Abstract
Planar Lightwave Circuit (PLC) technology provides an extremely effective method of printing optical waveguide based circuits onto simple mechanical substrates such as common Silicon wafers. PLCs have played a major role in low cost and high volume optical component manufacturing in the telecommunications industry. The impact of optical waveguide chips using the planar manufacturing technique is to provide solutions for integrating multiple optical components into a single chip platform, thus reducing the cost, improving consistency, and increasing yield and reliability by mass replication of complex optical devices. One premier application area of PLCs that has emerged is the manufacture of arrayed-waveguide gratings (AWGs) and/or Mach-Zehnder interferometers (MZIs) as linear filters for multiplexing, demultiplexing, and routing multiple closely-spaced wavelengths between individual fibers. The performance of these optical filters is very high and filters are routinely produced to multiplex and demultiplex optical signals having as little as 0.01% distinction between optical frequencies (i.e. 25GHz @ 1550nm). Since the accuracy of these filters depends on precise differences in multiple optical paths, they are very sensitive to any disturbance of those optical paths. The geometry of the PLC optical paths is solid within the waveguide structure, hence the PLC-based filter is essentially insensitive to any non-catastrophic mechanical disruption. An AWG is, for instance, unaffected by vibration. However, if the PLC filter is subjected to a temperature change, a slight change in the index of the waveguide glass occurs and, with lesser effect, the device changes size slightly due to the CTE of the substrate. These effects combine to produce a creep in the filter response of about 0.0007% / °C or about 1½ GHz / °C for wavelengths around 1550nm [1, 2]. Since the optical-frequency passband of a high-performance optical filter is required to be accurate and stable to as tight as 1 GHz, it is necessary to stabilize these filters against thermal drift.
© 2005 Optical Society of America
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