Optical Switching Technology

Modern telecom networks employ Wavelength Division Multiplexing (WDM) technique to transmit parallel optical channels at different wavelengths in fibres to maximise the capacity. At network nodes where different fibres meet, multiple Wavelength Selective Switches (WSSs) are used together to dynamically switch the WDM signals between fibres. This enables data to be sent between any two arbitrary points in the telecom network. The reconfigurable and future-proof nature of WSSs brings significant Capex and Opex savings to network operators.

ROADMap Systems have developed a high precision, sub-hologram based switching technology for two dimensional beam steering in Liquid Crystal on Silicon (LCOS) based Wavelength Selective Switching (WSS) systems. The precision sub-holograms use a much smaller area of the liquid crystal pixel array in comparison with the familiar beam elongation approach used in today’s products. This allows many WSS systems to be fabricated sharing a single LCoS device and shared optical components in the free space, light path coupled to the external fibre ports. The technology aims to help network operators to meet the burgeoning demand for bandwidth in an energy-efficient and cost-effective way.

The conventional WSS system based on the ‘disperse-and-switch’ architecture is depicted in the diagram below.

 

The input WDM signals are launched into the system via a fibre in the linear fibre array. A diffraction grating between the relay lenses is used to spatially separate the light, so that each WDM signal beam is projected onto a different area of the LCoS. Changing the pattern displayed on the LCoS device changes which output fibre the light couples into. The pattern can be changed independently for each wavelength channel. This allows each wavelength channel to be independently, reconfigurably switched to any chosen output fibre.

The cylindrical lens is used to elongate the beam projected on the LCoS device. The elongated beam occupies many pixels on the LCoS device as illustrated in the diagram below:

The ROADMap approach eliminates the cylindrical lens, so the optical beams have a much smaller footprint on the LCoS surface. This means beams can be steered in both x and y dimensions and that multiple independent WSSs can share the same LCoS device and optical components. One ROADMap WSS module can therefore contain multiple independent WSSs. The ROADMap system is shown below:

This structure gives the beam pattern on the LCoS device as shown below:

This highly-integrated universal flexible optical switch provides significant cost reduction, increased density and lower power consumption for each switch.

Switching capability increases by an order of magnitude, providing a step change in network capacity.