  Quantum memory is a fundamental building block for large-scale quantum
networks. On-demand optical storage with a large bandwidth, a high multimode
capacity and an integrated structure simultaneously is crucial for practical
application. However, this has not been demonstrated yet. Here, we fabricate an
on-chip waveguide in a $\mathrm {^{151}Eu^{3+}:Y_2SiO_5}$ crystal with
insertion losses of 0.2 dB, and propose a novel pumping scheme to enable
spin-wave atomic frequency comb (AFC) storage with a bandwidth of 11 MHz inside
the waveguide. Based on this, we demonstrate the storage of 200 temporal modes
using the AFC scheme and conditional on-demand storage of 100 temporal modes
using the spin-wave AFC scheme. The interference visibility between the readout
light field and the reference light field is $99.0\% \pm 0.6\%$ and $97\% \pm
3\%$ for AFC and spin-wave AFC storage, respectively, indicating the coherent
nature of this low-loss, multimode and integrated storage device.
