Method and Device for Altering Repetition Rate in a Mode-Locked Laser

Abstract

A mode locking device is disclosed for altering repetition rate in a mode-locked laser. In an example device, laser light is coupled from a fiber into a cavity through a sliding pigtail collimator with a diameter selected such that it is a close tolerance fit with a female snout on a package. A lens focuses laser light to an appropriate spot size onto a SAM or SESAM, such that back-reflection into the fiber is maximized, A piezoelectric transducer is mounted in cooperation with the SAM or SESAM for cavity tuning.

1 . A method of altering repetition rate in a mode-locked laser with a mode locking device, comprising:
 coupling laser light from a fiber through a pigtail collimator into a cavity;   focusing the laser light to an appropriate spot size onto a SAM or SESAM, wherein fluence at a focused spot closely matches saturation fluence of the SAM or SE SAM;   aligning the lens to maximize back reflection into the fiber; and   changing a position of the SAM or SESAM so as to change an optical path length of a laser cavity.   
     
     
         2 . The method of  claim 1 , further comprising free space aligning of the focused laser light onto the SAM or SESAM. 
     
     
         3 . The method of  claim 1 , further comprising mounting the SAM or SESAM onto a piezoelectric transducer to tune the cavity. 
     
     
         4 . The method of  claim 3 , further comprising providing a large stroke measured in hundreds of kilohertz and fast response while producing a useful stroke in a range of 1-2 um for long-term locking. 
     
     
         5 . The method of  claim 1 , further comprising a cat's-eye retro-reflector configuration aligning the laser light onto the SAM or SESAM to achieve robust fiber coupling. 
     
     
         6 . The method of  claim 1 , further comprising providing electrical connections to the SAM or SESAM while mounted on the piezoelectric transducer. 
     
     
         7 . The method of  claim 1 , further comprising providing one or more optical elements in a light path of the mode locking device, the optical elements selected from high-pass filters, low-pass filters, bandpass filters, notch filters, attenuators, electro-optic modulators, polarizers, bulk media, and waveguides. 
     
     
         8 . The method of  claim 1 , further comprising a dichoic mirror in a freespace section of the laser cavity to effectuate wavelength division multiplexing (pump light coupling). 
     
     
         9 . The method of  claim 1 , further comprising tuning of an optical pathlength of the cavity by allowing the pigtail collimator to translate over a given range within the cavity. 
     
     
         10 . The method of  claim 1 , further comprising providing a polarization-maintaining fiber configuration for the laser light. 
     
     
         11 . The method of  claim 1 , further comprising providing independent control of the temperature of the SAM or SESAM. 
     
     
         12 . A mode locking device for altering repetition rate of a mode-locked laser, comprising:
 a piezoelectric transducer controlled by an applied voltage;   a SAM or SESAM in association with the piezoelectric transducer, wherein translating a position of the SAM or SESAM back and forth along a mirror travel range adjusts the free space distance to tune the mode locking device;   an optical fiber in a collimator, the collimator configured to launch light at an angle substantially normal or perpendicular to a surface of the SESAM, wherein translation of the collimator enables coarsely tuning a free space optical path length of the mode locking device; and   a focusing lens to focus the light onto the SAM or SESAM.   
     
     
         13 . The mode locking device of  claim 12 , wherein the focusing lens is selected such that translation of the SAM or SESAM is smaller than the Rayleigh range of the focused light so that the retro-reflected beam is mostly, if not completely, insensitive to changes in the position of the SAM or SESAM. 
     
     
         14 . The mode locking device of  claim 12 , further comprising at least one of a high-pass filter, low-pass filter, notch filter, bandblock filter, attenuator, electro-optic modulator, polarizer, bulk media, and waveguide. 
     
     
         15 . The mode locking device of  claim 12 , further comprising a dichroic mirror in the free space section of the cavity to effectuate wavelength division multiplexing. 
     
     
         16 . The mode locking device of  claim 12 , further comprising a polarization-maintaining fiber configuration for the laser light. 
     
     
         17 . The mode locking device of  claim 12 , further comprising either or both of a thermoelectric cooler and a heating element to control a temperature of the SAM or SESAM. 
     
     
         18 . A mode locking device for altering repetition rate of a mode-locked laser, comprising:
 a piezoelectric material controlled by an applied voltage;   a SAM or SESAM in association with the piezoelectric material, wherein translating a position of the SAM or SESAM back and forth along a mirror travel range adjusts the free space distance to tune the mode locking device;   an optical fiber in a collimator, the collimator configured to launch light at an angle substantially normal or perpendicular to a surface of the SESAM, wherein translation of the collimator enables coarsely tuning a free space optical path length of the mode locking device;   a focusing lens to focus the light onto the SAM or SESAM; and   a mounting block to support the piezoelectric material and/or the SAM or SESAM, the mounting block dampening vibrations and resonant mechanical modes, thereby increasing the bandwidth of the piezoelectric transducer;   wherein a cat's eye retroreflector configuration translates a position of the SAM or SESAM without affecting the coupling efficiency.   
     
     
         19 . The mode locking device of  claim 18 , wherein the piezoelectric material provides a large stroke measured in hundreds of kilohertz and fast response while producing a useful stroke in a range of 1-turn for long-term locking. 
     
     
         20 . The mode locking device of  claim 18 , further comprising:
 at least one of a polarization-maintaining fiber configuration, a heating element on the SAM or SESAM, a thermoelectric cooler on the SAM or SESAM; and   one or more optical elements selected from high-pass filters, low-pass filters, bandpass filters, notch filters, attenuators, dichroic mirrors, electro-optic modulators, polarizers, bulk media, and waveguides.