Using air-trench bends, an ultracompact 8 8 arrayed waveguide grating (AWG) demultiplexer (200-GHz channel spacing) for wavelength-division multiplexing (WDM) has been designed and fabricated with perfluorocyclobutyl (PFCB) core and clad co-polymers on a polyimide substrate. Compared to a conventional AWG in the same material system, the air-trench bend AWG shrinks the required chip area by a factor of 20. The decreased size is a factor in reducing the measured thermal shift to 0.012 nm/ C and decreasing the polarization-dependent wavelength shift to 1.3 nm.

The authors have developed an anisotropic, high aspect ratio (18:1) etch for perfluorocyclobutyl (PFCB) polymers with trenches as narrow as 800nm using a CO∕O2 etch chemistry in an inductively coupled plasma reactive ion etcher. Anisotropy is achieved by carbon sidewall passivation. The motivation for this etch development is to use the air trenches as very compact waveguide splitters [S. Kim et al., Opt. Eng. 45, 054602 (2006)]. The authors report a new trench widening mechanism due to tensile stress of the PFCB films and a method of avoiding this widening through the use of additional stress relief trenches on both sides of the desired trench.

We demonstrate air-trench splitters in low index contrast perfluorocyclobutyl (PFCB) waveguides. Splitters are fabricated by etching 800 nm wide high aspect ratio (18:1) trenches. The measured optical loss is 0.4 dB/splitter. The reflection/transmission splitting ratio is 0.859/0.141, which closely matches two-dimensional finite difference time domain (2DFDTD) simulation results. Air-trench splitters and bends are used to demonstrate an ultra-compact ring resonator (RR) with a size reduction of 1,700 compared to a RR based on traditional curved waveguides in the same material system. A comparison between the RR's measured and analytically calculated performance shows close agreement when splitter and bend losses are taken into account.

A fabrication process for PFCB waveguide air-trench bends with scanning electron microscope (SEM)-based electron beam lithography (EBL) and autoalignment has been developed and high efficiency air-trench bends (97.2% for TE polarization and 96.2% for TM polarization) have been demonstrated. We have successfully developed a high aspect ratio (18:1) anisotropic PFCB etch using a CO/O 2 etch chemistry in an inductively coupled plasma reactive ion etcher (ICP RIE) for PFCB waveguide air-trench splitter fabrication. The fabricated splitters show a 90.1% overall efficiency and ~ 85-to-15 (85:15) splitting ratio for 950 nm wide splitter trench, which closely matches 2D-FDTD simulation results. Using air-trench bends, an ultracompact PFCB arrayed waveguide grating (AWG) 8 x 8 wavelength demultiplexer for Wavelength Division Multiplexing (WDM) application had been designed. Compared to a conventional AWG in the same material system, the air-trench bend AWG reduces the area required by a factor of 20. Compact ring resonators using these splitters and bends has been designed and fabrication and improvements are currently underway.

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