Microfabricated polymer analysis chip for optical detection

A coupling between multimode polymer waveguides and microfluidic channels on a polymethylmethacrylate (PMMA) capillary electrophoresis (CE)-chip for optical analytical applications has been successfully realised. This technology allows the integration of polymer optical waveguides together with hermetically sealed fluidic channels. The microchannels and waveguides are made in PMMA by the approved hot-embossing technology. The technology developed for the fabrication of polymer waveguides on the microfluidic chip offers the possibility of great flexibility in the choice of core materials, design and alignment of the polymer waveguides. The integration of polymer waveguides on an analysis chip enables highly spatially resolved optical detection without the large and expensive conventionally used apparatus. The optical properties of the analytical system developed are verified by transmission and propagation loss measurements. The results of measurements prove the suitability of the presented device for optical applications between 440 and 800 nm. This was shown with absorbance measurements of the dye Sulfanilazochromotrop (SPADNS) within 50 microm fluidic channels.     

Modeling photobleached optical polymer waveguides

One of the most efficient ways to prepare nonlinear optical polymer channel waveguides is by photobleaching. To control the index profile precisely and to design and improve the performance of active electro-optical devices, modeling of the photobleaching process is important. We report our phenomenological bleaching model, which uses a stretched exponential time dependency technique that predicts the index profile for polymer channel waveguides and present design rules for active optical switches and modulators. One way to verify the bleaching model is to calculate the effective index and compare this with our measured effective index obtained with prism-coupling techniques. The bleaching model shows good agreement with experiments.     

Fan-out routing and optical splitting techniques for compact optical interconnects using single-mode polymer waveguides

Polymer waveguide (WG) S-bends are necessary for fan-out routing techniques and optical splitting in high-density optical interconnects. Designing and manufacturing of optimal S-bends are critical for minimizing optical link loss while maintaining overall size and layout constraints. Complete structural loss analysis is demonstrated theoretically and shown experimentally utilizing both radial and transitional loss in single-mode (SM) polymer WG radial arc, cosine, and raised-sine S-bend profiles. SM polymer WG straights were first fabricated to measure standard propagation loss. SM WG S-bends were fabricated incorporating straight lead-in and lead-out sections to incorporate transitional loss present in workable designs. S-bend designs were measured at different dimensions and matched to theoretical losses. Compact cosine and radial arc S-bends exhibited the lowest structure loss for low and high NA WGs, respectively. High-speed performance of SM WG straights and S-bends was measured at 10 Gbit/s demonstrating low error rate. Optical splitters designed with S-bends and tapers were also evaluated and fabricated. Trade-off between optimal loss and minimal device size is discussed.     

Enhanced sensitivity of chemical dosimeters using liquid-core optical waveguides

The spectrophotometric sensitivity of chromophoric chemical dosimeters can be enhanced by increasing the optical path length through the light absorbing medium. This approach is used with optical waveguide (OWG) dosimeters, consisting of liquid-phase light-propagating media filling the core of a long, thin flexible polymer tubing. The liquid phase consists of dimethyl sulfoxide, N, N,-dimethylformamide, or triethyl phosphate solutions of hexa (hydroxyethyl) pararosaniline cyanide, a wellknown radiochromic dye precursor, which on irradiation converts from the leucoform into a brightly colored dye chromophore. The experimental design is described, as well as the influences of some experimental parameters: length of the OWG, curvature of the waveguide loops, cross section of the liquid light-guiding core, the temperature and the solvent. It was shown that concentrations of the radiation-generated dye as low as 5 × 10⁻⁸ mol dm⁻³ (corresponding to absorbed doses of about 10 mGy) can be measured on a standard spectrophotometer using a 100 cm long waveguide. It was also shown that sensitivity (optical absorbance increase per unit length per unit dose) was the same whether the light passed on a straight path or through a multiply looped waveguide as long as 150 cm. It is suggested that such long OWG assemblies can be used for enhancing the response of chemical dosimeters for medical and radiation protection applications, as well as in analytical chemistry and for chemical kinetics studies.     

Reflection photoelastic tomography for the detection of stress distribution in planar optical waveguides

A novel method for measuring local stress distributions and birefringence of films on substrates and planar optical waveguides, with submicrometric resolution, is presented. The technique relies on a reflective tomographic configuration, applied in conjunction with a polarimetric setup, which processes the stress-induced change of the state of polarization of a laser probe beam reflected at the waveguide-substrate (film-substrate) interface. By this means, theoretically foreseen stress behavior can be experimentally verified and spurious or induced local stress variations in integrated optics components can also be brought into evidence. The feasibility of the proposed method has been verified by reconstructing the two-dimensional axial stress distribution in the 4 x 2 microm(2) core region of a doped silica-on-silicon optical waveguide.     

Low loss, low refractive index fluorinated self-crosslinking polymer waveguides for optical applications

Synthesis and optical applications of low loss methacrylate-based fluorinated polymers are described. The synthesis of well defined self-crosslinking fluorinated polymers has been carried out in order to tune refractive index in the range of 1.390 < n < 1.450. After thermal crosslinking, one single lithographic step followed by reactive ion etching is necessary to monomode optical waveguide fabrication on silicon substrates. Optical losses lower than 1 dB/cm at 1300 nm and 2 dB/cm at 1550 nm were measured for highly confined modes. Efficient chip coupling to lensed optical fibers was obtained. Using waveguides with an effective index close to that of bulk silica, a significant coupling interaction between the guided modes and the whispering gallery modes of a silica microsphere was evidenced thus opening the way for new device applications.     

Characteristic analysis of absorptive multiple-quantum-well optical waveguides

Abstract

By extending the transfer matrix technique from the real domain to the complex, the complex eigenvalue equation is presented for both transverse electric and transverse magnetic modes of absorptive multiple-quantumwell optical waveguides, and a computer program is developed to solve the eigenvalue equation in the complex plane. On the basis of the computed results, the effects of the structural parameters and the refractive index profile on the mode propagation and loss properties are analysed and discussed for In^x Ga^1?xAs/Al^yGa^1?yAs absorptive multiple-quantum-well optical waveguides. The results indicate that, if approximate guided structural parameters and an appropriate refractive index profile are selected, higher-order modes can be controlled and single-mode propagation can be realized in the multiple-quantum-well optical waveguide with lower mode loss.     

Dispensed polymer waveguides and laser-fabricated couplers for optical interconnects on printed circuit boards

Optical interconnects can provide chip-to-chip data communication with much needed bandwidth as processor speed and density keep growing. Optical waveguides and couplers are essential components for implementing optical interconnections. Techniques for directly dispensing polymer waveguides in laser-ablated trenches on printed circuit boards and for fabricating optical couplers are presented for quick prototype of optical interconnects. High-quality UV curable polymer waveguides were routinely fabricated. High-efficiency couplers, blazed grating couplers on sloped waveguides, sloped facet metal film couplers, and reflective-undercut facet couplers can be fabricated by using excimer laser ablation.     

Slant-propagation characteristics in tapered optical waveguides: analysis

Although several analysis methods for tapered waveguides have been proposed, they dealt with the problem of a light wave traveling parallel to the tapered direction of the waveguide. Light waves that propagate at a slant in the tapered direction are discussed as mode-coupling problems, including radiation modes that are made discrete by the hypothetical boundary method. We propose a method of determining the three-dimensional wave vectors of the discrete radiation modes in the slant propagation; the slant-propagation characteristics, such as the transmission efficiency of the tapered waveguide, are analyzed.     

聚合物SiON波导的可变光衰减器性能研究

利用弯曲聚合物SiON波导设计了一种新型可变光衰减器,该器件由输入、输出直波导,S型的弯曲波导,以及在聚合物SiON波导弯曲部位镀上的电极组成.通过外加电场的作用来调节波导覆盖层的折射率,从而达到衰减波导中光能量的目的.现采用光束传播法(BPM)对设计的新型光衰减器进行了仿真设计,结果表明,设计的光衰减器具有大的动态可调衰减范围(45.3 dB),低的插入损耗(0.8 dB).     

Multichannel mode-filtered light detection based on an optical fiber for small-volume chemical analysis

A novel mode-filtered light detection method is described in which an unjacketed optical fiber is inserted into a transparent capillary tube and three or more detection channels are set on the capillary side for different distances from the port of the fiber. This new method is the basis of synchronization of separation and analysis, with which a modern multidimensional analysis apparatus will be constructed. For samples of different concentration, the more close to the laser incidence port of the fiber the detector has been set up, the greater the change of the intensity profile of mode-filtered light (deltaI(F)) that is obtained. Vice versa, if a parameter alpha = I0/In is established and, instead of a mode-filtered light signal, the reversed alteration trend of deltaalpha is found in comparison with the alteration trend of deltaI(F), the reason is that the background rapidly lowers with the increasing distance to the laser incidence port of the fiber; moreover, the mode-filtered light signal decreases slowly with it. With the present method and apparatus, glucose and glycerol have been determined, with good reproducibility and stability and a small sample volume. Furthermore, a real sample of glucose injection is measured for a detection volume of 5 microL, and an acceptable result is observed.     

Transmission properties in waveguides: an optical streamline analysis

We present a novel approach to study transmission through waveguides in terms of optical streamlines. This theoretical framework combines the computational performance of beam propagation methods with the possibility to monitor the passage of light through the guiding medium by means of these sampler paths. In this way, not only can the optical flow along the waveguide be followed in detail, but also a fair estimate of the transmitted light (intensity) can be accounted for by counting streamline arrivals with starting points statistically distributed according to the input pulse. Furthermore, this approach allows elucidation of the mechanism leading to energy losses, namely, a vortical dynamics, which can be advantageously exploited in optimal waveguide design.     

Integral equation analysis of coupling in symmetric grating-assisted optical waveguides

The propagation and coupling phenomena in grating-assisted optical couplers are analyzed by using an integral equation formulation and applying an entire-domain Galerkin technique. The proposed method constitutes a special type of the method of moments and provides high numerical stability and controllable accuracy. The electric field in the grating region is the unknown quantity and the resulting integral equation is subsequently solved by using Galerkin's method. The propagation constants of the guided waves are computed accurately by determining the singular points of the corresponding system's matrix. Numerical results regarding the propagation constants are presented for various coupler parameters, and the effect of the grating's physical and geometric characteristics on the coupling process is investigated.     

Integrated optical attenuated total reflection spectrometry of aqueous superstrates using prism-coupled polymer waveguides

Attenuated total reflection (ATR) spectrometry of aqueous solutions in contact with polystyrene integrated optical waveguides has been investigated. The mode-dependent absorption of evanescent energy by fluorescein solutions adjacent to the waveguide surface was measured and compared to theoretical predictions based on a ray optics approach. Although enhanced sensitivity was observed with increasing mode number, the sensitivity for the highest order mode was less than that predicted by theory.     

Fabrication of polymer waveguides between two optical fibers using spatially controlled light-induced polymerization

A new method for the fabrication of polymer waveguides between two optical fibers using a spatially controlled photopolymerization is reported. By taking advantage of the self-guiding effect of light through a photopolymerizable medium, polymer waveguides perfectly aligned with the fiber cores and strongly anchored to their surfaces are fabricated. The process is characterized by following in situ the coupling efficiency of a nonactinic laser source. Examples of waveguides exhibiting good coupling efficiency and high flexibility are given. By selecting the suitable monomers and adjusting the photonic parameters, the optical and mechanical waveguide properties (diameter, length, refractive index, rigidity, and flexibility) can be controlled in view of optical sensor applications.     

Accurate first-order leaky-wave analysis of antiresonant reflecting optical waveguides

We present a closed-form approximation for estimating both the field distribution and complex propagating constant of the antiresonant reflecting optical waveguide (ARROW) based on a first-order leaky-mode analysis. The formula was obtained from a novel coupled-electric-coupled-magnetic matrix method and provides six significant figures of the real part of the propagation constant beta of a SiO2/TiO2/SiO2/Si ARROW with an 8-microm core. The accuracy for the quantity of the imaginary part of beta is greater than 98.4% for the TE0 mode and 99.3% for TM0. The approximate values for field components are 96.1% accurate. In addition, a slight absorption by the substrate will result in modification of the initial improper leaky-mode behavior, which grows exponentially in the substrate, yielding a proper solution.