  We studied optical coherence properties of the 1.53 $\mu$m telecommunication
transition in an Er$^{3+}$-doped silicate optical fiber through spectral
holeburning and photon echoes. We find decoherence times of up to 3.8 $\mu$s at
a magnetic field of 2.2 Tesla and a temperature of 150 mK. A strong
magnetic-field dependent optical dephasing was observed and is believed to
arise from an interaction between the electronic Er$^{3+}$ spin and the
magnetic moment of tunneling modes in the glass. Furthermore, we observed
fine-structure in the Erbium holeburning spectrum originating from
superhyperfine interaction with $^{27}$Al host nuclei. Our results show that
Er$^{3+}$-doped silicate fibers are promising material candidates for quantum
state storage.
