Research On Wavelength Selective Switch Based On MEMS Technology

With the development of optical communication, especially the wide applications of dense wavelength division multiplexing (DWDM) technology, technologies such as optical cross connection (OXC) and reconfigurable optical add/drop multiplexer (ROADM) are attracting more and more attention. Wavelength selective switch (WSS) is characterized by free switching of individual wavelength, which enables it as an important part in above two technologies and thus becames a global research focus in optical communication.The present typical structures for a WSS were introduced and the respective characteristics were analyzed and compared. A new WSS structure based on MEMS (micro-electro-mechanical system) technology was presented. A transmitting phase grating and a MEMS mirror array were employed as the wavelength dispersiing and beam controlling elements respectively. The two elements were located on the front and rear focal plane of a resolution lens, which constructs a 2f optical system. An optical fiber collimator array was employed as the input/output ports. The optical beam is first expanded by a prism group and then incidents on the grating, thus the resolving power of the grating is improved. In order to reduce the WSS size, a mirror and a steering prism were employed to fold the optical path.The formula to calculate the power-coupling efficiency of the fundamental-mode gaussian beam was developed based on wave optics theory, thus the passband under given mirror array parameters, such as filling ratio and beam confining factor, was obtained. The relationship among the angular dispersion of the grating, the focal length of the resolution lens, the channel spacing and the pitch of the MEMS mirror array was analyzed. The beam expanding ratio of the prism group was deduced under a given prism angle and beam incident angle. The transforming and matching of Gaussian field in the optical system were anslyzed in emphasis. The power loss resulting from mismatch of Gaussian field was studied. These analyses are most important for the WSS design and optical adjustment.Based on above analyses, the elements for the WSS were designed and fabricated andd a 1×4 WSS was assembled. The device specifications were tested. The insertion loss is <5.08dB, the crosstalk between ports is <-45dB, the polarization dependent loss is <0.186dB. The results show that the designed WSS is characterized by simple structure, good scalibility and low loss. It can be employed as the key part in a ROADM and OXC, thus the flexibility and stability of network node is improved.