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.

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This paper presents a detailed investigation on the cause of ripples in the frequency response of a microwave photonic phase shifter implemented using a 90° hybrid coupler. It was found that an unwanted radio frequency (RF) modulation sideband is generated at the modulator output due to the 90° hybrid coupler amplitude and phase imbalance. This resulted in phase shifter output RF signal amplitude variation and phase deviation. Experimental results demonstrated that incorporating an optical filter in the phase shifter structure can reduce the amplitude variation and phase deviation from 4.2 dB to 2.2 dB and from ±12° to ±3.8°, respectively, over a wide frequency range. A comparison of the loss and the dynamic range of the microwave photonic phase shifter implemented using a 90° hybrid coupler with a conventional fiber optic link is also presented.

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