Laser doppler velocimeter

Abstract

A laser Doppler velocimeter is formed using erbium-doped fiber as the lasing medium. The fiber is diode-pumped. By properly modulating the lasing in the fiber, pulses of radiation may be generated. A telescope acts as the transmission device to focus the radiation at a specified point, and may also act as the receiving system for reflected radiation. The portion of the reflected radiation collected by the receiving system is analyzed to determine the Doppler shift caused by aerosols or objects at the focal point of the telescope.

1 . A laser Doppler velocimeter comprising:
 an optical fiber source of low power comprising: an optical fiber output port;   a bidirectional optical transmitter-receiver comprising:   an optical input-output port for transmitting a beam of radiation to be scattered at a predetermined location and for collection a portion of the scattered radiation: and an optical fiber input output port;   an optical fiber waveguide assembly comprising an optical fiber waveguide input port coupled to said optical fiber output port and an optical fiber output port coupled to said optical fiber input-output port;   a reference signal source:   a detector comprising a detector optical fiber input port for receiving collected scattered radiation and a reference signal; and   coupler means forming part of said waveguide assembly for transmitting at least a portion of the collected scattered radiation and a reference signal to the detector optical fiber input port.   
   
   
       2 . A laser Doppler velocimeter in accordance with  claim 1  characterized in that said source of optical radiation comprises a master oscillator power amplifier optical fiber signal source. 
   
   
       3 . A laser Doppler velocimeter in accordance with  claim 2  characterized in that said master oscillator is alternatively activated and deactivated to produce temporally long pulses. 
   
   
       4 . A laser Doppler velocimeter in accordance with  claim 1  characterized in that the detector is an interference fringe counter. 
   
   
       5 . A laser Doppler velocimeter in accordance with  claim 1  characterized in that the detector is a Doppler frequency detector. 
   
   
       6 . A laser Doppler velocimeter comprising: an optical wave guide formed from optical fiber;
 an optical fiber amplifier for generating or amplifying a beam of laser radiation in the wave guide fiber;   means for transmitting the beam of radiation through the wave guide fiber and out of the velocimeter to be scattered at a predetermined location;   means for collecting a portion of the scattered radiation and passing the collected scattered radiation through at least a portion of the wave guide fiber; and   means for measuring the collected scattered radiation.   
   
   
       7 . The velocimeter of  claim 6  further comprising means for continuously operating the laser. 
   
   
       8 . The velocimeter of  claim 6  further comprising means for alternatively activating and deactivating the laser. 
   
   
       9 . The velocimeter of  claim 6  further wherein the means for measuring the collected scattered radiation is a Doppler frequency detector. 
   
   
       10 . The velocimeter of  claim 6  further wherein the means for measuring the collected scattered radiation is an interference fringe detector. 
   
   
       11 . A system for measuring atmospheric conditions comprising:
 a laser source comprising an optical wave guide formed from a single-mode optical fiber connected to an erbium-doped optical fiber amplifier formed in a ring or linear configuration for providing a beam of coherent laser radiation in the wave guide fiber, and   an output optical system for directing said beam of laser radiation to a region for measuring said atmospheric conditions.   
   
   
       12 . A system according to  claim 11  wherein the wavelength of said beam of laser radiation is between 1.51 and 1.56 microns.