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optical switch


Conventional Wavelength Selective Switches (WSSs) steer light in one dimension. This fundamentally limits the number of output ports.

A typical WSS has one input fibre, and multiple output fibres. Light is launched into free space from the input fibre, at the centre of a linear fibre array. Relay lenses project the light onto a Liquid Crystal on Silicon (LCoS) beam steering device. A diffraction grating between the relay lenses is used to spatially separate the light, so that each Wavelength Division Multiplexed (WDM) signal beam is projected onto a different area of the LCoS.

The light is then reflected from the LCoS beam steering device back through the optical system, and couples into an output fibre in the linear fibre array. 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.

A cylindrical lens is used as part of the relay optics, to elongate the beam projected on the LCoS device. This allows each wavelength channel to be steered to a greater number of output ports, but each WSS is still limited to around 20 output ports. Our unique WSS technology steers light in two dimensions, not one. The cylindrical lens in the conventional WSS is replaced by a second spherical relay lens, and the linear fibre array by a 2D fibre array.This means the beams projected on the LCoS device are circular, not elongated. Our expertise in controlling the LCoS device means that the beams can be steered accurately in two dimensions. The number of output ports is therefore the same as for a conventional WSS, but far less of the LCoS device is used.Multiple independent WSSs can therefore share the same LCoS device. The other optical components can also be shared. One switch module can therefore contain multiple independent WSSs.

Introduction of CPDS

Centre for Photonic Devices and Sensors (CPDS) is in the Photonics area of the Electrical Engineering Division, with a research focus embracing photonic and sensing devices, functional materials and their integration at system level.

We aim to address future societal needs with new system functionalities through invention of novel device architectures based on in-depth understanding of basic material properties.

There is a wide range of activities within the group, including phase-only holography and its applications, high brightness multi-stable colour reflective displays, tunable dielectric materials and devices for radio frequencies, liquid crystal on silicon (LCOS) device development, and novel sensors.

As well as conducting highly focused studies, we also specialise in the development of demonstrators for business exploitation and commercialisation. This is facilitated by multi-disciplinary expertise within the group and by our highly experienced team approach. Some of the outcomes from the group have been successfully transferred to our industrial collaborators for production.