Fabrication and Charaterisation of Photonic Integrated Circuits

Abstract: The past few decades have seen an explosive increase ininformation transfer, fuelled by the enormous growth of theInternet, telecommunication applications, and mass mediasystems in general. Because of the very high bandwidthpotential promised by optical fibre communication technology,the area of all-optical networking has received a great amountof attention. However such systems require very expensiveoptical components for tasks such as (de)multiplexing,switching, and routing. A promising and exciting solution tohandle the ever-increasing demand for capacity with lower costsis to integrate optical elements into one common platform inorder to realize photonic integrated circuits (PICs), or planarlightwave circuits (PLCs). More versatile devices with greaterfunctionality for future all-optical networks are feasible withmonolithic integration of opto-electronic and semiconductorcomponents, which require very specialised low-temperatureprocessing techniques.This thesis presents the development of new techniques andmethodologies utilized in low temperature photonic devicefabrication, which can be used to facilitate integration oftemperature sensitive elements. The three-fold contributions tothe thesis are as follows. First, a low temperature plasmaenhanced chemical vapour deposition (PECVD) technology for therealization of silica-on-silicon photonic devices is developed.This technique readily lends itself to the monolithicintegration of devices such as planar optical amplifiers, lightsources, detectors and modulators. Absorption bands around1.48-mm and 1.51-mm wavelengths caused by N-H and Si-H bonds,respectively, had previously been thought to be intrinsic tothe PECVD deposition method when using N2O as the oxidant ofSiH4 and other dopings. The traditional method to eliminatethese absorption bands was high temperature (>10000C)annealing that seriously hinders device integration. Animportant achievement in this thesis is the completeelimination of these two absorption peaks while keeping thewhole fabrication process below 3000 C, and yet maintaining ahigh deposition rate.Second, optimisation of techniques in the device fabricationprocess flow and reports on the fabrication of state-of-the artdevices are presented. Important process steps in thefabrication of optical integrated devices such asphotolithography for patterning and reactive ion etching (RIE)in an inductively coupled plasma (ICP) reactor were alsodeveloped. These technologies were then applied to fabricatecomponents that implemented various concepts, such asMMI-couplers and -splitters, or state-of-the-art arrayedwaveguide gratings (AWG) based optical (de)multiplexers.Finally, applications of UV-processing on planar technologyare examined. Investigations of the UV-response on PECVDdeposited silica-on-silicon and germanosilicate systems arereported. UV-trimming was shown to be a versatile method toselectively control polarisation birefringence of devices. Atransmission dip of 47dB in a Bragg-grating imprinted on astraight channel waveguide was achieved without hydrogenloading, which led to a record for this simplified processflow. With the Bragg-grating inscription techniques, a novelconcept of a MMI based planar optical Add-Drop (de)multiplexerwas realised.The investigations carried out in this thesis show thatPECVD technology can provide low-loss and UV-sensitive materialsuitable for realising a variety of low-cost integrated devicesfor future all-optical networks.Keywords:Photonic integrated circuits,silica-on-silicon technology, plasma process, PECVD deposition,reactive ion etching, inductively coupled plasma (ICP),photolithography, planar devices, UV-photosensitivity, arrayedwaveguide gratings, multi-mode interference couplers, opticalAdd-Drop multiplexers