A new photonic microwave image rejection mixer that can achieve high conversion efficiency and has a wide bandwidth is presented. It is based on an integrated dual-parallel Mach-Zehnder modulator (MZM) with a 90° polarization rotator on one branch of the modulator. The two modulators connected in parallel are biased at the minimum transmission point to generate two sets of orthogonally polarized radio frequency (RF) and local oscillator (LO) modulation sidebands with the optical carrier being suppressed. Suppressing the optical carrier enables high RF and LO modulation sidebands to be detected by a photodiode without saturation. The LO modulation index is also designed to obtain a high conversion efficiency mixing operation. Experimental results demonstrate frequency downconversion with an image rejection function and a high conversion efficiency of > $-$ 5 dB over a wide 3 to 20 GHz frequency range. A technique for compensating the effect of coupler amplitude and phase imbalance to obtain a high image rejection ratio is also experimentally demonstrated.

A new dual-function photonic microwave signal processing structure that has the ability to realize both frequency up/down conversion and RF/IF phase shifting, is presented. In the proposed signal processor, a dual-polarization dual-parallel Mach Zehnder modulator (DP-DPMZM) is used to generate an orthogonally polarized single RF/IF signal and local oscillator (LO) modulation sideband without an optical carrier. The optical phase difference between the two sidebands can be controlled by controlling a DC voltage applied to a LiNbO3 electro-optic phase modulator that is connected after the DP-DPMZM. Beating between the two sidebands at a photodetector generates an RF/IF signal with a phase equal to the optical phase difference between the IF/RF signal and LO sidebands. The dual-function photonic microwave signal processor has a wide bandwidth and does not require a precise control of the laser wavelength. Experimental results demonstrate that a flat >-3 dB down/up conversion efficiency is achieved for an RF signal from 3.5 to 26.5 GHz and for an IF signal from 0.5 to 3 GHz, and a full 360° continuous phase shift of the output IF/RF signal.

A new microwave photonic phase controlling structure that can realize a continuously tunable 0° to 360° phase shift using only one DC voltage control is presented. Unlike other phase controlling structures, the radio-frequency (RF) signal phase shift produced by the new phase controller has a predefined linear relationship with the control voltage. This enables users to easily determine the control voltage needed to realize the desired RF signal phase shift. The microwave photonic phase controller is based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DPMZM) and a polarization-dependent optical phase shifter. It is suitable for realizing multiple RF signal phase shifts, which are required in beamforming applications. Experimental results are presented which demonstrate the realization of a continuously tunable -180° to 180° phase shift with little phase and amplitude variations over a wide frequency range, as well as a linear RF signal phase shift to control voltage relationship.

A high-speed refractive index sensing system based on the Fourier domain mode locked laser (FDML) and a microfiber Bragg grating (mFBG) is theoretically studied and experimentally demonstrated. Unlike traditional physical parameter sensing systems, which directly use the FDML as the wavelength scanning source and the optical sensor as the spectra shaping component, we inserted an mFBG into the FDML cavity in order to generate time domain pulse signals used for sensing. The wavelength shift in optical frequency domain is converted into time domain pulse drift. The sensitivity of the proposed refractive index (RI) sensing system is improved by two orders of magnitude, compared with the wavelength monitoring method. The scanning speed is as high as 43 kHz. Moreover, the sensitivity curve can be adjusted by tuning the direct current voltage. The nonlinear sensitivity and linear sensitivity with RI can be achieved.

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.

A microwave photonic signal processor that is capable of simultaneously realizing sub harmonic frequency down conversion and IF signal phase shifting operation is presented. The IF signal generated by the frequency down conversion process is obtained by the beating of the 2nd order LO sideband with the fundamental RF signal sideband at the photodetector. The phase of the IF signal can be tuned continuously from 0° to 360° by controlling the optical phase of the RF signal sideband. The optical carrier is eliminated at the signal processor output to achieve high conversion efficiency mixing operation. The signal processor can be designed to have a very wide bandwidth as it only involves optical components. Experimental results are presented that demonstrate frequency down conversion with > 8.8 dB conversion efficiency over 6 to 40 GHz RF signal bandwidth and 0.05 to 10 GHz IF signal bandwidth, and a continuous 0° to 360° phase shift on the output IF signal.