A new approach to optoelectronic integration is presented in which all optical and electronic devices are derived from a single crystal growth and a single fabrication sequence. The approach uses a self-aligned inversion channel capable of functioning as an FET or bipolar transistor, a detector, a modulator or a laser in either an analog or a digital mode. Topics discussed include a three-terminal switching laser, a bipolar inversion channel field-effect transistor, a three-terminal analogue laser, an HFET detector, and an HFET optical modulator.
Wideband modulators based on nonlinear optical (NLO) organic polymers are reviewed with particular attention given to the material properties, design guidelines, fabrication, and performance. Improvements in the efficiency of NLO polymers make it possible to significantly improve the performance of electrooptic devices. Major parameters to be considered for wideband modulator design include characteristic impedance, microwave and optical losses, and RF drive power as related to switching voltage efficiency.
A systematic optimization method for a wideband flat frequency response electrooptical modulator (EOM) with a reversal electrode structure is presented. The method is based on an optimization criterion and a systematic searching procedure to obtain better flatness of the amplitude frequency response and better linearity of the phase frequency response.
The wideband microwave performance of a laser link was improved using a lossless microwave impedance-matching network. Matching has been achieved from 3 to 9.5 GHz, which is more than one octave with a 5 dB associated improvement in both throughput loss and noise figure for the optical link. The improved noise figure makes it possible to use the laser link with lower-gain amplifiers in front of the laser, and the improved throughput loss reduces the gain needed after the link. It is concluded that impedance matching not only improves the performance but also reduces power consumption in the whole system.
A coherent fiber optic link employing wideband frequency modulation (FM) of the optical carrier is used to transfer radio frequency (RF) or microwave signals. This system is used to link a remotely located antenna to a conveniently located electronics processing site. The advantages of coherent analog fiber optic systems over non-coherent intensity modulated fiber optic analog transmission systems are described. An optical FM link employing an indirect transmitter to frequency modulate the optical carrier and a microwave delay line discriminator receiver is described. Measured performance data for a video signal centered at 60 MHz is presented showing the use of wideband FM in the link.
Attention is given to millimeter-wave electrooptic modulators (EOM), directly modulated semiconductor lasers, and solid state RF amplifiers for a laser transmitter system up to 100 GHz. Both millimeter-wave MESFET and HEMT amplifiers are considered to be feasible to drive laser diode and EOM. The state-of-the-art HEMT MMIC amplifiers are capable of driving frequencies beyond 100 GHz. The presently achieved HEMT medium power amplifier technology limits the LiNbO3 EOM operation frequency to 60 GHz because the LiNbO3 device requires more than 100 mW driving power. It is concluded that, for millimeter-wave operation frequency, new EOM configurations and substrate materials are urgently needed.
We demonstrate a 1.3 micron wavelength optical transmitter system with a 20 GHz RF center frequency and 2 GHz bandwidth. We accomplish this by actively modelocking a semiconductor diode laser at 14 GHz; the modelocked signal is then externally modulated between 5 GHz and 7 GHz, using a lithium niobate based Mach-Zehnder modulator. We show a hybrid prototype package for the modelocked laser source.
Ultra-high data rate optical communication links require multiplexing to separate channels. This is usually achieved electronically, limiting the data rate to the speed of the driving electronics. We describe a new means of optical-frequency division multiplexing which makes use of the spatial and frequency modulating characteristics of acoustooptic Bragg cells. A two channel proof-of-principal experiment is presented.
An electrically and optically optimized 18.5 to 19.0 GHz short-haul fiber optic (F.O.) link is presented. A theoretical link analysis of gain, system noise contributions, linearity, and dynamic range is shown as well as the corresponding measurements. Results indicate that by employing reactive matching and on-fiber lensing techniques, performance of high-speed F.O. links are still limited by high relative intensity noise levels and the limited frequency response of the laser. Alternative architectures are suggested to counteract these limiting problems of current high speed links.
An all optical circuit in GaAs/AlGaAs for control of phased-array systems using a single photonic integrated circuit chip has the potential for high performance control of phased-array system from a small, lightweight, package. Such a circuit based exclusively on combinations of reverse-biased optical phase modulators, waveguide interconnects, corner reflectors, and power splitter combiners with optical-fiber output to the antenna elements has been designed at Sandia National Laboratories. This paper presents some basic features of optical phase modulators for photonic circuit applications and provide relevant performance data as achieved to date. Current structures have been shown to operate with a 76.5 degree/V-mm figure of merit at 1.06 micron and losses as low as 2/cm. A digital phase shifter to allow direct digital control of phased arrays is also proposed and demonstrated.
This paper addresses the problem of dynamic optical processing for the control of phased array antennas. The significant result presented is the demonstration of a continuously variable photonic RF/microwave delay line. It is shown that by applying spatial frequency dependent optical phase compensation in an optical heterodyne process, variable RF delay can be achieved over a prescribed frequency band. Experimental results which demonstrate the performance of the delay line with regard to both maximum delay and resolution over a broad bandwidth are presented. Additionally, a spatially integrated optical system is proposed for control of phased array antennas. This approach uses a class of spatial light modulator known as a deformable mirror device and leads to a steerable arbitrary antenna radiation pattern of the true time delay type. Also considered is the ability to utilize the delay line as a general photonic signal processing element in an adaptive (reconfigurable) transversal frequency filter configuration.
A novel high speed, high on-off ratio (greater than 50 dB) fiber optical shutter switch for optically controlled phased array is proposed. Computer aided design tools for the development of the switch and the phased array have been developed. The beam steering, shaping, and forming are achieved by controlling the on-off status of the fiber shutter switches. The advantages of the phased array antenna using this new device are to possess higher antenna gain, lower sidelobes and higher speed. This fiber optic switch can also be used as fiber optic variable attenuator, isolator, and spatial light modulator for various other applications.
An all-fiber (6x6) optical shutter switch matrix with the control system for microwave phased array has been demonstrated. The device offers the advantages of integrated configuration, low cost, low power consumption, small size, and light weight. The maximum extinction ratio (among 36 individual pixel) of this switch matrix at 840 nm is 24.2 dB, and the switching time is less than 120 microsec. In addition to phased array application, this low cost switch matrix is extremely attractive for fiber optic switching networks.
In-line additive acousto-optic architectures for linear and planar phased arrays are described for one-dimensional (1D) and two-dimensional (2D) beam scanning, respectively, along with a simultaneous multiple beam forming architecture. A transmission mode acousto-optic processor is demonstrated in the laboratory. Electronic and optical receive mode systems are described.
Real-time multi-access laser communications employing an optical phased-array have many distinctive and attractive features, such as rapid beam forming and steering, efficient power combining, centimeter pointing accuracy, microradian beam width, and wide field-of-view. This paper presents both hardwares and analysis of belt and dome optical phased-arrays. Affordable and mass producible phased-array employing monolithic integration are also discussed.
A general computer analysis and design approach for beam steering phased array interaction in birefringent is presented. Two major classes interactions are derived: slow to fast interaction mode and fast to slow interaction mode. Experimental results on two tellurium dioxide phased arrays are also reported.
This paper reports the final experimental results and conclusions on the performance of an interferometric acousto-optic receiver (IAOR). The receiver is designed to acousto-optically channelize a 1 GHz RF bandwidth spectrum into 128 frequency bins, and generate digital frequency, pulse amplitude, pulse width and TOA words. Experimental results show that the predicted performance improvement over the power acousto-optic receiver (PAOR) is significantly below expectation. Key factors contributing to performance degradation are discussed along with supporting experimental data. Recommendations for further acousto-optic receiver work are presented.
We describe an acousto-optic signal processor which simultaneously determines target range, velocity (Doppler shift) and angle-of-arrival from pulsed Doppler radar signals. The two-dimensional processor combines a two-channel acousto-optic time-integrating correlator fed with radar signals from two antennas with an orthogonal acousto-optic time-integrating spectrum analyzer to simultaneously display target range, Doppler, and angle-of-arrival in orthogonal spatial dimensions on a two-dimensional photodetector array. By combining the pulsed Doppler and angle-of-arrival signal processing functions in a single acousto-optic processor, a compact, low power consuming package is possible.
This paper describes a novel pulse compressor concept based on optical coherent detection and associated implementation issues imposed by electro-optical component characteristics. The concept was developed to support pulse compression of wideband linear frequency modulation (LFM) waveforms in noncooperative bistatic/multistatic radar applications. Waveform bandwidths in excess of 1 GHz can be accommodated. Coherent optical detection is used to implement difference-mixing for subsequent digital active-correlation processing. This technique is noncooperative in that it requires no dedicated external reference or timing signals to be provided by the illuminating radar. Rather, the necessary reference signal is derived from intercepting the radar sidelobe emissions. Noncooperative narrow-band processing techniques have been developed, but the capability of this optical processing architecture to accommodate wideband signals appears unique.
An approach to optical processing of complex electronic systems operating on multiple radio frequency (or microwave) signals is presented. The approach is aimed at exploiting linear and nonlinear optics to synthesize transponders and receiving systems for satellites and other platforms. Emphasis is placed on the architecture of electronic functions for optical component realization. These elements perform the signal processing operations of AM, PM, and FM carrier modulation and demodulation; phase locked loop signal tracking; carrier element mixing; signal filtering; and signal matched filter detection. Analog optical processing techniques are capable of performing Fourier transforms readily. A second spatial dimension is available for parallel processing such as exhaustive search of signal space for signals and parameters of interest. The optical processors provide wide bandwidth, high carrier frequency capability, and fast response.
Nonparametric estimation of lower-order statistics from higher-order statistics of continuous processes is considered. Of particular interest is estimation of correlations and spectra (second-order statistics) from higher-order correlations and polyspectra (higher-order statistics). The use of higher-order statistics is motivated by their insensitivity to a wide class of additive noises including Gaussian noise of unknown covariance. The fact that lower-order correlations are projections of higher-order correlations is exploited. Experimental results are presented using an acousto-optic triple product processor to estimate the autocorrelation of a 1- D signal.
This paper describes the application of acousto-optic (AO) spectrum analysis techniques to astronomical spectrometers. The design of a 2 GHz bandwidth AO spectrometer and the performance limitations of the technology are discussed. Two alternative architectures are proposed. The new approaches appear promising for increasing the instantaneous bandwidth to greater than 5 GHz.
Distributed transmission line theory is used to accurately model circular microstrip resonant structures. The model incorporates the effects of microstrip dispersion, conductor and dielectric loss, curvature, and the coupling capacitance of the feed lines. It is applied to study electronically tuned resonators and excellent agreement is obtained between theory and experiment. Microwave optoelectronic mixing is obtained by heterodyning a microwave local oscillator with a modulated optical carrier in a microstrip ring resonator on semi-insulating GaAs substrate.
Based on the electro-optic (EO) sampling approach, a technique has been developed which offers high detection sensitivity for the measurement of two-dimensional electric field distribution in a GaAs microstrip line circuit. The interference effect in the EO sampling process was also investigated using this technique. The study resulted in a better understanding of the limitations of EO sampling. It is shown that correct use of the pulse width of the laser beam with respect to GaAs substrate thickness can lead to an accurate and consistent optical characterization of monolithic microwave integrated circuits (MMICs).
The use of III-V semiconductor heterojunction and quantum well optical modulators is considered for monitoring of shipboard radar and communication emissions. Both antenna- coupled and all-dielectric electro-optic electromagnetic environment monitoring systems are investigated with respect to sensitivity, linear dynamic range, and system bandwidth at optical wavelengths of 1.3 and 1.5 micrometers . Results are presented which indicate that these devices can, if carefully designed and utilized, be a useful alternative to interferometric modulators for this ultra-wideband analog fiberoptic application.
A novel bridge type optoelectric (OE) sample and hold circuit based upon current steering is proposed for the first time and is experimentally tested. Experimental comparison between this circuit and the conventional direct OE sample and hold circuit shows that the bridge type is clearly superior in performance to the direct OE circuit. When a high speed signal is sampled with high accuracy, the bridge type OE sample and hold circuit offers high charging capability, commanding signal isolation, and reduced time jitter, distinct advantages over electronic sample and hold circuits.
We demonstrate and characterize a silicon Fabry-Perot spatial light modulator in a fiber optic data transmission system at 1.3 micron wavelength. The device utilizes free carrier effects in silicon to achieve phase modulation, and a built-in Fabry-Perot cavity to convert the phase modulation into intensity modulation. The measured insertion loss is 3.5 dB, the modulation depth is 10 percent, and the bandwidth is 40 MHz.
A free space optical TDM switch at 1.32 micron is experimentally studied. The architecture of a TDM circuit switching system with a fixed transmitter and tunable receiver assignment is described. Since each user of the TDM switching system is assigned a time slot on the time frame, the corresponding receiver at the output looks only in the preassigned time slot for signal recovery. The electrical data signal from the input source is used to gate the optical pulses from the centralized source for the duration of the signal. It is concluded that large input/output switching systems are feasible.
We describe an optoelectronic microwave switch that exploits the high optical sensitivity of the air-GaAs interface. With an optical power of 100 micro-W, the switch has an insertion loss of 3.4 dB and an isolation of greater than 20 dB from 0 to 10 GHz. No electrical power is needed.
A hybrid optical/electronic A/D conversion technique is described which uses electrooptic sampling and time-demultiplexing together with multiple electronic A/D converters. A system which uses 4 parallel electronic A/D converters and a pulsed diode laser is demonstrated with a sample rate of 2 GHz. For single tone test signals in the range of 10 to 11 GHz, the precision of this system is as high as 2.8 effective bits, limited principally by laser jitter.
An electromagnetic-radiation diagnostics method is presented which is based on the interaction of intense microwave and laser infrared radiation with a semiconductor. Particular attention is given to the simultaneous effect of continuous microwave and optical infrared radiation on a crystalline silicon layer placed in a waveguide, the impact of this radiation on the mobility of free charge carriers and concentration of photocarriers, and an experimental method for studying the photocarrier diffusion caused by laser simulation of nonstationary microwave absorption in a semiconductor.
A compact 5-bit MMIC phase shifter has been developed utilizing EEl' switches and coplanar waveguide delay lines. The device has constant time delay over a bandwidth of more than 18% with an accuracy of±1 .2 Ps at X-band (±5°). An 1 1 .5 GHz version has less than 1 2 dB of insertion loss for any of its 32 states and an overall chip dimension of 2.25 x 2 .50 mm. A 20 GHz version has less than 1 1 dB of insertion loss and an overall chip dimension of 2.0 x 3.0 mm. Unit-to-unit variation in absolute time delay is less than 2 ps across two wafer lots andfour wafers.
Three new EOM structures are proposed for high efficiency nonlinearity compensation. A 30 dBc reduction in the 3rd order IMP is achieved at the expenses of 2.9X driving voltage increasing in the first approach. The second approach provides a theoretically total cancellation on the 2nd and 3rd order IMP at the expense of 2.8X driving voltage increasing. A 50 dBc reduction of 3rd order IMP is obtained, and a less than 100 dBc 2nd order IMP is achieved in the third approach at the expense of 1.6X driving voltage increasing. The sensitivity of the structure design parameters is also studied and discussed.
An optical based RF beam steering system is proposed for phased-array antenna systems. The system, COMPASS (Coherent Optical Monolithic Phased Array Steering System), is based on optical heterodyning employed to produce microwave phase shifting. At the heart of the system is a monolithic Photonic Integrated Circuit (PIC) constructed entirely of passive components. Microwave power and control signal distribution to the antenna is accomplished by optical fiber, thus separating the PIC and its control functions from the antenna. This approach promises to reduce size, weight, and complexity of future phased-array antenna systems.
A newly discovered slow acoustic surface wave (SAW) on a (-110) cut TeO2 surface is reported focusing on its properties studied using a PC based numerical method. It is concluded that the slow SAW is rather tolerant to crystal surface orientation errors and has unusually deep penetration of its shear component into the thickness of substrate, about 47 wavelengths for a half amplitude point. The deep shear field is considered to be beneficial for surface acoustooptic interaction with free propagating focused laser beams. Rotation of the substrate about the z-axis makes it possible to adjust a slow SAW velocity with the potential advantage of trading acoustic velocity for less acoustic attenuation. Wider-bandwidth long signal processing time Bragg cells may be feasible utilizing this trade-off. The slow SAW device is characterized by an extremely low power consumption which might be useful for compact portable or avionics signal processing equipment applications.