In the European project MORPHIC we develop a platform for programmable silicon photonic circuits enabled by waveguide-integrated micro-electro-mechanical systems (MEMS). MEMS can add compact, and low-power phase shifters and couplers to an established silicon photonics platform with high-speed modulators and detectors. This MEMS technology is used for a new class of programmable photonic circuits, that can be reconfigured using electronics and software, consisting of large interconnected meshes of phase shifters and couplers. MORPHIC is also developing the packaging and driver electronics interfacing schemes for such large circuits, creating a supply chain for rapid prototyping new photonic chip concepts. These will be demonstrated in different applications, such as switching, beamforming and microwave photonics.
We present a detailed study of parameter sweeps of silicon photonic arrayed waveguide gratings (AWG), looking into the effects of phase errors in the delay lines, which are induced by fabrication variation. We fabricated AWGs with 8 wavelength channels spaced 200 GHz and 400 GHz apart. We swept the waveguide width of the delay lines, and also performed a sweep where we introduced increments of length to the waveguides to emulate different AWG layouts and look into the effect of the phase errors. With this more detailed study we could quantitatively confirm the results of earlier studies, showing the wider waveguides reduce the effect of phase errors and dramatically improve the performance of the AWGs in terms of insertion loss and crosstalk. We also looked into the effect of rotating the layout of the circuit on the mask, and here we could show that, contrary to results with older technologies, this no longer has an effect on the current generation of devices.
In the Information and Communications Technology (ICT) sector, the demands on bandwidth continually grow due to
increased microprocessor performance and the need to access ever increasing amounts of stored data. The introduction of
optical data transmission (e.g. glass fiber) to replace electronic transmission (e.g. copper wire) has alleviated the
bandwidth issue for communications over distances greater than 10 meters, however, the need has arisen for optical data
transfer over shorter distances such as those found inside computers. A possible solution for this is the use of low–cost
single mode polymer based optical waveguides fabricated by direct patterning Nanoimprint Lithography (NIL). NIL has
emerged as a scalable manufacturing technology capable of producing features down to the hundred nanometer scale
with the potential for large scale (roll-to-roll) manufacturing.
In this paper, we present results on the modeling, fabrication and characterization of single mode waveguides and optical
components in low-loss ORMOCER™ materials. Single mode waveguides with a mode field diameter of 7 μm and
passive structures such as bends, directional couplers and multi-mode interferometers (MMIs) suitable for use in 1550
nm optical interconnects were fabricated using wafer scale NIL processes. Process issues arising from the nano-imprint
technique such as residual layers and angled sidewalls are modeled and investigated for excess loss and higher order
mode excitation. Conclusions are drawn on the applicability of nano-imprinting to the fabrication of circuits for intrachip/
board-level optical interconnect.
Polymer-based integrated optics is attractive for inter-chip optical interconnection applications, for instance, for coupling photonic devices to fibers in high density packaging. In such a hybrid integration scheme, a key challenge is to achieve efficient optical coupling between the photonic chips and waveguides. With the single-mode polymer waveguides, the alignment tolerances become especially critical as compared to the typical accuracies of the patterning processes. We study novel techniques for such coupling requirements. In this paper, we present a waveguide-embedded micro-mirror structure, which can be aligned with high precision, even active alignment method is possible. The structure enables 90 degree bend coupling between a single-mode waveguide and a vertical-emitting/detecting chip, such as, a VCSEL or photodiode, which is embedded under the waveguide layer. Both the mirror structure and low-loss polymer waveguides are fabricated in a process based mainly on the direct-pattern UV nanoimprinting technology and on the use of UVcurable polymeric materials. Fabrication results of the coupling structure with waveguides are presented, and the critical alignment tolerances and manufacturability issues are discussed.
We present designs for sharp bends in polymer waveguides using colloidal photonic crystal (PhC) structures. Both silica
(SiO2) sphere based colloidal PhC and core-shell colloidal PhC structures having a titania (TiO2) core inside silica (SiO2)
shells are simulated. The simulation results show that core-shell Face Centered Cubic (FCC) colloidal crystals have a
sufficient refractive index contrast to open up a bandgap in the desired direction when integrated into polymer
waveguides and can achieve reflection <70% for the appropriate plane. Different crystal planes of the FCC structure are
investigated for their reflection and compared with the calculated bandstructure. Different techniques for fabrication of
PhC on rectangular seed layers namely slow sedimentation; spin coating and modified doctor blading are discussed and
investigated. FCC and Random FCC silica structures are characterized optically to show realisation of (001) FCC.