Ming G. Li

Characterization of microwave integrated circuits using an optical phase-locking and sampling system

Using an optical technique, phase-locked microwave signals of up to 15 GHz from voltage-controlled oscillators have been achieved. Combining this technique with a photoconductive switch, a novel microwave waveform sampling system that displays the characteristics of oscillators and amplifiers has been demonstrated. The approach has potential applications for optically phase-locked microwave subsystems and monolithic integrated circuit characterizations.<<ETX>>

Intermixing optical and microwave signals in GaAs microstrip circuits for phase-locking applications

The microwave modulation of the interference generated by optical beams that are reflected from the top and bottom surfaces of GaAs substrate adjacent to a microstrip line is studied. The detected modulation is used to directly characterize the electrooptic effect. This optical-microwave intermixing technique is applied to phase-lock a free-running microwave oscillator with picosecond laser pulses. One potential application of this technique is for the optical on-wafer characterization of MMICs (monolithic microwave integrated circuits). >

Generation of high-power broad-band microwave pulses by picosecond optoelectronic technique

A single-picosecond GaAs photoconductive switch is used to pulse excite a microwave resonant cavity, thus generating a variety of RF (radiofrequency) waveforms with picosecond synchronization. The length of the transmission line that connects the photoconductive switch and the cavity and the strength of input/output cavity coupling elements provide for continuous variation of the frequency distribution of the generated RF power. The generation of greater than 7-kW broadband microwave bursts is demonstrated. >

Optoelectronic Devices For Millimeter-Waves

We discuss the dynamic behavior of the propagation parameters of millimeter-waves in semiconductor waveguides when they are controlled by a laser induced electron-hole plasma. Depending upon the laser source and the semiconducting material utilized, high speed millimeter-wave phase shifters, modulators, switches, and gating devices may be constructed. Gated millimeter-wave pulses of 1 ns duration have been observed in a Si waveguide. Modulated millimeter-wave signals with pulse durations of ~ 400 ps and a modulation bandwidth approaching 1 GHz are readily available using a Cr:GaAs waveguide controlled by a mode-locked Nd:YAG laser. Control of the propagation properties of a Si waveguide has also been demonstrated using a GaAs diode laser. Simultaneous measurements of phase shift and attenuation in the waveguide as a function of time have been performed and a theoretical model has been developed which is in excellent agreement with the measured data.

Direct DC to RF Conversion by Impulse Excitation of a Resonant Cavity

Conversion of energy from DC to RF has been demonstrated with an impulse-excited coaxial resonant cavity using picosecond optoelectronic switching techniques. A single pulse is capable of generating more than a hundred RF cycles with an energy conversion efficiency greater than 50%. Frequencies up to 3 GHz have been generated, and CW oscillations at 1.6 GHz have been obtained.

Modulation of millimeter-waves using diode laser illumination of a silicon waveguide

A quantitative study of the phase and/or amplitude modulation of millimeter-waves by a diode laser is reported. Using millimeter-waves as a probe, the transport properties of an optically induced electron-hole plasma in a bulk silicon waveguide may be measured. A theoretical model has been developed to predict the temporal behavior of the plasma in the case of low level optical injection. This model agrees well with the measured data.

Microwave modulation of optical signal by electro-optic effect in GaAs microstrips

A novel experimental scheme for detecting the electrooptic (EO) effect in a GaAs microstrip line is demonstrated. This scheme does not require the use of an analyzing polarizer but utilizes the modulation of the interference pattern generated by the multiple beams reflected from the top and bottom surfaces of the GaAs substrate. It is shown that even if an analyzing polarizer is used in the conventional EO sampling techniques, the interference effect has to be taken into account in order to explain the observed EO signal. For both detection schemes, it is demonstrated experimentally and theoretically that the amplitude of the EO signal varies very rapidly with the GaAs thickness. The absolute calibration in the electrooptic sampling technique for device or MMIC characterization is thus very difficult. In order to avoid the interference effect, laser pulses with a duration shorter than the round-trip time for the optical beam to travel through in the substrate must be used.<<ETX>>

Generation of Kilowatt/Kilovolt Broadband Micowave Bursts with a Single Picosecond Photoconductive Switch

A single picosecond GaAs photoconductive switch is used to pulse excite a microwave resonant cavity, generating various microwave waveforms. The generation of over 7 kW, with peak to peak voltage over 1.2 kV, of broadband microwave bursts is demonstrated.

On-Wafer Probing and Control of Microwave by Picosecond Optical Beam

to combine microwaves with ultrafast optics by intermixing them in monolithic microwave integrated circuits on a wafer. On-wafer phase locking of MMICs to the optical pulses and the display of high frequency waveforms by their low frequency replicas have been demonstrated. New techniques have been introduced

Microwave Phase Locking Using an Electro-optic Harmonic Mixer

A phase locked loop (PLL) which synchronizes the microwave source with laser pulses has been developed. An electro-optic broadband harmonic mixer has been used in the PLL loop.