<title>Micromachined two-chip WDM filters with stable half symmetric cavity</title>

Abstract

Wavelength Division Multiplexing has become a leading technology for long haul transmission systems which operate at 1550 nm wavelength. One of the key components of such systems are tunable filters. Beside low insertion loss, polarization insensitivity and large tuning range there is a strong demand for cost effectiveness and reliability. Two-chip micromachined filters are very promising candidates to fulfill these demands. Two Bragg mirrors are deposited on distinct chips. One of them is engineered as actuable membrane. The Fabry- Perot cavity is created by proper adjustment of the two chips one against the other. Modifying the cavity length by thermal induced heating of the membrane mirror or by applying an electrostatic force provides tunability of the transmission function. Tuning stability and insertion loss can be considerably improved if a stable half symmetric cavity containing a bend membrane instead of a flat one is used. This also helps to overcome some severe fabrication problems. On the other hand the half symmetric cavity is more sensitive to mismatch between filter geometry and phase fronts of the existing Gaussian beam. This aspect and the tolerances which can be accepted are discussed in this paper in detail.