Power stabilization of semiconductor laser harmonic frequency conversion modules
The invention relates to a fiber laser and harmonic frequency conversion module incorporating a 90 degree Polarization Maintaining (PM) fiber fusion splice therebetween for providing temperature insensitive power stabilization. The present invention has found that incorporating at least one 90 degree splice of the transmission axes of the PM fiber, coupling a fast axis to a slow axis, to create substantially equal optical path lengths of the two transmission axes of the fiber coupling can nearly eliminate output amplitude fluctuation within a practical operating temperature range.
1. An optical harmonic frequency conversion module comprising:
a semiconductor fiber laser generating a substantially linearly polarized light output;
a non-linear crystal waveguide device for converting the light output from the semiconductor fiber laser having a first frequency into an output light having a second frequency; and
an optical fiber link for coupling the substantially linearly polarized light output from the semiconductor fiber laser into the non-linear crystal waveguide device, the optical fiber link comprising birefringent optical fiber having a fast axis, and a slow axis orthogonal thereto, wherein the optical fiber link includes at least one 90 degree splice fusing a fast axis of a first segment of birefringent optical fiber to a slow axis of a second segment of birefringent optical fiber, wherein the optical fiber link includes two major PER (polarization extinction ratio) degradation points and the at least one 90 degree splice is disposed such that light launched into a fast axis of the optical fiber link has a substantially equal optical path length as light launched into a slow axis of the optical fiber link between the two major PER degradation points.
2. An optical harmonic frequency conversion module as defined in claim 1 , wherein the non-linear crystal waveguide device comprises a second harmonic generator (SHG).
3. An optical harmonic frequency conversion module as defined in claim 2 , wherein the optical fiber link comprises an optical fiber having a fiber Bragg grating (FBG) written therein.
4. An optical harmonic frequency conversion module as defined in claim 3 , wherein the 90 degree splice is located such that the temperature interval between maximum and minimum output of the harmonic frequency conversion module is greater than a selected operational temperature range.
5. An optical harmonic frequency conversion module as defined in claim 4 , wherein the at least one 90 degree splice comprises at least one fusion splice.
6. An optical harmonic frequency conversion module as defined in claim 4 , wherein a selected operational temperature range is less than 75 degrees Celsius.
7. An optical harmonic frequency conversion module as defined in claim 4 further including an output birefringent optical fiber for coupling light at a second frequency from the non-linear crystal waveguide device, the output birefringent fiber including at least one 90 degree splice such that light coupled into a fast axis of the birefringent optical fiber output from the non-linear crystal waveguide device has a substantially equal optical path length as light coupled into a slow axis of the birefringent optical fiber output.
8. An optical harmonic frequency conversion module as defined in claim 7 further including a polarizer coupled to an output end of the birefringent optical fiber output.
9. An optical harmonic frequency conversion module as defined in claim 8 further including a polarizing beam splitter for separating light from the polarizer and directing an unwanted polarization of the separated light to a photodetector for power monitoring.
10. An optical harmonic frequency conversion module as defined in claim 4 , wherein the first segment L 1 of the optical fiber link is coupled by a 90 degree splice to the second segment L 2 , such that L 1 is approximately equal to L 2 .
11. An optical harmonic frequency conversion module as defined in claim 4 , wherein the optical fiber link comprises a first segment L 1 optically coupled with a first 90 degree splice to a second segment L 2 optically coupled with a second 90 degree splice to a third segment L 3 , such that L 2 is substantially equal to L 1 +L 3 .