High-performance arrayed waveguide gratings

Planar technology and design have evolved significantly in the past decade, both in terms of performance and yield, reducing the cost/performance advantage of thin-film filters (TFF) over Array-Waveguide Grating (AWG) devices. This evolution is primarily due to two reasons. One of the reasons for this is the adoption of the latest in semi-conductor fabrication techniques with respect to wafer scale, process equipment automation, and yield engineering. The other reason is the many advancements made in the Planar Light Circuit (PLC) design front which have resulted in lower optical insertion loss, reduced crosstalk, increased channel bandwidth, decreased channel spacing, and minimal chromatic dispersion. We demonstrate here how such state-of-the-art fabrication technology in combination with advanced PLC designs can be effectively used to engineer the filter shape (ripple, bandwidth, and flatness) and chromatic dispersion of AWG's to match or exceed that of their thin-film counterparts. Low passband ripple is critical for cascading multiple nodes in ring network architecture whereas minimal chromatic dispersion (CD) is desired in high rate data systems to avoid signal distortion. The AWG device presented here has a 1 dB bandwidth that exceeds 80% of the channel spacing awhile exhibiting a high flatness (25 dB/1 dB ratio < 1.7), both of which are at least a 50% improvement over generic flat-top AWG designs available in the market and are equivalent in performance to TFF devices. At 100 GHz spacing, AWG's have intrinsic low-dispersion, but narrowing the spacing to 50 GHz leads to a four fold increase in the CD. Here, we have successfully overcome this limitation and have been able to design and fabricate a 50 GHz wide-band AWG with less than 1 ps/nm chromatic dispersion, which exceeds TFF performance.