Asher Madjar

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. >

A Large-Signal Model for the GaAs MESFET

An analytic Iarge-signal model for the GaAs FET is described which relates the terminal currents to the instantaneous terminal voltages and their time derivatives. It incorporates the device geometry and semiconductor parameters as well as the device parasitic circuit elements. The model is fast and efficient when implemented on a computer and is in a form suitable for large-signal circuit design and optimization.

Modeling the GaAs MESFET's response to modulated light at radio and microwave frequencies

In recent years, the usefulness of the MESFET as an optically sensitive microwave element on MMICs has generated much interest. A theoretical model for the device under steady illumination has been developed previously by the authors. This paper presents an extension of that model to include sinusoidally modulated illumination up to the microwave range. The dependence of the response on the bias conditions, the wavelength intensity and modulation frequency of the optical input, and the particulars of device structure are incorporated in the model. The importance of the internal photovoltaic effect, not properly accounted for in previous works, is emphasized. The theoretical model is validated by experimental results. >

Receiver for a coherent fiber-optic link with high dynamic range and low noise figure

Phase modulated coherent fiberoptic links can potentially provide exceptionally high spurious free dynamic range (SFDR) and low noise figure (NF). Critical issue is the development of a strictly linear phase demodulator. In this paper we describe a phase demodulator employing a phase locked loop discriminator. Implementing the PPLL on a single substrate using the state-of-the-art components could yield an SFDR better than 145 dB/Hz2/3 and NF lower than 3dB.

Design considerations for a uni-traveling carrier traveling wave photo detector for efficient generation of millimeter wave and sub-MM wave signals

In this paper the generation of MM and sub-wave signals by heterodyning two optical signals in a photo detector is considered. Previous work in this field has shown that this approach is feasible. However, the work demonstrated so far exhibits very low power efficiency (<1%) and low output power level (<1 mw) for frequencies in the MM wave range. In this paper design considerations for an efficient traveling wave unitraveling carrier PD are presented. Simple calculations are presented to estimate the bandwidth, microwave output power and power efficiency of this type of PD. The effect of the physical design parameters on the performance is discussed and design approach for high efficiency is presented. It is also shown that including the electron ballistic effect in the model suggests operation of the PD well into the sub-MM range.

Optical response of the GaAs MESFET at microwave frequencies and applications

The authors consider the MESFET as an optical port on MMICs (monolithic microwave integrated circuits). It is shown quantitatively how better optical coupling improves the photoresponse of the MESFET. It is pointed out that by modest redesign its frequency response can be significantly extended up to 10 GHz. How these can be converted to better optical control of MMIC circuits is demonstrated. A direct optical injection locking of a MESFET oscillator was performed. The measured optical injection locking bandwidth was 43.8 MHz.<<ETX>>

Impact of light illumination and passivation layer on silicon finite-ground coplanar-waveguide transmission-line properties

The modeling of silicon finite-ground coplanar-waveguide (FGCPW) transmission lines is presented in this paper. It is shown that the effective substrate conductivity increases in the presence of illumination and in the presence of a passivation layer in the slot regions independently. As a result, the losses of trenched FGCPW are lower than conventional FGCPW transmission lines. The strong dependence of the substrate conductivity on illumination suggests that optically controlled attenuators can be implemented with FGCPW transmission lines exhibiting practically no phase change between the different attenuation states. A new contrast ratio for optically controlled transmission lines is derived.

Large-Signal Microwave Performance Prediction of Dual-Gate GaAs MESFET Using an Efficient and Accurate Model (Short Paper)

This paper presents a microwave large-signal model for the dual-gate MESFET. The model enables prediction of device performance in small-signal and large-signal circuits. The model is an extension of a previously developed model for the ordinary MESFET. It relies on basic principles, thus correlating the device geometry and physical parameters to its performance. The speed and accuracy of the model are demonstrated by calculating three types of device performance: dc curves smell-signal scattering parameters, and huge-signal simulation of an amplifier. Good agreement was achieved between calculated and measured perfomance. The computed results are presented for comparison only, and no attempt was made to present a comprehensive analysis of the device performance.

Frequency response mechanisms for the GaAs MSM photodetector and electron detector

The GaAs metal-semiconductor-metal (MSM) device is a very useful planar and monolithic-microwave integrated-circuit compatible photodetector and electron-detector. As a photodetector, the MSM has been used for many applications in the past, however, in this paper we demonstrate its usefulness as an electron-beam detector as well. We present here a comprehensive analysis of the primary detection mechanism (electric field enhanced collection of generated electrons) as well as a newly identified secondary mechanism. This new mechanism is characterized by a high detection gain, but low speed. Experimental results are presented to verify the analysis, and possible applications are suggested by utilizing each one of the two detection mechanisms.

Microwave generation by regenerative mode-locking of a Nd:YVO/sub 4//MgO:LiNbO/sub 3/ microchip laser

This paper describes a 20 GHz experimental coupled optoelectronic oscillator based on the concept of active self mode-locking (regenerative mode locking) a Nd:YVO/sub 4//MgO:LiNbO/sub 3/ multi mode microchip laser. A millimeter wave signal is generated by beating the multiple longitudinal modes of the laser in a photo detector. In principle, the oscillator can be designed to operate to beyond 100 GHz. An important feature of this COEO is the absence of external narrowband RF filters and E/O modulators. The laser acts as an extremely narrowband filter in the microwave domain, which enables selection of one oscillation line. A phase noise of -102 dBc/Hz at 10 KHz offset was measured (limited by the noise floor of the analyzer used for the measurement). Lower phase noise is expected with optimization of the system and equipment.