Introduction Erbium-doped integrated optical amplifiers play an important role in fiber-optic telecommunication networks operating in the third window around 1.55 μm, due to their wide gain band and excellent noise behaviour. Applications can be found in e.g. amplifiers for loss compensation[l], lasers for signal generation in WDM-based systems (2] and cross-phase modulators for all-optical switching[3]. Driven by the rapid development of erbium-doped fiber amplifiers, a lot of research has been done on planar erbium-doped amplifiers, in a number of different host materials. Good results have been demonstrated in e.g. silica [4,5] and LiNb03 [6], where high amplification values of 10-15d.B have been demonstrated.

A novel type of integrated optical sensor has been evaluated theoretically. The sensing is based on the large effect of the refractive index of the measurand (generally a liquid) to the mode profile of a guided mode close to the cut-off. A special type turns over into a leaky mode-based sensor. The sensor has small size and is simple to fabricate. For the SiON technology-based structures used as a vehicle for the evaluation, a resolution of the refractive index in the range of 10−6 RIU has been achieved; however, with an operation range around a certain working index of ≈2×10−4 RIU only. This working index can be shifted to any desired value, within a certain range, by appropriately choosing the geometrical and material parameters. Because of technological tolerances, for practical operation, read-out based on wavelength scanning is required. The sensor can be used especially as an alarming sensor.

We demonstrate the versatility of a silicon nitride grated waveguide optical cavity as compact integrated optical sensors for (bulk) concentration detection, label-free protein sensing, and – with an integrated cantilever suspended above it – gas sensing.

A theoretical and experimental evaluation is given of a principle of direct, label-free opto-chemical sensing. According to this principle, which is applicable in compact planar optical sensors, measurand-induced wavelength shifts of the sharp fringes in the transmission spectra near the stop band edges of a resonant grating-based cavity are monitored. Such fringes are the results of Fabry–Perot resonances of the Bloch modes propagating in the cavity. Two sensor configurations have been considered, a first one for measuring the concentration of a single compound dissolved in water in the vicinity of the grating (bulk sensing), and a second one for determining the concentration of a specific compound adsorbed at the grating surface from a watery mixture of many compounds (surface sensing). In the latter, a thin interface layer which contains receptors specific to the targeted analyte, the PepN enzyme, is applied on top of the grated waveguide section. Filling of the receptors can be effectively seen as growth of an adlayer. Experimentally resolutions of 6×10−6 refractive index unit and ∼4pm adlayer growth have been obtained for bulk and surface sensing, respectively. With a statistical analysis the limitations to obtain lower resolutions with the current set-up are identified. The compact devices (footprint ∼200μm×15μm) are well suited for multi-sensing in lab-on-a-chip systems and can easily be fabricated with standard micro-fluidic and CMOS technologies.

Designing, implementing, refining, and assessing efficient modelling schemes for linear and nonlinear optical problem s constitutes one primary aim of our research. The Maxwell equ ations of classical electrodynamics are to be solved for a variety of structures and devices from the fields of guided w ave / integrated optics or, more general, photonics. Our approaches are typically a combination of — necessarily app roximate — analytical and numerical methods, such that they lead to accurate, moderately versatile computational sche mes that are sufficiently efficient for purposes of practical device design. Insight in the physical phenomena related to the lig ht propagation on the basis of the simulation tools is a secon d aim, as well as, based on this understanding, the conceptual design of optical devices for specific technical applicatio ns, typically in the areas of optical telecommunications or opt ical sensors. Some recent research topics are:

The paper presents a general theory for integrated optical (IO) sensing devices of the refractometric type, which relates noise and device parameters to the resolution of the measurand induced modal index changes. The theory is applied for length optimization of a number of integrated optical sensing devices. The results show the crucial importance of loss for the maximum attainable resolution of a given sensor. The presented theory is illustrated with numerical examples.

The potential of the classical “straight” integrated optical Mach-Zehnder interferometric (IO-MZI) sensor for monitoring thickness changes in bioreceptor layers is large: the achieved resolution in refractive index changes obtained in the past is as low as δn~10 [1], see Fig. 1. The MZI can be made selective after definition of sensing windows in the top cladding and by adding a target specific bioreceptor layer on one branch. The high resolution is a result of firstly the fact that the two branches of the device are made as equal as possible to minimise the effect of fluctuations in temperature, and secondly the use of electro-optical (EO) modulation. The EO-modulation enables the detection of a full response curve, including those parts of it that lead to a high sensitivity. As a result, the change in effective index (caused by a change in thickness of the bioreceptor layer) determined from the change in phase of the response curve is insensitive for fluctuations of the light source power.

We report the application of an integrated optical Young interferometer sensor for ultrasensitive, real-time, direct detection of viruses. We have validated the sensor by detecting herpes simplex virus type 1 (HSV-1), but the principle is generally applicable. Detection of HSV-1 virus particles was performed by applying the virus sample onto a sensor surface coated with a specific antibody against HSV-1. The performance of the sensor was tested by monitoring virus samples at clinically relevant concentrations. We show that the Young interferometer sensor can specifically and sensitively detect HSV-1 at very low concentrations (850 particles/mL). We have further demonstrated that the sensor can specifically detect HSV-1 suspended in serum. Extrapolation of the results indicates that the sensitivity of the sensor approaches the detection of a single virus particle binding, yielding a sensor of unprecedented sensitivity with wide applications for viral diagnostics.

In this paper, the design, fabrication, and application of a highly tolerant polarization-independent optical-waveguide structure suited for operation in the third communication window is presented. The waveguide structure has been optimized toward minimized sensitivity to technological tolerances and low fabrication complexity. The tolerance analysis has been based on the typical processing tolerances of the widely applied silicon-oxynitride technology, being plusmn3times10 -4 in refractive index, plusmn1% in thickness, and plusmn0.1 mum in channel width. The optimized waveguide design fulfills the criterion of a channel birefringence within 5times10 -5 , including processing tolerance. It also enables a fiber-to-chip coupling loss below 1 dB/facet and is suited for the realization of low-loss bends with a radius down to 600 mum. Based on this waveguide design, a passband-flattened optical wavelength filter with 50-GHz free spectral range has been realized and tested. The measured TE-TM shift of 0.03 nm confirms the polarization dependence of the optical waveguides being as low as 3times10 -5

The paper presents a general theory for sensing devices, relating noise and device parameters to resolution of modal index changes. The theory is applied to optimise the length of a few integrated optics sensing devices, being a Mac-Zehnder interferometers and two Fabry-Perot implementations. The results enable the determination of the maximum attainable resolution, and show the crucial importance of loss.

There is a strong parallelism between electronic integrated circuits (ICs) and integrated optics. In both cases micro- and increasingly nano-technology is applied resulting in devices for a broad spectrum of applications: communication, data processing, sensing and others. The most striking difference is the maturity and complexity. Electronic ICs have followed Moore’s law for about 40 years resulting in the currently more than 100 million transistors in a single chip, whereas in photonic circuitries 10 – 100 functional elements per chip represent state-of-the-art results. Photonics in this respect is clearly lagging behind and will do so also in future, as the minimum dimensions of the functional elements will be always in the order of the wavelength of light, i.e. at least some hundreds of nm. But even then, a density of 103 to 105 functional elements per optical chip is feasible, so that the term Very Large Scale Integrated (VLSI) photonics1 is not an exaggeration.

During the last decade there has been a rapidly growing interest in integrated optical (IO) sensors, especially because many of them principally allow for sensitive, real-time, label-free on-site measurements of the concentration of (bio-) chemical species. This review aims at giving an overview of the most relevant developments in this area. After a general introduction into the field of IO sensors for the chemical domain, relevant aspects of integrated optics and chemical sensing are presented in short. A large variety of IO sensing platforms are introduced and discussed: interferometers, resonators, coupling-based devices such as grating couplers and surface plasmon resonance based sensors and finally a new class of sensors based on chemically induced field profile changes. Strong and weak points of principle and of configurations based on these principles are indicated and the main performance data of the IO sensing platforms, especially the obtained resolution, are indicated. Best resolutions of the chemically induced refractive indices on the order of magnitude 10(-6)-10(-8) RIU can be obtained, corresponding to a resolution of 10(-3)-10(-5) nm in the chemically induced growth of layer thickness of chemo-optical transducer materials. Depending on the analyte and the type of transduction layer chemical concentrations down to some ppb or some pg ml(-1) can be determined. Several IO sensing systems are commercially available. Extension of individual sensors to sensor arrays is treated and finally an outlook for the future is given.

The performance of three novel integrated optical sensing structures is explored theoretically. The basic structure is a strip-loaded waveguide in which the strip consists of a several nanometers thick sensitive material. An attractive option is to realize this strip as a monomolecular antibody layer making the sensor capable to monitor chemical concentrations. All sensing structures rely on measurand induced changes of the field profile of the probing guided mode; this is in contrast to the big majority of the refractive IO-sensors in which the changes of the effective refractive index Neff are exploited. The potential of all sensing structures have been analyzed theoretically with a strong focus on obtaining good resolutions taking into account the effects of the imperfectness of the peripheral equipment. Resolutions expressed in terms of changes of the effective thickness in the range 10−3–3×10−5nm are expected to be feasible. Optical chips containing apart from the sensing structures also reference branches and fiber to chip couplings are discussed. A technological process for realizing the sensors in SiON technology is proposed.

Driving force of the research in Integrated Optics is the optical (tele-) communication, but in its slipstream a lot of research on Integrated Optical (IO-) sensors has been performed during last decade.

We demonstrate that in a sensor based on a multichannel Young interferometer, the phase information obtained for different pairs of channels can be used to correct the long-term instability (drift) due to temperature differences between measuring and reference channels, the drift in the alignment of the setup, etc. Experiments show that the nature of a major part of the drift is such that the drift present in one of the channels can be determined by interpolation of the drift measured in the two adjacent channels. It is shown that a drift reduction of 10 times can be achieved as compared with the situation in which no correction is applied. We anticipate that these findings will permit the exploitation of the extreme sensitivity of interference-based sensors to a much greater extent.

We report the fabrication and the characterization of the refractometric and thermo-optical properties of a quasi-one-dimensional waveguide photonic crystal-a strong, 76-/spl mu/m-long Bragg grating. The transmission spectra (around 660 nm) of the structure have been measured as a function of both the cladding refractive index and the temperature. The transmission stopband was found to shift by 0.8-nm wavelength for either a cladding refractive index change of 0.05 or a temperature change of 120 K. The steep stopband edges provide a sensitive detection method for this band shift, by monitoring the transmitted output power.

A novel type of chemooptical sensor has been designed, fabricated, and characterized. The sensor is simple to fabricate, places low demands on light source quality, and shows a resolution of the chemically induced refractive-index changes better than 5.10/sup -7/.

The European GROWTH project (Ref. G1RDCT-2000-00261) “Optical Characterisation Methods for MEMS Manufacturing” (OCMMM) will be finished in 2004. Starting in 2001 the proposed project aimed at strengthening MEMS testability at all stages, from the design to the end of life of a microsystem. Electrical characterisation of these devices is a well-proven technique. However, the micromechanical characterisation plays a crucial role as well, both during design and development of microstructures and during chip-production, assembling and life cycles of the finished products. Two optical approaches were pursued to improve the MEMS testability: on-chip integrated techniques as well as external fullfield interferometry. The ZfM activities were mainly focussed on the first one, the on-chip integrated optical demonstrators providing local in-situ measurements using Integrated Optics (IO). The micromechanical parameters of actuated MEMS structures are monitored by use of an optical read out, based on a Mach-Zehnder Interferometry (MZI). In loaded demonstrators, an MZI is monolithically integrated into the micromechanical part, while unloaded demonstrators use evanescent field MZI readout. The first demonstrator was a movable micromirror loaded with the sensing branch of an MZI in collaboration with LOPMD. As unloaded demonstrator a rotatable mirror with evanescent field read-out by MZI has been fabricated in collaboration with MESA+, research institute at the University of Twente, the Netherlands. 2 Loaded type demonstrator