  We characterize the optical coherence and energy-level properties of the 795
nm $^3$H$_6$ to $^3$H$_4$ transition of Tm$^{3+}$ in a Ti$^{4+}$:LiNbO$_{3}$
waveguide at temperatures as low as 0.65 K. Coherence properties are measured
with varied temperature, magnetic field, optical excitation power and
wavelength, and measurement time-scale. We also investigate nuclear
spin-induced hyperfine structure and population dynamics with varying magnetic
field and laser excitation power. Except for accountable differences due to
difference Ti$^{4+}$ and Tm$^{3+}$-doping concentrations, we find that the
properties of Tm$^{3+}$:Ti$^{4+}$:LiNbO$_{3}$ produced by indiffusion doping
are consistent with those of a bulk-doped Tm$^{3+}$:LiNbO$_{3}$ crystal
measured under similar conditions. Our results, which complement previous work
in a narrower parameter space, support using rare-earth-ions for integrated
optical and quantum signal processing.
