WHAT IS WAVELENGTH SELECTIVE SWITCH–WSS?

WSS stands for Wavelength Selective Switch. WSS has become the central heart of modern DWDM reconfigurable Agile Optical Network (AOC).

WSS can dynamically route, block and attenuate all DWDM wavelengths within a network node. The following figure shows WSS’s functionality.

The above figure shows that a WSS consists of a single common optical port and N opposing multi-wavelength ports where each DWDM wavelength input from the common port can be switched (routed) to any one of the N multi-wavelength ports, independent of how all other wavelength channels are routed.

This wavelength switching (routing) process can be dynamically changed through a electronic communication control interface on the WSS. So in essence, WSS switches DWDM channels or wavelengths.

There are also variable attenuation mechanism in WSS for each wavelength. So each wavelength can be independently attenuated for channel power control and equalization.

2. HOW DOES A WSS WORK?

There are several WSS switching engine technologies on the market today, here we will demonstrate a MEMS based design. The different switching technologies will be discussed in the next section.

A) 1X2 Configuration

The following figure shows a diffraction grating and MEMS based 1×2 wavelength selective swith

The light from a fiber is collimated by a lens with focal length f and demultiplexed by diffraction off the grating.

The direction of the beam after the grating will depend on the wavelength λ0?of the beam. The diffracted beams then pass through the lens for a second time, and the spectrally resolved light is focused on the reflective linear MEMS device, which is also referred as 1D (1 dimension) MEMS device. The MEMS device then either changes the amplitude (attenuate) or the direction of the beam.

The reflected light passes through the lens and is wavelength-multiplexed by diffraction off the grating, and finally the lens couples the light back into the fiber.? The output light is separated from the input light by a circulator.