The optical amplifier performance of Nd3+-doped polymer and amorphous Al2O3 channel waveguides with single-mode and multi-mode behavior around 880 nm is compared. Internal net gain in the wavelength range 865-930 nm is
investigated under continuous-wave excitation near 800 nm, for Nd3+ dopant concentrations typically in the range of 0.6-
1.0 × 1020 cm-3. A peak gain of 2.8 dB at 873 nm is obtained in a 1.9-cm-long polymer waveguide at a launched pump
power of 25 mW. The small-signal gain measured in a 1-cm-long sample is 2.0 dB/cm. In Al2O3, a peak gain of 1.57
dB/cm in a short and 3.0 dB in a 4.1-cm-long waveguide is obtained at 880 nm. Tapered multi-mode Nd3+-doped
amplifiers are embedded into an optical backplane and a maximum 0.21 dB net gain is demonstrated in a structure
consisting of an Al2O3:Nd3+ amplifier placed between two passive polymer waveguides on an optical backplane. The
gain can be further enhanced by increasing the pump power and improving the waveguide geometry, and the wavelength
of amplification can be adjusted by doping other rare-earth ions.
Integrated optical probes for detecting backscattered light in, e.g., Raman spectroscopy show desirable characteristics
compared to conventional optical fiber probes, although the latter ones may have better collection efficiency in many
cases. Major advantages of integrated probes include reduced size; reduced background noise due to scattering in the
probe because of reduced propagation length; potential for monolithic integration with filters and spectrometers; very
small collection volume, providing high spatial resolution; and polarization maintenance. We demonstrate that when
scattered light needs to be collected from a thin layer close to the probe surface, integrated probes can have better
collection efficiency than fiber probes do. We modeled a multimode integrated waveguide probe by adapting an
analytical model that had been developed for fiber probes. The model was extended in order to account for arbitrary
waveguide geometries and a low number of discrete waveguide modes compared to the quasi-continuum of modes in a
typical multimode fiber. Using this model we compared the collection efficiencies of integrated and fiber probes for a
thin scattering sample. We found that the integrated probe has a higher collection efficiency for scattering layer thickness
and probe-to-layer distance both smaller than ~100 μm.
Silicon oxynitride (SiON) is a highly attractive material for integrated optics, due to its excellent properties such as high
transparency, adjustable refractive index and good stability. In general, the growth of SiON layers by plasma enhanced
chemical vapor deposition (PECVD) is followed by a high temperature annealing step in order to remove hydrogen and
to achieve low propagation losses in the 1.5-μm wavelength window. The high annealing temperature (>1100°C)
required for sufficient hydrogen removal induces, however, side effects like significant inter-layer diffusion and micro-cracks
resulting in deterioration of the device performance.
In this paper compositional and optical properties of as-deposited and annealed boron (B) and phosphorous (P) doped
SiON layers were investigated. The doped layers have been fabricated by introducing PH3 and B2H6 gaseous precursors
into the PECVD process. Hydrogen contents of the samples have been studied by Fourier transform infrared (FTIR)
spectroscopy. Compared to undoped film, a 50% reduction of the hydrogen content was measured in as-deposited P-doped
SiON layers. Further reduction down to the FTIR detection limit was achieved upon annealing at temperatures as
low as 700°C.
Besides hydrogen reduction the reflow properties of B and P doped SiON are also highly relevant for the realization of
low-loss integrated optical circuits. Reactively ion etched channel waveguides have been reflown applying a temperature
of 900°C. Significant reduction of the sidewall roughness has been confirmed by scanning electron microscopy.
Fluorinated Epoxy waveguides doped with Nd complexes have been studied for optical amplification applications. The
fluorescent complex was Nd(TTA)3phen (TTA = thenoyltrifluoroacetone, phen = 1, 10-phenanthroline), which was
mixed with the host material 6-FDA (6-fluorinated-dianhydride ). The solution was spin coated in order to obtain
Nd(TTA)3phen-doped 6-FDA/epoxy slab and channel waveguides. The emission spectra of the Nd-complex doped
waveguides were measured at different pump powers by pumping at 800nm, and emission was observed at 890nm,
1060nm and 1330nm. The luminescence lifetime of the Nd complex within the waveguides was experimentally
determined. The results demonstrate that the neodymium ions within the polymer host have good transition properties.
Based on experimentally obtained parameters the optical gain of the Nd-complex doped waveguides was estimated with
the aid of rate equations. The results show that Nd complex doped polymer waveguides are promising gain media for
optical amplification.
We report the design and fabrication of small photonic crystal structures which are combined with conventional dielectric ridge waveguides. We describe in details the fabrication of both rough and smooth membranes, which are used as host for photonic crystals. Two Focused Ion Beam milling experiments are highlighted: the first one shows how photonic crystals can be fast and accurate milled into a Si membrane, whereas the second experiment demonstrates how focused ion beam milling can turn a rough surface into a well-patterned nano-smooth surface. The previously ultra rough surface showed no detectable roughness after milling due to the nanopolishing effect of the focused ion beam milling.
Different electro-optic polymer systems are analyzed with respect to their electro-optic activity, glass transition
temperature (Tg) and photodefinable properties. The polymers tested are polysulfone (PS) and SU8. The electro-optic
chromophore, tricyanovinylidenediphenylaminobenzene (TCVDPA), which was reported to have a high photochemical
stability 1 has been employed in the current work. Tert-butyl-TCVDPA, having bulky side groups, was synthesized and a doubling of the electro-optic coefficient (r33) compared to the unmodified TCVDPA was shown. A microring resonator
design was made based on the PS-TCVDPA system. SU8 (passive) and TCVDPA (active) channel waveguides were
fabricated by the photodefinition technique and the passive waveguide losses were measured to be 5 dB/cm at 1550 nm.
This paper presents novel ways of implementing waveguide components in photonic crystal slabs based on silicon-on-
insulator (SOT). The integration platform we consider consists of hexagonal holes arranged in a triangular lattice
('hexagon-type' photonic crystal). The waveguides are made of one missing row of holes (Wl) with triangular air
inclusions symmetrically added on each side of the waveguide.
Size and position of these inclusions are tuning parameters for the band diagram and can be used for minimizing the
distributed Bragg reflection (DBR) effect. The waveguides show single-mode behavior with reasanably high group
velocity and large transmission window, inside the gap between H-like modes**. These waveguides, closely resembling
conventional ridge waveguides, can be combined to form efficient bends and Y-junctions. The bends and Y-junctions
include intermediate short waveguide sections at haif the bend angle playing the role of corner 'mirrors'. Qualitative
design rules were obtained from 2D calculations based on effective index approximation.
On the foundation of joint experience acquired by several research centres there was defined the roadmap to the desired single technological platform for fabrication of a specific class of photonic integrated circuits, which are controlled by mechanical means. In the paper the challenges of fabrication of such photonic circuits are discussed. The main arguments in favour of the Silicon-on-Insulator materials system as the basis for the platform are presented. Options for the mechanics-to-optics arrangement, materials and processes are described and illustrated with the current achievements from the authors' labs. In the roadmap the preference is given to the vertical arrangement in which, the mechanical part is stacked above the waveguiding layer. A flexible trimming routine is designed to complement the process flow if the technologies developed cannot provide the required reproducibility.
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 that allow for a large number of functional elements within a given chip area: VLSI photonics. It is shown that optical microresonators can be considered 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+.
Polymeric optical waveguide components offer attractive properties for applications in optical telecom and datacom systems. These are high speed for electro-optic modulators, low power dissipation for thermo-optic (digital) switches and low-cost for all active and passive components. We report on active and passive components realized by utilizing polymer-specific attractive techniques such as planarizing spincoating, low-temperature reflowing and direct photodefinition. Examples are multimode photodefined passive polymeric waveguides for optical interconnect applications; photodefined monomode polymeric waveguides loaded with rare-earth doped nanoparticles for planar waveguide amplifiers and with non-linear chromophores for electro-optic modulators. We will show that polymer waveguide technology allows vertical stacking of electro-optic microringresonators with their port waveguides to realize high-speed modulators. By reflowing the reactive-ion-etched microring we could reduce the scattering by wall roughness considerably. Thermo-optic polymeric microringresonators combine the high thermo-optic coefficient and low thermal conductivity of polymers with the small size of the microring. It will be shown that this yields a broad wavelength tuning range at low power dissipation.
We present a novel design approach for line-defect waveguides integrated in a photonic crystal slab (PCS) with hexagonal holes in a triangular lattice (aka 'hexagon-type'). Triangular air inclusions are symmetrically added on each side of the waveguide. Size and position of these inclusions are tuning parameters for the band diagram and can be used for minimizing the distributed Bragg reflection (DBR) effect. The waveguides show single-mode behavior with reasonably high group velocity and large transmission window, inside the gap between even-like modes. Qualitative design rules were obtained from 2D calculations based on effective index approximation and full 3D calculations of the band structure were applied for fine-tuning of structural parameters of these high-index contrast systems. Transmission spectra and losses of finite-sized structures were estimated by means of 3D finite-difference time domain (FDTD) calculations. We present a pattern definition technique, which is an integration of optical lithography with focused ion beam (FIB) high-resolution etching. The mask pattern is transferred into the SOI stack by a subsequent reactive ion etching (RIE) process. The combination of moderate resolution optical lithography and FIB etching provides an excellent tool for fast prototyping of PCS-based devices.
A polarization independent optical waveguide structure suited for operation in the third communication window has been developed and optimized towards minimized dependence on deviations in the processing parameters and very low processing complexity. The tolerance analysis and optimization have been based on the thin film parameters of the widely applied silicon oxynitride technology. The silicon oxynitride layers have typically a material birefringence (nTMnTE) between 1-2 x 10-3 and can be deposited within a uniformity and reproducibility of 1% in thickness (d), 5x10-4 in refractive index (n) and 100 nm in channel width (w). The optimized waveguide structure meets the criterion of a channel birefringence (Δneff,TM-TE) within 5x10-5 taking the processing tolerance into account. Moreover, it was found
that the channel birefringence is thickness independent (within the 10-5 criterion) over a range of up to 200 nm
(δΔneff,TM-TE ,/ δd = 0). Furthermore, the optimized waveguide is fulfilling the remaining demands of the application
aimed at, such as monomodality, low fiber to chip coupling loss (< 0.5 dB/facet) and low loss bends with a radius down to 600 nm. This waveguiding structure has been applied for the realization of a passband flattened add-drop multiplexing device (or interleaver) with 0.4 nm free spectral range and 0.03 nm TE-TM shift. Based on this shift, a polarization dependence of 3 x 10-5 was calculated for the optical waveguides.
Integrated optics micoresonators (μ-resonators) are microstructures with dimensions typically in the order of tens of
microns down to a few microns, whose response depends critically on optical wavelength and material properties. Recent experimental studies have shown that they are suitable as refractive index sensors, absorption sensors, and microresonator-assisted single and two-photon fluorescence. The absorption and fluorescence spectra are material-specific properties, that the devices can readily detect by using different excitation wavelengths. Therefore, the devices
are suitable for non-specific agent detection. Due to their inherent small size and the ease of cascading several microresonators, they are suitable building blocks for a sensing array allowing sensing/detection of multiple quantities/agents on a single chip, by e.g., using different chemo-optical transduction layers on top of the
microresonators. Such devices have a chip-area of only a few 100 μm2, making them suitable for sensing ultra-small analyte volumes (which is advantageous for bio-chemical sensing). In this contribution, sensing arrays based on integrated optics microresonators and their prospects for Homeland Security applications are discussed. Several device-concepts based on integrated optics microresonators will be treated. Their performance is analyzed using realistic parameters and experimental results of microresonator devices realized in silicon oxynitride (SiON) technology. The potential integration of theses devices with microelectronics, micro-mechanics and micro total analysis systems is
discussed.
Recently an ever-increasing activity in the area of coupling between optical waveguide and ring or micro resonator has been developed. Devices based on this coupling held the promise of a new modality of light switching, amplifications and modulation. In this paper, the feasibility of an all optical switch based on the integration of the potentiality of microcavity resonator and organic materials having large nonlinearities, i.e. liquid crystals (LC's), is discussed. The device is based on silicon technology with hybrid integration of liquid crystals as a nonlinear material.
In this paper, we demonstrate a thermo-optically tunable periodic wavelength filter (interleaver) with a 50 GHz free spectral range (FSR). It has an almost rectangular wavelength response and consists of an asymmetric Mach-Zehnder Interferometer (MZI) consisting of two tunable 3dB couplers interconnected by two waveguide channels of unequal length, with a ring resonator coupled to one of the branches of the MZI. The filter is fabricated in silicon oxynitride (SiON) waveguide technology. The bar and cross transmission spectra and chromatic dispersion of the filter have been measured and passband flattening and stopband broadening was observed in good agreement with the simulation. The isolation was 15 dB and 12 dB for TM and TE polarized light respectively, which was lower than the designed 29 dB. The main cause of lower isolation is an inaccuracy of the realization of the power coupling coefficient to the ring (59% instead of the designed 82%). The measured dispersion of the filter varies from 0 ps/nm at the center to 1660 ps/nm at the edge of the passband.
The potential of integrated optical micro cavities (MC) for use in enhanced optical spectroscopy has been studied. The MC devices can sustain high morphological enhancement of optical field due to excitation of high-Q whispering gallery modes. The evanescent near field of the MC can be used to excite spectroscopic signal of molecules pout on top of the MC. Estimation shows that both local excitation field and emitted field can be increased y 2-3 orders of magnitude in the MC on resonance. In total, a gain of 4-8 orders of magnitude in the Raman/fluorescent signal of a molecule near the MC can be expected. In addition, the MC delivers a tunable and measurable enhancement, which is a real benefit in terms of enhanced optical microspectroscopy on-chip. High-Finesse integrated optics cylindrical micro cavities capable of significant field enhancement have been fabricated. Use of various waveguide/MC coupling schemes and design parameters allowed optimization of the devices for the largest intra-cavity power. The result for different micro cavities show prominent enhancement of intra-cavity field correlating with its mode spectrum. The characterization of MC and measurements performed demonstrate feasibility of the MC-based device for optical spectroscopy.
This paper describes the implementation and investigation of an all-optical amplified ring network with Phased Array based optical add/drop multiplexers (OADMs). From crosstalk analysis follows that an OADM with a foldback-structure and 1 X 2-switches has an outstanding crosstalk performance. From the investigation of the dynamic behavior of Erbium doped fiber amplifiers (EDFAs) in a ring configuration we found that EDFAs in a ring-configuration require a faster gain-control when compared to a cascade-configuration.
Integrated optical waveguides, as well as splitters and switches utilizing the principle of multimode interference have been realized in PECVD SiON/SiO2 technology. The waveguide design has been optimized to meet a number of requirements, such as small device size, polarization- independent operation, and low-power active operation. The design, fabrication, and initial experimental results for these devices are discussed.
The curriculum in Electrical Engineering at the University of Twente has been recently adjusted in order to increase the proficiency in optics of the graduates, providing a general background and preparing especially for integrated optics and optical communication techniques. This involves mainly three undergraduate courses during the second through fourth year of the five-year curriculum. Two of these courses involve intensive use of computer aids. In the first one, Electrodynamics, Maple worksheets are extensively used for diminishing the tedium of the mathematics and for visualizing (using animation) of traveling and standing wave patterns. In the last course, computer programs (a slab mode solver and an implementation of the beam propagation method) are used as design tools. We describe the aims, contents, and the relationship between the courses and some organizational issues. It is concluded that the courses meet our requirements: undergraduate students become productive quite fast in the field of integrated optics when they work in an internship or in their MSc-project. The background thus provided to our graduates seems to be well received in the relevant industry.
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