Optoelectronic Unit Research Articles

Optical sensor for interstitial pH measurements

An optical fiber sensor for measuring the pH in interstitial fluid is described. Microdialysis is the approach followed for extracting the sample from the subcutaneous adipose tissue. The interstitial fluid drawn flows through a microfluidic circuit formed by a microdialysis catheter in series with a pH glass capillary. The pH indicator (phenol red) is covalently immobilized on the internal wall of the glass capillary. An optoelectronic unit that makes use of LEDs and photodetectors is connected to the sensing capillary by means of optical fibers. Optical fibers are used to connect the interrogating unit to the sensing capillary. A resolution of 0.03 pH units and an accuracy of 0.07 pH units are obtained. Preliminary in vivo tests are carried out in pigs with altered respiratory function.

Doubly Ortho-Linked Quinoxaline/Diphenylfluorene Hybrids as Bipolar, Fluorescent Chameleons for Optoelectronic Applications

The titled dipolar hybrids bearing a central quinoxaline-fused dibenzosuberene optoelectronic unit with functional C5 and C8 appendages and spiro-fluorene junction act as fluorescent bipolar OLED chameleons. The emission colors can be tuned from blue, green, yellow, to red with operation brightness of 205, 1268, 1542, and 1102 cd/m2, respectively, at 20 mA/cm2.

Optical-fibre sensor system for monitoring the performance of the gas–propellant centrifuge separator of a spacecraft

An optical-fibre sensor system is presented for monitoring void fraction distribution in a spacecraft's gas and propellant centrifuge separator. The system could be used at the separator development stage or for monitoring, during ground tests, the elements of the spacecraft propulsion system. Our sensor system employs an array of point optical-fibre refractometric transducers installed in the form of several linear radial arrays on the separator rotating blades. We employed a small-size hemispherical optical detection element as the transducer and we optimized its parameters through numerical ray-tracing. The aim is to minimize the effect of the thin film of liquid that forms on the transducer's surface in this application. The features of this sensor system are: (1) an efficient matrix-type multiplexing scheme, (2) the installation of the main optoelectronic unit of the sensor in a hermetically sealed container inside the separator tank located on the rotating shaft and (3) the spark-proof and explosion-proof design of the sensor circuits and elements. The sensor is simple, reliable, low-cost and is capable of withstanding the factors involved during operation of the propulsion system such as cryogenic temperatures and chemically aggressive liquids. The novel elements and design concepts implemented in this sensor system can also find applications in other sensors for spacecraft propulsion systems and also in a variety of optical-fibre sensors used in scientific research and industry.

Error Estimation in a Fiber-Optic Dual Waveband Ratio Pyrometer

Noncontact sensor systems are able to measure high temperature work in very harsh environments, so they need the cooling system to work properly or they take measurements from long distances, introducing hazardous components in the measurement. In order to avoid the aforementioned problems, the hot-point optical radiation is captured by the all passive fiber transducer from a short distance, transmitted through the optical channel, and, hence, it is processed on the optoelectronic unit. Then, later, in order to be cost effective, we use a sandwich-type detector, which discriminates the light in two different optical widebands. Relative error less 4% is obtained from a study of the error estimation in order to evaluate its influence on the optical channel condition, and connection losses, among others, can modify the input light at optoelectronic units on the sensor system performances.

Reverse biased porous silicon light-emitting diodes for optical intra-chip interconnects

We have reported recent progress in development of the integrated optoelectronic unit on a Si chip. The developed optoelectronic unit includes a porous Si light-emitting diode (LED) connected with a photodetector by an alumina waveguide. Main attention has been devoted to the enhancement of LED parameters. Quantum efficiency as high as 0.4% has been reached. The delay time of 1.2 ns and the rise time of 1.5 ns have been measured for the diodes. Further improvements are also discussed.

Reversible and selective detection of NO 2 by means of optical fibres

A sandwich-type metal diphthalocyanine, bis(pthalocyaninato)titanium(IV) [Ti(Pc) 2], is proposed as a selective chemical transducer for the optical detection of nitrogen dioxide (NO 2). An alumina disc was used as a solid support for the immobilisation of the transducer, by means of evaporation from a Ti(Pc) 2 solution in toluene, and was placed in a suitable flow-cell. Through interaction with nitrogen dioxide, this compound underwent spectral changes in the red and green components of the visible spectrum. The optical characterisation of the optode was carried out by an appropriate optoelectronic unit, which was connected to the flow-cell by a single optical fibre. Appropriate treatment with UV light made the optode fully reversible. The optode developed was found to be very selective, and no interference coming from other gases was observed. A detection limit of 0.6 ppm was obtained.

Temperature measurement in soft tissue using a distributed fibre Bragg-grating sensor system

Currently used temperature sensor systems do not provide sufficient spatial resolution and can not be used as an integrated part of minimally invasive treatment. Few magnetic resonance (MR) compatible sensor systems are available. A distributed fibre Bragg-grating sensor system for use in biological tissue was constructed. Ten Bragg gratings were inscribed in the core of an optical fibre. The fibre was mounted into tubes made of MR-compatible materials. An opto-electronic unit connected to the fibre was used for signal generation and detection. Communication with a PC allowed presentation and logging of temperature data. The system was calibrated to the temperature range ‘195.8°C to 100°C. Experiments were conducted during freezing (cryoablation) of porcine liver in vivo. The system yielded a temperature profile with 6.5 mm spatial resolution and 5 s temporal resolution. Both mechanical stability and MR compatibility were acceptable and will allow routine use.

Permutation-network-based optoelectronic path-history units for Viterbi decoders

A concept, believed to be new, is introduced that enables the design and implementation of the path-history (PH) unit of Viterbi decoders with permutation networks. The rationale behind this concept is that the trace-back operation in the PH unit is nothing but propagation of a signal traveling from the rightmost end to the leftmost end in the trellis diagram controlled appropriately by the decision bits. On the basis of this observation, an optoelectronic PH unit, which consists of directional coupler switches and registers, is proposed. This unit can be treated as a direct implementation of the trellis diagram of the underlying convolutional code and carries out the trace-back operation by propagating a photonic signal rather than an electronic signal through a given permutation network controlled by the decision bits. Hence the speed is inherently faster than the equivalent electronic version. Here both unfolded and folded versions of optoelectronic PH units are proposed.

On the route towards Si-based optical interconnects

We have developed and fabricated a prototype of optical interconnects on a Si substrate. The original device design includes an aluminum–porous silicon light-emitting diode connected with a photodetector by an alumina waveguide. In order to minimize optical losses, the waveguide has been realized by subsequent deposition of three aluminum layers among which the intermediate one was doped with a titanium large refractive index layer. This multilayer structure was then anodically oxidized to form an Al 2O 3/Al 2O 3+TiO 2/Al 2O 3 layered waveguide. In the integrated optoelectronic unit it provides up to 50% increase of the detector response with respect to a waveguide of pure Al 2O 3. Optical losses in the visible range have been estimated to be about 1 dB/cm. Another method for increasing the detector response through the use of a microcavity is discussed.

Optoelectronic unit for the detection of diamonds by raman light scattering

Optoelectronic unit for the detection of diamonds by raman light scattering

Integrated Optoelectronic Unit Based on Porous Silicon

An original device design including an aluminum‐porous silicon light emitting diode connected with a photodetector by an alumina waveguide has been developed. Distinct photoconductivity and photovoltaic effects have been clearly revealed from current‐voltage curves of the photodetector. The comparison of external light excitation and internal light excitation has shown that photoresponse is considerably higher in case of the internal light source. Furthermore, the photoresponse from the internal light source can be increased by using a special reflector film along the edge of the aluminum electrode. The presented optoelectronic unit has been made by silicon technology and can be used for high speed optical interconnects within VLSI-IC.

Integrated Optoelectronic Unit Based on Porous Silicon

Integrated Optoelectronic Unit Based on Porous Silicon

The design of an optoelectronic arithmetic processor based on permutation networks

This paper introduces a new concept by which it is possible to design and implement arithmetic processors using permutation networks. To demonstrate this concept, several optoelectronic arithmetic units combining optical directional coupler switches and cyclic permutation networks are designed. The designs show that addition, subtraction, and multiplication can all be performed in O(log n) time in residue code domain and using O(n/sup 2/) directional coupler switches and gates, where n=log M, and M is the integer range of interest. These arithmetic units also have the capability of concurrent error detection and fault-tolerance, and they can be used to construct constant time inner product processors.

Linear phase tracking in a coherence modulation electrical sensor system using integrated LiNbO/sub 3/ modulator/demodulator

We report an interferometric sensor system, based on coherence modulation of light and LiNbO/sub 3/ integrated optics technology. We describe a phase detection scheme designed to retrieve the absolute phase variations produced by a sensor system where the sensor signal is electronically applied to an electro-optic modulator. The system consists of an imbalanced LiNbO/sub 3/ Mach-Zehnder transducer fed by a self-powered charge generating sensor, and an optoelectronic central processing unit including a second electrooptic Mach-Zehnder working as an optical demodulator and featuring a matched path-imbalance. Electrical feedback is applied to this second interferometer in an active demodulation scheme, allowing a linear tracking of the signal phase up to 7-/spl pi/ radians.

Design and application of double amplified recirculating ring structure for hybrid fibre buses

The design of a double-parallel amplified recirculating optical delay line utilizing an erbium-doped fibre amplifier for a fibre optical bus is described. This structure is used for amplifying, equalizing and filtering multicarrier signals coming from optoelectronic units attached to fibre couplers. The use of this structure for a hybrid multimode-singlemode fibre bus that includes optoelectronic units for sensors is also demonstrated.

Compact lenslet-array-based holographic correlator/convolver

Although electronic systems continue to shrink in size, optical processors, particularly correlators/convolvers, remain relatively bulky. Here a compact holographic correlator/convolver, based on the use of multiple lenslet arrays, is presented. This compact lenslet-array holographic correlator/convolver approach offers most of the advantages of conventional optical correlators, including fully parallel high-speed operation, yet its physical size is comparable with that of monolithic optoelectronic units such as VLSI spatial light modulators and CCD's. Thus hybrid optoelectronic systems based on the lenslet-array holographic correlator/convolver (pattern recognition, optically interconnected computers, artificial neural networks, etc.) can be both compact and fast.

Controlled-Pore Glasses Embedded in Plastic Optical Fibers for Gastric pH Sensing Purposes

The present work is concerned with the development of an optical-fiber pH sensor for gastric monitoring. Bromophenol blue is used as a chromophore, which is immobilized on controlled-pore glasses (CPGs) by means of a silylation process. As far as the optoelectronic unit is concerned, light-emitting diodes as sources and an appropriate electronic circuit as detection system are utilized. Treated CPGs are fixed at the end of two plastic optical fibers (core diameter = 500 μm) by means of a proprietary process; a reflector made of Teflon®, anchored to the distal end of the fibers, ensures good fibers/probe coupling efficiency. The behavior of the realized probe is carefully investigated, with particular attention devoted to the presence of hysteresis, to ionic strength and temperature effect, and to its lifetime. The fast response time, thanks to the absence of a mechanical envelope, the small dimensions of the probe, and the biocompatibility of the utilized materials make this sensor suitable for in vivo measurements.