Silicon photonics (SiPh) has emerged as a promising technology for photonic integrated circuits (PICs). One of the basic components in SiPh is the directional coupler (DC), which plays an important role in signal monitoring with the requirement of low wavelength dependence and low loss. This paper proposes a broadband and low-loss DC designed for signal power tapping on the 3 μm silicon-on-insulator (SOI) waveguide platform. By utilizing the advantages of multi-micron waveguides and replacing one of the straight waveguides with an optimized arc-shaped waveguide in the coupling region, the proposed DC enhances spectral stability and improves transmission with negligible loss. Experimental evidence indicates that the proposed DC showcases a minimal variation in the tapping ratio. From 1470 nm to 1630 nm, the largest deviation away from the tapping ratio at 1550 nm is 1.433%. Additionally, the device exhibits a low excess loss of −0.27 dB. These results suggest that the proposed device is well-suited to reliable signal power tapping and monitoring, particularly within PICs.