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.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present applicationThis is a Reissue application of U.S. Ser. No. 10 / 681,552, filed Oct. 7, 2003, now U.S. Pat. No. 7,072,543, granted Jul. 4, 2006, which is a continuation-in-part of U.S. patent application Ser. No. 10 / 128,953 filed Apr. 22, 2002, now U.S. Pat. No. 6,810,175, entitled “Off-Axis Mode Scrambler” by Jun Shan Wey et al., which is incorporated herein by reference. The present invention is also related to U.S. patent application Ser. No. 09 / 886,248 filed Jun. 20, 2001, entitled “Multimode Optical Signal Transmission in a Free-Space Optical Communication System” by Mark Lewis Plett.FIELD OF THE INVENTION[0002]The present invention generally relates to free-space optical communications systems (FSOCSs), and, more specifically, to a method and apparatus for increasing laser output power while maintaining compliance with eye safety standards.BACKGROUND INFORMATION[0003]With the increasing popularity of wide area networks (WAN5...

AI Technical Summary

Benefits of technology

[0007]According to aspects of the present invention, an apparatus and method is provided for generating a FSOCS optical signal via a spatially-extended light source. In one embodiment, the spatially-extended light source is in the form of a mode-scrambled optical fiber light distribution and the transmitter employs single-aperture optics. An optical beam having a “top hat” intensity profile is produced, which provides several advantages. One of these advantages is the transmitter power for a given laser product classification may be increased while still satisfying peak irradiance limits defined for eye safety.

Problems solved by technology

As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.

Transmission of optical signals through free space poses many challenges.

Notably, atmospheric conditions can greatly degrade signal strength, and consequently, reduce the maximum link distances.

Also, when launching a single-mode beam from a free-space optical terminal using conventional means, atmospheric scintillation and other wavefront distortion cause the beam to break up into chaotic bright and dark spots.

In some FSOCS applications, non-uniform power distributions far from the transmitter tend to undesirably limit the permissible overall power of the optical signal because the peak possible irradiance must meet specified eye safety standards.

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