Integration Of Optical Waveguides Research Articles

High index contrast polymer waveguide platform for integrated biophotonics

We present detailed characterization of a unique high-index-contrast integrated optical polymer waveguide platform where the index of the cladding material is closely matched to that of water. Single-mode waveguides designed to operate across a large part of the visible spectrum have been fabricated and waveguide properties, including mode size, bend loss and evanescent coupling have been modeled using effective-index approximation, finite-element and finite-difference time domain methods. Integrated components such as directional couplers for wavelength splitting and ring resonators for refractive-index or temperature sensing have been modeled, fabricated and characterized. The waveguide platform described here is applicable to a wide range of biophotonic applications relying on evanescent-wave sensing or excitation, offering a high level of integration and functionality. The technology is biocompatible and suitable for wafer-level mass production.

In-Plane Integration of Polymer Microfluidic Channels With Optical Waveguides– A Preliminary Investigation

The next major challenges for lab-on-a-chip (LoC) technology are 1) the integration of microfluidics with optical detection technologies and 2) the large-scale production of devices at a low cost. In this paper the fabrication and characterisation of a simple optical LoC platform comprising integrated multimode waveguides and microfluidic channels based on a photo-patternable acrylate based polymer is reported. The polymer can be patterned into both waveguides and microfluidic channels using photolithography. Devices are therefore both quick and cost-effective to fabricate, resulting in chips that are potentially disposable. The devices are designed to be highly sensitive, using an in-plane direct excitation configuration in which waveguides intersect the microfluidic channel orthogonally. The waveguides are used both to guide the excitation light and to collect the fluorescence signal from the analyte. The potential of the device to be used for fluorescence measurements is demonstrated using an aqueous solution of sodium fluorescein. A detection limit of 7 nM is achieved. The possibilities offered by such a device design, in providing a cost-effective and disposable measurement system based on the integration of optical waveguides with LoC technology is discussed.

Structure of modes of a smoothly irregular integrated-optical four-layer three-dimensional waveguide

The asymptotic method and the method of coupled waves used to study an integrated-optical multilayer three-dimensional waveguide satisfying the conditions of a continuously variable effective refractive index are considered. Three-dimensional fields of smoothly deforming modes of a four-layer integrated-optical waveguide are described analytically. Explicit dependences of the contributions of the first order of smallness to the electric and magnetic field amplitudes of quasi-waveguide modes are obtained. The canonical type of quasi-wave equations describing the structure of quasi-TE and quasi-TM modes in a smoothly irregular four-layer integrated-optical three-dimensional waveguide is presented for the asymptotic method. By using the perturbation theory, shifts of complex propagation constants are obtained in an explicit form for these modes. The elaborated theory can be used to analyse structures from dielectric, magnetic and metamaterials in a rather broad wavelength range of electromagnetic waves.

Inverse Algorithm With Built-In Spatial Filter to Obtain the 2-D Refractive Index Profile of Optical Waveguides From the Propagating Mode Near-Field Profile

We propose a modified inverse regularization algorithm for computing the 2-D refractive index profiles of integrated-optic waveguides from measured near-field data. The algorithm involves embedding of a spatial mean filter to remove impulses and high frequency noises from the near-field intensity as well as from its second derivative. The proposed filtering scheme is built-in to the inverse algorithm and does not require extra computation for filtering. The effectiveness of the proposed method is demonstrated by reconstructing the refractive index profile of a single mode lithium niobate channel waveguide from the propagating mode near-field intensity pattern.

Study of a computer-controlled integrated optical gas-concentration sensor

A computer-controlled integrated optical waveguide sensor based on an optical waveguide of the diffusion type with the low attenuation coefficient is developed and studied. It is shown that the response time of the sensor is ≈0.15 s. According to tests and computer simulations, the sensor can detect gaseous ammonia in air with the limiting theoretical concentration of ≈0.1 ppm for the signal-to-noise ratio no less than 20.

Integration of optical waveguides with micro-incandescent light

In this work, we propose the integration of optical waveguides with a simple light source device. Light is emitted from an incandescent chromium micro-resistor embedded in a self-supported region of silicon oxynitride (SiOxNy) film. The waveguide structure is fabricated on a (100) silicon substrate using silicon oxynitride as the core and cladding layers. Bulk micromachining of the silicon substrate in KOH solution is used to free from the substrate the embedded micro-resistor, reducing the thermal dissipation of that region, allowing the resistor to heat up to incandescent temperatures. A comparison between a theoretical calculation and the experimental data indicate that the microlamp reaches 1160K before failure. After a microannealing process realized on the microlamp structure, it is possible to couple light into the waveguide and control the output power by adjusting the current that flows through the microlamp.

Standardized bio-opto-fluidic chip technology using channel only process

The integration of optical waveguides within biological assay chips seems to be an interesting solution to increase their functionality as it will allow local optical probing of the samples. However, the techniques proposed to build such chips are generally complex requiring multiple steps to fabricate waveguides and channels, and at the same time losing the capacity to use cost-effective fabrication technique like injection moulding. We propose a techniques where the waveguides are actually built as empty channel in the optical chip and later filled with special liquid to be used as waveguide. In this way, the chip only necessitates the fabrication of channels, some carrying the biological samples and others used as waveguides. To simplify further the fabrication, we developed a standard holder that allows to address the issue of filling the waveguide channel with the special liquid and at the same time provide connection for the sample testing. The chip was fabricated in PDMS and it was tested together with the standard holder using different liquids. Although the optical loss is still high due to scattering, this type of system was able to easily detect the bubbles appearing in a bi-phasic flow, opening the way for further improvements in the technology.

Temperature-controlled UV-laser induced fabrication of planar polymeric waveguides

Integrated-optical waveguides may be written directly into the surface of a planar polymeric substrate by UV-excimer laser irradiation. The loss rate is relatively high due to the refractive index depth profile of waveguides produced in this way. The loss rate can be reduced significantly by use of a temperature-controlled fabrication process: during the UV-laser irradiation the polymeric substrate is heated in a controllable way by a hot plate. An explanation is given for this temperature-dependent effect.

Integration of optical waveguides and microfluidic channels both fabricated by femtosecond laser irradiation

A femtosecond laser is used to fabricate both microfluidic channels and high quality optical waveguides, intersecting each other on a single glass substrate. Fluorescence in fluids filling the microfluidic channels has been selectively excited in several points by coupling light in the optical waveguides. Waveguide-microchannel integration opens several prospects for in situ sensing in lab-on-a-chip devices.

High-accuracy IR polarimetry of waveguide optical elements

This paper discusses the main physical factors that affect the accuracy with which the polarization characteristics of waveguide optical elements are measured: distortions of the polarization when radiation is being introduced (focused) into optical waveguides, elastic strains of fiber lightguides when they are being attached, and depolarization of the radiation at inhomogeneities and defects of waveguides. An experimental apparatus for polarimetric studies of fiber and integrated-optics devices is described, in which the relative power of the polarization noise can be estimated to within 10−5 at a wavelength of 1.32 µm. The distribution of the degree of polarization of IR radiation in the cross section of a light beam is measured at the output of a single-mode lightguide, and the results are presented of measurements of the depolarization of IR radiation in locally deformed single- and multimode lightguides, a fiber coil polarizer, and straight and bent integrated-optics channel waveguides.

Selective detection of gas-phase TNT by integrated optical waveguide spectrometry using molecularly imprinted sol–gel sensing films

A chemical sensor was developed to detect the explosive 2,4,6-trinitrotoluene (TNT) utilizing planar integrated optical waveguide (IOW) attenuated total reflection spectrometry. Submicron thick films of organically modified sol–gel polymers were deposited on the waveguide surface as the sensing layer. Sol–gels were molecularly imprinted for TNT using covalently bound template molecules linked to the matrix through 1 or 2 carbamate linkages. Upon chemical cleavage of the template and displacement of the TNT-like pendant groups from the matrix, shape-selective binding sites were created that possess a primary amine group. The amine was used to deprotonate bound TNT yielding an anionic form that absorbs visible light. Binding of TNT and subsequent conversion to the anion results in the attenuation of light propagating through the waveguide, thus creating a spectrophotometric device. Sensitivity can be achieved by taking advantage of the substantial pathlength provided by the use of single mode IOWs. The limit-of-detection to gas-phase TNT was found to be five parts-per-billion (ppbV) in ambient air at a flow rate of 40 mL min −1 given a 60 s sampling time. The sensor is highly selective for TNT due to the selectivity of binding site recognition of TNT and the subsequent generation of the TNT anion. Response to TNT is not reversible which results in an integrating sensor device which, in theory, can improve the ability to detect small amounts of the explosive if the exposure time is sufficient in length.

Development of Specific Technologies and Assembly Systems for the New Challenge of Electro-Optical Devices

Today's information and communication systems are especially characterized by their capability and reliability of high data rate transmission. An integration of optical wave guides into printed circuit boards allows a hybrid electronics packaging in order to increase the data transmission rate. The success of this technology depends in particular on the availability of efficient production solutions. For this reason, the development of automated assembly systems for electro-optical components has become a main research field at the Institute for Manufacturing Automation and Production Systems. This paper describes the challenges of the placement systems and presents a continuous process chain for the automated assembly of electro-optical components.

Microfluidic sorting system based on optical waveguide integration and diode laser bar trapping

Effective methods for manipulating, isolating and sorting cells and particles are essential for the development of microfluidic-based life science research and diagnostic platforms. We demonstrate an integrated optical platform for cell and particle sorting in microfluidic structures. Fluorescent-dyed particles are excited using an integrated optical waveguide network within micro-channels. A diode-bar optical trapping scheme guides the particles across the waveguide/micro-channel structures and selectively sorts particles based upon their fluorescent signature. This integrated detection and separation approach streamlines microfluidic cell sorting and minimizes the optical and feedback complexity commonly associated with extant platforms.

Considerations on material composition for low-loss hollow-core integrated optical waveguides

The role of cladding bilayer material compositions to obtain low-loss hollow-core integrated optical waveguides was studied. Using the simple Fresnel reflection formulae, the optimal material composition was determined. It is shown that using bilayers with higher index-contrast does not always lead to a lower loss for (quasi-)linearly polarized modes. Based on that knowledge, structures that exhibit very low leakage loss for quasi-TE00 mode are proposed and designed using Si-compatible materials.

Propagation Losses in Curved Integrated Optical Waveguides Based on Oxidized Porous Silicon

The propagation losses are evaluated for the first time in curved integrated (buried) optical waveguides (WGs) based on oxidized porous silicon. In the visible red range, the losses decrease from 20 to 5 dB per 90° bending (for about 0.4 dB/cm loss in the straight WG) when the WG curvature radius increases from 125 to 2500 μm. The main component of the total bending losses in WGs is related to the coupling loss on the passage from straight to curved WG parts. Additional losses are introduced by the regions of incompletely oxidized porous silicon on the walls of curved WGs.

A Five-Order Mode Converter for Multimode Waveguide

A numerical model of five-order mode converter that converts the order of modes in an integrated-optic multimode waveguide is proposed. Such a structure is useful in optical guiding wave devices for mode control and mode shuffling. The dimensions and index profile of the device are well within the capabilities of the state of the art of integrated optics technology. We have successfully optimized the structural design of the device for propagation loss of less than 13.1 dB at an operating wavelength of 1.55 /spl mu/m. A cascaded form of the five-order mode converter is also proposed for selective mode conversion without the need of restructuring the connection within the device.

Determination of the refractive index depth profile of an UV-laser generated waveguide in a planar polymer chip

In this paper the optical-functional properties of integrated-optical waveguides in a planar polymer chip prepared by UV-laser irradiation have been investigated. Particularly the refractive index distribution of the waveguide is examined by a two-beam interferometric method. Also the waveguiding effect of this integrated-optical structure has been proved. The study shows that the refractive index depth profile strongly depends on the UV-irradiation dose. Several mostly independently occurring photochemical processes competing with one another can explain the formation and shape of the refractive index distribution.

PC software for analysis of versatile integrated optical waveguides by polarised semi-vectorial finite difference method

In this paper, a generic software package that provides an interactive and graphical environment for analysis by polarised semi-vectorial finite difference (SVFD) method of all kinds of integrated optical waveguides, such as buried channel, raised strip, rib, embedded, or ridge waveguides, is described. A coherent design rationale is formulated that takes into account the terms due to the interface between each layer as the basis of modal birefringence in integrated optics. Then, according to the opto-geometric parameters of a given waveguide, the modal propagation constants and the spatial fields patterns are calculated. Three examples regarding typical rib waveguides are dealt with, allowing to discuss the results (effective index values) compared with that of the Galerkin method. As fitted for personal computers, this software should be most useful for designing integrated optics components.

UV-laser assisted Fabrication of integrated-optical Waveguides

By UV-laser-irradiation a controllable change of the refractive index of some polymers can be attained in the irradiated zone. The detailed UV-photon-induced process mechanisms have been investigated on the basis of PMMA employed as an UV-modifiable model polymer. By mask lithographic methods the UV-laser-assisted technology for the modification of the polymer optical properties enables the local increase of the refractive index and thus the fabrication of integrated-optical waveguiding elements in the surface of a planar polymer chip. These elements are relevant for the manufacturing of complex integrated-optical components. The optical and functional properties of the integrated-optical waveguides have been characterized.

Fluorescence-based array biosensors for detection of biohazards.

Total internal reflection fluorescence (TIRF) is a process whereby fluorophores that are either attached to or are in close proximity with the surface of a waveguide are selectively excited via an evanescent wave. Planar waveguides provide the possibility of immobilizing multiple capture biomolecules onto a single surface and therefore, offer the exciting prospect of multi-analyte detection. The production of arrays and the results of various groups which use TIRF to interrogate such surfaces is reviewed, along with a look at how far the field has advanced toward the production of an automated, portable, multi-analyte array biosensor for real-time biohazard detection. In particular, a miniaturized, fully automated, stand-alone array biosensor developed at the Naval Research Laboratory is reported that monitors interactions between binding partners either as the final image or in real-time. A variety of analytes including toxins, bacteria and viruses have been detected both in buffer and complex matrices, such as blood and soil suspensions, with comparable detection limits. A number of developments have led to a TIRF array biosensor weighing only 5.5 kg which is automated for environmental, clinical and food monitoring or for detection of bioterrorist agents.