We present Si microlenses fabricated using dry ICP plasma etching of silicon and thermal photoresist reflow. The process is insensitive to thermal reflow time and it can be easily incorporated into fabrication flows for complex optical systems. Using this process, we were able to fabricate microlenses with diameter of 150 μm, radius of curvature of 682 μm and with a surface roughness of only 25 nm.
We have studied, for the first time, the sensing capabilities of plasma-enhanced chemical vapor deposition (PECVD) SiC-SiO2-SiC horizontal slot waveguides. Optical propagation losses were measured to be 23.9 dB/cm for the quasi-transverse magnetic mode. To assess the potential of this device as a sensor, we simulated the confinement factor in the slot. This simulation revealed that SiC-based slot waveguides can be used, advantangeously, for sensing as the confinement strongly varies with the refractive index of the slot material. A confinement factor change of 0.15/refractive index units was measured for different slot materials.
We fabricated horizontal slot waveguides using two low temperature deposition techniques ensuring the
full compatibility of the processes with CMOS technology. Slots width as thin as 45 nm with smooth slot
surfaces can easily be fabricated with simple photolithographic steps. Fundamental TM-like slot mode in
which the E-field is greatly enhanced within slot showed a 23.9 dB/cm and a 18 dB/cm in a PECVD
SiC/SiO<sub>2</sub>/SiC and a ALD TiO<sub>2</sub>/Al2O<sub>3</sub>/TiO<sub>2</sub> vertical slot waveguide, respectively.
Optical Coherence Tomography (OCT) has found applications in many fields of medicine and has a large
potential for the optical biopsy of tumors. One of the technological challenges impairing faster adoption of
OCT is the relative complexity of the optical instrumentation required, which translates into expensive and
bulky setups. In this paper we report an implementation of
Time-Domain Optical Coherence Tomography
based on Plasma Enhanced Chemical Vapor Deposition (PECVD) Silicon Carbide (SiC). The devices, with
a footprint of 0.3 cm<sup>2</sup>, are fabricated using rib waveguides defined in a SiC layer. While most of the
components needed are known when using this material , a fast delay line with sufficient scanning range
is a specific requirement of Time Domain (TD)-OCT. In the system reported here this is obtained making
use of the thermo-optical effect. Though the current implementation still requires external sources and
detectors to be coupled to the planar waveguide circuit, future work will include three-dimensional
integration of these components onto the substrate to achieve a fully autonomous and compact OCT chip.
With the potential to include the read-out and driving electronics on the same die, the reported approach
can yield extremely compact and low-cost TD-OCT systems in the visible, enabling a broad range of new
applications, including OCT devices for harsh environment.
Optical Coherence Tomography (OCT) is a promising medical imaging technique. It has found applications in many fields of medicine and has a large potential for the optical biopsy of tumours. One of the technological challenges impairing faster adoption of OCT is the relative complexity of the optical instrumentation required, which translates into expensive and bulky setups. In this paper we report an implementation of Time Domain OCT (TD-OCT) based on a silicon photonic platform. The devices are fabricated using Silicon-On-Insulator (SOI) wafers, on which rib waveguides are defined. While most of the components needed are well-known in this technology, a fast delay line with sufficient scanning range is a specific requirement of TD-OCT. In the system reported, this was obtained making use of the thermo-optical effect of silicon. By modulating the thermal resistance of the waveguide to the substrate, it is possible to establish a trade-off between maximum working frequency and power dissipation. Within this trade-off, the systems obtained can be operated in the kHz range, and they achieve temperature shifts corresponding to scanning ranges of over 2mm. Though the current implementation still requires external sources and detectors to be coupled to the Planar Lightwave Circuit (PLC), future work will include three-dimensional integration of these components onto the substrate. With the potential to include the read-out and driving electronics on the same die, the reported approach can yield extremely compact and low-cost TD-OCT systems, enabling a wealth of new applications, including gastrointestinal pills with optical biopsy capabilities.
Light delivery and optical monitoring during photodynamic therapy (PDT) is often limited by the need for a physical
optical link between the light source and detection devices and the treatment volume. This can be critical when sources
need to be implanted within the body for extended periods. We report on the latest developments for a telemetric PDT
delivery and monitoring device that can dynamically vary the local illumination parameters based on the in-situ fluence
rate within the PDT target volume. Local light delivery and collection is achieved using solid-state optodes, microfabricated
on a silicon substrate. Photodiodes have been produced using a standard bipolar process. Chip-form LEDs are
then assembled into micro-machined pits adjacent to the light fluence rate detectors. The devices (1.2×1.2mm<sup>2</sup>) are
bonded to a flexible PCB together with the remaining electronics. Power coupling and communications are achieved by
means of an inductive link while light delivery and fluence rate monitoring are digitally managed using a
microcontroller. These devices are being tested in optical phantoms and in pre-clinical models. Our results show that it is
possible to manufacture solid-state optodes of suitable dimensions and that it is feasible to telemetrically deliver and
control the local fluence rate using them. It can also be concluded from our work that while the optode is sufficiently
small to be useful as a light delivery and monitoring device, digital control, read-out electronics and power coupling can
benefit from further optimization and miniaturization.
Optical Coherence Tomography (OCT) is a powerful medical imaging technology. Its ability to non-invasively probe
tissues in depth with high resolution has lead to applications in many fields of medicine, with a large potential for
surgical guidance. One of the technological challenges impairing faster adoption of OCT is the relative complexity of the
corresponding optical instrumentation, which translates into expensive and bulky setups. In this paper a compact fast-scanning
optical delay line based on the thermo-optical effect of silicon is studied. Although this effect has been applied
to other optical components, the necessary frequency behaviour together with the relatively large scanning range
required are unique to the application. Cycling speeds of over 1kHz and ranges of more than 1mm are needed for video-rate
acquisition of relevant tissue volumes. A structure is proposed to meet these specifications. A bulk micro machined
freestanding waveguide is connected to the substrate by means of evenly spaced support beams. It is shown by means of
the Finite Element Method that the geometrical parameters of the beams modulate the thermal behaviour of the
waveguide. A linear trade-off between maximum working frequency and power dissipation for any given waveguide size
and required scanning range has been found. Our results show that the proposed implementation of a fast-scanning delay
line can match the requirements of Time Domain Optical Coherence Tomography.
Light transport in trabecular bone is not well understood despite its clinical interest. Recent experimental studies on optical bone biopsy are lacking models that relate their measurements to the underlying morphology and thus to tissue condition. Laser surgery can also benefit from a better understanding of energy distribution in cancellous bone. A Monte Carlo (MC) simulation environment, able to efficiently compute complex geometries and account for refraction and reflection on tissue boundaries has been developed to provide the missing insight. The geometry description is based on a 3D triangle mesh organised in a bounding-volume hierarchy. This efficient structure allows a fast photon-surface intersection test, ensuring a sufficient number of photon paths and thus a good signal-to-noise ratio. The simulation program has been validated against well-known problems of refractive optics and turbid media. This new tool has been applied to a set of numerical phantoms indicating that morphology may have a fundamental impact on long-range light transport. The simulation environment has also been used on high-resolution models of trabecular bone, based on micro-CT scans. Calculation of time resolved signals in transmission and reflectance geometries has been demonstrated, paving the way to numerical evaluation of new minimally invasive diagnostic techniques, and offering a link to evaluation of Optical Coherence Tomography (OCT) in complex heterogeneous geometries. Preliminary experimental results in support of the mentioned effects are presented.
A low temperature high quality gate dielectric process for bottom gate organic thin film transistors (OTFT) is introduced which is compatible to plastic substrates. The Al<sub>2</sub>O<sub>3 </sub>dielectric is grown from the aluminum gate electrode by anodic oxidation at room temperature and exhibits an exceptionally good electrical performance even for thin layers of 50nm. Finding an electrolyte which significantly reduces dielectric charges was instrumental for the desired OTFT application. The electrolyte and substrate dependent behaviour was characterized and compared to different dielectrics to point out the advantages of anodic oxidized aluminum. The characteristics of pentacene bottom contact OTFTs realized with anodized Al<sub>2</sub>O<sub>3</sub> gate dielectric on glass and plastic substrates are presented.