A Distribute Feedback Laser Diode Composed Microwave Photonic Bandpass Filter for SCM-Based Optical Transport Systems

In this paper, a distribute feedback laser diode (DFB LD) composed microwave photonic bandpass filter is proposed and experimentally demonstrated for subcarrier multiplexing (SCM)-based radio over fiber (RoF) transport systems. To realize the photonic filter, a multiwavelength laser, composed by directly modulating single-tone RF signal with a DFB LD, is developed to simultaneously generate six identical optical carriers. When these optical carriers are phase-modulated with SCM signals and communicated through optical fiber to optical network units (ONUs), a bandpass filter function is accomplished automatically due to the interaction of the accumulated chromatic dispersion and the optical interference among those transmitted optical carriers. Experimental results proof that the central frequency of the passband window of the photonic filter is not fixed, instead, it can be shifted accurately by alerting the optical channel spacing of the generated six optical carriers. By applying the proposed photonic filter for SCM-based RoF transport systems, each connected ONU will receive dedicated SCM signals only and the other SCM signals will be rejected, so no more electrical microwave filter is required to be deployed in the ONU. With the proposed scheme, the SCM-based RoF transport systems can be greatly simplified and the system transmission efficiency can be promoted and controlled centrally.