Wavelength-Division Demultiplexing Enhanced by Silicon-Photonic Tunable Filters in Ultra-Wideband Optical-Path Networks

With the recent growth of network traffic demands, a high-capacity optical-path network based on reconfigurable optical add-drop multiplexers (ROADMs) is highly desirable. Among the various technologies available, extending the useable frequency band is one of the most promising solutions since it can enlarge the network capacity with relatively small signal-quality degradation. However, increasing the number of wavelength signals detracts flexible signal-drop capabilities of the ROADM because the effective dynamic range of the digital coherent receiver is restricted by the number of wavelength signals input to the receiver. To overcome this difficulty, we adopt the ROADM structure that sets an optical wavelength-tunable filter in front of each receiver. This scheme retains the effective receiver dynamic range even if a large number of wavelength signals are multiplexed. In this paper, we demonstrate flexible signal drop in a C+L-band optical-path network by using an optical wavelength-tunable filter implemented on a single silicon-photonic chip. The prototype filter is monolithically implemented in conjunction with an input-port selector so as to reduce the total system loss. The filter comprises multiple asymmetric Mach-Zehnder interferometers for wavelength tuning and symmetric Mach-Zehnder interferometers for input-port selection. Its effectiveness is experimentally confirmed by measuring the bit-error ratios of 32-Gbaud/100-Gbps dual-polarization quadrature-phase-shift-keying signals and 32-Gbaud/200-Gbps dual-polarization 16-ary quadrature-amplitude-modulation signals. A single wavelength signal is extracted out of 285 wavelength signals multiplexed over the C+L band and successfully demodulated with negligible penalty in terms of the optical signal-to-noise ratio. The net fiber capacity reaches 57 Tbps.