A novel design of a core-based rib waveguide PN junction phase shifter of length 2 mm is proposed in this paper. Two PN junctions are formed on top and bottom of the core, and improved modulation efficiency is achieved. The unbalanced MZM with this proposed phase shifter is analysed for a wavelength of 1553.5 nm with the simulation results. The permissible loss of 7.8 dB occurred in this design. At 100 Gbps, an extinction ratio of 8.15 dB and bit error rate of 3.51 × 10-6 is obtained at VπL of 1V.cm. This device can be a better choice for high-speed data rate communication applications. © 2021, National Institute of Optoelectronics. All rights reserved.