Core networks are rapidly moving towards more efficient “colorless” operation, meaning that ROADM add and drop ports are not limited to fixed predetermined wavelength channels. Instead, a tunable transmitter can connect any wavelength to any add port and the ROADM can route any wavelength to any drop port receiver. Colorless operation improves the efficiency of valuable line cards and transponders in coherent transport networks, where a single DWDM channel carries 100Gbps of information.

In coherent optical communications systems the colorless channel drop operation is enabled by using the local oscillator laser and the VICR to select the receive channel, eliminating the need for a terminal optical filter. The VICR then detects the signal channel to which the local oscillator laser is matched, but all other channels are outside the device bandwidth. In colorless applications the remaining channels are not filtered out optically, so the incoming signal power to the VICR can vary significantly depending on how many other channels are present, resulting in up to 100 times higher power falling on the receiver than in the single channel case. The NeoPhotonics VICR integrates a PIC variable optical attenuator that provides control and stability to the input signal. In both colorless and conventional optically filtered systems, the VOA also improves performance by allowing system selection of the optimal operating point to enhance OSNR and reduce the effects of optical impairments such as polarization dependent loss (PDL).

NeoPhotonics Corp.