Low-cost Modulation Research Articles

An Efficient Technique for Designing High-Performance Millimeter-Wave Vector Modulators With Low Temperature Drift

Recently the demand for high-performance low-cost vector modulators for millimeter-wave direct carrier modulation applications is increasing. An efficient technique to improve the performance of the vector modulators has been proposed in this paper accordingly. This technique highlights the effect of the Lange coupler characteristic impedance and the cold pseudomorphic HEMT (pHEMT) total gatewidth on the performance. It is demonstrated by investigating two types of vector modulators, which employ unbalanced and balanced topologies. Furthermore, to reduce the temperature drift, a concise analysis of the thermal behavior of the vector modulators has been carried out. Based on the proposed technique, two types of monolithic vector modulators have been realized at 40 GHz on a 100-mum -thick GaAs substrate with 0.15-mum cold-pHEMT devices. The static constellations were obtained by using an automatic measurement system, and the temperature drifts were characterized by the measurement data from -55degC to 70degC . The results show that the technique is suitable for millimeter-wave vector modulator designs.

Errors analysis of transponder-based radiometric calibration for high-resolution imaging radars

Calibration is often required for precision measurement instruments like synthetic aperture radar (SAR) such that an image pixel intensity is directly expressed in terms of the surface backscatter coefficient. An active reflector named as transponder is an effective SAR calibration device which yields a larger radar cross-section than a corner reflector. Likewise, encoding the retransmitted signal can decouple the transponder from the background scatterers, hence, it can be used to calibrate SAR for radiometry, polarimetry and interferometry. However, as this transponder acts as an amplitude modulator, any signal errors in the transponder will result in degraded performance of radiation calibration. Literature search reveals that little work has been reported. As such, various kinds of signal errors and their effects on radiometric calibration are investigated. The system configuration and corresponding signal processing algorithms are detailed. Starting with an investigation of different errors, closed analytic expressions for calibration performance are derived. Furthermore, the most essential element of this transponder, one X-band wideband voltage-controlled attenuator, is developed. Experimental results show that, because of its low cost and wideband modulation technique, this transponder has extensive applications, not just for radiometric calibration.

A low cost modulation technique for magneto-optical measurements

A modulation–demodulation apparatus for magneto-optical Kerr effect measurements is presented. This system is based on an intensity modulated laser and on a specially designed demodulation circuit. This approach allows us to exploit the advantages offered by modulation at a much lower cost compared to the standard design based on expensive photoelastic modulators and general purpose lock-in amplifiers.

Micromachining for optical and optoelectronic systems

Micromachining technology opens up many new opportunities for optical and optoelectronic systems. It offers unprecedented capabilities in extending the functionality of optical devices and the miniaturization of optical systems. Movable structures, microactuators, and microoptical elements can be monolithically integrated on the same substrate using batch processing technologies. In this paper, we review the recent advances in this fast-emerging field. The basic bulk- and surface-micromachining technologies applicable to optical systems are reviewed. The free-space microoptical bench and the concept of optical prealignment are introduced. Examples of micromachined optical devices are described, including optical switches with low loss and high contract ratio, low-cost modulators, micromechanical scanners, and the XYZ micropositioners with large travel distance and fine positioning accuracy. Monolithically integrated systems such as single-chip optical disk pickup heads and a femtosecond autocorrelator have also been demonstrated.

Soft Switching for MW Solid-State Broadcast Transmitters

A new amplitude modulation strategy, suitable to solid-state RF transmitters (entirely transistorized) and operating in MW (Medium Wave: 530 kHz-1.6 MHz), is presented. Unlike current solutions used in broadcasting, this modulation strategy provides a simple and effective answer to customer requirements in terms of cost and reliability. Amplitude modulation strategies used in working solid-state transmitters are presented first, then the principle of the new strategy is described. It is based on the phase-shift of transmitter power amplifier control signals. However, this phase-shifting induces special switching modes which have to he studied. These switching modes are detailed as are their effects on the power amplifier’s reliability and efficiency. This leads to an optimization of the power amplifiers and to the definition of a modulatian strategy for high-frequency signals (over 1 MHz). A practical implementation with several power amplifiers is described. Efficiency and distortion measurements are given. The high-quality results highlight the interest in using phase-shifting control to realize a low cost, accurate and reliable amplitude modulation.

Polymer-waveguide-based photonic switch

Polymer waveguide technology was exploited to build a photonic switch with enormous bandwidth capabilities at extremely low cost per path. The properties of polymer waveguides allowed the use of a low-cost multielement spatial light modulator in a guided wave application. A 6 x 6 ferroelectric liquid crystal array was used as a switching element to block or transmit light signals between input and output fibers. Visible laser diodes, plastic fibers, PIN detectors, and our proprietary polymeric mixing rod couplers were used to construct the switch. The polymeric fibers, couplers, and switching element allowed eliminating the need to time-division multiplex photonic channels through the switch because the optical paths were no longer costly. This, in turn, eliminated the electronic buffering and synchronization requirements of the switch. This is critical, because signals that can be buffered and synchronized can be switched electronically using GaAs cross-point arrays. Although data-transparent wavelength conversion is acceptable at the inputs and outputs of a photonic switch, buffering and synchronization are not acceptable for some applications. Our low cost polymer waveguide approach also eliminates the need for costly multi-GHz lasers when they are not needed on a per channel basis.

High voltage modulator for pulsed ion implantation

Pulsed ion implantation is a relatively new technique which under appropriate application would be economically superior to the conventional line of sight ion implantation process. Such a system requires a high voltage pulse modulator with certain specifications for its waveform. This paper describes a low cost and reliable high voltage pulse modulator whose design is based on R- C circuits and uses triggered spark-gaps for switching. Oscilloscope traces of the output pulse indicate the success of this design in fulfilling the waveform requirements. Furthermore, this pulse modulator was used in the pulse implantation of aluminium with nitrogen ions.

Visual demonstrations with a low-cost PLZT modulator

Transparent ceramics enable visual demonstrations in large classrooms. These include computer music and data, obtaining of circularly polarized light etc.

Simple Acoustic Grating Modulators

Simple low-cost modulators based on the Raman-Nath regime of acoustooptic diffraction have been demonstrated. Experimental results on internal laser modulators constructed from some dense flint glasses and fused quartz are presented. 100% modulation of He-Ne lasers with rise times on the order of 1 musec are obtained with 10-MHz modulator drive powers of 100 mW. The theory necessary for the design of this class of modulators is reviewed and compared with the experiments.