We report the achievement of buried single-mode waveguides in special Boro-Aluminum-Silicate glass. The waveguides are characterized by very low propagation loss (< 0.1dB/cm) and negligible birefringence. The optical mode at the input and output ports is essentially identical to the mode of a standard single-mode optical fiber. We fabricated and tested several devices and report here 1x8 and 1x16 powers splitters and an interleaver defined for a 100GHz DWDM network.Due to the low birefringence of the waveguides, the TE and TM responses of the device are undistinguishable by customary characterization equipment. In addition we report a technique for permanent trimming of the optical circuit by localized heating. This unique advantage of ion-exchange technology, allowed us the adjustment of devices' parameters at post-fabrication stage. As an example, the trimming of a 2x2 directional coupler manifested here in the control of coupling coefficient value over a wide range (0.04-1 .5). The process control was such that a target value of 0.5 for the coefficient was accurately attained. The same process enabled us the tuning of the interleaver to the ITU grid within 1 Opm accuracy.