We present a design concept for an optimized surface-emitting two-dimensional second-order feedback structure
consisting of an array of holes within a dielectric material surrounded by a mirror rim. The mirror rim consists of a first
order photonic crystal structure. The lasing properties of such feedback structures with organic gain material are
investigated theoretically and experimentally.
We present the design of an optimized mixed-order photonic crystal laser structure. The lasing properties of
this two-dimensional photonic crystal structure with an organic gain material are investigated theoretically and
experimentally. A feedback structure fabricated in a thin film of Ta2O5 increases both the index contrast from
the gain material as well as the optical confinement. Furthermore, by combining first order photonic crystal
structures with second order ones losses occurring at the edge of the second order structure are dramatically
reduced leading to a lower laser threshold and / or to a much smaller footprint of the laser.
We investigate circular grating resonators (CGR) with a very small footprint. Photonic devices based on circular
grating resonators are computationally designed, optimized and studied in their functionality using finite
difference time-domain (FDTD) method. A wide variety of critical quantities such as transmission and reflection,
resonant modes, resonant frequencies, and field patterns are calculated. Due to their computational size some
of these calculations have to be performed on a supercomputer (e.g. parallel Blue Gene machine). The devices
are fabricated in SOI using the computational design parameters. First they are defined by electron-beam
lithography. Then the pattern transfer is achieved by an inductively coupled reactive-ion etch process. Finally,
the devices are characterized by coupling light from a tunable laser with a tapered lensed fiber. As predicted
from the simulations the measured transmission spectra exhibit a wide range of different type of resonances with
quality factors exceeding 1000.
Circular grating resonators could lead to the development of very advanced silicon-on-insulator (SOI) based
nano-photonic devices clearly beyond state of the art in terms of functionality, size, speed, cost, and integration
density. The photonic devices based on the circular grating resonators are computationally designed and studied
in their functionality using finite-difference time-domain (FDTD) method. A wide variety of critical quantities
such as transmission and field patterns are calculated.
Due to their computational size some of these calculations have to be performed on a supercomputer like a
massive parallel Blue Gene machine. Using the computational design parameters the devices are fabricated on
SOI substrates consisting of a buried oxide layer and a 340-nm-thick device layer. The devices are defined by
electron-beam lithography and the pattern transfer is achieved in a inductively coupled reactive-ion etch process.
Then the devices are characterized by coupling light in from a tunable laser with a lensed fiber. As predicted
the measured transmission spectra exhibit a wide range of different type of resonances with Q-factors over 1000
which compares very well with the computations.
Combining organic films with high Kerr-nonlinearities and highly
optimized photonic nanostructures could lead to new fast switching
elements. Fabry-Perot cavities are fabricated by incorporating an
organic material between two dielectric mirrors. Using femto-second
pump and probe measurements we characterize these hybrid 1-D
photonic band gap structures for various organic materials. By
varying the pump beam wavelength across the cavity resonance we are
able to delineate between the various underlying nonlinear
processes. Comparing these measurements with computations we are
able to quantify both the refractive and absorptive nonlinear
coefficients of various organic materials.
The temporal coupled mode theory is applied on the design of
filters and waveguide crossings that feature a resonator with
a high quality factor. To determine the transmission properties of the device we calculate the decay rate of the resonator. The analysis using the decay rates requires far less computational effort than conventional FDTD transmission calculations and therefore the
optimum device properties can be determined quickly.
Organic two-dimensional photonic bandgap structures (2D PBG) have been fabricated by spin-coating a thin polymer film onto a nano-patterned SiO2 circular-grating surface-emitting distributed Bragg reflectors (CG-SE-DBR). When optically pumped and for certain grating parameters, these structures exhibit a peak inside the stop band that
leads to lasing with a reduced threshold. An analytical model based on the transfer-matrix method has been developed to investigate the origin of this peak. The theoretical results are in excellent agreement with the experimental findings.
The phoenix project aims to develop all-optical switches based on
the combination of inorganic and organic materials in hybrid
devices. We present first results in developing low-loss ring
resonators fabricated in silicon-on-insulator (SOI) technology,
with Q-factors as high as 125.000, and losses of α≈3.5dB/cm in the ring.
We investigate both experimentally and theoretically the waveguiding
properties of the novel design of channel waveguides in
silicon-on-insulator (SOI) photonic crystal slabs. It is known that
the channel waveguides defined by a missing of one row of holes in a
triangular-lattice photonic crystal are characterized by a very narrow transmission bandwidth limited by large group velocity dispersion. In order to increase the bandwidth we investigate an alternative design, where the conventional single-mode strip waveguide is embedded into a photonic crystal slab -- a so-called double-trench waveguide. Such a design is intended to combine the best features of photonic crystal slabs, such as suppression of radiation losses at bends and imperfections, with broad bandwidth and small group velocity dispersion. We report the successful demonstration of this broad-bandwidth photonic crystal waveguide with propagation losses as low as 35 dB/cm, which are among the lowest reported in the literature. Furthermore, we found that the modes of positive (quasi-TE) and negative (quasi-TM) parity significantly interact in our structures due to the absence of the oxide layer on top of the SOI slab and the resulting asymmetry. As a result of this interaction multiple mini-stopbands appear in the areas of anti-crossing of the positive and negative parity modes. The results are successfully modeled by the plane-wave calculations confirming the nature of the experimentally observed mini-stopbands. To the best of our knowledge this is the first demonstration of the effects of asymmetry on the transmission characteristics of the photonic crystal slabs.