Wavelength Reuse in a UWB Over Fiber System Based on Phase-Modulation to Intensity-Modulation Conversion and Destructive Interferencing

A novel wavelength reuse scheme based on phase-modulation to intensity-modulation (PM-IM) conversion and destructive interferencing using a polarization modulator (PolM) and a fiber Bragg grating (FBG) in an ultra-wideband (UWB) over fiber (UWBoF) system is proposed and experimentally demonstrated. In the proposed scheme, a PolM and an FBG in the central station (CS) are used to generate intensity-modulated impulse UWB signal based on PM-IM conversion. The downstream UWB signal is sent to a base station (BS) over an optical fiber. At the BS, when the principle axis of the polarizer is aligned with one of the two orthogonal states of polarization (SOPs), the downstream UWB signal is received and detected. When the principle axis of the polarizer is oriented at a special angle to one of the two orthogonal SOPs, a clear optical carrier without intensity modulation is generated, which is then reused for upstream UWB data transmission. A theoretical analysis is performed which is verified by an experiment. A bidirectional point-to-point transmission of 1.25 Gb/s UWB signal over 25-km single-mode fiber (SMF) using a single light source from the CS is demonstrated. The receiver sensitivity and the BER performance for both downstream and upstream transmissions are measured.