Abstract

The rapid and global spread of the Internet is accelerating the growth not only of backbone networks but also of metro/access networks. Dense wavelength-division multiplexing (DWDM) has been employed to meet the recent explosive demand for backbone networks. However, in terms of cost, it is difficult to apply DWDM systems to metro/access networks because these systems require expensive temperature controllers and optical amplifiers. As an alternative, coarse wavelength-division multiplexing (CWDM) has been studied with a view to realizing cost-effective systems.¹ Here, uncooled distributed-feedback laser diodes (DFB-LDs) are used to reduce the system cost. This provides a CWDM system with a large channel spacing of 20 nm because DFB-LDs have a large temperature dependent wavelength shift of about 0.1 nm/degree. This wide wavelength tolerance of the light source requires a multi/de-multiplexing filter with a wide passband. Moreover, since the filter to light source cost ratio is greater than with a conventional DWDM system, the CWDM filter must be both inexpensive and compact. The planar waveguide filter is an attractive candidate because it can be mass-produced, is compact, and does not require complicated fiber handling. Lattice-form waveguide filters have been studied^2,3 and developed as wide pass-band DWDM interleave filters.^4,5 We recently reported a lattice-form planar waveguide CWDM filter, ⁶ however its crosstalk of –17 dB made it unsuitable for general application.

© 2002 Optical Society of America