; 
 passing the modulated optical signal through a collimating lens to output an optical beam comprising the FSOCS signal; 
 wherein the multimode fiber comprises two or more separate pieces of multimode fiber segments that are joined together to be a continuous single strand. 
 
     
     
       12. The method of  claim 11 , wherein the segment of multimode fiber consists of two or more separate pieces of multimode fiber, with possibly differing core sizes and index profiles, that have been joined together to form a continuous single strand. 
     
     
       13. The method of claim  12  11, wherein there are the two joined segments or more separate pieces of multimode fiber wherein the segments include a first segment of multimode fiber comprises having a 62.5 micron graded-index core, and the a second segment of multimode fiber comprises having a 200 micron step-index core. 
     
     
       14. The method of  claim 11 , wherein the optical signal laser beam is directed towards the first end of the segment of multimode fiber such that it is received at an offset angle relative to a centerline of an end portion of the segment of multimode fiber. 
     
     
       15. The method of  claim 11 , further comprising focusing the optical signal laser beam into an the first end of the segment of multimode fiber such that the optical signal laser beam is launched into the first end at a point that is offset from a centerline of the multimode fiber. 
     
     
       16. The method of  claim 11 , further comprising focusing the optical signal laser beam such that it converges at an angle that substantially matches a numerical aperture of the segment of multimode fiber. 
     
     
       17. A free-space optical communication system (FSOCS) transmitter An extended light source, comprising:
 means for generating a spatially-scrambled optical signal that functions as an extended light source, wherein the means for generating a spatially-scrambled optical signal comprises an optical fiber segment configured in a series of alternating loops and configured to generate a spatially-scrambled optical signal from a laser beam; and 
 focusing means, positioned to receive the spatially-scrambled optical signal that is generated and to direct the spatially-scrambled optical signal outward from the FSOCS transmitter as a spatially-scrambled optical beam; 
 wherein the optical fiber comprises two or more separate pieces of multimode fiber segments that are joined together to be a continuous single strand. 
 
     
     
       18. The FSOCS transmitter extended light source of  claim 17 , wherein the means for generating a spatially-scrambled optical signal optical fiber comprises:
 lasing means for generating a light signal; and 
 means for converting the light signal laser beam into a mode-scrambled signal.