Silicon photonics has attracted extensive attention in recent years as a promising solution for next generation high-speed, low energy consumption, and low cost data transmission systems. Although a few experiments indicated board-level and long haul communication capability, major and near-future application of silicon photonics is commonly seen as Ethernet at 100Gb/s and beyond, such as interconnects in data centers, where O-Band (near 1310 nm wavelength) has been standardized for its low fiber dispersion. However, almost all silicon photonics devices demonstrated up to date operate at C-Band (1530 nm to 1560 nm), the fiber loss and erbium amplification window, probably due to the wider availability of lasers and testing apparatus at this wavelength. Typical C-Band devices cannot operate at O-Band, thus the whole device library needs to be redesigned and recalibrated for O-Band applications. In this paper, we present an ultra compact, low loss, and low crosstalk waveguide crossing operating at O-Band. It is designed using the finite difference time domain method coupled with a particle swarm optimization. Device footprint is only 6 μm × 6 μm. The measured insertion loss is 0.19±0.02 dB across an 8-inch wafer. Cross talk is lower than -35 dB. We also report a second waveguide crossing with a 9 μm × 9 μm footprint with 0.017±0.005 dB insertion loss. Finally we summarize the performance of our overall O-Band device library, including low-loss waveguides, high-speed modulators, and photodetectors.