Integrated photonic devices for optical pulse shaping,udprocessing and measurement.

摘要

Over the last decade significant increase in internet access, high speed communication, highuddefinition media streaming and high volume cloud storage have affected our daily lives. This hasudresulted in an unprecedented demand in the speed and volume of data transfer. To overcome theudsevere speed limitations of present electronic circuits, which are practically limited to processingudand switching speeds below a few tens of GHz, all-optical or alternatively electro-optical solutionsudhave attracted considerable attention, offering generation/processing speeds from 10s of GHz toudseveral THz. Over the years engineers have moved light ever closer to the heart of computingudsystems, the microprocessor, in order to keep up with the switching and processing speeds requiredudto manipulate the gigantic amount of data being passed to telecommunication networks. This topicudis particularly important for applications in data centers (Data centers consist of a large group of networked computer servers typically used by organizations for theudremote storage, processing, or distribution of large amounts of data.), due to the limitations of electronicsudcircuits and copper wires in handling and processing high data rates.udIn particular, silicon photonics is seen as a great foundation for optics and electronics to meet.udLeveraging from mature complementary metal oxide semiconductor (CMOS) fabrication process,udsilicon photonics offers wafer scale testing, low cost packaging, scaling to high levels of integration,udsolves electrical interconnect limitation in data centers, supercomputers and integrated circuits.udDespite all the advantages offered by silicon photonics, it has been mostly implemented inudinterconnects and/or switching applications in industry. Significant effort has been put intouddevelopment of signal processing building blocks, which already exist in electronics, alternativelyudin optical domain with unprecedented operation bandwidths (processing speeds). These signaludprocessors generally fall into two categories: (1) linear optics and (2) nonlinear optics-baseduddevices. Linear optics signal processors are of higher interest in telecommunications, because theyudusually work with lower levels of power (few to tens of milliwatts). These processors offer 100 toud1000 times improvement in processing speed as compared with their electronic counterparts.udThe main objective of this Thesis is to develop integrated photonics devices for on-chip opticaludpulse shaping, processing and measurement. The Thesis includes proposals and developments ofudnovel theories, designs, numerical analysis, layout preparations and experimental demonstrations.udSpecific accomplishements of this Thesis include:uda) Proposal and development of a novel theoretical frame work, namely discrete space-totimeudmapping in cascaded co-directional couplers, enabling practical on-chip arbitraryudoptical pulse shaping with time resolutions ranging from a few femtoseconds up to the subnanosecondudregime.udb) Modelling, layout design and experimental demonstration of on-chip optical pulse shapinguddevices based on discrete space-to-time mapping theory. Demonstrated functionalitiesudinclude: (1) high quality sub-picosecond/picosecond flat-top pulse generation; (2)udTsymbol/s optical phase coded bit-packet generation; (3) Tsymbol/s optical phase andudamplitude coded bit-packet generation.udc) Proposal and development of a nondispersive, tunable band-pass/band-reject filteringudscheme using photonics Hilbert transformers (PHTs) incorporated in a Michelsonudinterferometer. By controlling the central frequency of PHTs with respect to each other,udboth the central frequency and the spectral width of the rejection/pass bands of the filterudare proved to be tunable. In this project bandwidth tuning from 260 MHz to 60 GHz isudnumerically demonstrated using two readily feasible fiber Bragg grating-based PHTs. Theuddesigned filter offers a high extinction ratio between the pass band and rejection bandud(>20dB in the narrow-band filtering case) with a very sharp transition with a slope of 170-uddB/GHz from rejection to pass band.udd) Proposal, modelling, layout design and experimental demonstration of on-chip fractionaludand integer-order PHTs on silicon-on-insulator (SOI) wafer, based on laterally apodizedudintegrated waveguide Bragg gratings. In this work high-performance photonic integer andudfractional-order Hilbert transformers, with processing bandwidths above 750 GHz, haveudbeen experimentally realized.ude) Experimental demonstration of on-chip, single-shot and real-time phase characterizationudof GHz-rate optical telecommunication signals. In particular, phase reconstruction basedudon optical ultrafast differentiation (PROUD) is implemented using an integratedwaveguideudMach-Zehnder Interferometer (MZI) to demonstrate self-referenced phaseudcharacterization of GHz-rate complex modulated signals (e.g. Quadrature Phase ShiftudKeying(QPSK), and Amplitude Phase Shift Keying (APSK) modulation formats), throughuda single-shot and real-time technique.udFinally, I strongly believe that the ideas, techniques and devices demonstrated throughout thisudThesis can contribute to the development of novel integrated-waveguide all-optical/electro-opticaludprocessors.