Abstract
This paper reviews the recent developments in microwave photonic devices based on liquid crystal on silicon (LCOS) technology. The operation principle, functions and important specifications of an LCOS based optical processor are described. Three microwave photonic devices, which are microwave photonic notch filters, phase shifters and couplers, reported in the past five years are focused on in this paper. In addition, a new multi-function signal processing structure based on amplitude and phase control functions in conjunction with a power splitting function in a commercial LCOS based optical processor is presented. It has the ability to realize multiple time -shifting operations and multiple frequency-independent phase shifting operations at the same time and control multiple RF signal amplitudes, in a single unit. The results for the new multi-function microwave photonic signal processor demonstrate multiple tunable true time delay and phase shifting operations with less than 3 dB amplitude variation over a very wide frequency range of 10 to 40 GHz.
Highlights
The low-loss and large available time-bandwidth product capability of fiber optic systems make them attractive for signal transmission, and for the generating, measuring and processing of microwave signals [1,2,3,4]
Since the fractional bandwidth of a microwave signal modulated onto an optical carrier is small, these qualities are virtually independent of the microwave frequency, making photonics suitable for broadband applications
Note that the two modulation optical processor amplitude and phase response profiles for realizing a continuous higher system signal-to-noise ratio (SNR) compared to the previously reported microwave photonic phase shifter based after optical signal processing
Summary
The low-loss and large available time-bandwidth product capability of fiber optic systems make them attractive for signal transmission, and for the generating, measuring and processing of microwave signals [1,2,3,4]. The microwave signal phase shifting operation in optical domain is of particular interest because it enables the operation over a wide bandwidth, together with a full phase shift range of 0◦ to 360◦ while keeping the amplitude of the microwave signal constant and fine tuning resolution, which are the fundamental requirements of phased array radar systems [6]. These requirements again cannot be achieved using electronic approaches. Experimental results are presented, which demonstrate the multi-function signal processor operating over a very wide frequency range
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