Tuning Bragg wavelength by writing gratings on prestrained fibers

Bragg gratings at a specific wavelength are made using an excimer KrF laser and a phase mask. The wavelength can be varied for fine tuning and multiplexing applications by straining the optical fiber during UV illumination. When the strain is removed, the grating formed is at a smaller wavelength than that dictated by the phase mask for the unstrained fiber. This technique was demonstrated by writing two gratings located at the same point in the optical fiber. The transmission from the first grating was used as a means for in situ absolute wavelength tuning. The second grating made with approximately 0.2% axial strain was at 1534.54 nm. Once the grating was made, the strain was removed from the fiber leaving the second grating tuned to 1532.04 nm, a wavelength shift of 2.5 nm.<
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