Fabrication of electron beam generated, chirped, phase mask (1070.11-1070.66 nm) for fiber Bragg grating dispersion compensator

We report on the fabrication of a chirped, phase mask that was used to crea te a fiber Bragg grating (FBG) device for the compensation of chromatic dis persion in longhaul optical transmission networks. Electron beam lithograph y was used to expose the grating onto a resist-coated quartz plate.; After etching, this phase mask was used to holographically expose an index gratin g into the fiber core [K. O. Hill, F. Bilodeau, D. C. Johnson, and J. Alber t, Appl. Phys. Lett. 62, 1035 (1993)]. The linear increase in the grating p eriod, ''chirp,'' is only 0.55 nm over the 10 cm grating. This is too small to be defined by computer aided design and a digital deflection system. In stead, the chirp was incorporated by repeatedly rescaling the analog electr onics used for field size calibration. Special attention must be paid to mi nimize any field stitching and exposure artifacts. This was done by using o verlapping fields in a ''voting'' method. As a result, each grating line is exposed by the accumulation of three overlapping exposures at 1/3 dose. Th is translates any abrupt stitching error into a small but uniform change in the line-to-space ratio of the grating. The phase mask was used with the d ouble-exposure photoprinting technique [K. O. Hill, F. Bilodeau, B. Male, T . Kitagawa, S. Theriault, D. C. Johnson, J. Albert, and K. Takiguchi, Opt. Lett. 19, 1314 (1994)]: a KrF excimer laser holographically imprints an apo dized chirped Bragg grating in a hydrogen loaded SMF-28 optical fiber. Our experiments have demonstrated a spectral delay of -1311 ps/nm with a linear ity of +/-10 ps over the 3 dB bandwidth of the resonant wavelength of the F BG. The reflectance, centered on 1550 nm, shows a side-lobe suppression of -25 dB. Fabrication processes and optical characterization will be discusse d. (C) 1998 American Vacuum Society. [S0734-211X(98)06406-3].