Wolfgang Karthe

Efficient Coupling into Polymer Waveguides by Gratings

Investigations of highly efficient grating couplers for polymer slab and strip waveguides fabricated by electron-beam lithography are reported. A maximum input efficiency of 67% is achieved. The electron-beam direct-writing technique allows one to replicate the original gratings into polymer substrates by embossing. An all-polymeric optical chip with efficient grating couplers is demonstrated. Waveguide grating couplers with blazed profile and variable grating depth are investigated. Thus, the intensity distribution of the outcoupled light is matched to a Gaussian-like profile. A focusing blazed grating that couples the light with an efficiency of 42% into a polymer strip waveguide is reported. A curvature correction of the grating lines allows one to improve the focusing properties.

Integrated optics toward the third dimension

The level of integration within standard waveguide devices is usually restricted to the use of a single plane per wafer containing waveguides. Recently, concepts for waveguide structures with several planes of waveguides gain some special interest. They are mainly due to intentions to increase the number of channels per chip, to reduce the chip size and to improve device characteristics. Dense vertical stacking of waveguides turns out to be an approach to 3D integrated optics, which is within the resolution limits of up-to-date waveguide technologies. Theoretical and experimental results for 3D directional couplers are reported in detail.

Directional coupler device using a three-dimensional waveguide structure

Abstract A new directional coupler device using a three-dimensional structure is presented. It consists of two stacked directional couplers (4 × 4-coupler as doubly stacked directional couplers). Coupling occurs both in horizontal and vertical direction. The device is intended to be the first of several devices employing three-dimensional structures. The presented device was fabricated by UV-patterning of a stack of spin-coated polymethylmethacrylate (PMMA) layers.

Polarization-independent integrated electro-optic phase modulator in polymers

Polymer multilayer waveguide technology was used to fabricate a polarization-independent phasemodulator. Refractive indices and electro-optic coefficient r33 of the materials used (Co. SANDOZ) were determined by waveguide methods.

Active and passive components of 3D integrated optics

The potential of 3D integrated optics based on different technological schemes is investigated. Theoretical and experimental results for waveguide geometries with stacked waveguide layers and with waveguide circuits prepared on topological structures are reported as well. Within waveguide geometries including individual guides in a sequence of stacked layers directional coupler arrays allow for short length passive signal distribution, and various schemes of single and multipath switching can be identified. Cost effective preparation technologies as spin coating of polymer and PECVD of SiON layers and their patterning by UV- exposure or RIE, respectively, have been prove to fulfill the critical tolerance requirements of a simultaneous directional coupling in two transversal directions. To realize waveguides with smooth height variation gray scale lithography was used to produce topological surfaces. Upon those surfaces waveguide paths and devices can be defined subsequently, which are useful e.g. for non-planar to planar fan out structures or interferometer configurations for sensing applications. The topological surfaces can be replicated very efficiently by reaction molding, a technology widely used for micro-optical structures, too.

Grating couplers in planar polymer waveguides with beam shaping properties

Investigations on input and output grating couplers with asymmetric triangular (blazed) profiles for planar polymer waveguides are reported. With blazed gratings a high outcoupling efficiency into one direction, either substrate or superstrate is achieved. The gratings are written directly into the waveguiding polymer layer by electron beam lithography and are replicated by embossing. Electron dose control across every grating period results in asymmetric blazed corrugation of the grating. Additionally, variation of the electron dose across the whole grating leads to a variable corrugation depth along the grating length. Two types of waveguide gratings were designed and produced, blazed corrugated gratings with constant groove depth and with variable groove depth, respectively. Input efficiencies of about 40% for gratings with constant grating depth were measured. The original gratings were replicated into nickel by electroplating. For a replicated grating we attained an efficiency of the outcoupled light into one diffraction order of about 74%. Waveguide grating couplers with blazed profile and variable grating groove depth are investigated. Thus, the intensity distribution of the outcoupled light can be varied and the field profile was matched to a Gaussian like profile.

Determination of thermo-optic coefficients in PE: and APE:LiNbO3 channel waveguides for phase-compensated sensor applications

Thermo-optic coefficients of the extraordinary effective refractive index in integrated optical channel waveguides in LiNbO3 have been measured with high accuracy by Mach-Zehnder and Fabry-Perot interferometer techniques. Single mode titanium-indiffused and single mode annealed proton-exchanged (APE) channel waveguides were found to have the same value as it is known for the substrate material. Multimode proton-exchanged (PE) channel waveguides specially designed for maximum field overlap to the APE waveguides show a reduction of the thermo-optic coefficient to one-fifth with negative sign. Phase shift dependent on temperature was examined in APE channel waveguides containing such a strip-shaped multimode PE segment. Possible phase-compensated wavelength sensor applications are proposed.

Electro-optic effects in polymer waveguide devices for optical communication

Electro-optic waveguide elements are fabricated in the polymer-on-silicon technology. Measured field distributions of the inverted rib waveguides show excellent agreement with vectorial FEM calculations. This method is also used for electro-optic phasemodulator design. The dynamics of electrode poling is studied by reflectrometry. An integrated waveguide interferometer with lateral electrodes allows the determination of the r33/r31 equals 3.5.

Optical carrier modulation by integrated optical devices in lithium niobate

Proton-exchanged LiNbO3 electrooptic waveguide devices are applicable to communications components employing phase and intensity modulation, in virtue of their (1) high optical damage threshold, (2) extremely high polarization maintenance, and (3) flexibility as to waveguide parameters, due to different annealing procedures. Attention is presently given to two examples of such devices, an LiNbO3 phase modulator and an LiNbO3 Mach-Zehnder interferometer modulator operating at 1300 nm.

Optimized design and fabrication of integrated optic 1x32 and 2x32 multifunnel power splitters in polymer

We present the optimized design and the fabrication of an integrated-optic 1 by 32 multifunnel power splitter and the extension to a 2 by 32 splitter of the same type which we are the first to report. This splitter type operates by receiving the radiated input power at the end of a slab waveguide by funnel shaped waveguides of increasing width to compensate for the power decrease towards the outer parts. Using cycle of BPM simulation and adapting the width of the receiver waveguides according to the calculated intensity distribution we achieved a maximum excess loss of 0.5 dB in the simulation. The 2 by 32 splitter was designed using two input waveguides placed symmetrically 8 micrometers off-center and facing the center of the receiver region. Both splitters were fabricated by UV exposure of PMMA with photo initiator BDK. The realized 1 by 32 splitter shows an excess loss of 0.7 dB compared to a reference waveguide and a standard deviation of 0.5 dB with a maximum loss of 1.8 dB at (lambda) equals 1320 nm, the 2 by 32 splitter has 1.3 dB excess loss, 0.8 dB standard deviation and 2.5 dB maximum loss.