摘要:

A sceptical view is advanced for the future of optical methods for signal processing, as a counterbalance to the implicit optimism usual in research papers concerning techniques with fascinating and elegant properties. Although optics is an extremely active field, and not yet fully exploited in providing general techniques for signal and image processing, it already appears to be conceding ground to the far less mature engineering discipline of electronic circuit integration. The glittering prizes of optics, in the shape of large bandwidths, high-order parallelism and freedom from limitations such as parasitic capacitances, carrier mobilities and crosstalk, are distanced from us by its mundane constraints of inadequate input-output techniques, large physical size, parametric inflexibility and dynamic-range limitations. Significant exceptions occur in specific cases such as where the signal itself is optical, or where a commonly required and complicated system function like an integrating spectrum analyser can be realised in a relatively simple opto-acoustic form.

DOI:10.1049/ip-j.1986.0002

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper discusses the processing of synthetic-aperture-radar (SAR) data from an optical perspective, with emphasis on real-time operations. To appreciate the problem of storing and processing the large quantity of data derived from recent, and projected, satellite-borneSARmissions a brief review of optical and digital techniques is presented. It is evident that there are still severe difficulties to be overcome in achieving real-time processing of satellite-borneSARdata with present digital electronic systems. In the paper several specific optical solutions to the data processing bottleneck are examined in detail, all are based on charge coupled devices (CCDs) configured to perform multichannel processing integrated with a variety of acoustooptic architectures. These systems have the potential to rival the performance of present digital electronic systems and offer substantial reductions in size, weight and power consumption. With future increases inSARdata throughput requirements in a wide range of applications it is argued that both present and future optical systems can offer a cost-effective processing facility which may complement digital electronic computers.

DOI:10.1049/ip-j.1986.0003

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The development and characterisation of an interferometric radio-frequency spectrum analyser based on two surface-acoustic-wave (SAW) Bragg cells illuminated by a semiconductor laser are reported. The local oscillator reference waveform is generated by a repetitive 31 bit pseudorandom noise sequence driven at 250Mbit/s, biphase modulated onto a suitable carrier. Spectrum-analyser measurements demonstrate a channelisation accuracy of 8MHz and a two-signal resolution of approximately 16MHz. For a collimated laser power of 11 mW, a dynamic range of 53 dBhas been achieved for signal pulses with 100 ns duration.

DOI:10.1049/ip-j.1986.0004

出版商:IEE    

年代:1986

数据来源: IET

摘要:

A computer model for simulating hybrid optical/digital cross correlators for pattern recognition is developed to investigate accuracy and limitations of a hybrid cross correlator compared to an ideal digital cross-correlator. The hybrid system is based on matrix-addressedLCDdisplays andCCDcamera chips as interface devices. Both joint-transform and frequency-plane correlators can be simulated, and different physical distortion effects from the optical components and from the interface devices can be included. The evaluation of the hybrid system is carried out in the correlation plane, which is the output of the system.

DOI:10.1049/ip-j.1986.0005

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes the design, construction and performance of a fully engineered and self-contained optical cross-ambiguity function processor. A matched pair of tellurium dioxide shear-mode acousto-optical cells are used to convert the two complex electrical input signals into a two-dimensional spatial modulation pattern on a light beam, which is then transformed optically into a light pattern representing the crossambiguity function for the two signals. A third acousto-optic cell controls light throughput, and the output pattern is recorded by a planarCCDphotodetector array. By slightly reconfiguring the optics, the processor may also be operated as a triple product time-integrating correlator. A brief description is given of the mode of operation of the acousto-optic cells. Details of the design and construction of the processor are covered in some depth. The principal performance parameters of the processor are presented, together with photographs of the output patterns obtained for various input test waveforms. Finally, the processor is assessed in terms of its suitability for use as a range-velocity indicator in a pulse compression radar system.

DOI:10.1049/ip-j.1986.0006

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper reports on a theoretical study of the two-Bragg-cell interferometric spectrum analyser system. This architecture offers an improvement in radio frequency (RF) dynamic range compared to that of the conventional power spectrum analyser. Bulkwave shear mode lithium niobate Bragg cells are assumed for the study together with shot noise limited detection by avalanche photodiodes. A theoretical model is presented which enables the temporal history of the intermediate frequency (IF) output on each channel of the detector array to be predicted. A time-domain model is employed in which the instantaneous Fourier transforms of the (Gaussian weighted) signal and reference waveforms are evaluated at intervals much less than theIFperiod. These are then coherently combined to simulate the heterodyne detection. A computer program based on this theory provides a realistic simulation of pulse responses, ringing and delay effects in theIFfilter, image and sidelobe levels, andIFbreakthrough due to the reference waveform. Results are presented for chirp, pseudonoise and Gaussian noise reference waveforms. It is concluded that for the detection ofRFpulses with durations as short as 100 ns, an instantaneous dynamic range of 50–55 dBrelative to rms noise should be achievable, for simultaneous signals.

DOI:10.1049/ip-j.1986.0007

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The effect of charge trapping on the resolution of a liquid crystal light valve using bulk bismuth silicon oxide (Bi12SiO20) as the photoconductor has been analysed. The method of solution is to set up and solve the appropriate differential equations for the light valve geometry. The variation of sensitivity and resolution is examined as a function of symmetric and asymmetric charge location and spatial frequency.

DOI:10.1049/ip-j.1986.0008

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The development of liquid crystal light valves (LCLVs) in the Sowerby Research Centre of British Aerospace is described. The device performance is found to be very dependent on the drive conditions, and this dependence is examined. Results for sensitivity, time response and resolution are presented for twoLCLVs. The resolution values obtained are compared with theoretically calculated ones.

DOI:10.1049/ip-j.1986.0009

出版商:IEE    

年代:1986

数据来源: IET

摘要:

The paper describes image correlation in a photorefractive based nondegenerate four-wave mixing system. The system is arranged such that the reference image may be changed arbitrarily quickly, and work is described which measures the rate at which the input image can be updated. It is shown that a photorefractive correlator may work at the maximum rate allowed by a TV system; i.e. the grating can be written during the flyback time of the TV camera. TV framelocked operation is described. It is shown that the correlator may provide a true correlation output or a weighted correlation, depending on the relative intensity of the write beams. Numerical simulation of a theoretical model of the correlation process supports the experimental results.

DOI:10.1049/ip-j.1986.0010

出版商:IEE    

年代:1986

数据来源: IET

摘要:

An nMOS-addressed liquid-crystal array has been designed, primarily for use as a spatial light modulator in the Fourier plane of a coherent optical processor. Specification of the performance of such filters in an ideal system is considered briefly, and a description is given of the operating parameters of our prototype device. Details are presented of the VLSI design for the integrated circuit, which consists of a square array of 16 × 16 pixels covering a total active area of 3.2 × 3.2 mm2on a silicon chip. An outline is also given of a simple interface circuit, built from discrete components, which allows the liquid-crystal filter to be controlled through the 8-bit port of a microcomputer. When illuminated with noncoherent light, the device acts as a liquid crystal display with ‘on-board’ memory.

DOI:10.1049/ip-j.1986.0011

出版商:IEE    

年代:1986

数据来源: IET