Dengcai Yang

Microchannel detection of microfluidic chips with digital holography imaging system

The quality of the microfluidic chip will influence the separations, injections, reactions and measurements of samples in the microfluidic system, it is essential to detect the structure such as the width, depth and roughness for evaluating its performance. Aiming at this requirement, digital holography microscope method is developed to achieve the quantitative, non-contact phase imaging with the full field. Firstly, the digital image plane holographic microscopy is designed, and the complex amplitude of the whole wave field is reconstructed by the angular spectrum method. The two-step phase subtraction and surface fitting methods are combined to eliminate the phase aberration, and the unwrapped phase information is extracted using the least-squares phase-unwrapping algorithm. Meanwhile, we acquire the profile parameters of the microchannel using white light interferometer, and the results demonstrate that the digital image plane holographic microscopy is feasible and effective for the profile measurement of microchannels in the microfluidic chip.

Microwave photonic frequency down-conversion link based on intensity and phase paralleled modulation

A photonic microwave down-conversion approach is proposed and experimentally demonstrated based on a Mach-Zehnder modulator paralleled with a phase modulator. The incident radio frequency signal and the local oscillator signal are feed to the MZM and PM, respectively, and these two modulated optical signals interfere in the coupler. The useless higher-order sidebands are removed by a tunable optical band-pass filter. The principle of microwave frequency down-conversion is analyzed theoretically, the MZM and PM paralleled frequency down-conversion system is built. Then the performance of system is tested, and the experimental results show that the spurious-free dynamic range achieves 104.8 dB:Hz2/3. Compared to the conventional MZM-MZM cascaded system, the SFDR has been improved by 16 dB. The MZM and PM paralleled frequency down-conversion system can balance the intensity of the two coherent beams easily, and only single DC bias is needed. The proposed method possesses simple structure and high dynamic range.

All-Optical Microwave Photonic Downconverter With Tunable Phase Shift

An all-optical microwave photonic frequency downconverter with tunable full range continuous phase shift is presented. In the proposed system, the radio frequency (RF) and local oscillator (LO) signals modulate two sub Mach–Zehnder modulators (MZMs) in an integrated dual-parallel MZM (DPMZM), respectively. The two sub-MZMs are both biased at the minimum transmission point to implement the carrier-suppressed double-sideband modulation. An optical bandpass filter is then used to retain the +1st order RF and LO sidebands. When the two sidebands are send to a photodetector, an intermediate frequency (IF) signal is produced, and the phase of the converted IF signal is linearly changed by adjusting the bias voltage of the parent MZM in the DPMZM. An experiment is carried out. An RF signal can be downconverted to a phase-tunable IF signal, and the measured spurious-free dynamic range reaches 100.2xa0dB·Hz2/3. The phase deviation and power ripple of the IF signal are less than 2° and 0.26xa0dB, respectively. The all-optical design makes the system bandwidth unlimited by electrical components. Meanwhile, since the proposed microwave photonic link can simultaneously implement frequency downconversion and full range phase shift of the converted IF signal, it provides a compact alternative for the applications including radio-over-fiber system and phased-array beamforming.

Ultra-wideband microwave photonic link based on single-sideband modulation

Comparing with the conventional double-sideband (DSB) modulation in communication system, single-sideband (SSB) modulation only demands half bandwidth of DSB in transmission. Two common ways are employed to implement SSB modulation by using optical filter (OF) or electrical 90° phase shift, respectively. However, the bandwidth of above methods is limited by characteristics of current OF and electrical phase shift. To overcome this problem, an ultra-wideband microwave photonic link based on SSB modulation is proposed and demonstrated. The radio frequency (RF) signal modulates a single-drive dual-parallel Mach-Zehnder modulator, and the SSB modulation is realized by combining an electrical 90° hybrid coupler and an optical bandpass filter. The experimental results indicate that the system can achieve SSB modulation for RF signal from 2 to 40 GHz. The proposed microwave photonic link provides an ultra-wideband approach based on SSB modulation for radio-over-fiber system.

Microwave photonic frequency downconverter based on single sideband modulation

A microwave photonic frequency downconverter is proposed and experimentally demonstrated based on an integrated polarization division multiplexing dual-parallel Mach-Zehnder (PDM-DPMZM) modulator. The radio frequency (RF) and the local oscillator (LO) signals are feed to the modulator through two electrical 90° hybrid couplers, respectively. The carrier suppress single sideband (CS-SSB) modulation can be achieved by adjusting the DC biases of the modulator. Then an intermediate frequency (IF) signal can be obtained by beating. The microwave photonic frequency downconversion link based on PDM-DPMZM is built. The result shows that both optical carrier sideband suppression ratio and sideband suppression ratio are over 20dB, and the spurious-free dynamic range achieves 98.0 dB·Hz2/3. No extra mixing spurs interferes the interested IF signal owing to the CS-SSB modulation. Besides, the proposed method has good isolation between the RF signal and LO signal.