The application of traditional coherent detection technology to optical access networks has been undermined due to its high complexity and high cost. In this paper, we propose a novel IQ-interleaved detection method which uses the preset frequency offset of the lasers at the transmitter and receiver to obtain the in-phase and quadrature components of the received signal. It keeps the simple structure of heterodyne detection and avoids the down-conversion process. Without Nyquist pulse shaping, the received signal bandwidth of the proposed scheme is theoretically 0.5B smaller than that of heterodyne detection for signal with a symbol rate of B. The 50-Gb/s NRZ transmission experiment proves that by using the proposed scheme, the receiving sensitivity and the frequency drift tolerance can be improved by ∼1 dB and 1 GHz compared with heterodyne detection under strong bandwidth limitation. Without pulse shaping, the receiving sensitivity, frequency drift tolerance (1-dB sensitivity penalty) and link power budget for 20-km fiber transmission are -31.8 dBm, 11 GHz and 43.5 dB, respectively. A higher power budget of 45 dB can be achieved when Nyquist pulse shaping is applied. The proposed scheme provides a low-complexity potential solution for a next-generation coherent PON.