Experimental Demonstration of Soft-ROADMs with Dual-Arm Drop Elements for Future Optical-Wireless Converged Access Networks

Digital signal processing (DSP)-enabled soft reconfigurable optical add/drop multiplexers (Soft-ROADMs) offer flexible add/drop optical switching at wavelength, sub-wavelength and spectrally-overlapped orthogonal (I and Q) sub-band (SB) levels, which makes them highly desirable for enabling flexible reconfigurable optical-wireless converged access networks where both fixed and wireless access services are consolidated in a shared network, enabling network resource efficient and cost-effective connectivity solutions. However, the performance of the targeted sub-band (TSB) extracted by the soft-ROADM drop element is extremely sensitive to drop RF signal phase offset, which is a major limitation impacting the technical feasibility of soft-ROADMs. To overcome this challenge, in this paper, a phase-offset-insensitive soft-ROADM dual-arm IQ drop operation is proposed and experimentally demonstrated. A DSP implemented multi-input multi-output (MIMO)-based I/Q crosstalk mitigation technique is employed to achieve the insensitivity to drop RF signal phase offset. It is shown that, the traditional single-arm I/Q soft-ROADM drop element has a limited drop RF signal phase offset dynamic range of ~±𝝅/𝟒 (