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Mode-couplings in a LPG

Phase shifted and cascaded long-period fiber grating written by using focused high-repetition-rate CO 2 laser pulses. Forward core-mode. Forward cladding modes. Resonant wavelength:. Core. Cladding. Long period fiber grating (LPG). Mode-couplings in a LPG. Phase matching condition:.

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Mode-couplings in a LPG

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  1. Phase shifted and cascaded long-period fiber grating written by using focused high-repetition-rate CO2 laser pulses

  2. Forward core-mode Forward cladding modes Resonant wavelength: Core Cladding Long period fiber grating (LPG) Mode-couplings in a LPG Phase matching condition:

  3. Spectral response of the LPG Transmission (dB) LP11 LP13 LP17 LP15 LP19 1400 1600 1800 Wavelength (nm)

  4. Applications of the LPG • Various kinds of filters used in fiber optic communications: • (Band-pass filter, band-rejection filter, gain flatten filter….) • All-fiber-type environmental parameters sensor • All-fiber-type biochemical sensor • All-optical signal processing devices • (Optical switching, optical differentiator and optical pulse shaper)

  5. Fabrication techniques for the LPG • Ultraviolet (UV) exposure • The electric-arc discharge • The mechanical pressure • The focused CO2 laser radiation

  6. Purpose of this study A simple scheme to write the LPFGs is proposed, which is based on the directly writing technique realized by using a high-repetition-rate CO2 laser pulses. Two particular gratings: The phase shifted LPFG The cascaded LPFGs where both the complex phase-mask and the time-tedious post-processing procedures can be avoided.

  7. Experimental setup

  8. Principle scheme for the formation of a LPFG • Temporal profile of the laser output at a site just after the shutter • The ideal profile of the resulted index-change of LPFG along the fiber

  9. Principle scheme for the formation of a phase-shifted LPFG • Index-change profile with a phase-shift inserted and (b) without phase-shift inserted.

  10. Theoretical Results Theoretical results for the transmission spectra of LPG with and without a phase-shift. (a) Without the phase shift inserted, (b) with the phase-shift of p, (c) with the phase-shift of 0.75p, and (d) with the phase-shift of 0.5p.

  11. Experimental results Experimental results for the measured transmission spectrum of LPG with and without phase-shift. (a) Without the phase shift inserted, (b) with the phase-shift of p, (c) with the phase-shift of 0.75p, and (d) with the phase-shift of 0.5p.

  12. Formation scheme for the cascaded two LPFGs

  13. Principle analysis for the cascaded LPGs Grating pitch Λ M-Z Interferometer Incident d Core mode Cladding mode T (dB) Wavelength (nm)

  14. Experimental results Experimental results for the measured transmission spectra the cascaded LPGs with a separation of (a) 0 cm, (b) 10.6 cm, (c) 13.0 cm, and (d) 37.0 cm.

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