Broadband IF-Over-Fiber Transmission Based on a Polarization Modulator

In this letter, we propose a novel broadband IF-over-fiber transmission system employing a polarization modulator (PolM). PolMs are special phase modulators, which can support both TE and TM modes with opposite phase modulation indices. If a polarizer is placed after the PolM with an angle of 45° to one principal axis of the PolM, then an equivalent intensity modulator (IM) can be achieved. On the other hand, if the direction of the polarizer is parallel to one principal axis of the PolM, an equivalent phase modulator (PM) can be achieved. As a result, we can utilize a PolM to achieve the functions of a parallel IM/PM transmitter, which is previously reported in mobile fronthaul to overcome the dispersion-induced power fading effect. Compared with the conventional parallel IM/PM transmitter based on an IM and a PM, our scheme only needs one modulator, which significantly reduces the cost and avoids the disparity in operation requirements between the IM and the PM. As a demonstration, we successfully transmit $14 \times 1$ GHz OFDM/OQAM signals with a data rate of 44.7 Gb/s over 25 km of a single-mode fiber.