In the last years, optical resonators have emerged as a promising tool for highly sensitive measurements. Especially for label-free measurements of biological substances, the resonators have to be functionalized by additional surface layers. Since the properties of the resonator, like the refractive index of the core and the layer as well as the layer thickness or the core radius can deeply in fluence the sensitivity. For this reason, a geometrical optics based theory is used to investigate the dependence of the resonance wavelength on the resonator properties.
This paper reports ex-situ preparation of conductive polymer/single-walled carbon nanotubes (SWNTs) nanocomposites by adding high conductive SWNTs to the polymer matrix. Sonication methods were used to disperse the SWNTs in the polymer. The conductivity of the nanocomposites is tuned by increasing the concentration of SWNTs. Furthermore, we present two-photon polymerization (2PP) method to fabricate structures on the basis of conductive photosensitive composites. The conductive structures were successfully generated by means of 2PP effect induced by a femtosecond laser.
Optical resonances of spherical microresonators are of great interest measurements with high sensitivity. Usually the quantity to be measured is determined by the shift of the resonances of a single particle. Unfortunately, for this purpose, an expensive low-bandwidth tunable laser system with high accuracy is needed. When using an array of microresonators with slightly different size, each particle has a different resonance behavior. A change of the quantity to be measured leads to a change of the intensity distribution over the entire array. Therefore, using a microresonator array it is sufficient to measure the intensity distribution over all particles at a fixed wavelength.
Since the early times of Arthur Ashkins groundbreaking experiments on optical tweezers, a great number of theoretical works was dedicated to this subject. Most of them treated the optical trapping of single spherical or elliptical particles. In the last years optical tweezers have become more and more a tool for assembling three dimensional structures using single microspheres as building blocks. Since all structures and particles inside the light beams influence the properties of the traps, we investigated theoretically the influence of additional single particles and particle arrays on the properties of optical traps. For this reason a geometrical optics based model is used with the inherent flexibility to be applied for various shapes and particle numbers.
Optical resonances of microresonators, also known as whispering gallery modes, are attracting considerable
interest as highly sensitive measuring devices with a variety of applications. Such resonators can be used for
pressure, force or strain measurement. Droplets, embedded in an appropriate substrate, form perfect spheres
due to their surface tension and can be used as optical resonators with high quality factors. The resonance
frequencies of these droplets depend sensitively on their size and shape. Pressure changes affect the droplet
shape. Therefore, pressure change can be measured with high sensitivity. In the work presented here, ethanol
droplets embedded in a silicone matrix are considered. The shift of the resonance frequencies of microdroplets
embedded in silicone as function of the applied pressure is investigated.
A new method to fabricate microstructures built by polymer microparticles using a bottom-up technique is presented.
The microstructures find broad application in micro-fluidics technology, photonics and tissue-engineering. The handling
of the particles is realized by a holographic optical tweezers setup, ensuring the precise allocation of the particles to the
desired structure. A biochemical technique ensures that the structure remains stable independent of the laser source. We
show that with this method complex two-dimensional durable structures can be assembled and cannot be separated by
optical forces. The structures are extendable during the entire fabrication process and can be linked to further particles
and structures as desired.
In recent years, optical microresonators have been extensively investigated for possible applications in many
different areas of research. In optical communications such resonators can be used for switching, filtering or
multiplexing devices. Due to its high quality factors, spherical microresonators are of great interest for optical
sensing. Here we will discuss the use of a microparticle array as a spectral sensing device. Especially the accuracy
in wavelength determination for broad light sources are in the focus of this work. Beside this, results for two
light sources with different wavelengths are given.
Microcavity optical resonators have been investigated in the last years extensively for possible applications in
optical communication (switching, filtering, and multiplexing), to investigate cavity quantum dynamic effects,
and for sensor applications. The most recent area of application is bio-sensing. The preferential resonator type
in the communication area is the disc resonator, the spherical resonator is the most prominent resonator type
in sensing applications and a rapidly growing number of groups are investigating the potential of hollow tube
resonators for detecting of bio-agents. Here we will present the concept of resonator arrays as sensing element.
Potential fields of application are similar to the single resonator sensor but also beyond. We will give an example
of an application that is not accessible for single resonators. We will describe the use of resonator arrays as
wavelength sensor and discuss several aspects such as the number of sensing elements or the line width on the
performance of such a device.