Q-switched all-fibre laser

Abstract

A Q-switched all-fiber laser utilizes a long period fibre grating (LPFG) modulator. The LPFG modulator is characterized by optical spectral characteristics that are controlled by application of stress via an actuator. In particular, the actuator applies stress to selected sections of the LPFG in order to modulate a light signal at a specified wavelength. Further, a controller is utilized to control the application of stress in the time domain, and thereby switch the Q-factor of the fiber laser cavity. In addition to the LPFG, the laser cavity comprises a pair of fiber Bragg gratings (FBGs) and a fiber gain medium.

1 . Apparatus comprising:
 at least one fiber Bragg grating reflector;   at least one pump light source;   a gain fibre; and   at least one long period fiber grating modulator employed to switch Q factor of the laser cavity, whereby a Q-switched fibre laser is provided.   
     
     
         2 . The apparatus of  claim 1  wherein the long period fiber grating modulator is operative in response to application of stress to at least one area of the fibre to change refractive index of the area while stress is applied. 
     
     
         3 . The apparatus of  claim 1  wherein the fiber Bragg grating is characterized by a center wavelength matching a modulating wavelength of the long period fiber grating modulator 
     
     
         4 . The apparatus of  claim 1  wherein the long period fiber grating modulator includes at least one phase shift section. 
     
     
         5 . The apparatus of  claim 1  wherein the long period fiber grating modulator includes first and second cascaded long period fibre gratings or more cascaded long period fiber gratings in series. 
     
     
         6 . The apparatus of  claim 1  further including a pump source which couples pump light into the laser cavity between the long period fiber grating modulator and the gain fibre. 
     
     
         7 . The apparatus of  claim 1  wherein the laser is a ring laser having a fibre loop, and wherein the long period fiber grating modulator is part of the fibre loop. 
     
     
         8 . The apparatus of  claim 1  wherein the laser is a ring laser having a fibre loop, and wherein the long period fiber grating modulator is outside of the fibre loop. 
     
     
         9 . The apparatus of  claim 1  wherein the laser is a ring laser having a fibre loop, and further including a pump source which couples pump light directly into the fibre loop. 
     
     
         10 . A method comprising:
 introducing pump light to laser cavity, the laser cavity includes at least one fiber Bragg grating reflector, a gain fibre, and at least one long period fiber grating modulator; and   switching the Q factor of laser cavity with the long period fiber grating modulator, whereby a Q-switched fibre laser is provided.   
     
     
         11 . The method of  claim 10  including the further step of controlling the long period fiber grating modulator via application of stress to at least one area of the fibre to change refractive index of the area while stress is applied. 
     
     
         12 . The method of  claim 10  including the further step of reflecting the light with at least one fiber Bragg grating characterized by a center wavelength matching a modulating wavelength of the long period fiber grating modulator 
     
     
         13 . The method of  claim 10  including the further step of switching the Q factor of the laser cavity with a long period fiber grating modulator having at least one phase shift section. 
     
     
         14 . The method of  claim 10  including the further step of switching the Q factor of the laser cavity with a long period fiber grating modulator having first and second cascaded long period fibre gratings or more cascaded long period fiber gratings in series. 
     
     
         15 . The method of  claim 10  including the further step of coupling pump light into the laser cavity between the long period fiber grating modulator and the gain fibre. 
     
     
         16 . The method of  claim 10  wherein the laser is a ring laser having a fibre loop, and including the further step of switching the Q factor of the laser cavity with a long period fiber grating modulator that is part of the fibre loop. 
     
     
         17 . The method of  claim 10  wherein the laser is a ring laser having a fibre loop, and including the further step of switching Q factor of the laser cavity with a long period fiber grating modulator that is outside of the fibre loop. 
     
     
         18 . The method of  claim 10  wherein the laser is a ring laser having a fibre loop, and further the pump light is coupled pump directly into the fibre loop.