Jihong Zheng

Tri-color composite volume H-PDLC grating and its application to 3D color autostereoscopic display.

A tri-color composite volume holographic polymer dispersed liquid crystal (H-PDLC) grating and its application to 3-dimensional (3D) color autostereoscopic display are reported in this paper. The composite volume H-PDLC grating consists of three different period volume H-PDLC sub-gratings. The longer period diffracts red light, the medium period diffracts the green light, and the shorter period diffracts the blue light. To record three different period gratings simultaneously, two photoinitiators are employed. The first initiator consists of methylene blue and p-toluenesulfonic acid and the second initiator is composed of Rose Bengal and N-phenyglycine. In this case, the holographic recording medium is sensitive to entire visible wavelengths, including red, green, and blue so that the tri-color composite grating can be written simultaneously by harnessing three different color laser beams. In the experiment, the red beam comes from a He-Ne laser with an output wavelength of 632.8 nm, the green beam comes from a Verdi solid state laser with an output wavelength of 532 nm, and the blue beam comes from a He-Cd laser with an output wavelength of 441.6 nm. The experimental results show that diffraction efficiencies corresponding to red, green, and blue colors are 57%, 75% and 33%, respectively. Although this diffraction efficiency is not perfect, it is high enough to demonstrate the effect of 3D color autostereoscopic display.

H-PDLC based waveform controllable optical choppers for FDMF microscopy

An electrically waveform controllable optical chopper based on holographic polymer dispersed liquid crystal grating (H-PDLC) is presented in this paper. The theoretical analyses and experimental results show that the proposed optical chopper has following merits: (1) controllable waveform, (2) no mechanical motion induced vibrational noise, and u2028(3) multiple-channel integration capability. The application of this unique electrically controllable optical chopper to frequency division multiplexed fluorescent microscopy is also addressed in this paper, which has the potential to increase the channel capacity, the stability and the reliability. This will be beneficial to the parallel detection, especially for dynamic studies of living biological samples.

Design of Dynamic Gain Equalizer With H-PDLC Reflection Gratings Doped With Ag Nanoparticles

In this letter, the characteristics of holographic polymer-dispersed liquid crystal reflection gratings doped with Ag nanoparticles (NPs) and their incorporation with dynamic gain equalizers are reported. Experimental results show that the addition of small quantities of Ag NPs causes considerable effects on holographic reflection gratings. Reflection efficiency of gratings improves with the addition of a 0.2% Ag NP solution. Refractive index modulation of doped gratings reached 4.8 × 10-3 experimentally. Taking advantage of reflective wavelength and electrically controlled refractive index modulation of gratings, cascades for several grating-based dynamic gain equalizers were proposed and testified. These can be incorporated with erbium-doped fiber amplifiers. Simulated results show that the fluctuation range of a typical gain spectrum for an erbium-doped fiber amplifier can be reduced from 3.3 to 0.23 dB.

The Frequency Modulation Electro-Optical Response of Holographic Polymer Dispersed Liquid Crystal Display Doped With Nano Ag

Holographic polymer dispersed liquid crystals (H-PDLCs), which is one of promising material for LC display, when doped with nanoscale silver (nano Ag) exhibit a unique electro-optical response to frequency modulation. We established an equivalent circuit model for H-PDLC doped nano Ag gratings according to Maxwell-Wagner effect and calculated relaxation frequency for three concentrations of nano Ag. We found that the frequency modulation and doping concentration have a close effect on threshold driving voltage of H-PDLC gratings. It is experimentally shown that the lowest threshold driving voltage can be obtained when the driving frequency is located just around the recipes dielectric relaxation frequency. It is possible to decrease the driving voltage of H-PDLC through selection of suitable driving frequency as well as via doping with appropriate concentration of nano Ag.

Improvement on the Performance of Holographic Polymer-Dispersed Liquid Crystal Gratings with Surface Plasmon Resonance of Ag and Au Nanoparticles

An investigation and comparison of the characteristics of holographic polymer-dispersed liquid crystal (H-PDLC) gratings doped with Ag and Au nanoparticles (NPs) is presented. The experimental results show that the diffraction efficiency and electro-optical properties of holographic gratings are improved through the addition of Ag and Au NPs. It is notable that Ag NP-doped gratings have far superior performance than those containing Au NPs. Furthermore, we find that the diffraction efficiency improvement can be explained as being due to the surface plasmon resonance of the metal NPs embedded in the PDLC. We theoretically simulate the surface plasmon resonance (SPR) wavelengths of the Ag and Au NPs within the PDLC and find that the laser wavelength used to fabricate the holographic gratings is much closer to the SPR wavelength of Ag NPs than that of Au NPs. Atomic force microscopy images show that the phase separation of the Ag-doped grating is improved, and the grating structure is much smoother than those of the undoped samples and the Au NP-doped samples, because of the SPR properties of the Ag NPs in the PDLC microstructure during the holographic recording process.

Electrically controlled optical choppers based on holographic polymer dispersed liquid crystal gratings

An electrically controlled optical chopper based on switchable holographic polymer dispersed liquid crystal (H-PDLC) gratings is demonstrated through a programmable, adjustable, and periodic external driving source. Compared with traditional mechanical optical choppers, the H-PDLC chopper exhibits many advantages, including faster response time, less waveform deformation, as well as easier integration, control, and fabrication, to name a few. Its excellent performance makes the device potentially useful in frequency modulation optical systems, such as frequency division multiplexed microscopy system.

Experiments and quantitative analysis of frequency division multiplexing confocal fluorescence microscopy with UV excitation

In this paper, we experimentally demonstrated a two‐channel frequency division multiplexing confocal fluorescence microscopy system using a UV laser as the excitation source. In our two‐channel frequency division multiplexing confocal fluorescence system, the incoming laser beam was divided into two beams and each beam was modulated with an individual carrier frequency. These two laser beams were then spatially combined with a small angle and focused into two diffraction‐limited spots on the targeted cell (rat neural cell) surface to generate fluorescent signal. As a result, the fluorescent signals from two spots of the rat neural cell surface can be demodulated and distinguished during data processing. Furthermore, a quantitative analysis on the cross‐talk among different frequencies was provided as well. The experimental results confirm that the two‐channel frequency division multiplexing confocal fluorescence technology can not only maintain the high spatial resolution, but also realize the multiple points detection simultaneously with high temporal resolution (within millisecond level range), which benefits the dynamic studies of living biological cells.

A four-channel frequency division multiplexed fluorescent microscope modulated by holographic polymer dispersed liquid crystal grating array

A four-channel frequency division multiplexed fluorescent microscope (FDMFM) modulated by holographic polymer dispersed liquid crystal (H-PDLC) grating array is presented in this paper. The four-channel H-PDLC grating array is developed and employed to generate frequency modulation. Fluorescent signals at four different locations on a rat neural cell have been successfully modulated with four different frequencies, collected by a single high-sensitivity photodetector, such as photomultiplier tubes, and distinguished by taking the Fourier transform of the detected sum signal. The experimental and simulation results agree well. The new system offers the advantages of (1) multiple channel modulation capability, (2) no mechanical noise and (3) flexible and controllable modulation profile (e.g. square wave, triangular wave, etc.). Thus this four-channel FDMFM system can be very helpful for studying fast-changing transient events in biological samples.

H-PDLC Based Electrically Controlled Optical Chopper Applied within the Fluorescence Microscopy System

An electrically controlled optical chopper based on holographic polymer dispersed liquid crystal grating (H-PDLC) and its application within the fluorescence microscopy has been investigated in this paper. The H-PDLC chopper has the characteristics such as free waveform, easy and precise tunable working frequency, no moving parts etc. In order to testify its application, a two-channel frequency division multiplexing confocal fluorescence microscopy (FDMCF) has been established, where the integrated H-PDLC chopper array modulates the individual exciting laser beam with different carrying frequency. The FDMCF microscopy detects two-channel fluorescent signals from the two different spots of the specimen’s surface synchronously. The successful experiments testified the optical chopper device based on H-PDLC technique, and explored its application possibility within the modern integrated optical system as well.