Electronic interconnects are reaching their limit in terms of speed, dimensions and permissible power consumption. This has been a major concern in data centers and large scale computing platforms, creating limits to their scalability especially with respect to power consumption. Silicon photonic-electronic integration is viewed as a viable alternative that enables reliability, high efficiency, low cost and small footprint. In particular, silicon with its high refractive index, has enabled the integration a many individual optical elements (ring resonators) in small areas. Though silicon has a high thermo-optic coefficient (1.8×10^-4/°C) compared to silica, small thermal fluctuations can affect the optical performance especially for WDM applications. Therefore, a passive athermal solution for silicon photonic devices is required in order to reduce thermal sensitivity and power consumption. We have achieved this goal by replacing the silica top cladding with negative thermo-optic coefficient (TOC) materials. While polymers and titanium dioxide(titania) have a negative TOC, polymers can’t handle high temperature processing and titania needs very tight thickness control and expensive deposition under vacuum. In this work we propose to use a sol-gel inorganic-organic hybrid material that has the benefits of both worlds. We were able to find optimum curing conditions to athermalize ring resonators by studying various sol-gel curing times and curing temperatures. Our athermal rings operate in a wide temperature range from 5C – 100C with thermal shifts below 1pm/C and low loss. Furthermore, we demonstrate that our athermal approach does not deleteriously effect critical device parameters, such as insertion loss and resonator Q factors.
A silicon waveguide in an electro-optic (EO) polymer cladding-based directional coupler switch was designed
and fabricated. Optimal dimensions for efficient coupling and minimal crosstalk are found analytically (coupled
mode theory) and numerically for 1550nm wavelength. Both coplanar electrode spacing and height are taken into
account for most effective poling conditions and performance. The design consists of two 255nm wide waveguides
separated by 500nm and is optimized for TE propagation. With an electrode separation of 4μm and coupling
length of 1.7cm, a switching voltage (Vs) < 10V at an r33 of 250pm/V is expected.
A Mach-Zehnder interferometer (MZI) is used to decouple the
electro-optic (EO) and piezoelectric tensor
components for a poled polymer film. In the past those using the MZI method failed to take into account the
piezoelectric contribution in the polymer which can lead to erroneous EO coefficient data. The typical poled sample of
polymer sandwiched between ITO glass and gold that was developed for the popular Teng-Man reflection ellipsometry
method is used, providing for easy comparison with that method. The sample serves as a mirror in one arm of the
interferometer with the gold side facing the beam for measuring the piezoelectric modulation and the glass side facing
the beam to measure the coupled piezoelectric and EO modulation. Optical biasing in the reference arm allows for the
baseline and modulated contrast of the system to be measured from which the tensor components are calculated. This
method has the advantage over the reflection ellipsometry method of allowing for the independent determination of the
Pockel's coefficients r13 and r33 and the piezoelectric coefficient d33. The r33 value of a guest host polymer that consists
of AJLZ53/amorphous polycarbonate (APC) was found to be 122.7 pm/V and 123.0 pm/V for the MZI and reflection
ellipsometry method respectively. The r33 data fits well to the dispersion of the second order susceptibility tensor
based on the two-level model approximation. Measurements were done from 100 Hz to 100 kHz with the results
showing that at higher frequencies the mechanical effects in the sample are negligible and modulation is almost entirely
due to the EO effect, as expected.
We investigate the dielectric and electrical properties of sol-gel/DNA-CTMA blends, with particular interest in capacitor
applications in energy storage. Methacryloyloxypropyltrimethoxysilane (MAPTMS) was the sol-gel precursor, and
DNA-CTMA was blended in to the resulting sol-gel at 5 weight%. The blend was then tested for its dielectric properties
and dielectric breakdown strength; at frequencies below 10kHz the blend was found to have a dielectric constant in the
range of 7.5, while the breakdown strength was greater than 800 V/μm, an exceptional value. We discuss these results
as well as other aspects of the dielectric and electrical properties of these blends.
Passive sol-gel materials play an important role in the development of electro-optic(EO) polymer-based modulators,
because of their variety of available refractive indices. They can be used to form passive waveguide transitions to
minimize coupling loss or as cladding layers for the EO polymer. The demands for these two applications are different.
For waveguide transitions the most important factor is the optical loss. Cladding layers should have a relatively high
conductivity at elevated temperatures to improve poling efficiency. Both demands are addressed in this study. The
synthesis of low loss (down to 0.45 dB/cm) sol-gel materials is shown. Slab waveguides as well as ridge waveguides
were fabricated and characterized by liquid prism measurements and cut-back loss measurements, respectively. For use
in cladding layers surrounding the EO polymer, materials with higher conductivity were developed. The conductivity of
the materials was increased, (3•10-9 S/m) through the use of a silane, which allows in situ formation of proton donating
functionalities. All developed materials can be used as solvent free resins, which enables classic photolithography as
well as patterning by UV-imprinting. The available refractive index range (at 1.55 μm) is from 1.495 to 1.562.
The handling of a continuously increasing amount of data leads to a strong need for high-speed short-range connections.
Conventional Cu technology between chips on a board is limited. Optical interconnects will dominate the market, since
they can overcome the limitations. One of the issues for materials used, e.g., for waveguides embedded in printed circuit
boards (PCBs) is the compatibility with standard epoxies used for PCBs during the entire board fabrication process.
Materials applied for optical interconnects should be mechanically and optically reliable, and also allow low-cost
production. From the material production side, the process should be easy to up-scale. Therefore, anticipatory research
strategy and suitable tailoring is asked for.
The handling of light in the UV and visible range often requires the use of specially designed materials. Most polymer
materials show an increased yellowing effect upon being exposed to shorter wavelength light. The major influence on the
absorption in the UV and visible range of a UV curable material is related to the UV initiator, beside any other
chromophores formed mainly during the exposure.
Different material approaches will be presented which fulfil the requirements for highly sophisticated applications in
optics / optical packaging technology. Firstly, an epoxy-based material system for optical chip-to-chip interconnection
will be introduced. Secondly, the adaptation of a UV patternable inorganic-organic hybrid material (ORMOCER®)
originally developed for waveguide applications in the data and telecom regime, will be discussed with respect to
applications in the visible regime. Spectroscopy and UV-DSC measurements were carried out to investigate the influence
of standard photoinitiators on the optical properties for an ORMOCER® system suitable for microoptic applications. The
results show that the resulting material properties were significantly improved by exchange of the initiators compared to
the originally incorporated one.