Research in the use of guided-wave optics for signal processing and sensing is reviewed, and advantages and limitations of the technology are discussed. The signal processors employ electrooptic, acoustooptic, and fiber-optic components to perform such functions as spectral analysis of radio-frequency signals, correlation and matched filtering, code and waveform synthesis, signal delay and storage, and analog-to-digital and digital-to-analog conversion. In most cases, the guided-wave approach is distinguished by the ability to perform a particular function at very high analog bandwidths or digital data rates. The second part of the review is concerned with sensor applications for guided-wave elements fabricated on planar substrates ("integrated optics"). Waveguides on an integrated optics chip have been used for sensing temperature, humidity, electric field, wavefront angle, and optical disc reflectivity. Also described are integrated optic phase and frequency shifters developed for use in fiber-optic sensors. In concluding remarks, an effort is made to provide some perspective on competing technologies and to indicate some areas where future research might prove fruitful.

Application of guided-wave optics in signal processing and sensing

7.1 – Fiber-Optic Delay-Line Signal Processors

Techniques for optical generation of microwave signals to 35 GHz, including direct laser diode modulation, FM sideband injection locking of laser diodes, and offset frequency phase locking of solid-state lasers, are reviewed. Optical methods for controlling microwave devices, including phased array radar and oscillators, are described. Recent advances in optical transmission of microwave signal are examined. >

Optical techniques for microwave generation, transmission and control

The multifiber array connector (MAC) is a FASTECH optical connector for simultaneously connecting up to 18 single-mode or multimode fibers through the backplane. A low reflection version of a single-mode, 12-fiber MAC was assembled and tested. The fiber end faces were polished at a slight angle to the plane perpendicular to the axis so that the reflection was cast outside the fiber acceptance angle of the transmitting fiber. When the bevel angle was 5.50 degrees , the reflection was less than -40 dB, and the connection loss averaged 0.6 dB with a maximum of 0.95 dB. Compared with samples with smaller bevel angles, these connection losses were within the range of scatter, and hence the effect of bevel on connection loss is deemed negligible. The measured reflections from both mated and unmated connectors followed the theoretical predictions closely for smaller bevel angles. For larger angles (e.g. 5.50 degrees ), the measured values exceeded the theoretical values. >

Low-reflection, single-mode multifiber array connector (MAC)

We demonstrate an inexpensive and easily fabricated, high-performance system for the generation of single and multiple optical pulse bursts. The system, which is comprised of commercially available components, provides single pulses as short as 190 ps full width half maximum. Used as an active, very low jitter, delay line for application to fast coincidence timing experiments, delays of much less than 1 ns to in excess of 1 I¼s are possible using 1300 nm standard telecommunications fiber. Optical fiber ladder networks containing differential fiber delays, connected together using single-mode fiber connectors have been used to construct flexible and reconfigurable optical burst generators. Precise delay time determination (Â±5 psecs) allows very accurate, discretely variable burst frequencies demonstrated at up to 3 GHz. Instruments capable of 4, 8, and 16 pulse trains are also demonstrated. A conservative estimate indicates pulse trains consisting of 128 pulses at 8 I¼W per pulse should be possible with a simple extension to the present apparatus.

High-speed optical pulse generation using single-mode optical fiber networks

A 0.5 ms delay line with a time-bandwidth product of > 105 is demonstrated by recirculating a 2 ns pulse around a 20.4 km single-mode fibre five times. Analogue signal regeneration is employed after each recirculation. System dynamic range, signal/noise ratio and cancellation ratio for a noncoherent moving target indicator radar application are given.

C.C. Wang

Papers

Fibre-optic recirculating analogue delay line