Low crosstalk polymer waveguide optical switch and switching matrix

Abstract

Polymer waveguide thermo-optic (TO) space switching elements show great promise for practical integrated photonic applications [1 - 4]. These devices are expected to be employed in future optical telecommunication systems as routing elements in optical cross-connects. One of the challenges of the optical waveguide space switches is to reduce the crosstalk which is vital to all-optical communication networks. All-optical communication networks have not been implemented in the real world because of the lack of a compact, low cost switching matrix with low crosstalk and insertion loss. For system applications, the crosstalk of a switching matrix should be <−30 dB, leading to the requirement for a single switching element to exhibit values <−40 dB. Up to now, such a switch can be only realized by fiber mechanical devices which, however, are bulky and not suitable for large switching matrices used in telecommunications. The switching matrix suitable for communications may be realized by integrated photonic technologies. The first polymer based (4×4)-switching matrix which integrated eight (2×2)-directional coupler switches and operated at λ = 1.55µm was reported in 1995 [3]. Due to the asymmetrical heating electrode configuration employed, crosstalk in the unbiased ‘cross’ state turned out to be limited to typically−25 dB, leading to a minimum crosstalk value of only−21.5 dB in the (4×4)-matrix. Low crosstalk in conjunction with low switching power operated at λ = 1.3 µm was obtained by NTT using a Mach-Zehnder interferometer (MZI) switch in 1993 [1]. However, in comparison with a directional coupler type switch the total length of a MZI is about three times as large which renders this type of switch less suitable for the implementation of larger switching matrices.