A buried polyimide waveguide fabricated on glass substrate using semiconductor processing technologies is presented. The proposed structure is applicable to planar lightwave circuits (PLCs) because of planar surface morphology of the device. Potential applications of the device range from passive optical coupler to active modulators. The fabrication steps of the buried polyimide waveguide include deep etching, polishing of polyimide, global planarization and formation of waveguide end facets. Deep glass etching requires a hard etching mask in order to prevent unwanted etching of the under laying material. Chromium(Cr) is one of the best making material because it is easy to grow and hard to etch. The Cr thin film was deposited the glass substrates using a thermal evaporation system. The glass substrate was etched by reactive ion etching (RIE) using SF6 and O2 (SF6:O2=20:1) mixture. Etching rate of glass and Cr were 0.1µm/min and 130Å/min, respectively. After etch, the polyimide guiding layer of the waveguide was spin-coating at a slow spinning speed onto the glass substrate, and was cured at 300¢Jfor 1.5 hr. The uneven surface of the device was planarized by lapping the polyimide down to the glass substrate. Both the abrasive paper and Al2O3 powder were used in the process. Then a thin layer of SOG (spin-on-glass) was coated on the top of the waveguide to isolated the polyimide from the air. Finally, the end facets of the waveguide were form by RIE etching without further polishing. The propagation loss of the waveguide was measured by conventional cut back method. The polarized lights at 1.3um were launched into the waveguide by end-face optical coupling. The propagation losses of the waveguide are 3dB/cm for TE wave and 4.6dB/cm for TM wave, respectively.

Abstract A novel buried hybrid polymer waveguide using semiconductor processing technologies is presented. It has advantage of low cost, ease of fabrication, planar surface morphology of the device, and it is applicable in dense wavelength division multiplex (DWDM) systems. The polymer waveguide consists of a polymer core buried in the SiO2 lower cladding on a Si substrate. The device was fabricated by first etching a trench into the SiO2 cladding. The surface of the waveguide was then planarized using the Benzocyclobutene (BCB) polymer. After etch back of the BCB polymer, the guiding core is formed in the trench region. Finally, a thin film layer of SOG (spin-on-glass) was coated on the top of the waveguide to isolate the core from the air. For TE polarized wave, the propagation loss as low as 0.59dB/cm is obtained. The propagation of TM wave is 0.65dB/cm. In addition, a multi-mode inference power splitter based on the buried waveguide structure is theoretically investigated.

A novel variable optical attenuator based on buried polymer waveguides and waveguide bends is proposed. The attenuator consists of three waveguide sections, separated for waveguide bending by two embedded micorprisms. The attenuation of device was achieved by steering the beam propagation direction in the waveguide by thermo-optical effects. Detailed simulation results using the Beam Propagation Method are presented. In addition, radiation losses of the waveguide bends are experimentally investigated. After two-10¢X bends, the normalized insertion losses as low as 65.7¢H are obtained. The propagation loss of the buried waveguide is 0.47dB/cm at l=1.3 mm.

In integrated optics, there are many adiabatic dielectric waveguides. Examples include bending waveguides, multi-mode interferometers (MMI), taper waveguides, grating assisted directional couplers (GADC), etc. Among these waveguide devices, adiabatic bending waveguides are the most important basic devices. They are used to connect various vertical or horizontally displaced waveguides. There are many approximate methods such as the beam propagation method (BPM), finite-difference time-domain, (FD-TD) and finite-difference frequency-domain (FD-FD) methods that have been used to analyze and optimize the waveguide designs. BPM can not calculate wide angle optical traffic due to its intrinsic paraxial limitation. Both FD-TD, FD-FD handle wide-angle bi-directional traffic but both demand tremendous computational resources. In this thesis, we develop a new formulation called full eigen-mode expansion technique (FEMET) that considers only forward propagating but all wide-angle traffic. It is a simplified version of our existing bidirectional, coupled transverse-mode integral-equation (CTMIE) formulation. FEMET includes all forward propagating, high-order mode field but neglects reflection at the dielectric discontinuities. Since FEMET uses no matrix equations, it is much faster than CTMIE. To verify the accuracy of FEMET we consider the titled straight waveguide (TSR) as our test example. TSR has an exact solution in its natural coordinate system which allows us to study computational characteristics of FEMET. The two FEMET computational control parameters are the total number of waveguide sections and the number of modes used in each section. Together they control the speed and accuracy of FEMET. We use FEMET to analyze radiation and mode interference of both S-bend waveguides and two-corner bends. These results compare well with result computed by other methods.

In this paper, a single mode buried polymer waveguide on silicon dioxide layer on silicon substrate is presented. The waveguide was completed by first obtaining the optical field distribution using a beam propagation method. The waveguide structure is carefully designed to ensure a single-mode operation of this device. The waveguide was fabricated by first etching a trench on SiO2 layer. Then Benezocy-clobutene (BCB) polymer was deposited onto the layer and cured in proper conditions. Finally, a thin hybrid sol-gel layer was used as the top cladding layer after the BCB polymer etch-back process. The propagation losses are 0.91dB/cm and 0.97dB/cm for TE and TM polarized lights. The polarization dependent loss is 0.06dB/cm. The coupling loss of the waveguide is 1.78dB.

Design and Analysis of Arrayed Waveguide Grating Abstract Fiber optic communication provides extremely broad bandwidth making transferring large quantities of voice/data possible. Dense Wavelength Division Multiplexing (DWDM) is the most critical technology of the optical communication system. It allows the simultaneous transmission of up to hundreds of channels within a single fiber across a distance of thousands of kilometers. Arrayed waveguide grating (AWG) is the most critical component in the DWDM system. It takes a single input and separates different optical ¡§channels¡¨ into different output fibers. It is critical that we develop our own ability to design and fabricate such a device, so that we will not be left behind in the technological realm. Although there are many commercially available AWG designing software such as the Phaser package of the BPMPRO software, they fail to provide a solution to aide in the final design of the optical mask for the AWG. In this thesis, we present a detailed, step-by-step analysis of an AWG device, as well as a description of how the AWG device works. In the process, we have classified the free parameters from that of depending parameters and have solved the routing problem in the layout of the waveguides. To summarize the primary result of this thesis, we use five main points, which are: 1) We discuss the function of each block, the subsystems of the AWG. 2) We propose a novel, yet intuitive theory based on geometric optics ¡V how the device is able to perform its de-multiplexing functions. 3) We present an analytic formula showing the linear property of the optical path difference along the source and the receiver arrays. 4) We solved the routing problem of the various waveguide sections of the AWG. 5) We have automated the process of generating optical masks in AutoCAD format from within a Matlab environment.

In this thesis, novel broadband waveguides capable of operating at terahertz (THz) frequencies are introduced. We explore in detail the two-wire waveguide showing that it can have absorption as low as 0.01 cm-1, fairly good coupling efficiency, and is free from group-velocity dispersion (GVD). We also propose two low loss, planar slot-line structures for guiding THz waves. Rigorous theoretical analyses, numerical simulations, and experimental results are presented to evaluate and verify the performance of the waveguides at THz frequencies. We also present a tapered structure to couple effectively THz waves from a photoconductive source to a two-wire waveguide. Finally, practical structures to realize the first THz low-loss cable using the two-wire waveguide are introduced. / Graduate

In the lower millimetre-wave frequency range, Substrate Integrated Waveguide (SIW) circuits have emerged as a reasonable compromise between rectangular waveguide and standard microstrip technologies. They are formed by a top- and bottom-metalized substrate and two arrays of plated or riveted holes (via holes) to replace the vertical metallic walls in conventional rectangular waveguide. Although many passive components known from traditional waveguide technology have been fabricated in SIW, one of the main challenges is to integrate active components with typical coaxial-type interfaces within the SIW environment. Therefore, the work presented in this dissertation focuses on new broadband transitions from SIW to other planar transmission-line technologies such as microstrip coplanar waveguide, coplanar strip line, slot line and coupled microstrips. Several of the new transitions are prototyped and experimentally verified. Two of these transitions are then used to integrate a low noise amplifier within SIW input and output ports. The measurements of fabricated SIW amplifier prototypes show very promising performance and clearly demonstrate successful integrations of active components within SIW. Finally, one of the new SIW-to-coplanar-waveguide transitions is employed as an interface to an SIW-based antenna, thus demonstrating the principle of connectivity of SIW to all currently used planar circuit technologies. / Graduate

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