Abstract
Tunable filters for wavelength division multiplexing (WDM) in optical fiber communication systems are key elements for the realization of reconfigurable optical networks. Desirable features for such filters include fast tuning speed, wide tuning range, low insertion loss, narrow channel bandwidth, low electric-power consumption, simple control mechanism, small size, and low cost. Various guided-wave optical approaches have been pursued for the development of such components.1–3 Of these technologies, only the electro-optic tunable filter (EOTF) can be tuned from one channel to another at the submicrosec-ond speeds that are needed for fast packet-switched networks.4 Such devices have been produced in lithium niobate (LiNbO3) based on a four-port Mach-Zehnder configuration by making use of phase-matched polarization conversion5 induced by a spatially periodic index perturbation which couples the TE and TM modes in waveguides which connect two polarizing beam splitters. However, the previous EOTFs in LiNbO3 required separate voltage controls for the polarization conversion and wavelength tuning sections, making them somewhat complex to control and inefficient in the use of the available length of the substrate. As an alternative, the concept of utilizing the static strain-optic effect from a surface film for making tunable filters in lithium tantalate (LiTaO3) was explored.6 In this scheme, a spatially periodic surface film induces the phase-matched polarization conversion and makes it possible to use the entire length of the waveguides in the arms of the interferometer for tuning. This paper reports the realization of the first high-speed electro-optically tunable wavelength filter at the 1.5 µm wavelength regime in LiNbO3 using static strain induced from a spatially periodic surface film for polarization mode conversion. Both electro-optic and thermo-optic wavelength tuning have been demonstrated. The temporal
© 2002 Optical Society of America
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