Hiroshi Kawashima, Noritaka Matsubara and Kazutaka Nara
In high bit rate optical transmission systems such as 40 Gbps, dispersion tolerances will be smaller than the dispersion fluctuations due to such factors as temperature change or power variation. To compensate for these fluctuations, tunable dispersion compensators (TDCs) are needed. Various types of tunable dispersion compensators have been demonstrated. Of these, integrated optic finite impulse response filter type TDCs in silica-based planar lightwave circuits (PLCs) are promising because of their flexibility with respect to dispersion curve shape, tunability of center wavelength and ability to compensate for multiple channels. Among these, the transversal filter, consisting of a splitter, N delay lines (called taps) connected in parallel and a combiner, is capable of having a large number of taps for high resolution and high controllability using monitor waveguides.
Owing to these advantages, we have fabricated an 8-tap transversal filter type TDC in a silica-based PLC with a high index contrast of 1.5 %, and have confirmed its operating principle using two types of dispersion curve shapes. We have been able to obtain good performance: chromatic dispersion of -71 ~ +109 ps/nm, insertion loss of <10 dB and operating wavelength range of 0.5 nm. We have also fabricated a 16-tap transversal filter type TDC and have confirmed a higher resolution than the 8-tap TDC.