Optical clock distribution is presented for the first time in an unmodified bulk CMOS chip. An H-tree distributes the signal using I-beam photonic waveguides operating at 780 nm, and avalanche photodiodes and transimpedance amplifiers bring the signal back to the electronic domain. All components are monolithically integrated on a 180nm bulk CMOS chip. The I-beam waveguides are also demonstrated in 22nm FDSOI CMOS technology without process modifications or design rule violations, making it the most advanced commercial process to monolithically demonstrate photonic waveguiding.