New Fields of investigation

PHOTONICS IS THE SCIENCE OF GENERATING AND MANIPULATING PHOTONS, elementary particles of light. It began with the 1960 construction of the laser by HRL scientists. Our current photonics thrust is applying state-of-the-art optoelectronics technologies to the development of new capabilities in microwave signal distribution, waveform generation, and signal processing. Using a multidisciplinary approach, HRL is leveraging knowledge in photonics, RF technology, and signal processing to create discriminators for future defense systems and commercial applications. To achieve our technical goals, we are combining our expertise in fiber optic link design and subsystem integration with selected capabilities for optoelectronic device design and fabrication.

In 2006, HRL focused on the development of several RF-photonic links and subsystems that form new enabling technologies for antenna remoting (locating antennas far away from demodulators and expensive, sensitive equipment; optical beamforming) management of large numbers of optical beams; and the generation of radar waveforms. To accomplish the high fidelity transmission of microwave signals via optical fibers, HRL designed coherent RF-photonic links that demonstrated more than 10 dB of linearity (spur free dynamic range) enhancement over conventional intensity-modulation approaches.

TREMENDOUS POTENTIALS

Photonic oscillators are a new generation of signal sources constructed by feeding the output of an RF-photonic link back to its electro-optic modulator. Its intrinsic design lends itself to the installation of both optical and RF outputs. Exploiting the long storage times of RF-photonic signals in low loss fibers (< 0.1 dB/km), we demonstrated tremendous potential for lowering the phase noise of continuous wave (CW) microwave signals. In 2006, HRL pushed the envelope of this technology further by demonstrating, for the first time, the generation of comb-waveforms that are frequency-locked to a low-noise RF-reference. We expect these RF-photonic links and subsystems to impact future radar development and signal distribution in large arrays.

In signal processing, HRL applied state-of-the-art wavelength division multiplexed (WDM) technologies (carrying multiple signals together as separate wavelengths) to form finite impulse response (FIR) RF-filters that possess instantaneous bandwidths and sampling rates greater than 10 GHz. We also developed in-house capabilities to fabricate silica/Si microdisks that demonstrated intrinsic quality-factors (Qo) higher than 10 million. When coupled to optical waveguides, these microresonators form infinite impulse response (IIR) optical filters with physical diameters that are less than 100 µm, making them attractive candidates in the formation of chip-scale filter arrays.

In 2006, HRL also demonstrated new time-interleaving capabilities for photonic analog-to-digital conversion (ADC) that utilized mode-locked laser pulses–only several picoseconds in duration–for front-end sampling. By combining fast, synchronized photonic switching with low-jitter optical sampling, we can direct optical signals into parallel electronic quantizers to accomplish time-interleaved ADC. Finally, HRL developed high-speed LiNbO3 electro-optic modulators with tandem sections designed for data-modulation and pulse-carving. This reduces intersymbol interference during the transition of bits in multi-GHz optical links.

developing technologies