Eric E. Funk

Two-dimensional synthetic aperture imaging in the optical domain

In scan-mode synthetic aperture imaging radar, spatial resolution in a range is given by a frequency-swept waveform, whereas resolution in the orthogonal direction is derived from the record of phase as the beam footprint executes linear motion over the object. We demonstrate here what is to our knowledge the first two-dimensional imaging that uses exactly this process in the optical domain for a 1 cm x 1 cm object with 90 mumx170 mum resolution.

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.

Phase performance of an eight-channel wavelength-division-multiplexed analog-delay line

The design of an eight-channel 25 /spl mu/s wavelength-division-multiplexed (WDM) microwave photonic delay line is described. The performance of the delay line was studied by measuring the temperature dependent relative phase drift between channels and the interchannel crosstalk. A simple method for measuring the maximum phase errors produced by the interchannel crosstalk is described and used to measure the maximum error on a channel in this system. The use of polarization interleaving and dispersion compensation to reduce the effects of crosstalk in the system is examined experimentally.

110 km 256-QAM digital microwave over fiber link

A 110 km digital microwave fiber-optic link has been designed and demonstrated with 256 QAM at 20 GHz. The design approach, involving the management of loss, dispersion, and Brillouin threshold throughout the link is discussed.

Nonlinear distortion and crosstalk in microwave fiber-radio links

Dispersion and fiber nonlinearities are potentially significant sources of impairment in fiber-radio links. An experimental study of second harmonic distortion and WDM crosstalk in externally modulated microwave fiber-radio links indicates that these impairments are much more significant than previously observed at CATV frequencies below 1 GHz.

RF phase distortion due to crosstalk in an 8 channel wavelength division multiplexed analog delay line

We present experimental results of crosstalk for an eight channel WDM 25 microsecond delay line. The total phase error produced by the crosstalk onto one channel from the other seven over a frequency of 0-20 GHz is measured.

Synthetic aperture imaging at 1.5μ: laboratory demonstration and potential application to planet surface studies

Two-dimensional imaging with synthetic aperture ladar (SAL) has been demonstrated in the laboratory. The method is entirely analogous to scan-mode synthetic aperture radar (SAR), which was used on the Magellan mission to Venus, but with 104-5 times shorter wavelength has the potential for much better resolution. The laboratory experiment is described and the theoretical limits placed on SNR by the combination of photon statistics and laser speckle are stated. SALs limitations of small ground footrpint size and SNR < 1 for single-look imagery can be alleviated by multiple images and mosaicking of scenes. Design equations are given that show what hardware capabilities are needed to implement a desired system. They show that a 10 μ SAL in orbit around Mars can give centimeter-class resolution with reasonable laser power (≤ 100 wt). Major engineering development hurdles must be overcome before any such system can be built.

Microwave photonic direct-sequence transmitter and heterodyne correlation receiver

This paper proposes and demonstrates a new architecture for the transmission, heterodyne reception, and correlation of direct-sequence (DS) signals encoded onto an optical carrier. The approach is practical for pseudo-noise in-modulated laser radar and free-space optical-code-division multiple-access communications. Although the local oscillator is free running, we show that the received signal is free from laser phase noise. Furthermore, by applying DS coding to both the transmitted signal and the local oscillator, the delay required for correlation can be realized via a combination of electrical and optical means.

Direct carrier modulation for wireless digital communications using an improved microwave-photonic vector modulator (MPVM) approach

This paper presents a demonstration of direct carrier modulation via the use of an improved microwave/photonic vector modulator (MPVM). This modulation approach is suitable for direct digital modulation of microwave and millimeter-wave signals and allows for tuning of the carrier frequency over wide bandwidths and dynamic reconfiguration of the modulation format. An all-optical control approach is used to achieve faster data rates and better carrier tunability than previously reported work in this area. Specifically, experimental results showing direct QPSK and 16 QAM modulation of carrier frequencies between 1.0 and 2.0 GHz with data rates to 8 Mbs are presented.

Hybrid fiber/millimeter-wave wireless for broadband last mile access

We have analyzed many of the technical issues involved in the development of a base-station to central office fiber link for last-mile wireless service. A power penalty due to the insertion of the fiber link has been determined for a chip laser based fiber radio downlink. Measurements have been performed to predict system performance, both for single channel and multi-channel operation.