Meirion Francis Lewis

A high-speed readout scheme for fast optical correlation-based pattern recognition

We describe recent developments to a novel form of hybrid electronic/photonic correlator, which exploits component innovations in both electronics and photonics to provide fast, compact and rugged target recognition, applicable to a wide range of security applications. The system benefits from a low power, low volume, optical processing core which has the potential to realise man portable pattern recognition for a wide range of security based imagery and target databases. In the seminal Vander Lugt correlator the input image is Fourier transformed optically and multiplied optically with the conjugate Fourier transform of a reference pattern; the required correlation function is completed by taking the inverse Fourier transform of the product optically. The correlator described here is similar in principle, but performs the initial Fourier transforms and multiplication electronically, with only the final most computationally demanding output Fourier transform being performed optically. In this scheme the Fourier transforms of both the input scene and reference pattern are reduced to a binary phase-only format, where the multiplication process simplifies to a simple Boolean logic XOR function. The output of this XOR gate is displayed on a state-of-the-art Fast Bit Plane Spatial Light Modulator (FBPSLM). A novel readout scheme has been developed which overcomes the previous system output bottleneck and for the first time allows correlation frame readout rates capable of matching the inherently fast nature of the SLM. Readout rates of up to ~1 MHz are now possible, exceeding current SLM capabilities and meeting potential medium term SLM developments promised by SLMs based on novel materials and architectures.

Low-phase-noise optoelectronic microwave source

A low phase noise optoelectronic source has been developed operating at 10 GHz. Custom surface acoustic wave (SAW) devices operating at high frequency and high acoustic power have been developed and are used as the critical element in an optical phase locked loop. Improved performance could be attained via lasers with larger control loop bandwidths. The source is antenna remoteable via the use of optical fibre and is compact and lightweight, suggesting applications in phased array radar.

Optically controlled phased-array antenna with PSK communications

An optically controlled RF/microwave/mm-wave phased array antenna has been developed operating at 10 GHz with 30 kHz reconfiguration rate via the use of a micromachined silicon Spatial Light Modulator. A communications function has been demonstrated with a variety of Phase Shift Keying modulation schemes (BPSK, QPSK, MSK) at data rates up to 200 Mbit/s and low BER (<1×10-9). A single channel has been demonstrated at 35 GHz. The properties of photonic components are taken advantage of in several ways: (i) since the carrier frequency is derived from heterodyning of lasers, it is tuneable from almost DC-100 GHz, (ii) the use of optical fiber allows for EMI immune antenna remoting, and (iii) the wide information bandwidth of optical modulators, which in this configuration is carrier frequency independent. The above is achieved in a lightweight and compact format, with considerable scope for further reductions in size and weight.

Laser stabilisation for coherent phased-array antenna beamforming

We describe a 50 dB improvement to the close-in phase noise spectra of diode-pumped YAG lasers and DFBs by locking the outputs to a fibre-optic delay line frequency discriminator. This forms a compact and rugged source.

MEMS and their applications in optical signal processing and beamforming for phased array antennas

A fast analogue phase-only SLM has been developed from MEMS technology. This device has been developed primarily for its speed and currently operates at 30 kHz. It has potential applications in many optical signal processing systems, the optical beamformer for the control of phased array antennas being the first to benefit.