Electro-optic Transducer Research Articles

Radiation Pattern Measurement of a Low-Profile Wearable Antenna Using an Optical Fibre and a Solid Anthropomorphic Phantom

This paper presents a study into radiation pattern measurements of an electrically small dielectric resonator antenna (DRA) operating between 2.4 and 2.5 GHz in the industrial, scientific and medical (ISM) radio band for body-centric wireless communication applications. To eliminate the distortion of the radiation pattern associated with the unwanted radiation from a metallic coaxial cable feeding the antenna we have replaced it with a fibre optic feed and an electro-optical (EO) transducer. The optical signal is then converted back to RF using an Opto-Electric Field Sensor (OEFS) system. To ensure traceable measurements of the radiation pattern performance of the wearable antenna a generic head and torso solid anthropomorphic phantom model has been employed. Furthermore, to illustrate the benefits of the method, numerical simulations of the co-polar and cross-polar H-plane radiation patterns at 2.4, 2.45, and 2.5 GHz are compared with the measured results obtained using: (i) an optical fibre; and (ii) a metallic coaxial cable.

On the feasibility of self-mixing interferometer sensing for detection of the surface electrocardiographic signal using a customized electro-optic phase modulator

Optical sensing offers an attractive option for detection of surface biopotentials in human subjects where electromagnetically noisy environments exist or safety requirements dictate a high degree of galvanic isolation. Such circumstances may be found in modern magnetic resonance imaging systems for example. The low signal amplitude and high source impedance of typical biopotentials have made optical transduction an uncommon sensing approach. We propose a solution consisting of an electro-optic phase modulator as a transducer, coupled to a vertical-cavity surface-emitting laser and the self-mixing signal detected via a photodiode. This configuration is physically evaluated with respect to synthesized surface electrocardiographic (EKG) signals of varying amplitudes and using differing optical feedback regimes. Optically detected EKG signals using strong optical feedback show the feasibility of this approach and indicate directions for optimization of the electro-optic transducer for improved signal-to-noise ratios. This may provide a new means of biopotential detection suited for environments characterized by harsh electromagnetic interference.

Comparison of theoretical and measured P1dB of a photonic microwave link: influence of some physical parameters of the DFB laser

This paper studies a microwave photonic link built as an IM/DD or intensity modulation–direct detection semiconductor laser system. The radiofrequency gain and 1 dB compression point of the link are both simulated with a modelling approach and compared to measurements. The electrical model of the electro-optic transducer, a distributed feedback laser, is first presented. Taking into account the nonlinearities and noise sources, it is developed on the commercial electrical software Advanced Design System. Owing to this accurate model, the impact of the relaxation oscillation frequency is presented on the system nonlinearity characteristic as for example the input 1 dB compression point. The comparison of simulated results to measured ones confirms the accuracy of this model.

Terahertz electrical response of nanoscale three-branch junctions

Ultrafast time-domain electro-optical characterization of the ballistic three-branch junctions (TBJs) has been performed to investigate their electrical response at terahertz (THz) frequencies. A TBJ rectifier consisting of two TBJs in parallel was placed in a coplanar waveguide (CPW) in which subpicosecond electrical pulses were generated by a photoconductive switch. A LiTaO3-based electro-optic transducer measured the waveform of the incident and transmitted voltage signals with a subpicosecond temporal resolution. This experimental configuration allowed the rectifier’s electrical response to be studied with a bandwidth of up to 1 THz. Detailed analysis of the TBJ rectifier and the photoconductive switch was performed in both the time domain and frequency domain. This analysis revealed poor coupling of the excitation signal into the rectifier because of a severe impedance mismatch between the rectifier and CPW as well as a parasitic capacitive coupling between the input and output ports of the rectifier. The poor coupling limited our ability to observe any substantial nonlinear response of the rectifier at THz frequencies. Possible solutions for enhancing the system bandwidth and efficient THz rectification are presented.

Femtosecond electro-optic effect in (Cd,Mn)Te single crystals

We present our studies on the femtosecond electro-optic (EO) effect in high quality Cd0.88Mn0.12Te (CMT) single crystals, grown using a modified vertical Bridgman method. Our time-resolved experiments were performed using a coplanar transmission line setup, which incorporated a free-standing, low-temperature-grown GaAs photoconductive switch as a sub-picosecond electrical pulse generator and the tested CMT crystal as an active EO transducer. We determined the r-coefficient (r41) of CMT at the high (THz) frequency range to be 29.4 pm/V, an order of magnitude greater than that measured for the same sample at low (MHz) frequencies. The observed suppression of the EO coefficient at low frequencies was due to effective electric field screening by free holes in the crystal volume. Comparison to the standard EO sampling scheme based on the LiTaO3 transducer showed that CMT exhibited the same sub-picosecond temporal resolution with significantly greater voltage sensitivity. We also did not observe, the so-called dielectric loading typical for LiTaO3-based samplers.

Low Invasive Internal Osteosynthesis in Fractures of Tibial Plateau

Outcomes of surgical treatment of 97 patients with intraarticular fractures of proximal tibial metaepiphysis were analyzed. In all patients internal osteosynthesis without arthrotomy and under either electro-optical transducer or arthroscopic control was performed. Cannulated screws and plates with angular stability were used for osteosynthesis. In fractures with impression of articular surface plasty of bone tissue defects using either autograft from the upper flaring portion of the ilium or -tricalcium phosphate was performed. In postoperative period partial weight bearing on the operated extremity was allowed starting from the 6th week. Complete weight bearing in fractures with impression was allowed in 10 week and in 6 weeks - in fractures without impression. Treatment results were followed up at terms from 6 to 70 months (mean - 35 months). Roentgenologic and functional evaluation was performed by Rusmussen and Resnik-Niwoyama systems. Achieved roentgenologic results were excellent in 57.7% of patients, good - in 24.7%, satisfactory - in 15.5% and unsatisfactory in 2.1% of patients. It was showed that at treatment of such fractures the application of modern fixators and arthroscopic control enabled to perform adequate reposition of the articular surface and visualize injuries of intraarticular structures. Plasty of subchondral bone defects and application of plates with angular stability eliminated the probability of secondary displacement of fragments thus creating the possibility of early functional treatment and rehabilitation.

Electrical detection of confined gap plasmons in metal–insulator–metal waveguides

Plasmonic waveguides offer promise in providing a solution to the bandwidth limitations of classical electrical interconnections1,2,3. Fast, low-loss and error-free signal transmission has been achieved in long-range surface plasmon polariton waveguides4,5. Deep subwavelength plasmonic waveguides with short propagation lengths have also been demonstrated6,7, showing the possibility of matching the sizes of optics and today's electronic components. However, in order to combine surface plasmon waveguides with electronic circuits, new high-bandwidth electro-optical transducers need to be developed. Here, we experimentally demonstrate the electrical detection of surface plasmon polaritons in metallic slot waveguides. By means of an integrated metal–semiconductor–metal photodetector, highly confined surface plasmon polaritons in a metal–insulator–metal waveguide are detected and characterized. This approach of integrating electro-optical components in metallic waveguides could lead to the development of advanced active plasmonic devices and high-bandwidth on-chip plasmonic circuits. Electrical detection and characterization of gap plasmons is achieved by means of an integrated metal–semiconductor–metal photodetector. Integration of electro–optical components in metallic waveguides may lead to active high-bandwidth on-chip nano-optical circuits.

PV-400 Time-Interval Analyzing Electro-Optical Transducer with Wide-Format Photocathode and Picosecond Resolution Time

A new time-interval analyzing electro-optical transducer with 4 × 40 mm2 photocathode, time resolution down to 2 psec, and spatial resolution down to 35 line pairs per millimeter is developed. The transducer is designed for use in the study of the spectra of optical radiation in the dynamic mode. The electro-optical system has a four-electrode design. The accelerating mesh electrode is situated a distance of about 1 mm from the photocathode. The deflecting plates are supplied with electron traps, making possible beam suppression.

Formation of charged particle tracks in glass-fiber microstructures

Glass-fiber disks intended for the image transfer in electrooptical transducers can be used as targets in microchannel Cerenkov track detectors. Calculated values of the coefficient of Cerenkov radiation trapping in the glass-fiber discs well agree with experiment, which confirms the hypothesis concerning a Cerenkov-type mechanism of the charged particle track formation in non-scintillating microfiber structures.

A theoretical model for ferroelectric polarization-controlled superconductor devices

Polarization-controlled superconductor devices could be used as a logic gate or other electronic units such as acoustic sensors, electro-optical transducers and image detectors. Lin and Wu (Appl. Phys. Lett. 65 (8) (1994) 1) have experimentally investigated the I–V characteristics of such a device. In this paper, we propose a theoretical model to calculate the polarization effect on the I–V curves. The polarization effects include the cause of the superconducting-normal state switching and exponential time dependence of the source-drain voltage. We fit the experimental data with the theoretical model. They agree quite well.

A novel electrooptical proximity sensor for robotics: calibration and active sensing

An electrooptical proximity sensor capable of measuring the distance and two-dimensional orientation of an object's surface is presented. The robustness of the sensor, targeted for utilization in robotic active sensing, is achieved via the development of a novel amplitude-modulated-based electrooptical transducer, an electronic-interface circuit that provides very good noise immunity and a wide dynamic operating range, and an effective multi-region calibration process that significantly improves pose-estimations at near proximities. An experimental setup was designed and implemented for the development and verification of the proposed proximity sensor in a simulated robotic environment. Experimental results using a variety of calibrated surfaces and materials are presented and discussed. It is shown that average accuracies of 0.01 mm and 0.03/spl deg/ can be achieved. The robustness of the proximity sensor is also verified for potential use in grasping objects with a priori noncalibrated surfaces.

A study and optoelectronic verification of AlGaAs/GaAs heterojunction bipolar transistor large-signal characteristics

A hybrid optoelectronic measurement system is constructed and used to obtain the large-signal characteristics of AlGaAs/GaAs heterojunction bipolar transistors. The measurement system utilizes a terahertz-bandwidth electrooptic transducer gated by 100-fs laser pulses to interrogate the time-domain waveforms at the device input and output nodes. A microwave signal phase-locked to the laser pulse-train is used to synchronously excite the device in both small-signal and large-signal regimes. The measurement system is capable of 50-GHz bandwidth and provides time-domain voltage waveforms that can be used directly to verify the time-domain results of the large-signal analysis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of Electro-Optic Sensor and Force Transducer on Leak Detection

Abstract The application of the Electro-Optic Sensor and Force transducer on leak detection began with reviewing various leak testing technologies and their associated problems. Specific applications of differential pressure sensors for leak testing are discussed and the specifications of the University of Arkansas Electro-Optic Sensor and Force Transducer are explained. A design for a new differential pressure transducer based on the University of Arkansas Electro-Optic is presented. A leak tester was assembled by using a prototype of a differential pressure transducer. The performance test and calibration of the unit was accomplished by using a standard calibrated leak. The calibration results were then used to estimate the leak rate of some unknown samples. In order to reduce the ambient effect, a balance volume was attached to the reference chamber. In conclusion, a discussion of the problems and limitations is presented.

Thin-film-transistor/liquid crystal display technology—An introduction

Liquid crystals are simple and very efficient electro-optic transducers, or light valves. Thin-film transistors are simple electronic control devices which can be fabricated on large transparent substrates. These two technologies, when combined, allow the fabrication of electronic displays which challenge the dominance of the cathode ray tube (CRT). This paper reviews the history of this important development, presents the current status in comparison to the color CRT, and describes the remaining challenges to be overcome if the color CRT is truly to be displaced.

A low-loss Ku-band directly modulated fibre-optic link

By optimizing electrooptic transducer gains, a Ku-band fiber-optic link that suffers only 12.6 dB of insertion loss at 12 GHz with a 3-dB bandwidth of 800 MHz was developed. The broad dynamic range (79.4 dB-MHz) exhibited by the link can be exploited in a number of analog communications applications where the small size, light weight, flexibility, and electromagnetic interference immunity of optical fibers are most desired. These applications include satellite communications systems, local area networks, and active phased-array harnesses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical data transmission at the Superconducting Super Collider

Digital and analog data transmission via fiber optics for the Superconducting Super Collider have been investigated. The state of the art of optical transmitters, low-loss fiber waveguides, receivers, and associated electronics components are reviewed and summarized. Emphasis is placed on the effects of the radiation environment on the performance of optical data transmission system components. The performance of candidate components of the wideband digital and analog transmission systems intended for deployment of the Superconducting Super Collider Detector is discussed. It is concluded that, using available digital ICs, electrooptical transducers, and fiber optic cable, the design and implementation of a digital optical wideband data transmission system with approximately 1-Gb/s data rate capability can be accomplished.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical analysis of the AMAC IIIS transducer

The AMAC IIIS electrooptical transducer for flow cytometry facilitates simultaneous measurements of electrical impedance and several optical properties of single cells. Ray-trace analysis demonstrates that its spherical exterior permits light rays to emerge effectively undeviated and thus lowers the required numerical aperture of the collecting lens as compared with a flat surfaced transducer. This feature results in an increased light-gathering ability, an increased depth of focus, minimum spherical and chromatic aberrations, and minimizes the optical volume observed.

High-speed optical digital transmitter/receiver module operating at 1.3 μm wavelength

Abstract Taking benefit of optical fibers' wide bandwidth and low attenuation, research and development were conducted in order to apply fiber optics to public telecommunications' networks mainly for long-distance and large-capacity transmissions. However, application of fiber has rapidly spread toward cornrnunication networks having relatively short transmission distances (within several kilometers) such as local area networks (LAN) and computer networks. Thus, requirements for the fiber optic transmitters and receivers used as electro-optic transducers, such as small-size, low-price, high-reliability and low-supply voltage operations, become stricter than those of the public telecommunication network.

A new method for the electro-optical measuring of fast high voltage pulses

This report describes a new method for measuring fast high voltage electric pulses based on one particular application of the Kerr effect. This work was carried out in order to further the development of optical particle detectors. At the present time with our method, the minimum risetime of the measured pulse reaches the nanosecond domain while the maximum voltage is limited only by the physical dimension of the electro-optical transducer. The measuring principle chosen requires a new calibration method in order to reconstruct the observed signal. The use of nitrobenzol as the active liquid allows the continuous modification of the cell sensitivity over a ratio of 1 to 3 without changing the geometry of the cell.

Experimental study of the lasing P/N junction as an electro-optical transducer

An experimental study of the small signal equivalent circuit of the lasing P/N junction itself is presented. The usual study examines the behavior of the packaged device through measurement of the dependence on dc current and on frequency of the modulus of the transfer function relating the stimulated power to the drive current. The present work features the study of the P/N junction itself through a new technique, the direct measurement of the modulus, and the argument of the ratio of the modulation of the stimulated power to the modulation of the spontaneous emission. The frequency modulation of the optical power is also studied, and the results compared with deductions from the present study of the spontaneous emission and from a published study of the amplitude and frequency transfer functions of a similar laser. All the studies support the new finding that the modulations of the junction voltage and the power are in phase with each other for frequencies up to the gigahertz range. The experimental values of the circuit elements show that the damping of the response is due to dissipation in the resistance representing the change in voltage with stimulated power. Comparison of the values of the circuit elements to the solutions of the multimode rate equations gives insight about the utility and limitations of existing formalism, in particular about the extent to which the formalism yields a single set of circuit elements which describes the transient response of all observables and about whether the observed responses are better modelled as those of a classical noise amplifier or a free running oscillator.