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 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 have fabricated a > 10 GHz high speed optoelectronic (OE), selector switch with high isolation (> 57 dB). This switch was used as a receiver for a microwave network demonstration with simulated satellite feeds of FM video and microwave BPSK digital channels.

A 5 bit photonic time shifter (switchable delay line) was developed for the applications of wideband array antennas. This module was used to steer the beam on the subarray level, which required up to 10 ns delay in the true delay beamforming network. The time shift module consists of four diode lasers and eight photodetectors in conjunction with fibre optic delay lines and a 4X8 optical coupler connected in between. The L-band module has a 38 dB loss at present. A silica waveguide-based delay line technology using monolithic/hybrid integration is under way. The miniaturised version will reduce the loss by combining a laser and detector switch array plus other OEIC components in the package.

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.

Optoelectronic integrated circuits (OEICs) may be the implementation choice over hybrid receivers for long-wavelength photoreceiver front-ends required to operate at data rates ≥ 10 Gbit/s. The OEIC advantage is primarily due to the achievement of reduced parasitics associated with the node connecting the photodiode and the preamplifier circuit, thereby permit-ting wider-bandwidth operation. Other potential advantages are higher reliability and lower manufacturing costs. Previously, the performance advantage has been offset by the complexities associated with the simultaneous realization of high-quality optical and electronic devices, and, as a result, hybrid receivers have offered, to date, better performance than OEICs, particularly for < 10-Gbit/s operation. However, promising results for OEIC receivers have been reported in recent years in a variety of technologies: p-i-n junction field-effect transistor (JFET),1 metal-semiconductor-metal (MSM) high-electron-mobility transistor (HEMT),2 p-i-n HEMT," and p-i-n hetero-junction bipolar transistor (HBT).4,5 In this paper we present results for broadband OEIC receivers based on InP-based HBT technology, which will be useful in applications requiring 20-Cbids operation and beyond.

An optoelectronic switch with a 4.5 GHz bandwidth has been fabricated and tested in a simulated antenna network environment. The experiment demonstrated the detection of L-band FM video channels and S-band microwave BPSK channels. The measured electrical crosstalk isolation was better than 29 dB.< >

Subcarrier-multiplexed (SCM) optical links combine high-speed digital and analog signals onto an optical carrier.1 Figure 1 shows how multiple antenna feeds could be distributed over a wavelength-division-multiplex (WDM) based system. At each port an optoelectronic (OE) switch selects the particular feed. Multiple users receive the full spectrum of signals simultaneously and can by way of the OE selector switch monitor a single desired feed.

It is well known that a key element in advanced photonic system architectures are arrays of sources and detectors. For example, such devices are useful in optoelectronic switching matrices,1 byte-wide communication, and active wavelength division multiplexing. The effective bandwidth of a system is equal to the bandwidth of a single optical channel multiplied by the total number of parallel channels. Hence, the achievement of very high frequency arrays is an important step in realizing systems which operate at terabit bandwidths and beyond.

The authors fabricated and packaged 1*4 arrays of In/sub 0.53/Ga/sub 0.47/As p-i-n photodetectors connected in a GaAs FET bias-switched, common cathode circuit. The bandwidth of the discrete (packaged) photodiodes in the arrays exceeds 11 GHz, and is 5 GHz for the packaged arrays. The on/off isolation ratio for fully packaged arrays using GaAs FET bias switches was measured at both low and high frequencies. It was found that the on/off isolation of the detectors in the array was 70 dB, and the bias switching times were less than 5 ns. The performance characteristics suggest that the p-i-n detector arrays used in a common cathode, current summing configuration have applications for high-freqeuncy digital and analog optical switching applications.< >

An optoelectronic crossbar switch has been fabricated and tested at 100-175 Mbit/s. The optoelectronic switching is achieved using bias switched detectors.<>

We have fabricated and tested channel guides and fibres made from photochromic glasses. The temporal response and the spectral response to UV radiation suggest that the fibres may be useful for monitoring processes involving UV irradiation.

For specialized applications, conventional optical fibers provide insufficient protection against high temperature, high stress conditions, and nuclear radiation. These conditions exist in optical sensor applications in nuclear reactors, fire-resistant cable deployment, and geothermal exploration.