New microwave photonic signal processing structures for generating in-phase and quadrature phase RF signals are presented. They are based on designing the bias angles of a dual-drive Mach Zehnder modulator (DDMZM) or a dual-parallel Mach Zehnder modulator (DPMZM) to introduce a specific phase shift to the optical carrier and using a wavelength division multiplexer to separate the lower and upper RF modulation sidebands. The optical carrier beat with the sidebands in a pair of photodetectors generate two output RF signals with a quadrature phase difference. The two proposed structures are simple, low cost and free of electrical components. The upper operating frequency of the two microwave photonic signal processors is only limited by the optical modulator bandwidth. Experimental results demonstrate the proposed microwave photonic signal processing structures have the ability to generate in-phase and quadrature phase signals with small phase and amplitude imbalance, over a wide frequency range.