Peter R. Herczfeld

Analytical model for optically generated currents in GaAs MESFETs

The MESFET as an optically sensitive microwave element in MMICs has attracted much attention. The theoretical modeling of the device, however, needs more consideration. The authors propose an analytical model for the illuminated MESFET, complete in that all major contributions to the optical response are considered. The dependence of the response on bias conditions, the wavelength and intensity of the optical input, and the particulars of device structure, are incorporated in the model. The importance of the internal photovoltaic effect, which has not been properly modeled previously, is emphasized. The novel theoretical model is verified by experimental results. >

An analytical model for the photodetection mechanisms in high-electron mobility transistors

The use of microwave high-electron mobility transistors (HEMTs) as photodetectors or optically controlled circuit elements have attracted interest. A model of the optical characteristics of HEMTs, which takes into account carrier transport as well as the quantum mechanical nature of the two-dimensional (2-D) electron gas channel, is presented. It is shown that the effect of illumination is equivalent to a shift in the gate to source bias voltage, referred to as the internal photovoltaic effect. The theoretical model is supported by experimental results that demonstrate that the HEMT photoresponse is a nonlinear function of light intensity with very high responsivity at low optical power levels.

Indirect Subharmonic Optical Injection Locking of a Millimeter-Wave IMPATT Oscillator

Large aperture phased-array antennas operating at millimeter-wave frequencies are designed for space-based communications and imaging. Array elements are composed of active transmit-receive (T/R) modules that are phase and frequency synchronized to a reference signal at the central processing unit by a fiber-optic (FO) distribution network. The implementation of FO links, synchronizing the millimeter-wave Iocal oscillators (LOs), imposes a great challenge. This paper presents results of indirect optical injection locking of a free-running 38-GHz (Ka-band) IMPATT oscillator over the Iocking range of 2-132 MHz, depending on the injected power level (amplifier gain). In the experiment, the nonlinearity of both the laser diode and the IMPATT oscillator is exploited to achieve 12th subharmonic injection locking. The overall system FM noise degradation of the reference signal is 16 dB at 500-Hz offset. The FM noise degradation is dominated by the theoretical limit of 20 log N, where N is the frequency multiplication factor used in subharmonic injection locking. Methods by which optical injection locking may be extended into 60 and 90 GHz are demonstrated.

Microwave Photonics—A Historical Perspective

Microwave photonics is a rapidly-growing interdisciplinary field linking microwave and optical technologies. This paper intends to trace the evolution of microwave photonics over the last three decades emphasizing some major research areas and application fields. Currently, microwave photonics is a vivid research area with several practical applications. In this paper, we attempt to project potential future trends as well.

Rapidly tunable millimeter-wave optical transmitter for lidar-radar

This paper reports on the optical generation of a rapidly tunable millimeter-wave subcarrier for lidar-radar. The millimeter-wave signal is generated by beating the output from two Nd:YVO/sub 4//MgO:LiNbO/sub 3/ electrooptical monomode microchip laser sections realized monolithically in a single composite crystal. The device has a continuous tuning range up to 45 GHz. The measured chirp rate is 3816 THz/s, the voltage sensitivity is 10.6 MHz/V, and the measured residual phase noise is -106 dBc/Hz at 10-kHz offset.

Design of phased arrays in terms of random subarrays

Analysis and systematic design of uniform phased arrays with subarrays of unequal sizes are absent from the literature, in spite of the appeal of such architectures to wide-bandwidth beam steering. Unequally sized subarrays are expected to outperform identical, contiguous subarrays in terms of array grating lobes, A uniform linear array that is divided into contiguous subarrays of random sizes is studied. Each array element is connected to a phase shifter, and each subarray is implemented with a common time delayer. Closed-form expressions for the average array factor and the variance of the array factor are developed. These expressions enable the formulation of a design procedure that includes the estimation of the peak-grating-lobe level in terms of the probability that the grating lobes will exceed a desired level. >

A mode-locked microchip laser optical transmitter for fiber radio

This paper is concerned with the optical domain generation of high-quality millimeter-wave signals for fiber-radio and other applications. The mode-locked millimeter-wave optical transmitter described is based on simple electrooptic microchip laser technology. The transmitter can be designed to operate from a few gigahertz to 100 GHz and beyond. The residual phase noise of the laser is below -100 dBc/Hz at 1-kHz offset, which makes it well suited for optically fed millimeter-wave wireless applications. A key feature of the transmitter is its simplicity, the very small number of elements it employs and the high level of integration of the millimeter-wave and photonic components that results in a small, rugged, and reliable package. The paper describes the design, fabrication, and experimental evaluation of the transmitter.

Theory of subharmonic synchronization of nonlinear oscillators

General expressions for the theoretical prediction of the subharmonic injection-locking range of oscillators with a nonlinear input-output relationship are presented. This analysis is extended to describe oscillators realized using real nonlinear input voltage and output current relationships. In particular, analytical results for an oscillator represented by a fifth-order polynomial describing a nonlinear current-voltage relationship for subharmonic factors of 2, 3, and 4 are given. Experiments relating the subharmonic locking range of a field-effect transistor oscillator at 18 GHz to the injected signal level are reported.<<ETX>>

Coherent PM Optical Link Employing ACP-PPLL

This paper concerns the modeling, design, and experimental validation of coherent phase modulated RF/optical link employing an ACP-PPLL linear phase demodulator. From theoretical modeling, the closed-form solutions for link gain, noise figure, and SFDR are derived. Then, two examples of link design are addressed: one with 100-MHz and one with 500-MHz bandwidth. Finally, experimental validation was performed using the 100-MHz design. The experimental results are in good agreement with the theoretical prediction.

MMIC compatible lightwave-microwave mixing techniques

The basic motivation for the research presented here is the chip-level integration of microwave and photonic components. It is demonstrated that a microwave signal can be mixed with a modulated optical signal in a MESFET. A brief theoretical analysis of the IF term of the drain current is given in terms of the input signal parameters and device characteristics. Experimental results for two mixing configurations using the MESFET are shown, along with biasing conditions which maximize the IF response.<<ETX>>