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We demonstrate a broadband and continuously tunable 14 optical beamforming network (OBFN), based on the hybrid integration of indium phosphide (InP) components in the silicon nitride (Si3N4) platform. The photonic integrated circuit (PIC) comprises a hybrid InP-Si3N4 external cavity laser, a pair of InP phase modulators, a Si3N4 optical single-sideband full carrier (SSBFC) filter followed by four tunable optical true time delay lines (OTTDLs), and four InP photodetectors. Each OTTDL consists of eight cascaded thermo-optical micro-ring resonators (MRRs) that impose tunable true time delay on the propagating optical signals. The OBFN-PIC is designed to facilitate the steering of a microwave signal with carrier frequency up to 40 GHz over a continuous set of beam angles. We evaluate the performance of the OBFN-PIC to handle and process microwave signals, measuring the link gain, the noise figure (NF), and the spurious-free dynamic range (SFDR) parameters. Moreover, we assess its beamforming capabilities assuming that the OBFN-PIC is part of a wireless system operating in the downlink direction and feeds a multi-element antenna array. Using microwave signals at 5 and 10 GHz with quadrature amplitude modulation (QAM) formats at 500 Mbaud, we evaluate the performance of the OBFN-PIC under various configurations. We show that error-free performance can be achieved at both operating frequencies and for all the investigated beam angles ranging from 45 to 135, thus validating its potential for high-quality beamforming performance.

We present our hybrid InP to SiN TriPleX integration interface with a novel alignment technique and its application to complex photonic integrated circuits. The integration interface comprises vertical alignment stops, which simplify the alignment process and allow for array integration with the same simplicity as for single dies. Horizontal alignment is carried out by utilizing optical backscatter reflectometry to get an active feedback signal without the need to operate the chip. Thus, typical contacting limitations of active flip-chip alignment are overcome. By using this method, we demonstrate the integration of InP DFB lasers with more than 60 mW of optical power coupled to a SiN waveguide with an averaged coupling loss of -2.1 dB. The hybrid integration process is demonstrated for single dies as well as full arrays. We evaluate the feasibility of the assembly process for complex photonic integrated circuits by integrating an InP gain chip to a SiN TriPleX external cavity. The process proves to be well suited and allows monitoring chip quality during assembly. A fully functional hybrid integrated tunable laser is fabricated, which is capable of full C-band tuning with optical output power of up to 60 mW.

Tunable semiconductor lasers with a narrow linewidth have found a wide range of important applications, reaching from coherent communications, remote optical sensing such as Lidar to arising applications such as microwave photonics (MWP). Especially, integrated microwave photonics [1,2] aims to achieve RF-to-RF signal processing in the optical domain with a small footprint while offering wide bandwidths. Recently, we developed a hybrid integrated photonic platform [3] based on active InP components such as gain sections, modulators, and detectors with passive silicon nitride-based TriPleX enabling low loss optical signal processing due to its low propagation losses (< 0.1 dB/cm). The combination of these two platforms enables fully integrated RF-to-RF analog photonic links (APL). The link gain of an APL quadratically depends on the sensitivity of the modulator, responsivity of the photodetector (PD) as well as the optical power at the receiving PD [2]. Therefore, to achieve an efficient APL with a high link gain an optical input power of typically more than 20 dBm is needed. Furthermore, high optical powers can keep the noise figure at a minimum by making the use of additional amplifiers obsolete. However, so far current hybrid as well as heterogeneously integrated lasers lack sufficient optical power to achieve such efficient APLs. Here, we present, to the best of our knowledge, the first hybrid integrated laser consisting of more than one InP gain sections sharing a common laser mirror. The resulting on-chip power of 20.7 dBm using two gain sections at a pump current of twice 300 mA is the highest optical power of a hybrid integrated laser to date. Furthermore, the laser shows a low intrinsic linewidth of 320 Hz as well as a low relative intensity noise ( The scheme and a photograph of the dual-gain section hybrid integrated laser is shown in Fig.1 (a) and (b), respectively. The laser comprises of two InP reflective semiconductor optical amplifier (RSOA) chips and a low-loss TriPleX frequency selective mirror chip. The frequency selective mirror is based on a well-known principle of Vernier mirror with two micro-resonators of slightly different length and, hence, free-spectral ranges of 208 GHz and 215 GHz. To achieve a higher optical output power the mirror chip is coupled to two individual InP RSOAs with a length of 700 μm instead of one [4]. The coupling losses from the InP RSOAs to TriPleX laser cavity are estimated to be about 1 dB. Each of the RSOAs has an individual electrical connection to apply a pump current. On the TriPleX chip, thermo-optic tuners are used to set the frequency selective mirror, to control the phases of the RSOAs within the cavity, two tunable Mach-Zehnder couplers are used to combine both output coupling of the cavity and the power in the output waveguide. The output waveguides are coupled to a fiber array with standard polarization maintaining fibers with a coupling loss of 0.5 dB.

An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper. The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit. All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements. The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches. Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures. Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform. This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks.

By using integrated optics, it is possible to reduce the size and cost of a bulky optical coherence tomography (OCT) system. One of the OCT components that can be implemented on-chip is the interferometer. In this work, we present the design and characterization of a Mach-Zehnder interferometer consisting of the wavelength-independent splitters and an on-chip reference arm. The Si3N4 was chosen as the material platform as it can provide low losses while keeping the device size small. The device was characterized by using a home-built swept source OCT system. A sensitivity value of 83 dB, an axial resolution of 15.2 μm (in air) and a depth range of 2.5 mm (in air) were all obtained.

We demonstrate supercontinuum generation in stoichiometric silicon nitride (Sisub3/subNsub4/subin SiOsub2/sub) integrated optical waveguides, pumped at telecommunication wavelengths. The pump laser is a mode-locked erbium fiber laser at a wavelength of 1.56 µm with a pulse duration of 120 fs. With a waveguide-internal pulse energy of 1.4 nJ and a waveguide with 1.0 µm × 0.9 µm cross section, designed for anomalous dispersion across the 1500 nm telecommunication range, the output spectrum extends from the visible, at around 526 nm, up to the mid-infrared, at least to 2.6 µm, the instrumental limit of our detection. This output spans more than 2.2 octaves (454 THz at the -30 dB level). The measured output spectra agree well with theoretical modeling based on the generalized nonlinear Schrödinger equation. The infrared part of the supercontinuum spectra shifts progressively towards the mid-infrared, well beyond 2.6 µm, by increasing the width of the waveguides.

Hybrid integrated semiconductor laser sources offering extremely narrow spectral linewidth as well as compatibility for embedding into integrated photonic circuits are of high importance for a wide range of applications. We present an overview on our recently developed hybrid-integrated diode lasers with feedback from low-loss silicon nitride (Si3N4 in SiO2) circuits, to provide sub-100-Hz-level intrinsic linewidths, up to 120 nm spectral coverage around 1.55 um wavelength, and an output power above 100 mW. We show dual-wavelength operation, dual-gain operation, laser frequency comb generation, and present work towards realizing a visible-light hybrid integrated diode laser., 25 pages, 16 figures

This paper describes a proof-of-concept of a miniaturized spectral-domain optical coherence tomography system, based on photonic integrated circuit (PIC) technology. The integrated optics 512-channel spectrometer consists of cascaded arrayed waveguide gratings (AWG) with the output waveguides directly attached to a CCD detector. The spectrometer has a center wavelength of 850 nm and a spectral sampling interval of 0.22 nm. The PIC has a footprint of 2.0 × 2.7 cm2. The wavelength response of the cascaded AWG spectrometer is calibrated with a tunable laser. Free space OCT measurements are done with a mirror as sample. The signal-to-noise ratio is ∼77 dB. Due to the ∼three times larger optical bandwidth incident on each CCD pixel, the sensitivity rolls off faster in depth than based on the spectral sampling interval. The axial resolution of the OCT system is determined at 5.9 ± 0.4 μm. We demonstrate the imaging capabilities of this PIC based system by imaging a multilayered phantom. Our results show the basis for the development of a handheld OCT system based on PIC technology, thereby facilitating the development of more applications of OCT.

The silicon nitride (Si3N4) planar waveguide platform has enabled a broad class of low-loss planar-integrated devices and chip-scale solutions that benefit from transparency over a wide wavelength range (400–2350 nm) and fabrication using wafer-scale processes. As a complimentary platform to silicon-on-insulator (SOI) and III–V photonics, Si3N4 waveguide technology opens up a new generation of system-on-chip applications not achievable with the other platforms alone. The availability of low-loss waveguides (

In this paper, we present the development of a photonic biosensor device for cancer treatment monitoring as a complementary diagnostics tool. The proposed device combines multidisciplinary concepts from the photonic, nano-biochemical, micro-fluidic and reader/packaging platforms aiming to overcome limitations related to detection reliability, sensitivity, specificity, compactness and cost issues. The photonic sensor is based on an array of six asymmetric Mach Zender Interferometer (aMZI) waveguides on silicon nitride substrates and the sensing is performed by measuring the phase shift of the output signal, caused by the binding of the analyte on the functionalized aMZI surface. According to the morphological design of the waveguides, an improved sensitivity is achieved in comparison to the current technologies (

We describe the first demonstration and characterization of an optically integrated InP-Si3 N4 hybrid laser. The laser is formed by integration of an InP-based reflective semiconductor optical amplifier with a InP-Si3 N4 based feedback waveguide circuit. The circuit comprises a frequency selective and tunable Vernier mirror composed of two microring resonators with slightly different radii. A wide tuning range of more than 43 nm is achieved via the thermo-optic effect. The typical side mode suppression ratio is 35 dB. The narrowest linewidth achieved is about 90 kHz, and the relative intensity noise is less than -135 dBc/Hz.

In this paper, we present the first results on a fully integrated optical beamforming module based on hybrid integration of TriPleX and InP. The Furthermore, we discuss the implementation of various beamforming architecture used in two European H2020 research projects.

In order to realize the multi-analyte assays for environmental contaminants, an optical biosensor utilizing laser-induced fluorescence-based detection via the binding of biomolecules to the surface of an integrated TriPleX™ waveguide chip on a glass substrate (fused silica, FS) is described. As far as we know, this is the first demonstration of using the TriPleX™ technology to fabricate the waveguide chip on a FS substrate. The sensor consists of 32 individually addressable sensor patches, which were formed on the chip surface by exploiting 3 Y-junction splitters, creating four equal rows of eight evanescently excited windows in parallel. The basic low-loss SiO2/Si3N4 TriPleX™ waveguide configuration in combination with on-chip spotsize convertors allows for both high fiber-to-chip coupling efficiency and enables at the same time individually optimized high chip surface intensity and low patch-to-patch deviation. Moreover, the complementary metal-oxide-semiconductor compatible fabrication of waveguide chip allows for its mass production at low cost. By taking MC-LR, 2,4-D, atrazine and BPA as the model analytes, the as-proposed waveguide based biosensor was proven sensitive with the detection limits of 0.22 μg/L for MC-LR, 1.18 μg/L for 2, 4-D, 0.2 μg/L for atrazine and 0.06 μg/L for BPA. Recoveries of the biosensor towards simultaneous detection of MC-LR, 2, 4-D, atrazine and BPA in spiked real water samples varied from 84% to 120%, indicating the satisfactory accuracy of the established technology.

Digital signal processing has achieved great success in the field of signal processing over the past several decades. However, as the bandwidth requirement increases, the power consumption and effective number of bits (ENOB) of the analog-to-digital convertor (ADC) have become bottlenecks. One solution is returning to analog and applying microwave photonic technologies, which shows potential for multiband signal processing. In this paper, a programmable integrated analog photonic signal processor based on cascaded Mach-Zehnder interferometers (MZIs) and a channelized filter has been proposed. Different shapes of the signal processor can be acquired for different applications. The highest processing resolution is 143 MHz, and the processing range of the signal processor can be higher than 112.5 GHz. An application of the signal processor for the signal extraction in a radio frequency (RF) photonic frontend operating from L-band to K-band is presented.

Photonic applications based on planar waveguide technology impose stringent requirements on properties such as optical propagation losses, light coupling to optical fibers, integration density, as well as on reliability and reproducibility. The latter is correlated to a high level of control of the refractive index and waveguide geometry. In this paper, we review a versatile dielectric waveguide platform, called TriPleX, which is based on alternating silicon nitride and silicon dioxide films. Fabrication with CMOS-compatible equipment based on low-pressure chemical vapor deposition enables the realization of stable material compositions being a prerequisite to the control of waveguide properties and modal shape. The transparency window of both materials allows for the realization of low-loss waveguides over a wide wavelength range (400 nm–2.35 μm). Propagation losses as low as 5×10-4 dB/cm are reported. Three basic geometries (box shell, double stripe, and filled box) can be distinguished. A specific tapering technology is developed for on-chip, low-loss (

The use of live bacterial reporters as sensing entities in whole-cell biosensors allows the investigation of the biological effects of a tested sample, as well as the bioavailability of its components. Here we present a proof of concept for a new design for online continuous water monitoring flow-cell biosensor, incorporating recombinant reporter bacteria, engineered to generate an optical signal (fluorescent or bioluminescent) in the presence of the target compound(s). At the heart of the flow-cell is a disposable chip made of porous aluminum oxide (PAO), which retains the sensor microorganisms on its rigid planar surface, while its high porosity allows an undisturbed access both to the sample and to essential nutrients. The ability of the bacterial reporters to detect model toxic chemicals was first demonstrated using a "naked" PAO chip placed on solid agar, and later in a chip encased in a specially designed flow-through configuration which enables continuous on-line monitoring. The applicability of the PAO chip to simultaneous online detection of diverse groups of chemicals was demonstrated by the incorporation of a 6-member sensor array into the flow-through chip. The selective response of the array was also confirmed in spiked municipal wastewater effluents. Sensing activity was retained by the bacteria after 12-weeks storage of freeze-dried biochips, demonstrating the biochip potential as a simple minimal maintenance "plug-in" cartridge. This low-cost and easy to handle PAO-based flow-cell biosensor may serve as a basis for a future platform for water quality monitoring.

Aflatoxins (AF) are naturally occurring mycotoxins, produced by many species of Aspergillus. Among aflatoxins, Aflatoxin M1 (AFM1) is one of the most frequent and dangerous for human health. The acceptable maximum level of AFM1 in milk according to EU regulation is 50 ppt, equivalent to 152 pM, and 25 ppt, equivalent to 76 pM, for adults and infants, respectively. Here, we study a photonic biosensor based on Si 3 N 4 asymmetric Mach&ndash, Zehnder Interferometers (aMZI) functionalized with Fab&rsquo, for AFM1 detection in milk samples (eluates). The minimum concentration of AFM1 detected by our aMZI sensors is 48 pM (16.8 pg/mL) in purified and concentrated milk samples. Moreover, the real-time detection of the ligand-analyte binding enables the study of the kinetics of the reaction. We measured the kinetic rate constants of the Fab&rsquo, AFM1 interaction.

We present the first demonstration of an optically integrated InP-Si 3 N 4 hybrid laser. The feasibility and viability of facet-to-facet, butt-coupled integration is proven by single-frequency operation, tunable across a wide range of 43 nm (including the entire telecom C-band) with sub-MHz spectral bandwidth.

In this work, we present a study of Aflatoxin M1 detection by photonic biosensors based on Si₃N₄ Asymmetric Mach-Zehnder Interferometer (aMZI) functionalized with antibodies fragments (Fab'). We measured a best volumetric sensitivity of 10⁴ rad/RIU, leading to a Limit of Detection below 5 × 10(-7) RIU. On sensors functionalized with Fab', we performed specific and non-specific sensing measurements at various toxin concentrations. Reproducibility of the measurements and re-usability of the sensor were also investigated.

A novel class of optical waveguides with a box-shaped cross section consisting of a low-index inner material surrounded by a thin high-index coating layer is presented. This original multilayered structure widens the traditional concept of index contrast for dielectric waveguides toward a more general concept of effective index contrast, which can be artificially tailored over a continuous range by properly choosing the thickness of the outer high-index layers. An electromagnetic analysis is reported, which shows that the transverse electric and transverse magnetic modes are spatially confined in different regions of the cross section and exhibit an almost 90degC rotational symmetry. Such unusual field distribution is demonstrated to open the way to new intriguing properties with respect to conventional waveguides. Design criteria are provided into details, which mainly focus on the polarization dependence of the waveguide on geometrical parameters. The possibility of achieving single-mode waveguides with either zero or high birefringence is discussed, and the bending capabilities are compared to conventional waveguides. The feasibility of the proposed waveguide is demonstrated by the realization of prototypal samples that are fabricated by using the emerging CMOS- compatible Si3N4-SiO2 TriPleX technology. An exhaustive experimental characterization is reported, which shows propagation loss as low as state-of-the-art low-index-contrast waveguides (< 0.1 dB/cm) together with enhanced flexibility in the optimization of polarization sensitivity and confirms the high potentialities of the proposed waveguides for large-scale integrated optics.

We report ultra-broadband supercontinuum generation in high-confinement Si3N4 integrated optical waveguides. The spectrum extends through the visible (from 470 nm) to the infrared spectral range (2130 nm) comprising a spectral bandwidth wider than 495 THz, which is the widest supercontinuum spectrum generated on a chip.

We will demonstrate a stress-optic phase modulator in the passive SiN-based TriPleX platform using a layer of piezoelectric material. Regarding the stress-optic effect, the piezoelectric layer deposited on top of an optical waveguide is employed to control the phase of propagating light in the structure by applying an electrical field across the layer. In this work, it is demonstrated that the stress-optic effect lowers the power consumption by a factor of one million for quasi-DC operation and increases the modulation speed by three orders of magnitude, compared to currently used thermo-optic modulation in the TriPleX platform.

Photonic chip based time-bin entanglement has attracted significant attention because of its potential for quantum communication and computation. Useful time-bin entanglement systems must be able to generate, manipulate and analyze entangled photons on a photonic chip for stable, scalable and reconfigurable operation. Here we report the first time-bin entanglement photonic chip that integrates time-bin generation, wavelength demultiplexing and entanglement analysis. A two-photon interference fringe with an 88.4% visibility is measured (without subtracting any noise), indicating the high performance of the chip. Our approach, based on a silicon nitride photonic circuit, which combines the low-loss characteristic of silica and tight integration features of silicon, paves the way for scalable real-world quantum information processors., 4 pages, 5 figures

We present a new approach to the dual-beam geometry for on-chip optical trapping and Raman spectroscopy, using waveguides microfabricated in TripleX technology. Such waveguides are box shaped and consist of SiO2 and Si3N4, so as to provide a low index contrast with respect to the SiO2 claddings and low loss, while retaining the advantages of Si3N4. The waveguides enable both the trapping and Raman functionality with the same dual beams. Polystyrene beads of 1 µm diameter can be easily trapped with the device. In the axial direction discrete trapping positions occur, owing to the intensity pattern of the interfering beams. Trapping events are interpreted on the basis of simulated optical fields and calculated optical forces. The average transverse trap stiffness is 0.8 pN/nm/W, indicating that a strong trap is formed by the beams emitted by the waveguides. Finally, we measure Raman spectra of trapped beads for short integration times (down to 0.25 s), which is very promising for Raman spectroscopy of microbiological cells.

This report describes an optical sensing hybrid system obtained by bonding a microfluidic system to an integrated optical (IO) four-channel Young interferometer (YI) chip. The microfluidic system implemented into a glass plate consists of four microchannels with cross-sectional dimensions of 200 microm x 15 microm. The microfluidic system is structured in such a way that after bonding to the IO chip, each microchannel addresses one sensing window in the four-channel YI sensor. Experimental tests show that the implementation of the microfluidics reduces the response time of the sensor from 100s, as achieved with a bulky cuvette, to 4s. Monitoring the anti-human serum albumine/human serum albumine (alpha-HSA/HSA) immunoreaction demonstrates the feasibility to use the microfluidic sensing system for immunosensing applications. In this case, a better discrimination between the bulk refractive index change and the layer formation can be made, resulting into higher accuracy and offering the prospect of being able to use the kinetics of the immunoreaction. The microfluidic sensing system shows an average phase resolution of 7 x 10(-5) x 2pi for different pairs of channels, which at the given interaction length of 4 mm corresponds to a refractive index resolution of 6 x 10(-8), being equivalent to a protein mass coverage resolution of 20 fg/mm2.

We extend our previous simulation study and we present experimental results regarding our Fast Fourier Transform method for the calculation of the resonance shifts in biosensors based on micro-ring resonators (MRRs). For the simulation study, we use a system model with a tunable laser at 850 nm, an MRR with 1.5∙10sup4/supquality factor, and a detection system with 50 dB maximum signal-to-noise ratio, and investigate the impact on the system performance of factors like the number of the resonance peaks inside the scanning window, the wavelength dependence of the laser power, and the asymmetry of the transfer functions of the MRRs. We find that the performance is improved by a factor of 2 when we go from single- to four-peak transfer functions, and that the impact of the wavelength dependence of the laser power is very low. We also find that the presence of asymmetries can lead to strong discontinuities of the transfer functions at the edges of the scanning window and can significantly increase the measurement errors, making necessary the use of techniques for their elimination. Using these conclusions, we build a system with sensing MRRs on TriPleX platform, and we experimentally validate our method using sucrose solutions with different concentrations. Involving techniques in order to exclude the noise originating from the microfluidic system, we achieve a wavelength resolution close to 0.08 pm, when the system operates with 0.5 pm scanning step. In combination with the sensitivity of the MRRs, which is measured to be equal to 93.7 nm/RIU, this wavelength resolution indicates the possibility for a limit of detection close to 8.5·10sup-7/supRIU, which represents to the best of our knowledge a record performance for this type of optical sensors and this level of scanning steps.

In this paper, we propose and experimentally demonstrate a novel wideband on-chip photonic modulation transformer for phase-modulated microwave photonic links. The proposed device is able to transform phase-modulated optical signals into intensity-modulated versions (or vice versa) with nearly zero conversion of laser phase noise to intensity noise. It is constructed using waveguide-based ring resonators, which features simple architecture, stable operation, and easy reconfigurability. Beyond the stand-alone functionality, the proposed device can also be integrated with other functional building blocks of photonic integrated circuits (PICs) to create on-chip complex microwave photonic signal processors. As an application example, a PIC consisting of two such modulation transformers and a notch filter has been designed and realized in TriPleXTM waveguide technology. The realized device uses a 2 × 2 splitting circuit and 3 ring resonators with a free spectral range of 25 GHz, which are all equipped with continuous tuning elements. The device can perform phase-to-intensity modulation transform and carrier suppression simultaneously, which enables high-performance phase-modulated microwave photonics links (PM-MPLs). Associated with the bias-free and low-complexity advantages of the phase modulators, a single-fiber-span PM-MPL with a RF bandwidth of 12 GHz (3 dB-suppression band 6 to 18 GHz) has been demonstrated comprising the proposed PIC, where the achieved spurious-free dynamic range performance is comparable to that of Class-AB MPLs using low-biased Mach-Zehnder modulators.

We present an overview of several microwave photonic processing functionalities based on combinations of Mach-Zehnder and ring resonator filters using the high index contrast silicon nitride (TriPleXTM) waveguide technology. All functionalities are built using the same basic building blocks, namely straight waveguides, phase tuning elements and directional couplers. We recall previously shown measurements on high spurious free dynamic range microwave photonic (MWP) link, ultra-wideband pulse generation, instantaneous frequency measurements, Hilbert transformers, microwave polarization networks and demonstrate new measurements and functionalities on a 16 channel optical beamforming network and modulation format transformer as well as an outlook on future microwave photonic platform integration, which will lead to a significantly reduced footprint and thereby enables the path to commercially viable MWP systems

This paper describes the design and fabrication of a sensitive integrated chemo-optical sensor supplied with on-chip fiber-to-waveguide connectors. The sensor is designed for TE-polarized light with wavelength of 633 nm. The fiber-to-chip connectors are based on easily fabricated silicon V-grooves combined with a smooth sawcut. The sawcut is defining the channel waveguide endface. The sensor is based on a phase modulated Mach-Zehnder interferometer, using the electro-optic effect of the waveguiding material zinc oxide (ZnO). The fiber-to-chip connector units have a typical coupling efficiency of 0.1?1%. The electro-optical voltage × length product V? is 15 ± 4 V cm at frequencies above 100 Hz. Preliminary experiments on the general (passive) sensor response showing its expected high sensitivity are discussed.

Thin (approx. 1 μm) crystalline ZnO films with a good optical quality and a good (0002) texture are grown under two considerably different process parameter sets using a r.f. planar magnetron sputtering unit. The optical parameters of the two corresponding ZnO layers are distinctly different: high refractive index (≅ 2.0 at λ = 632.8 nm) ZnO films resembling the single crystal form, and ZnO films with considerably lower (typical difference 0.05) refractive indices. The refractive index of the latter ZnO layers is adjustable (approx. 1.93-1.96 at λ = 632.8 nm) through the process deposition parameters. It is shown that the difference in refractive index between the two ZnO types most probably results from a difference in package density of the crystal columns. The optical waveguide losses of both ZnO types are typically 1-3 dB/cm at λ = 632.8 nm, however the low refractive index ZnO layers need a post-deposition anneal step to obtain these values. The two ZnO types are used to fabricate optical channel-and slab waveguides with small refractive index differences.

The feasibility of detecting small molecules such as pesticides using optical evanescent-wave sensors is discussed with emphasis on the Mach-Zehnder sensor and a newly developed sensor called a ‘critical’ sensor. For direct detection of an estimated average pesticide layer growth of 2×10−4 nm, the sensitivity of the Mach-Zehnder sensor is almost adequate (1×10−3 nm within one hour), whereas that of the ‘critical’ sensor (2×10−2 nm) is not sufficient. However, the simplicity of this latter sensor is very attractive. Results of α-hSA/hSA immunoreaction experiments obtained with this last type of sensor are presented.

It is still a common belief that ultra-high quality-factors (Q-factors) are a prerequisite in optical resonant cavities for high refractive index resolution and low detection limit in biosensing applications. In combination with the ultra-short steps that are necessary when the measurement of the resonance shift relies on the wavelength scanning of a laser source and conventional methods for data processing, the high Q-factor requirement makes these biosensors extremely impractical. In this work we analyze an alternative processing method based on the fast-Fourier transform, and show through Monte-Carlo simulations that improvement by 2-3 orders of magnitude can be achieved in the resolution and the detection limit of the system in the presence of amplitude and spectral noise. More significantly, this improvement is maximum for low Q-factors around 104 and is present also for high intra-cavity losses and large scanning steps making the designs compatible with the low-cost aspect of lab-on-a-chip technology. Using a micro-ring resonator as model cavity and a system design with low Q-factor (104), low amplitude transmission (0.85) and relatively large scanning step (0.25 pm), we show that resolution close to 0.01 pm and detection limit close to 10-7 RIU can be achieved improving the sensing performance by more than 2 orders of magnitude compared to the performance of systems relying on a simple peak search processing method. The improvement in the limit of detection is present even when the simple method is combined with ultra-high Q-factors and ultra-short scanning steps due to the trade-off between the system resolution and sensitivity. Early experimental results are in agreement with the trends of the numerical studies.

We propose and demonstrate a novel wideband microwave photonic fractional Hilbert transformer implemented using a ring resonator-based optical all-pass filter. The full programmability of the ring resonator allows variable and arbitrary fractional order of the Hilbert transformer. The performance analysis in both frequency and time domain validates that the proposed implementation provides a good approximation to an ideal fractional Hilbert transformer. This is also experimentally verified by an electrical Ssub21/subresponse characterization performed on a waveguide realization of a ring resonator. The waveguide-based structure allows the proposed Hilbert transformer to be integrated together with other building blocks on a photonic integrated circuit to create various system-level functionalities for on-chip microwave photonic signal processors. As an example, a circuit consisting of a splitter and a ring resonator has been realized which can perform on-chip phase control of microwave signals generated by means of optical heterodyning, and simultaneous generation of in-phase and quadrature microwave signals for a wide frequency range. For these functionalities, this simple and on-chip solution is considered to be practical, particularly when operating together with a dual-frequency laser. To our best knowledge, this is the first-time on-chip demonstration where ring resonators are employed to perform phase control functionalities for optical generation of microwave signals by means of optical heterodyning.

We present the first demonstration of a broadband and continuously tunable integrated optical true-time-delay line, operating over the complete DVB-S satellite communication band, realized with a CMOS-compatible TriPleXTM waveguide technology. The integrated optical chip includes a delay line and an optical sideband filter (OSBF) based on reconfigurable optical ring resonators (ORR). The filter and the delay responses are software programmable and have been configured for K u -band operation. For the first time, the continuous tunability between 0 and 277 ps is demonstrated over the complete for DVB-S satellite communication band (10.7–12.75 GHz).

A study on the immunoreactivity of adsorbed alpha hCG molecules as a function of substrate hydrophobicity and protein coverage is presented. The experiments were performed with a planar waveguide interferometrical immunosensor. The substrate hydrophobicity and the antibody density were found to be of major importance for the immunoreactivity of the adsorbed antibodies. A combination of a hydrophobic (contact angleor = 80 degrees) substrate and only a fraction (approximately 0.3) of a monolayer of antibodies gives the highest immunoreactivity. However, the immunoreaction affinity constant of the active antibodies is found to be essentially independent of the substrate hydrophobicity. The experimental results indicate that the orientation and not the conformation of the active antibodies on the substrate is dependent on the substrate hydrophobicity.

We describe a highly sensitive sensor which uses the evanescent field of a reusable planar optical waveguide as the sensing element. The waveguide used is optimized to obtain a steep dependence of the propagation velocity on the refractive-index profile near the surface. The adsorption of a layer of proteins thus results in a phase change, which is measured interferometrically using a Mach-Zehnder interferometer set-up. The stability of the interferometer is such that phase changes = (1 × 10-2)2pi per hour can be measured. Immunoreactions have been monitored down to concentrations of 5 × 10-11 M of a 40 kDa protein.

We describe a fiber optic interferometric refractive index sensor to illustrate that, by using the evanescent field of an optical waveguide, a potentially very sensitive determination of changes in the refractive index on the waveguide surface can be obtained. These changes can, e.g., be the result of immunoreactions. We used a Mach-Zehnder interferometer configuration with a flow-through cuvette in one arm with a decladded multimode glass fiber of 0.6-mm diameter and 2-cm interaction length. The obtained resolution in measuring refractive index changes is 1 x 10-(3). We also developed the theory describing the sensitivity of this sensor using the modal and the geometrical ray description.

For the modern radio astronomy instruments wide instantaneous bandwidth is a characteristic of great interest. This can be a difficult requirement for a phased array antenna (PAA)employing a traditional electronic beamformer: the performance of the constituting components, mainly combiners and delay elements, limits the bandwidth of the total system.

A squint-free, continuously tunable optical beamformer system for phased array receive antennas is proposed and experimentally demonstrated, which involves an integrated ring resonator-based optical beam forming network, filter-based optical SSB-SC modulation and balanced coherent detection.

One of the key research topics of the Telecommunication Engineering (TE) Group at the University of Twente (UT) is RF Photonics. The aim of this field is to develop schemes that utilize the advantages of optical technology for performing RF functions in wireless communication systems. Examples of such functions are high-frequency filtering, frequency conversion, antenna remoting, and beam forming for phased array antennas. The TE Group is currently involved in several Senter and NIVR projects on RF Photonics that are related to phased array antenna applications.

For enhanced communication on board an aircraft, novel antenna systems with broadband satellite based capabilities are required. The technology will enhance airline operations by providing in-flight connectivity for flight crew information and will bring live TV and high speed Internet connectivity to passengers. The installation of such systems on board an aircraft requires for aerodynamic reasons the development a very low-profile aircraft antenna, which can point to satellites anywhere in the upper hemisphere. To this end, phased array antennas which are conformal to the aircraft fuselage are attractive. In this paper, two key aspects of conformal phased array antenna arrays are addressed: the development of a broadband Ku-band antenna and an optical beam forming network for tracking satellites. The antenna elements of the conformal array are stacked patch antennas with dual linear polarization which have sufficient bandwidth. For tracking an optical circuit is proposed that consists of a cascade of optical ring resonators.

For enhanced communication on board of aircraft novel antenna systems with broadband satellite-based capabilities are required. The installation of such systems on board of aircraft requires the development of a very low-profile aircraft antenna, which can point to satellites anywhere in the upper hemisphere. To this end, phased array antennas which are conformal to the aircraft fuselage are attractive. In this paper two key aspects of conformal phased array antenna arrays are addressed: the development of a broadband Ku-band antenna and the beam synthesis for conformal array antennas. The antenna elements of the conformal array are stacked patch antennas with dual linear polarization which have sufficient bandwidth. For beam forming synthesis a method based on a truncated Singular Value Decomposition is proposed.

A novel squint-free, continuously tunable beamformer mechanism for a phased array antenna system is proposed. It consists of filter-based optical single-sideband suppressed-carrier modulation, a fully integrated optical beam forming network using cascades of optical ring resonators as tunable delay elements, and balanced coherent optical detection. The proposed system brings advantages in optical bandwidth requirement, system complexity, and dynamic range, without introducing the problem of beam squint or limited tuning resolution. Some experimental results are presented in order to demonstrate the feasibility of the proposed concept.

A novel optical beamformer system for phased array transmit antennas is proposed and experimentally demonstrated. It is based on an optical IM/DD link through a ring resonator-based optical beam forming network chip.

The activities of the Telecommunication Engineering (TE) group span the communications spectrum from copper cables, optical fibres, microwaves, radio and electromagnetic compatibility. Our research concentrates on optical signal processing and networks, mobile communications, microwave techniques and radiation from ICs and PCBs [1]. A considerable (and particularly interesting) part of it is related to optical beam forming for phased array antennas, using optical ring resonators. In this article the theoretical basics and practical challenges of this interesting research topic will be summarized.

In this paper we present a novel fabrication technique for silicon nitride (Si3N4) waveguides with a thickness of up to 900 nm, which are suitable for nonlinear optical applications. The fabrication method is based on etching trenches in thermally oxidized silicon and filling the trenches with Si3N4. Using this technique no stress-induced cracks in the Si3N4 layer were observed resulting in a high yield of devices on the wafer. The propagation losses of the obtained waveguides were measured to be as low as 0.4 dB/cm at a wavelength of around 1550 nm., 10 pages, 4 figures

— Optical ring resonators (ORRs) can be used as continuously tunable delay elements in a beam forming network for a phased-array antenna system. The bandwidth of such delay elements can be enhanced by cascading multiple ORRs. When delays and splitting/combining circuitry are integrated in one optical circuit, an optical beam forming network (OBFN) is obtained. In this paper, the principles of optical beam forming using ORRs are explained and demonstrated, by presenting measurements on a 1×4 OBFN chip, realized in LPCVD waveguide technology. To our knowledge, this is the first single-chip demonstration of continuous optical beam forming.

In this paper, we report the realization and characterization of a four-channel integrated optical Young interferometer (YI), which enables simultaneous and independent monitoring of three binding processes. The simultaneous and independent measurement of three different glucose concentrations shows the multi-purpose feature of such device. The phase resolution for different pairs of channels was /spl sim/1/spl times/10/sup -4/ fringes, which corresponds to a refractive index resolution of /spl sim/8.5/spl times/10/sup -8/ . The observed errors, which are caused due to mismatching of spatial frequencies of individual interference patterns with those determined from the CCD camera, have been reduced by using different reduction schemes. In addition, we have investigated a novel method for discrimination of the refractive index change from the thickness of a bound layer during an immunoreaction, as well as measuring the temperature change the takes place during such a process.