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In the past three decades, the volume of global data traffic has been growing at an astonishing rate with little sign to slow down. In responding to this need, the backbone of the network for long distance data communication has evolved from all electrical based on copper wires or radio, mixed optical and electrical with optical fibers in data transportation and electronics in switches and end-nodes, to all optical in which information is kept in the optical domain throughout the network until it reaches its final destination.
To make use of the vast bandwidth available, concurrency among multiple channels of optical transmission is necessary, and the wavelength division multiplexing (WDM) is the main technique in use. A wavelength selective switch (WSS) is able to route selectively individual WDM channels of any formats entering its input fibre port to any of the output fibre ports according to the optical configuration controlled via software by the service providers. Phase-only liquid crystal on silicon (LCOS) spatial light modulator (SLM) is currently the most flexible optical engine for WSSs, one of the key enabling technologies for software defined reconfigurable all optical networks.
We will review the advantages of LCOS WSSs and the use of holographic wavefront modulation for advanced switching functionalities and delivery of the key performance matrix. We will then introduce a new stacked WSS architecture based on 2D beam steering, where multiple independent WSSs can be integrated on a single LCOS device with common optics. This approach can significantly reduce the cost, footprint and power consumption and allow the WSSs to be reconfigured as ultra-high port count switches or non-blocking wavelength cross-connects (WXCs). Finally, we will address how this stacked WSS architecture can be utilized to meet the optical switching demand in large-scale data centres.
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