Thin-film lithium niobate (TFLN) modulators have gained significant attention for their high electro-optic modulation efficiency and large bandwidth. However, achieving efficient coupling to single-mode fibers remains a challenge. In this work, we present a large-bandwidth TFLN modulator with low fiber-to-fiber loss, employing grating couplers with metal mirrors for perfectly vertical coupling, which facilitates wafer-scale testing and packaging. The modulator with electrodes and metal mirrors is initially fabricated on an LN-on-insulator with silicon substrate, followed by bonding to a quartz wafer using UV adhesive, with subsequent removal of the silicon substrate. By incorporating periodic capacitively-loaded traveling-wave electrodes, the modulator achieves high modulation efficiency while maintaining a large bandwidth. The final device demonstrates a low fiber-to-fiber loss of 6.5 dB, a 3-dB bandwidth exceeding 67 GHz, and a half-wave voltage of 3.8 V in a 7 mm long modulation section. Additionally, successful data transmission using on-off keying (OOK) modulation at rates up to 100 Gbit/s is achieved. The proposed modulator is compatible with wafer-scale production and holds promising potential for high-capacity, low-loss optical communication systems.