This paper summarizes our recent work on high-speed photonic analog-to-digital conversion (A/D) technologies, where picosecond pulses generated by a 10 GHz mode-locked laser source were used to accomplish low-jitter photonic sampling. In addition, we describe our progress in the generation of 40 GHz wavelength-coded pulses for time-interleaved A/D, and the demonstration of photonic bandpass (at 1.6 GHz) Δ-∑ quantizers clocked at 10 GHz.
Integrated optoelectronic circuits that are capable of very high speeds or high functionality have been demonstrated using InP-based heterojunction bipolar transistors (HBTs). Optoelectronic receivers contain photodetectors fabricated from the same epitaxial material structure as the HBTs. High-functionality digital receivers, analog receiver arrays as well as analog-to-digital converters have been realized. Optoelectronic modulation circuits for signal transmission also contain separately grown, surface-coupled multiple- quantum-well (MQW) modulators.
We review our progress in the demonstration of photonically controlled phased arrays. In particular, we emphasize the impact made by photonic phased arrays steered via true-time- delay. We describe, in addition, a photonic beamforming architecture that combines RF-heterodyning with a Rotman lines feed for multiple beam formation.
We describe the architecture of an airborne SATCOM antenna that is photonically controlled. Specifically, the active array antenna is designed to transmit/receive in the SHF frequency band of 7.25 - 8.4 GHz. We emphasize, in particular, the remoting of the array front-end and the performance enhancements gained by adopting true-time-delay steering via the insertion of photonic technology.
In this paper, we discuss the applications and also several important system issues: insertion loss, noise figure, dynamic range and cost relating to photonics for wideband phased array antennas. This discussion is based on the work that we did on an L-band Optical Control of Phased Array Project funded by DARPA/Rome Lab. The antenna has been delivered to Rome Lab for further demonstration.
We describe the design of single frequency array transmitters and their application in RF-photonic systems. In addition, we present an array-based packaging technology that is based on passive-alignment with Si-waferboards.
Silicon waferboard technology based on etched and deposited passive-alignment features has been applied to the fabrication of optoelectronic transmitter and receiver arrays for rf applications. Using silicon waferboards, we have aligned both 1 by 4 buried-heterostructure laser arrays and 1 by 4 PIN photodetector arrays to optical fiber ribbons. Besides serving as mechanical carriers and alignment guides, the silicon wafers can also be used as rf or microwave substrates. We introduce rf-optoelectronic receiver arrays based on such enhanced silicon waferboards.
This paper describes the development of laser transmitter arrays for analog optoelectronic link applications up to 2 GHz. These modules have been developed in an attempt to utilize passive assembly and alignment operations for the purpose of reducing costs. To this end, silicon waferboard integration platforms and semiconductor laser arrays have been fabricated with special alignment features that allow passive assembly of flip-chip laser arrays to single-mode optical fiber arrays.
We report the demonstration of a 4-bit optoelectronic-switched silica-waveguide time-delay network. Targeted for insertion into a 96-element L-band conformal array, the optical time- shifter provides 16 programmable time-delays in steps of 0.248 nsec. By characterizing its RF insertion phase and synthesized pulse response, we verified that the relative time-delays generated by the waveguides were within 15 psec of their designed value. The antenna patterns obtained with the waveguide-module steering the central column of the phased array demonstrated greater than 50% instantaneous bandwidth for scan angles as wide as +/- 60 degrees.
We report the demonstration of a 4-bit optoelectronic-switched silica- waveguide time-delay network. Targeted for insertion into a 96-element L-band conformal array, the optical time-shifter provides 16 programmable time-delays in steps of 0.248 nsec. By characterizing its RF insertion phaser and synthesized pulse response, we verified that the relative time-delays generated by the waveguides were within 15 psec of their designed value.
We compare the GaAs and Silica-based approaches for realizing integrated time-shift networks. The performance of a fully functional 2-cm X 2-cm monolithic GaAs circuit is reviewed in detail. In addition, we describe the design of an optoelectronic- switched network that uses Silica-based star-couplers and waveguide arrays.
A monolithic optical time-shift network is described which is designed to steer a dual-band microwave phased array antenna at 2 and 10 GHz. The advantages of using cascade type network architectures to achieve the desired resolution are demonstrated. The implementation of different delay times in this optical time-shifter via bias control of detectors integrated monolithically on a GaAs wafer is described.
The first microwave-phased array antenna steered by optical delay lines is described. The optical ''time shifters'' utilize the propagation of light waves through a finite length of fiber to generate the time delays that control the beam pointing angle. Delay times specified by the antenna steering angle were implemented by switching bias currents of high speed lasers pigtailed to fiber optic delay lines.
A fiber-optic delay network consisting of eight different and selectable fiber delays has been demonstrated over a 1 to 11 GHz frequency range. The delay networks can be used as a three-bit resolution beam steerer for an electronically steered antenna. Discrete delay increments were selected by switching the bias current of high speed 1.3-micron laser diodes pigtailed to the delay lines.