The first demonstration of a 4-bit binary photonic delay line using ferroelectric liquid crystal (FLC) devices and externally modulated S/C band fiber-optic link is presented. A Mach-Zehnder integrated-optic modulator is used to modulate the light. This photonic delay line uses FLC optical on/off devices for optical path switching and active polarization noise filtering. Three dimensional imaging optics and antireflection coated optics are used to minimize photonic delay line insertion losses and interchannel crosstalk. Signal-to-noise ratio measurements as well as interchannel isolation crosstalk analysis is performed.

Conventional phased-array antennas are limited by the bandwidth and attenuation as well as mechanical rigidity of the coaxial cables employed to perform the microwave phase shift. Photonic technology offers advantages in distribution of the microwave signal including lightweight, compact delay lines, immunity from electromagnetic interference, low rf transmission loss and possibility of optical signal processing on the microwave encoded optical beam. Fiber optic delay lines have been demonstrated already but one requires a precision cut of the fiber length (accurate to a mm) to achieve accurate psec time delay. Guided-wave based approach allows precise definition of the waveguide delay line lengths. In addition, reproducible delays can be mass- produced ensuring low cost modules. In this paper, we demonstrate the first integrated optical delay lines in the silicon-on-insulator waveguide technology.

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.

Switched-volume-diffraction gratings are used to form free- space optical time delay systems with digitally selectable delays. In these systems, a cascade of n independently controlled gratings provides 2' evenly spaced time delay paths. An important feature of the approach described here is that the technology allows the use of compact micro-optic packaging, which in turn allows independent time delay channels to be tightly stacked. In one such scenario, the optical system for 75 5-bit optical time delay modules, each with a maximum selectable time delay of 1 ns, can be packed in a 3-inch cube. Recent results of theoretical modeling and experiments are presented which show that these systems have potential for excellent channel isolation, crosstalk suppression, and low insertion loss. Optical systems are discussed in the context of phased array applications: various configurations are described, including a multi-pass entire array driver that may replace many single channel time shifters with a single optical system.

Photonic microwave true-time delay eliminates the beam squint problem in broadband phased-array antenna. However the large insertion losses associated with the optical switching network that selects the appropriate delay line is a serious limitation. We have previously demonstrated a unique photonic filter that uses the optical carrier wavelength in the 1550 nm wavelength band to select the desired time delay. In this paper, dual band (1550/1300 nm) operation of this Recirculating Photonic Filter True-Time- Delay is demonstrated. This dual-band operation offers flexibility in system design, enhanced antenna functionality and is expected to lead to lower device and system cost.

We describe the design and development of an 8-element hardware-compressive receive true time delay steering system which employs wavelength division multiplexing. The laboratory system performance and the results from the system demonstration at the antenna range are discussed.

Phased array antennas (PAAs) offer many advantages including steering without physical movement, accurate beam pointing, increased scan flexibility in two dimensions, precise PAA element phase and amplitude control to obtain low sidelobes, and reduced power consumption and weight. The complexity associated with controlling the many thousand array elements, while handling the broad bandwidth required of a shared antenna, makes the marriage of photonics and microwave radar attractive. To satisfy the simultaneous requirements of wide bandwidth and large antenna scan angle, true-time-delay (TTD) steering techniques are required so that efficient elemental vector summation (in the receive mode) or distribution (in the transmit mode) can be obtained that is independent of frequency or angle. We describe here a new lower complexity and cost photonic TTD system which we call WDM Delay Broadcasting TTD. This approach (1) encodes fixed delays with wavelength, (2) makes available all of the delays at each of the subarrays, and (3) selects the appropriate delay using an optical filter (with correction via the element electric delay line). The results of this effort show that it is indeed possible to design and construct a photonically controlled TTD network that will exhibit the performance and cost benefits needed for widespread deployment in government and commercial systems.

A binary photonic delay line (PDL) module is proposed that gives balanced or equal gain/loss switched states. The module is based on a reflective and symmetric geometry and is adjustable to a wide range of time delays. Theoretical analysis as well as experimental demonstration of the proposed PDL architecture is performed. Issues such as electrical signal-to-noise ratio and relative output signal power between the two PDL settings are discussed.

The application of photonics technology in switched RF networks is discussed with emphasis on the benefits for avionics applications. System requirements and performance issues are addressed. A 16 X 16 photonic switch module prototype is described and results for RF fiber-optic links passing through the module are presented. RF channel isolation measured was at least 75 dB. A demonstration is described in which a photonic network using the switch module passed signals from a dynamic electromagnetic environment simulator to two radar warning systems under test. Demonstration modes included simulation of both aperture sharing and processor sharing. Finally, a novel alternative switch module architecture is described that is strictly non-blocking and has inherently better channel isolation.

We present a review of our recent work at WaveBand Corporation on optically controlled millimeter wave (MMW) steering antennas. Instead of relying on photonically controlled discreet microwave elements like phase-shifters, modulators, photodiodes, etc., our approaches are based on the interaction of MMWs with an electron-hole plasma grating created by optical means. We use silicon wafers as a medium for plasma recording as well as for plasma-MMW interaction. Electron-hole plasma is generated by illuminating the silicon wafer with near IR or visible light. The required plasma pattern is created by using a spatial-light- modulator, a set of photo-masks, or an optical fiber array connected to individually controlled LEDs. The new architectures promise flexible antenna designs and a cost reduction sizable enough to compare the proposed antennas with their phase-array counterparts.

Semiconductor optical amplifiers are investigated for use in large optical signal distributions systems requiring high dynamic range. The impact of amplifier length on the gain and noise figure of the microwave signal is illustrated experimentally. The performance of a device which simultaneously splits and amplifies the optical signal using the principle of multimode interference will be discussed, and it will be shown that this device has potentially higher performance that the previous generation Y-branch/amplifier combination.

Two photonic delay line structures are introduced that are based on the binary operation of Digital Micromirror DEvices (DMDs). These structures include a binary switched design based on multiple DMDs, and a non-binary delay line using a single DMD. These DMD-based delay lines do not require polarized light for operation.

A down-conversion photonic link implemented with a pair of parallel Mach-Zehnder modulators has been demonstrated. The block down-converter has a fixed local oscillator at 22 GHz and has demonstrated conversion of the 26 - 40 GHz millimeter-wave band down to the 4 - 18 GHz microwave intermediate frequency band. A conversion efficiency improvement over down-conversion links with serial modulator topologies with comparable components is predicted.

The generation of 84 GHz radiation was demonstrated using a mode-locked semiconductor laser (MLSL) pumped heterojunction bipolar transistor (HBT). The passively mode-locked MLSL was biased appropriately utilizing two diode laser drivers (current sources). Mode-locked behavior was achieved in a colliding pulse mode, resulting in a pulse repetition rate frequency of approximately equals 84 GHz. The mode-locked behavior was confirmed by utilizing both an interferometer-based correlation measurement and an optical spectrum analyzer. The MLSLO was then used to pump an HBT that was specially designed for optical pumping (a 10 mm X 10 mm window was fabricated in the HBT), allowing efficient optical excitation of the device. HBT-radiated MMW signals as high as 20 dB (above the noise floor) were achieved at approximately equals 84 GHz.

Planar photoelastic effect on compound semiconductor structures has been investigated for integrated optical transmitter in rf photonics system. While our prior works emphasized the investigation of low-loss photoelastic waveguide, photoelastic waveguide modulator, and photoelastic optical splitter, the present work focuses on the attainment of high performance laser which employs the photoelastic effect for waveguiding. Planar separate- confinement, double-heterostructure, single-quantum-well photoelastic GaAs/AlGaAs lasers have been fabricated using WNi stressors for waveguiding and ion implantation for isolation. Even without bonded on heat-sinks, these planar photoelastic lasers operate continuous wave at room temperature. The lowest threshold is 29 mA for a cavity length of 178 micrometers and a stressor width of 5 micrometers . The main waveguiding mechanism of the photoelastic lasers is determined to be weak index-guiding with the beam waist in the junction plane measured at 10 micrometers behind the end- facet.

Modern missile seekers operate in dual millimeter wave/infrared (MMW/IR) mode in order to enhance target detection. The same dual modality is required for their testing. The dual band test system calls for a combining element that can bring both MMW and IR beams to the same seeker head. Optical Holographic technique was used to overcome the fabrication problems associated with manufacturing large size (IR/MMW) beam combiner that should be transparent to MMW while reflecting IR beam. We designed and produced a surface relief holographic optical element (HOE) that satisfied beam combiner requirements. Since the uniform metal coating of any meaningful thickness would reflect most of MMW radiation, we have found a way to partially metalize the HOE, so that it becomes transparent for TM polarized MMW while maintaining excellent reflectance of IR.

A coherent, optical heterodyne approach to signal generation and beamforming is particularly advantageous in multi-beam mobile phased arrays. Use of optical technology allows an optimum distribution of weight and power to be achieved between the antenna face and central electronics, together with an efficient implementation of the beamforming function and a modular design approach in which the basic building blocks are frequency-independent. Systems of this type employ a pair of optical carriers with a difference frequency equal to the required microwave signal. Phased- locking is necessary in order to achieve sufficiently low phase noise in the radio communication link. Optical phase locked loops (OPLLs) have been shown to be potential candidates for this application, yet work still needs to be done to bring them from the laboratory to field demonstrations. This paper describes the construction of a laser-diode OPLL subsystem for evaluation in a proof-of- concept beamforming system. This involves optimization of the loop design, development of single-frequency laser diodes with the correct linewidth, modulation and tuning characteristics and integration into a micro-optic assembly with custom wideband electronics.

Optical interconnects have been designed, fabricated, and tested, and a graphics processor based on field-programmable gate arrays has been designed. The board-to-board connection approach is based on multi-channel integrated optical waveguides with novel optoelectronic active connectors, allowing multiple simultaneous data transfers among many boards. Data is transferred from chip to chip through optical data channels within an integrated chip. For electronic processing systems, we developed a preliminary design for a multiprocessor system suitable for both single instruction multiple data and multiple instruction multiple data, and using video random access memory and static random access memory for main memory, look-up table processing, and display interface.

An acousto-optic spectrum analyzer is combined with an analog artificial neural network classification technique to `understand' a complex signal environment and identify specific emitters.

Ultra-thin, electrically programmable, low control power optical devices are proposed as adaptive optical alignment correction devices for future deployable photonic modules for RF signal processing applications. A substantial relative optical/RF gain (i.e., 7.92 dB RF gain) in a free- space PDL that requires a fiber remoted feed in the infrared 1300 nm optical spectrum has been successfully demonstrated.

Acousto-optical devices which are intended for information transmission and conversion, may process both binary and analog signals. The theory which had been developed earlier for transmission of binary signals, has been expanded to the processing of analog signals. The system of resolving power and frequency bandwidth criteria has been studied in details, proceeding from the need to transmit the necessary amount of gray scale levels with the necessary reliability. It has also been shown that the basic equation of acousto- optics in which number of resolvable spots is determined as time-bandwidth product, must be modified for the case of gray scale transmission. The experimental results illustrating the proposed approach to basic parameters of acousto-optical devices, have been described and discussed.

It is usually considered that the theoretical limit of a single acousto-optical device frequency bandwidth is one octave. An acousto-optical device has been proposed which may operate in the frequency bandwidth significantly exceeding this theoretical limit without any division of this bandwidth into separate parts. Initially, in this device the wideband signal spectrum is created, and both first and second diffraction orders appear in the frequency plane overlapping each other partially. The negative image, correspondingly scaled and shifted, is created in the same plane in real time. The result of addition of all images is very close to the first diffraction order--light distribution describing the wideband signal spectrum.