D.J.W. Klunder

Sensor based on an integrated optical microcavity

A novel integrated optical sensor based on a cylindrical microcavity (MC) is proposed. A MC sustains so-called whispering-gallery modes (WGMs), in which the energy of the optical field can be efficiently stored. By monitoring the scattering intensity from the MC, one can detect minute changes in the refractive index of the WGM, for instance, as a result of analyte adsorption. Measurement of a change in refractive index of as little as 10(-4) is demonstrated experimentally. The MC-based integrated optical sensor may have a size of approximately 8mum , and it is rugged and inexpensive.

Stimulated emission and optical gain in LaF3:Nd nanoparticle-doped polymer-based waveguides

We report experiments which show evidence that stimulated emission at 863 nm takes place in hybrid monomode Si3N4 waveguides where LaF3 :Nd nanoparticle-doped polymethylmethacrylate (PMMA) was used as a top cladding material. Furthermore, optical gain at 1319 nm in LaF3:Nd nanoparticle dispersed PMMA s0.1 dB/cmd and photodefinable epoxy (Microchem SU-8) multimode waveguides has been observed at pump powers below 10 mW. This class of composite materials based on polymers with dispersed nanoparticles shows promising properties for planar optical amplifiers. Simulation showed that optical gain in the order of 10 dB can be achieved at 100 mW pump power in a 20 cm long monomode waveguide.

Integrated optical microcavities for enhanced evanescent-wave spectroscopy

The use of integrated optical microcavities (MCs) for enhanced optical spectroscopy and sensing is investigated. The MC sustains high- Q whispering-gallery modes, in which the energy of the optical field can be efficiently stored. The resulting enhanced field can be used to probe fluorescent molecules in the cladding of the MC. Enhanced fluorescence excitation with an integrated optical MC is demonstrated experimentally for what is believed to be the first time. A comparison between a MC and a straight waveguide shows that the MC may give an increase of 40 times in fluorescence excitation. Because of the ultrasmall size of the MC (15 microm in radius), the fluorescence signal may be observed from only 20 molecules in the cladding.

Visualizing the whispering gallery modes in a cylindrical optical microcavity.

Whispering gallery modes in cylindrical integrated optics microcavities have, for what is to our knowledge the first time, been mapped with a photon scanning tunneling microscope. Optical images were obtained with a spatial resolution of 50 nm. By combination of information on the spatial optical distributions with wavelength-dependent measurements, an unexpectedly rich variety of intracavity phenomena, such as polarization conversion and interference of copropagating and counterpropagating modes, could be directly observed. A quantitative comparison of the experimental data with computer simulations results in a comprehensive understanding of the various whispering gallery modes inside the microcavity.

Microresonators As Building Blocks For VLSI Photonics

In the last years much effort has been taken to arrive at optical integrated circuits with high complexity and advanced functionality. For this aim high index contrast structures are employed resulting in photonic wires in conventional index guiding waveguides or in photonic bandgap structures. In both cases the number of functional elements within a given chip area can be enhanced by several orders of magnitude: VLSI photonics. In this talk optical microresonators are presented as promising basic building blocks for filtering, amplification, modulation, switching and sensing. Active functions can be obtained by monolithic integration or a hybrid approach using materials with thermo‐, electro‐ and opto‐optic properties and materials with optical gain. Examples are mainly taken from work at MESA+.

Experimental and numerical study of SiON microresonators with air and polymer cladding

A systematic experimental and numerical study of the device performance of waveguide-coupled SiON microresonators with air and polymer cladding is presented. Values of device parameters like propagation losses of the microresonator modes, the off-resonance insertion losses, and the straight waveguide to microresonator coupling are determined by applying a detailed fitting procedure to the experimental results and compared to results of detailed numerical simulations. By comparing the propagation losses of the fundamental TE polarized microresonator mode obtained by fitting to the measured spectra to the also experimentally determined propagation losses in the adjacent straight waveguide and the materials losses, it is possible to identify the loss mechanisms in the microresonator. By comparing experimental results for microresonators with air and polymethylmethacrylate cladding and a detailed numerical study, the influence of the cladding index on the bend losses is evaluated. It is demonstrated that the presence of an upper cladding can, under the right conditions, actually be beneficial for loss reduction.

Propagation of a femtosecond pulse in a microresonator visualized in time

A noninvasive pulse-tracking technique has been exploited to observe the time-resolved motion of an ultrashort light pulse within an integrated optical microresonator. We follow a pulse as it completes several round trips in the resonator, directly mapping the resonator modes in space and time. Our time-dependent and phase-sensitive measurement provides direct access to the angular group and phase velocity of the modes in the resonator. From the measurement the coupling constants between the access waveguides and the resonator are retrieved while at the same time the loss mechanisms throughout the structure are directly visualized.

Detailed analysis of the intracavity phenomena inside a cylindrical microresonator

Based on a rigorous analysis of the intensity distribution inside a cylindrical microresonator (MR), a detailed description of the wavelength and spatial dependence of the intracavity intensity is given. The theory is in accordance with photon scanning tunneling microscopy (PSTM) of an integrated optics MR. Good agreement between the theory and the PSTM measurements is found.

Experimental analysis of the whispering-gallery modes in a cylindrical optical microcavity

A real-space study of a cylindrical integrated optical microcavity by means of a photon scanning-tunneling microscope with a resolution of 50 nm reveals optical intensity distributions in great detail. Moreover, novel phenomena such as polarization conversion and conversion from copropagation to counterpropagation are observed. We present detailed maps of the optical field distribution of the whispering-gallery modes inside the microcavity as a function of both wavelength and position. We have made a quantitative comparison between measured and calculated field distributions. As a result, the buildup of the various whispering-gallery modes is better understood.

High-resolution photon-scanning tunneling microscope measurements of the whispering gallery modes in a cylindrical microresonator

A detailed analysis of spatio-spectral photon scanning tunneling microscope scans of the light intensity inside a cylindrical microresonator has been carried out. By comparing the experimental results with theory, it is shown that the inclusion of spectral mode-beat phenomena is crucial for an accurate analysis of the modes present in the microresonator.